Affinity of various benzodiazepine site ligands in mice with a point mutation in the GABA A receptor γ2 subunit

Abstract The benzodiazepine binding site of GABA A receptors is located at the interface of the a and g subunits. Certain point mutations in these subunits have been demonstrated to dramatically reduce the affinity of benzodiazepine binding site ligands for these receptors. Recently, mice were generated with a phenylalanine (F) to isoleucine (I) substitution at position 77 in the g2 subunit of GABA A receptors. Here we tested the potency of 24 benzodiazepine binding site ligands from 16 different structural classes for inhibition of [ 3 H]flunitrazepam binding to brain membranes of these g2F77I mice. Results indicate that the potency of the classical 1,4-benzodiazepines, of the 1,4-thienodiazepine clotiazepam, the 1,5-benzodiazepine clobazam, or the pyrazoloquinoline CGS 9896 is only 2-7-fold reduced by this g2F77I point mutation. The potency of the imidazopyrimidines Ru 32698, Ru 33203, and Ru 33356, of the imidazoquinoline Ru 31719, or the pyrazolopyridine CGS 20625 is reduced 10-20-fold, whereas the potency of some imidazobenzodiazepines, b-carbolines, cyclopyrrolones, imidazopyridines, triazolopyridazines, or quinolines is 100-1000-fold reduced. Interestingly, the extent of potency reduction induced by the g2F77I point mutation varied within the structural classes of compounds. Results support and significantly extend previous observations indicating that the residue g2F77 is important for high affinity binding of some, but not all benzodiazepine site ligands

Serum Metal Ion Concentrations in Paediatric Patients following Total Knee Arthroplasty Using Megaprostheses

The purpose of this study was to determine the concentrations of cobalt, chromium, and molybdenum in the serum of paediatric tumour patients after fixed hinge total knee arthroplasty. Further, these metal ion levels were compared with serum metal ion levels of patients with other orthopaedic devices such as hip and knee prostheses with metal-on-metal or metal-on-polyethylene articulation to find differences between anatomical locations, abrasion characteristics, and bearing surfaces. After an average follow-up of 108 months (range: 67 to 163) of 11 paediatric patients with fixed hinge total knee arthroplasty, the mean concentrations for Co and Cr were significantly increased while Mo was within the limits compared to the upper values from the reference laboratory. Furthermore, these serum concentrations were significantly higher compared to patients with a standard rotating hinge device (P=0.002 and P<0.001) and preoperative controls (P<0.001). On the other hand, the serum levels of patients following MoM THA or rotating hinge arthroplasty using megaprostheses were higher. Therefore, periodic long-term follow-ups are recommended due to the rising concerns about systemic metal ion exposure in the literature. Upon the occurrence of adverse reactions to metal debris the revision of the fixed hinge implant should be considered