Toxicological Assessment of Flavor Ingredients in E-Vapor Products.

Many flavor ingredients are often used in potentially reduced-risk tobacco products (such as e-vapor products). Although most are "generally recognized as safe (GRAS)" when used in food, there is limited information available on their long-term health effects when delivered by inhalation. While obtaining route-of-exposure-specific toxicological data on flavor ingredients is critical to product evaluation, the large number of individual flavor ingredients available and their potential combinations render classical toxicological assessment approaches impractical, as they may require years of preclinical investigations and thousands of laboratory animals. Therefore, we propose a pragmatic approach in which flavor ingredients are initially assigned to groups of structurally related compounds (Flavor Groups), from which flavor group representatives (FGR) are then selected and tested individually and as a mixture in vitro and in vivo. The premise is that structurally related compounds would have comparable metabolic and biological activity and that the data generated using FGRs could support the toxicological assessment of other structurally related flavor ingredients of their respective Flavor Groups. This approach is explained in a step-wise manner and exemplified by a case study, along with its strengths, limitations as well as recommendations for further confirmatory testing. Once completed, this FGR approach could significantly reduce the time and resources required for filling the data gap in understanding the health risks of many flavor ingredients while also minimizing the need for laboratory animals.

Evaluation of toxicity of aerosols from flavored e-liquids in Sprague-Dawley rats in a 90-day OECD inhalation study, complemented by transcriptomics analysis.

The use of flavoring substances is an important element in the development of reduced-risk products for adult smokers to increase product acceptance and encourage switching from cigarettes. In a first step towards characterizing the sub-chronic inhalation toxicity of neat flavoring substances, a study was conducted using a mixture of the substances in a base solution of e-liquid, where the standard toxicological endpoints of the nebulized aerosols were supplemented with transcriptomics analysis. The flavor mixture was produced by grouping 178 flavors into 26 distinct chemical groups based on structural similarities and potential metabolic and biological effects. Flavoring substances predicted to show the highest toxicological effect from each group were selected as the flavor group representatives (FGR). Following Organization for Economic Cooperation and Development Testing Guideline 413, rats were exposed to three concentrations of the FGR mixture in an e-liquid composed of nicotine (23 µg/L), propylene glycol (1520 µg/L), and vegetable glycerin (1890 µg/L), while non-flavored and no-nicotine mixtures were included as references to identify potential additive or synergistic effects between nicotine and the flavoring substances. The results indicated that the inhalation of an e-liquid containing the mixture of FGRs caused very minimal local and systemic toxic effects. In particular, there were no remarkable clinical (in-life) observations in flavored e-liquid-exposed rats. The biological effects related to exposure to the mixture of neat FGRs were limited and mainly nicotine-mediated, including changes in hematological and blood chemistry parameters and organ weight. These results indicate no significant additive biological changes following inhalation exposure to the nebulized FGR mixture above the nicotine effects measured in this sub-chronic inhalation study. In a subsequent study, e-liquids with FGR mixtures will be aerosolized by thermal treatment and assessed for toxicity.

Systems toxicology assessment of a representative e-liquid formulation using human primary bronchial epithelial cells.

The development of reduced-risk products aims to provide alternatives to cigarettes that present less risk of harm for adult smokers. Responsible use of flavoring substances in these products may fulfill an important role in product acceptance. While most flavoring substances used in such products are also used by the food industry and are considered safe when ingested, their impact when inhaled may require further assessment. To aid in such an assessment, a three-step approach combining real-time cellular analysis, phenotypic high-content screening assays, and gene expression analysis was developed and tested in normal human bronchial epithelial cells with 28 flavoring substances commonly used in e-liquid formulations, dissolved individually or as a mixture in a base solution composed of propylene glycol, vegetable glycerin, and 0.6% nicotine. By employing this approach, we identified individual flavoring substances that potentially contribute greatly to the overall mixture effect (citronellol and alpha-pinene). By assessing modified mixtures, we showed that, although cytotoxic effects were found when assessed individually, alpha-pinene did not contribute to the overall mixture cytotoxicity. Most of the cytotoxic effect appeared to be attributable to citronellol, with the remaining substances contributing due to synergistic effects. We developed and used different scoring methods (Tox-Score, Phenotypic Score, and Biological Impact Factor/Network Perturbation Amplitude), ultimately enabling a ranking based on cytotoxicity, phenotypic outcome, and molecular network perturbations. This case study highlights the benefits of testing both individual flavoring substances and mixtures for e-liquid flavor assessment and emphasized the importance of data sharing for the benefit of consumer safety.

Respirable aerosol exposures of nicotine dry powder formulations to in vitro, ex vivo, and in vivo pre-clinical models demonstrate consistency of pharmacokinetic profiles.

Background: Nicotine, because of its volatility, has a complex dosimetry following inhalation as a vapor/aerosol mix. To better control the dosimetry, nicotine could be formulated with a suitable dry powder excipient for use in a clinical inhaler. Aim and Methods: The aim of this study was to investigate the pharmacokinetic PK profile of two dry powder formulations containing 2.5% or 5% nicotine using three experimental models associated to the PreciseInhale™ aerosolization system: the in vitro DissolvIt dissolution system; the ex vivo isolated, ventilated, and perfused lung (IPL) of the rat; and the in vivo intratracheally intubated rat. Results and Discussion: Following exposure, both nicotine formulations had very rapid and similar dissolution and absorption kinetics in both the DissolvIt and IPL exposure models, with an initial half-time of absorption to the single-pass perfusate of 34 and 72 seconds, respectively. In the intratracheally intubated rat, following a rapid initial equilibration between the lungs and systemic compartments, nicotine had a systemic elimination half-time of 2.3-2.4 hours for both formulations. The rapid pulmonary PK of nicotine was likely close to the theoretical equilibration of a low-binding substance with a tissue-blood partition coefficient close to 1. Conclusions: The data generated with the three experimental models provided a comprehensive picture of the inhalation PK of the two nicotine formulations. In particular, the results showed a very rapid dissolution and absorption of the two nicotine formulations and these results could be highly useful for improving the design and calibration of physiologically based PK models to produce more robust predictions. Abbreviations: AED: animal equivalent dose; BW: body weight; HPLC: high-performance liquid chromatography; IPL: isolated, ventilated, and perfused lung; PK: pharmacokinetics; SEM: scanning electron microscopy; USP: United States Pharmacopeia.

A 90-day OECD TG 413 rat inhalation study with systems toxicology endpoints demonstrates reduced exposure effects of the aerosol from the carbon heated tobacco product version 1.2 (CHTP1.2) compared with cigarette smoke. I. Inhalation exposure, clinical pathology and histopathology.

Within the framework of a systems toxicology approach, the inhalation toxicity of aerosol from a novel tobacco-heating potentially modified risk tobacco product (MRTP), the carbon-heated tobacco product (CHTP) 1.2, was characterized and compared with that of mainstream smoke (CS) from the 3R4F reference cigarette in a 90-day nose-only rat inhalation study in general accordance with OECD TG 413. CHTP1.2 is a heat-not-burn product using a carbon heat source to produce an aerosol that contains nicotine and tobacco flavor. At equal or twice the nicotine concentration in the test atmospheres, inhalation of CHTP1.2 aerosol led to a significantly lower exposure to harmful constituents and induced less respiratory tract irritation, systemic, and pathological effects compared with CS. Nasal epithelial changes were less pronounced in the CHTP1.2- than in the CS-exposed groups and reverted in the nicotine concentration-matched group after a recovery period. Lung inflammation was minimal in the CHTP1.2-treated groups compared with the moderate extent seen in the 3R4F groups. Many other toxicological endpoints evaluated did not show CHTP1.2 aerosol exposure-related effects, and no effects not seen for 3R4F were observed. These observations were consistent with findings from previous studies in which rats were exposed to MRTP aerosols containing similar nicotine concentrations.

Toxicity of the main electronic cigarette components, propylene glycol, glycerin, and nicotine, in Sprague-Dawley rats in a 90-day OECD inhalation study complemented by molecular endpoints.

While the toxicity of the main constituents of electronic cigarette (ECIG) liquids, nicotine, propylene glycol (PG), and vegetable glycerin (VG), has been assessed individually in separate studies, limited data on the inhalation toxicity of them is available when in mixtures. In this 90-day subchronic inhalation study, Sprague-Dawley rats were nose-only exposed to filtered air, nebulized vehicle (saline), or three concentrations of PG/VG mixtures, with and without nicotine. Standard toxicological endpoints were complemented by molecular analyses using transcriptomics, proteomics, and lipidomics. Compared with vehicle exposure, the PG/VG aerosols showed only very limited biological effects with no signs of toxicity. Addition of nicotine to the PG/VG aerosols resulted in effects in line with nicotine effects observed in previous studies, including up-regulation of xenobiotic enzymes (Cyp1a1/Fmo3) in the lung and metabolic effects, such as reduced serum lipid concentrations and expression changes of hepatic metabolic enzymes. No toxicologically relevant effects of PG/VG aerosols (up to 1.520  mg PG/L + 1.890 mg VG/L) were observed, and no adverse effects for PG/VG/nicotine were observed up to 438/544/6.6 mg/kg/day. This study demonstrates how complementary systems toxicology analyses can reveal, even in the absence of observable adverse effects, subtoxic and adaptive responses to pharmacologically active compounds such as nicotine.

Chromosome 7 gain and DNA hypermethylation at the HOXA10 locus are associated with expression of a stem cell related HOX-signature in glioblastoma.

BACKGROUND: HOX genes are a family of developmental genes that are expressed neither in the developing forebrain nor in the normal brain. Aberrant expression of a HOX-gene dominated stem-cell signature in glioblastoma has been linked with increased resistance to chemo-radiotherapy and sustained proliferation of glioma initiating cells. Here we describe the epigenetic and genetic alterations and their interactions associated with the expression of this signature in glioblastoma. RESULTS: We observe prominent hypermethylation of the HOXA locus 7p15.2 in glioblastoma in contrast to non-tumoral brain. Hypermethylation is associated with a gain of chromosome 7, a hallmark of glioblastoma, and may compensate for tumor-driven enhanced gene dosage as a rescue mechanism by preventing undue gene expression. We identify the CpG island of the HOXA10 alternative promoter that appears to escape hypermethylation in the HOX-high glioblastoma. An additive effect of gene copy gain at 7p15.2 and DNA methylation at key regulatory CpGs in HOXA10 is significantly associated with HOX-signature expression. Additionally, we show concordance between methylation status and presence of active or inactive chromatin marks in glioblastoma-derived spheres that are HOX-high or HOX-low, respectively. CONCLUSIONS: Based on these findings, we propose co-evolution and interaction between gene copy gain, associated with a gain of chromosome 7, and additional epigenetic alterations as key mechanisms triggering a coordinated, but inappropriate, HOX transcriptional program in glioblastoma.

MGMT methylation analysis of glioblastoma on the Infinium methylation BeadChip identifies two distinct CpG regions associated with gene silencing and outcome, yielding a prediction model for comparisons across datasets, tumor grades, and CIMP-status.

The methylation status of the O(6)-methylguanine-DNA methyltransferase (MGMT) gene is an important predictive biomarker for benefit from alkylating agent therapy in glioblastoma. Recent studies in anaplastic glioma suggest a prognostic value for MGMT methylation. Investigation of pathogenetic and epigenetic features of this intriguingly distinct behavior requires accurate MGMT classification to assess high throughput molecular databases. Promoter methylation-mediated gene silencing is strongly dependent on the location of the methylated CpGs, complicating classification. Using the HumanMethylation450 (HM-450K) BeadChip interrogating 176 CpGs annotated for the MGMT gene, with 14 located in the promoter, two distinct regions in the CpG island of the promoter were identified with high importance for gene silencing and outcome prediction. A logistic regression model (MGMT-STP27) comprising probes cg12434587 [corrected] and cg12981137 provided good classification properties and prognostic value (kappa = 0.85; log-rank p < 0.001) using a training-set of 63 glioblastomas from homogenously treated patients, for whom MGMT methylation was previously shown to be predictive for outcome based on classification by methylation-specific PCR. MGMT-STP27 was successfully validated in an independent cohort of chemo-radiotherapy-treated glioblastoma patients (n = 50; kappa = 0.88; outcome, log-rank p < 0.001). Lower prevalence of MGMT methylation among CpG island methylator phenotype (CIMP) positive tumors was found in glioblastomas from The Cancer Genome Atlas than in low grade and anaplastic glioma cohorts, while in CIMP-negative gliomas MGMT was classified as methylated in approximately 50 % regardless of tumor grade. The proposed MGMT-STP27 prediction model allows mining of datasets derived on the HM-450K or HM-27K BeadChip to explore effects of distinct epigenetic context of MGMT methylation suspected to modulate treatment resistance in different tumor types.

The Wnt inhibitory factor 1 (WIF1) is targeted in glioblastoma and has a tumor suppressing function potentially by induction of senescence.

Gene expression-based prediction of genomic copy number aberrations in the chromosomal region 12q13 to 12q15 that is flanked by MDM2 and CDK4 identified Wnt inhibitory factor 1 (WIF1) as a candidate tumor suppressor gene in glioblastoma. WIF1 encodes a secreted Wnt antagonist and was strongly downregulated in most glioblastomas as compared with normal brain, implying deregulation of Wnt signaling, which is associated with cancer. WIF1 silencing was mediated by deletion (7/69, 10%) or epigenetic silencing by promoter hypermethylation (29/110, 26%). Co-amplification of MDM2 and CDK4 that is present in 10% of glioblastomas was associated in most cases with deletion of the whole genomic region enclosed, including the WIF1 locus. This interesting pathogenetic constellation targets the RB and p53 tumor suppressor pathways in tandem, while simultaneously activating oncogenic Wnt signaling. Ectopic expression of WIF1 in glioblastoma cell lines revealed a dose-dependent decrease of Wnt pathway activity. Furthermore, WIF1 expression inhibited cell proliferation in vitro, reduced anchorage-independent growth in soft agar, and completely abolished tumorigenicity in vivo. Interestingly, WIF1 overexpression in glioblastoma cells induced a senescence-like phenotype that was dose dependent. These results provide evidence that WIF1 has tumor suppressing properties. Downregulation of WIF1 in 75% of glioblastomas indicates frequent involvement of aberrant Wnt signaling and, hence, may render glioblastomas sensitive to inhibitors of Wnt signaling, potentially by diverting the tumor cells into a senescence-like state.

Extent and patterns of MGMT promoter methylation in glioblastoma- and respective glioblastoma-derived spheres.

PURPOSE: Quantitative methylation-specific tests suggest that not all cells in a glioblastoma with detectable promoter methylation of the O6-methylguanine DNA methyltransferase (MGMT) gene carry a methylated MGMT allele. This observation may indicate cell subpopulations with distinct MGMT status, raising the question of the clinically relevant cutoff of MGMT methylation therapy. Epigenetic silencing of the MGMT gene by promoter methylation blunts repair of O6-methyl guanine and has been shown to be a predictive factor for benefit from alkylating agent therapy in glioblastoma. EXPERIMENTAL DESIGN: Ten paired samples of glioblastoma and respective glioblastoma-derived spheres (GS), cultured under stem cell conditions, were analyzed for the degree and pattern of MGMT promoter methylation by methylation-specific clone sequencing, MGMT gene dosage, chromatin status, and respective effects on MGMT expression and MGMT activity. RESULTS: In glioblastoma, MGMT-methylated alleles ranged from 10% to 90%. In contrast, methylated alleles were highly enriched (100% of clones) in respective GS, even when 2 MGMT alleles were present, with 1 exception (<50%). The CpG methylation patterns were characteristic for each glioblastoma exhibiting 25% to 90% methylated CpGs of 28 sites interrogated. Furthermore, MGMT promoter methylation was associated with a nonpermissive chromatin status in accordance with very low MGMT transcript levels and undetectable MGMT activity. CONCLUSIONS: In MGMT-methylated glioblastoma, MGMT promoter methylation is highly enriched in GS that supposedly comprise glioma-initiating cells. Thus, even a low percentage of MGMT methylation measured in a glioblastoma sample may be relevant and predict benefit from an alkylating agent therapy.

Expression of O6-methylguanine-DNA methyltransferase in childhood medulloblastoma.

Medulloblastomas (MB) are the most common malignant brain tumors in childhood. Alkylator-based drugs are effective agents in the treatment of patients with MB. In several tumors, including malignant glioma, elevated O(6)-methylguanine-DNA methyltransferase (MGMT) expression levels or lack of MGMT promoter methylation have been found to be associated with resistance to alkylating chemotherapeutic agents such as temozolomide (TMZ). In this study, we examined the MGMT status of MB and central nervous system primitive neuroectodermal tumor (PNET) cells and two large sets of primary MB. In seven MB/PNET cell lines investigated, MGMT promoter methylation was detected only in D425 human MB cells as assayed by the qualitative methylation-specific PCR and the more quantitative pyrosequencing assay. In D425 human MB cells, MGMT mRNA and protein expression was clearly lower when compared with the MGMT expression in the other MB/PNET cell lines. In MB/PNET cells, sensitivity towards TMZ and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) correlated with MGMT methylation and MGMT mRNA expression. Pyrosequencing in 67 primary MB samples revealed a mean percentage of MGMT methylation of 3.7-92% (mean: 13.25%, median: 10.67%). Percentage of MGMT methylation and MGMT mRNA expression as determined by quantitative RT-PCR correlated inversely (n = 46; Pearson correlation r (2) = 0.14, P = 0.01). We then analyzed MGMT mRNA expression in a second set of 47 formalin-fixed paraffin-embedded primary MB samples from clinically well-documented patients treated within the prospective randomized multicenter trial HIT'91. No association was found between MGMT mRNA expression and progression-free or overall survival. Therefore, it is not currently recommended to use MGMT mRNA expression analysis to determine who should receive alkylating agents and who should not.

Epigenetic deregulation of DNA repair and its potential for therapy.

Epigenetic silencing of essential components of DNA repair pathways is a common event in many tumor types, and comprise O6-methylguanine-DNA methyltransferase (MGMT), human mut L homolog 1 (hMLH1), Werner syndrome gene (WRN), breast cancer susceptibility gene 1 (BRCA1), and genes of the Fanconi anemia pathway. Most interestingly, some of these alterations become the Achilles heel of the affected tumors upon treatment with certain classes of anticancer agents. That is, patients whose tumors carry such defects can be stratified for respective therapy rendering some classic DNA damaging agents, such as alkylators or DNA crosslinking agents, into "targeted therapies." Here we review some of the affected repair pathways that, when inactivated, sensitize the tumors to specific drugs and are thus exploitable for individualized therapy.

Combination of doxorubicin and sulforaphane for reversing doxorubicin-resistant phenotype in mouse fibroblasts with p53Ser220 mutation.

Chemoresistance in cancer therapy is a multifactorial process, which includes alterations in drug accumulation, increased activity of gluthatione S-transferases, loss of function, and mutations of p53, etc. One strategy for reversing chemoresistance is the use of chemopreventive agents alongside standard chemotherapeutic protocols. Sulforaphane is one of the most promising chemopreventive agents. Sulforaphane inhibits cell proliferation and induces apoptosis in different tumor cell lines. Its proapoptotic potential could make it effective either alone or in combination with other therapeutic strategies in reversing chemoresistance. We investigated the effects of sulforaphane on mouse fibroblasts bearing a different p53 status (wild-type, knockout, mutated) for understanding whether its activity is prevented by a mutated p53 status. p53-knockout fibroblasts from newborn mice transfected with the p53(Ser220) mutation, observed in different human cancers, were used as a model of mutated p53 status. Moreover, since p53(Ser220) mutation fibroblasts showed a doxorubicin-resistant phenotype, we treated the cells with a combination of doxorubicin plus sulforaphane. Taken together, our results suggest that a mutated p53 status did not prevent the induction of apoptosis by sulforaphane and that sulforaphane was able to reverse the resistance to doxorubicin. The association of sulforaphane-doxorubicin may therefore allow doxorubicin to be administered at lower doses, thereby reducing its potential toxicity.

Cell-cycle specificity of sulforaphane-mediated apoptosis in Jurkat T-leukemia cells.

BACKGROUND: Sulforaphane (SFN) is an isothiocyanate that is present in widely consumed vegetables. Previous studies have shown that SFN is effective in preventing carcinogenesis induced by carcinogens in rodents. Recently it was found that SFN could also inhibit cell proliferation and induce apoptosis in several tumor cell lines. In the present study, the possible cell-cycle specificity of SFN-mediated apoptosis was investigated. MATERIALS AND METHODS: Cells were synchronized by thymidine block. Analysis of the cell-cycle and apoptosis induction was performed using flow cytometry. RESULTS: Flow cytometric assessment of the extent of apoptosis in cells synchronized by thymidine block revealed that cells were most sensitive to SFN in the G -phase, less sensitive in the G2/M-phase and least sensitive during the S-phase. CONCLUSION: These findings suggest that cell vulnerability to SFN-mediated apoptosis is subject to regulation by cell-cycle-dependent mechanisms.

Sulforaphane increases the efficacy of doxorubicin in mouse fibroblasts characterized by p53 mutations.

One novel strategy for increasing cancer chemotherapy efficacy and reversing chemoresistance involves co-administration of natural chemopreventive compounds alongside standard chemotherapeutic protocols. Sulforaphane is a particularly promising chemopreventive agent, which has been shown to exert proapoptotic effects on tumor cells containing p53 mutations. The p53(Ser220) mutation has been implicated in reduced efficacy and drug resistance in the context of osteosarcomas and breast tumors treated with doxorubicin-based protocols. We investigated the effects of a combination of doxorubicin and sulforaphane on cell viability and apoptosis induction in fibroblasts characterized by different p53 status (p53 wild-type, p53 knock-out, and p53(Ser220) mutation), and identified some of the molecular pathways triggered by the drug combination. Very high concentrations of doxorubicin were necessary to decrease the viability of p53(Ser220) and p53 knock-out (but not wild-type) cells. Treatment of p53(Ser220) and p53 knock-out cells with doxorubicin did not induce apoptosis, also at very high concentrations (10muM). Sulforaphane restored chemosensitivity and induced apoptosis in doxorubicin-resistant p53(Ser220) and p53 knock-out cells, irrespective of p53 status. The induction of apoptosis was caspase-3 dependent and caspase-8 independent. Bongkrekic acid, a mitochondrial membrane stabilizer, partially prevented the effects of doxorubicin plus sulforaphane on mitochondrial permeability but was unable to prevent the induction of apoptosis. N-acetyl-cysteine, a glutathione precursor, blocked the induction of apoptosis by doxorubicin plus sulforaphane. Considering the negligible safety profile of sulforaphane, our findings could prompt innovative clinical studies designed to investigate whether its coadministration can enhance the efficacy of doxorubicin-based regimens.

Toward refinement of the colony-forming unit-granulocyte/macrophage clonogenic assay: inclusion of a metabolic system.

This work represents a first attempt to refine the colony-forming unit-granulocyte/macrophage (CFU-GM) clonogenic assay by incorporating liver microsomes and co-factors as a metabolic system into the in vitro test system in response to an ECVAM recommendation. From the comparison of results obtained with the CFU-GM clonogenic assay currently used and with the new experimental protocol, different toxicity on granulocyte/macrophage precursors was demonstrated, when drugs with a known metabolism in vivo were tested.

A new experimental protocol as an alternative to the colony-forming unit-granulocyte/macrophage (CFU-GM) clonogenic assay to assess the haematotoxic potential of new drugs.

In this work, a first attempt to set-up a new in vitro experimental protocol with culture in liquid medium and flow cytometry analysis of bone marrow progenitors is described. This protocol is proposed as an alternative to the colony-forming unit-granulocyte/macrophage (CFU-GM) clonogenic in vitro assay currently used to assess the toxic potential of new drugs in the bone marrow. This new experimental approach should enable to speed up the procedure of the in vitro haematotoxic potential assessment, to reduce inter-experimental variability and to enhance result accuracy. Preliminary results obtained demonstrated that the progenitor cell count by flow cytometry replacing the light microscopy granulocyte/macrophage colony count represents a tremendous improvement in terms of accuracy and standardisation. Moreover, differential counts of cell sub-populations can be performed by using specific monoclonal antibodies. Furthermore, this method demonstrated to be time-saving, since 4 day cell incubation period is required instead of 7-14 day incubation in the CFU-GM clonogenic assay. On the basis of results obtained so far, the new experimental protocol proposed looks a promising alternative to the CFU-GM clonogenic assay currently used.