anhydrovitamin-a and Lymphoma

Retinyl palmitate (RP) is frequently used as an ingredient in cosmetics and other retail products. We previously reported that, under UVA light irradiation, RP is facilely decomposed into multiple products, including anhydroretinol (AR) and 5,6-epoxyretinyl palmitate (5,6-epoxy-RP). We also determined that combined treatment of mouse lymphoma cells with RP and UVA irradiation produced a photomutagenic effect. In this study, we evaluated the photomutagenicity of AR and 5,6-epoxy-RP, in L5178Y/Tk+/- mouse lymphoma cells. Treatment of cells with AR or 5,6-epoxy-RP alone at 10 and 25 microg/mL for 4 h did not show a positive mutagenic response. However, because these doses did not induce the required amount of cytotoxicity for mouse lymphoma assay, we are unable to determine whether or not these two compounds are mutagenic. Treatment of cells with 1-25 microg/mL AR or 5,6-epoxy-RP under UVA light (315-400 nm) for 30 min (1.38 mW/cm2) produced a synergistic photomutagenic effect. At 10 microg/mL (37.3 microM) AR with UVA exposure, the mutant frequency (MF) was about 3-fold higher than that for UVA exposure alone, whereas the MF for 25microg/mL (46.3microM) of 5,6-epoxy-RP + UVA was approximately 2-fold higher than that for UVA exposure alone. Compared with previous results for RP + UVA treatment, the potency of the induced phototoxicity and photomutagenicity was AR > RP > 5,6-epoxy-RP. To elucidate the underlying photomutagenic mechanism, we examined the loss of heterozygosity (LOH) at four microsatellite loci spanning the entire chromosome 11 for mutants induced by AR or 5,6-epoxy-RP. Most mutants lost the Tk+ allele, and more than 70% of the chromosome damage extended to 38 cM in chromosome length. AR + UVA induced about twice as many mutants that lost all four microsatellite markers from the chromosome 11 carrying the Tk+ allele as RP + UVA or 5,6-epoxy-RP + UVA. These results suggest that two of RP's photodecomposition products are photomutagenic in mouse lymphoma cells, causing events that affect a large segment of the chromosome.

Topics: Animals; Cell Line, Tumor; Loss of Heterozygosity; Lymphoma; Mice; Molecular Structure; Mutagenicity Tests; Mutagens; Palmitates; Photochemistry; Signal Transduction; Tretinoin; Ultraviolet Rays; Vitamin A

The retro-retinoids, metabolites of vitamin A (retinol), belong to a family of lipophilic signalling molecules implicated in regulation of cell growth and survival. Growth-promoting properties have been ascribed to 14-hydroxy-retro-retinol (14HRR), while anhydroretinol (AR) was discovered to act as a natural antagonist triggering growth arrest and death by apoptosis. Based on morphological studies and inhibition of apoptosis by the kinase blocker, herbimycin A, it has been suggested that retro-retinoids exhibit their function in the cytosolic compartment. F-actin emerged as a functional target for retro-retinoid action. By FACS analysis and fluorescence microscopy of phalloidin-FITC labeled cells we demonstrated that F-actin reorganization was an early event in AR-triggered apoptosis. Fluorescence images of AR-treated fibroblasts displayed short, thick, stick-like and punctate structures, and membrane ruffles at the cell periphery along with an increased diffuse staining pattern. Reversal of the AR effect by 14HRR or retinol indicates that F-actin is a common site for regulation by retro-retinoids. Inhibition of both cell death and actin depolymerisation by bcl-2 implies that cytoskeleton reorganization is downstream of bcl-2-related processes. Furthermore, stabilization of microfilaments by jasplakinolide increased the survival potential of AR treated cells, while weakening the cytoskeleton by cytochalasin B abetted apoptosis. Thus the cytoskeleton is an important way station in a communication network that decides whether a cell should live or die.

Topics: 3T3 Cells; Actins; Animals; Antineoplastic Agents; Apoptosis; Benzoquinones; Cell Survival; Cytochalasin B; Cytosol; Depsipeptides; Diterpenes; DNA Damage; Fibroblasts; Flow Cytometry; Kinetics; Lactams, Macrocyclic; Lymphoma; Mice; Peptides, Cyclic; Quinones; Retinoids; Rifabutin; Tumor Cells, Cultured; Vitamin A