NADPH-induced chemiluminescence and lipid peroxidation in kidney microsomes

Oxygen free radicals in nephrology

For living creatures with an aerobic metabolism, the univalent reduction of oxygen can lead to formation within the cell of intermediate products with marked chemical instability and strong potential toxicity. These are the free radicals (FR) superoxide and hydroxyl, hydrogen peroxide and the singlet 1O2. Their toxicity is primarily expressed through the peroxidation of membrane lipids, resulting in mitochondrial, lysosomal and parietal damage. It is enhanced by the presence of metals in trace amounts. Imbalance between the production of FR and the availability of FR scavengers (superoxide dismutase, catalase, glutathione peroxidase, etc.) may underlie different human pathologies. FR have been thought to play a part in inflammation; the aging process, carcinomatous transformations, damage due to recirculation and autoimmune diseases. As far as the kidney is concerned, the intervention of FR has been demonstrated or can be postulated in various contexts in the light of what has been observed in other pathologies: immunological nephritis, toxic nephropathies, microthrombotic and microangiopathic processes, damage caused by post-ischemic reflow, and problems in the preservation and rejection of transplants. FR have also been incriminated in lung lesions following intradialytic leukostasis and some aspects of toxicity ascribable to uremia. Subject to the precautions imposed by the need for theoretical, experimental and clinical verification, FR biochemistry offers new keys to the interpretation of a variety of kidney pathologies and opens up new prospects for treatment, both through a better understanding of the mechanism of action of drugs already known and employed, and with regard to the practical possibility of using alternative or combined forms of therapy.

Effect of t-butylhydroperoxide on p-aminohippurat uptake in rabbit renal cortical slices

OBJECTIVES

Oxygen free radical (superoxide radical, hydrogen peroxide, and hydroxyl radicals) have been considered to be responsible for the pathogenesis of ischemia reperfusion injury and toxic chemical injury in a variety of organs including myocardium, brain, intestine and kidneys. In in vitro models using a suspension of rat proximal tubule segments, t-butylhydroperoxide(t-BHP), a potent oxidant, induces the severity of tubular dysfunction as reflected by decreases in tubular respiration which is associated with a progressive increase in lipid peroxidation. The precise mechanism of t-BHP-induced cell injury remains to be determine. The study was carried out to determine the effect of oxygen free radicals on organic anion transport in renal proximal tubule.

METHODS

By renal cortical slices, we studied accumulation of organic ions, PAH efflux oxygen consumption, lactate dehydrogenase (LDH), lipid peroxidation. The data are expressed as the mean +/- SE and evaluated for significance using Student's t-test. A probability level of 0.05 was used to establish significance.

RESULTS

Effect of t-butylhydroperioxide(t-BHP), a potent oxidant, on organic anion p-amminohippurate(PAH) uptake was studied in rabbit renal cortical slices. t-BHP inhibited irreversibly PAH and organic cation tetraethylammonium(TEA) uptake in a dose dependent manner with IC50 of approximately 1.0 and 0.85 mM, respectively. The efflux rate constant pf PAH was not altered by the presence of 1 mM t-BHP, indicating that the inhibitory effect of t-BHP on the steady-state accumulation of PAH is due primary to the reduction in the influx of PAH across the basolateral membrane. The kinetic analysis showed that 1mM t-BHP caused a significant reduction in the maximum rate of PAH influx(Vmax) from 1.54 +/- 0.74 to 0.72 +/- 0.54 umol/g/10 min without an effect on Km, indicating that t-BHP depressed PAH influx across the basolateral membrane by reducing the number or turnover rate of active carrier for PAH transport, but not by altering substrate affinity of the carrier. Ouabain-sensitive and -insensitive oxygen consumption was not different between the control and t-BHP-treated slices. t-BHP caused an increase in LDH release and lipid peroxidation in a dose-dependent manner, which were highly correlated with changes in PAH uptake.

CONCLUSION

These results suggest that t-BHP inhibition of PAH uptake is attributed to renal tubular cell damage and lipid peroxidation plays an important role in the inhibitory effect of t-BHP on PAH transport in rabbit proximl tubules.

Free radical ablation for the prevention of post-ischemic renal failure following renal transplantation

The toxic metabolites of oxygen, including those which are free radicals, have been found to constitute a fundamental common pathway of tissue injury in a wide variety of disease processes, including injury in many organs resulting from post-ischemic reperfusion. Research efforts designed to prevent or ameliorate tissue injury have therefore centered on the pharmacologic inhibition of free radical-mediated mechanisms. This approach has particular application to post-ischemic renal failure seen in renal transplantation, after a well-defined period of graft ischemia, followed by reperfusion.

Effects of probucol on renal function in rats with bilateral ureteral obstruction

To ascertain the potential role of reactive oxygen metabolites in the pathophysiology of obstructive uropathy, we examined the effect of probucol, an antioxidant agent, on renal function in normal rats and rats with unilateral release of bilateral ureteral obstruction (BUO) of 24 hours duration. Rats were fed either a standard diet or a standard diet containing one percent probucol for two weeks prior to study. Probucol lowered serum cholesterol in both normal and BUO rats. Probucol did not significantly affect renal function in normal rats. BUO rats given probucol had greater inulin and PAH clearances at three to five hours and three days following release of BUO than rats with BUO not given probucol. Kidneys from obstructed rats had higher levels of malondialdehyde, an index of lipid peroxidation, a greater number of leukocytes in the cortex, decreased levels of reduced glutathione and increased levels of oxidized glutathione. Renal cortex from obstructed rats treated with probucol had significantly higher levels of reduced glutathione than kidneys of obstructed rats not given probucol. A decrease in cholesterol, using another lipid-lowering agent, lovastatin, did not modify renal function in rats with BUO. The data can be interpreted to indicate a role for reactive oxygen species in the pathophysiology of obstructive nephropathy. The improved renal function seen in probucol-treated rats with BUO may be due to an effect of this agent in affecting accumulation of reactive oxygen metabolites and/or decreasing the number of leukocytes infiltrating the renal cortex.

Evidence suggesting a role for hydroxyl radical in gentamicin-induced acute renal failure in rats

The protective effect of hydroxyl radical scavengers and iron chelators has strongly implicated the hydroxyl radical in several models of tissue injury. Based on in vitro studies showing gentamicin-enhanced generation of reactive oxygen metabolites in renal cortical mitochondria, we examined the effect of hydroxyl radical scavengers and iron chelators in gentamicin-induced acute renal failure. Rats treated with gentamicin (G) alone (100 mg/kg, s.c. x 8 d) developed advanced renal failure (BUN 215 +/- 30 mg/dl) compared to saline-treated controls (BUN 16 +/- 1 mg/dl, P less than 0.001). In contrast, rats treated with gentamicin and either dimethylthiourea (DMTU, an hydroxyl radical scavenger, 125 mg/kg, i.p. twice a day) or deferoxamine (DFO, an iron chelator, 20 mg/day by osmotic pump) had significantly lower BUN (G + DMTU 48.8 +/- 8 mg/dl, P less than 0.001, n = 8; G + DFO 30 +/- 7 mg/dl, P less than 0.001, n = 8). In separate experiments, treatment with two other hydroxyl radical scavengers (dimethyl sulfoxide or sodium benzoate) and a second iron chelator (2,3,dihydroxybenzoic acid) had a similar protective effect on renal function (as measured by both BUN and creatinine). In addition, histological evidence of damage was markedly reduced by the interventional agents. Finally, concurrent treatment with DMTU prevented the gentamicin induced increase in renal cortical malondialdehyde content (G: 4.4 +/- 0.2 nmol/mg; G + DMTU: 3.1 +/- 0.2 nmol/mg, P less than 0.0001, n = 8) suggesting that the protective effect of DMTU was related to free radical mechanisms rather than to some other effect. Taken together, these data strongly support a role for hydroxyl radical or a similar oxidant in gentamicin-induced acute renal failure.

Gentamicin enhanced production of hydrogen peroxide by renal cortical mitochondria

Agents that affect mitochondrial respiration have been shown to enhance the generation of reactive oxygen metabolites. On the basis of the well-demonstrated ability of gentamicin to alter mitochondrial respiration (stimulation of state 4 and inhibition of state 3), it was postulated that gentamicin may enhance the generation of reactive oxygen metabolites by renal cortical mitochondria. The aim of this study was to examine the effect of gentamicin on the production of hydrogen peroxide (measured as the decrease in scopoletin fluorescence) in rat renal cortical mitochondria. The hydrogen peroxide generation by mitochondria was enhanced from 0.17 +/- 0.02 nmol . mg-1 . min-1 (n = 14) in the absence of gentamicin to 6.21 +/- 0.67 nmol . mg-1 . min-1 (n = 14) in the presence of 4 mM gentamicin. This response was dose dependent with a significant increase observed at even the lowest concentration of gentamicin tested, 0.01 mM. Production of hydrogen peroxide was not increased when gentamicin was added to incubation media in which mitochondria or substrate was omitted or heat-inactivated mitochondria were used. The gentamicin-induced change in fluorescence was completely inhibited by catalase (but not by heat-inactivated catalase), indicating that the decrease in fluorescence was due to hydrogen peroxide. Thus this study demonstrates that gentamicin enhances the production of hydrogen peroxide by mitochondria. Because of their well-documented cytotoxicity, reactive oxygen metabolites may play a critical role in gentamicin nephrotoxicity.

A possible role for membrane lipid peroxidation in anthracycline nephrotoxicity

Adriamycin causes both glomerular and tubular lesions in kidney, which can be severe enough to progress to irreversible renal failure. This drug-caused nephrotoxicity may result from the metabolic reductive activation of Adriamycin to a semiquinone free radical intermediate by oxidoreductive enzymes such as NADPH-cytochrome P-450 reductase and NADH-dehydrogenase. The drug semiquinone, in turn, autoxidizes and efficiently generates highly reactive and toxic oxyradicals. We report here that the reductive activation of Adriamycin markedly enhanced both NADPH- and NADH-dependent kidney microsomal membrane lipid peroxidation, measured as malonaldehyde by the thiobarbituric acid method. Adriamycin-enhanced kidney microsomal lipid peroxidation was diminished by the inclusion of the oxyradical scavengers, superoxide dismutase and 1,3-dimethylurea, and by the chelating agents, EDTA and diethylenetriamine-pentaacetic acid (DETPAC), implicating an obligatory role for reactive oxygen species and metal ions in the peroxidation mechanism. Furthermore, the inclusion of exogenous ferric and ferrous iron salts more than doubled Adriamycin-stimulated peroxidation. Lipid peroxidation was prevented by the sulfhydryl-reacting agent, p-chloromercuribenzenesulfonic acid, by omitting NAD(P)H, or by heat-inactivating the kidney microsomes, indicating the requirement for active pyridine-nucleotide linked enzymes. Several analogs of Adriamycin as well as mitomycin C, drugs which are capable of oxidation-reduction cycling, greatly increased NADPH-dependent kidney microsomal peroxidation. Carminomycin and 4-demethoxydaunorubicin were noteworthy in this respect because they were three to four times as potent as Adriamycin. In isolated kidney mitochondria, Adriamycin promoted a 12-fold increase in NADH-supported (NADH-dehydrogenase-dependent) peroxidation. These observations clearly indicate that anthracyclines enhance oxyradical-mediated membrane lipid peroxidation in vitro, and suggest that peroxidation-caused damage to kidney endoplasmic reticulum and mitochondrial membranes in vivo could contribute to the development of anthracycline-caused nephrotoxicity.