Relationship of lead-induced proteins to stress response proteins in astroglial cells

Heme oxygenase-1 dysregulation in the brain: implications for HIV-associated neurocognitive disorders

Heme oxygenase-1 (HO-1) is a highly inducible and ubiquitous cellular enzyme that subserves cytoprotective responses to toxic insults, including inflammation and oxidative stress. In neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis, HO-1 expression is increased, presumably reflecting an endogenous neuroprotective response against ongoing cellular injury. In contrast, we have found that in human immunodeficiency virus (HIV) infection of the brain, which is also associated with inflammation, oxidative stress and neurodegeneration, HO-1 expression is decreased, likely reflecting a unique role for HO-1 deficiency in neurodegeneration pathways activated by HIV infection. We have also shown that HO-1 expression is significantly suppressed by HIV replication in cultured macrophages which represent the primary cellular reservoir for HIV in the brain. HO-1 deficiency is associated with release of neurotoxic levels of glutamate from both HIV-infected and immune-activated macrophages; this glutamate-mediated neurotoxicity is suppressed by pharmacological induction of HO-1 expression in the macrophages. Thus, HO-1 induction could be a therapeutic strategy for neuroprotection against HIV infection and other neuroinflammatory brain diseases. Here, we review various stimuli and signaling pathways regulating HO-1 expression in macrophages, which could promote neuronal survival through HO-1-modulation of endogenous antioxidant and immune modulatory pathways, thus limiting the oxidative stress that can promote HIV disease progression in the CNS. The use of pharmacological inducers of endogenous HO-1 expression as potential adjunctive neuroprotective therapeutics in HIV infection is also discussed.

Synergistic effects of toxic elements on heat shock proteins

Heat shock proteins show remarkable variations in their expression levels under a variety of toxic conditions. A research span expanded over five decades has revealed their molecular characterization, gene regulation, expression patterns, vast similarity in diverse groups, and broad range of functional capabilities. Their functions include protection and tolerance against cytotoxic conditions through their molecular chaperoning activity, maintaining cytoskeleton stability, and assisting in cell signaling. However, their role as biomarkers for monitoring the environmental risk assessment is controversial due to a number of conflicting, validating, and nonvalidating reports. The current knowledge regarding the interpretation of HSPs expression levels has been discussed in the present review. The candidature of heat shock proteins as biomarkers of toxicity is thus far unreliable due to synergistic effects of toxicants and other environmental factors. The adoption of heat shock proteins as "suit of biomarkers in a set of organisms" requires further investigation.

Induction of heme oxygenase-1 can halt and even reverse renal tubule-interstitial fibrosis

Background

The tubule-interstitial fibrosis is the hallmark of progressive renal disease and is strongly associated with inflammation of this compartment. Heme-oxygenase-1 (HO-1) is a cytoprotective molecule that has been shown to be beneficial in various models of renal injury. However, the role of HO-1 in reversing an established renal scar has not yet been addressed.

Aim

We explored the ability of HO-1 to halt and reverse the establishment of fibrosis in an experimental model of chronic renal disease.

Methods

Sprague-Dawley male rats were subjected to unilateral ureteral obstruction (UUO) and divided into two groups: non-treated and Hemin-treated. To study the prevention of fibrosis, animals were pre-treated with Hemin at days -2 and -1 prior to UUO. To investigate whether HO-1 could reverse established fibrosis, Hemin therapy was given at days 6 and 7 post-surgery. After 7 and/or 14 days, animals were sacrificed and blood, urine and kidney tissue samples were collected for analyses. Renal function was determined by assessing the serum creatinine, inulin clearance, proteinuria/creatininuria ratio and extent of albuminuria. Arterial blood pressure was measured and fibrosis was quantified by Picrosirius staining. Gene and protein expression of pro-inflammatory and pro-fibrotic molecules, as well as HO-1 were performed.

Results

Pre-treatment with Hemin upregulated HO-1 expression and significantly reduced proteinuria, albuminuria, inflammation and pro-fibrotic protein and gene expressions in animals subjected to UUO. Interestingly, the delayed treatment with Hemin was also able to reduce renal dysfunction and to decrease the expression of pro-inflammatory molecules, all in association with significantly reduced levels of fibrosis-related molecules and collagen deposition. Finally, TGF-β protein production was significantly lower in Hemin-treated animals.

Conclusion

Treatment with Hemin was able both to prevent the progression of fibrosis and to reverse an established renal scar. Modulation of inflammation appears to be the major mechanism behind HO-1 cytoprotection.

Reduction of myeloid suppressor cell derived nitric oxide provides a mechanistic basis of lead enhancement of alloreactive CD4(+) T cell proliferation

The persistent environmental toxicant and immunomodulator, lead (Pb), has been proposed to directly target CD4(+) T cells. However, our studies suggest that CD4(+) T cells are an important functional, yet indirect target. In order to identify the direct target of Pb in the immune system and the potential mechanism of Pb-induced immunotoxicity, myeloid suppressor cells (MSCs) were evaluated for their ability to modulate CD4(+) T cell proliferation after Pb exposure. Myeloid suppressor cells regulate the adaptive immune response, in part, by inhibiting the proliferation of CD4(+) T cells. It is thought that the mechanism of MSC-dependent regulation involves the release of the bioactive gas, nitric oxide (NO), blocking cell signaling cascades downstream of the IL-2 receptor and thus preventing T cells from entering cell-cycle. In mixed lymphocyte culture (MLC), increasing numbers of MSCs suppressed T cell proliferation in a dose-dependent manner, and this suppression is strikingly abrogated with 5 microM lead (Pb) treatment. The Pb-sensitive MSC population is CD11b(+), GR1(+)and CD11c(-) and thus phenotypically consistent with MSCs described in other literature. Inhibition of NO-synthase (NOS), the enzyme responsible for the production of NO, enhanced alloreactive T cell proliferation in MLC. Moreover, Pb attenuated NO production in MLC, and exogenous replacement of NO restored suppression in the presence of Pb. Significantly, MSC from iNOS-/- mice were unable to suppress T cell proliferation. An MSC-derived cell line (MSC-1) also suppressed T cell proliferation in MLC, and Pb disrupted this suppression by attenuating NO production. Additionally, Pb disrupted NO production in MSC-1 cells in response to treatment with interferon-gamma (IFN-gamma) and LPS or in response to concanavalin A-stimulated splenocytes. However, neither the abundance of protein nor levels of mRNA for the inducible isoform of NOS (iNOS) were altered with Pb treatment. Taken together these data suggest that Pb abrogates an MSC-dependent suppression of alloreactive T cell proliferation by inhibiting the function, but not the expression of iNOS.

Induction of Hsp22 (HspB8) by estrogen and the metalloestrogen cadmium in estrogen receptor-positive breast cancer cells

Estrogen (E2) plays a critical role in the etiology and progression of human breast cancer. The estrogenic response is complex and not completely understood, including in terms of the involved responsive genes. Here we show that Hsp22 (synonyms: HspB8, E2lG1, H11), a member of the small heat shock protein (sHSP) superfamily, was induced by E2 in estrogen receptor-positive MCF-7 breast cancer cells, resulting in an elevated Hsp22 protein level, whereas it was not induced in estrogen receptor-negative MDA-MB-231 cells. This induction was prevented by the pure anti-estrogen ICI182780 (faslodex, fulvestrant), whereas tamoxifen, a substance with mixed estrogenic and antiestrogenic properties, had no major inhibitory effect on this induction, nor did it induce Hsp22 on its own. Cadmium (Cd) is an environmental pollutant with estrogenic properties (metalloestrogen) that has been implicated in breast cancer. Treatment of MCF-7 cells with Cd also resulted in induction of Hsp22, and this induction was also inhibited by ICI182780. In live MCF-7 cells, Hsp22 interacted at the level of dimers with Hsp27, a related sHSP, as was shown by quantitative fluorescence resonance energy transfer measurements. In cytosolic extracts of MCF-7 cells, most of the E2- and Cd-induced Hsp22 was incorporated into high-molecular mass complexes. In part, Hsp22 and Hsp27 were components of distinct populations of these complexes. Finally, candidate elements in the Hsp22 promoter were identified by sequence analysis that could account for the induction of Hsp22 by E2 and Cd. Taken together, Hsp22 induction represents a new aspect of the estrogenic response with potential significance for the biology of estrogen receptor-positive breast cancer cells.

Effects of N-acetylcysteine on lead-exposed PC-12 cells

The neurotoxicity of lead has been well established through numerous studies. However, the cellular processes of lead neurotoxicity, as well as techniques to prevent or reverse cellular damage after lead exposure, remain unknown. If oxidative stress plays a primary role in lead-induced neurotoxicity, antioxidants should assist in reviving lead-exposed cells. The present study explores N-acetylcysteine (NAC) as an antioxidant agent in PC-12 cells after lead exposure. Selective oxidative stress parameters, including glutathione (GSH), glutathione disulfide (GSSG), and malondialdehyde (MDA), were measured in PC-12 cells exposed to various concentrations of lead acetate. Administering NAC after lead exposure improved cell survival as measured by Trypan Blue exclusion. NAC treatment also increased the GSH/GSSG ratio compared to the lead-only group, and reduced MDA to near control levels. These results imply that NAC protects cells from lead-induced oxidative damage by boosting the PC-12 cells' antioxidant defense mechanisms.

Arsenite pre-conditioning reduces UVB-induced apoptosis in corneal epithelial cells through the anti-apoptotic activity of 27 kDa heat shock protein (HSP27)

Exposure to ultraviolet (UV) light poses a health risk for eye disease, and solar ultraviolet in the B range (UVB, 280-320 nm) is known to be related to various corneal disorders. In this study, we investigated whether pre-conditioning of cells with arsenite (AsO2(-1)) can reduce UVB-induced apoptosis in human corneal epithelial cells, and whether the anti-apoptotic activity of 27 kDa heat shock protein (HSP27), a small heat shock protein, plays a role in this protection. UVB at levels comparable to physiologic solar exposure induces apoptosis of corneal epithelial cells in culture, demonstrated by activation of caspase 9 and caspase 3, and DNA fragmentation. When cells were pre-conditioned with arsenite prior to UVB exposure, the UVB-induced cell death was reduced, and UVB-induced activation of caspases and DNA fragmentation was inhibited. When cells were pre-treated with SB 203580, which inhibits HSP27 phosphorylation through inhibition of p38 MAP kinase activation, the arsenite-induced reduction of UVB-induced apoptosis was partially reversed. Arsenite pre-conditioning inhibited UVB-induced apoptosis in a two-phase pattern, which was temporally correlated with arsenite-induced HSP27 expression and phosphorylation. Neutralization of intracellular HSP27 with its antibody reduced arsenite's inhibition of UVB-induced caspase3 activation. Our results suggest that forms of stress that upregulate HSP27 and its phosphorylation may be useful as novel approaches to prevent adverse ocular effects arising from UV exposure in humans.

Distinct protective mechanisms of HO-1 and HO-2 against hydroperoxide-induced cytotoxicity

Heme oxygenases (HO-1 and HO-2) catalyze the NADPH-cytochrome P(450) reductase (CPR)-dependent degradation of heme into iron, carbon monoxide, and biliverdin, which is reduced into bilirubin. Under basal conditions, HO-1 is often undetected and can be induced by numerous stress conditions. Although HO-2 is constitutively expressed, its activity appears to be regulated by post-translational modifications. HO activity has been associated with cellular protection, by which it degrades heme, a prooxidant, into bioactive metabolites. Under given circumstances, overexpression of HO-1 can render cells more sensitive to free radicals. Here, we investigated the properties of human HO isoforms that protect against oxidative stress. Considering that CPR can be a limiting factor for optimal HO activity, we tested stable HO-1 and HO-2 cell lines that derived from the CPR cells. Results indicate that the HO-1 and HO-2 cells are more resistant than controls to hemin and to the organic tert-butyl hydroperoxide, t-BuOOH. However, HO-1 cells are less resistant than HO-2 cells to hydrogen peroxide (H(2)O(2)). The levels of oxidatively modified proteins of HO-1 and HO-2 cells in response to t-BuOOH toxicity are identical, but the level of oxidatively modified proteins of HO-2 cells is less than that of HO-1 cells in response to H(2)O(2) toxicity. Performing subcellular fractionations revealed that HO-2 and CPR are found together in the microsomal fractions, whereas HO-1 is partially present in the microsome and also found in other fractions, such as the cytosol. These same findings were observed in non-transfected primary neurons where HO-1 proteins were chemically induced with 15-deoxy-Delta(12,14)-prostaglandin J(2) (15dPGJ(2)). The differences in subcellular localization of HO-1 and HO-2 could explain some of the discrepancies in their cellular activity and enzymatic protective mechanisms.

Differential induction of heme oxygenase and other stress proteins in cultured hippocampal astrocytes and neurons by inorganic lead

We examined the effects of exposure to inorganic lead (Pb2+) on the induction of stress proteins in cultured hippocampal neurons and astrocytes, with particular emphasis on the induction of heme oxygenase-1 (HO-1). In radiolabeled neuronal cultures, Pb2+ exposure had no significant effect on the synthesis of any protein at any concentration (up to 250 microM) or duration of exposure (up to 4 days). In radiolabeled astrocyte cultures, however, Pb2+ exposure (100 nM to 100 microM; 1-4 days) increased synthesis of proteins with approximate molecular weights of 23, 32, 45, 57, 72, and 90 kDa. Immunoblot experiments showed that Pb2+ exposure (100 nM to 10 microM, 1-14 days) induces HO-1 synthesis in astrocytes, but not in neurons; this is probably the 32-kDa protein. The other heme oxygenase isoform, HO-2, is present in both neurons and astrocytes, but is not inducible by Pb2+ at concentrations up to 100 microM. HO-1 can be induced by a variety of stimuli. We found that HO-1 induction in astrocytes is increased by combined exposure to Pb2+ and many other stresses, including heat, nitric oxide, H2O2, and superoxide. One of the stimuli that may induce HO-1 is oxidative stress. Lead exposure causes oxidative stress in many cell types, including astrocytes. Induction of HO-1 by Pb2+ is reduced by the hydroxyl radical scavengers dimethylthiourea (DMTU) and mannitol, but not by inhibitors of calmodulin, calmodulin-dependent protein kinases, protein kinase C, or extracellular signal-regulated kinases (ERK). Therefore, we conclude that oxidative stress is an important mechanism by which Pb2+ induces HO-1 synthesis in astrocytes.

Acute lead exposure induces renal haeme oxygenase-1 and decreases urinary Na+ excretion

The effects of acute lead exposure on renal function, lipid peroxidation and the expression of haeme oxygenase (HO) in rat kidney were determined. A single injection of lead acetate (50 mg Pb/kg) was given to rats. Changes in renal function, characterized by a significant reduction in the Na+ excretion was observed six hours after Pb exposure; this effect persisted for 24 hours. TBARS levels increased in kidney cortex 24 hours after Pb administration. In kidney cortex, Pb exposure affected the expression of HO-1, a renal protein associated with oxidative stress. HO-1 mRNA increased 2.3-fold, three hours after Pb administration and remained increased for six, 12 and 24 hours. HO enzymatic activity and HO-1 protein increased six and three hours after Pb administration, respectively, and remained increased at 24 hours. HO inhibition by tin-protoporphyrin, potentiated Pb-induced increase in TBARS and prevented the Pb-induced reduction in Na+ excretion. Our data suggest that Pb may be acting through the generation of oxidant products and induction of HO.

Lead-stimulated p38MAPK-dependent Hsp27 phosphorylation

Lead (Pb2+) is a cytotoxic metal ion whose mechanism of action is not established. However, Pb2+ is known to interact with a wide variety of molecules involved in signal transduction. In this study the effect of Pb2+ on protein phosphorylation in bovine adrenal chromaffin cells and human SH SY5Y cells was examined. Cells were incubated with 32P(i) for 1 h in the presence of Pb2+ (1-10 microM) and the proteins were separated by two-dimensional PAGE. An increase in the phosphorylation of a number of proteins was observed in response to Pb2+, including three spots, MW 25 kDa, and pI's in the range 4.0-4.5. These proteins were immunoidentified as three isoforms of the heat-shock protein 27 kDa (Hsp27), and the identity of the most basic spot was confirmed by amino acid sequencing. Phosphorylation of p38MAPK was increased by Pb2+ and the effect of Pb2+ on Hsp27 phosphorylation was blocked by the p38MAPK inhibitor SB203580 (1 microM). The results were similar for bovine chromaffin cells and human SH SY5Y cells. This is the first report showing that Pb2+ can modulate the phosphorylation state of Hsp27 via activation of the p38MAPK pathway.

The influence of oxidative stress on catalase and MnSOD gene transcription in astrocytes

The brain is particularly vulnerable to oxygen free radicals, which have been implicated in the pathology of several neurological disorders. The antioxidant enzyme (AOE) system of the brain may play an important role in the protection against such oxidative stress. We investigated the influence of oxidative stress on the transcription of catalase and MnSOD mRNA. Primary rat astroglial cell cultures were treated either with hydrogen peroxide (H2O2), as a direct mediator of oxidative stress, or with the redox cycling compound paraquat. Both substances led to an increase of catalase and MnSOD mRNA levels. To further elucidate the mechanisms residing behind this increase, transfection experiments were performed. Transient transfection of primary astroglial cells with a reporter plasmid containing the upstream region of the catalase gene showed a decrease in reporter gene activity after exposure of transfected cells to either H2O2 or paraquat. In contrast, transfection experiments done with reporter plasmids for the MnSOD upstream region resulted in an increase of reporter gene activity after H2O2 as well as after paraquat treatment of transfected cells. These results indicate transcriptional regulation of MnSOD and post-transcriptional regulation of catalase gene expression after oxidative stress in primary rat astrocytes.

Biochemical approaches to studying neurotoxicity

This overview provides an introduction to biochemical analysis of toxicant effects on the nervous system. It includes a brief discussion of the salient features of the nervous system and a review of the various approaches used to detect and identify neurotoxicants and their modes of action.

Induction of heme oxygenase-1 in the brains of scrapie-infected mice

Heme oxygenase-1 (HO-1) is an inducible enzyme that catalyzes the rate-limiting step in the degradation of heme to biliverdin, carbon monoxide and iron, and its expression can be used as a marker for oxidative stress. Oxidative stress has been reported to be associated with neurodegenerative diseases including Alzheimer's disease. It is possible that oxidative stress is also involved in the disease process seen in scrapie, the archetype transmissible spongiform encephalopathy. In this study, we report that HO-1 is significantly increased in the scrapie-infected group compared to an age-matched control group. Immunohistochemistry showed a pronounced increase of immunostaining of this protein in the infected group compared to the minimal amount of staining in the control group. These results support that oxidative stress is closely associated with the pathogenesis of scrapie and that it might contribute to neurodegeneration in this disease.

Effect of lead exposure and accumulation on copper homeostasis in cultured C6 rat glioma cells

C6 rat glioma cells resemble rat astroglia in culture in that both cell types accumulate lead (Pb) intracellularly from the medium. As such, C6 cells are a model for Pb accumulation by the brain. In this study, an increase in intracellular Pb accumulation induced by p-chloromercuribenzoate (PCMB) after exposure to 10 microM Pb acetate suggests a role for sulfhydryl groups in Pb retention. Stimulation of Pb accumulation by nifedipine suggests the entry of Pb into these cells by a novel path. Most of the intracellular Pb from exposure for 7 days to 1 microM Pb was associated with high-molecular weight components in cytosol. Pb exposure increased the abundance of three proteins with the following characteristics on two-dimensional gels: 81 kDa with pI of 5.6, 81 kDa with pI of 4. 9, and 71 kDa with pI of 5.6. The levels of five other proteins, ranging in size from 37-41 kDa with pIs of 6.0-6.8 declined. Exposed C6 cells accumulated copper (Cu) intracellularly, and Cu accumulation after Pb exposure was shown by kinetic analysis with 67Cu to result from an increased uptake and a decreased efflux for Cu. Pb-exposed cells also showed increased Cu binding to membranes, which is consistent with the increase of Cu uptake. These data indicate that intracellular Pb interacts with high molecular weight proteins in C6 cells, and exposure also alters membrane transport properties for copper.

Protective role of heme oxygenase-1 in oxidative stress-induced neuronal injury

Heme oxygenase-1 (HO-1) is a stress protein induced in response to a variety of oxidative challenges. After treatment of the hybrid septal cells SN 56 with beta-amyloid peptide (beta-AP1-40) or hydrogen peroxide (H2O2), we detected high levels of reactive oxygen species, accompanied by a significant elevation in HO-1 expression. Levels of HO-1 increased and then decreased following cell loss. Pretreatment of SN 56 cells with HO-1 antisense oligonucleotides dramatically decreased the immunoreactivity of HO-1 and significantly enhanced the cytotoxicity of beta-AP1-40 and H2O2. In contrast, pretreatment with hemin, an HO-1 inducer, increased the expression of HO-1 and decreased the beta-AP1-40- and H2O2-induced cytotoxicity. These findings support the importance of HO-1 in protecting neurons against oxidative stress-induced injury.

Carboxyhemoglobin elevation in trauma victims

BACKGROUND

Products of the hemeoxygenase enzyme include carboxyhemoglobin (COH) and bilirubin, which have protective effects in stressed states. Hemeoxygenase-1 enzyme up-regulates in states of oxidative stress. We hypothesized that COH is elevated in septic trauma patients compared with nonseptic patients.

METHODS

A prospective study was carried out at a Level I trauma center involving all patients admitted to the trauma intensive care unit. During a 3.5-month period, 45 patients were enrolled, with 76 samples being drawn on admission and at later time points. The samples were classified as septic (Bone's criteria), stressed (based on expired gas analysis), or nonstressed nonseptic. Correlations with Acute Physiology and Chronic Health Evaluation III score, white blood cell count, temperature, partial pressure of oxygen, and percentage of inspired oxygen were evaluated.

RESULTS

COH levels in samples drawn from patients presenting in shock (systolic blood pressure < or =90 mm Hg) were significantly higher than levels in samples from patients not in shock (systolic blood pressure >90 mm Hg) (3.27+/-1.09 vs. 2.75+/-0.64; p = 0.013). Samples from septic patients with infection were associated with significantly higher Injury Severity Scores (34.1+/-11.2 vs. 21.8+/-18.3; p< or =0.05) and a lower percentage of inspired oxygen (41.6+/-10.3 vs. 61.0+/-26.3; p< or =0.05).

CONCLUSION

COH was significantly elevated in samples drawn during stress, sepsis, and shock states. There was overlap between sepsis and stress COH sample values, limiting the clinical usefulness of the assays in predicting sepsis. Further studies focusing on hemeoxygenase-1 expression and the role of its by-products in the outcomes of trauma patients are warranted.

Disruption of the intracellular sulfhydryl homeostasis by cadmium-induced oxidative stress leads to protein thiolation and ubiquitination in neuronal cells

Cadmium is a potent cell poison known to cause oxidative stress by increasing lipid peroxidation and/or by changing intracellular glutathione levels and to affect the ubiquitin/ATP-dependent proteolytic pathway. However, the cellular mechanisms involved in cadmium toxicity are still not well understood, especially in neuronal cells. To investigate the relationship between cadmium-induced oxidative stress and the ubiquitin/ATP-dependent pathway, we treated cultures of neuronal cells with different concentrations of the metal ion. In addition to decreases in glutathione levels, we observed marked increases in protein-mixed disulfides (Pr-SSGs) after exposure of HT4 cells (a mouse neuronal cell line) or rat primary mesencephalic cultures to Cd2+. The increases in intracellular levels of Pr-SSGs were concurrent with increases in the levels of ubiquitinated proteins (Ub proteins) when the HT4 cells were subjected to lower (25 microM or less) concentrations of cadmium. However, higher concentrations of cadmium (50 microM), which were toxic, led to increases in Pr-SSGs but inhibited ubiquitination, probably reflecting inhibition of ubiquitinating enzymes. The cadmium-induced changes in Pr-SSGs and Ub proteins were not affected when more than 85% of intracellular glutathione was removed from the cells by the glutathione synthetase inhibitor L-buthionine-(S,R)-sulfoximine. However, the reducing agent dithiothreitol, which prevented the build up of Pr-SSGs in the cell, also blocked the accumulation of Ub proteins induced by cadmium. In addition, dithiothreitol blocked the effects of the higher toxic (50 microM) concentrations of cadmium on cytotoxicity and on glutathione, Pr-SSGs, and Ub proteins. Together, these results strongly suggest that changes in the levels of intracellular Pr-SSGs and ubiquitin-protein conjugates in neuronal cells are responses closely associated with the disruption of intracellular sulfhydryl homeostasis caused by cadmium-mediated oxidative stress.

Opioids disrupt Ca2+ homeostasis and induce carbonyl oxyradical production in mouse astrocytes in vitro: transient increases and adaptation to sustained exposure

Pharmacologically distinct subpopulations of astroglia express mu, delta, and/or kappa opioid receptors. Activation of mu, delta, or kappa opioid receptors can destabilize intracellular calcium ([Ca2+]i) in astrocytes leading to cellular hypertrophy and reactive injury. To assess whether acute or sustained opioid exposure might adversely affect astroglial function by disrupting Ca2+ homeostasis or by producing reactive oxygen species, fura-2 and a novel fluorescent-tagged biotin-4-amidobenzoic hydrazide reagent, respectively, were used to detect [Ca2+]i and carbonyl oxidation products within individual murine astrocytes. Acute (3 h) exposure to mu; (H-Tyr-Pro-Phe (N-Me) -D-Pro-NH2; PLO17), delta ([D-Pen2, D-Pen5]-enkephalin), and kappa (trans-(+/-)-3, 4-dichloro-N-methyl-N-[2-(1-pyrr olidinyl) cyclohexyl] benzeneacetamide methanesulfonate; U50,488H) opioid agonists caused significant mean increases in [Ca2+]i and in the levels of oxidative products in astrocytes. In contrast, following 72 h of continuous opioid exposure, [Ca2+]i and carbonyl levels returned to normal, irrespective of opioid treatment. These preliminary findings indicate that opioids initially destabilize [Ca2+]i and increase reactive oxygen species in astrocytes; however, astrocytes later recover and adapt to sustained opioid exposure.