Effect of insulin on exocrine pancreatic secretion in healthy and diabetic anaesthetised rats

This investigation characterised the effects of exogenous insulin on exocrine pancreatic secretion in anaesthetised healthy and diabetic rats. Animals were rendered diabetic by a single injection of streptozotocin (STZ, 60 mg kg^–1 I.P.). Age-matched controls were injected citrate buffer. Rats were tested for hyperglycaemia 4 days after STZ injection and 7–8 weeks later when they were used for the experiments. Following anaesthesia (1 g kg^–1 urethane I.P.), laparotomy was performed and the pancreatic duct cannulated for collection of pure pancreatic juice. Basal pancreatic juice flow rate in diabetic rats was significantly (p < 0.001) increased whereas protein and amylase outputs were significantly (p < 0.001) decreased compared to control rats. Insulin (1 IU, I.P.) produced in healthy rats significant increases in pancreatic flow rate, amylase secretion and protein output compared to basal (p < 0.05). Insulin action also included a reduction in blood glucose (152.7 ± 16.9 mg dl^–1, n= 6, prior to insulin and 42.0 ± 8.4 mg dl^–1, n= 4, 100 min later). In fact, flow rate and glycaemia showed a strong negative correlation (p < 0.01, Pearson). Pretreatment with atropine (0.2 mg kg^–1, I.V.) abolished the effects of insulin on secretory parameters despite a similar reduction in glycaemia; in this series of experiments the correlation between flow rate and blood glucose was lost. In diabetic rats, insulin (4 IU, I.P.) did not modify exocrine pancreatic secretion. There was a fall in blood glucose (467.6 ± 14.0 mg dl^–1, n= 10, prior to insulin and 386.6 ± 43.6 mg dl^–1, n= 7, 120 min later). Rats, however, did not become hypoglycaemic. Similar results were observed in diabetic atropinized rats. The results of this study indicate that the effects of insulin on exocrine pancreatic secretion in anaesthetised healthy rats are mediated by hypoglycaemia-evoked vagal cholinergic activation. (Mol Cell Biochem 261: 105–110, 2004)     

Overexpression of protein-tyrosine phosphatase PTP sigma is linked to impaired glucose-induced insulin secretion in hereditary diabetic Goto-Kakizaki rats

The impaired glucose-induced insulin release in type 2 diabetes mellitus may be accounted for by reduced B-cell ATP/ADP ratio or decreased phosphorylation of proteins regulating exocytosis of insulin. This, in turn, could be due to enhanced phosphatase activity. Using in situ hybridization techniques to assess the expression of 11 different phosphotyrosine phosphatases (PTPases), known to be present in the B-cells, overexpression by approximately 60% of PTP sigma (also known as LAR-PTP2 or PTP NE-3) was demonstrated in pancreatic islets and liver of spontaneously type 2 diabetic Goto-Kakizaki (GK) rats. In agreement with these findings Western blot of islet lysates, using a polyclonal PTP sigma antiserum, showed increased amounts of the protein in GK relative to control rat islets. Exposure of isolated islets for 20 h to 5 muM antisense to PTP sigma, composed of an antisense PNA sequence of 15 bases linked to the cell penetrating peptide transportan, increased glucose-induced insulin secretion from GK rat islets, but not from control islets. In parallel, the amounts of the phosphatase decreased. In conclusion, increased expression of PTP sigma may be of pathogenetic significance for the defective insulin secretion in GK rat islets.     

硫化氢对糖尿病大鼠肾脏纤维化的影响及其机制

目的：观察硫化氢（H₂S）对糖尿病大鼠肾脏组织纤维化的影响并探讨其作用机制。方法：雄性SD大鼠随机分为正常对照（NC）组、糖尿病对照（DC）组、糖尿病+硫氢化钠（DM+NaHS）组和糖尿病+炔丙基甘氨酸（DM+PAG）组,每组8只。采用一次性腹腔注射链脲佐菌素的方法制备1型糖尿病大鼠模型。造模成功4周后,DM+NaHS组和DM+PAG组大鼠每天分别腹腔注射56 μmol/kg NaHS和40 mg/kg PAG溶液。处理4周后,测定各组大鼠空腹血糖（FBG）、尿素氮（BUN）和肌酐（SCr）水平;Masson染色观察肾脏组织胶原纤维变化,计算胶原容积分数（CVF）;透射电镜观察肾脏超微结构;利用试剂盒检测肾组织白细胞介素1β（IL-1β）、白细胞介素6（IL-6）、肿瘤坏死因子α（TNF-α）和羟脯氨酸（Hyp）水平;Western blot测肾组织TGF-β1、Smad3、磷酸化Smad3（p-Smad3）和IV型胶原（col-IV）的蛋白表达水平。结果：与NC组比较,DC组FBG、BUN、SCr、CVF、IL-1β、IL-6、TNF-α和Hyp均明显增高,肾脏胶原纤维沉积、超微结构损伤明显加重,TGF-β1、Smad3、p-Smad3、p-Smad3/Smad3和col-IV表达均明显增加。与DC组比较,除FBG外,DM+NaHS组中上述指标均明显改善;而DM+PAG组中上述指标损伤均进一步加重。结论：H₂S可以减轻糖尿病大鼠肾脏纤维化,其机制可能与减少促炎因子释放,下调TGF-β1/Smad3通路,抑制肾脏col-IV过量生成相关。     

乙醇激动ALDH2对糖尿病大鼠肾脏JNK表达的影响

目的：观察乙醇激动乙醛脱氢酶2（ALDH2）对糖尿病大鼠肾脏c-Jun氨基末端激酶（JNK）表达的影响。方法：18只健康雄性SD大鼠随机分为正常对照组、糖尿病组、乙醇＋糖尿病组（n=6）。造模8周后,测定血糖、糖化血红蛋白、肾功能、24h尿蛋白含量等指标,测定肾重指数,观察肾脏病理结构改变,检测肾脏组织ALDH2、p-JNK及JNK蛋白表达。结果：与正常对照组相比,糖尿病组血糖、糖化血红蛋白、尿素氮、肌酐、24h尿蛋白量及肾重指数均明显升高。病理切片显示：肾小球系膜基质增多、基底膜增厚、毛细血管腔变窄。肾脏组织ALDH2蛋白表达下降,p-JNK、JNK蛋白表达增加,p-JNK／JNK显著增高。给予乙醇干预后,肾功能损伤降低,病理改变减轻,肾脏组织ALDH2增高,p-JNK、JNK表达下降,p-JNK／JNK降低。结论：增加ALDH2表达可能通过抑制JNK信号通路的活性减轻糖尿病大鼠肾脏损伤。     

积雪草对早期糖尿病肾病大鼠TGF-β1表达及相关下游信号的影响

目的：通过研究积雪草（CA）对早期糖尿病肾病大鼠转化生长因子β₁（TGF-β₁）表达及相关下游信号的影响,阐明积雪草防治早期糖尿病肾病（DN）的分子机制。方法：60只雄性SD大鼠,按体重随机分为假手术组（n=10）和造模组（n=50）。造模组大鼠进行右肾切除术,1周后给以腹腔注射链脲佐菌素（STZ）30 mg/kg,连续给3 d;72 h后测血糖,以 ≥ 16.7 mmol/L,尿糖+++以上及尿量大于对照组的50%为DN模型成模标准。假手术组进行右肾被膜损伤,并注射相应量生理盐水。造模组通过灌胃给药,分为：DN模型组（模型组）、DN+福辛普利组（蒙组1.6 mg/kg·d）、DN+积雪草高剂量组（高剂量组16.8 mg/kg·d）、DN+积雪草中剂量组（中剂量组11.2 mg/kg·d）和DN+积雪草低剂量组（低剂量组5.6 mg/kg·d）（n=10）,连续给药16周,每日上午1次灌胃。利用实时荧光定量PCR和Western blot分别检测肾组织中TGF-β₁、TβR1、TβR2、Smad2/3、p-Smad2/3及Smad7 mRNA和蛋白的表达。结果：与假手术组相比,DN组TGF-β₁、TβR1、TβR2、Smad2/3 mRNA和蛋白表达及Smad2/3蛋白的磷酸化水平显著增加（P<0.05）、Smad7 mRNA和蛋白表达明显减少（P<0.05）,而福辛普利和高剂量积雪草能倒转DN引起的TGF-β₁、TβR1、TβR2、Smad2/3 mRNA和蛋白表达增加（P<0.05）及Smad7 mRNA和蛋白表达降低（P<0.05）。结论：积雪草可能通过调控TGF-β₁/Smad信号通路起到防治DN的作用。     

Renal mitochondrial oxidative stress is enhanced by the reduction of Sirt3 activity,in Zucker diabetic fatty rats

Objectives: Mitochondrial oxidative stress is involved in the pathogenesis of diabetic kidney disease. The objective of our study is to identify the mechanisms of renal mitochondrial oxidative stress, focusing on Sirt3, which is nicotinamide adenine dinucleotide (NAD⁺; oxidized NAD)-dependent deacetylase in mitochondria.

Methods: Renal mitochondrial oxidative stress and Sirt3 activity, using Zucker diabetic fatty rats (ZDFRs) and cultured proximal tubular cells under high-glucose condition were evaluated.

Results: At 28 weeks of age, ZDFRs exhibited the increased urinary albumin/liver-type fatty acid-binding protein (L-FABP)/8-hydroxy-2'-deoxyguanosine (8-OHdG) excretion, histological tubular cell damage, compared to non-diabetic Zucker Lean rats. In renal mitochondria, acetylated isocitrate dehydrogenase2 (IDH2) and superoxide dismutase2 (SOD2), accompanied with mitochondrial oxidative stress and mitochondrial morphologic alterations, were increased in ZDFRs, indicating inactivation of Sirt3. Additionally, expression of the NAD-degrading enzyme, CD38, was increased, and the NAD⁺/NADH (reduced NAD) ratio was reduced in the renal cortex of ZDFRs. High-glucose stimulation in cultured proximal tubular cells also resulted in an increase in acetylated IDH2/SOD2, CD38 overexpression and a reduction in the NAD⁺/NADH ratio.

Conclusions: Enhancement of mitochondrial oxidative stress in the diabetic kidney was mediated by the reduction of Sirt3 activity. CD38 overexpression may be related to a reduction in the NAD⁺/NADH ratio in the diabetic kidney.     

Combined insulin B:9-23 self-peptide and polyinosinic-polycytidylic acid accelerate insulitis but inhibit development of diabetes by increasing the proportion of CD4+Foxp3+ regulatory T cells in the islets in non-obese diabetic mice

Insulin peptide B:9-23 is a major autoantigen in type 1 diabetes. Combined treatment with B:9-23 peptide and polyinosinic-polycytidylic acid (poly I:C), but neither alone, induce insulitis in normal BALB/c mice. In contrast, the combined treatment accelerated insulitis, but prevented diabetes in NOD mice. Our immunofluorescence study with anti-CD4/anti-Foxp3 revealed that the proportion of Foxp3 positive CD4⁺CD25⁺ regulatory T cells (Tregs) was elevated in the islets of NOD mice treated with B:9-23 peptide and poly I:C, as compared to non-treated mice. Depletion of Tregs by anti-CD25 antibody hastened spontaneous development of diabetes in non-treated NOD mice, and abolished the protective effect of the combined treatment and conversely accelerated the onset of diabetes in the treated mice. These results indicate that poly I:C combined with B:9-23 peptide promotes infiltration of both pathogenic T cells and predominantly Tregs into the islets, thereby inhibiting progression from insulitis to overt diabetes in NOD mice.     

Regulation of insulin resistance by targeting the insulin‐like growth factor 1 receptor with microRNA‐122‐5p in hepatic cells

Insulin resistance (IR) is a common etiology of type 2 diabetes (T2D) defined by a state of decreased reactivity to insulin in multiple organs, such as the liver. This study aims to investigate how microRNA‐122‐5p (miR‐122) regulates the hepatic IR in vitro. We first found that the miR‐122 level was upregulated in the liver of rats fed with a high‐fat diet and injected with streptozotocin (T2D rats), while the expression level of insulin‐like growth factor 1 receptor (IGF‐1R), a potential target of miR‐122, was downregulated in the diabetic liver. In vitro, glucosamine‐induced IR was introduced in HepG2 hepatic cells, and the levels of miR‐122 and IGF‐1R were further assessed. An increase of miR‐122 level and a decrease of IGF‐IR level were observed in IR hepatic cells, which was the same as that in the diabetic liver. Results of the luciferase reporter assay validated IGF‐1R as a direct target of miR‐122. Moreover, in IR HepG2 cells, antagonizing miR‐122 with its specific inhibitor enhanced glucose uptake and suppressed the expression of glucose 6‐phosphatase and phosphoenolpyruvate carboxykinase, two key enzymes in regulating gluconeogenesis. Such alterations induced by the miR‐122 inhibitor in IR hepatic cells were impaired when IGF‐1R was simultaneously knocked down. In addition, the PI3K/Akt pathway was deactivated in IR cells, and then reactivated with miR‐122 inhibitor transfection. In conclusion, our study demonstrates that miR‐122 is able to regulate IR in hepatic cells by targeting IGF‐1R.     

Consumption of a high fat diet promotes protein O-GlcNAcylation in mouse retina via NR4A1-dependent GFAT2 expression

The incidence of type 2 diabetes, the most common cause of diabetic retinopathy (DR), is rapidly on the rise in developed countries due to overconsumption of calorie rich diets. Using an animal model of diet-induced obesity/pre-diabetes, we evaluated the impact of a diet high in saturated fat (HFD) on O-GlcNAcylation of retinal proteins, as dysregulated O-GlcNAcylation contributes to diabetic complications and evidence supports a role in DR. Protein O-GlcNAcylation was increased in the retina of mice fed a HFD as compared to littermates receiving control chow. Similarly, O-GlcNAcylation was elevated in retinal Müller cells in culture exposed to the saturated fatty acid palmitate or the ceramide analog Cer6. One potential mechanism responsible for elevated O-GlcNAcylation is increased flux through the hexosamine biosynthetic pathway (HBP). Indeed, inhibition of the pathway's rate-limiting enzyme glutamine-fructose-6-phosphate amidotransferase (GFAT) prevented Cer6-induced O-GlcNAcylation. Importantly, expression of the mRNA encoding GFAT2, but not GFAT1 was elevated in both the retina of mice fed a HFD and in retinal cells in culture exposed to palmitate or Cer6. Notably, expression of nuclear receptor subfamily 4 group A member 1 (NR4A1) was increased in the retina of mice fed a HFD and NR4A1 expression was sufficient to promote GFAT2 mRNA expression and O-GlcNAcylation in retinal cells in culture. Whereas palmitate or Cer6 addition to culture medium enhanced NR4A1 and GFAT2 expression, chemical inhibition of NR4A1 transactivation repressed Cer6-induced GFAT2 mRNA expression. Overall, the results support a model wherein HFD increases retinal protein O-GlcNAcylation by promoting NR4A1-dependent GFAT2 expression.