Postprandial hyperlipidemia in streptozotocin-induced diabetic rats is due to abnormal increase in intestinal acyl coenzyme A:cholesterol acyltransferase activity

Luteolin Mitigates Diabetic Dyslipidemia in Rats by Modulating ACAT-2, PPARα, SREBP-2 Proteins, and Oxidative Stress

Diabetic dyslipidemia is a crucial link between type-2 diabetes mellitus (T2DM) and atherosclerotic cardiovascular diseases (ASCVD). Natural biologically active substances have been advocated as complementary remedies for ASCVD and T2DM. Luteolin, a flavonoid, exhibits antioxidant, hypolipidemic, and antiatherogenic effects. Hence, we aimed to determine influence of luteolin on lipid homeostasis and hepatic damage in rats with T2DM induced by high-fat-diet (HFD) and streptozotocin (STZ). After being fed HFD for 10 days, male Wistar rats received 40 mg/kg STZ intraperitoneal injection on 11th day. Seventy-two hours later, hyperglycemic rats (fasting glucose > 200 mg/dL) were randomized into groups, and oral hydroxy-propyl-cellulose, atorvastatin (5 mg/kg), or luteolin (50 mg/kg or 100 mg/kg) administered daily, while continuing HFD for 28 days. Luteolin significantly ameliorated dyslipidemia levels and concomitantly improved atherogenic index of plasma in a dose-dependent manner. Increased levels of malondialdehyde and diminished levels of superoxide dismutase, catalase, and glutathione in HFD-STZ-diabetic rats were significantly regulated by luteolin. Luteolin significantly intensified PPARα expression while decreasing expression of acyl-coenzyme A:cholesterol acyltransferase-2 (ACAT-2) and sterol regulatory element binding protein-2 (SREBP-2) proteins. Moreover, luteolin effectively alleviated hepatic impairment in HFD-STZ-diabetic rats to near-normal control levels. The findings of the present study expound mechanisms by which luteolin mitigated diabetic dyslipidemia and alleviated hepatic impairment in HFD-STZ-diabetic rats by amelioration of oxidative stress, modulation of PPARα expression, and downregulation of ACAT-2 and SREBP-2. In conclusion, our results imply that luteolin may be efficacious in management of dyslipidemia in T2DM, and future research may be essential to substantiate our findings.

Streptozotocin-induced type 1 and 2 diabetes in rodents: a model for studying diabetic cardiac autonomic neuropathy

Background

Several animal models are continually being developed to study diabetic complication. Several conflicting regimen for diabetes induction exist in the literature with varying dose strength and regimen for different study interest in diabetes. This study aims to show the effect of high dose streptozotocin (STZ) on the one hand compared with multiple low doses after high fat diet induction on diabetic cardiac autonomic neuropathy (DCAN).

Methodology

Eighty-four Wistar rats were used to demonstrate DCAN induction using 2 approaches one for T1DM (STZ 50mg/kg) and the other for T2DM (HFD for 8 weeks with STZ 25mg/Kg daily for five days). DCAN features were assessed using invasive biomarkers, histology patterns and cardiac nerve densities.

Results

Diabetes induction rate was 76% and 89% in T1DM and T2DM model respectively. T1DM group had significant weight loss, reduced c-peptide, and insulin level post induction. The T2DM additionally showed significantly higher total cholesterol and Homeostatic model assessment (HOMA) compared with control. Serum levels of catecholamine, choactase, nerve growth factor and cardiac nerve density confirms development of DCAN.

Conclusion

High single dose of STZ and HFD with multiple low doses of STZ may be recommended for DCAN study in T1DM and T2DM rat model respectively.

Comparative Study on the Influence of Some Medicinal Plants on Diabetes Induced by Streptozotocin in Male Rats

Medicinal plants have played an important role in the treatment of many diseases. Medicinal plants are believed to be well appropriate with the human body and to produce less side influences than the pharmaceuticals. Kingdom of Saudi Arabia has abundant and wide variety of medicinal plants whose therapeutic effects have not been adequately studied. The aim of this study was to investigate the hypoglycemic activities of the extracts of three plant species collected from Albaha region of Saudi Arabia including Olea oleaster (Oleaceae family) leaves (OLE), Juniperus procera (Cupressaceae family) leaves (JLE), and Opuntia ficus-indica (Cactaceae family) stems (OSE) on streptozotocin (STZ) diabetic male rats. The animals were distributed into eight groups. The first group was used as normal control. The second group was diabetic control. Diabetic rats of the third, fourth, and fifth groups were supplemented with OLE, JLE, and OSE, respectively. Normal rats of the sixth, seventh, and eighth groups were treated with OLE, JLE, and OSE, respectively. As expected, the mean of body weight was significantly decreased in rats of the second group. Significant increase in the value of serum glucose and decline of insulin value were observed in rats of the second group. Several alterations of lipid and protein profile and oxidative stress markers were noted in diabetic control rats. Severe histopathological alterations of pancreatic tissues were observed in untreated diabetic rats. The obtained results showed that OLE, JLE, and OSE attenuated the physiological and histopathological alterations. These new data indicate that the attenuation influences of OLE, JLE, and OSE attributed to their antioxidant properties confirmed by oxidative stress markers evaluation.

Effect of aluminum chloride on blood glucose level and lipid profile in normal, diabetic and treated diabetic rats

OBJECTIVES

The objectives of the study were to assess evaluate the effects of aluminum chloride (AlCl₃) on blood glucose and lipid levels in normal, diabetic, and glibenclamide-treated diabetic rats.

MATERIALS AND METHODS

Forty-two male Wistar rats were divided into seven groups of six each. Group I was normal control, Groups II and III were given AlCl₃50 and 100 mg/kg, and Group IV to VII were administered with streptozotocin (STZ) (60 mg/kg) intraperitoneally. Group IV was diabetic control, Group V in addition was given AlCl₃50 mg/kg, Group VI glibenclamide (10 mg/kg), and Group VII glibenclamide and AlCl₃(50 mg/kg) per-oral daily for 28 days. Blood glucose and lipid levels were estimated at base line, after diabetes was set in and on the last day of study. Histopathological changes in pancreas, liver, and kidney were studied.

RESULTS

No significant change was observed in blood glucose and lipid levels in Group I. Group II and III showed a dose-dependent significant increase in blood glucose was observed. Group V had a reduction in blood glucose but not to the nondiabetic level. Group VI had significant reduction in blood sugar. In Group VII, treated with glibenclamide and AlCl₃, there was no significant change in blood glucose reduction compared to Group VI. Lipid levels were reduced in groups treated with AlCl₃ and glibenclamide and not in other groups. Gross tissue damage was seen in pancreas in STZ group and in liver and kidney in AlCl₃ groups.

CONCLUSION

AlCl₃ administration in Wistar rats caused in significant hyperglycemia in normal rats, hypoglycemia in diabetic rats, and did not influenced hypoglycemic effect of glibenclamide and in addition, resulted in reduction in lipid levels.

The Effects of Natural Clinoptilolite and Nano-Sized Clinoptilolite Supplementation on Lipid Profile, Food Intakes and Body Weight in Rats with Streptozotocin-Induced Diabetes

Purpose: To determine the effect of natural clinoptilolite (CLN) and nano-sized clinoptilolite (NCLN) on lipid profile, food intakes (FI) and weight changes in streptozotocin (STZ) induced diabetic rats. Methods: In this experimental study, 36 rats were randomly divided into two groups: diabetic group which was injected STZ (60 mg/kg BW), and a non-diabetic group. Three days after diabetes induction, each of these groups was randomly divided into 3 subgroups of 6 animals ((1) control, (2) 1%/food CLN, (3) 1%/food NCLN). The animals were supplemented for 28 days, starting three days after STZ administration. At the end of the study, blood was drawn for biochemical assays. The weights and FIs of the rats were measured at the beginning and end of each week. Results: Our findings revealed that there was no significant change in lipid profile, 28 days after administration of STZ in diabetic rats. Low density lipoprotein (LDL) was increased slightly in diabetic rats treated with NCLN without any significant changes in other lipid profile parameters in the other groups. Weight was reduced significantly in diabetic rats. Administration of CLN and NCLN prevented further weight loss in diabetic rats. All groups treated with STZ had higher food intake during the study. Conclusion: Lack of beneficial changes in lipid profile may be attributed to short study duration, insufficient for appearance of lipid abnormalities. Given the partial improvement in weight status and lack of undesirable effects of clinoptilolite supplementation, further research is recommended in subjects with typ1 diabetes mellitus.

Evaluation of Antidiabetic and Antihyperlipidemic Effects of Hydroalcoholic Extract of Leaves of Ocimum tenuiflorum (Lamiaceae) and Prediction of Biological Activity of its Phytoconstituents

Objective:

The aim was to evaluate the anti-diabetic and anti-hyperlipidemic effects of hydroalcoholic extract of leaves of Ocimum tenuiflorum (Lamiaceae) and prediction of biological activities of its phytoconstituents using in vivo anti-diabetic model and in silico analysis respectively.

Materials and Methods:

The leaves of O. tenuiflorum were extracted with 60% ethanol, and the extract was used for further pharmacological screening. The acute toxicity of the extract was evaluated as per the guidelines set by the Organization for Economic Co-operation and Development, revised draft guidelines 423. The oral anti-diabetic activity of the hydroalcoholic extract of O. tenuiflorum (125, 250 and 500 mg/kg) was studied against streptozotocin (STZ) (50 mg/kg; i.p.) + nicotinamide (120 mg/kg; i.p.) induced diabetes mellitus. The animals were treated with the investigational plant extract and standard drug (glibenclamide) for 21 consecutive days and the effect of hydroalcoholic extract of O. tenuiflorum on blood glucose levels was measured at regular intervals. At the end of the study, blood samples were collected from all the animals for biochemical estimation, then the animals were sacrificed and the liver and kidney were collected for organ weight analysis. Prediction for pharmacological and toxicological properties of phytoconstituents of O. tenuiflorum was carried out using online web tools such as online pass prediction and lazar toxicity prediction.

Results:

The hydroalcoholic extract of O. tenuiflorum showed significant anti-diabetic and anti-hyperlipidemic activity at 250 and 500 mg/kg, and this effect was comparable with that of glibenclamide. Predicted biological activities of phytoconstituents of O. tenuiflorum showed presence of various pharmacological actions, which includes anti-diabetic and anti-hyperlipidemic activities. Prediction of toxicological properties of phytoconstituents of O. tenuiflorum did not show any major toxic effects.

Conclusion:

The hydroalcoholic extract of O. tenuiflorum showed significant anti-diabetic and anti-hyperlipidemic activity against STZ + nicotinamide induced diabetes mellitus in rats. Further studies are required to confirm the anti-diabetic and anti-hyperlipidemic activities of individual phytoconstituents of O. tenuiflorum.

Antihyperglycemic, hypolipidemic, hepatoprotective and antioxidative effects of dietary clove (Szyzgium aromaticum) bud powder in a high-fat diet/streptozotocin-induced diabetes rat model

BACKGROUND

Syzygium aromaticum (L.) Merr. & Perry (clove) bud is an important spice used in the preparation of several delicacies and in folklore for diabetes management. The present study was convened to assess the effects of dietary clove bud powder (CBP) on biochemical parameters in a type 2 diabetes rat model, induced by a combination of high-fat diet and low-dose streptozotocin (35 mg kg⁻¹) for 30 days.

RESULTS

Diabetic rats were placed on dietary regimen containing 20-40 g kg⁻¹ clove bud powder. The results revealed that there was no significant (P > 0.05) difference in the average feed intake and weight changes between the rat groups. Furthermore, supplementation with CBP gradually reduced blood glucose level in diabetic rat compared to control diabetic rats without CBP supplementation (DBC). Moreover, reduced activity of α-glucosidase was observed in CBP and metformin-treated rat groups when compared to that of the DBC rat group. In addition, the DBC group had significantly (P < 0.05) higher lipid concentrations (except for high-density lipoprotein cholesterol) when compared to all other groups. Furthermore, CBP had significantly (P < 0.05) reduced activity of liver enzymes (alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase) and showed elevated levels of antioxidant status (glutathione, ascorbic acid, superoxide dismutase and catalase).

CONCLUSION

The results suggest that the clove bud diet may attenuate hyperglycemia, hyperlipidemia, hepatotoxicity and oxidative stress in the type 2 diabetic condition.

Postprandial changes in high density lipoproteins in rats subjected to gavage administration of virgin olive oil

Background and Aims

The present study was designed to verify the influence of acute fat loading on high density lipoprotein (HDL) composition, and the involvement of liver and different segments of small intestine in the changes observed.

Methods and Results

To address these issues, rats were administered a bolus of 5-ml of extra-virgin olive oil and sacrificed 4 and 8 hours after feeding. In these animals, lipoproteins were analyzed and gene expressions of apolipoprotein and HDL enzymes were assessed in duodenum, jejunum, ileum and liver. Using this experimental design, total plasma and HDL phospholipids increased at the 8-hour-time-point due to increased sphingomyelin content. An increase in apolipoprotein A4 was also observed mainly in lipid-poor HDL. Increased expression of intestinal Apoa1, Apoa4 and Sgms1 mRNA was accompanied by hepatic decreases in the first two genes in liver. Hepatic expression of Abcg1, Apoa1bp, Apoa2, Apoe, Ptlp, Pon1 and Scarb1 decreased significantly following fat gavage, while no changes were observed for Abca1, Lcat or Pla2g7. Significant associations were also noted for hepatic expression of apolipoproteins and Pon1. Manipulation of postprandial triglycerides using an inhibitor of microsomal transfer protein -CP-346086- or of lipoprotein lipase –tyloxapol- did not influence hepatic expression of Apoa1 or Apoa4 mRNA.

Conclusion

All these data indicate that dietary fat modifies the phospholipid composition of rat HDL, suggesting a mechanism of down-regulation of hepatic HDL when intestine is the main source of those particles and a coordinated regulation of hepatic components of these lipoproteins at the mRNA level, independently of plasma postprandial triglycerides.

Effects of Tribuli Saponins on Ventricular Remodeling after Myocardial Infarction in Hyperlipidemic Rats

This experiment was designed to determine whether Tribuli saponins (TS) relieve left ventricular remodeling (VR) after myocardial infarction (MI) in a murine hyperlipemia (HL) model. MI and HL models were induced and high and low doses of TS and simvastatin were administrated to the rats. Four weeks later, echocardiographic observation was performed and the left and right ventricular weight index (LVWI, RVWI) was calculated. Echocardiographic results showed that both high dose of TS and simvastatin had a beneficial effect on increasing fractional shortening (FS) and ejection fraction (EF), reducing left ventricular end diastolic volume (LVEDV), systolic volume (LVESV), left ventricular dimension end diastole (LVDd) and systole (LVDs), and decreasing LVWI, as compared to those in the HL-MI model group ( p < 0.05, 0.01). Both medicines had little impact on thickness of the anterior and posterior wall. No significant difference was observed between each treatment group ( p > 0.05). In conclusion, TS not only lowered serum lipidemia, but also relieved left ventricular remodeling, and improved cardiac function in the early stage after MI.

Isoform-specific inhibitors of ACATs: recent advances and promising developments

Acyl-CoA:cholesterol acyltransferase (ACAT) is a promising therapeutic target for cardiovascular diseases. Although a number of synthetic ACAT inhibitors have been developed, they have failed to show efficacy in clinical trials. Now, the presence of two ACAT isoforms with distinct functions, ACAT1 and ACAT2, has been discovered. Thus, the selectivity of ACAT inhibitors toward the two isoforms is important for their development as novel anti-atherosclerotic agents. The selectivity study indicated that fungal pyripyropene A (PPPA) is only an ACAT2-specific inhibitor. Furthermore, PPPA proved orally active in atherogenic mouse models, indicating it possessed cholesterol-lowering and atheroprotective activities. Certain PPPA derivatives, semi-synthetically prepared, possessed more potent and selective in vitro activity than PPPA against ACAT2. This review covers these studies and describes the future prospects of ACAT2-specific inhibitors.

Characterization of STZ-Induced Type 2 Diabetes in Zucker Fatty Rats

The Zucker fatty (ZF) rat is a disease model of obesity and metabolic syndrome, such as hyperlipidemia and insulin resistance, resulting from hyperphagia owing to the loss of function of the leptin receptor, but it rarely develops hyperglycemia. We examined the effects of different doses of streptozotocin (STZ). A low dosage of STZ (30 mg/kg body weight, i.p.) elevated blood glucose levels in ZF rats up to 300 mg/dl within a week, and to nearly 500 mg/dl by 5 weeks after injection of STZ. Besides hyperglycemia, STZ-treated ZF (STZ-ZF) rats retained metabolic syndrome features such as hyperlipidemia and hyperinsulinemia. The stimulated insulin secretion in response to orally-loaded glucose disappeared completely in STZ-ZF rats. Although there were no significant differences in the morphology of pancreatic islets between vehicle-treated ZF (Cont-ZF) and STZ-ZF rats, the insulin content was markedly decreased in STZ-ZF rats. The hepatic gene expression for gluconeogenic enzymes was upregulated in STZ-ZF rats compared with Cont-ZF rats. Metformin lowered the blood glucose levels of STZ-ZF rats in a dose-dependent manner. These results suggest that STZ-ZF rats are useful for studies of T2DM and for the evaluation of the efficacy of anti-diabetic drugs.

The myocardial infarct size-limiting and antiarrhythmic effects of acyl-CoA:cholesterol acyltransferase inhibitor VULM 1457 protect the hearts of diabetic-hypercholesterolaemic rats against ischaemia/reperfusion injury both in vitro and in vivo

The study was designed to characterise the influence of a novel acyl-CoA:cholesterol acyltransferase inhibitor, VULM 1457, on the severity of myocardial ischaemia-reperfusion injury in a model of diabetes mellitus and hypercholesterolaemia induced by co-administration of streptozotocin and a high fat-cholesterol diet. We used Langendorff-perfused rat hearts to measure the size of myocardial infarction after 30 min of regional ischaemia, followed by a 2-h reperfusion period, and open-chest rats were exposed to 6 min of ischaemia and 10 min of reperfusion to analyse ventricular arrhythmias. In addition to the high fat-cholesterol diet, VULM 1457 was administered to the diabetic-hypercholesterolaemic rats for 5 days. Decreased plasma and liver cholesterol levels and a significantly reduced occurrence of ventricular fibrillation (29% vs. 100%, P<0.01), determined via the mean number and duration of episodes (0.6+/-0.4 and 2.1+/-1.4 s vs. 2.8+/-0.8 and 53.5+/-14.4 s in diabetic-hypercholesterolaemic rats, both P<0.01), were observed in these animals. Lethal ventricular fibrillation was suppressed, and arrhythmia severity was also significantly decreased in these animals as compared to the non-treated animals (2.9+/-0.6 vs. 4.9+/-0.2; P<0.05). A smaller infarct size, normalised to the size of area at risk, was observed in the treated diabetic-hypercholesterolaemic group as compared to the non-treated group (16.3+/-1.9% vs. 37.3+/-3.1%; P<0.01). Aside from remarkable hypolipidaemic activity, VULM 1457 improved the overall myocardial ischaemia-reperfusion injury outcomes in the diabetic-hypercholesterolaemic rats by suppressing arrhythmogenesis as well as by reducing myocardial necrosis.

Hypercholesterolemia abrogates an increased resistance of diabetic rat hearts to ischemia-reperfusion injury

Both, diabetes mellitus (DM) and hypercholesterolemia (HCH) are known as risk factors of ischemic heart disease, however, the effects of experimental DM, as well as of HCH alone, on ischemia/reperfusion-induced myocardial injury are not unequivocal. We have previously demonstrated an enhanced resistance to ischemia-induced arrhythmias in rat hearts in the acute phase of DM. Our objectives were thus to extend our knowledge on how DM in combination with HCH, a model that is relevant to diabetic patients with altered lipid metabolism, may affect the size of myocardial infarction and susceptibility to arrhythmias. A combination of streptozotocin (STZ; 80 mg/kg, i.p.) and the fat-cholesterol diet (1% cholesterol, 1% coconut oil; FCHD) was used as a double-disease model mimicking DM and HCH simultaneosly occurring in humans. Following 5 days after STZ injection and FCHD leading to increased blood glucose and cholesterol levels, anesthetized open-chest diabetic, diabetic-hypercholesterolemic (DM-HCH) and age-matched control rats were subjected to 6-min ischemia (occlusion of LAD coronary artery) followed by 10 reperfusion to test susceptibility to ventricular arrhythmias in the in vivo experiments and to 30-min ischemia and subsequent 2-h reperfusion for the evaluation of the infarct size (IS) in the Langendorff-perfused hearts. The incidence of the most life-threatening ventricular arrhythmia, ventricular fibrillation, was significantly increased in the DM-HCH rats as compared with non-diabetic control animals (100% vs. 50%; p<0.05). Likewise, arrhythmia severity score (AS) was significantly higher in the DM-HCH rats than in the controls (4.9+/-0.2 vs. 3.5+/-0.5; p<0.05), but was not increased in the diabetic animals (AS 3.7+/-0.9; p>0.05 vs. controls). Diabetic hearts exhibited a reduced IS (15.1+/-3.0% of the area at risk vs. 37.6+/-2.8% in the control hearts; p<0.05), however, a combination of DM and HCH increased the size of myocardial infarction to that observed in the controls. In conclusion, HCH abrogates enhanced resistance to ischemia-reperfusion injury in the diabetic rat heart.

High-dose thiamine therapy counters dyslipidemia and advanced glycation of plasma protein in streptozotocin-induced diabetic rats

The streptozotocin-induced (STZ) diabetic rat experimental model of diabetes on insulin maintenance therapy exhibits dyslipidemia, mild thiamine deficiency, and increased plasma protein advanced glycation end products (AGEs). The reversal of thiamine deficiency by high-dose thiamine and S-benzoylthiamine monophosphate (benfotiamine) prevented the development of incipient nephropathy. Recently, we reported that high-dose thiamine (but not benfotiamine) countered diabetic dyslipidemia. To understand further the differences between the effects of thiamine and benfotiamine therapy, we quantified the levels of the AGEs in plasma protein. We found hydroimidazolone AGE residues derived from glyoxal and methylglyoxal, G-H1 and MG-H1, were increased 115% and 68% in STZ diabetic rats, with respect to normal controls, and were normalized by both thiamine and benfotiamine; whereas N-carboxymethyl-lysine (CML) and N-carboxyethyl-lysine (CEL) residues were increased 74% and 118% in STZ diabetic rats and were normalized by thiamine only. The lack of effect of benfotiamine on plasma CML and CEL residue concentrations suggests there may be important precursors of plasma protein CML and CEL residues other than glyoxal and methylglyoxal. These are probably lipid-derived aldehydes.

Effects of Tribuli saponins on left ventricular remodeling after acute myocardial infarction in rats with hyperlipidemia

OBJECTIVE

To observe the effect of Tribuli saponins (TS) on left ventricular remodeling after acute myocardial infarction (AMI) in rats with hyperlipemia.

METHODS

A composite model of myocardial infarction and hyperlipemia was established and treated with TS to observe its effect on cardiac structure and function by echocardiography.

RESULTS

(1) Cardiac function: As compared with the model group, the fractional shortening (FS) and ejection fraction (EF) got increased, and the left ventricular end diastolic volume (LVEDV) and systolic volume (LVESV) got lower in the groups treated with high dose TS and simvastatin (P < 0.05 or P < 0.01), but difference between the two treated groups was insignificant. (2) Cardiac structure: As compared with the model group, the left ventricular dimension end diastole (LVDd) and systole (LVDs) in the groups treated with high dose TS and simvastatin got lower (P < 0.05 or P < 0.01). No treatment showed any effect on the thickness of ventricular wall. (3)Ventricular weight index: Both high dose TS and simvastatin could decrease the left ventricular weight index (LVWI) (P < 0.05).

CONCLUSION

TS could attenuate the left ventricular remodeling after acute myocardial infarction to certain extent, and improve cardiac function in the early phase after AMI, thus playing an important role in controlling morbidity and mortality of cardiac events and long-term prognosis.

Combined effect of probucol and insulin on cataracts of diabetic rats fed a high cholesterol diet

We investigated the effects of long-term treatment with probucol, a hypolipidemic agent with antioxidative action, insulin, or their combination on cataracts of streptozotocin-induced diabetic rats fed a high cholesterol diet. Each rat was checked for cataracts at 0, 1, 2, 4, 8, 12 and 15 weeks after streptozotocin injection. Cataracts were observed from 8 weeks in untreated hypercholesterolemic and diabetic rats and the incidence of catarats increased to 100% by 15 weeks. The incidence of cataracts in rats treated with probucol, insulin and their combination was first seen at 12, 12 and 15 weeks, respectively, and was 86%, 63% and 33%, respectively, at 15 weeks. The preventive effects of both agents alone and their combination on the cataracts were confirmed by histopathological evaluation of eyeballs. The combined treatment with both agents markedly improved hyperglycemia, hyperlipidemia and increased serum lipid peroxide levels. These results indicate that the combined treatment with probucol and insulin is useful in preventing the development and progression of diabetic cataracts.

Combined effect of vitamin E and insulin on cataracts of diabetic rats fed a high cholesterol diet

In the present study we investigated the effects of a long-term treatment with vitamin E, an antioxidant vitamin, insulin or their combination on cataracts of streptozotocin (STZ)-induced diabetic rats fed a high cholesterol diet. Each rat was checked for cataracts at 0, 1, 2, 4, 8, 12 and 15 weeks after STZ injection. Cataracts were observed from 8 weeks in the control diabetic rats and their incidence of catarats increased to 100% by 12 weeks. The incidence of cataracts in rats treated with vitamin E, insulin and their combination was first seen at 12 weeks and 56%, 20% and 10%, respectively, at 12 weeks and 78%, 50% and 20%, respectively, at 15 weeks. The preventive effects of either agent alone and their combination on the cataracts were in agreement with those obtained by histopathological evaluation of eyeballs. The combined treatment with both agents markedly improved hyperglycemia, hyperlipidemia and increased serum lipid peroxide levels. These results indicate that the combined treatment with vitamin E and insulin is useful in preventing the development and progression of diabetic cataracts.

High-dose thiamine therapy counters dyslipidaemia in streptozotocin-induced diabetic rats

AIMS/HYPOTHESIS

Cardiovascular disease in diabetes is linked to increased risk of atherosclerosis, increased levels of triglyceride-rich lipoproteins and enhanced hepatic lipogenesis. The hepatic hexosamine pathway has been implicated in signalling for de novo lipogenesis by the liver. In this study, we assessed if decrease of flux through the hexosamine pathway induced by high-dose thiamine therapy counters diabetic dyslipidaemia.

METHODS

The model of diabetes used was the streptozotocin-induced diabetic rat with maintenance insulin therapy. Normal control and diabetic rats were studied for 24 weeks with and without oral high-dose therapy (7 and 70 mg/kg) with thiamine and benfotiamine. Plasma total cholesterol, HDL cholesterol and triglycerides were determined at 6-week intervals and hepatic metabolites and transketolase activity after death of the rats at 24 weeks.

RESULTS

We found that thiamine therapy (70 mg/kg) prevented diabetes-induced increases in plasma cholesterol and triglycerides in diabetic rats but did not reverse the diabetes-induced decrease of HDL. This was achieved by prevention of thiamine depletion and decreased transketolase activity in the liver of diabetic rats. There was a concomitant decrease in hepatic UDP-N-acetylglucosamine and fatty acid synthase activity. Thiamine also normalised food intake of diabetic rats. A lower dose of thiamine (7 mg/kg) and the thiamine monophosphate prodrug benfotiamine (7 and 70 mg/kg) were ineffective.

CONCLUSIONS/INTERPRETATION

High-dose thiamine therapy prevented diabetic dyslipidaemia in experimental diabetes probably by suppression of food intake and hexosamine pathway signalling but other factors may also be involved. Benfotiamine was ineffective.

Repeated Streptozotocin Injections Cause Early Onset of Glomerulosclerosis in Mice

Diabetic nephropathy (DN), a major cause of end-stage chronic renal failure, is histologically characterized by glomerulosclerosis. To investigate the molecular mechanisms of DN, it is important to establish a stable model of glomerulosclerosis in mice, because genomic manipulation techniques (such as gene destruction or transgene insertion) are well established in rodent species. In this study, we found that repeated administrations of streptozotocin led to early onset of glomerular sclerotic lesions in C57BL/6 mice, accompanied with renal dysfunction. During the natural course of DN, glomerular endothelial cells decreased at 10 weeks after the start of streptozotocin-injections, whereas myofibroblastic mesangial cells became evident. Our results provide an animal tool to elucidate the molecular mechanisms of DN, for example to investigate vascular pathology in diabetic glomerular diseases.

Antidiabetic effects of chitosan oligosaccharides in neonatal streptozotocin-induced noninsulin-dependent diabetes mellitus in rats

The antidiabetic effect of chitosan oligosaccharide (COS) was investigated in neonatal streptozotocin (STZ)-induced noninsulin-dependent diabetes mellitus rats. The fasting glucose level was reduced by about 19% in diabetic rats after treatment with 0.3% COS. Glucose tolerance was lower in the diabetic group compared with the normal group. After diabetic rats had been treated with 0.3% COS for 4 weeks, glucose tolerance increased significantly versus the diabetic control group, and glucose-inducible insulin expression increased significantly. In addition, fed-triglyceride (TG) levels in diabetic rats drinking 0.3% COS were reduced by 49% compared with those in diabetic control rats. The cholesterol levels of animals treated with COS were reduced by about 10% in fed or fasting conditions versus the corresponding controls, although the difference was not statistically significant. It was found that COS has a TG-lowering effect in diabetic rats, and that COS reduces signs of diabetic cardiomyopathy such as vacuolation of mitochondria and the separation and degeneration of myofibrils. In conclusion, these results indicate that COS can be used as an antidiabetic agent because it increases glucose tolerance and insulin secretion and decreases TG.

Experimental model of postprandial hypertriglyceridemia in sucrose-fed rats and the effectiveness of atorvastatin in the model

Although postprandial hypertriglyceridemia has drawn attention as an independent risk factor of cardiovascular disease, there is no established animal model that shows a physiological transitory change in lipoprotein metabolism after ingestion of a fatty meal. We developed an animal model of postprandial hypertriglyceridemia using sucrose-fed rats, and used this model to evaluate the effect of atorvastatin on this condition. Compared with normal rats, sucrose-fed rats orally loaded with olive oil showed a high and prolonged increase in plasma triglyceride (TG) concentration accompanied by both an increase in TG secretion and decrease in TG clearance. Atorvastatin (30 mg/kg orally) for 2 weeks reduced not only fasting plasma TG concentration, but also the postprandial TG concentration. Atorvastatin also suppressed rates of TG secretion in both chylomicron (CM)-rich (d < 0.96 g/mL) and very-low-density lipoprotein (VLDL) (d = 0.96 to 1.006 g/mL) fractions after oral fat loading. Further, atorvastatin improved the elimination time of exogenous TG emulsion only in the nonfasted, namely, high plasma TG condition. These results indicate that this animal model satisfactorily replicates the postprandial hypertriglyceridemia observed in humans and may therefore be useful in evaluation of lipid-lowering agents. Furthermore, atorvastatin not only improves fasting but also postprandial lipoprotein metabolism, presumably by reducing TG secretion from the liver or intestine or both, and by secondarily increasing TG-rich lipoprotein clearance by eliminating saturation.

Effects of a new single-nucleotide polymorphism in the Acyl-CoA:cholesterol acyltransferase-2 gene on plasma lipids and apolipoproteins in patients with hyperlipidemia

Acyl-CoA:cholesterol acyltransferase (ACAT) catalyzes cholesterol esterification in mammalian cells. Two isoforms of ACAT have been reported to date (ACAT-1 and ACAT-2). ACAT-1 protein is ubiquitously expressed in tissues, including macrophages, hepatocytes, adrenal glands, and intestines. In contrast, ACAT-2 is expressed mainly in the intestine in humans. However, the roles of ACAT-1 and ACAT-2 in lipoprotein metabolism in humans have not yet been reported. This study was carried out to clarify the relationship between ACAT-2 gene mutations and hyperlipidemia in humans. To identify gene mutations, we screened 30 subjects with hyperlipidemia (TC > 220 mg/dl or TG >150 mg/dl) by direct sequencing. As a result, we found a new single-nucleotide polymorphism (SNP; a point mutation in intron 1, IVS1 -8 G-->C) in the ACAT-2 gene. To investigate the relationship between this SNP and both plasma lipids and apolipoproteins, 91 unrelated hyperlipidemic subjects (40 males and 51 females), and 92 unrelated normolipidemic subjects (46 males and 46 females) were screened by direct sequencing. The frequencies of the IVS1 - 8G-->C allele in normolipidemic and hyperlipidemic subjects were 0.131 and 0.125, respectively. IVS1 -8 G-->C did not affect plasma concentrations of lipids or apolipoproteins in either normolipidemic or hyperlipidemic subjects. Although further studies are needed, our data suggest that the ACAT-2 gene may not affect lipid levels in humans.

Effect of SMP-500, a novel ACAT inhibitor, on hepatic cholesterol disposition in rats

The effects of SMP-500, a novel ACAT inhibitor, on serum lipid levels, hepatic lipid secretion rate, and hepatic lipid disposition in rats were studied to clarify its lipid-lowering action. SMP-500 reduced the serum cholesterol level in a dose-dependent manner in rats fed a hypercholesterolemic diet. SMP-500 also reduced hepatic free cholesterol content in addition to hepatic total and esterified cholesterol contents. Biliary concentrations of cholesterol and bile acid were increased by SMP-500; however, the bile flow and lithogenic index were not affected. SMP-500 increased cholesterol 7a-hydroxylase mRNA level. Therefore, it is suggested that the increase in concentrations of cholesterol and bile acid in bile is due to both the increase of bile acid production through the increase of cholesterol 7alpha-hydroxylase and the decrease of hepatic free cholesterol content. An inhibitory effect of SMP-500 both on the cholesterol secretion and on the TG secretion from liver was observed. SMP-500 reduced the serum TG level in sucrose-fed rats. From these results, one may hypothesize that the suppression of hepatic VLDL secretion probably plays an important role on both cholesterol- and TG-lowering effects of SMP-500.

[Lipid-lowering drugs]

Accumulating evidences in recent major clinical studies have shown the importance of anti-hyperlipidemic treatment in preventing atherosclerotic cardiovascular diseases. Lipid-lowering drugs can be divided into HMG-CoA reductase inhibitors (statins), bile-acid sequestrants (resins), nicotinic acid, fibrates and probucol. Among them, statins had revolutionary impact on the treatment of hyperlipidemia since pravastatin, which was developed in Japan, was launched in 1989. Several lipid-lowering drugs are now under development in Japan, including pitavastatin, rosuvastatin, F-1394 (ACAT inhibitor), CS-505 (ACAT inhibitor) and NO-1886 (LPL activator). In this review, characteristics of these new lipid-lowering drugs will be discussed.

Effect of F-1394, an acyl-CoA:cholesterol acyltransferase inhibitor, on atherosclerosis induced by high cholesterol diet in rabbits

Cholesterol-fed rabbits were used to study the anti-atherosclerotic effect of (1S,2S)-2-[3-(2,2-dimethylpropyl)-3-nonylureido]cyclohexane-1-yl 3-[(4R)-N-(2,2,5,5-tetramethyl-1,3-dioxane-4-carbonyl)amino]propionate (F-1394), an acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor. To test its effect on the development of atherosclerosis, rabbits were fed a high-cholesterol diet (HCD) for 6 weeks, followed by regular chow (RC) for 12 weeks plus 0 or 100 mg/kg per day F-1394. Serum total cholesterol (TC) rose to approximately 2000 mg/dl on HCD and then declined gradually after the change in diet in both groups. F-1394 significantly reduced the extent of the atherosclerotic lesions and the total and esterified cholesterol contents of the aorta (by 57,38, and 59%, respectively), without affecting the serum TC level. To clarify whether F-1394 accelerates the regression of preexisting atherosclerosis, rabbits were fed HCD for the first 6 weeks and then RC for the next 6 weeks. Then, the rabbits were given 0 or 100 x 2 mg/kg per day F-1394 for another 12 weeks while on RC. F-1394 significantly reduced the extent of the atherosclerotic lesions and the total and esterified cholesterol content in the aorta (by 31, 31, and 43%, respectively), without affecting the serum TC level. These results demonstrate that F-1394 both prevents the formation of atherosclerosis and accelerates its regression without affecting the serum TC level, indicating that F-1394 acts directly on the arterial wall.

In vitro toxicities of experimental jet fuel system ice-inhibiting agents

One research emphasis within the Department of Defense has been to seek the replacement of operational compounds with alternatives that pose less potential risk to human and ecological systems. Alternatives to glycol ethers, such as diethylene glycol monomethyl ether (M-DE), were investigated for use as jet fuel system ice-inhibiting agents (FSIIs). This group of chemicals includes three derivatives of 1,3-dioxolane-4-methanol (M-1, M-2, and M-3) and a 1,3-dioxane (M-27). In addition, M-DE was evaluated as a reference compound. Our approach was to implement an in vitro test battery based on primary rat hepatocyte cultures to perform initial toxicity evaluations. Hepatocytes were exposed to experimental chemicals (0, 0.001, 0.01, 0.1, 1, 10 mM dosages) for periods up to 24 h. Samples were assayed for lactate dehydrogenase (LDH) release, MTT dye reduction activity, glutathione level, and rate of protein synthesis as indicators of toxicity. Of the compounds tested, M-1, especially at the 10-mM dose, appeared to be more potent than the other chemicals, as measured by these toxicity assays. M-DE, the current FSII, elicited little response in the toxicity assays. Although some variations in toxicity were observed at the 10-mM dose, the in vitro toxicities of the chemicals tested (except for M-1) were not considerably greater than that of M-DE.

Postprandial hyperlipidemia in Zucker diabetic fatty fa/fa rats, an animal model of type II diabetes, and its amelioration by acyl-CoA:cholesterol acyltransferase inhibition

Postprandial hyperlipidemia (PH) is frequently observed in diabetic patients. We performed an oral fat-loading test in Zucker diabetic fatty (ZDF) fa/fa rats, a model for type II diabetes, to determine whether PH was induced in the rats. Post fat-loading changes in serum cholesterol and triglyceride levels were significantly greater in the fa/fa rats than those seen in their lean littermates and an acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor significantly reduced these levels by 24% and 31%, respectively. Therefore, we confirmed that PH appeared in ZDF fa/fa rats by fat loading and ACAT inhibition may be a potential treatment for PH.

Structure of the human acyl-CoA:cholesterol acyltransferase-2 (ACAT-2) gene and its relation to dyslipidemia

Acyl-CoA:cholesterol acyltransferase (ACAT) catalyzes cholesterol esterification in mammalian cells. Two isoforms of ACAT have been reported to date (ACAT-1 and ACAT-2). ACAT-1 is ubiquitously expressed in tissues except the intestine. In contrast, ACAT-2 is expressed mainly in the intestine in humans. To investigate the relationship between ACAT-2 and dyslipidemia, we determined the structure of the human ACAT-2 gene and then studied the relationship between mutations of the ACAT-2 gene and dyslipidemia. To isolate human ACAT-2 genomic DNA, we designed primers based on the human ACAT-2 cDNA sequence: forward primer 5'-ACACCTCGATCTTGGTCCTGCCATA-3' and reverse primer 5'-GGAATGCAGACAGGGAGTCCT-3'. Using these primers, a human P1-derived artificial chromosome (PAC) library was screened by PCR-based procedures. Isolated PAC clones were completely digested with BamHI and subcloned into plasmid vector. Subclones that contained exons were screened by dot-blot hybridization using partial ACAT-2 cDNA fragments. The coding region of the ACAT-2 gene was encoded in 15 exons from 51 to 265 base pairs on a 21 kilobase span of genomic DNA. The exonic sequences coincided completely with that of ACAT-2 cDNA, and each exon-intron junction conserved splicing consensus sequences. Next, 187 (91 dyslipidemic and 96 normolipidemic) subjects were screened by PCR single-strand conformational polymorphism analysis of the ACAT-2 gene. Three mutations were identified by DNA sequencing: two missense mutations (E14G in exon 1 and T254I in exon 7) and a point mutation in intron 7 (-35G-->A). Mutations in exon 1 and intron 7 were not associated with plasma concentrations of lipids and apolipoproteins (apo). However, plasma apoC-III levels in T254I heterozygotes were significantly higher than those in subjects without mutation. Plasma triglyceride (TG) levels in T254I heterozygotes were similar to those in subjects without mutation. Although further studies are needed, our data suggest that ACAT-2 may contribute to apoC-III gene expression and the assembly of apoC-III and TG, possibly in the intestine.

Abnormalities in apo B-containing lipoproteins in diabetes and atherosclerosis

Atherosclerosis is the major cause of death in patients with diabetes. Low-density lipoprotein (LDL) being the most important cholesterol-carrying lipoprotein has been studied extensively in both diabetes and non-diabetes. This paper reviews the literature but also focuses on the precursors of LDL and in particular the postprandial apo B-containing lipoproteins. Abnormalities in the postprandial lipoproteins and alteration in chylomicron assembly and clearance are discussed and the evidence presented suggesting the importance of dysregulation of these lipoproteins in atherosclerotic progression. The relationship between chylomicron production in the intestine and hepatic release of very low-density lipoproteins (VLDL) is explored, as is the interrelationship between clearance rates of these lipoproteins. The size of LDL influences its atherogenicity. VLDL composition and size in relation to its influence on LDL is discussed. The effect of diet on the composition of lipoproteins and the relationship between fatty acid composition and clearance is reviewed. Evidence that diabetic control beneficially alters lipoprotein composition is presented suggesting how improved diabetic control may reduce atherosclerosis. The review concludes with a discussion on the effect of the apo B-containing lipoproteins and their modification through glycation and oxidation on macrophage and endothelial function.