Adipose tissue inflammation is considered a major contributing factor in the development of obesity-associated insulin resistance and cardiovascular diseases. However, the cause of adipose tissue inflammation is presently unclear. The role of mitochondria in white adipocytes has long been neglected because of their low abundance. However, recent evidence suggests that mitochondria are essential for maintaining metabolic homeostasis in white adipocytes. In a series of recent studies, we found that mitochondrial function in white adipocytes is essential to the synthesis of adiponectin, which is the most abundant adipokine synthesized from adipocytes, with many favorable effects on metabolism, including improvement of insulin sensitivity and reduction of atherosclerotic processes and systemic inflammation. From these results, we propose a new hypothesis that mitochondrial dysfunction in adipocytes is a primary cause of adipose tissue inflammation and compared this hypothesis with a prevailing concept that “adipose tissue hypoxia” may underlie adipose tissue dysfunction in obesity. Recent studies have emphasized the role of the mitochondrial quality control mechanism in maintaining mitochondrial function. Future studies are warranted to test whether an inadequate mitochondrial quality control mechanism is responsible for mitochondrial dysfunction in adipocytes and adipose tissue inflammation.

Background: Ceramides are associated with metabolic complications including diabetic nephropathy in patients with diabetes. Recent studies have reported that podocytes play a pivotal role in the progression of diabetic nephropathy. Also, mitochondrial dysfunction is known to be an early event in podocyte injury. Thus, we tested the hypothesis that ceramide accumulation in podocytes induces mitochondrial damage through reactive oxygen species (ROS) production in patients with diabetic nephropathy. Methods: We used Otsuka Long Evans Tokushima Fatty (OLETF) rats and high-fat diet (HFD)-fed mice. We fed the animals either a control-or a myriocin-containing diet to evaluate the effects of the ceramide. Also, we assessed the effects of ceramide on intracellular ROS generation and on podocyte autophagy in cultured podocytes. Results: OLETF rats and HFD-fed mice showed albuminuria, histologic features of diabetic nephropathy, and podocyte injury, whereas myriocin treatment effectively treated these abnormalities. Cultured podocytes exposed to agents predicted to be risk factors (high glucose, high free fatty acid, and angiotensin II in combination [GFA]) showed an increase in ceramide accumulation and ROS generation in podocyte mitochondria. Pretreatment with myriocin reversed GFA-induced mitochondrial ROS generation and prevented cell death. Myriocin-pretreated cells were protected from GFA-induced disruption of mitochondrial integrity. Conclusion: We showed that mitochondrial ceramide accumulation may result in podocyte damage through ROS production. Therefore, this signaling pathway could become a pharmacological target to abate the development of diabetic kidney disease.

BackgroundEndogenous hyperinsulinemic hypoglycemia (EHH) is characterized by an inappropriately high plasma insulin level, despite a low plasma glucose level. Most of the EHH cases are caused by insulinoma, whereas nesidioblastosis and insulin autoimmune syndrome (IAS) are relatively rare.MethodsTo evaluate the relative frequencies of various causes of EHH in Korea, we retrospectively analyzed 84 patients who were diagnosed with EHH from 1998 to 2012 in a university hospital.ResultsAmong the 84 EHH patients, 74 patients (88%), five (6%), and five (6%) were diagnosed with insulinoma, nesidioblastosis or IAS, respectively. The most common clinical manifestation of EHH was neuroglycopenic symptoms. Symptom duration before diagnosis was 14.5 months (range, 1 to 120 months) for insulinoma, 1.0 months (range, 6 days to 7 months) for nesidioblastosis, and 2.0 months (range, 1 to 12 months) for IAS. One patient, who was diagnosed with nesidioblastosis in 2006, underwent distal pancreatectomy but was later determined to be positive for insulin autoantibodies. Except for one patient who was diagnosed in 2007, the remaining three patients with nesidioblastosis demonstrated severe hyperinsulinemia (157 to 2,719 µIU/mL), which suggests that these patients might have had IAS, rather than nesidioblastosis.ConclusionThe results of this study suggest that the prevalence of IAS may be higher in Korea than previously thought. Therefore, measurement of insulin autoantibody levels is warranted for EHH patients, especially in patients with very high plasma insulin levels.