Repeated five-day administration of L-BMAA, microcystin-LR, or as mixture, in adult C57BL/6 mice - lack of adverse cognitive effects

Beyond the blur: Scopolamine's utility and limits in modeling cognitive disorders across sexes - Narrative review

Scopolamine, widely regarded as the gold standard in preclinical studies of memory impairments, acts as a non-selective antagonist of central and peripheral muscarinic receptors. While its application in modeling dementia primarily involves antagonism at the M1 receptor, its non-selective peripheral actions may introduce adverse effects that influence behavioral test outcomes. This review analyzes preclinical findings to consolidate knowledge on scopolamine's use and elucidate potential mechanisms responsible for its amnestic effects. We focused on recognition, spatial, and emotional memory processes, alongside executive functions such as attention, cognitive flexibility, and working memory. The cognitive effects of scopolamine are highly dose-dependent, influenced by factors such as species, age, and sex of subjects. Notably, scopolamine rapidly induces observable memory impairments across species, from fish to rodents and primates, often with deficits that can persist for days. However, the compound's broad action on muscarinic receptors and its peripheral side effects, including pupil dilation and reduced salivation, complicates result interpretation, particularly in tasks requiring visual discrimination or food intake. The review also highlights scopolamine's translational value in modeling dementia and Alzheimer's disease, emphasizing the importance of considering individual factors and task-specific designs. Despite its widespread use, scopolamine's limited specificity for cholinergic dysfunction and inability to fully mimic the complex pathophysiology of cognitive disorders like Alzheimer's and Parkinson's disease point to the need for complementary models. This review aims to guide researchers in using scopolamine for modeling cognitive impairments, ensuring attention to factors impacting experimental outcomes.

Liver sinusoidal endothelial cells show reduced scavenger function and downregulation of Fc gamma receptor IIb, yet maintain a preserved fenestration in the Glmpgt/gt mouse model of slowly progressing liver fibrosis

Liver sinusoidal endothelial cells (LSECs) are fenestrated endothelial cells with a unique, high endocytic clearance capacity for blood-borne waste macromolecules and colloids. This LSEC scavenger function has been insufficiently characterized in liver disease. The Glmpgt/gt mouse lacks expression of a subunit of the MFSD1/GLMP lysosomal membrane protein transporter complex, is born normal, but soon develops chronic, mild hepatocyte injury, leading to slowly progressing periportal liver fibrosis, and splenomegaly. This study examined how LSEC scavenger function and morphology are affected in the Glmpgt/gt model. FITC-labelled formaldehyde-treated serum albumin (FITC-FSA), a model ligand for LSEC scavenger receptors was administered intravenously into Glmpgt/gt mice, aged 4 months (peak of liver inflammation), 9-10 month, and age-matched Glmpwt/wt mice. Organs were harvested for light and electron microscopy, quantitative image analysis of ligand uptake, collagen accumulation, LSEC ultrastructure, and endocytosis receptor expression (also examined by qPCR and western blot). In both age groups, the Glmpgt/gt mice showed multifocal liver injury and fibrosis. The uptake of FITC-FSA in LSECs was significantly reduced in Glmpgt/gt compared to wild-type mice. Expression of LSEC receptors stabilin-1 (Stab1), and mannose receptor (Mcr1) was almost similar in liver of Glmpgt/gt mice and age-matched controls. At the same time, immunostaining revealed differences in the stabilin-1 expression pattern in sinusoids and accumulation of stabilin-1-positive macrophages in Glmpgt/gt liver. FcγRIIb (Fcgr2b), which mediates LSEC endocytosis of soluble immune complexes was widely and significantly downregulated in Glmpgt/gt liver. Despite increased collagen in space of Disse, LSECs of Glmpgt/gt mice showed well-preserved fenestrae organized in sieve plates but the frequency of holes >400 nm in diameter was increased, especially in areas with hepatocyte damage. In both genotypes, FITC-FSA also distributed to endothelial cells of spleen and bone marrow sinusoids, suggesting that these locations may function as possible compensatory sites of clearance of blood-borne scavenger receptor ligands in liver fibrosis.

Freshwater Cyanobacterial Toxins, Cyanopeptides and Neurodegenerative Diseases

Cyanobacteria produce a wide range of structurally diverse cyanotoxins and bioactive cyanopeptides in freshwater, marine, and terrestrial ecosystems. The health significance of these metabolites, which include genotoxic- and neurotoxic agents, is confirmed by continued associations between the occurrence of animal and human acute toxic events and, in the long term, by associations between cyanobacteria and neurodegenerative diseases. Major mechanisms related to the neurotoxicity of cyanobacteria compounds include (1) blocking of key proteins and channels; (2) inhibition of essential enzymes in mammalian cells such as protein phosphatases and phosphoprotein phosphatases as well as new molecular targets such as toll-like receptors 4 and 8. One of the widely discussed implicated mechanisms includes a misincorporation of cyanobacterial non-proteogenic amino acids. Recent research provides evidence that non-proteinogenic amino acid BMAA produced by cyanobacteria have multiple effects on translation process and bypasses the proof-reading ability of the aminoacyl-tRNA-synthetase. Aberrant proteins generated by non-canonical translation may be a factor in neuronal death and neurodegeneration. We hypothesize that the production of cyanopeptides and non-canonical amino acids is a more general mechanism, leading to mistranslation, affecting protein homeostasis, and targeting mitochondria in eukaryotic cells. It can be evolutionarily ancient and initially developed to control phytoplankton communities during algal blooms. Outcompeting gut symbiotic microorganisms may lead to dysbiosis, increased gut permeability, a shift in blood-brain-barrier functionality, and eventually, mitochondrial dysfunction in high-energy demanding neurons. A better understanding of the interaction between cyanopeptides metabolism and the nervous system will be crucial to target or to prevent neurodegenerative diseases.

Environmental Neurotoxin β-N-Methylamino-L-alanine (BMAA) as a Widely Occurring Putative Pathogenic Factor in Neurodegenerative Diseases

In the present review we have discussed the occurrence of β-N-methylamino-L-alanine (BMAA) and its natural isomers, and the organisms and sample types in which the toxin(s) have been detected. Further, the review discusses general pathogenic mechanisms of neurodegenerative diseases, and how modes of action of BMAA fit in those mechanisms. The biogeography of BMAA occurrence presented here contributes to the planning of epidemiological research based on the geographical distribution of BMAA and human exposure. Analysis of BMAA mechanisms in relation to pathogenic processes of neurodegeneration is used to critically assess the potential significance of the amino acid as well as to identify gaps in our understanding. Taken together, these two approaches provide the basis for the discussion on the potential role of BMAA as a secondary factor in neurodegenerative diseases, the rationale for further research and possible directions the research can take, which are outlined in the conclusions.

Repeated exposure to microcystin-leucine-arginine potentiates excitotoxicity induced by a low dose of kainate

Microcystin-leucine-arginine (MLCR) is a cyanobacterial toxin, and has been demonstrated to cause neurotoxicity. In addition, MCLR has been identified as an inhibitor of protein phosphatase (PP)1 and PP2A, which are known to regulate the phosphorylation of various molecules related to synaptic excitability. Thus, in the present study, we examined whether MCLR exposure affects seizures induced by a low dose of kainic acid (KA; 0.05 μg, i.c.v.) administration. KA-induced seizure occurrence and seizure score significantly increased after repeated exposure to MCLR (2.5 or 5.0 μg/kg, i.p., once a day for 10 days), but not after acute MCLR exposure (2.5 or 5.0 μg/kg, i.p., 2 h and 30 min prior to KA administration), and hippocampal neuronal loss was consistently facilitated by repeated exposure to MCLR. In addition, repeated MCLR significantly elevated the membrane expression of kainate receptor GluK2 subunits, p-pan-protein kinase C (PKC), and p-extracellular signal-related kinase (ERK) at 1 h after KA. However, KA-induced membrane expression of Ca²⁺/calmodulin-dependent kinase II (CaMKII) was significantly reduced by repeated MCLR exposure. Consistent with the enhanced seizures and neurodegeneration, MCLR exposure significantly potentiated KA-induced oxidative stress and microglial activation, which was accompanied by increased expression of p-ERK and p-PKCδ in the hippocampus. The combined results suggest that repeated MCLR exposure potentiates KA-induced excitotoxicity in the hippocampus by increasing membrane GluK2 expression and enhancing oxidative stress and neuroinflammation through the modulation of p-CaMKII, p-PKC, and p-ERK.

Maternal exposure to a human based mixture of persistent organic pollutants (POPs) affect gene expression related to brain function in mice offspring hippocampus

Male and female mice pups were exposed to a low and high dose of a human relevant mixture of persistent organic pollutants (POPs) during pregnancy and lactation. Most compounds detected in the dams were found in offspring brains. The mice offspring exhibited changed expression of hippocampal genes involved in cognitive function (Adora2a, Auts2, Crlf1, Chrnb2, Gdnf, Gnal, Kcnh3), neuroinflammation (Cd47, Il1a), circadian rhythm (Per1, Clock), redox signalling (Hmox2) and aryl hydrocarbon receptor activation (Cyp1b1). A few genes were differentially expressed in males versus females. Mostly, similar patterns of gene expression changes were observed between the low and high dose groups. Effects on learning and memory function measured in the Barnes maze (not moving, escape latency) were found in the high dose group when combined with moderate stress exposure (air flow from a fan). Mediation analysis indicated adaptation to the effects of exposure since gene expression compensated for learning disabilities (escape latency, walking distance and time spent not moving in the maze). Additionally, random forest analysis indicated that Kcnh3, Gnal, and Crlf1 were the most important genes for escape latency, while Hip1, Gnal and the low exposure level were the most important explanatory factors for passive behaviour (not moving). Altogether, this study showed transfer of POPs to the offspring brains after maternal exposure, modulating the expression level of genes involved in brain function.

Interaction of Neuromelanin with Xenobiotics and Consequences for Neurodegeneration; Promising Experimental Models

Neuromelanin (NM) accumulates in catecholamine long-lived brain neurons that are lost in neurodegenerative diseases. NM is a complex substance made of melanic, peptide and lipid components. NM formation is a natural protective process since toxic endogenous metabolites are removed during its formation and as it binds excess metals and xenobiotics. However, disturbances of NM synthesis and function could be toxic. Here, we review recent knowledge on NM formation, toxic mechanisms involving NM, go over NM binding substances and suggest experimental models that can help identifying xenobiotic modulators of NM formation or function. Given the high likelihood of a central NM role in age-related human neurodegenerative diseases such as Parkinson’s and Alzheimer’s, resembling such diseases using animal models that do not form NM to a high degree, e.g., mice or rats, may not be optimal. Rather, use of animal models (i.e., sheep and goats) that better resemble human brain aging in terms of NM formation, as well as using human NM forming stem cellbased in vitro (e.g., mid-brain organoids) models can be more suitable. Toxicants could also be identified during chemical synthesis of NM in the test tube.

A Streptomyces globisporus strain kills Microcystis aeruginosa via cell-to-cell contact

Cyanobacterial harmful algal blooms (CyanoHABs) bring economic loss, damage aquatic ecosystems, and produce cyanobacterial toxins that threaten human health. Algicidal bacteria as pathogens can expediate the decline of CyanoHABs. In this study, a Streptomyces globisporus strain (designated G9), isolated from soil near a eutrophic pond, showed high algicidal activity against Microcystis aeruginosa. Experimental results show that G9 preyed on Microcystis through cell-to-cell contact: (1) the hyphae of G9 killed cyanobacterial cells by twining around them, while cells beyond the reach of G9 hyphae were in normal shapes; (2) No algicides were detectable in the supernatant of G9 cultures or G9-Microcystis cocultures. The algicidal ratio of G9 to M. aeruginosa reached 96.7% after 6 days. G9 selectively killed the tested cyanobacterial strains, while it had only minor impacts on the growth of tested Chlorophyceae. Differential gene expression studies show that G9 affected the expression of key genes of M. aeruginosa involved in photosynthesis, microcystin synthesis and cellular emergency responses. Further, the microcystin-LR content decreased gradually with G9 treatment. As the first reported Streptomyces sp. with algicidal (predation) activity requiring cell-to-cell contact with target prey, G9 is a good candidate for the exploration of additional cyanobacteria-bacteria interactions and the development of novel strategies to control CyanoHABs.

BMAA and MCLR Interact to Modulate Behavior and Exacerbate Molecular Changes Related to Neurodegeneration in Larval Zebrafish

Exposure to toxins produced by cyanobacteria (ie, cyanotoxins) is an emerging health concern due to their increasing prevalence and previous associations with neurodegenerative diseases including amyotrophic lateral sclerosis. The objective of this study was to evaluate the neurotoxic effects of a mixture of two co-occurring cyanotoxins, β-methylamino-l-alanine (BMAA) and microcystin leucine and arginine (MCLR), using the larval zebrafish model. We combined high-throughput behavior-based toxicity assays with discovery proteomic techniques to identify behavioral and molecular changes following 6 days of exposure. Although neither toxin caused mortality, morphological defects, nor altered general locomotor behavior in zebrafish larvae, both toxins increased acoustic startle sensitivity in a dose-dependent manner by at least 40% (p < .0001). Furthermore, startle sensitivity was enhanced by an additional 40% in larvae exposed to the BMAA/MCLR mixture relative to those exposed to the individual toxins. Supporting these behavioral results, our proteomic analysis revealed a 4-fold increase in the number of differentially expressed proteins in the mixture-exposed group. Additionally, prediction analysis reveals activation and/or inhibition of 8 enriched canonical pathways (enrichment p-value < .01; z-score≥|2|), including ILK, Rho Family GTPase, RhoGDI, and calcium signaling pathways, which have been implicated in neurodegeneration. We also found that expression of TDP-43, of which cytoplasmic aggregates are a hallmark of amyotrophic lateral sclerosis pathology, was significantly upregulated by 5.7-fold following BMAA/MCLR mixture exposure. Together, our results emphasize the importance of including mixtures of cyanotoxins when investigating the link between environmental cyanotoxins and neurodegeneration as we reveal that BMAA and MCLR interact in vivo to enhance neurotoxicity.

MicroRNA-181a regulates endoplasmic reticulum stress in offspring of mice following prenatal microcystin-LR exposure

Microcystin-LR (MCLR) was commonly regarded as a potent hepatotoxin and has been reported to cause neurotoxicity. This study was aimed to investigate how maternal MCLR exposure during pregnancy alters behavioral responses in offspring mice and the possible molecular mechanism involved in this procedure. Three doses of MCLR solutions (0, 3 or 15 μg/kg body weight) were administered subcutaneously to pregnant C57bl/6 from gestation day (GD) 6-19. Our results showed that MCLR prenatal exposure led to the impairment of learning and memory function in offspring on postnatal days (PND) 35, accompanied by endoplasmic reticulum (ER) stress and neuronal apoptosis in hippocampal CA1 regions of mice. Sixteen miRNAs in hippocampus of pups on PND 35 were significantly affected by MCLR exposure with the markedly decreased transcription of miR-181a-5p. We then found that miR-181a-5p was down-regulated, accompanied by activation of ER stress after prenatal exposure to MCLR using qPCR analysis. Furthermore, glucose-regulated protein, 78kDa/binding immunoglobulin protein (Grp78/BIP), a major ER chaperone and signaling regulator, was identified as a target of miR-181a-5p. Our study showed that miR-181a could lead to a decrease in the mRNA expression and protein levels of Grp78 by directly binding to its 3'-untranslated region (3'-UTR) in primary hippocampal neurons. Our findings indicate that the up-regulation of Grp78 mediated by inhibition of miR-181a-5p is a possible mechanism resulting in ER stress and cognitive impairment in pups following prenatal MCLR exposure.

Microcystin-LR induced oxidative stress, inflammation, and apoptosis in alveolar type II epithelial cells of ICR mice in vitro

Previous studies have shown that microcystin-LR (MC-LR) produced by toxic cyanobacterial blooms could inflict damage to the lung. However, the mechanisms underlying MC-induced pulmonary toxicity are not fully described. In this study, the primary' fetal alveolar type II epithelial cells (AEC II) from ICR mice, which are involved in formation of bioactive component of pulmonary epithelium and secretion of pulmonary surfactants, were exposed to MC-LR at different concentrations (0, 0.625, 1.25, 2.5, 5, 10, 20 μg/mL) for different time (12, 24, 36 h). Results showed that the viabilities of AEC II exposed to 10 and 20 μg MC-LR/mL were significantly decreased compared with the control group. Furthermore, MC-LR exposure resulted in overproduction of reactive oxygen species (ROS) and induced a significant reduction in superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). Expressions of apoptosis-related proteins including bax, cyt-c, and caspase-9 were significantly up-regulated by exposure to 2.5, 5, 10, or 20 μg MC-LR/mL. When exposed to 5, 10, or 20 μg MC-LR/mL, expressions of proteins involved in inflammatory, p-65 and iNOS were significantly greater than those of the controls. In conclusion, inflammation and apoptosis might be responsible for MC-LR-induced pulmonary injury.

Blood-brain barrier disruption and inflammation reaction in mice after chronic exposure to Microcystin-LR

Microcystin-leucine-arginine (MC-LR), which produced by toxic cyanobacteria and widely present in eutrophic waters, has been shown to have potent acute hepatotoxicity. MC-LR has been revealed to inflict damage to brain, while the neurotoxicity of chronic exposure to MC-LR and mechanisms underlying it are still confusing. Here, the mice were exposed to MC-LR dissolved in drinking water at dose of 1, 7.5, 15, and 30 μg/L for consecutive 180 days. MC-LR accumulated in mouse brains and impaired the blood-brain barrier by inducing the expression of matrix metalloproteinase-8 (MMP-8), which was regulated by NF-κB, c-Fos and c-Jun. Furthermore, MC-LR exposure induced microglial and astrocyte activation and resultant neuroinflammatory response. This study highlights the risks to human health of the current microcystin exposure.

Piperine Enhances the Antioxidant and Anti-Inflammatory Activities of Thymoquinone against Microcystin-LR-Induced Hepatotoxicity and Neurotoxicity in Mice

Microcystin- (MC-) LR is the most frequent cyanotoxin produced by Microcystis aeruginosa cyanobacteria in the contaminated freshwater environment. MC represents a health hazard to humans and animals. Therefore, the present study was designed to evaluate the potential ameliorative effect of thymoquinone (TQ) and/or piperine (PP) against MC toxicity in mice. Fifty-six mice were randomly divided into seven experimental groups. Group I is the normal control that received distilled water for 21 days; Group II (TQ) was treated with TQ (10 mg/kg, i.p) for 21 days; Group III (PP) was treated with PP (25 mg/kg, i.p) for 21 days; Group IV (MC) was treated with MC (10 μg/kg, i.p) for 14 days and served as the toxic control; and Groups V, VI, and VII received TQ and/or PP 7 days prior to MC and continued for 14 days with MC. The results revealed that MC elicited hepatotoxicity and neurotoxicity which was evident due to the significant elevation of serum AST, ALT, γGT, ALP, LDH, IL-1β, IL-6, and TNF-α levels. Furthermore, MC markedly increased MDA and NO contents along with reduction of GSH, SOD, CAT, and GSH-Px in liver and brain tissues. The electron transport chain may be a possible target for MC. TQ and/or PP ameliorated the MC-mediated oxidative damage in the liver and brain which might be attributed to their antioxidant properties. However, the concurrent treatment of TQ and PP showed the best regimen as a result of the PP-enhanced bioavailability of TQ.

Neurotoxin BMAA and its isomeric amino acids in cyanobacteria and cyanobacteria-based food supplements

Cyanobacteria are photosynthetic microorganisms distributed globally in aquatic and terrestrial environments. They are also industrially cultivated to be used as dietary supplements, as they have a high nutritional value; however, they are also known to produce a wide range of toxic secondary metabolites, called cyanotoxins. BMAA (β-methylamino-l-alanine) and its most common structural isomers, DAB (2,4-diaminobutyric acid) and AEG (N-2-aminoethylglycine) produced by cyanobacteria, are non-proteinogenic amino acids that have been associated with neurodegenerative diseases. A possible route of exposure to those amino acids is through consumption of food supplements based on cyanobacteria. The review critically discusses existing reports regarding the occurrence of BMAA, DAB and AEG in cyanobacteria and cyanobacteria-based food supplements. It is shown that inconsistencies in reported results could be attributed to performance of different methods of extraction and analysis applied and in ambiguities regarding determination of soluble and bound fractions of the compounds. The critical aspect of this review aims to grow awareness of human intake of neurotoxic amino acids, while results presented in literature concerning dietary supplements aim to promote further research, quality control as well as development of guidelines for cyanotoxins in food products.