Modulation of cholesterol-related sterols during Eimeria bovis macromeront formation and impact of selected oxysterols on parasite development

Atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization mass spectrometry imaging of Neospora caninum-infected cell monolayers

Neospora caninum is an obligate intracellular protozoan parasite of the phylum Alveolata (subphylum Apicomplexa) which has not been studied extensively in a biochemical context. N. caninum is a primary cause of reproductive disorders causing mummification and abortion not only in cattle but also in other small ruminant species resulting in a substantial economic impact on the livestock industry. In canids, which are the final hosts of N. caninum, clinical disease includes neuromuscular symptoms, ataxia, and ascending paralysis. Fatal outcomes of neosporosis have also been reported depending on the host species, age and immune status, however, its zoonotic potential is still uncertain. Therefore, N. caninum should be thoroughly investigated. Matrix-assisted laser desorption/ionisation (MALDI) mass spectrometry (MS) and MS imaging (MSI) were used, combined with high-performance liquid chromatography (HPLC) to investigate these intracellular parasites. The aim of this study was to identify molecular biomarkers for N. caninum tachyzoite-infected host cells and to further clarify their functions. By atmospheric-pressure scanning microprobe MALDI MS(I), sections of N. caninum-infected and non-infected host cell pellets were examined in order to determine potential markers. In vivo, N. caninum infects different types of nucleated cells, such as endothelial cells which represent a highly immunoreactive cell type. Therefore, primary bovine umbilical vein endothelial cells were here used as a suitable infection system. For comparison, the permanent MARC-145 cell line was used as an additional, simplified in vitro cell culture model. HPLC-tandem MS (HPLC-MS/MS) experiments combined with database search were employed for structural verification of markers. The statistically relevant biomarkers found by MS and identified by HPLC-MS/MS measurements were partly also found in infected monolayers. Marker signals were imaged in cell layers of N. caninum-infected and non-infected host cells at 5 µm lateral resolution.

Biochemical and Pathomorphological Investigations on Rabbits with Experimentally Induced Hepatic Eimeriosis

The present study aimed to evaluate the changes in concentrations of some biochemical parameters, as well as macro and microscopic alterations during Eimeria stiedae infection in rabbits. The experiment was performed using 12 three-month-old healthy rabbits, randomly allocated into 2 equal groups: G1 (controls, uninfected animals) and G2 (rabbits infected with E. stiedae). Blood samples were collected at time zero (prior to the infection), 6th, 24th, and 48th hours, and also 7th, 14th, 21st, 28th days after the infection. After sampling, the blood was centrifuged, plasma was separated and frozen at −20 ºC until analyzed. Thawed plasma was used for the quantitative determination of haptoglobin (Hp), total protein (TP), aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT), alkaline phosphatase (ALP), total cholesterol (TC), total bilirubin (TBIL), urea, and creatinine (CREA). The results in infected rabbits revealed a significant increase in Hp, AST, ALT, GGT, TBIL, and TC levels, as well as a significant decrease in ALP and urea. A weak hyperproteinemia was also observed. There were no changes in CREA concentration. At the end of the clinical investigation, all rabbits were humanely euthanized and necropsied. The post-mortem examination of the infected group revealed hepatomegaly, multifocal yellowish nodules diffusely spread over the liver surface and in the parenchyma, considerably dilated bile ducts, and biliary hyperplasia. Given the results obtained from this experiment, it can be affirmed that hepatic eimeriosis in rabbits is a severe parasitic disease leading to significant disturbances of liver histology and resulting changes in the biochemical profile of infected rabbits.

Novel Insights Into Sterol Uptake and Intracellular Cholesterol Trafficking During Eimeria bovis Macromeront Formation

Apicomplexan parasites are considered as defective in cholesterol synthesis. Consequently, they need to scavenge cholesterol from the host cell by either enhancing the uptake of extracellular cholesterol sources or by upregulating host cellular de-novo biosynthesis. Given that Eimeria bovis macromeront formation in bovine lymphatic endothelial host cells in vivo is a highly cholesterol-demanding process, we here examined host parasite interactions based on host cellular uptake of different low-density lipoprotein (LDL) types, i.e., of non-modified (LDL), oxidized (oxLDL), and acetylated LDL (acLDL). Furthermore, the expression of lipoprotein-oxidized receptor 1 (LOX-1), which mediates acLDL and oxLDL internalization, was monitored throughout first merogony, in vitro and ex vivo. Moreover, the effects of inhibitors blocking exogenous sterol uptake or intracellular transport were studied during E. bovis macromeront formation in vitro. Hence, E. bovis-infected primary bovine umbilical vein endothelial cells (BUVEC) were treated with inhibitors of sterol uptake (ezetimibe, poly-C, poly-I, sucrose) and of intracellular sterol transport and release from endosomes (progesterone, U18666A). As a read-out system, the size and number of macromeronts as well as merozoite I production were estimated. Overall, the internalization of all LDL modifications (LDL, oxLDL, acLDL) was observed in E. bovis-infected BUVEC but to different extents. Supplementation with oxLDL and acLDL at lower concentrations (5 and 10 µg/ml, respectively) resulted in a slight increase of both macromeront numbers and size; however, at higher concentrations (25-50 µg/ml), merozoite I production was diminished. LOX-1 expression was enhanced in E. bovis-infected BUVEC, especially toward the end of merogony. As an interesting finding, ezetimibe treatments led to a highly significant blockage of macromeront development and merozoite I production confirming the relevance of sterol uptake for intracellular parasite development. Less prominent effects were induced by non-specific inhibition of LDL internalization via sucrose, poly-I, and poly-C. In addition, blockage of cholesterol transport via progesterone and U18666A treatments resulted in significant inhibition of parasite development. Overall, current data underline the relevance of exogenous sterol uptake and intracellular cholesterol transport for adequate E. bovis macromeront development, unfolding new perspectives for novel drug targets against E. bovis.

Thiosemicarbazone Copper Chelator BLT-1 Blocks Apicomplexan Parasite Replication by Selective Inhibition of Scavenger Receptor B Type 1 (SR-BI)

Coccidian parasites are obligate intracellular pathogens that affect humans and animals. Apicomplexans are defective in de novo synthesis of cholesterol, which is required for membrane biosynthesis and offspring formation. In consequence, cholesterol has to be scavenged from host cells. It is mainly taken up from extracellular sources via LDL particles; however, little is known on the role of HDL and its receptor SR-BI in this process. Here, we studied effects of the SR-BI-specific blocker BLT-1 on the development of different fast (Toxoplasma gondii, Neospora caninum, Besnoitia besnoiti) and slow (Eimeria bovis and Eimeria arloingi) replicating coccidian species. Overall, development of all these parasites was significantly inhibited by BLT-1 treatment indicating a common SR-BI-related key mechanism in the replication process. However, SR-BI gene transcription was not affected by T. gondii, N. caninum and B. besnoiti infections. Interestingly, BLT-1 treatment of infective stages reduced invasive capacities of all fast replicating parasites paralleled by a sustained increase in cytoplasmic Ca⁺⁺ levels. Moreover, BLT1-mediated blockage of SR-BI led to enhanced host cell lipid droplet abundance and neutral lipid content, thereby confirming the importance of this receptor in general lipid metabolism. Finally, the current data suggest a conserved role of SR-BI for successful coccidian infections.

Eimeria bovis Macromeront Formation Induces Glycolytic Responses and Mitochondrial Changes in Primary Host Endothelial Cells

Eimeria bovis is an intracellular apicomplexan parasite that causes considerable economic losses in the cattle industry worldwide. During the first merogony, E. bovis forms large macromeronts with >140,000 merozoites I in host endothelial cells. Because this is a high-energy demanding process, E. bovis exploits the host cellular metabolism to fulfill its metabolic requirements. We here analyzed the carbohydrate-related energetic metabolism of E. bovis–infected primary bovine umbilical vein endothelial cells during first merogony and showed that during the infection, E. bovis–infected culture presented considerable changes in metabolic signatures, glycolytic, and mitochondrial responses. Thus, an increase in both oxygen consumption rates (OCR) and extracellular acidification rates (ECAR) were found in E. bovis–infected host cells indicating a shift from quiescent to energetic cell status. Enhanced levels of glucose and pyruvate consumption in addition to increased lactate production, suggesting an important role of glycolysis in E. bovis–infected culture from 12 days p.i. onward. This was also tested by glycolytic inhibitors (2-DG) treatment, which reduced the macromeront development and diminished merozoite I production. As an interesting finding, we observed that 2-DG treatment boosted sporozoite egress. Referring to mitochondrial activities, intracellular ROS production was increased toward the end of merogony, and mitochondrial potential was enhanced from 12 d p. i. onward in E. bovis–infected culture. Besides, morphological alterations of membrane potential signals also indicated mitochondrial dysfunction in macromeront-carrying host endothelial culture.

Ezetimibe blocks Toxoplasma gondii-, Neospora caninum- and Besnoitia besnoiti-tachyzoite infectivity and replication in primary bovine endothelial host cells

Coccidia are obligate apicomplexan parasites that affect humans and animals. In fast replicating species, in vitro merogony takes only 24–48 h. In this context, successful parasite proliferation requires nutrients and other building blocks. Coccidian parasites are auxotrophic for cholesterol, so they need to obtain this molecule from host cells. In humans, ezetimibe has been applied successfully as hypolipidaemic compound, since it reduces intestinal cholesterol absorption via blockage of Niemann−Pick C-1 like-1 protein (NPC1L1), a transmembrane protein expressed in enterocytes. To date, few data are available on its potential anti-parasitic effects in primary host cells infected with apicomplexan parasites of human and veterinary importance, such as Toxoplasma gondii, Neospora caninum and Besnoitia besnoiti. Current inhibition experiments show that ezetimibe effectively blocks T. gondii, B. besnoiti and N. caninum tachyzoite infectivity and replication in primary bovine endothelial host cells. Thus, 20 μm ezetimibe blocked parasite proliferation by 73.1−99.2%, via marked reduction of the number of tachyzoites per meront, confirmed by 3D-holotomographic analyses. The effects were parasitostatic since withdrawal of the compound led to parasite recovery with resumed proliferation. Ezetimibe-glucuronide, the in vivo most effective metabolite, failed to affect parasite proliferation in vitro, thereby suggesting that ezetimibe effects might be NPC1L1-independent.

Comparisons of the Sexual Cycles for the Coccidian Parasites Eimeria and Toxoplasma

Toxoplasma gondii and Eimeria spp. are widely prevalent Coccidian parasites that undergo sexual reproduction during their life cycle. T. gondii can infect any warm-blooded animal in its asexual cycle; however, its sexual cycle is restricted to felines. Eimeria spp. are usually restricted to one host species, and their whole life cycle is completed within this same host. The literature reviewed in this article comprises the recent findings regarding the unique biology of the sexual development of T. gondii and Eimeria spp. The molecular basis of sex in these pathogens has been significantly unraveled by new findings in parasite differentiation along with transcriptional analysis of T. gondii and Eimeria spp. pre-sexual and sexual stages. Focusing on the metabolic networks, analysis of these transcriptome datasets shows enrichment for several different metabolic pathways. Transcripts for glycolysis enzymes are consistently more abundant in T. gondii cat infection stages than the asexual tachyzoite stage and Eimeria spp. merozoite and gamete stages compared to sporozoites. Recent breakthroughs in host-pathogen interaction and host restriction have significantly expanded the understating of the unique biology of these pathogens. This review aims to critically explore advances in the sexual cycle of Coccidia parasites with the ultimate goal of comparing and analyzing the sexual cycle of Eimeria spp. and T. gondii.

Estimating fetal cholesterol synthesis rates by cord blood analysis in intrauterine growth restriction and normally grown fetuses

BACKGROUND

Cholesterol is an essential component in human development. In fetuses affected by intrauterine growth restriction (IUGR), fetal blood cholesterol levels are low. Whether this is the result of a reduced materno-fetal cholesterol transport, or due to low fetal de novo synthesis rates, remains a matter of debate. By analyzing cholesterol interbolites and plant sterols we aimed at deeper insights into transplacental cholesterol transport and fetal cholesterol handling in IUGR with potential targets for future therapy. We hypothesized that placental insufficiency results in a diminished cholesterol supply to the fetus.

METHODS

Venous umbilical cord sera were sampled post-partum from fetuses delivered between 24 weeks of gestation and at full term. IUGR fetuses were matched to 49 adequate-for-age delivered preterm and term neonates (CTRL) according to gestational age at delivery. Cholesterol was measured by gas chromatography-flame ionization detection using 5a-cholestane as internal standard. Cholesterol precursors and synthesis markers, such as lanosterol, lathosterol, and desmosterol, the absorption markers, 5α-cholestanol and plant sterols, such as campesterol and sitosterol, as well as enzymatically oxidized cholesterol metabolites (oxysterols), such as 24S- or 27-hydroxycholesterol, were analyzed by gas chromatography-mass spectrometry, using epicoprostanol as internal standard for the non-cholesterol sterols and deuterium labeled oxysterols for 24S- and 27-hydroxycholesterol.

RESULTS

Mean cholesterol levels were 25% lower in IUGR compared with CTRL (p < 0.0001). Lanosterol and lathosterol to cholesterol ratios were similar in IUGR and CTRL. In relation to cholesterol mean, desmosterol, 24S-hydroxycholesterol, and 27-hydroxycholesterol levels were higher by 30.0, 39.1 and 60.7%, respectively, in IUGR compared to CTRL (p < 0.0001). Equally, 5α-cholestanol, campesterol, and β-sitosterol to cholesterol ratios were higher in IUGR than in CTRL (17.2%, p < 0.004; 33.5%, p < 0.002; 29.3%, p < 0.021).

CONCLUSIONS

Cholesterol deficiency in IUGR is the result of diminished fetal de novo synthesis rates rather than diminished maternal supply. However, increased oxysterol- and phytosterol to cholesterol ratios suggest a lower sterol elimination rate. This is likely caused by a restricted hepatobiliary function. Understanding the fetal cholesterol metabolism is important, not only for neonatal nutrition, but also for the development of strategies to reduce the known risk of future cardiovascular diseases in the IUGR fetus.