Phosphoenolpyruvate carboxykinase (PEPCK) is involved in glycolysis in the cestode parasite, Raillietina echinobothrida; whereas, it executes a gluconeogenic role in its host, Gallus domesticus. Because of its differing primary function in the cestode parasite and its host, this enzyme is regarded as a plausible anthelmintic target. Hence, the biological significance of PEPCK in the parasite was analysed using siRNA against PEPCK from R. echinobothrida (RePEPCK). In order to find out the functional differences between RePEPCK and GdPEPCK (PEPCK from its host, G. domesticus), PEPCK genes from both sources were cloned, over-expressed, characterized, and some properties of the purified enzymes were compared. RePEPCK and GdPEPCK showed a standard Michaelis-Menten kinetics with Kmapp of 46.9 and 22.9 µm, respectively, for phosphoenolpyruvate and Kmapp of 15.4 µm for oxaloacetate in GdPEPCK decarboxylation reaction. Here, we report antagonist behaviours of recombinant PEPCKs derived from the parasite and its host. In search of possible modulators for PEPCK, few phytoestrogens were examined on the purified enzymes and their inhibitory constants were determined and discussed. This study stresses the potential of these findings to validate PEPCK as the anthelmintic drug target for parasitism management.

α-viniferin, an active component of the plant Carex baccans L., is known for its anticancer, antidiabetic, and anti-inflammatory properties. In Northeast India, different tribes traditionally consume C. baccans to control intestinal helminth infections. Therefore, the present study was carried out to assess the extent of tegumental alteration caused by α-viniferin in Raillietina echinobothrida, a widely prevalent poultry helminth in northeast India. Helminths were exposed in vitro to various doses of α-viniferin (50, 100, and 200 µM/mL of physiological buffered saline) and their motility and mortality were recorded. Stereoscan observations on the parasite exposed to the active compound showed extensive distortion and destruction of the surface fine topography of the tegument compared with controls. The compound also caused extensive damage to the tegument by disintegration of microtriches, disorganization of muscle bundles, and loss of cellular organelles combined with distortion and disruption of the plasma membrane, nuclear membrane, nucleolus, mitochondrial membrane, and cristae. Histochemical and biochemical studies carried out parasites exposed to α-viniferin revealed a decline in the activity of vital tegumental enzymes like acid phosphatase, alkaline phosphatase, and adenosine triphosphatase. Extensive structural and functional alterations observed in the treated parasites are indicative of efficient cestocidal activity of the compound.

Phosphoenolpyruvate carboxykinase (PEPCK, EC 4.1.1.32) is an essential regulatory enzyme of glycolysis in helminths in contrast to its role in gluconeogenesis in their host. Previously we have reported that phytochemicals from Flemingia vestita (Family: Fabaceae), genistein in particular, have vermifugal action and are known to affect carbohydrate metabolism in the cestode, Raillietina echinobothrida. In order to determine the functional differences of PEPCK from the parasite and its avian host (Gallus domesticus), we purified the parasite enzyme apparently to homogeneity, and characterized it. The native PEPCK is a monomer with a subunit molecular weight of 65 kDa. The purified enzyme displayed standard Michaelis-Menten kinetics with Km value of 42·52 μM for its substrate PEP. The Ki for the competitive inhibitors GTP, GMP, ITP and IMP for the carboxylation reaction were determined and discussed. In order to identify putative modulators from plant sources, phytochemicals from F. vestita and Stephania glabra were tested on the purified PEPCK, which resulted in alteration of its activity. From our results, we hypothesize that PEPCK may be a potential target site for anthelmintic action.

Ascorbic acid levels were found to be closely related to different stages of growth and maturity of Avitellina centripunctata, Moniezia expansa, and Stilesia globipunctata from goats and sheep and of Raillietina echinobothrida from fowl. The ascorbic acid level in avian parasites was higher than that in mammalian. The level was highest in immature proglottides and lowest in gravid proglottides.