l-Type Amino Acid Transporter 1 (LAT1/Lat1)-Utilizing Prodrugs Can Improve the Delivery of Drugs into Neurons, Astrocytes and Microglia

Abstract

l -Type Amino Acid Transporter 1 (LAT1/Lat1) is responsible for carrying large, neutral l -amino acids as well as several drugs and prodrugs across the blood-brain barrier (BBB). However, the BBB is not the only barrier that hinders drugs acting effectively within the brain; the brain parenchymal cell membranes represent a secondary barrier for the drugs with intracellular target sites. In this study, expression and function of Lat1 was quantified in mouse primary neuron, astrocyte and immortalized microglia (BV2) cultures. Moreover, ability of Lat1 to carry prodrugs inside these brain cells was evaluated. The results showed that Lat1 was localized at the similar level in all studied cells (3.07 ± 0.92–3.77 ± 0.91 fmol/µg protein). The transporter was also functional in all three cell types, astrocytes having the highest transport capacity and affinity for the LAT1/Lat1-substrate, [ 14 C]- l -leucine, followed by neurons and microglia. The designed prodrugs ( 1 - 6 ) were able to utilize Lat1 for their cellular uptake and it was mainly much higher than the one of their parent drugs. Interestingly, improved cellular uptake was also achieved in cells representing Alzheimer’s Disease phenotype. Therefore, improved delivery and intra-brain targeting of drugs can be attained by utilizing LAT1/Lat1 and prodrug approach.

L-Type Amino Acid Transporter 1-Utilizing Prodrugs of Ketoprofen Can Efficiently Reduce Brain Prostaglandin Levels

“…The efficacy of the drugs and their brain concentrations could be compared at multiple time points. Therefore, LAT1-utilisation can achieve not only targeted brain delivery but also improved intracellular brain delivery, as we have proven in our earlier studies [13,14,36]. Herein, it demonstrated the efficacy of the pro-drug, as measured by reduction in the concentrations of PGE2, which will permit an investigation of the chronic administration of NSAIDs in the treatment of neurodegenerative diseases while avoiding their peripheral adverse effects.…”

“…However, the amount of released KPF was quantified in this study from the whole brain tissue and, therefore, we cannot compare how much of KPF was delivered to the target cells, i.e., to activated astrocytes or microglia, in which the target enzymes, COXs, are located. We have previously shown that, although the total brain uptake of PD1 was comparable to KPF itself (K p, brain/plasma 0.0097 and 0.0098, respectively) [36], the LAT1-mediated uptake of PD1 into astrocytes and microglia has been 10-13 and 2-7 times greater, respectively, as compared to KPF [13]. This points to the superiority of LAT1 utilization in transporting the drugs into their intracellular targets and, hence, enhancing their potency and efficacy.…”

“…LAT1 is highly expressed in blood brain barrier (BBB) in comparison to other healthy tissues [11]. Moreover, this transporter is highly expressed in both the luminal and abluminal sides of the BBB [12] as well as in the brain parenchymal cells such as astrocytes, microglia, and neurons [13]. LAT1-utilization has not only been able to enable the brain delivery of ferulic acid, dopamine, valproic acid, and KPF prodrugs [14][15][16][17], but also to increase the extent of uptake in brain parenchymal cells in vitro [13].…”

“…Moreover, this transporter is highly expressed in both the luminal and abluminal sides of the BBB [12] as well as in the brain parenchymal cells such as astrocytes, microglia, and neurons [13]. LAT1-utilization has not only been able to enable the brain delivery of ferulic acid, dopamine, valproic acid, and KPF prodrugs [14][15][16][17], but also to increase the extent of uptake in brain parenchymal cells in vitro [13]. Unlike other transporters expressed at the BBB, the function and protein expression of LAT1 is not changed in Alzheimer's disease (AD)-like or Parkinson's disease (PD)-like pathology [18,19].…”

“…Alternatively, targeting the NSAIDs into the brain via a pro-drug approach seemed to be a promising solution [8]. Previously, we have reported a brain-targeted prodrug of KPF (PD1 in Figure 1) that utilizes LAT1 for its brain uptake across the BBB and its intracellular localization within the brain parenchymal cells [13,14]. Moreover, this pro-drug releases KPF into the brain and liver with a ratio of 0.5 and 0.1, respectively, as compared to the KPF treatment and with only a minor release of KPF in plasma [14].…”