Humin substances have been used as folk remedies for the last 3000 years. Recent studies have shown that humates possess anti-inflammatory properties, but the mechanism of how it affects inflammation is still unclear. In this study the anti-inflammatory properties of potassium humate, a water soluble humic acid salt, was investigated on different inflammatory pathways in vitro and in vivo. The effect of potassium humate on human mononuclear lymphocyte proliferation showed that potassium humate stimulated lymphocyte proliferation of resting-, PHA- and PWM-stimulated lymphocytes in vitro from concentrations of 20 to 80 µg/ml, in a dose dependant manner, where a maximum proliferation was observed at 80 µg/ml whereas lymphocyte proliferation decreased at 100 µg/ml. On the contrary potassium humate, at 40 µg/ml, significantly inhibited the supernatant concentrations of the following cytokines; TNF-α, IL-1ß, IL-6 and IL-10 by PHA stimulated lymphocytes. The effect of potassium humate on the alternative as well as the classical complement pathway was investigated in vitro using the haemolytic complement assay. Results indicated that potassium humate inhibits both the alternative and classical complement pathways without affecting the red blood cell membrane stability. Different inflammatory mechanisms were investigated in vivo, using the carrageenan-induced paw oedema model and the delayed type hypersensitivity reaction model. The carrageenan-induced paw oedema model was used to determine the effect of potassium humate on acute inflammation in the hind paw. Carrageenan was injected into the right hind footpad of a rat which caused an increase in paw volume due to oedema, which was measured with a plethysmometer. Potassium humate significantly inhibited the oedema at a dose of 60 mg/kg bodyweight and compared favourably with indomethacin at 10 mg/kg bodyweight. The effect of potassium humate on the delayed type hypersensitivity reaction model was also investigated whereby rats were sensitised with sheep erythrocytes. Potassium humate was administered daily by oral gavage at a dose of 60 mg/kg bodyweight. After 7 days, rats were challenged by injecting sheep erythrocytes into the right hind footpad. The degree of inflammation was determined by measuring the increase of paw volume with a plethysmometer. It was found that potassium humate did not have an anti-inflammatory effect on the delayed type hypersensitivity reaction as opposed to the inhibition caused by dexamethasone at a dose of 30 mg/kg bodyweight. This study showed that potassium humate selectively inhibited the inflammatory pathway of the carrageenan-induced paw oedema as opposed to the delayed type hypersensitivity. The mechanism of the anti-inflammatory property of potassium humate might possibly be due to the inhibition of the complement cascade. This study clearly shows that potassium humate possesses anti-inflammatory properties that can be utilised in the future as a potential treatment for inflammatory disorders associated with the activation of complement. However further investigation in the mechanism by which potassium humate inhibits complement activation needs to be done.
Dissertation (MSc (Pharmacology))--University of Pretoria, 2008.