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Kim D Vandegriff

Publications and source records attributed to Kim D Vandegriff.

8 recordsLinked to original sources
PubMed2006

Oxidation and haem loss kinetics of poly(ethylene glycol)-conjugated haemoglobin (MP4): dissociation between in vitro and in vivo oxidation rates.

Haemoglobin-based oxygen carriers can undergo oxidation of ferrous haemoglobin into a non-functional ferric form with enhanced rates of haem loss. A recently developed human haemoglobin conjugated to maleimide-activated poly(ethylene glycol), termed MP4, has unique physicochemical properties (increased molecular radius, high oxygen affinity and low cooperativity) and lacks the typical hypertensive response observed with most cell-free haemoglobin solutions. The rate of in vitro MP4 autoxidation is higher compared with the rate for unmodified SFHb (stroma-free haemoglobin), both at room temperature (20-22 degrees C) and at 37 degrees C (P<0.001). This appears to be attributable to residual catalase activity in SFHb but not MP4. In contrast, MP4 and SFHb showed the same susceptibility to oxidation by reactive oxygen species generated by a xanthine-xanthine oxidase system. Once fully oxidized to methaemoglobin, the rate of in vitro haem loss was five times higher in MP4 compared with SFHb in the fast phase, which we assign to the beta subunits, whereas the slow phase (i.e. haem loss from alpha chains) showed similar rates for the two haemoglobins. Formation of MP4 methaemoglobin in vivo following transfusion in rats and humans was slower than predicted by its first-order in vitro autoxidation rate, and there was no appreciable accumulation of MP4 methaemoglobin in plasma before disappearing from the circulation. These results show that MP4 oxidation and haem loss characteristics observed in vitro provide information regarding the effect of poly(ethylene glycol) conjugation on the stability of the haemoglobin molecule, but do not correspond to the oxidation behaviour of MP4 in vivo.

Animals↗
PubMed2004

Kinetics of NO and O2 binding to a maleimide poly(ethylene glycol)-conjugated human haemoglobin.

The hypertensive effect observed with most cell-free haemoglobins has been proposed to result from NO scavenging. However, a newly developed PEG [poly(ethylene glycol)]-conjugated haemoglobin, MalPEG-Hb [maleimide-activated PEG-conjugated haemoglobin], is non-hypertensive with unique physicochemical properties: high O2 affinity, low co-operativity and large molecular radius. It is therefore of interest to compare the ligand-binding properties of MalPEG-Hb with unmodified cell-free HbA (stroma-free human haemoglobin). NO association rates for deoxy and oxyMalPEG-Hb and HbA were found to be identical. These results confirm the lack of correlation between hypertension and NO for a similar modified haemoglobin with high molecular radius and low p50 (pO2 at which haemoglobin is half-saturated with O2) [Rohlfs, Bruner, Chiu, Gonzales, Gonzales, Magde, Magde, Vandegriff and Winslow (1998) J. Biol. Chem. 273, 12128-12134]. The R-state O2 association kinetic constants were also the same for the two haemoglobins. However, even though the p50 of MalPEG-Hb is approx. half of that of HbA, the biphasic O2 dissociation rates measured at relatively high pO2 (150 Torr) were 2-fold higher, giving rise to a 2-fold lower R-state equilibrium association constant for MalPEG-Hb compared with HbA. Thus the O2 affinity of MalPEG-Hb is higher only at pO2 values lower than the intersection point of the O2 equilibrium curves for MalPEG-Hb and HbA. In summary, the present studies found similar rates of NO binding to HbA and MalPEG-Hb, eliminating the possibility that the lack of vasoactivity of MalPEG-Hb is simply the result of reduced molecular reactivity with NO. Alternatively, the unique O2-binding characteristics with low p50 and co-operativity suggest that the 'R-state' conformation of MalPEG-Hb is in a more T-state configuration and restricted from conformational change.

Hemoglobins↗
PubMed2004

Comparison of PEG-modified albumin and hemoglobin in extreme hemodilution in the rat.

We have reported a new polyethylene glycol (PEG)-modified, hemoglobin-based O2 carrier (MP4) with novel properties, including a large molecular excluded volume and low PO2 necessary to obtain 50% O2 (approximately 6 Torr). To evaluate the ability of MP4 to transport O2, we compared it with PEG-modified albumin (MPA) using the identical chemistry of attachment of PEG chains. The resulting solutions were well matched with respect to all physical properties except that MP4 is an O2 carrier, whereas MPA is not. An additional solution, 10% pentastarch, was matched with the PEG-modified proteins with regard to oncotic activity and viscosity but does not contain PEG. The model used to evaluate O2 transport was continuous exchange transfusion in the rat until the hematocrit was virtually unmeasurable. Objective end points included survival and the onset of anaerobic metabolism, signaled by acid-base derangement and accumulation of lactic acid. Continuous exchange transfusion of 2.5 blood volumes in rats (n=5 in each treatment group) was carried out over 60 min, such that the final hematocrit was between 0 and 5% in all animals. Animals were observed for an additional 70 min, when survivors were killed. Overall survival for the MP4 animals was 100%; no animal that received either pentastarch or MPA survived. The hematocrit at which lactic acid began to rise was approximately 14.8% in both pentastarch and MPA animals and 7.4% in the animals that received MP4. In all groups, the total hemoglobin was approximately 5 g/dl at this point. We conclude that, despite its low PO2 necessary to obtain 50% O2, MP4 effectively substitutes for red blood cell hemoglobin in its ability to oxygenate tissues in extreme hemodilution.

Albumins↗
PubMed2004

Hemodynamic response and oxygen transport in pigs resuscitated with maleimide-polyethylene glycol-modified hemoglobin (MP4).

Cell-free Hb increases systemic and pulmonary pressure and resistance and reduces cardiac output and heart rate in animals and humans, effects that have limited their clinical development as "blood substitutes." The primary aim of this study was to evaluate the hemodynamic response to infusion of several formulations of a new polyethylene glycol (PEG)-modified human Hb [maleimide PEG Hb (MalPEGHb)] in swine, an animal known to be sensitive to Hb-induced vasoconstriction. Anesthetized animals underwent controlled hemorrhage (50% of blood volume), followed by resuscitation (70% of shed volume) with 10% pentastarch (PS), 4% MalPEG-Hb in lactated Ringer (MP4), 4% MalPEG-Hb in pentastarch (HS4), 2% MalPEG-Hb in pentastarch (HS2), or 4% stroma-free Hb in lactated Ringer solution (SFH). Compared with baseline, restoration of blood volume after resuscitation was similar and not significantly different for the PS (103%), HS2 (99%), HS4 (106%), and MP4 (87%) animals but significantly less for the SFH animals (66%) (P < 0.05). All solutions that contained MalPEG-Hb restored mean arterial and pulmonary pressure and cardiac output. Systemic vascular resistance was unchanged, and pulmonary arterial pressure and resistance were increased slightly. Both systemic and pulmonary vascular resistance increased significantly in animals that received SFH, despite less adequate blood volume restoration. Oxygen consumption was maintained in all animals that received MalPEG-Hb, but not PS. Base excess improved only with MalPEG-Hb and PS, but not SFH. Red blood cell O2 extraction was significantly increased in animals that received Hb, regardless of formulation. These data demonstrate resuscitation with MalPEG-human Hb without increasing systemic vascular resistance and support our previous observations in animals suggesting that the efficacy of low concentrations of PEG-Hb in the plasma results from reduced vasoconstriction.

Animals↗
PubMed2003

Oxygen transport in blood at high altitude: role of the hemoglobin-oxygen affinity and impact of the phenomena related to hemoglobin allosterism and red cell function.

Altitude hypoxia is a major challenge to the blood O2 transport system, and adjustments of the blood-O2 affinity might contribute significantly to hypoxia adaptation. In principle, lowering the blood-O2 affinity is advantageous because it lowers the circulatory load required to assure adequate tissue oxygenation up to a threshold corresponding to about 5,000 m altitude, whereas at higher altitudes an increased blood-O2 affinity appears more advantageous. However, the rather contradictory experimental evidence raises the question whether other factors superimpose on the apparent changes of the blood-O2 affinity. The most important of these are as follows: (1) absolute temperature and temperature gradients within the body; (2) the intracapillary Bohr effect; (3) the red cell population heterogeneity in terms of O2 affinity; (4) control of altitude alkalosis; (5) the possible role of hemoglobin as a carrier of the vasodilator nitric oxide; (6) the effect of varied red cell transit times through the capillaries.

Allosteric Regulation↗
PubMed2003

Targeted O2 delivery by low-P50 hemoglobin: a new basis for O2 therapeutics.

To assess O2 delivery to tissue by a new surface-modified, polyethylene glycol-conjugated human hemoglobin [MP4; Po2 at 50% saturation of hemoglobin (P50); 5.4 mmHg], we studied microcirculatory hemodynamics and O2 release in golden Syrian hamsters hemodiluted with MP4 or polymerized bovine hemoglobin (PolyBvHb; P50 54.2 mmHg). Comparisons were made with the animals' hemodiluted blood with a non-O2 carrying plasma expander with similar solution properties (Dextran-70). Systemic hemodynamics (arterial blood pressure and heart rate) and acid-base parameters were not correlated with microhemodynamics (arteriolar and venular diameter, red blood cell velocity, and flow). Microscopic measurements of Po2 and the O2 equilibrium curves permitted analysis of O2 release in precapillary and capillary vessels by red blood cells and plasma hemoglobin separately. No significant differences between the groups of animals with respect to arteriolar diameter, flow, or flow velocity were observed, but the functional capillary density was significantly higher in the MP4-treated animals (67%) compared with PolyBvHb-treated animals (37%; P < 0.05) or dextran-treated animals (53%). In the PolyBvHb-treated animals, predominant O2 release (both red blood cells and plasma hemoglobin) occurred in precapillary vessels, whereas in MP4 animals most of the O2 was released from both red blood cells and plasma hemoglobin in capillaries. Base excess correlated directly with capillary O2 release but not systemic O2 content or total O2 release. Higher O2 extraction of both red blood cell and plasma hemoglobin in capillaries represents a new mechanism of action of cell-free hemoglobin. High O2 affinity appears to be an important property for cell-free hemoglobin solutions.

Acid-Base Equilibrium↗
PubMed2003

MP4, a new nonvasoactive PEG-Hb conjugate.

BACKGROUND: Vasoconstriction has been an obstacle to clinical development of Hb-based O2 carriers. It is proposed that this limitation can be overcome by increasing molecular size and oxygen affinity. STUDY DESIGN AND METHODS: Surface-modified Hb (MP4) was designed, whose properties are consistent with the theory that cell-free Hb engages autoregulatory vasoconstrictive responses to Hb diffusion in the plasma space ("facilitated diffusion"). Human Hb was modified by reaction first with 2-iminothiolane to add sulfhydryl groups and then with monofunctional maleimide- activated 5-kDa PEG. RESULTS: MP4 was found to have a molecular weight of 90 kDa, a molecular radius increased relative to native Hb (9.3 +/- 1.4 vs. 3.2 nm), high oxygen affinity (p50 approximately 5-6 mmHg), and a Bohr effect approximately half that of native human Hb (-0.24Deltalogp50/DeltapH). At 4.2 g per dL in Ringer's lactate, its viscosity was 2.5 cP, and its oncotic pressure was 50 mmHg. The t50 of 14C-MP4 in rats was approximately 24 hours. No significant elevation in mean arterial pressure was observed. CONCLUSION: MP4 appears to be free of a pressor effect, a major limitation to the development of a safe and effective RBC substitutes in the past.

Animals↗