Treatment of Catecholaminergic Neurodegeneration

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Several findings in this reporting period relate to potential treatments to slow or prevent catecholaminergic neurodegeneration. We are especially interested in determining whether gene therapy with adeno-associated virus type 2 (AAV2) to increase endogenous production of glial cell line-derived neurotrophic factor (GDNF) slows the symptomatic progression of the rare disease multiple system atrophy (MSA) and improves clinical laboratory indices of central catecholaminergic functions. We also are testing experimental therapeutic predictions from the catecholaldehyde hypothesis, according to which 3,4-dihydroxyphenylacetaldehyde (DOPAL), an obligate intermediate in neuronal dopamine metabolism, causes or contributes to catecholaminergic neurodegeneration. (1) N-Acetylcysteine (NAC) mitigates DOPAL-induced protein modifications: Mechanisms of DOPAL neurotoxicity may include misfolding of intracellular proteins such as alpha-synuclein (AS). We found that DOPAL potently oligomerizes AS, converting AS to a toxic form, forms quinone-protein adducts with (quinonizes) AS, and evokes cytoplasmic AS deposition. In this regard DOPAL is far more potent than dopamine (Jinsmaa et al., J Pharmacol Exp Ther 2020;372:157-165). Co-incubation with NAC mitigates or prevents these alterations. These data rationalize treatment with NAC and a monoamine oxidase inhibitor (MAOI), to inhibit DOPAL formation and decrease formation of DOPAL-quinone (Jinsmaa et al., JPET 2018;366:113-124). (2) Substantial renal conversion of L-threo-3,4-dihydroxyphenylserine (L-DOPS) to norepinephrine in patients with neurogenic orthostatic hypotension: The norepinephrine precursor L-DOPS is approved for treatment of symptomatic orthostatic hypotension (OH). L-DOPS-induced increases in plasma norepinephrine levels are too small to explain the pressor effect of the drug. The kidneys contain abundant L-aromatic-amino-acid decarboxylase, which catalyzes the conversion of L-DOPS to norepinephrine. We assessed renal norepinephrine production from L-DOPS by comparing norepinephrine/L-DOPS ratios in urine to those in plasma in patients on L-DOPS. The ratio of norepinephrine/L-DOPS in urine averaged 63 times that in plasma. Thus, there is extensive renal production of norepinephrine from L-DOPS (Lamotte et al., Clin Auton Res 2019;29:113-117). (3) Coffee drinkers are relatively protected from developing PD, for reasons that are unclear. Almost all relevant research attention has focused on caffeine-induced inhibition of adenosine-2 receptors. We reported long ago that the plasma of coffee drinkers contains the anti-oxidant catechol 3,4-dihydrocaffeic acid (DHCA). We hypothesize that ingesting coffee increases plasma levels of DHCA and other catechols. We have found preliminarily that drinking coffee, whether caffeinated or decaffeinated, increases plasma DHCA levels as well as levels of at least 20 other catechols. Collaborations: (a) AAV2-GDNF treatment of MSA: Under an approved Bench-to-Bedside grant we will attempt to treat MSA by targeting the GDNF deficiency. A new clinical protocol is under IRB consideration at the Ohio State University. The NIH will be a site for evaluating patients who may be eligible for the trial and following them in terms of neuroimaging and CSF neurochemical measures of catecholaminergic functions. (b) Testing the catecholaldehyde hypothesis in vivo: In collaboration with Yehonatan Sharabi (Tel Aviv University) we are testing the catecholaldehyde hypothesis in animals by assessing whether combining the MAOI selegiline with NAC decreases DOPAL formation and prevents catecholaminergic neurodegeneration in the rat rotenone model of PD. (c) Mesenchymal stem cells to treat MSA: Intrathecal injection of mesenchymal stem cells might exert beneficial neurotrophic effects in this otherwise invariably lethal disease. In a collaborative study with investigators at the Mayo Clinic we are tracking CSF catechols as neurochemical biomarkers of treatment effects. (d) Renal sympathetic ablation to treat refractory hypertension: Renal sympathetic ablation is a possible non-pharmacologic treatment for refractory hypertension. In a collaborative study with the group headed by Dr. Benjamin Levine (Univ. of Texas), under NIH Clinical Protocol 18N0140 we used 18F-dopamine and 11C-methylreboxetine (11C-MRB) to assess the extent of local denervation. Preliminarily, we obtained the first evidence that a chemical denervation procedure actually decreases local sympathetic innervation in humans (Hearon et al., unpublished observations).. (e) Effects of atomoxetine on cerebrospinal fluid and plasma catechols: Atomoxetine is an FDA-approved drug that inhibits the cell membrane norepinephrine transporter (NET). As part of a collaborative study with Dr. Allan Levey (Emory) about whether atomoxetine improves cognitive dysfunction in people with mild cognitive impairment, we assayed cerebrospinal fluid (CSF) and plasma levels of catechols. Preliminarily, in both CSF and plasma atomoxetine treatment highly significantly increased levels of dopamine and norepinephrine without increasing levels of their respective neuronal metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenyglycol (DHPG). (f) AAV-mediated gene therapy in an animal model of Menkes disease: Menkes disease is a rare X-linked recessive disorder of a copper ATPase gene (ATP7A). Since dopamine-beta-hydroxylase (DBH), the enzyme that converts dopamine to norepinephrine, is a copper enzyme, increased levels of dopamine and its metabolites with respect to norepinephrine and its metabolites provides diagnostic biomarkers of Menkes disease in at-risk newborns. We are collaborating with Dr. Stephen Kaler (OSU) on animal models and gene therapy treatments of Menkes disease. (g) AAV-mediated gene therapy in an animal model of PD: Dopamine deficiency causes the movement disorder that defines PD. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in dopamine synthesis, and GTP cyclohydrolase-1 (GCH-1) is a key enzyme in the production of tetrahydrobiopterin, a required co-factor for TH. Under a Materials Cooperative Research and Development Agreement we carried out assays of CSF and tissue catechols in an exploratory study of intrathecal AAV2-TH/GCH1 in a rat PD model. (h) ALDH inhibition to treat opiate abuse: Opiate abuse is a major, increasing public health burden. Administration of opiates increases dopamine release in a particular brain system involved with reinforcement and learning. A possible treatment is to reduce rewarding effects of opiates by inhibiting dopamine synthesis. According to the hypothesis that aldehyde dehydrogenase inhibition leads to production of tetrahydropapaveroline, which feedback-inhibits TH, under the Helping to End Addiction Long-term (HEAL) initiative a clinical trial of an ALDH inhibitor is under way at the NIH Clinical Center. To determine whether the drug actually inhibits ALDH, we are collaborating by assaying plasma samples of protocol participants before and after drug administration. Preliminarily, we did not obtain neurochemical evidence for ALDH inhibition, with the dosing regimen being used.