The red blood cell phototoxicity test (photohaemolysis and haemoglobin oxidation): EU/COLIPA validation programme on phototoxicity (phase II)

Evaluating Hemolytic and Photo Hemolytic Potential of Organophosphorus by In Vitro Method as an Alternative Tool Using Human Erythrocytes

AIMS

The present study aims to determine the phototoxic and haemolytic activity of organophosphorus. The use of alternative in vitro assays with human erythrocytes is suggested to predict the polluting effect of these products on health.

METHODOLOGY

Human erythrocytes from Toluca Blood Bank were used. Sodium dodecyl sulfate was employed as a positive control. Additionally, the haemolysis percentage of three organophosphate (Acetate, Chlorpyrifos, Malathion, Methamidophos, Methyl Parathion) induced photo haemolysis formulated with surfactants on a concentration of 2 x 109 erythrocytes were evaluated. Finally, the products were classified as irritant or phototoxic.

RESULTS

Results showed that the HC50 red blood cells were similar for each organophosphate (Malathion and Methamidophos) indicating very irritant action with ratio classification (L/D) of 0.041 and 0.053, respectively. On the other hand, Chlorpyrifos was classified as an irritant with L/D= 0.14. On the other hand, the HC50 obtained photo hemolysis assays irradiated red blood cells was similar for each organophosphate (Acetate, Chlorpyrifos, Malathion, Methamidophos, Methyl Parathion) indicating no phototoxic action.

CONCLUSION

As a conclusion, it can be said that the parameters of haemolysis and denaturation of proteins are good indicators to classify organophosphorus formulated with surfactants as irritating or phototoxic.

Computational Investigation of Drug Phototoxicity: Photosafety Assessment, Photo-Toxophore Identification, and Machine Learning

One of the most appreciated capabilities of computational toxicology is to support the design of pharmaceuticals with reduced toxicological hazard. To this end, we have strengthened our drug photosafety assessments by applying novel computer models for the anticipation of in vitro phototoxicity and human photosensitization. These models are typically used in pharmaceutical discovery projects as part of the compound toxicity assessments and compound optimization methods. To ensure good data quality and aiming at models with global applicability we separately compiled and curated highly chemically diverse data sets from 3T3 NRU phototoxicity reports (450 compounds) and clinical photosensitization alerts (1419 compounds) which are provided as supplements. The latter data gives rise to a comprehensive list of explanatory fragments for visual guidance, termed phototoxophores, by application of a Bayesian statistics approach. To extend beyond the domain of well sampled fragments we applied machine learning techniques based on explanatory descriptors such as pharmacophoric fingerprints or, more important, accurate electronic energy descriptors. Electronic descriptors were extracted from quantum chemical computations at the density functional theory (DFT) level. Accurate UV/vis spectral absorption descriptors and pharmacophoric fingerprints turned out to be necessary for predictive computer models, which were both derived from Deep Neural Networks but also the simpler Random Decision Forests approach. Model accuracies of 83-85% could typically be reached for diverse test data sets and other company in-house data, while model sensitivity (the capability of correctly detecting toxicants) was even better, reaching 86%-90%. Importantly, a computer model-triggered response-map allowed for graphical/chemical interpretability also in the case of previously unknown phototoxophores. The photosafety models described here are currently applied in a prospective manner for the hazard identification, prioritization, and optimization of newly designed molecules.

Protection against oxidative damage in human erythrocytes and preliminary photosafety assessment of Punica granatum seed oil nanoemulsions entrapping polyphenol-rich ethyl acetate fraction

The main purpose of the present study is to evaluate the ability of nanoemulsion entrapping pomegranate peel polyphenol-rich ethyl acetate fraction (EAF) prepared from pomegranate seed oil and medium chain triglyceride to protect human erythrocyte membrane from oxidative damage and to assess preliminary in vitro photosafety. In order to evaluate the phototoxic effect of nanoemulsions, human red blood cells (RBCs) are used as a biological model and the rate of haemolysis and photohaemolysis (5 J cm(-2) UVA) is assessed in vitro. The level of protection against oxidative damage caused by the peroxyl radical generator AAPH in human RBCs as well as its effects on bilayer membrane characteristics such as fluidity, protein profile and RBCs morphology are determined. EAF-loaded nanoemulsions do not promote haemolysis or photohaemolysis. Anisotropy measurements show that nanoemulsions significantly retrain the increase in membrane fluidity caused by AAPH. SDS-PAGE analysis reveals that AAPH induced degradation of membrane proteins, but that nanoemulsions reduce the extension of degradation. Scanning electron microscopy examinations corroborate the interaction between AAPH, nanoemulsions and the RBC membrane bilayer. Our work demonstrates that Punica granatum nanoemulsions are photosafe and protect RBCs against oxidative damage and possible disturbance of the lipid bilayer of biomembranes. Moreover it suggests that these nanoemulsions could be promising new topical products to reduce the effects of sunlight on skin.

Phototoxicity: Its Mechanism and Animal Alternative Test Methods

The skin exposure to solar irradiation and photoreactive xenobiotics may produce abnormal skin reaction, phototoxicity. Phototoxicity is an acute light-induced response, which occurs when photoreacive chemicals are activated by solar lights and transformed into products cytotoxic against the skin cells. Multifarious symptoms of phototoxicity are identified, skin irritation, erythema, pruritis, and edema that are similar to those of the exaggerated sunburn. Diverse organic chemicals, especially drugs, are known to induce phototoxicity, which is probably from the common possession of UV-absorbing benzene or heterocyclic rings in their molecular structures. Both UVB (290~320 nm) and UVA (320~400 nm) are responsible for the manifestation of phototoxicity. Absorption of photons and absorbed energy (hv) by photoactive chemicals results in molecular changes or generates reactive oxygen species and depending on the way how endogenous molecules are affected by phototoxicants, mechanisms of phototoxcity is categorized into two modes of action: Direct when unstable species from excited state directly react with the endogenous molecules, and indirect when endogeneous molecules react with secondary photoproducts. In order to identify phototoxic potential of a chemical, various test methods have been introduced. Focus is given to animal alternative test methods, i.e., in vitro, and in chemico assays as well as in vivo. 3T3 neutral red uptake assay, erythrocyte photohemolysis test, and phototoxicity test using human 3-dimensional (3D) epidermis model are examples of in vitro assays. In chemico methods evaluate the generation of reactive oxygen species or DNA strand break activity employing plasmid for chemicals, or drugs with phototoxic potential.

Biphasic dose-response of antioxidants in hypericin-induced photohemolysis

In the present paper the photodynamic effect of hypericin on superoxide dismutase activity and the possibility of reduction of hypericin phototoxicity by antioxidants were studied. It was shown an almost twice decrease in superoxide dismutase activity of red blood cells under the photosensitization by hypericin. The influence of antioxidants (ascorbic acid and quercetin) on hypericin photodynamic action has revealed that these antioxidants suppress or stimulate photohemolysis caused by hypericin. The photosensitization reaction realized by hypericin could be shifted from type II to type I or vice versa by manipulating the antioxidant concentration. Strengthening of photohemolysis by antioxidants in some concentrations indicates the switching of alternative mechanisms of hypericin photodynamic action and its complicated manner. Thus the selection of antioxidant concentrations is of extreme importance for changing the efficacy of photodynamic therapy with hypericin.

A novel in vitro method for the detection and characterization of photosensitizers

Photoactivation and binding of photoactive chemicals to proteins is a known prerequisite for the formation of immunogenic photoantigens and the induction of photoallergy. The intensive use of products and the availability of new chemicals, along with an increasing exposure to sun light contribute to the risk of photosensitizing adverse reactions. Dendritic cells (DC) play a pivotal role in the induction of allergic contact dermatitis. Human peripheral blood monocyte derived dendritic cells (PBMDC) were thus perceived as an obvious choice for the development of a novel in vitro photosensitization assay using the modulation of cell surface protein expression in response to photosensitizing agents. In this new protocol, known chemicals with photosensitizing, allergenic or non-allergenic potential were pre-incubated with PBMDCs prior to UVA irradiation (1 J/cm(2)). Following a 48 h incubation, the expression of the cell surface molecules CD86, HLA-DR and CD83 was measured by flow cytometry. All tested photosensitizers induced a significant and dose-dependent increase of CD86 expression after irradiation compared to non-irradiated controls. Moreover, the phototoxicity of the chemicals could also be determined. In contrast, (i) CD86 expression was not affected by the chosen irradiation conditions, (ii) increased CD86 expression induced by allergens was independent of irradiation and (iii) no PBMDC activation was observed with the non-allergenic control. The assay proposed here for the evaluation of the photoallergenic potential of chemicals includes the assessment of their allergenic, phototoxic and toxic potential in a single and robust test system and is filling a gap in the in vitro photoallergenicity test battery.

Alternative Methods for Eye and Skin Irritation Tests: An Overview

The evaluation of eye and skin irritation potential is essential to ensuring the safety of individuals in contact with a wide variety of substances designed for industrial, pharmaceutical or cosmetic use. The Draize rabbit eye and skin irritancy tests have been used for 60 years to attempt to predict the human ocular and dermal irritation of such products. The Draize test has been the standard for ocular and dermal safety assessments for decades. However, several aspects of the test have been criticised. These include: the subjectivity of the method; the overestimation of human responses; and the method's cruelty. The inadequacies of the Draize test have led to several laboratories over the last 20 years making efforts to develop in vitro assays to replace it. Protocols that use different types of cell cultures and other methods have been devised to study eye and skin irritation. Different commercial kits have also been developed to study eye and skin irritation, based on the action of chemicals on these tissues. This article presents a review of the main alternatives developed to replace the use of animals in the study of chemical irritation. Particular attention is paid to the reproducibility of each method.

Potential irritation of lysine derivative surfactants by hemolysis and HaCaT cell viability

Surfactants represent one of the most common constituents in topical pharmaceutical and cosmetic applications or cleansers. Since adverse skin and ocular reactions can be caused by them, it is important to evaluate damaging effects. Amino acid-based surfactants deserve particular attention because of their low toxicity and environmental friendly properties. New lysine derivative surfactants associated with heavy and light counterions were tested. The ocular irritancy was assessed by hemolysis, and photohemolysis was employed to evaluate their phototoxicity. Cytotoxicity on HaCaT cells was determined by neutral red uptake and MTT assay to predict skin irritation. All lysine derivative surfactants were less hemolytic and thus less eye-irritating than the commercial surfactants used as model irritants. No phototoxic effects were found. All surfactants presented cytotoxic effects as demonstrated by decrease of neutral red uptake and reduction of MTT salt, with clear concentration-effect profiles. However, the rates of cytotoxicity on HaCaT for the new surfactants suggested that they were less cytotoxic and then, less skin-irritating than the reference ones; surfactants with heavy counterions were the less cytotoxic. The anionic surfactants investigated in the present work may constitute a promising class of surfactants given their low irritancy potential for pharmaceutical and cosmetic preparations.

Erythrocytes-the 'house elves' of photodynamic therapy

Photodynamic therapy (PDT) and fluorescence diagnosis (FD) are being developed for a number of clinical applications. Since fluorophores and photosensitising drugs are usually given systemically their effect on blood elements are of significant importance. Photodynamic effects on erythrocytes occur naturally in patients with erythropoietic protoporphyria (EPP). Exposure to small fluences, as obtained by the erythrocytes when they pass capillaries in the skin, leads to transfer of the photosensitiser protoporphyrin IX (PP IX), from EPP erythrocytes to endothelial cells. Thus, the erythrocytes are partly protected while the endothelial cells suffer photodamage. During photodynamic therapy in vivo erythrocytes are regularly photosensitised. This side effect is partly intended but mostly unwanted, and a summary of this topic is given. Furthermore, the effect of UV-A on erythrocytes that is accompanied with the formation of bilirubin is reviewed. Erythrocytes serve as convenient model cells for experimental research. Such use of erythrocytes to screen new photosensitisers may be of limited value. A combination of photohaemolysis and haemoglobin oxygenation may become the basis for an assay for in vitro phototoxicity. Erythrocytes from birds are good model cells for exploration of physiological and molecular mechanisms involved in PDT. A potential mechanism of PDT induced behaviour resembling apoptosis in erythrocytes is provided.PDT for sterilisation of erythrocyte concentrates has a potential for medical use. Photodynamic effects on the erythrocytes themselves should be avoided. This is realised by choosing a virus-selective photosensitiser, low fluences and treatment of the concentrates with agents like dipyridamole and antioxidants. Future aspects of applications of photosensitisation of red blood cells are discussed.

Assessment of the potential irritation and photoirritation of novel amino acid-based surfactants by in vitro methods as alternative to the animal tests

The ultraviolet-A radiation damage effects on skin and eyes will be increased by phototoxic compounds which could be present in pharmaceutical or cosmetic formulations. Great efforts have been made in the last years to find surfactants to replace those with phototoxic potential in commercial use. Series of different in vitro models for phototoxicity, included to validated neutral red uptake (NRU) 3T3 phototoxicity assay are useful screening tools. The phototoxic effects of a novel family of glycerol amino acid-based surfactant compounds were examined via these assays. Human red blood cells and two immortalised cell lines, murine fibroblast cell line 3T3, and one human keratinocyte cell line, HaCaT, were the in vitro models employed to predict potential photoirritation. The phototoxic end-points assessed were hemolysis (human red blood cell test) and resazurin transformation to resorufin and NRU in cell culture methods. The results suggest that no phototoxic effects by any new amino acid derived-surfactants, could be identified.

In vitro study of the antioxidant and immunomodulatory activity of aqueous infusion of Bidens pilosa

Bidens pilosa is an annual plant from tropical America with anti-inflammatory properties in hepatitis, laryngitis, headache and digestive disorders, among others. Its wide pharmacological applications can be attributed to its chemical composition, with inhibitory effects on pathogenic microorganisms and flavonoids, which show strong antioxidant capacities. We investigated the antioxidant activity of an aqueous infusion of Bidens pilosa by studying its protective effect on the hemolysis induced by an initiator of radicals such as 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). The immunomodulatory activity of the infusion was tested using whole blood cells. Cytokine production increased in whole blood stimulated or not by lipopolysaccharides (LPSs). The infusion is also characterized by its capacity to protect erythrocytes from the phototoxic effect of chlorpromazine, which allows its use as a potential photoprotector. Finally, it did not show ocular irritation, as demonstrated by the effect on hemoglobin denaturation. This study supports the health benefits of the ingestion of the infusion.

Photodegradation pathways and the in vitro phototoxicity of pyrazinamide, a phototoxic antitubercular drug

The phototoxic antitubercular drug pyrazinamide (1) is photolabile under irradiation with UV-A light as well as with a N2 laser (at 337 nm) in aerobic conditions. Irradiation in methanolic and in aqueous solutions of 1 produces four and three photoproducts, respectively. Their formation involves primary alpha-cleavage between the excited carbonyl of the amido group and the aromatic ring followed by hydrogen abstraction and dimerization. Pyrazinamide was able to cause photohemolysis in human erythrocytes and peroxidation of linoleic acid. Inhibition of both processes on addition of reduced glutathione (GSH) or ascorbic acid suggests the involvement of radicals. The absence of inhibition of the photohemolysis and lipid peroxidation processes in the presence of sodium azide (NaN3), or irradiation under argon, and the absence of singlet oxygen during the photolysis confirmed with 2,5-dimethylfuran rules out the possibility of participation of 1O2 in this process. Glutathione depletion was also observed. A radical intermediate was evidenced by thiobarbituric acid that was used as a radical probe, as well as by the dimerization of cysteine. No photohemolysis was detected in presence of the isolated photoproduct. We have also determined the relative efficiencies for the formation of single strand breaks after the irradiation of pBR322 DNA and pyrazinamide, which was also reduced in the presence of GSH.