Effect of uric acid on hypertension progression in spontaneously hypertensive rats

Exposure to low dose of Bisphenol A (BPA) intensifies kidney oxidative stress, inflammatory factors expression and modulates Angiotensin II signaling under hypertensive milieu

Humans are constantly exposed to low concentrations of ubiquitous environmental pollutant, Bisphenol A (BPA). Due to the prevalence of hypertension (one of the major risk factors of cardiovascular disease [CVD]) in the population, it is necessary to explore the adverse effect of BPA under hypertension associated pathogenic milieu. The current study exposed the Nω-nitro-l-arginine methyl ester (L-NAME) induced hypertensive Wistar rats to low dose BPA (50 μg/kg) for 30 days period. In tissue samples immunohistochemistry, real-time quantitative polymerase chain reaction and enzymatic assays were conducted. Moreover, studies on primary kidney cell culture were employed to explore the impact of low dose of BPA exposure at nanomolar level (20-80 nM range) on renal cells through various fluorescence assays. The observed results illustrate that BPA exposure potentiates/aggravates hypertension induced tissue abnormalities (renal fibrosis), oxidative stress (ROS generation), elevated angiotensin-converting enzyme activity, malfunction of the antioxidant and tricarboxylic acid cycle enzymes, tissue lipid abnormalities and inflammatory factor expression (both messenger RNA and protein level of TNF-α and IL-6). Further, in vitro exposure of nM levels of BPA to primary kidney cells modulates oxidative stress (both superoxide and total ROS), mitochondrial physiology (reduced mitochondrial transmembrane potential-∆ψm) and lipid peroxidation in a dose dependent manner. In addition, angiotensin II induced ROS generation was aggravated further by BPA during coexposure in kidney cells. Therefore, during risk assessment, a precise investigation on BPA exposure in hypertensive (CVD vulnerable) populations is highly suggested.

Ivabradine treatment lowers blood pressure and promotes cardiac and renal protection in spontaneously hypertensive rats

Hypertension is linked to hyperpolarization-activated cyclic nucleotide-gated (HCN) function, expressed in excitable and non-excitable cells. Considering that the reduction in heart rate (HR) improves coronary perfusion and cardiac performance, ivabradine (IVA) emerged as an important drug for the treatment of cardiovascular diseases.

AIM

Evaluate if IVA chronic treatment effect can mitigate hypertension and reverse the cardiac and renal damage in SHR.

MAIN METHODS

Rats were divided into 4 groups treated for 14 days with PBS (1 ml/kg; i.p) or IVA (1 mg/kg; i.p): 1) WKY PBS; 2) SHR PBS; 3) WKY IVA; and 4) SHR IVA. The systolic blood pressure (SBP) was measured, indirectly, before and during the treatment period with IVA (day 0, 1, 7 and 11). Rats were subjected to artery cannulation for direct blood pressure (BP) measurement. Morphofunctional and gene expression were evaluated in the heart and kidneys.

KEY FINDINGS

IVA reduced SBP only in SHR on the 7th day. Direct blood pressure measurement showed that IVA chronic treatment reduced HR in the SHR. Interestingly, mean arterial pressure (MAP) was reduced in SHR IVA when compared to SHR PBS. Serum and urinary biochemical data were not altered by IVA. Moreover, IVA reduced the renal inflammatory infiltrates and increased glomerular density, besides preventing the cardiac inflammatory and hypertrophic responses.

SIGNIFICANCE

IVA treatment lowered blood pressure, improved cardiac remodeling and inflammation, as well as decreasing renal damage in SHR. Further, IVA increased renal HCN2 mRNA and reduced cardiac HCN4 mRNA.

Febuxostat, a novel xanthine oxidoreductase inhibitor, improves hypertension and endothelial dysfunction in spontaneously hypertensive rats

Xanthine oxidase (XO) is an enzyme responsible for the production of uric acid. XO produces considerable amount of oxidative stress throughout the body. To date, however, its pathophysiologic role in hypertension and endothelial dysfunction still remains controversial. To explore the possible involvement of XO-derived oxidative stress in the pathophysiology of vascular dysfunction, by use of a selective XO inhibitor, febuxostat, we investigated the impact of pharmacological inhibition of XO on hypertension and vascular endothelial dysfunction in spontaneously hypertensive rats (SHRs). Sixteen-week-old SHR and normotensive Wistar-Kyoto (WKY) rats were treated with tap water (control) or water containing febuxostat (3 mg/kg/day) for 6 weeks. Systolic blood pressure (SBP) in febuxostat-treated SHR (220 ± 3 mmHg) was significantly (P < 0.05) decreased compared with the control SHR (236 ± 4 mmHg) while SBP in febuxostat-treated WKY was constant. Acetylcholine-induced endothelium-dependent relaxation in aortas from febuxostat-treated SHR was significantly (P < 0.05) improved compared with the control SHR, whereas relaxation in response to sodium nitroprusside was not changed. Vascular XO activity and tissue nitrotyrosine level, a representative indicator of local oxidative stress, were considerably elevated in the control SHR compared with the control WKY, and this increment was abolished by febuxostat. Our results suggest that exaggerated XO activity and resultant increase in oxidative stress in this experimental model contribute to the hypertension and endothelial dysfunction, thereby supporting a notion that pharmacological inhibition of XO is valuable not only for hyperuricemia but also for treating hypertension and related endothelial dysfunction in human clinics.

The association between blood pressure level and serum uric acid concentration in hemodialysis patients

Background: High blood pressure is a common condition in hemodialysis patients. Uric acid, which is high in these patients due to decreased clearance, had been shown to positively correlate with blood pressure in animal studies.

Objectives: The goal of this investigation was to evaluate the impact of high uric acid level on blood pressure in these patients.

Patients and Methods: Ninety-one patients, on three times weekly hemodialysis, were studied. Uric acid levels were measured just before and after hemodialysis along with blood pressures before, during and after each session. Data were analyzed by SPSS 15. A P value less than 0.05 was considered significant.

Results: 40 (44%) of patients had serum uric acid ≥6 mg/dl. Before dialysis 51 (61%) and 19 (21%) had high systolic blood and diastolic blood pressures respectively. Also, 50 (55%) were with wide pulse pressure and 63 (69%) had high mean arterial pressure (MAP). Additionally 62 (68%) developed inter-dialysis hypotension. After measuring odds ratio for hyperuricemia in each group, we observed low risk of hypruricemia in the group with high systolic pressure (OR = 0.352; 95% CI: 0.147-0.844; P = 0.01), the high MAP group (OR = 0.382; 95% CI: 0.153-0.955; P = 0.03) and wide pulse pressure group (OR = 0.416; 95% CI: 0.177-0.975; P = 0.04). There was no association between high uric acid level and diastolic pressure (P = 0.11) and inter-dialysis hypotension (P = 0.33). No relationship was found between serum uric acid and KT/V (P = 0.2), normalized protein catabolic rate (nPCR) (P = 0.07) and body mass index (BMI) (P = 0.4).

Conclusions: This study showed paradoxical association between high uric acid level and high systolic pressure, high MAP and wide pulse pressure and these effects were independent of dialysis duration, dialysis efficacy and nutrition, assuming that these relationships could be due to reverse epidemiology in dialysis patients.

Hyperuricemia: A Biomarker of Renal Hemodynamic Impairment

BACKGROUND

Many epidemiological, clinical, and experimental reports have demonstrated an association between serum uric acid concentration and a variety of cardiovascular and renal diseases, particularly in hypertension. At present, there seems to be no resolution to the question whether this relationship is causal or coincidental.

SUMMARY

This discussion examines a number of biological, pathophysiological, fundamental, and clinical relationships between serum uric acid concentration and several of these disorders. To this end, discussion and review provide some specific insight conclusions and recommendations related to their clinical relevance.

KEY MESSAGES

We suggest that, in most instances (especially in patients with essential hypertension), the increase in serum uric acid concentration is coincidental, serving as a useful biomarker that relates the magnitude of circulating plasma uric acid concentration with the extent of impaired cardiovascular and renal function. Moreover, the value of certain pharmaceutical agents affecting the serum uric acid level should be considered carefully by taking into consideration the associated pathophysiological derangements.

Endothelial dysfunction in femoral artery of the hypertensive rats is nitric oxide independent

This study examined nitric oxide (NO) production, oxidative load and endothelium-dependent relaxation (NO-dependent and NO-independent) in adult male borderline hypertensive (BHR) and spontaneously hypertensive (SHR) rats as compared to normotensive Wistar-Kyoto (WKY) rats. Systolic blood pressure (BP) was determined by tail-cuff. NO production was determined by conversion of [(3)H]-L-arginine. Conjugated dienes (CD) and concentrations of thiobarbituric acid-reactive substances (TBARS) were measured for assessment of oxidative load. Vascular function was investigated in rings of the femoral artery (FA) using a wire myograph. BP of WKY, BHR and SHR was 106+/-2, 143+/-3 and 191+/-3 mm Hg, respectively (p<0.01 for each). Significant left ventricle (LV) hypertrophy and elevated levels of CD and TBARS in the LV were present in BHR and SHR as compared to WKY. NO production was elevated significantly in the aorta of BHR and SHR vs. WKY as well as in the LV of SHR vs. WKY. Acetylcholine (ACh)-induced relaxation of the FA was reduced significantly in both BHR and SHR vs. WKY. The NO-dependent component of ACh-induced relaxation had increasing tendency in hypertensive groups and it correlated positively with BP. The NO-independent component of vasorelaxation was reduced significantly in BHR and SHR vs. WKY and it correlated negatively with BP. In conclusion, the results showed that endothelial dysfunction in the experimental model of borderline hypertensive and hypertensive rats is NO-independent. The results suggest that borderline hypertension represents a risk of other cardiovascular disorders which is qualitatively similar to that of fully developed hypertension.

Uric acid as one of the important factors in multifactorial disorders--facts and controversies

With considering serum concentration of the uric acid in humans we are observing hyperuricemia and possible gout development. Many epidemiological studies have shown the relationship between the uric acid and different disorders such are obesity, metabolic syndrome, hypertension and coronary artery disease. Clinicians and investigators recognized serum uric acid concentration as very important diagnostic and prognostic factor of many multifactorial disorders. This review presented few clinical conditions which are not directly related to uric acid, but the concentrations of uric acid might have a great impact in observing, monitoring, prognosis and therapy of such disorders. Uric acid is recognized as a marker of oxidative stress. Production of the uric acid includes enzyme xanthine oxidase which is involved in producing of radical-oxigen species (ROS). As by-products ROS have a significant role in the increased vascular oxidative stress and might be involved in atherogenesis. Uric acid may inhibit endothelial function by inhibition of nitric oxide-function under conditions of oxidative stress. Down regulation of nitric oxide and induction of endothelial dysfunction might also be involved in pathogenesis of hypertension. The most important and well evidenced is possible predictive role of uric acid in predicting short-term outcome (mortality) in acute myocardial infarction (AMI) patients and stroke. Nephrolithiasis of uric acid origin is significantly more common among patients with the metabolic syndrome and obesity. On contrary to this, uric acid also acts is an “antioxidant”, a free radical scavenger and a chelator of transitional metal ions which are converted to poorly reactive forms.