1alpha,25-dihydroxy-16-ene-23-yne-vitamin D3 and 1alpha,25-dihydroxy-16-ene-23-yne-20-epi-vitamin D3: analogs of 1alpha,25-dihydroxyvitamin D3 that resist metabolism through the C-24 oxidation pathway are metabolized through the C-3 epimerization pathway

The secosteroid hormone 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] is metabolized in its target tissues through modifications of both the side chain and the A-ring. The C-24 oxidation pathway, the previously well established main side chain modification pathway, is initiated by hydroxylation at C-24 of the side chain. The C-3 epimerization pathway, the newly discovered A-ring modification pathway, is initiated by epimerization of the hydroxyl group at C-3 of the A-ring. The end products of the metabolism of 1alpha,25(OH)2D3 through the C-24 oxidation and the C-3 epimerization pathways are calcitroic acid and 1alpha,25-dihydroxy-3-epi-vitamin-D3 respectively. During the past two decades, numerous noncalcemic analogs of 1alpha,25(OH)2D3 were synthesized. Several of the analogs have altered side chain structures and as a result some of these analogs have been shown to resist their metabolism through side chain modifications. For example, two of the analogs, namely, 1alpha,25-dihydroxy-16-ene-23-yne-vitamin D3 [1alpha,25(OH)2-16-ene-23-yne-D3] and 1alpha,25-dihydroxy-16-ene-23-yne-20-epi-vitamin D3 [1alpha,25(OH)2-16-ene-23-yne-20-epi-D3], have been shown to resist their metabolism through the C-24 oxidation pathway. However, the possibility of the metabolism of these two analogs through the C-3 epimerization pathway has not been studied. Therefore, in our present study, we investigated the metabolism of these two analogs in rat osteosarcoma cells (UMR 106) which are known to express the C-3 epimerization pathway. The results of our study indicate that both analogs [1alpha,25(OH)2-16-ene-23-yne-D3 and 1alpha,25(OH)2-16-ene-23-yne-20-epi-D3] are metabolized through the C-3 epimerization pathway in UMR 106 cells. The identity of the C-3 epimer of 1alpha,25(OH)2-16-ene-23-yne-D3 [1alpha,25(OH)2-16-ene-23-yne-3-epi-D3] was confirmed by GC/MS analysis and its comigration with synthetic 1alpha,25(OH)2-16-ene-23-yne-3-epi-D3 on both straight and reverse-phase HPLC systems. The identity of the C-3 epimer of 1alpha,25(OH)2-16-ene-23-yne-20-epi-D3 [1alpha,25(OH)2-16-ene-23-yne-20-epi-3-epi-D3] was confirmed by GC/MS and 1H NMR analysis. Thus, we indicate that vitamin D analogs which resist their metabolism through the C-24 oxidation pathway, have the potential to be metabolized through the C-3 epimerization pathway. In our present study, we also noted that the rate of C-3 epimerization of 1alpha,25(OH)2-16-ene-23-yne-20-epi-D3 is about 10 times greater than the rate of C-3 epimerization of 1alpha,25(OH)2-16-ene-23-yne-D3. Thus, we indicate for the first time that certain structural modifications of the side chain such as 20-epi modification can alter significantly the rate of C-3 epimerization of vitamin D compounds.

Reduced vitamin D receptor expression in parathyroid adenomas: implications for pathogenesis

BACKGROUND AND OBJECTIVES

Parathyroid adenomas discovered fortuitously grow very slowly and their cell birth rate greatly declines, features explicable by an initial increase in secretory set-point. In the nodules of severe uraemic parathyroid hyperplasia, there is an increased set-point and decreased expression of both the calcium sensing receptor (CaSR) and the vitamin D receptor (VDR). Accordingly, we examined VDR and CaSR expression in parathyroid adenomas.

PATIENTS AND DESIGN

We studied 24 patients with primary hyperparathyroidism with a wide range of vitamin D nutritional status (plasma 25-hydroxyvitamin D range 10-107 nmol/l). Eighteen patients discovered by biochemical screening were enrolled in a natural history or treatment option study, and six additional US patients matched a group studied concurrently in India with low plasma 25-hydroxyvitamin D level (< 37 nmol/l).

MEASUREMENTS

Receptor expression was determined by immunocytochemistry in each tumour and in 11 cases also in adjacent nonadenomatous tissue. VDR expression was reported as the proportion of positive cells (strongly rather than weakly stained) determined by systematic random sampling and CaSR expression as grey scale values of staining intensity in arbitrary units determined by image analysis.

RESULTS

The mean (SD) proportion of cells positive for VDR was 2.93 (2.17)% in the parathyroid adenomas and 95.7 (5.10)% in the nonadenomatous tissue. In about two-thirds of the cases VDR positive cells could have been remnants of a normal gland, but in the remaining one-third they were too numerous to be accounted for by this explanation. The mean (SD) intensity of CaSR expression was 151 (4.71) units in parathyroid adenomas and 218 (5.0) units in nonadenomatous tissue (P<0.001). The frequency of VDR loss and the changes in CaSR immunohistochemistry were unrelated to race, sex, or disease severity, except that the reduction in CaSR was significantly greater in patients with normal vitamin D nutrition (32.1% vs. 29.0%).

CONCLUSIONS

(1) There is reduction of vitamin D receptor expression in almost all cells in parathyroid adenomas. This defect was probably present in the founder cell of the tumour clone in the majority of cases. Since mutations in the vitamin D receptor gene have been sought but not found, possible explanations include inhibition of vitamin D receptor gene transcription, decreased amount of the corresponding mRNA, or failure of normal translation. (2) Reduction in calcium sensing receptor could be either the primary defect or (more commonly) secondary to loss of vitamin D receptor and is of sufficient magnitude to account for the increase in secretory set-point and consequent asymptotic growth and stable clinical course.

Bone mineral density (BMD) in obesity effect of weight loss

It is generally believed that bone mineral density (BMD) is increased in obese subjects, but the effect of weight loss on BMD has not been well studied. Therefore, we evaluated BMD among 11 obese women (mean age 45.5 +/- 14.2 years) before and after weight loss achieved by ingesting an 800 calorie diet for 12 weeks. BMD measurements were made at baseline, 6 months and 1 year intervals. Urinary hydroxyproline:creatinine (H:Cr), calcium:creatinine (Ca:Cr) ratios were measured as indices of bone turnover. Mean weight at baseline was 103.8 +/- 15.8 kg and decreased to 83.2 +/- 12.2 at six months and was 85.8 +/- 14.2 kg at one year. Total body, hip and lumbar spine BMD were 1.12 +/- 0.07, .87 +/- 0.11, and 1.02 +/- 0.12 gm/cm2, respectively. Total body BMD was significantly lower at 12 months compared to baseline. No significant change was observed in BMD of the lumbar spine. There was also a significant decrease in hip BMD at six months and 12 months compared to baseline. H:Cr and Ca:Cr ratios did not change over time. We conclude that weight loss achieved by VLCD is accompanied by a statistically significant change in BMD, but the BMD remained in the normal range.

A validated LC method for the quantitative determination of celecoxib in pharmaceutical dosage forms and purity evaluation in bulk drugs

A new reversed-phase, isocratic LC method was developed for the quantitative determination of COX-2 inhibitor celecoxib in bulk drugs and in pharmaceutical dosages. The proposed method is also applicable for the purity evaluation of celecoxib in bulk drugs. 5-Methyl 2-Nitro phenol has been used as internal standard for the quantitative determination of celecoxib. The method has been completely validated and proven to be rugged. The limit of detection (LOD) and limit of quantitation (LOQ) for celecoxib impurities namely, 4-hydrazino benzene sulfonamide (Intermediate I) and 1-(4-methyl phenyl)-4,4.4-trifluro butan-1,3-dione (Intermediate II) were found to be 32.0 and 97 ng. respectively. The active pharmaceutical ingredient was extracted from its finished dosage form (capsule) using methanol. The percentage recoveries ranged from 90.7 to 93.8. The stability studies were performed for celecoxib solution placed on laboratory bench and in refrigerator for hundred days. The samples were found to be stable for the study period.

Synthesis and biological activities of the two C(23) epimers of 1alpha,23,25-trihydroxy-24-oxo-19-nor-vitamin D(3): novel analogs of 1alpha,23(S),25-trihydroxy-24-oxo-vitamin D(3), a natural metabolite of 1alpha,25-dihydroxyvitamin D(3)

In a previous report, we indicated that 1alpha,23(S), 25-trihydroxy-24-oxovitamin D(3) [1alpha,23(S), 25(OH)(3)-24-oxo-D(3)], a natural metabolite of 1alpha, 25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] is almost equipotent to 1alpha,25(OH)(2)D(3) in suppressing parathyroid hormone (PTH) secretion (Lee et al., 1997. Biochemistry 36, 9429-9437). Also, 1alpha,23(S),25(OH)(3)-24-oxo-D(3) has been shown to possess only weak in vivo calcemic actions. Thus, vitamin D(3) analogs structurally related to 1alpha,23(S),25(OH)(3)-24-oxo-D(3) may have therapeutic value. Furthermore, biologic activity studies of various synthetic analogs of 1alpha,25(OH)(2)D(3) showed that the removal of carbon-19 (C-19) reduces the calcemic activity of 1alpha, 25(OH)(2)D(3.) Therefore, in an attempt to produce vitamin D(3) analogs with a better therapeutic index, we synthesized C(23) epimers of 1alpha,23,25(OH)(3)-24-oxo-19-nor-vitamin D(3) [1alpha,23, 25(OH)(3)-24-oxo-19-nor-D(3)]. The two epimers were compared to 1alpha,25(OH)(2)-19-nor-D(3) and 1alpha,25(OH)(2)D(3) in their ability to generate biologic activities in several in vitro assay systems. In the assay measuring the suppression of parathyroid hormone (PTH) secretion in bovine parathyroid cells, 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3) was as potent as 1alpha, 25(OH)(2)-19-nor-D(3) but was less potent than 1alpha,25(OH)(2)D(3). In the same assay 1alpha,23(R),25(OH)(3)-24-oxo-19-nor-D(3) exhibited greater potency than 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3). In the assays measuring the ability of vitamin D compounds to inhibit clonal growth and to induce differentiation of human promyelocytic leukemia (HL-60) cells, 1alpha,23(S),25(OH)(3)-24-oxo-19-nor-D(3) was less potent than 1alpha,25(OH)(2)-19-nor-D(3) but was equipotent to 1alpha, 25(OH)(2)D(3). More importantly, in the same assays, 1alpha,23(R), 25(OH)(3)-24-oxo-19-nor-D(3) was more potent than 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3) and was equipotent to 1alpha, 25(OH)(2)-19-nor-D(3). Also, the vitamin D receptor-mediated transcriptional activity of 1alpha,23(R), 25(OH)(3)-24-oxo-19-nor-D(3) was almost equal to that of 1alpha, 25(OH)(2)-19-nor-D(3), but higher than that of 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3). This finding explains in part the greater in vitro biologic activities of 1alpha,23(R), 25(OH)(3)-24-oxo-19-nor-D(3). In summary, our results indicate that 1alpha,23(R),25(OH)(3)-24-oxo-19-nor-D(3) and to a lesser extent 1alpha,23(S),25(OH)(3)-24-oxo-19-nor-D(3) are potent 19-nor vitamin D(3) analogs, which suppress PTH secretion in bovine parathyroid cells and strongly inhibit clonal growth and induce differentiation of HL-60 cells in vitro.

LC method for the quantitative determination of oxaprozin and its impurities in the bulk drug

A reversed phase linear gradient liquid chromatographic method was developed for the separation and quantitative determination of the seven known process related impurities and one degraded product of oxaprozin in the bulk drug material. An Inertsil-ODS 3V (150 x 4.6 mm), 5 microm column was operated with a phosphate buffer acetonitrile gradient. Detection was carried out on a UV detector at 254 nm. This method has been proved to be accurate and sensitive. The limits of detection (LOD) and limits of quantification (LOQ) of impurities were in the order of 5-60 ng and 16-200 ng, respectively. In addition to its ruggedness and robustness, this method offers identification of all eight impurities in a single run.

LC method for the determination of assay and purity of sibutramine hydrochloride and its enantiomers by chiral chromatography

Two isocratic liquid chromatography (LC) methods have been developed for the purity estimation and quantitative determination of sibutramine HCl, using 4-chloro aniline and lovastatin as internal standards, respectively. The precision has been checked in terms of F-test variance ratio using latter method as reference. The ratio of variances of the two methods is close to unity, confirming their good precision. The correlation coefficient for linear regression is more than 0.999. The inter and intra-day precision is found to be < 1.3% RSD. The accuracy determined as relative mean error (RME) for the intra-day assay is +/- 1.7%. The enantiomeric separation of sibutramine by chiral chromatography method has been described also. This method is capable of separating the two enantiomers with a selectivity of 1.4 and a resolution of 4.0. Both methods are found to be stability indicating and useful in the quality control of the bulk material.

A validated method for the determination and purity evaluation of benazepril hydrochloride in bulk and in pharmaceutical dosage forms by liquid chromatography

A gradient liquid chromatographic (LC) method has been developed for the determination and purity evaluation of benazepril hydrochloride in bulk and pharmaceutical dosage forms. The method is simple, rapid and selective. 5-Methyl-2-nitro phenol has been used as internal standard. The method is linear in the range of 50-800 microg. The precision for inter and intra-day assay variation of benazepril hydrochloride is below 1.6% RSD. The accuracy determined as relative mean error (RME) for the intra-day assay is within +/- 2.0%. The method is stability indicating, and is useful in the quality control of bulk manufacturing and also in pharmaceutical formulations.

Effect of vitamin D nutrition on parathyroid adenoma weight: pathogenetic and clinical implications

In primary hyperparathyroidism, adenoma size is a major determinant of disease severity and manner of presentation, but the reason for the large variation in size (>100-fold) is unknown. One factor could be the level of vitamin D nutrition, because in India, where vitamin D deficiency is endemic, adenomas are larger and the disease more severe than in the U.S. Accordingly, we determined the relationship between vitamin D nutrition, as measured by serum levels of 25-hydroxyvitamin D (25OHD), and parathyroid gland weight, expressed on a logarithmic scale, in 148 U.S. patients with primary hyperparathyroidism. A significant inverse relationship was found between log gland weight as dependent variable and serum 25OHD as independent variable (r = -0.365; P < 0.0001). The only other influence on gland weight was a weak inverse correlation with age. Log gland weight as an independent variable was significantly related to adjusted calcium, PTH, and alkaline phosphatase (AP) as dependent variables. In 51 patients with serum 25OHD levels less than 15 ng/mL, gland weight, PTH, AP, and adjusted calcium were each significantly higher than in 97 patients with 25OHD levels of 15 ng/mL or more, but 1,25-dihydroxyvitamin D levels were similarly increased in both groups. In the former group the response of adjusted calcium to PTH was blunted, and the response of AP was enhanced, based on significant differences in regression slopes (P = 0.0004 and 0.0022, respectively). Suboptimal vitamin D nutrition stimulates parathyroid adenoma growth by a mechanism unrelated to hypocalcemia or 1,25-dihydroxyvitamin D deficiency and reduces the calcemic response to PTH, so that a higher PTH level and more parathyroid cells are needed to raise the patient's serum calcium to the level corresponding to the increased set-point that is characteristic of the disease. Improved vitamin D nutrition in the population is partly, perhaps largely, responsible for the historical changes in disease severity and manner of presentation that have occurred over the last 50 yr.

Osteomalacia due to vitamin D depletion: a neglected consequence of intestinal malabsorption

PURPOSE

Osteomalacia due to vitamin D depletion is believed to be rare in the United States because of the routine fortification of milk and other dairy products with vitamin D. We present a series of patients with histologically verified osteomalacia due to vitamin D depletion to emphasize the need for more careful and systematic surveillance of patients at risk of this metabolic bone disease.

METHODS

Between 1989 and 1994, 17 patients with osteomalacia due to vitamin D depletion were seen in the Bone and Mineral Division of Henry Ford Health System, Detroit. All patients had a transiliac bone biopsy after in vivo double tetracycline labeling. Biochemical indexes of vitamin D nutritional status, parathyroid function, markers of bone turnover, and bone mineral density were assessed at the time of bone biopsy. The duration of symptoms, the lag between the cause of vitamin D depletion and the development of symptoms, and the radiologic findings were recorded.

RESULTS

Osteomalacia was suspected by the referring physician in only 4 of the 17 patients, although a gastrointestinal disorder that can lead to vitamin D depletion was present in every patient. Thirteen of the patients had sustained at least one osteoporotic fracture (wrist, spine, or hip), and most had low appendicular and axial bone mineral density. All patients had one or more biochemical abnormalities consistent with vitamin D depletion. In 4 patients, a progressive rise in the serum alkaline phosphatase level was recorded but was not investigated until the patient presented with bone pain, muscle weakness, or fracture.

CONCLUSIONS

Osteomalacia due to vitamin D depletion appears not to be suspected or diagnosed promptly in susceptible patients, perhaps because their physicians were not sufficiently aware of this condition.

Is there a difference between right and left femoral bone density?

Because of the known differences in bone mineral density (BMD) of the dominant and nondominant forearms, it has been customary to measure BMD of the nondominant forearm to reduce variance. However, it is less clear whether such systematic differences exist between BMD of the two hips. Accordingly, we measured BMD of both hips and the spine in 131 consecutive white women who presented to a community based private practitioner for evaluation and advice on osteoporosis. There was a highly significant correlation between BMD of the two hips at the femoral neck, trochanter, and Ward's triangle (r = 0.91, 0.93, and 0.89; p < 0.0001 for all three sites), and also between BMD at various measurement sites in the hip and the spine BMD (p < 0.0001). Although, there was no significant difference between the right and left femoral neck BMD, there were small (approximately 1-2.5%) but significant differences between BMD of the two hips at the trochanter and Ward's triangle (p = 0.008 and 0. 005, respectively). The left hip BMD was consistently higher than the right hip BMD at all measurement sites. Because of the small sample size of the left-handed persons, we were unable to determine the influence of dominant handedness on hip BMD. We concluded the following: (1) BMDs of the two hips are highly correlated at relevant measurement sites; (2) there does not appear to be a dominant hip as there is dominant forearm; (3) because of strong agreement between BMD of the two hips there is little justification to measure both hips in routine clinical practice.

Isolation and identification of 1alpha-hydroxy-24-oxovitamin D3 and 1alpha,23-dihydroxy-24-oxovitamin D3: metabolites of 1alpha,24(R)-dihydroxyvitamin D3 produced in rat kidney

1alpha,24(R)-Dihydroxyvitamin D3 [1alpha,24(R)(OH)2D3], a synthetic vitamin D3 analog, has been developed as a drug for topical use in the treatment of psoriasis. At present, the target tissue metabolism of 1alpha,24(R)(OH)2D3 is not understood completely. In our present study, we investigated the metabolism of 1alpha,24(R)(OH)2D3 in the isolated perfused rat kidney. The results indicated that 1alpha,24(R)(OH)2D3 is metabolized in rat kidney into several metabolites, of which 1alpha,24(R),25-trihydroxyvitamin D3, 1alpha,25-dihydroxy-24-oxovitamin D3, 1alpha,23(S),25-trihydroxy-24-oxovitamin D3, and 1alpha,23-dihydroxy-24,25,26,27-tetranorvitamin D3 are similar to the previously known metabolites of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3]. In addition to these aforementioned metabolites, we also identified two new metabolites, namely 1alpha-hydroxy-24-oxovitamin D3 and 1alpha,23-dihydroxy-24-oxovitamin D3. The two new metabolites do not possess the C-25 hydroxyl group. Thus, the metabolism of 1alpha,24(R)(OH)2D3 into both 25-hydroxylated and non-25-hydroxylated metabolites suggests that 1alpha,24(R)(OH)2D3 is metabolized in the rat kidney through two pathways. The first pathway is initiated by C-25 hydroxylation and proceeds further via the C-24 oxidation pathway. The second pathway directly proceeds via the C-24 oxidation pathway without prior hydroxylation at the C-25 position. Furthermore, we demonstrated that rat kidney did not convert 1alpha-hydroxyvitamin D3 [1alpha(OH)D3] into 1alpha,25(OH)2D3. This finding indicates that the rat kidney does not possess the classical vitamin D3-25-hydroxylase (CYP27) activity. However, from our present study it is apparent that prior hydroxylation of 1alpha(OH)D3 at the C-24 position in the 'R' orientation allows 25-hydroxylation to occur. At present, the enzyme responsible for the C-25 hydroxylation of 1alpha,24(R)(OH)2D3 is unknown. Our observation that the side chain of 1alpha,24(R)(OH)2D3 underwent 24-ketonization and 23-hydroxylation even in the absence of the C-25 hydroxyl group suggests that 1alpha,25(OH)2D3-24-hydroxylase (CYP24) can perform some steps of the C-24 oxidation pathway without prior C-25 hydroxylation. Thus, we speculate that CYP24 may be playing a dual role in the metabolism of 1alpha,24(R)(OH)2D3.

Meta-analysis of calcium bioavailability: a comparison of calcium citrate with calcium carbonate

OBJECTIVE

To perform a meta-analysis of data from available published trials comparing the bioavailability of calcium carbonate with that of calcium citrate.

DATA SOURCES

The whole set was comprised of 15 studies involving 184 subjects who underwent measurement of calcium absorption from calcium carbonate and calcium citrate. Category A excluded four studies for lack of physiological relevance, use of a mixed preparation with low content of calcium carbonate, or wide variability in results. Category B was comprised of five studies (from Category A) involving 71 subjects who took calcium supplements on an empty stomach. Category C was comprised of six studies (from Category A) involving 65 subjects who took calcium preparations with meals.

METHOD

The meta-analysis of calcium absorption data from calcium carbonate and calcium citrate, with calculation of effect size and 95% confidence intervals.

RESULTS

Calcium absorption from calcium citrate was consistently significantly higher than that from calcium carbonate by 20.0% in the whole set, by 24.0% in Category A, by 27.2% on an empty stomach, and by 21.6% with meals.

CONCLUSION

Calcium citrate is better absorbed than calcium carbonate by approximately 22% to 27%, either on an empty stomach or co-administered with meals.

Isolation and identification of 4,25-dihydroxyvitamin D2: a novel A-ring hydroxylated metabolite of vitamin D2

Vitamin D2 is less toxic in rats when compared to vitamin D3. Our laboratory has been involved in research projects which were directed towards identifying the possible mechanisms responsible for the toxicity differences between vitamins D2 and D3 in rats. The present research project was designed to isolate and identify new metabolites of vitamin D2 from serum of rats which were fed toxic doses of vitamin D2. Hypervitaminosis D2 was induced in 30 rats by feeding each rat with 1000 nmol of vitamin D2/day x 14 days. The rats were sacrificed on the 15th day and obtained 180 ml of serum. The lipid extract of the serum was directly analyzed by a straight phase HPLC system. The various vitamin D2 metabolites were monitored by their ultraviolet (UV) absorbance at 254 nm. One of the UV absorbing peaks did not comigrate with any of the known vitamin D2 metabolites. This unknown metabolite peak was further purified by HPLC and was then subjected to UV absorption spectrophotometry and mass spectrometry. The structure assignment of the new metabolite was established to be 4,25-dihydroxyvitamin D2 [4,25(OH)2D2] by the techniques of UV absorption spectrophotometry and mass spectrometry and by the new metabolite's susceptibility to sodium metaperiodate oxidation. At present the biological activity of this unique 'A-ring' hydroxylated vitamin D2 metabolite is not known. As this new metabolite is isolated from the serum of rats intoxicated with vitamin D2, we speculate that 4,25(OH)2D2 may be playing an important role in the deactivation of vitamin D2.

Calcitropic hormonal status in north Indian patients with end-stage renal disease

BACKGROUND

Bone disease in chronic renal failure has a wide spectrum that includes both high and low turnover conditions. Specific preventive and therapeutic measures require knowledge of the nature of bone involvement. Bone biopsy with static and dynamic histomorphometry is the gold standard for characterization of renal bone disease. However, non-invasive biochemical tests, especially serum intact parathyroid hormone (PTH), have a good correlation with histomorphometry. We studied the clinical and biochemical profile of bone disease in a sample of north Indian patients with chronic renal failure.

METHODS

Twenty-nine patients of chronic renal failure were evaluated clinically, radiologically (subperiosteal erosions on hand X-rays) and biochemically (serum calcium, phosphorus, total alkaline phosphatase, intact PTH, osteocalcin, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D). Bone histomorphometry could be done in 4 patients.

RESULTS

Serum intact PTH within or below the non-uraemic normal range, an index of low bone turnover, was seen in 17 (58.6%) patients. Serum osteocalcin, a bone formation marker, was within or below the non-uraemic normal range in 65.5% patients. Serum intact PTH and osteocalcin had a significant positive correlation (r = 0.6). Patient groups with clinical or radiological evidence of bone disease had serum intact PTH and osteocalcin levels comparable to those lacking such features. Serum intact PTH and total alkaline phosphatase were lower in haemodialysed (n = 25) patients than in those who had not received haemodialysis (n = 4). Low (< 10 ng/ml) serum 25-hydroxyvitamin D levels were seen in 7 (24%) patients while 1,25-dihydroxyvitamin D was low (< 15.9 pg/ml) in 20 (69%) patients. The biochemical parameters accurately reflected the bone histology (n = 4).

CONCLUSIONS

Our data show that the majority of north Indian patients with chronic renal failure have biochemical evidence of low bone turnover. Empirical use of calcium salts and active vitamin D analogues without documentation of parathyroid status carry the risk of further suppression of bone turnover.

In vitro cytotoxicity of 5-aminosubstituted 20(S)-camptothecins. Part 1

A number of 5-aminosubstituted 20(S)-camptothecin analogues were prepared via semi-synthesis starting from 20(S)-camptothecin and 9-methoxy 20(S)-camptothecin. In vitro anti-cancer activity of these analogues was determined using 60 human tumor cell line assay. Although water solubility of most of these compounds was improved compared to 20(S)-camptothecin, their anti-cancer activity was considerably diminished. However, only smaller substituents such as methylamine or hydroxylamine as present in 8s and 8t, respectively, showed good activity with improved water solubility.

Physiological significance of C-28 hydroxylation in the metabolism of 1alpha,25-dihydroxyvitamin D(2)

In our previous study, we indicated for the first time that C-28 hydroxylation plays a significant role in the metabolism of 1alpha, 25-dihydroxyvitamin D(2) [1alpha,25(OH)(2)D(2)] by identifying 1alpha,24(S),25,28-tetrahydroxyvitamin D(2) [1alpha,24(S),25, 28(OH)(4)D(2)] as a major renal metabolite of 1alpha,25(OH)(2)D(2) [G. S. Reddy and K-Y. Tserng Biochemistry 25, 5328-5336, 1986]. The present study was performed to establish the physiological significance of C-28 hydroxylation in the metabolism of 1alpha, 25(OH)(2)D(2). We perfused rat kidneys in vitro with 1alpha, 25(OH)(2)[26,27-(3)H]D(2) (5 x 10(-10)M) and demonstrated that 1alpha,24(R),25-trihydroxyvitamin D(2) [1alpha,24(R),25(OH)(3)D(2)] and 1alpha,24(S),25,28(OH)(4)D(2) are the only two major physiological metabolites of 1alpha,25(OH)(2)D(2). In the same perfusion experiments, we also noted that there is no conversion of 1alpha,25(OH)(2)D(2) into 1alpha,25,28-trihydroxyvitamin D(2 )[1alpha,25,28(OH)(3)D(2)]. Moreover, 1alpha,24(S),25,28(OH)(4)D(2) is not formed in the perfused rat kidney when synthetic 1alpha,25, 28(OH)(3)D(2) is used as the starting substrate. This finding indicates that C-28 hydroxylation of 1alpha,25(OH)(2)D(2) occurs only after 1alpha,25(OH)(2)D(2) is hydroxylated at C-24 position. At present the enzyme responsible for the C-28 hydroxylation of 1alpha, 24(R),25(OH)(3)D(2) in rat kidney is not known. Recently, it was found that 1alpha,25(OH)(2)D(3)-24-hydroxylase (CYP24) can hydroxylate carbons 23, 24, and 26 of various vitamin D(3) compounds. Thus, it may be speculated that CYP24 may also be responsible for the C-28 hydroxylation of 1alpha,24(R),25(OH)(3)D(2) to form 1alpha, 24(S),25,28(OH)(4)D(2). The biological activity of 1alpha,24(S),25, 28(OH)(4)D(2), determined by its ability to induce intestinal calcium transport and bone calcium resorption in the rat, was found to be almost negligible. Also, 1alpha,24(S),25,28(OH)(4)D(2) exhibited very low binding affinity toward bovine thymus vitamin D receptor. These studies firmly establish that C-28 hydroxylation is an important enzymatic reaction involved in the inactivation of 1alpha,25(OH)(2)D(2) in kidney under physiological conditions.

Routine screening for HIV and hepatitis B in patients undergoing cardiac catheterisation: the need to make it mandatory

Reuse of catheters during cardiac catheterisation and interventions is a routine practice in our country. However, the reuse of catheters is complicated by the inherent difficulties in adequate sterilisation of these devices. Gas sterilisation with ethylene oxide has been found to be ineffective when residual fluid was present. Recent reports indicate an increased prevalence of blood-borne viral infections especially Hepatitis B virus and Human Immunodeficiency virus in India. We analysed the data of patients from our Institute over the past seven years (1992-1998) who underwent routine screening for Human Immunodeficiency virus and Hepatitis B virus prior to cardiac catheterisation. During this period, the prevalence of Hepatitis B virus increased by 1.5 times and that of Human Immunodeficiency virus by 2.5 fold. In this changed scenario, it is advisable to perform a mandatory screening of all the patients undergoing invasive cardiac procedures so as to minimise the risk of transmission from one patient to another and also to the catheterisation laboratory personnel. In the patients with a positive result, proper precautions can be taken and the entire material used for cardiac catheterisation can be discarded.

Dielectric and high-pressure investigations on a thermotropic cubic mesophase

Optically isotropic cubic mesophases, which are commonly exhibited by lyotropic materials, have been observed in a few thermotropic liquid crystalline systems also. Although the first thermotropic cubic mesophase was reported about 40 years ago, its existence in diverse systems is only a recent finding. Moreover, the investigations on this mesophase have mainly concentrated on the structural aspects. While the effect of pressure has not been reported, only one dielectric measurement seems to have been carried out. In this paper we present the results of our dielectric and high pressure investigations on a compound exhibiting a thermotropic cubic mesophase. Two salient results are (i) a low frequency relaxation mode is observed with a large dielectric strength with appreciable changes across the columnar-cubic and cubic-smectic C transitions; and (ii) the cubic phase ceases to exist when the applied pressure exceeds about 400 bar.

Perspective on assessment of vitamin D nutrition

Although routine fortification of milk and a few other dairy products has been successful in preventing rickets in children, its impact on preventing vitamin D depletion in adults is less than satisfactory. The prevalence of vitamin D depletion in the elderly is on the rise again and appears to be more common than is currently appreciated. Several groups of individuals are at risk of developing vitamin D depletion, and a significant minority of otherwise healthy individuals is vitamin D insufficient. Unrecognized vitamin D depletion leads to secondary hyperparathyroidism, accelerates cortical bone loss, and increases the risk of hip fractures. With the availability of techniques to assess vitamin D nutrition, it is probably cost effective to routinely measure 25-hydroxyvitamin D levels in individuals at the greatest risk and in patients with various metabolic bone diseases to prevent vitamin D depletion. Early recognition and prompt treatment of vitamin D depletion improves functional well being of the individual, reduces morbidity related to bone loss and fractures, and is associated with a highly favorable cost/benefit ratio.