O-raffinose cross-linking markedly reduces systemic and renal vasoconstrictor effects of unmodified human hemoglobin

The hemodynamic effects of a 20% exchange-transfusion with different solutions of highly purified human hemoglobin A-zero (A0) were evaluated. We compared unmodified hemoglobin with hemoglobin cross-linked with O-raffinose. Unmodified hemoglobin increased systemic vascular resistance and mean arterial pressure more than the O-raffinose cross-linked hemoglobin solution (by approximately 45% and approximately 14%, respectively). Unmodified hemoglobin markedly reduced cardiac output (CO) by approximately 21%, whereas CO was unaffected by the O-raffinose cross-linked hemoglobin solution. Unmodified and O-raffinose cross-linked hemoglobin solutions increased mean arterial pressure to comparable extents ( approximately 14% and approximately 9%, respectively). Unmodified hemoglobin increased renal vascular resistance 2-fold and reduced the glomerular filtration rate by 58%. In marked contrast, the O-raffinose cross-linked hemoglobin had no deleterious effect on the glomerular filtration rate, renal blood flow, or renal vascular resistance. The extents to which unmodified and O-raffinose cross-linked hemoglobin solutions inactivated nitric oxide also were compared using three separate in vitro assays: platelet nitric oxide release, nitric oxide-stimulated platelet cGMP production, and endothelium-derived relaxing factor-mediated inhibition of platelet aggregation. Unmodified hemoglobin inactivated or oxidized nitric oxide to a greater extent than the O-raffinose cross-linked hemoglobin solutions in all three assays. In summary, O-raffinose cross-linking substantially reduced the systemic vasoconstriction and the decrease in CO induced by unmodified hemoglobin and eliminated the deleterious effects of unmodified hemoglobin on renal hemodynamics and function. We hypothesize that O-raffinose cross-linking reduces the degree of oxidation of nitric oxide and that this contributes to the reduced vasoactivity of this modified hemoglobin.