Purpose of Review: This study summarizes the applications of monoclonal antibodies (MAbs) against bioactive natural compounds for the functional analysis of crude drugs. Recent Findings: To date, we have established more than 40 kinds of MAbs against natural compounds and set up enzyme-linked immunosorbent assay (ELISA). The intracellular accumulation of harringtonine (HT) and its derivatives into cells was determined by ELISA using anti-HT MAb, and the uptake levels of these compounds conformed to their respective antiproliferative activities. Eastern blotting is an on-membrane quantitative analytical system that uses MAbs against natural compounds and it can also be used in a biological sample for pharmacokinetics study. Glycyrrhizin (GC) was detected in the serum of rats treated with GC by eastern blotting. Additionally, eastern blotting using MAb against 3-monoglucuronyl-glycyrrhetinic acid (3-MGA) could determine a potential causative agent of pseudoaldosteronism induced by excess intake of GC. The immunoaffinity column coupled with MAb made preparing an extract containing all components feasible except the target compound. Cell-based studies using GC-removed licorice extract, which was prepared by the immunoaffinity column conjugated with anti-GC MAb, revealed the potential functions of GC in licorice extract. Moreover, MAbs were used in determining cellular localization and target molecules of natural compounds. The combination of analysis using MAb and LC-MS/MS showed that aristolochic acid I (AA-I), a naturally occurring nephrotoxin and carcinogen, targets α-actinin-4 in the kidney cells. Summary: MAbs against natural compounds are useful tools to determine real pharmacological functions, cellular localization, and molecular targets of natural compounds in crude extracts.
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