Relationships among serum leptin, leptin receptor gene polymorphisms, and breast cancer in Korea

Genetic alterations in LEP and ADIPOQ genes and risk for breast cancer: a meta-analysis

Introduction

Breast cancer has a strong genetic predisposition, and its genetic architecture is not fully understood thus far. In this study, we aimed to perform a meta-analysis to evaluate the association of genetic alterations in LEP and ADIPOQ genes, as well as their receptor-encoded genes with risk for breast cancer.

Methods

Only published studies conducted in humans and written in English were identified by searching PubMed, SCOPUS, CINAHIL and Embase from their inception to October 2022. Eligibility assessment and data collection were completed independently by two researchers. Statistical analyses were done using the STATA software.

Results

After literature search, 33 publications were eligible for inclusion. Overall, LEP gene rs7799039-G allele (odds ratio [OR]: 0.78, 95% confidence interval [CI]: 0.62 to 0.98) and ADIPOQ gene rs1501299-T allele (OR: 1.41, 95% CI: 1.06 to 1.88) were associated with the significant risk of breast cancer. In subgroup analyses, differences in menopausal status, obesity, race, study design, diagnosis of breast cancer, genotyping method and sample size might account for the divergent observations of individual studies. Circulating leptin levels were comparable across genotypes of LEP gene rs7799039, as well as that of LEPR gene rs1137101 (P>0.05). Begg's funnel plots seemed symmetrical, with the exception of LEPR gene rs1137100 and ADIPOQ gene rs1501299.

Discussion

Taken together, we found, in this meta-analysis, that LEP gene rs7799039 and ADIPOQ gene rs1501299 were two promising candidate loci in predisposition to breast cancer risk.

Biochemical study on modifying role of variants of leptin gene and its receptor on serum leptin levels in breast cancer

The leptin is discharged from breast adipose tissue and is overexpressed in breast cancer (BC). Conflicting relation of leptin with BC was reported. We investigated this association and its impact on leptin level and disease characteristics. The study included 70 females (40 women with pathological proof of invasive BC patients and 30 controls). LEP and LEPR polymorphisms were evaluated by real-time PCR. Serum leptin was estimated by ELISA. Both LEPR and LEP disturbances increase the danger of BC where GG genotype and G allele frequencies of LEPR were higher in patients vs. control. GG genotype increases BC risk with OR (9.1) while G allele predisposes to disease with OR (3.8). Furthermore, LEP A allele was uniquely elevated in patients than healthy ones with OR (2.06). Precise relation of circulating leptin and its polymorphisms with predicting BC may authorize its utilization in early screening.

Investigation of leptin receptor rs1137101 G>A polymorphism with cancer risk: evidence from 35936 subjects

Leptin receptor (LEPR) signaling may be involved in promoting angiogenesis and proliferation, inhibiting apoptosis and playing a vital role in the progression of carcinogenesis. A number of studies have focused on the association of LEPR rs1137101 variants with susceptibility of cancer, however, the observed results were controversial. We searched literature on the relationship of LEPR rs1137101 G>A polymorphism with cancer risk by using PubMed and Embase databases, covering all publications up to 14 October 2018. In total, 44 case–control studies with 35,936 subjects were included. After combining all eligible studies, we identified null relationship between LEPR gene rs1137101 G>A polymorphism and overall cancer risk [A vs. G: odds ratio (OR ) =  0.97, 95% confidence interval (CI ) =  0.89–1.06, P = 0.547; AA vs. GG: OR  =  0.93, 95% CI  =  0.78–1.13, P = 0.476; AA/GA vs. GG: OR  =  0.99, 95% CI  =  0.91–1.09, P= 0.890 and AA vs. GA/GG: OR  = 0.92, 95% CI  =  0.82–1.04, P= 0.198]. However, in a subgroup analysis, there was an increased susceptibility of oral and oropharyngeal cancer in AA vs. GA/GG genetic model (OR, 1.83; 95% CI, 1.01–3.33; P=0.048). Considering the limited participants were included, the findings might be underpowered. Sensitivity analysis identified that any independent study omitted did not materially influence the pooled ORs and CIs. The results of publication bias detection showed that there was no evidence of bias. In summary, this analysis indicates that no significant association of cancer risk was identified to be correlated with rs1137101 G>A variants, even in stratified analyses.

LEPR polymorphisms and haplotypes in Mexican patients with colorectal cancer

INTRODUCTION

Obesity and colorectal cancer could be linked by adipocytokines, which are proteins associated with cell proliferation. High levels of the adipocytokine leptin promote the development of colorectal cancer through its receptor.

OBJECTIVE

To determine the association between c.326A>G and c.668A>G LEPR gene polymorphisms and colorectal cancer.

MATERIALS AND METHODS

DNA was extracted from the peripheral blood of 147 patients with sporadic colorectal cancer and 134 healthy people. Genotypes were obtained by PCRRFLP and the association was determined by the odds ratio (OR) test using the SPSS™, version 10.0, program. Haplotype frequencies and linkage disequilibrium were estimated by the Arlequin, version 3.5, software.

RESULTS

Both polymorphisms were in Hardy-Weinberg equilibrium. Only the c.326A>G heterozygous genotype revealed an increased risk for colorectal cancer development (OR=1.81, 95% CI=1.04-3.16, p=0.04). The AG haplotype showed a significant association with colorectal cancer (OR=0.58, 95% CI=0.35-0.96, p<0.03). Linkage disequilibrium between the variants was only evident for the patients group (r2=0.36).

CONCLUSION

Our results suggest that AG individuals heterozygous for the c.326A>G LEPR variant have a higher risk of colorectal cancer development whereas the AG haplotype (c.326A/c.668G) has a protective effect in the Mexican population.

Association of serum leptin with breast cancer: A meta-analysis

BACKGROUND

Accumulating evidence has demonstrated that leptin is associated to the tumorigenesis and progression of breast cancer (BC). However, these studies remain inconsistent. Thus, a meta-analysis was conducted to investigate the role of leptin in the patients with BC.

METHOD

A systematic search in PubMed, Embase, ISI Web of Science, and Chinese National Knowledge Infrastructure (CNKI) databases was conducted up to September 1, 2017. The standardized mean difference (SMD) with 95% confidence interval (CI) was applied to pool the effect size. A funnel plot and Egger test were used to evaluate publication bias.

RESULTS

Finally, 43 eligible studies were included in the current meta-analysis. Overall, serum leptin levels in BC cases were significantly higher compared with the controls (SMD = 0.61, P <.0001). When subgroup analyses were restricted to ethnicity and menstrual status, higher serum leptin concentration was also detected in patients with BC. Moreover, BC cases with body mass index (BMI) >25 indicated significantly higher serum leptin levels (SMD = 1.48, P = .034). Furthermore, the BC cases with lymph node metastases showed significantly higher serum leptin concentration (SMD = 0.53, P = .015).

CONCLUSION

The present meta-analysis suggests that the serum leptin may profiles as a pivotal role in the pathogenesis and metastasis of BC. In addition, leptin will provide useful information for a therapeutic target to treat BC.

Association between serum leptin levels and breast cancer risk: An updated systematic review and meta-analysis

BACKGROUND

Many studies have indicated that leptin is correlated with breast cancer occurrence and tumor behavior. However, this issue remains controversial. Therefore, we conducted an updated meta-analysis to investigate the role of leptin in breast cancer.

METHODS

We performed a systematic literature search and identified relevant papers up to 1 September 2017. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were used to evaluate effect sizes.

RESULTS

Thirty-five eligible studies were included in the current meta-analysis. Serum leptin levels were related to breast cancer risk as demonstrated by calculations of the overall SMD = 0.46 (95% CI = 0.31-0.60, I = 93.5%). A subgroup analysis of BMI identified an association between breast cancer and serum leptin levels in patients who are overweight and obese (overweight: SMD = 0.35, 95% CI = 0.13-0.57, I = 88.1%; obesity: SMD = 1.38, 95% CI = 0.64-2.12, I = 89.6%). Additionally, menopausal status subgroup analysis revealed a significant association in postmenopausal women (SMD = 0.26, 95% CI = 0.12-0.40, I = 77.9%). Furthermore, we identified a significant association between breast cancer and serum leptin levels in Chinese women (SMD = 0.61, 95% CI = 0.44-0.79, I = 40.6%).

CONCLUSION

The results of this meta-analysis suggested that leptin could be a potential biomarker for breast cancer risk in women, especially overweight/obese or postmenopausal women. Therefore, it may be useful for identifying subjects with a high risk for breast cancer who may benefit from preventive treatments.

Leptin and Leptin receptor polymorphisms, plasma Leptin levels and obesity in Tunisian volunteers

Adipose tissue is an important endocrine organ that secretes a number of adipokines, like Leptin (LEP). The aim this study was to investigate the prevalence of single nucleotide polymorphisms in LEP gene (LEP 3'UTR A/C, -2548 G/A) and LEPR (K109R and Q223R) and their association with Leptin level and obesity. We recruited 169 non-obese (body mass index [BMI] = 24.51-3.69 kg/m² ) and 160 obese (BMI = 36-4.78 kg/m² ) patients. Genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism, BMI was calculated, and Leptin level was measured by ELISA. Statistical analyses were performed by spss19.0. According to LEP 3'UTR A/C polymorphism, AC and CC genotype carriers had higher Leptin levels than AA genotype carriers, respectively, 31[0.05-148.8] (P = .008) vs 41[0.05-111.6] (P = .003). The K109R polymorphism was associated with obesity (P = .025) and seems to significantly decrease the LEP levels (P < .001). Concerning LEP G2548A polymorphism, our results showed that the OR of obesity associated with 2548 AA/GG was 1.87[1.106-2.78] P = .028 vs 1.41[1.035-1.85] P = .045 for 223AA/GG polymorphism. In our haplotype analysis, one haplotype seems to be the more protective and one other seems to be the highest risk to obesity. LEP 3'UTR A/C and LEPR K109R polymorphisms were associated with Leptin level and obesity.

Changes in Body Mass Index, Leptin, and Leptin Receptor Polymorphisms and Breast Cancer Risk

Obesity is a strong risk factor for breast cancer. The polymorphisms of leptin (LEP) and leptin receptor (LEPR) may be associated with breast cancer by regulator of adipose tissue mass and tumor cell growth. A total of 794 cases and 805 matched controls were sequentially enrolled. Time-of-flight mass spectrometry was used to determine the LEPrs7799039, LEPRrs1137100, and LEPRrs1137101 genotypes for each participant. Associations between polymorphisms of these genes, change in body mass index (BMI), and breast cancer risk were assessed by unconditional multivariable logistic regression models. The unconditional logistic regression model showed that persistent overweight (BMI ≥24 kg/m²) over the preceding 10 years was associated with increased breast cancer risk in premenopausal women (odds ratio [OR] = 1.67, 95% confidence interval [CI]: 1.19-2.35). No associations between LEPrs7799039, LEPRrs1137100, or LEPRrs1137101 polymorphisms alone and breast cancer risk were found. Persistent overweight over the preceding 10 years and carrying the LEPrs7799039 AA genotype together increased breast cancer risk in premenopausal women (OR_adj = 2.00, 95% CI: 1.26-3.16). Persistent overweight over the preceding 10 years and carrying the LEPRrs1137100 GG genotype increased breast cancer risk in premenopausal women (OR_adj = 1.68, 95% CI: 1.06-2.68). In premenopausal women, persistent overweight (BMI ≥24 kg/m²) over the preceding 10 years increases breast cancer risk. Persistent overweight along with LEPrs7799039 AA or LEPRrs1137100 GG genotypes synergistically increase risk of breast cancer among premenopausal women.

Association of two obesity-related gene polymorphisms LEPG2548A rs7799039 and LEPRQ223R rs1137101 with the risk of breast cancer

Many studies have been performed to investigate the correlation of leptin (LEP) and leptin receptor (LEPR) polymorphisms with breast cancer (BC) risk, however the results are inconclusive. To obtain a more precise estimation, we conducted this meta-analysis. We searched PubMed, EMBASE, and Web of Science databases to identify qualified studies. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were used to evaluate the association. Eight eligible studies (2,124 cases and 5,476 controls) for LEP G2548A (rs7799039) polymorphism, and thirteen studies (5,282 cases and 6,140 controls) for LEPR Q223R (rs1137101) polymorphism were included in our study. In general, no significant association between LEP G2548A polymorphism and BC susceptibility was found among five genetic models. In the stratified analysis by ethnicity and sources of controls, significant associations were still not detected in all genetic models. For LEPR Q223R polymorphism, we observed that the association was only statistically significant in Asians (G versus A: OR = 0.532, P = 0.009; GG versus AA: OR = 0.233, P = 0.002; GA versus AA: OR =0.294, P = 0.006; GG versus AA+AG: OR =0.635, P = 0; GA+GG versus AA: OR = 0.242, P = 0.003), but not in general populations and Caucasians. In conclusion, LEP G2548A polymorphism has no relationship with BC susceptibility, while LEPR Q223R polymorphism could decrease BC risk in Asians, but not in overall individuals and Caucasians. More multicenter studies with larger sample sizes are required for further investigation.

Leptin receptor Q223R polymorphism in Egyptian female patients with breast cancer

Aim of the study

Breast cancer is the most common cause of death in women. Obesity has been associated with increased risk of breast cancer in post-menopausal women. It induces chronic inflammation, which increases local and systemic levels of cytokines and adipokines such as leptin. Leptin (LEP) and leptin receptor (LEPR) genes have several polymorphisms in humans. This study aims to assess the association between blood levels of leptin and LEPR Q223R gene polymorphism in patients of cancer breast.

Material and methods

The current study was carried on 48 female breast cancer patients and 48 heathy female subjects. Carcinoembryonic antigen (CEA), cancer antibody CA15-3, and leptin hormone were determined. Single nucleotide polymorphism of LEPR Q223R was assessed by PCR/RFLP. Statistical analysis used: The statistical analysis of data was done by using SPSS version 20.

Results

There were significant increases in the concentrations of CEA (p = 0.004), CA15-3 (p < 0.001), and leptin hormone (p < 0.001) in BC patients in relation to the respective concentrations in control subjects. CEA and CA 15-3 showed significant differences between various BC stages. As regard to LEPR Q223R gene polymorphism, AA genotype showed significantly higher frequency in BC patients when compared to their respective controls, with higher risk to develop BC.

Conclusions

Leptin hormone shows significantly higher concentrations in BC patients. As regard to LEPR Q223R gene polymorphism, AA genotype showed significantly higher frequency in BC patients.

Leptin, obesity and breast cancer: progress to understanding the molecular connections

Obesity has a complicated connection to both breast cancer risk and the clinical behaviour of the established disease. The obese setting provides a unique adipose tissue microenvironment that, in association with systemic endocrine modifications, promotes tumor initiation, primary growth, invasion, and metastatic progression. This review presents an overview of the clinical and experimental evidences highlighting the adipokine leptin as the most important molecular mediator of obesity-breast cancer axis. The research of leptin network operating in this context could launch a new field not only in the knowledge of risk factors for breast cancer but also in the development of leptin targeting drugs as promising anticancer agents.

Impact of Weight Loss on Plasma Leptin and Adiponectin in Overweight-to-Obese Post Menopausal Breast Cancer Survivors

Women who are obese at the time of breast cancer diagnosis have higher overall mortality than normal weight women and some evidence implicates adiponectin and leptin as contributing to prognostic disadvantage. While intentional weight loss is thought to improve prognosis, its impact on these adipokines is unclear. This study compared the pattern of change in plasma leptin and adiponectin in overweight-to-obese post-menopausal breast cancer survivors during weight loss. Given the controversies about what dietary pattern is most appropriate for breast cancer control and regulation of adipokine metabolism, the effect of a low fat versus a low carbohydrate pattern was evaluated using a non-randomized, controlled study design. Anthropometric data and fasted plasma were obtained monthly during the six-month weight loss intervention. While leptin was associated with fat mass, adiponectin was not, and the lack of correlation between leptin and adiponectin concentrations throughout weight loss implies independent mechanisms of regulation. The temporal pattern of change in leptin but not adiponectin was affected by magnitude of weight loss. Dietary pattern was without effect on either adipokine. Mechanisms not directly related to dietary pattern, weight loss, or fat mass appear to play dominant roles in the regulation of circulating levels of these adipokines.

Polymorphisms of Leptin (-2548 G/A) and Leptin Receptor (Q223R) Genes in Iranian Women with Breast Cancer

Recent studies have shown that polymorphisms in leptin and leptin receptor genes are associated with increased risk for breast cancer. This study aimed at investigating -2548 G/A polymorphism in leptin gene and Q223R polymorphism in leptin receptor gene in patients with breast cancer. The study included 45 women with breast cancer and 41 healthy women. PCR-RFLP was used to determine the genotype of the subjects in terms of -2548 G/A polymorphism in leptin gene and Q223R polymorphism in leptin receptor gene. Serum levels of leptin were also measured by ELISA. For -2548 G/A polymorphism, the genotypes were homozygous AA (OR = 1.13; p = 0.8) and heterozygous GA (OR = 0.41; p = 0.2) and for Q223R polymorphism, the genotypes were homozygous RR (OR = 6.7; p = 0.09) and heterozygous QR (OR = 8.3; p = 0.06). The mean serum level of leptin was 33.22 ± 21.35 ng/mL in patients and 29.49 ± 23.27 ng/mL in the normal participants (p = 0.3). Although, despite the magnitude of the associations, the results suggested no statistically significant contribution of -2548 G/A polymorphism (in leptin gene), Q223R polymorphism (in leptin receptor gene), and serum leptin levels in predicting the risk of breast cancer, further studies with larger sample size are suggested.

Association of leptin receptor Lys109Arg and Gln223Arg polymorphisms with increased risk of clear cell renal cell carcinoma

BACKGROUND

Although roles of genetic polymorphisms of leptin receptor (LEPR) gene in several cancers have been documented, the association between polymorphisms of LEPR and clear cell renal cell carcinoma (CC-RCC) remains unknown. The aim of this study was to explore any relation.

MATERIALS AND METHODS

The study population consisted of 77 patients with CC-RCC and 161 healthy control subjects. Polymorphism analyses of Lys109Arg and Gln223Arg were performed by direct DNA sequencing and PCR-restriction fragment length polymorphism approaches respectively.

RESULTS

Comparisons of allelic and genotypic frequencies in Lys109Arg and Gln223Arg showed no significant difference between the cases and controls. However, when evaluating the combined genotype of Lys109Arg and Gln223Arg, risk with GG/GG was increased (OR=1.85, 95%CI=1.04-3.30) and with GA/GG or GG/GA was decreased (OR=0.07, 95%CI=0.01-0.54; OR and 95%CI of the latter could not be calculated for a value of zero) . Furthermore, the G-G haplotype frequency of Lys109Arg and Gln223Arg in the cases was higher (OR=1.68; 95%CI=1.02-2.76). In contrast, the A-G and G-A haplotype frequencies in the cases were lower than those in the controls (OR=0.06; 95%CI=0.01 to 0.47; OR and 95%CI of the latter could not be calculated for a value of zero). In addition, the Lys109Arg A allele was in LD with the Gln223Arg A allele (d'=0.9399) in the CC-RCC subjects, but not in the controls.

CONCLUSIONS

Our data suggest that the GG/GG combined genotype and G-G haplotype of Lys109Arg and Gln223Arg can act as evaluating factors for CC-RCC risk.

Leptin, adipocytes and breast cancer: Focus on inflammation and anti-tumor immunity

More than one million new cases of breast cancer are diagnosed worldwide each year and more than 400,000 deaths are caused by the disease. The origin of this pathology is multifactorial and involved genetic, hormonal, environmental and nutritional factors including obesity in postmenopausal women. The role played by the adipose tissue and their secretions, ie adipokines, is beginning to be recognized. Plasma adipokine levels, which are modulated during obesity, could have “remote” effects on mammary carcinogenesis. Breast cancer cells are surrounded and locally influenced by an adipocyte microenvironment, which is probably more extensive in obese people. Hence, leptin appears to be strongly involved in mammary carcinogenesis and may contribute to the local pro-inflammatory mechanisms, especially in obese patients, who have increased metastatic potential and greater risk of mortality. This review presents the multifaceted role of leptin in breast cancer development and the different molecular pathways involved such as inflammation, oxidative stress and antitumor immunity.

Lack of association between LEPR Lys656Asn or Ser343Ser polymorphisms and cancer susceptibility: A meta-analysis

Previous studies have shown conflicting results between the association of leptin receptor (LEPR) genetic polymorphisms and cancer risk. The frequent LEPR Lys656Asn or Ser343Ser genetic polymorphism has been demonstrated to be functional and may promote genetic susceptibility to cancers. However, the association between the LEPR Lys656Asn or Ser343Ser genetic polymorphism and cancer risk remains to be determined. To improve the understanding of the LEPR Lys656Asn or Ser343Ser genetic polymorphism role in global cancer, a comprehensive meta-analysis was conducted that comprised 2,480 cases and 3,162 controls. The LEPR Lys656Asn or Ser343Ser genetic polymorphism did not significantly affect the cancer risk. In the stratified analysis, there was no significant association of the LEPR Lys656Asn or Ser343Ser variants with any type of cancer under any model. In addition, significantly increased risks were found in the Asian population in heterozygous codominant [odds ratio (OR), 1.24 (1.01-1.53)] and dominant [OR, 1.24 (1.02-1.50)] genetic models. A significantly increased susceptibility to cancer was not found when stratified by study design. There were no significant differences found in genotype method and sample size in cases among the genotypes. These findings indicated a lack of association between LEPR Lys656Asn or Ser343Ser polymorphisms and cancer susceptibility, however, these polymorphisms may increase the cancer susceptibility among the Asian population, particularly in the dominant genetic model. The single-nucleotide polymorphism is also suggested to function as a dominant mutation, which requires verification or association with functional studies.

Lack of association between leptin levels and leptin gene polymorphism in obese women

The aim of the present study was to evaluate the relationship between oligopolymorphism in the 25th codon of leptin gene and obesity. Eighty-seven obese women and 75 healthy women were constituted obese and control groups. Body fat percent, fat mass and lean body mass were determined by bioimpedance meter and leptin levels were determined. The presence of 25th codon oligopolymorphism in the leptin gene was done by PCR-RFLP technique. Mean leptin levels were 38.5±22.0 ng/ml, and 147.9±44.8 ng/ml in the control and obese groups, respectively. The correlations of serum leptin level to body fat percentage and fat mass in the control group were significant. The correlations in the obese group were not significant. This data implies that the difference of leptin levels between control and obese groups are more likely to be associated with alterations in the leptin gene other than 25th codon or alterations in the leptin receptor gene.

Genetic variation in adipokine genes and associations with adiponectin and leptin concentrations in plasma and breast tissue

BACKGROUND

Circulating adipokines may be associated with breast cancer risk. Genetic variants governing adipokines and adipokine receptors may also predict risk, but their effect on breast adipokine concentrations is unknown.

METHODS

We conducted a cross-sectional analysis of functional SNPs in 5 adipokine genes [adiponectin, leptin (LEP), and their receptors] among 85 cancer-free women who were undergoing reduction mammoplasty.

RESULTS

In multivariable-adjusted regression models, compared with the common GG genotype, the AA genotype of the LEP A19G SNP was associated with 27% lower plasma adiponectin [ratio, 0.73; 95% confidence interval (CI), 0.54-0.98] and leptin (ratio, 0.73; 95% CI, 0.55-0.96). Women with the AG genotype of LEP A19G had 39% lower breast leptin (ratio, 0.61; 95% CI, 0.39-0.97) compared with those with the GG genotype. No associations were observed for SNPs in the remaining genes.

CONCLUSIONS

Genetic variation in LEP may alter endogenous adipokine concentrations in circulation and in breast tissues.

IMPACT

These preliminary findings may support the hypothesis that genetic variation in adipokine genes modifies circulating adipokine concentrations and possibly leptin concentrations in local breast tissues, which may be associated with breast cancer risk.

Favorable effects of low-fat and low-carbohydrate dietary patterns on serum leptin, but not adiponectin, among overweight and obese premenopausal women: a randomized trial

PURPOSE

The most effective dietary pattern for breast cancer prevention has been greatly debated in recent years. Studies have examined hypocaloric diets, with particular emphasis on macronutrient composition, yielding inconclusive data. The objective of this study was to examine the effects of calorie-restricted low-fat and low-carbohydrate diets (LFD and LCD, respectively) on circulating adipokines among overweight and obese premenopausal women.

METHODS

Seventy-nine overweight and obese premenopausal women were randomized to either LFD or LCD, with increased physical activity, for 52 weeks. Serum adiponectin, leptin and the adiponectin-to-leptin ratio (A/L) were measured at baseline, and at weeks 34 and 52 to assess intervention effects.

RESULTS

While there were no significant changes in serum adiponectin concentrations following the LCD and LFD interventions, leptin concentrations significantly decreased by week 34 of the intervention period (LCD: 35.3%, P = 0.004; LFD: 30.0%, P = 0.01), with no difference by intervention arm. At week 52, these reductions were statistically non-significant, indicating a return to baseline levels by the end of the intervention. While there were non-significant increases in the A/L ratio following the LCD and LFD intervention arms, the overall trend, across groups, was marginally significant (P = 0.05) with increases of 16.2% and 35.1% at weeks 34 and 52, respectively.

CONCLUSIONS

These findings suggest that caloric-restricted LCD and LFD dietary patterns favorably modify leptin and possibly the A/L ratio, and lend support to the hypothesis that these interventions may be effective for obesity-related breast cancer prevention through their effects on biomarkers involved in metabolic pathways.

TRIAL REGISTRATION

CLINICAL TRIAL REGISTRATION NUMBER

NCT01559194.

Leptin Receptor Gene Gln223Arg Polymorphism Is Not Associated with Hypertension: A Preliminary Population-Based Cross-Sectional Study

Hypertension is responsible for high morbidity and mortality as one of the most important cardiometabolic risk factors. The aim of the study was to investigate whether the Gln223Arg in the leptin receptor (LEPR) influences the prevalence of hypertension. A cross-sectional study was carried out in individuals aged ≥ 18 years. Polymorphism identification was performed using PCR-RFLP analysis. Participants with blood pressure ≥ 140/90 mmHg or medication use were considered hypertensive. Frequencies, means, cross-tabulations, and multivariate models were produced to study differences in hypertension prevalence by genotypes. The study includes 470 participants. The frequency of GG polymorphism variant was 10.43%, 46.81% AG, and 42.77% AA. The distribution of hypertension frequency by LEPR genotypes was the following: AA 43.8%, AG 40.4%, and GG 40.8%; there were no significant differences between groups. Comparative analysis which used multivariate Poisson regression adjusted by many potential confounders (age, sex, schooling, smoking, alcohol intake, obesity, and family history of parental obesity) did not modify this result. In this large sample of population-based study, the association of the LEPR Gln223Arg gene polymorphism with hypertension was not observed.

Multifaceted leptin network: the molecular connection between obesity and breast cancer

High plasma levels of leptin, a major adipocytokine produced by adipocytes, are correlated with increased fat mass in obese state. Leptin is emerging as a key candidate molecule linking obesity with breast cancer. Acting via endocrine, paracrine, and autocrine manner, leptin impacts various stages of breast tumorigenesis from initiation and primary tumor growth to metastatic progression. Leptin also modulates the tumor microenvironment mainly through supporting migration of endothelial cells, neo-angiogenesis and sustaining recruitment of macrophage and monocytes. Various studies have shown that hyperactive leptin-signaling network leads to concurrent activation of multiple oncogenic pathways resulting in enhanced proliferation, decreased apoptosis, acquisition of mesenchymal phenotype, potentiated migration and enhanced invasion potential of tumor cells. Furthermore, the capability of leptin to interact with other molecular effectors of obese state including, estrogen, IGF-1, insulin, VEGF and inflammatory cytokines further increases its impact on breast tumor progression in obese state. This article presents an overview of the studies investigating the involvement of leptin in breast cancer.

The Association between Leptin Level and Breast Cancer: A Meta-Analysis

Background

Contradictory results have been reported regarding the association between leptin level and breast cancer. Therefore, a meta-analysis was performed to investigate this issue.

Methods

Published literature from PubMed and the Chinese National Knowledge Infrastructure (CNKI) Database was retrieved. This study was performed based on different cases and control groups. The combined effect () with 95% confidence interval (CI) was calculated using fixed-effects or random-effects model analysis.

Results

Overall, the mean serum leptin level of case groups was significantly higher than that of control groups. A) For 9 studies comparing breast cancer cases and healthy controls the combined effect was 0.58 with 95% CI (0.48, 0.68). B) For 4 studies comparing premenopausal breast cancer cases and healthy controls the was 0.32 (0.12, 0.52). C) For 5 studies comparing postmenopausal cases and healthy controls the was 0.65 (0.46, 0.84). D) For 4 studies comparing breast cancer cases and breast benign controls the was 0.38 (0.17, 0.59). E) For 2 studies comparing premenopausal breast cancer cases and breast benign controls the was 0.33 (-0.25, 0.91). F) For 6 studies comparing postmenopausal breast cancer cases and breast benign controls the was 0.39 (0.19, 0.60). G) For 4 studies comparing lymph node metastasis positive cases and negative controls the was 0.72 (0.45, 1.00). H) For 3 studies comparing breast benign cases and healthy controls the was 0.71 (0.41, 1.01).

Conclusion

This meta-analysis suggests that leptin level plays a role in breast cancer and has potential for development as a diagnostic tool.

[Leptin: Involvement in the pathophysiology of breast cancer]

More than one million new cases of breast cancer are diagnosed each year worldwide and more than 400,000 deaths occur due to this pathology. Obesity is a risk factor for postmenopausal breast cancer and the place held by the adipose tissue and secretions (i.e. adipokines) begins to be recognized. Indeed, firstly, plasma adipokine levels, modulated in obesity situation, could have effects "remotely" on mammary carcinogenesis and, secondly, breast cancer cells are surrounded by adipocyte microenvironment, which is probably more important in the case of obesity, and may be locally influenced by it. In this context, leptin appears to be strongly involved in mammary carcinogenesis and may contribute to the angiogenesis process and local pro-inflammatory mechanisms, especially in obese patients for whom increased metastatic potential and risk of mortality are described.

Association of LEP G2548A and LEPR Q223R polymorphisms with cancer susceptibility: evidence from a meta-analysis

BACKGROUND

Numerous epidemiological studies have examined associations of genetic variations in LEP (G2548A, -2548 nucleotide upstream of the ATG start site) and LEPR (Q223R, nonsynonymous SNP in exon 6) with cancer susceptibility; however, the findings are inconsistent. Therefore, we performed a meta-analysis to comprehensively evaluate such associations.

METHODS

We searched published literature from MEDLINE, EMBASE, Web of Science and CBM for eligible publications. We also assessed genotype-based mRNA expression data from HapMap for rs7799039 (G2548A) and rs1137101 (Q223R) in normal cell lines derived from 270 subjects with different ethnicities.

RESULTS

The final analysis included 16 published studies of 6569 cases and 8405 controls for the LEP G2548A and 19 studies of 7504 cases and 9581 controls for the LEPR Q223R. Overall, LEP G2548A was statistically significantly associated with an increased risk of overall cancer (AA vs. GG: OR=1.27, 95% CI=1.05-1.54; recessive model: OR=1.19, 95% CI=1.00-1.41). Further stratifications by cancer type showed an increased risk for prostate cancer (recessive model: OR=1.26, 95% CI=1.05-1.51) but not for other cancers. For LEPR Q223R, no statistical evidence for an association with risk of cancer was found for all; however, further stratification by ethnicity showed an increased risk for Africans but not for other ethnicities. No significantly differences in LEP and LEPR mRNA expression were found among genotypes or by ethnicity.

CONCLUSIONS

Despite some limitations, this meta-analysis found some statistical evidence for an association between the LEP 2548AA genotype and overall risk of cancer, particularly for prostate cancer, but given this variant did not have an effect on mRNA expression, this association warrants additional validation in large and well-designed studies.

The association between polymorphisms in the leptin receptor gene and risk of breast cancer: a systematic review and pooled analysis

Many epidemiological studies have found that leptin correlates to body fat extent and breast cancer. Leptin exerts its physiological action through the leptin receptor (LEPR). However, published data on the association between LEPR alleles and breast cancer occurrence have led to in contradictory results. A total of 10 studies were identified to the meta-analysis, including 4,644 cases and 5,485 controls for LEPR rs1137101 polymorphism, 5 studies with 2,759 cases and 4,464 controls for rs1137100 polymorphism, and 2 studies for rs8051542, rs8051542, and rs8051542 polymorphisms. The pooled odds ratios (OR) with 95 % confidence intervals (CI) for breast cancer risk associated with LEPR genotypes were estimated. Elevated breast cancer risk was associated with LEPR rs1137101 polymorphism when all studies were pooled in the meta-analysis (allele contrast model: OR = 0.71, 95 % CI = 0.551-0.997). In the stratified analysis by ethnicity, significantly increased risks were also found among Asians for allele contrast model (OR 0.414, 95 % CI 0.312-0.550) and dominant model (OR 0.537, 95 % CI 0.370-0.781); for Africans, significantly increased risks were also found for allele contrast model (OR 0.716, 95 % CI 0.595-0.861), homozygote codominant (OR 0.537, 95 % CI 0.370-0.781) and dominant model (OR 1.595, 95 % CI 1.207-2.108). And significantly elevated breast cancer risk was associated with LEPR rs1137100 polymorphism for allele contrast (OR = 0.666, 95 % CI = 0.603-0.720) and homozygote codominant models (OR = 0.344, 95 % CI = 0.282-0.421). For LEPR rs8179183, rs4655537, and rs3762274 polymorphisms, no significant associations were detected in all comparison models. This pooled analysis suggested that rs1137101 and rs1137100 polymorphisms were significantly correlated with breast cancer risk and the A allele of LEPR rs1137101 variant and the G allele of LEPR rs1137100 variant were low-penetrant risk factors for developing breast cancer. Further, no significant associations existed between LEPR rs8179183, rs4655537, and rs3762274 polymorphisms and risk of breast cancer.

Adipokines in plasma and breast tissues: associations with breast cancer risk factors

BACKGROUND

Blood adipokines are associated with breast cancer risk; however, blood-breast adipokine correlations and factors that explain variation in adipokines are unknown.

METHODS

Plasma (n = 155) and breast (n = 85) leptin and adiponectin were assessed by immunoassays in women with no history of cancer. Multivariable-adjusted regression models were used to determine breast adipokine associations.

RESULTS

Through body mass index (BMI)-adjusted analyses, we initially observed positive plasma-breast correlations for leptin (r = 0.41, P = 0.0002) and adiponectin (r = 0.23, P = 0.05). The positive plasma-breast correlation for leptin was strongest among normal weight women (r = 0.62), whereas the correlation for adiponectin was strongest among obese women (r = 0.31). In multivariable models, adjusting for BMI, demographic, reproductive, and lifestyle factors, plasma leptin was not associated with breast leptin, and only the highest quartile of plasma adiponectin was associated with tissue levels. Of the risk factors investigated, those that contributed most to the variation in breast tissue adipokines were BMI and race for leptin, oral contraceptive use and smoking status for adiponectin.

CONCLUSIONS

Although we report positive plasma-breast adipokine correlations overall, plasma adipokine concentrations may not be good surrogates for breast concentrations among all women. Predictors of breast adipokines vary, depending on subject characteristics, possibly explaining inconsistent epidemiologic results and they implicate differing pathways toward carcinogenesis.

IMPACT

A clearer understanding of the relationships between plasma adipokines and their levels within the target organ is necessary to better understand the impact of these hormones on breast cancer risk. Future studies are needed to identify additional factors associated with breast adipokines in target tissues.

Susceptibility of gastric cancer according to leptin and leptin receptor gene polymorphisms in Korea

Purpose

Leptin plays an important role in the control of body weight and also has a growth-factor-like function in epithelial cells. Abnormal expression of leptin and leptin receptor may be associated with cancer development and progression. We evaluated the relationship among leptin and leptin receptors polymorphisms, body mass index (BMI), serum leptin concentrations, and clinicopathologic features with gastric cancer and determined whether they could be the risk factor of gastric cancer.

Methods

We measured the serum leptin concentrations of 48 Korean patients with gastric cancer and 48 age- and sex-matched controls. By polymerase chain reaction-restriction fragment length polymorphism, we investigated one leptin gene promoter G-2548A genotype and four leptin receptor gene polymorphisms at codons 223, 109, 343, and 656.

Results

There was no significant difference between the mean leptin concentrations of the patient and control groups, while BMI was significantly lower in gastric cancer cases (22.9 ± 3.6 vs. 24.5 ± 2.8 kg/m², P = 0.021). There was significant association between the LEPR Lys109Arg genotype and gastric cancer risk, heterozygotes for GA genotype had been proved to increased the risk of gastric cancer, and its corresponding odds ratio was 2.926 (95% confidence interval, 1.248 to 6.861).

Conclusion

Our results suggested that LEPR gene Lys109Arg polymorphism is associated with gastric cancer in Korean patients.

Genetic polymorphisms in obesity-related genes and endometrial cancer risk

BACKGROUND

Obesity is associated with circulating levels of adiponectin and leptin and endometrial cancer risk. Little is known about whether single nucleotide polymorphisms (SNPs) in the genes that encode adiponectin (ADIPOQ), leptin (LEP), adiponectin receptor 1 (ADIPOR1), adiponectin receptor 2 (ADIPOR2), and leptin receptor (LEPR) are associated with endometrial cancer.

METHODS

The authors selected 87 tagging SNPs to capture common genetic variants in these 5 genes. These SNPs were evaluated in 1028 endometrial cancer cases and 1932 community controls recruited from Chinese women. Logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (95% CIs).

RESULTS

Three of the 10 SNPs evaluated in the ADIPOQ gene were significantly associated with reduced cancer risk. The OR for women homozygous for the minor allele (A/A) for rs3774262 was 0.68 (95% CI, 0.48-0.97) compared with women homozygous for the major allele (G/G). Similar results were found for SNPs rs1063539 and rs12629945 in ADIPOQ, which were in linkage disequilibrium with rs3774262. These associations became nonsignificant after Bonferroni correction was applied. Controls with the minor allele A at rs3774262 had lower weight, smaller waist and hip circumferences, and lower body mass index than controls with the major allele G (all P < .05). Women homozygous for the minor allele (T/T) of rs2071045 in the LEP gene also had significantly lower risk (OR, 0.70; 95% CI, 0.54-0.90) than women homozygous for the major allele (C/C). No other SNPs in the LEP, ADIPOR1, ADIPOR2, or LEPR genes were found to be associated with cancer risk.

CONCLUSIONS

Although a chance finding cannot be ruled out, the consistency of findings for gene-endometrial cancer risk and gene-obesity measurements suggests that genetic polymorphisms in the ADIPOQ gene may play a role in endometrial cancer development.

Leptin and leptin receptor genes in relation to premenopausal breast cancer incidence and grade in Caucasian women

Body mass is inversely related to breast cancer risk among premenopausal women. Leptin, an essential cytokine regulating food intake, energy expenditure, glucose, and fat metabolism may be part of the mechanistic pathway. We investigated 50 tagging and candidate SNPs in the leptin (LEP) and leptin receptor (LEPR) genes for associations with premenopausal breast cancer incidence using 405 cases and 810 controls nested within the Nurses' Health Study II. We also examined associations between these SNPs and circulating leptin (among 910 women) and breast cancer grade (among 267 patients). Permutation tests were performed to adjust for multiple testing. We did not detect a significant association between SNPs in the LEP or LEPR gene and either breast cancer incidence or plasma leptin levels. Among cases, 14 SNPs of the LEPR gene were significantly associated with cancer grade, and rs1137101 (Q223R) survived multiple testing adjustment (adjusted P = 0.04). The G carriers of rs1137101 were more likely to have poorly differentiated than well-differentiated cancers. Our data suggest that common genetic variation in the LEP or LEPR gene has no strong association with premenopausal breast cancer risk. The LEPR gene might be associated with breast cancer grade.

The manner in which calories are restricted impacts mammary tumor cancer prevention

Although treatments for breast cancer have improved and long-term survival after diagnosis is now common, prevention of the disease is the ultimate goal. Weight loss or weight maintenance is one approach that has been recommended to reduce the risk of breast cancer, particularly for peri/postmenopausal women. This approach is supported by decades of data indicating that calorie restriction prevents spontaneous and chemically induced mammary tumor development in rodents. In most cases, calorie restriction was implemented by a consistent daily reduction of calories, i.e. chronic calorie restriction (CCR). There have also been several studies where periods of reduced caloric intake were followed by periods of refeeding, i.e. intermittent calorie restriction (ICR), resulting in the prevention of spontaneous mammary tumorigenesis. In most of the early studies, there were no direct comparisons of CCR to ICR. One study using moderate calorie restriction in a chemically induced breast cancer rat model found a slight increase in mammary tumor incidence compared with ad libitum fed and CCR rats. However, recently, it has been demonstrated in several transgenic mouse models of breast cancer that ICR consistently provided a greater degree of protection than CCR. This review will provide a detailed comparison of ICR and CCR for breast cancer prevention. It will also examine potential mechanisms of action that may include periods of reduced IGF-I and leptin as well as an increase in the adiponectin:leptin ratio. Application of this approach to at-risk women may provide an approach to lower the risk of breast cancer in overweight/obese women.

Polymorphisms in three obesity-related genes (LEP, LEPR, and PON1) and breast cancer risk: a meta-analysis

Common genetic variations in the leptin (LEP), leptin receptor (LEPR), and paraoxonase 1 (PON1) genes have been considered to be implicated in the development of breast cancer. However, the results were inconsistent. In this study, a meta-analysis was performed to assess the associations of five polymorphisms, including LEP G2548A, LEPR Q223R, LEPR Lys109Arg, PON1 L55M, and PON1 Q192R polymorphisms, with breast cancer risk. Published literature from PubMed, ISI Web of Science, Embase databases, CNKI, and Wanfang Data were retrieved. All studies evaluating the association between LEP G2548A, LEPR Q223R, LEPR Lys109Arg, PON1 L55M, or PON1 Q192R polymorphism and breast cancer risk were included. Pooled odds ratio (OR) with 95% confidence interval (CI) was calculated using fixed- or random-effects model. Three studies (2,003 cases and 1,967 controls) for LEP G2548A polymorphism, nine studies (4,627 cases and 5,476 controls) for LEPR Q223R polymorphism, five studies (2,759 cases and 2,573 controls) for LEPR Lys109Arg polymorphism, four studies (1,517 cases and 1,379 controls) for PON1 L55M polymorphism, and five studies (1,575 cases and 2,283 controls) for PON1 Q192R polymorphism were included in the meta-analysis. Overall, the results showed null significant association between LEP G2548A, LEPR Q223R, LEPR Lys109Arg, or PON1 Q192R polymorphism and breast cancer risk; however, PON1 L55M was significantly associated with breast cancer risk overall (MM vs. LL: OR = 2.16; 95% CI, 1.76-2.66). For LEPR Q223R polymorphism, further subgroup analysis suggested that the association was only statistically significant in East Asians (OR = 0.50; 95% CI, 0.36-0.70) but not in Caucasians (OR = 1.06; 95% CI, 0.77-1.45) or Africans (OR = 1.30; 95% CI, 0.83-2.03). The present meta-analysis suggested that LEPR Q223R polymorphism might be implicated in the development of breast cancer in East Asians; PON1 L55M might increase breast cancer risk. However, given the limited sample size, the findings warrant further investigation.

Effect of LEPR Gln223Arg polymorphism on breast cancer risk in different ethnic populations: a meta-analysis

Leptin and leptin receptor have been implicated in processes leading to breast cancer initiation and progression. An A to G transition mutation in codon 223, in exon 6 of the leptin receptor gene (LEPR) can result in glutamine to arginine substitution (Gln223Arg). A variety of case-control studies have been published evaluating the association between LEPR Gln223Arg polymorphism and breast cancer. However, published studies have yielded contradictory conclusions. This meta-analysis enrolled eight studies to estimate the overall risk of LEPR Gln223Arg polymorphism associated with breast cancer. The pooled ORs were performed for codominant model (Arg/Arg versus Gln/Gln; Arg/Gln versus Gln/Gln), dominant model (Arg/Arg + Arg/Gln versus Gln/Gln), recessive model (Arg/Arg versus Arg/Gln + Gln/Gln). Overall significantly elevated breast cancer risk was found for recessive model (OR 1.32, 95% CI 1.03-1.69) and for genotype Arg/Gln versus Gln/Gln (OR 1.16, 95% CI 1.01-1.34). In the stratified analysis by ethnicity, significantly increased risks were also found among Africans for genotype Arg/Arg versus Gln/Gln: OR 1.86, 95% CI 1.28-2.71, Arg/Gln versus Gln/Gln: OR 1.48, 95% CI 1.10-1.99, dominant model: OR 1.60, 95% CI 1.21-2.11 and recessive model: OR 1.48, 95% CI 1.07-2.05; for Asians, Arg/Arg versus Gln/Gln: OR 6.79, 95% CI 3.42-13.47 and dominant model: OR 2.03, 95% CI 1.42-2.90. However, no significantly increased risk was found among Europeans for all genetic models. In conclusion, the LEPR 223Arg is a low-penetrant risk for developing breast cancer, especially for black African women.

Plasma leptin levels and risk of breast cancer in premenopausal women

Body mass index (BMI) is inversely related to the risk of premenopausal breast cancer, but the underlying biological mechanisms of this association are poorly understood. Leptin, a peptide hormone produced primarily by adipocytes, is a potential mediator of the BMI association because BMI and total body fat are positively associated with circulating leptin levels and leptin and its receptor are overexpressed in breast tumors. We conducted a prospective case-control study nested within the Nurses' Health Study II cohort examining the association between plasma leptin levels in premenopausal women and breast cancer risk. Leptin was measured in blood samples collected between 1996 and 1999. The analysis included 330 incident breast cancer cases diagnosed after blood collection and 636 matched controls. Logistic regression models, controlling for breast cancer risk factors, were used to calculate ORs and 95% CIs. After adjustment for BMI at age 18, weight change since age 18 to blood draw, and other breast cancer risk factors, plasma leptin levels were inversely associated with breast cancer risk (OR for top vs. bottom quartile = 0.55; 95% CI = 0.31-0.99; P(trend) = 0.04). Adjustment for BMI at blood draw attenuated the association (OR = 0.69; 95% CI = 0.38-1.23; P(trend) = 0.26). Our results suggest that leptin may be inversely associated with breast cancer risk, but it is unclear whether any part of this association is independent of BMI.

Common genetic variation in adiponectin, leptin, and leptin receptor and association with breast cancer subtypes

Adipocytokines are produced by visceral fat, and levels may be associated with breast cancer risk. We investigated whether single nucleotide polymorphisms (SNPs) in adipocytokine genes adiponectin (ADIPOQ), leptin (LEP), and the leptin receptor (LEPR) were associated with basal-like or luminal A breast cancer subtypes. 104 candidate and tag SNPs were genotyped in 1776 of 2022 controls and 1972 (200 basal-like, 679 luminal A) of 2311 cases from the Carolina Breast Cancer Study (CBCS), a population-based case-control study of whites and African Americans. Breast cancer molecular subtypes were determined by immunohistochemistry. Genotype odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using unconditional logistic regression. Haplotype ORs and 95% CIs were estimated using Hapstat. Interactions with waist-hip ratio were evaluated using a multiplicative interaction term. Ancestry was estimated from 144 ancestry informative markers (AIMs), and included in models to control for population stratification. Candidate SNPs LEPR K109R (rs1137100) and LEPR Q223R (rs1137101) were positively associated with luminal A breast cancer, whereas ADIPOQ +45 T/G (rs2241766), ADIPOQ +276 G/T (rs1501299), and LEPR K656N (rs8129183) were not associated with either subtype. Few patterns were observed among tag SNPs, with the exception of 3 LEPR SNPs (rs17412175, rs9436746, and rs9436748) that were in moderate LD and inversely associated with basal-like breast cancer. However, no SNP associations were statistically significant after adjustment for multiple comparisons. Haplotypes in LEP and LEPR were associated with both basal-like and luminal A subtypes. There was no evidence of interaction with waist-hip ratio. Data suggest associations between LEPR candidate SNPs and luminal A breast cancer in the CBCS and LEPR intron 2 tag SNPs and basal-like breast cancer. Replication in additional studies where breast cancer subtypes have been defined is necessary to confirm these potential associations.

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.

Effect of chronic and intermittent calorie restriction on serum adiponectin and leptin and mammary tumorigenesis

The effect of chronic (CCR) and intermittent (ICR) caloric restriction on serum adiponectin and leptin levels was investigated in relation to mammary tumorigenesis. 10-wks old MMTV-TGF-α female mice were assigned to ad libitum fed (AL; AIN-93M diet), ICR (3-week 50% caloric restriction, AIN-93M-mod diet, 2× protein, fat, vitamins, and minerals followed by 3-wks 100% AL consumption of AIN-93M), and CCR (calorie and nutrient intake matched for each 6-wks ICR cycle, ∼ 75% of AL) groups. Mice were sacrificed at 79 (end of restriction) or 82 (end of refeeding) wks of age. Serum was obtained in cycles 1, 3, 5, 8, 11, and terminal. Mammary tumor incidence was 71.0%, 35.4%, and 9.1% for AL, CCR, and ICR mice, respectively. Serum adiponectin levels were similar among groups with no impact of either CCR or ICR. Serum leptin level rose in AL mice with increasing age but was significantly reduced by long-term CCR and ICR. The ICR protocol was also associated with an elevated adiponectin/leptin ratio. In addition, ICR-restricted mice had increased mammary tissue AdipoR1 expression and decreased leptin and ObRb expression compared with AL mice. Mammary fat pads from tumor-free ICR-mice had higher adiponectin expression than AL and CCR mice whereas all tumor-bearing mice had weak adiponectin signal in mammary fat pad. Although we did not show an association of either adiponectin or leptin with individual mice in relation to mammary tumorigenesis, we did find that reduced serum leptin and elevated adiponectin/leptin ratio were associated with the protective effect of intermittent calorie restriction.

Correlation of body mass index and leptin with tumor size and stage of disease in hormone-dependent postmenopausal breast cancer: preliminary results and therapeutic implications

Obesity is considered the most important risk and prognostic factor for estrogen-dependent breast cancer in postmenopausal women. Adipokines, in particular leptin, are at the center of the etiopathogenetic mechanisms by which obesity and related metabolic disorders influence breast cancer risk and its prognosis. The present prospective observational study aims to investigate the relationship between body mass index (BMI), serum levels of leptin and proinflammatory cytokines, and breast cancer prognostic factors. In the study, 98 postmenopausal and 82 premenopausal patients with ER-positive breast cancer participated. During the same study period, 221 control subjects were simultaneously recruited. Women underwent baseline measurements pre-operatively, before any surgical and systemic treatments. Pathologic characteristics of tumors were abstracted from pathology reports. Leptin and proinflammatory cytokines were assayed in stored fasting blood specimens. In postmenopausal breast cancer patients, BMI, leptin, and interleukin-6 significantly correlated with pathological tumor classification (pT) and TNM stage. Multivariate regression analysis showed that BMI and leptin, but not interleukin-6, were independent predictive variables of pT and TNM stage. Our results seem to suggest a twofold role of leptin in the etiopathogenesis of postmenopausal estrogen-positive breast cancer. Indeed, leptin reflects the total amount of fat mass, which correlates to aromatase activity and subsequent estrogens levels. Further studies are warranted to clarify the role of leptin and interleukin-6 in breast carcinogenesis and identify new therapeutic options, beyond the use of aromatase inhibitors, acting selectively on adipokine-driven pathways.

Leptin and leptin receptor expression in breast cancer

PURPOSE

Leptin is a multifunctional hormone that's produced by adipose tissue and leptin is involved in the regulation of food intake and energy balance. The aims of this study were to determine the leptin and leptin receptor (Ob-R) expressions in human breast cancer and their corresponding influence on the prognosis of patients with breast cancer.

MATERIALS AND METHODS

We examined the correlations between the leptin and Ob-R expressions and the breast cancer-related pathobiologic markers by performing immunohistochemistry in 517 patients with breast cancer. We analyzed the leptin and Ob-R expressions with respect to overall survival and relapse-free survival (RFS).

RESULTS

Positive cytoplasmic immunoreactivity for leptin was noted in 39% of the patients and 79% of the patients showed positive cytoplasmic immunoreactivity for Ob-R. The expression of leptin in breast cancer was correlated with a high Ki-67 labeling index (p=0.019). Based on the univariate survival analysis, the clinicopathologic variables with prognostic value included the histologic grade, the T stage, the N stage, the HER2 status, the Bcl-2, p53 and Ki-67 expressions (p<0.05). The patients with leptin-positive breast cancers and a negative hormone receptor status had a significantly longer overall survival (p=0.021). Multivariate survival analysis showed that a positive expression of leptin was an independent prognostic marker for overall survival (hazard ratio, 0.20; 95% CI, 0.04~0.99; p=0.05).

CONCLUSION

A leptin expression in breast cancer is significantly associated with the Ki-67 labeling index, and this suggests there is an association of a leptin expression with the proliferation activity. In addition, a leptin expression is an indicator of better survival for breast cancer patients.

No association between polymorphisms in LEP, LEPR, ADIPOQ, ADIPOR1, or ADIPOR2 and postmenopausal breast cancer risk

There is evidence that adipokines such as leptin and adiponectin may influence breast tumor development. We conducted a nested case-control study using women in the American Cancer Society Cancer Prevention Study II to examine the association between postmenopausal breast cancer and variability in the genes encoding leptin, the leptin receptor, adiponectin, adiponectin receptor 1, and adiponectin receptor 2. Using 648 cases and 659 controls, we found no statistically significant (P < 0.05) associations between breast cancer risk and any of the single nucleotide polymorphisms. Individual odds ratios ranged from 0.93 to 1.06. We found no evidence of effect modification by body mass index, adult weight gain, location of weight gain, or physical activity. Although we cannot rule out that these genes are involved in gene-gene or gene-environment interactions, our results suggest that individual single nucleotide polymorphisms in these genes do not substantially affect postmenopausal breast cancer risk.

Common genetic variations in the LEP and LEPR genes, obesity and breast cancer incidence and survival

Obesity is a strong risk factor for breast cancer in postmenopausal women and adverse prognostic indicator regardless of menopausal status. Leptin is an important regulator of adipose tissue mass and has been associated with tumor cell growth. Leptin exerts its effects through interaction with the leptin receptor (LEPR). We investigated whether genetic variations in the leptin (LEP) and LEPR genes are associated with risk of breast cancer, or once diagnosed, with survival. The polymorphisms LEP G-2548A and LEPR Q223R were characterized in population-based study consisting of mostly European-American women. The study examined 1,065 women diagnosed with first, primary invasive breast cancer between 1996 and 1997. Controls were 1,108 women frequency matched to the cases by 5-year age group. A modest increase in risk of developing breast cancer was associated with the LEP -2548AA genotype when compared to the LEP -2548GG genotype (age-adjusted OR = 1.30; 95% CI = 1.01-1.66). This association was stronger among postmenopausal women who were obese (OR = 1.86; 95% CI = 0.95-3.64) although the interaction was of borderline statistical significance (P = 0.07). We found no evidence of an association with polymorphisms of either LEP or LEPR in relation to all-cause or breast cancer-specific mortality among women with breast cancer (mean follow-up time = 66.7 months). The effects of these genotypes on breast cancer risk and mortality did not vary significantly when stratified by menopausal status. In summary, our results show that a common variant in LEP may be associated with the risk of developing breast cancer supporting the hypothesis that leptin is involved in breast carcinogenesis.

Physical activity and postmenopausal breast cancer: proposed biologic mechanisms and areas for future research

Convincing evidence now supports a probable preventive role for physical activity in postmenopausal breast cancer. The mechanisms by which long-term physical activity affect risk, however, remain unclear. The aims of this review were to propose a biological model whereby long-term physical activity lowers postmenopausal breast cancer risk and to highlight gaps in the epidemiologic literature. To address the second aim, we summarized epidemiologic literature on 10 proposed biomarkers, namely, body mass index (BMI), estrogens, androgens, sex hormone binding globulin, leptin, adiponectin, markers of insulin resistance, tumor necrosis factor-alpha, interleukin-6, and C-reactive protein, in relation to postmenopausal breast cancer risk and physical activity, respectively. Associations were deemed "convincing," "probable," "possible," or "hypothesized" using set criteria. Our proposed biological model illustrated the co-occurrence of overweight/obesity, insulin resistance, and chronic inflammation influencing cancer risk through interrelated mechanisms. The most convincing epidemiologic evidence supported associations between postmenopausal breast cancer risk and BMI, estrogens, and androgens, respectively. In relation to physical activity, associations were most convincing for BMI, estrone, insulin resistance, and C-reactive protein. Only BMI and estrone were convincingly (or probably) associated with both postmenopausal breast cancer risk and physical activity. There is a need for prospective cohort studies relating the proposed biomarkers to cancer risk and for long-term exercise randomized controlled trials comparing biomarker changes over time, specifically in postmenopausal women. Future etiologic studies should consider interactions among biomarkers, whereas exercise trials should explore exercise effects independently of weight loss, different exercise prescriptions, and effects on central adiposity.

Circulating levels of leptin, adiposity and breast cancer risk

The present case–control study was to investigate the relationships of plasma leptin level and anthropometric measures of adiposity with the risk of breast cancer. Questionnaire information, anthropometric measures and blood samples were taken before treatment from 297 incident cases with breast cancer and 593 controls admitted for health examination at the Tri-Service General Hospital, Taipei, between 2004 and 2006. Plasma levels of leptin were measured by RIA. Logistic regression analysis was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for assessing the associations. Overall, higher leptin concentrations were significantly associated with an increased risk of breast cancer (OR (95% CI) for top vs bottom tertile of leptin was 1.63 (1.07–2.49), P_trend=0.009). Waist circumference was a significant anthropometric factor for breast cancer in both pre- and postmenopausal women. Furthermore, the associations of leptin with breast cancer risk remained after adjustment for obesity indices. These results suggest that leptin may have an independent role in breast tumorigenesis. Regardless of the impact of circulating leptin, more research is needed to elucidate molecular mechanisms and local leptin levels that are critical for the development of breast cancers.

Involvement of the leptin receptor in the immune response in intestinal cancer

The incidence of colorectal cancers (CRC) may be influenced by environmental factors, including nutrition. The role of peptides regulating food intake in controlling the growth and recurrence of human tumors is controversial. Leptin, a cytokine-like peptide, regulates food intake. We investigated the expression of leptin and its receptor in 171 consecutive patients (78 female and 93 male; 71 years) with CRC. Leptin concentrations in the serum (ELISA) were determined before tumor removal. ObRb was characterized in tumors and normal homologous tissues and culture cells (HT29, HCT116, and HCT116 with a transferred chromosome 3) by using immunocytochemistry, immunohistochemistry, reverse transcription-PCR (RT-PCR), and Western blotting. Microsatellite instability (MSI) phenotype was characterized by immunohistochemistry and pentaplex PCR. mRNAs of cytokines and chemokines were quantified in tumors and in normal homologous tissues (RT-PCR) in 43 patients. Adequate statistical tests, including multivariate analysis adjusted for pathologic tumor-node-metastasis (pTNM), MSI-H, and ObRb phenotypes, were used. Higher expression of ObRb in tumors compared with the homologous normal mucosa, pTNM staging but not leptin serum level, was associated with patients' progression-free survival (PFS). Tumor ObRb phenotype and pTNM were independent predictive factors of PFS. ObRb was more strongly expressed in HCT116 cells than in HCT116-Ch3 cells as well as in MSI-H tumors than in microsatellite stability and potentially associated with efficient cytotoxic antitumoral response as assessed by immunohistochemistry and RT-PCR measurements. We suggest that leptin receptor expression in tumors is involved in adaptive immune response in sporadic colon and rectal tumors likely via MSI-H phenotype orientation.

Leptin receptor Gln223Arg polymorphism and breast cancer risk in Nigerian women: a case control study

Background

Leptin, a 16 kDa polypeptide hormone, implicated in various physiological processes, exerts its action through the leptin receptor, a member of the class I cytokine receptor family. Both leptin and leptin receptor have recently been implicated in processes leading to breast cancer initiation and progression in animal models and humans. An A to G transition mutation in codon 223 in exon 6 of the leptin receptor gene, resulting in glutamine to arginine substitution (Gln223Arg), lies within the first of two putative leptin-binding regions and may be associated with impaired signaling capacity of the leptin receptor. This study was designed to assess the role of this polymorphism in breast cancer susceptibility in Nigerian women.

Methods

We utilized a polymerase chain reaction (PCR)-based restriction fragment length polymorphism (RFLP) assay to evaluate the association between the Gln223Arg polymorphism of the leptin receptor gene and breast risk in Nigeria in a case control study involving 209 women with breast cancer and 209 controls without the disease. Study participants were recruited from surgical outpatient clinics and surgical wards of four University Teaching Hospitals located in Midwestern and southeastern Nigeria between September 2002 and April 2004.

Results

Premenopausal women carrying at least one LEPR 223Arg allele were at a modestly increased risk of breast cancer after adjusting for confounders (OR = 1.8, 95% confidence interval [CI] 1.0–3.2, p = 0.07). There was no association with postmenopausal breast cancer risk (OR = 0.9, 95% CI 0.4–1.8, p = 0.68).

Conclusion

Our results suggest that the LEPR Gln223Arg polymorphism in the extracellular domain of the LEPR receptor gene is associated with a modestly increased risk of premenopausal breast cancer in Nigerian women.

Effects of high-fat diet and/or body weight on mammary tumor leptin and apoptosis signaling pathways in MMTV-TGF-alpha mice

INTRODUCTION

Obesity is a risk factor for postmenopausal breast cancer and is associated with shortened mammary tumor (MT) latency in MMTV-TGF-alpha mice with dietary-induced obesity. One link between obesity and breast cancer is the adipokine, leptin. Here, the focus is on diet-induced obesity and MT and mammary fat pad (MFP) leptin and apoptotic signaling proteins.

METHODS

MMTV-TGF-alpha mice were fed low-fat or high-fat diets from 10 to 85 weeks of age. High-Fat mice were divided into Obesity-Prone and Obesity-Resistant groups based on final body weights. Mice were followed to assess MT development and obtain serum, MFP, and MT.

RESULTS

Incidence of palpable MTs was significantly different: Obesity-Prone > Obesity-Resistant > Low-Fat. Serum leptin was significantly higher in Obesity-Prone compared with Obesity-Resistant and Low-Fat mice. Low-Fat mice had higher MFP and MT ObRb (leptin receptor) protein and Jak2 (Janus kinase 2) protein and mRNA levels in comparison with High-Fat mice regardless of body weight. Leptin (mRNA) and pSTAT3 (phosphorylated signal transducer and activator of transcription 3) (mRNA and protein) also were higher in MTs from Low-Fat versus High-Fat mice. Expression of MT and MFP pro-apoptotic proteins was higher in Low-Fat versus High-Fat mice.

CONCLUSION

These results confirm a connection between body weight and MT development and between body weight and serum leptin levels. However, diet impacts MT and MFP leptin and apoptosis signaling proteins independently of body weight.

The roles of serum leptin concentration and polymorphism in leptin receptor gene at codon 109 in breast cancer

AIMS

We investigated the relationship between serum leptin concentrations and polymorphism of the leptin receptor gene and breast cancer.

METHODS

Serum leptin concentrations were measured by enzyme-linked immunosorbent assay in 47 women with invasive breast cancer compared with 41 age-matched controls without cancer. Genomic DNA was extracted from peripheral blood leukocytes. Genotyping of the leptin receptor gene at codon 109 (LEPR-109) was performed by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

Patients with breast cancer had a higher mean serum leptin concentration than women in the control group, but the difference was not statistically significant. Among those with breast cancer, the serum leptin concentration was higher in women with high-grade cancers (p = 0.020). The LEPR-109RR genotype was more frequent in premenopausal patients with tumors larger than 2 cm (p = 0.039) and in premenopausal women who were overweight (p = 0.029). Among patients with the LEPR-109RR genotype, higher mean serum leptin concentrations were present in those with triple-negative cancers (p = 0.048).

CONCLUSIONS

Our study suggests an association between serum leptin concentration and tumor progression. LEPR-109 polymorphism in premenopausal women appears to be associated with obesity and tumor progression.