Synergistic Effects of Adjuvants, Endotoxin, and Fasting on Induction of Diabetes With Multiple Low Doses of Streptozocin in Rats

Abstract

Three weekly intraperitoneal injections of complete Freund's adjuvant (CFA) and, 1 day later, low-dose streptozocin (STZ; 25 mg/kg i.p.) have been reported to cause immune destruction of β-cells and a gradual onset of diabetes mellitus. In this study, male Lewis rats were injected intraperitoneally with CFA and 1 day later with low-dose STZ; these were repeated at weekly intervals for 3 wk. The incidence of diabetes mellitus (nonfasted plasma glucose >200 mg/dl) in wk 1, 2, 3, and 4 was 50, 80, 93, and 100%, respectively. Rats receiving either CFA or STZ only did not develop diabetes. Injections of either the components of CFA (incomplete Freund's adjuvant and Mycobacterium butyricum), another granuloma-inducing organism (Listeria monocytogenes), or endotoxin before STZ induced diabetes, but the onset was slower and the diabetes was less severe than with CFA and STZ. Because intraperitoneal CFA injections caused peritoneal irritation, acute weight loss, and hypoglycemia on the day after injection, we examined whether fasting alone potentiated low-dose STZ. Fasting for 24 h before and 24 h after low-dose STZ caused diabetes that was similar in rapidity of onset and severity to that induced with CFA and STZ. Administration of CFA subcutaneously before STZ did not cause hypoglycemia or weight loss but did cause diabetes. Thus, the fasting effect of intraperitoneal CFA was not responsible for the induction of diabetes with CFA and STZ. These data indicate that immunologic adjuvants, endotoxin, and fasting all potentiate the diabetogenic action of low-dose STZ. The 50% incidence of diabetes in rats within 48 h of a single injection of CFA and low-dose STZ suggests that the immune system does not mediate diabetes in this model. Furthermore, transplants of islet isografts were not rejected by eight rats made diabetic with CFA and low-dose STZ.