Analysis of histidine and urocanic acid isomers by reversed-phase high-performance liquid chromatography

Effect of an Emollient Emulsion Containing 15.0% of Caprylic/Capric Triglyceride on the Urocanic Acid of the Stratum Corneum

Natural moisturizing factor (NMF) includes several compounds in the stratum corneum (SC), among them, urocanic acid (UCA). Ultraviolet (UV) exposure turns the trans-UCA of the SC into its cis isomer. We investigated the impact of a topical emollient emulsion treatment on the UCA isomers of the SC exposed to artificial UV stress. Aliquots of emollient emulsion were applied in healthy subjects for 2 h on delimited areas of the volar forearm, then, the SC was removed by tape stripping. Tapes were irradiated in a solar simulator chamber and a high performance liquid chromatograph was used to quantify UCA isomers from stripped SC extract. The amount of both UCA isomers were almost twice higher in the SC treated with the emollient emulsion. We also observed that the UV irradiation elevated the amount of the cis/trans UCA ratio on the SC (non-treated and treated), suggesting that the emollient sample was not able to avoid the UCA isomerization. The in vivo tests corroborated with the UCA data obtained ex vivo, since we found an increase in the superficial skin hydration with respective reduction of the TEWL, probably occurring by the occlusion performed by the emollient emulsion containing 15.0% w/w of caprylic/capric triglyceride.

BSA Capped gold Nanoclusters Modulated by Copper ion for Sensitive and Selective Detection of Histidine in Biological Fluid

This research proposed a sample and environmentally sustainable technique for the synthesis of bovine serum albumin capped gold nanoclusters (BSA-AuNCs) with outstanding fluorescence. The synthesized BSA-AuNCs were investigated using various ways before being combined with Cu2+ to produce a fluorescent switch probe (BSA-AuNCs-Cu2+) for histidine determination. After adding Cu2+, the fluorescence of the BSA-AuNCs was quenched, the fluorescence intensity was enhanced after adding histidine due to good coordination between Cu2+ and histidine. The significant chelation of histidine with Cu2+ demonstrated the viability of developing a selective "switch on" probe for histidine detecting over other amino acids. Unlike existing fluorescent nanomaterial-based approaches for detecting histidine, this study promises good selectivity, high efficiency, and the avoiding of chemical solvents. The designed BSA-AuNCs-Cu2+ fluorescent probe demonstrated an acceptable linear detection range of 0 to 240 µM under optimum circumstances, with a detection limit of 0.9 µM. The BSA-AuNCs-Cu2+ system was investigated in rat serum and human urine, with recoveries ranging from 97.2 to 108.2%, demonstrating its potential applicability for histidine detection with favorable results.

Analytical tools for urocanic acid determination in human samples: A review

Urocanic acid is a chromophore found in the skin that has been identified as an important immunosuppressant and carcinogenesis mediator through its photoisomerization from trans to cis form induced by ultraviolet radiation. Research on analytical methods that explore urocanic acid isomerization is indispensable to fully understand the deleterious effects mediated by this biomarker. In this context, the current relevant analytical methods for determination of these isomers in human samples are summarized in this review. The methods presented here are applicable to human samples collected by noninvasive methods (or minimally invasive), encompassing an array of analytical techniques, including high-performance capillary electrophoresis, confocal Raman spectroscopy, gas chromatography, high-performance liquid chromatography, and mass spectrometry, among others. Developed high-performance liquid chromatography methods have proven to be advantageous, allowing noninvasive collections for in vivo analysis and the confocal Raman, specially, for real-time analysis. Among all these methods, high-performance liquid chromatography is the most investigated one with mass spectrometry or ultraviolet detector, and the mass spectrometry detector being the most studied in the last years, demonstrating high sensitivity, very low detection limits, and accurate identification, especially for clinical investigations.

A novel label-free colorimetric detection of l-histidine using Cu2+-modulated G-quadruplex-based DNAzymes

We proposed a colorimetric method for l-histidine detection based on Cu²⁺-mediated DNAzyme and G-quadruplex-hemin complex catalyzed oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS). In this system, after the addition of l-histidine, the formation of G-quadruplex-hemin complex will be disturbed, thus the colorimetric signal intensity conversely corresponds to the concentration of histidine. In this assay, a lower detection limit of l-histidine (50 nM) is addressed comparing to previously reported colorimetric methods. The cost is extremely low as the proposed design is both label-free and enzyme-free. All the more vitally, the colorimetric detection procedure is substantially straightforward with no further modification processes. By and large, the sensor can provide a promising plan for the detection of l-histidine.

A supersandwich electrochemiluminescence immunosensor based on mimic-intramolecular interaction for sensitive detection of proteins

An electrochemiluminescence (ECL) immunoassay protocol was developed based on mimic-intramolecular interaction for sensitive detection of prostate specific antigen (PSA). It was constructed by integrating the ECL luminophore (tris(4,4'-dicarboxylicacid-2,2'-bipyridyl)-ruthenium(ii)dichloride (Ru(dcbpy)3(2+))) and coreactant (histidine) into the supersandwich DNA structure. This strategy was more effective in amplifying the ECL signal by shortening the electronic transmission distance, improving the ECL luminous stability and enhancing the ECL luminous efficiency. The ECL matrices denoted as MWCNTs@PDA-AuNPs were fabricated through spontaneous oxidative polymerization of dopamine (DA) on multiwalled carbon nanotubes (MWCNTs) and reducing HAuCl4 to produce gold nanoparticles (AuNPs) by DA simultaneously. Then, the prepared matrices were applied to bind capture antibodies. Moreover, supersandwich Ab2 bioconjugate was designed using a PAMAM dendrimer to immobilize the detection antibody and supersandwich DNA structure. The PAMAM dendrimer, with a plurality of secondary and tertiary amine groups, not only facilitated high-density immobilization of the detection antibody and supersandwich DNA structure, but also greatly amplified the ECL signal of Ru(dcbpy)3(2+). The supersandwich DNA structure contained multiple Ru(dcbpy)3(2+) and histidine, further amplifying the ECL signal. The proposed supersandwich immunosensor showed high sensitivity with a detection limit of 4.2 fg mL(-1) and a wide linear range of 0.01 pg mL(-1)-40.00 ng mL(-1). With the excellent stability, satisfying precision and reproducibility, the proposed immunosensor indicates promising practicability for clinical diagnosis.

Natural moisturizing factor components in the stratum corneum as biomarkers of filaggrin genotype: evaluation of minimally invasive methods

BACKGROUND

The carriers of loss-of-function mutations in the filaggrin gene (FLG) have reduced levels of natural moisturizing factor (NMF) in the stratum corneum. The concentration of NMF components which are formed by filaggrin protein breakdown in the stratum corneum might therefore be useful as a biomarker of the FLG genotype. OBJECTIVES To investigate the feasibility of different sampling methods for the determination of two NMF components, 2-pyrrolidone-5-carboxylic acid (PCA) and urocanic acid (UCA), in the stratum corneum as biomarkers for the FLG genotype.

METHODS

PCA and UCA from the stratum corneum were sampled by using a tape stripping technique and an extraction technique using skin patches containing potassium hydroxide (KOH). The concentrations of PCA and UCA were measured by high-performance liquid chromatography. Eleven carriers of an FLG mutation and 10 individuals wild type for the two most common FLG mutations (R501X and R2447X) [corrected] were included in the study.

RESULTS

The most significant difference between the FLG genotypes was found for PCA sampled by the tape stripping technique. The mean values of PCA obtained by the tape stripping technique were, respectively, 0.18, 0.50 and 1.64 mmol g(-1) protein in homozygous (or compound heterozygous), heterozygous and wild-type genotypes (P < 0.005 homozygous vs. heterozygous; P < 0.0001 heterozygous vs. wild type). The tape stripping technique showed less intrasubject variation compared with the KOH patches, in particular when the concentrations of UCA and PCA on the tape strips were normalized for protein amount.

CONCLUSIONS

The concentration of PCA in the stratum corneum collected by tape stripping showed it to be a feasible biomarker of the FLG genotype.

Recent advances in urocanic acid photochemistry, photobiology and photoimmunology

Urocanic acid (UCA), produced in the upper layers of mammalian skin, is a major absorber of ultraviolet radiation (UVR). Originally thought to be a 'natural sunscreen', studies conducted a quarter of a century ago proposed that UCA may be a chromophore for the immunosuppression that follows exposure to UVR. With its intriguing photochemistry, its role in immunosuppression and skin cancer development, and skin barrier function, UCA continues to be the subject of intense research effort. This review summarises the photochemical, photobiological and photoimmunological findings regarding UCA, published since 1998.

Topical exposure to exogenous ultraviolet-irradiated urocanic acid enhances Mycobacterium ulcerans infection in a Crl:IAF(HA)-hrBR hairless guinea-pig model of Buruli ulcer disease

BACKGROUND

Ultraviolet radiation (UVR) pre-exposure enhances Mycobacterium ulcerans infection in the Crl:IAF(HA)-hrBR hairless guinea-pig, possibly via a photoimmunosuppressive mechanism. The trans-cis photoisomerization of epidermal urocanic acid is an important initiator of the web of events leading to photoimmunosuppression. Thus, the hypothesis tested in this paper was that topical pre-exposure to UVR-irradiated urocanic acid mixture containing cis-urocanic acid (UVR-UCA) enhances the ulcerative form of M. ulcerans infection in the Crl:IAF(HA)-hrBR hairless guinea-pig model of human Buruli ulcer disease.

METHODS

Groups of six animals were subjected to daily topical treatment with either 0 (vehicle only), 0.1, 0.5 or 1 mg of trans (tUCA) or UVR-UCA (contained a cis : trans urocanic acid isomer ratio of 1 : 9) for three consecutive days. A sham treatment group was also included in the experiment. Three days following their final treatment, the guinea-pigs were intradermally infected in the right dorsal flank with 1.5 x 107 CFU of M. ulcerans in 0.1 ml of phosphate-buffered saline (PBS) and sham infected with 0.1 ml of PBS in the left dorsal flank. The resultant skin lesions were then measured over the next 21 days. At day 21 postinfection, the animals were tested for delayed-type hypersensitivity (DTH) reactivity to M. ulcerans cell fragment antigens (MCF).

RESULTS

Distinct, well-demarcated, dermally situated skin nodules were present at infected, but not sham-infected, skin sites by day 3 postinfection, and the lesions progressed to frank ulcers by day 5. Between days 5 and 21, the mean lesion diameters of the UVR-UCA-treated animals were significantly (P<0.001) greater than those of the sham, vehicle only or tUCA-treated groups. UVR-UCA-treated guinea-pigs also had significantly (P<0.001) suppressed DTH responses to MCF compared with the other treatment groups. There were no significant (P>0.4) differences between the lesion sizes and DTH responses of the tUCA, vehicle only or sham treatment groups. These results demonstrate that topical exposure to UVR-UCA promotes M. ulcerans infection and suppresses DTH responses to M. uclerans antigens in infected animals. These results lend credence to the hypothesis that UVR-mediated enhancement of Buruli ulcer disease in the Crl:IAF(HA)-hrBR hairless guinea-pig model occurs via modulation of cis-urocanic acid-susceptible immune pathways.

Simultaneous Determination of Histamine and Histidine by Liquid Chromatography Following Intramolecular Excimer-forming Fluorescence Derivatization with Pyrene-labeling Reagent

A highly sensitive and selective fluorometric method for the determination of histamine and histidine has been developed. This method is based on an intramolecular excimer-forming fluorescence derivatization with a pyrene reagent followed by reversed-phase liquid chromatography. The analytes, containing two amino moieties in a molecule, were converted to the corresponding dipyrene-labeled derivatives by derivatization. The derivatives afforded intramolecular excimer fluorescence (440 - 540 nm), which can clearly be discriminated from the normal fluorescence (360 - 420 nm) emitted from reagent blanks. The detection limits (signal-to-noise ratio = 3) were femto mole levels.

UV-induced skin changes due to regular use of commercial sunbeds

BACKGROUND/AIM

Increased pigmentation and thickening of the epidermis are the most important photoprotective skin reactions induced by ultraviolet (UV) radiation. The present study was designed to find out what changes are induced by regular use of commercial sunbeds twice weekly over a period of 6 weeks.

METHODS

The parameters analysed were skin pigmentation measured by chromametry, minimal erythema dose (MED) as a parameter of light sensitivity, epidermal thickening as determined by histology, induction of keratinocyte apoptosis as determined by TUNEL staining and antioxidant metabolism as measured by changes of cis- and trans-urocanic acid (UCA) content of the skin.

RESULTS

As expected, chromametry confirmed the clinically obvious increased skin pigmentation. However, no increase in MED was observed. In addition, neither epidermal thickening nor sunburn cells were seen. Significant detectable changes in proportion of the UCA isomer content of the UV-exposed skin were seen. The total UCA and cis-UCA content increased significantly between nearly all points of measurement. The amount of trans-UCA first decreased, then increased significantly between the different time points.

CONCLUSION

Our data indicate that sunbed-induced tanning is non-protective, which has to be addressed for persons looking for this effect before planning a stay in a sunny climate. However, sunbed-induced tanning may influence immunological reactions.