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Hypoxia can occur in pancreatic islets in type 2 diabetes mellitus. Pancreatic stellate cells (PSCs) are activated during hypoxia. Here we aimed to investigate whether PSCs within the islet are also activated in hypoxia, causing β-cell injury.
Islet and primary PSCs were isolated from Sprague Dawley rats, and cultured in normoxia (21% O2) or hypoxia (1% O2). The expression of α-smooth muscle actin (α-SMA), as measured by immunostaining and Western blotting, was used as a marker of PSC activation. Conditioned media (hypoxia-CM) were obtained from PSCs cultured in hypoxia.
Islets and PSCs cultured in hypoxia exhibited higher expressions of α-SMA than did those cultured in normoxia. Hypoxia increased the production of reactive oxygen species. The addition of N-acetyl-L-cysteine, an antioxidant, attenuated the hypoxia-induced PSC activation in islets and PSCs. Islets cultured in hypoxia-CM showed a decrease in cell viability and an increase in apoptosis.
PSCs within the islet are activated in hypoxia through oxidative stress and promote islet cell death, suggesting that hypoxia-induced PSC activation may contribute to β-cell loss in type 2 diabetes mellitus.
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Impaired β-cell function is the key pathophysiology of type 2 diabetes mellitus, and chronic exposure of nutrient excess could lead to this tragedy. For preserving β-cell function, it is essential to understand the cause and mechanisms about the progression of β-cells failure. Glucotoxicity, lipotoxicity, and glucolipotoxicity have been suggested to be a major cause of β-cell dysfunction for decades, but not yet fully understood. Fatty acid translocase cluster determinant 36 (CD36), which is part of the free fatty acid (FFA) transporter system, has been identified in several tissues such as muscle, liver, and insulin-producing cells. Several studies have reported that induction of CD36 increases uptake of FFA in several cells, suggesting the functional interplay between glucose and FFA in terms of insulin secretion and oxidative metabolism. However, we do not currently know the regulating mechanism and physiological role of CD36 on glucolipotoxicity in pancreatic β-cells. Also, the downstream and upstream targets of CD36 related signaling have not been defined. In the present review, we will focus on the expression and function of CD36 related signaling in the pancreatic β-cells in response to hyperglycemia and hyperlipidemia (ceramide) along with the clinical studies on the association between CD36 and metabolic disorders.
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Cardiovascular diseases represent the leading cause of death and moderate physical exercise is associated with a reduction in cardiovascular risk. The aim of the study was to evaluate the correlation between the amount of exercise recorded daily by a wearable gravitometer for 3 months and selected biochemical and clinical parameters. Nineteen sedentary type 2 diabetics were recruited and distributed into three homogenous groups, low, medium, and high exercise, according to the level of physical exercise monitored and expressed as MOVEs. Data showed an inverse correlation between MOVEs and oxidative stress indexes and a significant improvement in paraoxonase-1 activities and endothelial functionality. Decrease of visceral/total adipose tissue ratio, systolic blood pressure and a down-regulation of the inflammatory microRNA-146a in high exercise group were observed. Finally, a decrease of glycosylated hemoglobin and an up-regulation of the angiogenic microRNA-130a in medium exercise one was obtained. In this study, precise daily monitoring permitted to underline the importance of the amount of physical activity to counteract some cardiovascular risk factors persisting in diabetes. Finally, it identifies new microRNA biomarkers for future investigation on the same topic.
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Chronic exposure to elevated levels of free fatty acids contributes to pancreatic β-cell dysfunction. Although it is well known that metformin induces cellular energy depletion and a concomitant activation of AMP-activated protein kinase (AMPK) through inhibition of the respiratory chain, previous studies have shown inconsistent results with regard to the action of metformin on pancreatic β-cells. We therefore examined the effects of metformin on pancreatic β-cells under lipotoxic stress.
NIT-1 cells and mouse islets were exposed to palmitate and treated with 0.05 and 0.5 mM metformin. Cell viability, glucose-stimulated insulin secretion, cellular adenosine triphosphate, reactive oxygen species (ROS) levels and Rho kinase (ROCK) activities were measured. The phosphorylation of AMPK was evaluated by Western blot analysis and mRNA levels of endoplasmic reticulum (ER) stress markers and NADPH oxidase (NOX) were measured by real-time quantitative polymerase chain reaction analysis.
We found that metformin has protective effects on palmitate-induced β-cell dysfunction. Metformin at a concentration of 0.05 mM inhibits NOX and suppresses the palmitate-induced elevation of ER stress markers and ROS levels in a AMPK-independent manner, whereas 0.5 mM metformin inhibits ROCK activity and activates AMPK.
This study suggests that the action of metformin on β-cell lipotoxicity was implemented by different molecular pathways depending on its concentration. Metformin at a usual therapeutic dose is supposed to alleviate lipotoxic β-cell dysfunction through inhibition of oxidative stress and ER stress.
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Chronic hyperglycemia has deleterious effects on pancreatic β-cell function and turnover. Recent studies support the view that cyclin-dependent kinase 5 (CDK5) plays a role in β-cell failure under hyperglycemic conditions. However, little is known about how CDK5 impair β-cell function. Myricetin, a natural flavonoid, has therapeutic potential for the treatment of type 2 diabetes mellitus. In this study, we examined the effect of myricetin on high glucose (HG)-induced β-cell apoptosis and explored the relationship between myricetin and CDK5.
To address this question, we subjected INS-1 cells and isolated rat islets to HG conditions (30 mM) in the presence or absence of myricetin. Docking studies were conducted to validate the interaction between myricetin and CDK5. Gene expression and protein levels of endoplasmic reticulum (ER) stress markers were measured by real-time reverse transcription polymerase chain reaction and Western blot analysis.
Activation of CDK5 in response to HG coupled with the induction of ER stress via the down regulation of sarcoendoplasmic reticulum calcium ATPase 2b (
Myricetin protects the β-cells against HG-induced apoptosis by inhibiting ER stress, possibly through inactivation of CDK5 and consequent upregulation of PDX1 and SERCA2b.
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Chronic endoplasmic reticulum (ER) stress culminating in proteotoxicity contributes to the development of insulin resistance and progression to type 2 diabetes mellitus. Pharmacologic interventions targeting several different nuclear receptors have emerged as potential treatments for insulin resistance. The mechanistic basis for these antidiabetic effects has primarily been attributed to multiple metabolic and inflammatory functions. Here we review recent advances in our understanding of the association of ER stress with insulin resistance and the role of nuclear receptors in promoting ER stress resolution and improving insulin resistance in the liver.
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Oxidative stress is known to be associated with progression of diabetic kidney disease. Ceruloplasmin acts as a pro-oxidant under conditions of severe oxidative stress. Thus, we conducted a longitudinal observational study to evaluate whether the serum ceruloplasmin level is a predictive biomarker for progression of diabetic nephropathy.
A total of 643 Korean men with type 2 diabetes mellitus were enrolled. Serum ceruloplasmin was measured using a nephelometric method. Progression of diabetic nephropathy was defined as transition in albuminuria class (i.e., normoalbuminuria to microalbuminuria, microalbuminuria to macroalbuminuria, or normoalbuminuria to macroalbuminuria) and/or a greater than 2-fold increase of serum creatinine at follow-up compared with the baseline value.
During the follow-up period (median, 2.7 years; range, 0.3 to 4.4 years), 49 of 643 patients (7.6%) showed the progression of diabetic nephropathy and three patients (0.5%) developed end-stage renal disease. Baseline ceruloplasmin levels were higher in the progressors than in the nonprogressors (262.6±40.9 mg/L vs. 233.3±37.8 mg/L,
Baseline serum ceruloplasmin is an independent predictive factor for the progression of diabetic nephropathy in patients with type 2 diabetes mellitus.
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Diabetic cardiomyopathy (DCM), as one of the major cardiac complications in diabetic patients, is known to related with oxidative stress that is due to a severe imbalance between reactive oxygen species (ROS) and/or reactive nitrogen species (RNS) generation and their clearance by antioxidant defense systems. Transcription factor nuclear factor NF-E2-related factor 2 (Nrf2) plays an important role in maintaining the oxidative homeostasis by regulating multiple downstream antioxidants. Diabetes may up-regulate several antioxidants in the heart as a compensative mechanism at early stage, but at late stage, diabetes not only generates extra ROS and/or RNS but also impairs antioxidant capacity in the heart, including Nrf2. In an early study, we have established that Nrf2 protect the cardiac cells and heart from high level of glucose
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Fibroblast growth factor 21 (FGF21) is an endocrine hormone that is primarily expressed in the liver and exerts beneficial effects on obesity and related metabolic diseases. In addition to its remarkable pharmacologic actions, the physiological roles of FGF21 include the maintenance of energy homeostasis in the body in conditions of metabolic or environmental stress. The expression of FGF21 is induced in multiple organs in response to diverse physiological or pathological stressors, such as starvation, nutrient excess, autophagy deficiency, mitochondrial stress, exercise, and cold exposure. Thus, the FGF21 induction caused by stress plays an important role in adaptive response to these stimuli. Here, we highlight our current understanding of the functional importance of the induction of FGF21 by diverse stressors as a feedback mechanism that prevents excessive stress.
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We aimed to quantify stress-induced hyperglycemia and differentiate the glucose response between normal animals and those with diabetes. We also examined the pattern in glucose fluctuation induced by stress according to type of diabetes.
To load psychological stress on animal models, we used a predator stress model by exposing rats to a cat for 60 minutes and measured glucose level from the beginning to the end of the test to monitor glucose fluctuation. We induced type 1 diabetes model (T1D) for ten Sprague-Dawley rats using streptozotocin and used five Otsuka Long-Evans Tokushima Fatty rats as obese type 2 diabetes model (OT2D) and 10 Goto-Kakizaki rats as nonobese type 2 diabetes model (NOT2D). We performed the stress loading test in both the normal and diabetic states and compared patterns of glucose fluctuation among the three models. We classified the pattern of glucose fluctuation into A, B, and C types according to speed of change in glucose level.
Increase in glucose, total amount of hyperglycemic exposure, time of stress-induced hyperglycemia, and speed of glucose increase were significantly increased in all models compared to the normal state. While the early increase in glucose after exposure to stress was higher in T1D and NOT2D, it was slower in OT2D. The rate of speed of the decrease in glucose level was highest in NOT2D and lowest in OT2D.
The diabetic state was more vulnerable to stress compared to the normal state in all models, and the pattern of glucose fluctuation differed among the three types of diabetes. The study provides basic evidence for stress-induced hyperglycemia patterns and characteristics used for the management of diabetes patients.
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Numerous studies have established a link between autophagy and aging; however, the relationship has not been clearly defined. Aging is a very complex process caused by the accumulation of various factors due to the gradual failure of cellular maintenance. Recent studies have shown that autophagy reduces the stress responses induced by starvation, reactive oxygen species, and the accumulation of intracellular proteins and organelles through cytoprotection, clearance of damaged mitochondria, and lysosomal degradation. Here, we summarize our current understanding of the relationship between autophagy and the aging process.
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