Novel agents in the treatment of intestinal failure: humoral factors

Enhancement of Colonic Absorptive Function after the Massive Resection of the Small Intestine Based on the Creation of an Artificial Colonic Valve

The colon can have an absorptive function similar to that of the small intestine after the massive resection of the small bowel. To improve colonic absorptive function, we created a valve in the colon (artificial colonic valve, ACV). ACVs were created in 20 rats that had 80 percent of their small intestine resected, with an observation time of 30 weeks. The ACV rats were compared with those in the non-operated control group, the short bowel syndrome (SBS) group and the colon interposition (CI) group. The ACV rats were much heavier than those in the control group, SBS group and CI group. In terms of histology and the levels of α-amylase and the Na⁺-dependent bile salt transporter, the absorptive function of the colons before the valves resembled that of the small intestine. The colonic absorptive function was more obvious in ACV rats than in CI rats. An ACV can enhance colonic absorptive function after the massive resection of the small intestine. The colonic absorptive function of ACV rats was better than that of the rats in the CI group.

Teduglutide for the treatment of short bowel syndrome

Extensive resection of the intestine impairs its absorptive capacity and results in short bowel syndrome when the nutritional equilibrium is compromised. The remnant intestine adapts structurally to compensate, but nutritional autonomy cannot be achieved in patients with intestinal failure, requiring intravenous fluids and parenteral nutrition (PN) for sustenance of life. PN is expensive and associated with serious complications. Efforts to minimize or eliminate the need for PN heralded research focusing on the therapeutic utility of intrinsic gut factors involved in the postresection adaptation process. With the breakthrough recognition of the intestinotrophic properties of glucagon-like peptide-2, teduglutide, a recombinant analogue of glucagon-like peptide-2, is being investigated as a promising hope to mitigate the requirement of PN. Clinical studies to date have demonstrated a desirable benefit-to-risk profile in regards to its safety and efficacy. If approved for marketing, it will be the first of its class in short bowel syndrome management, offering an innovative therapeutic modality for this debilitating condition.

Early but not late administration of glucagon-like peptide-2 following ileo-cecal resection augments putative intestinal stem cell expansion

Expansion of intestinal progenitors and putative stem cells (pISC) occurs early and transiently following ileo-cecal resection (ICR). The mechanism controlling this process is not defined. We hypothesized that glucagon-like peptide-2 (GLP-2) would augment jejunal pISC expansion only when administered to mice immediately after ICR. Since recent reports demonstrated increases in intestinal insulin-like growth factor (IGF)-I following GLP-2 administration, we further hypothesized that increased intestinal IGF-I expression would correlate with pISC expansion following ICR. To assess this, GLP-2 or vehicle was administered to mice either immediately after resection (early) or before tissue harvest 6 wk following ICR (late). Histological analysis quantified proliferation and intestinal morphometrics. Serum levels of GLP-2 were measured by ELISA and jejunal IGF-I mRNA by qRT-PCR. Expansion of jejunal pISC was assessed by fluorescent-activated cell sorting of side population cells, immunohistochemistry for phosphorylated beta-catenin at serine 552 (a pISC marker), percent of crypt fission, and total numbers of crypts per jejunal circumference. We found that early but not late GLP-2 treatment after ICR significantly augmented pISC expansion. Increases in jejunal IGF-I mRNA correlated temporally with early pISC expansion and effects of GLP-2. Early GLP-2 increased crypt fission and accelerated adaptive increases in crypt number and intestinal caliber. GLP-2 increased proliferation and intestinal morphometrics in all groups. This study shows that, in mice, GLP-2 promotes jejunal pISC expansion only in the period immediately following ICR. This is associated with increased IGF-I and accelerated adaptive increases in mucosal mass. These data provide clinical rationale relevant to the optimal timing of GLP-2 in patients with intestinal failure.

Intestinal specific overexpression of interleukin-7 attenuates the alternation of intestinal intraepithelial lymphocytes after total parenteral nutrition administration

OBJECTIVE

Total parenteral nutrition (TPN), with the complete removal of enteral nutrition, results in marked changes in intestinal intraepithelial lymphocyte (IEL) function and phenotype. Previous work shows that TPN results in a loss of intestinal epithelial cell-derived interleukin-7 (IL-7), and this loss may play an important role in development of such TPN-associated IEL changes.

METHODS

To further understand this relation, we generated a transgenic mouse (IL-7), which overexpresses IL-7 specifically in intestinal epithelial cells. We hypothesized that this localized overexpression would attenuate many of the observed TPN-associated IEL changes.

RESULTS

Our study showed that TPN administration led to significant changes in IEL phenotype, including a marked decline in the CD8alphabeta+, CD4+, and alphabeta-TCR+ populations. IEL basal proliferation decreased 1.7-fold compared with wild-type TPN mice. TPN administration in wild-type mice resulted in several changes in IEL-derived cytokine expression. IL-7 mice given TPN, however, maintained IEL proliferation, and sustained normal IEL numbers and phenotype.

CONCLUSIONS

We conclude that specific intestinal IL-7 overexpression significantly attenuated many IEL changes in phenotype and function after TPN administration. These findings suggest a mechanism by which TPN results in observed IEL changes.

Modulation of mouse intestinal epithelial cell turnover in the absence of angiotensin converting enzyme

Angiotensin converting enzyme (ACE) has been shown to be involved in regulation of apoptosis in nonintestinal tissues. This study examined the role of ACE in the modulation of intestinal adaptation utilizing ACE knockout mice (ACE-/-). A 60% small bowel resection (SBR) was used, since this model results in a significant increase in intestinal epithelial cell (EC) apoptosis as well as proliferation. Baseline villus height, crypt depth, and intestinal EC proliferation were higher, and EC apoptosis rates were lower in ACE-/- compared with ACE+/+ mice. After SBR, EC apoptosis rates remained significantly lower in ACE-/- compared with ACE+/+ mice. Furthermore, villus height and crypt depth after SBR continued to be higher in ACE-/- mice. The finding of a lower bax-to-bcl-2 protein ratio in ACE-/- mice may account for reduced EC apoptotic rates after SBR in ACE-/- compared with ACE+/+ mice. The baseline higher rate of EC proliferation in ACE-/- compared with ACE+/+ mice may be due to an increase in the expression of several EC growth factor receptors. In conclusion, ACE appears to have an important role in the modulation of intestinal EC apoptosis and proliferation and suggests that the presence of ACE in the intestinal epithelium has a critical role in guiding epithelial cell adaptive response.

Specific overexpression of IL-7 in the intestinal mucosa: the role in intestinal intraepithelial lymphocyte development

IL-7 plays a crucial role in controlling T cell development and homeostasis. Since IL-7 may be derived from extraintestinal sources, and exogenous IL-7 broadly affects lymphoid populations, the actions of epithelial cell (EC)-derived IL-7 are not fully understood. The effect of intestinal specific expression of IL-7 on intestinal mucosal lymphocytes was investigated by using an IL-7 transgenic mouse model. We generated an intestinal EC-specific overexpressing IL-7 transgenic mouse model (IL-7(vill)) and compared their phenotype and function to wild-type C57BL/6J mice. EC-derived IL-7 overexpression was found to be exclusively in the small and large intestine. Numbers and subtypes of mucosal lymphocytes, including intraepithelial lymphocytes (IEL) and lamina propria lymphocytes (LPL), significantly changed in IL-7(vill) mice. From a functional standpoint, IEL proliferation also significantly increased in IL-7(vill) mice. IEL cytokine expression significantly changed in both T cell receptor (TCR)-alphabeta(+) and TCR-gammadelta(+) IEL subpopulations, including a significant increase in IFN-gamma and TNF-alpha as well as an increase in keratinocyte growth factor expression. EC expression of CD103 (integrin alpha(E)beta(7)), the ligand of E-cadherin, markedly upregulated and may account for a mechanism of the massive expansion of IEL in transgenic mice. Systemic lymphoid populations did not change in transgenic mice. IL-7 overexpression by intestinal EC significantly affected IEL phenotype and function. These results offer insight into the role of IL-7 in IEL development and suggest a critical role of EC-derived expression of IL-7 in the phenotype and function of IEL.

Short bowel syndrome

Treatment of short bowel syndrome (SBS) is often a difficult endeavor due to the high variability among patients with SBS in regard to remaining anatomical structure and functional capacity. Research efforts to substantiate the use of existing therapies in the treatment of SBS are ongoing, with newer developments yet to be fully explored. Current therapy for SBS begins with the implementation of a modified diet based on the presence or absence of the colon. Patients with difficulty ingesting enough nutrients and fluids for weight maintenance and fluid balance may benefit from nocturnal enteral nutrition and hydration. Those with inadequate absorptive capacity despite maximization of oral and enteral intake will need parenteral nutrition (PN) or hydration. Medications, including antisecretory agents, antidiarrheals, pancreatic enzymes, bile acid sequestrants, and antibiotics, often are useful in abating symptoms commonly associated with SBS. Growth factors, including recombinant human growth hormone and glucagon-like peptide 2, may be trialed to stimulate intestinal adaptation and enhance absorption in PN-dependent SBS patients. The gradual refinement of surgical procedures for SBS, including small bowel transplantation, has led to improved outcomes, and early referral of SBS patients to centers of excellence will optimize care.

Intestinal epithelial cell proliferation is dependent on the site of massive small bowel resection

Early intestinal adaptation after massive small bowel resection (SBR) is driven by increased epithelial cell (EC) proliferation. There is a clear clinical difference in the post-operative course of patients after the loss of proximal (P) compared to distal (D) small bowel. This study examined the effects of the site of SBR on post-resectional intestinal adaptation, and investigated the potential mechanisms involved. C57BL/6J mice (n = 7/group) underwent: (1) 60% P-SBR, (2) 60% D-SBR, (3) 60% mid (M)-SBR and (4) SHAM-operation (transection/reanastomosis). Mice were sacrificed at 7 days after surgery and ECs and adjacent mucosal lymphocytes (IELs) isolated. Adaptation was assessed in both jejunum and ileum by quantification of villus height, crypt depth, villus cell size, crypt cell size (microns), goblet cell number, and EC proliferation (%BrdU incorporation). Proliferation signalling pathways including keratinocyte growth factor (KGF)/KGFR(1), IL-7/IL-7R, and epidermal growth factor receptor (EGFR) were measured by RT-PCR. Expression of IL-7 was further analysed by immunofluorescence. Data were analyzed using ANOVA. All three SBR models led to significant increases in villus height, crypt depth, goblet cell numbers and EC proliferation rate when compared to respective SHAM groups. The strongest morphometric changes were found for jejunal segments after M-SBR and for ileal segments after P-SBR. Furthermore, morphometric analysis showed that at 1-week post-resection a tremendous increase in EC numbers occurred in jejunal villi (cell hyperplasia), whereas a significant increase in EC size predominated in ileal villi (cell hypertrophy). mRNA expression of KGF, KGFR(1), IL-7R, and EGFR showed a significant increase only after D-SBR, whereas IL-7 increased significantly after SBR in all investigated models, and this was confirmed by immunofluorescence studies. Early intestinal adaptation shows distinct differences depending on the site of SBR, and is predominately driven by cell hyperplasia in jejunal villi and cell hypertrophy in ileal villi. However, the exact mechanisms, which guide these signalling pathways are still unclear.

Intestinal epithelial cell-derived interleukin-7: A mechanism for the alteration of intraepithelial lymphocytes in a mouse model of total parenteral nutrition

Total parenteral nutrition (TPN), with the absence of enteral nutrition, results in profound changes to both intestinal epithelial cells (EC) as well as the adjacent intraepithelial lymphocyte (IEL) population. Intestinal EC are a rich source of IL-7, a critical factor to support the maintenance of several lymphoid tissues, and TPN results in marked EC changes. On this basis, we hypothesized that TPN would diminish EC-derived IL-7 expression and that this would contribute to the observed changes in the IEL population. Mice received enteral food and intravenous crystalloid solution (control group) or TPN. TPN administration significantly decreased EC-derived IL-7 expression, along with significant changes in IEL phenotype; decreased IEL proliferation; and resulted in a marked decrease in IEL numbers. To better determine the relevance of TPN-related changes in IL-7, TPN mice supplemented with exogenous IL-7 or mice allowed ad libitum feeding and treated with exogenous administration of anti-IL-7 receptor (IL-7R) antibody were also studied. Exogenous IL-7 administration in TPN mice significantly attenuated TPN-associated IEL changes, whereas blocking IL-7R in normal mice resulted in several similar changes in IEL to those observed with TPN. These findings suggest that a decrease in EC-derived IL-7 expression may be a contributing mechanism to account for the observed TPN-associated IEL changes.