Associations of antioxidant enzymes with cataract and age-related macular degeneration. The POLA Study. Pathologies Oculaires Liées à l'Age

OBJECTIVE

Oxidative mechanisms may play an important role in the etiology of cataract and age-related macular degeneration (AMD). The authors present the level of two antioxidant enzymes in relation to cataract and AMD.

DESIGN

Population-based, cross-sectional study on cataract and AMD and their risk factors.

PARTICIPANTS

This study includes 2584 participants recruited among the residents of the town of Sète (in the south of France), who were 60 years of age or older.

INTERVENTION/METHODS

Cataract was defined on the basis of slit-lamp examination, according to the Lens Opacities Classification System III, and AMD on the basis of fundus photographs according to an international classification. Biologic measurements were made centrally from blood samples for which the patient fasted.

MAIN OUTCOME MEASURES

The presence of early and late AMD and of subcapsular, cortical, nuclear, and mixed cataracts was assessed and related to the levels of plasma glutathione peroxidase and erythrocyte superoxide dismutase.

RESULTS

After multivariate adjustment, higher levels of plasma glutathione peroxidase (pIGPx) were significantly associated with a ninefold increase in late AMD prevalence, a sixfold increase in cortical cataract, and a twofold increase in nuclear and mixed cataracts. High levels of erythrocyte superoxide dismutase (SOD) activity were not associated with late AMD and early signs of AMD but were associated with a twofold increase in nuclear cataract.

CONCLUSION

The authors show here, for the first time, a strong association of high levels of pIGPx with age-related eye diseases. High levels of SOD also are associated with increased risk of nuclear cataract. More data are needed at the biochemical and epidemiologic levels for a better understanding of these findings.

[Risk factors of chronic rejection in kidney transplantation, results of a single center study]

Chronic rejection remains the single most important cause of renal allograft loss after the first year post-transplant. We performed a matched case control study within our cohort of 471 renal allograft recipients, comparing 66 patients with histologically proven chronic rejection with 66 controls. Analysis of immunological (transfusion, sensitisation, HLA matching, number of transplantation, number of acute rejections (AR), immunosuppression) and non-immunological (donors and recipients age and sex, CMV disease, post-transplant acute tubular necrosis, cold ischemia) factors which could predict the occurrence of chronic rejection (CR) was performed, using Wilcoxon rank test, Mac Nemar test and Cox model. Univariate analysis showed that potential risk factors for CR are: donor age > 45 years (p = 0.05), recipient age < 40 years (p = 0.008), CMV disease (p = 0.03), number of acute rejection episodes (p = 0.009), retransplantation (p = 0.002). Multivariate analysis showed that only the following factors significantly increased the risk of CR: AR episodes (p = 0.01) with an odds-ratio at 3.5 (95% CI = 1.3-3.9) for the second acute rejection episode and at 6.5 (95% CI = 1.5-29.4) for the third acute rejection episode, donor age > 45 years (p = 0.03) with an odds-ratio at 3.5 (95% CI = 1.1-10.6). Our data suggest that better matching at donor recipient age and more potent immunosuppressive protocols resulting in no acute rejection may improve the long term graft survival. They also show that the use of old donors (> 45 years), as a response to organ shortage is detrimental for long term renal function.

Oxidative stress and lipid abnormalities in renal transplant recipients with or without chronic rejection

BACKGROUND

The histological picture of chronic rejection with endothelial lesions and vascular hyperplasia resembles the early arteriosclerotic lesions. As increasing evidence suggests a role for oxidative stress in arteriosclerosis, we examined whether chronic rejection in renal transplant recipients was associated with increased oxidative stress markers.

METHODS

We investigated lipid metabolism and oxidative stress in 77 renal transplant recipients. Group I patients (n=34; 48+/-2 years old, 12 women, 22 men) had no clinical or histological signs of chronic rejection, whereas group II patients (n=43; 47+/-3 years old, 15 women, 28 men) had histologically proven chronic rejection. All patients were treated with cyclosporine and steroids. Lipid metabolism was evaluated by determining total cholesterol, triglycerides, high-density lipoprotein cholesterol, apolipoproteins AI and B, and lipoprotein (a). Oxidative stress was evaluated by determining: (i) the end product of lipid peroxidation, malonyldialdehyde (MDA), and erythrocyte polyunsaturated fatty acids; (ii) the nonenzymatic antioxidant system: erythrocyte alpha-tocopherol and glutathione; and (iii) the enzymatic antioxidant system: erythrocyte superoxide dismutase and plasma glutathione peroxidase. Results were compared with those of a control group (38 healthy volunteers).

RESULTS

Compared with controls, renal transplant recipients had significantly increased total cholesterol, triglyceride, and apolipoprotein B levels; they also had, in association with these lipid abnormalities, a significant increase in MDA and a significant decrease in erythrocyte polyunsaturated fatty acids, as well as a significant decrease in enzymatic and nonenzymatic antioxidant defense mechanisms. In contrast to lipid disturbances, where no difference was observed between groups I and II, markers of oxidative stress were significantly higher in group II compared with group I (MDA: 1.87+/-0.43 and 1.62+/-0.31 nmol/ml, respectively, P<0.05). The red blood cell antioxidative defense mechanisms were significantly decreased in group II compared with controls (erythrocyte alpha-tocopherol: 0.61+/-0.38 and 1.08+/-0.31 mg/L, respectively, P<0.01; superoxide dismutase: 1.08+/-0.2 and 1.32+/-0.31 U/mg Hb, respectively, P<0.01).

CONCLUSION

Our data show that oxidative stress with a decrease in antioxidant defenses is associated with kidney transplantation. In addition, oxidative stress markers are particularly increased in transplant recipients with chronic rejection, which suggests that oxidative stress may participate in the development and/or progression of vascular lesions observed in these patients.

[Evaluation of lipid peroxidation by measuring thiobarbituric acid reactive substances]

Malondialdehyde assay is the most generally used test in the appreciation of the role of oxidative stress in disease. Malondialdehyde is one of several products formed during the radical induced decomposition of polyunsaturated fatty acids. Most often, malondialdehyde assay used its reactivity at high temperature and low pH, towards thiobarbituric acid. This reaction is very sensitive but its specificity, even with improvement of pre-analytical (sampling, preservatives), and analytical stages (fluorescence, HPLC) is still a matter of debate. At present, the concept of "thiobarbituric acid reactive substances" (TBARS) have merged and progressively replaced the initial malondialdehyde assay. In this review, we presented the main results concerning the assays of TBARS and malondialdehyde in blood and different biological medium. In the future, oxidative stress appreciation will need the precise analytical determination of different molecules triggered by free radicals. The TBARS assay should be considered as a global test, allowing a global approach of lipoperoxidation whereas specific determination of malondialdehyde can only appreciate one of the end-product formed during oxidative stress.

[Oxidative stress and chronic renal insufficiency: what can be a prophylactic approach?]

Cardiovascular diseases represent the first cause of mortality in chronic renal failure patients treated by hemodialysis. Alterations in lipid metabolism and oxidative stress are recognized as vascular risk factors. Their corrections could be of interest for atherosclerosis prevention. In order to evaluate interest of an therapeutic intervention, we have analyzed oxidative metabolism in hemodialysis patients by determining the production of oxygen reactive species (ROS), the level of defense mechanisms, and the balance between nitric oxide (NO) and ROS, responsible for anti- or proxidant effects of NO. During dialysis sessions performed with cellulosic membrane (Cuprophan) an increase in hydroperoxide production by platelets was noted (12 HETE) (5.62 +/- 0.94 pg); similarly, superoxide anion (O2(0)-) production by monocytes (fluorescence index: 115 +/- 24) and by polynuclear cells (fluorescence index: 115 +/- 24) was enhanced. On the other hand, anti-oxidant defenses were significantly reduced with a decrease in RBC SOC activity (0.92 +/- 0.06 U/mg Hg) and in RBC vitamin E (0.7 +/- 0.07 mg/l) concentration. We have demonstrated a profound alteration in the L-arginine/NO pathway consequently to an accumulation of NO synthases inhibitors or activators. The necessity to reduce the production of ROS during dialysis sessions justifies the use of more biocompatible membranes, such as modified cellulosic or synthetic membranes, decreasing leucocyte activation. In addition, NO synthetase inhibitors can be preferentially eliminated by convection. Finally, a supplementation with an exogenous anti-oxidant, such as oral vitamin E (500 mg/day for 6 months) normalizes RBC vitamin E levels and concomitantly allows a decrease in MDA concentrations In conclusion, oxidative metabolism alterations observed in hemodialysis are multifactorial: preventive measures include the use of a more biocompatible material, the reequilibrium of the NO/ROS balance, and supplementation with exogenous anti-oxidants.

Erythropoietin and oxidative stress in haemodialysis: beneficial effects of vitamin E supplementation

Oxidative stress can produce profound alterations to cellular membrane lipids, impairing cell metabolism and viability. This phenomenon, previously observed in haemodialysis patients, has been proposed as a significant factor in regard to haemodialysis-related shortened red blood cells (RBC) survival. In the present study, several parameters associated with oxidative stress were evaluated in a group of haemodialysis patients either receiving erythropoietin therapy (n = 12, mean erythropoietin dose 88 +/- 24 U/kg/week) or not receiving such therapy (n = 30), and in 38 controls. Malonyldialdehyde (MDA, nmol/ml), an end-product of lipid peroxidation, and RBC antioxidant systems were measured, including RBC alpha-tocopherol (RBC vitamin E, mg/l), RBC glutathione (GSH, nmol/mgHb), and RBC superoxide dismutase activity (SOD, U/mgHb). Plasma vitamin E concentrations were also evaluated. Finally, oral vitamin E supplementation (500 mg daily), an exogenous antioxidant, was administered for 6 months to seven patients from the dialysis group receiving erythropoietin while oxidative parameters were repeatedly evaluated and erythropoietin requirements monitored, in order to appreciate the therapeutic relevance of an antioxidant supplementation. An elevation of serum MDA was observed in all haemodialysis patients and a significant decrease in RBC vitamin E, despite normal serum vitamin E levels. Furthermore, the reduction in RBC vitamin E was more important in patients treated with erythropoietin. Vitamin E supplementation resulted in a significant increase in RBC vitamin E (from 0.3 +/- 0.1 to 1.2 +/- 0.2 mg/l of pellet) and a reduction in erythropoietin dose (from 93 +/- 24 to 74 +/- 26 U/kg/week) while maintaining stable haemoglobin concentrations. These results suggest that the oxidative stress could be one of the resistance factors to erythropoietin response in haemodialysis and that vitamin E supplementation could have a sparing effect on erythropoietin dosage requirement.

Removal of constitutive and inducible nitric oxide synthase-active compounds in a modified hemodiafiltration with on-line production of substitution fluid: the contribution of convection and diffusion

Chronic renal failure and the uremic state lead to accumulation of various endogenous inhibitors of nitric oxide synthase. Previous studies on end-stage uremic patients nitric oxide synthase activity in murine vascular endothelium and cytokine-induced macrophage cell lines was shown to be modulated during treatment (Nephrol Dial Transplant 1995; 10: 1386-96). Paired filtration dialysis, a modified hemodiafiltration technique, physically separates convection from diffusion. Plasmas, ultrafiltrates and dialysates from seven uremic patients undergoing paired filtration dialysis performed using ultrapure apyrogen substitution fluid in the absence (first 120 min) or presence (last 120 min) of extracellular fluid reduction were tested for their inhibitory/stimulatory effect on ecNOS, constitutively expressed on t.End 1 cell line, a murine vascular endothelium, or for their inducing effect on iNOS, inducible on J774 cells, a macrophage cell line. On ecNOS, Group 1 (stimulatory, 3/7 patients) markedly enhanced the ecNOS activity as compared to control plasma, whereas group 2 plasma (inhibitory, 4/7 patients) inhibited ecNOS plasma. Post-dialysis plasma samples from all Group 1 and 2 patients showed a marked decrease of the predialysis stimulatory and inhibitory activity, respectively. On iNOS: all patient plasmas stimulated iNOS activity. The UF and particularly the dialysate had a remarkable iNOS inducing effect (Group 1). The substitution fluid obtained at 120 min during treatment in Group 1 and 2 had no effect on NOS activity. No correlation was found between predialysis ecNOS or iNOS activity values with mean systolic or diastolic pressures. These studies suggest a complex balance of ecNOS inhibitors/stimulators and iNOS inducers in uremia. Dialysis may remove ecNOS inhibitors and stimulators by convection and, in the latter case, by diffusion. iNOS inducers are removed during dialysis, suggesting the biocompatibility of the dialysis system with the on-line production of ultrapure substitution fluid.

[Lipoprotein glomerulopathy: a new French case with recurrence on the transplant]

Lipoprotein glomerulopathy is defined by the presence of lipidic deposits in the capillary lumen giving them a dialted and microaneurysmal aspect and the presence of quantitative and/or qualitative alterations of plasma apolipoprotein E. We describe here the long-term follow-up of a young female patient who presented with corticoresistant nephrotic syndrome in 1979 and progressed to chronic renal failure requiring dialysis in 1990. The three renal biopsies performed during the follow-up showed markedly enlarged capillary loops due to intra-luminal fibrinolipidic material deposition forming true intracapillary thrombi. She received a cadaver renal transplant in 1993. One year after transplantation, nephrotic syndrome reappeared and graft biopsy showed recurrence of the initial glomerular disease on the transplant. The plasma lipid profile showed hypercholesterolemia, hypertriglyceridemia, and elevated plasma ApoE levels with an abnormal Apo E phenotype. Our case report is a new typical case of lipoprotein glomerulopathy with recurrence of the initial disease on the renal allograft.

L-Arginine infusion after ischaemia-reperfusion of rat kidney enhances lipid peroxidation

To assess the role of superoxide (O2-) and nitric oxide (NO) in ischaemic-reperfusion-induced acute renal failure, we investigated whether an activation of the L-arginine-NO pathway contributes to ischaemia-reperfusion-induced kidney membrane peroxidation by measurement of 4-hydroxynonenal (HNE) content in anaesthetized rats submitted to acute renal ischaemia. Following ischaemia-reperfusion injury, renal blood flow (RBF) was significantly reduced, while renal vascular resistance was significantly increased. Infusion of neither L-arginine nor D-arginine led to a recovery of RBF. L-Arginine, but not D-arginine, caused a significant increase in HNE accumulation in the ischaemic kidney. L-Arginine infusion enhanced the degree of lipid peroxidation afforded by ischaemia-reperfusion injury in the kidney suggesting that products of the endogenous L-arginine-NO pathway may react with O2- to initiate lipid peroxidation.

Prognosis of acute renal failure in the elderly

Life expectancy is uncertain in the elderly with ARF. In order to determine whether a costly supportive management is worthwhile, we have studied a group of 68 elderly patients (over 65 years of age) admitted to the ICU with ARF.

PATIENTS

47 male; 21 female; 72 +/- 6 years old. Types of ARF include prerenal 24; obstructive 9; intrinsic 35 (acute tubular necrosis 30; glomerulonephritis 4; vascular 1). The mean simplified acute physiology score (SAPS) was 14 +/- 4; 39 patients (57.3%) had more than two underlying diseases; 42 patients (61.7%) were on mechanical ventilation; 40 patients (60%) underwent haemodialysis. The overall survival rate was 36.7%. Among the parameters studied, organic systemic failure index (OSF), diuresis, blood lactate, systolic blood pressure, urea appearance rate (UAR), differed significantly in survivors and deceased. From these results we conclude that the elderly with non-oliguric ARF, normal blood lactate, low catabolic state, and no more than two organ failures have a fair chance of recovering and should therefore be treated aggressively. In other cases, decisions to proceed with intensive supportive measures should be made according to individual characteristics.

[Protection of oxidation of LDL by nitric oxide: implication in atherogenesis]

Superoxide (O2-) and nitric oxide (.NO) are free radicals which are known to react together leading to peroxynitrite anions that can decompose to form nitrogen dioxide (NO2) and hydroxyl radical (OH degrees). .NO has been reported to have a dual effect on LDL oxidation (pro or antioxidant). In the present study we have investigated in vitro the action of exogenous .NO on human LDL oxidation promoted by oxygen, copper or (2,2'-azobis (2-aminodinopropane hydrochloride)(ABAP). .NO was given as NO donnor (sodium nitroprussiate or S-nitroso-L-glutathione) from 10 to 500 microM. Oxidation of LDL was measured by monitoring continuously conjugated diene formation at 234 nm. Exogenous .NO inhibited in a dose dependent manner the progress of spontaneous LDL oxidation. Copper--or ABAP--induced oxidation were characterized by lag, propagation and decomposition phases. Exogenous .NO decreased the propagation rate of LDL oxidation and the level of maximal diene production. These effects are different of these of alpha-tocopherol, a chain-breaking antioxidant. In our experimental conditions, .NO exhibited antioxidant activities. In vivo, the continuous release of endogenous .NO could protect LDL from cell-induced oxidation.

[Measurement of nitric oxide and biological systems]

Interest in NO measurement strongly increased with the discovery that NO is endogenously produced by living tissues. This review describes the major techniques for quantification of NO and derivatives in biological models.

Evidence from receptor antagonists of an important role for ETB receptor-mediated vasoconstrictor effects of endothelin-1 in the rat kidney

1. To characterize the receptor subtype(s) mediating the renal vasoconstrictor effects of the endothelin (ET) and sarafotoxin (SX) peptides in the isolated perfused kidney of the rat, we have examined the effects of endothelin-1 (ET-1), sarafotoxin 6b (SX6b) and sarafotoxin 6c (SX6c) as agonists, BQ-123 and FR 139317 as selective ETA receptor antagonists, and PD 145065 as a non-selective (ETA and ETB) receptor antagonist. We have also compared in the anaesthetized rat the systemic pressor and renal vasoconstrictor effects of ET-1 and SX6c alone or after pretreatment with PD 145065. 2. In the isolated perfused kidney, ET-1, SX6b and SX6c all gave similar concentration-dependent increases in perfusion pressure. The ETA receptor selective antagonists, BQ-123 and FR 139317, both partially blocked the increase in perfusion pressure induced by ET-1. In contrast, PD 145065 completely blocked the increase in perfusion pressure caused by ET-1. 3. Indomethacin (10 microM) had no effect on the ET-1-induced increases in perfusion pressure but significantly reduced the vasoconstriction induced by low concentrations of SX6c, without affecting responses to high concentrations. In the anaesthetized rat, indomethacin (5 mg kg-1) did not modify the systemic pressor or renal vasoconstrictor effects of ET-1 or SX6c. 4. In anaesthetized rats, bolus intravenous injections of ET-1 or SX6c (0.1, 0.25, 0.5 or 1.0 nmol kg-1) produced initial transient depressor responses followed by sustained and dose-dependent increases in mean arterial pressure (MAP). Both peptides caused an equipotent fall in renal blood flow (RBF).PD 145065 (5 mg kg-1) partially antagonized the systemic pressor effects of ET-1 and SX6c but completely blocked the fall in RBF and rise in renal vascular resistance (RVR) induced by ET-1 and SX6c. PD 145065 also antagonized the transient depressor effect following the bolus administration of either ET-1 or SX6c.5. These results indicate that ET/SX induced renal vasoconstriction is mediated via ETA and ETB-like receptors with ETB receptors having a predominant role in vivo. This may be of therapeutic relevance for an ETA receptor-selective antagonist may offer only limited protection against the deleterious renal effects of endogenous ETs.

Support of renal blood flow after ischaemic-reperfusion injury by endogenous formation of nitric oxide and of cyclo-oxygenase vasodilator metabolites

1. Ischaemia-reperfusion injury in the kidney is associated with a loss of autoregulation, an increase in renal vascular resistance (RVR), a decrease of renal blood flow (RBF) and ultimately acute renal failure. The aim of this study was to investigate the role of the release of endogenous nitric oxide (NO) in the recovery of RBF after ischaemic injury of the renal vascular bed. 2. Anaesthetized rats (thiopentone sodium; 120 mg kg-1, i.p.) were submitted to acute renal ischaemia followed by 2 or 6 h of reperfusion (I/R). Reperfusion was associated with a significant reduction in RBF, an increase in RVR, and an impairment of the vasodilator effect of acetylcholine (ACh). 3. NG-nitro-L-arginine methyl ester (L-NAME, 30 micrograms kg-1 min-1, i.v., n = 5) significantly prevented the recovery of RBF after I/R injury. Similarly, inhibition of prostanoid formation with indomethacin (5 mg kg-1, i.v., n = 4) significantly enhanced the rise in RVR associated with I/R injury. 4. Infusion of L-arginine (L-Arg; 1 or 3 mg kg-1 min-1, i.v., n = 5 and 4, respectively) or D-Arg (1 mg kg-1 min-1, i.v., n = 6), starting 30 min after occlusion, did not improve the recovery of RBF. Furthermore, infusion of L-Arg (20 mg kg-1 min-1 for 15 min; n = 4) had no effect on the I/R-induced impairment of the vasodilator responses to ACh. 5. To elucidate the relative importance of the constitutive and inducible NO synthase isoforms for the formation of NO after I/R, calcium-dependent (constitutive) and calcium-independent (inducible) NO synthase activities were measured in kidney homogenates obtained from ischaemic or non-ischaemic kidneys. A calcium-independent NO synthase activity was not detectable in kidney homogenates obtained from either sham-operated control rats or from animals subjected to I/R. Moreover, dexamethasone(3 mg kg-1, i.v., 60 min prior to I/R, n = 6), an inhibitor of the induction of NO synthase,had no effect on either RBF or RVR in rats subjected to I/R. In contrast to I/R, lipopolysaccaride(LPS, endotoxin; 5 mg kg-1, i.p., n = 3) caused a significant induction of a calcium-independent NO synthase activity in the kidney.6. These results confirm the importance of the release of vasodilator cyclo-oxygenase metabolites in the compromised renal circulation and indicate that the formation of NO derived from the constitutive, but not the inducible NO synthase, is also important for the maintenance of RBF after I/R injury of the renal vascular bed.

Mediation via different receptors of the vasoconstrictor effects of endothelins and sarafotoxins in the systemic circulation and renal vasculature of the anaesthetized rat

1. Using endothelin-1 (ET-1), endothelin-3 (ET-3), sarafotoxin 6b (SX6b) and sarafotoxin 6c (SX6c) as agonists and BQ-123 as a selective ETA receptor antagonist, we have examined the endothelin receptor subtypes mediating the systemic pressor and renal vasoconstrictor effects of the ET/SX family of peptides. 2. In anaesthetized rats, bolus intravenous injections of ET-1, ET-3, SX6b or SX6c (0.1, 0.25 and 0.50 nmol kg-1) produced initial transient depressor responses followed by sustained and dose-dependent increases in mean arterial pressure (MAP) with the following rank order of potency: SX6b > ET-1 >> SX6c > ET-3. In contrast, in the renal vasculature these peptides caused equipotent dose-dependent falls in renal blood flow (RBF) (ET-1 = ET-3 = SX6b = SX6c). 3. BQ-123 (1 mg kg-1, i.v. bolus) significantly reduced the systemic pressor effects of all the peptides but was largely ineffective against the renal vasoconstrictions. 4. These results indicate that although the systemic pressor effects of the ET/SX peptides are mediated via ETA receptors, the vasoconstriction in the kidney in vivo may be mediated predominantly via ETB-like receptors. This may be of therapeutic relevance, for an ETA-receptor-selective antagonist could offer only poor protection of the renal circulation from the deleterious effects of endogenously produced members of this peptide family.

[Post-transfusional anti-HLA hyperimmunization: importance of erythropoietin]

The use of erythropoietin (Epo) in chronic renal failure patients improves anemia and avoids iterative transfusions. As a consequence, a significant decrease of anti-HLA antibodies might be observed. From 31.12.1985 to 30.07.1991, among the 61 highly sensitized patients (pts) waiting for renal transplantation at our institution, 23 (7 men, 16 women, mean age 43.3 +/- 2.3 years) were treated with Epo during 21.4 +/- 1.7 months. After introduction of Epo, the mean number of transfusions significantly decreased from 35 +/- 8 to 0.5 +/- 0.4 (p < 0.0001) and the Panel Reactive Antibodies decreased from 88.1 +/- 1.7 to 18.8 +/- 5.6% (p < 0.0001). HLA antibodies totally disappeared in 12 patients, decreased more than 30% in 9 patients and remained stable in the 3 others. Renal transplantation was performed in 9 patients; 4 with a negative cross-match in both historical and current sera and 5 with a negative current cross-match but with a positive historical cross-match. 6/9 patients are doing well with a good graft function; 2 patients returned to hemodialysis for rejection and 1 patient died with a functioning kidney. Since Epo permits the transfusion withdrawal, its introduction in chronic renal failure treatment suppresses both the main factor of immunisation and one of the most important mechanisms of persistence of antibodies.