Identification of a small molecule that increases hemoglobin oxygen affinity and reduces SS erythrocyte sickling.

Small molecules that increase the oxygen affinity of human hemoglobin may reduce sickling of red blood cells in patients with sickle cell disease. We screened 38,700 compounds using small molecule microarrays and identified 427 molecules that bind to hemoglobin. We developed a high-throughput assay for evaluating the ability of the 427 small molecules to modulate the oxygen affinity of hemoglobin.

Hemodynamic responses to a hemoglobin bis-tetramer and its polyethylene glycol conjugate.

Background: The design of hemoglobin-based oxygen carriers (HBOCs) poses a significant challenge as clinical trials of many materials have reported adverse side effects that may come from the scavenging of the vasodilator nitric oxide (NO). A compensating reaction, reduction of endogenous nitrite by hemoglobin (Hb) and its derivatives, generates NO. Polyethylene glycol (PEG) conjugation of Hb enhances the rate of the reaction.

Hemoglobin bis-tetramers via cooperative azide-alkyne coupling.

Cross-linked hemoglobin-azides react with a bis-alkyne to form a bis-tetramer through sequential "click" reactions where the second step is promoted by the first.

Enhancing nitrite reductase activity of modified hemoglobin: bis-tetramers and their PEGylated derivatives.

The clinical evaluation of stabilized tetrameric hemoglobin as alternatives to red cells revealed that the materials caused significant increases in blood pressure and related problems and this was attributed to the scavenging of nitric oxide and extravasation. The search for materials with reduced vasoactivity led to the report that conjugates of hemoglobin tetramers and polyethylene glycol (PEG) chains did not elicit these pressor effects. However, this material does not deliver oxygen efficiently due to its lack of cooperativity and high oxygen affinity, making it unsuitable as an oxygen carrier.

Polyethylene glycol conjugation enhances the nitrite reductase activity of native and cross-linked hemoglobin.

Although stabilized hemoglobins have been evaluated as oxygen-carrying replacements for red cells in transfusions, in vivo evaluations have noted that these materials are associated with vasoactivity, a serious complication. Scavenging of endogenous nitric oxide by the deoxyheme sites of the stabilized proteins is one likely source of vasoactivity. Recent reports indicate that modification of cell-free hemoglobin derivatives with multiple chains of polyethylene glycol (PEG) suppresses vasoactivity.