Bacterial products primarily mediate fibroblast inhibition in biomaterial infection

PURPOSE

The stimulation of fibroblast growth is essential for the normal healing and tissue integration of biomaterials. The local elevation of proinflammatory mediators in infected perigraft fluid (PGF) may inhibit this growth. We sought to determine whether infected PGF inhibited fibroblast growth, and, if so, whether this was primarily dependent on the biomaterial, bacteria, or host.

METHODS

In vivo Dacron or expandable polytetra-fluoroethylene (ePTFE) grafts, sterile or colonized with slime-producing (RP-62A, viable or formalin-killed) or nonslime-producing (RP-62NA) Staphylococcus epidermidis (1 x 10(7) CFU/cm2), were implanted in Swiss Webster mice, and the PGF was harvested at 7 and 28 days. Antibodies to tumor necrosis factor alpha, interleukin 1 alpha, interferon gamma (7 micrograms/day), and indomethacin (50 micrograms/day) were administered by microinfusion pumps for 7 days and the PGF was harvested. Inhibition of the proinflammatory mediators was confirmed by enzyme-linked immunosorbant assay. The nontreated, heat-treated, or trypsin-digested in vivo PGF was incubated with an in vitro [3H]thymidine murine fibroblast (ATCC CCL-12) proliferation assay.

RESULTS

Fibroblast inhibition was significant at 7 and 28 days with infected PGF incubation compared with sterile and was not dependent on bacterial slime production or viability. Dacron sterile PGF did not significantly inhibit fibroblasts compared with control, whereas sterile ePTFE stimulated (P < 0.05) fibroblasts. Treatment of the PGF with proinflammatory cytokines, heat, and trypsin failed to reverse fibroblast inhibition in the infected state.

CONCLUSION

Biomaterial infection is associated with fibroblast inhibition that is dependent primarily on bacterial products and not the host or biomaterial. Conservative intervention strategies for graft infection need to address the problem of poor healing as well as bacterial clearance.

Platelet-activating factor contributes to immune cell and oxidant-mediated intestinal secretion

The sensitivity of the Ussing-chambered rat colon to stimulation of Cl- secretion (as measured by the change in short-circuit current) by exogenous platelet-activating factor (PAF) was increased significantly by washing the colon in vitro with Ringer's solution containing fatty acid-free albumin. When the wash solution was extracted with chloroform/methanol and the lipid extract was added back to Ussing-chambered colons, inhibition of PAF-stimulated short-circuit current was observed, whereas short-circuit current responses to bradykinin or vasoactive intestinal peptide were not affected. Hypoxia appears to be an important trigger for the down-regulation of the PAF response. These data suggest that hypoxia releases PAF or an endogenous lipid PAF inhibitor that desensitizes PAF receptors on colonic epithelial or mucosal cells. The short-circuit current response of rabbit colon to the chemotactic peptide formyl-methionyl-leucyl-phenylalanine was not inhibited by any PAF antagonist devoid of cyclooxygenase inhibitory activity but was strongly inhibited by indomethacin. In contrast, anti-IgE- or H2O2-stimulated short-circuit current in rat colon was inhibited by specific PAF antagonists, and this inhibition was additive with indomethacin. Both anti-IgE and H2O2 significantly increased PAF production by rat colon. These data suggest that PAF plays an important role in oxidant (H2O2)- and anti-IgE-mediated colonic Cl- secretion but not in Cl- secretion mediated by formyl-methionyl-leucyl-phenylalanine-stimulated phagocytes.

Phenotypic characterization of an intestinal subepithelial myofibroblast cell line

Subepithelial myofibroblasts are located at the interface between the epithelium and lamina propria in most mucosal tissues. Their biological functions are largely unknown because a long-term cell culture model for these cells has not been available. In this report, we define the phenotypic properties of a human colonic cell line (18Co) that exhibits most of the known characteristics of intestinal subepithelial myofibroblasts in situ. These characteristics include 1) a cell shape that can be reversibly interconverted between a flattened discoid and stellate morphology, 2) intracellular organelles reminiscent of myofibroblasts and smooth muscle cells in situ, 3) expression of alpha-smooth muscle actin, 4) plasma membrane receptors for endothelins and natriuretic peptides, and 5) regulation of epithelial sensitivity to calcium-dependent secretagogues by paracrine secretion of prostaglandins. 18Co cells provide an exploitable model to begin defining the physiological and pathophysiological functions of intestinal subepithelial myofibroblasts at the molecular level.

IL-1 stimulates intestinal myofibroblast COX gene expression and augments activation of Cl- secretion in T84 cells

Because interleukin-1 (IL-1) is an important mediator in the inflamed intestine, its effects on enterocyte-subepithelial myofibroblast (SEMF) interaction were investigated in vitro. Acutely juxtaposing T84 cells with 18Co or P2JF SEMF preincubated with IL-1 alpha significantly enhanced T84 short-circuit current (Isc) responsiveness to secretagogues in comparison to SEMF not activated by IL-1 alpha. The sensitivity of T84 cell Isc to Ca(2+)-dependent, but not adenosine 3',5'-cyclic monophosphate-dependent, secretagogues was augmented by IL-1 alpha-treated SEMF. These effects of IL-1 alpha are directly correlated with SEMF prostaglandin E2 (PGE2) production. Both IL-1 alpha augmentation of Cl secretagogue responsiveness and PGE2 formation were inhibited by IL-1 receptor antagonist. Within 5 h, IL-1 alpha stimulated a 10-fold increase in cyclooxygenase (COX)-2 steady-state mRNA levels in 18Co cells. In contrast, COX-1 message levels increased more slowly to two- to threefold above control levels after 24 h incubation. These results demonstrate that the proinflammatory cytokine IL-1 alpha accentuates intestinal SEMF augmentation of enterocyte responsiveness to Ca(2+)-dependent CI-secretagogues. PGE2 is an important mediator of SEMF-enterocyte interaction. The effects of IL-1 alpha on SEMF PGE2 productions are, at least in part, due to stimulation of COX gene expression.

Gastroenterology workforce modeling

OBJECTIVE

To examine the current supply and distribution of gastroenterologists and project future supply under various scenarios to provide a paradigm for workforce reform.

DESIGN

An analysis of current practices and distribution of gastroenterologists and a demographic model, using the 1992 gastroenterology workforce as a baseline.

MAIN OUTCOME MEASURE

Comparison of current supply, distribution, and practice profiles with past data and future projections, using analyses of data from the 1993 Area Resource File, 1992 Medicare Part B file, age- and sex-specific death and retirement rates from the Bureau of Health Professions, managed care staffing patterns, the National Survey of Internal Medicine Manpower, and the Bureau of the Census.

RESULTS

Rapid growth in the number of US gastroenterologists has resulted in a gastroenterologist-to-population ratio double that used on average by health maintenance organizations. In addition, the work profile of gastroenterologists is shared significantly by primary care physicians and other specialists, with the exception of a few specific and uncommon procedures.

CONCLUSIONS

Empirical evidence suggests that, even in the absence of detailed models to describe the desired supply/need balance for gastroenterology, the US health care system and clinicians may benefit from a reduction in gastroenterology training programs. The Gastroenterology Leadership Council endorsed a goal of 25% to 50% reduction in trainee numbers over 5 years, and recent National Resident Matching Program data indicate that a voluntary downsizing process is in full force. This study illustrates a paradigm for workforce planning that could be useful for other medical specialties.

Neuroimmunophysiology of the gastrointestinal mucosa: implications for inflammatory diseases

In conclusion, studies of the neuroimmunophysiology of the intestinal mucosa of the past 5-8 years have demonstrated an important role for the immune system in modulating water and electrolyte transport as well as intestinal motility in the gut. Activation of mast cells and phagocytes leads to heightened Cl- and water secretion, as well as changes in intestinal motility which leads to diarrheal states. These diarrheal responses are self-protective; they rid the intestine of offending microorganisms and antigens. Our investigation of this response has uncovered a new immune accessory cell Cz, the intestinal myofibroblast. This cell seems to play an important role in amplifying the immune signal. This cell is probably also important for the secretion of growth factors onto the epithelium and also the secretion of collagen which results in fibrosis under diseased states. These intestinal myofibroblasts are prolific prostaglandin producers, an important finding because prostaglandin synthesis inhibition has been shown to decrease the development of neoplasia in the gut. Thus, these intestinal myofibroblasts may have other important roles in addition to just modulating water and electrolyte secretion or gut motility. Our laboratory is now engaged in studying these intestinal myofibroblasts in some detail hoping to better understand the biology of these interesting cells.

Nonantibiotic therapy and pharmacotherapy of acute infectious diarrhea

The most important aspect of nonantibiotic treatment of diarrhea is to prevent or repair dehydration and thus prevent significant morbidity or death. Although intravenous fluid therapy is effective, it is expensive and requires personnel and equipment. ORT has saved millions of lives in emerging nations and should be more commonly used in developed countries. Although the simple concept of glucose-stimulated Na+ and fluid absorption remains the basic tenet of such ORT, grain-based solutions appear to have added efficacy and nutritional value. Mild, nondysenteric diarrheas can be safely and reasonably effectively treated either with loperamide or with bismuth subsalicylate compounds. Effective adjunctive therapy for severe secretory diarrheas has thus far escaped discovery. Somatostatin analogues such as octreotide have approximately 50% efficacy in reduction of the moderate secretory diarrheas such as those present in AIDS. There are pharmacologic leads that should be explored to develop more gut specific antisecretory forms of alpha 2-adrenergic agents, somatostatin, or phenothiazines. In addition, Cl- channel blockers still hold great theoretic promise. Effective antisecretory therapy has been sought for the past 20 years. It is disappointing that no effective new drugs have yet emerged. Undoubtedly, this speaks of our inexact understanding of the mechanisms that result in secretory diarrheas. Because of the continued loss of life from diarrhea in emerging nations, better understandings of these mechanisms and effective therapies remain appropriate goals for medical science.

Prostanoids inhibit intestinal NaCl absorption in experimental porcine cryptosporidiosis

BACKGROUND

Recent studies of piglet cryptosporidiosis have shown that impaired Na(+)-coupled glucose absorption is associated with a loss of two thirds of the villous absorptive surface and an inflammatory infiltration of the lamina propria. Because inflammatory cells release eicosanoids that may alter electrolyte transport, the present study examined the role of prostanoids on NaCl transport.

METHODS

Ileal mucosa was stripped of its muscle layers and mounted in Ussing chambers in the presence or absence of indomethacin. Adjacent tissue was also frozen for subsequent extraction and radioimmunoassay of prostaglandin E2 (PGE2).

RESULTS

Results showed that net Na+ absorption is inhibited and net Cl- secretion is induced in infected piglets. Indomethacin restored net Na+ and Cl- absorption to control levels and exogenous PGE reversed this effect. Radioimmunoassay of tissue extracts showed that PGE2 increased from 56.7 +/- 9.6 ng/cm2 in control to 134 +/- 16.8 ng/cm2 in infected ileum (P < 0.01).

CONCLUSIONS

These data indicate that in addition to the Na-glucose malabsorption arising from structural damage, part of the diarrhea of these infected animals must be attributed to local prostanoid production.

Studies on the effect of CL 306,293, a substituted quinoline carboxylic acid, on the clinical disease induced in mice with LP-BM5 virus

CL 306,293, a substituted quinoline carboxylic acid, is a potent inhibitor of dihydroorotic acid dehydrogenase, an enzyme essential for the biosynthesis of pyrimidines. In mammalian cell culture, the agent exhibits antiproliferative properties that can be reversed by the addition of uridine. CL 306,293 inhibits the development of the clinical disease in a murine model of immunodeficiency induced by a mixture of LP-BM5 retroviruses. In infected mice, the agent prevents the development of hypergammaglobulinemia, lymphadenopathy, splenomegaly and induction of an IL-2 deficiency. The CD4/CD8 ratio and the number of B cells in the lymph nodes are decreased if the infected animals are treated with CL 306,293. CL 306,293 was more efficacious and potent than 3'-azido-3'-deoxythymidine. The beneficial effects of CL 306,293 observed in this model are most probably related to its antiproliferative properties.

Fibroblasts modulate intestinal secretory responses to inflammatory mediators

Cultured colonic epithelial cells and fibroblasts were used to examine the interaction between these cell types during intestinal secretion. Secretory responses of T84 colonic epithelial cells, measured as changes in the short-circuit current in modified Ussing chambers to bradykinin, serotonin, hydrogen peroxide, and histamine, were enhanced in the presence of fibroblasts, either in cocultures or when separate cultures of fibroblasts were acutely juxtaposed with the T84 cultures. This effect was abolished by pretreatment with indomethacin and the fibroblasts were found to release prostaglandin E2 in response to these inflammatory mediators. Fibroblasts may exert a paracrine regulation on the secretory response of intestinal epithelial cells via the generation and release of cyclooxygenase products in response to inflammatory mediators. These studies suggest a novel function for the intestinal fibroblastic sheath: that of amplification of the inflammatory response through mesenchymal/epithelial interaction.

Hydrogen peroxide stimulates rat colonic prostaglandin production and alters electrolyte transport

The changes in short circuit current (electrogenic Cl- secretion) of rat colon brought about by xanthine/xanthine oxidase in the Ussing chamber were inhibited by catalase and diethyldithiocarbamate, but not by superoxide dismutase. These results, the reproduction of the response with glucose/glucose oxidase and with exogenous H2O2, and the lack of effect of preincubation with deferoxamine or thiourea implicate H2O2, and not O2- or OH., as the important reactive oxygen metabolite altering intestinal electrolyte transport. 1 mM H2O2 stimulated colonic PGE2 and PGI2 production 8- and 15-fold, respectively, inhibited neutral NaCl absorption, and stimulated biphasic electrogenic Cl secretion with little effect on enterocyte lactic dehydrogenase release, epithelial conductance, or histology. Cl- secretion was reduced by cyclooxygenase inhibition. Also, the Cl- secretion, but not the increase in prostaglandin production, was reduced by enteric nervous system blockade with tetrodotoxin, hexamethonium, or atropine. Thus, H2O2 appears to alter electrolyte transport by releasing prostaglandins that activate the enteric nervous system. The change in short circuit current in response to Iloprost, but not PGE2, was blocked by tetrodotoxin. Therefore, PGI2 may be the mediator of the H2O2 response. H2O2 produced in nontoxic concentrations in the inflamed gut could have significant physiologic effects on intestinal water and electrolyte transport.

Villous atrophy, crypt hyperplasia, cellular infiltration, and impaired glucose-Na absorption in enteric cryptosporidiosis of pigs

Intestinal morphology and fluid and electrolyte transport were examined in a neonatal porcine model of cryptosporidiosis. Sections of jejunum, ileum, and colon were obtained for morphometric analysis on days 3, 6, 9, and 12 postinfection, and in vivo perfusion studies of jejunum and ileum were conducted on days 3 and 4 postinfection. The most severe morphologic lesion was seen in the ileum on day 3, and consisted of villous atrophy, crypt hyperplasia, and cellular infiltration. Villous surface area was reduced from 2.1 +/- 0.4 x 10(5) microns2 in control ileum to 0.8 +/- 0.1 x 10(5) microns2 in infected ileum, a result associated with enterocytes that were fewer in number and reduced in cross-sectional area. Conversely, the number of inflammatory cells in the lamina propria of the villus increased from 456 +/- 116 in control to 1014 +/- 187 in infected villus without a significant change in the volume of the lamina propria. At the height of infection, there was an approximate 1:2 ratio of both organisms and inflammatory cells to villous enterocytes. In contrast, organisms were not observed in the crypts, and the concentration of inflammatory cells in crypt lamina propria was unaltered. Disappearance of organisms and polymorphonuclear cells from the ileum was associated with restoration of normal structure and was complete by day 12. Although organisms were seen in the colon, the general architecture was not severely affected. On days 3 and 4 postinfection, there was a complete impairment of the glucose-stimulated Na and water absorption in both jejunum and ileum of infected pigs; however, absorption of electrolytes and water from a basic Ringer's solution, in the absence of glucose, was not significantly affected. These results are consistent with a malabsorptive diarrheal disease associated with the morphological damage and are very similar to those seen in enteric viral disease in pigs, except that the upper intestine is more severely affected in the latter.

Serosal bicarbonate protects against acid injury to rabbit esophagus

The role of serosal bicarbonate ions (HCO3-) in protection against acid injury was investigated in rabbit esophageal mucosa mounted in Ussing chambers. Luminal acidification reduced potential difference and resistance in tissues exposed serosally to HCO3- or (unbuffered) HCO3-free solution. Whereas resistance declined similarly in both groups, potential difference declined less in HCO3- solution. After washout, HCO3-bathed tissues also had a greater increase in resistance, lower permeability to mannitol, and less histologic damage. Furthermore, as protection by HCO3- was not blocked by pretreatment with either the anion exchange blocker, 4 acetamido-4'-isothiocyanatostilbene 2-2'-disulfonic acid, or the carbonic anhydrase inhibitor, acetazolamide, and replacement of HCO3- with N-2-hydroxyethylpiperazine-N'-2-ethane sulfonic acid, a buffer impermeant to cells, was protective, an extracellular site for protection by HCO3- was likely. Where in the extracellular space HCO3- buffers H+ is unclear, but the absence of change in luminal pH and the inability to prevent the acid-induced increase in permeability in HCO3-bathed tissues argue against a luminal (preepithelial) site. Also, rapid repair was not demonstrated, indicating that a luminal site for protection after surface cell damage was unlikely. We conclude that serosal HCO3- is important in esophageal protection against acid damage by buffering H+ within the intercellular compartment of the extracellular space.

Immune system control of rat and rabbit colonic electrolyte transport. Role of prostaglandins and enteric nervous system

The role of the immune system in controlling intestinal electrolyte transport was studied in rat and rabbit colon in Ussing chambers. A phagocyte stimulus, the chemotactic peptide FMLP, and a mast cell stimulus, sheep anti-rat IgE, caused a brief (less than 10 min) increase in short-circuit current (Isc). Products of immune system activation, platelet-activating factor (PAF) and reactive oxygen species (ROS), caused a sustained, biphasic increase in the Isc. Ion replacement and flux studies indicated that these agonists stimulated electrogenic Cl secretion and inhibited neutral NaCl absorption; responses that were variably inhibited by the cyclooxygenase blockers indomethacin and piroxicam. Lesser degrees of inhibition by nordihydroguaiaretic acid could be accounted for by decreased prostaglandin synthesis rather than by lipoxygenase blockade. Tetrodotoxin, hexamethonium, and atropine also inhibited immune agonist-stimulated Isc, but had no effect on immune agonist-stimulated production of PGE2 or PGI2. These results indicate that immune system agonists alter intestinal epithelial electrolyte transport through release of cyclooxygenase products from cells in the lamina propria with at least 50% of the response being due to cyclooxygenase product activation of the enteric nervous system. The immune system, like the enteric nervous system and the endocrine system, may be a major regulating system for intestinal water and electrolyte transport in health and disease.

Colonic and esophageal transepithelial potential difference in cystic fibrosis

To evaluate differences in the expression of cystic fibrosis (CF) transport defects in the gastrointestinal tract of subjects with CF, in vivo measurements of colonic and esophageal transepithelial electrical potential difference (PD) were performed before and during amiloride superfusion in CF and healthy subjects. Esophageal PD before (-16 +/- 2 vs. -16 +/- 3 mV) and after (-14 +/- 2 vs. -15 +/- 0.3 mV) superfusion with amiloride were similar for CF and healthy subjects. Basal rectosigmoid colon PD was also similar (CF: mean -23 +/- 6 and maximal -37 +/- 9 mV; normal: mean -26 +/- 5 and maximal -45 +/- 11 mV) in both groups. However, with amiloride superfusion (10(-4) M) the colonic PD in CF subjects was almost abolished (95% +/- 15% inhibition), whereas the PD in healthy subjects was only partially reduced (42% +/- 6%) (p less than 0.05). The greater inhibition with amiloride in CF, which was evident in absolute terms (26 +/- 4 vs. 16 +/- 3 mV for controls, p less than 0.05) as well as relative terms, could not be ascribed to a difference in mineralocorticoid secretion rates, because 24-h urine excretion of aldosterone and 17 hydroxy and 17 ketosteroids were similar in both groups. Freshly excised colonic epithelia from 1 CF and 3 non-CF subjects were studied in Ussing chambers, and a similar difference in amiloride responsiveness noted: PD and short-circuit current declined 33% +/- 2% and 37% +/- 4%, respectively, in seven tissues from the colons of 3 patients without CF, whereas both PD and short-circuit current were fully inhibited (100%) in all three tissues from the CF patient. As the presence of an amiloride-insensitive component of short-circuit current in non-CF colon is largely due to electrogenic Cl- secretion, the demonstration that this component was absent both in vivo and in vitro in CF colon establishes the presence of a defect in electrolyte transport in CF colon, a defect consistent with recent reports of absent electrogenic Cl- secretion in CF intestine.

Altered intestinal chloride transport in cystic fibrosis

Sodium ion and chloride transport was studied in vitro in small intestinal and colonic tissue from patients with cystic fibrosis (CF) and from non-CF control subjects matched as to age and sex. Normal histological appearance and substantial response to mucosal glucose (5 mM, ileum) or mucosal amiloride (10(-5) M, colon) indicated normal tissue viability in both control and CF tissues. Electroneutral NaCl absorption was demonstrated in the small intestine of control subjects and CF patients. Small intestinal and colonic tissues of control subjects responded to four secretagogues (theophylline, 5 mM; prostaglandin E2, 10(-6) M; calcium ionophore (A23187), 10(-5) M; bethanechol, 5 x 10(-5) M), with electrogenic chloride secretion. The tissues of CF patients, however, did not respond to any of the test secretagogues. These studies demonstrate that an abnormality in chloride transport is present in the small intestinal and colonic epithelia of CF patients. Unlike airway epithelia, which secrete chloride in response to Ca ionophore, the intestinal epithelia of CF patients do not respond to either cAMP- or Ca-mediated secretagogues. This abnormality in intestinal electrolyte transport may play a role in the pathogenesis of meconium impactions in CF patients.

Effect of BW 942C, an enkephalinlike pentapeptide, on sodium and chloride transport in the rabbit ileum

BW 942C is a novel enkephalinlike pentapeptide that has been shown to have antidiarrheal action in model systems. The effect of BW 942C on rabbit ileal electrolyte transport was studied to gain insight into the mechanism of the antidiarrheal action of opiate-like compounds. Multiple effects were observed, differing with the basal state of the tissue. BW 942C increased Na absorption in tissues that were not absorbing in the basal state, whereas it had little effect on Na absorption in tissues that were previously absorbing at moderate to high rates (greater than 1 microEq/h.cm2. It increased Cl absorption and caused a dose-related decrease in short-circuit current in all tissues. This effect was reversed or inhibited by naloxone (10(-5) M), suggesting that it is mediated by opiate receptors. No significant change in residual flux was noted. BW 942C was effective from both the serosal and mucosal side; however, it required a 2-log higher dose on the mucosal side (10(-4) M, maximal) to achieve a response similar to that observed with serosal application (10(-6) M, maximal). The ability of BW 942C to alter stimulated secretion was studied using theophylline, prostaglandin E2, vasoactive intestinal peptide, and bethanechol. There was significantly less Cl secretion in BW 942C-treated tissues than in control tissues after stimulation with prostaglandin E2 (10(-7) M). However, this effect was not apparent at higher doses of prostaglandin E2 and there was no inhibition of the short-circuit current response to any of the secretory stimuli by BW 942C. Loperamide was also found to be unable to inhibit the Cl secretion or change in short-circuit current stimulated by theophylline. Although opiates have been shown to be moderately effective antidiarrheal agents, their ability to influence mucosal electrolyte transport is weak and may only account for part of their antidiarrheal action.