GLP-1 signalling and effects on glucose metabolism in myocytes from type 2 diabetic patients

Changes in the activity of glycogen synthase a and related kinases (phosphatidylinositol-3-kinase, protein kinase B, p44/42 MAP kinases and p70s6 kinase) evoked by GLP-1 in human myocytes from normal subjects were recently implied in the effect of this hormone upon D-glucose transport and glycogen synthesis in the same cells. The major aims of the present study were i) to investigate the possible extension of this knowledge to myocytes obtained from type 2 diabetic patients, ii) to compare in these patients the response to GLP-1, insulin or the structurally related GLP-1 peptides, exendin (1-39)amide and exendin(9-39)amide, and iii) to explore possible differences in the responsiveness to these agents between normal and diabetic subjects. Apart from the much higher basal PI3K activity and impaired response to insulin of p44/42 MAP kinases in the diabetic patients, the changes in enzyme activity caused by either hormone or peptide, although not identical, were essentially comparable. Nevertheless, significant differences in glucose transport and metabolism parameters were observed in the diabetic patients vs. normal subjects: in the diabetic patients, basal 2-deoxy-glucose uptake and glycogen synthase a activity were lower, accompanied by a similar increasing effect of GLP-1 or insulin; yet, the basal value for glycogen synthesis was higher, coinciding with a lesser relative increment in response to GLP-1 or insulin.     

Increased α1-adrenoceptor activity of the rat heart during adaptation to intermittent hypoxia

Research Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Research Institute of Experimental Cardiology, All-Union Cardiologic Scientific Center, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR A. D. Ado.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 111, No. 6, pp. 570–572, June, 1991.     

Effect of hypoxia on metabolism and contractile function of the heart in rats with type 2 diabetes mellitus and abdominal obesity

Type 2 diabetes mellitus was modeled in newborn albino rat pups. Metabolism and contractile activity of isolated heart under conditions of hypoxia were studied on adult rats. Contractile activity of the myocardium in animals with type 2 diabetes mellitus and abdominal obesity decreased during hypoxia. It was manifested in a decrease in systolic and developed pressure and disturbances in diastolic relaxation of the myocardium. Damage to cell membranes and increased secretion of aspartate transaminase into the coronary circulation were observed under conditions of energy deficit and activation of the anaerobic pathway of energy production. These changes became more pronounced with increasing the period of hypoxic exposure.Translated from Byulleten Eksperimentalnoi Biologii i Meditsiny, Vol. 138, No. 9, pp. 254–256, September, 2004     

Effect of hypoxia on metabolism and contractile function of the heart in rats with type 2 diabetes mellitus and abdominal obesity

Type 2 diabetes mellitus was modeled in newborn albino rat pups. Metabolism and contractile activity of isolated heart under conditions of hypoxia were studied on adult rats. Contractile activity of the myocardium in animals with type 2 diabetes mellitus and abdominal obesity decreased during hypoxia. It was manifested in a decrease in systolic and developed pressure and disturbances in diastolic relaxation of the myocardium. Damage to cell membranes and increased secretion of aspartate transaminase into the coronary circulation were observed under conditions of energy deficit and activation of the anaerobic pathway of energy production. These changes became more pronounced with increasing the period of hypoxic exposure. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 138, No. 9, pp. 254–256, September 2004     

Increased oxidative metabolism in middle suprasylvian cortex following removal of areas 17 and 18 from newborn cats

We measured changes in metabolic activity in middle suprasylvian (MS) cortex of cats subjected to early or late removal of areas 17 and 18 to localize shifts in activity possibly indicative of regions within MS cortex that may receive expanded inputs and be involved in the sparing of some visual behaviors following early primary visual cortex damage. Cytochrome oxidase (CO) activity was measured in MS cortex of mature, intact cats and of others with areas 17 and 18 removed in adulthood (P180), or on postnatal day 28 (P28) or postnatal day 1 (P1). Not less than 9 months after the ablation, brain sections were prepared and reacted for the presence of CO. The density of CO reactivity in each of the six cortical layers in MS cortex was measured and standardized against densities from ventral periaqueductal gray or hypothalamus on the same section. Following lesions on P1, significant increases in CO activity occurred in deep layer III and in layer IV of the medial bank of the MS sulcus, including all of area PMLS and the posterior portion of AMLS. In contrast, there were no significant differences in the level of CO activity among P28, P180, or intact cats for any of the cortical layers, and all had lower levels than the P1 cats. This metabolic change provides an anatomical marker for localizing adjustments in MS cortex and can be linked to amplified projections into MS cortex from the thalamus (LPm and A and C laminae of the dorsal lateral geniculate nucleus) and ventral posterior suprasylvian cortex following P1 ablations. Furthermore, this neurochemical analysis implicates a distinct region of MS cortex as the cortical locus of some spared visual functions following early primary visual cortex damage.     

Oxidative stress and adaptation of the infant heart to hypoxia and ischemia

The potential contribution of oxidative stress to cardioprotection in infants induced by adaptation to chronic hypoxia and by ischemic preconditioning is poorly understood. Under conditions of oxidative stress, reactive oxygen species and reactive nitrogen species may contribute to phenotypic changes in hearts adapted to chronic hypoxia and to the pathogenesis of myocardial injury during both ischemia/reperfusion and hypoxia/reoxygenation. Hearts from infant rabbits normoxic from birth can be preconditioned by brief periods of ischemia. In contrast, hearts from infant rabbits adapted to hypoxia from birth appear resistant to ischemic preconditioning. Chronically hypoxic infant rabbit hearts are already resistant to ischemia compared with age-matched normoxic controls, and thus additional cardioprotection by ischemic preconditioning may not be possible. Endothelial nitric oxide synthase (NOS3) protein and its product nitric oxide are increased, but not NOS3 message, in chronically hypoxic infant hearts to protect against ischemia. Chronic hypoxia from birth also increases cardioprotection of infant hearts by increasing association of heat shock protein 90 with NOS3. Normoxic infant hearts also generate more superoxide by an N(omega)-nitro-L-arginine methyl ester-inhibitable mechanism than chronically hypoxic hearts. Thus, NOS3 appears to be critically important in adaptation of infant hearts to chronic hypoxia and in resistance to subsequent ischemia by regulating the production of reactive oxygen and nitrogen species.     

Myocardial substrate metabolism in the normal and failing heart

The alterations in myocardial energy substrate metabolism that occur in heart failure, and the causes and consequences of these abnormalities, are poorly understood. There is evidence to suggest that impaired substrate metabolism contributes to contractile dysfunction and to the progressive left ventricular remodeling that are characteristic of the heart failure state. The general concept that has recently emerged is that myocardial substrate selection is relatively normal during the early stages of heart failure; however, in the advanced stages there is a downregulation in fatty acid oxidation, increased glycolysis and glucose oxidation, reduced respiratory chain activity, and an impaired reserve for mitochondrial oxidative flux. This review discusses 1) the metabolic changes that occur in chronic heart failure, with emphasis on the mechanisms that regulate the changes in the expression of metabolic genes and the function of metabolic pathways; 2) the consequences of these metabolic changes on cardiac function; 3) the role of changes in myocardial substrate metabolism on ventricular remodeling and disease progression; and 4) the therapeutic potential of acute and long-term manipulation of cardiac substrate metabolism in heart failure.     

Collagen metabolism in the myocardium of normal and diabetic rats

Myocardial collagen and total protein synthesis were studied in normal, diabetic, and insulin-treated diabetic rats after a single intraperitoneal injection of L-[2,3-3H]proline as a radioisotopic precursor. The incorporation of tritiated proline into myocardial protein was regarded as a measure of total protein synthesis and the incorporation into hydroxyproline as indicative of myocardial collagen synthesis. Both total protein and collagen synthesis were found to be significantly lower in diabetic rats. This was associated with decreased degradation of both total protein and collagen in diabetic rats, as suggested by prolonged turnover times. Collagen content was also found to be increased in diabetic myocardium. Early insulin therapy with normalization of blood sugars in diabetic rats returned myocardial collagen metabolism to normal. This suggests that maintenance of euglycemia in diabetic rats is necessary to prevent abnormal myocardial collagen metabolism.     

Increased urinary angiotensinogen precedes the onset of albuminuria in normotensive type 2 diabetic patients

It was previously reported that intrarenal renin angiotensin system (RAS) plays a pivotal role in the onset and progression of diabetic nephropathy (DN). Urinary angiotensinogen (UAGT) was employed as a special index of the intrarenal RAS status and enhanced significantly at a very early stage of chronic kidney disease and type 1 diabetes. On the basis of these findings, the present study was performed to test the hypothesis that UAGT levels are increase even before the development of DN in type 2 diabetic patients without hypertension. 102 patients with type 2 diabetes mellitus (T2DM) and 18 healthy volunteers were studied cross-sectionally. Clinical data were collected and morning spot urine samples were obtained from all participants. UAGT levels were detected by an enzyme-linked immunosorbent assay (ELISA). As a result, UAGT to creatinine ratio (UAGT/Cr) was significantly enhanced in T2DM patients before the appearance of urinary albumin (UALB) and further increased to a greater degree in albuminuric patients. UAGT/Cr levels were positively correlated with Log (UALB to creatinine ratio) and diastolic blood pressure, but negatively correlated with estimated glomerular filtration rate. These data indicate that elevated UAGT levels precede the onset of albuminuria in normotensive T2DM patients. UAGT might potentially serve as an early marker to determine intrarenal RAS activity and predict progressive kidney disease in T2DM patients without hypertension.     

Fibroblast growth factor-19 levels in type 2 diabetic patients with metabolic syndrome

This study aimed to examine fibroblast growth factor-19 (FGF-19) in type 2 diabetic (T2DM) patients with metabolic syndrome (MetS) and to evaluate the relationship between FGF-19 and other cardiovascular risk factors, such as atherogenic index of plasma (AIP) and hsCRP. 26 T2DM patients with MetS and 12 healthy controls were enrolled in the study. Serum FGF-19 levels were measured by sandwich ELISA, and compared with other cardiovascular risk factors; lipid profile, AIP, glucose, HbA1c, and hsCRP. AIP was calculated as log (TG/HDL-c). The median (1-3.quartile) FGF-19 levels in T2DM patients with MetS and healthy controls were 122.90 (108.63-237.60) pg/ml and 293.45 (153.64-370.31) pg/ml, respectively (P=0.003). Patients were also grouped by body mass index (BMI) <30 kg/m(2) (n=13) and ≥30 kg/m(2) (n=13) with median (1-3.quartile) FGF-19 values 168.70 (113.54-275.77) pg/mL and 115.89 (97.94-200.40) pg/mL, respectively (P=0.007). Significant negative correlations were found between FGF-19 and BMI, triglyceride, log (TG/HDL-c), hsCRP, and HbA1c (r=-0.526, P=0.001; r=-0.327, P=0.05; r=-0.312, P=0.05; r=-0.435, P=0.006; r=-0.357, P=0.028, respectively). We showed that FGF-19 levels are low in T2DM patients with MetS. The negative relationship between FGF-19 and several known cardiovascular risk factors such as TG, log (TG/HDL-c), hsCRP and HbA1c in diabetic patients with MetS suggests that FGF-19 can be used as a contributing marker.     

Increased angiotensin-converting enzyme activities in diabetes mellitus: analysis of diabetes type, state of metabolic control and occurrence of diabetic vascular disease

Serum angiotensin-converting enzyme activities were measured in 41 type 1 diabetics (16.4 +/- 4.0 U/ml), in 40 type 2 diabetics (15.0 +/- 5.2 U/ml) and in 52 controls (13.0 +/- 2.7 U/ml, mean +/- SD). Twenty six (32%) of 81 patients presented with serum angiotensin-converting enzyme activities above the normal range. No relation between serum angiotensin-converting enzyme activities and the presence or lack of diabetic vascular diseases in type 1 and type 2 diabetics could be detected. No significant differences in serum angiotensin-converting enzyme activities were found when comparing various types of diabetic vascular disease (retinopathy, neuropathy, renal failure, arterial vascular disease, diabetic vascular disease, coronary artery disease). However, mean serum angiotensin-converting enzyme activities were significantly increased in diabetics with retinopathy when compared with controls (p less than 0.0005). Correlation between metabolic long term control as determined by measuring glycohaemoglobin (HbA1) concentrations and serum angiotensin-converting enzyme activities could not be established. Serum angiotensin-converting enzyme activities did not show any correlations with duration of diabetes, age or sex of patients. A representative number of diabetics (32%) showed elevated serum angiotensin-converting enzyme activities, but a correlation with diabetic vascular disease, metabolic control or type of disease could not be established.     

Increased resistance of animals to X-ray irradiation following a period of acclimatization to hypoxia in the presence of a normal barometric pressure

Summary It was established as a result of experiment that the endurance of white mice to irradiation by x-rays is increased under the effect of acclimatization to hypoxia without decrease of barometric pressure. The activity of catalase in the blood and organs of acclimatized animals is increased.Presented by Academician K. M. Bykov     

强化胰岛素治疗减轻2型糖尿病大鼠氧化应激

近年来的研究表明氧化应激(oxidative stress,OS)参与了糖尿病的发生发展.糖尿病存在着OS水平的升高,而机体的OS决定于活性氧(reactive oxygen species,BOS)及其导致的过氧化脂质产生增多与抗氧化防御系统中各种抗氧化酶的减少.本研究旨在观察强化胰岛素治疗对2型糖尿病大鼠OS的影响及其机制.     

Muscle glycogen resynthesis, signalling and metabolic responses following acute exercise in exercise-trained pigs carrying the PRKAG3 mutation

Hampshire pigs carrying the PRKAG3 mutation in the AMP-activated protein kinase (AMPK) γ3 subunit exhibit excessive skeletal muscle glycogen storage and an altered glycogen synthesis signalling response following exercise. AMPK plays an important role as a regulator of carbohydrate and fat metabolism in mammalian cells. Exercise-trained muscles are repeatedly exposed to glycogen degradation and resynthesis, to which the signalling pathways adapt. The aim of this study was to examine the effect of acute exercise on glycogen synthesis signalling pathways, and the levels of insulin and other substrates in blood in exercise-trained pigs with and without the PRKAG3 mutation. After 5 weeks of training, pigs performed two standardized treadmill exercise tests, and skeletal muscle biopsies were obtained immediately after exercise and 3 h postexercise in the first test, and 6 h postexercise in the second test. The PRKAG3 mutation carriers had higher glycogen storage, and resynthesis of glycogen was faster after 3 h but not after 6 h of recovery. Alterations in the concentrations of insulin, glucose, lactate and free fatty acids after exercise did not differ between the genotypes. The carriers showed a lower expression of AMPK and increased phosphorylation of Akt Ser(473) after exercise, compared with non-carriers. Acute exercise stimulated the phosphorylation of AS160 in both genotypes, and the phosphorylation of GSK3α Ser(21) and ACC Ser(79) in the non-carriers. In conclusion, exercise-trained pigs carrying the PRKAG3 mutation show an altered Akt and AMPK signalling response to acute exercise, indicating that glucose metabolism is associated with faster resynthesis of muscle glycogen in this group.     

正常微量白蛋白尿的2型糖尿病患者肾脏磁共振扩散加权成像研究

目的 应用磁共振扩散加权成像(DWI)检测正常微量白蛋白尿(MAU)的2型糖尿病患者肾功能改变,评估其在2型糖尿病患者早期肾损害诊断中的价值.方法 2010年8月至12月在本院内分泌科门诊就诊的MAU在正常范围的2型糖尿病患者10例为观察组,同期健康体检者10例为健康对照组,每组20个肾,两组年龄、性别和体质量指数差异无统计学意义(均P＞0.05).应用单次激发平面回波DWI和常规MR序列进行双侧肾脏MRI检查,比较两组在弥散敏感梯度系数(b值)分别为400、500、600和800 s/mm2时肾实质表观扩散系数(ADC),并比较两组血清肌酐和胱抑素C水平.结果 MRI常规序列扫描显示两组肾脏形态、大小及解剖结构无明显差异,血清肌酐及胱抑素C水平差异无统计学意义(均P＞0.05).DWI检查显示,b值分别为500、600及800 s/mm2时,观察组ADC值分别为(2.15±0.06)×10-3、(2.05 ±0.07)×10-3、(1.87±0.05)×10-3 mm2/s,健康对照组ADC值分别为(2.32±0.07)×10-3、(2.16±0.04)×l0-3、( 1.95 ±0.04)×10-3 mm2/s,观察组ADC值较健康对照组均显著下降(均P＜0.05).结论 DWI可能有助于更早期地发现2型糖尿病患者肾功能损害.     

Changing pattern of gene expression is associated with ventricular myocyte dysfunction and altered mechanisms of Ca2+ signalling in young type 2 Zucker diabetic fatty rat heart

The association between type 2 diabetes and obesity is very strong, and cardiovascular complications are the major cause of morbidity and mortality in diabetic patients. The aim of this study was to investigate early changes in the pattern of genes encoding cardiac muscle regulatory proteins and associated changes in ventricular myocyte contraction and Ca(2+) transport in young (9- to 13-week-old) type 2 Zucker diabetic fatty (ZDF) rats. The amplitude of myocyte shortening was unaltered; however, time-to-peak shortening and time to half-relaxation of shortening were prolonged in ZDF myocytes (163 ± 5 and 127 ± 7 ms, respectively) compared with age-matched control rats (136 ± 5 and 103 ± 4 ms, respectively). The amplitude of the Ca(2+) transient was unaltered; however, time-to-peak Ca(2+) transient was prolonged in ZDF myocytes (66.9 ± 2.6 ms) compared with control myocytes (57.6 ± 2.3 ms). The L-type Ca(2+) current was reduced, and inactivation was prolonged over a range of test potentials in ZDF myocytes. At 0 mV, the density of L-type Ca(2+) current was 1.19 ± 0.28 pA pF(-1) in ZDF myocytes compared with 2.42 ± 0.40 pA pF(-1) in control myocytes. Sarcoplasmic reticulum Ca(2+) content, release and uptake and myofilament sensitivity to Ca(2+) were unaltered in ZDF myocytes compared with control myocytes. Expression of genes encoding various L-type Ca(2+) channel proteins (Cacna1c, Cacna1g, Cacna1h and Cacna2d1) and cardiac muscle proteins (Myh7) were upregulated, and genes encoding intracellular Ca(2+) transport regulatory proteins (Atp2a2 and Calm1) and some cardiac muscle proteins (Myh6, Myl2, Actc1, Tnni3, Tnn2, and Tnnc1) were downregulated in ZDF heart compared with control heart. A change in the expression of genes encoding myosin heavy chain and L-type Ca(2+) channel proteins might partly underlie alterations in the time course of contraction and Ca(2+) transients in ventricular myocytes from ZDF rats.