Acute regulation of multidrug resistance-associated protein 2 localization and activity by cAMP and estradiol-17β-D-glucuronide in rat intestine and Caco-2 cells

Regulation of ABC transporters by sex steroids may explain differences in drug resistance between sexes

Drug efficacy is dependent on the pharmacokinetics and pharmacodynamics of therapeutic agents. Tight junctions, detoxification enzymes, and drug transporters, due to their localization on epithelial barriers, modulate the absorption, distribution, and the elimination of a drug. The epithelial barriers which control the pharmacokinetic processes are sex steroid hormone targets, and in this way, sex hormones may also control the drug transport across these barriers. Thus, sex steroids contribute to sex differences in drug resistance and have a relevant impact on the sex-related efficacy of many therapeutic drugs. As a consequence, for the further development and optimization of therapeutic strategies, the sex of the individuals must be taken into consideration. Here, we gather and discuss the evidence about the regulation of ATP-binding cassette transporters by sex steroids, and we also describe the signaling pathways by which sex steroids modulate ATP-binding cassette transporters expression, with a focus in the most important ATP-binding cassette transporters involved in multidrug resistance.

Multidrug resistance-associated protein 2 is negatively regulated by oxidative stress in rat intestine via a posttranslational mechanism. Impact on its membrane barrier function

Oxidative stress (OS) is a key factor in the development of gastrointestinal disorders, in which the intestinal barrier is altered. However, the Multidrug resistance-associated protein 2 (Mrp2) status, an essential component of the intestinal transcellular barrier exhibiting pharmaco-toxicological relevance by limiting the orally ingested toxicants and drugs absorption, has not been investigated. We here evaluated the short-term effect of OS on Mrp2 by treatment of isolated rat intestinal sacs with tert-butyl hydroperoxide (TBH) for 30 min. OS induction by TBH (250 and 500 μM) was confirmed by increased lipid peroxidation end products, decreased reduced glutathione (GSH) content and altered antioxidant enzyme activities. Under this condition, assessment of Mrp2 distribution between brush border (BBM) and intracellular (IM) membrane fractions, showed that Mrp2 protein decreased in BBM and increased in IM, consistent with an internalization process. This was associated with decreased efflux activity and, consequently, impaired barrier function. Subsequent incubation with N-Acetyl-L-Cysteine (NAC, 1 mM) reestablished GSH content and reverted concomitantly the alteration in Mrp2 localization and function induced by TBH. Cotreatment with a specific inhibitor of classic calcium-dependent Protein Kinase C (cPKC) implicated this kinase in TBH-effects. In conclusion, we demonstrated a negative posttranslational regulation of rat intestinal Mrp2 after short-term exposition to OS, a process likely mediated by cPKC and dependent on intracellular GSH content. The concomitant impairment of the Mrp2 barrier function may have implications in xenobiotic absorption and toxicity in a variety of human diseases linked to OS, with notable consequences on the toxicity/safety of therapeutic agents.

Intraluminal nutrients acutely strengthen rat intestinal MRP2 barrier function by a glucagon-like peptide-2-mediated mechanism

AIM

MRP2 is an intestinal ABC transporter that prevents the absorption of dietary xenobiotics. The aims of this work were: (1) to evaluate whether a short-term regulation of intestinal MRP2 barrier function takes place in vivo after luminal incorporation of nutrients and (2) to explore the underlying mechanism.

METHODS

MRP2 activity and localization were assessed in an in vivo rat model with preserved irrigation and innervation. Nutrients were administered into distal jejunum. After 30-minutes treatments, MRP2 activity was assessed in proximal jejunum by quantifying the transport of the model substrate 2,4-dinitrophenyl-S-glutathione. MRP2 localization was determined by quantitative confocal microscopy. Participation of extracellular mediators was evaluated using selective inhibitors and by immunoneutralization. Intracellular pathways were explored in differentiated Caco-2 cells.

RESULTS

Oleic acid, administered intraluminally at dietary levels, acutely stimulated MRP2 insertion into brush border membrane. This was associated with increased efflux activity and, consequently, enhanced barrier function. Immunoneutralization of the gut hormone glucagon-like peptide-2 (GLP-2) prevented oleic acid effect on MRP2, demonstrating the participation of this trophic factor as a main mediator. Further experiments using selective inhibitors demonstrated that extracellular adenosine synthesis and its subsequent binding to enterocytic A2B adenosine receptor (A2BAR) take place downstream GLP-2. Finally, studies in intestinal Caco-2 cells revealed the participation of A2BAR/cAMP/PKA intracellular pathway, ultimately leading to increased MRP2 localization in apical domains.

CONCLUSION

These findings reveal an on-demand, acute regulation of MRP2-associated barrier function, constituting a novel physiological mechanism of protection against the absorption of dietary xenobiotics in response to food intake.

Acute regulation of apical ABC transporters in the gut. Potential influence on drug bioavailability

The extensive intestinal surface offers an advantage regarding nutrient, ion and water absorptive capacity but also brings along a high exposition to xenobiotics, including drugs of therapeutic use and food contaminants. After absorption of these compounds by the enterocytes, apical ABC transporters play a key role in secreting them back to the intestinal lumen, hence acting as a transcellular barrier. Rapid and reversible modulation of their activity is a subject of increasing interest for pharmacologists. On the one hand, a decrease in transporter activity may result in increased absorption of therapeutic agents given orally. On the other hand, an increase in transporter activity would decrease their absorption and therapeutic efficacy. Although of less relevance, apical ABC transporters also contribute to disposition of drugs systemically administered. This review article summarizes the present knowledge on the mechanisms aimed to rapidly regulate the activity of the main apical ABC transporters of the gut: multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein 2 (MRP2) and breast cancer resistance protein (BCRP). Regulation of these mechanisms by drugs, drug delivery systems, drug excipients and nutritional components are particularly considered. This information could provide the basis for controlled regulation of bioavailability of therapeutic agents and at the same time would help to prevent potential drug-drug interactions.

Roles of organic anion transporter 2 and equilibrative nucleoside transporter 1 in hepatic disposition and antiviral activity of entecavir during non-pregnancy and pregnancy

BACKGROUND AND PURPOSE

Entecavir (ETV), a first-line antiviral drug against hepatitis B virus (HBV), has the possibility to be used to prevent mother-to-child transmission. The aim of present study was to clarify the mechanism of ETV uptake into hepatocytes and evaluate the alteration of ETV's hepatic distribution during pregnancy.

EXPERIMENTAL APPROACH

The roles of equilibrative nucleotide transporter (ENT) 1 and organic anion transporter (OAT) 2 in ETV accumulation and anti-HBV efficacy were studied in human ENT1 or OAT2 overexpressed cell models and HepG2.2.15 cells, respectively; meanwhile, the liver-to-plasma ETV concentration ratios in non-pregnant and pregnant mice were measured to evaluate the effect of pregnancy on ETV hepatic distribution.

KEY RESULTS

ETV was shown to be a substrate of ENT1 and OAT2. An ENT1 inhibitor significantly decreased the efficacy of ETV in HepG2.2.15 cells, while overexpression of OAT2 increased susceptibility of HBV to ETV. The liver-to-plasma ETV concentration ratios in pregnant mice were sharply reduced; whereas, the absolute concentration of ETV in the liver did not obviously alter in pregnancy. Although oestradiol and progesterone showed a concentration-dependent inhibition on ETV accumulation both in hepatic cell lines and in primary human hepatocytes, a physiologically relevant concentration of oestradiol and progesterone did not affect antiviral activity of ETV.

CONCLUSIONS AND IMPLICATIONS

OAT2 and ENT1 are the main transporters involved in the hepatic uptake and anti-HBV efficacy of ETV. The concentration of ETV in the liver was not obviously altered during pregnancy, which indicates that dosage adjustment in pregnancy is not necessary.