Macrophage polarization induced by short-chain fatty acid attenuates acute lung injury in sepsis

Jinlan MA; Ge YANG; Yujie MA; Qinfu LIU; Xiaojun YANG

ABSTRACT

Objective:

To explore the effect of short-chain fatty acid (SCFA) on acute lung injury (ALI) in sepsis via macrophage polarization.

Methods:

① Clinical trial 30 sepsis patients admitted to the intensive care unit (ICU) of General Hospital of Ningxia Medical University from January to December in 2022 and 10 non-sepsis patients in the same period were enrolled, stool samples were collected on the first day of admission, and SCFA butyric acid level in the two groups were studied by targeted metabolomics. ② Animal experiment male C57BL/6J mice were selected and randomly divided into sham operation group (Sham group), sepsis caused by cecal ligation and perforation (CLP group) and SCFA intervention group (SCFA group, sodium butyrate 25 mg/kg was given by gavage 1 hour after CLP), with 6 animals in each group. Twenty-four hours after molding, the state of mice was evaluated by mouse sepsis score (MSS), the degree of pulmonary edema was evaluated by calculating the wet/dry ratio (W/D), and the pathological changes of lung tissue were observed by hematoxylin-eosin (HE) staining, and lung injury score was performed. The serum levels of tumor necrosis factor-α (TNF-α), interleukins (IL-1β, IL-6, IL-10), nuclear factor-κB (NF-κB), and transforming growth factor-β (TGF-β) were detected by enzyme-linked immunosorbent assay (ELISA). Real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) was used to measure the mRNA expressions of inflammatory factors TNF-α, IL-1β, IL-6 and antioxidant factor nuclear factor E2-related factor 2 (Nrf2) in lung tissue. The expressions of macrophage polarization markers arginin-1 (ARG-1), CD206, inducible nitric oxide synthase (iNOS) and IL-1β in lung tissue were detected by immunohistochemistry.

Results:

① Compared with non-sepsis patients, SCFA-butyric acid level was significantly reduced in patients with sepsis (μg/g 34.56±6.61 vs. 1 150.67±381.90, P < 0.01). ② Compared with the Sham group, MSS, lung W/D ratio, lung injury score, the levels of serum inflammatory factors TNF-α, TGF-β, NF-κB, IL-10, IL-6, IL-1β, the mRNA expressions of lung tissue inflammatory factors and antioxidant factor Nrf2, M1 macrophage polarization markers ARG-1, CD206 and M2 macrophage polarization markers iNOS and IL-1β were significantly increased in the CLP group. Compared with the CLP group, MSS, lung W/D ratio, lung injury score, the levels of serum inflammatory factors TNF-α, TGF-β, NF-κB, IL-10, IL-6, IL-1β, the mRNA expressions of lung tissue inflammatory factors and antioxidant factors Nrf2, and M1 macrophage polarization markers ARG-1 and CD206 were significantly reduced [MSS 14.50±3.16 vs. 20.00±1.55, lung W/D ratio 4.60±0.18 vs. 5.51±0.59, lung injury score 47.56±2.36 vs. 88.30±6.04, serum TNF-α (ng/L) 27.99±0.58 vs. 69.55±18.53, serum TGF-β (μg/L) 9.82±2.16 vs. 18.73±1.83, serum NF-κB (μg/L) 1.23±0.09 vs. 1.95±0.28, serum IL-10 (ng/L) 78.39±2.29 vs. 140.22±19.82, serum IL-6 (ng/L) 300.64±77.60 vs. 1 442.52±494.14, serum IL-1β (ng/L) 33.13±0.99 vs. 38.39±1.31, lung IL-1β mRNA expression (IL-1β/β-actin) 1.01±0.01 vs. 2.24±0.62, lung IL-6 mRNA expression (IL-6/β-actin) 0.63±0.09 vs. 1.46±0.31, lung TNF-α mRNA expression (TNF-α/β-actin) 0.81±0.33 vs. 2.57±0.64, lung Nrf2 mRNA expression (Nrf2/β-actin) 1.59±0.25 vs. 2.96±0.89, ARG-1 positive area (36.27±2.89)% vs. (49.75±5.03)%, CD206 positive area (20.02±3.26)% vs. (44.24±3.61)%, all P < 0.05]. However, there was no significant difference in M2 macrophage polarization markers iNOS and IL-1β expression [iNOS positive area (18.32±2.23)% vs. (21.77±3.57)%, IL-1β positive area (40.42±4.78)% vs. (42.14±4.22)%, both P > 0.05].

Conclusion:

SCFA may alleviate ALI in sepsis by reducing M1 polarization of pulmonary macrophages.