Differential kinetics at PK/PEPCK branch point in the cestode, Raillietina echinobothrida.

Pyruvate kinase (PK; EC 2.7.1.40) and phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.32) are essential regulatory enzymes of glucose oxidation in helminths, the PK/PEPCK branch point being the first divergent step between carbohydrate catabolism of the parasites and their hosts. Recently, PEPCK from the cestode parasite, Raillietina echinobothrida, has been purified and characterized. In order to find out the differential kinetics, if any, at PK/PEPCK branch point in the parasite, in this study, we purified and characterized the parasite PK and compared it with the parasite PEPCK. The purified PK displayed standard Michaelis-Menten kinetics with Kmapp of 77.8 µM for its substrate PEP, whereas the Kmapp was 46.9 µM for PEPCK. PEP exhibited differential kinetics at PK/PEPCK branch point of the parasite and behaved as a homotropic effector for PEPCK, but not for PK. The inhibitory constant (Ki) for genistein and daidzein (phytochemicals from Flemingia vestita) was determined and discussed. From these results, we hypothesize that PK/PEPCK branch point is a probable site for anthelmintic action.

GABA in the nervous system of the cestodes Diphyllobothrium dendriticum (Diphyllobothriidea) and Caryophyllaeus laticeps (Caryophyllidea), with comparative analysis of muscle innervation.

The nervous system (NS) of the cestodes Diphyllobothrium dendriticum (Diphyllobothriidea) and Caryophyllaeus laticeps (Caryophyllidea) was investigated using immunocytochemistry. The GABA neurotransmitter was identified in the NS of both species; GABAergic neurons were detected in the main nerve cords (MC). GABA-like immunoreactive neurons were predominantly unipolar and exhibited more intensive immunoreactivity in the neurite than in the perikaryon. In C. laticeps , GABA-like immunoreactive somas are located in both the MCs and peripheral NS near the longitudinal muscles. The innervation of the body musculature was studied using a combination of antibodies against GABA, serotonin (5-HT), and FMRFamide and with complementary staining of F-actin. In both species, the location of GABAergic neurites is associated with all muscle layers including the subtegumental, longitudinal, transverse, and dorsoventral muscles. The cytomorphology of 5-HTergic motoneurons in the MCs of both species is described and differences in muscle innervation between D. dendriticum and C. laticeps are demonstrated. No evidence for co-localization of GABA with 5-HT or FMRFamide neurotransmitters at any particular neuron was found. Neuropiles in MCs and peripheral NS had separate sets of immunoreactive neurites. A functional role for GABA in muscle innervation is discussed.

Effect of isoflavone from Flemingia vestita (Fabaceae) on the Ca2+ homeostasis in Raillietina echinobothrida, the cestode of domestic fowl.

The alcoholic crude root-peel extract of Flemingia vestita and its major isoflavone, genistein, have been shown to have a vermifugal/vermicidal effect by causing a flaccid paralysis accompanied by alterations in the structural architecture of the tegumental interface and metabolic activity in Raillietina echinobothrida, the cestode of domestic fowl. In the present study, the crude root-peel extract and pure genistein were tested in vitro with respect to Ca2+ homeostasis and the occurrence of some metal ions was detected in the parasite. Live cestodes were incubated in pre-defined concentrations of the crude root-peel extract, genistein and praziquantel (as reference drug), till the paralysis time with simultaneous maintenance of respective controls. In the parasite tissue, a significant amount of Ca2+ (approximately 400 microg/g dry tissue wt) was found to be present besides magnesium, iron, zinc, lead and chromium, whilst manganese, cadmium and nickel were below the level of detection. The Ca2+ concentration was decreased significantly by 39%-49%, in the parasite tissue exposed to the test materials in comparison to the respective controls. There was also an increase in Ca2+ efflux by 91%-160% into the culture medium under similar treatments. The changes in Ca2+ homeostasis may be related to the rapid muscular contraction and consequent paralysis in the parasite due to the anthelmintic stress caused by the phytochemicals of F. vestita.