Pathophysiology of insulin secretion

Effects of exogenous ghrelin treatment on oxidative stress, inflammation and histological parameters in a fat-fed streptozotocin rat model

In this study, the anti-inflammatory, antioxidative, and protective effects of ghrelin were investigated in a fat-fed streptozotocin (STZ) rat model and compared with metformin, diabetes and the healthy control groups. Histopathological evaluations were performed on H&E-stained pancreas and brain sections. Biochemical parameters were investigated by enzyme-linked immunosorbent assay. Blood glucose levels were significantly decreased with ghrelin or metformin treatments than the diabetes group. STZ administration increased brain, renal and pancreatic IL-1β, TNF-α and MDA while decreasing GPX, CAT, SOD, and NGF levels. Ghrelin increased renal GPX, CAT, NGF pancreatic GPX, SOD, CAT, NGF and brain SOD, NGF while it decreased renal, pancreatic and brain IL-1β, TNF-α and MDA levels. Ghrelin reduced neuronal loss and degeneration in the cerebral cortex and hippocampus and greatly ameliorated diabetes-related damage in pancreas. In conclusion, the data suggested that ghrelin is an effective candidate as a protectant for reducing the adverse effects of diabetes.

The Antioxidant Properties of Mushroom Polysaccharides can Potentially Mitigate Oxidative Stress, Beta-Cell Dysfunction and Insulin Resistance

Diabetes mellitus is a prevalent metabolic and endocrine illness affecting people all over the world and is of serious health and financial concern. Antidiabetic medicine delivered through pharmacotherapy, including synthetic antidiabetic drugs, are known to have several negative effects. Fortunately, several natural polysaccharides have antidiabetic properties, and the use of these polysaccharides as adjuncts to conventional therapy is becoming more common, particularly in underdeveloped nations. Oxidative stress has a critical role in the development of diabetes mellitus (DM). The review of current literature presented here focusses, therefore, on the antioxidant properties of mushroom polysaccharides used in the management of diabetic complications, and discusses whether these antioxidant properties contribute to the deactivation of the oxidative stress-related signalling pathways, and to the amelioration of β-cell dysfunction and insulin resistance. In this study, we conducted a systematic review of the relevant information concerning the antioxidant and antidiabetic effects of mushrooms from electronic databases, such as PubMed, Scopus or Google Scholar, for the period 1994 to 2021. In total, 104 different polysaccharides from mushrooms have been found to have antidiabetic effects. Most of the literature on mushroom polysaccharides has demonstrated the beneficial effects of these polysaccharides on reactive oxygen and nitrogen species (RONS) levels. This review discuss the effects of these polysaccharides on hyperglycemia and other alternative antioxidant therapies for diabetic complications through their applications and limits, in order to gain a better understanding of how they can be used to treat DM. Preclinical and phytochemical investigations have found that most of the active polysaccharides extracted from mushrooms have antioxidant activity, reducing oxidative stress and preventing the development of DM. Further research is necessary to confirm whether mushroom polysaccharides can effectively alleviate hyperglycemia, and the mechanisms by which they do this, and to investigate whether these polysaccharides might be utilized as a complementary therapy for the prevention and management of DM in the future.

Sodium meta-arsenite ameliorates hyperglycemia in obese diabetic db/db mice by inhibition of hepatic gluconeogenesis

Sodium meta-arsenite (SA) is implicated in the regulation of hepatic gluconeogenesis-related genes in vitro; however, the effects in vivo have not been studied. We investigated whether SA has antidiabetic effects in a type 2 diabetic mouse model. Diabetic db/db mice were orally intubated with SA (10 mg kg(-1) body weight/day) for 8 weeks. We examined hemoglobin A1c (HbA1c), blood glucose levels, food intake, and body weight. We performed glucose, insulin, and pyruvate tolerance tests and analyzed glucose production and the expression of gluconeogenesis-related genes in hepatocytes. We analyzed energy metabolism using a comprehensive animal metabolic monitoring system. SA-treated diabetic db/db mice had reduced concentrations of HbA1c and blood glucose levels. Exogenous glucose was quickly cleared in glucose tolerance tests. The mRNA expressions of genes for gluconeogenesis-related enzymes, glucose 6-phosphatase (G6Pase), and phosphoenolpyruvate carboxykinase (PEPCK) were significantly reduced in the liver of SA-treated diabetic db/db mice. In primary hepatocytes, SA treatment decreased glucose production and the expression of G6Pase, PEPCK, and hepatocyte nuclear factor 4 alpha (HNF-4α) mRNA. Small heterodimer partner (SHP) mRNA expression was increased in hepatocytes dependent upon the SA concentration. The expression of Sirt1 mRNA and protein was reduced, and acetylated forkhead box protein O1 (FoxO1) was induced by SA treatment in hepatocytes. In addition, SA-treated diabetic db/db mice showed reduced energy expenditure. Oral intubation of SA ameliorates hyperglycemia in db/db mice by reducing hepatic gluconeogenesis through the decrease of Sirt1 expression and increase in acetylated FoxO1.

[Insulin degludec--a new basal insulin for the treatment of type 1 and type 2 diabetes]

After subcutaneous injection, IDeg self-associates to form multihexamer chains that slowly dissociate into monomers. This results in a duration of action of more than 42 hours as well as a smooth level action profile with low intra-individual variability. Pharmacokinetic studies foun IDeg to have a half-life of approximately 25 hours which is considerably longer than that from other current insulin formulations. Based on these properties, IDeg demonstrated low risk for nocturnal hypoglycaemic events in the clinical study program. Concurrently, phase 3 studies have provided evidence for a non-inferior glucose lowering effect when compared to other currently available basal insulin formulations. Moreover, the long duration of action suggests a flexible handling which could be better adapted to patients' needs in daily routine. This article gives an overview of the mechanism of action of IDeg and the latest results from phase 2 and phase 3 studies.

A novel fluorescence imaging approach for comparative measurements of pancreatic islet function in vitro

Pancreatic islet dysfunction is a key element in the development of type 2 diabetes. Determining possible early warning signs of dysfunction is thus important to determining the underlying causes of diabetes. We describe an improved fluorescent imaging approach to detect potential islet dysfunction. Using Cell Tracker Red (CTR, a mildly thiol-reactive fluorescent probe) to positively label particular islets, we measured intracellular free calcium with fura-2 AM in both CTR-labeled and unlabeled sets of pancreatic islets simultaneously in vitro. This approach enhances sensitivity by controlling for differences in background fluorescence, temperature, and perifusion dynamics. We confirmed that 200 nM CTR produced no spectral overlap with fura-2 and no significant physiological effects in selective tests of islet function. To demonstrate the utility of dual-labeling, we compared untreated islets with islets pretreated with low-dose pro-inflammatory cytokines (IL-6 + IL-1B) to induce mild dysfunction. We alternated CTR-labeling between control and test islets and identified consistent reductions in the amplitude and trajectory of glucose-stimulated calcium responses (GSCa) among cytokine-treated islets that were independent of labeling. Observations were verified using a MATLAB program specifically designed to identify key features in the GSCa. Our findings thus demonstrate the utility of CTR-labeling in identifying islet dysfunction and propose that this technique can be adapted for other cells and tissues.

Associations of age with serum insulin, proinsulin and the proinsulin-to-insulin ratio: a cross-sectional study

BACKGROUND

Insulin responses and insulin levels seem to decline with age. However, the question of beta cell impairment attributable to ageing has been sparsely addressed in population-based studies. Non-fasting insulin levels are determined by the ambient degree of insulin resistance together with the capacity of beta cells to compensate by insulin secretion to prevent hyperglycaemia. A raised proinsulin-to-insulin ratio (proinsulin/insulin) due to impaired processing of proinsulin is an early marker of beta cell dysfunction. We hypothesised that in a general population, signs of beta cell failure with advancing age manifest not only by decreases in random insulin, but also with a corresponding increase in its precursor proinsulin.

METHODS

In the Tromsø Study 1994-95 we measured insulin and proinsulin concentrations in random blood samples from 6212 persons without self-reported diabetes mellitus and plotted the levels as percentiles according to age. In regression analyses we assessed the relationships between age and insulin, proinsulin, and proinsulin/insulin, while adjusting for the concomitant measurements of glucose and other metabolic variables, and the time since the last meal.

RESULTS

Median insulin concentrations declined significantly with advancing age group in men, but not in women. Proinsulin levels and proinsulin/insulin increased across age groups in both genders. After adjustment, greater age was associated with lower log10(insulin) and higher log10(proinsulin) and log10(proinsulin/insulin) (p = 0.0001 for all).

CONCLUSIONS

Negative associations of age with random insulin levels, together with positive associations of age with proinsulin and proinsulin/insulin, point towards a loss of beta cell function inherent in the ageing process.

Proteomics and islet research

The complementary disciplines of genomics and proteomics offer better insights into the molecular mechanisms of diseases. While genomics hunts for defining our static genetic substrate, proteomics explores the structure and function of proteins expressed by a cell or tissue type under specified conditions. In the past decade, proteomics has been revolutionized by the application of techniques such as two-dimensional gel electrophoresis (2DGE), mass spectrometry (MS), and protein arrays. These techniques have tremendous potential for biomarker development, target validation, diagnosis, prognosis, and optimization of treatment in medical care, especially in the field of islet and diabetes research. This chapter will highlight the contributions of proteomic technologies toward the dissection of complex network of signaling molecules regulating islet function, the identification of potential biomarkers, and the understanding of mechanisms involved in the pathogenesis of diabetes.

Role of insulin resistance in predicting progression to type 1 diabetes

OBJECTIVE

The purpose of this study was to determine whether insulin resistance is a risk factor for the development of type 1 diabetes in autoantibody-positive first-degree relatives of diabetic family members.

RESEARCH DESIGN AND METHODS

Subjects (n = 186) who had a projected 25-50% risk for diabetes and subjects (n = 170) who had a projected >50% risk for type 1 diabetes in 5 years were followed until clinical diabetes onset or the end of the study as part of the Diabetes Prevention Trial-Type 1. We assessed insulin secretion with the first-phase insulin response (FPIR) and insulin resistance with homeostasis model assessment of insulin resistance (HOMA-IR) from an intravenous glucose tolerance test. The median follow-up was 4.3 years for moderate-risk subjects and 3.7 years for high-risk subjects.

RESULTS

During the follow-up period, 53 subjects in the moderate-risk group and 70 subjects in the high-risk group developed type 1 diabetes. After adjustments for confounders using multivariate analysis, HOMA-IR and the FPIR-to-HOMA-IR ratio were significantly associated with type 1 diabetes in both risk groups. In the moderate-risk population, the hazard ratio (HR) of HOMA-IR was 2.70 (95% CI 1.45-5.06) and the HR of FPIR-to-HOMA-IR was 0.32 (95% CI 0.18-0.57). In the high-risk population, the HR of HOMA-IR was 1.83 (95% CI 1.19-2.82) and the HR of FPIR-to-HOMA-IR was 0.56 (95% CI 0.40-0.78).

CONCLUSIONS

There is clear evidence of the association between insulin resistance and progression to type 1 diabetes. The combination of FPIR and HOMA-IR could be used as a better metabolic indicator for type 1 diabetes risk for prediction and suggests possible intervention strategies for diabetes prevention.

Obesity and prostate cancer: epidemiology and clinical implications

OBJECTIVES

Both obesity and prostate cancer (PCa) are epidemic in Western society. Although initial epidemiological data appeared conflicting, recent studies have clarified the association between obesity and PCa. Therefore, we sought to review the epidemiological data linking obesity and PCa with an emphasis on the clinical implications and how to improve outcomes among obese men.

METHODS

A PubMed search using the keywords "prostate cancer" and "obesity" was performed. Relevant articles and references were reviewed for data on the association between obesity and PCa.

RESULTS

Recent data suggest obesity is associated with reduced risk of nonaggressive disease but increased risk of aggressive disease. This observation may be explained in part by an inherent bias in our ability to detect PCa in obese men (lower PSA values and larger sized prostates, making biopsy less accurate for finding an existent cancer), which ultimately leads to increased risk of cancer recurrence after primary therapy and increased PCa mortality. Despite this detection bias potentially contributing to more aggressive cancers, multiple biological links also exist between obesity and PCa including higher estradiol, insulin, free IGF-1, and leptin levels, and lower free testosterone and adiponectin levels, all of which may promote more aggressive cancers.

CONCLUSIONS

The association between obesity and PCa is complex. Emerging data suggest obesity increases the risk of aggressive cancer, while simultaneously decreasing the risk of more indolent disease. This is likely driven by both "biological" and "nonbiological" causes. Simple changes in clinical practice patterns can reduce the impact of nonbiological causes and may help improve PCa outcomes among obese men.

Drug-drug and food-drug pharmacokinetic interactions with new insulinotropic agents repaglinide and nateglinide

This review describes the current knowledge on drug-drug and food-drug interactions with repaglinide and nateglinide. These two meglitinide derivatives, commonly called glinides, have been developed for improving insulin secretion of patients with type 2 diabetes mellitus. They are increasingly used either in monotherapy or in combination with other oral antihyperglycaemic agents for the treatment of type 2 diabetes. Compared with sulfonylureas, glinides have been shown to (i) provide a better control of postprandial hyperglycaemia, (ii) overcome some adverse effects, such as hypoglycaemia, and (iii) have a more favourable safety profile, especially in patients with renal failure. The meal-related timing of administration of glinides and the potential influence of food and meal composition on their bioavailability may be important. In addition, some food components (e.g. grapefruit juice) may cause pharmacokinetic interactions. Because glinides are metabolised via cytochrome P450 (CYP) 3A4 isoenzyme, they are indeed exposed to pharmacokinetic interactions. In addition to CYP3A4, repaglinide is metabolised via CYP2C8, while nateglinide metabolism also involves CYP2C9. Furthermore, both compounds and their metabolites may undergo specialised transport/uptake in the intestine, another source of pharmacokinetic interactions. Clinically relevant drug-drug interactions are those that occur when glinides are administered together with other glucose-lowering agents or compounds widely coadministered to diabetic patients (e.g. lipid-lowering agents), with drugs that are known to induce (risk of lower glinide plasma levels and thus of deterioration of glucose control) or inhibit (risk of higher glinide plasma levels leading to hypoglycaemia) CYP isoenzymes concerned in their metabolism, or with drugs that have a narrow efficacy : toxicity ratio. Pharmacokinetic interactions reported in the literature appear to be more frequent and more important with repaglinide than with nateglinide. Rifampicin (rifampin) reduced repaglinide area under the plasma concentration-time curve (AUC) by 32-85% while it reduced nateglinide AUC by almost 25%. Reported increases in AUCs with coadministration of drugs inhibiting CYP isoenzymes never exceeded 80% for repaglinide (except with ciclosporin and with gemfibrozil) and 50% for nateglinide. Ciclosporin more than doubled repaglinide AUC (+144%), a finding that should raise caution when using these two drugs in combination. The most impressive pharmacokinetic interaction was reported with combined administration of gemfibrozil (a strong CYP2C8 inhibitor) and repaglinide (8-fold increase in repaglinide AUC). Although no studies have been performed in patients with type 2 diabetes, the latter combination should be avoided in clinical practice.

Antidiabetic agents in subjects with mild dysglycaemia: prevention or early treatment of type 2 diabetes?

Besides lifestyle, various pharmacological treatments have proven their efficacy to reduce the incidence of type 2 diabetes in high-risk individuals, especially in those with impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG). Major placebo-controlled clinical trials demonstrated favourable effects of various glucose-lowering drugs generally used for the treatment of type 2 diabetes, i.e. metformin, acarbose and thiazolidinediones (glitazones). These trials showed a lower rate of progression to overt diabetes and a higher regression rate to a normal glucose status with active treatment as compared to placebo after a follow up of several years. Ongoing trials should confirm such a favourable effect with those drugs and may demonstrate a similar protective effect with other pharmacological approaches such as glinides or even basal insulin regimen. However, the reported favourable effects were generally observed while the subjects were still on treatment, and partially vanished after a rather short period of wash-out of several weeks. Therefore, the distinction between a true preventing effect and simply a masking effect is difficult with glucose-lowering drugs. In addition, as type 2 diabetes is a progressive disease, it is still questionable whether the effect corresponds to a prevention effect or only to a postponing of the development of the disease. Owing to the pathophysiology of the disease, the only way to block the progression of type 2 diabetes is probably to avoid the progressive loss of beta-cell function and/or mass. Whatsoever, these data obtained in large clinical trials bring further argument to support early treatment of diabetes, even at a prediabetic state, in order to stop the vicious circle leading to an inevitable deterioration of glycaemia in predisposed subjects.

Diabetes mellitus in the elderly: insulin resistance and/or impaired insulin secretion?

Elderly people are more glucose intolerant and insulin resistant than young individuals, and many of them will develop type 2 diabetes. It remains, however, controversial whether this decrease in function is due to an inevitable consequence of "biological aging" or due to environmental or lifestyle variables. Indeed, increased adiposity/altered fat distribution, decreased fat free mass/abnormal muscle composition, poor dietary habits and physical inactivity all contribute to reduce insulin sensitivity. Insulin resistance in elderly people appears to predominate in skeletal muscle, whereas hepatic glucose output seems to be almost unaffected. Several abnormalities in islet beta-cell and insulin secretion were also pointed out in elderly people such as increased amyloid deposition and decreased amylin secretion, impaired insulin secretion pulsatility, decreased insulin sensitivity of pancreatic beta-cells to insulinotropic gut hormones and diminished insulin response to non-glucose stimuli such as arginine. Controversial results were reported concerning the effects of aging on absolute insulin secretion in response to oral or intravenous glucose. However, insulin secretion appears to decrease with age, with significantly diminished beta-cell sensitivity and acute insulin response to glucose, provided it is analyzed relative to concomitant decreased insulin sensitivity. Thus, there is an interplay between decreased insulin secretion and increased insulin resistance that largely explains the abnormal glucose metabolism seen in elderly. Weight loss, especially reduction of abdominal adiposity, and increased physical activity may contribute to improve insulin sensitivity and glucose tolerance, and prevent the development of type 2 diabetes in elderly people.

Subcutaneous insulin: pharmacokinetic variability and glycemic variability

The therapeutic goal in insulin-treated diabetic patients is to maintain on the long-term a tight glucose control (HbA1, < 6.5-7% or less) through an insulin regimen which "mimic" the physiological insulin profile: a basal insulin secretion to maintain glucose homeostasis and an acute post-prandial secretion in response to meal intake. Such goal represents a challenge for the clinician as conventional human insulins have major drawbacks: slow absorption and too late peak with regular insulins, delayed peak and often occuring at an unwanted time with intermediate and long-acting insulins. Furthermore, these insulins are characterised by a large within- and between-subjects variability, which complicate patients' task to self-adapt their daily doses, even for those well educated and compliants. These limitations and unpredictable variations in insulin action are responsible for an increased risk of hypoglycemic events, between meals as well as during the night period. As a consequence, glucose control is frequently insufficient in type 1 diabetic patients, and these limitations may contribute also to the delayed initiation of insulin therapy in type 2 diabetics when oral antidiabetic agents fail. This variability and the non-reproducibility of the conventional insulin pharmacodynamics are explained by several exogenous and endogenous factors describe in this review. Availability of new short-acting (lispro, aspart and glulisine) and long-acting analogs (glargine, detemir) of human insulin, with improved pharmacokinetic characteristics, and a lesser variability and better reproducibility, should facilitate a tight glucose control in insulin-treated patients. The main pharmacokinetic and pharmacodynamic characteristics of these new insulin analogs are presented and discussed in the light of there intra- and inter-individual variability. Their reduced variability should permit to reinforce near "physiological" insulin regimen such as "basal-bolus" technique and to consider new approaches and therapeutic strategies in type 1 and type 2 diabetic patients.

An immune origin of type 2 diabetes?

Subclinical, low-grade systemic inflammation has been observed in patients with type 2 diabetes and in those at increased risk of the disease. This may be more than an epiphenomenon. Alleles of genes encoding immune/inflammatory mediators are associated with the disease, and the two major environmental factors the contribute to the risk of type 2 diabetes-diet and physical activity-have a direct impact on levels of systemic immune mediators. In animal models, targeting of immune genes enhanced or suppressed the development of obesity or diabetes. Obesity is associated with the infiltration and proinflammatory activity of macrophages in adipose tissue, and immune mediators may be important regulators of insulin resistance, mitochondrial function, ectopic lipid storage and beta cell dysfunction or death. Intervention studies targeting these pathways would help to determine the contribution of an activated innate immune system to the development of type 2 diabetes.

Glucose-induced changes of multiple mouse islet proteins analysed by two-dimensional gel electrophoresis and mass spectrometry

AIMS/HYPOTHESIS

The aim of this study was to investigate molecular mechanisms of glucose-induced changes in islets of Langerhans by analysing global changes in protein patterns of islets exposed to elevated glucose concentrations.

METHODS

Islets were isolated from C57BL/6J mice and used either directly or after exposure to 11 mmol/l glucose for 24 h. Islet protein profiles were obtained by two-dimensional gel electrophoresis, and protein spots were identified by peptide mass fingerprinting using mass spectrometry.

RESULTS

Two-dimensional gels of freshly isolated islets and islets exposed to 11 mmol/l glucose contained 1,074 and 1,254 spots, respectively. The number of differentially expressed spots was 379, with 20 spots appearing as new proteins in islets exposed to 11 mmol/l glucose. We identified 124 spots corresponding to 77 protein entries and generated a reference map from freshly isolated islets. Actin, alpha enolase, cytokeratin 8, endoplasmin, glucose-regulated proteins, heat shock proteins, peroxiredoxins, prohormone convertase 2, protein disulphide isomerase, superoxide dismutase, tubulin, and V-type H+ -ATPase (V1 subunit A) were upregulated in islets exposed to 11 mmol/l glucose. In contrast, exocrine proteins and secretagogin were downregulated in these islets compared with in freshly isolated islets.

CONCLUSIONS/INTERPRETATION

The islet proteome approach revealed simultaneous changes in protein patterns of islets exposed to elevated glucose concentrations, indicating enhanced insulin synthesis, granular mobilisation and maturation, and increased stress response. The changes may be of relevance for the understanding of altered islet function in the hyperglycaemic state. It is expected that the islet reference map will become an important tool for dissecting multifactorial islet processes.

Renin-angiotensin system inhibition prevents type 2 diabetes mellitus

The inhibition of the renin-angiotensin system (RAS) with either angiotensin converting enzyme inhibitors (ACEIs) or AT1 angiotensin receptor blockers (ARBs) consistently and significantly reduces the incidence of type 2 diabetes in patients with hypertension or congestive heart failure. The mechanisms underlying this protective effect appear to be complex and may involve an improvement of both insulin sensitivity and insulin secretion. These two effects may result, at least in part, from the well known effects of these pharmacological agents on the vascular system on the one hand, on the ionic balance on the other hand. Indeed, the vasodilation induced by ACEIs or ARBs could improve the blood circulation in skeletal muscles, thus favouring peripheral insulin action, but also in the pancreas, thus promoting insulin secretion. Preserving cellular potassium and magnesium pools by blocking the aldosterone effects could also improve both cellular insulin action and insulin secretion. However, besides these classical effects, new mechanisms have been recently suggested. A direct effect of the inhibition of angiotensin and/or of the enhancement of bradykinin on various steps of the insulin cascade signalling has been described as well an increase in GLUT4 glucose transporters after RAS inhibition. Furthermore, it has been demonstrated that angiotensin II inhibits adipogenic differentiation of human adipocytes via A1 receptors and, therefore, it has been hypothesised that RAS blockade may prevent diabetes by promoting the recruitment and differentiation of adipocytes. Finally, some lipophilic ARBs appear to induce PPAR-gamma activity in the adipose tissue. Hence, the protection against type 2 diabetes observed after RAS inhibition may be partially linked to a thiazolidinedione-like effect. In conclusion, numerous physiological and biochemical mechanisms could explain the protective effect of RAS inhibition against the development of type 2 diabetes in individuals with arterial hypertension or congestive heart failure. What might be the main mechanism in the overall protection effect of ACEIs or ARBs remains an open question.