BIOLOGICAL EFFECTS OF ENCAPSULATED INSULIN ON TRANSFECTED CHINESE-HAMSTER OVARY CELLS

Oral administration of insulin incorporated into the wall of isobutylc yanoacrylate nanocapsule to diabetic rats induces a long-lasting norma lization of their fasting glycaemia. In this study, we examined the bi ological action of encapsulated insulin on DNA and glycogen syntheses in Chinese hamster ovary cells transfected with the human insulin rece ptor gene. In the 10(-11) mol/l - 10(-9) mol/l concentration range, en capsulated insulin elicited responses comparable to those induced by n ative insulin: at 10(-9) mol/l, the rates of glycogen and DNA synthesi s were enhanced by factors 3 and 2.5, respectively. Encapsulated insul in at 10(-7) mol/l evoked receptor desensitization although it did not induce receptor down-regulation and did not alter receptor recycling for up to 6 h. Chloroquine decreased the action of native insulin on g lycogen synthesis, but did not affect the dose-response characteristic s of encapsulated insulin. Acid-washing of the cells after 1 h of stim ulation decreased maximal insulin responsiveness and provoked a dose r esponse curve for encapsulated insulin similar to that of the native h ormone. Direct measurement of effective insulin binding activity showe d that encapsulated insulin (at 10(-8) and 10(-7) mol/l) was withdrawn from the incubation medium 5-8 times less efficiently than native ins ulin. These data are in agreement with previous results showing that t he polymeric wall protects encapsulated insulin from degradation. Pers istence of intact encapsulated insulin inside and outside the cell may result in modifying signalling events and thus be responsible for the observed cellular desensitization.