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Macrophages as a major source of oxygen radicals in the hyperoxic newborn rat lung
Robert P Jankov1, Leslie Johnstone, Xiaoping Luo
1Canadian Institutes of Health Research Group in Lung Development and Lung Biology Programme, Research Institute, The Hospital for Sick Children, Toronto, Canada.
Abstract:
The lungs of newborn rats exposed to 60% O(2) for 14 d were found to have a greatly increased cyanide-insensitive O(2) consumption, reflecting increased reactive oxygen species (ROS) formation. Exposure of the lung to hyperoxia is known to increase the production of ROS by mitochondria. We hypothesized that macrophages may also be a major contributor to this increase. Newborn rat pups were exposed to either air or 60% O(2) for 14 d and received either intraperitoneal gadolinium chloride (GdCl(3)) to abrogate macrophage influx, or inert vehicle. Lung homogenates were equilibrated in either 21% or 100% O(2) and total and cyanide-insensitive O(2) consumption, as well as nitric oxide accumulation were measured polarographically. Citrate synthase, a marker of mitochondrial mass, and nitrotyrosine, a marker of peroxynitrite formation, were quantified by Western blot. In addition to increased macrophage numbers, the lungs of 60% O(2)-exposed animals had greatly increased cyanide-insensitive O(2) consumption (p <.05 compared to air controls) and immunoreactive nitrotyrosine (p <.05), which were all completely abrogated by treatment with GdCl(3). Exposure to 60% O(2) for 14 d had no effect on peroxynitrite-independent nitric oxide release or mitochondrial mass. We conclude that increased ROS in the lungs of newborn rats exposed to 60% O(2) for 14 d was likely to be caused, in significant part, by the presence of increased numbers of macrophages.
Insights
In newborn rats exposed to high oxygen, increased reactive oxygen species (ROS) in lungs were linked to more macrophages. Gadolinium chloride treatment reduced ROS, indicating macrophages are a key source of lung oxidative stress.
Area of Science:
- Pulmonary Medicine
- Cellular Biology
- Toxicology
Background:
- Hyperoxia (high oxygen exposure) in newborns increases reactive oxygen species (ROS) production in the lungs, primarily attributed to mitochondria.
- The potential contribution of other cell types, such as macrophages, to this ROS increase remains less understood.
Purpose of the Study:
- To investigate the role of macrophages as a significant source of increased reactive oxygen species (ROS) in the lungs of newborn rats exposed to hyperoxia.
- To determine if inhibiting macrophage influx can mitigate hyperoxia-induced oxidative stress in the lungs.
Main Methods:
- Newborn rats were exposed to either 60% oxygen (hyperoxia) or air for 14 days.
- Animals received intraperitoneal injections of gadolinium chloride (GdCl(3)) to block macrophage influx or a vehicle control.
- Lung homogenates were analyzed for oxygen consumption (total and cyanide-insensitive), nitric oxide accumulation, citrate synthase (mitochondrial mass marker), and nitrotyrosine (peroxynitrite marker).
Main Results:
- Hyperoxia exposure led to increased macrophage numbers in the lungs.
- Cyanide-insensitive oxygen consumption and nitrotyrosine levels were significantly elevated in hyperoxia-exposed rats, indicating increased ROS and peroxynitrite formation.
- Gadolinium chloride treatment completely abrogated these hyperoxia-induced increases in ROS and nitrotyrosine.
- Hyperoxia did not affect nitric oxide release or mitochondrial mass.
Conclusions:
- Macrophages significantly contribute to the increased reactive oxygen species (ROS) formation in the lungs of newborn rats exposed to hyperoxia.
- Inhibiting macrophage influx with gadolinium chloride effectively reduces hyperoxia-induced lung oxidative stress.
- These findings highlight macrophages as a critical cellular target for mitigating hyperoxia-related lung injury in neonates.