Jun Jie Yin

The scavenging of reactive oxygen species and the potential for cell protection by functionalized fullerene materials

We demonstrated that three different types of water-soluble fullerenes materials can intercept all of the major physiologically relevant ROS. C(60)(C(COOH)(2))(2), C(60)(OH)(22), and Gd@C(82)(OH)(22) can protect cells against H(2)O(2)-induced oxidative damage, stabilize the mitochondrial membrane potential and reduce intracellular ROS production with the following relative potencies: Gd@C(82)(OH)(22)> or =C(60)(OH)(22)>C(60)(C(COOH)(2))(2). Consistent with their cytoprotective abilities, these derivatives can scavenge the stable 2,2-diphenyl-1-picryhydrazyl radical (DPPH), and the reactive oxygen species (ROS) superoxide radical anion (O(2)(*-)), singlet oxygen, and hydroxyl radical (HO(*)), and can also efficiently inhibit lipid peroxidation in vitro. The observed differences in free radical-scavenging capabilities support the hypothesis that both chemical properties, such as surface chemistry induced differences in electron affinity, and physical properties, such as degree of aggregation, influence the biological and biomedical activities of functionalized fullerenes. This represents the first report that different types of fullerene derivatives can scavenge all physiologically relevant ROS. The role of oxidative stress and damage in the etiology and progression of many diseases suggests that these fullerene derivatives may be valuable in vivo cytoprotective and therapeutic agents.

Metallofullerene nanoparticles circumvent tumor resistance to cisplatin by reactivating endocytosis

Cisplatin is a chemotherapeutic drug commonly used in clinics. However, acquired resistance confines its application in chemotherapeutics. To overcome the acquired resistance to cisplatin, it is reasoned, based on our previous findings of mediation of cellular responses by [Gd@C82(OH)22]n nanoparticles, that [Gd@C82(OH)22]n may reverse tumor resistance to cisplatin by reactivating the impaired endocytosis of cisplatin-resistant human prostate cancer (CP-r) cells. Here we report that exposure of the CP-r PC-3-luc cells to cisplatin in the presence of nontoxic [Gd@C82(OH)22]n not only decreased the number of surviving CP-r cells but also inhibited growth of the CP-r tumors in athymic nude mice as measured by both optical and MRI. Labeling the CP-r PC-3 cells with transferrin, an endocytotic marker, demonstrated that pretreatment of the CP-r PC-3-luc cells with [Gd@C82(OH)22]n enhanced intracellular accumulation of cisplatin and formation of cisplatin-DNA adducts by restoring the defective endocytosis of the CP-r cancer cells. The results suggest that [Gd@C82(OH)22]n nanoparticles overcome tumor resistance to cisplatin by increasing its intracellular accumulation through the mechanism of restoring defective endocytosis. The technology can be extended to other challenges related to multidrug resistance often found in cancer treatments.

Direct evidence for catalase and peroxidase activities of ferritin-platinum nanoparticles.

Using apoferritin (apoFt) as a nucleation substrate, we have successfully synthesized 1-2xa0nm platinum nanoparticles (Pt-Ft) which are highly stable. By directly measuring the products of Pt-Ft-catalyzed reactions, we showed, with no doubt, Pt-Ft possesses both catalase and peroxidase activities. With hydrogen peroxide as substrate, we observed oxygen gas bubbles were generated from hydrogen peroxide decomposed by Pt-Ft; the generation of oxygen gas strongly supports Pt-Ft reacts as catalase, other than peroxidase. While with organic dyes and hydrogen peroxide as substrates, distinctive color products were formed catalyzed by Pt-Ft, which indicates a peroxidase-like activity. Interestingly, these biomimetic properties showed differential response to pH and temperature for different reaction substrates. Pt-Ft showed a significant increase in catalase activity with increasing pH and temperature. The HRP-like activity of Pt-Ft was optimal at physiological temperature and slightly acidic conditions. Our current study demonstrates that Pt-Ft possesses both catalase and peroxidase activities for different substrates under different conditions.

Unraveling stress-induced toxicity properties of graphene oxide and the underlying mechanism.

Graphene oxide shows stress-induced toxicity properties in vivo under different pathophysiological conditions. A dual-path chemical mechanism, involving the overproduction of hydroxyl radicals and the formation of oxidizing cytochrome c intermediates, is responsible for the toxicity properties.

Inhibition of tumor growth by endohedral metallofullerenol nanoparticles optimized as reactive oxygen species scavenger.

Intraperitoneal injection of [Gd@C82(OH)22]n nanoparticles decreased activities of enzymes associated with the metabolism of reactive oxygen species (ROS) in the tumor-bearing mice. Several physiologically relevant ROS were directly scavenged by nanoparticles, and lipid peroxidation was inhibited in this study. [Gd@C82(OH)22]n nanoparticles significantly reduced the electron spin resonance (ESR) signal of the stable 2,2-diphenyl-1-picryhydrazyl radical measured by ESR spectroscopy. Like-wise, studies using ESR with spin-trapping demonstrated efficient scavenging of superoxide radical anion, hydroxyl radical, and singlet oxygen (1O2) by [Gd@C82(OH)22]n nanoparticles. In vitro studies using liposomes prepared from bovine liver phosphatidylcholine revealed that nanoparticles also had a strong inhibitory effect on lipid peroxidation. Consistent with their ability to scavenge ROS and inhibit lipid peroxidation, we determined that [Gd@C82(OH)22]n nanoparticles also protected cells subjected in vitro to oxidative stress. Studies using human lung adenocarcinoma cells or rat brain capillary endothelial cells demonstrated that [Gd@C82(OH)22]n nanoparticles reduced H2O2-induced ROS formation and mitochondrial damage. [Gd@C82(OH)22]n nanoparticles efficiently inhibited the growth of malignant tumors in vivo. In summary, the results obtained in this study reveal antitumor activities of [Gd@C82(OH)22]n nanoparticles in vitro and in vivo. Because ROS are known to be implicated in the etiology of a wide range of human diseases, including cancer, the present findings demonstrate that the potent inhibition of [Gd@C82(OH)22]n nanoparticles on tumor growth likely relates with typical capacity of scavenging reactive oxygen species.

Photodecomposition of vitamin A and photobiological implications for the skin.

Vitamin A (retinol), an essential human nutrient, plays an important role in cellular differentiation, regulation of epidermal cell growth and normal cell maintenance. In addition to these physiological roles, vitamin A has a rich photochemistry. Photoisomerization of vitamin A, involved in signal transduction for vision, has been extensively investigated. The biological effects of light‐induced degradation of vitamin A and formation of reactive species are less understood and may be important for light‐exposed tissues, such as the skin. Photochemical studies have demonstrated that excitation of retinol or its esters with UV light generates a number of reactive species including singlet oxygen and superoxide radical anion. These reactive oxygen species have been shown to damage a number of cellular targets, including lipids and DNA. Consistent with the potential for damaging DNA, retinyl palmitate has been shown to be photomutagenic in an in vitro test system. The results of mechanistic studies were consistent with mutagenesis through oxidative damage. Vitamin A in the skin resides in a complex environment that in many ways is very different from the chemical environment in solution and in in vitro test systems. Relevant clinical studies or studies in animal models are therefore needed to establish whether the pro‐oxidant activity of photoexcited vitamin A is observed in vivo, and to assess the related risks.

Deciphering the underlying mechanisms of oxidation-state dependent cytotoxicity of graphene oxide on mammalian cells

The promising broad applications of graphene oxide (GO) derivatives in biomedicine have raised concerns about their safety on biological organisms. However, correlations between the physicochemical properties, especially oxidation degree of GOs and their toxicity, and the underlying mechanisms are not well understood. Herein, we evaluated the cytotoxicity of three GO samples with various oxidation degrees on mouse embryo fibroblasts (MEFs). Three samples can be internalized by MEFs observed via transmission electron microscopy (TEM), and were well tolerant by MEFs at lower doses (below 25μg/ml) but significantly toxic at 50 and 100μg/ml via Cytell Imaging System. More importantly, as the oxidation degree decreased, GO derivatives led to a higher degree of cytotoxicity and apoptosis. Meanwhile, three GOs stimulated dramatic enhancement in reactive oxygen species (ROS) production in MEFs, where the less oxidized GO produced a higher level of ROS, suggesting the major role of oxidative stress in the oxidation-degree dependent toxicity of GOs. Results from electron spin resonance (ESR) spectrometry showed a strong association of the lower oxidation degree of GOs with their stronger indirect oxidative damage through facilitating H2O2 decomposition into OH and higher direct oxidative abilities on cells. The theoretical simulation revealed the key contributions of carboxyl groups and aromatic domain size of nanosheets to varying the energy barrier of H2O2 decomposition reaction. These systematic explorations in the chemical mechanisms unravel the key physicochemical properties that would lead to the diverse toxic profiles of the GO nanosheets with different oxygenation levels, and offer us new clues in the molecular design of carbon nanomaterials for their safe applications in biomedicine.

Photoirradiation of dehydropyrrolizidine alkaloids--formation of reactive oxygen species and induction of lipid peroxidation.

Pyrrolizidine alkaloid (PA)-containing plants are widespread in the world and are probably the most common poisonous plants affecting livestock, wildlife, and human. PAs require metabolic activation to generate pyrrolic metabolites (dehydro-PAs) that bind cellular protein and DNA, leading to hepatotoxicity and genotoxicity, including tumorigenicity. In this study we report that UVA photoirradiation of a series of dehydro-PAs, e.g., dehydromonocrotaline, dehydroriddelliine, dehydroretrorsine, dehydrosenecionine, dehydroseneciphylline, dehydrolasiocarpine, dehydroheliotrine, and dehydroretronecine (DHR) at 0-70 J/cm2 in the presence of a lipid, methyl linoleate, resulted in lipid peroxidation in a light dose-responsive manner. When irradiated in the presence of sodium azide, the level of lipid peroxidation decreased; lipid peroxidation was enhanced when methanol was replaced by deuterated methanol. These results suggest that singlet oxygen is a photo-induced product. When irradiated in the presence of superoxide dismutase, the level of lipid peroxidation decreased, indicating that lipid peroxidation is also mediated by superoxide. Electron spin resonance (ESR) spin trapping studies confirmed that both singlet oxygen and superoxide anion radical were formed during photoirradiation. These results indicate that UVA photoirradiation of dehydro-PAs generates reactive oxygen species (ROS) that mediated the initiation of lipid peroxidation. UVA irradiation of the parent PAs and other PA metabolites, including PA N-oxides, under similar experimental conditions did not produce lipid peroxidation. It is known that PAs induce skin cancer and are secondary (hepatogenous) photosensitization agents. Our results suggest that dehydro-PAs are the active metabolites responsible for skin cancer formation and PA-induced secondary photosensitization.

Structure and catalytic activities of ferrous centers confined on the interface between carbon nanotubes and humic acid

Preparation of heterogeneous catalysts with active ferrous centers is of great significance for industrial and environmental catalytic processes. Nanostructured carbon materials (NCM), which possess free-flowing π electrons, can coordinate with transition metals, provide a confinement environment for catalysis, and act as potential supports or ligands to construct analogous complexes. However, designing such catalysts using NCM is still seldom studied to date. Herein, we synthesized a sandwich structured ternary complex via the coordination of Fe-loaded humic acid (HA) with C=C bonds in the aromatic rings of carbon nanotubes (CNTs), in which the O/N-Fe-C interface configuration provides the confinement environment for the ferrous sites. The experimental and theoretical results revealed octahedrally/tetrahedrally coordinated geometry at Fe centers, and the strong hybridization between CNT C π* and Fe 3d orbitals induces discretization of the atomic charges on aromatic rings of CNTs, which facilitates O2 adsorption and electron transfer from carbon to O2, which enhances O2 activation. The O2 activation by the novel HA/Fe-CNT complex can be applied in the oxidative degradation of phenol red (PR) and bisphenol A (BPA) in aqueous media.