Lgr6-expressing functional nail stem-like cells differentiated from human-induced pluripotent stem cells.

The nail matrix containing stem cell populations produces nails and may contribute to fingertip regeneration. Nails are important tissues that maintain the functions of the hand and foot for handling objects and locomotion. Tumor chemotherapy impairs nail growth and, in many cases, loses them, although not permanently. In this report, we have achieved the successful differentiation of nail stem (NS)-like cells from human-induced pluripotent stem cells (iPSCs) via digit organoids by stepwise stimulation, tracing the molecular processes involved in limb development. Comprehensive mRNA sequencing analysis revealed that the digit organoid global gene expression profile fits human finger development. The NS-like cells expressed Lgr6 mRNA and protein and produced type-I keratin, KRT17, and type-II keratin, KRT81, which are abundant in nails. Furthermore, we succeeded in producing functional Lgr6-reporter human iPSCs. The reporter iPSC-derived Lgr6-positive cells also produced KRT17 and KRT81 proteins in the percutaneously transplanted region. To the best of our knowledge, this is the first report of NS-like cell differentiation from human iPSCs. Our differentiation method and reporter construct enable the discovery of drugs for nail repair and possibly fingertip-regenerative therapy.

Toenail and serum levels as biomarkers of iron status in pre- and postmenopausal women: correlations and stability over eight-year follow-up.

Iron status is often assessed in epidemiologic studies, and toenails offer a convenient alternative to serum because of ease of collection, transport, and storage, and the potential to reflect a longer exposure window. Very few studies have examined the correlation between serum and toenail levels for trace metals. Our aim was to compare iron measures using serum and toenails on both a cross-sectional and longitudinal basis. Using a subset of the US-wide prospective Sister Study cohort, we compared toenail iron measures to serum concentrations for iron, ferritin and percent transferrin saturation. Among 146 women who donated both blood and toenails at baseline, a subsample (59%, n = 86) provided specimens about 8 years later. Cross-sectional analyses included nonparametric Spearman's rank correlations between toenail and serum biomarker levels. We assessed within-woman maintenance of rank across time for the toenail and serum measures and fit mixed effects models to measure change across time in relation to change in menopause status. Spearman correlations at baseline (follow-up) were 0.08 (0.09) for serum iron, 0.08 (0.07) for transferrin saturation, and - 0.09 (- 0.17) for ferritin. The within-woman Spearman correlation for toenail iron between the two time points was higher (0.47, 95% CI 0.30, 0.64) than for serum iron (0.30, 95% CI 0.09, 0.51) and transferrin saturation (0.34, 95% CI 0.15, 0.54), but lower than that for ferritin (0.58, 95% CI 0.43, 0.73). Serum ferritin increased over time while nail iron decreased over time for women who experienced menopause during the 8-years interval. Based on cross-sectional and repeated assessments, our evidence does not support an association between serum biomarkers and toenail iron levels. Toenail iron concentrations did appear to be moderately stable over time but cannot be taken as a proxy for serum iron biomarkers and they may reflect physiologically distinct fates for iron.

Development of microemulgel formulations with varied permeation enhancers for transungual delivery of luliconazole in onychomycosis management.

Luliconazole-loaded microemulgels containing different permeation enhancers were formulated for transungual drug delivery for the management of onychomycosis, onychomycosis, which affects nails. The physicochemical properties like droplet size, zeta potential, pH, viscosity, spreadability, extrudability, oil binding capacity, drug content, and microscopic study were evaluated. The Pseudo-ternary phase diagram was constructed for the formulation of microemulsions (MEs) by keeping the Km ratio constant at 3:1 and characterized for clarity, mean droplet size, zeta potential, viscosity, pH, transmittance, refractive index, and stability. The ME mean droplet size and zeta potential were found in the range of 38.78 to 171.4 nm, and 0.00 to - 6.6 mV, respectively. Prepared MEs were converted into microemulgel by adding a 2.5% gelling agent (Carbapol 934) in the external phase, and a drug release study was conducted. Formulation E3 showed better drug release and was chosen as the control. Four different penetration enhancers were added separately within E3 and further evaluated for pH, viscosity, spreadability, extrudability, oil binding capacity, drug content, microscopic study, Compatibility study, XRD, and DSC. A favorable docking score was observed between luliconazole and Lanosterol 14-alpha-demethylase. In-vitro cumulative drug release at the end of 24 h from E3-SS, containing sodium sulfide as a penetration enhancer, was found to be 94.70% and was 2 times more than the control formulation. Ex-vivo transungual permeation studies through cutting nail clippings were found to be in the range of 28.18 - 36.52 µg/mm2. The microemulgels tagged as E3, E3-SS, and E3-SL showed a significant zone of inhibition against Candida albicans and Aspergillus fumigatus as compared to the marketed formulation.

Therapeutic treatment strategies for the management of onychomycosis: a patent perspective.

INTRODUCTION: Onychomycosis, a multifactorial fungal infection of the nails, shows a global prevalence of about 5.5% and is responsible for 50% of all nail infections. To develop effective management strategies, it is necessary to understand the etiology, pathophysiology, and risk factors of onychomycosis. Oral route of drug delivery is one of the routes utilized to deliver anti-fungal agents, but, has its own limitations like longer duration of treatment, increased adverse effects, and potential for drug interaction. The ungual route has received greater attention due to its localized, non- invasive action and improved patient compliance. AREAS COVERED: This review comprehensively discusses conventional onychomycosis therapies and patented novel drug delivery systems for the management of onychomycosis including chemical permeation enhancers, non-particulate drug delivery systems, penetration enhancing devices etc., Databases such as PubMed, ResearchGate, and Google Patents were searched by using the keywords onychomycosis and trans-ungual drug delivery. EXPERT OPINION: Enormous research has been conducted and is still ongoing to find the best possible novel drug delivery system for onychomycosis management. Approaches like incorporation of herbal constituents in nano-formulations, inkjet printing, laser devices, iontophoretic techniques, etc. can be employed to make safe and effective drug delivery systems which are regulatory compliant.

Identification of biomarkers in diabetic nails by Raman spectroscopy.

BACKGROUND: The growth of Diabetes Mellitus (DM) is a serious public health issue which is more prevalent in developing countries. The main problems related to DM are the gradual changes in the structural and functional integrity of tissues caused by hyperglycemia, which calls for early diagnosis and periodic monitoring exams. Recent studies suggest that the quality of the nail plate has great potential to assess the secondary complications of DM. Hence, this study aimed to determine the biochemical characteristics of the nails of individuals with DM2 by Raman confocal spectroscopy (CRS). METHODS: We collected fragments from the distal region of the fingernails of 30 healthy volunteers and 30 volunteers with DM2. The samples were analyzed by CRS (Xplora - Horiba) coupled to a 785 nm laser. RESULTS: Alterations in different biochemical components, such as proteins, lipids, amino acids, and final agents of advanced glycation, and alterations in the disulfide bridges, which are important in stabilizing keratin in nails were identified. CONCLUSION: The spectral signatures and new DM2 markers in nails were identified. Therefore, the possibility of acquiring biochemical information by evaluating the nails of diabetics, a simple and easily acquired material associated with the CRS technique, may allow health complications to be detected quickly.

Estimation of elemental concentrations in the toenail of young Saudi females with obesity.

Elemental homeostasis is essential for maintaining normal metabolic processes. Elements in the toenails are now considered in the diagnosis or screening and used as biomarkers of several metabolic disorders. The incidence of obesity is more prevalent in females than males globally. At the same time, females appeared more susceptible to elemental alterations than males. This study aimed to evaluate the variation in the levels of several elements in toenails as possible biomarkers of health conditions associated with obesity in young Saudi females. A cross-sectional study was performed, between February-November 2019. The study enrolled 79 young females divided into two groups: participants with obesity (n=39) and non-obese (n=40). The toenail was analyzed to estimate Fe, I, K, Na, Cd, Cr, Mn, Ca, Mg, Cu, Co, and Se levels. The study showed a significant elevation in the levels of Fe, Ca, K, and Na in the toenail sample of female participants with obesity compared to the non-obese group. The levels of Mn, Cd, Co, Cu, and Cr, were significantly decreased in the toenail of participants with obesity. Moreover, other elements (i.e., Mg, I, and Se) were not significantly lower in the female group with obesity. Our findings confirmed the alterations of several elements among Saudi females with obesity. The toenail elemental analysis may become a useful diagnostic technique in monitoring the nutritional status, predicting some metabolic disorders, and environmental exposure.

Comparative Spatial Transcriptomic and Single-Cell Analyses of Human Nail Units and Hair Follicles Show Transcriptional Similarities between the Onychodermis and Follicular Dermal Papilla.

The nail unit and hair follicle are both hard keratin-producing organs that share various biological features. In this study, we used digital spatial profiling and single-cell RNA sequencing to define a spatially resolved expression profile of the human nail unit and hair follicle. Our approach showed the presence of a nail-specific mesenchymal population called onychofibroblasts within the onychodermis. Onychodermis and follicular dermal papilla both expressed Wnt and bone morphogenetic protein signaling molecules. In addition, nail matrix epithelium and hair matrix showed very similar expressions profile, including the expression of hard keratins and HOXC13, a transcriptional regulator of the hair shaft. Integration of single-cell RNA sequencing and digital spatial profiling data through computational deconvolution methods estimated epithelial and mesenchymal cell abundance in the nail- and hair-specific regions of interest and revealed close transcriptional similarity between these major skin appendages. To analyze the function of bone morphogenetic proteins in nail differentiation, we treated cultured human nail matrix keratinocytes with BMP5, which are highly expressed by onychofibroblasts. We observed increased expressions of hard keratin and its regulator genes such as HOXC13. Collectively, our data suggest that onychodermis is the counterpart of dermal papilla and that BMP5 in onychofibroblasts plays a key role in the differentiation of nail matrix keratinocytes.

Comparative Analysis of Type I Keratin Expression By Nail Consistency: An Immunohistochemistry Study.

The nail plate is one of the essential structures of the nail apparatus and is highly keratinized, making it difficult to handle this tissue experimentally. Different types of nail consistency were identified by applying distal pressure to the nail plate. To analyze the relationship between the keratins expressed in the nail plate and nail consistency, we chose a sample of 32 adult individuals (age 49.81±3.21 y) with the same number of each sex, who had a similar percentage of nail consistency types (56.25% hard consistency nails and 43.75% soft consistency nails). Immunohistochemical analyses showed that hard consistency nails contain more keratin 17 than soft consistency nails (P=0.026). These novel results allow nail consistency to be defined by the differential expression of keratins in the nail plate, and have potential clinical implications for the diagnosis of possible nail disorders and/or systemic disease.

A drug-in-adhesive anti-onychomycotic nail patch: Influence of drug and adhesive nature on drug release, ungual permeation, in vivo residence in human and anti-fungal efficacy.

A nail patch is an attractive option for the topical treatment of onychomycosis, although no product is commercially available. We previously identified optimal nail patch formulations for two anti-onychomycotic drugs, based on their properties, as well as those of the other patch components. In this paper, our aim was to further investigate the potential of the patch formulations as topical nail medicines, in particular, whether the drug-in-adhesive patches release drug which then permeates into and through the nail plate and show anti-fungal efficacy, and whether and to what extent they remain adhered to the human nail plate in vivo when tested over 2 week durations. In addition, the influence of the drug (amorolfine HCl, ciclopirox olamine) and PSA (Duro-Tak 2852 or Duro-Tak 202A) on these parameters was determined. We found that both the nature of the drug and of the PSA influenced in vitro drug release. The nature of the drug, but not that of the PSA, influenced ungual drug permeation through human nail clippings, with considerably greater (almost double) permeation for ciclopirox olamine, the smaller and less lipophilic molecule. In vivo residence, tested with 3 out of the 4 patches, excluding the patch where ciclopirox olamine degraded with time, showed greater residence on toenails compared to fingernails reflecting their far lesser exposure to environmental stresses during daily activities. In vivo residence was enhanced when the patch was cut to the shape of the nail, was applied at bedtime, and when a clear colourless nail varnish was applied on top of the patch to 'seal' it into place on the nail. Comparison of the patches indicated greater residence of Duro-Tak 202A containing patches over those containing Duro-Tak 2852. Amorolfine HCl in Duro-Tak 202A based patch also showed antifungal efficacy in contrast to Duro-Tak 2852-based patch, and is particularly promising for further development as a potential toenail medicine, remaining almost fully adhered to toenails for at least two weeks.

Serum levels of survivin in patients with psoriasis and their relation to disease characteristics.

BACKGROUND: Psoriasis is a chronic inflammatory disease in which T helper 1 (Th1) and Th17 cells play a major role in its pathogenesis. Studies have shown that keratinocytes in psoriatic tissue are resistant to apoptosis and have a high proliferation rate. Survivin is a multifunctional protein belonging to an apoptosis inhibitor family, which has significant effects on the immune system, such as activation of dendritic cells and T cells and immunomodulation. OBJECTIVES: To investigate a possible relationship between serum survivin levels and psoriasis disease characteristics and severity. MATERIALS AND METHODS: The present study included 84 patients with psoriasis who did not receive any systemic treatment for psoriasis in the last three months and 84 volunteers without psoriasis. Demographic data, smoking status, and alcohol consumption of the participants were questioned, and body mass index (BMI) was calculated. In the patient group, disease duration, family history, accompanying arthritis, and nail involvement were questioned and psoriasis area severity index (PASI) scores were calculated. Serum survivin levels were measured in all subjects. RESULTS: Serum survivin level was significantly higher in the patients compared to the controls (p = 0.008). There was no relationship between serum survivin level and disease duration, family history, joint involvement, nail involvement, BMI, and PASI score (all p-values > 0.05). Serum survivin levels were significantly higher in smokers than non-smokers and in alcohol consumers than patients that did not drink alcohol in the psoriasis group (p = 0.034 and p = 0.006, respectively). CONCLUSION: Serum survivin levels were higher in psoriasis patients than the control group. This finding suggests that this molecule, which is both immunomodulatory and an apoptosis inhibitor, may play a role in the pathogenesis of psoriasis. Significantly high serum survivin level in psoriasis patients who smoke suggests that smoking may act through survivin. More comprehensive studies are needed to evaluate the role of survivin in the pathogenesis of psoriasis and its relationship with smoking.

Biomarkers of disease in human nails: a comprehensive review.

Diagnostic, monitoring, response, predictive, risk, and prognostic biomarkers of disease are all widely studied, for the most part in biological fluids or tissues, but there is steadily growing interest in alternative matrices such as nails. Here we comprehensively review studies dealing with molecular or elemental biomarkers of disease, as opposed to semiological, pharmacological, toxicological, or biomonitoring studies. Nails have a long history of use in medicine as indicators of pathological processes and have also been used extensively as a matrix for monitoring exposure to environmental pollution. Nail clippings are simple to collect noninvasively as well as to transport and store, and the matrix itself is relatively stable. Nails incorporate, and are influenced by, circulating molecules and elements over their several months of growth, and it is widely held that markers of biological processes will remain in the nail, even when their levels in blood have declined. Nails thus offer the possibility to not only look back into a subject's metabolic history but also to study biomarkers of processes that operate over a longer time scale such as the post-translational modification of proteins. Reports on ungual biomarkers of metabolic and endocrine diseases, cancer, and psychological and neurological disorders will be presented, and an overview of the sampling and analytical techniques provided.

The Influence of UV Varnishes on the Content of Cysteine and Methionine in Women Nail Plates-Chromatographic Studies.

The main purpose of this work was to determine if the use of hybrid nail polishes causes changes in concentration of the most important sulfur amino acids that build nail plate structures, cysteine and methionine. We found that the average contents of cysteine and methionine in studied samples before the use of hybrid manicure were 1275.3 ± 145.9 nmol mg-1 and 111.7 ± 23.8 nmol mg-1, respectively. After six months of hybrid manicure use, the average amount of these sulfur amino acids in studied samples were 22.1% and 36.5% lower in the case of cysteine and methionine, respectively. The average amounts of cysteine and methionine in nail plate samples after the use of hybrid manicures were 992.4 ± 96.2 nmol mg-1 and 70.9 ± 14.8 nmol mg-1, respectively. We also confirmed that in studied women the application of UV light varnishes reduced the thickness of the nail plate, from 0.50 ± 0.12 mm before to 0.46 ± 0.12 mm after the use of the hybrid manicure.

Patient Recovery from COVID-19 Infections: Follow-Up of Hair, Nail, and Cutaneous Manifestations.

BACKGROUND: COVID-19 is a pandemic disease worldwide. Although cutaneous manifestations may present in affected patients, there have been limited studies on the cutaneous findings and hair and nail abnormalities after discharge. OBJECTIVE: To establish the cutaneous manifestations, hair and scalp disorders, and nail abnormalities in patients who recovered from COVID-19 infections. METHODS: A retrospective chart review and telephone interviews were conducted to determine the cutaneous manifestations, hair and scalp disorders, and nail abnormalities of patients aged over 18 years who were diagnosed with COVID-19 infections at Siriraj Hospital, Bangkok, Thailand, between January and June 2020. RESULTS: Ninety-three patients with prior COVID-19 infections participated in the study. The COVID-19 severity had been mild for most (71%). Cutaneous manifestations were reported in 8 patients (8.6%), with the common skin conditions being maculopapular rash and urticaria. The onsets of the skin conditions were before admission (1%), during admission (4.3%), and after discharge (3.2%). Increased hair shedding was also reported in 22 patients (23.7%), with a female predominance. Three patients were affected during admission, while the others were affected after discharge. The patients with moderate, severe, and critical COVID-19 infections experienced significantly more hair shedding than those with asymptomatic and mild diseases. Only 2 patients with mild COVID-19 disease reported nail abnormalities (chromonychia and brittle nails). CONCLUSIONS: Cutaneous manifestations, hair disorders, and nail abnormalities can occur in patients with COVID-19 after their discharge from hospital. Patients should therefore be followed up in anticipation of dermatological problems.

Single-cell RNA sequencing of human nail unit defines RSPO4 onychofibroblasts and SPINK6 nail epithelium.

Research on human nail tissue has been limited by the restricted access to fresh specimen. Here, we studied transcriptome profiles of human nail units using polydactyly specimens. Single-cell RNAseq with 11,541 cells from 4 extra digits revealed nail-specific mesenchymal and epithelial cell populations, characterized by RSPO4 (major gene in congenital anonychia) and SPINK6, respectively. In situ RNA hybridization demonstrated the localization of RSPO4, MSX1 and WIF1 in onychofibroblasts suggesting the activation of WNT signaling. BMP-5 was also expressed in onychofibroblasts implicating the contribution of BMP signaling. SPINK6 expression distinguished the nail-specific keratinocytes from epidermal keratinocytes. RSPO4+ onychofibroblasts were distributed at close proximity with LGR6+ nail matrix, leading to WNT/ß-catenin activation. In addition, we demonstrated RSPO4 was overexpressed in the fibroblasts of onychomatricoma and LGR6 was highly expressed at the basal layer of the overlying epithelial component, suggesting that onychofibroblasts may play an important role in the pathogenesis of onychomatricoma.

A novel technique to evaluate nail softening effects of different urea formulations.

Urea has been incorporated into several topical ungual formulations to hydrate and soften the nail plate. In this study, we employed various characterization techniques (visual observation, scanning electron microscopy, measurement of thickness, transonychial water loss, nail electrical resistance, and mechanical study) to investigate the effect of urea concentration on the hydration of bovine hoof membranes - an in vitro model of infected human nails. We obtained inconsistent results in the thickness, transonychial water loss, nail electrical resistance, and scanning electron microscopy studies. In the mechanical study using a modified Texture Analyzer method, we reported an inverse and linear correlation between urea concentrations in the formulations and the force required to puncture the treated membrane (R2 = 0.9582, n ≥ 8). As the urea concentration decreased from 4x to 2x, 1x, and 0x % w/w, the puncture force increased significantly from 0.47 ± 0.07 to 0.77 ± 0.07, 0.91 ± 0.09, and 1.33 ± 0.26 N, respectively (p < 0.05). Thus, urea provided a positive softening effect on the membranes and the puncture force could indicate the urea level in topical formulations. In this study, we provided a novel, efficient, and reliable tool to evaluate the hydration level and physical properties of bovine hoof membranes.

Iontophoresis to Overcome the Challenge of Nail Permeation: Considerations and Optimizations for Successful Ungual Drug Delivery.

Iontophoresis is a widely used drug delivery technique that has been used clinically to improve permeation through the skin for drugs and other actives in topical formulations. It is however not commonly used for the treatment of nail diseases despite its potential to improve transungual nail delivery. Instead, treatments for nail diseases are limited to relatively ineffective topical passive permeation techniques, which often result in relapses of nail diseases due to the thickness and hardness of the nail barrier resulting in lower permeation of the actives. Oral systemic antifungal agents that are also used are often associated with various undesirable side effects resulting in low patient compliance. This review article discusses what is currently known about the field of transungual iontophoresis, providing evidence of its efficacy and practicality in delivering drug to the entire surface of the nail for extended treatment periods. It also includes relevant details about the nail structure, the mechanisms of iontophoresis, and the associated in vitro and in vivo studies which have been used to investigate the optimal characteristics for a transungual iontophoretic drug delivery system. Iontophoresis is undoubtedly a promising option to treat nail diseases, and the use of this technique for clinical use will likely improve patient outcomes.Graphical abstract.

Raman Spectroscopy, X-ray Diffraction, and Scanning Electron Microscopy as Noninvasive Methods for Microstructural Alterations in Psoriatic Nails.

Psoriasis is a chronic inflammatory disease associated with immune system dysfunction that can affect nails, with a negative impact on patient life quality. Usually, nail psoriasis is associated with skin psoriasis and is therefore relatively simple to diagnose. However, up to 10% of nail psoriasis occurs isolated and may be difficult to diagnose by means of current methods (nail biopsy, dermoscopy, video dermoscopy, capillaroscopy, ultrasound of the nails, etc.). Since the nail is a complex biological tissue, mainly composes of hard α-keratins, the structural and morphological techniques can be used to analyze the human fingernails. The aim of this study was to corroborate the information obtained using Raman spectroscopy with those obtained by scanning electron microscopy (SEM) and X-ray diffractometry and to assess the potential of these techniques as non-invasive dermatologic diagnostic tools and an alternative to current methods.

Human Nails Permeation of an Antifungal Candidate Hydroalcoholic Extract from the Plant Sapindus saponaria L. Rich in Saponins.

We evaluated a hydroalcoholic extract of Sapindus saponaria L. pericarps (ETHOSS), as a candidate to a topical antifungal medicine for onychomycosis. ETHOSS was produced by extracting the crushed fruits in ethanol. The saponin contents were identified and characterized by electrospray ionization mass spectrometry. We measured the in vitro antifungal activity against three dermatophyte fungi, isolated from onychomycosis: Trichophyton rubrum, T. mentagrophytes, and T. interdigitale, using broth microdilution tests. The minimum fungicide concentration of ETHOSS ranged from 195.31 to 781.25 µg/mL. The cytotoxicity of the crude extract was tested on the HeLa cell line, and its ability to permeate into healthy human nails by photoacoustic spectroscopy and Fourier transformation infrared spectrometer (FTIR) spectroscopy by attenuated total reflection. Besides its strong antifungal activity, ETHOSS showed low cytotoxicity in human cells. It was able to permeate and reach the full thickness of the nail in one hour, without the aid of facilitating vehicles, and remained there for at least 24 h. These results suggest that ETHOSS has great potential for treating onychomycosis.

Effect of Different Nail Penetration Enhancers in Solid Lipid Nanoparticles Containing Terbinafine Hydrochloride for Treatment of Onychomycosis.

Onychomycosis is considered a stubborn nail fungal infection that does not respond to conventional topical antifungal treatments. This study aimed to develop and characterize novel solid lipid nanoparticles (SLNs) formulae containing terbinafine HCl (TFH) and loaded with different nail penetration enhancers (nPEs). Three (nPEs) N-acetyl-L-cysteine, thioglycolic acid, and thiourea were used. Characterization of the prepared formulae was done regarding particle size, zeta potential, polydispersity index (PDI), entrapment efficiency (EE%), physical stability, in vitro release study, infrared (FT-IR), and their morphological structures. The selected formulae and the marketed cream Lamifen® were compared in terms of their antifungal activity against Trichophyton rubrum as well as their nail hydration and their drug uptake by the nail clippers. Thiourea was the nPE of choice; formulae (N2 and N8), with thiourea, were considered the optimum TFH SLNs containing nPEs. They were selected for their optimum particle size of 426.3 ± 10.18 and 450.8 ± 11.45 nm as well as their highest EE% of 89.76 ± 1.25 and 90.35 ± 1.33, respectively. The in vitro microbiological screening of the antifungal activity of these two formulae showed significantly larger zones of inhibition in comparison with the marketed product. The ex vivo screening of the drug uptake of the two selected formulae was significantly higher than that of the marketed product. The nPE formulae present a very promising option as they showed optimum physicochemical characterization with high antifungal activity and high drug uptake as well as good nail hydration effect.

Nail Melatonin Content: A Suitable Non-Invasive Marker of Melatonin Production.

Melatonin plays multiple physiological roles in the human body. Evaluation of melatonin production by the determination of urinary 6-sulfatoxymelatonin in 24-h samples has important drawbacks which hinder the successful evaluation of melatonin production in large cohorts. Here, we evaluated the potential of nail analysis for estimating melatonin production. Firstly, mass spectrometry methodology for the determination of melatonin in nails was optimized and successfully validated. The method was found to be linear in the range 6.5-830 fg/mg with intraday and interday accuracy in the range 100-104 %, precision below 15 % and a LOD of 3.5 fg/mg. Secondly, nail melatonin concentrations from 84 volunteers (age 5-96) were determined. The expected correlation between melatonin and age was obtained (correlation coefficient -0.615; p < 0.001). Additionally, we showed that fingernails are preferable to toenails to determine nail melatonin content. Finally, fingernails collected for 180 days after melatonin administration (two volunteers, 1.9 mg/night during 5 days) were analyzed. Nail melatonin concentrations immediately rose after administration and went back to pre-administration values after ≈100 days in both volunteers. Our results suggest that melatonin determination in nails is a suitable non-invasive tool for the estimation of global melatonin production. Due to the easy collection and storage of nails, the long-term information obtained and the multiple functions of melatonin, nail melatonin content might complement dim light melatonin onset, which is commonly measured from plasma/saliva samples, paving the way for melatonin research.