Determinants of drug entry into the developing brain

Entry of cannabidiol into the fetal, postnatal and adult rat brain

Cannabidiol is a major component of cannabis but without known psychoactive properties. A wide range of properties have been attributed to it, such as anti-inflammatory, analgesic, anti-cancer, anti-seizure and anxiolytic. However, being a fairly new compound in its purified form, little is known about cannabidiol brain entry, especially during development. Sprague Dawley rats at four developmental ages: embryonic day E19, postnatal day P4 and P12 and non-pregnant adult females were administered intraperitoneal cannabidiol at 10 mg/kg with [3H] labelled cannabidiol. To investigate the extent of placental transfer, the drug was injected intravenously into E19 pregnant dams. Levels of [3H]-cannabidiol in blood plasma, cerebrospinal fluid and brain were estimated by liquid scintillation counting. Plasma protein binding of cannabidiol was identified by polyacrylamide gel electrophoresis and its bound and unbound fractions measured by ultrafiltration. Using available RNA-sequencing datasets of E19 rat brain, choroid plexus and placenta, as well as P5 and adult brain and choroid plexus, expression of 13 main cannabidiol receptors was analysed. Results showed that cannabidiol rapidly entered both the developing and adult brains. Entry into CSF was more limited. Its transfer across the placenta was substantially restricted as only about 50% of maternal blood plasma cannabidiol concentration was detected in fetal plasma. Albumin was the main, but not exclusive, cannabidiol binding protein at all ages. Several transcripts for cannabidiol receptors were expressed in age- and tissue-specific manner indicating that cannabidiol may have different functional effects in the fetal compared to adult brain.

Effects of paracetamol/acetaminophen on the expression of solute carriers (SLCs) in late-gestation fetal rat brain, choroid plexus and the placenta

Solute carriers (SLCs) regulate transfer of a wide range of molecules across cell membranes using facilitative or secondary active transport. In pregnancy, these transporters, expressed at the placental barrier, are important for delivery of nutrients to the fetus, whilst also limiting entry of potentially harmful substances, such as drugs. In the present study, RNA-sequencing analysis was used to investigate expression of SLCs in the fetal (embryonic day 19) rat brain, choroid plexus and placenta in untreated control animals and following maternal paracetamol treatment. In the treated group, paracetamol (15 mg/kg) was administered to dams twice daily for 5 days (from embryonic day 15 to 19). In untreated animals, overall expression of SLCs was highest in the placenta. In the paracetamol treatment group, expression of several SLCs was significantly different compared with control animals, with ion, amino acid, neurotransmitter and sugar transporters most affected. The number of SLC transcripts that changed significantly following treatment was the highest in the choroid plexus and lowest in the brain. All SLC transcripts that changed in the placenta following paracetamol treatment were downregulated. These results suggest that administration of paracetamol during pregnancy could potentially disrupt fetal nutrient homeostasis and affect brain development, resulting in major consequences for the neonate and extending into childhood.

Exposure to Paracetamol in Early Pregnancy and the Risk of Developing Cerebral Palsy: A Case-Control Study Using Serum Samples

OBJECTIVE

To investigate whether maternal paracetamol use in early pregnancy is associated with cerebral palsy (CP) in offspring.

STUDY DESIGN

We conducted a registry and biobank-based case-control study with mother-child pairs. We identified CP cases (n = 322) born between 1995 and 2014 from a nationwide CP-registry. Randomly selected controls (n = 343) and extra preterm controls (n = 258) were obtained from a birth registry. For each mother, a single serum sample from early pregnancy (gestation weeks 10-14) was retrieved from a biobank and analyzed for serum concentrations of paracetamol, categorized into unexposed (<1 ng/ml), mildly exposed (1-100 ng/ml), and highly exposed (>100 ng/ml), and in quartiles. Analyses were performed using logistic regression and adjusted for potential confounders. Separate analyses were conducted including only those children born preterm and only those born term.

RESULTS

Of the 923 participants, 36.8% were unexposed, 53.2% mildly exposed, and 10% highly exposed to paracetamol. Overall, prenatal exposure to paracetamol was not associated with CP. Sensitivity and subgroup analyses showed no clear associations between paracetamol and CP across strata of term/preterm birth as well as subtypes of CP.

CONCLUSIONS

The present study does not support an association between intrauterine exposure to paracetamol in early pregnancy and the risk of CP. However, it is important to stress that the exposure estimate is based on a single serum sample.

Paracetamol use in pregnancy: Not as safe as we may think?

Paracetamol is used by more than 50% of women worldwide during pregnancy; headache representing the most frequent indication. Several studies report that long-term exposure to paracetamol in utero is associated with adverse neurodevelopmental outcomes in children, indicating a dose-response effect. However, less or no risk is found to be associated with short-term exposure. Paracetamol most likely crosses the placenta through passive diffusion, and there are several possible mechanisms for how paracetamol might affect fetal brain development. Although the literature suggests an association between prenatal paracetamol exposure and neurodevelopmental outcomes, the role of confounders cannot be ruled out. Consequently, as a precaution, we believe that pregnant women should be recommended ideally to only use paracetamol to treat conditions that might harm the fetus, such as severe pain or a high fever. This Comment aims to put focus on the potential fetal risks of paracetamol exposure in utero.

Developmental changes in the extent of drug binding to rat plasma proteins

Binding of therapeutics to proteins in blood plasma is important in influencing their distribution as it is their free (unbound) form that is able to cross cellular membranes to enter tissues and exert their actions. The concentration and composition of plasma proteins vary during pregnancy and development, resulting in potential changes to drug protein binding. Here, we describe an ultrafiltration method to investigate the extent of protein binding of six drugs (digoxin, paracetamol, olanzapine, ivacaftor, valproate and lamotrigine) and two water soluble inert markers (sucrose and glycerol) to plasma proteins from pregnant and developing rats. Results showed that the free fraction of most drugs was lower in the non-pregnant adult plasma where protein concentration is the highest. However, plasma of equivalent protein concentration to younger pups obtained by diluting adult plasma did not always exhibit the same extent of drug binding, reinforcing the likelihood that both concentration and composition of proteins in plasma influence drug binding. Comparison between protein binding and brain drug accumulation in vivo revealed a correlation for some drugs, but not others. Results suggests that plasma protein concentration should be considered when using medications in pregnant and paediatric patients to minimise potential for fetal and neonatal drug exposure.

The choroid plexus: a missing link in our understanding of brain development and function

Studies of the choroid plexus lag behind those of the more widely known blood-brain barrier, despite a much longer history. This review has two overall aims. The first is to outline long-standing areas of research where there are unanswered questions, such as control of cerebrospinal fluid (CSF) secretion and blood flow. The second aim is to review research over the past 10 years where the focus has shifted to the idea that there are choroid plexuses located in each of the brain's ventricles that make specific contributions to brain development and function through molecules they generate for delivery via the CSF. These factors appear to be particularly important for aspects of normal brain growth. Most research carried out during the twentieth century dealt with the choroid plexus, a brain barrier interface making critical contributions to the composition and stability of the brain's internal environment throughout life. More recent research in the twenty-first century has shown the importance of choroid plexus-generated CSF in neurogenesis, influence of sex and other hormones on choroid plexus function, and choroid plexus involvement in circadian rhythms and sleep. The advancement of technologies to facilitate delivery of brain-specific therapies via the CSF to treat neurological disorders is a rapidly growing area of research. Conversely, understanding the basic mechanisms and implications of how maternal drug exposure during pregnancy impacts the developing brain represents another key area of research.

Maternal and Fetal Expression of ATP-Binding Cassette and Solute Carrier Transporters Involved in the Brain Disposition of Drugs

Evidence from preclinical and clinical studies demonstrate that pregnancy is a physiological state capable of modifying drug disposition. Factors including increased hepatic metabolism and renal excretion are responsible for impacting disposition, and the role of membrane transporters expressed in biological barriers, including the placental- and blood-brain barriers, has received considerable attention. In this regard, the brain disposition of drugs in the mother and fetus has been the subject of studies attempting to characterize the mechanisms by which pregnancy could alter the expression of ATP-binding cassette (ABC) and solute carrier (SLC) transporters. This chapter will summarize findings of the influence of pregnancy on the maternal and fetal expression of ABC and SLC transporters in the brain and the consequences of such changes on the disposition of therapeutic drugs.

Urinary paracetamol (4-acetaminophenol) and its isomer 2-acetaminophenol of Chinese pregnant women: Exposure characteristics and association with oxidative stress biomarkers

N-Acetyl-4-aminophenol (NA4AP, paracetamol/acetaminophen), a widely used pharmaceutical, is ubiquitous in urine samples of general population, raising concern about human health risks; oxidative stress is considered to be a mechanism for its toxicities. N-Acetyl-2-aminophenol (NA2AP) is an isomer of NA4AP; until now, few studies characterized exposure characteristics of NA4AP and NA2AP in pregnant women. In this work, NA4AP and NA2AP concentrations in urine samples (n = 2124) collected at three different trimesters were measured to examine their internal body burden among Chinese pregnant women (n = 708) and their associations with three oxidative stress biomarkers (OSBs, 8-OHG, 8-OHdG, and HNE-MA). NA4AP was detected in 100% of the urine samples (median concentration: 7.96 ng/mL); NA2AP was detected in 94.9% of them (median: 3.05 ng/mL). The intraclass correlation coefficients of their concentrations across three trimesters were poor (<0.4); correlations of NA4AP and NA2AP were weak (r: 0.15-0.23). Pregnant women who had higher household income or urine samples provided in summer (vs. winter) had higher concentrations of NA4AP. Pregnant women who had a college degree or above (vs. less than a high school education) had higher concentrations of NA2AP but urine samples provided in summer (vs. winter) had lower concentrations of NA2AP. The 95th percentile estimated daily intake of NA4AP (2,331 ng/kg-bw/d) based on averaged concentrations of the three trimesters was 40 times lower than the cRfD for NA4AP (2.33 vs. 93 μg/kg-bw/d). Urinary concentrations of NA4AP and NA2AP were associated with higher levels of the selected OSBs. For example, an interquartile range increase in NA4AP was associated with a 26.5% (95% CI: 23.6-29.6%) increase in 8-OHG, a 27.5% (95% CI: 23.8-31.3%) increase in 8-OHdG, and a 33.4% (95% CI: 24.7-42.7%) increase in HNE-MA (p < 0.05). This is the first study to measure their concentrations repeatedly over three trimesters, examine their exposure characteristics, and reveal their associations with the selected OSBs in pregnant women. Further studies are needed to identify non-intentional exposure sources of NA4AP, NA2AP, and another isomer of them (i.e., N-acetyl-3-aminophenol), as well as more health risks related to their exposure.

Age dependent contribution of entry via the CSF to the overall brain entry of small and large hydrophilic markers

Background

Apparent permeability of the blood brain barrier to hydrophilic markers has been shown to be higher in the developing brain. Apart from synthesis in situ, any substance detected in the brain parenchyma can originate from two sources: directly through blood vessels of brain vasculature and/or indirectly by entry from the cerebrospinal fluid (CSF) after transfer across the choroid plexuses. The relative quantitative contribution of these two routes to the overall brain entry remains unclear.

Methods

In rats at embryonic day 16, 19 and postnatal day 4 and young adults, a small (sucrose, mw. 342 Da) or a large (dextran, mw. 70 kDa) radiolabelled hydrophilic marker was injected intravenously for very short periods of time (30 s to 5 min) before collection of plasma, cerebrospinal fluid (CSF) and brain samples. Results are presented as concentration ratios between radioactivity measured in CSF or brain and that in plasma (%).

Results

The dextran brain/plasma ratio five minutes post injection was similar (2–4%) from E16 to adulthood whereas the sucrose brain/plasma ratio was significantly higher in fetal brains, but was comparable to dextran values in the adult. Sucrose CSF/plasma ratios were also significantly higher in fetal animals and decreased with age. In very short experiments involving fetal animals, entry of sucrose into the CSF after only 30 s was similar to that of dextran and both markers showed similar brain/plasma ratios.

Conclusions

In the developing brain the apparent higher brain entry of a small hydrophilic marker such as sucrose can be attributed to its higher entry into the CSF and subsequent diffusion into the brain. By contrast, movement of a larger marker like 70 kDa dextran is restricted firstly by choroid plexus epithelial tight junctions and secondly by specialised junctions in the neuroependymal interface between the CSF and brain. Brain/plasma ratios of 70 kDa dextran were similar in fetal and adult rats. Therefore 70 kDa dextran should be considered an appropriate marker if brain residual vascular space is to be measured, especially in younger animals.

Entry of the antipsychotic drug, olanzapine, into the developing rat brain in mono- and combination therapies

Background: Olanzapine is used to treat schizophrenia and bipolar disorder in women of childbearing age. Continuation of psychotropic medications throughout pregnancy and lactation is often required as cessation could be dangerous for both mother and child. However, there is a lack of information on the transfer of these drugs into the developing brain. Methods: Sprague Dawley rats at three developmental ages: embryonic day E19, postnatal day P4 and non-pregnant adult females were administered unlabelled or radiolabelled ( ³H) olanzapine (0.15 mg/kg) either as monotherapy or in combination with each of seven other common medications. Similar injections were administered to pregnant E19 females to investigate placental transfer. Olanzapine in plasma, cerebrospinal fluid (CSF) and brain was measured by liquid scintillation counting after a single dose (acute) or following 5 days of treatment (prolonged). Results: Olanzapine entry into brain and CSF was not age-dependent. Prolonged olanzapine treatment reduced placental transfer from 53% to 46% (p<0.05). Co-administration of digoxin or lamotrigine with olanzapine increased its entry into the fetal brain, whereas paracetamol decreased its entry into the CSF. Placental transfer of olanzapine was increased by co-treatment with cimetidine and digoxin, whereas co-treatment with lamotrigine, paracetamol or valproate led to a substantial decrease. Repeated co-treatment of digoxin and olanzapine increased olanzapine transfer into the brain and CSF, but not across the placenta. Overall entry of olanzapine from maternally administered drugs into the fetal brain was higher after combination therapy with cimetidine and digoxin. Conclusions: Co-administration of olanzapine with some commonly used drugs affected its entry into the fetus and its developing brain to a greater extent than in adults. It appears that protection of the fetal brain for these drugs primarily comes from the placenta rather than from the fetal brain barriers. Results suggest that drug combinations should be used with caution particularly during pregnancy.

Lithium administered to pregnant, lactating and neonatal rats: entry into developing brain

Background

Little is known about the extent of drug entry into developing brain, when administered to pregnant and lactating women. Lithium is commonly prescribed for bipolar disorder. Here we studied transfer of lithium given to dams, into blood, brain and cerebrospinal fluid (CSF) in embryonic and postnatal animals as well as adults.

Methods

Lithium chloride in a clinically relevant dose (3.2 mg/kg body weight) was injected intraperitoneally into pregnant (E15–18) and lactating dams (birth-P16/17) or directly into postnatal pups (P0–P16/17). Acute treatment involved a single injection; long-term treatment involved twice daily injections for the duration of the experiment. Following terminal anaesthesia blood plasma, CSF and brains were collected. Lithium levels and brain distribution were measured using Laser Ablation Inductively Coupled Plasma-Mass Spectrometry and total lithium levels were confirmed by Inductively Coupled Plasma-Mass Spectrometry.

Results

Lithium was detected in blood, CSF and brain of all fetal and postnatal pups following lithium treatment of dams. Its concentration in pups’ blood was consistently below that in maternal blood (30–35%) indicating significant protection by the placenta and breast tissue. However, much of the lithium that reached the fetus entered its brain. Levels of lithium in plasma fluctuated in different treatment groups but its concentration in CSF was stable at all ages, in agreement with known stable levels of endogenous ions in CSF. There was no significant increase of lithium transfer into CSF following application of Na⁺/K⁺ ATPase inhibitor (digoxin) in vivo, indicating that lithium transfer across choroid plexus epithelium is not likely to be via the Na⁺/K⁺ ATPase mechanism, at least early in development. Comparison with passive permeability markers suggested that in acute experiments lithium permeability was less than expected for diffusion but similar in long-term experiments at P2.

Conclusions

Information obtained on the distribution of lithium in developing brain provides a basis for studying possible deleterious effects on brain development and behaviour in offspring of mothers undergoing lithium therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-021-00285-w.

Paracetamol use during pregnancy - a call for precautionary action

Paracetamol (N-acetyl-p-aminophenol (APAP), otherwise known as acetaminophen) is the active ingredient in more than 600 medications used to relieve mild to moderate pain and reduce fever. APAP is widely used by pregnant women as governmental agencies, including the FDA and EMA, have long considered APAP appropriate for use during pregnancy when used as directed. However, increasing experimental and epidemiological research suggests that prenatal exposure to APAP might alter fetal development, which could increase the risks of some neurodevelopmental, reproductive and urogenital disorders. Here we summarize this evidence and call for precautionary action through a focused research effort and by increasing awareness among health professionals and pregnant women. APAP is an important medication and alternatives for treatment of high fever and severe pain are limited. We recommend that pregnant women should be cautioned at the beginning of pregnancy to: forego APAP unless its use is medically indicated; consult with a physician or pharmacist if they are uncertain whether use is indicated and before using on a long-term basis; and minimize exposure by using the lowest effective dose for the shortest possible time. We suggest specific actions to implement these recommendations. This Consensus Statement reflects our concerns and is currently supported by 91 scientists, clinicians and public health professionals from across the globe.

Efflux transporters in rat placenta and developing brain: transcriptomic and functional response to paracetamol

Adenosine triphosphate binding cassette (ABC) transporters transfer lipid-soluble molecules across cellular interfaces either directly or after enzymatic metabolism. RNAseq analysis identified transcripts for ABC transporters and enzymes in rat E19, P5 and adult brain and choroid plexus and E19 placenta. Their functional capacity to efflux small molecules was studied by quantitative analysis of paracetamol (acetaminophen) and its metabolites using liquid scintillation counting, autoradiography and ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). Animals were treated acutely (30 min) and chronically (5 days, twice daily) with paracetamol (15 mg/kg) to investigate ability of brain and placenta barriers to regulate ABC transport functionality during extended treatment. Results indicated that transcripts of many efflux-associated ABC transporters were higher in adult brain and choroid plexus than at earlier ages. Chronic treatment upregulated certain transcripts only in adult brain and altered concentrations of paracetamol metabolites in circulation of pregnant dams. Combination of changes to metabolites and transport system transcripts may explain observed changes in paracetamol entry into adult and fetal brains. Analysis of lower paracetamol dosing (3.75 mg/kg) indicated dose-dependent changes in paracetamol metabolism. Transcripts of ABC transporters and enzymes at key barriers responsible for molecular transport into the developing brain showed alterations in paracetamol pharmacokinetics in pregnancy following different treatment regimens.

Ways to Address Perinatal Mast Cell Activation and Focal Brain Inflammation, including Response to SARS-CoV-2, in Autism Spectrum Disorder

The prevalence of autism spectrum disorder (ASD) continues to increase, but no distinct pathogenesis or effective treatment are known yet. The presence of many comorbidities further complicates matters, making a personalized approach necessary. An increasing number of reports indicate that inflammation of the brain leads to neurodegenerative changes, especially during perinatal life, "short-circuiting the electrical system" in the amygdala that is essential for our ability to feel emotions, but also regulates fear. Inflammation of the brain can result from the stimulation of mast cells-found in all tissues including the brain-by neuropeptides, stress, toxins, and viruses such as SARS-CoV-2, leading to the activation of microglia. These resident brain defenders then release even more inflammatory molecules and stop "pruning" nerve connections, disrupting neuronal connectivity, lowering the fear threshold, and derailing the expression of emotions, as seen in ASD. Many epidemiological studies have reported a strong association between ASD and atopic dermatitis (eczema), asthma, and food allergies/intolerance, all of which involve activated mast cells. Mast cells can be triggered by allergens, neuropeptides, stress, and toxins, leading to disruption of the blood-brain barrier (BBB) and activation of microglia. Moreover, many epidemiological studies have reported a strong association between stress and atopic dermatitis (eczema) during gestation, which involves activated mast cells. Both mast cells and microglia can also be activated by SARS-CoV-2 in affected mothers during pregnancy. We showed increased expression of the proinflammatory cytokine IL-18 and its receptor, but decreased expression of the anti-inflammatory cytokine IL-38 and its receptor IL-36R, only in the amygdala of deceased children with ASD. We further showed that the natural flavonoid luteolin is a potent inhibitor of the activation of both mast cells and microglia, but also blocks SARS-CoV-2 binding to its receptor angiotensin-converting enzyme 2 (ACE2). A treatment approach should be tailored to each individual patient and should address hyperactivity/stress, allergies, or food intolerance, with the introduction of natural molecules or drugs to inhibit mast cells and microglia, such as liposomal luteolin.

Entry of antiepileptic drugs (valproate and lamotrigine) into the developing rat brain

Background: Women with epilepsy face difficult choices whether to continue antiepileptic drug treatment during pregnancy, as uncontrolled seizures carry great risk to mother and fetus but continuing treatment may have adverse effects on baby’s development. This study aimed at evaluating antiepileptic drug entry into developing brain. Methods: Anaesthetised pregnant, non-pregnant adult females, postnatal and fetal rats were injected intraperitoneally with different doses, single or in combinations, of valproate and lamotrigine, all within clinical range. Injectate included 3H-labelled drug. After 30min, CSF, blood and brain samples were obtained; radioactivity was measured using liquid scintillation counting. Some animals were also exposed to valproate in feed throughout pregnancy and into neonatal period. Drug levels were measured by liquid chromatography coupled to mass spectrometry (LC-MS). Results are given as CSF or tissue/plasma% as index of drug entry. Results: Entry of valproate into brain and CSF was higher at E19 and P4 compared to adult but was not dose-dependent;  placental transfer increased significantly at highest dose of 100mg/Kg. Lamotrigine entry into the brain was dose dependent only at E19. Chronic valproate treatment, or combination of valproate and lamotrigine had little effect on either drug entry, except for reduced valproate brain entry in adult brain with chronic treatment. Placental transfer decreased significantly after chronic valproate treatment. LC-MS measurement of valproate in adults confirmed that rat plasma values were within the clinical range and CSF/plasma and brain/plasma ratios for LC-MS and 3H-valproate were similar. Conclusion: Results suggest that entry of valproate may be higher in developing brain, the capacity of barrier mechanism is mostly unaffected by doses within the clinical range, with or without addition of lamotrigine. Chronic valproate exposure may result in upregulation in cellular mechanisms restricting its entry into the brain. Entry of lamotrigine was little different at different ages and was not dose dependent.

Entry of antiepileptic drugs (valproate and lamotrigine) into the developing rat brain

Background: Women with epilepsy face difficult choices whether to continue antiepileptic drug treatment during pregnancy, as uncontrolled seizures carry great risk to mother and fetus but continuing treatment may have adverse effects on baby’s development. This study aimed at evaluating antiepileptic drug entry into developing brain.

Methods: Anaesthetised pregnant, non-pregnant adult females, postnatal and fetal rats were injected intraperitoneally with different doses, single or in combinations, of valproate and lamotrigine, within clinical range. Injectate included  ³H-labelled drug. After 30min, CSF, blood and brain samples were obtained; radioactivity measured using liquid scintillation counting. Some animals were also exposed to valproate in feed throughout pregnancy and into neonatal period. Drug levels measured by liquid chromatography coupled to mass spectrometry (LC-MS). Results given as CSF or tissue/plasma% as index of drug entry.

Results: Entry of valproate into brain and CSF was higher at E19 and P4 compared to adult and was dose-dependent except at E19; placental transfer increased significantly at highest dose of 100mg/kg. Lamotrigine entry into the brain was dose dependent only at E19. Chronic valproate treatment, or combination of valproate and lamotrigine had little effect on either drug entry, except for reduced valproate brain entry in adult brain with chronic treatment. Placental transfer decreased significantly after chronic valproate treatment. LC-MS measurement of valproate in adults confirmed that rat plasma values were within the clinical range and CSF/plasma and brain/plasma ratios for LC-MS and  ³H-valproate were similar.

Conclusion: Results suggest that entry of valproate may be higher in developing brain, the capacity of barrier mechanism is mostly unaffected by doses within the clinical range, with or without addition of lamotrigine. Chronic valproate exposure may result in upregulation in cellular mechanisms restricting its entry into the brain. Entry of lamotrigine was little different at different ages and was not dose dependent.

Coloring Molecules with Explainable Artificial Intelligence for Preclinical Relevance Assessment

Graph neural networks are able to solve certain drug discovery tasks such as molecular property prediction and de novo molecule generation. However, these models are considered "black-box" and "hard-to-debug". This study aimed to improve modeling transparency for rational molecular design by applying the integrated gradients explainable artificial intelligence (XAI) approach for graph neural network models. Models were trained for predicting plasma protein binding, hERG channel inhibition, passive permeability, and cytochrome P450 inhibition. The proposed methodology highlighted molecular features and structural elements that are in agreement with known pharmacophore motifs, correctly identified property cliffs, and provided insights into unspecific ligand-target interactions. The developed XAI approach is fully open-sourced and can be used by practitioners to train new models on other clinically relevant endpoints.

Transfer of rhodamine-123 into the brain and cerebrospinal fluid of fetal, neonatal and adult rats

Background

Adenosine triphosphate binding cassette transporters such as P-glycoprotein (PGP) play an important role in drug pharmacokinetics by actively effluxing their substrates at barrier interfaces, including the blood-brain, blood-cerebrospinal fluid (CSF) and placental barriers. For a molecule to access the brain during fetal stages it must bypass efflux transporters at both the placental barrier and brain barriers themselves. Following birth, placental protection is no longer present and brain barriers remain the major line of defense. Understanding developmental differences that exist in the transfer of PGP substrates into the brain is important for ensuring that medication regimes are safe and appropriate for all patients.

Methods

In the present study PGP substrate rhodamine-123 (R123) was injected intraperitoneally into E19 dams, postnatal (P4, P14) and adult rats. Naturally fluorescent properties of R123 were utilized to measure its concentration in blood-plasma, CSF and brain by spectrofluorimetry (Clariostar). Statistical differences in R123 transfer (concentration ratios between tissue and plasma ratios) were determined using Kruskal-Wallis tests with Dunn’s corrections.

Results

Following maternal injection the transfer of R123 across the E19 placenta from maternal blood to fetal blood was around 20 %. Of the R123 that reached fetal circulation 43 % transferred into brain and 38 % into CSF. The transfer of R123 from blood to brain and CSF was lower in postnatal pups and decreased with age (brain: 43 % at P4, 22 % at P14 and 9 % in adults; CSF: 8 % at P4, 8 % at P14 and 1 % in adults). Transfer from maternal blood across placental and brain barriers into fetal brain was approximately 9 %, similar to the transfer across adult blood-brain barriers (also 9 %). Following birth when placental protection was no longer present, transfer of R123 from blood into the newborn brain was significantly higher than into adult brain (3 fold, p < 0.05).

Conclusions

Administration of a PGP substrate to infant rats resulted in a higher transfer into the brain than equivalent doses at later stages of life or equivalent maternal doses during gestation. Toxicological testing of PGP substrate drugs should consider the possibility of these patient specific differences in safety analysis.

Acetaminophen Attenuates invasion and alters the expression of extracellular matrix enzymes and vascular factors in human first trimester trophoblast cells

Acetaminophen is one of the most common medications taken during pregnancy, considered safe for maternal health and fetal development. However, recent epidemiological studies have associated prenatal acetaminophen use with several developmental disorders in offspring. As acetaminophen can freely cross into and through the placenta, epidemiological associations with prenatal acetaminophen use may reflect direct actions on the fetus and/or the impact of altered placental functions. In the absence of rigorous mechanistic studies, our understanding of how prenatal acetaminophen exposure can cause long-term effects in offspring is limited. The objective of this study was to determine whether acetaminophen can alter key functions of a major placental cell type by utilizing immortalized human first trimester trophoblast cells. This study employed a comparative analysis with the nonsteroidal, anti-inflammatory drug aspirin, which has established effects in first trimester trophoblast cells. We report that immortalized trophoblast cells express the target proteins of acetaminophen and aspirin: cyclooxygenase (COX) -1 and -2. Unlike aspirin, acetaminophen significantly repressed the expression of angiogenesis and vascular remodeling genes in HTR-8/SVneo cells. Moreover, acetaminophen impaired trophoblast invasion by over 80%, while aspirin had no effect on invasion. Acetaminophen exposure reduced the expression of matrix metalloproteinase (MMP)-2 and -9 and increased the expression of tissue inhibitors of matrix metalloproteinases 2, leading to an imbalance in the ratio of proteolytic enzymes. Finally, a bioinformatic approach identified novel acetaminophen-responsive gene networks associated with key trophoblast functions and disease. Together these results suggest that prenatal acetaminophen use may interfere with critical trophoblast functions early in gestation, which may subsequently impact fetal development.

Effects of paracetamol (acetaminophen) on gene expression and permeability properties of the rat placenta and fetal brain

Background: Paracetamol (acetaminophen) is widely used in pregnancy and generally regarded as "safe" by regulatory authorities. Methods: Clinically relevant doses of paracetamol were administered intraperitoneally to pregnant rats twice daily from embryonic day E15 to 19 (chronic) or as a single dose at E19 (acute). Control samples were from un-treated age-matched animals. At E19, rats were anaesthetised, administered a final paracetamol dose, uteruses were opened and fetuses exposed for sample collection. For RNA sequencing, placentas and fetal brains were removed and flash frozen. Fetal and maternal plasma and cerebrospinal fluid were assayed for ⍺-fetoprotein and interleukin 1β (IL1β). Brains were fixed and examined (immunohistochemistry) for plasma protein distribution. Placental permeability to a small molecule ( 14C-sucrose) was tested by injection into either mother or individual fetuses; fetal and maternal blood was sampled at regular intervals to 90 minutes. Results: RNA sequencing revealed a large number of genes up- or down-regulated in placentas from acutely or chronically treated animals compared to controls. Most notable was down-regulation of three acute phase plasma proteins (⍺-fetoprotein, transferrin, transthyretin) in acute and especially chronic experiments and marked up-regulation of immune-related genes, particularly cytokines, again especially in chronically treated dams. IL1β increased in plasma of most fetuses from treated dams but to variable levels and no IL1β was detectable in plasma of control fetuses or any of the dams. Increased placental permeability appeared to be only from fetus to mother for both 14C-sucrose and ⍺-fetoprotein, but not in the reverse direction. In the fetal brain, gene regulatory changes were less prominent than in the placenta of treated fetuses and did not involve inflammatory-related genes; there was no evidence of increased blood-brain barrier permeability. Conclusion: Results suggest that paracetamol may induce an immune-inflammatory-like response in placenta and more caution should be exercised in use of paracetamol in pregnancy.

Effects of paracetamol (acetaminophen) on gene expression and permeability properties of the rat placenta and fetal brain

Background: Paracetamol (acetaminophen) is widely used in pregnancy and generally regarded as "safe" by regulatory authorities. Methods: Clinically relevant doses of paracetamol were administered intraperitoneally to pregnant rats twice daily from embryonic day E15 to 19 (chronic) or as a single dose at E19 (acute). Control samples were from un-treated age-matched animals. At E19, rats were anaesthetised, administered a final paracetamol dose, uteruses were opened and fetuses exposed for sample collection. For RNA sequencing, placentas and fetal brains were removed and flash frozen. Fetal and maternal plasma and cerebrospinal fluid were assayed for α-fetoprotein and interleukin 1β (IL1β). Brains were fixed and examined (immunohistochemistry) for plasma protein distribution. Placental permeability to a small molecule ( 14C-sucrose) was tested by injection into either mother or individual fetuses; fetal and maternal blood was sampled at regular intervals to 90 minutes. Results: RNA sequencing revealed a large number of genes up- or down-regulated in placentas from acutely or chronically treated animals compared to controls. Most notable was down-regulation of three acute phase plasma proteins (α-fetoprotein, transferrin, transthyretin) in acute and especially chronic experiments and marked up-regulation of immune-related genes, particularly cytokines, again especially in chronically treated dams. IL1β increased in plasma of most fetuses from treated dams but to variable levels and no IL1β was detectable in plasma of control fetuses or any of the dams. Increased placental permeability appeared to be only from fetus to mother for both 14C-sucrose and α-fetoprotein, but not in the reverse direction. In the fetal brain, gene regulatory changes were less prominent than in the placenta of treated fetuses and did not involve inflammatory-related genes; there was no evidence of increased blood-brain barrier permeability. Conclusion: Results suggest that paracetamol may induce an immune-inflammatory-like response in placenta and more caution should be exercised in use of paracetamol in pregnancy.

Medications for pregnant women: A balancing act between the interests of the mother and of the fetus

Drug entry into the adult brain is controlled by efflux mechanisms situated in various brain barrier interfaces. The effectiveness of these protective mechanisms in the embryo, fetus and newborn brain is less clear. The longstanding belief that "the" blood-brain barrier is absent or immature in the fetus and newborn has led to many misleading statements with potential clinical implications. Here we review the properties of brain barrier mechanisms in the context of drug entry into the developing brain and discuss the limited number of studies published on the subject. We noticed that most of available literature suffers from some experimental limitations, notably that drug levels in fetal blood and cerebrospinal fluid have not been measured. This means that the relative contribution to the overall brain protection provided by individual barriers such as the placenta (which contains similar efflux mechanisms) and the brain barriers cannot be separately ascertained. Finally, we propose that systematic studies in appropriate animal models of drug entry into the brain at different stages of development would provide a rational basis for use of medications in pregnancy and in newborns, especially prematurely born, where protection usually provided by the placenta is no longer present.