11-cis-retinal is the light-sensitive component in rod and cone photoreceptors, and its isomerization to all-trans retinal in the presence of light initiates the visual response. For photoreceptors to function normally, all-trans retinal must be converted back into 11-cis-retinal through a series of enzymatic steps known as the visual cycle. The interphotoreceptor retinoid-binding protein (IRBP...

Retinoids, synthetic and natural analogs of retinoic acid, exhibit potent growth inhibitory and cell differentiation activities that account for their beneficial effects in treating hyperproliferative diseases such as psoriasis, actinic keratosis, and certain neoplasias. Tazarotene is a synthetic retinoid that is used in the clinic for the treatment of psoriasis. To better understand the mechan...

Chemoprevention by retinoids of the progression of carci nomas induced in rats by azaserine was evaluated. Wistar/ Lewis rats were given 15 weekly injections of azaserine, 10 mg/kg, while fed a chow diet; after the completion of carcino gen treatment, they were fed a chow diet supplemented with four different retinoids at the level of 0.5 to 2 mmol/kg diet for 1 year. The incidence of neoplasms...

The embryonal carcinoma cell line F9 is known to differentiate when exposed to retinoic acid. We have examined the quantities of two intracellular retinoid-binding proteins in undifferentiated and differentiated F9 cells. The existence of a cell surface receptor that recognizes the plasma retinol-binding protein was also explored. It was shown that undifferentiated F9 cells contain low concentr...

INTRODUCTION The high rate of relapse of acne lesions following oral isotretinoin treatment is a common problem which remains unsolved. To avoid or minimize relapses, topical retinoids have been used for many years as maintenance treatment. However, adverse effects frequently occur. AIMS To determine the efficacy and safety of a new retinoid combination (Retinsphere technology) in maintaining...

PURPOSE The retinoid cycle maintains vision by regenerating bleached visual pigment through metabolic events, the kinetics of which have been difficult to characterize in vivo. Two-photon fluorescence excitation has been used previously to track autofluorescence directly from retinoids and pyridines in the visual cycle in mouse and frog retinas, but the mechanisms of the retinoid cycle are not ...

Retinol (the prototypic vitamin A) and its metabolites called retinoids play important physiologic roles in embryonal development, vision, maintenance of epithelial differentiation, immune functions, and reproduction (1). Many of these functions are mediated by retinol metabolites such as all-trans-retinoic acid (ATRA) (2). ATRA modulates gene expression by means of nuclear receptors that are m...

All-trans retinoic acid (atRA) is the active form of vitamin A, known to activate retinoid receptors, especially the heterodimer retinoid X receptor (RXR):retinoic acid receptor (RAR) that otherwise may play a role in regulation of some drug transporters. The present study was designed to characterize the nature of human hepatic transporters that may be targeted by atRA and the heterodimer RXR:...

All-trans-retinal, a retinoid metabolite naturally produced upon photoreceptor light activation, is cytotoxic when present at elevated levels in the retina. To lower its toxicity, two experimentally validated methods have been developed involving inhibition of the retinoid cycle and sequestration of excess of all-trans-retinal by drugs containing a primary amine group. We identified the first-i...

In HL-60 cells, retinoic acid (RA) and 9 cis-RA induce granulocytic differentiation, and calcitriol and sodium butyrate induce monocytic differentiation. To study the role of retinoid resistance on the response to these agents, we investigated their effects in HL-60 cells, retinoid-resistant HL-60R cells, and HL-GOR+ cells in which retinoid sensitivity has been restored. In HL-60 cells, catheps...