Skeletal toxicity resulting from exposure of growing male rats to coplanar PCB 126 is associated with disruption of calcium homeostasis and the GH-IGF-1 axis and direct effects on bone formation

Decrypting the skeletal toxicity of vertebrates caused by environmental pollutants from an evolutionary perspective: From fish to mammals

The rapid development of modern society has led to an increasing severity in the generation of new pollutants and the significant emission of old pollutants, exerting considerable pressure on the ecological environment and posing a serious threat to both biological survival and human health. The skeletal system, as a vital supportive structure and functional unit in organisms, is pivotal in maintaining body shape, safeguarding internal organs, storing minerals, and facilitating blood cell production. Although previous studies have uncovered the toxic effects of pollutants on vertebrate skeletal systems, there is a lack of comprehensive literature reviews in this field. Hence, this paper systematically summarizes the toxic effects and mechanisms of environmental pollutants on the skeletons of vertebrates based on the evolutionary context from fish to mammals. Our findings reveal that current research mainly focuses on fish and mammals, and the identified impact mechanisms mainly involve the regulation of bone signaling pathways, oxidative stress response, endocrine system disorders, and immune system dysfunction. This study aims to provide a comprehensive and systematic understanding of research on skeletal toxicity, while also promoting further research and development in related fields.

Indoxyl Sulfate Inhibits Osteogenesis in Bone Marrow Mesenchymal Stem Cells through the AhR/Hes1 Pathway

Uremic toxins cause bone disorders in patients with chronic kidney disease (CKD). These disorders are characterized by low turnover osteodystrophy and impaired bone formation in the early stages of CKD. Evidence indicates that the aryl hydrocarbon receptor (AhR) mediates signals that suppress early osteogenic differentiation in bone marrow mesenchymal stem cells (BMSCs). However, whether the AhR mediates the effects of indoxyl sulfate (IS), a uremic toxin, on BMSC osteogenesis remains unclear. We investigated whether IS affects osteogenesis through the AhR/Hes1 pathway. Expression levels of osteogenesis genes (Runx2, Bmp2, Alp, and Oc), AhR, and Hes1 were measured in mouse BMSCs (D1 cells). At concentrations of 2-50 μM, IS significantly reduced mineralization, particularly in the early stages of BMSC osteogenesis. Furthermore, IS significantly downregulated the expression of Runx2, Bmp2, Oc, and Alp. Notably, this downregulation could be prevented using an AhR antagonist and through Ahr knockdown. Mechanistically, IS induced the expression of Hes1 through AhR signaling, thereby suppressing the transcription of Runx2 and Bmp2. Our findings suggest that IS inhibits early osteogenesis of BMSCs through the AhR/Hes1 pathway, thus suppressing the transcription of Runx2 and Bmp2. Our findings may guide new therapeutic strategies against CKD-related bone disorders.

Insight into the mechanism of melatonin in attenuating PCB126-induced liver injury: Resistance to ROS-dependent NETs formation to alleviate inflammation and lipid metabolism dysfunction

3,3',4',4',5-Polychlorinated biphenyls (PCB126) is classified as a persistent organic environmental pollutant that can cause liver damage by producing excessive reactive oxygen species (ROS). ROS also can stimulate neutrophil extracellular traps (NETs) formation, which cause damage to organism if NETs are produced in excess. Melatonin is generally considered to possess strong antioxidant and anti-inflammation prosperities, but it is unclear whether it can alleviate PCB126-induced injury. To explore whether PCB126-induced liver injury is related to the formation of NETs and whether melatonin has a potent protective effect, we established PCB126 exposure/ PCB126 and melatonin co-treatment mouse models by gavage. To further clarify the specific mechanism, we also cultured neutrophils and AML12 cells to replicate in vivo model. Here, we found PCB126 exposure resulted in an elevation in the activities of MDA, LPO, PCO, and 8-OHdG, and a reduction in the activities of CAT, GSH-PX and SOD. We found that PCB126 exposure led to an elevation in the expression levels of chemokines (CCL2, CCL3, CCL4, CXCL12, and CXCL8) and marker factors for NETs formation (MPO, NE, NOX2, PKCα, and PKCζ) in the PCB126 group. IF, SYTOX staining, and SEM results also revealed that PCB126 could stimulate NETs formation. In addition, results of a co-culture system of PBNs and AML12 cells revealed that the expression levels of inflammatory cytokines (IL-1β, IL-6, and TNF-α) significantly decreased and the expression levels of metabolism factors (Fas, Acc, and Srebp) slightly decreased for scavenging NETs, indicating NETs formation aggravated PCB126-induced hepatic damages. Noteworthy, treatment with melatonin reversed these results. In summary, our findings revealed that melatonin alleviated hepatic damage aggravated by PCB126-induced ROS-dependent NETs formation through suppressing excessive ROS production. This finding not only enriches toxicological mechanism of PCB126, but more importantly extends biological effects of melatonin and its potential application values.

2,2',4,4'-Tetrabromodiphenyl ether and cadmium co-exposure activates aryl hydrocarbon receptor pathway to induce ROS and GSDME-dependent pyroptosis in renal tubular epithelial cells

We have previously found that a mixture exposure of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and cadmium (Cd) causes kidney damage; however, the mechanism was not fully understood. The aryl hydrocarbon receptor (AhR) is a ligand-receptor transcription factor that plays an important role in the adaptive response or metabolic detoxification of environmental toxins. Thus, this study aimed to examine the role of AhR in kidney toxicity. BDE-47 (50 μM) or Cd (5 μM) exposure reduced cell viability in renal tubular epithelial cells (HKC), with a larger effect observed in co-treatment. The cell morphology presented pyroptotic changes, including swollen cells, large bubbles, and plasma membrane pore formation. The gene expressions of AhR, heat shock protein 90 (Hsp90), AhR nuclear translocator (ARNT), and cytochrome P450 1B1 (CYP1B1) were increased, while CYP1A1 was decreased. Reactive oxygen species (ROS) were generated, which was reduced by the AhR antagonist CH223191. The apoptosis, necrosis, and intracellular lactated hydrogenase (LDH) release was elevated, and this was attenuated by N-acetylcysteine (NAC). Furthermore, the pyroptosis pathway was activated with increased protein levels of cleaved-caspase-3 and gasdermin E N-terminal (GSDME-NT), while caspase-8, caspase-3, and GSDME were decreased. These effects were alleviated by NAC and CH223191. Our data demonstrate a combined effect of BDE-47 and Cd on nephrotoxicity by activating AhR to induce ROS contributing to GSDME-dependent pyroptosis, and retardation of the AhR pathway could reduce this toxicity.

Epidemiology, Pathophysiology, and Genetics of Primary Hyperparathyroidism

In this narrative review, we present data gathered over four decades (1980-2020) on the epidemiology, pathophysiology and genetics of primary hyperparathyroidism (PHPT). PHPT is typically a disease of postmenopausal women, but its prevalence and incidence vary globally and depend on a number of factors, the most important being the availability to measure serum calcium and parathyroid hormone levels for screening. In the Western world, the change in presentation to asymptomatic PHPT is likely to occur, over time also, in Eastern regions. The selection of the population to be screened will, of course, affect the epidemiological data (ie, general practice as opposed to tertiary center). Parathyroid hormone has a pivotal role in regulating calcium homeostasis; small changes in extracellular Ca++ concentrations are detected by parathyroid cells, which express calcium-sensing receptors (CaSRs). Clonally dysregulated overgrowth of one or more parathyroid glands together with reduced expression of CaSRs is the most important pathophysiologic basis of PHPT. The spectrum of skeletal disease reflects different degrees of dysregulated bone remodeling. Intestinal calcium hyperabsorption together with increased bone resorption lead to increased filtered load of calcium that, in addition to other metabolic factors, predispose to the appearance of calcium-containing kidney stones. A genetic basis of PHPT can be identified in about 10% of all cases. These may occur as a part of multiple endocrine neoplasia syndromes (MEN1-MEN4), or the hyperparathyroidism jaw-tumor syndrome, or it may be caused by nonsyndromic isolated endocrinopathy, such as familial isolated PHPT and neonatal severe hyperparathyroidism. DNA testing may have value in: confirming the clinical diagnosis in a proband; eg, by distinguishing PHPT from familial hypocalciuric hypercalcemia (FHH). Mutation-specific carrier testing can be performed on a proband's relatives and identify where the proband is a mutation carrier, ruling out phenocopies that may confound the diagnosis; and potentially prevention via prenatal/preimplantation diagnosis. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Mechanisms and histopathological impacts of acetamiprid and azoxystrobin in male rats

Acetamiprid (neonicotinoid insecticide) and azoxystrobin (fungicide) are widespread pesticides used for pest management, but they have the potential for toxicity to mammals. The goal of this study was to look for oxidative stress, metabolic alterations, and reproductive problems in male rats' serum after 2 months of exposure to sub-lethal dosages of acetamiprid and azoxystrobin. Seven classes of male rats were formed: control, 3 groups of acetamiprid (1/10, 1/20, 1/40 LD₅₀), and 3 groups of azoxystrobin (1/10, 1/20, 1/40 LD₅₀) and were orally daily treated (n = 8/group). Our findings revealed that acetamiprid and azoxystrobin disrupted oxidative and metabolic processes in the examined rats throughout 30 and 60 days of testing. The levels of nitric oxide increased significantly, while catalase, a superoxide dismutase enzyme, and glutathione reductase activity were reduced. Serum levels of sex hormones, calcium, and total protein have all dropped substantially in rats. In comparison to the control group, the testis and liver structure, as well as spermatozoa parameters, had distinct histological characteristics. In conclusion, acetamiprid and azoxystrobin exhibit dose- and time-dependent effects on oxidative parameters that cause testis damage.

Endocrine disrupting chemicals and bone

Endocrine-disrupting chemicals (EDCs) are defined as chemicals that interfere with the function of the endocrine system. EDCs exert their hormonal effects through several mechanisms; modulating hormone receptors or changing metabolism of different hormones. EDCs also influence multiple signalling pathways while effecting the hormonal systems and possess complex dose-response curves. EDCs can exert deleterious effects on bone tissue through changing bone modelling and remodelling via altering bone paracrine hormone synthesis, the release of systemic hormones, cytokines, chemokines and growth factors, and effecting stem cell fate, as well as bone marrow mesenchymal stem cell differentiation. Evidence is accumulating of the bone disrupting effect of different groups of EDCs, such as; the perfluoroalkyl substances, the phthalate esters, the bisphenol A, the organotin compounds, the alkylphenols and the dioxin and dioxin-like compounds. This review highlights the recent discoveries of the effects of commonly found environmental chemicals on bone from basic molecular findings to clinical implications.

The insulin-like growth factor system: A target for endocrine disruptors?

The insulin-like growth factor (IGF) system is a critical regulator of growth, especially during fetal development, while also playing a central role in metabolic homeostasis. Endocrine disruptors (EDs) are ubiquitous compounds able to interfere with hormone action and impact human health. For example, exposure to EDs is associated with decreased birthweight and increased incidence of metabolic disorders. Therefore, the IGF system is a potential target for endocrine disruption. This review summarises the state of the science regarding effects of exposure to major classes of endocrine disruptors (dioxins and dioxin-like compounds, polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers, phthalates, perfluoroalkyl substances and bisphenol A) on the IGF system. Evidence from both experimental models (in vitro and in vivo) and epidemiological studies is presented. In addition, possible molecular mechanisms of action and effects on methylation are discussed. There is a large body of evidence supporting the link between dioxins and dioxin-like compounds and IGF disruption, but mixed findings have been reported in human studies. On the other hand, although only a few animal studies have investigated the effects of phthalates on the IGF system, their negative association with IGF levels and methylation status has been more consistently reported in humans. For polybrominated diphenyl ethers, perfluoroalkyl substances and bisphenol A the evidence is still limited. Despite a lack of studies for some ED classes linking ED exposure to changes in IGF levels, and the need for further research to improve reproducibility and determine the degree of risk posed by EDs to the IGF system, this is clearly an area of concern.

Bone tissue morphology of rat offspring lactationally exposed to polychlorinated biphenyl 169 and 155

Polychlorinated biphenyls (PCBs) are ubiquitous, persistent, organic pollutants also considered endocrine-disrupting chemicals. Our study examined the effects of lactational exposure to nondioxin-like PCB-155 and/or dioxin-like PCB-169 on longitudinal femur growth at the distal epiphyseal growth plate (EGP) in young rats at three different ages [postnatal days (PNDs) 9, 22, and 42]. After delivery, lactating rats were divided into four groups (PCB-169, PCB-155, PCB-155 + 169, and control) and administered PCBs intraperitoneally. The femurs of offspring were used to estimate growth rate (µm/day), and histomorphometric analysis on the distal femur included the thickness of the EGP and zones of proliferation and hypertrophy with calcification. Stereometry was used to determine trabecular bone volume density. In the PCB-169 and PCB-155 + 169 groups, PCB-169 affected longitudinal bone growth in the early postnatal period by interfering with chondrocytes in the EGP zone of proliferation and, to a lesser extent, the zone of hypertrophy. Morphometric alterations in EGP structure diminished until puberty. A slow growth rate persisted in the PCB-169 group until PND 42, while in the PCB-155 group, a fast growth rate between PNDs 9 to 22 was significantly reduced between PNDs 22 to 42. Sterometric assessment showed decreased trabecular bone volume in the PCB-155 + 169 group compared with that in the control on PND 9 and increased in the PCB-169 group compared with that in the PCB-155 group on PND 42. To summarize, studied PCB congeners exerted congener- and age-dependent effects on femur growth rate and its histomorphometric characteristics.

Skeletal Toxicity of Coplanar Polychlorinated Biphenyl Congener 126 in the Rat Is Aryl Hydrocarbon Receptor Dependent

Epidemiological evidence links polychlorinated biphenyls (PCBs) to skeletal toxicity, however mechanisms whereby PCBs affect bone are poorly studied. In this study, coplanar PCB 126 (5 μmol/kg) or corn oil vehicle was administered to N = 5 and 6 male and female, wild type (WT) or AhR -/- rats via intraperitoneal injection. Animals were sacrificed after 4 weeks. Bone length was measured; bone morphology was assessed by microcomputed tomography and dynamic histomorphometry. Reduced bone length was the only genotype-specific effect and only observed in males (p < .05). WT rats exposed to PCB 126 had reduced serum calcium, and smaller bones with reduced tibial length, cortical area, and medullary area relative to vehicle controls (p < .05). Reduced bone formation rate observed in dynamic histomorphometry was consistent with inhibition of endosteal and periosteal bone growth. The effects of PCB 126 were abolished in AhR -/- rats. Gene expression in bone marrow and shaft were assessed by RNA sequencing. Approximately 75% of the PCB-regulated genes appeared AhR dependent with 89 genes significantly (p < .05) regulated by both PCB 126 and knockout of the AhR gene. Novel targets significantly induced by PCB 126 included Indian hedgehog (Ihh) and connective tissue growth factor (Ctgf/Ccn2), which regulate chondrocyte proliferation and differentiation in the bone growth plate and cell-matrix interactions. These data suggest the toxic effects of PCB 126 on bone are mediated by AhR, which has direct effects on the growth plate and indirect actions related to endocrine disruption. These studies clarify important mechanisms underlying skeletal toxicity of dioxin-like PCBs and highlight potential therapeutic targets.