Effect of bombesin on gut mucosal impairment after severe burn

Insights into bombesin receptors and ligands: Highlighting recent advances

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

Contributions of severe burn and disuse to bone structure and strength in rats

Burn and disuse results in metabolic and bone changes associated with substantial and sustained bone loss. Such loss can lead to an increased fracture incidence and osteopenia. We studied the independent effects of burn and disuse on bone morphology, composition and strength, and microstructure of the bone alterations 14days after injury. Sprague-Dawley rats were randomized into four groups: Sham/Ambulatory (SA), Burn/Ambulatory (BA), Sham/Hindlimb Unloaded (SH) and Burn/Hindlimb Unloaded (BH). Burn groups received a 40% total body surface area full-thickness scald burn. Disuse by hindlimb unloading was initiated immediately following injury. Bone turnover was determined in plasma and urine. Femur biomechanical parameters were measured by three-point bending tests and bone microarchitecture was determined by micro-computed tomography (uCT). On day 14, a significant reduction in body mass was observed as a result of burn, disuse and a combination of both. In terms of bone health, disuse alone and in combination affected femur weight, length and bone mineral content. Bending failure energy, an index of femur strength, was significantly reduced in all groups and maximum bending stress was lower when burn and disuse were combined. Osteocalcin was reduced in BA compared to the other groups, indicating influence of burn. The reductions observed in femur weight, BMC, biomechanical parameters and indices of bone formation are primarily responses to the combination of burn and disuse. These results offer insight into bone degradation following severe injury and disuse.

Muscle contractile properties in severely burned rats

Burn induces a sustained catabolic response which causes massive loss of muscle mass after injury. A better understanding of the dynamics of muscle wasting and its impact on muscle function is necessary for the development of effective treatments. Male Sprague-Dawley rats underwent either a 40% total body surface area (TBSA) scald burn or sham burn, and were further assigned to subgroups at four time points after injury (days 3, 7, 14 and 21). In situ isometric contractile properties were measured including twitch tension (Pt), tetanic tension (Po) and fatigue properties. Body weight decreased in burn and sham groups through day 3, however, body weight in the sham groups recovered and increased over time compared to burned groups, which progressively decreased until day 21 after injury. Significant differences in muscle wet weight and protein weight were found between sham and burn. Significant differences in muscle contractile properties were found at day 14 with lower absolute Po as well as specific Po in burned rats compared to sham. After burn, the muscle twitch tension was significantly higher than the sham at day 21. No significant difference in fatigue properties was found between the groups. This study demonstrates dynamics of muscle atrophy and muscle contractile properties after severe burn; this understanding will aid in the development of approaches designed to reduce the rate and extent of burn induced muscle loss and function.

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.

“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.

Bombesin-induced gastroprotection

Bombesin is an endogenous gut peptide that is prominent in the stomach. In addition to its effects on modulating acid and gut peptide secretion, recent evidence indicates that bombesin is a potent gastroprotective agent. This review article examines the ability of bombesin to prevent gastric injury. Its protective actions appear to be mediated primarily via the release of endogenous gastrin, as gastroprotection is negated by blockade of gastrin receptors. Bombesin-induced gastroprotection and gastrin release are modified by somatostatin. Immunoneutralization of endogenous somatostatin increases the ability of bombesin to prevent gastric injury by increasing gastrin release. In mechanistic studies, ablation of capsaicin-sensitive afferent neurons abolishes bombesin-induced gastroprotection while cyclo-oxygenase inhibition partially reverses this effect. Nitric oxide synthase inhibition also negates bombesin-induced gastroprotection as well as the ability of bombesin to increase gastric mucosal blood flow. Taken together, the available evidence indicates that bombesin causes release of endogenous gastrin that activates sensory neurons located in the gastric mucosa. Activation of sensory neurons causes increased production of nitric oxide through activation of constitutive nitric oxide synthase, which leads to a resultant increase in gastric mucosal blood flow and renders the stomach less susceptible to damage from luminal irritants.

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.