Probing the heterogeneous structure of eumelanin using ultrafast vibrational fingerprinting

Eumelanin is a brown-black biological pigment with sunscreen and radical scavenging functions important to numerous organisms. Eumelanin is also a promising redox-active material for energy conversion and storage, but the chemical structures present in this heterogeneous pigment remain unknown, limiting understanding of the properties of its light-responsive subunits. Here, we introduce an ultrafast vibrational fingerprinting approach for probing the structure and interactions of chromophores in heterogeneous materials like eumelanin. Specifically, transient vibrational spectra in the double-bond stretching region are recorded for subsets of electronic chromophores photoselected by an ultrafast excitation pulse tuned through the UV-visible spectrum. All subsets show a common vibrational fingerprint, indicating that the diverse electronic absorbers in eumelanin, regardless of transition energy, contain the same distribution of IR-active functional groups. Aggregation of chromophores diverse in oxidation state is the key structural property underlying the universal, ultrafast deactivation behavior of eumelanin in response to photoexcitation with any wavelength.

Melanin distribution from the dermal-epidermal junction to the stratum corneum: non-invasive in vivo assessment by fluorescence and Raman microspectroscopy

The fate of melanin in the epidermis is of great interest due to its involvement in numerous physiological and pathological processes in the skin. Melanin localization can be assessed ex vivo and in vivo using its distinctive optical properties. Melanin exhibits a characteristic Raman spectrum band shape and discernible near-infrared excited (NIR) fluorescence. However, a detailed analysis of the capabilities of depth-resolved confocal Raman and fluorescence microspectroscopy in the evaluation of melanin distribution in the human skin is lacking. Here we demonstrate how the fraction of melanin at different depths in the human skin in vivo can be estimated from its Raman spectra (bands at 1,380 and 1,570 cm-1) using several procedures including a simple ratiometric approach, spectral decomposition and non-negative matrix factorization. The depth profiles of matrix factorization components specific to melanin, collagen and natural moisturizing factor provide information about their localization in the skin. The depth profile of the collagen-related matrix factorization component allows for precise determination of the dermal-epidermal junction, i.e. the epidermal thickness. Spectral features of fluorescence background originating from melanin were found to correlate with relative intensities of the melanin Raman bands. We also hypothesized that NIR fluorescence in the skin is not originated solely from melanin, and the possible impact of oxidized species should be taken into account. The ratio of melanin-related Raman bands at 1,380 and 1,570 cm-1 could be related to melanin molecular organization. The proposed combined analysis of the Raman scattering signal and NIR fluorescence could be a useful tool for rapid non-invasive in vivo diagnostics of melanin-related processes in the human skin.

Detection of a pheomelanin-like pigment by EPR spectroscopy in the mycelium of Plenodomus biglobosus

Melanin occurrence in Plenodomus biglobosus was investigated using electron paramagnetic (spin) resonance (EPR, ESR) spectroscopy. The fungus was isolated from living and dead leaves of European ash (Fraxinus excelsior L.). Dark pigmentation of P. biglobosus mycelium in vitro, especially on the reverse, was observed. The black coloration intensified with the age of the culture and inspired us to check if the analyzed fungus species synthesizes melanin. Melanin contains unpaired electrons, thus, EPR spectroscopy was applied, as a specific technique, to verify its presence in P. biglobosus. The EPR spectrum of the mycelium showed a very strong melanin signal, revealing pheomelanin-like features. Thus, the black pigment of P. biglobosus was clearly identified as melanin. However, no melanin was detected in the apparently dark culture medium even when zinc (II) acetate was added to increase the sensitivity of detection. Pheomelanin has many unusual biological functions but it is not commonly found in fungi. Detection of this type of melanin in P. biglobosus, which can be both endophytic or pathogenic, suggests a closer examination of the potential role of this melanin in host-parasite interaction.

Conidial Melanin of the Human-Pathogenic Fungus Aspergillus fumigatus Disrupts Cell Autonomous Defenses in Amoebae

The human-pathogenic fungus Aspergillus fumigatus is a ubiquitous saprophyte that causes fatal lung infections in immunocompromised individuals. Following inhalation, conidia are ingested by innate immune cells and can arrest phagolysosome maturation. How this virulence trait could have been selected for in natural environments is unknown. Here, we found that surface exposure of the green pigment 1,8-dihydroxynaphthalene-(DHN)-melanin can protect conidia from phagocytic uptake and intracellular killing by the fungivorous amoeba Protostelium aurantium and delays its exocytosis from the nonfungivorous species Dictyostelium discoideum To elucidate the antiphagocytic properties of the surface pigment, we followed the antagonistic interactions of A. fumigatus conidia with the amoebae in real time. For both amoebae, conidia covered with DHN-melanin were internalized at far lower rates than were seen with conidia lacking the pigment, despite high rates of initial attachment to nonkilling D. discoideum When ingested by D. discoideum, the formation of nascent phagosomes was followed by transient acidification of phagolysosomes, their subsequent neutralization, and, finally, exocytosis of the conidia. While the cycle was completed in less than 1 h for unpigmented conidia, the process was significantly prolonged for conidia covered with DHN-melanin, leading to an extended intracellular residence time. At later stages of this cellular infection, pigmented conidia induced enhanced damage to phagolysosomes and infected amoebae failed to recruit the ESCRT (endosomal sorting complex required for transport) membrane repair machinery or the canonical autophagy pathway to defend against the pathogen, thus promoting prolonged intracellular persistence in the host cell and the establishment of a germination niche in this environmental phagocyte.IMPORTANCE Infections with Aspergillus fumigatus are usually acquired by an inhalation of spores from environmental sources. How spores of a saprophytic fungus have acquired abilities to withstand and escape the phagocytic attacks of innate immune cells is not understood. The fungal surface pigment dihydroxynaphtalene-melanin has been shown to be a crucial factor for the delay in phagosome maturation. Here, we show that this pigment also has a protective function against environmental phagocytes. Pigmented conidia escaped uptake and killing by the fungus-eating amoeba Protostelium aurantium When ingested by the nonfungivorous phagocyte Dictyostelium discoideum, the pigment attenuated the launch of cell autonomous defenses against the fungal invader, such as membrane repair and autophagy, leading to prolonged intracellular retention. Membrane damage and cytoplasmic leakage may result in an influx of nutrients and thus may further promote intracellular germination of the fungus, indicating that A. fumigatus has acquired some of the basic properties of intracellular pathogens.

Photoprotection and Skin Pigmentation: Melanin-Related Molecules and Some Other New Agents Obtained from Natural Sources

Direct sun exposure is one of the most aggressive factors for human skin. Sun radiation contains a range of the electromagnetic spectrum including UV light. In addition to the stratospheric ozone layer filtering the most harmful UVC, human skin contains a photoprotective pigment called melanin to protect from UVB, UVA, and blue visible light. This pigment is a redox UV-absorbing agent and functions as a shield to prevent direct UV action on the DNA of epidermal cells. In addition, melanin indirectly scavenges reactive oxygenated species (ROS) formed during the UV-inducing oxidative stress on the skin. The amounts of melanin in the skin depend on the phototype. In most phenotypes, endogenous melanin is not enough for full protection, especially in the summertime. Thus, photoprotective molecules should be added to commercial sunscreens. These molecules should show UV-absorbing capacity to complement the intrinsic photoprotection of the cutaneous natural pigment. This review deals with (a) the use of exogenous melanin or melanin-related compounds to mimic endogenous melanin and (b) the use of a number of natural compounds from plants and marine organisms that can act as UV filters and ROS scavengers. These agents have antioxidant properties, but this feature usually is associated to skin-lightening action. In contrast, good photoprotectors would be able to enhance natural cutaneous pigmentation. This review examines flavonoids, one of the main groups of these agents, as well as new promising compounds with other chemical structures recently obtained from marine organisms.

Electron Paramagnetic Resonance Imaging of Melanin in Honey Bee

Honey bees play a crucial role in the nature by pollinating wild flowers. Over the past years, there has been an increasing concern regarding the honey bee colony decline. Pesticides or environmental effects targeting the biochemistry of insect chitin and cuticle coating may be in part responsible for honey bee pathologies. We here propose the use of electron paramagnetic resonance imaging (EPRI) as a tool to image the melanin-chitin complexes as part of the exoskeleton of the honey bee. EPRI at 9.65 GHz was applied on intact freeze-dried bees. The imaging data were collected on the melanin peak. High-resolution images revealed that this compound is extensively distributed in the periphery of the animal, data consistent with the localization in the cuticle of the bee. While EPR of melanin has been so far explored in the context of melanoma characterization, it may offer new opportunities in research on honey bees and other insects.

Adsorptive removal of trivalent and pentavalent arsenic from aqueous solutions using iron and copper impregnated melanin extracted from the marine bacterium Pseudomonas stutzeri

The metalloid arsenic is one of the most conspicuous groundwater contaminants in the Indian subcontinent and its removal from aqueous medium is the main focus of this study. The study aims at functionalising melanin using iron and copper for the efficient removal of arsenic and rendering water fit for consumption. Melanin obtained from the marine bacteria Pseudomonas stutzeri was functionalised by iron impregnation (Fe-melanin) and copper impregnation (Cu-melanin). Morphological studies using FESEM portrayed the impregnated iron and copper granules on the surface of melanin, while XRD analysis confirmed the presence of Fe₂O₃ and CuO on melanin. Adsorption studies on As (V) and As (III) were conducted using Fe-melanin and Cu-melanin for different operating variables like pH, temperature and contact time. More than 99% per cent of As (III) and As (V) from water was removed at a pH range between 4 and 6 within 50 min in the case of Fe-melanin and 80 min for Cu-melanin. Adsorption equilibrium studies showed better fit with Langmuir adsorption isotherm and had good agreement with Redlich-Peterson's three-parameter model. The maximum adsorption capacities of Fe-melanin and Cu-melanin obtained from Langmuir adsorption model are 50.12 and 20.39 mg/g, respectively, for As (V) and similarly 39.98 and 19.52 mg/g, respectively, for As (III). Arsenic-binding to the functionalised melanin was confirmed using FT-IR and the XPS analysis. Reuse of the adsorbent was effectively done by desorbing the iron and copper together with the bound As (III) and As (V) and further re-impregnation of iron and copper in melanin. Re-functionalised melanin showed 99% adsorption efficiency up to four cycles of adsorption/desorption.

The Guanidine Pseudoalkaloids 10-Methoxy-Leonurine and Leonurine Act as Competitive Inhibitors of Tyrosinase

Tyrosinase plays a key role in the production of melanin. A variety of industrial fields have shown interest in the development of tyrosinase inhibitors from plants. In this study, compounds 1–5 derived from Leonurus japonicas were evaluated to determine their ability to inhibit tyrosinase. Of these, 10-methoxy-leonurine (1) and leonurine (2) exhibited IC₅₀ values of 7.4 ± 0.4 and 12.4 ± 0.8 μM, respectively, and acted as competitive inhibitors of tyrosinase, with Ki values in the micromolar range. In silico modeling revealed a guanidine group located in the inner cavity and a benzene ring docked within the active site of these compounds. These guanidine pseudoalkaloids show potential not only as tyrosinase inhibitors but also as lead compounds in new scaffolds for the development of novel inhibitors.

A Dual-Modality MR/PA Imaging Contrast Agent Based on Ultrasmall Biopolymer Nanoparticles for Orthotopic Hepatocellular Carcinoma Imaging

BACKGROUND

Hepatocellular carcinoma (HCC) is the second leading cause of cancer death and early stage diagnosis can greatly increase the survival rate of patient. However, the accurate detection of HCC remains an urgent challenge in medical diagnosis. The combination of magnetic resonance imaging (MRI) and photoacoustic imaging (PAI) are conducive for accurate locating of cancerous tissue. Therefore, it is necessary to explore a more facile and biosafe dual-modal contrast agent for orthotopic HCC detection.

METHODS

In this study, a promising contrast agent had been identified based on gadolinium chelated melanin nanoparticles and evaluated its usage as a dual-modal T1 MRI and PAI contrast agent for orthotopic HCC detection.

RESULTS

The gadolinium-based melanin nanoparticles presented ultrasmall size, high chelation stability and negligible cytotoxicity estimated by CCK-8 assay. Moreover, the nanoparticle exhibited higher r1 relaxivity (45.762 mM-1 s-1) than clinically approved Gadodiamide (4.975 mM-1 s-1) at 1.5 T MR scanning. A linear regression analysis confirmed that the nanoparticles were ideal candidates for PAI in vitro. After the nanoparticles were injected into vein in mice with orthotopic HCC, a dramatic increase in signal of the liver was observed at 0.5 hr by MRI and PAI, while the tumor exerted remarkable signal enhancement at 7 hrs, showing excellent detection sensitivity. In addition, the nanoparticles exhibited excellent biocompatibility and they can be excreted through both hepatobiliary and renal pathways after diagnosis.

CONCLUSION

These results indicate that the ultrasmall gadolinium chelated melanin nanoparticles is a promising candidate as a dual-modal MRI/PAI contrast agent for the detection of orthotopic HCC.

Shedding light on melanins within in situ human eye melanocytes using 2-photon microscopy profiling techniques

Choroidal melanocytes (HCMs) are melanin-producing cells in the vascular uvea of the human eye (iris, ciliary body and choroid). These cranial neural crest-derived cells migrate to populate a mesodermal microenvironment, and display cellular functions and extracellular interactions that are biologically distinct to skin melanocytes. HCMs (and melanins) are important in normal human eye physiology with roles including photoprotection, regulation of oxidative damage and immune responses. To extend knowledge of cytoplasmic melanins and melanosomes in label-free HCMs, a non-invasive 'fit-free' approach, combining 2-photon excitation fluorescence lifetimes and emission spectral imaging with phasor plot segmentation was applied. Intracellular melanin-mapped FLIM phasors showed a linear distribution indicating that HCM melanins are a ratio of two fluorophores, eumelanin and pheomelanin. A quantitative histogram of HCM melanins was generated by identifying the image pixel fraction contributed by phasor clusters mapped to varying eumelanin/pheomelanin ratio. Eumelanin-enriched dark HCM regions mapped to phasors with shorter lifetimes and longer spectral emission (580-625 nm) and pheomelanin-enriched lighter pigmented HCM regions mapped to phasors with longer lifetimes and shorter spectral emission (550-585 nm). Overall, we demonstrated that these methods can identify and quantitatively profile the heterogeneous eumelanins/pheomelanins within in situ HCMs, and visualize melanosome spatial distributions, not previously reported for these cells.

Artificial Allomelanin Nanoparticles

Allomelanin is a type of nitrogen-free melanin most commonly found in fungi. Its existence enhances resistance of the organisms to environmental damage and helps fungi survive harsh radiation conditions such as those found on spacecraft and inside contaminated nuclear power plants. We report the preparation and characterization of artificial allomelanin nanoparticles (AMNPs) via oxidative oligomerization of 1,8-dihydroxynaphthalene (1,8-DHN). We describe the resulting morphological and size control of AMNPs and demonstrate that they are radical scavengers. Finally, we show that AMNPs are taken up by neonatal human epidermal keratinocytes and packaged into perinuclear caps where they quench reactive oxygen species generated following UV exposure.

Semi-automated standardisation of melanin bleaching procedures of heavily pigmented melanocytic lesions for immunohistochemical analysis on an automated platform

Background: The diagnosis of heavily pigmented melanocytic lesions is problematic. This is often compounded by lack of visibility of nuclear detail of tumour cells due to physical masking by melanin pigment. Similarly, there can be colour merging of chromogenic final reaction products with melanin, making an evidence of antigenic localisation problematic. There are a number of melanin bleaching techniques available for immunohistochemical assessments.Material and methods: All methods to date have involved the bleaching of melanin as a manually performed primary step before loading subsequently bleached slides onto automated immunohistochemical platforms. Here we define a semi-automated bleaching procedure that allows full integration on one of the most widely employed automated IHC staining platforms (Roche Ventana BenchMark Ultra). The bleaching protocol was defined on the BenchMark Ultra and involved the assessment of 24 histological cases of heavily pigmented malignant melanoma lesions (13 cutaneous and 11 metastatic) routinely fixed processed and paraffin wax embedded.Results: Completion of the bleaching was assessed on H&E preparations performed following the semi-automated bleaching step and employing the Roche Ventana BenchMark Ultra machine for 60 min at 42°C. Complete immunohistochemical staining was achieved on the automated platform within 5-6 h including the bleaching step. Results were consistent across all tissue evaluated.Discussion: This data provides evidence that the hydrogen peroxide bleaching procedure can be adapted for integration on one of the most widely employed automated IHC staining platforms and as a result, improve the efficiency and reproducibility of the technique.

Antioxidative Properties of Melanins and Ommochromes from Black Soldier Fly Hermetia illucens

A comparative study of melanin and ommochrome-containing samples, isolated from the black soldier fly (BSF) by enzymatic hydrolysis, alkaline and acid alcohol extraction or by acid hydrolysis, was carried out. Melanin was isolated both as a melanin-chitin complex and as a water-soluble melanin. Acid hydrolysis followed by delipidization yielded a more concentrated melanin sample, the electron spin resonance (ESR) signal of which was 2.6 × 1018 spin/g. The ommochromes were extracted from the BSF eyes with acid methanol. The antiradical activity of BSF melanins and ommochromes was determined by the method of quenching of luminol chemiluminescence. It has been shown that delipidization of water-soluble melanin increases its antioxidant properties. A comparison of the antioxidant activity of BSF melanins and ommochromes in relation to photoinduced lipid peroxidation was carried out. The ESR characteristics of native and oxidized melanins and ommochromes were studied. It is assumed that H. illucens adult flies can be a useful source of natural pigments with antioxidant properties.

Melanin-dot-mediated delivery of metallacycle for NIR-II/photoacoustic dual-modal imaging-guided chemo-photothermal synergistic therapy

Discrete Pt(II) metallacycles have potential applications in biomedicine. Herein, we engineered a dual-modal imaging and chemo-photothermal therapeutic nano-agent 1 that incorporates discrete Pt(II) metallacycle 2 and fluorescent dye 3 (emission wavelength in the second near-infrared channel [NIR-II]) into multifunctional melanin dots with photoacoustic signal and photothermal features. Nano-agent 1 has a good solubility, biocompatibility, and stability in vivo. Both photoacoustic imaging and NIR-II imaging in vivo confirmed that 1 can effectively accumulate at tumor sites with good signal-to-background ratio and favorable distribution. Guided by precise dual-modal imaging, nano-agent 1 exhibits a superior antitumor performance and less severe side effects compared with a single treatment because of the high efficiency of the chemo-photothermal synergistic therapy. This study shows that nano-agent 1 provides a promising multifunctional theranostic platform for potential applications in biomedicine.

Multimodality imaging of naturally active melanin nanoparticles targeting somatostatin receptor subtype 2 in human small-cell lung cancer

Somatostatin receptor subtype 2 (SSTR2) is highly expressed in pulmonary neuroendocrine tumors, which account for approximately 25% of all lung cancers including small-cell lung cancer (SCLC). It is possible to establish SCLC-specific imaging agents for multimodal imaging to obtain tumor integrity information. Herein, we constructed novel multifunctional organic melanin nanoparticles (MNPs) as a carrier and surface-loaded somatostatin analog octreotide to produce a human small-cell lung cancer-targeted nanoprobe OCT-PEG-MNPs. MNPs have an excellent photoacoustic imaging (PAI) function and can be directly chelated with the magnetic resonance contrast agent Mn2+, and N-bromo succinimide (NBS) can be used as an oxidant to label the nanoparticles with the long half-life radionuclide 124I by an electrophilic substitution reaction. Therefore, (124I, Mn) OCT-PEG-MNPs can not only be used for PAI but also be used for positron emission tomography (PET) and magnetic resonance imaging (MRI). The NCI-H69 SCLC tumor xenograft model with high SSTR2 expression was constructed to evaluate the multimodal imaging ability of (124I, Mn) OCT-PEG-MNPs. This nanoprobe showed good imaging abilities in PAI, MRI and PET. The PA images showed that the photoacoustic signal in the NCI-H69 tumor site gradually increased with time, and the NCI-H69 xenograft showed a clear increase in the T1-weighted signal intensity after injection of Mn-OCT-PEG-MNPs at 24 h compared to that in the prescan. MicroPET and biodistribution studies showed that the uptake of NCI-H69 tumors (8.03 ± 0.37% ID g-1) was significantly higher than that in the control A549 model (3.35 ± 0.54% ID g-1) after injection of (124I, Mn) OCT-PEG-MNPs at 24 h. The (124I, Mn) OCT-PEG-MNPs were successfully applied to multimodal imaging in a small-cell lung cancer model with high SSTR2 expression. This nanoprobe may be considered for clinical trials since it combines the numerous advantages of organic nanoparticles.

Bioinspired Production of Noniridescent Structural Colors by Adhesive Melanin-like Particles

Structural color printing of colloidal photonic films with tunable structures or optical properties is of great importance owing to their practical applications. In this article, we present a general method for the fabrication of colloidal particle films with tailored packing geometries by self-assembly of adhesive melanin-like polydopamine (PDA)-coated particles. The adhesion of particles is controlled by varying the thickness of the PDA coating, making it possible for dip coating of colloidal crystals, partly ordered or amorphous colloidal arrays (ACAs) with a tunable degree of order. We further studied the structural color printing of adhesive particles by infiltration-assisted or standard inkjet printing methods. Compared with bare particles, PDA-coated particles not only allow for control over color brightness/angle dependence of the photonic films but also significantly enhance the color quality of ACAs, both of which are useful for display, anticounterfeiting, or sensing applications. Owing to the inherent strong adhesiveness of PDA to virtually all types of surfaces, this PDA-based methodology can be potentially extended to a diverse range of colloidal particles toward the development of photonic devices.

The structural unit of melanin in the cell wall of the fungal pathogen Cryptococcus neoformans

Melanins are synthesized macromolecules that are found in all biological kingdoms. These pigments have a myriad of roles that range from microbial virulence to key components of the innate immune response in invertebrates. Melanins also exhibit unique properties with potential applications in physics and material sciences, ranging from electrical batteries to novel therapeutics. In the fungi, melanins, such as eumelanins, are components of the cell wall that provide protection against biotic and abiotic elements. Elucidation of the smallest fungal cell wall-associated melanin unit that serves as a building block is critical to understand the architecture of these polymers, its interaction with surrounding components, and their functional versatility. In this study, we used isopycnic gradient sedimentation, NMR, EPR, high-resolution microscopy, and proteomics to analyze the melanin in the cell wall of the human pathogenic fungus Cryptococcus neoformans We observed that melanin is assembled into the cryptococcal cell wall in spherical structures ∼200 nm in diameter, termed melanin granules, which are in turn composed of nanospheres ∼30 nm in diameter, termed fungal melanosomes. We noted that melanin granules are closely associated with proteins that may play critical roles in the fungal melanogenesis and the supramolecular structure of this polymer. Using this structural information, we propose a model for C. neoformans' melanization that is similar to the process used in animal melanization and is consistent with the phylogenetic relatedness of the fungal and animal kingdoms.

Melanins of Inonotus Obliquus: Bifidogenic and Antioxidant Properties

Extracts and melanins from Inonotus obliquus are widely used in medicine due to their high antioxidant properties. This study is dedicated to define the influence of the physicochemical and antioxidant properties of Inonotus obliquus melanins and their bifidogenic effects on Bifidobacterium bifidum 1 and Bifidobacterium animalis subsp. lactis. For this purpose, melanins precipitated from Inonotus obliquus aqueous extracts, obtained by a few methods, and separated melanin fractions by organic solvents were used. For the melanin physicochemical properties analysis spectrophotometry, electron paramagnetic resonance (EPR) spectroscopy and dynamic light scattering methods were applied. Melanins and their fractions difference in particle size and charge, antioxidant properties, and redox potential were revealed. It was shown that the redox potential, the size of melanin particles and the z-potential had maximum influence on bifidobacteria growth. The greatest activating effect on bifidobacteria was established by using melanin isolated from aqueous microwave extracts in concentrations of 10⁻¹³, 10⁻¹⁰, 10⁻⁵ g/cm³. The use of this melanin with antioxidant activity 0.67 ± 0.06 mg/g (expressed as ascorbic acid equivalent), and with redox potential −5.51 ± 2.22 mV as a prebiotic allowed the growth of Bifidobacterium bifidum 1 s to increase by 1.4 times in comparison with ascorbic acid by 24 h of cultivation.

Dopamine-melanin nanoparticles scavenge reactive oxygen and nitrogen species and activate autophagy for osteoarthritis therapy

Anti-oxidative agents hold great potential in osteoarthritis (OA) therapy. However, most radical scavengers have poor biocompatibility and potential cytotoxicity, which limit their applications. Herein we explore dopamine melanin (DM) nanoparticles as a novel scavenger of reactive oxygen species (ROS) and reactive nitrogen species (RNS). DM nanoparticles show low cytotoxicity and a strong ability to sequester a broad range of ROS and RNS, including superoxides, hydroxyl radicals, and peroxynitrite. This translates to excellent anti-inflammatory and chondro-protective effects by inhibiting intracellular ROS and RNS and promoting antioxidant enzyme activities. With an average diameter of 112.5 nm, DM nanoparticles can be intra-articularly (i.a.) injected into an affected joint and retained at the injection site. When tested in vivo in rodent OA models, DM nanoparticles showed diminished inflammatory cytokine release and reduced proteoglycan loss, which in turn slowed down cartilage degradation. Mechanistic studies suggest that DM nanoparticles also enhance autophagy that benefits OA control. In summary, our study suggests DM nanoparticles as a safe and promising therapeutic for OA.

Slow-Binding Inhibition of Tyrosinase by Ecklonia cava Phlorotannins

Tyrosinase inhibitors improve skin whitening by inhibiting the formation of melanin precursors in the skin. The inhibitory activity of seven phlorotannins (1-7), triphlorethol A (1), eckol (2), 2-phloroeckol (3), phlorofucofuroeckol A (4), 2-O-(2,4,6-trihydroxyphenyl)-6,6'-bieckol (5), 6,8'-bieckol (6), and 8,8'-bieckol (7), from Ecklonia cava was tested against tyrosinase, which converts tyrosine into dihydroxyphenylalanine. Compounds 3 and 5 had IC50 values of 7.0 ± 0.2 and 8.8 ± 0.1 μM, respectively, in competitive mode, with Ki values of 8.2 ± 1.1 and 5.8 ± 0.8 μM. Both compounds showed the characteristics of slow-binding inhibitors over the time course of the enzyme reaction. Compound 3 had a single-step binding mechanism and compound 5 a two-step-binding mechanism. With stable AutoDock scores of -6.59 and -6.68 kcal/mol, respectively, compounds 3 and 5 both interacted with His85 and Asn260 at the active site.

Photoacoustic properties of anterior ocular tissues

Clinical imaging techniques for the anterior segment of the eye provide excellent anatomical information, but molecular imaging techniques are lacking. Molecular photoacoustic imaging is one option to address this need, but implementation requires use of contrast agents to distinguish molecular targets from background photoacoustic signals. Contrast agents are typically selected based on a priori knowledge of photoacoustic properties of tissues. However, photoacoustic properties of anterior ocular tissues have not been studied yet. Herein, anterior segment anatomy and corresponding photoacoustic signals were analyzed in brown and blue porcine eyes ex vivo. Measured photoacoustic spectra were compared to known optical absorption spectra of endogenous chromophores. In general, experimentally measured photoacoustic spectra matched expectations based on absorption spectra of endogenous chromophores reported in the literature, and similar photoacoustic spectra were observed in blue and brown porcine eyes. However, unique light-tissue interactions at the iris modified photoacoustic signals from melanin. Finally, we demonstrated how the measured PA spectra established herein can be used for one application of molecular PA imaging, detecting photoacoustically labeled stem cells in the anterior segment for glaucoma treatment.

Ellipsoidal Artificial Melanin Particles as Building Blocks for Biomimetic Structural Coloration

Inspired by the structural coloration of anisotropic materials in nature, we demonstrate the preparation of structural color materials by the assembly of anisotropic particles. Spherical artificial melanin particles consisting of a polystyrene core and polydopamine shell were stretched asymmetrically to form uniform-sized ellipsoidal particles with different aspect ratios. The aspect ratio and assembly method of the ellipsoidal particles influence the structural coloration, indicating that the particle shape is one of the important parameters for controlling the structural coloration. The discovery of a method to control the structural color using ellipsoidal particles is useful in basic research on structural colors in nature and provides flexibility in material design and extends the application range of structural color materials.

Bioreduction of toxicity influenced by bioactive molecules secreted under metal stress by Azotobacter chroococcum

Heavy metal pollution destruct soil microbial compositions and functions, plant's performance and subsequently human health. Culturable microbes among many metal abatement strategies are considered inexpensive, viable and environmentally safe. In this study, nitrogen fixing bacterial strain CAZ3 recovered from chilli rhizosphere tolerated 100, 1000 and 1200 µg mL^-1 of cadmium, chromium and nickel, respectively and was identified as Azotobacter chroococcum by 16S rDNA sequence analysis. Under metal stress, cellular morphology of A. chroococcum observed under SEM was found distorted and shrinkage of cells was noticed when grown with 50 µg mL^-1 of Cd (cell size 1.7 µm) and 100 of µg mL^-1 Ni (cell size 1.3 µm) compared to untreated control (cell size 1.8 µm). In the presence of 100 µg mL^-1 of Cr, cells became elongated and measured 1.9 µm in size. Location of metals inside the cells was revealed by EDX. A dose dependent growth arrest and consequently the death of A. chroococcum cells was revealed under CLSM. A. chroococcum CAZ3 secreted 320, 353 and 133 µg EPS mL^-1 when grown with 100 µg mL^-1 each of Cd, Cr and Ni, respectively. The EDX revealed the presence of 0.4, 0.07 and 0.24% of Cd, Cr and Ni, respectively within EPS extracted from metal treated cells. Moreover, a dark brown pigment (melanin) secreted by A. chroococcum cells under metal pressure displayed tremendous metal chelating activity. The EDX spectra of melanin extracted from metal treated cells of A. chroococcum CAZ3 displayed 0.53, 0.22 and 0.12% accumulation of Cd, Cr and Ni, respectively. The FT-IR spectra of EPS and melanin demonstrated stretching vibrations and variations in surface functional groups of bacterial cells. The C-H stretching of CH₃ in fatty acids and CH₂ groups, stretching of N-H bond of proteins and O-H bond of hydroxyl groups caused the shifting of peaks in the EPS spectra. Similar stretching vibrations were recorded in metal treated melanin which involved CHO, alkyl, carboxylate and alkene groups resulting in significant peak shifts. Nuclear magnetic resonance (NMR) spectrum of EPS extracted from A. chroococcum CAZ3 revealed apparent peak signals at 4.717, 9.497, 9.369 and 9.242 ppm. However, ¹H NMR peaks were poorly resolved due largely to the impurity/viscosity of the EPS. The entrapment of metals by EPS and melanin was confirmed by EDX. Also, the induction and excretion of variable amounts of metallothioneins (MTs) by A. chroococcum under metal pressure was interesting. Conclusively, the present findings establish- (i) cellular damage due to Cd, Cr and Ni and (ii) role of EPS, melanin and MTs in adsorption/complexation and concurrently the removal of heavy metals. Considering these, A. chroococcum can be promoted as a promising candidate for supplying N efficiently to plants and protecting plants from metal toxicity while growing under metal stressed environment.

Unraveling the molecular nature of melanin changes in metastatic cancer

More people die from melanoma after a stage I diagnosis than after a stage IV diagnosis, because the tools available to clinicians do not readily identify which early-stage cancers will be aggressive. Near-infrared pump-probe microscopy detects fundamental differences in melanin structure between benign human moles and melanoma and also correlates with metastatic potential. However, the biological mechanisms of these changes have been difficult to quantify, as many different mechanisms can contribute to the pump-probe signal. We use model systems (sepia, squid, and synthetic eumelanin), cellular uptake studies, and a range of pump and probe wavelengths to demonstrate that the clinically observed effects come from alterations of the aggregated mode from "thick oligomer stacks" to "thin oligomer stacks" (due to changes in monomer composition) and (predominantly) deaggregation of the assembled melanin structure. This provides the opportunity to use pump-probe microscopy for the detection and study of melanin-associated diseases.

Photoacoustic-imaging-guided therapy of functionalized melanin nanoparticles: combination of photothermal ablation and gene therapy against laryngeal squamous cell carcinoma

Multimodality therapy under imaging-guidance is significant to improve the accuracy of cancer treatment. In this study, a photoacoustic imaging (PAI)-guided anticancer strategy based on poly-l-lysine functionalized melanin nanoparticles (MNP-PLL) was developed to treat laryngeal squamous cell carcinoma (LSCC). As a promising alternative to traditional therapies for LSCC, MNP-PLL/miRNA nanoparticles were combined with photothermal ablation against primary tumors and miR-145-5p mediated gene therapy for depleting the metastatic potential of tumor cells. Furthermore, taking advantage of the photoacoustic properties of melanin, PAI guided therapy could optimize the time point of NIR irradiation to maximize the efficacy of photothermal therapy (PTT). The in vitro and in vivo results proved that the combined treatments displayed the most significant tumor suppression compared with monotherapy. By integrating thermo-gene therapies into a theranostic nanoplatform, the MNP-PLL/miR-145-5p nanoparticles significantly suppressed the LSCC progression, indicating their great potential use for cancer therapy.