L-Arginine and asymmetric dimethylarginine (ADMA) transport across the mouse blood-brain and blood-CSF barriers: Evidence of saturable transport at both interfaces and CNS to blood efflux

PLoS One. 2024 Oct 24;19(10):e0305318. doi: 10.1371/journal.pone.0305318. eCollection 2024.

Abstract

L-Arginine is the physiological substrate for the nitric oxide synthase (NOS) family, which synthesises nitric oxide (NO) in endothelial and neuronal cells. NO synthesis can be inhibited by endogenous asymmetric dimethylarginine (ADMA). NO has explicit roles in cellular signalling and vasodilation. Impaired NO bioavailability represents the central feature of endothelial dysfunction associated with vascular diseases. Interestingly, dietary supplementation with L-arginine has been shown to alleviate endothelial dysfunctions caused by impaired NO synthesis. In this study the transport kinetics of [3H]-arginine and [3H]-ADMA into the central nervous system (CNS) were investigated using physicochemical assessment and the in situ brain/choroid plexus perfusion technique in anesthetized mice. Results indicated that L-arginine and ADMA are tripolar cationic amino acids and have a gross charge at pH 7.4 of 0.981. L-Arginine (0.00149±0.00016) has a lower lipophilicity than ADMA (0.00226±0.00006) as measured using octanol-saline partition coefficients. The in situ perfusion studies revealed that [3H]-arginine and [3H]-ADMA can cross the blood-brain barrier (BBB) and the blood-CSF barrier. [3H]-Arginine (11.6nM) and [3H]-ADMA (62.5nM) having unidirectional transfer constants (Kin) into the frontal cortex of 5.84±0.86 and 2.49±0.35 μl.min-1.g-1, respectively, and into the CSF of 1.08±0.24 and 2.70±0.90 μl.min-1.g-1, respectively. In addition, multiple-time uptake studies revealed the presence of CNS-to-blood efflux of ADMA. Self- and cross-inhibition studies indicated the presence of transporters at the BBB and the blood-CSF barriers for both amino acids, which were shared to some degree. Importantly, these results are the first to demonstrate: (i) saturable transport of [3H]-ADMA at the blood-CSF barrier (choroid plexus) and (ii) a significant CNS to blood efflux of [3H]-ADMA. Our results suggest that the arginine paradox, in other words the clinical observation that NO-deficient patients respond well to oral supplementation with L-arginine even though the plasma concentration is sufficient to saturate endothelial NOS, could be related to altered ADMA transport (efflux).

MeSH terms

  • Animals
  • Arginine* / analogs & derivatives
  • Arginine* / metabolism
  • Biological Transport
  • Blood-Brain Barrier* / metabolism
  • Kinetics
  • Male
  • Mice

Substances

  • Arginine
  • N,N-dimethylarginine

Grants and funding

This work was supported by a Biotechnology and Biological Sciences Research Council (BBSRC) centre for integrative biomedicine PhD studentship for Mr Fidanboylu to Dr Sarah Ann Thomas [BB/E527098/1]. https://www.ukri.org/councils/bbsrc/. This research was funded in whole, or in part, by the Wellcome Trust [080268]. https://wellcome.org/. The recipients of this Wellcome grant were: Dr Sarah Ann Thomas, Professors Paul Thomas Francis, Marzia Malcangio, Stephen Brendan McMahon and Marcus Rattray. For the purpose of Open Access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.