Applications of LC-MS in the study of the uptake, distribution, metabolism and excretion of bioactive polyphenols from dietary supplements

Abstract

Specific and quantitative analyses of the bioactive components and their metabolites in body fluids are essential to assess the interaction between groups of compounds in dietary supplements and preparations of psychoactives. Reverse-phase LC separations combined with tandem mass spectrometry provide the necessary specificity and sensitivity. In this paper, applications of these methods are described for the analysis of isoflavones, salvinorin A, synephrine isomers and their metabolites in serum, urine and aqueous humor.

Introduction

The use of dietary supplements in the USA has increased enormously following the passage of the Dietary Education Health and Safety Act (DSHEA) in 1994 (http://www.fda.gov/opacom/laws/dshea.html). Many of these dietary supplements are derived from plants and contain organic xenobiotics that are subject to the same issues of absorption, distribution, metabolism and excretion that control the effectiveness of synthetic pharmaceutical agents. Importantly, the plant compounds share the same transport systems and metabolizing enzymes. Therefore, interactions between dietary supplements and other pharmaceuticals are to be expected. To explore this issue it is necessary to examine the composition of dietary supplements as well as their metabolites in physiological materials (blood, urine and tissues).

The analysis of biologically relevant compounds both in their native forms in pharmaceutical or dietary supplement matrices and in physiological fluids and tissues has been enormously improved by the introduction of electrospray ionization (ESI) (Fenn et al., 1989). This method allows the facile transfer without damage of what in some cases are unstable organic compounds from the liquid to the gas phase at atmospheric pressure and at room temperature. This seemingly unlikely method has also had enormous impact in the study of peptides and proteins and deservedly earned John Fenn the 2002 Nobel Prize in Chemistry. When used in combination with reverse-phase HPLC, it offers all investigators a very powerful method for the analysis of compounds in complex biological matrices.

Many of the bioactive compounds in dietary supplements of botanical origin are conjugated with glycoside groups (Kudou et al., 1991, Coward et al., 1993). These are difficult to turn into volatile derivatives for gas chromatography analysis. LC-ESI-mass spectrometry has greatly simplified their measurement. Once the dietary supplements are ingested these conjugates are hydrolyzed either by intestinal bacteria or by enzymes in the cells lining the small intestine (Day et al., 1998, Day et al., 2000). In most cases, they undergo substantial metabolism within the intestinal wall, particularly to form glucuronides (Sfakianos et al., 1997). Again, LC-ESI-mass spectrometry is highly suited to the analysis of these metabolites (Barnes et al., 1994, Sfakianos et al., 1997).

Compounds with psychoactive properties are found both in botanicals and dietary supplements as well as in pharmaceutical and illicit drug formulations. Each of these compounds are subject to similar issues regarding intestinal uptake, phase I and phase II reactions in the gut wall, liver and other tissues to form metabolites, and biliary and/or urinary excretion. Each of the metabolic forms is readily analyzed by LC-ESI-mass spectrometry.

The goal of this article is to illustrate some of the applications of LC-ESI-MS, in particular tandem mass spectrometry, to the analysis of dietary supplements and psychoactive drugs.