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.


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.


CONCLUSIONS
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.
Vandegriff
Kim D
KD
Sangart, Inc., 11189 Sorrento Valley Road, Suite 104, San Diego, CA 92121, USA.
Malavalli
Ashok
A
Wooldridge
Jerod
J
Lohman
Jeff
J
Winslow
Robert M
RM
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002250:Carbon Radioisotopes; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002850:Chromatography, Gel; D006454:Hemoglobins / Q000009:adverse effects / Q000138:chemical synthesis* / Q000737:chemistry* / Q000493:pharmacokinetics; D006801:Humans; D007096:Imidoesters / Q000737:chemistry; D007700:Kinetics; D008297:Male; D008301:Maleimides / Q000494:pharmacology; D008970:Molecular Weight; D010100:Oxygen / Q000378:metabolism; D011092:Polyethylene Glycols / Q000009:adverse effects / Q000138:chemical synthesis* / Q000737:chemistry* / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D013438:Sulfhydryl Compounds / Q000737:chemistry; D014783:Viscosity
D002250:Carbon Radioisotopes; D006454:Hemoglobins; D007096:Imidoesters; D008301:Maleimides; C473626:PEG-Hb conjugate, MP4; D013438:Sulfhydryl Compounds; C043592:maleimide; D011092:Polyethylene Glycols; C005905:methyl 4-mercaptobutyrimidate; D010100:Oxygen