Metabolic and mitochondrial disturbances in streptozotocin-treated Sprague-Dawley and Sherman rats

This study provides explanation for conflicting evidence in the literature relating to changes in mitochondrial function and metabolic parameters during chemically induced diabetes. Diabetes of 3 days' duration (early ketosis) did not alter heart, kidney, or liver mitochondrial respiratory rates with glutamate or succinate even though serum glucose and triglycerides were elevated. Diabetes of 5 weeks' duration did not alter kidney or liver mitochondrial function in the fed adult rat although weight gain was depressed. The amount of kidney mitochondrial protein isolated per gram of tissue was increased by 30% in the diabetic. This increase was reversed by insulin treatment as were the other biochemical modalities measured. Superimposition of a 24-hr fast resulted in enhanced gluconeogenesis as measured by an animal weight loss of 17% within 24 hr (liver weight loss, 21%) and an elevation of serum urea nitrogen by 180% compared to fasted control. Respiratory rates of diabetic kidney mitochondria with glutamate were unaffected in the fasted animal whereas diabetic liver mitochondrial respiratory rates during succinate oxidation were reduced by 43%. Respiratory control was unchanged in the fasted diabetic rat. All the observed changes were reversed by insulin. Variation in the serum and liver metabolic indices (urea nitrogen, creatinine, glycerol, free fatty acids, free amino acids, triglycerides, and glucose) and liver mitochondrial responses to 7 weeks of chemically induced diabetes was affected by the rat strain, Sprague-Dawley versus Sherman, and rat weight, 72 g versus 222 g. Liver mitochondrial respirations in fed Sherman rats were not depressed by diabetes. Both rat strains had elevated liver free fatty acids and glutamate dehydrogenase activity in the diabetic state. Serum leucine, isoleucine, and valine were more elevated and serum lysine and arginine were more depressed in the diabetic Sprague-Dawley rat than in the Sherman rat. Conjectures on these results are presented in the text.     

Effect of iridoid glucoside on plasma lipid profile, tissue fatty acid changes, inflammatory cytokines, and GLUT4 expression in skeletal muscle of streptozotocin-induced diabetic rats

The present study was designed to examine the antihyperlipidaemic potential of iridoid glucoside isolated from Vitex negundo leaves in STZ-induced diabetic rats. The levels of cholesterol (TC), triglycerides, lipoproteins, free fatty acids, phospholipids, fatty acid composition, proinflammatory cytokines, muscle glycogen content, and glucose transporter 4 (GLUT4) expression were estimated in control and diabetic rats. Oral administration of iridoid glucoside at a dose of 50 mg/kg body weight per day to STZ-induced diabetic rats for a period of 30 days resulted in a significant reduction in plasma and tissue (liver and kidney) cholesterol, triglycerides, free fatty acids, and phospholipids. In addition, the decreased plasma levels of high-density lipoprotein-cholesterol and increased plasma levels of low density lipoprotein- and very low density lipoprotein-cholesterol in diabetic rats were restored to near normal levels following treatment with iridoid glucoside. The fatty acid composition of the liver and kidney was analyzed by gas chromatography. The altered fatty acid composition in the liver and kidney of diabetic rats was also restored upon treatment with iridoid glucoside. Moreover, the elevated plasma levels of proinflammatory cytokines and decreased levels of muscle glycogen and GLUT4 expression in the skeletal muscle of diabetic rats were reinstated to their normal levels via enhanced secretion of insulin from the remnant β cells of pancreas by the administration of iridoid glucoside. The effect produced by iridoid glucoside on various parameters was comparable with that of glibenclamide, a well-known antihyperglycemic drug.     

Metabolic origin of urinary 3-hydroxy dicarboxylic acids

3-Hydroxy dicarboxylic acids with chain lengths ranging from 6 to 14 carbons are excreted in human urine. The urinary excretion of these acids is increased in conditions of increased mobilization of fatty acids or inhibited fatty acid oxidation. Similar urinary profiles of 3-hydroxy dicarboxylic acids were also observed in fasting rats. The metabolic genesis of these urinary 3-hydroxy dicarboxylic acids was investigated in vitro with rat liver postmitochondrial and mitochondrial fractions. 3-Hydroxy monocarboxylic acids ranging from 3-hydroxyhexanoic acid to 3-hydroxyhexadecanoic acid were synthesized. In the rat liver postmitochondrial fraction fortified with NADPH, these 3-hydroxy fatty acids with carbon chains equal to or longer than 10 were oxidized to (omega - 1)- and omega-hydroxy metabolites as well as to the corresponding 3-hydroxy dicarboxylic acids. 3-Hydroxyhexanoic (3OHMC6) and 3-hydroxyoctanoic (3OHMC8) acids were not metabolized. Upon the addition of mitochondria together with ATP, CoA, carnitine, and MgCl2, the 3-hydroxy dicarboxylic acids were converted to 3-hydroxyoctanedioic, trans-2-hexenedioic, suberic, and adipic acids. In the urine of children with elevated 3-hydroxy dicarboxylic acid levels, 3OHMC6, 3OHMC8, 3-hydroxydecanoic, 3,10-dihydroxydecanoic, 3,9-dihydroxydecanoic, and 3,11-dihydroxydodecanoic acids were identified. On the basis of these data, we propose that the urinary 3-hydroxy dicarboxylic acids are derived from the omega-oxidation of 3-hydroxy fatty acids and the subsequent beta-oxidation of longer chain 3-hydroxy dicarboxylic acids. These urinary 3-hydroxy dicarboxylic acids are not derived from the beta-oxidation of unsubstituted dicarboxylic acids.     

In vivo and in vitro intervention with L-carnitine prevents abnormal energy metabolism in isolated diabetic rat heart: chemical and phosphorus-31 NMR evidence

The beneficial effects of in vivo injections (200 mg/kg, twice daily) or in vitro perfusion (5.0 mM) of L-carnitine on an intrinsic abnormality in energy metabolism was investigated in isolated, perfused diabetic rat heart. Hearts were aerobically perfused for 60 min with elevated fatty acid substrate to simulate diabetic conditions. Phosphorus-31 nuclear magnetic resonance spectroscopy revealed a temporal decline in myocardial ATP levels (to approx 82%) during perfusion of diabetic hearts, but not in control hearts. This reduction was prevented by prior treatment in vivo with L-carnitine or by providing L-carnitine acutely in the perfusion medium. Chemical analysis of tissue extracts indicated that L-carnitine injections were effective in replenishing the decrease in total myocardial carnitine content which was present in diabetic hearts and in preventing the accumulation of long chain fatty acyl CoA. Perfusion with L-carnitine also attenuated the elevation of long chain fatty acyl CoA in diabetic hearts. This study gives additional support to the hypothesis that decreases in ATP which occur in the isolated, perfused diabetic heart are correlated with a concomitant elevation in long chain fatty acyl CoA, a known inhibitor of adenine nucleotide translocase. In the presence of elevated exogenous fatty acids, a primary deficiency in the total myocardial carnitine pool would result in elevations in tissue concentrations of long chain fatty acyl CoA since carnitine is a required carrier for transport of fatty acids into mitochondria. Replenishment of the carnitine in vivo was shown to be sufficient to prevent subsequent alteration in long chain fatty acyl CoA and ATP in isolated perfused diabetic hearts despite the burden of elevated fatty acid substrates.     

Formation and degradation of dicarboxylic acids in relation to alterations in fatty acid oxidation in rats.

Dicarboxylic acids are excreted in urine when fatty acid oxidation is increased (ketosis) or inhibited (defects in beta-oxidation) and in Reye's syndrome. omega-Hydroxylation and omega-oxidation of C6-C12 fatty acids were measured by mass spectrometry in rat liver microsomes and homogenates, and beta-oxidation of the dicarboxylic acids in liver homogenates and isolated mitochondria and peroxisomes. Medium-chain fatty acids formed large amounts of medium-chain dicarboxylic acids, which were easily beta-oxidized both in vitro and in vivo, in contrast to the long-chain C16-dicarboxylic acid, which was toxic to starved rats. Increment of fatty acid oxidation in rats by starvation or diabetes increased C6:C10 dicarboxylic acid ratio in rats fed medium-chain triacylglycerols, and increased short-chain dicarboxylic acid excretion in urine in rats fed medium-chain dicarboxylic acids. Valproate, which inhibits fatty acid oxidation and may induce Reye like syndromes, caused the pattern of C6-C10-dicarboxylic aciduria seen in beta-oxidation defects, but only in starved rats. It is suggested, that the origin of urinary short-chain dicarboxylic acids is omega-oxidized medium-chain fatty acids, which after peroxisomal beta-oxidation accumulate as C6-C8-dicarboxylic acids. C10-C12-dicarboxylic acids were also metabolized in the mitochondria, but did not accumulate as C6-C8-dicarboxylic acids, indicating that beta-oxidation was completed beyond the level of adipyl CoA.     

Peroxisome-generated succinate induces lipid accumulation and oxidative stress in the kidneys of diabetic mice

Diabetes normally causes lipid accumulation and oxidative stress in the kidneys, which plays a critical role in the onset of diabetic nephropathy; however, the mechanism by which dysregulated fatty acid metabolism increases lipid and reactive oxygen species (ROS) formation in the diabetic kidney is not clear. As succinate is remarkably increased in the diabetic kidney, and accumulation of succinate suppresses mitochondrial fatty acid oxidation and increases ROS formation, we hypothesized that succinate might play a role in inducing lipid and ROS accumulation in the diabetic kidney. Here we demonstrate a novel mechanism by which diabetes induces lipid and ROS accumulation in the kidney of diabetic animals. We show that enhanced oxidation of dicarboxylic acids by peroxisomes leads to lipid and ROS accumulation in the kidney of diabetic mice via the metabolite succinate. Furthermore, specific suppression of peroxisomal β-oxidation improved diabetes-induced nephropathy by reducing succinate generation and attenuating lipid and ROS accumulation in the kidneys of the diabetic mice. We suggest that peroxisome-generated succinate acts as a pathological molecule inducing lipid and ROS accumulation in kidney, and that specifically targeting peroxisomal β-oxidation might be an effective strategy in treating diabetic nephropathy and related metabolic disorders.     

Amino acid metabolism in the Zucker diabetic fatty rat: effects of insulin resistance and of type 2 diabetes

We investigated amino acid metabolism in the Zucker diabetic fatty (ZDF Gmi fa/fa) rat during the prediabetic insulin-resistant stage and the frank type 2 diabetic stage. Amino acids were measured in plasma, liver, and skeletal muscle, and the ratios of plasma/liver and plasma/skeletal muscle were calculated. At the insulin-resistant stage, the plasma concentrations of the gluconeogenic amino acids aspartate, serine, glutamine, glycine, and histidine were decreased in the ZDF Gmi fa/fa rats, whereas taurine, alpha-aminoadipic acid, methionine, phenylalanine, tryptophan, and the 3 branched-chain amino acids were significantly increased. At the diabetic stage, a larger number of gluconeogenic amino acids had decreased plasma concentrations. The 3 branched-chain amino acids had elevated plasma concentrations. In the liver and the skeletal muscles, concentrations of many of the gluconeogenic amino acids were lower at both stages, whereas the levels of 1 or all of the branched-chain amino acids were elevated. These changes in amino acid concentrations are similar to changes seen in type 1 diabetes. It is evident that insulin resistance alone is capable of bringing about many of the changes in amino acid metabolism observed in type 2 diabetes.     

Effect of short- and long-term diabetes on carnitine and myo-inositol in rats.

1. The effect of short- (2 wk) and long-term (20 wk) streptozotocin diabetes was studied on urine, blood, liver, heart, brain, skeletal muscle, pancreas and kidney concentrations of acid-soluble carnitine and free myo-inositol. 2. Short-term diabetic rats excreted significantly higher concentrations of carnitine as well as myoinositol than normal rats. Blood carnitine and myo-inositol were not different between normal and diabetic rats. Diabetes caused a decrease in liver, brain and pancreatic carnitine, but not in heart, skeletal muscle and kidney. Myo-inositol concentration was decreased in liver, heart and kidney but not in brain, pancreas and skeletal muscle. 3. Long-term diabetic rats had higher urinary excretions of both carnitine and myo-inositol. Blood carnitine did not change; however, myo-inositol was higher in diabetic than in normal rats. Diabetes caused a significant increase in liver and a decrease in heart, brain, skeletal muscle and pancreatic content of carnitine; no difference in kidney carnitine was noted. Myo-inositol content was elevated only in liver of diabetic rats. 4. We suggest that carnitine and myo-inositol concentrations are influenced both by short- and long-term diabetes through changes in tissue metabolism.     

The biological origin of ketotic dicarboxylic aciduria. In vivo and in vitro investigations of the omega-oxidation of C6-C16-monocarboxylic acids in unstarved, starved and diabetic rats

The conversion of radioactive C6-C16-monocarboxylic acids to urinary adipic, suberic, sebacic and 3-hydroxybutyric acids was investigated in vivo in unstarved, starved and diabetic ketotic rats. Hexanoic, octanoic and decanoic acids were converted to C6-, C6-C8- and C6-C10-dicarboxylic acids, respectively, in fed and 72-h-starved rats. Lauric acid was converted to C6-C8-dicarboxylic acids in starved rats but not in unstarved rats. Decanoic and lauric acids were converted to relatively high amounts of C6-C8-dicarboxylic acids compared with myristic acid in myristic acid in ketotic diabetic rats, while radioactivity from [1-14C]-and [16-(14)] palmitic acid was not incorporated into C6-C8-dicarboxylic acids in diabetic ketotic rats. C6-C12-monocarboxylic acids in hydrolysed rat adipose tissue wee determined by gas-liquid chromatography-mass spectrometry (selected ion monitoring). Decanoic and lauric acids were found in amounts of 7.6-9.1 and 85.9-137.5 micrometers/100 mg tissue, respectively, whereas the amounts of hexanoic and octanoic acids were negligible. It is concluded that the biological origin of the C6-C8-dicarboxylic aciduria seen in ketotic rats are C10-C14-monocarboxylic acids, which are initially omega-oxidised solely or partly as free acids and subsequently beta-oxidised to adipic and suberic acids. The in vitro omega-oxidation of C6-C16-monocarboxylic acids to corresponding dicarboxylic acids in the 100,000 Xg supernatant fraction of rat liver homogenate was measured by selected ion monitoring. 0.09, 0.14, 16.1, 5.8, 7.0 and -6.9% of, respectively, hexanoic, octanoic, decanoic, lauric, myristic and palmitic acid were omega-oxidised to dicarboxylic acids of corresponding chain lengths after 90 min of incubation, when correction for the production of dicarboxylic acids in control assays was made. An in vitro production of C12-C16-dicarboxylic acids was detected in all assays ()including control assays), probably formed from"endogenous' monocarboxylic acids preexistent in the homogenate. Ths "endogenous' production of dicarboxylic acids was inhibited by C10-C16-monocarboxylic acids, where palmitic acid had the strongest effect. In fact, palmitic acid inhibited its own omega-oxidation when added in concentrations above 0.6 mM. Starvation of rats for 72 h did not alter the "endogenous' in vitro production of hexadecanedioic acid.     

Potential role of antioxidants during ethanol-induced changes in the fatty acid composition and arachidonic acid metabolites in male Wistar rats

Biochemical assessment of liver damage during ethanol-induced stress was done by measuring the activities of serum enzymes, viz., aspartate transaminase (AST) and alkaline phosphatase (ALP), which were significantly elevated in rats fed ethanol. Ethanol administration for a period of 60 days modifies the fatty acid composition, and the analysis of fatty acids showed that there was a significant increase in the concentrations of palmitic acid (16:0), stearic acid (18:0), and oleic acid (18:1) in liver, kidney, and brain, whereas the concentrations of palmitoleic (16:1) and arachidonic acid (20:4) were significantly decreased. The breakdown products of arachidonic acids (20:4), prostaglandins, were elevated. The antioxidants curcumin and N-acetylcysteine (NAC) decreased the activities of serum AST and ALP. Curcumin and NAC decreased the concentrations of fatty acids, viz., palmitic, stearic, and oleic acid, whereas arachidonic acid and palmitoleic acid were elevated. The prostaglandin concentrations were also decreased after curcumin and N-acetylcysteine treatment. Thus the present investigation shows that curcumin and N-acetylcysteine prevent the fatty acid changes produced by ethanol and also reduce the inflammatory response of ethanol by reducing the level of prostaglandins. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of cod liver oil on tissue antioxidant pathways in normal and streptozotocin-diabetic rats

Lipid disorders and increased oxidative stress may exacerbate some complications of diabetes mellitus. Previous studies have implicated the beneficial effects of some antioxidants, omega-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the protection of cells from the destructive effect of increased lipids and lipid peroxidation products. This study, therefore, was designed to investigate the effects of cod liver oil (CLO, Lysi Ltd. Island), which comprises mainly vitamin A, PUFAs, EPA and DHA. Effects were monitored on plasma lipids, lipid peroxidation products (MDA) and the activities of antioxidant enzymes, glutathione peroxidase (GSHPx) and catalase in heart, liver, kidney and lung of non-diabetic control and streptozotocin (STZ)-induced-diabetic rats. Two days after STZ-injection (55 mg kg(-1) i.p.), non-diabetic control and diabetic rats were divided randomly into two groups as untreated or treated with CLO (0.5 ml kg(-1) rat per day) for 12 weeks. Plasma glucose, triacylglycerol and cholesterol concentrations were significantly elevated in 12-week untreated-diabetic animals; CLO treatment almost completely prevented these abnormalities in triacylglycerol and cholesterol, but hyperglycaemia was partially controlled. CLO also provided better weight gain in diabetic animals. In untreated diabetic rats, MDA markedly increased in aorta, heart and liver but was not significantly changed in kidney and lung. This was accompanied by a significant increase in both GSHPx and catalase enzyme activities in aorta, heart, and liver of diabetic rats. In kidney and lung, diabetes resulted in reduced catalase while GSHPx was significantly activated. In aorta, heart, and liver, diabetes-induced changes in MDA were entirely prevented by CLO treatment. In the tissues of CLO-treated diabetic animals, GSHPx activity paralleled those of control animals. CLO treatment also caused significant improvements in catalase activities in every tissue of diabetic rats, but failed to affect MDA and antioxidant activity in control animals. The current study suggests that the treatment of diabetic rats with CLO provides better control of glucose and lipid metabolism, allows recovery of normal growth rate, prevents oxidative/peroxidative stress and ameliorates endogenous antioxidant enzyme activities in various tissues. Because CLO contains a plethora of beneficial compounds together, its use for the management of diabetes-induced complications may provide important advantages.     

The identification of a succinyl-CoA thioesterase suggests a novel pathway for succinate production in peroxisomes

Dicarboxylic acids are formed by omega-oxidation of fatty acids in the endoplasmic reticulum and degraded as the CoA ester via beta-oxidation in peroxisomes. Both synthesis and degradation of dicarboxylic acids occur mainly in kidney and liver, and the chain-shortened dicarboxylic acids are excreted in the urine as the free acids, implying that acyl-CoA thioesterases (ACOTs), which hydrolyze CoA esters to the free acid and CoASH, are needed for the release of the free acids. Recent studies show that peroxisomes contain several acyl-CoA thioesterases with different functions. We have now expressed a peroxisomal acyl-CoA thioesterase with a previously unknown function, ACOT4, which we show is active on dicarboxylyl-CoA esters. We also expressed ACOT8, another peroxisomal acyl-CoA thioesterase that was previously shown to hydrolyze a large variety of CoA esters. Acot4 and Acot8 are both strongly expressed in kidney and liver and are also target genes for the peroxisome proliferator-activated receptor alpha. Enzyme activity measurements with expressed ACOT4 and ACOT8 show that both enzymes hydrolyze CoA esters of dicarboxylic acids with high activity but with strikingly different specificities. Whereas ACOT4 mainly hydrolyzes succinyl-CoA, ACOT8 preferentially hydrolyzes longer dicarboxylyl-CoA esters (glutaryl-CoA, adipyl-CoA, suberyl-CoA, sebacyl-CoA, and dodecanedioyl-CoA). The identification of a highly specific succinyl-CoA thioesterase in peroxisomes strongly suggests that peroxisomal beta-oxidation of dicarboxylic acids leads to formation of succinate, at least under certain conditions, and that ACOT4 and ACOT8 are responsible for the termination of beta-oxidation of dicarboxylic acids of medium-chain length with the concomitant release of the corresponding free acids.     

Effect of diets rich in medium-chain and long-chain triglycerides on lipogenic-enzyme gene expression in liver and adipose tissue of the weaned rat.

The activity and mRNA concentrations of two lipogenic enzymes, fatty-acid synthase and acetyl-CoA carboxylase were measured in the liver and white adipose tissue of rats weaned to a carbohydrate-rich diet containing either long-chain or medium-chain fatty acids, and compared to those of rats weaned on a diet containing less than 1% (total energy) fat (high-carbohydrate diet). In the liver, the diet containing long-chain fatty acids inhibited the increase of both lipogenic-enzyme mRNA concentrations and activities seen at weaning on the high-carbohydrate diet but did not prevent the decrease in phosphoenolpyruvate carboxykinase mRNA and activity. In contrast, the diet containing medium-chain fatty acids induced a slower but finally similar increase in lipogenic-enzyme mRNA concentrations and activities. In adipose tissue, a similar trend was observed, although the inhibitory effect of the diet containing long-chain fatty acids was considerably less marked than in liver. It is concluded that medium-chain and long-chain fatty acids have not the same inhibitory potency of the gene expression of lipogenic enzymes, and that long-chain fatty acids have a more marked effect in the liver.     

Dietary ALA,EPA and DHA have distinct effects on oxylipin profiles in female and male rat kidney,liver and serum

There is much data on the effects of dietary n-3 fatty acids on tissue fatty acid compositions, but comparable comprehensive data on their oxygenated metabolites (oxylipins) is limited. The effects of providing female and male rats with diets high in α-linolenic acid (ALA), EPA or DHA for 6 weeks on oxylipins and fatty acids in kidney, liver and serum were therefore examined. The oxylipin profile generally reflected fatty acids, but it also revealed unique effects of individual n-3 fatty acids that were not apparent from fatty acid data alone. Dietary ALA increased renal and serum DHA oxylipins even though DHA itself did not increase, while dietary EPA did not increase DHA oxylipins in kidney or liver, suggesting that high EPA may inhibit this conversion. Oxylipin data generally corroborated fatty acid data that indicated that DHA can be retroconverted to EPA and that further retroconversion to ALA is limited. Dietary n-3 fatty acids decreased n-6 fatty acids and their oxylipins (except linoleic acid and its oxylipins), in order of effectiveness of DHA > EPA > ALA, with some exceptions: several arachidonic acid oxylipins modified at carbon 15 were not lower in all three sites, and EPA had a greater effect on 12-hydroxy-eicosatetraenoic acid and its metabolites in the liver. Oxylipins were predominantly higher in males, which was not reflective of fatty acids. Tissue-specific oxylipin profiles, therefore, provide further information on individual dietary n-3 fatty acid and sex effects that may help explain their unique physiological effects and have implications for dietary recommendations.     

The fatty acid composition of the tissues of streptozotocin-diabetic rats

The authors studied acute changes in the fatty acid composition of the tissues of streptozotocin-diabetic rats. They found that streptozotocin diabetes led to changes in the total lipids fatty acid spectrum in serum and in tissues (liver, adipose tissue, renal cortex diaphragm). After only 7 days' diabetes there was an increase in the percentual proportion of saturated fatty acids and a decrease in the amount of polyene fatty acids in the serum and in all the above tissue of diabetic animals. Palmitic acid (16:0) participated in the increase in the proportion of saturated fatty acids in all the given tissues, while stearic acid (18:0) played a role in the increase in the renal cortex and the serum. Among the monoene acids, there was a drop in the proportion of palmitoleic acid (16:1) in the adipose tissue and serum and in the amount of oleic acid (18:1) in the renal cortex, liver and muscle. Linoleic acid (18:2) played a role in the decrease in the proportion of polyene acids in all the given tissues and the serum, while arachidonic acid (20:4) was involved in the drop in the renal cortex, liver and muscle. The results show that diabetes leads to changes in the fatty acid composition of the renal cortex and muscle, as well as of the liver and adipose tissue. At present it is not yet clear whether there is an absolute decrease in the proportion of essential fatty acids, or whether diabetes is characterized by an increase in the amount of lipids in both serum and tissues.     

Effect of chromium supplementation on the diabetes induced-oxidative stress in liver and brain of adult rats

This study was designed to investigate the susceptibility of liver and brain tissues, as insulin-independent tissues, of normal adult male rats to the oxidative challenge of subchronic supplementation with chromium picolinate (CrPic) at low (human equivalent) and high doses (2.90 and 13.20 μg Cr kg⁻¹ day⁻¹, respectively). Also, the modulative effect of CrPic administration on the enhanced oxidative stress in the liver and brain tissues of alloxan-diabetic rats was studied. Fasting serum glucose level was not modified in normal rats but significantly reduced in diabetic rats that had received CrPic supplement. A mild oxidative stress was observed in the liver and brain of CrPic-supplemented normal rats confirmed by the dose-dependent reductions in the levels of hepatic and cerebral free fatty acids, superoxide dismutase and glutathione peroxidase activities, and in contrast increased tissue malondialdehyde concentration. On the other hand, hepatic and cerebral catalase activity was reduced in the high dose group only. CrPic supplementation did not act as a peroxisome proliferator confirmed by the significant reductions in liver and brain peroxisomal palmitoyl CoA oxidase activity. The non significant alterations in liver protein/DNA and RNA/DNA ratios indicate that CrPic did not affect protein synthesis per cell, and that mild elevations in hepatic total protein and RNA concentrations might be due to block or decrease in the export rate of synthesized proteins from the liver to the plasma. In diabetic rats, elevated levels of hepatic and cerebral free fatty acids and malondialdehyde, and in contrast the overwhelmed antioxidant enzymes, were significantly modulated in the low dose group and near-normalized in the high dose group. The significant increases observed in liver total protein and RNA concentrations, as well as protein/DNA and RNA/DNA ratios in diabetic rats supplemented with the high dose of Cr, compared to untreated diabetics, may be related to the improvement in the glycemic status of the diabetic animals rather than the direct effect of CrPic on protein anabolism.     

Brown adipose tissue activity controls triglyceride clearance

Brown adipose tissue (BAT) burns fatty acids for heat production to defend the body against cold and has recently been shown to be present in humans. Triglyceride-rich lipoproteins (TRLs) transport lipids in the bloodstream, where the fatty acid moieties are liberated by the action of lipoprotein lipase (LPL). Peripheral organs such as muscle and adipose tissue take up the fatty acids, whereas the remaining cholesterol-rich remnant particles are cleared by the liver. Elevated plasma triglyceride concentrations and prolonged circulation of cholesterol-rich remnants, especially in diabetic dyslipidemia, are risk factors for cardiovascular disease. However, the precise biological role of BAT for TRL clearance remains unclear. Here we show that increased BAT activity induced by short-term cold exposure controls TRL metabolism in mice. Cold exposure drastically accelerated plasma clearance of triglycerides as a result of increased uptake into BAT, a process crucially dependent on local LPL activity and transmembrane receptor CD36. In pathophysiological settings, cold exposure corrected hyperlipidemia and improved deleterious effects of insulin resistance. In conclusion, BAT activity controls vascular lipoprotein homeostasis by inducing a metabolic program that boosts TRL turnover and channels lipids into BAT. Activation of BAT might be a therapeutic approach to reduce elevated triglyceride concentrations and combat obesity in humans.     

Oral supplementation with l-aspartate and l-glutamate inhibits atherogenesis and fatty liver disease in cholesterol-fed rabbit

Previous studies have shown that dietary supplementation with l-aspartate and l-glutamate inhibits fatty streak initiation in cholesterol-fed rabbit. The present study investigates the role of dicarboxylic amino acids on the progression of fatty streaks and the development of fatty liver disease, which were caused in New Zealand White rabbits after a 0.5% w/w cholesterol diet for 7 weeks. A group of animals additionally received a combination of 12.5 mM l-aspartate and 12.5 mM l-glutamate per day through drinking water. Total cholesterol (TC), high-density lipoproteins cholesterol (HDLC), non-HDLC and triacylglycerol (TAG) concentrations were measured in plasma. Serum gamma-glutamyl transferase (γ-GT), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were also determined. At the end of dietary intervention, animals were sacrificed. Aortic, hepatic and brain lesions were evaluated after staining with hematoxylin and eosin. Supplementation with dicarboxylic amino acids inhibited the progression of aortic intima thickness (P < 0.05) and the development of liver lesions (P < 0.05). TC, non-HDLC and TAG were similarly increased in both cholesterol-fed groups. Serum γ-GT and AST activities elevated during the study in all cholesterol-fed animals but the elevation of γ-GT was milder and significantly lower in rabbits treated with l-aspartate and l-glutamate (P < 0.05). ALT activity was not affected by cholesterol feeding. In conclusion, oral supplementation with l-aspartate and l-glutamate inhibits the progression of atherogenesis and the development of fatty liver disease in the animal model of cholesterol-fed rabbit. The beneficial effects of dicarboxylic amino acids reflect the limited elevation of serum γ-GT activity.     

The fatty acid composition of glycerolipids in nerve,brain, and other tissues of the streptozotocin diabetic rat

The fatty acid composition of individual glycerolipids in brain and sciatic nerve of rats made diabetic with streptozotocin and sacrificed 8 weeks later was determined and compared to the alterations that occurred in liver and kidney glycerlipids. A substantial decrease in the proportion of arachidonic acid and increases in the relative content of linoleic and docosahexenoic (22∶6n3) acids occurred in the phosphoglycerides of visceral tissues from diabetic animals as reported by others. In contrast, except for a small rise in the percentage of linoleic acid, no consistent changes in fatty acid composition of phosphatidylcholine, phosphatidylethanolamine, ethanolamine plasmalogen, phosphatidylinositol or phosphatidylerrine from brain or nerve were detected. The fatty acids of triacylglycerol associated with nerve exhibited alterations similar to those characteristic of liver. The differences which developed as a result of diabetes were completely prevented if animals were maintained continuously on insulin commencing shortly after administration of streptozotocin. It is concluded that the fatty acid composition of brain and nerve phosphoglycerides are unusually resistant to alteration in the diabetic animal and that consequently, changes in bulk membrane fluidity are unlikely to contribute to functional abnormalities displayed by diabetic peripheral nerve. Special Issue dedicated to Dr. Eugene Kreps.     

Effect of ingestion of saline, glucose, and ethanol on mobilization and hepatic incorporation of epididymal pad palmitate-1-14C in rats

The effect of ingestion of saline, glucose, and ethanol (isocaloric with the glucose) on the mobilization of radiopalmitate from epididymal fat prelabeled in vivo and the incorporation of the mobilized label into liver lipids was investigated in rats. The mobilization of radiopalmitate from epididymal fat and the incorporation of the mobilized label into liver triglyceride were most markedly elevated by ingestion of ethanol. Increased mobilization and diversion of epididymal adipose tissue fatty acids to liver lipids of ethanol-treated rats were shown also by the close resemblance of the fatty acids of liver triglyceride to the fatty acids of epididymal fat. The amount of radiopalmitate mobilized by the saline-treated rats, comprising approximately a third of that mobilized by the ethanol-treated animals, was larger than the amount mobilized by the rats treated with glucose; most of it was oxidized rather than incorporated into the liver fats. In glucose-treated rats a larger fraction of radiopalmitate mobilized from one prelabeled epididymal pad was diverted to and incorporated into the lipids of the contralateral pad of the same animal. The specific activity of hepatic triglyceride of ethanol- and saline-treated rats was similar and significantly higher than that of animals treated with glucose. These data indicate that the ethanol-induced fatty liver can be attributed to an increased mobilization and incorporation of adipose tissue fatty acids into liver lipid and to an altered hepatic metabolism of fatty acids and triglyceride.