Methylene Blue Alleviates Inflammatory and Oxidative Lung Injury in a Rat Model of Feces-Induced Peritonitis.

Background and

Objectives

Feces-induced peritonitis (FIP), a clinically relevant model of polymicrobial sepsis, induces systemic inflammation and acute lung injury (ALI). Methylene blue (MB), a phenothiazine-based compound, exhibits vasoregulatory, antioxidant, and anti-inflammatory properties in the context of sepsis. This study aimed to evaluate the protective effects of MB on pulmonary injury in a rat model of FIP-induced sepsis. Materials and

Methods

Forty male Wistar rats were randomly assigned to four groups: control, FIP, FIP + Saline, and FIP + MB. MB was administered intraperitoneally at a dose of 20 mg/kg, 1 h after FIP induction. At 24 h post-induction, plasma levels of inflammatory markers [interleukin-6 (IL-6), interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), C-reactive protein (CRP)], oxidative stress marker [malondialdehyde (MDA)], metabolic indicator [lactic acid], and vascular signaling marker [cyclic guanosine monophosphate (cGMP)] were measured. Lung injury was evaluated through histopathological analysis and thoracic computed tomography (CT)-based Hounsfield unit (HU) quantification, while pulmonary function was assessed via arterial blood gas analysis, including arterial oxygen pressure (PaO2) and carbon dioxide pressure (PaCO2).

Results

FIP induction led to significant increases in plasma levels of IL-6, IL-1β, TNF-α, CRP, MDA, cGMP, and lactic acid, accompanied by elevated CT attenuation (HU) values and a marked reduction in arterial PaO2 and PaCO2. MB treatment significantly decreased the levels of IL-6, IL-1β, TNF-α, CRP, MDA, lactic acid, and cGMP, improved PaO2, and attenuated both histopathological lung injury and CT-assessed parenchymal density. No significant differences were observed in PaCO2 among the groups.

Conclusions

MB mitigates inflammation, oxidative damage, and pulmonary dysfunction in FIP-induced sepsis. Further studies are warranted to optimize dosing and timing and to evaluate long-term outcomes.