MK571 inhibits phase-2 conjugation of flavonols by Caco-2/TC7 cells, but does not specifically inhibit their apical efflux

ABCC1 transporter exports the immunostimulatory cyclic dinucleotide cGAMP

The DNA sensor cyclic GMP-AMP synthase (cGAS) is important for antiviral and anti-tumor immunity. cGAS generates cyclic GMP-AMP (cGAMP), a diffusible cyclic dinucleotide that activates the antiviral response through the adaptor protein stimulator of interferon genes (STING). cGAMP cannot passively cross cell membranes, but recent advances have established a role for extracellular cGAMP as an "immunotransmitter" that can be imported into cells. However, the mechanism by which cGAMP exits cells remains unknown. Here, we identifed ABCC1 as a direct, ATP-dependent cGAMP exporter in mouse and human cells. We show that ABCC1 overexpression enhanced cGAMP export and limited STING signaling and that loss of ABCC1 reduced cGAMP export and potentiated STING signaling. We demonstrate that ABCC1 deficiency exacerbated cGAS-dependent autoimmunity in the Trex1-/- mouse model of Aicardi-Goutières syndrome. Thus, ABCC1-mediated cGAMP export is a key regulatory mechanism that limits cell-intrinsic activation of STING and ameliorates STING-dependent autoimmune disease.

Transplacental transfer of acetaminophen in pregnant rats

Acetaminophen is among the most widely used analgesics; however, the proportion and mechanism of transplacental transfer of unbound acetaminophen with actual pharmacological activity remain unknown. Our hypothesis is that acetaminophen gradually penetrates the blood-placenta barrier to reach the fetus. A multiple microdialysis coupled to liquid chromatography with photodiode array detection method was developed to monitor acetaminophen levels in the maternal blood, placenta, fetus, and amniotic fluid of a pregnant rat and investigate this hypothesis. The pharmacokinetic data indicates that acetaminophen exhibits a nonlinear behavior in the maternal blood within the dosage regimen of 100 and 300 mg/kg. In addition, acetaminophen penetrates the placenta, fetus, and amniotic fluid during treatment. The transplacental transfer ratio represented by the area under the concentration curve (AUC) ratio for the conceptus (the collective term for the fetus, placenta, and amniotic fluid) and maternal blood (AUC_tissue/AUC_blood) was approximately 11-23 % after acetaminophen (100 and 300 mg/kg) administration. However, the transporter of multidrug resistance-associated protein (MRP) inhibitor MK-571 did not significantly change the transplacental transfer ratio. This basic study provides constructive information for the clinical application of acetaminophen in pregnant women.

O-Sulfation disposition of curcumin and quercetin in SULT1A3 overexpressing HEK293 cells: the role of arylsulfatase B in cellular O-sulfation regulated by transporters

Extensive phase II metabolic reactions (i.e., glucuronidation and sulfation) have resulted in low bioavailability and decreased biological effects of curcumin and quercetin. Compared to glucuronidation, information on the sulfation disposition of curcumin and quercetin is limited. In this study, we identified that BCRP and MRP4 played a critical role in the cellular excretion of curcumin-O-sulfate (C-O-S) and quercetin-O-sulfate (Q-O-S) by integrating chemical inhibition with transporter knock-down experiments. Inhibited excretion of sulfate (C-O-S and Q-O-S) caused significant reductions in cellular O-sulfation of curcumin (a maximal 74.4% reduction) and quercetin (a maximal 76.9% reduction), revealing a strong interplay of sulfation with efflux transport. It was further identified that arylsulfatase B (ARSB) played a crucial role in the regulation of cellular O-sulfation by transporters. ARSB overexpression significantly enhanced the reduction effect of MK-571 on the cellular O-sulfation (f_met) of the model compound (38.8% reduction for curcumin and 44.2% reduction for quercetin). On the contrary, ARSB knockdown could reverse the effect of MK-571 on the O-sulfation disposition of the model compound (29.7% increase for curcumin and 47.3% increase for quercetin). Taken together, ARSB has been proven to be involved in cellular O-sulfation, accounting for transporter-dependent O-sulfation of curcumin and quercetin. A better understanding of the interplay beneath metabolism and transport will contribute to the exact prediction of in vivo drug disposition and drug-drug interactions.

Modulation of the multixenobiotic resistance mechanism in Danio rerio hepatocyte culture (ZF-L) after exposure to glyphosate and Roundup®

The presence of the transmembrane proteins of the ATP-binding cassette (ABC) family, which perform the efflux of several substances, contributes to the survival of aquatic organisms in a contaminated environmental. Those proteins provide a phenotype named the multixenobiotic resistance mechanism (MXR) by performing the efflux of a wide range of endogenous and exogenous compounds (ABCB) and biotransformation products and anionic compounds (ABCC). The aim of the present study was to evaluate the cellular defense pathway of an established culture from zebrafish hepatocytes (ZF-L) after 24 and 48 h of exposure to glyphosate and Original Roundup®, an herbicide used globally. Through abcb4, abcc1, abcc2 and abcc4 gene expression, ABCB and ABCC2 protein expression and ABC pump activity in ZF-L cells exposed to glyphosate and Roundup®. The results showed an increase in ABCB gene and protein expression; however, although ABCC2 showed an increase in gene expression, its protein expression was lower than in the control group. Regarding ABC activity, only exposure to Roundup® at the lowest concentration showed an increase at 48 h, but in the presence of inhibitors, both glyphosate and Roundup® appeared to modulate ABC activity, reducing its inhibition and returning activity to levels without inhibitor.

Piperine enhances the bioavailability of silybin via inhibition of efflux transporters BCRP and MRP2

BACKGROUND

Although silybin serves as a well-known hepatoprotective agent with prominent anti-inflammatory, anti-oxidant and anti-fibrotic activities, its low bioavailability limits its application in the treatment of chronic liver diseases. However, novel formulation products with increased solubility were not sufficient to achieve pharmacologically meaningful concentrations of silybin in the clinical studies even used at high dosage.

HYPOTHESIS/PURPOSE

We hypothesized that inhibiting efflux transporter(s) and/or glucuronidation by piperine might enhance the bioavailability and efficacy of silybin.

METHODS

Pharmacokinetics of silybin given alone or in-combination with piperine was determined by a validated LC-MS method. A CCl₄ induced rat model of liver injury was prepared and verified for comparing the effects of silybin and combination treatment. To investigate the underlying mechanism, the inhibition effects of piperine on transportation of silybin were performed in Caco-2 and transfected MDCKII cell lines as well as sandwich-cultured rat hepatocytes (SCH). Human liver microsomes incubation was used for exploring the modulation effects of piperine on the phase-2 metabolism of silybin.

RESULTS

In the present study, we demonstrated for the first time that piperine as a bioenhancer increased the bioavailability of silybin (146%- 181%), contributing to a boosted therapeutic effect in CCl₄-induced acute liver-injury rat model. The underlying mechanisms involved that piperine enhanced the absorption of silybin by inhibiting the efflux transporters including MRP2 and BCRP but not MDR1 in Caco-2 and transfected MDCKII cell lines. Moreover, piperine could inhibit the biliary excretion of silybin and conjugated metabolites in sandwich-cultured rat hepatocytes. Notably, we found that piperine did not affect the phase-2 metabolism of silybin.

CONCLUSION

Efflux transporters play an important role in the pharmacokinetic behavior of flavolignans, and modulating these transporters by bioenhancer such as piperine could enhance the in vivo absorption of silybin, leading to more effective treatments.

Hepatic Transport of 25-Hydroxyvitamin D3 Conjugates: A Mechanism of 25-Hydroxyvitamin D3 Delivery to the Intestinal Tract

Vitamin D3 is an important prohormone critical for maintaining calcium and phosphate homeostasis in the body and regulating drug-metabolizing enzymes and transporters. 25-Hydroxyvitamin D3 (25OHD3), the most abundant circulating metabolite of vitamin D3, is further transformed to the biologically active metabolite 1α,25-dihydroxyvitamin D3 (1α,25-(OH)2D3) by CYP27B1 in the kidney and extrarenal tissues, and to nonactive metabolites by other cytochrome P450 enzymes. In addition, 25OHD3 undergoes sulfation and glucuronidation in the liver, forming two major conjugative metabolites, 25OHD3-3-O-sulfate (25OHD3-S) and 25OHD3-3-O-glucuronide (25OHD3-G), both of which were detected in human blood and bile. Considering that the conjugates excreted into the bile may be circulated to and reabsorbed from the intestinal lumen, deconjugated to 25OHD3, and then converted to 1α,25-(OH)2D3, exerting local intestinal cellular effects, it is crucial to characterize enterohepatic transport mechanisms of 25OHD3-S and 25OHD3-G, and thereby understand and predict mechanisms of interindividual variability in mineral homeostasis. In the present study, with plasma membrane vesicle and cell-based transport studies, we showed that 25OHD3-G is a substrate of multidrug resistance proteins 2 and 3, OATP1B1, and OATP1B3, and that 25OHD3-S is probably a substrate of breast cancer resistance protein, OATP2B1, and OATP1B3. We also demonstrated sinusoidal and canalicular efflux of both conjugates using sandwich-cultured human hepatocytes. Given substantial expression of these transporters in liver hepatocytes and intestinal enterocytes, this study demonstrates for the first time that transporters could play important roles in the enterohepatic circulation of 25OHD3 conjugates, providing an alternative pathway of 25OHD3 delivery to the intestinal tract, which could be critical for vitamin D receptor-dependent gene regulation in enterocytes.

Towards an Understanding of the Low Bioavailability of Quercetin: A Study of Its Interaction with Intestinal Lipids

We have studied the uptake of quercetin aglycone into CaCo-2/TC7 cells in the presence and absence of mixed micelles that are present in the human small intestine. The micelles inhibited the transport of quercetin into the cells. To gain an understanding of why this is the case we examined the solubilisation of quercetin in micelles of differing composition and into pure lipid phases. We did this by using the environmental sensitivity of quercetin’s UV-visible absorption spectra and measurement of free quercetin by filtration of the micellar solutions. The nature of the micelles was also studied by pyrene fluorescence. We found that the partitioning of quercetin into simple bile salt micelles was low and for mixed micelles was inhibited by increasing the bile salt concentration. The affinity of quercetin decreased in the order egg phosphatidylcholine (PC) = lysoPC > mixed micelles > bile salts. These results, together with the innate properties of quercetin, contribute to an understanding of the low bioavailability of quercetin.

ABCC2 (1249G > A) polymorphism implicates altered transport activity for sorafenib

1. Multidrug resistance-associated protein 2 (MRP2), encoded by the ABCC2 gene, is an efflux transporter of several endogenous substrates and xenobiotics. Here, we investigated whether the 1249G > A (rs2273697) polymorphism in ABCC2 affects the ability of MRP2 to pump the multi-tumor drug sorafenib out of cells. 2. Human embryonic kidney 293 (HEK 293) cell lines transfected with ABCC2-1249G and ABCC2-1249A were used to assess the sensitivity and accumulation to sorafenib. The isolated MRP2 were applied to estimate the ATPase activity. 3. The HEK293 cell line overexpressing the ABCC2 1249A allele showed a significantly higher 50% inhibitory concentration (IC₅₀) than a cell line overexpressing ABCC2-1249G or a non-overexpressing control cell line. Intracellular accumulation of sorafenib was much lower in ABCC2-1249A cells than in ABCC2-1249G cells expressing comparable levels of MRP2. Isolated ABCC2-1249A protein showed higher ATPase activity than ABCC2-1249G protein. 4. Our results suggest that the ABCC2 polymorphism 1249G > A increases the ATPase activity of MRP2, leading to greater efflux of sorafenib.