The impact of elevation of serum uric acid level on the natural history of glomerular filtration rate (GFR) and its sex difference.

BACKGROUND: The impact of elevation of the serum uric acid level (SUA) on the natural history of glomerular filtration rate (GFR) remains controversial. METHODS: If elevation of SUA is a result, rather than a cause, of a decline in GFR, the relationship between SUA and GFR should be the same in the same population over years except for shifts by age-dependent reduction of GFR. We tested this hypothesis using data from two cohorts and a group of allopurinol-treated patients. RESULTS: In Cohort 1 consisting of urban residents aged 40.6 ± 9.0 years (n = 3 446), SUA was inversely correlated with estimated GFR (eGFR) in both men and women, and the slope of the SUA-eGFR relationship was steeper in women than in men. The slopes of the regression lines became significantly steeper after a 6-year interval in both sexes, and the change in the slope was larger in women. A similar sex difference in the SUA-eGFR relationship and 6-year change in the slope were observed in Cohort 2 consisting of rural town residents aged 61.7 ± 12.2 years (n = 404). Multiple regression analyses showed that explanatory factors of eGFR after a 6-year interval were age and SUA at baseline in both cohorts, and partial regression coefficients of SUA were more negative in women than in men. The SUA-eGFR relationship in allopurinol-treated patients (n = 346, 63.5 ± 13.3 years old) was similar to that in Cohort 2. CONCLUSIONS: The results indicate that elevation of SUA accelerates the yearly decline in eGFR and that women are more susceptible to urate-induced decline in eGFR.

Angiotensin II type 1 receptor-mediated upregulation of calcineurin activity underlies impairment of cardioprotective signaling in diabetic hearts.

RATIONALE: The diabetic heart is resistant to ischemic preconditioning because of diabetes-associated impairment of phosphatidylinositol 3-kinase (PI3K)-Akt signaling. The mechanism by which PI3K-Akt signaling is impaired by diabetes remains unclear. OBJECTIVE: Here, we examined the hypothesis that phosphorylation of Jak2 upstream of PI3K is impaired in diabetic hearts by an angiotensin II type 1 (AT1) receptor-mediated mechanism. METHODS AND RESULTS: Infarct size (as percentage of risk area) after 20-minute ischemia/2-hour reperfusion was larger in a rat model of type 2 diabetes (Otsuka-Long-Evans-Tokushima fatty [OLETF] rat) than in its control (Long-Evans-Tokushima-Otsuka [LETO] rat) (60.4+/-1.6% versus 48.4+/-1.3%). Activation of Jak2-mediated signaling by erythropoietin or DADLE ([D-Ala2, D-Leu5]-enkephalin acetate), a delta-opioid receptor agonist, limited infarct size in LETO rats (27.7+/-3.4% and 24.8+/-5.0%) but not in OLETF rats (53.9+/-5.3% and 55.0+/-2.2%). Blockade of the AT1 receptor by valsartan or losartan for 2 weeks restored the myocardial response of OLETF rats to erythropoietin-induced infarct size limitation (39.4+/-4.9% and 31.2+/-7.5). In OLETF rats, erythropoietin failed to phosphorylate both Jak2 and Akt, and calcineurin activity was significantly higher than in LETO rats. Two-week treatment with valsartan normalized calcineurin activity in OLETF rats and restored the response of Jak2 to erythropoietin. This effect of AT1 receptor blockade was mimicked by inhibition of calcineurin by FK506. CONCLUSIONS: These results suggest that the diabetic heart is refractory to protection by Jak2-activating ligands because of AT1 receptor-mediated upregulation of calcineurin activity.

Screening of primary aldosteronism by clinical features and daily laboratory tests: combination of urine pH, sex, and serum K.

OBJECTIVE: To develop and validate a scoring system for selection of patients who should proceed to endocrinologic examinations of primary aldosteronism in newly diagnosed hypertensive patients. METHODS: A multivariate logistic regression analysis for primary aldosteronism was undertaken by use of seven possible primary aldosteronism markers, age less than 40 years, female sex, moderate-to-severe hypertension, hypokalemia, serum Na minus Cl at least 40 mmol/l, serum uric acid 237.92 µmol/l or less (4.0 mg/dl), and urine pH (U-pH) at least 7.0, in consecutive outpatients newly diagnosed with hypertension. The diagnostic criteria of primary aldosteronism were plasma aldosterone concentration-to-plasma renin activity ratio [ARR, (ng/dl)/(ng/ml per h)] at least 20 and at least one positive result in four types of challenge tests. RESULTS: Of 130 patients, 24 were diagnosed with primary aldosteronism. The area under the receiver operating characteristic curve (AUC) for a logistic model incorporating all possible primary aldosteronism markers was 0.73 [95% confidence interval (CI): 0.61-0.85]. Removing high U-pH, female sex, and hypokalemia from the full model decreased the AUC by 0.059, 0.035, and 0.011, respectively. We devised pH of urine, female sex, low serum K (PFK) score, in which one point each was assigned to high U-pH, female sex, and hypokalemia. The prevalences of primary aldosteronism in patients with 0, 1, 2, and 3 points were 11, 14, 42, and 60%, respectively. In external validation datasets (n = 106), AUC of PFK score was significantly higher than that of hypokalemia alone (0.73, 95% CI: 0.63-0.83 vs. 0.53, 95% CI: 0.44-0.63, P < 0.01). CONCLUSION: PFK score may be a better parameter than hypokalemia alone for identifying patients with a high probability of having primary aldosteronism.

Prevention and reversal of premature endothelial cell senescence and vasculopathy in obesity-induced diabetes by ebselen.

Although the accelerated atherosclerosis and premature aging of the cardiovascular system in patients with metabolic syndrome have been appreciated, the mechanisms of their development and potential therapeutic interventions remain unresolved. Our previous studies implicated advanced glycosylation end products in development of premature senescence preventable with a peroxynitrite scavenger, ebselen. Therefore, the effect of ebselen on endothelial senescence and vasculopathy in a model of metabolic syndrome--Zucker diabetic rats (ZDF)--was investigated. Ebselen decreased the abundance of 3-nitrotyrosine-modified proteins in ZDF rats. A 6-fold increase in the number of senescent endothelial cells in 22-week-old ZDF was prevented by ebselen. Development of vasculopathy, as collectively judged by the acetylcholine-induced vasorelaxation, NO production, angiogenic competence, and number of circulating microparticles, was almost completely prevented when ebselen was administered from 8 to 22 weeks and partially reversed when the treatment interval was 13 to 22 weeks. In conclusion, premature senescence of endothelial cells is progressively rampant in ZDF rats and is associated with the signs of severe vasculopathy. In addition, prevention of premature senescence of vascular endothelium through controlled decrease in nitrotyrosine formation was chronologically associated with the amelioration of vasculopathy, lending support to the idea of the pathogenetic role of premature senescence of endothelial cells in diabetic macrovasculopathy.

Olmesartan ameliorates insulin sensitivity by modulating tumor necrosis factor-alpha and cyclic AMP in skeletal muscle.

We have reported that tumor necrosis factor (TNF)-alpha in skeletal muscle is one of the determinants of insulin resistance and that the renin-angiotensin system may be related to the regulation of TNF-a in skeletal muscle. Recent studies have suggested the involvement of cyclic adenosine monophosphate (cAMP) in the regulation of TNF-a in vascular smooth muscle cells or monocytes. The aim of this study was to determine the relationship between cAMP and TNF-a in skeletal muscle in connection with the renin-angiotensin system. Six-week-old male Sprague-Dawley rats were fed either normal rat chow or fructose-rich chow for 6 weeks. For the last 2 weeks of a 6-week period, the rats were treated with a vehicle or with an angiotensin II type 1 receptor antagonist (olmesartan medoxomil, 0.1 mg/kg/day). TNF-alpha levels in the soleus muscle were significantly higher and cAMP levels in the soleus muscle were significantly lower in fructose-fed rats than in control rats. Olmesartan increased cAMP and reduced TNF-a simultaneously in fructose-fed rats. There was a significant negative correlation between levels of cAMP and TNF-alpha. Moreover, a cAMP analogue reduced TNF-a levels in the soleus muscle. These results indicate that the increase in TNF-alpha via suppression of cAMP may affect the induction of insulin resistance. In addition, the facts that olmesartan increased cAMP and decreased TNF-alpha suggest that a part of the TNF-alpha regulation by angiotensin II might consist of modulation of cAMP through Gi protein activation in skeletal muscle.

Tissue-specific impairment of insulin signaling in vasculature and skeletal muscle of fructose-fed rats.

The relation between insulin resistance/hyperinsulinemia and cardiovascular diseases has attracted much attention. Insulin affects not only glucose metabolism, but also protein synthesis and cell growth. Insulin stimulates both the phosphatidylinositol 3-kinase (PI3-K) and mitogen-activated protein kinase (MAPK) pathways, but the relationship between cardiovascular disease and selective insulin signal pathways is unclear. We investigated the tissue specificity and intracellular signal transduction selectivity of insulin resistance in the vasculature and skeletal muscle of fructose-fed rats (FFR). Sprague-Dawley rats were fed either normal rat chow (control rats) or fructose-rich chow. Normal saline with or without 1,000 (microg/kg) insulin was injected, and then the thoracic aorta or soleus muscle was removed under anesthetization. Insulin-induced tyrosine phosphorylation of insulin receptor beta subunit (IRbeta) and insulin receptor substrate-1 (IRS-1) and tyrosine/threonine phosphorylation of p44/42 MAPK (ERK-1/2) were evaluated. There were no significant differences in the degree of phosphorylation of IRbeta or ERK-1/2 in the thoracic aorta or in the soleus muscle between FFR and controls. However, tyrosine phosphorylation of IRS-1 in the soleus muscle of FFR was significantly reduced to 80% (p<0.001) of that in controls. The results suggest that PI3-K pathway in skeletal muscle is selectively impaired in FFR, and this impairment may induce hyperinsulinemia, which in turn may stimulate the MAPK pathway and lead to atherosclerosis. Thus PI3-K pathway may be one of the factors underlying the onset of cardiovascular disease in patients with insulin resistance.

Angiotensin II receptor activation in youth triggers persistent insulin resistance and hypertension--a legacy effect?

Although the involvement of angiotensin II (Ang II) in insulin resistance and hypertension has been established, the temporal relationships between Ang II receptor activation and changes in insulin sensitivity and blood pressure are not clear. To better understand this issue, we infused rats with Ang II (200 ng kg(-1) min(-1)) or vehicle for 4 weeks and assessed the residual effects after the discontinuation of the infusion on blood pressure, insulin sensitivity and tissue parameters of inflammation. Four weeks after the discontinuation of the Ang II infusion, the blood pressure was higher by 12.8 mm Hg, and insulin sensitivity as determined by a euglycemic hyperinsulinemic glucose clamp was reduced (glucose infusion rate: 11.1±0.7 vs. 17.6±0.5 mg kg(-1) min(-1)) in the Ang II-treated group compared with controls. The persistent hypertension and insulin resistance were associated with greater than two-fold increases in macrophage chemoattractant protein-1, tumor necrosis factor-α and thiobarbituric acid-reactive substrates in the soleus muscle. Furthermore, total and activated forms of Rac-1, a regulatory subunit of the NADPH oxidase complex, were increased by 144±14% and 277±82%, respectively, in the skeletal muscle of Ang II-treated rats. These residual effects after Ang II infusion were all attenuated by the co-administration of tempol, a free radical scavenger, or candesartan with Ang II. The effects of candesartan were not mimicked by hydralazine at an equidepressant dose. These findings suggest that Ang II receptor activation in youth triggers the upregulation of inflammatory cytokines and the production of reactive oxygen species, thereby inducing later insulin resistance and hypertension.

Deterioration of renal function by chronic heart failure is associated with congestion and oxidative stress in the tubulointerstitium.

OBJECTIVE: We examined the hypothesis that renal congestion is responsible for the decline in renal function in patients with heart failure (HF) via tubulointerstitial inflammation. METHODS: First, in a longitudinal study, we retrospectively examined the relationship between cardiac functions and the decline of renal function during a period of 6.4±3.2 years in 20 patients who had a left ventricular ejection fraction of <40% and an estimated glomerular filtration ratio (eGFR) of <60 mL/min/1.73 m(2). Second, we compared the renal histology in autopsy cases of HF-induced renal dysfunction (HF-RD), cases of nephrosclerosis (NSC) and cases of neither RD nor HF (controls) in a cross-sectional study. Third, we retrospectively examined renal function in HF patients with predominantly right, but not left, ventricular dysfunction. Results eGFR decreased at 9.4±4.6%/year in the cohort of the longitudinal study. The rate of eGFR decline was correlated with blood pressure and with diameter of the inferior vena cava (IVCd) (r=0.5) measured at the initial work-up. Multivariate analysis indicated that the IVCd is an independent determinant of decline of eGFR in HF. In the cross-sectional study, fibrosis, Rac1 expression, protein nitrosylation, and number of CD68-positive cells were increased in the tubulointerstitium in both cases of HF-RD and NSC. Peritubular capillaries in HF-RD were dilated by 35% without any change in density compared with those in the controls. In right sided HF, the reduction of IVCd after treatment was associated with improvement of eGFR. CONCLUSION: Venous congestion may contribute to HF-induced deterioration of renal function by augmenting oxidative stress-mediated inflammation in the tubulointerstitium.

Angiotensin II inhibits glucose uptake of skeletal muscle via the adenosine monophosphate-activated protein kinase pathway.

Adenosine monophosphate-activated protein kinase (AMPK) mediates metabolic responses of muscle to exercise and is involved in improvement of insulin resistance by endurance exercise. Recent studies have suggested that the renin-angiotensin system might negatively modulate insulin-mediated actions, but there has been little investigation of the correlation between the renin-angiotensin system and AMPK. To determine this correlation, we performed studies with glucose clamp in vivo, and glucose uptake by skeletal muscle ex vivo using 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR). Six-week-old male Sprague-Dawley rats were fed standard chow (standard-diet rats; SD) or fructose-rich chow (fructose-fed rats; FFR) for 6 weeks. At the age of 12 weeks, SD and FFR were treated by oral gavage, either with angiotensin II (Ang II) receptor blockade (ARB; valsartan 30 mg/kg) or vehicle. Thirty minutes after the treatment, we performed glucose clamp studies to measure glucose infusion rates during infusion of insulin (GIR(I)) and of AICAR (GIR(A)), which stimulates AMPK, and studied the effect of ARB on either GIR(I) or GIR(A). In an ex vivo study, we used bilateral fresh soleus muscles from 3-week-old male Sprague-Dawley rats to examine the glucose uptake (measured by (3)H-2-deoxyglucose uptake) of one side of soleus muscle incubated with AICAR with or without Ang II, or with tumor necrosis factor-alpha, in comparison with that of the other (untreated control) side of the muscle. Blood pressure of FFR was significantly higher than that of SD rats. GIR(I) was significantly lower in FFR than in SD, and treatment with ARB did not change GIR(I). GIR(A) of FFR was significantly lower than that of SD, but GIR(A) of FFR treated with ARB was significantly increased compared with that of FFR treated with vehicle. In the ex vivo study, incubation with AICAR significantly increased glucose uptake of soleus muscles, Ang II significantly decreased AICAR-activated glucose uptake in a dose-dependent manner, and ARB canceled the effect of Ang II. The results suggest that acute inhibition of the angiotensin 1 receptor improves glucose metabolism via not insulin but AMPK pathway through the angiotensin 1 receptor in FFR.

Effect of TNF-alpha--converting enzyme inhibitor on insulin resistance in fructose-fed rats.

Insulin resistance is associated with hypertension, obesity, dyslipidemia, and type 2 diabetes. It is well known that tumor necrosis factor (TNF)-alpha is one of the factors linked to obesity-induced insulin resistance; however, there have been no reports on the role of TNF-alpha in insulin resistance in nonobese insulin-resistant hypertensives. We tested the hypothesis that TNF-alpha affects insulin resistance in nonobese insulin-resistant hypertensive fructose-fed rats (FFR) and that a TNF-alpha--converting enzyme (TACE) inhibitor that blocks TNF-alpha secretion improves insulin resistance in FFR. Six-week-old male Sprague-Dawley rats were fed either standard chow (control) or fructose-rich chow (FFR) for 6 weeks. For the last two weeks of a six-week period of either diet, the rats were treated with a vehicle (control or FFR) or a TACE inhibitor (100 mg/kg/d of KB-R7785; FFR+TACE-I) in peritoneal injection. At the age of 12 weeks, insulin sensitivity was assessed in all conscious rats by the euglycemic hyperinsulinemic glucose clamp technique. While FFR had higher blood pressure than the control rats (P<0.01), the TACE inhibitor did not change blood pressure. Insulin sensitivity (M-value) was reduced in FFR compared with that in the control rats (16.7 +/- 1.1 mg/kg per min and 10.3 +/- 0.6 mg/kg per min in the control rats and FFR, respectively, P<0.001), and the TACE inhibitor improved insulin sensitivity to the level of the control rats (14.3 +/- 1.2 mg/kg per min in FFR+TACE-I, P<0.01). These data indicate that TNF-alpha plays a major role in insulin resistance in nonobese insulin-resistant models and also suggest that TACE would be a good target for controlling insulin resistance not only in obese models but also in nonobese insulin-resistant models.

Correlations of adiponectin level with insulin resistance and atherosclerosis in Japanese male populations.

OBJECTIVE: Adiponectin, which is secreted specifically by adipose tissue, has been shown to have an anti-atherosclerotic effect and to improve insulin resistance. The aim of this study was to determine the correlations of plasma adiponectin concentration with insulin resistance and atherosclerosis. DESIGN AND METHODS: We investigated the relationships of adiponectin concentration with insulin sensitivity, high-sensitivity C-reactive protein (hCRP) and pulse wave velocity (PWV) in male inhabitants of rural communities in Japan. hCRP and PWV were used as an indexes of atherosclerosis. RESULTS: A negative correlation was found between homeostasis model assessment (HOMA) as an index of insulin resistance and adiponectin concentration. Results of stepwise regression analysis for adiponectin showed that age, HOMA and serum triglyceride (TG) were independently correlated with adiponectin. Multiple regression analysis for lipid profile was also performed and revealed that adiponectin and HOMA were independently correlated with TG and serum high density lipoprotein (HDL)-cholesterol but not with serum total cholesterol. A significant negative correlation was found between adiponectin and hCRP in all subjects, and a significant negative correlation between adiponectin and PWV was also found in subjects equal or less than 70 years old. When HOMA was added to this analysis, HOMA was found to be independently correlated with hCRP and PWV, but the adiponectin level did not appear to be a significant predictor of hCRP or PWV. CONCLUSIONS: The results suggest that adiponectin plays a role in lipid metabolism and correlates with atherosclerosis either directly or through insulin resistance.

Acetylcholine-induced coronary spasm with a history of Kawasaki disease: case report.

A 21-year-old woman without any known coronary risk factors was found at coronary catheterization to have normal coronary angiograms, but demonstrated acethylcholine (ACh)-induced coronary spasm. She had a history of Kawasaki disease (KD) at 19 months of age and, although coronary angiography was not performed at that time, no coronary aneurysms were detected by echocardiography. To the best of our knowledge, this is the first case report of ACh-induced coronary spasm associated with normal coronary angiograms in a young person with a history of KD. The findings suggest that subclinical, persistent coronary endothelial dysfunction may exist in this patient; furthermore, the dysfunction appears diffuse and might be unrelated to coronary aneurysm formation. The long-term significance of coronary endothelial dysfunction in patients with KD, as suspected by coronary spasm, remains unknown but may be an important risk factor for future atherosclerosis.