The molecular basis of dapsone activation of CYP2C9-catalyzed nonsteroidal anti-inflammatory drug oxidation.

Positive heterotropic cooperativity, or "activation," results in an instantaneous increase in enzyme activity in the absence of an increase in protein expression. Thus, cytochrome P450 (CYP) enzyme activation presents as a potential drug-drug interaction mechanism. It has been demonstrated previously that dapsone activates the CYP2C9-catalyzed oxidation of a number of nonsteroidal anti-inflammatory drugs in vitro. Here, we conducted molecular dynamics simulations (MDS) together with enzyme kinetic investigations and site-directed mutagenesis to elucidate the molecular basis of the activation of CYP2C9-catalyzed S-flurbiprofen 4'-hydroxylation and S-naproxen O-demethylation by dapsone. Supplementation of incubations of recombinant CYP2C9 with dapsone increased the catalytic efficiency of flurbiprofen and naproxen oxidation by 2.3- and 16.5-fold, respectively. MDS demonstrated that activation arises predominantly from aromatic interactions between the substrate, dapsone, and the phenyl rings of Phe114 and Phe476 within a common binding domain of the CYP2C9 active site, rather than involvement of a distinct effector site. Mutagenesis of Phe114 and Phe476 abrogated flurbiprofen and naproxen oxidation, and MDS and kinetic studies with the CYP2C9 mutants further identified a pivotal role of Phe476 in dapsone activation. MDS additionally showed that aromatic stacking interactions between two molecules of naproxen are necessary for binding in a catalytically favorable orientation. In contrast to flurbiprofen and naproxen, dapsone did not activate the 4'-hydroxylation of diclofenac, suggesting that the CYP2C9 active site favors cooperative binding of nonsteroidal anti-inflammatory drugs with a planar or near-planar geometry. More generally, the work confirms the utility of MDS for investigating ligand binding in CYP enzymes.

Topological effects in ultrafast photoinduced processes between flurbiprofen and tryptophan in linked dyads and within human serum albumin.

The interaction dynamics between flurbiprofen (FBP) and tryptophan (Trp) has been studied in covalently linked dyads and within human serum albumin (HSA) by means of fluorescence and ultrafast transient absorption spectroscopy. The dyads have proven to be excellent models to investigate photoinduced processes such as energy and/or electron transfer that may occur in proteins and other biological media. Since the relative spatial arrangement of the interacting units may affect the yield and kinetics of the photoinduced processes, two spacers consisting of amino and carboxylic groups separated by a cyclic or a long linear hydrocarbon chain (1 and 2, respectively) have been used to link the (S)- or (R)-FBP with the (S)-Trp moieties. The main feature observed in the dyads was a strong intramolecular quenching of the fluorescence, which was more important for the (S,S)- than for the (R,S)- diastereomer in dyads 1, whereas the reverse was true for dyads 2. This was consistent with the results obtained by simple molecular modelling (PM3). The observed stereodifferentiation in (S,S)-1 and (R,S)-1 arises from the deactivation of 1Trp*, while in (S,S)-2 and (R,S)-2 it is associated with 1FBP*. The mechanistic nature of 1FBP* quenching is ascribed to energy transfer, while for 1Trp* it is attributed to electron transfer and/or exciplex formation. These results are consistent with those obtained by ultrafast transient absorption spectroscopy, where 1FBP* was detected as a band with a maximum at ca. 425 nm and a shoulder at ∼375 nm, whereas Trp did not give rise to any noticeable transient. Interestingly, similar photoprocesses were observed in the dyads and in the supramolecular FBP@HSA complexes. Overall, these results may aid to gain a deeper understanding of the photoinduced processes occurring in protein-bound drugs, which may shed light on the mechanistic pathways involved in photobiological damage.

Structure-activity relationships of flurbiprofen analogues as stabilizers of the amyloidogenic protein transthyretin.

The inherent amyloidogenic potentialof wild type transthyretin (TTR) is enhanced by a large number of point mutations, which destabilize the TTR tetramer, thereby promoting its disassembly and pathological aggregation responsible for TTR-related amyloidosis. TTR stabilizers are able to interact with the thyroxine-binding sites of TTR, stabilizing its tetrameric native state and inhibiting amyloidogenesis. Herein, we report on in vitro, ex vivo, and X-ray analyses to assess the TTR structural stabilization by analogues of flurbiprofen, a non-steroidal anti-inflammatory drug (NSAID). Overall, considering together binding selectivity and protective effects on TTR native structure by flurbiprofen analogues in the presence of plasma proteins, as determined by Western Blot,the aforementioned properties of analyzed compounds appear to be better (CHF5075 and CHF4802) or similar (CHF4795) or worse (CHF5074, also known as CSP-1103) as compared to those of diflunisal, used as a reference TTR stabilizer. Molecular details of the determinants affecting the interactionsof CHF5075, CHF4802, and CHF4795 with wild type TTRand of CHF5074 withtheamyloidogenic A25TTTR variant havebeen elucidated by X-ray analysis. Distinct interactions with TTR appear to characterize flurbiprofen analogues and the NSAID diflunisal and its analogues as TTR stabilizers. Relationships between stabilizing effect on TTR by flurbiprofen analogues determined experimentally and molecular details of their interactions with TTR have been established, providing the rationale for their protective effects on the native protein structure.

Validation of an analytical method to quantify the permeation and penetration of flurbiprofen into human pharynx tissue.

The aim of this investigation was to develop receiver and extraction fluids, and subsequently validate an analytical method to quantify the permeation and penetration of flurbiprofen into human pharynx tissue using a Franz diffusion cell. The solubility and stability of flurbiprofen in a suitable receiver fluid, and a suitable extraction method and fluid to recover and quantitate flurbiprofen from human pharynx tissue, were investigated using high-performance liquid chromatography (HPLC). The potential interference of human pharynx tissue in the receiver fluid was also investigated. The HPLC analytical method was successfully validated according to current guidelines. The final receiver fluid demonstrated sufficient solubility and stability, and the extraction method and fluid resulted in >95% recovery of flurbiprofen following exposure to human pharynx tissue. The lower limit of quantitation of flurbiprofen was 0.045 µg/mL in both the receiver and extraction fluids. There was no interference of the human pharynx tissue with the HPLC method. This investigation validated an analytical method for quantitating flurbiprofen, and determined a suitable receiver fluid and extraction method and fluid, which can be used to investigate the permeation and penetration of flurbiprofen through human pharynx tissue using the Franz diffusion cell method.

Prediction of Skin Permeation of Flurbiprofen from Neat Ester Oils and Their O/W Emulsions.

Although many in silico models were reported to predict the skin permeation of drugs from aqueous solutions, few studies were founded on the in silico estimation models for the skin permeation of drugs from neat oil formulations and o/w emulsions. In the present study, the cumulative amount of a model lipophilic drug, flurbiprofen (FP), that permeated through skin was determined from 12 different kinds of ester oils (Qoil) and an in silico model was developed for predicting the skin permeation of FP from these ester oils. Thus, the obtained Qoil values were well predicted with the FP solubility in the oils (Soil), the amount of FP uptake into the stratum corneum (SCoil) and molecular descriptors of dipolarity/polarizability (π2H) and molecular density. This model suggests that the thermodynamic activities of FP both in the formulations and skin are the key factors for predicting the skin permeation of FP from the ester oils. In addition, a high linear relationship was observed in the double-logarithm plots between the Qoil and the cumulative amount of FP permeated through skin from 20% ester oil in water emulsion (Qemul20%). Furthermore, the skin permeations of FP from 5 and 10% ester oil in water emulsions, Qemul5% and Qemul10%, respectively, were also predicted by the horizontal translation of the y-axis intercept of the liner equation for the relation between the Qoil and Qemul20%. These prediction methods must be helpful for designing topical oily and/or o/w emulsion formulations having suitable and high skin permeation rate of lipophilic drugs.

Novel Marmoset Cytochrome P450 2C19 in Livers Efficiently Metabolizes Human P450 2C9 and 2C19 Substrates, S-Warfarin, Tolbutamide, Flurbiprofen, and Omeprazole.

The common marmoset (Callithrix jacchus), a small New World monkey, has the potential for use in human drug development due to its evolutionary closeness to humans. Four novel cDNAs, encoding cytochrome P450 (P450) 2C18, 2C19, 2C58, and 2C76, were cloned from marmoset livers to characterize P450 2C molecular properties, including previously reported P450 2C8. The deduced amino acid sequence showed high sequence identities (>86%) with those of human P450 2Cs, except for marmoset P450 2C76, which has a low sequence identity (∼70%) with any human P450 2Cs. Phylogenetic analysis showed that marmoset P450 2Cs were more closely clustered with those of humans and macaques than other species investigated. Quantitative polymerase chain reaction analysis showed that all of the marmoset P450 2C mRNAs were predominantly expressed in liver as opposed to the other tissues tested. Marmoset P450 2C proteins were detected in liver by immunoblotting using antibodies against human P450 2Cs. Among marmoset P450 2Cs heterologously expressed in Escherichia coli, marmoset P450 2C19 efficiently catalyzed human P450 2C substrates, S-warfarin, diclofenac, tolbutamide, flurbiprofen, and omeprazole. Marmoset P450 2C19 had high Vmax and low Km values for S-warfarin 7-hydroxylation that were comparable to those in human liver microsomes, indicating warfarin stereoselectivity similar to findings in humans. Faster in vivo S-warfarin clearance than R-warfarin after intravenous administration of racemic warfarin (0.2 mg/kg) to marmosets was consistent with the in vitro kinetic parameters. These results indicated that marmoset P450 2C enzymes had functional characteristics similar to those of humans, and that P450 2C-dependent metabolic properties are likewise similar between marmosets and humans.

Effect of CYP2C9 genetic polymorphism on the metabolism of flurbiprofen in vitro.

CYP2C9 is an important member of the cytochrome P450 enzyme superfamily, and 57 cytochrome P450 2C9 alleles have been previously reported. To examine the enzymatic activity of the CYP2C9 alleles, kinetic parameters for 4'-hydroxyflurbiprofen were determined using recombinant human P450s CYP2C9 microsomes from insect cells Sf21 carrying wild-type CYP2C9*1 and other variants. The results showed that the enzyme activity of most of the variants decreased comparing with the wild type as the previous studies reported, while the enzyme activity of some of them increased, which were not in accordance with the previous researches. Of the 36 tested CYP2C9 allelic isoforms, two variants (CYP2C9*53 and CYP2C9*56) showed a higher intrinsic clearance value than the wild-type protein, especially for CYP2C9*56, exhibited much higher intrinsic clearance (197.3%) relative to wild-type CYP2C9*1, while the remaining 33 CYP2C9 allelic isoforms exhibited significantly decreased clearance values (from 0.6 to 83.8%) compared to CYP2C9*1. This study provided the most comprehensive data on the enzymatic activities of all reported CYP2C9 variants in the Chinese population with regard to the commonly used non-steroidal anti-inflammatory drug, flurbiprofen (FP). The results indicated that most of the tested rare alleles decreased the catalytic activity of CYP2C9 variants toward FP hydroxylation in vitro. This is the first report of all these rare alleles for FP metabolism providing fundamental data for further clinical studies on CYP2C9 alleles for FP metabolism in vivo.

Inhibition of FAAH, TRPV1, and COX2 by NSAID-serotonin conjugates.

Serotonin was linked by amidation to the carboxylic acid groups of a series of structurally diverse NSAIDs. The resulting NSAID-serotonin conjugates were tested in vitro for their ability to inhibit FAAH, TRPV1, and COX2. Ibuprofen-5-HT and Flurbiprofen-5-HT inhibited all three targets with approximately the same potency as N-arachidonoyl serotonin (AA-5-HT), while Fenoprofen-5-HT and Naproxen-5-HT showed activity as dual inhibitors of TRPV1 and COX2.

Metabolism and pathways for denitration of organic nitrates in the human liver.

Liver first-pass metabolism differs considerably among organic nitrates, but little information exists on the mechanism of denitration of these compounds in hepatic tissue. The metabolism of nitrooxybutyl-esters of flurbiprofen and ferulic-acid, a class of organic nitrates with potential therapeutic implication in variety of different conditions, was investigated in comparison with glyceryl trinitrate (GTN) in human liver by a multiple approach, using a spontaneous metabolism-independent nitric oxide (NO) donor [3-(aminopropyl)-1-hydroxy-3-isopropyl-2-oxo-1-triazene (NOC-5)] as a reference tool. Nitrooxybutyl-esters were rapidly and quantitatively metabolized to their respective parent compounds and the organic nitrate moiety nitrooxybutyl-alcohol (NOBA). Differently from GTN, which was rapidly and completely metabolized to nitrite, NOBA was slowly metabolized to nitrate. In contrast to the spontaneous NO donor NOC-5, NOBA and GTN did not generate detectable NO and failed to suppress the activity of cytochrome P450, an enzyme known to be inhibited by NO. The direct identification of NOBA after liver metabolism targets this compound as the functional organic nitrate metabolite of nitrooxybutyl-esters. Moreover, the investigation of the pathways for denitration of NOBA and GTN suggests that organic nitrates are not primarily metabolized to NO in the liver but to different extents of nitrite or nitrate depending in their different chemical structure. Therefore, cytochrome P450-dependent metabolism of concomitant drugs is not likely to be affected by oral coadministration of organic nitrates. However, the first pass may differently affect the pharmacological profile of organic nitrates in connection with the different extent of denitration and the distinct bioactive species generated and exported from the liver (nitrate or nitrite).

NO-donating tacrine derivatives as potential butyrylcholinesterase inhibitors with vasorelaxation activity.

To search for potent anti-Alzheimer's disease (AD) agents with multifunctional effects, 12 NO-donating tacrine-flurbiprofen hybrid compounds (2a-l) were synthesized and biologically evaluated. It was found that all the new target compounds showed selective butyrylcholinesterase (BuChE) inhibitory activity in vitro comparable or higher than tacrine and the tacrine-flurbiprofen hybrid compounds 1a-c, and released moderate amount of NO in vitro. The kinetic study suggests that one of the most active and highest BuChE selective compounds 2d may not only compete with the substrate for the same catalytic active site (CAS) but also interact with a second binding site. Furthermore, 2d and 2l exhibited significant vascular relaxation effect, which is beneficial for the treatment of AD. All the results suggest that 2d and 2l might be promising lead compounds for further research.

Alteration in plasma protein binding properties of propranolol and flurbiprofen during development of adjuvant-induced arthritis in rats.

Adjuvant-induced arthritis (AA) in the rat is used as a model for rheumatoid arthritis. In AA rats, the pharmacokinetics of various drugs is affected due to the alterations of plasma protein binding of drugs. We choose propranolol (PL) and flurbiprofen (FP) as model basic and acidic drugs, respectively, and investigated the effect of AA induction on their plasma protein binding at each developing stage of inflammation. The plasma protein binding of PL and FP was dramatically changed due to reduced albumin and increased α1-acid glycoprotein levels for at least 21 days after adjuvant treatment. Moreover, we illustrated the differences in protein binding in AA between both the drugs in each developing stage of inflammation. These results suggest that the changed plasma protein levels in AA rats accompanying the altered protein binding of drugs affect the pharmacokinetics of drugs which extensively bind to plasma protein under inflammatory condition.

A computational drug metabolite detection using the stable isotopic mass-shift filtering with high resolution mass spectrometry in pioglitazone and flurbiprofen.

The identification of metabolites in drug discovery is important. At present, radioisotopes and mass spectrometry are both widely used. However, rapid and comprehensive identification is still laborious and difficult. In this study, we developed new analytical software and employed a stable isotope as a tool to identify drug metabolites using mass spectrometry. A deuterium-labeled compound and non-labeled compound were both metabolized in human liver microsomes and analyzed by liquid chromatography/time-of-flight mass spectrometry (LC-TOF-MS). We computationally aligned two different MS data sets and filtered ions having a specific mass-shift equal to masses of labeled isotopes between those data using our own software. For pioglitazone and flurbiprofen, eight and four metabolites, respectively, were identified with calculations of mass and formulas and chemical structural fragmentation analysis. With high resolution MS, the approach became more accurate. The approach detected two unexpected metabolites in pioglitazone, i.e., the hydroxypropanamide form and the aldehyde hydrolysis form, which other approaches such as metabolite-biotransformation list matching and mass defect filtering could not detect. We demonstrated that the approach using computational alignment and stable isotopic mass-shift filtering has the ability to identify drug metabolites and is useful in drug discovery.

The Activity of Members of the UDP-Glucuronosyltransferase Subfamilies UGT1A and UGT2B is Impaired in Patients with Liver Cirrhosis.

BACKGROUND AND OBJECTIVE: The impact of liver cirrhosis on the activity of UDP-glucuronosyltransferases (UGTs) is currently not well characterized. We investigated the glucuronidation capacity and glucuronide accumulation in patients with liver cirrhosis. METHODS: We administered the Basel phenotyping cocktail (caffeine, efavirenz, flurbiprofen, omeprazole, metoprolol, midazolam) to patients with liver cirrhosis (n = 16 Child A, n = 15 Child B, n = 5 Child C) and n = 12 control subjects and obtained pharmacokinetic profiles of substrates and primary metabolites and their glucuronides. RESULTS: Caffeine and its metabolite paraxanthine were only slightly glucuronidated. The metabolic ratio (AUCglucuronide/AUCparent, MR) was not affected for caffeine but decreased by 60% for paraxanthine glucuronide formation in Child C patients. Efavirenz was not glucuronidated whereas 8-hydroxyefavirenz was efficiently glucuronidated. The MR of 8-hydroxyefavirenz-glucuronide formation increased three-fold in Child C patients and was negatively correlated with the glomerular filtration rate. Flurbiprofen and omeprazole were not glucuronidated. 4-Hydroxyflurbiprofen and 5-hydroxyomeprazole were both glucuronidated but the corresponding MRs for glucuronide formation were not affected by liver cirrhosis. Metoprolol, but not α-hydroxymetoprolol, was glucuronidated, and the MR for metoprolol-glucuronide formation dropped by 60% in Child C patients. Both midazolam and its metabolite 1'-hydroxymidazolam underwent glucuronidation, and the corresponding MRs for glucuronide formation dropped by approximately 80% in Child C patients. No relevant glucuronide accumulation occurred in patients with liver cirrhosis. CONCLUSIONS: Detailed analysis revealed that liver cirrhosis may affect the activity of UGTs of the UGT1A and UGT2B subfamilies according to liver function. Clinically significant glucuronide accumulation did not occur in the population investigated. CLINICAL TRIAL REGISTRATION: NCT03337945.

Influence of skin thickness on the in vitro permeabilities of drugs through Sprague-Dawley rat or Yucatan micropig skin.

The purpose of this study was to clarify the influence of skin thickness on the in vitro permeabilities of 3 model drugs with different physicochemical properties (nicorandil (NR), isosorbide dinitrate (ISDN) and flurbiprofen (FP)) through Sprague-Dawley rat (rat) or Yucatan micropig (YMP) skin. Intact, dermis-split, stratum corneum-stripped or stratum corneum-stripped and dermis-split rat or YMP skin (rat skin thickness: approximately 0.4, 0.9 or 1.2 mm; YMP skin thickness: approximately 0.4, 0.9, 1.8 or 2.8 mm) were set in Franz-type diffusion cells to determine the permeation rate, lag time and resistance ratio of the viable epidermis and dermis against whole skin (R(ved)/R(tot)) of the drugs. The YMP skin permeabilities of the drugs decreased with an increase in the skin thickness, and significant differences were observed in the permeation rates and lag times between intact and dermis-split (0.4 mm) YMP skins. The decreases in the permeabilities of the drugs through the YMP skin were larger than those through the rat skin. The influence of resistances of ISDN and FP through the dermis-split rat or YMP skin was greater at 0.9 mm skin thickness than 0.4 mm skin thickness. The R(ved)/R(tot) values for the YMP skins were relatively large for lipophilic drugs (ISDN and FP), and these ratios increased with an increase in the dermis thickness. These results suggest that in vitro skin permeation studies must be done using dermis-split (0.4 mm) skin with the thinnest dermis for predicting in vivo human percutaneous absorption rate.

Stereoselective binding of flurbiprofen enantiomers and their methyl esters to human serum albumin studied by time-resolved phosphorescence.

The interaction of the nonsteroidal anti-inflammatory drug flurbiprofen (FBP) with human serum albumin (HSA) hardly influences the fluorescence of the protein's single tryptophan (Trp). Therefore, in addition to fluorescence, heavy atom-induced room-temperature phosphorescence is used to study the stereoselective binding of FBP enantiomers and their methyl esters to HSA. Maximal HSA phosphorescence intensities were obtained at a KI concentration of 0.2 M. The quenching of the Trp phosphorescence by FBP is mainly dynamic and based on Dexter energy transfer. The Stern-Volmer plots based on the phosphorescence lifetimes indicate that (R)-FBP causes a stronger Trp quenching than (S)-FBP. For the methyl esters of FBP, the opposite is observed: (S)-(FBPMe) quenches more than (R)-FBPMe. The Stern-Volmer plots of (R)-FBP and (R)-FBPMe are similar although their high-affinity binding sites are different. The methylation of (S)-FBP causes a large change in its effect on the HSA phosphorescence lifetime. Furthermore, the quenching constants of 3.0 × 10(7) M(-1) s(-1) of the R-enantiomers and 2.5 × 10(7) M(-1) s(-1) for the S-enantiomers are not influenced by the methylation and indicate a stereoselectivity in the accessibility of the HSA Trp to these drugs.

Structural dynamics of the cooperative binding of small inhibitors in human cytochrome P450 2C9.

Some non-steroidal anti-inflammatory drugs (NSAIDs) exhibit atypical kinetic behavior when binding together with dapsone in CYP2C9. However, few studies about the detailed multi-drug binding dynamics in CYP2C9 have been reported. Here, molecular docking and molecular dynamics (MD) simulations are performed to explore the cooperative binding of dapsone and three NSAIDs in CYP2C9. The docking results show that dapsone bind to not only the distal primay bind site but also the active site above the heme group. Flurbiprofen/naproxen and piroxicam are located in the active site and the primary binding site of CYP2C9, respectively. It is noted that some key hydrogen bond (H-bond) and hydrophobic interactions mediate the conformational changes of substrates. Moreover, the calculated binding affinity is in line with experimental results. Further, the residue energy decomposition reveals that van der Waals energies of backbone/side-chain atoms dominate the substrate-binding and they can be ascribed to π···π, C-H···π, C-H⋯H-C interactions.

Drug metabolism in hemorrhagic shock: pharmacokinetics of selective markers of cytochrome-P450 2C9, 2D6, and 3A4 enzyme activities in a porcine model.

BACKGROUND: Cytochrome-P450 enzymes metabolize most administered drugs. A variety of clinical conditions affect the CYP system. However, the effect of hemorrhagic shock on CYP-mediated drug metabolism in clinical setting or in clinically applicable in-vivo models is largely unknown. Simultaneous administration of multiple CYP enzyme-selective drugs is a technique to ascertain a population's metabolic profile with a limited number of subjects. MATERIALS AND METHODS: Pigs were used as experimental animals as they possess CYP functionality similar to humans. Three probe drugs (dextromethorphan [CYP2D6], flurbiprofen [CYP2C9], and midazolam [CYP3A4]; doses: 0.5, 0.25, and 0.5 mg/kg, respectively) were administered intravenously to six Yorkshire-crossbred pigs in healthy state. Hemorrhagic shock was induced in six (four from healthy group after a 7-d washout period and two additional) pigs and the same doses of probe drugs were administered after a 14-h resuscitation phase. Blood samples were collected periodically in both phases and analyzed for parent drugs and metabolites (dextrorphan, 4'-hydroxy-flurbiprofen and 1'-hydroxy-midazolam) to calculate pharmacokinetic parameters. A comprehensive set of biochemical and physiologic markers of shock was also recorded. RESULTS: No changes in parent drug clearances were observed post-shock. Extensive metabolite formation with apparent higher exposure to total (conjugated and unconjugated) dextrorphan (p = 0.08), 4'-hydroxy-flurbiprofen (p = 0.11) and 1'-hydroxy-midazolam (p = 0.09) were observed post-shock. CONCLUSIONS: The metabolic capacity of CYP enzymes did not appear to be severely hindered in resuscitative phase of hemorrhagic shock. Diminished renal secretory function caused by hemorrhagic shock may be the cause of metabolite accumulation in plasma.

Development and evaluation of mucoadhesive buccal patches of flurbiprofen.

In the present study, an attempt was made to formulate mucoadhesive buccal patches of flurbiprofen (FBN) in order to enhance solubility. Solubity enhancement was attempted by making solid dispersion of drug with beta-CD (cyclodextrin). Initially preformulation were carried out using reported methods. Buccal patches were prepared by solvent casting technique using polymers like polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (SCMC), and hydroxypropyl methylcellulose (HPMC). The prepared patches were evaluated for their weight variation, thickness, folding endurance, surface pH, swelling index, in vitro residence time, in vitro permeation studies, drug content uniformity and bioadhesion test.

Bovine beta-lactoglobulin acts as an acid-resistant drug carrier by exploiting its diverse binding regions.

Binding of fluorine-containing drugs to bovine beta-lactoglobulin, the most abundant whey protein in bovine milk, was investigated by means of (19)F NMR and mass spectrometry. The stoichiometry of the binding and its stability in acidic medium, where beta-lactoglobulin is folded and stable, were also studied, along with competition from molecules that can be regarded as analogs of physiological ligands to bovine beta-lactoglobulin. Conditional binding data were combined with protein structural information derived from circular dichroism and limited proteolysis studies. Spectroscopic techniques were also used to assess whether the bound drugs stabilize the protein structure against denaturation by chaotropes or temperature at various pH values. The results obtained provide evidence for the presence of multiple binding regions on the protein, with a specific and different affinity for structurally different classes of hydrophobic drugs and, more generally, that bovine beta-lactoglobulin can bind and protect against low pH values various classes of drugs of pharmaceutical relevance.

Biotransformation of flurbiprofen by Cunninghamella species.

The biotransformation of the fluorinated anti-inflammatory drug flurbiprofen was investigated in Cunninghamella spp. Mono- and dihydroxylated metabolites were detected using gas chromatography-mass spectrometry and fluorine-19 nuclear magnetic resonance spectroscopy, and the major metabolite 4'-hydroxyflurbiprofen was isolated by preparative high-pressure liquid chromatography (HPLC). Cunninghamella elegans DSM 1908 and C. blakesleeana DSM 1906 also produced a phase II (conjugated) metabolite, which was identified as the sulfated drug via deconjugation experiments.