The inherent cytotoxicity of melanin precursors: a revision

Growth and longevity modulation through larval environment mediate immunosenescence and immune strategy of Tenebrio molitor

BACKGROUND

The Disposable Soma Theory of aging suggests a trade-off between energy allocation for growth, reproduction and somatic maintenance, including immunity. While trade-offs between reproduction and immunity are well documented, those involving growth remain under-explored. Rapid growth might deplete resources, reducing investment in maintenance, potentially leading to earlier or faster senescence and a shorter lifespan. However, rapid growth could limit exposure to parasitism before reaching adulthood, decreasing immunity needs. The insect immunity's components (cellular, enzymatic, and antibacterial) vary in cost, effectiveness, and duration. Despite overall immunity decline (immunosenescence), its components seem to age differently. We hypothesize that investment in these immune components is adjusted based on the resource cost of growth, longevity, and the associated risk of parasitism.

RESULTS

We tested this hypothesis using the mealworm beetle, Tenebrio molitor as our experimental subject. By manipulating the larval environment, including three different temperatures and three relative humidity levels, we achieved a wide range of growth durations and longevities. Our main focus was on the relationship between growth duration, longevity, and specific immune components: hemocyte count, phenoloxidase activity, and antibacterial activity. We measured these immune parameters both before and after exposing the individuals to a standard bacterial immune challenge, enabling us to assess immune responses. These measurements were taken in both young and older adult beetles. Upon altering growth duration and longevity by modifying larval temperature, we observed a more pronounced investment in cellular and antibacterial defenses among individuals with slow growth and extended lifespans. Intriguingly, slower-growing and long-lived beetles exhibited reduced enzymatic activity. Similar results were found when manipulating larval growth duration and adult longevity through variations in relative humidity, with a particular focus on antibacterial activity.

CONCLUSION

The impact of growth manipulation on immune senescence varies by the specific immune parameter under consideration. Yet, in slow-growing T. molitor, a clear decline in cellular and antibacterial immune responses with age was observed. This decline can be linked to their initially stronger immune response in early life. Furthermore, our study suggests an immune strategy favoring enhanced antibacterial activity among slow-growing and long-lived T. molitor individuals.

Secondary glaucoma: Toward interventions based on molecular underpinnings

Glaucoma is a heterogeneous group of progressive diseases that leads to irreversible blindness. Secondary glaucoma refers to glaucoma caused by a known underlying condition. Pseudoexfoliation and pigment dispersion syndromes are common causes of secondary glaucoma. Their respective deposits may obstruct the trabecular meshwork, leading to aqueous humor outflow resistance, ocular hypertension, and optic neuropathy. There are no disease-specific interventions available for either. Pseudoexfoliation syndrome is characterized by fibrillar deposits (pseudoexfoliative material) on anterior segment structures. Over a decade of multiomics analyses taken together with the current knowledge on pseudoexfoliative glaucoma warrant a re-think of mechanistic possibilities. We propose that the presence of nucleation centers (e.g., vitamin D binding protein), crosslinking enzymes (e.g., transglutaminase 2), aberrant extracellular matrix, flawed endocytosis, and abnormal aqueous-blood barrier contribute to the formation of proteolytically resistant pseudoexfoliative material. Pigment dispersion syndrome is characterized by abnormal iridolenticular contact that disrupts iris pigment epithelium and liberates melanin granules. Iris melanogenesis is aberrant in this condition. Cytotoxic melanogenesis intermediates leak out of melanosomes and cause iris melanocyte and pigment epithelium cell death. Targeting melanogenesis can likely decrease the risk of pigmentary glaucoma. Skin and melanoma research provides insights into potential therapeutics. We propose that specific prostanoid agonists and fenofibrates may reduce melanogenesis by inhibiting cholesterol internalization and de novo synthesis. Additionally, melatonin is a potent melanogenesis suppressor, antioxidant, and hypotensive agent, rendering it a valuable agent for pigmentary glaucoma. In pseudoexfoliative glaucoma, where environmental insults drive pseudoexfoliative material formation, melatonin's antioxidant and hypotensive properties may offer adjunct therapeutic benefits. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology.

Topical Application of No-Ozone Cold Plasma in Combination with Vitamin C Reduced Skin Redness and Pigmentation of UV-Irradiated Mice

Ultraviolet (UV) is the main cause of sunburn on the skin as it induces erythema and accelerates pigmentation. Vitamin C is one of the most frequently used compounds to reduce UV-induced skin pigmentation, but it has limitations in absorption through the skin. In this study, we tested whether a no-ozone cold plasma (NCP) treatment can improve UV-irradiated skin by helping the action of Vitamin C. For this, among five groups of HRM-2 hairless mice, four groups of mice were subjected to UVB irradiation, and three groups of UVB-treated mice were treated with NCP, Vitamin C, and NCP + Vitamin C, respectively. For evaluating the effect of each treatment, the melanin and erythema index was measured during animal experiments. Histological changes were monitored by performing H&E and MTS and IHC against tyrosinase and melanin. As a result, the naturally recovered mice showed a 28-point decrease in the melanin index, whereas a decrease of around 88, 74.3, and 106 points was detected in NCP-, Vitamin C-, and NCP + vitamin C-treated mice, respectively. Likewise, only a 39-point reduction in the erythema index was monitored in naturally recovered mice, but the NCP-, vitamin C-, and NCP + vitamin C-treated mice showed a 87.3-, 77-, and 111-point reduction, respectively. Interestingly, the skin tissues of the mice treated with NCP in combination with Vitamin C mostly recovered from UVB-induced damage. Altogether, this study elucidated the beneficial effect of the treatment of NCP in combination with Vitamin C on the UVB-irradiated skin, which might be helpful for treating sunburn on the skin.

Lrig1- and Wnt-dependent niches dictate segregation of resident immune cells and melanocytes in murine tail epidermis

The barrier-forming, self-renewing mammalian epidermis comprises keratinocytes, pigment-producing melanocytes and resident immune cells as first-line host defense. In murine tail skin, interfollicular epidermis patterns into pigmented ‘scale’ and hypopigmented ‘interscale’ epidermis. Why and how mature melanocytes accumulate in scale epidermis is unresolved. Here, we delineate a cellular hierarchy among epidermal cell types that determines skin patterning. Already during postnatal development, melanocytes co-segregate with newly forming scale compartments. Intriguingly, this process coincides with partitioning of both Langerhans cells and dendritic epidermal T cells to interscale epidermis, suggesting functional segregation of pigmentation and immune surveillance. Analysis of non-pigmented mice and of mice lacking melanocytes or resident immune cells revealed that immunocyte patterning is melanocyte and melanin independent and, vice versa, immune cells do not control melanocyte localization. Instead, genetically enforced progressive scale fusion upon Lrig1 deletion showed that melanocytes and immune cells dynamically follow epithelial scale:interscale patterns. Importantly, disrupting Wnt-Lef1 function in keratinocytes caused melanocyte mislocalization to interscale epidermis, implicating canonical Wnt signaling in organizing the pigmentation pattern. Together, this work uncovers cellular and molecular principles underlying the compartmentalization of tissue functions in skin.

Summary: Pigmentation and immune surveillance functions in murine tail skin are spatially segregated by Lrig1- and Wnt-Lef1-dependent keratinocyte lineages that control the partitioning of melanocytes and tissue-resident immune cells into distinct epidermal niches.

Theoretical Studies of Cyanophycin Dipeptides as Inhibitors of Tyrosinases

The three-dimensional structure of tyrosinase has been crystallized from many species but not from Homo sapiens. Tyrosinase is a key enzyme in melanin biosynthesis, being an important target for melanoma and skin-whitening cosmetics. Several studies employed the structure of tyrosinase from Agaricus bisporus as a model enzyme. Recently, 98% of human genome proteins were elucidated by AlphaFold. Herein, the AlphaFold structure of human tyrosinase and the previous model were compared. Moreover, tyrosinase-related proteins 1 and 2 were included, along with inhibition studies employing kojic and cinnamic acids. Peptides are widely studied for their inhibitory activity of skin-related enzymes. Cyanophycin is an amino acid polymer produced by cyanobacteria and is built of aspartic acid and arginine; arginine can be also replaced by other amino acids. A new set of cyanophycin-derived dipeptides was evaluated as potential inhibitors. Aspartate–glutamate showed the strongest interaction and was chosen as a leading compound for future studies.

Age-specific fecundity under pathogenic threat in an insect: Terminal investment versus reproductive restraint

The terminal investment hypothesis predicts that as an organism's prospects for survival decrease, through age or when exposed to a pathogenic infection, it will invest more in reproduction, which should trade-off against somatic maintenance (including immunity) and therefore future survival. Attempts to test this hypothesis have produced mixed results, which, in addition, mainly rely on the assessment of changes in reproductive effort and often overlooking its impact on somatic defences and survival. Alternatively, animals may restrain current reproduction to sustain somatic protection, increasing the chance of surviving for additional reproductive opportunities. We tested both of these hypotheses in females of the yellow mealworm beetle, Tenebrio molitor, an iteroparous insect with reproductive tactics similar to that of long-lived organisms. To achieve this, we mimicked pathogenic bacterial infections early or late in the life of breeding females by injecting them with a suspension of inactivated Bacillus cereus, a known natural pathogen of T. molitor, and measured female age-specific fecundity, survival, body mass and immunity. Inconsistent with a terminal investment, females given either an early or late-life immune challenge did not exhibit reduced survival or enhance their reproductive output. Female fecundity declined with age and was reduced by the early but not the late immune challenge. Both early and late-life fecundity correlated positively with life expectancy. Finally, young and old females exhibited similar antibacterial immune responses, suggesting that they both restrained reproduction to sustain immunity. Our results clearly demonstrate that age-specific reproduction of T. molitor females under pathogenic threat is inconsistent with a terminal investment. In contrast, our results instead suggest that females used a reproductive restraint strategy to sustain immunity and therefore subsequent reproductive opportunities. However, as infections were mimicked only, the fitness benefit of this reproductive restraint could not be shown.

Mucosal Melanoma: Pathological Evolution, Pathway Dependency and Targeted Therapy

Mucosal melanoma (MM) is a rare melanoma subtype that originates from melanocytes within sun-protected mucous membranes. Compared with cutaneous melanoma (CM), MM has worse prognosis and lacks effective treatment options. Moreover, the endogenous or exogenous risk factors that influence mucosal melanocyte transformation, as well as the identity of MM precursor lesions, are ambiguous. Consequently, there remains a lack of molecular markers that can be used for early diagnosis, and therefore better management, of MM. In this review, we first summarize the main functions of mucosal melanocytes. Then, using oral mucosal melanoma (OMM) as a model, we discuss the distinct pathologic stages from benign mucosal melanocytes to metastatic MM, mapping the possible evolutionary trajectories that correspond to MM initiation and progression. We highlight key areas of ambiguity during the genetic evolution of MM from its benign lesions, and the resolution of which could aid in the discovery of new biomarkers for MM detection and diagnosis. We outline the key pathways that are altered in MM, including the MAPK pathway, the PI3K/AKT pathway, cell cycle regulation, telomere maintenance, and the RNA maturation process, and discuss targeted therapy strategies for MM currently in use or under investigation.

Glyphosate inhibits melanization and increases susceptibility to infection in insects

Melanin, a black-brown pigment found throughout all kingdoms of life, has diverse biological functions including UV protection, thermoregulation, oxidant scavenging, arthropod immunity, and microbial virulence. Given melanin's broad roles in the biosphere, particularly in insect immune defenses, it is important to understand how exposure to ubiquitous environmental contaminants affects melanization. Glyphosate-the most widely used herbicide globally-inhibits melanin production, which could have wide-ranging implications in the health of many organisms, including insects. Here, we demonstrate that glyphosate has deleterious effects on insect health in 2 evolutionary distant species, Galleria mellonella (Lepidoptera: Pyralidae) and Anopheles gambiae (Diptera: Culicidae), suggesting a broad effect in insects. Glyphosate reduced survival of G. mellonella caterpillars following infection with the fungus Cryptococcus neoformans and decreased the size of melanized nodules formed in hemolymph, which normally help eliminate infection. Glyphosate also increased the burden of the malaria-causing parasite Plasmodium falciparum in A. gambiae mosquitoes, altered uninfected mosquito survival, and perturbed the microbial composition of adult mosquito midguts. Our results show that glyphosate's mechanism of melanin inhibition involves antioxidant synergy and disruption of the reaction oxidation-reduction balance. Overall, these findings suggest that glyphosate's environmental accumulation could render insects more susceptible to microbial pathogens due to melanin inhibition, immune impairment, and perturbations in microbiota composition, potentially contributing to declines in insect populations.

Depigmenting effect of Xanthohumol from hop extract in MNT-1 human melanoma cells and normal human melanocytes

Xanthohumol (XH) is the most abundant prenylated flavonoid found in the hop plant (Humulus lupulus L.) and has previously been shown to have depigmenting effects in B16F10 mouse melanoma cells; however, studies of its depigmenting efficacy in human melanocytes are still lacking. In this work, we explored the effects of XH on melanogenesis in MNT-1 human melanoma cells and normal human melanocytes from darkly-pigmented skin (HEM-DP). XH was screened for cytotoxicity over 48 h, and subsequently tested on melanogenesis in MNT-1 cells. XH was further tested in HEM-DP cells for melanin synthesis and melanosome export; dendricity was quantitated to assess effects on melanosome export. Melanosome degradation was studied in human keratinocytes (HaCaT). Our results showed that XH inhibited melanin synthesis in MNT-1 cells at 30 μM but increased intracellular tyrosinase activity without affecting ROS levels. In HEM-DP cells, XH robustly suppressed cellular tyrosinase activity at nontoxic concentrations (2.5–5 μM) without any effect on melanin synthesis. However, XH inhibited melanosome export by reducing dendrite number and total dendrite length. Further testing in HaCaT cells demonstrated that XH induced melanosome degradation at low micromolar concentrations without any cytotoxicity. In summary, our results demonstrate that XH at low micromolar concentrations might hold promise as a potent inhibitor of human pigmentation by primarily targeting melanin export and melanin degradation. Further studies to elucidate the signaling mechanisms of action of melanosome export inhibition by XH and in vivo efficacy are warranted.

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Xanthohumol (XH) inhibited melanin synthesis in MNT-1 human melanoma cells.

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XH did not inhibit melanin synthesis in primary human melanocytes but significantly suppressed both dendrite number and total dendrite length at low micromolar concentrations.

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Reduction of melanosome export by reduction in dendricity was correlated with the inhibition of intracellular tyrosinase activity.

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XH induced melanosome degradation in human keratinocytes.

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XH is a candidate for skin-lightning which inhibits human melanogenesis by targeting later steps in melanogenesis.

Non-invasive Reporter Gene Imaging of Cell Therapies, including T Cells and Stem Cells

Cell therapies represent a rapidly emerging class of new therapeutics. They are intended and developed for the treatment of some of the most prevalent human diseases, including cancer, diabetes, and for regenerative medicine. Currently, they are largely developed without precise assessment of their in vivo distribution, efficacy, or survival either clinically or preclinically. However, it would be highly beneficial for both preclinical cell therapy development and subsequent clinical use to assess these parameters in situ to enable enhancements in efficacy, applicability, and safety. Molecular imaging can be exploited to track cells non-invasively on the whole-body level and can enable monitoring for prolonged periods in a manner compatible with rapidly expanding cell types. In this review, we explain how in vivo imaging can aid the development and clinical translation of cell-based therapeutics. We describe the underlying principles governing non-invasive in vivo long-term cell tracking in the preclinical and clinical settings, including available imaging technologies, reporter genes, and imaging agents as well as pitfalls related to experimental design. Our emphasis is on adoptively transferred T cell and stem cell therapies.

Stem cell delivery to kidney via minimally invasive ultrasound-guided renal artery injection in mice

Cell-based therapies are promising treatments for various kidney diseases. However, the major hurdle in initiating therapeutic responses is the inefficiency of injection routes to deliver cells to the kidney parenchyma. Systemic injection, such as intravenous injection only delivers a small proportion of cells to the kidney. Whereas direct delivery, such as renal artery injection requires surgical procedures. A minimally invasive renal artery injection was therefore developed to enhance cell delivery to kidney. In this study, luciferase expressing human adipocyte derived stem cells (ADSC) were labelled with gold nanorods (GNR) and injected into the renal artery using ultrasound guidance. The ADSCs were tracked using bioluminescence and photoacoustic imaging serially over 7 days. Imaging confirmed that the majority of signal was within the kidney, indicative of successful injection and that the cells remained viable for 3 days. Histology showed co-localization of GNRs with ADSC staining throughout the kidney with no indication of injury caused by injection. These findings demonstrate that ultrasound-guided renal artery injection is feasible in mice and can successfully deliver a large proportion of cells which are retained within the kidney for 3 days. Therefore, the techniques developed here will be useful for optimising cell therapy in kidney diseases.

How Non-invasive in vivo Cell Tracking Supports the Development and Translation of Cancer Immunotherapies

Immunotherapy is a relatively new treatment regimen for cancer, and it is based on the modulation of the immune system to battle cancer. Immunotherapies can be classified as either molecular or cell-based immunotherapies, and both types have demonstrated promising results in a growing number of cancers. Indeed, several immunotherapies representing both classes are already approved for clinical use in oncology. While spectacular treatment successes have been reported, particularly for so-called immune checkpoint inhibitors and certain cell-based immunotherapies, they have also been accompanied by a variety of severe, sometimes life-threatening side effects. Furthermore, not all patients respond to immunotherapy. Hence, there is the need for more research to render these promising therapeutics more efficacious, more widely applicable, and safer to use. Whole-body in vivo imaging technologies that can interrogate cancers and/or immunotherapies are highly beneficial tools for immunotherapy development and translation to the clinic. In this review, we explain how in vivo imaging can aid the development of molecular and cell-based anti-cancer immunotherapies. We describe the principles of imaging host T-cells and adoptively transferred therapeutic T-cells as well as the value of traceable cancer cell models in immunotherapy development. Our emphasis is on in vivo cell tracking methodology, including important aspects and caveats specific to immunotherapies. We discuss a variety of associated experimental design aspects including parameters such as cell type, observation times/intervals, and detection sensitivity. The focus is on non-invasive 3D cell tracking on the whole-body level including aspects relevant for both preclinical experimentation and clinical translatability of the underlying methodologies.

Coriolus versicolor-derived protein-bound polysaccharides trigger the caspase-independent cell death pathway in amelanotic but not melanotic melanoma cells

We have investigated the potential cell death mechanism promoted by Coriolus versicolor fungus-derived protein-bound polysaccharides (PBPs) in melanoma cells. Knowing that melanogenesis has the potential to affect the tumor behavior and melanoma therapy outcome, the cytotoxic effects of PBPs were evaluated in human SKMel-188 melanoma cell line, whose phenotype, amelanotic versus pigmented, depends on the concentration of melanin precursors in the culture medium. Our results showed that inhibitory effect of PBPs (100 and 200 μg/ml) towards melanoma cells is inversely associated with the pigmentation level. This cytotoxicity induced in nonpigmented melanoma cells by PBPs was caspase-independent; however, it was accompanied by an increased intracellular reactive oxygen species (ROS) generation. The ROS production was controlled by c-Jun N-terminal kinase (JNK) because SP600125, a JNK inhibitor, significantly reduced ROS generation and protected cells against PBPs-induced death. We also found that PBPs-induced lactate dehydrogenase release in amelanotic melanoma cells was abolished by co-treatment with receptor-interacting serine/threonine-protein kinase 1 inhibitor, implying engagement of this kinase in PBPs-induced death pathway. The results suggest that PBPs induce an alternative programmed cell death, regulated by receptor-interacting protein-1 and ROS and that this process is modified by melanin content in melanoma cells. These findings are remarkable when considering the use of commercially available Coriolus versicolor by patients who suffer from melanoma cancer.

A QM protein from Bombyx mori negatively regulates prophenoloxidase activation and melanization by interacting with Jun protein

The QM gene that encodes for the ribosomal protein L10 was firstly identified from human tumour cells as a tumour suppressor. In this study, a QM gene was identified in silkworm Bombyx mori (BmQM) and its immunomodulatory function was explored. BmQM messenger RNA (mRNA) and protein were highly expressed in the silk gland and fat body, and expressed in all stages of silkworm growth. After challenged with four different microorganisms, the expression levels of BmQM mRNA in fat body or haemocytes were significantly upregulated compared with the control. After knock-down of BmQM gene, the expressions of some immune genes (PGRPS6, Gloverin0, Lysozyme and Moricin) were affected, and the transcripts of prophenoloxidase1 and prophenoloxidase2 have different degrees of change. The phenoloxidase activity was significantly reduced when the purified recombinant BmQM protein was injected. Recombinant BmQM protein inhibited systemic melanization and suppressed prophenoloxidase activation stimulated by Micrococcus luteus, but it did not affect phenoloxidase activity. Far-western blotting assays showed that the BmQM protein interacted with silkworm BmJun protein, which negatively regulates AP-1 expression. Our results indicated that BmQM protein could affect some immune gene expression and negatively regulate the prophenoloxidase-activating system, and it may play an important role in regulation of the innate immunity in insects.

Non-Synonymous variants in premelanosome protein (PMEL) cause ocular pigment dispersion and pigmentary glaucoma

Pigmentary glaucoma (PG) is a common glaucoma subtype that results from release of pigment from the iris, called pigment dispersion syndrome (PDS), and its deposition throughout the anterior chamber of the eye. Although PG has a substantial heritable component, no causative genes have yet been identified. We used whole exome sequencing of two independent pedigrees to identify two premelanosome protein (PMEL) variants associated with heritable PDS/PG. PMEL encodes a key component of the melanosome, the organelle essential for melanin synthesis, storage and transport. Targeted screening of PMEL in three independent cohorts (n = 394) identified seven additional PDS/PG-associated non-synonymous variants. Five of the nine variants exhibited defective processing of the PMEL protein. In addition, analysis of PDS/PG-associated PMEL variants expressed in HeLa cells revealed structural changes to pseudomelanosomes indicating altered amyloid fibril formation in five of the nine variants. Introduction of 11-base pair deletions to the homologous pmela in zebrafish by the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 method caused profound pigmentation defects and enlarged anterior segments in the eye, further supporting PMEL's role in ocular pigmentation and function. Taken together, these data support a model in which missense PMEL variants represent dominant negative mutations that impair the ability of PMEL to form functional amyloid fibrils. While PMEL mutations have previously been shown to cause pigmentation and ocular defects in animals, this research is the first report of mutations in PMEL causing human disease.

Anti‑inflammatory effects of Dendropanax morbifera in lipopolysaccharide‑stimulated RAW264.7 macrophages and in an animal model of atopic dermatitis

Dendropanax morbifera (D. morbifera), known as Dendro, means 'omnipotent drug' (Panax), and has been called the panacea tree. Various studies on D. morbifera are currently ongoing, aiming to determine its medicinal uses. The present study investigated the anti‑inflammatory effects and underlying mechanism of a natural extract of D. morbifera leaves (DPL) in lipopolysaccharide (LPS)‑stimulated RAW264.7 macrophages. In the present study, the following assays and models were used: MTT assay, nitric oxide (NO) assay, western blotting, ELISA and mouse models of atopic dermatitis. DPL extract markedly reduced the production of NO, inducible NO synthase and interleukin‑6, as well as the nuclear translocation of nuclear factor‑κB (NF‑κB). Additionally, the LPS‑induced activation of extracellular signal‑regulated kinase 1/2 (ERK1/2), P38 and c‑Jun N‑terminal kinase (JNK) was suppressed by DPL extract. Taken together, these results indicate that NF‑κB, ERK1/2, P38 and JNK may be potential molecular targets of DPL extract in the LPS‑induced inflammatory response. Subsequently, the present study investigated the effects of DPL extract in a 2,4‑dinitrochlorobenzene‑induced atopic dermatitis mouse model. Ear thickness, serum immunoglobulin E levels and histological analysis revealed that the DPL extract was effective in attenuating the inflammatory response. These results indicate that DPL extract has anti‑inflammatory potential and may be developed as a botanical drug to treat atopic dermatitis.

Molecular vibration as a novel explanatory mechanism for the expression of animal colouration

Animal colouration is characterized by the concentration of pigments in integumentary structures and by the nanoscale arrangement of constitutive elements. However, the influence of molecular vibration on colour expression has been overlooked in biology. Molecular vibration occurs in the infrared spectral region, but vibrational and electronic properties can influence each other. Thus, the vibration of pigment molecules may also affect their absorption properties and the resulting colours. We calculated for the first time the relative contribution of molecular vibration (by means of Raman spectroscopy) and concentration (by means of HPLC) of melanin polymers, the most common animal pigments, to generate diversity in plumage colour in 47 species of birds. Vibrational characteristics explained >9 times more variance in colour expression than the concentration of melanins. Additionally, we modelled melanin Raman spectra on the basis of the chemical structure of their constituent monomers and calculated the Huang-Rhys factors for each vibrational mode, which indicate the contribution of these modes to the electronic spectra responsible for the resulting colours. High Huang-Rhys factors frequently coincided with the vibrational modes of melanin monomers. Our results can be explained by the influence of molecular vibration on the absorption properties of melanins. The colour of organisms may thus mainly result from the vibrational properties of their molecules and only residually from their concentration. As a given melanin concentration can give rise to different colours because different structural melanin conformations can present different vibrational characteristics, vibrational effects may favour phenotypic plasticity and thus constitute an important evolutionary force.

Molecular Genetics of Pigment Dispersion Syndrome and Pigmentary Glaucoma: New Insights into Mechanisms

We explore the ideas and advances surrounding the genetic basis of pigment dispersion syndrome (PDS) and pigmentary glaucoma (PG). As PG is the leading cause of nontraumatic blindness in young adults and current tailored interventions have proven ineffective, a better understanding of the underlying causes of PDS, PG, and their relationship is essential. Despite PDS being a subclinical disease, a large proportion of patients progress to PG with associated vision loss. Decades of research have supported a genetic component both for PDS and conversion to PG. We review the body of evidence supporting a genetic basis in humans and animal models and reevaluate classical mechanisms of PDS/PG considering this new evidence.

On the Metal Cofactor in the Tyrosinase Family

The production of pigment in mammalian melanocytes requires the contribution of at least three melanogenic enzymes, tyrosinase and two other accessory enzymes called the tyrosinase-related proteins (Trp1 and Trp2), which regulate the type and amount of melanin. The last two proteins are paralogues to tyrosinase, and they appeared late in evolution by triplication of the tyrosinase gene. Tyrosinase is a copper-enzyme, and Trp2 is a zinc-enzyme. Trp1 has been more elusive, and the direct identification of its metal cofactor has never been achieved. However, due to its enzymatic activity and similarities with tyrosinase, it has been assumed as a copper-enzyme. Recently, recombinant human tyrosinase and Trp1 have been expressed in enough amounts to achieve for the first time their crystallization. Unexpectedly, it has been found that Trp1 contains a couple of Zn(II) at the active site. This review discusses data about the metal cofactor of tyrosinase and Trps. It points out differences in the studied models, and it proposes some possible points accounting for the apparent discrepancies currently appearing. Moreover, some proposals about the possible flexibility of the tyrosinase family to uptake copper or zinc are discussed.

Early-life inflammation, immune response and ageing

Age-related diseases are often attributed to immunopathology, which results in self-damage caused by an inappropriate inflammatory response. Immunopathology associated with early-life inflammation also appears to cause faster ageing, although we lack direct experimental evidence for this association. To understand the interactions between ageing, inflammation and immunopathology, we used the mealworm beetle Tenebrio molitor as a study organism. We hypothesized that phenoloxidase, an important immune effector in insect defence, may impose substantial immunopathological costs by causing tissue damage to Malpighian tubules (MTs; functionally equivalent to the human kidney), in turn accelerating ageing. In support of this hypothesis, we found that RNAi knockdown of phenoloxidase (PO) transcripts in young adults possibly reduced inflammation-induced autoreactive tissue damage to MTs, and increased adult lifespan. Our work thus suggests a causative link between immunopathological costs of early-life inflammation and faster ageing. We also reasoned that if natural selection weakens with age, older individuals should display increased immunopathological costs associated with an immune response. Indeed, we found that while old infected individuals cleared infection faster than young individuals, possibly they also displayed exacerbated immunopathological costs (larger decline in MT function) and higher post-infection mortality. RNAi-mediated knockdown of PO response partially rescued MTs function in older beetles and resulted in increased lifespan after infection. Taken together, our data are consistent with a direct role of immunopathological consequences of immune response during ageing in insects. Our work is also the first report that highlights the pervasive role of tissue damage under diverse contexts of ageing and immune response.

A common intronic variant of PARP1 confers melanoma risk and mediates melanocyte growth via regulation of MITF

Previous genome-wide association studies have identified a melanoma-associated locus at 1q42.1 that encompasses a ∼100-kb region spanning the PARP1 gene. Expression quantitative trait locus (eQTL) analysis in multiple cell types of the melanocytic lineage consistently demonstrated that the 1q42.1 melanoma risk allele (rs3219090[G]) is correlated with higher PARP1 levels. In silico fine-mapping and functional validation identified a common intronic indel, rs144361550 (-/GGGCCC; r2 = 0.947 with rs3219090), as displaying allele-specific transcriptional activity. A proteomic screen identified RECQL as binding to rs144361550 in an allele-preferential manner. In human primary melanocytes, PARP1 promoted cell proliferation and rescued BRAFV600E-induced senescence phenotypes in a PARylation-independent manner. PARP1 also transformed TERT-immortalized melanocytes expressing BRAFV600E. PARP1-mediated senescence rescue was accompanied by transcriptional activation of the melanocyte-lineage survival oncogene MITF, highlighting a new role for PARP1 in melanomagenesis.

Adhesive coatings based on melanin-like nanoparticles for surgical membranes

Adhesive coatings for implantable biomaterials can be designed to prevent material displacement from the site of implant. In this paper, a strategy based on the use of melanin-like nanoparticles (MNPs) for the development of adhesive coatings for polysaccharidic membranes was devised. MNPs were synthesized in vitro and characterized in terms of dimensions and surface potential, as a function of pH and ionic strength. The in vitro biocompatibility of MNPs was investigated on fibroblast cells, while the antimicrobial properties of MNPs in suspension were evaluated on E. coli and S. aureus cultures. The manufacturing of the adhesive coatings was carried out by spreading MNPs over the surface of polysaccharidic membranes; the adhesive properties of the nano-engineered coating to the target tissue (intestinal serosa) were studied in simulated physiological conditions. Overall, this study opens for novel approaches in the design of naturally inspired nanostructured adhesive systems.

Advanced optoacoustic methods for multiscale imaging of in vivo dynamics

Visualization of dynamic functional and molecular events in an unperturbed in vivo environment is essential for understanding the complex biology of living organisms and of disease state and progression. To this end, optoacoustic (photoacoustic) sensing and imaging have demonstrated the exclusive capacity to maintain excellent optical contrast and high resolution in deep-tissue observations, far beyond the penetration limits of modern microscopy. Yet, the time domain is paramount for the observation and study of complex biological interactions that may be invisible in single snapshots of living systems. This review focuses on the recent advances in optoacoustic imaging assisted by smart molecular labeling and dynamic contrast enhancement approaches that enable new types of multiscale dynamic observations not attainable with other bio-imaging modalities. A wealth of investigated new research topics and clinical applications is further discussed, including imaging of large-scale brain activity patterns, volumetric visualization of moving organs and contrast agent kinetics, molecular imaging using targeted and genetically expressed labels, as well as three-dimensional handheld diagnostics of human subjects.

The Role of DCT in HPV16 Infection of HaCaTs

Persistent infection with high-risk human papillomavirus (HPV) genotype is a major factor leading to many human cancers. Mechanisms of HPV entry into host cells and genome trafficking towards the nucleus are incompletely understood. Dopachrome tautomerase (DCT) was identified as a cellular gene required for HPV infection in HeLa cells on a siRNA screen study. Here, we confirm that DCT knockdown significantly decreases HPV infection in the human keratinocyte HaCaT cells as was observed in HeLas. We investigated the effects of DCT knockdown and found that DCT depletion caused increased reactive oxygen species (ROS) levels, DNA damage and altered cell cycle in HaCaT cells. We observed increased viral DNA localization at the endoplasmic reticulum but an overall decrease in infection in DCT knockdown cells. This observation suggests that viral DNA might be retained in the ER due to altered cell cycle, and viral particles are incapable of further movement towards the nucleus in DCT knockdown cells.

Autophagy deficient melanocytes display a senescence associated secretory phenotype that includes oxidized lipid mediators

Autophagy is a recycling program which allows cells to adapt to metabolic needs and to stress. Defects in autophagy can affect metabolism, aging, proteostasis and inflammation. Autophagy pathway genes, including autophagy related 7 (Atg7), have been associated with the regulation of skin pigmentation, and autophagy defects disturb the biogenesis and transport of melanosomes in melanocytes as well as transfer and processing of melanin into keratinocytes. We have previously shown that mice whose melanocytes or keratinocytes lack Atg7 (and thus autophagy) as a result of specific gene knockout still retained functioning melanosome synthesis and transfer, and displayed only moderate reduction of pigmentation. In cell culture the Atg7 deficient melanocytes were prone to premature senescence and dysregulation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling. To elucidate the biochemical basis of this phenotype, we performed a study on global gene expression, protein secretion and phospholipid composition in Atg7 deficient versus Atg7 expressing melanocytes. In cell culture Atg7 deficient melanocytes showed a pro-inflammatory gene expression signature and secreted higher levels of C-X-C motif chemokine ligand -1,-2,-10 and -12 (Cxcl1, Cxcl2, Cxcl10, Cxcl12), which are implicated in the pathogenesis of pigmentary disorders and expressed higher amounts of matrix metalloproteinases -3 and -13 (Mmp3, Mmp13). The analysis of membrane phospholipid composition identified an increase in the arachidonic- to linoleic acid ratio in the autophagy deficient cells, as well as an increase in oxidized phospholipid species that act as danger associated molecular patterns (DAMPs). The secretion of inflammation related factors suggests that autophagy deficient melanocytes display a senescence associated secretory phenotype (SASP), and we propose oxidized lipid mediators as novel components of this SASP.

Contrast agents for molecular photoacoustic imaging

Photoacoustic imaging (PAI) is an emerging tool that bridges the traditional depth limits of ballistic optical imaging and the resolution limits of diffuse optical imaging. Using the acoustic waves generated in response to the absorption of pulsed laser light, it provides noninvasive images of absorbed optical energy density at depths of several centimeters with a resolution of ∼100 μm. This versatile and scalable imaging modality has now shown potential for molecular imaging, which enables visualization of biological processes with systemically introduced contrast agents. Understanding the relative merits of the vast range of contrast agents available, from small-molecule dyes to gold and carbon nanostructures to liposome encapsulations, is a considerable challenge. Here we critically review the physical, chemical and biochemical characteristics of the existing photoacoustic contrast agents, highlighting key applications and present challenges for molecular PAI.

Promoter-Associated RNAs Regulate HSPC152 Gene Expression in Malignant Melanoma

The threshold of 200 nucleotides (nt) conventionally divides non-coding RNAs (ncRNA) into long ncRNA (lincRNA, that have more than 200 nt in length) and the remaining ones which are grouped as "small" RNAs (microRNAs, small nucleolar RNAs and piwiRNAs). Promoter-associated RNAs (paRNAs) are generally 200-500 nt long and are transcribed from sequences positioned in the promoter regions of genes. Growing evidence suggests that paRNAs play a crucial role in controlling gene transcription. Here, we used deep sequencing to identify paRNA sequences that show altered expression in a melanoma cell line compared to normal melanocytes. Thousands of reads were mapped to transcription start site (TSS) regions. We limited our search to paRNAs adjacent to genes with an expression that differed between melanoma and normal melanocytes and a length of 200-500 nt that did not overlap the gene mRNA by more than 300 nt, ultimately leaving us with 11 such transcripts. Using quantitative real-time PCR (qRT-PCR), we found a significant correlation between the expression of the mRNA and its corresponding paRNA for two studied genes: TYR and HSPC152. Ectopic overexpression of the paRNA of HSPC152 (designated paHSPC) enhanced the expression of the HSPC152 mRNA, and an siRNA targeting the paHSPC152 decreased the expression of the HSPC152 mRNA. Overexpression of paHSPC also affected the epigenetic structure of its putative promoter region along with effects on several biologic features of melanoma cells. The ectopic expression of the paRNA to TYR did not have any effect. Overall, our work indicates that paRNAs may serve as an additional layer in the regulation of gene expression in melanoma, thus meriting further investigation.

Melanin Precursor 5,6-Dihydroxyindol: Protective Effects and Cytotoxicity on Retinal Cells in vitro and in vivo

5,6-Dihydroxyindole (DHI) is a melanin pigment precursor with antioxidant properties. In the light of a report about cytotoxicity of DHI, the aim of this study was to assess possible toxic effects of DHI on cells related to the eye, such as human ARPE-19 cells and mouse retinal explants. Moreover, DHI was tested on its effects on retinal function in vivo using electroretinography. We found cytotoxicity of DHI against ARPE-19 cells at 100 μM, but not at 10 μM. 10 μM DHI exhibited a slight, though not significant protective activity against UV-A damage in ARPE-19 cells. We found cytoprotection in cultured mouse retinas by 50 μM DHI or its diacetylated derivative 5,6-diacetoxyindole (DAI), respectively. In ERG measurements in vivo, amplitudes were decreased only slightly by 100 μM DHI compared to saline, whereas a better preservation of amplitudes was visible at 10 μM DHI, in particular with respect to cones. In histological sections, more cones were found at 10 μM DHI than at 100 μM DHI. As a conclusion, DHI shows a slight protective effect at 10 μM both in vitro and in vivo. At 100 μM, it shows a strong cytotoxicity in vitro, which is strongly reduced in vivo.

Color measurement of the animal integument predicts the content of specific melanin forms

The slope of the reflectance spectra of feathers and hairs predicts their content of 5,6-dihydroxyindole-2-carboxylic acid (DHICA)-eumelanin and benzothiazole-pheomelanin.

Functional Characterization of MC1R-TUBB3 Intergenic Splice Variants of the Human Melanocortin 1 Receptor

The melanocortin 1 receptor gene (MC1R) expressed in melanocytes is a major determinant of skin pigmentation. It encodes a Gs protein-coupled receptor activated by α-melanocyte stimulating hormone (αMSH). Human MC1R has an inefficient poly(A) site allowing intergenic splicing with its downstream neighbour Tubulin-β-III (TUBB3). Intergenic splicing produces two MC1R isoforms, designated Iso1 and Iso2, bearing the complete seven transmembrane helices from MC1R fused to TUBB3-derived C-terminal extensions, in-frame for Iso1 and out-of-frame for Iso2. It has been reported that exposure to ultraviolet radiation (UVR) might promote an isoform switch from canonical MC1R (MC1R-001) to the MC1R-TUBB3 chimeras, which might lead to novel phenotypes required for tanning. We expressed the Flag epitope-tagged intergenic isoforms in heterologous HEK293T cells and human melanoma cells, for functional characterization. Iso1 was expressed with the expected size. Iso2 yielded a doublet of Mr significantly lower than predicted, and impaired intracellular stability. Although Iso1- and Iso2 bound radiolabelled agonist with the same affinity as MC1R-001, their plasma membrane expression was strongly reduced. Decreased surface expression mostly resulted from aberrant forward trafficking, rather than high rates of endocytosis. Functional coupling of both isoforms to cAMP was lower than wild-type, but ERK activation upon binding of αMSH was unimpaired, suggesting imbalanced signaling from the splice variants. Heterodimerization of differentially labelled MC1R-001 with the splicing isoforms analyzed by co-immunoprecipitation was efficient and caused decreased surface expression of binding sites. Thus, UVR-induced MC1R isoforms might contribute to fine-tune the tanning response by modulating MC1R-001 availability and functional parameters.

Tyrosinase Depletion Prevents the Maturation of Melanosomes in the Mouse Hair Follicle

The mechanisms that lead to variation in human skin and hair color are not fully understood. To better understand the molecular control of skin and hair color variation, we modulated the expression of Tyrosinase (Tyr), which controls the rate-limiting step of melanogenesis, by expressing a single-copy, tetracycline-inducible shRNA against Tyr in mice. Moderate depletion of TYR was sufficient to alter the appearance of the mouse coat in black, agouti, and yellow coat color backgrounds, even though TYR depletion did not significantly inhibit accumulation of melanin within the mouse hair. Ultra-structural studies revealed that the reduction of Tyr inhibited the accumulation of terminal melanosomes, and inhibited the expression of genes that regulate melanogenesis. These results indicate that color in skin and hair is determined not only by the total amount of melanin within the hair, but also by the relative accumulation of mature melanosomes.

Inhibitory effects of Taraxacum mongolicum with phreatic water on melanin synthesis

BACKGROUND

Recently, people have begun showing heightened interest in skin whitening. Melanin is an important factor that determines skin color. The purpose of this study is to investigate the inhibitory effect of Taraxacum mongolicum (TAM) with phreatic water (PW) from Dogo Hot Springs on melanin synthesis.

METHODS

We assessed the inhibitory effects of TAM on melanin synthesis in B16F10 mouse melanoma cells. The mRNA levels of tyrosinase related protein (TRP)-1, TRP-2, tyrosinase, MITF, ERK, and PKA protein were analyzed with reverse transcription polymerase chain reaction and Western blot analysis. We also assessed the inhibitory effects of TAM with PW on melanin synthesis in HRM-2 melanin-possessing hairless mice. After UVB irradiation, differences in melanin were analyzed with an image analysis software between the left dorsal skin (untreated part) and the right dorsal skin (treated part). The mRNA levels of TRP-1, TRP-2, and matrix metalloproteinase (MMP)-9 were analyzed with real-time quantitative polymerase chain reaction. The dorsal skins were analyzed with histological test by hematoxylin and eosin staining.

RESULTS

TAM inhibited the TRP-1, TRP-2, tyrosinase, MITF mRNA gene expression, and PKA protein expression on the concentration-dependent B16F10 cell. Moreover, TAM increased the ERK mRNA gene expression in the B16F10 cell. After UVB irradiation, TAM with PW increased the differences in melanin between the left dorsal skin (untreated part) and the right dorsal skin (treated part) in HRM-2 mice. TAM with PW inhibited the TRP-1, TRP-2, and MMP-9 mRNA gene expression in HRM-2 mice. TAM with PW decreased the epidermal thickness, around the cell deformation, keratinization, and infiltration in HRM-2 mice.

CONCLUSION

These results indicate that TAM with PW has the inhibitory effect of decreasing the melanin synthesis.

Melanin nanoparticles as a novel contrast agent for optoacoustic tomography

We describe the synthesis and characterization of melanin-like nanoparticles (MNP) as novel contrast agents for optoacoustic tomography. Good dispersion stability of high concentration MNPs in different biological media was achieved with thiol-terminated methoxy-poly(ethylene glycol), which can be used for further functional conjugation. MNP-PEG were found biocompatible with human MCF-7 and 3T3 cells. Cell toxicity of MNPs was found lower than that of gold nanorods for concentrations that provide equal optical absorbance. Optoacoustic tomography images were obtained with Laser Optoacoustic Imaging System (LOIS-3D) from tubes filled with contrast agents and live mice. Imaging of tubes permitted verification of the system resolution <300 μm and sensitivity Δμa=0.03/cm under safe laser fluence of 20 mJ/cm(2). Water suspensions of MNP demonstrated optoacoustic efficiency that is about equal to that of gold nanorods under conditions of equal optical absorption. We conclude that MNPs have the potential for biomedical imaging applications as optoacoustic contrast agents.

Melanin chemistry and the ecology of stress

Knowledge of melanin chemistry has important implications for the study of the evolutionary ecology of animal pigmentation, but the actual chemical diversity of these widely expressed biological pigments has been largely overlooked. Considering all melanin forms and the different conditions of endogenous oxidative stress during their synthesis provides information about physiological costs and benefits of different pigmentation patterns and opens a new perspective to understanding the evolution of color phenotypes in animals.

Mitochondrial function in melanoma

Melanoma is the most lethal form of skin cancer and its incidence is rapidly rising. Breakthroughs in the understanding of the basic biology of melanoma in the past decade have yielded several new treatments, and advances continue to be made on a variety of fronts. One such area involves the delineation of changes in mitochondria that occur during melanoma formation, and how these changes affect responses to therapy. In this review, we summarize recent developments on the multiple functions that mitochondria play in melanoma, and how these roles are currently being evaluated as new targets for clinical intervention.

Anti-melanogenic effects of δ-tocotrienol are associated with tyrosinase-related proteins and MAPK signaling pathway in B16 melanoma cells

Tocotrienols are known to possess potent antioxidant, anticancer, and cholesterol lowering activities. Being able to rapidly penetrate the skin, these vitamin E isoforms have been explored for potential treatment against melanoma. This study aimed to elucidate the mechanism involved in the anti-melanogenic effects of δ-tocotrienol (δT3) in B16 melanoma cells. Results showed that at 20 μM of δT3 significantly inhibited melanin formation and ROS generation. Treatment with δT3 also effectively suppressed the expression of melanogenesis-related proteins, including MC1R, MITF, TYRP-1, and TYRP-2. More importantly, we observed that the mitogen-activated protein kinase (MAPK) pathway was involved in mediating δT3's inhibitory effect against melanin production. Specifically, δT3 treatment markedly induced the activation of extracellular signal-regulated kinases (ERK). The use of ERK activation inhibitor (PD98059) abrogated the δT3-mediated downregulation expression melanogenesis-related proteins and restored melanin production. Furthermore, siRNA targeting ERK effectively blocked the δT3-induced repression of tyrosinase and TYRP-1 expression. These results suggest that δT3's inhibitory effect against melanogenesis is mediated by the activation of ERK signaling, thereby resulting in downstream repression of melanogenesis-related proteins and the subsequent melanin production. These data provide insight to δT3's effect and the targeting of ERK signaling for treatment against melanogenesis.

Effects of the melanin precursor 5,6-dihydroxy-indole-2-carboxylic acid (DHICA) on DNA damage and repair in the presence of reactive oxygen species

Eumelanin is a heterogeneous polymer composed of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and 5,6-dihydroxyindole (DHI). Studies have shown that DHICA promotes single strand breaks in plasmid DNA exposed to ultraviolet B radiation (UVB, 313 nm) and in DNA from human keratinocytes exposed to ultraviolet A radiation (UVA, 340-400 nm). Singlet molecular oxygen ((1)O2) is the main reactive species formed by UVA radiation on the skin. In this context, we now report that DHICA can cause single strand breaks in plasmid DNA even in the absence of light radiation. Interestingly, when DHICA was pre-oxidized by (1)O2, it lost this harmful capacity. It was also found that DHICA could interact with DNA, disturbing Fpg activity and decreasing its recognition of lesions by ∼50%. Additionally, the free nucleoside deoxyguanosine (dGuo) was used to evaluate whether DHICA would interfere with the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) and spiroiminodihydantoin (dSp) by (1)O2 or with the formation of 8-oxodGuo by hydroxyl radical (OH). We observed that when dGuo was oxidized by (1)O2 in the presence of DHICA, 8-oxodGuo formation was increased. However, when dGuo was oxidized by OH in the presence of DHICA, 8-oxodGuo levels were lower than in the absence of the precursor. Overall, our data reveal an important role for this eumelanin precursor in both the promotion and the protection of DNA damage and imply that it can impair DNA repair.

Tyrosine metabolic enzymes from insects and mammals: a comparative perspective

Differences in the metabolism of tyrosine between insects and mammals present an interesting example of molecular evolution. Both insects and mammals possess fine-tuned systems of enzymes to meet their specific demands for tyrosine metabolites; however, more homologous enzymes involved in tyrosine metabolism have emerged in many insect species. Without knowledge of modern genomics, one might suppose that mammals, which are generally more complex than insects and require tyrosine as a precursor for important catecholamine neurotransmitters and for melanin, should possess more enzymes to control tyrosine metabolism. Therefore, the question of why insects actually possess more tyrosine metabolic enzymes is quite interesting. It has long been known that insects rely heavily on tyrosine metabolism for cuticle hardening and for innate immune responses, and these evolutionary constraints are likely the key answers to this question. In terms of melanogenesis, mammals also possess a high level of regulation; yet mammalian systems possess more mechanisms for detoxification whereas insects accelerate pathways like melanogenesis and therefore must bear increased oxidative pressure. Our research group has had the opportunity to characterize the structure and function of many key proteins involved in tyrosine metabolism from both insects and mammals. In this mini review we will give a brief overview of our research on tyrosine metabolic enzymes in the scope of an evolutionary perspective of mammals in comparison to insects.

Structural and functional photoacoustic molecular tomography aided by emerging contrast agents

Photoacoustic tomography (PAT) can offer structural, functional and molecular contrasts at scalable observation level. By ultrasonically overcoming the strong optical scattering, this imaging technology can reach centimeters penetration depth while retaining high spatial resolution in biological tissue. Recent extensive research has been focused on developing new contrast agents to improve the imaging sensitivity, specificity and efficiency. These emerging materials have substantially accelerated PAT applications in signal sensing, functional imaging, biomarker labeling and therapy monitoring etc. Here, the potentials of different optical probes as PAT contrast agents were elucidated. We first describe the instrumental embodiments and the measured functional parameters, then focus on emerging contrast agent-based PAT applications, and finally discuss the challenges and prospects.

Melanins and melanogenesis: methods, standards, protocols

Despite considerable advances in the past decade, melanin research still suffers from the lack of universally accepted and shared nomenclature, methodologies, and structural models. This paper stems from the joint efforts of chemists, biochemists, physicists, biologists, and physicians with recognized and consolidated expertise in the field of melanins and melanogenesis, who critically reviewed and experimentally revisited methods, standards, and protocols to provide for the first time a consensus set of recommended procedures to be adopted and shared by researchers involved in pigment cell research. The aim of the paper was to define an unprecedented frame of reference built on cutting-edge knowledge and state-of-the-art methodology, to enable reliable comparison of results among laboratories and new progress in the field based on standardized methods and shared information.

Role of melanin in melanocyte dysregulation of reactive oxygen species

We have recently reported a potential alternative tumor suppressor function for p16 relating to its capacity to regulate oxidative stress and observed that oxidative dysregulation in p16-depleted cells was most profound in melanocytes, compared to keratinocytes or fibroblasts. Moreover, in the absence of p16 depletion or exogenous oxidative insult, melanocytes exhibited significantly higher basal levels of reactive oxygen species (ROS) than these other epidermal cell types. Given the role of oxidative stress in melanoma development, we speculated that this increased susceptibility of melanocytes to oxidative stress (and greater reliance on p16 for suppression of ROS) may explain why genetic compromise of p16 is more commonly associated with predisposition to melanoma rather than other cancers. Here we show that the presence of melanin accounts for this differential oxidative stress in normal and p16-depleted melanocytes. Thus the presence of melanin in the skin appears to be a double-edged sword: it protects melanocytes as well as neighboring keratinocytes in the skin through its capacity to absorb UV radiation, but its synthesis in melanocytes results in higher levels of intracellular ROS that may increase melanoma susceptibility.

The genetics of pigment dispersion syndrome and pigmentary glaucoma

We review the inheritance patterns and recent genetic advances in the study of pigment dispersion syndrome (PDS) and pigmentary glaucoma (PG). Both conditions may result from combinations of mutations in more than one gene or from common variants in many genes, each contributing small effects. We discuss the currently known genetic loci that may be related with PDS/PG in humans, the role of animal models in expanding our understanding of the genetic basis of PDS, the genetic factors underlying the risk for conversion from PDS to PG and the relationship between genetic and environmental--as well as anatomical--risk factors.

Nanobiotechnological Nanocapsules Containing Polyhemoglobin-Tyrosinase: Effects on Murine B16F10 Melanoma Cell Proliferation and Attachment

We have reported previously that daily intravenous infusions of a soluble nanobiotechnological complex, polyhemoglobin-tyrosinase [polyHb-Tyr], can suppress the growth of murine B16F10 melanoma in a mouse model. In order to avoid the need for daily intravenous injections, we have now extended this further as follows. We have prepared two types of biodegradable nanocapsules containing [polyHb-Tyr]. One type is to increase the circulation time and decrease the frequency of injection and is based on polyethyleneglycol-polylactic acid (PEG-PLA) nanocapsules containing [polyHb-Tyr]. The other type is to allow for intratumoural or local injection and is based on polylactic acid (PLA) nanocapsules containing [polyHb-Tyr]. Cell culture studies show that it can inhibit the proliferation of murine B16F10 melanoma cells in the “proliferation model”. It can also inhibit the attachment of murine B16F10 melanoma cells in the “attachment model.” This could be due to the action of tyrosinase on the depletion of tyrosine or the toxic effect of tyrosine metabolites. The other component, polyhemoglobin (polyHb), plays a smaller role in nanocapsules containing [polyHb-Tyr], and this is most likely by its depletion of nitric oxide needed for melanoma cell growth.