Even though miRNAs are considered as novel biomarkers for diagnosis of AHF, they are not established in clinical setting yet. These biomarkers have some advantages as compared to the established biomarkers such as NT-proBNP. The confounding factors which were indicated to affect the level of NT-proBNP such as age, obesity, sex, and renal function, do not have any significant influence on the level of miRNAs (17). Moreover, miRNAs can be detected in a variety of body fluids including blood, saliva, urine, milk, amniotic fluid, etc. (18). The current study investigated the applicability of selected miRNAs (including miR-1, -21, -23, and -423-5-p) in the diagnosis and prognosis of AHF patients. We found a significant elevation of these miRNAs in the plasma samples of AHF patients as compared to healthy control subjects. They also demonstrated impressive diagnostic power and significantly high sensitivity and specificity. The highest sensitivity and specificity in our study were seen in miR-423-5-p. However, we did not find any evidence supporting the prognostic value of these miRNAs. Even though, it does not rule out their applicability due to some limitations of our study which is discussed below. As far as the authors of the present study investigated, this is the first study that provides evidence for the diagnostic role of miR-21 in AHF patients. However, the diagnostic utility of miR-1, -23 and -423-5-p has been demonstrated in some previous studies (19-23), as well as, but there are some controversies. Corsten et al. (17) failed to detect any elevation in the level of miR-1 and -21 in AHF as compared to healthy controls. Also, Seronde et al. (20) postulated that the levels of miR-21 and miR-23 were similar among patients with AHF, stable CHF, and non-AHF with dyspnea. Moreover, miR-1 was significantly lower in AHF or stable CHF patients as compared to non-AHF with dyspnea. Zhang et al. (24) demonstrated a significant diagnostic value of miR-21 for CHF with a sensitivity of >99 percent, a specificity of 97.5 percent. A recent meta-analysis revealed that miR-423-5-p is an appropriate diagnostic biomarker for HF with a pooled sensitivity of 81 percent and a pooled specificity of 67 percent (25). Therefore, our study provided further confirmation on the diagnostic value of these miRNAs in AHF.
In the current study, we also investigated the levels of selected miRNAs in association with the cause of AHF and HF type based on EF and history of chronic HF (de novo or acute on chronic). However, we did not detect any significant differences in the levels of selected miRNAs in association with these outcomes, except for miR-21 and miR-23 which were significantly lower in patients with HF due to ischemic causes than those with non-ischemic causes. Previously, some similar unsuccessful results have been reported by other investigators. Elis et al. (19) also did not find any significant differences in the levels of miR-23 and miR-423-5-p between patients with HFrEF and HFpEF. Likewise, Seronde et al. (20) demonstrated no significant differences between de novo and acute on chronic AHF patients in terms of selected miRNAs including miR-1, -21, -23, and -423-5-p.
One year follow up of AHF patients in our study showed no applicability of these selected miRNAs in a one-year prognosis. Previously, Seronde et al. (20) also failed to detect any prognostic value for miR-1, -21, -23, and -423-5-p in terms of predicting readmission and one-year mortality. Cakmak et al. (26) postulated an upregulation of miR-21 in HF but reported that it had no significant prognostic value. However, Zhang et al. (10) demonstrated a significant correlation of miR-21 with patients’ two-year mortality but not with readmission rate. Schneider et al. (27) reported that increased level of miR‑21 at the time of clinical compensation was associated with better two-year survival and longer rehospitalization‑free. Furthermore, they demonstrated that higher miR‑423‑5p between the time of admission and clinical compensation was associated with fewer hospital readmissions in two-years. Therefore, the time of acquisition of plasma samples may affect the prognostic applicability of miRNAs.
Our study had some limitations. Although epidemiologic studies report that there are higher proportions of patients with HFpEF, there were few patients with HFpEF in our study. However, the inclusion of the patients in this study was completely random and we did not select the patients based on their HF type. Additionally, relatively small sample size in our study prevented us to evaluate accurately the level of miRNAs among AHF patients with different characteristics. Also, we had a relatively high rate of loss to follow up (20%), therefore, the same problem existed in the analysis of the patients’ follow up data. Even though, 20 percent is suggested to be an acceptable rate for loss to follow up (28). However, financial limitations prevented us to include more patients. Furthermore, it was better to compare AHF with other patients with dyspnea instead of healthy control. Moreover, a two-gated study design can be assumed as another source of bias for our study which should be avoided in future studies. Finally, although the diagnosis of the patients was assigned by two attending cardiologists and we tried to meticulously evaluate patients to assign the diagnosis according to the current established guidelines, it was better to confirm the patients’ diagnosis with an objective test such as NT-proBNP. However, performing this test was not feasible for us.