Joan E. Roberts

Enhanced Photodynamic Efficacy towards Melanoma Cells by Encapsulation of Pc4 in Silica Nanoparticles

Nanoparticles have been explored recently as an efficient means of delivering photosensitizers for cancer diagnosis and photodynamic therapy (PDT). Silicon phthalocyanine 4 (Pc4) is currently being clinically tested as a photosensitizer for PDT. Unfortunately, Pc4 aggregates in aqueous solutions, which dramatically reduces its PDT efficacy and therefore limits its clinical application. We have encapsulated Pc4 using silica nanoparticles (Pc4SNP), which not only improved the aqueous solubility, stability, and delivery of the photodynamic drug but also increased its photodynamic efficacy compared to free Pc4 molecules. Pc4SNP generated photo-induced singlet oxygen more efficiently than free Pc4 as measured by chemical probe and EPR trapping techniques. Transmission electron microscopy and dynamic light scattering measurements showed that the size of the particles is in the range of 25-30 nm. Cell viability measurements demonstrated that Pc4SNP was more phototoxic to A375 or B16-F10 melanoma cells than free Pc4. Pc4SNP photodamaged melanoma cells primarily through apoptosis. Irradiation of A375 cells in the presence of Pc4SNP resulted in a significant increase in intracellular protein-derived peroxides, suggesting a Type II (singlet oxygen) mechanism for phototoxicity. More Pc4SNP than free Pc4 was localized in the mitochondria and lysosomes. Our results show that these stable, monodispersed silica nanoparticles may be an effective new formulation for Pc4 in its preclinical and clinical studies. We expect that modifying the surface of silicon nanoparticles encapsulating the photosensitizers with antibodies specific to melanoma cells will lead to even better early diagnosis and targeted treatment of melanoma in the future.

Phototoxicity of Nano Titanium Dioxides in HaCaT Keratinocytes – Generation of Reactive Oxygen Species and Cell Damage

Nano-sized titanium dioxide (TiO(2)) is among the top five widely used nanomaterials for various applications. In this study, we determine the phototoxicity of TiO(2) nanoparticles (nano-TiO(2)) with different molecular sizes and crystal forms (anatase and rutile) in human skin keratinocytes under UVA irradiation. Our results show that all nano-TiO(2) particles caused phototoxicity, as determined by the MTS assay and by cell membrane damage measured by the lactate dehydrogenase (LDH) assay, both of which were UVA dose- and nano-TiO(2) dose-dependent. The smaller the particle size of the nano-TiO(2) the higher the cell damage. The rutile form of nano-TiO(2) showed less phototoxicity than anatase nano-TiO(2). The level of photocytotoxicity and cell membrane damage is mainly dependent on the level of reactive oxygen species (ROS) production. Using polyunsaturated lipids in plasma membranes and human serum albumin as model targets, and employing electron spin resonance (ESR) oximetry and immuno-spin trapping as unique probing methods, we demonstrated that UVA irradiation of nano-TiO(2) can induce significant cell damage, mediated by lipid and protein peroxidation. These overall results suggest that nano-TiO(2) is phototoxic to human skin keratinocytes, and that this phototoxicity is mediated by ROS generated during UVA irradiation.

Light and Immunomodulation

Abstract: The immune system is susceptible to a variety of stresses. Recent work in neuroimmunology has begun to define how mood alteration, stress, the seasons, and daily rhythms can have a profound effect on immune response through hormonal modifications. Central to these factors may be light through an eye‐brain hormonal modulation. In adult primates, only visible light (400‐700 nm) is received by the retina. This photic energy is then transduced and delivered to the visual cortex and, by an alternative pathway, to the supra‐chiasmatic nucleus (SCN), the hypothalamic region that directs circadian rhythm. Visible light exposure also modulates the pituitary and pineal glands, leading to neuroendocrine changes. Melatonin, norepinephrine, and acetylcholine decrease with light activation, whereas cortisol, serotonin, GABA, and dopamine levels increase. The synthesis of vasoactive intestinal polypeptide (VIP), gastrin releasing peptide (GRP), and neuropeptide Y (NPY) in rat SCN has been shown to be modified by light. These induced neuroendocrine changes can lead to alterations in mood and circadian rhythm as well as immune modulation. An alternative pathway for immune modulation by light is through the skin. Visible light (400‐700 nm) can penetrate epidermal and dermal layers of the skin and may directly interact with circulating lymphocytes to modulate immune function. In contrast to visible light, in vivo exposure to UV‐B (280‐320 nm) and UV‐A (320‐400 nm) radiation can alter normal human immune function only by a skin‐mediated response. It is therefore important, when reporting neuroendocrine immune findings, to control the intensity, timing and wavelength of ambient light.

Phototoxicity and cytotoxicity of fullerol in human retinal pigment epithelial cells

The water-soluble nanoparticle hydroxylated fullerene [fullerol, nano-C60(OH)(22-26)] has several clinical applications including use as a drug carrier to bypass the blood ocular barriers. We have previously found that fullerol is both cytotoxic and phototoxic to human lens epithelial cells (HLE B-3) and that the endogenous antioxidant lutein blocked some of this phototoxicity. In the present study we have found that fullerol induces cytotoxic and phototoxic damage to human retinal pigment epithelial cells. Accumulation of nano-C60(OH)(22-26) in the cells was confirmed spectrophotometrically at 405 nm, and cell viability, cell metabolism and membrane permeability were estimated using trypan blue, MTS and LDH assays, respectively. Fullerol was cytotoxic toward hRPE cells maintained in the dark at concentrations higher than 10 microM. Exposure to an 8.5 J x cm(-2) dose of visible light in the presence of >5 microM fullerol induced TBARS formation and early apoptosis, indicating phototoxic damage in the form of lipid peroxidation. Pretreatment with 10 and 20 microM lutein offered some protection against fullerol photodamage. Using time resolved photophysical techniques, we have now confirmed that fullerol produces singlet oxygen with a quantum yield of Phi=0.05 in D2O and with a range of 0.002-0.139 in various solvents. As our previous studies have shown that fullerol also produces superoxide in the presence of light, retinal phototoxic damage may occur through both type I (free radical) and type II (singlet oxygen) mechanisms. In conclusion, ocular exposure to fullerol, particularly in the presence of sunlight, may lead to retinal damage.

The Role of A2E in Prevention or Enhancement of Light Damage in Human Retinal Pigment Epithelial Cells

Abstract The process of sight (photostasis) produces, as a by-product, a chromophore called 2-[2,6-dimethyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E,3E,5E,7E-octatetraenyl]-1-(2-hydroxyethyl)-4-[4-methyl-6-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E,3E,5E-hexatrienyl]-pyridinium (A2E), whose function in the eye has not been defined as yet. In youth and adulthood, A2E is removed from human retinal pigment epithelial (h-RPE) cells as it is made, and so it is present in very low concentrations, but with advanced age, it accumulates to concentrations reaching 20 μM. In the present study we have used photophysical techniques and in vitro cellular measurements to explore the role of A2E in h-RPE cells. We have found that A2E has both pro- and antioxidant properties. It generated singlet oxygen (Φso = 0.004) much less efficiently than its precursor trans-retinal (Φso = 0.24). It also quenched singlet oxygen at a rate (108 M−1 s−1) equivalent to two other endogenous quenchers of reactive oxygen species in the eye: α-tocopherol (vitamin E) and ascorbic acid (vitamin C). The endogenous singlet oxygen quencher lutein, whose quenching rate is two orders of magnitude greater than that of A2E, completely prevented light damage in vitro, suggesting that singlet oxygen does indeed play a role in light-induced damage to aged human retinas. We have used multiphoton confocal microscopy and the comet assay to measure the toxic, phototoxic and protective capacity of A2E in h-RPE cells. At 1–5 μM, A2E protected these cells from UV-induced breaks in DNA; at 20 μM, A2E no longer exerted this protective effect. These results imply that the role of A2E is not simple and may change over the course of a lifetime. A2E itself may play a protective role in the young eye but a toxic role in older eyes.

In Vitro Phototoxicity and Hazard Identification of Nano-scale Titanium Dioxide

Titanium dioxide nanoparticles (nano-TiO(2)) catalyze reactions under UV radiation and are hypothesized to cause phototoxicity. A human-derived line of retinal pigment epithelial cells (ARPE-19) was treated with six samples of nano-TiO(2) and exposed to UVA radiation. The TiO(2) nanoparticles were independently characterized to have mean primary particle sizes and crystal structures of 22nm anatase/rutile, 25nm anatase, 31nm anatase/rutile, 59nm anatase/rutile, 142nm anatase, and 214nm rutile. Particles were suspended in cell culture media, sonicated, and assessed for stability and aggregation by dynamic light scattering. Cells were treated with 0, 0.3, 1, 3, 10, 30, or 100μg/ml nano-TiO(2) in media for 24hrs and then exposed to UVA (2hrs, 7.53J/cm(2)) or kept in the dark. Viability was assessed 24hrs after the end of UVA exposure by microscopy with a live/dead assay (calcein-AM/propidium iodide). Exposure to higher concentrations of nano-TiO(2) with UVA lowered cell viability. The 25nm anatase and 31nm anatase/rutile were the most phototoxic (LC(50) with UVA<5μg/ml), while the 142nm anatase and 214nm rutile were the least phototoxic. An acellular assay ranked TiO(2) nanoparticles for their UVA photocatalytic reactivities. The particles were found to be capable of generating thiobarbituric acid reactive substances (TBARS) under UVA. Flow cytometry showed that nano-TiO(2) combined with UVA decreased cell viability and increased the generation of reactive oxygen species (ROS, measured by Mitosox). LC(50) values under UVA were correlated with TBARS reactivity, particle size, and surface area.

Photooxidation of lens α-crystallin by hypericin (active ingredient in St. John's Wort).

Abstract Hypericin is the active ingredient in the over the counter antidepressant medication St. Johns Wort. Hypericin produces singlet oxygen and other excited state intermediates that indicate it should be a very efficient phototoxic agent in the eye. Furthermore it absorbs in the UV and visible range, which means it can potentially damage both the lens and the retina. Lens α-crystallin, isolated from calf lenses, was irradiated in the presence of hypericin (5 × 10−5 M, 10 mM ammonium bicarbonate, pH 7.0) and in the presence and absence of light (>300 nm, 24 mW/cm2). Hypericin-induced photosensitized photopolymerization as assessed by sodium dodecylsulfate-polyacrylamide gel electrophoresis. Further analysis of the oxidative changes occurring in α-crystallin using mass spectrometry showed specific oxidation of methionine, tryptophan and histidine residues, which increased with irradiation time. Hypericin did not damage the lens protein in the dark. Damage to α-crystallin could undermine the integrity of the lens directly by protein denaturation and indirectly by disturbing chaperone function. Therefore, in the presence of light, hypericin can induce changes in lens protein that could lead to the formation of cataracts. Appropriate precautions should be taken to protect the eye from intense sunlight while on this antidepressant medication.

Comparison of the aerobic photoreactivity of A2E with its precursor retinal.

A2E (2‐[2,6‐dimethyl‐8‐(2,6,6‐trimethyl‐1‐cyclohexen‐1‐yl)‐1E,3E,5E,7E‐octatetraenyl]‐1‐(2‐hydroxyethyl)‐4‐[4‐methyl‐6‐(2,6,6‐trimethyl‐1‐cyclohexen‐1‐yl)‐1E,3E,5E‐hexatrienyl]‐pyridinium) is a blue‐absorbing molecular constituent of human ocular lipofuscin and contributes to the golden‐yellow emission of this pigment. Lipofuscin photoproduces toxic reactive oxygen intermediates (ROI), but the specific molecular components responsible for this phototoxicity remain unidentified. In this article the aerobic photoreactivity of A2E is quantified by comparison with its biosynthetic precursor, all‐trans‐retinal, and with other appropriate standards. Under blue‐light exposure the efficacies for formation of cholesterol (Ch) hydroperoxides and the superoxide radical anion (O2·−) were determined using high‐pressure liquid chromatography with electrochemical detection and electron spin resonance oximetry and spin trapping, respectively. Photogeneration of singlet oxygen after blue‐light excitation of A2E was demonstrated unambiguously by the Ch peroxidation assay. After blue‐light irradiation of A2E, O2·− were detected, but the concentration was insufficient to account for the measured production of O2·− by the solvent extract of lipofuscin granules. The collective data support the conclusion that A2E does not produce sufficient concentrations of ROI to be the primary phototoxic constituent of lipofuscin.

Difference in Phototoxicity of Cyclodextrin Complexed Fullerene [(γ-CyD)2/C60] and Its Aggregated Derivatives toward Human Lens Epithelial Cells

The water-soluble fullerene derivative gamma-cyclodextrin bicapped C(60) [(gamma-CyD)(2)/C(60), CDF0] has several clinical applications, including use as a drug carrier to bypass the blood ocular barriers or a photosensitizer to treat tumors in photodynamic therapy. We have assessed the potential ocular toxicity of (gamma-CyD)(2)/C(60) and its aggregated derivatives induced by UVA and visible light in vitro in human lens epithelial cells (HLE B-3). Cell viability using the MTS assay demonstrated that 2 microM (gamma-CyD)(2)/C(60) was highly phototoxic to HLE B-3 cells with UVA irradiation, while no effect was observed in the presence of visible light or when maintained in the dark. In contrast, the aggregated derivative (CDF150) showed neither cytotoxicity nor any phototoxic effect even at 30 microM with either UVA or visible light irradiation. In lens cells treated with (gamma-CyD)(2)/C(60), phototoxicity was manifested as apoptosis. Singlet oxygen production measurement using the EPR/TEMP trapping technique determined that (gamma-CyD)(2)/C(60) (CDF0) efficiently produced singlet oxygen. The rate of singlet oxygen production decreased with increased aggregation, with no production by the fully aggregated sample formed after 150 min of heating (CDF150). UVA irradiation of HLE B-3 in the presence of (gamma-CyD)(2)/C(60) resulted in a significant rise in intracellular protein-derived peroxides. The singlet oxygen quenchers sodium azide and histidine each significantly protected lens cells against (gamma-CyD)(2)/C(60) photodamage, but lutein and Trolox (vitamin E) did not. Clearly, singlet oxygen is an important intermediate in the phototoxicity of monomeric (gamma-CyD)(2)/fullerene. Our results also demonstrate that UVA-blocking sunglasses can limit the ocular phototoxicity of this nanomaterial, while nontoxic endogenous antioxidants like lutein or Trolox cannot provide adequate protection.

Visible light induced changes in the immune response through an eye-brain mechanism (photoneuroimmunology).

The immune system is susceptible to a variety of stresses. Recent work in neuroimmunology has begun to define how mood alteration, stress, the seasons, and daily rhythms can have a profound effect on immune response through hormonal modifications. Central to these factors may be light through an eye-brain hormonal modulation. In adult primates, only visible light (400-700 nm) is received by the retina. This photic energy is then transduced and delivered to the visual cortex and by an alternative pathway to the suprachiasmatic nucleus (SCN). The SCN is a part of the hypothalamic region in the brain believed to direct circadian rhythm. Visible light exposure also modulates the pituitary and pineal gland which leads to neuroendocrine changes. Melatonin, norepinephrine and acetylcholine decrease with light activation, while cortisol, serotonin, gaba and dopamine levels increase. The synthesis of vasoactive intestinal polypeptide (VIP), gastrin releasing peptide (GRP) and neuropeptide Y (NPY) in rat SCN has been shown to be modified by light. These induced neuroendocrine changes can lead to alterations in mood and circadian rhythm. All of these neuroendocrine changes can lead to immune modulation. An alternative pathway for immune modulation by light is through the skin. Visible light (400-700 nm) can penetrate epidermal and dermal layers of the skin and may directly interact with circulating lymphocytes to modulate immune function. However, even in the presence of phototoxic agents such as eosin and rose bengal, visible light did not produce suppression of contact hypersensitivity with suppresser cells. In contrast to visible light, in vivo exposure to UV-B (280-320 nm) and UV-A (320-400 nm) radiation can only alter normal human immune function by a skin mediated response. Each UV subgroup (B, A) induces an immunosuppressive response but by differing mechanisms involving the regulation of differing interleukins and growth factors. Some effects observed in humans are: inhibition of allergic contact dermatitis; inhibition of delayed hypersensitivity to an injected antigen; prolongation of skin-graft survival and induction of a tumor-susceptible state. The following article will review much of the progress in this field and explore possible areas of future research.