Dennis Mulac

Differential cytotoxic actions of Shiga toxin 1 and Shiga toxin 2 on microvascular and macrovascular endothelial cells

Shiga toxin (Stx)-mediated injury to vascular endothelial cells in the kidneys, brain and other organs underlies the pathogenesis of haemolytic uraemic syndrome (HUS) caused by enterohaemorrhagic Escherichia coli (EHEC). We present a direct and comprehensive comparison of cellular injury induced by the two major Stx types, Stx1 and Stx2, in human brain microvascular endothelial cells (HBMECs) and EA.hy 926 macrovascular endothelial cells. Scanning electron microscopy of microcarrier-based cell cultures, digital holographic microscopy of living single cells, and quantitative apoptosis/necrosis assays demonstrate that Stx1 causes both necrosis and apoptosis, whereas Stx2 induces almost exclusively apoptosis in both cell lines. Moreover, microvascular and macrovascular endothelial cells have different susceptibilities to the toxins: EA.hy 926 cells are slightly, but significantly (∼ 10 times) more susceptible to Stx1, whereas HBMECs are strikingly (≥ 1,000 times) more susceptible to Stx2. These findings have implications in the pathogenesis of HUS, and suggest the existence of yet to be delineated Stx type-specific mechanisms of endothelial cell injury beyond inhibition of protein biosynthesis.

Metabolism and cytotoxic effects of T-2 toxin and its metabolites on human cells in primary culture.

T-2 toxin belongs to the large group of trichothecene mycotoxins synthesized by various Fusarium molds which can infect raw agriculture materials. Among the trichothecenes, T-2 toxin is one of the most potent mycotoxins and poses a potential health risk in human nutrition. Several acute and chronic toxic effects were observed in humans after consumption of contaminated food. Due to the rapid metabolism of T-2 toxin by esterases, several metabolites can be found in food and also in vivo after ingestion. The aim of this work was to determine the effects of T-2 toxin and of several of its metabolites, namely HT-2 toxin, neosolaniol, T-2-triol and T-2 tetraol, on two human cells in primary culture: human renal proximal tubule epithelial cells (RPTEC) and normal human lung fibroblasts (NHLF). Concerning the cytotoxicity of T-2 toxin and its metabolites, different studies were performed with animal cells and cell lines but there are only little data about cytotoxic effects in human cells. The use of human cells in primary culture gives a good completion of the already known data because these might be limited due to the disadvantages of cell lines (e.g., immortalization, tumor derivation, longtime cultivation). In order to study the cytotoxicity and mode of cell death, the parameters cell viability, caspase-3-activity and LDH-release were measured after exposure to T-2 toxin and several of its metabolites. With IC(50) values of 0.2 and 0.5 microM T-2 toxin showed the strongest cytotoxic effect in both cells with triggering apoptosis as kind of cell death starting at a concentration of 100nM. The metabolites HT-2 toxin and neosolaniol revealed weaker cytotoxic effects (IC(50): 0.7-3.0 microM) and induced apoptosis at higher concentrations (>1 microM). The other metabolites were less cytotoxic (IC(50): 8.3-25.1 microM) and did not activate caspase-3. In addition to the analysis of cytotoxic effects, we also studied the metabolism of T-2 toxin in these cells in primary culture. Using LC-ESI-MS/MS we could demonstrate that both cells are able to transform T-2 toxin into HT-2 toxin. Further metabolic activity could only be observed in renal proximal tubule (RPTEC) cells by forming neosolaniol as a second metabolite.

Cytotoxicity and accumulation of ergot alkaloids in human primary cells

Ergot alkaloids are secondary metabolites produced by fungi of the species Claviceps. Toxic effects after consumption of contaminated grains are described since mediaeval times. Of the more than 40 known ergot alkaloids six are found predominantly. These are ergotamine, ergocornine, ergocryptine, ergocristine, ergosine and ergometrine, along with their corresponding isomeric forms (-inine-forms). Toxic effects are known to be induced by an interaction of the ergot alkaloids as neurotransmitters, like dopamine or serotonin. Nevertheless data concerning cytotoxic effects are missing and therefore a screening of the six main ergot alkaloids was performed in human primary cells in order to evaluate the toxic potential. As it is well known that ergot alkaloids isomerize easily the stability was tested in the cell medium. Based on these results factors were calculated to correct the used concentration values to the biologically active lysergic (-ine) form. These factors range from 1.4 for the most stable compound ergometrine to 5.0 for the most unstable ergot alkaloid ergocristine. With these factors, reflecting the instability, several controverse literature data concerning the toxicity could be explained. To evaluate the cytotoxic effects of ergot alkaloids, human cells in primary culture were used. These cells remain unchanged in contrast to cell lines and the data allow a better comparison to the in vivo situation than using immortalized cell lines. To characterize the effects on primary cells, renal proximal tubule epithelial cells (RPTEC) and normal human astrocytes (NHA) were used. The parameters necrosis (LDH-release) and apoptosis (caspase-3-activation, DNA condensation and fragmentation) were distinguished. The results show that depending on the individual structure of the peptide ergot alkaloids the toxic properties change. While ergometrine as a lysergic acid amide did not show any effect, the peptide ergot alkaloids revealed a different toxic potential. Of all tested ergot alkaloids ergocristine was the most cytotoxic compound inducing apoptosis in human kidney cells starting at a concentration of 1μM in RPTEC. Uptake studies underline the cytotoxic properties, with an accumulation of peptide ergot alkaloids and no uptake of ergometrine. The results represent a new description of effects of ergot alkaloids regarding cytotoxicity and accumulation in human primary cells. For the first time apoptosis has been identified besides well described receptor effects. This gives a hint for a more complex mode of action of ergot alkaloids than described in literature so far.

Structural elucidation of T-2 toxin thermal degradation products and investigations toward their occurrence in retail food.

The stability of T-2 toxin under the conditions of baking or cooking was investigated using heating experiments with the model substances alpha-d-glucose, alpha-d-methyl-glucopyranosid, N-alpha-acetyl-l-lysine methyl ester, and N-alpha-acetyl-cysteine methyl ester. The reaction residue was screened for degradation products using gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography with evaporative light-scattering detection (HPLC-ELSD). Although T-2 toxin was degraded under all conditions, only heating of T-2 toxin with alpha-d-glucose produced a mixture of three degradation products, which were isolated and identified by MS and nuclear magnetic resonance (NMR) experiments. The reaction mechanism for the formation of the T-2 degradation products was elucidated by quantum chemical calculations. The relevance of these degradation products was investigated by baking experiments as well as the analysis of retail food samples. In cell-culture studies using immortalized human kidney epithelial (IHKE) cells, the T-2 degradation products were less cytotoxic (formazan dye cytotoxicity assay) compared to T-2 toxin.

Permeability of ergot alkaloids across the blood‐brain barrier in vitro and influence on the barrier integrity

Scope Ergot alkaloids are secondary metabolites of Claviceps spp. and they have been in the focus of research for many years. Experiments focusing on ergotamine as a former migraine drug referring to the ability to reach the brain revealed controversial results. The question to which extent ergot alkaloids are able to cross the blood-brain barrier is still not answered. Methods and results In order to answer this question we have studied the ability of ergot alkaloids to penetrate the blood-brain barrier in a well established in vitro model system using primary porcine brain endothelial cells. It could clearly be demonstrated that ergot alkaloids are able to cross the blood-brain barrier in high quantities in only a few hours. We could further identify an active transport for ergometrine as a substrate for the BCRP/ABCG2 transporter. Investigations concerning barrier integrity properties have identified ergocristinine as a potent substance to accumulate in these cells ultimately leading to a weakened barrier function. Conclusion For the first time we could show that the so far as biologically inactive described 8-(S) isomers of ergot alkaloids seem to have an influence on barrier integrity underlining the necessity for a risk assessment of ergot alkaloids in food and feed.

Comparative examination of adsorption of serum proteins on HSA- and PLGA-based nanoparticles using SDS–PAGE and LC–MS

The behavior of nanosized drug carrier systems under cell culture conditions and therefore also the destiny in the body are highly influenced by the protein corona, which is formed upon entering a biological environment. Some of the adsorbed proteins, named opsonins, lead to a shortened plasma circulation half-life of the nanoparticles. Others are attributed to promote the transport of nanoparticles into other compartments of the body, just to mention two examples. Hence, detailed knowledge concerning the composition of the protein corona is of great importance. The aim of this work was to investigate the influence of the nanoparticle starting material and the surface modification on the composition of the adsorbed serum proteins in a cell culture environment. Therefore, positively charged nanoparticles based on the biodegradable polymer poly(dl-lactide-co-glycolide) (PLGA) stabilized with didodecyldimethylammonium bromide (DMAB) and negatively charged nanoparticles based on human serum albumin (HSA) were prepared and modified with hydrophilic polymers. By incubating the nanoparticles with fetal bovine serum (FBS) the adsorption of serum proteins on the colloidal system was investigated. Using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) a semi-quantitative analysis of the protein corona was performed and after enzymatic in-solution-digestion the adsorbed proteins were identified using high resolution LC-MS. Our study accentuates the influence of the core material, surface charge, and surface modification on the amount and nature of the adsorbed proteins. The combination of SDS-PAGE and LC-MS turns out to be a simple and reliable method to investigate the protein corona of nanoparticles.

Cytotoxicity and Fluorescence Visualization of Ergot Alkaloids in Human Cell Lines

The ergot alkaloids as secondary metabolites from fungi of the genus Claviceps are the focus of many investigations because of their pharmacological and toxicological properties. The main effects of ergot alkaloids are referred to an interaction with several receptor systems in the human body. It is well-known that ergot alkaloids are able to isomerize with one isomer being biologically active and one being only weakly active, whereas the activity is restricted to receptor interactions. Latest investigations have proven that ergot alkaloids also show cytotoxic effects and induce apoptosis in human primary cells. These effects seem to correlate with accumulation properties. It was the aim of our current study to determine such effects in cancer cell lines, because ergot derivatives are also used in tumor therapy. Our results confirm the apoptotic effects in two cancer cell lines (HepG2 and HT-29) in a high range, and accumulation measurements show an interesting correlation between the alkaloid concentration in the cell lysate of the receptor-inactive isomers and cytotoxicity. In addition, the strong accumulative effects were first visualized by fluorescence microscopy by taking advantage of the natural fluorescence properties of ergot alkaloids.

Asymmetric flow field-flow fractionation (AF4) for the quantification of nanoparticle release from tablets during dissolution testing.

Nanoparticles composed of poly(DL-lactide-co-glycolide) (PLGA) represent promising colloidal drug carriers for improved drug targeting. Although most research activities are focused on intravenous application of these carriers the peroral administration is described to improve bioavailability of poorly soluble drugs. Based on these insights the manuscript describes a model tablet formulation for PLGA-nanoparticles and especially its analytical characterisation with regard to a nanosized drug carrier. Besides physico-chemical tablet characterisation according to pharmacopoeias the main goal of the study was the development of a suitable analytical method for the quantification of nanoparticle release from tablets. An analytical flow field-flow fractionation (AF4) method was established and validated which enables determination of nanoparticle content in solid dosage forms as well as quantification of particle release during dissolution testing. For particle detection a multi-angle light scattering (MALS) detector was coupled to the AF4-system. After dissolution testing, the presence of unaltered PLGA-nanoparticles was successfully proved by dynamic light scattering and scanning electron microscopy.

Investigation of the metabolism of ergot alkaloids in cell culture by fourier transformation mass spectrometry.

Ergot alkaloids are known toxic secondary metabolites of the fungus Claviceps purpurea occurring in various grains, especially rye products. The liver is responsible for converting the ergot alkaloids into metabolites; however, the toxic impact of these end products of metabolism is still unknown. The aim of this study was to analyze the metabolism of ergot alkaloids in colon and liver cell lines (HT-29, HepG2), as well as in human primary renal cells (RPTEC). It was shown that cells in vitro are able to metabolize ergot alkaloids, forming a variety of metabolic compounds. Significant differences between the used cell types could be identified, and a suitable model system was established using HT-29 cells, performing an intensive metabolism to hydroxylated metabolites. The formed substances were analyzed by coupling of high-performance liquid chromatography with fluorescence detection and Fourier transformation mass spectrometry (HPLC-FLD-FTMS) as a powerful tool to identify known and unknown metabolites.

New Perspective in the Formulation and Characterization of Didodecyldimethylammonium Bromide (DMAB) Stabilized Poly(Lactic-co-Glycolic Acid) (PLGA) Nanoparticles

Over the last few decades the establishment of nanoparticles as suitable drug carriers with the transport of drugs across biological barriers such as the gastrointestinal barrier moved into the focus of many research groups. Besides drug transport such carrier systems are well suited for the protection of drugs against enzymatic and chemical degradation. The preparation of biocompatible and biodegradable nanoparticles based on poly(lactic-co-glycolic acid) (PLGA) is intensively described in literature, while especially nanoparticles with cationic properties show a promising increased cellular uptake. This is due to the electrostatic interaction between the cationic surface and the negatively charged lipid membrane of the cells. Even though several studies achieved the successful preparation of nanoparticles stabilized with the cationic surfactants such as didodecyldimethylammonium bromide (DMAB), in most cases insufficient attention was paid to a precise analytical characterization of the nanoparticle system. The aim of the present work was to overcome this deficit by presenting a new perspective in the formulation and characterization of DMAB-stabilized PLGA nanoparticles. Therefore these nanoparticles were carefully examined with regard to particle diameter, zeta potential, the effect of variation in stabilizer concentration, residual DMAB content, and electrolyte stability. Without any steric stabilization, the DMAB-modified nanoparticles were sensitive to typical electrolyte concentrations of biological environments due to compression of the electrical double layer in conjunction with a decrease in zeta potential. To handle this problem, the present study proposed two modifications to enable electrolyte stability. Both polyvinyl alcohol (PVA) and polyethylene glycol (PEG) modified DMAB-PLGA-nanoparticles were stable during electrolyte addition. Furthermore, in contrast to unmodified DMAB-PLGA-nanoparticles and free DMAB, such modifications led to a lower cytotoxic activity against Caco-2 cells. In conclusion this study offers a closer and critical point of view on preparation, in vitro and analytical evaluation of DMAB-stabilized PLGA nanoparticles for the physiological use.