Estrogen mitogenic action. III. is phenol red a "red herring"?

Area of Science:

• Endocrinology
• Cell Biology
• Biochemistry

Background:

• Phenol red's potential estrogenic activity has led to the use of indicator-free media for in vitro endocrine studies.
• Recent advancements allow measurement of estrogen effects in phenol red-containing media, necessitating re-evaluation of the indicator's role.

Purpose of the Study:

• To evaluate the estrogenic potential of phenol red in standard cell culture media.
• To determine if phenol red interferes with estrogen receptor-positive (ER+) cell line responses to estradiol (E2) and tamoxifen.
• To identify critical factors for demonstrating sex steroid hormone-mitogenic effects in vitro.

Main Methods:

• Compared E2-responsive growth of nine ER+ cell lines in media with and without phenol red.
• Assessed phenol red's mitogenic potential and compared its dose-response to E2.
• Investigated tamoxifen's efficacy in both phenol red-containing and indicator-free media.
• Examined phenol red's ability to displace 3H-E2 binding and its role in progesterone receptor induction.

Main Results:

• Current concentrations of phenol red in culture media are insufficient to induce estrogenic effects.
• Phenol red did not interfere with E2-stimulated growth, tamoxifen inhibition, or E2 binding in the tested ER+ cell lines.
• Demonstration of sex steroid hormone-mitogenic effects is critically dependent on optimizing conditions to overcome serum-borne inhibitors.

Conclusions:

• Phenol red is not a significant confounding factor in current in vitro endocrine studies using standard media.
• The presence or absence of phenol red is inconsequential for demonstrating estrogenic effects when optimal conditions are employed.
• Effective demonstration of estrogenic effects relies on managing inhibitory factors in the culture system.