Energy dependency of glucocorticoid exacerbation of gp120 neurotoxicity

2022 ISPNE Bruce McEwen Lifetime Achievement award: Stress, from molecules to societies

The International Society for Psychoneuroendocrinology meeting in Chicago in 2022 was thrilled to recognize Dr. Robert Sapolsky with the Bruce McEwen Lifetime Achievement award. This is the second year for the award to be named to honor Bruce McEwen and it marks the completion of a special issue edited by Blazej Miziak and Robert Paul Juster in the journal Psychoneuroendocrinology dedicated to Bruce's legacy and the unfathomable contribution of Allostatic Load to the stress field. Yet, as our award winner writes, Bruce's legacy is more than scientific as he was well known for mentorship and being an exemplary person, theorist, and scientist. Perhaps understandably for a career favored by humble introverts and shy reclusives, the science shines in the spotlight and personal reflections are cut to accommodate word count limits. For scholars entering the field, stargazing at larger than life luminaries in the field is thrilling yet intimidating as it feels impossible that these experts have the same doubts and distractions as the rest of us primates. Thus, Psychoneuroendocrinology is thrilled to kick off the first perspectives piece in the Cell to Selves series with Dr. Robert Sapolsky sharing that, like his Baboon troops in Kenya, he too sometimes has a bad-hair day. This paper is a written version of a lecture I gave on September 8th, 2022, when receiving the first Bruce McEwen Lifetime Achievement Award from the ISPNE. This was a bittersweet honor; Bruce was my graduate advisor at Rockefeller University and over the next forty years, he was my mentor, teacher and father figure. His death in 2020 left a hole in my life.

Glucocorticoids, metabolism and brain activity

The review integrates different experimental approaches including biochemistry, c-Fos expression, microdialysis (glutamate, GABA, noradrenaline and serotonin), electrophysiology and fMRI to better understand the effect of elevated level of glucocorticoids on the brain activity and metabolism. The available data indicate that glucocorticoids alter the dynamics of neuronal activity leading to context-specific changes including both excitation and inhibition and these effects are expected to support the task-related responses. Glucocorticoids also lead to diversification of available sources of energy due to elevated levels of glucose, lactate, pyruvate, mannose and hydroxybutyrate (ketone bodies), which can be used to fuel brain, and facilitate storage and utilization of brain carbohydrate reserves formed by glycogen. However, the mismatch between carbohydrate supply and utilization that is most likely to occur in situations not requiring energy-consuming activities lead to metabolic stress due to elevated brain levels of glucose. Excessive doses of glucocorticoids also impair the production of energy (ATP) and mitochondrial oxidation. Therefore, glucocorticoids have both adaptive and maladaptive effects consistently with the concept of allostatic load and overload.

5α-reduced progestogens ameliorate mood-related behavioral pathology, neurotoxicity, and microgliosis associated with exposure to HIV-1 Tat

Human immunodeficiency virus (HIV) is associated with motor and mood disorders, likely influenced by reactive microgliosis and subsequent neural damage. We have recapitulated aspects of this pathology in mice that conditionally express the neurotoxic HIV-1 regulatory protein, trans-activator of transcription (Tat). Progestogens may attenuate Tat-related behavioral impairments and reduce neurotoxicity in vitro, perhaps via progesterone's 5α-reductase-dependent metabolism to the neuroprotective steroid, allopregnanolone. To test this, ovariectomized female mice that conditionally expressed (or did not express) central HIV-1 Tat were administered vehicle or progesterone (4mg/kg), with or without pretreatment of a 5α-reductase inhibitor (finasteride, 50mg/kg). Tat induction significantly increased anxiety-like behavior in an open field, elevated plus maze and a marble burying task concomitant with elevated protein oxidation in striatum. Progesterone administration attenuated anxiety-like effects in the open field and elevated plus maze, but not in conjunction with finasteride pretreatment. Progesterone also attenuated Tat-promoted protein oxidation in striatum, independent of finasteride pretreatment. Concurrent experiments in vitro revealed Tat (50nM)-mediated reductions in neuronal cell survival over 60h, as well as increased neuronal and microglial intracellular calcium, as assessed via fura-2 AM fluorescence. Co-treatment with allopregnanolone (100nM) attenuated neuronal death in time-lapse imaging and blocked the Tat-induced exacerbation of intracellular calcium in neurons and microglia. Lastly, neuronal-glial co-cultures were labeled for Iba-1 to reveal that Tat increased microglial numbers in vitro and co-treatment with allopregnanolone attenuated this effect. Together, these data support the notion that 5α-reduced pregnane steroids exert protection over the neurotoxic effects of HIV-1 Tat.

Saikosaponin D acts against corticosterone-induced apoptosis via regulation of mitochondrial GR translocation and a GR-dependent pathway

Saikosaponin D is an agonist of the glucocorticoid receptor (GR), and our preliminary study showed that it possesses neuroprotective effects in corticosterone-treated PC12 cells. However, further proof is required, and the molecular mechanisms of this neuroprotection remain unclear. This study sought to further examine the cytoprotective efficiency and potential mechanisms of action of Saikosaponin D in corticosterone-treated PC12 cells. The cells were treated with 250 μM corticosterone in the absence or presence of Saikosaponin D for 24 h; cell viability was then determined, and Hoechst 33342/propidium iodide (PI) and annexin/PI double staining, and TUNEL staining were performed. Next, mPTP, MMP, [Ca(2+)]i, translocation of the GR to the nucleus and Western blot analyses for caspase-3, caspase-9, cytochrome C, GR, GILZ, SGK-1, NF-Κb (P65), IκB-α, Bad, Akt, Hsp90 and HDAC-6 were investigated. The neuroprotective effects of Saikosaponin D were further confirmed by Hoechst 33342/PI, annexin/PI and TUNEL staining assays. These additional data suggested that Saikosaponin D partially reversed the physiological changes induced by corticosterone by inhibiting the translocation of the GR to the mitochondria, restoring mitochondrial function, down-regulating the expression of pro-apoptotic-related signalling events and up-regulating anti-apoptotic-related signalling events. These findings suggest that SSD exhibited its anti-apoptotic effects via differential regulation of mitochondrial and nuclear GR translocation, partial reversal of mitochondrial dysfunction, inhibition of the mitochondrial apoptotic pathway, and selective activation of the GR-dependent survival pathway.

Direct effects of corticosterone on ATP production by mitochondria from immortalized hypothalamic GT1-7 neurons

Glucocorticoids are known to decrease intracellular ATP levels in the brain. This study was performed to investigate whether corticosterone at physiological levels depresses mitochondrial ATP production by directly acting on mitochondria. Mitochondria were isolated from immortalized hypothalamic GT1-7 neurons. ATP levels were determined using a luciferase-luciferin assay. When malate, alpha-ketoglutarate or pyruvate was used as a respiration substrate, corticosterone at > or =100 nM decreased ATP production by 10%. In contrast, corticosterone did not affect ATP production when succinate or N,N,N',N'-tetramethyl-p-phenylenediamine+ascorbate were used. To investigate the specificity of corticosterone inhibition, we examined several steroids. All steroids tested suppressed mitochondrial ATP production by 10% at a concentration of 100 nM, in a manner similar to that of corticosterone. To examine the effects of corticosterone on GT1-7 cell physiology, we incubated GT1-7 cells with t-butyl hydroperoxide (t-BuOOH) with corticosterone. Corticosterone largely enhanced t-BuOOH-induced cell death. These results indicate that corticosterone non-specifically inhibits mitochondrial ATP production by suppressing electron transfer from NADH to the electron transfer chain through complex I. Partial inhibition of mitochondrial ATP production by corticosterone may contribute to oxidative stress-induced cell death.

The impact of environmental risk factors on HIV-associated cognitive decline in children

Both the human immunodeficiency virus (HIV) and environmental stress have been independently associated with decreased cognitive functioning in children. Given that they are also known to have a strong relationship with each other, the present study sought to test the hypothesis that children in conditions of high environmental risk would be at greater risk for the cognitive complications related to immunosuppression. A retrospective review was conducted to examine the records of 141 children treated at a large pediatric AIDS clinic from 1993 to 2000. CD4+ lymphocyte levels were recorded from laboratory results and IQ scores were recorded from routine psychological evaluations. Key indicators of environmental risk were collected and combined into one measure of overall environmental risk. Pearson product moment correlations were conducted to examine the relationship between environmental risk, age-adjusted CD4 and IQ. Results indicated a significant correlation between CD4 and IQ, with higher levels of immunocompetence predicting higher IQ scores. When subjects were dichotomized based on their environmental risk score, there was no relationship between CD4 count and IQ in the low environmental risk group. In contrast, CD4 was positively associated with IQ in the high environmental risk group. It is proposed that this may be due to gp120 levels in immunocompromised children being particularly toxic to the hippocampus and cortex under conditions of high stress but not so under conditions of low stress.

The dynamic localization of the glucocorticoid receptor in rat C6 glioma cell mitochondria

Glucocorticoids modify gene expression via the translocation of receptors from the cytosol to the nucleus following agonist-associated receptor activation. In this study, we have characterized mitochondrial glucocorticoid (GR) localization and associated translocation kinetics in the C6 mouse glioma cell line. Treatment of the cells, which were cultured in steroid-depleted culture medium, with the GR agonist dexamethasone (dex) resulted in a dramatic decrease in mitochondrial GR levels in parallel with those of the cytosolic receptor. The effect was not observed in isolated intact mitochondria suggesting that the effect is unlikely to be direct but is rather a component of the combined cellular response to GR activation. A marked stimulation of the expression of the mitochondrially-encoded cytochrome oxidase-1 (COX-1) gene was found following GR activation and its export from mitochondria. The effects were inhibited by RU486. Therefore, GR is likely to have a functional role at the level of the mitochondria within intact cells.

Effects of glucocorticoids in the gp120-induced inhibition of glutamate uptake in hippocampal cultures

Studies examining the development of AIDS Related Dementia have concentrated on neurotoxic properties of the HIV viral coat protein, gp120. We have previously shown that this neurotoxicity can be exacerbated by glucocorticoids (GCs), the stress hormones secreted by the adrenal. Moreover, GCs also worsen several of the mechanisms mediating gp120 neurotoxicity, such as increased calcium flux, ROS generation, and energy depletion. Gp120 interferes with the reuptake of glutamate in glia cultures, another possible mechanism by which it can be neurotoxic. This paper examines the role of GCs in exacerbating this phenomenon. It was found that while GCs do not exacerbate the decrease in reuptake of glutamate in glia cultures, they do enhance the decrease in mixed neuronal cultures and this latter effect appears to be energy-dependent.

Protection against gp120-induced neurotoxicity by an array of estrogenic steroids

gp120, the coat protein of HIV, can be neurotoxic and is thought to contribute to AIDS-related dementia complex. Such toxicity involves activation of glutamate receptors, mobilization of free cytosolic calcium, and generation of oxygen radicals. We have previously shown that the estrogen 17beta-estradiol, in concentrations of 100 nM or higher, lessens the neurotoxicity of gp120 in hippocampal and cortical cultures, blunts gp120-induced calcium mobilization, and lessens the oxidative consequences. In this study, we examined the protective potential of other estrogens. We found gp120 neurotoxicity in hippocampal cultures to be significantly lessened by estrone, equilin and estriol, although with an order of magnitude less potent than 17beta-estradiol. We also found all four estrogens to blunt gp120-induced calcium mobilization, with estriol being more efficacious than the other three estrogens. These findings give insight both into the mechanisms of estrogenic protection (e.g. receptor-dependent versus independent actions) as well as into the potential therapeutic use of estrogens against AIDS-related dementia complex.

Mixed lineage kinase 3 mediates gp120IIIB-induced neurotoxicity

Overexpression of gp120, the major coat protein of the HIV-1 virus, in central glial cells, or treatment of neurons with gp120 in culture, produces apoptotic neuronal death. Here we demonstrate that CEP-1347 (KT7515), an inhibitor of mixed lineage kinase 3 (MLK3), an upstream activator of JNK, inhibits gp120IIIB-induced apoptosis of hippocampal neurons. Furthermore, expression of wild type MLK3 in hippocampal pyramidal neurons enhanced gp120IIIB-induced neurotoxicity, whereas expression of a dominant negative MLK3 protected neurons from the toxic effects of the glycoprotein. These results indicate a role for MLK3 signaling in gp120IIIB-induced neuronal death, and suggest potential clinical utility of CEP-1347 in inhibiting the progression of AIDS dementia.

Effect of GP120 on glutathione peroxidase activity in cortical cultures and the interaction with steroid hormones

GP120 (the protein component of the HIV viral coat) is neurotoxic and may contribute to the cell loss associated with AIDS-related dementia. Previously, it has been shown in rat cortical mixed cultures that gp120 increased the accumulation of hydrogen peroxide and superoxide, two reactive oxygen species (ROS). We now demonstrate that gp120 increased activity of the key antioxidant glutathione peroxidase (GSPx), presumably as a defensive mechanism against the increased ROS load. Both estrogen and glucocorticoids (GCs), the adrenal steroid released during stress, blunted this gp120 effect on GSPx activity. The similar effects of estrogen and of GCs are superficially surprising, given prior demonstrations that GCs exacerbated and estrogens protected against gp120 neurotoxicity. We find that these similar effects of estrogen and GCs on GSPx regulation arose, in fact, from very different routes, which are commensurate with these prior reports. Specifically, estrogen has demonstrated antioxidant properties that may prevent the ROS increase (therefore acting as a neuroprotective agent) and rendered unnecessary the compensatory GSPx increased activity. To verify this we have added H2O2 to estrogen + gp120-treated cells, and GSPx activity was increased. However, with addition of H2O2 to GCs + gp120-treated cells there was no increase in activity. GCs appeared to decrease enzyme production and or activity and therefore under insult conditions ROS levels rose in the cell resulting in increased neurotoxicity. Overexpression of GSPx enzyme via herpes vector system reversed the GCs-induced loss of enzyme and eliminated the GCs exacerbation of gp120 neurotoxicity.

Glucocorticoids exacerbate peroxynitrite mediated potentiation of glucose deprivation-induced death of rat primary astrocytes

Glucocorticoids have been implicated in the exacerbation of several types of neurotoxicity in various neuropathological situations. In this study, we investigated the effect of a glucocorticoid dexamethasone on glucose deprivation induced cell death of immunostimulated rat primary astrocytes, which is dependent on the production of peroxynitrite from the immunostimulated cells [Choi et al. Glia, 31(2001) 155-164; J. Neuroimmunol. 112 (2001) 55-62]. Glucose deprivation in immunostimulated rat primary astrocytes results in the release of lactate dehydrogenase (LDH) after 5 h and co-treatment with dexamethasone (1-1000 nM) dose-dependently increased LDH release. Treatment of the exogenous peroxynitrite generator SIN-1 (20 microM), plus glucose deprivation, also increased LDH release after 6 h and co-treatment with dexamethasone dose-dependently increased LDH release. A glucocorticoid receptor antagonist, RU-486, reversed the potentiation of cell death by dexamethasone. Glucose deprivation in immunostimulated cells decreased the intracellular ATP levels, which preceded LDH release from the cell, and co-treatment with dexamethasone dose-dependently potentiated the depletion of intracellular ATP levels. In addition, dexamethasone further deteriorated SIN-1 plus glucose deprivation-induced decrease in mitochondrial transmembrane potential in rat primary astrocytes, which was reversed by RU-486. The results from the present study suggest that glucocorticoids may be detrimental to astrocytes in situations where activation of glial cells are observed, including ischemia and Alzheimer's disease, by mechanisms involving depletion of intracellular ATP levels and deterioration of mitochondrial transmembrane potentials.

Dexamethasone induces limited apoptosis and extensive sublethal damage to specific subregions of the striatum and hippocampus: implications for mood disorders

It has been shown previously that the synthetic corticosteroid dexamethasone induces apoptosis of granule cells in the dentate gyrus and striatopallidal neurons in the dorsomedial caudate-putamen. We investigated whether or not dexamethasone can induce damage to other neuronal populations. This issue was addressed using OX42 immunohistochemistry to visualise activated microglia and thereby gauge the extent of dexamethasone-induced neuronal death. A single dose of dexamethasone (20mg/kg, i.p.) administered to young male Sprague-Dawley rats induced a strong microglial reaction which was restricted to the striatum, the dentate gyrus and all of the CA subfields of the hippocampus. Some OX42-immunoreactive cells were also seen in the lateral septal nucleus. Subsequent quantitative analysis of silver/methenamine-stained sections confirmed that acute administration of dexamethasone induced apoptosis in the striatum and all regions of the hippocampus at doses as low as 0.7mg/kg. In contrast, dexamethasone failed to induce apoptosis in the lateral septal nucleus at doses up to 20mg/kg. The levels of dexamethasone-induced striatal and hippocampal apoptosis were attenuated by pretreatment with the corticosteroid receptor antagonist RU38486 (Mifepristone), which implies that the cell death was mediated by a corticosteroid receptor-dependent process. We further determined whether dexamethasone induced sublethal damage to neurons by quantifying reductions in the number of microtubule-associated protein-2-immunoreactive striatal and hippocampal cells following injection of the corticosteroid. Dexamethasone induced dramatic decreases in the striatum, with the dorsomedial caudate-putamen being particularly affected. Similar damage was seen in the hippocampus, with the dentate gyrus and CA1 and CA3 subfields being particularly vulnerable.Equivalent corticosteroid-induced neuronal damage may occur in mood disorders, where the levels of endogenous corticosteroids are often raised. Corticosteroid-induced damage of striatal and hippocampal neurons may also account for some of the cognitive deficits seen following administration of the drugs to healthy volunteers.

HIV-1-associated central nervous system dysfunction

Despite more than 15 years of extensive investigative efforts, a complete understanding of the neurological consequences of HIV-1 CNS infection remains elusive. Although the resources of numerous investigators have been focused on studies of HIV-1-associated CNS disease, the complex nature of the disease processes that underlie the clinical, pathological, and cellular manifestations of HIV-1 CNS infection have required a larger volume of studies than was initially envisioned. Several major areas remain as the focus of current research efforts. One of the more pressing issues facing researchers and clinicians alike is the search for correlates to the development of HIV-1-associated CNS neuropathology and the onset of HIVD. Although numerous parameters have been studied, none have been shown to be absolute predictors or markers of HIV-1-related CNS dysfunction. The identification of solid correlates of HIVD is an important goal that would permit clinical identification of individuals at risk for developing potentially crippling, life-threatening CNS abnormalities and would facilitate early treatment of nascent neurological problems. A more complete comprehension of the cellular foundations of CNS dysfunction and HIVD is also a fundamental part of strategies designed to treat or prevent HIV-1-associated CNS disease. Future investigations will strive to expand the body of knowledge concerning the complex interactions between infected and uninfected neuroglial cells and the roles of numerous cytokines, chemokines, and other soluble agents that are deregulated during HIV-1 CNS infection. In particular, a thorough understanding of the mechanisms of neurotoxicity may facilitate the development of new therapies that alleviate or eliminate the clinical consequences of CNS infection. Finally, investigators will continue to study HIVD within the context of single and combination drug therapies used in the treatment of HIV-1 infection and AIDS. As newer and more effective systemic treatments for HIV-1 infection and AIDS are introduced, the effects of these treatments on the onset, incidence, and severity of HIVD will also require intensive study. The impact of drug therapies on the ability of the CNS to act as an HIV-1 reservoir will also need to be addressed. Introduction of each new drug or drug combination will necessitate studies of drug penetration into the CNS and efficacy against the development of CNS abnormalities. Furthermore, as more effective treatments prolong the lifespan of individuals infected with HIV-1, the impact of extended survival on the occurrence and severity of HIVD will also require further investigations. The quest for answers to these and other questions will be complicated by the diversity of experimental systems used to study different aspects of HIV-1 CNS infection and HIVD. Each system has its own unique strengths and weaknesses. Clinical observations provide a continuous spectrum of symptomatic findings but reveal little about the underlying mechanisms of disease. In vivo imaging techniques, such as CT and MRI, also provide a continuum of observations, but the images are limited in their resolution. Neuropathological examinations of postmortem HIV-1-infected brains offer gross, cellular, and molecular views (including phenotypic and genotypic analyses of CNS viral isolates) of the diseased brain, but only provide a snapshot of the end-stage neurologic dysfunction. Studies that rely on animal surrogates for HIV-1, including SIV, simian-HIV (SHIV), feline immunodeficiency virus (FIV), visna virus, and HIV-1 SCID-hu models, permit experimental protocols that cannot be carried out in humans, but are limited by the fidelity with which each virus and animal model emulates the conditions and events observed in the human host. Finally, in vitro techniques, which include the use of primary cells and cell lines, adult or fetal human cell cultures, and BBB barrier model systems, are also convenient means by which aspe

Neuronal glycolytic pathway impairment induced by HIV envelope glycoprotein gp120

Neurological impairment is a common feature of Acquired Immunodeficiency Syndrome (AIDS); functional alterations have been reported both in central and peripheral nervous system and the Human Immunodeficiency Virus (HIV) envelope glycoprotein gp120 has been proposed as a neurotoxin acting through a calcium-dependent mechanism. On the other hand it has been reported that gp120 treatment also induce about a 20% decrease in the cerebral glucose utilization and in the cellular ATP levels. The reported observations were performed on experimental system where also non-neuronal cells where present; in order to evaluate whether a direct interaction between HIV proteins and neuronal cells takes place, we used a neuroblastoma cultures where only neuronal cells are present. We analysed the effects of gp120 on the N18TG2 neuroblastoma clone. Treatments were performed both on growing and confluent cultures. Short time treatment with gp120 of confluent cultures causes a 25% reduction in the level of neuron-specific enolase, resulting in a similar decrease of oxygen consumption. Long time exposure of growing cells also causes a reduction in cell survival. Furthermore, using a membrane-specific fluorescent probe we observed that gp120 produces an increase of membrane trafficking. These observations suggest a direct interaction between the viral envelope protein and neuronal cells, which results in an alteration of glycolytic metabolism. This alteration may be related to the neurologic impairments observed in AIDS patients.

The effects of steroid hormones in HIV-related neurotoxicity: a mini review

This review examines the interaction of steroid hormones, glucocorticoids and estrogen, and gp120, a possible causal agent of acquired immune deficiency syndrome-related dementia complex. The first part of the review examines the data and mechanisms by which gp120 may cause neurotoxicity and by which these steroid hormones effect cell death in general. The second part of the review summarizes recent experiments that show how these steroid hormones can modulate the toxic effects of gp120 and glucocorticoids exacerbating toxicity, and estrogen decreasing it. We then examine the limited in vivo and clinical data relating acquired immune deficiency syndrome-related dementia complex and steroid hormones and speculate on the possible clinical significance of these findings with respect to acquired immune deficiency syndrome-related dementia complex.

Glucocorticoids exacerbate the deleterious effects of gp120 in hippocampal and cortical explants

Glucocorticoids (GCs), the adrenal steroids secreted during stress, can compromise the ability of hippocampal neurons to survive numerous necrotic insults. We have previously observed that GCs worsen the deleterious effects of gp120, the glycoprotein of the acquired immune deficiency syndrome virus, which can indirectly damage neurons and which is thought to play a role in the neuropathological features of human immunodeficiency virus infection. Specifically, GCs augment gp120-induced calcium mobilization, ATP depletion, decline in mitochondrial potential, and neurotoxicity in fetal monolayer cultures from a number of brain regions. In the present report, we demonstrate a similar gp120/GC synergy in adult hippocampal and cortical explants. We generated explants from rats that were either adrenalectomized, adrenally intact, or intact and treated with corticosterone to produce levels seen in response to major stressors. Metabolic rates in explants were then indirectly assessed with silicon microphysiometry, and cytosolic calcium concentrations were assessed with fura-2 fluorescent microscopy. We observed that basal levels of GCs tonically augment the disruptive effects of gp120 on metabolism in the CA1 cell field of the hippocampus and in the cortex. Moreover, raising GC concentrations into the stress range exacerbated the ability of gp120 to mobilize cytosolic calcium in a number of hippocampal cell fields. Finally, we observed that the synthetic GC prednisone had similarly exacerbating effects on gp120. Thus, GCs can worsen the deleterious effects of gp120 in a system that is more physiologically relevant than the fetal monolayer culture and in a region-specific manner.

Glucocorticoid modulation of gp120-induced effects on calcium-dependent degenerative events in primary hippocampal and cortical cultures

The HIV coat protein gp120 has been implicated in damaging the nervous system and may play a role in AIDS-related dementia complex. The glycoprotein triggers the release of a glutamatergic agent from infected microglia and macrophages, causing NMDA receptor- and calcium-dependent excitotoxic damage to neurons. We have previously shown that glucocorticoids, the adrenal steroids secreted during stress, worsen gp120 neurotoxicity and calcium mobilization in various brain regions. This study explores events down-stream of gp120-induced calcium mobilization, specifically, generation of reactive oxygen species (ROS) and subsequent lipid peroxidation, destruction of the cytoskeleton through spectrin proteolysis, and the glucocorticoid modulation of these events in primary hippocampal cultures. We observe that 200 pM gp120 causes a significant accumulation of ROS, including superoxide, and of lipid peroxidation. Counter to our predictions, pretreatment with the glucocorticoid corticosterone (CORT) did not worsen the effects of gp120 on ROS accumulation, but did increase lipid peroxidation. We also observed that neither gp120 alone nor gp120 plus CORT caused detectable proteolysis of the cytoskeletal protein spectrin, whose breakdown has been shown to be a damaging consequence of calcium excess in other models of necrotic neuronal injury.

Quantification of neuron survival in monolayer cultures using an enzyme-linked immunosorbent assay approach, rather than by cell counting

The determination of neurotoxicity in monolayer mixed cultures has traditionally necessitated the time consuming and subjective procedure of counting neurons. In this paper, we propose a modification of an immunohistochemical staining method with a neuron-specific antibody against MAP2, that allows for quantification of neuron number to be done using an enzyme-linked immunosorbent assay (ELISA) plate reader. This new procedure involves the use of the compound 2,3'-azino-bis(ethylbenzothiazoline-6-sulphonic acid) (ABTS) at the last stage of the staining procedure. We employed two neurotoxicity models (the excitotoxin kainic acid and the interactions between gp120, the glycoprotein of HIV, and the stress hormone corticosterone) to compare the results obtained with this new method and the old method of immunohistochemical staining followed by 3,3'-daminobenzidine (DAB) and the counting of neurons. The ABTS/ELISA method was found to be a fast, reliable and objective procedure for the quantification of neurotoxicity.

Glucocorticoids interact with gp120 in causing neurotoxicity in striatal cultures

A significant subset of HIV-positive patients suffer from AIDS-Related Dementia Complex (ADC), an array of neurologic and neuropsychologic impairments. The HIV coat protein gp120 has been implicated in the deleterious neurologic consequences of HIV infection, damaging neurons through a glutamatergic and calcium-dependent pathway. We have previously reported that glucocorticoids, the adrenal steroids secreted during stress, can exacerbate the neurotoxic and calcium-mobilizing effects of gp120 in hippocampal and cortical cultures. Because both the symptomatology of ADC, as well as the neuropathologic profile of post-mortem HIV brains suggests an involvement of the striatum, we examined whether glucocorticoids could also augment the damaging effects of gp120 in primary striatal cultures. We observe that neither gp120 nor the glucocorticoid corticosterone, when administered alone, cause neurotoxicity or mobilization of free cytosolic calcium; however, a combination of the two caused significant toxicity and neuron death. This, along with our prior findings of gp120-glucocorticoid interactions, is striking, given the heavy clinical use of synthetic glucocorticoids for management of pulmonary complications of HIV infection.