High-Fat Diet and Environmentally Relevant Secondhand Smoke Co-exposure and Cardiovascular Regulation in Mice

BACKGROUND: Over the past few decades, cardiovascular disease incidence significantly decreased by 27%. Paradoxically, the number of deaths from cardiovascular diseases increased by 42% over the same period, owing to population growth and longevity. Consequently, cardiovascular diseases remain the leading cause of global death. Cardiovascular diseases are complex, multifactorial diseases that cannot be ascribed to a single factor. High-fat diet (HFD) and secondhand smoke (SHS) are two preventable risk factors for the development of cardiovascular diseases. Studies have shown that SHS exposure is associated with poor dietary habits, suggesting the importance of potential confounding diet effects on health effects of SHS exposure. We previously showed that, in mice, environmentally relevant SHS exposure resulted in 10% decrease in baroreflex sensitivity (BRS) and 13% decrease in measures of heart rate variability (HRV). Here, we sought to characterize how HFD interplay with SHS in inducing cardiovascular dysfunction. METHODS: Male C57BL/6J mice (11 wk) implanted with BP/ECG telemetry devices were fed with either normal diet (ND, 13.6 kcal% fat) or HFD (60 kcal% fat) and exposed to either filtered air (FA) or SHS (3 mg/m3 , 6 hr/d, 5 d/wk) for 11 weeks. 36-hr continuous BP/ECG recordings were performed. Data were divided into three 12-hour periods: the first dark cycle (dark 1) immediately after the last day of exposure, and the following light and dark (dark 2) cycles. Spontaneous baroreflex sensitivity (BRS) was determined with the sequence method. Standard time domain heart rate variability (HRV) parameters were obtained from normal-to-normal R-R intervals. RESULTS: HFD-fed mice had significantly greater weight gain than ND-fed group (+15.3 g and +2.8 g over 11 weeks, HFD and ND, respectively). SHS exposure had no effect on body weight. Compared to ND mice, HFD mice had significantly higher BP (~6.5 mmHg), HR (~98 bpm), and lower BRS (~15% decrease) in the light cycle. Furthermore, HFD significantly reduced overall and short-term HRV (36% and 47% reduction for SDNN and rMSSD, respectively, p < 0.05) across all three light cycles. The reduction in HRV is unlikely due to a higher HR in HFD mice because normalizing the HRV measures to baseline R-R intervals did not change the results. SHS exposure did not pose additional effects on these HFD-induced changes. While HFD alone did not affect BP variability, co-exposure of SHS and HFD significantly increased BP variability during the first dark cycle (16.8%, 15.6%, and 17.3% higher than HFD+FA group, for systolic, diastolic, and mean BP variability, respectively, p < 0.05), suggesting a co-exposure-induced BP dysregulation. CONCLUSIONS: This study emphasizes the importance of accounting for differences in diet when studying the cardiovascular effects of SHS. © FASEB.