PQBP1 promotes translational elongation and regulates hippocampal mGluR-LTD by suppressing eEF2 phosphorylation.

Eukaryotic elongation factor 2 (eEF2) mediates translocation of peptidyl-tRNA from the ribosomal A site to the P site to promote translational elongation. Its phosphorylation on Thr56 by its single known kinase eEF2K inactivates it and inhibits translational elongation. Extensive studies have revealed that different signal cascades modulate eEF2K activity, but whether additional factors regulate phosphorylation of eEF2 remains unclear. Here, we find that the X chromosome-linked intellectual disability protein polyglutamine-binding protein 1 (PQBP1) specifically binds to non-phosphorylated eEF2 and suppresses eEF2K-mediated phosphorylation at Thr56. Loss of PQBP1 significantly reduces general protein synthesis by suppressing translational elongation. Moreover, we show that PQBP1 regulates hippocampal metabotropic glutamate receptor-dependent long-term depression (mGluR-LTD) and mGluR-LTD-associated behaviors by suppressing eEF2K-mediated phosphorylation. Our results identify PQBP1 as a novel regulator in translational elongation and mGluR-LTD, and this newly revealed regulator in the eEF2K/eEF2 pathway is also an excellent therapeutic target for various disease conditions, such as neural diseases, virus infection, and cancer.

Novel Social Stimulation Ameliorates Memory Deficit in Alzheimer's Disease Model through Activating α-Secretase.

As the most common form of dementia in the world, Alzheimer's disease (AD) is a progressive neurological disorder marked by cognitive and behavioral impairment. According to previous researches, abundant social connections shield against dementia. However, it is still unclear how exactly social interactions benefit cognitive abilities in people with AD and how this process is used to increase their general cognitive performance. In this study, we found that single novel social (SNS) stimulation promoted c-Fos expression and increased the protein levels of mature ADAM10/17 and sAPPα in the ventral hippocampus (vHPC) of wild-type (WT) mice, which are hippocampal dorsal CA2 (dCA2) neuron activity and vHPC NMDAR dependent. Additionally, we discovered that SNS caused similar changes in an AD model, FAD4T mice, and these alterations could be reversed by α-secretase inhibitor. Furthermore, we also found that multiple novel social (MNS) stimulation improved synaptic plasticity and memory impairments in both male and female FAD4T mice, accompanied by α-secretase activation and Aß reduction. These findings provide insight into the process underpinning how social interaction helps AD patients who are experiencing cognitive decline, and we also imply that novel social interaction and activation of the α-secretase may be preventative and therapeutic in the early stages of AD.

Bi-allelic GOT2 Mutations Cause a Treatable Malate-Aspartate Shuttle-Related Encephalopathy.

Early-infantile encephalopathies with epilepsy are devastating conditions mandating an accurate diagnosis to guide proper management. Whole-exome sequencing was used to investigate the disease etiology in four children from independent families with intellectual disability and epilepsy, revealing bi-allelic GOT2 mutations. In-depth metabolic studies in individual 1 showed low plasma serine, hypercitrullinemia, hyperlactatemia, and hyperammonemia. The epilepsy was serine and pyridoxine responsive. Functional consequences of observed mutations were tested by measuring enzyme activity and by cell and animal models. Zebrafish and mouse models were used to validate brain developmental and functional defects and to test therapeutic strategies. GOT2 encodes the mitochondrial glutamate oxaloacetate transaminase. GOT2 enzyme activity was deficient in fibroblasts with bi-allelic mutations. GOT2, a member of the malate-aspartate shuttle, plays an essential role in the intracellular NAD(H) redox balance. De novo serine biosynthesis was impaired in fibroblasts with GOT2 mutations and GOT2-knockout HEK293 cells. Correcting the highly oxidized cytosolic NAD-redox state by pyruvate supplementation restored serine biosynthesis in GOT2-deficient cells. Knockdown of got2a in zebrafish resulted in a brain developmental defect associated with seizure-like electroencephalography spikes, which could be rescued by supplying pyridoxine in embryo water. Both pyridoxine and serine synergistically rescued embryonic developmental defects in zebrafish got2a morphants. The two treated individuals reacted favorably to their treatment. Our data provide a mechanistic basis for the biochemical abnormalities in GOT2 deficiency that may also hold for other MAS defects.

Transcriptome Regulation by Oncogenic ALK Pathway in Mammalian Cortical Development Revealed by Single-Cell RNA Sequencing.

Precise regulation of embryonic neurodevelopment is crucial for proper structural organization and functioning of the adult brain. The key molecular machinery orchestrating this process remains unclear. Anaplastic lymphoma kinase (ALK) is an oncogenic receptor-type protein tyrosine kinase that is specifically and transiently expressed in developing nervous system. However, its role in the mammalian brain development is unknown. We found that transient embryonic ALK inactivation caused long-lasting abnormalities in the adult mouse brain, including impaired neuronal connectivity and cognition, along with delayed neuronal migration and decreased neuronal proliferation during neurodevelopment. scRNA-seq on human cerebral organoids revealed a delayed transition of cell-type composition. Molecular characterization identified a group of differentially expressed genes (DEGs) that were temporally regulated by ALK at distinct developmental stages. In addition to oncogenes, many DEGs found by scRNA-seq are associated with neurological or neuropsychiatric disorders. Our study demonstrates a pivotal role of oncogenic ALK pathway in neurodevelopment and characterized cell-type-specific transcriptome regulated by ALK for better understanding mammalian cortical development.

Protective effect of nitronyl nitroxide against hypoxia-induced damage in PC12 cells.

Hypoxia induces cellular oxidative stress that is associated with neurodegenerative diseases. HPN (4'-hydroxyl-2-substituted phenyl nitronyl nitroxide), a stable nitronyl nitroxide, has excellent free radical scavenging properties. The purpose of this study was to investigate the protective effects of HPN on hypoxia-induced damage in PC12 cells. It was shown that HPN significantly attenuated hypoxia-induced loss of cell viability, release of lactate dehydrogenase (LDH), and morphological changes in PC12 cells. Moreover, hypoxic PC12 cells had increased levels of reactive oxygen species (ROS), malondialdehyde (MDA), and expression of HIF-1α and VEGF, but had reduced levels of superoxide dismutase (SOD) and catalase (CAT), and HPN reversed these changes. HPN also inhibited hypoxia-induced cell apoptosis via suppressing the expression of Bax, cytochrome c, and caspase-3, and inducing the expression of Bcl-2. These results indicate that the protective effects of HPN on hypoxia-induced damage in PC12 cells is associated with the suppression of hypoxia-induced oxidative stress and cell apoptosis. HPN could be a promising candidate for the development of a novel neuroprotective agent.

Rectification of radiotherapy-induced cognitive impairments in aged mice by reconstituted Sca-1+ stem cells from young donors.

BACKGROUND: Radiotherapy is widely used and effective for treating brain tumours, but inevitably impairs cognition as it arrests cellular processes important for learning and memory. This is particularly evident in the aged brain with limited regenerative capacity, where radiation produces irreparable neuronal damage and activation of neighbouring microglia. The latter is responsible for increased neuronal death and contributes to cognitive decline after treatment. To date, there are few effective means to prevent cognitive deficits after radiotherapy. METHODS: Here we implanted hematopoietic stem cells (HSCs) from young or old (2- or 18-month-old, respectively) donor mice expressing green fluorescent protein (GFP) into old recipients and assessed cognitive abilities 3 months post-reconstitution. RESULTS: Regardless of donor age, GFP+ cells homed to the brain of old recipients and expressed the macrophage/microglial marker, Iba1. However, only young cells attenuated deficits in novel object recognition and spatial memory and learning in old mice post-irradiation. Mechanistically, old recipients that received young HSCs, but not old, displayed significantly greater dendritic spine density and long-term potentiation (LTP) in CA1 neurons of the hippocampus. Lastly, we found that GFP+/Iba1+ cells from young and old donors were differentially polarized to an anti- and pro-inflammatory phenotype and produced neuroprotective factors and reactive nitrogen species in vivo, respectively. CONCLUSION: Our results suggest aged peripherally derived microglia-like cells may exacerbate cognitive impairments after radiotherapy, whereas young microglia-like cells are polarized to a reparative phenotype in the irradiated brain, particularly in neural circuits associated with rewards, learning, and memory. These findings present a proof-of-principle for effectively reinstating central cognitive function of irradiated brains with peripheral stem cells from young donor bone marrow.

Regulation of Neurotransmitter Release by Amyloid Precursor Protein Through Synapsin Phosphorylation.

Abnormal processing of amyloid precursor protein (APP) and aggregation of the Aß peptide are known to play a key role in the pathogenesis of Alzheimer disease, but the function of endogenous APP under normal physiological conditions remains poorly understood. In this study, we investigated presynaptic changes in APP knockout (KO) mice. We demonstrate that both sucrose-induced neurotransmission and synaptic depletion in response to high frequency stimulation are significantly enhanced in APP KO compared to wild type littermates. In addition, the level of phosphorylated forms of synapsins, but not total synapsins, is elevated in the KO mice. Furthermore, we show that the inhibition of L-type calcium channels normalizes phosphorylated synapsins and slows down the high frequency induced synaptic depletion in APP KO mice. These results suggest a new mechanism by which APP regulates synaptic vesicle dynamics through synapsin-dependent phosphorylation.

The neuronal protein Neurexin directly interacts with the Scribble-Pix complex to stimulate F-actin assembly for synaptic vesicle clustering.

Synaptic vesicles (SVs) form distinct pools at synaptic terminals, and this well-regulated separation is necessary for normal neurotransmission. However, how the SV cluster, in particular synaptic compartments, maintains normal neurotransmitter release remains a mystery. The presynaptic protein Neurexin (NRX) plays a significant role in synaptic architecture and function, and some evidence suggests that NRX is associated with neurological disorders, including autism spectrum disorders. However, the role of NRX in SV clustering is unclear. Here, using the neuromuscular junction at the 2-3 instar stages of Drosophila larvae as a model and biochemical imaging and electrophysiology techniques, we demonstrate that Drosophila NRX (DNRX) plays critical roles in regulating synaptic terminal clustering and release of SVs. We found that DNRX controls the terminal clustering and release of SVs by stimulating presynaptic F-actin. Furthermore, our results indicate that DNRX functions through the scaffold protein Scribble and the GEF protein DPix to activate the small GTPase Ras-related C3 Botulinum toxin substrate 1 (Rac1). We observed a direct interaction between the C-terminal PDZ-binding motif of DNRX and the PDZ domains of Scribble and that Scribble bridges DNRX to DPix, forming a DNRX-Scribble-DPix complex that activates Rac1 and subsequently stimulates presynaptic F-actin assembly and SV clustering. Taken together, our work provides important insights into the function of DNRX in regulating SV clustering, which could help inform further research into pathological neurexin-mediated mechanisms in neurological disorders such as autism.

Melatonin Receptor Agonist Piromelatine Ameliorates Impaired Glucose Metabolism in Chronically Stressed Rats Fed a High-Fat Diet.

Modern lifestyle factors (high-caloric food rich in fat) and daily chronic stress are important risk factors for metabolic disturbances. Increased hypothalamic-pituitary-adrenal (HPA) axis activity and the subsequent excess production of glucocorticoids (GCs) in response to chronic stress (CS) leads to increases in metabolic complications, such as type 2 diabetes and insulin resistance (IR). Melatonin (MLT), which protects several regulatory components of the HPA axis from GC-induced deterioration, might improve glucose homeostasis. Piromelatine is a melatonin receptor-1/melatonin receptor-2 (MT1/MT2) agonist with high affinity for MLT receptors and a longer duration of action than MLT. The objective of the present study was to explore the potential effects of piromelatine on glucose and lipid metabolism and insulin sensitivity in rats with IR induced by a high-fat diet combined with CS (CF). The results showed that piromelatine prevented the suppression of body weight gain and energy intake induced by CF and normalized CF-induced hyperglycemia and homeostasis model assessment-IR index, which suggests that piromelatine prevented whole-body IR. Piromelatine also prevented CF-induced dysregulation of genes involved in glucose and lipid metabolism, including proinflammatory cytokines, in adipose tissue. In addition, piromelatine also attenuated CF-induced excess free corticosterone release, increased glucocorticoid receptor expression, and decreased 11ß-hydroxysteroid dehydrogenase-1 expression, suggesting that piromelatine might ameliorate impaired glucose metabolism and prevent IR by normalizing HPA-axis functions. In conclusion, piromelatine might be a novel therapeutic agent for glucose intolerance and IR.

Acute and sub-chronic toxicological studies of the iridoid glycosides extract of Lamiophlomis rotata (Benth.) Kudo in rats.

Lamiophlomis rotata(Benth.) Kudo is widely used in traditional Chinese medicine and its iridoid glycosides extract (IGLR) was the main active ingredient with hemostatic, antinociceptive and anti-inflammatory effects. This study was aimed to evaluate the safety of IGLR using acute and sub-chronic toxicity study methods on Sprague-Dawley rats. In acute toxicity test, IGLR caused slight diarrhea in three dose groups and a decreased of RBC and increased of MCH and Ret (P < .05) were observed in 16 g/kg group. In sub-chronic toxicity study, unscheduled deaths occurred in 1 and 3 rats at 0.40 and 1.00 g/kg groups, respectively. A slight diarrhea was observed in 1.00 g/kg group. Hemolytic anemia was the main toxicity effects of IGLR found in 0.40 and 1.00 g/kg groups, with a significant decrease of RBC, HGB (P < .05) and increase of Ret, MCV, MCH (P < .05) in hematological parameters, a significant decrease of ALT, Crea (P < .05) and increase of TBIL (P < .05) in biochemical parameters, and a significant increase of the percentage of rubricyte, normoblast (P < .05) in bone marrow. Overall, this study found IGLR has a potential toxicity considering with hemolytic anemia and diarrhea to rat. These results provide an important reference for further IGLR-related drug exploration.

[Role of drug transporters in rational use of drugs at high altitude area].

Pharmacokinetics plays a key role in rational use of medicines. Many factors can affect the drug's pharmacokinetics. Previous studies mainly focused on the impact of hypoxia on hepatic drug metabolizing enzyme, but uncommon on drug transporters. Actually, drug transporter is a key factor for activation of the drugs transport across the cell membrane into the inside of cells, such as multidrug resistance protein (MDR), breast cancer resistance protein (BCRP), multidrug resistance associated protein (MRP), organic cation transporter (OCT), organic anion-transporting polypeptide (OATP), organic anion transporter (OAT), qligopeptide transporter (PEPT), etc. They are widely present in the small intestine villus epithelial cells, renal tubular epithelial cells, hepatocytes and biliary epithelial cells. They play a very important role in drug absorption, distribution, metabolism and excretion. The changes in drug transporters under hypoxia in intestinal could affect the bioavailability of drugs; the changes in drug transporters in organs could affect drug's distribution, subsequent drug's indications and adverse reactions; the changes in drug transporters in liver and kidney could affect the metabolism and excretion rate of drugs, thereby the drug's residence time and half-life.

The intellectual disability protein PAK3 regulates oligodendrocyte precursor cell differentiation.

Oligodendrocyte and myelin deficits have been reported in mental/psychiatric diseases. The p21-activated kinase 3 (PAK3), a serine/threonine kinase, whose activity is stimulated by the binding of active Rac and Cdc42 GTPases is affected in these pathologies. Indeed, many mutations of Pak3 gene have been described in non-syndromic intellectual disability diseases. Pak3 is expressed mainly in the brain where its role has been investigated in neurons but not in glial cells. Here, we showed that PAK3 is highly expressed in oligodendrocyte precursors (OPCs) and its expression decreases in mature oligodendrocytes. In the developing white matter of the Pak3 knockout mice, we found defects of oligodendrocyte differentiation in the corpus callosum and to a lesser extent in the anterior commissure, which were compensated at the adult stage. In vitro experiments in OPC cultures, derived from Pak3 knockout and wild type brains, support a developmental and cell-autonomous role for PAK3 in regulating OPC differentiation into mature oligodendrocytes. Moreover, we did not detect any obvious alterations of the proliferation or migration of Pak3 null OPCs compared to wild type. Overall, our data highlight PAK3 as a new regulator of OPC differentiation.

[Effect of hypoxia on expression of multidrug resistance protein 2 and its regulation mechanism].

Drug efflux transporters plays a key role in pharmacokinetics parameters changes. In recent years, in addition to P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), MRP2 has become an advanced research hotspot. Several signaling pathways andtranscription factors have been reported to be involved in regulation of MRP2 expression in hypoxic microenvironment of tumor, such as peroxisome proliferators-activated receptors (PPARα), nuclear factor κB (NF-κB), pregnane X receptor (PXR), farnesoid X receptor (FXR), constitutive androstane receptor (CAR) and microRNA. But it is not fully understood how MRP2 is regulated under hypoxia. MRP2 is one of the most important efflux transporter proteins. Many drugs or inhibitors have been shown to be its substrate. In the hypoxic environment, changes in expression of MRP2 can significantly affect drug's pharmacokinetics (absorption, distribution, metabolism, excretion). Simultaneously, the regulation of MRP2 expression under hypoxic might involve several signal pathways and many genes, which constitute an integral gene regulatory networks.

Effect of acetazolamide on cytokines in rats exposed to high altitude.

Acute mountain sickness (AMS) is a dangerous hypoxic illness that can affect humans who rapidly reach a high altitude above 2500m. In the study, we investigated the changes of cytokines induced by plateau, and the acetazolamide (ACZ) influenced the cytokines in rats exposed to high altitude. Wistar rats were divided into low altitude (Control), high altitude (HA), and high altitude+ACZ (22.33mg/kg, Bid) (HA+ACZ) group. The rats were acute exposed to high altitude at 4300m for 3days. The HA+ACZ group were given ACZ by intragastric administration. The placebo was equal volume saline. The results showed that hypoxia caused the heart, liver and lung damage, compared with the control group. Supplementation with ACZ significantly alleviated hypoxia-caused damage to the main organs. Compared with the HA group, the biochemical and blood gas indicators of the HA+ACZ group showed no difference, while some cytokines have significantly changed, such as activin A, intercellular adhesion molecule-1 (ICAM-1, CD54), interleukin-1α,2 (IL-1α,2), l-selectin, monocyte chemotactic factor (MCP-1), CC chemokines (MIP-3α) and tissue inhibitor of matrix metalloproteinase 1 (TIMP-1). Then, the significant difference pro-inflammatory cytokines in protein array were chosen for further research. The protein and mRNA content of pro-inflammatory cytokines MCP-1, interleukin-1ß (IL-1ß), tumor necrosis factor (TNF-α), interferon-γ (IFN-γ) in rat lung were detected. The results demonstrated that the high altitude affected the body's physiological and biochemical parameters, but, ACZ did not change those parameters of the hypoxia rats. This study found that ACZ could decrease the content of pro-inflammatory cytokines, such as MCP-1, IL-1ß, TNF-α and IFN-γ in rat lungs, and, the lung injury in the HA+ACZ group reduced. The mechanism that ACZ protected hypoxia rats might be related to changes in cytokine content. The reducing of the pro-inflammatory cytokines in rat lung might be other reason to explain ACZ against the acute mountain sickness.

[Changes of P-gp expression in rats' small intestine and effects on uptake of levofloxacin after acute exposure to hypoxia].

The drug transporter play a key role in the absorption of drugs. Investigation of the changes of drug transporters in response to hypoxia will provide insight into the mechanism of drug absorption. In this study we investigated the mRNA and protein expression of the transporter P-gp after acute hypoxia, and evaluated the effects of P-gp changes on absorption of levofloxacin in the intestine. The relative expression of m RNA and protein were reduced by 50.80% and 71.30%(P < 0.05). In the single-pass intestinal perfusion model, the intestinal wall permeability was increased by 56.16%, 226.00%, 77.74% and 141.00% in the time intervals at 30-60 min, 60-90 min, 90-120 min and 120-150 min although P-gp expression was decreased(P < 0.05). These results suggest that hypoxia may decrease the expression of P-gp in the intestine to reduce the excretion of levofloxacin and increase the absorption.

Partial deletion of ROCK2 protects mice from high-fat diet-induced cardiac insulin resistance and contractile dysfunction.

Obesity is associated with cardiac insulin resistance and contractile dysfunction, which contribute to the development of heart failure. The RhoA-Rho kinase (ROCK) pathway has been reported to modulate insulin resistance, but whether it is implicated in obesity-induced cardiac dysfunction is not known. To test this, wild-type (WT) and ROCK2(+/-) mice were fed normal chow or a high-fat diet (HFD) for 17 wk. Whole body insulin resistance, determined by an insulin tolerance test, was observed in HFD-WT, but not HFD-ROCK2(+/-), mice. The echocardiographically determined myocardial performance index, a measure of global systolic and diastolic function, was significantly increased in HFD-WT mice, indicating a deterioration of cardiac function. However, no change in myocardial performance index was found in hearts from HFD-ROCK2(+/-) mice. Speckle-tracking-based strain echocardiography also revealed regional impairment in left ventricular wall motion in hearts from HFD-WT, but not HFD-ROCK2(+/-), mice. Activity of ROCK1 and ROCK2 was significantly increased in hearts from HFD-WT mice, and GLUT4 expression was significantly reduced. Insulin-induced phosphorylation of insulin receptor substrate (IRS) Tyr(612), Akt, and AS160 was also impaired in these hearts, while Ser(307) phosphorylation of IRS was increased. In contrast, the increase in ROCK2, but not ROCK1, activity was prevented in hearts from HFD-ROCK2(+/-) mice, and cardiac levels of TNFα were reduced. This was associated with normalization of IRS phosphorylation, downstream insulin signaling, and GLUT4 expression. These data suggest that increased activation of ROCK2 contributes to obesity-induced cardiac dysfunction and insulin resistance and that inhibition of ROCK2 may constitute a novel approach to treat this condition.

MDR1 will play a key role in pharmacokinetic changes under hypoxia at high altitude and its potential regulatory networks.

Some newest studies indicated that drug transports may play the key role in pharmacokinetics changes under hypoxia at high altitude; MDR1 is now known to affect the disposition of many administered drugs and make a major contribution to absorption, distribution, metabolism, excretion. Different expression of MDR1 is frequently found in different normal tissues and tumor cells; it is important to better understand how MDR1 is regulated under hypoxia, which seems to be a complex and highly controlled process. Several signaling pathways and transcription factors have been described as being involved in the regulation of MDR1 expression, such as MAPK/ERK, nuclear factor-kappaB, hypoxia-inducible factor-1a, pregnane × receptor, constitutive androstane receptor and microRNA. Recently, researches have been increasingly appreciating long non-coding RNAs (lncRNAs) as an integral component of gene regulatory networks. lncRNAs play crucial roles in various biological processes ranging from epigenetic gene regulation, transcriptional control, post-transcriptional regulation, pre-mRNA processing and nuclear organization. A last recent research showed that H19 gene non-coding RNA is believed to induce P-glycoprotein expression under hypoxia.

Anti-hypoxia Activity of the Novel NO Donor Acetyl Ferulic Isosorbide Mononitrate in Acute High-Altitude Hypoxia Mice.

Nitric oxide (NO) may act as either a pro-oxidant or an antioxidant in biological systems. Previous work has found inhalation of NO improved survival in a high altitude rat model. NO donor isosorbide mononitrate derivants might have a protective effect against hypoxia. We synthesized a series of isosorbide mononitrate derivant compounds to test their anti-hypoxia activities. Normobaric hypoxia and hypobaric hypoxia models were used to study the protective role of NO donor in mice. The results showed isosorbide mononitrate derivants had protective effects in hypoxia mice. Among those compounds, acetyl ferulic isosorbide mononitrate (AFIM) was the most effective. It prolonged the survival time during the normobaric hypoxia test. It decreased malondialdehyde (MDA) and H2O2 in hypobaric hypoxia mice. The antioxidase activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) remained in normal ranges in the AFIM group. As a sign of mitochondrial dysfunction, the activities of ATPase were down regulated in mice under hypobaric hypoxia conditions. AFIM also protected ATPase activities. The protective effects of AFIM might come from a sustained NO supply and the release of acetyl ferulic acid with anti-oxidant activity.

Determination of rifampicin in rat plasma by modified large-volume direct injection RAM-HPLC and its application to a pharmcokinetic study.

A direct large volume injection high-performance liquid chromatography (HPLC) method with homemade restricted-access media (RAM) pre-column and combined with a column-switching valve was established and developed for determination rifampicin (RIP) in rat plasma. The rat plasma samples (100 µL) were injected directly onto pre-column, where RIP was retained and pre-concentrated, while proteins were washed to waste using a methanol-water (5:95) as the mobile phase at a flow rate of 1 mL/min. Then, by rotation of the switching valve at 5 min, the RIP were eluted from the pre-column and transferred to an Luna C18 analytical column by the chromatographic mobile phase consisting of methanol-acetonitrile-10 mm ammonium format (60:5:35) at a flow rate of 1 mL/min. The total analytical run time was 15 min with UV detection wavelength at 254 nm. Carbamazepine was used as the internal standard. Excellent linear correlation (r = 0.9993) was obtained in the range of 0.25-8 µg/mL for rat plasma. The intra-day and inter-day precisions of RIP were all <5.0%. The recoveries were in the range of from 99.98-113.66% for plasma. This on-line RAM-HPLC method was successfully applied to the pharmacokinetic study of RIP in rat plasma.