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Dyslipidemia is one of the most important cardiovascular disease (CVD) risk factors. Polyunsaturated fatty acids (FAs), and especially omega-3 FAs, could significantly contribute to the management of dyslipidemia and the prevention of CVD. The anti-hyperlipidemic effect of selected fish oils (eel, sardine, trout, cod liver) was comparatively evaluated in a high fat diet (HFD)-fed mouse model. At the end of 30 days on the HFD, all animals were hyperlipidemic and were switched to a diet consisting of 90% standard rodent chow plus 10% of oil from eel, sardine, cod liver, or trout. At the end of 60 days on these diets, blood glucose, total blood cholesterol, triglycerides (TGs), and high density lipoprotein (HDL) were quantitated. All diets, except sardine and standard rodent chow, showed statistically significant decreases in blood glucose from day 30 to 90. Total blood cholesterol decreased in all diets except the HFD group, which was continued on this diet until the end of the study. Eel and cod liver oil diets showed significant decreases in TGs. All dietary groups showed a decrease in HDL, but only the trout and standard chow groups exhibited statistically significant decreases. The fish oils tested here for effects on hyperlipidemia vary in per cent of omega-3 FAs and omega-6/-3 FA ratios as determined by gas chromatography Overall, smoked eel was the best source of omega-3 FA, with a balance of omega-6 FA, that ameliorated HFD-induced mixed hyperlipidemia.

Two dietary tenets of the free radical theory of cancer require refinement. The first was dietary reduction of vulnerable free-radical targets, e.g., polyunsaturated lipids. The second was the addition of one or more antioxidants to the diet. Further, it was reported in 1939 that high levels of dietary fat exacerbated UV-carcinogenesis. Both lines of enquiry (dietary lipid and antioxidant effects on UV-carcinogenesis) were investigated. Both dietary lipids and antioxidants modified carcinogenic expression. Increasing levels of omega-6 polyunsaturated fatty acids (PUFA) exacerbated UV-carcinogenesis. However, omega-3 PUFA dramatically inhibited carcinogenic expression. It is probable that the action of omega-6 and-3 PUFA rests with differential metabolic intermediates, both tumor promoting and immune-modulating, that each PUFA generates through lipoxygenase and cyclooxygenase pathways. Antioxidant supplementation with butylated hydroxytoluene or beta-carotene demonstrated that each exerted its own specific antioxidant mechanism(s). When introduced into the complex milieu of the cell with its own intricate and complex antioxidant defense system, detrimental effects may ensue. These results point to oversimplification of these dietary suggestions to reduce cancer risk and the necessity to refine these dietary recommendations.

Two of the dietary tenets of the free radical theory of cancer, put forth by Denham Harman in 1962, require, in deference to newly accrued knowledge, refinement. The first was a recommendation for dietary reduction of vulnerable free radical targets, for example, polyunsaturated lipids. The second was the addition of one or more antioxidants to the diet. With respect to the first, it is now known that the equivalent levels of dietary ω-6, -3 polyunsaturated fatty acids (PUFA) have opposite effects upon photocarcinogenesis. Increasing levels of ω-6 PUFA exacerbate photocarcinogenesis, with regard to decreased tumor latent period and tumor multiplicity. Dietary ω-3 PUFA inhibits photocarcinogenesis, increasing tumor latent period and reducing tumor multiplicity. Yet the degree of unsaturation in both types of fats is almost equal. It is almost certain that the action of these two types of PUFA rests with the intermediates that each generates through the lipoxygenase and cyclooxygenase pathways. The general ...

Epidemiological studies suggested that above average intake of beta-carotene (betaC) might reduce cancer risks. However, clinical trials found that betaC supplementation did not reduce the occurrence of non-melanoma skin cancer and that smokers suffered a significant increase in lung cancer incidence. Further, supplementing semi-defined diets with betaC failed to provide photoprotection as reported earlier for closed-formula rations, but actually exacerbated carcinogenesis. A redox mechanism, based upon one-electron transfer rate constants, proposed interactions between tocopherol, betaC and ascorbic acid in which the carotenoid radical cation, a strongly oxidizing radical, would be repaired by ascorbic acid. If the carotenoid radical cation remained unrepaired, this strongly oxidizing species could account for the pro-carcinogenic activity of betaC. Data from nutritional studies supported an interaction of tocopherol and betaC but not with ascorbic acid. The repair of the betaC radical cation must be dependent on factors other than ascorbic acid, e.g., other carotenoids or unidentified phytochemical(s).

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.

Pro-oxidants, reactive species and free radicals, are toxic substances that can cause oxidative damage to major constituents of biological systems. In contradistinction, antioxidants are defined as any substance that significantly prevents the pro-oxidant-initiated oxidation of a substrate. Consequently, it was suggested that it might be possible to reduce free radical damage and thus cancer risk through 3 dietary changes: (1) caloric reduction, that is, lowering the level of free radical reactions arising in the course of normal metabolism; (2) minimize dietary components that increase the level of free radical reactions (eg, polyunsaturated fats); and (3) supplement the diet with one or more free radical reaction inhibitors (antioxidants). Lipid peroxidation exemplifies the type of chain reaction initiated by free radicals in (2) and (3). Both the phenolic antioxidant butylated hydroxytoluene (BHT) and the carotenoid β-carotene can terminate such reactions and have been shown to influence ultraviolet (UV) carcinogenesis. However, there is a lack of correlation between physicochemical and patho-physiological responses in both instances. Whereas the influence on UV carcinogenesis of both antioxidants has been reported to diminish as the level of dietary fat decreases, pointing to the involvement of lipid peroxidative reactions, the mode of BHT’s action in inhibiting UV carcinogenesis appears to be related to UV dose diminution through increased spectral absorbance of the stratum corneum. β-carotene has no such effect and may actually exacerbate UV carcinogenesis under certain dietary conditions. This paradox points to the complex relationship between chemical mechanisms and biological mode of action of antioxidants. Recent clinical and experimental data suggest that antioxidant supplementation of the complex and intricately balanced natural antioxidant defense system as a cancer prevention strategy will demand extreme caution.

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.

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.

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.

Epithelial-to-mesenchymal cell Transition (EMT) was first recognized as a fundamental event in embryogenesis. EMT, and its reverse process, Mesenchymal-Epithelial Transition (MET), are critical to morphogenesis and are involved in the development of many tissues and organs and events occurring in the developing embryo [1]. EMT results in profound morphological and phenotypic changes to a cell [2]. In this process, epithelial cells disassemble cell-cell junctions [3]; there is reorganization of the cytoskeleton [4]; increased cell motility [1]; and invasion occurs, (requisite for metastasis) [5] – all hallmarks of cancer. EMT has been categorized into three types. Type I is developmental; Type II involves fibrosis and wound healing; and Type III is involved in cancer [6]. It is Type III that we are concerned with here.

The indictment of fat as a dietary constituent that potentiates carcinogenesis arose from a study of Watson and Mellanby in 1930 [1]. Animal diets containing high levels of butterfat (12.5-25%) were shown to enhance coal tar-induced skin tumor formation. After this seminal observation, intense investigations of the effects of dietary fat on chemically-induced carcinogenesis were conducted during the 1930s through the 1950s. There were several conclusions from these studies that are noteworthy [2]. These, however, must be tempered by the fact that many of these early studies failed to control for major dietary parameters, e.g., caloric density. And although much of the exacerbation of fat on tumor formation reported in these early studies could be explained on the basis of increased caloric intake, fat, per se, increased the rate of tumor formation, particularly when total caloric intake was restricted. Also, much of the exacerbation by fat on tumor formation occurred during the post initiation stage of carcinogenesis.

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.

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.

Considerable experimental evidence has accrued from animal studies that implicate dietary fats as important modulators of ultraviolet (UVR)-carcinogenic expression. These fats are composed of essential fatty acids (EFA) and are grouped into two families of polyunsaturated fatty acids (PUFA), omega (ω)-6 and omega (ω)-3 fatty acids (FA). They are essential in that they are precursors of a group of highly active hormones, eicosanoids, that are necessary for normal growth and maintenance of health. Relatively minor differences in molecular structure of these FA not only cause them to act differently in the body, but also to produce diverse effects in modulation of carcinogenic expression. Dietary ω-6 FA has been shown to exacerbate UVR carcinogenic expression (tumor latent period and tumor multiplicity) in a manner that is directly related to level of FA intake. Dietary ω-3 FA inhibits UVR carcinogenic expression. Pro-inflammatory and immunosuppressive eicosanoids, e.g. prostaglandin E2 (PGE2) levels increase in a linear fashion with the concentration of ω-6 FA intake. These levels are dramatically reduced with ω-3 FA intake. ω-6 FA intake suppresses the immunologic pathways manifested in delayed hypersensitivity (DTH) and the responses involved in tumor transplant rejection. ω-3 FA sustains the DTH response in UVR-irradiated animals. Clinical studies have found that supplementary ω-3 FA significantly raise the UVR-mediated erythema threshold and reduce the level of pro-inflammatory and immunosuppressive PGE2 in UVR-irradiated human skin. Taken in toto, these studies suggest that ω-3 supplementation could be beneficial in reducing the occurrence of non-melanoma skin cancer, particularly in those individuals who are at highest risk.

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.

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.

Considerable circumstantial evidence has accrued from both experimental animal and human clinical studies that support a role for omega-3 fatty acids (FA) in the prevention of non-melanoma skin cancer (NMSC). Direct evidence from animal studies has shown that omega-3 FA inhibit ultraviolet radiation (UVR) induced carcinogenic expression. In contrast, increasing levels of dietary omega-6 FA increase UVR carcinogenic expression, with respect to a shorter tumor latent period and increased tumor multiplicity. Both omega-6 and omega-3 FA are essential FA, necessary for normal growth and maintenance of health and although these two classes of FA exhibit only minor structural differences, these differences cause them to act significantly differently in the body. Omega-6 and omega-3 FA, metabolized through the lipoxygenase (LOX) and cyclooxygenase (COX) pathways, lead to differential metabolites that are influential in inflammatory and immune responses involved in carcinogenesis. Clinical studies have shown that omega-3 FA ingestion protects against UVR-induced genotoxicity, raises the UVR-mediated erythema threshold, reduces the level of pro-inflammatory and immunosuppressive prostaglandin E2 (PGE₂) in UVR-irradiated human skin, and appears to protect human skin from UVR-induced immune-suppression. Thus, there is considerable evidence that omega-3 FA supplementation might be beneficial in reducing the occurrence of NMSC, especially in those individuals who are at highest risk.

Several types of glass and plastic materials were shown to exhibit intense photoluminescence when irradiated with UV. Water or phosphate buffered saline (PBS) contained within vessels of the respective materials when irradiated, also demonstrated relatively long-lived luminescence. A significant percentage (30%) of cultured mammalian cells were killed when exposed to UV-irradiated glass beads. The nature of the luminescence of water or PBS, or whether this or the photoluminescence of glass is directly responsible for cell toxicity, is unknown. However, we call attention to this phenomenon as a potential complicating factor in photobiological studies.

Consumption of lycopene, a carotenoid without provitamin A activity, has been associated with a lower risk of prostate and breast cancer. Lutein is another carotenoid that may be associated with a reduced risk of age-related macular degeneration, the leading cause of blindness in adults 65 years of age and older. Bioactive compounds such as lycopene and lutein, derived from natural plant sources, have been shown to act at low substrate levels through the action of intrinsic cytokines and growth factors and their receptors within tissues, particularly those of the fibroblast growth factor and transforming growth factor beta families. The effects of grapefruit-derived and commercial lycopene and lutein preparations on androgen independent cultured malignant type II tumor cells [Dunning R3327AT3 or AT3 cells (androgen-responsive, slow-growing tumor cells with well developed epithelium and stroma)] were compared to their benign parent type I tumor epithelial cells (DTE). Results demonstrated that both lycopene, in an alpha -cyclodextrin water soluble carrier, and lutein inhibited malignant AT3 cells in a concentration and time-dependent manner. No such effect was observed when benign DTE cells were examined, demonstrating selective inhibition of extremely malignant AT3 prostate cancer cells relative to their benign parent. Lutein demonstrated a similar but slightly diminished response as lycopene. When cells were treated with cocktails of lycopene and lutein, no synergistic or additive effect occurred. These studies are consistent with epidemiological studies that show inverse relationships of these carotenoids with prostate cancer.

In toto, there is strong circumstantial evidence from both experimental and clinical studies to support a role for omega-3 FA in the prevention of non-melanoma skin cancer (NMSC). In experimental animal studies there is direct evidence that dietary omega-3 FA inhibits ultraviolet radiation (UVR) carcinogenic expression, with regard to both increased tumor latent period and reduced tumor multiplicity. Equivalent levels of omega-6 FA increase UVR carcinogenic expression. Dietary omega-3 FA dramatically reduces the plasma and cutaneous pro-inflammatory and immunosuppressive PGE(2) levels in mice. Dietary omega-6 FA increases prostaglandin E synthase type 2 (PGE(2)) level. Dietary omega-3 FA significantly reduces the inflammatory response and sustains, or enhances, the delayed type hypersensitivity immune response in mice when compared to an equivalent dietary level of omega-6 FA. Supplementary omega-3 FA significantly increases the UVR-mediated erythema threshold in humans. Supplementary omega-3 FA significantly reduces the level of pro-inflammatory and immunosuppressive PGE(2) levels in Ultraviolet B-irradiated human skin.

Nonmelanoma skin cancer is the most prevalent malignant disease among light-skinned individuals in the USA, accounting for approximately 1 million new cases annually. Solar ultraviolet radiation is known to be the major cause of skin cancer. The idea that diet, particularly dietary fat, may play a role in modulating cancer incidence has been based largely upon indirect epidemiologic evidence. However, few studies have found correlations of dietary fat intake with skin cancer incidence. Nevertheless, a large body of evidence with experimental animals and one clinical intervention trial, the latter avoiding the pitfalls of many epidemiologic investigations, clearly demonstrate that the level of dietary fat intake can have a significant influence on the occurrence of skin cancer in individuals at high risk.

Beta-carotene is a strong singlet oxygen quencher and antioxidant. Epidemiologic studies have implied that an above average intake of the carotenoid might reduce cancer risks. Earlier studies found that the carotenoid, when added to commercial closed-formula rodent diets, provided significant photoprotection against UV-carcinogenesis in mice. Clinical intervention trials found that beta-carotene supplementation evoked no change in incidence of nonmelanoma skin cancer. However, when smokers were supplemented with the carotenoid a significant increase in lung cancer resulted. Recently, employing a beta-carotene supplemented semi-defined diet, not only was no photoprotective effect found, but significant exacerbation of UV-carcinogenesis occurred. Earlier, a mechanism, based upon redox potential of interacting antioxidants, was proposed in which beta-carotene participated with vitamins E and C to efficiently repair oxy radicals and, thus, thought to provide photoprotection. In this schema, alpha-tocopherol would first intercept an oxy radical. In terminating the radical-propagating reaction, the tocopherol radical cation is formed which, in turn, is repaired by beta-carotene to form the carotenoid radical cation. This radical is repaired by ascorbic acid (vitamin C). As the carotenoid radical cation is a strongly oxidizing radical, unrepaired it could contribute to the exacerbating effect on UV-carcinogenesis. Thus, vitamin C levels could influence the levels of the pro-oxidant carotenoid radical cation. However, when hairless mice were fed beta-carotene supplemented semi-defined diet with varying levels of vitamin C (0-5590 mg kg(-1) diet) no effect on UV-carcinogenesis was observed. Lowering alpha-tocopherol levels did result in further increase of beta-carotene exacerbation, suggesting beta-carotene and alpha-tocopherol interaction. It was concluded that the non-injurious or protective effect of beta-carotene found in the closed-formula rations might depend on interaction with other dietary factors that are absent in the semi-defined diet. At present, beta-carotene use as a dietary supplement for photoprotection should be approached cautiously.

b-Carotene is a strong singlet oxygen quencher and, under most conditions, exhibits strong antioxidant properties. Based on these properties, and a number of epidemiological studies, it was suggested that an above average intake of the carotenoid might reduce cancer risks. Earlier studies had found that b-carotene, when added to commercial closed-formula rodent diets, provided significant photoprotection to ultraviolet light (UV) carcinogenesis. However, clinical trials found that b-carotene supplementation evoked no change in incidence of nonmelanoma skin cancer and that smokers suffered a significant increase in lung cancer incidence. Further, recent studies, employing b-carotene-supplemented semidefined diets, not only failed to find a photoprotective effect, but significant exacerbation of UV carcinogenic expression resulted. Based on the relative electron transfer rate constants for interactions between b-carotene, a-tocopherol (vitamin E), and vitamin C, a mechanism was proposed for the repair of b-carotene radical cation, a strongly oxidizing radical resulting from b-carotene interactions with many oxidizing species. It was theorized that vitamin C repaired the carotenoid radical cation. As mice have no nutritional requirement for vitamin C and smokers are known to exhibit low levels of the vitamin, it was suggested that differences in the relative levels of vitamin C in closed-formula rations (no vitamin C) in which photoprotection occurred, and semidefined diets (containing vitamin C) in which exacerbation resulted, might account for the differences in response. Hairless mice were fed b-carotene-supplemented semidefined diets containing varying levels of vitamins E and C (either increasing their concentrations or reducing them to reflect levels found in closed-formula rations) and subjected to a UV carcinogenesis protocol. Increasing levels of vitamins E and C did not ameliorate b-carotene exacerbation of UV carcinogenesis. Nor did elimination of vitamin C from the diet. Reduced levels of dietary vitamin E augmented b-carotene exacerbation of UV carcinogenic expression, suggesting vitamin E and b-carotene interaction. It is concluded that the photoprotective effect of b-carotene reported earlier by others, or the noninjurious effect of b-carotene found in our studies with closed-formula rations, might depend on interaction with other dietary factors that are either absent, or present in ineffectual concentrations, in the semidefined diet in which exacerbation of UV carcinogenesis occurs. Those factors could be other carotenoids, their isomers, or some yet unidentified phytochemical(s).

Solar ultraviolet radiation (UVR) is recognized as a major cause of non-melanoma skin cancer in man. Skin cancer occurs most frequently in the most heavily exposed areas and correlates with degree of outdoor exposure. The incidence of skin cancer is also increased by contact with photosensitizing drugs and chemicals such as psoralens, coal tars and petroleum stocks. Other substances which do not act as photosensitizers, such as immunosuppressants taken by organ transplant recipients, also increase the risk of skin cancer. The U.S. Food and Drug Administration requests, on a case-by-case basis, that risk of enhanced photocarcinogenesis is assessed for many classes of drugs. Health Canada's Therapeutic Products Programme has issued a Notice of Intent to regulate pharmaceutical products which may enhance carcinogenicity of the skin induced by ultraviolet radiation. Other national regulatory agencies review such data when they exist, but their own requirements emphasize batteries of short-term in vitro and in vivo tests. While they may support drug development strategies, short-term tests have yet to be validated as predictors of the ability of drugs or chemicals to enhance photocarcinogenesis. Published protocols now describe study designs and procedures capable of determining whether test agents enhance the rate of formation of UVR-induced skin tumors.

An hypothesis for the role of free radicals in cancer was elaborated by D. Harman in 1962 who suggested that it might be possible to reduce the extent of damage caused by free radicals through three dietary changes: (i) caloric reduction, i.e., lowering the level of free radical reactions arising in the course of normal metabolism; (ii) minimize dietary components that tend to increase the level of free radical reactions (e.g., polyunsaturated fats); and (iii) supplement the diet with one or more free radical reaction inhibitors (anti-oxidants). With respect to (ii) and (iii), lipid peroxidation exemplifies the type of chain reaction initiated by free radicals, with unsaturated fatty acids being the primary center of free radical attack. Anti-oxidants act as free radical scavengers and are able to terminate these reactions. Indeed, the phenolic anti-oxidant butylated hydroxytoluene (BHT), and the carotenoid beta-carotene, have both been shown to influence photocarcinogenesis, although the lack of correlation between physicochemical parameters and pathophysiological responses is apparent in both instances. The bimolecular rate constant for reaction of BHT with model peroxyl radicals is low while beta-carotene is highly reactive. However, both are able to efficiently inhibit lipid peroxidation reactions in biological membranes. Indeed, the influence of photocarcinogenesis by both BHT and beta-carotene is diminished as the level of dietary fat decreases, pointing to the involvement of lipid peroxidative reactions. Nevertheless, the mode of action of BHT in inhibiting photocarcinogenesis appears to be related to dose-diminution resulting from an increased spectral absorbance of the stratum corneum. On the other hand, beta-carotene has no such effect and may actually exacerbate photocarcinogenesis under certain dietary conditions. This paradox points to the complex relationship between chemical mechanisms and biological mode of action of anti-oxidants in photocarcinogenesis. Recent clinical and experimental data also suggest that supplementation of the complex and intricately balanced natural antioxidant defense system with one or more anti-oxidants as a cancer prevention strategy will demand extreme caution.

The quest to find or develop a systemic photoprotectant that would avoid the limitations associated with topical application of photoprotective agents has been a compelling endeavour. Such an agent would be expected to act by one or more of the following mechanisms, i.e.: (1) attenuation of the level of actinic insult by acting as a barrier to UV rays; (2) competing with the target molecules for the damaging products of the offending agent, e.g., the action of antioxidants; (3) restorative action; and (4) suppression of various stages of the inflammatory response. Several agents whose protective properties were presumed to result from one or more of these mechanisms have been examined in clinical trials. These include the antimalarials, psoralens, carotenoids, retinoids, vitamins C and E, and selenium. Whereas some agents show promise, others have limitations that preclude their consideration as an universal photoprotectant. However, recent attempts at dietary manipulation show some promise for protection against certain solar-induced effects. Specific strategies, namely reduction in total dietary fat and omega-3 fatty acid supplementation, have resulted in protection against non-melanoma skin cancer and other markers of UV-induced tissue damage, respectively. It is in these directions that future research is likely to be most beneficial with regard to systemic protection against UV-insult.

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 (P0.001). 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 (P0.02) in the last 8-month period. Patients in the DI group also had significantly (P0.01) 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.

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% O 2 , 10% CO 2 , and 83% N 2 ) 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

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.

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.

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.

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.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.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).In patients with a history of nonmelanoma skin cancer, a low-fat diet reduces the incidence of actinic keratosis.

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 (P0.04) 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 (P0.001) in ODC inducibility occurred with advancing age.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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.

Butylated hydroxytoluene (BHT) and certain carotenoid pigments have been found to inhibit photocarcinogenesis in animal models. In addition, BHT protects against UV-B-induced erythema and UV-B induction of ornithine decarboxylase. Studies on the photoprotective mechanism(s) of BHT suggested that changes in the physico-chemical properties of the keratin of the stratum corneum layer of skin occurred, leading to increases in UV absorption of that tissue. These changes might be exerted via the anti-radical action of BHT that retards oxidation and prevents cross-linking of the keratin chains, resulting in a diminution of UV-B radiation reaching potential target sites. The carotenoids beta-carotene, canthaxanthin and phytoene also inhibit UV-B carcinogenesis. beta-Carotene and canthaxanthin are excellent quenchers of singlet oxygen, and all three pigments can quench free radicals. beta-Carotene and canthaxanthin have been shown to quench singlet oxygen/free radical reactions in the skin of porphyric mice, and these two pigments as well as phytoene have been found to quench excited species formed on irradiation of mouse skin by UV-B.