Hemorrhagic shock resuscitation with an artificial oxygen carrier, hemoglobin vesicle, maintains intestinal perfusion and suppresses the increase in plasma tumor necrosis factor-alpha.

It is known that damage to the intestinal mucosa followed by systemic inflammatory response is one of the leading causes of shock related morbidity and mortality. In this study, we examined the ability of an artificial oxygen carrier hemoglobin vesicle (HbV) to sustain systemic and intestinal perfusion during hemorrhagic shock. In rabbits, hemorrhagic shock (40% of the estimated blood volume) was resuscitated with 5% albumin (alb group), HbV suspended in 5% albumin (HbValb group), or washed red blood cells suspended in 5% albumin (RBCalb group). Plasma tumor necrosis factor (TNF)-alpha level was measured in rats under the same experimental protocol. No significant intergroup differences were seen in systemic hemodynamics. In contrast, parameters of intestinal perfusion significantly deteriorated in the alb group but were equally well sustained in the HbValb and RBCalb groups. Also, a significant increase in plasma TNF-alpha level was seen in the alb group but not in the RBCalb or HbValb groups. These results indicate the proficient oxygen transporting capability of HbV and its potential efficacy in shock resuscitation.

Global allostery model of hemoglobin. Modulation of O(2) affinity, cooperativity, and Bohr effect by heterotropic allosteric effectors.

The O(2) equilibria of human adult hemoglobin have been measured in a wide range of solution conditions in the presence and absence of various allosteric effectors in order to determine how far hemoglobin can modulate its O(2) affinity. The O(2) affinity, cooperative behavior, and the Bohr effect of hemoglobin are modulated principally by tertiary structural changes, which are induced by its interactions with heterotropic allosteric effectors. In their absence, hemoglobin is a high affinity, moderately cooperative O(2) carrier of limited functional flexibility, the behaviors of which are regulated by the homotropic, O(2)-linked T/R quaternary structural transition of the Monod-Wyman-Changeux/Perutz model. However, the interactions with allosteric effectors provide such "inert" hemoglobin unprecedented magnitudes of functional diversities not only of physiological relevance but also of extreme nature, by which hemoglobin can behave energetically beyond what can be explained by the Monod-Wyman-Changeux/Perutz model. Thus, the heterotropic effector-linked tertiary structural changes rather than the homotropic ligation-linked T/R quaternary structural transition are energetically more significant and primarily responsible for modulation of functions of hemoglobin.

Heterotropic effectors control the hemoglobin function by interacting with its T and R states--a new view on the principle of allostery.

Careful analyses of precise oxygenation curves of hemoglobin (Hb) clearly indicate that, contrary to the common belief, allosteric effectors exert a dramatic control of the oxygenation characteristics of the protein by binding not only to the T (unligated), but also to the R (ligated) state, in a process that is proton-driven and involves proton uptake. The most striking functional changes were obtained when the allosteric effectors were bound to the fully ligated Hb: the oxygen affinity decreased dramatically, Bohr effect was enhanced, and cooperativity of oxygen ligation was almost absent, emulating a Root effect-like behavior. However, structural analysis, such as Cys beta 93 sulfhydryl reactivity and ultraviolet circular dichroism, confirmed that the ligated Hb was in fact in the R state, despite its extremely low affinity state features. These findings provide a new global view for allosteric interactions and invoke for a modern interpretation of the role of allosteric effectors and a reformulation of the Monod-Wyman-Changeaux model for control of allosteric systems, and other complementary models as well.