Modulation of Ras signaling alters the toxicity of hydroquinone, a benzene metabolite and component of cigarette smoke

An update on the safety of hydroquinone

Hydroquinone has been used for years for multiple conditions, including melasma, post-inflammatory hyperpigmentation, dyschromia from photoaging, and solar lentigines. It is known to be a very effective lightening agent, but several concerns have been raised about this widely used agent. The recent U.S. ban on over-the-counter skin lightening products containing hydroquinone has prompted further questioning of the safety of this widely used agent. While there have been prior informative, large-scale reviews on the safety of hydroquinone, new findings have since been reported. Here, we provide an updated review of studies published in the past 15 years on hydroquinone safety.

Hsa_circ_0001944 regulates apoptosis by regulating the binding of PARP1 and HuR in leukemia and malignant transformed cells induced by hydroquinone

Hydroquinone (HQ) is one of the major metabolites of benzene and can cause abnormal gene expression. It is a known carcinogen that alters cell cycle disruption and cell proliferation. However, its chemical mechanism remain a mystery. Circular RNAs (circRNAs) are a subtype of noncoding RNAs (ncRNAs) that play a variety of roles in biological processes. Hsa_circ_001944 expression was upregulated in 30 leukemia patients and HQ-induced malignant transformed TK6 cells. Hsa_circ_001944 silencing inhibited the growth of HQ-TK6 cells and halted the cell cycle. The silencing of hsa_circ_0001944 led to increased cell accumulation in G1 versus S phase, increased apoptosis in the sh1944 versus the shNC group, and increased levels of DNA damage (γ-H2AX), leading to cell cycle arrest. In summary, inhibition of hsa_circ_001944 restricted cell growth by inhibiting cell cycle arrest and induced growth of HQ-TK6 cells by modulating PARP1 expression. Hsa_circ_0001944 targeted HuR, which is a kind of RNA-binding protein, to control PARP1 expression via RNAinter, RBPmap, and RBPdb. Fluorescence in situ hybridization combined with immunofluorescent labeling and western blotting experiments showed that hsa_circ_001944 was able to dissociate HuR and PARP1 binding in HQ-TK6 cells, control PARP1 production, and ultimately alter the PARP1/H-Ras pathway.

The continuing evolution of barcode applications: Functional toxicology to cell lineage

DNA barcoding is a method to identify biological entities, including individual cells, tissues, organs, or species, by unique DNA sequences. With the advent of next generation sequencing (NGS), there has been an exponential increase in data acquisition pertaining to medical diagnosis, genetics, toxicology, ecology, cancer, and developmental biology. While barcoding first gained wide access in identifying species, signature tagged mutagenesis has been useful in elucidating gene function, particularly in microbes. With the advent of CRISPR/CAS9, methodology to profile eukaryotic genes has made a broad impact in toxicology and cancer biology. Designed homing guide RNAs (hgRNAs) that self-target DNA sequences facilitate cell lineage barcoding by introducing stochastic mutations within cell identifiers. While each of these applications has their limitations, the potential of sequence barcoding has yet to be realized. This review will focus on signature-tagged mutagenesis and briefly discuss the history of barcoding, experimental problems, novel detection methods, and future directions.

Topical Treatments for Melasma and Their Mechanism of Action

OBJECTIVE

We conducted a review of topical agents currently used in melasma, discussing their mechanism of action, efficacy, safety, and tolerability, with an update on newer treatments.

METHODS

A systematic review from PubMed database was performed, using PRISMA guidelines. The search was limited to English and Spanish studies that were double or single blinded, prospective, controlled or randomized clinical trials, reviews of literature, and meta-analysis studies.

RESULTS

348 studies were analyzed; 80 papers met inclusion criteria. Triple combination (TC) therapy and hydroquinone (HQ) are still the most well-studied agents with strong evidence-based recommendation. TC therapy remains the gold standard of care based on efficacy and patient tolerability. Evidence has shown ascorbic acid, azelaic acid, glycolic acid, kojic acid, salicylic acid, and niacinamide to be effective as adjuvant therapies with minimal side effects. Tranexamic acid (TA) and cysteamine have become recent agents of interest due to their good tolerability, however more trials and studies are warranted. Less evidence exists for other topical agents, such as linoleic acid, mulberry extract oil, rucinol, 2% undecylenoyl phenylalanine, and epidermal growth factors agents.

LIMITATIONS

Some studies discussed represented a low sample size, and there is an overall lack of recent studies with larger populations and long-term follow up.

CONCLUSIONS

TC therapy continues to be the gold standard of care. Topical cysteamine and TA are newer options that can be incorporated as adjuvant and maintenance treatments into a patient's regimen. Cysteamine and topical TA have no known severe adverse effects. Evidence comparing other topical adjuvant treatments to HQ, maintains HQ as the gold standard of care.

p16 loss facilitate hydroquinone-induced malignant transformation of TK6 cells through promoting cell proliferation and accelerating the cell cycle progression

The p16^INK4A is a multifunction gene that includes regulation of the cell cycle, apoptosis, senescence and tumor development. However, the effects of p16 in hydroquinone-induced malignant transformation of TK6 cells remain unclear. The present study aimed to explore whether p16 loss facilitate malignant transformation in TK6 cells. The results demonstrated that p16/Rb signal pathway was suppressed in hydroquinone-induced malignant transformation of TK6 cells. We further confirmed that p16 loss stimulated cell proliferation, and accelerated cell cycle progression in vitro and in vivo. The immunoblotting analysis indicated that p16 regulated cell cycle progression via Rb and p53. Therefore, we conclude that p16 is involved in HQ-induced malignant transformation associated with suppressing Rb and p53 which resulting in accelerating the cell cycle progression.

Quinone-thioether metabolites of hydroquinone play a dual role in promoting a vicious cycle of ROS generation: in vitro and in silico insights

Humans are exposed to hydroquinone (HQ) via diet, smoking, occupation, and even via inhalation of polluted air. Given its preferential distribution in kidney and liver, the impact of biotransformation on the nephrotoxicity and hepatotoxicity of HQ was evaluated. Indeed, HQ and its metabolites, benzoquinone, and quinone-thioethers (50, 100, 200, and 400 μM) all induced ROS-dependent cell death in both HK-2, a human kidney proximal epithelial cell line, and THLE-2, a human liver epithelial cell line, in a concentration-dependent manner. For a deeper insight into the biological mechanism of ROS stimulation, the bioinformatics database was reviewed. Intriguingly, 163 proteins were currently reported to form co-crystal complex with benzoquinone analogs, a large proportion of which are closely related to ROS generation. After a thorough assessment of the interaction affinity and binding energy, three key mitochondrial proteins that are particularly involved in electric transport, namely, cytochrome BC1, succinate dehydrogenase, and sulfide:quinone oxidoreductase, were highlighted for further verification. Their binding affinity and the action pattern were explored and validated by molecular docking and molecular dynamics simulations. Remarkably, quinone-thioether metabolites of HQ afforded high affinity to the above proteins that purportedly cause a surge in the generation of ROS. Therefore, HQ can be further converted into quinone-thioethers, which on one hand can function as substrates for redox cycling, and on the other hand may afford high affinity with key proteins evolved in mitochondrial electron transport system, leading to a vicious cycle of ROS generation. The combined data provide a prospective insight into the mechanisms of ROS motivation, expanding HQ-mediated toxicology profiles.

miR-7-5p overexpression suppresses cell proliferation and promotes apoptosis through inhibiting the ability of DNA damage repair of PARP-1 and BRCA1 in TK6 cells exposed to hydroquinone

Hydroquinone (HQ), one of the major metabolic products of benzene, is a carcinogen, which induces apoptosis and inhibit proliferation in lymphoma cells. microRNA-7-5p (miR-7-5p), a tumor suppressor, participates in various biological processes including cell proliferation and apoptosis regulation by repressing expression of specific oncogenic target genes. To explore whether miR-7-5p is involved in HQ-induced cell proliferation and apoptosis, we assessed the effect of miR-7-5p overexpression on induction of apoptosis analyzed by FACSCalibur flow cytometer in transfection of TK6 cells with miR-7-5p mimic (TK6- miR-7-5p). We observed an increased apoptosis by 25.43% and decreased proliferation by 28.30% in TK6-miR-7-5p cells compared to those negative control cells (TK6-shNC) in response to HQ treatment. Furthermore, HQ might active the apoptotic pathway via partly downregulation the expression of BRCA1 and PARP-1, followed by p53 activation, in TK6-miR-7-5p cells. In contrast, attenuated p53 and BRCA1 expression was observed in shPARP-1 cells than in NC cells after HQ treatment. Therefore, we conclude that HQ may activate apoptotic signals via inhibiting the tumor suppressive effects of miR-7-5p, which may be mediated partly by upregulating the expression of PARP-1 and BRCA1 in control cells. The increase of miR-7-5p expression further intensified downregulation of PARP-1 and BRCA1 in TK6-miR-7-5p cells, resulting in an increase of apoptosis and proliferation inhibited.

Inhibition of autophagy enhances Hydroquinone-induced TK6 cell death

Hydroquinone (HQ), one of the metabolic products of benzene, is a carcinogen. It can induce apoptosis in lymphoma cells. However, whether HQ can induce autophagy and what roles autophagy plays in TK6 cells exposured to HQ remains unclear. In this study, we found that HQ could induce autophagy through techniques of qRT-PCR, Western blot, immunofluorescent assay of LC3 and transmission electron microscope. Furthermore, inhibiting autophagy using 3-methyladenine (3-MA) or chloroquine (CQ) significantly enhanced HQ-induced cell apoptosis, suggesting that autophagy may be a survival mechanism. Our study also showed that HQ activated PARP-1. Moreover, knockdown of PARP-1 strongly exhibited decreased autophagy related genes expression. In contrast, the absence of SIRT1 increased that. Altogether, our data provided evidence that HQ induced autophagy in TK6 cells and autophagy protected TK6 from HQ attack-induced injury in vitro, and the autophagy was partially mediated via activation of the PARP-1-SIRT1 signaling pathway.

Tobacco Smoke and Ras Mutations Among Latino and Non-Latino Children with Acute Lymphoblastic Leukemia

BACKGROUND AND AIMS

Childhood acute lymphoblastic leukemia (ALL) is a biologically heterogeneous disease, and mutations in the KRAS and NRAS oncogenes are present at diagnosis in about one-fifth of cases. Ras mutations were previously associated with environmental exposures in leukemias as well as in many other cancer types. This study examined whether Ras mutation could define a unique etiologic group of childhood ALL associated with tobacco smoke, a well-established mutagen and carcinogen.

METHODS

We included 670 children with ALL enrolled in a case-control study in California (1995-2013), including 50.6% Latinos. Parental and child exposure to tobacco smoke was obtained from interviews. Sanger sequencing was used to detect the common KRAS and NRAS hotspot mutations in diagnostic bone marrow DNA. ALL cases were also characterized for common chromosome abnormalities. In case-case analyses, logistic regression analyses were used to estimate odds ratios to describe the association between tobacco smoke exposure and childhood ALL with Ras mutations.

RESULTS

KRAS or NRAS mutations were detected in ∼18% of children diagnosed with ALL. Ras mutations were more common among Latino cases compared with non-Latino whites and in high-hyperdiploid ALL. No associations were observed between parental smoking or child's passive exposure to smoke and Ras positive ALL.

CONCLUSIONS

The apparent lack of association between tobacco smoke and Ras mutation in childhood ALL suggests that Ras mutations do not specifically define a tobacco-related etiologic pathway. Reasons for racial and ethnic differences in ALL are not well understood and could reflect differences in etiology that warrant further examination.

Clinical nomogram to predict bone-only metastasis in patients with early breast carcinoma

BACKGROUND

Bone is one of the most common sites of distant metastasis in breast cancer. The purpose of this study was to combine selected clinical and pathologic variables to develop a nomogram that can predict the likelihood of bone-only metastasis (BOM) as the first site of recurrence in patients with early breast cancer.

METHODS

Medical records of patients with non-metastatic breast cancer were retrospectively collected. On the basis of the analysis of patient and tumour characteristics using the Cox proportional hazards regression model, a nomogram to predict BOM was constructed for a 4175-patient-training cohort. The nomogram was validated in an independent cohort of 579 patients.

RESULTS

Among 4175 patients with non-metastatic breast cancer, 314 developed subsequent BOM. Age, T classification, lymph node status, lymphovascular space invasion, and hormone receptor status were significantly and independently associated with subsequent BOM. The nomogram had a concordance index of 0.69 in the training set and 0.73 in the validation set.

CONCLUSIONS

We have developed a clinical nomogram to predict subsequent BOM in patients with non-metastatic breast cancer. Selection of a patient population at high risk for BOM could facilitate research of more specific staging approaches or the selective use of bone-targeted therapy.

Emerging approaches in predictive toxicology

Predictive toxicology plays an important role in the assessment of toxicity of chemicals and the drug development process. While there are several well-established in vitro and in vivo assays that are suitable for predictive toxicology, recent advances in high-throughput analytical technologies and model systems are expected to have a major impact on the field of predictive toxicology. This commentary provides an overview of the state of the current science and a brief discussion on future perspectives for the field of predictive toxicology for human toxicity. Computational models for predictive toxicology, needs for further refinement and obstacles to expand computational models to include additional classes of chemical compounds are highlighted. Functional and comparative genomics approaches in predictive toxicology are discussed with an emphasis on successful utilization of recently developed model systems for high-throughput analysis. The advantages of three-dimensional model systems and stem cells and their use in predictive toxicology testing are also described.

Application of toxicogenomic profiling to evaluate effects of benzene and formaldehyde: from yeast to human

Genetic variation underlies a significant proportion of the individual variation in human susceptibility to toxicants. The primary current approaches to identify gene-environment (GxE) associations, genome-wide association studies and candidate gene association studies, require large exposed and control populations and an understanding of toxicity genes and pathways, respectively. This limits their application in the study of GxE associations for the leukemogens benzene and formaldehyde, whose toxicity has long been a focus of our research. As an alternative approach, our published work has applied innovative in vitro functional genomics testing systems, including unbiased functional screening assays in yeast and a near-haploid human bone marrow cell line. Through comparative genomic and computational analyses of the resulting data, human genes and pathways that may modulate susceptibility to benzene and formaldehyde were identified, and the roles of several genes in mammalian cell models were validated. In populations occupationally exposed to low levels of benzene, we applied peripheral blood mononuclear cell transcriptomics and chromosome-wide aneuploidy studies in lymphocytes. In this review, we describe our comprehensive toxicogenomic approach and the potential mechanisms of toxicity and susceptibility genes identified for benzene and formaldehyde, as well as related studies conducted by other researchers.