Use of canine red blood cell with high concentrations of potassium, reduced glutathione, and free amino acid as host cells for in vitro cultivation of Babesia gibsoni

Establishment of Continuous In Vitro Culture of Babesia gibsoni by Using VP-SFM Medium with Low-Concentration Serum

The establishment of in vitro culture methods has greatly facilitated the research of Babesia. However, the current Babesia gibsoni in vitro culture medium requires high concentrations of canine serum, which intensively limits the culture and is unable to satisfy the demands of long-term studies. In this study, AlbuMAX I (2 mg/mL) and 2.5% dog serum (vol/vol) were added to VP-SFM medium to develop a low-concentration serum culture medium named VP-SFMAD (2.5%), and the effectiveness of this medium was assessed by the growth of B. gibsoni. The results showed that VP-SFMAD (2.5%) could support the continuous growth of the parasite, and the parasitemia has no difference with the cultivation in RPMI 1640 with 20% dog serum. In contrast, either a low concentration of dog serum or absence of AlbuMAX I will significantly lower the parasite growth or fail to maintain B. gibsoni growth in the long term. The strategy of reducing the hematocrit was also evaluated, and VP-SFMAD (2.5%) improved the parasitemia to over 50% within 5 days. The high parasitemia is helpful for larger numbers of parasite collection, which is valuable for studying the biology, pathogenesis, and virulence of Babesia and other intraerythrocytic parasites. In addition, VP-SFMAD (2.5%) medium was successfully used for monoclonal parasite screening, which obtained monoclonal strains with parasitized erythrocytes about 3%, which is similar to RPMI-1640D (20%) medium that obtains monoclonal strains on the 18th day. Those results showed that VP-SFMAD can be applied to B. gibsoni continuous long-term, expansion culture, and subclone culture. IMPORTANCE The VP-SFM as a base medium supplemented with AlbuMAX I and a low concentration of canine serum (2.5%) allowed the continuous in vitro culture of Babesia gibsoni at both small and large volumes, which was to meet different experimental needs, such as long-term culture and obtaining high parasitemia and subclone culture. The establishment of in vitro culture systems allows researchers to better understand the metabolism and growth patterns of Babesia. Importantly, several technical problems impeding such studies have been overcome.

The role of heat shock protein 90 in the proliferation of Babesia gibsoni in vitro

The present study investigated the role of heat shock protein 90 (HSP90) in the proliferation and survival of Babesia gibsoni in vitro. To detect the effect on the entry of B. gibsoni into host erythrocytes, the parasite was incubated with an antibody against B. gibsoni HSP90 (BgHSP90) for 24 hr. The results of this experiment demonstrated that both the incorporation of [³H]hypoxanthine into the nucleic acids of B. gibsoni and the number of parasites were not altered, indicating that an anti-BgHSP90 antibody did not directly inhibit the entry of the parasite into erythrocytes. Moreover, two HSP90 inhibitors, geldanamycin (GA) and tanespimycin (17-AAG), were used to evaluate the function of BgHSP90. GA and 17-AAG decreased both the incorporation of [³H]hypoxanthine and the number of infected erythrocytes, suggesting that BgHSP90 plays important roles in DNA synthesis and the proliferation of B. gibsoni. The effect of 17-AAG on the parasites was weaker than that of GA. Additionally, the effect of GA on the survival and superoxide generation of canine neutrophils was assessed. The survival of canine neutrophils was not affected. The superoxide generation was strongly suppressed by GA. This result indicated that GA inhibited the function of canine neutrophils. Additional studies are necessary to elucidate the role of BgHSP90 in the proliferation of the parasite.

In vitro and in vivo safety and efficacy studies of amphotericin B on Babesia gibsoni

Babesia gibsoni is a causative pathogen of canine babesiosis, which is commonly treated with anti-babesial drugs; however, the development of novel, more effective anti-babesial drugs is necessary because the currently used drugs cannot remove the parasites from dogs. Therefore we investigated the anti-babesial effect of amphotericin B (AmB), a membrane-active polyene macrolide antibiotic. The interaction of such compounds with sterols in bilayer cell membranes can lead to cell damage and ultimately cell lysis. AmB exhibits in vitro activity against B. gibsoni in normal canine erythrocytes within 12h. We also studied liposomal AmB (L-AmB), a liposomal formulation of AmB that required a longer incubation period to reduce the number of parasites. However, L-AmB completely inhibited the invasion of free parasites into erythrocytes. These results indicated that free parasites failed to invade erythrocytes in the presence of L-AmB. Both AmB and L-AmB induced mild hemolysis of erythrocytes. Moreover, the methemoglobin level and the turbidity index of erythrocytes were significantly increased when erythrocytes were incubated with AmB, suggesting that AmB induced oxidative damage in erythrocytes. Finally, the anti-babesial activity of AmB in vivo was observed. When experimentally B. gibsoni-infected dogs were administered 0.5 and 1mg/kg AmB by the intravenous route, the number of parasites decreased; however, recurrence of parasitemia was observed, indicating that AmB did not eliminate parasites completely. Blood urea nitrogen and creatinine of dogs were abnormally elevated after the administration of 1mg/kg AmB. These results indicate that AmB has in vivo activity against B. gibsoni; however, it does not eliminate parasites from infected dogs and affects kidney function at a high dose.

Effects and mechanisms of action of polyene macrolide antibiotic nystatin on Babesia gibsoni in vitro

Nystatin is a membrane-active polyene macrolide antibiotic and a channel-forming ionophore. Nystatin exhibits in vitro activity against Babesia gibsoni infecting normal canine erythrocytes containing low potassium (LK) and high sodium concentrations, i.e., LK erythrocytes. The calculated IC(50) value of nystatin against B. gibsoni infecting LK erythrocytes was 31.96 µg/ml. The anti-babesial activity of nystatin disappeared when B. gibsoni in LK erythrocytes were incubated in culture media containing high potassium concentrations (HK). Moreover, when the parasites were harbored in canine HK erythrocytes, which contained high potassium and low sodium concentrations as a result of high Na-K-ATPase activity, the in vitro anti-babesial activities of nystatin also disappeared, apparently due to protection by HK erythrocytes. This suggested that nystatin could show in vitro anti-babesial activity against B. gibsoni by its ionophorous activity, the same as other ionophores such as valinomycin. Subsequently, the effects of nystatin on the host cells were observed. Nystatin could not modify the intracellular concentrations of potassium, sodium, adenosine triphosphate, or glucose in either LK or HK erythrocytes, although it caused weak hemolysis in HK erythrocytes. In addition, nystatin did not affect the survival of canine peripheral polymorphonuclear leukocytes. In conclusion, nystatin destroyed B. gibsoni by ionophorous activity but did not affect either canine erythrocytes or leukocytes in vitro.

Clinical management of canine babesiosis

OBJECTIVE

To review and summarize current information regarding epidemiology, pathogenesis, and pathophysiology leading to the various clinical syndromes associated with canine babesiosis. Diagnosis, treatment, preventative strategies, and zoonotic implications are discussed.

ETIOLOGY

Babesiosis is caused by hemoprotozoa of the genus Babesia. Numerous species of Babesia exist worldwide. An increased incidence of babesiosis is described, especially in North America. The babesial organism spends the majority of its life cycle within the erythrocyte of the definitive host, resulting in hemolysis, with or without systemic complications.

DIAGNOSIS

Definitive diagnosis depends on direct visualization of the organism on blood smear or polymerase chain reaction. A positive serologic antibody test indicates exposure with or without active infection.

THERAPY

Antiprotozoal drugs, antimicrobials, and supportive care are the mainstays of babesiosis therapy.

PROGNOSIS

Prognosis depends on the severity of disease, which in turn depends on both organism and host factors. Clinical syndromes associated with a poorer prognosis include red biliary syndrome, acute renal failure, acute respiratory distress syndrome, neurologic dysfunction, acute pancreatitis, cardiac dysfunction, and hypoglycemia.

Suppressive effect of culture supernatant of erythrocytes and serum from dogs infected with Babesia gibsoni on the morphological maturation of canine reticulocytes in vitro

The present study evaluated the effects of infected culture supernatant of erythrocytes, fractionation of culture supernatant and serum from dogs infected with Babesia gibsoni (B. gibsoni) on the maturation of canine reticulocytes in vitro. The SDS-PAGE demonstrated that significantly broader bands were generated by both the infected culture supernatant of erythrocytes and the serum from dogs chronically infected with B. gibsoni. The culture supernatant of erythrocytes infected with B. gibsoni strongly suppressed the maturation of reticulocytes. Prior studies showed that chronically infected serum had inhibitory effects on both the maturation of reticulocytes and the canine pyrimidine 5'-nucleotidase subclass I and purine-specific 5'-nucleotidase activity. In addition, serum free infected culture supernatant of erythrocytes had an inhibitory effect on the morphological maturation of reticulocytes. These results suggest that infected serum and culture supernatant of erythrocytes might accumulate excess proteins and/or metabolites as a result of the inhibited maturation of reticulocytes and decreased activity of erythrocyte 5'-nucleotidase. Furthermore, the fractions observed at >150 kDa- and 150-70 kDa- in the infected culture supernatant and serum retarded the maturation of canine reticulocytes in vitro. The results obtained from the in vitro examinations, in the present study, suggested that B. gibsoni itself and/or its metabolites might release certain proteins in the infected culture supernatant and serum from infected dogs and as a result delay morphological maturation of canine reticulocytes.

Inhibition of Na,K-ATPase activity reduces Babesia gibsoni infection of canine erythrocytes with inherited high K, low Na concentrations

Babesia gibsoni multiplies well in canine red blood cells (RBCs) containing high concentrations of potassium (HK), reduced glutathione, and free amino acids as a result of an inherited high Na,K-ATPase activity, i.e., HK RBCs. To determine the role of Na,K-ATPase in the multiplication of B. gibsoni, the effect of ouabain on the proliferation of the parasites in HK RBCs was investigated. To determine the direct effect of ouabain on the parasites, the proliferation of the parasites in normal canine RBCs containing low potassium (LK) and high sodium concentrations, i.e., LK RBCs, which completely lack Na,K-ATPase activity, was observed. Ouabain at 0.1 mM significantly suppressed the multiplication of B. gibsoni in HK RBCs in vitro, whereas it had no effect on the parasites in LK RBCs. The results suggest that the multiplication of B. gibsoni in HK RBCs depends mainly on the presence of Na,K-ATPase in the cells. Therefore, the effects of ouabain on the intracellular cation and free amino acid composition of the HK RBCs were examined. In HK RBCs incubated with ouabain, a marked decrease in the concentration of potassium and an increase in sodium were observed, together with a decrease in the number of parasitized cells. These results suggest that the intracellular cation composition maintained by Na,K-ATPase might be advantageous to the parasites. Moreover, the concentrations of some free amino acids, i.e., asparagine, aspartate, glutamate, glutamine, glycine, and histidine, were markedly decreased in HK RBCs incubated with ouabain. Decreased concentrations of the free amino acids induced by inhibition of Na,K-ATPase seemed to affect the multiplication of B. gibsoni in HK RBCs. Based on these results, it is clear that the high Na,K-ATPase activity in HK RBCs contributes to the proliferation of B. gibsoni by maintaining high potassium and low sodium concentrations, as well as high concentrations of some free amino acids in the cells.

Antibabesial Activity of Protoberberine Alkaloids and 20-Hydroxyecdysone from Arcangelisia flava against Babesia gibsoni in Culture

Bioassay-guided fractionation of the boiled extract from the stems of Arcangelisia flava led to the isolation of palmatine (1), berberine (2), jatrorrhizine (3), dihydroberberine (4) and 20-hydroxyecdysone (5). The chemical structures of these compounds were elucidated on the basis of their chemical and spectral evidence. The isolated compounds were evaluated for their growth inhibiting effects on Babesia gibsoni in culture for a week. Compounds (1-4) showed significant inhibitions at concentrations from 100 to 1.0 microg/ml, while compound 5 at a concentration of 100 microg/ml, only.

Serum from dogs Infected with Babesia gibsoni inhibits maturation of reticulocytes and erythrocyte 5'-nucleotidase activity in vitro

Erythrocyte 5'-nucleotidase is thought to be involved in the maturation of erythrocytes. In the present study, in vitro incubation of canine erythrocytes demonstrated that significant inhibition of 5'-nucleotidase activity occurred in the presence of serum from dogs infected with Babesia gibsoni, when the enzyme was assayed with cytidine 5'-monophosphate (5'-CMP) and inosine 5'-monophosphate (5'-IMP) as substrates. The multiplication of B. gibsoni in in vitro culture also resulted in a significant decrease in the enzyme activity of erythrocytes in the culture. Furthermore, the infected serum and 5'-CMP retarded the maturation of canine reticulocytes in vitro. These results suggested 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 decreased activity of erythrocyte 5'-nucleotidase, resulting in the delayed maturation of reticulocytes.

BABESIA GIBSONI–SPECIFIC ISOENZYMES RELATED TO ENERGY METABOLISM OF THE PARASITE IN INFECTED ERYTHROCYTES

To clarify the cause of the predilection of Babesia gibsoni for reticulocytes and canine HK erythrocytes (containing high concentrations of potassium) with inherited high concentrations of some amino acids, including glutamate, 4 enzymes in B. gibsoni parasites were examined by polyacrylamide gel electrophoresis (PAGE). The enzymes, i.e., hexokinase, glucose phosphate isomerase, lactate dehydrogenase, and glutamate dehydrogenase (GDH), were found to be associated with B. gibsoni parasites. The parasite-specific enzymes were shown to have different mobility patterns in PAGE from those found in normal canine erythrocytes. GDH, which is able to oxidize glutamate to alpha-ketoglutarate, an intermediate in the citric acid cycle in mitochondria, was detected only in the parasites. Electron microscopy of the parasites revealed double-membraned organelles similar to mitochondria in their cytoplasm. The parasites in in vitro culture contained many more mitochondrialike organelles than those in the peripheral blood of infected dogs. In addition, the size of parasites cultured in vitro was significantly larger than that of parasites in the peripheral blood. Based on these results, it is suggested that B. gibsoni may use glucose as an energy source in its own glycolytic pathway. Moreover, the parasite may also be capable of oxidizing glutamate via GDH in the citric acid cycle, which may operate in the mitochondrialike organelles within the parasite. This may explain the predilection of B. gibsoni for canine reticulocytes and HK erythrocytes with a high concentration of glutamate.

Molecular cloning and phylogenetic analysis of Babesia gibsoni heat shock protein 70

The Babesia gibsoni heat shock protein 70 gene (BGHsp70) was cloned by polymerase chain reaction (PCR) and sequenced. The length of the gene was 1938 bp and the predicted polypeptide was 646 amino acids long with a calculated molecular weight of 70,627. The amino acid sequences of BGHsp70 from 17 isolates were identical, though there were six types of polymorphisms among the corresponding nucleotide sequences. There was no intron in the BGHsp70 gene. Phylogenetic analysis of the amino acid sequence of Hsp70 showed that B. gibsoni was most closely related to B. bovis and lies within a phylogenetic cluster with Theileria. These results suggest that Hsp70 was well conserved among intraerythrocytic protozoa.

Babesia gibsoni: preferential multiplication in reticulocytes is related to the presence of mitochondria and a high concentration of adenosine 5'-triphosphate in the cells

To determine the cause of the predilection of Babesia gibsoni for reticulocytes, the parasites were cultivated with various types of reconstituted erythrocyte ghosts, which were prepared by resealing erythrocyte ghosts together with variously treated erythrocyte lysate, in vitro. The level of parasitemia in the culture with reconstituted reticulocyte ghosts containing untreated reticulocyte lysate was significantly higher than that in the culture with reconstituted normocyte (mature erythrocyte) ghosts containing untreated normocyte lysate. The removal of mitochondria from reconstituted reticulocyte ghosts by filtration or centrifugation resulted in decreased of parasitemia in those cultures. In contrast, when mitochondria from reticulocytes were loaded into reconstituted normocyte ghosts, the parasitemia in the ghosts loaded mitochondria was increased to the same level as that in reconstituted reticulocyte ghosts. Furthermore, the parsitemia in the culture with reconstituted normocyte ghosts was proportional to the concentration of adenosine 5'-triphosphate in the ghosts. These results suggested that mitochondria of reticulocytes might enhance the multiplication of B. gibsoni through the generation of adenosine 5'-triphosphate within the cells.

Cultivation of Babesia and Babesia-like blood parasites: agents of an emerging zoonotic disease

Babesia and its close relatives are members of a group of organisms called piroplasms, a name which comes from their pear-shaped outlines. Long associated with blood diseases of cattle and other mammals, members of the genus Babesia have been recognized since the 1950s as infectious agents in humans. Species of this protozoan blood parasite that have routinely been isolated from mice (B. microti) or cattle (B. divergens) have also been isolated from humans. In addition to these familiar species, new isolates that resist being placed in existing taxonomic categories are the basis for rethinking their phylogenetic relationships based on sequencing data. The parasite represents a threat to the safety of the blood supply in that blood from asymptomatic humans can transmit Babesia to blood recipients. Such transmissions have occurred. The development of methods for cultivation of these organisms represents a significant opportunity to study their biology and disease potential. In addition, in vitro cultivation has provided a basis for studying immune responses of mammals to these infectious agents, with the hope of ultimately producing attenuated strains that could be used for immunizing of cattle and, perhaps, humans who live in areas of endemicity. The microaerophilous stationary phase culture technique, which uses a tissue culture medium base supplemented with appropriate serum and erythrocytes, has made it possible to obtain large numbers of parasitized erythrocytes for studying the biology of this parasite.

Increased generation of superoxide in erythrocytes infected with Babesia gibsoni

The present study was conducted to clarify the mechanism underlying the oxidative process in erythrocytes infected with Babesia gibsoni. The parasite B. gibsoni was cultured together with erythrocytes from normal dogs for 7 days. When parasitemia reached 12.0-13.4% at Day 7. the production of superoxide in erythrocytes was significantly higher in the parasitized culture than in the control culture (p<0.005). The concentration of thiobarbituric acid reactive substances (TBARS) in erythrocytes in parasitized culture was also significantly increased compared with the control culture (p<0.005), indicating that lipid peroxidation was greater in infected erythrocytes than in non-infected cells. In addition, the rates of superoxide generation in the blood of B. gibsoni-infected dogs were also significantly higher than in non-infected dogs (p<0.001). These results indicate that superoxide anions are increased in erythrocytes parasitized with B. gibsoni. and suggest that oxidative damage, due to lipid peroxidation, might be caused in host erythrocytes by the parasite.