RESUMO
The commercial feasibility of recombinant human Hb (rHb) as an O(2) delivery pharmaceutical is limited by the production yield of holoprotein in E. coli. Currently the production of rHb is not cost effective for use as a source in the development of third and fourth generation Hb-based oxygen carriers (HBOCs). The major problems appear to be aggregation and degradation of apoglobin at the nominal expression temperatures, 28-37 degrees C, and the limited amount of free heme that is available for holohemoglobin assembly. One approach to solve the first problem is to inhibit apoglobin precipitation by a comparative mutagenesis strategy to improve apoglobin stability. alpha Gly15 to Ala and beta Gly16 to Ala mutations have been constructed to increase the stability of the alpha helices of both subunits of HbA, based on comparison with the sequences of the more stable sperm whale hemoglobin subunits. Fetal hemoglobin is also known to be more stable than human HbA, and sequence comparisons between human beta and gamma (fetal Hb) chains indicate several substitutions that stabilize the alpha1beta1 interface, one of which, beta His116 to Ile, increases resistance to denaturation and enhances expression in E. coli. These favorable effects of enhanced globin stability can be augmented by co-expression of bacterial membrane heme transport systems to increase the rate and extent of heme uptake through the bacterial cell membranes. The combination of increased apoglobin stability and active heme transport appear to enhance holohemoglobin production to levels that may make rHb a plausible starting material for all extracellular Hb-based oxygen carriers.
Assuntos
Substitutos Sanguíneos/química , Hemoglobinas/química , Hemoglobinas/genética , Engenharia de Proteínas/métodos , Proteínas Recombinantes/química , Clonagem Molecular , Análise Custo-Benefício , Estabilidade de Medicamentos , Escherichia coli/genética , Globinas/química , Globinas/genética , Heme/metabolismo , Hemoglobinas/economia , Humanos , Engenharia de Proteínas/economia , Dobramento de Proteína , Proteínas Recombinantes/economiaRESUMO
This paper offers a model for the bias found in willingness-to-pay valuations against new treatments. For example, this bias provides an explanation for patient preferences that make it difficult for formularies to take treatments off their lists, even when newer treatments would appear to be clearly preferable. The appeal of the model, which is based on imperfect information, is that it is consistent with rational preferences and rational behavior by patients, which are necessary for standard models and methods related to decision theory, cost-effectiveness, and efficiency.
