Differential effects of human immunodeficiency virus type 1 envelope protein gp120 on interferon production by mononuclear cells from adults and neonates

While considerable progress in examining the course of human immunodeficiency virus (HIV) infection in adults has been made, a better understanding of the natural history of perinatal HIV infection remains to be obtained. Dysregulation of the production and functions of various cytokines, especially the interferons (IFNs), during HIV infections has been reported. Using an in vitro model system, we examined the effects of the HIV type 1 envelope protein, gp120 (10, 50, and 100 ng/ml), on gamma IFN (IFN-gamma) and IFN-alpha production by lymphocytes from neonates and adults and also examined the potential regulatory effects of gp120 on phorbol 12-myristate acetate (PMA)- and Sendai virus-induced IFN-gamma and IFN-alpha production by lymphocytes. PMA at a concentration of 50 ng/ml plus 50 ng of calcium ionophore A23187 per ml was used to induce IFN-gamma, while 150 hemagglutinating units of Sendai virus was used to induce IFN-alpha production. The antiviral activity of both IFN-alpha and IFN-gamma in leukocyte culture supernatants was assayed on BG-9 cells by a dye uptake technique using vesicular stomatitis virus as a challenge virus. Placental cord blood leukocyte (CBL) samples from healthy, term infants and adult peripheral blood leukocytes (APBL) produced no IFN in response to gp120. However, CBL produced significantly decreased levels of IFN-gamma compared with APBL in response to PMA plus ionophore. gp120 significantly suppressed both Sendai virus-induced IFN-alpha and PMA-induced IFN-gamma production by both CBL and APBL in a dose-dependent manner. However, gp120-induced suppression of IFN-alpha and IFN-gamma was significantly greater with CBL than with APBL. Treatment of CBL and APBL with gp120 did not induce any phenotypic alteration of the CD45 RO+ subset. Increased suppression of IFN-alpha and IFN-gamma production by gp120 in neonates may partially explain their apparent increased susceptibility to the clinical progression of HIV infections compared with that of adults.

Human immunodeficiency virus-1 gp120 and gp160 envelope proteins modulate mesangial cell gelatinolytic activity

Patients with human immunodeficiency virus (HIV) infection often develop glomerular lesions (mesangial expansion and sclerosis). Modulation of matrix degradation may be important in the expansion of the mesangium. We studied the effect of HIV sera and HIV-1 envelope glycoproteins on gelatinolytic activity of human mesangial cells. HIV serum-treated cells showed lower (P < 0.01) gelatinolytic activity when compared with cells treated with control serum (control serum, 4.3 +/- 0.1 versus HIV serum, 3.3 +/- 0.1 micrograms gelatin degraded/mg protein). Mesangial cells incubated with HIV-1 gp120 protein also showed decreased (P < 0.01) gelatinolytic activity (control, 4.6 +/- 0.2 versus HIV-1 gp120 protein, 1.7 +/- 0.2 micrograms gelatin degraded/mg protein). HIV-1 gp160 protein also inhibited (P < 0.05) mesangial cell gelatinolytic activity as judged by a biotin-avidin assay as well as by a 3H gelatin degradation assay. In contrast, gp alpha-1 acid, a nonviral glycoprotein, did not modulate mesangial cell gelatinolytic activity. These results suggest that the serum contents of HIV patients decrease gelatinolytic activity of mesangial cells. This effect of HIV sera seems to be mediated through HIV-1 gp proteins.

A molecular sensor system based on genetically engineered alkaline phosphatase

Binding and signaling proteins based on Escherichia coli alkaline phosphatase (AP; EC 3.1.3.1) were designed for the detection of antibodies. Hybrid proteins were constructed by using wild-type AP and point mutants of AP [Asp-101 --> Ser (D101S) and Asp-153 --> Gly (D153G)]. The binding function of the hybrid proteins is provided by a peptide epitope inserted between amino acids 407 and 408 in AP. Binding of anti-epitope antibodies to the hybrid proteins modulates the enzyme activity of the hybrids; upon antibody binding, enzyme activity can increase to as much as 300% of the level of activity in the absence of antibody or can decrease as much as 40%, depending on the presence or absence of the point mutations in AP. The fact that modulation is altered from inhibition to activation by single amino acid changes in the active site of AP suggests that the mechanism for modulation is due to structural alterations upon antibody binding. Modulation is a general phenomenon. The properties of the system are demonstrated by using two epitopes, one from the V3 loop of human immunodeficiency virus type 1 gp120 protein and one from hepatitis C virus core protein, and corresponding monoclonal antibodies. The trend of modulation is consistent for all hybrids; those in wild-type AP are inhibited by antibody, while those in the AP mutants are activated by antibody. This demonstrates that modulation of enzyme activity of the AP-epitope hybrid proteins is not specific to either a particular epitope sequence or a particular antibody-epitope combination.

HIV-1 gp120 produces DNA fragmentation in the cerebral cortex of rat

In the present experiments we have used morphological techniques to study the neuropathological profile of the brain of rats after intracerebroventricular (i.c.v.) injection of recombinant HIV-1 gp 120. Using brain cryostat sections (10 microns) from rats treated with a single, daily dose of gp120 (100 ng/rat) given for 7 and 14 consecutive days, in situ DNA fragmentation was revealed in the neocortex but not in the hippocampus by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end-labelling (TUNEL). In these rats, dark degenerating neurones were observed in the neocortex but not in the hippocampus. Treatment with bovine serum albumin (300 ng/rat, i.c.v.) for up to 14 days did not produce DNA fragmentation nor did it yield neuropathological lesions of the neocortex or hippocampus. In conclusion, the present data demonstrate that gp 120 given i.c.v. produced DNA fragmentation in the neocortex, thus suggesting that apoptosis is the mechanism through which neurones of the neocortex are killed.

Exposure to gp120 of HIV-1 induces an increased release of arachidonic acid in rat primary neuronal cell culture followed by NMDA receptor-mediated neurotoxicity

After incubation of highly enriched neurons from rat cerebral cortex with the HIV-1 coat protein gp120 for 18 h, cells showed fragmentation of DNA at internucleosomal linkers followed by NMDA receptor-mediated neurotoxicity. We report that in response to exposure to gp120 cells react with an increased release of arachidonic acid (AA) via activation of phospholipase A2. This process was not inhibited by NMDA receptor antagonists. To investigate the role of AA on the sensitivity of the NMDA receptor towards its agonist, low concentrations of NMDA were co-administered with AA. This condition enhanced the NMDA-mediated cytotoxicity. Administration of mepacrine reduced cytotoxicity caused by gp120. We conclude that gp120 causes an activation of phospholipase A2, resulting in the increased release of AA, which may in turn sensitize the NMDA receptor.

HIV-1 gp120 glycoprotein induces [Ca2+]i responses not only in type-2 but also type-1 astrocytes and oligodendrocytes of the rat cerebellum

Cultures of cerebellar cortex cells were exposed to the HIV-1 envelope glycoprotein, gp120, and investigated for cytosolic Ca2+ ion concentration ([Ca2+]i) changes by the fura-2 ratio videoimaging technique while bathed in complete, Na(+)-free or Mg(2+)-free Krebs-Ringer media. At the end of the [Ca2+]i experiments the cells were fixed and immunoidentified through the revelation of markers specific for neurons (microtubule associated protein-2), type-2 (A2B5) or all (glial fibrillary acidic protein) astrocytes, oligodendrocytes (galactocerebroside) or microglia (F4/80 antibody). In complete medium, rapid biphasic (spike-plateau) responses induced by gp120 (0.1-1 nM) were observed in a subpopulation of type-2 astrocytes. In addition, slow but progressive responses were observed in other type-2 cells and oligodendrocytes, whereas type-1 astrocytes showed small responses, if any, and granule neurons did not respond at all. Use of Na(+)-free medium (a condition that blocked another gp120-induced response, cytosolic alkalinization) resulted in an increase in [Ca2+]i response that was appreciable not only in type-2 but also in most type-1 astrocytes, possibly because of the inhibition of the Na+/Ca2+ exchanger and the ensuing decrease in Ca2+ extrusion. Granule neurons, including those in direct contact with responsive astrocytes, remained unresponsive, even when the experiments were carried out in Mg(2+)-free medium supplemented with glycine, a condition that favors activation of the glutamatergic N-methyl-D-aspartate (NMDA) receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

HIVgp120 activates autoreactive CD4-specific T cell responses by unveiling of hidden CD4 peptides during processing

T cells are made tolerant only to those self-peptides that are presented in sufficient amounts by antigen-presenting cells. They ignore cryptic self-determinants, such as either those not generated by processing machinery or generated in insufficient amounts. It is anticipated that mechanisms that either change antigen processing or increase the yield of previously "invisible" peptides may be capable of inducing T cell priming and, if they are self-maintained, may sustain autoimmune diseases. Herein, we demonstrate for the first time a mechanism by which the gp120 human immunodeficiency virus-I, by downregulating plasma membrane CD4 and increasing its processing, unveils hidden CD4 epitopes, inducing an autoimmune-specific T cell response.

An octapeptide analogue of HIV gp120 modulates protein tyrosine kinase activity in activated peripheral blood T lymphocytes

Following infection with HIV, patients exhibit lymphocyte dysfunction before the loss of CD4+ T cells. The major HIV surface glycoprotein, gp120, can modulate lymphocyte function in vitro; however, the mechanism by which gp120 affects T lymphocyte signal transduction is controversial. We have used Peptide T, a synthetic octapeptide derived from a conserved, CD4 binding region of gp120, to examine gp120-related modulation of lymphocyte signal transduction. Activation of lymphocytes through the T cell receptor (TCR) in collaboration with cell surface accessory molecules results in rapid increases in tyrosine phosphorylation, probably through the recruitment and activation of src-family protein tyrosine kinases (PTK) such as lck and fyn which have been implicated in mediating the proximal signalling events mediated through the TCR. To identify potential mechanisms by which gp120 could modulate the function of T lymphocytes, we determined the effect of Peptide T on normal, activated peripheral blood lymphoblasts. Treatment of normal, activated peripheral blood lymphoblasts with Peptide T (10(-9) M) for 60 min transiently reduced levels of protein tyrosine phosphorylation (ptyr). Reduction in levels of cellular ptyr was associated with transient inhibition of the activity of total cellular and CD4-associated p56lck kinase activity (80%). Peptide T also induced a small delayed reduction in the p59fyn activity (up to 42%). Despite the decrease in total cellular ptyr levels, pp60c-src kinase activity was increased 11-fold following treatment with Peptide T. Peptide T pretreatment also induced tyrosine phosphorylation of a 48-kD CD4-associated protein, indicating that Peptide T may have multiple effects. Peptide T did not alter the levels of total cellular p56lck enzyme, nor did it directly inhibit the activity of purified p56lck. These results are consistent with a Peptide T-dependent modulation of PTK regulation, and support the potential of gp120 to interfere with T lymphocyte signal transduction in activated T lymphocytes.

HIV-gp120 activates large-conductance apamin-sensitive potassium channels in rat astrocytes

Central nervous system (CNS) involvement usually occurs in individuals infected with human immunodeficiency virus type 1 (HIV-1). Evidence is now accumulating that neurons and astrocytes may be functionally compromised by exposure to viral components or cellular factors released from HIV-1-infected macrophages and/or microglia. We have previously reported that the HIV coat protein gp120 stimulates Na+/H+ exchange in primary cultured rat astrocytes, which, ultimately, results in the activation of a K+ conductance. In this report we characterize the electrophysiological and biophysical properties of the channels responsible for the gp120-induced increase in K+ conductance. These K+ channels had a relatively large unitary conductance (147 pS), were not gated by voltage, were sensitive to changes in H+ concentration at their cytosolic face, were specifically inhibited by apamin, and were insensitive to charybdotoxin and tetraethylammonium. The activation of these channels by gp120 is referable to cellular alkalinization subsequent to Na+/H+ exchange stimulation; gp120 failed to activate these K+ channels in the absence of external Na+ or in the presence of amiloride, an inhibitor of Na+/H+ exchange. Subsequent K+ loss from the astrocyte into the restricted extracellular space surrounding neurons can then lead to neuronal depolarization, activation of voltage-sensitive Ca2+ channels, and, eventually, cell death. Thus abnormal activation of astrocyte K+ channels by gp120 may contribute to the CNS pathophysiology associated with HIV-1 infection.

SPC3, a synthetic peptide derived from the V3 domain of human immunodeficiency virus type 1 (HIV-1) gp120, inhibits HIV-1 entry into CD4+ and CD4- cells by two distinct mechanisms

The third variable region (V3 loop) of gp120, the HIV-1 surface envelope glycoprotein, plays a key role in HIV-1 infection and pathogenesis. Recently, we reported that a synthetic multibranched peptide (SPC3) containing eight V3-loop consensus motifs (GPGRAF) inhibited HIV-1 infection in both CD4+ and CD4- susceptible cells. In the present study, we investigated the mechanisms of action of SPC3 in these cell types--i.e., CD4+ lymphocytes and CD4- epithelial cells expressing galactosylceramide (GalCer), an alternative receptor for HIV-1 gp120. We found that SPC3 was a potent inhibitor of HIV-1 infection in CD4+ lymphocytes when added 1 h after initial exposure of the cells to HIV-1, whereas it had no inhibitory effect when present only before and/or during the incubation with HIV-1. These data suggested that SPC3 did not inhibit the binding of HIV-1 to CD4+ lymphocytes but interfered with a post-binding step necessary for virus entry. In agreement with this hypothesis, SPC3 treatment after HIV-1 exposure dramatically reduced the number of infected cells without altering gp120-CD4 interaction or viral gene expression. In contrast, SPC3 blocked HIV-1 entry into CD4-/GalCer+ human colon epithelial cells when present in competition with HIV-1 but had no effect when added after infection. Accordingly, SPC3 was found to inhibit the binding of gp120 to the GalCer receptor. Thus, the data suggest that SPC3 affects HIV-1 infection by two distinct mechanisms: (i) prevention of GalCer-mediated HIV-1 attachment to the surface of CD4-/GalCer+ cells and (ii) post-binding inhibition of HIV-1 entry into CD4+ lymphocytes.

Interaction of HIV-1 gp120 molecule fragments with human monocytes: different requirements for tumor necrosis factor-alpha and IL-6 production

The HIV-1 gp120 recombinant protein fragment encompassing aa residues 410-511, that contains the CD4 binding region (rp120cd), and fragment aa 446-511, which lacks the sequence responsible for CD4 binding (rp120), were synthesized to study their ability to induce TNF synthesis in human monocytes. The rp120cd stimulated TNF alpha secretion by monocytes while the rp120 and full-length recombinant protein (FL gp120), used as control, failed to do so. However, FL gp120 stimulated peripheral blood mononuclear cells (PBMC) and lymphocytes for TNF production and this was inhibited by anti-CD4 MAb. The rp120cd also caused TNF secretion by PBMC that was not blocked by this antibody. Furthermore, FL gp120 but not rp120cd inhibited anti-CD4 mAb binding to CEM cells. Hence, FL gp120 may cause TNF release from lymphocytes by binding to CD4, while rp120cd interacts with monocytes but not lymphocytes and induces TNF production by a mechanism not involving CD4 binding. Unexpectedly, FL gp120 but not rp120cd stimulated IL-6 secretion and IL-6 mRNA synthesis in monocytes. The FL gp120-induced production of IL-6 by monocytes was inhibited by anti-CD4 monoclonal antibody (MAb). Thus, there may be different requirements for TNF induction in lymphocytes and monocytes stimulated with various preparations of gp120 and for the selective induction of cytokines in monocytes. The enhanced production of TNF in HIV infection and AIDS may involve distinct cellular sources and different mechanisms.

HIV-1 glycoprotein gp120 disrupts CD4-p56lck/CD3-T cell receptor interactions and inhibits CD3 signaling

Using the CD4+ human T cell clone P28, we demonstrated that the HIV-1 glycoprotein gp120 inhibited CD3-induced inositol trisphosphate production, calcium influx and T cell proliferation. Additionally, gp120 was shown to dissociate the tyrosine kinase p56lck from CD4 in CEM cells, with a concommittant inhibition of CD4-linked kinase activity. We have addressed the question whether disruption of CD4/p56lck or CD4/CD3-T cell receptor interactions, or both, could account for the inhibitory effect of gp120 in P28 cells. By comparing the effects of various anti-CD4 monoclonal antibodies (mAb) with those of gp120, we show that gp120 and IOT4a modulate CD4 expression, and decrease CD4-associated p56lck and CD4-linked kinase activity at the plasma membrane. In contrast, OKT4A and OKT4 anti-CD4 mAb have no inhibitory effect. Interestingly, gp120 also inhibits CD3-induced Lck activation and cellular tyrosine phosphorylation, particularly of phosphoinositide-specific phospholipase C-gamma-1. Kinetic experiments reveal that the inhibitory effect of gp120 on CD3-induced tyrosine phosphorylation appears as early as 30 min, but culminate when CD4-p56lck complexes disappear from the cell surface after 4 h. These results suggest that a negative signal is triggered by gp120 that results, after a few hours, in down-modulation of CD4-p56lck complexes and the impairment of CD3 signaling. Supporting this hypothesis, gp120 inhibits CD3-linked kinase activity as shown by the inhibition of the phosphorylation of CD3 chains, leading to the inhibition of subsequent signal transduction.

Modulation of CD4 lateral interaction with lymphocyte surface molecules induced by HIV-1 gp120

CD4, a lymphocyte surface glycoprotein, serves as co-receptor for antigen with the T cell receptor (TCR). It is also the lymphocyte receptor for HIV by binding the gp120 viral envelope protein. Interaction of gp120 with CD4 is crucial for viral infection, but is not sufficient to allow viral entry into cells. Recombinant gp120 alters CD4+ T cell responsiveness to activation stimuli. To express its co-receptor function fully, CD4 must be laterally associated with the TCR and CD45 to form multi-receptor complexes competent to transduce potent activation signals. Here, we examine the possibility that gp120/CD4 binding alters lateral associations of CD4 with other lymphocyte surface molecules, and that assembly of abnormal multi-molecular complexes is involved in the gp120-induced CD4+ T cell dysfunction and in viral entry. In the absence of gp120, CD4 displayed high association with CD3, CD5, CD45RC, CD25, CD28, CD44, and CD53; weak association with CD2, CD38, CD45RB, CD62L, and CD26; and no association with CD45RA, CD45RO, CD11b, CD11a, CD54, CD7, CD48, CD98, CD59 CD55, HLA class I and class II molecules. Treatment with gp120 significantly increased CD4 association with CD3, CD45RA, CD45RB, CD59, CD38, CD26 and HLA class I, and decreased that with CD45RC. Specificity of these results were assessed at various levels. First, gp120 did not influence lateral associations displayed by other molecules, such as HLA class II. Second, the Leu3 mAb which binds CD4 on a site overlapping the gp120 binding site, did not elicit the same CD4 lateral associations as gp120, and finally, a direct gp120/CD4+ interaction was needed to induce the lateral associations, as shown by the observation that blocking the gp120/CD4 binding by the Leu3 mAb inhibited the gp120-induced associations. These results can be interpreted in several ways gp120/CD4 interaction could trigger an inside-out signal responsible for the associations, or gp120 could induce steric modifications of CD4 that increase its affinity for the associating molecules. Alternatively, these molecules may interact directly with gp120, bridging them with CD4. It is also possible that th e associations may be mediated by additional components, interacting with both gp120 and the associating surface molecule. The last hypothesis is likely for CD59, whose gp120-induced association with CD4 required the presence of serum in the co-capping assay. Since both CD59 and gp120 bind complement, the observed association could be mediated by complement components.

HIV-1 coat protein gp120-induced increases in levels of intrasynaptosomal calcium

The effects of human immunodeficiency virus type-1 (HIV-1) coat protein gp120 on levels of intrasynaptosomal calcium ([Ca2+]i) were determined in rat cortical synaptosomes. gp120 at concentrations of > or = 400 pM, significantly (P < 0.05) increased levels of [Ca2+]i. Treatment with 20 mM KCl, reduced the concentrations of gp120 necessary to produce significant (P < 0.001) increases in [Ca2+]i. gp120-evoked increases in [Ca2+]i were prevented either by treatment with dantrolene or by removal of extracellular calcium with BAPTA. The peak levels of gp120-induced increases in [Ca2+]i were not affected by calcium channel blockers lanthanum and nicardipine, by glutamate receptor antagonists MK-801 and NBQX, or by removal of endogenous glutamate with glutamate dehydrogenase. gp120-induced [Ca2+]i increases in presynaptic terminals may play a role in HIV-mediated effects in the central nervous system.

Immunotoxicity of AZT: inhibitory effect on thymocyte differentiation and peripheral T cell responsiveness to gp120 of human immunodeficiency virus

3'-Azido-2',3'-dideoxythymidine (AZT) is extensively used in the treatment of human immunodeficiency virus (HIV) infection. Currently, it is debated whether AZT should be offered to symptomless HIV-infected individuals in the hope of delaying or even preventing progression to acquired immunodeficiency syndrome (AIDS). However, before the chronic use of AZT, it is essential to establish whether this drug alters the differentiation and functions of T cells particularly because HIV infects CD4+ T cells, as well as investigate whether AZT would alter the T cell response to HIV-encoded antigens. In the current study, therefore, we investigated the effect of administration of AZT into mice for 7-14 days on T cell differentiation in the thymus and the ability of T cells to respond to HIV antigens in the periphery. Our data demonstrated that AZT, when administered orally at 500 mg/kg body wt or higher concentrations for 14 days, caused marked thymic involution with significant decrease in the percentage of CD4+CD8+ T cells and increase in the percentage of CD4-CD8-, CD4+, and CD8+ T cells. AZT treatment did not affect the cellularity of the spleen or the ratios of T cells in the periphery. Also, splenic T cells from AZT-treated mice did not demonstrate marked decrease in their ability to respond to mitogens in vitro. However, when AZT-treated mice were immunized with foreign antigens, such as gp120 of HIV or conalbumin, the T cells demonstrated significant decrease in their ability to respond to these antigens. When AZT was added to cultures, it was found to inhibit the proliferation of T cells to mitogens as well as the differentiation of cytotoxic T lymphocytes (CTL). Interestingly, addition of exogenous IL-2 to CTL cultures reconstituted the decreased CTL response. Furthermore, administration of IL-2 into AZT-treated mice could also reconstitute the decrease in thymic cellularity induced by AZT. These data indicate that AZT, when present at the time of T cell differentiation or responsiveness to antigens in vivo, can mediate significant inhibition of such functions thereby suggesting that AZT may affect the immune response to HIV antigens.

gp120, an HIV-1 protein, increases susceptibility to hypoglycemic and ischemic brain injury in perinatal rats

Recent data suggest that gp120, a glycoprotein secreted by HIV-1-infected macrophages, is neurotoxic, and that toxicity is mediated, at least in part, by overactivation of NMDA-type excitatory amino acid receptors. In experimental animals, considerable evidence indicates that hypoglycemic and ischemic neuronal injury are mediated by endogenous excitatory amino acids. We hypothesized that in the presence of gp120 the severity of brain injury resulting from hypoglycemia and cerebral ischemia would increase. To test this hypothesis in vivo, we evaluated the influence of gp120 on the extent of brain injury resulting from these two clinically relevant pathophysiological insults in 7-day-old (P7) rats, the developmental stage of peak susceptibility to NMDA neurotoxicity. We compared the severity of hippocampal injury resulting from right intrahippocampal injections of gp120 (50 ng) in P7 rats rendered markedly hypoglycemic (n = 10) and in controls (n = 12). We also determined the influence of gp120 administration on the severity of hypoxic-ischemic injury, using a perinatal rat stroke model. P7 rats received intrahippocampal injections of gp120 (50 ng) (n = 23) or saline (n = 18) and then underwent right carotid ligation, followed by 2 h exposure to 8% oxygen. Brain injury was evaluated 5 days later, based on neuropathology evaluation and measurements of bilateral regional cross-sectional areas. The severity of hippocampal injury, based on cross-sectional area measurements, was considerably greater in animals from the hypoglycemic group than in litter-mate gp120-injected controls. Among the animals that underwent hypoxic-ischemic lesioning, the severity of injury, based on histopathology scoring and regional volume measurements, was considerably greater in animals that received gp120 than in those that received saline. These results provide support for the hypothesis that locally secreted HIV peptides, such as gp120, may potentiate the neurotoxicity of endogenous excitatory amino acid neurotransmitters in HIV-infected brain.

Multibranched peptide constructs derived from the V3 loop of envelope glycoprotein gp120 inhibit human immunodeficiency virus type 1 infection through interaction with CD4

The V3 loop of the gp120 of human immunodeficiency virus type 1 (HIV-1) is assumed to be involved in HIV-1-mediated membrane fusion. V3-derived peptides have been shown either to enhance or to prevent HIV-1 infection. Multibranched peptide constructs (MBPCs) derived from the V3 North American/European consensus sequence were designed to sort out these conflicting findings. At 5 microM, MBPC1 (8-branched GPGRAF) totally, and MBPC2 ([RKSIHIGPGRAFYT]4) partially, inhibited HIV-1LAI infection, whereas the GPGRAF monomer had only a limited effect. A peptide of the entire V3 consensus loop and a control MBPC had no detectable activity. The 5 microM MBPC1 HIV-1-inhibiting concentration was not cytotoxic, nor did it alter T lymphocyte allogeneic, antigen-, or mitogen-induced reactivities, and it was about 5- to 50-fold lower (MBPC2 and MBPC1, respectively) than that resulting in 50% cell death. Analysis of MBPC immunoreactivity showed that MBPC2, but not MBPC1, strongly reacted with human HIV-1 positive sera. Only MBPC2 elicited significant antibody responses in rabbits. The V3-derived MBPCs bound to CD4+ cells, as determined by immunofluorescence analysis. The binding was inhibited either by soluble CD4 or by CD4 monoclonal antibody (mAb) MT151, which recognizes the CDR3 region of the D1 domain of CD4, but not by other CD4 mAbs Leu3a, OKT4A, Q4021, 13B8-2, 5A8, RFT4, nor by the CD26 mAb BA5. Therefore, it appears likely that MBPCs inhibit HIV-1 infection by interacting with the CDR3 region of CD4 or with a region in its vicinity.

Synthetic multimeric peptides derived from the principal neutralization domain (V3 loop) of human immunodeficiency virus type 1 (HIV-1) gp120 bind to galactosylceramide and block HIV-1 infection in a human CD4-negative mucosal epithelial cell line

The glycosphingolipid galactosylceramide (GalCer), which binds gp120 with high affinity and specificity, is a potential alternative receptor for human immunodeficiency virus type 1 (HIV-1) in some CD4-negative neural and epithelial human cells, including the human colonic epithelial cell line HT-29. In the present study, we demonstrate that synthetic multibranched peptides derived from the consensus sequence of the HIV-1 V3 loop block HIV-1 infection in HT-29 cells. The most active peptide was an eight-branched multimer of the motif Gly-Pro-Gly-Arg-Ala-Phe which at a concentration of 1.8 microM induced a 50% inhibition of HIV-1 infection in competition experiments. This peptide was not toxic to HT-29 cells, and preincubation with HIV-1 did not affect viral infectivity, indicating that the antiviral activity was not due to a nonspecific virucidal effect. Using a high-performance thin-layer chromatography binding assay, we found that multibranched V3 peptides recognized GalCer and inhibited binding of recombinant gp120 to the glycosphingolipid. In addition, these peptides abolished the binding of an anti-GalCer monoclonal antibody to GalCer on the surface of live HT-29 cells. These data provide additional evidence that the V3 loop is involved in the binding of gp120 to the GalCer receptor and show that multibranched V3 peptides are potent inhibitors of the GalCer-dependent pathway of HIV-1 infection in CD4-negative mucosal epithelial cells.

AIDS-related dementia and calcium homeostasis

Approximately a third of adults and half of children with acquired immunodeficiency syndrome (AIDS) eventually suffer from neurological manifestations, including dysfunction of cognition, movement, and sensation. Among the various pathologies reported in the brain of patients with AIDS is neuronal injury and loss. A paradox arises, however, because neurons themselves are for all intents and purposes not infected by human immunodeficiency virus type 1 (HIV-1). This paper reviews evidence suggesting that at least part of the neuronal injury observed in the brain of AIDS patients is related to excessive influx of Ca2+. There is growing support for the existence of HIV- or immune-related toxins that lead indirectly to the injury or death of neurons via a potentially complex web of interactions between macrophages (or microglia), astrocytes, and neurons. Human immunodeficiency virus-infected monocytoid cells (macrophages, microglia, or monocytes), especially after interacting with astrocytes, secrete substances that potentially contribute to neurotoxicity. Not all of these substances are yet known, but they may include eicosanoids, that is, arachidonic acid and its metabolites, as well as platelet-activating factor. Macrophages activated by HIV-1 envelope protein gp120 also appear to release arachidonic acid and its metabolites. These factors can lead to increased glutamate release or decreased glutamate reuptake. In addition, gamma interferon (IFN-gamma) stimulation of macrophages induce release of the glutamate-like agonist quinolinate. Human immunodeficiency virus-infected or gp120-stimulated macrophages also produce cytokines, including tumor necrosis factor-alpha and interleukin-1 beta, which contribute to astrogliosis. A final common pathway for neuronal susceptibility appears to be operative, similar to that observed in stroke, trauma, epilepsy, neuropathic pain, and several neurodegenerative diseases, possibly including Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis. This mechanism involves the activation of voltage-dependent Ca2+ channels and N-methyl-D-aspartate (NMDA) receptor-operated channels, and therefore offers hope for future pharmacological intervention. This review focuses on clinically tolerated calcium channel antagonists and NMDA antagonists with the potential for trials in humans with AIDS dementia in the near future.

HIV-1 envelope protein gp120 potentiates NMDA-evoked noradrenaline release by a direct action at rat hippocampal and cortical noradrenergic nerve endings

Exposure of rat or human neocortical or hippocampal tissue to glutamate receptor agonists elicits as Ca(2+)-dependent, exocytotic-like release of previously accumulated [3H]noradrenaline through activation of both N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors colocalized on the noradrenergic axon terminals. Here we show that the NMDA (100 microM)-evoked release of [3H]noradrenaline from superfused thin layers of isolated rat hippocampal or cortical nerve endings was potentiated when the human immunodeficiency virus type 1 coat protein gp120 was added to the superfusion medium concomitantly with NMDA. The effect of gp120 (10 pM to 3 nM) on the 100 microM NMDA-evoked release of [3H]noradrenaline was concentration-dependent; the maximal effect (approximately 140% potentiation) was reached at 100 pM of gp120. The protein was inactive on its own. The [3H]noradrenaline release evoked by NMDA (100 microM)+gp120 (100 pM) was prevented by classical NMDA receptor antagonists, as well as by 10 microM memantine. Neither the release evoked by NMDA nor that elicited by NMDA+gp120 was sensitive to the nitric oxide synthase inhibitor NG-nitro-L-arginine, suggesting no involvement of nitric oxide. The [3H]noradrenaline release elicited by 100 microM AMPA was unaffected by gp120. The protein potentiated the release evoked by 100 microM glutamate; the effect of 100 pM gp120 was quantitatively identical to that of 1 microM glycine, with no apparent additivity between gp120 and glycine. The antagonism by 1 microM 7-chloro-kynurenic acid of the NMDA-induced [3H]noradrenaline release was reversed by glycine or gp120.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamate production by cultured microglia: differences between rat and mouse, enhancement by lipopolysaccharide and lack effect of HIV coat protein gp120 and depolarizing agents

Glutamate release from rat and mouse microglia subcultures grown in a serum-free medium was substantially greater in the presence than in the absence of a physiological concentration of glutamine (0.5 mM). Mouse microglia produced and released more glutamate than rat microglia. Glutamate accumulation in the medium increased with time and cell density, which is consistent with the virtual absence of glutamate reuptake. Lipopolysaccharide (LPS; 10-100 ng/ml), HIV coat protein gp120 (0.1-10 nM), high K+ (35 mM) or ATP (150 microM), did not affect glutamate release from cells maintained in serum-free medium. In the presence of 1% dialyzed serum, however, LPS induced a dose- and time-dependent increase in the accumulation of glutamate in the medium, suggesting that, as in other cell types, serum factors are required for LPS binding to its receptors.

Sulfated polyanions prevent HIV infection of lymphocytes by disruption of the CD4-gp120 interaction, but do not inhibit monocyte infection

Sulfated polyanions (SPs) bind variably to lymphocyte-expressed CD4 and inhibit binding of monoclonal antibodies to the first two domains of CD4. To further define this interaction, soluble recombinant CD4 (sCD4; four extracellular domains), its truncated amino-terminal two-domain derivative, and three linear peptide analogues spanning residues 6-60 (6-24, 20-40, 41-60) in the first domain were investigated for SP binding. Dextran sulfate (DXS) (500 kDa), polyvinyl sulfate, fucoidan, and carrageenan-kappa, each immobilized on carboxymethyl cellulose fibers, bound strongly to both the two-domain and four-domain recombinant CD4 molecules (similar to that observed with native CD4), whereas dextran sulfate (5 kDa), chondroitin 6-sulfate, and pentosan sulfate bound relatively poorly. No peptide binding to SPs was observed. Recombinant gp120 bound poorly (< 10%) to all of the immobilized polyanions, except pentosan sulfate (17%), for which some binding was noted. Binding of radiolabeled V3 loop peptide to SPs was slightly greater, with 20-30% binding to polyvinyl sulfate, dextran sulfate (500 kDa), and pentosan sulfate. Competitive binding studies demonstrated the predominance of sCD4 rather than rgp120 binding to SPs and supported previous data demonstrating a binding site for DXS (500 kDa) on the first domain of CD4 adjacent to the gp120 binding site and recognized by OKT4C and E monoclonal antibodies. Hence disruption of the CD4-gp120 interaction is probably responsible for most of the observed antiviral activity of SPs toward HIV infection of lymphocytes. However, HIV infection and gp120 binding to monocytes was unaffected by SPs, probably because SPs were unable to block the CD4-gp 120 interaction in monocytes.