Analysis of cross-linked human hemoglobin by conventional isoelectric focusing, immobilized pH gradients, capillary electrophoresis, and mass spectrometry

Synthesis and characterization of a novel DTPA polymerized hemoglobin based oxygen carrier

OBJECTIVE

The purpose of this study was to prepare a novel polymerized hemoglobin (Hb) based oxygen carrier (HBOC) designed to minimize Hb induced hypertension, while employing a simple and inexpensive method of preparation. Cyclic-diethylenetriaminepentaacetic acid (DTPA) was used to polymerize stroma free Hb (SF-Hb).

METHODS

SF-Hb was isolated from red blood cells and reacted with DTPA at a constant concentration, pH, and duration. Low molar mass fractions (<100 kDa) were removed using ultrafiltration. Reactions and subsequent ultrafiltration steps were determined to be reproducible by analyzing molar mass, colloid osmotic pressure and oxygen affinity. Finally, a model of 50% exchange transfusion (ET) in rats was used to evaluate the blood pressure response to DTPA polymerized SF-Hb (Poly-DTPA-Hb).

RESULTS

Poly-DTPA-Hb demonstrated a number averaged molar mass of 128.7 kDa and a weighted average of 223.0 kDa. Oxygen binding equilibrium indicated high oxygen affinity (P50 = 5.1+/-0.01 mm Hg) and little cooperativity (n = 1.4). Poly-DTPA-Hb and a control DTPA polymerized human serum albumin (Poly-DTPA-HSA) unexpectedly caused acute hypotension during the period of ET in rats (mean arterial pressure approximately 45% less than baseline). Hypotension occurring over the period of ET was determined to be mediated by calcium binding to protein associated DTPA. This effect was attenuated by the addition of calcium chloride (CaCl2) to the Poly-DTPA protein preparations.

CONCLUSIONS

Cyclic DTPA anhydride can be used to create cross-linked and polymerized hemoglobin, using a simple and inexpensive process. However, the addition of CaCl2 to the preparation appears to be required to prevent calcium chelation and subsequent hypotension during infusion.

Doping Control Analysis of Bovine Hemoglobin-Based Oxygen Therapeutics in Human Plasma by LC−Electrospray Ionization-MS/MS

Since January 2000, hemoglobin-based oxygen carriers, such as Hemopure, belong to the list of prohibited substances of the International Olympic Committee. Hemopure is based on bovine hemoglobin, which is intra- and intermolecularly cross-linked by glutaraldehyde units causing an average molecular weight of approximately 250,000. Bovine and human hemoglobins differ by 15% in amino acid sequence; hence, tryptic digestion of these proteins generates species-common and -unique peptides. Those specific fragments originate from the alpha- and beta-subunits of hemoglobin, such as bovine Hb peptides alpha(69-90) (2367.2 Da) or beta(40-58) (2089.9 Da). By means of LC-MS/MS, peptides of human and bovine hemoglobin can be separated and identified, enabling the determination of compounds based on Hb of bovine origin and thus the administration of oxygen carriers such as Hemopure. Blank plasma samples were spiked with Hemopure or human or bovine hemoglobin, filtered, enzymatically digested, and analyzed on an Agilent 1100 Series HPLC interfaced to an Applied Biosystems API 2000 triple quadrupole mass spectrometer. In plasma aliquots of 50 microL containing 50 microg of Hemopure (1 mg/mL), peptides of bovine hemoglobin were confirmed, and blank plasma samples as well as 68 specimens of high-performance athletes were tested with the developed procedure.

The lectin from the mushroom Pleurotus ostreatus: a phosphatase-activating protein that is closely associated with an alpha-galactosidase activity. A part of this paper has been presented as a preliminary report at the 17th Interlec. Meeting 1997 in Würzburg, Germany

The lectin from the mushroom Pleurotus ostreatus described earlier [F. Conrad, H. Rüdiger, The lectin from Pleurotus ostreatus: purification, characterization and interaction with a phosphatase, Phytochemistry 36 (1994) 277-283] was further characterized. Determination of the isoelectric point by capillary electrophoresis gave a value of 7.6. The dissociation constant of the lectin-alpha-lactose-1-phosphate complex determined by capillary electrophoresis is 3 mM. The activation of an endogenous phosphatase by the lectin as found earlier for the pseudosubstrate p-nitrophenylphosphate was confirmed also for naturally occurring substrates as ADP and ATP. We observed that at all purification steps the lectin is accompanied by an alpha-galactosidase activity. Both activities could neither be resolved by electrophoresis under non-denaturing conditions nor by affinity chromatography. However, carbohydrate binding by the lectin and carbohydrate processing by the enzyme are not due to the same site since: (i) the lectin accepts both alpha- and beta-glycosides whereas the enzyme activity is restricted to the alpha-anomer; (ii) the interaction with erythrocytes leads to a stable agglutinate, i.e. no 'clot-dissolving activity' [C.N. Hankins, J.I. Kindinger, L.M. Shannon, Legume alpha-galactosidases which have hemagglutinin properties, Plant Physiol. 65 (1980) 618-622] is observed; (iii) the alpha-galactosidase activity is inhibited by galactose but not by a beta-galactoside. Therefore, lectin and enzymatic activities are either properties of two tightly associated proteins, or of just one molecule. The kinetic parameters of the lectin-associated alpha-galactosidase activity for p-nitrophenyl-alpha-galactopyranoside are: K(M)=2.5 mM, k(cat)=66 s(-1), and K(I)=20mM for the inhibitor D-galactose.