HEPATIC ZONATION OF CARBOHYDRATE METABOLISM

Periportal cells synthesize twice as much glucose from lactate than do cells from the perivenous zone.     

Alterations in alanine metabolism in diabetic dogs during short-term treatment with an artificial B cell

Summary The flux rates of plasma glucose and alanine were studied isotopically (6-³H-glucose and U-¹⁴C-alanine simultaneously) in resting chronically diabetic dogs during short-term treatment with an artificial B cell where the insulin was infused into a peripheral vein. Despite perfect blood glucose control and normal glucose flux rates, the concentration and rates of appearance and disappearance of alanine were significantly elevated in the diabetic animals before, during and after an exogenous glucose load. The incorporation of the carbon moiety of alanine into circulating glucose was also increased, but diminished to a near-normal extent when exogenous glucose was given. The plasma clearance rates for alanine in the diabetic dogs were normal throughout the study. It is concluded that normal blood glucose control in diabetes does not necessarily mean normalization of the entire metabolic network. On the basis of peripheral hyperinsulinaemia alanine formation from glucose and branched chain amino acids is elevated in muscle. This may explain increased flux of alanine despite normal blood glucose control.     

黄芪甲苷调节PI3K/Akt/FoxO1通路抑制糖尿病大鼠肝糖异生

目的:探讨黄芪甲苷对2型糖尿病(T2DM)大鼠肝损伤保护潜在机制及肝组织磷酯酰肌醇3-激酶(PI3K)/蛋白激酶B(Akt)/叉头框转录因子1(FoxO1),磷酸烯醇式丙酮酸羧基酶(PEPCK)和葡萄糖6-磷酸酶(G6Pase)蛋白表达的影响。方法:6周高糖高脂饮食后,链脲佐菌素(STZ)一次性腹腔注射(0.035 g·kg^-1)建立T2DM大鼠模型,随机分为正常组、模型组、黄芪甲苷低、中、高剂量组及二甲双胍组。黄芪甲苷低、中、高剂量组灌胃黄芪甲苷0.02,0.04,0.08 g·kg^-1·d^-1,二甲双胍组灌胃二甲双胍0.2 g·kg^-1·d^-1;给药8周后,于末次灌胃24 h禁食不禁水后处死,测血清肝生化指标,肝脏指数等;采用苏木素-伊红(HE)染色观察肝脏组织病理形态学变化;马松(Masson)染色观察纤维化程度;过碘酸希夫(PAS)染色反应观察细胞内糖原等变化;免疫组化及蛋白免疫印迹法(Western blot)检测各组肝中PI3K/Akt/FoxO1信号蛋白及PEPCK,G6Pase蛋白表达水平。结果:与正常组比较,模型组肝脏指数显著升高(P<0.01),肝功能指标丙氨酸氨基转移酶(ALT),天门冬氨酸氨基转移酶(AST),总胆固醇(TC),甘油三酯(TG)的含量显著升高(P<0.01),高密度脂蛋白胆固醇(HDL-C)显著降低(P<0.01),大鼠体质量显著减轻(P<0.01),PI3K/Akt/Fox O1信号减弱(P<0.01),PEPCK,G6Pase蛋白表达水平显著增强(P<0.01);与模型组比较,黄芪甲苷中、高剂量组及二甲双胍组肝功能指标ALT,AST,TC,TG的含量明显降低(P<0.05,P<0.01),大鼠体质量明显增加(P<0.05,P<0.01),肝组织Fox O1,PEPCK及G6Pase蛋白水平明显降低(P<0.05,P<0.01),Fox O1的磷酸化水平明显增强(P<0.05,P<0.01)。结论:黄芪甲苷可能通过调节PI3K/Akt/Fox O1信号通路抑制高脂高糖加小剂量STZ诱导T2DM肝糖异生,从而起到延缓T2DM大鼠肝脏损伤作用。     

白花丹素改善高脂饮食小鼠肝脏脂代谢并降低糖异生的研究

目的 研究白花丹素（plumbagin,PLB）在非酒精性脂肪性肝病（nonalcoholic fatty liver disease,NAFLD）中的治疗效果。方法 将成年C57BL/6J小鼠分为4组：对照组（标准饮食,15%脂肪）,高脂肪饮食组（high fatty diet,HFD,58%脂肪）,HFD+PLB （5 mg·kg^-1·d^-1）组,HFD+PLB （15 mg·kg^-1·d^-1）组。HFD造模6周,PLB共灌胃4周,随后处死小鼠。通过HE染色和油红染色研究小鼠肝脏脂肪堆积情况,通过qRT-PCR试验研究肝脏脂代谢和糖异生相关基因表达情况,最后通过Western blotting研究活化蛋白-1（activator protein,AP-1）相关亚基的表达情况。结果 PLB可显著降低小鼠体质量和血液中葡萄糖水平,HE染色和油红染色结果显示PLB可显著降低小鼠肝脏脂质积累。PLB可显著降低脂肪代谢过程和糖异生相关基因表达,并可抑制AP-1亚基c-Jun,c-Fos和Fra1表达。结论 PLB可显著抑制HFD小鼠肝脏细胞脂肪累积,维持脂肪代谢和葡萄糖稳态,并抑制AP-1炎症反应。     

结合生物信息学和分子对接技术探讨基于肝糖异生抑制策略治疗2型糖尿病的靶标蛋白标志物

目的 基于肝糖异生抑制策略筛选2型糖尿病(type 2 diabetes mellitus,T2DM)的标志性靶标蛋白。方法 从NCBI数据库下载人类肝组织基因芯片数据集,使用GEO2R在线分析工具筛选T2DM易感性基因;利用GeneCards和OMIM数据库检索糖异生相关靶点;整合数据获取T2DM-肝糖异生交互靶点,并构建蛋白质间相互作用网络筛选标志性靶标蛋白;使用Metascape数据库对靶点进行基因本体论和通路富集分析;借助分子对接预测T2DM治疗药物与标志性靶标蛋白之间的相互作用能力;最后联合二甲双胍对标志性靶标蛋白在自发性T2DM KKAy小鼠肝组织中的影响进行验证。结果 共识别出1 143个T2DM易感性基因和958个糖异生相关靶点,获得56个T2DM-肝糖异生交互靶点,并经网络分析筛选出2个标志性靶标蛋白PTPRC和VCAM1;交互靶点主要富集在葡萄糖分解代谢、典型糖酵解、葡萄糖-6-磷酸糖酵解等生物过程,通过糖酵解/糖异生、糖尿病并发症中的AGE-RAGE信号通路、内分泌抵抗等通路调节发挥作用;26个降糖药物均与标志性靶点同时具有较好的空间匹配、能量匹配以及不同程度的结合能力;T2DM模型组小鼠血糖较正常组显著增高,且在治疗后显著降低;T2DM模型组小鼠肝组织中PTPRC、VCAM1的蛋白表达水平均较正常对照组显著增高,并且均在二甲双胍治疗后显著降低。结论 本研究系统筛选并验证了肝组织中可能影响T2DM肝糖异生的2个标志性靶标蛋白,揭示了T2DM中肝糖异生调控通路,为深入研究肝糖异生防治机制,寻找新的降糖药物作用靶点提供依据。     

Melatonin-induced modulation of glucose metabolism in primary cultures of rabbit kidney-cortex tubules

The effect of melatonin on glucose metabolism in the presence and absence of insulin has been investigated in the primary cultures of renal tubules grown in a defined medium. In the absence of glucose in the medium containing 5 microg/mL of insulin and 2 mm alanine + 5 mm glycerol + 0.5 mm octanoate, 100 nm melatonin stimulated both glucose and lactate synthesis, while in the medium devoid of insulin melatonin action was negligible. Melatonin-induced increase in glucose and lactate synthesis was accompanied by an enhancement of alanine and glycerol consumption. In view of measurements of [U-14C]L-alanine and [U-14C]L-glycerol incorporation into glucose, it is likely that melatonin increased alanine utilization for glucose production, while accelerated lactate synthesis was because of an enhanced glycerol consumption. As (i) 10 nm luzindole attenuated the stimulatory action of melatonin on glucose formation and (ii) the indole induced a decrease in intracellular cAMP level, it seems likely that in renal tubules melatonin binds to ML1 membrane receptor subtype. In view of a decline of intracellular fructose-1,6-bisphosphate content accompanied by a significant rise in hexose-6-phosphate and glucose levels, melatonin might result in an acceleration of flux through fructose-1,6-bisphosphatase probably because of an increase in the active, dephosphorylated form of this enzyme. Thus, the administration of melatonin in combination with insulin might be beneficial for diabetic therapy because of protection against hypoglycemia.     

Effect of insulin in vitro on the isolated,perfused alloxan-diabetic rat liver

Summary Withdrawal of exogenous insulin and a subsequent fast (24 h) of alloxan diabetic rats stimulated rates of gluconeogenesis, ureogenesis, ketogenesis, and amino acid release by in situ perfused livers when compared to those from normal, fasted rats. The contribution of liver glycogen to the high rates of gluconeogenesis observed with the diabetic liver could be excluded. Perfusate lactate concentrations remained constant during the period when the elevated rate of gluconeogenesis was observed with diabetic liver. Addition of insulin as a bolus (750 mU) and continuous infusion (12.5 mU/min) to the perfusion medium of diabetic livers resulted in constant perfusate levels of glucose, urea and -amino nitrogen indicating a suppression of the catabolic processes present in the fasted, diabetic liver. The rate of ketogenesis was also slowed by insulin to about half the rate prior to addition of the hormone. These data indicate that insulin has an immediate anti-catabolic effect in the perfused, diabetic liver.     

A differential action of phenformin in normal and diabetic rat livers

Summary Phenformin inhibited gluconeogenesis by livers from both normal and diabetic rats. However, the concentration of phenformin which inhibited gluconeogenesis by the diabetic livers was not effective in normal livers. It is suggested that an action which is differentially effective in the diabetic state is likely to be clinically relevant.     

The metabolic effects of sodium dichloroacetate in the suckling newborn rat

Summary Subcutaneous injection of sodium dichloroacetate (1 mg/g body wt every 3 h) in suckling newborn rats caused in 6 h a fall of 2.5 mmol/l in blood glucose concentrations, and a rise of 2.4 mmol/ l in total blood ketone body levels, but no change in the high levels of plasma non esterified fatty acids. Glucose utilization, measured after intraperitoneal injection of D-glucose (2 mg/g body wt), was not increased in newborns injected with dichloroacetate. The hypoglycaemia resulted from a decrease in gluconeogenic rate, secondarily to a lowering effect of dichloroacetate on blood levels of lactate, pyruvate and alanine. The hypoglycaemia induced by dichloroacetate was completely reversed by injecting newborn rats with a mixture of gluconeogenic precursors (lactate, pyruvate and alanine). It is concluded that the high rate of gluconeogenesis observed in suckling newborn rats in sustained by an increased release of lactate and, to a much smaller extent of pyruvate and alanine, by peripheral tissues. This probably resulted from the low pyruvate dehydrogenase activity found in peripheral tissues of the newborn rat. The hyperketonaemia induced by dichloroacetate could result from an increased ketogenesis and/or a decreased ketone body utilization.     

Lipid-dependent control of hepatic glycogen stores in healthy humans

Aims/hypothesis. Non-esterified fatty acids and glycerol could stimulate gluconeogenesis and also contribute to regulating hepatic glycogen stores. We examined their effect on liver glycogen breakdown in humans.¶Methods. After an overnight fast healthy subjects participated in three protocols with lipid/heparin (plasma non-esterified fatty acids: 2.2 ± 0.1 mol/l; plasma glycerol: 0.5 ± 0.03 mol/l; n = 7), glycerol (0.4 ± 0.1 mol/l; 1.5 ± 0.2 mol/l; n = 5) and saline infusion (control; 0.5 ± 0.1 mol/l; 0.2 ± 0.02 mol/l; n = 7). Net rates of glycogen breakdown were calculated from the decrease of liver glycogen within 9 h using ¹³C nuclear magnetic resonance spectroscopy. Endogenous glucose production was measured with infusion of D-[6,6-²H₂]glucose.¶Results. Endogenous glucose production decreased by about 25 % during lipid and saline infusion (p < 0.005) but not during glycerol infusion (p < 0.001 vs lipid, saline). An increase of plasma non-esterified fatty acids or glycerol reduced the net glycogen breakdown by about 84 % to 0.6 ± 0.3 μmol · kg^–1· min^–1 (p < 0.001 vs saline: 3.7 ± 0.5 μmol · kg^–1· min^–1) and by about 46 % to 2.0 ± 0.4 μmol · kg^–1· min^–1 (p < 0.01 vs saline and lipid), respectively. Rates of gluconeogenesis increased to 11.5 ± 0.8 μmol · kg^–1· min^–1 (p < 0.01) and 12.8 ± 1.0 μmol · kg^–1· min^–1 (p < 0.01 vs saline: 8.2 ± 0.7 μmol · l^–1· min^–1), respectively.¶Conclusion/interpretation: An increase of non-esterified fatty acid leads to a pronounced inhibition of net hepatic glycogen breakdown and increases gluconeogenesis whereas glucose production does not differ from the control condition. We suggest that this effect is not due to increased availability of glycerol alone but rather to lipid-dependent control of hepatic glycogen stores. [Diabetologia (2001) 44: 48–54]