Effects of benfluorex on in vivo patterns of insulin resistance induced by diets rich in fat or fructose

Jiangzhi Capsule improves fructose-induced insulin resistance in rats: Association with repair of the impaired sarcolemmal glucose transporter-4 recycling

ETHNOPHARMACOLOGICAL RELEVANCE

Jiangzhi Capsule, originated from an experienced formula in traditional Chinese Medicine, has been listed and used for the management of metabolic abnormalities in Australia for a long time. To better understand Jiangzhi Capsule, this study investigated its effect on insulin resistance.

MATERIALS AND METHODS

Male rats were treated with liquid fructose in their drinking water over 14 weeks. Jiangzhi Capsule was co-administered (once daily, by oral gavage) during the last 7 weeks. Indexes of lipid and glucose homeostasis were determined enzymatically, by ELISA and/or histologically. Gene expression was analyzed by real-time PCR, Western blot and/or immunohistochemistry.

RESULTS

Treatment with Jiangzhi Capsule (100mg/kg) attenuated fructose overconsumption-induced increases in basal plasma insulin concentrations, the homeostasis model assessment of insulin resistance index and the adipose tissue insulin resistance index in rats. The increased plasma glucose concentrations during oral glucose tolerance test were also inhibited. Furthermore, Jiangzhi Capsule had a trend to attenuate the decreased ratios of glucose and non-esterified fatty acids to plasma insulin concentrations. Mechanistically, this insulin-sensitizing action was accompanied by normalization of the downregulated sarcolemmal glucose transporter (GLUT)-4 protein expression and the decreased phosphorylated Akt to total Akt protein ratio in gastrocnemius.

CONCLUSIONS

These results suggest that Jiangzhi Capsule ameliorates fructose-induced insulin resistance with a link to repair of the impaired sarcolemmal GLUT-4 recycling through modulation of the ratio of phosphorylated Akt to total Akt in gastrocnemius. Our findings provide an evidence-based and mechanistic understanding of Jiangzhi Capsule for the management of insulin resistance-associated disorders.

Treatment with Rhodiola crenulata root extract ameliorates insulin resistance in fructose-fed rats by modulating sarcolemmal and intracellular fatty acid translocase/CD36 redistribution in skeletal muscle

Background

Rhodiola species have been used for asthenia, depression, fatigue, poor work performance and cardiovascular diseases, all of which may be associated with insulin resistance. To disclose the underlying mechanisms of action, the effect of Rhodiola crenulata root (RCR) on insulin resistance was investigated.

Methods

Male Sprague-Dawley rats were treated with liquid fructose in their drinking water over 18 weeks. The extract of RCR was co-administered (once daily by oral gavage) during the last 5 weeks. The indexes of lipid and glucose homeostasis were determined enzymatically and/or by ELISA. Gene expression was analyzed by Real-time PCR, Western blot and/or confocal immunofluorescence.

Results

RCR extract (50 mg/kg) suppressed fructose-induced hyperinsulinemia and the increases in the homeostasis model assessment of insulin resistance index and the adipose tissue insulin resistance index in rats. Additionally, this treatment had a trend to restore the ratios of glucose to insulin and non-esterified fatty acids (NEFA) to insulin. Mechanistically, RCR suppressed fructose-induced acceleration of the clearance of plasma NEFA during oral glucose tolerance test (OGTT), and decreased triglyceride content and Oil Red O staining area in the gastrocnemius. Furthermore, RCR restored fructose-induced sarcolemmal overexpression and intracellular less distribution of fatty acid translocase/CD36 that contributes to etiology of insulin resistance by facilitating fatty acid uptake.

Conclusion

These results suggest that RCR ameliorates insulin resistance in fructose-fed rats by modulating sarcolemmal and intracellular CD36 redistribution in the skeletal muscle. Our findings may provide a better understanding of the traditional use of Rhodila species.

Dietary fructose during the suckling period increases body weight and fatty acid uptake into skeletal muscle in adult rats

OBJECTIVE

The suckling period is one potentially "critical" period during which nutritional intake may permanently "program" metabolism to promote increased adult body weight and insulin resistance in later life. This study determined whether fructose introduced during the suckling period altered body weight and induced changes in fatty acid transport leading to insulin resistance in adulthood in rats.

METHODS AND PROCEDURES

Pups were randomly assigned to one of four diets: suckle controls (SCs), rat milk substitute formula (Rat Milk Substitute), fructose-containing formula (Fructose), or galactose-containing formula (Galactose). Starting at weaning, all pups received the same diet; at 8 weeks of age, half of the SC rats began ingesting a diet containing 65% kcal fructose (SC-Fructose). This continued until animals were 12 weeks old and the study ended.

RESULTS

At weeks 8, 10, and 11, the Fructose group weighed more than SC and SC-Fructose groups (P < 0.05). At weeks 8 and 10 of age, the Fructose group had significantly higher insulin concentrations vs. rats in the SC-Fructose group. (3)H-Palmitate transport into vesicles from hind limb skeletal muscle was higher in Fructose vs. SC rats (P < 0.05). CD36 expression was increased in the sarcolemma but not in whole tissue homogenates from skeletal muscle from Fructose rats (P < 0.05) suggesting a redistribution of this protein associated with fatty acid uptake across the plasma membrane. This change in subcellular localization of CD36 is associated with insulin resistance in muscle.

DISCUSSION

Consuming fructose during suckling may result in lifelong changes in body weight, insulin secretion, and fatty acid transport involving CD36 in muscle and ultimately promote insulin resistance.

Fish Oil Affects Pancreatic Fat Storage, Pyruvate Dehydrogenase Complex Activity and Insulin Secretion in Rats Fed a Sucrose-Rich Diet

Rats fed a sucrose-rich diet (SRD) develop hypertriglyceridemia and a marked decline in beta cell function. The purpose of this study was to determine whether changes in triglyceride concentration and/or altered pyruvate dehydrogenase complex (PDHc) activity contribute to the beta cell dysfunction, and to analyze the effect of dietary fish oil on the altered patterns of insulin secretion and peripheral insulin resistance. Rats were fed an SRD for 210 d. One-half of the rats continued consuming the SRD until d 270. The other half received an SRD in which fish oil (FO) was partially substituted for corn oil until d 270. A group of rats was fed a control diet (CD) throughout the experiment. The islets of rats fed the SRD had a greater triglyceride concentration and lower PDHc activity than those fed the CD. Insulin secretion patterns under the stimulus of glucose, palmitate or L-arginine were impaired in SRD-fed compared with CD-fed rats. This was accompanied by peripheral insulin resistance, mild hyperglycemia, a sharp increase of plasma triglyceride and free fatty acid levels and greater epididymal and retroperitoneal fat weights. FO normalized and/or improved these variables. Our results indicate that the increased fat storage and decreased PDHc activity in the beta cells play a key role in the abnormal insulin secretion of rats chronically fed an SRD. This is consistent with the reversion of these alterations by dietary FO.

Role of skeletal muscle on impaired insulin sensitivity in rats fed a sucrose-rich diet: effect of moderate levels of dietary fish oil

In the present study we investigated: (1) the contribution of the skeletal muscle to the mechanisms underlying the impaired glucose homeostasis and insulin sensitivity present in dyslipemic rats fed a sucrose-rich diet (SRD) over a long period of time and (2) the effect of fish oil on these parameters when there was a stable hypertriglyceridemia before the source of fat (corn oil) in the diet was replaced by isocaloric amounts of cod liver oil. Our results show an increased triglyceride content in the gastrocnemius muscle with an impaired capacity for glucose oxidation in the basal state and during euglycemic clamp. This was mainly due to a decrease of the active form of pyruvate dehydrogenase complex (PDHa) and an increase of PDH kinase activities. Hyperglycemia, normoinsulinemia, and diminished peripheral insulin sensitivity also were found. Even though there were no changes in the insulin levels, the former metabolic abnormalities were completely reversed when the source of fat was changed from corn oil to cod liver oil. The data also suggest that in the gastrocnemius muscle of rats fed a SRD over an extended period, an increased availability and oxidation of the lipid fuel, which in turn impairs the glucose oxidation, contributes to the abnormal glucose homeostasis and to the peripheral insulin insensitivity. Moreover, the parallel effect on insulin sensitivity, glucose, and lipid homeostasis attained through the manipulation of dietary fat (n-3) in the SRD suggests a role of n-3 fatty acid in the management of dyslipidemia and insulin resistance.

Therapeutic effect of benfluorex in type II diabetic patients on diet regimen alone

A randomized double-blind study of benfluorex (150 mg x 3 daily) versus placebo was conducted over 3 months in 32 type II diabetic patients (24 men and 8 women, aged 52 +/- 8.4 years) with mild stable obesity [body-mass index (BMI) 27 +/- 1.6 kg/ m2], moderate fasting hyperglycemia (fasting blood glucose 9 +/- 0.5 mmol/L, HbA1c 6.7 +/- 0.9%) and moderate hyperinsulinemia (18.6 +/- 3.0 microU/mL) when on treatment with diet alone. After a 1-month placebo run-in period, subjects were randomized to benfluorex or placebo three tablets daily. Inclusion parameters and end-of-study measures were body weight, BMI, fasting blood glucose, glycemic profile, HbA1c, fasting insulinemia, basal and stimulated C-peptide, and an insulin tolerance test (0.1 U/kg). The groups were homogeneous at baseline, except for glycemic profile (higher postprandial glycemia in the group randomized to benfluorex). At the end of the study, the groups did not differ in body weight or BMI; however, HbA1c decreased more with benfluorex (6.0 +/- 1.0% versus 6.8 +/- 0.9%, p = 0.024), as did the mean glycemic profile (7.8 +/- 1.4 versus 8.5 +/- 1.7 mmol/L, p < 0.001), including a particular decrease in postprandial glycemia. The decreases in fasting blood glucose and insulinemia appeared larger with benfluorex (7.7 +/- 1.3 versus 8.4 +/- 1.6 mmol/L and 13.5 +/- 4.5 versus 16.1 +/- 5.1 microU/mL, respectively), but were not statistically significant. The increase in the insulin sensitivity index (Kitt) was greater with benfluorex (+0.54 +/- 1.4 versus +0.25 +/- 1.3%/mn), but the difference was not statistically significant. The same was observed for the stimulated C-peptide. In type II diabetics with mild obesity and hyperglycemia previously managed with diet alone, benfluorex has significant long-term effect on HbA1c and mean daily blood glucose, and tends to lower insulinemia.

Therapeutic benefit of benfluorex in type II diabetic patients treated with sulfonylureas

The objective of this study was to evaluate the effect of benfluorex in type II diabetic patients already treated with sulfonylureas (SU) in a randomized placebo-controlled trial. After a 4-week placebo run-in, 68 patients (49 men and 19 women; age range 40-70 years; known duration of diabetes 0.5-19 years) were randomized to double-blind 12-week treatment with benfluorex (B) or placebo (P). Primary end points were HbA1c and fasting blood glucose (FBG). Secondary end points were glucose tolerance (meal test over 120 min), plasma insulin, C-peptide, and lipid profile. Results were analyzed using both intention-to-treat analysis (ITT) in patients completing at least one treatment visit and per protocol analysis in those completing the whole study. There were no baseline differences between the two groups in any study parameter. Fifty-eight patients completed the study (28 B, 30 P), and 66 patients (33 B, 33 P) were eligible for ITT analysis. Over the 12-week treatment period, FBG decreased by 14.9% in the B group (-1.39 mmol/L, p < 0.001), and 3.2% in the P group (-0.28 mmol/L, NS) according to the ITT analysis and by 17.4% (p < 0.001) and 3.8% (NS), respectively, in the per protocol analysis. The difference in FBG outcome between the two groups was significant (p = 0.009 and p = 0.004, respectively). In patients completing the study, mean HbA1c decreased in the B group (-0.66%, p = 0.005) and remained stable in the P group (+0.14%, NS). HbA1c outcome differed between the two groups (p = 0.007). The decrease in AUCglucose was greater in the B group than in the P group (-210 +/- 220 versus -60 +/- 270 mmol/L x 120 min, p = 0.026). Plasma insulin and C-peptide changes did not differ between the two groups. Low-density lipoprotein (LDL) cholesterol decreased in B patients and was stable in P patients (-0.43 versus -0.05 mmol/L, p = 0.026). Of the 68 randomized patients, six on B and four on P reported at least one adverse event, causing dropout in five and two patients, respectively. In conclusion, benfluorex is an effective agent for combination therapy in type II diabetic patients poorly controlled on SUs alone.

Fatty acids and fibrates are potent inducers of transcription of the phosphenolpyruvate carboxykinase gene in adipocytes

Cytosolic phosphoenolpyruvate carboxykinase (PEPCK) plays a critical role in adipose tissue glyceroneogenesis. We have previously shown that transcription of the PEPCK gene was stimulated by isoprenaline and retinoic acid in 3T3-F442A adipocytes. We also showed that oleate increased PEPCK mRNA. Here, we analysed the effect that fatty acids of various chain lengths and unsaturation degrees exerted on PEPCK gene expression in 3T3-F442A adipocytes. When maintained in serum-free, glucose-free medium, differentiated cells responded to unsaturated long-chain fatty acids by a large increase in PEPCK mRNA whereas saturated fatty acids were inefficient. A maximum fivefold stimulation by oleate was attained at 4 h of treatment with 1 mM fatty acid bound to albumin in a 6:1 ratio. The poly-unsaturated very long-chain fatty acid all-cis-4,7,10,13,16,19-docosahexaenoic acid (C22:6) was even more potent and produced a tenfold increase. The expression of the genes encoding glycerol-3-phosphate dehydrogenase, hormone-sensitive lipase or actin remained unaffected by oleate exposure. A 4-h treatment by the hypolipidemic drug clofibrate, 0.5-2 mM, also produced a large (3-9-fold) increase in PEPCK mRNA. When used at non-saturating concentrations, oleate and clofibrate acted in an additive manner. At maximally effective concentrations, additivity was lost, suggesting that fatty acids and fibrates might act through similar mechanisms. Nuclear transcription experiments showed that oleate and clofibrate stimulated the transcription rate of the gene. 3T3-F442A cells were stably transfected with a plasmid containing the base pairs -2100 to +69 of the PEPCK gene promoter fused to the chloramphenicol acetyltransferase gene. These differentiated stable transfectants responded to oleate and clofibrate by a specific increase in chloramphenicol acetyltransferase activity. Adipocytes express various isoforms of peroxisome-proliferator-activated receptors that can be activated by fibrates and fatty acids. Potential recognition sequences for peroxisome-proliferator-activated receptors are present in the -2100 to +69 fragment of the PEPCK gene promoter. Thus, this gene represents an ideal molecular target for understanding the complex transcriptional control exerted by fatty acids and peroxisome proliferators.

Fructose-induced hypertension in rats is concentration- and duration-dependent

The present study determined the most suitable concentration and duration of fructose treatment for inducing hypertension in Wistar rats. The correlation between fructose-induced hypertension and hyperinsulinemia was also evaluated. The rats were treated with 5%, 10%, or 20% fructose in drinking water. The greatest changes, including increases in blood pressure, fluid intake, and plasma levels of insulin, glucose, and triglycerides, and a decrease in food intake following fructose treatment, were observed with the 10% solution. The times of the onset and maximum response differed for the various parameters measured. The increase in blood pressure occurred earlier than the increase in the plasma insulin level. All abnormalities disappeared rapidly after fructose withdrawal. There was no significant correlation between plasma insulin level and systolic blood pressure. In conclusion, treatment with 10% fructose in drinking water (equivalent to a diet containing 48-57% fructose) for one week or longer is appropriate for the rapid production of fructose-induced hypertension in Wistar rats, which is associated with elevated levels of plasma insulin, glucose, and triglycerides.