Biomedical subjects
Publications and source records attributed to M L Traba.
Nephrolithiasis is presented in 18-40% of patients with primary hyperparathyroidism. Our work suggests that citrate, an inhibitor of calcium salts, could be involved in the presence of renal lithiasis because hyperparathyroid stone formers show less citrate elimination than nonstone formers.
Different mechanisms could explain the elevated calcium elimination, the main cause of calcium oxalate renal stones. Our results suggest that phosphate levels are decreased in patients with absorptive hypercalciuric nephrolithiasis and elevated serum dihydroxyvitamin D. This could be the reason why in this group of patients oral phosphate treatment prevented hypercalciuria and renal lithiasis.
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In order to analyze the role of 1,25(OH)2 D3 in bone and renal presentation forms of primary hyperparathyroidism (PHP), 61 patients, whose diagnosis had been confirmed surgically, were studied. An increase in serum 1,25(OH)2 D3 levels was found in PHP when compared to normal controls (49.1 +/- 2.8 pg/ml vs 34.1 +/- 1.4 pg/ml) (p less than 0.5). This increase directly correlates with serum alkaline phosphatase and creatinine clearance and inversely correlates with age. When patients were divided into two groups: A (n = 35) and B (n = 26) according to normal or increased 1,25(OH)2 D3 respectively, no difference was found in the clinical presentation forms of PHP. However, higher values of the biochemical parameters and bone remodeling markers were found in group B than in group A. This suggests the role of 1,25(OH)2 D3 as a modulator of metabolic activity in PHP and its possible therapeutic character in the clinical control of asymptomatic forms.
A small group of patients with nephrolithiasis who forms mixed (calcium oxalate and uric acid) calculi presents particular problems in their clinical management. In 3,158 stones analyzed in our laboratory, we found 158 mixed calculi in 86 of the patients. In this work, the clinical and biochemical results obtained from 27 patients with mixed stones were compared with those from 27 control patients with calcium oxalate renal lithiasis. A significant difference was found in oxalate and citrate urinary elimination (mean +/- SD) in mixed stone formers versus pure calcium oxalate stone formers: oxaluria (mg/24 h: 38 +/- 15 vs. 28 +/- 12; p less than 0.01) and citraturia (mg/24 h: 214 +/- 139 vs. 437 +/- 303; p less than 0.01). Citraturia was decreased in a high proportion (77%) in mixed stone formers, and only a reduced percentage of them (23%) presented normal values, although in the low limit of normality. As treatment and prophylactic measure, we proposed oral administration of citrates in mixed stone patients because citrate inhibits spontaneous nucleation of calcium salts and crystal growth, and it also increases the urinary pH with a consequent increase in uric acid solubility.
The role of magnesium in the regulation of 25(OH)D3-24R-hydroxylase and 25(OH)D3-1 alpha-hydroxylase in vitro remains to be clarified. Using a radiochemical assay, the effect of substrate concentration on both enzymes was measured in rat kidney homogenates as well as the alterations in their kinetic behaviour resulting from changes in the magnesium concentration in the incubation medium. The results showed that magnesium could be a modulator of 24- and 1 alpha-hydroxylases. Variations in magnesium caused alterations in the kinetic behaviour of both enzymes, which altered the synthesis rates of 24,25(OH)2D3 and 1,25(OH)2D3. Moreover, the substrate concentration was clearly involved in the response of both enzymes to the modulation by magnesium.
We have studied the possible correlation between serum 24,25-dihydroxyvitamin D [24,25-(OH)2D] and osteocalcin levels (sBGP) in Paget's disease of bone. We measured serum calcium, phosphate, PTH, 25-hydroxyvitamin D, 1,25-(OH)2D, 24,25-(OH)2D, alkaline phosphatase (sAP), and the urinary hydroxyproline/creatinine ratio (UOH prol/creat) in 19 patients with Paget's disease of bone and 16 age- and sex-matched controls. As expected, sAP, UOH prol/creat, and sBGP levels were significantly elevated, and there was a tendency to a decrease in serum levels of 24,25-(OH)2D in Pagetic patients with respect to the control group. There was no significant difference between patients and controls in serum calcium, phosphate, PTH, 25-hydroxyvitamin D, and 1,25-(OH)2D. The Pagetic patients were subdivided into two subgroups; subgroup A had normal sBGP levels (less than 5 ng/mL), and subgroup B had increased sBGP levels (greater than 5 ng/mL). Serum 24,25-(OH)2D levels in subgroup B were significantly lower than those in controls, while subgroup A showed levels similar to those in the control group. We also found a positive linear correlation between sAP and sBGP and between sAP and UOH prol/creat as well as a negative linear correlation between sBGP and 24,25-(OH)2D and between 24,25-(OH)2D and UOH prol/creat in Pagetic patients. These results point to a possible role of 24,25-(OH)2D in disease activity.
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We tested the existence of 25-hydroxyvitamin D-1 alpha-hydroxylase activity in the Walker carcinosarcoma 256 implanted in rats. This tumour has been shown to induce hypercalcaemia in the host animal. We found this enzyme activity in tumour homogenates, which was in the same range as that in the kidney of tumour-bearing rats. Our results suggest that 1,25-dihydroxyvitamin D synthesized by the Walker tumour might be involved in the mechanism responsible for the hypercalcaemia in the host rat.
Two cases of chondrocalcinosis associated with hypomagnesemia are presented and a literature review is carried out, revealing that half of the reported cases are associated with Bartter Syndrome. We describe the metabolic studies performed and discuss the possible role of calciotrope hormones in this type of clinical manifestation. The pathogenesis is thought to be a defect in the transport across the renal tubular cell (and also, possibly an alteration in the intestinal epithelial membrane) as well as the presence of other metabolic alterations (hypocalcemia, hypokalemia, hydrocarbon intolerance) associated with this not so rare disease.
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A method for perfusion of isolated canine tibia is described. With this procedure the influence of different albumins on the uptake of tritiated 25-hydroxyvitamin D3 (3H-25(OH)D3) by the tibia has been studied. Bovine serum albumin at 1% concentration seems to be optimum for this system. This experimental approach seems to be useful for the study of mineral metabolism.
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A new method for determination of oxalic acid in urine is described. The method encloses sample purification prior to the treatment by High Performance Liquid Chromatography (HPLC). The purification step consists in the passage of acidified urine through Sep-pak C18 cartridge (Waters), followed by the precipitation of the oxalic acid eluted with CaCl2, new dilution of the calcium oxalate precipitate, oxalic acid extraction with diethyl ether and total dryness of the sample. The losses of oxalic acid during this process are evaluated by the addition of oxalic acid (U-14C) before the precipitation step. The dried samples are redissolved in mobile phase (o-H3PO4, 0.05 M) and injected into a HPLC chromatograph, with reversed phase column (Lichrosorb RP-8, Merck). Oxalate peak is detected spectrophotometrically at 220 nm, with a retention time of 3.20 minutes. The method shows a mean recovery value of 98.25%, with an intra-run and between-run values of 5.13 and 8.06 respectively. The oxalic acid measured in urine by this method is 35.52 +/- 9.42 mg/24 h in normal subjects.
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