Epithelial secretory responses to inflammation. Platelet activating factor and reactive oxygen metabolites

Role of phospholipase A2 and tyrosine kinase in Clostridium difficile toxin A-induced disruption of epithelial integrity, histologic inflammatory damage and intestinal secretion

Clostridium difficile-associated disease causes diarrhea to fulminant colitis and death. We investigated the role of phospholipase A2 (PLA2) inhibitors, aristolochic acid (AA), bromophenacyl bromide (BPB) and quinacrine (QUIN) on the C. difficile toxin A-induced disruption of epithelial integrity, histologic inflammatory damage and intestinal secretion. Toxin A caused severe hemorrhagic and inflammatory fluid secretion at 6-8 h in rabbit ileal segments, an effect that was significantly inhibited by QUIN (71%, P < 0.01), AA (87%, P < 0.000l) or by BPB (51%, P < 0.01). The secretory effect of toxin A was also inhibited in segments adjacent to those with AA (89%, P < 0.01). Furthermore, QUIN or AA substantially reduced the histologic damage seen after 6-8 h in rabbit ileal segments. The cyclooxygenase inhibitor, indomethacin, also significantly inhibited (96%; n = 6) the secretory effects of toxin A in ligated rabbit intestinal segments. The destruction by toxin A of F-actin at the tight junctions of T-84 cell monolayers was not inhibited by AA or BPB. AA or QUIN had no effect on the T-84 cell tissue resistance reduction over 8-24 h after toxin A exposure. All the inhibitors were shown to be effective in the doses administered direct in ileal loops to inhibit PLA2 activity. The data suggest that PLA2 is involved in the major pathway of toxin A-induced histologic inflammatory damage and hemorrhagic fluid secretion.

Platelet-activating factor in the enteric nervous system of the guinea pig small intestine

Platelet-activating factor (PAF) is a proinflammatory mediator that may influence neuronal activity in the enteric nervous system (ENS). Electrophysiology, immunofluorescence, Western blot analysis, and RT-PCR were used to study the action of PAF and the expression of PAF receptor (PAFR) in the ENS. PAFR immunoreactivity (IR) was expressed by 6.9% of the neurons in the myenteric plexus and 14.5% of the neurons in the submucosal plexus in all segments of the guinea pig intestinal tract as determined by double staining with anti-human neuronal protein antibody. PAFR IR was found in 6.1% of the neurons with IR for calbindin, 35.8% of the neurons with IR for neuropeptide Y (NPY), 30.6% of the neurons with IR for choline acetyltransferase (ChAT), and 1.96% of the neurons with IR for vasoactive intestinal peptide (VIP) in the submucosal plexus. PAFR IR was also found in 1.5% of the neurons with IR for calbindin, 51.1% of the neurons with IR for NPY, and 32.9% of the neurons with IR for ChAT in the myenteric plexus. In the submucosal plexus, exposure to PAF (200-600 nM) evoked depolarizing responses (8.2 +/- 3.8 mV) in 12.4% of the neurons with S-type electrophysiological behavior and uniaxonal morphology and in 12.5% of the neurons with AH-type electrophysiological behavior and Dogiel II morphology, whereas in the myenteric preparations, depolarizing responses were elicited by a similar concentration of PAF in 9.5% of the neurons with S-type electrophysiological behavior and uniaxonal morphology and in 12.0% of the neurons with AH-type electrophysiological behavior and Dogiel II morphology. The results suggest that subgroups of secreto- and musculomotor neurons in the submucosal and myenteric plexuses express PAFR. Coexpression of PAFR IR with ChAT IR in the myenteric plexus and ChAT IR and VIP IR in the submucosal plexus suggests that PAF, after release in the inflamed bowel, might act to elevate the excitability of submucosal secretomotor and myenteric musculomotor neurons. Enhanced excitability of motor neurons might lead to a state of neurogenic secretory diarrhea.

Amelioration of experimental acute pancreatitis with a potent platelet-activating factor antagonist

The effect of a potent platelet-activating factor (PAF) antagonist, BB-882, on an experimental model of acute pancreatitis induced in male Wistar rats by a technique of microvascular ischaemia was studied. A single intraperitoneal injection of BB-882 (5 mg/kg) 30 min after induction of the disease in 12 animals significantly reduced (P < 0.001) the rise in the level of serum amylase (mean 2477 (range 2100-3280) units/l) compared with that in 12 control animals (mean 3928 (range 2800-5900) units/l) and significantly improved (P < 0.001) the mean pancreatic histology score (5.0 (range 3-10) versus 12.3 (range 8-18) in controls). PAF is a biologically active ether phosphorylcholine synthesized in cell membranes and a potent inflammatory mediator. Pancreatic tissue levels of this compound are increased in experimental acute pancreatitis and pretreatment with PAF receptor antagonists can ameliorate the progression of this disease. BB-882 alters the early course of experimental pancreatitis and may have a clinical therapeutic role.

Role of platelet activating factor in the intestinal epithelial secretory and Chinese hamster ovary cell cytoskeletal responses to cholera toxin

With the recent heightened concern about cholera around the world come new questions about the mechanism by which cholera toxin causes diarrhea. Peterson and Ochoa have suggested that prostaglandin synthesis is key to both the intestinal epithelial secretory and the CHO cell responses to cholera toxin [Peterson, J. W. and Ochoa, G. (1989) Science 245, 857-859]. Because platelet activating factor (PAF) can be a potent stimulus for prostaglandin synthesis, we examined its role in the intestinal and tissue culture effects of cholera toxin. We report that the specific PAF receptor antagonists BN 52021 and SR 27417 inhibit the effects of cholera toxin on intestinal secretion in rabbit ileal loops in vivo and on the cytoskeleton of Chinese hamster ovary cells in vitro. We also show that PAF itself can cause net fluid secretion in the rabbit model and that PAF potentiates the effects of cholera toxin on intestinal secretion. Finally, we demonstrate that cholera toxin stimulates significant PAF production (2.6-fold) in isolated T-84 intestinal epithelial cells. We conclude that cholera toxin stimulates PAF production and that PAF is involved in both the secretory and cytoskeletal responses to cholera toxin. These findings further support the involvement of additional mediators of cholera toxin effects other than mucosal cell cyclic AMP and help explain the effects of cholera toxin on prostaglandin synthesis.