Delta opioid agonists attenuate TAT 1–72 -induced oxidative stress in SK-N-SH cells David R. Wallace a, * , Summer L. Dodson b , Avindra Nath c , Rosemarie M. Booze d a Oklahoma State University, Center for Health Sciences, Departments of Pharmacology, Physiology and Forensic Sciences, 1111 West 17th Street, Tulsa, OK 74107-1898, USA b University of Tulsa, Department of Chemistry and Biochemistry, Tulsa, OK 74104-3189, USA c Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA d University of South Carolina, Department of Psychology, Columbia, SC 29208, USA Received 10 December 2004; accepted 22 July 2005 Available online 15 September 2005 Abstract Previous reports have indicated that the use of d agonists may prove to be a viable therapeutic tool as an analgesic agent without conventional opioid side effects. In addition, recent evidence suggests that d ligands may exert neuroprotective effects under a variety of toxin insults. The aim of the present studies was to assess the ability of d agonists (peptide: [D-Pen 2,5 ] enkephalin (DPDPE), non-peptide: (+)-4-[(aR)-a-((2S,5R)-4-allyl- 2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC-80)) and antagonists (naltrindole) to modify dichlorofluorescein (DCFH) fluorescence in the presence of the peroxynitrite generator, 3-morpholinylsydnoneimine chloride (SIN-1) or HIV-protein, TAT 1–72 (TAT) in SK-N-SH cells. Both DPDPE (100 nM) and SNC-80 (250 nM) attenuated (30–50%) the increased oxidative stress in the presence of SIN-1. This effect was partially reversed by addition of naltrindole, suggesting involvement of d receptors. Peroxynitrite radicals are involved in neurotoxicity associated with TAT. Incubation with TAT (10–250nM) demonstrated a concentration-dependent increase in oxidative stress up to 200% over control values. Preincubation with d agonists reduced 50 nM TAT-mediated oxidative stress 15–40%, which was partially reversed by naltrindole. Increasing log-concentrations of DPDPE or SNC-80 (0.01–100 mM) attenuated TAT-mediated oxidative stress up to 50% at 100 mM. In conclusion, these data demonstrate that both peptide and non-peptide delta agonists can partially attenuate intracellular oxidative stress, in part through a receptor-mediated mechanism. This suggests that delta ligands may have therapeutic usefulness in HIV patients beyond analgesia. # 2005 Elsevier Inc. All rights reserved. Keywords: TAT; Delta opioid; Oxidative stress; Peroxynitrite; HIV; Neurotoxicity 1. Introduction HIV dementia is a subcortical dementia associated with dysfunction in the basal ganglia (Berger and Nath, 1997). Currently, there are multiple HIV proteins that have been reported to exert neurotoxic effects. Several groups have demonstrated the presence of TAT protein brains of patients with HIV encephalitis by immunostaining (Hudson et al., 2000; Kruman et al., 1999). Additionally, mRNA levels for TAT are also elevated in brain tissue of patients with HIV dementia (Hudson et al., 2000; Wiley et al., 1996) TAT has been shown to be released by infected lymphoid (Ensoli et al., 1993), monocytic cells (Turchan et al., 2001) and glial cells (Tardieu et al., 1992) in vitro, by a leaderless but energy dependent pathway (Chang et al., 1997). Once released, TAT has been shown to exert toxicity through an oxidative stress pathway (Price et al., 2005; Bansal et al., 2000). One neurological system that is involved in TAT-induced neurotoxicity is the dopaminergic system. Recent evidence suggests a close relationship between d opioid receptor subtypes and dopamine receptor function in the striatum (Noble and Cox, 1995; Unterwald and Cuntapay, 2000). d Opioid receptors are localized on neuronal populations lost in Parkinson’s disease and may be effected by gp120 and TAT toxicity in late-stage AIDS (Noble and Cox, 1995). In addition to modulating the activity of dopaminergic neurons, d receptors have also been shown to affect the release of glutamate in the striatum (Rawls and McGinty, 2000). Glutamate receptor stimulation is one mechanism by which gp120 and TATexert their neurotoxicity, which suggests that d receptors may remain functional even following partial striatal degeneration. Collectively, these data NeuroToxicology 27 (2006) 101–107 * Corresponding author. Tel.: +1 918 699 8684; fax: +1 918 561 8276. E-mail address: walladr@chs.okstate.edu (D.R. Wallace). 0161-813X/$ – see front matter # 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.neuro.2005.07.008