GPR Expression in Intestinal Biopsies From SCT Patients Is Upregulated in GvHD and Is Suppressed by Broad-Spectrum Antibiotics

Microbiota can exert immunomodulatory effects by short-chain fatty acids (SCFA) in experimental models of graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (allo-SCT). Therefore we aimed to analyze the expression of SCFAs sensing G-protein coupled receptor GPR109A and GPR43 by quantitative PCR in 338 gastrointestinal (GI) biopsies obtained from 199 adult patients undergoing allo-SCT and assessed the interaction of GPR with FOXP3 expression and regulatory T cell infiltrates. GPR expression was strongly upregulated in patients with stage II-IV GvHD (p=0.000 for GPR109A, p=0.01 for GPR43) and at the onset of GvHD (p 0.000 for GPR109A, p=0.006 for GPR43) and correlated strongly with FOXP3 and NLRP3 expression. The use of broad-spectrum antibiotics (Abx) drastically suppressed GPR expression as well as FOXP3 expression in patients’ gut biopsies (p=0.000 for GPRs, FOXP3 mRNA and FOXP3+ cellular infiltrates). Logistic regression analysis revealed treatment with Abx as an independent factor associated with GPR and FOXP3 loss. The upregulation of GPRs was evident only in the absence of Abx (p=0.001 for GPR109A, p=0.014 for GPR43) at GvHD onset. Thus, GPR expression seems to be upregulated in the presence of commensal bacteria and associates with infiltration of FOXP3+ T regs, suggesting a protective, regenerative immunomodulatory response. However, Abx, which has been shown to induce dysbiosis, interferes with this protective response

Propagation and Chain-Length-Dependent Termination Rate Coefficients Deduced from a Single SP–PLP–EPR Experiment

The laser single pulse (SP)–pulsed laser polymerization (PLP)–electron paramagnetic resonance (EPR) technique allows for deducing propagation (<i>k</i>_p) and termination (<i>k</i>_t) rate coefficients, including the chain-length dependence of <i>k</i>_t, from a single pulsed-laser experiment. The method, which is particularly well suited for slowly terminating radicals, e.g., sterically hindered and ionic radicals, is illustrated for di­(<i>n</i>-butyl) itaconate in bulk at temperatures from 30 to 60 °C. The time evolution of the DBI radical concentration is measured with a high time resolution at constant magnetic field. Propagation is associated with a relatively low pre-exponential <i>A</i>(<i>k</i>_p), which is responsible for the small <i>k</i>_p value of 6.8 L mol^–1 s^–1 at 30 °C. The chain-length dependence (CLD) of <i>k</i>_t, deduced from the same SP–PLP–EPR signal as is <i>k</i>_p, turns out to be adequately represented by the composite model. Whereas typical numbers are found for the power-law exponents for short and long radicals and for the crossover chain length, the parameter <i>k</i>_t(1,1), which represents mutual termination of two radicals of chain length unity, is by 2 orders of magnitude below <i>k</i>_t(1,1) of monomers without significant steric hindrance

Termination and Transfer Kinetics of Acrylamide Homopolymerization in Aqueous Solution

The single pulse–pulsed laser polymerization–electron paramagnetic resonance (SP–PLP–EPR) method affords the detailed kinetic analysis of acrylamide polymerization in aqueous solution. Highly time-resolved SP–PLP–EPR experiments for 10 and 20 wt % AAm were first carried out at −5 °C, where only secondary propagating radicals (SPRs) occur. In a second step, the time evolution of midchain radicals (MCRs), produced from SPRs by backbiting, was measured at higher temperatures. The termination kinetics, including chain-length dependent termination of SPRs, the backbiting rate of SPRs, and the propagation rate of MCRs were determined. The rate coefficients from SP–PLP–EPR in conjunction with the known propagation rate coefficient of SPRs, enable the simulation of the kinetics and product properties of AAm radical polymerizations in aqueous solution

Chain-Length-Dependent Termination of Sodium Methacrylate Polymerization in Aqueous Solution Studied by SP-PLP-EPR

Via the single pulse–pulsed laser polymerization–electron paramagnetic resonance (SP-PLP-EPR) technique, the chain-length-dependent termination of 5 and 10 wt % sodium methacrylate (NaMAA) in aqueous solution was measured from 5 to 60 °C. The rate coefficients <i>k</i>_t(<i>i</i>,<i>i</i>) for termination of two ionized radicals of identical size <i>i</i> were analyzed by the composite model. Three out of the four composite-model parameters behave similarly to nonionized monomers, whereas the fourth parameter, the rate coefficient for termination of two radicals of chain length unity, <i>k</i>_t(1,1), exhibits a distinctly different behavior. The temperature dependence of <i>k</i>_t(1,1) is significantly below the one of fluidity (inverse solution viscosity). Moreover, absolute <i>k</i>_t(1,1) increases with NaMAA concentration, i.e., toward higher viscosity. Both observations indicate that the termination kinetics of ionized radicals largely differs from the Smoluchowski-type behavior

A stepwise kinetic approach to quantify rate coefficients for reactant-, auto- and non-catalyzed urethanization of phenyl isocyanate and 1-butanol

Limited kinetic information is available on the formation of polyurethanes with ongoing ambiguity in the exact reaction mechanism, which is complicated by the less understood competition between non-catalyzed and molecule-assisted reactions such as catalysis by the alcohol, the isocyanate, and the carbamate. In the present work, focusing on urethane formation based on the monofunctional analogues 1-butanol and phenyl isocyanate in dichloromethane, a two-step kinetic approach is presented, which is capable of first determining rate coefficients and Arrhenius parameters as kinetically significant under diluted conditions, and then determining extra rate coefficients as relevant in a large excess of one of the reactants. Gas chromatography and UV-vis analysis have been applied to quantify (carbamate) product yields as a function of time under quasi-stoichiometric concentrations and with a large 1-butanol excess, and reaction-event driven kinetic Monte Carlo modeling is applied to tune the rate coefficient of each kinetically relevant reaction pathway. It is shown that butanol catalyzed and carbamate catalyzed reactions are the most activated, and the formation of a complex based on two 1-butanol molecules and 1 phenyl isocyanate molecule has a significant influence on the kinetics, specifically in the case of high initial alcohol concentrations. The kinetic interpretations are supported by reaction probability variations as well as sensitivity analyses. The present two-step kinetic approach opens the door to delivering more reliable rate coefficients on the elementary reaction level for polyurethane systems and showcases that even under conventional conditions, as relevant for at least solution polyurethane formation, unconventional complex-based mechanisms can be more active than we currently anticipate based on conventional kinetic laws