Effect of Prolonged Repeated Exposure to Formaldehyde Donors with Doses Below the EC3 Value on Draining Lymph Node Responses

Abstract

In the Local Lymph Node Assay (LLNA), a stimulation index of 3 (SI = 3) is established as a threshold value for hazard identification of sensitization. The corresponding EC3 value, the effective concentration inducing a threefold increase compared to controls, can possibly predict threshold levels for sensitization in humans. Exposure to a dose below the threshold dose would not result in an induction of an immune response. Each repeated contact would be considered and viewed as a new contact and as long as the dose is below the threshold there will be no response, even after repeated exposures. However, repeated exposure may result in local accumulation eventually resulting in a dose that induces a response above the threshold for immunization. We investigated lymph node responses after short and prolonged exposure to formaldehyde donors, chemicals that are highly reactive with proteins and may thus persist in the skin. The studies were performed with formaldehyde and formaldehyde releasers (formaldehyde, paraformaldehyde, Quaternium-15, 2-Chloro-N-(hydroxymethyl)acetamide, and hexamethylenetetramine), at concentrations that induce a SI = 2, i.e., below the threshold for hazard identification. For all test chemicals investigated enhanced lymph node responses were obtained when comparing long-term prolonged exposure to short-term exposure, while three of five chemicals induced responses above SI = 3. Our results show that repeated and prolonged exposure to doses below the EC3 value can induce reactions above the SI = 3, the hazard identification threshold for sensitization in mice. So, when discussing the possible use of the EC3 as benchmark for risk assessment, one should consider duration of exposure and the possibility of local accumulation of the chemical under investigation.

Methylisothiazolinone in rinse-off products causes allergic contact dermatitis: a repeated open-application study

“…Under the conditions of our study, the relatively high, but realistic, frequency of exposure most likely had an impact on the response. Repeated low‐dose exposure has been shown to be an important factor for elicitation as well as sensitization . In the study by Jensen et al ., just two applications per day of a soap with 0·1% methyldibromo glutaronitrile (MDBGN) in MDBGN‐allergic individuals elicited a reaction in 37% of subjects.…”

Allergic contact dermatitis: epidemiology, molecular mechanisms, in vitro methods and regulatory aspects

“…Similar negative results were seen with paraformaldehyde and hexamethylenetetramine. However, formaldehyde, 2-chloro- N - (hydroxymethyl)acetamide and quaternium-15 showed positive results in an extended LLNA [199]. The underlying mechanisms leading to sensitisation at exposure levels below the LLNA thresholds are unclear.…”

Scientific Opinion on the re‐evaluation of hexamethylene tetramine (E 239) as a food additive

“…In a Local Lymph Node Assay (LLNA) a positive effect concentration (EC3) of 30.6% HMT was derived. A comparably low EC3 for formaldehyde was determined in the same study (De Jong et al, 2007). Thus, it may be concluded also for skin sensitization, that formaldehyde, which may be generated by hydrolysis of HMT in contact to skin, and not HMT, is the main causative agent of sensitization.…”