Binding of chemicals to melanins re-examined: adsorption of some drugs to the surface of melanin particles

Melanin Biopolymers in Pharmacology and Medicine-Skin Pigmentation Disorders, Implications for Drug Action, Adverse Effects and Therapy

Melanins are biopolymeric pigments formed by a multi-step oxidation process of tyrosine in highly specialized cells called melanocytes. Melanin pigments are mainly found in the skin, iris, hair follicles, and inner ear. The photoprotective properties of melanin biopolymers have been linked to their perinuclear localization to protect DNA, but their ability to scavenge metal ions and antioxidant properties has also been noted. Interactions between drugs and melanins are of clinical relevance. The formation of drug-melanin complexes can affect both the efficacy of pharmacotherapy and the occurrence of adverse effects such as phototoxic reactions and discoloration. Because the amount and type of melanin synthesized in the body is subject to multifactorial regulation-determined by both internal factors such as genetic predisposition, inflammation, and hormonal balance and external factors such as contact with allergens or exposure to UV radiation-different effects on the melanogenesis process can be observed. These factors can directly influence skin pigmentation disorders, resulting in hypopigmentation or hyperpigmentation of a genetic or acquired nature. In this review, we will present information on melanocyte biology, melanogenesis, and the multifactorial influence of melanin on pharmacological parameters during pharmacotherapy. In addition, the types of skin color disorders, with special emphasis on the process of their development, symptoms, and methods of treatment, are presented in this article.

Melanin: a unifying theory of disease as exemplified by Parkinson's, Alzheimer's, and Lewy body dementia

Melanin, a ubiquitous dark pigment, plays important roles in the immune system, including scavenging reactive oxygen species formed in response to ultraviolet radiation absorption, absorbing metals, thermal regulation, drug uptake, innate immune system functions, redox, and energy transduction. Many tissue types, including brain, heart, arteries, ovaries, and others, contain melanin. Almost all cells contain precursors to melanin. A growing number of diseases in which there is a loss of melanin and/or neuromelanin are increasingly thought to have infectious etiologies, for example, Alzheimer's disease (AD), Parkinson's disease (PD), Lewy Body Dementia (LBD), and vitiligo. AD, PD, LBD, and vitiligo have been linked with herpesvirus, which enters melanosomes and causes apoptosis, and with gut dysbiosis and inflammation. Herpesvirus is also linked with gut dysbiosis and inflammation. We theorize that under normal healthy states, melanin retains some of the energy it absorbs from electromagnetic radiation, which is then used to fuel cells, and energy from ATP is used to compliment that energy supply. We further theorize that loss of melanin reduces the energy supply of cells, which in the case of AD, PD, and LBD results in an inability to sustain immune system defenses and remove the plaques associated with the disease, which appear to be part of the immune system's attempt to eradicate the pathogens seen in these neurodegenerative diseases. In addition, in an attempt to explain why removing these plaques does not result in improvements in cognition and mood and why cognitions and moods in these individuals have ebbs and flows, we postulate that it is not the plaques that cause the cognitive symptoms but, rather, inflammation in the brain resulting from the immune system's response to pathogens. Our theory that energy retained in melanin fuels cells in an inverse relationship with ATP is supported by studies showing alterations in ATP production in relationship to melanin levels in melanomas, vitiligo, and healthy cells. Therefore, alteration of melanin levels may be at the core of many diseases. We propose regulating melanin levels may offer new avenues for treatment development.

The Assessment of the Phototoxic Action of Chlortetracycline and Doxycycline as a Potential Treatment of Melanotic Melanoma-Biochemical and Molecular Studies on COLO 829 and G-361 Cell Lines

Melanoma is still one of the most dangerous cancers. New methods of treatment are sought due to its high aggressiveness and the relatively low effectiveness of therapies. Tetracyclines are drugs exhibiting anticancer activity. Previous studies have also shown their activity against melanoma cells. The possibility of tetracycline accumulation in pigmented tissues and the increase in their toxicity under the influence of UVA radiation creates the possibility of developing a new anti-melanoma therapy. This study aimed to analyze the phototoxic effect of doxycycline and chlortetracycline on melanotic melanoma cells COLO 829 and G-361. The results indicated that tetracycline-induced phototoxicity significantly decreased the number of live cells by cell cycle arrest as well as a decrease in cell viability. The simultaneous exposure of cells to drugs and UVA caused the depolarization of mitochondria as well as inducing oxidative stress and apoptosis. It was found that the combined treatment activated initiator and effector caspases, caused DNA fragmentation and elevated p53 level. Finally, it was concluded that doxycycline demonstrated a stronger cytotoxic and phototoxic effect. UVA irradiation of melanoma cells treated with doxycycline and chlortetracycline allows for the reduction of therapeutic drug concentrations and increases the effectiveness of tested tetracyclines.

Preliminary Investigation on Simvastatin-Loaded Polymeric Micelles in View of the Treatment of the Back of the Eye

There is increasing consensus in considering statins beneficial for age-related macular degeneration and in general, for immune and inflammatory mediated diseases affecting the posterior segment of the eye. However, all available data relate to oral administration, and safety and effectiveness of statins directly administered to the eye are not yet known, despite their ophthalmic administration could be beneficial. The aim was the development and the characterization of polymeric micelles based on TPGS or TPGS/poloxamer 407 to increase simvastatin solubility and stability and to enhance the delivery of the drug to the posterior segment of the eye via trans-scleral permeation. Simvastatin was chosen as a model statin and its active hydroxy acid metabolite was investigated as well. Results demonstrated that polymeric micelles increased simvastatin solubility at least 30-fold and particularly TPGS/poloxamer 407 mixed micelles, successfully stabilized simvastatin over time, preventing the hydrolysis when stored for 1 month at 4 °C. Furthermore, both TPGS (1.3 mPas) and mixed micelles (33.2 mPas) showed low viscosity, suitable for periocular administration. TPGS micelles resulted the best performing in delivery simvastatin either across conjunctiva or sclera in ex vivo porcine models. The data pave the way for a future viable ocular administration of statins.

Minocycline Impact on Redox Homeostasis of Normal Human Melanocytes HEMn-LP Exposed to UVA Radiation and Hydrogen Peroxide

Minocycline is a semisynthetic tetracycline antibiotic. In addition to its antibacterial activity, minocycline shows many non-antibiotic, beneficial effects, including antioxidative action. The property is responsible, e.g., for anti-inflammatory, neuroprotective, and cardioprotective effects of the drug. However, long-term pharmacotherapy with minocycline may lead to hyperpigmentation of the skin. The reasons for the pigmentation disorders include the deposition of the drug and its metabolites in melanin-containing cells and the stimulation of melanogenesis. The adverse drug reaction raises a question about the influence of the drug on melanocyte homeostasis. The study aimed to assess the effect of minocycline on redox balance in human normal melanocytes HEMn-LP exposed to hydrogen peroxide and UVA radiation. The obtained results indicate that minocycline induced oxidative stress in epidermal human melanocytes. The drug inhibited cell proliferation, decreased the level of reduced thiols, and stimulated the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). The described changes were accompanied by an increase in the intracellular level of ROS. On the other hand, pretreatment with minocycline at the same concentrations increased cell viability and significantly attenuated the oxidative stress in melanocytes exposed to hydrogen peroxide and UVA radiation. Moreover, the molecular docking analysis revealed that the different influence of minocycline and other tetracyclines on CAT activity can be related to the location of the binding site.

Natural selection drives population divergence for local adaptation in a wheat pathogen

Evolution favors the emergence of locally-adapted optimum phenotypes that are likely to differ across a wide array of environmental conditions. The emergence of favorable adaptive characteristics is accelerated in agricultural pathogens due to the unique properties of agro-ecosystems. We performed a Q_ST - F_ST comparison using 164 strains of Parastagonospora nodorum sampled from eight global field populations to disentangle the predominant evolutionary forces driving population divergence in a wheat pathogen. We used digital image analysis to obtain quantitative measurements of growth rate and melanization at different temperatures and under different fungicide concentrations in a common garden experiment. F_ST measures were based on complete genome sequences obtained for all 164 isolates. Our analyses indicated that all measured traits were under selection. Growth rates at 18 °C and 24 °C were under stabilizing selection (Q_ST < F_ST), while diversifying selection (Q_ST > F_ST) was the predominant evolutionary force affecting growth under fungicide and high temperature stress. Stabilizing selection (Q_ST < F_ST) was the predominant force affecting melanization across the different environments. Melanin production increased at 30 °C but was negatively correlated with higher growth rates, consistent with a trade-off under heat stress. Our results demonstrate that global populations of P. nodorum possess significant evolutionary potential to adapt to changing local conditions, including warmer temperatures and applications of fungicides.

Adsorption of Paracetamol in Hospital Wastewater Through Activated Carbon Filters

In recent years, pharmaceutical products have been causing a serious environmental problem in hospital wastewater and water purification plants. The elimination of these pollutants is difficult due to their resistance to biological degradation. Paracetamol has been detected in higher concentrations in hospital wastewater than in other buildings. Activated carbons are a good material for removing paracetamol from hospital wastewater. One of the starting materials to obtain activated carbons is kenaf, which is an easy plant to cultivate. To study the elimination of paracetamol from hospital wastewater by activated carbon, the textural and chemical characterization of activated carbon, as well as the kinetic study and the analysis of the paracetamol adsorption mechanism by the adsorbent, have been carried out. The activated carbon samples studied are micro-mesoporous, with high specific surface values. The chemical composition with presence of oxygen groups favours the adsorption process. The adsorption kinetics were adjusted to a pseudo-second order model. The adsorption mechanism followed the intraparticular diffusion model, carried out in two stages: a fast first stage on the surface of the adsorbent and a slow one inside the pore. Based on the kinetic study, the use of this type of carbon is a good application for the removal of paracetamol from hospital wastewater.

Continuous removal of the model pharmaceutical chloroquine from water using melanin-covered Escherichia coli in a membrane bioreactor

Environmental release and accumulation of pharmaceuticals and personal care products is a global concern in view of increased awareness of ecotoxicological effects. Adsorbent properties make the biopolymer melanin an interesting alternative to remove micropollutants from water. Recently, tyrosinase-surface-displaying Escherichia coli was shown to be an interesting self-replicating production system for melanin-covered cells for batch-wise absorption of the model pharmaceutical chloroquine. This work explores the suitability of these melanin-covered E. coli for the continuous removal of pharmaceuticals from wastewater. A continuous-flow membrane bioreactor containing melanized E. coli cells was used for adsorption of chloroquine from the influent until saturation and subsequent regeneration. At a low loading of cells (10 g/L) and high influent concentration of chloroquine (0.1 mM), chloroquine adsorbed until saturation after 26 ± 2 treated reactor volumes (39 ± 3 L). The average effluent concentration during the first 20 h was 0.0018 mM, corresponding to 98.2% removal. Up to 140 ± 6 mg chloroquine bound per gram of cells following mixed homo- and heterogeneous adsorption kinetics. In situ low-pH regeneration released all chloroquine without apparent capacity loss over three consecutive cycles. This shows the potential of melanized cells for treatment of conventional wastewater or highly concentrated upstream sources such as hospitals or manufacturing sites.

Chlortetracycline and melanin biopolymer - The risk of accumulation and implications for phototoxicity: An in vitro study on normal human melanocytes

Tetracyclines belong to antimicrobial classes with the highest consumption in veterinary medicine and agriculture, which leads to the contamination of the environment and food products, as well as to antibiotic resistance and adverse drug reactions. Chloro-derivatives of tetracyclines are thought to be relatively more phototoxic than others and belong to the most frequently cited drugs as photosensitizers. Melanins are heterogenous biopolymers determining skin, hair and eye colour. They are biosynthesized in a multistep process in melanocytes. Melanins, besides photoprotective and antioxidant properties, may also contribute to adverse skin drug reactions, which involve e.g. hyperpigmentation disorders and phototoxic reactions. Furthermore, they have the ability to form a drug-melanin complex, which leads to deposition of the drug or its metabolites in pigmented tissues. The aim of the study was to examine the ability of chlortetracycline to form a complex with melanin, as well as the effect of the drug on viability, antioxidant defence system and melanogenesis in normal human epidermal melanocytes exposed to the UVA radiation. The obtained results show for the first time that chlortetracycline forms a complex with melanin polymers, which creates a possibility of the drug accumulation in pigmented tissues. A simultaneous exposition of normal melanocytes to chlortetracycline and to the UVA radiation decreases cell viability, proportionally to the drug concentration and the irradiation time. The phototoxic effect appears to be related to the induction of oxidative stress in melanocytes, mainly through an increase of SOD and a decrease of the CAT activity. Chlortetracycline itself does not influence the melanin content or the activity of tyrosinase. The UVA radiation appeared to be a conditioning factor stimulating melanogenesis, whereas the presence of the drug augmented this effect.

Potential effects of different natural antioxidants on inflammatory damage and oxidative-mediated hepatotoxicity induced by gold nanoparticles

Objective

The objective of this study was to verify and confirm the oxidative-mediated hepatotoxicity, inflammatory liver damage, and oxidative stress induced by intraperitoneal administration of gold nanoparticles (GNPs) in vivo; characterize the effect of different natural antioxidants on these hazardous changes; and finally choose the most powerful antioxidant among these different natural antioxidants.

Methods

Ten-nanometer GNPs were dissolved in aqueous solution of 0.01% concentration. A dose of 50 µL of 10 nm GNPs was administered intraperitoneally for 7 days to the rats, whereas the antioxidants were orally administered for the same time period. The antioxidants used in the study were vitamin E (Vit E), α-lipoic acid (ALA), quercetin (Qur), arginine (Arg), and melanin. Forty Wistar-Kyoto male rats were used. Rats were arbitrarily divided into seven groups after acclimatization for 1 week. For serum separation, blood samples were obtained from each animal. Serum liver function markers and tissue oxidative stress and lipid proxidation biomarkers were assessed.

Results

The increase in the levels of gamma-glutamyl transferase, alkaline phosphatase, total protein, alanine aminotransferase, and total bilirubin in the serum of rats and the increase of malondialdehyde in the hepatic tissue and decrease in reduced glutathione when compared with the control in this study confirmed the ability of GNPs to cause hazardous effects.

Conclusion

Treatment of rats with Vit E, ALA, Qur, Arg, and melanin along with GNPs significantly inhibited the inflammatory liver damage, lipid peroxidation, and the oxidative stress induced by GNPs in vivo, but with different responses due to their evaluated normalization values, and it has been confirmed that melanin is the most powerful antioxidant among these different natural antioxidants, ie, it has the most effective potential role against the hepatic inflammatory damage, oxidative stress, and lipid peroxidation.

Effect of melanin on gold nanoparticle-induced hepatotoxicity and lipid peroxidation in rats

Introduction

Melanin pigments are produced by melanocytes and are believed to act as antioxidants based on the belief that melanin can suppress electronically stirred states and scavenge the free radicals.

Materials and methods

The study was aimed to verify and prove the toxicity induced by administration of gold nanoparticles (GNPs) and to characterize the role of melanin as an antioxidant against inflammatory liver damage, oxidative stress, and lipid peroxidation induced intraperitoneally by GNPs in vivo.

Results

The findings from this study confirmed that administration of GNPs intraperitoneally caused liver damage in addition to producing oxidative stress and fatty acid peroxidation. The treatment of rats with melanin along with GNPs induced dramatic changes in all the measured biochemical parameters. Our data demonstrated that melanin completely inhibited inflammatory liver damage, oxidative stress, and lipid peroxidation, which was confirmed by the histological investigation of different liver sections stained by H&E.

Conclusion

These results suggest the beneficial use of melanin together with GNPs for alleviating its toxicity. Other studies should be implemented taking into consideration the role of melanin in comparison with other natural antioxidants.

Toxicological hair analysis: Pre-analytical, analytical and interpretive aspects

Background and aims Hair analysis for drug detection is one of the widely accepted imperative techniques in the field of forensic toxicology. The current study was designed to investigate the efficacy of chromatography for detection of drugs of abuse in hair. Method A comprehensive review of articles from last two decades on hair analyses via PubMed and similar resources was performed. Issues concerning collection, decontamination and analytical techniques are summarised. Physiochemical nature of hair, mechanism of drug incorporation and its stability in hair are briefly discussed. Furthermore, various factors affecting results and interpretation are elucidated. Result A hair sample is chosen over traditional biological samples such blood, urine, saliva or tissues due to its inimitable ability to provide a longer time frame for drug detection. Its collection is almost non-invasive, less cumbersome and does not involve any specialised training/expertise. Recent advances in analytical technology have resulted in better sensitivity, reproducibility and accuracy, thus providing a new arena of scientific understanding and test interpretation. Conclusion Though recent studies have yielded many insights into drug binding and drug incorporation in hair, the major challenge in hair analysis lies in the interpretation of results, which may be affected by external contamination and thus lead to false-positives. Therefore, there is a need for more sensitive and selective analysis methods to be developed in order to minimise factors that induce the effect of melanin, age and so on, and this would certainly provide a new dimension to hair analysis and its applications.

Melanins and melanogenesis: from pigment cells to human health and technological applications

During the past decade, melanins and melanogenesis have attracted growing interest for a broad range of biomedical and technological applications. The burst of polydopamine-based multifunctional coatings in materials science is just one example, and the list may be expanded to include melanin thin films for organic electronics and bioelectronics, drug delivery systems, functional nanoparticles and biointerfaces, sunscreens, environmental remediation devices. Despite considerable advances, applied research on melanins and melanogenesis is still far from being mature. A closer intersectoral interaction between research centers is essential to raise the interests and increase the awareness of the biomedical, biomaterials science and hi-tech sectors of the manifold opportunities offered by pigment cells and related metabolic pathways. Starting from a survey of biological roles and functions, the present review aims at providing an interdisciplinary perspective of melanin pigments and related pathway with a view to showing how it is possible to translate current knowledge about physical and chemical properties and control mechanisms into new bioinspired solutions for biomedical, dermocosmetic, and technological applications.

Ultrafast transient absorption of eumelanin suspensions: the role of inverse Raman scattering

An ultrafast investigation is carried out on synthetic eumelanin suspended either in water or in DMSO-methanol. Upon photoexcitation by visible femtosecond pulses, the transient absorption (TA) dynamics of the suspensions are probed in a broad visible spectral range, showing clear nonlinearities. The latter arise from pump-probe interactions that induce the inverse Raman scattering (IRS) effect. We show how eumelanin TA dynamics are modified in proximity of the solvent Stokes and anti-Stokes scattering peaks, demonstrating that IRS affects the sign of TA but not the relaxation times. We compare the results obtained in both suspensions, unveiling the role of the surrounding environment. Eventually, the intrinsic response of synthetic eumelanin to ultrafast photoexcitation is evaluated.

Methods to Inhibit Bacterial Pyomelanin Production and Determine the Corresponding Increase in Sensitivity to Oxidative Stress

Pyomelanin is an extracellular red-brown pigment produced by several bacterial and fungal species. This pigment is derived from the tyrosine catabolism pathway and contributes to increased oxidative stress resistance. Pyomelanin production in Pseudomonas aeruginosa is reduced in a dose dependent manner through treatment with 2-[2-nitro-4-(trifluoromethyl)benzoyl]-1,3-cyclohexanedione (NTBC). We describe a titration method using multiple concentrations of NTBC to determine the concentration of drug that will reduce or abolish pyomelanin production in bacteria. The titration method has an easily quantifiable outcome, a visible reduction in pigment production with increasing drug concentrations. We also describe a microtiter plate method to assay antibiotic minimum inhibitory concentration (MIC) in bacteria. This method uses a minimum of resources and can easily be scaled up to test multiple antibiotics in one microtiter plate for one strain of bacteria. The MIC assay can be adapted to test the affects of non-antibiotic compounds on bacterial growth at specific concentrations. Finally, we describe a method for testing bacterial sensitivity to oxidative stress by incorporating H2O2 into agar plates and spotting multiple dilutions of bacteria onto the plates. Sensitivity to oxidative stress is indicated by reductions in colony number and size for the different dilutions on plates containing H2O2 compared to a no H2O2 control. The oxidative stress spot plate assay uses a minimum of resources and low concentrations of H2O2. Importantly, it also has good reproducibility. This spot plate assay could be adapted to test bacterial sensitivity to various compounds by incorporating the compounds in agar plates and characterizing the resulting bacterial growth.

Chloroquine and hydroxychloroquine binding to melanin: Some possible consequences for pathologies

For many years chloroquine was used as a prophylactic agent against malaria, and more recently as a mild immunosuppressive. However, due to lengthy treatment periods, adverse effects have become apparent, which included retinopathy. The structurally related hydroxychloroquine is less toxic, thought to be owing to a lower tissue accumulation in melanin rich areas. This study primarily focused on quantifying melanin binding between chloroquine and hydroxychloroquine at physiological pH to investigate the potential link between binding and reported toxicity. In addition, for the first time this study quantified the actual extent of adsorption of chloroquine and hydroxychloroquine to melanin and examined the desorption profile of both drugs from melanin to demonstrate the affinity between the pigment and the solutes. The results suggest that there is a difference between the adsorption affinities of chloroquine and hydroxychloroquine, potentially explaining the differences in bioaccumulation in retinal tissue. In addition, both solutes displayed a strong physical attraction to the absorbent.

NTBC treatment of the pyomelanogenic Pseudomonas aeruginosa clinical isolate PA1111 inhibits pigment production and increases sensitivity to oxidative stress

Pyomelanin is a brown/black extracellular pigment with antioxidant and iron acquisition properties that is produced by a number of different bacteria. Production of pyomelanin in Pseudomonas aeruginosa contributes to increased resistance to oxidative stress and persistence in chronic infections. We demonstrate that pyomelanin production can be inhibited by 2-[2-nitro-4-(trifluoromethyl) benzoyl]-1,3-cyclohexanedione (NTBC). This treatment increases sensitivity of pyomelanogenic P. aeruginosa strains to oxidative stress, without altering the growth rate or resistance to aminoglycosides. As such, NTBC has potential to function as an anti-virulence factor in treating pyomelanogenic bacterial infections.

Small molecule modulators of aggregation in synthetic melanin polymerizations

There are numerous potential applications for melanin-binding compounds, and new methods are of interest to identify melanin-binding agents. A portion of the polymerization to eumelanin, the black to brown pigment in humans, is thought to be supramolecular aggregation of nanoparticles derived from dihydroxyindoles. Starting with chloroquine, a known eumelanin-binding compound, the ability of small molecules to influence aggregation in synthetic eumelanin polymerizations was investigated. Twenty-eight compounds were tested, including pharmaceuticals, dyes, aromatics, and amines. Compounds that either accelerate or delay the appearance of macroscopic particles in synthetic eumelanin polymerizations were uncovered.

Preclinical evaluation of an 131I-labeled benzamide for targeted radiotherapy of metastatic melanoma

Radiolabeled benzamides are attractive candidates for targeted radiotherapy of metastatic melanoma as they bind melanin and exhibit high tumor uptake and retention. One such benzamide, N-(2-diethylamino-ethyl)-4-(4-fluoro-benzamido)-5-iodo-2-methoxy-benzamide (MIP-1145), was evaluated for its ability to distinguish melanin-expressing from amelanotic human melanoma cells, and to specifically localize to melanin-containing tumor xenografts. The binding of [(131)I]MIP-1145 to melanoma cells in vitro was melanin dependent, increased over time, and insensitive to mild acid treatment, indicating that it was retained within cells. Cold carrier MIP-1145 did not reduce the binding, consistent with the high capacity of melanin binding of benzamides. In human melanoma xenografts, [(131)I]MIP-1145 exhibited diffuse tissue distribution and washout from all tissues except melanin-expressing tumors. Tumor uptake of 8.82% injected dose per gram (ID/g) was seen at 4 hours postinjection and remained at 5.91% ID/g at 24 hours, with tumor/blood ratios of 25.2 and 197, respectively. Single photon emission computed tomography imaging was consistent with tissue distribution results. The administration of [(131)I]MIP-1145 at 25 MBq or 2.5 GBq/m(2) in single or multiple doses significantly reduced SK-MEL-3 tumor growth, with multiple doses resulting in tumor regression and a durable response for over 125 days. To estimate human dosimetry, gamma camera imaging and pharmacokinetic analysis was performed in cynomolgus monkeys. The melanin-specific binding of [(131)I]MIP-1145 combined with prolonged tumor retention, the ability to significantly inhibit tumor growth, and acceptable projected human dosimetry suggest that it may be effective as a radiotherapeutic pharmaceutical for treating patients with metastatic malignant melanoma.

Adsorption of albumin and sodium hyaluronate on UHMWPE: a QCM-D and AFM study

The biotribological properties of artificial joints, in particular the efficiency of the lubrication, strongly determine their lifetime. The most commonly used artificial joints combine a metallic or ceramic part articulating against a ultra high molecular weight polyethylene (UHMWPE) counterface, and are lubricated by the periprosthetic fluid. This fluid contains several macromolecules, namely albumin and sodium hyaluronate (NaHA), that are known to be involved in the lubrication process. There are several studies in the literature concerning the interaction of the referred macromolecules with ceramic or metallic prosthetic materials. However, to our knowledge, information about their binding to the polymeric surface is practically inexistent. The objective of this work is to contribute to clarify the role played by albumin and NaHA on the biolubrication process, through the investigation of their interaction with the UHMWPE surface. The study involves adsorption measurements using a quartz crystal microbalance with dissipation (QCM-D), the characterization of the adsorbed films by atomic force microscopy (AFM) and wettability determinations. Albumin was found to adsorb strongly and extensively to the polymer, while NaHA led to a very low adsorption. In both cases rigid films were obtained, but with different morphology and porosity. The high binding affinity of the protein to the polymer was demonstrated both by the results of the fittings to Langmuir and Freundlich models and by the values of the adhesion forces determined by AFM. In the simultaneous adsorption of albumin and NaHA, protein adsorption is predominant and determines the surface properties.

Pharmacokinetic study of dexamethasone disodium phosphate using intravitreal, subconjunctival, and intravenous delivery routes in rabbits

Dexamethasone is a corticosteroid with proven efficacy for treating both anterior- and posterior-segment ocular diseases. Delivery of drugs to the back of the eye has always been a challenge, with dexamethasone being no exception. There are multiple delivery routes to the retina, with each exhibiting different pharmacokinetics, depending on the drug molecule and specific route of administration. In this study, we used intravenous (IV), subconjunctival (SC), and intravitreal (IVT) injections in rabbits to determine the pharmacokinetics of dexamethasone phosphate and its metabolic product, dexamethasone, at low (25 microg/kg) and high (250 microg/kg) doses. Plasma samples were collected from each group of animals at different time points up to 24 h after the injection. Using a liquid chromatographic mass spectrometric method with a limit of detection of 0.5 ng/mL, the plasma concentration for dexamethasone and its prodrug compound were quantified. IV delivery showed the fastest plasma elimination, followed by SC delivery. IVT delivery exhibited a depot effect, with very low plasma levels throughout the 24-h time course. At 24 h postinjection, only the high-dose IVT and low- and high-dose SC dexamethasone injections were still detectable in the plasma.

5,6-dihydroxyindole tetramers with "anomalous" interunit bonding patterns by oxidative coupling of 5,5',6,6'-tetrahydroxy-2,7'-biindolyl: emerging complexities on the way toward an improved model of eumelanin buildup

Chemical or enzymatic oxidation of 5,6-dihydroxyindole (1) leads to the rapid deposition of a black solid resembling eumelanin pigments by way of a complex oligomerization/polymerization process that proceeds in the early stages via dimers 2-3 and trimers 5-6 characterized by 2,4'- and 2,7'-couplings. Despite extensive efforts, the structures of the higher oligomers, which define the structural architecture and physicochemical properties of the eumelanin particles, have so far defied elucidation. Using a dimer-dimer coupling strategy that has recently allowed the first successful entry to a tetramer of 1, we report now three additional tetramers obtained by oxidation of 5,5',6,6'-tetrahydroxy-2,7'-biindolyl (3) with the peroxidase/H2O2 system. On the basis of extensive 2D NMR and mass spectrometric analysis, the products were identified as 5,5',5'',5''',6,6',6'',6'''-octaacetoxy-7,2':3',3'':2'',7'''-tetraindolyl (acetylated 8, 3%), 5,5',5'',5''',6,6',6'',6' ''-octaacetoxy-2,7':4',4'':7'',2'''-tetraindolyl (acetylated 9, 4%), and 5,5',5'',5''',6,6',6'',6'''-octaacetoxy-2,7':2',3'':2'',7'''-tetraindolyl (acetylated 10, 5%), in which the inner units are linked through unexpected 3,3'-, 4,4'-, and 2,3'-linkages. If verified in further studies, the newly uncovered coupling patterns would entail important consequences for current models of eumelanin structure based on one-dimensional structural chains with extended pi-electron conjugation or pi-stacked flat oligomer aggregates.

Differential effects of dopamine melanin on norharman-induced toxicity in PC12 cells

The food contaminant norharman structurally resembles MPTP a compound that selectively damages pigmented brain areas. Both compounds are sequestered and retained in melanin-containing neurons. The aim of the study was to examine whether intracellular melanin can modulate the toxicity of norharman in melanin-loaded PC12 cells. Dopamine melanin protected against norharman-induced upregulation of grp78, activation of caspase 3 and necrosis at low concentrations (5 and 50 microM). In contrast, at a high conentration (500 microM) there was a significantly increased expression of grp78, hsp90 and caspase 3 and a disassociation of melanin aggregates leading to dispersal of granules to swollen neurite terminals. In human populations, a long-term low-level exposure to toxicants with a high affinity to melanin will probably result in accumulation in melanin-containing neurons in vivo. Our data suggest that accumulation of a neurotoxicant in melanin-loaded cells may lead to increased cell stress, apoptotic signaling and disassociation of melanin aggregates.

Short-Lived Quinonoid Species from 5,6-Dihydroxyindole Dimers en Route to Eumelanin Polymers: Integrated Chemical, Pulse Radiolytic, and Quantum Mechanical Investigation

The transient species formed by oxidation of three dimers of 5,6-dihydroxyindole (1), a major building block of the natural biopolymer eumelanin, have been investigated. Pulse radiolytic oxidation of 5,5',6,6'-tetrahydroxy-2,4'-biindolyl (3) and 5,5',6,6'-tetrahydroxy-2,7'-biindolyl (4) led to semiquinones absorbing around 450 nm, which decayed with second-order kinetics (2k=2.8x10(9) and 1.4x10(9) M-1 s-1, respectively) to give the corresponding quinones (500-550 nm). 5,5',6, 6'-Tetrahydroxy-2,2'-biindolyl (2), on the other hand, furnished a semiquinone (lamdamax=480 nm) which disproportionated at a comparable rate (2k=3x10(9) M-1 s-1) to give a relatively stable quinone (lamdamax=570 nm). A quantum mechanical investigation of o-quinone, quinonimine, and quinone methide structures of 2-4 suggested that oxidized 2-4 exist mainly as 2-substituted extended quinone methide tautomers. Finally, an oxidation product of 3 was isolated for the first time and was formulated as the hydroxylated derivative 5 arising conceivably by the addition of water to the quinone methide intermediate predicted by theoretical analysis. Overall, these results suggest that the oxidation chemistry of biindolyls 2-4 differs significantly from that of the parent 1, whereby caution must be exercised before concepts that apply strictly to the mode of coupling of 1 are extended to higher oligomers.