Statistical optimisation of diclofenac sustained release pellets coated with polymethacrylic films

The objective of the present study was to evaluate three formulation parameters for the application of polymethacrylic films from aqueous dispersions in order to obtain multiparticulate sustained release of diclofenac sodium. Film coating of pellet cores was performed in a laboratory fluid bed apparatus. The chosen independent variables, i.e. the concentration of plasticizer (triethyl citrate), methacrylate polymers ratio (Eudragit RS:Eudragit RL) and the quantity of coating dispersion were optimised with a three-factor, three-level Box-Behnken design. The chosen dependent variables were cumulative percentage values of diclofenac dissolved in 3, 4 and 6 h. Based on the experimental design, different diclofenac release profiles were obtained. Response surface plots were used to relate the dependent and the independent variables. The optimisation procedure generated an optimum of 40% release in 3 h. The levels of plasticizer concentration, quantity of coating dispersion and polymer to polymer ratio (Eudragit RS:Eudragit RL) were 25% w/w, 400 g and 3/1, respectively. The optimised formulation prepared according to computer-determined levels provided a release profile, which was close to the predicted values. We also studied thermal and surface characteristics of the polymethacrylic films to understand the influence of plasticizer concentration on the drug release from the pellets.

Signal transduction in the Rhizobium meliloti dicarboxylic acid transport system

The gene products of the Rhizobium meliloti dctB and dctD genes, which control the expression of the C4-dicarboxylic acid transporter DctA, were overproduced in Escherichia coli and purified. The purified sensor protein, DctB, was shown to have autophosphorylation activity in vitro and could subsequently phosphorylate the transcriptional activator, DctD. The presence of C4-dicarboxylic acids did not affect either reaction. In vitro experiments aimed at investigating 'crosstalk' between cognate components demonstrated that the phospho-transfer activity was specific between DctB and DctD. Studies on truncated versions of the DctB protein in vitro revealed that the cytoplasmic domain of DctB had strong autophosphorylation activity. Data from gel retardation experiments demonstrated that once the activator protein, DctD, was phosphorylated it had increased affinity for binding to the dctA promoter DNA.