Potentiating effects of nonactive/active vitamin D analogues and ketoconazole in parathyroid cells.
OBJECTIVE
1,25-dihydroxyvitamin D(3)[1alpha,25(OH)(2)D(3), calcitriol], and its less calcaemic synthetic analogues have therapeutic potential in several diseases, including hyperparathyroidism (HPT). We have suggested that non-1alpha-hydroxylated (nonactive) vitamin D analogues may present an alternative in tumour cells expressing 25-hydroxyvitamin D(3) 1alpha-hydroxylase (1alpha-hydroxylase). The aim of this study was to investigate biological effects of a non-1alpha-hydroxylated vitamin D analogue in normal and tumour parathyroid cells.


METHODS
Effects of vitamin D analogues and ketoconazole on parathyroid hormone (PTH) secretion (radioimmunoassay) and PTH mRNA expression (reverse transcription-polymerase chain reaction) were studied in primary bovine parathyroid cells. Proliferation of tumour cells isolated from HPT patients was determined by thymidine incorporation.


RESULTS
EB1285, non-1alpha-hydroxylated precursor of the vitamin D analogue EB1089, suppressed PTH secretion and PTH mRNA level as well as increased expression of 25-hydroxyvitamin D(3)-24-hydroxylase (24-hydroxylase) in bovine parathyroid cells. EB1285 also inhibited cell proliferation of parathyroid tumour cells from primary (pHPT) and secondary HPT (sHPT) patients. Combined treatment with the cytochrome P450-dependent enzyme inhibitor ketoconazole and EB1285 or with active vitamin D compounds potentiated the suppressive effect on PTH secretion from bovine parathyroid cells. Ketaconazole alone displayed PTH suppression and increased 24-hydroxylase expression.


CONCLUSIONS
The results support the idea that a non-1alpha-hydroxylated vitamin D analogue may elicit vitamin D receptor (VDR) effects in 1alpha-hydroxylase expressing parathyroid tumour cells. Further studies are warranted to elucidate whether precursor vitamin D analogues as well as inhibitors of 24-hydroxylase present therapeutic alternatives in patients suffering from HPT.
Segersten
Ulrika
U
Department of Surgical Sciences, Endocrine Unit, Uppsala University Hospital, Sweden.
Björklund
Peyman
P
Hellman
Per
P
Akerström
Göran
G
Westin
Gunnar
G
D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000037:antagonists & inhibitors*; D000818:Animals; D002417:Cattle; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003864:Depression, Chemical; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007150:Immunohistochemistry; D007654:Ketoconazole / Q000494:pharmacology*; D010280:Parathyroid Glands / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000235:genetics / Q000378:metabolism*; D010282:Parathyroid Neoplasms / Q000378:metabolism*; D011355:Prodrugs / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D018167:Receptors, Calcitriol / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013250:Steroid Hydroxylases / Q000032:analysis / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000494:pharmacology*; D065668:Vitamin D3 24-Hydroxylase
D004791:Enzyme Inhibitors; D010281:Parathyroid Hormone; D011355:Prodrugs; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D014807:Vitamin D; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D007654:Ketoconazole