In the present study, the potential activity of two 5-nitroindazole derivatives previously proposed as suitable antichagasic prototypes was further evaluated on diverse Trypanosoma cruzi strains belonging to two discrete typing units (DTUs) frequently associated with human infection (i.e. DTUs TcII and TcVI). The trypanocidal profile that both 2-benzyl-1-propyl (22) and 2-benzyl-1-butyl (24) derivatives achieved on Tulahuen amastigotes (IC50 = 3·56 ± 0·99 and 6·31 ± 1·04 µ m, respectively) correlates with that of formerly obtained on CL Brener, corroborating an outstanding activity on DTU TcVI parasites. Moreover, a sequential screening on extracellular and intracellular stages of T. cruzi Y (DTU TcII) demonstrated also the effectiveness of 22 and 24 over this strain on a similar range of activity (IC50 epimastigotes = 3·55 ± 0·47 and 7·92 ± 1·63 µ m, IC50 amastigotes = 2·80 ± 0·46 and 9·02 ± 5·26 µ m, respectively). These results, supported by a lack of toxicity registered over either L929 fibroblasts or primary cultures of cardiomyocytes, confirm that 5-nitroindazolinones 22 and 24 display great selectivity on both drug-sensitive (CL and Tulahuen) and drug-moderately resistant (Y) T. cruzi strains, and therefore, represent an important outcome in the research of Chagas disease chemotherapy.

Trypanosoma cruzi is the aetiological agent of Chagas disease. Our group has focused on the study of ribosomal RNA and nucleolar structure in this organism. In this work, we address the cellular location of fibrillarin in epimastigotes. As a conserved and unreported feature in trypanosomatids, fibrillarin in T. cruzi is encoded by two genes that differ by approximately 35% in their deduced amino acid sequences (TcFib 1 and TcFib 2). Chimaeric fluorescent versions of TcFib1 and TcFib2 were individually expressed in T. cruzi cells. Both transfected cultures showed cells with a nucleolar fluorescent signal. We have not found any evident distinction between the structure or expression of Tcfibrillarins to propose a functional difference in cells. With the aid of an anti-TcFib 2 antibody, it was found that the endogenous protein relocates outside of the nucleolus in stationary epimastigotes. This was also the case in metacyclic trypomastigotes observed from aged cultures. The significance of this observation is not known, but a deficiency of fibrillarin nucleolar retention correlates with the observed reduction in the abundance of the pre-ribosomal RNAs species at stationary phase, and suggests that the nucleolar location of this protein depends on physiological processes.

Host manipulation is a common strategy of parasites employed to increase their fitness by changing the phenotype of their hosts. Whether host manipulation might be affected by environmental factors such as resource availability, has received little attention. We experimentally infected laboratory-bred copepods with the cestode Schistocephalus solidus, submitted infected and uninfected copepods to either a high or a low food treatment, and measured their behaviour. Infection reduced host activity and speed in both feeding treatments. However, the difference between the infected and uninfected copepods was smaller under low food conditions, because uninfected, but not infected, copepods moved slower under these conditions. We suggest that these differences are mediated by the physical condition of copepods rather than changes in how strongly the parasite manipulated host behaviour. Additionally, we measured three fitness-relevant traits (growth, development and infection rate in the next host) of the parasite to identify potential trade-offs with host manipulation. The largest parasites in copepods appeared the least manipulative, i.e. their hosts showed the smallest behavioural alterations, but this may again reflect variation in copepod condition, rather than life history trade-offs between parasite growth and host manipulation. Our results point to the possibility that parasite transmission depends on environmental conditions.