Postconditioning with inhaled carbon monoxide counteracts apoptosis and neuroinflammation in the ischemic rat retina

PLoS One. 2012;7(9):e46479. doi: 10.1371/journal.pone.0046479. Epub 2012 Sep 28.

Abstract

Purpose: Ischemia and reperfusion injury (I/R) of neuronal structures and organs is associated with increased morbidity and mortality due to neuronal cell death. We hypothesized that inhalation of carbon monoxide (CO) after I/R injury ('postconditioning') would protect retinal ganglion cells (RGC).

Methods: Retinal I/R injury was performed in Sprague-Dawley rats (n = 8) by increasing ocular pressure (120 mmHg, 1 h). Rats inhaled room air or CO (250 ppm) for 1 h immediately following ischemia or with 1.5 and 3 h latency. Retinal tissue was harvested to analyze Bcl-2, Bax, Caspase-3, HO-1 expression and phosphorylation of the nuclear transcription factor (NF)-κB, p38 and ERK-1/2 MAPK. NF-κB activation was determined and inhibition of ERK-1/2 was performed using PD98059 (2 mg/kg). Densities of fluorogold prelabeled RGC were analyzed 7 days after injury. Microglia, macrophage and Müller cell activation and proliferation were evaluated by Iba-1, GFAP and Ki-67 staining.

Results: Inhalation of CO after I/R inhibited Bax and Caspase-3 expression (Bax: 1.9 ± 0.3 vs. 1.4 ± 0.2, p = 0.028; caspase-3: 2.0 ± 0.2 vs. 1.5 ± 0.1, p = 0.007; mean ± S.D., fold induction at 12 h), while expression of Bcl-2 was induced (1.2 ± 0.2 vs. 1.6 ± 0.2, p = 0.001; mean ± S.D., fold induction at 12 h). CO postconditioning suppressed retinal p38 phosphorylation (p = 0.023 at 24 h) and induced the phosphorylation of ERK-1/2 (p<0.001 at 24 h). CO postconditioning inhibited the expression of HO-1. The activation of NF-κB, microglia and Müller cells was potently inhibited by CO as well as immigration of proliferative microglia and macrophages into the retina. CO protected I/R-injured RGC with a therapeutic window at least up to 3 h (n = 8; RGC/mm(2); mean ± S.D.: 1255 ± 327 I/R only vs. 1956 ± 157 immediate CO treatment, vs. 1830 ± 109 1.5 h time lag and vs. 1626 ± 122 3 h time lag; p<0.001). Inhibition of ERK-1/2 did not counteract the CO effects (RGC/mm(2): 1956 ± 157 vs. 1931 ± 124, mean ± S.D., p = 0.799).

Conclusion: Inhaled CO, administered after retinal ischemic injury, protects RGC through its strong anti-apoptotic and anti-inflammatory effects.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Inhalation
  • Animals
  • Anti-Inflammatory Agents / administration & dosage*
  • Apoptosis / drug effects*
  • Carbon Monoxide / administration & dosage*
  • Caspase 3 / genetics
  • Caspase 3 / metabolism
  • Cell Movement / drug effects
  • Enzyme Activation
  • Female
  • Gene Expression / drug effects
  • Heme Oxygenase-1 / genetics
  • Heme Oxygenase-1 / metabolism
  • Ischemia / drug therapy
  • Male
  • Mitogen-Activated Protein Kinases / metabolism
  • NF-kappa B / metabolism
  • Neuroglia / drug effects
  • Neuroglia / physiology
  • Neuroprotective Agents / administration & dosage*
  • Phosphorylation
  • Protein Processing, Post-Translational / drug effects
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Reperfusion Injury / drug therapy*
  • Retina / drug effects
  • Retina / pathology
  • Retinal Ganglion Cells / drug effects
  • Retinal Ganglion Cells / pathology
  • Retinal Vessels / pathology
  • Retinitis / prevention & control*
  • bcl-2-Associated X Protein / genetics
  • bcl-2-Associated X Protein / metabolism

Substances

  • Anti-Inflammatory Agents
  • Bax protein, rat
  • NF-kappa B
  • Neuroprotective Agents
  • Proto-Oncogene Proteins c-bcl-2
  • bcl-2-Associated X Protein
  • Carbon Monoxide
  • Heme Oxygenase-1
  • Mitogen-Activated Protein Kinases
  • Casp3 protein, rat
  • Caspase 3

Grant support

This work was supported by departmental funding. The article processing charge was funded by the German Research Foundation (DFG) and the Albert Ludwigs University Freiburg in the funding programme “Open Access Publishing”. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.