Molecular Pharmacology, Vol 13, 150-160, Copyright © 1977 by the American Society for Pharmacology and Experimental Therapeutics

Steroid-Stimulated Amino Acid Uptake in Cultured Human Fibroblasts Reflects Glucocorticoid and Anti-inflammatory Potency

¹ Division of Clinical Pharmacology, Department of Medicine, and Department of Pharmacology and Experimental Therapeutics, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

In cultured human skin-derived fibroblast monolayers, steroids which exhibit glucocorticoid and anti-inflammatory activity stimulate the uptake of the amino acid analogue -aminoisobutyric acid (AIB). Stimulation of AIB uptake is maximal after 5 hr of exposure to steroid, persists up to 24 hr in the presence of steroid, and is blocked by cycloheximide. Since the rate of AIB efflux from monolayers is also accelerated in the presence of steroid, the increase in the rate of AIB uptake is attributable to a greater stimulation of the rate of AIB influx. In the presence of steroid the apparent K_m of uptake of AIB is reduced without an appreciable effect on the apparent V_max of uptake. Steroid analogues lacking an 11 substituent (e.g., prednisone, cortisone) neither stimulate the uptake of AIB nor block the action of active analogues. The stimulation by active derivatives is concentration-dependent, and compounds can be ranked in potency according to their ED₅₀ values for stimulation of AIB uptake: cortisol (44 nM) < prednisolone (22 nM) < triamcinolone (13 nM) < beclomethasone (7 nM) = betamethasone (7 nM) < dichlorisone (4 nM) < dexamethasone (2 nM). The order of potencies broadly parallels the relative daily oral replacement doses of these compounds in humans and indicates a high intrinsic potency of the 21-alcohol chlorinated glucocorticoids, dichlorisone and beclomethasone.

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ACKNOWLEDGMENTS The author is grateful for the expert technical assistance of W. H. Shackelford. These studies were performed in the Alan Bernstein Memorial Laboratories of The Johns Hopkins University School of Medicine.