Affinity For Melanin Research Articles

Melanin-mediated accumulation of polycyclic aromatic hydrocarbons in human hair: Insights from biomonitoring and cell exposure studies

While human hair is widely used to monitor micro-organic contaminants (MOCs), their incorporation mechanisms are poorly understood. Melanin, known to facilitate the accumulation of drugs in hair, hasn’t been studied in the field of MOCs. Here, polycyclic aromatic hydrocarbons (PAHs), a class of priority MOCs, were investigated through hair biomonitoring as well as cell exposure experiments. PAH concentrations and melanin contents were measured in black and white hairs from the same individual. The results showed that five dominant PAHs (phenanthrene, fluoranthene, pyrene, benzo[a]anthracene and chrysene) in black hair (0.66 ng/g – 35.1 ng/g) were significantly higher than those in white hair (0.52 ng/g – 29.6 ng/g). Melanin contents in black hair (14.9 – 48.9 ng/g) were markedly higher than in white hair (0.35 – 2.15 ng/g) and were correlated to PAH concentrations, hinting melanin-mediated accumulation of PAHs in hair. The in vitro experiment using murine melanoma cells demonstrates that PAH levels in cells were affected by melanin, suggesting the affinity of melanin to PAHs. Both biomonitoring and cell exposure experiment implicate the pivotal role of melanin in PAH accumulation in hair. Therefore, to ensure the accuracy of hair biomonitoring for MOCs, attention must be paid to the melanin content uniformity.

Melanin-targeted [18F]-PFPN PET imaging may shed light for clear cell sarcoma.

Intracytoplasmic melanin pigment is a characteristic of clear cell sarcoma (CCS), which is a particularly deadly type of soft-tissue sarcoma. [18F]-N-(2-(diethylamino)ethyl)-5-(2-(2-(2-fluoroethoxy)ethoxy)ethoxy)picolinamide ([18F]-PFPN) is a positron emission tomography (PET) probe characterized by high melanin affinity. Therefore, this study aimed to investigate the feasibility of melanin-targeted [18F]-PFPN PET in patients with CCS. This prospective single-centre study recruited patients with pathologically confirmed CCS. [18F]-FDG PET/computed tomography and [18F]-PFPN PET/magnetic resonance imaging scans were performed within 1week of each other. The lesion numbers and [18F]-FDG and [18F]-PFPN PET parameters (maximum standardized uptake value [SUVmax], mean standardized uptake value [SUVmean], metabolic/melanotic tumour volume [MTV/MLTV], and total lesion glycolysis/melanin [TLG/TLM]) were collected. Three patients with CCS were recruited and received PET imaging. A total of 56 lesions were detected on [18F]-PFPN PET, including primary tumour and distant metastases. Identical lesions were not detected on [18F]-PFPN and [18F]-FDG PET. Twelve lesions (12/39, 30.77%) on [18F]-FDG imaging were missed on [18F]-PFPN, and 20 lesions (20/47,42.55%) on [18F]-PFPN imaging were missed on [18F]-FDG. In quantitative analysis, the [18F]-FDG SUVmean (4.60 ± 3.24) was higher than the [18F]-PFPN SUVmean (3.0 ± 2.63) in all lesions (P = 0.01). No significant correlations were found between the SUVmax, SUVmean, MLTV/MTV, and TLM/TLG values of [18F]-PFPN and [18F]-FDG (P > 0.05). Melanin-targeted [18F]-PFPN PET imaging is feasible for the diagnosis of CCS. Different imaging features were displayed on [18F]-PFPN and [18F]-FDG PET imaging, demonstrating the complementary role of the tracers. Combined use of the two imaging modalities would be preferred in patients with CCS. NCT05963035.

Removal of Unwanted Hair: Efficacy and Safety of 755-nm Alexandrite Laser Equipped with a 30 mm Spot Handpiece.

Background: Alexandrite 755 nm laser has been currently recognized one of the gold standards for the permanent hair removal business because of its sufficient tissue penetration and higher affinity for melanin compared with Nd:YAG, making the treatment more incisive and effective. Objective: In this study, we evaluated an Alexandrite 755 nm laser with a 30-mm spot for a new and fast hair removal treatment. Methods: Patients of both genders, with skin Fitzpatrick's types, ranging from II to III, were asked to avoid any epilation techniques 4 weeks before the laser hair removal session. Participants underwent a minimum of three to a maximum of eight sessions of treatment, every 6 weeks. Six months after the last treatment, the final evaluation was completed. The treated body areas included arms, legs, axillae, and trunk. The subjects used a numeric scale with a range of 0 to 10 (0: no pain, 10: unbearable), to indicate the associated pain level experienced. By comparing the percentage of terminal hairs before and after laser treatment, hair reduction was determined. Results: The patients reported only slight post-treatment erythema that disappeared after a few hours and only two patients showed persistent erythema lasting a few weeks. The pain was found to be 4.9 ± 0.9 after single pass emission. Conclusions: The 755 nm laser with the new handpiece has proven to be an ideal wavelength for hair removal, allowing efficient, safe, and faster treatments to be performed for the patient.

Aesthetic Gingival Melanin Pigmentation Treatment in Smokers and Non-Smokers: A Comparison Study Using Nd:YAG Laser and Ceramic Bur.

Aesthetic concerns are increasing rapidly; thus, several approaches have been suggested for treating gingival melanin pigmentation. Lasers have been reported as an effective new tool, and the Nd:YAG laser beam has an affinity for melanin and haemoglobin. However, ceramic gingival bur is simple and has less bleeding effect during operation than conventional techniques. This study aimed to compare the outcomes of gingival depigmentation using the Nd:YAG laser and ceramic bur in two different groups (smokers and non-smokers). A total of 40 patients presenting with gingival melanin pigmentation were enrolled in this split-mouth study. The sample was divided into two groups: smokers and non-smokers. Treatment was performed using the Nd:YAG laser (3 W, 60 mJ/pulse, and 50 Hz) and ceramic bur with a one-week interval between the two methods. Clinical indices were recorded, including intraoperative bleeding, wound healing, post-operative pain, and the recurrence of pigmentation, and follow-up periods were determined in the 3rd, 6th, and 9th months postoperatively. Both treatments promoted a similar pain experience and recurrence rate of pigmentation (p > 0.489, p = 1.000, respectively). Bleeding during surgery and complete healing recovery after one week were statistically significantly higher when using ceramic bur (p = 0.00, p = 0.041, respectively). Concerning the effect of smoking on the treatment, a higher recurrence rate was observed in SG than N-SG in laser sites (50%, and 95%, respectively) and bur sites (60%, and 85%, respectively), but statistically no significant difference was observed (p > 0.080). In conclusion, both procedures are adequate for aesthetic gingival depigmentation treatment. The Nd:YAG laser showed greater effectiveness in controlling bleeding, while ceramic bur showed a faster clinical recovery. Furthermore, smokers were more likely to have low depigmentation treatment stability.

18F-PFPN PET: A New and Attractive Imaging Modality for Patients with Malignant Melanoma.

18F-FDG PET has limited diagnostic applications in malignant melanoma (MM). 18F-N-(2-(diethylamino)ethyl)-5-(2-(2-(2-fluoroethoxy)ethoxy)ethoxy)picolinamide (18F-PFPN) is a novel PET probe with high affinity and selectivity for melanin. We conducted a clinical study with 2 aims, first to investigate the biodistribution and radiation dosimetry of 18F-PFPN in healthy volunteers, and second, to examine the diagnostic utility of 18F-PFPN PET imaging in patients with MM. Methods: 18F-PFPN was synthesized through a fluoro-for-tosyl exchange reaction. Five healthy volunteers were enrolled to investigate the biodistribution, pharmacokinetics, radiation dosimetry, and safety of the tracer. Subsequently, a total of 21 patients with clinically suspected or confirmed MM underwent both 18F-PFPN PET/MRI and 18F-FDG PET/CT scans. The normalized SUVmax of selected lesions was determined for both tracers and compared in patient- and lesion-based analyses. Results: 18F-PFPN has an elevated radiochemical yield and was highly stable invivo. In healthy volunteers, 18F-PFPN was safe and well tolerated, and its effective absorbed dose was comparable to that of 18F-FDG. In patient-based analysis, 18F-PFPN uptake was higher than 18F-FDG for both primary tumors and nodal metastases. In lesion-based analysis,18F-PFPN PET imaging could detect 365 metastases that were missed on 18F-FDG PET. Additionally, 18F-PFPN PET imaging had clinical value in distinguishing false-positive lesions on 18F-FDG PET. Conclusion: 18F-PFPN is a safe and well-tolerated melanin PET tracer. In a pilot clinical study, 18F-PFPN PET imaging outperformed traditional 18F-FDG PET in identifying both primary MM and its distant spread.

PHOTOBIOMODULATION THERAPY USED IN TREATMENT OF ORAL HEMATOMA WITH 940NM DIODE LASER – A CASE REPORT

Oral Hematoma generally occurs in the oral cavity due to sharp teeth by accidental biting of the cheeks, lips, tongue, oral mucosa or any soft tissues. These vascular lesions sometimes could have a feeder artery or blood vessel which could hinder the treatment protocol. Laser tissue interaction is basically dependent on the wavelength of laser used and the chromospheres within the host tissue which absorbs the laser light. Diode lasers have an affinity for blood, hemoglobin, haemosiderin and melanin predominantly as their chromophores. Hence shorter wavelength lasers such as Diode work very well in treatment of oral hematomas. Low level laser therapy or photobiomodulation works on the phenomena of light photons that are absorbed by cytochromes and porphyrins in the mitochondria of the cell thereby increasing cell respiration and transcription bringing about desired laser tissue interaction. This article highlights the use of diode lasers in the treatment of such oral hematomas. Key words: Low level laser therapy, photobiomodulation, oral haematoma, bloodless, painless, laser therapy, sutureless, laser healing, Diode laser, 940nm Diode laser, phototherapy, vascular lesions

A different insight in hair analysis: Simultaneous measurement of antipsychotic drugs and metabolites in the protein and melanin fraction of hair from criminal justice patients

BackgroundPrevious studies have postulated that four structural compartments may be differentiated in hair: surface protein domain, water-accessible protein domain, water-inaccessible protein domain, and melanin. Drugs contained in blood, sweat, sebum, and environment would be deposited in the first two domains, with primarily drugs in blood being incorporated in the latter two domains during hair synthesis. Drugs in the first two domains would be removed by washing procedures. Use of enzymatic extraction procedures and evaluation of hair for damage from harsh cosmetic treatments might help to separately identify and quantify the drugs incorporated in the second two domains. Aimsa) Development of an UPLC-MS/MS method for the simultaneous quantification of the following 19 antipsychotic drugs and metabolites in hair: amisulpride, aripiprazole, chlorpromazine, clotiapine, clozapine, desmethylclozapine, desmethylolanzapine, haloperidol, norchlorpromazine, 7-OH-quetiapine, 9-OH-risperidone, olanzapine, pimozine, pimpamperone, quetiapine, risperidone, sertindole, sulpride, and tiapride; b) evaluation of measurement of patient adherence to prescribed medication use, c) determination of the influence of biochemical individuality effects on hair drug content, d) evaluation of relative binding of antipsychotic drugs to protein and to melanin hair structures. MethodApproximately 10 mg of intact hair were decontaminated with isopropanol and phosphate buffer, and then enzymatically digested overnight with dithiothreitol. After centrifugation, the supernatant digest (protein fraction) was separated from the remaining melanin hair pellet (melanin fraction). Melanin fraction was washed with water, and the drugs were extracted with dimethyl sulfoxide with ball-mill pulverization. Both fractions were purified with solid-phase cation exchange cartridges and injected in the UHPLC-MS/MS system. Results and discussionValidation of the method was carried out on the protein fraction following international guidelines. The limits of quantification ranged from 1.6–40 pg/mg. The method was applied to 59 head hair samples from prisoners from an antipsychotic compliance study in the criminal justice system in US. The patients were under chlorpromazine, haloperidol, risperidone, olanzapine, or quetiapine multiple antipsychotic treatment, during incarceration. The first head hair centimeter, closest to the scalp, was analyzed. The results were evaluated in relation to the type of hair, colour, hair damage, drug melanin affinity, and prescribed dose. In general, no good correlation between the prescribed dose/concentration in hair was obtained. A wide range of antipsychotic concentrations were observed ‘dose mg/day (d); pg/mg protein fraction (A)’: chlorpromazine (d:50-400;A:<LOQ->1600) and its metabolite norchlorpromazine (A: <LOQ->1600), haloperidol (d:4-20;A: <LOQ-2902), olanzapine (d:5-20;A: <LOQ-223) and its metabolite desmethylolanzapine (A: <LOQ -136), quetiapine (d:4-400;A: <LOQ -2754) and its metabolite 7-OH-quetiapine (A: <LOQ -1448), risperidone (d:2-20;A: <LOQ->1600) and its metabolite 9-OH-quetiapine (A:<LOQ-296;B). Melanin was found to have a 2- to 85-fold higher drug-binding affinity relative to the protein fraction ConclusionThis report describes a different viewpoint method of quantifying the antipsychotics in the melanin and water-inaccessible protein fraction of hair, separately. No correlation between the prescribed dose and the concentrations found in the protein and melanin domains were observed. The results show that hair melanin would have a much higher affinity for the antipsychotic medications than do hair proteins, being influenced mainly by biochemical individuality effects and less by hair colour. Future studies would be of interest using the proposed extraction method applied to hair of different colours.

Melanin-instructed biomimetic synthesis of copper sulfide for cancer phototheranostics

Biomimetic synthesis is a promising strategy for the preparation of nanotheranostics with excellent biocompatibility. Herein, we report a biomimetic approach to synthesize folic acid (FA) modified copper sulfide (CuS) nanodots for cancer phototheranostics by using melanin as a biotemplate and FA as a stabilizer. Owing to the high affinity of melanin for metal ions, copper ions can be adsorbed on the surface of melanin and then reacted with S2− ions to form CuS nanodots. As a natural biomolecule, melanin has high biocompatibility and biodegradability, which can effectively improve the biosafety of the prepared CuS nanodots. More importantly, both melanin and CuS have strong near-infrared (NIR) absorption, the as-prepared CuS-Melanin-FA composite nanoprobes with high photothermal conversion efficiency are promising for augmented photoacoustic imaging and photothermal therapy of cancer, which is demonstrated on 4T1 tumor-bearing mice. Moreover, the biomimetic synthesis method for the preparation of CuS nanodots opens a new horizon for the biomimetic synthesis of other nanotheranostics.

Relationship between skin melanin index and nicotine pharmacokinetics in African American smokers

BackgroundBlacks bear a disproportionate burden of smoking-related diseases and experience greater difficulty quitting smoking than Whites. Nicotine has a high affinity for melanin, and it has been hypothesized that melanin levels might influence nicotine pharmacokinetics and enhance dependence. The aim of this study was to evaluate the hypothesis that melanin affects nicotine disposition kinetics in humans. MethodsForty-four Black participants were administered intravenous infusions of deuterium-labeled nicotine and cotinine. Plasma concentrations of nicotine and cotinine were measured, and pharmacokinetic parameters were estimated. The constitutive and facultative melanin indexes were measured using a dermaspectrophotometer. ResultsThe median constitutive melanin index was 60.7 (32.8–134.7) and the median facultative melanin index 68.1 (38.6–127.1). The mean (±SD) nicotine elimination half-life was 136 min (±33.5), clearance was 1237 mL/min (±331), and Vss was 204 L (±66), or 2.6 L/kg (±0.7). No evidence of significant differences was found in nicotine pharmacokinetic parameters by comparing participants in different melanin index quartiles (outliers with very high melanin index had similar pharmacokinetic values to others). Differences were not statistically significant when adjusted for age, BMI, sex and CYP2A6 genotype or the nicotine metabolite ratio (NMR), and no evidence of significant correlations were found between melanin (facultative or constitutive) and the pharmacokinetic parameters of nicotine or cotinine or tobacco dependence measures. ConclusionsBased on our finding in this group of Black smokers, we could not confirm the hypothesis that melanin significantly affects nicotine disposition kinetics or measures of tobacco dependence.

Chemotherapy-induced isolated right pan-retinal atrophy

INTRODUCTIONTopically applied ocular medications could be sufficiently absorbed to inflict untoward systemic consequences.1-4 Timolol, a non-selective beta blocker is capable of eliciting severe asthmatic attacks in susceptible individuals. Timolol absorption is via nasal mucosa to systemic circulation. On another hand, systemically administered medications could through ophthalmic and ciliary arteries reach ocular tissues to unleash lethal effects. For instance chloroquine and its derivative, hydroxychloroquine sulphate, which have been useful in treating malaria and in larger doses, collagen-vascular disease, cause a cumulative dose-related pigmentary retinopathy.5,6 Mechanisms of action include inhibition of critical enzymes and interference with the metabolic functions of Retinal Pigment Epithelium (RPE) and photoreceptors. Both drugs apparently have a selective affinity for melanin, so they get concentrated in RPE and uveal tissue and are retained for long periods, even after their usage is stopped.

The significance of a negative hair test result

Establish the interpretation criteria to document a negative hair test result. When using hair analysis as a specimen during investigative analysis, such as in workplace drug testing, doping confirmation, driving under the influence, or drug-facilitated crime, the question of importance is to know whether the analytical procedure is sensitive enough to identify traces of drug(s) in hair after exposure, even in single drug exposure. This is particularly important when the urine sample of the subject is positive and the corresponding hair test is negative. It has been accepted in the forensic community that a negative hair result cannot exclude the administration of a particular drug, or one of its precursors and that the negative findings should not overrule any positive urine result. Nevertheless, the negative hair findings can, on occasion, cast doubt on the positive urine analysis, resulting in substantial legal debate and various consequences for the subject and the final response to the police, lawyers, or judges. The concept of minimal detectable dosage in hair is of interest to document the negative findings, but limited data is currently available in the scientific literature. Such data includes cocaine, codeine, ecstasy, ketamine and some benzodiazepines or hypnotics. There is obviously a lack of data in the literature. As an example, the minimum detectable dosage in hair has not been established for common drugs of abuse, such as cannabis, heroin, morphine or amphetamines, most medicines or doping agents. Several reasons can account for the absence of analytical response in hair after controlled administration. Simply, the drug may not be incorporated in hair. That is the case for large biomolecules, such as hormones (growth hormone, insulin, erythropoietin…), which cannot be transferred from the blood capillaries to growing cells of hair. Although not supported by any data, it is the opinion of the authors that only compounds with a molecular weight lower than 1000 daltons may be incorporated in hair. It is also possible that the administered parent compound is not the target compound in hair, as highlighted with ethanol and ethyl glucuronide. However, given that drugs are incorporated into hair according to several parameters such as melanin affinity, lipophilicity and membrane permeability, some are well incorporated while others are poorly incorporated. The strategy to document any result will be presented, including which concentrations can be expected after single exposure and after repetitive/therapeutic use. It is accepted by the authors that some parameters have to be assessed: dose necessary to give a positive result, repeatability, robustness, contamination, carry-over, interferences, variable incorporation into hair, external factors that may have an impact, etc. The difficulties in interpreting results of hair analysis for new drugs must be documented. In particular, little is known about the incorporation into the keratin matrix after intake and the correlation between dosage frequency of use and hair concentrations. The interpretation of any result must considered different scenarios such as passive exposure vs. active consumption, mindful vs. unaware intake, and sporadic vs. chronic use. Therefore, hair results for unusual drugs should be interpreted with caution by experienced forensic toxicologists. A negative hair result is also a result. However, this can be interpreted in two different ways: – the owner of the hair did not take or was not exposed to the specific drug, or; – the procedure is not sensitive enough to detect the drug. Until laboratories will have sensitive enough methodologies to detect drugs following a single use, care should be taken to compare urine and hair findings.

High-Throughput Melanin-Binding Affinity and In Silico Methods to Aid in the Prediction of Drug Exposure in Ocular Tissue

Drugs possessing the ability to bind to melanin-rich tissue, such as the eye, are linked with higher ocular exposure, and therefore have the potential to affect the efficacy and safety profiles of therapeutics. A high-throughput melanin chromatographic affinity assay has been developed and validated, which has allowed the rapid melanin affinity assessment for a large number of compounds. Melanin affinity of compounds can be quickly assigned as low, medium, or high melanin binders. A high-throughput chromatographic method has been developed and fully validated to assess melanin affinity of pharmaceuticals and has been useful in predicting ocular tissue distribution in vivo studies. The high-throughput experimental approach has also allowed for a specific training set of 263 molecules for a quantitative structure-affinity relationships (QSAR) method to be developed, which has also been shown to be a predictor of ocular tissue exposure. Previous studies have reported the development of in silico QSAR models based on training sets of relatively small and mostly similar compounds; this model covers a broader range of melanin-binding affinities than what has been previously published and identified several physiochemical descriptors to be considered in the design of compounds where melanin-binding modulation is desired.

Physical factors affecting chloroquine binding to melanin

Chloroquine is an antimalarial drug but is also prescribed for conditions such as rheumatoid arthritis. Long-term users risk toxic side effects, including retinopathy, thought to be caused by chloroquine accumulation on ocular melanin. Although the binding potential of chloroquine to melanin has been investigated previously, our study is the first to demonstrate clear links between chloroquine adsorption by melanin and system factors including temperature, pH, melanin type, and particle size. In the current work, two Sepia melanins were compared with bovine eye as a representative mammalian melanin. Increasing the surface anionic character due to a pH change from 4.7 to 7.4 increased each melanin's affinity for chloroquine. Although the chloroquine isotherms exhibited an apparently strong interaction with each melanin, isosteric heat analysis indicated a competitive interaction. Buffer solution cations competed effectively at low surface coverage; chloroquine adsorption occurs via buffer cation displacement and is promoted by temperature-influenced secondary structure swelling.

Melanin affinity and its possible role in neurodegeneration

Certain drugs with melanin affinity are known to have caused pigmentary lesions in the eye and skin. This was the basis for the hypothesis that compounds with melanin affinity may cause damage also in other melanin-bearing tissues such as the substantia nigra. The heterogeneity of compounds that binds to melanin is large. Toxins, drugs, and several other compounds have melanin affinity. Compounds showing the highest affinity are mainly organic amines and metal ions. The binding of toxicants to melanin probably protects the cells initially. However, the binding is normally, slowly reversible and melanin may accumulate the toxicant and gradually release it into the cytosol. Several studies indicate that neuromelanin may play a significant role both in the initiation and in the progression of neurodegeneration. MPTP/MPP(+) that has been causally linked with Parkinsonism has high affinity for neuromelanin, and the induced dopaminergic denervation correlates with the neuromelanin content in the cells. This shows that the toxicological implications of the accumulation of toxicants in pigmented neurons and its possible role in neurodegeneration should not be neglected. Extracellular neuromelanin has been reported to activate dendritic cells and microglia. An initial neuronal damage induced by a neurotoxicant that leaks neuromelanin from the cells may therefore lead to a vicious cycle of neuroinflammation and further neurodegeneration. Although there are many clues to the particular vulnerability of dopaminergic neurons of substantia nigra in Parkinson's disease, the critical factors are not known. Further studies to determine the importance of neuromelanin in neurodegeneration and Parkinson's disease are warranted.

Development of gadolinium based nanoparticles having an affinity towards melanin

Small Rigid Platforms (SRPs) are sub-5 nanometre gadolinium based nanoparticles that have been developed for multimodal imaging and theranostic applications. They are composed of a polysiloxane network surrounded by gadolinium chelates. A covalent coupling with quinoxaline derivatives has been performed. Such derivatives have proven their affinity for melanin frequently expressed in primary melanoma cases. Three different quinoxaline derivatives have been synthesised and coupled to the nanoparticles. The affinity of the grafted nanoparticles for melanin has then been shown in vitro by surface plasmon resonance on a homemade melanin grafted gold chip.

Ex vivo models to evaluate the role of ocular melanin in trans-scleral drug delivery

Trans-scleral delivery is nowadays considered as a possible way to deliver drugs to the posterior segment of the eye. Despite the potentiality of this administration route, there is a lack of fundamental knowledge on the role of the numerous barriers involved.The aim of this work was to develop an easy and cheap ex vivo method to evaluate the barrier properties of the choroid–Bruch’s layer and in particular to estimate the role of melanin in drug diffusion through ocular tissues. In vitro binding studies were performed to estimate drug affinity for melanin; model molecules used were methylene blue, propranolol, levofloxacin and methylprednisolone sodium succinate. The ex vivo model set up is based on porcine eye bulbs with light blue iris or brown iris. While the choroid of brown eyes is dark, the choroid of blue eyes is transparent, due to the absence of melanin. Permeation experiments using pigmented and not-pigmented porcine tissues gave the opportunity to discriminate between the barrier role of choroid–Bruch’s membrane as such and the barrier role of melanin. Ex vivo permeation experiments can be performed using isolated choroid–Bruch’s or the sclera–choroid–Bruch’s layer. In this last case, it is possible to take into account also the barrier role of the sclera that tends to decrease the drug concentration at the sclera/choroid interface, thus amplifying the effect of melanin.The data obtained in this paper indicate that for some drugs melanin can really represent a barrier and the effect can imply a lower drug flux or simply a longer lag time depending on the kind of drug and the concentration applied. However, it is a saturable barrier, thus its effect can probably be overtaken by high doses or multiple administrations. The ex vivo model set up can help to refine computational models, to better evaluate the interplay among static, dynamic and metabolic barriers. Additionally, since human eyes display a full range of pigmentation, the model could also be useful to investigate the possible influence of pigmentation phenotype on trans-scleral delivery.

In vitro melanin binding of NS-49, a phenethylamine class alpha 1A-adrenoceptor agonist.

Characteristics of the in vitro binding of NS-49 ((R)-(-)-3'-(2-amino-1-hydroxyethyl)-4'-fluoromethanesulfonanilide hydrochloride, CAS 137431-04-0) to synthetic melanin were determined and compared with those of other drugs. At all the drug concentrations tested (12.5-200 mumol/l), chloroquine (CAS 54-05-7) had the highest melanin binding (%), followed by ofloxacin (CAS 82419-36-1), NS-49, norephedrine (CAS 154-41-6) and diazepam (CAS 439-14-5). Binding constants (Kb), calculated with the Langmuir adsorption isotherm were, in the order (largest to smallest) chloroquine, ofloxacin, NS-49, norephedrine, the Kb value for NS-49 being one-thirteenth that for chloroquine, one-seventh that for ofloxacin and ten times higher than that for norephedrine. 53% of NS-49 that was bound to synthetic melanin dissociated during 24 h of incubation after the binding experiment. The percent of dissociation for NS-49 was higher than the values for chloroquine (5%) and ofloxacin (39%). After 1 day incubation in the dissociation experiment, the amount of NS-49 bound per mg of melanin was 23 nmol, being less than the amounts of chloroquine (210 nmol) and ofloxacin (78 nmol). These findings indicate that NS-49 has a lower affinity for synthetic melanin than chloroquine and ofloxacin, which have high affinities and therefore accumulate in melanin containing ocular tissues.

99mTcI/ReI Tricarbonyl Complexes with Tridentate Cysteamine Based Ligands: Synthesis, Characterization and in vitro/in vivo Evaluation

AbstractTricarbonyl MI (M = Re, 99mTc) complexes of a new tridentate cysteamine based chelator have been synthesized and fully characterized. To gain an insight into the usefulness of this new chelator for labeling biomolecules with a fac‐[M(CO)3]+ core, the ligand framework has been functionalized with a N‐(dialkylaminoalkyl) pharmacophore. The corresponding 99mTcI complexes showed moderate affinity for melanin and moderate cell uptake by B16F1 murine melanoma cells, and therefore deserve further evaluation in vivo as radioactive probes for the detection of melanomas.

Value of the concept of minimal detectable dosage in human hair

The influence on drug incorporation of melanin affinity, lipophilicity, and membrane permeability is of paramount importance. Despite their high lipophilicity, some drugs have quite low incorporation rate into hair, suggesting that the higher incorporation rates of basic drugs (cocaine, amphetamines.) than neutral (steroids, benzodiazepines, cannabinoids…) or acidic ones are strongly related to the penetrating ability of the drug to break through the membrane based on the pH gradient between blood and the acidic hair matrix. When using hair analysis as a matrix during investigative analysis, e.g. workplace drug testing, doping, driving under the influence, drug-facilitated crime, the question of importance is to know whether the analytical procedure was sensitive enough to identify traces of drugs; this is particularly important when the urine sample(s) of the subject was positive and the hair sample(s) was negative. It has been accepted in the forensic community that a negative hair result cannot exclude the administration of a particular drug, or one of its precursors and the negative findings should not overrule a positive urine result. Nevertheless, the negative hair findings can, on occasion, cast doubt on the positive urine analysis, resulting in substantial legal debate and various consequences for the subject. The concept of minimal detectable dosage in hair is of interest to document the negative findings, but limited data is currently available in the scientific literature. Such data includes cocaine, codeine, ketamine, some benzodiazepines and some unusual compounds. Until laboratories will have sensitive enough methodologies to detect a single use of drug, care should be taken to compare urine and hair findings.

Evaluation of new iodinated acridine derivatives for targeted radionuclide therapy of melanoma using 125I, an Auger electron emitter

The increasing incidence of melanoma and the lack of effective therapy on the disseminated form have led to an urgent need for new specific therapies. Several iodobenzamides or analogs are known to possess specific affinity for melanoma tissue. New heteroaromatic derivatives have been designed with a cytotoxic moiety and termed DNA intercalating agents. These compounds could be applied in targeted radionuclide therapy using (125)I, which emits Auger electrons and gives high-energy, localized irradiation. Two iodinated acridine derivatives have been reported to present an in vivo kinetic profile conducive to application in targeted radionuclide therapy. The aim of the present study was to perform a preclinical evaluation of these compounds. The DNA intercalating property was confirmed for both compounds. After radiolabeling with (125)I, the two compounds induced in vitro a significant radiotoxicity to B16F0 melanoma cells. Nevertheless, the acridine compound appeared more radiotoxic than the acridone compound. While cellular uptake was similar for both compounds, SIMS analysis and in vitro protocol showed a stronger affinity for melanin with acridone derivative, which was able to induce a predominant scavenging process in the melanosome and restrict access to the nucleus. In conclusion, the acridine derivative with a higher nuclear localization appeared a better candidate for application in targeted radionuclide therapy using (125)I.