Effect of sodium 2-n-pentadecyl-benzimidazole-5-carboxylate (M & B 35347B), an inhibitor of acetyl-CoA carboxylase, on lipogenesis and fat deposition in obese hyperglycaemic (ob/ob) and lean mice

A high rate of lipogenesis in obese mice plays a major role in their excessive deposition of body lipid. Inhibition of lipogenesis may decrease their obesity. Therefore, we have investigated the effects of sodium 2-n-pentadecyl-benzimidazole-5-carboxylate (M & B 35347B), an inhibitor of acetyl-CoA carboxylase, on in-vivo lipogenesis in obese and lean mice. It significantly inhibited hepatic cholesterol and fatty acid synthesis, measured using 3H2O, in both lean and obese mice, with or without a glucose load. Brown adipose tissue (scapular) lipogenesis was decreased by M & B 35347B in obese mice but not in lean mice. In white adipose tissue, M & B 35347B did not affect the rates of lipogenesis in either scapular white, inguinal or epididymal depots of obese mice, or the inguinal and scapular white depot of lean mice. However, it doubled lipogenesis in the epididymal fat pad of lean mice. After a glucose load, lipogenesis in the lean epididymal fat pad was not inhibited but that in the inguinal depot was. M & B 35347B inhibited acetyl CoA carboxylase of adipose tissue in vitro but only a small inhibition was detected after in-vivo treatment. These different responses according to type of mouse, treatment and tissue site appear to stem from differences in inhibitor concentration and the importance of acetyl CoA carboxylase as the rate-limiting enzyme of lipogenesis. The weight gain of obese mice dosed orally (200 mg M & B 35347B/kg daily) for 60 days was unaffected and they continued to deposit excess body fat. This presumably occurred because of the lack of inhibition of fatty acid synthesis in white adipose tissue.     

Reduced lipogenesis in rats fed a high-protein carbohydrate-free diet

Rates of fatty acid synthesis were assessed in carcass, liver, and adipose tissue from rats fed for 30 to 40 days a balanced diet (66% wt/wt carbohydrate, 17% casein, 8% fat) or a high-protein carbohydrate-free diet (70% casein, 8% fat). Despite similar body weight increases, carcass fatty acid content of rats on the high-protein (HP) diet was 13% less, and the weight of their epididymal fat pads was reduced by 29% in relation to the controls. In vivo incorporation of 3H2O into carcass fatty acids (FA) and into liver triacylglycerol (TAG) was significantly reduced in HP-fed rats. FA synthesis from 14C-acetate, glucose, or leucine and from 3H2O was also markedly decreased in liver slices from HP rats. The amount of 3H-TAG that accumulated in plasma of rats injected with triton WR 1339 to block peripheral utilization of lipoprotein corresponded in HP and control rats to only 4.1% and 5.0%, respectively, of 3H-FA recovered in carcasses from animals not treated with triton, indicating that almost all of the carcass 3H-TAG was synthesized in situ. However, on a long term basis, the reduced hepatic lipogenesis and the resulting decreased transport of TAG might affect lipid accumulation in HP rats. In vivo lipogenesis from 3H2O and in vitro FA synthesis from 3H2O and from 14C-precursors did not differ significantly in retroperitoneal and epididymal adipose tissue from HP and control rats. In both groups of animals, in vivo rates of lipogenesis were higher in retroperitoneal than in epididymal adipose tissue but still did not account for rates of FA synthesis by carcasses, suggesting the existence of other sites with higher lipogenic activity.     

Lipogenesis in situ in the genetically obese Zucker fatty rat (fa/fa): Role of hyperphagia and hyperinsulinaemia

Summary In situ fatty acid synthesis has been measured with ³H₂O in anaesthetised lean and obese Zucker (fa/fa) rats. The accumulation of fatty acids was increased in both the liver and adipose tissue of young fa/fa rats as a result of both an increased rate of lipogenesis and an increase in tissue mass. Whereas total hepatic lipogenesis increased with age, total adipose tissue lipogenesis decreased in older fa/fa rats. Experiments with hepatectomized rats showed that the liver was the major site of the excess fatty acid synthesis in fa/fa rats. The enhanced rate of lipogenesis in fa/fa rats was abolished by either pairfeeding or streptozotocin treatment. The results suggest that the increased fatty acid synthesis in fa/fa rats is secondary to the hyperphagia, hpyerinsulinaemia, and increased mass of hepatic and adipose tissues.The authors are grateful to the M. R. C. for award of a project grant.     

De novo lipogenesis in adipose tissue of lean and obese women: application of deuterated water and isotope ratio mass spectrometry

OBJECTIVE: To evaluate the feasibility of using deuterated water and isotope ratio mass spectrometry to measure de novo fatty acid synthesis in adipose tissue, and to compare this parameter in obese and lean women. SUBJECTS: Six lean and six obese premenopausal Caucasian women in the main study and three obese Pima Indians in a pilot study. MEASUREMENTS: Deuterated water was administered orally twice daily for 14 days to create stable deuterium enrichment in body water, during which series of blood samples were collected to measure body water deuterium enrichment and deuterium incorporation into plasma total Triacylglycerol (TG) fatty acids and total cholesterol. Subcutaneous fat at different sites were sampled at the beginning and the end of deuterium administration to measure deuterium incorporation into TG fatty acids. RESULTS: Fractional de novo synthesis rate of TG fatty acids in adipose tissue was 0. 014+/-0.005 and 0.014+/-0.007% in lean and obese Caucasian women, corresponding to 2+/-0.7 and 5.6+/-3.2 g (P=0.3) of fatty acids synthesized daily, respectively. Plasma TG fatty acids and cholesterol synthesis rates were comparable to those reported previously. A pilot study showed that de novo lipid synthesis in adipose tissue of obese Pima Indians was also quantitatively minor. CONCLUSION: Human adipose tissue, like the liver, does not make a major contribution to whole body lipogenesis under eucaloric conditions. A combination of deuterated water and isotope ratio mass spectrometry is a useful research tool for studying accumulation of de novo synthesized lipids in human adipose tissue.     

Adrenalectomy reduces but does not reverse obesity in ob/ob mice

Bilateral adrenalectomy (ADX) of 4-month-old ob/ob mice led to reduced rates of body weight gain, a complete cessation of fat deposition and increased percentage carcass protein and ash during a 2-month observation period after surgery. However, ADX obese mice were still heavier and had more body fat and lower concentrations of carcass protein and ash than intact sex-matched littermate lean mice at the end of the experiment. When adrenalectomy was performed in younger obese mice before the syndrome was fully expressed (23 +/- 2 days of age), body weight gain was reduced by 40 per cent and fat deposition by 50 per cent during the next 3.5 months, but each was still greater than that of littermate lean mice. Despite the lower rate of weight gain after adrenalectomy, the skeletal and lean body growth of the early ADX obese mice equalled that of both obese and lean mice fed ad libitum. When the carcass composition of early ADX obese mice was compared with that of intact obese mice which were calorically restricted to the same rate of body weight gain, the ADX group had significantly less carcass fat (28 per cent) and more protein (50 per cent) and ash (20 per cent) than the dieted obese mice. In both experiments adrenalectomy led to reduced circulating immunoreactive insulin levels, although hyperinsulinemia persisted. The present results show that adrenalectomy is an effective tool for ameliorating the severity of many aspects of the ob/ob syndrome, particularly when compared with caloric restriction, but the procedure does not entirely reverse the deranged metabolism or abnormal carcass composition of these mice.     

Comparative study of the lipogenic potential of human and rat adipose tissue

The reported low activity of lipogenic enzymes (especially adenosine triphosphate [ATP]-citrate lyase) in human adipose tissue led to the general conclusion that in humans lipogenesis occurs primarily in the liver. However, recent studies indicate that the liver plays a minor role in de novo lipogenesis and suggest that adipose tissue may be the principal lipogenic human tissue. In an attempt to resolve these contradictions we reinvestigated the lipogenic potential of human adipose tissue and compared with adipose tissue of rats fed a high-fat diet for 2 weeks and fasted overnight before death. These conditions mimic the nutritional state of patients at the moment of tissue sampling. We found that overnight fasting of the rats maintained previously for 12 days on a high-fat diet caused a decrease of ATP-citrate lyase of about 7-fold. Thus, in human adipose tissue, the mean activity of ATP-citrate lyase was approximately 8 times lower than in rats fed a high-fat diet and fasted overnight, and about 50 times lower than in rats maintained on normal laboratory diet. Unlike ATP-citrate lyase, fatty acid synthase (FAS) activity was only slightly lower in human adipose tissue than in rats maintained on a normal laboratory diet. Comparable FAS activity was found when rats were fed a high-fat diet and fasted overnight. The average activities of human adipose tissue acetyl-coenzyme A carboxylase, malic enzyme, and glucose-6-phosphate dehydrogenase were approximately 3-, 4-, and 6-fold lower than in adipose tissue from rats fed a high-fat diet and fasted overnight before tissue sampling, while the activity of 6-phosphogluconate dehydrogenase in humans was higher than in rat adipose tissue. No significant differences in lipogenic enzyme activities were found between male and female and between lean and obese patients. The rate of fatty acid synthesis in intact pieces of human adipose tissue was approximately 5 times lower than in adipose tissue pieces of rats fed a high-fat diet and fasted overnight before tissue samples were taken. The comparison of the lipogenic potential of humans and rats (maintained on the diet to mimic the nutritional state of patients at the time of tissue sampling) suggests that human adipose tissue is an important site of fatty acid synthesis.     

Metabolism of the mouse made obese by a high-fat diet.

Lean mice were made obese by feeding, ad libitum, a high-lard diet. They showed an increased fat cell size and number which were maintained when this diet was replaced by the control high-carbohydrate diet for 10 weeks. Obese fed mice showed normal glucose and insulin serum levels, but insulinaemia was elevated after an overnight fast. The insulinaemic response after intraperitoneal injection of glucose was insignificant. Thus hyperinsulinism is not a prerequisite for the development of obesity. High-fat diet influenced, in vitro, glucose metabolism of adipose tissue, liver and muscle: basal lipogenesis was markedly reduced in adipose tissue and liver, and glucose oxidation was decreased in muscle. Insulin sensitivity was reduced by increased fat cell size. De novo formation of fatty acids in liver and adipose tissue did not contribute to the development of obesity. The increased lipoprotein lipase activity of the large fat cells suggested that obesity resulted from a direct storage of dietary fatty acids esterified by glycerol formed from circulating glucose.     

The postprandial rates of glycogen and lipid synthesis of lean and obese female Zucker rats

OBJECTIVE: To determine the relative rates of glycogenesis and lipogenesis following administration of a test meal in lean and obese Zucker rats. PROTOCOL: Nine-week-old lean and obese Zucker rats were fasted overnight, then tube-fed a test meal of balanced composition amounting to 16kJ (lean rats and one group of obese rats) or 24kJ (one group of obese rats) and containing 200 mg 1-(13)C glucose. Immediately after the meal the rats were injected intraperitoneally with 5 mCi of 3H2O and killed 1 h later. METHODS: Glycogenesis was calculated from the incorporation of 3H into liver glycogen divided by the specific activity of plasma water. Lipogenesis was calculated similarly from the incorporation of 3H into saponifiable lipids in liver and perirenal adipose tissue. The proportion of glycogen synthesized by the indirect pathway via pyruvate was determined from the ratio of 3H labelling at positions C6 and C2 in the glycogen glucose residues. Glycogen synthesis from glucose was determined from the ratio of 13C enrichment in liver glycogen to that in plasma glucose. RESULTS: The rate of synthesis of glycogen was considerably lower in the livers of obese rats than those of lean controls, with the larger meal causing a small but significant increase in glycogenesis. The proportion of glycogen synthesized via pyruvate showed a non-significant increase in the obese rats, while the amount of glycogen synthesized from glucose was significantly decreased. Hepatic lipogenic rates were about five times higher in both groups of obese rats than the lean controls. In adipose tissue, lipogenesis per g tissue was slightly reduced in the obese rats, although there was clearly an increase in adipose tissue lipogenic activity per whole animal. The larger meal caused a greater rise in plasma glucose and insulin concentrations but did not affect lipogenic rates, although it did cause a greater suppression of lipolysis, as indicated by a lower plasma glycerol concentration. CONCLUSION: Ingested carbohydrate is partitioned predominantly into hepatic fatty acid synthesis in obese Zucker rats. Hepatic glycogen synthesis is suppressed and comes mainly from precursors other than glucose. The suppression of hepatic glycogen synthesis may contribute to the increased energetic efficiency of obese Zucker rats.     

Skeletal muscle accretion and turnover in lean and obese (ob/ob) mice.

Skeletal muscle growth in obese (ob/ob) and lean mice was estimated from changes in fat-free carcass weight during development. No differences were observed at 2 wk of age, but fat-free carcasses of obese mice weighed less than those of lean mice at 5 wk of age. Fat-free carcasses of the adult obese mice were only 78% as heavy as those of lean mice, although the obese mice weighed up to twice as much as the lean mice. Even though obese mice accumulated less muscle than lean mice, urinary creatinine output of the obese mice was equal to that of the lean mice. The amount of 3-methylhistidine (3MH) in the carcasses of the mice and urinary output of 3MH were used to calculate the fractional breakdown rate (FBR) of myofibrillar proteins. Accumulation of 3MH in the carcasses paralleled carcass weight gain; thus, obese mice accumulated less 3MH than lean mice. Urinary output of 3MH was measured from 5 to 37 wk of age and was as great in the obese as in the lean mice; consequently, the FBR of the myofibrillar proteins was faster in the obese than in the lean mice. The FBR averaged 8.5 ± 0.6%/day for obese mice and 5.0 ± 0.1%/day for lean mice. The rate of 3MH accumulation in the carcass and the FBR were subsequently utilized to calculate a fractional synthesis rate (FSR) for the myofibrillar proteins. The FSR was not reduced in obese mice. The results suggest that obese mice accumulate less muscle because the rate of muscle degradation is increased.     

Role of pentoxifylline in non-alcoholic fatty liver disease in high-fat diet-induced obesity in mice

AIM:To study pentoxifylline effects in liver and adipose tissue inflammation in obese mice induced by high-fat diet(HFD).METHODS: Male swiss mice(6-wk old) were fed a highfat diet(HFD; 60% kcal from fat) or AIN-93(control diet; 15% kcal from fat) for 12 wk and received pentoxifylline intraperitoneally(100 mg/kg per day) for the last 14 d. Glucose homeostasis was evaluated by measurements of basal glucose blood levels and insulin tolerance test two days before the end of the protocol. Final body weight was assessed. Epididymal adipose tissue was collected and weighted for adiposity evaluation. Liver and adipose tissue biopsies were homogenized in solubilization buffer and cytokines were measured in supernatant by enzyme immunoassay or multiplex kit, respectively. Hepatic histopathologic analyses were performed in sections of paraformaldehyde-fixed, paraffin-embedded liver specimens stained with hematoxylin-eosin by an independent pathologist. Steatosis(macrovesicular and microvesicular), ballooning degeneration and inflammation were histopathologically determined. Triglycerides measurements were performed after lipid extraction in liver tissue. RESULTS: Pentoxifylline treatment reduced microsteatosis and tumor necrosis factor(TNF)-α in liver(156.3 ± 17.2 and 62.6 ± 7.6 pg/mL of TNF-α for non-treated and treated obese mice, respectively; P 0.05). Serum aspartate aminotransferase levels were also reduced(23.2 ± 6.9 and 12.1 ± 1.6 U/L for nontreated and treated obese mice, respectively; P 0.05) but had no effect on glucose homeostasis. In obese adipose tissue, pentoxifylline reduced TNF-α(106.1 ± 17.6 and 51.1 ± 9.6 pg/mL for non-treated and treated obese mice, respectively; P 0.05) and interleukin-6(340.8 ± 51.3 and 166.6 ± 22.5 pg/mL for non-treated and treated obese mice, respectively; P 0.05) levels; however, leptin(8.1 ± 0.7 and 23.1 ± 2.9 ng/mL for non-treated and treated lean mice, respectively; P 0.05) and plasminogen activator inhibitor-1(600.2 ± 32.3 and 1508.6 ± 210.4 pg/mL for non-treated and treated lean mice, respectively; P 0.05) levels increased in lean adipose tissue. TNF-α level in the liver of lean mice also increased(29.6 ± 6.6 and 75.4 ± 12.6 pg/mL for non-treated and treated lean mice, respectively; P 0.05) while triglycerides presented a tendency to reduction.CONCLUSION: Pentoxifylline was beneficial in obese mice improving liver and adipose tissue inflammation. Unexpectedly, pentoxifylline increased pro-inflammatory markers in the liver and adipose tissue of lean mice.     

Tissue-specific regulation of fatty acid synthesis by thyroid hormone.

It is generally agreed that thyroid hormone stimulates the hepatic synthesis of long chain fatty acids in the rat. However, there are conflicting data about its effects in white adipose tissue, while in brown adipose tissue, lipogenic rates are highest in hypothyroid animals. We have systematically examined the effect of thyroid state on lipogenesis in different rat tissues. Fatty acid synthesis was assessed in vivo, using the incorporation of tritiated water. Hepatic lipogenesis was induced 16-fold between hypothyroid (4.1 +/- 0.6 microns H incorporated/g.h) and hyperthyroid rats (66.5 +/- 13.2 microns H/g.h). Kidney and heart were much less lipogenically active, but also responded positively to thyroid hormone. Both hyper- and hypothyroidism diminished fatty acid synthesis in retroperitoneal fat and had similar, although not significant, effects in epididymal fat. However, epididymal adipocytes, taken from hyperthyroid rats and cultured in vitro, were 3 times more lipogenically active than cells from either hypo- or euthyroid animals. Lipogenesis in sc fat from hyperthyroid rats was enhanced when calculated per g tissue, but was not different when expressed per whole tissue. In brown adipose tissue, lipogenesis was inversely related to thyroid hormone status. Fatty acid synthesis in brain, lung, skin, and bone and muscle did not respond to changes in thyroid state. TLC confirmed that greater than 90% of the incorporated tritium was in fatty acids. Thus, in hypothyroid animals, lipogenesis primarily occurs in skin, bone, muscle, and other nonresponsive organs, whereas in hyperthyroid rats, the liver alone constitutes almost half of all fatty acid synthesis. The fatty acid synthetic pathway provides an excellent model for examining the tissue-specific regulation of gene expression by thyroid hormone.     

Urinary organic acid profiles in obese (ob/ob) mice: indications for the impaired omega-oxidation of fatty acids.

As a means of generating an hypothesis to explain genetic obesity of the C57BL/6J ob/ob mouse, we used gas chromatography-mass spectrometry to compare the urinary organic acid profiles of obese (ob/ob) and lean (+/?) mice on both a chow and a chemically simplified diet. More than 60 peaks were found and quantified; 45 peaks were identified. No acid was excreted in greater amounts by lean mice and none was excreted exclusively by either lean or obese mice. When normalized to body weight (obese mice being 40% heavier) and to creatinine excretion (30% greater in obese mice), however, only the daily excretion of malate, 2-hydroxyglutarate, aconitate, 3-hydroxy-3-methylglutarate, oxalate, ethylmalonate, and 4-hydroxyphenylacetate were significantly greater in obese mice. When allowed to eat only an all-fat (Crisco) diet for 4 days, the excretion of adipate rose 10-fold in lean mice, but only threefold in obese mice. Adipate excretion by Zucker rats also increased on the Crisco diet, but was indistinguishable between lean and fatty rats, suggesting that omega-oxidation might be impaired in obese mice but not in fatty rats. This suggestion complements an earlier proposal that a comparative increase in ethylmalonate excretion, which was also characteristic of fatty Zucker rats, might be explained by an increased concentration of butyryl-CoA due to inadequate beta-oxidation. An impairment of omega-oxidation in the obese mouse may also explain why urinary 3-hydroxy-3-methylglutarate, which is derived from short chain products of beta-oxidation, is increased in obese mice but not in fatty rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of carbohydrate overfeeding on whole body macronutrient metabolism and expression of lipogenic enzymes in adipose tissue of lean and overweight humans

OBJECTIVE: Lipids stored in adipose tissue can originate from dietary lipids or from de novo lipogenesis (DNL) from carbohydrates. Whether DNL is abnormal in adipose tissue of overweight individuals remains unknown. The present study was undertaken to assess the effect of carbohydrate overfeeding on glucose-induced whole body DNL and adipose tissue lipogenic gene expression in lean and overweight humans. DESIGN: Prospective, cross-over study. SUBJECTS AND METHODS: A total of 11 lean (five male, six female, mean BMI 21.0+/-0.5 kg/m(2)) and eight overweight (four males, four females, mean BMI 30.1+/-0.6 kg/m(2)) volunteers were studied on two occasions. On one occasion, they received an isoenergetic diet containing 50% carbohydrate for 4 days prior to testing; on the other, they received a hyperenergetic diet (175% energy requirements) containing 71% carbohydrates. After each period of 4 days of controlled diet, they were studied over 6 h after having received 3.25 g glucose/kg fat free mass. Whole body glucose oxidation and net DNL were monitored by means of indirect calorimetry. An adipose tissue biopsy was obtained at the end of this 6-h period and the levels of SREBP-1c, acetyl CoA carboxylase, and fatty acid synthase mRNA were measured by real-time PCR. RESULTS: After isocaloric feeding, whole body net DNL amounted to 35+/-9 mg/kg fat free mass/5 h in lean subjects and to 49+/-3 mg/kg fat free mass/5 h in overweight subjects over the 5 h following glucose ingestion. These figures increased (P<0.001) to 156+/-21 mg/kg fat free mass/5 h in lean and 64+/-11 mg/kg fat free mass/5 h (P<0.05 vs lean) in overweight subjects after carbohydrate overfeeding. Whole body DNL after overfeeding was lower (P<0.001) and glycogen synthesis was higher (P<0.001) in overweight than in normal subjects. Adipose tissue SREBP-1c mRNA increased by 25% in overweight and by 43% in lean subjects (P<0.05) after carbohydrate overfeeding, whereas fatty acid synthase mRNA increased by 66 and 84% (P<0.05). CONCLUSION: Whole body net DNL is not increased during carbohydrate overfeeding in overweight individuals. Stimulation of adipose lipogenic enzymes is also not higher in overweight subjects. Carbohydrate overfeeding does not stimulate whole body net DNL nor expression of lipogenic enzymes in adipose tissue to a larger extent in overweight than lean subjects.     

Deposition of dietary fatty acids in young Zucker rats fed a cafeteria diet.

The content and accretion of fatty acids in 30, 45 and 60-day-old Zucker lean Fa/? and obese fa/fa rats fed either reference chow or a cafeteria diet has been studied, together with their actual fatty acid intake during each period. Diet had little overall effect on the pattern of deposition of fatty acids, but quantitatively the deposition of fat was much higher in cafeteria-fed rats. The fat-rich cafeteria diet allowed the direct incorporation of most fatty acids into the rat lipids, whilst chow feeding activated lipogenesis and the deposition of a shorter chain and more saturated pattern of fatty acids. Genetic, obesity induced a significant expansion of net lipogenesis when compared with lean controls. Cafeteria-fed obese rats accrued a high proportion of fatty acids, which was close to that ingested, but nevertheless showed a net de novo synthesis of fatty acids. It is postulated that the combined effects of genetic obesity and a fat-rich diet result in high rates of fat accretion with limited net lipogenesis. Lean Zucker rats show a progressive impairment of their delta 5-desaturase system, a situation also observed in obese rats fed a reference diet. In Zucker obese rats, cafeteria feeding resulted in an alteration of the conversion of C18:2 into C20:3. The cafeteria diet fully compensated for these drawbacks by supplying very high amounts of polyunsaturated fatty acids.     

In vivo expression of carbohydrate responsive element binding protein in lean and obese rats

ChREBP (Carbohydrate response element binding protein) is considered to mediate the stimulatory effect of glucose on the expression of lipogenic genes. Its activity is stimulated by glucose. Less is known on the control of its expression. This expression could be controlled by nutritional (glucose, fatty acids) and hormonal (insulin) factors. We examined the in vivo nutritional control of ChREBP expression in liver and adipose tissue of Wistar rats. Compared respectively to the fed state and to a high carbohydrate diet, ChREBP mRNA concentrations were not modified by fasting or a high fat diet in rat liver and adipose tissue. FAS and ACC1 mRNA concentrations were on the contrary decreased as expected by fasting and high fat diets and these variations of FAS and ACC1 mRNA were positively related to those of SREBP-1c mRNA and protein, but not of ChREBP mRNA. Therefore i) ChREBP expression appears poorly responsive to modifications of nutritional condition, ii) modifications of the expression of ChREBP do not seem implicated in the physiological control of lipogenesis. To investigate the possible role of ChREBP in pathological situations we measured its mRNA concentrations in the liver and adipose tissue of obese Zucher rats. ChREBP expression was increased in the liver but not the adipose tissue of obese rats compared to their lean littermates. These results support a role of ChREBP in the development of hepatic steatosis and hypertriglyceridemia but not of obesity in this experimental model.     

Effects of diets containing medium-chain and long-chain triacylglycerols in the genetically obese Zucker fa/fa rat. Composition of fatty acids and triacylglycerols of the liver and adipose tissues

The effects of a hyperlipidic diet containing medium-chain triacylglycerols (MCT) or long-chain triacylglycerols (LCT) and a control diet on the lipid composition of liver and adipose tissue in the Zucker fa/fa and Fa/- rat are compared. The weights of liver and adipose tissues of the rats fed the MCT diet are little different from those of the two other groups, but they are always higher in obese rats than in lean rats. After feeding the MCT diet, the amounts of the constituent octanoic and decanoic acids in liver and adipose tissues are higher in the fa/fa rat than in the Fa/- rat. The rate of lipogenesis in liver and adipose tissues of the obese rat fed the MCT diet remains high.     

Bromocriptine/SKF38393 treatment ameliorates dyslipidemia in ob/ob mice.

Our previous studies have shown that the dopaminergic D1 receptor agonist SKF38393 (SKF) plus the D2 receptor agonist bromocriptine (BC) act synergistically to reduce obesity in obese C57BL/6J (ob/ob) mice. The present study investigated the effects of this combination on dyslipidemia in ob/ob mice. Female ob/ob mice were treated daily with vehicle or SKF (20 mg/kg body weight [BW]) plus BC (16 mg/kg BW [BC/SKF]) for 14 days. The animals were then used for the characterization of plasma lipoprotein profiles, hepatic triacylglycerol synthesis and secretion, adipocyte lipolysis, adipose and muscle lipoprotein lipase (LPL) activity, and muscle triglyceride (TG) content. The treatment significantly reduced plasma glucose 54%, TG 41%, cholesterol 21%, phospholipid 20%, and free fatty acid (FFA) 36% (P < .01). Hepatic triacylglycerol synthesis was 55% lower in treated mice versus control mice (P < .01). The cell size of isolated adipocytes was significantly reduced (41%) by treatment. LPL activity was increased in soleus skeletal muscle (25%, P < .05) but was sharply reduced in adipose tissue (91%, P < .01) in treated versus control mice. The TG content of hindlimb muscle was about 49% lower in treated versus control mice (P < .05). The basal and isoproterenol-stimulated lipolytic rate was decreased (approximately 53%) in adipocytes from treated animals compared with the control (P < .01). In conclusion, BC/SKF normalized the hypertriglyceridemia likely via its simultaneous antilipogenic action in liver tissue and antilipolytic action in adipose tissue. Decreased plasma flux of FFA partially contributed to the reduced hepatic lipogenesis, plasma very-low-density lipoprotein (VLDL)-TG, and TG in skeletal muscle. The above-described effects of BC/SKF treatment are largely independent of its effect to normalize hyperphagia in ob/ob mice.     

The metabolic fate of an oral 14C-alanine load in the obese Zucker rat.

Following an oral 14C-alanine load, obese Zucker rats showed the same rate of intestinal amino acid absorption as their lean counterparts. Alanine absorption was unchanged by a 24 h starvation period. The whole-body oxidation of the absorbed tracer was lower in the fa/fa rats and was significantly decreased in both lean and obese groups when the animals were submitted to starvation. The incorporation of the 14C-tracer into 14C-lipid was significantly higher in the carcass, skeletal muscle, white adipose tissue and liver of the obese animals, while that of brown adipose tissue was decreased as compared to that of the lean rats. Starvation induced no variation in 14C-lipid incorporation in the lean (+/?) animals while it sharply decreased this parameter in the obese. The incorporation of the tracer into 14C-glycogen and 14C-protein was also increased in the liver of the obese rats while no changes in incorporation into these fractions were observed in skeletal muscle. It is concluded that dietary amino acids significantly contribute to the hyperlipogenesis found in the liver and adipose tissue of the fa/fa rats.     

Relative importance of sympathetic outflow and insulin in the reactivation of brown adipose tissue lipogenesis in rats adapted to a high-protein diet

The effect of denervation or acute insulin deficiency on brown adipose tissue lipogenesis was investigated in rats adapted to a high-protein diet before and after diet reversion to a balanced diet. Denervation of rats fed the balanced diet induced a 50% reduction in in vivo rates of brown adipose tissue fatty acid synthesis, with decreased activities of acetyl-CoA carboxylase and adenosine triphosphate (ATP)-citrate lyase. The markedly (80%) reduced fatty acid synthesis and enzyme activities in brown adipose tissue from rats adapted to the high-protein diet were not affected by denervation. Replacement of the high-protein diet by the balanced diet for 24 hours restored fatty acid synthesis to normal levels, but recovery of enzyme activities was only partial. Lipogenesis restoration and partial recovery of enzyme activities were impaired in denervated tissue from high-protein diet-fed rats. In all experimental conditions, the activities of acetyl-CoA carboxylase and ATP-citrate lyase showed a better correlation with brown adipose tissue lipogenesis than the generators of H(+), glucose-6-P dehydrogenase, and malic enzyme. Anti-insulin serum administration during the 12- to 24-hour period after diet reversion completely blocked lipogenesis recovery in innervated and denervated tissues and drastically reduced brown adipose tissue lipogenesis of concomitantly injected rats fed the balanced diet. The data suggest that efficient and rapid adjustments of brown adipose tissue lipogenesis require sympathetic activation, and that this tissue can maintain significant, albeit reduced, rates of lipogenesis in the absence of sympathetic activation, but not in the absence of insulin.     

Modulation of fatty acid synthesis in vivo in brown adipose tissue, liver and white adipose tissue of cold-acclimated rats

The present experiment was an appraisal of the relative importance of fatty acid synthesis in brown adipose tissue (BAT) in young 28 or 5 degrees C adapted rats (9 weeks old). With a low-fat diet in vivo incorporation of 3H2O into BAT fatty acids was 8 times lower during the day than during the night and was not modified by a 6-hour fast during the day (28 degrees C). Cold acclimation doubled (night) or increased 8 times (day) BAT lipogenesis. Fasting led to a halving of the diurnal rate. A high-fat diet led to large decrease in synthesis rate during the night but had a weak effect on diurnal synthesis. The specific activity of fatty acids was 3 times lower in phospholipids than in neutral lipids. A comparison between 9- and 15-week-old rats indicated that in older warm-adapted rats BAT lipogenesis decreased by half but that cold stimulation was unaltered. These results were compared with hepatic and epididymal white adipose tissue lipogenesis. In conclusion, we showed that BAT of 5 degrees C rats is an important but not the major site for the conversion of carbohydrate to fat and that the proportional involvement of each tissue is age-dependent.