The effects of synbiotics on indoxyl sulphate level, constipation, and quality of life associated with constipation in chronic haemodialysis patients: a randomized controlled trial

Dysbiosis is an imbalance in the gut microbiota that causes changes in the number and activities of the microbiota in the gastrointestinal tract. Conditions in chronic kidney disease (CKD) that serve as risk factors for gut microbiota dysbiosis include a low-fibre diet, uraemia, prolonged colonic transit time, disturbance of protein assimilation, use of drugs such as antibiotics, phosphate-binding agents, and iron supplements, as well as other comorbidities [1]. Dysbiosis in CKD is characterized by an increase in the activity of proteolytic bacteria, such as the family Enterobacteriaceae (especially Enterobacter, Klebsiella and Escherichia), Enterococci, Clostridium perfringens and Pseudomonas, accompanied by a decrease in the activity of saccharolytic bacteria, such as the family Bifidobacteriaceae (especially Bifidobacterium, Lactobacillaceae and Prevotellaceae). This leads to an increase in the production of uraemic toxins, such as indoxyl sulphate (IS), p-cresyl sulphate (p-CS) and indole acetic acid (IAA), as well as a decrease in the production of short-chain fatty acids (SCFAs), such as butyrate and propionate [2].

Indoxyl Sulphate (IS) is a result of tryptophan metabolism by bacteria with the tryptophanase enzyme in the colon. In normal kidneys, this toxin is excreted through the secretion process in the tubules. This toxin is 90% bound to albumin in the circulation and, therefore, cannot be eliminated through the haemodialysis process [3]. As kidney function decreases, the accumulation of IS increases in the body of haemodialysis patients. IS activates nuclear factor-ƙB (NF-ƙB) and the expression of plasminogen activator inhibitor (PAI) type 1 in proximal tubular cells, mediating tubulointerstitial fibrosis, and is strongly associated with the progression of kidney damage. Additionally, IS is associated with aortic calcification, vascular stiffness, and increased oxidative stress in vascular endothelial cells, leading to increased cardiovascular risks in patients with CKD [4].

In addition to being associated with an increase in uraemic toxins, dysbiosis of the gut microbiota is also related to constipation, as it is one of the most frequent gastrointestinal symptoms experienced by haemodialysis patients [5]. Inflammation, increased uraemic toxin, and decreased butyrate acid are suspected to affect intestinal motility [6]. With inadequate treatment, persistent constipation affects patients’ mental and physical quality of life. Zhang et al. [7] reported that haemodialysis patients with constipation had lower scores on physical and mental health.

Improvement of dysbiosis by synbiotic administration is expected to lower IS toxin levels, improve constipation symptoms, and enhance constipation-related quality of life. However, currently available studies were conducted with small sample sizes, and not all of them were designed as double-blind randomized clinical trials. The results of these studies vary and cannot provide full evidence of the role of synbiotics in the improvement of gut dysbiosis, decreased uraemic toxins, and gastrointestinal symptoms [8‐11].

This study aimed to show the benefit of synbiotic administration in lowering uraemic toxins, specifically IS, and to investigate its benefits on constipation symptoms and the quality of life of haemodialysis patients in Indonesia.

Out of 100 screened patients, 60 met the inclusion criteria. These patients were randomized into either the synbiotics or the placebo group. Twenty-seven subjects in the synbiotics group and 30 subjects from the placebo group completed the study. In the synbiotics group, two subjects refused to continue the study, whereas one dropped out due to receiving antibiotics for 15 days during the course of the study. The research algorithm is shown in Fig. 1. Baseline demographic characteristics as well as IS levels and PAC-SYM and PAC-QOL scores are provided in Table 1.

The excretion of uraemic toxins, such as IS, decreases with declining kidney function. Although haemodialysis is an advanced kidney replacement therapy, IS still cannot be completely eliminated. This is because this toxin is large, and 90% is bound to albumin [14]. Various strategies to improve IS removal, including (using) haemodiafiltration machines, increasing dialysate flow, increasing dialyzer membrane size, or adding a sorbent to the dialysate, have not shown promising results [15‐17]. This suggests the need for an alternative way to lower the level of IS in CKD or CKD-HD patients. It was expected that the administration of synbiotics would suppress IS production in the gastrointestinal tract by improving gut microbiota dysbiosis. A previous study by Cossola C et al. found that a combination of prebiotics and probiotics restored the balance of gut microbiota and suppressed IS production [18]. However, some studies and a recent meta-analysis showed no correlation between synbiotics and IS reduction in CKD-HD subjects [8, 9, 19, 20]. Likewise, our study found nonsignificant results.

The reasons behind these findings might be because a 60-day administration and observation period were not sufficient to demonstrate a significant IS reduction. Thus, a longer observation period and serial examination of IS might be needed. Another factor that might have played a role in the findings is the fact that a previous study used a synbiotic combination that differed from ours. The synbiotics used by previous studies contained different strains of bacteria and higher amounts of prebiotics, which might have led to various effects [ 8,9,18‐20]. Furthermore, the results of these studies show the importance of determining the type, dosage and duration of administration of synbiotics to suppress IS levels [8, 9, 18‐20]. Additionally, this illustrates the need for faecal microbiota analysis to determine the most suitable synbiotics to be given to CKD-HD patients. In Indonesia, intestinal microbiota profile examination has never been performed on CKD-HD patients, and to date, there are no accurate data on the most suitable synbiotics for CKD-HD patients in Indonesia.

Saccharolytic bacteria provide benefits in improving intestinal microbiota homeostasis, lowering the amount of pathogenic bacteria, improving intestinal transit time, increasing the frequency of defecation, improving faecal consistency, decreasing bloating symptoms and producing butyric acid to increase intestinal barrier functions [21]. The presence of saccharolytic bacteria is expected to lower the amount and activity of proteolytic bacteria, which lowers the level of uraemic toxins, such as IS. The presence of fructooligosaccharides (FOS) modulates the growth of bacteria, such as Bifidobacterium, and increases the ratio of Roseburia/E. rectal, which plays a role in increasing the level of butyrate acid, which in turn serves as the source of energy in the regeneration of cells in the host’s intestines. Fructooligosaccharides also serve as substrates for saccharolytic bacteria contained in the synbiotic preparation, leading to increased SCFA production and suppressed uraemic toxin production by proteolytic bacteria [22].

Patients with CKD experience constipation more often than the normal population. This is due to the restriction of fibre and water, reduced physical activity, use of medications such as oral iron supplements, and gut microbiota dysbiosis in haemodialysis patients [23]. An in vitro study reported an inflammation process due to gut-derived uraemic toxin disrupting intestinal motility. Nishiyama et al. demonstrated that rats with CKD also had gut dysbiosis, reduced intestinal motility, reduced amounts of faeces, and intestinal inflammation [24]. A study by Ramos et al. showed that CKD patients suffering from constipation tended to have higher uraemic toxin levels [25]. Constipation increases colonic transit time, leading to an increase in the activity of proteolytic bacteria in metabolizing amino acids and producing uraemic toxins. The presence of uraemic toxin itself may worsen constipation. In other words, constipation and gut dysbiosis affect each other [26]. A study by Salmean et al. showed an improvement in defecation frequency among 13 CKD patients receiving high fibre supplementation for 12 weeks [27]. In our study, we found that the administration of synbiotics capsules improved complaints related to constipation symptoms patterns, as shown in the improved score on the PAC-SYM questionnaire. This is because the administration of synbiotics increases the amount and activity of saccharolytic bacteria in producing butyric acid. Butyric acid is the source of energy for the regeneration of colonocytes; thus, the increase in its production improves intestinal motility and contractility, lowering colonic transit time. Additionally, improving gut dysbiosis decreases intestinal inflammation, which causes disturbances in intestinal motility [6, 28].

Constipation, if not well treated, may affect the quality of life in haemodialysis patients. Zhang et al. reported that haemodialysis patients with constipation symptoms tended to have poorer quality of life and were prone to depression compared to subjects without constipation [7]. Ranganathan et al. reported that the administration of probiotics for six months in stage 3-4 CKD patients increased their quality of life [29]. A study by Haghihat et al. showed that the administration of synbiotics in haemodialysis patients improved their mental status, including depression and anxiety symptoms, but was not associated with significant improvement in terms of quality of life [30]. The results of this study were consistent with those of previous studies, which showed an improvement in terms of constipation-related quality of life as assessed using the PAC-QOL questionnaire. We observed significant improvements in terms of physical discomfort, psychosocial discomfort, and worries, although we did not observe significant improvement in terms of patient satisfaction. To date, current studies have shown various results. The pathogenesis of how synbiotics may affect the quality of life and the possibility of a gut-brain axis role are not yet completely understood. Hence, the need for further studies remains.

To the best of our knowledge, this is the first study in Indonesia that successfully showed the efficacy of synbiotic supplementation on the improvement of constipation symptoms and constipation-related quality of life in patients undergoing haemodialysis, although its efficacy in decreasing the IS level has not yet been established. This study has several limitations. We did not perform genomic analysis of gut microbiota on patients’ faecal samples to assess dysbiosis patterns in Indonesian CKD-HD patients and determine whether there was any change in dysbiosis patterns after synbiotic administration. Moreover, this study did not measure other uraemic toxins, such as p-cresyl sulphate and indole acetic acid, which may also increase gut microbiota dysbiosis. In addition, this study only included subjects who received haemodialysis twice a week, so attention is needed to generalize this study's results.

In conclusion, the administration of synbiotics containing Bifidobacterium longum, Lactobacillus acidophilus (5x10⁹ CFU), and 60 grams of fructo-oligosaccharides (FOS) in two capsules per day for 60 days has not been shown to reduce levels of IS toxin but can improve constipation symptoms and quality of life associated with constipation in CKD-HD patients.