Reactivity of bacterial and fungal laccases with lignin under alkaline conditions

The ability of Streptomyces ipomoea laccase to polymerize secoisolariciresinol lignan and technical lignins was assessed. The reactivity of S. ipomoea laccase was also compared to that of low redox fungal laccase from Melanocarpus albomyces using low molecular mass p-coumaric, ferulic and sinapic acid as well as natural (acetosyringone) and synthetic 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) mediators as substrates. Oxygen consumption measurement, MALDI-TOF MS and SEC were used to follow the enzymatic reactions at pH 7, 8, 9 and 10 at 30 °C and 50 °C. Polymerization of lignins and lignan by S. ipomoea laccase under alkaline reaction conditions was observed, and was enhanced in the presence of acetosyringone almost to the level obtained with M. albomyces laccase without mediator. Reactivities of the enzymes towards acetosyringone and TEMPO were similar, suggesting exploitation of the compounds and low redox laccase in lignin valorization under alkaline conditions. The results have scientific impact on basic research of laccases.     

Glibenclamide and HMR1098 normalize Cantú syndrome‐associated gain‐of‐function currents

Cantú syndrome (CS) is caused by dominant gain‐of‐function mutation in ATP‐dependent potassium channels. Cellular ATP concentrations regulate potassium current thereby coupling energy status with membrane excitability. No specific pharmacotherapeutic options are available to treat CS but I_KATP channels are pharmaceutical targets in type II diabetes or cardiac arrhythmia treatment. We have been suggested that I_KATP inhibitors, glibenclamide and HMR1098, normalize CS channels. I_KATP in response to Mg‐ATP, glibenclamide and HMR1098 were measured by inside‐out patch‐clamp electrophysiology. Results were interpreted in view of cryo‐EM I_KATP channel structures. Mg‐ATP IC₅₀ values of outward current were increased for D207E (0.71 ± 0.14 mmol/L), S1020P (1.83 ± 0.10), S1054Y (0.95 ± 0.06) and R1154Q (0.75 ± 0.13) channels compared to H60Y (0.14 ± 0.01) and wild‐type (0.15 ± 0.01). HMR1098 dose‐dependently inhibited S1020P and S1054Y channels in the presence of 0.15 mmol/L Mg‐ATP, reaching, at 30 μmol/L, current levels displayed by wild‐type and H60Y channels in the presence of 0.15 mmol/L Mg‐ATP. Glibenclamide (10 μmol/L) induced similar normalization. S1054Y sensitivity to glibenclamide increases strongly at 0.5 mmol/L Mg‐ATP compared to 0.15 mmol/L, in contrast to D207E and S1020P channels. Experimental findings agree with structural considerations. We conclude that CS channel activity can be normalized by existing drugs; however, complete normalization can be achieved at supraclinical concentrations only.     

Simultaneous dual-isotope 123I/99mTc acquisition using CZT-based cameras: Toward a one-stop-shop SPECT in heart failure patients

The CZT-cameras (DNM 530c and DSPECT) have only recently been introduced, and the impact of the increased energy resolution remains unknown. This paper summarizes the evidence on the assessment of: (i) the left ventricular function, (ii) the ¹²³I/^99mTc mismatch, and (iii) the heart-to-mediastinum ratio (HMR) of ¹²³I-metaiodobenzylguanidine (MIBG) uptake under dual-isotope conditions (^99mTc and ¹²³I) using cadmium-zinc-telluride (CZT) technology. The diagnostic accuracy of CZT cameras for myocardial sympathetic innervation imaging, left ventricular function and perfusion assessment using perfusion-gated SPECT have only been established in a few studies, under single-isotope conditions. Limited evidence is available regarding simultaneous dual-isotope acquisition using CZT-cameras. However, recently reported data have shown that CZT cameras allow, in dual-isotope (¹²³I and ^99mTc) acquisitions and under routine conditions: (i) a simultaneous and accurate segmental study of myocardial innervation and perfusion (match and mismatch), (ii) the ventricular function assessment (EDV, ESV and LVEF), and (iii) the determination of the late HMR of cardiac ¹²³I-MIBG uptake in patients with heart failure. However, this latter should be performed using transaxial reconstructed images and a linear correction based on phantom data acquisitions.