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A rapid, sensitive and selective LC-atmospheric pressure-chemical ionization-MS-MS method for the determination of the new antimicrobial agent, linezolid, in human plasma using selected reaction monitoring (SRM) was developed. Linezolid and the internal standard were extracted from the biological samples by solid phase extraction (SPE) and analyzed on a reversed-phase Shim Pack CLC-CN, C18 column with the mobile phase of acetonitrile and 20 mM ammonium acetate solution (4 + 1 v/v). Detection was accomplished using an LCQ mass spectrometer (Finnigan), which was programmed in positive MS-MS mode to permit measurement of the fragment ions of linezolid and internal standard at m/z 296.2 and 223.2, respectively. The assay run-time was less than 3.5 min. Quantitative analysis was based on peak area ratio of linezolid to the internal standard. Calibration plots were established over the concentration range of 0.1-20 micrograms ml-1 of linezolid with the lowest detection limit of 0.05 microgram ml-1 using 10 microliters sample volume. The SPE technique quantitatively recovered linezolid and the internal standard from the plasma samples at a percentage range of 89.1-93.7%. Determination of control samples of linezolid in plasma validated the LC-MS-MS-SRM method. Intra-assay and inter-assay precision were in the range of 5.1-11.4% relative standard deviation, whereas the intra- and inter-accuracy were in the range of 97.5-114.0% of the nominal concentrations of linezolid added. The data confirmed that the plasma samples of linezolid were stable at room temperature and when stored at -20 degrees C for at least 10 d. The developed LC-MS-MS-SRM method is recommended for the determination of linezolid in human plasma.

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Bone marrow stem cells (BMSCs) can differentiate into several cells that participate in the healing of meniscal wounds. To test this hypothesis, we examined the effects of injected BMSCs on the healing of meniscal wounds. Autologous BMSCs from eight adult dogs were injected into meniscal wounds (knee joints). After 12 weeks, the healing process was clinically and immunomorphologically evaluated using: (i) histochemical stains (haematoxylin and eosin, Masson trichrome and periodic acid-Schiff) and (ii) immunoperoxidase staining methods (CD3, CD79a, CD68, CD31 and alpha smooth-muscle actin for T, B lymphocytes, macrophages, endothelial cells and smooth-muscle lineage). Complete (six vs. three), partial (one vs. one) and no healing (one vs. four animals) of the meniscal wounds were observed in the injected and noninjected menisci. As compared with the noninjected menisci, examination of the tissues from the injected ones revealed: (i) marked angiogenesis (microvessel density: 3.22 +/- 0.66 vs. 6.50 +/- 2.10); (ii) chondrogenesis; (iii) prominent immune cell infiltrate (4.07 +/- 0.78 vs. 9.56 +/- 1.69, 8.33 +/- 0.77 vs. 3.67 +/- 1.00 and 4.38 +/- 0.62 vs. 11.1 +/- 1.43 for the total numbers of immune cells, lymphocytes and macrophages, respectively); and (iv) proliferation of the fibroblasts with marked deposition of collagen fibres (2.0 +/- 0.84 vs. 2.66 +/- 0.48). These values were statistically significantly higher for the injected menisci as compared with the noninjected ones (P >/= 0.05). Autologous BMSCs can improve meniscal wound healing. Whether this improvement occurs through BMSC differentiation into cells operational in the repair process, the release of certain mediator or other unknown mechanisms mandates further investigations.

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