Diet potentiates the UV-carcinogenic response to beta-carotene.

The role of beta-carotene as an anticancer agent has been questioned as a result of clinical trials in which the incidence of nonmelanoma skin cancer was unchanged in patients receiving a beta-carotene supplement and in beta-carotene-supplemented smokers who suffered a significant increase in lung cancer occurrence. In laboratory studies, beta-carotene-supplemented semidefined diets, in contrast to earlier studies employing commercial closed-formula diets, not only failed to provide a protective effect to ultraviolet (UV) carcinogenesis but resulted in significant exacerbation. A rationale for this distinct carcinogenic response to beta-carotene rests with the stability of the carotenoid radical cation, believed to be dependent on the presence of other antioxidants for rapid repair, and suggests that response to beta-carotene depends on the presence and interaction with other dietary factors. Here, we report that diet potentiates beta-carotene-mediated exacerbation of UV carcinogenesis. Although the dietary factor(s) responsible for this effect is unidentified, these studies underscore the potential risk of beta-carotene supplementation in free-living populations where dietary status is widely varied.

Radical interception by carotenoids and effects on UV carcinogenesis.

Studies employing time-resolved techniques have shown that beta-carotene, astaxanthin, and lycopene behave quite distinctly with respect to radical quenching and stability, lycopene being the least stable. These results are compatible with the relative effects of the various carotenoids on ultraviolet (UV)-mediated carcinogenesis in mice in which a statistically significant exacerbation by beta-carotene and astaxanthin, but not by lycopene, was observed. Interactions between these carotenoids and vitamin C and E radicals not only provide a chemical basis to explain the failure of beta-carotene to provide benefit in recent clinical trials but suggest that future carotenoid supplementation studies should proceed with caution until carotenoid interactions and radical repair mechanism(s) are elucidated.

Immunobiology of lipid-modulated UV-carcinogenesis.

Previous studies have demonstrated that high levels of dietary fat exacerbate UV-carcinogenic expression and suppress immunoresponsiveness. The latter may account for the former response. We have explored this possibility through T-lymphocyte transfer studies. Groups of HRA.HRII-c/+/Skh hairless mice were fed isocaloric diets containing high (12%, wt./wt.) or low (0.75%) levels of corn oil and irradiated 5 days/week (1.0 J cm-2/day) for 11 weeks with filtered FS-40 sunlamps. At weeks nine and 12, enriched T-cells from high-fat donors that had received 11 weeks of UV were transferred intravenously to low-fat recipients. Median tumor times for high-fat, low-fat recipient, and low-fat groups were 15.8, 18.5, and 21.6 weeks, respectively. The significantly (P < 0.03) shortened primary tumor latent period in low-fat-fed animals resulting from transfer of relatively low levels of T-cells derived from chronically irradiated high-fat donors demonstrates that the influence of dietary fat upon UV-carcinogenic expression is, at least partially, mediated via immunologic mechanisms. Further studies suggest that fat-modulated carcinogenesis can, itself, be regulated immunologically. A soluble T-14 (mouse squamous carcinoma cell line) cell-free fraction was injected subcutaneously at axillae and inguen of animals fed the high-fat diet during the first three weeks of UV or immediately post-UV. At week four post-UV, animals were challenged with T-14 cells injected subcutaneously at both flanks. 21 days post-challenge the tumor volumes of low-fat and high-fat immunized animals were zero versus 593 mm3 for the high-fat group (P < 0.007). Such treatment significantly (P < 0.03) increases the latent period of UV-induced primary tumors as well, when compared to non-treated high-fat-fed animals.

Influence of dietary lipid on hapten-specific UV-induced immunosuppression.

The influence of diets containing high (12%, w/w) and low (0.75%) levels of corn oil on hapten-specific antibody production to trinitrophenol-conjugated sheep red blood cells (TNP-SRBC) was examined in mice receiving 0, 3, 9, and 11 wk of UV radiation. Splenocytes from HRA HRII-c/+/Skh female hairless mice from the two dietary groups were incubated under a special atmosphere of low oxygen tension (7% O2, 10% CO2, and 83% N2) with TNP-SRBC to generate hapten-specific T-suppressor cells that, in turn, influence the number of direct plaque forming cells (PFC) in the Cunnigham-Szenberg plaque assay. Chronic UV irradiation reduced the number of direct PFC in both groups. After 11 wk of UV, the number of PFC in the high dietary fat group was significantly lower (P < 0.001) than that observed in the low fat group. These results suggest that dietary fat modulates UV-induced hapten-specific immunosuppression. Furthermore, the influence of dietary fat level, in this respect, was not realized until after 11 wk of UV, a time at which dietary fat has been shown to exert its influence on UV-carcinogenic expression.

Influence of dietary factors on actinically-induced skin cancer.

The first indication that high dietary fat intake could influence the development of ultraviolet (UV) radiation-induced skin cancer in experimental animals was reported in 1939. In the 1980s a series of animal studies showed that a high level of dietary fat intake markedly shortened the time between UV exposure and tumor appearance and increased the number of tumors that developed. Further, high levels of dietary fat affected skin cancer development at the promotional stage of UV-carcinogenesis, i.e., after the cancer causing dose of UV had been delivered. Perhaps more important, switching from a high-fat to a low-fat diet immediately after delivery of the UV-initiating dose negated the exacerbating effect of high fat intake. The latter finding suggested that dietary modification, even after a cancer-causing exposure to UV, might represent a potentially important intervention strategy in the prevention of non-melanoma skin cancer (NMSC) and provided the rationale for undertaking a dietary intervention trial. One hundred and fifteen skin cancer patients completed the 2-year clinical trial on the effect of a low-fat diet on occurrence of actinic keratosis (AK) and NMSC. Patients were randomly assigned to either continue their usual diet (control group, NI) or to adopt a diet with 20% of total caloric intake as fat (diet intervention group, DI). All patients were examined at 4-month intervals for new AK and NMSC. At baseline, the mean percent of caloric intake as fat was 40+/-4% in the NI group and 39+/-3% in the DI group. After 4 months of dietary therapy, the percent calories as fat had decreased to 21+/-7% in the DI group. The percent of calories as fat in the NI group did not drop below 37% during the study period. The cumulative number of new AK per patient from months 4 through 24 was 11.6+/-17 in the NI group and 3.2+/-6 in the DI group (P < 0.001). Numbers of new NMSC were analyzed in 8-month periods. There were no significant changes in NMSC occurrence in the NI group. However, NMSC occurrence in the DI group declined significantly (P < 0.02) in the last 8-month period. Patients in the DI group also had significantly (P < 0.01) fewer NMSC in the last 8-month period than did patients in the NI group (0.02 versus 0.26). Practical dietary advice, with respect to reduction of percent of calories as fat, could make an important contribution to the prevention and management of AK and NMSC.

Photocarcinogenesis: an overview.

Photocarcinogenesis represents the sum of a complex of simultaneous and sequential biochemical events that ultimately lead to the occurrence of skin cancer. These events, initiated by UV radiation of appropriate wavelength, include the formation of DNA photoproducts: DNA repair; mutation of proto-oncogenes and tumor suppressor genes; UV-production of radical species with subsequent effects on mutation and extra-nuclear function; and other epigenetic events that influence the course of carcinogenesis. The epigenetic influences may include immunological responses, antioxidant defenses, and dietary factors. This review represents an effort to provide current research results in the aforementioned areas and an attempt to meld these events into a comprehensive overview of photocarcinogenesis. If effective prevention and intervention strategies for skin cancer are to developed, a more thorough understanding of the disease process is imperative.

General guidelines for a low-fat diet effective in the management and prevention of nonmelanoma skin cancer.

A dietary intervention trial has shown a significant reduction in occurrence of actinic keratosis and nonmelanoma skin cancer in skin cancer patients who adopt diets in which the percentage of calories from fat is markedly lowered. The purpose of this study was to examine the dietary parameters of a low-fat diet found to be effective in reducing occurrence of skin cancer. Skin cancer patients were taught fat reduction strategies to complement their individual food preferences and life-styles. Diet composition was calculated using standard dietary assessment and nutrient analysis techniques. The dietary intervention was effective in reducing the percentage of calories from fat to 21% by Month 4 and maintaining that level for the remainder of the two-year study. Practical dietary advice with respect to reduction of percentage of calories from fat, along with an increase in the intake of grains, fruits, and vegetables, could make an important contribution to the management and prevention of skin cancer.

Signature p53 mutation at DNA cross-linking sites in 8-methoxypsoralen and ultraviolet A (PUVA)-induced murine skin cancers.

A combination of psoralen and ultraviolet A radiation (PUVA) is widely used in the treatment of psoriasis. However, PUVA treatment increases the risk of developing skin cancer in psoriasis patients and induces skin cancer in mice. Since the DNA damage induced by PUVA is quite different from that induced by UV, we investigated whether PUVA-induced mouse skin cancers display carcinogen-specific mutations in the p53 tumor suppressor gene. The results indicated that 10 of 13 (77%) PUVA-induced skin tumors contained missense mutations predominantly at exons 6 and 7. In contrast, tumor-adjacent, PUVA-exposed skin from tumor-bearing animals did not exhibit p53 mutation in exons 4-8. Interestingly, about 40% of all mutations in PUVA-induced skin tumors occurred at 5'-TA sites, and an equal number of mutations occurred at one base flanking 5'TA or 5'-TAT sites. Since PUVA induces DNA cross-links exclusively at these sites and since UV "signature" mutations were rarely detected in PUVA-induced skin cancers, we can conclude that PUVA acts as a carcinogen by inducing unique PUVA signature mutations in p53. This finding may have implications for identifying the etiology of skin cancer in psoriasis patients who have undergone PUVA therapy.

Reactivity of butylated hydroxytoluene.

Butylated hydroxytoluene (BHT) is a synthetic antioxidant that is widely used as an additive in foodstuffs to prevent spoiling. The physical-chemical properties of BHT and many related phenols have been examined previously although the mechanisms by which it exerts its antioxidant properties are poorly understood. The reactivity of BHT with singlet oxygen [O2(1 delta g)] and a number of radical species has been examined using the techniques of time resolved luminescence and pulse radiolysis. In benzene solution BHT reacted with O2(1 delta g) at a bimolecular rate constant of 1.3 x 10(6)M-1s-1. The one-electron oxidized, phenoxyl type BHT radical was generated using pulse radiolysis and the absorption spectrum showed a maximum at 400 nm. BHT reacts slowly with many radical species and upper limits for the bimolecular rate constant for reaction with several electron transfer processes are presented. The antioxidant role of BHT is discussed in terms of its reactivity, localization, and stability.

Dietary fat modulates immunoresponsiveness in UV-irradiated mice.

Previous studies have shown that a high level of dietary lipid (corn oil) exacerbates UV-carcinogenic expression in hairless mice. Furthermore, it was demonstrated that this effect occurs at the postinitiation, or promotion, stage of UV-carcinogenesis--a stage believed to be modulated immunologically. Thus, we sought to examine the influence of dietary lipid on specific immune parameters at various times within a UV-carcinogenic protocol, with the purpose of detecting potential relationships to UV carcinogenesis. Hairless mice were fed either a high- (12%, wt/wt, corn oil) or low-fat (0.75%, wt/wt, corn oil) diet for 2 weeks prior to start of the UV or experimental protocols. Animals were sensitized to dinitrochlorobenzene (DNCB) hapten and delayed-type hypersensitivity (DTH) was assessed. Delayed-type hypersensitivity was significantly suppressed (P = 0.01) in the high-fat group, even before UV irradiation. Although both groups exhibited UV-induced suppression of this response, the high-fat group was totally suppressed after 3 weeks of UV, whereas the low-fat group exhibited reactivity through week 8. The splenic T-lymphocyte (Thy 1.2+) population had declined by about 50% at the time of UV termination (11 weeks). Dietary lipid exerted no apparent influence upon this T-cell population. However, after 6 weeks of UV, I-J+ cells (a marker shown to be acquired adaptively by suppressor T lymphocytes) began to increase. By week 15 (4 weeks post-UV) I-J+ cells had increased by about 65% in the high-fat group, twice the % increase that occurred in the low-fat group. When UV-induced tumors were transplanted to recipient animals receiving various periods (0, 6, 11 weeks) of UV irradiation, no significant differences in median tumor rejection times between the two dietary groups occurred at 0 or 6 weeks. After 11 weeks of UV, the low-fat group exhibited a tumor rejection time that was comparable to that of nonirradiated animals, i.e. 21 days. However, median tumor rejection time for the high-fat group was greater than 63 days, significantly (P = 0.01) longer than that of the low-fat group. Thus, suppression of tumor rejection by high fat occurred at a time when high fat had been shown to exacerbate carcinogenic expression and when I-J+ cells had markedly increased. These data demonstrate that level of dietary lipid modulates immunoresponsiveness in UV-irradiated animals and is compatible with the thesis that immune suppression may account for the exacerbation of carcinogenic expression elicited by high dietary fat.

Evidence that a low-fat diet reduces the occurrence of non-melanoma skin cancer.

The effect of a low-fat diet on occurrence of non-melanoma skin cancer was examined in a 2-year dietary intervention trial. A total of 101 skin-cancer patients were randomized either to a control group that consumed, on average, 38% of caloric intake as fat, and in which no changes in dietary habits were introduced, or to a low-fat dietary-intervention group, in which patients were instructed to limit their calories from fat to 20% of total caloric intake. Patients were examined at 4-month intervals by dermatologists blinded to their dietary assignments. Nutrient analyses, conducted at each of the 4-month follow-up visits, indicated that the % calories of fat consumed in the intervention group had been reduced to 21% at 4 months and remained below this level throughout the 2-year period. There were no significant differences in total calories consumed, or in mean body weights, between the control and the intervention groups. Nor were there significant group differences in P/S ratios until month 24. Numbers of new skin cancers treated at each examination were analyzed in 8-month periods of the 2-year study. Comparisons of skin-cancer occurrences revealed no significant changes in the control group from baseline values. However, cancer occurrence in the low-fat intervention group declined after the first 8-month period and reached statistical significance by the last 8-month period. Patients in this group had significantly fewer cancers in the last 8-month period than did patients in the control group. In addition, there was a significant reduction in the number of patients developing skin cancer in the last 8-month period, as compared with the first 8-month period, within the low-fat intervention group. There were no significant changes in the control group. These data indicate that a low-fat diet can significantly reduce occurrence of a highly prevalent form of cancer.

Biochemical parameters of epidermal aging in the hairless mouse and the relationship to UV-carcinogenesis.

Epidemiological studies suggest that the incidence of cancer increases with age in both human and animal populations and that declining physiologic condition associated with aging might be responsible. Experimentally, the reverse has been most often observed, that is, older animals appear less susceptible to the induction of UV-carcinogenesis. Thus, we examined several biochemical parameters of epidermal macromolecular synthesis in hairless mice in an effort to gain insight into the role these processes play in physiological aging and their relationship to carcinogenesis. SKh-Hr-1 hairless mice were randomized into two groups (UV-irradiated and non-irradiated controls) and were two months of age at the start of irradiation and biochemical analyses. The UV group received 0.028 sunburn units (SBUs) daily (5 days wk-1) for 16 months from 40 watt BZS-WLG lamps. Stratum corneum turnover rates (SCR), cell label index (CLI), protein, DNA and RNA synthesis, and ornithine decarboxylase (ODC) induction were determined at monthly intervals over a period of two years. There were no age-related tendencies observed in SCR. CLI increased with age. Chronic, low-dose UV had no effect upon either of these parameters. Epidermal capacity for DNA and protein synthesis increased with age from 2 months to 12-15 months at which time both parameters peaked and then began to decline. UV significantly reduced (P < 0.04) the magnitude of DNA synthetic capacity at peak periods of synthesis but had no effect upon protein synthesis. RNA synthetic rates declined with age, reaching their lowest levels at 24 months. Further, a significant reduction (P < 0.001) in ODC inducibility occurred with advancing age.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a low-fat diet on the incidence of actinic keratosis.

BACKGROUND: Actinic keratoses are premalignant lesions and are a sensitive and important manifestation of sun-induced skin damage. Studies in animals have shown that dietary fat influences the incidence of sun-induced skin cancer, but the effect of diet on the incidence of actinic keratosis in humans is not known. METHODS: We randomly assigned 76 patients with nonmelanoma skin cancer either to continue their usual diet (control group) or to eat a diet with 20 percent of total caloric intake as fat (dietary-intervention group). For 24 months, the patients were examined for the presence of new actinic keratoses by physicians unaware of their assigned diets. RESULTS: At base line, the mean (+/- SD) percentage of caloric intake as fat was 40 +/- 4 percent in the control group and 39 +/- 3 percent in the dietary-intervention group. After 4 months of dietary therapy the percentage of calories as fat had decreased to 21 percent in the dietary-intervention group, and it remained below this level throughout the 24-month study period. The percentage of calories as fat in the control group did not fall below 36 percent at any time. The cumulative number of new actinic keratoses per patient from months 4 through 24 was 10 +/- 13 in the control group and 3 +/- 7 in the dietary-intervention group (P = 0.001). CONCLUSIONS: In patients with a history of nonmelanoma skin cancer, a low-fat diet reduces the incidence of actinic keratosis.

Effect of dietary omega-3 and omega-6 fatty acid sources on PUVA-induced cutaneous toxicity and tumorigenesis in the hairless mouse.

Because of concern about psoralen-induced phototoxicity and photocarcinogenesis, we investigated the effects of dietary lipids in a mouse model in which 8-methoxypsoralen (8-MOP) and UVA (PUVA) therapy has been shown to be carcinogenic. SKH-Hr-1 hairless albino mice were fed diets containing either omega-3 or omega-6 fatty-acid sources (menhaden oil and corn oil, respectively). After 2 weeks on the diets, the mice were treated topically with 8-MOP and then exposed to UVA (5 J/cm2). Mice receiving the omega-3 fatty-acid source exhibited a marked decrease in inflammatory response and a more rapid repair, as expressed both grossly and microscopically. In support of the latter response, i.e. repair, ornithine decarboxylase activity was about 20% greater in animals receiving the omega-3 fatty-acid source. The effects of the dietary fatty acid sources on PUVA tumorigenesis were examined in long-term studies in which animals were treated topically with 0.01% 8-MOP thrice weekly after which they were exposed to UVA (1 J/cm2). These studies indicated that a dietary lipid rich in omega-3 fatty acid and known to exhibit anti-inflammatory properties can markedly ameliorate the course of PUVA toxicity but does not impede the course of PUVA tumorigenesis.

A new Brevibacterium sp. isolated from infected genital hair of patients with white piedra.

A new aerobic gram-positive non-sporeforming bacillus has been isolated from infected genital hair of patients with white piedra in association with Trichosporon beigelii. This species has been characterised morphologically, nutritionally, by DNA base composition, cell-wall analysis and cellular fatty-acid profile on the basis of 14 isolates. The G+C content of DNA is 63.05 mol%. Cell walls possess meso-diaminopimelic acid (Type IV) and the sugars glucose, galactose, xylose and ribose; mycolic acids are not present. The species has a distinct colonial and microscopic morphology, is strongly proteolytic and produces methanethiol. These findings and the cellular fatty-acid profile are compatible with the genus Brevibacterium. A new species is proposed based on the following characters: colonial and microscopic growth and morphology; conditions for rod-to-coccus cycle; ribose utilisation; and tellurite reduction. The type strain has been named Brevibacterium mcbrellneri E2cr (ATCC 49030). The strong proteolytic properties may be the mechanism of pathogenesis.

Influence of dietary omega-6, -3 fatty acid sources on the initiation and promotion stages of photocarcinogenesis.

To determine the segment along the carcinogenic continuum at which dietary lipid exerts its principal effect, six groups of 35 Skh-HR-1 hairless mice were placed on defined isocaloric diets containing either 0.75%, 12% corn oil or 12% menhaden oil as sources of omega-6 or omega-3 fatty acids, respectively. All animals received an 11 week course of UV-radiation from fluorescent sunlamps. Upon termination of UV, diets of some groups were crossed-over to either low fat, high fat, omega-6 or omega-3 fatty acid sources. The first tumor appeared at week 14. Life-table analysis of the tumor incidence curves and Wilcoxon tests of tumor multiplicity provided evidence that high corn oil diets significantly (P less than 0.01) enhance carcinogenic expression; that tumor enhancement by the omega-6 fatty acid source occurs during the post-initiation, or promotion, stage; that replacement with a low corn oil diet after UV-initiation will negate the exacerbating effect of high corn oil; and that an omega-3 fatty acid source inhibits UV-carcinogenesis even at high dietary levels, although not during the post-initiation stage.

Beta-carotene does not act as an optical filter in skin.

Beta-carotene, when orally administered, only slightly increases the sunburn threshold in normal humans but effectively diminishes sunlight risk in patients suffering from erythropoietic protoporphyria. In addition, beta-carotene has been shown to inhibit UV-induced carcinogenesis in mice when administered either orally or intraperitoneally. To examine the photoprotective properties of beta-carotene, SKH-HR1 albino hairless mice received beta-carotene supplemented diets for either two or four weeks. At the end of each treatment period the skins were visibly yellow. Whole skin and epidermis from each animal were studied by forward scattering transmission spectroscopy and compared with age-matched controls. While no major optical differences were seen in the whole skin or in the epidermis, the presence of beta-carotene was optically demonstrated by weak but typical beta-carotene absorption peaks in the epidermis following the two week feeding period. The peaks were also apparent in the four week group. However, the beta-carotene peaks could not be resolved through full thickness skin. Despite the yellow appearance of the skin, the absorbance due to the carotene was insufficient to impart significant photoprotection. These results confirm previous theoretical arguments that oral beta-carotene treatment does not attain a sufficient concentration in the skin to produce a typical sunscreen effect by absorption of radiation. When beta-carotene is effective in the treatment of photosensitivity, it must produce its protectiveness through an alternative mechanism.

Influence of fish oil supplementation on the minimal erythema dose in humans.

A previous study using the hairless mouse model demonstrated that diets containing a fish-oil lipid source, which contained high levels of omega-3 fatty acids, markedly increased the minimum erythema dose (MED) when compared with diets containing other polyunsaturated fatty acids. To determine whether fish oil supplementation could produce a similar effect in humans, 20 subjects were randomized into two groups, a placebo group and a group receiving fish-oil supplements over a 4-week period. Results showed a small, but statistically significant, increase in MED in patients whose diet was supplemented with fish oil. Cholesterol and prostaglandin E2 levels were unchanged, while triglyceride levels were significantly decreased in the fish oil group. No significant changes in any of these parameters occurred in the placebo group.

Modification of membrane composition, eicosanoid metabolism, and immunoresponsiveness by dietary omega-3 and omega-6 fatty acid sources, modulators of ultraviolet-carcinogenesis.

Dietary sources of lipids containing predominantly n-3 or n-6 fatty acids (FA) have been examined for effect upon several potential pathophysiologic parameters. Epidermal, plasma, and red blood cell (RBC) membrane FA composition exhibited marked differences between animals fed the respective dietary lipid sources. Reduced levels of 18:1, 20:3 and 20:4 occurred in the n-3 FA fed animals which exhibited significantly higher levels of 20:5 and 22:6. Approximately equal levels of 18:2 were present in animals fed either diet. Despite marked differences in RBC membrane FA composition, only marginal effect upon osmotic fragility occurred. Lower levels of 20:3 and 20:4 found in n-3 fed animals could result from a deficit of elongase and/or delta 5-desaturase activity. Whether lower 20:4 levels in n-3 fed animals could rate-limit eicosanoid metabolism is unknown, but epidermal capacity to metabolise arachidonic acid in these animals was found to be closely related to n-6 FA intake. Animals fed n-3 FA exhibited markedly lower levels of plasma PGE2, even when the diet was supplemented with n-6 FA. In addition, UV-radiated animals receiving the n-3 FA source demonstrated a reduced (approximately 30%) response to inflammatory stimulus and a greater (4.5-fold) delayed hypersensitivity (DH) to dinitrochlorobenzene than animals fed the n-6 FA source. These data demonstrate that dietary lipid strongly influences tissue FA composition, eicosanoid metabolism, and, in the case of DH, at least one type of T-cell mediated immune response in UV-irradiated animals.