雷公藤甲素治疗db／db糖尿病小鼠的疗效观察

目的:利用db/db小鼠验证雷公藤甲素对糖尿病肾脏损伤的治疗作用,探讨雷公藤甲素防治糖尿病肾病的机制. 方法:9周龄的db/db和db/m小鼠分为五组:(1)db/m正常对照组;(2)dh/dh糖尿病对照组;(3)缬沙坦治疗纽;(4)雷公藤甲素低剂最治疗组;(5)雷公藤甲素高剂繁治疗组.于4周、8周及12周测定各组24h尿白蛋白、血生化和体重.光镜观察肾小球病变,电镜观察足突改变,并作定量分析.免疫病理观察足细胞裂孔膜蛋白nephrin,足细胞损伤标志物desmin,炎症反应标志物单核细胞趋化蛋白1(MCP-1),氧化应激标志物4羟壬烯醛(4-HNE)的表达. 结果:db/db小鼠经雷公藤甲素治疗后蛋白尿下降,肾小球肥大和足细胞损伤减轻,肾组织炎症和氧化应激状态改善,同时高血脂和肥胖减轻.该作用随治疗时间延长,效果更加明显,且高剂量疗效优于低剂量.雷公藤甲素降低蛋白尿、改善肾小球肥大的作用与缬沙坦相似,但降低肾组织炎症和氧化应激的作用雷公藤甲素比缬沙坦更强. 结论:雷公藤甲索能明显降低dh/db小鼠尿蛋白的排泄,减轻肾组织炎症反应,改善肾脏组织病变,对糖尿病肾脏损伤具有显著且更全面的治疗作用.     

Effect of cogent db,a herbal drug,on plasma insulin and hepatic enzymes of glucose metabolism in experimental diabetes

Aims: The present study was designed to investigate the effect of cogent db, a polyherbal drug on blood glucose, plasma insulin and the activities of hepatic glucose metabolic enzymes in alloxan-induced diabetic rats.
Methods: Male Wistar rats body weight of 180–200 g (six normal and 18 diabetic rats) were used in this study. The rats were divided into four groups after the induction of alloxan diabetes. In the experiment, six rats were used in each group: Group 1, normal rats given 2 ml of saline; Group 2, diabetic control rats given 2 ml of saline; Group 3, diabetic rats given aqueous solution of cogent db (0.45 g/body kg weight); and Group 4, diabetic rats given aqueous solution of glibenclamide (600 µg/kg body weight). The treatment was given for 40 days. After the treatment, fasting blood glucose, plasma insulin, urine sugar and the activities of hepatic glucose metabolic enzymes were determined in normal and experimental animals.
Results: Treatment with cogent db resulted in a significant reduction in blood glucose and the activities of glucose-6-phosphatase and fructose-1,6-bisphosphatase in the liver, whereas the level of plasma insulin and hepatic hexokinase activity were significantly increased in alloxan-diabetic rats.
Conclusions: The present investigation suggests that cogent db controls the blood glucose level by increasing glycolysis and decreasing gluconeogenesis with a lower demand of pancreatic insulin than in untreated rats. This is possible because it regulates the activities of hepatic glucose metabolic enzymes.     

胰激肽原酶对2型糖尿病小鼠肾小管病变的保护作用及机制

目的 探讨胰激肽原酶（PKK）对2型糖尿病（DM）肾病的作用及分子机制. 方法 将20只4周龄体重22～28 g的健康雄性db/db小鼠随机分为2组,PKK干预组（n=10,PKK腹腔注射60U·kg^-1·d^-1）和DM组（n=10,腹腔注射生理盐水1 ml/g）.以同窝出生的db/m小鼠为正常对照组（n=8,腹腔注射生理盐水1 ml/g）.每周检测小鼠的血糖和体重,每月监测小鼠收缩压与舒张压.干预16周后处死小鼠,留取肾脏组织标本.光镜观察各组小鼠肾小管病理学变化,电镜观察肾小管超微结构的改变.应用免疫组化方法检测肾脏组织中上皮型-钙黏附蛋白的表达水平,实时PCR方法检测小鼠肾脏组织白细胞介素1β（IL-1β）、纤维连接蛋白的mRNA表达水平.采用SPSS16.0软件进行统计学分析,多组资料用单因素方差分析. 结果 （1）干预16周后,DM组和PKK干预组小鼠血糖、体重均高于正常对照组小鼠,肾重/体重指数明显低于正常对照组,其差异有统计学意义[对照、DM、PKK组血糖分别为（5.4±0.6）、（27.4±4.6）、（26.9±3.0） mmol/L,F=86.35,P＜0.01;体重分别为（24.3±3.1）、（42.6±4.8）、（41.5±2.6）g,F=38.82,P＜0.01;肾重/体重指数分别为12.52±2.53、9.01±1.25、9.83±1.18,F=7.27,P＜0.01].DM与PKK组之间差异无统计学意义.3组之间的收缩压与舒张压差异均无统计学意义.（2）电镜提示PKK组DM小鼠肾脏近端与远端小管上皮细胞线粒体肿胀的情况、线粒体数目、近端小管上皮细胞的脂代谢障碍均较DM组改善.（3）免疫组化分析提示,与正常对照组相比,DM组E钙黏附蛋白表达明显减少,PKK干预组显著升高,分别为18.8±1.8、15.8±1.9、19.7±2.9 （F=9.70,P＜0.01）.3组IL-1β的表达分别为2.30±1.22、4.14±3.40、0.92±0.59（F=11.86,P＜0.01）;纤维连接蛋白的表达分别为1.67±0.53、8.45±2.02、2.04±0.79 （F=52.66,P＜0.01）. 结论 胰激肽原酶对2型糖尿病小鼠的肾小管具有保护作用,且机     

Comparison of the antidiabetic effects of brain-derived neurotrophic factor and thiazolidinediones in obese diabetic mice

AIMS: Brain-derived neurotrophic factor (BDNF) ameliorates glucose metabolism in obese diabetic db/db mice. The antidiabetic effect of BDNF is dependent on plasma insulin levels, and BDNF enhances insulin action by modulating insulin signalling in peripheral tissues. The aim of the study was to compare the antidiabetic effects of BDNF with those of thiazolidinediones (TZDs), which are insulin-sensitizing agents, through evaluation of the effects of BDNF and TZDs on glucose metabolism, energy expenditure, pancreatic function and hepatic steatosis in db/db mice. METHODS: The effects of BDNF, pioglitazone and rosiglitazone on blood glucose concentration, body weight and pancreatic insulin and glucagon contents and the effects of BDNF and troglitazone treatment for 3 weeks on blood glucose concentration, body and liver weights and histological liver images were examined in db/db mice. Furthermore, since BDNF reduces food intake in obese hyperphagic diabetic mice, the effects of BDNF treatment for 3 weeks on blood glucose concentration, body weight, fat pad and liver weights and rectal temparature in db/db mice were compared with those of troglitazone under pair-fed conditions. RESULTS: BDNF, pioglitazone and rosiglitazone all ameliorated hyperglycaemia in db/db mice, but BDNF increased the pancreatic insulin content more effectively than pioglitazone and rosiglitazone. The pancreatic glucagon content decreased with BDNF, but increased with pioglitazone and rosiglitazone compared with vehicle, and body weight and liver weight increased with troglitazone, but decreased with BDNF compared with vehicle. Histological analysis of the liver showed that BDNF treatment reduced the massive vacuolization observed with vehicle, whereas troglitazone worsened the vacuolization. Body weight, fat pad and liver weights in BDNF-treated mice were significantly lower than those in pair-fed troglitazone-treated db/db mice, and rectal temperature in BDNF-treated mice was significantly higher than that in pair-fed troglitazone-treated mice, suggesting that BDNF enhances energy expenditure. CONCLUSIONS: These data suggest that compared with TZDs, BDNF potently ameliorates pancreatic dysfunction, fatty liver and energy expenditure, thereby exerting favourable antidiabetic effects in type 2 diabetic mice.     

2型糖尿病模型db/db小鼠海马超微结构观察

目的：观察2型糖尿病动物模型－C57BL／KsJ(db/db)小鼠海马超微结构变化,方法：糖尿病组：6周龄C57BL／KsJ(db/db)小鼠5只,尾静脉空腹血糖高于11．1mmol/L且肥胖,对照组;非糖尿病小鼠C57BL／KsJ5只,尾静脉空腹血糖低于6．0mmol/L,体重正常,于30周龄（成模第6个月要）时,灌注固定取脑,透射电镜下观察海马CAI区,结果：糖尿病小鼠海马超微结构发生显著改变包括锥体细胞退变,髓鞘崩解,突触变性等。结论：糖尿病所致海马超微结构改变可能与糖尿病学习记忆功能减退有关。     

Effect of Cogent db,a herbal drug,on serum and tissue lipid metabolism in experimental hyperglycaemic rats

Aims:   We have previously reported the antidiabetic effect of Cogent db. The present study with alloxan-induced hyperglycaemic rats is focused on the mechanism of action, specifically on the activity of hepatic lipogenic enzymes, serum and tissue lipids.
Methods:   Male Wistar rats body weight of 180–200 g (six normal and 18 diabetic rats) were used in this study. The rats were divided into four groups after the induction of alloxan diabetes: normal rats; diabetic control; diabetic rats given Cogent db (0.45 g/kg body weight); diabetic rats given glibenclamide (600 µg/kg body weight). After 40 days treatment, fasting blood glucose, plasma insulin, activities of hepatic lipogenic enzymes, serum and tissue lipids were determined in normal and experimental animals.
Results:   Oral administration of Cogent db for 40 days resulted in significant reduction in blood glucose, serum and tissue (liver and kidney) lipids, whereas the level of plasma insulin and the activity of hepatic lipogenic enzymes were significantly increased in alloxan diabetic rats. Similar studies using glibenclamide have been conducted to compare the mode of action of these two drugs.
Conclusions:   Thus our study shows that Cogent db exhibits a strong antihyperlipidaemic effect, which could exert a beneficial action against macrovascular complications (cardiovascular disease) associated with diabetes mellitus.     

Phospholipid transfer activity of microsomal triglyceride transfer protein produces apolipoprotein B and reduces hepatosteatosis while maintaining low plasma lipids in mice

Microsomal triglyceride transfer protein (MTP), essential for apolipoprotein B (apoB) biosynthesis, evolved as a phospholipid transfer protein and acquired triglyceride transfer activity during a transition from invertebrates to vertebrates. But it is unknown whether MTP directly transfers lipids onto apoB in vivo and, if it does, whether both neutral and polar lipid transfer activities of MTP are critical for lipoprotein assembly. The molecular bases for differences in lipid transfer activities with respect to distinct domains in Drosophila MTP (dMTP) and human MTP (hMTP) are not obvious because both proteins have very similar primary, secondary, and tertiary structures. We used an in vivo approach to delineate physiological significance of these distinct lipid transfer activities by expressing dMTP (transfers phospholipids) and hMTP (transfers phospholipids and triglycerides) orthologs using adenoviruses in liver-specific MTP-deficient (L-MTP(-/-)) mice that have low plasma and high hepatic lipids. Both orthologs improved plasma lipids but plasma triglycerides were lower in dMTP mice due to lower hepatic triglyceride and apoB production. Hepatosteatosis in L-MTP(-/-) mice was ameliorated to similar levels by both. Attenuation of hepatosteatosis upon dMTP expression pertained to enhanced β-oxidation with no changes in lipogenesis. Phospholipid transfer activity of MTP promoted biogenesis of both apoB48 and apoB100-containing very low density lipoprotein in addition to a phospholipid-rich apoB48-containing high-density lipoprotein particle. Triglyceride transfer activity augmented the biosynthesis of triglyceride-rich lipoproteins by increasing the formation of these particles in the lumen of the endoplasmic reticulum. CONCLUSION: Based on these findings, we posit that the selective inhibition of MTP triglyceride transfer activity might reduce hyperlipidemia while protecting liver from excess lipid accumulation.     

Topiramate ameliorates hyperglycaemia and improves glucose-stimulated insulin release in ZDF rats and db/db mice

Topiramate (TPM) is a novel neurotherapeutic agent. Clinical studies reported that TPM treatment reduced body weight and decreased fasting blood glucose levels in obese patients with or without type 2 diabetes. It is unclear whether the blood glucose-normalizing phenomenon observed during TPM treatment is a primary effect or the consequence of reduced food intake and weight loss. In the present studies, we chronically treated female Zucker diabetic fatty (ZDF) rats (fed with a diabetogenic diet) and db/db mice with TPM (30-300 mg/kg/day) to examine the effect of TPM on hyperglycaemia and its relationship with food intake and body weight gain. Our data showed that TPM treatment markedly reduced blood glucose levels in both ZDF rats and db/db mice without a significant reduction in body weight gain. Pair-fed db/db mice treated with the vehicle alone did not exhibit a significant decrease in blood glucose levels compared with mice fed ad libitum. TPM treatment increased glucose-stimulated insulin release by 2-3-fold during an oral glucose tolerance test in both ZDF rats and db/db mice. We also observed a 1.4-fold increase of pancreatic insulin content and heightened insulin immunostaining in pancreatic beta cells in db/db mice treated with TPM. Our data suggest that the antidiabetic effect of TPM is independent of the changes in body weight gain and food intake. Improved glucose-induced insulin release may, in part, underlie the mechanisms by which TPM ameliorates the hyperglycaemia.     

Oxidative damage in cerebral vessels of diabetic db/db mice

BACKGROUND: Oxidative stress in diabetes mellitus has recently received increasing attention as it has been proven to be associated with the development of diabetic vascular complications. Our aim was to examine whether microvascular changes, including oxidative damage, were induced in the brains of diabetic animals. METHODS: The expression of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, the binding of cationized ferritin, a marker for evaluating endothelial glycocalyx, to the endothelial cells of capillaries and vascular permeability of intravenously injected horseradish peroxidase were examined in the cortices of 12- and 20-week-old db/db and db/+m mice. RESULTS: Immunostaining for 8-OHdG was clearly seen in the vessels of the cortex of 20-week-old db/db mice, but was hardly seen in those of mice in the other groups. The immunopositive area of 8-OHdG was significantly increased in the cortex of 20-week-old db/db mice compared with that of 20-week-old db/+m mice. No extravasated leakage of horseradish peroxidase was seen in any groups of mice, while the numbers of cationized ferritin particles binding to the endothelial cells was significantly decreased in 12- and 20-week-old db/db mice compared with that of db/+m mice at the same age, respectively. CONCLUSION: These findings suggest that changes in endothelial glycocalyx are induced in db/db mice and, in addition, the long-term diabetic condition of these mice induces oxidative DNA damage to the cerebral vessels.     

Genetic susceptibility to diabetes in inbred strains of mice: measurements of proinsulin mRNA and response to dexamethasone

Summary The insulin resistance produced by the recessive db mutation has led to more severe diabetes in C57BL/KsJ mice relative to that in C57BL/6J mice, suggesting genetic differences between the two strains affecting insulin production or insulin action. To assess these parameters blood glucose, serum insulin, pancreatic insulin, and proinsulin mRNA were measured in both normal and diabetic (db/db) KsJ and 6J strains. The mice were compared at 5 weeks of age, prior to the development of insulin lack known to occur with age in KsJ db/db mice. As a further provocation to insulin production, another group of the normal and db/db mice were given dexamethasone for 4 days. In normal mice there were no strain differences in blood glucose, serum insulin, pancreatic insulin, or proinsulin mRNA. Dexamethasone, presumably by augmenting insulin resistance, induced increases in serum insulin and proinsulin mRNA to the same extent in KsJ and 6J mice. In db/db mice, while blood glucose, serum insulin, and proinsulin mRNA were considerably higher than in normal mice, there were no strain differences observed. After dexamethasone the db/db mice exhibited strain differences which included higher blood glucose and higher serum insulin levels in KsJ mice. These findings were compatible with greater insulin resistance in KsJ than in 6J db/db mice. While dexamethasone treatment increased serum insulin in KsJ db/db mice, there was no augmentation of proinsulin mRNA in either strain, suggesting a limit to the insulin synthesis. Analysis of serum insulin/glucose and proinsulin mRNA/glucose ratios demonstrated a dexamethasone-induced increase in serum insulin/glucose in normal and diabetic mice of both strains. An increase in dexamethasone induced proinsulin mRNA/glucose ratio was observed in all but the KsJ db/db mice. This analysis suggested that although insulin secretion in KsJ db/db mice was augmented, the capacity for insulin synthesis had been exceeded. A limitation of insulin production at the level of insulin synthesis might explain the enhanced diabetes susceptibility of this strain.     

The effect of a high fibre diet on diabetic nephropathy in the db/db mouse

Summary Genetically diabetic mice (C57 BLKsJ db/ db) aged 5–6 weeks were given a diet containing 20% by weight of non-nutritive bulk and compared with age matched control diabetic mice on a normal diet (fibre content 4.5%) and non-diabetic mice. The duration of study was 12 weeks. No adverse effects were observed in animals given the high fibre diet. Total food consumption was greater in mice receiving the fibre enriched diet, but their absolute caloric intake was 6% less than control diabetic mice. Both groups exhibited similar rates of growth and development. Water intake in the experimental diabetic mice was reduced and similar to that of normal non-diabetic mice. Fasting blood glucose was significantly decreased in the experimental diabetic mice at 12 weeks. Renal pathological lesions in the control diabetic mice showed glomerular mesangial expansion and deposition of immunoglobulins within the mesangium. The experimental diabetic animals exhibited significantly less renal pathology, including light and immunofluorescent lesions. It is concluded that addition of non-absorbable fibre to the diet of genetically diabetic mice improves glycaemic control and retards the development of diabetic nephropathy.     

Combined therapy of rhein and benazepril on the treatment of diabetic nephropathy in db/db mice.

OBJECTIVE: Rhein and angiotensin-converting enzyme inhibitor (ACEI) have been reported to prevent the progression of diabetic nephropathy (DN). We further explore the unknown ability to induce renal-protection of rhein and ACEI combined therapy in DN compared with the therapeutic effects of single treatment of them by using db/db mouse of type 2 diabetes model. METHODS: db/db and db/m mice, 8 weeks of age, were divided into five groups according to the following treatments: (A) db/m, given saline treatment; (B) db/db, given saline treatment; (C) db/db, given rhein treatment (150 mg/kg/day); (D) db/db, given benazepril treatment (10 mg/kg/day); (E) db/db, given rhein (150 mg/kg/day) with benazepril (10 mg/kg/day). Body weight, plasma glucose, plasma lipid and 24 h urinary albumin excretion levels were measured every 4 weeks. Morphometry of renal tissue and immunohistology of transforming growth factor-beta1 (TGF-beta) and fibronectin were determined for all groups at the end of the treatment. RESULTS: It was found that after treatment urinary albumin excretion was reduced after 4 weeks treatment in group E and after 8 weeks treatment in groups C and D, when compared to group B (p<0.05). Plasma creatinine levels dropped significantly for group E, compared with the diabetic control group by the end of the treatment period. Furthermore, after the treatment body weight, plasma glucose, cholesterol, triglyceride and low density lipoprotein all decreased in groups C and E compared to group B (p<0.05). Histological morphometric analysis revealed that the whole glomerular area and extracellular matrix area was significantly reduced in groups C, D and E compared to group B, at 20 weeks of age, an effect most pronounced in group E. Using immunohistochemistry, the expression of fibronectin and TGF-beta1 in groups C, D and E was found to have decreased compared to group B, after 12 weeks treatment, again the effect being more pronounced in group E. CONCLUSIONS: There appeared to be a similar renal protective effect of rhein compared with benazepril in diabetic nephropathy. A combined therapy may offer a more beneficial complementary effect on kidney injury in db/db mice, as reflected by urinary albumin excretion, renal function and histological changes. Our findings suggest that a therapeutic approach that combines rhein with ACEI provides a more effective therapy for DN than does either agent alone.     

Exercise restores endothelial function independently of weight loss or hyperglycaemic status in <Emphasis Type="Italic">db/db</Emphasis> mice

AIMS/HYPOTHESIS: Exercise ameliorates oxidative stress-mediated diabetic vascular endothelial dysfunction through poorly defined mechanisms. We hypothesised that, in addition to improving metabolic parameters, upregulation of antioxidants such as superoxide dismutase (SOD) mediates exercise-induced reductions of oxidative stress and increased nitric oxide (NO) bioavailability, and also restores vasodilatation. METHODS: Type 2 diabetic db/db and normoglycaemic wild-type mice were exercised at moderate intensity for 1 h a day for 7 weeks, leading to a 10% body weight loss. Sedentary animals or those undergoing a low-intensity exercise regimen causing non-significant weight loss were also used. We examined aortic endothelial cell function, NO bioavailability and various biomarkers of oxidative stress. RESULTS: Moderate-intensity exercise lowered body weight, increased mitochondrial manganese SOD (MnSOD) and both total and phosphorylated (Ser1177) endothelial nitric oxide synthase (eNOS) protein production; it also reduced whole-body (plasma 8-isoprostane) and tissue oxidative stress (nitrotyrosine immunostaining or protein carbonyl levels in the aorta). Low-intensity exercise did not alter body weight; however, it upregulated cytosolic Cu/Zn-SOD instead of MnSOD, and still demonstrated all the above benefits in the db/db aorta. Importantly, both exercise protocols improved endothelial-dependent vasodilatation and NO bioavailability without altering hyperglycaemic status in db/db mice. CONCLUSIONS/INTERPRETATION: Exercise reverses diabetic vascular endothelial dysfunction independently of improvements in body weight or hyperglycaemia. Our data suggest that upregulation of eNOS and specific SOD isoforms could play important roles in improving NO bioavailability, as well as in reversing endothelial dysfunction in type 2 diabetes patients through lifestyle modifications in the management of diabetes.     

Long-term effects of vanadate treatment on glycogen metabolizing and lipogenic enzymes of liver in genetically diabetic (db/db) mice

The effect of long-term (12 weeks) oral treatment with sodium orthovanadate on hepatic glycogen metabolizing and lipogenic enzymes was studied in genetically diabetic db/db mice. These mice were characterized by significant (P less than .001) obesity, hyperglycemia, and hyperinsulinemia. Vanadate administration led to significant decreases in body weight (P less than .001) and plasma insulin levels (P less than .01) and the mice became normoglycemic. The total glycogen synthase (EC 2.4.1.11) activity in the livers of diabetic mice showed a 47% increase, which did not undergo any significant change after treatment with vanadate. Hepatic phosphorylase (EC 2.4.1.1) activities (a and total) showed twofold increases in db/db mice when compared with the nondiabetic ones. Vanadate caused significant decreases in phosphorylase a (P less than .02) and total phosphorylase (P less than .001) activities. Glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and malic enzyme (EC 1.1.1.40) in diabetic liver had differential alterations, as indicated by a 50% decrease in glucose-6-phosphate dehydrogenase and 160% increase in malic enzyme activities. Vanadate administration led to normalization of both enzyme activities. In nondiabetic mice, vanadate treatment did not cause changes in any parameter, except for a 46% decrease in plasma insulin levels. This investigation indicates that vanadate can normalize many of the metabolic abnormalities seen in the liver of genetically diabetic db/db mice, a model for non-insulin-dependent diabetes mellitus (NIDDM). Vanadate also causes a decrease in plasma insulin level, along with normalization of plasma glucose, which suggests a partial reversal of insulin resistance.     

Enteroinsular axis of db/db mice and efficacy of dipeptidyl peptidase IV inhibition

In type 2 diabetic patients, the administration of glucagon-like peptide-1 (GLP-1), known as an incretin, exerts antidiabetic effects. However, GLP-1 is rapidly degraded by dipeptidyl peptidase IV (DPPIV) after its release. DPPIV inhibition is thought to be a rational strategy to treat type 2 diabetes. In this study, using C57BLKS/J-db/db (db/db) mice as a model of type 2 diabetes, we examined the effect of acute DPPIV inhibition on glucose tolerance at the early and later stages of diabetes, determining plasma active GLP-1 and insulin levels. In addition, we investigated changes of plasma DPPIV activity. Compared with normal C57BL6/J (B6) and db/+ mice, significantly increased plasma DPPIV activities were observed in db/db mice. Expression of the proglucagon gene encoding GLP-1 was significantly upregulated in the colon of db/db mice. The administration of valine-pyrrolidide, a DPPIV inhibitor, resulted in potentiated insulin secretion mediated by increased endogenous GLP-1 action, leading to improved glucose tolerance in db/db mice at 6 weeks of age. However, although acute DPPIV inhibition with valine-pyrrolidide resulted in higher plasma active GLP-1 and insulin levels in db/db mice at 23 weeks of age, it did not improve glucose tolerance. The function of the enteroinsular axis is preserved in both stage of diabetes and the DPPIV inhibitor potentiated it, but the progression of insulin resistance appeared to block the improvement of glucose tolerance through DPPIV inhibition. Our results suggest that DPPIV inhibition is a suitable approach for treatment of impaired glucose tolerance (IGT), and type 2 diabetes in the early stage.     

Dehydroepiandrosterone suppresses elevated hepatic glucose-6-phosphatase mRNA level in C57BL/KsJ-db/db mice: comparison with troglitazone

Dehydroepiandrosterone (DHEA) is known to improve hyperglycemia of diabetic C57BL/KsJ-db/db mice that are obese and insulin resistant. In a previous study, we reported that DHEA as well as troglitazone suppresses the elevated hepatic gluconeogenic enzymes, glucose-6-phosphatase (G6Pase) and fructose-1,6-bisphosphatase (FBPase) activities in C57BL/KsJ-db/db mice. In the present study, we evaluated the changes in mRNA of G6Pase and FBPase in db/db mice. Despite hyperinsulinemia, the G6Pase mRNA level of db/db mice was elevated as compared to their heterozygote littermate db/+m mice. In contrast, the FBPase mRNA level was not elevated in db/db mice. Administration of DHEA for two weeks significantly decreased the blood glucose level and the elevated G6Pase mRNA level in db/db mice. No significant changes were seen in the FBPase mRNA level after the administration of DHEA. Administration of troglitazone also decreased the blood glucose and G6Pase mRNA level in db/db mice although no changes were seen in the FBPase mRNA level. These results suggest that the elevation of G6Pase mRNA is important in elucidating the cause of insulin resistance, and that the G6Pase gene is at least one target for the hypoglycemic effects of DHEA as an insulin sensitizing agent in db/db mice.     

Molecular mapping of the mouse db mutation.

Diabetes (db) is an autosomal recessive mutation located in the midportion of mouse chromosome 4 that results in profound obesity with hyperphagia, increased metabolic efficiency, and insulin resistance. To clone this gene and generate a molecular map of the region around this mutation, two genetic crosses were established: an intraspecific backcross between C57BL/6J db/db females and C57BL/6J db/db x DBA/2J +/+ F1 (B6D2 db/+ F1) male mice and an interspecific intercross between B6D2 db/+ F1 males and C57BL/6J db/db x Mus spretus F1 (B6spretus db/+ F1) females. The progeny of both crosses were characterized for genotype at the db locus to map a series of restriction fragment length polymorphisms relative to the db locus. Measurements of body weight, body length, and plasma concentrations of glucose and insulin in the animals allowed the assignment of genotype (db/db vs. db/+ or +/+). A total of 132 progeny of the intraspecific cross and 48 db/db progeny of the interspecific cross were typed for individual restriction fragment length polymorphisms to generate a gene order of: centromere-brown (Mt4)-P lambda Mm3(2)-Ifa (Inta)-Cjun-db-D4Rp1-Glut1-Mtv-13-Lck. Several of the genes that are linked to db [Cjun, glucose transporter (Glut1) and Lck] map to human chromosome 1p, suggesting that db may be part of a syntenic group between human 1p and the distal portion of mouse chromosome 4. In addition, phenotyping of the progeny of these crosses revealed a wide range in plasma concentrations of glucose and insulin among the obese progeny, with some animals developing overt diabetes and other remaining euglycemic. Distributions of age-controlled plasma [glucose] and [insulin] among the intraspecific-cross obese progeny were not bimodal, suggesting a role for polygenic differences between the progenitor strains (C57BL/6J and DBA/2J) in the development of overt diabetes.     

Phosphodiesterase 3B gene expression is enhanced in the liver but reduced in the adipose tissue of obese insulin resistant db/db mouse.

Phosphodiesterase (PDE) 3B, when activated by insulin, causes a decrease in intracellular cAMP concentration. The activation of this enzyme results in the reduced output of free fatty acids (FFA) from adipocytes, and an increased lipogenesis in liver. We have recently shown that PDE3B gene expression is reduced in adipose tissues of KKAy mice. We intend to further elucidate the regulation of PDE3B in liver as well as adipose tissues in relation to the insulin resistant state. We examined PDE3B gene expression in liver and adipose tissues of obese, insulin-resistant diabetic db/db mice and also checked the effect of an insulin-sensitizing drug, troglitazone, on this gene expression. In the liver of db/db mice, PDE3B mRNA, its corresponding protein, and the associated catalytic activity were all increased by 2.1, 1.9 and 1.6-fold, respectively, over those in db/+ control mice. Histological examination revealed substantial triglyceride storage in the liver of db/db mice. Conversely, in the adipose tissue of db/db mice, PDE3B mRNA, protein, and its associated activity were all decreased by 0.38, 0.33 and 0.36-fold, respectively. Troglitazone, which has no effect on PDE3B in liver, increased the expression of this gene in adipocytes. This increase is associated with a reduction in the elevated levels of serum insulin, glucose, FFA and triglycerides. The reduced PDE3B gene expression in adipose tissues, which results in the elevation of serum FFA, could be the primary event in the development of insulin resistance in db/db mice. The enhanced PDE3B gene expression may correlate with changes in triglyceride storage in the liver of these mice.