Inhibitory Effect of Pyrimidine and Purine Nucleotides on the Multiplication of <i>Babesia gibsoni</i>: Possible Cause of Low Parasitemia and Simultaneous Reticulocytosis in Canine Babesiosis

Abstract

ABSTRACT. The present study was conducted to determine the cause of low parasitemia and simultaneous reticulocytosis in canine babesiosis. The parasitemia was significantly decreased in in vitro cultures of Babesia gibsoni by the pretreatment of host canine erythrocytes with lead acetate, which is a specific inhibitor of pyrimidine 5'-nucleotidase subclass I (P5N-I). The serum from dogs chronically infected with B. gibsoni did not decrease the activities of hexokinase, glucose-6-phosphate dehydrogenase or 6-phosphogluconate dehydrogenase in canine reticulocytes, although it was previously reported that this serum had inhibitory effects on both the maturation of reticulocytes and the canine P5N-I and purine-specific 5'-nucleotidase activities. Furthermore, the in vitro multiplication of B. gibsoni was significantly inhibited by pyrimidine nucleotides such as cytidine 5'-monophosphate (5'-CMP), which is preferentially catalyzed by P5N-I and also inhibits the morphological maturation of canine reticulocytes. Purine nucleotides such as inosine 5'-monophospha te (5'-IMP) also had an inhibitory effect on the multiplication of this parasite. These results suggest that nucleotides such as 5'-CMP and 5'-IMP might accumulate in young erythrocytes and/or serum in dogs infected with B. gibsoni as a result of the decreased activity of erythrocyte 5'-nucleotidase, and the accumulation of these nucleotides might inhibit the multiplication of this parasite and simultaneously retard the maturation of reticulocytes. The results obtained from the in vitro examinations in the present study may partially clarify the relationship between low parasitemia and simultaneous reticulocytosis in vivo in canine babesiosis. KEY WORDS: Babesia gibsoni, erythrocyte 5'-nucleotidase, purine nucleotide, pyrimidine nucleotide, reticulocyte.

Babesia microti Primarily Invades Mature Erythrocytes in Mice

“…Whether Babesia itself reduces erythropoiesis in susceptible strains remains to be investigated. Studies of B. gibsoni infection have shed some light on how an intraerythrocytic pathogen can hijack erythropoiesis (13,14). B. gibsoni inhibits the activity of 5Ј nucleotidase, an enzyme that degrades rRNA in reticulocytes (13).…”

“…The reduced 5Ј-nucleotidase activity leads to an accumulation of pyrimidine and purine nucleotides, such as CMP and IMP. The former inhibits parasite replication and retards reticulocyte maturation, whereas the latter inhibits parasite replication (14). As reticulocyte maturation is halted and parasite growth curtailed, this scenario favors survival of both parasite and host.…”

Electrochemical oxidation of inosine 5′-monophosphate in neutral aqueous solution

“…Such an oxidation is well documented for purines and substituted purines [45,46]. The -O-radical species (18) formed at C 8 position combines rapidly with radical species (13) to form -C-O-N-linked dimer (19). Similar to the dimer (15) both the ribose-phosphate moieties are hydrolyzed and all the three reactive H atoms are replaced with (CH 3 ) 3 Si-units during silylation.…”

“…The radical species (12) can have several possible resonating structures as shown in Scheme 1. The radical species (13) in which the odd electron is present at position N 1 seems to rapidly dimerize to form a N-N linked dimer (15) with the loss of both the ribose-phosphate moieties due to the addition of 0.1 M HCl to the electrolyzed sample, which was added in order to convert the sodium salt into free acid. Such observation about the hydrolysis of sugar units is also well documented in the literature [44].…”

“…Besides this, 5 0 -IMP has been used as flavor enhancers in poultry feed [11]. 5 0 -IMP induces a delayed paralysis effect in termites [12] and is reported to exhibit an inhibitory effect on the multiplication of the parasite Babesia gibsonic in infected young erythrocytes and simultaneously retard the maturation of reticulocytes [13]. 5 0 -IMP holds potential as pharmacological agent to enhance the effect of bacterial and viral vaccines [14].…”