The research on the therapeutic use of pyruvate is actually voluminous, but the articles are sort of hidden in plain sight (one has to search for "ethyl pyruvate," which is essentially a pyruvate prodrug, or for "sodium pyruvate" or "calcium pyruvate," which are the commonly-used salts of pyruvate: http://scholar.google.com/scholar?as_q=&num=100&btnG=Search+Scholar&as_epq=&as_oq=++sodium-pyruvate+calcium-pyruvate+ethyl-pyruvate&as_eq=hydrogenation+enantioselective&as_occt=any&as_sauthors=&as_publication=&as_ylo=&as_yhi=&as_allsubj=all&hl=en&lr=).
The end of that url should include an "=" sign, and I don't know if the link will work without it. But ethyl pyruvate is just the ethyl ester of pyruvate and is more stable in solution than pyruvate itself. The ethyl group is just cleaved by nonspecific esterase enzymes, as far as I understand it, evidently either in the gastrointestinal tract or in cells in the target tissues. A lot of the research is being done on the uses of ethyl pyruvate in acute inflammatory states, apparently, or situations of acute trauma to organs. But that doesn't mean pyruvate is just an "anti-inflammatory" drug, etc. Here are some articles evaluating the neuroprotective effects of pyruvate (from ethyl pyruvate):
(http://scholar.google.com/scholar?num=100&hl=en&q=ischemia+sodium-pyruvate+OR+calcium-pyruvate+OR+ethyl-pyruvate&spell=1). In my opinion, something like pyruvate (from ethyl pyruvate, which could be used at higher dosages without overloading the body with calcium or sodium, as Brunengraber and Roe (2006) (http://hardcorephysiologyfun.blogspot.com/2009/02/anaplerotic-compounds-free-form-glycine.html) noted.
One thing that is worth noting is that pyruvate, from calcium pyruvate, for example, can degrade to parapyruvate in a water solution. The authors of some of the articles about ethyl pyruvate mention that, and parapyruvate can evidently cause problems. One would probably not, in my opinion, want to "store" pyruvate in solution for a long time or make some sports drink with pyruvate in it. I say that because some people who are serious athletes do that, and some coaches or other people suggest that people make these dilute solutions of sugar in water and drink them during exercise, etc. (like home-made sports drinks with low concentrations of sugars). But I looked at the articles showing the lability of pyruvate, and they're almost unintelligible. It is the case that pyruvate is volatile in solution, but I don't know how long it would take to degrade. Those old articles, from the 1960s...I just can't tell what time frame they're talking about, but the use of sodium pyruvate in mitochondrial disorders [Tanaka et al., 2007: (http://www.orifund.org/doc/treatment.pdf) (http://www.ncbi.nlm.nih.gov/pubmed/17881297)] would suggest, in my opinion, that pyruvate is stable enough to survive the few minutes, in solution, before its absorption. My guess is that the degradation would only become significant after many minutes to hours, but that's just my guess. Haas et al. (2007) did note that testing the blood for pyruvate requires a blood sample to be treated with 8 percent perchlorate and put in an ice bath and then tested "rapidly" for the concentration of pyruvate that's in the sample [Haas et al., 2007: (http://pediatrics.aappublications.org/cgi/reprint/120/6/1326.pdf) (http://www.ncbi.nlm.nih.gov/pubmed/18055683)].
That article by Tanaka et al. (2007) is actually really good. It's a short communication but discusses some of the mechanisms, such as an increase in the NAD+/NADH ratio in the liver (presumably intramitochondrially), in response to exogenous pyruvate. The authors also note that surprisingly low doses of pyruvate have benefited some people with mitochondrial disorders, and the authors are evidently planning a multicenter trial to test sodium pyruvate in the treatment of people who have mitochondrial disorders.
Even though pyruvate looks useful, there could be some kind of theoretical concern, in my opinion, with elevation of plasma or intracellular alanine levels, in the sense that exogenous alanine was found to decrease creatine biosynthesis in humans [Crim et al., 1976: (http://jn.nutrition.org/cgi/reprint/106/3/371.pdf)]. Haas et al. (2007) noted that elevations in plasma alanine can be an indication that pyruvate levels have been elevated for a prolonged period of time [even in the context of an elevated lactate/pyruvate ratio that occurs in the context of an elevation in the absolute lactate and pyruvate levels (i.e. both [lactate+pyruvate] and [lactate]/[pyruvate] are elevated over controls, etc.)]. Pyruvate can be transaminated to alanine, as far as I know, but I don't know if alanine would actually accumulate during the conditions under which pyruvate would be administered therapeutically. Fritsche et al. (1999) [Fritsche et al., 1999: (http://www.jbc.org/cgi/reprint/274/5/3026) (http://www.ncbi.nlm.nih.gov/pubmed/9915841?dopt=Abstract)] showed that L-alanine can inhibit arginine:glycine amidinotransferase (the first enzyme of creatine biosynthesis), but I doubt that effect would occur in the short term. That's just my opinion, and there would probably be some way of preventing it. I'm not sure that alanine would even be elevated in people taking pyruvate, but, in my opinion, it's conceivable that alanine could become elevated in response to very large doses of pyruvate or pyruvate prodrugs. It's the only theoretical concern I can think of, but I'm not sure it would even occur.
Pyruvate and ethyl pyruvate have very distinct pharmacological effects. Numerous publications support this view. Ethyl pyruvate's pharmacological effects may be mediated by inhibition of the enzyme, glyoxalase-1, which is responsible for detoxifying the glycolytic side product, methylglyoxal. Or, ethyl pyruvate may exert pharmacological effects by covalently modifying a critical cysteine residue in the p65 component of the transcription factor, NF-kappaB. These two potential mechanisms are not mutually exclusive. Both pyruvate and ethyl pyruvate are good hydrogen peroxide scavengers, but being more lipohilic, ethyl pyruvate may be transported into cells more readily.
ReplyDeleteAlong similar lines, pyruvate anion does not induce insulin secretion by pancreatic islet cells. But, methyl pyruvate (another simple pyruvate ester) is a very potent insulin secretagogue.
Thanks--that's interesting. Do significant amount of ethyl or methyl pyruvate reach different cell types intact, before they've been hydrolyzed, and then exert cell-type specific effects that depend on the content of different esterase enzymes in the different cell types, etc.? They used to say or imply that the acetyl groups of 2',3',5'-tri-O-acetyluridine (PN401/RG2133) were mainly removed in the intestinal tract or liver, etc., but maybe that wasn't always true. I think one of those pharmaceutical companies has tested an acyluridine compound that's more lipophilic, too, but, for some reason, I didn't think to consider the lipophilicity of ethyl pyruvate as being a factor. That's interesting.
ReplyDeleteThe calculated logP for pyruvate anion is about -3.5, whereas the calculated logP for ethyl pyruvate is about 0.1 (more positive numbers indicate greater lipophilicity).
ReplyDeletePyruvate is transported into cells via the monocarboxylate transporter system, which normally functions in the other direction to transport lactate out of cells.
Presumably, ethyl pyruvate and methyl pyruvate enter cells by passive diffusion across the membrane. Published data from studies of insulin secretion by islets suggest that much greater permeation into beta cells is the basis for methyl pyruvate being an insulin secretatgogue, whereas pyruvate anion is not.
Similarly, published data from high-field NMR studies of neonatal rat brain slices suggest that ethyl pyruvate is much more neuroprotective than pyruvate even the metabolic fate of both compounds in the cells is the same. Again, greater permeability is thought to be the mechanism.
The fate of ethyl pyruvate in vivo is not known. However, in some studies, the effective dose of ethyl pyruvate for neuroprotection is about 40 mg/kg (~0.3 mMole/kg). In contrast, in some published studies of sodium pyruvate as a neuroprotective agent, there has been no positive treatment effect. In other published studies, neuroprotection was observed with sodium pyruvate, but the effective dose was 500 mg/kg (~4 mMole/kg). Huge difference.
That's interesting. I seem to remember reading that pyruvate also causes nausea and other side effects, and maybe something about its weak basicity causes that. One of those articles on (alpha-ketoglutarate)(2-) showed nausea and vomiting in people at really low doses--like 3-4 grams per day or something. That would limit its usefulness as a neuroprotective. Those types of things tend to be big problems, in a lot of cases. People were talking about something similar with arginine hydrochloride (which is neutral) vs. free-form L-arginine (which is an anion). Those mechanisms of neuroprotection are interesting. Pyruvate seems to have a really interesting effect on the redox state, and, to some extent, it seems to have the opposite effect that a lot of these other physiological activators of glycolysis have. Ribose-5-phosphate, from nucleotides or ribose, elevates the NADH/NAD+ ratio in the cytosol, and that article by Tanaka et al. (2007) is saying that pyruvate has the opposite effect but still activates glycolysis. That reducing effect that can occur with ribose and even glutamine is not, in my view, necessarily good. Also, I don't see how pyruvate could cause any of the problems with redox cycling that something like coenzyme Q10 causes. That Tanaka article also talks about activation of the pyruvate dehydrogenase complex by pyruvate, via inhibition of pyruvate dehydrogenase kinases 1-4, in the pyruvate dehydrogenase complex, without the peripheral neuropathy that dichloroacetate can cause. They used to use dichloroacetate in mitochondrial disorders and encephalopathies, but I guess the peripheral neuropathy must have showed up a lot. That's interesting about the directionality of the monocarboxylate transporter. I wonder if someone could use esters of alpha-ketoglutarate or some other TCA cycle intermediates in combination with ethyl pyruvate or something, to potentiate its effects. There's this article showing neuroprotective effects of alpha-ketoglutarate or pyruvate in cultured neurons or astrocytes [Ying et al., 2002: (http://www.ncbi.nlm.nih.gov/pubmed/12142562)].
ReplyDelete