Modeling long-term diabetes and related complications in rats.

INTRODUCTION: Accurate preclinical modeling of diabetic complications such as retinopathy, nephropathy and neuropathy is crucial to enable the development of novel preventative therapies. The aims of this study were to establish a model of long-term diabetes with sustained medium scale hyperglycemia and characterize the pathological changes detectable after 4months, with particular respect to dependence on the degree of hyperglycemia. METHODS: Streptozotocin-induced diabetic CFY rats were subjected to four different insulin substitution protocols to achieve different levels of glycemic control (Diabetic 1-4 groups). Eyes were investigated by ophthalmoscopy, kidney function by urine analysis, and neuropathy by functional tests. Retinal and renal morphological evaluations were performed by histology, immuno-histochemistry and electron microscopy. RESULTS: Rats of the Diabetic 3 group showed massive hyperglycemia-dependent anterior segment neovascularization, enhanced total retinal score and retinal apoptotic cell number, degeneration of dopaminergic amacrine cells, increased glomerular PAS-positivity, altered excreted total protein/creatinine ratio and cold allodynia, parallel with medium scale hyperglycemia (blood glucose level between 22 and 25mmol/L) and satisfying state of health. DISCUSSION: We established a treatment protocol in rats enabling complex investigation of diabetic retinopathy, nephropathy and neuropathy on a long-term period. Clearly hyperglycemic dependent parameters of these complications serve as good outcome measures for preclinical trials. Our results provide a useful basis for designing studies for testing preventative treatments as well as other translational medical research in this field.

Biochemical background of toxic interaction between tiamulin and monensin.

Tiamulin, a diterpene antibiotic, is used for treatment of pulmonary and gastrointestinal infections in swine and poultry. Combined administration of tiamulin and ionophores (e.g. monensin) to farm animals may lead to intoxication manifested in severe clinical symptoms. Tiamulin metabolite complex with cytochrome P450 has been suggested to be the basis of drug-interactions. However, the formation of metabolic intermediate complex is questionable. The effect of tiamulin-treatment on cytochrome P450 activities was investigated in rats. Ethylmorphine and aminopyrine N-demethylation activities as well as monensin metabolism (O-demethylation) increased in liver microsomes of tiamulin-treated (200 mg/kg) animals. CYP3A1 induction caused by tiamulin was confirmed by the results of Western blot analysis. To test metabolic intermediate complex formation as a result of tiamulin treatment, cytochrome P450 activities were also determined in the presence of potassium ferricyanide. The findings together with those of in vitro complex formation suggested that formation of metabolic intermediate complexes of tiamulin with cytochrome P450 could be excluded. On the other hand, the results of inhibition studies showed significant decrease of ethylmorphine or aminopyrine as well as monensin demethylation in the presence of tiamulin. Our results proved that tiamulin has dual effect on cytochromes P450. It is able to induce and directly inhibit CYP3A enzymes, which are predominantly responsible for monensin O-demethylation. The direct effect of tiamulin as an inhibitor might play a more important role in toxicity than its putative effect as a chemical inducer of CYP3A enzymes.