Thermogenesis-independent metabolic benefits conferred by isocaloric intermittent fasting in ob/ob mice.

Intermittent fasting (IF) is an effective dietary intervention to counteract obesity-associated metabolic abnormalities. Previously, we and others have highlighted white adipose tissue (WAT) browning as the main underlying mechanism of IF-mediated metabolic benefits. However, whether IF retains its efficacy in different models, such as genetically obese/diabetic animals, is unknown. Here, leptin-deficient ob/ob mice were subjected to 16 weeks of isocaloric IF, and comprehensive metabolic phenotyping was conducted to assess the metabolic effects of IF. Unlike our previous study, isocaloric IF-subjected ob/ob animals failed to exhibit reduced body weight gain, lower fat mass, or decreased liver lipid accumulation. Moreover, isocaloric IF did not result in increased thermogenesis nor induce WAT browning in ob/ob mice. These findings indicate that isocaloric IF may not be an effective approach for regulating body weight in ob/ob animals, posing the possible limitations of IF to treat obesity. However, despite the lack of improvement in insulin sensitivity, isocaloric IF-subjected ob/ob animals displayed improved glucose tolerance as well as higher postprandial insulin level, with elevated incretin expression, suggesting that isocaloric IF is effective in improving nutrient-stimulated insulin secretion. Together, this study uncovers the insulinotropic effect of isocaloric IF, independent of adipose thermogenesis, which is potentially complementary for the treatment of type 2 diabetes.

CD36 mediates albumin transcytosis by dermal but not lung microvascular endothelial cells: role in fatty acid delivery.

In healthy blood vessels, albumin crosses the endothelium to leave the circulation by transcytosis. However, little is known about the regulation of albumin transcytosis or how it differs in different tissues; its physiological purpose is also unclear. Using total internal reflection fluorescence microscopy, we quantified transcytosis of albumin across primary human microvascular endothelial cells from both lung and skin. We then validated our in vitro findings using a tissue-specific knockout mouse model. We observed that albumin transcytosis was saturable in the skin but not the lung microvascular endothelial cells, implicating a receptor-mediated process. We identified the scavenger receptor CD36 as being both necessary and sufficient for albumin transcytosis across dermal microvascular endothelium, in contrast to the lung where macropinocytosis dominated. Mutations in the apical helical bundle of CD36 prevented albumin internalization by cells. Mice deficient in CD36 specifically in endothelial cells exhibited lower basal permeability to albumin and less basal tissue edema in the skin but not in the lung. Finally, these mice also exhibited a smaller subcutaneous fat layer despite having identical total body weights and circulating fatty acid levels as wild-type animals. In conclusion, CD36 mediates albumin transcytosis in the skin but not the lung. Albumin transcytosis may serve to regulate fatty acid delivery from the circulation to tissues.

Cilostazol protects hepatocytes against alcohol-induced apoptosis via activation of AMPK pathway.

Alcoholic liver disease (ALD) is a worldwide health problem and hepatocyte apoptosis has been associated with the development/progression of ALD. However, no definite effective pharmacotherapy for ALD is currently available. Cilostazol, a selective type III phosphodiesterase inhibitor has been shown to protect hepatocytes from ethanol-induced apoptosis. In the present study, the underlying mechanisms for the protective effects of cilostazol were examined. Primary rat hepatocytes were treated with ethanol in the presence or absence of cilostazol. Cell viability and intracellular cAMP were measured. Apoptosis was detected by Hoechst staining, TUNEL assay, and caspase-3 activity assay. The roles of cAMP and AMP-activated protein kinase (AMPK) pathways in the action of CTZ were explored using pharmacological inhibitors and siRNAs. Liver from mice received ethanol (5 g/kg body weight) by oral gavage following cilostazol treatment intraperitoneally was obtained for measurement of apoptosis and activation of AMPK pathway. Cilostazol inhibited ethanol-induced hepatocyte apoptosis and potentiated the increases in cAMP level induced by forskolin. However, the anti-apoptotic effect of cilostazol was not reversed by an inhibitor of adenylyl cyclase. Interestingly, cilostazol activated AMPK and increased the level of LC3-II, a marker of autophagy. The inhibition of AMPK abolished the effects of cilostazol on LC3-II expression and apoptosis. Moreover, the inhibition of LKB1 and CaMKK2, upstream kinases of AMPK, dampened cilostazol-inhibited apoptosis as well as AMPK activation. In conclusion, cilostazol protected hepatocytes from apoptosis induced by ethanol mainly via AMPK pathway which is regulated by both LKB1 and CaMKK2. Our results suggest that cilostazol may have potential as a promising therapeutic drug for treatment of ALD.

Evaluation of tissue Doppler ultrasonographic and strain imaging for assessment of myocardial dysfunction in dogs with type 1 diabetes mellitus.

OBJECTIVE To investigate cardiac structural and functional changes by tissue Doppler imaging (TDI) and strain imaging in dogs with spontaneous type 1 diabetes mellitus. ANIMALS 30 client-owned dogs, of which 10 had normotensive type 1 diabetes mellitus and 20 were healthy. PROCEDURES All dogs underwent physical examination, laboratory analyses, standard echocardiography, and TDI. RESULTS On TDI and strain imaging, transmitral peak early diastolic velocity (E)-to-tissue Doppler-derived peak early diastolic velocity at basal segment (E') of septum ratio, E:lateral E' ratio, and septal tissue Doppler-derived peak late diastolic velocity at basal segment (A') were significantly higher and the septal E':A' ratio and lateral longitudinal strain were significantly lower for diabetic dogs than for control dogs. Furthermore, in diabetic dogs, serum glucose and fructosamine concentrations after a 12-hour period of food withholding were positively correlated with regional systolic functional variables (septal and lateral longitudinal strain) and left ventricular filling pressure indices (E:septal E' and E:lateral E' ratios) but were negatively correlated with diastolic functional variables (E:transmitral peak late diastolic velocity and septal and lateral E':A' ratios). CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that myocardial function in diabetic dogs may be altered before the development of clinical heart-associated signs and that the change may be more readily detected by TDI and strain imaging than by conventional echocardiography. In addition, findings indicated that hyperglycemia could have detrimental effects on myocardial function, independent of hypertension, other cardiac diseases, and left ventricular hypertrophy, in dogs with type 1 diabetes.

Rate of left ventricular pressure change by Doppler echocardiography in dogs with chronic mitral valve disease at different stages of congestive heart failure.

Although the major pathological feature of chronic mitral valve disease is mitral regurgitation, myocardial dysfunction has been suggested to be present in dogs with chronic mitral valve disease. However, accurate assessment of myocardial function remains challenging. Doppler-derived rate of left ventricular pressure change is a simple, less load-dependent method for evaluating myocardial function. We aimed to evaluate Doppler-derived rate of left ventricular pressure change for assessing myocardial function in different stages of dogs with chronic mitral valve disease. This analytical cross-sectional study recruited 55 client-owned dogs with chronic mitral valve disease prospectively. Based on physical examination, indirectly measured blood pressure, routine hematologic and biochemistry examinations, thoracic radiography, electrocardiography, and echocardiography, dogs were diagnosed as mitral valve disease and excluded for systemic diseases and other cardiac diseases. They were classified according to the International Small Animal Cardiac Health Council scales. Doppler-derived rates of left ventricular pressure rise and fall (dP/dt and -dP/dt) were analyzed by two investigators using continuous-wave Doppler imaging. Doppler-derived dP/dt was higher in dogs of class IIIa than in those of the other classes, whereas values of -dP/dt decreased significantly with the severity of congestive heart failure. The peak velocity of the early diastolic wave and -dP/dt were identified as independent predictors of congestive heart failure. Our findings suggested that Doppler-derived dP/dt and -dP/dt, used in combination with conventional echocardiographic variables, could allow a better understanding of myocardial dysfunction and a possibility for prediction of the risk of heart failure in dogs with chronic mitral valve disease.

Intermittent fasting promotes adipose thermogenesis and metabolic homeostasis via VEGF-mediated alternative activation of macrophage.

Intermittent fasting (IF), a periodic energy restriction, has been shown to provide health benefits equivalent to prolonged fasting or caloric restriction. However, our understanding of the underlying mechanisms of IF-mediated metabolic benefits is limited. Here we show that isocaloric IF improves metabolic homeostasis against diet-induced obesity and metabolic dysfunction primarily through adipose thermogenesis in mice. IF-induced metabolic benefits require fasting-mediated increases of vascular endothelial growth factor (VEGF) expression in white adipose tissue (WAT). Furthermore, periodic adipose-VEGF overexpression could recapitulate the metabolic improvement of IF in non-fasted animals. Importantly, fasting and adipose-VEGF induce alternative activation of adipose macrophage, which is critical for thermogenesis. Human adipose gene analysis further revealed a positive correlation of adipose VEGF-M2 macrophage-WAT browning axis. The present study uncovers the molecular mechanism of IF-mediated metabolic benefit and suggests that isocaloric IF can be a preventive and therapeutic approach against obesity and metabolic disorders.

Effect of exercise intensity on unfolded protein response in skeletal muscle of rat.

Endoplasmic reticulum (ER) stress, unfolded protein response (UPR), and mitochondrial biogenesis were assessed following varying intensities of exercise training. The animals were randomly assigned to receive either low- (LIT, n=7) or high intensity training (HIT, n=7), or were assigned to a control group (n=7). Over 5 weeks, the animals in the LIT were exercised on a treadmill with a 10° incline for 60 min at a speed of 20 m/min group, and in the HIT group at a speed of 34 m/min for 5 days a week. No statistically significant differences were found in the body weight, plasma triglyceride, and total cholesterol levels across the three groups, but fasting glucose and insulin levels were significantly lower in the exercise-trained groups. Additionally, no statistically significant differences were observed in the levels of PERK phosphorylation in skeletal muscles between the three groups. However, compared to the control and LIT groups, the level of BiP was lower in the HIT group. Compared to the control group, the levels of ATF4 in skeletal muscles and CHOP were significantly lower in the HIT group. The HIT group also showed increased PGC-1α mRNA expression in comparison with the control group. Furthermore, both of the trained groups showed higher levels of mitochondrial UCP3 than the control group. In summary, we found that a 5-week high-intensity exercise training routine resulted in increased mitochondrial biogenesis and decreased ER stress and apoptotic signaling in the skeletal muscle tissue of rats.