Increased diaphragm expression of GLUT4 in control and streptozotocin-diabetic rats by fish oil-supplemented diets

Acute and Subacute Toxicity and Cytotoxicity of Opuntia Dillenii (Ker-Gawl) Haw. Seed Oil and Its Impact on the Isolated Rat Diaphragm Glucose Absorption

This study aims to assess the safety of the Opuntia dillenii (Ker-Gawl) haw. seed oil (ODSO) and its effect on the glucose absorption activity of the isolated rat hemidiaphragm. This oil's safety was studied by exploring its acute (doses 1, 3, 5, and 7 mL/kg) and subacute (doses 1 and 2 mL/kg) toxicities in albino mice and Wistar rats, respectively. The safety of the ODSO was also assessed by studying its effect on the HepG2 cell viability in vitro. The effect of ODSO, or combined with the insulin, on the glucose absorption activity of isolated rat hemidiaphragm was evaluated at the dose 1 g/L in vitro. The results demonstrated the safety of ODSO. Indeed, this study showed that this oil does not produce any mortality or signs of toxicity after the single-dose administration in mice. Additionally, the daily intake of the ODSO during four weeks does not induce a significant variation in the biochemical parameters and body weight of rats compared with the control group. Besides, the cell viability of HepG2 did not change in the presence of ODSO. On the other hand, the ODSO increased the glucose absorption activity of the isolated rat hemidiaphragm, and this activity was significantly enhanced when combined with insulin. This study confirms, on one side, the safety of this oil and its efficacy and, on the other side, encourages its potential use as a complement to treat diabetes.

The Effect of n-3 Fatty Acids on Glucose Homeostasis and Insulin Sensitivity

Type 2 diabetes (T2D) as well as cardiovascular disease (CVD) represent major complications of obesity and associated metabolic disorders (metabolic syndrome). This review focuses on the effects of long-chain n-3 polyunsaturated fatty acids (omega-3) on insulin sensitivity and glucose homeostasis, which are improved by omega-3 in many animal models of metabolic syndrome, but remain frequently unaffected in humans. Here we focus on: (i) mechanistic aspects of omega-3 action, reflecting also our experiments in dietary obese mice; and (ii) recent studies analysing omega-3’s effects in various categories of human subjects. Most animal experiments document beneficial effects of omega-3 on insulin sensitivity and glucose metabolism even under conditions of established obesity and insulin resistance. Besides positive results obtained in both cross-sectional and prospective cohort studies on healthy human populations, also some intervention studies in prediabetic subjects document amelioration of impaired glucose homeostasis by omega-3. However, the use of omega-3 to reduce a risk of new-onset diabetes in prediabetic subjects still remains to be further characterized. The results of a majority of clinical trials performed in T2D patients suggest that omega-3 have none or marginal effects on metabolic control, while effectively reducing hypertriglyceridemia in these patients. Despite most of the recent randomized clinical trials do not support the role of omega-3 in secondary prevention of CVD, this issue remains still controversial. Combined interventions using omega-3 and antidiabetic or hypolipidemic drugs should be further explored and considered for treatment of patients with T2D and other diseases.

Fish oil reverses the altered glucose transporter, phosphorylation, insulin receptor substrate-1 protein level and lipid contents in the skeletal muscle of sucrose-rich diet fed rats

The role and underlying mechanisms by which n-3 polyunsaturated fatty acids (PUFA) prevent/reverse SRD-induced insulin resistance (IR) in the muscle are not completely understood. Therefore, we examined: triglyceride, diacylglycerol, PKCθ, Glut-4, enzymatic hexokinase activity, IRS-1 protein mass level, and fatty acid composition of muscle phospholipids. Rats were fed a SRD during 6 months. Thereafter, half the animals continued with SRD up to 8 months; the other half was fed a SRD in which CO (8% wt/wt) was replaced by FO (7%+1% CO) for 2 months. Results were compared with those obtained in rats fed a control diet (CD). In SRD-fed rats, FO oil normalized/improved lipid storage and PKCθ protein mass level. Effects of insulin were comparable with those of CD-fed rats. FO reversed impaired glucose phosphorylation, IRS-1, and, under insulin stimulation, Glut-4 protein mass level. FO normalized insulin resistance and increased n-3 PUFAs in muscle phospholipids.

Dietary (n-3) long chain polyunsaturated fatty acids prevent sucrose-induced insulin resistance in rats

This study was designed to determine the effect of substituting (n-3) long-chain PUFAs (LCPUFAs) for linoleic acid and hence decreasing the (n-6):(n-3) fatty acid ratio on sucrose-induced insulin resistance in rats. Weanling male Wistar rats were fed casein-based diets containing 100 g/kg fat for 12 wk. Insulin resistance was induced by replacing starch (ST) with sucrose (SU). The dietary fats were formulated with groundnut oil, palmolein, and fish oil to provide the following ratios of (n-6):(n-3) fatty acids: 210 (ST-210, SU-210), 50 (SU-50), 10 (SU-10), and 5 (SU-5). Compared with starch (ST-210), sucrose feeding (SU-210) significantly increased the plasma insulin and triglyceride concentrations and the plasma insulin area under the curve (AUC) in response to an oral glucose load. Adipocytes isolated from rats fed SU-210 had greater lipolytic rate, lower insulin stimulated glucose transport, and lower insulin-mediated antilipolysis than those from rats fed ST-210. Decreasing the dietary (n-6):(n-3) ratio in sucrose-fed rats (SU-10 and SU-5) normalized the plasma insulin concentration and the AUC of insulin after a glucose load. The sucrose-induced increase in plasma triglyceride concentration was normalized in rats fed SU-50, SU-10 and SU-5. Further, sucrose-induced alterations in adipocyte lipolysis and antilipolysis were partially reversed and glucose transport improved in rats fed diets SU-5 and SU-10. In diaphragm phospholipids, decreasing the (n-6):(n-3) ratio in the diet increased the concentration of (n-3) LCPUFAs with concomitant decreases in the concentration of (n-6) LCPUFAs. These results suggest that (n-3) LCPUFAs at a level of 2.6 g/kg diet [0.56% energy (n-3) LCPUFAs, (n-6):(n-3) ratio = 10] may prevent sucrose-induced insulin resistance by improving peripheral insulin sensitivity.

Differential effects of dietary saturated and trans-fatty acids on expression of genes associated with insulin sensitivity in rat adipose tissue

OBJECTIVE

Trans-fatty acids (TFAs) are formed during partial hydrogenation of vegetable oils and are shown to be more atherogenic than saturated fatty acids (SFAs). Our previous study showed that dietary TFAs decrease adipose tissue insulin sensitivity to a greater extent than SFAs in rats. We hypothesized that the effects of these fatty acids on insulin sensitivity could be mediated through an alteration in gene expression. In the current study we have investigated the effects of dietary TFAs or SFAs on expression of genes associated with insulin sensitivity in rat adipose tissue.

DESIGN AND METHODS

Male weanling Wistar/NIN rats were divided into four groups and fed one of the following diets containing 10% fat (g/100 g diet) differing only in the fatty acid composition for 3 months: control diet (3.7% linoleic acid (LA)), SFA diet (5% SFA), TFA diet 1 (1.5% TFA + 1% LA) and TFA diet 2 (1.5% TFA + 2% LA). The mRNA expression of peroxisome proliferator-activated receptor gamma (PPARgamma), lipoprotein lipase (LPL), glucose transporter-4 (GLUT4), resistin and adiponectin was analyzed in epididymal fat using RT-PCR. The effects of TFA were studied at two levels of LA to understand the beneficial effects of LA over the effects of TFA.

RESULTS

Both dietary SFA and TFA upregulated the mRNA levels of resistin. Dietary SFA downregulated adiponectin and GLUT4 and upregulated LPL, while TFA downregulated PPARgamma and LPL. The effects of dietary TFA on PPARgamma and resistin were not counteracted by increased LA (TFA diet 2).

CONCLUSION

The effects of SFAs on the aforementioned genes except PPARgamma could be extrapolated towards decreased insulin sensitivity, while only the alteration in the mRNA levels of PPARgamma and resistin could be associated with insulin resistance in TFA-fed rats. These findings suggest that dietary SFAs and TFAs alter the expression of different genes associated with insulin sensitivity in adipose tissue.

Substituting dietary linoleic acid with alpha-linolenic acid improves insulin sensitivity in sucrose fed rats

This study describes the effect of substituting dietary linoleic acid (18:2 n-6) with alpha-linolenic acid (18:3 n-3) on sucrose-induced insulin resistance (IR). Wistar NIN male weanling rats were fed casein based diet containing 22 energy percent (en%) fat with approximately 6, 9 and 7 en% saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) respectively for 3 months. IR was induced by replacing starch (ST) with sucrose (SU). Blends of groundnut, palmolein, and linseed oil in different proportions furnished the following levels of 18:3 n-3 (g/100 g diet) and 18:2 n-6/18:3 n-3 ratios respectively: ST-220 (0.014, 220), SU-220 (0.014, 220), SU-50 (0.06, 50), SU-10 (0.27, 10) and SU-2 (1.1, 2). The results showed IR in the sucrose fed group (SU-220) as evidenced by increase in fasting plasma insulin and area under the curve (AUC) of insulin in response to oral glucose load. In SU-220, the increase in adipocyte plasma membrane cholesterol/phospholipid ratio was associated with a decrease in fluidity, insulin stimulated glucose transport, antilipolytic effect of insulin and increase in basal and norepinephrine stimulated lipolysis in adipocytes. In SU-50, sucrose induced alterations in adipocyte lipolysis and antilipolysis were normalized. However, in SU-2, partial corrections in plasma insulin, AUC of insulin and adipocyte insulin stimulated glucose transport were observed. Further, plasma triglycerides and cholesterol decreased in SU-2. In diaphragm phospholipids, the observed dose dependent increase in long chain (LC) n-3 PUFA was associated with a decrease in LC-n-6 PUFA but insulin stimulated glucose transport increased only in SU-2. Thus, this study shows that the substitution of one-third of dietary 18:2 n-6 with 18:3 n-3 (SU-2) results in lowered blood lipid levels and increases peripheral insulin sensitivity, possibly due to the resulting high LCn-3 PUFA levels in target tissues of insulin action. These findings suggest a role for 18:3 n-3 in the prevention of insulin resistant states. The current recommendation to increase 18:3 n-3 intake for reducing cardiovascular risk may also be beneficial for preventing IR in humans.

What Do Hormones Have to Do with Aging? What Does Aging Have to Do with Hormones?

It is clear that aging results in alterations of endocrine physiology, which in turn appear to contribute to development of the senescent phenotype. How the underlying basic aging process or processes cause the endocrine cell dysfunctions leading to hormone imbalance is far from clear, but oxidative alteration of cell membranes is an attractive candidate mechanism that might be susceptible to some degree of global remediation.

Modulation of glucose transporters in rat diaphragm by sodium tungstate

Oral administration of sodium tungstate is an effective treatment for diabetes in animal models. We examined the effects of 6 weeks of oral administration of tungstate on glucose transporters (GLUT) in streptozotocin-induced diabetic rat diaphragm. Diabetes decreased GLUT4 expression while tungstate treatment normalized not only GLUT4 protein but also GLUT4 mRNA in the diabetic rats. Furthermore, treatment increased GLUT4 protein in plasma and internal membranes, suggesting a stimulation of its translocation to the plasma membrane. Tungstate had no effect on healthy animals. There were no differences in the total amount of GLUT1 transporter in any group. We conclude that the normoglycemic effect of tungstate may be partly due to a normalization of the levels and subcellular localization of GLUT4, which should result in an increase in muscle glucose uptake.

Omega-3 polyunsaturated fatty acids inhibit the accumulation of PAS-positive material in the myocardium of STZ-diabetic wistar rats

This study was conducted to investigate the effect of Omega-3 PUFA on streptozotocin (STZ)-induced diabetic cardiomyopathy in wistar rats. After 4 weeks of STZ (60 mg/kg, i.v.) administration, the diabetic animals were randomly divided into two groups: Diabetic control and Omega-3 PUFA treated diabetic rats. Omega-3 PUFA (0.5 ml/kg) was administered to the latter group for 10 weeks. Age matched normal rats served as Normal controls. During the study, plasma glucose, glycosylated hemoglobin, plasma cholesterol, LDL and HDL cholesterol, triglyerides were evaluated in all the groups. Omega-3 PUFA treatment did not normalise but instead blunted the effect of diabetes with regards to the above parameters significantly (P<0.01). At the end of the experiment, morphometric and histochemical studies were performed on heart and myocardial enzyme markers were studied. In the diabetic control group, diabetic cardiomyopathy was characerised by elevated CPK (DC 110+/-8.85 vs. NC 39+/-5.83) and morphological changes in heart. Gravimetric ratios showed increased heart-to-body weight ratio in diabetic control over normal control group. (DC 3.38+/-0.05 vs. NC 2.48+/-0.03). Histochemical evidence showed increased accumulation of PAS-positive material in myocardial interstitium (++++). The Omega-3 PUFA treatment blunted all these adverse effects of diabetes on heart significantly (P<0.001). However, further studies are warranted to elucidate the mechanism by which Omega-3 PUFA decreases the accumulation of PAS-positive material in diabetic myocardium.

Effect of age receptor blocker and/or anti-inflammatory coadministration in relation to glycation, oxidative stress and cytokine production in stz diabetic rats

Until now the relation between advanced glycation end products (AGEs) and vascular lesion is still controversial. However, the interaction of the former with a receptor triggers the synthesis of cytokines particularly interleukin 1- beta(IL-1 beta) and tumour necrosis factor- alpha(TNFalpha ). Subsequent release of nitric oxide (NO) may in turn induce certain damage to beta cell islets. Several arguments indicated that AGEs and reactive oxygen intermediates (ROIs) could alter the function of the vessel wall. Therefore, this study was undertaken to investigate the effectiveness of aminoguanidine, AG (inhibitor of AGE formation) joined with omega -3-fatty acids, omega 3FAs (anti-inflammatory immunosuppressive drug) in STZ diabetic rats. Diabetes was induced in 48 female albino Wistar rats by a single intraperitoneal (i.p.) injection of streptozotocin (STZ, 50 mg kg (-1)). Diabetic animals were treated with AG (50 mg kg(-1) ) and/or omega 3FAs (12 mg kg (-1)) daily and orally for 4 weeks. Groups of age matched diabetic rats ( n= 10) and healthy animals ( n= 10) served as positive and negative controls. At the end of the study, plasma glucose, fructosamine, total cholesterol (TC), high density lipoprotein cholesterol (HDLC), low density lipoprotein cholesterol (LDLC), the susceptibility of LDL to copper-catalysed oxidation, catalase activity, NO, IL-1 beta, TNF alpha were measured. Histopathological assessment of pancreatic slices were also determined. Diabetes remarkably increased plasma glucose, fructosamine and dyslipidaemia (increased TC, LDLC and decreased HDLC). Oxidative markers like oxidative susceptibility of LDL, catalase activity and NO levels were greatly enhanced. Finally, it increased the synthesis and release of cytokine (IL-1beta and TNF alpha). Treatment of diabetic rats with AG and omega 3FAs markedly reduced the above mentioned parameters. Combined form therapy has a better effect regarding oxidative cell markers, specifically NO level. Finally, omega 3FAs coadministration with AG nearly restored the atrophy of islets of Langerhan's and the peripheral lymphocytic infiltration compared to diabetic and AG treated groups. In conclusion, there is a direct correlation between glycation, oxidative stress and cytokine production with increased propensity of microvascular disorder in STZ diabetic rats. omega 3FA administration with AGE receptor blocker may represent a possible avenue of research for therapeutics directed for alleviating the complication associated with diabetes.