Artificial space weathering to mimic solar wind enhances the toxicity of lunar dust simulants in human lung cells

During NASA's Apollo missions, inhalation of dust particles from
lunar regolith was identified as a potential occupational hazard
for astronauts. These fine particles adhered tightly
to spacesuits and were unavoidably brought into the living areas
of the spacecraft. Apollo astronauts reported that exposure to the dust
caused intense respiratory and ocular irritation. This problem is
a potential challenge for the Artemis Program, which aims to return humans
to the Moon for extended stays in this decade. Since lunar dust is
“weathered” by space radiation, solar wind, and the incessant
bombardment of micrometeorites, we investigated whether treatment of lunar
regolith simulants to mimic space weathering enhanced their toxicity. Two
such simulants were employed in this research, Lunar Mare
Simulant-1 (LMS-1), and Lunar Highlands Simulant-1 (LHS-1), which were
added to cultures of human lung epithelial cells (A549) to simulate lung
exposure to the dusts. In addition to pulverization, previously shown to
increase dust toxicity sharply, the simulants were exposed to hydrogen gas
at high temperature as a proxy for solar wind exposure. This treatment
further increased the toxicity of both simulants, as measured by
the disruption of mitochondrial function, and damage to DNA both in
mitochondria and in the nucleus. By testing the effects of supplementing
the cells with an antioxidant (N-acetylcysteine), we showed that a
substantial component of this toxicity arises from free radicals. It
remains to be determined to what extent the radicals arise from the dust
itself, as opposed to their active generation by inflammatory processes in
the treated cells.