Inhibitors of Prostaglandin Transport and Metabolism Augment Protease-Activated Receptor-2-Mediated Increases in Prostaglandin E2 Levels and Smooth Muscle Relaxation in Mouse Isolated Trachea

Stimulants of protease-activated receptor-2 (PAR(2)), such as Ser-Leu-Ile-Gly-Arg-Leu-NH(2) (SLIGRL), cause airway smooth muscle relaxation via the release of the bronchodilatory prostanoid prostaglandin E(2) (PGE(2)). The principal aim of the current study was to determine whether compounds that inhibit PGE(2) reuptake by the prostaglandin transporter [bromocresol green and U46619 (9,11-dideoxy-9alpha,11alpha-methanoepoxy PGF2alpha) and PGE(2) metabolism by 15-hydroxyprostaglandin dehydrogenase (thiazolidenedione compounds rosiglitazone and ciglitazone) significantly enhanced the capacity of SLIGRL to elevate PGE(2) levels and produce relaxation in isolated segments of upper and lower mouse trachea. SLIGRL produced concentration-dependent increases in PGE(2) levels and smooth muscle relaxation, although both effects were significantly greater in lower tracheal segments than in upper tracheal segments. SLIGRL-induced increases in PGE(2) levels were significantly enhanced in the presence of ciglitazone and rosiglitazone, and these effects were not inhibited by GW9662 (2-chloro-5-nitrobenzanilide), a peroxisome proliferator-activated receptor-gamma antagonist. SLI-GRL-induced relaxation responses were also significantly enhanced by ciglitazone and rosiglitazone, whereas responses to isoprenaline, a PGE(2)-independent smooth muscle relaxant, were unaltered. Ciglitazone and rosiglitazone alone produced concentration-dependent increases in PGE(2) levels and smooth muscle relaxation, and these responses were inhibited by indomethacin, a cyclooxygenase inhibitor. Bromocresol green, an inhibitor of prostaglandin transport, significantly enhanced SLIGRL-induced increases in PGE(2) levels and relaxation. Immunohistochemical staining for 15-hydroxyprostaglandin dehydrogenase was relatively intense over airway smooth muscle, as was staining for the prostaglandin transporter over both airway smooth muscle and epithelium. In summary, inhibitors of PGE(2) reuptake and metabolism significantly potentiate PAR(2)-mediated increases in PGE(2) levels and smooth muscle relaxation in murine-isolated airways.

Study on bromocresol green-cetyltrimethylammonium-deoxyribonucleic acids system by resonance light scattering spectrum methods

An assay of deoxyribonucleic acids (DNA) determination, with the sensitivity at nanogram level, was established in the present study by using a common spectrofluorometer to detect the intensity of resonance light scattering (RLS). In hexamethylene tetramine (HMTA) buffer (pH 11.00), Bromocresol Green (BCG) and deoxyribonucleic acids (DNA) react with cetyltrimethylammonium bromide (CTMAB) to form large particles of three-component complex, which results in strong enhanced RLS signals characterized by three peaks at 336, 390, and 622 nm and at 336 nm that is the strongest of the three enhanced RLS peaks. Mechanistic studies showed that the enhanced RLS stems from the aggregation of BCG on DNA through the bridged and synergistic effect of CTMAB. Yeast DNA (yDNA), in the range of 0.05-0.90 ngml(-1), fish sperm DNA (fsDNA) in the range of 0.05-0.80 ngml(-1), and calf thymus DNA (ctDNA) in the range of 0.05-0.80 ngml(-1) can be determined if 2.0 x 10(-6) moll(-1) BCG was employed. The determination limit of yDNA was 12.7 ngml(-1). Three synthetic samples of yDNA were analyzed with good reproducibility.

Transport of prostaglandin E1 across the blood-brain barrier in rats

The transport of prostaglandin E(1) (PGE(1)) across the blood-brain barrier (BBB) was characterized using an in-situ rat brain perfusion technique. The uptake of [(3)H]PGE(1) was not affected by shortchain monocarboxylic acids (butyric acid and valeric acid). On the other hand, uptake of [(3)H]PGE(1) was significantly inhibited by medium-chain monocarboxylic acids such as hexanoic acid, enanthic acid and octanoic acid. These medium-chain monocarboxylic acids showed a more potent inhibitory effect on [(3)H]PGE(1) uptake with increasing number of carbon atoms. In contrast, there was no decrease in [(3)H]PGE(1) transport by any dicarboxylic acids with 5-8 carbon atoms. Valproic acid decreased [(3)H]PGE(1) uptake, whereas p-aminohippuric acid, a substrate for the organic anion transporter family, did not inhibit [(3)H]PGE(1) transport. Bromocresol green, an inhibitor of prostaglandin transporter (PGT), strongly decreased [(3)H]PGE(1) transport across the BBB. In addition, digoxin and taurocholate, substrates for organic anion transporting polypeptide subtype 2 (Oatp2), significantly inhibited [(3)H]PGE(1) uptake. RT-PCR analysis revealed that PGT mRNA and Oatp2 mRNA are expressed in a capillary-rich fraction from rat brain. Thus, it is suggested that PGE(1) transport across the BBB is mediated by some specific transport systems, possibly by the members of the Oatp family.

Expression of PGT in MDCK cell monolayers: polarized apical localization and induction of active PG transport

The PG transporter (PGT) is expressed in subapical vesicles in the kidney collecting duct. To gain insight into the possible function of the PGT in this tubule segment, we tagged rat PGT with green fluorescent protein at the COOH terminus and generated stable PGT-expressing Madin-Darby canine kidney cell lines. When grown on permeable filters, green fluorescent protein-PGT was expressed predominantly at the apical membrane. Although the basal-to-apical transepithelial flux of [(3)H]PGE(2) was little changed by PGT expression, the apical-to-basolateral flux was increased 100-fold compared with wild-type cells. Analysis of driving forces revealed that this flux represents PGT-mediated active transepithelial PGE(2) transport. We propose that endogenous PGT is exocytically inserted into the collecting duct apical membrane, where it could control the concentration of luminal PGs.

Taurine secretion in primary monolayer cultures of flounder renal epithelium: stimulation by low osmolality

Transepithelial taurine fluxes determined in short-circuited monolayer cultures of flounder renal proximal cells in Ussing chambers revealed net taurine secretion. Both unidirectional secretory and reabsorptive taurine fluxes exhibited saturation kinetics contributed by two distinct saturable transepithelial taurine transport systems operating at different taurine concentration ranges. The taurine secretory system operating below 0. 5 mM had lower affinity but higher capacity than the reabsorptive system, whereas the one operating at high concentrations (0.5-3.0 mM) had higher affinity but the same capacity as the corresponding reabsorptive system. Exposure (2 h) of the cultures to hyposmotic medium in the presence of taurine increased taurine secretory flux twofold with no effect on the reabsorptive flux. The hyposmolality-induced increase in taurine secretion was associated with a decreased peritubular taurine efflux and a concurrent increased luminal taurine efflux; the latter occurred via a pathway that was not affected by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid but inhibited by probenecid. The culture response in hyposmotic medium mimics the in vivo response of the intact marine fish kidney to dilution.

Functional role of high-affinity anandamide transport, as revealed by selective inhibition

Anandamide, an endogenous ligand for central cannabinoid receptors, is released from neurons on depolarization and rapidly inactivated. Anandamide inactivation is not completely understood, but it may occur by transport into cells or by enzymatic hydrolysis. The compound N-(4-hydroxyphenyl)arachidonylamide (AM404) was shown to inhibit high-affinity anandamide accumulation in rat neurons and astrocytes in vitro, an indication that this accumulation resulted from carrier-mediated transport. Although AM404 did not activate cannabinoid receptors or inhibit anandamide hydrolysis, it enhanced receptor-mediated anandamide responses in vitro and in vivo. The data indicate that carrier-mediated transport may be essential for termination of the biological effects of anandamide, and may represent a potential drug target.

Heterogeneity of dog-liver glutathione S-transferases. Evidence for a unique temperature dependence of the catalytic process

Dog liver glutathione S-transferase activities are associated with five cytosolic proteins and to approximately 1.5% with microsomal proteins determined on the basis of activity conjugating to 1-chloro-2,4-dinitrobenzene. The four major cytosolic enzymes were purified to apparent homogeneity by sequential use of ion-exchange, hydrophobic, hydroxyapatite and affinity chromatography. The isolated transferases are binary combinations of three classes of subunits: alpha (Mr = 26,000), beta (Mr = 27,000), gamma (Mr = 28,500). They were classified by roman numerals assigned in order of increasing isoelectric point as DI alpha gamma (pI 6.4), DII alpha alpha (pI 6.9), DIII beta gamma (pI 8.1), and DIV beta gamma (pI 8.7). Additionally, traces of conjugating activity may be attributed to a, beta monomeric or dimeric protein with cationic character. The differences in catalytic specificity, temperature and pH dependence of activity, and sensitivity and kinetic response to inhibitory ligands may reflect the intrinsic structural heterogeneity of the transferases. At physiological glutathione concentrations DI alpha gamma accounted for roughly 60% of the total 1-chloro-2,4-dinitrobenzene-conjugating activity, the rank order of activity being DI alpha gamma greater than DII alpha alpha greater than DIV beta gamma greater than DIII beta gamma. The glutathione-dependent denitration of organic nitrates seems to be restricted to the cationic enzymes, whereas 1,2-dichloro-4-nitrobenzene-conjugating activity is exclusively associated with the anionic transferases, DI alpha gamma much greater than DII alpha alpha. Arrhenius plots from initial rate experiments performed over a range of temperatures (15-40 degrees C) exhibit an upward bend for DI alpha gamma, an apparently constant slope for DII alpha alpha and DIII beta gamma, and a downward bend for DIV beta gamma.

Influence of plasma protein on the inhibitory effects of indocyanine green and bromcresol green on pulmonary prostaglandin E1 extraction

The purpose of this study was to examine the influence of plasma protein on the inhibitory effects of the anionic dyes indocyanine green and bromcresol green on prostaglandin E1 (PGE1) uptake by the lungs. Dog lung lobes were isolated and perfused with either autologous plasma or Krebs-Ringer bicarbonate solution (KRB) containing no protein but with dextran used as a colloid. PGE1 uptake was determined by injecting a bolus, containing radiolabelled PGE1 into the lobar artery and then analysing ethanolic extracts of the venous effluent for radioactivity in PGE1 and PGE1 metabolites by thin layer chromatography and scintillation counting. When the lobes were perfused with KRB, bromcresol green at an average initial concentration of 28.5 microM, reduced PGE1 by an average of 56%. When the lobes were perfused with plasma, similar concentrations of bromcresol green reduced the uptake by less than 2%. A similar result was obtained with indocyanine green, which at an average initial concentration of 17.5 microM reduced uptake by about 70% when the lobes were perfused with KRB, but when the lobes were perfused with plasma similar concentrations of the dye reduced uptake by less than 3.5%. The results suggest that plasma protein binding interferes with the inhibitory effects of these dyes on PGE1 uptake in the lungs.

Thromboxane B2 (TxB2) metabolism in rat isolated lung and its inhibition by drugs

In rat isolated lung perfused via the pulmonary circulation, 3H-TxB2 was metabolized to another radioactive species. About 60% of effluent 3H was metabolite and the same proportion of metabolite was found in lung at 5 min after the injection of 3H-TxB2. Metabolism of TxB2 was prevented by bromcresol green, dipyridamole and frusemide apparently by decreasing uptake of TxB2 by the lung. Our results support the possibility of TxB2 competing with PGE2 for metabolism in lung, although TxB2 is not a substrate for PGDH in vitro.

The effects of prostaglandins and arachidonic acid on the electroretinogram: evidence for functional cyclooxygenase activity in the retina

The effects of intravitreally injected prostaglandins (PGs) and arachidonic acid (AA) on the electrical activity of the retina were studied by monitoring the electroretinogram (ERG) of rabbits. In normal rabbits, intravitreal injection of PGE1, PGE2, or AA caused a gradual depression of b-wave amplitude as measured either in low (2 lux) or normal (300 lux) background illumination: up to 45% depression was observed within 1 hr and no recovery was noted during 4 hr of monitoring. The depression of the b-wave amplitude after the intravitreal injection of AA and PGs was similar in time course. Bromcresol green, an inhibitor of PG transport, significantly potentiated the effects of low doses of PGE1 and PGE2 and, to a lesser extent, that of AA. Indomethacin, a known inhibitor of cyclooxygenase activity, prevented the AA-induced, but not the PG-induced depression of the b-wave amplitude. It is concluded that PGs can have a direct effect on the retina and that this region of the eye contains sufficient cyclooxygenase activity to produce pathophysiologically significant amounts of PGs and/or related autacoids.

PAH transport in rock crab (Cancer irroratus) urinary bladder

Crab urinary bladder appears to possess several morphological and functional similarities to vertebrate renal proximal tubule. Sections of intermolt rock crab bladder accumulated PAH by a process that was concentrative (60 min tissue-to-medium ratio (T/M) for 10 microM PAH averaged 24), Na dependent, powered by glycolytic metabolism, and inhibitable by other organic anions. Initial section uptakes exhibited saturation kinetics and a double-reciprocal plot of uptake vs. concentration yielded a single line with a Km of 70 microM and a Vmax of 5 nmol . mg tissue-1 . h-1. Chlorophenol red and bromocresol green (BCG) competitively inhibited PAH uptake. When bladder sheets were mounted in a flux chamber, they exhibited a large, net lumen-to-serosa (L leads to S) flux of 10 microM PAH that was abolished by 1 mM BCG. The small unidirectional S leads to L flux was not BCG-inhibitable. Bladder sheets exhibited PAH T/M greater than 1 after luminal, but not serosal, exposure. BCG only reduced bladder sheet T/M after luminal exposure. The data are consistent with uphill, Na-dependent, and carrier-mediated entry of PAH at the luminal membrane and nonmediated exit at the serosal membrane.

The fate of exogenous arachidonic acid in guinea-pig isolated lung

1. The fate of [14C]arachidonic acid perfused through the pulmonary circulation was studied in guinea-pig lungs perfused with Krebs solution. 2. Radioactivity in the lung effluent fell rapidly and by 10 min about 20% of the infused radioactivity had emerged. 3. Most (70%) of the effluent radioactivity was associated with products of cyclo-oxygenase activity, whereas in the lung tissue most of the retained radioactivity was present as phospholipid. 4. Radioactivity in phospholipid was distributed equally between three groups: phosphatidyl choline, phosphatidyl ethanolamine and the other phosphatides. 5. Addition of albumin to the Krebs solution perfusing the lung increased the proportion of effluent radioactivity to 50%, decreased the cyclo-oxygenase products but increased the label in phospholipid in lung. 6. Indomethacin, frusemide, bromcresol green and diethylcarbamazine all decreased biological activation of arachidonic acid. 7. Indomethacin, bromcresol green and diethylcarbamazine also decreased effluent radioactivity and cyclo-oxygenase products with minimal effects on the distribution of radioactivity in lung lipid. 8. It appears that the major metabolic pathway for exogenous arachidonic acid perfused through the pulmonary circulation was incorporation into phospholipid. Metabolism via cyclo-oxygenase only involved about 15% of the total substrate infused.

Kinetics studies on the renal transport of probenecid in vitro

1. The kinetic parameters of renal transport of probenecid have been assessed by studying the uptake of the drug in rabbit kidney tubules incubated in an electrolyte medium under various conditions. 2. The added compounds inhibited the uptake of probenecid both by kidney cortical slices and separated renal tubule preparations in the following order: p-aminohippurate less than phenol red less than bromophenol blue less than bromocresol green. A reversible competitive inhibitory effect of these organic anions on the renal accumulation of the drug was observed. 3. The Km for renal uptake of probenecid in separated tubules (0.04 mM) and the KI values calculated in this system for p-aminohippurate (0.5 mM), phenol red (0.09 mM), bromophenol blue (0.02 mM) and bromocresol green (0.015 mM) were found to be in good agreement with the corresponding KI value of probenecid and Km values of these compounds previously observed in various kidney tissue preparations. 4. On the basis of above mentioned findings, it is concluded that probenecid, p-aminohippurate and various phenolsulphonphthalein dyes are transported by the common renal organic anion transport system.

The effects of intravitreally injected prostaglandin E1 on retinal function and their enhancement by a prostaglandin-transporter inhibitor

The effects of intravitreally injected prostaglandins (PG's) E1 and F2alpha were studied on conscious, bromcresol green (BrCG)-pretreated and control rabbits. The electroretinogram (ERG) of both the PG-injected and the contralateral control eyes was recorded with contact lens electrodes; and electrocorticogram and the visually evoked response (VER) were recorded from both hemispheres with previously implanted supradural electrodes. In normal rabbits, intravitreal injection of 0.70 mg of PGE1 resulted in a small reduction in the amplitude of the ERG b-wave and of the slow negative wave (SNW) of the contralateral VER. In BrCG-pretreated rabbits, intravitreal injection of 0.70 mg of PGE1 caused a statistically significant decrease in the amplitude of the ERG b-wave and the SNW. Intravitreal injection of 0.7 mg of PGE1 also caused a significantly prolonged inhibition of the ERG in BrCG-pretreated, but not in normal rabbits, following exposure of the eye to a bright light flash. A smaller dose of PGE1 (0.35 mg/eye) caused more moderate effects on some of these parameters. These effects could not be explained by the PG-induced miosis. PGF2alpha (0.7 mg/eye) caused no significant changes in any of the parameters studied. These results indicate that exogenous PG's can have adverse effects on retinal function and that these effects are enhanced by BrCG, a PG-transport inhibitor. Presumably, this inhibitor blocks the PG-removal mechanisms across the blood-retinal barriers and hence allows the accumulation of PG's in the extracellular fluids of the retina.

Enhancement of pulmonary drug absorption in the rat by bromphenol blue and related dyes

1. Pulmonary absorption studies in the rat showed that intratracheally administered 5-10 mM bromphenol blue, bromcresol green and bromthymol blue markedly increased the absorption rate of 0.1 mM phenol red. 2. Similarly, 1-10 mM bromphenol blue increased the absorption rate of 0.1 mP p-,minohippuric acid, tetraethylammonium and mannitol by 2- to 18-fold in a concentration-dependnet manner. 3. Mannitol absorption was enhanced more by bromthymol blue, sulphobromophthalein, bromcresol purple, thymol blue and bromcresol green than by bromphenol blue or m-cresol purple. Chlorphenol red and phenol red had no effect on mannitol absorption. 4. The results indicated that certain sulphonic acid dyes increase the permeability of the respiratory tract epithelium, perhaps by increasing its porosity.

Dependence of pulmonary prostaglandin metabolism on carrier-mediated transport processes

Inhibitors of prostaglandin (PG) transport (probenecid, indomethacin, or bromcresol green) were found to eliminate the difference between the pulmonary transit time of 3H and 14C when [3H]PGF2alpha and E114C]sucrose were injected as a single intra-arterial bolus into the isolated perfused rat lung. Similar results were obtained with PGE1. The transit time of [3H]PGA1 was not significantly different from that of [14C]sucrose even in the absence of an inhibitor. These inhibitors increased the amount of [3H]PGF2alpha or [3H]PGE1 and decreased the amount of [3H]PG metabolites found in the venous effluent: these agents also inhibited the pulmonary metabolism of continously infused, nonradioactive PGF2alpha. One of the three inhibitors, bromcresol green, was shown not to be an effective inhibitor of PG metabolism in cell-free preparations of rat lung homogenates. These results indicated that under normal conditions, PG's are rapidly transported into intracellular compartment(s) where they are metabolized. Inhibition of this transport process prevents rapid access of PG's to the cytoplasmic enzymes and therefore inhibits pulmonary PG metabolism. This implies that inhibitors of PG transport, including anti-inflammatory organic acids, and some PG antagonists, metabolites, and analogues, can be expected to inhibit the pulmonary metabolism of PG's and thus could potentiate the systemic effects endogenous or exogenous PG's.