Distribution of lignin–carbohydrate complex in plant kingdom and its functionality as alternative medicine

Lignin–carbohydrate complexes (LCCs) are major cell wall components formed by the dehydrogenation of three monolignols, p-coumaryl, coniferyl and sinapyl alcohols. Diverse pharmacological activities of LCCs distributed into various plants were summarized. LCCs showed one order higher anti-HIV activity than tannins and flavonoids. Mechanism of anti-HIV activity induction includes the inhibition of HIV adsorption to and penetration into the cells, and inhibition of reverse transcriptase and protease. Limited digestion experiments demonstrated that a phenylpropenoid polymer, but not a sugar moiety, is important for anti-HIV activity. Dehydrogenation polymers of phenylpropenoids without carbohydrate showed higher anti-HIV activity, whereas phenylpropenoid monomers were inactive, suggesting the importance of highly polymerized structure. LCCs inhibited the plaque formation and RNA polymerase activity of influenza virus, and reduced the lethality of virus infection in mice. LCCs inhibited the plaque formation of HSV-1, and oral intake of LCC-vitamin C tablet reduced the symptoms in HSV-1-infected patients. LCCs stimulated the iodination of myeloperoxidase-positive human monocytes, neutrophiles and promyelocytic leukemia that may be involved in the bacterial killing mechanism. LCCs stimulated splenocyte proliferation, and showed both pro- and anti-inflammatory activity in activated macrophage. Preliminary DNA array analysis demonstrated the activation of the signal pathway of chemokine expression via TLR2. The molecular weight, solubility, sterilization method and association with other components during extraction step may produce diverse biological activity of LCCs. Broad and potent anti-viral activity and synergism with vitamin C suggest functionality of LCC as alternative medicine.