The Use of Tannic Acid in the Local Treatment of Burn Wounds: Intriguing Old and New Perspectives

Wounds. 2001;13(4) 

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Tannins Used as Medicinal Agents: Structural Characteristics and Origin

Tannins comprise a large group of natural products widely distributed in the plant kingdom. They have a great structural diversity, but in general, two classes are distinguished, the hydrolyzable type and the condensed type.[6] Hydrolyzable tannins are esters of sugars, mainly glucose, and phenol carboxylic acids, such as gallic acid, hexahydroxydiphenic acid, or its stable dilactone ellagic acid. As their name infers, hydrolyzable tannins are readily degraded under hydrolytic conditions into these fundamental components. Hydrolyzable tannins are present in many different plant species but are found in particularly high concentrations in nutgalls growing on Rhus semialata (Chinese and Korean gallotannins) and Quercus infectoria (Aleppo or Turkish gallotannins), the seedpods of Caesalpinia spinosa (Tara tannins), and the fruits of Terminalia chebula.[7] The condensed tannins are much more resistant to decomposition and merely yield polymers or amorphous precipitates under the influence of acids. The basic monomer of condensed tannins is (epi)catechin, which is extended by the successive addition of similar units to form oligomers and polymers. Traditionally, important commercial sources of condensed tannins are the heartwood of Schinopsis lorentzii and S. balansae (Quebracho tannins), the bark and/or heartwood of Acacia catechu (Catechu tannins) and A. mollisima (Wattle or Mimosa tannins), and the bark of Rhizophora and Eucalyptus species.[8,9]

Although both types of tannin have been used to treat diseases in traditional medicine, the hydrolyzable tannins are generally considered as officinal in Europe and North America. They have been included in many pharmacopoeias, in the older editions in particular, and are specifically referred to as "acidum tannicum" or tannic acid.[10,11,12,13] Few accounts with respect to the use of condensed tannins originate from China, where plant extracts containing these tannins as their major constituents are also applied as medicinal agents for the treatment of burns.[14,15,16]


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