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Chapter 2: Application of Microspheres to Measure Cell Surface- Associated Proteolytic Enzyme Activities
Published in Alan Rembaum, Zoltán A. Tökés, Micro spheres: Medical and Biological Applications, 2017
HBL-100 and MCF-7 cells were further tested with microspheres carrying 125I-labeled glycophorin. The question was raised whether integral membrane components are also substrates for the cell-surface associated proteolytic activity. Glycophorin is a major erythrocyte membrane constituent which contains a high number of negatively charged sialic acid residues. This glycoprotein was purified to homogeneity from human erythrocyte stroma using lithium diiodosalicylate.17 It was treated with DIFP and iodinated the same way as casein. The 125I-labeled glycophorin was coupled to the microspheres and its rate of digestion while in contact or without contact with cells was measured. The results are summarized in Table 4. The unique finding is that, at all times, the amount of peptides released in nocontact configuration was indistinguishable or higher than in-contact configuration. Three interpretations can be proposed. The first one is the possibility that different types of enzymes are assayed for in-contact and no-contact positions. Thus, the enzymes retained at the cell surface are less effective in cleaving glycophorin than the released enzyme.
Evaluation of potential health effects associated with occupational and environmental exposure to styrene – an update
Published in Journal of Toxicology and Environmental Health, Part B, 2019
M.I. Banton, J.S. Bus, J.J. Collins, E. Delzell, H.-P. Gelbke, J.E. Kester, M.M. Moore, R. Waites, S.S. Sarang
In addition to the large genetic toxicology literature, there is an extensive literature using genetic damage biomarkers evaluated in the blood cells of humans occupationally exposed to styrene. There are reports for CA, MN, SCE, and gene mutation. ATSDR (2010) provides a compilation of the human chromosomal aberration and mutation studies through the review’s time period. Two mutation assays have been used in humans to study styrene, the Hprt gene mutation test and the Glycophorin A (GPS) assay. The studies that evaluated occupationally exposed subjects for increases in the frequency of Hprt mutants in relation to control individuals were reported by Vodicka et al. (1995, 1999, 2001) and Lambert et al. (1995). Two studies are reported that used the GPA gene to assess mutation induction (Bigbee et al. 1996; Compton-Quintana et al. 1993). None of these studies provides a clear conclusion as to whether styrene can induce mutation in human lymphocytes. Although there are a relatively large number of cytogenetic studies in occupationally exposed humans, as with the mutation studies, the study designs of these studies lack key elements important for understanding the results.