High-performance liquid chromatography method for the quantification of non-radiolabelled cinnamic compounds in analytes derived from human skin absorption and metabolism experiments

Anthelmintic efficacy of cinnamaldehyde and cinnamic acid from cortex cinnamon essential oil against Dactylogyrus intermedius

Utilization of chemical pesticide to control monogenean diseases is often restricted in many countries due to the development of pesticide resistance and concerns of chemical residues and environmental contamination. Thus, the use of antiparasitic agents from plants has been explored as a possible way for controlling monogenean infections. Extracts from Cinnamomum cassia were investigated under in vivo conditions against Dactylogyrus intermedius in goldfish. The two bioactive compounds, cinnamaldehyde and cinnamic acid, were identified using nuclear magnetic resonance and electrospray ionization mass spectrometry. The 48 h median effective concentrations (EC(50)) for these compounds against D. intermedius were 0·57 and 6·32 mg L(-1), respectively. The LD(50) of cinnamaldehyde and cinnamic acid were 13·34 and 59·66 mg L(-1) to goldfish in 48 h acute toxicity tests, respectively. These data confirm that cinnamaldehyde is effective against D. intermedius, and the cinnamaldehyde exhibits potential for the development of a candidate antiparasitic agent.

Allergic contact dermatitis--formation, structural requirements, and reactivity of skin sensitizers

Contact allergy is caused by a wide range of chemicals after skin contact. Its clinical manifestation, allergic contact dermatitis (ACD), is developed upon repeated contact with the allergen. This perspective focuses on two areas that have yielded new useful information during the last 20 years: (i) structure-activity relationship (SAR) studies of contact allergy based on the concept of hapten-protein binding and (ii) mechanistic investigations regarding activation of nonsensitizing compounds to contact allergens by air oxidation or skin metabolism. The second area is more thoroughly reviewed since the full picture has previously not been published. Prediction of the sensitizing capacity of a chemical is important to avoid outbreaks of ACD in the population. Much research has been devoted to the development of in vitro and in silico predictive testing methods. Today, no method exists that is sensitive enough to detect weak allergens and that is robust enough to be used for routine screening. To cause sensitization, a chemical must bind to macromolecules (proteins) in the skin. Expert systems containing information about the relationship between the chemical structure and the ability of chemicals to haptenate proteins are available. However, few designed SAR studies based on mechanistic investigations of prohaptens have been published. Many compounds are not allergenic themselves but are activated in the skin (e.g., metabolically) or before skin contact (e.g., via air oxidation) to form skin sensitizers. Thus, more basic research is needed on the chemical reactions involved in the antigen formation and the immunological mechanisms. The clinical importance of air oxidation to activate nonallergenic compounds has been demonstrated. Oxidized fragrance terpenes, in contrast to the pure terpenes, gave positive patch test reactions in consecutive dermatitis patients as frequently as the most common standard allergens. This shows the importance of using compounds to which people are exposed when screening for ACD in dermatology clinics.

Simultaneous determination of cinnamaldehyde, eugenol and paeonol in traditional Chinese medicinal preparations by capillary GC-FID

A capillary GC method was established for simultaneous determination of cinnamaldehyde (CNMD), eugenol (EL) and paeonol (PL) in two traditional Chinese herbal medicinal preparations, Weitongding tablet (WTDT) and Guifu Dihuang pill (GDHP). The assays were based on a programmed temperature GC in a 30 m x 0.53 mm capillary column with nitrogen as carrier and FID detector. Good linearities were obtained over ranges of 0.45-452 mg/l CNMD, 0.31-625 mg/l EL and 0.30-610 mg/l PL, respectively. The spike recoveries were within 84-111%.

Protein binding and metabolism influence the relative skin sensitization potential of cinnamic compounds

Skin protein modification (haptenation) is thought to be a key step in the manifestation of sensitization to low molecular mass chemicals (<500 g/mol). For sensitizing chemicals that are not protein reactive, it is hypothesised that metabolic activation can convert such chemicals into protein reactive toxins within the skin. trans-Cinnamaldehyde, alpha-amyl cinnamaldehyde, and trans-cinnamic alcohol are known sensitizers with differing potencies in man, where the former two are protein reactive and the latter is not. Here, we have used immunochemical methods to investigate the extent of protein-cinnamaldehyde binding in rat and human skin homogenates that have been incubated (for either 5, 15, 30, or 60 min) at 37 degrees C with cinnamaldehyde, alpha-amyl cinnamaldehyde (at concentrations of between 1 and 40 mM), and cinnamic alcohol (at higher concentrations of 200 or 400 mM). Cinnamaldehyde specific antiserum was raised specially. A broad range (in terms of molecular mass) of protein-cinnamaldehyde adducts was detected (as formed in a time- and concentration-dependent manner) in skin treated with cinnamaldehyde and cinnamic alcohol but not with alpha-amyl cinnamaldehyde. Mechanistic observations have been related to relative skin sensitization potential, as determined using the local lymph node assay (LLNA) as a biological read-out. The work presented here suggests that there is a common hapten involved in cinnamaldehyde and cinnamic alcohol sensitization and that metabolic activation (to cinnamaldehyde) is involved in the latter. Conversely, there does not appear to be a common hapten for cinnamaldehyde and alpha-amyl cinnamaldehyde. Such mechanistic work on protein modification is important in understanding the early mechanisms of skin sensitization. Such knowledge can then be used in order that effective and appropriate in vitro/in silico tools for predicting sensitization potential, with a high confidence, can be developed.

Cinnamic compound metabolism in human skin and the role metabolism may play in determining relative sensitisation potency

BACKGROUND

trans-Cinnamaldehyde and trans-cinnamic alcohol cause allergic contact dermatitis (ACD) in humans; cinnamaldehyde is a more potent sensitiser than cinnamic alcohol. These two chemicals are principal constituents of the European Standard 'Fragrance Mix', as used in patch testing diagnostics of sensitisation to fragrances by clinical dermatologists. As contact sensitisers are usually protein reactive compounds, it is hypothesised that cinnamic alcohol (not protein-reactive) is a 'prohapten' that requires metabolic activation, presumably by cutaneous oxidoreductases, to the protein-reactive cinnamaldehyde (a 'hapten'). It is postulated that cinnamaldehyde can be detoxified by aldehyde dehydrogenase (ALDH) to cinnamic acid and/or by alcohol dehydrogenase (ADH) to cinnamic alcohol. Hence, a variety of metabolic pathways may contribute to the relative exposures and hence sensitising potencies of cinnamic alcohol and cinnamaldehyde.

OBJECTIVE

To evaluate the extent of cinnamaldehyde and cinnamic alcohol metabolism in human skin and provide evidence for the role of cutaneous ADH and ALDH in such metabolism.

METHODS

The extent of cinnamic alcohol and aldehyde metabolism was investigated in human skin homogenates and sub-cellular fractions. A high performance liquid chromatography method was used for analysis of skin sample extracts. Studies were conducted in the presence and absence of the ADH/cytochrome P450 inhibitor 4-methylpyrazole and the cytosolic ALDH inhibitor, disulfiram.

RESULTS

Differential metabolism of cinnamic alcohol and cinnamaldehyde was observed in various subcellular fractions: skin cytosol was seen to be the major site of cinnamic compound metabolism. Significant metabolic inhibition was observed using 4-methylpyrazole and disulfiram in whole skin homogenates and cytosolic fractions only.

CONCLUSIONS

This study has demonstrated that cutaneous ADH and ALDH activities, located within defined subcellular compartments, play important roles in the activation and detoxification of CAlc and CAld in skin. Such findings are important to the development of computational hazard prediction tools for sensitisation (e.g. the DEREK program) and also to dermatologists in understanding observed interindividual differences, cross-reactivities or co-sensitisation to different cinnamic compounds in the clinic.

Human skin absorption and metabolism of the contact allergens, cinnamic aldehyde, and cinnamic alcohol

trans-Cinnamaldehyde and trans-cinnamic alcohol have been commonly reported to cause allergic contact dermatitis (ACD) in humans. Cinnamaldehyde is a more potent skin sensitizer than cinnamic alcohol. It has been hypothesized that cinnamic alcohol is a "prohapten" that requires metabolic activation, presumably by oxidoreductase enzymes such as alcohol dehydrogenase (ADH) or cytochrome P450 2E1 (CYP2E1), to the protein-reactive cinnamaldehyde (a hapten). In this study, the in vitro percutaneous absorption and metabolism of cinnamaldehyde and cinnamic alcohol (78 micromol dose) has been examined using freshly excised, metabolically viable, full-thickness breast and abdomen skin from six female donors. Penetration rates and total cumulative recoveries of cinnamic compounds that were present in receptor fluid, extracted from within the skin, evaporated from the skin surface, or remained unabsorbed on the skin surface after 24 h were quantified by reversed-phase high-performance liquid chromatography. Biotransformation of cinnamaldehyde to both cinnamic alcohol and cinnamic acid was observed. Topically applied cinnamic alcohol was converted to cinnamaldehyde (found on the skin surface only) and cinnamic acid. To establish whether these biotransformations were enzymatic, experiments were performed in the absence and presence of varying concentrations (80-320 micromol) of the ADH/CYP2E1 inhibitors pyrazole or 4-methylpyrazole. The observation that pyrazole significantly reduced (p < 0.05) the total penetration of cinnamic metabolites into receptor fluid, following either cinnamaldehyde or cinnamic alcohol treatment, but did not significantly affect parent chemical penetration, suggests that we are measuring cutaneous metabolic products of ADH activity. The skin absorption and metabolism of cinnamaldehyde and cinnamic alcohol will play an important role in the manifestation of ACD following topical exposure to these compounds.