Decreased Chitotriosidase Activity and Levels in Familial Mediterranean Fever

Familial Mediterranean fever (FMF) is an autosomal recessive autoinflammatory disease. Recurrent fever, abdominal attacks, pleural attacks, prodromes, and pericarditis are common clinical manifestations of FMF. Mutations in the Mediterranean fever (MEFV) gene encoding of a protein called pyrin appear to cause the disease in many cases. Mutations have been widely found in exons 1, 2, 3, 5, 9, and 10 of the MEFV gene. The five most frequent mutations are E148Q, M680I, M694V, M694I, and V726A (1, 2, 3). Whereas FMF is widely found among Mediterranean and Middle Eastern populations, sporadic cases have been reported in the Far East (4).

Abnormal innate immune system activation, which is responsible for activating inflammasome, is the main player in the pathogenesis of autoinflammatory diseases (5). The proposed molecular mechanism in the pathogenesis of FMF is increased inflammasome activation due to restricted pyrin expression (6). Inflammasomes activate caspase 1 and trigger the release of pro-inflammatory cytokines, such as interleukin-1β (IL-1β) and IL-18. These cytokines stimulate neutrophils and macrophages and induce an inflammatory response (7).

Two different phenotypes (types 1 and 2) might be seen in patients with FMF. Type 1 is characterized by short recurrent episodes of inflammation. The episodes may last from 24 to 72 hours and have variable frequency. The frequency of attacks may vary from once per week to once every 5–10 years. Approximately half of the affected individuals report experiencing a prodrome of discomfort and/or psychological uneasiness up to 24 hours before the actual attack (1, 2). Colchicine is used in the treatment of FMF. It reduces the frequency of attacks and prevents amyloidosis (8).

Chitotriosidase (ChT) is a member of the chitinase family capable of hydrolyzing chitin. This enzyme is mainly secreted from activated and differentiated macrophages, therefore, ChT is a marker of macrophage activation (9). Human ChT is associated with Gaucher’s disease, lysosomal storage disorders, sarcoidosis, Crimean Congo hemorrhagic fever, and beta-thalassemia (10, 11, 12, 13). It has also been indicated that ChT can be up-regulated during the immunological response in other acute or chronic inflammatory conditions (14). Therefore, we wanted to investigate whether differences in ChT concentrations or activity could be seen in patients with FMF.

The purpose of this study was to investigate the changes in the activity and concentration of ChT in FMF patients compared to healthy controls. To the best of our knowledge, this is the first study to evaluate both ChT activity and concentrations in FMF patients.

The patients had a median duration of illness of 72 (2–360) months. The baseline characteristics of the study population are given in Table 1. The genotype and frequency of the detected mutations in the patients are provided in Table 2. Median ChT activity was 10.00 (6.00–15.00) nmol/mL/hr and 14.00 (6.25–20.75) nmol/mL/hr in the patients and controls, respectively. A statistically significant difference was found in the ChT activity between the controls and the patients (P = 0.027). The median ChT concentrations were 65.40 (46.20–84.92) pg/mL and 125.00 (75.72–143.95) pg/mL in the patients and controls, respectively. There was also a statistically significant difference between the controls and patients in terms of ChT concentrations (P < 0.001). The results are expressed as median percentiles (25th–75th). ChT activity, ChT levels and CRP concentrations in controls and patients have been given with boxplot in Fig. 1A, 1B and 1C, respectively. The mean C-reactive protein (CRP) was 2.58 ± 1.83 mg/dL and 34.20 ± 4.5 mg/dL in patients with an acute attack and an attack-free period, respectively. A statistically significant difference was observed in patients with an acute FMF attack compared to those in an attack-free period in terms of C-reactive protein (CRP) (P < 0.001). However, we did not find any significant difference in terms of the activity (P = 0.136) and concentrations (P = 0.331) of ChT between patients with an acute attack and an attack-free period. We also did not find any statistically significant correlation between ChT activity (P = 0.978, r = 0.003) or concentrations (P = 0.446, r = −0.87) and C-reactive protein concentrations in the patients.

Table 1 Baseline characteristics of study population Click for larger imageClick for full tableDownload as Excel file

Table 2 Genotype and frequency of detected mutations in patients Click for larger imageClick for full tableDownload as Excel file

Fig. 1 Box plots for patients and controls. (A) Chitotriosidase activity. (B) Chitotriosidase levels. (C) CRP levels. The image of each group shows the box with median (horizontal line within the box); the interquartile range (IQR), corresponding to the 25th–75th percentiles (lower and upper limit of the box); nearest observations within 1.5 IQRs (the whiskers) and outliers (circles within 3 IQR). Click for larger imageDownload as PowerPoint slide

Human ChT is a chitin fragmenting enzyme. Although the physiological functions of this enzyme are still unclear, there is evidence that ChT plays a role in the innate immune system (16, 17, 18). Different studies have demonstrated changes in ChT activity and concentrations in multiple diseases (10, 11, 12, 13). However, these changes have not been concurrently evaluated in patients with FMF. FMF is a chronic inflammatory and autosomal recessive disorder. Turkey is one of the countries that has the highest number of patients with FMF. Proteins encoded by Mediterranean fever (MEFV) called pyrin and marenostrin are secreted by neutrophils and macrophages. These proteins regulate the secretion of proteins in neutrophils and macrophages. Point mutations (single substitutions) in the MEFV gene have an important role in FMF pathogenesis. However, the diagnosis of FMF has been made principally according to clinical findings, and has been frequently applied to the MEVF mutation analysis in the case of patients in whom FMF is suspected (19, 20, 21).

Taylan et al. (22) demonstrated increased concentrations of ChT in patients with FMF. Contrary to this study, we found lower ChT activity and concentrations in patients with FMF. To date, it has been thought that the main, and even the only, source of serum ChT is activated macrophage (12, 23, 24, 25). However, it has been demonstrated that polymorphonuclear neutrophils are also a source of ChT (26). Colchicine inhibits the chemotaxis of neutrophils and the release of arachidonate and 5-lipoxygenase in macrophages (27). In our study, 76 patients were receiving colchicine. We thought that the reason for the reduced ChT concentrations and activity in patients with FMF was colchicine use. Colchicine might reduce the expression and activity of ChT by preventing neutrophil leucocytes chemotaxis and macrophage activity.

Familial Mediterranean fever is characterized by periodic attacks that last 1–3 days. The major inflammatory process in acute FMF attacks is the activation of neutrophils in serosal and synovial surfaces. It has been determined that CRP is the only acute phase protein raised during the acute attacks of patients with FMF (28). In our study, we found higher CRP concentrations in patients with an acute FMF attack than in those in an attack-free period. However, we did not find any statistically significant differences in the ChT activity and concentrations in patients with an acute FMF attack compared to those in an attack-free period. Additionally, we did not find any correlation between CRP and the activity and concentration of ChT. Our results are inconsistent with the results of Taylan et al. (22). The discrepancy between results might rely on the great differences in the study population number, the selection criteria for the patients, and differences in the received doses of colchicine. We believe that both ChT activity and concentrations cannot be used to determine and evaluate the acute attack period of FMF.

One of the limitations of the study was that the study population was made up of the same ethnic group, which cannot be generalized to other ethnic groups. Also, we did not adjust our data for body mass index. Another limitation was the lack of data about the patients’ ChT polymorphism.

In conclusion, the findings of the present study demonstrate that FMF patients have decreased ChT concentrations and activity compared to healthy controls. Additionally, we did not find any statistically significant correlation between enzyme activity and concentrations and disease activity. Our study is the first report that shows decreasing ChT concentrations and activity in FMF patients. According to our findings, serum ChT enzyme activity and concentrations may not be considered as a biomarker to evaluate disease activity and the prognosis of disease. However, more studies are needed to evaluate the changes in enzyme activity and the role of ChT in patients compared to colchicine negative patients.