Interaction and Transport of Methamphetamine and its Primary Metabolites by Organic Cation and Multidrug and Toxin Extrusion Transporters

An unconventional cancer-promoting function of methamphetamine in hepatocellular carcinoma

For the past decade, the prevalence and mortality of methamphetamine (METH) use have doubled, suggesting that METH use could be the next substance use crisis worldwide. Ingested METH is transformed into other products in the liver, a major metabolic organ. Studies have revealed that METH causes deleterious inflammatory response, oxidative stress, and extensive DNA damage. These pathological damages are driving factors of hepatocellular carcinoma (HCC). Nonetheless, the potential role of METH in HCC and the underlying mechanisms remain unknown. Herein, we found a higher HCC incidence in METH abusers. METH promoted cellular proliferation, migration, and invasion in two human-derived HCC cells. Consistently, METH uptake promoted HCC progression in a xenograft mouse model. Mechanistically, METH exposure induced ROS production, which activated the Ras/MEK/ERK signaling pathway. Clearance of ROS by NAC suppressed METH-induced activation of Ras/ERK1/2 pathways, leading to arrest of HCC xenograft formation in nude mice. To the best of our knowledge, this is the first study to substantiate that METH promotes HCC progression and inhibition of ROS may reverse this process.

Interaction Profiles of Central Nervous System Active Drugs at Human Organic Cation Transporters 1-3 and Human Plasma Membrane Monoamine Transporter

Many psychoactive compounds have been shown to primarily interact with high-affinity and low-capacity solute carrier 6 (SLC6) monoamine transporters for norepinephrine (NET; norepinephrine transporter), dopamine (DAT; dopamine transporter) and serotonin (SERT; serotonin transporter). Previous studies indicate an overlap between the inhibitory capacities of substances at SLC6 and SLC22 human organic cation transporters (SLC22A1-3; hOCT1-3) and the human plasma membrane monoamine transporter (SLC29A4; hPMAT), which can be classified as high-capacity, low-affinity monoamine transporters. However, interactions between central nervous system active substances, the OCTs, and the functionally-related PMAT have largely been understudied. Herein, we report data from 17 psychoactive substances interacting with the SLC6 monoamine transporters, concerning their potential to interact with the human OCT isoforms and hPMAT by utilizing radiotracer-based in vitro uptake inhibition assays at stably expressing human embryonic kidney 293 cells (HEK293) cells. Many compounds inhibit substrate uptake by hOCT1 and hOCT2 in the low micromolar range, whereas only a few substances interact with hOCT3 and hPMAT. Interestingly, methylphenidate and ketamine selectively interact with hOCT1 or hOCT2, respectively. Additionally, 3,4-methylenedioxymethamphetamine (MDMA) is a potent inhibitor of hOCT1 and 2 and hPMAT. Enantiospecific differences of R- and S-α-pyrrolidinovalerophenone (R- and S-α-PVP) and R- and S-citalopram and the effects of aromatic substituents are explored. Our results highlight the significance of investigating drug interactions with hOCTs and hPMAT, due to their role in regulating monoamine concentrations and xenobiotic clearance.

How do psychostimulants enter the human brain? Analysis of the role of the proton-organic cation antiporter

BACKGROUND

Although psychostimulants apparently do cross the BBB, it is poorly understood how these hydrophilic and positively charged molecules can pass the blood-brain barrier (BBB). That may be mediated by a genetically still uncharacterized H⁺/OC antiporter with high activity at the BBB.

METHODS

We studied the uptake of 16 psychostimulants and hallucinogens with hCMEC/D3 cells using the prototypic inhibitor imipramine (cis-inhibition), exchange transport with diphenhydramine and clonidine (trans-stimulation), proton dependency of the uptake, and we characterized the concentration-dependent uptake.

RESULTS

Cell uptake of methylenedioxyamphetamines, amphetamines and dimethyltryptamine (DMT) were strongly inhibited (to about 10% of the controls) by imipramine and diphenhydramine, whereas uptake of cathine was only weakly inhibited and mescaline not significantly. Amphetamine, methylamphetamine, para-Methoxy-N-methylamphetamine (PMMA), Methylenedioxymethamphetamine (MDMA), phentermine and DMT exhibited the highest exchange after preloading with diphenhydramine with only 5.5%, 5.2%, 7.8%, 6%, 1.9%, 7.6% remaining in the cells. Less and no exchange were seen with cathine and mescaline, respectively. Dependence on intracellular pH was most pronounced with the methylendioxyamphetamines while uptake of cathine, DOI and cocaine were only moderately affected and mescaline not at all.

CONCLUSION

Except for mescaline, all psychostimulants studied here were substrates of the H⁺/OC antiporter, implicating a strong need for a better characterization of this transport protein.

Pharmacology of Drugs Used as Stimulants

Psychostimulant, cardiovascular, and temperature actions of stimulants involve adrenergic (norepinephrine), dopaminergic (dopamine), and serotonergic (serotonin) pathways. Stimulants such as amphetamine, 3,4-methylenedioxymethamphetamine (MDMA), or mephedrone can act on the neuronal membrane monoamine transporters NET, DAT, and SERT and/or the vesicular monoamine transporter 2 to inhibit reuptake of neurotransmitter or cause release by reverse transport. Stimulants may have additional effects involving pre- and postsynaptic/junctional receptors for norepinephrine, dopamine, and serotonin and other receptors. As a result, stimulants may have a wide range of possible actions. Agents with cocaine or MDMA-like actions can induce serious and potentially fatal adverse events via thermodysregulatory, cardiovascular, or other mechanisms. MDMA-like stimulants may cause hyperthermia that can be life threathening. Recreational users of stimulants should be aware of the dangers of hyperthermia in a rave/club environment.

Transport of Drugs and Endogenous Compounds Mediated by Human OCT1: Studies in Single- and Double-Transfected Cell Models

Organic Cation Transporter 1 (OCT1, gene symbol: SLC22A1) is predominately expressed in human liver, localized in the basolateral membrane of hepatocytes and facilitates the uptake of endogenous compounds (e.g. serotonin, acetylcholine, thiamine), and widely prescribed drugs (e.g. metformin, fenoterol, morphine). Furthermore, exogenous compounds such as MPP⁺, ASP⁺ and Tetraethylammonium can be used as prototypic substrates to study the OCT1-mediated transport in vitro. Single-transfected cell lines recombinantly overexpressing OCT1 (e.g., HEK-OCT1) were established to study OCT1-mediated uptake and to evaluate transporter-mediated drug-drug interactions in vitro. Furthermore, double-transfected cell models simultaneously overexpressing basolaterally localized OCT1 together with an apically localized export protein have been established. Most of these cell models are based on polarized grown MDCK cells and can be used to analyze transcellular transport, mimicking the transport processes e.g. during the hepatobiliary elimination of drugs. Multidrug and toxin extrusion protein 1 (MATE1, gene symbol: SLC47A1) and the ATP-driven efflux pump P-glycoprotein (P-gp, gene symbol: ABCB1) are both expressed in the canalicular membrane of human hepatocytes and are described as transporters of organic cations. OCT1 and MATE1 have an overlapping substrate spectrum, indicating an important interplay of both transport proteins during the hepatobiliary elimination of drugs. Due to the important role of OCT1 for the transport of endogenous compounds and drugs, in vitro cell systems are important for the determination of the substrate spectrum of OCT1, the understanding of the molecular mechanisms of polarized transport, and the investigation of potential drug-drug interactions. Therefore, the aim of this review article is to summarize the current knowledge on cell systems recombinantly overexpressing human OCT1.

Electrochemiluminescent screening for methamphetamine metabolites

The abuse of methamphetamine (MA) is to date detected and subsequently verified through the monitoring of MA and its metabolites within biological specimens. Current approaches require complex sample purification strategies alongside significant analysis time. Given the high prevalence of MA within the global drug market, there remains a need for rapid, portable and alternative screening approaches appropriate for direct detection within biological matrices for employment across the forensic and clinical environments. This contribution illustrates the use of an electrochemiluminescence (ECL) strategy for the screening of MA, amphetamine (AMP) and para hydroxy-methamphetamine (pOH-MA) for such applications. The sensing system showed ideal analytical performance with linear ranges at forensically relevant concentrations of 0.1 μM to 0.5 mM for MA, 10 μM to 1 mM AMP and 10 μM to 5 mM for pOH-MA, and superb detection limits of 74.6 nM, 6 μM and 82. μM for MA, AMP and pOH-MA respectively. Furthermore, the sensor was successful in the detection of MA, AMP and pOH-AMP within human pooled serum, artificial urine and saliva, without any prior purification strategies. Here a portable ECL sensor is detailed for the successful employment of the direct screening of these amphetamine type substances and their corresponding metabolites at clinically and forensically relevant concentrations within a range of biological matrices. This approach successfully represents a strong proof-of-concept, for a novel, simple and rapid screening method with significant potential for high-throughput screening of biological samples for drug metabolites, widening the avenues where ECL sensors could be employed.

A Review of the Metabolism and Potential Drug-drug Interactions With Addictive Drugs

People who use drugs (PWUD) are at increased risk for drug-related harms such as overdose. Additionally, they are also at increased risk of secondary harms from bacterial and other infections such as hepatitis B, hepatitis C, and Human Immunodeficiency Virus. These secondary harms, along with other medical conditions, typically require treatment with prescription medications. When considering treatment options, drug-drug interactions (DDIs) must be considered, unfortunately these interactions are often overlooked with addictive drugs. Although DDIs in PWUD have been reviewed for certain drug classes and specific drugs of abuse, no comprehensive list could be found. The objective of this article is to compile a list of potential DDIs between prescription drugs and addictive drugs to create a list allowing prescribers to make more informed decisions when prescribing a medication to PWUD.

The Interaction of Organic Cation Transporters 1-3 and PMAT with Psychoactive Substances

Organic cation transporters 1-3 (OCT1-3, SLC22A1-3) and the plasma membrane monoamine transporter (PMAT, SLC29A4) play a major role in maintaining monoaminergic equilibrium in the central nervous system. With many psychoactive substances interacting with OCT1-3 and PMAT, a growing literature focuses on characterizing their properties via in vitro and in vivo studies. In vitro studies mainly aim at characterizing compounds as inhibitors or substrates of murine, rat, and human isoforms. The preponderance of studies has put emphasis on phenylalkylamine derivatives, but ketamine and opioids have also been investigated. Studies employing in vivo (knockout) models mostly concentrate on the interaction of psychoactive substances and OCT3, with an emphasis on stress and addiction, pharmacokinetics, and sensitization to psychoactive drugs. The results highlight the importance of OCT3 in the mechanism of action of psychoactive compounds. Concerning in vivo studies, a veritable research gap concerning OCT1, 2, and PMAT exists. This review provides an overview and summary of research conducted in this field of research.

General Overview of Organic Cation Transporters in Brain

Inhibitors of Na⁺/Cl^- dependent high affinity transporters for norepinephrine (NE), serotonin (5-HT), and/or dopamine (DA) represent frequently used drugs for treatment of psychological disorders such as depression, anxiety, obsessive-compulsive disorder, attention deficit hyperactivity disorder, and addiction. These transporters remove NE, 5-HT, and/or DA after neuronal excitation from the interstitial space close to the synapses. Thereby they terminate transmission and modulate neuronal behavioral circuits. Therapeutic failure and undesired central nervous system side effects of these drugs have been partially assigned to neurotransmitter removal by low affinity transport. Cloning and functional characterization of the polyspecific organic cation transporters OCT1 (SLC22A1), OCT2 (SLC22A2), OCT3 (SLC22A3) and the plasma membrane monoamine transporter PMAT (SLC29A4) revealed that every single transporter mediates low affinity uptake of NE, 5-HT, and DA. Whereas the organic transporters are all located in the blood brain barrier, OCT2, OCT3, and PMAT are expressed in neurons or in neurons and astrocytes within brain areas that are involved in behavioral regulation. Areas of expression include the dorsal raphe, medullary motoric nuclei, hypothalamic nuclei, and/or the nucleus accumbens. Current knowledge of the transport of monoamine neurotransmitters by the organic cation transporters, their interactions with psychotropic drugs, and their locations in the brain is reported in detail. In addition, animal experiments including behavior tests in wildtype and knockout animals are reported in which the impact of OCT2, OCT3, and/or PMAT on regulation of salt intake, depression, mood control, locomotion, and/or stress effect on addiction is suggested.

Substrates and Inhibitors of Organic Cation Transporters (OCTs) and Plasma Membrane Monoamine Transporter (PMAT) and Therapeutic Implications

The gene products of the SLC22A gene family (hOCT1, hOCT2, and hOCT3) and of the SLC29A4 gene (hPMAT or hENT4) are all polyspecific organic cation transporters. Human OCTs (including hPMAT) are expressed in peripheral tissues such as small intestine, liver, and kidney involved in the pharmacokinetics of drugs. In the human brain, all four transporters are expressed at the blood-brain barrier (BBB), hOCT2 is additionally expressed in neurons, and hOCT3 and hPMAT in glia. More than 40% of the presently used drugs are organic cations. This chapter lists and discusses all known drugs acting as substrates or inhibitors of these four organic cation transporters, independently of whether the transporter is expressed in the central nervous system (CNS) or in peripheral tissues. Of interest is their involvement in drug absorption, distribution, and excretion as well as potential OCT-associated drug-drug interactions (DDIs), with a focus on drugs that act in the CNS.

Organic Cation Transporters in Health and Disease

The organic cation transporters (OCTs) OCT1, OCT2, OCT3, novel OCT (OCTN)1, OCTN2, multidrug and toxin exclusion (MATE)1, and MATE kidney-specific 2 are polyspecific transporters exhibiting broadly overlapping substrate selectivities. They transport organic cations, zwitterions, and some uncharged compounds and operate as facilitated diffusion systems and/or antiporters. OCTs are critically involved in intestinal absorption, hepatic uptake, and renal excretion of hydrophilic drugs. They modulate the distribution of endogenous compounds such as thiamine, L-carnitine, and neurotransmitters. Sites of expression and functions of OCTs have important impact on energy metabolism, pharmacokinetics, and toxicity of drugs, and on drug-drug interactions. In this work, an overview about the human OCTs is presented. Functional properties of human OCTs, including identified substrates and inhibitors of the individual transporters, are described. Sites of expression are compiled, and data on regulation of OCTs are presented. In addition, genetic variations of OCTs are listed, and data on their impact on transport, drug treatment, and diseases are reported. Moreover, recent data are summarized that indicate complex drug-drug interaction at OCTs, such as allosteric high-affinity inhibition of transport and substrate dependence of inhibitor efficacies. A hypothesis about the molecular mechanism of polyspecific substrate recognition by OCTs is presented that is based on functional studies and mutagenesis experiments in OCT1 and OCT2. This hypothesis provides a framework to imagine how observed complex drug-drug interactions at OCTs arise. Finally, preclinical in vitro tests that are performed by pharmaceutical companies to identify interaction of novel drugs with OCTs are discussed. Optimized experimental procedures are proposed that allow a gapless detection of inhibitory and transported drugs.

Impact of Recent Methamphetamine Use on Vancomycin Clearance

PURPOSE

To determine whether recent methamphetamine use increases vancomycin clearance.

METHODS

This was a multi-center, retrospective, IRB-approved study at two tertiary care medical centers. Adult patients with a urine drug screen, ≥3 consecutive vancomycin doses, and an appropriately drawn vancomycin trough were assessed and classified as amphetamine positive or amphetamine negative. The primary outcome was vancomycin clearance.

RESULTS

88 patients were included in the analysis, with 44 patients in each group. Vancomycin clearance was greater in the amphetamine positive group (94.54 vs. 86.84 mL/min, p = 0.042, 95% CI 0.29-15.09). There was no significant difference in goal vancomycin trough achievement between groups (34.1% amphetamine positive vs. 43.2% amphetamine negative; p = 0.512). Per multifactorial logistic regression analysis, older age and male gender were associated with decreased vancomycin clearance, while higher BMI and cocaine positive urine drug screen were associated with increased vancomycin clearance.

CONCLUSION

Recent methamphetamine use may increase vancomycin clearance. Larger prospective trials with protocolized vancomycin dosing strategies are needed to further elucidate the impact of methamphetamine use on attainment of goal vancomycin troughs in addition to the potential impact on vancomycin clearance.

Characterization of Meta-Iodobenzylguanidine (mIBG) Transport by Polyspecific Organic Cation Transporters: Implication for mIBG Therapy

Radiolabeled meta-iodobenzylguanidine (mIBG) is an important radiopharmaceutical used in the diagnosis and treatment of neuroendocrine cancers. mIBG is known to enter tumor cells through the norepinephrine transporter. Whole-body scintigraphy has shown rapid mIBG elimination through the kidney and high accumulation in several normal tissues, but the underlying molecular mechanisms are unclear. Using transporter-expressing cell lines, we show that mIBG is an excellent substrate for human organic cation transporters 1-3 (hOCT1-3) and the multidrug and toxin extrusion proteins 1 and 2-K (hMATE1/2-K), but not for the renal organic anion transporter 1 and 3 (hOAT1/3). Kinetic analysis revealed that hOCT1, hOCT2, hOCT3, hMATE1, and hMATE2-K transport mIBG with similar apparent affinities (K _m of 19.5 ± 6.9, 17.2 ± 2.8, 14.5 ± 7.1, 17.7 ± 10.9, 12.6 ± 5.6 µM, respectively). Transwell studies in hOCT2/hMATE1 double-transfected Madin-Darby canine kidney cells showed that mIBG transport in the basal (B)-to-apical (A) direction is much greater than in the A-to-B direction. Compared with control cells, the B-to-A permeability of mIBG increased by 20-fold in hOCT2/hMATE1 double-transfected cells. Screening of 23 drugs used in the treatment of neuroblastoma identified several drugs with the potential to inhibit hOCT- or hMATE-mediated mIBG uptake. Interestingly, irinotecan selectively inhibited hOCT1, whereas crizotinib potently inhibited hOCT3-mediated mIBG uptake. Our results suggest that mIBG undergoes renal tubular secretion mediated by hOCT2 and hMATE1/2-K, and hOCT1 and hOCT3 may play important roles in mIBG uptake into normal tissues. SIGNIFICANCE STATEMENT: mIBG is eliminated by the kidney and extensively accumulates in several tissues known to express hOCT1 and hOCT3. Our results suggest that hOCT2 and human multidrug and toxin extrusion proteins 1 and 2-K are involved in mIBG renal elimination, whereas hOCT1 and hOCT3 may play important roles in mIBG uptake into normal tissues. These findings may help to predict and prevent adverse drug interaction with therapeutic [¹³¹I]mIBG and develop clinical strategies to reduce [¹³¹I]mIBG accumulation and toxicity in normal tissues and organs.

Mechanistic PBPK Modeling of Urine pH Effect on Renal and Systemic Disposition of Methamphetamine and Amphetamine

The effect of urine pH on renal excretion and systemic disposition has been observed for many drugs and metabolites. When urine pH is altered, tubular ionization, passive reabsorption, renal clearance, and systemic exposure of drugs and metabolites may all change dramatically, raising clinically significant concerns. Surprisingly, the urine pH effect on drug disposition is not routinely explored in humans, and regulatory agencies have neither developed guidance on this issue nor required industry to conduct pertinent human trials. In this study, we hypothesized that physiologically based pharmacokinetic (PBPK) modeling could be used as a cost-effective method to examine potential urine pH effect on drug and metabolite disposition. Our previously developed and verified mechanistic kidney model was integrated with a full-body PBPK model to simulate renal clearance and area under the plasma concentration-time curve (AUC) with varying urine pH statuses using methamphetamine and amphetamine as model compounds. We first developed and verified drug models for methamphetamine and amphetamine under normal urine pH condition [absolute average fold error (AAFE) < 1.25 at study level]. Then, acidic and alkaline urine scenarios were simulated. Our simulation results show that the renal excretion and plasma concentration-time profiles for methamphetamine and amphetamine could be recapitulated under different urine pH (AAFE < 2 at individual level). The methamphetamine-amphetamine parent-metabolite full-body PBPK model also successfully simulated amphetamine plasma concentration-time profiles (AAFE < 1.25 at study level) and amphetamine/methamphetamine urinary concentration ratios (AAFE < 2 at individual level) after dosing methamphetamine. This demonstrates that our mechanistic PBPK model can predict urine pH effect on systemic and urinary disposition of drugs and metabolites. SIGNIFICANCE STATEMENT: Our study shows that integrating mechanistic kidney model with full-body physiologically based pharmacokinetic model can predict the magnitude of alteration in renal excretion and area under the plasma concentration-time curve (AUC) of drugs and metabolites when urine pH is changed. This provides a cost-effective method to evaluate the likelihood of renal and systemic disposition changes due to varying urine pH. This is important because multiple drugs and diseases can alter urine pH, leading to quantitatively and clinically significant changes in drug and metabolite disposition that may require adjustment of therapy.

Detection, pharmacokinetics, and selected pharmacodynamic effects of methamphetamine following a single transmucosal and intravenous administration to exercised Thoroughbred horses

Methamphetamine is a central and peripheral nervous system stimulant. There is only a single study that describes exposure to and disposition of this compound in horses. The potential for abuse and inadvertent exposure in equine athletes along with the limited data available necessitates further study. The objectives of the current study were to describe drug and metabolite concentrations, develop an analytical method that could be used to regulate its use, and describe selected pharmacodynamic effects. In phase 1, six horses were randomized into three transmucosal dose groups (n = 2/group; 0.5, 1.0 or 10 mg). In phase 2, horses received a single 10 mg intravenous dose. In phase 3, the effects of urinary pH on elimination were studied. Blood and urine samples were collected for up to 72 hours post drug administration. Concentrations of methamphetamine were measured using liquid chromatography-tandem mass spectrometry. Methamphetamine was below the limit of detection (LOD) in blood by 2, 4, and 18 hours following transmucosal administration of 0.5, 1, and 10 mg, respectively. Following intravenous administration, methamphetamine fell below the LOD between 12 and 18 hours. Following urinary acidification, methamphetamine fell below the limit of quantitation (LOQ) by 12 hours. In urine, methamphetamine was no longer detected at 48, 48, and 72 hours in the 0.5, 1, and 10 mg transmucosal groups and 18 hours in the intravenous group. Increased urinary pH resulted in urinary concentrations of methamphetamine falling below detectable levels by 48 hours post transmucosal administration. While the number of animals was small, behavioral, stimulatory, and cardiac effects were minimal.

Roles of Renal Drug Transporter in Drug Disposition and Renal Toxicity

The kidney plays an important role in maintaining total body homeostasis and eliminating toxic xenobiotics and metabolites. Numerous drugs and their metabolites are ultimately eliminated in the urine. The reabsorption and secretion functions of the nephron are mediated by a variety of transporters located in the basolateral and luminal membranes of the tubular cells. In the past decade, many studies indicated that transporters play important roles in drug pharmacokinetics and demonstrated the impact of renal transporters on the disposition of drugs, drug-drug interactions, and nephrotoxicities. Here, we focus on several important renal transporters and their roles in drug elimination and disposition, drug-induced nephrotoxicities and potential clinical solutions.

Organic Cation Transporter 3 Facilitates Fetal Exposure to Metformin during Pregnancy

Metformin, an oral antihyperglycemic, is increasingly being prescribed to pregnant women with gestational diabetes. Metformin is a hydrophilic cation and relies on organic cation transporters to move across cell membranes. We previously demonstrated that human and mouse placentas predominantly express organic cation transporter 3 (OCT3), but the impact of this transporter on maternal and fetal disposition of metformin is unknown. Using immunofluorescence colocalization studies in term human placenta, we showed that OCT3 is localized to the basal (fetal-facing) membrane of syncytiotrophoblast cells with no expression on the apical (maternal-facing) membrane. OCT3 positive staining was also observed in fetal capillaries. To determine the in vivo role of OCT3 in maternal and fetal disposition of metformin, we determined metformin maternal pharmacokinetics and overall fetal exposure in wild-type and Oct3-null pregnant mice. After oral dosing of [¹⁴C]metformin at gestational day 19, the systemic drug exposure (AUC_0-∞) in maternal plasma was slightly reduced by ∼16% in the Oct3^-/- pregnant mice. In contrast, overall fetal AUC_0-∞ was reduced by 47% in the Oct3^-/- pregnant mice. Consistent with our previous findings in nonpregnant mice, metformin tissue distribution was respectively reduced by 70% and 52% in the salivary glands and heart in Oct3^-/- pregnant mice. Our in vivo data in mice clearly demonstrated a significant role of Oct3 in facilitating metformin fetal distribution and exposure during pregnancy. Modulation of placental OCT3 expression or activity by gestational age, genetic polymorphism, or pharmacological inhibitors may alter fetal exposure to metformin or other drugs transported by OCT3.

Disposition of Methamphetamine and Major Metabolites in Mice: Role of Organic Cation Transporter 3 in Tissue-Selective Accumulation of Para-Hydroxymethamphetamine

Methamphetamine is one of the most widely abused illicit drugs. Although human intoxication and multiple tissue toxicities frequently occur in abusers, little is known about the distribution of methamphetamine or its primary metabolites, amphetamine and para-hydroxymethamphetamine (p-OHMA), to their sites of toxicity. This study determined the pharmacokinetics, tissue exposure, and partition ratios of methamphetamine and major metabolites in various mouse tissues and investigated the impact of organic cation transporter 3 (Oct3) following i.v. injection of methamphetamine to male Oct3^+/+ and Oct3^-/- mice. Methamphetamine, amphetamine, and p-OHMA were readily detectable in plasma with Oct3^+/+ and Oct3^-/- mice displaying similar plasma pharmacokinetic profiles for all three analytes. In addition to kidney and liver, salivary glands highly accumulated methamphetamine, amphetamine, and p-OHMA with total exposure 3.3- to 9.4-fold higher than plasma area under the concentration-time curve (AUC). Consistent with being an Oct3 substrate, p-OHMA AUC in salivary glands is reduced by 50% in Oct3^-/- mice. p-OHMA AUC in skeletal muscle is also significantly reduced in Oct3^-/- mice. Our data identified salivary glands as a novel site of high accumulation of methamphetamine and metabolites, which may underlie methamphetamine toxicity in this tissue. Furthermore, our study identified Oct3 as an important determinant of tissue uptake and exposure to p-OHMA in salivary glands and skeletal muscle. Our findings suggest that local tissue accumulation of methamphetamine and/or its metabolites may play a role in several of the reported peripheral toxicities of methamphetamine, and Oct3 can significantly impact tissue exposure to its substrates without affecting systemic elimination.