A novel LC‐MS/MS method to quantify eumelanin and pheomelanin and their relation to UVR sensitivity – A study on human skin biopsies

Melanin in the skin can be divided into eumelanin and pheomelanin subtypes. Simultaneous quantification of these subtypes could clarify their relation to skin type and skin cancer development. We describe a novel, sensitive liquid chromatography–tandem mass spectrometry method to quantify two eumelanin markers, pyrrole‐2,3,5‐tricarboxylic acid (PTCA) and pyrrole‐2,3‐dicarboxylic acid (PDCA), and two pheomelanin markers, thiazole‐4,5‐dicarboxylic acid (TDCA) and thiazole‐2,4,5 tricarboxylic acid (TTCA), performed in a single run using the same biopsy. Volunteers with either Fitzpatrick skin type (FST) I/II or III/IV (n = 30) each provided a 4‐mm punch biopsy from the buttock. Upon analysis, the FST I + II group had significantly less of all four melanin biomarkers (PTCA, 0.75 ng/mm²; PDCA, 0.08 ng/mm²; TTCA, 0.24 ng/mm²; and TDCA, 0.10 ng/mm²) versus the FST III + IV group (PTCA, 4.89 ng/mm²; PDCA, 0.22 ng/mm²; TTCA, 2.61 ng/mm²; and TDCA, 0.72 ng/mm²), p ≤ 0.003. We find that this new LC‐MS/MS method is sensitive enough to quantify eumelanin and pheomelanin markers even in the lightest skin types.     

Understanding the Role of Cesium and Rubidium Additives in Perovskite Solar Cells: Trap States,Charge Transport,and Recombination

Adding cesium (Cs) and rubidium (Rb) cations to FA_0.83MA_0.17Pb(I_0.83Br_0.17)₃ hybrid lead halide perovskites results in a remarkable improvement in solar cell performance, but the origin of the enhancement has not been fully understood yet. In this work, time‐of‐flight, time‐resolved microwave conductivity, and thermally stimulated current measurements are performed to elucidate the impact of the inorganic cation additives on the trap landscape and charge transport properties within perovskite solar cells. These complementary techniques allow for the assessment of both local features within the perovskite crystals and macroscopic properties of films and full devices. Strikingly, Cs‐incorporation is shown to reduce the trap density and charge recombination rates in the perovskite layer. This is consistent with the significant improvements in the open‐circuit voltage and fill factor of Cs‐containing devices. By comparison, Rb‐addition results in an increased charge carrier mobility, which is accompanied by a minor increase in device efficiency and reduced current–voltage hysteresis. By mixing Cs and Rb in quadruple cation (Cs‐Rb‐FA‐MA) perovskites, the advantages of both inorganic cations can be combined. This study provides valuable insights into the role of these additives in multiple‐cation perovskite solar cells, which are essential for the design of high‐performance devices.     

A Simple and Rapid Staining Technique for Plastic Embedded Cartilage and Bone

In this report we describe a simple and rapid staining technique for cartilage and bone embedded in Araldite. Semitbin sections of embryonic vertebrae obtained from 15 to 17 day mouse fetuses were stained using an aqueous solution 0.25% with respect to methylene blue, 0.25% with respect to azure A, and 0.5% with respect to Na₂ CO₃, then counterstained with 1% aqueous pararosaniline chloride (MAP). Results were compared with toluidine blue stained sections. MAP permitted good discrimination of developmental stages of both cells and extracellular matrix within vertebral ossification centers during endochondral ossification. The technique is simple, rapid and applicable to plastic embedded sections, and can be used prior to ultrastructural examination.     

Significance of Thiol-Disulfide Exchange in Resting Stages of Plant Development

Abstract: Desiccation tolerance is a fundamental principle for resting stages of plant development which include the dormancy of seeds and the quiescent stages of resurrection plants. To prevent the deleterious effects of cellular desiccation, a complex interplay of several adaption mechanisms is required. The ability to cope with free radicals, the formation of which is well documented in desiccated tissues, is one of these basic requirements. Detoxification of free radicals by several antioxidants and scavenging enzymes include reactions of reduced glutathione (GSH) resulting in the formation of glutathione disulfide (GSSG). In free radical processing pathways GSSG is considered to be immediately reduced back to GSH by the action of glutathione reductase (EC 1.6.4.2.). However, in desiccated tissues GSSG accumulates. Protein-glutathione mixed disulfides (PSSG) are also reported to increase in plants under drought leading to the hypothesis that glutathione protects protein thiol groups from auto-oxidation. The irreversible formation of intramolecular disulfides resulting in denaturation of proteins would be one of the primary sites of desiccation injury. We suggest that PSSG is formed by the reaction of GSSG with high molecular weight thiols and introduce a thiol-disulfide cycle that involves reduction/oxidation processes of glutathione and protein thiol groups during the dehydration/rehydration processes in desiccation tolerant tissues.     

Evaluation of Brucella abortus S19 vaccine strains by bacteriological tests, molecular analysis of ery loci and virulence in BALB/c mice.

Two Brucella abortus S19 commercial vaccine strains used for vaccination against brucellosis in India and three S19 strains available as international reference were examined by microbiological assays and molecular analysis of the ery loci involved in erythritol metabolism, and tested for residual virulence in BALB/c mice. According to the sensitivity to penicillin and i-erythritol, the five strains tested had the phenotypic characteristics of strain S19. However, on culture medium containing i-erythritol, all strains developed spontaneous i-erythritol resistant colonies at mutation rates ranging from 1.42x10(-2) to 1.33x10(-6). The S19 characteristic 702 bp deletion in the erythrulose 1-phosphate dehydrogenase gene of the ery locus was present only in the three reference strains but not in the two commercial vaccines. Both commercial strains and one of the reference strains showed reduced virulence in BALB/c mice. The presence or absence in S19 strains of the 702 bp deletion in the ery locus had no correlation with either the rates of spontaneous mutation to erythritol resistance or the residual virulence in mice.     

Chordoma in children: Case-report and review of literature

We report an exceptional case of a very late local failure in a 9-year-old boy presenting with a chordoma of the cranio-cervical junction. The child was initially treated with a combination of surgical resection followed by high dose photon–proton radiation therapy. This aggressive therapy allowed a 9-year remission with minimal side-effects. Unfortunately, he subsequently presented with a local failure managed with a second full-dose course of protons. The child died one year later from local bleeding of unclear etiology.Keyword: Chordoma, Sarcoma, Protontherapy, Children     

Differences in the taste quality of maltose and sucrose in rats: issues involving the generalization of conditioned taste aversions

The present study employed a conditioned taste aversion generalizationparadigm to test the hypothesis that maltose produces tastesensations in the rat which are qualitatively distinguishablefrom sucrose. Since stimulus generalization can occur in boththe quality and intensity domains, an intrachemical (acrossconcentration) generalization gradient was established to aidin the interpretation of the interchemical (across molecules)generalization gradient. Moreover, since the commonly used intaketest is vulnerable to nontaste post-ingestional influences,the present study measured immediate responses to 100 µlstimulus samples, thus increasing our confidence that the behaviorwas under orosensory control. In Experiment 1, naive water deprivedrats were trained in a specially designed gustometer to maintaindrinking-spout contact for intermittent water reinforcement.Following this, rats in the experimental group were given threeexposures to 0.1 M sucrose on separate days, with the firsttwo exposures immediately preceding an injection of LiCl. Acontrol group was treated identically but received distilledwater instead of sucrose. Rats were then tested in the gustometerfor their avoidance of three equimolar concentrations of sucroseand maltose. Rats received ten trials of each stimulus quasi-randomlypresented in two sessions. Results indicated that all sucroseconcentrations were avoided (in experimental group only), butonly the 0.3 M concentration of maltose was avoided. The lowestsucrose concentration was significantly less avoided than thehigher concentrations. Intensity generalization gradients aresuch that intensities weaker than the conditioned stimulus (CS)produce just as much or less of a conditioned response (CR)and intensities stronger than the CS produce just as much ora greater CR than that elicited by the CS itself. Therefore,based on the results of Experimental, it was predicted thatif 0.1 M maltose served as the CS, the order of avoidance shouldbe: 0.3 M sucrose 0.1 M sucrose 0.03 M sucrose 0.3 M maltose 0.1 M maltose 0.03 M maltose, if it were true that maltoseand sucrose produce identical sensations that differ only inintensity. Experiment 2 explicitly tested this prediction usingthe same procedure as Experiment 1 except that 0.1 M maltoseserved as the CS. The observed order of avoidance was 0.3 Mmaltose > 0.1 M maltose > 0.03 M maltose = 0.3 M sucrose= 0.1 M sucrose = 0.03 M sucrose. In both experiments the intrachemicalgeneralization gradient broadened and the interchemical generalizationgradient steepened upon retesting. In conclusion, qualitativedifferences between maltose and sucrose explain the outcomesof these experiments better than differences in the relativeintensity of these sugars at isomolar concentrations.