Beneficial effect of nicotinamide on the proportion of insulin cells in developing chick pancreas

Previous studies have suggested that nicotinamide increases the number of insulin cells both in vivo and in vitro. However, the question remains as to whether there is in fact an increase and whether this increase is caused by the proliferation of progenitor cells, or by replication of existing insulin cells. In order to investigate this, the endodermal component of dorsal pancreatic buds of 5-day-old chick embryos was cultured on Matrigel in a serum-free medium (Ham's F12-ITS) to which nicotinamide, at a concentration of 5 and 10 mM, respectively, was added. Control explants were cultured in Ham's F12-ITS medium without nicotinamide. After 7 days in culture the buds were incubated with bromodeoxyuridine (BrdU) and then processed for immunocytochemistry. Localization of insulin, BrdU and glucagon was carried out on adjacent serial sections. The proportion of insulin cells was 6.76, 11.32 and 16.86% in control, 5 and 10 mM nicotinamide-treated explants, respectively. Hence adding nicotinamide to the culture medium induced a 1.7- and 2.5-fold increase in the proportion of insulin cells when compared to the controls. These proportions were significantly different from that of control explants (P < 0.05). However, a very small number of insulin cells were found to be proliferating, suggesting that the increase in the proportion of insulin cells had resulted from stimulation of progenitor cells and not proliferation of existing insulin cells.