Polymerized Urushiol of the Commercially Available Rhus Product in Korea

Systemic contact dermatitis commonly occurs with the intake of lacquer (rhus) in Korea, because rhus lacquer is thought to be effective for the treatment of gastrointestinal problems and good for health1-3. Recently, rhus products have been commercialized due to a national project of the Ministry of Agriculture and Forestry of Korea, and also, manufacturers have insisted that they possess proprietary technology for rhus poison detoxification. However, there have been many people visiting dermatologic clinics who are suffering from the ingestion of rhus products. Urushiol, the sap of the Japanese lacquer tree, is the active immunogen of rhus. Urushiol, acting as hapten, binds with self-protein to then generate neo-antigenic determinants4, 5. The principle of current rhus poison detoxification techniques is the elimination of urushiol. Current methods that induce the oxidation and the polymerization of urushiol include heating, boiling with botanical materials or high protein foods, as well as a process that uses an oxidizing agent or enzyme6. The process diminishes the allergenicity of urushiol through reduction of an effector, but polymerized urushiol still has antigenicity - although to a diminished degree6, 7. The Korean Food and Drug Administration (KFDA) has regulations to control urushiol use as a food. However, the KFDA laboratory method for urushiol detection can detect only the rhus monomer. Accordingly, present rhus products that were considered not to include urushiol by KFDA possibly do contain polymerized urushiol. Therefore, we conducted experiments for detection of polymerized urushiol in rhus products approved by the KFDA.

Many Koreans consume rhus extract (Japanese lacquer tree, Rhus verniciflua) in various forms such as lacquer with boiled chicken, duck and rabbit, a lacquer sap drink, or via inhalation, relying on folk medicine beliefs that rhus is good for the health. For that reason, systemic contact dermatitis caused by rhus occurs frequently in Korea1-3. Adverse effects, due to ingestion of this rhus, have been significant. Yun et al.8 reported that 32% of the people who ingested boiled chicken with rhus, for the first time, exhibited a rash. Won et al.3 conducted a clinical study of 147 patients with systemic contact dermatitis from ingestion of boiled chicken with rhus. They reported that when people ingested boiled chicken with rhus, 1 out of 4 exhibited systemic contact dermatitis. Erythematous maculopapules, erythroderma and erythema multiforme-like lesions were among the cutaneous manifestations: 50.6%, 40.9% and 8.4%, respectively. They also reported that leukocytosis and abnormal liver function were identified in 61.2% and 16.3% of those who exhibited cutaneous manifestations, respectively. Simultaneously, systemic symp toms such as pyrexia, rigor, headache, chest tightness and dyspnea have also been reported1, 2, 8, 9.

Urushiol, an antigen of rhus, acts as a hapten and exhibits antigenicity, binding with self-protein4, 5. Urushiol is a catechol complex that is comprised of either a C15 or C17-alkyl or alkenyl group on the side chain. Depending on side chain type, the complex can consist of 10 or more slightly different similar structures. Both saturated and unsaturated side chains were identified1, 6, 10, 11. Urushiol is stabilized by inducing oxidation and polymerization with laccase (p-diphenol oxidase enzyme) under appropriate humidity1, 6. Its antigenicity decreases through this stabilization process, but does not completely disappear, and may cause an immune reaction7.

Rhus detoxification means removing urushiol. Currently, available rhus detoxification is accomplished through simple heating, methods involving oxidizing agents or enzymes, methods utilizing plant materials such as medicinal herbs, or heating with protein6. Urushiol reacts with self-protein at the catechol phenol ring and with unsaturated side chain sites, which are the primary active sites for oxidation and polymerization10. Accordingly, reactivity differs depending on the extent of unsaturation on the side chains. Therefore, urushiol, with saturated side chains, reacts in less than 50% of the subjects; whereas, urushiol with unsaturated side chains reacts in more than 90%10. Simple heating, methods accompanying oxidizing agents or enzymes, and methods accompanying heating with protein use these characteristics, and induce generation of urushiol polymers through oxidation and polymerization of the urushiol catechol phenol ring and unsaturated side chains. In this way, reactivity of urushiol is mitigated, reducing active sites that bind with self-protein6, 10, 12. However, as active sites that bind with self-protein can remain within a urushiol polymer, too, antigenicity does not completely disappear. So, if it is exposed to those who are already sensitized, symptoms such as contact dermatitis can be induced6, 7, 10.

Now, the KFDA has appointed rhus as an 'ingredient that cannot be used in the food', and the standardized laboratory test method for urushiol identification as a high performance liquid chromatography (HPLC)-UV absorption detector with a gas chromatography-mass spectrometer. In case of rhus-related foods, the KFDA approves a food product if urushiol is not detected in accordance with this norm. However, these test methods use samples pretreated several times with a filtration of acetone, hexane and acetonitrile as solvents, so that the urushiol polymer is filtered and not detected. In addition, as only the presence of 4 types of urushiol monomer peaks (C₁₅monoene, diene, triene, saturated) is determined, urushiol polymer cannot be identified6. In other words, present rhus products, which were considered not to include urushiol potentially by KFDA, potentially contain urushiol polymer, in which antigenicity still remains.

For this reason, in order to identify the existence of polymers, we prepared samples fractionated with chloroform solvent - which can dissolve polymers - utilizing one of the commercially available rhus extract products that were considered not to include urushiol by the KFDA. Then, we used a method to obtain fractions with a recycle preparative HPLC system. Also, we carried out ¹H NMR analysis using DMSO-d₆ as a solvent, which can dissolve polymers of high molecular weight. As a result, a substance with molecular weight 638 that is suspected to be urushiol dimer was identified. This means that urushiol polymers - such as dimmers - in which antigenicity potentially remains, exist in the rhus products approved by the KFDA. So, if these rhus products are exposed to those who are already sensitized, adverse effects, such as contact dermatitis, may present. Even if the antigenicity of this rhus product is low, the product is not completely detoxified.

The present experiments have some limitations. First, we used only one rhus extract product approved by the KFDA as a sample. So, a reproducibility test, which checks if the same results from experiments with other products will be obtained or not, should be carried out. Secondly, some impurities might exist in the samples as a result of simplifying filtration processes in order to identify urushiol polymers. These impurities may be interfering in the precise mass spectrometry and structure analysis. Thirdly, structure analyses using 2-dimensional or 3-dimensional NMR, in addition to ¹H NMR, were not conducted.

In this study, we identified a substance, suspected to be urushiol dimer, present in one of the commercially available rhus products. Therefore, even if the antigenicity of the rhus products is low, the products may cause adverse effects, such as skin eruptions, due to inomplete detoxification. Thus, imprudent public relations and distribution of potentially unsafe rhus products should be banned; efforts to enhance the approval standards for the distribution of rhus-related products are required.