Productive HIV-1 infection of primary CD4+ T cells induces mitochondrial membrane permeabilization leading to a caspase-independent cell death.

We have explored in vitro the mechanism by which human immunodeficiency virus, type 1 (HIV-1) induces cell death of primary CD4+ T cells in conditions of productive infection. Although HIV-1 infection primed phytohemagglutinin-activated CD4+ T cells for death induced by anti-CD95 antibody, T cell death was not prevented by a CD95-Fc decoy receptor, nor by decoy receptors of other members of the TNFR family (TNFR1/R2, TRAILR1/R2/OPG, TRAMP) or by various blocking antibodies, suggesting that triggering of death receptors by their cognate ligands is not involved in HIV-induced CD4 T cell death. HIV-1 induced CD4 T cell shrinkage, cell surface exposure of phosphatidylserine, loss of mitochondrial membrane potential (Deltapsim), and mitochondrial release of cytochrome c and apoptosis-inducing factor. A typical apoptotic phenotype (nuclear chromatin condensation and fragmentation) only occurred in around half of the dying cells. Treatment with benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone, a broad spectrum caspase inhibitor, prevented nuclear chromatin condensation and fragmentation in HIV-infected CD4+ T cells and in a cell-free system (in which nuclei were incubated with cytoplasmic extracts from the HIV-infected CD4+ T cells). Nevertheless, benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone did not prevent mitochondrial membrane potential loss and cell death, suggesting that caspases are dispensable for HIV-mediated cell death. Our findings suggest a major role of the mitochondria in the process of CD4 T cell death induced by HIV, in which targeting of Bax to the mitochondria may be involved

Transport and pharmacological properties of nine different human Na, K-ATPase isozymes.

Na,K-ATPase plays a crucial role in cellular ion homeostasis and is the pharmacological receptor for digitalis in man. Nine different human Na,K-ATPase isozymes, composed of 3 alpha and beta isoforms, were expressed in Xenopus oocytes and were analyzed for their transport and pharmacological properties. According to ouabain binding and K(+)-activated pump current measurements, all human isozymes are functional but differ in their turnover rates depending on the alpha isoform. On the other hand, variations in external K(+) activation are determined by a cooperative interaction mechanism between alpha and beta isoforms with alpha2-beta2 complexes having the lowest apparent K(+) affinity. alpha Isoforms influence the apparent internal Na(+) affinity in the order alpha1 > alpha2 > alpha3 and the voltage dependence in the order alpha2 > alpha1 > alpha3. All human Na,K-ATPase isozymes have a similar, high affinity for ouabain. However, alpha2-beta isozymes exhibit more rapid ouabain association as well as dissociation rate constants than alpha1-beta and alpha3-beta isozymes. Finally, isoform-specific differences exist in the K(+)/ouabain antagonism which may protect alpha1 but not alpha2 or alpha3 from digitalis inhibition at physiological K(+) levels. In conclusion, our study reveals several new functional characteristics of human Na,K-ATPase isozymes which help to better understand their role in ion homeostasis in different tissues and in digitalis action and toxicity

Comparative in vitro activity of penicillin G, levofloxacin, moxifloxacin, telithromycin, pristinamycin, quinupristin–dalfopristin and linezolid against ofloxacin-intermediate and -resistant Streptococcus pneumoniae

AbstractScreening by ofloxacin disk was carried out on 1158 strains of Streptococcus pneumoniae in order to investigate the in vitro bacteriostatic activity of penicillin G, levofloxacin, moxifloxacin, telithromycin, linezolid, pristinamycin and quinupristin–dalfopristin against ofloxacin-intermediate and -resistant S. pneumoniae strains. It was concluded that these new antimicrobial agents could be useful for the treatment of pneumococcal infections caused by penicillin-sensitive and -resistant S. pneumoniae, and would represent a valid therapeutic option for patients allergic to β-lactams, should they prove to be potent in vivo