Cytotoxicity and Cytoprotective Activity of Naphthalenediols in Rat Cortical Neurons

Abstract

Some members of the naphthalenediol family have been shown in previous work on PC-12 cells to act as effective antioxidants while being relatively nontoxic. In the present work, we extend that study to examine the effect of naphthalenediols on rat primary cortical neurons exposed to AAPH (2,2'-azobis (2-amidinopropane) hydrochloride), a source of peroxyl radicals. Compounds tested included the acetylated forms of 1,2-naphthalenediol, that is, 1,2-ND, as well as 1,4-ND, 2,3-ND, 1,8-ND, and the known highly potent antioxidant (-)-epigallocatechin gallate (EGCG). In cytoxicity studies, cells were exposed to the compounds for 24 h, leading to observed toxicity in the order of 1,4-ND > 1,2 ND >> 2,3-ND approximately EGCG > 1,8-ND. In cytoprotection studies, the desired compounds were incubated with neurons prior to AAPH exposure, and live cell counts were determined by trypan blue and/or MTT assays. Excellent protection, superior to EGCG, was provided by 2,3-ND and 1,8-ND. Additional studies using glutamate as a stressor showed that 1,8-ND had a significant protective effect at concentrations as low as 500 nM. The results can be understood on the basis of the tendency (or lack thereof) to form the corresponding quinone, which in turn depends on whether or not there is a loss of aromaticity in the ring adjacent to the quinone moiety. Thus, certain members of the family of naphthalenediols are quite cytotoxic, whereas others show promise as neuroprotective antioxidants.

Oxidative modification of citrate synthase by peroxyl radicals and protection with novel antioxidants

“…Thus, the NDs were tested as synthetic alternatives to PG. The high antioxidant potential of 1,8-ND seen here is in accordance with our previous studies on rat adrenal pheochromocytoma cells 14 and cortical neurons 15 , where 1,8-ND acted as an effective cytoprotector against AAPHmediated oxidative stress, showing low cytotoxicity. Of the NDs tested, 1,8-ND is the most effective antioxidant due to its ability to donate hydrogen atoms to peroxyl radicals without forming quinones (see references 14, 15, and 27 for an exhaustive overview of antioxidant properties of these phenols).…”

“…EGCG has been previously shown to provide pronounced cytoprotection against AAPH-mediated damage, similar to 1,8-ND 14,15 , in whole cell treatments. In this study, EGCG failed to protect CS against AAPH-dependent inactivation at concentrations of 0.25-1 mM ( Figure 9A).…”

“…CS is found in both prokaryotes and eukaryotes, and in the latter, it is located exclusively in the mitochondrial matrix 11 . CS activity has been widely used as an indicator of cellular mitochondrial content, function, and integrity [12][13][14][15] (for a review, see reference 16). However, recent evidence 17 suggests that changes in CS activity do not parallel changes in mitochondrial DNA content and other mitochondrial respiratory enzymes.…”

“…To our knowledge, ours is the first study to examine the effects of peroxyl radicals on mitochondrial enzymes. Naphthalenediols (NDs) constitute a novel class of phenolic antioxidants that may be used to restore CS activity, provided that the mechanism of CS inactivation involves free radical attack 14,15 . NDs are thought to work by transferring a hydrogen atom to either the attacking free radical or to an oxidized amino acid (such as a tyrosyl radical (R-Tyr-O • )) 27 .…”

Role of catalpol in ameliorating the pathogenesis of experimental autoimmune encephalomyelitis by increasing the level of noradrenaline in the locus coeruleus

“…A total of 7 days following plating, the culture media was replaced with fresh media (controls) or media containing 1, 5, 10 or 20 µM catalpol, followed by incubation for 24 h at 37°C. Oxidative damage was initiated by a water-soluble initiator 2,2′-azobis (2-amidinopropane) hydrocholoride (AAPH; 20 µM) ( 46 ). Following incubation for 3 h at 37°C, cell viability was analyzed by CCK-8.…”