Effect of 1,24R‐dihydroxyvitamin D₃ on the Growth of Human Keratinocytes

Abstract

The effect of 1,24R-dihydroxyvitamin D3 (1,24R(OH)2D3), a synthetic analogue of a biologically active form of vitamin D3 (1,25-dihydroxyvitamin D3, 1,25(OH)2D3), on the growth of human keratinocytes cultured in serum-free medium was investigated. The growth of cultured normal human keratinocytes was inhibited by 65% by 10(-8)M 1,24R(OH)2D3 and by 90% by 10(-7)M 1,24(OH)2D3. It inhibited cell growth almost completely at 10(-6)M. The DNA synthesis of keratinocytes was also inhibited with 1,24R(OH)2D3 by 27% at 10(-8)M, 59% at 10(-7)M, and 92% at 10(-6)M. The inhibition of cell growth and DNA synthesis were more remarkable by 1,24R(OH)2D3 than by 1,25(OH)2D3. 1,24R(OH)2D3 also inhibited the growth of keratinocytes derived from patients with psoriasis vulgaris; the growth inhibitory effect was again more remarkable with 1,24R(OH)2D3 than with 1,25(OH)2D3. The viability and protein synthesis of keratinocytes were not affected by 1,24R(OH)2D3, suggesting that the growth inhibitory effect is due to its biological activity, not to cytotoxicity. The binding of [3H]-labeled 1,25(OH)2D3 to its receptor in the cytosolic fraction of cultured keratinocytes was competitively substituted by unlabeled 1,24R(OH)2D3 as well as 1,25(OH)2D3, suggesting that 1,24R(OH)2D3 binds to the 1,25(OH)2D3 receptor. It was found that the affinity of 1,24R(OH)2D3 for the receptor was slightly higher than that of 1,25(OH)2D3. These results demonstrate that 1,24R(OH)2D3 functions as a potent growth inhibitor in vitro in human keratinocytes from both normal and psoriatic epidermis, and it possesses a higher affinity for the 1,25(OH)2D3 receptor in cultured human keratinocytes. The difference in affinity of 1,24R(OH)2D3 for the 1,25(OH)2D3 receptor correlates with its greater inhibition of keratinocyte growth than 1,25(OH)2D3. 1,24R(OH)2D3 may be useful in the treatment of psoriasis.

Influence of Tacalcitol on Cell Cycle Kinetics of Human Keratinocytes following Standardized Injury

“…This is in contrast with studies which showed that tacalcitol affects keratinization to some extent [2,7,24]. However, most authors conclude that the effect of tacalcitol on differentiation is limited [4,6,8].…”

“…Several in vitro and in vivo studies showed the effect of tacalcitol on epidermal proliferation and differentiation, and the effect on inflammatory processes in skin [2][3][4][5][6][7][8]. Especially the effect on epidermal proliferation has shown to be most substantial [2,6,7]. This finding strongly suggests that the antipsoriatic effect of tacalcitol may be mediated by the normalization of epidermal cell cycle kinetics.…”

Transcriptional activation of the wild-type and mutant vitamin D receptors by vitamin D3 analogs

“…For maxacalcitol, the affinity is slightly weaker than that of calcitriol (Valaja et al 1990) and is almost the same as that of calcipotriol (Binderup & Bramm 1988). The affinity of tacalcitol is comparable with that of calcitriol (Matsumoto et al 1990). Alfacalcidol does not directly bind to the WT-VDR in vitro because it is a prodrug converted to calcitriol via hydroxylation in the liver (Orimo & Schacht 2005).…”

“…Synthetic VD 3 analogs are important therapeutic agents for treating renal osteodystrophy, psoriasis vulgaris, osteoporosis, and other diseases (Matsumoto et al 1990, Brown & Coyne 2002, Morii et al 2004, Tsukamoto 2004, O'Neill & Feldman 2010. Among the VD 3 analogs, calcitriol is the physiologically active form of VD 3 , and alfacalcidol is a prodrug that requires hydroxylation in the liver.…”

Assessment of the Clinical Effect of Topical Tacalcitol on Ichthyoses with Retentive Hyperkeratosis

“…Tacalcitol, a chemically synthesized vitamin D 3 analog, has been demonstrated to produce equivalent dose-dependent inhibition of proliferation and stimulation in the terminal differentiation of human keratinocytes [5, 6, 7]. Tacalcitol is as active as calcitriol (1α,25-dihydroxyvitamin D 3 ) on mineral metabolism, but is less toxic than 1α-hydroxyvitamin D 3 [8].…”