Applicability of fluorescamine as a fluorogenic reagent for highly sensitive fluorimetric analysis of the tyrosine kinase inhibitor (avapritinib) in pharmaceuticals and biological samples

Avapritinib (AVP) was the first precision drug to be approved by the US Food and Drug Administration (FDA) in 2020 for patients suffering from metastatic gastrointestinal stromal tumors (GISTs) and progressive systemic mastocytosis. The analysis of AVP in pharmaceutical tablets and human plasma was then carried out using a fast, efficient, sensitive, and simple fluorimetric method using a fluorescamine reagent. The procedure is based on the interaction between fluorescamine as a fluorogenic reagent and the primary aliphatic amine moiety in AVP using borate buffer solution at pH 8.8. The produced fluorescence was measured at 465 nm (Excitation at 395 nm). The calibration graph's linearity range was discovered to be 45.00-500.0 ng mL-1 . Utilizing the International Council for Harmonization (ICH) and US-FDA recommendations, the research technique was validated and bioanalytically validated. The proposed approach was effectively employed for determining the stated pharmaceuticals in plasma with a high percentage of recovery ranging from 96.87 to 98.09 and pharmaceutical formulations with a percentage of recovery equal to 102.11% ± 1.05%. In addition, the study was extended to a pharmacokinetic study of AVP with 20 human volunteers as a step for AVP management in therapeutic cancer centers.

Salvage Parenteral Antibiotics for Multidrug-Resistant (MDR) Gram-Negative Bacteria; A Fluorescamine-Based Technique for Ultrasensitive Spectrofluorimetric Measurement of Polymyxins; Human Plasma Application

Polymyxins (PMS), namely Colistin (CS) and Polymyxin B (Poly B), are antimicrobial drugs that recently used to treat multi-resistant gram-negative bacteria infections and their resurgence owing to a lack of new antibiotics. A speedy, simple, and ultrasensitive spectrofluorimetric screening of PMS in pharmaceutical formulations and biological fluids was urgently required from this point forward. A reaction between fluorescamine and the aliphatic amino moiety found in both drugs was performed in a slightly alkaline borate buffer (pH 8.5) resulted in highly fluorescent products measured at λ_em 460 (after λ_ex 390.5 nm). Linear calibration curves were constructed over the concentration range of 70 to 1800 ng mL^-1 and 100 to 1400 ng mL^-1 , with slope values of 0.273 and 0.286, correlation coefficients of 0.9998 and 0.9997, and determination coefficient of 0.9997 and 0.9994 for Poly B and CS, respectively. The ultra sensitivity of the proposed method was demonstrated by the very low limits of quantifications values of 67.56 ng mL^-1 and 94.89 ng mL^-1 for Poly B and CS, respectively. The cited drugs were successfully determined in their intravenous market preparations by the prescribed method. Moreover, due to the high sensitivity, the suggested method was employed to assay the investigated drugs in biological fluids.

Green and sensitive spectrofluorimetric method for the determination of two cephalosporins in dosage forms

Using two green and sensitive spectrofluorimetric methods, we quantified two cephalosporins, cefepime (CFM) and cefazolin (CFZ), in raw and pharmaceutical formulations. The first method is based on the reaction between CFM and fluorescamine (borate buffer, pH 8), which yields a highly fluorescent product. After excitation at 384 nm, the fluorescent product emits light at 484 nm. At concentration ranges from 12.0 to 120.0 ng ml^-1, the relative fluorescence intensity/concentration curve was linear with a limit of quantification (LOQ) of 2.46 ng ml^-1. The second method relied on measuring the CFZ quenching action on acriflavine fluorescence through formation of an ion-associate complex using Britton-Robinson buffer at pH 8. We measured acriflavine fluorescence at 505 nm after excitation at 265 nm. The decrease in acriflavine fluorescence intensity was CFZ concentration-dependent. Using this method, we quantified CFZ in concentrations ranging from 1 to 10 µg ml^-1 with a LOQ of 0.48 µg ml^-1. We studied and optimized the factors influencing reaction product formation. Moreover, we adapted our methods to the investigation of the mentioned drugs in raw and pharmaceutical formulations with greatly satisfying results. We statistically validated our methods according to International Council on Harmonisation Guidelines. The obtained results were consistent with those obtained with the official high-performance liquid chromatography methods.

LC-MS/MS quantification of asymmetric dimethyl arginine and symmetric dimethyl arginine in plasma using surrogate matrix and derivatization with fluorescamine

Aim: A novel LC-MS/MS method using a surrogate matrix and derivatization with fluorescamine was developed and validated for simultaneous quantification of asymmetric dimethyl arginine and symmetric dimethyl arginine. Methods & results: Asymmetric dimethyl arginine, symmetric dimethyl arginine and corresponding internal standards were extracted using protein precipitation and derivatization with fluorescamine followed by SPE. Derivatives were analyzed by turbo ion spray LC-MS/MS in the positive ion mode. Methodology was successfully transferred across multiple preclinical species and utilized in the support of several investigative studies. Conclusion: A new LC-MS/MS analytical methodology that utilizes a surrogate matrix and derivatization with fluorescamine was successfully developed and validated.

[Determination of Nonvolatile Amines in Foods by HPLC Following Fluorescamine Derivatization]

A method was developed for the determination of nonvolatile amines, such as histamine, tyramine, putrescine, and cadaverine, in foods. These nonvolatile amines were extracted from a sample with 5% trichloroacetic acid, and the extract was purified using an InertSep MC-1 cartridge column. The four amines were derivatized with fluorescamine, determined by HPLC with a fluorescence detector, and confirmed by LC-MS/MS. The average recoveries (n=5) and the relative standard deviations from 11 foods (pacific saury, dried mackerel, canned mackerel in brine, canned tuna in oil, fish sauce, surimi, rice-koji miso, soy sauce, gouda cheese, red wine, and beer) spiked at 100 mg/kg were 81-100% and 0.4-3.1%, respectively.

The convenient use of fluorescamine for spectrofluorimetric determination of midodrine hydrochloride in pure form and its tablets formulation: Application to content uniformity testing

A novel sensitive and simple spectrofluorimetric method was developed then validated for determination of midodrine in both its authentic pure form and its tablets. This method is based on the reaction between midodrine's aliphatic primary amine moiety with fluorescamine reagent, using borate buffer at pH 7.8 and yielding a highly fluorescent product whose fluorescence intensity was measured at 462 nm after excitation at 388 nm. This method represents the first attempt for determination of midodrine spectrofluorimetrically. A calibration curve was constructed showing that the linear range was 0.2-3.0 μg/ml. The limit of detection and limit of quantitation values were 0.06 and 0.19 μg/ml respectively. The correlation coefficient (r) and the determination coefficient (r² ) values were 0.9992 and 0.9984 respectively. The proposed method was validated according to ICH guidelines and successfully applied for determination of midodrine in its tablets with an overall % recovery of 99.56 ± 0.95. Finally, the presented method was adapted to study the content uniformity test according to United States Pharmacopeia guidelines.

[Determination of Histamine by a Rapid Fluorescamine-UPLC Method]

We have developed a rapid analysis method for determination of histamine using ultra-performance liquid chromatography and fluorescamine derivatization. Histamine was extracted from foods with trichloroacetic acid after homogenization. The supernatant obtained by centrifugation was filtered and derivatized without solid-phase extraction. The mobile phase was 10 mM phosphate-acetonitrile (75 : 25) without ion-pairing. Recovery tests of histamine from fishes, seasoning and fish products gave acceptable recovery (95.8-117.7%). This method should be useful for rapid evaluation of food poisoning outbreaks.

A mix-and-click method to measure amyloid-β concentration with sub-micromolar sensitivity

Aggregation of amyloid-β (Aβ) protein plays a central role in Alzheimer's disease. Because protein aggregation is a concentration-dependent process, rigorous investigations require accurate concentration measurements. Owing to the high aggregation propensity of Aβ protein, working solutions of Aβ are typically in the low micromolar range. Therefore, an ideal Aβ quantification method requires high sensitivity without sacrificing speed and accuracy. Absorbance at 280 nm is frequently used to measure Aβ concentration, but the sensitivity is low with only one tyrosine and no tryptophan residues in the Aβ sequence. Here we present a fluorescence method for Aβ quantification using fluorescamine, which gives high fluorescence upon reaction with primary amines. We show that, using hen egg white lysozyme as a standard, fluorescence correlates linearly with primary amine concentration across a wide range of fluorescamine concentrations, from 62.5 to 1000 µM. The maximal sensitivity of detection is achieved at a fluorescamine concentration of 250 µM or higher. The fluorescamine method is compatible with the presence of dimethyl sulfoxide, which is commonly used in the preparation of Aβ oligomers, and limits the use of absorbance at 280 nm due to its high background reading. Using aggregation kinetics, we show that the fluorescamine method gives accurate concentration measurements at low micromolar range and leads to highly consistent aggregation data. We recommend the fluorescamine assay to be used for routine and on-the-fly concentration determination in Aβ oligomerization and fibrillization experiments.

KDAC8 substrate specificity quantified by a biologically relevant, label-free deacetylation assay

Analysis of the human proteome has identified thousands of unique protein sequences that contain acetylated lysine residues in vivo. These modifications regulate a variety of biological processes and are reversed by the lysine deacetylase (KDAC) family of enzymes. Despite the known prevalence and importance of acetylation, the details of KDAC substrate recognition are not well understood. While several methods have been developed to monitor protein deacetylation, none are particularly suited for identifying enzyme-substrate pairs of label-free substrates across the entire family of lysine deacetylases. Here, we present a fluorescamine-based assay which is more biologically relevant than existing methods and amenable to probing substrate specificity. Using this assay, we evaluated the activity of KDAC8 and other lysine deacetylases, including a sirtuin, for several peptides derived from known acetylated proteins. KDAC8 showed clear preferences for some peptides over others, indicating that the residues immediately surrounding the acetylated lysine play an important role in substrate specificity. Steady-state kinetics suggest that the sequence surrounding the acetylated lysine affects binding affinity and catalytic rate independently. Our results provide direct evidence that potential KDAC8 substrates previously identified through cell based experiments can be directly deacetylated by KDAC8. Conversely, the data from this assay did not correlate well with predictions from previous screens for KDAC8 substrates using less biologically relevant substrates and assay conditions. Combining results from our assay with mass spectrometry-based experiments and cell-based experiments will allow the identification of specific KDAC-substrate pairs and lead to a better understanding of the biological consequences of these interactions.

Titration of lysine residues on adenine nucleotide translocase by fluorescamine induces permeability transition

Chemical modification of primary amino groups of mitochondrial membrane proteins by the fluorescent probe fluorescamine induces non-specific membrane permeabilisation. Titration of the lysine ϵ-amino group promoted efflux of accumulated Ca(2+), collapse of transmembrane potential and mitochondrial swelling. Ca(2+) release was inhibited by cyclosporin A. Considering the latter, we assumed that fluorescamine induces permeability transition. Carboxyatractyloside also inhibited the reaction. Using a polyclonal antibody for adenine nucleotide translocase, Western blot analysis showed that the carrier appeared labelled with the fluorescent probe. The results point out the importance of the ϵ-amino group of lysine residues, located in the adenine nucleotide carrier, on the modulation of membrane permeability, since its blockage suffices to promote opening of the non-specific nanopore.

Utility of Experimental Design in Pre-Column Derivatization for the Analysis of Tobramycin by HPLC-Fluorescence Detection: Application to Ophthalmic Solution and Human Plasma

A novel, selective, and sensitive reversed phase high-performance liquid chromatography (HPLC) method coupled with fluorescence detection has been developed for the determination of tobramycin (TOB) in pure form, in ophthalmic solution and in spiked human plasma. Since TOB lacks UV absorbing chromophores and native fluorescence, pre-column derivatization of TOB was carried out using fluorescamine reagent (0.01%, 1.5 mL) and borate buffer (pH 8.5, 2 mL). Experimental design was applied for optimization of the derivatization step. The resulting highly fluorescent stable derivative was chromatographed on C₁₈ column and eluted using methanol:water (60:40, v/v) at a flow rate of 1 mL min⁻¹. A fluorescence detector (λ_ex 390 and λ_em 480 nm) was used. The method was linear over the concentration range 20–200 ng mL⁻¹. The structure of the fluorescent product was proposed, the method was then validated and applied for the determination of TOB in human plasma. The results were statistically compared with the reference method, revealing no significant difference.

A highly sensitive fluorimetric method for determination of lenalidomide in its bulk form and capsules via derivatization with fluorescamine

BACKGROUND

Lenalidomide (LND) is a potent novel thalidomide analog which demonstrated remarkable clinical activity in treatment of multiple myeloma disease via a multiple-pathways mechanism. The strong evidences-based clinical success of LND in patients has led to its recent approval by US-FDA under the trade name of Revlimid® capsules by Celgene Corporation. Fluorimetry is a convenient technique for pharmaceutical quality control, however there was a fluorimetric method for determination of LND in its bulk and capsules.

RESULTS

A novel highly sensitive and simple fluorimetric method has been developed and validated for the determination of lenalidmide (LND) in its bulk and dosage forms (capsules). The method was based on nucleophilic substitution reaction of LND with fluorescamine (FLC) in aqueous medium to form a highly fluorescent derivative that was measured at 494 nm after excitation at 381 nm. The factors affecting the reaction were carefully studied and optimized. The kinetics of the reaction was investigated, and the reaction mechanism was postulated. Under the optimized conditions, linear relationship with good correlation coefficient (0.9999) was found between the fluorescence intensity and LND concentration in the range of 25-300 ng/mL. The limits of detection and quantitation for the method were 2.9 and 8.7 ng/mL, respectively. The precision of the method was satisfactory; the values of relative standard deviations did not exceed 1.4%. The proposed method was successfully applied to the determination of LND in its bulk form and pharmaceutical capsules with good accuracy; the recovery values were 97.8-101.4 ± 1.08-2.75%.

CONCLUSIONS

The proposed method is selective and involved simple procedures. In conclusion, the method is practical and valuable for routine application in quality control laboratories for determination of LND.

Spectrofluorimetric and spectrophotometric determination of pregabalin in capsules and urine samples

Three new, simple, sensitive and selective spectrofluorimetric and spectrophotometric methods were developed for the determination of the γ-amino-n-butyric acid derivative, pregabalin. Pregabalin as a primary amine reacts with fluorescamine to yield a fluorescent product (Method I), with 2,4-dinitrofluorobenzene (Method II) and 2,3,5,6-tetrachloro-1,4-benzoquinone (Method III) in aqueous alkaline buffered media to form colored products which could be measured spectrophotometrically. The optimum conditions for each reaction were ascertained and the methods were applied for the determination of pregabalin over the concentration range of 20-280 ng mL(-1) and 1-7 μg mL(-1) for spectrofluorimetry and spectrophotometry, respectively with good correlation (≥0.999). The limits of assays detection ranged from 9.6 × 10(-4) μg mL(-1) to 0.42 μg mL(-1) for spectrofluorimetry and spectrophotometry, respectively. The suggested methods were applied to the determination of the drug in capsules. No interference could be observed from the additives listed to be in capsules. Furthermore, the spectrofluorimetric method was extended to the in-vitro determination of pregabalin in spiked urine, interference from endogenous amino acids could be eliminated through selective complexation with copper acetate; the percentage recovery was found to be 98% ± 1.42 (n=6). Co- administered drugs such as chlordiazepoxide, clonazepam, diazepam, nitrazepam and lamotrigine did not interfere with the assay. The methods were validated with respect to linearity, accuracy, precision and robustness. The results obtained were determined to be in good agreement with those obtained using a previously reported method.

A hyperglycemic peptide from pituitary growth hormone: preparation with pepsin and assay in ob-ob mice

A fragment that induces glucose intolerance in hereditarily obese mice has been prepared from pituitary growth hormone(sheep and human) by controlled digestion with pepsin in 0.05 M sodium acetate buffer, pH 3.7. The digest was purified by column chromatography on Bio-Gel P-6, followed by chromatography on Bio-Rex 70 and Bio-Gel P-2; in each successive step peptide was quantitated with the fluorescamine procedure. The fragment from sheep growth hormone has these characteristics: (1) It induces glucose intolerance in fasted ob/ob female mice when injected subcutaneously in a divided dose 15 min before, and concurrently with, glucose. (2) It is a basie peptide, as judged from its elution behavior on Bio-Rex 70, H(+) form. (3) It does not crossreact with antiserum to human growth hormone in radioimmunoassay. Further purification and initial sequence determinations have been undertaken.