No abstract

Metabolism, excretion, and tissue distribution of [uC]photodieldrin were studied in male rabbits following single oral and intraperitoneal treatments. About 55 to 60% of the administered dose was eliminated in the urine and 1 to 3% was excreted in the feces, in 9 days, in oral or intraperitoneal treated rabbits. Less than 1% radioactivity of urine and feces was extractable in the organic phase showing that most of it was water soluble or conjugated in nature. All 23 tissue samples obtained at autopsy, 9 days after the treatment, showed a minimum of 0.001% of the given dose. Higher concentrations of 14C residues were found in fat followed by liver and then other tissues. Relatively higher concentrations of residues were present in tissues of intraperitoneally treated animals. Analysis of the organic extract of the urine, feces, and liver by TLC showed the presence of seven metabolites along with photodieldrin. Kidney extracts showed, along with photodieldrin, only two of the metabolites detected in urine, feces, and liver. Quantitative analyses of watersoluble and conjugated radioactive photodieldrin or its metabolites, present in the urine, feces, liver, and kidney, were performed after their enzyme and acid hydrolysis.

1 alpha, 25-Dihydroxyvitamin D3 [1 alpha, 25-(OH)2D3], the hormonal form of vitamin D3, is further metabolized in the kidney and intestine through the carbon 24 (C-24) oxidation pathway initiated by C-24 hydroxylation, and the carbon 23 (C-23) oxidation pathway initiated by C-23 hydroxylation. The C-24 oxidation pathway leading to the formation of calcitroic acid has been previously reported to be present in bone cells, but the C-23 oxidation pathway leading to the formation of 1 alpha, 25-(OH)2D3-26,23-lactone has not been described in bone cells, even though 1 alpha, 25-(OH)2D3-26,23-lactone is noted to have a significant effect on bone formation. Therefore, in the present study, we investigated the production of 1 alpha, 25-(OH)2D3-26,23-lactone in normal human osteoblasts, and our studies revealed that human osteoblasts possess the activity of both 24- and 23-hydroxylases constitutively. Thus, 1 alpha, 24(R),25-(OH)3D3, 1 alpha, 25-(OH)2-24-oxo-D3, 1 alpha, 23(S), 25-(OH)3-24-oxo-D3, 1 alpha, 23-(OH)2-24,25,26,27-tetranor D3, and calcitroic acid formed through the C-24 oxidation pathway and 1 alpha, 23(S),25-(OH)3D3 and 1 alpha, 25-(OH)2D3-26,23-lactone formed through the C-23 oxidation pathway were detected under basal conditions. Also, the synthesis of these metabolites was increased significantly when the cells were treated with 1 alpha, 25-(OH)2D3 (50 nM) for 24 h before incubation with the tracer. As 25-hydroxyvitamin D3 (25OHD3) follows similar side-chain modifications as 1 alpha, 25-(OH)2D3, the metabolism of 25OHD3 in normal human osteoblasts was studied under basal conditions. We found that 25OHD3 was also metabolized through both C-24 and C-23 oxidation pathways, resulting in significant synthesis of 24(R),25-(OH)2D3 along with 25OH-24-oxo-D3, 23(S),25-(OH)2-24-oxo-D3, 23(S),25-(OH)2D3, and 25OHD3-26,23-lactone. Under the same experimental conditions, we looked for 1 alpha, 25-(OH)2D3 synthesis, as earlier studies have shown production of 1 alpha, 25-(OH)2D3 in human bone cells. During a time-course study ranging from 1-24 h, we found that by 2 h, the 24(R), 25-(OH)2D3 concentration rose and accumulated considerably during the following 24 h, but 1 alpha, 25-(OH)2D3 did not accumulate at any time. However, other 1-hydroxylated metabolites, 1 alpha, 23(S),25-(OH)3D3, 1 alpha, 23(S),25-(OH)3-24-oxo-D3, as well as 1 alpha, 25-(OH)2D3-26,23-lactone were detected.(ABSTRACT TRUNCATED AT 400 WORDS)

Recent evidence suggests that the bone anabolic effects of the active hormone 1a, 25(OH) 2 D 3 ] are mediated via a direct action on cells of the osteoblastic lineage.1) In a number of studies, however, the doses required for anabolic effects were associated with toxicity due to hypercalcaemia and hypercalciuria.2,3) Previous studies have reported the syntheses of a number of analogs of 1a,25(OH) 2 D 3 , and these analogs can mimic the effects of the parent compound without causing hypercalcaemia.4) As such, these analogs may prove to be useful as potential therapeutic agents for the treatment for osteoporosis 5,6) and other metabolic bone diseases associated with bone loss. 7)The mechanisms of action of 1a,25(OH) 2 D 3 are far from clear although its effects on osteoblastic function have been well-documented. 4,8) Briefly, 1a,25(OH) 2 D 3 has been shown to affect alkaline phosphatase (ALP) activity, 9-13) the production, 14,15) and gene expression 16,17) of osteocalcin (OC) and insulin-like growth factor-1, 18,19) cell proliferation, 9,20) collagen synthesis 9,21,22) and expression, 16,17) parathyroid hormone (PTH)-stimulated adenylate cyclase activity, 8,23) as well as the regulation of its own receptor levels.14,24-26) The effects of 1a,25(OH) 2 D 3 have been reported to be dependent upon the stage of osteoblast maturation. 8,10,12,13) On the other hand, while the actions of several analogs have been well documented on calcium mobilization in mice or chicks 4,27) and on cell differentiation and proliferation in leukemic, 28,29) prostate, 30) and breast cancer 31) cells and human retinoblastoma tumors, 32) little is known of its effects on bone cells including the bone-forming osteoblasts. We recently showed that differences exist in the actions of 1a,25(OH) 2 D 3 and the analog 1a,25(OH) 2 -16-ene-23-yne-D 3 in the osteosarcoma SaOS-2 cells. 33) In the present report, our objective was to investigate the actions of another analog, 1a,25(OH) 2 -16-ene-D 3 , on osteoblast function. In addition, we wanted to compare its effects with those of the parent compound and their modulation by 17b -estradiol (E 2 ) in our two human cell models representing two stages of differentiation, the more differentiated cells grown in the presence of dexamethasone (DEX), the normal human osteoblasts HOBϩDEX and osteosarcoma SaOSϩDEX cells, and the corresponding less differentiated cells grown in the absence of DEX, the HOB-DEX and SaOS-DEX cells.