Jon D. Gower

Intracellular iron redistribution: An important determinant of reperfusion damage to rabbit kidneys

These studies were designed to examine the possible role of low molecular weight intracellular iron chelates (desferrioxamine-available (DFX-A) iron) in the damage which occurs during cold storage and subsequent reperfusion of kidneys. The level of DFX-A iron increased significantly (P less than 0.005) in the cortex of rabbit kidneys rendered cold ischaemic (CI) for 24 hr and the amount of iron available for DFX chelation increased significantly (P less than 0.05) in both the cortex and medulla of kidneys stored for 48 or 72 hr compared with fresh non-ischaemic controls. During ex vivo reperfusion of the organs with an oxygenated asanguinous perfusate, DFX-A iron returned rapidly to pre-ischaemic levels in 24 hr CI kidneys, but remained elevated following 48 and 72 hr CI (P less than 0.05 compared with 24 hr CI kidneys after 5 min reperfusion), returning to control levels only after 30 min reperfusion. There was no concurrent increase in total iron levels, indicating that a redistribution of iron to more accessible pools had occurred within the tissue. We suggest that decompartmentalization of intracellular iron during ischaemia and raised DFX-A iron levels over an extended period during subsequent reperfusion are responsible for increased catalysis of oxygen-derived free radical-mediated lipid peroxidation, and are an important factor in the deterioration of physiological function observed in rabbit kidneys following extended periods of cold storage.

Determination of desferrioxamine-available iron in biological tissues by high-pressure liquid chromatography

Intracellular iron loosely bound to proteins such as ferritin or in the form of low molecular weight chelates is available to catalyze adverse reactions such as the formation of reactive free radicals. A method to measure this small but important iron pool by utilizing the highly specific iron-chelator desferrioxamine is described. Following incubation of tissue fractions with desferrioxamine, the parent compound and its iron-bound form, ferrioxamine, are extracted using solid-phase cartridges and quantitated by reversed-phase HPLC using uv detection. Calculation of the ferrioxamine:desferrioxamine ratio and comparison with a standard curve constructed using a series of known iron concentrations allow the determination of micromolar amounts of desferrioxamine-available iron in biological samples.

Lipid peroxidation and ultrastructural changes in rat lung isografts after single-passage organ flush and 48-hour cold storage with and without one-hour reperfusion in vivo.

Rat lung isografts were preserved for 48 hr at 0 degrees C using a simple organ flush technique. After storage alone, isotonic saline flush resulted in significantly raised indices of lipid peroxidation in vitro (Schiff bases and thiobarbituric-acid-reactive material [TBAR]). Lungs flushed with hypertonic citrate (HCA) had significantly less oxidative damage than saline-flushed lungs. The addition to the HCA flush of verapamil, a calcium channel blocker, or desferrioxamine, an iron chelator, significantly reduced TBA reactivity in stored lungs compared with HCA alone. After 1-hr reperfusion in vivo, lipid peroxidation was reduced in HCA-flushed lungs compared with saline flush (TBAR alone), but no additional protection from the use of desferrioxamine or verapamil was demonstrated. Electron microscopy after saline flush and storage alone showed gross endothelial swelling and fragmentation. Reperfusion with blood for 1 hr resolved cell swelling, but alveolar/capillary wall rupture occurred. HCA protected against cell swelling, but endothelial vesiculation and widening of the basement membrane were observed. After reperfusion, HCA-flushed lungs developed much endothelial loss that was considerably reduced by the use of desferrioxamine and verapamil. The lipid peroxidation results suggest that iron- and calcium-mediated free radical production may be important mechanisms in oxidative damage to stored rat lungs. Electron microscopy findings correlated with biochemical evidence of free-radical-mediated injury. Reduction of endothelial loss on reperfusion by the use of verapamil and desferrioxamine provides circumstantial evidence that ischemia and reperfusion damage of organs stored for transplantation is partly due to Fe++(+)- and Ca+(+)-dependent mechanisms that probably involve increased free radical production.

Oxidative damage to kidney membranes during cold ischemia. Evidence of a role for calcium.

Storage of rabbit kidneys at 0°C for periods of 72 hr after flushing with hypertonic citrate solution, or 24 hr when flushed with isotonic saline, resulted in significant increases in Schiff base and thiobarbituric acid-reactive markers of lipid peroxidation in vitro. The extent of lipid peroxidation was not significantly altered by addition of verapamil (100 μM), a Ca++ channel blocking agent, or calcium 1 mM (CaCl2) to the HCA storage solution. In contrast, verapamil significantly reduced the extent of lipid peroxidation in kidneys stored in saline solution, and a significant increase in oxidative damage occurred when CaCl2 was added to this storage solution. Thus the extent of lipid peroxidation in kidneys stored in saline was significantly mediated by extracellular Ca++, whereas in HCA this was probably chelated by the large excess of citrate (55 mM) in this medium that prevented, or at least slowed, its entry into the renal cells. Lipid peroxidation was however significantly increased in kidneys stored in both HCA and saline solutions by addition of the calcium ionophore A23187 (10 μM) or the polysaccharide dye ruthenium red (5 μM) that inhibits mitochondrial uptake of Ca++. This strongly suggested that altered intracellular Ca++ homeostasis during the storage period played an important role in the development of oxidative damage to kidneys stored in both these media.

The oxidation of benzo[a]pyrene-7,8-dihydrodiol mediated by lipid peroxidation in the rat intestine and the effect of dietary lipids

This study has demonstrated that the microsomal fraction of the rat small intestinal mucosa has the capacity to catalyse the oxidation of benzo[a]pyrene(BP)-7,8-diol to BP-diol-epoxides (BPDEs) both by a mechanism involving the mixed-function oxidase system (NADPH-dependent) and as a result of the initiation of peroxidation of the membrane phospholipids by ferrous ions, ascorbate and ADP. The NADPH-dependent reaction was fastest in the proximal part of the intestine and resulted in the formation of approximately equal amounts of BPDE I and BPDE II. The lipid peroxidation-catalysed reaction favoured the production of BPDE I and was maximal in the middle region of the intestine, closely paralleling the rate of lipid peroxidation in the intestinal sections. Feeding rats on a cod liver oil diet, rich in C20:5 and C22:6, significantly increased the incorporation of these fatty acids into the microsomal fractions. This resulted in a greatly increased rate of lipid peroxidation in vitro and a significantly higher rate of lipid peroxidation-catalysed BP-7,8-diol oxidation compared to rats fed fat-free, mono-unsaturated lard or corn oil (58% C18:2) diets. Thus the rate of conversion of BP-7,8-diol to its ultimate carcinogenic forms during lipid peroxidation in the intestinal fractions of rats fed a polyunsaturated fat was quantitatively more important than the NADPH-catalysed reaction as measured in vitro.

The effect of dietary lipids and antioxidants on the activity of epoxide hydratase in the rat liver and intestine

The effect of varying the fatty acid composition of the lipid components of the diet on the activity of epoxide hydratase in the rat liver and intestinal mucosa has been studied. Feeding a 10% cod liver oil diet (containing 18% C20:5 and 11% C22:6) resulted in a 3-fold increase in epoxide hydratase activity in the liver and a 1.6-fold increase in the intestine compared to rats fed a fat-free diet. The activity of epoxide hydratase in rats fed a cod liver oil diet was significantly greater than that for the group fed a lard diet (containing mainly saturated and mono-unsaturated fatty acids) containing the same quantity of vitamin E. Thus, the enhancing effect of the cod liver oil diet was due to the polyunsaturated fatty acids in this oil. Dietary corn oil (58% C18:2) also stimulated epoxide hydratase activity in the liver but not in the intestine. Vitamin E levels of up to 500 mg/kg diet were ineffective at inducing epoxide hydratase activity in both the liver and intestine. Significant changes in the fatty acid composition of hepatic and intestinal microsomes took place when rats were fed diets of different fatty acid composition. These changes were such that the proportions of polyunsaturated fatty acids in the microsomal fractions reflected the amounts of these fatty acids in the dietary fat. Hepatic epoxide hydratase activity was found to be positively correlated to the proportion of polyunsaturated fatty acids in the microsomal fractions of the liver.

Function of single rat lung isografts after 48-hour cold storage. The effect of treatment with free radical antagonists and prostacyclin PGI2.

Single orthotopic rat lung isografts were carried out in adult male AS rats after 48-hour cold storage (0 degrees C). Grafts were preserved by simple organ flush followed by low-temperature immersion. Hypertonic citrate (HCA) without additives was evaluated as the basic flush solution. In other groups desferrioxamine (an iron chelator), verapamil (a calcium channel blocker) and prostacyclin (PGI2) were added separately to HCA and given intravenously to donor and recipient animals in an attempt to improve the preservation. Baseline controls were fresh HCA-flushed lungs grafted immediately after harvest. Negative controls to the HCA assessment were lungs flushed with isotonic saline (NaCl) stored for 48 hr at 0 degrees C. Functional studies were carried out at weekly intervals until sacrifice (in the fifth postoperative week) and included assessment of blood flow, aeration and gas transfer by perfusion scintigraphy, chest roentgenograms, and blood gas analysis. Of the baseline control animals, 10/10 survived to the end of the study period; all grafts appeared macroscopically normal and blood gas analysis showed good function. Of the animals grafted with HCA-flushed, 48-hr-stored lungs 2/10 died postoperatively; 7/10 grafts appeared macroscopically normal at the end of the study, and one was slightly reduced in size. Blood gas analysis of HCA-flushed, 48-hr-stored lungs showed function similar to that of baseline control grafts. NaCl-flushed lungs (negative controls) survived surprisingly well: 3/10 animals died postoperatively, 6/10 lungs appeared normal, and one was reduced in size. Assessment of graft function showed no significant benefit of HCA flush compared with NaCl. Treatment with desferrioxamine, verapamil or prostacyclin (PGI2) failed to improve the outcome after HCA flush; in fact desferrioxamine gave significantly poorer results. The study has shown that successful 48-hr preservation of rat lung isografts can be achieved by simple organ flush with HCA and storage at 0 degrees C. Contrary to expectation and experience with preservation of other organs, rat lungs were remarkably well preserved after flush with NaCl.

Iron Redistribution and Lipid Peroxidation in the Cold Ischaemic Kidney

Oxygen-derived free radicals may play an important role in the damage which occurs to organs subjected to extended periods of cold storage followed by reperfusion with oxygenated blood upon transplantation into the recipient1. One damaging radical-mediated process is the peroxidation of membrane-bound polyunsaturated fatty acids and we have previously demonstrated significant elevations in lipid peroxidation markers in kidneys subjected to cold storage and autotransplantation2. Iron is required for the initiation of lipid peroxidation3 which may be the consequence of highly reactive OH. radical formation from O 2 .- and H2O2 via the Haber-Weiss reaction or direct attack on polyunsaturated fatty acids by iron complexes with oxygen4. In addition, iron also catalyses the decomposition of lipid hydroperoxides (LOOH) to alkoxy (LO.) and peroxy (LOO.) radicals which stimulate the chain reaction of lipid peroxidation4. In order to minimize the likelihood of these damaging reactions, iron is transported and stored in specific proteins. However, a small pool of iron exists in the cell as low molecular weight chelates5 which are able to exert catalytic activity.

The dependence of the rate of BP metabolism in the rat small intestinal mucosa on the composition of the dietary fat

We studied the effects that dietary fat has on the capacity of preparations of rat small intestinal mucosal cells to metabolize benzo[a]pyrene (BP) in vitro and on the composition of fatty acids in the endoplasmic reticulum of the intestinal mucosa. When rats were fed diets containing different types of fat, there were significant changes in the incorporation of fatty acids into the endoplasmic reticulum of the mucosal cells of the small intestine: the proportions of polyunsaturated fatty acids in the endoplasmic reticulum reflected the amounts of these fatty acids in the dietary fat. The rate of BP oxidation in the intestinal mucosa was dependent on the amount and composition of the dietary fat, but the range and proportions of the metabolites produced were not affected. Dietary C18:2 was particularly important in elevating the rate of BP oxidation, but dietary C20:5 and C22:6 also effectively increased the rate of BP oxidation. The rate of BP oxidation in the small intestine of rats fed different diets was positively correlated with the proportion of polyunsaturated fatty acids in the endoplasmic reticulum of the mucosal cells.

Reoxygenation following hypoxia stimulates lipid peroxidation and phosphatidylinositol breakdown in kidney cortical slices

Reoxygenation of hypoxic (120 min at 37 degrees) rabbit kidney cortical slices in vitro resulted in a rapid increase in lipid peroxidation and phosphatidylinositol hydrolysis. No changes in phosphatidylinositol breakdown occurred during hypoxia or upon reoxygenation in the absence of calcium. Incubation of renal slices with carbon tetrachloride resulted in increased lipid peroxidation but had no effect on phosphatidylinositol breakdown. It is concluded that altered intracellular calcium homeostasis during reoxygenation is involved in mediating increased phosphatidylinositol hydrolysis through activation of a specific phospholipase C, but that oxidative stress per se does not have a significant effect on the inositol phosphate secondary messenger response in this model system.