Vitamin A/retinoids signalling in the human lung

Vitamin A is used as a generic term for all vitamin A derivatives with retinol-like biological activity. Retinol is the main parent compound for vitamin A. It derives from carotenoids (provitamin A) and also directly from the pre-formed vitamin A contained in the diet. The term "retinoid" is a generic descriptor of compounds structurally related to vitamin A and the synthetic analogues of retinol with or without biological activity. Retinoic acid is the active cellular catabolite. Vitamin A/retinoids have been given cancer-preventive functions and subsequently used in clinical trials to reduce lung cancer incidence in high-risk individuals. The results obtained have been in contradiction with both in vivo and in vitro promising studies. It seems therefore necessary to develop a better understanding of the vitamin A/retinoids signalling pathways in the lung. With this aim, we summarise the relevant knowledge focussed on the lung.