Bernard Lacour

Type 2 Diabetes Increases the Risk for Uric Acid Stones

An increased prevalence of nephrolithiasis has been reported in patients with diabetes. Because insulin resistance, characteristic of the metabolic syndrome and type 2 diabetes, results in lower urine pH through impaired kidney ammoniagenesis and because a low urine pH is the main factor of uric acid (UA) stone formation, it was hypothesized that type 2 diabetes should favor the formation of UA stones. Therefore, the distribution of the main stone components was analyzed in a series of 2464 calculi from 272 (11%) patients with type 2 diabetes and 2192 without type 2 diabetes. The proportion of UA stones was 35.7% in patients with type 2 diabetes and 11.3% in patients without type 2 diabetes (P < 0.0001). Reciprocally, the proportion of patients with type 2 diabetes was significantly higher among UA than among calcium stone formers (27.8 versus 6.9%; P < 0.0001). Stepwise regression analysis identified type 2 diabetes as the strongest factor that was independently associated with the risk for UA stones (odds ratio 6.9; 95% confidence interval 5.5 to 8.8). The proper influence of type 2 diabetes was the most apparent in women and in patients in the lowest age and body mass index classes. In conclusion, in view of the strong association between type 2 diabetes and UA stone formation, it is proposed that UA nephrolithiasis may be added to the conditions that potentially are associated with insulin resistance. Accordingly, it is suggested that patients with UA stones, especially if overweight, should be screened for the presence of type 2 diabetes or components of the metabolic syndrome.

Uremia Accelerates both Atherosclerosis and Arterial Calcification in Apolipoprotein E Knockout Mice

Chronic renal failure (CRF) favors the development of atherosclerosis and excessive calcification of atheromatous lesions. CRF was induced in apolipoprotein E knockout (apoE(-/-)) mice to study (1) a possible acceleration of aortic atherosclerosis, (2) the degree and type of vascular calcification, and (3) factors involved in the calcification process. For creating CRF, 8-wk-old apolipoprotein E gene knockout (apoE(-/-)) mice underwent partial kidney ablation. Control animals underwent sham operation. Aortic atherosclerotic plaques and calcification were evaluated using quantitative morphologic image processing. At 6 wk after nephrectomy, CRF mice had significantly higher serum urea, cholesterol, and triglyceride concentrations than non-CRF controls. The serum levels of advanced oxidation protein products were elevated in the uremic group and were correlated with serum urea levels. Atherosclerotic lesions in thoracic aorta were significantly larger in uremic apoE(-/-) mice than in nonuremic controls. The relative proportion of calcified area to total surface area of both atherosclerotic lesions and lesion-free vascular tissue was increased in aortic root of uremic apoE(-/-) mice when compared with controls. The calcium deposits were made of hydroxyapatite and calcite crystals. In addition, plaques from uremic animals showed a significant increase in collagen content, whereas the degree of macrophage infiltration was comparable in both groups. There was no difference in mean arterial BP. These findings demonstrate that CRF aggravates atherosclerosis in apoE(-/-) mice. Moreover, CRF enhances arterial calcification at both atheromatous intimal sites and atheroma-free medial sites. We anticipate that this experimental model will be useful to test treatment strategies aimed at decreasing the accelerated atherosclerosis and arterial calcification in uremia.

Changes in stone composition according to age and gender of patients: a multivariate epidemiological approach

Urinary stone incidence and composition have changed markedly over the past half-century in industrialized countries, in parallel with profound changes in living standards and dietary habits, with a dramatic increase in the incidence of calcium oxalate stones. However, studies evaluating the influence of age and gender on the distribution of the various types of urinary calculi are scarce. We report the results of a study based on 27,980 calculi (from 19,442 males and 8,538 females) analyzed by infrared spectroscopy between 1976 and 2001. The relationships between age and sex and stone composition were investigated using a multivariate approach, based on correspondence factor analysis (CFA). We found a male predominance for calcium oxalate and uric acid, a female preponderance for calcium phosphate and struvite stones, and an increasing prevalence of uric acid stones with age in both genders. CFA was able to reconstruct in blind the age curve from stone composition. The first two axes of the multidimensional classification, which correspond to age, included 86.9% of the total variance, indicating that age was the main factor involved in stone type. Superimposition of age classes and stone components showed a strong relationship between age and whewellite, weddellite, brushite, carbapatite, octacalcium phosphate and uric acid, while other substances (whitlockite, amorphous carbonated calcium phosphate, struvite, proteins, mucopolysaccharides, triglycerides or ammonium urate) appeared weakly related to age. In addition, CFA suggests the role of common lithogenic factors between weddellite, carbapatite and brushite, which clustered in the same area, whereas the various crystalline forms of phosphate stones segregated into two different clusters, suggesting distinct pathogenic factors. In conclusion, this study provides a picture of the present epidemiology of urinary stones in France. CFA helped to confirm: (1) an etiopathogenic distinction between weddellite and whewellite, (2) etiopathogenic associations between chemical compounds, which were only suspected on a clinical basis, and (3) suggested yet unrecognized associations, especially with respect to the heterogeneous group of phosphate stones.

Influence of body size on urinary stone composition in men and women.

A larger body size has been shown to be associated with increased excretion of urinary lithogenic solutes, and an increased risk of nephrolithiasis has been reported in overweight patients. However, the type of stones produced in these subjects has not been ascertained. Based on a large series of calculi, we examined the relationship between body size and the composition of stones, in order to assess which type of stone is predominantly favoured by overweight. Among 18,845 consecutive calculi referred to our laboratory, 2,100 came from adults with recorded body height and weight. Excluding calculi from patients with diabetes mellitus, as well as struvite and cystine stones, the study material consisted of 1,931 calcium or uric acid calculi. All calculi were analysed by infrared spectroscopy and categorized according to their main component. Body mass index (BMI) values were stratified as normal BMI (<25xa0kg/m2), overweight (BMI 25–29.9) or obese (BMI≥30). Overall, 27.1% of male and 19.6% of female stone formers were overweight, and 8.4 and 13.5% were obese, respectively. In males, the proportion of calcium stones was lower in overweight and obese groups than in normal BMI group, whereas the proportion of uric acid stones gradually increased with BMI, from 7.1% in normal BMI to 28.7% in obese subjects (P<0.0001). The same was true in females, with a proportion of uric acid stones rising from 6.1% in normal BMI to 17.1% in obese patients (P=0.003). In addition, the proportion of uric acid stones markedly rose with age in both genders (P<0.0001). The average BMI value was significantly higher in uric acid stone formers aged <60xa0years than in all other groups, whereas it did not differ from other groups in those aged ≥60xa0years. Stepwise regression analysis identified BMI and age as significant, independent covariates associated with the risk of uric acid stones. Our data provide evidence that overweight is associated with a high proportion of uric acid stones in patients less than 60xa0years of age, whereas beyond this limit, advancing age is the main risk factor.

Sevelamer Prevents Uremia-Enhanced Atherosclerosis Progression in Apolipoprotein E–Deficient Mice

Background— The novel phosphate binder sevelamer has been shown to prevent the progression of aortic and coronary calcification in uremic patients. Whether it also decreases the progression of atheromatous plaques is unknown. The aim of our study was to examine the effect of sevelamer administration on the development of atherosclerosis and aortic calcification in the uremic apolipoprotein E–deficient mouse as an established model of accelerated atherosclerosis. Methods and Results— Female mice were randomly assigned to 4 groups: 2 groups of nonuremic mice (sevelamer versus control) and 2 groups of uremic mice (sevelamer versus control). Sevelamer was given at 3% with chow. The increases in serum phosphorus concentration and calcium-phosphorus product observed in uremic control mice were prevented by sevelamer. Serum total cholesterol was increased in the 2 uremic mouse groups and remained unchanged in response to sevelamer. After 8 weeks of sevelamer treatment, uremic mice exhibited a significantly lower degree of atherosclerosis (P<0.001) and vascular calcification than uremic control mice. Of interest, sevelamer exerted an effect on both intima and media calcification (P=0.005) in uremic mice. Among possible mechanisms involved, we found no evidence for the modulation by sevelamer of inflammation or selected uremic toxins. In contrast, nitrotyrosine staining as a measure of oxidative damage was significantly decreased in response to sevelamer treatment in control and uremic mice (P<0.005). Conclusions— Sevelamer delays not only vascular calcification but also atherosclerotic lesion progression in uremic apolipoprotein E–deficient mice. It opens the possibility of a cholesterol-independent action of sevelamer on atheroma formation via effects on mineral metabolism, oxidative stress, or both.

The calcimimetic R-568 retards uremia-enhanced vascular calcification and atherosclerosis in apolipoprotein E deficient (apoE―/―) mice

OBJECTIVEnSecondary hyperparathyroidism of chronic kidney disease promotes vascular calcification. Calcimimetics reduce serum parathyroid hormone, calcium (Ca), and phosphorus by calcium-sensing receptor (CaR) activation. Here we examined possible effects of the calcimimetic R-568 (R-568) on the progression of aortic calcification and atherosclerosis in apoE(-/-) mice with chronic renal failure (CRF) and the potential implication of aortic smooth muscle cell CaR.nnnMETHODS AND RESULTSnApoE(-/-) mice were assigned to 3 CRF groups and 1 non-CRF group receiving daily gavage with R-568, calcitriol, or vehicle. Serum Ca and phosphorus and parathyroid gland volume of CRF mice were decreased by R-568, whereas elevated serum FGF23 and total cholesterol remained unchanged. Both aortic plaque and non-plaque calcification was lower in R-568 mice, and so was atherosclerotic plaque area fraction. In vitro, R-568 induced a decrease in smooth muscle cell calcification when cultured in high phosphate medium. This decrease was abolished in CaR-SiRNA-transfected cells.nnnCONCLUSIONSnThe calcimimetic R-568 delayed the progression of both aortic calcification and atherosclerosis in uremic apoE(-/-) mice. This effect was mediated via a better control of hyperparathyroidism including serum Ca and phosphorus. Direct vascular CaR activation also could have played a role in the observed effects.

Role of reactive oxygen species and Bax in oxidized low density lipoprotein-induced apoptosis of human monocytes

This study investigated the proapoptotic effects of oxidized low density lipoprotein (oxLDL), which plays a key role in atherogenesis, on normal fresh human monocytes isolated from peripheral blood (PBMs), on human monocyte-derived macrophages, and on U937 monocytic cell line. OxLDL were generated by hypochlorous acid (HOCl) treatment of native LDL. We demonstrated that HOCl-oxLDL (200 microg/ml) induced apoptosis in PBMs and U937 cells via the mitochondrial pathway, whereas it failed to induce apoptosis in human monocyte-derived macrophages. OxLDL-induced U937 cells apoptosis involved ROS generation, mitochondrial Bax translocation with a disruption of mitochondrial membrane potential, cytosolic liberation of cytochrome c and subsequently activation of caspases-9 and -3. The interference of ROS scavengers N-acetylcysteine and catalase with HOCl-oxLDL-induced apoptosis further supports the importance of mitochondrial ROS production in this process. Bcl-2 overexpression prevented Bax translocation whereas it failed to prevent ROS generation indicating that ROS is an upstream signal for inducing mitochondrial apoptotic damages. Because monocyte apoptosis could limit early atheroma formation, it will be interesting to identify the signaling pathway(s) induced by HOCl-oxLDL leading to ROS generation. In contrast, monocyte-derived macrophages, which resist to HOCl-oxLDL-induced oxidative stress, may promote atherosclerosis.

Lanthanum carbonate, like sevelamer-HCl, retards the progression of vascular calcification and atherosclerosis in uremic apolipoprotein E-deficient mice

BACKGROUNDnAtherosclerosis and vascular calcification (VC) progression in chronic kidney disease is favored by disturbances of mineral metabolism. We compared the effect of phosphate binder lanthanum (La) carbonate with sevelamer-HCl on atherosclerosis, VC and bone structure and function in mice with chronic renal failure (CRF).nnnMETHODSnApolipoprotein E-deficient (apoE(-/-)) mice were randomized to one non-CRF and three CRF groups, fed with standard diet (one non-CRF and one CRF) or diet supplemented with either 3% lanthanum carbonate (La3%) or 3% sevelamer-HCl (Sev3%).nnnRESULTSnBoth La3% and Sev3% supplemented CRF mice displayed a decrease of serum phosphorus, calcification at both intimal and medial aortic sites and atherosclerosis. This was associated with a reduction of plaque Type I collagen expression by both binders and of positive nitrotyrosine staining in response to sevelamer-HCl only. Increased mineral apposition and bone formation rates in unsupplemented CRF mice were reduced by Sev3% but not by La3%.nnnCONCLUSIONSnThe beneficial effects of La carbonate and sevelamer-HCl on the progression of VC and atherosclerosis in CRF mice could be mainly due to a decrease in phosphate retention and likewise a reduction of arterial Type I collagen expression. The effect of La carbonate differed from that of sevelamer-HCl in that it did not appear to exert its vascular effects via changes in oxidative stress or bone remodeling in the present model.

Increased Plasma S-Nitrosothiol Concentrations Predict Cardiovascular Outcomes among Patients with End-Stage Renal Disease: A Prospective Study

The plasma concentrations of S-nitrosothiols, which are circulating nitric oxide metabolites with potential biologic activity, are increased among patients undergoing chronic hemodialysis (HD). However, the ability of S-nitrosothiols to release nitric oxide at physiologically relevant sites may be reduced among HD patients, because of impaired availability and/or activity of factors involved in S-nitrosothiol breakdown. The resultant lack of S-nitrosothiol bioavailability could contribute to the high cardiovascular risk for such patients. A possible relationship between plasma S-nitrosothiol levels and cardiac outcomes, as well as all-cause mortality rates, was investigated in a cohort of 250 chronic HD patients and who were undergoing regular dialysis three times per week were monitored for 1 yr. During that follow-up period, major cardiac events and all-cause deaths were prospectively recorded. At baseline, high plasma S-nitrosothiol levels (>2 micro M, corresponding to the top quartile of all measured values) were independently associated with pulse pressure in an adjusted multivariate analysis (odds ratio, 1.03; 95% confidence interval, 1.01 to 1.05; P = 0.007). During the follow-up period, 36 patients died (16 as a result of cardiac causes) and 33 patients experienced major adverse cardiac events. In an adjusted Cox proportional-hazards model, high plasma S-nitrosothiol concentrations (i.e., the top quartile versus the three other quartiles) were an independent predictor of cardiac events (hazard ratio, 3.30; 95% confidence interval, 1.61 to 6.76; P = 0.001) but not of all-cause death. Therefore, among chronic HD patients, markedly elevated plasma S-nitrosothiol levels are associated with pulse pressure and predict cardiovascular outcomes. These findings support the hypothesis that impaired S-nitrosothiol bioavailability in uremia is an important factor for the excessive cardiovascular risk among HD patients.

Paracellular calcium transport across Caco-2 and HT29 cell monolayers

Abstractu2002Intestinal calcium absorption has been shown to include two processes, a saturable transcellular movement and a non-saturable paracellular pathway. The potential utility of cell monolayers for studying transepithelial intestinal calcium transport has already been demonstrated; however, simultaneous evaluation of the contribution of the saturable transcellular and of the non-saturable paracellular processes to the total transepithelial transport has not yet been attempted. The aim of this study was to investigate the contribution both of transcellular and paracellular transport processes to the total transepithelial calcium transport in two cell culture monolayers. Caco-2 cells and a clone derived from HT-29 cells (HT29-Cl.19A), two cell lines derived from colon adenocarcinomas which are known to be able to exhibit typical enterocytic differentiation, were used. Cell monolayers were grown on a permeable support and used after 15 days of culture when these cells express enterocytic differentiation and high transepithelial resistance. Isotopic transport rate measurements were performed in the absence of a chemical gradient. The paracellular route was evaluated using [3H]mannitol. Calcium and [3H]mannitol transport rates across cell monolayers were not significantly different. Augmentation of calcium uptake by 200 mM sorbitol did not significantly increase calcium or mannitol transepithelial transport; however, calcium accumulation in the cells was increased by about 200%. Modulation of the monolayer permeability by addition of 10 nM vasoactive intestinal polypeptide (VIP) or 0.5 mM carbachol treatment, which respectively increased and decreased the transepithelial resistance, consequently modified calcium and mannitol transport in a parallel manner. Our results show that Caco-2 and HT29-Cl.19A cell monolayers are good models for studying the calcium paracellular transport pathway.