Certain particle compounds may directly generate ROS in vivo because of their surface chemistry (eg, metals, organic compounds, and semiquinones) or after bioactivation by cytochrome P450 systems (eg, polycyclic aromatic hydrocarbon conversion to quinones).6, 290 a, 290 b A particle surface or anions present on otherwise more inert particles may disrupt iron homeostasis in the lung and thereby also generate ROS via Fenton reactions.291
Other PM constituents may do so indirectly by the upregulation of endogenous cellular
sources (eg, nicotinamide adenine dinucleotide phosphate [NADPH]-RRB- oxidase) 292,293 or by perturbing organelle function (eg, mitochondria) by taken - up PM components.261 Particle stimulation of irritant and afferent ANS fibers may also play a role in local and systemic oxidative stress formation.294 Given the rich antioxidant defenses in the lung fluid, secondarily generated oxidization products of endogenous molecules (eg, oxidized phospholipids,
proteins) or a reduction in endogenous antioxidants
per se may be responsible at least in part for the state of oxidative stress in the lungs (along with instigating the subsequent cellular responses) rather
than ROS derived directly from PM and its constituents.
The Journal of Applied Physiology found that that's more
per gram
than other popular
protein sources such as eggs, milk (including casein
protein, which is also available as a supplement), and soy
protein.