Psoriasis and vitamin A. Plasma transport and skin content of retinol, dehydroretinol and carotenoids in adult patients versus healthy controls.

The vitamin-A status of 107 patients with psoriasis and 37 healthy controls was investigated. The mean serum level of retinol-binding protein (RBP) was normal in the 79 patients with chronic plaque psoriasis covering 25% or less of the skin surface. In the 28 patients with more extensive plaque lesions or pustular/erythrodermic psoriasis, the mean serum RBP level was significantly lower than in the controls (P less than 0.05). The cutaneous concentrations of retinol (vitamin A1), dehydroretinol (vitamin A2) and carotenoids were measured in extracts of saponified shave-biopsy specimens of uninvolved and involved skin from 33 patients with plaque psoriasis. Their retinol values did not differ significantly from those found in control skin (mean, 252 ng/g), whereas the carotenoid levels in both uninvolved and involved skin were 25%-50% lower. In contrast, the dehydroretinol concentration was higher in the patients' involved skin (mean, 237 ng/g) than in their uninvolved skin (94 ng/g) and healthy control skin (70 ng/g; P less than 0.01). Although the origin of increased dehydroretinol levels in involved psoriatic skin is unknown, similar increments were observed in control epidermis in which proliferation had been induced by tape stripping. In 7 patients treated with oral etretinate (aromatic retinoid) for 2-3 weeks, the median retinol and dehydroretinol levels in involved skin increased by 107% and 212%, respectively; the vitamin-A concentrations in uninvolved skin did not change significantly. Oral treatment with beta-carotene/canthaxanthin raised the median carotenoid levels in uninvolved and involved skin by 170% and 610%, respectively, without significantly affecting the vitamin-A composition.