Collagen synthesis in explants from rat intestine

Sepsis impairs anastomotic collagen gene expression and synthesis: a possible role for nitric oxide

Although intra-abdominal sepsis is known to impair colon healing by inhibiting anastomotic collagen synthesis, the effect of systemic sepsis on this process is unknown. Endotoxins and cytokines associated with sepsis induce nitric oxide synthesis both systemically and locally within colonic tissue. We hypothesized that systemic sepsis impairs colonic healing and examined a possible correlation with nitric oxide expression. Male Sprague-Dawley rats received intraperitoneal injections of either saline (sham group) or Escherichia coli endotoxin (lipopolysaccharide 1 mg/100 g body weight) at Times -24 and -12 hr (LPS group). All animals underwent laparotomy and left colonic anastomosis at Time 0. At 24 and 96 hr postlaparotomy rats were sacrificed, the anastomoses excised, and [3H]-proline incorporation into protein measured as an index of total new protein synthesis (TNP). Digestion with purified collagenase yielded incorporation into the collagen fraction (CDP). Additional sham and LPS-treated rats were sacrificed at 24, 72, and 120 hr, the anastomoses excised, and nitric oxide synthase activity in the tissue measured by the conversion of [3H]-arginine to [3H]citrulline in an ex vivo culture system. Finally, sham and LPS rats were sacrificed at 120 hr for measurement of colon anastomotic bursting pressure. Systemic sepsis significantly impaired new collagen synthesis in anastomotic tissue at 24 hr compared to control samples (P < 0.02). No difference was noted at 96 hr. TNP synthesis was similar in both groups at 24 or 96 hr. Northern blot analysis confirmed a significant decrease in Type I and Type III collagen mRNA expression at 24 hr in septic rats. Anastomotic bursting pressure was also decreased in the septic group (P < 0.003). Sepsis elevated nitric oxide synthase activity in anastomotic tissue 24 hr postanastomosis, when compared to sham tissue (P < 0.0001). These data suggest that systemic endotoxin induces nitric oxide synthesis at the anastomotic site. The simultaneous dysregulation of collagen gene expression and synthesis with decreased anastomotic strength suggests a possible regulatory role for nitric oxide in gastrointestinal healing.

Intra-abdominal sepsis impairs colonic reparative collagen synthesis

BACKGROUND

Intra-abdominal infection is generally considered a contraindication to primary colon anastomosis. In order to elucidate the mechanisms by which sepsis affects colonic healing, we studied anastomotic new collagen and protein synthesis and collagen gene expression in a relevant animal model.

METHODS

Forty male Sprague-Dawley rats (240 to 260 g) underwent sham laparotomy (SHAM, n = 18) or cecal ligation and single puncture (CLP, n = 22). After 24 hours, animals underwent single-layer left colon anastomosis. Animals were sacrificed either 1 or 4 days postanastomosis. Anastomotic segments of colon were excised, minced, and incubated with 4.5 muCi 3H-proline. After 3 hours, tissue 3H-proline incorporation was quantitated as an index of total new protein synthesis. The protein fraction was then digested with purified collagenase enzyme to determine 3H-proline incorporation into collagenase-digestible protein, an index of new collagen synthesis. Total RNA was extracted from anastomotic tissue samples and subjected to Northern blot analysis for type I and type III collagen genes.

RESULTS

Intra-abdominal sepsis resulted in markedly less new collagen synthesis 1 day postanastomosis (9,163 +/- 1,234 versus 3,744 +/- 444 disintegrates per minute 3H-proline/mg of protein, P < 0.0001) and 4 days postanastomosis (8,462 +/- 956 versus 5,708 +/- 802 dpm/mg of protein P < 0.05). Noncollagenous protein synthesis was also impaired in anastomotic tissue from CLP rats on postanastomosis day 1 (37,497 +/- 3,740 versus 18,593 +/- 2,695 dpm/mg of of protein, P < 0.001) and postanastomosis day 4 (28,238 +/- 834 versus 17,784 +/- 1,415 dpm/mg of of protein, P < 0.0001). The expression of type I and type III collagen was altered relative to the normal temporal sequence observed in SHAM animals.

CONCLUSION

Intra-abdominal infection impairs colonic reparative collagen and protein synthesis. In addition, regulation of type I and type III collagen genes is altered by intra-abdominal sepsis, and the alteration likely contributes to impaired new collagen synthesis and decreased colonic mechanical strength.

Diabetes impairs the development of early strength, but not the accumulation of collagen, during intestinal anastomotic healing in the rat

The evidence that diabetes mellitus adversely affects healing is derived from data on skin, where diminished wound strength is accompanied by a reduced collagen content. As no such data are available on intestinal anastomotic repair, and it has been reported that collagen metabolism in skin and intestine is affected differently by the diabetic state, anastomotic healing in the rat intestine during uncontrolled diabetes was examined. Wistar rats underwent resection and anastomosis of both ileum and colon 1 week after a single injection of streptozotocin (diabetic group) or citrate (control group). After 3 days the mean bursting pressure of ileal anastomoses was 4.1 kPa in controls and 1.0 kPa in diabetic animals (P < 0.05). For colon, these values were 12.0 and 4.9 kPa respectively (P < 0.05). This negative effect of diabetes persisted after 7 days in ileum but not in colon. Diabetic animals had more anastomotic abscesses, especially in the ileum: nine of 16 animals at 3 days after operation versus one of 15 in the control group (P < 0.01). Anastomotic hydroxyproline concentration and content in diabetic animals were not reduced. The postoperative collagen synthetic capacity, as measured in tissue explants, was strongly stimulated in the wound area and appeared essentially unchanged in the diabetic animals. Uncontrolled streptozotocin-induced diabetes severely impairs the development of anastomotic strength in the rat intestine but, unlike impaired wound healing in skin, this phenomenon is not caused by deficient accumulation of collagen.

Collagen synthetic capacity throughout the uninjured and anastomosed intestinal wall

The capacity to synthesize collagen was measured throughout the intestinal tract of the rat, using an in vitro technique. In addition, the effect of anastomotic construction in either the ileum or the colon on collagen synthetic capacity at specific distant locations both 1 and 4 days after operation was investigated. Collagen synthetic capacity is relatively uniform throughout the large bowel. However, in the small bowel in which synthesis is lower than in the large bowel, synthesis is significantly higher in the most proximal and distal segments than in the intermediate tissue. Anastomotic construction in either part of the bowel strongly increases collagen synthetic capacity at the immediate wound site. The synthetic response is not restricted to the anastomotic site but appears to be more generalized and is, in the small bowel, to some extent specific for collagen since the collagen synthetic capacity is increased far more than the capacity to produce noncollagenous protein. Anastomotic construction in the colon has only minor, although sometimes significant, effects on collagen synthetic capacity in the ileum, and vice versa.

Intraperitoneal cytostatics impair early post-operative collagen synthesis in experimental intestinal anastomosesP6

Collagen synthesis in intestinal anastomoses has been measured in rats after in vivo administration of cytostatics. The cytostatics were administered during 5 consecutive days either intravenously or intraperitoneally. On day 3 of the course the rats received both an ileal and a colonic anastomosis. The animals were sacrificed 3 and 7 days after operation. The cytostatics regimen used was a combination of 5-fluorouracil, bleomycin and cisplatinum in a dose of 10, 2 and 0.35 mg kg-1 day-1, respectively. In an additional group, a twice higher dose was given intraperitoneally. Three days after operation a severe inhibition of the collagen synthesis was observed in all the cytostatics treated groups, both in ileum and in colon. The effects of intraperitoneal administration were much more pronounced than those observed after an equal dose given intravenously. Seven days after operation the collagen synthesis in the intravenously treated groups was restored to the level of the control group. However, in the intraperitoneal groups the collagen synthesis in ileal anastomoses was still inhibited. Thus, cytostatics suppress collagen synthesis in intestinal anastomoses. The effect is more severe after intraperitoneal than after intravenous administration, confirming our earlier hypothesis that the former mode of administration comprises a higher risk for anastomotic integrity.

Postoperative changes in collagen synthesis in intestinal anastomoses of the rat: differences between small and large bowel

Collagen synthesis is an essential feature of anastomotic healing in the intestine. Postoperative collagen synthesis, measured in vitro in intestinal anastomoses was studied from three hours to 28 days after operation. For this purpose, an ileal and a colonic anastomosis were constructed within the same animal and the results in both intestinal segments were compared. In the ileum, collagen synthesis was significantly increased, with respect to unoperated controls, three hours after operation. It remained raised during the period of study, with a maximal 10-fold stimulation four days after operation, and had nearly returned to the preoperative level after four weeks. The general pattern was the same in the colon, although quantitatively different: the increase in synthetic activity was delayed in comparison with the ileum. Maximal stimulation was approximately six-fold. In addition, we calculated the ratio for each rat between anastomotic collagen synthesis and the average value found in non-operated control animals. Postoperative stimulation in the ileum was higher than in the colon in almost every animal examined. The results show that the ileum responds more quickly and strongly to wounding than the colon, at least as far as the production of new collagen is concerned. Possibly, this phenomenon contributes to the lower failure rate apparent for anastomoses in the small bowel.

Healing of experimental intestinal anastomoses. Parameters for repair

Anastomotic dehiscence remains a major complication in surgery of the large bowel, and studies on the healing sequence of experimental anastomoses are necessary to define underlying mechanisms and find ways to improve surgical outcome, particularly in high-risk situations. For the quantitative description of anastomotic repair, both mechanical and biochemical parameters are employed, each with their own limitations. Mechanical parameters, either bursting pressure or breaking strength, only reflect growing anastomotic strength as long as disruption occurs within the anastomotic area, which is less than one week after surgery for the bursting pressure and probably up to two weeks for the breaking strength. The biochemical description of anastomotic repair has been limited to behavior of collagen, as represented by its rather unique constituent amino acid hydroxyproline. Conclusions based on collagen concentrations--per unit weight--should be considered with caution since they may change as a consequence of changes in noncollagenous substances. In this respect, collagen content, per unit length, is probably a better parameter to describe anastomotic collagen levels. Few investigations have addressed the quality of collagen (e.g., crosslinking or type). Since, at this time, no distinct correlations have been demonstrated between development of mechanical strength or occurrence of leakage and collagen levels in the healing anastomosis, attention should not be restricted to a description of the quantity of collagen present: the quality of anastomotic collagen should be investigated, perhaps even more so.