Multi-constituent identification in Australian cane toad skin extracts using high-performance liquid chromatography high-resolution tandem mass spectrometry

Abstract

Toad skins and venom glandular secretions have been widely used for centuries in traditional Chinese and Japanese medicine for the treatment of various ailments such as cancer, sores, toothache, local inflammation and pain. The active chemical constituents from traditional oriental medicines have demonstrated potential in the development of effective therapeutic pharmaceuticals. Our primary focus in this research was to identify and characterise 'active' compounds or groups of compounds for their potential as neuropsychiatric disorder therapeutics. For this aim, we utilised a variety of solvents, i.e., the aqueous, 60% ethanol (aqueous) and acetic acid (aq) (at two different pHs) for extractions of Australian cane toad skins to identify chemical constituents. The identification of compounds was carried out using HPLC-ESI-Q-TOF-MS/MS based on the accurate mass measurement for molecular ions and MS/MS analysis, whereby accurate mass pseudo-molecular ions and characteristic fragment ions were compared to published reference data, including mass bank and NIST. As a result, we have to date identified 42 major constituents including alkaloids, amino acids, bufadienolides, fatty acids, nucleobases, nucleosides and vitamins mostly from the aqueous and 60% ethanol extracts. Of the 42 constituents identified, 29 were found in the aqueous extract, 35 were found in the ethanol (aq) extract and only 10 in the pH 1.78 acetic acid extract and 11 in the pH 2.17 acetic acid extract of the cane toad skins. Therefore, the aqueous and 60% ethanolic extracts present the greatest potential for ongoing development in our assays. There have been no previous reports on the identification of many of the constituents we have here identified in Australian cane toad skins. These findings, while somewhat consistent with findings in toad skins in other countries, identifies the presence of potential bioactive constituents. Our results showed that HPLC-ESI-Q-TOF-MS/MS is an effective method to characterise and identify components in Australian cane toad skin extracts. Chemical profiling is an essential initial step in the identification and therapeutic exploitation of bioactive agents present in Australian cane toad skin extracts.

Keywords: Aqueous extract; Australian cane toad skin; Constituents; Ethanolic extract; Q-TOF-MS.