Functional induction of P-glycoprotein in the blood-brain barrier of streptozotocin-induced diabetic rats: evidence for the involvement of nuclear factor-kappaB, a nitrosative stress-sensitive transcription factor, in the regulation

ABCB1 and ABCG2 Regulation at the Blood-Brain Barrier: Potential New Targets to Improve Brain Drug Delivery

The drug efflux transporters ABCB1 and ABCG2 at the blood-brain barrier limit the delivery of drugs into the brain. Strategies to overcome ABCB1/ABCG2 have been largely unsuccessful, which poses a tremendous clinical problem to successfully treat central nervous system (CNS) diseases. Understanding basic transporter biology, including intracellular regulation mechanisms that control these transporters, is critical to solving this clinical problem.In this comprehensive review, we summarize current knowledge on signaling pathways that regulate ABCB1/ABCG2 at the blood-brain barrier. In Section I, we give a historical overview on blood-brain barrier research and introduce the role that ABCB1 and ABCG2 play in this context. In Section II, we summarize the most important strategies that have been tested to overcome the ABCB1/ABCG2 efflux system at the blood-brain barrier. In Section III, the main component of this review, we provide detailed information on the signaling pathways that have been identified to control ABCB1/ABCG2 at the blood-brain barrier and their potential clinical relevance. This is followed by Section IV, where we explain the clinical implications of ABCB1/ABCG2 regulation in the context of CNS disease. Lastly, in Section V, we conclude by highlighting examples of how transporter regulation could be targeted for therapeutic purposes in the clinic. SIGNIFICANCE STATEMENT: The ABCB1/ABCG2 drug efflux system at the blood-brain barrier poses a significant problem to successful drug delivery to the brain. The article reviews signaling pathways that regulate blood-brain barrier ABCB1/ABCG2 and could potentially be targeted for therapeutic purposes.

Effects of Diabetes Mellitus-Related Dysglycemia on the Functions of Blood-Brain Barrier and the Risk of Dementia

Diabetes mellitus is one of the most common metabolic diseases worldwide, and its long-term complications include neuropathy, referring both to the peripheral and to the central nervous system. Detrimental effects of dysglycemia, especially hyperglycemia, on the structure and function of the blood-brain barrier (BBB), seem to be a significant backgrounds of diabetic neuropathy pertaining to the central nervous system (CNS). Effects of hyperglycemia, including excessive glucose influx to insulin-independent cells, may induce oxidative stress and secondary innate immunity dependent inflammatory response, which can damage cells within the CNS, thus promoting neurodegeneration and dementia. Advanced glycation end products (AGE) may exert similar, pro-inflammatory effects through activating receptors for advanced glycation end products (RAGE), as well as some pattern-recognition receptors (PRR). Moreover, long-term hyperglycemia can promote brain insulin resistance, which may in turn promote Aβ aggregate accumulation and tau hyperphosphorylation. This review is focused on a detailed analysis of the effects mentioned above towards the CNS, with special regard to mechanisms taking part in the pathogenesis of central long-term complications of diabetes mellitus initiated by the loss of BBB integrity.

Effects of 1α,25-dihydroxyvitamin D3 on the pharmacokinetics and biodistribution of ergothioneine, an endogenous organic cation/carnitine transporter 1 substrate, in rats

Purpose

This study aimed to investigate the effects of 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) on the expression levels of organic cation/carnitine transporter 1 (OCTN1) as well as the pharmacokinetics and biodistribution of ergothioneine, an OCTN1 substrate, in rats.

Methods

Rats pretreated with 1,25(OH)₂D₃ (2.56 nmol/kg/day) for four days were administered ergothioneine (2 mg/kg) intravenously. The expression levels of rat OCTN1 (rOCTN1) in organs were determined using real-time quantitative polymerase chain reaction. Ergothioneine levels in plasma, urine, and organs (with and without intravenous injection of exogenous ergothioneine) were determined using liquid chromatography-tandem mass spectrometry.

Results

1,25(OH)₂D₃ pretreatment resulted in a significant decrease in rOCTN1 mRNA expression levels in the kidney and brain, a significant increase in basal plasma levels of ergothioneine (from 48 h), and a significant decrease in the tissue-plasma partition coefficient (K_p) in all tissues (except the heart and lungs) and the basal urine levels of ergothioneine. After intravenous administration, the pharmacokinetic profiles of ergothioneine were consistent with the basal levels of endogenous ergothioneine, with an increase in AUC_∞ by 85%, a significant decrease in total clearance by 49%, and a decrease in V_ss by 32% in 1,25(OH)₂D₃-treated rats. The K_p value and urinary recovery of ergothioneine also decreased in the 1,25(OH)₂D₃-treated group.

Conclusion

This study showed the effects of 1,25(OH)₂D₃ on the expression and function of rOCTN1 by investigating the interaction between 1,25(OH)₂D₃ and ergothioneine. Dose adjustment and possible changes in bioavailability should be considered before the co-administration of vitamin D or its active forms and OCTN1 substrates.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40005-022-00563-1.

Blood-Brain Barrier Transporters: Opportunities for Therapeutic Development in Ischemic Stroke

Globally, stroke is a leading cause of death and long-term disability. Over the past decades, several efforts have attempted to discover new drugs or repurpose existing therapeutics to promote post-stroke neurological recovery. Preclinical stroke studies have reported successes in identifying novel neuroprotective agents; however, none of these compounds have advanced beyond a phase III clinical trial. One reason for these failures is the lack of consideration of blood-brain barrier (BBB) transport mechanisms that can enable these drugs to achieve efficacious concentrations in ischemic brain tissue. Despite the knowledge that drugs with neuroprotective properties (i.e., statins, memantine, metformin) are substrates for endogenous BBB transporters, preclinical stroke research has not extensively studied the role of transporters in central nervous system (CNS) drug delivery. Here, we review current knowledge on specific BBB uptake transporters (i.e., organic anion transporting polypeptides (OATPs in humans; Oatps in rodents); organic cation transporters (OCTs in humans; Octs in rodents) that can be targeted for improved neuroprotective drug delivery. Additionally, we provide state-of-the-art perspectives on how transporter pharmacology can be integrated into preclinical stroke research. Specifically, we discuss the utility of in vivo stroke models to transporter studies and considerations (i.e., species selection, co-morbid conditions) that will optimize the translational success of stroke pharmacotherapeutic experiments.

HMGB1 plays an important role in pyroptosis induced blood brain barrier breakdown in diabetes-associated cognitive decline

Diabetes mellitus increases the risk of dementia, and evidence suggests hyperglycemia is a key contributor to neurodegeneration. However, our understanding of diabetes-associated cognitive decline, an important complication of diabetes mellitus, is lacking and the underlying mechanism is unclear. Blood brain barrier (BBB) breakdown is a possible cause of dementia in diabetes mellitus and Alzheimer's disease. Accumulating evidence shows BBB dysfunction caused by hyperglycemia contributes to cognitive decline. A specific type of inflammatory programmed cell death, called pyroptosis, has potential as a therapeutic target for BBB-associated diseases. Potential inducers of pyroptosis include inflammasomes such as NLRP3, whose activation relies on damage-associated molecular patterns. High mobility group box 1 (HMGB1) is a highly conserved, ubiquitous protein found in most cell types, and acts as a damage-associated molecular pattern when released from the nucleus. We propose that HMGB1 influences vascular inflammation by activating the NLRP3 inflammasome and thereby initiating pyroptosis in vascular cells. Moreover, HMGB1 plays a pivotal role in the pathogenesis of diabetes mellitus and diabetic complications. Here, we review the role of HMGB1 in BBB dysfunction induced by hyperglycemia and propose that HMGB1 is a promising therapeutic target for countering diabetes-associated cognitive decline.

Cardiotoxic Effects of the Antineoplastic Doxorubicin in a Model of Metabolic Syndrome: Oxidative Stress and Transporter Expression in the Heart

ABSTRACT

The aim of the present work was to examine whether metabolic syndrome-like conditions in rats with fructose (F) overload modify the cardiotoxic effects induced by doxorubicin (DOX) and whether the treatment altered the expression of P-gp, breast cancer resistance protein, and organic cation/carnitine transporters in the heart. Male Sprague-Dawley rats received either tap water (control group [C]; n = 16) or water with F 10% wt/vol (n = 16) during 8 weeks. Three days before being killed, the animals received a single dose of DOX (6 mg/kg, ip, md) (C-DOX and F-DOX groups) or vehicle (VEH; ISS 1 mL/kg BW; ip) (C-VEH and F-VEH groups) (n = 8 per group). F overload enhanced thiobarbituric acid-reactive substance levels in the left ventricle, and DOX injection further increased those values. DOX did not alter thiobarbituric acid-reactive substance production in C animals. DOX caused a decrease of 30% in the ejection fraction and a nearly 40% reduction in the fractional shortening in F animals, but not in C rats. Cardiac tissue levels of P-gp decreased by about 30% in F rats compared with the C groups. DOX did not modify cardiac P-gp expression. Breast cancer resistance protein and organic cation/carnitine transporter (OCTN 1/2/3) protein levels did not change with either F or DOX. It is suggested that DOX could cause greater cardiotoxicity in rats receiving F, probably due to enhanced cardiac lipid peroxidation and lower expression of cardiac P-gp. These results support the hypothesis that the cardiotoxicity of DOX could be increased under metabolic syndrome-like conditions or in other health disorders that involve cardiovascular risk factors.

P-glycoprotein associated with diabetes mellitus and survival of patients with pancreatic cancer: 8-year follow-up

Diabetes mellitus (DM) has a high prevalence in patients with pancreatic cancer (PaC), but the prognostic value of DM in PaC remains controversial. Alterations of P-glycoprotein (P-gp) and cytochrome P450 3A4 (CYP3A4) contribute to multidrug resistance and intestinal metabolism in a variety of cancer types, which may be implicated in DM development. This study aimed to explore the potential prognostic value of P-gp and CYP3A4 in PaC patients in the context of DM through long-term follow-up. We retrospectively reviewed the medical records of patients with PaC admitted at The First People's Hospital of Changzhou, Jiangsu, China, from January 2011 to November 2019 and identified two cohorts of adult patients with PaC, including 24 with DM and 24 without DM (non-DM). The baseline clinical characteristics and outcomes were compared. Immunohistochemistry showed that protein expression of P-gp, but not CYP3A, in duodenum tissues was significantly upregulated in PaC patients with DM compared with those without DM. Kaplan-Meier analysis and log-rank test showed that the survival of patients with PaC and DM/high expression of P-gp was not significantly reduced compared with that of patients without DM/low expression of P-gp. These findings suggested that P-gp expression levels were different in the DM and non-DM groups of patients with PaC, but DM and duodenal P-gp levels were not associated with the long-term survival of patients with PaC. It appears that the presence of DM or P-gp expression levels may not serve as effective prognostic markers for PaC.

The regulation of drug-metabolizing enzymes and membrane transporters by inflammation: Evidences in inflammatory diseases and age-related disorders

Drug-metabolizing enzymes (DMEs) and membrane transporters play important roles in the absorption, distribution, metabolism, and excretion processes that determine the pharmacokinetics of drugs. Inflammation has been shown to regulate the expression and function of these drug-processing proteins. Given that inflammation is a common feature of many diseases, in this review, the general mechanisms for inflammation-mediated regulation of DMEs and transporters are described. Also, evidences regarding the aberrant expression of these drug-processing proteins in several inflammatory diseases and age-related disorders are provided.

Neurovascular unit transport responses to ischemia and common coexisting conditions: smoking and diabetes

Transporters at the neurovascular unit (NVU) are vital for the regulation of normal brain physiology via ion, water, and nutrients movement. In ischemic stroke, the reduction of cerebral blood flow causes several complex pathophysiological changes in the brain, one of which includes alterations of the NVU transporters, which can exacerbate stroke outcome by increased brain edema (by altering ion, water, and glutamate transporters), altered energy metabolism (by altering glucose transporters), and enhanced drug toxicity (by altering efflux transporters). Smoking and diabetes are common risk factors as well as coexisting conditions in ischemic stroke that are also reported to change the expression and function of NVU transporters. Coexistence of these conditions could cause an additive effect in terms of the alterations of brain transporters that might lead to worsened ischemic stroke prognosis and recovery. In this review, we have discussed the effects of ischemic stroke, smoking, and diabetes on some essential NVU transporters and how the simultaneous presence of these conditions can affect the clinical outcome after an ischemic episode. Further scientific investigations are required to elucidate changes in NVU transport in cerebral ischemia, which can lead to better, personalized therapeutic interventions tailor-made for these comorbid conditions.

Intermittent streptozotocin administration induces behavioral and pathological features relevant to Alzheimer's disease and vascular dementia

RATIONALE

Diabetes mellitus (DM) is a major risk factor for Alzheimer's disease and vascular dementia. Few animal models exist that focus on the metabolic contributions to dementia onset and progression. Thus, there is strong scientific rationale to explore the effects of streptozotocin (STZ), a diabetogenic compound, on vascular and inflammatory changes within the brain.

OBJECTIVE AND METHODS

The present study was designed to evaluate the effect of staggered, low-dose administration of STZ on behavioral and cognitive deficits, neuroinflammation, tau pathology, and histopathological alterations related to dementia.

RESULTS

Staggered administration (Days 1, 2, 3, 14, 15) of streptozotocin (40 mg/kg/mL) induced a diabetic-like state in mice, resulting in sustained hyperglycemia. STZ-treated animals displayed memory deficits in the novel object recognition task as well as increased tau phosphorylation and increased neuroinflammation. Additionally, STZ led to altered insulin signaling, exhibited by decreased plasma insulin and decreased levels of insulin degrading enzyme and pAKT within the hippocampus.

CONCLUSIONS

STZ-treated animals exhibit cognitive deficits and histopathological changes seen in dementia. This model of dementia warrants continued investigation to better understand the role that DM plays in dementia-related alterations.

Altered Transport and Metabolism of Phenolic Compounds in Obesity and Diabetes: Implications for Functional Food Development and Assessment

Interest in the application of phenolic compounds from the diet or supplements for the prevention of chronic diseases has grown substantially, but the efficacy of such approaches in humans is largely dependent on the bioavailability and metabolism of these compounds. Although food and dietary factors have been the focus of intense investigation, the impact of disease states such as obesity or diabetes on their absorption, metabolism, and eventual efficacy is important to consider. These factors must be understood in order to develop effective strategies that leverage bioactive phenolic compounds for the prevention of chronic disease. The goal of this review is to discuss the inducible metabolic systems that may be influenced by disease states and how these effects impact the bioavailability and metabolism of dietary phenolic compounds. Because current studies generally report that obesity and/or diabetes alter the absorption and excretion of these compounds, this review includes a description of the absorption, conjugation, and excretion pathways for phenolic compounds and how they are potentially altered in disease states. A possible mechanism that will be discussed related to the modulation of phenolic bioavailability and metabolism may be linked to increased inflammatory status from increased amounts of adipose tissue or elevated plasma glucose concentrations. Although more studies are needed, the translation of benefits derived from dietary phenolic compounds to individuals with obesity or diabetes may require the consideration of dosing strategies or be accompanied by adjunct therapies to improve the bioavailability of these compounds.

PPARγ agonists regulate bidirectional transport of amyloid-β across the blood-brain barrier and hippocampus plasticity in db/db mice

BACKGROUND AND PURPOSE

There is emerging evidence suggesting that abnormal transport of amyloid-β (Aβ) across the blood-brain barrier (BBB) is involved in diabetes-associated cognitive decline. We investigated whether PPARγ agonists restore Aβ transport across the BBB and hippocampal plasticity in db/db mice.

EXPERIMENTAL APPROACH

Efflux and influx of Aβ across the BBB were determined by stereotaxic intra-cerebral or i.a. infusion of [(125) I]-Aβ1-40 respectively. Receptor for advanced glycation end products (RAGE) and low-density lipoprotein receptor-related protein 1 (LRP1), which are involved in Aβ influx and efflux, PPARγ and NF-κB p65 at the BBB, as well as hippocampal Aβ, caspase-3, Bax and Bcl-2 were assayed by Western blot, immunohistochemistry and RT-PCR. In vivo, hippocampal LTP was recorded, and Morris water maze and Y-maze tasks were performed.

KEY RESULTS

Treatment with PPARγ agonists, rosiglitazone (0.8 mg·kg(-1) ) and pioglitazone (9.0 mg·kg(-1) ), for 6 weeks significantly increased Aβ efflux and decreased Aβ influx across the BBB in db/db mice. Concomitantly, they decreased hippocampal Aβ1-40 and Aβ1-42 , suppressed neuronal apoptosis, as indicated by decreased caspase-3 activity and increased ratio of Bcl-2/Bax, and increased hippocampal plasticity, characterized by an enhanced in vivo LTP and better performance in behavioural tests. Furthermore, the PPARγ agonists induced the expression of LRP1 gene by activation of PPARγ and suppressed RAGE gene expression by inactivation of NF-κB signalling at the BBB of db/db mice.

CONCLUSIONS AND IMPLICATIONS

PPARγ agonists modify abnormal Aβ transport across the BBB and this is accompanied by amelioration of β-amyloidosis and an improvement in hippocampal plasticity in diabetic mice.

Increased intestinal P-glycoprotein expression and activity with progression of diabetes and its modulation by epigallocatechin-3-gallate: Evidence from pharmacokinetic studies

The aim of this study was to evaluate the change in the expression and the activity of intestinal P-glycoprotein (efflux transporter) with progression of diabetes in rats. Diabetes was induced in Wistar rats using a combination of low dose streptozotocin along with high fat diet. The expression of intestinal P-glycoprotein significantly increased (P≤0.05) with the progression of diabetes which was inferred from the mRNA analysis of mdr1a and mdr1b genes in the ileum segment of rat intestine. Furthermore, a significant increase (P≤0.05) in Na(+)-K(+) ATPase activity was observed in the ileum segment of rat intestine with the progression of diabetes. As a result of this, a significant decrease in the intestinal uptake and peroral bioavailability of the P-glycoprotein substrates (verapamil and atorvastatin) was observed along with the progression of diabetes as compared to normal animals. To address this problem of impaired drug uptake and bioavailability, a reported P-glycoprotein inhibitor, epigallocatechin-3-gallate, was experimentally evaluated. The treatment with epigallocatechin-3-gallate resulted in significant reduction in the expression and activity of P-glycoprotein and subsequent improvement in the intestinal uptake and peroral bioavailability of both verapamil and atorvastatin in normal as well as in diabetic animals. The findings of this study rationalised the use and established the mechanism of action of epigallocatechin-3-gallate to overcome P-glycoprotein mediated drug efflux and will also be helpful in therapeutic drug monitoring in diabetes.

Antidiabetic drugs restore abnormal transport of amyloid-β across the blood-brain barrier and memory impairment in db/db mice

Previous studies have shown significant changes in amyloid-β (Aβ) transport across the blood-brain barrier (BBB) under diabetic conditions with hypoinsulinemia, which is involved in diabetes-associated cognitive impairment. Present study employed db/db mice with hyperinsulinemia to investigate changes in Aβ transport across the BBB, hippocampal synaptic plasticity, and restorative effects of antidiabetic drugs. Our results showed that db/db mice exhibited similar changes in Aβ transport across the BBB to that of insulin-deficient mice. Chronic treatment of db/db mice with antidiabetic drugs such as metformin, glibenclamide and insulin glargine significantly decreased Aβ influx across the BBB determined by intra-arterial infusion of (125)I-Aβ(1-40), and expression of the receptor for advanced glycation end products (RAGE) participating in Aβ influx. Insulin glargine, but not, metformin or glibenclamide increased Aβ efflux across the BBB determined by stereotaxic intra-cerebral infusion of (125)I-Aβ(1-40), and expression of the low-density lipoprotein receptor related protein 1 (LRP1) participating in Aβ efflux. Moreover, treatment with these drugs significantly decreased hippocampal Aβ(1-40) or Aβ(1-42) and inhibited neuronal apoptosis. The drugs also ameliorated memory impairment confirmed by improved performance on behavioral tasks. However, insulin glargine or glibenclamide, but not metformin, restored hippocampal synaptic plasticity characterized by enhancing in vivo long-term potentiation (LTP). Further study found that these three drugs significantly restrained NF-κB, but only insulin glargine enhanced peroxisome proliferator-activated receptor γ (PPARγ) activity at the BBB in db/db mice. Our data indicate that the antidiabetic drugs can partially restore abnormal Aβ transport across the BBB and memory impairment under diabetic context.

Impact of cigarette smoke extract and hyperglycemic conditions on blood-brain barrier endothelial cells

Background

Diabetes and tobacco smoking are significant public health concerns which have been shown to independently impact the blood–brain barrier (BBB). Since smoking is a risk factor for diabetes and shares some of the common pathological pathways leading to metabolic abnormalities, it is hypothesized that their combination would produce additive or synergistic BBB dysfunction. Therefore, the objective of this study was to assess this hypothesis and evaluate the magnitude of these effects in vitro using hCMEC/D3 cells; a well-established human BBB endothelial cell line.

Methods

Monolayers of hCMEC/D3 cells were exposed to hyperglycemic conditions (HG; 35 mM) or 5% soluble cigarette smoke extracts (CSE, model of mainstream smoke exposure) for 12–24 h. Cells were then harvested for subsequent biochemical analyses. Transendothelial electrical resistance (TEER) and paracellular permeability to florescent dextrans were used to assess monolayer integrity. Analysis of released factors and cytokines was carried out by ELISA. Western blot (WB) analysis/immunofluorescence of relevant molecular targets was carried out. P-gp efflux activity was measured using rhodamine 123.

Results

Immunofluorescence and WB data showed a significant ZO-1 down-regulation by HG and/or CSE over 24 h exposure. CSE in presence of HG produced a synergistic increase in release of vascular endothelial growth factor that was accompanied by decreased TEER and augmented permeability to labeled dextrans in a size-dependent manner. Moreover, CSE increased the expression of GLUT-1 and SGLT-1 in isolated membrane fractions of hCMEC/D3 cells. The effect was amplified by HG. Both, HG and CSE elicited the membrane upregulation of P-glycoprotein (P-gp) expression which however, was not paralleled by a comparable efflux activity. Interestingly, concomitant exposure to HG and CSE evoked a marked upregulation of PECAM-1 and other pro-inflammatory markers including IL-6 and -8, when compared to each condition alone. Moreover, exposure to all tested conditions amplified (to a different degree) cellular oxidative stress response denoted by increased Nrf2 nuclear translocation.

Conclusion

Overall, our results have clearly shown an additive pattern in the release of angiogenic and inflammatory factors following concomitant exposure to HG and CSE. This suggests the involvement of common key modulators in BBB impairment by both CS and HG possibly through the activation of oxidative stress responses.

Altered glycaemia differentially modulates efflux transporter expression and activity in hCMEC/D3 cell line

The unique phenotype of blood-brain barrier (BBB) endothelium is partly maintained by abundant expression of ATP-binding cassette superfamily of efflux transporters that strictly restrict the CNS access to toxic substances including xenobiotics in circulation. Previously, we have shown that diabetes-related altered glycemic conditions differentially affect and compromise BBB integrity. However, the impact of diabetes on BBB efflux transporters is less understood. In this study, we examined the effects of single or repeated episodes of hypo-and hyperglycemia on major BBB efflux transporters expression/function in human cerebromicrovascular endothelial cell line (hCMEC/D3). Cells were exposed to normal (5.5 mM), hypo (2.2 mM) or hyper (25 or 35 mM)-glycemic media containing D-glucose for 12h (acute) or two 3h episodes/day of hypo- or hyperglycemia with an intercalated 2h normalglycemic exposure for 3 days ("glycemic variability", see Methods). Acute hypoglycemic exposure (12h) up-regulated BBB endothelial mRNA and protein expression of P-glycoprotein, BCRP and other multidrug resistance associated proteins (MRP1 and 4) paralleled by an increase in transporter-specific efflux activity (∼ 2-fold vs. control). Although, 12h hyperglycemia did not affect the efflux transporter expression (except for MRP4), a significant increase in BCRP activity was observed. By contrast, DNA microarray data revealed that repeated hyperglycemic episodes (but not hypoglycemia) significantly up-regulate P-glycoprotein expression and activity. Thus, this study suggests a differential impact of altered glycemic conditions on major BBB drug efflux transporters expression/function, sensitive to the length of exposure (acute vs. repeated), with an implication for altered CNS drug disposition in diabetic population.

Effects of 1α,25-dihydroxyvitamin D3 , the natural vitamin D receptor ligand, on the pharmacokinetics of cefdinir and cefadroxil, organic anion transporter substrates, in rat

Evidence in the literature suggests that 1α,25-dihydroxyvitamin D3 [1,25(OH)2 D3 ], the vitamin D receptor ligand, down-regulated the expression of the rat renal organic anion (renal organic anion transporter, rOAT) and oligopeptide (rPEPT) transporters, but increased intestinal rPEPT1 expression. We investigated, in rats, the intravenous and oral pharmacokinetics of 2 mg/kg cefdinir and cefadroxil, two cephalosporins that are eliminated via renal OAT1/OAT3 and are substrates of PEPT1/PEPT2, with and without 1,25(OH)2 D3 treatment. The area under the plasma concentration-time curve (AUC) of cefdinir or cefadroxil after 1,25(OH)2 D3 treatment was increased significantly because of decreased clearance (CL). Both kidney uptake and cumulative urinary recovery were significantly decreased, whereas liver uptake and fecal recovery remained unchanged in 1,25(OH)2 D3 -treated rats. Similar changes in AUC and CL were observed for both drugs upon coadministration of probenecid, the OAT inhibitor. Oral availability of cefdinir and cefadroxil remained unchanged with 1,25(OH)2 D3 treatment, suggesting lack of a role for intestinal rPEPT1. Rather, reduction of rOAT1/rOAT3 mRNA expression in kidney with 1,25(OH)2 D3 -treatment was observed, confirmed by decreased function in MDCKII cells overexpressing human OAT1 and OAT3. These composite results suggest that 1,25(OH)2 D3 treatment reduces cefdinir and cefadroxil clearances by diminution of renal OAT1/OAT3 expression, implicating a role for 1,25(OH)2 D3 in eliciting transporter-based drug interactions.

Diabetes Mellitus and Blood-Brain Barrier Dysfunction: An Overview

A host of diabetes-related insults to the central nervous system (CNS) have been clearly documented in type-1 and -2 diabetic patients as well as experimental animal models. These host of neurological disorders encompass hemodynamic impairments (e.g., stroke), vascular dementia, cognitive deficits (mild to moderate), as well as a number of neurochemical, electrophysiological and behavioral alterations. The underlying causes of diabetes-induced CNS complications are multifactorial and are relatively little understood although it is now evident that blood-brain barrier (BBB) damage plays a significant role in diabetes-dependent CNS disorders. Changes in plasma glucose levels (hyper- or hypoglycemia) have been associated with altered BBB transport functions (e.g., glucose, insulin, choline, amino acids, etc.), integrity (tight junction disruption), and oxidative stress in the CNS microcapillaries. Last two implicating a potential causal role for upregulation and activation of the receptor for advanced glycation end products (RAGE). This type I membrane-protein also transports amyloid-beta (Aβ) from the blood into the brain across the BBB thus, establishing a link between type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD, also referred to as "type 3 diabetes"). Hyperglycemia has been associated with progression of cerebral ischemia and the consequent enhancement of secondary brain injury. Difficulty in detecting vascular impairments in the large, heterogeneous brain microvascular bed and dissecting out the impact of hyper- and hypoglycemia in vivo has led to controversial results especially with regard to the effects of diabetes on BBB. In this article, we review the major findings and current knowledge with regard to the impact of diabetes on BBB integrity and function as well as specific brain microvascular effects of hyper- and hypoglycemia.

Comparative pharmacokinetic study of paclitaxel and docetaxel in streptozotocin-induced diabetic rats

The pharmacokinetics of paclitaxel and docetaxel were compared in diabetic rats induced by streptozotocin (DMIS rats) and the impact of altered expression of cytochrome P450 3A (Cyp3A) and P-glycoprotein (P-gp) in the diabetic state. The pharmacokinetics of paclitaxel and docetaxel were determined after intravenous (5 mg/kg) and oral (30 and 40 mg/kg, respectively) administration to both groups and the mRNA expression levels of Cyp3A isozymes and Mdr1a and Mdr1b in the liver and small intestine were determined in control and DMIS rats. After intravenous administration, the AUC and clearance of paclitaxel and docetaxel were not significantly different in DMIS vs control rats. After oral administration, the AUC and C(max) of paclitaxel in DMIS rats were significantly greater than those in the control rats, whereas those of docetaxel was not changed significantly. The mRNA expression levels of hepatic Cyp3A1, Cyp3A9 and Mdr1b were significantly increased in DMIS compared with the control rats. In the intestine, Cyp3A62 expression decreased in the DMIS rats compared with the controls. Thus the pharmacokinetic changes of taxanes observed in the DMIS rats were attributed to changes in P-gp and Cyp3A, predominant factors that control the absorption of paclitaxel and docetaxel, respectively. It seemed that there were different susceptibilities to intestinal P-gp and Cyp3A between the two taxanes.

Functional impairment of P-glycoprotein by sodium nitroprusside pretreatment in mouse brain capillary endothelial cells

We examined whether pretreatment of mouse brain blood vessel endothelial cell clone 4 (MBEC4) cells with sodium nitroprusside (SNP), a NO(x) donor, as an in vitro model of the bloodbrain barrier could affect P-glycoprotein (P-gp) functional activity. Uptake into the cells and MBEC4 plasma membrane vesicles (MPMVs) in the presence or absence of SNP pretreatment was used to investigate functional changes. Increased accumulation of [(3)H]vincristine, a widely used substrate for P-gp, into MBEC4 was observed upon SNP pretreatment, likely due to impaired P-gp function. To better understand the mechanism of the impairment, MPMVs were prepared and characterized in terms of purity and Na(+)-dependent glucose uptake. [(3)H]daunomycin uptake into MPMVs was diminished after SNP pretreatment in the presence of an ATP-regenerating system, indicating that the functional activity of P-gp was impaired after exposure to SNP. Under conditions of excess ATP, daunomycin uptake into the vesicles was still decreased after SNP pretreatment, indicating that SNP interacted directly with the transport system, but not with the ATP-regenerating system. Together, these results suggest that NO or NO(x) functionally impairs P-gp in the in vitro blood-brain barrier model with SNP pretreatment.

Biphasic regulation of P-glycoprotein function and expression by NO donors in Caco-2 cells

AIM

To investigate the effects of nitric oxide (NO) donors on the function and expression of P-glycoprotein (P-gp) in Caco-2 cells.

METHODS

Caco-2 cells were exposed to NO donors for designated times. P-gp function and expression were assessed using Rhodamine123 uptake assay and Western blotting, respectively. Intracellular reactive oxygen species (iROS) and intracellular reactive nitrogen species (iRNS) levels were measured using ROS and RNS assay kits, respectively.

RESULTS

Exposure of Caco-2 cells to 0.1 or 2 mmol/L of sodium nitroprusside (SNP) affected the function and expression of P-gp in concentration- and time-dependent manners. A short-term (4 h) exposure reduced P-gp function and expression accompanied with significantly increased levels of iROS and iRNS. In contrast, a long-term (24 h) exposure stimulated the P-gp function and expression. The stimulatory effects of 2 mmol/L SNP was less profound as compared to those caused by 0.1 mmol/L SNP. The other NO donors SIN-1 and SNAP showed similar effects. Neither the NO scavenger PTIO (2 mmol/L) nor soluble guanylate cyclase inhibitor ODQ (50 μmol/L) reversed the SNP-induced alteration of P-gp function. On the other hand, free radical scavengers ascorbate, glutathione and uric acid (2 mmol/L for each), PKC inhibitor chelerythrine (5 μmol/L), PI3K/Akt inhibitor wortmannin (1 μmol/L) and p38 MAPK inhibitor SB203580 (10 μmol/L) reversed the upregulation of P-gp function by the long-term exposure to SNP, but these agents had no effect on the impaired P-gp function following the short-term exposure to SNP.

CONCLUSION

NO donors time-dependently regulate P-gp function and expression in Caco-2 cells: short-term exposure impairs P-gp function and expression, whereas long-term exposure stimulates P-gp function and expression. The regulation occurs via a NO-independent mechanism.

High glucose decreases expression and activity of p-glycoprotein in cultured human retinal pigment epithelium possibly through iNOS induction

Inhibition of p-glycoprotein under hyperglycemic conditions has been reported in various barrier tissues including blood-brain barrier, intestine, and kidney, and has been linked to significant clinical complications. However, whether this is also true for the outer blood-retinal barrier constituted by retinal pigment epithelium, or has a role in pathogenesis of diabetic retinopathy is not yet clear. In this study, using cultured human retinal pigment epithelium cell line D407, we found that high glucose exposure induced a significant decrease in p-glycoprotein expression both at mRNA and at protein levels, accompanied by an attenuated p-glycoprotein activity determined by intracellular rhodamine 123 retention. In marked contrast, the expressions of both mRNA and protein levels of inducible nitrate oxide synthase (iNOS) increased, and were accompanied by increased extracellular nitrate/nitrite production by Griess reaction. In addition, mRNA levels of nuclear receptors revealed a decreased expression of pregnane X receptor after the exposure of high glucose. However, the subsequent alterations in production of nitrate/nitrite, functional expression of p-glycoprotein, and mRNA levels of pregnane X receptor were partially blocked when pretreated with S,S′-1,3-phenylene-bis(1,2-ethanediyl)-bis-isothiourea•2HBr (PBITU), a selective iNOS inhibitor. Moreover, the effects of PBITU were antagonized with the addition of L-arginine, a substrate for NO synthesis. Our in vitro results suggest for the first time that iNOS induction plays a novel role in decreased p-glycoprotein expression and transport function at the human outer blood-retinal barrier under hyperglycemic conditions and further support the concept of inhibiting iNOS pathway as a therapeutic strategy for diabetic retinopathy.

Nitric oxide contributes to hypoxia-reoxygenation-induced P-glycoprotein expression in rat brain endothelial cells

Ischemia-reperfusion leads to increased levels at the blood-brain barrier of the multidrug efflux transporter, P-glycoprotein that provides protection to the brain by limiting access of unwanted substances. This is coincident with the production of nitric oxide. This present study using immortalized rat brain endothelial cells (GPNTs) examines whether following hypoxia-reoxygenation, nitric oxide contributes to the alterations in P-glycoprotein levels. After 6 h of hypoxia, both nitric oxide and reactive oxygen species, detected intracellularly using fluorescent monitoring dyes, were produced in the subsequent reoxygenation phase coincident with increased P-glycoprotein. The evidence that nitric oxide can directly affect P-glycoprotein expression was sought by applying S-nitroso-N-acetyl-DL: -penicillamine that as shown increased the nitric oxide generation. Sodium nitroprusside, though more effective at increasing P-glycoprotein expression, appeared to produce different reactive species. Real time RT-PCR analysis revealed the predominant form of nitric oxide synthase in these cells to be endothelial, inhibition of which partially prevented the increase in P-glycoprotein during reoxygenation. These data indicate that the production of nitric oxide by endothelial nitric oxide synthase during reoxygenation can influence P-glycoprotein expression in cells of the blood-rat brain barrier, highlighting another route by which nitric oxide may protect the brain.

Induction of drug efflux protein expression by venlafaxine but not desvenlafaxine

Venlafaxine and its metabolite desvenlafaxine are serotonin-norepinephrine reuptake inhibitors currently prescribed for the treatment of depression. Previously, it was reported that venlafaxine is an inducer of MDR1, the gene responsible for P-glycoprotein (P-gp). The present study expanded upon these findings by examining the effect of venlafaxine and desvenlafaxine on the expression of both P-gp and the breast cancer resistance protein (BCRP) in human brain endothelial cells (HBMEC), an in vitro model of the blood-brain barrier (BBB). The HBMEC were treated for 1 h with various concentrations (500 nM to 50 µM) of venlafaxine and desvenlafaxine. Western blot analysis revealed treatment with venlafaxine significantly induced the expression of P-gp (2-fold) and BCRP (1.75-fold) in a dose-dependent manner, while treatment with desvenlafaxine had no effect on drug efflux transporter expression. To determine the functional significance of this effect, the permeability of a known drug efflux probe, rhodamine 123, across the BBB model and Caco-2 cells, a model of intestinal absorption, were examined. Treatment with venlafaxine (1-50 µM) for 1 h significantly reduced the apical-to-basolateral permeability of R123 across the BBB model (30%) and Caco-2 cell monolayers (25%), indicative of increased drug efflux transporter expression at the apical membrane. Conversely, desvenlafaxine had no effect on R123 permeability in either cellular model. These studies indicate that venlafaxine, but not desvenlafaxine is an inducer of drug efflux transporter expression, which consequently increases the potential for clinical drug-drug interactions. Therefore, based on these preliminary results, caution should be taken when prescribing venlafaxine with other P-gp substrates.

Nuclear factor-kappa B activity regulates brain expression of P-glycoprotein in the kainic acid-induced seizure rats

This study was aimed to investigate the effect of NF-κB activity on the seizure susceptibility, brain damage, and P-gp expression in kainic acid- (KA-) induced seizure rats. Male SD rats were divided into saline control group (NS group), KA induced epilepsy group (EP group), and epilepsy group intervened with NF-κB inhibitor-pyrrolidine dithiocarbamate salt (PDTC group) or with dexamethasone (DEX group). No seizures were observed in the rats of NS group. Compared with NS group, increased P-gp expression and NF-κB activation in the rat brain of the EP group were observed after KA micro-injection. Both PDTC and DEX pre-treatment significantly increased the latency to grade III or V seizure onset compared to EP group but failed to show neuron-protective effect as the number of survival neurons didn't significantly differ from that in EP group. Furthermore, PDTC pre-treatment significantly decreased P-gp expression along with NF-κB activation in the hippocampus CA3 area and amygdala complex of rats compared with the EP group, implying that NF-κB activation involved in the seizure susceptibility and seizure induced brain P-gp over-expression. Additionally, DEX pre-treatment only decreased P-gp expression level without inhibition of NF-κB activation, suggesting NF-κB independent pathway may also participate in regulating seizure induced P-gp over-expression.

P-glycoprotein and breast cancer resistance protein expression and function at the blood-brain barrier and blood-cerebrospinal fluid barrier (choroid plexus) in streptozotocin-induced diabetes in rats

The aim of the study was to investigate the influence of diabetes mellitus type 1 on expression and function of the ATP-binding cassette transport proteins P-glycoprotein (Pgp, Abcb1) and breast cancer resistance protein (Bcrp, Abcg2) at the blood-brain barrier and the blood-cerebrospinal fluid barrier formed by the choroid plexus. In brain capillary endothelial cells forming the blood-brain barrier, Pgp and Bcrp are located in the luminal membrane while apical/sub-apical localization was described for Pgp in choroid plexus epithelial cells. Alterations in expression or function may lead to damages in barrier integrity and may cause brain defects after long term diabetes. Diabetes was induced by i.p.-streptozotocin injection 14days prior to performing experiments. RNA and protein expression were analyzed in choroid plexus and blood-brain barrier capillaries by RT-PCR and Western blot, respectively. Pgp and Bcrp expression was increased in blood-brain barrier capillaries; in choroid plexus, only Bcrp showed elevated gene expression. Protein expression was not altered. Functional analyses were carried out using confocal laser-scanning microscopy in intact isolated brain capillaries with the fluorescent Pgp substrate NBD-Cyclosporin A (NBD-CsA) and BODIPY® FL prazosin as substrate for Bcrp. Consistent with protein expression data, no changes in diabetic animals occurred, suggesting an unaltered function of Pgp and Bcrp.

Amyloid efflux transporter expression at the blood-brain barrier declines in normal aging

Reduced clearance of amyloid β peptides (Aβ) across the blood-brain barrier contributes to amyloid accumulation in Alzheimer disease. Amyloid β efflux transport is via the endothelial low-density lipoprotein receptor-related protein 1 (LRP-1) and P-glycoprotein (P-gp), whereas Aβ influx transport is via the receptor for advanced glycation end products. Because age is the major risk factor for developing Alzheimer disease, we measured LRP-1 and P-gp expression and associated transporter expression with Aβ accumulation in aging rats. Quantitative LRP-1 and P-gp microvessel expression was measured by immunohistochemistry (IHC); LRP-1 and P-gp expression were assessed in microvessel isolates by Western blotting. There was an age-dependent loss of capillary LRP-1 across all ages (3-36 months) by IHC (linear trend p = 0.0004) and between 3 and 20 months by Western blotting (linear trend p < 0.0001). There was a late (30-36 months) P-gp expression loss by IHC (p < 0.05) and Western blotting (p = 0.0112). Loss of LRP-1 correlated with Aβ42 accumulation (p = 0.0121) and very nearly with Aβ40 (p = 0.0599) across all ages. Expression of LRP-1 correlated negatively with the expression of receptor for advanced glycation end products (p < 0.0004). These data indicate that alterations in LRP-1 and P-gp expression seem to contribute progressively to Aβ accumulation in aging.

Evidence of carrier-mediated transport in the penetration of donepezil into the rat brain

The objective of this study was to characterize the mechanism that controls the transport of donepezil into the brain. The apparent brain uptake clearance (CL(app,br)) was decreased as a function of the dose of donepezil, suggesting an involvement of a saturable transport process via transporter(s) in the penetration across the blood-brain barrier (BBB). Consistent with in vivo results, the uptake of substrates for organic cation transporters was significantly reduced by donepezil in both MBEC4 cells (i.e., a model for BBB) and HEK 293 cells expressing the transporters found in the brain, indicative of the involvement of organic cation transporters in the transport of the drug. Furthermore, donepezil transport was enhanced (p < 0.01) in HEK 293 cells expressing rOCNT1, rOCTN2, or rCHT1. The CL(app,br) was reduced up to 52.8% of the control in rats that had been pretreated with choline, while the CL(app,br) was unaffected with pretreatments with organic cations other than choline, suggesting that choline and donepezil share a common transport mechanism in the penetration across the BBB in vivo. Taken together, these observations suggest that the transport of donepezil across the BBB is mediated by organic cation transporters such as choline transport system(s).

Inducible nitric oxide synthase-mediated decrease of intestinal P-glycoprotein expression under streptozotocin-induced diabetic conditions

AIMS

P-glycoprotein (P-gp), one of the important drug-efflux pumps, is known to be affected by pathological conditions such as inflammation or infection. Recently, it is reported that high glucose or hyperglycemia can alternate P-gp expression levels at the blood-brain barrier or in the kidney, although the details are still unknown. Here, we analyzed the alteration of intestinal P-gp expression and function in the development of diabetes and elucidated the mechanisms.

MAIN METHODS

Type 1 diabetes was induced in male ddY mice by an i.p. injection of streptozotocin (STZ) (230 mg/kg). We analyzed ileal P-gp expression and function using Western blot analysis and an in situ closed loop method, respectively.

KEY FINDINGS

A significant reduction of P-gp expression level in ileum was found 9 days after STZ administration. In contrast, a remarkable decrease in P-gp function was observed on the 3rd and 9th days. Interestingly, nitric oxide synthase (NOS) activity in ilea was significantly increased on the 9th day. The decrease of P-gp expression levels observed on the 9th day was completely suppressed by L-N(G)-nitroarginine methyl ester (L-NAME), a broad range NOS inhibitor, or aminoguanidine, a specific inducible NOS (iNOS) inhibitor.

SIGNIFICANCE

These results indicate the possibility that nitric oxide (NO), produced by iNOS in the ileum, is involved in the reduction of ileal P-gp expression under STZ-induced diabetic conditions.

Pharmacokinetics of drugs in rats with diabetes mellitus induced by alloxan or streptozocin: comparison with those in patients with type I diabetes mellitus

Objectives

In rats with diabetes mellitus induced by alloxan (DMIA) or streptozocin (DMIS), changes in the cytochrome P450 (CYP) isozymes in the liver, lung, kidney, intestine, brain, and testis have been reported based on Western blot analysis, Northern blot analysis, and various enzyme activities. Changes in phase II enzyme activities have been reported also. Hence, in this review, changes in the pharmacokinetics of drugs that were mainly conjugated and metabolized via CYPs or phase II isozymes in rats with DMIA or DMIS, as reported in various literature, have been explained. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized in the kidney, and that were excreted mainly via the kidney or bile in DMIA or DMIS rats were reviewed also. For drugs mainly metabolized via hepatic CYP isozymes, the changes in the total area under the plasma concentration–time curve from time zero to time infinity (AUC) of metabolites, AUCmetabolite/AUCparent drug ratios, or the time-averaged nonrenal and total body clearances (CLNR and CL, respectively) of parent drugs as reported in the literature have been compared.

Key findings

After intravenous administration of drugs that were mainly metabolized via hepatic CYP isozymes, their hepatic clearances were found to be dependent on the in-vitro hepatic intrinsic clearance (CLint) for the disappearance of the parent drug (or in the formation of the metabolite), the free fractions of the drugs in the plasma, or the hepatic blood flow rate depending on their hepatic extraction ratios. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized via the kidney in DMIA or DMIS rats were dependent on the drugs. However, the biliary or renal CL values of drugs that were mainly excreted via the kidney or bile in DMIA or DMIS rats were faster.

Summary

Pharmacokinetic studies of drugs in patients with type I diabetes mellitus were scarce. Moreover, similar and different results for drug pharmacokinetics were obtained between diabetic rats and patients with type I diabetes mellitus. Thus, present experimental rat data should be extrapolated carefully in humans.

Change in P-glycoprotein and caveolin protein expression in brain striatum capillaries in New Zealand obese mice with type 2 diabetes

AIMS

To investigate the expression of P-gp and caveolins in brain striatum capillaries in inbred mice with type 2 diabetes.

MAIN METHODS

Inbred mice with type 2 diabetes (male New Zealand obese; NZO) were compared with related mice without diabetes (female NZO and New Zealand White). Protein expression of P-gp and caveolins in capillaries of the brain striatum was examined by immunohistochemical analysis. P-gp efflux pump activity in the blood-brain barrier (BBB) was measured by in vivo brain microdialysis. Regulation of P-gp and caveolin expression was examined in cultured adult rat brain endothelial cells (ARBEC).

KEY FINDINGS

In capillaries in the brain striatum, expression of P-gp and caveolins was higher and lower, respectively, in mice with type 2 diabetes compared with non-diabetic mice. Brain extracellular concentrations of intravenously injected rhodamine 123 were more than 50-60% lower in type 2 diabetic mice. Insulin and PMA treatments significantly increased P-gp expression, whereas the same treatments decreased caveolin expression in ARBEC.

SIGNIFICANCE

Protein expression of P-gp and caveolins can be regulated in animals with type 2 diabetes. These changes may be important in modulating P-gp activity in the BBB in type 2 diabetes.

P-glycoprotein expression in immortalised rat brain endothelial cells: comparisons following exogenously applied hydrogen peroxide and after hypoxia-reoxygenation

Levels of multidrug efflux transporter P-glycoprotein (P-gp) on endothelial cells lining brain blood vessels are important for limiting access of many compounds to the brain. In vivo studies have indicated that ischaemia-reperfusion that generates reactive oxygen species also increases P-gp levels in brain endothelial cells. To investigate possible mechanisms, in vitro studies were performed on immortalised (GPNT) and primary rat brain endothelial cells. Exposure to hydrogen peroxide (200 microM) resulted in intracellular oxidative stress as detected from higher levels of dichlorofluorescein fluorescence and raised levels of P-gp protein, mdr1a and mdr1b transcripts and, in GPNT cells, increased mdr1a and mdr1b promoter activity. The P-gp protein increases were abolished by pre-treatment with polyethylene glycol-catalase and were curtailed by co-culture with primary rat astrocytes. Exposure of GPNT cells to 6 h hypoxia followed by 24 h reoxygenation produced less intracellular oxidative stress as judged from smaller increments in dichlorofluorescein fluorescence but still resulted in raised levels of P-gp protein, an effect partially abolished by pre-treatment with polyethylene glycol-catalase. However, transcript levels and promoter activities were not significantly increased. These data suggest that hydrogen peroxide contributes to P-gp up-regulation following hypoxia-reoxygenation but the underlying mechanisms of its actions differ from those occurring after direct hydrogen peroxide application.