3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole Induces Apoptosis and Necrosis with Activation of Different Caspases in Rat Splenocytes

Comparative metabolomic analysis of exudates of microcystin-producing and microcystin-free Microcystis aeruginosa strains

Cyanobacterial harmful algal blooms (cHABs) dominated by Microcystis aeruginosa threaten the ecological integrity and beneficial uses of lakes globally. In addition to producing hepatotoxic microcystins (MC), M. aeruginosa exudates (MaE) contain various compounds with demonstrated toxicity to aquatic biota. Previously, we found that the ecotoxicity of MaE differed between MC-producing and MC-free strains at exponential (E-phase) and stationary (S-phase) growth phases. However, the components in these exudates and their specific harmful effects were unclear. In this study, we performed untargeted metabolomics based on liquid chromatography-mass spectrometry to reveal the constituents in MaE of a MC-producing and a MC-free strain at both E-phase and S-phase. A total of 409 metabolites were identified and quantified based on their relative abundance. These compounds included lipids, organoheterocyclic compounds, organic acid, benzenoids and organic oxygen compounds. Multivariate analysis revealed that strains and growth phases significantly influenced the metabolite profile. The MC-producing strain had greater total metabolites abundance than the MC-free strain at S-phase, whereas the MC-free strain released higher concentrations of benzenoids, lipids, organic oxygen, organic nitrogen and organoheterocyclic compounds than the MC-producing strain at E-phase. Total metabolites had higher abundance in S-phase than in E- phase in both strains. Analysis of differential metabolites (DMs) and pathways suggest that lipids metabolism and biosynthesis of secondary metabolites were more tightly coupled to growth phases than to strains. Abundance of some toxic lipids and benzenoids DMs were significantly higher in the MC-free strain than the MC-producing one. This study builds on the understanding of MaE chemicals and their biotoxicity, and adds to evidence that non-MC-producing strains of cyanobacteria may also pose a threat to ecosystem health.

Antiapoptotic effects of dietary antioxidants towards N-nitrosopiperidine and N-nitrosodibutylamine-induced apoptosis in HL-60 and HepG2 cells

The aim of this work was to determine the effect of vitamin C, diallyl disulfide (DADS) and dipropyl disulfide (DPDS) towards N-nitrosopiperidine (NPIP) and N-nitrosodibutylamine (NDBA)-induced apoptosis in human leukemia (HL-60) and hepatoma (HepG2) cell lines using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. None of the vitamin C (5-50 microm), DADS and DPDS (1-5 microm) concentrations selected induced a significant percentage of apoptosis. In simultaneous treatments, vitamin C, DADS and DPDS reduced the apoptosis induced by NPIP and NDBA in HL-60 and HepG2 cells (around 70% of reduction). We also investigated its scavenging activities towards reactive oxygen species (ROS) produced by NPIP and NDBA using 2',7'-dichlorodihydrofluorescein diacetate in both cell lines. ROS production induced by both N-nitrosamine was reduced to control levels by vitamin C (5-50 microm) in a dose-dependent manner. However, DADS (5 microm) increased ROS levels induced by NPIP and NDBA in HL-60 (40 and 20% increase, respectively) and HepG2 cells (18% increase), whereas DPDS was more efficient scavenger of ROS at the lowest concentration (1 microm) in both HL-60 (52 and 25% reduction, respectively) and HepG2 cells (24% reduction). The data demonstrated that the scavenging ability of vitamin C and DPDS could contribute to inhibition of the NPIP- and NDBA-induced apoptosis. However, more than one mechanism, such as inhibition of phase I and/or induction of phase II enzymes, could be implicated in the protective effect of dietary antioxidants towards NPIP- and NDBA-induced apoptosis in HL-60 and HepG2 cells.

Investigating the caffeine effects in the yeast Saccharomyces cerevisiae brings new insights into the connection between TOR, PKC and Ras/cAMP signalling pathways

Caffeine is a natural purine analogue that elicits pleiotropic effects leading ultimately to cell's death by a largely uncharacterized mechanism. Previous works have shown that this drug induces a rapid phosphorylation of the Mpk1p, the final mitogen-activated protein (MAP) kinase of the Pkc1p-mediated cell integrity pathway. In this work, we showed that this phosphorylation did not necessitate the main cell wall sensors Wsc1p and Mid2p, but was abolished upon deletion of ROM2 encoding a GDP/GTP exchange factor of Rho1p. We also showed that the caffeine-induced phosphorylation of Mpk1p was accompanied by a negligible activation of its main downstream target, the Rlm1p transcription factor. This result was consolidated by the finding that the loss of RLM1 had no consequence on the increased resistance of caffeine-treated cells to zymolyase, indicating that the cell wall modification caused by this drug is largely independent of transcriptional activation of Rlm1p-regulated genes. Additionally, the transcriptional programme elicited by caffeine resembled that of rapamycin, a potent inhibitor of the TOR1/2 kinases. Consistent with this analysis, we found that the caffeine-induced phosphorylation of Mpk1p was lost in a tor1Delta mutant. Moreover, a tor1Delta mutant was, like mutants defective in components of the Pkc1p-Mpk1p cascade, highly sensitive to caffeine. However, the hypersensitivity of a tor1 null mutant to this drug was rescued neither by sorbitol nor by adenine, which was found to outcompete caffeine effects specially on mutants in the PKC pathway. Altogether, these data indicated that Tor1 kinase is a target of caffeine, whose inhibition incidentally activates the Pkc1p-Mpk1p cascade, and that the caffeine-dependent phenotypes are largely dependent on inhibition of Tor1p-regulated cellular functions. Finally, we found that caffeine provoked, in a Rom2p-dependent manner, a transient drop in intracellular levels of cAMP, that was followed by change in expression of genes implicated in Ras/cAMP pathway. This result may pose Rom2p as a mediator in the interplay between Tor1p and the Ras/cAMP pathway.

3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), a food-born carcinogenic heterocyclic amine, promotes nitric oxide production in murine macrophages

A heterocyclic amine, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) is one of the potent food-born dietary carcinogens derived mainly from burnt meat products. In the present study, we investigated the inductive effect of Trp-P-1 on nitric oxide (NO) production in murine macrophages since NO and its oxidized derivatives are directly involved in triggering mutagenesis and carcinogenesis. Our results show that Trp-P-1 induced mRNA expression of inducible NO synthase (iNOS) and NO production without co-stimulation in murine peritoneal macrophages and RAW 264.7 cells. Trp-P-1 further enhanced both iNOS mRNA expression and NO production, which were primarily induced by lipopolysaccharide (LPS). Electrophoretic mobility shift assay demonstrated that Trp-P-1, alone or in the presence of LPS, facilitated the DNA binding activity of the transcription factor NF-kappaB, and the trans-acting activity of the NF-kappaB was confirmative as determined by in vitro transfection and a luciferase reporter gene assay. Moreover, Trp-P-1 induced increasing intracellular reactive oxygen species (ROS), which play an important role in NF-kappaB activation. These results suggest that Trp-P-1 induces NO production mediated by an increased intracellular ROS, NF-kappaB activation, and subsequent iNOS gene expression.