Alkylating agents are possible inducers of glioblastoma and other brain tumors.

Epidemiological evidence of an association between exposure to chemical carcinogens and an increased risk for development of glioblastoma (GBM) is limited to weak statistical associations in cohorts of firefighters, farmers, residents exposed to air pollution, and soldiers exposed to toxic chemicals (e.g., military burn pits, oil-well fire smoke). A history of ionizing radiation therapy to the head or neck is associated with an increased risk of GBM. Ionizing radiation induces point mutations, frameshift mutations, double-strand breaks, and chromosomal insertions or deletions. Mutational profiles associated with chemical exposures overlap with the broad mutational patterns seen with ionizing radiation. Data on 16 agents (15 chemicals and radio frequency radiation) that induced tumors in the rodent brain were extracted from 602 Technical Reports on 2-years cancer bioassays found in the National Toxicology Program database. Ten of the 15 chemical agents that induce brain tumors are alkylating agents. Three of the 15 chemical agents have idiosyncratic structures and might be alkylating agents. Only two of the 15 chemical agents are definitively not alkylating agents. The rat model is thought to be of possible relevance to humans suggesting that exposure to alkylating chemicals should be considered in epidemiology studies on GBM and other brain tumors.

Risk factors for glioblastoma are shared by other brain tumor types.

The reported risk factors for glioblastoma (GBM), i.e., ionizing radiation, Li-Fraumeni syndrome, Neurofibromatosis I, and Turcot syndrome, also increase the risk of other brain tumor types. Risk factors for human GBM are associated with different oncogenic mutation profiles. Pedigreed domestic dogs with a shorter nose and flatter face (brachycephalic dogs) display relatively high rates of glioma formation. The genetic profiles of canine gliomas are also idiosyncratic. The association of putatively different mutational patterns in humans and canines with GBM suggests that different oncogenic pathways can result in GBM formation. Strong epidemiological evidence for an association between exposure to chemical carcinogens and an increased risk for development of GBM is currently lacking. Ionizing radiation induces point mutations, frameshift mutations, double-strand breaks, and chromosomal insertions or deletions. Mutational profiles associated with chemical exposures overlap with the broad mutational patterns seen with ionizing radiation. Weak statistical associations between chemical exposures and GBM reported in epidemiology studies are biologically plausible. Molecular approaches comparing reproducible patterns seen in spontaneous GBM with analogous patterns found in GBMs resected from patients with known significant exposures to potentially carcinogenic chemicals can address difficulties presented by traditional exposure assessment.

Qualitative and Quantitative Analyses of the Enantiomers of Nicotine and Nornicotine Employing Chiral Supercritical Fluid Chromatography.

An optimized method employing chiral supercritical fluid chromatography with diode array UV-VIS detection has been developed for the quantitative analysis of nicotine and nornicotine enantiomer distributions. The method parameters that were optimized included: column type (stationary phases, Chiralpak IG-3), column temperature (40°C), modifier types and concentration (isopropyl alcohol, 10%), additive types and concentrations (diethylamine, 0.2%), elution times (<6 min, flow rate 3 mL/min) and resolution factor (>1.2). These optimized conditions led to nicotine and nornicotine enantiomer detection limits of ~5 ng/µL with accompanying %RSD values of <2% from the analyses of commercially available nicotine-containing formulations.

Bruce Nathan Ames - Paradigm shifts inside the cancer research revolution.

Dr. Bruce Ames turned 92 on December 16, 2020. He considers his most recent work linking adequate consumption of 30 known vitamins and minerals with successful aging to be his most important contribution. With the passage of time, it is not uncommon for the accomplishments of a well-known scientist to undergo a parsimonious reductionism in the public mind - Pasteur's vaccine, Mendel's peas, Pavlov's dogs, Ames' test. Those of us in the research generation subsequent to Dr. Ames' are undoubtedly affected by our own unconscious tendencies toward accepting the outstanding achievements of the past as commonplace. In doing so, seminal advances made by earlier investigators are often inadvertently subsumed into common knowledge. But having followed Ames' work since the mid-1970s, we are cognizant that the eponymous Ames Test is but a single chapter in a long and rich narrative. That narrative begins with Ames' classic studies on the histidine operon of Salmonella, for which he was elected to the National Academy of Sciences. A summary of the historical progression of the understanding of chemical carcinogenesis to which Ames and his colleagues contributed is provided. Any summary of a topic as expansive and complex as the ongoing unraveling of the mechanisms underlying chemical carcinogenesis will only touch upon some of the major conceptual advances to which Ames and his colleagues contributed. We hope that scientists of all ages familiar with Ames only through the eponymous Ames Test will further investigate the historical progression of the conceptualization of cancer caused by chemical exposure. As the field of chemical carcinogenesis gradually moves away from primary reliance on animal testing to alternative protocols under the rubric of New Approach Methodologies (NAM) an understanding of where we have been might help to guide where we should go.

Categorizing the characteristics of human carcinogens: a need for specificity.

The International Agency for Research on Cancer (IARC) has recently proposed employing "ten key characteristics of human carcinogens" (TKCs) to determine the potential of agents for harmful effects. The TKCs seem likely to confuse the unsatisfactory correlation from testing regimes that have ignored the differences evident when cellular changes are compared in short and long-lived species, with their very different stem cell and somatic cell phylogenies. The proposed characteristics are so broad that their use will lead to an increase in the current unacceptably high rate of false positives. It could be an informative experiment to take well-established approved therapeutics with well-known human safety profiles and test them against this new TKC paradigm. Cancers are initiated and driven by heritable and transient changes in gene expression, expand clonally, and progress via additional associated acquired mutations and epigenetic alterations that provide cells with an evolutionary advantage. The genotoxicity testing protocols currently employed and required by regulation, emphasize testing for the mutational potential of the test agent. Two-year, chronic rodent cancer bioassays are intended to test for the entire spectrum of carcinogenic transformation. The use of cytotoxic doses causing increased, sustained cell proliferation that facilitates accumulated genetic damage leads to a high false-positive rate of tumor induction. Current cancer hazard assessment protocols and weight-of-the-evidence analysis of agent-specific cancer risk align poorly with the pathogenesis of human carcinoma and so need modernization and improvement in ways suggested here.

Clinical epidemiology studies on potential effects of endocrine disrupting chemicals (EDCs) should exclude subjects with obesity as determined by BMI.

Obesity as determined by BMI is a confounder in clinical evaluations of the effects of endocrine disrupting chemicals (EDCs). Validated regulatory tests are used to determine whether a chemical acts via a mode of action (MOA) that affects estrogen, androgen, thyroid or steroidogenic pathways. Test batteries for evaluating EDCs include QSAR, in vitro assays, and animal testing. Studies suggest that EDCs pose the greatest risk during prenatal and early infant development when organ systems are developing. Health effects include lowered fertility, endometriosis, and cancers associated with estrogenic activity. Epidemiology studies on adverse effects of EDCs in the general population are difficult to conduct due to very low exposures of EDCs in non-occupational cohorts, and lack of exposure measurements between cases and controls. In contrast with very low levels of hormonal perturbation from nano-molar to micro-molar exposures to EDCs, adipose tissue in obesity alters estrogen, testosterone, thyroid stimulating hormone, and inflammation levels. Obesity in pregnancy and gestational diabetes are associated with adverse outcomes in infants and children including autism, poor motor skills, lowered IQ, and altered birth weight. Neonatal effects of obesity are confounded by average lower socio-economic status. The already perturbed endocrine balance in overweight or obese persons renders them particularly worthy subjects for clinical epidemiology investigations on the possible effects of endocrine disrupting chemicals. However, inclusion of subjects with obesity requires accounting for potentially confounding effects of the hormonal influences arising from excess adiposity. If subjects with obesity are to be included in clinical epidemiological evaluations related to hormonal effects, the subjects should be classified by body fat percentage rather than by the much less exact measure of body mass index (BMI).

Obesity as a Source of Endogenous Compounds Associated With Chronic Disease: A Review.

In 2014, it was estimated that more than 1.9 billion adults were overweight with over 600 million classifiable as obese. Approximately two-thirds of U.S. adults over 20 years of age are currently overweight with about 35% classified as obese, a figure thought likely to reach 42% by 2030 in those over 18 years of age. Adipose cells from stored body fat secrete estrogen and a very large number (> 500) of biologically active substances termed adipokines, in addition to inducing, by other cell-driven effects, pathological alterations in insulin pathways. The U.S. National Cancer Institute reports that exposure to the hormone disrupting and proinflammatory effects of excess adipose tissue are associated with an increased risk for 11 different cancers. Obesity is also associated with a number of serious non-neoplastic conditions including metabolic syndrome and type 2 diabetes; menstrual cycle irregularities and lowered fertility (men and women); and abnormal bone morphology in a subset of female patients. In men hypogonadism, low testosterone levels, benign prostatic hyperplasia, and lowered sperm counts have been reported. In developed countries, the endogenous adverse health burden associated with obesity is only matched, quantitatively and qualitatively, by the exogenous toxicity of cigarette smoking. The investigation of possible hormonal and/or proinflammatory effects of chemicals should include an assessment of the profound endocrine alterations associated with obesity.

Utility of the mouse dermal promotion assay in comparing the tumorigenic potential of cigarette mainstream smoke.

The International Agency for Research on Cancer (IARC) has classified a number of the chemical constituents reported in cigarette mainstream smoke (MS) as carcinogens. In the international literature, 81 IARC classified carcinogens have been reported historically in MS. Cigarette smoke is a complex aerosol of minute liquid droplets (termed the particulate phase) suspended within a mixture of gases (CO(2), CO, NO(x), etc.) and semi-volatile compounds. The gases and semi-volatiles are termed the vapor phase. Due to early difficulties in inducing carcinomas in laboratory animals following inhalation exposure to MS, the mouse dermal promotion assay became the standard method of comparing the tumorigenic potential of cigarette smoke condensates (the particulate phase of MS nearly devoid of MS gases and having a significant reduction of the semi-volatile components of the vapor phase). Of the 81 IARC carcinogens reported in MS, 48 are found exclusively in the particulate phase, 29 in the vapor phase only, and four IARC carcinogens in both phases. A general comparison of the quantity and potency of the individual carcinogenic constituents of the MS vapor and particulate phases illustrates that the potential carcinogenic contribution from the vapor phase might be significant. Therefore, the mouse dermal promotion assay may not be a sensitive comparator of the tumorigenic potential of different MSs displaying a diversity of vapor phase components. However, when used in a weight-of-the-evidence approach that includes smoke chemistry, in vitro studies using whole smoke and human exposure studies evaluating both vapor and particulate phase smoke constituents, the mouse dermal promotion assay remains an important risk assessment tool as the only test that reproducibly measures the tumorigenic potential of cigarette smoke condensate.

Perspectives on pulmonary inflammation and lung cancer risk in cigarette smokers.

Cigarette mainstream smoke (MSS) inhaled by smokers is a complex aerosol composed of minute liquid droplets suspended within a mixture of combustion gases (CO, CO2, NOx, etc.) and semivolatile compounds. The minute liquid droplets represent the particulate or "tar" phase, while the combustion gases and semivolatiles comprise the vapor phase. For historical and technical reasons, the vast majority of studies on the carcinogenicity of MSS have focused on the particulate phase. The particulate phase is mutagenic and cytotoxic in vitro, proinflammatory, and promotes tumor formation in animal models. In addition to cytotoxic compounds found in the particulate phase, the vapor phase of MSS contains a number of cytotoxic constituents including reactive aldehydes and carbonyls capable of damaging cells and inducing pulmonary inflammation. A large body of evidence suggests that smoking-induced pulmonary inflammation may play an important role in increasing lung cancer risk in smokers. Use of aspirin and nonsteroidal anti-inflammatory drugs is associated with reduced cancer development in animal models and lower lung cancer rates in smokers. A number of benign nonpulmonary and pulmonary diseases characterized by chronic inflammation increase the risk of cancer at the affected site in the absence of chemical exposure. Animal models displaying tumorigenic responses following exposure to either whole smoke or smoke fractions show elevated rates of cellular proliferation. A relationship between pulmonary inflammation and lung cancer is mechanistically plausible because inflammatory cells secrete activated oxygen species, inflammatory mediators, and proteolytic enzymes that can both damage DNA and lead to increases in reparative cell proliferation rates.

Percutaneous penetration enhancers in cigarette mainstream smoke.

Percutaneous penetration enhancers (PPEs) are chemicals used to enhance the transdermal delivery of drugs. Fifty-eight of the approximately 150 PPEs used for the transdermal delivery of drugs have been reported in cigarette mainstream smoke (MS). MS is a complex aerosol of minute liquid droplets (termed the particulate phase) suspended within a mixture of gases (CO(2), CO, NO(x), etc.) and semi-volatile compounds. The gases and many of the semi-volatiles are termed the vapor phase. Twenty-nine of the 58 PPEs have been identified in MS vapor phase, 15 in the particulate phase and 14 in both the vapor and particulate phases. There is a tendency for MS PPEs to be hydrophobic, with 40 of the 58 compounds (69%) being either hydrophobic or strongly hydrophobic, and only 24% being hydrophilic. Many of the 4800 known constituents of MS are hydrophilic and would not be expected to readily cross cell membranes or penetrate tissue when delivered as single compounds. The in vivo effect on biological activity of the juxtaposition within the cigarette smoke aerosol of the large number of hydrophilic constituents with the 58 PPEs is currently unknown. As an initial step in understanding this potential complex interaction, the 58 PPEs in MS have been identified and a number of molecular parameters related to the ability to penetrate tissue have been calculated, including MS concentration, measured and calculated base ten logarithm of the octanol-water partition coefficient (Mlog P and Clog P), molecular volume (MgVol) and calculated molar refractivity (CMR).

The relative toxicity of substituted phenols reported in cigarette mainstream smoke.

Cigarette mainstream smoke (MS) contains a number of structurally diverse substituted phenols. Recent quantitative structure activity relationship (QSAR) studies on phenols show that substituted phenols with electron-releasing groups can form potentially toxic phenoxyl-free radicals. In contrast, substituted phenols with electron-withdrawing groups do not form phenoxyl-free radicals but exert their toxicity primarily through lipophilicity. The chemical structures of 253 different substituted phenols reported in MS have been described in sufficient detail to allow identification of the individual compounds. From a laterally validated equation based on published data on the toxic effects of phenols on cultured cells, the relative toxicity, on a molar basis, of the 253 MS phenols has been determined. Based on this scheme, the most toxic phenols in MS include, in descending order of toxicity, 2-(dimethylamino)-phenol, 2-ethyl-6-methyl-1,4-benzenediol, 2-methoxy-1,4-benzenediol, and 4-ethyl-2-methoxy-6-methylphenol. The least toxic phenols include, in ascending order of toxicity, 4-hydroxybenzoic acid and 3-hydroxybenzenepropanoic acid. In the human exposure situation, the toxicity of MS phenols is a complex interaction, with contributions made by the following factors: toxicity per mole; MS concentration; synergistic, additive or antagonistic interactions with other MS components; host susceptibility; metabolism; and individual smoking behavior and inhalation patterns. In the absence of data to the contrary, reduction in the number and concentration of toxic MS smoke components may be considered to be advantageous. Studies of this type can play an important role in identifying MS components for reduction or removal.