Effects of outdoor and indoor airborne particulate matter on thyroid hormone and vitamin A metabolism.

Vitamin A is an important regulator of normal epithelial differentiation and proliferation and might act in the promotion phase of carcinogenesis. Vitamin A and thyroid hormone metabolism are linked by a common plasma carrier protein transthyretin (TTR). Results indicated that extracts of outdoor and indoor airborne particulate matter (APM), originating from different pollution sources, significantly interfered with thyroxine (T4) binding to TTR. The neutral fraction accounted for most of the inhibitory activity. Polycyclic aromatic hydrocarbons and nitrated derivatives were not responsible for the activity of the neural fraction. A single treatment of rats with an outdoor and cigarette smoke APM extract depleted plasma T4 and triiodothyronine levels and increased plasma retinol levels, while liver and lung retinol levels were depleted. The studies show that APM extracts have the potency to interfere with thyroid hormone metabolism both in vitro and in vivo and to deplete lung vitamin A in vivo.