Continuous inhalation of carbon monoxide induces right ventricle ischemia and dysfunction in rats with hypoxic pulmonary hypertension

Localized delivery of carbon monoxide

The heme oxygenase (HO)/carbon monoxide (CO) system is a physiological feedback loop orchestrating various cell-protective effects in response to cellular stress. The therapeutic use of CO is impeded by safety challenges as a result of high CO-Hemoglobin formation following non-targeted, systemic administration jeopardizing successful CO therapies as of this biological barrier. Another caveat is the use of CO-Releasing Molecules containing toxicologically critical transition metals. An emerging number of local delivery approaches addressing these issues have recently been introduced and provide exciting new starting points for translating the fascinating preclinical potential of CO into a clinical setting. This review will discuss these approaches and link to future delivery strategies aiming at establishing CO as a safe and effective medication of tomorrow.

Rapid quantification of myocardial fibrosis: a new macro-based automated analysis

Background

Fibrosis is associated with various cardiac pathologies and dysfunction. Current quantification methods are time-consuming and laborious. We describe a semi-automated quantification technique for myocardial fibrosis and validated this using traditional methods.

Methods

Pulmonary Hypertension (PH) was induced in adult Wistar rats by subcutaneous monocrotaline (MCT) injection(40 mg/kg). Cryosections of myocardial tissue (5 μm) of PH rats (n = 9) and controls (n = 9) were stained using Picrosirius red and scanned with a digital microscopic MIRAX slide scanner. From these sections 21 images were taken randomly of each heart. Using ImageJ software a macro for automated image analysis of the amount of fibrosis was developed. For comparison, fibrosis was quantified using traditional polarisation microscopy. Both methods were correlated and validated against stereology as the gold standard. Furthermore, the method was tested in paraffin-embedded human tissues.

Results

Automated analysis showed a significant increase of fibrosis in PH hearts vs. control. Automated analysis correlated with traditional polarisation and stereology analysis (r² = 0.92 and r² = 0.95 respectively). In human heart, lungs, kidney, and liver, a similar correlation with stereology (r² = 0.91) was observed. Time required for automated analysis was 22% and 33% of the time needed for stereology and polarisation analysis respectively.

Conclusion

Automated quantification of fibrosis is feasible, objective, and time-efficient.

Electronic supplementary material

The online version of this article (doi:10.1007/s13402-011-0035-7) contains supplementary material, which is available to authorized users.

Divergent cardiopulmonary actions of heme oxygenase enzymatic products in chronic hypoxia

Background

Hypoxia and pressure-overload induce heme oxygenase-1 (HO-1) in cardiomyocytes and vascular smooth muscle cells (VSMCs). HO-1^−/− mice exposed to chronic hypoxia develop pulmonary arterial hypertension (PAH) with exaggerated right ventricular (RV) injury consisting of dilation, fibrosis, and mural thrombi. Our objective was to indentify the HO-1 product(s) mediating RV protection from hypoxic injury in HO-1^−/− mice.

Methodology/Principal Findings

HO-1^−/− mice were exposed to seven weeks of hypoxia and treated with inhaled CO or biliverdin injections. CO reduced right ventricular systolic pressure (RVSP) and prevented hypoxic pulmonary arteriolar remodeling in both HO-1^−/− and control mice. Biliverdin had no significant effect on arteriolar remodeling or RVSP in either genotype. Despite this, biliverdin prevented RV failure in the hypoxic HO-1^−/− mice (0/14 manifested RV wall fibrosis or thrombus), while CO-treated HO-1^−/− mice developed RV insults similar to untreated controls. In vitro, CO inhibited hypoxic VSMC proliferation and migration but did not prevent cardiomyocyte death from anoxia-reoxygenation (A-R). In contrast, bilirubin limited A-R-induced cardiomyocyte death but did not inhibit VSMC proliferation and migration.

Conclusions/Significance

CO and bilirubin have distinct protective actions in the heart and pulmonary vasculature during chronic hypoxia. Moreover, reducing pulmonary vascular resistance may not prevent RV injury in hypoxia-induced PAH; supporting RV adaptation to hypoxia and preventing RV failure must be a therapeutic goal.

Inhalation of carbon monoxide ameliorates collagen-induced arthritis in mice and regulates the articular expression of IL-1beta and MCP-1

Carbon monoxide (CO), long considered a toxic gas, has recently been shown to mediate anti-inflammatory effects in various animal models. The aim of this study was to investigate whether the inhalation of CO ameliorated collagen-induced arthritis (CIA) in mice. CIA was induced in female DBA/1 mice by the injection of an anti-type II collagen antibody and lipopolysaccharide. The CO treatment group was exposed to CO gas at a concentration of 200 ppm in a closed cage starting on the day of the injection with an anti-type II collagen antibody and throughout the remaining study period. The clinical arthritis scores was examined daily for swelling of the paws as a sign of arthritis. For histopathology, the sections of the hind legs were evaluated by hematoxylin-eosin staining. Moreover, we evaluated the expression of interleukin (IL)-1beta and monocyte chemoattractant protein-1 (MCP-1) mRNA in the hind paws. Both clinical arthritis scores as well as histological findings of joint inflammation were significantly reduced in mice treated with CO gas inhalation compared to untreated mice. Further, CO significantly inhibited the increased expression of IL-1beta and MCP-1 mRNA in paws at day 3 after the induction of arthritis. In conclusion, the inhalation of CO protected mice from the synovial inflammation of CIA. Based on these data, the beneficial effects of CO in murine RA model may be attributed to its anti-inflammatory properties.

CO-MP4, a polyethylene glycol-conjugated haemoglobin derivative and carbon monoxide carrier that reduces myocardial infarct size in rats

BACKGROUND AND PURPOSE

MP4 (Hemospan) is a Hb-based oxygen therapeutic agent, based on polyethylene-glycol (PEG) conjugation to Hb, undergoing clinical trials as an oxygen carrier. This study describes the functional interaction between MP4 and carbon monoxide (CO), as a CO delivery agent, and the effects of CO-MP4 on myocardial infarct size following ischaemia and reperfusion in rats.

EXPERIMENTAL APPROACH

Kinetic measurements of CO-MP4 binding were used to evaluate the effects of PEG modification on Hb subunit structure/function and to calculate CO-MP4 equilibrium constants. CO transport by CO-MP4 was shown by ligand (O2/CO) partitioning between MP4 and red blood cell (RBC)-Hb. Pharmacological effects of CO-MP4 were studied on myocardial infarction in rats.

KEY RESULTS

CO binding kinetics show primary structural/functional effects on beta chains in MP4, with alpha chains maintaining the ability to undergo tertiary conformational transition. CO confers long-term, room-temperature stability and is able to rapidly re-equilibrate between MP4 and RBCs. In a rat model of myocardial infarct, in contrast to oxy-MP4, CO-MP4 reduced infarct size when administered prior to the induction of ischaemia.

CONCLUSIONS AND IMPLICATIONS

MP4 PEGylation chemistry modifies the individual function of Hb subunits, but results in an overall CO equilibrium constant similar to that for unmodified Hb. CO-MP4 is able to deliver CO to the circulation and reduces ischaemia/reperfusion injury in rats, providing the first evidence for this drug as a CO therapeutic agent.