Molecular dynamics simulations of the internal mobility of Gd3+-based MRI contrast agents: consequences for water proton relaxivity

The increasing use of contrast agents in magnetic resonance imaging (MRI) for medical diagnosis is due to the ability, called relaxivity, of these paramagnetic compounds to accelerate the relaxation of the surrounding water proton spins. A new classical force field for molecular dynamics simulations of Gd3+ polyaminocarboxylates has recently been published, which allows the study of the chelate internal mobility. We present two selected examples where such motions can affect relaxivity. Knowing the relationship between the bound water proton and oxygen mobility is important for the combined analysis of multinuclear NMR studies, and we show that they differ significantly. Next, we observe symmetry changes over time in the Gd3+ coordination polyhedron of the acyclic complexes. We propose that such rearrangements can play a role in the electron spin relaxation of Gd3+ chelates, an important result considering the uncertainty still attached to this particular factor

Impact of the M184V/I Mutation on the Efficacy of Abacavir/Lamivudine/Dolutegravir Therapy in HIV Treatment-Experienced Patients.

Objective The impact of the M184V/I mutation on the virological failure (VF) rate in HIV-positive patients with suppressed viremia switching to an abacavir/lamivudine/dolutegravir regimen has been poorly evaluated. Method This is an observational study from 5 European HIV cohorts among treatment-experienced adults with ≤50 copies/mL of HIV-1 RNA who switched to abacavir/lamivudine/dolutegravir. Primary outcome was the time to first VF (2 consecutive HIV-1 RNA >50 copies/mL or single HIV-1 RNA >50 copies/mL accompanied by change in antiretroviral therapy [ART]). We also analyzed a composite outcome considering the presence of VF and/or virological blips. We report also the results of an inverse probability weighting analysis on a restricted population with a prior history of VF on any ART regimen to calculate statistics standardized to the disparate sampling population. Results We included 1626 patients (median follow-up, 288.5 days; interquartile range, 154-441). Patients with a genotypically documented M184V/I mutation (n = 137) had a lower CD4 nadir and a longer history of antiviral treatment. The incidence of VF was 29.8 cases (11.2-79.4) per 1000 person-years in those with a previously documented M184V/I, and 13.6 cases (8.4-21.8) in patients without documented M184V/I. Propensity score weighting in a restricted population (n = 580) showed that M184V/I was not associated with VF or the composite endpoint (hazard ratio [HR], 1.27; 95% confidence interval [CI], 0.35-4.59 and HR 1.66; 95% CI, 0.81-3.43, respectively). Conclusions In ART-experienced patients switching to an abacavir/lamivudine/dolutegravir treatment, we observed few VFs and found no evidence for an impact of previously-acquired M184V/I mutation on this outcome. Additional analyses are required to demonstrate whether these findings will remain robust during a longer follow-up

Multiexponential Electronic Spin Relaxation and Redfield's Limit in Gd(III) Complexes in Solution: Consequences for 17O/1H NMR and EPR Simultaneous Analysis

Multiple experiments (17O NMR, 1H NMR, and EPR) have been performed in the past to understand the microscopic parameters that control the magnetic relaxation rate enhancement induced by paramagnetic molecules on neighboring water protons, the so-called relaxivity. The generally accepted theories of the electron spin relaxation of S = 7/2 ions such as Gd3+ (Solomon-Bloembergen-Morgan or simplified Hudson-Lewis) are unsatisfactory for a simultaneous analysis. Recently, an improved theory, where the electron spin relaxation is due to the combination of a static (thus explicitly linked to the molecular structure) and a dynamic zero field splitting, has been developed and tested on experimental EPR data. The model has also been extended beyond the electronic Redfield limit using Monte Carlo simulations. Using the aqua ion [Gd(H2O)8]3+ as a test case, we present here the first simultaneous analysis of 17O NMR, 1H NMR, and EPR relaxation data using this rigorous approach of the electron spin relaxation. We discuss the physical meaning of the calculated parameters. The consequences on future experiments are also considered, especially regarding the analysis of nuclear magnetic relaxation dispersion (NMRD) profiles in the study of Gd3+ complexes

Molecular Dynamics Simulations of the Internal Mobility of Gd3+-Based MRI Contrast Agents: Consequences for Water Proton Relaxivity

The increasing use of contrast agents in magnetic resonance imaging (MRI) for medical diagnosis is due to the ability, called relaxivity, of these paramagnetic compounds to accelerate the relaxation of the surrounding water proton spins. A new classical force field for molecular dynamics simulations of Gd3+ polyaminocarboxylates has recently been published, which allows the study of the chelate internal mobility. We present two selected examples where such motions can affect relaxivity. Knowing the relationship between the bound water proton and oxygen mobility is important for the combined analysis of multinuclear NMR studies, and we show that they differ significantly. Next, we observe symmetry changes over time in the Gd3+ coordination polyhedron of the acyclic complexes. We propose that such rearrangements can play a role in the electron spin relaxation of Gd3+ chelates, an important result considering the uncertainty still attached to this particular factor