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Osteoarthritis (OA) is a joint pathology characterized by progressive cartilage degradation. Medical care is mainly based on alleviating pain symptoms. Compelling studies report the presence of empty lacunae and hypocellularity in cartilage with aging and OA progression, suggesting that chondrocyte cell death occurs and participates to OA development. However, the relative contribution of apoptosis per se in OA pathogenesis appears complex to evaluate. Indeed, depending on technical approaches, OA stages, cartilage layers, animal models, as well as in vivo or in vitro experiments, the percentage of apoptosis and cell death types can vary. Apoptosis, chondroptosis, necrosis, and autophagic cell death are described in this review. The question of cell death causality in OA progression is also addressed, as well as the molecular pathways leading to cell death in response to the following inducers: Fas, Interleukin-1β (IL-1β), Tumor Necrosis factor-α (TNF-α), leptin, nitric oxide (NO) donors, and mechanical stresses. Furthermore, the protective role of autophagy in chondrocytes is highlighted, as well as its decline during OA progression, enhancing chondrocyte cell death; the transition being mainly controlled by HIF-1α/HIF-2α imbalance. Finally, we have considered whether interfering in chondrocyte apoptosis or promoting autophagy could constitute therapeutic strategies to impede OA progression.

One high affinity (nM) and one low affinity (M) macroscopic dissociation constant for the binding of metal ions were found for the wild-type metallo-␤-lactamase from Bacillus cereus as well as six single-site mutants in which all ligands in the two metal binding sites were altered. Surprisingly, the mutations did not cause a specific alteration of the affinity of metal ions for the sole modified binding site as determined by extended x-ray absorption fine structure (EXAFS) and perturbed angular correlation of ␥-rays spectroscopy, respectively. Also UV-visible absorption spectra for the mono-cobalt enzymes clearly contain contributions from both metal sites. The observations of the very similar microscopic dissociation constants of both binding sites in contrast to the significantly differing macroscopic dissociation constants inevitably led to the conclusion that binding to the two metal sites exhibits negative cooperativity. The slow association rates for forming the binuclear enzyme determined by stopped-flow fluorescence measurements suggested that fast metal exchange between the two sites for the mononuclear enzyme hinders the binding of a second metal ion. EXAFS spectroscopy of the mono-and di-zinc wild type enzymes and two di-zinc mutants provide a definition of the metal ion environments, which is compared with the available x-ray crystallographic data.Two zinc binding sites in close proximity are conserved in all metallo-␤-lactamases studied so far. Only two of the metal ion ligands undergo variations between the three different subclasses of the enzyme family (1). The enzyme from Bacillus cereus 569/H/9 (BcII) 1 represents a member of subclass B1 with 3 His ligands in one site and 1 Asp, 1 Cys, and 1 His ligand in the other site (3H 1 and DCH 1 sites, respectively). Various crystal structures of BcII are available, representing mononuclear (2) and binuclear species (3, 4). It was shown earlier that both mono-and binuclear zinc enzymes from B. cereus (5) and Bacteroides fragilis (6) are catalytically active.Although catalytic mechanisms for the enzyme with either one or two zinc ions bound have been discussed (for review see Ref. 7) the respective roles of the two binding sites during catalysis are still unclear. Generally the 3H site is considered to be the primary catalytic site. However, the importance of the DCH site for catalysis became obvious from studies of the C168A mutant. When only one zinc ion is bound to this mutant, it shows a very low activity compared with the wild type, whereas wild type-like activity is almost restored when a second metal ion is bound (5).Perturbed angular correlation (PAC) of ␥-ray spectroscopy provides information on the metal ion coordination geometry through measurement of the nuclear quadrupole interaction (NQI) between the nuclear electric quadrupole moment and the electric field gradient from the surrounding charge distribution. With this method it was possible to demonstrate that the Cd(II) ions in the mononuclear wild type BcII are distributed between the two m...

When expressed by pathogenic bacteria, Zn2؉ -␤-lactamases induce resistance to most ␤-lactam antibiotics. A possible strategy to fight these bacteria would be a combined therapy with non-toxic inhibitors of Zn 2؉ -␤-lactamases together with standard antibiotics. For this purpose, it is important to verify that the inhibitor is effective under all clinical conditions. We have investigated the correlation between the number of zinc ions bound to the Zn 2؉ -␤-lactamase from Bacillus cereus and hydrolysis of benzylpenicillin and nitrocefin for the wild type and a mutant where cysteine 168 is replaced by alanine. It is shown that both the mono-Zn 2؉ (mononuclear) and di-Zn 2؉ (binuclear) Zn 2؉ -␤-lactamases are catalytically active but with different kinetic properties. The mono-Zn2؉ -␤-lactamase requires the conserved cysteine residue for hydrolysis of the ␤-lactam ring in contrast to the binuclear enzyme where the cysteine residue is not essential. Substrate affinity is not significantly affected by the mutation for the mononuclear enzyme but is decreased for the binuclear enzyme. These results were derived from kinetic studies on two wild types and the mutant enzyme with benzylpenicillin and nitrocefin as substrates. Thus, targeting drug design to modify this residue might represent an efficient strategy, the more so if it also interferes with the formation of the binuclear enzyme.