[Protective effect of the endoplasmic reticulum stress inhibitor 4-phenylbutyric acid against myocardial injury in septic mice].

OBJECTIVES

Endoplasmic reticulum stress (ERS) is an important pathophysiological mechanism involved in the development and progression of sepsis-related myocardial injury (SRMI). This study aims to investigate the protective effect of the ERS inhibitor 4‑phenylbutyric acid (4PBA) against myocardial injury in lipopolysaccharide (LPS)‑induced SRMI.

METHODS

An SRMI mouse model was established by intraperitoneal injection of LPS in male C57BL/6J mice. In experiment 1, mice were randomly assigned to 5 groups (n=6 per group): Control, LPS 6 h, LPS 12 h, LPS 24 h, and LPS 48 h groups. In experiment 2, mice were randomly assigned to 4 groups (n=6 per group): Control, LPS, tunicamycin (TM), and TM+LPS groups. In experiment 3, mice were randomly assigned to 4 groups (n=6 per group): Control, LPS, 4PBA, and 4PBA+LPS groups. In experiment 4, mice were randomly assigned to 4 groups (n=8 per group): LPS, TM, TM+LPS, and 4PBA+LPS groups. TM (0.5 mg/kg) was administered intraperitoneally 6 h before LPS injection, and 4PBA (10 mg/kg) was administered 6 h before and 6 h after LPS injection. Cardiac function was evaluated by echocardiography. Plasma cardiac troponin I (cTnI) and creatine kinase-MB (CK-MB) levels and cardiac tissue interleukin-1β (IL-1β) levels were measured by enzyme-linked immunosorbent assay (ELISA). Histopathological changes in myocardial tissue were examined using hematoxylin-eosin (HE) staining. Western blotting was performed to determine the expression of ERS-related proteins, including inositol-requiring enzyme 1α (IRE1α), phosphorylated protein kinase R-like endoplasmic reticulum kinase (p-PERK), cleaved-activating transcription factor 6 (cleaved-ATF6), spliced X-box binding protein 1 (XBP1s), CCAAT enhancer binding protein-homologous protein (CHOP), and glucose-regulated protein 78 (GRP78), as well as the inflammatory factor tumor necrosis factor-α (TNF-α), in cardiac tissue. An in vitro sepsis model was established by treating HL-1 mouse cardiomyocytes with LPS. Cardiomyocyte apoptosis and mitochondrial membrane potential (ΔΨm) were evaluated using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and JC-1 mitochondrial membrane potential assays, respectively.

RESULTS

Compared with the control group, left ventricular ejection fraction (EF) and fractional shortening (FS) in the LPS 6 h, LPS 12 h, LPS 24 h, and LPS 48 h groups initially decreased and subsequently recovered over time, whereas plasma cTnI and CK-MB levels and myocardial IL-1β levels initially increased and subsequently decreased; these differences were statistically significant (all P<0.05). The expression levels of the ERS-related proteins IRE1α, XBP1s, p-PERK, CHOP, cleaved-ATF6, and GRP78 in cardiac tissues were significantly increased (all P<0.05). Marked myocardial edema, myofibrillar disruption, and loss of vascular spaces were observed. Compared with the LPS group, the 4PBA+LPS group showed significantly increased EF and FS, significantly decreased plasma cTnI and CK-MB levels and myocardial IL-1β level, and significantly reduced expression of ERS-related proteins and the inflammatory factor TNF-α in cardiac tissues (all P<0.05). The 5-day survival rate of mice showed an increasing trend, accompanied by marked amelioration of myocardial histopathological injury. The TM+LPS group showed changes in the opposite direction to those observed in the 4PBA+LPS group. In the LPS-treated HL-1 cardiomyocyte model, mitochondrial membrane potential was significantly improved in the 4PBA+LPS group compared with the LPS group (P<0.05), while the proportion of TUNEL-positive cells was significantly reduced (P<0.05).

CONCLUSIONS

Activation of ERS aggravates LPS-induced SRMI, whereas 4PBA attenuates excessive ERS activation, alleviates the inflammatory response, reduces cardiomyocyte apoptosis, improves cardiac function, and decreases mortality. Targeting ERS may represent a potential therapeutic strategy for sepsis-related myocardial injury.