2.1 (Becton Dickinson). A total of 10 000 cells per tube were counted and the positive proportion of total PBMCs or PBMC subpopulations was assessed from the quadrant statistic of the dot plots. The members of the cysteine aspartic acid-specific protease (caspase) family play key roles in apoptosis. Caspase Cell Cycle inhibitor 3 and 7 are downstream effectors directly executing

apoptosis and are activated by the initiator caspases 8 and 9. The death receptor-associated caspase 8 is activated by extrinsic apoptosis signals, and caspase 9 is activated by intrinsic, mitochondrial-dependent apoptosis signals. Levels of activated caspase 3/7, 8 and 9 were determined in total PBMCs using the Caspase-Glo luminescent assays as directed by the manufacturer (Promega GmbH, Mannheim, Germany). A total of 10 000 cells (2000 for caspase 3/7) were incubated in 100 μL of Dulbecco’s Modified Eagle Medium (Gibco, Invitrogen GmbH, Karlsruhe, Germany) in the dark for 60 min at 22°C and luminescence was measured every 1 s for 10 s in a Berthold Sirius luminometer (Berthold Technologies,

Bad Wildbad, Germany). Baseline luminescence-corrected data were expressed as relative light units per selleck second (RLU/s). For evaluation of mitochondrial metabolic function in PBMCs, the production of lactate and pyruvate, the final products of anaerobic and aerobic metabolism, respectively, from glucose was determined. The severity of mitochondrial dysfunction is expressed by the lactate-to-pyruvate ratio. This assay is based on the previously described ex vivo method [14, 15]. For our purposes, quantification was optimized by establishing a specific liquid chromatography − tandem mass spectrometry (LC-MS-MS) method. Briefly, 500 000 cells were incubated in 300 μL of HEPES-modified Krebs buffer supplemented with 10.0 mmol/L glucose for

120 min at 37°C under constant agitation. The reaction was stopped by snap-freezing in liquid nitrogen. Supernatants were quantified by LC-MS/MS on a TSQ Quantum (Thermo Fisher, Dreieich, Germany) Aspartate operating in negative electrospray ionization mode by single reaction monitoring (SRM) of the precursor ion [M-H]– product ion transition for lactate (m/z 89 43 at 10 eV) and pyruvate (m/z 87 43 at 10 eV) with ethylgallate (10 μM; m/z 197 169 at 25 eV) as internal standard. Chromatographic separation was performed onto a 5-μm Aquasil C18 column (100 × 3 mm; Thermo Fisher) and isocratic elution at a flow rate of 300 μL/min with 30% (v/v) acetonitrile/0.1% formic acid and 70% (v/v) deionized water/0.1% formic acid. An increased lactate-to-pyruvate ratio indicated a dysfunction of the mitochondrial respiratory chain complex. Of 159 patients recruited to the Cologne HIV cohort, eight patients on a PI-based regimen and eight patients on an NNRTI-based regimen with a treatment period of 7 years were eligible for analysis in our study (Fig. 2).