Thermal injury effects on intestinal crypt cell proliferation and death are cell position dependent

Exogenous glucagon-like peptide-2 improves outcomes of intestinal adaptation in a distal-intestinal resection neonatal piglet model of short bowel syndrome

BACKGROUND

Endogenous glucagon-like peptide-2 (GLP-2) levels and intestinal adaptation are reduced in distal-intestinal resection animal models of short bowel syndrome (SBS) that lack remnant ileum. We hypothesized that exogenous GLP-2 would improve intestinal adaptation in a distal-intestinal resection neonatal piglet model of SBS.

METHODS

In all, 35 piglets were randomized to 2 treatment and 3 surgical groups: control (sham), 75% mid-intestinal resection (JI), and 75% distal-intestinal resection (JC). Parenteral nutrition (PN) commenced on day 1 and was weaned as enteral nutrition (EN) advanced. IV GLP-2 (11 nmol/kg/d) or saline was initiated on day 2. Piglets were maintained for 14 d. Clinical, functional, morphological, and histological outcomes were obtained.

RESULTS

JC-GLP-2 piglets had fewer days on PN (10.0 ± 0.6 vs. 13.8 ± 0.2), more days on EN (4.0 ± 0.6 vs. 0.2 ± 0.2), a higher percentage of EN at termination (92 ± 5 vs. 52 ± 10%), fewer days of diarrhea (8.0 ± 0.7 vs. 12.3 ± 0.4), increased intestinal length (19 ± 4 vs. -5 ± 3%), and deeper jejunal crypts (248 ± 21 vs. 172 ± 12 μm), compared with saline piglets.

CONCLUSION

GLP-2 therapy improves clinical, morphological, and histological outcomes of intestinal adaptation in a distal-intestinal resection model of SBS. Since this anatomical subtype represents the majority of clinical cases of neonatal SBS, these results support a potential role for GLP-2 therapy in pediatric SBS.

Patterns of proliferative activity in the colonic crypt determine crypt stability and rates of somatic evolution

Epithelial cells in the colon are arranged in cylindrical structures called crypts in which cellular proliferation and migration are tightly regulated. We hypothesized that the proliferation patterns of cells may determine the stability of crypts as well as the rates of somatic evolution towards colorectal tumorigenesis. Here, we propose a linear process model of colonic epithelial cells that explicitly takes into account the proliferation kinetics of cells as a function of cell position within the crypt. Our results indicate that proliferation kinetics has significant influence on the speed of cell movement, kinetics of mutation propagation, and sensitivity of the system to selective effects of mutated cells. We found that, of all proliferation curves tested, those with mitotic activities concentrated near the stem cell, including the actual proliferation kinetics determined in in vivo labeling experiments, have a greater ability of delaying the rate of mutation accumulation in colonic stem cells compared to hypothetical proliferation curves with mitotic activities focused near the top of the crypt column. Our model can be used to investigate the dynamics of proliferation and mutation accumulation in spatially arranged tissues.

Mathematical and computational models have a long and rich history in enhancing our understanding of intestinal epithelial cells. A plethora of models have been proposed to describe different aspects of cellular behavior, including cell proliferation, migration, differentiation, and mutation accumulation. Here, we present a novel approach to examine the effects of proliferation kinetics on the rate of somatic evolution in a spatially arranged model of the colon. Based on our simulation results, we demonstrate that spatially determined proliferation kinetics has the ability to delay the rate of somatic evolution, and changes in proliferation patterns can significantly affect the speed of mutation accumulation. Our work highlights the importance of considering proliferation kinetics as well as the spatial organization of tissues when investigating the dynamics of cancer initiation.

Heat-stress-induced damage to porcine small intestinal epithelium associated with downregulation of epithelial growth factor signaling

Extreme heat during certain days of the summer renders pigs susceptible to severe heat stress, which negatively affects their growth performance. We hypothesized that such heat stress impaired the small intestinal mucosa, a site responsible for nutrient absorption. To simulate heat stress, Chinese experimental mini-pigs were treated with 5 h of continual 40 degrees C temperature each day for 10 d in succession. Pigs were killed at 1, 3, 6 and 10 d after treatment, and small intestinal epithelia were sampled for histochemical examination and biochemical analyses. The duodenum and jejunum were seriously damaged within 3 d of initiation of treatment. Subsequent study of the process of jejunum recovery showed that the initiation of recovery started within 6 d following heat stress. Such damage was associated with the downregulation of epithelial growth factor signaling. In conclusion, heat stress induced short-term damage to the epithelium of porcine intestine. Because the intestinal epithelium is crucial for nutrient uptake, such damage should partially account for the impairment of growth performance of pigs under heat stress.

“Systemic apoptotic response” after thermal burns

The systemic pathophysiologic changes following thermal injuries affect multiple organs and body systems leading to clinical manifestations including shock, intestinal alterations, respiratory and renal failure, immunosuppression and others. Recent advances in the comprehension of mechanisms underlying systemic complications of thermal injuries have contributed to uncover part of the cellular and molecular basis that underlie such changes. Recently, programmed cell death (apoptosis) has been considered playing an important role in the development of such pathological events. Therefore, investigators utilizing animal models and clinical studies involving human primates have produced a large body of information suggesting that apoptosis is associated with most of the tissue damages triggered by severe thermal injuries. In order to draw the attention on the important role of apoptosis on systemic complications of thermal injuries, in this review we describe most of these studies, discuss possible cellular and molecular mechanisms and indicate ways to utilize them for the development of therapeutic strategies by which apoptosis may be prevented or counteracted.

The effects of propofol and ketamine on gut mucosal epithelial apoptosis in rats after burn injury

BACKGROUND AND OBJECTIVES

Apoptosis occurs after thermal injury and may result from either ischaemic intestinal insult or inflammatory mediators released after burn injury. The aim of the study was to investigate the effects of propofol and ketamine on gut epithelium apoptosis after burn injury.

METHODS

Sixty male Wistar Albino rats were randomly assigned into four groups. Anaesthesia was induced and maintained with propofol in Groups 1 and 2, and ketamine in Groups 3 and 4 over 12 h. Groups 2 and 4 received 30% total body surface area burn. Groups 1 and 3 had no burn injury. Mean arterial pressure was maintained within 10% of baseline levels in all animals. At 12 h postburn, animals were sacrificed and tissue samples were taken from small intestine for determination of lipid peroxidation, apoptosis and proliferation. Also blood samples were taken for measurement of serum tumor necrosis factor-alpha (TNF-alpha) levels.

RESULTS

Ileal malondialdehyde (MDA) concentration (extent of lipid peroxidation) increased significantly in Group 4 (112.4 +/- 10.2 nmol g-1) compared to Group 3 (48.4 +/- 5.6 nmol g-1) and Group 2 (59.8 +/- 3.2 nmol g-1). The mean TNF-alpha level in Group 4 (118.9 +/- 10.5 pg mL-1) at 12 h postburn was significantly higher than the mean in Group 2 (56.4 +/- 4.3 pg mL-1). Group 4 had the highest mean TUNEL index (terminal deoxyuridine nick-end labelling--an index of extent of apoptosis) of all the groups (265/10). Also the mean TUNEL index value in Group 2 (53/10) was higher than that of Group 1 (3/10) and Group 3 (5/10). The proliferating cell nuclear antigen index (extent of proliferation) remained unchanged among groups.

CONCLUSIONS

Propofol could offer a protection against apoptosis of enterocytes with a stable tissue MDA and serum TNF-alpha level compared to ketamine anaesthesia in an animal model of burn injury.

Mechanisms of postburn intestinal barrier dysfunction in the rat: Roles of epithelial cell renewal, E-cadherin, and neutrophil extravasation*

OBJECTIVE

Our group has previously shown that the intestinal epithelium exhibits increased postburn barrier permeability and bacterial translocation associated with deranged neutrophil activity. The purpose of this investigation is to explore possible underlying intestinal structural mechanisms, leading to those functional changes with emphasis on (1) neutrophil influx and extravasation in the intestinal lamina propria 1-3 days after burn and (2) enterocyte proliferation, migration, apoptosis, and E-cadherin junctional epithelium levels 3 days after burn.

DESIGN

Freshly isolated ileum specimens were quick frozen, then cut by a cryostat into 30-micron-thick sections. Sections from day 1 postburn rats were immunostained with (1) anti-granulocyte or anti-elastase antibodies to assess neutrophil influx or (2) combined anti-granulocyte and anti-von Willebrand factor double immunolabeling to compare levels of neutrophil extravasation. Sections from day 3 postburn rats were immunostained with (1) bromodeoxyuridine immunohistochemistry 1, 3, 6, or 18 hrs after bromodeoxyuridine injection to assess enterocyte proliferation and migration, (2) cytokeratin-18 M30-immunohistochemistry to compare levels of enterocyte apoptosis, and (3) E-cadherin immunohistochemistry to compare junctional E-cadherin integrity. Ileal myeloperoxidase activity and bacterial translocation of Enterococcus faecalis were assessed biochemically and by E. faecalis-specific bacterial cultures, respectively, in day 3 postburn rats.

SETTING

: Research laboratories in a medical center and an academic institution.

SUBJECTS

Male Sprague-Dawley rats given sham treatment or treatment as a burn model with full-thickness skin scald over 30% total body surface area.

CONCLUSIONS

We report (1) increased levels of neutrophil influx and extravasation in villi lamina propriae, including elastase-positive cells (postburn day 1), (2) heightened levels of intestinal myeloperoxidase activity (postburn day 3), (3) decreased levels of epithelial cell proliferation, migration, and E-cadherin (postburn day 3), and (4) increased enterocyte apoptosis and E. faecalis bacterial translocation (postburn day 3). Based on these structural and functional abnormalities, we propose a mechanism for burn injury-related intestinal barrier dysfunction that includes increased trans- and para-cellular leakage caused by impaired enterocyte renewal and decreased junctional E-cadherin levels subsequent to increased neutrophil influx and extravasation within the villus lamina propria microenvironment.

Burn-Induced Gut Mucosal Homeostasis in TCR ?? Receptor-Deficient Mice

Gammadelta T lymphocytes make up approximately 50% of lymphocytes in the intestine. These cells have been shown to prime macrophages for TNF-alpha production after burn. We previously showed that neutralizing anti-TNF-alpha antibodies reduce mucosal atrophy by decreasing gut epithelial apoptosis after severe burn. We hypothesized that burn-induced mucosal turnover is diminished in T cell receptor delta gene knockout (TCR delta-/-) mice through diminished TNF-alpha activity. Forty-two wild-type and 42 TCR delta-/- mice (C57-BL6) were randomly assigned to burn and sham burn groups. The burn group underwent a 25% total body surface area (TBSA) scald burn. The proximal small intestine was harvested at 2, 12, and 48 h. To assess mucosal atrophy, mucosal height and cell numbers in the villi and crypts were determined on hematoxylin and eosin-stained tissue sections. Apoptotic gut epithelium was identified by terminal deoxyuridine nick-end labeling (TUNEL) staining, and cell proliferation was detected by immunostaining for proliferative cell nuclear antigen (PCNA). TNF-alpha mRNA expression was measured by RT-PCR. Caspase-8 activity was measured by colorimetric assay. Statistical analysis was performed with two-way analysis of variance and t testing. Significance was accepted at P < 0.05. Data are expressed as means +/- SEM. TNF-alpha mRNA expression was significantly decreased in TCR delta-/- mice at 2 h after burn. Gut epithelial apoptosis and proliferation in both wild-type and TCR delta-/- mice were significantly increased after burn, but TCR delta-/- mice had a significantly lower levels of apoptosis (P < 0.01) and proliferation (P < 0.05) when compared with wild-type mice. Burn-induced mucosal atrophy was identified in groups by decreasing villus height, crypt depth, and villus and crypt cell number (P < 0.001) compared with sham, but no difference was found between wild-type and TCR delta-/- mice. Caspase-8 activity was significantly diminished in TCR delta-/- mice compared with wild-type mice. Gammadelta T cells are associated with increased TNF-alpha expression and gut epithelial turnover in the small bowel after severe burn. However, absence of delta T cell receptor did not inhibit mucosal atrophy after severe burn. This study suggests that gut mucosal atrophy after severe burn is a multifactorial process associated with increased TNF-alpha activity.

Morphological changes of cell proliferation and apoptosis in rat jejunal mucosa at different ages

AIM: To study the changes of cell proliferation and apoptosis in rat jejunal epithelium at different ages.

METHODS: Cell proliferation and apoptosis of the jejunal mucosal and glandulous epithelia from birth to postnatal 12^th month were observed using immunocytochemistry (ICC), and TUNEL method. The height of villus, the thickness of muscle layer and the number of goblet cells in jejunal mucosal and glandulous epithelia were measured by BeiHang analytic software and analyzed by STAT.

RESULTS: (1) Proliferating cell nuclear antigen (PCNA) positive cells of jejunal glandulous recess were found and increased in number from birth to the postnatal 3^rd month. The number of PCNA positive cells peaked in the postnatal 3^rd month, and decreased from then on. (2) The number of apoptotic cells also peaked in the postnatal 3^rd month, showing a similar trend to that of the PCNA positive cells. (3) The height of jejunal villus increased after birth, peaked in the postnatal 3^rd month and decreased from then on. The jejunal muscle layer became thicker in the postnatal 3^rd week and the postnatal 12^th month. The number of goblet cells of the jejunal mucosal and glandulous epithelia had a linear correlation with age.

CONCLUSION: (1) PCNA positive cells are distributed in the jejunal glandulous recess. (2) Apoptotic cell number peaks in the postnatal 3^rd month, indicating that cell proliferation and apoptosis are developed with the formation of digestive metabolism as rat grows to maturity. (3) The thickness of jejunal muscle layer increases to a maximum in the postnatal 3^rd week, which may be related to the change in diet from milk to solid food. (4) The number of goblet cells increases rapidly in the postnatal 3^rd week, probably due to ingestion of solid food.

Effect of bombesin on gut mucosal impairment after severe burn

Severe cutaneous bum alters gut epithelial homeostasis. In previous studies, treatment with bombesin decreased mucosal atrophy and improved maintenance of gut mucosal integrity after severe burn. Our current hypothesis is that bombesin reduces burn-induced gut impairment by decreasing gut epithelial cell death. Fifty-four adult male Fisher-344 rats were randomly assigned to three groups: control, sham burn (I), burn (II), and burn + bombesin (III). Animals in groups II and III received a 60% total body surface area full thickness scald burn, and the treatment group (III) received bombesin subcutaneously (10 microg/kg, every 8 h) beginning immediately before the experiment. The proximal small bowel was harvested at 12 and 72 h after burn with measurement of wet and dry weight, mucosal weight, and protein content, and a 1-cm length of proximal end was excised and fixed in fomalin for histological and immunohistochemical observation. Data are expressed as means +/- SEM. Statistical analysis was by done by analysis of variance (significance at P < 0.05). Bombesin treatment attenuated mucosal atrophy demonstrated by restoration of the mucosal weight, mucosal protein content, and maintenance of mucosal height and total mucosal epithelial cell count. Gut epithelial cell apoptosis was, at least in part, inhibited by bombesin compared with a significant increase of gut cell apoptosis at 12 h after burn. Gut epithelial proliferation was not affected. Bombesin diminished burn-induced gut mucosal atrophy and gut epithelial cell apoptosis, suggesting that bombesin treatment may play an important role in the recovery of gut impairment after severe burn.