Mechanism(s) Underlying Toxicity and the Development of Tolerance to Methamphetamine

Transkript

1 Mechanism(s) Underlying Toxicity and the Development of Tolerance to Methamphetamine Diana G. Wilkins, PhD. Center for Human Toxicology University of Utah Salt Lake City, Utah

2 Methamphetamine METH, ice, crank or speed; Schedule II stimulant Various routes of administration

3 How is METH Used? Dependent upon route of administration; mg/episode; as much as 1-2 g in a binge (i.e., very high doses) Effect persists 6-8 hours

4 How is METH Used? Immediately after inhalation or i.v. administration, user experiences brief flash or rush Snorting or oral administration produces euphoria, but not an intense rush; effects last as long as 12 hours Snorting produces effects within 3-5 minutes; oral administration within 15 minutes Tolerance to euphoric effects occurs within minutes

5 METH Trends Mentions Methamp Amphet

6 METH Lab Seizures Source: US Department of Justice

7 Why is METH Abused? Long duration of action (especially relative to cocaine) Inexpensive, easy to manufacture

8 What are METH s Adverse Effects? After initial rush, often agitation and perhaps violent behavior Extremely addicting Severe craving Hyperthermia Weight loss

9 What Does METH Do? What happens at the synapse after a single dose of METH?

10 Brain Regions of Interest * * *

11 Neuronal Morphology

12 Model of a Dopaminergic Synapse

13 Model of a Serotonergic Synapse

14 Synaptosomes (P2) Homogenize Centrifuge 1000 x g Resuspend Centrifuge 22,000 x g Osmotic Lysis And 100,000 x g Vesicles (P3) Membranes (P3)

15 Mechanism of Action Causes release of dopamine via reversal of the dopamine transporter Causes some release of serotonin and norepinephrine as well

16 What Does METH Do? What happens after multiple doses of METH (neurotoxic regimen)?

17 Neurotoxicity A neurotoxic regimen of METH: - Causes long-term reduction in TH and TPH enzyme activities (Koda and Gibb, 1973; Hotchkiss and Gibb 1980; Bakhit and Gibb, 1980) Hotchkiss and Gibb, 1980

18 Neurotoxicity A neurotoxic regimen of METH: - Causes long-term depletion of dopamine in striatum and other brain regions (Kogan and Gibb, 1976; Morgan and Gibb,1980; Ricaurte et al., 1980) Morgan and Gibb, 1980

19 Neurotoxicity A neurotoxic regimen of METH: - Causes hyperthermia that is linked to depletion in dopamine. Blocking hyperthermia attenuates the dopamine deficits (Bowyer et al., 1992; 1993; 1994 ) Bowyer et al., 1994

20 Neurotoxicity A neurotoxic regimen of METH: - Increases free radical formation in striatum (Giovanni et al., 1995; Fleckenstein et al. 1999)

21 Neurotoxicity A neurotoxic regimen of METH: - Decreases DA transporter re-uptake (Kokoshka et al., 1998; Metzger et al., 2000)

22 Adverse Effects Persistent dopaminergic deficits McCann et al., J. Neurosci. 1998

23 Neurotoxicity A neurotoxic regimen of METH: - Decreases VMAT2 uptake (Brown et al., 2000)

24 Neurotoxicity A neurotoxic regimen of METH: - Demonstrates age-dependent changes for DAT uptake and TH (Kokoshka( et al., 2000)

25 Neurotoxicity A neurotoxic regimen of METH: - Demonstrates age-dependent differential responses in METH concentrations. Kokoshka et al., 2000

26 Neurotoxicity A neurotoxic regimen of METH: - Causes a redistribution of synaptic vesicles (Riddle et al., 2002; 2003) Synaptosome Membrane Vesicle * Saline METH Saline METH Saline METH 0 *

27 Dopaminergic Synapse : Neurotoxicity

28 Neurotoxicity: Important Concepts METH causes persistent dopaminergic deficits Hyperthermia contributes to deficits Reactive oxygen species contribute to deficits METH causes trafficking of vesicles

29 What Does METH Do? What happens when multiple doses of METH are given at frequent intervals?

30 Tolerance Tolerance is defined as a diminished response to a drug after repeated doses. - Can be behavioral, pharmacokinetic, etc. - For this presentation, tolerance will be defined in terms of striatal dopamine and serotonin (outcome markers).

31 Tolerance Protocols

32 Tolerance A tolerance-inducing METH regimen: - Attenuates the depletion in striatal dopamine and serotonin observed after a neurotoxic regimen Treatment SAL Pretxt + METH Challenge METH PreTxt + METH Challenge ( mg/kg/day) Dopamine * % of control * # % of control 5-HT * % of control * # % of control Schmidt et al., 1985

33 What Does METH Do? So, integrating what the lab is exploring in neurotoxicity,, what happens during tolerance with respect to: - Temperature? - Persistence of tolerance? - Alterations in distribution of drug? - Effects on transporters? - Reactive oxygen species?

34 Tolerance A tolerance-inducing METH regimen: - Attenuates the dopamine depletion after a neurotoxic regimen given 24 hours after pre- treatment Dopamine Concentrations in Striatum DA (ng/mg protein) SS MS SM MM * Mean +/- S.D. METH Pretxt: : 5 escalating s.c.. doses of 2.5, 5.0, hr 6 intervals METH Challenge: : 5 s.c.. doses of hr 4 intervals

35 Tolerance A tolerance-inducing METH regimen: - Attenuates the hyperthermia observed during a neurotoxic regimen Temp 0 C Temp Data Tolerance Experiment Ptx with 5x2.5, 5, 6 Hr Int Challenge with 5x Hr Int * * * Time (hrs) * * * * SS MS SM MM Dosing

36 Tolerance A tolerance-inducing METH regimen: - With this protocol, does not alter the brain concentration of METH METH Concentrations in Three Brain Regions Tolerance Experiment 10 Meth (n g /m g) SM MM 0 Frontal Cortex Hippocampus Striatum

37 Tolerance A tolerance-inducing METH regimen: - Attenuates deficits in several brain regions 1 week after challenge STRIATUM STRIATUM HIPPOCAMPUS FRONTAL CORTEX DOPAMINE (pg /µg protein) SEROTONIN (pg /µg protein) 4 3 * * SEROTONIN (pg /µg protein) * * SEROTONIN (pg /µg protein) * SALINE/SALINE SALINE/METH METH/SALINE METH/METH Davis et al., 2003 (In Press)

38 Tolerance A tolerance-inducing METH regimen: - No significant alteration in DAT re-uptake of dopamine DA Uptake (fmol / mg protein) SALINE/SALINE SALINE/METH METH/SALINE METH/METH

39 Tolerance A tolerance-inducing METH regimen: - Decreases the attenuation of VMAT2 dopamine uptake (function of VMAT) Vesicular DA Uptake (fmol / mg protein) * * + * # * 0 SALINE/SALINE SALINE/METH METH/SALINE METH/METH

40 Tolerance A tolerance-inducing METH regimen: - Attenuated the redistribution of VMAT2 within nerve terminal Non-membrane-associated fraction Band Density (Arbitrary Units) * * ** 0 SALINE/SALINE METH/SALINE 0 SALINE/SALINE SALINE/METH 0 METH/SALINE METH/METH 0 SALINE/METH METH/METH

41 Dopaminergic Synapse : Tolerance

42 Tolerance: Important Concepts Development of tolerance is dependent on the dosing paradigm Tolerance protocols attenuate persistent dopaminergic deficits Temperature and tolerance are linked Tolerance protocols appear to alter trafficking of vesicles

43 Acknowledgements Kamisha Johnson-Davis*, B.S. Jonathan Danaceau,, PhD.* Jayme Day, B.S., Brad Charles, B.S., Cassie Deering,, B.S. and Stacy Smeal,, B.S. Annette Fleckenstein, PhD. and Laboratory NIDA Program Project Grant No. DA 13367