Zirconium-based hydrophobic-MOFs as innovative electrode modifiers for flibanserin determination: Exploring the electrooxidation mechanism using a comprehensive spectroelectrochemical study

Three different types of Zr-based MOFs derived from benzene dicarboxylic acid (BDC) and naphthalene dicarboxylic acid as organic linkers (ZrBDC, 2,6-ZrNDC, and 1,4-ZrNDC) were synthesized. They were characterized using X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform IR spectroscopy (FT-IR), and Transmission electron microscopy (TEM). Their hydrophilic/hydrophobic nature was investigated via contact angle measurements; ZrBDC MOF was hydrophilic and the other two (ZrNDC) MOFs were hydrophobic. The three MOFs were combined with MWCNTs as electrode modifiers for the determination of a hydrophobic analyte, flibanserin (FLB), as a proof-of-concept analyte. Under the optimized experimental conditions, a significant enhancement in the oxidation peak current of FLB was observed when utilizing 2,6-ZrNDC and 1,4-ZrNDC, being the highest when using 1,4-ZrNDC. Furthermore, a thorough investigation of the complex oxidation pathway of FLB was performed by carrying out simultaneous spectroelectrochemical measurements. Based on the obtained results, it was verified that the piperazine moiety of FLB is the primary site for electrochemical oxidation. The fabricated sensor based on 1,4-ZrNDC/MW/CPE showed an oxidation peak of FLB at 0.8 V vs Ag/AgCl. Moreover, it showed excellent linearity for the determination of FLB in the range 0.05 to 0.80 μmol L-1 with a correlation coefficient (r) = 0.9973 and limit of detection of 3.0 nmol L-1. The applicability of the developed approach was demonstrated by determination of FLB in pharmaceutical tablets and human urine samples with acceptable repeatability (% RSD values were below 1.9% and 2.1%, respectively) and reasonable recovery values (ranged between 97 and 103% for pharmaceutical tablets and between 96 and 102% for human urine samples). The outcomes of the suggested methodology can be utilized for the determination of other hydrophobic compounds of pharmaceutical or biological interest with the aim of achieving low detection limits of these compounds in various matrices.

A Different Perspective on the Characterization of a New Degradation Product of Flibanserin With HPLC-DAD-ESI-IT-TOF-MSn and Its Pharmaceutical Formulation Analysis With Inter-Laboratory Comparison

BACKGROUND

Flibanserin (FLB) was first synthesized as an antidepressant drug; however, due to its enhancing effects on sexual activity, it was approved for treatment of hypoactive sexual desire disorder in women in 2015.

OBJECTIVE

The aim of this study was to develop a new and fully validated HPLC method for analysis of FLB in pharmaceutical formulations besides its degradation products, and identification of possible formation mechanisms by using HPLC-DAD-ESI-IT-TOF-MSn.

METHOD

The HPLC separation was achieved in a Supelco Ascentis® Express series phenyl hexyl column (100 × 4.6 mm, ID 2.7 µm). The mobile phase was acetonitrile-ammonium acetate solution (50:50, v/v, 10 mM, pH 5.4) mixture, which was pumped at the rate of 0.5 mL/min. Chromatography, detection, and structural identification was performed by using a LCMS-IT-TOF instrument (Shimadzu, Japan).

RESULTS

1-(2-(4-(3-hydroxy-5-(trifluoromethyl)phenyl)piperazine-1-yl)ethyl)-1,3-dihydro-2H-benzo[d]imidazol-2-one is proposed as a novel degradation product, with a mass of 407.1695 and a formula of C20H21F3N4O2 with a margin of error about 0.001 ppm. The developed method is applicable with 98% accuracy within the 2.5-50.0 µg/mL range. The LOD and LOQ were about 500 ng/mL and 1.50 µg/mL, respectively. The transferability and variation between laboratories were tested by inter-laboratory comparison and evaluated with one-way analysis of variance.

CONCLUSIONS

A novel FLB degradation product, which was produced under oxidative forced degradation conditions was observed and identified for the first time; in addition, the formation kinetics of the degradation product besides decomposition of FLB was studied. Furthermore, an inter-laboratory comparison was carried out, and application of the proposed method on a pseudo Addyi® (Sprout Pharmaceuticals, Inc.) sample was tested using both instrument configurations.

HIGHLIGHTS

A novel stability-indicating assay method was developed and fully validated according to the International Council on Harmonization (Q2) R1 for the analysis of FLB in the pharmaceutical preparations. A new degradation product was identified in the oxidative forced degradation condition and characterized using HPLC-DAD-ESI-IT-TOF-MS3. Moreover, the possible mechanism and the formation kinetic of the degradation product were revealed. In addition, the developed method was transferred to another LC-PDA instrument for inter-laboratory comparison. Finally, the current method was applied to a pseudo formulation of Addy in both instruments, and ANOVA was applied for evaluation.

Emphasis on the incorporation of Tropaeolin OO dye and silver nanoparticles for voltammetric estimation of flibanserin in bulk form, tablets and human plasma

A novel electrochemical sensor based on the electro-deposition of silver nanoparticles (AgNPs) on Tropaeolin OO (poly-TO) layers over pencil graphite electrode (PGE) surface was fabricated for the first time for voltammetric determination of flibanserin (FBS); a drug enhances female sexual performance. Further characterization studies using cyclic voltammetry (CV), square wave voltammetry (SWV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were conducted. The AgNPs synergistic effect on poly-TO layers facilitates the FBS electro-oxidation in phosphate buffer solution (pH 6.0) and its determination in bulk form, tablets and in human plasma. Following ICH guidelines, validation of the proposed SWV method for FBS analysis was successfully achieved using the fabricated sensor (AgNPs@poly-TO/PGE). Under the optimal instrumental and experimental conditions, the anodic oxidation peak current was directly proportional to FBS concentration in the range from 0.1 to 8.5 μmol L^-1 with low detection and quantitation limits (0.0286 and 0.0867 μmol L^-1, respectively). High sensitivity, selectivity as well as easiness of fabrication are the main advantages of the modified sensor.

Development and validation of a novel evaporation setup-assisted TLC method with fluorescence detection for determination of flibanserin in pharmaceutical and biological samples

A specific and sensitive thin layer chromatographic method coupled with fluorescence detection for determination of flibanserin (FLN) that treats woman hypoactive sexual desire disorder was developed. The proposed method depends on the enhancement of FLN native fluorescence intensity via the exposure of the developed TLC plate to concentrated hydrochloric acid vapors. Herein, an evaporation setup needed for HCl vapors exposure step was designed for the first time to ensure a uniform distribution of the vapors throughout the developed bands on the plate. Chloroform: methanol (9.5: 0.5, v/v) was the optimum mobile phase that gave a compact band (R_f= 0.44 ± 0.02) using TLC aluminium plates precoated with silica gel G 60F₂₅₄ as a stationary phase. After exposure of the developed TLC plate to HCl vapors, the FLN bands emission intensities were measured after excitation at 275 nm. Conferring ICH guidelines, the linearity range was 20.0 - 1500.0 ng/band with a good linear relationship (r= 0.9998). Detection and quantitation limits were 5.12 and 15.50 ng/band, respectively. Also, the method was validated for accuracy, precision, robustness, specificity and selectivity. Statistical analysis verified the suitability of the proposed method for estimation of FLN in tablets and in human plasma with acceptable recoveries (98.07-101.45%).

A systematic UHPLC-Q-TOF-MS/MS based analytical approach for characterization of flibanserin metabolites and establishment of biotransformation pathway

A systematic metabolite profiling approach has paramount importance in detecting, identifying, and characterizing drug metabolites. Till date, there is no report published on the comprehensive metabolic fate of flibanserin (FLB). In this study, the structure of entire potential metabolites of FLB has been elucidated by execution of in silico tool and high resolution mass spectrometry based metabolite profiling strategy employing data-dependent and data-independent approaches. In vitro metabolism profile was investigated after incubating FLB with liver microsomes (rat and human) and S9 fractions in presence of their respective co-factors. In vivo metabolites were identified from rat plasma, urine, feces, and brain tissue samples. An efficient extraction technique was developed that made it possible to identify the metabolites generated even in extremely low concentrations. Extraction was carried out by precipitating protein and thereafter solid-phase extraction to enrich their concentration in the sample before analysis. Fourteen new metabolites have been identified and characterized. Most of the metabolites of FLB were generated due to hydrolysis and oxidation followed by glucuronide, sulfate, and methyl conjugation. Additionally, a spiking study was employed to confirm the presence of N-oxide metabolite in human liver S9 fraction and rat urine samples. Moreover, we have established the probable biotransformation pathway of FLB and successfully analyzed the toxicity potential of the metabolites using Pro Tox-II software.

Second-derivative synchronous fluorimetry and time-programmed HPLC-fluorescence detection for simultaneous estimation of flibanserin and sitagliptin phosphate in synthetic mixtures and human plasma samples

Diabetes Mellitus is directly related to female anaphrodesia. Female Viagra or Flibanserin (FLB), U.S. FDA approved in 2015, is specifically indicated for premenopausal Hypoactive Sexual Desire Disorder, HSDD, which is one of the primary consequences of Diabetes Mellitus. Simultaneous analysis of the concomitantly administered, FLB and oral antidiabetics, as Sitagliptin phosphate (STG), is a crucial demand to investigate mutual drug-drug interaction. The latter is responsible for uncontrolled glycaemia and higher risk of sudden hypoglycemia. Two simple, sensitive, economical and direct analytical methods, namely, Second-Derivative Synchronous Fluorimetric Spectroscopy, D₂-SFS, and High Performance Liquid Chromatography with fluorimetric detection, HPLC-FD, are established for simultaneous determination of FLB and STG in their binary mixtures. First method relies on measuring D₂-SFS spectra of both drugs, at Δλ = 25 nm, along linearity ranges of 0.05-1 μg/mL for both drugs. The second method is a chromatographic one with gradient elution of FLB and STG on RP-ZORBAX Eclipse C₁₈ column (5 µm, 4.6 × 150 mm). Mobile phase; phosphate buffer: acetonitrile, pH 4.5, with a flow rate of 1 mL/min at room temperature has been used. Time programmed fluorimetric detection is optimized at λem = 305 nm for STG (0.0-5.9 min), at λem = 375 nm for FLB (6-9 min) after both excitation at λex = 257 nm, in the linear ranges of 1-40 μg/mL and 5-60 μg/mL for FLB and STG, respectively. Proposed methods have been validated according to ICH guidelines, then applied for simultaneous quantitation of FLB and STG in their laboratory-prepared mixtures and in spiked human plasma samples. Satisfactory Student's t-value and F-variance ratio have been obtained upon comparing the results of both methods.

Insights into flibanserin oxidative stress degradation pathway: in silico – in vitro toxicity assessment of its degradates

Characterization of the degradation products of pharmaceutical drugs is essential to assess their safety.

Development and Greenness Evaluation of Spectrofluorometric Methods for Flibanserin Determination in Dosage Form and Human Urine Samples

Green, economic and sensitive two spectrofluorometric methods were developed for the quantitation of flibanserin (FB) in different matrices, which are based on FB native fluorescence properties. The first technique depends on measuring the relative fluorescence intensity of FB directly at emission and excitation wavelengths(λ_em/λ_ex) (371 nm/247 nm), while the second technique is a first derivative (D¹) spectrofluorometric method, which depends on measuring the peak amplitudes at 351 nm. Linear regressions were observed in the range of 0.1–1.5 μg/mL for both methods. Moreover, both methods were efficiently extended to analyze FB in human urine, indicating the ultra-sensitivity of the methods, and linear regression was found within a range 0.05–0.7 μg/mL for both methods. Excellent selectivity of the proposed methods and good recoveries were obtained upon the analysis of FB in pharmaceutical dosage form and human urine samples without interference from matrix components with acceptable ranges, from 98.86 to 101.46% and from 98.08 to 102.37%, respectively. Greenness of the developed methods was assessed using the national environmental method index (NEMI) and Analytical Eco-scale and Green Analytical Procedure Index (GAPI). The three approaches confirmed that the developed methods are green, safe and environment-friendly.

Surface-enhanced Raman spectroscopy for rapid identification and quantification of Flibanserin in different kinds of wine

Wine has always been a popular carrier for psychedelic drugs, with the rapid identification and quantification of psychedelic drugs in wine being the focus of regulating illegal behavior. In this study, surface-enhanced Raman spectroscopy (SERS) is used for the rapid detection of Flibanserin in liquor, beer and grape wine. First, the theoretical Raman spectrum with characteristic Flibanserin peaks was calculated and identified, and the limit of detection of 1 μg mL-1 for Flibanserin in liquor was determined. The curve equation was obtained by fitting using the least squares method, and the correlation coefficient was 0.995. The recovery range of the Flibanserin liquor solution ranged from 93.70% to 108.32%, and the relative standard deviation (RSD) range was 2.77% to 7.81%. Identification and quantification of Flibanserin in liquor, beer and grape wine were done by principal component analysis (PCA) and support vector machine (SVM). Machine learning algorithms were used to reduce the workload and the possibility of manual misjudgements. The classification accuracies of the Flibanserin liquor, beer and grape wine spectra were 100.00%, 95.80% and 92.00%, respectively. The quantitative classification accuracies of the Flibanserin liquor, beer and grape wine spectra were 92.30%, 91.70% and 92.00%, respectively. The machine learning algorithms were used to verify the advantages and feasibility of this method. This study fully demonstrates the huge application potential of combining SERS technology and machine learning in the rapid on-site detection of psychedelic drugs.

Drug interaction study of flavonoids toward OATP1B1 and their 3D structure activity relationship analysis for predicting hepatoprotective effects

Organic anion transporting polypeptide 1B1 (OATP1B1), a liver-specific uptake transporter, was associated with drug induced liver injury (DILI). Screening and identifying potent OATP1B1 inhibitors with little toxicity is of great value in reducing OATP1B1-mediated DILI. Flavonoids are a group of polyphenols ubiquitously present in vegetables, fruits and herbal products, some of them were reported to produce transporter-mediated DDI. Our objective was to investigate potential inhibitors of OATP1B1 from 99 flavonoids, and to assess the hepatoprotective effects on bosentan induced liver injury. Eight flavonoids, including biochanin A, hispidulin, isoliquiritigenin, isosinensetin, kaempferol, licochalcone A, luteolin and sinensetin exhibited significant inhibition (>50 %) on OATP1B1 in OATP1B1-HEK293 cells, which reduced the OATP1B1-mediated influx of methotrexate, accordingly decreased its cytotoxicity in OATP1B1-HEK293 cells and increased its AUC_0-t in different extents in rats, from 28.27%-82.71 %. In bosentan-induced rat liver injury models, 8 flavonoids reduced the levels of serum total bile acid (TBA) and the liver concentration of bosentan in different degrees. Among them, kaempferol decreased the concentration most significantly, by 54.17 %, which indicated that flavonoids may alleviate bosentan-induced liver injury by inhibiting OATP1B1-mediated bosentan uptake. Furthermore, the pharmacophore model indicated the hydrogen bond acceptors and hydrogen bond donors may play critical role in the potency of flavonoids inhibition on OATP1B1. Taken together, our findings would provide helpful information for predicting the potential risks of flavonoid-containing food/herb-drug interactions in humans and alleviating bosentan -induced liver injury by OATP1B1 regulation.

Mass Spectrometry-Based Rapid Quantitative Bioanalysis of Flibanserin: Pharmacokinetic and Brain Tissue Distribution Study in Female Rats

Flibanserin (FLB) is the first United States Food and Drug Administration (USFDA) approved serotonin modulator recently marketed to treat acquired generalized women hypoactive sexual desire disorder. The scope of this study was to develop and validate a sensitive, selective and reliable ultra-performance liquid chromatography–mass spectroscopy/mass spectroscopy-based quantification method for FLB in rat plasma as well as brain tissue samples. The method includes a simple liquid–liquid sample extraction procedure. FLB was subjected to chromatographic separation using a poroshell C18 column with the mobile phase comprising a mixture of acetonitrile (ACN), 10 mM ammonium acetate and acetic acid (90:10:0.1, v/v/v). Detection and quantification of FLB after positive electrospray ionization were carried out in selective ion monitoring mode. The fragment ions (m/z) of FLB (parent ion: 391.1741) and IS (parent ion: 448.1550) were monitored at 161.0704 and 285.0917, respectively. A linear response of FLB was observed over a concentration range of 2.5–600 ng/mL in plasma and 5–500 ng/mL in brain tissue homogenate. The intra- and inter-day precision and accuracy of the method met the acceptable limits specified in the USFDA bioanalytical method validation guideline. The analyte was found to be stable in benchtop, freeze-thaw, auto-injector and dry extract stability studies. The developed method was used to quantitate FLB in the plasma and brain tissue of a single-dose oral pharmacokinetic and brain tissue distribution study in female rats. Maximum FLB concentration in plasma and brain was achieved within an hour; however, the total amount of the drug that reached the brain was significantly less than in plasma. Rate of elimination of FLB from brain was also faster resulting in a lesser half-life in brain compared to the plasma.

Determination of flibanserin in the presence of confirmed degradation products by a third derivative emission spectrofluorometric method: Application to pharmaceutical formulation

Flibanserin is a new drug used for the treatment of hypoactive sexual desire disorder. This work is considered the first study concerning the fluorimetric behaviour of flibanserin and its new florescent degradation products. A fast, cost-effective, stability-indicating spectrofluorometric method was developed and validated for the determination of flibanserin in the presence of oxidative degradation products. Stability studies are performed to predict the behaviour of substances under various harsh conditions. Thus, flibanserin was subjected to degradation using hydrogen peroxide. The stability-indicating method was developed and validated per ICH guidelines; it was linear in the range of 0.1-3 μg/mL. The method was accurate and precise as it showed good recoveries between 98.50 and 100.90% and relative standard deviation less than 2%, respectively, and no significant differences were found after statistical comparison with the in-house HPLC method. In addition, the structures of the oxidative degradation products were confirmed using infrared spectroscopy and mass spectrometry, and the proposed degradation pathway was predicted.

Simultaneous determination of evobrutinib and its metabolite evobrutinib-diol in dog plasma by liquid chromatography combined with electrospray ionization tandem mass spectrometry

A rapid and sensitive liquid chromatography hyphenated with electrospray ionization tandem mass spectrometric method (LC-ESI-MS/MS) was developed and validated for simultaneous determination of evobrutinib and evobrutinib-diol in dog plasma. The plasma sample was processed using acetonitrile and chromatographic separation was carried out on a Waters Acquity BEH C₁₈ column (50 × 2.1 mm, 1.7 μm). The mobile phase was composed of 0.1% formic acid and acetonitrile, with an optimized gradient elution at a flow rate of 0.4 mL/min. Detection was accomplished in selective reaction monitoring mode via electrospray ionization interface operated in positive ion mode. The precursor-to-product transitions for quantification were m/z 430.2 → 98.1 for evobrutinib, m/z 464.2 → 98.1 for evobrutinib-diol and m/z 441.2 → 138.1 for ibrutinib (internal standard). The developed assay was linear over the tested concentration ranges with correlation coefficient >0.995. The LLOQ was 0.1 ng/mL for both analytes. The inter- and intra-day precisions were <9.65% and the accuracy ranged from -3.94 to 6.37%. The extraction recovery was >85.41% and no significant matrix effect was observed. The developed assay was successfully applied to the pharmacokinetic study of evobrutinib and evobrutinib-diol in dogs after oral administration of evobrutinib at a single dose of 5 mg/kg.

Development and validation of liquid chromatography-electrospray-tandem mass spectrometry method for determination of flibanserin in human plasma: Application to pharmacokinetic study on healthy female volunteers

A novel rapid and highly sensitive ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) bioanalytical method was established for the analysis of flibanserin in human plasma. Flibanserin d4 was used as internal standard (IS). Flibanserin and the internal standard (IS) were extracted from the plasma using protein precipitation technique with acetonitrile. A Kinetex C₁₈ (2.6 μm, 2.1 × 50 mm) column was used for chromatographic separation and the mobile phase was a mixture of 20 mm ammonium acetate buffer (pH 4.5)-acetonitrile (50:50, v/v) with an isocratic elution mode and a flow rate of 0.3 mL/min. The analysis was performed on a Xefo TQD Waters mass spectrometer in multiple reaction monitoring mode with a positive electrospray ionization interface. The US Food and Drug Administration guidelines were followed during the bio-analytical methods validation regarding linearity, precision, accuracy, carryover, selectivity, dilution integrity and stability. The analysis run time was carried out within 2 min over a wide linear concentration range of 5-1000 ng mL^-1 . Finally, the proposed method was successfully used in a pharmacokinetic study that measured flibanserin concentration in healthy, non-pregnant female volunteers after a single 100 mg oral dose of flibanserin.