16th GCC Closed Forum: ICH M10 implementation; NGS, qPCR/dPCR, flow cytometry validation; tissue biomarkers; IS response; immunogenicity harmonization; bioanalytical industry status.

The 16th GCC Closed Forum was held in Orlando, FL, USA, on 23 June 2023. Representatives from international bioanalytical Contract Research Organizations were in attendance in order to discuss scientific and regulatory issues specific to bioanalysis. The issues discussed at the meeting included: IS response, flow cytometry, changes to the bioanalytical industry, NGS assays, biomarker assay for tissues, dPCR validation, immunogenicity harmonization and ICH M10 implementation. Conclusions and consensus from discussions of these topics are included in this article.

Recommendations on qPCR/ddPCR assay validation by GCC.

Gene therapy, cell therapy and vaccine research have led to an increased use of qPCR/ddPCR in bioanalytical laboratories. CROs are progressively undertaking the development and validation of qPCR and ddPCR assays. Currently, however, there is limited regulatory guidance for the use of qPCR and a complete lack of any regulatory guidelines for the use of the newer ddPCR to support regulated bioanalysis. Hence, the Global CRO Council in Bioanalysis (GCC) has issued this White Paper to provide; 1) a consensus on the different validation parameters required to support qPCR/ddPCR assays; 2) a harmonized approach to their validation and 3) a consistent development of standard operating procedures (SOPs) for all the bioanalytical laboratories using these techniques.

Intact quantitative bioanalytical method development and fit-for-purpose validation of a monoclonal antibody and its related fab fragment in human vitreous and aqueous humor using LC-HRMS.

Ranibizumab is an FDA-approved drug used to treat wet age-related macular degeneration (AMD), diabetic retinopathy, macular edema, and myopic choroidal neovascularization. Bevacizumab is another drug often used off-label to treat wet AMD. In order to reduce unwanted angiogenesis, ranibizumab and bevacizumab target circulating VEGF-A in the eye. Concentration levels in human vitreous and aqueous humor can be used to provide valuable efficacy information. However, vitreous and aqueous humor's aqueous environment, and vitreous humor's viscosity, as well as the stickiness of the analytes can provide bioanalytical challenges. In this manuscript, we describe the development, optimization, and fit-for-purpose validation of an LC-HRMS method designed for intact quantitative bioanalysis of ranibizumab and bevacizumab in human vitreous and aqueous humor following intravitreal administration. In order to fully develop this method, evaluations were conducted to optimize the conditions, including the data processing model (extracted ion chromatograms (XICs) vs deconvolution), carryover mitigation, sample preparation scheme optimization for surrogate and primary matrices, use of internal standard/immunocapture/deglycosylation, and optimization of the extraction and dilution procedure, as well as optimization of the liquid chromatography and mass spectrometry conditions. Once the method was fully optimized, a fit-for-purpose validation was conducted, including matrix parallelism, with a linear calibration range of 10 to 200 µg/mL. The development of this intact quantitative method using LC-HRMS provides a proof-of-concept template for challenging, but valuable new and exciting bioanalytical techniques.

Recommendations on ELISpot assay validation by the GCC.

Gene therapy, cell therapy and vaccine research have led to an increased need to perform cellular immunity testing in a regulated environment to ensure the safety and efficacy of these treatments. The most common method for the measurement of cellular immunity has been Enzyme-Linked Immunospot assays. However, there is a lack of regulatory guidance available discussing the recommendations for developing and validating these types of assays. Hence, the Global CRO Council has issued this white paper to provide a consensus on the different validation parameters required to support Enzyme-Linked Immunospot assays and a harmonized and consistent approach to Enzyme-Linked Immunospot validation among contract research organizations.

Multifaceted Bioanalytical Methods for the Comprehensive Pharmacokinetic and Catabolic Assessment of MEDI3726, an Anti-Prostate-Specific Membrane Antigen Pyrrolobenzodiazepine Antibody-Drug Conjugate.

Complex biotherapeutic modalities, such as antibody-drug conjugates (ADC), present significant challenges for the comprehensive bioanalytical characterization of their pharmacokinetics (PK) and catabolism in both preclinical and clinical settings. Thus, the bioanalytical strategy for ADCs must be designed to address the specific structural elements of the protein scaffold, linker, and warhead. A typical bioanalytical strategy for ADCs involves quantification of the Total ADC, Total IgG, and Free Warhead concentrations. Herein, we present bioanalytical characterization of the PK and catabolism of a novel ADC. MEDI3726 targets prostate-specific membrane antigen (PMSA) and is comprised of a humanized IgG1 antibody site-specifically conjugated to tesirine (SG3249). The MEDI3726 protein scaffold lacks interchain disulfide bonds and has an average drug to antibody ratio (DAR) of 2. Based on the structural characteristics of MEDI3726, an array of 4 bioanalytical assays detecting 6 different surrogate analyte classes representing at least 14 unique species was developed, validated, and employed in support of a first-in-human clinical trial (NCT02991911). MEDI3726 requires the combination of heavy-light chain structure and conjugated warhead to selectively deliver the warhead to the target cells. Therefore, both heavy-light chain dissociation and the deconjugation of the warhead will affect the activity of MEDI3726. The concentration-time profiles of subjects dosed with MEDI3726 revealed catabolism of the protein scaffold manifested by the more rapid clearance of the Active ADC, while exhibiting minimal deconjugation of the pyrrolobenzodiazepine (PBD) warhead (SG3199).

Cell-type specific differences in antiretroviral penetration and the effects of HIV-1 Tat and morphine among primary human brain endothelial cells, astrocytes, pericytes, and microglia.

The inability to achieve adequate intracellular antiretroviral concentrations may contribute to HIV persistence within the brain and to neurocognitive deficits in opioid abusers. To investigate, intracellular antiretroviral concentrations were measured in primary human astrocytes, microglia, pericytes, and brain microvascular endothelial cells (BMECs), and in an immortalized brain endothelial cell line (hCMEC/D3). HIV-1 Tat and morphine effects on intracellular antiretroviral concentrations also were evaluated. After pretreatment for 24 h with vehicle, HIV-1 Tat, morphine, or combined Tat and morphine, cells were incubated for 1 h with equal concentrations of a mixture of tenofovir, emtricitabine, and dolutegravir at one of two concentrations (5 µM or 10 µM). Intracellular drug accumulation was measured using LC-MS/MS. Drug penetration differed depending on the drug, the extracellular concentration used for dosing, and cell type. Significant findings included: 1) Dolutegravir (at 5 µM or 10 µM) accumulated more in HBMECs than other cell types. 2) At 5 µM, intracellular emtricitabine levels were higher in microglia than other cell types; while at 10 µM, emtricitabine accumulation was greatest in HBMECs. 3) Tenofovir (5 or 10 µM extracellular dosing) displayed greater accumulation inside HBMECs than in other cell types. 4) After Tat and/or morphine pretreatment, the relative accumulation of antiretroviral drugs was greater in morphine-exposed HBMECs compared to other treatments. The opposite effect was observed in astrocytes in which morphine exposure decreased drug accumulation. In summary, the intracellular accumulation of antiretroviral drugs differed depending on the particular drug involved, the concentration of the applied antiretroviral drug, and the cell type targeted. Moreover, morphine, and to a lesser extent Tat, exposure also had differential effects on antiretroviral accumulation. These data highlight the complexity of optimizing brain-targeted HIV therapeutics, especially in the setting of chronic opioid use or misuse.

Multiplex LC-MS/MS Assays for Clinical Bioanalysis of MEDI4276, an Antibody-Drug Conjugate of Tubulysin Analogue Attached via Cleavable Linker to a Biparatopic Humanized Antibody against HER-2.

Bioanalysis of complex biotherapeutics, such as antibody-drug conjugates (ADCs), is challenging and requires multiple assays to describe their pharmacokinetic (PK) profiles. To enable exposure-safety and exposure-efficacy analyses, as well as to understand the metabolism of ADC therapeutics, three bioanalytical methods are typically employed: Total Antibody, Antibody Conjugated Toxin or Total ADC and Unconjugated Toxin. MEDI4276 is an ADC comprised of biparatopic humanized antibody attached via a protease-cleavable peptide-based maleimidocaproyl linker to a tubulysin toxin (AZ13599185) with an approximate average drug-antibody ratio of 4. The conjugated payload of MEDI4276 can undergo ester hydrolysis to produce the conjugated payload AZ13687308, leading to the formation of MEDI1498 (de-acetylated MEDI4276). In this report, we describe the development, validation and application of three novel multiplex bioanalytical methods. The first ligand-binding liquid chromatography coupled with tandem mass spectrometry (LBA-LC-MS/MS) method was developed and validated for simultaneous measurement of total antibody and total ADC (antibody-conjugated AZ13599185) from MEDI4276. The second LBA-LC-MS/MS assay quantified total ADC (antibody-conjugated AZ13687308) from MEDI1498. The third multiplex LC-MS/MS assay was used for simultaneous quantification of unconjugated AZ13599185 and AZ13687308. Additional stability experiments confirmed that quantification of the released warhead in the presence of high concentrations of MEDI4276 was acceptable. Subsequently, the assays were employed in support of a first-in-human clinical trial (NCT02576548).

Simultaneous determination of intracellular concentrations of tenofovir, emtricitabine, and dolutegravir in human brain microvascular endothelial cells using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Combination antiretroviral therapy (cART) regimens are recommended for HIV patients to better achieve and maintain plasma viral suppression. Despite adequate plasma viral suppression, HIV persists inside the brain, which is, in part thought to result from poor brain penetration of antiretroviral drugs. In this study, a simple and ultra-sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous determination of tenofovir, emtricitabine, and dolutegravir in cell lysates of an immortalized human brain microvascular endothelial cell line (hCMEC/D3) was developed and validated. Analytes were separated on a reverse phase C18 column using water and 0.1% formic acid in acetonitrile as mobile phases. The analytes were detected using positive electrospray ionization mode with multiple reaction monitoring (MRM). The assay was linear in the concentration range of 0.1-100 ng mL-1 for all analytes. Intra- and inter-assay precision and accuracy were within ±13.33% and ±10.53%, respectively. This approach described herein was used to determine the intracellular accumulation of tenofovir, emtricitabine, dolutegravir simultaneously in hCMEC/D3 cells samples.

Preanalytical approaches to improve recovery of amyloid-ß peptides from CSF as measured by immunological or mass spectrometry-based assays.

BACKGROUND: Amyloid-ß 1-42 (Aß1-42) peptide is a well-established cerebrospinal fluid (CSF) biomarker for Alzheimer's disease (AD). Reduced levels of Aß1-42 are indicative of AD, but significant variation in the absolute concentrations of this analyte has been described for both healthy and diseased populations. Preanalytical factors such as storage tube type are reported to impact Aß recovery and quantification accuracy. Using complementary immunological and mass spectrometry-based approaches, we identified and characterized preanalytical factors that influence measured concentrations of CSF Aß peptides in stored samples. METHODS: CSF from healthy control subjects and patients with AD was aliquoted into polypropylene tubes at volumes of 0.1 ml and 0.5 ml. CSF Aß1-42 concentrations were initially measured by immunoassay; subsequent determinations of CSF Aß1-42, Aß1-40, Aß1-38, Aß1-37, and Aß1-34 concentrations were made with an absolute quantitative mass spectrometry assay. In a second study, CSF from healthy control subjects and patients with dementia was denatured with guanidine hydrochloride (GuHCl) at different stages of the CSF collection and aliquoting process and then measured with the mass spectrometry assay. RESULTS: Two distinct immunoassays demonstrated that CSF Aß1-42 concentrations measured from 0.5-ml aliquots were higher than those from 0.1-ml aliquots. Tween-20 surfactant supplementation increased Aß1-42 recovery but did not effectively resolve measured concentration differences associated with aliquot size. A CSF Aß peptide mass spectrometry assay confirmed that Aß peptide recovery was linked to sample volume. Unlike the immunoassay experiments, measured differences were consistently eliminated when aliquots were denatured in the original sample tube. Recovery from a panel of low-retention polypropylene tubes was assessed, and 1.5-ml Eppendorf LoBind® tubes were determined to be the least absorptive for Aß1-42. A comparison of CSF collection and processing methods suggested that Aß peptide recovery was improved by denaturing CSF earlier in the collection/aliquoting process and that the Aß1-42/Aß1-40 ratio was a useful method to reduce variability. CONCLUSIONS: Analyte loss due to nonspecific sample tube adsorption is a significant preanalytical factor that can compromise the accuracy of CSF Aß1-42 measurements. Sample denaturation during aliquoting increases recovery of Aß peptides and improves measurement accuracy. The Aß1-42/Aß1-40 ratio can overcome some of the quantitative variability precipitated by preanalytical factors affecting recovery.

Comparison of a stable isotope labeled (SIL) peptide and an extended SIL peptide as internal standards to track digestion variability of an unstable signature peptide during quantification of a cancer biomarker, human osteopontin, from plasma using capillary microflow LC-MS/MS.

Human osteopontin (hOPN) is a secreted plasma protein which is elevated in various cancers and is indicative of poor prognosis. Here we describe investigations involving an extended peptide internal standard to track an unstable signature peptide followed by further method development and validation for quantitative measurement of hOPN from plasma using microflow liquid chromatography and tandem mass spectrometry (MFLC-MS/MS). A biologically relevant tryptic peptide 'GDSVVYGLR' was used as a signature peptide for this method. The optimized method involved immunocapture of the analyte protein using hOPN specific antibodies followed by trypsin digestion to obtain the signature peptide. Analysis was carried out on a Waters IonKey/MS system using a flow rate of 2.5µL/min. Immunocapture buffer was used as a surrogate matrix for the validation studies. The method was validated over a range of 25-600ng/mL. Intra-assay and inter-assay accuracies were within ±13%. Intra-assay and inter-assay precision were within 17%. A stable isotope labeled (SIL) peptide GDSVVYGLR* and an extended SIL peptide TYDGRGDSVV*YGLRSKSKKF were evaluated as internal standards (IS) to account for signature peptide digestion instability and variability. Inherent digestion variability i.e., under controlled conditions, was within ±20% with both IS peptides. In digestion variability studies, where trypsin activity was varied (20-180%), the use of the extended SIL peptide as an internal standard limited the variability to within ±30% of the normalized response. Alternatively, when the SIL peptide was used as the internal standard, the variability ranged from -67.4% to 50.6% of the normalized response. The applicability of the validated method was demonstrated by quantification of OPN from plasma samples obtained from 10 healthy individuals and 10 breast cancer patients. The plasma OPN concentrations in healthy individuals ranged from 38 to 85ng/mL with a mean concentration of 55.4±15.3ng/mL. A 1.5-12 fold increase in OPN concentrations, ranging from 85 to 637ng/mL, was seen in breast cancer patient samples.

An extended stable isotope-labeled signature peptide internal standard for tracking immunocapture of human plasma osteopontin for LC-MS/MS quantification.

A stable isotope-labeled signature peptide, whose sequence corresponds to the human osteopontin (hOPN) specific antibody epitope, was evaluated as an internal standard to compensate for immunocapture variability during quantification of hOPN by immunoaffinity-coupled LC-MS/MS. Immunocapture variability was induced by varying the antibody amount per well from 150 to 4500 ng and analysis was carried out with internal standards added before and after the immunocapture step. The immunocapture variability ranged from -80.9 to 77.0% when the IS was added after immunocapture and from -37.5 to 20.3% when the internal standard was added before immunocapture. The lower variability demonstrates the ability of stable labeled isotope internal standard peptide to compensate for variation during immunocapture.

A validated HPLC-MS/MS assay for quantifying unstable pharmacologically active metabolites of clopidogrel in human plasma: application to a clinical pharmacokinetic study.

Clopidogrel is prescribed for the treatment of Acute Coronary Syndrome and recent myocardial infarction, recent stroke, or established peripheral arterial disease. A sensitive and reliable high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) assay was developed and validated to enable reliable quantification of four diastereomeric and chemically reactive thiol metabolites, two of which are pharmacologically active, in human plasma. The metabolites were stabilized by alkylation of their reactive thiol moieties with 2-bromo-3'-methoxyacetophenone (MPB). Following organic solvent mediated-protein precipitation in a 96-well plate format, chromatographic separation was achieved by gradient elution on an Ascentis Express RP-amide column. Chromatographic conditions were optimized to ensure separation of the four derivatized active metabolites. Derivatized metabolites and stable isotope-labeled internal standards were detected by positive ion electrospray tandem mass spectrometry. The HPLC-MS/MS assay was validated over concentration ranges of 0.125-125 ng/mL for metabolites H1-H3 and 0.101-101 ng/mL for H4. Intra- and inter-assay precision values for replicate quality control samples were within 14.3% for all analytes during the assay validation. Mean quality control accuracy values were within ±6.3% of nominal values for all analytes. Assay recoveries were high (>79%). The four derivatized analytes were stable in human blood for at least 2 h at room temperature and on ice. The analytes were also stable in human plasma for at least 25 h at room temperature, 372 days at -20 °C and -70 °C, and following at least five freeze-thaw cycles. The validated assay was successfully applied to the quantification of all four thiol metabolites in human plasma in support of a human pharmacokinetic study.

An improved LC-MS/MS method for the determination of taspoglutide in plasma and urine using orthogonal HILIC-RP column switching, ultra-performance LC separation and 'wrong-way-round' electrospray ionization.

The synthetic peptide drug taspoglutide, developed for treatment of diabetes, must be quantified at low pg/mL levels in biological samples. This manuscript describes the improvement of a previous method, featuring orthogonal hydrophilic interaction to reversed-phase chromatography column switching and tandem mass spectrometric detection. Signal-to-noise ratio was enhanced and isobaric interferences were reduced by ultra-performance separation using a basic mobile phase in 'wrong-way-round' ionization mode and monitoring a selective fragment ion. Tedious solid-phase extraction cleanup was abandoned in favor of simple protein precipitation. Urine required the addition of surfactants to prevent adsorptive drug loss. Dissociation of complexes with possibly formed anti-drug antibodies was achieved with formic acid. Lower limits of quantitation (LLOQ) were 4 pg/mL in human plasma and 10 pg/mL in urine using a 250 µL sample, and an LLOQ of 50 pg/mL was obtained in animal plasma using 50 µL. Precision, accuracy and incurred samples reproducibility fulfilled regulatory requirements. Simultaneous determination of unlabeled and stable isotope labeled taspoglutide, interesting for clearance studies in which both compounds are co-administered, was realized using a structural analog as internal standard. The described method offered excellent sensitivity with low sample consumption, reasonable throughput, moderate costs and high robustness for routine analysis.

Microcystin analysis in human sera and liver from human fatalities in Caruaru, Brazil 1996.

In 1996, an extensive exposure of Brazilian hemodialysis patients at a dialysis center, using a municipal water supply water contaminated with cyanotoxins, provided the first evidence for acute lethal human poisoning from the cyclic peptide hepatotoxins called microcystins. During this outbreak, 100 of 131 patients developed acute liver failure and 52 of these victims were confirmed to have been exposed to lethal levels of microcystins. Detection and quantitation of microcystins in these biological samples posed some analytical challenges since there were no well-established and routine analytic methods to measure total microcystins in tissue or sera samples. At the time of the 1996 exposure we used analytic methods that combined the use of enzyme linked immunosorbant assay (ELISA), analytical high performance liquid chromatography (HPLC), electrospray ionization ion-trap mass spectroscopy (ES-ITMS) and matrix assisted laser desorption ionization-time of flight spectroscopy (MALDI-TOF). In the intervening years these methods have been improved and others developed that allow a more quantitative and critical analysis of microcystin contaminated tissue and sera. For these reasons, and to see how storage with time might effect the detection and stability of microcystins in these matrices, we reanalyzed selected liver tissues and sera from the Caruaru victims in Brazil. We developed and validated a procedure to measure total microcystins in Caruaru human sera and liver tissue using a combination of ELISA, liquid chromatography and liquid chromatography-mass spectrometry (LC/MS), GC/MS and MS/MS techniques. GC/MS and LC/MS were followed by MS/MS to obtain a fingerprint fragment spectra for the microcystins. The validity of the extraction procedure for free microcystins was confirmed by recovery experiments with blood sera spiked with microcystin-LR. We removed proteins with the Microcon Centrifugal Filter prior to LC/MS and ELISA analysis. A solid phase extraction (SPE) procedure was used for analysis of protein bound microcystins by conversion of ADDA to erythro-2-methyl-3-methoxy-4-phenylbutyric acid (MMPB) combined with GC/MS. We found that the GC/MS method yielded a higher concentration of microcystin than that obtained by ELISA and LC/MS. We hypothesize that this difference is due to better GC/MS detection of the covalently bound form of microcystins in human liver tissue. We also concluded that microcystins are very stable when stored under these conditions for periods of almost 10 years.

Sublethal exposure from microcystins to renal insufficiency patients in Rio de Janeiro, Brazil.

In November 2001, a cyanobacterial bloom dominated by Microcystis and Anabaena occurred in the Funil Reservoir and the Guandu River, both of which supply drinking water to Rio de Janeiro, Brazil. Using ELISA, microcystins were detected at a concentration of 0.4 microg/L in the drinking water, whereas a concentration of 0.32 microg/L was detected in activated carbon column-treated water for use at the renal dialysis center of Clementino Fraga Filho Hospital (HUCFF) at the Federal University of Rio de Janeiro. A total of 44 hemodialysis patients who received care at this center were believed to be exposed. Initial ELISA analyses confirmed the presence of serum microcystin concentrations > or = 0.16 ng/mL in 90% of serum samples collected from these patients. Twelve patients were selected for continued monitoring over the following 2-month period. Serum microcystin concentrations ranged from < 0.16 to 0.96 ng/mL during the 57 days after documented exposure. ELISA-positive samples were found throughout the monitoring period, with the highest values detected 1 month after initial exposure. ESI LC/MS analyses indicated microcystins in the serum; however, MS/MS fragmentation patterns typical of microcystins were not identified. LC/MS analyses of MMPB for control serum spiked with MCYST-LR. and patient sera revealed a peak at retention time of 8.4 min and a mass of 207 m/z. These peaks are equivalent to the peak observed in the MMPB standard analysis. Taken together ELISA, LC/MS, and MMPB results indicate that these renal dialysis patients were exposed to microcystins. This documents another incident of human microcystin exposure during hemodialysis treatment.

A simple colorimetric method to detect biological evidence of human exposure to microcystins.

Toxic cyanobacteria are contaminants of surface waters worldwide. Microcystins are some of the most commonly detected cyanotoxins. Biological evidence of human exposure may be difficult to obtain due to limitations associated with cost, laboratory capacity, analytic support, and expertise. We investigated the application of an enzyme-linked immunosorbant assay (ELISA) to detect microcystins in human serum. We analyzed ten serum samples collected from dialysis patients who were known to be exposed to a mixture of microcystins during a 1996 outbreak in Brazil. We applied a commercially available ELISA method to detect microcystins in serum, and we compared the ELISA results to a more specific method, liquid chromatography/mass spectrometry (LC/MS) that was also used to detect microcystins in serum. The Spearman correlation coefficient was calculated using serum microcystin concentrations in split samples obtained by the two methods. Serum microcystin concentrations were similar, and we found good correlation of microcystin concentrations between the two methods. The ELISA detected total microcystins, median=19.9 ng/ml; LC/MS detected microcystin-LR equivalents, median=21.2 ng/ml; Spearman r=0.96, p<0.0001. We found that ELISA is a simple, accessible method to screen human serum for evidence of microcystin exposure.

The uptake kinetics and immunotoxic effects of microcystin-LR in human and chicken peripheral blood lymphocytes in vitro.

Microcystin-LR is a cyanobacterial heptapeptide that presents acute and chronic hazards to animal and human health. We investigated the influence of this toxin on human and chicken immune system modulation in vitro. Peripheral blood lymphocytes were treated with microcystin-LR at environmentally relevant doses of 1, 10 and 25 microg/ml for 12, 24, 48, 72 h (for proliferation assay cells were treated for 72 h). T-cell and B-cell proliferation as well as apoptosis and necrosis were determined in human and chicken samples. IL-2 and IL-6 production by human lymphocytes also was measured. In addition, uptake kinetics of microcystin-LR into human and chicken peripheral blood lymphocytes were calculated by Liquid Chromatography (LS) /Mass Spectrometry (MS) analysis. At the highest dose microcystin-LR decreased T-cell proliferation and all doses of microcystin-LR inhibited B-cell proliferation. The frequency of apoptotic and necrotic cells increased in a dose and time-dependent manner. Human lymphocytes responded to stimulation with microcystin-LR by increased production of IL-6 and decreased production of IL-2. Human lymphocytes were able to uptake from 0.014 to 1.663 microg/ml and chicken lymphocytes from 0.035 to 1.733 microg/ml of the microcystin-LR added to the cultures, depending on the treatment time and dose. In conclusion, microcystin-LR acted as an immunomodulator in cytokine production and down-regulated lymphocyte functions by induction of apoptosis and necrosis. However, further studies dealing with the influence of microcystin-LR on expression cytokine genes and transcription factors are necessary to confirm these hypotheses.

Detection and analysis of the cyanobacterial peptide hepatotoxins microcystin and nodularin using SELDI-TOF mass spectrometry.

Surface-enhanced laser desorption ionization mass spectrometry (SELDI-TOFMS) was used to develop a new and useful method for determination and identification of the cyanobacterial (blue-green algae) toxins: microcystin and nodularin. The technique, combining chromatography and MS, enables microcystin/nodularin capture, purification, analysis, and processing from complex biological mixtures directly onto a hydrophobic chip. Factors affecting ion intensities, including matrix concentration and laser intensity, were investigated to optimize sensitivity of the method. Microcystins and nodularin were analyzed for femtomolar sensitivity (about 2.5 pg microcystin-LR in 2 microl water). Samples of blood sera and liver tissue were spiked with microcystin-LR and analyzed. The detection limit was 1 ng in 2 microl blood sera solution. Reactions of microcystins by compounds containing mercaptan groups, such as dithiothreitol, aminoethanethiol and protein phosphatase 1, were examined on the chip by mass spectrometry. Formation of the microcystin-dithiothreitol conjugate was used to confirm the target compounds. The MS/MS data obtained showed the presence of the microcystin conjugate. The reaction position of the toxin with target compound was confirmed by a series of MS/MS fragment ions. The protein profile of microcystins reacting with protein phosphatase 1 was also obtained from the SELDI-TOF mass spectra.