Beta-cells in type 2 diabetes: a loss of function and mass

Transferring to insulin detemir from NPH insulin or insulin glargine in type 2 diabetes patients on basal-only therapy with oral antidiabetic drugs improves glycaemic control and reduces weight gain and risk of hypoglycaemia: 14-week follow-up data from PREDICTIVE

AIM

The aim of this study was to evaluate the safety and efficacy of insulin detemir in type 2 diabetes patients previously receiving NPH insulin (NPH group, n = 175) or insulin glargine (glargine group, n = 118) in combination with oral antidiabetic drugs (OADs).

METHODS

Patients were transferred to insulin detemir, while the OAD regimen and number of injections remained the same. The incidence of serious adverse drug reactions, including major hypoglycaemia, and haemoglobin A(1c) (HbA(1c)), fasting glucose, within-patient fasting glucose variability and body weight change were measured at 14 weeks.

RESULTS

Glycaemic control improved in both NPH (HbA(1c) = -0.2%, p < 0.05; fasting glucose -1.0 mmol/l, p < 0.0001) and glargine (HbA(1c) = -0.6%, p < 0.0001; fasting glucose -1.4 mmol/l, p < 0.0001) groups, including a reduction in fasting glucose variability (p < 0.01 for both). The incidence of total and nocturnal hypoglycaemia was reduced in both NPH and glargine groups. The incidence of major hypoglycaemia was low and did not change significantly during the follow-up period. Mean body weight was significantly reduced in the NPH (-0.7 kg, p < 0.01) and glargine (-0.5 kg, p < 0.05) groups.

CONCLUSIONS

These results indicate that in type 2 diabetes, transferring from other basal insulins to insulin detemir in combination with OADs was associated with improvements in glycaemic control, which were accompanied by a reduced risk of hypoglycaemia and a reduction in body weight.

Metabolic mechanisms of failure of intraportally transplanted pancreatic beta-cells in rats: role of lipotoxicity and prevention by leptin

The objective of this study was to determine whether the late failure of beta-cells in islets transplanted via the portal vein is caused by excess insulin-stimulated lipogenesis and lipotoxicity and, if so, whether the damage can be prevented by reducing lipogenesis surrounding the islets. Based on the premise that high portal vein levels of nutrients and incretins would stimulate hyperinsulinemia, thereby inducing intense lipogenesis in nearby hepatocytes, normal islets were transplanted into livers of syngeneic streptozotocin-induced diabetic recipients. Hydrolysis of the surrounding fat would flood the islet grafts with fatty acids that could damage and destroy the beta-cells. Reducing lipogenesis by leptin or caloric restriction should prevent or reduce the destruction. After a rise after transplantation, insulin levels gradually declined and hyperglycemia increased. Four weeks after transplantation mRNA of the lipogenic transcription factor, sterol regulatory element-binding protein-1c (SREBP-1c) and its lipogenic target enzymes were elevated in livers of these recipients, as was triacylglycerol content. Positive oil red O staining for lipids and immunostaining for SREBP-1 were observed in hepatocytes surrounding islets with damaged beta-cells. Leptin-induced lipopenia prevented and caloric restriction reduced steatosis, hyperglycemia, and apoptotic beta-cell destruction. Excessive SREBP-1c-mediated lipogenesis, induced in hepatocytes by insulin hypersecretion, is followed by beta-cell destruction in the grafts and reappearance of diabetes. Graft failure is prevented by blocking lipogenesis. The results suggest that strict antilipogenic intervention might improve outcomes after human islet transplantation.

Inflammatory process in type 2 diabetes: The role of cytokines

Population-based studies have shown strong relationship between inflammatory markers and metabolic disturbances, obesity, and atherosclerosis, whereas inflammation has been considered as a "common soil" between these clinical entities and type 2 diabetes (T2D). The accumulation of macrophages in adipose tissue (AT), the common origin of macrophages and adipocytes, the prevalent presence of peripheral mononuclear cells, and apoptotic beta cells by themselves seem to be the sources of inflammation present in T2D, since they generate the mediators of the inflammatory processes, namely cytokines. The main cytokines involved in the pathogenesis of T2D are interleukin-1beta (IL-1beta), with an action similar to the one present in type 1 diabetes, tumor necrosis factor-alpha (TNF-alpha), and IL-6, considered as the main regulators of inflammation, leptin, more recently introduced, and several others, such as monocyte chemoattractant protein-1, resistin, adiponectin, with either deleterious or beneficial effects in diabetic pathogenesis. The characterization of these molecules targeted diabetes treatment beyond the classical interventions with lifestyle changes and pharmaceutical agents, and toward the determination of specific molecular pathways that lead to low grade chronic inflammatory state mainly due to an immune system's unbalance.

Pro-survival role of gelsolin in mouse beta-cells

We have previously shown that the Ca(2+)-dependent actin-severing protein gelsolin plays an important role in regulated insulin secretion. The aim of this study was to determine the role of gelsolin in beta-cell survival as it has been shown to play a dual role in apoptosis in other cell types. MIN6 subclones B1 and C3, shown previously to express gelsolin at different levels (B1>>C3 cells), were used for this purpose. We demonstrate that B1 cells have lower levels of apoptosis and active caspase-3 when compared with C3 cells, in both standard (25 mmol/l glucose and 15% FCS) and deprived (5 mmol/l glucose and 1% FCS) conditions. Overexpression of gelsolin resulted in a decrease in the percentage of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)(+) and active caspase-3(+) cells. Conversely, knockdown of gelsolin by RNA interference in B1 cells caused an increase in the number of TUNEL(+) and active caspase-3(+) cells. Finally, the anti-apoptotic role of gelsolin was confirmed in purified primary mouse beta-cells where overexpression of gelsolin resulted in a decrease in the percentage of TUNEL(+) cells. In summary, our results show for the first time that gelsolin plays a pro-survival role in pancreatic beta-cells.

Activation of peroxisome proliferator-activated receptor-γ protects pancreatic β-cells from cytokine-induced cytotoxicity via NFκB pathway

Diabetes mellitus is characterized by cytokine-induced insulitis and a deficit in beta-cell mass. Ligands for peroxisome proliferator-activated receptor-gamma (PPAR-gamma) have been shown to have anti-inflammatory effects in various experimental models. We questioned whether activation of endogenous PPAR-gamma by either PPAR-gamma ligands or adenoviral-directed overexpression of PPAR-gamma (Ad-PPAR-gamma) could inhibit cytokine-induced beta-cell death in RINm5F (RIN) cells, a rat insulinoma cell line. Treatment of RIN cells with interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN-gamma) induced beta-cell damage through NF kappaB-dependent signaling pathways. Activation of PPAR-gamma by PPAR-gamma ligands or Ad-PPAR-gamma inhibited IL-1 beta and IFN-gamma-stimulated nuclear translocation of the p65 subunit and DNA binding activity. NF kappaB target gene expression and their product formation, namely inducible nitric oxide synthase and cyclooxygenase-2 were decreased by PPAR-gamma activation, as established by real-time PCR, Western blots and measurements of NO and PGE(2). The mechanism by which PPAR-gamma activation inhibited NF kappaB-dependent cell death signals appeared to involve the inhibition of I kappa B alpha degradation, evidenced by inhibition of cytokine-induced NF kappaB-dependent signaling events by Ad-I kappaB alpha (S32A, S36A), non-degradable I kappaB alpha mutant. I kappaB beta mutant, Ad-I kappaB beta (S19A, S23A) was not effective in preventing cytokine toxicity. Furthermore, a protective effect of PPAR-gamma ligands was proved by assaying for normal insulin secreting capacity in response to glucose in isolated rat pancreatic islets. The beta-cell protective function of PPAR-gamma ligands might serve to counteract cytokine-induced beta-cell destruction.

Exenatide and biotin in conjunction with a protein-sparing fast for normalization of beta cell function in type 2 diabetics

The dysdifferentiation of beta cells in type 2 diabetes appears to be caused and maintained by a vicious cycle of glucolipotoxicity: chronic elevations of glucose and free fatty acids induce beta cell dysdifferentiation as well as apoptosis; the resulting failure of glucose-stimulated insulin secretion tends to maintain the elevations of glucose and free fatty acids. Since extended fasts restore normoglycemia in diabetics, the resulting relief from glucotoxicity has been associated with a marked improvement in beta cell function that can be conserved after the fast if the factors precipitating diabetes--obesity, fatty and high-glycemic-index diets, sedentary lifestyle--have been adequately addressed. The new drug exenatide, an analog of the incretin hormone glucagon-like peptide-1, may be a worthwhile adjuvant to such fasting therapy, since it tends to counteract the glucolipotoxicity-induced down-regulation of the crucially important beta cell transcription factor IDX-1. Exenatide also exerts trophic effects on beta cell mass that in the longer term might help to restore diminished beta cell mass. Supraphysiological concentrations of biotin, possibly because they activate the soluble guanylate cyclase, also promote induction of IDX-1 and counteract the adverse impact of glucolipotoxicity in this regard; thus, high-dose biotin, which is well tolerated, may represent an additional adjuvant for therapeutic fasting intended to normalize beta cell function in type 2 diabetics.

Low concentration of interleukin-1beta induces FLICE-inhibitory protein-mediated beta-cell proliferation in human pancreatic islets

High glucose concentrations have a dual effect on beta-cell turnover, inducing proliferation in the short-term and apoptosis in the long-term. Hyperglycemia leads to beta-cell production of interleuking (IL)-1beta in human pancreatic islets. Fas, a death receptor regulated by IL-1beta, is involved in glucose-induced beta-cell apoptosis. Fas engagement can be switched from death signal to induction of proliferation when the caspase 8 inhibitor, FLICE-inhibitory protein (FLIP), is active. Here, we show that IL-1beta at low concentrations may participate in the mitogenic actions of glucose through the Fas-FLIP pathway. Thus, exposure of human islets to low IL-1beta concentrations (0.01-0.02 ng/ml) stimulated proliferation and decreased apoptosis, whereas increasing amounts of IL-1beta (2-5 ng/ml) had the reverse effects. A similarly bimodal induction of FLIP, pancreatic duodenal homeobox (PDX)-1, and Pax4 mRNA expression, as well as glucose-stimulated insulin secretion, was observed. In contrast, Fas induction by IL-1beta was monophasic. Low IL-1beta also induced the IL-1 receptor antagonist (IL-1Ra), suppression of which by RNA interference abrogated the beneficial effects of low IL-1beta. The Fas antagonistic antibody ZB4 and small interfering RNA to FLIP prevented low IL-1beta-stimulated beta-cell proliferation. Consistent with our in vitro results, IL-1beta knockout mice displayed glucose intolerance along with a decrease in islet Fas, FLIP, Pax4, and PDX-1 transcripts. These findings indicate that low IL-1beta levels positively influence beta-cell function and turnover through the Fas-FLIP pathway and that IL-1Ra production prevents harmful effects of high IL-1beta concentrations.

Targeting postprandial hyperglycemia

In healthy individuals, blood glucose levels in the fasting state are maintained by the continuous basal-level insulin secretion. After a meal, the rise in postprandial glucose (PPG) is controlled by the rapid pancreatic release of insulin, stimulated by both glucose and the intestinal production of the incretins glucose-dependent insulinotropic polypeptide and glucagon-like peptide 1. In diabetic individuals, postprandial insulin secretion is insufficient to suppress an excessive rise in PPG. There is increasing evidence that elevated PPG exerts a more deleterious effect on the vascular system than elevation of fasting plasma glucose. In particular, individuals with normal fasting plasma glucose but impaired glucose tolerance have significantly increased risk of cardiovascular events. With the recognition of the importance of PPG and the availability of new pharmacologic options, management of diabetes will shift to greater attention to PPG levels. The prototype for such an approach is in the treatment of gestational diabetes and diabetic pregnancies where PPG is the primary target of efforts at glycemic control. These efforts have been extremely successful in improving the outlook for diabetic pregnant women. There are many approaches to reduction of PPG; dietary management and promotion of exercise are very effective. Sulfonylureas, meglitinides, metformin, thiazolidinediones, and disaccharidase inhibitors all counteract PPG elevation. The development of glucagon-like peptide 1 agonists such as exendin and dipeptidyl peptidase IV inhibitors such as vildagliptin offers a new approach to suppression of PPG elevation. New semisynthetic insulin analogues permit a more aggressive response to postprandial glucose elevation, with lower risk of hypoglycemia, than with regular insulin. Inhaled insulin also has a rapid onset of action and offers benefits in PPG control. It is proposed that an aggressive treatment approach focusing on PPG, similar to the current standards for diabetic pregancies, be directed at individuals with diabetes and impaired glucose tolerance.

Upregulation of aspartoacylase activity in the duodenum of obesity induced diabetes mouse: implications on diabetic neuropathy

Aspartoacylase (ASPA) hydrolyzes N-acetylaspartic acid (NAA) into aspartate and acetate. Normal hydrolysis of NAA is important to maintain healthy neurons. Since enteric neuropathy is one of the events seen in diabetes, whether ASPA activity is affected in diabetic condition is not known. In order to investigate the possibility, ASPA activity was examined in the duodenum and brain of obesity induced diabetes model mouse. Aspartoacylase activity was high in the diabetic mouse duodenum compared to control duodenum. The same result was also observed by immunostaining of the mouse duodenum. The activity of ASPA was found to be elevated in the brain of diabetic mouse compared to the control brain. These data suggest that normal hydrolysis of NAA is affected by ASPA activity seen in the type 2 diabetes model mouse and this change is likely to contribute to neuropathy seen in diabetes, if documented also in patients with type 2 diabetes.

Oxidative stress in type 2 diabetes: the role of fasting and postprandial glycaemia

Oxidative stress, through the production of reactive oxygen species (ROS), has been proposed as the root cause underlying the development of insulin resistance, beta-cell dysfunction, impaired glucose tolerance and type 2 diabetes mellitus (T2DM). It has also been implicated in the progression of long-term diabetes complications, including microvascular and macrovascular dysfunction. Excess nourishment and a sedentary lifestyle leads to glucose and fatty acid overload, resulting in production of ROS. Additionally, reaction of glucose with plasma proteins forms advanced glycation end products, triggering production of ROS. These ROS initiate a chain reaction leading to reduced nitric oxide availability, increased markers of inflammation and chemical modification of lipoproteins, all of which may increase the risk of atherogenesis. With the postulation that hyperglycaemia and fluctuations in blood glucose lead to generation of ROS, it follows that aggressive treatment of fasting and postprandial hyperglycaemia is important for prevention of micro and macrovascular complications in T2DM.

Early use of insulin in type 2 diabetes

Type 2 diabetes is a disease characterised by peripheral insulin resistance, as well as by pancreatic beta cell dysfunction. This process is in part due to elevated blood glucose and free fatty acids--termed glucolipotoxicity. The traditional pathway of treating type 2 diabetes in a stepwise manner, beginning with life style modifications and continuing with oral hypoglycaemic agents leads to a protracted period of unnecessary hyperglycaemia. A new approach, targeted at alleviating the deleterious effects of hyperglycaemia and elevated free fatty acids by acutely lowering both with intensive insulin therapy, has yielded prolonged remissions in therapy in which only diet was necessary to maintain normoglycaemia. This new approach, its rationale, benefits and misgivings are discussed in this review.