Effects of the dual PPAR-α/γ agonist aleglitazar on glycaemic control and organ protection in the Zucker diabetic fatty rat.

AIMS: To evaluate the effects of aleglitazar, a dual peroxisome proliferator-activated receptor-α/γ agonist, on the development of diabetes-related organ dysfunction, in relation to glycaemic and lipid changes, in Zucker diabetic fatty (ZDF) rats. METHODS: Six-week-old, male ZDF rats received aleglitazar 0.3 mg/kg/day or vehicle as food admix for 13 weeks (n = 10 per group). Age-matched male Zucker lean rats served as non-diabetic controls. Plasma and renal markers were measured at several time points. Histopathology and quantitative immunohistochemistry were performed at 13 weeks. RESULTS: Glycated haemoglobin (5.4 vs. 9.2%) and blood glucose (8.3 ± 0.3 vs. 26.1 ± 1.0 mmol/l) were significantly reduced at 12 weeks with aleglitazar versus vehicle-treated ZDF rats (both p < 0.01), while aleglitazar preserved near-normal plasma insulin levels. Aleglitazar prevented the development of hypertriglyceridaemia (1.4 ± 0.1 vs. 8.5 ± 0.9 mmol/l) and reduced plasma non-esterified fatty acids (0.09 ± 0.02 vs. 0.26 ± 0.04 mmol/l) relative to vehicle-treated animals (both p < 0.01). Urinary glucose and protein concentrations were significantly reduced at 13 weeks with aleglitazar versus vehicle-treated rats (both p < 0.01). Consistent with its effect on glycaemic control, aleglitazar protected ß-cell morphology, as evidenced by preservation of islet integrity, and reduction of ß-cell apoptosis and islet fibrosis. Aleglitazar prevented renal glomerular hypertrophy, podocyte degeneration, glomerulosclerosis, tubulo-interstitial lesions and development of cataracts. CONCLUSIONS: Aleglitazar strongly improved glycaemic and lipid parameters while protecting key tissues, including the pancreas, kidneys and eyes, against diabetes-associated structural and functional changes in the ZDF rat.

Taspoglutide, a novel human once-weekly GLP-1 analogue, protects pancreatic ß-cells in vitro and preserves islet structure and function in the Zucker diabetic fatty rat in vivo.

AIM: Glucagon-like peptide-1 (GLP-1) has protective effects on pancreatic ß-cells. We evaluated the effects of a novel, long-acting human GLP-1 analogue, taspoglutide, on ß-cells in vitro and in vivo. METHODS: Proliferation of murine pancreatic ß (MIN6B1) cells and rat islets in culture was assessed by imaging of 5-ethynyl-2'-deoxyuridine-positive cells after culture with taspoglutide. Apoptosis was evaluated with the transferase-mediated 2'-deoxyuridine 5'-triphosphate nick-end labelling assay in rat insulinoma (INS-1E) cells and isolated human islets exposed to cytokines (recombinant interleukin-1ß, interferon-γ, tumour necrosis factor-α) or lipotoxicity (palmitate) in the presence or absence of taspoglutide. Islet morphology and survival and glucose-stimulated insulin secretion in perfused pancreata were assessed 3-4 weeks after a single application of taspoglutide to prediabetic 6-week-old male Zucker diabetic fatty (ZDF) rats. RESULTS: Proliferation was increased in a concentration-dependent manner up to fourfold by taspoglutide in MIN6B1 cells and was significantly stimulated in isolated rat islets. Taspoglutide almost completely prevented cytokine- or lipotoxicity-induced apoptosis in INS-1E cells (control 0.5%, cytokines alone 2.2%, taspoglutide + cytokines 0.6%, p < 0.001; palmitate alone 8.1%, taspoglutide + palmitate 0.5%, p < 0.001) and reduced apoptosis in isolated human islets. Treatment of ZDF rats with taspoglutide significantly prevented ß-cell apoptosis and preserved healthy islet architecture and insulin staining intensity as shown in pancreatic islet cross sections. Basal and glucose-stimulated insulin secretion of in situ perfused ZDF rat pancreata was normalized after taspoglutide treatment. CONCLUSIONS: Taspoglutide promoted ß-cell proliferation, prevented apoptosis in vitro and exerted multiple ß-cell protective effects on islet architecture and function in vivo in ZDF rats.

High prevalence of prediabetes and diabetes in a population exposed to high levels of an organochlorine cocktail.

AIMS/HYPOTHESIS: A heavily polluted area of Eastern Slovakia was targeted by the PCBRISK cross-sectional survey to search for possible links between environmental pollution and both prediabetes and diabetes. METHODS: Associations of serum levels of five persistent organic pollutants (POPs), namely polychlorinated biphenyls (PCBs), 2,2'-bis(4-chlorophenyl)-1,1-dichloroethylene (p,p'-DDE), 2,2'-bis(4-chlorophenyl)-1,1,1-trichloro-ethane (p,p'-DDT), hexachlorobenzene (HCB) and beta-hexachlorocyclohexane (beta-HCH), with prediabetes and diabetes were investigated in 2,047 adults. Diabetes and prediabetes were diagnosed by fasting plasma glucose in all participants and by OGTT in 1,220 compliant participants. RESULTS: Our population was stratified in terms of individual POPs quintiles and associations between environmental pollution, prediabetes and diabetes were investigated. Prevalence of prediabetes and diabetes increased in a dose-dependent manner, with individuals in upper quintiles of individual POPs showing striking increases in prevalence of prediabetes as shown by OR and 95% CI for PCBs (2.74; 1.92-3.90), DDE (1.86; 1.17-2.95), DDT (2.48; 1.77-3.48), HCB (1.86; 1.7-2.95) and beta-HCH (1.97; 1.28-3.04). Interestingly, unlike PCBs, DDT and DDE, increased levels of HCB and beta-HCH seemed not to be associated with increased prevalence of diabetes. Nevertheless, individuals in the 5th quintile of the variable expressing the cumulative effect of all five POPs (sum of orders) had a more than tripled prevalence of prediabetes and more than six times higher prevalence of diabetes when compared with the 1st referent quintile. CONCLUSIONS/INTERPRETATION: Increasing serum concentrations of individual POPs considerably increased prevalence of prediabetes and diabetes in a dose-dependent manner. Interaction of industrial and agricultural pollutants in increasing prevalence of prediabetes or diabetes is likely.

Taspoglutide, a novel human once-weekly analogue of glucagon-like peptide-1, improves glucose homeostasis and body weight in the Zucker diabetic fatty rat.

AIM: Glucagon-like peptide-1 (GLP-1) receptor agonists are a novel class of pharmacotherapy for type 2 diabetes. We investigated the effects of a novel, long-acting human GLP-1 analogue, taspoglutide, in the Zucker diabetic fatty (ZDF) rat, an animal model of type 2 diabetes. METHODS: Blood glucose and plasma levels of insulin, peptide YY (PYY), glucose-dependent insulinotropic polypeptide (GIP) and triglycerides were measured during oral glucose tolerance tests (oGTT) conducted in ZDF rats treated acutely or chronically with a single long-acting dose of taspoglutide. Pioglitazone was used as a positive control in the chronic study. Postprandial glucose, body weight, glycaemic control and insulin sensitivity were assessed over 21 days in chronically treated animals. RESULTS: Acute treatment with taspoglutide reduced glucose excursion and increased insulin response during oGTT. In chronically treated rats, glucose excursion and levels of GIP, PYY and triglycerides during oGTT on day 21 were significantly reduced. Postprandial glucose levels were significantly lower than vehicle controls by day 15. A significant reduction in body weight gain was noticed by day 8, and continued until the end of the study when body weight was approximately 7% lower in rats treated with taspoglutide compared to vehicle. Glycaemic control (increased levels of 1,5-anhydroglucitol) and insulin sensitivity (Matsuda index) were improved by taspoglutide treatment. CONCLUSIONS: Taspoglutide showed typical effects of native GLP-1, with improvement in glucose tolerance, postprandial glucose, body weight, glycaemic control and insulin sensitivity.

Concerted action of leptin in regulation of fatty acid oxidation in skeletal muscle and liver.

Central action of leptin on food intake and energy expenditure is integrated with leptin's peripheral action modulating the fatty acid and glucose metabolism and preventing the accumulation of lipids in nonadipose tissues. However, exact mechanism(s) of the leptin's action in the peripheral tissues has not yet been fully elucidated. Therefore, we investigated the effect of a single intravenous injection of leptin on palmitoyl-CoA and palmitoyl-carnitine oxidation rate in liver and skeletal muscle followed by measurements of the carnitine-palmitoyl transferase 1 (CPT1) activity and activities of ss-oxidation enzymes in mitochondria (acyl-CoA dehydrogenase) and in peroxisomes (acyl-CoA oxidase) of rats. Animals were euthanized and tissues and serum harvested 15 min, 1 hour, 3 hours and 6 hours after leptin administration. Intravenous leptin injection increased mitochondrial palmitoyl-CoA oxidation rate in both liver (95%; P<0.025) and skeletal muscle (2.7-fold; P<0.05). This was paralleled by lowering hepatic (-156%; P<0.001) and skeletal muscle (-191%; P<0.001) triglyceride content. Leptin-induced elevation of palmitoyl-CoA oxidation rate in liver was paralleled by increased CPT1 activity (52%; P<0.05) and ss-oxidation capacity (52%; P<0.05). Lack of the leptin's effect on the CPT1-activity in muscle (20%; p=0.09) suggests the existence of an alternative pathway for increasing the palmitoyl-CoA-oxidation rate bypassing the CPT1 regulatory step. Interestingly, leptin stimulated the overall ss-oxidation capacity in muscle by 69% (P=0.027). This may indicate to an involvement of mitochondrial acyl-CoA dehydrogenases as well as of peroxisomal fat catabolism. Taken together, we showed that leptin acutely increases palmitoyl-CoA oxidation rate in liver and in skeletal muscle, which was associated with tissue specific effect on the CPT1 activity as well as on the downstream enzymes of fatty acid oxidation pathways in rat mitochondria and peroxisomes. Tangible evidence for the leptin-induced increase of fatty acid catabolism was provided by a lowered skeletal muscle and hepatic lipid deposition.

Insulin sensitivity indices: a proposal of cut-off points for simple identification of insulin-resistant subjects.

Demanding measurement of insulin sensitivity using clamp methods does not simplify the identification of insulin resistant subjects in the general population. Other approaches such as fasting- or oral glucose tolerance test-derived insulin sensitivity indices were proposed and validated with the euglycemic clamp. Nevertheless, a lack of reference values for these indices prevents their wider use in epidemiological studies and clinical practice. The aim of our study was therefore to define the cut-off points of insulin resistance indices as well as the ranges of the most frequently obtained values for selected indices. A standard 75 g oral glucose tolerance test was carried out in 1156 subjects from a Caucasian rural population with no previous evidence of diabetes or other dysglycemias. Insulin resistance/sensitivity indices (HOMA-IR, HOMA-IR2, ISI Cederholm, and ISI Matsuda) were calculated. The 75th percentile value as the cut-off point to define IR corresponded with a HOMA-IR of 2.29, a HOMA-IR2 of 1.21, a 25th percentile for ISI Cederholm, and ISI Matsuda of 57 and 5.0, respectively. For the first time, the cut-off points for selected indices and their most frequently obtained values were established for groups of subjects as defined by glucose homeostasis and BMI. Thus, insulin-resistant subjects can be identified using this simple approach.

Mapping of genetic determinants of the sympathoneural response to stress.

Activation of the sympathoadrenal system (SAS, comprising the sympathetic nervous system and the adrenal medulla) in response to stressful stimuli is an important defense mechanism as well as a contributor to several cardiovascular diseases. There is variability in the SAS response to stress, although the extent to which this is genetically regulated is unclear. Some rodent models, including the hereditary hypertriglyceridemic (hHTg) rat, are hyperresponsive to stress. We investigated whether quantitative trait loci (QTLs) that affect sympathoadrenal response to stress could be identified. Second filial generation rats (n = 189) derived from a cross of the hHTg rat and the Brown Norway rat had plasma norepinephrine (NE) and epinephrine (Epi) levels, indices of activation of the sympathoneural and adrenal medulla components, respectively, measured in the resting state and in response to an immobilization stress. Responses were assessed early (20 min) and late (120 min) after the application of the stress. A genome scan was conducted using 153 microsatellite markers. Two QTLs (maximum peak LOD scores of 4.17 and 3.52, respectively) influencing both the early and late plasma NE response to stress were found on chromosome 10. Together, the QTLs accounted for approximately 20% of the total variation in both the early and late NE responses in the F(2) rats. Interestingly, the QTLs had no effect on plasma Epi response to stress. These findings provide evidence for a genetic determination of the response of a specific component of the SAS response to stress. Genetically determined variation in sympathetic nervous system response to stress may contribute to cardiovascular diseases.

Regulation of gene expression for lipogenic enzymes in the liver and adipose tissue of hereditary hypertriglyceridemic, insulin-resistant rats: effect of dietary sucrose and marine fish oil.

Hypertriglyceridemia is closely linked to insulin resistance. Increased dietary intake of n-3 polyunsaturated fatty acids reverses both hypertriglyceridemia and insulin resistance. To evaluate molecular mechanisms responsible for the hypotriglyceridemic effects of n-3 polyunsaturated fatty acids, the expression of genes for lipogenic enzymes in liver and white and brown adipose tissue was estimated in hereditary hypertriglyceridemic rats which underwent an euglycemic hyperinsulinemic clamp. Before the clamp, animals were fed a basal or a high (63%) sucrose diet with or without fish oil for two weeks. Results were compared to data obtained from control animals subjected to the identical protocol. In hereditary hypertriglyceridemic rats, gene expression for malic enzyme was increased in liver and in brown adipose tissue but not in white adipose tissue. The high sucrose diet raised malic enzyme mRNA levels in liver of both hereditary hypertriglyceridemic and control rats, and this effect was more pronounced in brown adipose tissue. Supplementing the high sucrose diet with fish oil led to a suppression of malic enzyme gene expression in liver and brown adipose tissue of control rats. However, this inhibitory effect was not as pronounced in the hereditary hypertriglyceridemic rats. Raised levels of fatty acid synthase mRNA in liver and brown adipose tissue of control rats fed high sucrose diet were suppressed by consumption of diet high in n-3 fatty acids. On the other hand, in hereditary hypertriglyceridemic rats fed high sucrose diet, fish oil supplementation failed to suppress increased levels of fatty acid synthase mRNA in liver and in brown adipose tissue. It appears that hereditary hypertriglyceridemic rats have elevated levels of mRNA for lipogenic enzymes in liver and brown adipose tissue and dietary control leading to an alteration of hypertriglyceridemia influences gene expression of lipogenic enzymes only under special dietary circumstances.

Modulation of rat testicular LH/hCG receptors by membrane lipid fluidity.

The specific binding of [125I]hCG to rat testicular membrane preparations was investigated as a function of membrane fluidity changed by lipids. Membrane fluidity was measured either by fluorescence depolarization of diphenylhexatriene or ESR spectra of I(1,14), I(12,3) and CAT 16 incorporated into the membrane. Incubation of membrane with cholesteryl-hemisuccinate increased both the rigidity of membrane lipids and the specific binding of [125I]hCG. A similar rigidifying action of saturated fatty acids was, however, not accompanied by increased accessibility of LH/hCG receptors. Treatment of testicular membranes with unsaturated fatty acids enhanced membrane fluidity but specific binding of the gonadotropin disappeared. In spite of the increase of LH/hCG receptors in cell membranes treated with cholesteryl-hemisuccinate, Leydig cells showed decreased sensitivity to cAMP response to LH stimulation. The results indicate that newly exposed LH/hCG receptors are not coupled with the adenylate cyclase system.

The effect of hyperlipidemia on serum fatty acid composition in type 2 diabetics.

Fatty acid (FA) profiles of total serum lipids were determined by capillary gas chromatography in Type 2 diabetic patients (NIDDM) with diverse types of hyperlipidemia. In patients with hypertriglyceridemia (DM-HTG) and combined hypertriglyceridemia and hypercholesterolemia (DM-HLP), a significantly different total FA composition was found compared with healthy controls or diabetics with normal serum lipids. In particular, the proportions of saturated and monounsaturated FA were increased and the proportions of n-6 polyunsaturated FA were decreased. In DM-HLP patients, PUFA n-6 metabolites and C20-C22 PUFA were also decreased. Thus, hyperlipidemia shifts significantly the serum FA composition in NIDDM patients into an atherogenic profile. More study is needed, however, to understand if serum FA changes may contribute to the increased atherogenesis commonly found in these patients.

Fatty acid composition in fractions of structural and storage lipids in liver and skeletal muscle of hereditary hypertriglyceridemic rats.

The fatty acid (FA) compositions of liver and skeletal muscle structural lipids, overall phospholipids and phosphatidylcholine, and triglycerides (TG) were determined in the hereditary hypertriglyceridemic (HTG) rat, a nonobese animal model of the insulin resistance syndrome. Four groups of HTG rats and four groups of control animals were fed equal-energy diets for two weeks: basal (B), high-sucrose (HS), or fish oil-supplemented basal (BFO) or high-sucrose (HSFO) diets. In the liver of HTG rats, a decrease of n-6 long-chain polyunsaturated FA (PUFA), especially in 20:4n-6, in comparison with controls was found. Moreover, a concomitant accumulation of 18:2n-6 in structural lipids was observed. These differences were more pronounced in liver than in skeletal muscle. HS feeding raised the proportion of 18:1n-9 and decreased 18:2n-6 in lipid fractions. In both tissues and in both strains, the amounts of long-chain n-3 PUFA, as well as the level of total C20-22 PUFA, went up after fish oil feeding. However, the effects were somewhat less pronounced in the HTG rats. The increase in n-3 PUFA occurred mainly at the expense of reduced levels of 18:2n-6 in structural lipids and of 18:1n-9 in triglycerides. These changes were associated, in companion studies reported in this volume, with improved insulin action in HTG rats. In conclusion, the FA composition in lipid subclasses of HTG rats differs significantly from the controls mainly in liver structural lipids, suggesting the impairment of PUFA desaturation. Dietary change effected a similar modulation of FA profile across both strains, with fish oil increasing the levels of long-chain PUFA toward control values in the NTG rats. The HTG rat thus provides an interesting animal model for the study of impaired fatty acid metabolism.

Structural changes in the aorta of the hereditary hypertriglyceridemic rat.

Structural changes in the ascending thoracic aorta of hereditary hypertriglyceridemic (hHTG), insulin-resistant, and hypertensive rats were studied using transmission electron microscopy. Normotensive Wistar rats were used as controls. The most-pronounced morphological changes were observed in the tunica intima. Endothelial cells of hHTG rats formed a continual layer around the whole circumference. Subendothelial space was enlarged. Some endothelial cells were delaminated from the subendothelial space by big lipid droplets that were often present in the subendothelial space, and the endothelial cells bulged out towards the lumen. Big electron-lucent lipid droplets were present in the majority of the endothelial cells and occupied the main part of the cytoplasm. Degenerative microvesicular and membranous material was present in the cytoplasm. Increased numbers of vesicles of Golgi apparatus and cisternae of endoplasmic reticulum were found. Similar morphological alterations, but in less-extended form, were observed in smooth muscle cells. The organization and orientation of smooth muscle cells were essentially intact. In muscle cells, lipid droplets were localized in close relation to Golgi complex and in dilated cisternae of the sarcoplasmic reticulum. Lipid droplets, degenerative material, myelin figures, myelinoid membranes, and vesicular components were also sporadically found in the intercellular space among muscle cells. This pilot morphological investigation provides further arguments for a thorough and more-focused electron microscopy study of conductance arteries of the hHTG rats.

Effect of dietary fish oil on 2-deoxy-D-3H glucose uptake in isolated adipocytes of rats fed various diets.

High sucrose diet-induced insulin resistance and mild glucose intolerance are associated with decreased insulin binding to isolated adipocytes and reduced insulin action in adipose tissue. Enhanced dietary intake of omega-3 polyunsaturated fatty acids (n-3-FA) counteracts these disorders. To provide more information on the possible role of membrane-related glucose transport processes, basal and insulin-stimulated 2-deoxy-D-3H glucose uptake was evaluated in isolated adipocytes obtained from rats on various dietary regimens. For 2 weeks animals were fed three different isocaloric (18 cal% proteins, 19 cal% fat, and 63 cal% carbohydrate) diets: (1) a standard rat chow (B), (2) a high sucrose diet (S, 63 cal% sucrose), or (3) an S diet supplemented with marine fish oil (S + FO, Martens, 30 wt% of n-3-FA). High dietary n-3-FA intake resulted in a significant decline in both basal (0.05 +/- 0.01 pmol/10(6) fat cells; mean +/- SEM) and insulin-stimulated (10(-6) M) (0.20 +/- 0.01) glucose uptake when compared with the control (basal: 0.12 +/- 0.02; insulin: 0.35 +/- 0.02) and/or the S group (basal: 0.18 +/- 0.03; insulin: 0.43 +/- 0.03), indicating decreases in insulin responsiveness and sensitivity (ED50: B: 0.03 +/- 0.01; S: 0.03 +/- 0.01; S + FO: 0.73 +/- 0.2 nM; p < 0.01 for S + FO vs B and S + FO vs S). Fish oil supplementation induced an increase in adipocyte size (B: 69 +/- 1.6; S: 70 +/- 2.5 and S + FO: 76 +/- 2.2 microns; B: S + FO p < 0.05) and a decrease in plasma membrane microviscosity (B: 4.08 +/- 0.3; S: 5.39 +/- 0.5; S + FO: 3.10 +/- 0.3; p < 0.05). Rates of basal and insulin-stimulated glucose uptake did not correlate with plasma membrane microviscosity; however, a negative relation to fat cell size was found (r = -0.484; p < 0.05). On the other hand, a positive correlation between both basal (r = 0.504; p < 0.05) and insulin-stimulated (10(-6) M, r = 0.640; p < 0.02) glucose uptake and blood glucose levels was observed. In conclusion, these data (a) suggest a less important role of diet-induced changes in plasma membrane microviscosity for glucose uptake in adipose tissue, and (b) leave unclear the mechanism of why dietary fish oil decreases the sensitivity of glucose uptake to insulin in isolated rat adipocytes.

Insulin resistance in the hereditary hypertriglyceridemic rat is associated with an impairment of delta-6 desaturase expression in liver.

Our previous studies have shown that insulin resistance (IR) in the hereditary hypertriglyceridemic (hHTg) rat is accompanied by a specific fatty acid (FA) profile in insulin target tissues, possibly due to a defect in the desaturation pathway. Increased dietary intake of n-3 polyunsaturated fatty acids (PUFAs) was shown to shape FA composition and to improve insulin sensitivity in this animal strain. Thus, the aim of this study is twofold: (1) to evaluate a defect in the FA desaturation by direct measurement of enzyme activity and gene expression for Delta-6 desaturase (Delta-6 D) in liver of hHTg rats and (2) to investigate the effect of dietary n-3 PUFAs on hepatic Delta-6 D in relation to tissue FA composition. Male Wistar or hHTg rats were fed ad libitum for 21 days either the basal or fish oil (FO)-supplemented diets. Triglyceride (Tg) levels in serum and tissue lipid extracts were measured with the aid of a commercially available enzymatic set. Hepatic activity of the Delta-6 D was determined radiometrically in a microsomal fraction using 1-(14)C-linoleic acid as a substrate. The Delta-6 D mRNA levels were measured using the Northern blot technique. Tissue FA composition was determined by gas chromatography in the total phospholipid fraction after TLC separation. Increased levels of Tg in hHTg rat circulation were accompanied by raised accumulation of Tg in skeletal muscles. FO feeding lowered the concentration of Tg in serum and prevented their accumulation in skeletal muscles of hHTg rats. A pronounced decrease in the hepatic Delta-6 D activity in hHTg rats (by about 80%) was not further diminished by FO feeding. On the other hand, the activity of Delta-6 D in liver of control rats was reduced by about 40% after FO supplementation. These changes were paralleled by a decrease in the Delta-6 D index as calculated from the liver phospholipid FA profile. In particular, an increase in the amount of 18:2 n-6 and a decrease in arachidonic acid and PUFA n-6 metabolites were found. The results indicate that a decrease of insulin action in hHTg rats is accompanied by an impairment of the hepatic Delta-6 D activity already at the gene level, which is not further affected by n-3 PUFA supplementation.

Lipids and insulin resistance: what we've learned at the Fourth International Smolenice Symposium.

A summary of the Fourth International Smolenice Symposium on Lipids and Insulin Resistance focusing on "The Role of Fatty Acid Metabolism and Fuel Partitioning" is provided. Highlights and issues of the conference are mentioned, as well as strategies for the future.

Modulation of the hypolipidemic effect of fish oil by inhibition of adipose tissue lipolysis with acipimox, a nicotinic acid analog.

To assess the possible benefits of combined hypolipidemic therapy (acipimox+marine fish oil) on lipid and lipoprotein metabolism, male Wistar rats were fed for 14 days a high sucrose diet (70 cal% sucrose) alone or a high sucrose diet supplemented with acipimox (0.2 g/100 g diet) and/or fish oil (1 ml orally daily; 30 wt% of n-3 PUFA). Feeding a high sucrose diet increased (control: 61 +/- 6 vs HS: 110 +/- 8 nmol.min-1.mg-1, p < 0.001) the activity of acetyl CoA carboxylase in the liver, this was normalized by fish oil but not acipimox alone (HS+FO: 68 +/- 4; HS+ACI: 95 +/- 4; HS+ACI+FO: 71 +/- 2 nmol.min-1.mg-1). Increased triglyceride concentration in serum and muscle tissue (m. soleus and heart) of high sucrose-fed animals was suppressed equally by fish oil, acipimox, and/or both. The cholesterol-lowering effect of fish oil was also present in the liver (p < 0.005). The cholesterol-lowering action of acipimox was accompanied by the accumulation of cholesterol in the liver (p < 0.005), whereas the combination of acipimox+fish oil did not change the liver cholesterol content. After fish oil the LDL binding capacity of liver plasma membranes was increased 1.6-fold (p < 0.001). LDL receptor activity was significantly decreased in HS+ACI group (p < 0.05), but remained unchanged in HS+FO+ACI-fed animals. In summary, (a) the hypotriglyceridemic effect of fish oil in high sucrose-induced HTG is due to its inhibitory effects at the level of fatty acid synthesis; (b) decreased triglyceride production and output from the liver prevent triglyceride accumulation in muscle tissue; (c) the cholesterol-lowering action of acipimox but not fish oil was accompanied by an accumulation of cholesterol in the liver; (d) the latter phenomenon may be due to the opposite effects of both drugs on cholesterol catabolism via hepatic LDL receptors.

Muscle GLUT 4 protein levels and impaired triglyceride metabolism in streptozotocin diabetic rats. Effect of a high sucrose diet and fish oil supplementation.

Our data indicate that (a) the existence of a defect in the clearance of circulating TG and persistence of muscle TG deposition in the high sucrose-fed neonatal streptozotocin diabetic rat, which (b) can only be partially corrected by raised dietary n-3 PUFA intake. (c) Skeletal muscle of STZ type II-like diabetic rats contains about 40% less glucose transporters, and (d) this situation cannot be changed by any of the dietary treatments employed. (e) These findings indicate that muscle TG accumulation may have no direct relation to glucose transport in muscle.

Nuclear all-trans retinoic acid receptors in liver of rats with diet-induced insulin resistance.

Retinoic acid receptor alpha (RAR alpha) expression and RAR binding characteristics were investigated in the liver of rats with high-sucrose (HS) diet-induced insulin resistance. Animals were fed a basal (B) or HS (63 cal%) diet with or without fish oil (FO) (30% w/w of total fatty acids) for two weeks. A significant augmentation (p < 0.01) in the RAR alpha mRNA accumulation in rats fed HS diet when compared to rats fed B diet was demonstrated. In comparison with rats fed B + FO diet, a significant increase (p < 0.005) in the RAR alpha expression was found in rats fed HS + FO diet. In [3H]-retinoic acid (RA) binding studies, Scatchard plots confirmed a significant increase (p < 0.05) in the RAR maximal binding capacity (Bmax) only in rats fed HS + FO diet when compared to rats fed B diet. No significant changes in the association constant (Ka) were found among the groups when compared to rats fed B diet. In contrast to RAR alpha, a significant decrease (p < 0.005) in nuclear thyroid hormone receptor alpha 1 (TR alpha 1) expression was found in rats fed HS diet when compared to rats fed B diet. A significant decrease (p < 0.05) in the TR alpha 1 expression was also detected in rats fed HS + FO diet in comparison with rats fed B + FO diet. In addition, an analogous pattern in the expression of the TR isoform (TR alpha 2) was evaluated as well. In conclusion, the high-sucrose diet-induced insulin resistance might be associated with an increased RAR alpha expression and RAR population, and also with a decreased TR alpha 1 and TR alpha 2 mRNA accumulation.

Diet-induced insulin resistance is associated with decreased activity of type I iodothyronine 5'-deiodinase in rat liver.

The effect of feeding Wistar rats with high-sucrose (63 wt% of sucrose, HS) or high-fat (30 wt% of fat, HF) diets for two weeks on serum selenium concentration and type I iodothyronine 5'-deiodinase (5'-DI) activity in liver was investigated. No significant differences in serum selenium concentration (as determined by graphite-furnace atomic absorption spectrometry) were found among the groups of rats fed basal, HS, or HF diets. A significant reduction of the 5'-DI activity (p < 0.005-0.05) was found in groups of rats fed either HS or HF diet in comparison with rats fed B diet. In conclusion, it is suggested that decreased 5'-DI activity in HS or HF diet-induced insulin resistance is not due to selenium status, but it may involve other dietary-related factors.

Effect of a low salt diet on blood pressure and vasoactive hormones in the hereditary hypertriglyceridemic rat.

In hereditary HTG rats, basal systolic blood pressure using tail-cuff sphygmomanometry was significantly higher (122.1 +/- 2.1 mm Hg; n = 16) than that in NTG animals (107.1 +/- 1.52; n = 16). A low salt diet did not influence blood pressure in NTG rats during the consecutive 4 weekly periods. However, in the second week blood pressure in HTG rats rose significantly in both the control rats on a normal salt diet and those on a low salt diet (132.5 +/- 1.89, n = 8, and 132.6 +/- 1.93, n = 8). No further changes were registered in the third and fourth week in control HTG rats. On the other hand, blood pressure fell significantly in HTG rats on a low salt diet in the third week in comparison with the second week (119.5 +/- 3.2, n = 8), and it increased again in the fourth week (123.0 +/- 2.35, n = 8). Hormones in plasma were determined at the end of the experiment. Plasma levels of norepinephrine were not influenced by differences in salt intake and were significantly higher by about 45% in HTG than in NTG animals. The lowest concentration of corticosterone in plasma was found in control HTG rats (1.2 +/- 0.2 vs 4.6 +/- 0.8 micrograms/100 ml in control NTG rats). Nevertheless, corticosterone concentration increased in HTG rats on a low salt diet at comparable values found in NTG rats on a low salt diet (3.1 +/- 0.8 vs 4.3 +/- 1.5). Plasma renin activity and plasma aldosterone concentrations were not different in the NTG and HTG groups and were uninfluenced by the diets (Table 1). We conclude that the elevated blood pressure in HTG rats and its variations during the experiment may reflect more pronounced sympathetic activity in HTG rats rather than blood pressure dependency on different salt intake.