Biology subjects

Fidanboylu, M.

Publications and source records attributed to Fidanboylu, M..

3 recordsLinked to original sources

bioRxiv2025

Saturation kinetics and specificity of transporters for L-arginine and asymmetric dimethylarginine (ADMA) at the blood-brain and blood-CSF barriers.

Nitric oxide synthases (NOS) synthesize nitric oxide (NO) from L-arginine in endothelial and neuronal cells. Asymmetric dimethylarginine (ADMA) is a homologue of arginine and an endogenous inhibitor of NOS. As NO is a critical signalling molecule and influences physiological pathways in health and disease, the transfer of arginine and ADMA across the blood-CNS barriers is of interest. Our research group have previously demonstrated the presence of saturable transporters for [3H]-L-arginine and [3H]-ADMA at the blood-brain and blood-CSF barriers using in vitro and in situ methods. In this study, we determine the identity and kinetic characteristics of these transporters by means of the in situ brain/choroid plexus perfusion technique in anaesthetised mice. Results indicated that [3H]-arginine and [3H]-ADMA could be transported across blood-brain and blood-CSF barriers by the cationic amino acid transporter, system-y+. In contrast to the results obtained with arginine where transport was predominately by a single transport system (system-y+), ADMA delivery to the CNS was more complex and involved multiple transport systems (system y+, B0,+, y+L and b0,+) suggesting its concentration is tightly regulated. System y+ and system y+L transporters could be involved in the CNS to blood efflux of ADMA that we have previously observed. The half-saturation constant (Km) and maximal influx rate of the saturable component (Vmax) for [3H]-ADMA transport into the frontal cortex was 29.07{+/-}7.19 M and 0.307{+/-}0.017 nmol.min-1.g-1, respectively, and into the CSF was 30.59{+/-}25.41 M and 2.07{+/-}0.38 nmol.min-1.g-1, respectively. This information could help explain the arginine paradox providing evidence that ADMA interacts with transporters that can remove ADMA from cells. These removal mechanisms could be stimulated by excess arginine in the plasma resulting in increased NO production. It remains to be seen if arginine supplementation could be used to increase NO production and improve hypoperfusion observed in disease states such as Alzheimers and stroke.

neuroscience↗

bioRxiv2024

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.

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 l.min-1.g-1, respectively, and into the CSF of 1.08{+/-}0.24 and 2.70{+/-}0.90 l.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 easily sufficient to saturate endothelial NOS, could be related to ADMA transport.

neuroscience↗

bioRxiv2019

Drug reformulation for a neglected disease. The NANOHAT project to develop a safer more effective sleeping sickness drug.

Human African trypanosomiasis (HAT or sleeping sickness) is caused by the parasite Trypanosoma brucei sspp. The disease has two stages, a haemolymphatic stage after the bite of an infected tsetse fly, followed by a central nervous system stage where the parasite penetrates the brain, causing death if untreated. Treatment is stage-specific, due to the blood-brain barrier, with less toxic drugs such as pentamidine used to treat stage 1. The objective of our research programme was to develop an intravenous formulation of pentamidine which increases CNS exposure by some 10-100 fold, leading to efficacy against a model of stage 2 HAT. This target candidate profile is in line with drugs for neglected diseases inititative recommendations. To do this, we evaluated the physicochemical and structural characteristics of formulations of pentamidine with Pluronic micelles (triblock-copolymers of polyethylene-oxide and polypropylene oxide), selected candidates for efficacy and toxicity evaluation in vitro, quantified pentamidine CNS delivery of a sub-set of formulations in vitro and in vivo, and progressed one pentamidine-Pluronic formulation for further evaluation using an in vivo single dose brain penetration study. Screening pentamidine against 40 CNS targets did not reveal any major neurotoxicity concerns, however, pentamidine had a high affinity for the imidazoline2 receptor. The reduction in insulin secretion in MIN6 {beta}-cells by pentamidine maybe secondary to pentamidine-mediated activation of {beta}-cell imidazoline receptors and impairment of cell viability. Pluronic F68 (0.01%w/v)-pentamidine formulation had a similar inhibitory effect on insulin secretion as pentamidine alone and an additive trypanocidal effect in vitro. However, all Pluronics tested (P85, P105 and F68) did not significantly enhance brain exposure of pentamidine. These results are relevant to further developing block-copolymers as nanocarriers, improving BBB drug penetration and understanding the side effects of pentamidine.

pharmacology and toxicology↗