New horizon of MDR1 (P-glycoprotein) study

Relationship between blood-brain barrier changes and drug metabolism under high-altitude hypoxia: obstacle or opportunity for drug transport?

The blood-brain barrier is essential for maintaining the stability of the central nervous system and is also crucial for regulating drug metabolism, changes of blood-brain barrier's structure and function can influence how drugs are delivered to the brain. In high-altitude hypoxia, the central nervous system's function is drastically altered, which can cause disease and modify the metabolism of drugs in vivo. Changes in the structure and function of the blood-brain barrier and the transport of the drug across the blood-brain barrier under high-altitude hypoxia, are regulated by changes in brain microvascular endothelial cells, astrocytes, and pericytes, either regulated by drug metabolism factors such as drug transporters and drug-metabolizing enzymes. This article aims to review the effects of high-altitude hypoxia on the structure and function of the blood-brain barrier as well as the effects of changes in the blood-brain barrier on drug metabolism. We also hypothesized and explore the regulation and potential mechanisms of the blood-brain barrier and associated pathways, such as transcription factors, inflammatory factors, and nuclear receptors, in regulating drug transport under high-altitude hypoxia.

Glycosphingolipid storage in Fabry mice extends beyond globotriaosylceramide and is affected by ABCB1 depletion

Aim:

Fabry disease is caused by α-galactosidase A deficiency leading to accumulation of globotriaosylceramide (Gb₃) in tissues. Clinical manifestations do not appear to correlate with total Gb₃ levels. Studies examining tissue distribution of specific acyl chain species of Gb₃ and upstream glycosphingolipids are lacking.

Material & methods/Results:

Thorough characterization of the Fabry mouse sphingolipid profile by LC-MS revealed unique Gb₃ acyl chain storage profiles. Storage extended beyond Gb₃; all Fabry tissues also accumulated monohexosylceramides. Depletion of ABCB1 had a complex effect on glycosphingolipid storage.

Conclusion:

These data provide insights into how specific sphingolipid species correlate with one another and how these correlations change in the α-galactosidase A-deficient state, potentially leading to the identification of more specific biomarkers of Fabry disease.

Fabry disease is caused by a shortage of the enzyme α-galactosidase A leading to storage of a fat called globotriaosylceramide (Gb₃) in tissues. Disease severity does not appear to correlate directly with total Gb₃. Importantly, Gb₃ is comprised of many highly related but distinct species. We examined levels of Gb₃ species and precursor molecules in Fabry mice. Gb₃ species and storage are unique to each tissue. Furthermore, storage is not limited to Gb₃; precursor fats are also elevated. Detailed analyses of differences in storage between the normal and α-galactosidase A-deficient state may provide a better understanding of the causes of Fabry disease.

Dexamethasone protects normal human liver cells from apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand by upregulating the expression of P-glycoproteins

Glucocorticoids are effective for the treatment of acute-on-chronic pre-liver failure, severe chronic hepatitis B and acute liver failure; however, the mechanism underlying the effects of treatment by glucocorticoids remains to be fully elucidated. The role and detailed mechanism of how glucocorticoids prevent liver disease progression can be elucidated by investigating the apoptosis of hepatocytes following glucocorticoid treatment. P‑glycoproteins (P‑gps) also confer resistance to apoptosis induced by a diverse range of stimuli. Glucocorticoids, particularly dexamethasone (DEX), upregulate the expression of P‑gp in several tissues. In the present study, the normal human L‑02 liver cell line was used, and techniques, including immunocytochemistry, western blot analysis, flow cytometry and reverse transcription‑quantitative polymerase chain reaction analysis were used for determining the expression levels of P‑gps, and for evaluating the effect of DEX pretreatment on the expression of P‑gps. DEX (1‑10 µM) was added to the cell culture media and incubated for 24‑72 h. The results revealed that DEX upregulated the mRNA and protein levels of P‑gp in a dose‑ and time‑dependent manner. Subsequently, tumor necrosis factor‑related apoptosis‑inducing ligand (TRAIL) was used for the induction of apoptosis in the cells, followed by a terminal deoxynucleotidyl transferase dUTP nick end labeling assay to assess the apoptotic stages. The results demonstrated that apoptosis in the group of cells, which were pre‑treated with DEX was significantly lower than that in the control group. Treatment with tariquidar, a P‑gp inhibitor, reduced the anti‑apoptotic effects of DEX. These results established that DEX protects normal human liver cells from TRAIL‑induced apoptosis by upregulating the expression of P-gp. These observations may be useful for elucidating the mechanism of DEX for preventing the progression of liver disease.

Combined use of anticancer drugs and an inhibitor of multiple drug resistance-associated protein-1 increases sensitivity and decreases survival of glioblastoma multiforme cells in vitro

Glioblastoma multiforme (GBM) is a brain tumour characterised by a remarkably high chemoresistance and infiltrating capability. To date, chemotherapy with temozolomide has contributed only poorly to improved survival rates in patients. One of the most important mechanisms of chemoresistance comes about through the activity of certain proteins from the ATP-binding cassette superfamily that extrudes antitumour drugs, or their metabolites, from cells. We identify an increased expression of the multiple drug resistance-associated protein 1 (Mrp1) in glioblastoma multiforme biopsies and in T98G and G44 cell lines. The activity of this transporter was also confirmed by measuring the extrusion of the fluorescent substrate CFDA. The sensitivity of GBM cells was low upon exposure to temozolomide, vincristine and etoposide, with decreases in cell viability of below 20% seen at therapeutic concentrations of these drugs. However, combined exposure to vincristine or etoposide with an inhibitor of Mrp1 efficiently decreased cell viability by up to 80%. We conclude that chemosensitization of cells with inhibitors of Mrp1 activity might be an efficient tool for the treatment of human GBM.

Liposome-encapsulated doxorubicin reverses drug resistance by inhibiting P-glycoprotein in human cancer cells

The most frequent drawback of doxorubicin is the onset of drug resistance, due to the active efflux through P-glycoprotein (Pgp). Recently formulations of liposome-encapsulated doxorubicin have been approved for the treatment of tumors resistant to conventional anticancer drugs, but the molecular basis of their efficacy is not known. To clarify by which mechanisms the liposome-encapsulated doxorubicin is effective in drug-resistant cancer cells, we analyzed the effects of doxorubicin and doxorubicin-containing anionic liposomal nanoparticles ("Lipodox") on the drug-sensitive human colon cancer HT29 cells and on the drug-resistant HT29-dx cells. Interestingly, we did not detect any difference in drug accumulation and toxicity between free doxorubicin and Lipodox in HT29 cells, but Lipodox was significantly more effective than doxorubicin in HT29-dx cells, which are rich in Pgp. This effect was lost in HT29-dx cells silenced for Pgp and acquired by HT29 cells overexpressing Pgp. Lipodox was less extruded by Pgp than doxorubicin and inhibited the pump activity. This inhibition was due to a double effect: the liposome shell per se altered the composition of rafts in resistant cells and decreased the lipid raft-associated amount of Pgp, and the doxorubicin-loaded liposomes directly impaired transport and ATPase activity of Pgp. The efficacy of Lipodox was not increased by verapamil and cyclosporin A and was underwent interference by colchicine. Binding assays revealed that Lipodox competed with verapamil for binding Pgp and hampered the interaction of colchicine with this transporter. Site-directed mutagenesis experiments demonstrated that glycine 185 is a critical residue for the direct inhibitory effect of Lipodox on Pgp. Our work describes novel properties of liposomal doxorubicin, investigating the molecular bases that make this formulation an inhibitor of Pgp activity and a vehicle particularly indicated against drug-resistant tumors.

Targeted genome modification in mice using zinc-finger nucleases

Homologous recombination-based gene targeting using Mus musculus embryonic stem cells has greatly impacted biomedical research. This study presents a powerful new technology for more efficient and less time-consuming gene targeting in mice using embryonic injection of zinc-finger nucleases (ZFNs), which generate site-specific double strand breaks, leading to insertions or deletions via DNA repair by the nonhomologous end joining pathway. Three individual genes, multidrug resistant 1a (Mdr1a), jagged 1 (Jag1), and notch homolog 3 (Notch3), were targeted in FVB/N and C57BL/6 mice. Injection of ZFNs resulted in a range of specific gene deletions, from several nucleotides to >1000 bp in length, among 20-75% of live births. Modified alleles were efficiently transmitted through the germline, and animals homozygous for targeted modifications were obtained in as little as 4 months. In addition, the technology can be adapted to any genetic background, eliminating the need for generations of backcrossing to achieve congenic animals. We also validated the functional disruption of Mdr1a and demonstrated that the ZFN-mediated modifications lead to true knockouts. We conclude that ZFN technology is an efficient and convenient alternative to conventional gene targeting and will greatly facilitate the rapid creation of mouse models and functional genomics research.

Toxicity of xanthene food dyes by inhibition of human drug-metabolizing enzymes in a noncompetitive manner

The synthetic food dyes studied were rose bengal (RB), phroxine (PL), amaranth, erythrosine B (ET), allura red, new coccine, acid red (AR), tartrazine, sunset yellow FCF, brilliant blue FCF, and indigo carmine. First, data confirmed that these dyes were not substrates for CYP2A6, UGT1A6, and UGT2B7. ET inhibited UGT1A6 (glucuronidation of p-nitrophenol) and UGT2B7 (glucuronidation of androsterone). We showed the inhibitory effect of xanthene dye on human UGT1A6 activity. Basic ET, PL, and RB in those food dyes strongly inhibited UGT1A6 activity, with IC₅₀ values = 0.05, 0.04, and 0.015 mM, respectively. Meanwhile, AR of an acidic xanthene food dye showed no inhibition. Next, we studied the inhibition of CYP3A4 of a major phase I drug-metabolizing enzyme and P-glycoprotein of a major transporter by synthetic food dyes. Human CYP3A4 and P-glycoprotein were also inhibited by basic xanthene food dyes. The IC₅₀ values of these dyes to inhibit CYP3A4 and P-glycoprotein were the same as the inhibition level of UGT1A6 by three halogenated xanthene food dyes (ET, PL, and RB) described above, except AR, like the results with UGT1A6 and UGT2B7. We also confirmed the noninhibition of CYP3A4 and P-gp by other synthetic food dyes. Part of this inhibition depended upon the reaction of ¹O₂ originating on xanthene dyes by light irradiation, because inhibition was prevented by ¹O₂ quenchers. We studied the influence of superoxide dismutase and catalase on this inhibition by dyes and we found prevention of inhibition by superoxide dismutase but not catalase. This result suggests that superoxide anions, originating on dyes by light irradiation, must attack drug-metabolizing enzymes. It is possible that red cosmetics containing phloxine, erythrosine, or rose bengal react with proteins on skin under lighting and may lead to rough skin.

Identification of putative steroid-binding sites in human ABCB1 and ABCG2

Homology modelling was used to generate three-dimensional structures of the nucleotide-binding domains (NBDs) of human ABCB1 and ABCG2. Interactions between a series of steroidal ligands and transporter NBDs were investigated using an in silico docking approach. C-terminal ABCB1 NBD (ABCB1 NBD2) was predicted to bind steroids within a cavity formed partly by the P-Loop, Tyr1044 and Ile1050. The P-Loop within ABCG2 NBD was also predicted to be involved in steroid binding. No overlap between ATP- and RU-486-binding sites was predicted in either NBD, though overlaps between ATP- and steroid-binding sites were predicted in the vicinity of the P-Loop in both nucleotide-binding domains.

Role of Ss-A/Ro ribonucleoprotein 60 ku subunit variant 1 in multi-drug resistance of gastric cancer

AIM: To investigate the possible role of Ro 60 variant 1 in multi-drug resistance (MDR) of gastric cancer.

METHODS: Ro 60 variant 1 encoding gene was cloned using RT-PCR method. Ro 60 variant 1 sense eukaryotic expression vector was constructed using DNA recombination technique and transfected into SGC7901 cells with LipofectamineTM 2000. Drug sensitivity was detected by MTT assay. IC50 values of gastric cancer cells for chemotherapy drugs were calculated. Intracellular accumulation of adriamycin in gastric cancer cells was measured by sorting fluorescence- activated cells.

RESULTS: The expression level of Ro 60 variant 1 in SGC7901 cells was increased after transfection with sense genes. In vitro drug sensitivity assay showed that the sensitivity of SGC7901 cells transfected with Ro 60 variant 1 genes was significantly decreased compared with SGC7901 and SGC7901-pcDNA3.1 cells on vincristine (IC₅₀: 2.87 ± 0.10 mg/L vs 0.47 ± 0.07 mg/L, 0.63 ± 0.08 mg/L, P < 0.01), 5-FU(IC₅₀: 3.89 ± 0.12 mg/L vs 0.59 ± 0.17 mg/L, 0.92 ± 0.12 mg/L, P<0.01), mitomycin (IC₅₀: 1.02 ± 0.06 mg/L vs 0.50 ± 0.04 mg/L, 0.73 ± 0.09 mg/L, P < 0.05), cisplatin (IC₅₀: 1.15 ± 0.06 mg/L vs 0.46 ± 0.04 mg/L, 0.52 ± 0.05 mg/L, P < 0.01) and adriamycin (IC₅₀: 0.45 ± 0.03 mg/L vs 0.15 ± 0.03 mg/L, 0.16 ± 0.02 mg/L, P < 0.01). Flow cytometry revealed that accumulation of adriamycin in SGC7901 cells transfected with Ro 60 variant 1 gene was decreased (50.39 ± 2.09 mg/L vs 94.99 ± 4.07 mg/L, 88.06 ± 2.67 mg/L, P < 0.01), when compared with SGC7901 and SGC7901-pcDNA3.1 cells.

CONCLUSION: SGC7901 cells transfected with Ro 60 variant 1 sense genes exhibit MDR. Ro 60 variant 1 might play a certain role in MDR of gastric cancer.

Interaction between valproic acid and carbapenem antibiotics

The serum concentration of valproic acid (VPA) in epilepsy patients decreased by the administration of carbapenem antibiotics, such as meropenem, panipenem or imipenem, to a sub-therapeutic level. This review summarized several case reports of this interaction between VPA (1-4 g dose) and carbapenem antibiotics to elucidate the possible mechanisms decreasing VPA concentration by carbapenem antibiotics. Studies to explain the decrease were carried out using rats by the following sites: absorption of VPA in the intestine, glucuronidation in the liver, disposition in blood and renal excretion. In the intestinal absorption site, there are two possible mechanisms: inhibition of the intestinal transporter for VPA absorption by carbapenem antibiotics, and the decrease of beta-glucuronidase supplied from enteric bacteria, which were killed by antibiotics. This is consistent with a view that the decrease of VPA originated from VPA-Glu, relating to entero-hepatic circulation. The second key site is in the liver, because of no decreased in VPA level by carbapenem antibiotics in hepatectomized rats. There are three possible mechanisms in the liver to explain the decreased phenomenon: first, decrease of the UDPGA level by carbapenem antibiotics. UDPGA is a co-factor for UDP-glucuronosyltransferase (UGT)-mediated glucuronidation of VPA. Second, the direct activation of UGT by carbapenem antibiotics. This activation was observed after pre-incubation of human liver microsomes with carbapenem antibiotics. Third, the inhibition of beta-glucuronidase in liver by carbapenem antibiotics and the decreased VPA amount liberated from VPA-Glu. The third site is the distribution of VPA in blood (erythrocytes and plasma). Plasma VPA distributed to erythrocytes by the inhibition of transporters (Mrp4), which efflux VPA from erythrocytes to plasma, by carbapenem antibiotics. The increase of renal excretion of VPA as VPA-Glu depends on the increase of VPA-Glu level by UGT. One or a combination of some factors in these mechanisms might relate to the carbapenem-mediated decrease of the plasma VPA level.

Reversal of multidrug resistance in gastric cancer cell line by Ss-A/Ro ribonucleoprotein 60-ku subunit antisense nucleic acid

AIM: To investigate the possible function of Ro 60 antisense nucleic acid in multidrug resistant cell line of gastric cancer.

METHODS: Ro 60 antisense eukaryotic expression vector was constructed using DNA recombination technique, then transfected into SGC7901-VCR by Lipofectamine^TM2000. Drug sensitivity assay was performed using MTT assay, and IC₅₀ values of gastric cancer cells to chemotherapy drugs were calculated. The intracellular accumulation of adriamycin in gastric cancer cells was measured using fluorescence-activated cell sorting.

RESULTS: The expression level of Ro 60 in SGC7901-VCR cells was decreased after transfection with antisense genes. In vitro drug sensitivity assay show that SGC7901-VCR cells transfected with Ro 60 antisense genes showed significantly increased sensitivity to vincristine (IC₅₀: 7.66 ± 0.45 mg/L vs 19.56 ± 0.38, 17.48 ± 0.85 mg/L, P < 0.01), mitomycin (IC₅₀: 0.84 ± 0.03 mg/L vs 1.62 ± 0.06, 1.80 ± 0.03 mg/L, P < 0.01), cisplatin (IC₅₀: 0.51 ± 0.03 mg/L vs 0.87 ± 0.03, 0.88 ± 0.03 mg/L, P < 0.01) and adriamycin (IC₅₀: 0.22 ± 0.01 mg/L vs 0.52 ± 0.02, 0.43 ± 0.03 mg/L, P < 0.01), as compared with SGC7901-VCR and SGC7901-VCR-pcDNA3.1 cells. As showed by flow cytometry, the intracellular accumulation of adriamycin in the cells transfected with Ro 60 antisense gene was markedly increased in comparison with that in SGC7901-VCR or SGC7901-VCR-pcDNA3.1 cells (51.94 ± 1.26 mg/L vs 36.27 ± 0.98, 37.01 ± 0.91 mg/L, P < 0.01).

CONCLUSION: After transfected into multidrug resistant cell line of gastric cancer, Ro 60 antisense nucleic acid can inhibit the multidrug resistant phenotype of gastric cancer.

Preparation of HCT-8/5-fluorouracil multidrug resistant cell line and detection of P-glycoprotein

AIM: To develop HCT-8/5-fluorouracil multidrug resistant cell line and explore the mechanism its drug resistance.

METHODS: High concentration of 5-FU was used in the beginning to induce drug resistance of HCT-8 cell line, and thereafter, the concentration of 5-FU was increased in gradient. About 7 mo later, the cells could stably grow in 2.0 mg/L 5-FU, which was named HCT-8/5-FU multidrug resistant cell line. The resistant index of HCT-8/5-FU cells to 5-FU, adriamycin (ADM), and cisplatin (DDP) was examined with MTT assay, and growth curve was drawn. The morphological changes were observed by both light and electron microscopy. The function of P-glycoprotein (P-gp) was detected by flow cytometry using rhodamine staining.

RESULTS: The resistant index of HCT-8/5-FU cells to 5-FU is 16.6, and a cross-resistance to ADM and DDP was also noticed. In comparison with that of the parental cells, the growth rate of HCT-8/5-FU cells did not changed significantly, but the morphology of the cells was remarkably changed. Irregular nucleus, double nucleus and polymorphic nucleus appeared in HCT-8/5-FU cells, and the cells shaped as polygon-like and leptosomatic. The numbers of mitochondria, endoplasmic reticulum and lysosome were increased, and over-expression of P-gp was observed in HCT-8/5-FU cells.

CONCLUSION: HCT-8/5-FU multidrug resistant cell line is successfully developed. The drug-resistance mechanism of HCT-8/5-FU cell line may be related to the over-expression of P-gp.