Cytotoxicity and cytoprotective activity of naphthalenediols in rat cortical neurons

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 ≈ 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

Development of novel antioxidants: Design, synthesis, and reactivity

We are attempting to develop novel synthetic antioxidants aimed at retarding the effects of free-radical induced cell damage. In this paper we discuss the design strategy and report the synthesis of seven novel antioxidants, including six catechols and a benzylic phenol. The bond dissociation enthalpy (BDE) for the most active (weakest) OH bond in each molecule was calculated by theoretical methods, as well as the BDE for the semiquinone radical. Reaction rates with the nitrogen-centered free radical DPPH . were measured in ethyl acetate. The log of k DPPH for bimolecular reaction correlated well with the primary BDE. The correlation between rate constants and calculated BDEs shows that the BDE is a good predictor of antioxidant activity with DPPH ., suggesting that our design criteria are useful and that these compounds should undergo further testing in cell cultures and in animal models

Cytotoxicity and cytoprotective activity in naphthalenediols depends on their tendency to form naphthoquinones

We consider the cytotoxicity and the protection against oxidative stress for members of the naphthalenediol family and the known antioxidant epigallocatechin gallate (EGCG). Compounds include the 1,2-naphthalenediol (1,2-ND), 1,4-ND, 2,3-ND, 1,8-ND, and 1,4-dipropyl-2,3-naphthalenediol (DPND). The cell line is an adherent clone of rat pheochromocytoma (PC12-AC). Oxidative stress was induced by the peroxyl radical generator AAPH. The relative order of cytotoxicity was 1,4-ND > 1,2-ND > DPND > 2,3-ND > 1,8-ND > EGCG, with EC50's of 15, 40, 160, >250, >250, >>250 μM, respectively. Despite their high toxicity, both 1,4-ND and 1,2-ND showed narrow zones of protective behavior whereas DPND, 2,3-ND and 1,8-ND and especially EGCG showed an extended protective range. The total protection obtained for the combination of cells/oxidative stressor/protective compounds (PC12-AC/AAPH/naphthalenediols) was defined by an integrated measure, the cytoprotective area (CPA). We relate the observed cytotoxicity and CPA to the different electronic structures of the naphthalenediols, characterized by the first and second bond dissociation enthalpies and the pKa's for parent (diol) and semiquinone. Since the 2,3- and 1,8-naphthalenediols do not form quinones, their cytotoxicit

Mechanism of cytotoxicity of catechols and a naphthalenediol in PC12-AC cells: The connection between extracellular autoxidation and molecular electronic structure

ortho-Hydroxyphenols (catechols) form a common structural unit in naturally occurring antioxidants such as polyphenols. They also show pro-oxidant characteristics which depend on their particular structure. Here we examined the acetylated versions of three catechols and a naphthalenediol for cytotoxicity to adrenal PC12-AC cells. We found that the three catechols H1 (a p-methoxycatechol), H2 (a catechol analog of α-tocopherol), and H4 (a dioxymethylene-substituted catechol) strongly upregulate glutathione (GSH) in 24 h, whereas 1,4-dipropyl-2,3-naphthalenediol (DPND) does not. Upregulation of GSH is primarily caused by oxidative stress in the form of hydrogen peroxide generation, and both GSH upregulation and the rate of H 2O 2 generation correlate well with the cytotoxicity. The major source of H 2O 2 is autoxidation in the extracellular space, which results from transport of the (deacetylated) hydroquinone form outside the cell, rather than internal redox cycling