The anomalous behaviour of exogenous 25-hydroxyvitamin D in competitive binding assays

Abstract Purpose MK6240 is a second-generation tau PET tracer designed to detect the neurofibrillary tangles in the brains of patients with Alzheimer’s disease (AD). The aim of the study was to characterize 3H-MK6240 in AD and control brain tissue and to compare its binding properties with those of first-generation tau PET tracers. Methods Saturation binding assays with 3H-MK6240 were carried out in the temporal and parietal cortices of AD brains to determine the maximum number of binding sites (Bmax) and the dissociation constants (Kd) at these sites. Competitive binding assays were carried out between 3H-MK6240 and unlabelled MK6240, AV-1451 (aka T807, flortaucipir) and THK5117, and between 3H-THK5351 and unlabelled MK6240. Regional binding studies with 3H-MK6240 were carried out in homogenates from six AD and seven control brains and, using autoradiography, on large frozen sections from two AD brains and one control brain. Results The saturation binding assays gave Bmax and Kd values of 59.2 fmol/mg and 0.32 nM in the temporal cortex and 154.7 fmol/mg and 0.15 nM in the parietal cortex. The competitive binding assays revealed two binding sites with affinities in the picomolar and nanomolar range shared by 3H-MK6240 and all the tested unlabelled compounds. There were no binding sites in common between 3H-THK5351 and unlabelled MK6240. Regional binding of 3H-MK6240 was significantly higher in AD brain tissue than in controls. Binding in brain tissue from AD patients with early-onset AD was significantly higher than in brain tissue from patients with late-onset AD. Binding of 3H-MK6240 was not observed in off-target regions. Autoradiography showed high regional cortical binding in the two AD brains and very low binding in the control brain. Conclusions 3H-MK6240 has a high binding affinity for tau deposits in AD brain tissue but also has different binding characteristics from those of the first-generation tau tracers. This confirms the complexity of tau tracer binding on tau deposits with different binding affinities for different binding sites.

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Further probes into quantitative aspects of competitive binding assays: Allowance for effects of antigen multivalency in immunoassays

Archives of Biochemistry and Biophysics ◽

10.1016/0003-9861(87)90084-1 ◽

1987 ◽

Vol 254 (1) ◽

pp. 92-101 ◽

Cited By ~ 14

Author(s):

Philip J. Hogg ◽

Donald J. Winzor

Keyword(s):

Competitive Binding ◽

Binding Assays ◽

Competitive Binding Assays

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Potential misinterpretation of the competitive binding assays

Trends in Biochemical Sciences ◽

10.1016/0968-0004(89)90100-x ◽

1989 ◽

Vol 14 (11) ◽

pp. 443-444 ◽

Cited By ~ 2

Author(s):

Elena Presecan ◽

Horea Porumb ◽

Ioan Lascu

Keyword(s):

Competitive Binding ◽

Binding Assays ◽

Competitive Binding Assays

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Adapting Homogeneous Enzyme-Linked Competitive Binding Assays to Microtiter Plates

Analytical Biochemistry ◽

10.1006/abio.1994.1135 ◽

1994 ◽

Vol 218 (1) ◽

pp. 14-19 ◽

Cited By ~ 8

Author(s):

B. Kim ◽

J.M. Buckwalter ◽

M.E. Meyerhoff

Keyword(s):

Competitive Binding ◽

Binding Assays ◽

Microtiter Plates ◽

Competitive Binding Assays

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Some theoretical aspects of competitive binding assays

Human Pathology ◽

10.1016/s0046-8177(74)80096-1 ◽

1974 ◽

Vol 5 (1) ◽

pp. 6-8 ◽

Cited By ~ 2

Author(s):

Alfred Zettner

Keyword(s):

Competitive Binding ◽

Binding Assays ◽

Competitive Binding Assays

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Binding specificities of heat-labile enterotoxins isolated from porcine and human enterotoxigenic Escherichia coli for different gangliosides

Canadian Journal of Microbiology ◽

10.1139/m89-109 ◽

1989 ◽

Vol 35 (6) ◽

pp. 670-673 ◽

Cited By ~ 12

Author(s):

Shunji Sugii ◽

Takao Tsuji

Keyword(s):

Escherichia Coli ◽

Competitive Binding ◽

Enterotoxigenic Escherichia Coli ◽

Type B ◽

Binding Assays ◽

B Subunit ◽

Human Type ◽

Heat Labile ◽

Sepharose 4B ◽

Competitive Binding Assays

The binding specificities of heat-labile enterotoxins (LTp and LTh) isolated from porcine and human enterotoxigenic Escherichia coli on human erythrocytes were studied by competitive binding assays using different gangliosides as inhibitors. The binding of 125I–labeled LTp to neuraminidase-treated human type A erythrocytes was most effectively inhibited by ganglioside GM1 Ganglioside GM1 was 11 and 105 times more potent than gangliosides GD1b and GM2, respectively. Gangliosides GD1a, GT1b, and GM3 were much less potent. Similar results were also obtained in competitive binding assays with the 125I-labeled B subunit of LTh and neuraminidase-treated human type B erythrocytes, and in those with 3H-labeled ganglioside GM1 and LTp-coupled Sepharose 4B. The binding of 3H-labeled ganglioside GM1 to LTp was not effectively inhibited by galactose-β(1 → 3)N-acetyl-D-galactosamine at the highest concentration used. These findings suggest that the combining sites of LTp and LTh may be specific for at least the galactose-N-acetyl-D-galactosamine-galactose (N-acetyl-neuraminic acid) portion of ganglioside GM1.Key words: binding specificity, heat-labile enterotoxin, enterotoxigenic Escherichia coli, ganglioside.

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