A, Brain section from an SIV-infected untreated macaque demonstrating
typical changes of severe SIV encephalitis with numerous epithelioid macrophages
(arrows) and multinucleated giant cells (arrowheads) in perivascular spaces.
B, Brain section from an SIV-infected macaque treated with minocycline, showing
no inflammation. Hematoxylin-eosin; original magnification ×200.
A, Expression of major histocompatibility complex class II antigens,
which detects activated macrophages and microglia and endothelial cells. B,
Expression of macrophage marker CD68, which marks activated macrophages and
microglia. C, Expression of T-cell intracytoplasmic antigen 1, a protein found
in cytotoxic cytoplasmic granules of natural killer cells and CD8 T cells.
D, Expression of activated p38 mitogen-activated protein kinase (p-p38); up-regulated
most in neurons and astrocytes in our model. E, Expression of β-amyloid
precursor protein, a marker of axonal degeneration. Each data point represents
the mean of 20 repeated measures of major histocompatibility complex class
II, CD68, T-cell intracytoplasmic antigen 1, p-p38, or β-amyloid precursor
protein. The P values were determined by comparing
the replicate data from each group of animals with the data from the other
group. For graphical presentation, only the animal-specific means are depicted.
Horizontal bars indicate group means.
Monocyte chemoattractant protein 1 (MCP-1) expression in cerebrospinal
fluid (CSF) is expressed as the ratio of MCP-1 in the CSF vs that in the plasma.
A, After 28 days after inoculation, untreated macaques with moderate to severe
encephalitis had increased CSF:plasma MCP-1 ratios. B, Minocycline-treated
macaques had significantly lower CSF:plasma MCP-1 ratios (P = .001) after 28 days. C, Simian immunodeficiency virus–infected,
minocycline-treated macaques had significantly lower MCP-1 protein in brain
homogenates than untreated macaques. Horizontal bars indicate group means.
Cerebrospinal fluid (CSF) viral RNA quantitated by real-time reverse
transcription–polymerase chain reaction in the simian immunodeficiency
virus (SIV)–infected, untreated macaques, A, was significantly higher
from 28 to 84 days after inoculation (P = .05)
than in SIV-infected, minocycline-treated macaques during the same period,
B. The area to the right of the vertical dashed line indicates samples taken
after the initiation of minocycline treatment. C, Minocycline-treated animals
had significantly less viral RNA in brain homogenates. D, Minocycline-treated
animals also had significantly less viral glycoprotein 41 protein in the brain.
For C and D, each data point represents the mean of 20 repeated measures of
glycoprotein 41. The P value was determined by comparing
the replicate data from each group of animals with the data from the other
group. For graphical presentation, only the animal-specific means are depicted.
Horizontal bars indicate group means.
A and B, Simian immunodeficiency virus (SIV)–infected primary
macaque lymphocytes, C, Human immunodeficiency virus (HIV)–infected
primary human lymphocytes, D and E, SIV-infected primary macaque macrophages,
and F, HIV-infected primary human macrophages.
Western blot analysis of total p38 and activated p38 (p-p38) in minocycline-treated,
human immunodeficiency virus [HIV]–infected primary human lymphocytes,
A, and macrophages, B, demonstrating minocycline-induced suppression of activation
of p38 in lymphocytes but not macrophages.
Zink MC, Uhrlaub J, DeWitt J, Voelker T, Bullock B, Mankowski J, Tarwater P, Clements J, Barber S. Neuroprotective and Anti–Human Immunodeficiency Virus Activity of Minocycline. JAMA. 2005;293(16):2003-2011. doi:10.1001/jama.293.16.2003
Author Affiliations: Department of Comparative
Medicine, Johns Hopkins University School of Medicine, Baltimore, Md (Drs
Zink, Mankowski, Clements, and Barber; Mss Uhrlaub, and Voelker; and Messrs
DeWitt and Bullock); Department of Biostatistics and Epidemiology, University
of Texas Health Science Center at Houston, School of Public Health, El Paso
Regional Campus, El Paso (Dr Tarwater).
Context The prevalence of human immunodeficiency virus (HIV) central nervous
system (CNS) disease has not decreased despite highly active antiretroviral
therapy. Current antiretroviral drugs are expensive, have significant adverse
effects including neurotoxicity, and few cross the blood-brain barrier.
Objective To examine the ability of minocycline, an antibiotic with potent anti-inflammatory
and neuroprotective properties, to protect against encephalitis and neurodegeneration
using a rapid, high viral load simian immunodeficiency virus (SIV) model of
HIV-associated CNS disease that constitutes a rigorous in vivo test for potential
Design and Subjects Five SIV-infected pigtailed macaques were treated with 4 mg/kg per day
of minocycline beginning at early asymptomatic infection (21 days after inoculation).
Another 6 macaques were inoculated with SIV but remained untreated. Blood
and cerebrospinal fluid (CSF) samples were taken on days 7, 10, 14, 21, 28,
35, 43, 56, 70, 77, and 84, and all macaques were humanely killed at 84 days
after inoculation, a time that corresponds to late-stage infection in HIV-infected
Main Outcome Measures Blood and CSF samples were tested for viral load by real-time reverse
transcription–polymerase chain reaction and levels of monocyte chemoattractant
protein 1 were quantitated by enzyme-linked immunosorbent assay. The presence
and severity of encephalitis was determined by microscopic examination of
tissues. Central nervous system inflammation was further assessed by measuring
infiltration and activation of macrophages, activation of p38 mitogen-activated
protein kinase and expression of amyloid precursor protein by quantitative
Results Minocycline-treated macaques had less severe encephalitis (P = .02), reduced CNS expression of neuroinflammatory markers
(major histocompatibility complex class II, P = .03;
macrophage marker CD68 , P = .07;
T-cell intracytoplasmic antigen 1, P = .03;
CSF monocyte chemoattractant protein 1, P = .001),
reduced activation of p38 mitogen-activated protein kinase (P<.001), less axonal degeneration (β-amyloid precursor protein, P = .03), and lower CNS virus replication (viral
RNA, P = .04; viral antigen, P = .04). In in vitro analysis, minocycline suppression of
HIV and SIV replication in cultured primary macrophages did not correlate
with suppression of activation of p38-mitogen-activated protein kinase pathways,
whereas suppression in primary lymphocytes correlated with suppression of
Conclusions In this experimental SIV model of HIV CNS disease, minocycline reduced
the severity of encephalitis, suppressed viral load in the brain, and decreased
the expression of CNS inflammatory markers. In vitro, minocycline inhibited
SIV and HIV replication. These findings suggest that minocycline, a safe,
inexpensive, and readily available antibiotic should be investigated as an
Human immunodeficiency virus (HIV) central nervous system (CNS) disease
is characterized by infiltration and activation of macrophages and microglia,
production of proinflammatory cytokines, expression of proapoptotic and neurotoxic
mediators, and neuronal loss.1- 3 Although
many antiretroviral drugs suppress HIV replication in peripheral blood, few
drugs achieve effective levels in the brain or alter the inflammatory responses
that accompany viral infection in the CNS. In addition, many reverse transcriptase
and protease inhibitors are expensive and have significant adverse effects,
including neurotoxicity.4,5 A
number of neuroprotective agents for HIV-infected individuals are being examined
in clinical trials,6- 9 but
no single agent has emerged as a solution to both the inflammatory and neurodegenerative
effects of HIV in the CNS.
The simian immunodeficiency virus (SIV)–macaque model provides
an excellent system to dissect the pathogenesis of HIV-induced CNS disease
because it recapitulates key features of HIV CNS infection, including the
development of encephalitis with active virus replication in the CNS, characteristic
histopathological changes, psychomotor impairment, and neurodegeneration.10- 13 However,
the prolonged course of infection (years) and the unpredictable incidence
of SIV CNS disease in the classic SIV-macaque model have limited its usefulness
to elucidate pathogenic mechanisms of HIV CNS disease that may be vulnerable
to therapeutic intervention. We therefore developed an accelerated, consistent
SIV-macaque model of HIV CNS disease in which more than 90% of infected animals
develop encephalitis with neurodegeneration 3 months after inoculation.13,14 Because of the high viral loads in
plasma and CSF of infected animals, the rapidity of immunosuppression and
the high incidence of severe neurological disease, this model provides a rigorous
test for evaluation of anti-HIV and neuroprotective therapeutics.
We tested the ability of the tetracycline derivative minocycline to
protect against SIV neurodegeneration for several reasons. First, minocycline
has potent anti-inflammatory properties and effectively crosses the blood-brain
barrier.15- 17 Second,
minocycline is neuroprotective in animal models of amyotrophic lateral sclerosis,
multiple sclerosis, Parkinson disease, Huntington disease, and ischemic or
traumatic brain injury and has recently been shown to reduce gadolinium-enhancing
lesions in the CNS of patients with multiple sclerosis.18- 24 Third,
the anti-inflammatory and neuroprotective properties of minocycline in several
animal models have been linked to suppressed activation of p38 mitogen-activated
protein kinase, and we recently demonstrated increased p38 activation in SIV
encephalitis.25 Finally, minocycline is readily
available, inexpensive, relatively safe when administered long term, and it
is approved by the US Food and Drug Administration for treatment of other
Twelve juvenile pigtailed macaques (Macaca nemestrina) were intravenously inoculated as previously described with SIV/DeltaB670
(50 AID50) and SIV/17E-Fr (10 000 AID50).12 Minocycline at a dose of 4 mg/kg per day divided
over 2 doses was administered orally in a cherry-flavored tablet to 6 macaques
starting 21 days after innoculation.26 One
macaque in the treated group who frequently refused to eat the minocycline
tablet was removed from the study. There were no recognizable adverse effects
of minocycline treatment. Cerebrospinal fluid and plasma samples were taken
on days 7, 10, 14, 21, 28, 35, 43, 56, 70, 77, and 84 for quantitation of
viral RNA and monocyte chemoattractant protein 1 (MCP-1).12,27 All
macaques were killed 84 days after inoculation in accordance with federal
guidelines and institutional policies. At death, macaques were perfused with
sterile saline to remove blood from the vasculature prior to freezing or fixing
tissues. These animal studies were approved by the Johns Hopkins Animal Care
and Use Committee. All the animals were humanly treated in accordance with
federal guidelines and institutional policies.
Pathological Assessment. All tissues were examined
microscopically by 2 pathologists (M.C.Z., J.M.). Sections of frontal and
parietal cortex, basal ganglia, thalamus, midbrain, cerebellum, brain stem,
and spinal cord were examined microscopically and scored independently as
mild, moderate, or severe according to previously described criteria.12
Quantitation of RNA in Plasma, CSF, and Brain. Viral
RNA in plasma and CSF and viral RNA in brain tissue (basal ganglia) were quantitated
by real-time reverse transcription–polymerase chain reaction using a
protocol previously described.12
Quantitation of MCP-1 in Plasma, CSF, and Brain. Monocyte
chemoattractant protein 1 levels in CSF, plasma, and brain homogenates were
measured by enzyme-linked immunosorbent assay (R&D Systems, Minneapolis,
Minn) as described previously.27
Quantitative Immunohistochemical Analysis. Our
methods for quantitative immunohistochemical analysis of macrophage marker
CD68, major histocompatibility complex class II, T-cell intracytoplasmic antigen
1, SIV glycoprotein 41, β-amyloid precursor protein, and activated p38
have been described previously.12,25,27,28
Cell Culture, In Vitro Infection, and Treatment With
Minocycline. Peripheral blood lymphocytes and macrophages were cultured
as described.29 Minocycline was added to cultures
24 hours before inoculation with HIV-1IIIB, HIV-1Ba-L, SIV/17E-Fr, or SIV/DeltaB670.
Peripheral blood lymphocytes and macrophages were infected (multiplicity of
infection, 0.005 and 0.05, respectively), washed, and cultured with or without
minocycline. Virus replication was assessed by quantitating p27 or p24 by
enzyme-linked immunosorbent assay (Coulter, Miami, Fla) in supernatants collected
periodically after infection. Viabilities of infected peripheral blood lymphocytes
(assessed by trypan blue exclusion) were not affected by minocycline. Minocycline
concentrations of 20 μg/mL or less were not toxic to macrophages; however,
concentrations of 40 μg/mL resulted in an approximate 30% reduction in
viability after 9 days.
Western Blot Analysis of p38 Activation. For
HIV- and SIV-infected cultures, whole cell lysates were prepared from the
above cultures 9 days after inoculation and were subjected to Western blot
analysis for total p38 or activated p38 (Cell Signaling, Beverly, Mass).
Fisher exact P value was used to compare the
proportions of animals with moderate or severe encephalitis between treated
and control groups to properly account for the small number of observations.
The dichotomization of CNS severity (moderate to severe vs none to mild) has
been used in previous research using this model27 and
was conducted prior to data analysis. The comparison between treated and control
groups’ mean MCP-1 level in the brain was conducted using a 2-sample t test. Expression of major histocompatibility complex
class II, CD68, T-cell intracytoplasmic antigen 1, p-p38, β-amyloid precursor
protein, and viral protein in the brain were quantitated using 20 repeated
measures on each tissue sample. The P values were
determined by comparing the replicate data from each group of animals with
the data from the other group although only the means were depicted graphically
in the figures. Comparisons between the 2 treatment groups were conducted
using a linear regression model with a dichotomous variable indicating membership
in the treatment group, a method analogous to the 2-sample t test. In addition, the coefficient and SE estimates were calculated
using generalized estimating equations,30 a
robust estimation procedure that properly accounts for the inherent correlation
among replicated or repeated measurements observed on the same animal. For
variables with measurements taken repeatedly overtime (ie, CSF viral RNA and
CSF:plasma MCP-1 ratio) we again used generalized estimating equations in
a linear regression model but with time from inoculation and treatment by
time interaction included as independent variables. The model estimates of
the coefficient and standard error for the interaction term were used to test
the differences, if any, of the rates of change over time between the 2 treatment
groups. All statistical tests were performed as 2-sided tests. Analyses were
performed using Stata statistical software version 8 (StataCorp, College Station,
Tex). Statistical significance was P<.05.
In this study, a rapid, high viral load SIV model of HIV CNS disease
was used to test the ability of minocycline to suppress SIV CNS inflammation
and neurodegeneration. Because all macaques develop rapid immunosuppression
and express high viral loads in plasma and CSF and because the majority develops
encephalitis within 84 days after virus inoculation, this model provides a
rigorous test for potential therapeutic treatments. Five macaques were infected
with SIV12 and received minocycline treatment
(4 mg/kg per day)26 that was initiated during
asymptomatic infection (21 days after inoculation).31 By
day 84 after inoculation, of the untreated macaques, 3 developed moderate,
2 developed severe, and 1 developed no SIV encephalitis (Figure 1).12 In contrast, 3 of 5
minocycline-treated animals did not develop encephalitis while the remaining
2 macaques had only mild encephalitis. This decreased incidence of moderate
and severe encephalitis in the minocycline-treated macaques was statistically
significant (P = .02).
To assess the ability of minocycline to suppress SIV-induced CNS inflammation,
we quantitated infiltration and activation of macrophages and infiltration
of cytotoxic lymphocytes into the CNS, activation of p38 mitogen-activated
protein kinase in the brain and expression of β-amyloid precursor protein,
a marker of axonal degeneration, by quantitative immunohistochemical analysis.12,25,27,28 Minocycline
significantly reduced expression of major histocompatibility complex class
II antigens (P = .03; Figure 2A), indicating suppressed activation of macrophages, endothelial
cells, or both in the brain.
Decreased infiltration and activation of macrophages in minocycline-treated
animals also was suggested by reduced expression of the macrophage marker
CD68 (P = .07, Figure 2B). Minocycline also reduced the infiltration of cytotoxic
lymphocytes into the brain as evidenced by significantly reduced expression
of the cytotoxic lymphocyte marker T-cell intracytoplasmic antigen 1 (P = .03, Figure 2C) in treated animals. The effects of minocycline were not only
limited to macrophages and lymphocytes as suggested by the finding of significantly
reduced activation of p38 in neurons and astrocytes in the brain of minocycline-treated
macaques (P<.001, Figure 2D). Expression of β-amyloid precursor protein, an established
marker of axonal degeneration, also was significantly lower (P = .03, Figure 2E)
in minocycline-treated macaques compared with untreated SIV-infected animals.
Proinflammatory chemokines, particularly MCP-1, provide signals from
the CNS that promote infiltration of macrophages and to a lesser extent inflammatory
T lymphocytes from the periphery into the brain. Increased CSF expression
of MCP-1 has been correlated with the development of HIV and SIV CNS disease.27,32,33 Quantitation of CSF:plasma
MCP-1 levels provides a measure of the gradient of the MCP-1 that exists between
the CNS and the periphery.27 To determine whether
minocycline affects expression of this important proinflammatory signal in
the CNS, MCP-1 levels in CSF and plasma were quantitated throughout infection
and MCP-1 in brain was quantitated at necropsy. Cerebrospinal fluid MCP-1
levels (as measured by CSF:plasma ratios) of several treated and untreated
SIV-infected macaques increased during acute infection and then declined after
10 to 14 days after inoculation (Figure 3A,
B), a pattern typical of acute SIV infection.27 In
the untreated SIV-infected macaques, CSF MCP-1 levels increased again after
28 days in contrast to the minocycline-treated macaques in which CSF MCP-1
levels remained significantly lower (P = .001).
The low levels of MCP-1 in the CSF of the minocycline-treated macaques during
late-stage infection were confirmed by measuring MCP-1 protein levels in brain
homogenates by enzyme-linked immunosorbent assay. Minocycline-treated macaques
had significantly lower levels of MCP-1 protein in the brain than SIV-infected
macaques (P = .03; Figure 3C). Thus, minocycline has an impact on the release of chemokines
that mediate influx of inflammatory cells into the brain.
Because previous studies in this model demonstrated that macaques with
more severe encephalitis had higher levels of viral RNA in the CSF and brain,
we quantitated viral RNA in the CSF and in brain tissue from SIV-infected
minocycline-treated and untreated macaques by real-time reverse transcription–polymerase
chain reaction.12 Minocycline significantly
suppressed levels of viral RNA in the CSF after 28 days. (P = .05; Figure 4A,
B). Comparison of the change in CSF viral load from day 28 after inoculation
onward using a linear regression model demonstrated declining CSF viral loads
in minocycline-treated macaques (dark line after 28 days in Figure 4A, B) in contrast to increasing CSF viral loads in untreated
macaques. Furthermore, minocycline-treated macaques had reduced expression
of viral RNA in the basal ganglia region of the brain (P = .04, Figure 4C).
The suppressive effect of minocycline on SIV replication was confirmed by
quantitative image analysis on brain sections stained immunohistochemically
for SIV glycoprotein 41. Minocycline-treated macaques had significantly lower
expression of viral antigen in brain than untreated SIV-infected macaques
(P = .04; Figure 4D).
Since minocycline suppressed SIV replication in the CNS, we examined
whether it also would inhibit SIV and HIV replication in the predominant target
cells productively infected by these viruses—macrophages and lymphocytes.
Cultured primary macaque and human peripheral blood monoculear cells–derived
macrophages and lymphocytes29 were treated
with 10, 20, or 40 μg/mL of minocycline20,34 for
24 hours prior to inoculation with the appropriate viruses. Virus replication
was quantitated over time by p24 (HIV) or p27 (SIV) enzyme-linked immunosorbent
assay on culture supernatants. Minocycline inhibited HIV and SIV replication
in primary lymphocytes (Figure 5A, B,
E) and macrophages (Figure 5C, D, and
F), in a dose-dependent manner. At the highest dose, minocycline inhibited
HIV replication by 92% and 99% and SIV replication by 99% and 85% in lymphocytes
and macrophages, respectively.
To investigate the mechanism(s) involved in minocycline-mediated suppression
of HIV and SIV replication, we examined activation of p38 in cultured, HIV-infected
minocycline-treated primary lymphocytes and macrophages. p38 is ubiquitously
expressed and although activation of p38 in astrocytes and neurons accompanies
neurodegeneration in our model and others, this kinase also has critical signaling
functions in other cells including T lymphocytes and monocytes or macrophages.16,25,34 We specifically examined
p38 activation as a potential mechanism for virus suppression because 2 reports
have suggested that activation of p38 is required for replication of HIV in
lymphocytes35 and in U1 promonocytic cells36 and because minocycline suppresses activation of
p38 in response to proinflammatory cytokines and neurotoxic products.16,34 Cells were treated with minocycline
for 24 hours prior to HIV infection and activation of p38 was assessed by
Western blot analysis of whole cell lysates prepared days 9 after inoculation.
Minocycline inhibited activation of p38 (and to some extent constitutive expression
of p38) in HIV-infected primary lymphocytes but not in macrophages (Figure 6A, B). Similar results were obtained
from SIV-infected primary lymphocytes and macrophages (data not shown). These
data indicate that although inhibition of virus replication in minocycline-treated
primary lymphocytes correlates with inhibition of p38 activation, inhibition
of HIV and SIV replication in primary macrophages occurs via p38-independent
mechanisms. They further indicate that the known activators of p38 in both
lymphocytes and macrophages, mitogen-activated protein kinase kinase 3 and
6, are not direct targets of minocycline.
In this study, we demonstrate that minocycline significantly inhibits
HIV and SIV replication in vitro and also reduces the incidence and severity
of encephalitis in a rigorous SIV-macaque model of HIV CNS disease. The latter
observation is particularly impressive, given the rapidity and severity of
SIV encephalitis in our model and the ability of minocycline to intervene
effectively when treatment is initiated during asymptomatic infection and
continued during the short period between 21 and 84 days. To the best of our
knowledge, this is the first report demonstrating anti-inflammatory and neuroprotective
activity of an antibiotic against a highly pathogenic virus infection and
that minocycline suppresses HIV and SIV replication in lymphocytes and macrophages,
the main target cells in vivo for these viruses. Given that the prevalence
of HIV CNS disease has not declined in the era of highly active antiretroviral
treatment, this finding may have important implications for future studies
on the prevention and treatment of HIV-infected individuals.37- 39
The ability of minocycline to prevent increased expression of MCP-1
in the brain is unquestionably one factor mediating the neuroprotective effect
in our SIV model of HIV CNS disease.27 Monocyte
chemoattractant protein 1, which is produced by macrophages and astrocytes
in the brain, is the major inflammatory chemokine responsible for the influx
of macrophages into the brain. Macrophages provide a primary mode of transport
for HIV and SIV into the brain, are the major sources for HIV and SIV replication
in the CNS and produce toxic mediators during HIV CNS disease. Our finding
of reduced activation of macrophages or microglia and decreased influx of
cytotoxic lymphocytes in minocycline-treated SIV-infected macaques is consistent
with the suppression of MCP-1 expression in the CNS by this antibiotic. This
study is the first, to our knowledge, to link MCP-1 to the mechanisms mediating
the neuroprotective effects of minocycline. This finding suggests that minocycline
may have clinical applicability to neurodegenerative disorders in which MCP-1-induced
infiltration and activation of macrophages is an important determinant of
neuropathology, such as multiple sclerosis. A recent report suggested that
minocycline may be an effective therapy for multiple sclerosis.24 Furthermore,
it is possible that minocycline treatment may have a role in treatment of
HIV-infected individuals who are at higher risk for development of HIV CNS
disease by virtue of a genetic polymorphism in the MCP-1 promoter region that
increases MCP-1 levels.33
The dose of minocycline that was used in these macaques (4 mg/kg per
day) is within in the tolerated range for humans. Although it can be difficult
to compare effective or toxic doses from one species to another, studies in
nonhuman primates come as close to actual human trials as possible. Two double-blind,
randomized, placebo-controlled feasibility trials of minocycline in patients
with amyotrophic lateral sclerosis have been reported recently.40 In
the first, 19 patients were treated with 200 mg/d of minocycline (3 mg/kg
per day for a 70-kg individual) for 6 months with no difference in adverse
events compared with those in the placebo group. In a second, 23 patients
received up to 400 mg per day in an 8-month crossover trial. The mean tolerated
dose in this study was 387 mg/d (5.5 mg/kg per day for a 70 kg individual).
These findings suggest that minocycline at the dose that suppressed CNS inflammation
and virus replication in macaques may be well tolerated in HIV-infected individuals.
Although minocycline treatment initiated at 21 days after SIV inoculation
significantly reversed the pattern of increasing levels of viral RNA in the
CSF as infection progressed, its effect on plasma viral load was less marked,
likely because of the early high plasma viral loads ( ≈ 108 copy Eq/mL by 10 days after inoculation) in this accelerated SIV-macaque
model. Nevertheless, plasma viral RNA levels were significantly lower in the
3 minocycline-treated macaques that did not develop encephalitis than in the
2 treated macaques with encephalitis (data not shown; P = .05).
Perhaps the most unexpected result of these studies was the ability
of minocycline to substantially inhibit replication of SIV and HIV in primary
cultures of macrophages and lymphocytes. A recent study describing minocycline
inhibition of HIV in cultured microglia was recently reported.41 It
seems unlikely that minocycline has classic antiviral activity as do reverse
transcriptase and protease inhibitors because the antibiotic was not engineered
to target a specific viral protein.
We propose that rather than exerting direct antiviral activity, minocycline
modifies the intracellular or extracellular environment making it nonpermissive
for HIV or SIV replication. The ability of minocycline to modify environments
differentially in primary macrophages and T lymphocytes (as evidenced by the
differential effect of minocycline on p38 activation) raises the possibility
that each cell type has a unique minocycline-sensitive target and hence, a
unique mechanism of suppression.35,36,42 An
important potential therapeutic advantage of this differential effect is that
if the virus develops mutations that confer resistance to minocycline in one
target cell type, that resistance might not confer a replicative advantage
in the other cell type. Minocycline represents a second immunodulatory agent
to suppress HIV replication in macrophages in a p38-independent manner. Murabutide,
which is currently being studied in clinical trials of HIV-infected patients,
also acts to suppress HIV replication in a p38-independent manner in macrophages.42,43
Minocycline is a semisynthetic second-generation tetracycline that readily
crosses the blood-brain barrier, is inexpensive and safe, has been prescribed
for years, and is available in generic form. Our findings that minocycline
inhibits SIV and HIV replication in primary macrophages and lymphocytes in
vitro and suppresses SIV replication in the brain and the accompanying neuropathology
provide evidence for designing human studies to examine the potential role
of minocycline as a supplement to highly active antiretroviral therapy in
the treatment of HIV-associated cognitive disorders and in maintaining low
viral loads in patients for whom highly active antiretroviral therapy must
be discontinued. Furthermore, minocycline is efficacious against a variety
of infectious diseases, including toxoplasmosis, malaria, and several sexually
transmitted diseases and thus has potential for long-term use in global areas
in which individuals frequently harbor multiple infections besides HIV.
Corresponding Author: M. Christine Zink,
DVM, PhD, Johns Hopkins University School of Medicine, 733 N Broadway, Room
839, Baltimore, MD 21205 (email@example.com).
Author Contributions: Dr Zink had full access
to all of the data in the study and takes responsibility for the integrity
of the data and the accuracy of the data analysis.
Study concept and design: Zink, Tarwater, Clements,
Acquisition of data: Zink, Uhrlaub, DeWitt,
Voelker, Bullock, Mankowski, Tarwater, Barber.
Analysis and interpretation of data: Zink,
Mankowski, Tarwater, Clements, Barber.
Drafting of the manuscript: Zink, Uhrlaub,
DeWitt, Voelker, Bullock, Mankowski, Tarwater, Clements, Barber.
Critical revision of the manuscript for important
intellectual content: Zink, Clements, Barber.
Statistical analysis: Tarwater.
Obtained funding: Zink, Clements.
Administrative, technical, or material support:
Zink, Uhrlaub, DeWitt, Voelker, Bullock, Mankowski, Clements, Barber.
Study supervision: Zink, Barber.
Financial Disclosures: Drs Zink and Barber
are named as inventors on a patent pending for minocycline to treat HIV infection.
The patent will be held by the Johns Hopkins University. Otherwise no other
authors reported financial disclosures.
Funding/Support: These studies were supported
by grants MH069116 and NS44815 from the National Institutes of Health.
Role of the Sponsor: The National Institutes
of Health did not participate in the design and conduct of the study, in the
collection, analysis, and interpretation of the data, or in the preparation,
review, or approval of the manuscript.
Acknowledgment: We thank April Hargrove, John
Anderson, Lucio Gama, and Ming Li for technical assistance and Jessica Carman
for fruitful discussions.