Insulin-stimulated glucose disposal in patients with type I (IDDM) and type II (NIDDM) diabetes mellitus

Resistência à insulina e síndrome metabólica no diabetes melito do tipo 1

A resistência à insulina (RI) pode desempenhar um papel, na história natural do diabetes melito do tipo 1 (DM1), maior do que o habitualmente reconhecido. Nas últimas décadas, este papel se tornou mais evidente com o aumento da obesidade e da diminuição da atividade física nos jovens. Esta revisão tem como objetivo apresentar e discutir a RI nas diferentes fases do DM1, bem como a prevalência da Síndrome Metabólica (SM) nessa condição. O aumento na RI, concomitante a uma diminuição da massa de células beta, pode alterar o equilíbrio entre a sensibilidade à insulina e a secreção de insulina, e precipitar a hiperglicemia nos indivíduos com pré-DM1. A RI poderia refletir uma forma mais agressiva de doença autoimune, mediada por fatores imuno-inflamatórios, comuns a ambos os processos, que também mediassem a destruição das células beta (TNF-alfa e IL-6). Estes conceitos fazem parte da "Hipótese Aceleradora". A história familiar de DM2 e a hiperglicemia crônica (glicotoxicidade), durante a fase clínica do DM1, estão associadas a uma diminuição da captação periférica de glicose. A nefropatia diabética (ND), através da inflamação subclínica e do aumento no estresse oxidativo, contribui para a RI e o desenvolvimento da SM. A prevalência da SM no DM1 varia entre 12 a 40%, sendo mais freqüente nos pacientes com ND e controle glicêmico insatisfatório. Estes achados possuem implicações na terapêutica e no prognóstico cardiovascular dos pacientes com DM1.

Insulin resistance and its contribution to colon carcinogenesis

The insulin resistance-colon cancer hypothesis, stating that insulin resistance may be associated with the development of colorectal cancer, represents a significant advance in colon cancer, as it emphasizes the potential for this cancer to become a modifiable disease. The fact that the incidence of insulin resistance has been increasing in the United States and much of the rest of the Western world where colon cancer remains the second leading cause of cancer death makes the exploration of the interrelationship of these conditions a subject of high priority. Here, we review the salient features of insulin resistance, defined as impaired biological response to the action of insulin. Recent epidemiological studies, evaluating potential associations between colon cancer risk and diabetes mellitus, dietary intake and metabolic factors, and IGF levels in several clinical settings, provide strong support of the insulin resistance-colon cancer hypothesis (without establishing causality). Mechanistically, insulin resistance has been associated with hyperinsulinemia, increased levels of growth factors including IGF-1, and alterations in NF-kappaB and peroxisome proliferator-activated receptor signaling, which may promote colon cancer through their effects on colonocyte kinetics. It is a reasonable expectation that in the not too distant future, critical interventions to the already mapped molecular sequence of events, which link two apparently disparate entities, combined with lifestyle changes could abrogate the development of colon cancer.

Mechanisms of vanadium action: insulin-mimetic or insulin-enhancing agent?

The demonstration that the trace element vanadium has insulin-like properties in isolated cells and tissues and in vivo has generated considerable enthusiasm for its potential therapeutic value in human diabetes. However, the mechanisms by which vanadium induces its metabolic effects in vivo remain poorly understood, and whether vanadium directly mimics or rather enhances insulin effects is considered in this review. It is clear that vanadium treatment results in the correction of several diabetes-related abnormalities in carbohydrate and lipid metabolism, and in gene expression. However, many of these in vivo insulin-like effects can be ascribed to the reversal of defects that are secondary to hyperglycemia. The observations that the glucose-lowering effect of vanadium depends on the presence of endogenous insulin whereas metabolic homeostasis in control animals appears not to be affected, suggest that vanadium does not act completely independently in vivo, but augments tissue sensitivity to low levels of plasma insulin. Another crucial consideration is one of dose-dependency in that insulin-like effects of vanadium in isolated cells are often demonstrated at high concentrations that are not normally achieved by chronic treatment in vivo and may induce toxic side effects. In addition, vanadium appears to be selective for specific actions of insulin in some tissues while failing to influence others. As the intracellular active forms of vanadium are not precisely defined, the site(s) of action of vanadium in metabolic and signal transduction pathways is still unknown. In this review, we therefore examine the evidence for and against the concept that vanadium is truly an insulin-mimetic agent at low concentrations in vivo. In considering the effects of vanadium on carbohydrate and lipid metabolism, we conclude that vanadium acts not globally, but selectively and by enhancing, rather than by mimicking the effects of insulin in vivo.