Blood-to-brain influx transport of nicotine at the rat blood?brain barrier: Involvement of a pyrilamine-sensitive organic cation transport process

The putative proton-coupled organic cation antiporter is involved in uptake of triptans into human brain capillary endothelial cells

BACKGROUND

Triptans are anti-migraine drugs with a potential central site of action. However, it is not known to what extent triptans cross the blood-brain barrier (BBB). The aim of this study was therefore to determine if triptans pass the brain capillary endothelium and investigate the possible underlying mechanisms with focus on the involvement of the putative proton-coupled organic cation (H+/OC) antiporter. Additionally, we evaluated whether triptans interacted with the efflux transporter, P-glycoprotein (P-gp).

METHODS

We investigated the cellular uptake characteristics of the prototypical H+/OC antiporter substrates, pyrilamine and oxycodone, and seven different triptans in the human brain microvascular endothelial cell line, hCMEC/D3. Triptan interactions with P-gp were studied using the IPEC-J2 MDR1 cell line. Lastly, in vivo neuropharmacokinetic assessment of the unbound brain-to-plasma disposition of eletriptan was conducted in wild type and mdr1a/1b knockout mice.

RESULTS

We demonstrated that most triptans were able to inhibit uptake of the H+/OC antiporter substrate, pyrilamine, with eletriptan emerging as the strongest inhibitor. Eletriptan, almotriptan, and sumatriptan exhibited a pH-dependent uptake into hCMEC/D3 cells. Eletriptan demonstrated saturable uptake kinetics with an apparent Km of 89 ± 38 µM and a Jmax of 2.2 ± 0.7 nmol·min-1·mg protein-1 (n = 3). Bidirectional transport experiments across IPEC-J2 MDR1 monolayers showed that eletriptan is transported by P-gp, thus indicating that eletriptan is both a substrate of the H+/OC antiporter and P-gp. This was further confirmed in vivo, where the unbound brain-to-unbound plasma concentration ratio (Kp,uu) was 0.04 in wild type mice while the ratio rose to 1.32 in mdr1a/1b knockout mice.

CONCLUSIONS

We have demonstrated that the triptan family of compounds possesses affinity for the H+/OC antiporter proposing that the putative H+/OC antiporter plays a role in the BBB transport of triptans, particularly eletriptan. Our in vivo studies indicate that eletriptan is subjected to simultaneous brain uptake and efflux, possibly facilitated by the putative H+/OC antiporter and P-gp, respectively. Our findings offer novel insights into the potential central site of action involved in migraine treatment with triptans and highlight the significance of potential transporter related drug-drug interactions.

A review on the effect of COX-2-mediated mechanisms on development and progression of gastric cancer induced by nicotine

Smoking is a documented risk factor for cancer, e.g., gastric cancer. Nicotine, the principal tobacco alkaloid, would exert its role of contribution to gastric cancer development and progression through nicotinic acetylcholine receptors (nAChRs) and β-adrenergic receptors (β-ARs), which then promote cancer cell proliferation, migration and invasion. As a key isoenzyme in conversion of arachidonic acid to prostaglandins, cyclooxygenase-2 (COX-2) has been demonstrated to have a wide range of effects in carcinogenesis and tumor development. At present, many studies have reported the effect of nicotine on gastric cancer by binding to nAChR, as well as indirectly stimulating β-AR to mediate COX-2-related pathways. This review summarizes these studies, and also proposes more potential COX-2-mediated mechanisms. These events might contribute to the growth and progression of gastric cancer exposed to nicotine through tobacco smoke or cigarette substitutes. Also, this review article has therefore the potential not only to make a significant contribution to the treatment and prognosis of gastric cancer for smokers but also to the clinical application of COX-2 antagonists. In addition, this work also discusses the considerable challenges of this field with special reference to the future perspective of COX-2-mediated mechanisms in development and progression of gastric cancer induced by nicotine.

Targeting Transporters for Drug Delivery to the Brain: Can We Do Better?

Limited drug delivery to the brain is one of the major reasons for high failure rates of central nervous system (CNS) drug candidates. The blood–brain barrier (BBB) with its tight junctions, membrane transporters, receptors and metabolizing enzymes is a main player in drug delivery to the brain, restricting the entrance of the drugs and other xenobiotics. Current knowledge about the uptake transporters expressed at the BBB and brain parenchymal cells has been used for delivery of CNS drugs to the brain via targeting transporters. Although many transporter-utilizing (pro)drugs and nanocarriers have been developed to improve the uptake of drugs to the brain, their success rate of translation from preclinical development to humans is negligible. In the present review, we provide a systematic summary of the current progress in development of transporter-utilizing (pro)drugs and nanocarriers for delivery of drugs to the brain. In addition, we applied CNS pharmacokinetic concepts for evaluation of the limitations and gaps in investigation of the developed transporter-utilizing (pro)drugs and nanocarriers. Finally, we give recommendations for a rational development of transporter-utilizing drug delivery systems targeting the brain based on CNS pharmacokinetic principles.

Differences in Cerebral Distribution between Imipramine and Paroxetine via Membrane Transporters at the Rat Blood-Brain Barrier

PURPOSE

The present study aimed to elucidate the transport properties of imipramine and paroxetine, which are the antidepressants, across the blood-brain barrier (BBB) in rats.

METHODS

In vivo influx and efflux transport of imipramine and paroxetine across the BBB were tested using integration plot analysis and a combination of brain efflux index and brain slice uptake studies, respectively. Conditionally immortalized rat brain capillary endothelial cells, TR-BBB13 cells, were utilized to characterize imipramine and paroxetine transport at the BBB in vitro.

RESULTS

The in vivo influx clearance of [3H]imipramine and [3H]paroxetine in rats was determined to be 0.322 mL/(min·g brain) and 0.313 mL/(min·g brain), respectively. The efflux clearance of [3H]imipramine and [3H]paroxetine was 0.380 mL/(min·g brain) and 0.126 mL/(min·g brain), respectively. These results suggest that the net flux of paroxetine, but not imipramine, at the BBB in vivo was dominated by transport to the brain from the circulating blood. The uptake of imipramine and paroxetine by TR-BBB13 cells exhibited time- and temperature-dependence and one-saturable kinetics with a Km of 37.6 μM and 89.2 μM, respectively. In vitro uptake analyses of extracellular ion dependency and the effect of substrates/inhibitors for organic cation transporters and transport systems revealed minor contributions to known transporters and transport systems and the difference in transport properties in the BBB between imipramine and paroxetine.

CONCLUSIONS

Our study showed the comprehensive outcomes of imipramine and paroxetine transport at the BBB, implying that molecular mechanism(s) distinct from previously reported transporters and transport systems are involved in the transport.

Mechanistic insights into the efficacy of memantine in treating certain drug addictions

The deleterious effects of the drug addiction epidemic are compounded by treatment strategies that are only marginally efficacious. Memantine is a unique glutamatergic medication with proven ability to attenuate drug addiction in preclinical models. However, clinical translational studies are inconsistent. In this review, we summarize preclinical evidences and clinical trials that investigated the efficacy of memantine in treating patients with alcohol, opiate, cocaine, and nicotine use disorders and discuss the results from a mechanistic point of view. Memantine has shown efficacy in reducing alcohol and opiate craving, consumption, and withdrawal severity. However, in cocaine and nicotine use disorders, memantine did not have significant effect on cravings or consumption. Additionally, memantine was associated with increased subjective effects of alcohol, cocaine, and nicotine. We discuss possible mechanisms behind this variability. Since memantine transiently blocks NMDA receptors and protects neurons from overstimulation by excessive synaptic glutamate, its efficacy should be observed in drug phases that cause hyperglutamatergic states, while hypoglutamatergic drug use states would not resolve with blocking NMDA receptors. Second, memantine pharmacokinetic studies have been done in rodents and healthy volunteers, but not in patients with substance use disorder. Memantine, opiates, cocaine, and nicotine share the same transporter family at the blood brain barrier. This shared transport mechanism could impact brain concentrations of memantine and its effects. In conclusion, memantine remains an intriguing compound in our pharmacopeia with controversial results in treating certain aspects of drug addiction. Further studies are needed to understand the clinical and biological correlates of its efficacy.

Total Synthesis of Decahydroquinoline Poison Frog Alkaloids ent-cis-195A and cis-211A

The total synthesis of two decahydroquinoline poison frog alkaloids ent-cis-195A and cis-211A were achieved in 16 steps (38% overall yield) and 19 steps (31% overall yield), respectively, starting from known compound 1. Both alkaloids were synthesized from the common key intermediate 11 in a divergent fashion, and the absolute stereochemistry of natural cis-211A was determined to be 2R, 4aR, 5R, 6S, and 8aS. Interestingly, the absolute configuration of the parent decahydroquinoline nuclei of cis-211A was the mirror image of that of cis-195A, although both alkaloids were isolated from the same poison frog species, Oophaga (Dendrobates) pumilio, from Panama.

Structural Requirements for Uptake of Diphenhydramine Analogs into hCMEC/D3 Cells Via the Proton-Coupled Organic Cation Antiporter

There is increasing evidence that a proton-coupled organic cation (H⁺/OC) antiporter facilitates uptake of various central nervous system-active drugs, such as the histamine H1 receptor antagonist diphenhydramine, into the brain. The purpose of this study was to clarify the structural requirements for H⁺/OC antiporter-mediated uptake into hCMEC/D3 cells, an established in vitro model of the human blood-brain barrier, by using a series of diphenhydramine analogs. For this purpose, we synthesized seven tertiary amine analogs and three amide analogs. Uptake of all the amines was facilitated by an outwardly directed H⁺ gradient and inhibited by pyrilamine, a typical substrate and a strong inhibitor of the H⁺/OC antiporter. Further, uptake of most of the amines was trans-stimulated by pyrilamine. Uptake of the amines was 21 times faster than that of the amides on average, even though the lipophilicity (log D_7.4) of the amines is lower than that of the amides. Amines containing a pyrrolidine or piperidine ring showed the highest uptake rates. Our results suggest that an amine moiety, especially a heterocyclic amine moiety, is important for recognition and transport by the H⁺/OC antiporter.

Involvement of a Novel Organic Cation Transporter in Paeonol Transport Across the Blood-Brain Barrier

Paeonol has neuroprotective function, which could be useful for improving central nervous system disorder. The purpose of this study was to characterize the functional mechanism involved in brain transport of paeonol through blood-brain barrier (BBB). Brain transport of paeonol was characterized by internal carotid artery perfusion (ICAP), carotid artery single injection technique (brain uptake index, BUI) and intravenous (IV) injection technique in vivo. The transport mechanism of paeonol was examined using conditionally immortalized rat brain capillary endothelial cell line (TR-BBB) as an in vitro model of BBB. Brain volume of distribution (V_D) of [³H]paeonol in rat brain was about 6-fold higher than that of [¹⁴C]sucrose, the vascular space marker of BBB. The uptake of [3H]paeonol was concentration-dependent. Brain volume of distribution of paeonol and BUI as in vivo and inhibition of analog as in vitro studies presented significant reduction effect in the presence of unlabeled lipophilic compounds such as paeonol, imperatorin, diphenhydramine, pyrilamine, tramadol and ALC during the uptake of [³H]paeonol. In addition, the uptake significantly decreased and increased at the acidic and alkaline pH in both extracellular and intracellular study, respectively. In the presence of metabolic inhibitor, the uptake reduced significantly but not affected by sodium free or membrane potential disruption. Similarly, paeonol uptake was not affected on OCTN2 or rPMAT siRNA transfection BBB cells. Interestingly. Paeonol is actively transported from the blood to brain across the BBB by a carrier mediated transporter system.

Molecular Insights Into Memory-Enhancing Metabolites of Nicotine in Brain: A Systematic Review

Background: The alleged procognitive effects of nicotine and its metabolites in brain are controversial. Objective: Here, we review the pharmacologically active metabolites of nicotine in brain and their effects on neuronal mechanisms involving two main cognitive domains, i.e., learning and memory. Methods: We searched Embase, Medline via PubMed, Scopus, and Web of Science databases for entries no later than May 2018, and restricted the search to articles about nicotine metabolites and cognitive behavior or cognitive mechanisms. Results: The initial search yielded 425 articles, of which 17 were eligible for inclusion after application of exclusion criteria. Of these, 13 were experimental, two were clinical, and two were conference papers. Conclusions: The results revealed three pharmacologically active biotransformations of nicotine in the brain, including cotinine, norcotinine, and nornicotine, among which cotinine and nornicotine both had a procognitive impact without adverse effects. The observed effect was significant only for cotinine.

Role of cationic drug-sensitive transport systems at the blood-cerebrospinal fluid barrier in para-tyramine elimination from rat brain

Background

para-Tyramine (p-TA) is a biogenic amine which is involved in multiple neuronal signal transductions. Since the concentration of p-TA in dog cerebrospinal fluid (CSF) has been reported to be greater than that in plasma, it is proposed that clearance of cerebral p-TA is important for normal function. The purpose of this study was to examine the role of the blood–brain barrier and blood-cerebrospinal fluid barrier (BCSFB) in p-TA clearance from the brain.

Methods

In vivo [³H]p-TA elimination from rat cerebral cortex and from CSF was examined after intracerebral and intracerebroventricular administration, respectively. To evaluate BCSFB-mediated p-TA transport, [³H]p-TA uptake by isolated rat choroid plexus and conditionally immortalized rat choroid plexus epithelial cells, TR-CSFB3 cells, was performed.

Results

The half-life of [³H]p-TA elimination from rat CSF was found to be 2.9 min, which is 62-fold faster than that from rat cerebral cortex. In addition, this [³H]p-TA elimination from the CSF was significantly inhibited by co-injection of excess unlabeled p-TA. Thus, carrier-mediated p-TA transport process(es) are assumed to take part in p-TA elimination from the CSF. Since it is known that transporters at the BCSFB participate in compound elimination from the CSF, [³H]p-TA transport in ex vivo and in vitro models of rat BCSFB was examined. The [³H]p-TA uptake by isolated rat choroid plexus and TR-CSFB3 cells was time-dependent and was inhibited by unlabeled p-TA, indicating carrier-mediated p-TA transport at the BCSFB. The p-TA uptake by isolated choroid plexus and TR-CSFB3 cells was not reduced in the absence of extracellular Na⁺ and Cl⁻, and in the presence of substrates of typical organic cation transporters. However, this p-TA uptake was significantly inhibited by cationic drugs such as propranolol, imipramine, amantadine, verapamil, and pyrilamine. Moreover, p-TA uptake by TR-CSFB3 cells took place in an oppositely-directed H⁺ gradient manner. Therefore, this suggested that p-TA transport at the BCSFB involves cationic drug-sensitive transport systems which are distinct from typical plasma membrane organic cation transporters.

Conclusion

Our study indicates that p-TA elimination from the CSF is greater than that from the cerebral cortex. Moreover, it is suggested that cationic drug-sensitive transport systems in the BCSFB participate in this p-TA elimination from the CSF.

Nicotine transport in lung and non-lung epithelial cells

AIMS

Nicotine is rapidly absorbed from the lung alveoli into systemic circulation during cigarette smoking. However, mechanism underlying nicotine transport in alveolar epithelial cells is not well understood to date. In the present study, we characterized nicotine uptake in lung epithelial cell lines A549 and NCI-H441 and in non-lung epithelial cell lines HepG2 and MCF-7.

MATERIALS AND METHODS

Characteristics of [³H]nicotine uptake was studied using these cell lines.

KEY FINDINGS

Nicotine uptake in A549 cells occurred in a time- and temperature-dependent manner and showed saturation kinetics, with a Km value of 0.31mM. Treatment with some organic cations such as diphenhydramine and pyrilamine inhibited nicotine uptake, whereas treatment with organic cations such as carnitine and tetraethylammonium did not affect nicotine uptake. Extracellular pH markedly affected nicotine uptake, with high nicotine uptake being observed at high pH up to 11.0. Modulation of intracellular pH with ammonium chloride also affected nicotine uptake. Treatment with valinomycin, a potassium ionophore, did not significantly affect nicotine uptake, indicating that nicotine uptake is an electroneutral process. For comparison, we assessed the characteristics of nicotine uptake in another lung epithelial cell line NCI-H441 and in non-lung epithelial cell lines HepG2 and MCF-7. Interestingly, these cell lines showed similar characteristics of nicotine uptake with respect to pH dependency and inhibition by various organic cations.

SIGNIFICANCE

The present findings suggest that a similar or the same pH-dependent transport system is involved in nicotine uptake in these cell lines. A novel molecular mechanism of nicotine transport is proposed.

Imperatorin is Transported through Blood-Brain Barrier by Carrier-Mediated Transporters

Imperatorin, a major bioactive furanocoumarin with multifunctions, can be used for treating neurodegenerative diseases. In this study, we investigated the characteristics of imperatorin transport in the brain. Experiments of the present study were designed to study imperatorin transport across the blood-brain barrier both in vivo and in vitro. In vivo study was performed in rats using single intravenous injection and in situ carotid artery perfusion technique. Conditionally immortalized rat brain capillary endothelial cells were as an in vitro model of blood-brain barrier to examine the transport mechanism of imperatorin. Brain distribution volume of imperatorin was about 6 fold greater than that of sucrose, suggesting that the transport of imperatorin was through the blood-brain barrier in physiological state. Both in vivo and in vitro imperatorin transport studies demonstrated that imperatorin could be transported in a concentration-dependent manner with high affinity. Imperatorin uptake was dependent on proton gradient in an opposite direction. It was significantly reduced by pretreatment with sodium azide. However, its uptake was not inhibited by replacing extracellular sodium with potassium or N-methylglucamine. The uptake of imperatorin was inhibited by various cationic compounds, but not inhibited by TEA, choline and organic anion substances. Transfection of plasma membrane monoamine transporter, organic cation transporter 2 and organic cation/carnitine transporter 2/1 siRNA failed to alter imperatorin transport in brain capillary endothelial cells. Especially, tramadol, clonidine and pyrilamine inhibited the uptake of [³H]imperatorin competitively. Therefore, imperatorin is actively transported from blood to brain across the blood-brain barrier by passive and carrier-mediated transporter.

Involvement of Proton-Coupled Organic Cation Antiporter in Varenicline Transport at Blood-Brain Barrier of Rats and in Human Brain Capillary Endothelial Cells

Varenicline is a selective partial α₄β₂ nicotinic acetylcholine receptor agonist, which is used to help achieve smoking cessation. Here, we investigated varenicline transport at the blood-brain barrier by means of in vivo microdialysis, in situ brain perfusion, and brain efflux index measurements in rats, and in vitro uptake studies in human brain capillary endothelial cells. Microdialysis demonstrated that varenicline is actively transported from blood to brain in rats. Blood-to-brain uptake transport of varenicline, as measured by the in situ brain perfusion technique, was strongly inhibited by diphenhydramine, a potent inhibitor of proton-coupled organic cation (H⁺/OC) antiporter. However, brain efflux index study showed that brain-to-blood efflux transport of varenicline was not inhibited by diphenhydramine. In human brain capillary endothelial cells, varenicline was taken up time- and concentration-dependently. The uptake was dependent on an oppositely directed proton gradient, but was independent of extracellular sodium and membrane potential. The uptake was inhibited by a metabolic inhibitor, and by substrates of H⁺/OC antiporter, but not by substrates or inhibitors of OCTs, OCTNs, PMAT, and MATE1, which are known organic cation transporters. The present results suggest that the H⁺/OC antiporter contributes predominantly to varenicline uptake at the blood-brain barrier.

Involvement of a proton-coupled organic cation antiporter in the blood-brain barrier transport of amantadine

The blood-to-brain transport of amantadine, a weak N-methyl-d-aspartate (NMDA) antagonist, has been shown previously to participate in the cationic drug-sensitive transport system across the mouse blood-brain barrier (BBB). The purpose of the present study was to characterize the influx transport system by means of both an in situ mouse brain perfusion technique and in vitro studies using rat immortalized brain capillary endothelial cells (GPNT). The observed concentration-dependent initial uptake rate of [(3) H]amantadine suggested the involvement of a carrier-mediated transport mechanism. The normal uptake at physiological pH 7.4 was decreased by 72.9% in acidic perfusate, while it was increased by 35.3% in alkaline perfusate. These results suggest that pH-dependent transport is regulated by utilizing an oppositely directed proton gradient as a driving force. In addition, the [(3) H]amantadine uptake was moderately inhibited by the adamantane structural analogs (rimantadine and memantine) and other cationic drugs (pyrilamine, clonidine, nicotine, etc.), but not by substrates or inhibitors of the well-characterized organic cation transporters (tetraethylammonium, l-carnitine and choline). A similar inhibition pattern was observed between the in vivo studies and the in vitro experiments. These results indicate that the influx transport for amantadine across the BBB involves a proton-coupled organic cation antiporter. Copyright © 2016 John Wiley & Sons, Ltd.

Reduction of nicotine self-administration by chronic nicotine infusion with H1 histamine blockade in female rats

RATIONALE

Chronic nicotine infusion via transdermal patches has been widely shown to assist with smoking cessation. In particular, transdermal nicotine treatment prior to quitting smoking helps reduce ad libitum smoking and aids cessation Rose et al. (Nicotine Tob Res 11:1067-75, 2009). However, despite this success, the majority of smokers who use transdermal nicotine fail to permanently quit smoking. Additional treatments are needed. Tobacco addiction does not just depend on nicotinic receptor systems; a variety of neural systems are involved, including dopamine, norepinepherine, serotonin, and histamine.

OBJECTIVES

Given the involvement of a variety of neural systems in the circuits of addiction, combination therapy may offer improved efficacy for successful smoking cessation beyond single treatments alone. We have found that pyrilamine, an H1 histamine antagonist, significantly decreases nicotine self-administration in rats.

METHODS

The current study was conducted to confirm the effect of chronic nicotine infusion on ongoing nicotine self-administration and resumed access after enforced abstinence and to determine the interaction of chronic nicotine with an H1 antagonist treatment.

RESULTS

Chronic nicotine infusion via osmotic minipump (2.5 and 5 mg/kg/day for 28 days) significantly reduced nicotine self-administration in a dose-dependent manner. Chronic nicotine infusion also reduced the resumption of nicotine self-administration after enforced abstinence. Chronic pyrilamine infusion (25 mg/kg/day for 14 days) also significantly reduced nicotine self-administration.

CONCLUSION

The combination of chronic nicotine and pyrilamine reduced nicotine self-administration to a greater extent than treatment with either drug alone.

Effect of Transient Nicotine Load Shock on the Performance ofPseudomonassp. HF-1 Bioaugmented Sequencing Batch Reactors

Bioaugmentation with degrading bacteria can improve the treatment of nicotine-containing tobacco industrial wastewater effectively. However, the transient and extremely high feeding of pollutants may compromise the effectiveness of the bioaugmented reactors. The effect of transient nicotine shock loads on the performance ofPseudomonassp. HF-1 bioaugmented SBRs were studied. The results showed that, under 500–2500 mg/L of transient nicotine shocks, all the reactors still could realize 100% of nicotine degradation in 4 days of recovery, while the key nicotine degradation enzyme HSP hydroxylase increased in expression. Though the dramatic increase of activities of ROS, MDA, SOD, and CAT suggested that transient nicotine shock loads could induce oxidative stress on microorganisms in activated sludge, a decrease to control level demonstrated that most of the microorganisms could resist 500–1500 mg/L of transient nicotine shock under the protection from strain HF-1. After 8 cycles of recovery, high ROS level and low TOC removal in high transient shock reactors implied that 2000–2500 mg/L of transient nicotine shock was out of its recovery of strain HF-1 bioaugmented system. This study enriched our understanding on highly efficient nicotine-degrading strain bioaugmented system, which would be beneficial to tobacco waste or wastewater treatment in engineering.

Mechanism of brain targeting by dexibuprofen prodrugs modified with ethanolamine-related structures

The first molecular insights into how prodrugs modified with ethanolamine-related structures target the brain were generated using an in vitro BBB model and in situ perfusion technique. Prodrugs were delivered safely and efficiently to the brain through tight interaction with the anionic membrane of brain capillary endothelial cells, observed as a shift in zeta potential, followed by uptake into the cells. Prodrugs III and IV carrying primary and secondary amine modifications appeared to enter the brain via energy-independent passive diffusion. In contrast, besides the passive diffusion, prodrugs I and II carrying tertiary amine modifications also appeared to enter via an active process that was energy and pH dependent but was independent of sodium or membrane potential. This active process involved, at least in part, the pyrilamine-sensitive H(+)/OC antiporter, for which the N,N-diethyl-based compound II showed a much lower affinity than the N,N-dimethyl-based compound I, likely due to steric hindrance. These new insights into brain-targeting mechanisms may help guide efforts to design new prodrugs.

[Carrier-mediated Transport of Cationic Drugs across the Blood-Tissue Barrier]

Studies of neurological dysfunction have revealed the neuroprotective effect of several cationic drugs, suggesting their usefulness in the treatment of neurological diseases. In the brain and retina, blood-tissue barriers such as blood-brain barrier (BBB) and blood-retinal barrier (BRB) are formed to restrict nonspecific solute transport between the circulating blood and neural tissues. Therefore study of cationic drug transport at these barriers is essential to achieve systemic delivery of neuroprotective agents into the neural tissues. In the retina, severe diseases such as diabetic retinopathy and macular degeneration can cause neurological dysfunction that dramatically affects patients' QOL. The BRB is formed by retinal capillary endothelial cells (inner BRB) and retinal pigment epithelial cells (outer BRB). Blood-to-retina transport of cationic drugs was investigated at the inner BRB, which is known to nourish two thirds of the retina. Blood-to-retinal transport of verapamil suggested that the barrier function of the BRB differs from that of the BBB. Moreover, carrier-mediated transport of verapamil and pyrilamine revealed the involvement of novel organic cation transporters at the inner BRB. The identified transport systems for cationic drugs are sensitive to several cationic neuroprotective and anti-angiogenic agents such as clonidine and propranolol, and the involvement of novel transporters was also suggested in their blood-to-retina transport across the inner BRB.

Effect of experimental kidney disease on the functional expression of hepatic reductases

Chronic kidney disease (CKD) affects the nonrenal clearance of drugs by modulating the functional expression of hepatic drug-metabolizing enzymes and transporters. The impact of CKD on oxidative and conjugative metabolism has been extensively studied. However, its effect on hepatic drug reduction, an important phase I drug-metabolism pathway, has not been investigated. We aimed to assess the effect of experimental CKD on hepatic reduction using warfarin as a pharmacological probe substrate. Cytosolic and microsomal cellular fractions were isolated from liver tissue harvested from five-sixths-nephrectomized and control rats (n = 10 per group). The enzyme kinetics for warfarin reduction were evaluated in both fractions, and formation of warfarin alcohols was used as an indicator of hepatic reductase activity. Selective inhibitors were employed to identify reductases involved in warfarin reduction. Gene and protein expression of reductases were determined using quantitative real-time polymerase chain reaction and Western blotting, respectively. Formation of RS/SR-warfarin alcohol was decreased by 39% (P < 0.001) and 43% (P < 0.01) in cytosol and microsomes, respectively, in CKD rats versus controls. However, RR/SS-warfarin alcohol formation was unchanged in the cytosol, and a trend toward its decreased production was observed in microsomes. Gene and protein expression of cytosolic carbonyl reductase 1 and aldo-keto reductase 1C3/18, and microsomal 11β-hydroxysteroid dehydrogenase type 1 were significantly reduced by >30% (P < 0.05) in CKD rats compared with controls. Collectively, these results suggest that the functional expression of hepatic reductases is selectively decreased in kidney disease. Our findings may explain one mechanism for altered nonrenal clearance, exposure, and response of drugs in CKD patients.

Drug abuse and the neurovascular unit

Drug abuse continues to create a major international epidemic affecting society. A great majority of past drug abuse research has focused mostly on the mechanisms of addiction and the specific effects of substance use disorders on brain circuits and pathways that modulate reward, motivation, craving, and decision making. Few studies have focused on the neurobiology of acute and chronic substance abuse as it relates to the neurovascular unit (brain endothelial cell, neuron, astrocyte, microglia, and pericyte). Increasing research indicates that all cellular components of the neurovascular unit play a pivotal role in both the process of addiction and how drug abuse affects the brain response to diseases. This review will focus on the specific effects of opioids, amphetamines, alcohol, and nicotine on the neurovascular unit and its role in addiction and adaption to brain diseases. Elucidation of the role of the neurovascular unit on the neurobiology associated with drug addiction will help to facilitate the development of better therapeutic approaches for drug-dependent individuals.

Bioaugmentation of activated sludge with Acinetobacter sp. TW enhances nicotine degradation in a synthetic tobacco wastewater treatment system

Bioaugmentation (BA) using Acinetobacter sp. TW with high nicotine-degrading efficiency was applied in a bioreactor receiving a load of COD (3,200 ± 50 mg/L) and nicotine (1.0 ± 0.1g/L). The results showed that because of the colonization of strain TW, the COD removal was stable at 80-90%, while nicotine removal reached 98% in the BA system. Furthermore, according to PCR-DGGE fingerprinting, compared with the originally activated sludge, more bacteria existed in the BA systems while some bacteria disappeared from the non-BA system. In terms of the quorum sensing, short chain AHLs increased to assist colonization of strain TW, and long chain AHLs were secreted and helped to resist the nicotine toxicity. Compared with the non-BA system, the amounts of ROS, protein carbonyls and 8-OHdG were significant lower in the BA systems, which suggested that strain TW played an important role in eliminating the nicotine toxicity from the bioreactors.