Одредување на ензимска активност на тиопурин метилтрансфераза и концентрација на 6-тиогванин и 6-метил меркаптопурин кај пациенти со воспалителни цревни заболувања третирани со азатиоприн

Abstract

Objectives: Thiopurine methytransferase (TPMT) is the most frequently analyzed enzyme, and usually routinely assessed in clinical practice in patients with inflammatory bowel disease (IBD) receiving azathioprine (AZA) therapy. By monitoring the concentration of active metabolites of AZA, 6-thioguanine-nucleotide (6-TGN) and 6-Methylmercaptopurine (6-MMP), the thiopurine treatment can be adjusted and personalized, and its adverse events minimized. Material and Methods: This study included a total of 63 patients with IBD (45 with Crohn's disease (CD) and 18 with ulcerative colitis (UC): patients that had indication for treatment with AZA, patients treated with AZA at the moment of this study and patients that had used AZA in the past, but due to some reason they had stopped. TPMT assessment was done using the ELISA method, according to which patients were divided into three subgroups: patients with low enzyme activity (<5.0 U/ml Er), patients with intermediate enzyme activity (5.0-13.7 U/ml Er) and patients with normal or high enzyme activity (>13.8 U/ml Er). Each of these groups was then analyzed according to the concentration of the metabolites, 6-TGN and 6-MMP (only in patients currently receiving AZA, determined with high performance liquid chromatography); therapeutic response, and the adverse events (AEs). Results: The mean value of TPMT enzyme in all patients was 18.49 U/mL Еr ± 8.27 U/mL Еr (min. 1.9 U/mL Еr, max. 35.8 U/mL Еr). 69.84% of patients had normal or high TPMT activity, 25.4% intermediate, while 4.76% had low enzyme activity. In patients who had AEs, a significantly lower mean value of TPMT enzyme was assessed in comparison with patients without AEs (13.96 U/mL Еr ± 8.69 U/mL Еr v.s. 18.43 U/mL Еr ± 7.22 U/mL Еr ) (p<0.05). Most of the patients with AEs belonged to the group with low TPMT enzyme activity, followed by the group with intermediate activity and normal or high TPMT enzyme activity (50% v.s. 18.38% v.s. 15.38%, respectively) (p>0.05). The majority of patients who achieved remission belonged to the group with normal or high TPMT enzyme activity (65.38%) (p>0.05). The mean value of 6-TGN concentration was 437.46 pmol/8x108 Er ± 198.82 pmol/8x108 (min. 64.8 pmol/8x108, max. 905.5 pmol/8x108). As the TPMT activity was increasing, the concentration of 6-TGN was decreasing (R=-0.3632). The largest percentage of patients with observed AEs had high 6-TGN concentration (18.75%), followed by the therapeutic group (14.29%). None of the patients who belonged to the sub-dosed group had AEs. As the concentration of 6-TGN was increasing, the remission rate was increasing, too (R=0.0819). The mean value of 6-MMP was 6497.87 pmol/8x108 Er ± 7462.02 pmol/8x108 Er (min. 283.3 pmol/8x108 Er, max. 31324.4 pmol/8x108 Er). As the TPMT activity was increasing, the concentration of 6-MMP was increasing, too (R=0.3431). Patients with AEs had higher mean value of 6-MMP when compared to those who were without AEs (7592.92 pmol/8x108Er ± 7534.19 pmol/8x108Er v.s. 6295.08 pmol/8x108Er ± 7575.19 pmol/8x108Er) (p>0.05). In 50% of patients in the group with AEs the mean value of 6-MMP concentration was >5877 pmol/8x108Er, in comparison with the group without AEs, where it was >2891 pmol/8x108Er in 50% of them. Conclusion: Patients with IBD who have low TPMT enzyme activity are at an increased risk of developing AE after azathioprine treatment. Both, patients with intermediate and those with normal or high TPMT enzyme activity are more likely to achieve remission when using AZA (54.55% v.s. 65.38%). Most of the patients with AEs belonged to the group with high AZA metabolites levels, 6-TGN concentration >400 pmol/8x108 Er and 6-MMP >5700 pmol/8x108 Er.