[Oral administration of insulin inhibits islet beta cell apoptosis and prevents diabetes in NOD mice].
OBJECTIVE
To investigate the effect of oral administration of insulin on insulitis beta cell apoptosis and diabetes in non-obese diabetic (NOD) mice, and to explore the mechanism of immune tolerance induced by insulin.


METHODS
Eighty-six female NOD mice were randomly divided into an insulin group (n=43) and a phosphate buffered saline (PBS) group (n=43). From 4 weeks of age, the recombinant human insulin (Humulin R) 1 mg (70 microL) was administrated in the oral insulin group and 70 microL PBS in the control group respectively, twice per week before 12 weeks of age and then once weekly until 30 weeks. Insulitis and beta cell apoptosis of islets were observed at 12 weeks. IL-4 and IFN-gamma in the sera were measured by enzyme linked immunosorbent assay (ELISA). The expression levels of I-Abeta(g7), IL-4, IFN-gamma, IL-1beta, Fas and TGF-beta mRNA of islets, and IL-4, IFN-gamma, TGF-beta mRNA of Peyer's patch were measured by reverse transcription-polymerase chain reaction (RT-PCR) at 12 weeks.


RESULTS
The incidences in the insulin group were significantly lower than those in the PBS group (55.6% vs 85.7% at 30 weeks, 70.4% vs 96.4% at 52 weeks, P<0.05). The insulitis scores in the insulin group were lower than those in the PBS group, but there was no statistical significance. Fas expression on islets and apoptotic beta cell rates in the insulin group were lower than those in the PBS group (P<0.05). In the insulin group, serum IL-4 levels were higher, and IFN-gamma levels were lower than those in the PBS group (P<0.05). The levels of I-Abeta(g7), IFN-gamma, IL-1beta and Fas mRNA transcription in islets and IFN-gamma mRNA transcription in Peyer's patch were both lower in the insulin group, and IL-4, TGF-beta mRNA levels were higher than those in the PBS group (P<0.05).


CONCLUSIONS
The specific autoantigen insulin may induce the immune tolerance and prevent the diabetes in NOD mice, but it cannot block the progression of insulitis. Oral administration of insulin can induce the regulatory T cells, and make Th1 to Th2 cytokine shifts in the system and islets, thus preventing the Fas-mediated beta-cell apoptosis and diabetes.
Jiang
Tie-Jian
TJ
Department of Endocrinology, Xiangya Hospital, Central South University, Changsha 410008, China.
Zhou
Zhi-Guang
ZG
D000284:Administration, Oral; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D016207:Cytokines / Q000378:metabolism; D003922:Diabetes Mellitus, Type 1 / Q000188:drug therapy* / Q000473:pathology; D005260:Female; D061386:Insulin, Regular, Human / Q000008:administration & dosage / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects*; D051379:Mice; D016688:Mice, Inbred NOD; D058408:Th1-Th2 Balance; D019014:fas Receptor / Q000378:metabolism
D016207:Cytokines; C491899:Fas protein, mouse; D061386:Insulin, Regular, Human; D019014:fas Receptor