Interaction of Organic Anion Transporter 3-Mediated Uptake of Steviol Acyl Glucuronide, a Major Metabolite of Rebaudioside A, with Selected Drugs.

Organic anion transporter 3 (OAT3) plays a critical role in the renal excretion of many xenobiotics. Because steviol acyl glucuronide (SVAG), an OAT3 substrate, is the major circulating metabolite after oral ingestion of steviol glycosides and is excreted into the urine, inhibition of OAT3 activity may alter pharmacokinetic profiles of SVAG. The present study showed that drugs such as probenecid and glimepiride displayed potent inhibition toward the OAT3-mediated SVAG transport, with IC50 values of 4.9 and 0.8 µM, respectively. No species differences were observed. Probenecid and glimepiride could significantly elevate plasma concentrations of SVAG after oral administration of rebaudioside A, with significant increases in plasma maximum (Cmax) and area under the plasma time-concentration curve values. The inhibitory effect on the OAT3-mediated SVAG transport exemplified a unique case between drugs and the metabolite of a food additive. Our data suggest that caution should be exercised when giving steviol glycoside products to human subjects with compromised renal function.

Andrographolide is neither a human organic anion transporter 1 (hOAT1) substrate nor inhibitor.

Andrographolide, a major bioactive compound isolated from Andrographis paniculata (Burm. F.) Nees, was evaluated for its effects on the hOAT1 membrane transporter. Substrate determination and inhibition of hOAT1-mediated uptake transport assay was carried out using recombinant CHO-hOAT1 cells. The results showed that the uptake ratio of andrographolide was less than 2.0 at all concentrations tested, indicating that andrographolide is not a hOAT1 substrate. Andrographolide has no significant effects on the p-aminohippuric acid uptake and on the mRNA and protein expression of hOAT1. In conclusion, andrographolide may not pose a drug-herb interaction risk related to hOAT1.

A one-pot synthesis of tetrazolones from acid chlorides: understanding functional group compatibility, and application to the late-stage functionalization of marketed drugs.

A one-pot and scalable synthesis of tetrazolones (tetrazol-5-ones) from acid chlorides using azidotrimethylsilane is presented. The reaction tolerates many functional groups and can furnish aryl-, heteroaryl-, alkenyl-, or alkyl-substituted tetrazolone products in moderate to excellent yield (14-94%). No reduction in yield was observed when the reaction was undertaken on a larger-scale (20-36 g). The method could be used for the late-stage functionalization of pharmaceuticals, to provide tetrazolone congeners of the marketed drugs aspirin, indomethacin, probenecid, telmisartan, bexarotene, niacin (vitamin B3), and the active metabolite of the recently-launched immuno-modulatory agent, BG-12 (Tecfidera®). The ability of a tetrazolone group to serve as a bioisostere of a carboxylic acid, and to improve drug pharmacokinetic profiles is also highlighted.

Effect of Known Inhibitors of Ion Transport on Pendrin (SLC26A4) Activity in a Human Kidney Cell Line.

BACKGROUND/AIMS: Pendrin is a Cl-/I-/HCO3- exchanger playing a fundamental role in controlling blood pressure and airway function, therefore representing an attractive target for the treatment of hypertensive states and respiratory distresses. A review of the literature regarding the ability of some compounds (namely several known inhibitors of ion transport) to block pendrin activity revealed discordant findings. These incongruous findings may be due, in part, to the concentration of compound and/or the nature of the model system used in the study. METHODS: Pendrin activity was evaluated by measuring pendrin-dependent iodide influx following overexpression of the transporter in a human kidney cell line, in the presence of selected test compounds or the respective vehicles. RESULTS: Pendrin activity was significantly hampered by 0.1 mM 5-nitro-2-[(3-phenylpropyl)amino]benzoic acid (NPPB), niflumic acid and tenidap, but was resistant to 0.1 mM 4, 4'-diisothiocyano-2, 2'-stilbene-disulfonic acid (DIDS), furosemide and probenecid. CONCLUSIONS: The results of the present study indicate that clinically effective non-steroidal anti-inflammatory drugs (niflumic acid and tenidap) directly inhibit pendrin activity.

"Predicting" Polymorphs of Pharmaceuticals Using Hydrogen Bond Propensities: Probenecid and Its Two Single-Crystal-to-Single-Crystal Phase Transitions.

The recently developed hydrogen-bonding propensity tool in the Cambridge Structural Database software package (Mercury) was tested to predict polymorphs. The compounds for the study were chosen from a list of approximately 300 pharmaceutically important compounds, for which multiple crystal forms had not been previously reported. The hydrogen-bonding propensity analysis was carried out on approximately 60 randomly selected compounds from this list. Several compounds with a high probability for exhibiting polymorphism in the analysis were chosen for a limited experimental crystal form screening. One of the compounds, probenecid, did not yield polymorphs by traditional solution crystallization screening, but differential scanning calorimetry revealed three polymorphs. All of them exhibit the same hydrogen bonding and transform via two reversible single-crystal-to single-crystal transformations, which have been characterized in detail through three single-crystal structure determinations at appropriate temperatures.

Selective inhibition of human carbonic anhydrases by novel amide derivatives of probenecid: synthesis, biological evaluation and molecular modelling studies.

Novel amide derivatives of probenecid, a well-known uricosuric agent, were synthesized and evaluated as inhibitors of human carbonic anhydrases (hCAs, EC 4.2.1.1). The transmembrane isoforms (hCA IX and XII) were potently and selectively inhibited by some of them. The proposed chemical modification led to a complete loss of hCA II inhibition (K(i)s>10,000 nM) and enhanced the inhibitory activity against the tumour-associated hCA XII (compound 4 showed a K(i) value of 15.3 nM). The enzyme inhibitory data have also been validated by docking studies of the compounds within the active site of hCA XII.

A technique for quantifying intracellular free sodium ion using a microplate reader in combination with sodium-binding benzofuran isophthalate and probenecid in cultured neonatal rat cardiomyocytes.

BACKGROUND: Intracellular sodium ([Na+]i) kinetics are involved in cardiac diseases including ischemia, heart failure, and hypertrophy. Because [Na+]i plays a crucial role in modulating the electrical and contractile activity in the heart, quantifying [Na+]i is of great interest. Using fluorescent microscopy with sodium-binding benzofuran isophthalate (SBFI) is the most commonly used method for measuring [Na+]i. However, one limitation associated with this technique is that the test cannot simultaneously evaluate the effects of several types or various concentrations of compounds on [Na+]i. Moreover, there are few reports on the long-term effects of compounds on [Na+]i in cultured cells, although rapid changes in [Na+]i during a period of seconds or several minutes have been widely discussed. FINDINGS: We established a novel technique for quantifying [Na+]i in cultured neonatal rat cardiomyocytes attached to a 96-well plate using a microplate reader in combination with SBFI and probenecid. We showed that probenecid is indispensable for the accurate measurement because it prevents dye leakage from the cells. We further confirmed the reliability of this system by quantifying the effects of ouabain, which is known to transiently alter [Na+]i. To illustrate the utility of the new method, we also examined the chronic effects of aldosterone on [Na+]i in cultured cardiomyocytes. CONCLUSIONS: Our technique can rapidly measure [Na+]i with accuracy and sensitivity comparable to the traditional microscopy based method. The results demonstrated that this 96-well plate based measurement has merits, especially for screening test of compounds regulating [Na+]i, and is useful to elucidate the mechanisms and consequences of altered [Na+]i handling in cardiomyocytes.

The history and future of probenecid.

Probenecid was initially developed with the goal of reducing the renal excretion of antibiotics, specifically penicillin. It is still used for its uricosuric properties in the treatment in gout, but its clinical relevance has sharply fallen and is rarely used today for either. Interestingly, throughout the last 60 years, there have been a host of apparently unrelated studies using probenecid in the clinical and basic research arena, including its potential use in the diagnosis and treatment of depression and its use to prevent fura-2 leakage in calcium transient studies. Recently, it has been shown that it is also an agonist of the Transient Receptor Potential Vanilloid 2 channel. Due to its unique action and new findings implicating TRPV channels in physiology and in disease, probenecid may have a new future as a research tool, and perhaps as a clinical agent in the neurology and cardiology fields. We review the history of probenecid in this paper and its potential future uses.

Thermodynamics of cosolvent action: phenacetin, salicylic acid and probenecid.

The solubility of phenacetin, salicylic acid, and probenecid in ethanol-water and ethanol-ethyl acetate mixtures at several temperatures (15-40 degrees C) was measured. The solubility profiles are related to medium polarity changes. The apparent thermodynamic magnitudes and enthalpy-entropy relationships are related to the cosolvent action. Salicylic acid and probenecid show a single peak against the solubility parameter delta(1) of both solvent mixtures, at 40% (delta(1) = 21.70 MPa(1/2)) and 30% (delta(1) = 20.91 MPa(1/2)) ethanol in ethyl acetate, respectively. Phenacetin displays two peaks at 60% ethanol in ethyl acetate (23.30 MPa(1/2)) and 90% ethanol in water (delta(1) = 28.64 MPa(1/2)). The apparent enthalpies of solution display a maximum at 30% (phenacetin and salicylic acid) and 40% (probenecid) ethanol in water, respectively. Two different mechanisms, entropy at low ethanol ratios, and enthalpy at high ethanol ratios control the solubility enhancement in the aqueous mixture. In the nonaqueous mixture (ethanol-ethyl acetate) enthalpy is the driving force throughout the whole solvent composition for salicylic acid and phenacetin. For probenecid, the dominant mechanism shifts from entropy to enthalpy as the ethanol in ethyl acetate concentration increases. The enthalpy-entropy compensation plots corroborate the different mechanisms involved in the solubility enhancement by cosolvents.

Capillary electrophoresis of diuretics and probenecid in methanol.

Actual mobilities and dissociation constants of six diuretics (benzthiazide, bumetanide, ethacrynic acid, furosemide, hydrochlorothiazide and chlorothiazide) and probenecid were investigated in methanol by capillary zone electrophoresis (CZE). The actual mobilities were derived from the dependence of the effective mobilities of the analytes on the pH(*) of the methanolic background electrolyte (BGE) solution. The measurement of effective mobilities was carried out mainly by a pressure-mediated capillary electrophoresis (CE) method. For comparison, parallel measurements were carried for two of the analytes by the conventional capillary electrophoresis approach, without pressure. The pK(a)(*) values in methanol were calculated by non-linear curve fitting to the measured mobility values. The difference between the pK(a) values in water and methanol was about 5 units for the loop diuretics (furosemide, bumetanide, ethacrynic acid) and probenecid and around 3-4 units for the thiazide diuretics. Knowledge of the ionisation behaviour of compounds in methanol paves the way for the wider use of methanol as background electrolyte solvent in capillary electrophoresis. Moreover, as is demonstrated in the current study, the calculation of actual mobilities and pK(a) values facilitates the optimisation of pH conditions for the separation, thereby applications can be expanded, and the combination of capillary electrophoresis with electrospray ionisation mass spectrometry becomes easier.

Quantitation of Armillarisin A in human plasma by liquid chromatography-electrospray tandem mass spectrometry.

A rapid and sensitive LC-MS/MS method for quantifying Armillarisin A in human plasma after a single oral dose (40 mg) has been developed and validated. Sample preparation used liquid-liquid extraction with a mixture of diethyl ether-dichloromethane (60:40, v/v) in an acidic environment. The retention times of Armillarisin A and the internal standard, probenecid, were 1.63 and 1.78 min, respectively. The calibration curve was linear over the range 0.15-50 ng/mL with a limit of quantitation of 0.15 ng/mL. The coefficient of variation as a measure of intra- and inter-day precision was <9.3% and the accuracy was in the range 92.5-108.0%. The Armillarisin A concentration-time profile in human plasma was determined after an oral dose of a 40 mg tablet.

Comparison of permeation enhancing strategies for an oral factor Xa inhibitor using the Caco-2 cell monolayer model.

FXai, a direct inhibitor of the clotting factor Xa, provides high water solubility but poor membrane permeability due to multiple sites of ionization and a molecular weight exceeding 500 Da, making it a Class III drug according to the Biopharmaceutics Classification System. To overcome the ionization problem and increase the transcellular permeability, various ester and hydroxyamidine prodrugs exhibiting a reduced number of ionization sites were studied in the Caco-2 monolayer model for intestinal permeation. Alternatively, the potential transcellular permeation enhancement of Imwitor 742 and the potential paracellular enhancement of three chitosan formulations were investigated in the same model. FXai has an apparent permeability (P(app)) of about 1 nm/s, which is generally regarded as very low. The butylester-hydroxyamidine double-prodrug was found to provide a markedly increased permeability (40.4 nm/s) as did the co-application of chitosan (43.3 nm/s). Other prodrugs slightly increased permeability (1.3-9.2 nm/s) but were inferior to the previous attempts to enhance permeability while the Imwitor admixture showed no effect (1.1 nm/s). Moreover, a bioactivating metabolism towards the hydroxyamidine mono-prodrug was detected in the Caco-2 cell permeation model. Although esterases were overexpressed and mainly located apically, an acceptable permeation was reached. In addition, the prodrugs triggered an efflux system that is not inhibited by verapamil but by quinidine, suggesting the involvement of an organic cation transporter.

Rapid internal acyl migration and protein binding of synthetic probenecid glucuronides.

Internal acyl migration reactions of drug 1-O-acyl-beta-D-glucopyranuronates (1beta-acyl glucuronides) are of interest because of their possible role in covalent binding to proteins and consequent adverse effects. The reactivity of the synthetic probenecid 1beta-acyl glucuronide (PRG), the principal metabolite of probenecid (PR) in humans, has been investigated in terms of acyl migration, hydrolysis, and covalent binding to proteins in phosphate buffer (pH 7.4) and human plasma at 37 degrees C. PRG primarily degraded by acyl migration according to apparent first-order kinetics and the 2-, 3-, and 4-acyl isomers sequentially appeared as both alpha- and beta-anomeric forms. In addition, small amounts of PRG and extremely labile 1alpha-acyl isomer existed in the equilibrated mixture favoring the 2alpha/beta-acyl isomer, that provided significant information regarding the mechanism of acyl migration. All of the positional isomers and anomers were characterized using preparative HPLC and NMR spectroscopy. Acyl migration was observed to predominate over hydrolysis in both media although the extent of hydrolysis in plasma was larger than that in the buffer. The overall degradation half-lives (h) in the buffer and plasma were 0.27 +/- 0.003 and 0.17 +/- 0.007, respectively. The covalent binding rapidly proceeded mainly via the Schiff's base mechanism and reached a plateau after 2 h of incubation. The maximal binding was 146 +/- 4.8 pmol/mg of protein, and ca. 10% of the initial concentration of PRG. These results indicated that PRG is most labile and susceptible to acyl migration of all the drug acyl glucuronides reported to date in the physiological conditions, and highly reactive to plasma proteins, that could provide a possible explanation for the immunologically based adverse effects of PR.