Tibor Kovács

Exenatide induces aortic vasodilation increasing hydrogen sulphide, carbon monoxide and nitric oxide production

BackgroundIt has been reported that GLP-1 agonist exenatide (exendin-4) decreases blood pressure. The dose-dependent vasodilator effect of exendin-4 has previously been demonstrated, although the precise mechanism is not thoroughly described. Here we have aimed to provide in vitro evidence for the hypothesis that exenatide may decrease central (aortic) blood pressure involving three gasotransmitters, namely nitric oxide (NO) carbon monoxide (CO), and hydrogen sulphide (H2S).MethodsWe determined the vasoactive effect of exenatide on isolated thoracic aortic rings of adult rats. Two millimetre-long vessel segments were placed in a wire myograph and preincubated with inhibitors of the enzymes producing the three gasotransmitters, with inhibitors of reactive oxygen species formation, prostaglandin synthesis, inhibitors of protein kinases, potassium channels or with an inhibitor of the Na+/Ca2+-exchanger.ResultsExenatide caused dose-dependent relaxation of rat thoracic aorta, which was evoked via the GLP-1 receptor and was mediated mainly by H2S but also by NO and CO. Prostaglandins and superoxide free radical also play a part in the relaxation. Inhibition of soluble guanylyl cyclase significantly diminished vasorelaxation. We found that ATP-sensitive-, voltage-gated- and calcium-activated large-conductance potassium channels are also involved in the vasodilation, but that seemingly the inhibition of the KCNQ-type voltage-gated potassium channels resulted in the most remarkable decrease in the rate of vasorelaxation. Inhibition of the Na+/Ca2+-exchanger abolished most of the vasodilation.ConclusionsExenatide induces vasodilation in rat thoracic aorta with the contribution of all three gasotransmitters. We provide in vitro evidence for the potential ability of exenatide to lower central (aortic) blood pressure, which could have relevant clinical importance.

Oxidative stress and non-enzymatic glycation in IgA nephropathy.

AIM Approximately 20-50% of IgA nephropathy patients develop end-stage renal disease. We have previously found enhanced oxidative stress and decreased antioxidant capacity in red blood cells of IgA nephropathy patients. In this study we assess oxidative stress, non-enzymatic glycation, oxidative resistance of low-density lipoprotein and its alpha-tocopherol content in these patients. PATIENTS AND METHODS Non-enzymatic glycation and oxidative stress were assessed in 88 IgA nephropathy patients by measuring advanced glycation end products, Nepsilon-carboxymethyl-lysine, thiobarbituric acid reactive substances, oxidative resistance of low-density lipoprotein and its alpha-tocopherol content. RESULTS Advanced glycation end products (2659 +/- 958 a.u.) and Nepsilon-carboxymethyl-lysine (563 +/- 215 ng/ml) were significantly higher in IgA nephropathy patients with decreased renal function compared to those with normal renal function (p < 0.002) or controls (p < 0.001). Thiobarbituric acid-reactive substances in plasma and associated with low-density lipoprotein were significantly elevated and oxidative resistance of low-density lipoprotein was significantly reduced in all groups of IgA nephropathy patients. There was no significant difference in circulating fluorescent advanced glycation end products, Nepsilon-carboxymethyl-lysine, thiobarbituric acid-reactive substances levels, oxidative resistance of low-density lipoprotein and its alpha-tocopherol content between patients with normal vs. impaired glucose metabolism. Low alpha-tocopherol content of low-density lipoprotein was accompanied with decreased oxidative resistance, depletion in polyunsaturated fatty acids, elevated saturated fatty acids and thiobarbituric acid-reactive substances within low-density lipoprotein suggesting enhanced lipid peroxidation. CONCLUSIONS Decreased oxidative resistance of low-density lipoprotein and enhanced oxidative stress are common features in IgA nephropathy, while increased non-enzymatic glycation occurs as renal function declines.

Different Effect of IgA Nephropathy and Polycystic Kidney Disease on Arterial Stiffness

Background: Renal function is a major predictor of vascular function and cardiovascular diseases. Little information exists about the effect of specific renal diseases on vascular function in chronic kidney diseases (CKD). Methods: One hundred and twenty patients (60 with IgA nephropathy, IgAN, and 60 with polycystic kidney disease, PKD) with CKD stages 1–4 were studied and compared. Pulse-wave velocity was measured by the digital volume pulse (DVP) method and stiffness index (SIDVP) was derived. Results: All CKD (IgAN and PKD) patients had increased SIDVP compared to controls (10.39 vs. 8.87 ± 1.79 m/s, p = 0.008). PKD patients had increased SIDVP compared to IgAN and controls (11.14 ± 2.19, 9.66 ± 2.02 and 8.87 ± 1.79 m/s, respectively, p < 0.001). An inverse correlation was found between SIDVP and glomerular filtration rate in all CKD (IgAN and PKD) patients (p = 0.001) and in IgAN alone (p < 0.01), but not in PKD. With multivariate regression analysis, only age and 24-hour systolic blood pressure exerted independent effects on SIDVP. Conclusions: Compared to controls, arterial stiffness was increased in CKD patients. However, arterial stiffening was more pronounced in PKD than in IgAN, suggesting that vascular function is not similarly altered in etiologically different CKD groups. The fact that blood pressure was an independent risk factor underscores a therapeutic opportunity.

Circadian blood pressure changes and cardiac abnormalities in IgA nephropathy.

The absence of diurnal blood pressure rhythm is characteristic of patients with chronic glomerulonephritis already before they develop hypertension. The prognostic importance and possible target organ-damaging effect of the absence are unknown. Simultaneously, 24-hour ambulatory blood pressure monitoring and echocardiographic investigations were done in 12 normotensive and 38 hypertensive IgA nephropathy patients. The hypertensive patients were treated with either angiotensin-converting enzyme inhibitor (ACEI) alone or in combination with a non-dihydropyridine calcium channel blocker. The absence of a night-time blood pressure reduction was frequent in both groups (5/12 vs. 20/38). In the hypertensive patients, blood pressure and left ventricular mass index were higher (124.6 ± 23.3/81.2 ± 15.3 vs. 106.6 ± 33.4/67.4 ± 21.8 mm Hg, p < 0.001, and 124.1 ± 46.2 vs. 89.2 ± 45.6 g/m2, p < 0.01). Diastolic left ventricular function was better in normotensive patients, in whom E wave/A wave ratio (E/A) and decelaration time values correlated closely with the diastolic diurnal index (E/A, r = 0.86, p < 0.01; DT, r = –0.70, p < 0.01). In the hypertensive patients, both the left ventricular wall thickness and diastolic function were significantly related to nighttime blood pressure and diurnal index values, but there was no relationship with daytime blood pressure. In conclusion, in IgA nephropathy patients there are mild cardiac abnormalities before they develop hypertension, the abnormalities bearing the closest correlation with the decrease in diurnal blood pressure rhythm. These data suggest the inefficacy of ACEI and calcium channel blockers in treating nighttime hypertension and in reestablishing diurnal rhythm. These phenomena are of great importance in the development of left ventricular hypertrophy and diastolic malfunction.

Prevalence of α1-antitrypsin phenotypes in patients with IgA nephropathy

Background: α 1 -antitrypsin (AAT) is the main protease inhibitor in the blood. Several different AAT phenotypes exist. The most common variant is the MM phenotype, which is also associated with normal AAT levels. The less common phenotypes with Z and S variants are associated with low AAT levels. AAT deficiency is a risk factor for pulmonary emphysema, liver impairment and some immune-mediated diseases, some of which are also associated with IgA nephropathy (IgAN). In fact, liver impairment resulting from AAT deficiency may directly contribute to renal abnormalities resembling IgAN. Patients and methods: We investigated AAT phenotype and AAT levels in 100 IgAN patients who did not have end-stage liver disease. Fifteen patients in our sample had secondary IgAN. We also tested for the presence of renal deposition of AAT in patients heterozygous for AAT variants as well as in a randomly chosen group of patients with MM phenotype. We checked for any association between AAT phenotype and the progression of IgAN as well as the prevalence of diseases associated with IgAN (i.e. secondary IgAN). Results: Twelve patients in our sample were heterozygous for AAT variants. Phenotypes were MZ in 5 patients, MS in 3, MF in 1, ML in 2 and ME in 1 patient. AAT levels were lower in these 12 patients than in those homozygous for the M variant (1.17 ± 0.46 vs. 1.44 ± 0.34 g/l, p < 0.05). We found renal deposition of AAT in 2 heterozygous patients and in 1 of the 12 patients which were randomly chosen. End-stage renal (ESRF) failure developed in 3 of the 12 heterozygous patients and in 6 of the 88 homozygous patients (p = 0.07) during the follow-up. The prevalence of heterozygosity was significantly higher in patients with secondary IgAN than in those with primary IgAN ((5/15 vs. 7/85; p < 0.02). Conclusions: AAT phenotype is not associated with the risk of primary IgA nephropathy, but might have an impact on disease outcome as well as on the risk of secondary IgAN.

Role of iron in the interaction of red blood cells with methylglyoxal. Modification of L-arginine by methylglyoxal is catalyzed by iron redox cycling.

Diabetes mellitus is characterized by increased methylglyoxal (MG) production. The aim of the present study was to investigate the role of iron in the cellular and molecular effects of MG. A red blood cell (RBC) model and L-arginine were used to study the effects of MG in the absence and presence of iron. Intracellular free radical formation and calcium concentration were measured using dichlorofluorescein and Fura-2-AM, respectively. Effects of MG were compared to the effect of ferrous iron. Reaction of L-arginine with MG was investigated by electron spin resonance (ESR) spectroscopy and by a spectrophotometric method. MG caused an iron dependent oxidative stress in RBCs and an elevation of the intracellular calcium concentration due to formation of reactive oxygen species. Results of co-incubation of MG with ferrous iron in the RBC model suggested an interaction of MG and iron; one interaction was a reduction of ferric iron by MG. A role of iron in the MG-L-arginine reaction was also verified by ESR spectroscopy and by spectrophotometry. Ferric iron increased free radical formation as detected by ESR in the MG-L-arginine reaction; however, ferrous iron decreased it. The reaction of MG with L-arginine yielded a brown product as detected spectrophotometrically and this reaction was catalyzed at a lower rate with ferric iron but at a higher rate with ferrous iron. These data suggest that MG causes oxidative stress in cells, which is due at least in part to ferric iron reduction by MG and to the modification of amino acids e.g. L-arginine by MG, which is catalyzed by iron redox cycling.

Metabolic syndrome and other cardiovascular risk factors associated with the progression of IgA nephropathy

Background The metabolic syndrome is associated with modest but independent and additive risk of new onset chronic kidney disease (CKD) in several studies. The purpose of our study was to determine whether metabolic syndrome and other cardiovascular risk factors (hyperuricaemia and smoking) are associated with the progression of IgA nephropathy (IgAN). Methods Two hundred and twenty three IgAN patients (107 with and 116 without metabolic syndrome) were examined. The primary renal end point was doubling of serum creatinine; secondary end points were reaching eGFR of ≤ 60 ml/min/1,73m2 or eGFR of ≤30 ml/min/1.73 m2, and end-stage renal disease, ESRD (the composite of serum creatinine ≥500 μmol/l, initiation of dialysis treatment or transplantation). The association of metabolic syndrome with renal end points was examined using the Kaplan-Meier method and Cox models. Results Metabolic syndrome established at the diagnosis or during follow-up of IgAN patients was significantly associated with the primary renal end point (unadjusted hazard ratio of doubling of serum creatinine, 95% confidence interval: 1.96 (1.17–1.33, p = 0.011). The association remained significant after adjustment for confounders: 1.70 (1.02–3.83, p = 0.040). Results were similar for secondary end points except ESRD which was not associated with the presence of metabolic syndrome. Hyperuricaemia and smoking were independent risk factors of progression. Survival curves stratified on metabolic syndrome status showed significant differences for the end points (p = 0.017–0.001) except for ESRD. Conclusions Early diagnosis and treatment of metabolic syndrome, hyperuricaemia and smoking may be an additional cost-effective strategy for preventing the progression of IgAN.

Histological Diagnosis Determines Complications of Percutaneous Renal Biopsy: A Single-Center Experience in 353 Patients

Background: We studied the connection between complication occurrence related to renal biopsies and histological diagnoses of the biopsy specimen. We also analyzed the distribution of diagnoses in our population. Methods: We retrospectively studied 353 patients undergoing renal biopsy at the same center. Biopsies were performed after marking the site of puncture by ultrasound imaging. Connection of complications with diagnoses and clinical parameters was evaluated. Results: Complication rate was 44.5% in our study. There was a significantly lower rate of complications in patients with diabetic nephropathy (likelihood ratio, LR = 0.44) or acute tubular necrosis (LR = 0.38), while patients with thin basement membrane syndrome had a more than 6-fold higher risk for development of intrarenal hemorrhage than others. Patients with vasculitis (LR = 2.88) and acute interstitial nephritis (LR = 3.18) have a more than doubled risk for arteriovenous shunts, while in patients with severe arteriosclerosis the prevalence of this complication was lower (LR = 0.46). Arteriovenous shunts developed also at a significantly higher rate in patients with rapidly progressive glomerulonephritis. Conclusion: Patients with thin basement membrane syndrome, vasculitis, rapidly progressive glomerulonephritis or acute interstitial nephritis should be observed more carefully after renal biopsy due to the significantly higher risk for certain complications.

Elevated Vascular Level of ortho-Tyrosine Contributes to the Impairment of Insulin-Induced Arterial Relaxation

Previous studies have shown that in diabetes mellitus, insulin-induced relaxation of arteries is impaired and the level of ortho-tyrosine (o-Tyr), an oxidized amino acid is increased. Thus, we hypothesized that elevated vascular level of o-Tyr contributes to the impairment of insulin-induced vascular relaxation. Rats were fed with o-Tyr for 4 weeks. Insulin-induced vasomotor responses of isolated femoral artery were studied using wire myography. Vascular o-Tyr content was measured by HPLC, whereas immunoblot analyses were preformed to detect eNOS phosphorylation. Sustained oral supplementation of rats with o-Tyr increased the content of o-Tyr in the arterial wall and significantly reduced the relaxations to insulin. Sustained supplementation of cultured endothelial cells with o-Tyr increased the incorporation of o-Tyr and mitigated eNOS Ser (1 177) phosphorylation to insulin. Increasing arterial wall o-Tyr level attenuates insulin-induced relaxation - at least in part - by decreasing eNOS activation. Elevated level of o-Tyr could be an underlying mechanism for vasomotor dysfunction in diabetes mellitus.

Heart rate recovery after exercise is associated with renal function in patients with a homogenous chronic renal disease

BACKGROUND Attenuated heart rate recovery (HRR) is an independent predictor of cardiac and total mortality. Diminished renal function is a similar predictor. There are no data concerning the interaction between the two risk factors. We studied HRR in patients with a homogeneous renal disease, IgA nephropathy. METHODS One hundred and seven patients with biopsy-proven chronic IgA nephropathy (71 males, 36 females aged 45 +/- 11 years) performed a graded exercise treadmill stress test. HRR was measured as the heart rate difference between the peak value and the heart rate 1 min after exercise. The patients were divided into three groups based on estimated glomerular filtration rate (eGFR): CKD 1, eGFR >or= 90 ml/min (n = 46); CKD 2, eGFR 60-89 ml/min (n = 38), CKD 3-4, eGFR 15-59 ml/min (n = 23). We compared these data with 29 normal controls (aged 46 +/- 14 years). RESULTS HRR values corresponded to eGFR as follows: 29.9 +/- 8.8 bpm normal controls, 27.8 +/- 9.2 bpm CKD 1, 24.5 +/- 10.5 bpm CKD 2 and 16.3 +/- 9.3 bpm CKD 3-4. The latter differed from the other groups significantly (P < 0.05). Metabolic syndrome was common in IgA nephropathy patients (27%). Metabolic syndrome patients had a HRR of 19.6 +/- 10.1 bpm, compared to 25.8 +/- 10.4 bpm in patients without metabolic syndrome (P = 0.007). Nevertheless, a multivariate regression analysis accepted only eGFR as an independent predictor of HRR. CONCLUSION eGFR predicts HRR in patients with a homogenous renal disease. Metabolic syndrome influences HRR, albeit not independently in this cohort.