Serum lipids and lipoprotein composition in spontaneously diabetic BB Wistar rats

Susceptibility to fatty acid-induced β-cell dysfunction is enhanced in prediabetic diabetes-prone biobreeding rats: a potential link between β-cell lipotoxicity and islet inflammation

β-Cell lipotoxicity is thought to play an important role in the development of type 2 diabetes. However, no study has examined its role in type 1 diabetes, which could be clinically relevant for slow-onset type 1 diabetes. Reports of enhanced cytokine toxicity in fat-laden islets are consistent with the hypothesis that lipid and cytokine toxicity may be synergistic. Thus, β-cell lipotoxicity could be enhanced in models of autoimmune diabetes. To determine this, we examined the effects of prolonged free fatty acids elevation on β-cell secretory function in the prediabetic diabetes-prone BioBreeding (dp-BB) rat, its diabetes-resistant BioBreeding (dr-BB) control, and normal Wistar-Furth (WF) rats. Rats received a 48-h iv infusion of saline or Intralipid plus heparin (IH) (to elevate free fatty acid levels ~2-fold) followed by hyperglycemic clamp or islet secretion studies ex vivo. IH significantly decreased β-cell function, assessed both by the disposition index (insulin secretion corrected for IH-induced insulin resistance) and in isolated islets, in dp-BB, but not in dr-BB or WF, rats, and the effect of IH was inhibited by the antioxidant N-acetylcysteine. Furthermore, IH significantly increased islet cytokine mRNA and plasma cytokine levels (monocyte chemoattractant protein-1 and IL-10) in dp-BB, but not in dr-BB or WF, rats. All dp-BB rats had mononuclear infiltration of islets, which was absent in dr-BB and WF rats. In conclusion, the presence of insulitis was permissive for IH-induced β-cell dysfunction in the BB rat, which suggests a link between β-cell lipotoxicity and islet inflammation.

Involvement of eotaxin, eosinophils, and pancreatic predisposition in development of type 1 diabetes mellitus in the BioBreeding rat

Allergy and autoimmunity are both examples of deregulated immunity characterized by inflammation and injury of targeted tissues that have until recently been considered disparate disease processes. However, recent findings have implicated mast cells, in coordination with granulocytes and other immune effector cells, in the pathology of these two disorders. The BioBreeding (BB) DRlyp/lyp rat develops an autoimmune insulin-dependent diabetes similar to human type 1 diabetes mellitus (T1DM), whereas the BBDR+/+ rat does not. To better understand immune processes during development of T1DM, gene expression profiling at day (d) 40 (before insulitis) and d65 (before disease onset) was conducted on pancreatic lymph nodes of DRlyp/lyp, DR+/+, and Wistar-Furth (WF) rats. The eosinophil-recruiting chemokine, eotaxin, and the high-affinity IgE receptor (FcepsilonRI) were up-regulated >5-fold in d65 DRlyp/lyp vs d65 DR+/+ pancreatic lymph nodes by microarray (p < 0.05) and quantitative RT-PCR studies (p < 0.05). DR+/+, WF, and d40 DRlyp/lyp animals possessed normal pancreatic histology; however, d65 DRlyp/lyp animals possessed eosinophilic insulitis. Therefore, immunohistochemistry for pancreatic eotaxin expression was conducted, revealing positive staining of d65 DRlyp/lyp islets. Islets of d65 DR+/+ rats also stained positively, consistent with underlying diabetic predisposition in the BB lineage, whereas WF islets did not. Other differentially expressed transcripts included those associated with eosinophils, mast cells, and lymphocytes. These data support an important role for these inflammatory mediators in BB rat T1DM and suggest that the lymphopenia due to the Ian5/(lyp) mutation may result in a deregulation of cells involved in insulitis and beta cell destruction.

Plasma and lipoprotein lipid composition and hepatic antioxidant status in spontaneously hypertensive (SHR) and normotensive (WKY) rats

Plasma and lipoprotein lipid composition and endogenous hepatic antioxidant status were investigated in hypertensive, 14-week-old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats fed a standard commercial rat chow. Total plasma calcium and magnesium concentrations were similar between both rat strains; however, systolic blood pressure in SHR was greater than in WKY at 13 weeks of age (197 ± 12 vs. 132 ± 14 mmHg; p <= 0.05), confirming hypertension in SHR. Total plasma cholesterol and triacylglycerol concentrations were lower (p <= 0.05) in SHR compared with WKY. A lower (p < 0.05) HDL cholesterol level in SHR plasma resulted in a higher LDL to HDL cholesterol ratio compared with WKY counterparts. No significant differences in the relative proportion of HDL apolipoprotein A-I fraction were observed between SHR and WKY. Both SHR VLDL and HDL triacylglycerol fractions were lower (p < 0.05) in SHR than WKY. Analysis of liver antioxidant enzyme activities showed no differences in rat liver superoxide dismutase (SOD), but lower (p < 0.05) liver glutathione peroxidase (GSH-Px) activity in SHR. However, liver glutathione (GSH) levels were similar in SHR and WKY counterparts. A possible compensatory effect to the oxidative status of SHR was suggested by the significant (p < 0.05) increase in both liver catalase (CAT) and glutathione reductase (GSSG-Red) activities. Despite these results, in vitro oxidative challenge studies with H2O2demonstrated a greater susceptibility of liver to GSH depletion in the SHR, although no parallel change in thiobarbituric acid reactive substances (TBARS) production was observed. The comparatively lower plasma cholesterol observed in hypertensive SHR paralleled specific differences in liver catalase and glutathione redox antioxidant enzyme activities.Key words: liver antioxidant status, plasma and lipoprotein lipids, spontaneously hypertensive rat.

Estrogen inhibits cuff-induced intimal thickening of rat femoral artery: effects on migration and proliferation of vascular smooth muscle cells

The present study was performed to elucidate the mechanism underlying the anti-atherogenic action of estrogen. We investigated the effect of estrogen on intimal thickening of the rat femoral artery induced by cuff placement and further examined the effect of estrogen on migration and proliferation of vascular smooth muscle cells (VSMCs) in culture. Intimal thickening was significantly greater in males than in control females. Intimal thickening in females was increased to the level in males by ovariectomy. Estrogen replacement to ovariectomized rats reversed this effect. Proliferating cell nuclear antigen immunohistochemistry showed that in vivo proliferation of VSMCs contributed to the difference in intimal thickening. There was no difference in blood pressure and serum lipids, suggesting that estrogen directly acted on artery and inhibited intimal thickening. 17 beta-Estradiol (E2, 1-100 nmol/l) inhibited migration of cultured rat VSMCs, assayed using a microchemotaxis chamber, in a concentration-dependent manner. E2 (0.01-100 nmol/l), but not progesterone or testosterone, also inhibited [3H]thymidine incorporation in rat VSMCs in a concentration-dependent manner. Indomethacin, NG-monomethyl-L-arginine and methylene blue did not influence the inhibitory action of E2 on [3H]thymidine incorporation, suggesting that prostanoids and nitric oxide are not involved in the action of E2. E2 did not provoke VSMC injury, as measured by the release of incorporated [3H]2-deoxy-D-glucose. These results suggest that the inhibition of migration and proliferation of VSMCs contributes to the inhibitory effect of estrogen on intimal thickening.

Mechanism of hypertriglyceridemia in Dahl salt-sensitive rats, an animal model of spontaneous nephrotic syndrome

It has been reported that focal and segmental glomerulosclerosis (FSGS) with pronounced proteinuria rapidly develop in Dahl salt-sensitive hypertensive (DS) rats fed a high-salt diet. We found that even when they are fed a standard rat chow (0.3% NaCl), DS rats, especially males, exhibit marked proteinuria, hypoalbuminemia, and hypertriglyceridemia without marked hypertension at 32 to 38 weeks of age. The nephrosis was associated with spontaneously developed FSGS. We therefore investigated the mechanism of hypertriglyceridemia in nephrotic animals. Plasma triglyceride (TG) and apoprotein (apo) B levels were markedly increased in DS rats compared with Sprague-Dawley (SD) rats, and this was mainly attributable to an increase in the concentration of very-low-density lipoprotein (VLDL). The TG secretion rate estimated by the Triton WR1339 method was significantly greater in DS rats. VLDL-TGs isolated from both the DS and SD rats were endogenously radiolabeled with different isotopes, and a mixture of these was then injected into DS and SD recipients. The half-life of VLDL-TG was about three times longer in DS recipients, regardless of the source of VLDL. In SD recipients, VLDL from DS rats was cleared at a slower rate than VLDL from SD rats. The activity of lipoprotein lipase in postheparin plasma was substantially decreased in DS rats. Isoelectric focusing gel electrophoresis (IEF) showed that the ratio of apo E/C or apo C-II/C-III in VLDL was markedly decreased and the ratio of apo E or apo C to apo A1 in high-density lipoprotein (HDL) was slightly decreased in DS rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of atherosclerosis in alloxan diabetic rats

Rats with alloxan-induced diabetes developed severe atherosclerotic lesions when they were maintained on a 0.25% cholesterol diet for one year. The atheromatous changes developed at the aortic arch, appeared as early as 3 months after the start of the experiment, and increased thereafter. The diabetic rats also developed atherosclerosis when they were fed standard rat chow, but the area of the atheromatous lesion was about one tenth of that in rats fed the high-cholesterol diet. Normal rats did not develop atherosclerosis even when fed the high-cholesterol diet for one year. The alloxan diabetic rats showed no increase in body weight, but developed serum glucose levels as high as 600-800 mg/dl as well as high serum cholesterol levels and lower serum HDL-cholesterol levels. The development of atherosclerosis in these rats was significantly related to an increase in the serum cholesterol/phospholipid ratio, the atherogenic index (TC-HDLC/HDLC), and the serum total cholesterol level, but was not related to the serum glucose, HDL-cholesterol, triglyceride, or lipid peroxide levels. These relationships were found as early as B-16 weeks after the start of the experiment. These data suggest that the serum cholesterol/phospholipid ratio, the atherogenic index, and the total cholesterol level are important risk factors for the development of atherosclerosis in rats with alloxan diabetes.

Hypersensitivity to ADP of platelets from diabetic rats associated with enhanced fibrinogen binding

Platelets from diabetic humans and animals are hypersensitive to ADP. The hypersensitivity to ADP of platelets from diabetic rats occurs independently of activation of the arachidonate pathway or release of dense granule contents. During platelet aggregation by ADP, fibrinogen binds to its receptor on platelets. We examined if the hypersensitivity to ADP of platelets from diabetic rats is associated with enhanced early binding of fibrinogen to its receptor on these platelets. Fibrinogen association with platelets from rats with spontaneous or streptozotocin-induced diabetes was significantly greater 10 s or 1 min after addition of ADP (10 microM) than with platelets from their corresponding control rats. Since enhanced fibrinogen association occurred with platelets from insulin-treated rats with spontaneous diabetes, and from rats with streptozotocin-induced diabetes that did not receive insulin, the enhanced fibrinogen binding is likely due to the diabetic state rather than to the administration of insulin or the mechanism responsible for the diabetes. Therefore, enhanced early fibrinogen association with platelets from diabetic rats is associated with their hypersensitivity to ADP.

Secretion of triglyceride and ketogenesis by livers from spontaneous diabetic BB Wistar rats

Livers from male and female BB Wistar spontaneously diabetic rats were perfused in vitro to determine the effects of spontaneously occurring insulin-dependent diabetes on the metabolism of fatty acid. The secretion of triglyceride and the incorporation of [1-14C] oleic acid into perfusate and hepatic triglyceride was reduced by the diabetic state, whereas beta-hydroxybutyrate production and output of total ketone bodies were increased. The spontaneous diabetic Wistar rat clearly is a suitable model to study the derangements induced in lipid/plasma lipoprotein metabolism by the insulin-dependent diabetic state; the data obtained with this model confirm our earlier observations on experimental insulin deficiency induced with alloxan, streptozotocin, and anti-insulin serum.

Apolipoprotein distribution in plasma HDL subfractions in alcohol consumers

Alcohol intake is known to increase plasma HDL subfractions and apo A levels. Few data are available, however, with regard to precise apoprotein composition of plasma lipoproteins in alcohol consumers. The aim of the present study was to examine the lipid and apoprotein distribution in plasma lipoproteins of subjects with different levels of alcohol intake. Thirty-six male regular drinkers were classified as social (n = 10, average daily consumption greater than or equal to 5 and less than or equal to 20 g), moderate (n = 11, average daily consumption greater than 20 g and less than 70 g) and heavy drinkers (n = 15, average daily consumption greater than or equal to 70 g). Reference data were obtained from 11 subjects, all lifelong abstainers. Lipoproteins were fractioned by sequential ultracentrifugation and apolipoprotein distribution in VLDL, HDL-2 and HDL-3 was determined by isoelectrofocusing in polyacrylamide-urea gel. HDL-2 cholesterol was significantly higher in heavy drinkers (P less than 0.005). A parallel trend for HDL-3 cholesterol was observed. In alcohol consumers HDL-2 particles were enriched in apos C, in particular apo C-II (P 0.005), displacing apo A-I. These data suggest that apolipoprotein distribution in the HDL-2 subfraction is influenced by alcohol intake even at the lowest level.

Isoform patterns of apolipoprotein E in diabetes mellitus

Apolipoproteins in delipidated VLDL preparations from normal, diabetic, and non-diabetic hyperlipidaemic subjects were analysed by SDS-polyacrylamide gel electrophoresis, and by isoelectric focusing. On electrophoresis, diabetic VLDL contained more apolipoprotein E (17.3 +/- 7.3 (+/- SD) %, n = 54) than did VLDL from hyperlipidaemic (13.4 +/- 4.2%, n = 52; p less than 0.005) or normal (12.4 +/- 2.6%, n = 29; p less than 0.001) subjects. Apolipoprotein E excess was also seen when subgroups were characterized by apolipoprotein E phenotype. In diabetic patients of E3/E3 phenotype, apolipoprotein E was 16.4 +/- 6.0% (n = 25), compared with 12.9 +/- 2.5% in control subjects (n = 14; p = 0.008). Acidic isoforms were more common in 44 diabetic patients with E3/E3 phenotype; E3, E2, E1, and E1' as percentage of total E apolipoprotein were 58.3 +/- 7.6, 24.5 +/- 4.4, 13.7 +/- 4.5, and 3.8 +/- 4.3% respectively, compared with 63.5 +/- 10.4 (p = 0.034), 19.1 +/- 5.3 (p less than 0.001), 13.7 +/- 6.5 (NS), and 3.7 +/- 2.1% (NS) in 21 normal subjects. In 31 diabetic patients, of apolipoprotein E3/E3 phenotype, E3, E2, E1 and E1' were 60.2 +/- 7.3, 23.4 +/- 9.4, 11.1 +/- 4.1, and 5.4 +/- 3.7%, respectively, compared with 68.0 +/- 7.1 (p less than 0.001), 21.9 +/- 6.4 (NS), 6.3 +/- 3.9 (p less than 0.001), and 3.7 +/- 2.5 (p less than 0.05) % in 32 hyperlipidaemic patients. Diabetic patients of E3/E2 phenotype showed less apolipoprotein E3 than normal or hyperlipidaemic subjects, with a similar trend for apolipoprotein E4 in those of E4/E3 phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma lipoproteins and cholesterol metabolism in spontaneously hyperlipemic rats

The aim of this study was to characterize the plasma lipoprotein pattern and some aspects of cholesterol metabolism in a line of hyperlipemic male rats. Plasma cholesterol and triglycerides were increased about 3-fold as compared to control animals (238 vs. 75 and 185 vs. 59 mg/dl respectively). The plasma lipoprotein distribution and the chemical composition of the isolated lipoproteins was unaffected. Plasma triglyceride production rate was increased (40%, P less than 0.01) and post-heparin lipoprotein lipase activity in plasma decreased (-28%, P less than 0.01) in the hyperlipemic rat. The activity of 3 enzymes involved in cholesterol metabolism (HMG-CoA reductase, cholesterol 7 alpha-hydroxylase, and acyl-CoA cholesterol-acyltransferase) did not differ from control values. 3H2O incorporation into digitonin-precipitable sterols, however, was significantly higher than in controls. This finding was due, in part, to an increased liver weight in the hyperlipemic animals. Furthermore kinetic data using 125I-LDL showed that the fractional catabolic rate of lipoprotein was within the normal range, while the synthetic rate of LDL protein was increased (0.67 vs. 0.3 mg/kg/h, P less than 0.01) in the hyperlipemic rat. These observations suggest that multiple metabolic defects underline the hyperlipemia observed in this animal model.

Serum lipoprotein and apoprotein concentrations in 4-(4-chlorophenyl)-2-hydroxytetronic acid and clofibrate-treated cholesterol and cholic acid-fed rats

Influence of clofibrate and an aci-reductone, 4-(4-chlorophenyl)-2-hydroxytetronic acid (CHTA) on lipoproteins and apoproteins was studied in cholesterol- plus cholic acid-fed rats. CHTA (0.4 mmol/kg body wt, twice daily) significantly lowered serum total cholesterol and triglyceride concentrations at both 10 and 16 days, whereas clofibrate at the same dose did not alter serum cholesterol levels, but elevated serum triglyceride concentrations at 16 days. The abnormal cholesterol-rich very low density lipoproteins (VLDL), intermediate density lipoproteins (IDL) and low density lipoproteins (LDL) produced by cholesterol plus cholic acid were significantly reduced in their cholesterol content by treatment with CHTA, a compound having an oxidation reduction potential. Conversely, clofibrate administration increased VLDL-cholesterol with concomitant decreases in IDL- and LDL-cholesterol concentrations. Administration of CHTA to cholesterol- plus cholic acid-fed rats significantly increased concentrations of VLDL and IDL, but had no effect on HDL protein. Both CHTA and clofibrate administration to cholesterol- plus cholic acid-fed rats significantly lowered IDL protein concentrations. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) studies of apoproteins revealed that clofibrate treatment significantly reduced apoC-III and C-II in VLDL, C-II in IDL, and apoA-IV and A-I in HDL. Rats treated with CHTA significantly raised apoC-II and C-III in HDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Combination insulin/glyburide therapy in type II diabetes mellitus. Effects on lipoprotein metabolism and glucoregulation

A randomized double-blind, placebo-controlled trial of insulin plus glyburide was carried out in 22 insulin-treated patients with poorly controlled type II diabetes mellitus. Glycemic control and lipoprotein responses were assessed for 16 weeks. Oral glucose tolerance testing was performed at weeks 0, 4, and 16. Clinical characteristics and glycemic control were similar at week 0 in the placebo/insulin group (n = 12) and the glyburide/insulin group (n = 10). Throughout the study, the dose of insulin was fixed. The placebo group had no change in any metabolic parameter throughout the protocol period. After four weeks, glyburide significantly lowered fasting blood glucose and integrated glucose areas (p less than 0.01) after oral glucose testing compared with week 0 (fasting blood glucose 225 +/- 20 mg/dl versus 286 +/- 27 mg/dl, p less than 0.02). Associated with this were mean fasting, stimulated, and integrated C-peptide levels that were significantly higher (p less than 0.02) at week 4 versus week 0. After 16 weeks, mean fasting blood glucose remained significantly lower compared with baseline values (252 +/- 25 mg/dl versus 286 +/- 27 mg/dl, p less than 0.05). Glycosylated hemoglobin (hemoglobin A1c) levels decreased significantly (p less than 0.05) at weeks 4 to 16 compared with the baseline value. Although integrated areas were no different after oral glucose, fasting and stimulated C-peptide levels were significantly higher (p less than 0.05) at week 16 versus week 0. Total cholesterol, triglycerides, low-density lipoprotein cholesterol, very-low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol did not change during the study. After the code was broken, comparisons were made between those with response to combination therapy (reduction of fasting blood glucose by at least 50 mg/dl or fasting blood glucose of 140 mg/dl or less at the end of the first week of treatment that persisted for four consecutive weeks) and those without response. Baseline clinical and laboratory characteristics were identical in both groups. Mean fasting and stimulated serum C-peptide levels after oral glucose, however, were significantly higher in the patients with response at week 4 compared with the patients without response. The mean maximal incremental C-peptide level was 1.50 +/- 0.19 ng/ml at week 0 in the patients with response compared with 0.67 +/- 0.28 ng/ml in the patients without response (p less than 0.01). Lipoproteins were not different in the two groups.(ABSTRACT TRUNCATED AT 400 WORDS)