EDITORIAL: IS THERE A ROLE FOR FIRST GENERATION BLOOD SUBSTITUTES IN THE RESUSCITATION OF HEMORRHAGIC SHOCK ? also in "Artif Cells, Blood Substitutes & Immob. Biotechnology, an international journal. 26(5-6);i-iii,1998"
T.M.S.Chang,OC,MD.CM,PhD,FRCP(C), Director, Artificial Cells & Organs Research Centre, Professor of Physiology, Medicine & Biomedical Engineering, MRC Career Investigator, McGill University, Montreal, Quebec, Canada H3G 1Y6
There have been much recent discussions and controversies in the use and design of clinical trials of first generation modified hemoglobin blood substitutes for the resuscitation of severe hemorrhagic shock. There is no blood group antigen in blood substitutes and they can be stored and used at anytime. Thus it would be an ideal resuscitation fluid for use in emergency situations as in the case of severe hemorrhagic shock. However, it would be extremely important to consider the following points in the potential uses of the first generation blood substitutes for the resuscitation of severe hemorrhagic shock.
Severe hemorrhagic shock results in extensive vasoconstriction and marked decrease in blood supply to a number of important organs including the intestine, the kidney and others with resulting ischemia in these organs. When the condition persists for sufficient length of time, reperfusion of oxygen carrying fluid can result in the generation of sufficient amount of oxygen radicals to result in ischemica-reperfusion injuries. Indeed, one of the potential problems in the resuscitation of severe hemorrhagic shock is ischemia-reperfusion injuries when oxygen carrying fluid is administered, especially when hemorrhagic shock has persisted for some time before reperfusion.
The present first generation modified hemoglobin blood substitutes (1-5) are prepared from ultrapure hemoglobin with nearly all of the red blood cell enzymes removed. As a result, the red blood cell antioxidant enzymes, superoxide dismutase and catalase, are no longer present in these preparations to lessen the potential problems related to ischemia-reperfusion injuries. Furthermore, Alayash has shown that in the absence of antioxidant enzymes, hemoglobin is a very reactive molecule in ischemia-reperfusion conditions(1).
Nearly all the published preclinical animal studies in the use of first generation modified hemoglobin blood substitutes in resuscitation are based on replacement within a very short time after severe hemorrhagic shock (1-5). Under these conditions, whole blood and modified hemoglobin appear to be superior to other fluids for improving the long term survival rates. However, we should not immediately apply these results to all cases of hemorrhagic shock. We have recently asked the following question. The intestine is one of the organs that can be severely affected by ischemia-reperfusion in severe hemorrhagic shock. What would be the effect of reperfusion of modified hemoglobin prepared from ultrapure hemoglobin on intestine with sustained ischemia? Our result shows that after 90 minutes of ischemia, reperfusion with polyhemoglobin results in a 13-fold increase in oxygen radicals in the effluence from the intestine, from the baseline level of 0.05 +/- 0.04 to a maximal level of 0.67 +/- 0.17 (nanomole/ml +/- standard deviation) (6). Oxygen radical generation is measured by the hydroxylation of 4-hydroxybenzoate to 3,4-dihydroxybenzoate (3,4 DHBA) using electrochemical detection. We carried out another study under the exact conditions but using polyhemoglobin crosslinked with superoxide dismutase and catalase (PolyHb-SOD-CAT) instead of polyhemoglobin prepared from ultrapure hemoglobin (6). Reperfusion with PolyHb-SOD-CAT results only in a minimal increase in oxygen radicals, from the baseline level of 0.05 +/- 0.04 nanomole/ml to 0.19 +/- 0.08 nanomole/ml. This shows the role of the red blood cell enzymes superoxide dismutase and catalase in lessening the generation of oxygen radicals in those conditions that can lead to ischemia-reperfusion injuries.
Thus in the use or design of clinical trial for the resuscitation of severe hemorrhagic shock it will be extremely important to take the above factors into consideration. If the resuscitation takes place almost immediately after hemorrhagic shock, then there may not be too much of a problem with ischemia-reperfusion injury. However, if the resuscitation takes place after sustained period of hemorrhagic shock, then resuscitation with the first generation blood substitutes may result in ishemic-reperfusion injuries and causing more harm than without such resuscitation. This would also apply to other ischemic conditions including reperfusion in stroke and other situations.
The first generation modified hemoglobin blood substitutes now in phase II and phase III clinical trials have important clinical potential for certain clinical conditions, especially for short-term use in surgery (1-5). However, it will be disastrous to think of the first generation modified hemoglobin blood substitutes as an universal blood substitute for use in all conditions. This further points to the need for the research and development of new generations of modified hemoglobin blood substitutes. For example, 2nd generation system like our Poly-SOD-CAT (6) or those specially prepared from recombinant technology or Hsias chemical modification of hemoglobin with similar properties. There are also 3rd generations system like encapsulated hemoglobin with hemoglobin, SOD and CAT in liposomes from the groups of Tsuchida (5) and Rudolphs(2) or in biodegradable polymeric nanocapsules from Changs group of Yu & Chang(1).
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