Genotoxicity assessment of 4-methylimidazole: regulatory perspectives

Drosophila Toxicogenomics: genetic variation and sexual dimorphism in susceptibility to 4-Methylimidazole

BACKGROUND

4-methylimidazole is a ubiquitous and potentially carcinogenic environmental toxicant. Genetic factors that contribute to variation in susceptibility to its toxic effects are challenging to assess in human populations. We used the Drosophila melanogaster Genetic Reference Panel (DGRP), a living library of natural genetic variation, to identify genes with human orthologs associated with variation in susceptibility to 4-methylimidazole.

RESULTS

We screened 204 DGRP lines for survival following 24-hour exposure to 4-methylimidazole. We found extensive genetic variation for survival, with a broad sense heritability of 0.82; as well as genetic variation in sexual dimorphism, with a cross-sex genetic correlation of 0.59. Genome-wide association analyses identified a total of 241 candidate molecular polymorphisms in or near 273 unique genes associated with survival. These polymorphisms had either sex-specific or sex-antagonistic effects, and most had putative regulatory effects. We generated interaction networks using these candidate genes as inputs and computationally recruited genes with known physical or genetic interactions. The network genes were significantly over-represented for gene ontology terms involving all aspects of development (including nervous system development) and cellular and organismal functions as well as canonical signaling pathways, and most had human orthologs.

CONCLUSIONS

The genetic basis of variation in sensitivity to acute exposure to 4-methylimidazole in Drosophila is attributable to variation in genes and networks of genes known for their effects on multiple developmental and cellular processes, including possible neurotoxicity. Given evolutionary conservation of the underlying genes and pathways, these insights may be applicable to humans.

Electrochemical detection of 4(5)-methylimidazole in aqueous solutions

4(5)-methylimidazole (4-MeI) is a potential carcinogen widely used in food colours. EU regulations specify a maximum allowable concentration of 200 ppm for 4-MeI in caramel colours. This study reports an electrochemical determination technique for 4-MeI in caramel colours for the first time. The effect of pH and interference from air were studied to optimize the detection conditions on a glassy carbon electrode in aqueous alkaline solutions using square wave voltammetry (SWV) technique. The concentration of 4-MeI was quantitatively measured down to 10 μM (∼0.8 ppm). Traditional methods such as HPLC, GC, spectrometry and immunoassays involve either expensive instrumentation and reagents or time consuming preparation and detection processes. This study demonstrates the possibility of rapid and simple electrochemical determination of (4-MeI) in food colours with minimum workup using a portable potentiostat.

Consumption of Sugar-Sweetened Soft Drinks and Risk of Gastrointestinal Cancer: A Systematic Review and Meta-Analysis of Observational Studies

INTRODUCTION

Previous observational studies have reported inconsistent findings on the association between consumption of sugar-sweetened soft drinks (SSSDs) and the risk of gastrointestinal (GI) cancer. This study investigated the associations between SSSD consumption and the risk of GI cancer using a systematic review and meta-analysis.

METHODS

Observational epidemiological studies were searched from the PubMed and EMBASE databases until June 2021. We conducted a meta-analysis of all included studies and subgroup meta-analyses based on various factors.

RESULTS

In a meta-analysis of 27 studies with nine case-control studies and 18 cohort studies, the consumption of SSSDs was modestly associated with an increased risk of GI cancer (odds ratio [OR]/relative risk [RR]: 1.08; 95% confidence interval [CI]: 1.01-1.16), with a significant positive dose-response relationship. In the subgroup meta-analysis by study design, there was a significant positive association between the consumption of SSSDs and GI cancer in cohort studies (RR: 1.11; 95% CI: 1.03-1.20; n = 18), but not in case-control studies. In the subgroup meta-analysis by type of cancer, consumption of SSSDs was significantly associated with an increased risk of colorectal cancer (OR/RR: 1.13; 95% CI: 1.07-1.19).

CONCLUSIONS

This meta-analysis suggests that SSSD consumption significantly increases the risk of GI cancer, specifically colorectal cancer.

4-Methylimidazole, a carcinogenic component in food, amount, methods used for measurement; a systematic review

4-methylimidazole (4-MEI) is widely used industrially. This carcinogenic component has been reported in some types of food. It is usually produced by the caramelization process in food, drinks and caramel coloring. The possible mechanism for the formation of this compound in food is the Maillard reaction. In order to estimate the amount of substance 4-MEI in food, a systematic study was conducted. The selected keywords were 4-methylimidazole, 4-MEI, beverage, drink, meat, milk, and coffee. 144 articles were obtained from the initial search. The articles were evaluated and finally, the data of 15 manuscripts were extracted. Based on the data extracted from selected articles, the highest amount is reported in caramel color, coffee, and cola drinks. In 70% of the selected studies, the analytical method was based on liquid chromatography. In this method, there is no need for derivatization. SPE columns were used to extract samples in most manuscripts. According to per capita consumption, the most exposure to 4-MEI is through coffee. In high risk food products, regular monitoring with analytical methods with high sensitivity is recommended. Furthermore, most of the selected studies were about the validation method, so few samples were selected. It is recommended to design more studies with a high sample size to accurately evaluate this carcinogenic compound in food.

Food-Borne Chemical Carcinogens and the Evidence for Human Cancer Risk

Commonly consumed foods and beverages can contain chemicals with reported carcinogenic activity in rodent models. Moreover, exposures to some of these substances have been associated with increased cancer risks in humans. Food-borne carcinogens span a range of chemical classes and can arise from natural or anthropogenic sources, as well as form endogenously. Important considerations include the mechanism(s) of action (MoA), their relevance to human biology, and the level of exposure in diet. The MoAs of carcinogens have been classified as either DNA-reactive (genotoxic), involving covalent reaction with nuclear DNA, or epigenetic, involving molecular and cellular effects other than DNA reactivity. Carcinogens are generally present in food at low levels, resulting in low daily intakes, although there are some exceptions. Carcinogens of the DNA-reactive type produce effects at lower dosages than epigenetic carcinogens. Several food-related DNA-reactive carcinogens, including aflatoxins, aristolochic acid, benzene, benzo[a]pyrene and ethylene oxide, are recognized by the International Agency for Research on Cancer (IARC) as causes of human cancer. Of the epigenetic type, the only carcinogen considered to be associated with increased cancer in humans, although not from low-level food exposure, is dioxin (TCDD). Thus, DNA-reactive carcinogens in food represent a much greater risk than epigenetic carcinogens.

Application of gas flow headspace liquid phase micro extraction coupled with gas chromatography-mass spectrometry for determination of 4-methylimidazole in food samples employing experimental design optimization

Background

4-Methylimidazole (4-MeI) or 4-methyl-1H-imidazole, a slightly yellowish solid with molecular formula C₄H₆N₂, is a heterocyclic compound which supposedly does not exist as a natural product and is formed when carbohydrates are heating with ammonium compounds. This compound is used in pharmaceuticals, agriculture and photography chemicals, dyes and pigments, and rubber manufacturing. In the present study, a simple and efficient sample preparation method designated gas flow headspace liquid phase microextraction (GF-HS-SDME) was employed for the extraction and preconcentration of 4-methylimidazole (4-MeI) from food and beverage samples, before its determination by gas chromatography-mass spectrometry.

Result

To investigate the optimal conditions for the extraction process in GF-HS-SDME method, factors affecting extraction, including selection of extraction solvent, vial volume, extraction solvent ratio, position of extracting solvent, drop volume, sample volume, stirring speed, temperature, extraction time, sample pH, ionic strength of the sample solution and gas flow rate were optimized by utilizing both one-variable-at-a-time method and Plackett–Burman design. The investigation of protocol was carried out by using a standard solution containing 100.0 μg L⁻¹ of 4-MeI in deionized water.

Conclusion

In this study, a simple and green analytical method based on GF-HS-SDME was proposed for the extraction and preconcentration of 4-MeI from foodstuffs, followed by GC–MS determination. The main advantage of this method is its high preconcentration factor and fastness due to the application of an inert gas stream during microextraction.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13065-022-00823-z.

Toxic effects of 4-methylimidazole on the maturation and fertilization of mouse oocytes

Individuals of all ages, including children and teenagers, consume 4-methylimidazole (4-MI) in their food. 4-MI is a caramel-colored waste product that has previously been linked to human carcinogenesis and has shown possible signs of reproductive toxicity. This study aimed to determine whether 4-MI is harmful to oocytes during meiosis and fertilization. Female mice were intragastrically administered 0, 50, or 100 mg/kg body weight of 4-MI daily for 10 days. We found that 4-MI affects the quality of oocytes by affecting their meiotic ability and fertility potential. Specifically, 4-MI rendered the meiotic spindles and chromosomes less stable, which halted oocyte maturation and resulted in aneuploidy. 4-MI also slowed the decrease in the levels of cortical granules and their component ovastacin; consequently, sperms could not be bound and fertilization could not occur. We also found that mitochondrial dysfunction was associated with oocytes deterioration. This led to reactive oxygen species accumulation and cell death. Altogether, our findings reveal that the poor condition of oocytes subjected to 4-MI is primarily attributable to mitochondrial malfunction and redox alterations.

Consumption of artificially sweetened soft drinks and risk of gastrointestinal cancer: a meta-analysis of observational studies

OBJECTIVE

There remain inconclusive findings from previous observational epidemiological studies on whether consumption of artificially sweetened soft drinks (ASSD) increases the risk of gastrointestinal (GI) cancer. We investigated the associations between the consumption of ASSD and the risk of GI cancer using a meta-analysis.

DESIGN

Systematic review and meta-analysis.

SETTING

PubMed and EMBASE were searched using keywords until May 2020 to identify observational epidemiological studies on the association between the consumption of ASSD and the risk of GI cancer.

SUBJECTS

Twenty-one case-control studies and seventeen cohort studies with 12 397 cancer cases and 2 474 452 controls.

RESULTS

In the random-effects meta-analysis of all the studies, consumption of ASSD was not significantly associated with the risk of overall GI cancer (OR/relative risk (RR), 1·02; 95 % CI, 0·92, 1·14). There was no significant association between the consumption of ASSD and the risk of overall GI cancer in the subgroup meta-analyses by study design (case-control studies: OR, 0·95; 95 % CI, 0·82, 1·11; cohort studies: RR, 1·14; 95 % CI, 0·97, 1·33). In the subgroup meta-analysis by type of cancer, consumption of ASSD was significantly associated with the increased risk of liver cancer (OR/RR, 1·28; 95 % CI, 1·03, 1·58).

CONCLUSIONS

The current meta-analysis of observational epidemiological studies suggests that overall, there is no significant association between the consumption of ASSD and the risk of GI cancer.

A Review of the Analytical Methods for the Determination of 4(5)-Methylimidazole in Food Matrices

4(5)-Methylimidazole (4(5)MEI) is a product of the Maillard reaction between sugars and amino acids, which occurs during the thermal processing of foods. This compound is also found in foods with caramel colorants additives. Due to its prevalence in foods and beverages and its potent carcinogenicity, 4(5)MEI has received federal and state regulatory agency attention. The aim of this review is to present the extraction procedures of 4(5)MEI from food matrices and the analytical methods for its determination. Liquid and gas chromatography coupled with mass spectrometry are the techniques most commonly employed to detect 4(5)MEI in food matrices. However, the analysis of 4(5)MEI is challenging due to the high polarity, water solubility, and the absence of chromophores. To overcome this, specialized sample pretreatment and extraction methods have been developed, such as solid-phase extraction and derivatization procedures, increasing the cost and the preparation time of samples. Other analytical methods for the determination of 4(5)MEI, include capillary electrophoresis, paper spray mass spectrometry, micellar electrokinetic chromatography, high-performance cation exchange chromatography, fluorescence-based immunochromatographic assay, and a fluorescent probe.

Caramel colors in terms of scientific research, with particular consideration of their toxicity

Caramel colors, the most common food additives in the world, are divided into four classes (IIV), marked with the symbols E150 a-d, respectively. Individual classes of caramel colors differ from each other in physico-chemical properties and the method of preparation, which affects the formation of various compounds that are important for the assessment of food safety A number of studies on all caramel classes of have been performed, including toxicokinetic, genotoxic, carcinogenic and reproductive and developmental toxicity studies, which have not shown harmful effects of these additives at doses not exceeding ADI. However, there is an increasing number of scientific reports of the possible toxic effects present in caramels of low-molecular compounds. Currently, three compounds are considered to be toxicologically important and resulting from the possible concentration in the final product: 5-HMF (present in all classes), 4(5)-MeI (present in caramel classes III and IV) or THI (present in caramel class III). 4(5)-MeI has a neurotoxic effect and was considered in 2011 as a possible human carcinogen (class 2B, according to IARC). In the case of THI, studies have confirmed its lymphopenic activity, probably secondary to its immunosuppressive effect. Consequently, in the 1980s, JECFA set acceptable levels 4(5)-MeI and THI, for the caramel classes in which these compounds may be present. The toxicity of 5-HMF has not been confirmed unequivocally, but studies have shown that this compound is not neutral to living organisms. Currently, most international organizations and scientific institutes recognize these additives as safe for consumers, but at the same time scientists emphasize the need for further research.

Multigenerational reproductive assessment of 4-methylimidazole administered in the diet to Hsd:Sprague Dawley SD rats

The general population, including children and adolescents, is exposed to 4-methylimidazole (4-MI) in the diet. 4-MI is a by-product of caramel color manufacturing. It has been previously classified as a possible human carcinogen and displays potential reproductive toxicity. A follow up assessment of reproductive toxicity was conducted in rats utilizing the reproductive assessment by continuous breeding paradigm, in which multiple generations were exposed to 4-MI in diet at 750, 2500, and 5000 ppm. 4-MI exposure was associated with delays in preputial separation and vaginal opening, impairment in reproductive performance, and concomitant histopathological findings in the prostate, testis, and epididymis at 2500 and 5000 ppm. The Lowest Observed Adverse Effect Level for reproductive (based on prostate atrophy) and developmental toxicity (based on delays in preputial separation and vaginal opening) was 750 ppm, equivalent to approximately 50-60 mg/kg bw/day.

Comparison of acute respiratory epithelial toxicity for 4-Methylimidazole and naphthalene administered by oral gavage in B6C3F1 mice

4-Methylimidazole (4MEI) is a contaminant in food and consumer products. Pulmonary toxicity and carcinogenicity following chronic dietary exposures to 4MEI is a regulatory concern based on previous rodent studies. This study examined acute pulmonary toxicity in B6C3F1 mice from 6 h to 5 days after oral gavage with a single dose of 150 mg/kg 4MEI, a double dose delivered 6 h apart, or vehicle controls. Oral gavage of 150 mg/kg naphthalene, a prototypical Club cell toxicant, was used as a positive control. Intrapulmonary conducting airway cytotoxicity was assessed in fixed-pressure inflated lungs using qualitative histopathology scoring, quantitative morphometric measurement of vacuolated and exfoliating epithelial cells, and immunohistochemistry. 4MEI treatment did not change markers of cytotoxicity including the mass of vacuolated epithelium, the thickness of the epithelium, or the distributions of epithelial proteins: secretoglobin 1A1, proliferating cell nuclear antigen, calcitonin gene-related peptide, and myeloperoxidase. 4MEI and vehicle controls caused slight cytotoxicity with rare vacuolization of the epithelium relative to the severe bronchiolar epithelial cell toxicity found in the naphthalene exposed mice at terminal bronchioles, intrapulmonary airways, or airway bifurcations. In summary, 4MEI caused minimal airway epithelial toxicity without characteristic Club Cell toxicity when compared to naphthalene, a canonical Club Cell toxicant.

A weight of evidence assessment of the genotoxic potential of 4-methylimidazole as a possible mode of action for the formation of lung tumors in exposed mice

4-Methylimidazole (4-MeI) is a byproduct formed during the cooking of foods containing carbohydrates and amino acids, including the production of flavors and coloring substances, e.g., class III and IV caramel colors, used in many food products with extensive human exposure. Two-year rodent bioassays via oral exposure conducted by the National Toxicology Program reported evidence of carcinogenicity only in B6C3F₁ mice (increased alveolar/bronchial neoplasms). In 2011, the International Agency for Research on Cancer classified 4-MeI as Group 2B, "possibly carcinogenic to humans". An expert panel was commissioned to assess the genotoxic potential of 4-MeI and the plausibility of a genotoxic mode of action in the formation of lung tumors in mice when exposed to high doses of 4-MeI. The panel defined and used a weight-of-evidence (WOE) approach that included thorough evaluation of studies assessing the genotoxic potential of 4-MeI. The panelists categorized each study, consisting of study weight, degree of technical performance, study reliability, and contribution to the overall WOE. Based on the reviewed studies' weighted contribution, the panel unanimously concluded that the WOE supports no clear evidence of in vivo genotoxicity of 4-MeI and no association for a genotoxic mode of action in the formation of mouse lung tumors.

Evaluation of two in silico programs for predicting mutagenicity and carcinogenicity potential for 4-methylimidazole (4-MeI) and known metabolites

4-Methylimidazole (4-MeI) is a nitrogen-containing heterocyclic compound that is used in the manufacture of chemicals, dyes and pharmaceuticals and may be found in a variety of foods following formation during heating. The purpose of this study was to use two different in silico programs, CASE Ultra and Toxtree, to investigate potential structure-activity relationships in 4-MeI and its metabolites for mutagenicity and carcinogenicity, and combine that information with the available literature to draw conclusions regarding the strength of the predictions observed. Neither CASE Ultra nor Toxtree identified any structural alerts that were associated with mutagenic activity. Data for 4-MeI from a single study were used in the development of the CASE Ultra mouse and rat carcinogenicity models, but no additional similar structures were identified in the carcinogenicity model training set. One metabolite, 5-methylhydantoin, was predicted to be positive in the CASE Ultra carcinogenicity male and female mouse models; positive predictivity percentages of 60.9% and 73.7%, respectively. However, low structural similarity between 5-methylhydantoin and the compounds identified in the training set (<25%) decreases confidence in the positive prediction. Three metabolites were predicted to be positive in the CASE Ultra mouse micronucleus model, but again suffered from low structural similarity. Both limited structural similarity and inconsistent responses among the other clastogenicity models suggest that additional structurally similar compounds are needed to assess the predictive capacity of these alerts for biological activity of these compounds.

Chronic intake of 4-Methylimidazole induces Hyperinsulinemia and Hypoglycaemia via Pancreatic Beta Cell Hyperplasia and Glucose Dyshomeostasis

Caramel colours are the preferential food colouring agent globally, reaches wide age groups through eatables. Colas, a sweetened carbonated drink are most common caramel coloured beverage and its consumption is linked with diabetes, obesity, pancreatic cancer and other endocrine disorders. A major by-product produced during caramelization is 4-methylimidazole (4-MEI) that is detected in noteworthy concentrations in colas and other beverages. Previous studies revealed the neurotoxic and carcinogenic potential of 4-MEI in animals at higher doses but the effect of 4-MEI at theoretical maximum daily intake dose on glucose homeostasis is unexplored. Here, mice treated with 4-MEI (32 µg/kg bodyweight/day) for seven weeks exhibited severe hypoglycaemia and hyperinsulinemia mediated by hyperplasia of pancreatic beta cells and induces metabolic alterations. On combinatorial treatment, 4-MEI suppressed the glucogenic potential of non-artificial sweeteners and promotes lipogenesis. Furthermore, increased levels of C-peptide, LDL-cholesterol and triglycerides were observed in the humans with regular intake of 4-MEI containing beverages. In summary, 4-MEI induced pancreatic beta cell hyperplasia and leads to disruption of glucose and lipid homeostasis. This study suggests the need for further assessment and reconsideration of the wide usage of 4-MEI containing caramels as food additives.