Genetic Differences in Vulnerability to Methamphetamine-related Brain Dysfunction: Implications for HIV
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Genetic Differences in Vulnerability to Methamphetamine-related Brain Dysfunction: Implications for HIV Mariana Cherner, PhD Associate Professor In Residence Department of Psychiatry UCSD AIDS Rounds 02/22/13
Objectives Overview of methamphetamine CNS effects Results of neuropsychological study of methamphetamine Preliminary evidence for individual differences in methamphetamine-associated neurocognitive impairment: role of metabolism Relevance for HIV and HCV Future study
Methamphetamine-related brain injury Damage / loss of dopamine terminals and transporters Oxidative stress Mitochondrial injury Glutamatergic excitotoxic injury Glial activation Increase in inflammatory cytokines/chemokines Cerebrovascular pathology Brain metabolic and perfusion changes Loss of neurons in subcortical regions
Meta-analysis: Neuropsychological Effects of Methamphetamine Scott, et al. (2007). Neuropsychol Rev 17:275–297
Problems with published studies Studies of methamphetamine users show cognitive and psychomotor abnormalities, but » Few documented HIV serostatus » None documented HCV serostatus » Control Ss typically have less other substance abuse » Control Ss often have better premorbid functioning
Cognitive impairment in subjects withsingle or co-morbid HIV and Meth Risks (N=398) Rippeth et al, JINS, 2004
Rates of NP Impairmentby Number of Meth, HIV, and HCV Risk Factors
Predictors of NP Impairment amongMethamphetamine Dependent Individuals
Objectives1. Determine prevalence of NP impairment in HIV-, HCV- meth users compared to healthy controls with similar demographic characteristics and estimated premorbid functioning.2. Determine which meth use characteristics are associated with NP impairment.
Greater proportion NP impairmentamong methamphetamine dependent based on age, education, sex, and ethnicity adjusted test scores
Confounding Variables did not Predict Global Neuropsychological Impairmentalcohol cannabiswhole model test: X2 = 6.99 p = .03 whole model test: X2 = 5.80 p = .05alcohol effect: X2 = 1.56 p = .21 cannabis effect: X2 = .44 p = .50meth effect: X2 = 6.37 p = .01 meth effect: X2 = 5.4 p = .02cocainewhole model test: X2 = 5.60 p = .06 MDD lifetime: X2 = .06 p = .81cocaine effect: X2 = 0.21 p = .62 MDD current: X2 = .45 p = .50meth effect: X2 = 5.28 p = .02 ASPD: X2= .04 p = .85 ADHD: X2 = .02 p = .89
Methamphetamine use characteristics did not predict neuropsychological impairmentMean (sd) or Proportion NP Impaired (n=22) NP Normal (n=32) p valueLength of abstinence in days 125.2 (96.1) 131.1 (103.2) NSYears of use 11.8 (5.2) 12.1 (5.4) NSLifetime grams consumed 4234 (3421) 4415 (4603) NSAverage grams per year of use 413 (395) 363 (340) NSn (%) using in the last 30 days 3 (14%) 4 (13%) NSPrimary mode of METH use NS n (%) ingest 0 1 (3%) n (%) inject 2 (9%) 5 (16%) n (%) insufflate 7 (32%) 12 (37%) n (%) smoke 13 (59%) 14 (44%) Cherner, et al. (2002). JINS
Conclusions from previous findings:The lack of correspondence betweenmethamphetamine exposure and NP impairment suggests individual differences in vulnerability to methamphetamine neurotoxicity
Possible targets to investigate Pharmacodynamic NP impairment could be » Metabolic pathways/enzymes related to » Receptors » Genes associated with » Transporters drug response » Intracellular signaling » Genes associated with pathways neuropathologic vulnerability » DNA binding proteins » Their combination Pharmacokinetic » Metabolism » Distribution » Absorption From: K. Heinzerling, 2007
Cytochrome P450, family 2, subfamily D, polypeptide 6 Enzyme that metabolizes many psychoative compounds Highly polymorphic Located on chromosome 22q13.1Source: Detectable in brainhttp://en.wikipedia.org/wiki/Image:CYP2D6_structure.png. Borislav Mitev Responsible for primary oxidative metabolism of methamphetamine Source: Lin et al, 1997
CYP2D6 Metabolic Activity Over 80 known genetic polymorphisms, many affecting metabolic rate Resulting phenotypes (%= prevalence in Caucasians): » Extensive metabolizer is wildtype - 65 to 70% » Intermediate metabolizer - 20-30% » Poor metabolizer - 5 to 14% » Ultra-rapid metabolizer - rare
Poor Metabolizers Have no active CYP2D6 alleles (or 1 partially active) Are at greater risk of drug-induced side effects due to diminished drug elimination most common mutant alleles in Caucasians: CYP2D6*3, CYP2D6*4, CYP2D6*5, CYP2D6*6, which account for 93-97% of the PM phenotypes Low prevalence among Asians, higher in Africans Gonzalez et al, 1988; Gough et al, 1990; Kimura et al, 1989; Marez et al, 1997
Study Objective and Hypothesis Primary Aim: To determine the influence of CYP2D6 phenotype corresponding to high or low metabolic activity on cognitive functioning in abstinent methamphetamine addicts Hypothesis: Extensive metabolizers will clear methamphetamine more effectively and therefore will show better NP functioning
RESULTS: Methamphetamine UseCharacteristics by Metabolic Phenotype Mean (SD) or % Extensive (n=33) Intermediate (n=17) Poor (n=3) Age Onset 22 (9) 24 (6) 18 (2) Total Years of Use 12 (5) 12 (5) 11 (9) Days Abstinent 131 (107) 113 (80) 117 (63) METH Density (g/yr) 413 (324) 370 (448) 240 (279) Lifetime grams 4719 (4237) 3559 (3787) 4267 (5869) Last Year grams 347 (314) 267 (304) 333 (422) Binge use predominant 4% 5% 0% Route* injection 6% 25% 33% (1/3) intranasal 29% 50% 33% (1/3) smoke 65% 25% 33% (1/3) *p < .05
Greater Prevalence of Neuropsychological Impairment in Extensive Metabolizers *p<.05 †p<.10
CYP2D6 Rank Ordered Activity Metabolic activity rank:Activity Phenotype n 1: two non-functional alleles 1 PM 3 2: one decreased function and one non-functional allele 2 IM 4 3: one normal function and one non-functional allele, or two 3 IM 13 decreased function alleles 4: one normal function and one 4 EM 14 decreased function allele 5 EM 18 5: two normal function alleles (based on activity data by Zanger, 2004)
Correlations between NP Deficit Scores and CYP2D6 metabolic activity based on combination of alleles Deficit Score Spearman Ρ Prob>|ρ| Global 0.36 0.009 Processing Speed 0.31 0.025 Attn/Wk Memory 0.16 0.257 Verbal Fluency 0.18 0.192 Learning 0.39 0.004 Delayed Recall 0.20 0.156 Executive 0.35 0.010 Motor 0.02 0.868
Summary Methamphetamine use parameters are poor predictors of cognitive impairment, suggesting individual differences in vulnerability to neurotoxic effects Results of CYP2D6 study implicate the products of methamphetamine metabolism as a source of brain injury High CYP2D6 metabolic activity is associated with worse neurocognitive outcomes, possibly as a result of greater formation of harmful methamphetamine oxidative metabolites Low metabolic activity may also be associated with worse neurocognitive outcome, perhaps as a result of lower clearance of the parent compound Other factors may be at play: cannabis? antidepressants? meth dose?
Summary (cont) First study to suggest that differential meth metabolism is associated with neurocognitive outcomes Findings are supported by in vitro studies showing greater cellular toxicity of methamphetamine1 and other substituted amphetamines (MDMA, MTA)2 under conditions of normal vs. low CYP2D6 activity Recent study of MDMA users showed ultra-rapids had worse cognitive performance
The case for toxic metabolites Hydroxy metabolites of amphetamine and meth are neurochemically and behaviorally active have a much longer half-life than the parent compound (e.g., 1.5 days compared 45 minutes, in rat brain) can induce release and inhibit uptake of norepinephrine and dopamine with almost equivalent potency to the unmetabolized substances. are taken up by dopaminergic terminals accumulate in striatum and hypothalamus after chronic administration. can induce hyperlocomotion and stereotyped behaviors
in vitro evidence Meth hydroxy metabolite causes greater cytotoxicity than unmetabolized meth Cells expressing the active form of CYP2D6 show greater MDMA toxicity than cells with less active forms toxicity of MDMA metabolite (N-methyl-α- methyldopamine) was found 100-fold stronger than unmetabolized MDMA
Brain CYP2D6 Activity CYP2D6 protein and mRNA are detectable in a number of brain regions, both in neurons and glia CYP2D6 metabolic activity is detectable in animal brain microsomes CYP2D6 involved in biotransformation of dopamine and serotonin from trace amines in brain – thought to influence DA – 5HT balance.
Infectious Disease Rationale CYP2D6 activity is dysregulated in HCV and HIV there are no studies investigating whether the meth- associated brain dysfunction observed in HIV is mitigated by genotypes influencing meth metabolism. it is not known how the bioavailability of meth or its metabolic products may contribute to the added neuropsychological sequelae that meth abuse confers in the context of HIV and HCV Ritonavir and SSRI’s (and other Rx) commonly prescribed are CYP2D6 inhibitors
CYP2D6 Genotype and Cognitive Deficits inMethamphetamine Users with/without HIV new R01 study to begin April 2013
Aim 1 To determine effects of CYPD6 genotype on methamphetamine-associated neurocognitive deficits. Address whether CYP2D6 genotype contributes to differences in frequency or severity of neurocognitive deficits among meth users, and explore alternative explanations of the data, including whether CYP2D6 genotype explains differences in meth consumption or mode of use.
Aim 2 To identify factors that mitigate CYP2D6 effects on methamphetamine-associated deficits. Whether the relationship between CYP2D6 genotype and cognitive outcomes is altered in the context of HIV or HCV infection, and how concomitant use of substances that interact with CYP2D6 (e.g., ritonavir, antidepressants) affects that relationship.
Exploratory Aim To explore effects of interactions between CYP2D6 and other genes on neurocognitive outcomes. Given the role of CYP2D6 in biotransformation of dopamine and serotonin, focus on common polymorphisms that code for dopamine and serotonin activity/availability.Catechol-o-methyl transferase COMT Val158Met Dopamine transporterDopamine receptors 2, 3, 4 Tryptophan Hydroxylase 2DOPA/tryptophan decarboxylase Monoamine oxidase ASerotonin receptor 2A Serotonin-transporterSerotonin-transporter-gene-linked polymorphic region
Current & Future Directions Determine degree of brain injury as a function of CYP2D6 phenotype in autopsy tissues from deceased methamphetamine users (R03 funded study) Measure actual relationship between meth metabolites cellular injury in an in vitro model with mixed brain cell cultures (submitted R21 application)
Public Health Importance Tools for providers to make advantageous treatment choices. » e.g., if findings are replicated: prescribe a CYP2D6 inhibitor to turn a genotypically extensive metabolizer into a poor metabolizer. » if findings are reversed: avoid further inhibiting CYP2D6 activity by choosing alternate medications. » educate patients/clients about particularly risky practices (e.g., what are the risks of using meth while being on a ritonavir- containing cART regimen?