Melanin, a promising radioprotector: Mechanisms of actions in a mice model

Morphological changes in melanized and non-melanized Cryptococcus neoformans cells post exposure to sparsely and densely ionizing radiation demonstrate protective effect of melanin

There is a need for novel and effective prophylactic treatments and radioprotective materials to protect civilians and military personnel from ionizing radiation in contaminated environments. Melanin, a naturally occurring, ubiquitous pigment, has been shown to confer radioresistance, acting as a potential radioprotective agent. We have demonstrated that melanized Cryptococcus neoformans (CN) cells had improved survival post ionizing irradiation than non-melanized ones. The goal of this study was to identify morphological changes in melanized and non-melanized CN cells following irradiation with densely-ionizing deuterons and alpha particles relative to sparsely-ionizing gamma radiation. We observed significant differences between the melanized and non-melanized CN cellular ultrastructure following irradiation. Melanized CN cells were relatively resistant to mid and max-dose levels of alpha particles and deuterons irradiation. Following irradiation the capsule was stripped, but the cell wall was intact and structural integrity was maintained. At the maximum dose, cytoplasmic vacuolization, and mitochondrial swelling started to occur. In contrast, the non-melanized CN strain was sensitive to the mid-dose radiation. Non-melanized cells presented two morphologies: small condensed, and swollen, lacking structural integrity. This morphological investigation provides the first direct evidence of the radioprotective properties of melanin in CN cells subjected to high RBE and high LET ionizing radiation.

Effect of Low-Dose Selenium Supplementation on the Genotoxicity, Tissue Injury and Survival of Mice Exposed to Acute Whole-Body Irradiation

The aim of the present study is to evaluate the radioprotective effect of low-dose selenium supplementation (multiple administrations) on radiation toxicities and mortality induced by lethal dose of whole-body irradiation (WBI). For this, BALB/c mice received sodium selenite (4 μg/kg body wt) intraperitoneally for five consecutive days and subjected to WBI at an absorbed dose of 8 Gy (⁶⁰Co, 1 Gy/min). Administration of sodium selenite was continued even during the post irradiation days three times a week till the end of the experiment. The radioprotective effect was evaluated in terms of the improvement in 30 days post irradiation survival, protection from DNA damage, and biochemical and histological changes in radiosensitive organs. The results indicated that low-dose sodium selenite administration did not protect the mice from radiation-induced hematopoietic and gastrointestinal injuries and subsequent mortality. However, it significantly prevented the radiation-induced genotoxicity or DNA damage in peripheral leukocytes. Further sodium selenite administration modulated the messenger RNA (mRNA) expression of GPx1, GPx2, and GPx4 in the spleen and intestine differentially and led to a significant increase in GPx activity (∼1.5 to 2-folds) in these organs. In line with this observation, sodium selenite administration reduced the level of lipid peroxidation in the intestine. In conclusion, our study shows that low-dose sodium selenite supplementation can be an effective strategy to prevent WBI-induced genotoxicity but may not have an advantage against mortality sustained during nuclear emergencies.

Eumelanin-releasing spongy-like hydrogels for skin re-epithelialization purposes

Melanin function in the skin has been associated with pigmentation but other properties such as electrical conductance, photoprotection, and antioxidant and antimicrobial activity have also been recognized. Nonetheless, the use of melanin in a skin wound healing context has never been considered. In this sense, eumelanin particles with a typical round and nano-sized morphology and electrical conductivity of 2.09 × 10^-8 S cm^-1 were extracted from the ink of Sepia officinalis. The ability of primary human keratinocytes (hKCs) to phagocyte eumelanin, which was then accumulated in cytosolic vesicles and nuclei surroundings, was demonstrated. Keratinocyte viability and maturation was not affected by eumelanin contact, but at eumelanin amounts higher than 0.1 mg l^-1 cell morphology was altered and cell proliferation was inhibited. A time and eumelanin amount-dependent reduction of reactive oxygen species (ROS) released by eumelanin-containing ultraviolet (UV)-irradiated keratinocytes was observed. Eumelanin-containing gellan gum (GG) spongy-like hydrogels allowed a sustained release of eumelanin in the range of 0.1 to 5 mg l^-1, which was shown in vitro to not be harmful to hKCs, and the absence of a strong host reaction after subcutaneous implantation in mice. Herein, we propose spongy-like hydrogels as sustained release matrices of S. officinalis eumelanin for predicting a beneficial role in skin wound healing through a direct effect over keratinocytes.

Pharmacological Properties of Melanin and its Function in Health

The biological pigment melanin is present in most of the biological systems. It manifests a host of biological and pharmacological properties. Its role as a molecule with special properties and functions affecting general health, including photoprotective and immunological action, are well recognized. Its antioxidant, anti-inflammatory, immunomodulatory, radioprotective, hepatic, gastrointestinal and hypoglycaemic benefits have only recently been recognized and studied. It is also associated with certain disorders of the nervous system. In this MiniReview, we consider the steadily increasing literature on the bioavailability and functional activity of melanin. Published literature shows that melanin may play a number of possible pharmacological effects such as protective, stimulatory, diagnostic and curative roles in human health. In this MiniReview, possible health roles and pharmacological effects are considered.

Adult Mesenchymal Stem Cells and Radiation Injury

Recent understanding of the cellular and molecular signaling activations in adult mesenchymal stem cells (MSCs) has provided new insights into their potential clinical applications, particularly for tissue repair and regeneration. This review focuses on these advances, specifically in the context of self-renewal for tissue repair and recovery after radiation injury. Thus far, MSCs have been characterized extensively and shown to be useful in mitigation and therapy for acute radiation syndrome and cognitive dysfunction. Use of MSCs for treating radiation injury alone or in combination with additional trauma is foreseeable.

Multimodal-Imaging-Guided Cancer Phototherapy by Versatile Biomimetic Theranostics with UV and γ-Irradiation Protection

A versatile biomimetic theranostic agent based on magnetic melanin nanoparticles is developed for positron-emission tomography/magnetic resonance/photoacoustic/photothermal multimodal-imaging-guided cancer photothermal therapy and UV and γ-irradiation protection.

Evaluation of gamma ray-induced gastrointestinal tract morphological and proliferative activity changes in rhesus monkeys

To provide support for future pharmacology and preclinical studies, we have established a stable nonhuman primate animal model to demonstrate the histopathological changes in the gastrointestinal tract following gamma ray irradiation. In this study, 12 healthy rhesus monkeys were divided into 2 groups (control and radiation groups). Animals in the radiation group were exposed to gamma rays (cobalt 60 source) at a dose level of 6.5 Gy total body irradiation bilaterally (i.e. 3.25 Gy on each side). Control animals were sham exposed using identical procedures. After a 5-day in-life observation period, gastrointestinal tract tissues (esophagus, stomach, duodenum, jejunum, ileum, colon, and rectum) were collected and fixed in 10% neutral-buffered formalin for subsequent hematoxylin and eosin and 5-bromo-2-deoxyuridine (BrdU) immunohistochemistry processing. The results showed that the esophagus was undergoing degeneration without obvious inflammatory changes, while the stomach and duodenum exhibited both degeneration and inflammation. From the jejunum to the rectum, late-stage inflammation with glandular regeneration, as well as a high-level BrdU labeling index, was present.

Hemorrhage Exacerbates Radiation Effects on Survival, Leukocytopenia, Thrombopenia, Erythropenia, Bone Marrow Cell Depletion and Hematopoiesis, and Inflammation-Associated microRNAs Expression in Kidney

Exposure to high-dose radiation results in detrimental effects on survival. The effects of combined trauma, such as radiation in combination with hemorrhage, the typical injury of victims exposed to a radiation blast, on survival and hematopoietic effects have yet to be understood. The purpose of this study was to evaluate the effects of radiation injury (RI) combined with hemorrhage (i.e., combined injury, CI) on survival and hematopoietic effects, and to investigate whether hemorrhage (Hemo) enhanced RI-induced mortality and hematopoietic syndrome. Male CD2F1 mice (10 weeks old) were given one single exposure of γ- radiation (60Co) at various doses (0.6 Gy/min). Within 2 hr after RI, animals under anesthesia were bled 0% (Sham) or 20% (Hemo) of total blood volume via the submandibular vein. In these mice, Hemo reduced the LD50/30 for 30-day survival from 9.1 Gy (RI) to 8.75 Gy (CI) with a DMF of 1.046. RI resulted in leukocytopenia, thrombopenia, erythropenia, and bone marrow cell depletion, but decreased the caspase-3 activation response. RI increased IL-1β, IL-6, IL-17A, and TNF-α concentrations in serum, bone marrow, ileum, spleen, and kidney. Some of these adverse alterations were magnified by CI. Erythropoietin production was increased in kidney and blood more after CI than RI. Furthermore, CI altered the global miRNAs expression in kidney and the ingenuity pathway analysis showed that miRNAs viz., let-7e, miR-30e and miR-29b that were associated with hematopoiesis and inflammation. This study provides preliminary evidence that non-lethal Hemo exacerbates RI-induced mortality and cell losses associated with high-dose γ-radiation. We identified some of the initial changes occurring due to CI which may have facilitated in worsening the injury and hampering the recovery of animals ultimately resulting in higher mortality.

Structural Characterization of Melanin Pigments from Commercial Preparations of the Edible Mushroom Auricularia auricula

Many of the most widely consumed edible mushrooms are pigmented, and these have been associated with some beneficial health effects. Nevertheless, the majority of the reported compounds associated with these desirable properties are non-pigmented. We have previously reported that melanin pigment from the edible mushroom Auricularia auricula can protect mice against ionizing radiation, although no physicochemical characterization was reported. Consequently, in this study we have characterized commercial A. auricula mushroom preparations for melanin content and carried out structural characterization of isolated insoluble melanin materials using a panel of sophisticated spectroscopic and physical/imaging techniques. Our results show that approximately 10% of the dry mass of A. auricula is melanin and that the pigment has physicochemical properties consistent with those of eumelanins, including hosting a stable free radical population. Electron microscopy studies show that melanin is associated with the mushroom cell wall in a manner similar to that of melanin from the model fungus C. neoformans. Elemental analysis of melanin indicated C, H, and N ratios consistent with 5,6-dihydroxyindole-2-carboxylic acid/5,6-dihydroxyindole and 1,8-dihydroxynaphthalene eumelanin. Validation of the identity of the isolated product as melanin was achieved by EPR analysis. A. auricula melanin manifested structural differences, relative to the C. neoformans melanin, with regard to the variable proportions of alkyl chains or oxygenated carbons. Given the necessity for new oral and inexpensive radioprotective materials coupled with the commercial availability of A. auricula mushrooms, this product may represent an excellent source of edible melanin.

Coniferyl aldehyde reduces radiation damage through increased protein stability of heat shock transcriptional factor 1 by phosphorylation

PURPOSE

We previously screened natural compounds and found that coniferyl aldehyde (CA) was identified as an inducer of HSF1. In this study, we further examined the protective effects of CA against ionizing radiation (IR) in normal cell system.

METHODS AND MATERIALS

Western blotting and reverse transcription-polymerase chain reaction tests were performed to evaluate expression of HSF1, HSP27, and HSP70 in response to CA. Cell death and cleavage of PARP and caspase-3 were analyzed to determine the protective effects of CA in the presence of IR or taxol. The protective effects of CA were also evaluated using animal models.

RESULTS

CA increased stability of the HSF1 protein by phosphorylation at Ser326, which was accompanied by increased expression of HSP27 and HSP70. HSF1 phosphorylation at Ser326 by CA was mediated by EKR1/2 activation. Cotreatment of CA with IR or taxol in normal cells induced protective effects with phosphorylation- dependent patterns at Ser326 of HSF1. The decrease in bone marrow (BM) cellularity and increase of terminal deoxynucleotidyl transferase dUTP nick end labeling-positive BM cells by IR were also significantly inhibited by CA in mice (30.6% and 56.0%, respectively). A549 lung orthotopic lung tumor model indicated that CA did not affect the IR-mediated reduction of lung tumor nodules, whereas CA protected normal lung tissues from the therapeutic irradiation.

CONCLUSIONS

These results suggest that CA may be useful for inducing HSF1 to protect against normal cell damage after IR or chemotherapeutic agents.

On-column enzymatic synthesis of melanin nanoparticles using cryogenic poly(AAM-co-AGE) monolith and its free radical scavenging and electro-catalytic properties

“Novel approach for biosynthesis of melanin nanoparticles by sequestrial biotransformation of l-DOPA using immobilized tyrosinase enzyme in macroporous poly(AAm-co-AGE) monolith”.

One-pot green synthesis of eumelanin: process optimization and its characterization

Herein, we propose the importance of Taguchi’s design of experiment methodology for increasing the yield of eumelanin using l-Dopa as the substrate and tyrosinase enzyme from Amorphophallus campanulatus as the biocatalyst.

Inhibition of nitric oxide and tumour necrosis factor-α production in peritoneal macrophages by Aspergillus nidulans melanin

The naturally occurring pigment, melanin is found in organisms of all phylogenetic kingdoms, including fungi, and exhibits a wide range of biological activities. Our objective was to investigate the effects of melanin extracted from the fungus Aspergillus nidulans on the production of the pro-inflammatory mediators nitric oxide (NO) and tumour necrosis factor-α (TNF-α) in peritoneal macrophages and on the viability of McCoy mouse fibroblasts. The results showed that A. nidulans melanin did not stimulate NO production in macrophages, but it inhibited the NO production in lipopolysaccharide (LPS)-stimulated macrophages by approximately 82%. Similarly, A. nidulans melanin inhibited LPS-stimulated TNF-α production by 52% and showed a slight stimulatory effect on TNF-α production in macrophages. In addition, the toxicity of A. nidulans melanin to McCoy cells was much lesser (IC50=373.5±2.4 µg/mL) than that of known agents such as cisplatin (IC50=41.2 µg/mL). The viability of peritoneal macrophages was greater than 90% at the highest melanin concentration tested (100 µg/mL). Thus, the combination of low cytotoxicity and marked inhibition of TNF-α and NO production suggests that A. nidulans melanin has potential as an anti-inflammatory agent and may be used in the future for development of new drugs with therapeutic utility.

Singlet molecular oxygen generation by light-activated DHN-melanin of the fungal pathogen Mycosphaerella fijiensis in black Sigatoka disease of bananas

In pathogenic fungi, melanin contributes to virulence, allowing tissue invasion and inactivation of the plant defence system, but has never been implicated as a factor for host cell death, or as a light-activated phytotoxin. Our research shows that melanin synthesized by the fungal banana pathogen Mycosphaerella fijiensis acts as a virulence factor through the photogeneration of singlet molecular oxygen O2 (1Δg). Using analytical tools, including elemental analysis, ultraviolet/infrared absorption spectrophometry and MALDI-TOF mass spectrometry analysis, we characterized both pigment content in mycelia and secreted to the culture media as 1,8-dihydroxynaphthalene (DHN)-melanin type compound. This is sole melanin-type in M. fijiensis. Isolated melanins irradiated with a Nd:YAG laser at 532 nm produced monomol light emission at 1270 nm, confirming generation of O2 (1Δg), a highly reactive oxygen specie (ROS) that causes cellular death by reacting with all cellular macromolecules. Intermediary polyketides accumulated in culture media by using tricyclazole and pyroquilon (two inhibitors of DHN-melanin synthesis) were identified by ESI-HPLC-MS/MS. Additionally, irradiation at 532 nm of that mixture of compounds and whole melanized mycelium also generated O2 (1Δg). A pigmented-strain generated more O2 (1Δg) than a strain with low melanin content. Banana leaves of cultivar Cavendish, naturally infected with different stages of black Sigatoka disease, were collected from field. Direct staining of the naturally infected leaf tissues showed the presence of melanin that was positively correlated to the disease stage. We also found hydrogen peroxide (H2O2) but we cannot distinguish the source. Our results suggest that O2 (1Δg) photogenerated by DHN-melanin may be involved in the destructive effects of Mycosphaerella fijiensis on banana leaf tissues. Further studies are needed to fully evaluate contributions of melanin-mediated ROS to microbial pathogenesis.