Effects of probiotics, prebiotics, and synbiotics on mineral metabolism in ovariectomized rats — impact of bacterial mass, intestinal absorptive area and reduction of bone turn-over

BackgroundDefined prebiotics were shown to improve calcium balance and diminish bone loss. However, the effect of their combination with probiotics on gut ecology and bone metabolism has not yet been studied. We investigated whether the combination of a probiotic with a defined microbial strain results in improved bone mineralization, and whether this effect is associated with changes in gut ecology.MethodsEighty ovariectomized adult rats were allocated to five groups: group 1, sham-operated (SHAM); group 2–5, ovariectomized (OVX). Semipurified diets containing 0.7% calcium and 0.5% phosphorus were fed for 16 weeks, group 1 and group 2 got no supplements, group 3 (PRO) was supplemented with a potential probiotic (Lactobacillus acidophilus NCC90), group 4 (PRE) with prebiotics (oligofructose + acacia gum) and group 5 (SYN) with synbiotics (probiotics + prebiotics).ResultsOvariectomy increased body weight and reduced bone weight, content of calcium, phosphorus and ash of bone, bone alkaline phosphatase (BAP), and bone structure. This was indicated by lower trabecular bone area, trabecular perimeter, and connectivity but higher epiphyseal breadth. Ovariectomy elevated the jejunal pH. The probiotic alone did not significantly affect bone mineralization and gut ecology. Rats on prebiotics had significantly higher amounts of cecal contents and lower pH in cecal and colonic contents. Their calcium balance tended to be increased (p < 0.1). Synbiotics reduced pH in different intestinal segments, significantly in cecum. They stimulated most the colonic absorption surface as indicated by colon weight. Only feeding synbiotics significantly prevented OVX-induced loss of calcium content in lumbar vertebrae (mg) with final values (mean ± SD) of 44.44 ± 2.94 (SHAM), 41.20 ± 4.59 (OVX), 41.63 ± 3.78 (PRO), 43.42 ± 3.07 (PRE), and 44.68 ± 2.28 (SYN). This effect was associated with higher counts of bifidobacteria in the short-term and Bacteroides in the long-term, and with a tendency for lower BAP with 128.7 ± 28.5 U/L vs. 155.3 ± 28.1 U/L in OVX (p < 0.1).ConclusionSYN exerted a synergistic effect on bone mineralization, presumably due to changes in gut microbiota and ecology associated with large bowel digesta weight (most likely reflecting microbial mass) and with large bowel weight (reflecting absorptive area), while bone turnover tended to be reduced as indicated by BAP.