Nutrients, Vol. 17, Pages 2107: Vitamin D3, 25-Hydroxyvitamin D3, and 1,25-Dihydroxyvitamin D3 Uptake in Cultured Human Mature Adipocytes
Nutrients doi: 10.3390/nu17132107
Authors:
Nazlı Uçar
Richard. T. Pickering
Peter M. Mueller
Jude T. Deeney
María Morales Suárez-Varela
José Miguel Soriano
Michael F. Holick
Background/Objectives: Vitamin D3 is predominantly sequestered in adipose tissue, where it is slowly mobilized under conditions of deficiency in vivo. However, the kinetics of its uptake, release, and interaction with its major metabolites, 25(OH)D3 and 1,25(OH)2D3, remain poorly understood. Given the close relationship between obesity, low-grade chronic inflammation, and disrupted vitamin D metabolism, a clearer understanding of these dynamics in adipocytes is essential. Thus, we sought to characterize time-dependent uptake and metabolites in differentiated human adipocytes. Methods: Human pre-adipocytes were differentiated in vitro and exposed to either vitamin D3 and 1,25(OH)2D3 or the combination of vitamin D3, 25(OH)D3 and 1,25(OH)2D3. Intracellular concentrations were quantified through HPLC at various time points. A separate efflux experiment assessed vitamin D3 release under basal and isoproterenol-stimulated conditions using 3H-vitamin D3 and scintillation counting. Results: Vitamin D3 uptake showed a gradual and sustained increase over 96 h, suggesting ongoing accumulation within lipid-rich compartments. In contrast, 25(OH)D3 and 1,25(OH)2D3 peaked rapidly within the first hour and declined sharply. Isoproterenol stimulation significantly enhanced vitamin D3 release into the extracellular medium from the adipocytes, indicating increased efflux during lipolytic activation. Conclusions: Adipocytes selectively retain vitamin D3 while rapidly clearing its hydroxylated forms. These findings highlight the distinct intracellular handling of vitamin D metabolites and suggest that tailored supplementation strategies—particularly in individuals with excess adiposity—may improve bioavailability and metabolic efficacy.
Background/Objectives: Vitamin D3 is predominantly sequestered in adipose tissue, where it is slowly mobilized under conditions of deficiency in vivo. However, the kinetics of its uptake, release, and interaction with its major metabolites, 25(OH)D3 and 1,25(OH)2D3, remain poorly understood. Given the close relationship between obesity, low-grade chronic inflammation, and disrupted vitamin D metabolism, a clearer understanding of these dynamics in adipocytes is essential. Thus, we sought to characterize time-dependent uptake and metabolites in differentiated human adipocytes. Methods: Human pre-adipocytes were differentiated in vitro and exposed to either vitamin D3 and 1,25(OH)2D3 or the combination of vitamin D3, 25(OH)D3 and 1,25(OH)2D3. Intracellular concentrations were quantified through HPLC at various time points. A separate efflux experiment assessed vitamin D3 release under basal and isoproterenol-stimulated conditions using 3H-vitamin D3 and scintillation counting. Results: Vitamin D3 uptake showed a gradual and sustained increase over 96 h, suggesting ongoing accumulation within lipid-rich compartments. In contrast, 25(OH)D3 and 1,25(OH)2D3 peaked rapidly within the first hour and declined sharply. Isoproterenol stimulation significantly enhanced vitamin D3 release into the extracellular medium from the adipocytes, indicating increased efflux during lipolytic activation. Conclusions: Adipocytes selectively retain vitamin D3 while rapidly clearing its hydroxylated forms. These findings highlight the distinct intracellular handling of vitamin D metabolites and suggest that tailored supplementation strategies—particularly in individuals with excess adiposity—may improve bioavailability and metabolic efficacy. Read More