Endoplasmic reticulum stress participates in the pathophysiology of mercury-caused acute kidney injury

Mercury-induced toxicity: Mechanisms, molecular pathways, and gene regulation

Mercury is a well-known neurotoxicant for humans and wildlife. The epidemic of mercury poisoning in Japan has clearly demonstrated that chronic exposure to methylmercury (MeHg) results in serious neurological damage to the cerebral and cerebellar cortex, leading to the dysfunction of the central nervous system (CNS), especially in infants exposed to MeHg in utero. The occurrences of poisoning have caused a wide public concern regarding the health risk emanating from MeHg exposure; particularly those eating large amounts of fish may experience the low-level and long-term exposure. There is growing evidence that MeHg at environmentally relevant concentrations can affect the health of biota in the ecosystem. Although extensive in vivo and in vitro studies have demonstrated that the disruption of redox homeostasis and microtube assembly is mainly responsible for mercurial toxicity leading to adverse health outcomes, it is still unclear whether we could quantitively determine the occurrence of interaction between mercurial and thiols and/or selenols groups of proteins linked directly to outcomes, especially at very low levels of exposure. Furthermore, intracellular calcium homeostasis, cytoskeleton, mitochondrial function, oxidative stress, neurotransmitter release, and DNA methylation may be the targets of mercury compounds; however, the primary targets associated with the adverse outcomes remain to be elucidated. Considering these knowledge gaps, in this article, we conducted a comprehensive review of mercurial toxicity, focusing mainly on the mechanism, and genes/proteins expression. We speculated that comprehensive analyses of transcriptomics, proteomics, and metabolomics could enhance interpretation of "omics" profiles, which may reveal specific biomarkers obviously correlated with specific pathways that mediate selective neurotoxicity.

Influence of increasing acclimation temperature on growth, digestion, antioxidant capacity, liver transcriptome and intestinal microflora of Ussruri whitefish Coregonus ussuriensis Berg

For effective restoration, conservation of Ussruri whitefish Coregonus ussuriensis Berg and coping with global climate change, effects of environmental temperature on Ussruri whitefish urgently need to be explored. In current study, the effects of different acclimation temperatures on the growth, digestive physiology, antioxidant ability, liver transcriptional responses and intestinal microflora patterns of Ussruri whitefish were investigated. Ussruri whitefish (15.20 g ± 1.23 g) were reared for 42 days under different acclimation temperatures, i.e., 10, 13, 16, 19, 22 and 25 °C, respectively. Result first determined 28 °C as the semi-lethal temperature in order to design the temperature gradient test. Highest main gain rate (MGR) and specific growth rate (SGR) were observed in fish group having acclimation temperature of 19 °C. Significantly decrease (P < 0.05) in triglyceride (TG) content appeared at 19 °C as compared to the 10 °C and 13 °C temperature groups. 19 °C notablely increased protease activities of stomach and intestine and intestinal lipase and amylase activities. 19 °C group obtained the highest activities of chloramphnicol acetyltransferase (CAT) and total antioxidant capacity (T-AOC) and higher activities of superoxide dismutase (SOD). The intestinal microflora composition was most conducive to maintaining overall intestinal health when the temperature was 19 °C, compared to 10 °C and 25 °C. Ussruri whitefish exposed to 10 °C and 25 °C possessed the lower Lactobacillus abundance compared to exposure to 19 °C. Temperature down to 10 °C or up to 25 °C, respectively, triggered cold stress and heat stress, which leading to impairment in intestinal digestion, liver antioxidant capacity and intestinal microflora structure. Liver transcriptome response to 10 °C, 19 °C and 25 °C revealed that Ussruri whitefish might require the initiation of endoplasmic reticulum stress to correct protein damage from cold-temperature and high-temperature stress, and it was speculated that DNAJB11 could be regarded as a biomarker of cold stress response.Based on the quadratic regression analysis of MGR and SGR against temperature, the optimal acclamation temperature were, respectively, 18.0 °C and 18.1 °C. Our findings provide valuable theoretical insights for an in-depth understanding of temperature acclimation mechanisms and laid the foundation for conservation and development of Ussruri whitefish germplasm resources.

Acute kidney injury: exploring endoplasmic reticulum stress-mediated cell death

Acute kidney injury (AKI) is a global health problem, given its substantial morbidity and mortality rates. A better understanding of the mechanisms and factors contributing to AKI has the potential to guide interventions aimed at mitigating the risk of AKI and its subsequent unfavorable outcomes. Endoplasmic reticulum stress (ERS) is an intrinsic protective mechanism against external stressors. ERS occurs when the endoplasmic reticulum (ER) cannot deal with accumulated misfolded proteins completely. Excess ERS can eventually cause pathological reactions, triggering various programmed cell death (autophagy, ferroptosis, apoptosis, pyroptosis). This article provides an overview of the latest research progress in deciphering the interaction between ERS and different programmed cell death. Additionally, the report consolidates insights into the roles of ERS in AKI and highlights the potential avenues for targeting ERS as a treatment direction toward for AKI.

Metabolomics in Acute Kidney Injury: The Experimental Perspective

Acute kidney injury (AKI) affects increasing numbers of in-hospital patients in Central Europe and the USA, the prognosis remains poor. Although substantial progress has been achieved in the identification of molecular/cellular processes that induce and perpetuate AKI, more integrated pathophysiological perspectives are missing. Metabolomics enables the identification of low-molecular-weight (< 1.5 kD) substances from biological specimens such as certain types of fluid or tissue. The aim of the article was to review the literature on metabolic profiling in experimental AKI and to answer the question if metabolomics allows the integration of distinct pathophysiological events such as tubulopathy and microvasculopathy in ischemic and toxic AKI. The following databases were searched for references: PubMed, Web of Science, Cochrane Library, Scopus. The period lasted from 1940 until 2022. The following terms were utilized: "acute kidney injury" OR "acute renal failure" OR "AKI" AND "metabolomics" OR "metabolic profiling" OR "omics" AND "ischemic" OR "toxic" OR "drug-induced" OR "sepsis" OR "LPS" OR "cisplatin" OR "cardiorenal" OR "CRS" AND "mouse" OR "mice" OR "murine" OR "rats" OR "rat". Additional search terms were "cardiac surgery", "cardiopulmonary bypass", "pig", "dog", and "swine". In total, 13 studies were identified. Five studies were related to ischemic, seven studies to toxic (lipopolysaccharide (LPS), cisplatin), and one study to heat shock-associated AKI. Only one study, related to cisplatin-induced AKI, was performed as a targeted analysis. The majority of the studies identified multiple metabolic deteriorations upon ischemia/the administration of LPS or cisplatin (e.g., amino acid, glucose, lipid metabolism). Particularly, abnormalities in the lipid homeostasis were shown under almost all experimental conditions. LPS-induced AKI most likely depends on the alterations in the tryptophan metabolism. Metabolomics studies provide a deeper understanding of pathophysiological links between distinct processes that are responsible for functional impairment/structural damage in ischemic or toxic or other types of AKI.

Assessing Kidney Injury Induced by Mercuric Chloride in Guinea Pigs with In Vivo and In Vitro Experiments

Acute kidney injury, which is associated with high levels of morbidity and mortality, affects a significant number of individuals, and can be triggered by multiple factors, such as medications, exposure to toxic chemicals or other substances, disease, and trauma. Because the kidney is a critical organ, understanding and identifying early cellular or gene-level changes can provide a foundation for designing medical interventions. In our earlier work, we identified gene modules anchored to histopathology phenotypes associated with toxicant-induced liver and kidney injuries. Here, using in vivo and in vitro experiments, we assessed and validated these kidney injury-associated modules by analyzing gene expression data from the kidneys of male Hartley guinea pigs exposed to mercuric chloride. Using plasma creatinine levels and cell-viability assays as measures of the extent of renal dysfunction under in vivo and in vitro conditions, we performed an initial range-finding study to identify the appropriate doses and exposure times associated with mild and severe kidney injuries. We then monitored changes in kidney gene expression at the selected doses and time points post-toxicant exposure to characterize the mechanisms of kidney injury. Our injury module-based analysis revealed a dose-dependent activation of several phenotypic cellular processes associated with dilatation, necrosis, and fibrogenesis that were common across the experimental platforms and indicative of processes that initiate kidney damage. Furthermore, a comparison of activated injury modules between guinea pigs and rats indicated a strong correlation between the modules, highlighting their potential for cross-species translational studies.

Role of endoplasmic reticulum stress and autophagy in the transition from acute kidney injury to chronic kidney disease

Acute kidney injury (AKI) and chronic kidney disease (CKD) are global health concerns with increasing rates in morbidity and mortality. Transition from AKI-to-CKD is common and requires awareness in the management of AKI survivors. AKI-to-CKD transition is a main risk factor for the development of cardiovascular disease and progression to end-stage kidney disease. The mechanisms driving AKI-to-CKD transition are being explored to identify potential molecular and cellular targets for renoprotective drug interventions. Endoplasmic reticulum (ER) stress and autophagy are involved in the process of AKI-to-CKD transition. Excessive ER stress results in the persistent activation of unfolded protein response, which is an underneath cause of kidney cell death. Moreover, ER stress modulates autophagy and vice-versa. Autophagy is a degradation defensive mechanism protecting cells from malfunction. However, the underlying pathological mechanism involved in this interplay in the context of AKI-to-CKD transition is still unclear. In this review, we discuss the crosstalk between ER stress and autophagy in AKI, AKI-to-CKD transition, and CKD progression. In addition, we explore possible therapeutic targets that can regulate ER stress and autophagy to prevent AKI-to-CKD transition to improve the long-term prognosis of AKI survivors.

C-Phycocyanin prevents acute myocardial infarction-induced oxidative stress, inflammation and cardiac damage

CONTEXT

C-Phycocyanin is a protein with anti-scavenger, antioxidant and anti-inflammatory actions against agents that cause cellular damage. The cardioprotective action of C-phycocyanin against acute myocardial infarction (AMI) has not been studied in animal models.

OBJECTIVE

To investigate C-phycocyanin's effect on oxidative stress, inflammation and cardiac damage in a model of isoproterenol-induced AMI.

MATERIALS AND METHODS

Wistar rats were divided into four groups: (1) sham + vehicle (0.9% saline solution by oral gavage, OG); (2) sham + C-phycocyanin (50 mg/kg/d, OG); (3) AMI + vehicle, and (4) AMI + C-phycocyanin. AMI was induced by administering isoproterenol (20, 10, 5 and 3 mg/kg each dose per day), and serum cardiac enzymes were quantified. After five days, the animals were euthanized; the heart was dissected to determine oxidative stress, redox environment, inflammation and cardiac damage markers.

RESULTS

We observed that C-phycocyanin reduced AMI-increased cardiac enzymes (CK by about 53%, CKMB by about 60%, AST by about 16% and ALT by about 21%), lipid peroxidation (57%), reactive oxygen species (50%), nitrites (46%), oxidized glutathione (41%), IL1β (3%), INFγ (5%), TNFα 3%), Bcl2 (37%), Bax (43%), COX2 (21%) and caspase 9 (61%). Finally, C-phycocyanin reduced AMI-induced aberrant histological changes related to myonecrosis, interstitial oedema and inflammatory infiltration in the heart muscle.

CONCLUSIONS

C-Phycocyanin prevents AMI-induced oxidative stress, inflammation and heart damage. This study is the first report that employed C-phycocyanin in an animal model of AMI and supports the potential use of C-phycocyanin in the management of AMI.

Emerging links between endoplasmic reticulum stress responses and acute kidney injury

All cell types must maintain homeostasis under periods of stress. To prevent the catastrophic effects of stress, all cell types also respond to stress by inducing protective pathways. Within the cell, the endoplasmic reticulum (ER) is exquisitely stress-sensitive, primarily because this organelle folds, posttranslationally processes, and sorts one-third of the proteome. In the 1990s, a specialized ER stress response pathway was discovered, the unfolded protein response (UPR), which specifically protects the ER from damaged proteins and toxic chemicals. Not surprisingly, UPR-dependent responses are essential to maintain the function and viability of cells continuously exposed to stress, such as those in the kidney, which have high metabolic demands, produce myriad protein assemblies, continuously filter toxins, and synthesize ammonia. In this mini-review, we highlight recent articles that link ER stress and the UPR with acute kidney injury (AKI), a disease that arises in ∼10% of all hospitalized individuals and nearly half of all people admitted to intensive care units. We conclude with a discussion of prospects for treating AKI with emerging drugs that improve ER function.

Molecular Mechanisms of Cellular Injury and Role of Toxic Heavy Metals in Chronic Kidney Disease

Chronic kidney disease (CKD) is a progressive disease that affects millions of adults every year. Major risk factors include diabetes, hypertension, and obesity, which affect millions of adults worldwide. CKD is characterized by cellular injury followed by permanent loss of functional nephrons. As injured cells die and nephrons become sclerotic, remaining healthy nephrons attempt to compensate by undergoing various structural, molecular, and functional changes. While these changes are designed to maintain appropriate renal function, they may lead to additional cellular injury and progression of disease. As CKD progresses and filtration decreases, the ability to eliminate metabolic wastes and environmental toxicants declines. The inability to eliminate environmental toxicants such as arsenic, cadmium, and mercury may contribute to cellular injury and enhance the progression of CKD. The present review describes major molecular alterations that contribute to the pathogenesis of CKD and the effects of arsenic, cadmium, and mercury on the progression of CKD.

Mercuric chloride induces sequential activation of ferroptosis and necroptosis in chicken embryo kidney cells by triggering ferritinophagy

Mercuric chloride (HgCl₂) is an environmental pollutant with serious nephrotoxic effects, but the underlying mechanism of HgCl₂ nephrotoxicity is not well understood. Ferroptosis and necroptosis are two programmed cell death (PCD) modalities that have been reported singly in heavy metal-induced kidney injury. However, the interaction between ferroptosis and necroptosis in HgCl₂-induced kidney injury is unclear. Here, we established a model of HgCl₂-exposed chicken embryo kidney (CEK) cells to dissect the progresses and mechanisms of these two PCDs. We found that ferroptosis was initially activated in CEK cells after HgCl₂ exposure for 12 h, and necroptosis was activated subsequently at 24 h. Importantly, further study indicated that the shift from ferroptosis to necroptosis was driven by ROS, which was produced by iron-dependent Fenton reaction, and the iron chelation by DFO prevented the sequential activation of both ferroptosis and necroptosis. To investigate the source of intracellular iron, the regulation of iron homeostasis was first explored and demonstrated a tendency for intracellular iron overload in CEK cells. Interestingly, the cellular ferritin, a free iron depository, decreased in a time-dependent manner. Further studies revealed that the degradation of ferritin was attributed to the activation of selective cargo receptor nuclear receptor coactivator 4 (NCOA4)-mediated ferritinophagy, and the inhibition of ferritinophagy by CQ prevented the HgCl₂-induced cell death. In conclusion, our study demonstrated that HgCl₂ released excess free iron via ferritinophagy, led to a sustained accumulation of ROS and ultimately activated ferroptosis and necroptosis sequentially. These findings provide a new understanding for the nephrotoxic mechanism of HgCl₂.

Effect of inorganic mercury exposure on reproductive system of male mice: Immunosuppression and fibrosis in testis

Mercury as a toxic heavy metal will accumulate in the body and induce various diseases through the food chain. However, it is unknown that the detailed mechanism of reproductive disorder induced by inorganic mercury in male mice to date. This study investigated the toxicological effect of mercuric chloride (HgCl₂ ) exposure on reproductive system in male mice. Male Kunming mice received normal saline daily or HgCl₂ (3 mg/kg bodyweight) by intraperitoneal injection for a week. The reproductive function was evaluated, and the HgCl₂ exposure induced the decline of sperm quality, pregnancy rate, mean litter size, and survival rate. Notably, we firstly found the HgCl₂ -induced immunosuppression and fibrosis in mice testis according to the results of RNA sequencing. Collectively, these findings demonstrate that HgCl₂ exposure disrupts the reproductive system and induces testicular immunosuppression and fibrosis via inhibition of the CD74 signaling pathway in male mice.

C-phycoerythrin from Phormidium persicinum Prevents Acute Kidney Injury by Attenuating Oxidative and Endoplasmic Reticulum Stress

C-phycoerythrin (C-PE) is a phycobiliprotein that prevents oxidative stress and cell damage. The aim of this study was to evaluate whether C-PE also counteracts endoplasmic reticulum (ER) stress as a mechanism contributing to its nephroprotective activity. After C-PE was purified from Phormidium persicinum by using size exclusion chromatography, it was characterized by spectrometry and fluorometry. A mouse model of HgCl₂-induced acute kidney injury (AKI) was used to assess the effect of C-PE treatment (at 25, 50, or 100 mg/kg of body weight) on oxidative stress, the redox environment, and renal damage. ER stress was examined with the same model and C-PE treatment at 100 mg/kg. C-PE diminished oxidative stress and cell damage in a dose-dependent manner by impeding the decrease in expression of nephrin and podocin normally caused by mercury intoxication. It reduced ER stress by preventing the activation of the inositol-requiring enzyme-1α (IRE1α) pathway and avoiding caspase-mediated cell death, while leaving the expression of protein kinase RNA-like ER kinase (PERK) and activating transcription factor 6α (ATF6α) pathways unmodified. Hence, C-PE exhibited a nephroprotective effect on HgCl₂-induced AKI by reducing oxidative stress and ER stress.

Bioaccumulation of mercury and transcriptional responses in tusk (Brosme brosme), a deep-water fish from a Norwegian fjord

High concentrations of mercury (Hg) have been documented in deep-water fish species from some Norwegian fjords. In this study, tusk (Brosme brosme) was sampled from four locations in the innermost parts of Sognefjorden in Western Norway. Total Hg and methylmercury (MeHg) levels were measured in liver tissue. To search for potential sublethal effects of Hg, we characterized the hepatic transcriptome in tusk with high and low levels of Hg bioaccumulation using global transcriptomics analysis (RNA-seq). The results showed that there was a significant correlation between fish weight and accumulated concentrations of MeHg but not total Hg. MeHg accounted for 30-40% of total Hg in liver of most of the fish, although at concentrations above 2-3 mg Hg/kg wet weight the percentage of MeHg dropped considerably. Transcriptome analysis resulted in hundreds of differentially expressed genes in the liver of tusk with high Hg levels. Functional enrichment analysis suggested that the top affected pathways are associated with protein folding, adipogenesis, notch signaling, and lipid metabolism (beta-oxidation and phospholipids). Based on transcriptional responses pointing to well-known effects of Hg compounds in fish, the study suggests that tusk in Sognefjorden could be negatively impacted by Hg bioaccumulation.

Arthrospira maxima (Spirulina) prevents endoplasmic reticulum stress in the kidney through its C-phycocyanin

Arthrospira maxima (Spirulina) is a cyanobacterium which is considered a nutraceutical because it has antioxidant, anti-inflammatory, and cytoprotective properties in different renal disease models (Rodriguez-Sánchez et al., 2012; Aziz et al., 2018; Memije-Lazaro et al., 2018). The therapeutic effects are due to the presence of metabolites with biological effects similar to those of essential fatty acids ω-3 and ω-6, vitamins A, C and E, and accessory pigments such as phycobiliproteins. One of the most abundant phycobiliproteins in A. maxima is C-phycocyanin (Mysliwa-Kurdziel and Solymosi, 2017). This molecule is responsible for nephroprotective action in a model of acute kidney injury (AKI) because it reduces oxidative stress and caspase activation (Rodriguez-Sánchez et al., 2012; Rojas-Franco et al., 2018). However, both A. maxima and its C-phycocyanin are related to the reduction of the redox environment. Thus, they probably help to maintain the adequate function of the intracellular organelles like the endoplasmic reticulum. However, this therapeutic action has not been evaluated previously.

Injectable Affinity and Remote Magnetothermal Effects of Bi-Based Alloy for Long-Term Bone Defect Repair and Analgesia

As alternatives, metallic/nonmetallic bone graft materials play significant roles in bone defect surgery to treat external trauma or bone disease. However, to date, there are rather limited long-term implantable materials owning to in situ molding incapability of metallics and poor mechanical property of nonmetallics. Here, Bi-based low melting point alloy, with unique properties of injectability, solid-liquid phase transition, mechanical capability, and biocompatibility, present obvious long-lasting bone affinity as the excellent artificial bone-substitute. It is particularly necessary to point out that the targeted injected Bi alloy remains in its original position for up to 210 days without moving, as well as, displays good osseointegration ability to resolve repeated revision trauma caused by losing bone repair material. Additionally, with outstanding electrical and thermal conductivity, an unconventional way using Bi alloy to realize very beneficial hyperthermia analgesia via non-invasive wireless energy delivery is first proposed, which avoids adverse effects on bone remodeling inflicted by traditional drugs. The significantly decreased expression of pain sensitizing factor, such as, interleukin-6, neuropeptide substance, and transient receptor potential vanilloid 1 reveals the potential mechanism of hyperthermia analgesia. The present findings suggest the combination therapy of Bi alloy in bone repair and analgesia, which owns far-reaching clinical application value.

Response of selenoproteins gene expression profile to mercuric chloride exposure in chicken kidney

Kidney is a primary target organ for mercuric chloride (HgCl₂) toxicity. Selenium (Se) can exert antagonistic effect on heavy metals-induced organ toxicity by regulating the expression of selenoproteins. The objective of this study was to investigate the effect of HgCl₂ on the gene expression of selenoproteins in chicken kidney. Sixty male Hyline brown chickens were randomly and evenly divided into two groups. After acclimatization for one week, chickens were provided with the standard diet as well as non-treated water (CON group), and standard diet as well as HgCl₂-treated water (250 ppm, HgCl₂ group). After seven weeks, kidney tissues were collected to examine the mRNA expression levels of 25 selenoproteins genes and protein expression levels of 4 selenoproteins. Moreover, correlation analysis and principal component analysis (PCA) were used to analyze the expression patterns of 25 selenoproteins. The results showed that HgCl₂ exposure significantly decreased the mRNA expression of Glutathione peroxidase 1 (GPX1), GPX4, Thioredoxin reductase 2 (TXNRD2), Iodothyronine deiodinase 1 (DIO1), Methionine-Rsulfoxide reductase 1 (SELR), 15-kDa selenoprotein (SEP15), selenoprotein I (SELI), SELK, SELM, SELN, SELP, SELS, SELT, SELW, and SEPHS2. Meanwhile, HgCl₂ exposure significantly increased the mRNA expression of GPX3, TXNRD1, and SELU. Western blot analysis showed that the expression levels of GPX3, TXNRD1, SELK, and SELN were concordant with these mRNA expression levels. Analysis results of selenoproteins expression patterns showed that HgCl₂-induced the main disorder expression of selenoproteins with antioxidant activity and endoplasmic reticulum resident selenoproteins. In conclusion, selenoproteins respond to HgCl₂ exposure in a characteristic manner in chicken kidney.