Bacterial adhesion inhibitor prevents infection in a rodent surgical incision model

Surgical site infection risk continues to increase due to lack of efficacy in current standard of care drugs. New methods to treat or prevent antibiotic-resistant bacterial infections are needed. Multivalent Adhesion Molecules (MAM) are bacterial adhesins required for virulence. We developed a bacterial adhesion inhibitor using recombinant MAM fragment bound to polymer scaffold, mimicking MAM7 display on the bacterial surface. Here, we test MAM7 inhibitor efficacy to prevent Gram-positive and Gram-negative infections. Using a rodent model of surgical infection, incision sites were infected with antibiotic-resistant bioluminescent strains of Staphylococcus aureus or Pseudomonas aeruginosa. Infections were treated with MAM7 inhibitor or control suspension. Bacterial abundance was quantified for nine days post infection. Inflammatory responses and histology were characterized using fixed tissue sections. MAM7 inhibitor treatment decreased burden of S. aureus and P. aeruginosa below detection threshold. Bacterial load of groups treated with control were significantly higher than MAM7 inhibitor-treated groups. Treatment with inhibitor reduced colonization of clinically-relevant pathogens in an in vivo model of surgical infection. Use of MAM7 inhibitor to block initial adhesion of bacteria to tissue in surgical incisions may reduce infection rates, presenting a strategy to mitigate overuse of antibiotics to prevent surgical site infections.

Aromatase is increased in astrocytes in the presence of elevated pressure

After traumatic brain injury (TBI), a progressive injury and death of neurons and glia leads to decreased brain function. Endogenous and exogenous estrogens may protect these vulnerable cells. In this study, we hypothesized that increased pressure leads to an increase in aromatase expression and estrogen production in astrocytes. In this study, we subjected rat glioma (C6) cells and primary cortical astrocytes to increased pressure (25 mm Hg) for 1, 3, 6, 12, 24, 48, and 72 h. Total aromatase protein and RNA levels were measured using Western analysis and RT-PCR, respectively. In addition, we measured aromatase activity by assaying estrone levels after administration of its precursor, androstenedione. We found that increased pressure applied to the C6 cells and primary cortical astrocytes resulted in a significant increase in both aromatase RNA and protein. To extend these findings, we also analyzed aromatase activity in the primary astrocytes during increased pressure. We found that increased pressure resulted in a significant (P < 0.01) increase in the conversion of androstenedione to estrone. In conclusion, we propose that after TBI, astrocytes sense increased pressure, leading to an increase in aromatase production and activity in the brain. These results may suggest mechanisms of brain estrogen production after increases in pressure as seen in TBI patients.

Potential of hemoglobin-based oxygen carriers in trauma patients

Injured patients have a unique requirement for early blood transfusion. A product that can be used in the prehospital setting that adequately carries and delivers oxygen to peripheral tissues would potentially be life saving for severely injured patients. Allogeneic blood is not the ideal agent in the pre-hospital setting. Present limitations in the allogeneic blood supply include the need for cross-matching, refrigeration, marginal supply, transfusion reactions, infectious disease transmission and immunomodulation increasing the risk of organ dysfunction after transfusion.Hemoglobin-based oxygen carriers have been under present development for the last 25 years. These compounds use either human or bovine hemoglobin that is then chemically altered to improve safety. These compounds exhibit many desirable characteristics that make them potential therapeutic agents in the treatment of the injured patient. These compounds do not need to be cross-matched, have favorable oxygen dissociation characteristics, long half lives, do not transmit disease, appear to be less immunoreactive than blood and theoretically can be used in the pre-hospital setting as a low volume oxygen carrying solution without need for refrigeration. There are at least three agents presently under development that use different techniques to alter the basic hemoglobin tetramer. While there is no FDA approved hemoglobin-based oxygen carrier approved for use in injured patients at this writing, phase III studies are currently either underway or being developed. There is high likelihood that one or more of these agents will be approved for clinical use in the near future.

Contribution of age and gender to outcome of blunt splenic injury in adults: multicenter study of the eastern association for the surgery of trauma

BACKGROUND

The purpose of this study was to examine the contribution of age and gender to outcome after treatment of blunt splenic injury in adults.

METHODS

Through the Multi-Institutional Trials Committee of the Eastern Association for the Surgery of Trauma (EAST), 1488 adult patients from 27 trauma centers who suffered blunt splenic injury in 1997 were examined retrospectively.

RESULTS

Fifteen percent of patients were 55 years of age or older. A similar proportion of patients > or = 55 went directly to the operating room compared with patients < 55 (41% vs. 38%) but the mortality for patients > or = 55 was significantly greater than patients < 55 (43% vs. 23%). Patients > or = 55 failed nonoperative management (NOM) more frequently than patients < 55 (19% vs. 10%) and had increased mortality for both successful NOM (8% vs. 4%, p < 0.05) and failed NOM (29% vs. 12%, p = 0.054). There were no differences in immediate operative treatment, successful NOM, and failed NOM between men and women. However, women > or = 55 failed NOM more frequently than women < 55 (20% vs. 7%) and this was associated with increased mortality (36% vs. 5%) (both p < 0.05).

CONCLUSION

Patients > or = 55 had a greater mortality for all forms of treatment of their blunt splenic injury and failed NOM more frequently than patients < 55. Women > or = 55 had significantly greater mortality and failure of NOM than women < 55.

Alternative case definitions of ventilator-associated pneumonia identify different patients in a surgical intensive care unit

Diagnostic criteria that define ventilator-associated pneumonia (VAP) remain controversial. The purpose of this study was to evaluate common definitions of VAP and determine their relationship to each other and clinical treatment. This study prospectively evaluated several diagnostic criteria that define VAP in a cohort of 255 consecutive SICU patients ventilated for < 48 h. Definitions evaluated include the CDC definitions, the Johanson definitions which do not rely on culture data, the Physician's Probable diagnosis which relies on positive quantitative cultures, and the antibiotic treatment group. Forty-four patients (17%) received antibiotic treatment for VAP. Depending on the definition evaluated, criteria were met for a diagnosis of VAP from as low as 4% of patients by the Johanson definition to as high as 48% of patients by the CDC definition. There was poor agreement among the definitions in their ability to select the same patient as having VAP. Besides duration of mechanical ventilation and tube feeding, which were risk factors that predicted meeting the criteria for all groups, risk factors predicting VAP varied among the definitions. This study demonstrates that in a surgical ICU, the candidate definitions of pneumonia evaluated show little agreement. The particular case definition chosen to diagnose VAP will determine the incidence rate of pneumonia, the time to onset of pneumonia, and the risk factors of the type of patient treated.

Blunt splenic injury in adults: Multi-institutional Study of the Eastern Association for the Surgery of Trauma

BACKGROUND

Nonoperative management of blunt injury to the spleen in adults has been applied with increasing frequency. However, the criteria for nonoperative management are controversial. The purpose of this multi-institutional study was to determine which factors predict successful observation of blunt splenic injury in adults.

METHODS

A total of 1,488 adults (>15 years of age) with blunt splenic injury from 27 trauma centers in 1997 were studied through the Multi-institutional Trials Committee of the Eastern Association for the Surgery of Trauma. Statistical analysis was performed with analysis of variance and extended chi2 test. Data are expressed as mean +/- SD; a value of p < 0.05 was considered significant.

RESULTS

A total of 38.5 % of patients went directly to the operating room (group I); 61.5% of patients were admitted with planned nonoperative management. Of the patients admitted with planned observation, 10.8% failed and required laparotomy; 82.1% of patients with an Injury Severity Score (ISS) < 15 and 46.6% of patients with ISS > 15 were successfully observed. Frequency of immediate operation correlated with American Association for the Surgery of Trauma (AAST) grades of splenic injury: I (23.9%), II (22.4%), III (38.1%), IV (73.7%), and V (94.9%) (p < 0.05). Of patients initially managed nonoperatively, the failure rate increased significantly by AAST grade of splenic injury: I (4.8%), II (9.5%), III (19.6%), IV (33.3%), and V (75.0%) (p < 0.05). A total of 60.9% of the patients failed nonoperative management within 24 hours of admission; 8% failed 9 days or later after injury. Laparotomy was ultimately performed in 19.9% of patients with small hemoperitoneum, 49.4% of patients with moderate hemoperitoneum, and 72.6% of patients with large hemoperitoneum.

CONCLUSION

In this multicenter study, 38.5% of adults with blunt splenic injury went directly to laparotomy. Ultimately, 54.8% of patients were successfully managed nonoperatively; the failure rate of planned observation was 10.8%, with 60.9% of failures occurring in the first 24 hours. Successful nonoperative management was associated with higher blood pressure and hematocrit, and less severe injury based on ISS, Glasgow Coma Scale, grade of splenic injury, and quantity of hemoperitoneum.

Is octreotide beneficial following pancreatic injury?

BACKGROUND

Pancreatic injury is often associated with multiple complications related to uncontrolled pancreatic exocrine secretion, including pancreatic fistula, pseudocyst, and intra-abdominal abscesses. Somatostatin analogues such as octreotide have been shown to decrease pancreas-related morbidity following major pancreatic resection in patients with pancreatic neoplasms and acute severe pancreatitis. This study was conducted to determine whether or not the administration of octreotide influences the incidence and severity of abdominal complications following pancreatic injury.

PATIENTS AND METHODS

Patients with intraoperative diagnosis of pancreatic injury over a 6-year period were studied retrospectively. Specific complications assessed include abdominal abscesses, pseudocyst, pancreatitis, and pancreatic fistula. Statistical analysis of qualitative variables was by chi-square analysis, and analysis of quantitative variables by Student's t-test (P < 0.05).

RESULTS

Injury to the pancreas was identified in 96 patients. Sixteen early deaths (< 48 hours) and one late death occurred, for a mortality of 18%, leaving 80 patients as the study population; 21 patients received octreotide and 55 patients did not. Pancreatic fistula occurred in 32 patients (40%). When stratified by pancreatic injury severity, there was no significant difference in complication rates, although patients treated with octreotide had a higher rate of fistula formation (48% versus 40%), longer duration of fistula drainage, and longer hospital stay compared with untreated patients.

CONCLUSION

Although adverse patient selection may be a factor in this retrospective survey, the magnitude of observed differences raises concerns regarding the empiric administration of octreotide to such patients pending prospective study.

Differential effects of acute thermal injury on rat splanchnic and renal blood flow and prostanoid release

This study examines the hypothesis that acute thermal injury decreases renal and splanchnic blood flow which correlates with altered endogenous vasodilator eicosanoid release. Anesthetized male Wistar rats were subjected to sham or a non-resuscitated 30% total body surface area burn. At 1, 2, 4, 8, and 24 h post-burn mean arterial pressure as well as superior mesenteric and renal artery in vivo blood flow were measured. The superior mesenteric and renal arteries were cannulated and perfused in vitro with their end organs with Krebs buffer (pH 7.4, 37 degrees C). Renal and splanchnic 6-keto-PGF1 alpha (PGI2), PGE2, and thromboxane B2 (TXB2) release were measured by EIA at 15 min of perfusion. Renal and superior mesenteric artery blood flow decreased by 40% or more at 1 and 2 h post-burn despite mean arterial pressure remaining unchanged. The major eicosanoids released were PGI2 from the splanchnic bed and PGI2 and PGE2 from the kidney. Splanchnic PGI2 and TXB2 release and renal TXB2 increased 2-3 fold at 1 h post-burn but returned to the sham level at 2 h post-burn. By 24 h post-burn the vasodilator eicosanoids were increased in both the splanchnic and renal vascular beds. These data show that decreased renal and splanchnic blood flow was associated with increased endogenous release of the potent vasoconstrictor TXB2. By 2 h post-burn, renal and splanchnic blood flow began returning toward the sham level as endogenous release of TXB2 from both organs fell to sham levels. These data suggest that increased endogenous release of TXB2 may contribute to the short-term decrease in renal and splanchnic blood flow in the immediate post-burn period and thus may contribute to ischemia of both vascular beds.

Augmented tumor necrosis factor response to lipopolysaccharide after thermal injury is regulated posttranscriptionally

BACKGROUND AND OBJECTIVE

Thermal injury has been shown to enhance macrophage sensitivity to lipopolysaccharide (LPS), resulting in augmented tumor necrosis factor alpha (TNF-alpha) production. This study was designed to examine whether enhanced TNF-alpha response after thermal injury and LPS stimulation is regulated at the level of transcription.

DESIGN

Tumor necrosis factor alpha release in alveolar macrophages harvested from sham- or thermal-injured Wistar rats was determined using an L929 cytotoxicity bioassay on days 1, 3, and 5 following 40% scald burn and incubation for 24 hours with LPS (0 or 10 micrograms/mL). Separate groups of rats underwent intraperitoneal injection of LPS (5 mg/kg) 3 days following sham or thermal injury. Lung tissue RNA was isolated and probed for TNF-alpha messenger RNA (mRNA), using nuclease protection analysis. Finally, pooled alveolar macrophages were harvested 3 days following sham or thermal injury and cultured in the presence or absence of LPS (10 micrograms/mL) for 4 hours. The RNA from the pooled alveolar macrophages was extracted and probed for TNF-alpha mRNA levels.

RESULTS

Thermal injury alone did not significantly increase alveolar macrophage TNF-alpha bioactivity, whole-lung TNF-alpha mRNA levels, or pooled alveolar macrophages TNF-alpha mRNA levels when compared with levels in sham-injured rats. However, alveolar macrophages from postburn day 3 (PBD 3) demonstrated increased sensitivity to LPS (10 micrograms/mL) compared with alveolar macrophages from sham-injured animals undergoing similar LPS treatment (2365 +/- 1011 vs 169 +/- 79 ng/mL; P < .05). Whole-lung mRNA levels in both sham-injured and PBD-3 rats receiving intraperitoneal LPS, while elevated approximately 2.5-fold from those of non-LPS treated rats, were not different from each other. Finally, pooled alveolar macrophages from sham-injured and PBD-3 rats cultured in the presence of LPS had approximately 1.7-fold and threefold increased TNF-alpha mRNA levels, respectively, compared with alveolar macrophages not cultured with LPS.

CONCLUSIONS

Thermal injury induces priming of alveolar macrophages, resulting in significant increases in macrophage TNF-alpha production after exposure to LPS. The majority of this effect appears to be regulated at a posttranscriptional level, since there were only moderate increases in TNF-alpha mRNA levels after LPS stimulation, which did not coincide with large differences in bioactivity.

Burn injury enhances alveolar macrophage endotoxin sensitivity

Systemic activation of inflammatory cascades has been implicated in the pathogenesis of the multiple organ dysfunction syndrome. To begin to determine whether dysregulation of macrophage cytokine expression after burn plays a role in organ failure, we examined tumor necrosis factor alpha bioactivity of liver and lung macrophages under two conditions: (1) at 1, 3, 5, and 7 days after 40% scald burn, and (2) after sequential insult consisting of 40% scald burn followed by in vitro incubation with endotoxin. Burn alone did not significantly alter alveolar macrophage or Kupffer cell tumor necrosis factor alpha bioactivity at any of the timepoints examined. Sequential insult did not result in significant changes in Kupffer cell tumor necrosis factor alpha, but tumor necrosis factor alpha was increased 11.1 times in alveolar macrophages harvested on postburn day 3. Therefore macrophage cytokine responses to thermal injury are apparently both tissue-specific and time-dependent.

Effect of cyclosporine on adrenocortical response to injury and infection

The effects of cyclosporine administration on the adrenocortical response to the severe stress of burn wound sepsis were studied in Wistar rats. Animals were treated with cyclosporine (10 mg/kg/day) or saline by gavage for 10 days, then subjected to 30% scald burns with wound inoculation with Pseudomonas. Animals were sacrificed on Postburn Days (PBDs) 1, 4, and 7 for determination of serum corticosterone and ACTH levels and adrenal weights and histology. Adrenal glands from animals sacrificed on PBD 7 were also analyzed for DNA, RNA, and protein content. Cyclosporine treatment without injury had no significant effect on body weight gain, adrenal mass, or baseline ACTH or corticosterone levels. During sepsis, cyclosporine-treated animals demonstrated a significantly diminished adrenocortical response compared to those given only saline. Serum corticosterone levels in the cyclosporine group were 45, 53, and 62% lower on PBDs 1, 4, and 7, respectively, than in saline-treated controls (P < 0.01 on each day). ACTH levels were 43 and 36% lower in cyclosporine-treated animals on PBDs 4 and 7, respectively, compared to the saline-treated group (P < 0.05 on each day). Adrenal hyperplasia occurred in both groups by PBD 7, but increases in adrenal mass and in histologic changes associated with hyperplasia (lipid depletion, vascular dilation) were less pronounced in cyclosporine-treated animals compared to those receiving saline, while adrenal composition remained similar between the two groups. Thus, cyclosporine administration is associated with an attenuated adrenocortical response to the stress of sepsis due to diminished circulating levels of ACTH.

Splanchnic vasoconstriction and bacterial translocation after thermal injury

Gut barrier failure and bacterial translocation (BT) after thermal injury may result from splanchnic vasoconstriction and intestinal ischemia. The role of the renin-angiotensin system in intestinal blood flow and BT after thermal injury was studied by pretreatment with the angiotensin-converting enzyme (ACE) inhibitor enalapril in Wistar rats before sham or 30% scald burn. Adequacy of ACE inhibition was documented by the absence of a hypertensive response to angiotensin I, and intestinal blood flow was determined using 51Cr-labeled microspheres. Small bowel blood flow was decreased by 46% at 4-h postburn (P less than 0.05) in untreated burned animals despite maintenance of normal cardiac index but returned to baseline levels by 24 h after injury. Enalapril pretreatment resulted in maintenance of small bowel blood flow after thermal injury and was associated with a significantly reduced incidence of BT (20% vs. 75% in untreated burned animals, P less than 0.01). These findings further implicate intestinal ischemia in the etiology of gut barrier dysfunction after thermal injury, mediated in part by activation of the renin-angiotensin system.

Skeletal muscle amino acid and myofibrillar protein mRNA response to thermal injury and infection

Skeletal muscle changes associated with severe injury were investigated in male Wistar rats subjected to 30% full thickness scald injury (burn) and thermal injury followed by immediate colonization with 10(8) colony-forming units of Pseudomonas aeruginosa (BI). Freely fed animals (FF) and animals pair fed to the BI animals (PF) served as controls. Thermal injury in conjunction with infection produced a rapid and sustained muscle cellular membrane depolarization (transmembrane potential difference at 12 h after injury: FF 92.1 +/- 0.3 and BI 85.2 +/- 2.3 mV; P less than 0.05). This was followed by body weight loss and skeletal muscle protein wasting (gastrocnemius protein at 7 days: FF 0.35 +/- 0.01 and BI 0.16 +/- 0.03 g; P less than 0.05) and intracellular high-energy phosphate depletion (ATP at 10 days: FF 6.6 +/- 0.4 and BI 4.5 +/- 0.4 mumol/g tissue; P less than 0.05). These body and cellular changes were not accounted for by the anorexia alone. Marked alterations in intracellular free amino acids were also noted in the BI group characterized by increases in levels of all amino acids (total intracellular free amino acids at 7 days: FF 51 +/- 7 and BI 91 +/- 12 mM; P less than 0.05) except intracellular glutamine (at 7 days: FF 6.0 +/- 0.2 and BI 2.4 +/- 0.6 mM; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential pathophysiology of bacterial translocation after thermal injury and sepsis

Bacterial translocation (BT) occurs transiently after thermal injury and may result from an ischemic intestinal insult. To evaluate continued intestinal ischemia in the ongoing BT associated with sepsis after injury, rats were randomized to (1) 30% burn injury with Pseudomonas wound infection (BI), (2) BI + fluid resuscitation (BI + Fluid), (3) BI after allopurinol pretreatment to inhibit xanthine oxidase (BI + Allo), or (4) BI after azapropazone pretreatment to inhibit neutrophil degranulation (BI + Aza). On postburn days (PBD) 1, 4, and 7, animals were studied for evidence of BT and intestinal lipid peroxidation. BI + Fluid, BI + Allo, and BI + Aza significantly (p less than 0.05) reduced rates of BT and ileal lipid peroxidation acutely after thermal injury (PBD 1) compared to BI. All four groups had equally high rates of BT associated with the onset of sepsis (PBDs 4 and 7), without evidence of further intestinal lipid peroxidation. These data indicate that the chronic gut barrier failure associated with sepsis after injury occurs independently of continued intestinal ischemia.

Bacterial overgrowth and intestinal atrophy in the etiology of gut barrier failure in the rat

Bacterial translocation occurs in animal models of shock, trauma, sepsis, and parenteral or elemental enteral alimentation. Bowel atrophy and cecal bacterial overgrowth have both been implicated in the pathophysiology of bacterial translocation in many of these models. To further define the etiology of bacterial translocation resulting from dietary manipulations, rats were fed a elemental/defined-formula diet (DFD) for 2 weeks ad libitum and then randomized to either intestinal decontamination with a nonabsorbable antibiotic (neomycin) or no antibiotic treatment. Neomycin treatment significantly (p less than 0.01) reduced the incidence of bacterial translocation after DFD, in association with a significant reduction in the number of cecal gram-negative bacteria. Neither loss of bowel mass after DFD nor bowel composition was affected by oral neomycin. Bacterial translocation after DFD would thus appear to be the result of cecal bacterial overgrowth rather than a loss of a physical intestinal barrier due to atrophy.

Pathophysiologic glucocorticoid levels and survival of translocating bacteria

Burn wound sepsis in rats results in sustained corticosterone elevations and the prolonged presence of translocated bacteria in the mesenteric lymph nodes (MLNs). To determine if survival of bacteria in the MLNs may be influenced by pathophysiologic corticosterone levels, MLNs were quantitatively analyzed from rats randomized to the following groups: burn wound sepsis (BI); BI with adrenocortical response attenuated by cyclosporine (cyclosporine/BI); or cyclosporine/BI with corticosterone replacement (cyclosporine/BI + P). Although rates of bacterial translocation were similar, corticosterone levels were significantly different among the three groups and correlated with the number of lymphocytes and the number of enteric bacteria present per gram of MLN. Thus, pathophysiologic elevations of corticosterone levels during sepsis may exert an effect that allows survival of translocated bacteria in the MLNs of rats, perhaps due to glucocorticoid-associated alterations in regional immunity.

Pathophysiologic glucocorticoid elevations promote bacterial translocation after thermal injury

Thermal injury results in transient elevations of plasma glucocorticoids and promotes translocation of bacteria from the gut to the mesenteric lymph nodes (MLN) in rats. Translocated organisms are quickly cleared following uncomplicated thermal injury. However, subsequent burn wound infection, in temporal association with sustained pathophysiologic elevations of plasma corticosterone, results in the continued presence of enteric bacteria in the MLN. To study the role of sustained pathophysiologic steroid elevations in the mediation of this prolonged bacterial translocation, Wistar rats were randomly placed in groups receiving one of the following: (i) a 30% total body surface area scald injury with placement of a subcutaneous corticosterone pellet, (ii) a 30% total body surface area scald and a sham pellet implantation, (iii) a sham burn and a corticosterone pellet implantation, or (iv) a sham burn and a sham pellet implantation. The animals were sacrificed on days 1 and 4 after injury, and cultures of the MLN, as well as the liver and spleen, were taken. Implantation of corticosterone pellets resulted in sustained elevations of plasma corticosterone compared with controls not receiving corticosterone pellets, similar to results seen in association with injury and infection. These pathophysiologic elevations were associated with the prolonged presence of organisms in the MLN (90% of burned rats with implanted corticosterone pellets versus 25% of rats with uncomplicated burns on postburn day 4; P less than 0.01), but only in the presence of burn injury. Pathophysiologic glucocorticoid elevations did not lead to progression of translocation to the viscera or blood. Thus, the pathophysiologic glucocorticoid response contributes to the translocation of enteric bacteria and their prolonged presence in the MLN after systemic injury.

Additive effects of thermal injury and infection on the small bowel

Thermal injury is associated with functional alterations of multiple organ systems, including the gastrointestinal tract. To study the effects of ongoing infection after thermal injury on bowel mass, composition, and blood flow, male Wistar rats were randomized to receive either 30% scald burn, 30% scald burn with Pseudomonas aeruginosa wound inoculation, sham burn, or sham burn with pair feeding to burned and infected animals. On days 3 and 7 after injury, intestinal blood flow was measured with 51Cr-labeled microspheres, and intestinal mass and composition were analyzed. Burned and infected animals demonstrated a chronic loss of small bowel mass not seen in burned animals without infection by day 7 after injury. Compositional alterations of the small bowels of burned and infected animals included protein wasting similar to but occurring earlier than that seen with anorexia alone and significantly decreased deoxyribonucleic acid and ribonucleic acid content, whereas tissue water content remained unchanged. These chronic intestinal alterations in the burned and infected group could not be explained by ongoing ischemia because intestinal blood flow in these animals was not significantly altered at either time point, implying mediation by other pathophysiologic mechanisms.

Harry M. Vars award. Glutamine or fiber supplementation of a defined formula diet: impact on bacterial translocation, tissue composition, and response to endotoxin

Despite provision of adequate calories, defined formula diets in rats lead to bacterial translocation (BT), fatty infiltration of the liver, and an increased susceptibility to endotoxin. These deleterious effects may be due in part to a loss of intestinal barrier integrity resulting from bowel atrophy. Defined formula diets lack both glutamine and fiber, substances which may help maintain intestinal mass. To determine whether supplementation of defined formula diets with either glutamine or fiber might prevent bowel atrophy and, thus, BT, hepatic steatosis, and the altered response to endotoxin, Wistar rats were fed (1) defined formula diet ad libitum (DFD), (2) (DFD + 2% (w/v) glutamine, (GLUT), or (3) DFD + 2% (w/v) psyllium (FIBER). Rats given standard food isocalorically pair-fed to DFD were used as controls. Nutritional status was assessed by daily weight gain, as well as the ability to maintain serum albumin, hematocrit and white blood counts. After 2 weeks of these feeding regimens, animals were sacrificed, and organ weights and composition were determined, with rates of bacterial translocation determined by mesenteric lymph node, abdominal viscera, and cecal cultures. Additional animals receiving the same experimental diets were subsequently challenged with endotoxin and observed for mortality with rates of post-endotoxin BT and the responses of acute phase proteins and cytokines measured. All dietary regimens resulted in equivalent weight gain and other nutritional parameters. Both glutamine and fiber supplementation maintained small bowel mass, but only GLUT preserved normal jejunal mucosal architecture. Neither fiber nor glutamine supplementation prevented cecal bacterial overgrowth or BT, resulting from the DFD.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibiotic prophylaxis diminishes bacterial translocation but not mortality in experimental burn wound sepsis

Pseudomonas (PSA) burn wound sepsis results in prolonged bacterial translocation (BT) of enteric organisms such as E. coli to the mesenteric lymph nodes (MLN) and organs in rats. Intestinal decontamination with oral antibiotics may improve mortality after burn injury, perhaps due to decreased BT. To determine the effect of oral antibiotic prophylaxis effective against E. coli but not PSA on BT and subsequent mortality in a model of PSA burn wound sepsis, rats were given a 30% scald burn and wound inoculation with 10(8) PSA followed by randomization to either ampicillin (50 mg/kg/d) or saline gavage. Cultures of MLN, organs, blood, and cecal contents were obtained on days 1, 4, and 7 after injury, with additional animals observed for 14-day mortality. Although oral antibiotic prophylaxis resulted in increased cecal colony counts, the incidence of BT was unchanged. The number of organisms present in both the MLN and organs, however, was significantly reduced with prophylaxis, indicating cecal overgrowth by non-translocating bacteria. Reduction of the number of translocating organisms did not result in improved mean survival time after injury, suggesting that mortality from PSA burn wound sepsis occurs independently of bacterial translocation.

Bacterial translocation and intestinal atrophy after thermal injury and burn wound sepsis

Bacterial translocation (BT) occurs after thermal injury in rodents in association with intestinal barrier loss. Infection complicating thermal injury may also affect the intestine producing bowel atrophy. To study these relationships, Wistar rats received either 30% scald followed by wound inoculation with Pseudomonas; 30% scald with pair feeding to infected animals; or sham injury as controls. On days 1, 4, and 7 after injury animals were killed with examination of the bowel and culture of the mesenteric lymph nodes (MLN), livers, spleens, and blood. All burned animals demonstrated BT to the MLN on day 1 after injury, but only burn-infected animals had continued BT on days 4 and 7, with progression of BT to the abdominal organs and blood. Burn injury and infection also resulted in significant atrophy of small bowel mucosa temporally associated with continued BT. Thus injury complicated by infection results in prolonged and enhanced bacterial translocation, perhaps due to failure to maintain the mucosal barrier.

Cytokine production in a model of wound healing: the appearance of MIP-1, MIP-2, cachectin/TNF and IL-1

Macrophages are essential for normal wound repair and many of their effects on healing wounds are likely to be mediated by the secretion of cytokines. This study examines the appearance of messenger RNA (mRNA) for cachectin/tumor necrosis factor (TNF), IL 1, and macrophage inflammatory proteins 1 and 2 (MIP-1 and MIP-2), as well as the mature peptides, in a model of wound healing using wound chambers. RNA for all four cytokines can be detected in wound inflammatory cells by polymerase chain reaction amplification throughout the first 7 days. Cachectin/TNF and IL 1 protein levels peaked on the first day after wound chamber implantation, and MIP-1 and MIP-2 were detected only on day 3. The data suggest that these cytokines participate in the early inflammatory response to wounding.

In vivo myocyte sodium activity and concentration during hemorrhagic shock

The increase in intracellular Na+ concentration ([ Na+]i) and H2O content and decrease in K+ concentration during hemorrhagic shock have been observed. However, the state of the increased [Na+]i has never been defined. In this investigation double-barreled Na(+)-selective microelectrodes were used to directly measure in vivo intracellular Na+ activity (alpha Na) in skeletal muscle cells during prolonged hemorrhagic shock. Resting membrane potential, [Na+]i, and H2O content were also studied concomitantly. Sustained hemorrhagic shock with metabolic acidosis was produced in 12 rabbits after removal of approximately 40% of estimated blood volume under light anesthesia. During prolonged shock, resting membrane potentials of skeletal muscle cells depolarized to -74.7 +/- 1.7 mV from a base-line value of -92.6 +/- 0.4 mV. [Na+]i increased to 14.22 +/- 0.45 mmol/l from a base-line value of 11.50 +/- 0.32 mmol/l. Intracellular H2O content also had a 2.2% increase, whereas levels of [K+]i and extracellular H2O content decreased significantly. However, alpha i(Na) remained unchanged (4.07 +/- 0.19 mmol/l in base line and 4.04 +/- 0.20 mmol/l during shock). This makes the intracellular apparent activity coefficient for Na+ fall significantly from 0.356 in base line to 0.286 during shock. This result indicates that the extra Na+ that diffused into cell because of membrane dysfunction was bound to the fixed charges and/or compartmentalized into subcellular organelles. The unchanged alpha i(Na) also indicates that the depolarization of resting membrane potentials during sustained severe hypovolemia was not caused by the increased [Na+]i. The increase in extracellular [K+] during shock could account for the fall of the resting membrane potentials.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a novel tumor necrosis factor alpha/cachectin from the livers of burned and infected rats

Tumor necrosis factor alpha (TNF-alpha)/cachectin is a monocyte/macrophage-derived cytokine implicated as a proximal mediator of many of the catastrophic host responses to infection or endotoxin. However, circulating levels of TNF-alpha/cachectin have only been episodically detected in hospitalized patients with life-threatening bacterial infections. In the present report, increased quantities of immune-reactive TNF-alpha/cachectin were recovered from the livers of rats 3 days following a lethal burn and infection. Two species of TNF-alpha/cachectin were detected, one of approximately 29 kd and the other 17 kd, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In murine peritoneal macrophages and rat Kupffer cells stimulated in vitro with endotoxin, a 29-kd cell-associated and 17-kd secreted form were also detected. We conclude that the increased appearance in vivo of a 29-kd form of TNF-alpha/cachectin from the livers of lethally burned and infected rats represents a novel cell-associated form of the protein.

Role of leukocytes in reperfusion injury of skeletal muscle after partial ischemia

These experiments evaluated the leukocyte as a potential source of oxygen free radical (OFR) generation during reperfusion injury in post-ischemic skeletal muscle. The infrarenal aorta of heparinized Sprague-Dawley rats was clamped for 90 min, declamped, and reperfused for 60 min. Hindlimb muscle resting transmembrane potential difference (Em) and high-energy phosphate content were determined at base line, during ischemia, and on reperfusion. Four groups were studied: a control group, a second group receiving superoxide dismutase and catalase (SOD + CAT) on declamping, a third group receiving dimethylmyleran (DMM) 7 days before the experiment to obtain a selective leukopenia (white blood cells = 1,210 +/- 144/mm3, neutrophils = 1.2%), and a fourth group pretreated with allopurinol (ALLO). During the ischemic period, resting Em was significantly depolarized (-78.6 +/- 0.5 mV from -90.3 +/- 0.3; P less than 0.05) in the control group, whereas creatine phosphate (CP) was depleted and ATP maintained. Data collected during the ischemic phase of the three other groups were similar to the control group (P = NS). On reperfusion, persistent depolarization of resting Em was observed despite restoration of muscle CP content in the control and ALLO groups (-75.4 and -77.0 mV, respectively). In contrast, significant repolarization of resting Em was noted after reperfusion in the SOD + CAT and DMM groups (-86.5 and -88.6 mV, respectively). These data implicate leukocyte-generated OFR as mediators of reperfusion-associated cellular membrane injury in postischemic skeletal muscle.

Hepatocellular membrane function during chronic burn injury

Hepatocellular membrane dysfunction, as indicated by depolarization of the membrane potential, occurs after acute injury and early bacteremia. To determine whether hepatocellular membrane dysfunction occurs in the setting of ongoing thermal injury and infection, Wistar rats were divided into four groups: (1) sham-burned, freely fed controls (FF); (2) rats sustaining approximately 30% total body surface area dorsal full-thickness scald burn (Burn); (3) rats sustaining burns as in group 2 followed by immediate inoculation of 1 x 10(8) CFU Pseudomonas aeruginosa (Burn/Inf); and (4) sham-burned rats pair-fed to the food intake of the Burn/Inf group (PF). On the third and seventh days postburn, body and liver weights were determined. In vivo hepatocellular transmembrane potentials were measured and hepatic ATP, RNA, DNA, and protein contents were assayed. By Day 7, despite greater weight loss in the Burn/Inf group than due to starvation alone (P less than 0.01 Burn/Inf vs FF and PF), hepatic mass was conserved. This was associated with hyperpolarization of the hepatic transmembrane potential (-46.6 +/- 1.5 vs -32.1 +/- 0.6 mV, Burn/Inf vs FF, P less than 0.01) and increases in RNA (141 +/- 9 vs 91 +/- 4 mg/liver, Burn/Inf vs FF, P less than 0.01) and DNA (37 +/- 5 vs 22 +/- 2 mg/liver, Burn/Inf vs FF, P less than 0.05) contents, with no change in ATP or hepatic protein contents. There was a significant hypercorticosteronemia observed in the Burn/Inf group (43 +/- 9 vs 2.8 +/- 0.7 micrograms/dl, Burn/Inf vs FF, P less than 0.01). This hepatic membrane hyperpolarization and augmented RNA content were not secondary to burn or starvation alone as the response in these groups was significantly less than that of the Burn/Inf group. It is suggested that this hepatic membrane hyperpolarization is one mechanism by which hepatic function is maintained during ongoing burn infection in the rat.

Effect of hormonal and substrate backgrounds on cell membrane function in normal males

Hormonal and substrate influences on in vivo cellular membrane function were evaluated in 15 healthy male volunteers. Each subject underwent serial evaluations of membrane function in the anterior tibialis muscle, as assessed by transcutaneous measurement of resting membrane potential (Em). Group A subjects (n = 9) underwent measurement of resting Em in the basal state and again during the 10th day of intravenous feeding (IVF). Group B subjects (n = 6) underwent measurement of resting Em in the basal state during epinephrine infusion and again during epinephrine infusion on the 7th day of IVF. Percutaneous needle biopsy of the vastus lateralis muscle permitted calculation of transmembrane electrolyte distribution from the Nernst equation, using the measured Em and the chloride space method. Hospitalization with intake of a defined-formula enteral diet for 3 days resulted in depolarization (P less than 0.05) of resting Em (-75.3 +/- 1.6 mV) compared with normal (-79.8 +/- 0.9 mV). Despite 10 days of subsequent IVF, further depolarization (P less than 0.05) of resting Em (-71.2 +/- 1.2 mV) was observed. In the dual presence of IVF and exogenous epinephrine infusion, there was an increase (P less than 0.05) in intracellular potassium concentration and repolarization of resting Em (-80.6 +/- 0.8 mV) to normal levels. These data indicate that hormonal background and substrate availability contribute to the in vivo modulation of cellular membrane function in human skeletal muscle, possibly through facilitation of sodium-dependent amino acid transport across the cell membrane.

Replacement of the anterior cruciate ligament using a synthetic prosthesis. An evaluation of graft biology in the dog

The ACL of 21 adult mongrel dogs was replaced with a knitted dacron velour prosthesis. The biologic fate of these synthetic grafts was then evaluated at various intervals from 1 to 12 months postoperatively using routine histology and a vascular injection (Spalteholz) technique. Following implantation the knitted dacron prosthesis was encapsulated with a vascular synovial tissue in a manner similar to that observed with autogenous patellar tendon grafts. This revascularization process was followed by a proliferation of fibroblasts throughout the extent of the prosthesis. While the grafts appeared to support a fibrous tissue proliferation in and around the design of the prosthesis, this tissue demonstrated only a random orientation of collagen fibers as late as 1 year postoperatively. It would appear, therefore, that although the knitted dacron prosthesis is capable of inducing and supporting tissue encapsulation and ingrowth, it does not allow for the functional orientation of this tissue.