Undaria pinnatifida (Wakame) alga contains high amounts of hexadeca‐4Z,7Z,10Z,13Z‐tetraenoic acid which was reported to decrease the efficiency of cisplatin chemotherapeutics. To obtain a fatty acid enriched extract of this ω‐3 poly‐unsaturated fatty acid as an analytical standard, Wakame was used as source material for its extraction. A two‐step extraction protocol consisting of a liquid‐liquid extraction followed by solid‐phase extraction with 3‐aminopropyl silica in accordance to a normal‐phase elution mode was developed. An ultra high performance liquid chromatography with electrospray ionization tandem mass spectrometry method based on sequential windowed acquisition of all theoretical fragment ion mass spectra allowed a simultaneous comprehensive group selective fatty acids profiling in untargeted manner and quantitative analysis of the targeted fatty acid. Hexadeca‐4Z,7Z,10Z,13Z‐tetraenoic acid was identified using high‐resolution product ion spectra. The quantitative method was based on d5‐deuterated hexadeca‐4Z,7Z,10Z,13Z‐tetraenoic acid which was employed as surrogate calibrant. Preliminary method validation was performed by evaluating detection and quantification limits, linear range, intra‐assay and inter‐day precision. Finally, a concentration of 421.2 ± 14.9 ng/mL (4% CV) of hexadeca‐4Z,7Z,10Z,13Z‐tetraenoic acid was determined in the extract which was further used as analytical standard.
Dental plaque is a structurally organized biofilm which consists of diverse microbial colonies and extracellular matrix. Its composition may change when pathogenic microorganisms become dominating. Therefore, dental biofilm or plaque has been frequently investigated in the context of oral health and disease. Furthermore, its potential as an alternative matrix for analytical purposes has also been recognized in other disciplines like archeology, food sciences, and forensics. Thus, a careful in-depth characterization of dental plaque is worthwhile. Most of the conducted studies focused on the screening of microbial populations in dental plaque. Their lipid membranes, on the other hand, may significantly impact substance (metabolite) exchange within microbial colonies as well as xenobiotics uptake and incorporation into teeth. Under this umbrella, a comprehensive lipidomic profiling for determination of lipid compositions of in vivo dental plaque samples and of in vitro cultivated biofilm as surrogate matrix to be used for analytical purposes has been performed in this work. An untargeted lipidomics workflow utilizing a ultra-high-performance liquid chromatography (UHPLC)-quadrupole-time-of-flight (QTOF) platform together with comprehensive SWATH (sequential window acquisition of all theoretical fragment ion mass spectra) acquisition and compatible software (MS-DIAL) that comprises a vast lipid library has been adopted to establish an extensive lipidomic fingerprint of dental plaque. The main lipid components in dental plaque were identified as triacylglycerols, followed by cholesterol, cholesteryl esters as well as diacylglycerols, and various phospholipid classes. In vivo plaque is a rare matrix which is usually available in very low amounts. When higher quantities for specific research assays are required, efficient ways to produce an appropriate surrogate matrix are mandatory. A potential surrogate matrix substituting dental plaque was prepared by cultivation of in vitro biofilm from saliva and similarities and differences in the lipidomics profile to in vivo plaque were mapped by statistical evaluation post-analysis. It was discovered that most lipid classes were highly elevated in the in vitro biofilm samples, in particular diacylglycerols, phosphatidylglycerols, and phosphatidylethanolamines (PEs). Furthermore, an overall shift from even-chain lipid species to odd-chain lipids was observed in the cultivated biofilms. On the other hand, even-chain phosphatidylcholines (PCs), lysoPCs, cholesteryl esters, and cholesterol-sulfate were shown to be specifically increased in plaque samples.
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