Effects of a potent antioxidant, platinum nanoparticle, on the lifespan of Caenorhabditis elegans

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Abstract

We have shown that platinum nanoparticles (nano-Pt) are a superoxide dismutase (SOD)/catalase mimetic. Various data have shown extension of the Caenorhabditis elegans lifespan by antioxidant treatment. The present study was designed to elucidate the survival benefit conferred by nano-Pt, as compared to the well-known SOD/catalase mimetic EUK-8. At 0.5 mM, nano-Pt significantly extended the lifespan of wild-type N2 nematodes and at 0.25 and 0.5 mM, nano-Pt recovered the shortened lifespan of the mev-1(kn1) mutant, which is due to excessive oxidative stress. In both instances, EUK-8 at 0.05, 0.5, and 5 mM did not extend nematode lifespan. Even when 0.4 M paraquat was loaded exogenously, nano-Pt (0.1 and 0.5 mM) and EUK-8 (0.5 and 5 mM) were effective in rescuing worms. Moreover, 0.5 mM nano-Pt significantly reduced the accumulation of lipofuscin and ROS induced by paraquat. We measured the in vitro dose-dependent quenching of O2 and H2O2, indicating that nano-Pt is a more potent SOD/catalase mimetic than EUK-8. Nano-Pt prolonged the worm lifespan, regardless of thermotolerance or dietary restriction. Taken together, nano-Pt has interesting anti-ageing properties.

Introduction

It is well known that the accumulation of molecular damage caused by free radicals, which are derived from the reactive oxygen species (ROS) side-products of normal metabolic pathways, is a major factor in ageing (Beckman and Ames, 1998, Bokov et al., 2004, Finkel and Holbrook, 2000). ROS oxidize endogenous molecules, such as lipids (Packer, 1992), proteins (Ishii et al., 2002, Stadtman, 1992), and DNA (Beckman and Ames, 1997). Although most organisms have developed antioxidant defense systems, which include superoxide dismutase (SOD), catalase, and glutathione peroxidase (Fridovich, 1995), not all excess ROS are detoxified. In addition, while oxidized molecules are repaired and replaced by biological protective systems, biomolecules are irreversibly oxidized over time. These irreversibly oxidized molecules accumulate, leading to deleterious consequences during ageing (Raha and Robinson, 2000). Thus, the free radical theory of ageing proposed by Harman (1956) has been supported.

The correlation between delayed ageing progression and oxidative stress resistance has been demonstrated in several model organisms (Beckman and Ames, 1998, Orr and Sohal, 1994). Using wild-type N2 Caenorhabditis elegans (C. elegans), it has been shown that vitamin E (Harrington and Harley, 1988), tocotrienols (Adachi and Ishii, 2000), CoQ10 (Ishii et al., 2004), and EGb761, which is an extract of Ginkgo biloba leaves (Wu et al., 2002), can extend the lifespan of the worms by increasing resistance to oxidative stress. These results suggest that exogenous administration of antioxidants can prolong life. Since SOD/catalase mimetics decrease excessive ROS, they appear to extend the lifespan of C. elegans. However, the effect of well-known SOD/catalase mimetic EUK-8 on lifespan is controversial (Keaney and Gems, 2003, Keaney et al., 2004, Melov et al., 2000, Sampayo et al., 2003, Uchiyama et al., 2005). Thus, further clarification of the effects of SOD/catalase mimetics on lifespan is needed.

Recently, polymer-protected metal nanoparticles have been developed. These metal nanoparticles can function as catalysts in various reactions, such as hydrogenation, oxidation, and hydration (Aiken and Finke, 1999, Toshima and Yonezawa, 1998). In biosciences, gold nanoparticles have been primarily used as nanoprobes for transmission electron microscopy (Mannweiler et al., 1982). As platinum nanoparticles (nano-Pt) are known to act as reductive catalysts, they may have utility as antioxidants to reduce ROS in living organisms. Indeed, we have shown that nano-Pt has the ability to scavenge ROS, superoxide anion radicals (O2), and hydrogen peroxide (H2O2), indicating that in functional terms, nano-Pt can act as a SOD/catalase mimetic (Kajita et al., 2007).

In the present study, we compared the effects of nano-Pt and EUK-8 on the lifespan of C. elegans strains, i.e., the wild-type N2 and the short-lived mev-1(kn1) mutant. We found that nano-Pt was more effective than EUK-8 in extending the lifespan of C. elegans.

Section snippets

C. elegans strains and growth conditions

The wild-type N2 strain and the mev-1(kn1) mutant were provided by the Caenorhabditis Genetic Center (University of Minnesota, St. Paul, MN, USA). These strains were maintained at 20 °C, according to the procedures established by Brenner (1974). Age-synchronous populations were prepared, as previously described (Emmons et al., 1979). Briefly, collected eggs were allowed to hatch overnight at 20 °C in S-basal buffer, which consisted of 100 mM NaCl, 0.01 mM cholesterol, and 50 mM potassium phosphate

Lifespan

The survival curve for N2 worms under normal conditions (Fig. 1A and Table 1) was in good accordance with those reported previously (Keaney et al., 2004, Uchiyama et al., 2005). Treatment with 0.5 mM nano-Pt extended the average lifespan by 22.3 ± 2.8% (p < 0.001), while significant lifespan extension was not observed at other concentrations of nano-Pt (Fig. 1A and C and Table 1). PVP (40 mM) alone did not increase the lifespan. EUK-8 did not prolong, but rather reduced the mean lifespan in a

Discussion

In the present study, we examined the effects of nano-Pt, which is a new SOD/catalase mimetic, on the lifespan of C. elegans strains. In the lifespan assay, at 0.5 mM, nano-Pt extended the lifespan of N2 nematode but at 0.1 and 1 mM, nano-Pt did not (Fig. 1). Cellular damage caused by oxidative stress is one of the key factors in ageing so that we examined whether nano-Pt affect the accumulation of the autofluorescent pigment lipofuscin. Lipofuscin is generated by oxidative degeneration and

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  • Cited by (0)

    1

    Present address: Department of Aging Control, Graduate School of Medicine, Juntendo University, Tokyo, Japan.

    2

    Present address: Department of Global Infectious Diseases and Tropical Medicine, National Defense Medical College, 3-2 Namiki, Tokorozawa, Saitama 359-8513, Japan.

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