Acute Redox Effects of Butyrate or Propionate in Mitochondria: Stimulation of the Glycine Cleavage System, etc.

This is a really great article [Hampson et al., 1984a: (http://www.ncbi.nlm.nih.gov/pubmed/6498157)], and the authors discuss a lot of things that are not directly related to the glycine cleavage system (GCS). The authors note that butyrate, propionate, or acetate stimulated the overall activity of the GCS multienzyme complex by, in preparations of mitochondria, causing an increase in ATP consumption, as a result of the formation of acyl-CoA thioesters, and thereby decreasing the intramitochondrial NADH/NAD+ ratio. The authors noted that the ATP-depleting effect of the acyl-CoA synthetase reaction in the intact cells of the intact liver had previously been found to be much less pronounced than the effect in mitochondria alone [Hampson et al., 1984b: (http://www.jbc.org/cgi/reprint/259/2/1180.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/6420402)], evidently because intact cells have a supply of glucose and other energy substrates. This article seems strange at first glance, because most of the research has shown that short-chain acyl-CoA's, such as propionyl-CoA, inhibit different enzymes of the GCS [one of many: Hayasaka et al., 1983: (http://www.ncbi.nlm.nih.gov/pubmed/6679320)]. But the initial effects of butyrate and propionate and other free organic anions can be different. The stimulation was not due to an action of propionyl-CoA, because Hampson et al. (1984) added L-carnitine and found a decrease in the levels of propionyl-CoA, formed in response to the exogenous propionate, but not an attenuation of the effect of propionate on the intramitochondrial redox potential.

The way Hampson et al. (1984) present the data on the redox state is potentially confusing, because they keep referring to the transhydrogenase equilibrium. The transhydrogenase enzyme is in the inner mitochondrial membrane and essentially, based on my somewhat limited knowledge of it, serves to buffer changes in the intramitochondrial pyridine (NAD+ based) nucleotide redox couples. The authors discuss the fact that the energy-linked equilibrium constant for the transhydrogenase enzymatic reaction:

NADH + NADP+ <---> NAD+ + NADPH

can be 500, but the Keq can be near 1 in the absence of a proton gradient, such as in response to the presence of an uncoupler. The authors said that propionate had appeared, at first glance, to behave like an uncoupler in the isolated mitochondria but that it had probably just decreased the intramitochondrial NADH/NAD+ ratio via the acyl-CoA-synthetase-dependent consumption of ATP, in the formation of propionyl-CoA. The authors noted that similar experiments had shown the oxygen to be depleted from the media containing isolated mitochondria, in response to propionate. There's similar research in humans that shows that beta-hydroxybutyrate (BHB), a ketone, can increase the oxygen uptake into cells and produce a transient thermal effect, when researchers administer it intravenously [Chiolero et al., 1993: (http://www.ajcn.org/cgi/reprint/58/5/608.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/8237864)]. That effect essentially balances out the acute increase in urinary bicarbonate excretion that evidently results from the oxidation of BHB. Ketone oxidation, even in the absence of ketoacidosis, tends to produce low-level, extracellular acidosis, but the effect can be opposed by the increase in oxygen consumption in response to the oxidation of ketones.

Incidentally, Vamecq et al. (2005) [Vamecq et al., 2005: (http://www.ncbi.nlm.nih.gov/pubmed/15713528)] also discussed the possibility that the formation of acyl-CoA thioesters, in response to a large influx of ketones (similar to the apparent effect of a large influx of propionate or butyrate), could conceivably produce transient ATP depletion. Vamecq et al. (2005) focused a bit too much on the idea that ketones produce anticonvulsant effects by causing mild ATP depletion. Most research has shown the opposite effect, in my view, although I think they make a valid point, to some extent. At very high levels, ketones, upon their metabolism into acetyl-CoA or long-chain acyl-CoA's, will tend to inhibit TCA cycle enzymes by leading to the accumulation of acyl-CoA's. But at lower dosages or levels, the oxidation, in the presence of other substrates, will tend to increase ATP production, in my opinion. But Hampson and colleagues also did some interesting experiments with different combinations of alpha-ketoglutarate and other TCA cycle intermediates and found, from what I can tell, that the additions of excesses of single TCA cycle intermediates produced the opposite effect on the intramitochondrial redox potential and inhibited the stimulatory effects of butyrate and propionate on the overall activity of the GCS. I don't have time to get into this, but it's relevant to anaplerosis and energy metabolism. This and the related articles from 1984 and 1983, by that group (Hampson et al.), have a lot of information that's very relevant to the study of energy metabolism and the ketogenic diet, etc. A lot of these older articles on energy metabolism are really terrific and filled with insights that everyone's forgotten about.

These articles are relevant to the use of sodium butyrate for various purposes, some of which I've discussed in past postings. These types of effects would be another reason, in my opinion, to start at lower dosages of sodium butyrate and not increase to massive dosages, etc. For example, there's research using 4 grams/day of sodium butyrate to treat ulcerative colitis. They've used much higher dosages of arginine butyrate, mainly given intravenously, to treat sickle cell disease, etc. Incidentally, the use of some calcium salts of butyrate could be more problematic than the use of sodium butyrate, in my opinion. Also, some manufacturers are using enteric-coated tablets to administer butyrate, and that's a major mistake, in my opinion. Enteric-coated tablets tend to be quite problematic, in my opinion, and manufacturers seem to be, in many cases, incapable of manufacturing them properly. That's just my opinion, but, in my eyes, it's an intractable problem that people just seem to be incapable of addressing. I've discussed that issue, at length, in past postings.

Incidentally, one approach would be to use small amounts of pantothenic acid (i.e. 100-200 mg/d or something) to partially compensate for any supposed increase in the fatty acyl-CoA/CoA ratio, in response to sodium butyrate, but I don't know how effective that would be. The point of those articles is that pantothenic acid could, by providing more coenzyme A, simply amplify the mild and transient ATP depletion that butyrate could produce. In my opinion (and much as the authors of the first article state), butyrate doesn't appear to behave like something that produces much ATP depletion, even transiently. It behaves like an energy substrate, in my opinion. But the effect of 4 grams/d may be quite different from the effects of higher dosages, both because of the acute effect of butyryl-CoA formation and because of the effects of butyryl-CoA (or longer-chain acyl-CoA's formed from butyrate) on mitochondrial enzymes.

This is also relevant to some research that supposedly rules out or discounts the roles of methylmalonic acid and propionyl-CoA accumulation in subacute combined degeneration and other neuropathic effects of vitamin B12 deficiency. In some of that research, which is summarized in an annual review of nutrition article [Metz, 1992: (http://www.ncbi.nlm.nih.gov/pubmed/1354465)], researchers apparently found that propionate or isoleucine administration or both (I forget the details, and I can't look it up right now) didn't acutely worsen the neurological dysfunction in animals with chronic B12 deficiency. I think some of the conclusions based on that research may have been erroneous, though, because the acute effects of the free organic anions [organic anions, or "ketoacids" (branched-chain fatty acids), formed from isoleucine, for example, could be quite different from the "intermediate-term" effects of the extra 2-methylbutyryl-CoA (formed from isoleucine) or from other acyl-CoA's that could accumulate after the prolonged administration of organic anions.

Notes on HMB; Leucine as a Supposedly-Ketogenic Amino Acid

This article [Kuhara et al., 1982: (http://www.ncbi.nlm.nih.gov/pubmed/7116632)] describes leucine as being a "potent ketogenic amino acid," and I guess there can be a significant contribution of leucine-derived branched chain organic acids, such as HMB/3-hydroxyisovalerate, to ketogenesis. About 5 percent of leucine normally is converted into HMB, apparently. The only other thing I thought of is that the slight elevation in plasma branched-chain amino acids (Holocek et al., 2009) [Holecek et al., 2009: (http://www.ncbi.nlm.nih.gov/pubmed/19056452)] might conceivably produce tryptophan (TRP) and tyrosine (TYR) and phenylalanine (PHE) depletion from the brain, in my opinion, but it looks like the effect is probably not even as pronounced as the increase in the plasma BCAA (leucine+isoleucine+valine)/(TYR+TRP+PHE) ratio from a high-protein meal. In dietary protein, 20-30 percent of the amino acids are BCAA's, if memory serves, and this causes the plasma BCAA/(TYR+TRP+PHE) ratio to increase progressively as the dietary protein intake increases [Fernstrom et al., 1979: (http://www.ajcn.org/cgi/reprint/32/9/1912.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/573061)]. There's the potential that that effect, to the extent that it could occur in response to the mild, apparent "leucine-sparing" effect of HMB (Holocek et al., 2009), could, in my opinion, produce transient worsening of mood or other psychiatric complications in people. Although some of those trials with HMB suggest that the opposite effect would occur, I can't really put a lot of faith in some of these articles on the effects of BCAAs on the brain. They're used as neuroprotectives and as a treatment for mania (leucine and other BCAAs), and I doubt HMB would have the same effects. It's not an amino acid and wouldn't be expected to compete with tyrosine, tryptophan, and phenylalanine for entry into the brain. But I can't be sure about that, and it's obviously something a person would want to discuss with one's doctor. It's possible that the supposed neuroprotective effects of leucine and BCAAs, as in spinocerebellar degeneration, etc., are not mediated by glutamine or 2-oxoglutarate sparing or whatever mechanism has been suggested but are the result of a ketogenic effect of leucine in astrocytes (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=BCAA+spinocerebellar). The authors of those BCAA-as-neuroprotective articles view the BCAAs as being energy substrates or as being capable of decreasing glutamate, though, I think. I don't know what the proposed mechanisms are, besides those mechanisms. HMB can also act as a precursor of fatty acids and could conceivably cause problems in people with liver disease, but those old articles show that it's, evidently, preferentially incorporated into cholesterol. I discussed the BCAA issues in a past posting (http://hardcorephysiologyfun.blogspot.com/2009/02/potential-psychiatric-pitfalls-in.html).