Cadmium and lead implication in testis cancer; is there a connection?

Lead (Pb) in biological samples in association with cancer risk and mortality: A systematic literature review

BACKGROUND AND AIM

Lead (Pb) is a toxic heavy metal and pervasive environmental contaminant, and a class 2 A carcinogen according to the IARC classification, yet its link with cancer at several body sites remains uncertain. Here, we aimed at summarizing the scientific evidence regarding its association with cancer risk and mortality, focusing on studies that carried out Pb measurements in biological samples.

METHODS

We reviewed articles published in PubMed and EMBASE until January 2nd, 2024, that quantified the epidemiological association between Pb measured in blood, urine, nails, and other biological media, and cancer risk and mortality (overall and by cancer site/type).

RESULTS

We included 46 articles (out of 8022 screened) published in 1995-2023 and reporting on investigations conducted in fifteen countries. In terms of design, 20 were prospective, 24 were retrospective case-control studies, and 2 were cross-sectional. Pb levels were determined in blood in the majority of studies (n=28). The most consistent evidence was for the association of Pb with cancer of the gastrointestinal tract, particularly the oesophagus, stomach (RR ranging from 0.80 to 2.66), colon-rectum, and pancreas; and of the bladder and urinary tract (RR from 1.10 to 2.89). For other specific malignancies, the data were conflicting or too limited to draw reliable conclusions. Finally, increased Pb concentration in blood and urine was consistently associated with higher overall cancer incidence and mortality.

CONCLUSIONS

Lead is a widespread and highly persistent environmental pollutant associated with cancer at multiple body sites. Comprehensive primary prevention interventions aiming at reducing opportunities for Pb exposure need to be continuously promoted and implemented.

Cadmium in biological samples and site-specific cancer risk and mortality: A systematic review of original articles and meta-analyses

BACKGROUND

Cadmium (Cd) is classified as a class 1 carcinogen by the IARC, yet uncertainty persists regarding the total burden of cancer (incidence and mortality) caused by exposure to it, due to the still limited evidence with regard to its aetiological role in cancer at several body sites.

OBJECTIVES AND METHODS

We searched PubMed and EMBASE for meta-analyses and original articles published by February 1st, 2024, that focused on the link between cadmium measured in biological samples (blood, urine, finger-/toe-nails, and hair) and site-specific cancer risk and mortality.

RESULTS

We included 9 meta-analyses and 57 original articles (of these, the design was retrospective in 38 and prospective in 19, and Cd levels were quantified in blood, n=33, urine, n=19, both blood and urine, n=2, or finger-/toenail, n=3). Current data consistently suggest a causal role of exposure to cadmium in pancreas, lung, and bladder carcinogenesis. Total cancer risk and mortality are also positively correlated with Cd levels in biological samples. The evidence is weak or inconclusive for the remaining cancer sites (including breast and prostate), mostly due to the limited number of studies available to date and/or methodological limitations.

DISCUSSION

Exposure to cadmium poses a risk for increased cancer incidence and mortality. Cadmium-related cancer burden might indeed be currently underestimated, as the amount of available evidence for most cancer sites and types is currently limited, and more research in the field is warranted. Continuing efforts to contain Cd pollution and mitigate associated health risk are also needed.

Concentrations, Sources, and Health Risk of Heavy Metals in Edible Parts of Broilers from Northeast of Algeria

Heavy metals contamination of poultry products is a major concern for public health. This study aimed to determine the concentration of mercury (Hg), lead (Pb), and iron (Fe) in the edible parts of broilers, as well as in feed, drinking water, and litter as sources of contamination and to assess their possible human health risk in the province of Jijel (Northeast Algeria). The range of Hg, Pb, and Fe in edible parts were 0.004-0.007, 0.185-0.480, and 28.536-88.306 mg/kg, respectively, and the difference in content was only significant (p < 0.05) for lead. Breast and thigh samples had Pb concentrations above the maximum limit. Spearman coefficient analysis revealed that most correlations were positive between metals detected in feed, water, and litter and those in the edible parts of broilers. But most of them were insignificant (p > 0.05). The estimated daily intake (EDI) values of examined metal exceeded the tolerable daily intake (PTDI). The target hazard quotients (THQ) and hazard index (HI) of all metals were lower than 1, suggesting no significant carcinogenic risks. The calculated incremental lifetime cancer risk (ILCR) of Pb was higher than 10-4 for men, women, and children, indicating the presence of carcinogenic risk. Considering the wide consumption of broiler meat, regular national monitoring of heavy metals in the broiler production chain is recommended to protect population health.

Mitigating lead-induced osteoporosis: The role of butyrate in gut-bone axis restoration

Lead (Pb) is an environmentally widespread bone toxic pollutant, contributes to the development of osteoporosis. Butyric acid, mainly produced by the fermentation of indigestible dietary fiber by gut microbiota, plays a pivotal role in the maintenance of bone homeostasis. However, the effects of butyric acids on the Pb induced osteoporosis have not yet been elucidated. In this study, our results showed that Pb exposure was negatively related to the abundance of butyric acid, in the Pb-exposed population and Pb-exposed mice. Pb exposure caused gut microbiota disorders, resulting in the decline of butyric acid-producing bacteria, such as Butyrivibrio_crossotus, Clostridium_sp._JN9, and the butyrate-producing enzymes through the acetyl-CoA pathway. Moreover, results from the NHANES data suggested that dietary intake of butyrate was associated with a reduced risk of osteoporosis in lead-burdened populations, particularly among men or participants aged 18-60 years. In addition, butyrate supplementation in mice with chronic Pb exposure improved the bone microarchitectures, repaired intestinal damage, upregulated the proportion of Treg cells. Taken together, these results demonstrated that chronic Pb exposure disturbs the gut-bone axis, which can be restored by butyric acid supplement. Our results suggest that butyrate supplementation is a possible therapeutic strategy for lead-induced bone toxicity.

Thyroid under siege: Unravelling the toxic impact of real-life metal mixture exposures in Wistar rats

This study explored the effect of a toxic metal(oid) mixture (cadmium, lead, arsenic, mercury, chromium, and nickel) on thyroid function in Wistar rats exposed for 28 or 90 days. Dose levels were determined based on prior human-biomonitoring investigation. The experiment included control (male/female rats, 28 and 90 days) and treated groups, reflecting the lower confidence limit of the Benchmark Dose (BMDL) for hormone levels (M1/F1, 28 and 90 days), median concentrations (M2/F2, 28 and 90 days), 95th percentile concentrations (M3/F3, 28 and 90 days) measured in a human study, and reference values for individual metals extracted from the literature (M4/F4, 28 days only). Blood and thyroid gland samples were collected at the experimental termination. Serum TSH, fT3, fT4, T3, and T4 levels were measured, and SPINA-GT and SPINA-GD parameters were calculated. In silico analysis, employing the Comparative Toxicogenomic Database and ToppGene Suite portal, aimed to reveal molecular mechanisms underlying the observed effects. Results showed greater sensitivity in the female rats, with significant effects observed at lower doses. Subacute exposure increased TSH, fT3, and T3 levels in females, while subchronic exposure in males decreased TSH and fT3 levels and increased fT4. Subacute exposure induced changes even at allegedly safe doses, emphasizing potential health risks. Histological abnormalities were observed in all the treated groups. In silico findings suggested that toxic metal exposure contributes to thyroid disorders via oxidative stress, disruption of micronutrients, interference with hormone synthesis, and gene expression dysregulation. These results indicate that seemingly safe doses in single-substance research can adversely affect thyroid structure and function when administered as a mixture. These findings highlight the complex impact of toxic metal exposure on thyroid health, emphasizing that adhering to accepted safety limits for single-substance research fails to account for adverse effects on thyroid structure and function upon exposures to metal mixtures.

Emerging insights into the impacts of heavy metals exposure on health, reproductive and productive performance of livestock

Heavy metals, common environmental pollutants with widespread distribution hazards and several health problems linked to them are distinguished from other toxic compounds by their bioaccumulation in living organisms. They pollute the food chain and threaten the health of animals. Biologically, heavy metals exhibit both beneficial and harmful effects. Certain essential heavy metals such as Co, Mn, Se, Zn, and Mg play crucial roles in vital physiological processes in trace amounts, while others like As, Pb, Hg, Cd, and Cu are widely recognized for their toxic properties. Regardless of their physiological functions, an excess intake of all heavy metals beyond the tolerance limit can lead to toxicity. Animals face exposure to heavy metals through contaminated feed and water, primarily as a result of anthropogenic environmental pollution. After ingestion heavy metals persist in the body for an extended duration and the nature of exposure dictates whether they induce acute or chronic, clinical or subclinical, or subtle toxicities. The toxic effects of metals lead to disruption of cellular homeostasis through the generation of free radicals that develop oxidative stress. In cases of acute heavy metal poisoning, characteristic clinical symptoms may arise, potentially culminating in the death of animals with corresponding necropsy findings. Chronic toxicities manifest as a decline in overall body condition scoring and a decrease in the production potential of animals. Elevated heavy metal levels in consumable animal products raise public health concerns. Timely diagnosis, targeted antidotes, and management strategies can significantly mitigate heavy metal impact on livestock health, productivity, and reproductive performance.

The adverse role of endocrine disrupting chemicals in the reproductive system

Reproductive system diseases pose prominent threats to human physical and mental well-being. Besides being influenced by genetic material regulation and changes in lifestyle, the occurrence of these diseases is closely connected to exposure to harmful substances in the environment. Endocrine disrupting chemicals (EDCs), characterized by hormone-like effects, have a wide range of influences on the reproductive system. EDCs are ubiquitous in the natural environment and are present in a wide range of industrial and everyday products. Currently, thousands of chemicals have been reported to exhibit endocrine effects, and this number is likely to increase as the testing for potential EDCs has not been consistently required, and obtaining data has been limited, partly due to the long latency of many diseases. The ability to avoid exposure to EDCs, especially those of artificially synthesized origin, is increasingly challenging. While EDCs can be divided into persistent and non-persistent depending on their degree of degradation, due to the recent uptick in research studies in this area, we have chosen to focus on the research pertaining to the detrimental effects on reproductive health of exposure to several EDCs that are widely encountered in daily life over the past six years, specifically bisphenol A (BPA), phthalates (PAEs), polychlorinated biphenyls (PCBs), parabens, pesticides, heavy metals, and so on. By focusing on the impact of EDCs on the hypothalamic-pituitary-gonadal (HPG) axis, which leads to the occurrence and development of reproductive system diseases, this review aims to provide new insights into the molecular mechanisms of EDCs' damage to human health and to encourage further in-depth research to clarify the potentially harmful effects of EDC exposure through various other mechanisms. Ultimately, it offers a scientific basis to enhance EDCs risk management, an endeavor of significant scientific and societal importance for safeguarding reproductive health.