The protective effect of naringenin on ulcerative colitis in mice through increasing Nrf2 pathway activity

Abstract

Ulcerative colitis (UC) is a chronic inflammatory disease with an increasing prevalence worldwide. Naringenin (NAR) has been proven effective in preventing UC, but its mechanism has not been fully elucidated. In this study, network pharmacology and bioinformatics methods are used to screen the genes associated with NAR and UC. A mouse model of dextran sulfate sodium (DSS)-induced UC is established. After treatment with NAR, the disease activity index (DAI) is scored, and colonic histopathology is observed via hematoxylin-eosin (HE) staining. The expressions of the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway and inflammation-related factors in the colons of UC mice are examined via western blot analysis and immunohistochemistry (IHC). The results of the animal experiments reveal that the model group of UC mice present the most severe weight loss and the highest DAI scores. After the administration of NAR, weight loss is alleviated, and DAI scores are reduced (P < 0.05). NAR improves pathological manifestations in the mouse colon, such as reducing inflammatory cell infiltration and restoring goblet cell loss (P < 0.05). NAR significantly increases the protein expression levels of Nrf2, heme oxygenase 1 (HO-1), and NAD(P)H dehydrogenase [quinone] 1 (NQO1) in the colon (P < 0.05) but decreases the protein expression levels of nuclear factor kappa-B (NF-κB), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) (P < 0.05), thus alleviating the inflammatory response in UC model mice.

1. Introduction

Ulcerative colitis (UC) is a chronic inflammatory disease characterized by symptoms such as abdominal pain, diarrhea, rectal bleeding, urgency to have bowel movements, bloating, anemia and weight loss [1]. The incidence of UC is increasing annually worldwide [2]. Its incidence is approximately 0.63 per thousand in Asia and the Middle East, 2.14 per thousand in the United States, 2.48 per thousand in Canada and even 5.05 per thousand in Europe [3]. The gradually increasing incidence of UC has become a global health concern.

The etiology and pathogenesis of UC are not fully understood, but they are believed to be associated with factors such as immune dysfunction, genetic predisposition, environmental influences, gut microbiota, and psychological factors [4]. Nrf2 is a basic leucine zipper protein that is capable of regulating the expression of antioxidant proteins. It plays a key role in various physiological and pathological processes, such as metabolism, inflammation, autophagy, and the immune response [5]. Under oxidative stress stimulation, Nrf2 transcriptionally activates the expression of heme oxygenase 1 (HO-1). HO-1 can catalyze the conversion of heme into carbon monoxide (CO), bilirubin, and free iron. Therefore, CO can inhibit the nuclear factor kappa-B (NF-κB) pathway, leading to a reduction in the expressions of proinflammatory cytokines. HO-1 can also inhibit the production of tumor necrosis factor-α (TNF-α), IL-6, and other inflammatory factors, thereby suppressing the development of inflammation [6]. During the occurrence of UC, NF-κB is activated, resulting in the transcription of various cytokine genes, such as cyclooxygenase-2 (COX-2), TNF-α, and interleukin-1β (IL-1β). TNF-α and IL-1β prompt the generation of matrix metalloproteinases, resulting in the impairment of the extracellular matrix and mucosa [7]. In colonic myofibroblasts, the activation of NF-κB may increase the expressions of chemokines. This process plays a vital role in attracting neutrophils to the site of inflammation and contributes to the onset and progression of inflammation [8].

Previous studies have shown that NAR activates Nrf2, leading to increased expressions of HO-1, NQO1, and superoxide dismutase (SOD). It also reduces the production of reactive oxygen species (ROS), thereby inhibiting the NF-κB-mediated inflammatory response [9]. The NF-κB signaling pathway is intimately associated with the inflammatory response of the immune system. It plays a crucial role in regulating the body’s inflammatory response and transcription of various inflammatory cytokine genes, leading to excessive production of inflammatory cytokines such as TNF-α and IL-1β. This disruption of intestinal mucosal homeostasis contributes to inflammation in UC [10].

UC cannot be completely cured, and its chronic course can lead to the progression of this inflammatory disease to colorectal cancer, increasing the risk of mortality for patients [11]. Currently, the main treatment options for patients with UC include aminosalicylates, corticosteroids, immunosuppressants, biologics, and probiotics. However, these med