Fasting-induced intestinal apoptosis is mediated by inducible nitric oxide synthase and interferon-{gamma} in rat

Nitric oxide (NO) is associated with intestinal apoptosis in health and disease. This study aimed to investigate the role of intestinal NO in the regulation of apoptosis during fasting in rats. Male Wistar rats were divided into two groups and subcutaneously injected with saline (SA) or aminoguanidine (AG), followed by fasting for 24, 48, 60, and 72 h. At each time point, the jejunum was subjected to histological evaluation for enterocyte apoptosis by histomorphometric assessment and TUNEL analysis. We performed immunohistochemistry for inducible NO synthase (iNOS) expression in the jejunum and measured tissue nitrite levels using HPLC and 8-hydroxydeoxyguanosine adduct using ELISA, indicative of endogenous NO production and reactive oxygen species (ROS) production, respectively. Jejunal transcriptional levels of iNOS, neuronal NO synthase (nNOS), and interferon-gamma (IFN-gamma) were also determined by RT-PCR. Fasting caused significant jejunal mucosal atrophy due to attenuated cell proliferation and enhanced apoptosis with increase in iNOS transcription, its protein expression in intestinal epithelial cells (IEC), and jejunal nitrite levels. However, AG treatment histologically reduced apoptosis with inhibition of fasting-induced iNOS transcription, protein expression, and nitrite production. We also observed fasting-induced ROS production and subsequent IFN-gamma transcription, which were all inhibited by AG treatment. Furthermore, we observed reduced transcriptional levels of nNOS, known to suppress iNOS activation physiologically. These results suggest that fasting-induced iNOS activation in IEC may induce apoptosis mediators such as IFN-gamma via a ROS-mediated mechanism and also a possible role of nNOS in the regulation of iNOS activity in fasting-induced apoptosis.