IRIS II Study: Sensitivity and specificity of intact proinsulin, adiponectin, and the proinsulin/adiponectin ratio as markers for insulin resistance

Hyperproinsulinemia in obesity and in type 2 diabetes and its relation to cardiovascular disease

Disproportionately elevated fasting levels of proinsulin immunoreactive material (PIM)relative to insulin immunoreactivity (IRI) are a well-established abnormality in type 2 diabetes. Thesignificance of this abnormality has been investigated and discussed in several studies. Areas covered: The present review focuses on the role of proinsulin and its conversion intermediates inthe development of type 2 diabetes, obesity and insulin resistance, and the potential role as a marker ofcardiovascular risk, including the most important studies in this field. Expert commentary: The composition of plasma PIM is heterogeneous comprising des(31,32)-proinsulin,intact proinsulin and small amounts of des(64,65)-proinsulin. Disproportionate hyperproinsulinemiaseems to occur early in the development and before the diagnosis of type 2 diabetes, and seemsassociated to disease progression. Obesity and insulin resistance does not influence fasting PIM/IRI levels in type 2 diabetes. Fasting PIM/IRI levels in type 2 diabetes are closely associated with the degree of impairment in insulin secretory capacity. Different type 2 diabetes alleles have been described associated with elevated PIM/IRI levels. Recent data suggests that proinsulin and its conversion intermediates may have a role as markers of increased risk of cardiovascular disease in glucose intolerance and type 2 diabetes.

Total and High Molecular Weight Adiponectin Levels and Prediction of Cardiovascular Risk in Diabetic Patients

The study aimed at assessing the potential use of lower total and HMW adiponectin levels for predicting cardiovascular risk in patients with type 2 diabetes mellitus (T2DM). Concentrations of total adiponectin or high molecular weight (HMW) adiponectin decrease in association with the development of metabolic dysfunction such as obesity, insulin resistance, or T2DM. Increased adiponectin levels are associated with a lower risk for coronary heart disease. A total of 551 individuals were assessed. The first group comprised metabolically healthy participants (143 females, and 126 males) and the second group were T2DM patients (164 females, and 118 males). Both total adiponectin and HMW adiponectin in diabetic patients were significantly lower when compared with the group of metabolically healthy individuals. There was a weak monotonic correlation between HMW adiponectin levels and triglycerides levels. Binary logistic regression analysis, gender adjusted, showed a higher cardiovascular risk in diabetic persons when both total adiponectin (OR = 1.700) and HMW adiponectin (OR = 2.785) levels were decreased. A decrease in total adiponectin levels as well as a decrease in its HMW adiponectin is associated with a higher cardiovascular risk in individuals with T2DM. This association suggests that adiponectin levels may be potentially used as an epidemiological marker for cardiovascular risk in diabetic patients.

Clinical use of adiponectin as a marker of metabolic dysregulation

Adiponectin concentrations exhibit strong cross-sectional relationships with obesity, inflammation, and diabetes. Adiponectin concentrations have been extensively evaluated as epidemiologic markers of diabetes and cardiovascular disease risk. In the present review we will provide an overview of these epidemiologic relationships as the backdrop for an evaluation of the clinical applications of adiponectin measurements. These include using adiponectin as an indicator of need for preventive or therapeutic intervention, as a predictor of response to therapy, and as a marker of therapeutic effectiveness. These efforts are laying the groundwork for the transition of adiponectin measurements from the laboratory to the clinic.

Effects of acarbose treatment on markers of insulin sensitivity and systemic inflammation

BACKGROUND

This study assessed the effect of postprandial glucose reduction by acarbose on insulin sensitivity and biomarkers of systemic inflammation.

METHODS

This was a single-center, double-blind, randomized, placebo-controlled, crossover study <40 weeks in duration, involving 66 subjects with varying degrees of glucose tolerance. Eligible patients completed a 3-week run-in period and were randomized to receive either 100 mg of acarbose three times daily followed by placebo, or vice versa, lasting 12 weeks each with a 12-week washout between interventions. Liquid meal challenges and hyperinsulinemic-euglycemic glucose clamp were performed at weeks 0, 12, 24, and 36.

RESULTS

Fasting proinsulin levels and proinsulin-to-adiponectin ratios but not fasting adiponectin levels were significantly lower during acarbose versus placebo treatment. Clamp-derived insulin sensitivity index and body weight were unchanged by the intervention. Levels of fasting insulin, fasting glucose, monocyte chemoattractant protein-1, interleukin-6, and interleukin-1β were comparable between treatments. In the liquid meal challenge tests, postprandial glucose and insulin responses were significantly lower during acarbose versus placebo treatment. The effects of acarbose on the reduction of fasting proinsulin was most pronounced in subjects with impaired fasting glucose/impaired glucose tolerance (n = 24).

CONCLUSIONS

Reduction of the glycemic load by acarbose decreased fasting levels of proinsulin but had no effect on adiponectin and whole-body insulin sensitivity as well as biomarkers reflecting inflammation. The preventive effects of acarbose on type 2 diabetes mellitus and cardiovascular risk need further investigation and cannot be explained by changes of insulin resistance and inflammatory biomarkers.

Elevated intact proinsulin levels are indicative of Beta-cell dysfunction, insulin resistance, and cardiovascular risk: impact of the antidiabetic agent pioglitazone

BACKGROUND

Insulin resistance (IR) and deterioration of beta-cell secretion are main features in the development of type 2 diabetes, which is reflected in increasing serum intact proinsulin levels in later disease stage. Introduction of stable assays that are able to distinguish between intact proinsulin and its specific and unspecific cleavage products has resulted in the finding that serum intact proinsulin values can serve as a direct marker for beta-cell dysfunction, are a highly specific indicator of IR, and can predict cardiovascular risk.

METHOD

Determination of fasting intact proinsulin may be used to monitor and optimize antidiabetic therapeutic approaches. Our study group has been involved in a variety of clinical studies investigating drug effects on beta-cell secretory capacity, IR, and intact proinsulin levels. One focus was on the impact of insulin-sensitizing therapy with pioglitazone on the pancreatic beta-cell load.

RESULTS

Treatment with pioglitazone resulted in significant decreases in elevated proinsulin levels in type 2 diabetes patients. This effect was independent from glycemic control.

CONCLUSIONS

Measurement of fasting intact proinsulin values allows a staging of beta-cell dysfunction and evaluation of IR, thus providing an interesting diagnostic tool for both selection of appropriate therapy and monitoring of treatment success.

A review of islet of Langerhans degeneration in rodent models of type 2 diabetes

Type 2 diabetes mellitus (TTDM) is characterized by progressive loss of glucose control through multifactorial mechanisms. The search for an understanding of TTDM has relied on animal models since the realization of the importance of the pancreas in controlling plasma glucose concentration. Rodent models of TTDM are developed to express hyperglycemia and not islet degeneration per se. Degeneration of the islets of Langerhans with beta-cell loss is secondary to insulin resistance and is regarded as the more important lesion. Despite this, differences between models are seen in the development and progression of islet degeneration. Assessing the differences between the models is important to appreciate the various aspects of TTDM and understand their advantages as well as their deficiencies. Relevant animal models of TTDM provide opportunities to investigate important physiological and cell biological processes that may ultimately lead to development of targeted therapies. This article reviews the importance, advantages, and limitations of rodent models of TTDM in relation to the histopathological changes that characterize islet degeneration. Pathophysiological mechanisms that contribute to islet degeneration are also discussed and are placed into the context of changes in islet histological appearances.

Metabolic syndrome and mitochondrial function: molecular replacement and antioxidant supplements to prevent membrane peroxidation and restore mitochondrial function

Metabolic syndrome consists of a cluster of metabolic conditions, such as hypertriglyceridemia, hyper-low-density lipoproteins, hypo-high-density lipoproteins, insulin resistance, abnormal glucose tolerance and hypertension, that-in combination with genetic susceptibility and abdominal obesity-are risk factors for type 2 diabetes, vascular inflammation, atherosclerosis, and renal, liver and heart disease. One of the defects in metabolic syndrome and its associated diseases is excess cellular oxidative stress (mediated by reactive oxygen and nitrogen species, ROS/RNS) and oxidative damage to mitochondrial components, resulting in reduced efficiency of the electron transport chain. Recent evidence indicates that reduced mitochondrial function caused by ROS/RNS membrane oxidation is related to fatigue, a common complaint of MS patients. Lipid replacement therapy (LRT) administered as a nutritional supplement with antioxidants can prevent excess oxidative membrane damage, restore mitochondrial and other cellular membrane functions and reduce fatigue. Recent clinical trials have shown the benefit of LRT plus antioxidants in restoring mitochondrial electron transport function and reducing moderate to severe chronic fatigue. Thus LRT plus antioxidant supplements should be considered for metabolic syndrome patients who suffer to various degrees from fatigue.

Fixed-dose combination of pioglitazone and glimepiride in the treatment of Type 2 diabetes mellitus

Type 2 diabetes is characterized by impaired insulin sensitivity and disturbances in β-cell function. While glimepiride stimulates β-cell secretion and leads to a reduction of blood glucose levels, pioglitazone activates peroxisome proliferator-activated receptor-γ and improves insulin resistance. Combining these two modes of action has been shown to improve glucose and lipid metabolism, and to improve the overall cardiovascular risk in patients with Type 2 diabetes. The combination of glimepiride and pioglitazone is generally well tolerated and a fixed combination may lead to an improved compliance in patients. The purpose of this review is to evaluate the clinical data that has been published on this combination, appearing to represent a convenient way to obtain therapeutic targets in patients with Type 2 diabetes mellitus.