A scanning electron microscope study on the route of entry of clorsulon into the liver fluke, Fasciola hepatica

Abstract

Three experiments were carried out in vitro to determine the roles of the tegument and gut of Fasciola hepatica in the uptake of the flukicidal drug, clorsulon. Changes to the two surfaces were assessed by scanning electron microscopy. In the first experiment, the flukes were ligatured to prevent the oral ingestion of drug and treated for 24 h in clorsulon (10 microg/ml). The gastrodermal surface remained normal and few changes to the tegumental surface were observed. In the second experiment, flukes were fed for 24 h on red blood cells isolated from rats dosed with clorsulon at 12.5 mg/kg body weight; this experiment was designed to prevent the exposure of the tegumental surface to the drug. The gastrodermal surface was severely disrupted and the gut lamellae were disorganised and necrotic. Swelling of the tegument and blebbing on the tegumental surface were evident, but the changes were not severe. More severe swelling of the tegument was observed in the third experiment, in which flukes were incubated for 24 h in clorsulon (10 microg/ml), with both absorptive surfaces being available for drug uptake. The gastrodermal surface was badly disrupted and the gut lamellae were disorganised and necrotic. Taking the results of the three experiments together, the gastrodermal surface was more affected than the tegument and the greatest disruption to the two surfaces was seen when both routes of entry were available to the fluke. The data support a previous study which indicated that entry of clorsulon into the fluke in vivo is principally by the oral ingestion of drug bound to the red blood cells.

Ultrastructural observations on oral ingestion and trans-tegumental uptake of clorsulon by the liver fluke, Fasciola hepatica

“…The relatively more rapid effect in vitro may be due to the more direct exposure of the tegument to clorsulon under in vitro conditions. The present results can also be compared to those obtained for the midbody region of the fluke in the parallel set of SEM experiments (Meaney et al 2005). The severe swelling of the basal infolds in the non-ligatured flukes may have given rise to the swelling of the tegument observed by SEM and the relatively flat, smooth apical surface of the tegumental syncytium seen by TEM.…”

“…Comparing the present results with the results of the parallel SEM study, the disruption to the lamellae appeared to be more striking from SEM observations for the non-ligatured clorsulon-treated and the clorsulon-bound RBC-fed flukes. For these two groups, the lamellae were badly disrupted, disorganised and appeared necrotic (Meaney et al 2005). However, from the TEM study, such a gross disruption of the gastrodermal lamellae was not so evident, although some disruption of the lamellae, particularly along their bases, was evident in clorsulon-bound RBC-fed flukes.…”

“…Consequently, disruption to the gastrodermis is likely to be more severe than to the outer tegumental covering of the fluke. However, previous scanning and transmission electron microscopy (SEM and TEM) studies involving clorsulon have shown that the tegument is affected (Meaney et al 2003(Meaney et al , 2004(Meaney et al , 2005. To assess the relative impact of clorsulon treatment on the tegument and gastrodermis, experiments have been designed to eliminate one or other of the two routes of entry.…”

“…In a separate experiment, flukes were exposed to clorsulon with both routes being available for drug uptake. The investigation has been carried out in two parts: the first part involved SEM and the results of this study have been published (Meaney et al 2005). This paper presents the results of a parallel TEM study, focussing on internal changes within the tegument and gastrodermis as a consequence of the three treatments.…”

Metabolic enzymes of helminth parasites: potential as drug targets

“…It also has weak activity against carbonic anhydrase (EC 2.4.1.1) in the host and, most likely, the parasite [52,53]. The drug causes widespread damage to the ultrastructure of F. hepatica [54][55][56][57].…”