In vitro inhibition of lysine decarboxylase activity by organophosphate esters

Structure-dependent destructive adsorption of organophosphate flame retardants on lipid membranes

The widespread use of organophosphate flame retardants (OPFRs), a serious type of pervasive environmental contaminants, has led to a global concern regarding their diverse toxicities to living beings. Using a combination of experimental and theoretical approaches, we systematically studied the adsorption, accumulation, and influence of a series of OPFRs on the lipid membranes of bacteria and cells. Our results revealed that OPFRs can aggregate in lipid membranes, leading to the destruction of membrane integrity. During this process, the molecular structure of the OPFRs is a dominant factor that significantly influences the strength of their interaction with the lipid membrane, resulting in varying degrees of biotoxicity. Triphenyl phosphate (TPHP), owing to its large molecular size and strong hydrophobicity, causes severe membrane disruption through the formation of nanoclusters. The corresponding severe toxicity originates from the phase transitions of the lipid membranes. In contrast, smaller OPFRs such as triethyl phosphate (TEP) and tris(2-chloroethyl) phosphate (TCEP) have weaker hydrophobicity and induce minimal membrane disturbance and ineffective damage. In vivo, gavage of TPHP induced more severe barrier damage and inflammatory infiltration in mice than TEP or TCEP, confirming the higher toxicity of TPHP. Overall, our study elucidates the structure-dependent adsorption of OPFRs onto lipid membranes, highlighting their destructive interactions with membranes as the origin of OPFR toxicity.

Cucurbit[n]uril-based fluorescent indicator-displacement assays for sensing organic compounds

The widespread conversion of synthetic receptors into luminescent sensors has been achieved via the use of fluorescent-indicator displacement assays (F-IDAs). Due to their rigid structures and efficient binding affinities, cucurbit[n]urils, combined with a variety of fluorescent guests, have gained extensive utilization in fluorescent-indicator displacement assays for sensing non-fluorescent or weakly fluorescent organic compounds (analytes) in a selective and specific manner. This mini-review summarizes recent advances in the design of cucurbit[n]uril-based fluorescent-indicator displacement assays and discusses the current challenges and future prospects in this area.

Enzyme assays with supramolecular chemosensors - the label-free approach

Enzyme activity measurements are essential for many research areas, e.g., for the identification of inhibitors in drug discovery, in bioengineering of enzyme mutants for biotechnological applications, or in bioanalytical chemistry as parts of biosensors. In particular in high-throughput screening (HTS), sensitive optical detection is most preferred and numerous absorption and fluorescence spectroscopy-based enzyme assays have been developed, which most frequently require time-consuming fluorescent labelling that may interfere with biological recognition. The use of supramolecular chemosensors, which can specifically signal analytes with fluorescence-based read-out methods, affords an attractive and label-free alternative to more established enzyme assays. We provide herein a comprehensive review that summarizes the current state-of-the-art of supramolecular enzyme assays ranging from early examples with covalent chemosensors to the most recent applications of supramolecular tandem enzyme assays, which utilize common and often commercially available combinations of macrocyclic host molecules (e.g. cyclodextrins, calixarenes, and cucurbiturils) and fluorescent dyes as self-assembled reporter pairs for assaying enzyme activity.

Decarboxylases as hypothetical targets for actions of organophosphates: Molecular modeling for prediction of hidden and unexpected health threats

The rise of various neurodegenerative disorders are somewhat correlating with the worldwide application of multiple anthropogenic toxicants. Though different possible targets were revealed to date, for example, for organophosphorus compounds (OPs), plenty of questions remain. Several decarboxylases (aromatic amino acid decarboxylase, AADC; histidine decarboxylase, HDC; glutamate decarboxylase, GAD) catalyze the biosynthesis of neurotransmitters and neuromodulators and contain pyridoxal phosphate (PLP) as a cofactor. In the current work, 18 OPs which have different neurotoxicity (chemical warfare agents and pesticides) and can penetrate through the blood-brain barrier, were selected. Then, their possible interaction with these decarboxylases in both apo- and holoforms was revealed using computer modeling methods (molecular docking and dynamics). The main amino acid residues of the enzymes responsible for binding OPs have been identified. Individual substances that are most dangerous from the point of view of a possible negative effect on the activity of several decarboxylases were revealed among studied OPs. Glyphosate should be of special interest, since it is not highly toxic towards serine hydrolases, but may prove to be a strong inhibitor for decarboxylases. Holo-AADC could be the most inhibition-prone enzyme among all those investigated.

Occurrence, distribution and risk assessment of organophosphate ester flame retardants and plasticizers in surface seawater of the West Pacific

Twenty-eight samples of surface seawater were collected from the West Pacific Ocean during 2019 using a high-volume solid-phase extraction with high-throughput organic analysis (Hi-throat/Hi-volume SPE) method, and concentrations of 10 organophosphate ester flame retardants and plasticizers (OPEs) were determined. The total OPE concentration in the samples was 3.02-48.4 ng L^-1 (mean 25.0 ± 10.5 ng L^-1), with tris(2-chloroethyl) phosphate (TCEP) being the largest contributor. Cluster analysis results showed off-shore input from the coast of East and Southeast Asia was an important source of these chemicals. Tri-p-tolyl phosphate (TpTP) should also be considered for long-term monitoring, because of its high detection frequency. Results of a risk assessment indicated low ecological risk to species in the West Pacific Ocean for TPhP and ΣOPEs. Hazard quotients (HQs) were all <1, indicating that the health risk to humans from these chemicals was at acceptable levels.

New insights into the mechanism of hepatocyte apoptosis induced by typical organophosphate ester: An integrated in vitro and in silico approach

Apoptosis is one of the typical features of liver diseases, therefore molecular targets of hepatic apoptosis and regulatory mechanisms need to be further investigated. The caspases play important functions in the execution of apoptosis and many studies have focused on classical caspase-dependent cell death pathways. However, other types of cell death pathways (such as mitochondrial poly (ADP-ribose) polymerase-1 (PARP1) pathway) are suggested to be also as important as the caspase-mediated pathways in reflection of early toxic effects in hepatocytes, which requires additional research. In this work, an approach integrated in silico and in vitro was used to investigate the underlying toxicological mechanisms of hepatocyte apoptosis through the PARP1 dependent cell death pathway induced by triphenyl phosphate (TPP). Docking view showed that TPP could interact with helix αJ to affect the activation of PARP1 as a molecular initial event. In vitro assays suggested some biochemical events downstream of PARP1 activation, such as mitochondrial injury, apoptosis inducing factor (AIF) release, reactive oxygen species (ROS) production, and DNA damage. Moreover, the apoptosis was alleviated when cells were pretreated with PJ34 hydrochloride (PARP1 inhibitor), suggesting the mitochondrial PARP1 dependent pathway played a pivotal role in L02 cells apoptosis. This study indicated that PARP1 was an important molecular target in this process. And it also helped to understand the mechanism of hepatocytes apoptosis, early hepatic toxicity, and even liver diseases.

A review of organophosphate flame retardants and plasticizers in the environment: Analysis, occurrence and risk assessment

Organophosphate esters (OPEs) are used as additives in flame retardants and plasticizers. Due to phase out of several congeners of polybrominated diphenyl ethers (PBDEs), the application of organophosphorus flame retardants (OPFRs) is continuously increasing over the years. As a consequence, large amounts of OPEs enter the environment. Sewage and solid waste (especially e-waste) treatment plants are the important sources of OPEs released to the environment. Other sources include emissions of OPE-containing materials and vehicle fuel into the atmosphere. OPEs are widely detected in air, dust, water, soil, sediment and sludge. To know the pollution situation of OPEs, a variety of methods on their pretreatment and determination have been developed. We discussed and compared the analytical methods of OPEs, including extraction, purification as well as GC- and LC-based determination techniques. Much attention has been paid to OPEs because some of them are recognized highly toxic to biota, and the toxicological investigations of the most concerned OPEs were summarized. Risk assessments showed that the aquatic and benthic environments in some regions are under considerable ecological risks of OPEs. Finally, we pointed out problems in the current studies on OPEs and provided some suggestions for future research.

Derivation of the predicted no-effect concentration for organophosphate esters and the associated ecological risk in surface water in China

Organophosphate esters (OPEs), as re-emerging contaminants considered to be a potential health concern, are ubiquitous in the environment and have been widely investigated. However, little is known on the safe OPE concentrations in the water quality criteria for the protection of the aquatic environment, which is an indispensable part of environmental management. In the present study, aquatic acute and chronic predicted no-effect concentrations (PNECs) of six frequently detected OPEs were derived from the hazardous concentrations for 5% of species (HC₅s), respectively. The acute PNECs for the selected OPEs ranged from 17.70 to 3562 μg/L, while the chronic PNECs ranged from 4.6 × 10^-4 to 61.85 μg/L. Among these OPEs, tricresyl phosphate (TCrP) exhibited the lowest acute PNEC, while tris(1,3-dichloro-2-propyl) phosphate (TDCPP) presented chronic PNEC, which indicated that it has a higher toxicity effect on the aquatic environment. Furthermore, the aquatic ecological risks of individual OPEs (except for TDCPP) were deemed to be relatively low in Chinese surface water; however, the aquatic ecological risks of TDCPP and ΣOPEs indicated that they have potential adverse effects and should be considered as a potential health concern. The probability of 5% of aquatic organisms being affected by ΣOPEs was in the range of 0.21 to 17.39% based on the joint probability curve method.

The critical factors affecting typical organophosphate flame retardants to mimetic biomembrane: An integrated in vitro and in silico study

Organophosphate flame retardants (OPFRs) have been reported to induce cytotoxicity in a structure-dependent manner. The toxic effects may be due to the damage of biomembrane integrity and/or the interference of membrane signal pathway. In this study, the damages of fifteen typical OPFRs (chlorinated phosphates, alkyl phosphates, aryl phosphates, and alkoxy phosphates) to mimetic biomembrane were determined by the electrochemical impedance spectroscopy (EIS). The molecular structure descriptors that characterized the action mechanisms were screened by stepwise regression. The six molecular descriptors (MATS7e, DLS_05, Mor19m, Mor22v, Mor12v and MATS8m) were screened to study the actions between OPFRs and mimetic biomembrane. A quantitative structure-activity relationship (QSAR) model was developed by the partial least squares (PLS) method. Statistical results indicated that the QSAR model had good robustness and mechanism interpretability. The distribution of atomic electronegativities (MATS7e) and atomic masses in three dimensional spaces (Mor19m) were the key factors influencing the actions between OPFRs and simulated biofilms. The compounds with strong electron-withdrawing property could invade the inner layer of membrane and destroy its integrity. High levels of steric hindrance could impair the damage capacity caused by electronegativity. Moreover, drug-like index (DLS_05), spatial structures of particle (Mor22v, Mor12v) and atomic masses (MATS8m) also affected the actions. The results revealed the mechanism of the actions of OPFRs with simulated biofilms and elucidated the key structural characteristics affecting the actions of OPFRs, which could provide theoretical basis for ecological risk assessment of OPFRs.

Occurrence, distribution and risk assessment of organophosphate esters in surface water and sediment from a shallow freshwater Lake, China

Organophosphate esters (OPEs) are ubiquitous in the environment and pose a potential threat to ecosystem and human health. This study investigated the concentrations, distributions and risk of 12 OPEs in surface water and sediment from Luoma Lake, Fangting River and Yi River. Solid-phase extraction (SPE) method were used to extract OPEs from water samples, ultrasonic process and SPE method were used to extract OPEs from sediment samples, and the extracts were finally analyzed using the HPLC-MS/MS. The results revealed that the median and maximum concentrations of ΣOPEs were 73.9 and 1066 ng/L in surface water, and were 28.7 and 35.9 ng/g in sediment, respectively. Tris(2-chloroethyl) phosphate (TCEP) and trimethyl phosphate (TMP) were the most abundant OPEs in the surface water with median concentrations of 24.3 and 16.4 ng/L in Luoma Lake, respectively. Triethyl phosphate (TEP) was the most abundant OPE in the sediment with a median concentrations of 28.9 ng/g. However, tricresyl phosphate (TCrP) and ethylhexyl diphenyl phosphate (EHDPP) predominantly contributed to the ecological risk with respective median risk quotients 0.07 and 0.01 for surface water in Luoma Lake. TEP and TCrP were the most significant contributors to the ecological risk with respective median risk quotients of 6.4 × 10^-4 and 5.6 × 10^-4 for sediment. It was also found that inflowing Fangting River could be the major pollution source to Luoma Lake. The no-cancer and carcinogenic risks of OPEs were lower than the theoretical threshold of risk. The study found that the ecological and human health risks due to the exposure to OPEs were currently acceptable. In other words, the Luoma Lake was relatively safer to use as a drinking water source in urban areas in the context of OPEs pollution.

Organophosphate esters in East Greenland polar bears and ringed seals: Adipose tissue concentrations and in vitro depletion and metabolite formation

East Greenland is a contamination "hot spot" for long-range transported anthropogenic chemicals, including organophosphate esters (OPEs). High concentrations of OPEs have been reported in arctic air while very little is known for wildlife where OPE tissue residues levels appear to be strongly influenced by biotransformation. In the present study, the hepatic in vitro metabolism of six environmentally relevant organophosphate (OP) triesters and corresponding OP diester formation were investigated in East Greenland polar bears (PBs) and ringed seals (RSs). The in vitro metabolism assay results were compared to adipose levels in field samples from the same individuals. In vitro OP triester metabolism was generally rapid and structure-dependent, where PBs metabolized OPEs more rapidly than RSs. Exceptions were the lack of triethyl phosphate (TEP) metabolism and slow metabolism of tris(2-ethylhexyl) phosphate (TEHP) in both species. OP diester metabolites were also formed with the exception of TEP which was not metabolized at all. Tris(1,3-dichloro-2-propyl) phosphate was completely converted to its corresponding diester. However, the mass balances showed that OP diester formation corresponding to TEHP, tri(n-butyl) phosphate, and tris(2-butyoxyethyl) phosphate did not account for 100% of the OP triester depletion, which indicated alternate pathways of OP triester metabolism had occurred. Triphenyl phosphate was completely converted to its OP diester metabolite in PBs but not in RSs suggesting species-specific differences. The results demonstrated that OP triester bioaccumulation and fate in PBs versus their RS prey is substantially influenced by biotransformation.