The effect of oxidative stress induced by tert-butylhydroperoxide under distinct folic acid conditions: An in vitro study using cultured human trophoblast-derived cells

Recent Advances in Folates and Autoantibodies against Folate Receptors in Early Pregnancy and Miscarriage

Though firstly identified in cerebral folate deficiency, autoantibodies against folate receptors (FRAbs) have been implicated in pregnancy complications such as miscarriage; however, the underlying mechanism needs to be further elaborated. FRAbs can be produced via sensitization mediated by folate-binding protein as well as gene mutation, aberrant modulation, or degradation of folate receptors (FRs). FRAbs may interfere with folate internalization and metabolism through blocking or binding with FRs. Interestingly, different types of FRs are expressed on trophoblast cells, decidual epithelium or stroma, and macrophages at the maternal-fetal interface, implying FRAbs may be involved in the critical events necessary for a successful pregnancy. Thus, we propose that FRAbs may disturb pregnancy establishment and maintenance by modulating trophoblastic biofunctions, placental development, decidualization, and decidua homeostasis as well as the functions of FOLR2+ macrophages. In light of these findings, FRAbs may be a critical factor in pathological pregnancy, and deserve careful consideration in therapies involving folic acid supplementation for pregnancy complications.

Interactions of arsenic exposure, arsenic metabolism with red blood cell folate on the risk of hypertension: NHANES 2007-2016

PURPOSE

Arsenic exposure was associated with hypertension, and arsenic metabolism might be influenced by folate concentrations. Thus, this study aimed to explore the interaction between arsenic exposure and metabolism with folate concentrations on hypertension.

METHODS

We studied 6643 adults aged 20 years and older who participated in the National Health and Nutrition Examination Survey from 2007 through 2016. Urinary total arsenic (UTAs), the percentage of urinary dimethylarsinic acid (DMA%), serum and red blood cell (RBC) folate were collected. Logistic regression and restricted cubic spline (RCS) analyses were performed to determine the association and dose-response relationship. Interaction analyses were conducted on both additive and multiplicative scales.

RESULTS

UTAs (median: 7.05 μg/L) was positively associated with hypertension risk, and the adjusted OR was 1.44 (95% CI: 1.06-1.95) when comparing the third with the lowest quartile. And participants with the highest quintile of RBC folate had increased hypertension risk than those with the lowest quintile (adjusted OR = 1.43, 95% CI: 1.06-1.94). Significant additive interaction was observed between excessive RBC folate with high UTAs (AP = 0.323, 95% CI: 0.083-0.564) and low DMA% (AP = 0.381, 95% CI: 0.119-0.643) on hypertension risk.

CONCLUSION

Our results suggested significant interactions between high UTAs and low DMA% with excessive RBC folate on hypertension risk.

High Folate, Perturbed One-Carbon Metabolism and Gestational Diabetes Mellitus

Folate is a dietary micronutrient essential to one-carbon metabolism. The World Health Organisation recommends folic acid (FA) supplementation pre-conception and in early pregnancy to reduce the risk of fetal neural tube defects (NTDs). Subsequently, many countries (~92) have mandatory FA fortification policies, as well as recommendations for periconceptional FA supplementation. Mandatory fortification initiatives have been largely successful in reducing the incidence of NTDs. However, humans have limited capacity to incorporate FA into the one-carbon metabolic pathway, resulting in the increasingly ubiquitous presence of circulating unmetabolised folic acid (uFA). Excess FA intake has emerged as a risk factor in gestational diabetes mellitus (GDM). Several other one-carbon metabolism components (vitamin B12, homocysteine and choline-derived betaine) are also closely entwined with GDM risk, suggesting a role for one-carbon metabolism in GDM pathogenesis. There is growing evidence from in vitro and animal studies suggesting a role for excess FA in dysregulation of one-carbon metabolism. Specifically, high levels of FA reduce methylenetetrahydrofolate reductase (MTHFR) activity, dysregulate the balance of thymidylate synthase (TS) and methionine synthase (MTR) activity, and elevate homocysteine. High homocysteine is associated with increased oxidative stress and trophoblast apoptosis and reduced human chorionic gonadotrophin (hCG) secretion and pancreatic β-cell function. While the relationship between high FA, perturbed one-carbon metabolism and GDM pathogenesis is not yet fully understood, here we summarise the current state of knowledge. Given rising rates of GDM, now estimated to be 14% globally, and widespread FA food fortification, further research is urgently needed to elucidate the mechanisms which underpin GDM pathogenesis.

Folic Acid Levels During Pregnancy Regulate Trophoblast Invasive Behavior and the Possible Development of Preeclampsia

Background

One of the unique features of placentation is its similarity to tumorigenesis yet being very well regulated. It allows rapid proliferation, migration, and invasion of mononuclear trophoblast cells into the maternal uterus and remodeling the maternal vasculature. This pseudomalignant nature of trophoblastic cells is strictly regulated and its importance becomes evident in abnormal pregnancies that are characterized by aberrant trophoblast proliferation/invasion like preeclampsia. In addition to this, the importance of folic acid supplementation during pregnancy is well documented. We aimed to analyze the molecular and epigenetic regulation of the pseudomalignant nature of placentation via folic acid levels.

Methods

Placental tissue samples were collected from different pregnancies in three different gestational stages. We estimated the impact of folic acid levels on global methylation, LINE1 methylation, and expression of DNMTs in all three gestational stages in pregnant women and preeclampsia pregnancies. We also analyzed the effect of folic acid supplementation on trophoblastic invasion using placental derived cells viz, JEG-3 and HTR-8/SVneo cell line and verified the molecular and epigenetic mechanisms involved in this regulation.

Results

Development of preeclampsia was observed to be associated with lower folate levels in placental tissue, higher global methylation level, and higher expression of DNMT1and DNMT3A. Folic acid supplementation was found to increase the invasive potential of placental trophoblasts by almost two folds which were associated with the decreased expression of tumor suppressor genes and tissue inhibitors of matrix metalloproteinases; and increased expression of oncogenes, telomerase gene, and matrix metalloproteinases. These folic acid-mediated changes were observed to be regulated by CpG methylation in the case of many genes. Folic acid supplementation was also observed to significantly decrease global methylation in placental trophoblasts related to decreasing expression of DNMT1 and DNMT3A.

Conclusion

Lower folic acid levels are associated with preeclampsia development and folic acid supplementation regulates the invasive potential of placental trophoblasts as mediated by various epigenetic changes in the placenta suggesting the protective effect of folic acid against preeclampsia.

α-tocopherol prevents oxidative stress-induced proliferative dysfunction in first-trimester human placental (HTR-8/SVneo) cells

Extravillous trophoblasts (EVTs) are the main participants in the process of placentation, an early process critical for placental growth and function involving an adequate invasion and complete remodelling of the maternal spiral arteries during early pregnancy. An increase in oxidative stress during pregnancy is associated with the onset and progression of several pregnancy disorders, including preeclampsia and gestational diabetes mellitus and it also occurs due to exposure of pregnant women to some xenobiotics (eg. alcohol). This study aimed to investigate how oxidative stress affects EVTs, and the ability of several distinct antioxidant agents to prevent these changes. For this, we exposed HTR8/SVneo cells to tert-butylhydroperoxide (0.5 μM; 24 h), which was able to increase lipid peroxidation and protein carbonyl levels. Under these conditions, there was a decrease in proliferation rates, culture growth, migratory and angiogenic capacities and an increase in the apoptosis rates. The antiproliferative effect of TBH was supressed by simultaneous treatment of the cells with α-tocopherol, but other antioxidants (vitamin C, allopurinol, apocynin, N-acetylcysteine, quercetin and resveratrol) were ineffective. α-tocopherol was also able to abolish the effect of TBH on lipid peroxidation and protein carbonyl levels. Overall, our results show that oxidative stress interferes with EVT characteristics essential for the placentation process, which may contribute to the association between oxidative stress and pregnancy disorders. Our results also show that the nature of the in vitro model of oxidative stress-induction is an important determinant of the cellular consequences of oxidative stress and, therefore, of the efficacy of antioxidants.

Interaction between Metformin, Folate and Vitamin B12 and the Potential Impact on Fetal Growth and Long-Term Metabolic Health in Diabetic Pregnancies

Metformin is the first-line treatment for many people with type 2 diabetes mellitus (T2DM) and gestational diabetes mellitus (GDM) to maintain glycaemic control. Recent evidence suggests metformin can cross the placenta during pregnancy, thereby exposing the fetus to high concentrations of metformin and potentially restricting placental and fetal growth. Offspring exposed to metformin during gestation are at increased risk of being born small for gestational age (SGA) and show signs of ‘catch up’ growth and obesity during childhood which increases their risk of future cardiometabolic diseases. The mechanisms by which metformin impacts on the fetal growth and long-term health of the offspring remain to be established. Metformin is associated with maternal vitamin B₁₂ deficiency and antifolate like activity. Vitamin B₁₂ and folate balance is vital for one carbon metabolism, which is essential for DNA methylation and purine/pyrimidine synthesis of nucleic acids. Folate:vitamin B₁₂ imbalance induced by metformin may lead to genomic instability and aberrant gene expression, thus promoting fetal programming. Mitochondrial aerobic respiration may also be affected, thereby inhibiting placental and fetal growth, and suppressing mammalian target of rapamycin (mTOR) activity for cellular nutrient transport. Vitamin supplementation, before or during metformin treatment in pregnancy, could be a promising strategy to improve maternal vitamin B₁₂ and folate levels and reduce the incidence of SGA births and childhood obesity. Heterogeneous diagnostic and screening criteria for GDM and the transient nature of nutrient biomarkers have led to inconsistencies in clinical study designs to investigate the effects of metformin on folate:vitamin B₁₂ balance and child development. As rates of diabetes in pregnancy continue to escalate, more women are likely to be prescribed metformin; thus, it is of paramount importance to improve our understanding of metformin’s transgenerational effects to develop prophylactic strategies for the prevention of adverse fetal outcomes.

Mitochondrial Lon protease - depleted HeLa cells exhibit proteome modifications related to protein quality control, stress response and energy metabolism

The ATP-dependent Lon protease is located in the mitochondrial matrix and oxidized proteins are among its primary targets for their degradation. Impairment of mitochondrial morphology and function together with apoptosis were observed in lung fibroblasts depleted for Lon expression while accumulation of carbonylated mitochondrial proteins has been reported for yeast and HeLa Lon deficient cells. In addition, age-related mitochondrial dysfunction has been associated with an impairment of Lon expression. Using a HeLa cell line stably transfected with an inducible shRNA directed against Lon, we have previously observed that Lon depletion results in a mild phenotype characterized by an increase of both production of reactive oxygen species and level of oxidized proteins (Bayot et al., 2014, Biochimie, 100: 38-47). In this study using the same cell line, we now show that Lon knockdown leads to modifications of the expression of a number of specific proteins involved in protein quality control, stress response and energy metabolism, as evidenced using a 2D gel-based proteomic approach, and to alteration of the mitochondrial network morphology. We also show that these effects are associated with decreased proliferation and can be modulated by culture conditions in galactose versus glucose containing medium.

Pathobiological Mechanisms of Endothelial Dysfunction Induced by tert-Butyl Hydroperoxide via Apoptosis, Necrosis and Senescence in a Rat Model

Background: Endothelial dysfunction is one of the underlying causes for vascular diseases. tert-Butyl hydroperoxide (t-BHP), a short-chain lipid hydroperoxide analog, has been reported to cause adverse effects in different systems. However, the adverse actions of t-BHP on inducing endothelial dysfunction are unclear and remain under investigation. Aim of the present study was to identify the pathobiological mechanisms of t-BHP in rat aortic endothelial cells and thoracic aorta. Methods: Primary cultured cells were treated with vehicle or t-BHP (50, 100, 250, 500, and 1,000 μM). Cells were harvested and specific analyses regarding cellular apoptosis, necrosis, and senescence were conducted. Additionally, t-BHP (0.1, 0.2, and 0.4 mmol/kg body weight) or vehicle were administered to male rats (the young group at 6 weeks of age and the mature adult group at 24 weeks of age) daily through intraperitoneal injections. At 10 days after the first drug treatment apoptotic endothelial toxicity was evaluated by biochemical, histological, and immunofluorescent staining analyses. Results: Dose-dependent effects of t-BHP were observed for the reduction of cell viability, deterioration of cell toxicity, initiation of cell cycle arrest, and triggering of apoptosis and necrosis. Moreover, increase of cells stained positive for senescence-associated beta-galactosidase (SA-β-Gal), amelioration of telomerase activity, and precipitations of necrotic, cell cycle, and apoptotic signaling regulatory proteins were also found in the in vitro model. In the in vivo study, results indicated that t-BHP at higher doses enlarged the intima-medial thickness of descending aorta in the mature adult group, but led to aortic narrowing in the young group. Increased injuries were observed by upregulating endothelial apoptosis- and senescence-positive staining, along with caspase-3 activity and down-regulating telomerase activity. Conclusion: These results confirmed that t-BHP impaired aortic endothelial cell survival at least partially by the activation of p53-mediated signaling pathways, inhibition of cell cycle regulatory proteins, and initiation of cellular senescence-related signaling pathways. In conclusion, t-BHP was found to be a major trigger for impairing aortic endothelial cell survival and deteriorating vascular dysfunction in experimental practice.