Ozonized carbon black induces mitochondrial dysfunction and DNA damage

Area of Science:

• Environmental Toxicology
• Cellular and Molecular Toxicology
• Air Pollution Health Effects

Background:

• Black carbon and tropospheric ozone (O3) are significant air pollutants in China with known inhalation hazards.
• Ozone can oxidize black carbon, forming secondary particles whose health impacts remain largely unknown.
• Understanding the toxicity of these secondary particles is crucial for public health risk assessment.

Purpose of the Study:

• To characterize the cytotoxicity of secondary particles formed from ozone-oxidized carbon black (OCB) compared to untreated carbon black (UCB).
• To investigate the molecular pathways involved in OCB-induced toxicity in bronchial epithelial cells (16HBE) and mice.
• To assess the genotoxicity and mitochondrial dysfunction induced by UCB and OCB.

Main Methods:

• Carbon black (untreated and ozonized) was used as a proxy for black carbon.
• In vitro assays in 16HBE cells assessed cell viability, reactive oxygen species (ROS), glutathione redox state, mitochondrial membrane potential (MMP), and ATP levels.
• Genotoxicity was evaluated using alkaline comet assays, cytokinesis-block micronucleus (CBMN) tests, and in vivo bone marrow micronucleus (BMN) tests, alongside serum 8-hydroxy-2'-deoxyguanosine (8-OHdG) measurement.

Main Results:

• Ozonized carbon black (OCB) exposure led to decreased cell viability, increased cell death, and reduced mitochondrial membrane potential (MMP) in 16HBE cells compared to untreated carbon black (UCB).
• UCB induced higher intracellular ROS levels than OCB, suggesting oxidative stress is not the primary driver of OCB toxicity.
• OCB exposure showed increased comet length, indicating enhanced genotoxicity, while CBMN and BMN tests were negative for both UCB and OCB.

Conclusions:

• Ozonization significantly enhances the mitochondrial toxicity and genotoxicity of carbon black particles.
• The toxic effects of OCB appear to be mediated by mechanisms beyond oxidative stress.
• These findings highlight the potential health risks associated with secondary air pollutants formed from black carbon.