Cerebellar level of neurotransmitters in rats exposed to paracetamol during development

A quantitative weight-of-evidence review of preclinical studies examining the potential developmental neurotoxicity of acetaminophen

Acetaminophen [paracetamol; N-acetyl-para-aminophenol (APAP)] is an antipyretic/analgesic commonly used in the treatment of fever and mild to moderate pain, headache, myalgia, and dysmenorrhea. Recent literature has questioned the safety of acetaminophen use during pregnancy, with an emphasis on whether exposure to the developing nervous system results in behavioral changes consistent with autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), and/or other cognitive deficits in the offspring. No previous review has used a fully detailed, quantitative weight-of-evidence (QWoE) approach to critically examine the preclinical acetaminophen data with regards to potential developmental neurotoxicity (DNT). Following regulatory guidance, a QWoE framework using prespecified scoring criteria was developed consistent with previous approaches to characterize potential adverse DNT outcomes with considerations for biological relevance of the response to adverse outcomes (outcome score) and the strength of methods and study design (methods score). Considerations for the methods score included (1) experimental design, (2) details/reliability of measurement(s), (3) data transparency, and (4) translational/methodological relevance. Considerations for the outcome score included response-related (1) statistical significance, (2) dose-response, (3) relevance/reliability/magnitude, (4) plausibility, and (5) translational relevance, including consideration of systemic toxicity/hepatotoxicity and therapeutic and/or non-systemically toxic doses and durations of use. Application of this QWoE framework to the 34 in vivo studies identified that assess the potential DNT of acetaminophen resulted in 188 QWoE entries documented across 11 DNT endpoints: social behavior, stereotypic behavior, behavioral rigidity, attention/impulsivity, hyperactivity, anxiety-like behavior, sensorimotor function, spatial learning/memory, nonspatial learning/memory, neuroanatomy, and neurotransmission. For each endpoint, the mean outcome score and methods score were calculated for total entries and for entries segregated by sex to assist in determining data quality and potential adversity. Informed by all 188 entries, the QWoE analysis demonstrated data of moderate quality showing no consistent evidence of DNT in male and female rodents following exposure to acetaminophen at therapeutic and/or nonsystemically toxic doses. Although some of the DNT endpoints (behavioral rigidity, attention/impulsivity, spatial learning/memory, neuroanatomy, and neurotransmission) generally displayed a more limited dataset and/or relatively lower data quality, similar conclusions were drawn based on results indicating a lack of biological relevance and reliability of reported adverse effects. Overall, this QWoE analysis on the preclinical in vivo data demonstrates no consistent evidence of adverse effects following developmental exposure to acetaminophen at therapeutic and/or non-systemically toxic doses on the structure and function of the nervous system, including neuroanatomical, neurotransmission, and behavioral endpoints.

Impaired brainstem auditory evoked potentials after in utero exposure to high dose paracetamol exposure

Paracetamol is an analgesic and antipyretic medication regarded as the safest over-the-counter pain and fever relief option during pregnancy. Paracetamol and its metabolites are known to reach the developing fetus through direct placental transfer and can cross the blood brain barrier. Several recent, large-scale epidemiologic studies suggest that in utero paracetamol exposure can increase the risk of neurodevelopmental conditions, including autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD) and developmental delay (DD). Since auditory processing deficits are a common feature of ASD, we hypothesized that animals exposed to paracetamol in utero will have impaired auditory brainstem function. We investigated this hypothesis by recording and analyzing click-evoked auditory brainstem responses (ABR) at postnatal day 21 and 29 in Sprague-Dawley rats. In utero exposure to high dose paracetamol exposure had no impact on body or brain weight. However, high dose paracetamol exposure did significantly delay ear opening and resulted in elevated ABR thresholds, and longer wave and interwave latencies. These changes in wave latency extended to the highest click intensity tested but were most severe near threshold. This data suggests that development and function of the auditory brainstem may be impacted by high dose paracetamol exposure and that simple, non-invasive tests of auditory function have utility as an early screening tool for neurodevelopmental disorders.

Examining the relationship of acetaminophen use during pregnancy with early language development in children

BACKGROUND

Acetaminophen is the only analgesic considered safe for use throughout pregnancy. Recent studies suggest that use during pregnancy may be associated with poorer neurodevelopmental outcomes in children, but few have examined language development.

METHODS

The Illinois Kids Development Study is a prospective birth cohort in east-central Illinois. Between December 2013 and March 2020, 532 newborns were enrolled and had exposure data available. Participants reported the number of times they took acetaminophen six times across pregnancy. Language data were collected at 26.5-28.5 months using the MacArthur-Bates Communicative Development Inventories (CDI; n = 298), and 36-38 months using the Speech and Language Assessment Scale (SLAS; n = 254).

RESULTS

Taking more acetaminophen during the second or third trimester was associated with marginally smaller vocabularies and shorter utterance length (M3L) at 26.5-28.5 months. More acetaminophen use during the third trimester was also associated with increased odds of M3L scores ≤25th percentile in male children. More use during the second or third trimester was associated with lower SLAS scores at 36-38 months. Third trimester use was specifically related to lower SLAS scores in male children.

CONCLUSIONS

Higher prenatal acetaminophen use during pregnancy may be associated with poorer early language development.

IMPACT

Taking more acetaminophen during pregnancy, particularly during the second and third trimesters, was associated with poorer scores on measures of language development when children were 26.5-28.5 and 36-38 months of age. Only male children had lower scores in analyses stratified by child sex. To our knowledge, this is the first study that has used a standardized measure of language development to assess the potential impact of prenatal exposure to acetaminophen on language development. This study adds to the growing body of literature suggesting that the potential impact of acetaminophen use during pregnancy on fetal neurodevelopment should be carefully evaluated.

The relationship of prenatal acetaminophen exposure and attention-related behavior in early childhood

Acetaminophen is currently the only analgesic considered safe for use throughout pregnancy, but recent studies indicate that prenatal exposure to acetaminophen may be related to poorer neurodevelopmental outcomes. Multiple studies have suggested that it may be associated with attention problems, but few have examined this association by trimester of exposure. The Illinois Kids Development Study is a prospective birth cohort located in east-central Illinois. Exposure data were collected between December 2013 and March 2020, and 535 newborns were enrolled during that period. Mothers reported the number of times they took acetaminophen at six time points across pregnancy. When children were 2, 3, and 4 years of age, caregivers completed the Child Behavior Checklist for ages 1.5-5 years (CBCL). Associations of acetaminophen use during pregnancy with scores on the Attention Problems and ADHD Problems syndrome scales, the Internalizing and Externalizing Behavior composite scales, and the Total Problems score were evaluated. Higher acetaminophen exposure during the second trimester of fetal development was associated with higher Attention Problems, ADHD Problems, Externalizing Behavior, and Total Problems scores at ages 2 and 3. Higher second trimester exposure was only associated with higher Externalizing Behavior and Total Problems scores at 4 years. Higher cumulative exposure across pregnancy was associated with higher Attention Problems and ADHD Problems scores at ages 2 and 3. Findings suggest that prenatal acetaminophen exposure, especially during the second trimester, may be related to problems with attention in early childhood.

Investigating Paracetamol's Role as a Potential Treatment for Parkinson's Disease: Ab Initio Analysis of Dopamine, l-DOPA, Paracetamol, and NAPQI Interactions with Enzymes Involved in Dopamine Metabolism

Recently, it was found that paracetamol can extend the therapeutic window of l-DOPA treatment for Parkinson's disease [Golding (2019) BJPharm, 4(2), Article 619]. It has been posited that the effect could be due to paracetamol and its metabolite, NAPQI, inhibiting pain signals in the spinal column. In this work, we examine the possibility that the therapeutic effect of the paracetamol for the Parkinson's disease patient may be due to an inhibition of the enzymes that metabolize dopamine and/or l-DOPA, thus effectively extending the lifetime of the l-DOPA treatment. In this work, we use the M062X/6-311+G* level of theory to calculate the electronic binding energies (including explicit desolvation) of several ligands (paracetamol, NAPQI, dopamine, and l-DOPA) with a series of enzymes important to the production and metabolism of dopamine and compare them to calculated binding energy values for the natural substrates for those enzymes in order to predict possible inhibition. Benchmark interaction energies for a subset of the systems studied are calculated using the more accurate second-order Møller-Plesset perturbation (MP2) method in order to calibrate the accuracy of the M062X method. If we assume that the interaction energies calculated here can serve as a proxy for in vivo inhibition, then we can predict that paracetamol and NAPQI should not inhibit the natural production of dopamine and may in fact inhibit the metabolism of l-DOPA and dopamine, thus extending the length of l-DOPA treatments.

Perinatal exposure to paracetamol: Dose and sex-dependent effects in behaviour and brain's oxidative stress markers in progeny

Paracetamol (PAR) has been employed worldwide for pain and fever treatment during pregnancy and lactation. Epidemiologic studies have shown that exposure to PAR can increase the risk for developmental disorders, such as attention-deficit hyperactive disorder and autism spectrum disorder. This study aimed to investigate if gestational and lactational exposure to human-relevant doses of PAR could alter behavioural and brain oxidative stress parameters in the rat`s offspring. Wistar dams were gavaged daily with water or PAR (35 mg/kg/ or 350 mg/kg) during gestational day 6 to weaning (postnatal day 21). Behavioural assessments occurred at post-natal days 10 (nest seeking test), 27 (behavioural stereotypy) and 28 (three chamber sociability test and open field). Concentration of advanced oxidation protein products (AOPP), reduced glutathione (GSH), lipid hydroperoxides (LOOH) and activity of superoxide dismutase (SOD) were estimate in prefrontal cortex, hippocampus, striatum and cerebellum of 22-day-old rats. Compared to CON animals, males exposed to PAR during pregnancy and lactation augmented apomorphine-induced stereotyped behaviour (350 mg/kg) and ambulation in open-field test (35 mg/kg). Reduced exploratory behaviour in three chamber sociability test was observed in pups exposed to PAR at 350 mg/kg in both sexes. PAR treatment decreased hippocampal GSH level and striatal SOD activity in males exposed to 35 mg/kg, suggesting the vulnerability of these areas in PAR-induced developmental neurotoxicity. Findings suggest PAR use during pregnancy and lactation as a potential risk factor for neurodevelopmental disorders with males being more susceptible.

Early exposure to paracetamol reduces level of testicular testosterone and changes gonadal expression of genes relevant for steroidogenesis in rats offspring

In this study, we investigated the effects of early paracetamol treatment on the testicular level of testosterone and expression of genes important for steroid biosynthesis and reproduction in male rats offspring. Rats were continuously exposed to paracetamol at doses of 5 or 15 mg/kg b.w. during pregnancy and the first two months of the postpartum development. Testosterone level was determined by ELISA. Profile of gene expression for the testicular steroidogenic factors were evaluated using the Real-Time PCR. Our results showed that paracetamol reduces testicular testosterone level and causes compensatory transactivation of genes important for steroidogenesis and reproductive capacity. We have observed significant over-expression of several genes involved in cholesterol transport and steroid biosynthesis e.g., genes for steroidogenic acute regulatory protein, hydroxysteroid dehydrogenases, luteinizing hormone subunit beta, gonadotropin and androgen receptors. Up-regulation of these genes with parallel testosterone reduction in the testicles could be the possible mechanism that maintains and prevents the loss of the steroidogenic function.

Paracetamol - An old drug with new mechanisms of action

Paracetamol (acetaminophen) is the most commonly used over-the-counter (OTC) drug in the world. Despite its popularity and use for many years, the safety of its application and its mechanism of action are still unclear. Currently, it is believed that paracetamol is a multidirectional drug and at least several metabolic pathways are involved in its analgesic and antipyretic action. The mechanism of paracetamol action consists in inhibition of cyclooxygenases (COX-1, COX-2, and COX-3) and involvement in the endocannabinoid system and serotonergic pathways. Additionally, paracetamol influences transient receptor potential (TRP) channels and voltage-gated Kv7 potassium channels and inhibits T-type Cav3.2 calcium channels. It also exerts an impact on L-arginine in the nitric oxide (NO) synthesis pathway. However, not all of these effects have been clearly confirmed. Therefore, the aim of our paper was to summarize the current state of knowledge of the mechanism of paracetamol action with special attention to its safety concerns.

How to translate neurocognitive and behavioural outcome data in animals exposed to paracetamol to the human perinatal setting?

Introduction

There are epidemiological - not necessary causal - observations that link perinatal paracetamol (acetaminophen) exposure to impaired neuro-cognition and behaviour, but animal models may assist to better understand the mechanisms.

Material and methods

To provide an overview on preclinical data and mechanisms explored, we conducted a structured literature search on animal models and neuro-cognition and behavioural outcome following perinatal paracetamol exposure.

Results

This search resulted in 20 papers (rat (n = 9), zebrafish larvae (n = 6), mice (n = 5)), published between 2009 and 2020. Eight discussed pregnancy/fetal paracetamol exposure, 6 juvenile, 6 studies combined pregnancy and juvenile exposure. Quality assessment (SYRCLE's bias risk) showed a heterogeneous pattern with blinding issues. Most papers (n = 16) described paracetamol exposure without indication, except for an induced fever and repetitive needle pricking (rat), brain injury (mice), and a zebrafish nociception model. Reported outcomes related to biochemistry (mono-amines, amino acids, protein expression), anatomy (teratogen, morphology, nuclear size) or behaviour (spatial memory, motor, social behaviour and exploration, sexual behaviour). On mechanisms, the cumulative data support an interesting 'cannabinoid' hypothesis to link paracetamol to neuro-cognitive and behavioural outcome. Besides limited species diversity, there is relevant within-species paracetamol dosing variability (dose, duration) with undocumented exposure.

Conclusions

Models should further integrate clinical indications, as non-exposure is the obvious safest setting in the absence of an indication. Besides pain and fever and related to the cannabinoid hypothesis, this should include perinatal brain injury, as there is animal experimental evidence that cannabinoids are neuroprotective in newborn brain injury or asphyxia, further supported by evidence from non-perinatal models of paracetamol-related neuroprotective effects.

Narcotic-Sparing Approaches and the Shift Toward Paracetamol in Neonatal Intensive Care

Effective analgesia in neonates is relevant not only because of ethical aspects or empathy, but it is a crucial and integral part of medical and nursing care. However, there is also emerging evidence - although mainly in animal models - on the relation between the exposure to narcotics and impaired neurodevelopmental outcome, resulting in a CATCH-22 scenario. Consequently, a balanced approach is needed with the overarching intention to attain adequate pain management with minimal side effects. Despite the available evidence-based guidance on narcotics in ventilated neonates, observations on drug utilization still suggest an overall increase in exposure with extensive variability between units. This increased exposure over time and the extensive variability is concerning given the limited evidence of benefits and potential harm.Implementation strategies are effective to reduce exposure to narcotics but result in increased paracetamol exposure. We therefore summarized the evidence on paracetamol use in procedural pain management, in minor to moderate as well as major pain syndromes in neonates. While there are sufficient data on short-term safety, there are still concerns on long-term side effects. These concerns relate to neurobehavioral outcome, atopy or fertility, and are at present mainly driven by epidemiological perinatal observations, together with postulated mechanisms.We conclude that future clinical research objectives should still focus on the need to develop better assessment tools to quantify pain and on the need for high-quality data on long-term outcome of therapeutic interventions - also for paracetamol - and exploration of the mechanisms involved.

Anthropogenic contaminants of high concern: Existence in water resources and their adverse effects

Existence of anthropogenic contaminants (ACs) in different environmental matrices is a serious and unresolved concern. For instance, ACs from different sectors, such as industrial, agricultural, and pharmaceutical, are found in water bodies with considerable endocrine disruptors potency and can damage the biotic components of the environment. The continuous ACs exposure can cause cellular toxicity, apoptosis, genotoxicity, and alterations in sex ratios in human beings. Whereas, aquatic organisms show bioaccumulation, trophic chains, and biomagnification of ACs through different entry route. These problems have been found in many countries around the globe, making them a worldwide concern. ACs have been found in different environmental matrices, such as water reservoirs for human consumption, wastewater treatment plants (WWTPs), drinking water treatment plants (DWTPs), groundwaters, surface waters, rivers, and seas, which demonstrate their free movement within the environment in an uncontrolled manner. This work provides a detailed overview of ACs occurrence in water bodies along with their toxicological effect on living organisms. The literature data reported between 2017 and 2018 is compiled following inclusion-exclusion criteria, and the obtained information was mapped as per type and source of ACs. The most important ACs are pharmaceuticals (diclofenac, ibuprofen, naproxen, ofloxacin, acetaminophen, progesterone ranitidine, and testosterone), agricultural products or pesticides (atrazine, carbendazim, fipronil), narcotics and illegal drugs (amphetamines, cocaine, and benzoylecgonine), food industry derivatives (bisphenol A, and caffeine), and personal care products (triclosan, and other related surfactants). Considering this threatening issue, robust detection and removal strategies must be considered in the design of WWTPs and DWTPs.

Prenatal paracetamol exposure and child neurodevelopment: A review

BACKGROUND

The non-prescription medication paracetamol (acetaminophen, APAP) is currently recommended as a safe pain and fever treatment during pregnancy. However, recent studies suggest a possible association between APAP use in pregnancy and offspring neurodevelopment.

OBJECTIVES

To conduct a review of publications reporting associations between prenatal APAP use and offspring neurodevelopmental outcomes.

METHODS

Relevant sources were identified through a key word search of multiple databases (Medline, CINAHL, OVID and TOXNET) in September 2016. All English language observational studies of pregnancy APAP and three classes of neurodevelopmental outcomes (autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), and intelligence quotient (IQ)) were included. One reviewer (AZB) independently screened all titles and abstracts, extracted and analyzed the data.

RESULTS

64 studies were retrieved and 55 were ineligible. Nine prospective cohort studies fulfilled all inclusion criteria. Data pooling was not appropriate due to heterogeneity in outcomes. All included studies suggested an association between prenatal APAP exposure and the neurodevelopmental outcomes; ADHD, ASD, or lower IQ. Longer duration of APAP use was associated with increased risk. Associations were strongest for hyperactivity and attention-related outcomes. Little modification of associations by indication for use was reported.

CONCLUSIONS

Together, these nine studies suggest an increased risk of adverse neurodevelopmental outcomes following prenatal APAP exposure. Further studies are urgently needed with; precise indication of use and exposure assessment of use both in utero and in early life. Given the current findings, pregnant women should be cautioned against indiscriminate use of APAP. These results have substantial public health implications.

Perinatal and neonatal use of paracetamol for pain relief

Paracetamol (acetaminophen) is the most widely used drug to treat pain or fever in pregnant women or neonates, but its pharmacokinetics (PK) and pharmacodynamics (PD) warrant a focused analysis. During pregnancy, there is an important increase in paracetamol clearance. Consequently, it is reasonable to anticipate that the analgesic effect of paracetamol will decrease faster, whereas higher doses may result in even higher oxidative toxic metabolites. Therefore, most peripartal PD data relate to multimodal analgesia strategies. In neonates, weight/size is the most relevant covariate of paracetamol PK. This resulted in proposed dosing regimens containing higher doses than currently prescribed in the label for term neonates. Using adequate dosing, paracetamol is a poor procedural analgesic, is effective for mild-to-moderate pain, and has morphine-sparing effects. Short-term safety has been well documented, and there is active research investigating the potential association between paracetamol exposure and atopy, fertility, and neurobehavior.