Probiotics combined with aminosalicylic acid affiliates remission of ulcerative colitis: a meta-analysis of randomized controlled trial

Ulcerative colitis (UC) is a chronic intestinal inflammatory disease with increasing prevalence worldwide [1]. Chronic inflammation and colitis in colonic mucosa are the main features of UC. The disease course of UC could be very long and usually accompanied by persistent symptoms. It is quite difficult for UC to be cured [2]. UC affects the life quality of patients. Patients who have longer disease course of UC are more likely to get colon cancer [3]. The etiology and pathogenesis of UC have been extensively studied. Various hypotheses were proposed by different researchers. But until now, none of those hypotheses are perfect. At present, scholars believe that genetic factors, immune factors, intestinal mucosa barrier function factors, environmental factors, and microorganism factors might be related to UC [4]. Since UC is considered as an autoimmune disease, immune factors seem to play an important role in UC [5].

The treatment of UC is mainly anti-inflammation and immune response regulation [6]. In recent years, studies have found that severe intestinal flora imbalances are closely related to the occurrence of UC, so the research and application of microecological agents are getting more and more attention [7–9]. Accumulating evidences have suggested that intestinal microbiota plays an important role in the pathogenesis of this disorder [10,11]. Therefore, increasing clinical trials have been carried out to explore the effects of different probiotics in treating UC and suggested that probiotics could have beneficial effects on UC patients. However, many of these studies either have relatively small sample size or are not randomized controlled trials (RCTs). The meta-analysis based on a large data of RCTs could make the evidence more convincing. The present paper summarized the available literature before June 2018, which concerned the probiotic intervention studies for the management of UC, comparing the effects between probiotics and placebo, no additive treatment to standard therapy or mesalazine, addressing the clinical outcome parameters in UC subjects.

We followed the Cochrane Handbook for Systematic Reviews of Intervention to conduct this meta-analysis [12]. The results were reported in compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) [13]. The ethical approval is not applicable to the present study.

We conducted systematical online searches in the PubMed, Web of science, Embase, Wanfang, VIP (VIP Database for Chinese Technical Periodicals), and China National Knowledge Infrastructure database from inception to June 10, 2018. The following search words were used: probiotics, UC, RCTs, induction of remission, aminosalicylic acid, mesalazine, and sulfasalazine. We placed language restriction to Chinese and English. We also checked the reference lists of previous reviews to identify potentially eligible studies.

Two investigators (P.L.J. and Z.Y.) independently carried out the initial search. Any discrepancy was resolved by discussion and consensus. The included study had to meet the following criteria: (1) Population: children or adults with UC regardless of clinical setting. (2) Intervention: probiotics in conjunction with mesalazine or sulfasalazine or aminosalicylic acid. (3) Comparison: mesalazine or sulfasalazine or aminosalyicylic acid alone (4) Primary outcomes: remission rate. The latest data were used for duplicates. The reviews, comments, letters, animal study, or experimental study was excluded. Study with unavailable data were also excluded.

Two authors independently performed the data extraction using a standard excel sheet. Any disagreements were solved by consensus. For each study, the following information was extracted: the first author, publication year, degree of severity (mild to moderate, active stage), intervention versus comparison, probiotics types and number, doses for probiotics, treatment period (week), trial group (event and non-event), control (event vs non-event) sample size. We also contacted the corresponding authors to obtain the information, if required. We only focused on remission rate of patients with UC in the present study.

We used the Cochrane risk of bias tool to assess the quality of included studies [14]. This evaluation tool consists of random sequence generation, allocation concealment, blinding of participants, personnel-to-study protocol, blinding of outcome assessment, incomplete outcomes data, selective reporting, and other bias. The studies were classified as high risk, low risk, and unclear risk of bias according to the above criteria. The studies with more than one key domains were considered high risk of bias, those without all domains were considered low risk of bias. Otherwise, they were considered to be at unclear risk of bias.

In the present study, the relative risks (RRs) with 95% confidence intervals (CIs) were calculated to quantify the effect of probiotics combined with aminosalicylic acid on UC. Heterogeneity within studies was evaluated using I² statistic and Chi-square test, the I²>50% or P<0.05 indicated significant heterogeneity [15,16]. The random-effect model was used for heterogeneity. Subgroup analyses were also conducted in the following category: severity (mild to moderate vs active stage), number of probiotics (one type, two types, and three types), type of drug (mesalazine vs salicylazosulfapyridine [SASP]) and treatment period (4, 8, and 12 weeks). Sensitivity analysis was conducted to test the stability of pooled results. Publication bias was assessed by visually inspecting a funnel plot and trim and filled funnel plot, and the Begg and Egger’s test was also used [17]. All statistical analyses were completed using Stata 13.0 and RevMan 5.0. P<0.05 was considered significance.

The flowchart of study selection was presented in Figure 1. We first obtained 716 records from 6 online databases. After 314 duplicates records were removed, 402 records were prepared for further screening. 327 records were excluded by scanning titles and abstracts. We got 75 records for full-text articles assessed for eligibility. 49 studies were excluded including 28 unrelated topics, 4 studies with insufficient data, 7 reviews, and case reports. Twenty-seven studies were finally included in the qualitative and quantitative synthesis (Supplementary File S1).

The general characteristics of included studies were presented in Table 1. These studies were published from 2007 to 2018. The sample sizes ranged from 34 to 129, with a total of 1942 patients. Among these studies, 10 studies were conducted among patients with active stage UC, and 16 studies were conducted in patients with mild-to-moderate UC. For control group, 4 studies used SASP only, and 23 studies used mesalazine only. Twenty studies involved seven types of bacterium, including Bifidobacterium, Lactobacillus, Streptococcus thermophilus, Enterococcus faecalis, Clostridium butyricum, Bacillus subtilis, and Saccharum. Nine studies had one type of bacterium, two studies had two types of bacterium, and fifteen studies included three types of bacterium. The treatment period of most studies were 8 weeks, and eight studies were 4 weeks, and three studies were 12 weeks. The remission rate of trial group ranged from 15.4 to 82.9%, and the control group ranged from 7.7 to 71.9%.

The Supplementary Figures S2 and S3 presented the details of risk of bias. Overall, 12 studies were categorized as being at high risk, and the rest of studies were unclear risk of bias. The primary reason is the blinding of participants and personnel (performance bias). These studies did not report whether blinding method was used. The random sequence generation was perfect in all studies.

Twenty-seven studies totaling 1942 provided data on remission rate. Compared with aminosalicylic acid alone, the combination with probiotics significantly increased remission rate (RR = 1.40, 95% CI: 1.27–1.53, P=0.000, Figure 2) without heterogeneity (I²=0.0%, P=0.659). The subgroup analysis indicated that probiotics combined with aminosalicylic acid can significantly elevate the remission rate in both mild to moderate (RR = 1.33, 95% CI: 1.16–1.54, P=0.000, Figure 3A) and active stage (RR = 1.40, 95% CI: 1.27–1.64, P=0.000, Figure 3B) UC. One and three types showed that combination with probiotics can affiliate the remission of UC (RR = 1.36, 95% CI: 1.20–1.53, P=0.000; RR = 1.45, 95% CI: 1.24–1.70, P=0.000, Figure 4). There was no significance for two types of bacterium between the trial and control group (RR = 1.54, 95% CI: 0.88–2.69, P=0.130, Figure 4). For different mesalazine or SASP, the combination was still better than drug only. Significant differences were found in both types of drug (Figure 5, RR = 1.37, 95% CI: 1.23–1.52, P=0.000 vs RR = 1.56, 95% CI: 1.23–1.98, P=0.000). We also conducted subgroup analysis in different treatment periods, the results from fixed-effect model indicated that significant remission rate differences were found (8 weeks: RR = 1.51, 95% CI: 1.32–1.73, P=0.000; 4 weeks: RR = 1.36, 95% CI: 1.14–1.61, P=0.001, Figure 6). For 12 weeks, there were no significant differences (RR = 1.16, 95% CI: 0.95–1.43, Figure 6).

The sensitivity analysis was conducted by excluding one study each time and pooled the rest studies. The results indicated that no significant alteration was found (Supplementary Figure S4), which showed that the pooled results were stable.

The funnel plot was presented in Figure 7. There was a slight asymmetry in the funnel plot, which means publication bias may exists. The Begg and Egger’s test indicated that some publication bias existed (Z=2.000, P=0.045, t=7.050, P=0.000). We also used the trim and filled funnel plot to assess the publication bias. Eleven studies were needed to make the funnel plot balance (Supplementary Figure S5).

The present study comprehensively and systematically reviewed the current available literature and found that: (1) probiotics in conjunction with aminosalicylic acid can significantly increase the remission rate of UC compared with aminosalicylic acid alone. There was no significant difference between combined with mesalazine group and SASP group. (2) The results remained consistent in different number of bacterium, severity of UC, type of combined drug, and treatment periods (4 vs 8 weeks). (3) For a 12-week treatment, no significant effect difference was found between drug combination and single drug.

The pathological and physiological mechanism of UC was complicated, including at least four interacting factors: gene, immune system, intestinal flora, and environment [18]. Compared with normal healthy people, the intestinal flora of most patients with UC had changed. It was reported that the intestinal flora had changed regardless of active period or the relieved period for patients with UC [19]. The number of Pseudomonas, Bifidobacterium, Helicobacter spiralis, Fragile pseudomonas, and Clostridium difficile had decreased while the number of Enterococcus and Bacillus increased. Therefore, it is theoretically possible to alleviate the active period of UC by correcting the imbalance of bacterial flora through probiotics [20]. The possible mechanisms of probiotics in the treatment of UC included inhibiting the growth pathogenic bacteria, improving the function of epithelial mucosal barrier, regulating immunity, and reducing the secretion of proinflammatory factors. Previous studies evaluated the maintenance effect of probiotics versus that of aminosalicyates on UC. A meta-analysis with six RCTs and a total of 721 participants indicated that no significant difference was observed between probiotics and aminosalicylate (RR = 1.08, 95% CI: 0.91–1.28). However, the number of this meta-analysis was limited [21]. Sang et al. [22] evaluated the induction of remission and maintenance effect of probiotics of UC. Compared with the non-probiotics group, the remission rate for UC patients who received probiotics was not significantly altered (RR = 1.35, 95% CI: 0.98–1.85). Nevertheless, the remission rate of UC which received probiotics was increased (RR = 2.00, 95% CI: 1.35–2.96). Another study with 23 RCTs and a total of 1763 patients evaluated whether probiotics were beneficial at all stages of the treatment in inflammatory bowel disease or superior to placebo. They found that probiotics can significantly increase the remission rate in patients with active UC (P=0.010) compared with placebo group. Unfortunately, similar effect on maintaining remission rate of UC was found between probiotics and 5-aminosalicylic acid [23]. These studies suggested that probiotic treatment was more effective than placebo in maintaining remission of UC and was equivalent compared with aminosalicylic acid.

In the past several years, more and more researchers have focused on combined drugs.

Previous studies indicated that the maintaining effect of probiotics for active stage UC was unclear, and the induction remission of aminosalicylic acid was obvious [24]. Whether patients with UC can benefit a lot from combination of probiotics with aminosalicylic acid still remains unclear. Currently, the aminosalicylic acid agents are commonly used in the treatment of UC, including SASP and mesalazine. Patients with UC tended to use large amounts of antibiotics for a long time [25]. The number of normal bacteria in the intestinal tract is reduced. The SASP was decomposed into 5-aminosalicylic acid by bacteria. The effect of aminosalicylic acid greatly decreased. At the same time, SASP itself has a certain bacteriostatic effect, and also inhibited the intestinal bacteria decomposition of SASP [26]. Both of the two reasons lowered the concentration of 5-aminosalicylic acid, which makes the therapy effect not ideal. Therefore, if probiotics was used when aminosalicylic acid was taken, this plan can regulate the intestinal flora and increase the concentration of 5-aminopylic acid and improve the curative effect. The present study confirmed this theory and gave a stronger evidence.

The main strengthen of the present study is that we did not find any significant heterogeneity within studies. The present study still has several limitations. First, the quality of included study was moderate, and the primary reason was the lack of blinding methods. Second, a number of included studies are few in some subgroup settings, and more rigorous and well-designed RCTs are needed to confirm our results. Third, most of the studies are from Asian populations that may cause publication bias. In fact, the funnel plot, Begg and Egger’s test also indicated that there was a slight publication bias, which may influence the stability of pooled results. Finally, although we carefully selected published studies, some unpublished data and grey literature were not included, which may influence the estimation.

In conclusion, our meta-analysis suggested that probiotics in conjunction with aminosalicylic can obviously increase the clinical remission rate of activity UC than drug alone. This effect was not influenced by probiotic types, severity of disease, and type of drugs. After a 12-week treatment, no significant difference was observed between combined and single drugs. This result from subgroup analysis should be cautious because of the limited number of studies.

We thank the colleagues of the Pediatric Academy of University of South China.

P.L.J. and J.Z.S. conceived and designed the research. Z.Y. and W.A.P. analyzed the data. P.L.J. and J.Z.S. created all tables and figures. P.L.J. drafted the manuscript. Z.Y. and W.A.P. made critical revisions of the manuscript. All authors read and approved the final manuscript.

The authors declare that there are no sources of funding to be acknowledged.

The authors declare that there are no competing interests associated with the manuscript.

CI

confidence interval

PRISMA

preferred reporting items for systematic reviews and meta-analysis

RCT

randomized controlled trial

RR

relative risk

SASP

salicylazosulfapyridine

UC

ulcerative colitis