Protective Effect of ELI-21C-76C Against Poison Ivy and Poison Oak Dermatitis in a Guinea Pig Model

Poison ivy (Toxicodendron radicans), poison oak (T. diversilobum), and poison sumac (T. vernix) are the primary causes of contact dermatitis in the United States, affecting 10–50 million Americans every year. The prevalence of sensitivity to poison ivy and poison oak in the general adult population ranges from 50% to 70% with peak frequency for sensitization occurring between the ages of 8 and 14. Outdoor activities as well as outdoor occupations which relate to firefighting, forestry and agriculture are at high risk, costing significant medical expenses and worker's disability. During our ongoing studies aimed at the discovery of an effective prophylactic treatment for toxicodendron dermatitis, we have developed a series of novel agents and tested the efficacy of these agents in an in vivo animal model. Here, we present the protective effect of our pro-drug ELI-21C-76C in our guinea pig experimental model.

Guinea pigs were sensitized with poison ivy extract (1.0mg/100µL acetone) in the neck region. Two weeks later they were challenged with 4.5 and 6.0µg of poison ivy extract on the abdominal skin. The erythema and edema scores were recorded. Non-reactive guinea pigs were eliminated from the study. The remaining guinea pigs were divided into four groups of 8 animals. Two weeks later three groups were inoculated intramuscular (IM) with different doses of ELI-21C-76C in the thigh muscle. A fourth group was given vehicle (5% Ethanol) IM. Two weeks post inoculation these guinea pigs were challenged with poison ivy and poison oak extracts on the abdominal skin. Erythema and edema scores were recorded.

The results showed that ELI-21C-76C at the doses of 2.0mg/kg and 1.0mg/kg was significantly effective in decreasing the degree of skin reaction to poison ivy challenge. At the dose of 0.1mg/kg there was reduction in the severity of skin reaction but it was not significantly different from those in the control animals. These results also confirmed that ELI-21C-76C at the dose of 2.0mg/kg was significantly effective against poison oak challenge. The dose of 1.0mg/kg and 0.1mg/kg showed reduction in the skin reaction to challenge; however, it was not significantly different than those of the control animals. In conclusion, the dose of 2.0mg/kg was effective in protecting severe skin reaction upon exposure to either poison ivy or poison oak.