Objective: Pinellia Tuber, the dried tuber of Pinellia ternata, is widely used in Japanese Kampo medicines and traditional Chinese medicines. The unprocessed Pinellia Tuber is known to cause very strong acrid irritation at oral and laryngopharynx mucosa. Recent studies have shown that the sharp needle-like crystals called raphides, that are composed of calcium oxalate and proteins, are the main causative substances of the irritation. Ginger, the rhizome of Zingiber officinale, has been used in the processing to reduce the acridity of Pinellia Tuber since before the sixth century, however, the mechanisms of reducing acridity have not been scientifically proved yet.Methods: We developed the raphides denaturation assay (RDA) to quantify the degree of denaturation in the raphides to cause irritation. By their lipophilic characters, the raphides could be extracted in petroleum ether (PE) layer from powdered Pinellia Tuber suspended in water, and the contents of the raphides in PE layer were measured by the absorbance. By this assay, we conducted the activity-guided fractionation from the boiling water extract of ginger to find the ingredients to denature the raphides. We also conducted the gustatory tests to detect the change of the irritation of the denatured raphides.Results: The treatment of powdered Pinellia Tuber suspension with ginger extract reduced the distribution of raphides in PE layer in RDA in a concentration-dependent manner. The activity-guided fractionation using RDA revealed that oxalic acid was the main active ingredient in ginger extract to denature the raphides of Pinellia Tuber. Oxalic acid reduced the lipophilicity of the raphides in the thermo-, time-, and concentration-dependent manners, and its activity was affected by pH. The treatment of powdered Pinellia Tuber suspension with oxalic acid significantly reduced its acrid irritation in gustatory test in human.Conclusions: We found that oxalic acid is the main active ingredient in ginger to reduce the acrid irritation of Pinellia Tuber.
Objective: Pinellia tuber, the dried tuber of Pinellia ternata, causes severe acrid irritation in the mouth and throat when swallowed in its raw form. Based on the theory of traditional Chinese medicine, this acridity is reduced by heating or processing using ginger, licorice, alum, or lime. Although these detoxification methods have been known since ancient times, only little is known about the mechanisms by which they detoxify Pinellia tubers. In the present study, we aimed to reveal the effectiveness of α-starch, and glycyrrhizin in licorice for the detoxification of Pinellia tubers. Methods: Previously, we found that intact raphides of raw Pinellia tuber have a lipophilic character, and denaturation of the raphides reduced their lipophilicity and acridity. Accordingly, we developed a raphide denaturation assay (RDA) to quantify the degree of denaturation of raphides by measuring the absorbance of the petroleum ether (PE) layer comprising the raphides. The effect of α-starch or the decoction of licorice (the root and stolon of Glycyrrhiza uralensis) on raphide denaturation was then determined using this assay. Results: The treatment of raphides with α-starch markedly enhanced heat denaturation of the raphides. Licorice decoction, glycyrrhizin, and glycyrrhetinic acid significantly denatured raphides in a calcium-dependent manner at high pH. Glycyrrhizin and glycyrrhetinic acid are also attached to the denatured raphides. Conclusions: α-starch in Pinellia tubers contributes to detoxification by heating. In the traditional processing method for Pinellia tubers using licorice and lime, glycyrrhizin in licorice and calcium ions play important roles in denaturing raphides. Graphical abstract: http://links.lww.com/AHM/A42.
Pinellia tuber, the dried tuber of Pinellia ternata, causes a very strong acridity sensation in the oral and laryngopharynx mucosa when taken orally in its unprocessed form. In traditional Chinese medicine (TCM), this sensation has been called "toxicity", and Pinellia tuber must be processed using ginger extract, licorice, or alum. In Japanese traditional Kampo medicine, since “toxicity” can be eliminated by decocting, it should not be processed. However, little is known about the mechanism underlying the "detoxification" of Pinellia tubers. In this study, we produced murine antiserum using recombinant P. ternata lectin (PTL), developed an immuno-fluorescence staining method for PTL in the needle-shaped crystals (raphides) that were prepared by petroleum ether extraction (PEX) from Pinellia tuber, and elucidated the mechanism of the processing of Pinellia tuber using heat or ginger extract. After heating the raphides in water, the amount of PTL contained in the raphides was significantly reduced by the immunostaining, although the shape of the raphides was not changed. Incubating raphides with dried ginger extract also significantly reduced the amount of PTL in the raphides in a concentration-dependent manner. By the activity-guided fractionation of ginger extract, the active ingredients in the ginger extract were oxalic acid, tartaric acid, malic acid, and citric acid. Among these four organic acids, oxalic acid mainly contributed to the effect of dried ginger extract by its content in ginger extract and its activity. These results exhibit scientific evidences for the traditional theories of processing to "detoxify" Pinellia tuber in TCM and Kampo medicine. Graphical abstract
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