Extended Data Fig. 5: Additional control analyses for the mediation effect of Lac-Phe on metformin-associated BMI reduction.
From: Lac-Phe mediates the effects of metformin on food intake and body weight
(a) Schematic of the two subgroups of MESA in the post-hoc subgroup analysis stratified by ΔBMI. The change in BMI of the complete MESA sample prior to subgroup analysis was 0.24 ± 0.04 kg/m2, n = 3645. Participants with increased BMI are shown in red; participants with decreased BMI are shown in blue. (b-d) The mediation model in Fig. 3b was reordered to test if ΔBMI partially mediates the relationship between metformin use (exposure) and Lac-Phe levels (outcome). (b) Among MESA participants with decreased BMI, the total effect of metformin use on Lac-Phe levels was assessed in an ‘unmediated model’ using an age- and sex-adjusted linear regression model. (c) To construct mediation models, the individual associations of metformin use, lac-phe, lactate, and ΔBMI were assessed using linear regression models as described in Methods. The direct effect of metformin use on Lac-Phe levels was then assessed using an age- and sex-adjusted linear regression model adjusted for ΔBMI. No reduction in the direct effect of metformin on Lac-Phe levels was appreciated compared to the total effect of metformin on Lac-Phe in the unmediated model suggesting no meditation. (d) The mediation effect of ΔBMI derived from the mediation models in (c), n = 1184. Values are median with 95% confidence intervals. Statistical significance were calculated using nonparametric bootstrapping with the percentile method. (e-g) The mediation effects of Lac-Phe and lactate on the effect of metformin-associated BMI increase. (e) Among MESA participants with increased BMI, the total effect of metformin use on ΔBMI was assessed in an ‘unmediated model’ using an age- and sex-adjusted linear regression model. (f) To construct mediation models, the individual associations of metformin use, Lac-Phe, lactate, and ΔBMI were assessed using linear regression models as described in Methods. The direct effect of metformin use on ΔBMI was then assessed using an age- and sex-adjusted linear regression model adjusted for either Lac-Phe (left) or lactate (right). No reduction in the direct effects of metformin on ΔBMI compared to the total effect of metformin on ΔBMI in the unmediated model suggested no meditation effect of either Lac-Phe or lactate. (g) The mediation effects of Lac-Phe and lactate. derived from the mediation models in (f), n = 1460. Values are plotted as mean with 95% confidence intervals. Confidence intervals and statistical significance (unadjusted p values) were calculated using nonparametric bootstrapping with the percentile method, as described in Methods. (h) The mediation effects of additional 136 metabolites measured in MESA participants with decreased BMI using the amide negative LC-MS method. Seven out of the 136 tested metabolites were found to have a predicted mediation effect with unadjusted p-value ≤ 0.05 (right). Values are median values with 95% confidence intervals. The confidence intervals and statistical significance of the predicted mediation effects for these seven metabolites were calculated using nonparametric bootstrapping with the percentile method (n = 1619), as described in Methods.
