Human pharmacokinetic profile of 1,25-dihydroxyvitamin D3-glycoside of herbal origin.

A natural form of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active metabolite of vitamin D, was identified in glycosylated form in Solanum glaucophyllum (SG). Solbone P, an extract of SG with high and homogenous content of glycosylated 1,25(OH)2D3, was chemically characterized and produced under GMP conditions. Three different doses of glycosylated 1,25(OH)2D3 were given as single oral dose to 16 healthy volunteers in a first-in-man trial. The oral pharmacokinetic properties of 1,25(OH)2D3 of SG origin were established and the subjects were monitored until day 28 for safety reasons. This included regular monitoring of vital signs, electrocardiogram (ECG) data, calcium, phosphate and creatinine values. Subjects were exposed to up to the equivalent of a 40-fold level of the recommended human daily dose for synthetic 1,25(OH)2D3 (0.5μg/subject/day) without experiencing any untoward effects. When compared with the historically established pharmacokinetics profile of synthetic 1,25(OH)2D3, glycosylated 1,25(OH)2D3 of herbal origin exhibited delayed absorption characteristics. The phenomenon is species independent, as similar pharmacokinetic patterns were observed in rats and chickens. This modified release pattern may be attributed to the glycosylation of herbal 1,25(OH)2D3 because de-glycosylation by ubiquitous intestinal enzymes prior to intestinal uptake of the unmodified 1,25(OH)2D3 is the rate-limiting step. The major relevance of this finding is that the human pharmacokinetic profile of glycosylated 1,25(OH)2D3 of herbal origin is reminiscent of a delayed release formulation of free 1,25(OH)2D3, resulting in a wider therapeutic window, a potentially longer therapeutic effectiveness, and thus, a better pharmacologic tolerance. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.