The albumin to globulin ratio is associated with mucosal healing in Japanese patients with ulcerative colitis: A cross-sectional study

Ulcerative colitis (UC) is a chronic inammatory disease. Mucosal healing (MH) is inversely associated with clinical outcome. The albumin to globulin ratio (AGR) is known as chronic inammation marker. some evidence regarding an association between AGR and some chronic diseases has been no study evaluated the between AGR and among patients with UC.


Results
The mean age was 51.2 years, and the percentage of male patients was 59.0%. The percentage of MH was 26.4%. High AGR (1.483 < AGR ≤ 1.643) and very high AGR (> 1.643) was signi cantly positively associated with MH (OR 2.21 [95% CI: 1.12-4.47], p for trend = 0.001) after adjustment for confounding factors. No association between AGR and partial MH was found. The independent positive association between AGR and MH was found in only low C-reactive protein group.

Conclusion
Among Japanese patients with UC, AGR was signi cantly positively associated with MH, was signi cantly positively associated with MH especially in the low C-reactive protein group.

Background
Ulcerative colitis (UC) is a chronic in ammatory bowel disease (IBD) characterized by a disease course involving relapses and remissions [1]. Mucosal healing (MH) is inversely associated with clinical relapse, rates of hospitalization and surgery, and incidence of colorectal cancer [2][3][4][5][6][7]. Thus, MH has been indicated as the therapeutic goal for UC.
The prospective studies have shown that strict control based on monitoring of in ammatory biomarkers and maintenance of MH [8]. The concept of the treat-to-target in UC had accepted to improve the prognosis. The implications of MH had led to improved endoscopic and clinical outcomes. Colonoscopy ndings are essential for assessing MH and Fecal calprotectin (FC) is most reliable marker for MH. However, repeated endoscopy and stool examination are extremely burdensome for patients. repeated fecal examinations may be distressing for women, the young, or patients without symptoms. More serum markers for MH that can be measured repeatedly, easily, and rapidly is needed for achieve the concept of the treat-to-target among ulcerative colitis.
Albumin and globulin are the two major components of serum proteins. The albumin to globulin ratio (AGR), calculated as serum albumin/ (total protein -albumin), has been used one of marker for chronic in ammation. AGR has been reported to be a prognostic marker in patients with cancers [9][10][11][12][13][14][15], chronic heart failure [16], stroke [17], and sarcoidosis [18]. However, no evidence regarding association between AGR and clinical outcomes among patients with UC exits. Thus, we aimed to evaluate the association between AGR and MH among Japanese patients with UC.

Study population
The study subjects consisted of 387 Japanese patients with UC at the Department of Gastroenterology and Metabology at the Ehime University Graduate School of Medicine, and at several a liated hospitals in Ehime prefecture (The Ehime Clinical Network for Alimentary Diseases study group). All patients were diagnosed with UC according to endoscopic, radiological, histological, and clinical criteria. After 114 patients were excluded due to incomplete data, the nal analysis sample in this study consisted of 273 patients assessed for endoscopy examination, medication, serum albumin, and serum globulin. The study protocol conforms to the ethical guidelines of the 1975 Declaration of Helsinki (6th revision, 2008). This protocol was approved by the Institutional Review Board of the Ehime University Graduate School of Medicine (1505011). Well trained staff obtained written informed consent from all patients enrolled.

Measurements
Information on endoscopic ndings, age at onset of UC, use of drugs for UC, C-reactive protein (CRP), AGR was collected using medical records and self-. Serum albumin, globulin and CRP were determined from routine blood levels obtained from patient les at the time the patients were included in the study. Blood samples were taken the morning after overnight fasting. Blood examination was collected when a colonoscopy is reserved or when the colonoscopy examination is performed. There could be a time difference of about two months. Height was measured to the nearest millimeter using a stadiometer with the patients standing completely erect. Weight was measured in light clothing. BMI was calculated as weight in kilograms divided by square height in meters.

De nition of mucosal healing
We evaluated mucosal status by total colonoscopy. The Mayo endoscopic score (MES) consists of the following four categories [19]: 0, normal or inactive disease; 1, mild disease with erythema, decreased vascular patterns, and mild friability; 2, moderate disease with marked erythema, absence of vascular patterns, friability, and erosions; 3, severe disease with spontaneous bleeding and ulceration. MH and partial MH were de ned as category 0 and 0-1, respectively, in this study. One endoscopic specialist was responsible for evaluating MES and MH, and was blinded to AGR.

Statistical analysis
AGR was divided into quartiles on the basis of the distribution of all study subjects. AGR level was classi ed into four categories: 1) low AGR, < 1.281 (reference); 2) moderate AGR, 1.281-1.483; 3) high AGR, 1.483-1.643; and 4) very high AGR, > 1.643. Estimations of crude odds ratios (ORs) and their 95% con dence intervals (CIs) for MH and partial MH in relation to AGR were performed using logistic regression analysis. Multiple logistic regression analyses were used to adjust for potential confounding factors. Age, sex, steroid use, BMI, onset age, and anti-TNFα preparation were selected a priori as potential confounding factors. A receiver operating characteristic (ROC) curve was generated, and the area under the curve was calculated to indicate the utility of the AGR for mucosal healing. We used Youden Index to calculate the cut off value of platelet. Statistical analyses mainly were performed using SAS software package version 9.4 (SAS Institute Inc., Cary, NC, USA). ROC curve, cut off value of AGR, sensitivity and speci city were analyzed using JMP 14.2 (SAS Institute Inc., Cary, NC, USA). All probability values for statistical tests were two-tailed, and P < 0.05 was considered statistically signi cant. Table 1 shows the characteristics of the 273 study participants. The mean age was 51.2 years, and the percentage of male patients was 59.0%. Use of 5-aminoasalicylates, prednisolone, and TNF-α monoclonal antibody preparations were reported at 90.8%, 21.3%, and 5.9%, respectively. The percentage of MH was 26.4%, and the mean AGR was 1.461 ± 0.291. In this cohort, median CRP was 0.099 mg/dl. The ROC curve of AGR for identifying the mucosal healing had an area under curve of 0.613 ( Fig. 1)    OR, odds ratio; CI, con dence interval; AGR, albumin to globulin ratio; CRP, C-reactive protein

Discussion
In the present study, AGR was independently positively associated with MH among 273 Japanese patients with UC, and ours is the rst such study to show a signi cant positive association between AGR and MH among patients with UC. AGR is independently positively associated with MH but not partial MH among patients with only low CRP UC.
Albumin and globulin are the two major components of serum proteins, and their levels correlate with systemic in ammation [11][12][13]. Albumin maintains osmotic pressure and functions [20]. Low serum albumin is associated with not only nutritional status but also chronic in ammation [13,21]. Low serum albumin could weaken the human immune system, thus increasing susceptibility to infection and resulting in cytokine-induced suppression [22,23]. On the other hand, globulin consists of all types of proin ammatory proteins. A high level of globulin indicated a systematic in ammatory response [24]. Serum globulin level is thought to re ect the degree of continuous systemic in ammation. AGR is less sensitive and less susceptible to measurement variability such as dehydration or uid retention since it is a ratio rather than an absolute value [9].
AGR has been reported to be a prognostic marker in patients with colorectal [8], lung [10], and breast cancers [11]. Furthermore, AGR is an independent predictor of mortality in patients with chronic heart failure [16]. AGR is signi cantly inversely associated with cardiovascular diseases and incidence of stroke [17,25]. Additionally, an inverse association between AGR and the clinical activity was reported among patients with sarcoidosis [18]. The ndings in the present study consistent with these ndings regarding the AGR and clinical outcomes.
Colonoscopy ndings are essential for assessing mucosal status in patients with UC and determining treatment strategies. FC is useful and reliable marker for MH. However, repeated endoscopy is extremely burdensome for patients. Similarly, repeated fecal examinations may be distressing for the young, women, or patients without symptoms. Additionally, colonoscopy and FC might be not suitable for assessment for early response for medication. AGR is simple, rapid, relatively non-invasive, repeatable, and can be measured at all medical institutions. AGR monitoring might be useful to assessment disease activity, treatment response, and prognosis especially among UC patients with low CRP level. However, further research is needed for assessment AGR as a biomarker for diseases activity among patients with UC.
The underlying mechanism linking AGR and MH remains unclear, but there are several biologically plausible options. Serum albumin is known to decrease during in ammation [26]. In fact, in 43 patients with UC, CRP was signi cantly inversely associated with serum albumin [27]. Because of intestinal tract in ammation, protein loss from the gut and malnutrition may in uence serum albumin levels [28]. AGR was associated with plasma TNF-α levels in community-dwelling Japanese elderly women [29]. Levels of α1 globulins (α1-antitrypsin, thyroid-binding globulin, and transcortin) and α2 globulins (ceruloplasmin, α2-macroglobulin, and haptoglobin) are also increased in acute in ammation [30]. Intestinal tract in ammation might elevate AGR with protein loss and elevated TNF-α.
This study has several limitations. First, this was a cross-sectional analysis; therefore, we cannot conclude that there is a causal association between AGR and MH. Second, in this cohort, the sample size was small. Third, the exclusion rate was high. Fourth, we could not estimate the dietary intake of protein.
Fifth, most of the patients have been receiving treatment for UC. The long duration of medication might therefore might affect AGR value. Finally, the current study patients might be an unrepresentative sample of Japanese patients with UC. The use of medication in Japanese study based on claims data were similar to those in the present study [31]. However, since this cohort consist of Japanese patients, the ndings in the present study might not be generalized to other cohorts.

Conclusions
Among Japanese patients with UC, AGR may be independently positively associated with MH was signi cantly positively associated with MH especially in the low C-reactive protein group. The study protocol was approved by the institutional review board of the Ehime University Graduate School of Medicine (1505011). Well-trained staff obtained written informed consent from all patients enrolled.

Consent for publication
Not applicable.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Funding
Not applicable.  Receiver operating characteristic curve of AGR for identifying the mucosal healing based on Mayo endoscopic subscore 0. The receiver operating characteristic (ROC) curve AGR for identifying the mucosal healing had an area under curve of 0.613. When cut off value of AGR was determined as 1.52, the sensitivity and speci city were 60.6% and 62.1%, respectively. We used Youden Index to calculate the cut off value of AGR