CSF penetration by antiretroviral drugs

A helping HAND: therapeutic potential of MAGL inhibition against HIV-1-associated neuroinflammation

Background

Human immunodeficiency virus (HIV) affects nearly 40 million people globally, with roughly 80% of all people living with HIV receiving antiretroviral therapy. Antiretroviral treatment suppresses viral load in peripheral tissues but does not effectively penetrate the blood-brain barrier. Thus, viral reservoirs persist in the central nervous system and continue to produce low levels of inflammatory factors and early viral proteins, including the transactivator of transcription (Tat). HIV Tat is known to contribute to chronic neuroinflammation and synaptodendritic damage, which is associated with the development of cognitive, motor, and/or mood problems, collectively known as HIV-associated neurocognitive disorders (HAND). Cannabinoid anti-inflammatory effects are well documented, but therapeutic utility of cannabis remains limited due to its psychotropic effects, including alterations within brain regions encoding reward processing and motivation, such as the nucleus accumbens. Alternatively, inhibiting monoacylglycerol lipase (MAGL) has demonstrated therapeutic potential through interactions with the endocannabinoid system.

Methods

The present study utilized a reward-related operant behavioral task to quantify motivated behavior in female Tat transgenic mice treated with vehicle or MAGL inhibitor MJN110 (1 mg/kg). Brain tissue was collected to assess dendritic injury and neuroinflammatory profiles, including dendritic microtubule-associated protein (MAP2ab) intensity, microglia density, microglia morphology, astrocyte density, astrocytic interleukin-1ß (IL-1ß) colocalization, and various lipid mediators.

Results

No significant behavioral differences were observed; however, MJN110 protected against Tat-induced dendritic injury by significantly upregulating MAP2ab intensity in the nucleus accumbens and in the infralimbic cortex of Tat(+) mice. No or only minor effects were noted for Iba-1+ microglia density and/or microglia morphology. Further, Tat increased GFAP+ astrocyte density in the infralimbic cortex and GFAP+ astrocytic IL-1ß colocalization in the nucleus accumbens, with MJN110 significantly reducing these measures in Tat(+) subjects. Lastly, selected HETE-related inflammatory lipid mediators in the striatum were downregulated by chronic MJN110 treatment.

Conclusions

These findings demonstrate anti-inflammatory and neuroprotective properties of MJN110 without cannabimimetic behavioral effects and suggest a promising alternative to cannabis for managing neuroinflammation.

Antiretroviral drugs from multiple classes induce loss of excitatory synapses between hippocampal neurons in culture

Introduction: Antiretroviral (ARV) drugs have improved prognoses for people living with HIV. However, HIV-associated neurocognitive disorders (HAND) persist despite undetectable viral loads. Some ARVs have been linked to neuropsychiatric effects that may contribute to HAND. Synapse loss correlates with cognitive decline in HAND and synaptic deficits may contribute to the neuropsychiatric effects of ARV drugs. Methods: Using an automated high content assay, rat hippocampal neurons in culture expressing PSD95-eGFP to label glutamatergic synapses and mCherry to fill neuronal structures were imaged before and after treatment with 25 clinically used ARVs. Results and Discussion: At a concentration of 10 μM the protease inhibitors nelfinavir and saquinavir, the non-nucleoside reverse transcriptase inhibitors etravirine and the 8-OH metabolite of efavirenz, the integrase inhibitor bictegravir, and the capsid inhibitor lenacapavir produced synaptic toxicity. Only lenacapavir produced synapse loss at the nanomolar concentrations estimated free in the plasma, although all 4 ARV drugs induced synapse loss at Cmax. Evaluation of combination therapies did not reveal synergistic synaptic toxicity. Synapse loss developed fully by 24 h and persisted for at least 3 days. Bictegravir-induced synapse loss required activation of voltage-gated Ca2+ channels and bictegravir, etravirine, and lenacapavir produced synapse loss by an excitotoxic mechanism. These results indicate that select ARV drugs might contribute to neuropsychiatric effects in combination with drugs that bind serum proteins or in disease states in which synaptic function is altered. The high content imaging assay used here provides an efficient means to evaluate new drugs and drug combinations for potential CNS toxicity.

Cerebrospinal fluid immune markers and HIV-associated neurocognitive impairments: A systematic review

HIV-1 is responsible for the development of a spectrum of cognitive impairments known as HIV-associated neurocognitive disorder (HAND). In the era of antiretroviral therapy (ART), HAND remains prevalent in people living with HIV (PLWH), despite low or undetectable viral loads. Persistent neuroinflammation likely plays an important role in the contributing biological mechanisms. Multiple cerebrospinal fluid (CSF) immune markers have been studied but it is unclear which markers most consistently correlate with neurocognitive impairment. We therefore conducted a systematic review of studies of the association of CSF immune markers with neurocognitive performance in ART-experienced PLWH. We aimed to synthesize the published data to determine consistent findings and to indicate the most noteworthy CSF markers of HAND. Twenty-nine studies were included, with 20 cross-sectional studies and 9 longitudinal studies. From the group of markers most often assayed, specific monocyte activation (higher levels of Neopterin, sCD163, sCD14) and neuroinflammatory markers (higher levels of IFN-γ, IL-1α, IL-7, IL-8, sTNFR-II and lower levels of IL-6) showed a consistent direction in association with HIV-associated neurocognitive impairment. Furthermore, significant differences exist in CSF immune markers between HIV-positive people with and without neurocognitive impairment, regardless of viral load and nadir/current CD4⁺ count. These markers may be useful in furthering our understanding of the neuropathology, diagnosis and prognosis of HAND. Studies using prospective designs (i.e. pre- and post-interventions), "multi-modal" methods (e.g. imaging, inflammation and neurocognitive evaluations) and utilizing a combination of the markers most commonly associated with HAND may help delineate the mechanisms of HAND.

Brain HIV-1 latently-infected reservoirs targeted by the suicide gene strategy

Reducing the pool of HIV-1 reservoirs in patients is a must to achieve functional cure. The most prominent HIV-1 cell reservoirs are resting CD4 + T cells and brain derived microglial cells. Infected microglial cells are believed to be the source of peripheral tissues reseedings and the emergence of drug resistance. Clearing infected cells from the brain is therefore crucial. However, many characteristics of microglial cells and the central nervous system make extremely difficult their eradication from brain reservoirs. Current methods, such as the "shock and kill", the "block and lock" and gene editing strategies cannot override these difficulties. Therefore, new strategies have to be designed when considering the elimination of brain reservoirs. We set up an original gene suicide strategy using latently infected microglial cells as model cells. In this paper we provide proof of concept of this strategy.

Beneficial and Adverse Effects of cART Affect Neurocognitive Function in HIV-1 Infection: Balancing Viral Suppression against Neuronal Stress and Injury

HIV-associated neurocognitive disorders (HAND) persist despite the successful introduction of combination antiretroviral therapy (cART). While insufficient concentration of certain antiretrovirals (ARV) may lead to incomplete viral suppression in the brain, many ARVs are found to cause neuropsychiatric adverse effects, indicating their penetration into the central nervous system (CNS). Several lines of evidence suggest shared critical roles of oxidative and endoplasmic reticulum stress, compromised neuronal energy homeostasis, and autophagy in the promotion of neuronal dysfunction associated with both HIV-1 infection and long-term cART or ARV use. As the lifespans of HIV patients are increased, unique challenges have surfaced. Longer lives convey prolonged exposure of the CNS to viral toxins, neurotoxic ARVs, polypharmacy with prescribed or illicit drug use, and age-related diseases. All of these factors can contribute to increased risks for the development of neuropsychiatric conditions and cognitive impairment, which can significantly impact patient well-being, cART adherence, and overall health outcome. Strategies to increase the penetration of cART into the brain to lower viral toxicity may detrimentally increase ARV neurotoxicity and neuropsychiatric adverse effects. As clinicians attempt to control peripheral viremia in an aging population of HIV-infected patients, they must navigate an increasingly complex myriad of comorbidities, pharmacogenetics, drug-drug interactions, and psychiatric and cognitive dysfunction. Here we review in comparison to the neuropathological effects of HIV-1 the available information on neuropsychiatric adverse effects and neurotoxicity of clinically used ARV and cART. It appears altogether that future cART aiming at controlling HIV-1 in the CNS and preventing HAND will require an intricate balancing act of suppressing viral replication while minimizing neurotoxicity, impairment of neurocognition, and neuropsychiatric adverse effects. Graphical abstract Schematic summary of the effects exerted on the brain and neurocognitive function by HIV-1 infection, comorbidities, psychostimulatory, illicit drugs, therapeutic drugs, such as antiretrovirals, the resulting polypharmacy and aging, as well as the potential interactions of all these factors.

Treating viruses in the brain: Perspectives from NeuroAIDS

Aggressive use of antiretroviral therapy has led to excellent viral suppression within the systemic circulation. However, despite these advances, HIV reservoirs still persist. The persistence of HIV within the brain can lead to the development of HIV-associated neurocognitive disorders (HAND). Although the causes of the development of neurocognitive disorders is likely multifactorial, the inability of antiretroviral therapy to achieve adequate concentrations within the brain is likely a major contributing factor. Information about antiretroviral drug exposure within the brain is limited. Clinically, drug concentrations within the cerebrospinal fluid (CSF) are used as markers for central nervous system (CNS) drug exposure. However, significant differences exist; CSF concentration is often a poor predictor of drug exposure within the brain. This article reviews the current information regarding antiretroviral exposure within the brain in humans as well as preclinical animals and discusses the impact of co-morbidities on antiretroviral efficacy within the brain. A more thorough understanding of antiretroviral penetration into the brain is an essential component to the development of better therapeutic strategies for neuroAIDS.

Zidovudine and lamivudine reach higher concentrations in ventricular than in lumbar human cerebrospinal fluid

OBJECTIVE

For the treatment of HIV-1-related brain disease and for the prevention of the brain becoming a viral reservoir, it is important that antiretroviral agents reach sufficient concentrations in the CNS. To date, human brain pharmacokinetic data are solely derived from lumbar cerebrospinal fluid (CSF) and mostly originate from single samples.

DESIGN

We determined concentrations of antiretroviral drugs in serial samples of ventricular CSF and compared these to the concentrations in serum and lumbar CSF of these patients.

METHODS

Two treatment-naïve HIV-1-infected patients received external ventricular drainage for obstructive hydrocephalus. Starting with a combination antiretroviral regimen (cART), ventricular CSF, and subsequently lumbar CSF, with parallel serum, was frequently collected. Drug concentrations were determined and CSF-to-serum ratios were calculated.

RESULTS

High concentrations, resulting in high CSF-to-serum ratios, were found in the ventricular CSF of the three substances zidovudine, lamivudine and indinavir, whereas this was not observed for stavudine, ritonavir, saquinavir and efavirenz. Concentrations of zidovudine and lamivudine were up to four times greater in CSF from the ventricles than in lumbar CSF of the same patient. The zidovudine concentrations in the ventricular CSF exceeded serum concentrations by a factor of 1.4.

CONCLUSION

Unexpectedly high concentrations of some antiretrovirals in the ventricular CSF, the site close to the brain parenchyma where HIV is located, should be considered when the cART regimen is aiming at CNS viral replication.

Peripheral immune dysregulation in the ART era of HIV-associated neurocognitive impairments: A systematic review

Human immunodeficiency virus-associated neurocognitive impairment (HANI) remains problematic despite the effective use of antiretroviral therapy (ART) and viral suppression. A dysregulated immune response contributes to the development of HANI but findings on the association between peripheral blood immune markers and HANI have been inconsistent. We therefore conducted a systematic review of studies of the association of peripheral blood immune markers with neurocognitive performance in ART experienced HIV-positive participants. Thirty-seven studies were eligible, including 12 longitudinal studies and 25 cross-sectional studies. Findings consistently show that HIV-positive participants have altered immune marker levels, including elevated markers of monocyte activation (neopterin, sCD14, sCD163) and inflammation (CCL2, IL-8, IL-18, IP-10, IFN-α, sTNFR-II and TNF-α). These elevated levels persist in HIV-positive participants despite ART. The majority of studies found associations of HANI with immune markers, including those linked to monocyte activation (sCD14 and sCD163) and inflammation (IL-18 and IP-10). Despite the heterogeneity of studies reviewed, due to the presence of raised peripheral markers, our narrative review provides evidence of chronic inflammation despite ART. The raised levels of these markers may suggest certain mechanisms are active, potentially those involved in the neuropathophysiology of HANI.

Pharmacokinetics of nucleoside/nucleotide reverse transcriptase inhibitors for the treatment and prevention of HIV infection

INTRODUCTION

Despite dramatic increases in new drugs and regimens, a combination of two nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) remains the backbone of many regimens to treat HIV.

AREA COVERED

This article summarizes the pharmacokinetic characteristics of approved NRTIs that are currently in the international treatment and prevention guidelines.

EXPERT OPINION

Compared to other NRTIs, tenofovir alafenamide fumarate (TAF) is more advantageous in terms of potency and safety. It is therefore a preferred choice in combination with emtricitabine (FTC) in most HIV treatment guidelines. The efficacy of the two-drug combination of NRTI/Integrase strand-transfer inhibitor, i.e. lamivudine/dolutegravir has been approved as an option for initial therapy. This regimen however has some limitations in patients with HBV coinfection. The two NRTI combinations tenofovir disproxil fumarate (TDF)/FTC and TAF/FTC have also been approved for pre-exposure prophylaxis (PrEP). Interestingly, a promising long-acting nucleoside reverse transcriptase translocation inhibitor, islatravir, formulated for implant was well tolerated and remained effective for up to a year, suggesting its potential as a single agent for PrEP. In the next decade, it remains to be seen whether NRTI-based regimens will remain the backbone of preferred ART regimens, or if the treatment will eventually move toward NRTI-sparing regimens to avoid long-term NRTI-toxicity.

Mass Spectrometry Imaging Demonstrates the Regional Brain Distribution Patterns of Three First-Line Antiretroviral Drugs

HIV in the central nervous system (CNS) contributes to the development of HIV-associated neurological disorders (HAND), even with chronic antiretroviral therapy. In order for antiretroviral therapy to be effective in protecting the CNS, these drugs should have the ability to localize in brain areas known to be affected by HIV. Consequently, this study aimed to investigate the localization patterns of three first-line antiretroviral drugs, namely, efavirenz, tenofovir, and emtricitabine, in the rat brain. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) were utilized to assess the pharmacokinetics and brain spatial distribution of the three drugs. Each drug was administered (50 mg/kg) to healthy female Sprague-Dawley rats via intraperitoneal administration. LC-MS/MS results showed that all three drugs could be delivered into the brain, although they varied in blood-brain barrier permeability. MALDI-MSI showed a high degree of efavirenz localization across the entire brain, while tenofovir localized mainly in the cortex. Emtricitabine distributed heterogeneously mainly in the thalamus, corpus callosum, and hypothalamus. This study showed that efavirenz, tenofovir, and emtricitabine might be a potential drug combination antiretroviral therapy for CNS protection against HAND.

Simultaneous determination of intracellular concentrations of tenofovir, emtricitabine, and dolutegravir in human brain microvascular endothelial cells using liquid chromatography-tandem mass spectrometry (LC-MS/MS)

Combination antiretroviral therapy (cART) regimens are recommended for HIV patients to better achieve and maintain plasma viral suppression. Despite adequate plasma viral suppression, HIV persists inside the brain, which is, in part thought to result from poor brain penetration of antiretroviral drugs. In this study, a simple and ultra-sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of tenofovir, emtricitabine, and dolutegravir in cell lysates of an immortalized human brain microvascular endothelial cell line (hCMEC/D3) was developed and validated. Analytes were separated on a reverse phase C18 column using water and 0.1% formic acid in acetonitrile as mobile phases. The analytes were detected using positive electrospray ionization mode with multiple reaction monitoring (MRM). The assay was linear in the concentration range of 0.1-100 ng mL-1 for all analytes. Intra- and inter-assay precision and accuracy were within ±13.33% and ±10.53%, respectively. This approach described herein was used to determine the intracellular accumulation of tenofovir, emtricitabine, dolutegravir simultaneously in hCMEC/D3 cells samples.

Viral infections of the central nervous system in Africa

Viral infections are a major cause of human central nervous system infection, and may be associated with significant mortality, and long-term sequelae. In Africa, the lack of effective therapies, limited diagnostic and human resource facilities are especially in dire need. Most viruses that affect the central nervous system are opportunistic or accidental pathogens. Some of these viruses were initially considered harmless, however they have now evolved to penetrate the nervous system efficiently and exploit neuronal cell biology thus resulting in severe illness. A number of potentially lethal neurotropic viruses have been discovered in Africa and over the course of time shown their ability to spread wider afield involving other continents leaving a devastating impact in their trail. In this review we discuss key viruses involved in central nervous system disease and of major public health concern with respect to Africa. These arise from the families of Flaviviridae, Filoviridae, Retroviridae, Bunyaviridae, Rhabdoviridae and Herpesviridae. In terms of the number of cases affected by these viruses, HIV (Retroviridae) tops the list for morbidity, mortality and long term disability, while the Rift Valley Fever virus (Bunyaviridae) is at the bottom of the list. The most deadly are the Ebola and Marburg viruses (Filoviridae). This review describes their epidemiology and key neurological manifestations as regards the central nervous system such as meningoencephalitis and Guillain-Barré syndrome. The potential pathogenic mechanisms adopted by these viruses are debated and research perspectives suggested.

The clinical pharmacology of integrase inhibitors

Introduction: Treatment of HIV infection has consistently evolved in the last three decades. A steady improvement in efficacy tolerability, safety, and practical aspects of treatment intake has made HIV infection much easier to manage over the long term, and in optimal treatment conditions the life expectancy of persons living with HIV infection now approaches the values of the general population. The last category of antiretrovirals to be fully developed for clinical use is the one of strand-transfer integrase inhibitors (INSTIs). Areas covered: In this review, the evolution of the knowledge on INSTIs use in the clinical setting is reviewed, analyzed, and interpreted. Emphasis is placed on the properties possibly accounting for several superiority results achieved by INSTIs in non-inferiority designed comparative clinical trials, which led to their inclusion as first line options in all versions of HIV therapeutic guidelines. Expert commentary: Some unprecedented clinical-pharmacological properties of INSTIs, such as their rapid and sustained action against HIV replication, the optimal tolerability and safety profile and a clinically proven robust genetic barrier are the main factors justifying the successful clinical use of INSTIs. Based on these unique features, novel INSTIs-based treatment modalities are being developed, including the reduction of antiretroviral regimens to two drugs only.

Autophagy: The multi-purpose bridge in viral infections and host cells

Autophagy signaling pathway is involved in cellular homeostasis, developmental processes, cellular stress responses, and immune pathways. The aim of this review is to summarize the relationship between autophagy and viruses. It is not possible to be fully comprehensive, or to provide a complete "overview of all viruses". In this review, we will focus on the interaction of autophagy and viruses and survey how human viruses exploit multiple steps in the autophagy pathway to help viral propagation and escape immune response. We discuss the role that macroautophagy plays in cells infected with hepatitis C virus, hepatitis B virus, rotavirus gastroenteritis, immune cells infected with human immunodeficiency virus, and viral respiratory tract infections both influenza virus and coronavirus.

Nucleoside Reverse Transcriptase Inhibitors (NRTIs) Induce Pathological Pain through Wnt5a-Mediated Neuroinflammation in Aging Mice

Highly Active Antiretroviral Therapy (HAART) has significantly contributed to the increase of HIV-infected survivors over 50 years of age. Unfortunately, patients are required to stay on long-term HAART, which may be causally related to the development of neurological problems such as chronic pain. Little is known about the contribution of HAART or its therapeutic agents to the pathogenesis of pain during aging. In this study, we determined the effect of nucleoside reverse transcriptase inhibitors (NRTIs) on the development of mechanical allodynia and the potential underlying mechanism in aging mice (15.5 months). We found that systemic administration of individual NRTIs, including ddC (2'-3'-dideoxycytidine), ddI (didanosine), AZT (3'-azido-3'-deoxythymidine) and d4T (2', 3'-didehydro-2', 3'-dideoxythymidine), induced allodynia in similar magnitudes and temporal profiles. We used ddC as a representative to investigate cellular and molecular processes induced by NRTIs in the spinal cord that probably underlie the development of allodynia. The results showed that ddC caused evident neuroinflammation in the spinal cord, suggested by the up-regulation of proinflammatory cytokines TNF-α and IL-1β and the reactions of microglia and astrocytes. In addition, we found that Wnt5a, a critical regulator of neuroinflammation, was also up-regulated. Pharmacological inhibition of Wnt5a blocked ddC-induced up-regulation of TNF-α and astrocyte reaction, while activation of Wnt5a signaling potentiated these processes. Furthermore, our data showed that inhibition of Wnt5a significantly reversed ddC-induced mechanical allodynia in aging mice. The results collectively suggest that NRTIs may contribute to the development of chronic pain in aging patients by inducing Wnt5a-regulated neuroinflammation.

Contrasting effect of the latency-reversing agents bryostatin-1 and JQ1 on astrocyte-mediated neuroinflammation and brain neutrophil invasion

Background

Despite effectiveness of the combined antiretroviral therapy, HIV-1 persists in long-lived latently infected cells. Consequently, new therapeutic approaches aimed at eliminating this latent reservoir are currently being developed. A “shock and kill” strategy using latency-reversing agents (LRA) to reactivate HIV-1 has been proposed. However, the impact of LRA on the central nervous system (CNS) remains elusive.

Methods

We used human fetal astrocytes and investigated the effects of several LRA on their functional and secretory activities. Astrocytes were infected with VSV-G-pseudotyped HIV-1 before treatment with various blood-brain barrier (BBB)-permeable LRA at subcytotoxic doses, which allow HIV-1 reactivation based on previous in vitro and clinical studies. Cells and supernatants were then used to evaluate effects of infection and LRA on (i) viability and metabolic activity of astrocytes using a colorimetric MTS assay; (ii) chemokines and proinflammatory cytokines secretion and gene expression by astrocytes using ELISA and RT-qPCR, respectively; (iii) expression of complement component 3 (C3), a proxy for astrogliosis, by RT-qPCR; (iv) glutamate uptake capacity by a fluorometric assay; and (v) modulation of neutrophil transmigration across an in vitro BBB model.

Results

We demonstrate that bryostatin-1 induces secretion of chemokines CCL2 and IL-8 and proinflammatory cytokines IL-6 and GM-CSF, whereas their production is repressed by JQ1. Bryostatin-1 also increases expression of complement component 3 and perturbs astrocyte glutamate homeostasis. Lastly, bryostatin-1 enhances transmigration of neutrophils across an in vitro blood-brain barrier model and induces formation of neutrophil extracellular traps.

Conclusions

These observations highlight the need to carefully assess the potential harmful effect to the CNS when selecting LRA for HIV-1 reactivation strategies.

Electronic supplementary material

The online version of this article (10.1186/s12974-017-1019-y) contains supplementary material, which is available to authorized users.

Mechanisms of HIV Neuropathogenesis: Role of Cellular Communication Systems

BACKGROUND

One of the major complications of Human Immunodeficiency Virus (HIV) infection is the development of HIV-Associated Neurocognitive Disorders (HANDs) in approximately 50-60% of HIV infected individuals. Despite undetectable viral loads in the periphery owing to anti-retroviral therapy, neuroinflammation and neurocognitive impairment are still prevalent in HIV infected individuals. Several studies indicate that the central nervous system (CNS) abnormalities observed in HIV infected individuals are not a direct effect of viral replication in the CNS, rather these neurological abnormalities are associated with amplification of HIV specific signals by unknown mechanisms. We propose that some of these mechanisms of damage amplification are mediated by gap junction channels, pannexin and connexin hemichannels, tunneling nanotubes and microvesicles/exosomes.

OBJECTIVE

Our laboratory and others have demonstrated that HIV infection targets cell to cell communication by altering all these communication systems resulting in enhanced bystander apoptosis of uninfected cells, inflammation and viral infection. Here we discuss the role of these communication systems in HIV neuropathogenesis.

CONCLUSION

In the current manuscript, we have described the mechanisms by which HIV "hijacks" these host cellular communication systems, leading to exacerbation of HIV neuropathogenesis, and to simultaneously promote the survival of HIV infected cells, resulting in the establishment of viral reservoirs.

Efavirenz: What is known about the cellular mechanisms responsible for its adverse effects

The HIV infection remains an important health problem worldwide. However, due to the efficacy of combined antiretroviral therapy (cART), it has ceased to be a mortal condition, becoming a chronic disease instead. Efavirenz, the most prescribed non-nucleoside analogue reverse transcriptase inhibitor (NNRTI), has been a key component of cART since its commercialization in 1998. Though still a drug of choice in many countries, its primacy has been challenged by the arrival of newer antiretroviral agents with better toxicity profiles and treatment adherence. The major side effects related to EFV have been widely described in clinical studies, however the mechanisms that participate in their pathogenesis remain largely ununderstood. This review provides an insight into the cellular and molecular mechanisms responsible for the development of the most significant undesired effects induced by efavirenz, both short- and long-term, revealed by in vitro and in vivo experimental pharmacological research. Growing evidence implicates the drug in energy metabolism, mitochondrial function, and other cellular processes involved in stress responses including oxidative stress, inflammation and autophagy.

On the way to find a cure: Purging latent HIV-1 reservoirs

Introduction of cART in 1996 has drastically increased the life expectancy of people living with HIV-1. However, this treatment has not allowed cure as cessation of cART is associated with a rapid viral rebound. The main barrier to the eradication of the virus is related to the persistence of latent HIV reservoirs. Evidence is now accumulating that purging the HIV-1 reservoir might lead to a cure or a remission. The most studied strategy is the so called "shock and kill" therapy. This strategy is based on reactivation of dormant viruses from the latently-infected reservoirs (the shock) followed by the eradication of the reservoirs (the kill). This review focuses mainly on the recent advances made in the "shock and kill" therapy. We believe that a cure or a remission will come from combinatorial approaches i.e. combination of drugs to reactivate the dormant virus from all the reservoirs including the one located in sanctuaries, and combination of strategies boosting the immune system. Alternative strategies based on cell and gene therapy or based in inducing deep latency, which are evoked in this review reinforce the idea that at least a remission is attainable.

The role of connexin and pannexin containing channels in the innate and acquired immune response

Connexin (Cx) and pannexin (Panx) containing channels - gap junctions (GJs) and hemichannels (HCs) - are present in virtually all cells and tissues. Currently, the role of these channels under physiological conditions is well defined. However, their role in the immune response and pathological conditions has only recently been explored. Data from several laboratories demonstrates that infectious agents, including HIV, have evolved to take advantage of GJs and HCs to improve viral/bacterial replication, enhance inflammation, and help spread toxicity into neighboring areas. In the current review, we discuss the role of Cx and Panx containing channels in immune activation and the pathogenesis of several infectious diseases. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Neuronal Stress and Injury Caused by HIV-1, cART and Drug Abuse: Converging Contributions to HAND

Multiple mechanisms appear to contribute to neuronal stress and injury underlying HIV-associated neurocognitive disorders (HAND), which occur despite the successful introduction of combination antiretroviral therapy (cART). Evidence is accumulating that components of cART can itself be neurotoxic upon long-term exposure. In addition, abuse of psychostimulants, such as methamphetamine (METH), seems to compromise antiretroviral therapy and aggravate HAND. However, the combined effect of virus and recreational and therapeutic drugs on the brain is still incompletely understood. However, several lines of evidence suggest a shared critical role of oxidative stress, compromised neuronal energy homeostasis and autophagy in promotion and prevention of neuronal dysfunction associated with HIV-1 infection, cART and psychostimulant use. In this review, we present a synopsis of recent work related to neuronal stress and injury induced by HIV infection, antiretrovirals (ARVs) and the highly addictive psychostimulant METH.

Targeting the Brain Reservoirs: Toward an HIV Cure

One of the top research priorities of the international AIDS society by the action “Towards an HIV Cure” is the purge or the decrease of the pool of all latently infected cells. This strategy is based on reactivation of latently reservoirs (the shock) followed by an intensifying combination antiretroviral therapy (cART) to kill them (the kill). The central nervous system (CNS) has potential latently infected cells, i.e., perivascular macrophages, microglial cells, and astrocytes that will need to be eliminated. However, the CNS has several characteristics that may preclude the achievement of a cure. In this review, we discuss several limitations to the eradication of brain reservoirs and how we could circumvent these limitations by making it efforts in four directions: (i) designing efficient latency-reversal agents for CNS-cell types, (ii) improving cART by targeting HIV transcription, (iii) improving delivery of HIV drugs in the CNS and in the CNS-cell types, and (iv) developing therapeutic immunization. As a prerequisite to these efforts, we also believe that a better comprehension of molecular mechanisms involved in establishment and persistence of HIV latency in brain reservoirs are essential to design new molecules for strategies aiming to achieve a cure for instance the “shock and kill” strategy.

Neurotoxicity in the Post-HAART Era: Caution for the Antiretroviral Therapeutics

Despite the advent of highly active antiretroviral therapy (HAART), HIV-associated neurological disorders (HAND) remain a major challenge in human immunodeficiency virus (HIV) treatment. The early implementation of HAART in the infected individuals helps suppress the viral replication in the plasma and other compartments. Several studies also report the beneficial effect of drugs that successfully penetrate central nervous system (CNS). However, recent data in both clinical setup and in in vitro studies indicate CNS toxicity of the antiretrovirals (ARVs). Although the evidence is limited, correlation between prolonged use of ARVs and neurotoxicity strongly suggests that it is essential to study the underlying mechanisms responsible for such toxicity. Furthermore, closer attention toward clinical outcomes is required to screen various ARV regimens for their association with HAND and other comorbidities. A growing body of literature also indicates a possible role of accelerated aging in the antiretroviral therapy-associated neurotoxicity. Lastly, owing to high pill burden, multiple drugs in the HIV treatment also invite a possible role of drug-drug interaction via various cytochrome P450 enzymes. The particular emphasis of this review is to highlight the need to identify alternative approaches in reducing the CNS toxicity of the ARV drugs in HIV-infected individuals.

Neurocognitive Function at the First-Line Failure and on the Second-Line Antiretroviral Therapy in Africa: Analyses From the EARNEST Trial

OBJECTIVE

To assess neurocognitive function at the first-line antiretroviral therapy failure and change on the second-line therapy.

DESIGN

Randomized controlled trial was conducted in 5 sub-Saharan African countries.

METHODS

Patients failing the first-line therapy according to WHO criteria after >12 months on non-nucleoside reverse transcriptase inhibitors-based regimens were randomized to the second-line therapy (open-label) with lopinavir/ritonavir (400 mg/100 mg twice daily) plus either 2-3 clinician-selected nucleoside reverse transcriptase inhibitors, raltegravir, or as monotherapy after 12-week induction with raltegravir. Neurocognitive function was tested at baseline, weeks 48 and 96 using color trails tests 1 and 2, and the Grooved Pegboard test. Test results were converted to an average of the 3 individual test z-scores.

RESULTS

A total of 1036 patients (90% of those >18 years enrolled at 13 evaluable sites) had valid baseline tests (58% women, median: 38 years, viral load: 65,000 copies per milliliter, CD4 count: 73 cells per cubic millimeter). Mean (SD) baseline z-score was -2.96 (1.74); lower baseline z-scores were independently associated with older age, lower body weight, higher viral load, lower hemoglobin, less education, fewer weekly working hours, previous central nervous system disease, and taking fluconazole (P < 0.05 in multivariable model). Z-score was increased by mean (SE) of +1.23 (0.04) after 96 weeks on the second-line therapy (P < 0.001; n = 915 evaluable), with no evidence of difference between the treatment arms (P = 0.35).

CONCLUSIONS

Patients in sub-Saharan Africa failing the first-line therapy had low neurocognitive function test scores, but performance improved on the second-line therapy. Regimens with more central nervous system-penetrating drugs did not enhance neurocognitive recovery indicating this need not be a primary consideration in choosing a second-line regimen.

The neurobiology of HIV and its impact on cognitive reserve: A review of cognitive interventions for an aging population

The medications used to treat HIV have reduced the severity of cognitive deficits; yet, nearly half of adults with HIV still exhibit some degree of cognitive deficits, referred to as HIV-associated neurocognitive disorder or HAND. These cognitive deficits interfere with everyday functioning such as emotional regulation, medication adherence, instrumental activities of daily living, and even driving a vehicle. As adults are expected to live a normal lifespan, the process of aging in this clinical population may exacerbate such cognitive deficits. Therefore, it is important to understand the neurobiological mechanisms of HIV on cognitive reserve and develop interventions that are either neuroprotective or compensate for such cognitive deficits. Within the context of cognitive reserve, this article delivers a state of the science perspective on the causes of HAND and provides possible interventions for addressing such cognitive deficits. Suggestions for future research are also provided.

The physical and psychological effects of HIV infection and its treatment on perinatally HIV-infected children

INTRODUCTION

As highly active antiretroviral therapy (HAART) transforms human immunodeficiency virus (HIV) into a manageable chronic disease, new challenges are emerging in treating children born with HIV, including a number of risks to their physical and psychological health due to HIV infection and its lifelong treatment.

METHODS

We conducted a literature review to evaluate the evidence on the physical and psychological effects of perinatal HIV (PHIV+) infection and its treatment in the era of HAART, including major chronic comorbidities.

RESULTS AND DISCUSSION

Perinatally infected children face concerning levels of treatment failure and drug resistance, which may hamper their long-term treatment and result in more significant comorbidities. Physical complications from PHIV+ infection and treatment potentially affect all major organ systems. Although treatment with antiretroviral (ARV) therapy has reduced incidence of severe neurocognitive diseases like HIV encephalopathy, perinatally infected children may experience less severe neurocognitive complications related to HIV disease and ARV neurotoxicity. Major metabolic complications include dyslipidaemia and insulin resistance, complications that are associated with both HIV infection and several ARV agents and may significantly affect cardiovascular disease risk with age. Bone abnormalities, particularly amongst children treated with tenofovir, are a concern for perinatally infected children who may be at higher risk for bone fractures and osteoporosis. In many studies, rates of anaemia are significantly higher for HIV-infected children. Renal failure is a significant complication and cause of death amongst perinatally infected children, while new data on sexual and reproductive health suggest that sexually transmitted infections and birth complications may be additional concerns for perinatally infected children in adolescence. Finally, perinatally infected children may face psychological challenges, including higher rates of mental health and behavioural disorders. Existing studies have significant methodological limitations, including small sample sizes, inappropriate control groups and heterogeneous definitions, to name a few.

CONCLUSIONS

Success in treating perinatally HIV-infected children and better understanding of the physical and psychological implications of lifelong HIV infection require that we address a new set of challenges for children. A better understanding of these challenges will guide care providers, researchers and policymakers towards more effective HIV care management for perinatally infected children and their transition to adulthood.

Efavirenz and the CNS: what we already know and questions that need to be answered

The NNRTI efavirenz has long been one of the most frequently employed antiretroviral drugs in the multidrug regimens used to treat HIV infection, in accordance with its well-demonstrated antiretroviral efficacy and favourable pharmacokinetics. However, growing concern about its adverse effects has sometimes led to efavirenz being replaced by other drugs in the initial treatment selection or to switching of therapy to efavirenz-free regimens in experienced patients. Neurological and neuropsychiatric reactions are the manifestations most frequently experienced by efavirenz-treated patients and range from transitory effects, such as nightmares, dizziness, insomnia, nervousness and lack of concentration, to more severe symptoms including depression, suicidal ideation or even psychosis. In addition, efavirenz has recently been associated with mild/moderate neurocognitive impairment, which is of specific relevance given that half of the patients receiving ART eventually suffer some form of HIV-associated neurocognitive disorder. The mechanisms responsible for efavirenz-induced neurotoxicity are unclear, although growing evidence points to disturbances in brain mitochondrial function and bioenergetics. This review offers a comprehensive overview of the current evidence on the interaction that efavirenz displays with the CNS, including the penetration and concentration of the drug in the brain. We discuss the prevalence, types and specificities of its side effects and recently uncovered cellular mechanisms that may be involved in their development.

Pharmacokinetics and pharmacodynamics of antiretrovirals in the central nervous system

HIV-positive patients may be effectively treated with highly active antiretroviral therapy and such a strategy is associated with striking immune recovery and viral load reduction to very low levels. Despite undeniable results, the central nervous system (CNS) is commonly affected during the course of HIV infection, with neurocognitive disorders being as prevalent as 20-50 % of treated subjects. This review discusses the pathophysiology of CNS infection by HIV and the barriers to efficacious control of such a mechanism, including the available data on compartmental drug penetration and on pharmacokinetic/pharmacodynamic relationships. In the reviewed articles, a high variability in drug transfer to the CNS is highlighted with several mechanisms as well as methodological issues potentially influencing the observed results. Nevirapine and zidovudine showed the highest cerebrospinal fluid (CSF) to plasma ratios, although target concentrations are currently unknown for the CNS. The use of the composite CSF concentration effectiveness score has been associated with better virological outcomes (lower HIV RNA) but has been inconsistently associated with neurocognitive outcomes. These findings support the CNS effectiveness of commonly used highly antiretroviral therapies. The use of antiretroviral drugs with increased CSF penetration and/or effectiveness in treating or preventing neurocognitive disorders however needs to be assessed in well-designed prospective studies.

HIV-associated Neurocognitive Disorders and Antiretroviral Therapy: Current Concepts and Controversies

Antiretroviral drugs may help prevent neurological decline in individuals with HIV infection by suppressing viral replication and associated chronic immune activation in the central nervous system. However, HIV control in the brain may come at the price of drug-induced neurotoxicity. Herein, we review recent advances in the balance between adequate viral suppression in the nervous system and adverse effects of the medications used in HIV treatment.

The Effect of Central Nervous System Penetration Effectiveness of Highly Active Antiretroviral Therapy on Neuropsychological Performance and Neuroimaging in HIV Infected Individuals

The incidence of HIV-associated dementia has been greatly reduced in the era of highly active antiretroviral therapy (HAART); however milder forms of cognitive impairment persist. It remains uncertain whether HAART regimens with a high degree of central nervous system penetration effectiveness (CPE) exert beneficial neurological outcomes in HIV-infected (HIV+) individuals on stable treatment. Sixty-four HIV-infected adults on HAART were assigned a CPE score using a published ranking system and divided into high (≥7; n = 35) and low (<7; n = 29) CPE groups. All participants completed neuropsychological testing in addition to structural neuroimaging. Neuropsychological tests included measures known to be sensitive to HIV with values converted into standardized scores (NPZ-4) based on published normative scores. A semi-automated methodology was utilized to assess brain volumetrics within cortical (grey and white matter) and subcortical (thalamus, caudate, putamen) regions of interest. Analyses assessed NPZ-4 and brain volumetric differences between HIV+ individuals with high and low CPE scores. No significant differences in brain integrity were observed between the two groups. Long-term HAART regimens with a high degree of CPE were not associated with significantly improved neuropsychological or neuroimaging outcomes in HIV+ adults. Results suggest that alternate mechanisms may potentially contribute to better neurological outcomes in the era of HAART.

Significance and clinical management of persistent low-level viremia and very-low-level viremia in HIV-1-infected patients

A goal of HIV therapy is to sustain suppression of the plasma viral load below the detection limits of clinical assays. However, widely followed treatment guidelines diverge in their interpretation and recommended management of persistent viremia of low magnitude, reflecting the limited evidence base for this common clinical finding. Here, we review the incidence, risk factors, and potential consequences of low-level HIV viremia (LLV; defined in this review as a viremia level of 50 to 500 copies/ml) and very-low-level viremia (VLLV; defined as a viremia level of <50 copies/ml detected by clinical assays that have quantification cutoffs of <50 copies/ml). Using this framework, we discuss practical issues related to the diagnosis and management of patients experiencing persistent LLV and VLLV. Compared to viral suppression at <50 or 40 copies/ml, persistent LLV is associated with increased risk of antiretroviral drug resistance and overt virologic failure. Higher immune activation and HIV transmission may be additional undesirable consequences in this population. It is uncertain whether LLV of <200 copies/ml confers independent risks, as this level of viremia may reflect assay-dependent artifacts or biologically meaningful events during suppression. Resistance genotyping should be considered in patients with persistent LLV when feasible, and treatment should be modified if resistance is detected. There is a dearth of clinical evidence to guide management when genotyping is not feasible. Increased availability of genotypic assays for samples with viral loads of <400 copies/ml is needed.

Developments in HIV-1 immunotherapy and therapeutic vaccination

Since the human immunodeficiency virus (HIV-1) pandemic began, few prophylactic vaccines have reached phase III trials. Only one has shown partial efficacy in preventing HIV-1 infection. The introduction of antiretroviral therapy (ART) has had considerable success in controlling infection and reducing transmission but in so doing has changed the nature of HIV-1 infection for those with access to ART. Access, compliance, and toxicity alongside the emergence of serious non-AIDS morbidity and the sometimes poor immune reconstitution in ART-treated patients have emphasized the need for additional therapies. Such therapy is intended to contribute to control of HIV-1 infection, permit structured treatment interruptions, or even establish a functional cure of permanently suppressed and controlled infection. Both immunotherapy and therapeutic vaccination have the potential to reach these goals. In this review, the latest developments in immunotherapy and therapeutic vaccination are discussed.

Evidence of the innate antiviral and neuroprotective properties of progranulin

BACKGROUND

Compelling data exist that show that normal levels of progranulin (PGRN) are required for successful CNS aging. PGRN production is also modulated by inflammation and infection, but no data are available on the production and role of PGRN during CNS HIV infection.

METHODS

To determine the relationships between PGRN and HIV disease, neurocognition, and inflammation, we analyzed 107 matched CSF and plasma samples from CHARTER, a well-characterized HIV cohort. Levels of PGRN were determined by ELISA and compared to levels of several inflammatory mediators (IFNγ, IL-6, IL-10, IP-10, MCP-1, TNFα, IL-1β, IL-4 and IL-13), as well as clinical, virologic and demographic parameters. The relationship between HIV infection and PGRN was also examined in HIV-infected primary human microglial cultures.

RESULTS

In plasma, PGRN levels correlated with the viral load (VL, p<0.001). In the CSF of subjects with undetectable VL, lower PGRN was associated with neurocognitive impairment (p = 0.046). CSF PGRN correlated with CSF IP-10, TNFα and IL-10, and plasma PGRN correlated with plasma IP-10. In vitro, microglial HIV infection increased PGRN production and PGRN knockdown increased HIV replication, demonstrating that PGRN is an innate antiviral protein.

CONCLUSIONS

We propose that PGRN plays dual roles in people living with HIV disease. With active HIV replication, PGRN is induced in infected macrophages and microglia and functions as an antiviral protein. In individuals without active viral replication, decreased PGRN production contributes to neurocognitive dysfunction, probably through a diminution of its neurotrophic functions. Our results have implications for the pathogenesis, biomarker studies and therapy for HIV diseases including HIV-associated neurocognitive dysfunction (HAND).

Neurologic disease in HIV-infected children and the impact of combination antiretroviral therapy

The prevalence of HIV-associated neurocognitive impairment in perinatally HIV-infected children has declined since the introduction of combination antiretroviral therapy (cART). Early initiation of cART in infancy has been shown to positively impact neurodevelopment; however, children continue to be diagnosed with HIV outside of the early infancy period and can experience subtle to severe neurocognitive deficits despite cART. The causes of these neurocognitive deficits despite effective cART are multifactorial and likely include continued viral replication in the CNS, ongoing neuroinflammation, irreversible CNS injury prior to cART initiation, neurotoxic effects of cART, and socioeconomic and psychosocial effects. Many aspects of our understanding of HIV-associated neurocognitive disorders have emerged from research in adult patients, but perinatally HIV-infected children represent a very different population. These children were exposed to HIV during a period of rapid brain development and have lifelong infection and potential lifelong cART exposure. HIV is no longer a rapidly fatal disease, and most HIV-infected children in resource-rich countries are living into adulthood. It is therefore critical to optimize neurocognitive outcomes of these youth. This review summarizes current understanding of the pathogenesis of HIV-associated CNS infection and the impact of cART on neurocognitive function in children and adolescents and discusses important areas for future research.

An overview of the biological and psychosocial context surrounding neurocognition in HIV

The presence of a psychiatric illness increases the risk of exposure to HIV and disease complications; however, effective treatments have substantially reduced mortality in adults with HIV. Despite such effective treatments, nearly half of adults with HIV experience neurocognitive deficits that can affect job-related and everyday tasks, thus reducing their quality of life. This article provides an overview of the context in which neurocognitive deficits occur in adults with HIV; it also includes implications for treatment and mitigation of such neurocognitive deficits. Understanding the underlying neurocognitive changes related to HIV can help psychiatric nurses provide better care to patients that may improve medication compliance and everyday functioning.

Involvement of extracellular signal-regulated kinase (ERK1/2)-p53-p21 axis in mediating neural stem/progenitor cell cycle arrest in co-morbid HIV-drug abuse exposure

Neurological complications in opioid abusing Human Immunodeficiency Virus-1 (HIV-1) patients suggest enhanced neurodegeneration as compared to non-drug abusing HIV-1 infected population. Neural precursor cells (NPCs), the multipotent cells of the mammalian brain, are susceptible to HIV-1 infection and as opiates also perturb their growth kinetics, detailed mechanistic studies for their co-morbid exposure are highly warranted. Using a well characterized in vitro model of human fetal brain-derived neural precursor cells, we investigated alterations in NPC properties at both acute and chronic durations. Chronic morphine and Tat treatment attenuated proliferation in NPCs, with cells stalled at G1-phase of the cell cycle. Furthermore HIV-Tat and morphine exposure increased activation of extracellular signal-regulated kinase-1/2 (ERK1/2), enhanced levels of p53 and p21, and decreased cyclin D1 and Akt levels in NPCs. Regulated by ERK1/2 and p53, p21 was found to be indispensible for Tat and morphine mediated cell cycle arrest. Our study elaborates on the cellular and molecular machinery in NPCs and provides significant mechanistic details into HIV-drug abuse co-morbidity that may have far reaching clinical consequences both in pediatric as well as adult neuroAIDS.

Brain viral burden, neuroinflammation and neurodegeneration in HAART-treated HIV positive injecting drug users

The long-term impact of chronic human immunodeficiency virus (HIV) infection on brain status in injecting drug users (IDU) treated with highly active antiretroviral therapy (HAART) is unknown. Viral persistence in the brain with ongoing neuroinflammation may predispose to Alzheimer-like neurodegeneration. In this study, we investigated the brains of ten HAART-treated individuals (six IDU and four non-DU), compared with ten HIV negative controls (six IDU and four non-DU). HIV DNA levels in brain tissue were correlated with plasma and lymphoid tissue viral loads, cognitive status, microglial activation and Tau protein and amyloid deposition. Brain HIV proviral DNA levels were low in most cases but higher in HIV encephalitis (n = 2) and correlated significantly with levels in lymphoid tissue (p = 0.0075), but not with those in plasma. HIV positive subjects expressed more Tau protein and amyloid than HIV negative controls (highest in a 58 year old), as did IDU, but brain viral loads showed no relation to Tau and amyloid. Microglial activation linked significantly to HIV positivity (p = 0.001) and opiate abuse accentuated these microglial changes (p = 0.05). This study confirms that HIV DNA persists in brains despite HAART and that opiate abuse adds to the risk of brain damage in HIV positive subjects. Novel findings in this study show that (1) plasma levels are not a good surrogate indicator of brain status, (2) viral burden in brain and lymphoid tissues is related, and (3) while Tau and amyloid deposition is increased in HIV positive IDU, this is not specifically related to increased HIV burden within the brain.

The effects of neurotrophins and the neuropeptides VIP and PACAP on HIV-1 infection: histories with opposite ends

The nerve growth factor (NGF) and other neurotrophins, and the neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) are largely present in human tissue and can exert modulatory activities on nervous, endocrine and immune system functions. NGF, VIP and PACAP receptors are expressed systemically in organisms, and thus these mediators exhibit pleiotropic natures. The human immunodeficiency virus type 1 (HIV-1), the causal agent of the acquired immunodeficiency syndrome (AIDS), infects immune cells, and its replication is modulated by a number of endogenous factors that interact with HIV-1-infected cells. NGF, VIP and PACAP can also affect HIV-1 virus particle production upon binding to their receptors on the membranes of infected cells, which triggers cell signaling pathways that modify the HIV-1 replicative cycle. These molecules exert opposite effects on HIV-1 replication, as NGF and other neurotrophins enhance and VIP and PACAP reduce viral production in HIV-1-infected human primary macrophages. The understanding of AIDS pathogenesis should consider the mechanisms by which the replication of HIV-1, a pathogen that causes chronic morbidity, is influenced by neurotrophins, VIP and PACAP, i.e. molecules that exert a broad spectrum of physiological activities on the neuroimmunoendocrine axis. In this review, we will present the main effects of these two groups of mediators on the HIV-1 replicative cycle, as well as the mechanisms that underlie their abilities to modulate HIV-1 production in infected immune cells, and discuss the possible repercussion of the cross talk between NGF and both neuropeptides on the pathogenesis of HIV-1 infection.