Exploration of the mechanisms underlying the beneficial effect of Luo Tong formula on retinal function in diabetic rats via the “gut microbiota–inflammation–retina” axis

Abstract

Background Diabetic retinopathy (DR) is a common microvascular complication of diabetes. Luo Tong formula (LTF), a classical traditional Chinese medicine (TCM) prescription, consists of four plants that have been widely and effectively used to treat DR. Previous work in our laboratory has confirmed that LTF can effectively ameliorate DR. However, the potential mechanism underlying the therapeutic effect of LTF on DR has not been fully elucidated. To explore the potential mechanism of action through which LTF prevents and alleviates DR from an inflammation and gut microbiota perspective. Materials and methods Metabolite profiling of LTF was performed using liquid chromatography–mass spectrometry (LC–MS) and gas chromatography–mass spectrometry (GC–MS). Type 1 diabetes was induced in male Sprague Dawley (SD) rats via tail vein injection of 45 mg/kg streptozotocin. Next, 100 SD rats were randomly divided into four groups, normal control; diabetic control; diabetic + insulin + calcium dobesilate; and diabetic + insulin + LTF. After 12 weeks of treatment, glucose metabolism, fundus oculi, blood-retinal barrier permeability, retinal thickness, microvascular damage, as well as cell junction expression in retinas were measured and the changes observed in different groups were compared. Finally, the alteration in gut microbiota and inflammatory cytokine expression in serum and tissues were monitored, and their correlation was analyzed. Results A total of 1024 valid peaks were obtained for LTF using GC–MS. The HbA1c and fasting blood glucose (FBG) levels in the LTF group were slightly decreased. LTF exerted protective effects on fundus oculi and the retina structure to different degrees. LTF attenuated systemic and local retinal inflammation by significantly decreasing the levels of seven pro-inflammatory cytokines, including ICAM-1, IL-6, IL-8, MCP-1, VCAM-1, VEGF, and IL-1β. LTF restored the intestinal microbiota of diabetic rats to levels that were similar to those of normal rats. Further analysis revealed that Enterobacteriales, Prevotellaceae, Enterobacteriaceae, Bacteroides, and Klebsiella were significantly and positively correlated with the inflammatory factors in DR after LTF treatment. Conclusions Our results revealed the mechanisms underlying the preventive effects of LTF on DR development and progression. LTF inhibited pathological changes in retinal histopathology, cell composition, and cell junction proteins while effectively ameliorating systemic and local retinal inflammation via regulating pivotal gut microbiota.

Clinical observations and mechanistic insights of traditional Chinese medicine in the management of diabetic retinopathy

“…This finding led researchers to propose the concept of the ‘gut microbiota inflammatory visual network axis’ (Di et al. 2022 ). The association of this axis with chronic inflammatory states has been increasingly demonstrated in the development of DR.…”

Guiding modern traditional Chinese medicine research using the theory of state‐target differentiation and treatment—Maintaining the validity of traditional Chinese medicine and creating new medical science

“…Further investigations on the intervention mechanism of Luo Tong formula demonstrated that it could enhance the expression of cellular tight junction proteins and peripheral proteins to protect the blood–retinal barrier and reduce pathological damage. In addition, Luo Tong formula can significantly enrich beneficial bacteria such as Faecali and Corynebacterium and markedly decrease harmful bacteria such as Enterobacteriales and Bacteroides to effectively reduce systemic and local retinal inflammation [23].…”

Dysregulations of metabolites and gut microbes and their associations in rats with noise induced hearing loss

“…Recently, noise exposure was found to be associated with the imbalance of the host gut microbiota (Berlow et al, 2021;Chi et al, 2021). Chronic noise exposure was found to have promotive roles in the development of Alzheimer's disease (AD) and diabetes through the dysregulation of host gut microbiota (Verhaar et al, 2021;Di et al, 2022;Park and Wu, 2022;Wang et al, 2022). To provide new clues for the prevention and treatment of noise related disorders, it is necessary to investigate the dysregulations of metabolism and host gut microbes and explore their associations.…”