Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011860 (type 2 diabetes)
 57,723 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The resistance to insulin (insulin resistance, IR) is a common feature and a possible link between such frequent disorders as non-insulin dependent diabetes mellitus (NIDDM), hypertension and obesity. Pharmacological amelioration of IR and understanding its pathophysiology are therefore essential for successful management of these disorders. In this review, we will discuss the mechanisms of action of thiazolidinediones (TDs), a new family of insulin-sensitizing agents. Experimental studies of various models of IR and an increasing number of clinical studies have shown that TDs normalize a wide range of metabolic abnormalities associated with IR. By improving insulin sensitivity in skeletal muscles, the adipose tissue and hepatocytes, TDs reduce fasting hyperglycaemia and insulinaemia. Furthermore, TDs markedly influence lipid metabolism--they decrease plasma triglyceride, free fatty acid and LDL-cholesterol levels, and increase plasma HDL-cholesterol concentrations. Although TDs do not stimulate insulin secretion, they improve the secretory response of beta cells to insulin secretagogues. TDs act at various levels of glucose and lipid metabolism--ameliorate some defects in the signalling cascade distal to the insulin receptor and improve glucose uptake in insulin-resistant tissues via increased expression of glucose transporters GLUT1 and GLUT4. TDs also activate glycolysis in hepatocytes, oppose intracellular actions of cyclic AMP, and increase intracellular magnesium levels. TDs bind to peroxisome proliferator activating receptors gamma (PPAR gamma), members of the steroid/thyroid hormone nuclear receptor superfamily of transcription factors involved in adipocyte differentiation and glucose and lipid homeostasis. Activation of PPAR gamma results in the expression of adipocyte-specific genes and differentiation of various cell types in mature adipocytes capable of active glucose uptake and energy storage in the form of lipids. Furthermore, TDs inhibit the pathophysiological effects exerted by tumour-necrosis factor (TNF alpha), a cytokine involved in the pathogenesis of IR. These effects are most likely also mediated by stimulation of PPAR gamma. In mature adipocytes, PPAR gamma stimulation inhibits stearoyl-CoA desaturase 1 (SCD1) enzyme activity resulting in a change of cell membrane fatty acid composition. Apart from their metabolic actions, TDs modulate cardiovascular function and morphology independently of the insulin-sensitizing effects. TDs decrease blood pressure in various models of hypertension as well as in hypertensive insulin-resistant patients, and inhibit proliferation, hypertrophy and migration of vascular smooth muscle cells (VSMC) induced by growth factors. These processes are considered to be crucial in the development of vascular remodelling, atherosclerosis and diabetic organ complications. TDs induce vasodilation by blockade of Ca2+ mobilisation from intracellular stores and by inhibition of extracellular calcium uptake via L-channels. Furthermore, TDs interfere with pressor systems (catecholamines, renin-angiotensin system) and enhance endothelium-dependent vasodilation. A key role of TDs effects in vascular remodelling is played by inhibition of the mitogen-activated protein (MAP) kinase pathway. This signalling pathway is important for VSMC growth and migration in response to stimulation with tyrosine-kinase dependent growth factors. In addition to the vasoprotective mechanisms mentioned above, troglitazone, the latest representative of this pharmacological group, possesses antioxidant actions comparable to vitamin E. In summary, TDs have the unique ability to attack mechanisms responsible for metabolic alterations as well as for vascular abnormalities characteristic for IR. Therefore, TDs represent a powerful research tool in attempts to find a common denominator underlying the pathophysiology of the metabolic syndrome X. A recently reported link between MAP kinase signalling pathway and PPAR gamma
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PMID:Thiazolidinediones--tools for the research of metabolic syndrome X. 980 67

Hypertension often complicates type 2 diabetes mellitus, and angiotensin converting enzyme inhibitor treatment has been shown to improve insulin resistance in such cases. However, the effect of angiotensin II type-1 (AT(1)) receptor antagonists on insulin resistance is still controversial. To gain further information on this effect, we examined the effect of losartan on insulin resistance in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of type 2 diabetes mellitus. Losartan administration alone lowered systolic blood pressure, but did not improve oral glucose tolerance test or insulin resistance in OLETF rats. However, the administration of losartan with exercise significantly improved both systolic blood pressure and insulin resistance relative to control OLETF rats. On the other hand, losartan treatment, regardless of exercise, increased glucose uptake in excised soleus muscle and fat cells. To explore the beneficial effect of losartan on skeletal muscle glucose uptake, we examined intracellular signaling of soleus muscle. Although Akt activity and glucose transporter type 4 (GLUT4) expressions were not affected by losartan with or without exercise, extracellular signal-regulated kinase (ERK1/2) and p38 mitogen-activated protein (MAP) kinase activities were increased by both interventions. These results indicate that angiotensin AT(1) receptor antagonist improved local insulin resistance, but not systemic insulin resistance. These findings may explain the controversy over the effect of angiotensin AT(1) receptor antagonists on insulin resistance in clinical use. The enhancing effect of angiotensin AT(1) receptor antagonist on skeletal muscle glucose uptake may be attributable to MAP kinase activation or other mechanisms rather than phosphatidylinositol 3-kinase activation.
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PMID:Effects of losartan in combination with or without exercise on insulin resistance in Otsuka Long-Evans Tokushima Fatty rats. 1171 Oct 55

Serine and threonine kinases may contribute to insulin resistance and the development of type 2 diabetes. To test the potential for members of the mitogen-activated protein (MAP) kinase family to contribute to type 2 diabetes, we examined basal and insulin-stimulated Erk 1/2, JNK, and p38 phosphorylation in adipocytes isolated from healthy and type 2 diabetic individuals. Maximal insulin stimulation increased the phosphorylation of Erk 1/2 and JNK in healthy control subjects but not type 2 diabetic patients. Insulin stimulation did not increase p38 phosphorylation in either healthy control subjects or type 2 diabetic patients. In type 2 diabetic adipocytes, the basal phosphorylation status of these MAP kinases was significantly elevated and was associated with decreased IRS-1 and GLUT4 in these fat cells. To determine whether MAP kinases were involved in the downregulation of IRS-1 and GLUT4 protein levels, selective inhibitors were used to inhibit these MAP kinases in 3T3-L1 adipocytes treated chronically with insulin. Inhibition of Erk 1/2, JNK, or p38 had no effect on insulin-stimulated reduction of IRS-1 protein levels. However, inhibition of the p38 pathway prevented the insulin-stimulated decrease in GLUT4 protein levels. In summary, type 2 diabetes is associated with an increased basal activation of the MAP kinase family. Furthermore, upregulation of the p38 pathway might contribute to the loss of GLUT4 expression observed in adipose tissue from type 2 diabetic patients.
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PMID:Enhanced basal activation of mitogen-activated protein kinases in adipocytes from type 2 diabetes: potential role of p38 in the downregulation of GLUT4 expression. 1260 2

Although it is known that diabetic nephropathy is accelerated by hypertension, the mechanisms involved in this process are not clear. In this study we aimed to clarify these mechanisms using male Wistar fatty rats (WFR) as a type 2 diabetic model and male Wistar lean rats (WLR) as a control. Each group was fed a normal or high sodium diet from the age of 6 to 14 weeks. We determined the blood pressure and urinary albumin excretion (UAE). At the end of the study, the expressions of mitogen-activated protein kinases (MAPK) and transforming growth factor-beta1 (TGF-beta1) were examined in the isolated glomeruli by Western blot analysis, and the number of glomerular lesions was determined by conventional histology. High sodium load caused hypertension and a marked increase in UAE in the WFR but not in the WLR. Glomerular volume was increased in the hypertensive WFR. There was no difference among the four groups in the expression of c-Jun-NH2-terminal kinase (JNK). In contrast, the expressions of extracellular signal-regulated kinase 1/2 (ERK1/2) and its upstream regulator, MAPK/ERK kinase 1 (MEK1), were augmented in the hypertensive WFR. Expression of p38 MAPK was increased in the normotensive WFR, and further enhanced in the hypertensive WFR. Moreover, administration of high sodium load to WFR augmented the expression of TGF-beta1. In conclusion, systemic hypertension in WFR accelerates the diabetic nephropathy in type 2 diabetes via MEK-ERK and p38 MAPK cascades. TGF-beta1 is also involved in this mechanism.
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PMID:Hypertension accelerates diabetic nephropathy in Wistar fatty rats, a model of type 2 diabetes mellitus, via mitogen-activated protein kinase cascades and transforming growth factor-beta1. 1273 3

Lectin-like oxidized LDL receptor-1 (LOX-1) is a newly identified receptor for oxidized LDL that is expressed by vascular cells. LOX-1 is upregulated in aortas of diabetic rats and thus may contribute to the pathogenesis of human diabetic atherosclerosis. In this study, we examined the regulation of human monocyte-derived macrophage (MDM) LOX-1 expression by high glucose and the role of LOX-1 in glucose-induced foam cell formation. Incubation of human MDMs with glucose (5.6 to 30 mmol/L) enhanced, in a dose- and time-dependent manner, LOX-1 gene and protein expression. Induction of LOX-1 gene expression by high glucose was abolished by antioxidants, protein kinase C (PKC), mitogen-activated protein kinases (MAPKs), nuclear factor-kappaB (NF-kappaB), and activated protein-1 (AP-1) inhibitors. In human MDMs cultured with high glucose, increased expression of PKCbeta2 and enhanced phosphorylation of extracellular signal-regulated protein kinase 1/2 was observed. Activation of these kinases was inhibited by the antioxidant N-acetyl-L-cysteine (NAC) and by the PKCbeta inhibitor LY379196. High glucose also enhanced the binding of nuclear proteins extracted from human MDMs to the NF-kappaB and AP-1 regulatory elements of the LOX-1 gene promoter. This effect was abrogated by NAC and PKC/MAPK inhibitors. Finally, high glucose induced human macrophage-derived foam cell formation through a LOX-1-dependent pathway. Overall, these results demonstrate that high glucose concentrations enhance LOX-1 expression in human MDMs and that this effect is associated with foam cell formation. Pilot data showing that MDMs of patients with type 2 diabetes overexpress LOX-1 support the relevance of this work to human diabetic atherosclerosis.
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PMID:Glucose enhances human macrophage LOX-1 expression: role for LOX-1 in glucose-induced macrophage foam cell formation. 1500 26

Both type 1 and type 2 diabetes can lead to altered retinal microvascular function and diabetic retinopathy. Insulin signaling may also play a role in this process, and mice lacking insulin receptors in endothelial cells are protected from retinal neovascularization. To define the role of diabetes in retinal function, we compared insulin signaling in the retinal vasculature of mouse models of type 1 (streptozotocin) and type 2 diabetes (ob/ob). In streptozotocin mice, in both retina and liver, insulin receptor (IR) and insulin receptor substrate (IRS)-2 protein and tyrosine phosphorylation were increased by insulin, while IRS-1 protein and its phosphorylation were maintained. By contrast, in ob/ob mice, there was marked down-regulation of IR, IRS-1, and IRS-2 protein and phosphorylation in liver; these were maintained or increased in retina. In both mice, Phosphatidylinositol 3,4,5-trisphosphate generation by acute insulin stimulation was enhanced in retinal endothelial cells. On the other hand, protein levels and phosphorylation of PDK1 and Akt were decreased in retina of both mice. Interestingly, phosphorylation of p38 mitogen-activated protein kinase and ERK1 were responsive to insulin in retina of both mice but were unresponsive in liver. HIF-1alpha and vascular endothelial growth factor were increased and endothelial nitric-oxide synthase was decreased in retina. These observations indicate that, in both insulin-resistant and insulin-deficient diabetic states, there are alterations in insulin signaling, such as impaired PDK/Akt responses and enhanced mitogen-activated protein kinases responses that could contribute to the retinopathy. Furthermore, insulin signaling in retinal endothelial cells is differentially altered in diabetes and is also differentially regulated from insulin signaling in classical target tissues such as liver.
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PMID:Altered insulin signaling in retinal tissue in diabetic states. 1520 Dec 86

Recent reports have suggested that PKCepsilon contributes to systemic insulin resistance, and is involved in the pathogenesis of type 2 diabetes, however, the exact mechanism is still unknown. To elucidate the possible involvement of PKCepsilon in the pathogenesis of type 2 diabetes, we examined the role of PKCepsilon in differentiated adipocytes using mouse 3T3-L1 adipocytes. We found that the over-expression of PKCepsilon resulted in the increase of IL-6 expression in differentiated adipocytes. This PKCepsilon-induced IL-6 expression could be completely inhibited by U0126, an inhibitor of mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase. We also demonstrated that PKCepsilon increased the transcriptional activity of Est-like transcription factor (Elk-1) as well as the DNA-binding activity of activator protein-1 (AP-1) in differentiated 3T3-L1 adipocytes. These results suggest that PKCepsilon is able to increase IL-6 expression via the ERK-AP-1 pathway in differentiated adipocytes, and that PKCepsilon is involved in systemic insulin resistance by regulating plasma IL-6 concentrations.
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PMID:PKCepsilon induces interleukin-6 expression through the MAPK pathway in 3T3-L1 adipocytes. 1564 4

Although the target of hepatitis C virus (HCV) infection is the liver, it has become progressively more evident that HCV can induce diseases in numerous organs. Recently, much attention has been drawn to metabolic disorders in HCV infection. Initially, hepatic steatosis and disturbances in lipid metabolism were found to be characteristic of HCV infection, and, subsequently, a correlation was noted between HCV infection and diabetes. It is now evident that HCV, by itself, can induce insulin resistance by way of disturbing the intracellular signaling pathway of insulin by the function of HCV core protein. Insulin resistance, caused by HCV infection, evolves to type 2 diabetes when superimposed on a high-fat diet and obesity. The fact that HCV infection induces insulin resistance by the virus itself may influence the progression of chronic hepatitis and open up novel therapeutic approaches. When hepatitis C is compared with nonalcoholic steatohepatitis (NASH), there are a number of similarities and several differences. From the metabolic aspect, hepatitis C resembles NASH in numerous features, such as the presence of steatosis, serum dyslipidemia, and oxidative stress in the liver, suggesting that hepatitis C is a steatohepatitis. In contrast, there are noticeable differences between hepatitis C and NASH, in that HCV modulates cellular gene expression and intracellular signal transduction, including the activation of mitogen-activated protein (MAP) kinase and transcription factor activator protein (AP)-1, while such details have not been noted for NASH. This difference may explain the markedly higher incidence of HCC development in chronic hepatitis C compared with that in NASH. HCV infection needs to be viewed not only as a liver disease but also as a metabolic disease, and this viewpoint could open up a novel way to the molecular understanding of the pathogenesis of hepatitis C, as a virus-associated steatohepatitis (VASH).
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PMID:Metabolic aspects of hepatitis C viral infection: steatohepatitis resembling but distinct from NASH. 1586 69

Adipocyte cell proliferation is an important process in body fat mass development in obesity. Adiponectin or Acrp30 is an adipocytokine exclusively expressed and secreted by adipose tissue that regulates lipid and glucose metabolism and plays a key role in body weight regulation and homeostasis. Adiponectin mRNA expression in adipose tissue and plasma level of adiponectin are decreased in obesity and type 2 diabetes. In obese rodents, the selective CB(1) receptor antagonist rimonabant reduces food intake and body weight and improves lipid and glucose parameters. We have reported previously that rimonabant stimulated adiponectin mRNA expression in adipose tissue of obese fa/fa rats, by a direct effect on adipocytes. We report here that rimonabant (10-400 nM) inhibits cell proliferation of cultured mouse 3T3 F442A preadipocytes in a concentration-dependent manner. In parallel to this inhibitory effect on preadipocyte cell proliferation, rimonabant (25-100 nM) stimulates mRNA expression and protein levels of two late markers of adipocyte differentiation (adiponectin and glyceraldehyde-3-phosphate dehydrogenase) with a maximal effect at 100 nM, without inducing the accumulation of lipid droplets. Furthermore, treatment of mouse 3T3 F442A preadipocytes with rimonabant (100 nM) inhibits basal and serum-induced p42/44 mitogen-activated protein (MAP) kinase activity. These results suggest that inhibition of MAP kinase activity by rimonabant may be one of mechanisms involved in the inhibition of 3T3 F442A preadipocyte cell proliferation and stimulation of adiponectin and GAPDH expression. The inhibition of preadipocyte cell proliferation and the induction of adipocyte late "maturation" may participate in rimonabant-induced antiobesity effects, particularly the reduction of body fat mass.
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PMID:The cannabinoid CB1 receptor antagonist rimonabant (SR141716) inhibits cell proliferation and increases markers of adipocyte maturation in cultured mouse 3T3 F442A preadipocytes. 1628 21

Type 1 and type 2 diabetes are characterized by progressive beta-cell failure. Apoptosis is probably the main form of beta-cell death in both forms of the disease. It has been suggested that the mechanisms leading to nutrient- and cytokine-induced beta-cell death in type 2 and type 1 diabetes, respectively, share the activation of a final common pathway involving interleukin (IL)-1beta, nuclear factor (NF)-kappaB, and Fas. We review herein the similarities and differences between the mechanisms of beta-cell death in type 1 and type 2 diabetes. In the insulitis lesion in type 1 diabetes, invading immune cells produce cytokines, such as IL-1beta, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma. IL-1beta and/or TNF-alpha plus IFN-gamma induce beta-cell apoptosis via the activation of beta-cell gene networks under the control of the transcription factors NF-kappaB and STAT-1. NF-kappaB activation leads to production of nitric oxide (NO) and chemokines and depletion of endoplasmic reticulum (ER) calcium. The execution of beta-cell death occurs through activation of mitogen-activated protein kinases, via triggering of ER stress and by the release of mitochondrial death signals. Chronic exposure to elevated levels of glucose and free fatty acids (FFAs) causes beta-cell dysfunction and may induce beta-cell apoptosis in type 2 diabetes. Exposure to high glucose has dual effects, triggering initially "glucose hypersensitization" and later apoptosis, via different mechanisms. High glucose, however, does not induce or activate IL-1beta, NF-kappaB, or inducible nitric oxide synthase in rat or human beta-cells in vitro or in vivo in Psammomys obesus. FFAs may cause beta-cell apoptosis via ER stress, which is NF-kappaB and NO independent. Thus, cytokines and nutrients trigger beta-cell death by fundamentally different mechanisms, namely an NF-kappaB-dependent mechanism that culminates in caspase-3 activation for cytokines and an NF-kappaB-independent mechanism for nutrients. This argues against a unifying hypothesis for the mechanisms of beta-cell death in type 1 and type 2 diabetes and suggests that different approaches will be required to prevent beta-cell death in type 1 and type 2 diabetes.
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PMID:Mechanisms of pancreatic beta-cell death in type 1 and type 2 diabetes: many differences, few similarities. 1630 47


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