A Calcium-Rich Multimineral Intervention to Modulate Colonic Microbial Communities and Metabolomic Profiles in Humans: Results from a 90-Day Trial

Abstract

Aquamin is a calcium-, magnesium-, and multiple trace element-rich natural product with colon polyp prevention efficacy based on preclinical studies. The goal of this study was to determine the effects of Aquamin on colonic microbial community and attendant metabolomic profile. Thirty healthy human participants were enrolled in a 90-day trial in which Aquamin (delivering 800 mg of calcium per day) was compared with calcium alone or placebo. Before and after the intervention, colonic biopsies and stool specimens were obtained. All 30 participants completed the study without serious adverse event or change in liver and renal function markers. Compared with pretreatment values, intervention with Aquamin led to a reduction in total bacterial DNA (P = 0.0001) and a shift in the microbial community measured by thetaYC (θYC; P = 0.0087). Treatment with calcium also produced a decline in total bacteria, but smaller than seen with Aquamin, whereas no reduction was observed with placebo in the colon. In parallel with microbial changes, a reduction in total bile acid levels (P = 0.0375) and a slight increase in the level of the short-chain fatty acid (SCFA) acetate in stool specimens (P < 0.0001) from Aquamin-treated participants were noted. No change in bile acids or SCFAs was observed with calcium or placebo. We conclude that Aquamin is safe and tolerable in healthy human participants and may produce beneficial alterations in the colonic microbial community and the attendant metabolomic profile. Because the number of participants was small, the findings should be considered preliminary.

Conflict of interest statement

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

©2019 American Association for Cancer Research.

Figures

Figure 1.

Study design. Study flow diagram highlighting enrollment, group randomization, intervention allocation, study duration, and study sample collection plan.

Figure 2.

Decrease in bacterial DNA with Aquamin. qPCR for bacterial DNA in colon (A) and stool (B) samples. The average cycle quantification (Cq) value from duplicate qPCR runs was plotted except for one post-Aquamin colon sample which failed to reach the amplification threshold in one duplicate and was therefore represented by a single Cq value (34.4) rather than the average. Another post-Aquamin colon sample failed to reach the amplification threshold in both duplicates and was, therefore, not plotted or included in the statistical analysis. A decrease in the total bacterial DNA is indicated by a higher Cq value (longer time to reach amplification threshold). There was no difference in pre- vs. postsupplementation for the placebo group. *, P < 0.05; ***, P < 0.001; and ****, P < 0.0001 compared with the corresponding pretreatment value.

Figure 3.

θYCdistances for comparison of pre- vs. postsupplementation values in gut bacterial community composition for colon (A) and stool (B) samples. Higher values reflect greater differences. **, P = 0.0087 relative to calcium. The insets show that the majority of the Aquamin (colon and stool) samples were above the median value for all samples. The majority of placebo and calcium samples were at or below the combined median value. C, Correlation between θYC in colon biopsy and stool specimens based on pre- vs. postsupplementation values (P = 0.0041).

Figure 4.

Segregation of gut microbial communities and gut microbial diversity. Biplot figures depicting PCoAs of θYC distances between colon biopsy and stool samples based on Illumina sequencing of the V4 region of 16S rRNA. θYC distance is a measure of difference in pre- and posttreatment microbial populations from individual participants with each of the three interventions. Data from colon specimens are shown in A and B, whereas stool specimen data are presented in C and D. Some of the OTUs driving the observed segregation between the groups are shown in the biplots. A, Differences in colon microbiota between postintervention Aquamin compared with postintervention placebo and calcium were seen: Aquamin samples with AMOVA P values of 0.005 (compared with placebo) and 0.009 (compared with calcium). B, Postintervention colon samples from Aquamin group were also significantly different relative to preintervention Aquamin samples with an AMOVA P value of 0.022. C and D, There were no significant differences found in stool samples. E and F, Shannon diversity index. Aquamin intervention reduced gut microbial (alpha) diversity as compared with the placebo in colon biopsy samples (*, P < 0.05). No significant change was observed in the gut microbial diversity in stool samples. G and H, Alterations in the relative abundance of major gut phyla with Aquamin supplementation. The change in the relative abundances of the top 1,000 OTUs (pooled by phyla) and assessed by pre- and postintervention analysis among three interventions in colon and stool specimens. For this analysis, 43 to 48 OTUs across the three treatment groups were pooled for Actinobacteria, 101 to 110 OTUs for Bacteroidetes, 543 to 591 OTUs for Firmicutes, 31 to 39 OTUs for Proteobacteria, and 4 to 6 OTUs for Verrucomicrobia phyla. **, P < 0.01; ***, P < 0.001; and ****, P < 0.0001.

Figure 5.

Decrease in bile acids and increase in SCFAs in stool specimens. Bile acids and SCFA were assessed as described in the Materials and Methods Section. Values shown represent concentration differences between preintervention and postintervention samples. Asterisks represent statistical significance. A, Total bile acids (sum of the total conjugated and total unconjugated bile acids) are shown along with conjugated and unconjugated forms. * reflects decrease with Aquamin at P = 0.0375 (total) and at P = 0.0527 (unconjugated) versus calcium. B, Primary bile acids. CA and CDCA measured concurrently with DCA were significantly decreased with Aquamin at P = 0.0074 (CA) and P = 0.0310 (DCA/CDCA) versus calcium. C, Secondary bile acids. HDCA was significantly decreased with Aquamin and calcium versus placebo with P value < 0.0001 and = 0.0149 respectively. HCA and TUDCA, measured concurrently with THDCA were decreased with Aquamin relative to calcium, whereas α and ω muricholic acids were also reduced relative to calcium. For HCA, P = 0.015; for TUDCA/THDCA, P = 0.0287; for αMCA, P = 0.0012; and for ωMCA, P = 0.0003. With calcium supplementation, HDCA was also decreased relative to placebo (P = 0.0149). Inset: TUDCA/THDCA. D, SCFA. Acetate was significantly increased with Aquamin relative to calcium alone (P < 0.0001).