Characterization of Catecholaldehyde Adducts with Carnosine and l-Cysteine Reveals Their Potential as Biomarkers of Catecholaminergic Stress.

Rachel A Crawford,T Blake Monroe,Luca Regazzoni,Jonathan A Doorn,Ettore Gilardoni,Ethan J Anderson

doi:10.1021/acs.chemrestox.1c00153

Rachel A Crawford, T Blake Monroe + Show 4 more

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https://doi.org/10.1021/acs.chemrestox.1c00153

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Abstract

Monoamine oxidase (MAO) catalyzes the oxidative deamination of dopamine and norepinephrine to produce 3,4-dihydroxyphenylacetaldehyde (DOPAL) and 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL), respectively. Both of these aldehydes are potently cytotoxic and have been implicated in pathogenesis of neurodegenerative and cardiometabolic disorders. Previous work has demonstrated that both the catechol and aldehyde moieties of DOPAL are reactive and cytotoxic via their propensity to cause macromolecular cross-linking. With certain amines, DOPAL likely reacts via a Schiff base before oxidative activation of the catechol and rearrangement to a stable indole product. Our current work expands on this reactivity and includes the less-studied DOPEGAL. Although we confirmed that antioxidants mediated DOPAL’s reactivity with carnosine and N-acetyl-l-lysine, antioxidants had no effect on reactivity with l-cysteine. Therefore, we propose a non-oxidative mechanism where, following Schiff base formation, the thiol of l-cysteine reacts to form a thiazolidine. Similarly, we demonstrate that DOPEGAL forms a putative thiazolidine conjugate with l-cysteine. We identified and characterized both l-cysteine conjugates via HPLC-MS and additionally identified a DOPEGAL adduct with carnosine, which is likely an Amadori product. Furthermore, we were able to demonstrate that these conjugates are produced in biological systems via MAO after treatment of the cell lysate with norepinephrine or dopamine along with the corresponding nucleophiles (i.e., l-cysteine and carnosine). As it has been established that metabolic and oxidative stress leads to increased MAO activity and accumulation of DOPAL and DOPEGAL, it is conceivable that conjugation of these aldehydes to carnosine or l-cysteine is a newly identified detoxification pathway. Furthermore, the ability to characterize these adducts via analytical techniques reveals their potential for use as biomarkers of dopamine or norepinephrine metabolic disruption.

Highlights

Monoamine oxidase (MAO)-catalyzed deamination of norepinephrine (NE) and dopamine (DA) yields 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL) and 3,4-dihydroxyphenylacetaldehyde (DOPAL), respectively, as well as H2O2.1 Under physiological conditions, these catecholaldehyde metabolites are detoxified primarily by aldehyde dehydrogenase (ALDH) to their corresponding carboxylic acid or by aldose reductase (AR) to their corresponding alcohol.[2]
We demonstrate that MAO activity is necessary and sufficient for conjugate formation in a cell lysate, suggesting that the formation of these adducts may be novel detoxification pathways for catecholaldehydes and that the resultant conjugates could be biomarkers for neuro or cardiac injury
Inactive Cell Lysate: Carnosine or L-cysteine was incubated with DOPEGAL or DOPAL at a final concentration of 1 mM and 100 μM, respectively, in 100 μg/mL cell lysate at 37 °C, which represents at 10:1 ratio of reactants

Summary

Introduction

Monoamine oxidase (MAO)-catalyzed deamination of norepinephrine (NE) and dopamine (DA) yields 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL) and 3,4-dihydroxyphenylacetaldehyde (DOPAL), respectively, as well as H2O2.1 Under physiological conditions, these catecholaldehyde metabolites are detoxified primarily by aldehyde dehydrogenase (ALDH) to their corresponding carboxylic acid or by aldose reductase (AR) to their corresponding alcohol.[2] Under conditions of oxidative stress, a multilevel dysregulation of catecholamine metabolism occurs, resulting in an accumulation of the aldehyde intermediates.[1] Aberrant production of these aldehydes, which are highly reactive and cytotoxic, has been implicated in disease etiopathology.[1,3] This is often referred to as the “catecholaldehyde hypothesis”.1. DOPAL has been studied for its role in the pathogenesis of Parkinson’s disease: DOPAL can covalently modify proteins,[4,5,6] generate reactive oxygen species and radicals,[7] and promote oligomerization of α-synuclein, a hallmark of Parkinson’s.8,9 Both DOPAL10 and DOPEGAL11 have recently been implicated in Alzheimer’s disease pathogenesis due to their potent activation of asparagine endopeptidase, the enzyme involved in amyloid precursor protein and Tau accumulation.

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