Inhibition of polyisoprenylated methylated protein methyl esterase by synthetic musks induces cell degeneration

Global distribution and ecological risk assessment of synthetic musks in the environment

Synthetic musks, as an alternative product of natural musks, are widely used in almost all fragrances of consumer products, such as perfumes, cosmetics and detergents. During the past few decades, the production of synthetic musks has been increasing year by year, subsequently followed by large concern about their adverse effects on ecosystems and human beings. Until now, several studies have reviewed the latest development of analytical methods of synthetic musks in biological samples and cosmetics products, while there is still lack of a systematic analysis of their global distribution in different environmental media. Thus, this review summarizes the occurrence of synthetic musks in the environment including biota around the world and explores their global distribution patterns. The results show that galaxolide (HHCB), tonalide (AHTN), musk xylene (MX) and musk ketone (MK) are generally the most frequently detected synthetic musks in different samples with HHCB and AHTN being predominant. Higher concentrations of HHCB and AHTN are normally found in western countries compared to Asian countries, indicating more consumptions of these musks in western countries. The persistence, bioaccumulation and toxicity (PBT) of synthetic musks (mainly for polycyclic musks and nitro musks) are also discussed. The risk quotients (RQs) of HHCB, AHTN, MX and MK in most waters and sediments are below 0.1, reflecting a low risk to aqueous and sediment-dwelling species. In some sites, e.g., close to STPs, high risks (RQs>1) are characterized. Currently, limited data are available for macrocyclic musks and alicyclic musks in terms of either occurrence or PBT properties. More studies with an expanded scope of chemical type, geographical distribution and (synergic) toxicological effects especially from a long-term point of view are needed.

Interactions between polycyclic musks and human lactoferrin: Multi-spectroscopic methods and docking simulation

Galaxolide (1,3,4,6,7,8-hexahydro-4,6,6,7,8-hexamethylcyclopenta-γ-2-benzopyrane; HHCB) and Tonalide (7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene; AHTN) are "pseudo-persistent" pollutants that can cause DNA damage, endocrine disruption, organ toxicity, and reproductive toxicity in humans. HHCB and AHTN are readily enriched in breast milk, so exposure of infants to HHCB and AHTN is of concern. Here, the molecular mechanisms through which HHCB and AHTN interact with human lactoferrin (HLF) are investigated using computational simulations and spectroscopic methods to identify indirectly how HHCB and AHTN may harm infants. Molecular docking and kinetic simulation studies indicated that HHCB and AHTN can interact with and alter the secondary HLF structure. The fluorescence quenching of HLF by HHCB, AHTN was static with the forming of HLF-HHCB, HLF-AHTN complex, and accompanied by non-radiative energy transfer and that 1:1 complexes form through interaction forces. Time-resolved fluorescence spectroscopy indicated that binding to small molecules does not markedly change the HLF fluorescence lifetime. Three-dimensional fluorescence spectroscopy indicated that HHCB and AHTN alter the peptide chain backbone structure of HLF. Ultraviolet-visible absorption spectroscopy, simultaneous fluorescence spectroscopy, Fourier-transform infrared spectroscopy, and circular dichroism spectroscopy indicated that HHCB and AHTN change the secondary HLF conformation. Antimicrobial activity experiments indicated that polycyclic musks decrease lactoferrin activity and interact with HLF. These results improve our understanding of the mechanisms involved in the toxicities of polycyclic musks bound to HLF at the molecular level and provide theoretical support for mother-and-child health risk assessments.

A Comparative Multi-System Approach to Characterizing Bioactivity of Commonly Occurring Chemicals

A 2019 retrospective study analyzed wristband personal samplers from fourteen different communities across three different continents for over 1530 organic chemicals. Investigators identified fourteen chemicals (G14) detected in over 50% of personal samplers. The G14 represent a group of chemicals that individuals are commonly exposed to, and are mainly associated with consumer products including plasticizers, fragrances, flame retardants, and pesticides. The high frequency of exposure to these chemicals raises questions of their potential adverse human health effects. Additionally, the possibility of exposure to mixtures of these chemicals is likely due to their co-occurrence; thus, the potential for mixtures to induce differential bioactivity warrants further investigation. This study describes a novel approach to broadly evaluate the hazards of personal chemical exposures by coupling data from personal sampling devices with high-throughput bioactivity screenings using in vitro and non-mammalian in vivo models. To account for species and sensitivity differences, screening was conducted using primary normal human bronchial epithelial (NHBE) cells and early life-stage zebrafish. Mixtures of the G14 and most potent G14 chemicals were created to assess potential mixture effects. Chemical bioactivity was dependent on the model system, with five and eleven chemicals deemed bioactive in NHBE and zebrafish, respectively, supporting the use of a multi-system approach for bioactivity testing and highlighting sensitivity differences between the models. In both NHBE and zebrafish, mixture effects were observed when screening mixtures of the most potent chemicals. Observations of BMC-based mixtures in NHBE (NHBE BMC Mix) and zebrafish (ZF BMC Mix) suggested antagonistic effects. In this study, consumer product-related chemicals were prioritized for bioactivity screening using personal exposure data. High-throughput high-content screening was utilized to assess the chemical bioactivity and mixture effects of the most potent chemicals.

Prolonged sub-lethal exposure to galaxolide (HHCB) and tonalide (AHTN) promotes the metastatic potential of glioblastoma tumor spheroids

Galaxolide and tonalide are well-known polycyclic musks whose intensive use without limitations in numerous cleaning, hygiene, and personal care products has resulted in widespread direct human exposure via absorption, inhalation, and oral ingestion. Latest data shows that long-term, low-dose exposure to toxic chemicals can induce unpredictable harmful effects in a variety of living systems, however, interactions between synthetic musks and brain tumours remain largely unexplored. Glioblastoma (GB) accounts for nearly half of all tumours of the central nervous system and is characterized by very poor prognosis. The aims of this study were (1) to investigate the potential effect of long-term (20-generation) single and combined application of galaxolide and tonalide at sub-lethal doses (5-2.5 u M) on the angiogenesis, invasion, and migration of human U87 cells or tumour spheroids, and (2) to explore the underlying molecular mechanisms. Random amplified polymorphic DNA assays revealed significant DNA damage and increased total mutation load in galaxolide- and/or tonalide-treated U87 cells. In those same groups, we also detected remarkable tumour spheroid invasion and up-regulation of both HIF1-α/VEGF/MMP9 and IL6/JAK2/STAT3 signals, known to have important roles in hypoxia-related angiogenesis and/or proliferation. Prolonged musk treatment further altered angio-miRNA expression in a manner consistent with poor prognosis in GB. We also detected significant over-expression of the genes Slug, Snail, ZEB1, and Vimentin, which are biomarkers of epithelial to mesenchymal transition. In addition, matrigel, transwell, and wound healing assays clearly showed that long-term sub-lethal exposure to galaxolide and/or tonalide induced invasion and migration proposing a high metastatic potential. Our results suggest that assessing expression of HIF-1a, VEGF, STAT3, and the miR-17-92 cluster in biopsy samples of GB patients who have a history of possible long-term exposure to galaxolide or tonalide could be beneficial for deciding a therapy regime. Additionally, we recommend that extensively-used hygiene and cleaning materials be selected from synthetic musk-free products, especially when used in palliative care processes for GB patients.

Endocrine disruptors also function as nervous disruptors and can be renamed endocrine and nervous disruptors (ENDs)

Endocrine disruption (ED) and endocrine disruptors (EDs) emerged as scientific concepts in 1995, after numerous chemical pollutants were found to be responsible for reproductive dysfunction. The World Health Organization established in the United Nations Environment Programme a list of materials, plasticizers, pesticides, and various pollutants synthesized from petrochemistry that impact not only reproduction, but also hormonal functions, directly or indirectly. Cells communicate via either chemical or electrical signals transmitted within the endocrine or nervous systems. To investigate whether hormone disruptors may also interfere directly or indirectly with the development or functioning of the nervous system through either a neuroendocrine or a more general mechanism, we examined the scientific literature to ascertain the effects of EDs on the nervous system, specifically in the categories of neurotoxicity, cognition, and behaviour. To date, we demonstrated that all of the 177 EDs identified internationally by WHO are known to have an impact on the nervous system. Furthermore, the precise mechanisms underlying this neurodisruption have also been established. It was previously believed that EDs primarily function via the thyroid. However, this study presents substantial evidence that approximately 80 % of EDs operate via other mechanisms. It thus outlines a novel concept: EDs are also neurodisruptors (NDs) and can be collectively termed endocrine and nervous disruptors (ENDs). Most of ENDs are derived from petroleum residues, and their various mechanisms of action are similar to those of "spam" in electronic communications technologies. Therefore, ENDs can be considered as an instance of spam in a biological context.

Polyisoprenylated Cysteinyl Amide Inhibitors: A Novel Approach to Controlling Cancers with Hyperactive Growth Signaling

Aberrant activation of monomeric G-protein signaling pathways drives some of the most aggressive cancers. Suppressing these hyperactivities has been the focus of efforts to obtain targeted therapies. Polyisoprenylated methylated protein methyl esterase (PMPMEase) is overexpressed in various cancers. Its inhibition induces the death of cancer cells that harbor the constitutively active K-Ras proteins. Furthermore, the viability of cancer cells driven by factors upstream of K-Ras, such as overexpressed growth factors and their receptors or the mutationally-activated receptors, is also susceptible to PMPMEase inhibition. Polyisoprenylated cysteinyl amide inhibitors (PCAIs) were thus designed to target cancers with hyperactive signaling pathways involving the G-proteins. The PCAIs were, however, poor inhibitors of PMPMEase, with K_i values ranging from 3.7 to 20 μM. On the other hand, they inhibited cell viability, proliferation, colony formation, induced apoptosis in cells with mutant K-Ras and inhibited cell migration and invasion with EC₅₀ values of 1 to 3 μM. HUVEC tube formation was inhibited at submicromolar concentrations through their disruption of actin filament organization. At the molecular level, the PCAIs at 2 to 5 μM depleted monomeric G-proteins such as K-Ras, RhoA, Cdc42 and Rac1. The PCAIs also deplete vinculin and fascin that are involved in actin organization and function while disrupting vinculin punctates in the process. These demonstrate a polyisoprenylation-dependent mechanism that explains the observed PCAIs' inhibition of the proliferative, invasive and angiogenic processes that promote both tumor growth and metastasis.

Study of conformational and functional changes caused by binding of environmental pollutant tonalide to human serum albumin

Tonalide (AHTN) is a new category of pollutants with a wide range of potential environmental and organismal hazards due to its persistence and lipophilicity, and the safety evaluation of this pollutant under physiological condition is a pressing issue. This study investigated the mechanism of interaction between AHTN and human serum albumin (HSA) that is an important transporter in plasma using multiple spectroscopic, molecular docking, and dynamics simulation methods. The steady-state fluorescence and fluorescence lifetime experiments showed that AHTN quenches the inherent fluorescence of HSA through a static quenching mechanism. Thermodynamic parameters exhibited that the binding constant of AHTN and HSA is of the order of 10^{^4} L/mol, and the binding is a spontaneous process of moderate strength with hydrophobic forces as the main driving force. Site competition revealed that AHTN binds to site I of HSA IIA subdomain, which was evidenced by the molecular docking results. AHTN altered the HSA amino acid microenvironment and conformation can be derived from three-dimensional fluorescence, circular dichroism spectroscopy, and molecular dynamics simulation. The computer simulations corroborate the experimental results positively. Moreover, AHTN acted as a competitive inhibitor to weaken the esterase-like activity of HSA, leading to impaired function of HSA. Results suggest that interactions between AHTN and HSA may affect the normal structure and activities of the protein, this insight will be helpful to provide some basic information to further explore the potential hazards of AHTN in humans.

Antioxidative enzyme activities in the Rhodeinae sinensis Gunther and Macrobrachium nipponense and multi-endpoint assessment under tonalide exposure

Tonalide or acetyl hexamethyl tetralin (AHTN) is used as a fragrance additive in various household products. Recently, AHTN has drawn attention owing to its negative health effects on aquatic organisms. Data on AHTN toxicity toward aquatic species are limited. Therefore, this study tested the oxidative stress induced by AHTN exposure on the Rhodeinae sinensis Gunther and Macrobrachium nipponense. In this study, malonaldehyde (MDA) content and the activities of acetyl cholinesterase (AchE), superoxide dismutase (SOD), glutathione S-transferase (GST), and catalase (CAT) in R. sinensis Gunther were tested after 30 days of exposure to 30.093, 34.005, 38.426, 43.421, 49.067, 55.444, 62.652, 70.800, and 80.000 μg/L AHTN, respectively. The MDA, AchE, SOD, GST and CAT in M. nipponense were tested after 40 days of exposure to 60.000, 72.000, 86.400, 103.680, 124.416, 149.299, 179.159, 214.991, and 257.989 μg/L AHTN, respectively. In addition, an integrated biomarker response (IBR) index was utilised to evaluate the integrated toxic effects of AHTN on R. sinensis Gunther and M. nipponense. Finally, the predicted no-effect concentrations (PNECs) of AHTN, based on reproduction, biochemistry, survival, chronic toxicity, and acute toxicity endpoints were derived. The results indicated that low concentrations of AHTN can induce significant changes of oxidative stress biomarkers. The no observed effect concentrations (NOECs) of SOD, GST, AchE, CAT, and MDA were 103.680, 72.000, <60.000, 72.000, and <60.000 μg/L for R. sinensis Gunther and 38.426, 43.421, 30.093, 30.093, and 38.426 μg/L for M. nipponense, respectively. The IBR calculation results showed that 149.299 μg/L AHTN caused the highest toxic effect on R. sinensis Gunther after 30 days of exposure, whereas 70.797 μg/L AHTN caused the greatest damage to M. nipponense after 40 days of exposure. The PNECs of AHTN based on the non-traditional endpoints of biochemistry and reproduction were 0.00145 μg/L and 0.000395 μg/L, respectively, which were significantly lower than the PNEC of 2.636 μg/L for traditional endpoint survival. Therefore, the protection of aquatic organisms based on non-traditional toxicity endpoints should be considered in ecological risk assessment.

Neurotoxicity of fragrance compounds: A review

Fragrance compounds are chemicals belonging to one of several families, which are used frequently and globally in cosmetics, household products, foods and beverages. A complete list of such compounds is rarely found on the ingredients-list of such products, as "fragrance mixtures" are defined as "trade secrets" and thus protected by law. While some information regarding the general toxicity of some of these compounds is available, their neurotoxicity is known to a lesser extent. Here, we discuss the prevalence and neurotoxicity of fragrance compounds belonging to the three most common groups: phthalates, synthetic musks and chemical sensitizers.

Disruption of actin filaments and suppression of pancreatic cancer cell viability and migration following treatment with polyisoprenylated cysteinyl amides

Pancreatic cancer is characterized by K-Ras mutations in over 90% of the cases. The mutations make the tumors aggressive and resistant to current therapies resulting in very poor prognoses. Valiant efforts to drug mutant K-Ras and related proteins for the treatment of cancers with Ras mutations have been elusive. The need thus persists for therapies to target and suppress the hyperactive K-Ras mutant proteins to normal levels of activity. Polyisoprenylated cysteinyl amide inhibitors (PCAIs) of polyisoprenylated methylated protein methyl esterase (PMPMEase) were designed to disrupt polyisoprenylated protein metabolism and/or functions. The potential for PCAIs to serve as targeted anticancer agents for pancreatic cancer was evaluated in pancreatic ductal adenocarcinoma (PDAC) cell lines expressing mutant (MIAPaCa-2 and Panc-1) and wild type (BxPC-3) K-Ras proteins. The PCAIs inhibited MIAPaCa-2 and BxPC-3 cell viability and induced apoptosis with EC₅₀ values as low as 1.9 µM. The PCAIs, at 0.5 µM, inhibited MIAPaCa-2 cell migration by 50%, inhibited colony formation and disrupted F-actin filament organization. The PCAIs blocked MIAPaCa-2 cell progression at the G0/G1 phase. These results reveal that the PCAIs disrupt pertinent biological processes that lead to pancreatic cancer progression and thus have the potential to act as targeted effective treatments for pancreatic cancer.

Polyisoprenylated methylated protein methyl esterase as a putative drug target for androgen-insensitive prostate cancer

Prostate cancer (CaP) is the most frequently diagnosed cancer in US men, with an estimated 236,590 new cases and 29,720 deaths in 2013. There exists the need to identify biomarkers/therapeutic targets for the early/companion diagnosis and development of novel therapies against the recalcitrant disease. Mutation and overexpression-induced abnormal activities of polyisoprenylated proteins have been implicated in CaP. Polyisoprenylated methylated protein methyl esterase (PMPMEase) catalyses the only reversible and terminal reaction of the polyisoprenylation pathway and may promote the effects of G proteins on cell viability. In this review, the potential role of PMPMEase to serve as a new drug target for androgen-insensitive CaP was determined. Specific PMPMEase activities were found to be 3.5- and 4.5-fold higher in androgen-sensitive 22Rv1 and androgen-dependent LNCaP and 1.5- and 9.8-fold higher in castration-resistant DU 145 and PC-3 CaP cells compared to normal WPE1-NA22 prostate cells. The PMPMEase inhibitor, L-28, induced apoptosis with EC50 values ranging from 1.8 to 4.6 μM. The PMPMEase activity in the cells following treatment with L-28 followed a similar profile, with IC50 ranging from 2.3 to 130 μM. L-28 disrupted F-actin filament organisation at 5 μM and inhibited cell migration 4-fold at 2 μM. Analysis of a CaP tissue microarray for PMPMEase expression revealed intermediate, strong, and very strong staining in 94.5% of the 92 adenocarcinoma cases compared to trace and weak staining in the normal and normal-adjacent tissue controls. The data are an indication that effective targeting of PMPMEase through the development of more potent agents may lead to the successful treatment of metastatic CaP.

Polyisoprenylated methylated protein methyl esterase: a putative biomarker and therapeutic target for pancreatic cancer

Pancreatic cancer is the most deadly neoplasm with a 5-year survival rate of less than 6%. Over 90% of cases harbor K-Ras mutations, which are the most challenging to treat due to lack of effective therapies. Here, we reveal that polyisoprenylated methylated protein methyl esterase (PMPMEase) is overexpressed in 93% of pancreatic ductal adenocarcinoma. We further present polyisoprenylated cysteinyl amide inhibitors (PCAIs) as novel compounds designed with structural elements for optimal in vivo activities and selective disruption of polyisoprenylation-mediated protein functions. The PCAIs inhibited PMPMEase with Ki values ranging from 3.7 to 20 μM. The 48 h EC50 values for pancreatic cancer Mia PaCa-2 and BxPC-3 cell lines were as low as 1.9 μM while salirasib and farnesylthiosalicylamide were ineffective at 20 μM. The PCAIs thus have the potential to serve as effective therapies for pancreatic and other cancers with hyperactive growth signaling pathways mediated by Ras and related G-proteins.

Polyisoprenylated methylated protein methyl esterase is both sensitive to curcumin and overexpressed in colorectal cancer: implications for chemoprevention and treatment

Inhibition of PMPMEase, a key enzyme in the polyisoprenylation pathway, induces cancer cell death. In this study, purified PMPMEase was inhibited by the chemopreventive agent, curcumin, with a K(i) of 0.3 μM (IC50 = 12.4 μM). Preincubation of PMPMEase with 1 mM curcumin followed by gel-filtration chromatography resulted in recovery of the enzyme activity, indicative of reversible inhibition. Kinetics analysis with N-para-nitrobenzoyl-S-trans,trans-farnesylcysteine methyl ester substrate yielded K M values of 23.6 ± 2.7 and 85.3 ± 15.3 μM in the absence or presence of 20 μM curcumin, respectively. Treatment of colorectal cancer (Caco2) cells with curcumin resulted in concentration-dependent cell death with an EC50 of 22.0 μg/mL. PMPMEase activity in the curcumin-treated cell lysate followed a similar concentration-dependent profile with IC50 of 22.6 μg/mL. In colorectal cancer tissue microarray studies, PMPMEase immunoreactivity was significantly higher in 88.6% of cases compared to normal colon tissues (P < 0.0001). The mean scores ± SEM were 91.7 ± 11.4 (normal), 75.0 ± 14.4 (normal adjacent), 294.8 ± 7.8 (adenocarcinoma), and 310.0 ± 22.6 (mucinous adenocarcinoma), respectively. PMPMEase overexpression in colorectal cancer and cancer cell death stemming from its inhibition is an indication of its possible role in cancer progression and a target for chemopreventive agents.