Long-term enteral arginine supplementation in rats with intestinal ischemia and reperfusion

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.

Protective effect of intestinal ischemic preconditioning on ischemia reperfusion-caused lung injury in rats

Intestinal ischemia reperfusion (IR) causes injury of distant critical organs. Remote intestinal ischemic preconditioning (IP) may confer the cytoprotection in critical organs including lung. The authors hypothesized that intestinal IP would be a prophylactic factor in the prevention of distant lung injury induced by IR. Rats were randomly divided into IR, IP, and Sham (S) group. Compared with IR group in the serum and lung tissue, MPO, MDA, TNF-α, and IL-1 levels were significantly decreased in the IP group. Following the same pattern, NO level in the serum and lung tissue was significantly increased in the IP group. And intestinal IP markedly abolished lung injury scores in contrast to IR group. Moreover, intestinal IP significantly attenuated caspase-3 expression, leading to the low expression of Bax and the high expression of Bcl-2. The present study showed that intestinal IP ameliorates the capacity of anti-oxygen free radical, inhibits the release of pro-inflammatory cytokines and alleviates apoptosis in IR-induced lung injury in rats. Intestinal IP may provide a novel prophylactic strategy for treatment of IR-induced lung injury.

Guanylyl cyclase-G modulates jejunal apoptosis and inflammation in mice with intestinal ischemia and reperfusion

Background

Membrane bound guanylyl cyclase-G (mGC-G), a novel form of GC mediates ischemia and reperfusion (IR)-induced renal injury. We investigated the roles of mGC-G in intestinal IR-induced jejunal damage, inflammation, and apoptosis.

Materials and methods

Male C57BL/6 wild-type (WT) and mGC-G gene knockout (KO) mice were treated with a sham operation or 45 min of superior mesenteric arterial obstruction followed by 3, 6, 12, or 24 h of reperfusion.

Results

Sham-operated KO mice had significantly lower plasma nitrate and nitrite (NOx) levels and jejunal villus height, crypt depth, and protein expression of phosphorylated-nuclear factor-kappa-B (NF-κB), phosphorylated-c-Jun N-terminal kinases (JNK) 2/3, phosphorylated-p38, and B-cell lymphoma-2 (Bcl-2). They had significantly greater jejunal interleukin-6 mRNA, cytochrome c protein, and apoptotic index compared with sham-operated WT mice. Intestinal IR significantly decreased plasma NOx in WT mice and increased plasma NOx in KO mice. The jejunal apoptotic index and caspase 3 activities were significantly increased, and nuclear phosphorylated-NF-κB and phosphorylated-p38 protein were significantly decreased in WT, but not KO mice with intestinal IR. After reperfusion, KO mice had an earlier decrease in jejunal cyclic GMP, and WT mice had an earlier increase in jejunal proliferation and a later increase in cytosol inhibitor of kappa-B-alpha. Intestinal IR induced greater increases in plasma and jejunal interleukin-6 protein in WT mice and a greater increase in jejunal interleukin-6 mRNA in KO mice.

Conclusions

mGC-G is involved in the maintenance of jejunal integrity and intestinal IR-induced inflammation and apoptosis. These results suggest that targeting cGMP pathway might be a potential strategy to alleviate IR-induced jejunal damages.

New insights in intestinal ischemia-reperfusion injury: implications for intestinal transplantation

PURPOSE OF REVIEW

Ischemia-reperfusion injury is inevitable during intestinal transplantation and can negatively affect the transplant outcome. Here, an overview is provided of the recent advances in the pathophysiological mechanisms of intestinal ischemia-reperfusion injury and how this may impact graft survival.

RECENT FINDINGS

The intestine hosts a wide range of microorganisms and its mucosa is heavily populated by immune cells. Intestinal ischemia-reperfusion results in the disruption of the epithelial lining, affecting also protective Paneth cells (antimicrobials) and goblet cells (mucus), and creates a more hostile intraluminal microenvironment. Consequently, both damage-associated molecular patterns as well as pathogen-associated molecular patterns are released from injured tissue and exogenous microorganisms, respectively. These 'danger' signals may synergistically activate the innate immune system. Exaggerated innate immune responses, involving neutrophils, mast cells, platelets, dendritic cells, as well as Toll-like receptors and complement proteins, may shape the adaptive T-cell response, thereby triggering the destructive alloimmune response toward the graft and resulting in transplant rejection.

SUMMARY

Innate immune activation as a consequence of ischemia-reperfusion injury may compromise engraftment of the intestine. More dedicated research is required to further establish this concept in man and to design more effective therapeutic strategies to better tolerize intestinal grafts.

Arginine de novo and nitric oxide production in disease states

Arginine is derived from dietary protein intake, body protein breakdown, or endogenous de novo arginine production. The latter may be linked to the availability of citrulline, which is the immediate precursor of arginine and limiting factor for de novo arginine production. Arginine metabolism is highly compartmentalized due to the expression of the enzymes involved in arginine metabolism in various organs. A small fraction of arginine enters the NO synthase (NOS) pathway. Tetrahydrobiopterin (BH4) is an essential and rate-limiting cofactor for the production of NO. Depletion of BH4 in oxidative-stressed endothelial cells can result in so-called NOS3 "uncoupling," resulting in production of superoxide instead of NO. Moreover, distribution of arginine between intracellular transporters and arginine-converting enzymes, as well as between the arginine-converting and arginine-synthesizing enzymes, determines the metabolic fate of arginine. Alternatively, NO can be derived from conversion of nitrite. Reduced arginine availability stemming from reduced de novo production and elevated arginase activity have been reported in various conditions of acute and chronic stress, which are often characterized by increased NOS2 and reduced NOS3 activity. Cardiovascular and pulmonary disorders such as atherosclerosis, diabetes, hypercholesterolemia, ischemic heart disease, and hypertension are characterized by NOS3 uncoupling. Therapeutic applications to influence (de novo) arginine and NO metabolism aim at increasing substrate availability or at influencing the metabolic fate of specific pathways related to NO bioavailability and prevention of NOS3 uncoupling. These include supplementation of arginine or citrulline, provision of NO donors including inhaled NO and nitrite (sources), NOS3 modulating agents, or the targeting of endogenous NOS inhibitors like asymmetric dimethylarginine.