Effects of enteral arginine supplementation on the structural intestinal adaptation in a rat model of short bowel syndrome

Short bowel syndrome in infants: the critical role of luminal nutrients in a management program

Short bowel syndrome develops when the remnant mass of functioning enterocytes following massive resections cannot support growth or maintain fluid–electrolyte balance and requires parenteral nutrition. Resection itself stimulates the intestine’s inherent ability to adapt morphologically and functionally. The capacity to change is very much related to the high turnover rate of enterocytes and is mediated by several signals; these signals are mediated in large part by enteral nutrition. Early initiation of enteral feeding, close clinical monitoring, and ongoing assessment of intestinal adaptation are key to the prevention of irreversible intestinal failure. The length of the functional small bowel remnant is the most important variable affecting outcome. The major objective of intestinal rehabilitation programs is to achieve early oral nutritional autonomy while maintaining normal growth and nutrition status and minimizing total parenteral nutrition related comorbidities such as chronic progressive liver disease. Remarkable progress has been made in terms of survivability and quality of life, especially in the context of coordinated multidisciplinary programs, but much work remains to be done.

Effect of intestinal resections on arginine metabolism: practical implications for nutrition support

PURPOSE OF REVIEW

The present review relates recent developments in the understanding of arginine and citrulline metabolism and complementation after intestinal resection.

RECENT FINDINGS

Arginine metabolism is disturbed after significant intestinal resection, with reduced fluxes and circulating and tissue concentrations. There is also a reduction in citrulline production, a major source of endogenous arginine by enterocyte metabolism. There is evidence to suggest that arginine or citrulline supplementation may be important in this situation.

SUMMARY

In experimental intestinal resection, arginine availability decreases as intestinal citrulline synthesis decreases. In this setting, there is debate over the efficiency of arginine supplementation on intestinal adaptation, perhaps due to different doses used. In contrast, citrulline, a precursor for arginine synthesis, whether provided enterally or parenterally, is more efficient at 1 g/kg/day than complementation with arginine (at the same dose) in sustaining arginine pools. In addition, citrulline is more effective than arginine in maintaining nitrogen homeostasis. Clinical studies are vital in order to establish the value of citrulline supplementation in short bowel patients.

Bilirubin impairs intestinal regrowth following massive small bowel resection in a rat model

OBJECTIVES

The purpose of the present study was to evaluate the effects of exogenous bilirubin on structural intestinal adaptation, cell proliferation, and apoptosis in a rat model of short bowel syndrome (SBS).

MATERIALS AND METHODS

Male Sprague-Dawley rats were divided into 5 experimental groups: Sham rats underwent bowel transection and reanastomosis, sham multiple doses of bilirubin (MDB) rats underwent bowel transection and were treated with bilirubin, SBS rats underwent a 75% small bowel resection, SBS-SDB (single dose bilirubin) rats underwent a bowel resection and were treated with a single dose of bilirubin, and SBS-MDB underwent a bowel resection and were treated with 3 doses of bilirubin. Bilirubin was administered intraperitoneally from the 7th day through the 14th day postoperatively. Serum total bilirubin concentration over time was evaluated in 5 SBS-SDB rats following a single intraperitoneal dose. Total bilirubin, alanine aminotransferase, and aspartate aminotransferase in serum and parameters of intestinal adaptation, enterocyte proliferation, and enterocyte apoptosis were determined on day 15.

RESULTS

SBS-SDB and SBS-MDB animals demonstrated lower ileal bowel and mucosal weights, jejunal mucosal DNA and ileal mucosal protein, and jejunal and ileal villus height and crypt depth (vs SBS animals). Bilirubin-treated rats showed a lower apoptotic index in jejunum and ileum and a trend toward an increase in cell proliferation in jejunum and ileum (vs SBS group).

CONCLUSIONS

In a rat model of SBS, exogenous bilirubin inhibits structural intestinal adaptation. Increased cell proliferation and decreased apoptosis may be considered adaptive mechanisms that maintain cell mass.

Impairment of arginine metabolism in rats after massive intestinal resection: effect of parenteral nutrition supplemented with citrulline compared with arginine

Arginine homoeostasis is impaired in short bowel syndrome, but its supplementation in short bowel syndrome patients remains controversial. Recently, we demonstrated the benefits of citrulline supplementation by the enteral route in resected rats. Since the first step in managing short bowel syndrome is to initiate total parenteral nutrition, we hypothesized that parenteral citrulline supplementation would be more appropriate in this situation than arginine supplementation. In the present study, 24 rats were assigned to four groups. The sham group underwent transection whereas the three other groups underwent resection (R) of 80% of the small intestine. All rats were then fed exclusively by total parenteral nutrition as follows: supplementation with citrulline (R+CIT), with arginine (R+ARG) or no supplementation (R). All of the rats received isocaloric and isonitrogenous nutrition for 4 days. Nitrogen balance was measured daily. Rats were then killed and the blood was collected and the intestinal mucosa and extensor digitorum longus muscle were removed for amino acid and protein analysis. Citrulline and arginine increased mucosal protein content in the ileum (compared with sham and R, P<0.05). However, only citrulline prevented extensor digitorum longus atrophy (R+CIT, 130±3 mg compared with R, 100±6 mg and R+ARG, 110±2 mg, P<0.05). In addition, arginine worsened nitrogen balance (R+ARG, 104±46 mg/72 h compared with R, 249±69 mg/72 h, P<0.05). Only citrulline was able to prevent muscle atrophy and it was achieved independently from any noticeable effect on the gut in particular because citrulline and arginine share the same effect on mucosal ileal protein content. These results suggest that citrulline should be considered as a potential supplement for total parenteral nutrition of short bowel syndrome patients.

Intestinal intraepithelial lymphocyte derived angiotensin converting enzyme modulates epithelial cell apoptosis

BACKGROUND & AIMS

Intestinal adaptation in short bowel syndrome (SBS) consists of increased epithelial cell (EC) proliferation as well as apoptosis. Previous microarray analyses of intraepithelial lymphocytes (IEL) gene expression after SBS showed an increased expression of angiotensin converting enzyme (ACE). Because ACE has been shown to promote alveolar EC apoptosis, we examined if IEL-derived ACE plays a role in intestinal EC apoptosis.

METHODS

Mice underwent either a 70% mid-intestinal resection (SBS group) or a transection (Sham group) and were studied at 7 days. ACE expression was measured, and ACE inhibition (ACE-I, enalaprilat) was used to assess ACE function.

RESULTS

IEL-derived ACE was significantly elevated in SBS mice. The addition of an ACE-I to SBS mice resulted in a significant decline in EC apoptosis. To address a possible mechanism, tumor necrosis factor alpha (TNF-alpha) mRNA expression was measured. TNF-alpha was significantly increased in SBS mice, and decreased with ACE-I. Interestingly, ACE-I was not able to decrease EC apoptosis in TNF-alpha knockout mice.

CONCLUSIONS

This study shows a previously undescribed expression of ACE by IEL. SBS was associated with an increase in IEL-derived ACE. ACE appears to be associated with an up-regulation of intestinal EC apoptosis. ACE-I significantly decreased EC apoptosis.

Mechanisms of enteral nutrient-enhanced intestinal adaptation

The role of enteral nutrients in maintaining small intestinal structure and function is well established. Evidence that enteral nutrients induce intestinal adaptation include the structural and functional gradient along the length of the healthy intestine, the atrophy and functional compromise induced by fasting and parenteral nutrition, and the enhanced adaptive capacity of the distal intestine following partial enterectomy. Key mechanisms contributing to enteral nutrient-induced intestinal adaptation include nonspecific luminal stimulation and that provided by specific nutrients, "functional workload" induced by polymeric nutrients, potential stimulation of pancreaticobiliary secretions, secretion of humoral mediators, and induction of intestinal hyperemia.

Advances in short bowel syndrome: an updated review

Short bowel syndrome (SBS) continues to be an important clinical problem due to its high mortality and morbidity as well as its devastating socioeconomic effects. The past 3 years have witnessed many advances in the investigation of this condition, with the aim of elucidating the cellular and molecular mechanisms of intestinal adaptation. Such information may provide opportunities to exploit various factors that act as growth agents for the remaining bowel mucosa and may suggest new therapeutic strategies to maintain gut integrity, eliminate dependence on total parenteral nutrition, and avoid the need for intestinal transplantation. This review summarizes current research on SBS over the last few years.

Intestinal adaptation after massive intestinal resection

Patients with short bowel syndrome require long term parenteral nutrition support. However, after massive intestinal resection the intestine undergoes adaptation and nutritional autonomy may be obtained. Given that the complications of parenteral nutrition may be life threatening or result in treatment failure and the need for intestinal transplantation, a more attractive option is to wean patients off nutrition support by optimising the adaptive process. The article examines the evidence that after extensive small bowel resection adaptation occurs in humans and focuses on the factors that influence adaptation and the strategies that have been used to optimise this process. The review is based on an English language Medline search with secondary references obtained from key articles. There is evidence that adaptation occurs in humans. Adaptation is a complex process that results in response to nutrient and non-nutrient stimuli. Successful and reproducible strategies to improve adaptation remain elusive despite an abundance of experimental data. Nevertheless given the low patient survival and quality of life associated with other treatments for irreversible intestinal failure it is imperative that clinical research continues into the optimisation of the adaptation.

Intestinal adaptation after massive intestinal resection

Patients with short bowel syndrome require long term parenteral nutrition support. However, after massive intestinal resection the intestine undergoes adaptation and nutritional autonomy may be obtained. Given that the complications of parenteral nutrition may be life threatening or result in treatment failure and the need for intestinal transplantation, a more attractive option is to wean patients off nutrition support by optimising the adaptive process. The article examines the evidence that after extensive small bowel resection adaptation occurs in humans and focuses on the factors that influence adaptation and the strategies that have been used to optimise this process. The review is based on an English language Medline search with secondary references obtained from key articles. There is evidence that adaptation occurs in humans. Adaptation is a complex process that results in response to nutrient and non-nutrient stimuli. Successful and reproducible strategies to improve adaptation remain elusive despite an abundance of experimental data. Nevertheless given the low patient survival and quality of life associated with other treatments for irreversible intestinal failure it is imperative that clinical research continues into the optimisation of the adaptation.

Parenteral arginine impairs intestinal adaptation following massive small bowel resection in a rat model

The nitric oxide precursor L-arginine (ARG) has been shown to influence intestinal structure and absorptive function. It is also well known that the route of administration modulates the effects of ARG. The present study evaluated the effects of parenteral ARG on structural intestinal adaptation, cell proliferation, and apoptosis in a rat model of short bowel syndrome (SBS). Male Sprague-Dawley rats were divided into three experimental groups: Sham rats underwent bowel transection and reanastomosis, SBS rats underwent a 75% small bowel resection, and SBS-ARG rats underwent a 75% small bowel resection and were treated with ARG given subcutaneously at a dose of 300 mug/kg, once daily, from days 3 to 14. Parameters of intestinal adaptation, enterocyte proliferation, and enterocyte apoptosis were determined on day 15 following operation. The SBS rats demonstrated a significant increase in jejunal and ileal bowel and mucosal weight, villus height and crypt depth, and cell proliferation index compared with the sham group. The SBS-ARG animals demonstrated lower ileal bowel and mucosal weights, jejunal mucosal DNA and ileal mucosal protein, and jejunal and ileal villus height and crypt depth compared with SBS animals. The SBS-ARG rats also had a lower cell proliferation index in both jejunum and ileum and a greater enterocyte apoptotic index in ileum compared with the SBS-untreated group. In conclusion, in a rat model of SBS, parenteral arginine inhibits structural intestinal adaptation. Decreased cell proliferation and increased apoptosis are the main mechanisms responsible for decreased cell mass.