The effect of growth hormone on gut mucosal homeostasis and cellular mediators after severe trauma

Kinetics of Inflammatory Mediators in the Immune Response to Burn Injury: Systematic Review and Meta-Analysis of Animal Studies

Burns are often accompanied by a dysfunctional immune response, which can lead to systemic inflammation, shock, and excessive scarring. The objective of this study was to provide insight into inflammatory pathways associated with burn-related complications. Because detailed information on the various inflammatory mediators is scattered over individual studies, we systematically reviewed animal experimental data for all reported inflammatory mediators. Meta-analyses of 352 studies revealed a strong increase in cytokines, chemokines, and growth factors, particularly 19 mediators in blood and 12 in burn tissue. Temporal kinetics showed long-lasting surges of proinflammatory cytokines in blood and burn tissue. Significant time-dependent effects were seen for IL-1β, IL-6, TGF-β1, and CCL2. The response of anti-inflammatory mediators was limited. Burn technique had a profound impact on systemic response levels. Large burn size and scalds further increased systemic, but not local inflammation. Animal characteristics greatly affected inflammation, for example, IL-1β, IL-6, and TNF-α levels were highest in young, male rats. Time-dependent effects and dissimilarities in response demonstrate the importance of appropriate study design. Collectively, this review presents a general overview of the burn-induced immune response exposing inflammatory pathways that could be targeted through immunotherapy for burn patients and provides guidance for experimental set-ups to advance burn research.

Characterization of an intestine-specific GH receptor knockout (IntGHRKO) mouse

OBJECTIVE

Growth hormone (GH) has been reported to enhance the intestinal barrier; as such, recombinant GH has been administered for several intestinal diseases. However, excess GH action has been implicated in increasing the risk of intestinal dysfunction. The goal of this study was to examine the direct effects of GH on the small and large intestines to clarify the role GH plays in intestinal function through the use of a mouse model.

DESIGN

An intestinal epithelial-specific GH receptor (GHR) knockout (IntGHRKO) mouse line was generated using Cre-lox with the villin promoter driving Cre expression. The generated mice were characterized with respect to growth and intestinal phenotypes.

RESULTS

IntGHRKO mice showed no significant changes in body length, weight, or composition compared to floxed controls. Male IntGHRKO mice had significantly shorter large intestines at 4 and 12 months of age. Intestinal barrier function was assessed by measuring the expression of tight junction related genes, as well as levels of serum endotoxin and fecal albumin. Results showed sex differences as males had an increase in occludin levels but normal serum endotoxin and fecal albumin; while, females had changes in fecal albumin levels with normal occludin and serum endotoxin. Evaluation of glucose tolerance and fat absorption also showed sex differences as females were glucose intolerant, while males had impaired fat absorption. Histopathology revealed a trend towards decreased villus height in males, which could explain the sex difference in glucose homeostasis.

CONCLUSIONS

Overall, the data demonstrate that disruption of GH on the intestinal epithelial cells modestly affects the intestinal gross anatomy, morphology, and function in a sex-specific manner.

Molecular Mechanisms of Melatonin Protection from Gastric Mucosal Apoptotic Injury in Experimental Burns

Melatonin, a basic secretory pineal gland product, is a nontoxic, multifunctional molecule. It has antioxidant and anti-apoptotic activities and protects tissues from injury. The objective of the present study was to determine the molecular mechanism of melatonin anti-apoptotic effect on gastric injury in a rat burn model. We hypothesized that melatonin gastric protection may be related to the activation of transcription erythroid 2-related factor 2 (Nrf2). Using a 30% total body surface area (TBSA) rat burn model, melatonin (10 mg/kg, i.p.) was injected immediately and 12 h after thermal skin injury. Via light immunohistochemistry, we determined the tissue level of 4-hydroxy-2-nonenal (4-HNE) as a marker of lipid peroxidation, Bcl-2 and Bax as apoptosis-related proteins, and Nrf2. Results are presented as medians (interquartile range (IQR)). Thermal trauma in burned animals, compared with the controls, increased the expression of pro-apoptotic Bax protein (1.37 (0.94–1.47)), decreased anti-apoptotic Bcl-2 protein (1.16 (1.06–1.23), p < 0.001) in epithelial cells, and elevated Bax/Bcl-2 ratios (p < 0.05). Tissue 4-HNE and Nrf2 levels were increased following severe burns (1.55 (0.98–1.61) and 1.16 (1.01–1.25), p < 0.05, respectively). Melatonin significantly decreased 4-HNE (0.87 (0.74–0.96), p < 0.01) and upregulated Nrf2 (1.55 (1.52–1.65), p < 0.001) levels. It also augmented Bax (1.68 (1.5–1.8), p < 0.001) and Bcl-2 expressions (1.96 (1.89–2.01), p < 0.0001), but reduced Bax/Bcl-2 ratios (p < 0.05). Our results suggest that experimental thermal trauma induces oxidative gastric mucosal injury. Melatonin manifests a gastroprotective effect through Nrf2 activation, lipid peroxidation attenuation, and Bax/Bcl-2 ratio modification as well.

Targeting palmitoyl acyltransferase ZDHHC21 improves gut epithelial barrier dysfunction resulting from burn-induced systemic inflammation

Clinical studies in burn patients demonstrate a close association between leaky guts and increased incidence or severity of sepsis and other complications. Severe thermal injury triggers intestinal inflammation that contributes to intestinal epithelial hyperpermeability, which exacerbates systemic response leading to multiple organ failure and sepsis. In this study, we identified a significant function of a particular palmitoyl acyltransferase, zinc finger DHHC domain-containing protein-21 (ZDHHC21), in mediating signaling events required for gut hyperpermeability induced by inflammation. Using quantitative PCR, we show that ZDHHC21 mRNA production was enhanced twofold when intestinal epithelial cells were treated with TNF-α-IFN-γ in vitro. In addition, pharmacological targeting of palmitoyl acyltransferases with 2-bromopalmitate (2-BP) showed significant improvement in TNF-α-IFN-γ-mediated epithelial barrier dysfunction by using electric cell-substrate impedance-sensing assays, as well as FITC-labeled dextran permeability assays. Using acyl-biotin exchange assay and click chemistry, we show that TNF-α-IFN-γ treatment of intestinal epithelial cells results in enhanced detection of total palmitoylated proteins and this response is inhibited by 2-BP. Using ZDHHC21-deficient mice or wild-type mice treated with 2-BP, we showed that mice with impaired ZDHHC21 expression or pharmacological inhibition resulted in attenuated intestinal barrier dysfunction caused by thermal injury. Moreover, hematoxylin and eosin staining of the small intestine, as well as transmission electron microscopy, showed that mice with genetic interruption of ZDHHC21 had attenuated villus structure disorganization associated with thermal injury-induced intestinal barrier damage. Taken together, these results suggest an important role of ZDHHC21 in mediating gut hyperpermeability resulting from thermal injury.NEW & NOTEWORTHY Increased mucosal permeability in the gut is one of the major complications following severe burn. Here we report the novel finding that zinc finger DHHC domain-containing protein-21 (ZDHHC21) mediates gut epithelial hyperpermeability resulting from an experimental model of thermal injury. The hyperpermeability response was significantly attenuated with a pharmacological inhibitor of palmitoyl acyltransferases and in mice with genetic ablation of ZDHHC21. These findings suggest that ZDHHC21 may serve as a novel therapeutic target for treating burn-induced intestinal barrier dysfunction.

Effectiveness of Recombinant Human Growth Hormone for Pharyngocutaneous Fistula Closure

Objectives

In laryngeal cancer, which comprises 25% of head and neck cancer, chemotherapy has come into prominence with the increase in organ-protective treatments. With such treatment, salvage surgery has increased following recurrence; the incidence of pharyngocutaneous fistula has also increased in both respiratory and digestive system surgery. We investigated the effects of recombinant human growth hormone on pharyngocutaneous fistula closure in Sprague-Dawley rats, based on an increase in amino acid uptake and protein synthesis for wound healing, an increase in mitogenesis, and enhancement of collagen formation by recombinant human growth hormone.

Methods

This study was experimental animal study. Forty Sprague-Dawley rats were separated into two groups, and pharyngoesophagotomy was performed. The pharyngoesophagotomy was sutured with vicryl in both groups. Rats in group 1 (control group) received no treatment, while those in group 2 were administered a subcutaneous injection of recombinant human growth hormone daily. On day 14, the pharynx, larynx, and upper oesophagus were excised and examined microscopically.

Results

Pharyngocutaneous fistula exhibited better closure macroscopically in the recombinant human growth hormone group. There was a significant difference in collagen formation and epithelisation in the recombinant human growth hormone group compared to the control group.

Conclusion

This study is believed to be the first in which the effect of recombinant human growth hormone on pharyngocutaneous fistula closure was evaluated, and the findings suggest the potential of use of growth hormone for treatment of pharyngocutaneous fistula.

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.

Activation of Wnt3a signaling stimulates intestinal epithelial repair by promoting c-Myc-regulated gene expression

In response to mucosal injury, epithelial cells modify the patterns of expressed genes to repair damaged tissue rapidly. Our previous studies have demonstrated that the transcription factor c-Myc is necessary for stimulation of epithelial cell renewal during mucosal healing, but the up-stream signaling initiating c-Myc gene expression after injury remains unknown. Wnts are cysteine-rich glycoproteins that act as short-range ligands to locally activate receptor-mediated signaling pathways and correlate with the increased expression of the c-Myc gene. The current study tested the hypothesis that Wnt3a signaling is implicated in intestinal epithelial repair after wounding by stimulating c-Myc expression. Elevated Wnt3a signaling in intestinal epithelial cells (IEC-6 line) by coculturing with stable Wnt3a-transfected fibroblasts or ectopic overexpression of the Wnt3a gene enhanced intestinal epithelial repair after wounding. This stimulatory effect on epithelial repair was prevented by silencing the Wnt coreceptor LRP6 or by c-Myc silencing. Activation of the Wnt3a signaling pathway increased β-catenin nuclear translocation by decreasing its phosphorylation and stimulated c-Myc expression during epithelial repair after wounding. In stable Wnt3a-transfected IEC-6 cells, increased levels of c-Myc were associated with an increase in expression of c-Myc-regulated genes cyclcin D1 and cyclin E, whereas c-Myc silencing inhibited expression of cyclin D1 and cyclin E and delayed epithelial repair. These results indicate that elevated Wnt3a signaling in intestinal epithelial cells after wounding stimulates epithelial repair by promoting c-Myc-regulated gene expression.

Growth hormone-dependent pathogenesis of human hepatic steatosis in a novel mouse model bearing a human hepatocyte-repopulated liver

Clinical studies have shown a close association between nonalcoholic fatty liver disease and adult-onset GH deficiency, but the relevant molecular mechanisms are still unclear. No mouse model has been suitable to study the etiological relationship of human nonalcoholic fatty liver disease and human adult-onset GH deficiency under conditions similar to the human liver in vivo. We generated human (h-)hepatocyte chimeric mice with livers that were predominantly repopulated with h-hepatocytes in a h-GH-deficient state. The chimeric mouse liver was mostly repopulated with h-hepatocytes about 50 d after transplantation and spontaneously became fatty in the h-hepatocyte regions after about 70 d. Infusion of the chimeric mouse with h-GH drastically decreased steatosis, showing the direct cause of h-GH deficiency in the generation of hepatic steatosis. Using microarray profiles aided by real-time quantitative RT-PCR, comparison between h-hepatocytes from h-GH-untreated and -treated mice identified 14 GH-up-regulated and four GH-down-regulated genes, including IGF-I, SOCS2, NNMT, IGFLS, P4AH1, SLC16A1, SRD5A1, FADS1, and AKR1B10, respectively. These GH-up- and -down-regulated genes were expressed in the chimeric mouse liver at lower and higher levels than in human livers, respectively. Treatment of the chimeric mice with h-GH ameliorated their altered expression. h-Hepatocytes were separated from chimeric mouse livers for testing in vitro effects of h-GH or h-IGF-I on gene expression, and results showed that GH directly regulated the expression of IGF-I, SOCS2, NNMT, IGFALS, P4AH1, FADS1, and AKR1B10. In conclusion, the chimeric mouse is a novel h-GH-deficient animal model for studying in vivo h-GH-dependent human liver dysfunctions.

Can we protect the gut in critical illness? The role of growth factors and other novel approaches

The intestine plays a central role in the pathophysiology of critical illness and is frequently called the "motor" of the systemic inflammatory response. Perturbations to the intestinal barrier can lead to distant organ damage and multiple organ failure. Therefore, identifying ways to preserve intestinal integrity may be of paramount importance. Growth factors and other peptides have emerged as potential tools for modulation of intestinal inflammation and repair due to their roles in cellular proliferation, differentiation, migration, and survival. This review examines the involvement of growth factors and other peptides in intestinal epithelial repair during critical illness and their potential use as therapeutic targets.

Effects of recombinant human growth hormone on enterocutaneous fistula patients

AIM: To explore the effects of recombinant human growth hormone (rhGH) on intestinal mucosal epithelial cell proliferation and nutritional status in patients with enterocutaneous fistula.

METHODS: Eight patients with enterocutaneous fistulas received recombinant human growth hormone (10 μg/d) for 7 d. Image analysis and immunohisto-chemical techniques were used to analyse the expression of proliferating cell nuclear antigen (PCNA) in intestinal mucosal epithelial cells in biopsy samples from the patients who had undergone an endoscopic biopsy through the fistula at day 0, 4 and 7. Body weights, nitrogen excretion, serum levels of total proteins, albumin, prealbumin, transferrin and fibronectin were measured at day 0, 4 and 7.

RESULTS: Significant improvements occurred in the expression of PCNA in the intestinal mucosal epithelial cells at day 4 and 7 compared to day 0 (24.93 ± 3.41%, 30.46 ± 5.24% vs 12.92 ± 4.20%, P < 0.01). These changes were accompanied by the significant improvement of villus height (500.54 ± 53.79 μm, 459.03 ± 88.98 μm vs 210.94 ± 49.16 μm, P < 0.01), serum levels of total proteins (70.52 ± 5.13 g/L, 74.89 ± 5.16 g/L vs 63.51 ± 2.47 g/L, P < 0.01), albumin (39.44 ± 1.18 g/L, 42.39 ± 1.68 g/L vs 35.74 ± 1.75 g/L, P < 0.01) and fibronectin (236.3 ± 16.5 mg/L, 275.8 ± 16.9 mg/L vs 172.5 ± 21.4 mg/L, P < 0.01) at day 4 and 7, and prealbumin (286.38 ± 65.61 mg/L vs 180.88 ± 48.28 mg/L, P < 0.05), transferrin (2.61 ± 0.12 g/L vs 2.41 ± 0.14 g/L, P < 0.05) at day 7. Nitrogen excretion was significantly decreased at day 7 (3.40 ± 1.65 g/d vs 7.25 ± 3.92 g/d, P < 0.05). No change was observed in the body weight.

CONCLUSION: Recombinant human growth hormone could promote intestinal mucosal epithelial cell proliferation and protein synthesis in patients with enterocutaneous fistula.

Prevention and treatment of gastrointestinal dysfunction following severe burns: A summary of recent 30-year clinical experience

AIM: To sum up the recent 30-year experience in the prevention and treatment of gastrointestinal dysfunction in severe burn patients, and propose practicable guidelines for the prevention and treatment of gastrointestinal (GI) dysfunction.

METHODS: From 1980 to 2007, a total of 219 patients with large area and extraordinarily large area burns (LAB) were admitted, who were classified into three stages according the therapeutic protocols used at the time: Stage 1 from 1980 to 1989, stage 2 from 1990 to 1995, and stage 3 from 1996 to 2007. The occurrence and mortality of GI dysfunction in patients of the three stages were calculated and the main causes were analyzed.

RESULTS: The occurrence of stress ulcer in patients with LAB was 8.6% in stage 1, which was significantly lower than that in stage 1 (P < 0.05). No massive hemorrhage from severe stress ulcer and enterogenic infections occurred in stages 2 and 3. The occurrence of abdominal distension and stress ulcer and the mortality in stage 3 patients with extraordinarily LAB was 7.1%, 21.4% and 28.5%, respectively, which were significantly lower than those in stage 1 patients (P < 0.05 or P < 0.01), and the occurrence of stress ulcer was also significantly lower than that in stage 2 patients (P < 0.05).

CONCLUSION: Comprehensive fluid resuscitation, early excision of necrotic tissue, staged food ingestion, and administration of specific nutrients are essential strategies for preventing gastrointestinal complications and lowering mortality in severely burned patients.

Laparoscopic surgery induced interleukin-6 levels in serum and gut mucosa: implications of peritoneum integrity and gas factors

BACKGROUND

The peritoneum serves as an integral part of host immunity, and the homeostasis of intraperitoneal environment is held to be beneficial for patient recovery after abdominal surgery. How minimal invasive access to the abdomen by laparoscopy and incisions would alter the intraperitoneal immune response is not fully defined. This study examined the levels of IL-6 in serum and gut mucosa following laparoscopic surgery with reference to the peritoneum integrity and gas factors.

METHODS

BALB/c mice were divided into three groups (ten animals in each group) that underwent different abdominal surgical treatments: laparotomy (open group), laparoscopy with atmospheric air (air group) or carbon dioxide pneumoperitoneum (CO(2) group). A 3-cm incision of the skin and muscle was made in all animals except the peritoneum was left intact in the latter two animal groups in order to cancel out the incisional tissue injury present in laparotomy. Four hours after surgery, serum, and jejunal mucosa were extracted for IL-6 measurement by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Open laparotomy resulted in significant elevation of serum IL-6 level when compared to the laparoscopic procedures in the descending order of open > air > CO(2) groups. For the mucosal IL-6 level, both the open and air groups were significantly higher than the CO(2) group. Data from multivariate analysis revealed that breaching or incision of the peritoneum was an important factor for the elevated levels of IL-6 in serum (p < 0.001) and jejunal mucosa (p = 0.032).

CONCLUSION

The present study suggests that laparoscopic techniques to minimize the size of the peritoneal incision as well as exposure to atmospheric air can potentially reduce postoperative stress responses associated with abdominal surgery and prompt early recovery.

“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.

Ghrelin improves burn-induced delayed gastrointestinal transit in rats

Delayed gastrointestinal transit is common in patients with severe burn. Ghrelin is a potent prokinetic peptide. We aimed at testing the effect of ghrelin on burn-induced delayed gastrointestinal transit in rats. Gastric emptying (GE), intestinal transit (IT), and colonic transit (CT) studies were performed in male Sprague-Dawley rats. Rats were randomized into two main groups as follows: sham injury and ghrelin-treated burn injury with doses of 0, 2, 5, and 10 nmol/rat ip 6 h after burn. Sham/burn injury was induced under anesthesia. Rats received a phenol red meal 20 min following ghrelin injection. Based on the most effective ghrelin dose, 1 mg/kg sc atropine was given 30 min before the ghrelin in one group of rats for each study. The rats in each group were killed 30-90 min later; their stomachs, intestines, and colons were harvested immediately, and the amount of phenol red recovered was measured. Percentage of gastric emptying (GE%) and geometric center for IT and CT were calculated. We found 1) severe cutaneous burn injury significantly delayed GE, IT, and CT compared with sham injury (P < 0.05); 2) ghrelin normalized both GE and IT, but not the CT; 3) the most effective dose of ghrelin was 2 nmol/rat; and 4) atropine blocked the prokinetic effects of ghrelin on GE% and IT. In conclusion, ghrelin normalizes burn-induced delayed GE and IT but has no effect on CT in rats. The prokinetic effects of ghrelin are exerted via the cholinergic pathway. Ghrelin may have a therapeutic potential for burn patients with delayed upper gastrointestinal transit.