The “intrinsic toxicity” of the hemoglobin molecule is likely to be responsible for these side effects.
Oxidative stress produces highly reactive “ferryl” intermediates at the heme iron and free radicals elsewhere in the protein.
At the University of Essex basic science funded by the UK Biotechnology and Biological Sciences Research Council (BBSRC) has revealed that introducing specific amino acid residues (tyrosine) on the hemoglobin protein can detoxify the protein. This is achieved by enabling the body’s own defences - vitamin C and uric acid - to better reduce the potentially damaging oxidative intermediates.
The University of Essex has engineered a range of novel hemoglobin molecules that have additional tyrosine residues; consequently they are less likely to induce oxidative damage. Patents have been granted in the USA and Australia and are pending in other territories.