Detrimental association between quadriceps strength and exposure to polycyclic aromatic hydrocarbons in elderly adults

Benzo[a]pyrene exposure in muscle triggers sarcopenia through aryl hydrocarbon receptor-mediated reactive oxygen species production

BACKGROUND

Benzo[a]pyrene (BaP), a toxic carcinogen, is associated with various adverse effects but is rarely discussed in muscle-related disorders. This study investigated in vitro and in vivo effects triggered by BaP exposure in muscles and hypothesized that exposure might induce conditions similar to sarcopenia due to the shared mechanism of oxidative stress. In vitro experiments used C2C12 mouse myoblasts to examine effects induced by BaP exposure in control (untreated) and BaP-treated (10 µM/ml) muscle cells. An established TNF-α-treated sarcopenia model was utilized to verify our results. In vivo experiments compared immunohistochemical staining of sarcopenia-related markers in rats exposed to clean air and polluted air.

RESULTS

In C2C12 cells, after 2-72 h of BaP exposure, elevated mRNA and protein expressions were observed in aryl hydrocarbon receptor (AhR) and cytochrome P450 1A1, subsequently in ROS (NOX2 and NOX4) production, inflammatory cytokines (IL-6, TNF-α, and NF-kB), and proteins mediating apoptotic cell death (caspase-3 and PARP). Two myokines also altered mRNA and protein expressions akin to changes in sarcopenia, namely decreased irisin levels and increased myostatin levels. In addition, N-acetylcysteine, a well-known antioxidant, led to decrease in oxidative markers induced by BaP. The validation by TNF-α-treated sarcopenia model revealed comparable biological responses in either TNF-α or BaP treated C2C12 cells. In vivo experiments with rats exposed to air pollution showed increased expression of BaP, AhR, 8-hydroxydeoxyguanosine, and myostatin and decreased irisin expression in immunohistochemical staining.

CONCLUSIONS

Our results suggest that BaP exerts deleterious effects on the muscle, leading to conditions indicative of sarcopenia. Antioxidant supplementation may be a treatment option for BaP-induced sarcopenia, but further validation studies are needed.

The relationship between polycyclic aromatic hydrocarbons exposure and serum klotho among adult population

Background

Klotho is an important factor involving aging process. Recently, polycyclic aromatic hydrocarbons (PAHs) exposure was reported to have adverse impact on DNA methylation associated with aging. The aim of the current study was to determine the relationship between serum klotho and PAHs exposure in an adult population.

Methods

A total of 2597 participants obtained from NHANES 2015–2016 were included in this cross-sectional study. Serum klotho levels were analyzed by enzyme-linked immunosorbent assay (ELISA). PAHs exposure was estimated by urinary sample using liquid chromatography-tandem mass spectrometry. The relationship between serum klotho and exposure to PAHS was analyzed by a multivariable linear regression model.

Results

2-napthol and 3-fluorene were significantly associated with decreased klotho. After fully adjusting pertinent variables, PAH exposure was significantly associated with decreased klotho, particularly in men.

Conclusion

In the present study we highlighted the significant association between PAHs exposure and serum klotho levels. The importance of environmental effect on aging process and age-related disorders should be paid more attention and clinical intervention is necessary.

The gender-specific adverse association of polycyclic aromatic hydrocarbons on skeletal muscle mass and strength in the general adults and the possible mechanisms in experimental rats

Whether polycyclic aromatic hydrocarbons (PAHs) exposure is associated with muscle mass and muscle strength has been scantly investigated. The cross-sectional associations of urinary PAH metabolites with appendicular skeletal muscle mass and hand grip strength in adults were first investigated in the National Health and Nutrition Examination Survey (NHANES). Laboratory study was further carried out to examine the effect of PAHs on skeletal muscle mass and strength. 2742 and 2462 US adults were finally analyzed for muscle mass and muscle strength, respectively. In male participants, urinary PAH metabolites were found to show an inverse relationship with muscle mass and grip strength. In female participants, no significant relationship was found between urinary PAH metabolites with muscle mass or grip strength. In male Sprague-Dawley (SD) rats, administration of B [a]P induced muscle atrophy when compared with the control. However, muscle mass and strength were not significantly altered in female rats. The variations in muscle morphology parameters were accompanied by significant decrease in plasma testosterone levels in the B [a]P-treated male rats. Testosterone co-treatment significantly mitigated B [a]P mediated damages in skeletal muscle in male rats. The results of the present study indicate that there may be a gender-specific causal relationship between the PAHs and muscle atrophy.