The role of kidney in glucose homeostasis – SGLT2 inhibitors,a new approach in diabetes treatment

The role of the kidney in blood glucose-level regulation was until recently underestimated. Renal gluconeogenesis, renal glucose uptake and tubular glucose reabsorption are the three ways of renal involvement in glucose homeostasis. In the postabsorptive state, 20% of total glucose release is attributed to renal gluconeogenesis. Tubular glucose reabsorption is performed by the combined action of Na⁺/D-glucose SGLTs co-transporters and GLUT-facilitated diffusion glucose transporters. SGLT2 inhibitors are a new family of agents, which occlude the path of SGLT2 glucose reabsorption and cause glucosuria. Efficacy of SGLT2 inhibitors includes reduction of HbA1c, fasting and postprandial blood glucose level and slight body weight and systolic blood pressure decrease. The most common adverse events of them are genital mycotic and urinary tract infections. Dapagliflozin and canagliflozin are the first agents of this class, approved from the European Medicine Agency and FDA, respectively.     

Maternal di‐(2‐ethylhexyl) phthalate exposure alters hepatic insulin signal transduction and glucoregulatory events in rat F1 male offspring

Di‐(2‐ethylhexyl) phthalate (DEHP) is a commonly used plasticizer with endocrine disrupting properties. Its widespread use resulted in constant human exposure including fetal development and postnatal life. Epidemiological and experimental data have shown that DEHP has a negative influence on glucose homeostasis. However, the evidence regarding the effect of maternal DEHP exposure on hepatic glucose homeostasis is scarce. Hence, we investigated whether DEHP exposure during gestation and lactation disrupts glucose homeostasis in the rat F₁ male offspring at adulthood. Pregnant rats were divided into three groups and administered with DEHP (10 and 100 mg/kg/day) or olive oil from gestational day 9 to postnatal day 21 (lactation period) through oral gavage. DEHP‐exposed offspring exhibited hyperglycemia, impaired glucose and insulin tolerances along with hyperinsulinemia at postnatal day 80. DEHP exposure significantly reduced the levels of insulin signaling molecules such as insulin receptors, IRS1, Akt and its phosphorylated forms. GSK3β and FoxO1 proteins increased in DEHP‐exposed groups whereas its phosphorylated forms decreased. Treated groups showed decreased glycogen synthase activity and glycogen concentration. Glucose‐6‐phosphatase and phosphoenolpyruvate carboxykinase mRNA level and enzyme activity increased in DEHP‐treated groups. The interaction between FoxO1‐glucose‐6‐phosphatase and FoxO1‐phosphoenolpyruvate carboxykinase was also increased. This study suggests that DEHP exposure impairs insulin signal transduction and alters glucoregulatory events leading to the development of type 2 diabetes in F₁ male offspring.     

Diurnal variations in blood intermediary metabolites in mild gestational diabetic patients and the effect of a carbohydrate-restricted diet

Summary Twenty-four-hour metabolic profiles were performed in the third trimester of pregnancy in seven non-diabetic women (group A) and in two groups of mild gestational diabetics, at diagnosis (group B, seven patients) and after treatment with a 150-g carbohydrate diet (group C, seven patients). Mean 24-h blood metabolite levels (± SD) in groups A, B and C were: glucose: 4.65±0.82, 5.35±3.06 and 5.40±1.7 mmol/l; lactate: 1.05±0.18, 1.14±0.42 and 0.78 ±0.22mmol/l; alanine: 0.31±0.03, 0.31±0.10 and 0.27±0.07 mmol/l; ketone bodies: 0.11±0.04, 0.19 ±0.05 and 0.26±0.15mmol/l. Glucose levels were not significantly different between the groups. Ketone body levels were elevated in the diabetics prior to treatment (p < 0.01) and rose higher on diet. Lactate levels were reduced on the diet (0.05 < P < 0.10). Abnormalities in the concentrations of total blood ketone body levels in gestational diabetics may be detrimental to fetal development and therapy should be designed to minimise changes in intermediary metabolites.     

饥饿、糖尿病和肥胖状态对小鼠肝脏SOCS2基因表达的影响

目的确定小鼠肝脏SOCS2基因在饥饿、糖尿病和肥胖状态下的表达水平,并初步研究SOCS2对糖异生的影响。方法动物分3组:C57BL/6J小鼠、对照组(饱食)和实验组(饥饿24 h);糖尿病模型小鼠db/db及对照小鼠db/m饱食;肥胖模型小鼠ob/ob及其对照C57BL/6J小鼠(饱食)。处死小鼠后提取肝脏RNA做反转录PCR,荧光实时定量PCR检测小鼠肝脏SOCS2及糖异生相关基因在3组小鼠中的表达水平;使用腺病毒表达系统在C57BL/6J小鼠原代肝细胞中过表达SOCS2,Western blot检测SOCS2蛋白的表达,葡萄糖生成实验检测糖输出。结果饥饿使C57BL/6J小鼠肝脏中SOCS2 mRNA水平下调,db/db和ob/ob小鼠肝脏SOCS2基因表达比其对照小鼠均明显下降(P0.05),调节糖异生的关键基因PGC-1α、PEPCK和G6Pase的mRNA水平均上升。在C57BL/6J小鼠原代肝细胞中过表达SOCS2,得到大小为Mr 23 000的蛋白,糖输出受到明显抑制。结论初步认定SOCS2可抑制C57BL/6J小鼠原代肝细胞糖异生,可能是治疗糖尿病的一个新靶点。     

Comparative effects of phenformin,metformin and glibenclamide on metabolic rhythms in maturity-onset diabetics

Summary Twelve hour metabolic rhythms have been performed on six maturity-onset diabetic subjects during successive periods of therapy with phenformin, metformin, and glibenclamide. Moderate control of blood glucose concentration was achieved with phenformin and metformin, the lowest concentrations being found with glibenclamide. Mean blood lactate concentration was grossly elevated during phenformin therapy, moderately elevated with metformin and normal during glibenclamide treatment. Similar patterns were found for the lactate/pyruvate ratio, alanine, glycerol and ketone bodies. Serum triglyceride concentrations were significantly higher during phenformin treatment than with the other two regimes. Serum insulin concentration was higher on glibenclamide than with either biguanide. Most of these effects of the biguanides could be accounted for by an inhibitory effect on hepatic gluconeogenesis. It is concluded that the use of biguanides as hypoglycaemic agents in diabetes is associated with the production of multiple metabolic abnormalities.     

Zonation of alanine metabolism in the bivascularly perfused rat liver.

AIMS/BACKGROUND: Zonation of alanine metabolism was investigated in the bivascularly perfused rat liver, a technique in which a selective area of the periportal region can be reached via the hepatic artery. METHODS: Bivascular liver perfusion was done in both the antegrade and retrograde modes. Predominance of a given metabolic parameter in the periportal or perivenous area was deduced from comparisons of the changes caused by alanine infusion into the hepatic artery in antegrade and retrograde perfusion. RESULTS: Confirming previous notions, glutamine synthesis predominated in the perivenous area, however, the contribution of the periportal area was significant. Gluconeogenesis and the associated extra oxygen consumption were more pronounced in the periportal region. The capacity of urea synthesis in the periportal region was relatively small as indicated by the ratios of urea to glucose production, which were lower in this region. Ammonia in the periportal region was considerably above the mean ammonia production of whole the liver parenchyma. The overflows of pyruvate and lactate were considerably smaller in the periportal region. CONCLUSION: The distribution of alanine metabolism seems to reflect mainly zonation of the fates of the carbon skeleton (mainly gluconeogenesis). The production of glutamine in the periportal area is in agreement with recent reports about the presence of glutamine synthetase in Kupffer and endothelial cells.