Type I Diabetes Mellitus Suppresses Experimental Skin Carcinogenesis.

This study explores the previously uncharted territory of the effects of ultraviolet (UV) radiation on diabetic skin, compared to its well-documented impact on normal skin, particularly focusing on carcinogenesis and aging. Employing hairless SKH-hr2, Type 1 and 2 diabetic, and nondiabetic male mice, the research subjected these to UV radiation thrice weekly for eight months. The investigation included comprehensive assessments of photoaging and photocarcinogenesis in diabetic versus normal skin, measuring factors such as hydration, trans-epidermal water loss, elasticity, skin thickness, melanin, sebum content, stratum corneum exfoliation and body weight, alongside photo documentation. Additionally, oxidative stress and the presence of hydrophilic antioxidants (uric acid and glutathione) in the stratum corneum were evaluated. Histopathological examination post-sacrifice provided insights into the morphological changes. Findings reveal that under UV exposure, Type 1 diabetic skin showed heightened dehydration, thinning, and signs of accelerated aging. Remarkably, Type 1 diabetic mice did not develop squamous cell carcinoma or pigmented nevi, contrary to normal and Type 2 diabetic skin. This unexpected resistance to UV-induced skin cancers in Type 1 diabetic skin prompts a crucial need for further research to uncover the underlying mechanisms providing this resistance.

A Synopsis of the Associations of Oxidative Stress, ROS, and Antioxidants with Diabetes Mellitus.

The Greek physician, Aretaios, coined the term "diabetes" in the 1st Century A.D. "Mellitus" arose from the observation that the urine exhibits a sweetness due to its elevated glucose levels. Diabetes mellitus (DM) accounted for 6.7 million deaths globally in 2021 with expenditures of USD 966 billion. Mortality is predicted to rise nearly 10-fold by 2030. Oxidative stress, an imbalance between the generation and removal of reactive oxygen species (ROS), is implicated in the pathophysiology of diabetes. Whereas ROS are generated in euglycemic, natural insulin-regulated glucose metabolism, levels are regulated by factors that regulate cellular respiration, e.g., the availability of NAD-linked substrates, succinate, and oxygen; and antioxidant enzymes that maintain the cellular redox balance. Only about 1-2% of total oxygen consumption results in the formation of superoxide anion and hydrogen peroxide under normal reduced conditions. However, under hyperglycemic conditions, about 10% of the respiratory oxygen consumed may be lost as free radicals. Under hyperglycemic conditions, the two-reaction polyol pathway is activated. Nearly 30% of blood glucose can flux through this pathway-a major path contributing to NADH/NAD+ redox imbalance. Under these conditions, protein glycation and lipid peroxidation increase, and inflammatory cytokines are formed, leading to the further formation of ROS. As mitochondria are the major site of intracellular ROS, these organelles are subject to the deleterious effects of ROS themselves and eventually become dysfunctional-a milestone in Metabolic Syndrome (MetS) of which insulin resistance and diabetes predispose to cardiovascular disease.

Influence of Omega-3 Fatty Acid-Rich Fish Oils on Hyperlipidemia: Effect of Eel, Sardine, Trout, and Cod Oils on Hyperlipidemic Mice.

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.

The Benefits and Risks of Certain Dietary Carotenoids that Exhibit both Anti- and Pro-Oxidative Mechanisms-A Comprehensive Review.

Carotenoid pigments, particularly ß-carotene and lycopene, are consumed in human foodstuffs and play a vital role in maintaining health. ß-carotene is known to quench singlet oxygen and can have strong antioxidant activity. As such, it was proposed that ß-carotene might reduce the risk of cancer. Epidemiological studies found inverse relationships between cancer risk and ß-carotene intake or blood levels. However, clinical trials failed to support those findings and ß-carotene supplementation actually increased lung cancer incidence in male smokers. Early experimental animal studies found dietary ß-carotene inhibited UV-induced skin cancers. Later studies found that ß-carotene supplementation exacerbated UV-carcinogenic expression. The discrepancies of these results were related to the type of diet the animals consumed. Lycopene has been associated with reduced risk of lethal stage prostate cancer. Other carotenoids, e.g., lutein and zeaxanthin, play a vital role in visual health. Numerous studies of molecular mechanisms to explain the carotenoids' mode of action have centered on singlet oxygen, as well as radical reactions. In cellular systems, singlet oxygen quenching by carotenoids has been reported but is more complex than in organic solvents. In dietary ß-carotene supplement studies, damaging pro-oxidant reactivity can also arise. Reasons for this switch are likely due to the properties of the carotenoid radicals themselves. Understanding singlet oxygen reactions and the anti-/pro-oxidant roles of carotenoids are of importance to photosynthesis, vision and cancer.

Potential Benefits of Omega-3 Fatty Acids in Non-Melanoma Skin Cancer.

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.

The role of nutritional lipids and antioxidants in UV-induced skin cancer.

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.

Interaction of ascorbic acid and tocopherol on beta-carotene modulated carcinogenesis.

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).

Lycopene and lutein inhibit proliferation in rat prostate carcinoma cells.

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.

The potential of omega-3 fatty acids in the prevention of non-melanoma skin 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.

Can diet prevent nonmelanoma skin cancer progression?

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.

Reassessment of a free radical theory of cancer with emphasis on ultraviolet carcinogenesis.

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 beta-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. beta-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.

Pro-carcinogenic activity of beta-carotene, a putative systemic photoprotectant.

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.

Modulation of dietary vitamins E and C fails to ameliorate b-carotene exacerbation of UV carcinogenesis in mice.

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).

Standardized protocols for photocarcinogenesis safety testing.

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.

Celecoxib, a cyclooxygenase 2 inhibitor as a potential chemopreventive to UV-induced skin cancer: a study in the hairless mouse model.

OBJECTIVE: To assess the preventive effect of a cyclooxygenase 2 inhibitor, celecoxib (Celebrex; G.D. Searle & Co, Skokie, Ill), in UV-induced skin cancer in hairless mice. DESIGN: Randomized dose-response study. A total of 75 SKH-HR-1 female hairless mice, aged 2 months, were randomized into control, low-dose (200 mg twice daily human dose equivalent), and high-dose (400 mg twice daily human dose equivalent) celecoxib treatment groups. Animals received 1 J/cm(2) daily (5 d/wk) total irradiation. The animals were evaluated weekly for appearance of tumors, and the data were analyzed with respect to tumor latency period and tumor multiplicity using statistical software and Wilcoxon rank sum analyses, respectively. Prostaglandin E(2) levels in the blood and skin were assessed in each group. SETTING: Veterans Affairs Medical Center, Research and Dermatology Services. INTERVENTION: Animals received restricted diets containing the Food and Drug Administration-approved human equivalent doses of 200 mg (low dose) and 400 mg (high dose) of celecoxib twice daily. Controls received no drug. Tumors were induced in all animals with an equivalent UV dose. MAIN OUTCOME MEASURES: Animals were evaluated weekly for the appearance of tumors, and data were analyzed with regard to tumor latency period and tumor multiplicity. Constitutive prostaglandin E(2) levels in blood and epidermis were assessed in each group. RESULTS: Low doses and high doses of celecoxib significantly lengthened the tumor latency period (P<.03 and P<.003, respectively) and reduced tumor multiplicity (P<.005 and P<.001, respectively) compared with controls. There were no differences in the constitutive levels of blood or epidermal prostaglandin E(2) in the low- or high-dose treated animals compared with controls when analyzed at study termination. CONCLUSIONS: Celecoxib is an effective and safe chemopreventive agent in UV carcinogenesis. The epidemiologic, laboratory, and animal studies of the influence of celecoxib on cancer incidence and its low association with systemic adverse effects have led to a potentially new therapeutic approach for the prevention of skin cancer.

Pro-oxidant and anti-oxidant mechanism(s) of BHT and beta-carotene in photocarcinogenesis.

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.