Analytical and Bioanalytical Methods for the Determination of Dipeptidyl Peptidase-4 Inhibitors in Various Matrices: A Comprehensive Review

BACKGROUND

DPP-4 inhibitors, or gliptins, are new oral antidiabetic drugs for type 2 diabetes. They help to regulate insulin and glucagon. These drugs have the advantage of a lower risk of hypoglycemia compared to some other diabetes medications and are typically prescribed when metformin and sulphonylureas have become less effective.

OBJECTIVE

This review analyses a range of analytical and bioanalytical methods for DPP-4 inhibitors, that use spectroscopic techniques, chromatographic, and hyphenated techniques for analysis. So far, no review comprising all DPP-4 inhibitors has been presented. The primary objective of this review is to present the analysts with various analytical and bioanalytical methods for the quantification and estimation of DPP-4 inhibitors in different matrices.

METHODS

To improve understanding, a review was carried out by creating a database of pre-existing research from digital sources such as ScienceDirect, and PubMed. The methodology is shown in the flowchart of the literature selection process.

CONCLUSION

The comprehensive assessment of methods for analysing DPP-4 inhibitors can be a valuable resource for researchers and healthcare practitioners. Hitherto, no review encompassing all DPP-4 inhibitors has been presented. Therefore, gaps in the data available on a particular subject, need to be required to collect data on a particular construct. The review suggests that chromatographic techniques were majorly used for analysis wherein solvents like acetonitrile, methanol, and buffer solutions were used as mobile phases that can deteriorate HPLC columns and equipment. So, scientists could investigate new methods for the assessment of DPP-4 inhibitors using more eco-friendly solvents.

Green Multiplex Chromatographic Determination of Nine Penicillin Antibiotics Residues in Industrial Air Dust and Wastewater Environmental Samples

Determination of penicillin residues in different industrial effluents including wastewater and air samples is important to prevent exposure to residual amounts of penicillin and the development of antibiotic resistance. A green high performance liquid chromatography (HPLC) method coupled with diode array detection has been developed and validated for multiplex determination of nine penicillin antibiotics in the industrial air dust and wastewater environmental samples of penicillin facility in addition to the monitoring of facility surface cleaning. Separation was performed on C18 column with gradient elution of methanol and phosphate buffer (pH 4) at a flow rate of 1.5 mL min-1 and ultra violet (UV) detection at 220 nm. Low limits of detection were achieved (0.1-0.3 μg mL-1) indicating good sensitivity of the proposed. The method was applied for ensuring the efficiency of cleaning validation after worst-case selection. Recovery studies of the studied penicillins from fortified stainless steel and polycarbonate surfaces and swabs were between 91.91 and 100.22% with relative standard deviation 0.11-1.79%. The presence of any of the studied penicillins in wastewater samples from penicillin plant drainage was checked. Also, total air dust concentration (mg m-3) and % of penicillin active material residues in air dust were calculated from the area of the exposed group in suspension, tablet and vial production lines. The proposed method can be recommended for routine analysis of air and wastewater environmental samples for the detection of penicillin antibiotics at low levels as well as monitoring of facility surface cleaning with high accuracy and precision.

Development and validation of a new analytical method for determination of linagliptin in bulk by visible spectrophotometer

A simple, economical, and specific analytical method has been developed for determining and validating linagliptin (LNG) in bulk. This method is based on a condensation reaction between a primary amine in LNG and an aldehyde group in P-dimethylaminobenzaldehyde (PDAB) to form the yellow Schiff base with a wavelength of 407 nm. The optimum experimental conditions for the formulation of the colored complex have been studied. The optimum conditions were 1 mL of 5% w/v reagent solution with methanol and distilled water as a solvent for both PDAB, LNG respectively, also adding 2 mL of HCl as an acidic medium, heating to 70-75 °C on a water bath for 35 min. Furthermore, the stoichiometry of the reaction has been studied according to Job's and Molar ratio method which was expressing 1:1 for LNG and PDAB. The researcher modified the method. The results show that the linearity in the concentration range (5-45 µg/mL) with correlation coefficient R² = 0.9989 with percent recovery (99.46-100.8%) and RSD was less than 2%, LOD and LOQ 1.5815 - 4.7924 μg/mL respectively. This method can show high quality and there is no significant interference with excipients and in pharmaceutical forms. None of the studies showed the development of this method before.

Eco-friendly stability-indicating HPTLC micro-determination of the first FDA approved SARS-CoV-2 antiviral prodrug Remdesivir: Study of degradation kinetics and structural elucidation of the degradants using HPTLC-MS

The worldwide spread coronavirus (covid-19) pandemic caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) represents a global health crisis. The world was forced to face a great challenge to control and overcome this health disaster through various containment measures including efficient vaccination side by side with effective medication. Remdesivir (RMD) is the first FDA approved antiviral agent for treatment of covid-19 pandemic and hence regarded as the first-in-class medication of this highly contagious respiratory disease. The current study represents the first stability indicating HPTLC method for the estimation of RMD in bulk form and pharmaceutical formulation. The method employed TLC silica gel aluminum plates 60 F₂₅₄ as stationary phase and green mobile phase composed of ethyl acetate and ethanol (96: 4, v/v) with densitometric detection at 245 nm. Comprehensive validation of the adopted method was accomplished according to the ICH guidelines regarding linearity, ranges, detection and quantification limits, precision, accuracy and robustness. The developed method offered a neat separation of the drug in presence of pharmaceutical excipients as well as in presence of acidic, alkaline, neutral hydrolytic, oxidative and photolytic degradants. Additionally, structural elucidation of alkaline and hydrolytic oxidation degradation products was carried out using HPTLC-MS. Furthermore, for the first time the acidic and alkaline degradation kinetics of RMD were studied and its degradation rate constants and half-lives were calculated. Moreover, greenness appraisal of the developed method as well as comparison with previously published stability indicating HPLC methods were performed using analytical Eco-scale, GAPI and AGREE metrics.

Investigation of an artificial solution degradant of linagliptin: An undesired linagliptin urea derivative generates in sample preparation of linagliptin tablet treated by sonication in acetonitrile containing diluent

During the related substances testing method development for linagliptin tablet, an unknown peak was observed in HPLC chromatograms with a level exceeding the identification threshold. By using a strategy that combines LC-PDA/UV-MSⁿ with mechanism-based stress studies, the unknown peak was rapidly identified as linagliptin urea, a solution degradant that is caused by the reaction between the API and hydrocyanic acid with sonication treatment to accelerate dissolution of the drug substance in sample preparation of linagliptin tablets, and hydrocyanic acid is a known impurity in HPLC grade acetonitrile and acetonitrile is used as part of diluent. The mechanism of the solution degradation chemistry was verified by stressing linagliptin API with trimethylsilyl cyanide (TMSCN, which can give off HCN slowly in the presence of water) treated with sonication in the sample preparation. Further investigation found that when the sonication treatment was replaced by vortex vibration in the process of the sample preparation, the RRT 1.28 species was decreased to below the level of the detection limit (0.02%). The structure of this impurity was further confirmed through the synthesis of the impurity and subsequent structure characterization by 1D and 2D NMR. Due to the presence of trace amount of HCN in HPLC grade acetonitrile, these types of solution degradation would likely occur in analysis of pharmaceutical finished products containing APIs with primary and secondary amine moieties drug product during sample preparations, particularly when sonication treatment is used to accelerate dissolution of drug substance from the finished drug product. In the GMP quality control laboratories, such events may trigger undesirable out-of-specification (OOS) events. Hence, the results of this paper can help to prevent these events from happening in the first place or resolve these OOS events in GMP laboratories.

Analysis of Metformin and Five Gliptins in Counterfeit Herbal Products: Designs of Experiment Screening and Optimization

BACKGROUND

Drug counterfeiting is a rising problem due to difficulties with identifying counterfeit drugs and the lack of regulations and legislation in developing countries.

OBJECTIVE

This study aims to develop a robust and economic reversed phase high performance liquid chromatography (LC) method for simultaneously determining metformin HCl, vildagliptin, saxagliptin, alogliptin benzoate, sitagliptin phosphate monohydrate, and linagliptin to target counterfeiting.

METHODS

Plackett-Burman (PB) and Box-Behnken (BB) designs were used to screen and optimize the mobile phase composition. Chromatographic separation was carried out on an Inertsil® ODS-3 C18 column with isocratic elution mode and the mobile phase was a mixture of acetonitrile-methanol-ammonium formate buffer, pH 3.5 (25:10:65, v/v/v). This method was applied to analyze synthetic drugs in three traditional Chinese and Indian herbal medicines. To identify the adulterants, thin-layer chromatography (TLC), nuclear magnetic resonance (NMR), and mass spectrometry (MS) were used on counterfeit herbal medicines.

RESULTS

The developed method is sensitive, simple, rapid, economical, accurate, and highly robust. Student's t-test and variance ratio (F-test at P < 0.05) were used to compare the results statistically with the reference methods.

CONCLUSION

The study found that the analyzed herbal medicines were adulterated with metformin and the quantification of anti-diabetic counterfeits was therefore applied.

HIGHLIGHTS

This study determined counterfeited anti-diabetic drugs in Indian and Chinese traditional herbal medicines(THMs). Design-of-experiment, PB, and BB designs were used. Method validation was also performed in accordance with the International Conference on Harmonization guidelines.

Electrochemical Detection of Linagliptin and its Interaction with DNA

Objectives

Linagliptin (Lin) is a drug used in treatment of type 2 diabetes mellitus. In this study, the electrochemical detection of Lin and its interaction with DNA was analyzed for the first time using voltammetric methods by measuring the oxidation currents of the adenine bases of DNA before and after the interaction. In addition, the electrochemical properties of the Lin were studied.

Materials and Methods

The interaction between Lin and DNA was evaluated using differential pulse voltammetry. A three-electrode system comprising of a pencil graphite electrode as the working electrode, reference electrode (Ag/AgCl), and platinum wire as the auxiliary electrode was used in the electrochemical studies. Experimental conditions, such as the concentration, pH of the supporting electrolyte, and immobilization time were optimized to obtain maximum analytical signals.

Results

The adenine bases of DNA were evaluated as an analytical signal obtained at approximately +1.2 V vs. Ag/AgCl. After the Lin-DNA interaction, the oxidation currents of adenine decreased as proof of interaction. No reports have been published on Lin interacting with DNA. Based on our results, a diffusion-controlled irreversible redox process involving independent oxidation was revealed for Lin. Under optimum conditions, the detection limit was 6.7 µg/mL for DNA and 21.5 µg/mL for Lin. Based on the observations, Lin has a toxic effect on DNA.

Conclusion

We successfully demonstrated that Lin interacts with DNA, and its influence on DNA could play a vital role in the medical effect of the drug.

An RP-HPLC Method for Quantitative Analysis of Linagliptin Entrapped in Nanotransfersomes and its Application to Skin Permeation Studies

Background:

Linagliptin (LNG) is an oral hypoglycemic agent that acts by inhibiting the enzyme dipeptidyl peptidase - 4 (DPP-4) and reduces blood sugar levels in type-II diabetic patients. To date, the literature presents few analytical methods for the determination of LNG. However, no reversed phase-high performance liquid chromatography (RP-HPLC) method has been reported for the determination of LNG in nanotransfersomes and in vitro skin permeation samples.

Objective:

The present study involves the development and validation of RP-HPLC method to quantify LNG in both nanotransfersomes and in vitro skin permeation and deposition samples.

Methods:

The chromatographic analysis was performed on Luna C18 (2) column (250 x 4.6 mm, 5μm particle size) with a mobile phase consisting of a mixture of methanol: 0.2% orthophosphoric acid (50:50, v/v) at a flow rate of 1.0 mL/min, detection wavelength of 227 nm, and column temperature of 40 °C.

Results:

The method was found to be specific, linear (r2 ≥ 0.999; 2-12 μg/mL), precise at both intra and inter-day levels (percentage relative standard deviation; % RSD < 2.00), accurate (percentage recovery 100.21-103.83%), and robust. The detection and quantification limits were 0.27 and 0.82 μg/mL, respectively. The mean % entrapment efficiency and the cumulative amount of LNG permeated across the rat skin from different transfersomal formulations ranged between 40.78 ± 2.54 % to 52.26 ± 2.15 % and 79.54 ± 16.67 to 200.74 ± 35.13 μg/cm2 respectively.

Conclusion:

The method was successfully applied to determine the entThe method was successfully applied to determine the entrapment efficiency, in vitro skin permeation and deposition behavior of LNG-nanotransfersomes.rapment efficiency, in vitro skin permeation and deposition behavior of LNG-nanotransfersomes.

Application of online liquid chromatography/quadrupole time-of-flight electrospray ionization tandem mass spectrometry for structural characterization of linagliptin degradation products and related impurities

RATIONALE

Linagliptin is a drug used for the management of type 2 diabetes, which is a leading cause of global ill health and mortality. Impurities can affect the quality and safety of drug products and eventually may affect human health. A robust, sensitive and reliable analytical method is required to detect, characterize, quantify and control the presence of impurities in finished pharmaceutical products such as linagliptin.

METHODS

Linagliptin was stressed under harsh conditions as in the ICH Q1A (R2) guidelines to generate degradation products. The degradation products and process-related impurities were separated using an InertSustain C8 column (4.6 mm × 150 mm, 5 μm) and characterized by tandem quadrupole time-of-flight mass spectrometry in positive mode electrospray ionization. The developed method was validated according to the ICH Q2 (R1) guidelines.

RESULTS

Upon forced degradation, 12 degradation products were obtained (6 in oxidative stress and 3 in each of acid and alkaline hydrolysis). The special finding here was the presence of a pair of isomeric degradation products in acid hydrolysis and the formation of degradation products in base hydrolysis and oxidative degradation caused by the use of acetonitrile as a diluent. The 12 degradation products and 6 process-related substances were successfully identified using liquid chromatography/tandem mass spectrometry.

CONCLUSIONS

A reversed-phase high-performance liquid chromatography method was developed and validated for the separation of the 12 degradation products and 6 process-related impurities. Structural characterization of all impurities was carried out using fragmentation pathways obtained from tandem mass spectrometry. The method was sufficiently sensitive and reproducible for quality control of linagliptin and for further research studies.

A Glassy Carbon Electrode for the Determination of Linagliptin, an Antidiabetic Drug in Pure Form, Tablets and Some Biological Fluids by Adsorptive Stripping Voltammetry

AIM

The present work provides a fast, simple, accurate, and inexpensive analytical method for the determination of Linagliptin (anti-diabetic drug).

METHODS

The analysis was performed using a square wave adsorptive anodic stripping voltammetric technique (SWAASV) and glassy carbon electrode (GCE) as a working electrode. The experimental and instrumental parameters were studied and discussed to ensure the validity of the method.

RESULTS

The method has a very good linearity (R² = 0.9984), wide concentration range (0.189 - 2.268 μg mL^-1), low detection limit of 0.052 μg mL^-1 and low quantitation limit of 0.172 μg mL^-1.

CONCLUSION

Linagliptin was identified successfully using the proposed method in pharmaceutical formulations, spiked human urine and plasma with 99.67, 91.96, and 92.78% recovery, respectively, and the results obtained were compared with other reported methods.

Square-wave Adsorptive Anodic Stripping Voltammetric Determination of Antidiabetic Drug Linagliptin in Pharmaceutical Formulations and Biological Fluids Using a Pencil Graphite Electrode

A simple, sensitive, low-cost, quick and reliable square-wave anodic stripping voltammetric method is described for the determination of the antidiabetic drug Linagliptin (LNG) in pure form, tablets, and spiked human urine and plasma samples. Using a pencil graphite electrode (PGE), cyclic voltammetry (CV) was applied to study the electrochemical behavior of LNG. In a Teorell-Stenhagen buffer (pH 5.5) containing 0.1 M NaClO₄ as a supporting electrolyte, the LNG yields an irreversible well-defined oxidation peak at about 1.2 V vs. Ag/AgCl electrode. The various affecting factors, such as the pH, buffer type, supporting electrolyte, accumulation potential, scan rate and accumulation time, were tested and optimized. Also, square-wave adsorptive anodic stripping voltammetric (SWAdASV) studies show that the peak current various linearly over the LNG concentration range of 0.24 - 5.20 μg mL^-1 (R² = 0.9994). The detection and quantification limits were calculated to be 0.10 and 0.33 μg mL^-1, respectively. The proposed procedure exhibits a good precision, selectivity, and stability and was applied successfully to determine the LNG in pharmaceutical formulations (tablets) and biological fluids (spiked human urine and plasma samples).

Pharmacokinetic interaction between linagliptin and tadalafil in healthy Egyptian males using a novel LC–MS method

Aim: Assessment of pharmacokinetic interaction between linagliptin (LNG) and tadalafil (TDL) in healthy males. Methods: First, a novel LC–MS method was developed; second, a Phase IV, open-label, cross-over study was performed. Volunteers took single 20-mg TDL dose on day 1 followed by wash out period of 2 weeks then multiple oral dosing of 5-mg/day LNG for 13 days. On day 13, volunteers were co-administered 20-mg TDL. Results: LNG and TDL single doses did not affect QTc interval. Smoking did not alter pharmacokinetics/pharmacodynamics of LNG and TDL. Co-administration of LNG with TDL resulted in TDL longer time to reach maximum plasma concentration (Tmax), decreased oral clearance (Cl/F) and oral volume of distribution (Vd/F), increased its maximum plasma concentration (Cmax), area under concentration-time curve (AUC), muscle pain and QTc prolongation. Conclusion: LNG and TDL co-administration warrants monitoring and/or TDL dose adjustment.

A new stability indicating reverse phase high performance liquid chromatography method for the determination of enantiomeric purity of a DPP-4 inhibitor drug linagliptin

A simple, sensitive, and stability indicating isocratic reverse phase high performance liquid chromatography method has been developed, optimized and validated for the separation and quantification of S-enantiomer in linagliptin (R-enantiomer) drug substance. Enantiomeric separation was achieved on a Cellulose tris(4-chloro-3-methylphenylcarbamate) stationary phase. Mobile phase consists of aqueous diammonium hydrogen phosphate buffer and acetonitrile in the ratio of 35:65 v/v. Isocratic elution was performed at a flow rate of 1.0 mL/min, the column oven temperature was set at 40°C and detection was at 226 nm. The resolution between R and S enantiomers is found to be more than 4.0. The impact of mobile phase composition, pH of buffer and temperature on the resolution has been studied. The detector response is found to be linear over the concentration range of 0.17-1.7 μg/mL. LOD and LOQ levels of S-enantiomer are found to be 0.057 and 0.172 μg/mL respectively. The recovery of S-enantiomer is 99.8% w/w. The proposed method is validated for specificity, precision, linearity, accuracy and robustness.

Structural re-positioning, in silico molecular modelling, oxidative degradation, and biological screening of linagliptin as adenosine 3 receptor (ADORA3) modulators targeting hepatocellular carcinoma

Chemical entities with structural diversity were introduced as candidates targeting adenosine receptor with different clinical activities, containing 3,7-dihydro-1H-purine-2,6-dione, especially adenosine 3 receptors (ADORA3). Our initial approach started with pharmacophore screening of ADORA3 modulators; to choose linagliptin (LIN), approved anti-diabetic drug as Dipeptidyl peptidase-4 inhibitors, to be studied for its modulating effect towards ADORA3. This was followed by generation, purification, analytical method development, and structural elucidation of oxidative degraded product (DEG). Both of LIN and DEG showed inhibitory profile against hepatocellular carcinoma cell lines with induction of apoptosis at G2/M phase with increase in caspase-3 levels, accompanied by a downregulation in gene and protein expression levels of ADORA3 with a subsequent increase in cAMP. Quantitative in vitro assessment of LIN binding affinity against ADORA3 was also performed to exhibit inhibitory profile at Ki of 37.7 nM. In silico molecular modelling showing binding affinity of LIN and DEG towards ADORA3 was conducted.