High level nitrosamines in rat faeces with colorectal cancer determined by a sensitive GC-MS method.

N-nitrosamines (NAs) are common toxic substances that have a strong correlation with many human diseases, such as liver damage and cancer. However, there is a lack of studies on methods involving the detection of NAs in biological samples, possibly owing to the interference of complex biological matrices and the influence of endogenous NAs. In this work, solid-phase extraction with mixed solid phases and adsorption sedimentation were used to successfully establish a gas chromatography-mass spectrometry (GC-MS) method for detecting eight NAs in rat faeces. Chromatographic separation of analytes was performed with Agilent VF-WAXms (30 m × 0.25 mm, 0.25 µm) GC columns. The LLOQs of eight NAs were set to the concentration of 0.5 ng/g and the obtained standard curves were linear, and correlation coefficients (r) were ≥ 0.99 for samples with concentration ranges of 0.5-500 ng/g. The inter and intra-assay precisions were< 15% for all analytes in the quality control samples, and the accuracies ranged from 88.67% to 108.33%. The extraction recoveries were above 78.56% for seven NAs, and a significant matrix effect was not observed. The application of this method revealed that the levels of NAS in the faeces of rats with colorectal cancer were higher than those of normal rats. Additionally, the effect of a high nitrite diet on NAs in faeces was analysed; the results confirmed that a high nitrite diet might contribute to an abnormal increase in NAs. Our work provides an analytical method for further in vivo study of NAs. Furthermore, a pilot study on the relationship between NAs and colorectal cancer was completed.

Melaxillines A and B, monoterpenoid indole alkaloids from Melodinus axillaris.

Two new monoterpenoid indole alkaloids, melaxillines A (1) and B (2), together with four known alkaloids (3-6), were isolated from the roots of Melodinus axillaris. The structures were determined by extensive spectroscopic methods, including 1D and 2D-NMR spectroscopy, high resolution mass spectrometric data, and by comparison to literature data. New compounds 1-2 might be derived from a common precursor (3) by proposing their biogenetic route, and compound 1 represents the first Melodinus alkaloid featuring an ethyl acetate group skeleton at C-18. The anti-inflammatory effects of all the isolated compounds were evaluated by measuring the inhibitory ratios of ß-glucuronidase release in rat polymorphonuclear leukocytes (PMNs) induced by platelet-activating factor. Compounds 1-4 showed significant anti-inflammatory activities with IC50 values ranging from 1.51 to 21.56µM, respectively.