Biodegradable core crosslinked star polymer nanoparticles as 19F MRI contrast agents for selective imaging

With the aim of developing stimuli-responsive imaging agents, we report here the synthesis of core crosslinked star (CCS) polymers and their evaluation as pH-sensitive 19F magnetic resonance imaging (19F MRI) contrast agents. Block copolymers consisting of poly(ethylene glycol)methyl ether methacrylate (PPEGMA) as the first block and a copolymer of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 2,2,2-trifluoroethyl methacrylate (TFEMA) as the second block were synthesised using RAFT polymerisation. The polymerisation kinetics were studied in detail. The block copolymers were then used as arm precursors for the arm-first synthesis of CCS polymers through RAFT dispersion polymerisation. The synthetic conditions were investigated and optimised. CCS polymers with a degradable core were also synthesised and evaluated as 19F MRI contrast agents. The degradation of the core was confirmed by treatment with various reducing agents. The particle size, 19F NMR signal and relaxation times as well as 19F MRI imaging performance of the CCS polymers were studied at a range of value of solution pH. Significant enhancement of the image intensity was observed when the pH was decreased from 8 to 5, indicating that the CCS nanoparticles could be used as 19F MRI contrast agents for the detection of the acidic environment within tumour tissue

Monitoring children and adolescents with severe obesity: body mass index (BMI), BMI z-score or percentage above the International Obesity Task Force overweight cut-off?

AIM: Body mass index (BMI) metrics are widely used as a proxy for adiposity in children with severe obesity. The BMI expressed as the percentage of a cut-off percentile for overweight or obesity has been proposed as a better alternative than BMI z-scores when monitoring children and adolescents with severe obesity. METHODS: Annual changes in BMI, BMI z-score and the percentage above the International Obesity Task Force overweight cut-off (%IOTF-25) were compared with dual-energy X-ray absorptiometry (DXA) derived body fat (%BF-DXA) in 59 children and adolescents with severe obesity. RESULTS: The change in %BF-DXA was correlated with the change in %IOTF-25 (r = 0.68) and BMI (r = 0.70), and somewhat less with the BMI z-score (r = 0.57). Cohen's Kappa statistic to detect an increase or decrease in %BF-DXA was fair for %IOTF-25 (κ = 0.25; p = 0.04) and BMI (κ = 0.33; p = 0.01), but not for the BMI z-score (κ = 0.08; p = 0.5). The change in BMI was positively biased due to a natural increase with age. CONCLUSION: Changes in the BMI metrics included in the study are associated differently with changes in %BF-DXA. The BMI z-score is widely used to monitor changes in adiposity in children and adolescents with severe obesity, but the %IOTF-25 might be a better alternative.status: publishe