iridoids and thiazolyl-blue

Previously, we reported that genipin, a herbal iridoid, had neuritogenic and neuroprotective actions on PC12 cells. Although nitric oxide (NO)-activated signalings were proposed to be neuritogenic, the neuroprotective action of genipin remains to be elucidated. From the standpoint of NO activation, we tested a possible protective mechanism through the nitrosative Kelch-like ECH-associated protein (Keap1)/NF-E2-related factor 2 (Nrf2)-antioxidant response element pathway in rat retinal ganglion cells (RGC-5 cells) in culture, and in vivo, against hydrogen peroxide and optic nerve injury (ONI), respectively, using a long-acting (1R)-isoPropyloxygenipin (IPRG001). IPRG001 induced NO generation and the expressions of antioxidative enzymes, such as heme oxygenase-1 (HO-1), in RGC-5 cells. The protective action of IPRG001 depended on HO-1 and NO induction. We found that S-nitrosylation of Keap1 by IPRG001 may contribute to translocation of Nrf2 to the nucleus and triggered transcriptional activation of antioxidative enzymes. Furthermore, apoptotic cells were increased and 4-hydroxy-2-nonenal was accumulated in rat retina following ONI. Pre-treatment with IPRG001 almost completely suppressed apoptosis and accumulation of 4-hydroxy-2-nonenal in RGCs following ONI accompanied by HO-1 induction. These data demonstrate for the first time that IPRG001 exerts neuroprotective action in RGCs in vitro and in vivo, through the Nrf2/antioxidant response element pathway by S-nitrosylation against oxidative stress.

Topics: Aldehydes; Animals; Antioxidants; Blotting, Western; Cell Death; Cell Line; Chromatin; Coloring Agents; Cysteine Proteinase Inhibitors; Heme Oxygenase-1; Humans; Immunohistochemistry; Immunoprecipitation; In Situ Nick-End Labeling; Intracellular Signaling Peptides and Proteins; Iridoid Glycosides; Iridoids; Kelch-Like ECH-Associated Protein 1; NF-E2-Related Factor 2; Nitric Oxide; Oxidative Stress; Rats; Rats, Sprague-Dawley; Response Elements; Retinal Ganglion Cells; Reverse Transcriptase Polymerase Chain Reaction; RNA; RNA, Small Interfering; Signal Transduction; Tetrazolium Salts; Thiazoles

Catalpol is an iridoid glycoside, distributed in the roots of Rehmannia glutinosa Libosch. In vitro results showed that preincubation with catalpol (0.5-0.5 mM) for 0.5 hours before and during 48 hour exposure to 0.2 mM MPP+ appeared to be significant protective effect while catalopl was considerably less effective at the doses of 0.001 to 0.01 mM. The addition of catalpol at the dose of 0.05-0.5 mM significantly increased DA and DOPAC to MPP+ treated group. C57bl/6 mice received administration of catalpol for 12 hours before and during the 7 day treatment with MPTP. Such treatment at doses of 15 mg/kg significantly and dramatically blocked tyrosine hydroxylase-positive cell loss in mice. DA turnover in MPTP mice was reversed in the nigrostriatal pathway. In conclusion, data obtained in the above study suggested that catalpol exerted neuroprotective action in vitro and in vivo PD model.

Topics: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; 3,4-Dihydroxyphenylacetic Acid; Analysis of Variance; Animals; Brain; Cell Survival; Dopamine; Dose-Response Relationship, Drug; Glucosides; Iridoid Glucosides; Iridoids; Male; Mice; Mice, Inbred C57BL; Neuroprotective Agents; Neurotoxicity Syndromes; Neurotoxins; PC12 Cells; Rats; Tetrazolium Salts; Thiazoles; Time Factors; Tyrosine 3-Monooxygenase