Subcellular fractionation of human intestinal mucosa by large-scale zonal centrifugation. I. Characterization of subcellular organelles in the distal part of the ileum

Lysophosphatidylcholine and the inflammatory action of neutrophils

Lysophosphatidylcholine (lysoPC) is a polar lipid formed in cells and tissues under normal conditions and is known to cause tissue damage in a variety of experimental systems. We have therefore examined the possibility that increased amounts of lysoPC are formed in activated inflammatory cells and are involved in their tissue-damaging action. Human neutrophil leucocytes were labelled with [14C]arachidonic acid (AA), activated with the calcium ionophore A23187, and the degradation of phospholipids, with subsequent release of AA and AA metabolites, was studied. We also studied neutrophil metabolism of [14C]lysoPC in the presence of different concentrations of cold lysoPC, and the relation between phospholipid degradation and release of N-acetyl-beta-glucosaminidase (NAG), a lysosomal enzyme. We found that the release of both AA and NAG was coupled to a degradation of phosphatidylcholine (PC), and that the neutrophils were able to metabolise lower, but not higher, concentrations of lysoPC. Moreover, the phospholipase A2 inhibitor, nordihydroguaiaretic acid significantly inhibited PC degradation, lysoPC formation, and NAG release, whereas the lipoxygenase inhibitor, BW 755C had little effect on these parameters. These findings demonstrate that the AA mobilization in activated neutrophils is associated with PC degradation, and point to be possibility that the ensuing lysoPC formation might mediate lysosomal enzyme release.

Phospholipase activation and arachidonic acid release in isolated intestinal epithelial cells

A novel method for studying the mobilization of free arachidonic acid (AA) in isolated intestinal epithelial cells is described. The method is based on labeling the cellular phospholipids with 14C-AA and studying the release of this 14C-AA on subsequent phospholipase activation. Cells of high viability were isolated from the small intestine of guinea pigs and incubated with 14C-AA for 2 h; most of the incorporated 14C-AA was then esterified into phosphatidylethanolamine and phosphatidylcholine. When the labeled cells were stimulated with the calcium ionophore A23187 in the presence of external calcium, they released significant amounts of AA. In contrast, the cells released no AA when stimulated with A23187 in the absence of external calcium or in the presence of chlorpromazine or 4-bromophenacyl bromide, both of which are known to inhibit phospholipase A2 activity. On the other hand, the cells released significant AA in response to exogenous phospholipase C from Clostridium perfringens. These findings indicate that AA release in intestinal cells may be caused by calcium-mediated phospholipase A2 activation or by products of microbial phospholipase C activity. They also suggest the further use of 14C-AA-labeled cells for studying agents and mechanisms that may influence the release of AA in the gastrointestinal tract.

Lysophosphatidylcholine increases rat ileal permeability to macromolecules

The influence of lysophosphatidylcholine (LPC) on macromolecular permeability in the distal ileum has been studied. Using a rat experimental model, we determined the intestinal permeability to different sized dextrans (3000-70 000 daltons) and bovine serum albumin (BSA) in the absence and presence of LPC. We also examined the morphology of the ileal mucosa after deposition of LPC in the gut lumen, and determined N-acetyl-beta-glucosaminidase, 5'-nucleotidase, and alkaline phosphatase activities in suspensions of isolated mucosal cells and different concentrations of LPC. We found that 20 mM LPC damaged the ileal mucosa and that it increased its permeability to all the molecules investigated. Moreover, mixtures of mucosal cells and 0.01-1 mM LPC showed increased N-acetyl-beta-glucosaminidase activity: the higher the LPC concentration, the higher the enzyme activity. These findings indicate that LPC, a naturally occurring surfactant in the intestine, might damage mucosal cells and release lysosomal enzyme activity, and that higher LPC concentrations may impair the mucosal barrier function and increase the gut permeability to macromolecules such as proteins. This could have relevance to the development of various disease states, in which increased intestinal absorption of macromolecules is of importance.

Studies of the phospholipase A2 activity of rat ileal mucosa

A rapid and simple procedure has been used to determine phospholipase A2 activity (EC 3.1.1.4) in rat ileal mucosa. We used 14C-oleate-labeled Escherichia coli as substrate for the phospholipase activity and a 0.45-micron Millipore filter to separate the product of hydrolysis--the 14C-oleic acid--from the unhydrolyzed substrate. The phospholipase A2 activity was optimal at pH 9.8 and at 2 mM Ca2+, but another peak of activity appeared at pH 7.2. In addition, cell fractionation revealed yet another phospholipase A2 activity at pH 5.0 in the absence of Ca2+. These findings suggest the presence of more than one phospholipase A2 in the ileal mucosa and points to the possible use of a simple procedure for studying their distribution and properties.