Cutaneous melanin pigment plays a critical role in camouflage, mimicry, social communication, and protection against harmful effects of solar radiation. Melanogenesis is under complex regulatory control by multiple agents interacting via pathways activated by receptor-dependent and -independent mechanisms, in hormonal, auto-, para-, or intracrine fashion. Because of the multidirectional nature and heterogeneous character of the melanogenesis modifying agents, its controlling factors are not organized into simple linear sequences, but they interphase instead in a multidimensional network, with extensive functional overlapping with connections arranged both in series and in parallel. The most important positive regulator of melanogenesis is the MC1 receptor with its ligands melanocortins and ACTH, whereas among the negative regulators agouti protein stands out, determining intensity of melanogenesis and also the type of melanin synthesized. Within the context of the skin as a stress organ, melanogenic activity serves as a unique molecular sensor and transducer of noxious signals and as regulator of local homeostasis. In keeping with these multiple roles, melanogenesis is controlled by a highly structured system, active since early embryogenesis and capable of superselective functional regulation that may reach down to the cellular level represented by single melanocytes. Indeed, the significance of melanogenesis extends beyond the mere assignment of a color trait.

https://www.physiology.org/doi/pdf/10.1152/physrev.00044.2003

Melanin Pigmentation in Mammalian Skin and Its Hormonal Regulation

The epidemiologic literature in the English language regarding intake of tomatoes and tomato-based products and blood lycopene (a compound derived predominantly from tomatoes) level in relation to the risk of various cancers was reviewed. Among 72 studies identified, 57 reported inverse associations between tomato intake or blood lycopene level and the risk of cancer at a defined anatomic site; 35 of these inverse associations were statistically significant. No study indicated that higher tomato consumption or blood lycopene level statistically significantly increased the risk of cancer at any of the investigated sites. About half of the relative risks for comparisons of high with low intakes or levels for tomatoes or lycopene were approximately 0.6 or lower. The evidence for a benefit was strongest for cancers of the prostate, lung, and stomach. Data were also suggestive of a benefit for cancers of the pancreas, colon and rectum, esophagus, oral cavity, breast, and cervix. Because the data are from observational studies, a cause-effect relationship cannot be established definitively. However, the consistency of the results across numerous studies in diverse populations, for case-control and prospective studies, and for dietary-based and blood-based investigations argues against bias or confounding as the explanation for these findings. Lycopene may account for or contribute to these benefits, but this possibility is not yet proven and requires further study. Numerous other potentially beneficial compounds are present in tomatoes, and, conceivably, complex interactions among multiple components may contribute to the anticancer properties of tomatoes. The consistently lower risk of cancer for a variety of anatomic sites that is associated with higher consumption of tomatoes and tomato-based products adds further support for current dietary recommendations to increase fruit and vegetable consumption.

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Tomatoes, Tomato-Based Products, Lycopene, and Cancer: Review of the Epidemiologic Literature

Pomegranate (Punica granatum L.) fruits are widely consumed as juice (PJ). The potent antioxidant and anti-atherosclerotic activities of PJ are attributed to its polyphenols including punicalagin, the major fruit ellagitannin, and ellagic acid (EA). Punicalagin is the major antioxidant polyphenol ingredient in PJ. Punicalagin, EA, a standardized total pomegranate tannin (TPT) extract and PJ were evaluated for in vitro antiproliferative, apoptotic and antioxidant activities. Punicalagin, EA and TPT were evaluated for antiproliferative activity at 12.5-100 microg/ml on human oral (KB, CAL27), colon (HT-29, HCT116, SW480, SW620) and prostate (RWPE-1, 22Rv1) tumor cells. Punicalagin, EA and TPT were evaluated at 100 microg/ml concentrations for apoptotic effects and at 10 microg/ml concentrations for antioxidant properties. However, to evaluate the synergistic and/or additive contributions from other PJ phytochemicals, PJ was tested at concentrations normalized to deliver equivalent amounts of punicalagin (w/w). Apoptotic effects were evaluated against the HT-29 and HCT116 colon cancer cell lines. Antioxidant effects were evaluated using inhibition of lipid peroxidation and Trolox equivalent antioxidant capacity (TEAC) assays. Pomegranate juice showed greatest antiproliferative activity against all cell lines by inhibiting proliferation from 30% to 100%. At 100 microg/ml, PJ, EA, punicalagin and TPT induced apoptosis in HT-29 colon cells. However, in the HCT116 colon cells, EA, punicalagin and TPT but not PJ induced apoptosis. The trend in antioxidant activity was PJ>TPT>punicalagin>EA. The superior bioactivity of PJ compared to its purified polyphenols illustrated the multifactorial effects and chemical synergy of the action of multiple compounds compared to single purified active ingredients.

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In vitro antiproliferative, apoptotic and antioxidant activities of punicalagin, ellagic acid and a total pomegranate tannin extract are enhanced in combination with other polyphenols as found in pomegranate juice

Dietary consumption of the carotenoid lycopene (mostly from tomato products) has been associated with a lower risk of prostate cancer. Evidence relating other carotenoids, tocopherols, and retinol to prostate cancer risk has been equivocal. This prospective study was designed to examine the relationship between plasma concentrations of several major antioxidants and risk of prostate cancer. We conducted a nested case-control study using plasma samples obtained in 1982 from healthy men enrolled in the Physicians’ Health Study, a randomized, placebo-controlled trial of aspirin and β-carotene. Subjects included 578 men who developed prostate cancer within 13 years of follow-up and 1294 age- and smoking status-matched controls. We quantified the five major plasma carotenoid peaks (α- and β-carotene, β-cryptoxanthin, lutein, and lycopene) plus α- and γ-tocopherol and retinol using high-performance liquid chromatography. Results for plasma β-carotene are reported separately. Odds ratios (ORs), 95% confidence intervals (CIs), and P s for trend were calculated for each quintile of plasma antioxidant using logistic regression models that allowed for adjustment of potential confounders and estimation of effect modification by assignment to either active β-carotene or placebo in the trial. Lycopene was the only antioxidant found at significantly lower mean levels in cases than in matched controls ( P = 0.04 for all cases). The ORs for all prostate cancers declined slightly with increasing quintile of plasma lycopene (5th quintile OR = 0.75, 95% CI = 0.54–1.06; P , trend = 0.12); there was a stronger inverse association for aggressive prostate cancers (5th quintile OR = 0.56, 95% CI = 0.34–0.91; P , trend = 0.05). In the placebo group, plasma lycopene was very strongly related to lower prostate cancer risk (5th quintile OR = 0.40; P , trend = 0.006 for aggressive cancer), whereas there was no evidence for a trend among those assigned to β-carotene supplements. However, in the β-carotene group, prostate cancer risk was reduced in each lycopene quintile relative to men with low lycopene and placebo. The only other notable association was a reduced risk of aggressive cancer with higher α-tocopherol levels that was not statistically significant. None of the associations for lycopene were confounded by age, smoking, body mass index, exercise, alcohol, multivitamin use, or plasma total cholesterol level. These results concur with a recent prospective dietary analysis, which identified lycopene as the carotenoid with the clearest inverse relation to the development of prostate cancer. The inverse association was particularly apparent for aggressive cancer and for men not consuming β-carotene supplements. For men with low lycopene, β-carotene supplements were associated with risk reductions comparable to those observed with high lycopene. These data provide further evidence that increased consumption of tomato products and other lycopene-containing foods might reduce the occurrence or progression of prostate cancer.

/pdf/lower-prostate-cancer-risk-in-men-with-elevated-plasma-3e7uz43j2l.pdf

Lower prostate cancer risk in men with elevated plasma lycopene levels: results of a prospective analysis.

Reactive oxygen species (ROS) and the coupled oxidative stress have been associated with tumor formation. Several studies suggested that ROS can act as secondary messengers and control various signaling cascades. In the present studies, we characterized the oxidative stress status in three different prostate cancer cells (PC3, DU145, and LNCaP) exhibiting various degree of aggressiveness and normal prostate cells in culture (WPMY1, RWPE1, and primary cultures of normal epithelial cells). We observed increased ROS generation in cancer cells compared with normal cells, and that extramitochondrial source of ROS generator, NAD(P)H oxidase (Nox) systems, are associated with the ROS generation and are critical for the malignant phenotype of prostate cancer cells. Moreover, diphenyliodonium, a specific Nox inhibitor, blocked proliferation, modulated the activity of growth signaling cascades extracellular signal-regulated kinase (ERK)1/ERK2 and p38 mitogen-activated protein kinase as well as AKT protein kinase B, and caused cyclin B-dependent G(2)-M cell cycle arrest. We also observed higher degrees of ROS generation in the PC3 cells than DU145 and LNCaP, and that ROS generation is critical for migratory/invasiveness phenotypes. Furthermore, blocking of the ROS production rather than ROS neutralization resulted in decreased matrix metalloproteinase 9 activity as well as loss of mitochondrial potential, plausible reasons for decreased cell invasion and increased cell death. Taken together, these studies show, for the first time, the essential role of ROS production by extramitochondrial source in prostate cancer and suggest that therapies aimed at reducing ROS production might offer effective means of combating prostate cancer in particular, and perhaps other malignancies in general.

https://cancerres.aacrjournals.org/content/canres/68/6/1777.full.pdf

Oxidative stress is inherent in prostate cancer cells and is required for aggressive phenotype.

Background: Prostate cancer is a disease associated with aging. Also commonly associated with increasing age is a shift in the prooxidant‐antioxidant balance of many tissues toward a more oxidative state, i.e., increased oxidative stress. We hypothesize that androgen exposure, which has long been associated with the development of prostate cancer, may be a means by which the prooxidant‐antioxidant balance of prostate cells is altered. Purpose: Using established prostate carcinoma cell lines, we studied the effect of androgens on various parameters of oxidative state (e.g., generation of hydrogen peroxide and hydroxyl radicals, lipid peroxidation, and oxygen consumption) and antioxidant defense mechanisms (e.g., the glutathione system and catalase). Methods: The androgen-responsive LNCaP and the androgen-independent DU145 prostate carcinoma cell lines were exposed to 5a-dihydrotestosterone (DHT) and to the synthetic androgen R1881. The cellular proliferation responses were measured by use of a fluorometric assay to quantitate the amount of DNA. The generation of reactive oxygen species was measured by use of 2*,7*-dichlorofluorescin diacetate, a dye that fluoresces in the presence of hydrogen peroxide or hydroxyl radicals. Lipid peroxidation was quantitated by use of a chromogen specific for malonaldehyde and 4-hydroxy-2(E)-nonenal. General mitochondrial activity was determined by assaying 3-(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide (MTT) reduction. A Clarktype electrode was used to assess oxygen consumption per cell. Intracellular glutathione concentrations and the activities of catalase and g-glutamyl transpeptidase were measured spectrophotometrically. All P values resulted from two-sided tests. Results: DHT at less than 1 to 100 nM (a concentration range encompassing the physiologic levels of DHT considering all ages) and R1881 at 0.1-1 nM concentrations were effective in inducing in LNCaP cells comparable proliferative responses and changes in oxidative stress. In contrast, neither DHT nor R1881 had any effect on the oxidative stress in DU145 cells. The mitochondrial activity in LNCaP cells, as measured by MTT reduction, was significantly elevated above the levels of the untreated controls by DHT (0.1-1000 nM) and R1881 (0.05-1 nM )( P<.001 in both). Oxygen consumption and catalase activity were increased in LNCaP cells in the presence of 1 nM R1881 by 60% and 40%, respectively, over the values in the untreated control cells (P<.03 and P<.01, respectively). The same concentration of R1881 resulted in a decrease in intracellular glutathione concentrations and an increase in g-glutamyl transpeptidase activity in LNCaP ells. Treatment with the oxidizing agents H2O2 and menadione produced an increase in g-glutamyl transpeptidase activity in LNCaP cells, whereas treatment with the antioxidant compound ascorbic acid (100 mM) reduced the oxidative stress produced in LNCaP cells by 1 nM R1881 and completely blocked the g-glutamyl transpeptidase activity. Conclusions: Physiologic levels of androgens are capable of increasing oxidative stress in androgenresponsive LNCaP prostate carcinoma cells. The evidence suggests that this result is due in part to increased mitochondrial activity. Androgens also alter intracellular glutathione levels and the activity of certain detoxification enzymes, such as g-glutamyl transpeptidase, that are important for maintenance of the cellular prooxidant‐antioxidant balance. [J Natl Cancer Inst 1997;89:40-8]

/pdf/prooxidant-antioxidant-shift-induced-by-androgen-treatment-ldevvtjxcs.pdf

Prooxidant-Antioxidant Shift Induced by Androgen Treatment of Human Prostate Carcinoma Cells

BACKGROUND Previous studies have suggested that male hormones (androgens) and certain forms of oxygen (reactive oxygen species) are linked to the development of prostate cancer. We hypothesized that androgens contribute to prostate carcinogenesis by increasing oxidative stress. We further hypothesized that antioxidants reduce prostate cancer risk by modulating androgen effects on cellular processes. METHODS To test these hypotheses, we looked for 1) a change in the level of reactive oxygen species in the presence of androgens, 2) androgen-induced binding activity of transcriptional activators AP-1 and NF-kappaB, whose activities are known to be altered during cell proliferation, and 3) the effect of antioxidants on androgen-induced transcription factor binding. RESULTS Physiologic concentrations (1 nM) of 5alpha-dihydrotestosterone or 1-10 nM R1881, a synthetic androgen, produced sustained elevation of AP-1 and NF-kappaB DNA-binding activity in LNCaP cells, an androgen-responsive human prostate carcinoma cell line. Androgen-independent DU145 cells (another human prostate carcinoma cell line) were unaffected by R1881 treatment. AP-1-binding activity increased 5 hours after 1 nM R1881 treatment; NF-kappaB DNA-binding activity increased after 36 hours. Both activities remained elevated for at least 120 hours. Nuclear AP-1 and NF-kappaB protein levels were not elevated. Antioxidant vitamins C plus E blocked both androgen-induced DNA-binding activity and production of reactive oxygen species. CONCLUSION Physiologic concentrations of androgens induce production of reactive oxygen species and cause prolonged AP-1 and NF-kappaB DNA-binding activities, which are diminished by vitamins C and E.

/pdf/effect-of-antioxidants-on-androgen-induced-ap-1-and-nf-kb-2ijqzwd3km.pdf

William F. Henry

Papers

Prooxidant-Antioxidant Shift Induced by Androgen Treatment of Human Prostate Carcinoma Cells

Effect of Antioxidants on Androgen-Induced AP-1 and NF-κB DNA-Binding Activity in Prostate Carcinoma Cells