THE CARBODIIMIDE PRODUCT OF DIAFENTHIURON INHIBITS MITOCHONDRIA INVIVO

There is convincing evidence that the thiourea diafenthiuron is a proinsecticide which is converted to the carbodiimide CGA 140408. We have previously shown that CGA 140408 covalently binds to the proteolipid subunit of the F0 moiety of mitochondrial ATPase, thereby inhibiting ATPase activity, and to porin, a channel forming protein of the outer mitochondrial membrane. We now demonstrate by studying whole insect respiration and locomotive activity that CGA 140408 has a depressing effect like other mitochondrial inhibitors. In Calliphora, the reduction of respiration is due to decreased locomotive activity since biochemical studies on thoraces show that only 10-20% of total mitochondrial ATP synthesis capacity is blocked shortly before death. Furthermore, we find no inhibition of the energy metabolism of thoracic flight muscles as evidence by 31P NMR studies. In contrast to the flight muscles studied in Calliphora, mitochondrial inhibition is prominent in several tissues as shown in Locusta where mitochondrial ATPase is blocked up to 80% in vivo. Not all locust tissues are affected to the same extent. Blocking of ATPase activity correlates well with the extent of intoxication and paralysis. In the nervous system, the block of mitochondrial ATPase is further paralleled by a reduction of ATP concentration by more than 50%. We conclude that not all mitochondria of a tissue have to be blocked to achieve a lethal effect, and that it may be sufficient if only some mitochondria are inhibited. Our data suggest that inhibition of energy metabolism is the primary mode of action of CGA 140408 in vivo. The results explain the observed paralytic symptoms and the stop of feeding as the early sign of poisoning. © 1993 Academic Press.