l-Homocysteine Sulfinic Acid and Other Acidic Homocysteine Derivatives Are Potent and Selective Metabotropic Glutamate Receptor Agonists

Abstract

Moderate hyperhomocysteinemia is associated with several diseases, including coronary artery disease, stroke, Alzheimer's disease, schizophrenia, and spina bifida. However, the mechanisms for their pathogenesis are unknown but could involve the interaction of homocysteine or its metabolites with molecular targets such as neurotransmitter receptors, channels, or transporters. We discovered that L-homocysteine sulfinic acid (L-HCSA), L-homocysteic acid, L-cysteine sulfinic acid, and Lcysteic acid are potent and effective agonists at several rat metabotropic glutamate receptors (mGluRs). These acidic homocysteine derivatives 1) stimulated phosphoinositide hydrolysis in the cells stably expressing the mGluR1, mGluR5, or mGluR8 (plus G␣ qi9 ) and 2) inhibited the forskolin-induced cAMP accumulation in the cells stably expressing mGluR2, mGluR4, or mGluR6, with different potencies and efficacies depending on receptor subtypes. Of the four compounds, L-HCSA is the most potent agonist at mGluR1, mGluR2, mGluR4, mGluR5, mGluR6, and mGluR8. The effects of the four agonists were selective for mGluRs because activity was not discovered when L-HCSA and several other homocysteine derivatives were screened against a large panel of cloned neurotransmitter receptors, channels, and transporters. These findings imply that mGluRs are candidate G-protein-coupled receptors for mediating the intracellular signaling events induced by acidic homocysteine derivatives. The relevance of these findings for the role of mGluRs in the pathogenesis of homocysteine-mediated phenomena is discussed.

Salvinorin A, an Active Component of the Hallucinogenic SageSalvia divinorumIs a Highly Efficacious κ-Opioid Receptor Agonist: Structural and Functional Considerations

“…Salvinorin B and all other tested salvinorin derivatives were devoid of with the response induced by U69593 defined as 100%. The salvinorin A derivatives listed above were also screened at a large number of cloned receptors and found to have no significant activity, when tested at 10 M at the following receptors: serotonin (5-HT1A, 5-HT1B, 5-HT1D, 5-HT1E, 5-HT2A, 5-HT2B, 5-HT2C, 5-HT3, 5-HT5a, 5-HT6, 5-HT7), dopamine (D1, D2, D3, D4, D5), muscarinic (m1, m2, m3, m4, m5), , ␦, and ORL-1 opioid receptors, 1, 2, ␣1-adrenergic (1a, 1b, 1d), ␣2-adrenergic (2A, 2B, 2C) ␤2-adrenergic, and CB-1 cannabinoid receptors [assayed as previously detailed (Shi et al, 2003)]. significant activity.…”

Evidence for the Preferential Involvement of 5-HT2A Serotonin Receptors in Stress- and Drug-Induced Dopamine Release in the Rat Medial Prefrontal Cortex

“…Cell lines stably transfected with recombinant cDNA encoding receptors or cell lines that express endogenous receptors were used for the comprehensive screening using the resources of the National Institute of Mental Health's Psychoactive Drug Screening Program (PDSP) as previously detailed . The recombinant receptors included (1) human adrenergic receptors, a1A, a1B, a2A, a2B, a2C, and rat adrenergic receptors, b1 and b2; (2) rat cannabanoid CB1 receptor; (3) dopaminergic receptors, hD1, rD2, rD3, rD4, and hD5; (4) human histamine receptors, H1, H2, and H4; (5) rat imidazoline receptor; (6) human muscarinic acetylcholine receptors, M1, M2, M3, M4, and M5; (7) human nicotinic acetylcholine receptors, a2/b2, a2/b4, a3/b2, a3/b4, a4/b2, and a4/b4; (8) human opiate receptors, m, d, and k; (9) human peptide receptors, V1, V2, V3, and OT; (10) serotonergic receptors, h5-HT1A, r5-HT1B, h5-HT1E, r5-HT2A, h5-HT2B, r5-HT2C, h5-HT3, h5-HT5A, h5-HT6, and h5-HT7; (11) human transporters of serotonin, norepinephrine, and dopamine as previously described (Roth et al, 1998;Rothman et al, 2000;Roth et al, 2001;Roth et al, 2002;Shapiro et al, 2002); and (12) rat metabotropic glutamate receptors, mGluR1a, mGluR2, mGluR4, mGluR5a, mGluR6, and mGluR8 as previously described (Gomeza et al, 1996;Wroblewska et al, 1997;Kozikowski et al, 1998;Shi et al, 2003). The endogenous receptors included (1) GABA receptors, GABA A , GABA B , and GABA BZP from rat forebrain; (2) histamine receptor H1 from rat forebrain; (3) rat nicotinic acetylcholine receptor, a4/b2; (4) ionotropic NMDA glutamate receptor from rat forebrain; and (5) voltage-sensitive Ca 2 þ channel from rat heart.…”

“…The conditions for the different binding assays and K i values for reference ligands are as described previously (Shi et al, 2003). On-line protocols for binding assays are available at http:// pdsp.cwru.edu/nimh/binding.htm.…”

In Vitro Characterization of Ephedrine-Related Stereoisomers at Biogenic Amine Transporters and the Receptorome Reveals Selective Actions as Norepinephrine Transporter Substrates

“…Stably and transiently transfected cells expressing mainly human cloned Gprotein coupled receptors, ion channels, and transporters were maintained as detailed previously (Rothman et al, 2000;Roth et al, 2002;Setola et al, 2003) with radioligand binding and functional assays performed as described previously using the resources of the National Institute of Mental Health Psychoactive Drug Screening Program (Rothman et al, 2000;Roth et al, 2002). Details of all assay conditions have been published previously (Shi et al, 2003). Initial screening of test compounds was performed in quadruplicate at 10 M concentration.…”