Michael E. Grossmann

Minireview: Obesity and breast cancer: the estrogen connection.

There is now substantial evidence that overweight and/or obesity and/or weight gain are risk factors for the development of postmenopausal breast cancer. In addition, obesity and/or elevated body mass index at breast cancer diagnosis has a negative impact on prognosis for both premenopausal and postmenopausal women. Therefore, understanding the mechanism of how obesity affects the mammary tumorigenesis process is an important health issue. Elevated serum estrogen levels as well as enhanced local production of estrogen have been considered primary mediators of how increased body weight promotes breast cancer development in postmenopausal women. Here, we provide an overview of estrogens relationship with both obesity and breast cancer as separate entities. Human and relevant preclinical studies are cited. In addition, other growth factors that may be involved in this relationship are considered.

Obesity and breast cancer: status of leptin and adiponectin in pathological processes

It is well recognized that obesity increases the risk of various cancers, including breast malignancies in postmenopausal women. Furthermore, obesity may adversely affect tumor progression, metastasis, and overall prognosis in both pre- and postmenopausal women with breast cancer. However, the precise mechanism(s) through which obesity acts is/are still elusive and this relationship has been the subject of much investigation and speculation. Recently, adipose tissue and its associated cytokine-like proteins, adipokines, particularly leptin and adiponectin, have been investigated as mediators for the association of obesity with breast cancer. Higher circulating levels of leptin found in obese subjects could be a growth-enhancing factor as supported by in vitro and preclinical studies, whereas low adiponectin levels in obese women may be permissive for leptin’s growth-promoting effects. These speculations are supported by in vitro studies which indicate that leptin promotes human breast cancer cell proliferation while adiponectin exhibits anti-proliferative actions. Further, estrogen and its receptors have a definite impact on the response of human breast cancer cell lines to leptin and adiponectin. More in-depth studies are needed to provide additional and precise links between the in vivo development of breast cancer and the balance of adiponectin and leptin.

Intermittent Calorie Restriction Delays Prostate Tumor Detection and Increases Survival Time in TRAMP Mice

Prostate cancer is the most frequently diagnosed cancer in men. Whereas chronic calorie restriction (CCR) delays prostate tumorigenesis in some rodent models, the impact of intermittent caloric restriction (ICR) has not been determined. Here, transgenic adenocarcinoma of the mouse prostate (TRAMP) mice were used to compare how ICR and CCR affected prostate cancer development. TRAMP mice were assigned to ad libitum (AL), ICR (2 wk 50% AL consumption followed by 2 wk pair feeding to AL consumption), and CCR (25% AL consumption) groups at 7 wk of age and followed until disease burden necessitated euthanasia or mice reached terminal endpoints (48 or 50 wk of age). Body weights fluctuated in response to calorie intake (P < 0.0001). ICR mice were older at tumor detection than AL (P = 0.0066) and CCR (P = 0.0416) mice. There was no difference for age of tumor detection between AL and CCR mice (P = 0.3960). Similar results were found for survival. Serum leptin, adiponectin, insulin, and IGF-I were all significantly different among the groups. These results indicate that the way in which calories are restricted impacts both time to tumor detection and survival in TRAMP mice, with ICR providing greater protective effect compared to CCR.

Eleostearic Acid Inhibits Breast Cancer Proliferation by Means of an Oxidation-Dependent Mechanism

Eleostearic acid (α-ESA) is a conjugated linolenic acid that makes up ∼60% of Momordica charantia (bitter melon) seed oil. Prior work found that water extract from bitter melon was able to inhibit breast cancer. Here, we investigated effects of α-ESA on both estrogen receptor (ER)–negative MDA-MB-231 (MDA-wt) and ER-positive MDA-ERα7 human breast cancer cells. We found that α-ESA inhibited proliferation of both MDA-wt and MDA-ERα7 cells, whereas conjugated linoleic acid had comparatively weak antiproliferative activity at 20 to 80 μmol/L concentrations. We also found that α-ESA (40 μmol/L) treatment led to apoptosis in the range of 70% to 90% for both cell lines, whereas conjugated linoleic acid (40 μmol/L) resulted in only 5% to 10% apoptosis, similar to results for control untreated cells. Addition of α-ESA also caused loss of mitochondrial membrane potential and translocation of apoptosis-inducing factor as well as endonuclease G from the mitochondria to the nucleus. Additionally, α-ESA caused a G2-M block in the cell cycle. We also investigated the potential for lipid peroxidation to play a role in the inhibitory action of α-ESA. We found that when the breast cancer cells were treated with α-ESA in the presence of the antioxidant α-tocotrienol (20 μmol/L), the growth inhibition and apoptosis effects of α-ESA were lost. An AMP-activated protein kinase inhibitor (Dorsomorphin) was also able to partially abrogate the effects of α-ESA, whereas a caspase inhibitor (BOC-D-FMK) did not. These results illustrate that α-ESA can block breast cancer cell proliferation and induce apoptosis through a mechanism that may be oxidation dependent.

The balance between leptin and adiponectin in the control of carcinogenesis - focus on mammary tumorigenesis.

A number of studies indicate that a growing list of cancers may be influenced by obesity. In obese individuals these cancers can be more frequent and more aggressive resulting in reduced survival. One of the most prominent and well characterized cancers in this regard is breast cancer. Obesity plays a complex role in breast cancer and is associated with increased inflammation, angiogenesis and alterations in serum levels of potential growth factors such as insulin, adiponectin, leptin and estrogen. Reduced levels of serum adiponectin have been reported in breast cancer patients compared to healthy controls, particularly in postmenopausal women and the level of adiponectin has been shown to be inversely associated with insulin resistance. The role of serum leptin levels in breast cancer appears to be more complex. Some studies have shown leptin to be increased in women with breast cancer but other studies have found leptin to be decreased or unchanged. This may be due to a number of confounding issues. We and others propose that it may be the levels of adiponectin and leptin as well as the balance of adiponectin and leptin that are the critical factors in breast and other obesity related cancer tumorigenesis. This review will focus on the current understanding of the interplay between obesity and the functions of leptin and adiponectin. It will then examine what is known about their potential roles in cancer particularly as pertains to breast cancer and how the ratio of adiponectin to leptin may play a role in tumorigenesis.

Prevention of mammary tumorigenesis by intermittent caloric restriction: does caloric intake during refeeding modulate the response?

Chronic caloric restriction (CCR) prevents mammary tumorigenesis in rodents, but a protective effect for intermittent caloric restriction (ICR) is less well documented. We recently reported that ICR reduced mammary tumor (MT) incidence of mouse mammary tumor virus–transforming growth factor (MMTV-TGF)-α mice to a greater extent than did CCR. Here, we repeated this protocol and obtained serum and tissue samples. Ad libitum (AL) MMTV-TGF-α mice were fed AIN-93M diet. Beginning at 10 weeks of age, ICR mice received isocaloric AIN-93M-mod diet (2-fold increases in protein, fat, vitamins, and minerals) at 50% of ad libitum for 3 weeks followed by 3 weeks refeeding with AIN-93M diet. CCR mice were pair-fed AIN-93M:AIN-93M-mod (2:1) matching intakes for restriction/refeeding cycles. Mice were sacrificed for MT size, at 79 (end of 12th restriction) or at 80 (1 week after 12th refeeding) weeks of age. AL and ICR-80 mice had heavier body weights than ICR-79 and CCR mice (P < 0.0001). Cumulative food intakes of ICR and CCR mice were reduced 12% and 15% versus AL mice (P < 0.0001). However, ICR mice consumed significantly (P < 0.0001) more food than did AL mice during refeeding. MT incidence was 84%, 13%, and 27% for AL, ICR, and CCR mice, respectively. MT weight (P < 0.0011) and number (P < 0.01) were higher for AL mice compared with ICR and CCR mice. AL and ICR-80 mice had similar serum IGF-I levels, but only AL values were higher than those of ICR-79 and CCR mice (P < 0.0017). ICR mice had more MT DNA breaks compared with AL and CCR mice, suggesting enhanced apoptosis (P < 0.02). AL mice had higher mammary fat pad ObR and ObRb leptin receptor mRNA expression than did ICR and CCR mice (P < 0.001), but there was no effect on MTs. These results confirm that ICR prevents development of MTs to a greater extent than does CCR, although “overeating” during refeeding may compromise this protection.

Epidermal Fatty Acid Binding Protein Promotes Skin Inflammation Induced by High-Fat Diet

Defining specific cellular and molecular mechanisms in most obesity-related diseases remains an important challenge. Here we report a serendipitous finding that consumption of a high-fat diet (HFD) greatly increased the occurrence of skin lesions in C57BL/6 mice. We demonstrated that HFD induced the accumulation of a specific type of CD11c(+) macrophages in skin preceding detectable lesions. These cells primed skin to induce IL-1β and IL-18 signaling, which further promoted the cytokines IFN-γ- and IL-17-mediated skin inflammation. Mechanistically, epidermal fatty acid binding protein (E-FABP) was significantly upregulated in skin of obese mice, which coupled lipid droplet formation and NLRP3 inflammasome activation. Deficiency of E-FABP in obese mice decreased recruitment of CD11c(+) macrophages in skin tissues, reduced production of IL-1β and IL-18, and consequently dampened activation of effector T cells. Furthermore, E-FABP-deficient mice are completely resistant to HFD-induced skin lesions. Collectively, E-FABP represents a molecular sensor triggering HFD-induced skin inflammation.

Cross-sectional analysis of intermittent versus chronic caloric restriction in the TRAMP mouse

Previously we found that intermittent calorie restriction (ICR) delayed the age of prostate tumor detection and death in TRAMP mice in comparison to chronic calorie restricted (CCR) and ad libitum fed (AL) TRAMP mice.

Role of the adiponectin leptin ratio in prostate cancer.

We hypothesize that adiponectin and leptin may be capable of mediating some of the effects that body weight has on prostate cancer and that a mouse model may be effective to examine this hypothesis. We found that tumors from the TRAMP prostate cancer model expressed adiponectin and leptin receptors. TRAMP-C2 prostate cancer cell proliferation was reduced by adiponectin. Leptin was able to block the ability of adiponectin to reduce cell proliferation through altered signaling of the ERK pathway. Overall, this work suggests that adiponectin, leptin, and their receptors may play an important role in prostate cancer.

Combination of Intermittent Calorie Restriction and Eicosapentaenoic Acid for Inhibition of Mammary Tumors

There are a number of dietary interventions capable of inhibiting mammary tumorigenesis; however, the effectiveness of dietary combinations is largely unexplored. Here, we combined 2 interventions previously shown individually to inhibit mammary tumor development. The first was the use of the omega-3 fatty acid, eicosapentaenoic acid (EPA), and the second was the implementation of calorie restriction. MMTV-Her2/neu mice were used as a model for human breast cancers, which overexpress Her2/neu. Six groups of mice were enrolled. Half were fed a control (Con) diet with 10.1% fat calories from soy oil, whereas the other half consumed a diet with 72% fat calories from EPA. Within each diet, mice were further divided into ad libitum (AL), chronic calorie-restricted (CCR), or intermittent calorie-restricted (ICR) groups. Mammary tumor incidence was lowest in ICR-EPA (15%) and highest in AL-Con mice (87%), whereas AL-EPA, CCR-Con, CCR-EPA, and ICR-Con groups had mammary tumor incidence rates of 63%, 47%, 40%, and 59%, respectively. Survival was effected similarly by the interventions. Consumption of EPA dramatically reduced serum leptin (P < 0.02) and increased serum adiponectin in the AL-EPA mice compared with AL-Con mice (P < 0.001). Both CCR and ICR decreased serum leptin and insulin-like growth factor I (IGF-I) compared with AL mice but not compared with each other. These results illustrate that mammary tumor inhibition is significantly increased when ICR and EPA are combined as compared with either intervention alone. This response may be related to alterations in the balance of serum growth factors and adipokines. Cancer Prev Res; 6(6); 540–7. ©2013 AACR.