Quantitative Determination of Microcystins in Rat Plasma by LC–ESI Tandem MS

Harmful Algal Bloom Toxins in Aerosol Generated from Inland Lake Water

Harmful algal blooms (HABs) caused by cyanobacteria in freshwater environments produce toxins (e.g., microcystin) that are harmful to human and animal health. HAB frequency and intensity are increasing with greater nutrient runoff and a warming climate. Lake spray aerosol (LSA) released from freshwater lakes has been identified on lakeshores and after transport inland, including from lakes with HABs, but little is known about the potential for HAB toxins to be incorporated into LSA. In this study, freshwater samples were collected from two lakes in Michigan: Mona Lake during a severe HAB with microcystin concentrations (>200 μg/L) well above the Environmental Protection Agency (EPA) recommended "do not drink" level (1.6 μg/L) and Muskegon Lake without a HAB (<1 μg/L microcystin). Microcystin toxins were identified in freshwater, as well as aerosol particles generated in the laboratory from Mona Lake water by liquid chromatography-tandem mass spectrometry (LC-MS/MS) at atmospheric concentrations up to 50 ± 20 ng/m3. Enrichment of hydrophobic microcystin congeners (e.g., microcystin-LR) was observed in aerosol particles relative to bulk freshwater, while enrichment of hydrophilic microcystin (e.g., microcystin-RR) was lower. As HABs increase in a warming climate, understanding and quantifying the emissions of toxins into the atmosphere is crucial for evaluating the health consequences of HABs.

Stable-isotope dilution LC-MS/MS method for quantitative determination of microcystin conjugates with cysteine and glutathione in biotic matrices

Microcystins are cyclic peptide toxins with hepatotoxic and tumor-promoting properties, which are produced in significant quantities (up to tens of μg/L) in freshwater cyanobacterial water blooms. Several studies reported microcystin accumulation in fish with possible food transfer to humans. These compounds are further metabolized to cysteine and glutathione conjugates which can be present in tissues in significant concentrations. In this study, we focused on the development and evaluation of robust and highly sensitive SPE-LC-MS/MS method for the analysis of microcystin conjugates in fish tissue samples. For the first time, we demonstrate the use of isotopically labeled internal standards which are essential for accurate and precise determination of analytes in complex biotic matrices. LLOQs of respective microcystin conjugates (signal-to-noise ratio; S/N > 10, peak-to-peak method) ranged from 3.3 to 5.0 ng/g of tissue fresh weight (FW). The calibration was linear within a range of concentrations from 1 to 70 ng/mL for all analyzed conjugates. The precision and repeatability of the method were very good with recoveries in the range of 88.5-107.6% and relative standard deviations between 8.8 and 13.2% for all analytes. In the follow-up study, fully validated method was used for the determination of microcystin conjugate levels in common carp exposed to microcystin-containing cyanobacterial biomass under controlled conditions. Significant amounts of microcystin conjugates (up to 55 ng/g) were found in the tissues of fish after 7 weeks of exposure. Our method was shown to be robust, sensitive, selective, and suitable for the determination of trace levels of microcystin conjugates in fish tissues.

Development and applications of solid-phase extraction and liquid chromatography-mass spectrometry methods for quantification of microcystins in urine, plasma, and serum

The protocols for solid-phase extraction (SPE) of six microcystins (MCs; MC-LR, MC-RR, MC-LA, MC-LF, MC-LW, and MC-YR) from mouse urine, mouse plasma, and human serum are reported. The quantification of those MCs in biofluids was achieved using HPLC-orbitrap-MS in selected-ion monitoring (SIM) mode, and MCs in urine samples were also quantified by ultra-HPLC-triple quadrupole-tandem mass spectrometry (UHPLC-QqQ-MS/MS) in multiple reaction monitoring (MRM) mode. Under optimal conditions, the extraction recoveries of MCs from samples spiked at two different concentrations (1 μg/L and 10 μg/L) ranged from 90.4% to 104.3% with relative standard deviations (RSDs) ≤ 4.7% for mouse urine, 90.4-106.9% with RSDs ≤ 6.3% for mouse plasma, and 90.0-104.8% with RSDs ≤ 5.0% for human serum. Matrix-matched internal standard calibration curves were linear with R2 ≥ 0.9950 for MC-LR, MC-RR and MC-YR, and R2 ≥ 0.9883 for MC-LA, MC-LF, and MC-LW. The limits of quantification (LOQs) in spiked urine samples were ∼0.13 μg/L for MC-LR, MC-RR, and MC-YR, and ∼0.50 μg/L for MC-LA, MC-LF, and MC-LW, while the LOQs in spiked plasma and serum were ∼0.25 μg/L for MC-LR, MC-RR, and MC-YR, and ∼1.00 μg/L for MC-LA, MC-LF, and MC-LW. The developed methods were applied in a proof-of-concept study to quantify urinary and blood concentrations of MC-LR after oral administration to mice. The urine of mice administered 50 μg of MC-LR per kg bodyweight contained on average 1.30 μg/L of MC-LR (n = 8), while mice administered 100 μg of MC-LR per kg bodyweight had average MC-LR concentration of 2.82 μg/L (n = 8). MC-LR was also quantified in the plasma of the same mice. The results showed that increased MC-LR dosage led to larger urinary and plasma MC-LR concentrations and the developed methods were effective for the quantification of MCs in mouse biofluids.

Simultaneous quantification of microcystins and nodularin in aerosol samples using high-performance liquid chromatography/negative electrospray ionization tandem mass spectrometry

RATIONALE

Cyanobacteria are a small group of photosynthetic planktonic bacteria, producing a large group of strong hepatotoxins called microcystins (MCs). Many studies have been conducted to evaluate the presence of MCs and nodularin (NOD) in water or in marine organisms, but little research has been done on the atmospheric environment. Waterborne toxins can be found in the aerosol phase due to bubble-bursting processes.

METHODS

The aim of this study was to obtain a sensitive method for the simultaneous determination of trace concentrations of individual cyanotoxins in aerosol samples, using liquid chromatography coupled with a triple quadrupole (HPLC/MS/MS). During method development improved electrospray ionization was found in negative ion mode. In contrast with other authors, we have developed a chromatographic separation using alkaline conditions, thus achieving good resolution, improved electrospray ionization and therefore better sensitivity.

RESULTS

A sensitive analytical method was set up to simultaneously measure trace concentrations of cyanotoxins in aerosol samples in a single chromatographic analysis using the internal standard method. The limit of detection for all the toxins was determined to be between 1 fg/μL (MC LA and LF) and 9 fg/μL (NOD).

CONCLUSIONS

The method was applied to ten aerosol samples from the Venice Lagoon. In these samples, trace concentrations of MC-LA ranging between 90 fg m(-3) and 706 fg m(-3), MC-LF between n.d. and 369 fg m(-3) and MC-LW between n.d. and 262 fg m(-3). This is the first study to quantify the cyanotoxins in Venetian aerosol samples using the HPLC/(-)ESI-MS/MS.