Red blood cells with
abnormal hemoglobins (Hb) are frequently associated with increased
hemoglobin autoxidation, accumulation of
iron in membranes, increased membrane damage and a shorter red cell life span. The mechanisms for many of these changes have not been elucidated. We have shown in our previous studies that
hydrogen peroxide formed in association with
hemoglobin autoxidation reacts with
hemoglobin and initiates a cascade of reactions that results in
heme degradation with the formation of two fluorescent emission bands and the release of
iron.
Heme degradation was assessed by measuring the fluorescent band at ex 321 nm. A 5.6 fold increase in fluorescence was found in red cells from sickle transgenic mice that expressed exclusively human
globins when compared to red cells from control mice. When sickle transgenic mice co-express the gamma M transgene, that expresses HbF and inhibits polymerization,
heme degradation is decreased. Mice expressing exclusively
hemoglobin C had a 6.9 fold increase in fluorescence compared to control.
Heme degradation was also increased 3.5 fold in beta-thalassemic mice generated by deletion of murine beta(major). Membrane bound
IgG and red cell metHb were highly correlated with the intensity of the fluorescent
heme degradation band. These results suggest that degradation of the
heme moiety in intact
hemoglobin and/or degradation of free
heme by
peroxides are higher in pathological RBCs. Concomitant release of
iron appears to be responsible for the membrane damage that leads to
IgG binding and the removal of red cells from circulation.