Nicholas Ieronimakis

Human gestation is characterized by dynamic changes in maternal physiology and maturation of tissue functions before and after birth. The fetus and neonate are highly dependent upon transfer of maternal nutrients via the placenta and lactating mammary gland, which frequently involve selective membrane transporter proteins. At the same time, developmental changes in fetal and infant transport mechanisms critical for regulating absorption at the intestinal and blood–brain barriers are occurring. Coordinate regulation of cellular entry and efflux of nutrients, supplements, and xenobiotics, including drugs and environmental chemicals, must occur during this critical developmental period. In 2023, the National Institutes of Health launched the Transporter Elucidation Network (TEN) across four centers. This initiative applies experimental, computational, and translational approaches to (1) identify S o L ute C arrier (SLC) superfamily and A TP‐ b inding c assette (ABC) transporters in the human placenta, mammary gland, as well as the pediatric brain and intestinal barriers and, (2) characterize their localization, expression, function, and regulation. The Network seeks to identify functional determinants of transporters as gatekeepers of entry to placenta, mammary gland and brain, and applies structural biology, proteomics, metabolomics, organoids, liquid biopsies, and microphysiological systems to this end. Computational strategies, such as machine learning, virtual screening, physiologically based pharmacokinetics, and perinatal epidemiology complement our experimental approaches. This paper highlights the TEN's multidisciplinary strategies to address current challenges in perinatal and pediatric transporter research and its commitment to advancing state‐of‐the‐art tools and new approach methodologies to fill critical gaps in our understanding of nutrient and xenobiotic exposure during early human development.

Solute carriers ( SLC ) and ATP‐binding cassette ( ABC ) transporters are essential for placental solute exchange and fetal protection, yet their transcriptomic profiles in the human placenta remain poorly characterized. Although fetal sex influences placental development and function, its impact on transporter expression is unclear. Using RNA sequencing, we profiled SLC and ABC transporter expression in two anatomical regions of term human placentas ( N = 10) with balanced fetal sex distribution and controlled clinical features. In the intervillous region, 276 SLC s were detected, with 60% expressed at low levels (CPM < 25) and 110 (40%) expressed at higher levels (CPM 25–1650). Four transporters— SLC2A1 (GLUT1), SLC44A2 (CTL2), SLC38A2 (SNAT2), and SLC38A1 (SNAT1)—showed the highest expression (CPM > 500). Functional annotation of 110 SLC s revealed transporters for amino acids, metals, and inorganic ions each accounted for ~9%. Other well‐represented SLC s included xenobiotic and vitamin transporters. Mitochondrial, lysosomal, and endoplasmic reticulum and Golgi transporters together accounted for ~37%, while 11% were orphan transporters. Thirty‐seven ABC transporter transcripts were detected, primarily associated with xenobiotic and lipid transport. Compared with the intervillous region, 1676 genes—including 32 SLC and 2 ABC transporters—were differentially expressed in the decidual region. Although 117 genes in the intervillous region and 79 genes in the decidual region exhibited sexually dimorphic expression, none were SLC s. Notably, male placentas showed higher expression of ABCB1 (P‐gp), confirmed by qPCR and western blot. Our findings provide a transcriptomic map of placental transporters and highlight a potential sex‐specific difference on ABCB1 expression and xenobiotic protection.

Background: Chronic pain is a major cause of distress and disability, and biomarkers may aid in the assessment and treatment of it. Urine metabolites may be valuable bioindicators that can provide biological insight regarding chronic pain. Objectives: To investigate the relationship between a multimarker composite measure of metabolites and patient-reported outcomes scores in adults with chronic pain, using data from a pragmatic clinical trial with a sequential, multiple-assignment randomized trial design. Methods: Self-reported measures and urine samples from 169 active-duty service members with chronic pain were collected. Urine was analyzed using a preestablished panel of metabolites, including four previously identified biomarkers of pain: kynurenic acid, pyroglutamic acid, ethylmalonic acid, and methylmalonate. Multivariable linear regression models—adjusted for participant characteristics such as age and sex—were used to cross-sectionally examine the relationship between 11 patient-reported outcomes (fatigue, sleep-related impairment, anxiety, depression, anger, pain catastrophizing, physical function, pain interference, satisfaction with participation with social roles, pain intensity, and pain impact score) and the four urine metabolites both individually and as a composite (urine metabolite pain indicator, or UMPI). Given the study’s small sample size and exploratory nature, a significance threshold of p ≤ .10 was used for all analyses. Results: The UMPI showed statistically significant associations with five self-reported measures (fatigue, anxiety, depression, physical functioning, and pain impact score); adjusted Pearson correlations ranged from .18 to .25. Individual metabolite analyses supported these findings, with all relationships between individual metabolites and self-reported measures showing positive associations. Kynurenic acid and ethylmalonic acid showed the strongest associations, each having statistically significant relationships with four individual self-reported measures, while pyroglutamic acid had statistically significant relationships with three self-reported measures and methylmalonate with none. The UMPI demonstrated feasible reliability. Discussion: Our finding of associations between the UMPI and components of the self-reported measures supports the development of the UMPI and these four urine metabolites as biomarkers for chronic pain outcomes. Further research is planned and will be essential for establishing mechanistic insight and guiding biomarker development within the context of pain management.

Longitudinal changes in the blood proteome during gestation relate to fetal development and maternal homeostasis. Charting the maternal blood proteome in normal pregnancies is critical for establishing a baseline reference when assessing complications and disease. Using mass spectrometry-based shotgun proteomics, we surveyed the maternal plasma proteome across uncomplicated pregnancies. Results indicate a significant rise in proteins that govern placentation and are vital to the development and health of the fetus. Importantly, we uncovered proteome signatures that strongly correlated with gestational age. Fold increases and correlations between the plasma concentrations of ADAM12 (ρ = 0.973), PSG1 (ρ = 0.936), and/or CSH1/2 (ρ = 0.928) with gestational age were validated with ELISA. Proteomic and validation analyses demonstrate that the maternal plasma concentration of ADAM12, either independently or in combination with either PSG1 or CSH1/2, correlates with gestational age within ±8 days throughout pregnancy. These findings suggest that the gestational age in healthy pregnancies may be determined by referencing the concentration of select plasma proteins.

Zika virus infection can result in devastating pregnancy outcomes when it crosses the placental barrier. For human pregnancies, the mechanisms of vertical transmission remain enigmatic. Utilizing a human placenta-cotyledon perfusion model, we examined Zika virus exposure in the absence of maternal factors. To distinguish responses related to viral infectionvs. recognition, we evaluated cotyledons perfused with either active or inactivated Zika virus. Active Zika virus exposure resulted in infection, cell death and syncytium injury. Pathology corresponded with transcriptional changes related to inflammation and innate immunity. Inactive Zika virus exposure also led to syncytium injury and related changes in gene expression but not cell death. Our observations reveal pathologies and innate immune responses that are dependent on infection or virus placenta interactions independent of productive infection. Importantly, our findings indicate that Zika virus can infect and compromise placentas in the absence of maternal humoral factors that may be protective.

Objective: The proliferation of improvised masks during the COVID-19 pandemic has raised questions regarding filter effectiveness and safety. We sought to compare the effectiveness of commonly used improvised filter materials against N95 industry standards. Methods: Six different filter materials commonly used in the community were tested using both single- and multi-layer configurations with the TSI 8130 automated filter tester in accordance with National Institute for Occupational Safety and Health (NIOSH) standards for N95 respirators. Results: Only three of the tested filter material configurations met N95 parameters with regard to filtration efficiency and pressure drop across the filter material–the: True-HEPA filter, 4-layer MERV 13 and 14 HVAC filters. Conclusions: Many proposed filter materials for improvised masks do not meet current industry standards and may pose safety and efficacy concerns. Care should be taken when selecting materials for this critical respirator component, particularly for health care workers or others at high risk for pathogen exposure.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Prematurity is associated with perinatal neuroinflammation and injury. Screening for genetic modulators in an LPS murine model of preterm birth revealed the upregulation of Nr4a1, an orphan nuclear transcription factor that is normally absent or limited in embryonic brains. Concurrently, Nr4a1 was downregulated with magnesium sulfate (MgSO₄) and betamethasone (BMTZ) treatments administered to LPS exposed dams. To understand the role of Nr4a1 in perinatal brain injury, we compared the preterm neuroinflammatory response in Nr4a1 knockout (KO) versus wild type (wt) mice. Key inflammatory factors Il1b, Il6 and Tnf, and Iba1+ microglia were significantly lower in Nr4a1 KO versus wt brains exposed to LPS in utero. Treatment with MgSO₄/BMTZ mitigated the neuroinflammatory process in wt but not Nr4a1 KO brains. These results correspond with a reduction in cerebral hemorrhage in wt but not mutant embryos from dams given MgSO₄/BMTZ. Further analysis with Nr4a1-GFP-Cre × tdTomato loxP reporter mice revealed that the upregulation of Nr4a1 with perinatal neuroinflammation occurs in the cerebral vasculature. Altogether, this study implicates Nr4a1 in the developing vasculature as a potent mediator of neuroinflammatory brain injury that occurs with preterm birth. It is also possible that MgSO₄/BMTZ mitigates this process by direct or indirect inhibition of Nr4a1.