Exposure to cadmium and head and neck cancers: a meta-analysis of observational studies

The dynamic face of cadmium-induced Carcinogenesis: Mechanisms, emerging trends, and future directions

Cadmium (Cd) is a malleable element with odorless, tasteless characteristics that occurs naturally in the earth's crust, underground water, and soil. The most common reasons for the anthropological release of Cd to the environment include industrial metal mining, smelting, battery manufacturing, fertilizer production, and cigarette smoking. Cadmium-containing products may enter the environment as soluble salts, vapor, or particle forms that accumulate in food, soil, water, and air. Several epidemiological studies have highlighted the association between Cd exposure and adverse health outcomes, especially renal toxicity, and the impact of Cd exposure on the development and progression of carcinogenesis. Also highlighted is the evidence for early-life and even maternal exposure to Cd leading to devastating health outcomes, especially the risk of cancer development in adulthood. Several mechanisms have been proposed to explain how Cd mediates carcinogenic transformation, including epigenetic alteration, DNA methylation, histone posttranslational modification, dysregulated non-coding RNA, DNA damage in the form of DNA mutation, strand breaks, and chromosomal abnormalities with double-strand break representing the most common DNA form of damage. Cd induces an indirect genotoxic effect by reducing p53's DNA binding activity, eventually impairing DNA repair, inducing downregulation in the expression of DNA repair genes, which might result in carcinogenic transformation, enhancing lipid peroxidation or evasion of antioxidant interference such as catalase, superoxide dismutase, and glutathione. Moreover, Cd mediates apoptosis evasion, autophagy activation, and survival mechanisms. In this review, we decipher the role of Cd mediating carcinogenic transformation in different models and highlight the interaction between various mechanisms. We also discuss diagnostic markers, therapeutic interventions, and future perspectives.

Toxicity Tolerance in the Carcinogenesis of Environmental Cadmium

Cadmium (Cd) is an environmental toxicant of worldwide public health significance. Diet is the main non-workplace Cd exposure source other than passive and active smoking. The intestinal absorption of Cd involves transporters for essential metals, notably iron and zinc. These transporters determine the Cd body burden because only a minuscule amount of Cd can be excreted each day. The International Agency for Research on Cancer listed Cd as a human lung carcinogen, but the current evidence suggests that the effects of Cd on cancer risk extend beyond the lung. A two-year bioassay demonstrated that Cd caused neoplasms in multiple tissues of mice. Also, several non-tumorigenic human cells transformed to malignant cells when they were exposed to a sublethal dose of Cd for a prolonged time. Cd does not directly damage DNA, but it influences gene expression through interactions with essential metals and various proteins. The present review highlights the epidemiological studies that connect an enhanced risk of various neoplastic diseases to chronic exposure to environmental Cd. Special emphasis is given to the impact of body iron stores on the absorption of Cd, and its implications for breast cancer prevention in highly susceptible groups of women. Resistance to cell death and other cancer phenotypes acquired during Cd-induced cancer cell transformation, under in vitro conditions, are briefly discussed. The potential role for the ZnT1 efflux transporter in the cellular acquisition of tolerance to Cd cytotoxicity is highlighted.

Prevalence of Self-Reported Voice Concerns and Associated Risk Markers in a Nonclinical Sample of Military Service Members

INTRODUCTION

Difficult communication environments are common in military settings, and effective voice use can be critical to mission success. This study aimed to estimate the prevalence of self-reported voice disorders among U.S. military service members and to identify factors that contribute to their voice concerns.

METHOD

A nonclinical sample of 4,123 active-duty service members was recruited across Department of Defense hearing conservation clinics. During their required annual hearing evaluation, volunteers provided responses to voice-related questions including a slightly adapted version of the Voice Handicap Index-10 (VHI-10) as part of a larger survey about communication issues. Changepoint detection was applied to age and years of service to explore cohort effects in the reporting of voice concerns. Logistic regression analyses examined multiple available factors related to communication to identify factors associated with abnormal results on the VHI-10.

RESULTS

Among the respondents, 41% reported experiencing vocal hoarseness or fatigue at least several times per year, and 8.2% (n = 336) scored above the recommended abnormal cut-point value of 11 on the VHI-10. Factors independently associated with the greatest risk for self-reported voice concerns were sex (female), cadmium exposure, vocal demands (the need for a strong, clear voice), and auditory health measures (frequency of experiencing temporary threshold shifts; self-reported hearing difficulties).

CONCLUSIONS

Based on self-reported voice concerns and false negative rates reported in the literature, the prevalence of dysphonia in a large sample of active-duty service members is estimated to be 11.7%, which is higher than that in the general population. Certain predictors for voice concerns were expected based on previous literature, like female sex and voice use, but frequency of temporary threshold shifts and exposure to cadmium were surprising. The strong link between voice and auditory problems has particular implications regarding the need for effective communication in high-noise military and other occupational environments.

Exposure to arsenic, polycyclic aromatic hydrocarbons, metals, and association with skin cancers in the US adults

Worldwide, skin cancer affects millions of people yearly and is broadly classified into melanoma and nonmelanoma types of skin cancer. The toxicity of metals to human health is a public and clinical health problem due to their widespread use in tools, machinery, and appliances as well as their widespread distribution in the air, water, and soil. Arsenic is a carcinogenic metalloid and available in the Earth's crust. Polycyclic aromatic hydrocarbons (PAHs) are toxic to humans, and incomplete combustion of fossil fuels is the main source of PAHs. Human populations exposed to metals from various sources can lead to various diseases including cancer. Limited studies are conducted to simultaneously assess the correlation of multiple arsenic, PAHs, metals with the occurrence of skin cancer. This study aimed to analyze the association between six PAHs compounds, seven types of arsenic, and fourteen metals from urine specimen with skin cancer in US adults. We performed a cross-sectional analysis using data from a total of 14,716 adults from the National Health Examination and Nutrition Survey (NHANES) database for three cycles ranging from 2011-2012 to 2015-2016. Specialized weighted complex survey logit regressions were conducted. Linear logit regression models using only main effects were performed first to identify the correlation between the selected demographic and lifestyle variables and melanoma, nonmelanoma, and unknown types of skin cancer. A second set of linear, main-effects logit regression models were constructed to examine the correlation between melanoma, nonmelanoma, and other types of skin cancers and seven types of arsenic (arsenous acid, arsenic acid, arsenobetaine, arsenocholine, dimethylarsinic acid, monomethylacrsonic acid, and total arsenic), six PAHs (1-hydroxynaphthalene, 2-hydroxynaphthalene, 3-hydroxyfluorene, 2-hydroxyfluorene, 1-hydroxyphenathrene, and 1-hydroxypyrene), and fourteen metals (barium, cadmium, cobalt, cesium, molybdenum, manganese, lead, antimony, tin, strontium, thallium, tungsten, uranium, and mercury) when adjusted for the selected covariates. The statistical analysis was conducted using R software, version 4.0.4. A marginal positive significant correlation between total arsenic and nonmelanoma was observed. This study identified a significant positive association between barium, cadmium, cesium, mercury, tin, and melanoma development. Cesium showed a significant positive statistical association for nonmelanoma, and thallium showed a borderline significant statistical association for nonmelanoma. A statistically significant positive association was found between cadmium and an unknown type of skin cancer. The findings of this study indicated a statistically significant positive association between skin cancer and barium, cadmium, cesium, tin, mercury, and thallium. Further studies are recommended in humans to refute or confirm these findings.

Estimation of health risks associated with dietary cadmium exposure

In much of the world, currently employed upper limits of tolerable intake and acceptable excretion of cadmium (Cd) (ECd/Ecr) are 0.83 µg/kg body weight/day and 5.24 µg/g creatinine, respectively. These figures were derived from a risk assessment model that interpreted β2-microglobulin (β2MG) excretion > 300 μg/g creatinine as a "critical" endpoint. However, current evidence suggests that Cd accumulation reduces glomerular filtration rate at values of ECd/Ecr much lower than 5.24 µg/g creatinine. Low ECd/Ecr has also been associated with increased risks of kidney disease, type 2 diabetes, osteoporosis, cancer, and other disorders. These associations have cast considerable doubt on conventional guidelines. The goals of this paper are to evaluate whether these guidelines are low enough to minimize associated health risks reliably, and indeed whether permissible intake of a cumulative toxin like Cd is a valid concept. We highlight sources and levels of Cd in the human diet and review absorption, distribution, kidney accumulation, and excretion of the metal. We present evidence for the following propositions: excreted Cd emanates from injured tubular epithelial cells of the kidney; Cd excretion is a manifestation of current tissue injury; reduction of present and future exposure to environmental Cd cannot mitigate injury in progress; and Cd excretion is optimally expressed as a function of creatinine clearance rather than creatinine excretion. We comprehensively review the adverse health effects of Cd and urine and blood Cd levels at which adverse effects have been observed. The cumulative nature of Cd toxicity and the susceptibility of multiple organs to toxicity at low body burdens raise serious doubt that guidelines concerning permissible intake of Cd can be meaningful.

DNA Damage Response Mechanisms in Head and Neck Cancer: Significant Implications for Therapy and Survival

Head and neck cancer (HNC) is a term collectively used to describe a heterogeneous group of tumors that arise in the oral cavity, larynx, nasopharynx, oropharynx, and hypopharynx, and represents the sixth most common type of malignancy worldwide. Despite advances in multimodality treatment, the disease has a recurrence rate of around 50%, and the prognosis of metastatic patients remains poor. HNCs are characterized by a high degree of genomic instability, which involves a vicious circle of accumulating DNA damage, defective DNA damage repair (DDR), and replication stress. Nonetheless, the damage that is induced on tumor cells by chemo and radiotherapy relies on defective DDR processes for a successful response to treatment, and may play an important role in the development of novel and more effective therapies. This review summarizes the current knowledge on the genes and proteins that appear to be deregulated in DDR pathways, their implication in HNC pathogenesis, and the rationale behind targeting these genes and pathways for the development of new therapies. We give particular emphasis on the therapeutic targets that have shown promising results at the pre-clinical stage and on those that have so far been associated with a therapeutic advantage in the clinical setting.

Effect of liposomal drug based on interferon and extract from Silybum marianum on antioxidative status of bulls against the background of contamination of fodders by cadmium and plumbum

The balance between anti- and prooxidants in animal organisms in general and in each cell in particular is responsible for the regulation of many metabolic processes that provide immunocompetence, growth, development and protection of animals from oxidative stress, related to inflow of cadmium and plumbum. Therefore, the objective of our study was the influence of a liposomal drug based on interferon and milk thistle (Silybum marianum (L.) Gaertn.) on the antioxidative status of the organism of bulls in the conditions of cadmium and plumbum loading. The experiments were performed on six-months-old Black Motley dairy cattle. The fodders in the farm were determined to contain high levels of plumbum and cadmium. The liposomal drug Lipointersyl inhibited the lipid peroxidation processes in the bulls. The drug components promoted the decrease in the level of intermediate and end products of lipid peroxidation, in particular 22% decrease in the level of diene conjugates and 20% decrease in TBA-active products. Intramuscular injection of the liposomal drug to bulls of the experimental group strengthened the antioxidant protection of their organism. On the 30th day of the experiment, blood from experimental group animals was seen to have a 9.8% increase in reduced glutathione. Assay of the enzymatic link of the glutathione system revealed that the activity of glutathione peroxidase and glutathione reductase in the blood of the animals that had been injected the liposomal drug Lipointensyl had increased by 24.0% and 27.7% respectively by the 30th day of the experiment. The experiments conducted on young cattle demonstrated that intermuscularly injected the Lipointensyl liposomal drug – against the background of cadmium and plumbum loading – promoted the activation of the glutathione system of antioxidant protection as a result of increase in the activity of its enzymatic and non-enzymatic links. The study of catalase and superoxide dismutase activities revealed that on the 30th and 40th days of the experiment, the activity of those enzymes varied within the physiological norms. Therefore, the analyzed Silybum marianum-based liposomal drug has antioxidant properties, it is recommended for young cattle in the conditions of contamination with heavy metals in order to prevent the development of oxidative stress.

Systematic review and meta-analysis of cancer risks in relation to environmental waste incinerator emissions: a meta-analysis of case-control and cohort studies

OBJECTIVES

Various toxic substances can be generated from incinerators, exposing nearby residents, and epidemiological studies have shown wide variations in risk estimates for cancer risk in populations living close to incinerators.

METHODS

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a literature search and systematic review were conducted to identify studies conducted on general populations exposed to environmental incinerator emissions and cancer outcomes. Meta-analysis was performed according to the cancer types for which 2 or more studies were reported. Subgroup analysis was done for sex, the exposure estimation method, the study period, and the type of outcome.

RESULTS

Eleven studies were found for the qualitative review and meta-analysis. Seven studies had a case-control design, and 4 had a cohort design. The pooled effect size was not significant for breast, colorectal, liver, lung, lymphohematopoietic, stomach, bladder, central nervous system, and laryngeal cancers, non-Hodgkin lymphoma, sarcoma, leukemia, and all cancers. In the subgroup analysis, the pooled effect size of laryngeal cancer in females was 1.82 (95% confidence interval, 1.10 to 3.01), although only 2 studies were identified.

CONCLUSIONS

The meta-analysis did not provide evidence of an increased risk for any cancer among populations living near waste incinerators, except for laryngeal cancer in females. However, since relatively few studies were reviewed and some cancer types showed significant increases in individual studies, this evidence needs to be updated regularly.

Neutrophil‑to‑lymphocyte ratio as a prognostic predictor for patients with cancer treated with stereotactic body radiation therapy: A meta‑analysis

Stereotactic body radiation therapy (SBRT) is effective for the treatment of cancer. Neutrophil-to-lymphocyte ratio (NLR) is a common prognostic factor in predicting survival of patients with cancer. Previous studies have reported that NLR may be able to predict survival of patients with cancer treated with SBRT; however, the results are inconsistent. Therefore, the present study performed a meta-analysis to pool the data of prognostic prediction using NLR for patients with cancer who underwent SBRT. PubMed, Google Scholar, Embase and The Cochrane Library were used to search for articles published before October 2020. Pooled hazard radios (HRs) with 95% confidence intervals (CIs) were used to evaluate the association of NLR levels with patient outcome following SBRT. The primary endpoint was overall survival (OS). Subgroup analyses were used to detect sources of heterogeneity. Publication bias was assessed by Egger's test and Begg's test. A total of nine studies involving 1,010 participants were included in the present meta-analysis. Univariate and multivariate analyses revealed that elevated NLR predicted a worse outcome for OS (HR, 1.35; 95% CI, 1.22-1.49; P<0.001 and HR, 1.29; 95% CI, 1.16-1.44; P<0.001, respectively), regardless of pre- and post-treatment groups. Subgroup analysis demonstrated that the prospective group showed more significant heterogeneity (I²=57.7%; P=0.124) than the retrospective group (I²=0%) and overall (I²=47.5%). In conclusion, both pre- and post-SBRT elevated NLRs were revealed to be independently associated with poor survival in patients with cancer who received SBRT.