DISCRIMINATION AND QUANTIFICATION OF GLYCOSAMINOGLYCANS IN PHARMACEUTICAL FORMULATIONS USING micro-raman SPECTROSCOPY

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1 DISCRIMINATION AND QUANTIFICATION OF GLYCOSAMINOGLYCANS IN PHARMACEUTICAL FORMULATIONS USING micro-raman SPECTROSCOPY Eleni Kamilari 1, Christos Kontoyannis 1, 2, Fotini Lamari 1 and Malvina Orkoula 1,* 1 Department of Pharmacy, University of Patras 2 ICE/HT-FORTH, Patras Keywords: Glycosaminoglycans, Raman spectroscopy, pharmaceutical formulations ABSTRACT Glycosaminoglycans (GAGs), heteropolysaccharides of great biological importance, are found in biological systems, pharmaceutical formulations, as well as food supplements. A methodology based on Raman spectroscopy was constructed and successfully applied for the qualitative analysis of pharmaceutical formulations, as well as the qualitative and quantitative analysis of a Chondroitin Sulfate and Hyaluronic acid mixture found in a pharmaceutical formulation administrated by intrarticular injection in osteoarthritis. Identification of GAGs in the pharmaceutical formulations was performed by comparing their Raman spectra with those of pure substances. Spectral differences were used to identify individual glycosaminoglycans. Discrimination between various types of GAGs was achieved based on characteristic vibrational frequencies of the functional groups of these molecules. INTRODUCTION Glycosaminoglycans (GAGs) are complex negatively charged carbohydrate molecules that are present in the extracellular matrix of all animal cell surfaces. Glycosaminoglycans participate in many biological processes through the regulation of numerous cellular physiological functions, such as cell proliferation, differentiation, adhesion, cell-cell and cell-matrix interactions [1]. They are also thought to be involved in a variety of diseases and pathological conditions, including cancer and joint diseases [2, 3]. Glycosaminoglycans, including chondroitin sulfate (CS), hyaluronic acid (HA) and heparin (HEP), are found in pharmaceutical formulations, as well as in food supplements. Hyaluronic acid (HA) and chondroitin sulfate (CS) are used in ophthalmic solutions and in formulations administrated as drugs by intrarticular injection in cases of osteoarthritis in order to reduce pain. Nowadays, there are many nutritional supplements containing the above glycosaminolycans into the marketplace. Their use improves joint function and slows progression of osteoarthritis. Heparin is widely used as an anticoagulant agent. Several methods for the qualitative and quantitative determination of glycosaminoglycans require the enzymatic digestion of the polysaccharide in disaccharide units. Then, the disaccharides are separated using reverse-phase high performance liquid chromatography (HPLC) [4], anion exchange chromatography [5], agarose gel electrophoresis [6], capillary electrophoresis [7] or fluorophore-assisted carbohydrate electrophoresis [8]. Another analytical method most commonly used for the determination of total amount of GAG is the carbazole reaction method [9]. However, the methods mentioned above, despite some advantages, are relatively time consuming and demand a high level of skill. Moreover, enzymes are expensive. Scope of the present study is the development of an easy to use, accurate and rapid method for the analysis of mixtures of GAGs. For this purpose, Raman spectroscopy was chosen. Raman spectroscopy is a vibrational technique that provides information related to the vibrations of chemical bonds that exist in the specimen and thus make it suitable not only for the qualitative analysis but also for the quantitative analysis of the specimen. Raman analysis is done simultaneously for all constituents and no previous separation is needed. The collected Raman signal is the sum of individual signals of the components of the specimen. MATERIALS AND METHODS Various pharmaceutical products in the form of solutions or tablets containing chondroitin sulfate (CS), hyaluronic acid (HA) or heparin (HEP) were examined in the present study and are presented in the following table.

2 Table 1. Pharmaceuticals analyzed in this study, type of GAG contained, their form, as well as their use (HA: hyaluronic acid, CS: chondroitin sulfate, HEP: heparin) Name GAG contained Pharmaceutical form Use Hye HA Solution Ophthalmic solution Hyalart HA Solution Intra-articular injection for osteoarthritis Heparin Leo HEP Solution Anticoagulant Solgar CS Tablet Food supplement Synovium HA, CS Solution Intra-articular injection for osteoarthritis No sample pre-treatment was performed. Specimens were deposited on a highly reflectivity gold-coated glass slide. In cases of solutions, one droplet of each sample was deposited on the slide and was left to dry. Raman spectra were recorded using a Renishaw spectrometer coupled with an optic microscope (Renishaw, InVia, Raman microscope, UK). A laser line at 785 nm (diode laser) was used for excitation. The system was equipped with a charge-coupled device (CCD) air-cooled detector. Raman spectra were acquired from various points of the specimen under the same conditions, by focusing the laser line through the objective lens (50x) of the optic microscope onto the sample s surface. In order to construct calibration curves, mixtures of chondroitin sulfate with increasing amounts of hyaluronic acid (0%, 1% and 2% w/v), as well as mixtures of hyaluronic acid with increasing amounts of chondroitin sulfate were prepared by adding the appropriate amounts of solids and dissolving in ultrapure water. Raman spectra of each sample prepared were acquired after the deposition and dehydration of a droplet on the highly reflectivity gold-coated glass slide. RESULTS AND DISCUSSION Raman spectra of pure substances Pure chondroitin sulfate, hyaluronic acid and heparin were characterized by means of Raman spectroscopy and the recorded spectra are presented in figure 1. The stronger in intensity peak in the Raman spectrum of chondroitin sulfate and heparin is located at approximately 1070 cm -1 and is attributed to the symmetric stretching vibration of the sulfate groups (OSO - 3 ) [10, 11]. The absence of the particular vibration is observed in the Raman spectrum of hyaluronic acid (HA) which is the only unsulfated glycosaminoglycan. Other important vibrations which are related to the functional groups of these molecules are found in the spectral regions: cm -1 (spectral region A), cm -1 (spectral region B) and cm -1 (spectral region C)..

3 Figure 1. Raman spectra of chondroitin sulfate (CS), heparin (HEP) and hyaluronic acid (HA). Qualitative analysis of glycosaminoglycans in pharmaceutical formulations Two pharmaceutical preparations containing hyaluronic acid were analyzed with Raman spectroscopy and the results are demonstrated in figure 2. Figure 2. Raman spectra of two pharmaceuticals (Hye and Hyalart ) which contain hyaluronic acid and pure hyaluronic acid (HA).

4 As shown in figure 2, the Raman spectra of the hyaluronic acid formulations present similar spectral profile with that of hyaluronic acid and consequently the presence of hyaluronic acid is easily verified in the samples. The same methodology was applied as a means of determination of heparin in an anticoagulant drug. The acquired Raman spectra are depicted in figure 3. Despite the presence of excipients (Figure 3 Spot B), heparin (HEP) can be identified in the spectrum of the pharmaceutical product (Figure 3 Spot A) based on the characteristic vibrations of the sulfate group (OSO 3 - ) at 1070 cm -1 [10] and the bands at 825 cm -1 and 894 cm -1. The former is ascribed to the coupling of C-O-S and ring C-O-C vibrations, while the latter arises from C-O-S linkages [12]. In the case of the nutritional supplement in the form of tablet which contains chondroitin sulfate (CS), spectral analysis was challenging, as shown in figure 4, due to the presence of other components-excipients (Figure 4 Spot B). However, chondroitin sulfate was spotted in the examined sample (Figure 4 Spot A) due to characteristic Raman vibrations in the three regions of interest. Figure 3. Raman spectra of a drug (Spot A and Spot B) which contains heparin and pure heparin (HEP).

5 Figure 4. Raman spectra of a nutritional supplement (Spot A and Spot B) which contains chondroitin sulfate and pure chondroitin sulfate (CS). Simultaneous determination of chondroitin sulfate and hyaluronic acid in a pharmaceutical formulation The same methodology was applied for the simultaneous determination and discrimination of chondroitin sulfate (CS) and hyaluronic acid (HA) in a commercial preparation. The results are presented in figure 5. Identification of both GAGs in the specimen was easily performed comparing the Raman spectrum of the formulation with those of pure substances, but spectral differentiation was proved burdensome, due to structural similarities of the analyzed molecules. As a result, it is difficult to ascribe bands in the spectrum of the specimen to chondroitin sulfate or hyaluronic acid. However, discrimination between GAGs was accomplished based on characteristic vibrational frequencies of the functional groups of these molecules. Bands at 858 cm -1 and 940 cm -1 correspond to chondroitin sulfate s vibrations. The former arises from vibrations of C-O-S linkages, while the latter is correlated to C-O-C linkage vibration [11]. Bands at 897 cm -1 and 950 cm -1 arise from hyaluronic acid and are ascribed to C-H vibrations and C-O-C linkage vibrations respectively [13]. The peaks in the Raman spectra of chondroitin sulfate and hyaluronic acid at 1344 cm -1 and 1332 cm -1 respectively are identified as the CH 2 deformation modes. Another significant distinguishing feature is chondroitin s sulfate band at 1071 cm -1 arising from sulfate group (OSO 3 - ) as hyaluronic acid has no sulfate groups. Quantitative analysis of chondroitin sulfate or hyaluronic acid in a pharmaceutical formulation Mixtures of hyaluronic acid (HA) and increasing amounts of chondroitin sulfate (CS) (0%, 1% and 2% w/v) were prepared and analyzed with the aid of Raman spectroscopy in order to quantify chondroitin sulfate in a pharmaceutical preparation. Deconvolution of overlapped bands and band fitting was achieved using an appropriate software (Peakfit v4.0, Jandel Scientific, San Rafael, CA). Figure 6 shows the deconvoluted Raman spectra of the hyaluronic acid - chondroitin sulfate mixtures under the cm -1 spectral region. In this region major spectral differences between the examined glycosaminoglycans are observed and are related to the vibration of the sulfate group which is present only in chondroitin sulfate s spectrum (at 1070 cm -1 ) and the vibration at 1128 cm -1 which is characteristic in hyaluronic acid s spectrum.

6 Figure 5. Raman spectra of a commercial pharmaceutical which contains hyaluronic acid and chondroitin sulfate (Synovium ), pure chondroitin sulfate (CS) and pure hyaluronic acid (HA). Figure 6. Deconvolution and band fitting under the envelope cm -1 on Raman spectra of HA-CS mixtures; A: 1% w/v HA+1% w/v CS, B: 1% w/v HA+2% w/v CS. As explained above, the ratio of peak amplitudes of the deconvoluted bands at approximately 1070 cm -1 and 1128 cm -1, attributed to chondroitin sulfate and hyaluronic acid respectively, were used for the construction of the calibration curve. Similarly, mixtures of chondroitin sulfate (CS) and increasing amounts of hyaluronic acid (HA) (0%, 1% and 2% w/v) were prepared in order to construct a calibration curve and to quantify hyaluronic acid in a pharmaceutical preparation. Figure 7 shows the deconvoluted Raman spectra of chondroitin sulfate - hyaluronic acid mixtures.

7 Figure 7. Deconvolution and band fitting under the envelope cm -1 on Raman spectra of CS-HA mixtures; A: 1% w/v CS+1% w/v HA, B: 1% w/v CS+2% w/v HA. The calibration curve was constructed using the ratio of peak amplitudes of Raman bands at approximately 1128 cm -1 and 1069 cm -1. The equations of both calibration curves, as well as the correlation coefficients, are tabulated in table 2. Table 2. Types of mixtures studied and values of intercept, slope and correlation coefficient (R 2 ) of calibration curves No. Mixtures studied Intercept Slope R 2 I HA-CS R 2 = II CS-HA R 2 = The concentration of chondroitin sulfate (CS) in the diluted formulation is estimated to be 0.79 % w/v and the relative error value is 1.25% against the theoretical value (0.80% w/v). The measured concentration of hyaluronic acid (HA) is 0.81% w/v with a relative error value of 1.25% compared to the theoretical concentration 0.80% w/v). The results are summarized in table 3. Table 3. Quantification of chondroitin sulfate (CS) or hyaluronic acid (HA) from a pharmaceutical GAG contained Theoretical concentration Determined amount (% w/v) (% w/v) Relative error (%) CS HA Note. Calibration curve No I (Table 2) was used for the determination of CS in the formulation, whereas the concentration of HA was calculated based on the calibration curve No II (Table 2). CONCLUSIONS The qualitative and the quantitative evaluation of glycosaminoglycans in pharmaceutical formulations play an important role in pharmaceutics. The absence of sample pretreatment, the ease of use, the accuracy, along with the fact that Raman spectroscopy offers the possibility of simultaneous and rapid analysis of all components with no need for previous separation, make it applicable for this kind of analysis.

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