Walter Zidek

The Antioxidant Acetylcysteine Reduces Cardiovascular Events in Patients With End-Stage Renal Failure A Randomized, Controlled Trial

Background—Patients with end-stage renal failure have increased oxidative stress and show elevated cardiovascular mortality. Whether increased cardiovascular events can be prevented by the administration of antioxidants is unknown. Methods and Results—We evaluated the effects of acetylcysteine, a thiol-containing antioxidant, on cardiovascular events in patients undergoing hemodialysis. A prospective, randomized, placebo-controlled trial was conducted between October 1, 1999, and September 30, 2001, in 134 patients (76 male and 58 female) with a mean age of 62±16 years (mean±SD) who had been undergoing maintenance hemodialysis for a minimum of 3 months 3 times weekly in an ambulatory center. Median (range) follow-up was 14.5 (1 to 24) months. Patients were randomly assigned either to receive acetylcysteine (600 mg BID) or placebo. The primary end point was a composite variable consisting of cardiac events including fatal and nonfatal myocardial infarction, cardiovascular disease death, need for coronary angioplasty or coronary bypass surgery, ischemic stroke, peripheral vascular disease with amputation, or need for angioplasty. Secondary end points included each of the component outcomes, total mortality, and cardiovascular mortality. A total of 18 (28%) of the 64 hemodialysis patients assigned to acetylcysteine group and 33 (47%) of the 70 hemodialysis patients assigned to control group had a primary end point (relative risk, 0.60 [95% CI, 0.38 to 0.95], P =0.03). No significant differences in secondary end points or total mortality were detected. Conclusions—In hemodialysis patients, treatment with acetylcysteine (600 mg BID) reduces composite cardiovascular end points.

Influence of treatment on leptin levels in patients with obstructive sleep apnoea

Obstructive sleep apnoea syndrome (OSAS) is a common disorder in obesity. Leptin, an adipocyte-derived signalling factor, plays an important role in metabolic control. There is growing evidence that leptin regulation is altered in OSAS. Therefore, the aim of this study was to test the hypothesis that effective treatment will influence leptin levels in OSAS patients. Serum leptin levels were determined in 86 consecutive patients (aged 57.5±11.0 yrs) with polysomnographically verified OSAS. In addition, leptin levels were reassessed and treatment efficacy was evaluated by polysomnography after 6 months of therapy. Patients were treated with continuous or bilevel positive airway pressure, a mandibular advancement device or conservatively, depending on the clinical symptoms. Mean serum leptin levels did not change with treatment in the whole study group (7.3±5.0 versus 7.5±4.8 ng·mL−1), however, leptin levels decreased in effectively treated patients (8.5±5.0 versus 7.4±5.1 ng·mL−1) while they increased in ineffectively treated patients (5.0±4.0 versus 7.7±4.1 ng·mL−1). Furthermore, not only was there a significant and independent correlation between the change in leptin levels with treatment and the change in body mass index, but also with the change in apnoea/hypopnoea index. Effective treatment of sleep-disordered breathing may have significant effects on leptin levels in obstructive sleep apnoea syndrome patients. Changes in leptin levels are related to changes in apnoea/hypopnoea index in obstructive sleep apnoea syndrome patients.

Right ventricular dysfunction in patients with obstructive sleep apnoea syndrome.

There is conclusive evidence that obstructive sleep apnoea syndrome (OSAS) influences right heart haemodynamics and can also induce pulmonary hypertension. It is not known, however, whether right ventricular dysfunction can occur in patients with OSAS in the absence of lung disease. We studied 107 patients (94 males, 13 females, mean age 55 +/- 11 yrs) with polysomnographically verified OSAS in whom clinically significant lung disease was excluded. Right ventricular ejection fraction (RVEF) was determined by radionuclide ventriculography. In addition, pulmonary function tests, arterial blood gas analysis and right heart catheterization were performed. RVEF was impaired in 19 patients (18%). Eighteen (95%) had signs or symptoms consistent with mild right ventricular failure. Patients with or without impaired RVEF did not differ with respect to body mass index, age or lung function. Stepwise multiple logistic regression analysis revealed that RVEF was significantly associated with the apnoea/hypopnoea index (r = -0.68; p = 0.0009) and the extent of nocturnal oxyhaemoglobin saturation (r = 0.42; p = 0.035), but not with age, body mass index, blood gas analysis, gender, lung function, pulmonary artery pressure and left ventricular ejection fraction. We conclude that in patients with otherwise unexplained right ventricular failure, obstructive sleep apnoea syndrome may underlie the right ventricular dysfunction.

Influence of proteinuria on long-term transplant survival in kidney transplant recipients

Long-term prognosis in kidney transplant recipients depends on multiple factors. To investigate whether mild proteinuria within the first 6 months following transplantation is a determinant of the long-term function and survival of kidney transplants, 357 patients transplanted between 1980 and 1990 were retrospectively examined over a period of 5 years. 25.5% of the patients developed an early proteinuria between 0.25 and 1.0 g/day over 6 or more months. This group was well matched concerning gender, age of recipient, underlying disease, time on hemodialysis, donor age, cold ischemia time and HLA mismatches with the group without proteinuria (n = 266). Five-year transplant survival in the group with proteinuria was 58.9% in contrast to 85.6% in recipients without proteinuria. Intermittent proteinuria did not worsen long-term prognosis. Proteinuria of 12 months or longer further reduced 5-year transplant survival to 42.6%. Over the whole observation period, serum creatinine in recipients with proteinuria was about 0.5 mg/dl higher as compared with patients without proteinuria. No correlation between proteinuria and gender, age of recipient, duration of hemodialysis, age of donor, cold ischemia time and mismatches could be detected. In conclusion, early proteinuria apparently is not due to established donor or recipient factors. However, there is a strong correlation of proteinuria with worse transplant function and survival.

Effect of continuous positive airway pressure therapy on 24-hour blood pressure in patients with obstructive sleep apnea syndrome.

BACKGROUND Patients with obstructive sleep apnea syndrome (OSAS) are subject to an increased cardiovascular morbidity including systemic hypertension. Little is known about the effects of treatment with nasal continuous positive airway pressure (CPAP) on systemic hypertension. METHODS Automated ambulatory 24-h blood pressure (BP) monitoring was performed in 88 consecutive patients who were referred for evaluation of snoring or suspected OSAS. In addition, the long-term effects of CPAP therapy on 24-h BP were assessed. RESULTS A total of 62 patients had OSAS and 26 habitual snoring. Patients with OSAS had significantly higher mean arterial BP values than snorers (102.7 +/- 10.7 v 94.0 +/- 10.2 mm Hg; P < .01). Multiple stepwise linear regression analysis disclosed that the degree of systemic hypertension was independently associated with the severity of OSAS as determined by the apnea/hypopnea index (R = 0.43; P < .001), but not with age, body mass index, or smoking habits. Of the 62 patients with OSAS, 52 were treated with CPAP and reevaluated after 9 months. The CPAP resulted in a significant decrease in mean arterial BP (from 103.7 +/- 10.4 to 99.1 +/- 10.8 mm Hg; P < .05). For those patients with systemic hypertension whose BP improved with CPAP therapy, 24-h mean pulse pressure at baseline (r = -0.36; P < .05) as well as average heart rate during the day (r = -0.35; P < .05) turned out as predictors. CONCLUSIONS Obstructive sleep apnea syndrome contributes, at least in part, to the development of systemic hypertension, and CPAP may improve BP values in treated OSAS patients. Predictors of a beneficial CPAP effect on BP are a high heart rate and a high pulse pressure before treatment.

Differential effects of diadenosine phosphates on purinoceptors in the rat isolated perfused kidney

The activation of various purinoceptors in rat renal vasculature by P1,P2‐diadenosine pyrophosphate (Ap2A), P1,P3‐diadenosine triphosphate (Ap3A), P1,P4‐diadenosine tetraphosphate (Ap4A), P1,P5‐diadenosine pentaphosphate (Ap5A), P1,P6‐diadenosine hexaphosphate (Ap6A) was studied by measuring their effects of perfusion pressure of a rat isolated perfused kidney. The vasoconstrictive response to Ap5A was completely due to P2X purinoceptor activation, that to Ap4A and Ap6 was P2X purinoceptor mediated to a large extent, as evidenced by the inhibitory effects of suramin and pyridoxal‐phosphate‐6‐azophenyl‐2′,4′‐disulphonic acid tetrasodium (PPADS). The vasoconstrictive effects of Ap2A and Ap3A were mostly due to stimulation of A1‐receptors, as shown by the inhibitory effect of 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX). The vasoconstrictive response to Ap6A was partially insensitive to A1 and P2X purinoceptor blockers. In raised tone preparations Ap2A and Ap3A evoked vasodilatation, which was blocked by the A2 receptor blocker, 3,7‐dimethyl‐1‐propargylxanthine (DMPX). In raised tone preparations Ap4A evoked vasodilatation when the P2‐purinoceptors were blocked by suramin. The activation of different purinoceptor subtypes by diadenosine phosphates critically depends on the number of phosphate groups.

Reactive oxygen species in essential hypertension and non–insulin-dependent diabetes mellitus

To evaluate whether increased levels of reactive oxygen species (ROS) are involved in the pathogenesis of essential hypertension (EH) and non-insulin-dependent diabetes mellitus (NIDDM), both resting and stimulated levels of intracellular ROS were measured in lymphocytes from patients with EH (n = 10), NIDDM (n = 16) and age-matched healthy individuals (control subjects, n = 19). ROS was monitored with the dye, dihydrorhodamine-123 (DHR; 1 micromol/L) in the presence or absence of superoxide dismutase (superoxide scavenger), sodium azide (singlet oxygen/hydrogen peroxide scavenger), genistein (tyrosine kinase inhibitor), or bisindolylmaleimide (protein kinase C inhibitor). Simultaneous monitoring of cytosolic [Ca2+]i was done with fura-2. Resting ROS levels were significantly higher in NIDDM (4.71+/-0.25 nmol/10(6) cells; mean +/- SEM, P<.05) compared with EH (4.03+/-0.22 nmol/10(6) cells) or controls (4.05+/-0.15 nmol/10(6) cells). The formyl-Met-Leu-Phenylalanine-(fMLP)-induced ROS generation was significantly higher in NIDDM (21.92+/-2.23 nmol/10(6) cells; P<.05) compared with EH (14.58+/-1.90 nmol/10(6) cells) or control (16.06+/-1.22 nmol/10(6) cells). The fMLP-induced ROS increase was significantly reduced in the presence of sodium azide in all groups (P<.01) but was largely unaffected in the presence of SOD. Genistein and bisindolylmaleimide significantly inhibited the fMLP-induced ROS in all groups. The fMLP-induced [Ca2+]i increase was significantly higher in NIDDM (71+/-12 nmol/L, P <.01) compared with EH (42+/-4 nmol/L) and control subjects (35+/-3 nmol/L). Phytohemagglutinin was more effective in increasing [Ca2+]i than ROS. It is concluded that ROS may play a role in the metabolic syndrome of NIDDM but not in EH.

Identification and characterization of diadenosine 5′,5‴-P1,P2 -diphosphate and diadenosine 5′,5‴-P1,P3-triphosphate in human myocardial tissue

We examined whether human cardiac tissue contains diadenosine polyphosphates and investigated their physiological role. Extracts from human cardiac tissue from transplant recipients were fractionated by size exclusion‐, affinity‐, anion exchange‐ and reversed‐phase chromatography. MALDI‐MS analysis of two absorbing fractions revealed molecular masses of 676.2 Da and 756.0 Da. The UV spectra of both fractions were identical to that of adenosine. Postsource decay MALDI mass spectrometry indicated that the molecules with a mass of 676.2 Da and 757.0 Da contained AMP and ATP, respectively. As shown by enzymatic cleavage, both molecules consist of two adenosines interconnected by either two or three phosphates in 5′‐positions of the riboses. Two substances can be identified as 5′,5‴‐P1,P2‐diphosphate (Ap2A) and 5′,5‴‐P1,P3‐triphosphate (Ap3A). Ap2A and Ap3A, together with ATP and ADP, are stored in myocardial‐specific granules in biologically active concentrations. In the isolated perfused rat heart, Ap2A and Ap3A caused dose‐dependent coronary vasodilations. In myocardial preparations, Ap2A and Ap3A attenuated the effect of isoproterenol, exerting a negative inotropic effect. The calcium current of guinea pig ventricular myocytes, stimulated by isoproterenol, was also attenuated by Ap2A and Ap3A. The presence of Ap2A and Ap3A in cardiac‐specific granules and the actions of these substances on the myocardium and coronary vessels indicate a role for these substances as endogenous modulators of myocardial functions and coronary perfusion.—Luo, J., Jankowski, J., Knobloch, M., van der Giet, M., Gardanis, K., Russ, T., Vahlensieck, U., Neumann, J., Schmitz, W., Tepel, M., Deng, M. C., Zidek, W., Schlüter, H. Identification and characterization of diadenosine 5′,5‴‐P1,P2‐diphosphate and diadenosine 5′,5‴‐P1,P3‐triphosphate in human myocardial tissue. FASEB J. 13, 695–705 (1999)

Evidence of Altered Homocysteine Metabolism in Chronic Renal Failure

The fasting serum concentrations of total homocysteine and metabolites of transsulfuration (cystathionine, cysteine, methylmalonic acid, 2-methylcitric acid) and remethylation (methionine) were determined by gas chromatography-mass spectrometry in 40 nondialyzed patients with chronic renal disease and in 50 patients with end-stage renal disease requiring chronic maintenance hemodialysis. The nondialyzed patients and 28 of the dialysis patients did not receive additional vitamin supplementations. Twenty-two of the dialysis patients received daily oral vitamin preparations containing 10 mg pyridoxine (vitamin B6), 6 µg cyanocobalamin (vitamin B12), and 1 mg folic acid. In the nondialyzed patients, linear regression analysis showed positive correlations between serum concentrations of creatinine and total homocysteine (r = 0.68, p < 0.0001), cystathionine (r = 0.73, p < 0.0001), methylmalonic acid (r = 0.77, p < 0.0001), and 2-methylcitric acid (r = 0.81, p < 0.0001). Serum homocysteine was positively correlated with serum concentrations of cystathionine (r = 0.59, p < 0.0001), cysteine (r = 0.69, p = 0.004), methylmalonic acid (r = 0.64, p = 0.0001), and 2-methylcitric acid (r = 0.64, p < 0.0001). There was no significant correlation between serum concentrations of homocysteine and methionine (r = –0.14, p = 0.63). In the hemodialysis patients receiving oral vitamin supplementation, serum homocysteine and cystathionine concentrations were significantly lower than in hemodialysis patients not receiving vitamins (homocysteine 21.8 ± 1.1 vs. 33.2 ± 3.7 µmol/l, p = 0.0004; cystathionine 2,075.9 ± 387.1 vs. 3,171.3 ± 680.2 nmol/l, p = 0.02; mean ± SEM). In summary, our results show increased intermediate products of the transsulfuration pathway, but no increase in remethylation of homocysteine in chronic renal disease, including end-stage renal disease requiring chronic maintenance dialysis.

Identification and Characterization ofP 1,P 7-Di(adenosine-5′)-heptaphosphate from Human Platelets

Diadenosine pentaphosphate and diadenosine hexaphosphate have been isolated in human platelets and have been postulated to play an important role in the control of vascular tone. Here we describe the isolation and identification of diadenosine heptaphosphate from human platelets. Dinucleoside polyphosphates were concentrated by affinity chromatography from a nucleotide-containing fraction from deproteinated human platelets. Dinucleoside polyphosphates were purified by anion-exchange and reversed phase high performance liquid chromatography to homogeneity. Analysis of one of these fractions with matrix-assisted laser desorption/ionization mass spectrometry revealed a molecular mass of 1076.4 (1077.4 = [M + H]+) Da. UV spectroscopic analysis of this fraction showed the spectrum of an adenosine derivative. Comparison of the postsource decay matrix-assisted laser desorption/ionization mass spectrum of the fraction minus that of diadenosine heptaphosphate (Ap7A) demonstrated that the isolated substance was identical to Ap7A. The identity of the retention times of the authentic and the isolated compound confirmed this result. Enzymatic analysis demonstrated an interconnection of the phosphate groups with the adenosines in the 5′-positions of the riboses. With thrombin-induced platelet aggregation, Ap7A is released from the platelets into the extracellular space. The vasoconstrictive action of Ap7A on the vasculature of the isolated perfused rat kidney Ap7A was slightly less than that of Ap6A. The threshold of the vasoconstrictive action of Ap7A was 10−5mol/liter. The vasoconstrictive effect was abolished by suramin and pyridoxal phosphate 6-azophenyl-2′,4′-disulfonic acid, suggesting an activation of P2x receptors. Furthermore, Ap7A inhibits ADP-induced platelet aggregation. Thus, the potent vasoconstrictor Ap7A derived from human platelets, like other diadenosine polyphosphates, may play a role in the regulation of vascular tone and hemostasis.