Effects of pantethine on lipogenesis and CO2 production in the isolated hepatocytes of the chick (Gallus domesticus)

Nutritional regulation of glucokinase: a cross-species story

The glucokinase (GK) enzyme (EC 2.7.1.1.) is essential for the use of dietary glucose because it is the first enzyme to phosphorylate glucose in excess in different key tissues such as the pancreas and liver. The objective of the present review is not to fully describe the biochemical characteristics and the genetics of this enzyme but to detail its nutritional regulation in different vertebrates from fish to human. Indeed, the present review will describe the existence of the GK enzyme in different animal species that have naturally different levels of carbohydrate in their diets. Thus, some studies have been performed to analyse the nutritional regulation of the GK enzyme in humans and rodents (having high levels of dietary carbohydrates in their diets), in the chicken (moderate level of carbohydrates in its diet) and rainbow trout (no carbohydrate intake in its diet). All these data illustrate the nutritional importance of the GK enzyme irrespective of feeding habits, even in animals known to poorly use dietary carbohydrates (carnivorous species).

Pantethine, a derivative of vitamin B5, favorably alters total, LDL and non-HDL cholesterol in low to moderate cardiovascular risk subjects eligible for statin therapy: a triple-blinded placebo and diet-controlled investigation

High serum concentration of low-density lipoprotein cholesterol (LDL-C) is a major risk factor for coronary heart disease. The efficacy of pantethine treatment on cardiovascular risk markers was investigated in a randomized, triple-blinded, placebo-controlled study, in a low to moderate cardiovascular disease (CVD) risk North American population eligible for statin therapy, using the National Cholesterol Education Program (NCEP) guidelines. A total of 32 subjects were randomized to pantethine (600 mg/day from weeks 1 to 8 and 900 mg/day from weeks 9 to 16) or placebo. Compared with placebo, the participants on pantethine showed a significant decrease in total cholesterol at 16 weeks (P=0.040) and LDL-C at 8 and 16 weeks (P=0.020 and P=0.006, respectively), and decreasing trends in non-high-density lipoprotein cholesterol at week 8 and week 12 (P=0.102 and P=0.145, respectively) that reached significance by week 16 (P=0.042). An 11% decrease in LDL-C from baseline was seen in participants on pantethine, at weeks 4, 8, 12, and 16, while participants on placebo showed a 3% increase at week 16. This decrease was significant between groups at weeks 8 (P=0.027) and 16 (P=0.010). The homocysteine levels for both groups did not change significantly from baseline to week 16. Coenzyme Q10 significantly increased from baseline to week 4 and remained elevated until week 16, in both the pantethine and placebo groups. After 16 weeks, the participants on placebo did not show significant improvement in any CVD risk end points. This study confirms that pantethine lowers cardiovascular risk markers in low to moderate CVD risk participants eligible for statins according to NCEP guidelines.

Expression of the glucokinase gene in mule duck liver and glucokinase activities in chicken and mule duck livers

The presence of glucokinase (GK), a critical enzyme controlling glucose homeostasis, particularly liver glucose utilization in mammals, has long been a matter of debate in avian species because a number of investigators have failed to detect GK activity in the livers of chickens and several other avian species. In this study, we cloned a partial GK cDNA from mule duck livers and measured GK-like activity in the livers of mule ducks and broiler chickens under 2 nutritional states. Liver samples from 5-wk-old meal-fed male broiler chickens (Ross) were obtained from overnight-fasted chickens (BC) and 5 h after an oral saccharose load (6 mL/kg of BW of a 50% saccharose solution) given just before the meal (BS). Liver samples from 15-wk-old mule ducks were collected after an overnight fast (DC) and 12 h after the last overfeeding meal (DO). A partial cDNA ( approximately 600 bp) was obtained from duck livers. It presented 99% identity with chicken partial GK cDNA (gi 44888789) and 82% identity with human GK (gi 15967158). Chicken liver weights represented 1.8 and 3.3% of BW, respectively, for BC and BS (n = 8, P < 0.05). Glucokinase and low-Michaelis constant hexokinase (HK) activity levels were similar in BC (respectively, 0.88 and 1.00 mU/mg of protein). In response to the meal load, GK activity increased significantly (+57%), whereas HK decreased (-46%) in BS. Duck liver weights represented 1.4 and 7.6% of BW, respectively, for DC and DO (n = 8, P < 0.05). In DC livers, GK activity was significantly higher than HK activity (respectively, 1.76 and 0.63 mU/mg of protein). Both activities were significantly increased in DO (2 times, n = 8, P < 0.05). In conclusion, GK is present in ducks as well as chickens, and it is nutritionally regulated in avian species as well as in mammals. Further work will determine whether the higher liver GK activity and GK:HK ratio in DC compared with BC is related to age or BW or linked to the high lipogenic capacity of the duck liver.

Increased lipogenesis in isolated hepatocytes from cold-acclimated ducklings

Thermogenic endurance and development of metabolic cold adaptation in birds may critically depend on their ability to synthesize and use fatty acids (FA) as fuel substrates. Hepatic lipogenesis and the capacity to oxidize FA in thermogenic tissues were measured in cold-acclimated (CA) ducklings (Cairina moschata) showing original mechanisms of metabolic cold adaptation in the absence of brown adipose tissue, the specialized thermogenic tissue of rodents. The rate of FA synthesis from [U-(14)C]glucose and from [1-(14)C]acetate, measured in incubated hepatocytes isolated from 5-wk-old thermoneutral (TN; 25 degrees C) or CA (4 degrees C) fed ducklings, was higher than in other species. Hepatic de novo lipogenesis was further increased by cold acclimation with both glucose (+194%) and acetate (+111%) as precursor. Insulin slightly increased (+11-14%) hepatic lipogenesis from both precursors in CA ducklings, whereas glucagon was clearly inhibitory (-29 to -51%). Enhanced de novo lipogenesis was associated with higher (+171%) hepatocyte activity of glucose oxidation and larger capacity (+50 to +100%) of key lipogenic enzymes. The potential for FA oxidation was higher in liver (+61%) and skeletal muscle (+29 to +81%) homogenates from CA than from TN ducklings, suggesting that the higher hepatic lipogenesis may fuel oxidation in thermogenic tissues. Present data underline the high capacity to synthesize lipids from glucose in species like muscovy ducks susceptible to hepatic steatosis. Lipogenic capacity can be further increased in the cold and may represent an important step in the metabolic adaptation to cold of growing ducklings.

Hepatothermic therapy of obesity: rationale and an inventory of resources

Hepatothermic therapy (HT) of obesity is rooted in the observation that the liver has substantial capacities for both fatty acid oxidation and for thermogenesis. When hepatic fatty acid oxidation is optimized, the newly available free energy may be able to drive hepatic thermogenesis, such that respiratory quotient declines while basal metabolic rate increases, a circumstance evidently favorable for fat loss. Effective implementation of HT may require activation of carnitine palmitoyl transferase-1 (rate-limiting for fatty acid beta-oxidation), an increase in mitochondrial oxaloacetate production (required for optimal Krebs cycle activity), and up-regulation of hepatic thermogenic pathways. The possible utility of various natural agents and drugs for achieving these objectives is discussed. Potential components of HT regimens include EPA-rich fish oil, sesamin, hydroxycitrate, pantethine, L-carnitine, pyruvate, aspartate, chromium, coenzyme Q10, green tea polyphenols, conjugated linoleic acids, DHEA derivatives, cilostazol, diazoxide, and fibrate drugs. Aerobic exercise training and very-low-fat, low-glycemic-index, high-protein or vegan food choices may help to establish the hormonal environment conducive to effective HT. High-dose biotin and/or metformin may help to prevent an excessive increase in hepatic glucose output. Since many of the agents contemplated as components of HT regimens are nutritional or food-derived compounds likely to be health protective, HT is envisioned as an on-going lifestyle rather than as a temporary 'quick fix'. Initial clinical efforts to evaluate the potential of HT are now in progress.

Inhibition of acetyl-CoA carboxylase by cystamine may mediate the hypotriglyceridemic activity of pantethine

Pantethine is a versatile and well-tolerated hypolipidemic agent whose efficacy in this regard appears to be mediated by its catabolic product cystamine, a nucleophile which avidly attacks disulfide groups. An overview of pantethine research suggests that the hypotriglyceridemic activity of pantethine reflects cystamine-mediated inhibition of the hepatic acetyl-CoA carboxylase, which can be expected to activate hepatic fatty acid oxidation. Inhibition of HMG-CoA reductase as well as a more distal enzyme in the cholesterol synthetic pathway may account for pantethine's hypocholesterolemic effects. If pantethine does indeed effectively inhibit hepatic acetyl-CoA carboxylase, it may have adjuvant utility in the hepatothermic therapy of obesity. As a safe and effective compound of natural origin, pantethine merits broader use in the management of hyperlipidemias.

Peroxisome proliferators as adjuvants for the reverse-electron-transport therapy of obesity: an explanation for the large increase in metabolic rate of MEDICA 16-treated rats

The efficacy of reverse-electron-transport therapy of obesity should be promoted by agents which up-regulate hepatocyte enzymes that are potentially rate-limiting for mitochondrial fatty acid oxidation and electron shuttles. Peroxisome proliferator drugs, including the fibrates used to treat hyperlipidemia, may be useful in this regard, as they induce malic enzyme, the mitochondrial glycerol-3-phosphate dehydrogenase, and carnitine palmitoyl transferase I in rodent hepatocytes. An agent of this class, MEDICA 16, has the additional property of potently inhibiting both citrate lyase and acetyl-CoA carboxylase. As a result, methyl-substituted diacarboxylic acids (MEDICA) 16 can be expected to disinhibit hepatic fatty acid oxidation while up-regulating electron shuttle mechanisms, and thus should stimulate reverse electron transport. This may explain the remarkable 40% increase in basal metabolic rate observed in normal rats ingesting MEDICA 16--an effect not associated with any compensatory increase in food intake. Relative to controls, the MEDICA 16-treated rats achieved a 50% reduction in body fat and a modest increase in lean mass, such that weight and growth were not changed. In other rodent strains, MEDICA 16 has prevented obesity diabetes and atherogenesis. However, whether MEDICA 16 and other peroxisome proliferator drugs will have clinical utility in reverse-electron-transport therapy may hinge on their ability to induce key enzymes in human hepatocytes; cell culture studies to evaluate this are required.

Pantethine stimulates lipolysis in adipose tissue and inhibits cholesterol and fatty acid synthesis in liver and intestinal mucosa in the normolipidemic rat

In vitro effects of pantethine on adipose tissue lipolysis and on both hepatic and intestinal cholesterol and fatty acid synthesis in normolipidemic rats are determined and related to their respective in vivo hypolipidemic effects after acute oral administration. At 3, 5, 7 and 24 h after a single high dose of pantethine to rats, free fatty acids (FFA), cholesterol and triglycerides levels decreased whereas plasma glycerol increased, the effect becoming significant at 7 h. The release of glycerol and FFA by epididymal fat pad pieces from rats was measured in Krebs Ringer bicarbonate-albumin buffer supplemented or not with epinephrine and several concentrations of pantethine (0, 10(-5), 10(-4), or 10(-3) M), and it turned out to be enhanced as pantethine concentration increased. Besides, when glucose was present in the medium, this drug lowered fatty acid re-esterification in a dose-dependent manner, the effect being specially evident in the presence of epinephrine. In vitro synthesis of both cholesterol and fatty acids by slices of liver or intestinal epithelial cells was depressed as the concentration of pantethine increased in the medium. Thus, an inhibition of both cholesterolgenesis and lipogenesis seems to contribute to the hypocholesterolemic and hypotriglyceridemic effects of pantethine. On the other hand, the stimulation of lipolysis and the inhibition of fatty acid re-esterification on adipose tissue caused by pantethine must be counteracted by a high fatty acid oxidation in the liver which would explain the decrease in FFA and the increase in glycerol levels detected in the plasma of the pantethine-treated animals.