Increased human immunodeficiency virus (HIV) type 1 DNA content and quinolinic acid concentration in brain tissues from patients with HIV encephalopathy

HIV-associated neurocognitive disorder: key implications of the microbiota-gut-brain axis

HIV-associated neurocognitive disorder (HAND) is now recognized to be relatively common in people living with HIV (PLWH), and remains a common cause of cognitive impairment. Unfortunately, the fundamental pathogenic processes underlying this specific outcome of HIV infection have not as yet been fully elucidated. With increased interest in research related to the microbiota-gut-brain axis, the gut-brain axis has been shown to play critical roles in regulating central nervous system disorders such as Alzheimer's disease and Parkinson's disease. PLWH are characterized by a particular affliction, referred to as gut-associated dysbiosis syndrome, which provokes an alteration in microbial composition and diversity, and of their associated metabolite composition within the gut. Interestingly, the gut microbiota has also been recognized as a key element, which both positively and negatively influences human brain health, including the functioning and development of the central nervous system (CNS). In this review, based on published evidence, we critically discuss the relevant interactions between the microbiota-gut-brain axis and the pathogenesis of HAND in the context of HIV infection. It is likely that HAND manifestation in PLWH mainly results from (i) gut-associated dysbiosis syndrome and a leaky gut on the one hand and (ii) inflammation on the other hand. In other words, the preceding features of HIV infection negatively alter the composition of the gut microbiota (microbes and their associated metabolites) and promote proinflammatory immune responses which singularly or in tandem damage neurons and/or induce inadequate neuronal signaling. Thus, HAND is fairly prevalent in PLWH. This work aims to demonstrate that in the quest to prevent and possibly treat HAND, the gut microbiota may ultimately represent a therapeutically targetable "host factor."

Tryptophan catabolism via the kynurenine pathway regulates infection and inflammation: from mechanisms to biomarkers and therapies

BACKGROUND

L-Tryptophan (L-Trp), an essential amino acid, is the only amino acid whose level is regulated specifically by immune signals. Most proportions of Trp are catabolized via the kynurenine (Kyn) pathway (KP) which has evolved to align the food availability and environmental stimulation with the host pathophysiology and behavior. Especially, the KP plays an indispensable role in balancing the immune activation and tolerance in response to pathogens.

SCOPE OF REVIEW

In this review, we elucidate the underlying immunological regulatory network of Trp and its KP-dependent catabolites in the pathophysiological conditions by participating in multiple signaling pathways. Furthermore, the KP-based regulatory roles, biomarkers, and therapeutic strategies in pathologically immune disorders are summarized covering from acute to chronic infection and inflammation.

MAJOR CONCLUSIONS

The immunosuppressive effects dominate the functions of KP induced-Trp depletion and KP-produced metabolites during infection and inflammation. However, the extending minor branches from the KP are not confined to the immune tolerance, instead they go forward to various functions according to the specific condition. Nevertheless, persistent efforts should be made before the clinical use of KP-based strategies to monitor and cure infectious and inflammatory diseases.

Regional Analysis of Intact and Defective HIV Proviruses in the Brain of Viremic and Virally Suppressed People with HIV

Here, we provide the first regional analysis of intact and defective HIV reservoirs within the brain. Brain tissue from both viremic and virally suppressed people with HIV (PWH) harbored HIV pol DNA in all regions tested, with lower levels present in basal ganglia and cerebellum relative to frontal white matter. Intact proviruses were primarily found in the frontal white matter but also detected in other brain regions of PWH, demonstrating frontal white matter as a major brain reservoir of intact, potentially replication competent HIV DNA that persists despite antiretroviral therapy. ANN NEUROL 2023;94:798-802.

HIV-1 differentially modulates autophagy in neurons and astrocytes

Autophagy, a lysosomal degradative pathway that maintains cellular homeostasis, has emerged as an innate immune defense against pathogens. The role of autophagy in the deregulated HIV-infected central nervous system (CNS) is unclear. We have found that HIV-1-induced neuro-glial (neurons and astrocytes) damage involves modulation of the autophagy pathway. Neuro-glial stress induced by HIV-1 led to biochemical and morphological dysfunctions. X4 HIV-1 produced neuro-glial toxicity coupled with suppression of autophagy, while R5 HIV-1-induced toxicity was restricted to neurons. Rapamycin, a specific mTOR inhibitor (autophagy inducer) relieved the blockage of the autophagy pathway caused by HIV-1 and resulted in neuro-glial protection. Further understanding of the regulation of autophagy by cytokines and chemokines or other signaling events may lead to recognition of therapeutic targets for neurodegenerative diseases.

Disturbed Amino Acid Metabolism in HIV: Association with Neuropsychiatric Symptoms

Blood levels of the amino acid phenylalanine, as well as of the tryptophan breakdown product kynurenine, are found to be elevated in human immunodeficiency virus type 1 (HIV-1)-infected patients. Both essential amino acids, tryptophan and phenylalanine, are important precursor molecules for neurotransmitter biosynthesis. Thus, dysregulated amino acid metabolism may be related to disease-associated neuropsychiatric symptoms, such as development of depression, fatigue, and cognitive impairment. Increased phenylalanine/tyrosine and kynurenine/tryptophan ratios are associated with immune activation in patients with HIV-1 infection and decrease upon effective antiretroviral therapy. Recent large-scale metabolic studies have confirmed the crucial involvement of tryptophan and phenylalanine metabolism in HIV-associated disease. Herein, we summarize the current status of the role of tryptophan and phenylalanine metabolism in HIV disease and discuss how inflammatory stress-associated dysregulation of amino acid metabolism may be part of the pathophysiology of common HIV-associated neuropsychiatric conditions.

Anti-tat Hutat2:Fc mediated protection against tat-induced neurotoxicity and HIV-1 replication in human monocyte-derived macrophages

BACKGROUND

HIV-1 Tat is essential for HIV replication and is also a well-known neurotoxic factor causing HIV-associated neurocognitive disorder (HAND). Currently, combined antiretroviral therapy targeting HIV reverse transcriptase or protease cannot prevent the production of early viral proteins, especially Tat, once HIV infection has been established. HIV-infected macrophages and glial cells in the brain still release Tat into the extracellular space where it can exert direct and indirect neurotoxicity. Therefore, stable production of anti-Tat antibodies in the brain would neutralize HIV-1 Tat and thus provide an effective approach to protect neurons.

METHODS

We constructed a humanized anti-Tat Hutat2:Fc fusion protein with the goal of antagonizing HIV-1 Tat and delivered the gene into cell lines and primary human monocyte-derived macrophages (hMDM) by an HIV-based lentiviral vector. The function of the anti-Tat Hutat2:Fc fusion protein and the potential side effects of lentiviral vector-mediated gene transfer were evaluated in vitro.

RESULTS

Our study demonstrated that HIV-1-based lentiviral vector-mediated gene transduction resulted in a high-level, stable expression of anti-HIV-1 Tat Hutat2:Fc in human neuronal and monocytic cell lines, as well as in primary hMDM. Hutat2:Fc was detectable in both cells and supernatants and continued to accumulate to high levels within the supernatant. Hutat2:Fc protected mouse cortical neurons against HIV-1 Tat86-induced neurotoxicity. In addition, both secreted Hutat2:Fc and transduced hMDM led to reducing HIV-1BaL viral replication in human macrophages. Moreover, lentiviral vector-based gene introduction did not result in any significant changes in cytomorphology and cell viability. Although the expression of IL8, STAT1, and IDO1 genes was up-regulated in transduced hMDM, such alternation in gene expression did not affect the neuroprotective effect of Hutat2:Fc.

CONCLUSIONS

Our study demonstrated that lentivirus-mediated gene transfer could efficiently deliver the Hutat2:Fc gene into primary hMDM and does not lead to any significant changes in hMDM immune-activation. The neuroprotective and HIV-1 suppressive effects produced by Hutat2:Fc were comparable to that of a full-length anti-Tat antibody. This study provides the foundation and insights for future research on the potential use of Hutat2:Fc as a novel gene therapy approach for HAND through utilizing monocytes/macrophages, which naturally cross the blood-brain barrier, for gene delivery.

Synaptic dysfunction in the hippocampus accompanies learning and memory deficits in human immunodeficiency virus type-1 Tat transgenic mice

BACKGROUND

Human immunodeficiency virus (HIV) associated neurocognitive disorders (HAND), including memory dysfunction, continue to be a major clinical manifestation of HIV type-1 infection. Viral proteins released by infected glia are thought to be the principal triggers of inflammation and bystander neuronal injury and death, thereby driving key symptomatology of HAND.

METHODS

We used a glial fibrillary acidic protein-driven, doxycycline-inducible HIV type-1 transactivator of transcription (Tat) transgenic mouse model and examined structure-function relationships in hippocampal pyramidal cornu ammonis 1 (CA1) neurons using morphologic, electrophysiological (long-term potentiation [LTP]), and behavioral (Morris water maze, fear-conditioning) approaches.

RESULTS

Tat induction caused a variety of different inclusions in astrocytes characteristic of lysosomes, autophagic vacuoles, and lamellar bodies, which were typically present within distal cytoplasmic processes. In pyramidal CA1 neurons, Tat induction reduced the number of apical dendritic spines, while disrupting the distribution of synaptic proteins (synaptotagmin 2 and gephyrin) associated with inhibitory transmission but with minimal dendritic pathology and no evidence of pyramidal neuron death. Electrophysiological assessment of excitatory postsynaptic field potential at Schaffer collateral/commissural fiber-CA1 synapses showed near total suppression of LTP in mice expressing Tat. The loss in LTP coincided with disruptions in learning and memory.

CONCLUSIONS

Tat expression in the brain results in profound functional changes in synaptic physiology and in behavior that are accompanied by only modest structural changes and minimal pathology. Tat likely contributes to HAND by causing molecular changes that disrupt synaptic organization, with inhibitory presynaptic terminals containing synaptotagmin 2 appearing especially vulnerable.

Ianthellamide A, a selective kynurenine-3-hydroxylase inhibitor from the Australian marine sponge Ianthella quadrangulata

Ianthellamide A (1), a novel octopamine derivative, was isolated from the Australian marine sponge Ianthella quadrangulata. Compound 1 selectively inhibited the activity of kynurenine 3-hydroxylase with an IC(50) value of 1.5 μM. It also significantly increased the level of endogenous kynurenic acid in rat brain and hence has the potential as a neuroprotective agent in the treatment of neurodegenerative disorders.

Human immunodeficiency virus type 1 clade B and C gp120 differentially induce neurotoxin arachidonic acid in human astrocytes: implications for neuroAIDS

HIV-1 clades (subtypes) differentially contribute to the neuropathogenesis of HIV-associated dementia (HAD) in neuroAIDS. HIV-1 envelop protein, gp120, plays a major role in neuronal function. It is not well understood how these HIV-1 clades exert these neuropathogenic differences. The N-methyl-D: -aspartate (NMDA) receptor-reduced glutamine synthesis could lead to secretion of neurotoxins such as arachidonic acid (AA) which plays a significant role in the neuropathogenic mechanisms in neuroAIDS. We hypothesize that clade B and C gp120 proteins exert differential effects on human primary astrocytes by production of the neurotoxin arachidonic acid. Our results indicate that clade B gp120 significantly downregulated NMDA receptor gene and protein expression, and level of glutamine while increasing expression of prostaglandin E2 (PGE(2)) and thromboxane A2 receptor (TBXA(2) R) compared to HIV-1 clade C gp120 protein. Thus, our studies for the first time demonstrate that HIV-1 clade B-gp120 protein appears to induce higher levels of expression of the neuropathogenic molecule cyclooxygenase-2 (COX-2)-mediated arachidonic acid by-products, PGE(2), and TBXA(2) R compared to HIV-1 clade C gp120 protein. These studies suggest that HIV-1 clade B and C gp120 proteins may play a differential role in the neuropathogenesis of HAD in neuroAIDS.

Human immunodeficiency virus type 1 clade B and C Tat differentially induce indoleamine 2,3-dioxygenase and serotonin in immature dendritic cells: Implications for neuroAIDS

Human immunodeficiency virus type 1 (HIV-1) is commonly associated with immune dysfunctions and the suppression of antigen-presenting cells. This results in immune alterations, which could lead to impaired neuronal functions, such as neuroAIDS. The neurotoxic factor kynurenine (KYN), the rate-limiting enzyme indoleamine 2,3-dioxygenase (IDO), serotonin (5-HT), and serotonin transporter (5-HTT) may play a role in tryptophan deficiency and serotogenic dysfunction in neuroAIDS. HIV-1 transactivator regulatory protein (Tat) is known to play a major role in immune dysfunction. Previous studies suggest that HIV-1 B and C clades differentially manifest neuronal dysfunctions in the infected host. In the present study we examine the effect of HIV-1 B and C clade-derived Tat on IDO and 5-HTT gene and protein expressions by dendritic cells as studied by quantitative polymerase chain reaction (qPCR) and Western blot. In addition, the intracellular IDO expression, IDO enzyme activity, and the levels of 5-HT and KYN were also measured. Results indicate that HIV-1 clade B Tat up-regulates IDO and down-regulates 5-HTT gene and protein expressions. Further, HIV-1 clade B Tat caused a reduction of 5-HT with simultaneous increase in KYN levels as compared to HIV-1 clade C Tat. These studies suggest that HIV-1 clade B and C Tat proteins may play a differential role in the neuropathogenesis of HIV-associated dementia (HAD) or HIV-associated neurocognitive disorder (HAND).

Substituent effects on the reaction of beta-benzoylalanines with Pseudomonas fluorescens kynureninase

Kynureninase is a pyridoxal 5'-phosphate-dependent enzyme that catalyzes the hydrolytic cleavage of l-kynurenine to give l-alanine and anthranilic acid. beta-Benzoyl-l-alanine, the analogue of l-kynurenine lacking the aromatic amino group, was shown to a good substrate for kynureninase from Pseudomonas fluorescens, and the rate-determining step changes from release of the second product, l-Ala, to formation of the first product, benzoate [Gawandi, V. B., et al. (2004) Biochemistry 43, 3230-3237]. In this work, a series of aryl-substituted beta-benzoyl-dl-alanines was synthesized and evaluated for substrate activity with kynureninase from P. fluorescens. Hammett analysis of k(cat) and k(cat)/K(m) for 4-substituted beta-benzoyl-dl-alanines with electron-withdrawing and electron-donating substituents is nonlinear, with a concave downward curvature. This suggests that there is a change in rate-determining step for benzoate formation with different substituents, from gem-diol formation for electron-donating substituents to C(beta)-C(gamma) bond cleavage for electron-withdrawing substituents. Rapid-scanning stopped-flow kinetic experiments demonstrated that substituents have relatively minor effects on formation of the quinonoid and 348 nm intermediates but have a much greater effect on the formation of the aldol product from reaction of benzaldehyde with the 348 nm intermediate. Since there is a kinetic isotope effect on its formation from beta,beta-dideuterio-beta-(4-trifluoromethylbenzoyl)-dl-alanine, the 348 nm intermediate is proposed to be a vinylogous amide derived from abortive beta-deprotonation of the ketimine intermediate. These results provide additional evidence for a gem-diol intermediate in the catalytic mechanism of kynureninase.

CNS inflammation and macrophage/microglial biology associated with HIV-1 infection

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system (CNS) can result in neurological dysfunction with devastating consequences in a significant proportion of individuals with acquired immune deficiency syndrome. HIV-1 does not infect neurons directly but induces damage indirectly through the accumulation of activated macrophage/microglia (M/M) cells, some of which are infected, that release neurotoxic mediators including both cellular activation products and viral proteins. One mechanism for the accumulation of activated M/M involves the development in infected individuals of an activated peripheral blood monocyte population that traffics through the blood-brain barrier, a process that also serves to carry virus into CNS and establish local infection. A second mechanism involves the release by infected and activated M/M in the CNS of chemotactic mediators that recruit additional monocytes from the periphery. These activated M/M, some of which are infected, release a number of cytokines and small molecule mediators as well as viral proteins that act on bystander cells and in turn activate them, thus amplifying the cascade. These viral proteins and cellular products have neurotoxic properties as well, both directly and through induction of astrocyte dysfunction, which ultimately lead to neuronal injury and death. In patients effectively treated with antiretroviral therapy, frank dementia is now uncommon and has been replaced by milder forms of neurocognitive impairment, with less frequent and more focal neuropathology. This review summarizes key findings that support the critical role and mechanisms of monocyte/macrophage activation and inflammation as a major component for HIV-1 encephalitis or HIV-1 associated dementia.

Human immunodeficiency virus type-1 protein Tat induces tumor necrosis factor-alpha-mediated neurotoxicity

HIV-1 infection causes, with increasing prevalence, neurological disorders characterized in part by neuronal cell death. The HIV-1 protein Tat has been shown to be directly and indirectly neurotoxic. Here, we tested the hypothesis that a non-neurotoxic epitope of Tat can, through actions on immune cells, increase neuronal cell death. Tat(1-72) and a mutant Tat(1-72) lacking the neurotoxic epitope (Tat(Delta31-61)) concentration-dependently and markedly increased TNF-alpha production in macrophage-like differentiated human U937 and THP-1 cells, in mouse peritoneal macrophages and in mouse brain microglia. Tat(1-72) was but Tat(Delta31-61) was not neurotoxic when applied directly to neurons. Supernatants from U937 cells treated with either Tat(1-72) or Tat(Delta31-61) were neurotoxic and their immunoneutralization with an anti-TNF-alpha antibody decreased Tat(1-72)- and Tat(Delta31-61)-induced neurotoxicity. Together, these results demonstrate that the neurotoxic epitope of Tat(1-72) is different from the epitope that is indirectly neurotoxic following production of TNF-alpha from immune cells, and suggest that therapeutic interventions against TNF-alpha might be beneficial against HIV-1 associated neurological disorders.

Crystal structure of Homo sapiens kynureninase

Kynureninase is a member of a large family of catalytically diverse but structurally homologous pyridoxal 5'-phosphate (PLP) dependent enzymes known as the aspartate aminotransferase superfamily or alpha-family. The Homo sapiens and other eukaryotic constitutive kynureninases preferentially catalyze the hydrolytic cleavage of 3-hydroxy-l-kynurenine to produce 3-hydroxyanthranilate and l-alanine, while l-kynurenine is the substrate of many prokaryotic inducible kynureninases. The human enzyme was cloned with an N-terminal hexahistidine tag, expressed, and purified from a bacterial expression system using Ni metal ion affinity chromatography. Kinetic characterization of the recombinant enzyme reveals classic Michaelis-Menten behavior, with a Km of 28.3 +/- 1.9 microM and a specific activity of 1.75 micromol min-1 mg-1 for 3-hydroxy-dl-kynurenine. Crystals of recombinant kynureninase that diffracted to 2.0 A were obtained, and the atomic structure of the PLP-bound holoenzyme was determined by molecular replacement using the Pseudomonas fluorescens kynureninase structure (PDB entry 1qz9) as the phasing model. A structural superposition with the P. fluorescens kynureninase revealed that these two structures resemble the "open" and "closed" conformations of aspartate aminotransferase. The comparison illustrates the dynamic nature of these proteins' small domains and reveals a role for Arg-434 similar to its role in other AAT alpha-family members. Docking of 3-hydroxy-l-kynurenine into the human kynureninase active site suggests that Asn-333 and His-102 are involved in substrate binding and molecular discrimination between inducible and constitutive kynureninase substrates.

Synthesis and anti-HIV properties of new hydroxyquinoline-polyamine conjugates on cells infected by HIV-1 LAV and HIV-1 BaL viral strains

To find new derivatives that block different virus strains entry in cells bearing specific surface receptors represent an interesting challenge for medicinal chemists. Here, we report the synthesis and the anti-HIV properties of a new series of analogues based on the introduction of quinoline moiety on various polyamine backbones, including polyazamacrocycles. Three compounds 7, 8, and 10 of this series were found active on PBMCs cells infected by HIV-1 LAV or by HIV-1 BaL, in contrast the well-known reference compound 1a (AMD 3100) was found only active on HIV-1 LAV strain.

Involvement of quinolinic acid in AIDS dementia complex

Human immunodeficiency virus (HIV) infection is often complicated by the development of acquired immunodeficiency syndrome (AIDS) dementia complex (ADC). Quinolinic acid (QUIN) is an end product of tryptophan, metabolized through the kynurenine pathway (KP) that can act as an endogenous brain excitotoxin when produced and released by activated macrophages/microglia, the very cells that are prominent in the pathogenesis of ADC. This review examines QUIN's involvement in the features of ADC and its role in pathogenesis. We then synthesize these findings into a hypothetical model for the role played by QUIN in ADC, and discuss the implications of this model for ADC and other inflammatory brain diseases.

NAD biosynthesis: identification of the tryptophan to quinolinate pathway in bacteria

Previous studies have demonstrated two different biosynthetic pathways to quinolinate, the universal de novo precursor to the pyridine ring of NAD. In prokaryotes, quinolinate is formed from aspartate and dihydroxyacetone phosphate; in eukaryotes, it is formed from tryptophan. It has been generally believed that the tryptophan to quinolinic acid biosynthetic pathway is unique to eukaryotes; however, this paper describes the use of comparative genome analysis to identify likely candidates for all five genes involved in the tryptophan to quinolinic acid pathway in several bacteria. Representative examples of each of these genes were overexpressed, and the predicted functions are confirmed in each case using unambiguous biochemical assays.

Regulation of indoleamine 2,3-dioxygenase expression in simian immunodeficiency virus-infected monkey brains

The human immunodeficiency virus type 1-associated cognitive-motor disorder, including the AIDS dementia complex, is characterized by brain functional abnormalities that are associated with injury initiated by viral infection of the brain. Indoleamine 2,3-dioxygenase (IDO), the first and rate-limiting enzyme in tryptophan catabolism in extrahepatic tissues, can lead to neurotoxicity through the generation of quinolinic acid and immunosuppression and can alter brain chemistry via depletion of tryptophan. Using the simian immunodeficiency virus (SIV)-infected rhesus macaque model of AIDS, we demonstrate that cells of the macrophage lineage are the main source for expression of IDO in the SIV-infected monkey brain. Animals with SIV encephalitis have the highest levels of IDO mRNA, and the level of IDO correlates with gamma interferon (IFN-gamma) and viral load levels. In vitro studies on mouse microglia reveal that IFN-gamma is the primary inducer of IDO expression. These findings demonstrate the link between IDO expression, IFN-gamma levels, and brain pathology signs observed in neuro-AIDS.

Neuroimmune and neurovirological aspects of human immunodeficiency virus infection

Like most lentiviruses, HIV-1 causes both immune suppression and neurological disease. Neurological disease may occur at any stage of HIV infection but is most apparent with severe immune suppression. Cognitive impairment, reflected strikingly by HIV-associated dementia, has attracted intense interest since the outset of the HIV epidemic, and understanding of its pathogenesis has been spurred on by the emergence of several hypotheses outlining potential pathogenic mechanisms. The release of inflammatory molecules by HIV-infected microglia and macrophages and the concurrent neuronal damage play central roles in the conceptualization of HIV neuropathogenesis. Many inflammatory molecules appear to contribute to the pathogenic cascade and their individual roles remain undefined. At the same time, the abundance of virus in the brain and the type or strain of virus found in the brain may also be important codeterminants of neurological disease, as shown for other neurotropic viruses. Coreceptor use by HIV found in the brain appears to closely mirror what has been reported in systemic macrophages. The impact of HAART on viral genotype and phenotype found in the brain, and its relationship to clinical disease, remain uncertain. Several interesting animal models have been developed, using other lentiviruses, transgenic animals, and HIV-infected SCID mice, that may prove useful in future pathogenesis and therapeutic studies. Despite the progress in the understanding of HIV neuropathogenesis, many questions remain unanswered.

Progress in clinical neurosciences: The neuropathogenesis of HIV infection: host-virus interaction and the impact of therapy

Despite the availability of highly active antiretroviral therapy (HAART), primary HIV-related neurological diseases remain major problems in HIV clinics. The present review examines the pathogenesis of HIV-related dementia and the less severe minor cognitive and motor deficit, together with distal sensory and drug-induced toxic polyneuropathies. Abnormal host immune responses within the nervous system and the role of viral expression and diversity are emphasized in relation to neurovirulence. Induction of innate immune responses within the central and peripheral nervous systems, largely mediated by cells of macrophage lineage, appear to be common to the development of primary HIV-related neurological disease. Activation of these cell types results in the release of a cascade of inflammatory molecules including cytokines, chemokines, matrix metalloproteinases, and arachidonic acid metabolites that influence neuronal survival. Individual viral proteins encoded by envelope and tat genes and discrete sequences within these genes influence the extent to which these pro-inflammatory molecules are induced. At the same time, systemic immune suppression may influence the occurrence and severity of HIV-related neurological diseases. Implementation of HAART and neuroprotective treatments improves neurological function although the evolution of drug-resistant viral strains limits the sustained benefits of HAART.

Protective effect of CCR5 delta 32 heterozygosity is restricted by SDF-1 genotype in children with HIV-1 infection

OBJECTIVE

To determine the influences on pediatric AIDS of a heterozygous 32 base pair deletion in the CC-chemokine receptor 5 gene (CCR5 wt/Delta 32) and a common polymorphism in the 3' untranslated region of stromal cell-derived factor-1 beta gene transcript (SDF1-3'A).

DESIGN

The rate of HIV-1 disease progression and viral burden were compared according to the CCR5 and SDF-1 genotypes in 127 (58 Caucasians, 60 African-Americans and nine Hispanics) perinatally HIV-1-infected children.

RESULTS

Regardless of ethnic background, the CCR5 wt/Delta 32 genotype was associated with a delayed onset of AIDS-defining infectious complications during the first 5 years of infection [relative hazard (RH) = 0.22; 95% confidence interval (CI), 0.012--1.02; P = 0.053]. Similarly, CCR5 wt/Delta 32 conferred an early protection against severe immune suppression and HIV-1 encephalopathy, but only in those without SDF1-3'A (RH = 0; 95% CI, 0--0.70; P = 0.020, and RH = 0; 95% CI, 0--0.71; P = 0.021, respectively). When examined before 5 years of age (n = 81), the children with CCR5 wt/Delta 32 had significantly lower levels of cell-associated HIV-1 DNA than wild-type homozygotes (P = 0.016, adjusted by race), while SDF1-3'A carriers had relatively higher levels (P = 0.047, adjusted by race). Although the disease-retarding effect of CCR5 wt/Delta 32 subsequently disappeared, time to death was still significantly delayed in the CCR5 Delta 32 heterozygotes without SDF1-3'A (RH = 0; 95% CI, 0--0.53; P = 0.008).

CONCLUSION

In pediatric AIDS, the protective effect of CCR5 wt/Delta 32 is more pronounced in early years of infection and appears to be abrogated by the SDF1-3'A genotype.

Induction of indoleamine 2,3-dioxygenase in primary human macrophages by HIV-1

Increased kynurenine pathway metabolism has been implicated in the aetiology of the AIDS dementia complex (ADC). The rate limiting enzyme for this pathway is indoleamine 2,3-dioxygenase (IDO). We tested the efficacy of different strains of HIV-1 (HIV1-BaL, HIV1-JRFL and HIV1-631) to induce IDO in cultured human monocyte-derived macrophages (MDM). A significant increase in both IDO protein and kynurenine synthesis was observed after 48 h in MDM infected with the brain derived HIV-1 isolates, laboratory adapted (LA) HIV1-JRFL, and primary isolate HIV1-631. In contrast, almost no kynurenine production or IDO protein was evident in MDM infected with the high replicating macrophage tropic LA strain, HIV1-BaL. The induction of IDO and kynurenine synthesis by HIV1-JRFL and HIV1-631 declined to baseline levels by day-8 post-infection. Together, these results indicate that only selected strains of HIV-1 are capable of inducing IDO synthesis and subsequent oxidative tryptophan catabolism in MDM.

Reservoirs for HIV-1: mechanisms for viral persistence in the presence of antiviral immune responses and antiretroviral therapy

The success of combination antiretroviral therapy for HIV-1 infection has generated interest in mechanisms by which the virus can persist in the body despite the presence of drugs that effectively inhibit key steps in the virus life cycle. It is becoming clear that viral reservoirs established early in the infection not only prevent sterilizing immunity but also represent a major obstacle to curing the infection with the potent antiretroviral drugs currently in use. Mechanisms of viral persistence are best considered in the context of the dynamics of viral replication in vivo. Virus production in infected individuals is largely the result of a dynamic process involving continuous rounds of de novo infection of and replication in activated CD4(+) T cells with rapid turnover of both free virus and virus-producing cells. This process is largely, but not completely, interrupted by effective antiretroviral therapy. After a few months of therapy, plasma virus levels become undetectable in many patients. Analysis of viral decay rates initially suggested that eradication of the infection might be possible. However, there are several potential cellular and anatomical reservoirs for HIV-1 that may contribute to long-term persistence of HIV-1. These include infected cell in the central nervous system and the male urogenital tract. However, the most worrisome reservoir consists of latently infected resting memory CD4(+) T cells carrying integrated HIV-1 DNA. Definitive demonstration of the presence of this form of latency required development of methods for isolating extremely pure populations of resting CD4(+) T cells and for demonstrating that a small fraction of these cells contain integrated HIV-1 DNA that is competent for replication if the cells undergo antigen-driven activation. Most of the latent virus in resting CD4(+) T cells is found in cells of the memory phenotype. The half-life of this latent reservoir is extremely long (44 months). At this rate, eradication of this reservoir would require over 60 years of treatment. Thus, latently infected resting CD4(+) T cells provide a mechanism for life-long persistence of replication-competent forms of HIV-1, rendering unrealistic hopes of virus eradication with current antiretroviral regimens. The extraordinary stability of the reservoir may reflect gradual reseeding by a very low level of ongoing viral replication and/or mechanisms that contribute to the intrinsic stability of the memory T cell compartment. Given the substantial long-term toxicities of current combination therapy regimens, novel approaches to eradicating this latent reservoir are urgently needed.

Induction of indolamine 2,3-dioxygenase in primary human macrophages by human immunodeficiency virus type 1 is strain dependent

Increased kynurenine pathway metabolism has been implicated in the etiology of AIDS dementia complex (ADC). The rate-limiting enzyme for this pathway is indolamine 2,3-dioxygenase (IDO). We tested the efficacy of different strains of human immunodeficiency virus type 1 (HIV1-BaL, HIV1-JRFL, and HIV1-631) to induce IDO in cultured human monocyte-derived macrophages (MDM). A significant increase in both IDO protein and kynurenine synthesis was observed after 48 h in MDM infected with the brain-derived HIV-1 isolates, laboratory-adapted (LA) HIV1-JRFL, and primary isolate HIV1-631. In contrast, almost no kynurenine production or IDO protein was evident in MDM infected with the highly replicating macrophage-tropic LA strain HIV1-BaL. The induction of IDO and kynurenine synthesis by HIV1-JRFL and HIV1-631 declined to baseline levels by day 8 postinfection. Abundant HIV-1 replication did not reduce the ability of exogenous gamma interferon (IFN-gamma) to induce IDO and kynurenine synthesis in HIV-infected MDM. The addition of anti-IFN-gamma antibody to MDM infected with HIV1-JRFL resulted in an absence of detectable IDO protein after 48 h and a decrease of 64% +/- 1% in supernatant kynurenine concentration. Together, these results indicate that only selected strains of HIV-1 are capable of inducing IDO synthesis and subsequent kynurenine metabolism in MDM. The induction of IDO, while apparently independent of replication capacity, appears to be mediated by a transient production of IFN-gamma in MDM responding to the initial infection with selected strains of HIV-1.

Nutritional Contributions to the CNS Pathophysiology of HIV-1 Infection and Implications for Treatment

Nutritional deficiencies are commonplace in patients with human immunodeficiency virus type 1 (HIV-1) infection, and recent research has indicated that nutritional factors may play an important role in the pathogenesis of HIV-1 disease. Although nutritional deficiencies are unlikely to be the primary causative factor in disease progression, they may contribute to cognitive dysfunction, neurologic abnormalities, mood disturbance, and immune dysregulation associated with HIV-1 infection. Furthermore, deficiencies of specific micronutrients have been associated with increased risk of HIV-1-associated mortality. This article will briefly summarize the role of macronutrient deficiency, the interactions of specific micronutrient deficiencies with neuropsychiatric functioning, and the role of these factors in HIV-1 disease progression. Since recent research has shown that normalization of many nutritional deficits and supplementation beyond normal levels are associated with improvements in neuropsychiatric functioning, potential treatment implications will also be discussed.

Stereospecificity of Pseudomonas fluorescens kynureninase for diastereomers of beta-methylkynurenine

The diastereomers of beta-methyl-L-kynurenine were prepared by preparative ozonolysis of the respective diastereomers of beta-methyl-L-tryptophan. A practical method for preparative enzymatic resolution of the diastereomers of beta-methyltryptophan was developed using carboxypeptidase A digestion of the N-trifluoroacetyl derivatives. The stereochemical assignment was confirmed by X-ray crystal structure determination of (2S, 3R)-threo-beta-methyl-L-tryptophan. (2S,3S)-erythro-beta-Methyl-L-kynurenine is a slow substrate for kynureninase from Pseudomonas fluorescens (k(cat)/K(m) = 0.1% that of L-kynurenine), producing anthranilic acid, while (2S,3R)-threo-L-kynurenine is about 390-fold less reactive than erythro. Rapid-scanning stopped-flow measurements show that beta-methyl substitution affects the rate of alpha-deprotonation of the L-kynurenine-pyridoxal-5'-phosphate Schiffs base. This is consistent with the stereoelectronic requirements of the reaction. These results are the first demonstration that beta-substituted kynurenines can be substrates for kynureninase, and may be useful in the design of mechanism-based inhibitors.

Species differences in L-tryptophan-kynurenine pathway metabolism: quantification of anthranilic acid and its related enzymes

Anthranilic acid (AA) has attracted considerable attention as one of the L-tryptophan-kynurenine pathway metabolites in the central nervous system. In this study, a highly sensitive and accurate method for the quantification of AA has been developed using reversed-phase high-performance liquid chromatography with electrochemical detection. Serum and cerebrospinal fluid (CSF) AA concentrations in different animal species were measured. CSF AA concentrations in rabbits were 1.1 +/- 0.1 nmol/liter, which were 5. 7-33.0 times lower than those in other species studied. Serum AA concentrations, however, were slightly higher in rabbits than in other species. In contrast, the concentrations of L-kynurenine (L-KYN) in both serum and CSF were substantially higher in rabbits than in other species. Tissue kynurenine pathway enzymes, indoleamine 2,3-dioxygenase (IDO), tryptophan 2,3-dioxygenase, kynurenine 3-hydroxylase, and kynureninase were determined in rabbits, rats, gerbils, and mice. These enzymes varied among species, especially lung IDO activities in rabbits were 146-516 times higher than those found in other species, but rabbit liver kynurenine 3-hydroxylase activities were lower by one order of magnitude than those of the other species tested. Furthermore, brain kynurenine 3-hydroxylasae activities were 12.3-23.2 times higher in gerbils than those in the other species tested. In addition, AA concentrations in serum following intravenous administration of L-KYN (5 mg/kg) were also measured in rabbits. AA levels peaked sharply within 5 min after administration and decreased in a time-dependent manner. At 5 min after administration, CSF L-KYN and AA concentrations were also increased by 1.76- and 2.56-fold, respectively, compared with basal levels. Increased AA concentrations in CSF following L-KYN administration may reflect the entry of AA into the CSF after conversion to AA in systemic tissue and/or the local synthesis of AA from L-KYN in the CNS.

Sources of the neurotoxin quinolinic acid in the brain of HIV-1-infected patients and retrovirus-infected macaques

This study investigated the sources of quinolinic acid, a neurotoxic tryptophan-kynurenine pathway metabolite, in the brain and blood of HIV-infected patients and retrovirus-infected macaques. In brain, quinolinic acid concentrations in HIV-infected patients were elevated by > 300-fold to concentrations that exceeded cerebrospinal fluid (CSF) by 8.9-fold. There were no significant correlations between elevated serum quinolinic acid levels with those in CSF and brain parenchyma. Because nonretrovirus-induced encephalitis confounds the interpretation of human postmortem data, rhesus macaques infected with retrovirus were used to examine the mechanisms of increased quinolinic acid accumulations and determine the relationships of quinolinic acid to encephalitits and systemic responses. The largest kynurenine pathway responses in brain were associated with encephalitis and were independent of systemic responses. CSF quinolinic acid levels were also elevated in all infected macaques, but particularly those with retrovirus-induced encephalitis. In contrast to the brain changes, there was no difference in any systemic measure between macaques with encephalitis vs. those without. Direct measures of the amount of quinolinic acid in brain derived from blood in a macaque with encephalitis showed that almost all quinolinic acid (>98%) was synthesized locally within the brain. These results demonstrate a role for induction of indoleamine-2,3dioxygenase in accelerating the local formation of quinolinic acid within the brain tissue, particularly in areas of encephalitis, rather than entry of quinolinic acid into the brain from the meninges or blood. Strategies to reduce QUIN production, targeted at intracerebral sites, are potential approaches to therapy.

Encephalopathy and progression of human immunodeficiency virus disease in a cohort of children with perinatally acquired human immunodeficiency virus infection. Women and Infants Transmission Study Group

OBJECTIVE

To describe the incidence, predictors, and survival of children with human immunodeficiency virus (HIV) encephalopathy followed in the Women and Infants Transmission Study cohort.

STUDY DESIGN

Retrospective review of clinical and immunologic staging of perinatally HIV-infected infants, based on the 1994 Centers for Disease Control and Prevention Classification System.

RESULTS

Data were available for 128 HIV-infected children, with a median follow-up of 24 months. HIV encephalopathy was diagnosed in 27 (21%) of children. Median survival after diagnosis was 14 months. Of children with encephalopathy, 74% had at least moderate immunosuppression by the time of diagnosis. Encephalopathy represented the first acquired immunodeficiency syndrome-defining condition in 67%, and the only one in 26% of children. Hepatosplenomegaly or lymphadenopathy during the first 3 months of life was diagnosed in 63%, in contrast to 29% of those without encephalopathy (p value = 0.001). Cardiomyopathy was present in 30% of the children with encephalopathy versus 2% of those without encephalopathy. High viral load in infancy was associated with increased risk of encephalopathy but was not predictive of age at onset.

CONCLUSIONS

Encephalopathy in children with HIV is common and is associated with high viral load, immunodeficiency, and shortened survival. Encephalopathy was more likely to develop in infants with early signs and symptoms of HIV, although age at onset could not be predicted.

Inhibition of murine embryonic growth by human immunodeficiency virus envelope protein and its prevention by vasoactive intestinal peptide and activity-dependent neurotrophic factor

Intrauterine growth retardation and neurodevelopmental handicaps are common among infants born to HIV-positive mothers and may be due to the actions of virions and/or maternally derived viral products. The viral envelope protein, gp120, is toxic to neurons, induces neuronal dystrophy, and retards behavioral development in neonatal rats. Vasoactive intestinal peptide, a neuropeptide regulator of early postimplantation embryonic growth, and the neuroprotective protein, activity-dependent neurotrophic factor, prevent gp120-induced neurotoxicity. Whole embryo culture of gestational day 9.5 mouse embryos was used to assess the effect of gp120 on growth. Embryos treated with gp120 exhibited a dose-dependent inhibition of growth. gp120-treated embryos (10(-8) M) grew 1.2 somites in the 6-h incubation period, compared with 3.9 somites by control embryos. Embryos treated with gp120 were significantly smaller in cross-sectional area and had significantly less DNA and protein than controls. Growth inhibition induced by gp120 was prevented by cotreatment with vasoactive intestinal peptide or activity-dependent neurotrophic factor. gp120 may play a role in the growth retardation and developmental delays experienced by infants born to HIV-positive mothers. Vasoactive intestinal peptide and related factors may provide a therapeutic strategy in preventing developmental deficits.

Cigarette smoking, bacterial pneumonia, and other clinical outcomes in HIV-1 infection. Terry Beirn Community Programs for Clinical Research on AIDS

Cigarette smoking has been associated with impaired immune defenses and an increased risk of certain infectious and neoplastic diseases in HIV-1 seronegative populations. We examined the relationship between cigarette smoking and clinical outcome in a prospective cohort of 3221 HIV-1-seropositive men and women enrolled in the Terry Beirn Community Programs for Clinical Research on AIDS. Differences in clinical outcomes between never, former, and current cigarette smokers were assessed using proportional hazards regression analysis. After adjustment for CD4+ cell count, prior disease progression, use of antiretroviral therapy, and other covariates, there was no difference between current smokers and never smokers in the overall risk of opportunistic diseases [relative hazard (RH) = 1.05; 95% confidence interval (CI) 0.90-1.23; p = 0.52] or death (RH = 1.00; 95% CI 0.86-1.18; p = 0.97). However, current smokers were more likely than never smokers to develop bacterial pneumonia (RH = 1.57; 95% CI 1.14-2.15; p = 0.006), oral candidiasis (RH = 1.37; 95% CI 1.16-1.62; p = 0.0002), and AIDS dementia complex (RH = 1.80; 95% CI 1.11-2.90; p = 0.02). In addition, current smokers were less likely to develop Kaposi's sarcoma (RH = 0.58; 95% CI 0.39-0.88; p = 0.01) and several other non-respiratory tract diseases. If confirmed by other studies, these findings have important clinical implications.