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How does paracetamol work?

How does paracetamol work?



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Hinz et al. 2008 found that COX-2 may be inhibited by paracetamol, and this is attributed to it's analgesic and antipyretic properties. However, there are other more recent claims from Andersson et al., 2011 that a toxic intermediate metabolite, NAPQI, may be acting on TRPA1-receptors in the spinal cord. Whilst I'm vaguely aware that the end goal is to affect prostaglandins, to me at least it remains unclear how that translates to painkilling.

There are also other theories I would imagine.

This exceedingly common drug seems shrouded in mystery. I know very little about pharmacology (evidently!), so some expert insight into the popular theories, and why they're popular, would be greatly appreciated.

  • What are the most popular theories in a nutshell?
    • Why are they a popular theory?
    • Which protein is targeted?
    • How does that inhibition introduce the analgesic and antipyretic properties?
  • Is it possible multiple theories are correct?

  • Why is so little known about paracetamol? Is it exceptionally difficult, or the norm in pharmaceutical research of relatively old effective drugs? If it ain't broken, why fix it!


What are the most popular theories in a nutshell?

To date, the mechanism of action of paracetamol is not fully understood. There are some experimental evidences, but it is difficult to put things togheter. It is now clear that paracetamol acts contemporaneously via at least three pathways:

  • The inhibition of cyclo-oxigenase (COX)

The main mechanism proposed is the inhibition of COX, it's highly selective for COX-2.
COX are molecules involved in the metabolism of arachidonic acid (aa). It catalyzes the reaction to form prostaglandin H2, a pro-inflammatory compound, from aa. Paracetamol, as other NSAIDs, block this step , thus reduce the amount of prostaglandin H2. The reduced amount of prostaglandin H2 in the CNS, lowers the hypothalamic set-point in the thermoregulatory centre.

The exact mechanisms by which COX is inhibited in various circumstances are still a subject of discussion.

Some authors state that paracetamol works by inhibiting the COX-3 isoform-a COX-1 splice variant-of the COX family of enzymes.
This variant is expressed mostly in brain, so it is the one supposed to be involved in the antalgic effect of this compound.

There is another physiopathologic possibility to explain its action, that is: paracetamol would block COX, but in an inflammatory environment where the concentration of peroxides is high, paracetamol itself is oxydated and thus inactive. When it founds a non inflammatory environment, such as CNS, it become reduced and thus active (it reduces temperature, it has anti-dolorific action, etc).

  • The modulation of the endogenous cannabinoid system, through its metabolite AM404, a compound that inhibits the reuptake of the endogenous cannabinoid/vanilloid anandamide by neurons.

The COX model can explain quite well the action of paracetamol, altought it has been demonstrated an important role of the endocannabinoid system aside of COX. When cannabinoid receptors are blocked with synthetic antagonists, paracetamol's analgesic effects are prevented. This is tought to be due by an active metabolite of paracetamol, that is called AM404 and inhibits the reuptake of anandamide.

Anandamide reuptake lowers synaptic levels of anandamide. This results in a more activated pain receptor (at least the main one, called TRPV1, or according to an old nomenclature: vanilloid receptor). The high levels of anandamine, due to inhibition of its reuptake, desensitise this receptor in a way similar to the capsaicine. Furthermore, this active metabolite (AM404) inhibits sodium channels, this chemical behaviour is shared with lidocaine and procaine, two common anesthetic drugs.

These two actions by themselves have been shown to reduce pain, and are a possible explanation of paracetamol's mechanism of action; but one other specific activity of this compound remains unexplained by these two models.

  • Serotonin receptor agonism.

It has been observed that this compound can reduce the social rejection in humans. This can't be explained with COX or type I endocannabinoid system modulation. Increase of social behavior in mice dosed with paracetamol, wich models a reduction of social rejection response in humansdoes not appear to be due to cannabinoid receptor type 1 activity… In the animal model, it seems a result from serotonin receptor agonism.

  • Aside of this main features, some other evidences are in bibliography.

In 2011 a debate started on scientific journals. Some has found a hint to the analgesic mechanism of paracetamol, being that the metabolites of paracetamol e.g. NAPQI, act on TRPA1-receptors in the spinal cord to suppress the signal transduction from the superficial layers of the dorsal horn, to alleviate pain. This findings has been contested in a new hypothesis paper on how paracetamol might act. This second study concedes that NAPQI is the active metabolite but that this reactive compound should react not only with the thiol in TRPA1 but also with any other suitably available nucleophile that it happens to encounter. This broad interaction with thiol groups in cysteine proteases, like the ones that process procytokines, might be the targets giving rise to overall analgesic effects, changing the global cytokyne environment. Even if there are evidences of drug-body interaction with formation of active metabolites and there are some models of drug action, many things are not fully cleared and the debate is still open.

Why are they a popular theory?

Are popular because are based on experimental and clinical evidence. Also, this theories can model lot of the biological effects of this compound.

Which protein is targeted?

Not any time it can be possible to reduce a pharmacological interaction at this level. For instance, in one theory it inhibits an enzyme, the cyclooxygenase (COX); in one other model entire classes of molecules, the sodium channels, are modulated… Unfortunately many times, dealing with living organisms, it is not possible to offer an hard, mechanicistic explanation of things.

How does that inhibition introduce the analgesic and antipyretic properties?

In the COX inhibition model, the analgesic properties can be explained trough an affinity for COX3; and the antipyretic activity can be due to the reduced amount of prostaglandin E2 in the CNS, in the thermoregulatory centre it lowers the hypothalamic set-point. The endocannabinoid model can explain preety well the anti dolorific actions, as well as the serotonin receptor interaction the behavioral one.

Is it possible multiple theories are correct?

Yes, there is a substantial overlap between different regulatory systems, so that is straight to think that the same chemical (or some of its different active metabolites) can modulate different systems.

Why is so little known about paracetamol? Is it exceptionally difficult, or the norm in pharmaceutical research of relatively old effective drugs? If it ain't broken, why fix it!

Is it not that difficult topic! One can say that is as tricky as any clinical pharmacology topic. The problem is that many compound are clinically used as drugs even if their molecular functionig is unknown if they are safe and of proved usefullness. This is true for paracetamol as well as many other drugs, like a lot of anaesthetic agents as Propofol.


Ibuprofen, Paracetamol and COVID-19: Here’s What You Need to Know

There’s been some confusion recently on whether we should or shouldn’t take ibuprofen to treat symptoms of COVID-19, especially after the World Health Organization (WHO) changed its stance. After initially recommending people avoid taking ibuprofen to treat symptoms of the new coronavirus disease, as of March 19 the WHO now does not recommend avoiding ibuprofen to treat COVID-19 symptoms.

France’s Minister of Solidarity and Health Oliver Véran announced that taking anti-inflammatory drugs could be a factor in worsening a COVID-19 infection. Image credit: StockSnap.

The confusion began after France’s Minister of Solidarity and Health Oliver Véran announced on Twitter that taking anti-inflammatory drugs (such as ibuprofen or cortisone) could be a factor in worsening a COVID-19 infection.

He recommended that paracetamol should be taken instead to treat the associated fever.

At the moment, the NHS only recommends taking paracetamol for COVID-19 symptoms, even though it admits there is no strong evidence showing ibuprofen worsens symptoms.

The BMJ also states that ibuprofen should be avoided when managing COVID-19 symptoms.

Ibuprofen is a non-steroidal anti-inflammatory drug (NSAID).

NSAIDs, including ibuprofen, normally have three main uses: they help with inflammation, pain, and fever. People might also take them for inflammatory conditions such as arthritis and for pain. However, paracetamol can also help treat pain and fever.

Fever is a higher than normal body temperature, and is one of the signs of COVID-19, along with a persistent cough and shortness of breath.

The body develops a fever as a defense mechanism, where the immune system produces a chain of molecules that tell the brain to make and keep more heat inside to fight the infection.

While getting fever during an infection is part of the body’s defense mechanism, a serious rise in body temperature can be fatal and should be treated.

Having fever is also uncomfortable because it often comes with shivering, headaches, nausea and stomach upsets.

Taking an anti-inflammatory like ibuprofen or paracetamol will bring down a high temperature by lowering some of the fever molecules.

However, doctors who compared the two in 2013 suggested taking paracetamol over ibuprofen for normal chest infections because they found a small number of people’s illness got worse with ibuprofen.

This scanning electron microscope image shows SARS-CoV-2 (yellow) isolated from a patient in the U.S., emerging from the surface of cells (blue/pink) cultured in the lab. Image credit: NIAID.

Cause for concern?

Some of the reasons that there’s a concern taking ibuprofen will make COVID-19 symptoms worse comes from previous studies that have shown people with other serious chest infections (such as pneumonia) experienced worse symptoms and prolonged illness after taking an NSAID, including ibuprofen.

But it’s difficult to say if taking ibuprofen in these instances directly causes worse symptoms and prolonged illness, or if it’s because taking ibuprofen or other anti-inflammatories help manage pain, which may hide how serious the illness is and could stop people from asking for help earlier – delaying treatment.

Or, it might be to do with ibuprofen’s anti-inflammatory effects. One theory is that anti-inflammatory medicines can interfere with some of the body’s immune response, although this is not proven for ibuprofen.

However, two French studies warn doctors and pharmacists not to give NSAIDs when they see signs of chest infections, and that NSAIDs shouldn’t be given when children are infected with viruses.

There’s no agreement on why ibuprofen could make chest infections worse, but both studies reported worse outcomes in patients who had taken a NSAID to treat their condition.

A recent letter to The Lancet suggested that ibuprofen’s harm in COVID-19 is to do with its effect on an enzyme in the body called angiotensin-converting enzyme 2 (ACE2) — though this has yet to be proven.

This caused additional worries for patients taking angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) for existing heart conditions.

Several leading organizations have rightly warned patients not to stop taking their regular medicines in light of unconfirmed theories.

Because novel coronavirus is a new type of virus, there is currently no evidence proving that taking ibuprofen will be harmful or make COVID-19 symptoms worse.

Research in this area is developing fast, but with so much misinformation about COVID-19 and ibuprofen use, the cautious approach is to avoid ibuprofen with COVID-19 if at all possible – especially for those with pre-existing health conditions.

Anyone who thinks they might have COVID-19 can consider using paracetamol instead of ibuprofen for managing their fever, unless they’re told otherwise by their doctor or pharmacist.

In the meantime, the UK’s Committee of Human Medicines and the National Institute for Health and Care Excellence (NICE) have been asked to review all the evidence to understand ibuprofen’s impact on COVID-19 symptoms.

Naturally, people already prescribed an anti-inflammatory drug for a health condition should ask their doctor’s opinion and not just stop their medication.

It’s worth noting, however, that ibuprofen and NSAIDs can trigger stomach ulcers and indigestion and might not be suitable for some people with heart disease, kidney and liver problems, and asthma, as well as people over 65, and those who drink more alcohol.

These drugs should not be used in people with very high blood pressure, and women trying to get pregnant or already pregnant.

Paracetamol, which can also treat pain and fever, may be preferred.

Though it takes up to an hour to work, it’s safe to use for women who are pregnant or breastfeeding, and can be taken with or without food.

Some people need to take extra care with paracetamol and should speak with their doctor or pharmacist first, for example if they have liver or kidney problems.

The usual dose of paracetamol for adults is one or two 500 milligram tablets up to four times in 24 hours, with at least four hours in between doses. Most people use a syrup to give paracetamol to children. How much to give depends on your child’s age, but again paracetamol should only be given up to four times in 24 hours, with at least four hours between doses.

Pharmacies have been running short of paracetamol and some shops have been rationing sales.

For those exhibiting symptoms, a box of 32 tablets should last for at least four days.

At this time of crisis, it’s important people make sure they’re not stockpiling medicines unnecessarily and depriving others who are equally in need of paracetamol and other vital drugs.

Author: Parastou Donyai , professor and director of pharmacy practice at the University of Reading.

This article was originally published on The Conversation .


How does Paracetamol toxicity work?

Okay, this is a bit of a strange one I know. There is a lot of rubbish regarding paracetamol out there. Many believe that using it long term can be bad for your liver for example. However the truth is that you're fine as long as you stay within the 'therapeutic' range.

I was at work today (Admin at a GP surgery) and I scanned a letter regarding a patient that attempted suicide by consuming 30 paracetamol tablets and went to sleep. Apparently she was annoyed to have woken up seemingly fine. So what happened to this patient? Did she get lucky?

Also, if it's safe to have up to 8 in a day does it matter how you divide the dosage throughout the day? For example could one take 3 two times a day instead? Why is the suggested dosage 2 four times a day? What if an individual took 4 twice a day? Would this be dangerous?

It seems to me that paracetamol toxicity works quite differently to a lot of other drug overdoses?

But that is basically my main question. If it's okay to have 4000 mg of paracetamol a day, does it matter how that is divided throughout the day? What may be the long term effects of taking more than 1000 mg every 4 hours?

This is one of my favourite toxicity questions!

The reason it seems different to 'other' cases is because of how easy it is to do despite the fact it's a commonly used, easy to obtain drug.

Paracetamol is taken up by the body and relieves pain, high temperature, etc. ➯ter' that, like many drugs, it's metabolised, in this case in the Liver. That means that the chemical structure is changed, inactivating it and/or making it easier to excrete. It's a foreign compound so your body is going to remove it.

In this case, paracetamol itself is not toxic. However, one of the 'metabolites' (something it gets metabolised into) is. Paracetamol is metabolism into three different compounds initally. NAPQI is toxic, and damages the liver.

NAPQI is usually detoxified quickly in the liver ("GSH conjugation" in the graph), so normal use of paracetamol is not necessarily dangerous. For individuals with very low body mass it can be.

There are different types of overdose. You can accidentally take more than recommended, for example taking lemsip and paracetamol tablets. There are excessive single doses, such as taking 30 tablets at once. And there are also excessive staggered doses, which is what you're referring to with "4 twice a day". This wouldn't necessarily be bad on its own as a one off, as people taking lemsip and cocodamol and paracetamol effectively do this. Sadly people do do that when they're unwell.

Now, back to NAPQI. It's usually removed very quick so you only get toxic doses when you go above the recommended dosage, but this can be as low as 75mg/kg to start seeing toxic effects. It's normally 150mg/kg. For 75mg/kg, thats a dose of 5250mg for an adult, or around 11 500mg tablets. Doses of 10-15g are when it typically starts to get lethal. This is because the liver cannot work fast enough to clear out NAPQI, so it continues to damage your liver. Even if you take large doses you don't die instantly—it takes 3-4 days normally and you can feel fine in this time. This is why its incredibly important to seek medical attention after overdosing on paracetamol, "even if you feel fine", as the packages say.

15g of paracetamol is 30 tablets so it could be lethal, but not necessarily. People survive massive overdoses by chance.

Yes, though, it does matter how you spread the doses and the dose regimen (how many and how often) is designed around making it work but stopping it killing you. You shouldn't double up doses of paracetamol to "make it work longer".

Interesting side note, alcohol use can lower the amount of damage your liver can take and so alcoholics should avoid paracetamol use.


Contents

Glutathione biosynthesis involves two adenosine triphosphate-dependent steps:

  • First, gamma-glutamylcysteine is synthesized from L-glutamate and cysteine. This conversion requires the enzyme glutamate–cysteine ligase (GCL, glutamate cysteine synthase). This reaction is the rate-limiting step in glutathione synthesis. [3]
  • Second, glycine is added to the C-terminal of gamma-glutamylcysteine. This condensation is catalyzed by glutathione synthetase.

While all animal cells are capable of synthesizing glutathione, glutathione synthesis in the liver has been shown to be essential. GCLC knockout mice die within a month of birth due to the absence of hepatic GSH synthesis. [4] [5]

The unusual gamma amide linkage in glutathione protects it from hydrolysis by peptidases. [6]

Occurrence Edit

Glutathione is the most abundant thiol in animal cells, ranging from 0.5 to 10 mM. It is present both in the cytosol and the organelles. [6]

Humans synthesize glutathione, but a few eukaryotes do not, including Fabaceae, Entamoeba, and Giardia. The only archaea that make glutathione are halobacteria. Some bacteria, such as cyanobacteria and proteobacteria, can biosynthesize glutathione. [7] [8]

Glutathione exists in reduced (GSH) and oxidized (GSSG) states. The ratio of reduced glutathione to oxidized glutathione within cells is a measure of cellular oxidative stress [9] [10] where increased GSSG-to-GSH ratio is indicative of greater oxidative stress. In healthy cells and tissue, more than 90% of the total glutathione pool is in the reduced form (GSH), with the remainder in the disulfide form (GSSG). [11]

In the reduced state, the thiol group of cysteinyl residue is a source of one reducing equivalent. Glutathione disulfide (GSSG) is thereby generated. The oxidized state is converted to the reduced state by NADPH. [12] This conversion is catalyzed by glutathione reductase:

NADPH + GSSG + H2O → 2 GSH + NADP + + OH −

Antioxidant Edit

GSH protects cells by neutralising (i.e., reducing) reactive oxygen species. [13] [6] This conversion is illustrated by the reduction of peroxides:

2 GSH + R2O2 → GSSG + 2 ROH (R = H, alkyl)

Regulation Edit

Aside from deactivating radicals and reactive oxidants, glutathione participates in thiol protection and redox regulation of cellular thiol proteins under oxidative stress by protein S-glutathionylation, a redox-regulated post-translational thiol modification. The general reaction involves formation of an unsymmetrical disulfide from the protectable protein (RSH) and GSH: [14]

Glutathione is also employed for the detoxification of methylglyoxal and formaldehyde, toxic metabolites produced under oxidative stress. This detoxification reaction is carried out by the glyoxalase system. Glyoxalase I (EC 4.4.1.5) catalyzes the conversion of methylglyoxal and reduced glutathione to S-D-lactoyl-glutathione. Glyoxalase II (EC 3.1.2.6) catalyzes the hydrolysis of S-D-lactoyl-glutathione to glutathione and D-lactic acid.

It maintains exogenous antioxidants such as vitamins C and E in their reduced (active) states. [15] [16] [17]

Metabolism Edit

Among the many metabolic processes in which it participates, glutathione is required for the biosynthesis of leukotrienes and prostaglandins. It plays a role in the storage of cysteine. Glutathione enhances the function of citrulline as part of the nitric oxide cycle. [18] It is a cofactor and acts on glutathione peroxidase. [19]

Conjugation Edit

Glutathione facilitates metabolism of xenobiotics. Glutathione S-transferase enzymes catalyze its conjugation to lipophilic xenobiotics, facilitating their excretion or further metabolism. [20] The conjugation process is illustrated by the metabolism of N-acetyl-p-benzoquinone imine (NAPQI). NAPQI is a reactive metabolite formed by the action of cytochrome P450 on paracetamol (acetaminophen). Glutathione conjugates to NAPQI, and the resulting ensemble is excreted.

Potential neurotransmitters Edit

Glutathione, along with oxidized glutathione (GSSG) and S-nitrosoglutathione (GSNO), bind to the glutamate recognition site of the NMDA and AMPA receptors (via their γ-glutamyl moieties). GSH and GSSG may be neuromodulators. [21] [22] [23] At millimolar concentrations, GSH and GSSG may also modulate the redox state of the NMDA receptor complex. [22] Glutathione binds and activates ionotropic receptors, potentially making it a neurotransmitter. [24]

GSH activates the purinergic P2X7 receptor from Müller glia, inducing acute calcium transient signals and GABA release from both retinal neurons and glial cells. [25] [26]

In plants Edit

In plants, glutathione is involved in stress management. It is a component of the glutathione-ascorbate cycle, a system that reduces poisonous hydrogen peroxide. [27] It is the precursor of phytochelatins, glutathione oligomers that chelate heavy metals such as cadmium. [28] Glutathione is required for efficient defence against plant pathogens such as Pseudomonas syringae and Phytophthora brassicae. [29] Adenylyl-sulfate reductase, an enzyme of the sulfur assimilation pathway, uses glutathione as an electron donor. Other enzymes using glutathione as a substrate are glutaredoxins. These small oxidoreductases are involved in flower development, salicylic acid, and plant defence signalling. [30]

Systemic bioavailability of orally consumed glutathione is poor because the tripeptide is the substrate of proteases (peptidases) of the alimentary canal, and due to the absence of a specific carrier of glutathione at the level of cell membrane. [31] [32] In another study, researchers reported long term glutathione supplementation offers protection from oxidative damage. In this study 500 mg oral GSH supplementation not only increased erythrocytic GSH but also decreased 8-OHdG significantly within three months in elderly (age above 55 years) diabetic individuals [33]

Because direct supplementation of glutathione is not successful, supply of the raw nutritional materials used to generate GSH, such as cysteine and glycine, may be more effective at increasing glutathione levels. Other antioxidants such as ascorbic acid (vitamin C) may also work synergistically with glutathione, preventing depletion of either. The glutathione-ascorbate cycle, which works to detoxify hydrogen peroxide (H2O2), is one very specific example of this phenomenon.

Oral supplementation with gamma-glutamylcysteine has been shown to effectively increase cellular glutathione levels. [34]

Additionally, compounds such as N-acetylcysteine [35] (NAC) and alpha lipoic acid [36] (ALA, not to be confused with the unrelated alpha-linolenic acid) are both capable of helping to regenerate glutathione levels. NAC in particular is commonly used to treat overdose of acetaminophen, a type of potentially fatal poisoning which is harmful in part due to severe depletion of glutathione levels. It is a precursor of cysteine.

Calcitriol (1,25-dihydroxyvitamin D3), the active metabolite of vitamin D3, after being synthesized from calcifediol in the kidney, increases glutathione levels in the brain and appears to be a catalyst for glutathione production. [37] About ten days are needed for the body to process vitamin D3 into calcitriol. [38]

S-adenosylmethionine (SAMe), a cosubstrate involved in methyl group transfer, has also been shown to increase cellular glutathione content in persons suffering from a disease-related glutathione deficiency. [39] [40] [41]

Low glutathione is commonly observed in wasting and negative nitrogen balance, as seen in cancer, HIV/AIDS, sepsis, trauma, burns, and athletic overtraining. Low levels are also observed in periods of starvation. These effects are hypothesized to be influenced by the higher glycolytic activity associated with cachexia, which result from reduced levels of oxidative phosphorylation. [42] [43]

Ellman's reagent and monobromobimane Edit

Reduced glutathione may be visualized using Ellman's reagent or bimane derivatives such as monobromobimane. The monobromobimane method is more sensitive. In this procedure, cells are lysed and thiols extracted using a HCl buffer. The thiols are then reduced with dithiothreitol and labelled by monobromobimane. Monobromobimane becomes fluorescent after binding to GSH. The thiols are then separated by HPLC and the fluorescence quantified with a fluorescence detector.

Monochlorobimane Edit

Using monochlorobimane, the quantification is done by confocal laser scanning microscopy after application of the dye to living cells. [44] This quantification process relies on measuring the rates of fluorescence changes and is limited to plant cells.

CMFDA has also been mistakenly used as a glutathione probe. Unlike monochlorobimane, whose fluorescence increases upon reacting with glutathione, the fluorescence increase of CMFDA is due to the hydrolysis of the acetate groups inside cells. Although CMFDA may react with glutathione in cells, the fluorescence increase does not reflect the reaction. Therefore, studies using CMFDA as a glutathione probe should be revisited and reinterpreted. [45] [46]

ThiolQuant Green Edit

The major limitation of these bimane-based probes and many other reported probes is that these probes are based on irreversible chemical reactions with glutathione, which renders these probes incapable of monitoring the real-time glutathione dynamics. Recently, the first reversible reaction based fluorescent probe-ThiolQuant Green (TQG)-for glutathione was reported. [47] ThiolQuant Green can not only perform high resolution measurements of glutathione levels in single cells using a confocal microscope, but also be applied in flow cytometry to perform bulk measurements.

RealThiol Edit

The RealThiol (RT) probe is a second-generation reversible reaction-based GSH probe. A few key features of RealThiol: 1) it has a much faster forward and backward reaction kinetics compared to ThiolQuant Green, which enables real-time monitoring of GSH dynamics in live cells 2) only micromolar to sub-micromolar RealThiol is needed for staining in cell-based experiments, which induces minimal perturbation to GSH level in cells 3) a high-quantum-yield coumarin fluorophore was implemented so that background noise can be minimized and 4) equilibrium constant of the reaction between RealThiol and GSH has been fine-tuned to respond to physiologically relevant concentration of GSH. [48] RealThiol can be used to perform measurements of glutathione levels in single cells using a high-resolution confocal microscope, as well as be applied in flow cytometry to perform bulk measurements in high throughput manner.

Organelle-targeted RT probe has also been developed. A mitochondria targeted version, MitoRT, was reported and demonstrated in monitoring the dynamic of mitochondrial glutathione both on confocoal microscope and FACS based analysis. [49]

Protein-based glutathione probes Edit

Another approach, which allows measurement of the glutathione redox potential at a high spatial and temporal resolution in living cells, is based on redox imaging using the redox-sensitive green fluorescent protein (roGFP) [50] or redox-sensitive yellow fluorescent protein (rxYFP). [51] Because its very low physiological concentration, GSSG is difficult to measure accurately. GSSG concentration ranges from 10 to 50 μM in all solid tissues, and from 2 to 5 μM in blood (13–33 nmol per gram Hb). GSH-to-GSSG ratio of whole cell extracts is estimated from 100 to 700. [52] Those ratios represent a mixture from the glutathione pools of different redox states from different subcellular compartments (e.g. more oxidized in the ER, more reduced in the mitochondrial matrix), however. In vivo GSH-to-GSSG ratios can be measured with subcellular accuracy using fluorescent protein-based redox sensors, which have revealed ratios from 50,000 to 500,000 in the cytosol, which implies that GSSG concentration is maintained in the pM range. [53]

Comprehensive reviews on the significance of glutathione in human disease have been published on a regular basis in peer reviewed medical journals. [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] Indisputable cause and effect links between GSH metabolism and diseases, such as diabetes, cystic fibrosis, cancer, neurodegenerative diseases, HIV and aging have been demonstrated. A variety of explanations as to why the depletion of GSH is linked to oxidative stress in these disease states have been proposed.

Cancer Edit

Once a tumor has been established, elevated levels of glutathione may act to protect cancerous cells by conferring resistance to chemotherapeutic drugs. [64] The antineoplastic mustard drug canfosfamide was modeled on the structure of glutathione.

Cystic fibrosis Edit

Several studies have been completed on the effectiveness of introducing inhaled glutathione to people with cystic fibrosis with mixed results. [65] [66]

Alzheimer's disease Edit

While extra Cellular amyloid beta (Aβ) plaques, neurofibrillary tangles (NFT), inflammation in the form of reactive astrocytes and microglia, and neuronal loss are all consistent pathological features of Alzheimer's disease (AD), a mechanistic link between these factors is yet to be clarified. Although the majority of past research has focused on fibrillar Aβ, soluble oligomeric Aβ species are now considered to be of major pathological importance in AD. Upregulation of GSH may be protective against the oxidative and neurotoxic effects of oligomeric Aβ. [ medical citation needed ]

Depletion of the closed form of GSH in the hippocampus may be a potential early diagnostic biomarker for AD. [67] [68]

Winemaking Edit

The content of glutathione in must, the first raw form of wine, determines the browning, or caramelizing effect, during the production of white wine by trapping the caffeoyltartaric acid quinones generated by enzymic oxidation as grape reaction product. [69] Its concentration in wine can be determined by UPLC-MRM mass spectrometry. [70]

Cosmetics Edit

Glutathione is the most common agent taken by mouth in an attempt to whiten the skin. [71] It may also be used as a cream. [71] Whether or not it actually works is unclear as of 2019. [72] Due to side effects that may result with intravenous use, the government of the Philippines recommends against such use. [73]


First study to reveal how paracetamol works could lead to less harmful pain relief medicines

Researchers at King's College London have discovered how one of the most common household painkillers works, which could pave the way for less harmful pain relief medications to be developed in the future

Researchers at King's College London have discovered how one of the most common household painkillers works, which could pave the way for less harmful pain relief medications to be developed in the future.

Paracetamol, often known in the US and Asia as acetaminophen, is a widely-used analgesic (painkiller) and the main ingredient in everyday medications such as cold and flu remedies. Although discovered in the 1890s and marketed as a painkiller since the 1950s, exactly how it relieves pain was unknown.

This study, funded by the UK Medical Research Council (MRC) and published online today in Nature Communications, shows for the first time the principal mechanism of action for one of the most-used drugs in the world.

The researchers from King's, with colleagues from Lund University in Sweden, have identified that a protein called TRPA1, found on the surface of nerve cells, is a key molecule needed for paracetamol to be an effective painkiller.

Dr David Andersson, from the Wolfson Centre for Age Related Diseases at King's, said: 'This is an extremely exciting finding, which unlocks the secrets of one of the most widely-used medicines, and one which could impact hugely on the development of new pain relief drugs.

'Paracetamol is the go-to medicine for treating common aches and pains, but if the recommended dose is significantly exceeded it can lead to fatal complications.

'So now we understand the underlying principal mechanism behind how this drug works, we can start to look for molecules that work in the same way to effectively relieve pain, but are less toxic and will not lead to serious complications following overdose.'

The team of researchers used a 'hot-plate' test to observe the effects of paracetamol in mice. This involved measuring the number of seconds it takes for a mouse to withdraw its paw from a slightly hot surface. They found that paracetamol increased the time it took for mice to withdraw their paw, showing that the drug reduced the heat-induced pain.

The scientists then carried out experiments to observe what happened when a protein called TRPA1 was not present at all in the mice. They found that when they removed the TRPA1 protein and repeated the hot-plate test, the paracetamol had no analgesic effect. This identifies the protein as a key molecule needed for paracetamol to be an effective painkiller.

However, paracetamol on its own does not activate the TRPA1 protein. The study showed that when paracetamol is administered, a break-down product called NAPQI is formed in the spinal cord (where 'painful' information is processed). This product is also formed in the liver and is responsible for the toxic side effects seen following overdoses.

Furthermore, they demonstrated that other compounds that, unlike NAPQI, are not toxic can activate TPRA1 in the spinal cord when injected into mice. Because these compounds are not reactive, they are less likely to be harmful.

Professor Stuart Bevan, co-author from King's, said: 'What we saw happening in the mice was that the break-down product formed from paracetamol in turn stimulates a protein found on the surface of nerve cells called TRPA1. When this protein was activated, it appeared to interfere with the transmission of information from that nerve cell to other nerve cells, which would normally send a signal up to the brain, signalling pain. So in this case the NAPQI product that was formed from paracetamol acted on the TRPA1 protein to reduce transmission of information from pain-sensing nerves to the brain.

'These results are surprising because previous studies have shown that TRPA1 can actually produce pain, coughs and hypersensitivities - it is the receptor for many common irritants like onion, mustard and tear gas. So our discovery shows for the first time that the opposite is in fact true - this protein is a novel mechanism of action for a painkiller.'

The researchers say that if they can identify other analgesic compounds similar to paracetamol that use the same TRPA1 pathway to prevent pain signals sent by nerve cells to the brain, it is possible that they can find a compound that does not have toxic effects and will reduce the risk of overdose.

Dr Andersson concludes: 'This study validates TRPA1 as a new target for pain relief drugs. Many targets have been identified in the past, but as paracetamol is a medicine that we know works well in humans, this gives us a head-start in looking for effective molecules that utilise the same pathways but are less harmful.'

CONTACT
Katherine Barnes
International Press Officer
King's College London
Tel: 44-207-848-3076
Email: [email protected]

About King's College London (http://www. kcl. ac. uk)

King's College London is one of the top 30 universities in the world (2011/12 QS World University Rankings), and the fourth oldest in England. A research-led university based in the heart of London, King's has nearly 23,500 students (of whom more than 9,000 are graduate students) from nearly 140 countries, and some 6,000 employees. King's is in the second phase of a £1 billion redevelopment programme which is transforming its estate.

King's has an outstanding reputation for providing world-class teaching and cutting-edge research. In the 2008 Research Assessment Exercise for British universities, 23 departments were ranked in the top quartile of British universities over half of our academic staff work in departments that are in the top 10 per cent in the UK in their field and can thus be classed as world leading. The College is in the top seven UK universities for research earnings and has an overall annual income of nearly £450 million.

King's has a particularly distinguished reputation in the humanities, law, the sciences (including a wide range of health areas such as psychiatry, medicine, nursing and dentistry) and social sciences including international affairs. It has played a major role in many of the advances that have shaped modern life, such as the discovery of the structure of DNA and research that led to the development of radio, television, mobile phones and radar. It is the largest centre for the education of healthcare professionals in Europe no university has more Medical Research Council Centres.

King's College London and Guy's and St Thomas', King's College Hospital and South London and Maudsley NHS Foundation Trusts are part of King's Health Partners. King's Health Partners Academic Health Sciences Centre (AHSC) is a pioneering global collaboration between one of the world's leading research-led universities and three of London's most successful NHS Foundation Trusts, including leading teaching hospitals and comprehensive mental health services. For more information, visit: http://www. kingshealthpartners. org.

King's College London is one of the top 30 universities in the world (2011/12 QS international world rankings), and was The Sunday Times 'University of the Year 2010/11', and the fourth oldest in England. A research-led university based in the heart of London, King's has nearly 23,500 students (of whom more than 9,000 are graduate students) from nearly 140 countries, and some 6,000 employees. King's is in the second phase of a £1 billion redevelopment programme which is transforming its estate.

King's has an outstanding reputation for providing world-class teaching and cutting-edge research. In the 2008 Research Assessment Exercise for British universities, 23 departments were ranked in the top quartile of British universities over half of our academic staff work in departments that are in the top 10 per cent in the UK in their field and can thus be classed as world leading. The College is in the top seven UK universities for research earnings and has an overall annual income of nearly £450 million.

King's has a particularly distinguished reputation in the humanities, law, the sciences (including a wide range of health areas such as psychiatry, medicine, nursing and dentistry) and social sciences including international affairs. It has played a major role in many of the advances that have shaped modern life, such as the discovery of the structure of DNA and research that led to the development of radio, television, mobile phones and radar. It is the largest centre for the education of healthcare professionals in Europe no university has more Medical Research Council Centres.

King's College London and Guy's and St Thomas', King's College Hospital and South London and Maudsley NHS Foundation Trusts are part of King's Health Partners. King's Health Partners Academic Health Sciences Centre (AHSC) is a pioneering global collaboration between one of the world's leading research-led universities and three of London's most successful NHS Foundation Trusts, including leading teaching hospitals and comprehensive mental health services. For more information, visit: http://www. kingshealthpartners. org.

The College is in the midst of a five-year, £500 million fundraising campaign - World questions|King's answers - created to address some of the most pressing challenges facing humanity as quickly as feasible. The campaign's three priority areas are neuroscience and mental health, leadership and society, and cancer. More information about the campaign is available at http://www. kcl. ac. uk/ kingsanswers.

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


Acetaminophen

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Acetaminophen, also called paracetamol, drug used in the treatment of mild pain, such as headache and pain in joints and muscles, and to reduce fever. Acetaminophen is the major metabolite of acetanilid and phenacetin, which were once commonly used drugs, and is responsible for their analgesic (pain-relieving) effects. Acetaminophen relieves pain by raising the body’s pain threshold, and it reduces fever by its action on the temperature-regulating centre of the brain. The drug inhibits prostaglandin synthesis in the central nervous system, but it lacks an anti-inflammatory effect in peripheral nerves.

Acetaminophen is much less likely to cause gastrointestinal side effects than aspirin, but overdoses of it can cause fatal liver damage. For prolonged use, aspirin is considered safer. Acetaminophen has also been implicated as a hormone disruptor, with prenatal exposure to the drug possibly linked to hyperkinetic and behavioral disorders in children. Research has also linked acetaminophen use to alterations in risk perception and decision making and increased risk-taking behaviour.

The drug is marketed under several trade names, including Tylenol, Tempra, and Panadol.

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Kara Rogers, Senior Editor.


Paracetamol (acetaminophen)

The equilibrium position lies very far to the left.
The vast majority of paracetamol molecules in an aqueous solution will be found as the undissociated paracetamol molecules.

At 25 o C, paracetamol (acetaminophen) has a 3 Ka = 3.09 x 10 -10

Solubility

solvent cold water hot water ethanol The difference in the solubility of paracetamol (acetaminophen) in water of different temperatures can be used to separate paracetamol (acetaminophen) from commercially available panadol® or tylenol® as described below.
solubility (g/100 mL) 1.43 5 14

Procedure to determine the paracetamol (acetaminophen) content in commercially available tablets:

Wear eye protection (safety glasses or goggles).

It is possible to buy fizzy paracetamol tablets.
In these tablets the paracetamol has been mixed with citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) and sodium hydrogencarbonate (sodium bicarbonate).
When placed in water, the citric acid and sodium hydrogencarbonate in the tablet react to produce bubbles of carbon dioxide.
The bubbles of carbon dioxide gas help break the tablet up into smaller pieces that are easier to swallow.

Synthesis of Paracetamol (acetaminophen)

Step 1:nitration of phenol

Phenol (hydroxybenzene) will react with sodium nitrate (an oxidizing agent) in the presence of sulfuric acid to produce a mixture of structural isomers of nitrophenol.

H2SO4
&rarr
NaNO3(aq)
+
phenol
(hydroxybenzene)
4-nitrophenol
( p -nitrophenol)
25% yield
2-nitrophenol
( o -nitrophenol)
36% yield

When concentrated sulfuric acid (H2SO4) is added to sodium nitrate (NaNO3) the following reaction occurs:

Then, in excess sulfuric acid, reactive nitronium ion, NO2 + , is produced:

The nitronium ion, NO2 + , attacks the benzene ring of phenol to produce a mixture of various structural isomers of nitrophenol.

The OH (hydroxyl) functional group of phenol (hydroxybenzene) is said to activate the benzene ring at the 2- and 4- positions. This results in the formation of 2-nitrophenol and 4-nitrophenol.
The 3- and 5- positions of the benzene ring are not activated so 3-nitrophenol and 5-nitrophenol are NOT produced.

4-nitrophenol can be separated from the mixture containing 2-nitrophenol:

Step 2: reduction of a nitro group to an amine

In carbon chemistry (organic chemistry) a reduction reaction has occurred if 4 :

In the reaction shown below, oxygen is lost from the nitro group of 4-nitrophenol and hydrogen is added to form 4-aminophenol, so the reaction is a reduction reaction:

In the laboratory: Industrial preparation:
NaBH4
&rarr
Pd/1 M NaOH
H2
&rarr
Pt catalyst
4-nitrophenol 4-aminophenol
74% yield
4-nitrophenol 4-aminophenol

A catalyst such as palladium in the laboratory reaction, or platinum in the industrial reaction, is required to provide a surface for the reaction to take place on.
The 4-nitrophenol molecules are held to the surface of the catalyst by weak forces of attraction, which then weakens the strong covalent bonds in the nitro group making it vulnerable to attack by hydrogen.

Step 3: formation of an amide

With the exception of tertiary amines, amines undergo reaction with anhydrides to produce amides.

4-aminophenol, an amine, suspended in water at room temperature readily reacts with ethanoic anhydride (acetic anhydride) to produce a precipitate of the amide paracetamol (acetaminophen) as shown below:

Reactions of Paracetamol (acetaminophen)

Acid Hydrolysis

Hydrolysis (reaction with water) of amides in acidic solution produces an amine and a carboxylic acid.

Hydrolysis of paracetamol (acetaminophen) in acidic solution produces an amine (4-aminophenol) and a carboxylic acid (acetic acid)

1 Paracetamol was marketed as Panadol by Sterling-Winthrop Co in 1953 in the UK.

2 Paracetamol was marketed as Tylenol by McNeil Laboratories in 1955 in the USA.

4 This is only a general 'rule of thumb' but it is useful because it can be difficult to determine whether a carbon atom has 'gained' or 'lost' electrons.


First study to reveal how paracetamol works could lead to less harmful pain relief medicines

Researchers at King's College London have discovered how one of the most common household painkillers works, which could pave the way for less harmful pain relief medications to be developed in the future.

Paracetamol is a widely-used analgesic (painkiller) and the main ingredient in everyday medications such as cold and flu remedies. Although discovered in the 1890s and marketed as a painkiller since the 1950s, exactly how it relieves pain was unknown.

This study, funded by the Medical Research Council (MRC) and recently published in Nature Communications, shows for the first time the principal mechanism of action for one of the most-used drugs in the world.

A research team at King's led by Professor Stuart Bevan, with colleagues from Lund University in Sweden, have identified that a protein called TRPA1, found on the surface of nerve cells, is a key molecule needed for paracetamol to be an effective painkiller.

Dr David Andersson, from the Wolfson Centre for Age Related Diseases at King's, said: 'This is an extremely exciting finding, which unlocks the secrets of one of the most widely-used medicines, and one which could impact hugely on the development of new pain relief drugs.

'Paracetamol is the go-to medicine for treating common aches and pains, but if the recommended dose is significantly exceeded it can lead to fatal complications.

'So now we understand the underlying principal mechanism behind how this drug works, we can start to look for molecules that work in the same way to effectively relieve pain, but are less toxic and will not lead to serious complications following overdose.'

The team of researchers used a 'hot-plate' test to observe the effects of paracetamol in mice. This involved measuring the number of seconds it takes for a mouse to withdraw its paw from a slightly hot surface. They found that paracetamol increased the time it took for mice to withdraw their paw, showing that the drug reduced the heat-induced pain.

The scientists then carried out experiments to observe what happened when a protein called TRPA1 was not present at all in the mice. They found that when they removed the TRPA1 protein and repeated the hot-plate test, the paracetamol had no analgesic effect. This identifies the protein as a key molecule needed for paracetamol to be an effective painkiller.

However, paracetamol on its own does not activate the TRPA1 protein. The study showed that when paracetamol is administered, a break-down product called NAPQI is formed in the spinal cord (where 'painful' information is processed). This product is also formed in the liver and is responsible for the toxic side effects seen following overdoses.

Furthermore, they demonstrated that other compounds that, unlike NAPQI, are not toxic can activate TPRA1 in the spinal cord when injected into mice. Because these compounds are not reactive, they are less likely to be harmful.

Professor Bevan, co-author from King's, said: 'What we saw happening in the mice was that the break-down product formed from paracetamol in turn stimulates a protein found on the surface of nerve cells called TRPA1. When this protein was activated, it appeared to interfere with the transmission of information from that nerve cell to other nerve cells, which would normally send a signal up to the brain, signalling pain. So in this case the NAPQI product that was formed from paracetamol acted on the TRPA1 protein to reduce transmission of information from pain-sensing nerves to the brain.

'These results are surprising because previous studies have shown that TRPA1 can actually produce pain, coughs and hypersensitivities -- it is the receptor for many common irritants like onion, mustard and tear gas. So our discovery shows for the first time that the opposite is in fact true -- this protein is a novel mechanism of action for a painkiller.'

The researchers say that if they can identify other analgesic compounds similar to paracetamol that use the same TRPA1 pathway to prevent pain signals sent by nerve cells to the brain, it is possible that they can find a compound that does not have toxic effects and will reduce the risk of overdose.

Dr Andersson concludes: 'This study validates TRPA1 as a new target for pain relief drugs. Many targets have been identified in the past, but as paracetamol is a medicine that we know works well in humans, this gives us a head-start in looking for effective molecules that utilise the same pathways but are less harmful.'


Summary

Paracetamol is a useful medicine. Its benefits as an analgesic and antipyretic are widely known but it should be used with caution and an appreciation of its mechanism of action. It works optimally when the right dose is given by the right route. As with all medicines, adverse effects can (and do) occur as a result of poor prescribing and following accidental or purposeful ingestion. There may be longer term effects on general health that should not be overlooked—and it certainly should not be simply ‘prescribed routinely’ to all children admitted to hospital or given indiscriminately to all children who are febrile.

Test your knowledge

Which of the following conditions is most likely to result in oral paracetamol being ineffective?