Acrylamide (AA) is commonly used in industry for gel experiments, water purification, and plastic production(Friedman 2003; E. A. Smith and Oehme 1991), workers can be exposed to acrylamide through the skin and respiratory tract. In addition, smoking and diet in daily life are potential sources of acrylamide exposure for the general population. Then, AA is widely found in foods such as French fries and bread, and is formed by the Maillard reaction between free aspartic acid and reducing sugars at high temperatures(Mottram, Wedzicha, and Dodson 2002; Stadler and Scholz 2004). Due to the widespread presence of acrylamide in foods, several studies have estimated dietary acrylamide exposure(Andačić et al. 2020; Eicher et al. 2020; Kawahara et al. 2019). Studies have found that consumer estimates of average intake of AA may vary by country and dietary habits but the average intake can be considered to be about 0.4 µg/kg per day, with an average intake of about 1.0 µg/kg for advanced consumers(Chuang, Chiu, and Chen 2006).
Acrylamide is readily soluble in water and can be rapidly absorbed in the body as well as rapidly distributed in various tissues(Chaudhry, Cotterill, and Watkins 2006). Acrylamide is metabolized in vivo by two pathways, the first being biotransformation via cytochrome P450 (CYP2E1) to produce GA (glycidyl amide) (Calleman, Bergmark, and Costa 1990; Duale et al. 2009), the second pathway is coupled to glutathione in the presence of glutathione S-transferase (GST): acrylamide to N-Acetyl-S-(2-carbamoylethyl)-L-cysteine (AAMA), glycidyl amide to N-Acetyl-S-(2-carbamoyl-2-hydroxyethyl)-L-cysteine (GAMA) (S. C. Sumner, MacNeela, and Fennell 1992). Metabolites of acrylamide and glycidyl amide are excreted in the urine as thioglycolic acid derivatives(Eva K. Kopp et al. 2008).
The risk of human exposure to acrylamide is usually estimated based on its occurrence in food, and a health reference value is determined by comparing this risk to the baseline lower confidence limit for dose in animals (BMDL 10) (Chain (CONTAM) 2015), however, this method is influenced by various factors such as dietary frequency and bias in the estimation of acrylamide levels in food. Therefore, human biomonitoring (HBM) is currently used to obtain exposure to acrylamide in urine or blood to better estimate total exposure (Goerke et al. 2019; Pedersen et al. 2022). In general, urine is the specimen of choice for acrylamide biomonitoring (F Fernández et al. 2022), because of its stability, high specificity and sensitivity, and its easy availability in large quantities (Louro et al. 2019).
Urinary metabolite levels of acrylamide have been reported in several studies(Thomas Bjellaas et al. 2007; Melanie Isabell Boettcher et al. 2005; Ruenz et al. 2016; S.-Y. Wang et al. 2020). Due to the high enzymatic activity of CYP2E1, AA is more readily metabolized oxidatively than GA. In a study of urinary acrylamide metabolism in mice, a GAMA/AAMA ratio of 0.23 was calculated(Twaddle et al. 2004). Sumner et al. also found that AAMA accounted for 41% of total urinary metabolites and GAMA for only 21% after oral administration of 50 mg/kg AA body weight to mice, with a GAMA/AAMA ratio close to 0.51(S. C. J. Sumner et al. 2003), and the same was found in the population metabolic pattern(Mojska et al. 2020). AAMA seems to be more advantageous than GAMA in excretion, but GAMA is converted from GA, which may play a role in cancer, neurotoxicity, etc. Therefore, GAMA/AAMA ratio has been explored again as a specific indicator of AA metabolic activation. However, a recent study has shown that the GAMA/AAMA ratio changes substantially even in a single participant after oral acrylamide administration due to differences in the elimination kinetics of the two metabolites(T. Bjellaas et al. 2005; Melanie I. Boettcher et al. 2006). Therefore, this ratio is unreliable for assessing potential polymorphisms between individuals, so using a single AAMA as a short-term exposure biomarker remains advantageous.
The health effects of acrylamide have received increasing attention in recent years, and its neurotoxicity has been demonstrated in occupational populations(He et al. 1989). The general symptoms of neurotoxicity in humans are skeletal muscle weakness, ataxia, weight loss, and axonal degeneration of the central and peripheral nervous system(Hagmar et al. 2001). Studies have found that the specific neurotoxicity index (Nin) of acrylamide-induced peripheral neuropathy correlates with workers' 24-hour urine Mercapturic acid levels in the urine of workers were significantly correlated(Calleman et al. 1994). In addition, the carcinogenicity of acrylamide has been well documented in experimental animals(Klaunig 2008). Therefore, acrylamide has been classified by the World Health Organization's International Agency for Research on Cancer (IARC) as a "probable human cancer risk"(IARC 1994, 60). Studies on dietary acrylamide and hemoglobin adducts and various cancers have been reported repeatedly(Kito et al. 2020; Obón-Santacana et al. 2016; Zha et al. 2020), but studies on cancer and urinary biomarkers of acrylamide are scarce, and only a dose-response relationship between urinary AAMA and uroepithelial carcinoma (UC) has been found(Chung et al. 2020). Therefore, studying the role of urinary biomarkers of acrylamide will help researchers to discuss its relationship with various diseases in the future.
With this review, we aim to summarize the published levels of the urinary metabolite of acrylamide, AAMA, as a reference for the exposure dose in the studied population. In addition, we discuss the association of AAMA with other factors and diseases, aiming to illustrate the role of the urinary metabolite of acrylamide, AAMA, and to explore research gaps and future needs.