ANALYTICAL METHODS TO DETECT THE AUTOOXIDATION OF ADRENOLUTIN AS A STEP IN CATECHOLAMINE METABOLISM

The acute hemodynamic effects of organophosphate (OP) intoxication include positive chronotropic and inotropic changes along with increases in intraventricular pressure and coronary blood flow. These observations are consistent with an enhanced sympathetic tone that correlates neurogenic cardiomyopathy to adrenergic overactivity and subsequent, focal catecholamine (CA) release and cellular oxidative stress. Several mechanisms have been proposed to explain the cardiotoxicity associated with elevated CA concentrations. However, it is suggested that the oxidative metabolites of CA's, rather than (or in addition to) the parent CA's per se, may initiate or be in part responsible for the cardiotoxicity. The chromatographic profile of adrenochrome (1) and adrenolutin (2) (Figure 1) are described in this study in an isocratic, reverse phase HPLC method using UV/VIS and electrochemical (EC) detection. The aqueous adrenochrome standard shows a retention time of 1.9 minutes under employed conditions. Furthermore, using a flow rate of 0.6 mL/min and a UV/VIS detector set at a wavelength of 490 nm, several chromatographic peaks were detected, indicative of different species after injection of the aqueous adrenolutin standard. A similar multiple peak chromatographic profile was observed with EC detection. We hypothesized from the literature and observed complexity of the chromatogram (i.e. multiple intermediate species of the adrenolutin) that adrenolutin is being autooxidized over time. Based upon EPR spin trapping, we found the generation of a carbon-centered radical at the C-2 position that will interact with oxygen to give an intermediate peroxy radical. This may be eventually transformed to 5,6-dihydroxy-1-methyl-2,3-indoledione. The production of these proposed carbon- and oxygen-centered radicals in the autooxidation of adrenolutin was confirmed by spin trapping experiments using the spin trap, f -phenyl N-tert-butyl nitrone (PBN). When adrenolutin is dissolved in water at neutral pH in the presence of PBN, two different EPR spectra of PBN adducts are obtained. One observed PBN adduct has hyperfine splitting constants (hfsc's) of a N = 1.54 mT, a g H = 0.40 mT, and a n H = 0.13 mT; the other observed PBN adduct H H has the following hfsc's a N = 1.50 mT and a g H = 0.33 mT. The detection of these H reactive intermediates during the continued autooxidation of adrenolutin may account for the biochemical toxicity of catecholamine metabolism. These methods may allow for the quantification and/or characterization of the cardiotoxicity observed after organophosphate (OP) intoxication.