Reduction in hemoglobin-oxygen affinity results in the improvement of exercise capacity in mice with chronic heart failure.

OBJECTIVES: This study examined whether a reduction in hemoglobin-oxygen affinity improves exercise capacity in mice with heart failure. BACKGROUND: Exercise intolerance is a major determinant of quality of life in patients with chronic heart failure. One of the major goals of the treatment for chronic heart failure is to improve quality of life. METHODS: Four weeks after left coronary ligation, we transplanted bone marrow cells isolated from the transgenic mice expressing a hemoglobin variant with low oxygen affinity, Presbyterian, into the lethally irradiated mice with heart failure or administered a synthetic allosteric modifier of hemoglobin. The mice were then exercised on a treadmill. RESULTS: Four weeks after the left coronary artery ligation, mice showed cardiac dysfunction and chamber dilation, which were characteristics of heart failure. The transplantation led to a reduction in hemoglobin-oxygen affinity and an increase in oxygen supply for skeletal muscle without changes in muscle properties. The transplanted mice showed improved running performance on a treadmill despite impaired cardiac contractility. Furthermore, administration of the synthetic allosteric modifier of hemoglobin showed a similar effect. CONCLUSIONS: Allosteric modification of hemoglobin represents a therapeutic option for improving exercise capacity in patients with chronic heart failure. One mechanism of improvement in exercise capacity is enhanced oxygen delivery in the skeletal muscle.

Heme structures of five variants of hemoglobin M probed by resonance Raman spectroscopy.

The alpha-abnormal hemoglobin (Hb) M variants show physiological properties different from the beta-abnormal Hb M variants, that is, extremely low oxygen affinity of the normal subunit and extraordinary resistance to both enzymatic and chemical reduction of the abnormal met-subunit. To get insight into the contribution of heme structures to these differences among Hb M's, we examined the 406.7-nm excited resonance Raman (RR) spectra of five Hb M's in the frequency region from 1700 to 200 cm(-1). In the high-frequency region, profound differences between met-alpha and met-beta abnormal subunits were observed for the in-plane skeletal modes (the nu(C=C), nu(37), nu(2), nu(11), and nu(38) bands), probably reflecting different distortions of heme structure caused by the out-of-plane displacement of the heme iron due to tyrosine coordination. Below 900 cm(-1), Hb M Iwate [alpha(F8)His --> Tyr] exhibited a distinct spectral pattern for nu(15), gamma(11), delta(C(beta)C(a)C(b))(2,4), and delta(C(beta)C(c)C(d))(6,7) compared to that of Hb M Boston [alpha(E7)His --> Tyr], although both heme irons are coordinated by Tyr. The beta-abnormal Hb M variants, namely, Hb M Hyde Park [beta(F8)His --> Tyr], Hb M Saskatoon [beta(E7)His --> Tyr], and Hb M Milwaukee [beta(E11)Val --> Glu], displayed RR band patterns similar to that of metHb A, but with some minor individual differences. The RR bands characteristic of the met-subunits of Hb M's totally disappeared by chemical reduction, and the ferrous heme of abnormal subunits was no longer bonded with Tyr or Glu. They were bonded to the distal (E7) or proximal (F8) His, and this was confirmed by the presence of the nu(Fe-His) mode at 215 cm(-1) in the 441.6-nm excited RR spectra. A possible involvement of heme distortion in differences of reducibility of abnormal subunits and oxygen affinity of normal subunits is discussed.

Changes of near-UV CD spectrum of human hemoglobin upon oxygen binding: a study of mutants at alpha 42, alpha 140, beta 145 tyrosine or beta 37 tryptophan.

The deoxy-form of human adult hemoglobin (Hb A) exhibits a distinct negative CD band at 287 nm that disappears in the oxy-form. It has been suggested that the negative CD band is due to the environmental alteration of Tyr-alpha 42 or Trp-beta 37 at the alpha(1)beta(2) contact upon deoxygenation. To evaluate the contributions of the aromatic residues at the alpha(1)beta(2) contact and the penultimate tyrosine residues of the alpha and beta subunits (alpha 140 and beta 145) to the negative CD band, three recombinant (r) Hbs (rHb Ser-alpha 42, rHb His-beta 37, and rHb Thr-beta 145) were produced in Escherichia coli, and we compared the near-uv CD spectra of these three rHbs and Hb Rouen (Tyr-alpha 140-->His) with the spectra of Hb A under the condition in which all mutant Hbs were able to undergo the T-->R transition (Hill's n > 2.0). The contributions of Tyr-alpha 42, Trp-beta 37, Tyr-alpha 140, and Tyr-beta 145 to the negative CD band were estimated from changes in the ellipticity of the negative CD band at 287 nm to be 4, 18, 32, and 27%, respectively. These results indicate that environmental alteration of the penultimate tyrosine residues caused by the formation of salt bridges upon the R-->T transition is primarily responsible for the negative CD band.

Changes in the abnormal alpha-subunit upon CO-binding to the normal beta-subunit of Hb M Boston: resonance Raman, EPR and CD study.

Heme-heme interaction in Hb M Boston (His alpha 58-->Tyr) was investigated with visible and UV resonance Raman (RR), EPR, and CD spectroscopies. Although Hb M Boston has been believed to be frozen in the T quaternary state, oxygen binding exhibited appreciable co-operativity (n=1.4) and the near-UV CD spectrum indicated weakening of the T marker at pH 9.0. Binding of CO to the normal beta-subunit gave no change in the EPR and visible Raman spectra of the abnormal alpha-subunit at pH 7.5, but it caused an increase of EPR rhombicity and significant changes in the Raman coordination markers as well as the Fe(III)-tyrosine related bands of the alpha-subunit at pH 9.0. The UVRR spectra indicated appreciable changes of Trp but not of Tyr upon CO binding to the alpha-subunit at pH 9.0. Therefore, we conclude that the ligand binding to the beta heme induces quaternary structure change at pH 9.0 and is communicated to the alpha heme, presumably through His beta 92-->Trp beta 37-->His alpha 87.