Inhibition of human phenol and estrogen sulfotransferase by certain non-steroidal anti-inflammatory agents.

We hypothesized that aryl acetate- and aryl carboxylate-containing drugs would inhibit human phenol sulfotransferase (SULT1A1), and that selectivity would depend upon the interaction of the aryl portion of the molecule with the sulfotransferase acceptor binding site. This hypothesis was based on results with the rat orthologue showing that oxidation of phenolic substrates to carboxylate derivatives resulted in competitive inhibition of rat phenol sulfotransferase. We chose nine structurally representative non-steroidal anti-inflammatory agents and determined their inhibitory potency and selectivity toward SULT1A1 and expressed human estrogen sulfotransferase (SULT1E1). The results show that the tested agents reversibly inhibit SULT1A1 activity with IC(50) ranging from 0.1 microM to 3800 microM. These agents also inhibited SULT1E1 (IC(50) = 6 microM to 9000 microM). The agents were clearly isoform selective, with IC(50) ratios (1E1/1A1) ranging from 0.01 to 200. Nimesulide, meclofenamate, and piroxicam were more selective towards SULT1A1 inhibition, while sulindac and ibuprofen were more selective towards SULT1E1 inhibition. Sulfotransferase inhibition was maintained after substituting the carboxylate with enolate (nimesulide) or methylsulfonamide (piroxicam). Kinetic studies determined the type of inhibition of SULT1A1 for three agents (meclofenamate, nimesulide, aspirin) to be non-competitive or partial non-competitive versus both substrate (p-nitrophenol) and cofactor (PAPS). This inhibition mechanism indicates that meclofenamate, nimesulide and aspirin bind near enough to the substrate binding site to prevent catalysis but not affect dissociation of the substrate-enzyme complex. The inhibition of SULT1A1 by meclofenamate, nimesulide, salicylate and aspirin may be clinically relevant based on ratio of inhibition constant to predicted in vivo inhibitor concentration ([I]/IC(50) > 1).

Fluoride and silicon intake in normal and endemic fluorotic areas.

Precise quantitative information on (a) the contribution of diet to the daily intake of fluoride; and (b) the intake of silicon, which the current work suggests can aggravate fluorosis, is not available for fluorotic and non-fluorotic areas of India. Therefore, an attempt has been made in the present study to collect the above information in normal and fluorotic villages. The daily intake of fluoride (mean +/- SD) over water and diet in normal villages was 1.2 +/- 0.67 mg and 1.0 +/- 0.60 mg, while the corresponding values in a normal urban area were 0.5 +/- 0.03 mg and 1.2 +/- 0.73 mg, respectively. With respect to the intake over water the mean values in normal areas (urban vs. rural) were significantly different (P < 0.001), while there was no significant difference in dietary contribution in the normal areas. In fluorotic villages the daily intake of fluoride was 12.1 +/- 4.11 mg over water and 3.4 +/- 2.43 mg over the diet. These values from fluorotic villages were significantly higher (P < 0.001) than those observed in the normal rural areas. The total intake of silicon (mean +/- SD) in rural and urban normal areas was 204 +/- 58.6 mg and 143 +/- 29.4 mg per day, respectively. The corresponding value from fluorotic villages was 277 +/- 65.5 mg, which was significantly higher (P < 0.01) than those observed in both the normal areas. The situation was similar in fluorotic villages with respect to silicon intake over diet and water. However, the intake of this element over water in the normal rural area (74.0 +/- 18.51 mg per day) was significantly higher (P < 0.001) than the value obtained in the normal urban area (7.5 +/- 1.82 mg per day). This study clearly shows that in the fluorosis-affected areas studied, (a) the total intake of both fluoride and silicon is significantly higher than the intake in non-fluorotic areas; and (b) diets contribute significantly to the intake of both these elements. Our observations on silicon intake and its probable relation to fluorosis are the first of their kind in the literature.

Contribution of vitamin A deficiency to calculogenic risk factors of urine: studies in children.

Studies in experimental animals showed that vitamin A deficiency enhanced the severity of urinary calculi disease. In India, children with low socioeconomic status are the major victims of bladder stone disease, and vitamin A deficiency is also more prevalent among these children. However, no systematic study is available to correlate the vitamin A-deficient status of children with their predisposition to urinary calculi disease. Vitamin A-deficient and normal boys were the subjects of this study. Twenty-four-hour samples of urine were collected from all the children at the beginning of the study and after normalizing the vitamin A status of the deficient children. Important risk factors were estimated in urine. Plasma vitamin A levels were also measured in these children. Among the deficient group, only children with plasma vitamin A levels of 15 micrograms and lower exhibited calcium oxalate crystalluria. Most importantly, abnormal crystalluria was observed in all children whose plasma vitamin A levels were 13 micrograms/dl or less. Compared to normal children the urine of vitamin A-deficient children showed the following changes: (a) reduced concentration of crystal growth inhibitors, namely citrate and glycosaminoglycans; (b) a decline in inhibitory activity toward calcium oxalate crystal growth; and (c) enhanced excretion of high risk factors, namely calcium and oxalate. Correction of vitamin A status normalized the above abnormal properties of urine. The results of this study strongly support the hypothesis that the vitamin A-deficient state is one of the factors that can enhance the risk of urolithiasis in susceptible populations.

Effect of fluoride, silicon, and magnesium on the mineralizing capacity of an inorganic medium and stone formers urine tested by a modified in vitro method.

An in vitro mineralizing system using bovine achilles tendon developed by Thomas and Tomita (3) was modified to enable quantitative evaluation of mineralization. Using this modified method, the potential effect of various ions on the rate of calcium uptake from inorganic mineralization medium was measured. Of the elements tested, only silicon and fluoride accelerated calcium uptake, whereas magnesium had an inhibitory effect. The simultaneous presence of silicon and fluoride in the medium had a synergistic action on calcium uptake. Urine of stone formers showed high propensity to mineralize tendon collagen, but not the urine of non-stone formers. Total content, and concentration of silicon in urine of stone formers was significantly higher than in normal urine. Addition of silicon to non-stone formers urine enhanced its capacity to mineralize collagen in vitro. These results strongly suggest the possible involvement of silicon and fluoride in the genesis of urinary calculi in man.

Role of fluoride in formation of urinary calculi: studies in rats.

The effect of fluoride on urinary calculi formation in young rats was investigated. Two studies, in which rats received diets that included either higher calcium (9 g/kg diet) or normal calcium (5 g/kg diet), were conducted At each level of calcium, one group of rats received a high level of fluoride and another a low level of fluoride in the diet. Rats ingesting high fluoride diets exhibited a higher incidence of crystalluria and bladder stones compared with those receiving low fluoride diets. However, compared with higher calcium diets, normal calcium diets delayed the appearance of crystalluria and produced smaller calculi. Calcium and oxalate were the major components of the calculi. Calculi of rats fed the higher calcium and high fluoride diet contained relatively less protein and more calcium compared with calculi formed in rats ingesting the higher calcium and low fluoride diet. The concentration of fluoride in calculi from rats fed high fluoride diets was significantly higher than that of calculi from rats fed low fluoride diets. A significant positive correlation between calcium and fluoride concentration of calculi was observed in rats fed the higher calcium diet only. These studies indicate that ingestion of excess fluoride facilities calcium oxalate crystalluria and promotes the formation of bladder stones in rats, under the experimental conditions used.