Clinical Characteristics of the Participants
A total of 56 cases were collected in OA group, including 22 males and 34 females, and 52 healthy controls (HC group), including 24 males and 28 females. It was found that there was no significant difference in age, gender and BMI between the two groups (p = 0.729, p = 0.471, p = 0.902). (Table 2)
Table 2
Clinical characteristics of the two groups
Clinical characteristics
|
Healthy group
(n = 52)
|
OA group
(n = 56)
|
P-value
|
Age (year)
|
63.8(48–82)
|
63.3(40–79)
|
0.729
|
Gender
|
|
|
|
Female (%)
|
28(53.8%)
|
34(60.7%)
|
0.471
|
Male (%)
|
24(46.2%)
|
22(39.3%)
|
|
BMI (kg/m2)
|
23.0(16–28)
|
22.9(17–28)
|
0.902
|
Two-tailed Student’s t test was used to compare the continuous variables; Chisquare exact test compared categorical variables. BMI, body mass index
|
Cluster Analysis and Species Annotation
A total of 2145 OTUs were obtained from 108 samples, including 1861 OTUs in the OA group and 1784 OUTs in the HC group. There were 1500 OTUs overlapping in the two groups of samples. The number of peculiar OTUs in the OA group (361) was greater than that in the HC group (284). (Fig. 1a).
In the experiment, the Rarefaction Curves of the samples are gradually flat, indicating that the sequencing depth of the experimental samples was reasonable. In addition, the Good's Coverage index of each sample is more than 97%, which also shows that the sequencing has covered almost all the species in the sample. (Fig. 1b, Table 3)
Table 3
Alpha diversity associated indexes and Good's Coverage
Index
|
OA group
|
HC group
|
P-value
|
Chao1
|
391.1(131.1-618.6)
|
361.3(105.5-781.9)
|
0.208
|
Shannon-Wiener Index
|
5.1(2.4–6.7)
|
5.0(1.9–6.8)
|
0.485
|
Simpson's diversity Index
|
0.9(0.5-1.0)
|
0.9(0.6-1.0)
|
0.831
|
Good coverage
|
0.98(0.98–0.99)
|
0.99(0.97-1.00)
|
0.130
|
Community structure distribution
According to the composition of microbes at different levels (phylum, class and family), we draw histograms about the composition of the gut microbiome in two groups (Fig. 2a, 2b, 2c). And use box plots to show microorganisms with significant differences at each level (Fig. 2d, 2e, 2f).
Differences in abundance and composition
Alpha diversity analysis can reflect the abundance and evenness of microbial community. The main indicators include Chao1, Shannon-Wiener Index, Simpson's diversity Index and Rank Abundance analysis. Shannon-Wiener Index and Simpson's diversity Index are mostly used to reflect sample diversity, and the higher the index is, the higher the community diversity is. While the value of Chao1 is equal to the estimated number of OTUs. In this experiment, Chao1, Shannon index and Simpson index in OA group were higher than those in HC group (difference: 29.7 [95% CI: -16.7-76.4], 0.13 [95% CI: -0.24-0.50], 0.01[95% CI: -0.03-0.03]), but the difference was not significant. It can also be seen from the Rank Abundance analysis that there was no significant difference in richness and evenness between two groups. (Fig. 1c, Table 3)
Beta diversity analysis is to compare the composition of microbial communities in different samples. In this study, based on Weighted Unifrac and Unweighted Unifrac distance algorithms, PCoA analysis and NMDS analysis were used to compare the differences of microbial community composition between OA group and HC group. Through PCoA analysis and NMDS analysis, it can be seen that the OA group and the HC group have different aggregation tendencies, suggesting that there are differences in the composition of community between two groups. Besides, through Anosim analysis and Adonis analysis, based on four different distance algorithms, the difference of community composition between two groups was statistically analyzed. The results showed that there was significant difference in community composition between two groups. (Fig. 3a, 3b, Table 4)
Table 4
Results of four different distance algorithms
|
|
Binary_jaccard
|
Bray_curtis
|
Unweighted_unifrac
|
Weighted_unifrac
|
Adonis
|
R2
|
0.01264
|
0.01507
|
0.01491
|
0.02221
|
|
P
|
0.016
|
0.048
|
0.025
|
0.036
|
Anosim
|
R
|
0.0226
|
0.0253
|
0.0355
|
0.0203
|
|
P
|
0.027
|
0.045
|
0.010
|
0.060*
|
Based on four different algorithms, only one of the P values is equal to 0.06, and the rest are less than 0.05.
|
In this study, Linear discriminant analysis Effect Size (LEfSe) was used to find the Biomarker with statistical difference between the two groups. As can be seen from the figures, Actinobacteria, Bifidobacteriaceae, Bifidobacterium and Alistipes were significantly enriched in osteoarthritis patients. While the abundance of Prevotellaceae and Faecalibacterium was lower than that of the healthy group. Combined the main difference bacteria at the genus level obtained by the Wilcoxon rank-sum test, it was found that Bifidobacterium, Alistipes and Faecalibacterium could be used as biomarkers for osteoarthritis (Fig. 4a, 4b, Fig.S1). In addition, Index analysis and random forest analysis confirmed the effectiveness of biomarkers (Fig. S2). Unfortunately, it is not accurate to use only three biomarkers to distinguish the osteoarthritis group from healthy group (AUC = 0.62 ± 0.16). However, based on 14 optimal genera bacteria ( Faecalibacterium, Alistipes, Bifidobacterium, Lactobacillus, Anaerostipes, Parasutterella, Anaerotruncus, Desulfovibrio, Megamonas, Mucispirillum, Prevotella_9, Ambiguous, Ruminococcaceae_UCG_010, Prevotellaceae_NK3B31), it can achieve an area under the curve (AUC) of 0.74 ± 0.12.
Correlation between main differential bacteria and clinical characteristics
This study analyzed the correlation between the first 13 significantly different bacteria (Faecalibacterium, Megamonas, Lactobacillaceae, Alistipes, Lactobacillus, Bifidobacteriaceae, Bifidobacterium, p_Actinobacteria, c_Actinobacteria, Prevotellaceae, Melainabacteria, Cyanobacteria, Bifidobacteriales, Bifidobacterium, obtained by the LEfSe algorithm) and clinical characteristics (age, gender and BMI). The results showed that the relative abundance of Prevotellaceae is positively correlated with BMI, (r = 0.219 [95%CI: 0.033-0.4], p = 0.023), while the relative abundance of Bifidobacterium, Actinobacteria and Actinobacteria was negatively correlated with BMI ( r= -0.236 [95%CI: -0.41 to -0.04], r= -0.248 [95%CI: -0.42 to -0.07], r = -0.196 [95%CI: -0.38 to -0.01], p = 0.014, p = 0.010, p = 0.043).
Functional prediction
Combined with the KEGG database, the 16S sequencing data were analyzed, and the results showed that the number of genes which were related to lipid metabolism, glycan biosynthesis and metabolism involved in gut microbiome in OA group was significantly lower than that in HC group at level 2 KEGG signaling pathway (p = 0.049, p = 0.005), and in the level 3 KEGG signal transduction, the enrichment of OA group in signal pathways such as glycan biosynthesis and metabolism, lipopolysaccharide biosynthesis and Adipocytokine signaling pathway were also significantly lower than that of the control group (p = 0.009, p = 0.001, p = 0.012), but in signal pathways related to apoptosis, the degree of enrichment was significantly higher than that of healthy people (p = 0.006).
In addition, the sequencing data were also analyzed by combining with COG database. The results showed that the proteins related to Na+-transporting NADH: ubiquinone oxidoreductase ( subunit NqrA, subunit NqrB and subunit NqrF ) of OA group were significantly lower than that of the control group (p<0.001, p<0.001, p<0.001).