Double-antibody enzyme immunoassay for nortriptyline

Area of Science:

• Biochemistry
• Enzyme Assays
• Analytical Chemistry

Background:

• Development of sensitive and precise immunoassays is crucial for therapeutic drug monitoring.
• Radioimmunoassays (RIA) are established methods but involve radioactive isotopes.
• Enzyme immunoassays offer a non-radioactive alternative with comparable performance.

Purpose of the Study:

• To develop a novel enzyme immunoassay for the quantification of nortriptyline.
• To conjugate beta-D-galactosidase to desmethylnortriptyline for use in the assay.
• To evaluate the performance of the developed enzyme immunoassay compared to existing methods.

Main Methods:

• Conjugation of beta-D-galactosidase (from Escherichia coli) to desmethylnortriptyline using dimethyl adipimidate.
• Development of a double-antibody immunoassay utilizing the enzyme conjugate.
• Quantification of enzyme activity using o-nitrophenyl-beta-D-galactopyranoside as substrate.
• Validation of the assay by comparing results with radioimmunoassay and gas-chromatography.

Main Results:

• High enzyme activity was retained post-conjugation (80%).
• Significant enzyme conjugation to desmethylnortriptyline was achieved (75%).
• The developed enzyme immunoassay demonstrated comparable sensitivity, precision, and simplicity to radioimmunoassay.
• Plasma nortriptyline levels determined by the enzyme immunoassay correlated well with RIA and gas-chromatography results.

Conclusions:

• A robust enzyme immunoassay for nortriptyline has been successfully developed.
• The assay provides a sensitive, precise, and non-radioactive alternative for nortriptyline quantification.
• This method holds promise for routine clinical use in therapeutic drug monitoring of nortriptyline.