[Molecular engineering of hemoglobin for transfusion]

Abstract

The search for a safe alternative to conventional blood transfusion has been directed towards either the use of synthetic perfluorochemicals or the biochemical manipulation of highly purified stroma-free Hb solutions prepared from outdated bank blood. However when using human blood, one does not eliminate the risks of viral infections. A novel source of Hb appeared with recent biotechnology techniques enabling one to synthesize recombinant Hb from microorganisms (E coli or S. cerevisiae) whose genome has been modified to contain globin genes. Normal human Hb A in solution, i.e. outside the red cells, is not suited for direct usage as a blood substitute because i) its high oxygen affinity, due to the absence of 2,3 DPG in the plasma, precludes sufficient O2 unloading to the tissues; ii) at low concentration, relative to that in the red cells, tetrameric Hb dissociates into dimers which escape the circulatory system by renal filtration or rapidly oxidize to the non functional metHb form. Expression of alpha- and beta-globins in Escherichia coli and in Saccharomyces cerevisiae enables one to introduce appropriate mutation(s) in the globin genes resulting in the expression of a synthetic Hb with low oxygen affinity, resembling that of normal whole blood; functional Hb has also been produced in a soluble form either in E. coli or in yeast. The coexpression of beta globin chains and alpha globin subunits linked by a peptide bond results in the direct synthesis of stabilized and fully functional Hb tetramers. Lastly, dilute haemoglobin solutions are prone to autooxidize and the rate of oxidation appears to be inversely proportional with the oxygen affinity of the heme groups.(ABSTRACT TRUNCATED AT 250 WORDS)