Stimulatory effect of voluntary exercise or fat removal (partial lipectomy) on apoptosis in the skin of UVB light-irradiated mice

Possible involvement of CXC motif chemokine ligand 10 in exercise-induced collagen production of mouse dermal fibroblasts

Evidence suggests that exercise can regulate skin functions such as promoting wound healing and inhibiting aging. Physical exercise modulates the secretion of proteins and peptides from skeletal muscles, called myokines, which play a role in transmitting exercise signals throughout the body. Therefore, exercise-regulated myokines may play a role in controlling skin functions; however, the precise mechanisms remain elusive. In this study, we focused on the recently identified CXC motif chemokine ligand 10 (CXCL10), an exercise-reduced myokine, and attempted to elucidate its role in regulating collagen synthesis in dermal fibroblasts. Mouse C2C12 myotubes were stimulated with or without electrical pulse stimulation (EPS) to induce contraction for 24 h, and conditioned medium was collected (EPS-CM or Ctrl-CM, respectively). The reduction in CXCL10 concentration by EPS was confirmed using ELISA. Next, mouse dermal fibroblasts were isolated from the dorsal skin of C57BL6/J mice (2 weeks old) and were stimulated with Ctrl-CM or EPS-CM for 24 h. EPS-CM treatment significantly increased collagen production compared to Ctrl-CM treatment. Even in the Ctrl-CM condition, the addition of an antagonist for CXCR3 (CXCL10 receptor) increased collagen production. In contrast, recombinant CXCL10 abolished EPS-CM-dependent collagen induction. Overall, this study raises the possibility that CXCL10 secretion from skeletal muscles may control collagen production in mouse dermal fibroblasts.

Enhancing Effects of Environmental Enrichment on the Functions of Natural Killer Cells in Mice

The environment of an organism can convey a powerful influence over its biology. Environmental enrichment (EE), as a eustress model, has been used extensively in neuroscience to study neurogenesis and brain plasticity. EE has also been used as an intervention for the treatment and prevention of neurological and psychiatric disorders with limited clinical application. By contrast, the effects of EE on the immune system are relatively less investigated. Recently, accumulating evidence has demonstrated that EE can robustly impact immune function. In this review, we summarize the major components of EE, the impact of EE on natural killer (NK) cells, EE's immunoprotective roles in cancer, and the underlying mechanisms of EE-induced NK cell regulation. Moreover, we discuss opportunities for translational application based on insights from animal research of EE-induced NK cell regulation.

Exercise and cancer: a position statement from the Spanish Society of Medical Oncology

Due to improvements in the number of cancer survivors and survival time, there is a growing interest in healthy behaviors, such as physical activity (PA), and their potential impact on cancer- and non-cancer-related morbidity in individuals with cancer. Commissioned by the Spanish Society of Medical Oncology (SEOM), in this review, we sought to distill the most recent evidence on this topic, focusing on the mechanisms that underpin the effects of PA on cancer, the role of PA in cancer prevention and in the prognosis of cancer and practical recommendations for clinicians regarding PA counseling. Despite the available information, the introduction of exercise programs into the global management of cancer patients remains a challenge with several areas of uncertainty. Among others, the most effective behavioral interventions to achieve long-term changes in a patient’s lifestyle and the optimal intensity and duration of PA should be defined with more precision in future studies.

Molecular Mechanisms Linking Exercise to Cancer Prevention and Treatment

The benefits of exercise training for cancer patients are becoming increasingly evident. Physical exercise has been shown to reduce cancer incidence and inhibit tumor growth. Here we provide the status of the current molecular understanding of the effect of exercise on cancer. We propose that exercise has a role in controlling cancer progression through a direct effect on tumor-intrinsic factors, interplay with whole-body exercise effects, alleviation of cancer-related adverse events, and improvement of anti-cancer treatment efficacy. These findings have wide-ranging societal implications, as this understanding may lead to changes in cancer treatment strategies.

PDE2 is a novel target for attenuating tumor formation in a mouse model of UVB-induced skin carcinogenesis

Our previous studies demonstrated that the topical application of caffeine is a potent inhibitor of UVB-induced carcinogenesis and selectively increases apoptosis in tumors but not in non-tumor areas of the epidermis in mice that are at a high risk for developing skin cancer. While this effect is mainly through a p53 independent pathway, the mechanism by which caffeine inhibits skin tumor formation has not been fully elucidated. Since caffeine is a non-specific phosphodiesterase inhibitor, we investigated the effects of several PDE inhibitors on the formation of sunburn cells in mouse skin after an acute exposure to ultraviolet light B (UVB). The topical application of a PDE2 inhibitor, erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride (EHNA hydrochloride), stimulated epidermal apoptosis compared to control (P<0.01) and to a greater extent than caffeine whereas a PDE4 inhibitor attenuated the epidermal apoptosis compared to control (P<0.01). Since PDE2 hydrolyzes cyclic nucleotides, mainly cGMP, the effects of EHNA hydrochloride on epidermal apoptosis following UVB exposure may be mediated, in part, by increased cGMP signaling. Data demonstrated that the topical application of dibutyryl cGMP stimulated epidermal apoptosis (P<0.01) following an acute exposure to UVB. Treating UVB-pretreated mice topically with 3.1 µmole or 0.8 µmole of EHNA hydrochloride attenuated tumor formation to a greater extent than treating with 6.2 µmole caffeine when these compounds were applied once a day, five days a week for 18 weeks. These observations suggest a novel role for PDE2 in UVB-induced tumorigenesis and that PDE2 inhibitors that mediate cGMP signaling may be useful for the prevention and treatment of skin cancer.

Parametrial fat tissue from high fat diet-treated SKH-1 mice stimulates transformation of mouse epidermal JB6 cells

Our previous studies indicated that decreasing visceral adipose tissue by surgical removal of the parametrial fat pads inhibited UVB-induced carcinogenesis in SKH-1 mice fed a high fat diet (HFD), but not a low fat diet (LFD) indicating that the parametrial fat tissue from mice fed a HFD played a role in skin carcinogenesis.

OBJECTIVE

In the present study, we sought to investigate how a HFD may influence the intrinsic properties of the parametrial fat tissue to influence UVB-induced skin tumor formation.

METHODS AND RESULTS

Immunohistochemical staining, adipokine array, and flow cytometry showed that parametrial fat tissue from mice fed a HFD had a higher density of macrophage-fused dead adipocytes (crown-like structures), more adipokines, and stimulated the production of more reactive oxygen species compared with parametrial fat tissue from mice fed a LFD. These differences between parametrial fat tissue from mice fed a HFD and LFD were associated with their effect on the in vitro transformation of mouse epidermal JB6 cells. Our results indicated that fat tissue filtrate (an aqueous filtrate made from the parametrial fat pad) from mice fed a HFD enhanced the conversion of JB6 cells from an epithelial-like morphology to cells with a fibroblast-like morphology to a greater extent than fat tissue filtrate from mice fed a LFD. Studies indicated that the fibroblast-like cells had decreased levels of E-cadherin, increased levels of Twist as assayed by western blot. Fat tissue filtrate made from the parametrial fat tissue of mice fed a HFD had 160% more transforming activity than that from mice fed a LFD and formed malignant mesenchymal tumors in vivo.

CONCLUSION

These studies provide the first in vitro demonstration of a parametrial fat tissue-induced transformation of an epidermal cell.

Oral caffeine during voluntary exercise markedly inhibits skin carcinogenesis and decreases inflammatory cytokines in UVB-treated mice

Ultraviolet B (UVB)-pretreated SKH-1 mice were treated with water, caffeine (0.1 mg/ml), voluntary running wheel exercise (RW) or caffeine together with RW for 14 wk. Treatment of the mice with caffeine, RW, or caffeine plus RW decreased skin tumors per mouse by 27%, 35%, and 62%, respectively, and the tumor volume per mouse was decreased by 61%, 70%, and 85%, respectively. In mechanistic studies, mice were treated with water, caffeine, RW, or caffeine plus RW for 2 wk prior to a single irradiation with UVB. Caffeine plus RW increased RW activity by 22% when compared with RW alone. Caffeine ingestion was not significantly different between groups. Treatment of mice with caffeine plus RW for 2 wk decreased the weight of the parametrial fat pads and stimulated the formation of UVB-induced apoptosis to a greater extent than treatment with caffeine or RW alone. An antibody array revealed that caffeine plus RW administered to mice fed a high-fat diet and irradiated with UVB decreased the epidermal levels of lipopolysaccharide-induced CXC chemokine, soluble TNF alpha receptor-1, and macrophage inflammatory protein-1γ. Overall, caffeine during RW exerts a stronger effect than either treatment alone for decreasing tissue fat, increasing UVB-induced apoptosis, lowering the levels of cytokines associated with inflammation and for inhibiting UVB-induced carcinogenesis.

Mechanisms of Caffeine-Induced Inhibition of UVB Carcinogenesis

Sunlight-induced non-melanoma skin cancer is the most prevalent cancer in the United States with more than two million cases per year. Several studies have shown an inhibitory effect of caffeine administration on UVB-induced skin cancer in mice, and these studies are paralleled by epidemiology studies that indicate an inhibitory effect of coffee drinking on non-melanoma skin cancer in humans. Strikingly, decaffeinated coffee consumption had no such inhibitory effect. Mechanism studies indicate that caffeine has a sunscreen effect that inhibits UVB-induced formation of thymine dimers and sunburn lesions in the epidermis of mice. In addition, caffeine administration has a biological effect that enhances UVB-induced apoptosis thereby enhancing the elimination of damaged precancerous cells, and caffeine administration also enhances apoptosis in tumors. Caffeine administration enhances UVB-induced apoptosis by p53-dependent and p53-independent mechanisms. Exploration of the p53-independent effect indicated that caffeine administration enhanced UVB-induced apoptosis by inhibiting the UVB-induced increase in ATR-mediated formation of phospho-Chk1 (Ser345) and abolishing the UVB-induced decrease in cyclin B1 which resulted in caffeine-induced premature and lethal mitosis in mouse skin. In studies with cultured primary human keratinocytes, inhibition of ATR with siRNA against ATR inhibited Chk1 phosphorylation and enhanced UVB-induced apoptosis. Transgenic mice with decreased epidermal ATR function that were irradiated chronically with UVB had 69% fewer tumors at the end of the study compared with irradiated littermate controls with normal ATR function. These results, which indicate that genetic inhibition of ATR (like pharmacologic inhibition of ATR via caffeine) inhibits UVB-induced carcinogenesis support the concept that ATR-mediated phosphorylation of Chk1 is an important target for caffeine’s inhibitory effect on UVB-induced carcinogenesis.

Inhibition of progression of androgen-dependent prostate LNCaP tumors to androgen independence in SCID mice by oral caffeine and voluntary exercise

The effect of oral caffeine or voluntary running wheel exercise (RW) alone or in combination on the progression of human androgen-dependent LNCaP prostate tumors to androgen independence in male severe combined immunodeficiency mice was determined. The mice were injected subcutaneously with LNCaP cells, and when the tumors reached a moderate size, the mice were surgically castrated and treated with caffeine (0.40 mg/ml drinking water) or RW alone or in combination for 42 days. We found that caffeine administration or RW inhibited the progression and growth of androgen-dependent LNCaP tumors to androgen independence, and a combination of the 2 regimens was more effective than the individual regimens alone. The ratios of the percent mitotic cells/caspase-3 positive cells in tumors from the caffeine-treated, RW-treated, or combination-treated mice were decreased by 34%, 38%, and 52%, respectively. Caffeine treatment increased the percentage of mitotic tumor cells undergoing apoptosis (lethal mitosis) whereas RW inhibited the increase in interleukin-6 that occurred during the progression of LNCaP tumors from androgen dependence to androgen independence. Our results indicate that oral administration of caffeine in combination with voluntary exercise may be an effective strategy for the prevention of prostate cancer progression from androgen dependence to androgen independence.

Inhibition of UVB-induced nonmelanoma skin cancer: a path from tea to caffeine to exercise to decreased tissue fat

Oral administration of green tea, black tea, or caffeine (but not the decaffeinated teas) inhibited ultraviolet B radiation (UVB)-induced skin carcinogenesis in SKH-1 mice. Studies with caffeine indicated that its inhibitory effect on the ATR/Chk1 pathway is an important mechanism for caffeine's inhibition of UVB-induced carcinogenesis. The regular teas or caffeine increased locomotor activity and decreased tissue fat. In these studies, decreased dermal fat thickness was associated with a decrease in the number of tumors per mouse. Administration of caffeine, voluntary exercise, and removal of the parametrial fat pads all stimulated UVB-induced apoptosis, inhibited UVB-induced carcinogenesis, and stimulated apoptosis in UVB-induced tumors. These results suggest that caffeine administration, voluntary exercise, and removal of the parametrial fat pads inhibit UVB-induced carcinogenesis by stimulating UVB-induced apoptosis and by enhancing apoptosis in DNA-damaged precancer cells and in cancer cells. We hypothesize that tissue fat secretes antiapoptotic adipokines that have a tumor promoting effect.

Surgical removal of the parametrial fat pads stimulates apoptosis and inhibits UVB-induced carcinogenesis in mice fed a high-fat diet

Removal of the parametrial fat pads (partial lipectomy) from female SKH-1 mice fed a high-fat diet inhibited UVB-induced carcinogenesis, but this was not observed in mice fed a low-fat chow diet. Partial lipectomy in high-fat-fed mice decreased the number of keratoacanthomas and squamous cell carcinomas per mouse by 76 and 79%, respectively, compared with sham-operated control mice irradiated with UVB for 33 wk. Immunohistochemical analysis indicated that partial lipectomy increased caspase 3 (active form) positive cells by 48% in precancerous epidermis away from tumors, by 68% in keratoacanthomas, and by 224% in squamous cell carcinomas compared with sham-operated control mice. In addition, partial lipectomy decreased cell proliferation away from tumors and in tumors. RT-PCR analysis for adipokines revealed that mRNAs for TIMP1, MCP1, and SerpinE1 (proinflammatory/antiapoptotic cytokines) in the parametrial fat pads of sham-operated control mice were 54- to 83-fold higher than levels in compensatory fat that returned after surgery in partially lipectomized mice at the end of the tumor study. Feeding mice high-fat diets for 2 wk increased levels of TIMP1 and other adipokines in serum and epidermis, and these increases were inhibited by removal of the parametrial fat pads. Our results are a unique demonstration that surgical removal of a specific tissue fat results in inhibition of carcinogenesis in obese mice. This inhibition was associated with an increase in apoptosis and a decrease in proliferation in tumors and in precancerous areas away from tumors.

Inhibition of UVB-induced nonmelanoma skin cancer: a path from tea to caffeine to exercise to decreased tissue fat

Oral administration of green tea, black tea, or caffeine (but not the decaffeinated teas) inhibited ultraviolet B radiation (UVB)-induced skin carcinogenesis in SKH-1 mice. Studies with caffeine indicated that its inhibitory effect on the ATR/Chk1 pathway is an important mechanism for caffeine's inhibition of UVB-induced carcinogenesis. The regular teas or caffeine increased locomotor activity and decreased tissue fat. In these studies, decreased dermal fat thickness was associated with a decrease in the number of tumors per mouse. Administration of caffeine, voluntary exercise, and removal of the parametrial fat pads all stimulated UVB-induced apoptosis, inhibited UVB-induced carcinogenesis, and stimulated apoptosis in UVB-induced tumors. These results suggest that caffeine administration, voluntary exercise, and removal of the parametrial fat pads inhibit UVB-induced carcinogenesis by stimulating UVB-induced apoptosis and by enhancing apoptosis in DNA-damaged precancer cells and in cancer cells. We hypothesize that tissue fat secretes antiapoptotic adipokines that have a tumor promoting effect.

Effects of high-fat diets rich in either omega-3 or omega-6 fatty acids on UVB-induced skin carcinogenesis in SKH-1 mice

Our previous studies reported that caffeine or voluntary exercise decreased skin tumor multiplicity, in part, by decreasing fat levels in the dermis. These data suggest that tissue fat may play an important role in regulating ultraviolet light (UV) B-induced skin tumor development. In the present study, we explored the effects of high-fat diets rich in either omega-3 or omega-6 fatty acids on UVB-induced skin carcinogenesis. SKH-1 mice were irradiated with 30 mJ/cm(2) of UVB once a day, two times per week for 39 weeks. During UVB treatment, one group of mice was given a high-fat fish oil (HFFO) diet rich in omega-3 fatty acids and the other group of mice was given a high-fat mixed-lipids (HFMLs) diet rich in omega-6 fatty acids. The results showed that, compared with HFML diet, HFFO treatment (i) increased latency for the development of UVB-induced skin tumors; (ii) decreased the formation of papilloma, keratoacanthoma and carcinoma by 64, 52 and 46%, respectively and (iii) decreased the size of papilloma, keratoacanthoma and carcinoma by 98, 80 and 83%, respectively. Mechanistic studies with antibody array revealed that compared with HFML diet, administration of HFFO to the mice significantly decreased the UVB-induced increases in the levels of TIMP-1, LIX and sTNF R1 as well as other several proinflammatory cytokines and stimulated the UVB-induced apoptosis in the epidermis. Our results indicate that omega-3 fatty acids in HFFO diet have beneficial effects against UVB-induced skin carcinogenesis, and these effects may be associated with an inhibition on UVB-induced inflammatory response.

Effect of physical activity on nonmelanoma skin cancer risk in kidney, liver, and pancreatic transplant patients

BACKGROUND

Physical activity has been associated with a lower risk of cancer, including melanoma, but the effect has not yet been assessed for nonmelanoma skin cancer (NMSC).

OBJECTIVE

To determine whether the risk of skin cancer differs according to physical activity level in patients at high risk for NMSC.

METHODS

We conducted a retrospective cohort study in kidney, liver, and pancreatic transplant patients via telephone interview. Physical activity scores were calculated for each patient using a previously validated questionnaire. Sun exposure history and skin type were also recorded. The outcome of interest was a biopsy-proven diagnosis of at least one NMSC.

RESULTS

Of 142 subjects, 45 (32%) developed NMSC. There was no significant effect of physical activity on the development of NMSC.

CONCLUSIONS

Physical activity level may not be a major predictor of skin cancer risk in organ transplant patients. Controlled trials and population-based studies are needed to determine whether exercise can decrease the risk of NMSC in the general population. The authors have indicated no significant interest with commercial supporters.

Environmental and genetic activation of a brain-adipocyte BDNF/leptin axis causes cancer remission and inhibition

Cancer is influenced by its microenvironment, yet broader, environmental effects also play a role but remain poorly defined. We report here that mice living in an enriched housing environment show reduced tumor growth and increased remission. We found this effect in melanoma and colon cancer models, and that it was not caused by physical activity alone. Serum from animals held in an enriched environment (EE) inhibited cancer proliferation in vitro and was markedly lower in leptin. Hypothalamic brain-derived neurotrophic factor (BDNF) was selectively upregulated by EE, and its genetic overexpression reduced tumor burden, whereas BDNF knockdown blocked the effect of EE. Mechanistically, we show that hypothalamic BDNF downregulated leptin production in adipocytes via sympathoneural beta-adrenergic signaling. These results suggest that genetic or environmental activation of this BDNF/leptin axis may have therapeutic significance for cancer.

Weight Loss via exercise with controlled dietary intake may affect phospholipid profile for cancer prevention in murine skin tissues

Exercise has been linked to a reduced cancer risk in animal models. However, the underlying mechanisms are unclear. This study assessed the effect of exercise with dietary consideration on the phospholipid profile in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mouse skin tissues. CD-1 mice were randomly assigned to one of the three groups: ad libitum-fed sedentary control; ad libitum-fed treadmill exercise at 13.4 m/min for 60 min/d, 5 d/wk (Ex+AL); and treadmill-exercised but pair-fed with the same amount as the control (Ex+PF). After 14 weeks, Ex+PF but not Ex+AL mice showed approximately 25% decrease in both body weight and body fat when compared with the controls. Of the total 338 phospholipids determined by electrospray ionization-tandem mass spectrometry, 57 were significantly changed, and 25 species could distinguish effects of exercise and diet treatments in a stepwise discriminant analysis. A 36% to 75% decrease of phosphatidylinositol (PI) levels in Ex+PF mice occurred along with a significant reduction of PI 3-kinase in TPA-induced skin epidermis, as measured by both Western blotting and immunohistochemistry. In addition, approximately 2-fold increase of the long-chain polyunsaturated fatty acids, docosahexaenoic and docosapentaenoic acids, in phosphatidylcholines, phosphatidylethanolamines, and lysophosphatidylethanolamines was observed in the Ex+PF group. Microarray analysis indicated that the expression of fatty acid elongase-1 increased. Taken together, these data indicate that exercise with controlled dietary intake, but not exercise alone, significantly reduced body weight and body fat as well as modified the phospholipid profile, which may contribute to cancer prevention by reducing TPA-induced PI 3-kinase and by enhancing omega-3 fatty acid elongation.

Oral administration of caffeine during voluntary exercise markedly decreases tissue fat and stimulates apoptosis and cyclin B1 in UVB-treated skin of hairless p53-knockout mice

Treatment of p53(-/-) mice orally with caffeine, voluntary exercise or their combination for 2 weeks prior to a single irradiation with UVB (i) decreased the weight of the epididymal fat pads by 22, 40 and 56%, (ii) decreased the thickness of the dermal fat layer by 10, 26 and 42%, (iii) increased the number of apoptotic sunburn cells by 29, 100 and 489%, (iv) increased the number of caspase-3-positive cells by 33, 117 and 667% and (v) increased the number of mitotic cells with cyclin B1-positive staining by 40, 210 and 510%, respectively. Pearson's correlation coefficient indicated a statistically significant inverse relationship between the level of tissue fat and the number of mitotic cells with cyclin B1 in p53(-/-) mice but not in p53(+/+) littermates. Western blot analysis indicated that treatment of p53(-/-) mice with caffeine together with exercise increased the level of cyclin B1 significantly more than in p53(+/+) mice. p53(-/-) mice, but not p53(+/+) mice, treated with caffeine during exercise exhibited a dramatic decrease in the level of survivin. Our results suggest that voluntary exercise in combination with oral caffeine may exert a synergistic increase in UVB-induced apoptosis and that tissue fat may be a more important modulator of apoptosis and carcinogenesis in p53-deficient mice than in p53-normal mice. The stimulatory effects on apoptosis in p53(-/-) mice by the combination treatment might be associated with increased levels of cyclin B1 and decreased levels of survivin.

Rapid body weight gain increases the risk of UV radiation-induced skin carcinogenesis in SKH-1 hairless mice

Although it is well known that caloric restriction reduces the risk of chronic diseases including cancer, the role of weight gain in the development of UV light-induced tumors has not, to our knowledge, been investigated. In view of the increase in obesity worldwide, we asked the question whether there is any relationship between body weight gain and skin tumor development. We subjected 3 groups, each composed of 30 SKH-1 hairless female mice, to UV radiation (30 mJ/cm(2), twice weekly for 17 weeks) and observed tumor formation over the ensuing 8 to 13 weeks: group 1 received pelleted diet; group 2 received pellets during the irradiation period and was then switched to powder; and group 3 received powder exclusively. At the end of the experiment, the mean body weight of group 1 was 32.1 +/- 0.5 g, whereas that of groups 2 and 3 was 39.0 +/- 1.5 and 39.5 +/- 1.4 g, respectively. Tumor incidence reached 90% at 8 weeks after completion of irradiation for the animals in group 3 and at 13 weeks for the animals in group 2. Similarly, at 8 weeks after irradiation when all animals of group 3 were euthanized, tumor multiplicity was 0.8, 1.2, and 3.2 for groups 1, 2, and 3, respectively. Thus, in comparison with the mice consuming pellets, the powder-fed mice gained weight more rapidly and developed tumors much faster. Considering the escalating numbers of individuals worldwide who are overweight or obese, our findings provide further impetus for advocating healthier diets and maintenance of constant body weight in adults.

Physical activity and cancer prevention : pathways and targets for intervention

The prevalence of obesity, an established epidemiological risk factor for many cancers, has risen steadily for the past several decades in the US and many other countries. Particularly alarming are the increasing rates of obesity among children, portending continuing increases in the rates of obesity and obesity-related cancers for many years to come. Modulation of energy balance, via increased physical activity, has been shown in numerous comprehensive epidemiological reviews to reduce cancer risk. Unfortunately, the effects and mechanistic targets of physical activity interventions on the carcinogenesis process have not been thoroughly characterized. Studies to date suggest that exercise can exert its cancer-preventive effects at many stages during the process of carcinogenesis, including both tumour initiation and progression. As discussed in this review, exercise may be altering tumour initiation events by modifying carcinogen activation, specifically by enhancing the cytochrome P450 system and by enhancing selective enzymes in the carcinogen detoxification pathway, including, but not limited to, glutathione-S-transferases. Furthermore, exercise may reduce oxidative damage by increasing a variety of anti-oxidant enzymes, enhancing DNA repair systems and improving intracellular protein repair systems. In addition to altering processes related to tumour initiation, exercise may also exert a cancer-preventive effect by dampening the processes involved in the promotion and progression stages of carcinogenesis, including scavenging reactive oxygen species (ROS); altering cell proliferation, apoptosis and differentiation; decreasing inflammation; enhancing immune function; and suppressing angiogenesis. A paucity of data exists as to whether exercise may be working as an anti-promotion strategy via altering ROS in initiated or preneoplastic models; therefore, no conclusions can be made about this possible mechanism. The studies directly examining cell proliferation and apoptosis have shown that exercise can enhance both processes, which is difficult to interpret in the context of carcinogenesis. Studies examining the relationship between exercise and chronic inflammation suggest that exercise may reduce pro-inflammatory mediators and reduce the state of low-grade, chronic inflammation. Additionally, exercise has been shown to enhance components of the innate immune response (i.e. macrophage and natural killer cell function). Finally, only a limited number of studies have explored the relationship between exercise and angiogenesis; therefore, no conclusions can be made currently about the role of exercise in the angiogenesis process as it relates to tumour progression. In summary, exercise can alter biological processes that contribute to both anti-initiation and anti-progression events in the carcinogenesis process. However, more sophisticated, detailed studies are needed to examine each of the potential mechanisms contributing to an exercise-induced decrease in carcinogenesis in order to determine the minimum dose, duration and frequency of exercise needed to yield significant cancer-preventive effects, and whether exercise can be used prescriptively to reverse the obesity-induced physiological changes that increase cancer risk.

Inhibitory effect of voluntary running wheel exercise on the growth of human pancreatic Panc-1 and prostate PC-3 xenograft tumors in immunodeficient mice

In the present study, we investigated the effect of voluntary exercise on the formation and growth of the human pancreas Panc-1 and prostate PC-3 tumors in immunodeficient mice. Female severe combined immunodeficient (SCID) mice were injected subcutaneously with human pancreatic cancer Panc-1 cells, and male SCID mice were injected subcutaneously with human prostate cancer PC-3 cells. Voluntary running wheel exercise for 63 days, starting one week before the subcutaneous injection of Panc-1 or PC-3 tumor cells into SCID mice, suppressed the growth of Panc-1 and PC-3 tumors. The exercise regimen increased the food and fluid consumption in the female and male mice. Exercise also decreased the size of the parametrial fat pads in the female mice and the paradidymis fat pads in the male mice, but there was no effect on the body weight. Mechanistic studies showed that voluntary running wheel exercise inhibited proliferation as reflected by a decreased mitosis, and the exercise regimen also stimulated apoptosis as reflected by the increased caspase-3 (active form) expression in the Panc-1 and PC-3 tumors. Voluntary running wheel exercise decreased the ratio of the percent mitotic cells/apoptotic cells in Panc-1 and PC-3 tumors by 38 and 32%, respectively. The present study demonstrated an inhibitory effect of voluntary exercise on the growth of pancreas and prostate tumors in a SCID mouse xenograft model.

Voluntary exercise together with oral caffeine markedly stimulates UVB light-induced apoptosis and decreases tissue fat in SKH-1 mice

Treatment of SKH-1 mice orally with caffeine (0.1 mg/ml in the drinking water), voluntary running wheel exercise, or a combination of caffeine and exercise for 2 weeks (i) decreased the weight of the parametrial fat pads by 35, 62, and 77%, respectively; (ii) decreased the thickness of the dermal fat layer by 38, 42, and 68%, respectively; (iii) stimulated the formation of UVB-induced apoptotic sunburn cells in the epidermis by 96, 120, and 376%, respectively; and (iv) stimulated the formation of UVB-induced caspase 3 (active form)-positive cells in the epidermis by 92, 120, and 389%, respectively (average of two experiments). Oral administration of caffeine (0.4 mg/ml in the drinking water) in combination with voluntary exercise was less effective than administration of the low dose of caffeine in combination with exercise in stimulating UVB-induced apoptosis. Although orally administrated caffeine (0.1 mg/ml in the drinking water) or voluntary exercise for 2 weeks caused only a small nonsignificant stimulation of UVB-induced increase in the percentage of phospho-p53 (Ser-15)-positive cells in the epidermis (27 or 18%, respectively), the combination of the two treatments enhanced the UVB-induced increase in phospho-p53 (Ser-15)-positive cells by 99%. The plasma concentration of caffeine in mice ingesting caffeine (0.1-0.4 mg/ml drinking water) is similar to that in the plasma of most coffee drinkers (one to four cups per day). Our studies indicate a greater than additive stimulatory effect of combined voluntary exercise and oral administration of a low dose of caffeine on UVB-induced apoptosis.