Developmental pharmacogenetics: a general paradigm for application to neonatal pharmacology and toxicology

CYP3A4/5 genotypes and age codetermine tacrolimus concentration and dosage in pediatric heart transplant recipients

Tacrolimus (TAC) is the cornerstone of immunosuppressive therapy for pediatric heart transplantation (HTx) recipients. However, little information is known on the interaction of developmental and genetic variants on TAC disposition in this population, which makes TAC dose optimization more difficult. The aim of study was to investigate the relationship between genotypes and age on TAC concentrations and dosage during the early post-operation period in pediatric HTx recipients. Sixty-six pediatric HTx recipients were enrolled and divided into three groups according to the age (<6, ≥6-≤12, 12-18 years old). CYP3A4/5, POR and ABCB1 polymorphisms were genotyped. The associations between genotypes and age on TAC dose-adjusted trough concentrations (C₀/D), dose requirement as well as acute kidney injury (AKI) were evaluated. CYP3A5*3 and CYP3A4*1G were significantly correlated with TAC C₀/D and dose requirement in the pediatric recipients ≥ 6 years. The C₀/D in children aged ≥ 6-≤12 years and 12-18 years is 2.8 and 4.2 fold of these < 6 years old, respectively. TAC dose requirements in children aged < 6 years were 2.4 times and 3.5 times of these aged ≥ 6-≤12 years and 12-18 years, respectively. Among the same CYP3A5*3 or CYP3A4*1G genotypes, age was positively increased with TAC C₀/D and negatively correlated with targeted dose. No genetic variants were found to be associated with AKI during the early post-operation period. CYP3A4/5 genotypes and age should be taken into consideration to TAC dosage in pediatric HTx recipients.

Integrated in a systems pharmacology approach, pharmacogenetics holds the promise for personalized medicine in neonates

Tweetable abstract Integrated in a systems pharmacology approach, pharmacogenetics holds the promise for personalized medicine in neonates. This has been illustrated for some diseases specific to neonates.

The Impact of Pharmacogenetics on Pharmacokinetics and Pharmacodynamics in Neonates and Infants: A Systematic Review

In neonates, pharmacogenetics has an additional layer of complexity. This is because in addition to genetic variability in genes that code for proteins relevant to clinical pharmacology, there are rapidly maturational changes in these proteins. Consequently, pharmacotherapy in neonates has unique challenges. To provide a contemporary overview on pharmacogenetics in neonates, we conducted a systematic review to identify, describe and quantify the impact of pharmacogenetics on pharmacokinetics and -dynamics in neonates and infants (PROSPERO, CRD42022302029). The search was performed in Medline, Embase, Web of Science and Cochrane, and was extended by a PubMed search on the ‘top 100 Medicines’ (medicine + newborn/infant + pharmacogen*) prescribed to neonates. Following study selection (including data in infants, PGx related) and quality assessment (Newcastle–Ottawa scale, Joanna Briggs Institute tool), 55/789 records were retained. Retained records relate to metabolizing enzymes involved in phase I [cytochrome P450 (CYP1A2, CYP2A6, CYP2B6, CYP2C8/C9/C18, CYP2C19, CYP2D6, CYP3A5, CYP2E1)], phase II [glutathione-S-transferases, N-acetyl transferases, UDP-glucuronosyl-transferase], transporters [ATP-binding cassette transporters, organic cation transporters], or receptor/post-receptor mechanisms [opioid related receptor and post-receptor mechanisms, tumor necrosis factor, mitogen-activated protein kinase 8, vitamin binding protein diplotypes, corticotrophin-releasing hormone receptor-1, nuclear receptor subfamily-1, vitamin K epoxide reductase complex-1, and angiotensin converting enzyme variants]. Based on the available overview, we conclude that the majority of reported pharmacogenetic studies explore and extrapolate observations already described in older populations. Researchers commonly try to quantify the impact of these polymorphisms in small datasets of neonates or infants. In a next step, pharmacogenetic studies in neonatal life should go beyond confirmation of these associations and explore the impact of pharmacogenetics as a covariate limited to maturation of neonatal life (ie, fetal malformations, breastfeeding or clinical syndromes). The challenge is to identify the specific factors, genetic and non-genetic, that contribute to the best benefit/risk balance.

Development of a generic lifelong physiologically based biokinetic model for exposome studies

The current study within the frame of the HEALS project aims at the development of a lifelong physiologically based biokinetic (PBBK) model for exposome studies. The aim was to deliver a comprehensive modelling framework for addressing a large chemical space. Towards this aim, the delivered model can easily adapt parameters from existing ad-hoc models or complete the missing compound specific parameters using advanced quantitative structure activity relationship (QSAR). All major human organs are included, as well as arterial, venous, and portal blood compartments. Xenobiotics and their metabolites are linked through the metabolizing tissues. This is mainly the liver, but also other sites of metabolism might be considered (intestine, brain, skin, placenta) based on the presence or not of the enzymes involved in the metabolism of the compound of interest. Each tissue is described by three mass balance equations for (a) red blood cells, (b) plasma and interstitial tissue and (c) cells respectively. The anthropometric parameters of the models are time dependent, so as to provide a lifetime internal dose assessment, as well as to describe the continuously changing physiology of the mother and the developing fetus. An additional component of flexibility is that the biokinetic processes that relate to metabolism are related with either Michaelis-Menten kinetics, as well as intrinsic clearance kinetics. The capability of the model is demonstrated in the assessment of internal exposure and the prediction of expected biomonitored levels in urine for three major compounds within the HEALS project, namely bisphenol A (BPA), Bis(2-ethylhexyl) phthalate (DEHP) and cadmium (Cd). The results indicated that the predicted urinary levels fit very well with the ones from human biomonitoring (HBM) studies; internal exposure to plasticizers is very low (in the range of ng/L), while internal exposure to Cd is in the range of μg/L.

Tacrolimus treatment in childhood refractory nephrotic syndrome: A retrospective study on efficacy, therapeutic drug monitoring, and contributing factors to variable blood tacrolimus levels

Tacrolimus, an immunosuppressive drug, was recommended by the 2012 KDIGO guidelines to treat nephrotic syndrome (NS) in children and adults. However, it has high interpatient pharmacokinetic variability and exposure levels should be monitored, although there are no specified target concentrations. This retrospective study aimed to review efficacy and safety after concomitant treatment with tacrolimus and prednisone, and to identify factors that contribute to the variable blood-trough-concentration-to-dose (C₀/Dose) ratio in children with refractory NS (RNS). A 6-month therapy induced complete or partial remission in 95% of patients. One-year follow-up indicated a high remission rate and low nephrotoxicity. Under maintenance dosages, approximately 95% of the C₀ values were 2-7 ng/mL. Body weight (BW), age, CYP3A5 polymorphisms were the factors affecting the C₀/Dose ratio. The C₀/Dose ratio in patients with a BW of <20 kg was 1.5-fold than that in patients with BW of ≥40 kg. Moreover, the C₀/Dose ratio in patients aged 1-≤6 and 6-≤12 years was significantly lower than that in patients aged 12-≤18 years, by 25% and 48%, respectively. There were no significant association between CYP3A5 genotyping and C₀/Dose ratio in younger children (1-≤6 years), rather than older children (6-≤18 years). In conclusion, routine CYP3A5 genotyping should be considered in children aged over 6 years and exposure levels (C₀) of 2-7 ng/mL may be feasible when tacrolimus is combined with low-dose prednisone to treat childhood RNS.

Pediatric Age Groups and Approach to Studies

Pediatric clinical trials are often requested according to specific age ranges. In the past and still today, these ages may correspond to developmental stages, such as newborn, infancy, childhood, and adolescence. Selection of ages for pediatric participation in medication studies should correspond to ages of rapid changes in pharmacokinetics and pharmacodynamics. Age-related changes in several enzymes involved in drug metabolism and glomerular filtration are described as examples of optimal ages for study of specific drugs according to their pathways of disposition.

Physiology-based toxicokinetic modelling in the frame of the European Human Biomonitoring Initiative

Given the opportunities provided by internal dosimetry modelling in the interpretation of human biomonitoring (HBM) data, the assessment of the links between exposure to chemicals and observed HBM data can be effectively supported by PBTK modelling. This paper gives a comprehensive review of available human PBTK models for compounds selected as a priority by the European Human Biomonitoring Initiative (HBM4EU). We highlight their advantages and deficiencies and suggest steps for advanced internal dose modelling. The review of the available PBTK models highlighted the conceptual differences between older models compared to the ones developed recently, reflecting commensurate differences in research questions. Due to the lack of coordinated strategies for deriving useful biomonitoring data for toxicokinetic properties, significant problems in model parameterisation still remain; these are further increased by the lack of human toxicokinetic data due to ethics issues. Finally, questions arise as well as to the extent they are really representative of interindividual variability. QSARs for toxicokinetic properties is a complementary approach for PBTK model parameterisation, especially for data poor chemicals. This approach could be expanded to model chemico-biological interactions such as intestinal absorption and renal clearance; this could serve the development of more complex generic PBTK models that could be applied to newly derived chemicals. Another gap identified is the framework for mixture interaction terms among compounds that could eventually interact in metabolism. From the review it was concluded that efforts should be shifted toward the development of generic multi-compartmental and multi-route models, supported by targeted biomonitoring coupled with parameterisation by both QSAR approach and experimental (in-vivo and in-vitro) data for newly developed and data poor compounds.

Risk characterization of bisphenol-A in the Slovenian population starting from human biomonitoring data

The current study aims to characterize exposure and risk associated to bisphenol-A (BPA) exposure in Slovenia, starting from biomonitoring data. Based on the urinary data, daily intake for the individuals was back-calculated using a physiology based biokinetic (PBBK) model properly parameterized for BPA, coupled with an exposure reconstruction algorithm. Re-running the PBBK model in forward mode allowed the estimation of biologically effective dose (free plasma BPA) and the respective daily area under the curve (AUC). Finally, risk characterization ratio was derived using both external and internal dose metrics. The urinary BPA levels were found low, with GM of 0.79, 1.51 and 0.20 μg/g creatinine for mothers, children and fathers respectively, similar to the levels of other European countries. Based on the above and accounting for the dynamics of exposure and biokinetics, daily intake was estimated, median exposure levels have been estimated equal to 0.019, 0.035 and 0.005 μg/kg_bw/d for mothers, fathers and children respectively. The highest estimated intake level was found in a child, equal to 0.87 μg/kg_bw/d, while the maximum intake for mothers and fathers were 0.7 and 0.8 μg/kg_bw/d respectively. The respective RCR levels using the EFSA t-TDI of 4 μg/kg_bw/d were 2 magnitudes of order lower below 1, independently of the selected method. It has to be noted that had daily intake been estimated solely based on the urinary concentrations mass balance, the estimated intake would be lower, as a result of the oversimplification on exposure and elimination time dynamics. This highlights the importance for using PBBK modelling based exposure reconstruction schemes for rapidly metabolized and excreted compounds such as BPA, as well as the study design of efficient sampling for rapidly metabolized compounds.

Advancing Chemical Risk Assessment through Human Physiology-Based Biochemical Process Modeling

Physiology-Based BioKinetic (PBBK) models are of increasing interest in modern risk assessment, providing quantitative information regarding the absorption, metabolism, distribution, and excretion (ADME). They focus on the estimation of the effective dose at target sites, aiming at the identification of xenobiotic levels that are able to result in perturbations to the biological pathway that are potentially associated with adverse outcomes. The current study aims at the development of a lifetime PBBK model that covers a large chemical space, coupled with a framework for human biomonitoring (HBM) data assimilation. The methodology developed herein was demonstrated in the case of bisphenol A (BPA), where exposure analysis was based on European HBM data. Based on our calculations, it was found that current exposure levels in Europe are below the temporary Tolerable Daily Intake (t-TDI) of 4 μg/kg_bw/day proposed by the European Food Safety Authority (EFSA). Taking into account age-dependent bioavailability differences, internal exposure was estimated and compared with the biologically effective dose (BED) resulting from translating the EFSA temporary total daily intake (t-TDI) into equivalent internal dose and an alternative internal exposure reference value, namely biological pathway altering dose (BPAD); the use of such a refined exposure metric, showed that environmentally relevant exposure levels are below the concentrations associated with the activation of biological pathways relevant to toxicity based on High Throughput Screening (HTS) in vitro studies.

Pharmacogenetics: Applications to Pediatric Patients

Individual genomic differences may affect drug disposition and effects of many drugs, and identification of biomarkers are crucial to personalize dosage and optimize response. In children, developmental changes associated with growth and maturation translate into different relationships between genotype and phenotype and different responses to treatment compared to adults. This review aims to summarize some developmental aspects of pharmacogenetics, based on practical examples.

Safety, dosing, and pharmaceutical quality for studies that evaluate medicinal products (including biological products) in neonates

The study of medications among pediatric patients has increased worldwide since 1997 in response to new legislation and regulations, but these studies have not yet adequately addressed the therapeutic needs of neonates. Additionally, extant guidance developed by regulatory agencies worldwide does not fully address the specificities of neonatal drug development, especially among extremely premature newborns who currently survive. Consequently, an international consortium from Canada, Europe, Japan, and the United States was organized by the Critical Path Institute to address the content of guidance. This group included neonatologists, neonatal nurses, parents, regulators, ethicists, clinical pharmacologists, specialists in pharmacokinetics, specialists in clinical trials and pediatricians working in the pharmaceutical industry. This group has developed a comprehensive, referenced White Paper to guide neonatal clinical trials of medicines - particularly early phase studies. Key points include: the need to base product development on neonatal physiology and pharmacology while making the most of knowledge acquired in other settings; the central role of families in research; and the value of the whole neonatal team in the design, implementation and interpretation of studies. This White Paper should facilitate successful clinical trials of medicines in neonates by informing regulators, sponsors, and the neonatal community of existing good practice.

Integrated exposure and risk characterization of bisphenol-A in Europe

The current study aims at a comprehensive risk characterization of bisphenol A (BPA) supported by an integrated exposure modelling framework that comprises far field and near field exposure modelling coupled to a dynamic lifetime PBTK model. Exposure analysis was done on European data of BPA food residues and human biomonitoring (HBM). The latter were further assimilated through an advanced exposure reconstruction modelling framework to estimate the corresponding external and internal systemic dose of BPA and its metabolites. Special attention was paid on the assessment of exposure to BPA during critical developmental stages such as gestation by modelling the mother-fetus toxicokinetic interaction. Our findings showed that current exposure levels in Europe are below the temporary Tolerable Daily Intake (t-TDI) of 4 μg/kg_bw/d proposed by the European Food Safety Authority. Taking into account age-dependent bioavailability differences, internal exposure of premature neonates hosted in intensive care units was reckoned close to the biologically effective dose (BED) resulting from translating the EFSA temporary total daily intake (t-TDI) into equivalent internal dose. Use of the ToxCast21 Biological Pathway Altering Dose (BPAD) as an alternative internal exposure reference value, resulted in increased margins of safety compared to the conventional exposure/risk characterization scheme.

Neonatal pain management: still in search for the Holy Grail

Inadequate pain management but also inappropriate use of analgesics in early infancy has negative effects on neurodevelopmental outcome. As a consequence, neonatal pain management is still in search for the Holy Grail. At best, effective pain management is based on prevention, assessment, and treatment followed by a re-assessment of the pain to determine if additional treatment is still necessary. Unfortunately, epidemiological observations suggest that neonates are undergoing painful procedures very frequently, unveiling the need for effective preventive, non-pharmacological strategies. In addition, assessment is still based on validated, multimodal, but subjective pain assessment tools. Finally, in neonatal intensive care units, there is a shift in clinical practices (e.g., shorter intubation and ventilation), and this necessitates the development and validation of new pharmacological treatment modalities. To illustrate this, a shift in the use of opioids to paracetamol has occurred and short-acting agents (remifentanil, propofol) are more commonly administered to neonates. In addition to these new modalities and as part of a more advanced approach of the developmental pharmacology of analgesics, pharmacogenetics also emerged as a tool for precision medicine in neonates. To assure further improvement of neonatal pain management the integration of pharmacogenetics with the usual covariates like weight, age and/or disease characteristics is needed.

Pharmacokinetics in neonatal prescribing: evidence base, paradigms and the future

Paediatric patients, particularly preterm neonates, present many pharmacological challenges. Due to the difficulty in conducting clinical trials in these populations dosing information is often extrapolated from adult populations. As the processes of absorption, distribution, metabolism and excretion of drugs change throughout growth and development extrapolation presents risk of over or underestimating the doses required. Information about the development these processes, particularly drug metabolism pathways, is still limited with weight based dose adjustment presenting the best method of estimating pharmacokinetic changes due to growth and development. New innovations in pharmacokinetic research, such as population pharmacokinetic modelling, present unique opportunities to conduct clinical trials in these populations improving the safety and effectiveness of the drugs used. More research is required into this area to ensure the best outcomes for our most vulnerable patients.

Neonatal drug therapy: The first frontier of therapeutics for children

Knowledge about the safe and effective use of medicines in neonates has increased substantially but has resulted in few label changes. Drugs developed for use in adults are reshaped and tailored to specific neonatal indications. However, the use of drugs in neonates should not only mirror adult pharmacotherapy, but should be driven by their own specific needs. Therefore, building collaborative networks may assist to develop a newborn-driven research agenda addressing their clinical needs and diseases.

Pharmacogenomics and pharmacoepigenomics in pediatric medicine

In the past several years, human genetics studies have progressed from monogenic to complex and common diseases because of the advancement in technologies. There is increased knowledge of the pharmacokinetics and pharmacogenomics of the drugs in adults as well as in children. These technological developments provided new diagnostic, prognostic, and therapeutic opportunities. We are now in a position to address many additional ambitious questions. For instance, in clinical medicine, interindividual variation in drug response is a major problem. Some of the heterogeneity of drug safety and efficacy among individuals can be explained by pharmacogenomics. It has also the potential to improve the treatment in both adults and children. In pediatrics however, there is ontogeny and metabolic capacity in children is different compared to adults. Several specific developmental changes may underlie some of the variability in drug response seen in children. They may also be responsible for adverse drug reactions (ADRs). Therefore, much of the diversity in drug effects cannot be explained by studying the genomic diversity alone. It is necessary to include the effect of growth (involves variations in gene expression) along with genetic differences when explaining the variability in treatment response. In this respect epigenomics may expand the scope of pharmacogenomics towards optimization of drug therapy. Future studies must focus on periods of maturation of the drug-metabolizing enzymes and polymorphisms in their genes by using candidate gene approach, gene expression analysis, genome-wide haplotype mapping, and proteomics. The integration of genetic data and clinical phenotypes along with the role of other factors is necessary to evaluate both efficacy and ADRs of any drug. It may require extensive genetic epidemiological studies spanning over many years.

Clinical pharmacology of intravenous paracetamol in perinatal medicine

Clinical pharmacology aims to predict drug-related effects based on compound and population specific pharmacokinetics (PK, concentration-time), and pharmacodynamics (PD, concentration-effect). Consequently, dosing needs to be based on the physiological characteristics of the individual patient. Pregnancy and early infancy hereby warrant focused assessment. The specific characteristics of both subpopulations will be illustrated based on observations on intravenous (iv) paracetamol PK and PD collected in these specific populations. At delivery, there is a significant higher paracetamol clearance (+ 45%, L/h) when compared to non-pregnant observations. This higher clearance is in part explained by a proportional increase in oxidative metabolite production, but mainly an increase in glucuronidation. When focusing on PD, an association between maternal paracetamol exposure and atopy in infancy and fetal gastroshizis has been reported. In early infancy, paracetamol clearance is significantly lower and mainly depends on size (weight 0.75), while also the distribution volume is higher (L/kg). Reports on hepatic tolerance, haemodynamic stability and impact of body temperature have been published while the concentration effect profile for analgesia seems to be similar between neonates and children. Similar to maternal exposure, there are reports on the association with atopy. Studies on the use of paracetamol to close the patent ductus arteriosus are ongoing. At least, these observations provide evidence on the need to study commonly administered anesthetics in such specific subpopulations with specific focus on both population specific PK and PD to further improve patient tailored pharmacotherapy.

Developmental pharmacogenetics of immunosuppressants in pediatric organ transplantation

Cyclosporine, tacrolimus, sirolimus, and mycophenolate mofetil are the primary immunosuppressants used on pediatric organ transplantation. Therapeutic drug monitoring is used in daily practice, because their clinical use is hampered by a narrow therapeutic index and large variability. Tailoring immunosuppressive therapy to the individual patient to optimize efficacy and minimize toxicity is therefore essential. Because research in pharmacogenetics already identified polymorphisms impacting their pharmacokinetic parameters in adults, developmental pharmacogenetics of immunosuppressants holds promises for optimizing dosage regimens and improving clinical outcome in children. In this review, we focus on the impact of age and pharmacogenetics on these immunosuppressants in children undergoing organ transplantation.

Fetal medicine and treatment

Fetal medicine covers a broad spectrum of conditions that can be diagnosed before birth. Different disorders will require different treatment strategies and there is often an important ontogenetic aspect on how and when treatment can be implemented. Due to the limited availability there is a general lack of knowledge on how pharmacotherapy can be provided in the most efficient way. Until recently most knowledge about how different drugs are transferred and metabolized in the human fetus is based on very limited observational studies on concentrations of drugs in fetal blood and other fetal compartments. It might be that the rapid development of other non-invasive methods for fetal diagnostics such as isolation of fetal DNA and RNA in maternal serum, NMR imaging and other techniques could in the future be explored in fetal pharmacotherapy. Introduction of new treatment strategies are often based on extrapolation from experience in neonates and adults. However some fetal conditions are very specific for this time period in life. This especially entails disturbances in development as malformations, early growth restriction and several congenital disorders. Here it might be required to introduce new treatment strategies without any previous experience in humans. Example of this ethical dilemma is gene therapy for lung growth in severe cases of diaphragmatic hernia and early growth restriction. The risk-benefit issues need to be discussed in all these alternatives. However, it is likely that the concept of the human fetus as a potential patient is still in its infancy and with an improved understanding about fetal patho-physiology there will be a continued need for better knowledge of pharmacotherapy during this crucial time period in life.

Identifying genomic and developmental causes of adverse drug reactions in children

Adverse drug reactions are a concern for all clinicians who utilize medications to treat adults and children; however, the frequency of adult and pediatric adverse drug reactions is likely to be under-reported. In this age of genomics and personalized medicine, identifying genetic variation that results in differences in drug biotransformation and response has contributed to significant advances in the utilization of several commonly used medications in adults. In order to better understand the variability of drug response in children however, we must not only consider differences in genotype, but also variation in gene expression during growth and development, namely ontogeny. In this article, recommendations for systematically approaching pharmacogenomic studies in children are discussed, and several examples of studies that investigate the genomic and developmental contribution to adverse drug reactions in children are reviewed.

Developmental pharmacogenetics in pediatric rheumatology: utilizing a new paradigm to effectively treat patients with juvenile idiopathic arthritis with methotrexate

Although methotrexate is widely used in clinical practice there remains significant lack of understanding of its mechanisms of action and the factors that contribute to the variability in toxicity and response seen clinically. In addition to differences in drug administration, factors that affect pharmacokinetics and pharmacodynamics such as genetic variation may explain individual differences in drug biotransformation. However, the pediatric population has an additional factor to consider, namely the ontogeny of gene expression which may result in variation throughout growth and development. We review the current understanding of methotrexate biotransformation and the concept of ontogeny, with further discussion of how to implement a developmental pharmacogenomics approach in future studies.