A low-glucose eating pattern is associated with improvements in glycemic variability among women at risk for postmenopausal breast cancer: an exploratory analysis

Background

High glycemic variability (GV) is a biomarker of cancer risk, even in the absence of diabetes. The emerging concept of chrononutrition suggests that modifying meal timing can favorably impact metabolic risk factors linked to diet-related chronic disease, including breast cancer. Here, we examined the potential of eating when glucose levels are near personalized fasting thresholds (low-glucose eating, LGE), a novel form of timed-eating, to reduce GV in women without diabetes, who are at risk for postmenopausal breast cancer.

Methods

In this exploratory analysis of our 16-week weight loss randomized controlled trial, we included 17 non-Hispanic, white, postmenopausal women (average age = 60.7 ± 5.8 years, BMI = 34.5 ± 6.1 kg/m2, HbA1c = 5.7 ± 0.3%). Participants were those who, as part of the parent study, provided 3-7 days of blinded, continuous glucose monitoring data and image-assisted, timestamped food records at weeks 0 and 16. Pearson's correlation and multivariate regression were used to assess associations between LGE and GV, controlling for concurrent weight changes.

Results

Increases in LGE were associated with multiple unfavorable measures of GV including reductions in CGM glucose mean, CONGA, LI, J-Index, HBGI, ADDR, and time spent in a severe GV pattern (r = -0.81 to -0.49; ps < 0.044) and with increases in favorable measures of GV including M-value and LBGI (r = 0.59, 0.62; ps < 0.013). These associations remained significant after adjusting for weight changes.

Conclusion

Low-glucose eating is associated with improvements in glycemic variability, independent of concurrent weight reductions, suggesting it may be beneficial for GV-related disease prevention. Further research in a larger, more diverse sample with poor metabolic health is warranted.Clinical trial registration: ClinicalTrials.gov, NCT03546972.

Metformin and Breast Cancer: Current Findings and Future Perspectives from Preclinical and Clinical Studies

Over the last several decades, a growing body of research has investigated the potential to repurpose the anti-diabetic drug metformin for breast cancer prevention and/or treatment. Observational studies in the early 2000s demonstrated that patients with diabetes taking metformin had decreased cancer risk, providing the first evidence supporting the potential role of metformin as an anti-cancer agent. Despite substantial efforts, two decades later, the exact mechanisms and clinical efficacy of metformin for breast cancer remain ambiguous. Here, we have summarized key findings from studies examining the effect of metformin on breast cancer across the translational spectrum including in vitro, in vivo, and human studies. Importantly, we discuss critical factors that may help explain the significant heterogeneity in study outcomes, highlighting how metformin dose, underlying metabolic health, menopausal status, tumor subtype, membrane transporter expression, diet, and other factors may play a role in modulating metformin's anti-cancer effects. We hope that these insights will help with interpreting data from completed studies, improve the design of future studies, and aid in the identification of patient subsets with breast cancer or at high risk for the disease who are most likely to benefit from metformin treatment.

Trends in Diet and Cancer Research: A Bibliometric and Visualization Analysis

Diet plays a critical role for patients across the cancer continuum. The World Cancer Research Fund International and the American Cancer Society have published evidence supporting the role of nutrition in cancer prevention. We conducted an analysis of the literature on dietary nutrients and cancer to uncover opportunities for future research. The objective of the bibliometric analysis was to describe trends in peer-reviewed publications on dietary components and cancer and to highlight research gaps. PubMed was queried for manuscripts with diet- and cancer-related keywords and Medical Subject Headings (MeSH) terms. Metadata covering 99,784 publications from 6469 journals were analyzed to identify trends since 1970 on diet topics across 19 tumor types. Publications focused largely on breast, colorectal, and liver cancer, with fewer papers linking diet with other cancers such as brain, gallbladder, or ovarian. With respect to "unhealthy" diets, many publications focused on high-fat diets and alcohol consumption. The largest numbers of publications related to "healthy" diets examined the Mediterranean diet and the consumption of fruits and vegetables. These findings highlight the need for additional research focused on under-investigated cancers and dietary components, as well as dietary studies during cancer therapy and post-therapy, which may help to prolong survivorship.

Abstract 3030: Effect of 6 months of bazedoxifene and conjugated estrogen on measures of insulin resistance in postmenopausal women at increased risk for breast cancer

Background: Bazedoxifene 20 mg (BZA) + Conjugated estrogen 0.45 mg (CE) as Duavee™ is FDA approved for treatment of hot-flashes and prevention of osteoporosis. We are investigating 6 months of BZA + CE vs wait list control in a multisite Phase IIB trial for primary prevention of breast cancer in high-risk peri-and postmenopausal women with vasomotor symptoms. Primary endpoints are change in mammographic fibroglandular volume and normal breast epithelial proliferation as assessed by Ki-67. Menopause transition is marked by an increase in insulin resistance and incidence of metabolic syndrome which in turn are implicated in the development of breast cancer. Tamoxifen can induce insulin resistance due to effects on small adipocytes, pancreatic beta cells, and hepatic lipid accumulation. In contrast, preclinical studies suggest that BZA + CE may have favorable effects on insulin resistance, particularly in obese animals. Consequently, we are exploring effects of BZA + CE on measures of insulin resistance in our clinical trial.

Methods: Fasting plasma was assessed for insulin and glucose in a CLIA laboratory the same day as drawn. HOMA-IR (insulin resistance) was computed as insulin (µU/ml) × glucose (mg/dl)]/405) and HOMA-%S (measure of insulin sensitivity) as 100/HOMA-IR. HOMA-IR ≥ 1.9 is considered an indication of early insulin resistance and HOMA-IR &gt;2.8 significant insulin resistance. HOMA-%S values of ≥100% are considered an indication of insulin sensitivity.

Results: 21 women have been randomized in the initial 10 months of accrual at the University of Kansas Cancer Center with 8 women completing the 6 -month randomized period to date. Median age was 53 (48-56), and median BMI was 25 kg/m2 (22-35 kg/m2). All women were normoglycemic. However, 2 women (1 each BZA + CE and wait list) had baseline evidence of insulin resistance by HOMA IR (≥1.9). In the woman randomized to BZA + CE, HOMA-IR improved from 2.29 at baseline to 1.0 at 6 months and HOMA-%S improved from 44 to 100%. There was little change in insulin resistance measures in the woman with baseline insulin resistance randomized to wait list. HOMA-IR was 2.83 at baseline and 2.76 at 6 months and HOMA-%S 35% at baseline and 36% at 6 months. Another waitlist participant with normal baseline HOMA-%S of 141% dropped to 71% at 6 months. Results will be available for 20 study participants at the meeting.

Summary: In our initial accrual group there is no indication that 6 months of BZA +CE is associated with development of insulin resistance. Funded in part by NIH grant CA249437 and Breast Cancer Research Foundation grants BCRF-21-049 and BCRF-22-049.

Citation Format: Carol J. Fabian, Erin D. Giles, Katherine L. Cook, Kandy Powers, Christy Altman, Amy Kreutzjans, Teresa Phillips, Adrian Zelenchuk, Krystal Pittman, Stephen D. Hursting, Bruce Kimler. Effect of 6 months of bazedoxifene and conjugated estrogen on measures of insulin resistance in postmenopausal women at increased risk for breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3030.

SIM2s directed Parkin-mediated mitophagy promotes mammary epithelial cell differentiation

The functionally differentiated mammary gland adapts to extreme levels of stress from increased demand for energy by activating specific protective mechanisms to support neonatal health. Here, we identify the breast tumor suppressor gene, single-minded 2 s (SIM2s) as a novel regulator of mitophagy, a key component of this stress response. Using tissue-specific mouse models, we found that loss of Sim2 reduced lactation performance, whereas gain (overexpression) of Sim2s enhanced and extended lactation performance and survival of mammary epithelial cells (MECs). Using an in vitro model of MEC differentiation, we observed SIM2s is required for Parkin-mediated mitophagy, which we have previously shown as necessary for functional differentiation. Mechanistically, SIM2s localizes to mitochondria to directly mediate Parkin mitochondrial loading. Together, our data suggest that SIM2s regulates the rapid recycling of mitochondria via mitophagy, enhancing the function and survival of differentiated MECs.

Preventing ovariectomy-induced weight gain decreases tumor burden in rodent models of obesity and postmenopausal breast cancer

BACKGROUND

Obesity and adult weight gain are linked to increased breast cancer risk and poorer clinical outcomes in postmenopausal women, particularly for hormone-dependent tumors. Menopause is a time when significant weight gain occurs in many women, and clinical and preclinical studies have identified menopause (or ovariectomy) as a period of vulnerability for breast cancer development and promotion.

METHODS

We hypothesized that preventing weight gain after ovariectomy (OVX) may be sufficient to prevent the formation of new tumors and decrease growth of existing mammary tumors. We tested this hypothesis in a rat model of obesity and carcinogen-induced postmenopausal mammary cancer and validated our findings in a murine xenograft model with implanted human tumors.

RESULTS

In both models, preventing weight gain after OVX significantly decreased obesity-associated tumor development and growth. Importantly, we did not induce weight loss in these animals, but simply prevented weight gain. In both lean and obese rats, preventing weight gain reduced visceral fat accumulation and associated insulin resistance. Similarly, the intervention decreased circulating tumor-promoting growth factors and inflammatory cytokines (i.e., BDNF, TNFα, FGF-2), with greater effects in obese compared to lean rats. In obese rats, preventing weight gain decreased adipocyte size, adipose tissue macrophage infiltration, reduced expression of the tumor-promoting growth factor FGF-1 in mammary adipose, and reduced phosphorylated FGFR indicating reduced FGF signaling in tumors.

CONCLUSIONS

Together, these findings suggest that the underlying mechanisms associated with the anti-tumor effects of weight maintenance are multi-factorial, and that weight maintenance during the peri-/postmenopausal period may be a viable strategy for reducing obesity-associated breast cancer risk and progression in women.

Noxious Stimulation Induces Acute Hemorrhage and Impairs Long-Term Recovery after Spinal Cord Injury (SCI) in Female Rats: Evidence Estrous Cycle May Have a Modulatory Effect

Spinal cord injuries (SCIs) are often the result of traumatic accidents, which also produce multiple other injuries (polytrauma). Nociceptive input from associated injuries has been shown to significantly impair recovery post-SCI. Historically, work in our laboratory has focused exclusively on male animals; however, increasing incidence of SCI in females requires research to determine whether pain (nociceptive) input poses the same risk to their recovery. Some animal studies have shown that females demonstrate greater tissue preservation and better locomotor recovery post-SCI. Given this, we examined the effect of sex on SCI recovery in two pain models—intermittent electrical stimulation (shock) to the tail or capsaicin injection to the hindpaw. Female rats received a lower thoracic contusion injury and were exposed to noxious stimulation the next day. The acute effect of noxious input on cardiovascular function, locomotor performance, and hemorrhage were assessed. Treatment with capsaicin or noxious electrical stimulation disrupted locomotor performance, increased blood pressure, and disrupted stepping. Additional experiments examined the long-term consequences of noxious input, demonstrating that both noxious electrical stimulation and capsaicin impair long-term recovery in female rats. Interestingly, injury had a greater effect on behavioral performance when progesterone and estrogen were low (metestrus). Conversely, nociceptive input led to a greater disruption in locomotor performance and produced a greater rise in blood pressure in animals injured during estrus.

A Low-Glucose Eating Pattern Improves Biomarkers of Postmenopausal Breast Cancer Risk: An Exploratory Secondary Analysis of a Randomized Feasibility Trial

Postmenopausal breast cancer is the most common obesity-related cancer death among women in the U.S. Insulin resistance, which worsens in the setting of obesity, is associated with higher breast cancer incidence and mortality. Maladaptive eating patterns driving insulin resistance represent a key modifiable risk factor for breast cancer. Emerging evidence suggests that time-restricted feeding paradigms (TRF) improve cancer-related metabolic risk factors; however, more flexible approaches could be more feasible and effective. In this exploratory, secondary analysis, we identified participants following a low-glucose eating pattern (LGEP), defined as consuming energy when glucose levels are at or below average fasting levels, as an alternative to TRF. Results show that following an LGEP regimen for at least 40% of reported eating events improves insulin resistance (HOMA-IR) and other cancer-related serum biomarkers. The magnitude of serum biomarkers changes observed here has previously been shown to favorably modulate benign breast tissue in women with overweight and obesity who are at risk for postmenopausal breast cancer. By comparison, the observed effects of LGEP were similar to results from previously published TRF studies in similar populations. These preliminary findings support further testing of LGEP as an alternative to TRF and a postmenopausal breast cancer prevention strategy. However, results should be interpreted with caution, given the exploratory nature of analyses.

Rapid Escalation of High-Volume Exercise during Caloric Restriction; Change in Visceral Adipose Tissue and Adipocytokines in Obese Sedentary Breast Cancer Survivors

Simple Summary

Aerobic exercise reduces risk for developing breast cancer or for breast cancer recurrence. In obese women exercise can significantly augment the effects of caloric restriction on visceral fat, reducing metabolic abnormalities and cancer. Women who are older, obese, and sedentary, especially those who have been treated for breast cancer, find it difficult to initiate and achieve the minimum or optimum levels of exercise. In a two-part pilot we found that by providing older, obese, sedentary breast cancer survivors 12 weeks of twice weekly personal training sessions, they could safely increase exercise to ≥200 min/week by 9 weeks during caloric restriction. At 24 weeks, high levels of exercise were still observed with continued behavioral support and study-provided exercise facility. Substantial improvement in visceral fat and breast cancer risk biomarkers were observed with this affordable intervention that is readily exportable to the community.

Abstract

Aerobic exercise reduces risk for breast cancer and recurrence and promotes visceral adipose tissue (VAT) loss in obesity. However, few breast cancer survivors achieve recommended levels of moderate to vigorous physical activity (MVPA) without supervision. In a two-cohort study, feasibility of 12 weeks of partially supervised exercise was started concomitantly with caloric restriction and effects on body composition and systemic risk biomarkers were explored. In total, 22 obese postmenopausal sedentary women (including 18 breast cancer survivors) with median age of 60 and BMI of 37 kg/m² were enrolled. Using personal trainers twice weekly at area YMCAs, MVPA was escalated to ≥200 min/week over 9 weeks. For cohort 2, maintenance of effect was assessed when study provided trainer services were stopped but monitoring, group counseling sessions, and access to the exercise facility were continued. Median post-escalation MVPA was 219 min/week with median 12-week mass and VAT loss of 8 and 19%. MVPA was associated with VAT loss which was associated with improved adiponectin:leptin ratio. In total, 9/11 of cohort-2 women continued the behavioral intervention for another 12 weeks without trainers. High MVPA continued with median 24-week mass and VAT loss of 12 and 29%. This intervention should be further studied in obese sedentary women.

Designing Relevant Preclinical Rodent Models for Studying Links Between Nutrition, Obesity, Metabolism, and Cancer

Diet and nutrition are intricately related to cancer prevention, growth, and treatment response. Preclinical rodent models are a cornerstone to biomedical research and remain instrumental in our understanding of the relationship between cancer and diet and in the development of effective therapeutics. However, the success rate of translating promising findings from the bench to the bedside is suboptimal. Well-designed rodent models will be crucial to improving the impact basic science has on clinical treatment options. This review discusses essential experimental factors to consider when designing a preclinical cancer model with an emphasis on incorporating these models into studies interrogating diet, nutrition, and metabolism. The aims of this review are to (a) provide insight into relevant considerations when designing cancer models for obesity, nutrition, and metabolism research; (b) identify common pitfalls when selecting a rodent model; and (c) discuss strengths and limitations of available preclinical models. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Change in Blood and Benign Breast Biomarkers in Women Undergoing a Weight-Loss Intervention Randomized to High-Dose ω-3 Fatty Acids versus Placebo

The inflammation-resolving and insulin-sensitizing properties of eicosapentaenoic (EPA) and docosahexaenoic (DHA) fatty acids have potential to augment effects of weight loss on breast cancer risk. In a feasibility study, 46 peri/postmenopausal women at increased risk for breast cancer with a body mass index (BMI) of 28 kg/m² or greater were randomized to 3.25 g/day combined EPA and DHA (ω-3-FA) or placebo concomitantly with initiation of a weight-loss intervention. Forty-five women started the intervention. Study discontinuation for women randomized to ω-3-FA and initiating the weight-loss intervention was 9% at 6 months and thus satisfied our main endpoint, which was feasibility. Between baseline and 6 months significant change (P < 0.05) was observed in 12 of 25 serum metabolic markers associated with breast cancer risk for women randomized to ω-3-FA, but only four for those randomized to placebo. Weight loss (median of 10% for trial initiators and 12% for the 42 completing 6 months) had a significant impact on biomarker modulation. Median loss was similar for placebo (-11%) and ω-3-FA (-13%). No significant change between ω-3-FA and placebo was observed for individual biomarkers, likely due to sample size and effect of weight loss. Women randomized to ω-3-FA exhibiting more than 10% weight loss at 6 months showed greatest biomarker improvement including 6- and 12-month serum adiponectin, insulin, omentin, and C-reactive protein (CRP), and 12-month tissue adiponectin. Given the importance of a favorable adipokine profile in countering the prooncogenic effects of obesity, further evaluation of high-dose ω-3-FA during a weight-loss intervention in obese high-risk women should be considered. PREVENTION RELEVANCE: This study examines biomarkers of response that may be modulated by omega-3 fatty acids when combined with a weight-loss intervention. While focused on obese, postmenopausal women at high risk for development of breast cancer, the findings are applicable to other cancers studied in clinical prevention trials.

Abstract 2567: Duavee® improves metabolic health without increasing cancer risk: findings from a preclinical model of obesity and postmenopausal breast cancer

Introduction: Many women at high risk for breast cancer will not take standard selective estrogen receptor modulators (SERMs) for cancer prevention due to concern of side effects, especially vasomotor symptoms. Duavee®, a tissue selective complex of the SERM bazedoxifene (BZA; 20mg) + conjugated estrogen (CE; 0.45mg), is FDA approved for relief of hot-flashes. Preclinical and early phase human studies suggest Duavee® has potential for breast cancer prevention, with favorable change in mammographic fibroglandular volume and proliferation. Given the &gt;40% incidence of obesity in postmenopausal women, and that obesity increases breast cancer risk, the current study was aimed at identifying the effects of obesity on response to Duavee® in a rodent model of obesity and postmenopausal breast cancer.

Methods: This study used our well-characterized rat model of diet-induced obesity and postmenopausal ER-positive breast cancer. Rats were injected with N-methylnitrosourea (MNU, 50 mg/kg) at 7 weeks of age to induce mammary tumors and fed a high fat diet (HF; 46% kcal fat) to promote obesity. Lean and obese rat were selected based on % body fat at 16 weeks. Tumors were monitored by manual palpation weekly and measured using digital calipers. Tumor-bearing rats were ovariectomized (OVX) when a tumor reached 0.7cm3. Rats were then maintained on ad libitum HF diet or HF diet plus a daily oral dose of Duavee® (3mg BZA+ 0.07mg CE/kg body weight) for 8 weeks. Body composition was analyzed biweekly (qMR) and fat pads weighed at study end to determine regional fat distribution.

Results: Like menopause in women, OVX induces weight gain in this model. Duavee® significantly blunted the OVX-induced weight gain in both lean (-65%, p&lt;0.001) and obese (-88%, p&lt;0.001) rats compared to controls. Similarly, Duavee®-treated rats gained less body fat after OVX vs controls (-50% lean; -97% obese, p&lt;0.001). Duavee® administration was associated with reduction in glucose in obese rats after 2 weeks and in lean and obese rats after 8 weeks (-11% vs controls, p=0.03). The effects of Duavee® on regional fat deposition varied by adiposity. Obese Duavee®-treated rats had significantly lower pericardial fat (-17%, p&lt;0.05) and tended to have lower mammary fat (-19%, p=0.08); lean rats had less gonadal fat (-20%, p&lt;0.05), while deposition in this region was not altered by Duavee® in obese rats. At 8 weeks there was no evidence that Duavee® promoted tumor development or growth in lean or obese OVX rats.

Conclusions: These data suggest that Duavee® may provide beneficial effects on body composition and metabolism in obese OVX animals without promotion of tumor growth. Further analyses will include study of direct effects of Duavee® on tumors, the tumor microenvironment, and systemic markers of insulin resistance and mammary cancer risk in our rat model of pre-and postmenopausal obesity and breast cancer.

Citation Format: Karen A. Corleto, Tara N. Mahmood, Danilo Landrock, Stephen D. Hursting, Carol J. Fabian, Bruce F. Kimler, Erin D. Giles. Duavee® improves metabolic health without increasing cancer risk: findings from a preclinical model of obesity and postmenopausal breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2567.

Abstract PD11-02: Randomized trial of 12 months of omega-3 fatty acids vs placebo during a weight loss intervention in post-menopausal women at increased risk for breast cancer

Objectives: The primary objective was to determine tolerability of ω-3 fatty acids (2150 mg of eicosapentaenoic acid (EPA) and 1050 docosahexaenoic acid (DHA) ethyl esters) vs placebo in women in undergoing a behavioral weight loss intervention (6 months loss and 6 months maintenance). Secondary objectives were to explore potential differences in modulation of blood and benign breast tissue risk biomarkers, satiety and quality of life indices, and weight loss. Results: 46 peri and postmenopausal women were randomized and 42 completed the 6 months of the weight loss intervention and were biomarker evaluable (22 placebo and 20 ω-3 FA). Median baseline BMI in the 42 evaluable women was 31 kg/m2 with a median 6-month relative weight loss of 11% and relative fat mass loss of 20% (DXA). Median 12-month relative mass loss was 10% in the 35 women completing 12 months of the intervention. ω-3 fatty acids increased the ratio of (EPA+DHA): arachidonic acid 2.6-fold (median, range 1.8 - 3.8) vs no change for placebo. There was no difference by randomization group in relative weight or fat mass loss at 6 or 12 months, grade 2 and 3 adverse events, early discontinuation, satiety or other quality of life measures. More serum biomarkers exhibited significant within-group improvement at 6 and 12 months for evaluable women randomized to ω-3 FA than to placebo. At 6 months, significant change (P&lt;0.05) was observed for adiponectin, leptin, adiponectin:leptin ratio, insulin, lipocalin-2, resistin, PAI-1, HGF, CRP, SHBG, and bioavailable testosterone in women randomized to ω-3 FA but only for leptin, adiponectin: leptin ratio and SHBG in those randomized to placebo. At 6 months, the 21 women who lost &gt;10% weight (median 15%) showed significant within-group improvement in adiponectin, leptin, adiponectin:leptin ratio, insulin, lipocalin-2, resistin, PAI-1, HGF, CRP, SHBG, bioavailable estradiol and bioavailable testosterone. For women with &lt;10% weight loss (median 6%) there was significant within-group improvement only for leptin, the adiponectin: leptin ratio, and SHBG. Little change was observed for inflammatory cytokines IL-6, TNF-alpha, MCP-1 or FABP4, or FGF-21 with ω-3 FA or &gt;10% weight loss. Given the dramatic effect of weight loss on biomarkers, we examined within-group and between-group change from baseline to 6 and 12 months for the four subgroups (10-11 women in each) defined by ω-3 FA or placebo and &lt; or &gt; 10% weight loss at 6 months. The subgroup of &gt;10% loss + ω-3 FA had the greatest within-group change in the proportion of significantly modulated biomarkers at 6 months. &gt;10% loss + ω-3 FA was the only subgroup with a significant within-group increase in adiponectin at both 6 and 12 months and achievement of a beneficial ratio of adiponectin (ug/ml) to leptin (ng/ml) of &gt; 1.0 in 100% of participants. There was a significant between-group effect for adiponectin for &gt;10% loss + ω-3 FA vs each of the other groups. Biomarkers were assessed in tissue acquired by random periareolar fine needle aspiration (RPFNA). There were no significant differences in change in cytomorphology or Ki-67 between women randomized to ω-3 FA or placebo but there were significant within-group increases in benign breast adiponectin (pg/ug protein) at 12 months (p=0.014) for women randomized to ω-3 FA. Conclusions: EPA + DHA ethyl esters (3150 mg/day), added to a behavioral weight loss program in overweight women at increased risk for breast cancer, is well-tolerated and may further improve risk biomarker modulation. The increase in adiponectin when ω-3 FA is added to weight loss is of particular interest given that adiponectin opposes the oncogenic effect of leptin and is associated with improved insulin sensitivity and reduced mTOR signaling. Further study is warranted with enough subjects to detect between-group differences.

Citation Format: Carol J Fabian, Christie A Befort, Debra K Sullivan, Susan E Carlson, Jennifer L Nydegger, Amy L Kreutzjans, Kandy R Powers, Teresa A. Phillips, Trina Metheny, Carola M Zalles, Erin D Giles, Stephen D Hursting, Bruce F Kimler. Randomized trial of 12 months of omega-3 fatty acids vs placebo during a weight loss intervention in post-menopausal women at increased risk for breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD11-02.

Preclinical Models to Study Obesity and Breast Cancer in Females: Considerations, Caveats, and Tools

Obesity increases the risk for breast cancer and is associated with poor outcomes for cancer patients. A variety of rodent models have been used to investigate these relationships; however, key differences in experimental approaches, as well as unique aspects of rodent physiology lead to variability in how these valuable models are implemented. We combine expertise in the development and implementation of preclinical models of obesity and breast cancer to disseminate effective practices for studies that integrate these fields. In this review, we share, based on our experience, key considerations for model selection, highlighting important technical nuances and tips for use of preclinical models in studies that integrate obesity with breast cancer risk and progression. We describe relevant mouse and rat paradigms, specifically highlighting differences in breast tumor subtypes, estrogen production, and strategies to manipulate hormone levels. We also outline options for diet composition and housing environments to promote obesity in female rodents. While we have applied our experience to understanding obesity-associated breast cancer, the experimental variables we incorporate have relevance to multiple fields that investigate women's health.

Impact of Exercise and Activity on Weight Regain and Musculoskeletal Health Post-Ovariectomy

The purpose of this study was to determine whether obesity and/or exercise training alters weight regain and musculoskeletal health after ovariectomy (OVX). Female rats were fed high-fat diet (HFD) to reveal obesity-prone (OP) and obesity-resistant (OR) phenotypes. The OP and OR exercising (EX) and sedentary (SED) rats were calorically restricted to lose 15% of body weight using medium-fat diet. Rats were then maintained in energy balance for 8 wk before OVX. After OVX and a brief calorically limited phase, rats were allowed to eat ad libitum until body weight plateaued. Starting at weight loss, EX ran 1 h·d, 6 d·wk, 15 m·min. Energy intake, spontaneous physical activity (SPA), and total energy expenditure were evaluated at the end of weight maintenance pre-OVX, and at three time points post-OVX: before weight regain, during early regain, and after regain. Data are presented as mean ± SE. Exercise attenuated weight regain after OVX in OP only (OP-EX, 123 ± 10 g; OP-SED, 165 ± 12 g; OR-EX, 121 ± 6 g; OR-SED, 116 ± 6 g), which was primarily an attenuation of fat gain. The early post-OVX increase in energy intake explained much of the weight regain, and was similar across groups. Exercising improved bone strength, as did maintaining SPA. Group differences in muscle mitochondrial respiration were not significant. The large decrease in SPA due to OVX was persistent, but early weight regain was dependent on decreased SPA. In conclusion, leanness and exercise do not necessarily protect from OVX-induced weight gain. Exercise prevented weight gain in obese rats, but loss of SPA was the greatest contributor to post-OVX weight gain. Thus, understanding the mechanisms resulting in reduction in SPA after ovarian hormone loss is critical in the prevention of menopause-associated metabolic dysfunction.

Regular exercise potentiates energetically expensive hepatic de novo lipogenesis during early weight regain

Exercise is a potent facilitator of long-term weight loss maintenance (WLM), whereby it decreases appetite and increases energy expenditure beyond the cost of the exercise bout. We have previously shown that exercise may amplify energy expenditure through energetically expensive nutrient deposition. Therefore, we investigated the effect of exercise on hepatic de novo lipogenesis (DNL) during WLM and relapse to obesity. Obese rats were calorically restricted with (EX) or without (SED) treadmill exercise (1 h/day, 6 days/wk, 15 m/min) to induce and maintain weight loss. After 6 wk of WLM, subsets of WLM-SED and WLM-EX rats were allowed ad libitum access to food for 1 day to promote relapse (REL). An energy gap-matched group of sedentary, relapsing rats (REL-GM) were provided a diet matched to the positive energy imbalance of the REL-EX rats. During relapse, exercise increased enrichment of hepatic DN-derived lipids and induced hepatic molecular adaptations favoring DNL compared with the gap-matched controls. In the liver, compared with both REL-SED and REL-GM rats, REL-EX rats had lower hepatic expression of genes required for cholesterol biosynthesis; greater hepatic expression of genes that mediate very low-density lipoprotein synthesis and secretion; and greater mRNA expression of Cyp27a1, which encodes an enzyme involved in the biosynthesis of bile acids. Altogether, these data provide compelling evidence that the liver has an active role in exercise-mediated potentiation of energy expenditure during early relapse.

Metformin inhibits stromal aromatase expression and tumor progression in a rodent model of postmenopausal breast cancer

BACKGROUND

Obesity and type II diabetes are linked to increased breast cancer risk in postmenopausal women. Patients treated with the antidiabetic drug metformin for diabetes or metabolic syndrome have reduced breast cancer risk, a greater pathologic complete response to neoadjuvant therapy, and improved breast cancer survival. We hypothesized that metformin may be especially effective when targeted to the menopausal transition, as this is a lifecycle window when weight gain and metabolic syndrome increase, and is also when the risk for obesity-related breast cancer increases.

METHODS

Here, we used an 1-methyl-1-nitrosourea (MNU)-induced mammary tumor rat model of estrogen receptor (ER)-positive postmenopausal breast cancer to evaluate the long-term effects of metformin administration on metabolic and tumor endpoints. In this model, ovariectomy (OVX) induces rapid weight gain, and an impaired whole-body response to excess calories contributes to increased tumor glucose uptake and increased tumor proliferation. Metformin treatment was initiated in tumor-bearing animals immediately prior to OVX and maintained for the duration of the study.

RESULTS

Metformin decreased the size of existing mammary tumors and inhibited new tumor formation without changing body weight or adiposity. Decreased lipid accumulation in the livers of metformin-treated animals supports the ability of metformin to improve overall metabolic health. We also found a decrease in the number of aromatase-positive, CD68-positive macrophages within the tumor microenvironment, suggesting that metformin targets the immune microenvironment in addition to improving whole-body metabolism.

CONCLUSIONS

These findings suggest that peri-menopause/menopause represents a unique window of time during which metformin may be highly effective in women with established, or at high risk for developing, breast cancer.

Is regular exercise an effective strategy for weight loss maintenance?

Weight regain after weight loss is one of the most significant challenges to successful obesity treatment. Regular exercise has long been touted as a strategy for weight loss maintenance, but the lack of clear evidence in clinical trials has caused some to question its effectiveness. In this review, we present the arguments both questioning and in support of exercise as an obesity therapeutic. Our purpose is to bring clarity to the literature, present a unified perspective, and identify the gaps in knowledge that need to be addressed in future studies. Critical questions remain including sex differences, individual variability and compensatory behaviors in response to exercise, exercise adherence, the role of energy flux and the molecular mechanisms mediating the beneficial effects of exercise after weight loss and during weight regain. Future research should focus on these critical questions to provide a more complete understanding of the potential benefits of exercise on weight loss maintenance.

Prior weight loss exacerbates the biological drive to gain weight after the loss of ovarian function

Both the history of obesity and weight loss may change how menopause affects metabolic health. The purpose was to determine whether obesity and/or weight loss status alters energy balance (EB) and subsequent weight gain after the loss of ovarian function. Female lean and obese Wistar rats were randomized to 15% weight loss (WL) or ad libitum fed controls (CON). After the weight loss period, WL rats were kept in EB at the reduced weight for 8 weeks prior to ovariectomy (OVX). After OVX, all rats were allowed to eat ad libitum until weight plateaued. Energy intake (EI), spontaneous physical activity, and total energy expenditure (TEE) were measured with indirect calorimetry before OVX, immediately after OVX, and after weight plateau. Changes in energy intake (EI), TEE, and weight gain immediately after OVX were similar between lean and obese rats. However, obese rats gained more total weight and fat mass than lean rats over the full regain period. Post-OVX, EI increased more (P ≤ 0.03) in WL rats (58.9 ± 3.5 kcal/d) than CON rats (8.5 ± 5.2 kcal/d), and EI partially normalized (change from preOVX: 20.5 ± 4.2 vs. 1.5 ± 4.9 kcal/day) by the end of the study. As a result, WL rats gained weight (week 1:44 ± 20 vs. 7 ± 25 g) more rapidly (mean = 44 ± 20 vs. 7 ± 25 g/week; P < 0.001) than CON Prior obesity did not affect changes in EB or weight regain following OVX, whereas a history of weight loss prior to OVX augmented disruptions in EB after OVX, resulting in more rapid weight regain.

Ibuprofen before Exercise Does Not Prevent Cortical Bone Adaptations to Training

Using a nonsteroidal anti-inflammatory drug (NSAID) before a single bout of mechanical loading can reduce bone formation response. It is unknown whether this translates to an attenuation of bone strength and structural adaptations to exercise training.

PURPOSE

This study aimed to determine whether nonsteroidal anti-inflammatory drug use before exercise prevents increases in bone structure and strength in response to weight-bearing exercise.

METHODS

Adult female Wistar rats (n = 43) were randomized to ibuprofen (IBU) or vehicle (VEH) and exercise (EX) or sedentary (SED) groups in a 2 × 2 (drug and activity) ANCOVA design with body weight as the covariate, and data are reported as mean ± SE. IBU drops (30 mg·kg BW) or VEH (volume equivalent) were administered orally 1 h before the bout of exercise. Treadmill running occurred 5 d·wk for 60 min·d at 20 m·min with a 5° incline for 12 wk. Micro-CT, mechanical testing, and finite element modeling were used to quantify bone characteristics.

RESULTS

Drug-activity interactions were not significant. Exercise increased tibia cortical cross-sectional area (EX = 5.67 ± 0.10, SED = 5.37 ± 0.10 mm, P < 0.01) and structural estimates of bone strength (Imax: EX = 5.16 ± 0.18, SED = 4.70 ± 0.18 mm, P < 0.01; SecModPolar: EX = 4.01 ± 0.11, SED = 3.74 ± 0.10 mm, P < 0.01). EX had increased failure load (EX = 243 ± 9, SED = 202 ± 7 N, P < 0.05) and decreased distortion in response to a 200-N load (von Mises stress at tibia-fibula junction: EX = 48.2 ± 1.3, SED = 51.7 ± 1.2 MPa, P = 0.01). There was no effect of ibuprofen on any measurement tested. Femur results revealed similar patterns.

CONCLUSION

Ibuprofen before exercise did not prevent the skeletal benefits of exercise in female rats. However, exercise that engenders higher bone strains may be required to detect an effect of ibuprofen.

Metformin Accumulation Correlates with Organic Cation Transporter 2 Protein Expression and Predicts Mammary Tumor Regression In Vivo

Several epidemiologic studies have associated metformin treatment with a reduction in breast cancer incidence in prediabetic and type II diabetic populations. Uncertainty exists regarding which patient populations and/or tumor subtypes will benefit from metformin treatment, and most preclinical in vivo studies have given little attention to the cellular pharmacology of intratumoral metformin uptake. Epidemiologic reports consistently link western-style high fat diets (HFD), which drive overweight and obesity, with increased risk of breast cancer. We used a rat model of HFD-induced overweight and mammary carcinogenesis to define intratumoral factors that confer metformin sensitivity. Mammary tumors were initiated with 1-methyl-1-nitrosourea, and rats were randomized into metformin-treated (2 mg/mL drinking water) or control groups (water only) for 8 weeks. Two-thirds of existing mammary tumors responded to metformin treatment with decreased tumor volumes (P < 0.05), reduced proliferative index (P < 0.01), and activated AMPK (P < 0.05). Highly responsive tumors accumulated 3-fold greater metformin amounts (P < 0.05) that were positively correlated with organic cation transporter-2 (OCT2) protein expression (r = 0.57; P = 0.038). Importantly, intratumoral metformin concentration negatively associated with tumor volume (P = 0.03), and each 10 pmol increase in intratumoral metformin predicted >0.11 cm³ reduction in tumor volume. Metformin treatment also decreased proinflammatory arachidonic acid >1.5-fold in responsive tumors (P = 0.023). Collectively, these preclinical data provide evidence for a direct effect of metformin in vivo and suggest that OCT2 expression may predict metformin uptake and tumor response. Cancer Prev Res; 10(3); 198-207. ©2017 AACR.

Modeling Diet-Induced Obesity with Obesity-Prone Rats: Implications for Studies in Females

Obesity is a worldwide epidemic, and the comorbidities associated with obesity are numerous. Over the last two decades, we and others have employed an outbred rat model to study the development and persistence of obesity, as well as the metabolic complications that accompany excess weight. In this review, we summarize the strengths and limitations of this model and how it has been applied to further our understanding of human physiology in the context of weight loss and weight regain. We also discuss how the approach has been adapted over time for studies in females and female-specific physiological conditions, such as menopause and breast cancer. As excess weight and the accompanying metabolic complications have become common place in our society, we expect that this model will continue to provide a valuable translational tool to establish physiologically relevant connections to the basic science studies of obesity and body weight regulation.

Weight restoration on a high carbohydrate refeeding diet promotes rapid weight regain and hepatic lipid accumulation in female anorexic rats

Background

There is currently no standard clinical refeeding diet for the treatment of anorexia nervosa (AN). To provide the most efficacious AN clinical care, it is necessary to define the metabolic effects of current refeeding diets.

Methods

An activity-based model of anorexia nervosa (AN) was used in female rats. AN was induced over 7d by timed access to low fat (LF) diet with free access to a running wheel. Plasma hormones/metabolites and body composition were assessed at baseline, AN diagnosis (day 0), and following 28d of refeeding on LF diet. Energy balance and expenditure were measured via continuous indirect calorimetry on days −3 to +3.

Results

AN induction caused stress as indicated by higher levels of corticosterone versus controls (p < 0.0001). The rate of weight gain during refeeding was higher in AN rats than controls (p = 0.0188), despite lower overall energy intake (p < 0.0001). This was possible due to lower total energy expenditure (TEE) at the time of AN diagnosis which remained significantly lower during the entire refeeding period, driven by markedly lower resting energy expenditure (REE). AN rats exhibited lower lipid accumulation in visceral adipose tissues (VAT) but much higher liver accumulation (62 % higher in AN than control; p < 0.05) while maintaining the same total body weight as controls. It is possible that liver lipid accumulation was caused by overfeeding of carbohydrate suggesting that a lower carbohydrate, higher fat diet may be beneficial during AN treatment. To test whether such a diet would be accepted clinically, we conducted a study in adolescent female AN patients which showed equivalent palatability and acceptability for LF and moderate fat diets. In addition, this diet was feasible to provide clinically during inpatient treatment in this population.

Conclusion

Refeeding a LF diet to restore body weight in female AN rats caused depressed TEE and REE which facilitated rapid regain. However, this weight gain was metabolically unhealthy as it resulted in elevated lipid accumulation in the liver. It is necessary to investigate the use of other diets, such as lower carbohydrate, moderate fat diets, in pre-clinical models to develop the optimal clinical refeeding diets for AN.

Exercise Decreases Lipogenic Gene Expression in Adipose Tissue and Alters Adipocyte Cellularity during Weight Regain After Weight Loss

Exercise is a potent strategy to facilitate long-term weight maintenance. In addition to increasing energy expenditure and reducing appetite, exercise also favors the oxidation of dietary fat, which likely helps prevent weight re-gain. It is unclear whether this exercise-induced metabolic shift is due to changes in energy balance, or whether exercise imparts additional adaptations in the periphery that limit the storage and favor the oxidation of dietary fat. To answer this question, adipose tissue lipid metabolism and related gene expression were studied in obese rats following weight loss and during the first day of relapse to obesity. Mature, obese rats were weight-reduced for 2 weeks with or without daily treadmill exercise (EX). Rats were weight maintained for 6 weeks, followed by relapse on: (a) ad libitum low fat diet (LFD), (b) ad libitum LFD plus EX, or (c) a provision of LFD to match the positive energy imbalance of exercised, relapsing animals. 24 h retention of dietary- and de novo-derived fat were assessed directly using ¹⁴C palmitate/oleate and ³H₂0, respectively. Exercise decreased the size, but increased the number of adipocytes in both retroperitoneal (RP) and subcutaneous (SC) adipose depots, and prevented the relapse-induced increase in adipocyte size. Further, exercise decreased the expression of genes involved in lipid uptake (CD36 and LPL), de novo lipogenesis (FAS, ACC1), and triacylglycerol synthesis (MGAT and DGAT) in RP adipose during relapse following weight loss. This was consistent with the metabolic data, whereby exercise reduced retention of de novo-derived fat even when controlling for the positive energy imbalance. The decreased trafficking of dietary fat to adipose tissue with exercise was explained by reduced energy intake which attenuated energy imbalance during refeeding. Despite having decreased expression of lipogenic genes, the net retention of de novo-derived lipid was higher in both the RP and SC adipose of exercising animals compared to their energy gap-matched controls. Our interpretation of this data is that much of this lipid is being made by the liver and subsequently trafficked to adipose tissue storage. Together, these concerted effects may explain the beneficial effects of exercise on preventing weight regain following weight loss.

The role for adipose tissue in weight regain after weight loss

Weight regain after weight loss is a substantial challenge in obesity therapeutics. Dieting leads to significant adaptations in the homeostatic system that controls body weight, which promotes overeating and the relapse to obesity. In this review, we focus specifically on the adaptations in white adipose tissues that contribute to the biological drive to regain weight after weight loss. Weight loss leads to a reduction in size of adipocytes and this decline in size alters their metabolic and inflammatory characteristics in a manner that facilitates the clearance and storage of ingested energy. We present the hypothesis whereby the long-term signals reflecting stored energy and short-term signals reflecting nutrient availability are derived from the cellularity characteristics of adipose tissues. These signals are received and integrated in the hypothalamus and hindbrain and an energy gap between appetite and metabolic requirements emerges and promotes a positive energy imbalance and weight regain. In this paradigm, the cellularity and metabolic characteristics of adipose tissues after energy-restricted weight loss could explain the persistence of a biological drive to regain weight during both weight maintenance and the dynamic period of weight regain.

Developmental windows of breast cancer risk provide opportunities for targeted chemoprevention

The magnitude of the breast cancer problem implores researchers to aggressively investigate prevention strategies. However, several barriers currently reduce the feasibility of breast cancer prevention. These barriers include the inability to accurately predict future breast cancer diagnosis at the individual level, the need for improved understanding of when to implement interventions, uncertainty with respect to optimal duration of treatment, and negative side effects associated with currently approved chemoprevention therapies. None-the-less, the unique biology of the mammary gland, with its postnatal development and conditional terminal differentiation, may permit the resolution of many of these barriers. Specifically, lifecycle-specific windows of breast cancer risk have been identified that may be amenable to risk-reducing strategies. Here, we argue for prevention research focused on two of these lifecycle windows of risk: postpartum mammary gland involution and peri-menopause. We provide evidence that these windows are highly amenable to targeted, limited duration treatments. Such approaches could result in the prevention of postpartum and postmenopausal breast cancers, correspondingly.

Obesity and overfeeding affecting both tumor and systemic metabolism activates the progesterone receptor to contribute to postmenopausal breast cancer

Obese postmenopausal women have increased risk of breast cancers with poorer clinical outcomes than their lean counterparts. However, the mechanisms underlying these associations are poorly understood. Rodent model studies have recently identified a period of vulnerability for mammary cancer promotion, which emerges during weight gain after the loss of ovarian function (surgical ovariectomy; OVX). Thus, a period of transient weight gain may provide a life cycle-specific opportunity to prevent or treat postmenopausal breast cancer. We hypothesized that a combination of impaired metabolic regulation in obese animals prior to OVX plus an OVX-induced positive energy imbalance might cooperate to drive tumor growth and progression. To determine if lean and obese rodents differ in their metabolic response to OVX-induced weight gain, and whether this difference affects later mammary tumor metabolism, we performed a nutrient tracer study during the menopausal window of vulnerability. Lean animals preferentially deposited excess nutrients to mammary and peripheral tissues rather than to the adjacent tumors. Conversely, obese animals deposited excess nutrients into the tumors themselves. Notably, tumors from obese animals also displayed increased expression of the progesterone receptor (PR). Elevated PR expression positively correlated with tumor expression of glycolytic and lipogenic enzymes, glucose uptake, and proliferation markers. Treatment with the antidiabetic drug metformin during ovariectomy-induced weight gain caused tumor regression and downregulation of PR expression in tumors. Clinically, expression array analysis of breast tumors from postmenopausal women revealed that PR expression correlated with a similar pattern of metabolic upregulation, supporting the notion that PR+ tumors have enhanced metabolic capacity after menopause. Our findings have potential explanative power in understanding why obese, postmenopausal women display an increased risk of breast cancer.

Exercise reduces appetite and traffics excess nutrients away from energetically efficient pathways of lipid deposition during the early stages of weight regain

The impact of regular exercise on energy balance, fuel utilization, and nutrient availability, during weight regain was studied in obese rats, which had lost 17% of their weight by a calorie-restricted, low-fat diet. Weight reduced rats were maintained for 6 wk with and without regular treadmill exercise (1 h/day, 6 days/wk, 15 m/min). In vivo tracers and indirect calorimetry were then used in combination to examine nutrient metabolism during weight maintenance (in energy balance) and during the first day of relapse when allowed to eat ad libitum (relapse). An additional group of relapsing, sedentary rats were provided just enough calories to create the same positive energy imbalance as the relapsing, exercised rats. Exercise attenuated the energy imbalance by 50%, reducing appetite and increasing energy requirements. Expenditure increased beyond the energetic cost of the exercise bout, as exercised rats expended more energy to store the same nutrient excess in sedentary rats with the matched energy imbalance. Compared with sedentary rats with the same energy imbalance, exercised rats exhibited the trafficking of dietary fat toward oxidation and away from storage in adipose tissue, as well as a higher net retention of fuel via de novo lipogenesis in adipose tissue. These metabolic changes in relapse were preceded by an increase in the skeletal muscle expression of genes involved in lipid uptake, mobilization, and oxidation. Our observations reveal a favorable shift in fuel utilization with regular exercise that increases the energetic cost of storing excess nutrients during relapse and alterations in circulating nutrients that may affect appetite. The attenuation of the biological drive to regain weight, involving both central and peripheral aspects of energy homeostasis, may explain, in part, the utility of regular exercise in preventing weight regain after weight loss.

Effect of the estrous cycle and surgical ovariectomy on energy balance, fuel utilization, and physical activity in lean and obese female rats

This study presents an in-depth analysis of the effects of obesity on energy balance (EB) and fuel utilization in adult female rats, over the estrous cycle and immediately after surgical ovariectomy (OVX), to model pre- and postmenopausal states, respectively. Female Wistar rats were fed a high-fat (46%) diet for 16 wk to produce mature lean and obese animals. Stage of estrous was identified by daily vaginal lavage, while energy intake (EI), total energy expenditure (TEE), and fuel utilization were monitored in a multichamber indirect calorimeter and activity was monitored by infrared beam breaks. Metabolic monitoring studies were repeated during the 3-wk period of rapid OVX-induced weight gain. Component analysis of TEE was performed to determine the nonresting and resting portions of energy expenditure. Obesity was associated with a greater fluctuation in EB across the estrous cycle. Cycling obese rats were less active, expended more energy per movement, and oxidized more carbohydrate than lean rats. The changes in EB over the cycle in lean and obese rats were driven by changes in EI. Finally, OVX induced a large positive energy imbalance in obese and lean rats. This resulted primarily from an increase in EI in both groups, with little change in TEE following OVX. These observations reveal a dominant effect of obesity on EB, fuel utilization, and activity levels in cycling rats, which has implications for studies focused on obesity and EB in female rodents.

Abstract 72: Metformin enhances tumor regression and reduces tumor burden in a preclinical paradigm modeling obesity's impact on postmenopausal breast cancer

BACKGROUND: Obesity and type II diabetes have been linked to a higher risk of breast cancer in post-menopausal women. Patients treated with the anti-diabetic drug metformin (1,1-dimethylbiguanide hydrochloride) for type II diabetes or metabolic syndrome have shown a reduced risk of breast cancer, a greater pathologic complete response for neoadjuvant therapy and an improved breast cancer survival. The purpose of this study was to examine the effects of metformin on tumor promotion in a rodent model of obesity and postmenopausal breast cancer.

METHODS: Rats were injected with N-methylnitrosourea (MNU, 50 mg/kg) at 8 weeks of age to induce mammary tumors, and fed a high fat diet (from 5 weeks of age) to promote obesity. Obesity-resistant and obesity-prone rats were selected, based upon weight gain (between 10 and 14 weeks of age) and were matured under these conditions to produce adult, tumor-bearing lean and obese rats (24±1 vs 29±1 % body fat). Tumors were monitored by manual palpation at weekly intervals from the time of MNU administration. Obese animals were randomly assigned to either metformin treatment (2mg/mL in their drinking water, n=8) or control group (water only, n=6), after at least 1 tumor reached a volume &gt;1cm3. Rats were maintained on their respective treatments for the duration of the study. One week following the initiation of treatment, animals were ovariectomized (OVX) to mimic the post-menopausal state, and tumor palpations were continued for an additional 9 weeks.

RESULTS: Prior to OVX, control and metformin treated obese rats were similar in weight (413±21 vs 397±20 g) and tumor burden (3.3±1.2 vs 3.7±2.3 g). In response to OVX, tumor burden decreased in all animals, as predicted, based on the hormone responsiveness of MNU-induced tumors. Compared to untreated obese rats, the percent of pre-OVX tumor burden was lower in metformin-treated rats (weeks 1-3 post-OVX; 67±10 vs 26± 8%, p&lt;0.05). A tendency for metformin to attenuate the subsequent rebound in tumor burden was observed at week 7 (126±67 vs 41±35%, p=0.06), week 8 (170±112 vs 35±29%, p=0.06), and week 9 (249±165 vs 41±30%, p=0.09).

CONCLUSIONS: These preliminary observations indicate that metformin enhances OVX-induced tumor regression in obese rats and may reduce long term tumor growth and survival in these animals after the surgery. These findings suggest that metformin may have therapeutic benefits in obese, peri- or post-menopausal patients who are at risk for breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 72.

A surprising link between the energetics of ovariectomy-induced weight gain and mammary tumor progression in obese rats

Obesity increases the risk for postmenopausal breast cancer. We have modeled this metabolic context using female Wistar rats that differ in their polygenic predisposition for obesity under conditions of high-fat feeding and limited physical activity. At 52 days of age, rats were injected with 1-methyl-1-nitrosourea (MNU, 50 mg/kg) and placed in an obesogenic environment. At 19 weeks of age, the rats were separated into lean, mid-weight, and obese rats, based upon their weight gained during this time. The rats were ovariectomized (OVX) at approximately 24 weeks of age and the change in tumor multiplicity and burden, weight gain, energy intake, tumor estrogen receptor (ER) status, and humoral metabolite and cytokine profiles were examined. The survival and growth of tumors increased in obese rats in response to OVX. OVX induced a high rate of weight gain during post-OVX weeks 1-3, compared to SHAM-operated controls. During this time, feed efficiency (mg gain/kcal intake) was lower in obese rats, and this reduced storage efficiency of ingested fuels predicted the OVX-induced changes in tumor multiplicity (r = -0.64, P < 0.001) and burden (r = -0.57, P < 0.001). Tumors from obese rats contained more cells that expressed ERalpha, and post-OVX plasma from rats with the lowest feed efficiency had lower interleukin (IL)-2 and IL-4 levels. Our observations suggest a novel link between obesity and mammary tumor promotion that involves impaired fuel metabolism during OVX-induced weight gain. The metabolically inflexible state of obesity and its inability to appropriately respond to the OVX-induced energy imbalance provides a plausible explanation for this relationship and the emergence of obesity's impact on breast cancer risk after menopause.

Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss

Weight loss is accompanied by several metabolic adaptations that work together to promote rapid, efficient regain. We employed a rodent model of regain to examine the effects of a regular bout of treadmill exercise on these adaptations. Obesity was induced in obesity-prone rats with 16 wk of high-fat feeding and limited physical activity. Obese rats were then weight reduced (approximately 14% of body wt) with a calorie-restricted, low-fat diet and maintained at that reduced weight for 8 wk by providing limited provisions of the diet with (EX) or without (SED) a daily bout of treadmill exercise (15 m/min, 30 min/day, 6 days/wk). Weight regain, energy balance, fuel utilization, adipocyte cellularity, and humoral signals of adiposity were monitored during eight subsequent weeks of ad libitum feeding while the rats maintained their respective regimens of physical activity. Regular exercise decreased the rate of regain early in relapse and lowered the defended body weight. During weight maintenance, regular exercise reduced the biological drive to eat so that it came closer to matching the suppressed level of energy expenditure. The diurnal extremes in fuel preference observed in weight-reduced rats were blunted, since exercise promoted the oxidation of fat during periods of feeding (dark cycle) and promoted the oxidation of carbohydrate (CHO) later in the day during periods of deprivation (light cycle) . At the end of relapse, exercise reestablished the homeostatic steady state between intake and expenditure to defend a lower body weight. Compared with SED rats, relapsed EX rats exhibited a reduced turnover of energy, a lower 24-h oxidation of CHO, fewer adipocytes in abdominal fat pads, and peripheral signals that overestimated their adiposity. These observations indicate that regimented exercise altered several metabolic adaptations to weight reduction in a manner that would coordinately attenuate the propensity to regain lost weight.

The use of proliferating cell nuclear antigen immunohistochemistry with a unique functional marker to detect postnatal neurogenesis in paraffin-embedded sections of the mature pig brain

Until recently, evidence supporting postnatal neurogenesis was controversial. Much of the debate has centered on the identification of the dividing cells as neurons versus glia. Because neurogenesis has become a well-documented phenomenon, there is a need for reliable protocols to identify recently divided neurons in a wide range of situations. To facilitate the investigation of postnatal neurogenesis of magnocellular neurons in the pig hypothalamus, a sequential immunohistochemical staining technique was developed for use on serial sections of paraffin-embedded tissue. Proliferating neurons were labeled using mouse-derived monoclonal antibodies to detect proliferating cell nuclear antigen (PCNA) and vasopressin (VP). PCNA, a nuclear protein essential for cell division, identifies recently divided cells in the brains of healthy animals. VP is a unique functional marker for a mature neuron. The presence of a cell with VP positive cytoplasm and a PCNA positive nucleus demonstrates the presence of a VP-producing neuron that has recently divided. This protocol allowed us to safely and accurately label recently proliferated neurons in the mature pig hypothalamus and can be used on archived tissue. This data can be used for further morphometric analysis, as serial sectioning allows for three-dimensional reconstruction of hypothalamic nuclei.

Role of insulin-like growth factor binding proteins (IGFBPs) in breast cancer proliferation and metastasis

Cancers of the breast, prostate, and lung commonly metastasize to the bone resulting in osteolysis, pathologic fracture, pain and significant clinical morbidity. To date, the reason for such selectivity in the site of metastasis remains largely unknown. The bone is a rich source of many chemokines and growth factors, including: insulin-like growth factor (IGF) I and II, transforming growth factor-beta (TGF-beta), interleukins, and tumour necrosis factor-alpha (TNF-alpha). We propose that exposure of breast cancer cells to the bone microenvironment results in alterations in gene expression that favour the growth and proliferation of tumour cells in the bone. To investigate this hypothesis, MDA-MB-231 breast carcinoma cells were exposed to bone-derived conditioned media (BDCM) generated by culturing fetal rat calvaria for 24 h under serum free conditions. Using cDNA microarray technology, we have identified the insulin-like growth factor family of binding proteins (IGFBPs) as genes whose expression profiles are consistently and significantly altered with exposure to this simulated bone environment in vitro, when compared to untreated controls. Our data suggests that the upregulation of IGFBP-3 seen with exposure to the bone microenvironment is directly linked to an increase in TGF-beta mediated cell proliferation. Furthermore, this process appears to be functioning through an IGF-independent mechanism.

Postnatal neurogenesis in the vasopressin and oxytocin-containing nucleus of the pig hypothalamus

The vasopressin and oxytocin-containing nucleus (VON) of the pig hypothalamus demonstrates dramatic postnatal growth in nucleus size, both volume and neuron number, during puberty, and continues to increase in size in the adult sexually mature female pig throughout its reproductive prime. This study was designed to show that postnatal neurogenesis is responsible for the VON growth that occurs between adolescence and maturity. Recently divided neurosecretory cells of the hypothalamus were identified in adolescent and mature non-lactating female pigs using a sequential immunohistochemistry double-labeling technique with monoclonal mouse antibodies to detect vasopressin and proliferating cell nuclear antigen (PCNA), a protein associated with the S phase of the cell cycle. A computer-assisted image-analysis system was used to assess nucleus volume and neuron counts. The VON of the mature dry sows was significantly larger in volume and number of vasopressin neurons than the VON of the adolescent pigs. Double-labeled cells were noted in the VON of both adolescent and mature dry sows, but the number and proportion of double-labeled cells was significantly higher in adolescent pigs. Our results indicate the presence of neurons containing PCNA in the VON of the pig hypothalamus. This suggests that mitosis of neurogenic precursors plays a role in the growth of the nucleus.