Cerebral folate receptor α (FRα) is essential for transporting folate into the central nervous system, supporting normal biological functions and fetal neurodevelopment. We aimed to provide in vivo measurements of folic acid dynamics at FRα in non-human primate brains using positron emission tomography (PET) and [18F]AzaFol, a high-affinity FRα radioligand. A 0.01 mg/kg intravenous dose of folic acid, comparable to pregnancy supplementation doses (400–800 µg), dramatically reduced FRα availability in the choroid plexus (CP), based on uptake profiles and exploratory kinetic modeling. Following this dose, [18F]AzaFol uptake increased, potentially capturing (1) FRα-mediated transport of folic acid and (2) real-time FRα recycling, which may restore binding sites as serum folic acid levels decline, reducing receptor competition. Experiments with constant infusion of folic acid during PET imaging aimed to identify the possible folic acid transport rate and serum concentrations at which this process reaches a steady state. Pharmacokinetic analysis suggests full FRα blockage with serum folic acid concentrations within the range of 63–90 ng/mL and cumulative dose slightly above 0.01 mg/kg. Findings enhance the understanding of folic acid’s in vivo pharmacology at cerebral FRα and may inform future studies on disorders in which impaired folic acid transport is suspected, either at the CP or at the placenta.
AlamCKondoMO’ConnorDL, et al. Clinical implications of folate transport in the central nervous system. Trends Pharmacol Sci2020; 41: 349–361.
2.
Centers for Disease Control and Prevention (CDC). Spina bifida and anencephaly before and after folic acid mandate—United States, 1995-1996 and 1999-2000. JAMA2004; 53: 362–365.
3.
Food and Drug Administration (FDA). Food standards: amendment of standards of identity for enriched grain products to require addition of folic acid. Fed Regist1996; 61: 8781–8797.
4.
US Preventive Services Task Force; BarryMJNicholsonWK, et al. Folic acid supplementation to prevent neural tube defects: US Preventive Services Task Force reaffirmation recommendation statement. JAMA2023; 330: 454–459.
5.
EryilmazHDowlingKFHuntingtonFC, et al. Association of prenatal exposure to population-wide folic acid fortification with altered cerebral cortex maturation in youths. JAMA Psychiatry2018; 75: 918–928.
6.
CzeizelAE.Folic acid in the prevention of neural tube defects. J Pediatr Gastroenterol Nutr1995; 20: 4–16.
7.
CanfieldMACollinsJSBottoLD, et al. Changes in the birth prevalence of selected birth defects after grain fortification with folic acid in the United States: findings from a multi-state population-based study. Birth Defects Res A Clin Mol Teratol2005; 73: 679–689.
8.
LevineSZKodeshAViktorinA, et al. Association of maternal use of folic acid and multivitamin supplements in the periods before and during pregnancy with the risk of autism spectrum disorder in offspring. JAMA Psychiatry2018; 75: 176–184.
9.
SchmidtRJTancrediDJOzonoffS, et al. Maternal periconceptional folic acid in-take and risk of autism spectrum disorders and developmental delay in the CHARGE (CHildhood Autism Risks from Genetics) case-control study. Am J Clin Nutr2012; 96: 80–89.
RamaekersVTRothenbergSPSequeiraJM, et al. Autoantibodies to folate receptors in the cerebral folate deficiency syndrome. N Engl J Med2005; 352: 1985–1991.
13.
RamaekersVTQuadrosEV.Cerebral folate deficiency syndrome: early diagnosis, intervention and treatment strategies. Nutrients2022; 14: 3096.
14.
KanmazSSimsekEYilmazS, et al. Cerebral folate transporter deficiency: a potentially treatable neurometabolic disorder. Acta Neurol Belg2023; 123: 121–127.
GrappMWredeASchweizerM, et al. Choroid plexus transcytosis and exosome shuttling deliver folate into brain parenchyma. Nat Commun2013; 4: 2123.
17.
SpectorRLorenzoAV.Folate transport by the choroid plexus in vitro. Science (1979)1975; 187: 540–542.
18.
PapadopoulouMTDalpaEPortokalasM, et al. Cerebral folate deficiency in two siblings caused by biallelic variants including a novel mutation of FOLR1 gene: Intrafamilial heterogeneity following early treatment and the role of ketogenic diet. JIMD Rep2021; 60: 3–9.
19.
SteinfeldRGrappMKraetznerR, et al. Folate receptor alpha defect causes cerebral folate transport deficiency: a treatable neurodegenerative disorder associated with disturbed myelin metabolism. Am J Hum Genet2009; 85: 354–363.
20.
MancoCCorteseRAlbertiM, et al. FOLR1 gene variation with adult-onset cerebral folate deficiency and stable clinical and MRI features up to 2 years. Neurol Genet2023; 9: e200104.
21.
BrunettiSMalerbaLGiordanoL, et al. Cerebral folate transporter deficiency syndrome in three siblings: Why genetic testing for developmental and epileptic encephalopathies should be performed early and include the FOLR1 gene. Am J Med Genet A2021; 185: 2526–2531.
22.
SpectorRJohansonCE.Choroid plexus failure in the Kearns-Sayre syndrome. Cerebrospinal Fluid Res2010; 7: 14.
23.
Bobrowski-KhouryNRamaekersVTSequeiraJM, et al. Folate receptor alpha autoantibodies in autism spectrum disorders: diagnosis, treatment and prevention. J Pers Med2021; 11: 710.
24.
FryeREDelheyLSlatteryJ, et al. Blocking and binding folate receptor alpha autoantibodies identify novel autism spectrum disorder subgroups. Front Neurosci2016; 10: 80.
25.
RossignolDAFryeRE.Cerebral folate deficiency, folate receptor alpha autoantibodies and leucovorin (folinic acid) treatment in autism spectrum disorders: a systematic review and meta-analysis. J Pers Med2021; 11: 1141.
26.
FryeRESequeiraJMQuadrosEV, et al. Cerebral folate receptor autoantibodies in autism spectrum disorder. Mol Psychiatry2013; 18: 369–381.
27.
RothenbergSPda CostaMPSequeiraJM, et al. Autoantibodies against folate receptors in women with a pregnancy complicated by a neural-tube defect. N Engl J Med2004; 350: 134–142.
28.
DongYWangLLeiY, et al. Gene variants in the folate pathway are associated with increased levels of folate receptor autoantibodies. Birth Defects Res2018; 110: 973–981.
29.
GnesinSMüllerJBurgerIA, et al. Radiation dosimetry of 18F-AzaFol: a first in-human use of a folate receptor PET tracer. EJNMMI Res2020; 10: 32.
30.
BetzelTMüllerCGroehnV, et al. Radiosynthesis and preclinical evaluation of 3’-Aza-2’-[(18)F]fluorofolic acid: a novel PET radiotracer for folate receptor targeting. Bioconjug Chem2013; 24: 205–214.
31.
Herrick-DavisKGrindeELindsleyT, et al. Native Serotonin 5-HT2C receptors are expressed as homodimers on the apical surface of choroid plexus epithelial cells. Mol Pharmacol2015; 87: 660–673.
32.
LoganJFowlerJSVolkowND, et al. Distribution volume ratios without blood sampling from graphical analysis of PET data. J Cereb Blood Flow Metab1996; 16: 834–840.
33.
RohlfingTKroenkeCDSullivanEV, et al. The INIA19 template and NeuroMaps atlas for primate brain image parcellation and spatial normalization. Front Neuroinform2012; 6: 27.
34.
NagaoTHirokawaM.Diagnosis and treatment of macrocytic anemias in adults. J Gen Fam Med2017; 18: 200–204.
35.
ObeidRHolzgreveWPietrzikK.Folate supplementation for prevention of congenital heart defects and low birth weight: an update. Cardiovasc Diagn Ther2019; 9: S424–S433.
36.
GebremichaelTGWelesamuelTG.Adherence to iron-folic acid supplement and associated factors among antenatal care attending pregnant mothers in governmental health institutions of Adwa town, Tigray, Ethiopia: cross-sectional study. PLoS One2020; 15: e0227090.
37.
RidlerKRizzoGBursteinES, et al. Imaging the 5-HT2C receptor with PET: Evaluation of 5-HT2C and 5-HT2A affinity of pimavanserin in the primate brain. J Cereb Blood Flow Metab2024; 45: 352–364.
38.
BalashovaOAVisinaOBorodinskyLN.Folate action in nervous system development and disease. Dev Neurobiol2018; 78: 391–402.
39.
KamenBASmithAK.A review of folate receptor alpha cycling and 5-methyltetrahydrofolate accumulation with an emphasis on cell models in vitro. Adv Drug Deliv Rev2004; 56: 1085–1097.
40.
ČarnaMOnyangoIGKatinaS, et al. Pathogenesis of Alzheimer’s disease: involvement of the choroid plexus. Alzheimers Dement2023; 19: 3537–3554.
41.
RiciglianoVAGLouapreCPoirionE, et al. Imaging characteristics of choroid plexuses in presymptomatic multiple sclerosis: a retrospective study. Neurol Neuroimmunol Neuroinflamm2022; 9: e200026.
42.
KlistornerSBarnettMHParrattJ, et al. Choroid plexus volume in multiple sclerosis predicts expansion of chronic lesions and brain atrophy. Ann Clin Transl Neurol2022; 9: 1528–1537.
43.
LizanoPLutzOLingG, et al. Association of choroid plexus enlargement with cognitive, inflammatory, and structural phenotypes across the psychosis spectrum. Am J Psychiatry2019; 176: 564–572.
44.
BraviBMelloniEMTPaoliniM, et al. Choroid plexus volume is increased in mood disorders and associates with circulating inflammatory cytokines. Brain Behav Immun2024; 116: 52–61.
45.
HartenP.Reducing toxicity of methotrexate with folic acid. Z Rheumatol2005; 64: 353–358.
46.
HallertCSvenssonMTholstrupJ, et al. Clinical trial: B vitamins improve health in patients with coeliac disease living on a gluten-free diet. Aliment Pharmacol Ther2009; 29: 811–816.
47.
LevLPetersenKRobertsJL, et al. Exploring the impact of folic acid supplementation and vitamin B12 deficiency on maternal and fetal outcomes in pregnant women with celiac disease. Nutrients2024; 16: 3194.
48.
MeltzerCCLealJPMaybergHS, et al. Correction of PET data for partial volume effects in human cerebral cortex by MR imaging. J Comput Assist Tomogr1990; 14: 561–570.
49.
Müller-GärtnerHWLinksJMPrinceJL, et al. Measurement of radiotracer concentration in brain gray matter using positron emission tomography: MRI-based correction for partial volume effects. J Cereb Blood Flow Metab1992; 12: 571–583.
50.
RoussetOGMaYEvansAC.Correction for partial volume effects in PET: principle and validation. J Nucl Med1998; 39: 904–911.
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