Rapid and structure-specific cellular uptake of selected steroids

Area of Science:

• Endocrinology and Molecular Biology
• Cellular Biology and Biochemistry

Background:

• Steroid hormones regulate vital physiologic and pathophysiologic processes, including metabolism, immune function, reproduction, and hormone-dependent cancers.
• Cellular uptake is critical for steroid hormone action, yet mechanisms remain incompletely understood.
• Current assumptions about diffusion-driven vs. active uptake need direct testing.

Purpose of the Study:

• To investigate the mechanisms of cellular steroid uptake.
• To determine if steroid uptake is structure-dependent and identify specific structural preferences.
• To elucidate the roles of passive and active transport in cellular steroid accumulation.

Main Methods:

• Experiments using intact cells to measure free steroid accumulation.
• Varying steroid structures and lipophilicity to assess uptake differences.
• Comparing uptake in viable vs. non-viable cells and across different cell types.
• Investigating the effect of serum proteins on steroid uptake in vitro.

Main Results:

• Intact cells accumulate free steroids to markedly elevated concentrations.
• Steroid uptake is structure-dependent, with more lipophilic steroids reaching higher concentrations.
• Specific structural features (3β-OH, Δ5 vs. 3-keto, Δ4) and steroid classes (progestogens vs. androgens) show distinct preferences.
• Structure-specific preferences occur passively (independent of cell viability) and across multiple cell types.
• Serum proteins partially inhibit passive uptake but permit substantial active uptake for some steroids.

Conclusions:

• Both passive and active mechanisms contribute significantly to cellular steroid uptake.
• Passive, lipophilicity-driven steroid accumulation is a previously underappreciated factor.
• Findings provide crucial context for in vitro and in vivo studies of steroid transport and action.