Crosstalk of tight junction components with signaling pathways. Biochim Biophys Acta. 2008;1778:729-756. [PMID: 17950242 DOI: 10.1016/j.bbamem.2007.08.018]

The control of vascular integrity by endothelial cell junctions: molecular basis and pathological implications

Human pathologies such as vascular malformations, hemorrhagic stroke, and edema have been associated with defects in the organization of endothelial cell junctions. Understanding the molecular basis of these diseases requires different integrated approaches which include basic cell biology, clinical studies, and studies in animal models such as mice and zebrafish. In this review we discuss recent findings derived from these approaches and their possible integration in a common picture.

The investigation of synovial genomic targets of bucillamine with microarray technique

OBJECTIVE

To identify the molecular mechanisms of bucillamine activity, global gene expression analysis and pathway analysis were conducted using IL-1 beta-stimulated human fibroblast-like synovial cells (FLS).

METHODS

Normal human FLS were treated with IL-1 beta in the presence or absence of 10 and 100 microM bucillamine for 6 h. Total RNA was extracted and global gene expression levels were detected using a 44 k human whole genome array. Data were analyzed using Ingenuity pathway analysis.

RESULTS

Numerous pathways were activated by IL-1 beta stimulation. At both concentrations, bucillamine suppressed nine signal pathways stimulated by IL-1 beta.

CONCLUSIONS

Bucillamine effectively inhibited fibroblast growth factor (FGF) signaling and tight junction signaling activated by IL-1 beta in FLS. Suppression of these signal pathways may correlate with the pharmacologic mechanisms of bucillamine. In particular, the suppression of FGF signaling by bucillamine is remarkable because the activation of FGF signaling may be involved in rheumatoid arthritis pathology.

TNFalpha up-regulates claudin-2 expression in epithelial HT-29/B6 cells via phosphatidylinositol-3-kinase signaling

Our aim has been to characterize the molecular mechanisms regulating the expression of the channel-forming tight-junctional protein claudin-2 in response to the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFalpha), which is elevated, for example, in active Crohn's disease. TNFalpha caused an 89% decrease of the paracellular resistance in colonic HT-29/B6 cells, whereas transcellular resistance was unaltered. The claudin-2 protein level was increased by TNFalpha without changes in subcellular tight-junctional protein localization as revealed by confocal laser scanning microscopy. Enhanced gene expression was identified as the source of this increase, since claudin-2-specific mRNA and promoter activity was elevated, whereas mRNA stability remained unaltered. Specific inhibitors and phospho-specific antibodies revealed that the increased gene expression of claudin-2 after TNFalpha treatment was mediated by the phosphatidylinositol-3-kinase pathway. Thus, the up-regulation of claudin-2 by TNFalpha is attributable to the regulation of the expression of the gene, as a result of which epithelial barrier function is disturbed, for example, during chronic intestinal inflammation.

Phosphoinositide 3-kinases in cell migration

Cell migration is essential for many biological processes in animals and is a complex highly co-ordinated process that involves cell polarization, actin-driven protrusion and formation and turnover of cell adhesions. The PI3K (phosphoinositide 3-kinase) family of lipid kinases regulate cell migration in many different cell types, both through direct binding of proteins to their lipid products and indirectly through crosstalk with other pathways, such as Rho GTPase signalling. Emerging evidence suggests that the involvement of PI3Ks at different stages of migration varies even within one cell type, and is dependent on the combination of external stimuli, as well as on the signalling status of the cell. In addition, it appears that different PI3K isoforms have distinct roles in cell polarization and migration. This review describes how PI3K signalling is regulated by pro-migratory stimuli, and the diverse ways in which PI3K-mediated signal transduction contributes to different aspects of cell migration.

Reprint of "The role of cytoskeleton in the regulation of vascular endothelial barrier function" [Microvascular Research 76 (2008) 202-207]

The cytoskeleton is vital to the function of virtually all cell types in the organism as it is required for cell division, cell motility, endo- or exocytosis and the maintenance of cell shape. Endothelial cells, lining the inner surface of the blood vessels, exploit cytoskeletal elements to ensure the integrity of cell monolayer in quiescent endothelium, and to enable the disintegration of the formed barrier in response to various agonists. Vascular permeability is defined by the combination of transcellular and paracellular pathways, with the latter being a major contributor to the inflammation-induced barrier dysfunction. This review will analyze the cytoskeletal elements, which reorganization affects endothelial permeability, and emphasize signaling mechanisms with barrier-protective or barrier-disruptive potential.

Prostaglandin E2-EP1 and EP2 receptor signaling promotes apical junctional complex disassembly of Caco-2 human colorectal cancer cells

BACKGROUND

The apical junctional complex (AJC) is a dynamic structure responsible to maintain epithelial cell-cell adhesions and it plays important functions such as, polarity, mechanical integrity, and cell signaling. Alteration of this complex during pathological events leads to an impaired epithelial barrier by perturbation of the cell-cell adhesion system. Although clinical and experimental data indicate that prostaglandin E(2) (PGE2) plays a critical function in promoting cell motility and cancer progression, little is known concerning its role in AJC disassembly, an event that takes place at the beginning of colorectal tumorigenesis. Using Caco-2 cells, a cell line derived from human colorectal cancer, we investigated the effects of prostaglandin E(2) (PGE(2)) treatment on AJC assembly and function.

RESULTS

Exposition of Caco-2 cells to PGE(2) promoted differential alteration of AJC protein distribution, as evidenced by immunofluorescence and immunoblotting analysis and impairs the barrier function, as seen by a decrease in the transepithelial electric resistance and an increase in the permeability to ruthenium red marker. We demonstrated the involvement of EP1 and EP2 prostaglandin E(2) receptor subtypes in the modulation of the AJC disassembly caused by prostanoid. Furthermore, pharmacological inhibition of protein kinase-C, but not PKA and p38MAPK significantly prevented the PGE(2) effects on the AJC disassembly.

CONCLUSION

Our findings strongly suggest a central role of Prostaglandin E2-EP1 and EP2 receptor signaling to mediate AJC disassembly through a mechanism that involves PKC and claudin-1 as important target for the TJ-related effects in human colorectal cancer cells (Caco-2).

A lipid-protein hybrid model for tight junction

The epithelial tight junction (TJ) was first described ultrastructurally as a fusion of the outer lipid leaflets of the adjoining cell membrane bilayers (hemifusion). The discovery of an increasing number of integral TJ and TJ-associated proteins has eclipsed the original lipid-based model with the wide acceptance of a protein-centric model for the TJ. In this review, we stress the importance of lipids in TJ structure and function. A lipid-protein hybrid model accommodates a large body of information supporting the lipidic characteristics of the TJ, harmonizes with the accumulating evidence supporting the TJ as an assembly of lipid rafts, and focuses on an important, but relatively unexplored, field of lipid-protein interactions in the morphology, physiology, and pathophysiology of the TJ.

Ca(2+)-dependent protein kinase C isoforms are critical to estradiol 17beta-D-glucuronide-induced cholestasis in the rat

The endogenous estradiol metabolite estradiol 17beta-D-glucuronide (E(2)17G) induces an acute cholestasis in rat liver coincident with retrieval of the canalicular transporters bile salt export pump (Bsep, Abcc11) and multidrug resistance-associated protein 2 (Mrp2, Abcc2) and their associated loss of function. We assessed the participation of Ca(2+)-dependent protein kinase C isoforms (cPKC) in the cholestatic manifestations of E(2)17G in perfused rat liver (PRL) and in isolated rat hepatocyte couplets (IRHCs). In PRL, E(2)17G (2 mumol/liver; intraportal, single injection) maximally decreased bile flow, total glutathione, and [(3)H] taurocholate excretion by 61%, 62%, and 79%, respectively; incorporation of the specific cPKC inhibitor Gö6976 (500 nM) in the perfusate almost totally prevented these decreases. In dose-response studies using IRHC, E(2)17G (3.75-800 muM) decreased the canalicular vacuolar accumulation of the Bsep substrate cholyl-lysylfluorescein with an IC50 of 54.9 +/- 7.9 muM. Gö6976 (1 muM) increased the IC50 to 178.4 +/- 23.1 muM, and similarly prevented the decrease in the canalicular vacuolar accumulation of the Mrp2 substrate, glutathione methylfluorescein. Prevention of these changes by Gö6976 coincided with complete protection against E(2)17G-induced retrieval of Bsep and Mrp2 from the canalicular membrane, as detected both in the PRL and IRHC. E(2)17G also increased paracellular permeability in IRHC, which was only partially prevented by Gö6976. The cPKC isoform PKCalpha, but not the Ca(2+)-independent PKC isoform, PKCepsilon, translocated to the plasma membrane after E(2)17G administration in primary cultured rat hepatocytes; Gö6976 completely prevented this translocation, thus indicating specific activation of cPKC. This is consistent with increased autophosphorylation of cPKC by E(2)17G, as detected via western blotting.

CONCLUSION

Our findings support a central role for cPKC isoforms in E(2)17G-induced cholestasis, by inducing both transporter retrieval from the canalicular membrane and opening of the paracellular route.

Tight junctions as targets of infectious agents

The epithelial barrier is a critical border that segregates luminal material from entering tissues. Essential components of this epithelial fence are physical intercellular structures termed tight junctions. These junctions use a variety of transmembrane proteins coupled with cytoplasmic adaptors, and the actin cytoskeleton, to attach adjacent cells together thereby forming intercellular seals. Breaching of this barrier has profound effects on human health and disease, as barrier deficiencies have been linked with the onset of inflammation, diarrhea generation and pathogenic effects. Although tight junctions efficiently restrict most microbes from penetrating into deeper tissues and contain the microbiota, some pathogens have developed specific strategies to alter or disrupt these structures as part of their pathogenesis, resulting in either pathogen penetration, or other consequences such as diarrhea. Understanding the strategies that microorganisms use to commandeer the functions of tight junctions is an active area of research in microbial pathogenesis. In this review we highlight and overview the tactics bacteria and viruses use to alter tight junctions during disease. Additionally, these studies have identified novel tight junction protein functions by using pathogens and their virulence factors as tools to study the cell biology of junctional structures.

The junctional integrity of epithelial cells is modulated by Pseudomonas aeruginosa quorum sensing molecule through phosphorylation-dependent mechanisms

In Pseudomonas aeruginosa, cell-cell communication based on acyl-homoserine lactone (HSL) quorum sensing molecules is known to coordinate the production of virulence factors and biofilms by the bacterium. Incidentally, these bacterial signals can also modulate mammalian cell behaviour. We report that 3O-C(12)-HSL can disrupt adherens junctions in human epithelial Caco-2 cells as evidenced by a reduction of the expression and distribution of E-cadherin and beta-catenin. Using co-immunoprecipitation we also found that P. aeruginosa 3O-C(12)-HSL-treatment resulted in tyrosine hyperphosphorylation of E-cadherin, beta-catenin, occludin and ZO-1. Similarly, serine and threonine residues of E-cadherin and ZO-1 became more phosphorylated after 3O-C(12)-HSL treatment. On the contrary, occludin and beta-catenin underwent dephosphorylation on serine and threonine residues after exposition of 3O-C(12)-HSL. These changes in the phosphorylation state were paralleled by alteration in the structure of junction complexes and increased paracellular permeability. Moreover, pre-treatment of the Caco-2 cells with protein phosphatase and kinase inhibitors prevented 3O-C(12)-HSL-induced changes in paracellular permeability and interactions between occludin-ZO-1 and the E-cadherin-beta-catenin. These findings clearly suggest that an alteration in the phosphorylation status of junction proteins are involved in the changes in cell junction associations and enhanced paracellular permeability, and that bacterial signals are indeed sensed by the host cells.

Claudin Tight Junction Proteins: Novel Aspects in Paracellular Transport

Claudins are essential components of the intercellular tight junction and major determinants of paracellular solute fluxes across epithelia and endothelia. Many members of this family display a distinct charge or size specificity, whereas others render the epithelium impermeable to transport. Due to intercellular localization, claudin-mediated transport processes are passive and driven by an electrochemical gradient. In epithelial tissues, claudins exhibit a temporal–spatial expression pattern corresponding with regional and local solute transport profiles. Whereas paracellular transport mechanisms in organs such as intestine and kidney have been extensively investigated, little is known about the molecular mechanisms determining solute transport in the peritoneum, and thus the determinants of peritoneal dialysis. Given the ubiquitous expression of claudins in endothelia and epithelia, it is predictable that claudins also contribute to pore formation and determination in the peritoneum, and that they are involved in solute flux. Therefore, we review the basic characteristics of claudin family members and their function as exemplified in renal tubular transport and give an outlook to what extent claudin family members might be of importance for solute reabsorption across the peritoneal membrane.

Organization and signaling of endothelial cell-to-cell junctions in various regions of the blood and lymphatic vascular trees

Adhesive intercellular junctions between endothelial cells are formed by tight junctions and adherens junctions. In addition to promoting cell-to-cell adhesion, these structures regulate paracellular permeability, contact inhibition of endothelial cell growth, cell survival, and maintenance of cell polarity. Furthermore, adherens junctions are required for the correct organization of new vessels during embryo development or during tissue proliferation in the adult. Extensive research on cultured epithelial and endothelial cells has resulted in the identification of many molecular components of tight junctions and adherens junctions. Such studies have revealed the complexity of these structures, which are formed by membrane-associated adhesion proteins and a network of several intracellular signaling partners. This review focuses on the structural organization of junctional structures and their functional interactions in the endothelium of blood vessels and lymphatics. We emphasize the way that these structures regulate endothelial cell homeostasis by transferring specific intracellular signals and by modulating activation and signaling of growth factor receptors.

Biology of claudins

Claudins are a family of tight junction membrane proteins that regulate paracellular permeability of epithelia, likely by forming the lining of the paracellular pore. Claudins are expressed throughout the renal tubule, and mutations in two claudin genes are now known to cause familial hypercalciuric hypomagnesemia with nephrocalcinosis. In this review, we discuss recent advances in our understanding of the physiological role of various claudins in normal kidney function, and in understanding the fundamental biology of claudins, including the molecular basis for selectivity of permeation, claudin interactions in tight junction formation, and regulation of claudins by protein kinases and other intracellular signals.

Age-dependent responses of glial cells and leptomeninges during systemic inflammation

Systemic inflammation causes the age-dependent differential glial responses, but little is known about how age influences the barrier function of leptomeninges during systemic inflammation. This study was conducted to elucidate the relationship between the glial responses and the levels of tight junction proteins, occludin and ZO-1, in adjuvant arthritis (AA) rats. In young AA rats, microglia and astrocytes localized to the proximity of the leptomeninges expressed interleukin (IL)-10 and transforming growth factor (TGF)-beta1. The level of occludin significantly increased. In middle-aged AA rats, however, glial cells expressed IL-1beta and prostaglandin E(2) (PGE(2))-synthesizing enzymes. Furthermore, occludin and ZO-1 significantly decreased, resulting in the increased permeability of leptomeninges. In the cultured leptomeningeal cells, IL-1beta and PGE(2) caused a marked loss of occludin and ZO-1, respectively. Pretreatment with IL-10 and TGF-beta1 significantly antagonized their effects. These findings establish that age strongly influences the barrier functions of the leptomeninges through the age-dependent differential glial responses during systemic inflammation.

Peroxynitrite-dependent activation of protein phosphatase type 2A mediates microvascular endothelial barrier dysfunction

Aims

We investigated the mechanism by which proinflammatory stimulation induces microvascular endothelial barrier dysfunction. Since protein phosphatase type 2A (PP2A) can mediate paracellular leak and can be inactivated by tyrosine phosphorylation in its catalytic subunit (PP2Ac), we hypothesized that microvascular endothelial cells exposed to proinflammatory stimulation produce peroxynitrite that nitrates PP2Ac, and this nitration inhibits tyrosine phosphorylation of PP2Ac and thereby increases PP2A activity to mediate endothelial barrier dysfunction.

Methods and results

Exposure of mouse skeletal muscle microvascular endothelial cell monolayers to a proinflammatory stimulus [lipopolysaccharide (LPS) + interferon (IFN)γ] increased permeability to albumin, and this barrier dysfunction was attenuated by PP2A inhibitor okadaic acid or by siRNA (small interfering ribonucleic acid) against PP2Ac. LPS + IFNγ increased synthesis of peroxynitrite precursors nitric oxide (NO) and superoxide by inducible NO synthase (iNOS) and NADPH oxidase, respectively. PP2Ac immunoprecipitates isolated from LPS + IFNγ- or peroxynitrite-treated cells showed increased tyrosine nitration, decreased tyrosine phosphorylation and increased phosphatase activity. 3-Nitrotyrosine immunoprecipitates from LPS + IFNγ-stimulated cells also exhibited increased PP2A activity. Further, iNOS inhibitor 1400W, iNOS deficiency, NADPH oxidase inhibitor apocynin, or p47phox deficiency prevented the increase in PP2A activity and preserved barrier function.

Conclusion

LPS + IFNγ stimulates endothelial cells to produce iNOS-derived NO and NADPH oxidase-derived superoxide, which form peroxynitrite that nitrates tyrosine residues in PP2Ac and inhibits their phosphorylation. This nitration in PP2Ac is correlated with PP2A activation that mediates endothelial barrier dysfunction.

Tight junction protein ZO-2 expression and relative function of ZO-1 and ZO-2 during mouse blastocyst formation

Apicolateral tight junctions (TJs) between epithelial cells are multiprotein complexes regulating membrane polarity and paracellular transport and also contribute to signalling pathways affecting cell proliferation and gene expression. ZO-2 and other ZO family members form a sub-membranous scaffold for binding TJ constituents. We investigated ZO-2 contribution to TJ biogenesis and function during trophectoderm epithelium differentiation in mouse preimplantation embryos. Our data indicate that ZO-2 is expressed from maternal and embryonic genomes with maternal ZO-2 protein associated with nuclei in zygotes and particularly early cleavage stages. Embryonic ZO-2 assembled at outer blastomere apicolateral junctional sites from the late 16-cell stage. Junctional ZO-2 first co-localised with E-cadherin in a transient complex comprising adherens junction and TJ constituents before segregating to TJs after their separation from the blastocyst stage (32-cell onwards). ZO-2 siRNA microinjection into zygotes or 2-cell embryos resulted in specific knockdown of ZO-2 mRNA and protein within blastocysts. Embryos lacking ZO-2 protein at trophectoderm TJs exhibited delayed blastocoel cavity formation but underwent normal cell proliferation and outgrowth morphogenesis. Quantitative analysis of trophectoderm TJs in ZO-2-deficient embryos revealed increased assembly of ZO-1 but not occludin, indicating ZO protein redundancy as a compensatory mechanism contributing to the mild phenotype observed. In contrast, ZO-1 knockdown, or combined ZO-1 and ZO-2 knockdown, generated a more severe inhibition of blastocoel formation indicating distinct roles for ZO proteins in blastocyst morphogenesis.

A cross-link between protein kinase A and Rho-family GTPases signaling mediates cell-cell adhesion and actin cytoskeleton organization in epithelial cancer cells

Disassembly of the apical junctional complex (AJC) together with actin cytoskeleton alterations are among the initial events for the development of epithelial cancer. The cell signaling pathways for these processes have been analyzed separately. However, the existence of a link between these two events has not been defined. In this study, using the extracellular calcium depletion model, we analyzed the signaling pathways regulating AJC disassembly together with actin cytoskeleton organization in colon adenocarcinoma cells (Caco-2). Changes in the location of AJC proteins were examined by immunofluorescence and immunoblotting, and tight junction (TJ) functionality was observed by measuring the transepithelial electrical resistance and permeation to ruthenium red. The actin cytoskeleton was stained with rhodamine-phalloidin and analyzed by confocal microscopy. Rho-GTPase activation was assessed by its translocation to the membrane (a hallmark of RhoA activation) and immunoblotting. Pharmacological inhibition of protein kinase A (PKA) with H-89 [N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide)] prevented AJC disassembly and actin disorganization at the apical and medial regions caused by calcium depletion. Rho inhibition using toxin A induced AJC disassembly and actin cytoskeleton reorganization. Y-27632 [(R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-ciclohexanecarboxamide], a Rho-associated kinase inhibitor, reversed redistribution of E-cadherin, but not of TJ proteins and actin disorganization caused by calcium depletion. Calcium depletion and forskolin treatment caused activation of Rho, as evidenced by their translocation to the membrane, an event concurrent to Rac and RhoGDI translocation, and this effect was also reverted by H-89. Thus, our findings demonstrate a central role of a regulatory cascade that integrates PKA and Rho-family GTPases in the AJC disassembly and actin organization in tumor epithelial cells.

Biphasic regulation of mammary epithelial resistance by serotonin through activation of multiple pathways

Mammary gland homeostasis and the lactation-to-involution switch are regulated by serotonin (5-hydroxytryptamine (5-HT)). Mammary epithelial tight junctions are physiological targets of 5-HT, and their disruption marks an early stage of mammary gland involution. In these studies, we have identified signal transduction mechanism employed by 5-HT during regulation of mammary gland transepithelial resistance. Transepithelial electrical resistance and tight junction protein architecture were studied in cultures of MCF10A human mammary epithelial cells. Serotonin had biphasic effects on mammary epithelial resistance. At lower concentrations and earlier time points, 5-HT potentiated epithelial transmembrane resistance, whereas at higher concentrations and later time points, 5-HT decreased transepithelial electrical resistance and disrupted tight junctions. Both the early and delayed actions of 5-HT were mediated by the 5-HT7 receptor through activation of G(s)/cAMP. 5-HT induced the activities of both protein kinase A and p38 mitogen-activated protein kinase. Inhibition of p38 mitogen-activated protein kinase abrogated 5-HT-induced disruption of mammary epithelial tight junctions (the delayed effect). In contrast, inhibition of protein kinase A prevented the increased epithelial resistance in response to 5-HT (the transient effect). These studies imply an integrated set of mechanisms whereby transient, modest activation of 5-HT7 promotes tight junction integrity, and sustained 5-HT7 activation drives involution by disrupting tight junctions.

Occludin oligomeric assembly at tight junctions of the blood-brain barrier is disrupted by peripheral inflammatory hyperalgesia

Tight junctions (TJs) at the blood-brain barrier (BBB) dynamically alter paracellular diffusion of blood-borne substances from the peripheral circulation to the CNS in response to external stressors, such as pain, inflammation, and hypoxia. In this study, we investigated the effect of lambda-carrageenan-induced peripheral inflammatory pain (i.e., hyperalgesia) on the oligomeric assembly of the key TJ transmembrane protein, occludin. Oligomerization of integral membrane proteins is a critical step in TJ complex assembly that enables the generation of tightly packed, large multiprotein complexes capable of physically obliterating the interendothelial space to inhibit paracellular diffusion. Intact microvessels isolated from rat brains were fractionated by detergent-free density gradient centrifugation, and gradient fractions were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis/ Western blot. Injection of lambda-carrageenan into the rat hind paw produced after 3 h a marked change in the relative amounts of oligomeric, dimeric, and monomeric occludin isoforms associated with different plasma membrane lipid raft domains and intracellular compartments in endothelial cells at the BBB. Our findings suggest that increased BBB permeability (i.e., leak) associated with lambda-carrageenan-induced peripheral inflammatory pain is promoted by the disruption of disulfide-bonded occludin oligomeric assemblies, which renders them incapable of forming an impermeant physical barrier to paracellular transport.

The role of cytoskeleton in the regulation of vascular endothelial barrier function

The cytoskeleton is vital to the function of virtually all cell types in the organism as it is required for cell division, cell motility, endo- or exocytosis and the maintenance of cell shape. Endothelial cells, lining the inner surface of the blood vessels, exploit cytoskeletal elements to ensure the integrity of cell monolayer in quiescent endothelium, and to enable the disintegration of the formed barrier in response to various agonists. Vascular permeability is defined by the combination of transcellular and paracellular pathways, with the latter being a major contributor to the inflammation-induced barrier dysfunction. This review will analyze the cytoskeletal elements, which reorganization affects endothelial permeability, and emphasize signaling mechanisms with barrier-protective or barrier-disruptive potential.

Azaspiracid shellfish poisoning: a review on the chemistry, ecology, and toxicology with an emphasis on human health impacts

Azaspiracids (AZA) are polyether marine toxins that accumulate in various shellfish species and have been associated with severe gastrointestinal human intoxications since 1995. This toxin class has since been reported from several countries, including Morocco and much of western Europe. A regulatory limit of 160 μg AZA/kg whole shellfish flesh was established by the EU in order to protect human health; however, in some cases, AZA concentrations far exceed the action level. Herein we discuss recent advances on the chemistry of various AZA analogs, review the ecology of AZAs, including the putative progenitor algal species, collectively interpret the in vitro and in vivo data on the toxicology of AZAs relating to human health issues, and outline the European legislature associated with AZAs.