Activities of ectonucleotidases and adenosine deaminase in platelets of dogs experimentally infected with Rangelia vitalii.

Rangeliosis is a disease which affects dogs in Brazil, caused by a piroplasm known as Rangelia vitalii. This disease causes a lot of clinico-pathological features, including the coagulation disorders associated with bleeding. The cause of these changes has not yet been determined. Considering the association of purinergic system and hemostasis this study aimed to evaluate the activity of enzymes that hydrolyze ATP, ADP and AMP; and deamination of adenosine in platelets from dogs experimentally infected with R. vitalii. For this study, 12 healthy young dogs (females) were used, separated in two groups. Group A (n=5) were uninfected controls, and group B were experimentally infected with R. vitalii (n=7). After being inoculated with R. vitalii-infected blood, animals were monitored by blood smear examinations, which showed intra-erythrocytic forms of the parasite after five days post-inoculation (PI). Blood samples were collected to quantitate and separate platelets (Day 0, 12 and 21 PI) and to measure the enzymatic activities (Day 12 and 21 PI). The activity of NTPDase, 5'-nucleotidase and adenosine deaminase (ADA) was measured in platelets. A reduction (P<0.01) in the number of platelets was observed in R. vitalii-infected blood at Days 12 and 21 PI. At Day 12 PI, a reduction (P<0.01) in the hydrolysis of ATP, ADP and AMP, and deamination of adenosine was observed in dogs infected with R. vitalii. At Day 21 PI the ADA activity remained decreased, unlike the activity of NTPDase which increased (P<0.05). Based on these results we can conclude that ATP, ADP and AMP hydrolysis and adenosine deamination were altered in platelets of R. vitalii-infected dogs. Considering the importance of the purinergic system in hemostasis, it is believed that those changes contribute to the coagulation disorders and bleeding observed in R. vitalii-infected dogs and discussed in this manuscript.

Babesia rodhaini: the protective effect of pyruvate kinase deficiency in mice.

Despite the evidence suggesting that mouse pyruvate kinase (PK) deficiency provides protection against malaria in rodents, there has been no investigation of a parallel protective effect against babesiosis caused by Babesia rodhaini. Here, we examined whether a PK-deficient co-isogenic mouse strain (CBA-Pk-1(slc)) was protected against B. rodhaini infection. We demonstrated that deficiency in pyruvate kinase correlated with a significant protective effect, with survival rates of 50%, 58% and 56% in groups inoculated with 10, 10(3) and 10(5) parasitized erythrocytes, respectively. In contrast, control CBA (CBA-Pk-1(+)) mice exhibited 100% lethality, regardless of the infectious dose. In addition, CBA-Pk-1(slc) mice showed decreased levels of parasitemia when compared to CBA-Pk-1(+) mice, in groups given 10, 10(3) or 10(5) parasitized erythrocytes. These results indicate that similar to PK deficiency in rodents, PK deficiency in mice affects the in vivo growth of B. rodhaini and protects the mice from lethal babesiosis.

Plasma levels of zinc, copper, copper/zinc ratio, and activity of carbonic anhydrase in equine piroplasmosis.

We have determined the plasma concentrations of copper, zinc, copper/zinc ratio, and carbonic anhydrase activity in horses infected with Babesia equi. The study was conducted in 14 horses with the disease and 10 healthy animals that served as controls. The infection was confirmed by the clinical manifestations of the disease and by Giemsa staining of thin blood smears showing the parasites inside red blood cells. The horses with piroplasmosis had lower plasma levels of zinc, elevated copper, and increased activity of carbonic anhydrase. Consequently, the copper/zinc ratio was also higher than in the healthy controls.

Serum carboxypeptidase B levels during acute and mild Babesia divergens infections of adult cattle.

Serum carboxypeptidase B levels were measured in adult cows suffering from both acute and mild babesiosis caused by Babesia divergens. In severe infections serum carboxypeptidase B levels started to fall three days after infection and were significantly lower than both preinfection levels and those of mildly affected cows for a period of 10 days starting at the time of maximum parasitaemia. Normal levels were regained on the 23rd day after infection.

The effect of diminazene aceturate on cholinesterase activity in dogs with canine babesiosis.

A clinical trial was designed to evaluate the effects of diminazene aceturate and its stabiliser antipyrine on serum pseudocholinesterase (PChE) and red blood cell acetylcholinesterase (RBC AChE) in dogs with babesiosis. The trial was conducted on naturally occurring, uncomplicated cases of babesiosis (n = 20) that were randomly allocated to groups receiving a standard therapeutic dose of diminazene aceturate with antipyrine stabiliser (n = 10) or antipyrine alone (n = 10). Blood was drawn immediately before and every 15 minutes for 1 hour after treatment. Plasma PChE showed a 4% decrease between 0 and 60 min within the treatment group (p < 0.05). No statistically significant differences were found between the treatment and control groups at any of the time intervals for PChE. There was an increase in RBC AChE activity at 15 min in the treatment group (p < 0.05). No significant differences were found between the treatment and control groups at any time interval for RBC AChE. In view of the difference in PChE, samples from additional, new cases (n = 10) of canine babesiosis were collected to identify the affect of the drug over 12 hours. No significant depression was identified over this time interval. The results suggests that the underlying mechanism in producing side-effects, when they do occur, is unlikely to be through cholinesterase depression.

Downregulation of hepatic cytochrome P450 3A in mice infected with Babesia microti.

To investigate effects of Babesia infection on drug metabolism, we intraperitoneally inoculated B. microti into ICR mice and measured the expression and activity of hepatic cytochrome P450 (CYP) 3A, a major drug-metabolizing enzyme. Twelve days after infection, CYP3A11 mRNA, CYP3A protein and activity and mRNAs of nuclear receptors, which participate in CYP3A expression, were significantly reduced. These results suggest that B. microti infection suppresses CYP3A-dependent drug metabolism. Additionally, tumor necrosis factor (TNF)-α and nitric oxide synthase (NOS) 2 mRNAs were induced in the infected mouse liver. Since TNF-α is one of the potent mediators that induce NOS2 and repress CYP3A transcription, the possible involvement of TNF-α in this downregulation of CYP3A was discussed.

Serum carboxypeptidase B levels during acute and mild Babesia bovis and acute Babesia bigemina infections of cattle.

Serum carboxypeptidase B (SCPB) levels were measured in splenectomised calves and in non-splenectomised cattle infected with three virulent and one avirulent strains of Babesia bovis, and in splenectomised calves infected with virulent Babesia bigemina parasites. SCPB levels commenced falling three days post-infection in animals infected with virulent B. bovis strains and fell significanttly terminally. In animals infected with the avirulent B. bovis strain, the SCPB levels were not significantly altered. Animals infected with B. bigemina had no significant changes in their SCPB levels. Fatal infections were uniformly observed in animals with virulent B. bovis, but only two of six animals infected with B. bigemina and none infected with avirulent B. bovis, died.

The enzymes of pyrimidine biosynthesis in Babesia bovis and Babesia bigemina.

All six enzymes of de novo pyrimidine biosynthesis leading to the formation of UMP have been demonstrated in whole homogenates from two bovine Babesia species, B. bovis and B. bigemina. The specific activities of the respective enzymes were of the same order of magnitude as observed for the related parasite, Plasmodium berghei. The results indicate that both these parasites have the potential of obtaining their pyrimidine requirements by de novo synthesis. Subcellular fractionation established that dihydroorotate dehydrogenase, the fourth enzyme of the pathway, was of a particulate nature. Mammalian respiratory chain inhibitors and ubiquinone analogues caused inhibition of the Babesia dihydroorotate dehydrogenase. As observed for other eukaryotic systems, the dehydrogenase appears to be linked to a respiratory chain via ubiquinone.