Impact of cell‐free hemoglobin on contracting skeletal muscle oxygen pressure dynamics: Potential therapeutic role of haptoglobin

Abstract

Free hemoglobin (Hb) associated with hemolytic diseases (i.e., sickle cell anemia) extravasates into vascular tissue and depletes nitric oxide (NO), which leads to impaired vascular function and could disrupt skeletal muscle metabolic control during exercise. We tested the hypothesis that: 1) free Hb would extravasate into skeletal muscle tissue impairing the contracting skeletal muscle O2 delivery/O2 utilization ratio (microvascular PO2, PO2mv) to a similar extent as that observed following NO synthase (NOS) blockade, and 2) that the Hb scavenging protein haptoglobin (Hp) would prevent Hb extravasation and inhibit these skeletal muscle tissue effects. PO2mv was measured in eight healthy rats (phosphorescence quenching) at rest and during 180s of electrically induced (1‐Hz) twitch spinotrapezius muscle contractions (experiment 1). A second subset of seven rats was also used to investigate the effects of Hb+Hp (experiment 2). For both experiments, measurements were made: 1) during control conditions, 2) following a bolus infusion of either Hb (50 mg/kg) or Hb+Hp (50 mg/kg, bound Hb), and 3) following local superfusion of NG‐nitro‐l‐arginine methyl ester (L‐NAME; 10 mg/kg). Additional experiments were completed to visualize Hb extravasation into the muscular tissue using Click chemistry techniques. There were no significant differences in the PO2mv observed at rest for any condition in either experiment (p>0.05 for all). In experiment 1, both Hb and L‐NAME reduced the PO2mv significantly during the steady‐state of muscle contractions when compared to control conditions with no differences between Hb and L‐NAME conditions (control: 24 ± 1, Hb: 21 ± 1, L‐NAME: 20 ± 1 mmHg, p<0.05). In experiment 2, only L‐NAME resulted in a significantly lower PO2mv during the steady‐state of muscle contractions (control: 25 ± 1, Hb+Hp: 22 ± 2, L‐NAME: 18 ± 1 mmHg, p<0.05). Free Hb lowered the blood‐myocyte O2 driving force to a level not significantly different from L‐NAME. However, infusing Hb bound to Hp resulted in no significant differences in steady‐state PO2mv during muscle contractions when compared to control. Surprisingly, we did not observe Hb accumulation in skeletal muscle tissue. Taken together these data suggest that free Hb impairs O2 delivery/utilization via a NO scavenging effect which would presumably disrupt oxidative metabolism and shorten the onset of fatigue during exercise. Furthermore, the unchanged PO2mv steady‐state observed following Hb+Hp further suggests that therapeutic administration of the Hb binding protein haptoglobin may restore skeletal muscle metabolic control and potentially exercise tolerance in those afflicted with hemolytic diseases.Support or Funding InformationFunded by NIH (R01HL125642) to DCI and Colorado Nutrition and Obesity Research Center (P30DK048520) award to SKF.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.