Mechanisms of interference of p-diphenols with the Trinder reaction

Nanozyme-integrated alcogel colorimetric sensor for rapid and on-site detection of tert-butyl hydroquinone

Tert-butyl hydroquinone (TBHQ) stand as one of the most widely used antioxidants in food and daily chemical products. Rapid and sensitive monitoring of TBHQ holds considerable importance in safeguarding human health due to its potential risks. In this study, we devised an alcogel-based colorimetric sensor enabling the portable and visual detection of TBHQ. The Ce-UiO-66 nanozyme exhibiting remarkable oxidase-like activity, was synthesized and characterized, facilitating the catalysis of TBHQ oxidation to 2-tert-butyl-1,4-benzoquinone (TBBQ). The ensuing chromogenic reaction between TBBQ and ethylenediamine produced a stable and colored product, serving as a reliable indicator for the rapid and specific detection of TBHQ. Building upon this discovery, a portable and low-cost colorimetric sensor was fashioned by integrating the nanozyme into κ-carrageenan alcogel, thereby enabling on-site TBHQ detection via a smartphone-based sensing platform. The colorimetric sensor exhibited a detection limit of 0.8 μg mL-1, demonstrating robust performance across various matrices such as edible oils, cosmetics, and surface water. Recoveries ranged from 84.9 to 95.5%, with the sensor's accuracy further validated through gas chromatography-mass spectrometry. Our study presents an effective approach to rapid and convenient monitoring of TBHQ, exhibiting good extensibility and practicability.

Emergency medicine pharmacotherapy compromises accuracy of plasma creatinine determination by enzyme-based methods: real-world clinical evidence and implications for clinical practice

Background

Assessment of kidney function in emergency settings is essential across all medical subspecialties. Daily assessment of patient creatinine results from emergency medical services showed that some deviated from expected values, implying drug-related interference.

Methods

Real-time clinical evaluation of an enzyme method (Roche CREP2) in comparison with the Jaffé gen. 2 method (Roche CREJ2) was performed. During the period of December 2022 and January 2023, we analyzed 8,498 patient samples, where 5,524 were heavily medicated STAT patient specimens, 500 were pediatric specimens, and 2,474 were from a distant general population in a different region using the same methods.

Results

In 109 out of 5,524 hospital specimens (1.97%, p < 0.001), the CREP2 value was apparently (25% or more) lower than CREJ2. Suspect interfering medication was found in a sample of 43 out of 46 reviewed patients where medication data were available. This phenomenon was not observed in the general population.

Conclusion

In a polymedicated urgent care hospital population, a creatinine enzyme method produces unreliable results, apparently due to multiple drug-related interferences.

Oxidation of anti-thyroid drugs and their selenium analogs by ABTS radical cation

Lactoperoxidase was previously used as a model enzyme to test the inhibitory activity of selenium analogs of anti-thyroid drugs with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a substrate. Peroxidases oxidize ABTS to a metastable radical ABTS•+, which is readily reduced by many antioxidants, including thiol-containing compounds, and it has been used for decades to measure antioxidant activity in biological samples. We showed that anti-thyroid drugs 6-n-propyl-2-thiouracil, methimazole, and selenium analogs of methimazole also reduced it rapidly. This reaction may explain the anti-thyroid action of many other compounds, particularly natural antioxidants, which may reduce the oxidized form of iodine and/or tyrosyl radicals generated by thyroid peroxidase thus decreasing the production of thyroid hormones. However, influence of selenium analogs of methimazole on the rate of hydrogen peroxide consumption during oxidation of ABTS by lactoperoxidase was moderate. Direct hydrogen peroxide reduction, proposed before as their mechanism of action, cannot therefore account for the observed inhibitory effects. 1-Methylimidazole-2-selone and its diselenide were oxidized by ABTS•+ to relatively stable seleninic acid, which decomposed slowly to selenite and 1-methylimidazole. In contrast, oxidation of 1,3-dimethylimidazole-2-selone gave selenite and 1,3-dimethylimidazolium cation. Accumulation of the corresponding seleninic acid was not observed.

Probing the mechanism of flavin action in the oxidative decarboxylation catalyzed by salicylate hydroxylase

Salicylate hydroxylase (NahG) is a FAD-dependent monooxygenase in which the reduced flavin activates O₂ coupled to the oxidative decarboxylation of salicylate to catechol or uncoupled from substrate oxidation to afford H₂O₂. This chapter presents different methodologies in equilibrium studies, steady-state kinetics, and identification of reaction products, which were important to understand the S_EAr mechanism of catalysis in NahG, the role of the different FAD parts for ligand binding, the extent of uncoupled reaction, and the catalysis of salicylate's oxidative decarboxylation. These features are likely familiar to many other FAD-dependent monooxygenases and offer a potential asset for developing new tools and strategies in catalysis.

Fluorescence-Amplified Origami Microneedle Device for Quantitatively Monitoring Blood Glucose

Exploration of clinically acceptable blood glucose monitors has been engaging in the past decades, yet the ability to quantitatively detect blood glucose in a painless, accurate, and highly sensitive manner remains limited. Herein, a fluorescence-amplified origami microneedle (FAOM) device is described that integrates tubular DNA-origami nanostructures and glucose oxidase molecules into its inner network to quantitatively monitor blood glucose. The skin-attached FAOM device can collect glucose molecules in situ and transfer the input into a proton signal after the oxidase's catalysis. The proton-driven mechanical reconfiguration of DNA-origami tubes separates fluorescent molecules and their quenchers, eventually amplifying the glucose-correlated fluorescence signal. The function equation established on clinical examinees suggests that FAOM can report blood glucose in a highly sensitive and quantitative manner. In clinical blind tests, the FAOM achieves well-matched accuracy (98.70 ± 4.77%) compared with a commercial blood biochemical analyzer, fully meeting the requirements of accurate blood glucose monitoring. The FAOM device can be inserted into skin tissue in a trivially painful manner and with minimal leakage of DNA origami, substantially improving the tolerance and compliance of the blood glucose test.

Rifampicin is not an inhibitor of tyrosinase

Rifampicin has been previously described as an inhibitor of tyrosinase (Chai et al., Int. J. Biol. Macromol. 102 (2017) 425-430). However, rifampicin contains a p-diphenol group and compounds with such a moiety have been shown before to reduce tyrosinase-generated o-quinones. Rifampicin also shows strong absorption in a region completely overlapping with the visible absorption band of dopachrome, the oxidation product of L-tyrosine and L-dopa, whose concentration is measured spectrophotometrically in the standard enzymatic assay to monitor the activity of tyrosinase. We have demonstrated that rifampicin is also rapidly oxidized by o-quinones generated from catechols by tyrosinase or by treatment with sodium periodate. Smaller changes of absorbance at 475 nm during oxidation of L-dopa by tyrosinase in the presence of rifampicin do not result from enzyme inhibition but from oxidation of rifampicin by dopaquinone, which leads to rapid decrease of rifampicin absorption in this range. The actual reaction rates are not affected, which we have demonstrated by measurements of oxygen consumption. Rifampicin behaves therefore as other compounds with reducing properties, such as ascorbic acid, hydroquinone, hydrazine derivatives, and flavonoids, some of which have also been incorrectly described before as inhibitors of tyrosinase.

In vitro oxidation of hispidin and gallic acid by horseradish peroxidase

Gallic acid and hispidin have been previously described by us as inhibitors of horseradish peroxidase (Benarous, K., Benali, F. Z., Bekhaoua, I. C., and Yousfi, M. Journal of Biomolecular Structure & Dynamics, (2021) 39(18), 7168-7180). However, additional experiments have demonstrated that under the applied assay conditions both compounds are rapidly oxidized by this enzyme. After oxidation, the components of the reaction mixture undergo complex reactions giving products with much weaker absorption at the detection wavelength. This was interpreted by us as enzyme inhibition, which, however, is only apparent. In fact, the activity of horseradish peroxidase is not affected by these compounds, which was demonstrated by measurements of hydrogen peroxide consumption.Communicated by Ramaswamy H. Sarma.

Plasma creatinine below limit of quantification in a patient with acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is an infrequent complication of inflammatory bowel disease and can be exceptionally linked to interstitial nephritis secondary to anti-inflammatory drugs, such as Pentasa® (5-ASA).

CASE PRESENTATION

We present an case of an 80-year-old man who presented chronic diarrheas treated by Pentasa®. He developed AKI, evidenced by high plasma creatinine dosed in his local laboratory. At the hospital admission, plasma creatinine was exceptionally undetectable by the enzymatic method while Jaffe's method successfully determined it. Creatinine measurement by the enzymatic method was gradually restored during hospital stay, concomitant with the discontinuation of 5-ASA administration, suggesting that this drug could interfere with creatinine enzymatic assay. Creatinine enzymatic assays combine serial reactions. The last one called Trinder reaction, catalyzed by a peroxidase, uses H₂O₂ to convert uncolored dye in a colored compound, proportionally to creatinine concentration. We showed that AKI related-plasma accumulation of 5-ASA, could participate in the negative interference observed on creatinine measurement, by scavenging H₂O₂. Interestingly, all Trinder reaction-based measurements (uric acid, lipase, lactate, triglycerides and cholesterol) were affected. Negative interference of 5-ASA was confirmed by interferogram experiments on all Trinder reaction-dependent assays.

CONCLUSION

All Trinder-dependent parameters should be interpreted with the patient's treatment knowledge, in particular salicylate derivatives.