Antioxidant and pharmacological effects
Antioxidants are materials that prevent the oxidation reaction of oxygen-containing reactive free radicals.They are important in health/cosmetic applications to prevent the destruction of healthy cells in the human body, and in materials science applications to prevent the degradation of the materials used as (for example) composites. Lignin and lignosulfonates have been examined for their antioxidant abilities in both cases, due to the phenolate and carboxylate groups, which impart antioxidant effects.
The syringyl units of the lignosulfonates (methoxyl group ortho to the phenolic hydroxyl group) aid in enhancing antioxidant effects.This is due to the increased chelating properties of the phenolic hydroxyl group and the radical-scavenging capability.
One study showed that lignosulfonates completely inhibited hemolysis of human blood induced by 2,2′-azobis(2-aminidopropane) (AAPH; a radical initiator) at a concentration of approximately 200 μg mL−1 in blood.Another study reported the partial inhibition of 2,2-diphenyl-1-picrylhydrazyl (DPPH) with an increase in lignosulfonate-grafted copolymer.The phenolic content increased from 0 to 0.97 wt % due to the incorporation of lignosulfonates, which caused an increase in DPPH inhibition from 0 to 31 %.
Additionally, lignosulfonates are nonirritant to eyes and skin; thus, they have potential to be used in cosmetic products.The lignin incorporated in the polypropylene blends increased the antioxidant abilities of the composite from an oxidation induction period of 7.18 to 11.12 min; this indicates prevention of the oxidation reaction.
In addition to antioxidant capabilities, studies have shown that lignosulfonates have antiviral properties; these most likely stem from their polyanionic characteristics and molecular structures. Lignosulfonates have anticoagulant, antiulcerogenic, and antitumor activities when used in vivo on 180 sarcoma tumor cells.
Lignosulfonates activate macrophages, which results in growth in murine (rat) bone marrow cells at a minimum concentration of 10 μg mL−1 lignosulfonates in the culture medium of murine peritoneal resident macrophages, which is comparable to that of typical macrophage activators.Consequently, lignosulfonates may be used as a part of immunochemotherapy drugs for some diseases.
In particular, lignosulfonates dosed at 50 μg mL−1 resulted in the complete inhibition of cell death caused by HIV, HIV-specific antigen production, along with syncytia formation, possibly due to the prevention of the CD-4 receptor and HIV interaction. This means that lignosulfonates could be used to develop anti-HIV drugs to stimulate the immune system. Another study showed vaginal contraceptive potential for lignosulfonic acid; a derivative of lignosulfonates.
At a dosage of 1.5 mg mL−1, lignosulfonic acid blocked fertilization in macaque oocytes. This interesting property, along with its antiviral potential properties, may allow for lignosulfonic acid/lignosulfonate containing materials to act as both contraceptives and antimicrobials.