Effects of Two Natural Bisbenzylisoquinolines, Curine and Guattegaumerine, Extracted from Isolona hexaloba on Rhodamine Efflux by Abcb1b from Rat Glycocholic-Acid-Resistant Hepatocarcinoma Cells.

To develop new therapeutic molecules, it is essential to understand the biological effects and targets of clinically relevant compounds. In this article, we describe the extraction and characterization of two alkaloids from the roots of Isolona hexaloba-curine and guattegaumerine. The effect of these alkaloids on the multidrug efflux pump ABCB1 (MDR1/P-Glycoprotein) and their antiproliferative properties were studied. Compared to verapamil, a widely used inhibitor of P-gp, curine and guattegaumerine were found to be weak inhibitors of MDR1/P-Glycoprotein. The highest inhibition of efflux produced by verapamil disappeared in the presence of curine or guattegaumerine as competitors, and the most pronounced effect was achieved with curine. Altogether, this work has provided new insights into the biological effects of these alkaloids on the rat Mdr1b P-gp efflux mechanism and would be beneficial in the design of potent P-gp inhibitors.

Effects of Verapamil and Two Bisbenzylisoquinolines, Curine and Guattegaumerine Extracted from Isolona hexaloba, on the Inhibition of ABC Transporters from Pseudomonas aeruginosa.

The biological effects of alkaloids, curine, guattegaumerine, and verapamil, on Pseudomonas aeruginosa were investigated. These molecules did not inhibit P. aeruginosa growth but increased the sensitivity of this bacterium to carbenicillin, novobiocin, and erythromycin. The results of another study indicate that curine and guattegaumerine were competitors of verapamil and acted as inhibitors of eukaryotic ABCB1 efflux pump. A BLAST-P carried out between a bacterial MDR transporter LmrA from Lactococcus lactis, a human MDR1/P-glycoprotein (ABCB1), and ABC proteins of P.aeruginosa highlighted five potential candidates that have this bacterium. A study on the sensitivity to carbenicillin in the presence of verapamil allowed us to identify the product of gene PA1113 as the ABC transporter involved in the influx of carbenicillin. Similarly, novobiocin transport performed in the presence of verapamil and a docking analysis highlighted protein MsbA (Lipid A flippase, gene PA4997) as a potential candidate in novobiocin efflux. MsbA has previously been identified as a multidrug transporter in E. coli, and as P. aeruginosa MsbA presented 76% identity with E. coli MsbA, it is possible that novobiocin efflux involves this ABC transporter, accounting for about 30% of the bacterium resistance to this antibiotic.

Identification of the PA1113 Gene Product as an ABC Transporter Involved in the Uptake of Carbenicillin in Pseudomonas aeruginosa PAO1.

The resistance of Pseudomonas aeruginosa to antibiotics is multi factorial and complex. Whereas efflux pumps such as MexAB-OprM have been thought to predominate, here we show that a novel ATP Binding Cassette (ABC) transporter that mediates influx of carbenicillin from the periplasm to the cytoplasm and away from its cell wall target plays an important role in the resistance of P. aeruginosa to this antibiotic. Treatment of P. aeruginosa with verapamil, an inhibitor of ABC transporters in eukaryotic cells, increases its sensitivity to carbenicillin. Using amino acid sequence homology with known verapamil protein targets as a probe, we determined that the PA1113 gene product, an ABC transporter, mediates carbenicillin uptake into the bacterial cytoplasm. Docking and pharmacological analyses showed that verapamil and carbenicillin compete for the same site on the PA1113 gene protein, explaining the inhibitory effect of verapamil on carbenicillin uptake, and furthermore suggest that the PA1113 ABC transporter accounts for about 30% of P. aeruginosa carbenicillin resistance. Our findings demonstrate that the PA1113 gene product helps mediate carbenicillin resistance by transporting it away from its cell wall target and represents a promising new therapeutic target.

Tumor necrosis factor-alpha down-regulates human Cu/Zn superoxide dismutase 1 promoter via JNK/AP-1 signaling pathway.

Overexpression of Cu/Zn superoxide dismutase 1 (SOD1) in monocytes blocks reactive oxygen species-induced inhibition of cell growth and apoptosis and renders cells resistant to the toxic effect of tumor necrosis factor (TNF)-alpha, suggesting that TNF-alpha represses the SOD1 gene in these cells. We herein show that TNF-alpha decreases SOD1 mRNA, protein, and promoter activity in U937 cells. Electrophoretic mobility-shift assays (EMSA) show that TNF-alpha decreased binding of three different complexes. Ectopic Sp1 overexpression markedly increased SOD1-basal promoter activity and partially antagonized the TNF-alpha inhibitory effect. In contrast, ectopic c-Jun overexpression mimics TNF-alpha inhibitory effects and antagonizes Sp1 stimulatory effects. In agreement with these findings, EMSA shows a TNF-alpha-induced increase in AP-1 and a decrease in Sp1 DNA binding. Disruption of the C/EBP site decreases, whereas mutation in the Sp1/Egr-1 site completely abolishes DNA-binding and promoter activity. A JNK inhibitor antagonized the negative effects of TNF-alpha on SOD1 promoter activity, suggesting that JNK signaling through c-Jun protein activation is critical for the TNF-alpha-dependent SOD1 repression. A greater understanding of the mechanisms of TNF-alpha-induced SOD1 repression could facilitate the design and development of novel therapeutic drugs for inflammatory conditions.

Thyroid hormone export varies among primary cells and appears to differ from hormone uptake.

We characterized T3 efflux in primary cultures of cells derived from human placenta, neonatal rat cardiac myocytes, and rat inner medullary collecting ducts (IMCD). The T3 efflux rate was highest in placenta cells, followed by ventriculocytes, atriocytes, and IMCD cells. Verapamil reversibly blocked [125I]T3 efflux in these cells in a manner that correlated with their T3 efflux rate. Thus, verapamil inhibition of [125I]T3 efflux in placenta cells led to a 432% increase in the [125I]T3 content compared with 33% increase in IMCD cells. Several unlabeled iodothyronines, but not TRIAC, differentially blocked [125I]T3 efflux such as (T4 > T3 > rT3 = D-T3 > D-T4) in placenta cells and (T4 > rT3 = D-T4 = T3 > D-T3) in ventriculocytes, suggesting tissue-specific differences in the carriers/transporters responsible for T3 efflux. This hypothesis draws further support from the fact that D-T3 inhibited [125I]T3 efflux in placenta cells, but not in ventriculocytes. TRIAC did not affect T3 efflux in ventriculocytes or placenta cells, but it greatly inhibited [125I]T3 uptake in these cells, suggesting that [125I]T3 uptake and efflux mechanisms are distinct and appear to be mediated by distinct carrier/transporter proteins. Collectively, these data suggest that differences in thyroid hormone transport in target cells may provide an important mechanism for regulating hormone action in a tissue-specific fashion.

Altered hepatobiliary gene expressions in PFIC1: ATP8B1 gene defect is associated with CFTR downregulation.

Recent reports in patients with PFIC1 have indicated that a gene defect in ATP8B1 could cause deregulations in bile salt transporters through decreased expression and/or activity of FXR. This study aimed to: (1) define ATP8B1 expression in human hepatobiliary cell types, and (2) determine whether ATP8B1 defect affects gene expressions related to bile secretion in these cells. ATP8B1 expression was detected by RT-PCR in hepatocytes and cholangiocytes isolated from normal human liver and gallbladder. ATP8B1 mRNA levels were 20- and 200-fold higher in bile duct and gallbladder epithelial cells, respectively, than in hepatocytes. RT-PCR analyses of the liver from two patients with PFIC1, one with PFIC2, one with biliary atresia, showed that, compared to normal liver, hepatic expressions of FXR, SHP, CYP7A1, ASBT were decreased at least by 90% in all cholestatic disorders. In contrast, NTCP transcripts were less decreased (by < or = 30% vs. 97%) in PFIC1 as compared with other cholestatic disorders, while BSEP transcripts, in agreement with BSEP immunohistochemical signals, were normal or less decreased (by 50% vs. 97%). CFTR hepatic expression was decreased (by 80%), exclusively in PFIC1, while bile duct mass was not reduced, as ascertained by cytokeratin-19 immunolabeling. In Mz-ChA-2 human biliary epithelial cells, a significant decrease in CFTR expression was associated with ATP8B1 invalidation by siRNA. In conclusion, cholangiocytes are a major site ofATP8B1 hepatobiliary expression. A defect of ATP8B1 along with CFTR downregulation can impair the contribution of these cells to bile secretion, and potentially explain the extrahepatic cystic fibrosis-like manifestations that occur in PFIC1.

Negative regulation of superoxide dismutase-1 promoter by thyroid hormone.

The role of thyroid hormone [L-3,5,3'-triiodothyronine (T3)] and the thyroid hormone receptor (TR) in regulating growth, development, and metabolic homeostasis is well established. It is also emerging that T3 is associated with oxidative stress through the regulation of the activity of superoxide dismutase-1 (SOD-1), a key enzyme in the metabolism of oxygen free radicals. We found that T3 reverses the activation of the SOD-1 promoter caused by the free radical generators paraquat and phorbol 12-myristate 13-acetate through the direct repression of the SOD-1 promoter by liganded TR. Conversely, the SOD-1 promoter is significantly stimulated by unliganded TRs. This regulation requires the DNA-binding domain of the TR, which is recruited to an inhibitory element between -157 and +17 of the SOD-1 promoter. TR mutations, which abolish recruitment of coactivator proteins, block repression of the SOD-1 promoter. Conversely, a mutation that inhibits corepressor binding to the TR prevents activation. Together, our findings suggest a mechanism of negative regulation in which TR binds to the SOD-1 promoter but coactivator and corepressor binding surfaces have an inverted function. This effect may be important in T3 induction of oxidative stress in thyroid hormone excess.

Thyroid hormone receptor binding to DNA and T3-dependent transcriptional activation are inhibited by uremic toxins.

BACKGROUND: There is a substantial clinical overlap between chronic renal failure (CRF) and hypothyroidism, suggesting the presence of hypothyroidism in uremic patients. Although CRF patients have low T3 and T4 levels with normal thyroid-stimulating hormone (TSH), they show a higher prevalence of goiter and evidence for blunted tissue responsiveness to T3 action. However, there are no studies examining whether thyroid hormone receptors (TRs) play a role in thyroid hormone dysfunction in CRF patients. To evaluate the effects of an uremic environment on TR function, we investigated the effect of uremic plasma on TRbeta1 binding to DNA as heterodimers with the retinoid X receptor alpha (RXRalpha) and on T3-dependent transcriptional activity. RESULTS: We demonstrated that uremic plasma collected prior to hemodialysis (Pre-HD) significantly reduced TRbeta1-RXRalpha binding to DNA. Such inhibition was also observed with a vitamin D receptor (VDR) but not with a peroxisome proliferator-activated receptor gamma (PPARgamma). A cell-based assay confirmed this effect where uremic pre-HD ultrafiltrate inhibited the transcriptional activation induced by T3 in U937 cells. In both cases, the inhibitory effects were reversed when the uremic plasma and the uremic ultrafiltrate were collected and used after hemodialysis (Post-HD). CONCLUSION: These results suggest that dialyzable toxins in uremic plasma selectively block the binding of TRbeta1-RXRalpha to DNA and impair T3 transcriptional activity. These findings may explain some features of hypothyroidism and thyroid hormone resistance observed in CRF patients.

Analysis of P-glycoprotein-mediated membrane transport in human peripheral blood lymphocytes using the UIC2 shift assay.

BACKGROUND: During transport-associated adenosine triphosphate hydrolysis, P-glycoprotein (Pgp) undergoes conformation transitions detected by UIC2, a functional anti-Pgp monoclonal antibody. A newly developed UIC2 shift assay is based on increased UIC2 reactivity in the presence of Pgp substrates. All peripheral blood leukocytes express low Pgp levels. The existing antibody-based detection methods are limited in their sensitivity and require additional techniques to simultaneously analyze Pgp expression and efflux, making it difficult to ascertain the physiologic role of Pgp-mediated transport. METHODS: We validated the UIC2 shift assay against UIC2 immunostaining and DiOC(2) efflux. The UIC2 shift assay was then used to characterize Pgp functional expression and its physiologic substrates in peripheral blood leukocytes. RESULTS: A strong correlation was observed between the UIC2 shift assay versus immunostaining and dye efflux tests. The UIC2 shift assay showed improved sensitivity (compared with conventional UIC2 staining) and allowed for simultaneous detection of Pgp expression and function. Using this assay, we identified several new Pgp substrates, including monensin and retinol, and confirmed that interleukin-2 and interferon-gamma can be transported by Pgp. CONCLUSIONS: Our findings validate the use of the UIC2 shift assay in MDR1 detection and support the idea that Pgp plays a physiologic role in immunoregulation.

Thyroid hormone transport is disturbed in erythrocytes from patients with chronic renal failure on hemodialysis.

AIMS: To now, there are no studies reporting whether thyroid hormones (THs) transport play a role in thyroid hormone dysfunction observed in chronic renal failure (CRF). Therefore, the aim of this study was to investigate the transport of THs in erythrocytes from patients with CRF on hemodialysis (HD). METHODS: [125I]-L-triiodothyronine ([125I]T3) and [125I]-L-thyroxine ([125I]T4) erythrocytes uptake was measured at 1 min and 5 min. To study L-triiodothyronine (LT3) and L-thyroxine (LT4) efflux from erythrocytes, we preloaded the cells during 180 min with [125I]T3 or [125I]T4 and measured their [125I]T3 or [125I]T4 efflux during 60 min. RESULTS: [125I]T3 uptake in erythrocytes from uremic patients pre-HD was higher than control subjects by 50% at 1 min and by 55% at 5 min. However, [125I]T4 uptake in erythrocytes from uremic patients was significantly lower at 1min (88%) and at 5 min (63%). LT3 efflux rate was lower and LT4 efflux was significantly higher than in control subjects. After 60-min of efflux, LT3 remained in erythrocytes was 80% higher and LT4 was 57% lower than in normal individuals. Neither [125I]T3 and [125I]T4 uptake, nor efflux rates were changed by hemodialysis. CONCLUSION: Despite the fact that uremic patients on hemodialysis show low serum levels of LT3, changes in LT3 influx and efflux could act as a compensatory mechanism that neutralize thyroid hormone dysfunction in order to maintain the euthyroid state.