Effects of Shiga toxin type 2 on maternal and fetal status in rats in the early stage of pregnancy

Progression of renal damage and tubular regeneration in pregnant and non-pregnant adult female rats inoculated with a sublethal dose of Shiga toxin 2

BACKGROUND

Shiga toxin-producing Escherichia coli is the main cause of post-diarrheal hemolytic uremic syndrome (HUS) which produces acute kidney injury mainly in children, although it can also affect adults. The kidneys are the organs most affected by Shiga toxin type 2 (Stx2) in patients with HUS. However, previous studies in pregnant rats showed that a sublethal dose of Stx2 causes severe damage in the uteroplacental unit and induces abortion, whereas produces mild to moderate renal damage. The aim of the present work was to study the progression of renal injury caused by a sublethal dose of Stx2, as well as renal recovery, in pregnant and non-pregnant rats, and to investigate whether pregnancy physiology may affect renal damage progression mediated by Stx2.

METHODS

Renal function and histopathology was evaluated in pregnant rats intraperitoneally injected with a sublethal dose of Stx2 (0.5 ng/g bwt) at the early stage of gestation (day 8 of gestation), and results in these rats were compared over time with those observed in non-pregnant female rats injected with the same Stx2 dose. Hence, progression of cell proliferation and dedifferentiation in renal tubular epithelia was also investigated.

RESULTS

The sublethal dose of Stx2 induced abortion in pregnant rats as well as a significant more extended functional and histological renal injury in non-pregnant rats than in pregnant rats. Stx2 also caused decreased ability to concentrate urine in non-pregnant rats compared to their controls. However, renal water handling in pregnant rats was not altered by Stx2, and was significantly different than in non-pregnant rats. The greatest renal injury in both pregnant and non-pregnant rats was observed at 4 days post-Stx2 injection, and coincided with a significant increase in tubular epithelial proliferation. Expression of mesenchymal marker vimentin in tubular epithelia was consistent with the level of tubular damage, being higher in non-pregnant rats than in pregnant rats. Recovery from Stx2-induced kidney injury was faster in pregnant rats than in non-pregnant rats.

CONCLUSIONS

Adaptive mechanisms developed during pregnancy such as changes in water handle and renal hemodynamic may contribute to lessen the Stx2-induced renal injury, perhaps at the expense of fetal loss.

Detection and characterization of circulating microvesicles containing Shiga toxin type 2 in a rat model of Hemolytic Uremic Syndrome

Shiga toxin producing Escherichia coli (STEC) are foodborne pathogens that release Shiga toxin (Stx), virulence factor responsible for the development of Hemolytic Uremic Syndrome (HUS). Stx causes endothelial cell damage, which leads to platelets deposition and thrombi formation within the microvasculature. It has been described that Stx activates blood cells and induces the shedding of proinflammatory and prothrombotic microvesicles (MVs) containing the toxin. In this sense, it has been postulated that MVs containing Stx2 (MVs-Stx2+) can contribute to the physiopathology of HUS, allowing Stx2 to reach the target organs while evading the immune system. In this work, we propose that circulating MVs-Stx2+ can be a potential biomarker for the diagnosis and prognosis of STEC infections and HUS progression. We developed a rat HUS model by the intraperitoneal injection of a sublethal dose of Stx2 and observed: decrease in body weight, increase of creatinine and urea levels, decrease of creatinine clearance and histological renal damages. After characterization of renal damages, we investigated circulating total MVs and MVs-Stx2+ by flow cytometry at different times after Stx2 injection. Additionally, we evaluated the correlation of biochemical parameters such as creatinine and urea in plasma with MVs-Stx2+. As a result, we found a significant circulation of MVs-Stx2+ at 72 and 96 h after Stx2 injection, nevertheless no correlation with creatinine and urea plasma levels were detected. Our results suggest that MVs-Stx2+ may be an additional biomarker for the characterization and diagnosis of HUS progression. A further analysis is required in order to validate MVs-Stx2+ as biomarker of the disease.

Detection of Shiga Toxin-Producing Escherichia coli (STEC) in the Endocervix of Asymptomatic Pregnant Women. Can STEC Be a Risk Factor for Adverse Pregnancy Outcomes?

The presence of Escherichia coli in the vaginal microbiome has been associated with pregnancy complications. In previous works, we demonstrated that Shiga toxin-producing Escherichia coli (STEC) can produce abortion and premature delivery in rats and that Shiga toxin type 2 (Stx2) can impair human trophoblast cell lines. The hypothesis of this work was that STEC may colonize the lower female reproductive tract and be responsible for adverse pregnancy outcomes. Thus, the aim of this work was to evaluate the presence and prevalence of virulence factor genes from STEC in the endocervix of asymptomatic pregnant women. For that purpose, endocervical swabs were collected from pregnant women during their prenatal examination. Swab samples were enriched in a differential medium to select Enterobacteria. Then, positive samples were analyzed by PCR to detect genes characteristic of Escherichia sp. (such as uidA and yaiO), genes specific for portions of the rfb (O-antigen-encoding) regions of STEC O157 (rfb_O157), and STEC virulence factor genes (such as stx1, stx2, eae, lpfA_O113, hcpA, iha, sab, subAB). The cytotoxic effects of stx2-positive supernatants from E. coli recovered from the endocervix were evaluated in Vero cells. Our results showed that 11.7% of the endocervical samples were positive for E. coli. Additionally, we found samples positive for stx2 and other virulence factors for STEC. The bacterial supernatant from an isolate identified as E. coli O113:NT, carrying the stx2 gene, exhibited cytotoxic activity in Vero, Swan 71 and Hela cells. Our results open a new perspective regarding the presence of STEC during pregnancy.

The limited knowledge of placental damage due to neglected infections: ongoing problems in Latin America

The placenta works as a selective barrier, protecting the fetus from potential infections that may affect the maternal organism during pregnancy. In this review, we will discuss several challenging infections that are common within Latin American countries and that may affect the maternal-fetal interface and pose risks to fetal development. Specifically, we will focus on emerging infectious diseases including the arboviruses, malaria, leishmaniasis, and the bacterial foodborne disease caused by Shiga toxin-producing Escherichia coli. We will also highlight some topics of interest currently being studied by research groups that comprise an international effort aimed at filling the knowledge gaps in this field. These topics address the relationship between exposure to microorganisms and placental abnormalities, congenital anomalies, and complications of pregnancy.

ABBREVIATIONS

ADE: antibody-dependent enhancement; CCL2: monocyte chemoattractant protein-1; CCL3: macrophage inflammatory protein-1 α; CCL5: chemokine (C-C motif) ligand 5; CHIKV: chikungunya virus; DCL: diffuse cutaneous leishmaniasis; DENV: dengue virus; Gb3: glycolipid globotriaosylceramyde; HIF: hypoxia-inducible factor; HUS: hemolytic uremic syndrome; IFN: interferon; Ig: immunoglobulins; IL: interleukin; IUGR: intrauterine growth restriction; LCL: localized cutaneous leishmaniasis; LPS: lipopolysaccharid; MCL: mucocutaneous leishmaniasis; NO: nitric oxide; PCR: polymerase chain reaction; PGF: placental growth factor; PM: placental malaria; RIVATREM: Red Iberoamericana de Alteraciones Vasculares em transtornos del Embarazo; sVEGFR: soluble vascular endothelial growth factor receptor; STEC: shiga toxin-producing Escherichia coli; stx: shiga toxin protein; TNF: tumor necrosis factor; TOAS: T cell original antigenic sin; Var2CSA: variant surface antigen 2-CSA; VEGF: vascular endothelial growth factor; VL: visceral leishmaniasis; WHO: world health organization; YFV: yellow fever virus; ZIKV: Zika virus.

Shiga Toxin-Producing Escherichia coli Infections during Pregnancy

Gastrointestinal infection with Shiga toxin-producing Escherichia coli (STEC) causes diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome (HUS), characterized by hemolytic anemia, thrombocytopenia and acute renal failure. The main virulence factor of STEC is Shiga toxin (Stx), which is responsible for HUS development. STEC can produce Stx type 1 and/or 2 (Stx1, Stx2) and their variants, Stx2 being more frequently associated with severe cases of HUS. This pathology occurs in 5⁻15% of cases with STEC infection when Stx gain access to the bloodstream and causes damage in the target organs such as the kidney and brain. STEC infections affect mainly young children, although the large HUS outbreak with a new Stx2-producing STEC O104:H4 in Europe in 2011 involved more adults than children, and women were over-represented. Maternal infections during pregnancy are associated with adverse pregnancy outcomes. Studies in rats showed that Stx2 binds to the utero-placental unit and causes adverse pregnancy outcomes. In this article, we provide a brief overview of Stx2 action on placental tissues and discuss whether they might cause pregnancy loss or preterm birth.

Immunization with BLS-Stx2B chimera totally protects dams from early pregnancy loss induced by Shiga toxin type 2 (Stx2) and confers anti-Stx2 immunity to the offspring

Shiga toxin producing Escherichia coli (STEC) are bacterial pathogens involved in food-borne diseases. Shiga toxin (Stx) is the main virulence factor of STEC and is responsible for systemic complications including Hemolytic Uremic Syndrome (HUS). It has been previously demonstrated that Shiga toxin type 2 (Stx2) induces pregnancy loss in rats in early stage of pregnancy. The main purpose of this study was to determine if an active immunization prevents Stx2 mediated pregnancy loss and confers passive protective immunity to the offspring. For that purpose Sprague Dawley female rats were immunized with the chimera based on the enzyme lumazine synthase from Brucella spp. (BLS) and the B subunit of Shiga toxin 2 (Stx2B) named BLS-Stx2B. After immunization females were mated with males. At day 8 of gestation, dams were challenged intraperitoneally with a sublethal and abortifacient dose of Stx2. The immunization induced high anti-Stx2B-specific antibody titers in sera and most important, prevented pregnancy loss. Pups born and breastfeed by immunized dams had high anti-Stx2B-specific antibody titers in sera. Cross-fostering experiments indicated that passive protective immunity against Stx2 was transmitted through lactation. These results indicate that immunization of adult female rats with BLS-Stx2B prevents Stx2-induced pregnancy loss and confers anti Stx2 protective immunity to the offspring.