Apoptosis and the pattern of DNase I expression following massive small bowel resection

The effect of hepatocyte growth factor on intestinal adaption in an experimental model of short bowel syndrome

PURPOSE

Nowadays, the standard therapy for patients with short bowel syndrome is parenteral nutrition (PN). Various growth factors have been tested to achieve weaning from prolonged PN administration. We evaluated the effect of hepatocyte growth factor (HGF) on structural intestinal adaptation and cell proliferation in a rat model of SBS.

METHODS

Thirty Sprague-Dawley rats were divided into three groups; group A rats (sham) underwent bowel transection, group B rats underwent a 75% bowel resection, and group C rats underwent the same procedure but were treated postoperatively with HGF. Histopathologic parameters of intestinal adaptation were determined, while microarray and rt-PCR analyses of ileal RNA were also performed.

RESULTS

Treatment with HGF resulted in significant increase in body weight, while the jejunal and ileal villus height and crypt depth were increased in HGF rats (36%, p < 0.05 and 27%, p < 0.05 respectively). Enterocyte proliferation was also significantly increased in HGF rats (21% p < 0.05). Microarray and quantitative rt-PCR analyses showed that the genes hgfac, rac 1, cdc42, and akt 1 were more than twofold up-regulated after HGF treatment.

CONCLUSION

HGF emerges as a growth factor that enhances intestinal adaptation. The future use of HGF may potentially reduce the requirement for PN in SBS patients.

Anti-TNF-α Therapy Exerts Intestinal Anti-inflammatory and Anti-apoptotic Effects After Massive Bowel Resection in a Rat

OBJECTIVES

The aim of this study was to examine the effect of massive small bowel resection on proinflammatory cytokine intestinal expression and the effect of anti-TNF-α antibodies (ATA) on intestinal inflammation, epithelial cell turnover, and intestinal adaptation after bowel resection in rats.

METHODS

Male Sprague-Dawley rats were divided into 4 experimental groups: Sham-rats underwent bowel transection; Sham-ATA rats underwent bowel transection and were treated with ATA; SBS-animals underwent 75% bowel resection; and SBS-ATA rats underwent bowel resection and were treated with ATA similarly to Group B. Parameters of intestinal adaptation, enterocyte proliferation, and apoptosis were determined at sacrifice. TNF-α and apoptosis-related gene and protein levels were determined by Illumina's Digital Gene Expression (DGE) analysis, Real Time PCR, Western blotting, and immunohistochemistry.

RESULTS

From 25 genes related to TNF-α signalling that were investigated, 8 genes in the jejunum and 10 genes in the ileum were found to be up-regulated in resected versus sham animals. SBS rats demonstrated a significant increase in tissue and plasma TNF-α, IL-6 levels, intestinal mucosal TNF-α related gene expression, and microscopic parameters of inflammation. Treatment of resected animals with ATA resulted in a significant decrease in TNF-α levels, intestinal mucosal TNF-α-related gene expression, decreased number of intraepithelial lymphocytes and macrophages, and lower apoptotic index compared with SBS animals.

CONCLUSIONS

In a rat model of SBS, ATA decreased plasma and tissue TNF-α levels, diminished mucosal inflammation, and inhibited cell apoptosis. Anti-apoptotic effects of ATA appear to be associated with an inhibited extrinsic apoptotic pathway.

The role of intermediate filaments in maintaining integrity and function of intestinal epithelial cells after massive bowel resection in a rat

PURPOSE

Intermediate filaments (IFs) are a part of the cytoskeleton that extend throughout the cytoplasm of all cells and function in the maintenance of cell-shape by bearing tension and serving as structural components of the nuclear lamina. In normal intestine, IFs provide a tissue-specific three-dimensional scaffolding with unique context-dependent organizational features. The purpose of this study was to evaluate the role of IFs during intestinal adaptation in a rat model of short bowel syndrome (SBS).

MATERIALS AND METHODS

Male rats were divided into two groups: Sham rats underwent bowel transection and SBS rats underwent a 75% bowel resection. Parameters of intestinal adaptation, enterocyte proliferation and apoptosis were determined 2 weeks after operation. Illumina's Digital Gene Expression (DGE) analysis was used to determine the cytoskeleton-related gene expression profiling. IF-related genes and protein expression were determined using real-time PCR, Western blotting and immunohistochemistry.

RESULTS

Massive small bowel resection resulted in a significant increase in enterocyte proliferation and concomitant increase in cell apoptosis. From the total number of 20,000 probes, 16 cytoskeleton-related genes were investigated. Between these genes, only myosin and tubulin levels were upregulated in SBS compared to sham animals. Between IF-related genes, desmin, vimentin and lamin levels were down-regulated and keratin and neurofilament remain unchanged. The levels of TGF-β, vimentin and desmin gene and protein were down-regulated in resected rats (vs sham animals).

CONCLUSIONS

Two weeks following massive bowel resection in rats, the accelerated cell turnover was accompanied by a stimulated microfilaments and microtubules, and by inhibited intermediate filaments. Resistance to cell compression rather that maintenance of cell-shape by bearing tension are responsible for contraction, motility and postmitotic cell separation in a late stage of intestinal adaptation.

Accelerated intestinal epithelial cell turnover after bowel resection in a rat is correlated with inhibited hedgehog signaling cascade

PURPOSE

The hedgehog (Hh) signaling pathway is one of the key regulators of gastrointestinal tract development. Recent studies point to the role of hedgehog signaling in regulating adult stem cells involved in maintenance and regeneration of intestinal stem cells. The purpose of this study was to evaluate the role of Hh signaling during intestinal adaptation in a rat model of short bowel syndrome (SBS).

METHODS

Male rats were divided into two groups: Sham rats underwent bowel transection and SBS rats underwent a 75 % bowel resection. Parameters of intestinal adaptation, enterocyte proliferation, and apoptosis were determined 2 weeks after operation. Illumina's Digital Gene Expression analysis was used to determine the Hh signaling gene expression profiling. Hh-related genes and protein expression were determined using Real-Time PCR, Western blotting, and immunohistochemistry.

RESULTS

Massive small bowel resection resulted in a significant increase in enterocyte proliferation and concomitant increase in cell apoptosis. From the total number of 20,000 probes, 13 genes related to Hh signaling were investigated. In jejunum, eight genes were down-regulated, three genes up-regulated, and two genes remained unchanged. In ileum, five genes were down-regulated and six genes were unchanged in SBS vs sham animals. SBS rats also demonstrated a significant three- to fourfold decrease in SMO, GIL, and PTCH mRNA, and protein levels (determined by Real-Time PCR and Western blot) compared to control animals.

CONCLUSION

Two weeks following massive bowel resection in rats, the accelerated cell turnover was accompanied by an inhibited Hh signaling pathway. Hh signaling may serve as an important mediator of reciprocal interactions between the epithelium and the underlying mesenchymal stroma during intestinal adaptation following massive bowel resection in a rat.

PDGF-α stimulates intestinal epithelial cell turnover after massive small bowel resection in a rat

Numerous cytokines have been shown to affect epithelial cell differentiation and proliferation through epithelial-mesenchymal interaction. Growing evidence suggests that platelet-derived growth factor (PDGF) signaling is an important mediator of these interactions. The purpose of this study was to evaluate the effect of PDGF-α on enterocyte turnover in a rat model of short bowel syndrome (SBS). Male rats were divided into four groups: Sham rats underwent bowel transection, Sham-PDGF-α rats underwent bowel transection and were treated with PDGF-α, SBS rats underwent a 75% bowel resection, and SBS-PDGF-α rats underwent bowel resection and were treated with PDGF-α. Parameters of intestinal adaptation, enterocyte proliferation and apoptosis were determined at euthanasia. Illumina's Digital Gene Expression analysis was used to determine PDGF-related gene expression profiling. PDGF-α and PDGF-α receptor (PDGFR-α) expression was determined by real-time PCR. Western blotting was used to determine p-ERK, Akt1/2/3, bax, and bcl-2 protein levels. SBS rats demonstrated a significant increase in PDGF-α and PDGFR-α expression in jejunum and ileum compared with sham animals. SBS-PDGF-α rats demonstrated a significant increase in bowel and mucosal weight, villus height, and crypt depth in jejunum and ileum compared with SBS animals. PDGF-α receptor expression in crypts increased in SBS rats (vs. sham) and was accompanied by an increased cell proliferation following PDGF-α administration. A significant decrease in cell apoptosis in this group was correlated with lower bax protein levels. In conclusion, in a rat model of SBS, PDGF-α stimulates enterocyte turnover, which is correlated with upregulated PDGF-α receptor expression in the remaining small intestine.

Oral insulin stimulates intestinal epithelial cell turnover following massive small bowel resection in a rat and a cell culture model

PURPOSE

We have recently reported that oral insulin (OI) stimulates intestinal adaptation after bowel resection and that OI enhances enterocyte turnover in correlation with insulin receptor expression along the villus-crypt axis. The purpose of the present study was to evaluate the effect of OI on intestinal epithelial cell proliferation and apoptosis in a rat model of short bowel syndrome (SBS) and in a cell culture model.

METHODS

Caco-2 cells were incubated with increasing concentrations of insulin. Cell proliferation and apoptosis were determined by FACS cytometry. Cell viability was investigated using the Alamar Blue technique. Male rats were divided into three groups: Sham rats underwent bowel transection, SBS rats underwent a 75% bowel resection, and SBS-OI rats underwent bowel resection and were treated with OI given in drinking water (1 U/ml) from the third postoperative day. Parameters of intestinal adaptation, enterocyte proliferation and apoptosis were determined on day 15. Real time PCR was used to determine the level of bax and bcl-2 mRNA and western blotting was used to determine bax, bcl-2, p-ERK and AKT protein levels. Statistical analysis was performed using the one-way ANOVA test, with P < 0.05 considered statistically significant.

RESULTS

Treatment of Caco-2 cells with insulin resulted in a significant increase in cell proliferation (twofold increase after 24 h and 37% increase after 48 h) and cell viability (in a dose-dependent manner), but did not change cell apoptosis. In a rat model of SBS, treatment with OI resulted in a significant increase in all parameters of intestinal adaptation. Elevated cell proliferation rate in insulin treated rats was accompanied by elevated AKT and p-ERK protein levels. Decreased cell apoptosis in SBS-INS rats corresponded with a decreased bax/bcl-2 ratio.

CONCLUSIONS

Oral insulin stimulates intestinal epithelial cell turnover after massive small bowel resection in a rat model of SBS and a cell culture model.

Effect of alpha-naphthylisothiocyanate-induced liver injury on intestinal adaptation in a rat model of short bowel syndrome

BACKGROUND/PURPOSE

Progressive hyperbilirubinemia and end-stage liver failure are among the most serious complications of short bowel syndrome (SBS), representing the principle cause of death in a majority of fatal cases. In the current study, we examined the effects of alpha-naphthylisothiocyanate (ANIT)-induced liver injury on intestinal adaptation in a rat model of SBS.

METHODS

Male rats were divided into four groups: Sham rats underwent bowel transection (n = 8), Sham liver-injury rats underwent bowel transection and IP injection of ANIT (100 mg/kg, n = 8), SBS rats underwent a 75% bowel resection, and SBS-ANIT rats underwent bowel resection and liver injury similar to group sham-ANIT (n = 8). Fourteen days after intervention, liver biopsies and intestinal samples were obtained and evaluated for liver damage and measures of intestinal adaptation. Real time PCR and Western blotting were used to determine the level of bax and bcl-2 mRNA and protein, and p-ERK protein levels. Statistical analysis was performed using the one-way ANOVA test, with p < 0.05 considered statistically significant.

RESULTS

All ANIT-treated animals exhibited histological evidence of liver damage that was associated with the expansion of atypical ductal proliferation near the periportal areas, intense neutrophil infiltration in the liver, increased mitotic activity, Kupfer cells hyperplasia and fatty liver degeneration. ANIT-induced liver damage in bowel resected animals was associated with a significant decrease in all parameters of intestinal adaptation including bowel and mucosal weight in jejunum (twofold decrease) and ileum (twofold decrease), mucosal DNA in jejunum (fourfold decrease), mucosal protein in jejunum (threefold decrease) and ileum (threefold decrease), villus height in jejunum (38%) and ileum (34%), and crypt depth in jejunum (24%) and ileum (30%) compared to SBS animals. Both Sham-ANIT and SBS-ANIT rats demonstrated decreased enterocyte proliferation rates that were accompanied by decreased p-ERK protein levels. Lower apoptotic rates in jejunum (40%) and ileum (52%) in SBS-ANIT rats (vs. SBS) coincided with decreased bax mRNA and protein levels.

CONCLUSIONS

In a rat model of SBS, ANIT-induced liver injury was associated with decreased enterocyte proliferation and inhibited intestinal adaptation.

Parenteral but not enteral omega-3 fatty acids (Omegaven) modulate intestinal regrowth after massive small bowel resection in rats

BACKGROUND

The purpose of the present study was to evaluate the effects of ω-3 fatty acids (Omegaven) on early intestinal adaptation in rats with short bowel syndrome (SBS).

METHODS

Male Sprague-Dawley rats were randomly assigned to 1 of 4 groups: sham rats underwent bowel transection; SBS rats underwent 75% bowel resection; SBS-O ω-3 rats underwent bowel resection and were treated with oral Omegaven given by gavage; and SBS-I ω-3 rats underwent bowel resection and were treated with Omegaven given intraperitoneally. Rats were killed on day 14. Parameters of intestinal adaptation (bowel and mucosal weight, mucosal DNA and protein, villus height and crypt depths, cell proliferation and apoptosis) were determined at time of death. Real-time polymerase chain reaction was used to determine the level of Bax and Bcl-2 messenger RNA (mRNA). Statistical analysis was performed using Kruskal-Wallis test followed by post hoc test, with P < .05 considered statistically significant.

RESULTS

Oral ω-3 supplementation did not significantly change intestinal regrowth. In contrast, parenteral ω-3 in rats that underwent resection resulted in higher bowel and mucosal weights, mucosal DNA and protein in ileum, villus height in ileum, crypt depth in jejunum and ileum, and greater rates of cell proliferation in jejunum and ileum compared with SBS animals. The initial decreased levels of apoptosis corresponded with the early decrease in Bax and increase in Bcl-2 mRNA levels.

CONCLUSIONS

Parenteral but not enteral Omegaven augments and accelerates structural bowel adaptation in a rat model of SBS. Increased cell proliferation and decreased apoptosis reflect increased cell turnover in Omegaven-treated animals.

Leptin affects intestinal epithelial cell turnover in correlation with leptin receptor expression along the villus-crypt axis after massive small bowel resection in a rat

In this study, we examine the responsiveness of intestinal epithelial cell turnover to leptin (LEP) in correlation with leptin receptor (LEPr) expression along the villus-crypt axis in a rat with short bowel syndrome (SBS). Adult rats underwent either a 75% intestinal resection or a transection. SBS-LEP rats underwent bowel resection and were treated with LEP starting from the fourth postoperative day. Parameters of intestinal adaptation, enterocyte proliferation, and enterocyte apoptosis were determined at sacrifice. RT-PCR technique was used to determine Bax and Bcl-2 gene expression in ileal mucosa. Villus tips, lateral villi, and crypts were separated using laser capture microdissection. LEPr expression for each compartment was assessed by quantitative real-time PCR (Taqman). Treatment with LEP significantly stimulated all parameters of adaptation. LEPr expression in crypts significantly increased in SBS rats (vs Sham rats) and was accompanied by a significant increase in enterocyte proliferation and decreased apoptosis after LEP administration. A significant increase in LEPr expression at the tip of the villus in SBS rats was accompanied by decreased cell apoptosis. In conclusion LEP accelerated enterocyte turnover and stimulated intestinal adaptation. The effect of LEP on enterocyte proliferation and enterocyte apoptosis correlated with receptor expression along the villus-crypt axis.

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.

Dietary palmitic acid modulates intestinal re-growth after massive small bowel resection in a rat

PURPOSE

Among factors promoting intestinal adaptation after bowel resection, dietary fatty acids have a special role. The purpose of the present study was to evaluate the effects of palmitic acid (PA) on early intestinal adaptation in rats with short bowel syndrome (SBS).

MATERIALS

Male Sprague-Dawley rats underwent either a bowel transection with re-anastomosis (sham rats) or 75% small bowel resection (SBS rats). Animals were randomly assigned to one of four groups: sham rats fed normal chow (sham-NC); SBS rats fed NC (SBS-NC), SBS rats fed high palmitic acid diet (SBS-HPA), and SBS rats fed low palmitic acid diet (SBS-LPA). Rats were sacrificed on day 14. Parameters of intestinal adaptation, overall bowel and mucosal weight, mucosal DNA and protein, villus height and crypt depth, cell proliferation and apoptosis were determined at sacrifice. RT-PCR and Western blotting were used to determine the level of bax and bcl-2 mRNA and protein (parameters of apoptosis), and ERK protein levels (parameter of proliferation). Statistical analysis was performed using Kruskal-Wallis test followed by post hoc test for multiple comparisons with P values of less than 0.05 considered statistically significant.

RESULTS

SBS-HFD rats demonstrated higher bowel and mucosal weight, mucosal DNA and protein in ileum, while deprivation of PA (SBS-LPA) inhibited intestinal re-growth both in jejunum and ileum compared to SBS-NC rats. A significant up-regulation of ERK protein coincided with increased cell proliferation in SBS-HFD rats (vs. SBS-NC). Also, the initial decreased levels of apoptosis corresponded with the early decrease in bax and increase in bcl-2 at both mRNA and protein levels.

CONCLUSION

Early exposure to HPA both augments and accelerates structural bowel adaptation in a rat model of SBS. Increased cell proliferation and decreased cell apoptosis may be responsible for this effect. Deprivation of PA in the diet inhibits intestinal re-growth.

Effect of lactulose on bacterial translocation and intestinal adaptation in a rat model of short bowel syndrome

BACKGROUND

It is frequently assumed that dietary nondigestible carbohydrates improve host resistance to intestinal infections by stimulating proliferation of the protective gut microflora. Therefore, the aim of this study was to define the effect of lactulose, a nondigestible carbohydrate, on bacterial translocation and intestinal adaptation in a rat model of short bowel syndrome (SBS).

MATERIALS AND METHODS

Male Sprague-Dawley rats were divided into 3 experimental groups. Sham rats underwent bowel transection, SBS rats underwent 75% small bowel resection, and SBS-LAC rats underwent bowel resection and were treated with oral lactulose given in drinking water at a dose of 1.5 g x kg(-1) x day(-1) from the 3rd to the 15th postoperative day. Bacterial translocation (to mesenteric lymph nodes, liver, and portal and peripheral blood) and parameters of intestinal adaptation were determined on day 15.

RESULTS

Treatment with lactulose did not change bacterial translocation, but decreased ileal mucosal weight (20%; P < 0.05), ileal mucosal DNA (2-fold decrease; P < 0.05) and protein (26%; P < 0.05), villus height in jejunum (21%; P < 0.05) and crypt depth in ileum (17%; P < 0.05), proliferation rates in jejunum (18%; P < 0.05) and ileum (15%; P < 0.05), and apoptotic index in jejunum (40%; P < 0.05) and ileum (36%; P < 0.05) compared with SBS animals. Bax expression was upregulated in SBS rats compared with control animals, but decreased following treatment with lactulose.

CONCLUSIONS

In a rat model of SBS, oral lactulose does not improve bacterial translocation from the intestine, but inhibits intestinal adaptation.

Responsiveness of intestinal epithelial cell turnover to TGF-alpha after bowel resection in a rat is correlated with EGF receptor expression along the villus-crypt axis

Recent evidence suggests that transforming growth factor alpha (TGF-alpha) enhances enterocyte proliferation and stimulates intestinal adaptation after massive bowel resection. In the present study, we evaluated the effects of TGF-alpha on enterocyte turnover and correlated it with epidermal-growth factor (EGF) receptor expression along the villus-crypt axis in a rat model of short bowel syndrome (SBS). Male rats were divided into three groups, sham rats underwent bowel transection (group A); SBS rats underwent a 75% bowel resection (group B); and SBS/TGF-alpha rats underwent bowel resection and were treated with TGF-alpha (75 microg/kg) (group C) from the seventh postoperative day. Parameters of intestinal adaptation, enterocyte proliferation and apoptosis were determined on day 15. Villus tips, lateral villi and crypts were separated using laser capture microdissection. EGF receptor expression for each compartment was assessed by quantitative real-time PCR (Taqman). Statistical analysis was performed using one-way ANOVA test, with P < 0.05 considered statistically significant. Treatment with TGF-alpha resulted in a significant increase in all parameters of intestinal adaptation. EGF receptor expression in crypts significantly increased in SBS rats (vs sham rats) (0.035 +/- 0.013 vs 0.010 +/- 0.002 Log ng Total RNA/18 s) and was accompanied by a significant increase in enterocyte proliferation (169 +/- 8 vs 138 +/- 5 BrdU positive cells/per 10 crypts, P < 0.05) and decreased apoptosis following TGF-alpha administration (group C). A significant decrease in EGF receptor expression at the tip of the villus (0.005 +/- 0.002 vs 0.029 +/- 0.014 Log ng Total RNA/18 s) and in the lateral villus (0.003 +/- 0.001 vs 0.028 +/- 0.006 Log ng Total RNA/18 s) in SBS (group B) rats (vs sham, group A) was accompanied by increased cell apoptosis in these compartments following treatment with TGF-alpha (group C). In a rat model of SBS, TGF-alpha increased enterocyte proliferation and stimulated intestinal adaptation. The effect of TGF-alpha on enterocyte turnover is correlated with EGF receptor expression along the villus-crypt axis.

Bombesin stimulates enterocyte turnover following massive small bowel resection in a rat

Recent evidence suggests that bombesin (BBS) is involved in modulation of growth and differentiation of normal small intestine. The purpose of the present study was to evaluate the effects of BBS on enterocyte turnover after massive small bowel resection in a rat. Male Sprague-Dawley rats were divided into three experimental groups: Sham rats underwent bowel transection and re-anastomosis, short bowel syndrome (SBS) rats underwent a 75% small bowel resection, and SBS-BBS rats underwent bowel resection and were treated with BBS given subcutaneously at a dose of 20 mug/kg, once daily, from postoperative day 3 through 14. Parameters of intestinal adaptation (bowel and mucosal weights, mucosal DNA and protein, villus height and crypt depth), enterocyte proliferation and enterocyte apoptosis were determined in jejunum and ileum on day 15 following operation. RT-PCR technique was used to determine Bax and Bcl-2 gene expression in ileal mucosa. Statistical analysis was performed using the non-parametric Kruskal-Wallis ANOVA test, with P less than 0.05 considered statistically significant. Treatment with BBS resulted in a significant increase in ileal bowel and mucosal weight, ileal mucosal DNA and protein, jejunal and ileal villus height, jejunal crypt depth, and jejunal and ileal proliferation index compared to SBS-animals. SBS rats showed a significant increase in Bax and Bcl-2 expression in ileum that was accompanied by a significant increase in cell apoptosis compared to sham animals. SBS-BBS rats demonstrated a significant decrease in Bax and Bcl-2 expression in ileum and a decrease in apoptotic index compared to SBS-animals. In conclusion, in a rat model of SBS, BBS enhances enterocyte turnover and stimulates structural intestinal adaptation. Decreased Bax expression may be responsible for the inhibitory effect of BBS on enterocyte apoptosis.

Oral insulin enhances intestinal regrowth following massive small bowel resection in rat

Experimental studies have suggested that insulin (INS) plays an important role in small intestinal growth and development. In the present study we investigated the effect of oral INS on structural intestinal adaptation and enterocyte proliferation and loss via 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, SBS rats underwent 75% small bowel resection, and SBS-INS rats underwent bowel resection and were treated with oral INS given in the drinking water from the 3rd to the 15th postoperative day. Parameters of intestinal adaptation (bowel and mucosal weight, mucosal DNA and protein, villous height, and crypt depth), enterocyte proliferation, and apoptosis were determined on day 15. SBS-INS rats demonstrated a significant increase (vs SBS rats) in jejunal and ileal overall bowel and mucosal weight, ileal mucosal DNA and protein, ileal villous height, and crypt depth. SBS-INS rats also showed an increased cell proliferation index in jejunum and ileum and decreased apoptotic index in jejunum compared to SBS animals. In conclusion, in a rat model of SBS, oral INS strongly enhances intestinal adaptation. Possible mechanisms may include increased cell proliferation and decreased enterocyte loss via apoptosis.

Mucosal expression of p21, p27, p53, Bcl-2, and bax after small bowel resection and autotransplantation in pigs

Massive small bowel resection increases ileal villus height as part of normal adaptation. However, despite no gut loss, autotransplantation of the entire small intestine also increases ileal villus height. Our aim was to test whether similar modulation of enterocyte proliferation and apoptosis underpin these comparable increases in villus height. Fifteen pigs were randomly assigned for laparotomy (n=5), 75% proximal small bowel resection (n=5), or jejunoileal autotransplantation (n=5). Eight weeks postoperatively, full-thickness small bowel sections underwent routine immunohistochemistry for cell cycle inhibitors (p53, p21, and p27), antiapoptotic Bcl-2, and proapoptotic bax. The specimens were analyzed semiquantitatively, and the number of intensively positive epithelial cells for each group was compared from 20 digital images (0.32 mm(2)/image). Compared with laparotomy, small bowel resection decreased the number of p27-positive enterocytes in both jejunum and ileum, increased the number of bax-expressing cells in ileum, but decreased the number of bax-expressing cells in jejunum. In contrast, compared with laparotomy, jejunoileal autotransplantation altered neither mucosal bax nor p27 expression. In all groups, Bcl-2 expression was similarly confined to inflammatory cells of the lamina propria, while both p53 and p21 were negative. We conclude that long-term alterations in the enterocytic expression of certain cell cycle and apoptosis markers (p27 and bax) accompany small bowel resection. These changes differ between the jejunum and the ileum and are not seen after whole small bowel autotransplantation. Therefore, increased ileal villus height after autotransplantation, despite resembling postresectional intestinal adaptation, is underpinned by different regulation of enterocyte proliferation and apoptosis.

Gene alteration of intestinal intraepithelial lymphocytes in response to massive small bowel resection

BACKGROUND

The intestinal adaptive response [increased epithelial cell (EC) proliferation and apoptosis] after massive small bowel resection (SBR) is partially controlled by intraepithelial lymphocytes (IEL). To identify IEL factors contributing to EC adaptation post-SBR we utilized microarray assays.

METHODS

Mice underwent a 70% SBR (SBR1w/SBR4w) or sham operation (Sham1w/Sham4w). After 1 or 4 weeks (1w, 4w) small bowel was harvested, and IEL isolated. Determination of the EC-proliferation rate used BrdU incorporation, and of the EC-apoptotic rate used Annexin V staining. Affymetrix system microarrays (12,491 genes) were performed to examine IEL-mRNA expression. Results were considered significant if fold-change (FC) between groups was >2 and P<0.05 (F-test), or FC>3 and 0.05> P >0.01, or FC>4 and P>0.05. Significant genes were confirmed by conventional RT-PCR.

RESULTS

The SBR EC-proliferation rate increased significantly in both 1w and 4w groups compared to Sham: SBR1w 0.24+/-0.07 vs. Sham1w 0.12+/-0.02 (P=0.03); SBR4w 0.35+/-0.04 vs. Sham4w 0.19+/-0.02 ( P<0.01). The EC-apoptotic rate was unchanged in the 1w group, but significantly differed from controls after 4 weeks: SBR4w 39.92+/-6.78 vs. Sham4w 12.56+/-6.44 ( P<0.01). Microarray results were analyzed to identify potential growth-modifying IEL genes. The following were identified (function in parenthesis; A, apoptosis; P, proliferation): lipocalin 2 (promotes A), angiotensin converting enzyme (increases A), Rap2 interacting protein (reduces A, promotes P), amphiregulin (promotes P) and leucine-rich-alpha2-glycoprotein (promotes A, reduces P). Based on RT-PCR results these genes showed significant changes between groups. The increase in ACE at 1w preceded the observed apoptotic changes. The alterations in lipocalin 2, Rap2 and amphiregulin at 4w coincided with the marked changes in growth and apoptosis in the SBR mice.

CONCLUSIONS

IEL undergo temporal changes after SBR. These findings provide profound insight into potential IEL-dependent regulation of EC homeostasis post-SBR.

The distribution of cofilin and DNase I in vivo

Actin is the principal component of the cytoskeleton, a structure that can be disassembled and reassembled in a matter of seconds in vivo. The state of assembly of actin in vivo is primarily regulated by one or more actin binding proteins (ABPs). Typically, the actions of ABPs have been studied one by one, however, we propose that multiple ABPs, acting cooperatively, may be involved in the control of actin filament length. Cofilin and DNase I are two ABPs that have previously been demonstrated to form a ternary complex with actin in vitro. This is the first report to demonstrate their co-localisation in vivo, and differences in their distributions. Our observations strongly suggest a physiological role for higher order complexes of actin in regulation of cytoskeletal assembly during processes such as cell division.

Identification and expression of deoxyribonuclease (DNase) I alternative transcripts in the rat

Deoxyribonuclease (DNase) I has been implicated in the induction of DNA fragmentation and cell death, however little is known about its regulation in vivo. In the present study, we describe that DNase I messenger RNA (mRNA) is alternatively spliced in rat kidney, and the activity of the DNase I correlates with the alternative splicing during the course of renal ischemia/reperfusion. Northern blot analysis with mRNA from control rat kidneys and kidneys subjected to ischemia/reperfusion in vivo yielded two bands of approximately 1.3 and 1.5 kb, suggesting the possibility of alternative splicing. However, prolonged reperfusion up to 16 h resulted in the predominant expression of 1.3 kb transcript. The disappearance of the 1.5 kDa band was associated with the increased DNase I activity in the kidney during ischemia/reperfusion. To study the alternative splicing of the DNase I mRNA, rat kidney cortex DNA complementary to RNA library was screened using rat DNase I probe. Twenty-one positive clones were obtained and were compared with the reported DNase I mRNA transcript cloned from rat parotid gland. All clones showed 100% homology with the reported DNase I coding sequence and part of 5'-untranslated region (5'-UTR), named exon 1a by us. Twelve out of 21 isolated clones had longer 5'-UTR than previously described, and DNase I pre-mRNA was alternatively spliced in this region. Six out of these 12 clones contained extra up to 153 bp in extreme 5' end, whereas, in six other clones, an internal 132 bp segment (exon 1b) of this additional sequence was absent, and only the extreme 5'UTR sequence (exon 1c) was found in these clones. The nucleotide analysis showed that alternating exon 1b has the possibility of a secondary structure with high internal homology and potential for at least one major stable stem-loop. Both newly identified segments, exons 1b and 1c, were also identified in genomic DNA. The long splice variant, containing exon 1b, is expressed only in the kidney among different tissues tested. Exon 1b inhibited translational activity of DNase I mRNA in vitro. Our data suggest that alternative splicing in 5'-UTR in the kidney may provide a prompt DNA-independent regulation of DNase I activity when DNA is damaged during ischemic injury.

Molecular and cellular biology of small-bowel mucosa

Study of the molecular and cellular biology of the small-intestinal mucosa is providing insights into the remarkable properties of this unique tissue. With its structured pattern of cell proliferation, differentiation, and apoptosis, and its ability to adapt following exposure to luminal nutrients or injury from surgery or pathogens, it functions in a regulated but responsive manner. We review recent publications on factors affecting development, gene expression, cell turnover, and adaptation.

Epidermal growth factor is critical for intestinal adaptation following small bowel resection

The loss of small intestinal mucosal surface area is a relatively common clinical situation seen in both the pediatric and adult population. The most frequent causes include mesenteric ischemia, trauma, inflammatory bowel disease, necrotizing enterocolitis, and volvulus. Following surgical resection, the remnant intestine compensates or adapts to the loss of native bowel by increasing its absorptive surface area and functional capacity. Unfortunately, many patients fail to adapt adequately, and are relegated to lifelong intravenous nutrition. Research into intestinal adaptation following small bowel resection (SBR) has evolved only recently from the gross and microscopic level to the biochemical and genetic level. As understanding of this process has increased, numerous therapeutic strategies to augment adaptation have been proposed. Epidermal growth factor (EGF) is an endogenous peptide that is secreted into the gastrointestinal tract and able to influence gut ontogeny, as well as mucosal healing. Early studies have demonstrated its ability to augment the adaptive process. Focusing on a murine model of massive intestinal loss, the morphological, structural, biochemical, and genetic changes that occur during the intestinal adaptive process will be reviewed. The role of EGF and its receptor as critical mediators of the adaptive process will be discussed. Additionally, the ability of EGF to augment intestinal proliferation and diminish programmed cell death (apoptosis) following SBR will be examined. Enhancing adaptation in a controlled manner may allow patients to transition off parenteral nutrition to enteral feeding and, thereby, normalize their lifestyle.

Epidermal growth factor is critical for intestinal adaptation following small bowel resection

The loss of small intestinal mucosal surface area is a relatively common clinical situation seen in both the pediatric and adult population. The most frequent causes include mesenteric ischemia, trauma, inflammatory bowel disease, necrotizing enterocolitis, and volvulus. Following surgical resection, the remnant intestine compensates or adapts to the loss of native bowel by increasing its absorptive surface area and functional capacity. Unfortunately, many patients fail to adapt adequately, and are relegated to lifelong intravenous nutrition. Research into intestinal adaptation following small bowel resection (SBR) has evolved only recently from the gross and microscopic level to the biochemical and genetic level. As understanding of this process has increased, numerous therapeutic strategies to augment adaptation have been proposed. Epidermal growth factor (EGF) is an endogenous peptide that is secreted into the gastrointestinal tract and able to influence gut ontogeny, as well as mucosal healing. Early studies have demonstrated its ability to augment the adaptive process. Focusing on a murine model of massive intestinal loss, the morphological, structural, biochemical, and genetic changes that occur during the intestinal adaptive process will be reviewed. The role of EGF and its receptor as critical mediators of the adaptive process will be discussed. Additionally, the ability of EGF to augment intestinal proliferation and diminish programmed cell death (apoptosis) following SBR will be examined. Enhancing adaptation in a controlled manner may allow patients to transition off parenteral nutrition to enteral feeding and, thereby, normalize their lifestyle.

Effect of massive small bowel resection on the Bax/Bcl-w ratio and enterocyte apoptosis

Following small bowel resection (SBR), the remnant intestine undergoes adaptation. Enterocyte proliferation is increased and counterbalanced by increased rates of apoptosis. To elucidate a mechanism for increased enterocyte apoptosis, this study tested the hypothesis that the ratio between pro-apoptotic Bax and pro-survival Bcl-w correlates with the apoptosis that occurs following SBR. Mice (C57Bl/6; n = 76) underwent a 50% proximal SBR or sham operation. After 12 hours and 1, 2, 3, and 7 days, the ileum was removed, the apoptotic index (apoptotic bodies/crypt) was recorded, and the messenger RNA and protein for Bax and Bcl-w were quantified. The apoptotic index was equivalent in the sham and SBR mice at 12 hours; however, it was significantly elevated following SBR at every other day measured. The ratio of Bax to Bcl-w messenger RNA relative to sham operation increased after SBR at 24 hours, decreased by day 3, and returned to baseline levels by 1 week. The protein ratio showed an increase by day 1, which remained elevated through day 7. An augmented ratio of Bax to Bcl-w messenger RNA and protein corresponded with the increase in enterocyte apoptosis. Alterations in the expression ratio of these genes may play a role in establishing a new homeostatic set point between proliferation and apoptosis during adaptation.