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The delay time in sickle cell disease after 40 years: A paradigm assessed
Journal article   Open access   Peer reviewed

The delay time in sickle cell disease after 40 years: A paradigm assessed

Frank A Ferrone
American journal of hematology, v 90(5), pp 438-445
May 2015
PMID: 25645011
url
https://doi.org/10.1002/ajh.23958View
Published, Version of Record (VoR)Maybe Open Access (Publisher Bronze) Open

Abstract

Anemia, Sickle Cell - blood Anemia, Sickle Cell - diagnosis Anemia, Sickle Cell - drug therapy Anemia, Sickle Cell - pathology Antisickling Agents - therapeutic use Cell Movement - drug effects Erythrocyte Deformability - drug effects Erythrocytes, Abnormal - drug effects Erythrocytes, Abnormal - metabolism Erythrocytes, Abnormal - pathology Hemoglobin, Sickle - antagonists & inhibitors Hemoglobin, Sickle - chemistry Hemoglobin, Sickle - metabolism Humans Hydroxyurea - therapeutic use Kinetics Lung - blood supply Lung - drug effects Lung - metabolism Lung - pathology Oxygen - blood Polymerization - drug effects Severity of Illness Index Time Factors
Sickle hemoglobin polymerization commences with a striking latency period, called a "delay time" followed by abrupt polymer formation. The delay time is exceedingly concentration dependent. This discovery (40 years ago) led to the "kinetic hypothesis," that is, that the pathophysiology was related to the relationship between the delay time and the capillary transit. The delay time is well described by a double-nucleation mechanism of polymer formation. In macroscopic volumes, the delay time is highly reproducible, but in small volumes such as erythrocytes, under certain conditions, the intrinsic delay time can be augmented by a stochastic delay owing to random waiting times for the first nucleus to form. This lengthens the average delay and adds further protection from vaso-occlusion. When oxygen removal is not sudden, the growth of polymers after the delay time is limited by the rate of oxygen removal, further lengthening the time before occlusion may occur. This is important if some polymers have remained in the cell after pulmonary transit as their presence otherwise would obliterate any delay. The difficulty of deforming a cell once polymerized rationalizes the "two-step" model of vaso-occlusion in which a postcapillary adhesion event is followed by a sickling logjam. The delay time that is required is therefore generalized to be the delay time for an erythrocyte to move beyond regions in the venuoles where adherent cells have reduced the available lumen. The measurements of delay times correlate well with the severity of sickling syndromes. They also correlate with the improvements owing to the administration of hydroxyurea.

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