[Treatment of diabetes in experimental animals by metallocomplexes]

The number of patients suffered from diabetes mellitus has increased over the decades probably because of both lifestyle- and diet-changes. There are two types of diabetes mellitus. Type 1 diabetes mellitus is due to the autoimmune-mediated destruction of pancreatic B cells, which results in absolute insulin deficiency, thus the patients require insulin injections. Type 2 diabetes mellitus is due to the insulin resistance and abnormal insulin secretion, thus the patients require exercise, diet control and/or oral hypoglycemic medicines. Each treatment, however, has some problems involving physical and mental burden, and formation of self-antibodies for insulin injections, and the severe side effects and discontinuation of insulin synthesis in the pancreas for hypoglycemic medicines. To overcome these important problems and find the replacements for the insulin injections and synthetic medicines, we attempted to develop new antidiabetic metallocomplexes with novel structures and mechanisms. In 1990, we first presented orally active vanadyl (+4 oxidation state of oxo-vanadium) complexes including vanadyl-cysteine methyl ester complex, which normalized hyperglycemia in the streptozocin (STZ)-induced type 1 diabetic rats. Based on these findings, we have developed a wide variety of vanadyl complexes with different coordination environments around vanadyl ion. Following the study, we also challenged to develop orally active zinc complexes since 2002. This review focuses on our recent development of vanadyl and zinc complexes for anti-diabetic and anti-metabolic syndromes, together with the propose for the possible action mechanism of these complexes in adipocytes.