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Increased Phospholipase A2 and Decreased Lysophospholipase Activity in the Small Intestinal Mucosa After Ischaemia and Revascularisation

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Increased Phospholipase A2 and Decreased Lysophospholipase Activity in the Small Intestinal Mucosa After Ischaemia and Revascularisation Gut: first published as 10.1136/gut.28.11.1445 on 1 November 1987. Downloaded from Gut, 1987, 28, 1445-1453 Increased phospholipase A2 and decreased lysophospholipase activity in the small intestinal mucosa after ischaemia and revascularisation T OTAMIRI, L FRANZEN, D LINDMARK, AND C TAGESSON From the Clinical Research Center and Departments ofSurgery, Pathology II, Occupational Medicine and Clinical Chemistry, Linkipinlg University Hospital, Linkoping, Sweden SUMMARY The influence of ischaemia and revascularisation on lipid peroxidation and phospho- lipid metabolism in the rat small intestinal mucosa was investigated. Two hours of total ischaemia followed by five minutes of revascularisation caused not only accumulation of malondialdehyde in the mucosa, but also increased activity of phospholipase A2, decreased activity of lysophospho- lipase, and increased ratio between lysophosphatidylcholine and phosphatidylcholine. Pretreat- ment with the phospholipase A7 inhibitor, quinacrine, prevented the increases in mucosal phospholipase A2 activity and lysophosphatidylcholine/phosphatidylcholine ratio after ischaemia and morphological examinations revealed that the mucosa was then also protected against ischaemic injury. These findings point to the possibility that activation of phospholipase A2 and accumulation of lysophosphoglycerides could be involved in mediating the mucosal injury caused by small intestinal ischaemia. http://gut.bmj.com/ The mechanisms underlying mucosal injury caused affected by lysoPC concentrations that had no effect by small intestinal ischaemia have not been fully on the non-ischaemic intestine, and it was therefore elucidated. Intraluminal proteolytic enzymes like suggested that increased amounts of lysoPC was pancreatic trypsin have been claimed to be of being formed in the ischaemic gut mucosa, perhaps importance,' although ischaemic mucosal damage by the action of phospholipase A2 on phosphatidyl- occurs also in animals who have had their pancreatic choline (PC).' This possibility would be consistent ducts ligated five to six days before the ischaemia. It with the recent findings that lysoPC and other has also been suggested that the countercurrent lysophosphoglycerides accumulate in the ischaemic on September 29, 2021 by guest. Protected copyright. exchange of oxygen in the intestinal villi could heart""' and are important mediators of sequelae aggravate the mucosal hypoxia and initiate necrosis after myocardial ischaemia. 12 1' in the epithelial cells near the villous tips.4 More In order to further examine this possibility, we recently, oxygen-derived free radicals produced in have now investigated the influence of ischaemia and the tissue during a postocclusive hyperaemia have revascularisation on phospholipase A, activity, lyso- been put forward. Such free radicals can increase phospholipase activity, and lysoPC/PC ratio in the lipid peroxidation and damage cellular membranes" small intestinal mucosa. In addition, we have but a precise molecular mechanism by which they examined the effect of a phospholipase A2 inhibitor, might injure the intestinal mucosa during ischaemia quinacrine, on the accumulation of lysoPC and on the has not been substantiated. mucosal damage after ischaemia and revascularisa- We recently found7 that the intestinal permeability tion. increase after ischaemia was potentiated by lysophos- phatidylcholine (lysoPC), a potentially membrane Methods damaging surfactant ocurring naturally in the gut but also known to induce mucosal injury -at higher ANIMALS concentrations."9 The ischaemic intestine was thus Female Sprague/Dawley rats (225-250 g body Addrcess for corrcspodiiciicc: C TIaess'.on. MI) I)cpairtnicnt of Occupational weight) were anaesthetised by an intraperitonal Mcdicinc. Iinkoping UJnicrrsity. S-581X5I .Inkoping. Swcdcnli injection of ketamine (KetalarR, Parke Davis and Co Rcccavcd for phublic.tion 9 April. 1987. Inc, USA, 50 mg/kg body weight) and xylazin 1445 Gut: first published as 10.1136/gut.28.11.1445 on 1 November 1987. Downloaded from 1446 4()tamniri, I r(llleIl, Lindmiiark, (111(1 lagcsson (Rompun', Bayer Ag. Leverkusen, West Germany. After cooling with tap watcr, I ml distilled water was 5 mg/kg body weight). Laparotomy was carried out added and the red pigmenit produced was extracted and the most distal 1) cm of the ileum was ligated at with 5-) ml n-butanol:pyrarmide (15:1, v/v) and both ends. In order to minimise evaporaition from the assayed fluorometrically. Results were expressed as tissue, the smlall intestine was covered with sterile nmol MDA/mg protein. gauze pads soaked with saline at 37°C. In addition, Phospholipase A2 (PLA2, EC 3. 1. 1.4) was deter- 5 ml Ringerdex solution was given subcutaneously to mined as described previously.'- The reaction prevent dehydration of the animals. mixture contained, in a final volulmle of 450 [tl radiolabelled E coli (5000 cpm), 70 mM buffer of EXPERIMENTAL DESIGN suitable pH (pH 9-8 glycine-NaOll, pli 7 2 Tris- An experimental model described in detail pre- maleate, and pH 5-5 citrate), 2 mM CaCl2 (this was viously14 was used to create ischaemia and revascu- included when assaying PLA, at pH 9-8 and 7-2 but larisation. A thin thread (5-0) was placed under the excluded at pH 5-5), 0)010 (wt/vol) bovinle serumI mesenteric vessels supporting the tied loop. The albumin (BSA), and mucosal cells correspoindinig to thread was heightened about 2 cm, which lifted the 2-X8 tg protein. The mixture was incubated at 37°C' vessels up and caused the blood flow to the tied loop and the reaction stopped by adding 3 ml 0( 15 M NaCI to stop. After two hours, the animal was killed and with I(XO BSA. The suspenisionI was then passed the tied loop excised. In another group of animals the through a 0(45 [tm Millipore filter (Millex SFIJA 0(25 vessels were brought down again and the intestinal BO, Millipore AB. V Fr6lunda, Sweden) and the segment revascularised for five minutes before the radioactivity in the filtrate was counted and animal was killed. In yet another group (the non- expressed as percentage of total radioactivity. ischaemic controls), the vessels were left untreated Lysophospholipase (EC 3.1 1.15) was determined for two hours and five minutes. using lysoPC as substrate. The reaction mixture The blood flow in the tied loop before, during, and contained, in a total volume of 50)0( 1I mM lysoPC after the ischaemia was recorded using laser Doppler (Sigma type 1), 15,000 cpm radiolabelled lysoPC flowmetry.' As described previously,'4 lifting the (I - acyl-"4C-palmitoyl-sti-glycero-3-phosporylcholine, vessels 2 cm caused total ischaemina in the bowel wall 52 3 mCi/mmol; NEN Chemicals, GmbH, Dreici- whereas bringing the vessels down again reestab- chenheim, West Germany), 400 1t Trismaleate, pH lished the blood flow to starting values. 7-3, and 0(-20 ug homogeinised mucosal cells. The To study the influence of a phospholipase A mixture was incubated at 37°C and the reaction http://gut.bmj.com/ inhibitor, rats were given intravenous injections of stopped by the addition of I ml cold 20%( trichloro- quinacrine (10 mg/kg body weight) dissolved in 0-5 acetic acid. To the reaction products were added 0(5 ml 150 mM NaCl. After 30 minutes, the animals were ml 16% Triton X-100 and 5 ml hexane. One millilitre prepared as described above. Controls were given 0(5 of the top layer (the hexane phase) was then counted ml 150 mM NaCl only. The animals were then for radioactivity and the total radioactivity in the subjected to two hours ischaemia and five minutes hexane phase expressed as percentage of total revascularisation as described above. radioactivity. on September 29, 2021 by guest. Protected copyright. Lysophosphatidylcholine (lysoPC) and phos- SAMPl.F PREP'ARATION phatidylcholine (PC) were determined essentially as The excised segment was opened and the mucosa described by Chen and Kou.x Lipids were extracted washed with cold saline and scraped off with a according to Folch et al/, the extracts evaporated to curette. Special precaution was taken to remove only dryness under vacuum, and the residues dissolved in the superficiail layers of the mucosa. The mucosal 250 ,ul CHC13:CH3OH (2:1, v/v). The extracted phos- cells were suspended in 150 mM NaCl, weighed, and pholipids were then subjected to high performance disintegrated in a Dounce homogeniser by five liquid chromatography (HPLC). The HPLC equip- strokes with a Teflon pestle. The homogenised cells ment was an LKB 2152 controller, a LKB 2150 pump, were then Ianalysed as described below. a Rhenodyne 7125 injector with a 20 l loop, a LDC spectromonitor III, and a Hewlett Packard 3393 A CHEMICAI. ANAL YSIS integrator. The column was an Apex Silica 5 (250x Malondialdehyde (MDA) was determined using the 4-5 mm, Jones Chromatography Ltd, Colnbrook, thiobatrbituric acid (TBA) reaction.' The reaction UK) and the mobile phase CH3CN: CH3OH: H3PO4 mixture contained 0(2 ml 8- 1 o sodium dodecyl (100:3:1). The column was equilibrated overnight sulphate (SDS), 15 ml 2(0 acetic acid pH1 3-5, 1-5 ml with mobile phase (0-05 ml/min) before analysis. A 0(8)X TBA, and 0(2 ml homogenised cclls (2-3 mg flow program was used to speed up elution of the protein). The mixture was made up to 44) ml with phospholipids and to narrow and point the chromato- distilled waiter and heated at 950C for 60 minutes. graphic peaks; this program (0 min: 1 ml/min, 18 Gut: first published as 10.1136/gut.28.11.1445 on 1 November 1987. Downloaded from Increasedphospholipase A, atid decreased lysophosplholipase activity in the .small intestinal mucosa 1447 PE 006 5.1g lipid AUFS PS PC PC SM Fig. I Reversedphase HPLCseparation ofphosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylcholine (PC), IVsophosp)hatidyklholine (lvsoPC), and sphingomyelin (SM). One [tg ofJeach phospholipid was inijected. Details concerning the chromnatographi cctnditionts are given in Methods. A UFS=absorbance units Jull scale. min:1b5 ml/min, 20 min:2 ml/min, 21 min:3 ml/min, The morphological changes in the villous tips were 30 min:1 ml/min) was started at the time of sample quantitatively assessed by examining five intestinal injection.
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