Isolation and Characterization of Allomelanin from Pathogenic Black Knot Fungus-a Sustainable Source of Melanin

Interactions of Melanin with Electromagnetic Radiation: From Fundamentals to Applications

Melanin, especially integumentary melanin, interacts in numerous ways with electromagnetic radiation, leading to a set of critical functions, including radiation protection, UV-protection, pigmentary and structural color productions, and thermoregulation. By harnessing these functions, melanin and melanin-like materials can be widely applied to diverse applications with extraordinary performance. Here we provide a unified overview of the melanin family (all melanin and melanin-like materials) and their interactions with the complete electromagnetic radiation spectrum (X-ray, Gamma-ray, UV, visible, near-infrared), which until now has been absent from the literature and is needed to establish a solid fundamental base to facilitate their future investigation and development. We begin by discussing the chemistries and morphologies of both natural and artificial melanin, then the fundamentals of melanin-radiation interactions, and finally the exciting new developments in high-performance melanin-based functional materials that exploit these interactions. This Review provides both a comprehensive overview and a discussion of future perspectives for each subfield of melanin that will help direct the future development of melanin from both fundamental and applied perspectives.

Melanin/melanin-like nanoparticles: As a naturally active platform for imaging-guided disease therapy

The development of biocompatible and efficient nanoplatforms that combine diagnostic and therapeutic functions is of great importance for precise disease treatment. Melanin, an endogenous biopolymer present in living organisms, has attracted increasing attention as a versatile bioinspired functional platform owing to its unique physicochemical properties (e.g., high biocompatibility, strong chelation of metal ions, broadband light absorption, high drug binding properties) and inherent antioxidant, photoprotective, anti-inflammatory, and anti-tumor effects. In this review, the fundamental physicochemical properties and preparation methods of natural melanin and melanin-like nanoparticles were outlined. A systematical description of the recent progress of melanin and melanin-like nanoparticles in single, dual-, and tri-multimodal imaging-guided the visual administration and treatment of osteoarthritis, acute liver injury, acute kidney injury, acute lung injury, brain injury, periodontitis, iron overload, etc. Was then given. Finally, it concluded with a reasoned discussion of current challenges toward clinical translation and future striving directions. Therefore, this comprehensive review provides insight into the current status of melanin and melanin-like nanoparticles research and is expected to optimize the design of novel melanin-based therapeutic platforms and further clinical translation.

Melanin: insights into structure, analysis, and biological activities for future development

Melanin, a widely distributed pigment found in various organisms, possesses distinct structures that can be classified into five main types: eumelanin (found in animals and plants), pheomelanin (found in animals and plants), allomelanin (found in plants), neuromelanin (found in animals), and pyomelanin (found in fungi and bacteria). In this review, we present an overview of the structure and composition of melanin, as well as the various spectroscopic identification methods that can be used, such as Fourier transform infrared (FTIR) spectroscopy, electron spin resonance (ESR) spectroscopy, and thermogravimetric analysis (TGA). We also provide a summary of the extraction methods of melanin and its diverse biological activities, including antibacterial properties, anti-radiation effects, and photothermal effects. The current state of research on natural melanin and its potential for further development is discussed. In particular, the review provides a comprehensive summary of the analysis methods used to determine melanin species, offering valuable insights and references for future research. Overall, this review aims to provide a thorough understanding of the concept and classification of melanin, its structure, physicochemical properties, and structural identification methods, as well as its various applications in the field of biology.

The Enigmatic World of Fungal Melanin: A Comprehensive Review

Synthetic dyes are generally not safe for human health or the environment, leading to the continuous search and growing demand for natural pigments that are considered safer, biodegrade more easily, and are environmentally beneficial. Among micro-organisms, fungi represent an emerging source of pigments due to their many benefits; therefore, they are readily viable on an industrial scale. Among all the bioactive pigments produced by fungi, melanin is an enigmatic, multifunctional pigment that has been studied for more than 150 years. This dark pigment, which is produced via the oxidative polymerization of phenolic compounds, has been investigated for its potential to protect life from all kingdoms, including fungi, from biotic and abiotic stresses. Over time, the research on fungal melanin has attracted a significant amount of scientific interest due to melanin's distinct biological activities and multifarious functionality, which is well-documented in the literature and could possibly be utilized. This review surveys the literature and summarizes the current discourse, presenting an up-to-date account of the research performed on fungal melanin that encompasses its types, the factors influencing its bioactivity, the optimization of fermentation conditions to enhance its sustainable production, its biosynthetic pathways, and its extraction, as well as biochemical characterization techniques and the potential uses of melanin in a wide range of applications in various industries. A massive scope of work remains to circumvent the obstacles to obtaining melanin from fungi and exploring its future prospects in a diverse range of applications.

Insight into the Antioxidant Activity of 1,8-Dihydroxynaphthalene Allomelanin Nanoparticles

Melanins are stable and non-toxic pigments with great potential as chemopreventive agents against oxidative stress for medical and cosmetic applications. Allomelanin is a class of nitrogen-free melanin often found in fungi. The artificial allomelanin obtained by the polymerization of 1,8-dihydroxynaphthalene (DHN), poly-DHN (PDHN), has been recently indicated as a better radical quencher than polydopamine (PDA), a melanin model obtained by the polymerization of dopamine (DA); however, the chemical mechanisms underlying this difference are unclear. Here we investigate, by experimental and theoretical methods, the ability of PDHN nanoparticles (PDHN-NP), in comparison to PDA-NP, to trap alkylperoxyl (ROO•) and hydroperoxyl (HOO•) radicals that are involved in the propagation of peroxidation in real conditions. Our results demonstrate that PDHN-NP present a higher antioxidant efficiency with respect to PDA-NP against ROO• in water at pH 7.4 and against mixed ROO• and HOO• in acetonitrile, showing catalytic cross-termination activity. The antioxidant capacity of PDHN-NP in water is 0.8 mmol/g (ROO• radicals quenched by 1 g of PDHN-NP), with a rate constant of 3 × 105 M-1 s-1 for each reactive moiety. Quantum-mechanical calculations revealed that, thanks to the formation of a H-bond network, the quinones in PDHN-NP have a high affinity for H-atoms, thus justifying the high reactivity of PDHN-NP with HOO• observed experimentally.

Isolation and characterization of blackish-brown BY2-melanin accumulated in cultured tobacco BY-2 cells

The tobacco BY-2 cell line is one of the most utilized plant cell lines. After long-term culture, the cells turn brown to black, but the causal pigment is unknown. We successfully isolated a blackish-brown pigment from BY-2 cells cultured for 3 weeks. Morphological and spectroscopic analyses indicated that the pigment had similar features to a melanin-like substance reported previously. Furthermore, physicochemical analyses revealed that this pigment possessed most of the properties of melanin-like pigments. In addition, the high nitrogen content suggested that it differed from common plant melanins classified as allomelanins, suggesting a novel eumelanin-like pigment: "BY2-melanin". This is the first example showing that eumelanin-like pigments are produced in the cultures of plant cells for which the accumulation of melanin has not been reported. This tobacco BY-2 cell culture technique may represent a customizable and sustainable alternative to conventional melanin production platforms, with significant potential for industrial and pharmacological applications.

Nanoparticles derived from naturally occurring metal chelators for theranostic applications

Metals are indispensable for the activities of all living things, from single-celled organisms to higher organisms, including humans. Beyond their intrinsic quality as metal ions, metals help creatures to maintain requisite biological processes by forming coordination complexes with endogenous ligands that are broadly distributed in nature. These types of naturally occurring chelating reactions are found through the kingdoms of life, including bacteria, plants and animals. Mimicking these naturally occurring coordination complexes with intrinsic biocompatibility may offer an opportunity to develop nanomedicine toward clinical applications. Herein, we introduce representative examples of naturally occurring coordination complexes in a selection of model organisms and highlight such bio-inspired metal-chelating nanomaterials for theranostic applications.

Melanin of fungi: from classification to application

Melanin is a secondary metabolite composed of complex heterogeneous polymers. Fungal melanin is considered to be a sustainable and biodegradable natural pigment and has a variety of functional properties and biological activities. On one hand, due to its own specific properties it can play the role of antioxidant, anti-radiation, adsorption, and photoprotection. On the other hand, it has good biological activities such as hepatoprotective effect, hypolipidemic effect and anti-cancer. Therefore, it is widely used in various fields of daily life, including dyeing, food, biomedical and commercial industry. It is conducive to environmental protection and human health. However, the insolubility of fungal melanin in water, acids and organic solvents has been an obstacle to its commercial applications. Thus, the chemical modification methods of fungal melanin are summarized to increase its solubility and expand the application fields. Although fungal melanin has been used in many industries, as the structure and function of fungal melanin and modified melanin are further studied, more functional properties and bioactivities are expected to be discovered for a wide range of applications in the future.