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The detection of non-covalent complexes in the mass range 19,000-34,000 Da, using electrospray ionization mass spectrometry (ESI-MS), is reviewed. The examples discussed include (1) a protein-ligand interaction (ras-GDP), (2) an inhibitor-protein-ligand interaction (SCH 54292/SCH 54341-ras-GDP), (3) a protein-protein interaction (gamma-IFN homodimer) and (4) a protein-metal complex [HCV (1-181)-Zn]. In each case, the ESI-MS method is capable of releasing the intact non-covalent complex from its native solution state into the gas phase in the form of multiply-charge ions. The molecular masses of these complexes were determined with a mass accuracy of better than 0.01%, which is far superior to the traditional methods of sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel permeation chromatography. The method provides the researcher with a quick, reliable and reproducible method for probing difficult biological problems. The key to success in the study of non-covalent complexes depends on careful understanding and manipulation of ESI source parameters and sample solution conditions; special care must be taken with the source orifice potential and the solution pH and organic co-solvents must be avoided. This paper also illustrates the usefulness of ESI-MS for addressing biological problems leading to the discovery of new therapeutics; the approach involves the rapid screening of potential drug candidates, such as weakly bound inhibitors.

The use of an active Nafion substrate is shown to enhance the performance of MALDI MS. The use of a Nafion substrate with certain matrices can significantly enhance the signals obtained over those observed with a stainless steel probe substrate. Analytes can often be observed with the use of the Nafion substrate that cannot be easily observed with the standard MALDI procedure, and usually a much wider range of peaks can be observed using MALDI from the Nafion substrate than with any single matrix on a stainless steel substrate. This enhancement of signal from the Nafion substrate is observed only with the sequential deposition of the sample and the matrix onto the Nafion film. If the analyte and matrix are premixed, then the effect is not observed. The use of the Nafion substrate has been shown to be particularly effective in analyzing real biological mixtures without prepurification. This has been demonstrated for various samples including the analysis of the products of chemical digests of proteins, protein profiling in milk and egg white samples, cell lysate analysis, and oligonucleotide detection.

This study was carried out in 121 pigs to develop a population pharmacokinetic ( PPK) model by oral (p.o.) administration of valnemulin at a single dose of 10 mg/kg. Serum biochemistry parameters of each pig were determined prior to drug administration. Three to five blood samples were collected at random time points, but uniformly distributed in the absorption, distribution, and elimination phases of drug disposition. Plasma concentrations of valnemulin were determined by high-performance liquid chromatography-tandem mass spectrometry ( HPLC- MS/ MS). The concentration-time data were fitted to PPK models using nonlinear mixed effect modeling ( NONMEM) with G77 FORTRAN compiler. NONMEM runs were executed using Wings for NONMEM. Fixed effects of weight, age, sex as well as biochemistry parameters, which may influence the PK of valnemulin, were investigated. The drug concentration-time data were adequately described by a one-compartmental model with first-order absorption. A random effect model of valnemulin revealed a pattern of log-normal distribution, and it satisfactorily characterized the observed interindividual variability. The distribution of random residual errors, however, suggested an additive model for the initial phase (<12 h) followed by a combined model that consists of both proportional and additive features (≥12 h), so that the intra-individual variability could be sufficiently characterized. Covariate analysis indicated that body weight had a conspicuous effect on valnemulin clearance ( CL/ F). The featured population PK values of Ka, V/ F and CL/ F were 0.292/h, 63.0 L and 41.3 L/h, respectively. [ABSTRACT FROM AUTHOR]

Wang, R., Yuan, L.G., He, L.M., Zhu, L.X., Luo, X.Y., Zhang, C.Y., Yu, J.J., Fang, B.H., Liu, Y.H. Pharmacokinetics and bioavailability of valnemulin in broiler chickens. J. vet. Pharmacol. Therap., 247-251. The objective of this study was to investigate the pharmacokinetics and bioavailability of valnemulin in broiler chickens after intravenous (i.v.), intramuscular (i.m.) and oral administrations of 10 mg/kg body weight (bw). Plasma samples were analyzed by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Pharmacokinetic characterization was performed by non-compartmental analysis using WinNonlin program. After intravenous administration, distribution was wide with the volume of distribution based on terminal phase(V) of 4.27 ± 0.99 L /kg. Mean valnemulin t(h), Cl(L /h /kg), V (L /kg) and AUC(μg·h /mL) values were 2.85, 0.99, 2.72 and 10.34, respectively. After intramuscular administration, valnemulin was rapidly absorbed with a C of 2.2 μg/mL achieved at 0.43 h (t), and the absolute bioavailability (F) was 88.81%; and for the oral route the same parameters were 0.66 ± 0.15 μg/mL, 1.54 ± 0.27 h and 74.42%. A multiple-peak phenomenon was present after oral administration. The plasma profile of valnemulin exhibited a secondary peak during 2-6 h and a tertiary peak at 32 h. The favorable PK behavior, such as the wide distribution, slow elimination and acceptable bioavailability indicated that it is likely to be effective in chickens. [ABSTRACT FROM AUTHOR]