Characterization of the effect of Cr(VI) on humoral innate immunity using Drosophila melanogaster

Transfer of heavy metals along the food chain: A review on the pest control performance of insect natural enemies under heavy metal stress

Heavy metal contamination represents a critical global environmental concern. The movement of heavy metals through the food chain inevitably subjects insect natural enemies to heavy metal stress, leading to various adverse effects. This review assesses the risks posed by heavy metal exposure to insect natural enemies, evaluates how such exposure impacts their pest control efficacy, and investigates the mechanisms affecting their fitness. Heavy metals transfer and accumulate from soil to plants, then to herbivorous insects, and ultimately to their natural enemies, impeding growth, development, and reproduction of insect natural enemies. Typically, diminished growth and reproduction directly compromise the pest control efficacy of these natural enemies. Nonetheless, within tolerable limits, increased feeding may occur as these natural enemies strive to meet the energy demands for detoxification, potentially enhancing their pest control capabilities. The production of reactive oxygen species and oxidative damage caused by heavy metals in insect natural enemies, combined with disrupted energy metabolism in host insects, are key factors contributing to the reduced fitness of insect natural enemies. In summary, heavy metal pollution emerges as a significant abiotic factor adversely impacting the pest control performance of these beneficial insects.

Symbiotic hemolymph bacteria reduce hexavalent chromium to protect the host from chromium toxicity in Procambarus clarkii

Hexavalent chromium (Cr(VI)) is a cytotoxic heavy metal pollutant that adversely affects all life forms. Interestingly, the crustacean Procambarus clarkii exhibits a relatively high tolerance to heavy metals. The underlying mechanisms remain unclear. In this study, we investigated the role of symbiotic bacteria in P. clarkii in alleviating Cr(VI)-induced damage and explored their potential mechanisms of action. Through transcriptomic analysis, we observed that Cr(VI) activated P. clarkii's antimicrobial immune responses and altered the bacterial composition in the hemolymph. After antibiotic treatment to reduce bacterial populations, Cr(VI)-induced intestinal and liver damage worsened, and crayfish exhibited lower levels of GSH/CAT/SOD activity. The Exiguobacterium, the symbiotic bacteria in the hemolymph of P. clarkii, were proved to be primary contributor to Cr(VI) tolerance. Further investigation suggested that it resists Cr(VI) through the activation of the ABC transporter system and the reduction of Cr(VI) via the reductase gene nfsA. To validate the role of Exiguobacterium in Cr(VI) tolerance, crayfish treated with antibiotics then supplemented with Exiguobacterium H6 and recombinant E. coli (with the nfsA gene), reduced Cr(VI)-induced ovarian damage. Overall, this study revealed that the symbiotic bacteria Exiguobacterium can absorb and reduce hexavalent chromium, mitigating Cr(VI)-induced damage in P. clarkii. These findings provide new insights into hexavalent chromium tolerance mechanisms in crustaceans.

The immunotoxicity of Cd exposure to gypsy moth larvae: An integrated analysis of cellular immunity and humoral immunity

Heavy metal exposure-triggered growth retardation and physiology disorder in phytophagous insects have been widely understood, but only a few studies have investigated its immunomodulatory effects on herbivorous insects. Here, the innate immunity of gypsy moth (Lymantria dispar) larvae under Cd stress was evaluated by integrating cellular and humoral immunity, and the immunomodulation mechanism of Cd stress was further understood by the proteomics analysis of larval hemolymph. Our results showed that the total hemocyte count, as well as phagocytic, encapsulation and bacteriostatic activity, of hemolymph in gypsy moth larvae exposed to Cd stress was significantly lower than that in un-treated larvae. Further proteomic analysis revealed that Cd exposure may reduce the total hemocyte count in larval hemolymph by inducing endoplasmic reticulum pathway-mediated hemocyte apoptosis, thereby causing the collapse of cellular immunity in gypsy moth larvae. In addition, the transcriptional level of signal transduction genes (IMD, Toll, Relish, JAK and STAT) and antimicrobial peptide genes (cecropin and lebocin), as well as the protein abundance of pattern recognition receptors (PGRP and GNBP3) in the Toll, IMD and JAK/STAT signaling pathways was significantly decreased in Cd-treated larvae, clearly implying an immunosuppresive effect of Cd stress on pathogen recognition, signal transduction and effector synthesis of humoral immunity in gypsy moth larvae. Taken together, these results suggest that Cd exposure decreases both cellular immunity and humoral immunity of gypsy moth larvae, and provides a new entry point for systematically and comprehensively unraveling the heavy metal pollutants-caused immunotoxicity.

Blood chromium exposure, immune inflammation and genetic damage: Exploring associations and mediation effects in chromate exposed population

Both genetic damage and inappropriate immune function are relevant to cancer of hexavalent chromium [Cr(VI)]. However, its associations with immune response and genetic damage development are poorly understood. To explore their associations and mediating effects, 1249 participants were included from the Occupational Chromate Exposure Dynamic Cohort, and their blood Cr concentrations were measured as internal exposure. A set of biomarkers including urinary 8-hydroxy-2' - deoxyguanosine (8-OHdG), micronucleus frequency (MNF) and mitochondrial DNA copy number (mtCN) was developed to evaluate the landscape of genetic damage of Cr(VI). Serum C-reactive protein (CRP) and first component of complement q (C1q) were measured to reflect immune inflammation. Multivariate linear regression and mediation analyses were applied to assess the potential associations and mediation effects. It was found that blood Cr level showed significant dose-dependent relationships with increasing of MNF and urinary 8-OHdG, while negative association with CRP and C1q. Furthermore, a 1-unit increase in CRP was associated with decreases of - 0.765 to - 0.254 in MNF, - 0.400 to - 0.051 in urinary 8-OHdG. 4.97% of the association between blood Cr level and the increased MNF was mediated by CRP. 11.58% of the relationship between concentration of blood Cr and urinary 8-OHdG was mediated by C1q. These findings suggested that Cr(VI) exposures might prompt genetic damage, possibly partial via worsening immune inflammation.

Single and mixed exposure to cadmium and mercury in Drosophila melanogaster: Molecular responses and impact on post-embryonic development

Heavy metals, like many other chemical elements, are naturally present in the environment; however, the concentrations of these metals in various environmental matrices have increased through their intensive use in many human activities (such as industry, mining and agriculture). Among the heavy metals, cadmium (Cd) and mercury (Hg) induce a wide variety of defects in animals. While the effects of these heavy metals have been widely documented, a single exposure paradigm is typically used. Few studies have focused on evaluating combined exposure to these metals. However, in the environment, animals are confronted with a plethora of substances simultaneously; thus, the presence and origin of such substances must be determined to reduce the sources of contamination. Using the model of the fruit fly Drosophila melanogaster, for which many tools are readily available, we investigated how different concentrations of Cd and Hg in single and combined exposures impact post-embryonic development. In parallel, we evaluated the extended expression pattern of 38 molecular targets used as potential biomarkers of exposure through qPCR. Our results showed that both metals caused developmental delays and mortality in dose-dependent responses. Both metals were able to deregulate genes involved in hormonal control, general stress, and oxidative stress. Importantly, we confirmed synergistic interactions between Cd and Hg. Our results indicate the importance of assessing several biomarkers and their kinetics in mixtures. Drosophila represents a useful model for monitoring the toxicity of substances in polluted environments.

Transfer of heavy metal along food chain: a mini-review on insect susceptibility to entomopathogenic microorganisms under heavy metal stress

The development and physiological status of pest insects are important factors that affect the effectiveness of biological control. Current knowledge reveals that heavy metals can be transferred to phytophagous insects through food chains and cause various chronic toxicological effects on the growth and physiology of phytophagous insects. These findings potentially attribute heavy metal contamination to an environmental factor governing biocontrol efficiency against pest insects, pointing to an urgent demand to better understand the effects of heavy metal exposure on insect susceptibility to entomopathogenic microorganisms. Here we discuss the transfer characteristics of heavy metals along the food chains to phytophagous insects and conclude that heavy metal exposure may promote insect susceptibility to entomopathogenic microorganisms in the heavy metal-contaminated regions. Furthermore, we propose a 'combined effect' hypothesis that combination of entomopathogenic agent and heavy metal stress can cause a much higher overall insect mortality than does the entomopathogenic agent or the heavy metal stress alone. This is a new and relatively unexplored area in the microbial-based biocontrol research, which might have great potential for future optimization of biocontrol strategies against economically and ecologically important agricultural or forest pests in the heavy metal polluted areas. © 2020 Society of Chemical Industry.

Drosophila melanogaster Models of Metal-Related Human Diseases and Metal Toxicity

Iron, copper and zinc are transition metals essential for life because they are required in a multitude of biological processes. Organisms have evolved to acquire metals from nutrition and to maintain adequate levels of each metal to avoid damaging effects associated with its deficiency, excess or misplacement. Interestingly, the main components of metal homeostatic pathways are conserved, with many orthologues of the human metal-related genes having been identified and characterized in Drosophila melanogaster. Drosophila has gained appreciation as a useful model for studying human diseases, including those caused by mutations in pathways controlling cellular metal homeostasis. Flies have many advantages in the laboratory, such as a short life cycle, easy handling and inexpensive maintenance. Furthermore, they can be raised in a large number. In addition, flies are greatly appreciated because they offer a considerable number of genetic tools to address some of the unresolved questions concerning disease pathology, which in turn could contribute to our understanding of the metal metabolism and homeostasis. This review recapitulates the metabolism of the principal transition metals, namely iron, zinc and copper, in Drosophila and the utility of this organism as an experimental model to explore the role of metal dyshomeostasis in different human diseases. Finally, a summary of the contribution of Drosophila as a model for testing metal toxicity is provided.

Chromium alters lipopolysaccharide-induced inflammatory responses both in vivo and in vitro

We demonstrated that pretreatment with chromium (Cr) significantly alters inflammatory responses of mice or macrophage cell lines. The mice were pretreated with 50 and 200 mg L(-1) of Cr dissolved in drinking water for 7 or 21 d, respectively. Then, the mice were challenged with lipopolysaccharide (LPS) or saline for 3 h. The body and liver weights significantly decreased after exposure to 200 mg L(-1) of Cr for both 7 and 21 d. Serious infiltration of inflammatory cells around the artery was found in the liver treated with 200 mg L(-1) of Cr for 7 and 21 d. The levels of tumor necrosis factor-α (TNFα) and interleukin-6 (IL6) in peritoneal macrophage significantly increased after the treatment with 200 mg L(-1) of Cr for 7 d. Moreover, LPS-induced increases in the serum levels and the transcriptional status of some cytokine genes were amplified by the Cr pretreatment. In the in vitro test, the RAW264.7 cell line was pretreated with Cr for 3, 6, 12, and 24 h, followed by stimulation with LPS (1 μg mL(-1)) for 6 h. LPS-induced the increases in TNFα, IL6, Interleukin-1α (IL1α), Interleukin-1β (IL1β), inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX2) mRNA levels were significantly promoted by the pretreatment with Cr for 3, 6, and 12 h, whereas they were weakened by the pre-exposure to Cr for 24 h in a concentration-dependent manner. In addition, LPS-induced the release of TNFα and IL6 in the medium was also significantly enhanced or suppressed by the different Cr pretreatment. The results suggested that Cr had the potential to induce immunotoxicity by altering the inflammatory responses.

Metabolomic Analysis Provides Insights on Paraquat-Induced Parkinson-Like Symptoms in Drosophila melanogaster

Paraquat (PQ) exposure causes degeneration of the dopaminergic neurons in an exposed organism while altered metabolism has a role in various neurodegenerative disorders. Therefore, the study presented here was conceived to depict the role of altered metabolism in PQ-induced Parkinson-like symptoms and to explore Drosophila as a potential model organism for such studies. Metabolic profile was generated in control and in flies that were fed PQ (5, 10, and 20 mM) in the diet for 12 and 24 h concurrent with assessment of indices of oxidative stress, dopaminergic neurodegeneration, and behavioral alteration. PQ was found to significantly alter 24 metabolites belonging to different biological pathways along with significant alterations in the above indices. In addition, PQ attenuated brain dopamine content in the exposed organism. The study demonstrates that PQ-induced alteration in the metabolites leads to oxidative stress and neurodegeneration in the exposed organism along with movement disorder, a phenotype typical of Parkinson-like symptoms. The study is relevant in the context of Drosophila and humans because similar alteration in the metabolic pathways has been observed in both PQ-exposed Drosophila and in postmortem samples of patients with Parkinsonism. Furthermore, this study provides advocacy towards the applicability of Drosophila as an alternate model organism for pre-screening of environmental chemicals for their neurodegenerative potential with altered metabolism.