Oxidant Mechanisms in Response to Ambient Air Particles Beatriz González-Flecha Department of Environmental Health Harvard School of Public Health Boston, MA, USA

Rats Mice Paramecia Oxygen toxicity: early evidence Mice Drosophila Rats Paramecia

Oxygen poisoning and X-irradiation: A mechanism in common R. Gershman et al. Nature, 1954 First demonstration of the involvement of oxygen free radicals in the mechanism of oxygen toxicity

Oxygen Free Radicals = Reactive Oxygen Species (ROS) O 2 e-e- e-e- e-e- e-e- O 2 -. H2O2H2O2 HO H2OH2O Produced in association to aerobic metabolism (1952)(1970’s) Toxic at high concentrations (1954) (1970’s) Able to promote cell proliferation and enzyme induction at sublethal concentrations (1962)(1990) Superoxide anion Hydrogen peroxide Hydroxyl radical

Main sources of ROS in mammalian tissues Intracellular sourceSpecies 1. Mitochondrial Respiratory Chain Ubiquinone O 2 -. NADH dehydrogrenase O Enoplasmic Reticulum NADH-cytochrome reductase O 2 -. or H 2 O 2 Cytochrome P450 O 2 -. Cytochrome b5 O Plasma Membrane Lipoxygenase 1 O 2 Prostaglandin synthase 1 O 2 NADH oxidase (PMN) O Cytosol a) soluble enzymes and proteins Hemoglobin O 2 -. Xanthine oxidase O 2 -. b) small molecules Flavins O 2 -. or H 2 O 2 Thiols O 2 -.

O 2 O 2 - H 2 O 2 HO 1 O 2 O 2 + H 2 O 2 SOD O 2 + H 2 O Catalase Carotene O 2 Radical Chain Protective mechanisms M M M Modified from Chance et al. Physiol. Rev. 59, (1979).

O 2 O 2 - H 2 O 2 HO 1 O 2 O 2 + H 2 O 2 SOD O 2 + H 2 O Catalase Carotene O 2 Radical Chain Protective mechanisms Modified from Chance et al. Physiol. Rev. 59, (1979). Damage to cellular components

Post-100% O 2 Reparative responses: Epithelial remodeling Enzyme induction Pulmonary Responses to Oxygen 20% O 2 Normoxia 85% O 2 Adaptive responses: Proliferation of epithelial cells Induction of antioxidant enzymes 100 % O 2 Damage to the lung epithelium Inflammation Edema

Cellular Responses to ROS ROS concentration

Health Effects of Ambient Air Particles

1943- Los Angeles, CA Visibility 3 Blocks. Numerous complaints watery eyes, nausea, & respiratory discomfort

20 People and 1,000's animals dead, 6,000 ill

1952- London, England 4,000 Dead

Ambient air particles have intrinsic toxicity Particle pollution, and not other pollutants, leads to increased death across much of the USA (HEI:

Particle Sources Anthropogenic sources Transportation Power plants Incinerators Wood burning Natural Sources Volcanoes Erosion Forest fires Sea spray Soil Biological (pollen, spores)

Ambient Air Particles and Oxidants CAPs increase luminol-enhanced chemiluminescence, and the oxidation of redox- sensitive fluorescent markers in PMN and alveolar macrophages in vitro Quinone radicals were detected in air per mg PM inhalation induces anti-oxidant enzymes Oxidants induce expression of pro-inflammatory cytokines

Mechanism of Pulmonary Oxidative Stress and Toxicity by PM Particle/cell interactions Direct action on intracellular sources of ROS Potentiation by macrophage-derived cytokines TNF-alpha, IL-8, etc.

Cardiac Effects of PM Neural mechanisms sympathetic/parasympathetic stimulation of the heart Direct action on the heart Soluble components (inorganic and organic) Insoluble (ultrafine/fine particles) Inflammatory mechanisms release of cytokine/chemokine into circulation

Summary The health effects of PM in humans as well as the biological effects of CAPs in animal and cell models are well documented The existing evidence strongly suggests that ROS are involved in the initiation steps of the mechanistic pathways leading from PM exposure to inflammatory effects and cardiopulmonary toxicity The cellular mechanisms of PM toxicity are currently under investigation