High performance liquid chromatography analysis of MESNA (2-mercaptoethane sulfonate) in biological samples using fluorescence detection

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1 BIOMEDICAL CHROMATOGRAPHY Biomed. Chromatogr. 19: (2005) Published 80 online ORIGINAL in Wiley RESEARCH InterScience ( ORIGINAL RESEARCH DOI: /bmc.420 High performance liquid chromatography analysis of MESNA (2-mercaptoethane sulfonate) in biological samples using fluorescence detection Suneetha Mare, Suman Penugonda and Nuran Ercal* Department of Chemistry, University of Missouri-Rolla, 142 Schrenk Hall, Rolla, MO 65409, USA Received 26 February 2004; revised 29 April 2004; accepted 6 May 2004 ABSTRACT: MESNA is the sodium salt of 2-mercaptoethane sulfonate, a thiol-containing drug. It is an antioxidant used particularly in renal protection. Several studies have proved that MESNA has beneficial effects in ischemic acute renal failure where it scavenges reactive oxygen species (ROS), due to the presence of the thiol group. It also reduces the size of urinary bladder cancer. MESNA was proved to be effective in preventing hemorrhagic cystitis induced by high doses of several chemotherapeutic regimens such as cyclophosphamide and ifosfamide. It has been shown that MESNA functions as an uroprotective substance in drug-induced experimental bladder cancer models. Moreover, recent studies have suggested that it is also effective in reducing intestinal inflammation in colitis. Because of the increased level of interest in using MESNA for treating various disorders, a new and sensitive method was needed to understand the pharmacokinetics of this drug. Accordingly, we developed a new method for determining free MESNA in biological samples by using ThioGlo-3 [3H-Naphto [2,1-b] pyran, 9-acetoxy-2-(4-(2,5-dihydro-2, 5-dioxo-1H-pyrrol-1-yl) phenyl- 3-oxo)] as the derivatizing agent. MESNA was detected fluorimetrically by reverse-phase HPLC using acetonitrile:water (75:25) along with acetic acid and phosphoric acid (1 ml/l each) as the mobile phase. The detection limit was 1.64 nm per 20 µl injection volume, with a linearity (r = 0.999) in the calibration curve extending over a range nm. The coefficients of variation for within-run and between-run precision were 0.43 and 3.31%, respectively. The relative recoveries in the biological samples were in the range 87 ± 6 to 93 ± 2.4%. The concentrations of MESNA in the biological samples (lungs, liver, kidney and brain) were determined. The highest concentration of MESNA was found in plasma. Of all the tissues, the kidney was found to have the highest concentration while the liver had the lowest concentration. Copyright 2004 John Wiley & Sons, Ltd. KEYWORDS: sodium 2-mercaptoethane sulfonate; thiols; ThioGlo 3; reactive oxygen species; ischemic acute renal failure; hemorrhagic cystitis INTRODUCTION Sodium salt of 2-mercaptoethane sulfonate (MESNA) is a thiol-containing drug which is mainly used as a uroprotectant, when given orally and intravenously, due to its ability to increase the levels of free thiol groups in the urinary tract. It especially helps prevent hemorrhagic cystitis, ulcerative colitis and bladder tumors induced by anti-tumor agents and external nephrotoxins (Nishikawa et al., 2003; Stofer-Vogel et al., 1993; Shusterman et al., 2003; Mashiach et al., 2001). MESNA has the capability to scavenge reactive oxygen species (ROS). We believe that these protective effects of MESNA could be partially due to its potential antioxidant function because it has a thiol functional group. Almost all known thiol-containing compounds tend to scavenge free radicals. Recent studies indicate that *Correspondence to: N. Ercal, Department of Chemistry, University of Missouri-Rolla, 142 Schrenk Hall, Rolla, MO 65409, USA. nercal@umr.edu Abbreviations used: MESNA, 2-mercaptoethane sulfonate; ROS, reactive oxygen species; SBB, serine borate buffer. Published online 15 September 2004 numerous disorders originate from free radical attacks on biological macromolecules such as proteins, lipids and DNA. Therefore, the search for a new antioxidant is essential and subsequent analysis in biological samples is critical. In 1959, the first analysis of MESNA was performed using non-specific colorimetric assay (Ellman, 1959). In this technique, however the concentration of free thiol groups already present in biological samples cannot be distinguished from that of MESNA. Considering these problems, several HPLC methods coupled with electrochemical, UV and fluorescence detections have recently been reported for the analysis of MESNA. Even though electrochemical detection is more sensitive and selective, its maintenance and use are more difficult than those of UV and fluorescence (Sidau and Shaw, 1984; el-yazigi et al., 1995; James and Rogers, 1986; Verschraagen et al., 2001, 2003). Moreover, responses from other chemical groups could cause interference and invalidate results. The HPLC- UV detection method used for determining MESNA, as reported by Glowacki et al. (2001), seemed to be less Copyright 2004 John Wiley & Sons, Ltd. Biomed. Chromatogr. 19: (2005)

2 HPLC analysis of MESNA ORIGINAL RESEARCH 81 Figure 1. Scheme of formation of fluorescent ThioGlo 3 MESNA adduct. specific with the UV-tag used to derivatize MESNA. With this method, the chromatogram from plasma sample showed several other peaks which could interfere with biological thiols. Gatti et al. (1990) developed a method for determining aliphatic thiols including MESNA by using HPLC fluorescence detection. However, this method did not show its applicability to determining MESNA in biological tissues. Therefore, we believe that a new and sensitive method is needed to monitor MESNA levels in biological samples. This study describes the determination of free MESNA in plasma and biological tissues (lungs, liver, kidney, brain) using ThioGlo-3 as the derivatizing agent. Owing to its high affinity for free thiol groups, ThioGlo-3 forms a fluorescent derivative (Fig. 1) with MESNA, which can be detected fluorimetrically by reverse phase HPLC. EXPERIMENTAL Reagents and chemicals Acetonitrile, acetic acid, methanol, and phosphoric acid (all HPLC grade) were purchased from Fischer (FairLawn, NJ, USA). MESNA, l-serine and Tris HCl (Trizma hydrochloride) were obtained from Sigma (St Louis, MO, USA), and ThioGlo 3 was purchased from Covalent Associates Inc. (Woburn, MA, USA). Diethylenetriaminepentaacetic acid (DETAPAC) was from Aldrich (Milwaukee, WI, USA). Animals Adult male C57BL/6 mice, weighing g each, were obtained from Charles River Laboratories. The mice were housed in a temperature-controlled (25 C) room equipped to maintain a 12 h light dark cycle. Standard rat chow (Purina rat chow) and water were given ad libitum. After overnight fasting, MESNA was administered intraperitoneally at 800 mg/kg of body weight in 1 ml of saline. The animals were then anesthetized according to the University of Missouri Animal Care regulations. After 30 min, blood samples were collected via intracardiac puncture into the sterile polystyrene tubes containing heparin as an anticoagulant, and the animals were then sacrificed to obtain liver, lung, kidney and brain samples. Plasma was obtained by centrifugation of blood for 5 min at 3000 rpm and immediately derivatized with ThioGlo 3. Solutions Required concentrations (1 mm, 100 µm, 10 µm) of MESNA stock solutions were prepared in HPLC-grade or nanopure water (0.16 mg/ml). These stock solutions were used to prepare standards for the calibration curve. Serine borate buffer (SBB) was prepared by adding g Tris HCl, g borate, g serine and g diethylenetriaminepentaacetic acid in 1 L of HPLC grade water. ThioGlo 3 (0.05 mm) was prepared by adding g in 10 ml acetonitrile. HPLC system The HPLC system (Shimadzu Corporation, Kyoto, Japan) consisted of a model LC-10A pump, a Rheodyne injection valve with a 20 µl filling loop, and a Model RF 535 flourometer (Shimadzu Corporation, Kyoto, Japan) operating at an excitation wavelength of 365 nm and an emission wavelength of 445 nm. The HPLC column (Column Engineering, Ontario, CA, USA) was mm i.d. and was packed with 5 µm particles of C 18 silica packing material. Quantitation of the peaks was performed with a Chromatopac model CR601 integrator (Shimadzu). The mobile phase used was acetonitrile:water (75:25, v/v) along with acetic acid and

3 82 ORIGINAL RESEARCH Figure 2. Reaction time of ThioGlo 3 MESNA adduct (n = 5). Peak areas are reported as mean values ± standard deviations (SD). phosphoric acid (1 ml/l each) to adjust the ph to 2.5. The ThioGlo 3 derivatives were eluted from the column isocratically at a flow rate of 1 ml/min. Assay procedures Derivatization of MESNA. Tissue samples (0.14 mg/ml) were homogenized in SBB (100 mm Tris HCl, 10 mm borate, 5mm serine, 1 mm diethylenetriamine pentaacetic acid, ph 7.00), as described by Neal et al. (1997). The homogenates of the liver, lung, kidney, brain tissues and plasma from C57BL/6 mice were appropriately diluted with SBB and then derivatized with ThioGlo 3 to form fluorescent derivatives under room temperature. A 0.5 mm ThioGlo 3 solution in acetonitrile (375 µl) was added to 25 µl of water and 100 µl of the diluted samples. Standards without tissue matrix were prepared by taking appropriate volume of MESNA stock solutions (to obtain the concentrations 2.5, 5, 25, 125, 250, 1250 and 2500 nm) and diluting with water (HPLC grade) to bring the volume to 125 µl and then they were derivatized by adding 0.5 mm ThioGlo 3 solution in acetonitrile (375 µl). The resulting solutions were mixed and incubated at room temperature for min. After the reaction time was complete (Fig. 2), 10 µl of the 2 N HCl solution were added to stop the reaction. The final ph of the solution was maintained at about 1, which is important for stabilizing the derivatives. The derivatized samples were filtered through a 0.2 µm acrodisk and then injected onto a 5 µm C 18 column in a reverse-phase HPLC system. Tissue protein concentrations were determined by the Bradford method (Bradford, 1976). Protein assay. Protein content of the tissue and cell samples was determined by using the Bradford method (Bradford, 1976) in order to compare the concentration levels of MESNA obtained from different tissue samples (Table 2). The homogenized samples were appropriately diluted before the protein was determined. Concentrated Coomasie blue (Bio-Rad) was diluted 1:5 (v/v) with distilled water; then 2.5 ml of this diluted dye was added to 50 µl of the homogenized sample. The mixture was incubated at room temperature for 5 min and the absorbance was measured at 595 nm by a spectrophotometer. The concentration of protein present in these homogenized samples was obtained by comparing these absorbance values against the standard curve. A standard curve was constructed using bovine serum albumin (BSA), mg/ml. Validation studies Validation studies on MESNA were done by measuring lower limit of detection, linearity, selectivity, stability, accuracy, between run and within run precision and relative recoveries. Calibration curve. Calibration curves for MESNA were obtained by injecting 20 µl of ThioGlo 3-derivatized standards containing tissue matrix and standards without tissue matrix. These standards were prepared as explained under Derivatization of MESNA. Linearity in the tissue standards was obtained over a full range of nm with a regression constant r = 0.998, while linearity in the standards was obtained over a full range of nm with r = as the regression constant. Accuracy and precision. Accuracy was assessed with five replicates of MESNA-free liver tissue matrix samples at five different concentrations in the range nm of MESNA, which were derivatized and then analyzed on seven different days to determine the day-to-day CVs and the accuracy (%). The between-run precision was determined by analyzing the seven replicates of the same homogenate at seven different times on each of seven different days. Withinrun precision was determined by successively injecting the seven replicates of the same biological sample in the single analytical run and comparing the peak areas of the MESNA derivatives for each of the injections.

4 HPLC analysis of MESNA ORIGINAL RESEARCH 83 Relative recovery. Relative recovery was determined by spiking tissue samples (n = 3) with 500 nm of MESNA and comparing the results to those obtained from aqueous samples supplemented with the same concentration of MESNA. Selectivity, stability and lower limit of detection. The interference due to the hydrolysis products and endogenous thiols such as glutathione, cysteine and homocysteine with that of MESNA was determined. Stability studies were done by the analysis of the derivatized samples stored at 4 C and also the plasma and tissue samples stored at 70 C for at least 2 weeks. Lower limit of detection was determined by analyzing seven replicates of blank samples without the interference of noise (signal-to-noise, S/N = 3:1). RESULTS Calibration curve Calibration curves were obtained by using integrated peak areas as the y-axis vs standard MESNA concentrations as the x-axis. Linearity was obtained with a regression constant of (r = 0.999) for MESNA concentrations over the range nm. Similar linearity, with a regression constant of r = 0.998, was also observed for another calibration curve (average of seven different standard curves) obtained by injecting 20 µl of ThioGlo 3 derivative standards containing liver tissue (Fig. 6). Accuracy and precision MESNA-free liver tissue matrix samples were analyzed using five different concentrations and the coefficients of variation and the accuracy were reported in Table 1. The coefficients of variation for within run and between Table 1. Precision and accuracy of the determination of MESNA in the MESNA-free liver tissue matrix (n = 5) MESNA Accuracy concentration (nm) CV (%) (%) run precisions in the standards and also in the biological samples were shown in Table 2. Between-run and within-run precisions for MESNA in plasma were 8.7 and 3.6% respectively, and for the other tissue samples it was less than 15%. The concentrations of MESNA in plasma and in all of the tissue samples are reported in Table 3. Sensitivity, reproducibility and relative recovery The detection limit for MESNA was observed to be 1.64 nm (S/N = 3). The retention time for MESNA ThioGlo 3 adduct was found to be reproducible through out the experiment. Relative recoveries in the plasma and tissue samples were presented as mean ± standard deviation (Table 2). Selectivity and stability After in situ derivatization of the biological samples, the resulting ThioGlo 3-MESNA fluorescent derivatives were separated using the HPLC system. The retention time for ThioGlo 3-MESNA adduct was 2.3 min. Figure 3(A) shows the chromatogram of Thio- Glo 3 peak and Fig. 3(B) confirms the separation Table 2. MESNA in sample matrices and standards for within-run and between-run precision (n = 5). Relative recovery is reported as the average relative recovery of three samples spiked with 500 nm MESNA in each sample matrix Sample matrix Liver Lung Kidney Brain Plasma Standard Between run precision (n = 7) 2.60% 14.8% 1.20% 9.10% 8.70% 3.30% Within run precision (n = 7) 6.90% 8.50% 0.30% 2.80% 3.60% 0.43% Percentage relative recovery 87.4 ± ± ± ± ± 3.0 N/A N/A = not applicable. Table 3. MESNA in tissues 30 min after intraperitoneal admistration of 800 mg/kg of MESNA MESNA concentration Sample MESNA, nmol/l Protein, ml/mg Control Liver 565 ± ± 0.01 ND Lung ± ± 0.04 ND Kidney ± ± 0.01 ND Brain ± ± 0.04 ND Plasma ± 15.0 nmol/l ND

5 84 ORIGINAL RESEARCH Figure 3. (A) Chromatogram A is a blank chromatogram prepared by substituting water for MESNA containing sample which shows a ThioGlo 3 hydrolysis peak without MESNA. (B) Chromatogram B shows the separation of a ThioGlo 3 MESNA adduct (250 nm) from a ThioGlo 3 hydrolysis peak. A 12.5 µl sample of 10 µm MESNA was added to 25 µl of serine borate buffer (its composition was stated in the text) followed by a 375 µl of 0.5 mm ThioGlo 3 solution in acetonitrile. Separation was performed by using acetonitrile:water (75:25, v/v) as a mobile phase at a flow rate of 1mL/min on a column ( mm i.d.) packed with 5 µm particles of C 18 packing material; the fluorescent adducts were detected flourimetrically (λ ex = 365 nm; λ em = 445 nm). Figure 5. (A) Chromatogram obtained from a control C57BL/ 6 mouse kidney tissue sample (no MESNA peak). (B) Chromatogram showing separation of ThioGlo 3 MESNA adduct from a ThioGlo hydrolysis peak obtained from a C57BL/6 mouse kidney tissue sample after spiking with 500 nm of MESNA. Details of the derivatization steps used for the tissue samples are stated in the text. being spiked with 500 nm of MESNA are shown in Fig. 5. All of the tissue and plasma samples that had been derivatized and maintained at 4 C remained stable for at least 2 weeks with less than 2% deviation in all the samples. And the plasma and tissue samples stored at 70 C remained stable for at least two freeze thaw cycles. DISCUSSION Figure 4. A representative chromatogram of a mixture of GSH, CYS, HCYS and MESNA ThioGlo 3 derivatized samples. Peak identifications and experimental conditions were the same as those of Figure 3. GSH, glutathione; CYS, cysteine; HCYS, homocysteine; MESNA, sodium 2- mercaptoethane sulfonate. of ThioGlo 3-MESNA adduct from ThioGlo 3 hydrolysis peaks. The chromatogram pictured in Fig. 4 shows the separation of ThioGlo 3-MESNA adduct from the biological thiols such as GSH, Cys and HCys. The chromatograms of kidney samples before and after MESNA, sodium salt of 2-mercaptoethane sulfonate, has a dominant advantage as a potent drug in treating nephrotoxicity (Stofer-Vogel et al., 1993; Turrill et al., 1995). According to some studies, MESNA can also be used as a prophylactic agent in chemotherapy-induced nephrotoxicity. The prevalence of chemotherapyinduced nephrotoxicity was significantly reduced when the patients were given MESNA as a prophylactic drug (Hensley et al., 1999). Another study by Mashiach et al. (2001) showed that MESNA helped in minimizing renal ishemic reperfusion injury because of its ability to concentrate in the

6 HPLC analysis of MESNA ORIGINAL RESEARCH 85 Figure 6. Standard curves obtained from MESNA and MESNA in liver tissue matrix. Calibration curves are plotted using integrated peak areas as y-axis vs the standard concentration as x-axis. Peak areas are reported as mean values ± standard deviations (SD). kidneys. There is a critical need to develop new techniques and to conduct studies to determine clinically acceptable methods for measuring the concentration of MESNA in kidneys. Accordingly, we have described a simple, reproducible method for determining the concentrations of free MESNA in kidneys, along with other tissues such as livers, lungs and brains including plasma. The highest and lowest concentrations of MESNA in the tissue samples were observed in the kidneys and in the livers, respectively. Our results also support the fact that MESNA concentrates more in the kidneys than in all other tissues. The lower limit of detection was found to be 1.64 nm. Each sample requires a 7 min run time; however, the retention time of MESNA was 2.3 min. The concentration of MESNA in plasma was found to be higher than that in the tissue samples, and the relative recoveries in plasma were even larger than those reported by James and Rogers (1986). In plasma, MESNA rapidly oxidizes into DIMESNA (the inactive form of MESNA) which, in turn, reduces and converts into the active thiol form (MESNA) in the renal tubular epithelia by cytosolic enzymes (Leeuwenkamp et al., 1991; Nishikawa et al., 2003; Lahdetie et al., 1990). In order to obtain the actual concentration of reduced MESNA in plasma and tissue samples, we believed that the samples should be immediately derivatized. Many reagents, especially N-substituted maleimides, were tried in order to derivatize the thiol groups. ThioGlo 3, one of the derivatizing agents we used, had added advantages (Ercal et al., 2001). First, it showed little or no fluorescence before reacting with the thiol groups (Yang and Langmuir, 1991; Langmuir et al., 1995). Second, the hydrolysis products generated by the reaction of ThioGlo 3 with the thiol groups in the samples had no fluorescence. Thus only a few ThioGlo 3 hydrolysis peaks were seen in the chromatograms and interference due to these hydrolysis peaks was ultimately less. Last but not the least, the derivatizing steps were very simple, plus this method of derivatization can be carried out under ambient temperature conditions. Moreover our derivatized samples that had been stored at 4 C were found to be stable for at least 2 weeks. Although we have not conducted a detailed stability study of MESNA in our laboratory, several stability studies have been done that showed MESNA in deproteinized plasma which had been stored at 20 C remained stable for 35 days (Verschraagen et al., 2001). In deproteinized kidney tissue, MESNA decreased by 96% in 2 weeks, whereas its concentration in deproteinized kidney tissue that had been stored at 80 C remained stable for more than 12 weeks (Verschraagen et al., 2003). In addition, James and Rogers (1986) reported a stability study of MESNA in plasma sample. Depending upon the preliminary results of relative recoveries of MESNA obtained from biological samples, we believe that this method of derivatization can be used to determine the concentrations of free MESNA in plasma as well as in tissue samples and also that it can be effectively used in certain pharmacokinetic studies.

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