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REVIEW ARTICLE
published: 12 January 2015
doi: 10.3389/fnins.2014.00445
Impact of methamphetamine on infection and immunity
Sergio A. Salamanca 1, Edra E. Sorrentino 1, Joshua D. Nosanchuk 2,3 and Luis R. Martinez 4*
1 Department of Biomedical Sciences, Long Island University-Post, Brookville, NY, USA
2 Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY, USA
3 Medicine (Division of Infectious Diseases), Albert Einstein College of Medicine, Bronx, NY, USA
4 Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY, USA
Edited by:
The prevalence of methamphetamine (METH) use is estimated at ∼35 million people
Jacob Raber, Oregon Health and
worldwide, with over 10 million users in the United States. METH use elicits a myriad of
Science University, USA
social consequences and the behavioral impact of the drug is well understood. However,
Reviewed by:
new information has recently emerged detailing the devastating effects of METH on host
Eugene A. Kiyatkin, National
immunity, increasing the acquisition of diverse pathogens and exacerbating the severity
Institute on Drug Abuse, USA
Gillian Grafton, University of
of disease. These outcomes manifest as modifications in protective physical and chemical
Birmingham, UK
defenses, pro-inflammatory responses, and the induction of oxidative stress pathways.
*Correspondence:
Through these processes, significant neurotoxicities arise, and, as such, chronic abusers
Luis R. Martinez, New York Institute
with these conditions are at a higher risk for heightened consequences. METH use also
of Technology, College of
Osteopathic Medicine, Northern
influences the adaptive immune response, permitting the unrestrained development of
Boulevard, PO Box 8000 Riland
opportunistic diseases. In this review, we discuss recent literature addressing the impact
Building, Room 28 Old Westbury,
of METH on infection and immunity, and identify areas ripe for future investigation.
NY 11568-8000, USA
e-mail: [email address]
Keywords: methamphetamine, infectious diseases, immunity, drug abuse, HIV, neurotoxicity
METHAMPHETAMINE (METH), A MAJOR PUBLIC HEALTH
control policies has significantly limited the availability of precur-
PROBLEM
sor chemicals essential for METH production, raising purchase
The growing popularity of Methamphetamine (METH), a street
prices and reducing the overall demand for the product (Drug
drug associated with the severe neurological and physical con-
Enforcement Administration,
2007; Gong et al., 2012). General
sequences afflicting its users, has created an increasingly serious
METH use is seen as minimal exposure to the drug, primar-
public health problem worldwide. In a 2011 United Nations sur-
ily involving first time users; whereas, chronic METH abuse and
vey, approximately 2.5% of Australians over the age of 14 have
dependence expose the user to a diverse range of adverse physical
tried METH, a prevalence rate three to five times higher than
and cognitive health consequences
(Panenka et al., 2013). The rate
those seen in the United States (USA), Canada, and the United
of treatment admissions for primary METH abuse has increased
Kingdom
(United Nations, 2011). In the USA, over one mil-
over 3-fold in recent years
(Colfax and Shoptaw, 2005).
lion individuals aged 12 years and older—roughly 0.5% of the
Diverse routes for METH use exist, including oral ingestion,
American population—were reported to have sampled METH
smoking, snorting, intravenous injection, and anal insertion. The
(Colfax and Shoptaw, 2005; United Nations, 2011). According
intravenous administration of METH has become a popular
to the USA Department of Justice, after alcohol and marijuana,
usage mechanism due to its ability to deliver almost immedi-
METH is the most commonly used recreational drug in many
ate effects of euphoria
(Hart et al., 2008). The sharing of drug
states
(Drug Enforcement Administration, 2007).
paraphernalia combined with METH’s perceived enhancement of
METH is a potent central nervous system (CNS) stimulant
sexual pleasure and the association of its use with unsafe sex-
that mimics the pharmacological effects of cocaine. The “rush”
ual practices greatly increases the likelihood of the acquisition
that follows METH use is associated with the release of neu-
of human immunodeficiency virus (HIV) and other infectious
rotransmitters, including adrenaline, dopamine, and serotonin
diseases
(Ellis et al., 2003; Urbina et al., 2004; Mansergh et al.,
(Downes and Whyte,
2005; Collins et al., 2014). Whereas the half-
2006; Nakamura et al., 2011). In addition, animal studies demon-
life of cocaine is measured in minutes, however, that of METH
strate that METH suppresses both innate and adaptive immunity
is measured in hours (∼8 to 24 h). Thus, the pharmacological
(In et al., 2005; Peerzada et al., 2013). This review explores
effects of METH are thus longer lasting than cocaine. In spite
recent research developments related to the effects of METH on
of the potentially dangerous consequences of METH use, the
infection and immunity.
drug retains its popularity as a low-cost alternative to cocaine
and heroin. The relative ease of METH production has ensured
PHARMACOLOGICAL METH LEVELS IN HUMANS
that prices remain low, particularly in Australia, where METH
The S-(+) enantiomer of METH ((S)-N-Methyl-1-phenyl-
use is more prevalent and widespread than in most other coun-
propan-2-amine), dextromethamphetamine, is popularly used
tries
(Marwick, 2000; United Nations, 2011; Gong et al., 2012).
among METH users for its potent effect on the cardiovascular
In recent years, however, the upsurge of drug enforcement and
system and CNS
(Li et al., 2010; Volkow et al., 2010). Patterns
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Salamanca et al.
Methamphetamine on infection and immunity
of METH intake are variable depending on the user; a self-
Female, 270 ng/g) within the first hours after the initial injec-
reporting study indicated that a majority of chronic METH
tion
(Saito et al., 2008). However, a typical dose of METH that
users consume the drug more than 20 days per month, at a
is self-administered (i.v.) by rats is 0.1–0.2 mg/kg that is equiv-
frequency of 1–3 doses per day
(Saito et al., 2008). Typically,
alent to a human dose (7–14 mg/70 kg)
(Cook et al., 1992; Hart
people take 5–15 mg (low stimulation), 10–30 (common dose),
et al.,
2008; Kuczenski et al., 2009; Krasnova et al., 2010; Kousik
and 20–60 mg (strong) with both per-oral and intravenous
et al.,
2014). Also, pigeons injected i.v. and intramuscularly (i.m.)
(i.v.) administration
(Hart et al., 2008; Cruickshank and Dyer,
with 0.8 mg/kg of METH showed 100% of bioavailability; how-
2009). Following ingestion, the metabolism of METH takes
ever, i.v. absorption was three times higher than i.m. In this
place in the liver, where the cytochrome P4502D6 causes N-
regard, some studies support that injection of METH in ranges
demethylation and aromatic hydroxylation, forming the pri-
of 3.6–10 mg/Kg are considered lethal in animals (Hendrickson
mary metabolites para-hydroxymethamphetamine (pOH-MA)
et al.,
2008). Similarly, a recent study showed an 8-fold higher cat-
and amphetamine (AMP). Afterwards, the primary and other
alytic activity of METH in rhesus macaques compared to humans
minor metabolites (norephedrine, 4-hydroxyamphetamine, 4-
due to enzymatic differences
(Earla et al., 2014).
hydroxynorephenedrine, benzyl methyl ketoxime and benzoic
acid) are absorbed across the gastrointestinal tract. The con-
MECHANISMS OF NEUROTOXICITY
centration peak of METH in plasma after oral ingestion can be
Administration of METH can increase blood–brain barrier (BBB)
detected at 3.13–6.3 h post-consumption and its metabolites peak
permeability in rodents. Moderate to high doses of METH disrupt
at 10–24 h
(Gartner and Liu, 2002). The metabolite pOH-MA is
the BBB in several regions, including the cortex, hippocampus,
therefore one of the most stable biomarkers of METH abuse (Li
thalamus, hypothalamus, cerebellum, amygdala, and striatum
et al.,
2010).
that, in turn, are further injured by hyperthermia and, poten-
METH is often used in binges, and as the drug exhibits a
tially, by seizures
(Sharma and Kiyatkin, 2009; Yamamoto et al.,
half-life of 11.4–12 h
(Cho et al., 2001; Harris et al., 2003).
2010). Although it is unclear whether there is a relationship
Recently published studies modeling binge patterns show that
between BBB injury and the damage to neurotransmitter systems,
after the fourth administration of 260 mg during a single day,
BBB injury appears to contribute to striatal neuron degenera-
subsequently, produces blood levels of 2.5 mg/L, reaching as high
tion rather than dopaminergic terminal damage
(Bowyer et al.,
as 3 mg/L on the second day
(Melega et al., 2007). Thus, binge
2008).METH stimulates astrocytes to produce high levels of IL-
doses of 260 mg–1 g produce 2.5–12 mg/L blood levels. A study
6 and IL-8, resulting in an inflammatory response that inhibits
conducted in Australia between 2000 and 2005 found that 68%
neurogenesis in the brain, affects sub-ventricular and hippocam-
of 371 deaths in which individuals tested positive for AMPs
pal cells, reduces hippocampal progenitor cells. Similarly, METH
could be attributed directly to METH toxicity. METH concentra-
alters gene expression on astrocytes, halting their cell cycle and
tion ranged from 0.2 to 15 mg/L (median, 0.2 mg/L), with AMP
proliferation
(Shah et al., 2012; Jackson et al., 2014).
levels registering at 0.01–2.0 mg/L (median, 0.07 mg/L) (Kaye
Mechanisms underlying METH-induced BBB damage include
et al.,
2008). It is important to establish that these concentra-
alterations of expression and structure in tight junctions,
tions and peak values vary greatly depending upon the routes of
microglial activation, remodeling of BBB cytoskeleton, induc-
administration and detection technique.
tion of neuroinflammatory factors, and energy related disruption.
Although the brain receives around 15% of the cardiac output
METH, especially at high doses combined with physical exer-
(114 ± 24 mL/100 mL/min) the concentration of METH, its dis-
tion, can cause hyperthermia and enhance reactive oxygen species
tribution and metabolism varied in all the organs
(Ito et al., 2003).
(ROS) production, thus triggering BBB breakdown (Sharma
Interestingly, the effect of METH in brain structure and activity is
et al.,
2007; Ramirez et al., 2009; Northrop and Yamamoto,
extensive. A study determined the distribution and bioavailabil-
2012). METH can induce the polymerization of proteins nec-
ity of METH in several human organs using Positron Emission
essary for the stability of the BBB. Therefore, when alterations
Tomography, revealing a low rate of drug uptake in the brain
in proteins occur, the permeability of the barrier is affected and
(9 min) compared to the other organs examined. Nevertheless,
migration of inflammatory cells, such as monocytes, arises more
the prolonged clearing period (
>75 min), suggests a neurotoxic
frequently
(Park et al., 2013). In murine models, the administra-
effect due to the extended exposure to the drug
(Volkow et al.,
tion of low and high doses of METH shows an increase in IgG
2010).
immunoreactivity in the striatum
(Urrutia et al., 2013).
Notably, administration of antioxidants attenuates BBB injury
PHARMACOLOGICAL METH LEVELS IN ANIMALS
in acute METH toxicity models and further implicates oxidative
The use of animal models has been widely used to evaluate the
stress in pathological effects
(Sharma et al., 2007). One study sug-
effect of METH in the immune and nervous system, among oth-
gests that METH induces the opening of the BBB by activating
ers. One study employing a murine model estimated how METH
the nitric oxide synthases (NOS) present in the endothelial cells of
is distributed to tissues. Tissue-to-serum METH ratios in rats are:
the brain capillary network
(Martins et al., 2013). Oxidative stress
brain, 9.7; kidney, 35.3; spleen, 14.3
(Rivière et al., 2000). Levels
represents an imbalance between the production of ROS and the
of METH and AMP in both female and male murine spleens
BBB’s ability to readily detoxify the reactive intermediates or to
measured within a 72 h period after treatment with 5 mg/Kg
repair the resulting damage.
demonstrated high concentrations of METH (Male, 870, Female,
METH also alters the expression of several tight junction pro-
1310 ng/g) in comparison to lower levels of AMP (Male, 130,
teins and increases the permeability of brain-derived primary
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Salamanca et al.
Methamphetamine on infection and immunity
microvascular endothelial cells
(Mahajan et al., 2008; Ramirez
sensation akin to insects crawling on or under the skin. The
et al.,
2009). The use of acute high doses of METH increases
result of formication is that users engage in constant skin “pick-
the permeability of the BBB principally in the hippocampus,
ing,” often causing the formation of ulcers that frequently scar.
while downregulation of tight junction proteins such as ZO-1,
A marked lack of hygiene among users may also be correlated to
Claudin-5, and occludin cause failure in the BBB, thus increas-
higher rates of skin infections, abscess, and cellulitis
(Rusyniak,
ing the expression of matrix metalloproteinase (MMP)-9 in the
2013).
hippocampal neurons
(Martins et al., 2011). The regulation of
Another common sign of METH abuse is extreme tooth decay,
occludin levels is important to maintain the stability of the
a condition known in the media as “METH mouth.” Users
endothelial tissue; however, METH causes the polymerization of
with “METH mouth” have blackened, stained, or rotting teeth,
actin thereby hindering rearrangements, ultimately leading to a
even among young and/or short-term users. The exact causes of
functional disruption of the BBB
(Park et al., 2013). MMP activa-
“METH mouth” are not fully understood. A common miscon-
tion is thought to occur through several mechanisms, including
ception is that METH directly causes the caries
(Shaner et al.,
oxidative stress and cytokine production
(Haorah et al., 2007;
2006). The leading hypothesis is that METH constricts blood ves-
McColl et al., 2008).
sels, thereby, limiting blood supply resulting in “dry mouth” or
Collectively, these findings suggest that AMP-driven oxidative
xerostomia
(Saini et al., 2005; Goodchild and Donaldson, 2007;
stress followed by the activation of MMPs and breakdown of
Heng et al., 2008; Hamamoto and Rhodus, 2009). A reduction in
tight junctions mediate BBB disruption; both the activation of
saliva impairs the mouth’s capacity to neutralize harsh acids pro-
MMPs and oxidative stress can induce inflammation which could
duced by oral bacteria after metabolizing carbohydrates, resulting
be accompanied by an increase in cytokine production within
in erosion of the teeth and gums and increasing the susceptibil-
microglia, perpetuating damage and increasing BBB permeability
ity of teeth to damage
(Shaner et al., 2006; Evans et al., 2012).
(Kim et al., 2005; Amantea et al., 2007; Block and Hong, 2007).
A more recent pilot study, however, found no difference in saliva
The consequences of BBB disruption are widespread and may
flow rates between users and non-users despite increased saliva
enhance the vulnerability of the brain to microbial toxins and
acidity in users and decreased buffer capacity in saliva.
infection
(Eugenin et al., 2013).
The extent of tooth decay varies widely among METH users.
Richards et al., found that users who snorted METH had sig-
EFFECTS OF METH ON HOST IMMUNITY
nificantly worse tooth decay than users who smoked or injected
The effects of METH on host immune response have not yet been
it, although all types of users suffered from dental problems
extensively described. Limited studies about the effects of METH
(Richards and Brofeldt, 2000); however, a newer study suggests
on immune function have, however, revealed that METH use has
the oral route, in contrast to intravenous or intranasal, as a better
profound immunological implications. Findings in humans, with
predictor of “METH mouth” severity
(Brown et al., 2013).
slight variance across ethnic groups, reveal that the uptake of a
particular METH isotope targets specific organ types, in which
ROLE OF METH ON INNATE IMMUNITY
concentrations (per/mL of tissue) were highest in the kidneys and
METH administration induces modifications in cellular compo-
lungs; intermediate in the stomach, pancreas, liver, and spleen;
nents including natural killer cells (NK), dendritic cells (DCs),
and lower in the brain and heart
(Volkow et al., 2010). METH
monocytes, macrophages, and granulocytes, indicating complex
use leads to profound consequences in both, innate and adaptive
mechanisms of immunosuppression
(Harms et al., 2012). METH
immunity. Hence, investigations have begun to further elucidate
alkalizes normally acidic organelles within macrophages, lead-
the cellular and molecular basis for METH’s induced immune
ing to the inhibition of phagocytosis and antigen presentation
suppression, examples of which are discussed subsequently.
processes
(Tallóczy et al., 2008). Similar to chloroquine, METH
is a weak base capable of inducing a collapse of the pH gradi-
METH ALTERATIONS OF NATURAL PHYSICAL AND CHEMICAL
ent across acidic organelles. The microbicidal capacity of DCs
BARRIERS
and macrophages is significantly decreased after METH expo-
The skin acts as a primary physical barrier to prevent the entrance
sures
(Tallóczy et al., 2008; Martinez et al., 2009). Furthermore,
of pathogens, thereby serving as one of the innate immune
the drug reduces the number of DCs and NK cells (Saito
response’s first lines of defense
(Proksch et al., 2008). Sweat glands
et al.,
2006; Harms et al., 2012). The reduction of monocytes
in the skin release various bactericidal and regulatory peptides,
(Harms et al., 2012) and macrophages in the peritoneal zone
restricting the development of pathogenic microbiota
(Rieg et al.,
after METH administration has also been reported
(Saito et al.,
2006). METH has been detected in sweat 2 h after ingestion, with
2008). Similarly, antigen presentation in professional phagocytes
traces remaining for periods of more than a week in cases wherein
are dysregulated, diminishing the processing capacity of these
multiple doses were administered
(Barnes et al., 2008). No pre-
cells
(Harms et al., 2012). METH-treated macrophages in tissue
vious studies exist, however, aiming to understand the effect of
culture displayed increased levels of pro-inflammatory cytokine
METH on microbiota and metabolites present in the skin (e.g.,
TNF-α, whereas similar cells stimulated with lipopolysaccharide
lactate, glycerol, pyruvate, ammonium cation, urea) (Kutyshenko
(LPS) showed increased amounts of IL-1β and IL-8 in addi-
et al.,
2011). In this regard, the administration of drugs such
tion to TNF-α
(Liu et al., 2012). These modifications of the
as METH via injection is associated with the development of
innate immune response can result in impaired inflammatory
necrotizing fasciitis. Significantly, heavy daily users of METH
responses and the degradation of physical and chemical protective
frequently develop neurological manifestation of formication, a
barriers.
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Salamanca et al.
Methamphetamine on infection and immunity
METH AND INFLAMMATION
in rat thymic and splenic lymphocytes and produces severe
Much of the existing literature related to METH’s impact on
immunosuppression, which could contribute to the higher rate of
inflammation derives from research focusing on CNS toxic-
infections observed in chronic METH users
(Harms et al., 2012;
ity. For instance, METH increases glutamate (GLU) levels (Ito
Peerzada et al., 2013). For instance, rodent studies demonstrate
et al.,
2006) and GLU receptor stimulation increases microglial
that METH alters cytokine response in retroviral-infections (Yu
activation
(Thomas and Kuhn, 2005). Activation of GLU recep-
et al.,
2002; Liang et al., 2008), alters gene expression of immune
tors increases the production of TNF-α, IL-1β, IL-6, and IL-
cells
(Mahajan et al., 2006), and disturbs thymic CD4+/CD8+
8
(Chaparro-Huerta et al., 2005; Liu et al., 2012), resulting
T-cell ratios
(Yu et al., 2002; In et al., 2005).
in increased extracellular GLU levels by either inhibiting GLU
METH reduces T cell infiltrates in the lungs, inhibiting T cell
uptake or increasing GLU release from activated microglia (Zou
proliferation and reducing the capacity of these cells to main-
and Crews,
2005). Additionally, astrocytes play a role in METH-
tain a protective immune response against respiratory pathogens
induced toxicity through the modulation of GLU-mediated exci-
(Martinez et al., 2009). Similarly, METH-exposed mice demon-
totoxicity and inflammation. Astrocytes regulate extracellular
strated elevated levels of early response IL-6 and IL-10 in tissue
concentrations of GLU, mainly via neurotransmitter uptake. For
homogenates, which could indicate the development of a non-
METH, the activation of cortical astrocytes appears to be caused
protective Th2 response against bacterial and fungal pathogens
by GLU release and protein kinase C activation, and is inhibited
in the respiratory tract, even when Th1 cytokines are present
by GLU receptor antagonism
(Miyatake et al., 2005). Moreover,
(Peerzada et al., 2013).
METH’s stimulation of excitatory neurotransmitters and subse-
An alternative mechanism for altered T-cell function is that
quent mGluR5-mediated activation of Akt/PI3K signaling path-
METH modifies oxidative stress responses. As discussed earlier,
ways leads to the release of NF-kB, which then translocates from
the effects of oxidative stress on suppressed signal transduction,
the cytoplasm to the nucleus for the enhanced expression of IL-6
transcription factor activities, and diminished cytokine produc-
and IL-8 in astrocytes
(Shah et al., 2012). The release of NF-
tion in response to antigen stimulation in T cells has been docu-
kB into the cytoplasm occurs via the phosphorylation of IKK by
mented in several model systems
(Flora et al., 2003; Shah et al.,
activated Akt/PI3K, which subsequently phosphorylates p-IkB, a
2012). The ability of reactive oxidative free radicals to impair T
regulatory protein for NF-kB
(Shah et al., 2012). Under normal
lymphocyte function has been documented in various human
physiologic conditions, however, astrocytes suppress microglial
pathologic conditions, specifically AIDS, in which oxidative stress
activation through the release of anti-inflammatory cytokines and
can hamper host control of retroviral replication
(Potula et al.,
neurotrophic factors
(Neumann, 2001). For instance, astrocytes
2010).
suppress microglial activation by releasing TGF-β or IL-10 (Loftis
Interestingly, a recent finding suggests that METH alters intra-
et al.,
2011).
cellular calcium mobilization in T cells, resulting in subsequent
Another mechanism by which METH facilitates inflamma-
production of oxidative free radicals, a phenomenon associated
tory response is through the induction of oxidative stress. METH
with mitochondrial damage and weakened T cell function (Potula
administration stimulates a substantial production of dopamine
et al.,
2010). Mitochondria serve as a source of both intra-
and the release of serotonin, which can undergo autoxidation pro-
cellular ROS and ATP production, a process regulated by the
cesses and produce hydrogen peroxide and super-oxide radicals
second messenger, calcium. METH exposure elevates levels of
(Flora et al., 2003). In addition, METH can intensify cellular oxi-
cytosolic calcium, however, and leads to the saturation of the
dation via the depolarization of mitochondria and, as mentioned
electron transport chain, which contributes to the acute produc-
previously, enhanced production of extracellular GLU, both of
tion of oxidative free radicals and ultimately results in oxidative
which are well known to boost levels of ROS
(Shah et al., 2012).
alteration of proteins, loss of intracellular ATP levels in T cells
These oxidative disturbances in cellular redox status can incite the
and mitochondrial dysfunction
(Potula et al., 2010). A compen-
activation of various transcription factors, such as NF-kB, AP-1
satory down-regulation of mitochondrial proteins from chronic
or CREB, which, in turn, stimulate specific redox-regulated tran-
METH treatment can incite a long-term cellular redox imbalance,
scription factors that regulate gene expression for inflammatory
weakening T cells’ ability to effectively respond to opportunistic
cytokines and adhesion molecules
(Shah et al., 2012).
pathogens
(Potula et al., 2010; Chandramani Shivalingappa, 2012;
Martins et al., 2013).
METH AND ADAPTIVE IMMUNITY
T-cells play critical roles in orchestrating immune responses
METH FACILITATES THE ACQUISITION OF INFECTIOUS
(Anderton, 2006) because their activation and proliferation are
DISEASES
characteristic of adaptive immune responses. The mechanisms
In addition to psychosocial aberrations, infections are serious
underlying the interplay between cells of the adaptive immune
complications of chronic METH use. Moreover, the intoxicating
system and METH are currently unclear. However, the data firmly
effects of METH alter judgment and reduce inhibitions, leading
establishes that METH adversely impacts adaptive responses that
people to engage in unsafe activities, increasing risk for acquiring
render the host more susceptible to progressive diseases, particu-
transmissible microbes and other opportunistic infections; these
larly HIV
(In et al., 2005; Martinez et al., 2009).
findings have been documented worldwide
(Plankey et al., 2007;
Murine models show that METH modifies thymic and splenic
Volkow et al., 2007; Ye et al., 2008; Sutcliffe et al., 2009; Parry
cellularity and alters peripheral T lymphocyte populations (In
et al.,
2011; Borders et al., 2013; Eugenin et al., 2013; Heninger
et al.,
2005). High dose METH intake induces apoptotic death
and Collins,
2013; Khan et al., 2013; Stahlman et al., 2013; Liao
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Salamanca et al.
Methamphetamine on infection and immunity
et al.,
2014). Former and current drug users have higher risks to
2013). In particular, METH use is associated with increased risk
acquired sexually transmitted diseases (STDs)
(Barry et al., 2009;
for syphilis and gonorrhea in gay and bisexual men (Shoptaw
Miller et al., 2009; Cranston et al., 2012; Javanbakht et al., 2012;
et al.,
2002; Wong et al., 2005; Taylor et al., 2007). In this regard,
Wang et al., 2012; Chew Ng et al., 2013). These infections result
METH use is associated with the syphilis cases reported in China,
from the high association of METH use and inconsistent condom
including heterosexual and homosexual men and female sex
use, unprotected sex incentivized by money, and high-risk sexual
workers
(Kang et al., 2011; Liao et al., 2013, 2014).Furthermore,
partner types
(Johnston et al., 2010; Borders et al., 2013; Stahlman
syphilis infection increases the transmission and acquisition of
et al.,
2013). Hence, there are increased risks for diverse infectious
HIV
(Xiao et al., 2010). The minimal amount of studies aiming to
diseases and these impaired individuals have a reduced capacity
address the correlation between METH use and syphilis cases in
to combat microbial challenges
(Cohen et al., 2007; Patel et al.,
several countries may dampen what role this drug plays in disease
2013). In this regard, current clinical and empirical knowledge on
transmission and resistance to antibiotics.
the impact of METH on the acquisition of infectious diseases is
discussed here.
HEPATITIS
METH abuse, hepatitis C virus (HCV) infection and HIV disease
METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (MRSA)
are overlapping epidemics in the USA and worldwide (Soriano
MR
SA is the single most important bacterial pathogen in infec-
et al.,
2002; Letendre et al., 2005). Illicit drug-using individuals
tions among injection drug users, with skin and soft-tissue infec-
are at especially high risk for acquisition of and disease from HCV
tions (SSTI) being extremely common
(Gordon and Lowy, 2005).
(Day et al., 2003; Hagan et al., 2005; Smyth et al., 2005). HCV
Their incidence is difficult to estimate because such infections are
results in ∼20,000 infections and 8000–10,000 deaths annually
often self-treated. In this regard, a study revealed that MR
SA was
in the USA
(Ye et al., 2008; Klevens et al., 2009). HCV infec-
isolated from 61% of abscesses and 53% of purulent wounds eval-
tion is particularly associated with injection use
(Gonzales et al.,
uated in the US emergency departments in all type of patients
2006). Notably, HCV is prevalent in HIV patients
(Ranger et al.,
suggesting that it is likely that complicated cutaneous lesions in
1991). In fact, HIV-HCV co-infection is found in 50–90% of
drug users are caused by this bacterium A cross-sectional study of
HIV-infected drug users and chronic HCV infection increases the
IDUs in San Francisco found that 32% had an abscess, cellulitis,
morbidity and mortality rates
(Letendre et al., 2005; Soriano et al.,
or both
(Binswanger et al., 2000). Nasal carriage of MR
SA is sig-
2002). Hence, a substantial proportion of METH users with or
nificantly increased in METH uses and MR
SA disease occurs in
without HIV infection has HCV
(Hahn et al., 2001; Miller et al.,
over half of colonized drug addicts
(El-Sharif and Ashour, 2008).
2004; Lea et al., 2013), suggesting that METH abuse is a risk fac-
In addition, skin-picking is also associated with MR
SA SSTI.
tor for HCV. Importantly, METH abuse significantly increases
As previously stated, METH use causes formication, which
HCV penetration into the brain of HIV-infected patients, exac-
can lead to skin-picking behavior and skin breakdown. METH
erbating cognitive impairments
(Letendre et al., 2007). Although
abusers often live in unhygienic circumstances. Moreover, unsafe
risky behavioral practices, such as sharing contaminated nee-
injection of METH and poor injection hygiene (e.g., lack of skin
dles and sexual activity after using METH may play an impor-
cleaning before injecting), injecting with unsterile equipment and
tant role in HCV transmission, there is relatively little infor-
contaminated drug solutions can introduce high bacterial loads
mation available about whether METH directly enhances HCV
(Frontera and Gradon, 2000). Significantly, drug solutions may
replication.
contain particulate matter (e.g., talc) that damage cardiac valves
METH inhibits immune responses in the liver, facilitating
if injected intravenously
(Frontera and Gradon, 2000). Chronic
HCV replication in human hepatocytes
(Ye et al., 2008). METH
METH use may increase the incidence of cardiovascular pathol-
inhibits intracellular interferon alpha (IFN-α) expression in
ogy
(Wijetunga et al., 2003; Yu et al., 2003) and, if injected,
human hepatocytes, which is associated with increased HCV
infective staphylococcal endocarditis
(Cooper et al., 2007).
replication. In addition, METH compromises the anti-HCV effect
of IFN-α. In this regard, METH inhibits the expression of the sig-
STDs
nal transducer and activator of transcription 1, a key modulator
The mind-altering effects of METH cause behavioral modifica-
in IFN-mediated responses. METH down-regulates the expres-
tions, leading people to engage in sexual activities that put them
sion of IFN regulatory factor-5, a crucial transcriptional factor
at risk for acquiring transmissible diseases
(Ellis et al., 2003). In
that activates the IFN pathway
(Ye et al., 2008). The fact that
addition to HIV and hepatitis, METH use is associated with an
METH compromises IFN-α-mediated innate immunity against
increased risk for and incidence of other STDs, including gen-
HCV indicates that this drug may have a cofactor role in HCV
ital warts, syphilis, gonorrhea, and chlamydia
(Hirshfield et al.,
pathogenesis.
2004a,b; Mansergh et al., 2006; Rhodes et al., 2007; Mimiaga et al.,
Although less well studied, METH also appears to increase
2008; Barry et al., 2009; Cranston et al., 2012; Javanbakht et al.,
the risk for disease due to hepatitis A virus and hepatitis B virus
2012; Valencia et al., 2012). In a USA study, bacterial and viral
(HBV)
(Gonzales et al., 2008). The factors associated with these
STDs were significantly more common in METH users (odds
infections are similar to that of HCV acquisition. For instance,
ratio 3.8), and the risk to acquire STDs in METH users was
an outbreak of HBV occurred in a group of METH-abusing indi-
even greater than that associated with cocaine
(Hirshfield et al.,
viduals sharing injection drug paraphernalia
(Vogt et al., 2006).
2004b). Furthermore, high levels of METH use are observed in a
Furthermore, fulminant liver failure due to HBV may be more
poly-drug use lifestyle, raising sexual risky behaviors
(Khan et al.,
common in the setting of METH injection
(Garfein et al., 2004).
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Salamanca et al.
Methamphetamine on infection and immunity
HIV
to CD4+ T-lymphocytes, mononuclear phagocytes are primary
There is compelling evidence, although limited in quantity, from
targets for HIV. HIV-infected macrophages survive for months,
both animal and
in vitro studies that illicit drugs and alcohol
actively producing and spreading the virus. METH enhances
directly affect intracellular HIV multiplication, progression to
HIV replication in human macrophages by up-regulation of
AIDS, and death. Previous research indicated that METH might
CCR5 expression, augmenting infectivity and reinforcing the
influence viral entry and integration at the host genome level,
transport of infected leukocytes across the blood brain barrier
promoting HIV production and viremias
(Liang et al., 2008;
(Liang et al., 2008). METH administration significantly increases
Toussi et al., 2009; Marcondes et al., 2010; Nair and Saiyed,
HIV-1 production by both HIV-infected monocytes and CD4+
2011). Specifically, findings suggest an indirect dysregulation of
T-lymphocytes
in vitro. METH increases HIV production and
chemokines and costimulatory molecules via DCs, macrophages,
viremia in mice transgenic for a replication-competent HIV
and CD4+ T lymphocytes, enabling the pathogenesis of HIV.
provirus and human cyclin T1
(Toussi et al., 2009). Interestingly,
HIV infection is highly regulated by the expression of the HIV
METH’s interaction with macrophages has illustrated the down-
entry co-receptors CXCR4 and CCR5. METH-treated groups
regulation of TLR9 expression, aiding in the HIV infection of
demonstrated that both of these receptors exhibited up-regulated
these innate cells by mitigating the receptor’s antiviral effects (Cen
expression after METH treatment on dendritic cells, signifying
et al.,
2013).
increased susceptibility to HIV infection
(Liang et al., 2008; Nair
METH and HIV-1 appear to cause more neurocognitive
et al.,
2009; Nair and Saiyed, 2011). In addition, METH exposure
deficits than either alone, but their interaction is poorly under-
significantly reduced expression of ERK2 and up-regulated p32
stood
(Rippeth et al., 2004; Cadet and Krasnova, 2007). A trans-
MAPK genes. In general, the genes from these signaling pathways
genic mouse expressing the viral envelope protein gp120 in
govern the regulation of cytokines (IL-2, IL-10, and TNF-α) and
the CNS has significantly more pronounced stereotypic behav-
if altered, can enhance the production of new HIV virions and
ioral responses to METH relative to parental mice, providing
deplete CD4+ T cells from the host’s immune system
(Nair et al.,
in vivo evidence that HIV affects the brain’s response to the drug
2009; Nair and Saiyed, 2011). Similarly, METH has demonstrated
(Roberts et al., 2010). Additionally, METH serves as an agonist
influence over dopaminergic receptors in previous findings, caus-
for the NMDA (N-Methyl-D-aspartate) receptor, activating IDO
ing increases in dopamine concentration in extracellular spaces.
and COX-2 expression as well as facilitating the eventual produc-
This excessive accumulation eventually leads to the degeneration
tion of QUIN, a neurotoxin also induced during HIV infection
of the striatal dopamine terminals and the formation of reac-
and can expedite neuronal apoptosis when these mechanisms are
tive oxidative stress molecules. In a recent study, D1 and D2
combined
(Nair and Samikkannu,
2012). Lastly, an evaluation
receptors were deleted and METH-treated cells were observed
of the impact of METH and Tat on the Wnt/β-catenin signaling
for changes in genetic expression of CCR5
(Nair et al., 2009).
pathway, a neuroprotective pathway vital in various CNS func-
Results showed that both D1 and D2 deficient cells reversed the
tions and negatively regulates HIV-1 replication in astrocytes,
up-regulatory effects of METH on DCs, indicating their involve-
revealed that they amplified the inhibitory effect, yet employed
ment in METH-induced HIV infectivity
(Reynolds et al., 2007;
individual cascades in an astrocytoma cell line (U87MG) to
Nair et al., 2009).
suppress β-catenin-mediated signaling
(Sharma et al., 2011).
Some factors associated with METH abuse include emotional
HIV pathogenesis can also be enhanced through METH abuse
reasons, social stigmas, depression, heritability, patterns of child-
via regulation of members from the signaling lymphocytic acti-
hood abuse, and low income
(Semple et al., 2008). A growing
vation family (SLAM), which potentially indicates a mechanism
body of research supports the relationship between METH use
by which the drug exacerbates HIV infection
(Harms et al.,
and an increase in behaviors (sexual and those related to IDU)
2012). CD150, a SLAM molecule, was up-regulated on CD4+
that increase risk for HIV infection. Chronic METH use is asso-
T cells after METH treatment making these cells susceptible to
ciated with a 2-fold higher risk of HIV acquisition
(Plankey et al.,
HIV infection
(Harms et al., 2012). METH use enhances HIV
2007). Among gay and bisexual men, METH is associated with
neuropathogenesis magnifying the effect of dopamine on HIV
high-risk sexual behavior, HIV infection, and predicts a high inci-
infection of macrophages
(Gaskill et al., 2009). Although we are
dence of AIDS
(Marshall et al., 2011; Nakamura et al., 2011; Lea
just beginning to understand the multifaceted, complex effects of
et al.,
2013). In addition to the above-mentioned factors, in a
METH in the context of HIV infection, the limited information
multi-cohort analysis of the LGBT (Lesbian, Gay, Bisexual and
available suggests that METH facilitates HIV spread, increasing
Transgender) community, other risk factors for HIV in METH
immune cell dysfunction, and exacerbating neuroAIDS.
users strongly correlated with young age, IDU, and depression.
METH exacerbates HIV pathology, including cognitive deficits,
OPPORTUNISTIC FUNGI
cardiovascular compromise, dental decay, and is strongly sus-
Fungal pathogens have been recently used as empirical models
pected to inhibit normal immunological response to secondary
to understand the impact of METH use on host homeostasis
infections, such as HCV
(Carey et al., 2006; Gonzales et al., 2006;
and increased permissiveness to opportunistic microorganisms.
Cruickshank and Dyer, 2009).
Histoplasma capsulatum is the most prevalent cause of fungal
HIV infection is associated with progressive CD4+ T-cell
respiratory infections, representing 53.19% of cases of endemic
depletion and immune dysregulation. Direct neurotoxic effects
mycoses in the US
(Chu et al., 2006). Since
H. capsulatum is
of METH putatively aggravate HIV-associated neuronal injury
endemic to the Midwestern USA, where METH is a critical
(Gartner and Liu, 2002; Williams and Hickey, 2002). In addition
public health issue; the fungus is an ideal model organism to
Frontiers in Neuroscience | Neuropharmacology
January 2015 | Volume 8 | Article 445 |
6
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Salamanca et al.
Methamphetamine on infection and immunity
study the impact of METH in a systemic disease model. METH
T- and B-cells in METH-exposed hosts require further study.
abrogates normal macrophage function, resulting in accelerated
Identification of these underlying mechanisms will highlight new
disease in murine histoplasmosis
(Martinez et al., 2009). METH
therapeutic and prophylactic methods to improve immunity in
decreases phagocytosis and killing of
H. capsulatum by primary
the context of drug abuse. These goals are of considerable signif-
macrophages. METH exposed
H. capsulatum-infected mice have
icance in the fields of immunity, host-pathogen interactions and
increased fungal burdens, increased pulmonary inflammation,
drug abuse.
and decreased survival. METH exposure results in cytokine dys-
There is an urgent need for innovative METH treatment inter-
regulation, aberrant processing of yeasts within macrophages, and
ventions to prevent the acquisition and transmission of infec-
immobilization of MAC-1 receptors on the macrophage surface.
tious diseases. Through utilization of drug abuse treatment and
Additionally, METH inhibits T cell proliferation and alters anti-
community-based outreach programs, drug abusers can change
body production, both important components of adaptive immu-
their HIV risk behaviors
(Garfein et al., 2010; Miller et al., 2010;
nity. Hence, it is established that METH alters the immune system
Naar-King et al., 2010). Through targeted outreach and aware-
of a mammalian host, resulting in enhanced disease (Martinez
ness programs, the prevalence of drug abuse and drug-related
et al.,
2009).
risk behaviors, such as needle-sharing and unsafe sexual practices,
The encapsulated fungus
Cryptococcus neoformans is the most
can be reduced significantly, thus decreasing the risk of disease
common cause of fungal meningitis in patients with AIDS
acquisition. This is a challenge because due to recent reduction
killing = 600,000 people worldwide
(Park et al., 2009). Using
in healthcare funding usually compromises the viability of these
a systemic mouse model of infection and
in vitro assays, it was
preventive programs. Healthcare providers should be trained to
recently demonstrated that METH stimulates fungal adhesion,
recognize signs of METH addiction, and work openly and hon-
capsular polysaccharide release, and biofilm formation in pul-
estly with their patients to address the detrimental effects of
monary tissue
(Patel et al., 2013). Interestingly, structural analysis
METH addiction.
of the capsular polysaccharide of METH-exposed cryptococci
At this time, cognitive behavioral and contingency manage-
revealed that METH alters the carbohydrate composition of this
ment interventions are the most effective treatments for METH
virulence factor, highlighting the fungus’s ability to adapt to envi-
addiction
(Rawson et al., 2004; Roll et al., 2006). For example, the
ronmental stimuli, a possible explanation for its pathogenesis.
Matrix Model is a comprehensive behavioral treatment approach
Additionally, METH facilitates
C. neoformans dissemination from
for the reduction of METH abuse that merges cognitive therapy,
the respiratory tract into the CNS. METH alters BBB integrity and
drug testing, family education, 12-Step support, individual coun-
modifies the expression of tight junction and adhesion molecules
seling and reinforcement for nondrug-related activities (Rawson
(Eugenin et al., 2013). These findings provide novel evidence
et al.,
2004). Contingency management interventions also offer
of the impact of METH abuse on the integrity of the cells that
tangible incentives in exchange for participating in therapy and
comprise the BBB and protect the brain from infection.
sustaining abstinenc
e.(Roll et al., 2006) Currently, no specific
medications exist that counteract the effects of METH or that pro-
CONCLUSION AND FUTURE PERSPECTIVES
long abstinence from the abuse of METH by an addict. However,
METH use has become increasingly prevalent in recent years, cre-
novel anti-METH immunotherapies, primarily in the form of
ating a severe public health epidemic and societal burden. The
monoclonal antibodies and lipid-based vaccines, are in early clin-
drug adversely changes user behavior, including putting METH
ical trial phases and act as pharmacokinetic antagonists, isolating
users at high risk for the acquisition of diverse infectious dis-
METH and its metabolites from vulnerable areas in the brain and
eases. Recent studies have identified a causal linkage between
minimizing the toxic effects of the drug
(Peterson et al., 2013;
METH and immune dysfunction in mature mammals. METH
Rüedi-Bettschen et al., 2013; Collins et al., 2014; Hambuchen
immunosuppression may underlie the mechanism for the rapid
et al.,
2014).
development of AIDS in METH users, progressing from HIV
Finally, the research described to date is likely to be only the tip
to AIDS within only a few months
(CDC, 2007). Investigators
of the proverbial iceberg, such that numerous other diseases, espe-
are just beginning to decipher the complex effects of METH in
cially infectious diseases, are likely to be significantly modified by
the context of HIV infection, but the limited nature of available
METH. The propagation of this disease, along with many other
information suggests that this drug dramatically impacts disease.
viral and bacterial contagions, demonstrates the necessity for con-
Understanding the specific mechanisms of METH abuse and HIV
tinued studies in this area of healthcare and substance abuse. Until
will require large epidemiological studies as well as the utilization
the use of METH is strictly curtailed, the impact of METH on our
of relevant animal models that reproduce salient features of HIV
society will continue to be severe.
infection in humans and are devoid of numerous confounding
factors present in human studies.
ACKNOWLEDGMENTS
Another important question yet to be answered is how METH
Luis R. Martinez is supported by the NYIT College of Osteopathic
disarms the adaptive immune system, further rendering the host
Medicine Start-up funds.
more susceptible to opportunistic infections. We recently showed
that the impairment of adaptive immunity by METH dimin-
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This article was submitted to Neuropharmacology, a section of the journal Frontiers in
Prevalence and correlates of HIV and syphilis infections among men who
Neuroscience.
have sex with men in seven provinces in China with historically low HIV
Copyright © 2015 Salamanca, Sorrentino, Nosanchuk and Martinez. This is an open-
prevalence.
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Yamamoto, B. K., Moszczynska, A., and Gudelsky, G. A. (2010). Amphetamine tox-
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