Steven Lewis Ramsay

Rapid sample preparation and simultaneous quantitation of prostaglandins and lipoxygenase derived fatty acid metabolites by liquid chromatography-mass spectrometry from small sample volumes

Abstract Background: Fatty acid metabolites play a key role in numerous physiological and pathological processes. A rapid liquid chromatography-mass spectrometry assay for the simultaneous determination of prostanoids, isoprostane and lipoxygenase (LOX) derived fatty acid metabolites in a small biological sample of only 20 μL was developed. Methods: Human plasma samples were applied to a filter spot, extracted without prior derivatization and analyzed within 13 min. Detection of metabolites was performed on a triple quadrupole mass spectrometer in negative multiple-reaction monitoring detection mode. Application of this assay to various biological matrices was performed. Results: The validated assay was linear over the concentration range of 5–500 nmol/L for prostanoids and isoprostane, 50–5000 nmol/L for LOX-derived metabolites and 400–40,000 nmol/L for fatty acids. Limits of quantitation were 0.4–233 nmol/L, depending on the metabolite. Plasma samples from diabetic patients and controls showed significant increases in (±)9-HODE and 15(S)-HETE with p-values of 0.019 and 0.024, respectively. Conclusions: The small amount of 20 μL sample volume used in this assay and the demonstrated application to various sample types makes it an ideal routine analysis method for fatty acid metabolites. The resulting values for LOX-derived metabolites in diabetes mellitus type 2 samples support earlier findings about the role of lipid oxidation products in diabetes. Clin Chem Lab Med 2008;46:1589–97.

New caerin antibacterial peptides from the skin glands of the Australian tree frog Litoria xanthomera

The secretion of the skin glands of the ‘orange‐thighed frog’ Litoria xanthomera contains seven peptides. One of these is the known hypotensive peptide caerulein. Two new peptides, caerin 1.6 [GLFSVLGAVAKHVLPHVVPVIAEKL(NH2)], and caerin 1.7 [GLFKVLGSVAKHLLPHVAPVIAEKL(NH2)] show antibacterial properties. Two other peptides lack the first two amino acid residues of caerins 1.6 and 1.7 and show no antibacterial activity. The identification of the peptides in Litoria xanthomera confirms that this species is related to Litoria caerula, Litoria gilleni and Litoria splendida but not as closely as those three species are related to each other.

Isotope correction of mass spectrometry profiles

Isotope correction of a profile is an important step in the analysis of mass spectrometry derived data. The problem is mathematically formulated as a system of linear equations which is general enough to include previous correction methods. For the solution of these equations when applied to the whole profile an efficient algorithm is developed. In experimental tests the resulting algorithm corrected the profile fast and successfully.

The negative ion mass spectra of (M – H) – ions from phenylthiohydantoin derivatives of amino acids

The mass spectra of (M – H)− ions of phenylthiohydantoin (PTH) amino acids show characteristic fragmentations through the side chain (the α-side chain of the original amino acid) which may be used to identify each of the common amino acids. Some of these fragmentations are Leu (C3H8), Ile (CH4, C2H6), Phe (PhH), Tyr (CH2=C6H4=O), Trp (CH2=C8H5N), Ser (CH2O), Thr (MeCHO) and Met (MeSH). The formulae in parentheses represent the neutrals lost.