Protective action of beta-carotene against lethal photosensitization of fibroblasts in vitro

beta-Carotene uptake and effects on intracellular levels of retinol in vitro

The purpose of the present study was to determine beta-carotene uptake and resultant effects on intracellular levels of retinol in cell lines of varied origin. Human skin fibroblasts, mouse embryonic fibroblasts, rabbit corneal epithelial cells, and rat liver cells were studied. Cells were cultured in medium supplemented with beta-carotene in a water-dispersible beadlet formulation. At selected intervals, cells and media were sampled and analyzed by high-performance liquid chromatography for beta-carotene and retinol content. beta-Carotene was taken up by all four cell lines. An increase in the intracellular levels of retinol was concomitant with beta-carotene uptake in all cell lines. The uptake of beta-carotene and the increase in intracellular retinol were highest in the two fibroblast cell lines. Incubation with media supplemented with crystalline beta-carotene, dissolved in tetrahydrofuran, resulted in significantly lower beta-carotene uptake and intracellular retinol levels. We view these results as a demonstration that a wide variety of cells, cultured in vitro, are able to convert beta-carotene to retinol. Therefore, beta-carotene's provitamin A activity should be carefully considered when the protective effects of beta-carotene in vitro are interpreted.

beta-Carotene uptake, metabolism, and distribution in BALB/c 3T3 cells

Although a growing number of epidemiological studies indicate that dietary beta-carotene has anticarcinogenic activity, the mechanism(s) of beta-carotene protection remains to be definitively established. In this context, in vitro studies of beta-carotene have been, and continue to be, valuable. We examined the following critical features in designing an in vitro system for studying the protection action of beta-carotene: 1) form of beta-carotene used for cellular uptake, 2) cellular metabolism of beta-carotene, and 3) subcellular distribution of beta-carotene. It was determined that beta-carotene added to medium in a water-dispersible formulation is readily taken up by BALB/c 3T3 cells and is located predominantly in cellular membranes. Cellular uptake of beta-carotene added to medium in an organic solvent is greatly reduced. It was also found that intracellular retinol increased significantly after a three-day exposure of BALB/c 3T3 cells to media containing beta-carotene. This result suggests that the ability to metabolize beta-carotene to retinoids is not limited to cells of intestinal origin. The results and methodology described here will be useful in the rational design of in vitro assays for elucidating the mechanism(s) of beta-carotene protective effects at the cellular level.

Concentration and fluence dependence of the disturbance of the membrane integrity of human fibroblasts by the photodynamic action of Photosan III

Two human fibroblast cell lines were treated with varying concentrations of the photosensitizer Photosan III for different incubation times, and subsequently irradiated with an He-Ne laser. The biological parameter investigated was trypan blue exclusion by the cells. For each given drug concentration and incubation time, a threshold fluence was observed, which resulted in the complete loss of the cell membrane integrity. Using the equation tcr = b X CPS-a, the correlation between threshold light dose (tcr) and the concentration of the photosensitizer (CPS) can be described for all three incubation times (10 min, 2 h, 20 h) characterized by different sets of a and b values. This power function implies that these parameters are inversely correlated to each other. A correlation of incubation time with critical exposure time for different drug concentrations gave saturation curves. No differences were observed between the two cell lines. The method applied may be useful for a fast comparison of the sensitizing efficiencies of different treatment protocols for the in vitro investigation of photodynamic laser therapy.

Relationship between changes in antigen expression and protein synthesis in human melanoma cells after hyperthermia and photodynamic treatment

Hyperthermia and photoactivated hematoporphyrin derivative induce a dose-dependent reduction in the expression of the p250 surface melanoma-associated antigen on the human FME cell line. Expression of this glycoprotein antigen was quantitated by immunofluorescence flow cytometry based on the monoclonal antibody 9.2.27. Decrease in antigen expression was followed by a transient increase above the level for untreated cells, before normalization occurred about one week after treatment. These treatment-induced changes in antigen expression could partly be explained by changes in protein synthesis. This conclusion was based on the following observations: Hyperthermia and photoactivated hematoporphyrin derivative both inhibited protein synthesis. The latter increased again rapidly to rates above normal until antigen expression reached normal level, whereupon the protein synthesis rate decreased to normal. Inhibition of protein synthesis by cycloheximide 1 day after heating, prevented the recovery of antigen expression, demonstrating that protein synthesis is necessary for resumption of normal antigen expression. The changes in both antigen expression and protein synthesis were dose-dependent, and the magnitude and duration of the changes increased with increasing dose. The time courses of the changes in protein synthesis after two different treatments which both inactivated two logs of cells were almost identical, as were the time courses after two lower heat doses inactivating one log of cells. These similarities were reflected in the changes in antigen expression. At the same time as protein synthesis reached its maximum and antigen expression resumed normal level, an increase in the Golgi apparatus was observed ultrastructurally, indicating an increased synthesis rate and transportation of glycoproteins to the cell surface.

Do oral carotenoids protect human skin against ultraviolet erythema, psoralen phototoxicity, and ultraviolet-induced DNA damage?

This study was performed in order to (1) assess the magnitude of a possible protective effect of oral carotenoids on ultraviolet B (UVB)-, ultraviolet A (UVA)-, and psoralen ultraviolet A (PUVA)-induced erythema in human skin and (2) to evaluate whether the postulated prevention of skin cancer by prophylactic administration of carotenoids is based on a decrease in UVB-induced DNA damage. Twenty-three healthy volunteers received oral carotenoids (150 mg/day) for 4 weeks. Serum levels were quantitated, and ranged from 390 to 1710 micrograms/dl. Before and after carotenoid administration, the UVA- and UVB-MEDs and the PUVA-MPD were determined by standard phototesting. DNA damage was assessed by autoradiographical measurement of unscheduled DNA synthesis (UDS) following UVB exposure before and after treatment. No statistically significant carotenoid-dependent protection was found against UVA, UVB, and PUVA erythema by comparing the pre- and postcarotenoid erythema doses. Also at the DNA level there was no indication of a protective effect that could be detected with the methods employed: the amount of UVB-induced UDS was not decreased after carotenoid treatment. We conclude that (1) carotenoids do not reduce UVB-, UVA-, or PUVA-induced erythema in human skin; that (2) reactive oxygen species may not be involved in PUVA-erythema production or, alternatively, carotenoids may not quench these radicals sufficiently in vivo; and that (3) carotenoid protection against UVB-induced carcinogenesis does not operate by reducing the number of mutagenic lesions in DNA.

Uptake and localisation of haematoporphyrin derivative in normal rat liver

Fluorescence microscopy and analytical subcellular fractionation were used to investigate the hepatic localisation of haematoporphyrin derivative (HPD) after intraperitoneal administration. HPD was found to rapidly accumulate in the liver and then to slowly decline over 48 hr. Fluorescence microscopy showed that although at early times porphyrins could not be localised to a particular cell type, at 24 hr porphyrins were preferentially localised to the Kupffer cells of the liver. Subcellular fractionation studies indicated that the initial rapid uptake of HPD was to the cytosol. However, at 24 hr, porphyrins appeared to be localised to lysosomes. Lysosomal localisation was confirmed using the selective organelle perturbant, Triton WR 1339. No evidence was found either at the light microscope level or by subcellular fractionation to suggest association of HPD with other organelles. HPLC analysis showed that the porphyrins present in the plasma and in the cytosol and lysosome fractions were mainly the (RS, SR) and (RR, SS) diastereoisomers of haematoporphyrin and the two position isomers 8-(1-hydroxyethyl)-3-vinyldeuteroporphyrin and 3-(1-hydroxyethyl)-8-vinyldeuteroporphyrin. There was no evidence for the involvement of dimers such as dihaematoporphyrin ether.

Photodynamic therapy of rat liver cancer: protection of the normal liver by indocyanine green

The application of photodynamic therapy (PDT) to hepatocellular carcinoma (HCC) has been difficult because hematoporphyrin derivatives (HpD) accumulate not only in cancer cells but also in normal hepatocytes and, hence, laser irradiation causes injuries in both tissues. Protection of the normal liver tissue from laser phototoxicity was demonstrated using indocyanine green (ICG) as a protective agent. In vitro, argon laser irradiation decolored the green tint of ICG much faster in solutions containing HpD than those without, suggesting that ICG captured singlet oxygen from HpD. Degeneration of Change hepatocytes induced by HpD and laser irradiation was prevented by an addition of ICG into the medium. In vivo, laser irradiation of the rat liver surface caused hyperemia when HpD was injected two days before, while the hyperemia was much milder in rats additionally receiving ICG injection 10 minutes before the irradiation. ICG injected into rat HCC accumulated only in the normal liver tissue. Laser irradiation of rat HCC preinjected with both HpD and ICG destroyed only the cancer tissue, while the surrounding liver tissue was preserved. Both in vitro and in vivo results suggest that ICG has a scavenger effect against excited oxygen and it might be used as a protective agent in PDT of HCC.

Photomodification of biological membranes with emphasis on singlet oxygen mechanisms

This review discusses photomodification of biological membranes and model membrane systems. Current concepts of membrane structure are first reviewed briefly. The role of preillumination association of sensitizer with membranes as it relates to photomodification rate is discussed, as well as the role of singlet oxygen in membrane photomodification. Finally the characteristics of singlet oxygen generation in membranes are considered. The evidence clearly indicates that membrane photomodification cannot be understood based only on the properties of sensitizers and singlet oxygen in aqueous solution. Rather the properties of sensitizers in association with membranes are the determinants of membrane photomodifcation. These properties differ significantly in aqueous solution and in membranes.

Retention and photodynamic effects of haematoporphyrin derivative in cells after prolonged cultivation in the presence of porphyrin

Photoradiation therapy of cancer in the presence of haematoporphyrin derivative is based on a retention of porphyrin in malignant tissue. After long term incubation of NHIK 3025 cells in the presence of 25 microgram ml-1 haematoporphyrin derivative, one fraction is easily removed from the cells by washing with a serum-rich medium. Another fraction remains bound to the cells for a prolonged time. The former does not contribute to the photosensitivity of the cells while the latter, the tightly-bound component, results in a photosensitivity proportional to the cellular contents of porphyrin. Transformed cells are shown to be slightly more sensitive and to retain 25-50% more haematoporphyrin derivative than non-transformed cells. Cytological effects of light absorbed by the tightly-bound component have been studied. The growth of treated cells is similar to that of control cells after a dose-dependent post irradiation lag period. A relatively slow leakage of lactate dehydrogenase (LDH) out of the cells takes place after treatment. The treatment induces a significant increase in the frequency of sister chromatid exchanges (SCE). We conclude that photoactivation of the tightly-bound fraction of haematoporphyrin derivative induces less damage to the outer cell membrane and probably more intracellular damage than irradiation of cells after a short period in contact with the derivative.