Type 2 Diabetes Mellitus: Pathogenic Features and Experimental Models in Rodents

Type 2 diabetes mellitus (T2DM) is the most common endocrine disorder (90%) in the world; it has numerous clinical, immunological, and genetic differences from type 1 diabetes mellitus. The pathogenesis of T2DM is complex and not fully clear. To date, animal models remain the main tool by which to study the pathophysiology and therapy of T2DM. Rodents are considered the best choice among animal models, because they are characterized by a small size, short induction period, easy diabetes induction, and economic efficiency. This review summarizes data on experimental models of T2DM that are currently used, evaluates their advantages and disadvantages vis-a-vis research, and describes in detail the factors that should be taken into account when using these models. Selection of a suitable model for tackling a particular issue is not always trivial; it affects study results and their interpretation.

[Molecular mechanisms of action and physiological effects of the proinsulin C-peptide (a systematic review)]

The C-peptide is a fragment of proinsulin, the cleavage of which forms active insulin. In recent years, new information has appeared on the physiological effects of the C-peptide, indicating its positive effect on many organs and tissues, including the kidneys, nervous system, heart, vascular endothelium and blood microcirculation. Studies on experimental models of diabetes mellitus in animals, as well as clinical trials in patients with diabetes, have shown that the C-peptide has an important regulatory effect on the early stages of functional and structural disorders caused by this disease. The C-peptide exhibits its effects through binding to a specific receptor on the cell membrane and activation of downstream signaling pathways. Intracellular signaling involves G-proteins and Ca2+-dependent pathways, resulting in activation and increased expression of endothelial nitric oxide synthase, Na+/K+-ATPase and important transcription factors involved in apoptosis, anti-inflammatory and other intracellular defense mechanisms. This review gives an idea of the C-peptide as a bioactive endogenous peptide that has its own biological activity and therapeutic potential.

[Diabetes mellitus and chronic liver diseases. Part 1: general mechanisms of etiology and pathogenesis]

In recent years there has been an active discussion about the relationship between diabetes mellitus (DM) and chronic liver diseases (CLD). On the one hand, patients with diabetes have an increased risk of developing CLD. On the other hand, patients with CLD very often identify abnormal glucose metabolism which ultimately leads to impaired glucose tolerance and the development of diabetes. This review outlines potential causal relationships between some CLD and DM. Common mechanisms that provoke metabolic and autoimmune disorders in the development of various nosologies of the CKD group, leading to steatosis, insulin resistance, impaired glucose tolerance and the development of diabetes are described. Certain features of the assessment of carbohydrate metabolism compensation in patients with hepatic dysfunction, anemia and protein metabolism disorders are described.

Type 2 diabetes and metabolic syndrome: identification of the molecular mechanisms, key signaling pathways and transcription factors aimed to reveal new therapeutical targets

Type 2 diabetes mellitus (T2DM) is a socially important disease with only symptomatic therapy developed due to lack of knowledge about its pathogenesis and underlying mechanism. Insulin resistance (IR) is the first link of T2DM pathogenesis and results in decrease of ability of insulin to stimulate glucose uptake by target cells. Development of IR involves genetic predisposition, excessive nutrition, stress, obesity or chronic inflammation due to disruption of insulin signaling within cells. Molecular mechanisms and markers of IR are characterized rather poorly, which prevents early diagnosis and creation of preventive therapy. Euglycemic clamp test is still a golden standard for IR diagnosis in clinic. Hyperglycemia is a distant consequence of IR in which damaging effect of oxidative and carbonyl stress is realized and diagnosis of T2DM is stipulated. Molecular chaperones and small heat-shock proteins have a protective effect at the early stages of T2DM pathogenesis, preventing development of reticulum stress and apoptosis. Endothelial dysfunction is related to T2DM and its cardiovascular complications, however, it is unknown on which stage of pathogenesis these changes occur and what are their molecular inductors. Finally, transcriptional activity and adipogenic differentiation play an important role in formation of new fat depots from predecessor cells and activation of brown and beige fat demonstrating hypolipidemic and hypoglycemic properties. The aim of this study was investigation of pathophysiological mechanisms of development of IR and endothelial dysfunction, role of transcription factor Prep1 and small heat shock proteins, evaluation of novel methods of diagnostics of IR and therapeutic potential of brown and beige fat, determination of biotargets for new antidiabetic drugs.

Nonalcoholic fatty liver disease: cause or consequence of insulin resistance?

Nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM) are pathological conditions that are co-occurring, and have been reaching epidemic proportions. One of the most significant risk factors for the development of both T2DM and NAFLD is obesity, which increases existing insulin resistance (IR). IR thought to be one of the main pathogenic causes linking T2DM and NAFLD. In recent years, there has been increased interest in obtaining non-invasive methods for assessing fibrosis and determining indications for liver biopsy, such as the NAFLD fibrosis score, extended liver fibrosis panel, and transient elastography. However, liver biopsy remains the gold standard for diagnosing NAFLD. Given that patients with T2DM are at higher risk of NAFLD than the general population, and that the presence of diabetes is a risk factor for the progression of NAFLD, patients with T2DM should be more closely monitored by clinicians. The present review paper is devoted to the search for causeeffect relationships of concurrent diseases such as NAFLD and disorders of carbohydrate metabolism, and priority areas of diagnosis of NAFLD.