LEAF EXTRACTS OF ACER SPP. CAUSE DIFFERENT PATTERNS OF TOXICITY IN BIOASSAYS OF EQUINE ERYTHROCYTES

While red maple (Acer rubrum) is the most common maple reported to cause maple toxicosis (i.e., a debilitating condition that occurs in equines after the consumption of dried or wilted maple leaves), other maple species are also toxic. Previously reported is that extracts from A. saccharinum cause similar levels of damage to equine erythrocytes. While the toxic agent(s) is unknown, the development of hemolytic anemia and methemoglobinemia in equines suggests it is a strong oxidant. The objective of this research is to evaluate the toxicity of dried samples of 35 maple species. Leaves (n = 10 to 15) were collected, dried, and ground. The toxin(s) were extracted in buffer and incubated with erythrocytes. Toxicity, as measured by area under hemolytic curve (AUHC) and percentage methemoglobin (%M), was quantified based on the absorbencies of erythrocyte/ extract suspensions at 560, 576, and 630 nm. Species were ranked for AUHC and %M. Levels of toxicity for A. buergerianum (AUHC = 56, %M = 82) and A. freemanii (AUHC = 53, %M = 64) were higher than levels for A. rubrum for both AUHC and %M (35 and 59, respectively), while levels for A. campestre (AUHC = 21, %M = 0) and A. japonicum (AUHC = 29, %M = 47) were lower for both. Levels of toxicity for A. cappidociumand and A. pensylvanicum were higher than A. rubrum for AUHC (51 and 58, respectively) but lower for %M (2 and 7, respectively) while the level of toxicity for A. griseum x nikoense showed the opposite trend (low AUHC = 24, high %M = 66). These four different patterns support the possibility of more than one toxic compound responsible for causing maple toxicosis.