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Abstract: As biomarkers, endogenous neurotransmitters play critical roles in the process of neuropsychiatric diseases, and neurotransmitter levels in different brain regions can contribute to neurological disease diagnosis and treatment. Due to the lack of a blank matrix for endogenous neurotransmitters, surrogate‐matrix and surrogate‐analyte approaches have been used for the determination of neurotransmitters to solve this problem. In this study, we capitalised on the high accuracy, precision, and throughput of UHPLC‐MS/MS and developed new methods based on the two approaches. Both approaches satisfied FDA and EMA validation criterias after an appropriate parallelism assessment, and they were used to further quantify the three endogenous neurotransmitters, including dopamine (DA), serotonin (5‐HT) and γ‐aminobutyric acid (GABA) in rat brain four regions (cortex, striatum, hypothalamus and hippocampus) which represent the catecholamines, indolamines, and amino acids, respectively. Comparison of the results in the same rats (n = 10) showed there was no significant difference in DA, 5‐HT, or GABA levels between the two approaches (P > 0.05). The concentrations of DA and GABA were highest in striatum and hypothalamus, respectively, and the levels of 5‐HT were paralleled in striatum and hippocampus almost 2‐fold higher than other regions. This is the first study to compare these two approaches in the determination of endogenous neurotransmitter content in the rat brain, and the surrogate‐matrix approach proved to be simple, rapid, and reliable, considering cost, matrix similarity, and practicality. [ABSTRACT FROM AUTHOR]

Background: Rotigotine is a potent and selective D1, D2, and D3 dopaminergic receptor agonist. Due to an extensive first-pass effect, it has a very low oral bioavailability (approximately 0.5% in rats)., Purpose: The present investigation aimed to develop a microemulsion-based hydrogel for transdermal rotigotine delivery with lower application site reactions., Methods: Pseudoternary phase diagrams were constructed to determine the region of oil in water (o/w)-type microemulsion. Central composite design was used to support the pseudoternary phase diagrams and to select homogeneous and stable microemulsions with an optimal amount of rotigotine permeation within 24 hours. In vitro skin permeation experiments were performed, using Franz diffusion cells, to compare rotigotine-loaded microemulsions with rotigotine solutions in oil. The optimized formulation was used to prepare a microemulsion-based hydrogel, which was subjected to bioavailability and skin irritancy studies., Results: The selected formulations of rotigotine-loaded microemulsions had enhanced flux and permeation coefficients compared with rotigotine in oil. The optimum microemulsion contained 68% water, 6.8% Labrafil(®), 13.44% Cremophor(®) RH40, 6.72% Labrasol(®), and 5.04% Transcutol(®) HP; the drug-loading rate was 2%. To form a microemulsion gel, 1% Carbomer 1342 was added to the microemulsion. The bioavailability of the rotigotine-loaded microemulsion gel was 105.76%±20.52% with respect to the marketed rotigotine patch (Neupro(®)). The microemulsion gel irritated the skin less than Neupro., Conclusion: A rotigotine microemulsion-based hydrogel was successfully developed, and an optimal formulation for drug delivery was identified. This product could improve patient compliance and have broad marketability.

Superoxide dismutase (SOD) is used to manage chronic pain, including neuropathic and inflammatory pain. However, data regarding the clinical effectiveness are conflicting and the neurophysiological mechanism of SOD has yet to be elucidated. The aim of the present study was to investigate whether SOD relieved chronic central pain (CCP) following spinal cord injury (SCI) and the possible underlying mechanisms. A CCP model was established using the Allen method and the CCP of the rats was measured using the paw withdrawal threshold. SOD was administered intraperitoneally following the establishment of CCP as a result of SCI. The results demonstrated that SOD relieved CCP in rats following SCI. In addition, the expression of spinal phosphorylated N-methyl-D-aspartate(NMDA) receptor subunit 1 (pNR-1) was inhibited in the CCP rats that had been treated with SOD. These observations indicated that SOD reduced mechanical allodynia and attenuated the enhancement of spinal pNR1 expression in rats with CCP. In addition, the results indicated that superoxide, produced via xanthine oxidase, and the participation of superoxide and nitric oxide (NO) as a precursor of peroxynitrite in NMDA, were involved in the mediation of central sensitization. Therefore, the observations support the hypothesis that SOD may have a potential therapeutic role for the treatment of CCP following SCI via the manipulation of superoxide and NO.

The aim of this study was to investigate the effect of Poly(amidoamine) (PAMAM) dendrimers on corneal permeation of puerarin (PUE). Permeation studies were performed using excised cornea of rabbits by a Valia-Chien diffusion apparatus. Drug-treatment studies were carried out by measuring the penetration of puerarin on cornea in PAMAM-PUE physical mixture or PAMAM-PUE complex, and cornea-treatment studies were carried out by measuring the penetration of puerarin on PAMAM dendrimer pretreated cornea in puerarin solution. The results showed that the permeability coefficient of puerarin in PAMAM-PUE physical mixture was enhanced by 2.48 (G3), 1.99 (G4) and 1.36 (G5) times on average, respectively compared to control. However, no significant permeability enhancement of puerarin in PAMAM-PUE complex was found compared to control. This may attribute to free drug concentration was lower in PAMAM-PUE complex which served as a depot and exhibited slow-released behavior of drug. Cornea-treatment studies showed that the lag time of puerarin was decreased, while the cumulative amount within 2.5 h (Q(2.5)) and the permeability coefficient of puerarin increased compared to control. The permeability coefficient of puerarin was linear correlated to the molecular weight of PAMAM dendrimer (r(2)=0.99). This indicates that higher generation of PAMAM dendrimer more easily interact with cornea or loosen the epithelium cell junctions than lower generation to increase the flux of puerarin. Overall, the study showed that PAMAM dendrimer increased the corneal permeation of puerarin mainly by altering the corneal barrier.