A high glycemic index starch diet affects lipid storage-related enzymes in normal and to a lesser extent in diabetic rats.

The of this study was to evaluate the chronic effects of a high (waxy corn) vs. a low (mung beans) glycemic index starch diet on the lipogenic enzymes, fatty acid synthase (FAS) and lipoprotein lipase (LPL). Normal and diabetic (streptozotocin-injected on d 2 of life) male Sprague-Dawley rats consumed a diet containing 575 g/kg carbohydrates either as waxy cornstarch (WCS) or as mung bean starch (MBS). After 3 wk, neither body weights nor relative epididymal fat pad weights differed. In diabetic rats, the WCS diet induced high basal plasma insulin levels. Plasma triglycerides were not significantly affected by diet in either normal or diabetic rats. Adipose tissue and liver LPL activities were not modified by the type of starch in the diet. In normal rats, FAS activity and gene expression in epididymal adipose tissue but not in liver were greater in rats consuming the WCS diet than in those consuming MBS. To evaluate the implication of insulin in this regulation, two genes regulated by insulin [GLUT4 and phosphoenolpyruvate carboxykinase (PEPCK)] were also studied. The high glycemic index WCS diet compared with the low glycemic index MBS diet resulted in lower hepatic PEPCK mRNA in both normal and diabetic rats. Normal, but not diabetic rats fed WCS had greater GLUT4 gene expression in adipocytes than did those fed MBS. We conclude that the total replacement of 575 g/kg low glycemic index starch by a high glycemic index starch for 3 wk caused the following in normal rats: 1) high FAS activity and mRNA in adipose tissue but not in liver and 2) high GLUT4 gene expression in adipose tissue. In both normal and diabetic rats this same diet resulted in lower hepatic PEPCK mRNA. Therefore, high glycemic index starch diet is implicated in stimulating FAS activity and lipogenesis and might have undesirable long-term metabolic effects.

Evidence for a sustained genetic effect on fat storage capacity in cultured adipose cells from Zucker rats.

Using mature adipocytes and preadipocytes from genetically obese Zucker rats, we investigated the cells' ability to maintain abnormal fat storage capacity when withdrawn from their in vivo environment. Long-term adipocyte cultures from obese rats displayed an increase in both glucose consumption (GC) and enzyme activities, including fatty acid synthase (4-fold), glycerol-3-phosphate dehydrogenase (4.5-fold), lipoprotein lipase (LPL; 6-fold), and malic enzyme (2.5-fold). Fully differentiated obese predipocytes exhibited a twofold increase in these enzyme activities, together with higher glucose metabolism. In obese cells, LPL mRNA was increased in both adipocytes (6-fold) and differentiated preadipocytes (2-fold). Insulin mediated an increase in GC and lipogenic enzymes in both adipocytes and preadipocytes regardless of the genotype; this effect was more marked in obese cells. Examining cultured adipocytes from rats fed a high-fat diet, we showed that the nutritional effect upon GC and lipogenic enzymes was abolished after culture. These results demonstrated that fatty mutation may be intrinsically expressed in prolonged cultured mature adipocytes and in newly differentiated adipocytes.

Gene expression of lipid storage-related enzymes in adipose tissue of the genetically obese Zucker rat. Co-ordinated increase in transcriptional activity and potentiation by hyperinsulinaemia.

The genetically obese Zucker rat displays excessive fat storage capacity which is due to a tissue-specific increase in the activities of a number of lipid storage-related enzymes in adipose tissue. The aim of this study was to investigate the molecular mechanism responsible for this phenomenon. Lean (Fa/fa) and obese (fa/fa) Zucker rats were studied during the early stages of adipose tissue overdevelopment, both before (at 16 days of age) and after (at 30 days of age) the emergence of hyperinsulinaemia, in order to delineate the effects of the fatty genotype independently of those of hyperinsulinaemia. Lipoprotein lipase (LPL), glycerophosphate dehydrogenase (GPDH), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and malic enzyme (ME) mRNA levels in the adipose tissue of lean and obese rats were assessed by Northern blot analysis, and the relative transcription rates of the corresponding genes were compared in the two genotypes by a nuclear run-on assay. In normoinsulinaemic 16-day-old pre-obese rats, mRNA levels were increased over control values (LPL, 5-fold; ME, 2-fold; GAPDH, 3-fold), in close correlation with genotype-mediated differences in enzyme activities. Stimulation of the transcription rates of the ME and GAPDH genes was observed in obese rats, which could fully account for differences in steady-state mRNA levels. At this age, GPDH activity, mRNA level and transcription rate were similar in the two genotypes. In hyperinsulinaemic 30-day-old obese rats, a 6-7-fold increase in both mRNA and the transcription rate of GPDH emerged, together with an amplification of the genotype-mediated differences observed in younger animals (GAPDH, 6-fold; ME, 7.9-fold; LPL, 10-fold). These results demonstrate that the obese genotype exerts a co-ordinated control on the expression of these genes in adipose tissue, mainly at the transcriptional level. This genotype effect is greatly amplified by the development of hyperinsulinaemia.

Evidence of enhanced storage capacity in adipose tissue of genetically fat chickens.

The storage capacity for plasma triglyceride in abdominal adipose tissue has been investigated in two lines of chickens selected for either high or low adiposity (fat line and lean line, respectively). Adipose tissue cellularity and lipoprotein lipase (LPL) activity were estimated in 2- and 5-wk-old birds. In 2-wk-old birds, cellularity and LPL and glycerophosphate dehydrogenase (GPDH) activity were evaluated in the stromavascular fraction. At both ages studied, the fat line exhibited a twofold increase in mature fat cell number and a marked hypertrophy. LPL activity per cell did not differ with genotype, regardless of the nutritional state; however, LPL activity per whole fat pad was higher in fat birds. In 2-wk-old fat chickens, the stromavascular fraction was characterized by an increase in cell number and a decrease in LPL activity, while GPDH was unchanged. Finally, adipocyte hyperplasia in the fat line appeared to reflect an excessive proliferation of precursor cells. The higher LPL activity in fat birds resulted mainly from cell hyperplasia, rather than from a greater intrinsic activity of adipocytes. Consequently, enhanced fatty acid uptake by adipose tissue represents a major factor in determination of adiposity in the chicken.

Glucocorticoid binding during the differentiation of 3T3-F442A fibroblasts into adipocytes. A possible regulatory effect of insulin.

Until recently, few studies had been carried out on receptors for glucocorticoids in adipocytes, although the role of these steroids is considerable. In the present studies, we chose the pre-adipocyte line 3T3-F442A, which constitutes an excellent model for investigating the differentiation and function of adipocytes. Using a whole cell assay system, we showed the existence of a homogenous class of sites with the characteristics of glucocorticoid receptors, that is, high-affinity binding which is reversible, specific and saturable. Whatever the state of cellular differentiation, the affinity of the receptor for dexamethasone did not vary, although we observed an increase in the number of sites during differentiation. When cells were differentiated in the presence of insulin, there was a further increase in the binding capacity; moreover, insulin deprivation of such adipocytes caused a decrease in the number of sites. Our results therefore suggest that factors other than the glucocorticoids themselves influence dexamethasone binding. It is suggested that insulin plays a role in the regulation of the number of glucocorticoid receptors.

Growth hormone binding to cultured preadipocytes from obese fa/fa rats increases during cell differentiation.

Preadipocytes from 7 day-old obese Zucker rats and from their lean littermates were grown in primary culture. Specific binding of human growth hormone (hGH) to the cells is demonstrated. There is no change in hGH binding to preadipocytes from lean animals before (day 5 of the culture) and after adipose conversion (day 12). Moreover, addition of insulin to the culture medium does not affect the specific binding of 125I-hGH to the cells. On the contrary, when 1 nM insulin is added to the culture medium of preadipocytes from obese rats, the specific binding of 125I-hGH is enhanced during the cell differentiation, with a 3-fold increase in the number of binding sites. The functional significance of these additional GH sites in differentiated preadipocytes from obese rats has to be examined.

A method for separating cultured preadipocytes according to their density: application to stromal cells from overfed suckling rats.

The stroma vascular fraction of adipose tissue consists of a heterogeneous cell population; not all the cells in this compartment undergo adipose conversion in primary culture. A density gradient centrifugation procedure was used to separate cultured cells on the basis of their triglyceride content. This method was applied to both stroma vascular cells from rat adipose tissue and to a 3T3 F442A preadipose cell line as a reference. Comparison of the results obtained from these two cell types suggests that this separation procedure can lead to a quantification of adipose differentiation in the heterogeneous stromal cell population. Separation procedures were applied to cultured stromal cells derived from young rats during the onset of nutritional obesity induced by overfeeding in early life. Results show that early overfeeding induced an increase in the stromal cell differentiation capacity which is expressed in vitro.

Dietary no-effect level of a dithiocarbamate fungicide, thiram, evaluated from measurement data on rats. I. Choice of the model of the dose-response relationship.

Rats were fed diets containing various amounts of added thiram, a dithiocarbamate fungicide. As thiram feeding resulted in decreased appetite, control rats not receiving thiram were pair-fed to the experimental ones. On d 30 of the experiment the animals were weighed and sacrificed, and the following organs were weighed: liver, kidneys, heart, epididymal and perirenal fat pads, testes, seminal vesicles, tibia, adrenals, and thyroid. Liver concentrations of lactate, pyruvate, beta-hydroxybutyrate, acetoacetate, ATP, and ADP were determined by enzymatic-spectrofluorimetric assay. For each parameter studied and each thiram dosage, values for treated rats were compared to those for control rats and the probability under the null hypothesis was computed. These probabilities were transformed into probits, logits, or "Weibull transforms" and plotted against the logarithms of the respective doses. Models were fitted to the data by linear regression techniques. Finally, the dose inducing the least significant difference (LSD dose), and the dose considered "safe" at P = 0.95, 0.99, and 0.999 were calculated. Significant pesticide-induced changes in the following parameters were found: food intake; weights of the whole body, kidneys, epididymal and perirenal fat pads, testes, and seminal vesicles; and liver beta-hydroxybutyrate/acetoacetate and lactate/pyruvate ratios. As the models did not differ in fit to the experimental data or in computed LSD doses, they were discriminated on the grounds of their underlying theoretical assumptions and their prediction of safe doses in a long-term study. The log-probit model was rejected for the former reason, and it was shown that the Weibull model foresees a nonnegligible risk of change, with thiram feeding at low doses, for too many parameters. The analysis resulted in the selection of the log-probit model for further use. Weight of fatty tissues was the most sensitive parameter and, using the log-probit model, the predicted no-effect dose at the 95 percent confidence level was 38 ppm thiram in the diet.

[Cellular energy metabolism in rats receiving diets contaminated with lindane]. / Métabolisme énergétique cellulaire chez des rats recevant un régime contaminé par du lindane.

Young male rats, Wistar CF strain, about 70 g body weight, were fed a well-balanced diet containing 0 (control), 60 or 240 ppm lindane. The day before the experiment, all the animals were fasted, and some of them placed in a restraint wheel forcing them to walk on during 18 hrs; another group was given an i.p. injection of 2.6 g/kg glucose 30 minutes before their sacrifice. The redox and energy potentials of liver and muscle tissues were estimated after the determination of the following compounds: lactate, pyruvate, beta-hydroxybutyrate, acetoacetate, ATP, ADP, AMP, inorganic phosphate, NADP and NADPH. No effect of lindane was observed on muscle metabolism and the 60 ppm dose was without significant effect on liver metabolism. At the 240 ppm dosage: a. Lindane ingestion increased the liver betaHOB/AcAc ratio and decreased the Lac/pyr ratio. The ATP/ADP ratio was not significantly lowered, although the ATP concentration was diminished and, conversely, the AMP and inorganic P ones were elevated; b. Whereas lindane lowered the glucose effect on the mitochondrial redox potential, it had no influence on the increasing of the ATP/ADP ratio by glucose, or on the antiketogenic effect of this sugar; c. In the animals fed the lindane-contaminated diet, muscular exercise increased the liver betaHOB/AcAc and NADPH/NADP ratios, while the lac/pyr and ATP/ADP ratios were unaltered. But blood pyruvate was increased. The following interpretation has been given. Lindane ingestion inhibits liver mitochondrial activity and increases ketogenesis. The glucose treatment results in a poor glucose utilization for energy needs in the contaminated animals and the forced muscular exercise shows that gluconeogenesis proceeds at a slower rate than in the controls. It is suggested that an increased demand in NADPH, as resulting from the induction of the microsomal enzymes by lindane, is one of the mechanisms by which the pesticide inhibits the activity of the tricarboxylic acid cycle.

[Lipid metabolism in rats fed a diet rich in various carbohydrates. I. Results after I.P. injection of lipogenic precursors]. / Métabolism lipidique chez le rat recevant un régime riche en certains glucides. I. Résultats obtenus après injection I.P. de précurseurs lipogéniques

Male rats, Wistar CF strain, weighing 120 g at the beginning of the experiment, were fed during 7 months with one of the following diets, containing 72 p. 100 (w/w) carbohydrate: starch, fructose, glucose and sucrose. These diets were about 18% (w/w) in protein content and were conveniently balanced with respect to vitamins and mineral nutrients. After an overnight fast, the animals received by the i.p. way, 30 mn before their killing, one of the following lipogenic precursors: glucose (considered as the control treatment), fructose ethanol or acetate, thus forming 16 experimental groups. In their liver, heart and blood were determined the concentrations of 6 lipid compounds: triglycerides, non-esterified fatty acids, free, esterified and total cholesterol, phospholipide. a. The sucrose diet gave the heaviest animals, with a liver and heart which were the richest in triglyceride content. They had also the highest liver and blood cholesterol, but their blood phospholipid was the lowest. The starch diet also increased, compared to the glucose diet, liver and heart triglycerides and liver cholesterol. As regards the fructose diet, it had the same effects than the sucrose one in elevating liver weight, blood triglycerides and cholesterol; conversely, it lowered liver and chiefly heart triglycerides and increased blood phospholipide. The glucose diet was for almost all parameters the one which displayed the lowest values. b. Relative to the glucose injection, other ones increased liver triglycerides, cholesterol and phospholipids and non-esterified fatty acids of the 3 assayed tissues. We observed that some differences between the effects of two given injections varied according to the previous diet, e.g. the sucrose-fed rats had more liver triglycerides and cholesterol, more heart and blood cholesterol after i.p. fructose than after i.p. glucose, which was not the case for the starch-fed animals. The importance of liver esterification reactions, which are increased with a long-term administration of a fructose-containing diet, is emphasized in the discussion. However dietary fructose could not be able to display its lipogenic effets in the absence of dietary glucose and that is why sucrose is more efficient than glucose in promoting a net lipid synthesis.