Intra-articular dysplasia of the femoral head in developmental dysplasia of the hip.

Central to the current treatment of dysplasia of the hip (DDH) is the concept of congruent reduction of the hip. If the femoral head is aspherical in DDH, this concept needs reconsideration. MRI scans are used to examine the femoral head in children. Diameters of 14 DDH and 12 normal hips were measured in three planes by eight observers on two occasions. Femoral head sphericity was determined using the mathematical concept of eccentricity. In DDH, the femoral head was less spherical, most marked in the coronal plane, yielding a 'rugby ball'-shaped femoral head. Accordingly, concentric reduction of the femoral head in DDH is impossible.

Probing interactions of Vpu from HIV-1 with amiloride-based compounds.

Viral ion channels or viroporins are short membrane proteins that participate in wide-ranging functions including virus replication and entry, assembly, and virus release. One such viroporin is the 81 amino acid residue Vpu protein derived from HIV-1. This protein consists of one transmembrane (TM) and two cytoplasmic helical domains, the former of which oligomerises to form cation-selective ion channels. In this study, we investigate the binding properties of amiloride compounds to Vpu embedded into liposomes using surface plasmon resonance (SPR). We explore the Vpu ion channel inhibitor, hexamethylene amiloride (HMA), as a molecular tool to examine the potential interactive role of key TM residues, Trp23, Ser24, and Glu29, in terms of positioning of these residues on the channel pore and the orientation of its constituent helices. The study provides experimental support that a direct interaction between Ser24 and HMA occurs and that this residue is most likely located in the channel pore. Mutation of Trp23 does not impact HMA affinity suggesting no direct involvement in binding and that this residue is lipid facing. These findings indicate that small molecules such as amilorides are capable of specifically interacting with Vpu ion channels. Although a correlation between ion channel and functional activity cannot be dismissed, alternative mechanisms involving protein-protein interactions may play an important role in the efficacy of these compounds.

Design and synthesis of pinanamine derivatives as anti-influenza A M2 ion channel inhibitors.

The adamantanes are a class of anti-influenza drugs that inhibit the M2 ion channel of the influenza A virus. However recently, the clinical effectiveness of these drugs has been called into question due to the emergence of adamantane-insensitive A/M2 mutants. Although we previously reported (1R,2R,3R,5S)-3-pinanamine 3 as a novel inhibitor of the wild type influenza A virus M2 protein (WT A/M2), limited inhibition was found for adamantane-resistant M2 mutants. In this study, we explored whether newly synthesized pinanamine derivatives were capable of inhibiting WT A/M2 and selected adamantane-resistant M2 mutants. Several imidazole and guanazole derivatives of pinanamine were found to inhibit WT A/M2 to a comparable degree as amantadine and one of these compounds 12 exhibits weak inhibition of A/M2-S31N mutant and it is marginally more effective in inhibiting S31NM2 than amantadine. This study provides a new insight into the structural nature of drugs required to inhibit WT A/M2 and its mutants.

Coexistence of two adamantane binding sites in the influenza A M2 ion channel.

The influenza A virus contains a proton-selective ion channel (M2) that is the target of the adamantane family of drug inhibitors. Two recently published studies relating to adamantane binding of the M2 ion channel using X-ray crystallography and solution NMR have reignited interest in the potential use of adamantanes in combating the spread of influenza A. However, these two studies propose different binding sites for the adamantane drugs with the X-ray M2/amantadine structure favoring an ion channel pore-binding model and the solution NMR M2/rimantadine structure suggesting the existence of a lipid-facing binding pocket. We conducted a series of surface plasmon resonance (SPR) experiments designed to accurately measure the affinity of amantadine and rimantadine to M2 ion channels embedded in 1,2-dimyristoyl-sn-glycero-phosphocholine (DMPC) liposomes. We find that this class of drug is capable of binding M2 with two different affinities in the order of 10(-4) and 10(-7) M, suggesting that both proposed binding sites are feasible. Furthermore, by examining drug binding to M2 mutant constructs (V27A, S31N, and D44A), it was possible to probe the location of the two binding sites. We show that a high-affinity binding site corresponds to the M2 ion channel pore whereas the secondary, low-affinity binding site can be attributed to the lipid face of the pore. These SPR results are in excellent agreement with the most recent solid-state NMR study of amantadine-bound M2 in lipid bilayers and provide independent support that the ion channel pore-binding site is responsible for the pharmacological activity elicited by the adamantane drugs.