The toxic and lethal effects of the trehalase inhibitor trehazolin in locusts are caused by hypoglycaemia

Abstract

SUMMARY The main blood sugar of locusts is trehalose, which is hydrolysed to two glucose units by trehalase. Homogenates of locust flight muscles are rich in trehalase activity, which is bound to membranes. A minor fraction of trehalase is in an overt form while the remainder is latent, i.e. active only after impairing membrane integrity. Trehazolin, an antibiotic pseudosaccharide,inhibits locust flight muscle trehalase with apparent Ki-and EC50 values of 10–8 mol l–1and 10–7 mol l–1, respectively. Trehazolin is insecticidal: 50 μg injected into locusts completely and selectively blocked the overt form of muscle trehalase (with little effect on latent activity) and killed 50% of the insects within 24 h. Here, it is demonstrated for the first time that trehazolin causes dramatic hypoglycaemia. Injection of 10 μg trehazolin caused glucose levels to fall by over 90% in 24 h, from 2.8 mmol l–1 to 0.23 mmol l–1, while trehalose increased from 61 mmol l–1 to 111 mmol l–1. Feeding glucose to the locusts fully neutralized the effects of a potentially lethal dose of trehazolin. This indicates that hypertrehalosaemia is not acutely toxic, whereas lack of glucose causes organ failure (presumably of the nervous system), and that sufficient haemolymph glucose can only be generated from trehalose by trehalase. The results also suggest that overt flight muscle trehalase is located in the plasma membrane with the active site accessible to the haemolymph. Trehalase inhibitors are valuable tools for studying the molecular physiology of trehalase function and sugar metabolism in insects.

Long-term effects of the trehalase inhibitor trehazolin on trehalase activity in locust flight muscle

“…Injection of 20g of trehazolin markedly reduced motor activity and food consumption in experimental locusts (see also Wegener et al, 2003;Liebl et al, 2010). This is regarded as a consequence of the fact that the poisoned locusts were unable to utilize carbohydrates properly.…”

“…When injected into insects, these inhibitors affect motor activity, feeding, metabolism, growth, development, reproduction and flight (Kono et al, 1993;Kono et al, 1994a;Kono et al, 1994b;Ando et al, 1995a;Tanaka et al, 1998), thus indicating that trehalose metabolism is involved in many aspects of insect physiology. The inhibitors interfere specifically with the hydrolysis of trehalose (Ando et al, 1995b) but apparently do not block its production and release into the haemolymph by the fat body (Kono et al, 1995;Wegener et al, 2003;Liebl et al, 2010). The prominent inhibitor-induced increase in haemolymph trehalose was noticed early and has been reported repeatedly (Kono et al, 1993;Kono et al, 1999).…”

“…The potential activity of trehalase in the flight muscle of locusts is high and the reaction is strongly exergonic, so that the activity of trehalase in flight muscle must be strictly controlled in a reversible manner, lest all available trehalose be split. How trehalase activity is regulated in locust flight muscle is still unknown, as none of the established mechanisms for the control of enzyme activities seems to operate (Worm, 1981;Vaandrager et al, 1989;Becker et al, 1996;Wegener et al, 2003;Liebl et al, 2010).…”

Comparison of gut morphology and distribution of trehalase activity in the gut of wood-feeding and fungus-growing termites (Isoptera: Termitidae)

“…Trehalase activity in both termites decreased markedly 1 d after treatment. The percentage mortality was concentration dependent and the high percentage mortality recorded indicates that validamycin could be used as an insecticide for controlling both wood-feeding and fungusgrowing termites, as it prevents the hydrolysis of trehalose, leading to a lack of glucose (Wegener et al, 2003). Validamycin is absorbed through the gut membrane into the haemocoel and may be absorbed into other tissues (Tatun et al, 2014b).…”

New synthesis and biological evaluation of uniflorine A derivatives: towards specific insect trehalase inhibitors

“…Proteins were measured according to Bradford using bovine serum albumin as a standard. 22 Trehalase activity was measured through a coupled assay with glucose-6-phosphate dehydrogenase and hexokinase, according to Wegener et al 23 To examine the potential of each compound as a trehalase inhibitor, screening assays of potential inhibitors were carried out at a fixed concentration of 1 mM, and dose-response curves were established to determine IC 50 values. Experiments were performed at fixed substrate concentration close to the K m value (0.5 mM for C. riparius and S. littoralis trehalases and 2.5 mM for porcine trehalase) in the presence of increasing inhibitor concentrations.…”