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.

The "Liberalized Ketogenic Diet," Insulin Sensitivity, Resistance Exercise

The authors of this article [Pfeifer and Thiele, 2005: (http://www.direct-ms.org/pdf/NutritionNonAuto/KetogenicDietModifiedEpilepsy.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/16344529)] used a liberalized ketogenic diet in people who had epilepsy, and this essentially meant that the people ate low glycemic index carbohydrates instead of no carbohydrates at all. A food with a low glycemic index is one that doesn't create a spike in plasma glucose and therefore does not cause a lot of insulin to be released. The glycemic index (GI) is the ratio of the area under the plasma glucose vs. time curve for the food in question (a bowl of a specific cereal, for example) [AUC(food)] to the AUC of pure glucose, times 100. So it's AUC(food)/AUC(glucose), and pure glucose has a GI of 100. The concept has been applied to the management of the diets of people who have diabetes, but there's research showing that it may be more important to keep the size of a meal small than to eat big meals with low GI foods. So a person who ate a giant meal of the best quality bread, with a low-GI, the amount of insulin released over the period following the meal (and hence the suppressive effect on ketone formation in the liver or in astrocytes, in theory at least) might well be larger than if a person ate a small meal of candy or something. I don't know the details on the amounts of carbohydrates used in that study, and so this is obviously something a person would want to discuss with one's doctor.

I'm mentioning this because it's relevant to other supposed applications of the "ketogenic diet," and the effect of the use of low GI foods, in combination with the use of low doses of some sort of ketogenic supplement (such as HMB or sodium butyrate, which doesn't provide a lot of calcium and phosphate, added to supposedly compensate for the phosphate-sequestering effect, in the GI tract, of a calcium salt of an organic anion), would be similar to the use of those low-doses of ketogenic substrates with resistance exercise, in my opinion. I'm just saying that resistance exercise generally has, in my opinion, a much stronger insulin-sensitizing effect than endurance exercise, and that's the idea behind this type of modified ketogenic diet. The idea is to increase insulin sensitivity, but it's also relevant that the growth hormone release and elevations of serum IGF-1 (or even IGF-1 released locally from satellite cells, in the muscles) are known to contribute to ketogenesis [so is epinephrine (adrenaline), released much more during resistance exercise than aerobic exercise] [(http://scholar.google.com/scholar?num=100&hl=en&lr=&q=ketogenesis+%22growth+hormone%22+OR+IGF); (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=epinephrine+ketogenesis)]. Doing that type of exercise may or may not be practical for everyone, and a person would obviously want to talk to one's doctor before starting an exercise program. But the other implication of that article is that some factors that improve insulin sensitivity could, under some circumstances, produce "beneficial" effects by increasing ketogenesis and not just by maintaining low plasma glucose and insulin levels, etc.

Neuroprotective and Supposed Antidepressant-Like Effects of Sodium Butyrate: Relevance to HMB Research and Energy Metabolism

A lot of these articles showing that butyrate (usually administered or used in vitro as sodium butyrate, or SB), a short-chain fatty acid similar in structure to HMB (3-hydroxy-3-methylbutyrate or 3-hydroxyisovalerate, discussed in the two previous postings), reduces the degradation of numerous proteins by proteasomes are relevant to research on HMB. There are many similarities among the effects of butyrate and HMB. HMB is thought to exert its anticatabolic effects by inhibiting proteasomal activity (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=proteasome+methylbutyrate+OR+%223-hydroxyisovalerate%22) and also by acting as a precursor of HMG-CoA and of cholesterol. The extent to which an HMB-induced increase in cholesterol formation contributes to the HMB-induced inhibition of proteasomal activity is unknown. SB is a nonselective inhibitor of histone deacetylase enzymes in vitro, and its histone deacetylase inhibitory effect, at least in vitro, is thought to contribute to its inhibition of TNF-alpha-induced NFkappaB (NFkB) transcription factor [a.k.a. the "Rel" family of subunits that form the dimers that comprise NFkB transcription factors: (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=RelA+RelB)] activation in the cytosol (Yin et al., 2001: (http://www.jbc.org/cgi/reprint/276/48/44641)(http://www.ncbi.nlm.nih.gov/pubmed/11572859?dopt=Abstract); (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=%22sodium+butyrate%22+proteasome)]. Butyrate doesn't prevent the ubiquitination of IkB proteins (inhibitors of NFkB activation) but causes them to acccumulate as ubiquitin-conjugated proteins, without being degraded in proteasomes, evidently (Yin et al., 2001). HMB is also thought to exert anti-inflammatory effects by suppressing NFkB activation, as a result of the HMB-induced suppression of "proteasomal activity" [Baxter et al., 2005: (http://www.ncbi.nlm.nih.gov/pubmed/16006030)].

I don't doubt that some of those mechanisms are important, and a decrease in the activation of NFkB transcription factors can be antiproliferative and can downregulate the expression of numerous pro-inflammatory cytokines (cytokines that suppress mitochondrial functioning), etc., but SB is produced by microorganisms in the GI tract and is known to be the major energy substrate for colonocytes in the submucosal layers (I forget the terminology) of the colon (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=%22sodium+butyrate%22+energy). The in vitro research probably uses bizarre conditions and shows that SB can induce apoptosis of colon cancer cells. It looks like SB is pro-apoptotic at high but not low concentrations (0.5 mM to 2 mM) [Singh et al., 1997: (http://carcin.oxfordjournals.org/cgi/reprint/18/6/1265.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/9214612)]. But SB supposedly doesn't produce very strong histone deacetylase inhibition in the brain in vivo in animals, but it does produce neuroprotective effects in all sorts of different models (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=%22sodium+butyrate%22+neurodegenerative+OR+neurological+OR+neuroprotective+OR+Parkinson%27s+OR+Huntington%27s+OR+ischemia+OR+ischaemia+OR+hypoxia+OR+anoxia). Sodium butyrate has also produced some "antidepressant-like" effects in animal models of depression (http://scholar.google.com/scholar?q=%22sodium+butyrate%22+antidepressant&hl=en&lr=). Sodium butyrate is also sold as a supplement (http://www.google.com/products?q=sodium+butyrate&hl=en&aq=f).

Anyway, I just put this information up here, but I have no idea what the dosage range would be. One would obviously want to discuss this type of thing with one's doctor, and the most obvious, potential problem would be the disturbances in phosphate or calcium homeostasis in response to something like this. The infusion of 3-hydroxybutyrate, a "ketone" that doesn't have a carbonyl group but is defined as being a ketone, and acetate, for example, can increase plasma bicarbonate, and this effect appears to be the result of the metabolism of the organic acids/fatty acids and not from effects on phosphate homeostasis, in some articles. But these organic anions can just have strange effects, and it's something to be aware. Many medications can affect acid-base homeostasis and could interact with sodium butyrate or HMB. Some anticonvulsants act as carbonic anhydrase inhibitors, for example, and could interact with these types of short-chain fatty acids (such as sodium butyrate) or branched-chain organic acids/fatty acids (such as HMB).

In my opinion, sodium butyrate probably acts mostly as an energy substrate, but that doesn't exclude other mechanisms. I also think the research on sodium butyrate is likely to be relevant to future research on the mechanisms of action of HMB. Both compounds inhibit proteasomal activity and may have overlapping or similar effects, but I don't think it's going to be as simple as testing HMB as a "histone deacetylase inhibitor." Histone acetylation is extraordinarily complex and dynamic, and to think that one can treat a multitude of conditions with histone deacetylase inhibitors is not realistic, in my opinion. Vitamin D receptor activation can increase histone acetylation (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=%22vitamin+D%22+histone+acetyltransferase+OR+acetylation), much as sodium butyrate supposedly does (histone deacetylase inhibition leads to increases in the acetylation of histone proteins). But it's clear, in my opinion, that a lot of the effects of sodium butyrate cannot be explained in terms of histone acetylation.

Mechanisms Underlying the Mild Anticonvulsant Effects of Increases in Ketone Oxidation: Glutamate Availability, GABA Biosynthesis, and Anaplerosis

This article [Yudkoff et al., 2001: (http://www.ncbi.nlm.nih.gov/pubmed/11746421)] is interesting, and the authors hypothesize that increases in ketone availability to neurons, in the brain, produce their mild anticonvulsant effects by increasing the pool of glutamate that is available for GABA synthesis (this would be in GABAergic neurons, presumably, although the authors do not rule out the possibility that an increase in glutamate availability in astrocytes could increase the output of glutamine from astrocytes and thereby enhance GABA formation in neurons, etc.). Even though increases in the availabilities of beta-hydroxybutyrate and acetoacetate to the brain have been associated with antidepressant or anxiolytic and anticonvulsant effects (http://scholar.google.com/scholar?num=100&hl=en&lr=&q=ketogenic+antidepressant+OR+anxiolytic+OR+mood), I don't think the 80% fat diet ("ketogenic diet") is a very realistic approach. The use of medium-chain triglycerides (octanoate, decanoate, etc.) has also been associated with fatty liver disease, and the entry of octanoate and decanoate into the mitochondria is not entirely carnitine-independent, as the authors of some articles have argued. Glycogen-depleting resistance exercise can elevate plasma free fatty acids (FFAs) for 2-4 days and can also elevate plasma ketone levels transiently, at least [(http://hardcorephysiologyfun.blogspot.com/2009/04/protection-against-ischemic-damage-by.html); (http://hardcorephysiologyfun.blogspot.com/2009/04/expression-of-creatine-kinase-by.html); (http://hardcorephysiologyfun.blogspot.com/2009/04/low-cholesterol-levels-and-risk-of.html)]. But circulating FFAs can be used in the biosynthesis of ketones by astrocytes, and adjacent astrocytes or neurons can then oxidize those ketones, etc. The mechanism by which ketones may produce anticonvulsant effects, as described by Yudkoff et al. (2001), is very similar to (essentially identical, to the extent that an increase in ketone oxidation can increase the pool of glutamate available for GABA synthesis by glutamic acid decarboxylase) the proposed mechanism by which exogenous glutamine can increase GABA formation in vivo in rats (http://hardcorephysiologyfun.blogspot.com/2009/03/gabaergic-effect-of-l-glutamine-in-rats.html). In my opinion, low-dose glutamine, which was used as an antidepressant augmentation approach in one small and obscure trial [Cocchi, 1976, cited here: (http://hardcorephysiologyfun.blogspot.com/2009/03/gabaergic-effect-of-l-glutamine-in-rats.html)], could substitute for or potentially work in concert with elevations in ketones as an energy substrate for astrocytes and neurons, but, past a certain dose, the glutamine-induced reductions in plasma FFAs may begin to become counterproductive with respect to astrocyte energy metabolism. Researchers have also found that glutamine can help to preserve the adenylate charge and total adenosine nucleotide content during ischemia, in many different tissues. That may be relevant to depression, and I've discussed various aspects of purine metabolism, in the brain, etc., in many past postings [(http://hardcorephysiologyfun.blogspot.com/2009/04/increase-in-nucleotide-absorption-and.html); (http://hardcorephysiologyfun.blogspot.com/2009/04/adenosine-pka-activity-creb-activation.html); (http://hardcorephysiologyfun.blogspot.com/2009/04/research-on-use-of-creatine-monohydrate.html); (http://hardcorephysiologyfun.blogspot.com/2009/03/adenosine-and-guanosine-in-animal.html); (http://hardcorephysiologyfun.blogspot.com/2009/01/details-on-nucleotides-bioavailability.html)].

Yudkoff et al. (2001) think that the oxidation of ketones increases the intramitochondrial acetyl-CoA pool and leads to a shift in the equilibrium of the reversible aspartate aminotransferase (AA) enzymatic reaction, so as to favor glutamate formation. The authors suggest that this shift results from an increase in the consumption of oxaloacetate, one of the products of the AA reaction, by citrate synthase. Acetyl-CoA and oxaloacetate are substrates of citrate synthase, which forms citrate. The authors also note that ketone oxidation is likely to decrease the free CoA pool and thereby decrease the flux through the alpha-ketoglutarate dehydrogenase (KGDH) reaction of the TCA cycle. One issue I see is the fact that citrate synthase activity tends to be inhibited by a high acetyl-CoA/CoA ratio, but this is nonetheless a really good article. Also, they're basically saying that ketone oxidation lessens the flux of substrates through the TCA cycle (http://hardcorephysiologyfun.blogspot.com/2009/01/coenzyme-sequestration.html), given that the inhibition of the KGDH step limits the anaplerotic addition and removal of TCA cycle intermediates from the mitochondria by the malate-aspartate and malate-citrate shuttles that transfer those intermediates in and out of the mitochondria, thereby sustaining the TCA cycle. So ketone oxidation expands the pool of TCA cycle intermediates but diminishes oxidative metabolism by exacerbating the inhibition of the KGDH reaction? Are they saying ketone oxidation inhibits anaplerosis, by producing more inhibition of KGDH activity, and then increases anaplerosis by expanding the pools of citrate and citrate-derived TCA cycle intermediates that will supposedly enhance anaplerosis? The activity of AA is very high, normally, and increases in the transports of intermediates by the malate-aspartate (as discussed by the authors) and malate-citrate shuttles are not necessarily consistent with the inhibition of oxidative metabolism. It's possible that ketones buffer the pool of TCA cycle intermediates by slowing down oxidative metabolism and preventing the derangements in the cytosolic NADH/NAD+ ratio that can occur during, for example, "hyperglycolysis," following traumatic brain injuries. Then, when ketone levels fall, there's a larger pool of TCA cycle intermediates and more capacity for sustaining oxidative metabolism. What they say has a lot of truth to it, I think, but I also think that the effects of increases in ketone oxidation could be ironed out a little more.

Effects of Free Fatty Acids on ACTH and CRH Release and Responsivenes, on Sympathetic Activity, and, Potentially, Cerebral Blood Flow

This article [Migrenne et al., 2006: (http://diabetes.diabetesjournals.org/cgi/content/full/55/Supplement_2/S139)(http://cat.inist.fr/?aModele=afficheN&cpsidt=18366946)] (why is the journal Diabetes not indexed in Pubmed?) is really interesting, and the authors discuss research showing that the infusion of oleate or other free fatty acids (FFAs) into the carotid artery can cause those FFAs to enter hypothalamic neurons and either augment or decrease insulin release, in either a plasma-glucose-dependent or a glucose-independent manner, by altering the sympathetic outflow from the brain to the pancreas and other sites. The beta-oxidation of FFAs, in the hypothalamus and other parts of the brain, is required for many of these effects to occur, as discussed by Migrenne et al. (2006). This is relevant to the possibility that elevations in some saturated FFAs may produce mood-elevating or mild anticonvulsant effects, even as they may contribute to insulin resistance and other undesirable conditions, etc. [(http://hardcorephysiologyfun.blogspot.com/2009/04/protection-against-ischemic-damage-by.html)(http://hardcorephysiologyfun.blogspot.com/2009/04/low-cholesterol-levels-and-risk-of.html)]. Kok et al. (2004) [Kok et al., 2004: (http://ajpendo.physiology.org/cgi/content/full/287/5/E848)(http://www.ncbi.nlm.nih.gov/pubmed/15280154?dopt=Abstract)] cite research (reference 63) showing that high-fat diets tend to increase FFA levels, and this is fairly well-known to be the case, in my opinion. Kok et al. (2004) found that the acipimox-induced decreases in FFA levels had reduced ACTH levels in obese people. Although the authors of many articles present research to show that FFAs produce sympathetic activation or increase ACTH release, Lanfranco et al. (2004) [Lanfranco et al., 2004: (http://jcem.endojournals.org/cgi/content/full/89/3/1385)(http://www.ncbi.nlm.nih.gov/pubmed/15001638?dopt=Abstract)] found that an acute increase in plasma FFA levels reduced both cortisol and ACTH, and the authors discussed evidence suggesting the FFAs had exerted their inhibitory influence on ACTH secretion by acting on the hypothalamus (i.e. acting on neurons or astrocytes). There's some evidence that FFAs can increase sympathetic activation by acting on plasma membrane ion channels, and unsaturated FFAs can inhibit or otherwise affect beta-adrenoreceptor activation. FFAs can modify ligand binding to a number of different G-protein coupled receptors. Many of the effects on the sympathetic outflow from the CNS appear to be the result of the beta-oxidation of FFAs in the hypothalamus, though, presumably in astrocytes. Tataranni et al. (1999) [Tataranni et al., 1999: (http://www.pnas.org/cgi/content/full/96/8/4569)(http://www.ncbi.nlm.nih.gov/pubmed/10200303)] found that the elevation in plasma FFA levels after a meal correlated positively with regional cerebral blood flow (rCBF) to the dorsolateral prefrontal cortex, in association with an increase in satiety after the meal. That's a significant finding, and it could partly be a result of the beta-oxidation of those FFAs in cerebral vascular endothelial cells. The dorsolateral prefrontal cortex is obviously a site whose neuronal activity is thought to be crucially important in cognitive functioning and mood regulation, etc. [(http://scholar.google.com/scholar?q=%22dorsolateral+prefrontal+cortex%22+%22cerebral+blood+flow%22+depression&hl=en&lr=); (http://scholar.google.com/scholar?hl=en&lr=&q=%22dorsolateral+prefrontal+cortex%22+%22cerebral+blood+flow%22+cognitive)]. The recovery from depression was associated with increases in rCBF to the dorsolateral prefrontal cortex, for example [Bench et al., 1995: (http://www.ncbi.nlm.nih.gov/pubmed/7675913)]. It should be noted that something like resistance exercise tends to elevate both FFAs and ACTH and cortisol levels. The elevations in cortisol levels following resistance exercise can be very significant, and they're not really "bad," in my opinion. One can view that type of elevation as being a "strong signal" to essentially override glucocorticoid resistance at the level of the CNS or even in cells outside the brain. In asthma, for example, responsiveness to beta-adrenoreceptor agonists, which can produce anti-inflammatory effects on many cell types, can be restored within 24 hours by glucocorticoid administration. In chronic stress and depression, the issue tends not to be elevations in cortisol per se but resistance to feedback inhibition of ACTH release, by the pituitary, and CRH release from the hypothalamus. CRH generally activates noradrenergic neurons in the locus ceruleus, and an acute increase in noradrenaline availability in the hypothalamus can decrease CRH release from hypothalamic neurons [Hillhouse et al., 1975: (http://www.ncbi.nlm.nih.gov/pubmed/1079076); Valentino et al., 1988: (http://www.jneurosci.org/cgi/reprint/8/3/1016.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/3258021)]. Those types of regulatory mechanisms don't work very effectively, even under the best of circumstances, and the regulation of CRH release is very complex.

Increase in Nucleotide Absorption and Retention During the Fasted State: Bioavailability Issues and Potential Problems With Enteric-Coated Tablets

These articles [Gross et al., 1988: (http://www.ncbi.nlm.nih.gov/pubmed/3390463); Gross and Savaiano, 1991: (http://www.ncbi.nlm.nih.gov/pubmed/2009279)] are really good and show that the retention, by the intestinal tissues themselves, of intrajejunally-administered nucleosides or nucleic acids can be roughly twice as great in the fasted state as in the "fed" state. Those articles are potentially confusing, because, normally, the retention of nucleosides or nucleotides in the intestines (i.e. the salvage of nucleosides and incorporation into nucleotide pools in the epithelial or smooth muscle cells, etc.) would be less-than desirable, from the standpoint of bioavailability. But what those authors are saying is that xanthine oxidase activity is lower in the fasted state. Those articles tell me that administering purines, in particular, during the fasted state, as discussed below and in past postings [see Carver and Walker, 1995, cited and discussed here: (http://hardcorephysiologyfun.blogspot.com/2009/03/adenosine-and-guanosine-in-animal.html); see here, also: (http://hardcorephysiologyfun.blogspot.com/2009/01/details-on-nucleotides-bioavailability.html)], is likely to produce both greater bioavailability, as discussed in those past postings, and greater salvage, by the target cells that the nucleotides or their metabolites enter, of those purines. That's just my opinion. I didn't know the effect had been shown to be that large. Ho et al. (1979) [Ho et al., 1979: (http://jn.nutrition.org/cgi/reprint/109/8/1377.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/458492)] found even larger increases in the absorption of nucleosides or nucleic acids in the fasted state, although those large, relative increases in tissue content, in the fasted state vs. the fed state, appear to be partially or largely due to increases in the absorption of the nucleotides or nucleic acids (purine bases).

It's important to note that the bioavailability is also likely, in my opinion, to be enhanced in the fasted state. The bioavailability is partly a function of how rapidly a physiological compound, such as a nucleotide, enters solution in the intraluminal fluid. I forget where the reference is, but the intraluminal fluid volume in the stomach or along a segment of the small intestine can be remarkably small and can be something like 15-20 mL. The general concept is that many physiological compounds (nucleotides in particular) can be transported into and metabolized by any cell they come in contact with. If a person takes something like guanosine or adenosine, as a free nucleoside, the low solubilities will, in my opinion, significantly limit the bioavailability of those nucleosides by slowing the rate of dissolution in the GI tract. The undissolved nucleosides will slowly enter solution, as the fraction that is dissolved is transported into cells or has diffused away, by passive diffusion. Savaiano et al. (1980) [Savaiano et al., 1980: (http://jn.nutrition.org/cgi/reprint/110/9/1793.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/7411237)] found evidence suggestive of extreme differences in the bioavailabilities of nucleic acids and nucleosides, such that the intravenous (i.v.) administration produced levels of tissue retention that were 3-59 times the levels produced by oral administration. Usually, the ratio of the i.v. to oral bioavailability of a drug, expressed as the ratio of the areas under the serum concentration vs. time curves [AUC(i.v.)/AUC(oral)], is maybe between 2 and 5 or 7 or something like that. Those differences found by Savaiano et al. (1980) are not especially relevant for human dosing, however, because the solubilities of both nucleic acids and nucleosides are drastically lower than the solubilities of the disodium salts of guanosine monophosphate (GMP and adenosine monophosphate (AMP) or triphosphate (ATP), for example [or the disodium salt of inosine monophosphate (IMP)]. Those solubility differences could essentially mean that most of the nucleic acids or nucleosides would be degraded to uric acid, in humans, or to uric acid and then allantoin, in animals, before they could even enter the portal circulation, etc, in my opinion. Other salts of AMP or GMP or ATP also display deficient solubilities, and those solubility data are freely available on countless sites on the internet. Many of the researchers who have used oral guanosine or GMP as anticonvulsants, in animal experiments, have discussed those solubility issues. The authors of many of those older articles were evidently not aware of those issues, however, in my opinion, and they're very important issues.

Another major problem with oral purine dosing is the use of enteric coatings, and I've discussed this in detail previously (http://hardcorephysiologyfun.blogspot.com/2009/01/details-on-nucleotides-bioavailability.html). Most enteric coatings would be expected to severely and unnecessarily reduce the bioavailabilities of orally-administered nucleotides or nucleosides, in my opinion. Many enteric coated tablets could potentially not dissolve in the GI tract, in my opinion, because the pH in many people would not be expected to be high enough to allow the coatings to dissolve, as discussed by Fallingborg et al. (1999), cited below. Additionally, the use of tablets could be expected to produce the same, drastic slowing of entry into solution that a low level of solubility would be expected to produce, in my opinion. Persky et al. (2003) [Persky et al., 2003: (http://www.pharmacy.unc.edu/pkpd/AMP%20Articles/Persky%20et%20al%20Clin%20Pharmacok%202003.pdf)(http://www.ncbi.nlm.nih.gov/pubmed/12793840)] discussed the fact that the rate of dissolution of physiological substrates, such as creatine, can be an important pharmacokinetic variable to consider, and these types of pharmacokinetic considerations are potentially more important for maximizing the bioavailabilities of nucleotides or other physiological compounds, in my opinion, than those considerations are for maximizing the bioavailabilities of drugs. Many drugs cannot be extensively or even partially metabolized by every cell in the body. With physiological substrates, time (i.e. pharmacokinetics) is of the essence, so to speak, because there is both the rate of uptake, by endothelial cells or cells in the liver, and the rates of degradation by every cell the substrates are available to. Even in the case of creatine, Deldicque et al. (2008) [Deldicque et al., 2008: (http://www.ncbi.nlm.nih.gov/pubmed/17851680)], discussed here (http://hardcorephysiologyfun.blogspot.com/2009/03/adenosine-and-guanosine-in-animal.html), found that the Cmax of plasma creatine, a reflection of an "improvement" in the kinetics of absorption or entry into the systemic circulation, etc., was higher in response to the administration of creatine monohydrate in a water solution (i.e. pre-dissolved) than in response to its administration in foods, which slow the rate of entry of creatine monohydrate into solution. A lower Cmax could be expected, in my opinion, to decrease the fraction of nucleotides, for example, that would gain entry into the brain and be salvaged, as opposed to being degraded into uric acid, by cells in the brain.

Some of the confusion surrounding these issues may be the result of some lingering misconceptions that many people, even researchers, evidently are holding onto. The fasted state in a human means any time 12 or more hours after the previous meal, although I've seen the 10-hour time point used as a marker for the beginning of the "fasted" state. So this means the only true fasted state is likely to be the time period in the morning, before breakfast. Why is this the case? Fallingborg (1999) [Fallingborg et al., 1999: (http://www.ncbi.nlm.nih.gov/pubmed/10421978)] discussed large numbers of studies on the time course with which food moves out of the stomach and into the duodenum and jejunum and so on, and much of the data that Fallingborg (1999) discussed had been collected from experiments using different types of devices that transmit data on the pH and other variables in the gastrointestinal (GI) tract. Some of those are pill-sized devices that have tiny video cameras in them, but I'm not sure those were in use in 1999. After a person eats the first meal of the day, that food may, depending on the sizes and frequencies of the subsequent meals (meaning any food that is eaten), remain in the stomach for between ~2.6 and 14.5 hours (Fallingborg et al., 1999). The gastric residence time (GRT) of tiny, mechanized capsules, with pH sensors in them (the pH is a measure of acidity, such that pH values below or above 7 are "acidic" or "basic"/"alkaline," respectively) is between 1.1 and 1.9 hours in the fasted state, but the GRT for the same capsule can be *up to 14.5 hours* in a person who takes the capsule at breakfast and eats every couple of hours during the rest of the day. Fallingborg (1999) discusses the fact that a single, small meal, eaten in the morning, has been shown to only increase the GRT of the capsule to ~2.6 hours. Fallingborg (1999) discusses the fact that, in the fasted state, the interdigestive migrating myoelectric complex (IMMC), which is phase III of a series of cyclic, contractile events in the smooth muscle that lines the stomach, allows solid food to exit the stomach about every 2 hours. When a person eats a single meal or, in particular, meals every 2-3 hours, the cyclic or "phasic" aspects of these contractions are abolished or "frozen", and food may not exit the stomach for many hours (up to 14 or 14.5). This is very important for understanding the major problems that exist, in my opinion, with enteric coatings for many preparations of (i.e. products containing) SAM-e or ATP disodium, etc., as discussed previously (http://hardcorephysiologyfun.blogspot.com/2009/01/details-on-nucleotides-bioavailability.html).

This residence time applies to solid substances that cannot enter solution and diffuse into the small intestine. If a person eats a water-soluble nutrient or sugar or amino acid or nucleotide, those substances can exit the stomach in aqueous (water) solution very rapidly. But even the slowing effect that is produced by the food in the stomach can limit the bioavailability of a water-soluble substance, such as creatine, in the "fed" state. So the stomach may not be completely empty until ~4 am or even later, if a person eats his or her last meal at 6 pm or something. The paper by Fallingborg (1999) is superb, and the author cites 183 papers and goes into exhaustive detail on all of these considerations.

A major point that Fallingborg (1999) makes is that statements about taking enteric-coated (acid-resistant) tablets "between meals" or "on an empty stomach, between meals" make no sense, because the stomach does not empty between meals. When a person is told to take some of these enteric-coated SAM-e or ATP disodium tablets (or other enteric-coated tablets) "between meals, on an empty stomach," the tablet may not exit the stomach and have any hope of releasing its contents until up to 14.5 hours after the person has taken it and eaten many subsequent meals. More importantly, Fallingborg (1999) discusses research showing that the mean pH in the duodenum of humans is ~6.22. The duodenal pH has been shown to range from 5.66 to 6.4 in other articles (Fallingborg, 1999). In the jejunum, the upper part of the true small intestine proper, is about 4.92 in the fasted state (a median value) and 6.08 after a meal. The pH is thought to only increase to above 7, to 7.4-7.6 (Fallingborg, 1999), in the distal ileum, which is an almost shocking fact that helps to explain the many problems, such as intestinal strictures and so on, with enteric-coated tablets that have been reported in the literature. The pH in the proximal small intestine, therefore, ranges from ~6.08 to ~6.49 (Fallingborg, 1999), when one looks at the data from multiple articles. But many of the enteric coatings do not dissolve until the pH is some amount greater than 7, and yet the jejunum is the site at which enteric-coated tablets are supposed to dissolve. Enteric coatings are polymeric substances, generally, whose solubility is pH-dependent. That means they can't dissolve in fluids that display pH values below some critical range of numbers, and the lower limit of the range may be 7.5 or 8 or some other value and may depend on the particular formulation used by the manufacturer.

Those data on the pH of the intraluminal fluid mean that the dissolution of enteric coatings could be very problematic, in my opinion. One explanation for the misconceptions about the pH in the intraluminal fluid might be that the pH of bile is ~8.03 (Fallingborg, 1999), and maybe people have thought that the pH of bile will be equivalent to the pH of the intraluminal fluid. It's just not the case. There can be a tendency to rely on 30- and 40-year-old data or research in some of these areas, and that tendency can become problematic, in my opinion. I should mention that, in many disease states, such as in people with liver disease, the jejunal pH can be substantially lower than those median or mean values, measured in apparently healthy people and can decrease progressively throughout the day. The pH-sensitivities of something like an enteric coating should obviously, in my opinion, be engineered so as to allow dissolution at the lower range of intraluminal pH values for anyone. This would not be difficult to do, but it's not something that many manufacturers or other people seem to be aware of the need for (if enteric coatings are still going to be used). Here are some articles reporting gastric or intestinal injuries (i.e. obstruction of the pyloric sphincter or intestinal obstructions/strictures) from poorly-formulated enteric-coated tablets (this poor formulation extends to more or less all enteric-coated tablets, in my opinion, when one looks at the data on the pH-dependences of the polymers used in the coatings) [Harris, 1973: (http://www.ncbi.nlm.nih.gov/pubmed/4764749); Sogge et al., 1977: (http://www.ncbi.nlm.nih.gov/pubmed/22308); Davies, 1999: (http://www.ualberta.ca/~csps/JPPS2(1)/N.Davies/NSAID.htm)(http://www.ncbi.nlm.nih.gov/pubmed/10951657); Sherry, 1979: (http://www.ncbi.nlm.nih.gov/pubmed/287936); (http://scholar.google.com/scholar?num=50&hl=en&lr=&safe=off&q=%22enteric+coated%22+stricture+OR+obstruction)]. Obviously, non-enteric-coated aspirin could cause damage to the stomach or small intestine for other reasons, and one should always talk to one's doctor before making any change in any medication. The benefits of enteric-coated preparations may outweigh any potential problems with the preparations, for many people in many specific disease states. But my point is to show the many problems that exist with the approach, in a functional sense, and with many of the individual preparations, in my opinion.

When researchers refer to a "pyloric obstruction" from an enteric-coated aspirin tablet, the researchers mean that the tablet become "stuck" in the valve-like muscle that opens, periodically, to allow food to pass from the stomach into the duodenum. In some cases, minor or not-so-minor surgical procedures are required to remove these obstructions from the undissolved tablets.