Strontium absorption and excretion in normocalciuric subjects : relation to calcium metabolism

The relationships of Sr intestinal absorption and renal excretion with biohumoral factors regulating Ca metabolism were studied in 47 normocalciuric subjects with Ca kidney stones. Sr concentrations were measured in serum and urine after an oral load of stable Sr (30.2 mumol/kg body wt). Enteral absorption of the ion (9.77 +/- 0.438 mmol.L-1.min, 240 min after Sr administration), expressed as the area under the plasma concentration-time curve (AUC), and renal clearance (CRE) in these subjects during the test (2.80 +/- 0.336 mL/min) were not different from values for 27 controls. CRE was not correlated with AUCs. Plasma concentrations of parathyroid hormone (PTH) negatively correlated with AUCs (P < 0.01) and correlated with CRE after one outlier was excluded (P < 0.05). Plasma concentrations of 1,25-dihydroxyvitamin D correlated positively with AUCs (P < 0.01) when normalized to the plasma concentration of PTH. Multiple stepwise regression showed that PTH and phosphatemia were significantly related to AUC values at 240 min (P < 0.01). These findings suggest that Sr absorption and excretion reflect the regulation of Ca metabolism, but some differences in renal handling of the two ions may exist

Plasma homocysteine levels and cardiovascular mortality in patients with end-stage renal disease

Hyperhomocysteinemia is considered an independent risk factor for atherosclerosis in patients with normal renal function. Plasma homocysteine (Hcy) is increased in patients with chronic renal failure (CRF) and could be linked to their high cardiovascular (CV) morbidity and mortality. We prospectively studied 77 patients (47 males and 30 females aged 62.85 \ub1 1.53 yrs) who had been on maintenance hemodialysis (HD) (4 hr/ 73/week) for 65.5 \ub1 7.23 months. Patients were followed-up for 44 months. At baseline, blood samples were taken for hemoglobin (Hb), total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides, serum calcium, serum phosphates, parathyroid hormone (PTH), Hcy, vitamin B12, serum and erythrocyte folate and methylentetrahydrofolate-reductase (t-MTH-FR) genotype determination. Plasma Hcy levels of patients were divided into four quartiles. The univariate analysis demonstrated a significant relationship between Hcy and diastolic blood pressure (BP) (r=0.45; p=0.003), and both plasma (r=-0.30; p=0.03) and erythrocyte (r=-0.48; p=0.01) folate levels and CV score (r=0.39; p=0.007). Kaplan-Meier analysis showed that the mortality rate due to CV events was statistically significantly higher in the 4th Hcy quartile (68%; 12 patients) vs. the 3rd quartile (12%; two patients), the 2nd quartile (28%; four patients) and the 1st quartile (14%; two patients) (log-rank test p=0.02). Cox's regression analysis for CV survival showed that Hcy was a positive CV mortality predictor (\u3b2=0.02; hazard ratio=1.031; 95% confidence interval (95% CI): 1.013-1.050; p=0.001), while LDL cholesterol and albumin related negatively to CV mortality (LDL cholesterol: \u3b2=-0.02; hazard ratio=0.095; 95% CI: 0.0957-0.0997; p=0.035; albumin: P=-2.35; hazard ratio=0.097; 95% CI: 0.011-0.847; p=0.026). Our results show that Hcy is a strong independent mortality predictor in HD patients with a 3% increase in mortality for each 1 \u3bcmol/L increase in plasma Hcy concentration. This agrees with previous findings confirming the role of Hcy in predicting CV risk factors in uremic patients

Nonacidotic proximal tubulopathy transmitted as autosomal dominant trait

The family of a patient with a nonacidotic and hypercalciuric proximal tubulopathy was studied. The proband showed glycosuria, aminoaciduria, tubular proteinuria, renal hypophosphatemia, and urate tubular hyporeabsorption without bicarbonate loss. He also presented increased urine calcium excretion, plasma 1,25-dihydroxyvitamin D, and enteral calcium absorption. Clinical consequences of the tubulopathy were osteopenia and calcium kidney stones. Fifteen of the proband's relatives were studied; six of them had renal hypophosphatemia, 10 presented hypercalciuria, and three showed both hypercalciuria and hypophosphatemia. No other reabsorption defects were observed. High plasma levels of 1,25-dihydroxyvitamin D were found in 13 family members; their values correlated positively with calcium excretion and negatively with tubular phosphate reabsorption. None produced stones or had reduced mineral bone density. Hypophosphatemia and hypercalciuria occurred in the two generations studied; their transmission was independent of gender, and male-to-male transmission occurred for both defects. Our findings suggest that a genetic alteration of proximal tubular function could cause multiple reabsorption defects in the proband or renal phosphate leakage in the proband's relatives. The genotypic alteration causing the proximal dysfunctions may be monogenic, with an autosomal dominant pattern of inheritance and variable expressivity. Increased calcium excretion may be due to the proximal tubular alteration; alternatively, it may be the result of a genetic background predisposing to idiopathic hypercalciuria. Phosphate and calcium loss could stimulate 1,25-dihydroxyvitamin D synthesis in proximal tubular cells

Supplementazione e.v. di acido folinico e vitamina B12 e concentrazioni di omocisteina nei pazienti emodializzati

INTRODUCTION: Hyperhomocysteinemia is one of the causes of the increased incidence of cardiovascular disease in uremia. Since homocysteine (Hcy) metabolism depends on the availability of folate and vitamin B12, we have measured the effects of chronic i.v. supplementation of folinic acid and vitamin B12 in a group of patients on maintenance hemodialysis. METHODS: We compared the blood concentration of total Hcy (tHcy), vitamin B12 and folate and the intraerythrocyte concentration of folate in a group of 27 hemodialysis patients (Treated group), given an i.v supplementation with folinic acid (0.9 mg) and Vitamin B12 (cyanocobalamine 1.5 mg and hydroxycobalamine 1.5 mg) three times per week at the end of each dialysis session with those measured in a similar group of 28 hemodialysis patients without supplementation (No Treatment group). The patients were also characterized for the thermolabile variant (mutation C667-->T) of the enzyme methylene-tetrahydrofolate reductase (tMTHFR). RESULTS: High plasma levels (< 11.7 micromol/L) of tHcy were observed in 54/55 patients. T patients had Hcy values significantly lower than NT ones (31.7+/-3.6 vs. 1.1+/-8.3micromol/L, p < 0.05). Serum vitamin B12 (1200 73.6 vs. 762+/-72.2 pmol/L, p < 0.001) and intraerythrocyte folate levels were also significantly higher in the T group (2176+/-127 vs. 1511+/-156, p < 0.005), while no significant difference was observed for serum folate. The distribution of tMTHFR genotypes was similar in the two groups. Homozygous patients showed higher levels of Hcy in comparison with wild type patients both in the whole population (62.32+/-15.9 vs.30.43+/-3.2, p < 0.05) and in the NT group (87.8+/-25.3 vs.36.8+/-13.1., p < 0.05), while no significant difference was observed among genotypes in the T group. CONCLUSIONS: Uremic patients on hemodialysis, when supplemented with even low i.v. dose of folinic acid and vitamin B12, show significantly lower plasma levels of tHcy than non-supplemented patients