The novel finding of the present study is that of VitD3 play a potential protective role in RE at an early stage. This study of the effects of VitD3 treatment in rat models of acute and chronic RE has the following major novel findings: (1) esophageal impairments occurred in rats with surgery-induced acute and chronic RE, as evidenced by macrographic and histopathological findings; (2) no significant differences in morphologic grading of esophageal mucosa were observed after VitD3 treatment in RE rats; (3) the protein expression levels of the pro-inflammatory cytokines, including IL-1β, IL-6, and IL-8, were significantly increased in both the acute and chronic RE groups, compared with the sham-surgery group; (4) VitD3 treatment significantly reduced the levels of these pro-inflammatory cytokines in both low-dose and high-dose VitD3 groups compared with the DMSO control group; and (5) serum calcium levels increased significantly in response to VitD3 treatment, while no abnormal alterations were observed on histological examination of the kidney tissues of these rats.
RE is considered a consequence of chronic inflammation of the esophagus occurring when mainly when the tissue is irritated by reflux of gastric acid. In the present study, rat models of acute and chronic RE were surgically induced using modified procedures, namely PNL-CARE, as we reported previously[16–18]. Macrographic and histopathological findings showed characteristic esophageal impairments in rats after surgical induction of acute or chronic RE. In addition, a number of key pro-inflammatory cytokines, specifically IL-1β, IL-6, and IL-8, were significantly elevated in the rat models of acute and chronic RE, which may be attributed to the inflammatory response in the esophagus after it is irritated by gastric acid reflux[20, 21]. Furthermore, using the rat models established in this study, we subsequently tested our hypothesis that VitD3 treatment could exert a beneficial effect in the inflammatory process occurring in acute or chronic RE.
It may merit attention that VitD3 treatment, either at a low dose or high dose, significantly reduced the levels of these important pro-inflammatory cytokines or mediators of the inflammatory process, including IL-1β, IL-6, and IL-8, in comparison with the cytokine levels in the control group. Especially, with the rat model of acute RE, we found that the experimental rats in the high-dose and low-dose VitD3 groups showed significant reductions in the levels of IL-1β, IL6, and IL-8 protein expression compared with those in the control groups. However, VitD3 seemed to affect the levels of IL-1β, IL6, and IL-8 protein expression differently between acute and chronic RE. In the chronic RE rats, VitD3 treatment slightly diminished the expression levels of IL-1β, IL6, and IL-8 protein in contrast to the control groups, and no difference between groups was observed. Although VitD3 treatment significantly suppressed the expression of these pro-inflammatory factors (IL-1β, IL6, and IL-8), there was no significant difference in the morphologic grading of the esophageal mucosa between the VitD3 treatment groups and control groups of rats with acute RE. Furthermore, considering that VitD3 was given after RE occurred, these findings suggest that VitD3 alone may not improve the esophageal impairments arising from the reflux of gastric acid into the esophagus in RE. We also noted that the serum level of calcium was markedly elevated after VitD3 treatment in rats, while histological findings of the kidney tissues detected no abnormality, indicating no renal toxicity in relation to excessive serum calcium. Collectively, excessive secretion of the pro-inflammatory factors is proposed as an early event in the development of RE[22], and our findings suggest that VitD3 has the potential to slow the development of RE.
This study has a number of limitations to consider. Although we showed that VitD3 diminished the expression of pro-inflammatory cytokines (IL-1β, IL-6, and IL-8) in rats, a further in-depth mechanistic study is needed to determine the molecular pathways through which it occurs. Additionally, two doses of VitD3 were used in the present study, and more doses of VitD3 should be tested for their effects on the pro-inflammatory cytokines and to examine if the effect could be dose-dependent. These studies are currently underway in our laboratory.
In conclusion, IL-1β, IL-6, and IL-8 are markedly elevated in RE, and abnormal increases in these important pro-inflammatory cytokines are suppressed by VitD3 in rats. Although no morphologic and histopathologic changes are observed with VitD3 treatment, these novel findings suggest a potential protective role for VitD3 in RE at an early stage. VitD3 holds promise to slow down the progression of ER or prevent ER, but further studies are needed in the future.