The effects of humic acid-arsenate complexes on human red blood cells

Humic acid (HA) has been proposed as factor in the cause of Blackfoot disease (BFD) among individuals who live along the southwest coast of Taiwan. In this study, the interaction of the synthetic humic acid, made from catechol, with sodium arsenate (As(V)) was investigated and assessed with respect to damage to human red blood cells. HA is characterized as phenolic and phenolic carboxylic polymer structures containing both -COOH and -OH as their main functional groups. HA and As(V) alone are able to hemolyze 60-100 and 5-20% human red blood cells at concentrations of 50-300 microg/ml and 5-100 mM, respectively, after 6 h. HA is shown to be relatively ineffective in causing ATP depletion of red blood cells. For organometallic complexes composed of HA-As(V) the inhibition effect of EDTA was completely abolished and the use of the triple complex HA-As(V)-EDTA resulted in an enhancement of hemolysis. HA caused lipid peroxidation in a concentration- and time-dependent manner. However, HA-As(V) and As(V) decreased lipid peroxidation. These results indicated that HA initiates oxidative stress on red blood cells and this results in their dysfunction. HA-chelated high-concentration metal complexes inhibited the structures containing the main functional groups involved in decreasing hemolysis, and, thus, HA may be a significant factor in the etiology of BFD.