Interactive Effects of Omega-3 Polyunsaturated Fatty Acids and Secondhand Smoke in Mice and Human Subjects

Abstract

Active smoking and secondhand smoke (SHS) exposure increase the risk of cardiovascular morbidity and mortality. Active smoking is associated with reduced levels of omega-3 polyunsaturated fatty acids (n-3 PUFA) and studies show that n-3 PUFA supplementation can improve smoking-induced vascular dysfunction. However, the relationship between n-3 PUFA and SHS exposure has not been studied. Fat-1 transgenic mice, which convert n-6 to n-3 PUFA, were fed diets with n-3 PUFA or without (n-6 PUFA diet), exposed to air or SHS for 4 weeks, and vasoreactivity, antioxidant indices, and omega-3 index (percent eicosapentaenoic + docosahexaenoic acids in RBC) measured. Compared to air-exposed mice, SHS-enhanced aortic constriction in mice fed the n-6 PUFA diet (omega-3 index, 5.9 ± 0.2%; mean ± SE), but not in mice fed the n-3 PUFA diet (omega-3 index, 7.8 ± 0.6%). SHS also significantly induced mRNA expression of cytochrome P4501A1, NADPH:quinone oxidoreductase, heme oxygenase-1, and angiotensinogen in adipose tissue, and increased antioxidant capacity only in mice on the n-6 PUFA diet. Notably, SHS reduced the omega-3 index by 1.0 percentage point (p = 0.003), compared to air-exposed mice irrespective of diet. Additionally, we recruited human nonsmokers (NS) with and without SHS exposure (n = 40) 19-40 years old and measured the omega-3 index and antioxidant capacity. In human subjects SHS exposure was associated with a significantly lower omega-3 index (NS, 4.4 ± 1.1%; NS + SHS, 3.2 ± 1.0%; mean ± SD, p = 0.002) and higher antioxidant capacity (p < 0.001) than unexposed NS. Thus, SHS exposure is associated with lower levels of n-3 PUFA in mice and humans; however, an omega-3 index of ~ 8% in mice has vasoprotective and antioxidant properties.

Keywords: Antioxidant capacity; Fat-1 transgenic mice; Omega-3 polyunsaturated fatty acids; Secondhand smoke; Vascular dysfunction.

Fig. 1

Total particulate matter concentration during secondhand smoke exposure of mice. Variation of total particulate matter concentration in the whole-body exposure chamber during 120 min exposure of fat-1 transgenic mice to secondhand smoke.

Fig. 2

Effect of diet and secondhand smoke (SHS) exposure on aortic constriction to phenylephrine (PE). (a, b) Dose-dependent aortic constriction with and without L-NNA from fat-1 mice exposed to filtered air (open squares) or SHS (solid squares) and fed an n-3 PUFA diet. (c, d) Dose-dependent aortic constriction with and without L-NNA from fat-1 mice exposed to filtered air (open triangles) or SHS (solid triangles) and fed an n-6 PUFA diet. Data were analyzed by two-way (exposure and dose) repeated measures ANOVA within diet followed by post hoc Holm-Sidak comparisons. In the absence of L-NNA there was a significant exposure- (p = 0.014) and dose-exposure interaction (p < 0.001) in mice fed the n-6 PUFA diet. In the presence of L-NNA, there was a significant dose-exposure interaction (p < 0.001) in mice fed the n-6 PUFA diet. *p < 0.05 versus air-exposed controls (n = 6–9/group).

Fig. 3

Effect of diet and secondhand smoke (SHS) exposure on aortic constriction to U46619. (a, b) Dose-dependent aortic constriction with and without L-NNA from fat-1 mice exposed to filtered air (open squares) or SHS (solid squares) and fed an n-3 PUFA diet. (c, d) Dose-dependent aortic constriction with and without L-NNA from fat-1 mice exposed to filtered air (open triangles) or SHS (solid triangles) and fed an n-6 PUFA diet. Data were analyzed by two-way (exposure and dose) repeated measures ANOVA within diet followed by post hoc Holm-Sidak comparisons. In the absence of L-NNA there was a significant dose-exposure interaction (p = 0.018) in mice fed the n-6 PUFA diet. In the presence of L-NNA, there was a significant dose-exposure interaction (p = 0.032) in mice fed the n-6 PUFA diet. *p < 0.05 versus air-exposed controls (n = 6–9/group).

Fig. 4

Effect of diet and secondhand smoke (SHS) exposure on mRNA expression in adipose tissue. mRNA expression, relative to the housekeeping gene hypoxanthine-guanine phosphoribosyltransferase (Hprt), of (a) heme oxygenase-1 (Hmox1), (b) NADPH:quinone oxidoreductase (Nqo1), (c) cytochrome P4501A1 (Cyp1a1), and (d) angiotensinogen (Agt) is adipose tissue of fat-1 mice was assessed by qPCR. Data were analyzed by two-way ANOVA followed by post hoc Holm-Sidak comparisons. For Hmox1 there was a significant exposure (p = 0.027) and diet-exposure interaction (p = 0.010). For Nqo1 there was a significant diet-exposure interaction (p= 0.037). For Cyp1a1 there was a significant diet (p < 0.001), exposure (p = 0.03) and diet-exposure interaction (p = 0.013). For Agt there was a significant exposure (p = 0.017) and diet-exposure interaction (p = 0.017). *p < 0.05 versus air-exposed controls within diet. ^#p < 0.05 versus the same exposure group fed the n-3 PUFA diet (n = 6–9/group).

Fig. 5

Effect of diet and secondhand smoke (SHS) exposure on total antioxidant capacity in mice. Serum total antioxidant capacity in fat-1 mice was compared by two-way ANOVA followed by post hoc Holm-Sidak comparisons. There was a significant diet (p < 0.001) and exposure (p = 0.007) on total antioxidant capacity. *p < 0.05 versus air-exposed controls within diet. ^#p < 0.05 versus the same exposure group fed the n-3 PUFA diet (n = 6–9/group).

Fig. 6

Effect of secondhand smoke (SHS) exposure of human nonsmokers on total antioxidant capacity. Serum total antioxidant capacity was compared between nonsmokers with and without SHS exposure by t-test (n = 20/group).