Abstract
目的
探讨脂联素、瘦素、可溶性瘦素受体（soluble leptin receptor，sOB-R）对女性绝经前后乳腺癌的单独或联合效应，为揭示肥胖与乳腺癌之间的分子机制提供证据。
方法
序贯纳入乳腺癌新发患者469例及同期按1∶1年龄频数匹配的469例健康女性为研究对象。采用问卷收集研究对象基线信息，并采用ELISA法检测血浆中脂联素、瘦素、sOB-R水平。采用多因素非条件logistic回归，并进一步按照腰臀比（waist-to-hip ratio，WHR）和体质量指数（body mass index，BMI）分层，分析观察指标对绝经前后乳腺癌发生风险的影响。
结果
本研究共纳入480例绝经前和458例绝经后女性。绝经前病例组249例，对照组231例，中位BMI分别为22.9 kg/m2、23.2 kg/m2，中位WHR分别为0.80、0.83。绝经后病例组220例，对照组238例，中位BMI分别为23.4 kg/m2、23.7 kg/m2；中位WHR分别为0.82、0.86。多因素logistics回归发现，模型校正前后，sOB-R、脂联素的升高与绝经前后的乳腺癌风险降低相关（P<0.05），而瘦素/可溶性瘦素受体比值（FLI） 、瘦素/脂联素比值（leptin/adiponectin，L/A）仅与绝经后乳腺癌的发生风险升高有关。进一步按WHR和BMI分层，脂联素、FLI与绝经后乳腺癌的关联在所有亚组仍有统计学意义。在体质量正常的中心型肥胖（18.5 kg/m2≤BMI<24 kg/m2且WHR≥0.85）妇女中，高L/A比值与绝经后乳腺癌风险增加有关。未发现瘦素与绝经前后乳腺癌的关联。
结论
sOB-R、脂联素水平降低，FLI、L/A升高的绝经后女性，sOB-R、脂联素水平降低的绝经前女性，乳腺癌的发生风险高。
Keywords: 乳腺癌, 肥胖, 瘦素, 可溶性瘦素受体, 脂联素
Abstract
Objective
To explore the individual or combined effects of adiponectin, leptin, and soluble leptin receptor (sOB-R) on risks for premenopausal and postmenopausal breast cancer, and to provide evidence for revealing the molecular mechanism between obesity and breast cancer.
Methods
469 newly-diagnosed breast cancer cases were sequentially recruited for the study and 469 age-frequency-matched healthy women were enrolled as the controls over the same period of time. The participant baseline information was collected with questionnaires, and plasmic levels of adiponectin, leptin and sOB-R were checked with ELISA. Multivariate unconditional logistic regression was conducted and the analyses were further stratified according to waist-to-hip ratio (WHR) and body mass index (BMI) to explore the effect of the indicators on the risks for premenopausal and postmenopausal breast cancer.
Results
A total of 480 premenopausal and 458 postmenopausal women were included in the study. Among the premenopausal subjects, 249 were breast cancer patients and 231 were controls. The median BMI was 22.9 kg/m2and 23.2 kg /m2, respectively, and the median WHR was 0.80 and 0.83, respectively. Among the postmenopausal subjects, 220 were breast cancer patients and 238 were controls. The median BMI was 23.4 kg/m2 and 23.7 kg/m2, respectively, and the median WHR was 0.82 and 0.86, respectively. Multivariate logistic regression analysis showed that before and after model adjustment, the increase in sOB-R and adiponectin levels was correlated to reduced risks of premenopausal and postmenopausal breast cancer (P<0.05), while the increase in the leptin/sOB-R ratio (also known as free leptin index, FLI) and leptin/adiponectin (L/A) ratio was only correlated to increased risks of postmenopausal breast cancer. After further stratification by WHR and BMI, the association between adiponectin, FLI and postmenopausal breast cancer remained statistically significant in all subgroups. Among subjects with normal-BMI central obesity (18.5 kg/m2≤BMI<24 kg/m2 & WHR≥0.85) , higher L/A ratio was associated with an increased risk of postmenopausal breast cancer. No clear association between leptin and premenopausal and risks for postmenopausal breast cancer was found in the study.
Conclusion
Postmenopausal women with decreased levels of sOB-R and adiponectin, and increased FLI and L/A, and premenopausal women with decreased levels of sOB-R and adiponectin were found to be at high risks for breast cancer.
Keywords: Breast cancer, Obesity, Leptin, Soluble leptin receptor, Adiponectin
乳腺癌是我国女性最常见的恶性肿瘤之一。据估计，2018年中国乳腺癌新发病例达416 371例，死亡病例117 174例[1]。肥胖与乳腺癌的发生密切相关，2014年，中国成年人肥胖率达到12.9% [2]，体脂分布以中心型为特点[3]。肥胖参与乳腺癌发生的机制尚不明确，但脂肪组织分泌的脂肪因子，如瘦素、脂联素等，可能在其中发挥重要作用[4]。
瘦素是由肥胖基因编码、脂肪细胞合成的蛋白。瘦素与膜瘦素受体结合可发挥促进肿瘤细胞增殖、转移等作用[5-6]。可溶性瘦素受体（soluble leptin receptor，sOB-R）主要由膜瘦素受体的胞外结构域发生溶蛋白性裂解，脱落入血形成，是血液循环瘦素的主要结合蛋白，可决定大部分瘦素活性[7-8]。脂联素具有多种功能，包括调节糖脂代谢、抗炎、抗癌细胞增殖和促癌细胞凋亡等，可能与乳腺癌的风险降低有关[9-10]。此外，脂联素还可抑制瘦素诱导的细胞增殖，二者之间的平衡可有效调节乳腺癌细胞的增殖[11-12]。因此，为了探讨这三种单一指标对乳腺癌细胞的联合作用，部分研究[8, 13-14]也将比值指标——瘦素/可溶性瘦素受体比值（亦称游离瘦素指数，free leptin index，FLI）和瘦素/脂联素比值（leptin/adiponectin，L/A）纳入分析。
目前血浆瘦素、脂联素水平与绝经前后乳腺癌的关系结论尚不一致，且很少有调查研究这些关联是否会受到肥胖程度的影响。sOB-R与乳腺癌的关系也尚未得到充分的研究，尤其是在中国妇女中。由此，本研究通过病例对照设计，按绝经状态分层，分别探讨血浆脂联素、瘦素及sOB-R水平对中国西南地区绝经前后女性乳腺癌发生风险的单独和联合效应，并进一步分析效应在不同肥胖程度女性中的变化。
1. 对象与方法
1.1. 研究对象
病例组：2018年4月−2019年5月，从四川大学华西医院和四川省肿瘤医院序贯收集经穿刺活检的病理学明确诊断的新发乳腺癌病例469例，其中绝经前对象249例，绝经后对象220例。纳入标准：汉族，在四川省居住3年以上。排除转移性乳腺癌、精神疾病或内分泌疾病患者。
对照组：同期按年龄频数匹配，序贯收集四川省人民医院体检中心、成都市双流县全国乳腺癌农村筛查点的健康女性469例，其中绝经前对象231例，绝经后对象238例。纳入标准：经超声和钼靶检查排除患有乳腺癌，汉族，在四川省居住3年以上者。排除其他恶性肿瘤、精神疾病患者。
本研究由四川大学华西第四医院（华西公共卫生学院）伦理委员会批准实施，所有研究对象均同意并签署研究知情同意书。
1.2. 资料收集
采用课题组统一编制的《女性乳腺癌危险因素调查表》，由调查员询问调查对象并逐一填写。调查内容包括：①一般人口学特征，包括年龄、家庭人均月收入、教育水平等；②生活习惯，包括主动吸烟等；③人体测量指标，测量对象在接受调查时的身高、体质量、腰围、臀围；④女性生殖生育史，包括月经状况、初潮年龄、是否怀过孕、初产年龄、生育数等；⑤肿瘤家族史、乳腺/卵巢/子宫良性疾病史。
1.3. 血样收集及实验室检测
病例在临床治疗前采样，对照在体检时采样。抽取空腹抗凝血全血5 mL，采血后4 h内分离血浆2 mL分装保存于−80 ℃。采用ELISA法测定血浆瘦素、sOB-R和脂联素水平，试剂盒来自武汉伊莱瑞特生物科技有限公司。瘦素、sOB-R和脂联素蛋白检测灵敏度分别为46.88 pg/mL、0.19 ng/mL和0.47 ng/mL，批间、批内变异系数均小于10%。
1.4. 变量定义
① FLI：瘦素（ng/mL）/可溶性瘦素受体（ng/mL），可反映有活性的游离瘦素水平；② L/A：瘦素（ng/mL）/脂联素（µg/mL），可反映瘦素与脂联素对乳腺癌细胞的联合效应；③ 体质量指数（body mass index，BMI）：体质量（kg）/身高（m2）。BMI<18.5 kg/m2定义为体质量不足，18.5 kg/m2≤BMI<24 kg/m2定义为正常体质量，24 kg/m2≤BMI<28 kg/m2定义为超重，BMI≥28 kg/m2定义为一般性肥胖[15]；④ 腰臀比（waist-to-hip ratio，WHR）：腰围（cm）/臀围（cm）。WHR≥0.85定义为中心型肥胖[16]。进一步联合BMI和WHR综合评估肥胖程度，按BMI和WHR分层：WHR<0.85且BMI<24 kg/m2；WHR<0.85且BMI≥24 kg/m2；WHR≥0.85且18.5 kg/m2≤BMI<24 kg/m2；WHR≥0.85且BMI≥24 kg/m2。
1.5. 统计学方法
本研究连续型变量均不符合正态分布，采用中位数（Q1，Q4）进行描述，组间比较采用Mann-Whitney U检验。分类变量采用例数（%）表示，组间比较采用χ2检验。以病例/对照为因变量建立非条件logistic回归模型进行多因素分析，将单因素分析中差异有统计学意义的变量以及蛋白指标纳入，建立多因素logistic回归模型，以病例/对照作为因变量，对照编码为0，病例编码为1，基于对照组的暴露水平将蛋白及比值指标按四分位数分组，转换为四分位等级变量Q1、Q2、Q3、Q4。以最低水平暴露组Q1作为参照，其余更高水平组设为哑变量，分析不同等级下的指标水平与绝经前后乳腺癌发生风险的关联；同时，利用各指标Q1、Q2、Q3、Q4等级变量计算 P趋势值。按BMI和WHR分层，分析蛋白指标与绝经前后乳腺癌的风险关联，并采用Wald检验进行异质性分析；为尽量保证分层下的研究数量足够，将选择不同的四分位数作为蛋白指标的截断值，转换为二分类变量，因此，绝经前：将瘦素水平的Q1，sOB-R、脂联素、FLI、L/A比值的Q2作为截断值；绝经后：将瘦素、sOB-R和脂联素水平的Q2，FLI的Q3，L/A比值的Q1作为截断值，转换为二分类变量。α=0.05。
2. 结果
2.1. 基线特征
见表1。共纳入480例绝经前和458例绝经后女性。绝经前病例组249例，对照组231例，中位BMI分别为22.9、23.2 kg/m2，中位WHR分别为0.80、0.83。绝经后病例组220例，对照组238例，中位BMI分别为23.4 、23.7 kg/m2；中位WHR分别为0.82、0.86。对于绝经前女性，病例与对照组间的教育水平、生育子女数、WHR差异有统计学意义（P<0.05）；对于绝经后的女性，病例组与对照组间的教育水平、主动吸烟、生育子女数、乳腺/卵巢/子宫良性疾病史、肿瘤家族史、WHR差异有统计学意义（P<0.05）。
表 1. The distribution and comparison of characteristics in the premenopausal and postmenopausal breast cancer patients and controls.
绝经前后病例组和对照组基线特征的分布与比较
| Characteristic | Premenopausal | Postmenopausal | |||||||
| Cases (n=249) | Controls (n=231) | U/F | P | Cases (n=220) | Controls (n=238) | U/F | P | ||
| BMI: Body mass index; WHR: Waist-to-hip ratio.* Mann-Whitney U test; † χ2 test. | |||||||||
| Age/yr., median (Q1, Q4) | 44 (40.5, 48.5) | 44 (40, 47) | 1.218 | 0.223* | 57 (53, 62) | 57 (52, 61) | 1.245 | 0.213* | |
| Menarche age/years, median (Q1, Q4) | 13 (13, 14) | 14 (13, 15) | −0.872 | 0.383* | 15 (13, 16) | 14 (13, 16) | 1.317 | 0.188* | |
| Age at first live birth/years, median (Q1, Q4) | 24 (22, 26) | 24 (22, 26) | 0.190 | 0.850* | 24 (23, 26) | 25 (23, 27) | −0.710 | 0.477* | |
| Education level/case (%) | 12.367 | <0.001† | 12.957 | <0.001† | |||||
| Below high school | 202 (81.1) | 155 (67.1) | 197 (89.6) | 183 (76.9) | |||||
| High school and above | 47 (18.9) | 76 (32.9) | 23 (10.4) | 55 (23.1) | |||||
| Family monthly income per capita/case (%) | 0.212 | 0.645† | 0.044 | 0.834† | |||||
| ≤ ¥ 1 500 | 93 (37.4) | 91 (39.4) | 94 (42.7) | 104 (43.7) | |||||
| > ¥ 1 500 | 156 (62.6) | 140 (60.6) | 26 (57.3) | 134 (56.3) | |||||
| Active smoking/case (%) | 2.188 | 0.139† | 4.583 | 0.032† | |||||
| Yes | 8 (3.2) | 2 (0.9) | 8 (3.6) | 1 (0.4) | |||||
| No | 241 (96.8) | 229 (99.1) | 212 (96.4) | 237 (99.6) | |||||
| Family history of cancers/case (%) | 1.624 | 0.203† | 10.676 | 0.001† | |||||
| Yes | 57 (22.9) | 42 (18.2) | 63 (28.6) | 38 (16.0) | |||||
| No | 192 (77.1) | 189 (81.8) | 157 (71.4) | 200 (84.0) | |||||
| Number of live birth/case (%) | 21.977 | <0.001† | 13.783 | 0.003† | |||||
| 0 | 6 (2.4) | 9 (3.9) | 7 (3.2) | 3 (1.3) | |||||
| 1 | 156 (62.7) | 184 (79.7) | 122 (55.5) | 163 (68.5) | |||||
| 2 | 76 (30.5) | 35 (15.1) | 58 (26.4) | 57 (23.9) | |||||
| ≥3 | 11 (4.4) | 3 (1.3) | 33 (14.9) | 15 (6.3) | |||||
| History of benign breast, ovarian and
uterine disease/case (%) |
0.206 | 0.650† | 4.330 | 0.037† | |||||
| Yes | 89 (35.7) | 78 (33.7) | 79 (35.9) | 64 (26.9) | |||||
| No | 160 (64.3) | 153 (66.3) | 141 (64.1) | 174 (73.1) | |||||
| History of pregnancy/case (%) | 0.193 | 0.660† | 0.752 | 0.386† | |||||
| Yes | 245 (98.4) | 225 (97.4) | 215 (97.7) | 236 (99.2) | |||||
| No | 4 (1.6) | 6 (2.6) | 5 (2.3) | 2 (0.8) | |||||
| WHR (median (Q1, Q4)) | 0.80 (0.74, 0.86) | 0.83 (0.79, 0.87) | −4.091 | <0.001* | 0.82 (0.76, 0.88) | 0.86 (0.81, 0.90) | −5.759 | <0.001* | |
| BMI/(kg/m2), median (Q1, Q4) | 22.9 (20.8, 24.9) | 23.2 (21.2, 25.0) | −1.172 | 0.241* | 23.4 (21.5, 25.3) | 23.7 (21.6, 25.7) | −1.215 | 0.224* | |
关于蛋白指标，绝经前女性中，病例组与对照组间的血浆sOB-R、脂联素、FLI差异有统计学意义（P<0.05）；绝经后女性中，病例组与对照组间的sOB-R、脂联素、FLI、L/A比值差异有统计学意义（P<0.05）；绝经前后，瘦素在病例组与对照组间的差异均无统计学意义。见表2。
表 2. The distribution and comparison of biomarker levels in the premenopausal and postmenopausal breast cancer patients and controls.
绝经前后病例组和对照组蛋白指标水平的分布与比较
| Characteristic | Cases | Controls | U | P |
| sOB-R: Soluble leptin receptor; FLI: Leptin/sOB-R; L/A: Leptin/adiponectin.
| ||||
| Premenopausal | ||||
| n | 249 | 231 | — | — |
| Leptin/(ng/mL), median (Q1, Q4) | 7.77 (3.66, 13.42) | 8.42 (4.68, 14.06) | −1.269 | 0.204 |
| sOB-R/(ng/mL), median (Q1, Q4) | 23.76 (14.05, 38.43) | 30.45 (19.65, 46.71) | −3.513 | <0.001 |
| Adiponectin/(µg/mL), median (Q1, Q4) | 10.85 (7.38, 14.93) | 13.37 (9.04, 17.08) | −3.920 | <0.001 |
| FLI (median (Q1, Q4)) | 0.35 (0.20, 0.49) | 0.29 (0.20, 0.39) | 2.957 | 0.003 |
| (L/A)/(ng/µg), median (Q1, Q4) | 0.75 (0.35, 1.36) | 0.63 (0.38, 1.10) | 1.220 | 0.222 |
| Postmenopausal | ||||
| n | 220 | 238 | — | — |
| Leptin/(ng/mL), median (Q1, Q4) | 8.03 (4.75, 13.35) | 8.28 (4.73, 13.56) | 0.027 | 0.979 |
| sOB-R/(ng/mL), median (Q1, Q4) | 23.56 (13.85, 40.26) | 31.03 (18.12, 48.89) | −2.896 | 0.004 |
| Adiponectin/(µg/mL), median (Q1, Q4) | 12.47 (9.24, 17.53) | 17.77 (10.31, 24.95) | −5.735 | <0.001 |
| FLI (median (Q1, Q4)) | 0.37 (0.23, 0.49) | 0.27 (0.19, 0.36) | 4.720 | <0.001 |
| (L/A)/(ng/µg), median (Q1, Q4) | 0.68 (0.35, 1.15) | 0.50 (0.21, 0.86) | 3.508 | <0.001 |
2.2. 脂联素、瘦素、sOB-R与绝经前后乳腺癌的关联
2.2.1. 绝经前乳腺癌的风险分析
多因素logistic回归发现，校正前，sOB-R、脂联素、FLI的升高与绝经前乳腺癌相关（P趋势<0.05）。与Q1组相比，Q3、Q4组的sOB-R、脂联素预示绝经前乳腺癌的发生风险降低，Q4组的FLI预示绝经前乳腺癌的发生风险升高。校正后，sOB-R、脂联素与绝经前乳腺癌的发生风险的关系不变，但FLI不再具有统计学意义。校正前后，未发现瘦素、L/A比值与绝经前乳腺癌发生风险的明显关联。见表3。
表 3. Correlation between premenopausal breast cancer risks and adiponectin, leptin, and sOB-R.
脂联素、瘦素及可溶性瘦素受体与绝经前乳腺癌的风险分析
| Variable | Cases/controls | Basic model | Adjusted model† | |||
| OR (95% CI) | P trend | OR (95% CI) | P trend | |||
| sOB-R: Soluble leptin receptor; FLI: Leptin/sOB-R; L/A: Leptin/adiponectin;
OR: Odds ratio; CI: Confidence interval; † Adjusted foreducation level (<high school/≥high school), number of live birth (nulliparous, 1, 2, ≥3 children). | ||||||
| Leptin/(ng/mL) | 0.285 | 0.143 | ||||
| Q1 (≤4.68) | 82/58 | 1.00 | 1.00 | |||
| Q2 (4.69−) | 49/59 | 0.59 (0.35−0.98) | 0.54 (0.32−0.92) | |||
| Q3 (8.43−) | 60/57 | 0.75 (0.45−1.22) | 0.70 (0.42−1.17) | |||
| Q4 (>14.06) | 58/57 | 0.72 (0.44−1.18) | 0.64 (0.38−1.07) | |||
| sOB-R/(ng/mL) | 0.002 | 0.024 | ||||
| Q1 (≤19.65) | 94/59 | 1.00 | 1.00 | |||
| Q2 (19.66−) | 65/57 | 0.72 (0.44−1.16) | 0.65 (0.39−1.07) | |||
| Q3 (30.47−) | 44/58 | 0.48 (0.29−0.79) | 0.44 (0.26−0.75) | |||
| Q4 (>46.71) | 46/57 | 0.51 (0.31−0.84) | 0.49 (0.29−0.83) | |||
| Adiponectin/(µg/mL) | 0.001 | 0.001 | ||||
| Q1 (≤9.04) | 91/57 | 1.00 | 1.00 | |||
| Q2 (9.05−) | 72/59 | 0.76 (0.47−1.23) | 0.68 (0.42−1.12) | |||
| Q3 (13.39−) | 43/58 | 0.46 (0.28−0.78) | 0.42 (0.25−0.72) | |||
| Q4 (>17.08) | 43/57 | 0.47 (0.28−0.79) | 0.48 (0.28−0.81) | |||
| FLI | 0.011 | 0.060 | ||||
| Q1 (≤0.20) | 65/59 | 1.00 | 1.00 | |||
| Q2 (0.21−) | 37/62 | 0.54 (0.32−0.93) | 0.59 (0.34−1.03) | |||
| Q3 (0.30−) | 46/55 | 0.76 (0.45−1.29) | 0.74 (0.43−1.26) | |||
| Q4 (>0.39) | 101/55 | 1.67 (1.03−2.70) | 1.51 (0.92−2.47) | |||
| (L/A)/(ng/µg) | 0.448 | 0.778 | ||||
| Q1 (≤0.38) | 69/57 | 1.00 | 1.00 | |||
| Q2 (0.39−) | 48/59 | 0.67 (0.40−1.13) | 0.70 (0.41−1.19) | |||
| Q3 (0.64−) | 51/58 | 0.73 (0.43−1.22) | 0.68 (0.40−1.16) | |||
| Q4 (>1.10) | 81/57 | 1.17 (0.72−1.91) | 1.07 (0.65−1.78) | |||
2.2.2. 绝经后乳腺癌的风险分析
多因素logistic回归发现，校正前，sOB-R、脂联素、FLI、L/A比值的升高与绝经后乳腺癌的风险相关（P趋势<0.05）。与Q1组相比，Q3、Q4组sOB-R、脂联素预示绝经后乳腺癌的风险降低，Q4组的FLI 及Q2、Q3、Q4组的L/A比值预示绝经后乳腺癌的发生风险升高。校正后，sOB-R、FLI 、L/A比值与绝经后乳腺癌的发生风险的关系不变，脂联素仅Q4组与绝经后乳腺癌的发生风险降低有关。校正前后，未发现瘦素与绝经后乳腺癌风险之间的明显关联。见表4。
表 4. Correlation between postmenopausal breast cancer risk and adiponectin, leptin, and sOB-R.
脂联素、瘦素及可溶性瘦素受体与绝经后乳腺癌的风险分析
| Variable | Cases/controls | Basic model | Adjusted model† | |||
| OR(95% CI) | P trend | OR(95% CI) | P trend | |||
| sOB-R: Soluble leptin receptor; FLI: Leptin/sOB-R; L/A: Leptin/adiponectin;
OR: Odds ratio; CI: Confidence interval. † Adjusted for active smoking (yes/no), education level (<high school/≥high school), number of live birth (nulliparous, 1, 2, ≥3 children), family history of cancers (yes/no), history of benign breast, ovarian and uterine disease (yes/no). | ||||||
| Leptin/(ng/mL) | 0.827 | 0.931 | ||||
| Q1 (≤4.73) | 54/59 | 1.00 | 1.00 | |||
| Q2 (4.74−) | 60/60 | 1.09 (0.65−1.83) | 1.13 (0.66−1.95) | |||
| Q3 (8.29−) | 53/60 | 0.97 (0.57−1.63) | 0.95 (0.55−1.66) | |||
| Q4 (>13.56) | 53/59 | 0.98 (0.58−1.66) | 1.10 (0.63−1.91) | |||
| sOB-R/(ng/mL) | 0.004 | 0.009 | ||||
| Q1 (≤18.12) | 75/59 | 1.00 | 1.00 | |||
| Q2 (18.13−) | 65/60 | 0.85 (0.52−1.39) | 0.73 (0.44−1.22) | |||
| Q3 (31.04−) | 41/60 | 0.54 (0.32−0.91) | 0.51 (0.29−0.88) | |||
| Q4 (>48.89) | 39/59 | 0.52 (0.31−0.88) | 0.53 (0.30−0.92) | |||
| Adiponectin/(µg/mL) | <0.001 | <0.001 | ||||
| Q1 (≤10.31) | 71/59 | 1.00 | 1.00 | |||
| Q2 (10.32−) | 98/61 | 1.34 (0.83−2.14) | 1.33 (0.81−2.17) | |||
| Q3 (17.78−) | 42/59 | 0.59 (0.35−1.00) | 0.63 (0.36−1.09) | |||
| Q4 (>24.95) | 9/59 | 0.13 (0.06−0.28) | 0.12 (0.05−0.27) | |||
| FLI | <0.001 | <0.001 | ||||
| Q1 (≤0.19) | 40/64 | 1.00 | 1.00 | |||
| Q2 (0.20−) | 34/56 | 0.97 (0.54−1.74) | 1.19 (0.64−2.23) | |||
| Q3 (0.28−) | 42/60 | 0.85 (0.48−1.53) | 0.78 (0.42−1.47) | |||
| Q4 (>0.36) | 114/58 | 3.15 (1.90−5.22) | 3.48 (2.01−6.02) | |||
| (L/A)/(ng/µg) | 0.001 | 0.001 | ||||
| Q1 (≤0.21) | 24/59 | 1.00 | 1.00 | |||
| Q2 (0.22−) | 64/61 | 2.58 (1.43−4.65) | 2.55 (1.36−4.76) | |||
| Q3 (0.52−) | 54/59 | 2.25 (1.23−4.11) | 2.24 (1.19−4.22) | |||
| Q4 (>0.86) | 78/59 | 3.25 (1.82−5.82) | 3.35 (1.80−6.23) | |||
2.3. 按WHR和BMI分层分析脂联素、瘦素、sOB-R与绝经前后乳腺癌的关联
分层分析中，未发现蛋白及比值指标与绝经前女性乳腺癌风险的明显关联。在所有亚组的绝经后女性中，脂联素、FLI与乳腺癌的关联仍有统计学意义。相较于WHR<0.85的绝经后女性，脂联素更能降低WHR≥0.85的绝经后女性乳腺癌的发生风险。在体质量正常的中心型肥胖女性中，L/A比值与绝经后乳腺癌的发生仍有关联，见表5～表6。
表 5. Correlation between premenopausal breast cancer risk and adiponectin, leptin, and sOB-R stratified by WHR and BMI.
按WHR、BMI分层分析脂联素、瘦素、sOB-R与绝经前乳腺癌的风险关联
| Variable | WHR<0.85 | WHR≥0.85 | ||||||||||
| BMI<24 kg/m2 | BMI≥24 kg/m2 | 18.5 kg/m2≤BMI<24 kg/m2* | BMI≥24 kg/m2 | P# | ||||||||
| Cases/controls | OR(95% CI)† | Cases/controls | OR(95% CI)† | Cases/controls | OR(95% CI)† | Cases/controls | OR(95% CI)† | |||||
| sOB-R: Soluble leptin receptor; FLI: Leptin/sOB-R; L/A: Leptin/adiponectin; WHR: Waist-to-hip ratio; BMI: Body mass index;
OR: Odds ratio; CI: Confidence interval. * We did not have any woman with WHR≥0.85&BMI<18.5 kg/m2in our study; † Adjusted for education level (<high school/≥high school), number of live birth (nulliparous, 1, 2, ≥3 children); # Heterogeneity, determined using Wald test. | ||||||||||||
| Leptin/(ng/mL) | <0.001 | |||||||||||
| ≤4.68 | 60/36 | 1.00 | 7/5 | 1.00 | 12/9 | 1.00 | 3/8 | 1.00 | ||||
| >4.68 | 67/63 | 0.67 (0.39−1.17) | 41/36 | 0.84 (0.22−3.20) | 27/28 | 0.68 (0.23−1.99) | 32/46 | 1.99 (0.46−8.50) | ||||
| sOB-R/(ng/mL) | <0.001 | |||||||||||
| ≤30.46 | 98/66 | 1.00 | 24/17 | 1.00 | 22/17 | 1.00 | 15/16 | 1.00 | ||||
| >30.46 | 29/33 | 0.65 (0.36−1.20) | 24/24 | 0.87 (0.35−2.14) | 17/20 | 0.49 (0.18−1.30) | 20/38 | 0.91 (0.33−2.54) | ||||
| Adiponectin/(µg/mL) | <0.001 | |||||||||||
| ≤13.38 | 87/56 | 1.00 | 32/16 | 1.00 | 21/16 | 1.00 | 23/28 | 1.00 | ||||
| >13.38 | 40/43 | 0.61 (0.35−1.06) | 16/25 | 0.30 (0.12−0.75) | 18/21 | 0.67 (0.25−1.76) | 12/26 | 0.73 (0.28−1.88) | ||||
| FLI | 0.045 | |||||||||||
| ≤0.29 | 56/55 | 1.00 | 18/18 | 1.00 | 16/22 | 1.00 | 12/26 | 1.00 | ||||
| >0.29 | 71/44 | 1.38 (0.80−2.39) | 30/23 | 0.90 (0.34−2.36) | 23/15 | 1.95 (0.75−5.11) | 23/28 | 1.56 (0.60−4.01) | ||||
| (L/A)/(ng/µg) | 0.010 | |||||||||||
| ≤0.63 | 74/62 | 1.00 | 18/16 | 1.00 | 19/20 | 1.00 | 6/18 | 1.00 | ||||
| >0.63 | 53/37 | 1.21 (0.70−2.11) | 30/25 | 1.06 (0.43−2.64) | 20/17 | 0.91 (0.35−2.40) | 29/36 | 2.46 (0.78−7.76) | ||||
表 6. Correlation between postmenopausal breast cancer risk and adiponectin, leptin, and sOB-R stratified by WHR and BMI.
按WHR、BMI分层分析脂联素、瘦素、sOB-R与绝经后乳腺癌的风险关联
| Variable | WHR<0.85 | WHR≥0.85 | ||||||||||
| BMI<24 kg/m2 | BMI≥24 kg/m2 | 18.5 kg/m2≤BMI<24 kg/m2* | BMI≥24 kg/m2 | P # | ||||||||
| Cases/controls | OR(95% CI)† | Cases/controls | OR(95% CI)† | Cases/controls | OR(95% CI)† | Cases/controls | OR(95% CI)† | |||||
| sOB-R: Soluble leptin receptor; FLI: Leptin/sOB-R; L/A: Leptin/adiponectin; WHR: Waist-to-hip ratio; BMI: Body mass index;
OR: Odds ratio; CI: Confidence interval. * We did not find the woman with WHR≥0.85&BMI<18.5 kg/m2in our study; † Adjusted foractive smoking (yes/no), education level (<high school/≥high school), number of live birth (nulliparous, 1, 2, ≥3 children), family history of cancers (yes/no), history of benign breast, ovarian and uterine disease (yes/no); # Heterogeneity, determined using Wald test. | ||||||||||||
| Leptin/(ng/mL) | <0.001 | |||||||||||
| ≤8.28 | 66/54 | 1.00 | 16/7 | 1.00 | 18/33 | 1.00 | 13/24 | 1.00 | ||||
| >8.28 | 25/21 | 1.29 (0.66−2.55) | 33/21 | 1.66 (0.51−5.45) | 23/20 | 2.75 (1.08−6.96) | 25/57 | 0.83 (0.35−1.98) | ||||
| sOB-R/(ng/mL) | <0.001 | |||||||||||
| ≤31.03 | 71/54 | 1.00 | 27/7 | 1.00 | 26/34 | 1.00 | 15/23 | 1.00 | ||||
| >31.03 | 20/21 | 0.82 (0.38−1.75) | 22/21 | 0.20 (0.06−0.67) | 15/19 | 1.51 (0.58−3.95) | 23/58 | 0.67 (0.28−1.58) | ||||
| Adiponectin/(µg/mL) | <0.001 | |||||||||||
| ≤17.77 | 68/37 | 1.00 | 35/13 | 1.00 | 35/30 | 1.00 | 30/40 | 1.00 | ||||
| >17.77 | 23/38 | 0.41 (0.20−0.81) | 14/15 | 0.33 (0.11−0.99) | 6/23 | 0.22 (0.07−0.63) | 8/41 | 0.22 (0.08−0.58) | ||||
| FLI | 0.089 | |||||||||||
| ≤0.36 | 42/56 | 1.00 | 22/21 | 1.00 | 19/38 | 1.00 | 22/64 | 1.00 | ||||
| >0.36 | 49/19 | 3.32 (1.65−6.70) | 27/7 | 5.84 (1.74−19.57) | 22/15 | 2.64 (1.02−6.83) | 16/17 | 2.95 (1.23−7.11) | ||||
| (L/A)/(ng/µg) | 0.003 | |||||||||||
| ≤0.21 | 17/25 | 1.00 | 1/2 | 1.00 | 3/19 | 1.00 | 2/13 | 1.00 | ||||
| >0.21 | 74/50 | 2.02 (0.92−4.42) | 48/26 | 5.04 (0.34−74.06) | 38/34 | 7.24 (1.89−27.77) | 36/68 | 3.83 (0.72−20.37) | ||||
3. 讨论
脂联素可激活AMPK途径、GSK-3β/β-catenin等信号通路，直接抑制癌细胞的增殖和促进癌细胞凋亡，也可通过增加胰岛素敏感性、降低炎性因子分泌，改善肿瘤微环境，间接抑制乳腺癌细胞的增殖[4-5, 9-10]。YU等[17]通过meta分析，纳入27篇文献，发现在亚洲人中，脂连素在绝经前后对照组的水平均更高。本研究未发现总瘦素水平与绝经前后乳腺癌的明显关联，但sOB-R与绝经前后乳腺癌的风险呈显著负相关。sOB-R主要来源于膜瘦素受体的脱落，完全由细胞外结构域组成，无信号转导功能，主要在血液中循环[7]。瘦素在血液中可以游离的形式或与sOB-R结合的形式存在，与sOB-R结合的瘦素因为无法与细胞膜瘦素受体结合导致其作用受到抑制，瘦素的生物可利用度减少[7-8, 18]。目前sOB-R与绝经前后乳腺癌关联的人群研究非常少，RODRIGO等[14]通过纳入80对病例对照发现了与本研究一致的结果，均发现sOB-R升高与绝经前后的乳腺癌发生风险降低有关。
由于瘦素的活性主要由瘦素受体控制，而瘦素与脂联素均为脂肪细胞因子，存在共同或相互作用，3个指标之间关系密切，仅分析单一指标可能无法反映指标间对乳腺癌的综合作用，而部分研究提出指标间的比值形式可能反映其综合作用[8, 11-14]，故本研究进一步分析了比值指标对绝经前后乳腺癌的效应。
游离瘦素可能是瘦素的生物活性形式[8]，而FLI可反映游离瘦素水平。本研究观察到FLI与绝经后乳腺癌风险有显著正向关联。游离瘦素可能通过激活受体介导的信号通路直接作用于乳腺癌细胞，也可通过降低胰岛素敏感性、促进炎症反应、增加雌激素合成间接作用[5-6]。同样，RODRIGO等[14]也发现高FLI可显著增加绝经后乳腺癌的发生风险（OR=12.308, 95%CI: 1.203～12.588）。FLI可能是瘦素活性更加准确的测量指标，能够更准确地反映瘦素对绝经后乳腺癌风险的影响。
本研究也发现L/A比值与绝经后乳腺癌呈正向关联。NKHATA等[12]通过体外细胞实验发现随着L/A比值增加，MCF-7和T47-D两种乳腺癌细胞的增殖均增加。脂联素可以抑制瘦素介导的细胞增殖，二者之间的平衡可有效地调节乳腺癌细胞的增殖[11-12, 19]。与本研究结果相似，CHEN、张家鑫等[20-21]均发现高L/A比值与乳腺癌的发生以及乳腺肿瘤的侵袭性有强相关性。因此，未来的前瞻性研究应该包括两个比值指标的测量，二者可能作为绝经后乳腺癌风险评估的重要指标。
由于3个蛋白均为脂肪相关因子，与肥胖的关联较强，有必要探讨不同肥胖程度的中国女性中，指标对绝经前后乳腺癌的风险效应。同时，中国成年人的体脂分布具有中心型特点[3]，联合WHR和BMI能够更加综合地评估中国成年人的肥胖程度。因此，本研究进一步按BMI和WHR进行分层分析。
在各体质量分层下，sOB-R与绝经前后乳腺癌的关联消失，其可能与肥胖的关联较强[22]。脂联素、FLI与绝经后乳腺癌风险的关联仍然有统计学意义，其中脂连素更能降低WHR≥0.85的绝经后女性乳腺癌风险。FLI代表游离瘦素水平，对绝经后乳腺癌的效应较稳定，其可能作为绝经后乳腺癌发生风险的独立预测指标。
同时，在体质量正常但中心型肥胖（18.5 kg/m2≤BMI<24 kg/m2且WHR≥0.85）的女性中，L/A比值对绝经后乳腺癌风险有显著效应。有研究提出中心型肥胖反映大量的腹部及内脏脂肪的堆积，瘦素、脂联素可能与腹部脂肪相互作用，通过雌激素、胰岛素抵抗等途径，在绝经后乳腺癌的发生发展中发挥重要作用[21, 23]。
本研究探讨了指标对绝经前后乳腺癌的单独和联合效应，并进一步联合BMI和WHR综合评估中国成年人的肥胖程度，分析指标效应在不同肥胖程度女性中的变化，为揭示肥胖与绝经前后乳腺癌之间的分子机制提供了证据。然而，本研究仍有一定的局限性。首先，研究样本量较小；其次，本研究是回顾性病例对照研究，无法证明其因果关系。今后，应开展大规模的前瞻性研究进一步验证单个及联合指标对绝经前后乳腺癌的作用。
Funding Statement
国家自然科学基金项目（No. 81874282）和四川省科技计划项目（No. 2017SZ0005）资助
Contributor Information
芳 易 (Fang YI), Email: 1940941323@qq.com.
佳圆 李 (Jia-yuan LI), Email: lijiayuan@scu.edu.cn.
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