The contribution of larval zebrafish transcriptomics to chemical risk assessment.

In Canada, the Canadian Environmental Protection Act (1999) requires human health and environmental risk assessments be conducted for new substances prior to their manufacture or import. While this toxicity data is historically obtained using rodents, in response to the international effort to eliminate animal testing, Health Canada is collaborating with the National Research Council (NRC) of Canada to develop a New Approach Method by refining existing NRC zebrafish models. The embryo/larval zebrafish model evaluates systemic (whole body) general toxicity which is currently unachievable with cell-based testing. The model is strengthened using behavioral, toxicokinetic and transcriptomic responses to assess non-visible indicators of toxicity following chemical exposure at sub-phenotypic concentrations. In this paper, the predictive power of zebrafish transcriptomics is demonstrated using two chemicals; Raloxifene and Resorcinol. Raloxifene exposure produced darkening of the liver and malformation of the nose/mandible, while Resorcinol exposure produced increased locomotor activity. Transcriptomic analysis correlated differentially expressed genes with the phenotypic effects and benchmark dose calculations determined that the transcriptomic Point of Departure (POD) occurred at subphenotypic concentrations. Correlating gene expression with apical (phenotypic) effects strengthens confidence in evaluation of chemical toxicity, thereby demonstrating the significant advancement that the larval zebrafish transcriptomics model represents in chemical risk assessment.

Assessing the Morphological and Behavioral Toxicity of Catechol Using Larval Zebrafish.

Catechol is a ubiquitous chemical used in the manufacturing of fragrances, pharmaceuticals and flavorants. Environmental exposure occurs in a variety of ways through industrial processes, during pyrolysis and in effluent, yet despite its prevalence, there is limited information regarding its toxicity. While the genotoxicity and gastric carcinogenicity of catechol have been described in depth, toxicological studies have potentially overlooked a number of other effects relevant to humans. Here, we have made use of a general and behavioral larval zebrafish toxicity assay to describe previously unknown catechol-based toxicological phenomena. Behavioral testing revealed catechol-induced hypoactivity at concentrations an order of magnitude lower than observable endpoints. Catechol exposure also resulted in punctate melanocytes with concomitant decreases in the expression of pigment production and regulation markers mitfa, mc1r and tyr. Because catechol is converted into a number of toxic metabolites by tyrosinase, an enzyme found almost exclusively in melanocytes, an evaluation of the effects of catechol on these cells is critical to evaluating the safety of this chemical. This work provides insights into the toxic nature of catechol and highlights the benefits of the zebrafish larval testing platform in being able to dissect multiple aspects of toxicity with one model.

Comparative toxicological assessment of 2 bisphenols using a systems approach: evaluation of the behavioral and transcriptomic responses of Danio rerio to bisphenol A and tetrabromobisphenol A.

The zebrafish (Danio rerio) is becoming a critical component of new approach methods (NAMs) in chemical risk assessment. As a whole organism in vitro NAM, the zebrafish model offers significant advantages over individual cell-line testing, including toxicokinetic and toxicodynamic competencies. A transcriptomic approach not only allows for insight into mechanism of action for both apical endpoints and unobservable adverse outcomes, but also changes in gene expression induced by lower, environmentally relevant concentrations. In this study, we used a larval zebrafish model to assess the behavioral and transcriptomic alterations caused by subphenotypic concentrations of 2 chemicals with the same structural backbone, the endocrine-disrupting chemicals bisphenol A and tetrabromobisphenol A. Following assessment of behavioral toxicity, we used a transcriptomic approach to identify molecular pathways associated with previously described phenotypes. We also determined the transcriptomic point of departure for each chemical by modeling gene expression changes as continuous systems which allows for the identification of a single concentration at which toxic effects can be predicted. This can then be investigated with confirmatory cell-based testing in an integrated approach to testing and assessment to determine risk to human health and the environment with greater confidence. This paper demonstrates the impact of using a multi-faceted approach for evaluating the physiological and neurotoxic effects of exposure to structurally related chemicals. By comparing phenotypic effects with transcriptomic outcomes, we were able to differentiate, characterize, and rank the toxicities of related bisphenols, which demonstrates methodological advantages unique to the larval zebrafish NAM.

Identification of minimum essential therapeutic mixtures from cannabis plant extracts by screening in cell and animal models of Parkinson's disease.

Medicinal cannabis has shown promise for the symptomatic treatment of Parkinson's disease (PD), but patient exposure to whole plant mixtures may be undesirable due to concerns around safety, consistency, regulatory issues, and psychoactivity. Identification of a subset of components responsible for the potential therapeutic effects within cannabis represents a direct path forward for the generation of anti-PD drugs. Using an in silico database, literature reviews, and cell based assays, GB Sciences previously identified and patented a subset of five cannabinoids and five terpenes that could potentially recapitulate the anti-PD attributes of cannabis. While this work represents a critical step towards harnessing the anti-PD capabilities of cannabis, polypharmaceutical drugs of this complexity may not be feasible as therapeutics. In this paper, we utilize a reductionist approach to identify minimal essential mixtures (MEMs) of these components that are amenable to pharmacological formulation. In the first phase, cell-based models revealed that the cannabinoids had the most significant positive effects on neuroprotection and dopamine secretion. We then evaluated the ability of combinations of these cannabinoids to ameliorate a 6-hydroxydopmamine (OHDA)-induced change in locomotion in larval zebrafish, which has become a well-established PD disease model. Equimolar mixtures that each contained three cannabinoids were able to significantly reverse the OHDA mediated changes in locomotion and other advanced metrics of behavior. Additional screening of sixty-three variations of the original cannabinoid mixtures identified five highly efficacious mixtures that outperformed the original equimolar cannabinoid MEMs and represent the most attractive candidates for therapeutic development. This work highlights the strength of the reductionist approach for the development of ratio-controlled, cannabis mixture-based therapeutics for the treatment of Parkinson's disease.

Reciprocal expression of integration host factor and HU in the developmental cycle and infectivity of Legionella pneumophila.

Legionella pneumophila is an intracellular parasite of protozoa that differentiates late in infection into metabolically dormant cysts that are highly infectious. Regulation of this process is poorly understood. Here we report that the small DNA binding regulatory proteins integration host factor (IHF) and HU are reciprocally expressed over the developmental cycle, with HU expressed during exponential phase and IHF expressed postexponentially. To assess the role of these regulatory proteins in development, chromosomal deletions were constructed. Single (ihfA or ihfB) and double deletion (Deltaihf) IHF mutants failed to grow in Acanthamoeba castellanii unless complemented in trans when expressed temporally from the ihfA promoter but not under P(tac) (isopropyl-beta-d-thiogalactopyranoside). In contrast, IHF mutants were infectious for HeLa cells, though electron microscopic examination revealed defects in late-stage cyst morphogenesis (thickened cell wall, intracytoplasmic membranes, and inclusions of poly-beta-hydroxybutyrate), and were depressed for the developmental marker MagA. Green fluorescent protein promoter fusion assays indicated that IHF and the stationary-phase sigma factor RpoS were required for full postexponential expression of magA. Finally, defects in cyst morphogenesis noted for Deltaihf mutants in HeLa cells correlated with a loss of both detergent resistance and hyperinfectivity compared with results for wild-type cysts. These studies establish IHF and HU as markers of developmental stages and show that IHF function is required for both differentiation and full virulence of L. pneumophila in natural amoebic hosts.

Molecular cloning, ontogeny and tissue distribution of zebrafish (Danio rerio) prohormone convertases: pcsk1 and pcsk2.

Prohormone convertase subtilisin/kexin (PCSK) enzymes are a family of nine related serine proteases, found in a multitude of tissues, and responsible for the maturation of a variety of protein and peptide precursors. Pcsk1 and Pcsk2 are found within dense core secretory granules in endocrine and neuroendocrine cells and are responsible for cleaving several hormones and neuropeptide precursors. In this work, we cloned and sequenced the cDNA of pcsk1 and pcsk2 from zebrafish (Danio rerio). pcsk1 is a 2268bp ORF, whose 755 amino acid protein product is identical to that predicted from the genome sequence. pcsk2 is a 1941bp ORF, encoding a 646 amino acid peptide. Both Pcsk1 and Pcsk2 display high degrees of similarity to their counterparts in other species, including the conservation of the catalytic triad and other essential residues. The brain contained the highest expression levels of both pcsk1 (1.49+/-0.21) (displayed as ratio to EF-1a), and pcsk2 (0.23+/-0.04). Both transcripts were also detectable in the fore, mid and distal gut. pcsk1 and 2 were detectable at 4.5h post-fertilization, and while pcsk1 expression increased throughout development (0.12+/-0.01 maximum at 3 days post-fertilization), pcsk2 expression was highest at day 5 post-fertilization (0.03+/-0.01), and decreased prior. For the first time, we have identified and characterized a pcsk1 transcript in fish. We have also identified and characterized the pcsk2 transcript in zebrafish, and have assessed the tissue distribution and ontogeny of both.

Analysis of the Uptake, Metabolism, and Behavioral Effects of Cannabinoids on Zebrafish Larvae.

The Cannabis sativa plant contains numerous phytocannabinoids and terpenes with known or potential biological activity. For decades, plant breeders have been breeding the Cannabis plant to control for a desired ratio of the major cannabinoids. A high-throughput in vivo model to understand the relationship between the chemical composition of different strains and their therapeutic potential then becomes of value. Measuring changes in the behavioral patterns of zebrafish larvae is an established model with which to test the biological activity of neuroactive compounds. However, there is currently little information regarding the uptake kinetics and metabolism of compounds by larvae. In this study, we chose to compare the uptake kinetics and metabolism of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) alone or in combination with their effects on larval behavior. We have shown that both compounds have distinct behavioral patterns and concentration response profiles. Additionally, the uptake kinetics observed for each compound appears to correlate with the change in behavior observed in the behavioral assays. When combinations of THC and CBD were tested there were shifts in both the behavioral activity and the uptake kinetics of each compound compared with when they were tested alone. Finally, the THC/CBD-derived metabolites detected in the larvae are similar to those found in mammalian systems. This study thus provides a model for further testing of additional cannabinoids and potentially plant extracts.

Use of the zebrafish larvae as a model to study cigarette smoke condensate toxicity.

The smoking of tobacco continues to be the leading cause of premature death worldwide and is linked to the development of a number of serious illnesses including heart disease, respiratory diseases, stroke and cancer. Currently, cell line based toxicity assays are typically used to gain information on the general toxicity of cigarettes and other tobacco products. However, they provide little information regarding the complex disease-related changes that have been linked to smoking. The ethical concerns and high cost associated with mammalian studies have limited their widespread use for in vivo toxicological studies of tobacco. The zebrafish has emerged as a low-cost, high-throughput, in vivo model in the study of toxicology. In this study, smoke condensates from 2 reference cigarettes and 6 Canadian brands of cigarettes with different design features were assessed for acute, developmental, cardiac, and behavioural toxicity (neurotoxicity) in zebrafish larvae. By making use of this multifaceted approach we have developed an in vivo model with which to compare the toxicity profiles of smoke condensates from cigarettes with different design features. This model system may provide insights into the development of smoking related disease and could provide a cost-effective, high-throughput platform for the future evaluation of tobacco products.

Prohormone processing in zebrafish.

Proprotein convertases (PCs) are secretory proteolytic enzymes that activate precursor proteins into biologically active forms by limited proteolysis at one or multiple internal sites. PCs are implicated in the processing of multiple protein precursors, including hormones, proteases, growth factors, angiogenic factors, and receptors. PCs have been linked recently to various pathologies such as Alzheimer's disease, tumorigenesis, and infections. The zebrafish has emerged as an attractive model for studying the role of PCs not only in substrate production but also in development. Herein we describe methods that are used to characterize DNA sequences of PCs in zebrafish, as well as to evaluate the ontogeny and tissue distribution of their transcripts. We also provide information on the morpholino-mediated knockdown of proprotein convertases.

The zebrafish embryo as a tool for screening and characterizing pleurocidin host-defense peptides as anti-cancer agents.

The emergence of multidrug-resistant cancers and the lack of targeted therapies for many cancers underscore an unmet need for new therapeutics with novel modes of action towards cancer cells. Host-defense peptides often exhibit selective cytotoxicity towards cancer cells and show potential as anti-cancer therapeutics. Here, we screen 26 naturally occurring variants of the peptide pleurocidin for cytotoxic and anti-cancer activities, and investigate the underlying mechanism of action. Cytotoxicities were assessed in vitro using cell-based assays and in vivo using zebrafish embryos. Morphological changes were assessed by both transmission and scanning electron microscopy, and functional assays were performed on zebrafish embryos to investigate the mechanism of cell death. A total of 14 peptides were virtually inactive against HL60 human leukemia cells, whereas 12 caused >50% death at ≤32 µg/ml. Morphological changes characteristic of oncosis were evident by electron microscopy after only 1 minute of treatment with 32 µg/ml of variant NRC-03. Only two peptides were hemolytic. Four peptides showed no toxicity towards zebrafish embryos at the highest concentration tested (25 µM; ∼64 µg/ml) and one peptide was highly toxic, killing 4-hour-post-fertilization (hpf) embryos immediately after exposure to 1 µM peptide. Four other peptides killed embryos after 24 hours of exposure at 1 µM. Most peptides caused mortality at one or more developmental stages only after continuous exposure (24 hours) with higher lethal doses (≥5 µM). Pleurocidin NRC-03 bound to embryos and induced the release of superoxide, caused an increase in the number of TUNEL-positive nuclei, and caused membrane damage and the loss of embryonic epithelial integrity, marked by the exclusion of cells from the outer epithelium and the appearance of F-actin within the circumferential cells of the repair site. Our results indicate that specific pleurocidin variants are attractive cancer-selective agents that selectively induce cell death in target cells but leave non-target cells such as erythrocytes and non-transformed cells unaffected.

Tissue distribution and effects of fasting and obesity on the ghrelin axis in mice.

Ghrelin is a 28 amino acid peptide hormone derived from the 117 amino acid proghrelin, following cleavage by proprotein convertase 1 (PC1). In this study, we comprehensively assessed the tissue distribution and the effect of fasting and obesity on preproghrelin, Exon-4D, PC1 and GOAT expression and proghrelin-derived peptide (PGDP) secretion. The stomach was the major source of preproghrelin expression and PDGPs, followed by the small intestine. The remaining peripheral tissues (including the brain and pancreas) contained negligible expression levels. We detected obestatin in all stomach proghrelin cells, however, 22% of proghrelin cells in the small intestine did not express obestatin. There were strain differences in ghrelin secretion in response to fasting between CD1 and C57BL/6 mice. After a 24 hour-fast, CD1 mice had increased plasma levels of total ghrelin and obestatin with no change in preproghrelin mRNA or PGDP tissues levels. C57BL/6 mice showed a different response to a 24 hour-fast having increased proghrelin mRNA expression, stomach acylated ghrelin peptide and no change in plasma obestatin in C57BL/6 mice. In obese mice (ob/ob and diet-induced obesity (DIO)) there was a significant increase in preproghrelin mRNA levels while tissue and plasma PGDP levels were significantly reduced. Fasting did not affect PGDP in obese mice. Obese models displayed differences in GOAT expression, which was elevated in DIO mice, but reduced in ob/ob mice. We did not find co-localization of the leptin receptor in ghrelin expressing stomach cells, ruling out a direct effect of leptin on stomach ghrelin synthesis and secretion.

Antiparasitic drug nitazoxanide inhibits the pyruvate oxidoreductases of Helicobacter pylori, selected anaerobic bacteria and parasites, and Campylobacter jejuni.

Nitazoxanide (NTZ) exhibits broad-spectrum activity against anaerobic bacteria and parasites and the ulcer-causing pathogen Helicobacter pylori. Here we show that NTZ is a noncompetitive inhibitor (K(i), 2 to 10 microM) of the pyruvate:ferredoxin/flavodoxin oxidoreductases (PFORs) of Trichomonas vaginalis, Entamoeba histolytica, Giardia intestinalis, Clostridium difficile, Clostridium perfringens, H. pylori, and Campylobacter jejuni and is weakly active against the pyruvate dehydrogenase of Escherichia coli. To further mechanistic studies, the PFOR operon of H. pylori was cloned and overexpressed in E. coli, and the multisubunit complex was purified by ion-exchange chromatography. Pyruvate-dependent PFOR activity with NTZ, as measured by a decrease in absorbance at 418 nm (spectral shift from 418 to 351 nm), unlike the reduction of viologen dyes, did not result in the accumulation of products (acetyl coenzyme A and CO(2)) and pyruvate was not consumed in the reaction. NTZ did not displace the thiamine pyrophosphate (TPP) cofactor of PFOR, and the 351-nm absorbing form of NTZ was inactive. Optical scans and (1)H nuclear magnetic resonance analyses determined that the spectral shift (A(418) to A(351)) of NTZ was due to protonation of the anion (NTZ(-)) of the 2-amino group of the thiazole ring which could be generated with the pure compound under acidic solutions (pK(a) = 6.18). We propose that NTZ(-) intercepts PFOR at an early step in the formation of the lactyl-TPP transition intermediate, resulting in the reversal of pyruvate binding prior to decarboxylation and in coordination with proton transfer to NTZ. Thus, NTZ might be the first example of an antimicrobial that targets the "activated cofactor" of an enzymatic reaction rather than its substrate or catalytic sites, a novel mechanism that may escape mutation-based drug resistance.

A 65-kilobase pathogenicity island is unique to Philadelphia-1 strains of Legionella pneumophila.

Nucleotide sequence analysis of an approximately 80-kb genomic region revealed an approximately 65-kb locus that bears hallmarks of a pathogenicity island. This locus includes homologues of a type IV secretion system, mobile genetic elements, and known virulence factors. Comparative studies with other Legionella pneumophila strains and serogroups indicated that this approximately 65-kb locus is unique to L. pneumophila serogroup 1 Philadelphia-1 strains.