Participants characteristics
Out of 160 volunteers, only 17 qualified participants were selected based on the inclusion and exclusion criteria. These individuals were then divided into two groups: a diabetes group (T2D) consisting of five cases with FPG levels ≥ 7.0 mmol/dl (126mg/dl), and a normal glucose control group (Control) consisting of twelve cases with FPG levels < 7.0 mmol/dl. The male-to-female sex ratio in the T2D group was 2:3, while that in the control group was 5:7. An individual case-control study was designed, in which each T2D case was matched with 2–3 control cases of the same gender and similar age. The waist circumference and waist-to-hip ratio (WHR) of the participants exhibited statistically significant differences between the T2D and Control groups, with T2D patients displaying higher values for both measures than those in the Control group. (Table 1). The comprehensive information of each participant is presented in Supplementary Table 1.
Table 1
Characteristics of the participants in both groups
Group | T2D | Control | t value | p value |
FPG, mmol/L | 11.58 ± 5.83 | 5.52 ± 0.29 | 3.77 | 0.00 |
Age, years | 60.80 ± 8.50 | 55.08 ± 7.79 | 1.35 | 0.20 |
BMI | 27.96 ± 2.38 | 24.97 ± 3.44 | 1.76 | 0.10 |
Waistlin, cm | 102.60 ± 6.80 | 88.46 ± 7.44 | 3.65 | 0.00 |
Hipline, cm | 105.00 ± 6.44 | 99.58 ± 7.01 | 1.48 | 0.16 |
WHR | 0.98 ± 0.33 | 0.89 ± 0.42 | 4.22 | 0.00 |
SBP, mmHg | 133.80 ± 18.73 | 129.92 ± 17.30 | 0.73 | 0.48 |
DBP, mmHg | 83.60 ± 13.26 | 85.50 ± 11.34 | -0.30 | 0.77 |
Differential gut microbial species identified by metagenomic analysis between T2D and Control group
The relative abundance of the seven taxonomic levels, including kingdom, phylum, class, order, family, genus and species were analyzed. Four kingdoms, Bacteria, Viruses, Archaea and Eukaryota, and 120 phyla, 101 classes, 210 orders, 433 families, 1526 genera and 6638 species from fecal samples of the participants have been detected. Although Principal Component Analysis (PCA) (Ringnér M. 2008) and Non-Metric Multidimensional Scaling (NMDS) (Young MP et al. 1995) were employed to assess the diversity differences among groups at each level, no statistically significant differences were observed. However, there were significant variations observed in the bacterial composition at both genus and species levels between group with T2D and those without. In the bacteria, Blautia genus with the highest quantity was dominant, and it was higher in T2D than Control. However, the number of most different bacteria was higher in Control than that in T2D and the Control had more abundance of microorganisms belonged to Flavobacteriia class. The detailed information of the different bacteria is shown in Supplementary table 2.
Then we measured different species among groups by rank sum test, reduced the dimension by linear discriminant analysis (LDA) (Segata N et al. 2011) and evaluated the influence of different species through LDA score. The criteria was 4, that meant the bacteria significantly impacted to the group when it’s LDA Score over 4. It is evident that, the microorganisms with higher LDA score in T2D all belonged to the Firmicutes phylum, especially the Clostridium genus, and that in Control all belonged to the Bacteroidetes phylum, especially the Flavobacteriia and Bacteroidia class (Fig. 1).
Comparative analysis of metabolic enzyme abundance by metagenomic analysis
After searching the KEGG database and conducting statistical analysis, it was found that 103 metabolic enzymes of gut microbiota exhibited significant differences in relative abundance between groups, with 80% of them increased in the T2D group. (Fig. 2).
Figure 2A cluster heat map was generated to compare the abundance of 103 metabolic enzymes between individuals with type 2 diabetes and a control group. The color red indicated an increase in enzyme abundance, while blue represented a decrease. The intensity of the color reflects the quantity of enzymes present; deeper shades indicate higher or lower quantities.
Compare the metabolic profiles between T2D and control group by Untargeted metabolomics analyses
A total of 4597 metabolites were detected, which mainly were Amino acid and its metabolites, Benzene and substituted derivatives, Heterocyclic compounds, Aldehyde, Ketones, Esters, Organic acid And Its derivatives. We analyzed the difference of metabolites between groups by OPLS-DA (Thévenot EA et al. 2015) and a significant difference was shown (Fig. 3). The OPLS-DA model evaluate was R2Y = 0.993, Q2 = 0.318 and R2X = 0.441.
Figure 3 The OPLS-DA analysis revealed significant differences in metabolite profiles between the T2D and Control groups. The abscissa represented the score value of the prediction component, and the difference between groups could be seen in the abscissa direction. The ordinate represented the score value of the orthogonal component, and the ordinate direction could see the difference within the group. Percentage represented extent of explanation of components to the data set.
Differential metabolites observed in the T2D group
There were 144 metabolites had significant difference between the two groups in relative abundance, including 100 positive ions and 44 negative ions. Compared to the Control group, in the T2D group, there were 137 gut metabolites reduced including 97 positive ions and 40 negative ions and only 7 raised including three positive ions and four negative ions (Fig. 4). The detail information of all the differential metabolites was described in supplementary table 3 and the information of every sample can be got from supplementary table 4. This result was inverse of that of metabolic enzymes, that may reflect a compensatory mechanism of the disordered microbiota in that the metabolic function of the gut decreased in the T2D group.
The various sources of the differential metabolites were revealed by the Origin analysis
By using MetOrigin, eleven metabolites originated from intestinal microorganism or host were found out, and three metabolites, fusidate Sodium, 3-Hydroxyphenylacetic acid and beta-Tocotrienol (β-Tocotrienol/β-T3) were from intestinal microorganism, four of that originated from host, four of that originated from Co-Metabolism (host and microorganism co-produce) (Fig. 5). The information of the eleven metabolites was showed in Table 2, and that were all decreased in the T2D group. The detail information of all the results can be found in supplementary table 3.
Table 2
The information of the eleven metabolites from intestinal microorganism or host or Co-Metabolism
HMDBID | KEGGID | Name | Origin |
HMDB0015570 | C06694 | Fusidate Sodium | Microbiota |
HMDB0000440 | C05593 | 3-Hydroxyphenylacetic acid | Microbiota |
HMDB0030554 | C14154 | beta-Tocotrienol | Microbiota |
HMDB0006845 | C15776 | 4alpha-Methylfecosterol | Co-Metabolism |
HMDB0000619 | C00695 | cholic acid | Co-Metabolism |
HMDB0001337 | C00909 | Leukotriene A4 | Co-Metabolism |
HMDB0012453 | C17333 | 3beta-Hydroxy-5-cholestenoic acid | Co-Metabolism |
HMDB0000879 | C13713 | Tetrahydrodeoxycorticosterone | Host |
HMDB0001335 | C01312 | Prostaglandin I2 | Host |
HMDB0060407 | C18040 | 5alpha-Dihydrodeoxycorticosterone | Host |
HMDB0004026 | C05485 | 21-Hydroxypregnenolone | Host |
Enrichment analysis of metabolic pathways
The differential metabolites between groups were enriched in three metabolic pathways, Ubiquinone and other terpenoid-quinone biosynthesis was from intestinal microorganism, Arachidonic acid metabolism and Steroid hormone biosynthesis were both from host. In the Arachidonic acid metabolism pathway, there were four metabolites decreased in the T2D group, which were Prostaglandin I2, Leukotriene A4, 15-Keto-Prostaglandin F2a and Trioxilin B3. In the Steroid hormone biosynthesis pathway, the 5alpha-Dihydrodeoxycorticosterone decreased in the T2D group.
Biological and statistical correlation analysis in Ubiquinone and other terpenoid-quinone biosynthesis pathway
Sankey networks from the MetOrigin can describe biological and statistical correlation of gut microbiome and metabolites. In the Ubiquinone and other terpenoid-quinone biosynthesis pathway(https://www.kegg.jp/pathway/ko00130), the beta-Tocotrienol decreased in T2D group and several gut bacteria had biological and statistical significant correlation with that. The Firmicutes, Proteobacteria, Actinobacteria phylum and the Bacilli class negatively correlated with the beta-Tocotrienol. Conversely, the Bacteroidetes phylum positively correlated with that (Fig. 6).
Correlation analysis of gut bacteria and metabolites
We analyzed the statistical correlation between the gut microorganisms and metabolites in all metabolic pathways using Spearman nonparametric inertia analysis. We found out that many species belonged to Clostridium genus were negatively correlated to most metabolites including beta-Tocotrienol (Fig. 7).