NTP-CERHR monograph on the potential human reproductive and developmental effects of acrylamide

Acrylamide, used in the manufacture of polyacrylamide and grouting agents, is produced during the cooking of foods. Workplace exposure to acrylamide can occur through the dermal and inhalation routes. The objectives of this study were to evaluate the metabolism of acrylamide in humans following oral administration, to compare hemoglobin adduct formation on oral and dermal administration, to measure hormone levels, and to monitor the safety of acrylamide in people exposed under controlled conditions. Prior to conducting exposures in humans, a low-dose study was conducted in rats administered 3 mg/kg 1,2,3-¹³C₃acrylamide by gavage. The study protocol was reviewed and approved by Institute Review Boards both at RTI which performed the sample analysis, and the clinical research center conducting the study. 1,2,3-¹³C₃Acrylamide (AM) was administered in an aqueous solution orally (single dose of 0.5, 1.0,or 3.0 mg/kg) or dermally (3 daily doses of 3.0 mg/kg) to sterile male volunteers. Urine samples (3 mg/kg oral dose) were analyzed for AM metabolites using 13C NMR spectroscopy. Approximately 86 % of the urinary metabolites were derived from GSH conjugation, and excreted as N-acetyl-S-(3-amino-3-oxopropyl)cysteine and its S-oxide.Glycidamide, glycer amide, and low levels of N-acetyl-S-(3-amino-2-hydroxy-3-oxopropyl)cysteine were detected in urine. On oral administration, a linear dose response was observed for N-(2-carbamoylethyl)valine (AAVal) and N-(2-carbamoyl-2-hydroxyethyl)valine (GAVal) in hemoglobin. Dermal administration resulted in lower levels of AAVal and GAVal. This study indicated that humans metabolize acrylamide via glycidamide to a lesser extent than rodents, and dermal uptake was approximately 5%of that observed with oral uptake. Acrylamide is used in the manufacture of water- soluble polymers (European Union,2002). These polymers are then used for wastewater and sludge treatment, paper manufacture, soil stabilization, mining and many other uses (European Union, 2002).Acrylamide is also a chemical intermediate in the manufacture of other monomeric chemicals and used for grouting and preparation of laboratory gels for electrophoresis.Human exposure through these applications is very small (European Union, 2002).Previously, it has been postulated that dermal absorption was the major route of human exposure to acrylamide (European Union, 2002). The magnitude of this dermal absorption is highly relevant as one of the uses of acrylamide based polymers is in the formulation of skin creams (European Union, 2002). Estimates of dermal absorption based on in vitro and rodent studies have ranged from 3% to 100 (European Union,2002). Recently, exposure to acrylamide in a variety of cooked foods has been described(Rosen and Hellen as, 2002; Tareke et al., 2002). Human exposure via this route is substantial, with estimated exposures as high as 70 μg per day proposed (Tareke et al.,2002). Acrylamide is metabolized by two main pathways: glutathione conjugation (Dixit et al.,1982; Edwards, 1975; Hashimoto and Aldridge, 1970; Miller et al., 1982; Sumner et al.,1992), and oxidation to glycidamide (Calleman et al., 1990; Sumner et al., 1992). The metabolism of acrylamide in vivo results in the formation of a number of metabolites.These metabolism of acrylamide in vivo has been investigated by administration of 1,2,3-13C3 acrylamide to rodents, with the detection and quantitation of metabolites by 13 CNMR spectroscopy (Sumner et al., 1999; Sumner et al., 1992; Sumner et al., 2003). The oxidation reaction to glycidamide is catalyzed by cytochrome P450 2E1 in rodents(Sumner et al., 1999). Both acrylamide and glycidamide react with hemoglobin producing a stable adduct which can be measured as an indicator of exposure.Correlations have been made with hemoglobin adducts and neurotoxicity, but there has been no systematic standardization of hemoglobin adducts with dose. Glycidamide is weakly mutagenic in the Salmonella test (Hashimoto and Tanii, 1985). It can react with DNA in vitro to produce a guanine derivative N7-(2-carbamoyl-2-hydroxyethyl)guanine(Gamboa da Costa et al., 2003; Segerback et al., 1995). In vivo, administration of acrylamide to rats and mice produces low levels of N7-(2-carbamoyl-2-hydroxyethyl)guanine (Gamboa da Costa et al., 2003; Segerback et al., 1995).Acrylamide induces a characteristic peripheral neurotoxicity in animals and man(Spencer and Schaumburg, 1974a, b, 1975). This toxicity manifests itself as a distal to proximal loss of nerve function and dying back of cells. Acrylamide also effects rodent reproduction, namely smaller litter size. At elevated acrylamide doses other reproductive effects are seen, likely as a consequence of the neurotoxicity. Acrylamide is carcinogenic in drinking water studies in laboratory rats (Friedman et al.,1995; Johnson et al., 1986). In male rats, it induces tumors of the tunica vaginalis testes and the thyroid, while in females, it induces mammary fibroadenomas and thyroid tumors(Friedman et al., 1995). The mechanism for this tumorigenicity is unclear, although interaction with the dopamine receptor has been postulated as well as genotoxicity (Tyland Friedman, 2003). If the mechanism were genotoxicity, then conversion of acrylamide to glycidamide is directly proportional to carcinogenic activity.Understanding the mechanism of tumorigenicity is important, since conventional risk assessment techniques place the order of magnitude of the risk at approximately 10-3 with exposures of 70 μg/ day.The relative contributions of acrylamide and glycidamide in the mode of action of acrylamide are the subject of debate and current research. Understanding the conversion of acrylamide to glycidamide and differences that may occur between species, exposure route, and dose are important considerations in assessing the risk of the possible effects of acrylamide exposures in the diet, in consumer products, and in the workplace.The primary objectives of this study were to evaluate the conversion of acrylamide to glycidamide in people exposed to acrylamide, and to evaluate the extent of uptake following dermal administration. This was conducted by administering a low dose of 13C labeled acrylamide to volunteers orally or dermally, and by measuring urinary metabolites or hemoglobin adducts derived from the glycidamide pathway and comparing them to metabolites and hemoglobin adducts derived from acrylamide directly. More specifically, we intended to evaluate urinary metabolites and hemoglobin adducts, and to measure hormone levels after exposure to a known dose of acrylamide. As a secondary and no less important objective, we intended to monitor the safety of acrylamide in people exposed under controlled conditions.