title: Characteristic ion clusters as determinants for the identification of pyrrolizidine alkaloid N-oxides in pyrrolizidine alkaloid-containing natural products using HPLC-MS analysis.
abstract: Pyrrolizidine alkaloid (PA)-containing plants are widely distributed in the world. PAs are hepatotoxic, affecting livestock and humans. PA N-oxides are often present together with PAs in plants and also exhibit hepatotoxicity but with less potency. HPLC-MS is generally used to analyze PA-containing herbs, although PA references are unavailable in most cases. However, to date, without reference standards, HPLC-MS methodology cannot distinguish PA N-oxides from PAs because they both produce the same characteristic ions in mass spectra. In the present study, the mass spectra of 10 PA N-oxides and the corresponding PAs were systemically investigated using HPLC-MS to define the characteristic mass fragment ions specific to PAs and PA N-oxides. Mass spectra of toxic retronecine-type PA N-oxides exhibited two characteristic ion clusters at m/z 118-120 and 136-138. These ion clusters were produced by three unique fragmentation pathways of PA N-oxides and were not found in their corresponding PAs. Similarly, the nontoxic platynecine-type PA N-oxides also fragmented via three similar pathways to form two characteristic ion clusters at m/z 120-122 and 138-140. Further application of using these characteristic ion clusters allowed successful and rapid identification of PAs and PA N-oxides in two PA-containing herbal plants. Our results demonstrated, for the first time, that these characteristic ion clusters are unique determinants to discriminate PA N-oxides from PAs even without the availability of reference samples. Our findings provide a novel and specific method to differentiate PA N-oxides from PAs in PA-containing natural products, which is crucial for the assessment of their intoxication.
authors.affiliation: School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Jianqing
authors.initials: J
authors.lastname: Ruan
authors.forename: Na
authors.initials: N
authors.lastname: Li
authors.forename: Qingsu
authors.initials: Q
authors.lastname: Xia
authors.forename: Peter P
authors.initials: PP
authors.lastname: Fu
authors.forename: Shuying
authors.initials: S
authors.lastname: Peng
authors.forename: Yang
authors.initials: Y
authors.lastname: Ye
authors.forename: Ge
authors.initials: G
authors.lastname: Lin
mesh_terms: D019659:Asteraceae / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003497:Cyclic N-Oxides / Q000032:analysis / Q000737:chemistry; D007477:Ions / Q000032:analysis / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods*; D010936:Plant Extracts / Q000737:chemistry*; D018517:Plant Roots / Q000737:chemistry; D011763:Pyrrolizidine Alkaloids / Q000032:analysis* / Q000737:chemistry
chemical_list: D003497:Cyclic N-Oxides; D007477:Ions; D010936:Plant Extracts; D011763:Pyrrolizidine Alkaloids