Roles of neuronal nitric oxide synthase and inducible nitric oxide synthase in intestinal transplantation of rats

Nitric oxide protects intestinal mucosal barrier function and prevents acute graft rejection after intestinal transplantation: A mini-review

Intestinal transplantation is a complex technical procedure that provides patients suffering from end-stage intestinal failure an opportunity to enjoy improved quality of life, nutrition and survival. Compared to other types of organ transplants, it is a relatively new advancement in the field of organ transplantation. Nevertheless, great advances have been made over the past few decades to the present era, including the use of ischemic preconditioning, gene therapy, and addition of pharmacological supplements to preservation solutions. However, despite these strides, intestinal transplantation is still a challenging endeavor due to several factors. Notable among them is ischemia-reperfusion injury (IRI), which results in loss of cellular integrity and mucosal barrier function. In addition, IRI causes graft failure, delayed graft function, and decreased graft and recipient survival. This has necessitated the search for novel therapeutic avenues and improved transplantation protocols to prevent or attenuate intestinal IRI. Among the many candidate agents that are being investigated to combat IRI and its associated complications, nitric oxide (NO). NO is an endogenously produced gaseous signaling molecule with several therapeutic properties. The purpose of this mini-review is to discuss IRI and its related complications in intestinal transplantation, and NO as an emerging pharmacological tool against this challenging pathological condition. i.

Inducible and neuronal nitric oxide synthases exert contrasting effects during rat intestinal recovery following fasting

We investigated the effects of endogenous inducible (iNOS) and neuronal nitric oxide synthase on recovery from intestinal mucosal atrophy caused by fasting-induced apoptosis and decreased cell proliferation during refeeding in rats. Rats were divided into five groups, one of which was fed ad libitum, and four of which underwent 72 h of fasting, followed by refeeding for 0, 6, 24, and 48 h, respectively. iNOS and neuronal nitric oxide synthase mRNA and protein levels in jejunal tissues were measured, and mucosal height was histologically evaluated. Apoptotic indices, interferon-γ (IFN-γ) transcription levels, nitrite levels (as a measure of nitric oxide [NO] production),8-hydroxydeoxyguanosine formation (indicating reactive oxygen species [ROS] levels), crypt cell proliferation, and the motility indices (MI) were also estimated. Associations between mucosal height and NOS protein levels were determined using Spearman's rank correlation test. Notably, we observed significant increases in mucosal height and in neuronal nitric oxide synthase mRNA and protein expression as refeeding time increased. Indeed, there was a significant positive correlation between neuronal nitric oxide synthase protein level and mucosal height during the 48-h refeeding period ( r = 0.725, P < 0.01). Conversely, iNOS mRNA and protein expression decreased according to refeeding time, with a significant negative correlation between iNOS protein level and mucosal height being recorded during the 48-h refeeding period ( r = -0.898, P < 0.01). We also noted a significant negative correlation between jejunal neuronal nitric oxide synthase and iNOS protein concentrations over this same period ( r = -0.734, P < 0.01). Refeeding also restored the decreased jejunal MI caused by fasting. Our finding suggests that refeeding likely repairs fasting-induced jejunal atrophy by suppressing iNOS expression and subsequently inhibiting NO, ROS, and IFN-γ as apoptosis mediators, and by promoting neuronal nitric oxide synthase production and inducing crypt cell proliferation via mechanical stimulation. Impact statement Besides providing new data confirming the involvement of iNOS and nNOS in intestinal mucosal atrophy caused by fasting, this study details their expression and function during recovery from this condition following refeeding. We demonstrate a significant negative correlation between iNOS and nNOS levels during refeeding, and associate this with cell proliferation and apoptosis in crypts and villi. These novel findings elucidate the relationship between these NOS isoforms and its impact on recovery from intestinal injury. A mechanism is proposed comprising the up-regulation of nNOS activity by mechanical stimulation due to the presence of food in the intestine, restricting iNOS-associated apoptosis and promoting cell proliferation and gut motility. Our investigation sheds light on the molecular basis behind the repercussions of total parenteral nutrition on intestinal mucosal integrity, and more importantly, the beneficial effects of early enteral feeding.

Endothelium-dependent vasodilation effects of Panax notoginseng and its main components are mediated by nitric oxide and cyclooxygenase pathways

Panax notoginseng, a traditional Chinese herbal medicine, has been used for the treatment of cardiovascular diseases. The main bioactive components of this species are Panax notoginseng saponins (PNS). The present study aimed to investigate the effects of PNS and five of its main components (ginsenosides Rg1, Re, Rb1 and Rd, and notoginsenoside R1) on rat aorta rings pre-contracted with norepinephrine (NE) and to determine the underlying mechanism of action. Isolated aorta rings (with or without intact endothelium) from adult male Wistar rats were stimulated with NE to induce vasoconstriction, and subsequently treated with different concentrations of PNS and its five main components (Rg1, Re, Rb1, R1 and Rd) separately. This procedure was repeated after pre-incubation with the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and the cyclooxygenase (COX) inhibitor indomethacin (INDO), in order to elucidate the mechanism of action of PNS and its components. The results demonstrated that PNS and the components Rg1, Re, Rb1 and R1, but not Rd, induced vessel relaxation in a concentration-dependent manner when the endothelium lining was intact. NO synthase inhibitor L-NAME and guanylate cyclase inhibitor ODQ attenuated the diastolic effects of PNS, Rg1, Re, Rb1 and R1 in aortic rings with intact endothelium. By contrast, INDO, a known COX inhibitor weakened the vasodilation effects of PNS, Re and Rb1 but demonstrated no effect on Rg1 and R1. In conclusion, PNS and two of its main components (Re and Rb1) exert vasodilating effects through the NO and COX pathways.

Oral Citrulline Mitigates Inflammation and Jejunal Damage via the Inactivation of Neuronal Nitric Oxide Synthase and Nuclear Factor-κB in Intestinal Ischemia and Reperfusion

BACKGROUND

Intestinal ischemia and reperfusion (I/R) is a life-threatening emergency accompanied by inflammation and organ damage. We compared the mechanisms and the effects of arginine, citrulline, and glutamine on inflammation and intestinal damage.

MATERIALS AND METHODS

Male Wistar rats underwent 60 minutes of superior mesenteric artery occlusion and either 3 (I/R3) or 24 (I/R24) hours of reperfusion and were orally administered vehicle, arginine, citrulline, or glutamine 15 minutes before reperfusion and at 3, 9, and 21 hours of reperfusion.

RESULTS

I/R3 rats experienced jejunal damage and apoptosis, and I/R24 rats had liver dysfunction compared with normal rats (one-way ANOVA, P < .05). Arginine and citrulline administrations improved jejunal morphology, and citrulline and glutamine administrations alleviated the loss of jejunal mass in I/R3 rats. I/R3-increased circulating nitrate/nitrite (NOx), tumor necrosis factor-α, and interleukin-6 were significantly decreased by citrulline, glutamine and citrulline, and arginine, glutamine, and citrulline, respectively. These amino acids decreased plasma NOx and interferon-γ in I/R24, decreased jejunal neuronal nitric oxide synthase (NOS) protein in I/R3 rats, and alleviated jejunal apoptosis in I/R3 and I/R24 rats. In addition, the jejunal phosphorylated to total nuclear factor-κB (NF-κB) ratio was decreased by arginine and citrulline in I/R24 rats.

CONCLUSION

Oral administration of arginine, citrulline, and glutamine may alleviate systemic inflammation, jejunal apoptosis, and neuronal NOS in intestinal I/R. Citrulline may further attenuate jejunal damage by preserving jejunal mass, partially via the inactivation of NOS and the NF-κB pathway. In conclusion, oral citrulline may have more benefits than arginine and glutamine in mitigating intestinal ischemia and reperfusion-induced adverse effects.

Lifor Solution: An Alternative Preservation Solution in Small Bowel Transplantation

Background and Objectives. The intestinal mucosa is extremely sensitive to ischemia. Better intestinal preservation is the first step to improve the results of intestinal transplantation. The aim of the study is to investigate the effect of cold Lifor solution on preservation of swine small bowel. Methods. Swine ileum segments (200 cm) were allotransplanted heterotopically after 9-hour cold storage with UW solution (group 1, n = 6), with Lifor solution (group 2, n = 6), or without storage (group 3, n = 6), respectively. After cold storage, mucosal adenosine triphosphate (ATP) concentrations and histopathologic analysis after preservation were performed. At day 7 after the transplantation, intestinal absorptive function was also observed. Results. After 9 h cold preservation, pathological changes, the content of ATP in the intestinal mucosa, and the intestinal absorptive function after transplantation in group 2 were similar to those of group 1. Conclusion. The effect of cold storage of swine small bowel with Lifor solution is similar to that of UW solution. It may provide additional rationale for further exploration of Lifor as an alternative preservation solution in small bowel transplantation.