The effect of 5-thioglucose on the energy metabolism of Schistosoma mansoni in vitro

Using our understanding of interactions between helminth metabolism and host immunity to target worm survival

Helminths can adapt to environmental conditions in the host, utilising anaerobic processes like fermentation and malate dismutation to produce energy from carbohydrate. Although targeting carbohydrate metabolism is an established therapeutic strategy to combat helminth infection, questions remain over the metabolic pathways they employ as adults to survive and evade host immunity. Helminths also use amino acid, polyunsaturated fatty acid (PUFA), and cholesterol metabolism, a possible strategy favouring the production of immunomodulatory compounds that may influence survival in the host. Here, we discuss the significance of these differing metabolic pathways and whether targeting of helminth metabolic pathways may allow for the development of novel anthelmintics.

Unlocking the Potential of HK2 in Cancer Metabolism and Therapeutics

Glycolysis is a tightly regulated process in which several enzymes, such as Hexokinases (HKs), play crucial roles. Cancer cells are characterized by specific expression levels of several isoenzymes in different metabolic pathways and these features offer possibilities for therapeutic interventions. Overexpression of HKs (mostly of the HK2 isoform) have been consistently reported in numerous types of cancer. Moreover, deletion of HK2 has been shown to decrease cancer cell proliferation without explicit side effects in animal models, which suggests that targeting HK2 is a viable strategy for cancer therapy. HK2 inhibition causes a substantial decrease of glycolysis that affects multiple pathways of central metabolism and also destabilizes the mitochondrial outer membrane, ultimately enhancing cell death. Although glycolysis inhibition has met limited success, partly due to low selectivity for specific isoforms and excessive side effects of the reported HK inhibitors, there is ample ground for progress. The current review is focused on HK2 inhibition, envisaging the development of potent and selective anticancer agents. The information on function, expression, and activity of HKs is presented, along with their structures, known inhibitors, and reported effects of HK2 ablation/inhibition. The structural features of the different isozymes are discussed, aiming to stimulate a more rational approach to the design of selective HK2 inhibitors with appropriate drug-like properties. Particular attention is dedicated to a structural and sequence comparison of the structurally similar HK1 and HK2 isoforms, aiming to unveil differences that could be explored therapeutically. Finally, several additional catalytic- and non-catalytic roles on different pathways and diseases, recently attributed to HK2, are reviewed and their implications briefly discussed.

Sativa seeds against Schistosoma mansoni different stages

The schistosomicidal properties of Nigella sativa seeds were tested in vitro against Schistosoma mansoni miracidia, cercariae, and adult worms. Results indicate its strong biocidal effects against all stages of the parasite and also showed an inhibitory effect on egg-laying of adult female worms. In the present work we also studied the effects of crushed seeds on some antioxidant enzymes; which have a role in protection of adult worms against host oxidant killing; as well as some enzymes of glucose metabolism; which have a crucial role in the survival of adult worms inside their hosts. The data revealed that the used drug induce an oxidative stress against adult worms which indicated by a decrease in the activities of both antioxidant enzymes, superoxide dismutase, glutathione peroxidase, and glutathione reductase and enzymes of glucose metabolism, hexokinase and glucose-6-phosphate dehydrogenase. Disturbing of such enzymes of adult worms using N. sativa seeds could in turn render the parasite vulnerable to damage by the host and may play a role in the antischistosomal potency of the used drug.

Glucose Transport and Metabolism in Mammalian-stage Schistosomes

Adult schistosomes transport nutrients from the host bloodstream across their outer body covering or tegument. The tegument is a cytologically unusual structure; it is a syncytium bounded externally by two lipid bilayer membranes. In this review, Patrick Skelly, Louis Tielens and Chuck Shoemaker reconsider our understanding of how glucose enters schistosomes across this unusual outer covering in the light of recent papers characterizing glucose transport proteins and glucose metabolism pathways in these parasites.

The reversible effect of glucose on the energy metabolism of Schistosoma mansoni cercariae and schistosomula

This study on isolated cercarial bodies demonstrates that the biological transformation from cercaria to schistosomulum and the biochemical transition from an aerobic to an anaerobic energy metabolism are separate processes, which are not necessarily linked. The metabolic transition depends on the external glucose concentration and is fully reversible. In the presence of only a tracer amount of [6-14C]glucose, carbon dioxide was the major end product, but at higher glucose concentrations mainly lactate was formed. This effect could be demonstrated in cercarial bodies in water as well as in fully transformed schistosomula. In non-transformed cercariae a change towards a more anaerobic energy metabolism could be induced by an increase in the external glucose concentration, which demonstrated that the biochemical transition can occur in the absence of the biological transformation. Furthermore, the biological transformation can occur without a concomitant biochemical transition: in the presence of 5 mM glucose, lactate production by cercarial bodies during transformation was increased 50-fold, whereas in the presence of only a tracer amount of glucose the metabolic profile remained that of cercariae. Also, in fully transformed schistosomula, this transition to a more anaerobic energy metabolism was induced by increased glucose concentrations, but at low glucose concentrations carbon dioxide was the major end product, as in cercariae. The effect of external glucose on the metabolism was fully reversible. After a high glucose concentration had induced a more anaerobic metabolism in cercariae in water, the metabolism returned to an aerobic one upon removal of the glucose. Likewise, the metabolism in schistosomula switched back and forth between anaerobic and aerobic patterns, following successive changes in the glucose concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

The energy metabolism of Schistosoma mansoni during its development in the hamster

A detailed study was made of the changes in the carbohydrate metabolism of Schistosoma mansoni occurring during both the penetration of the skin of a hamster and the subsequent development of the schistosome in the lung, liver, and mesenteric veins of the host. During infection, within a few hours a transition occurs from a fully aerobic to a largely anaerobic energy metabolism. By 5 h postinfection, about 6% of carbohydrate breakdown occurs in the aerobic reactions of the Krebs cycle, whereas the rest occurs in the anaerobic formation of lactate. The contribution of aerobic processes to carbohydrate breakdown remains at this level of 6% until 3 weeks postinfection and then gradually declines to the adult level of 2.5%. Measurement of the protein content of developing schistosomes shows that an exponential growth occurs over a 15-day period after the arrival of the schistosomes in the liver (days 11-25 postinfection). During this period the protein content of the parasites increases about 100-fold, but despite this change in size, no major changes occur in the end-product pattern of carbohydrate breakdown. We conclude that during this period the rate of oxygen diffusion into the tissues is not a limiting factor for aerobic metabolism. A limited diffusion of oxygen may play a role in the decreasing contribution of aerobic processes during the later stages of maturation of the schistosomes.

Glycogen metabolism in Schistosoma mansoni worms after their isolation from the host

Adult Schistosoma mansoni worms rapidly degrade their endogenous glycogen stores immediately after isolation from the host. In NCTC 109 or in a diphasic culture medium the glycogen levels slowly recovered again after the initial decrease. The rapid degradation of glycogen could be prevented, even in a simple salt medium, if 100 mM glucose and 1% bovine serum albumin were present. Incubations with 14C-labelled glucose under different conditions revealed that the degradation of glycogen was induced by the limited catabolism of external glucose. Conditions are described which induce glycogen degradation or resynthesis by S. mansoni. The physiological function of the glycogen stores is probably to provide substrate during periods of insufficient supply of external glucose. It is speculated that such periods occur when the worm pair moves into the small mesenteric veins of the host. This hypothesis explains the remarkable wandering behaviour of the parasite in the mesenteric veins, since the schistosomes would have to return to larger vessels when their endogenous glycogen stores are exhausted.