In this prospective observational study, FGF-21 and Irisin levels were found to decrease in the sarcopenic patient group compared to non-sarcopenic patients, while CRP was found to increase in comparison with non-sarcopenic patients. In this context, this study is the first one for new patients diagnosed with operated colorectal cancer, which has shown that FGF-21 and irisin can be associated with sarcopenia and inflammation, and inflammation may also play a role.
Previously, there were discussions about the relationship between levels of irisin in circulation and aerobic capacity [29, 30]. Some previous studies have demonstrated that circulating irisin levels are not associated with fat-free mass [31] but also ALM (appendicular fat-free mass) and HGS (muscle strength) [32, 33]. Building on them in the present study, we have shown reduced irisin levels in sarcopenic patients with cancer, despite other studies conducted on certain non-cancer patients that reported no association with sarcopenia. In a study conducted in healthy women, the levels of irisin circulating were shown to be in a positive relationship with the biceps muscle circumference (used as a backup marker for muscle mass) [34]. Stengel et al. reported that concentrations of irisin in circulation showed a positive correlation with fat-free mass using a bioelectric impedance analyzer [35]. In a study conducted by Chang et al. in 715 Korean individuals without cancer, the average levels of irisin in the sarcopenic group were lower than the non-sarcopenic group. The same study determined that in logistic regression models, the relationship between serum irisin concentration and event sarcopenia continued even after being adjusted to potential contradictions such as gender, age and fat indices [36]. In another study of non-cancer patients, the levels of irisin in circulation in sarcopenic patients were determined to be no different than those of control subjects, and skeletal muscle mass index was reported to indicate no correlation with such levels [37]. Although there are contradicting studies in the literature, these studied differed in terms of design and sarcopenia definitions as well as the methods they used to identify sarcopenia, which may account for inconsistent results. In our study, we determined sarcopenia by measuring it based on the current definition and recommended test method recommended by the EGSWOP. Moreover, unlike other studies, we conducted it in cancer patients. All these findings suggest a positive relationship between irisin and muscle physiology and metabolism, and that irisin also has a potential regulatory role.
Although FGF21 is shown to play a role in energy metabolism [15–17], it is a myokine that has been treated very poorly in the studies of cachexia and sarcopenia, and the available data are limited. Some studies have found a positive correlation between serum FGF21 levels and aging-sarcopenia [38, 39]. A study conducted by Hojman et al. reported a negative relationship between the FGF-21 level and the fat-free mass [40]. The degeneration of various body tissues and changes in metabolic activity, considered as part of the aging process, may affect the synthesis and release of FGF21. Adipocytes have been shown to be an important source of FGF21 production, whereas the liver was previously considered to be the main source of FGF21 in circulation [41]. More recently, the skeletal muscle expression and the release of FGF21 have been shown to cause a five-fold increase in the concentration of FGF21 in circulation [42]. This suggests that there may be a relationship between the quantity of muscle tissue and the level of FGF-21. Although our understanding of the systemic effects of muscular FGF21 has increased, FGF21's direct contribution to muscle function has not yet been investigated. With this study, we have shown that there may be a relationship between sarcopenia and FGF-21.
Our study detected a positive relationship between sarcopenia and CRP. Moreover, this relationship was maintained in the logistical regression analysis as well. In a study evaluating 100 patients with advanced lung cancer, 69% and 47% of patients presented cachexia and sarcopenia, respectively. That study found no significant difference in terms of CRP, IL-6 and albumin concentrations when compared with non-cachectic patients (p = 0.020, p = 0.040, p = 0.003); however, the relationship between inflammatory markers and sarcopenia was not investigated [43]. Although some studies detected a relationship between inflammation and sarcopenia [44–46], there are others that reported no relation [47]. A meta-analysis that did not include cancer patients showed no difference between basal sarcopenia and inflammatory markers (IL-6, TNF-a), but a positive relationship with CRP was reported [47]. Another study was reported to have a positive relationship between sarcopenia and highly-sensitive CRP (HsCRP), which continued in logistic regression [48].
In the present study, when assessing factors that may be associated with sarcopenia (age, gender, BMI, ECOG performance score, chronic disease, albumin level) there was an association only with male gender and BMI < 25. (p values, respectively: 0.015 and 0.019). The results of the present study were confirmed in a study conducted by Oflazoglu et al. in cancer patients [49]. Also, a meta-analysis published by Pamoukdjian on sarcopenia in patients with cancer reported that sarcopenia was more frequent in men [50]. In addition, we found that the incidence of sarcopenia was lower in obese and overweight patients (BMI > 25) than those with normal and low weight (BMI < 25). Supporting the findings of the present study, a study conducted by Brougmann et al. in 87 patients over the age of 70 with early-stage colorectal cancer reported that sarcopenia was associated with low BMI (p = 0.03) [51].
The present study was designed as a prospective observational study, but there were certain limitations. The first is that it was conducted with a limited number of patients. On the other hand, the recommended gold standard method for detecting sarcopenia is computed tomography. However, we used the bioelectric impedance device, which is a non-invasive method. Although the bioelectric impedance analyzer is a fast, non-invasive method for measuring body composition, its reliability can vary with an individual's hydration level, ethnicity, physical suitability, even if optimal conditions are provided.
In conclusion, the present study has shown that sarcopenia, irisin and FGF-21 have a negative relationship in operated non-metastatic colorectal cancer patients and pointed to a potential relationship between sarcopenia and inflammation. This suggests that these biomarkers could play a role in the physiopathology of sarcopenia. It further suggests that there may be a positive relationship between sarcopenia and inflammation. However, our results should be validated with different types of cancer and more patients.