Oral administration of Bifidobacterium longum in a gastro-resistant seamless capsule decreases serum phosphate levels in patients receiving haemodialysis

When kidney function decreases, phosphate (P) per se can initiate and promote hyperparathyroidism and vascular calcification. Therefore, hyperphosphataemia is a widely recognized risk factor for mortality and cardiovascular disease in patients with chronic kidney disease (CKD) [1]. Despite the introduction in the market of new P-binders, such as sevelamer hydrochloride and lanthanum carbonate, the control of hyperphosphataemia in haemodialysis (HD) patients remains difficult because of adverse effects such as constipation and faecal impaction, drug compliance and metal accumulation. We here report an interesting observation that serum P levels can be reduced by modifying the intestinal flora with probiotic administration. This may suggest a new potential approach to better control hyperphosphataemia in HD patients.

In patients receiving HD, intestinal aerobic bacteria, such as enterobacteria and enterococci, occur in numbers ∼100 times higher than those in healthy subjects. These aerobes produce putrefactive substances [2]. Oral administration of antibiotic-resistant lactic acid bacteria for 4 weeks can restore the composition of disturbed microflora characterized by overgrowth of aerobes and decreased levels of serum uraemic toxins, including indicant, in HD patients [2].

When administered orally, Bifidobacteria cannot survive exposure to gastric juice before they reach the intestine. In order to enable Bifidobacteria to reach the intestine, a colony-forming unit of Bifidobacterium longum JBL01, a strain of human Bifidobacteria, measuring 2.0 × 10⁹, combined with 0.11 g of oligosaccharides (lactulose and raffinose) as a stimulant to bacteria proliferation, were encapsulated in a gastro-resistant seamless capsule (B capsule, MorishitaJintan Co., Ltd, Osaka, Japan). Bifidobacteria can survive in this gastro-resistant capsule even in a solution of 1.2 pH at 37°C for 120 min. In contrast, Bifidobacteria without the capsule (a powder formulation) cannot be detected immediately after mixing with the solution [3]. Moreover, significant decreases in serum levels of indoxyl sulphate and homocysteine were observed by oral administration of B. longum in the gastro-resistant capsule, but not by the administration of B. longum without the capsule in HD patients [4].

Thus, to improve the composition of disturbed microflora and alleviate faecal impaction, B capsules containing B. longum JBL01 were administered orally once daily for 4 weeks in 15 patients receiving HD [age: 62.2 ± 9.8 years; 10 males, 5 females; 5 diabetes mellitus (DM), 10 non-DM; HD duration: 9.3 ± 7.0 years; serum albumin levels: 3.9 ± 0.3 g/dL; serum corrected calcium (Ca) levels: 9.1 ± 0.8 mg/dL; serum P levels: 6.7 ± 0.6 mg/dL; serum intact parathyroid hormone (PTH) levels: 363 ± 221 pg/mL]. Results were compared with those of 16 HD patients who did not receive B capsules as a control group (age:58.1 ± 15.6 years; 10 males, 6 females; 3 DM, 13 non-DM; HD duration: 9.1 ± 6.8 years; serum albumin levels: 3.8 ± 0.3 g/dL; serum-corrected Ca levels: 9.0 ± 0.9 mg/dL; serum P levels: 7.0 ± 0.8 mg/dL; serum intact PTH levels: 219 ± 124 pg/mL). No patient had undergone treatment with B. longum preparations before participating in this study. The dose of drugs affecting P metabolism were fixed through the study period in the control group (Ca carbonate: 2.79 ± 1.44 g, n= 14; sevelamer hydrochloride: 3.20 ± 2.94 g, n= 5; calcitriol injection: 1.67 ± 0.24 μg/week, n= 3; maxacalcitol: 15.0 ± 4.1 μg/week, n= 3; oral alfacalcidol: 0.5 μg, n= 2, oral calcitriol: 0.38 μg, n= 2) and in the B capsule-treated group (Ca carbonate: 2.50 ± 0.71 g, n= 12; sevelamer hydrochloride: 3.75 ± 0.53 g, n= 4; calcitriol injection: 2.75 μg/week, n= 2; maxacalcitol: 12.5 ± 8.5 μg/week, n= 4; oral alfacalcidol: 0.25 ± 0 μg, n= 3, oral calcitriol: 0.25 μg, n= 1). No patients received lanthanum carbonate or cinacalcet hydrochloride in either group. All data are expressed as mean ± SD or without SD in n= 1 or 2.

Oral administration of B capsules for 4 weeks had no significant effect on defecation frequency or faecal hardness determined by the Bristol stool form scale (data not shown). The explanation for this result may be related to the low incidence of obstinate constipation from the beginning in this study (mean defecation frequency: 0.9/day). Serum P levels unexpectedly decreased significantly in the second and fourth weeks due to oral administration of the B capsule (Figure 1). Serum P levels remained unchanged in the control group. Subsequently, serum P levels returned to original levels 2 weeks after the completion of oral treatment. No significant changes were found in other serum parameters in the B capsule-treated group compared with baseline data and with the control group (data not shown).

Fig. 1.

Effect of once-daily oral administration of encapsulated B. longum JBL01 with oligosaccharides (B capsule) for 4 weeks on serum P levels in patients on haemodialysis. Open circle: untreated control group (n= 16); filled circle: B capsule-treated group (n= 15). Data are expressed as mean ± SD. **P< 0.01 and ***P< 0.001 versus baseline data (paired t-test). ^#P< 0.05 and ^###P< 0.001 versus the control group (Student's t-test).

The main mechanism for a decrease in serum P levels during B capsule treatment is its ability to lower intestinal pH levels. In the faeces of HD patients, pH levels and ammonia concentrations are elevated due to bacteria-mediated hydrolysis of urea [4]. High levels of ammonia are responsible for elevated pH in faeces and lead to overgrowth of aerobic and putrefactive bacteria. Bifidobacteria can ferment carbohydrates to produce acetic acid and lactic acid, resulting in acidification of the intestinal lumen [4]. Low pH levels in the intestinal milieu inhibit the growth of aerobic and putrefactive bacteria, thus normalizing the intestinal flora. In another study, the administration of B. longum decreased faecal pH levels, and pretreatment levels were restored 1 week after the completion of treatment [5]. Decreased intestinal pH levels due to B capsule treatment may increase the ionization of intestinal Ca. Ca²⁺ binds with intestinal P ions as an intrinsic P binder. In this study, increased intestinal Ca²⁺ did not lead to elevated serum Ca levels. Ca²⁺ may be immediately used in the formation of calcium phosphate in the intestine, and thus not absorbed. Further studies measuring faecal pH, P and Ca excretions will examine this as a possible mechanism in B capsule-treated patients.

In this study, although the number of faecal bacteria was not determined during B capsule treatment, the decrease in serum P levels cannot be due to increased uptake of P into the intestinal B. longum for their proliferation. Because feeding of B. longum increases their number, but does not affect the total number of bacteria through a reduction in aerobes in the faeces of healthy subjects [5]. In addition, increased faecal volume and water content are not responsible for low serum P levels, as evidenced by unchanged defecation frequency and faecal hardness among the patients in the present study.

It is increasingly recognized that uraemic toxins originating from intestinal microbial metabolism may contribute to the deterioration of renal function, cardiovascular calcification, metabolic bone disease and mortality in CKD/HD patients [6, 7]. The administration of Bifidobacteria can decrease the serum concentrations of indoxyl sulphate and P-cresol in HD patients [4, 7]. In addition, Bifidobacteria produce vitamin B12 and folate, which can normalize serum homocysteine levels in HD patients [3]. This is an important property since most HD patients show hyperhomocysteinaemia, which is a risk factor for cardiovascular disease. Although further investigation is clearly required to clarify the mechanism for the P-reducing effect of the B capsule, Bifidobacteria preparation is a simple and safe treatment for persistent hyperphosphataemia in patients receiving HD. Further studies may identify additional potential benefits of probiotic treatments in CKD/HD patients [6, 7].

Conflict of interest statement

N.N. is a member of the speaker's bureau for Kyowa Hakko Kirin Co., Ltd.