A total of 24 participants, aged 45.5 ± 10.2 (mean ± SD) years were recruited into four groups, with seven, four, seven and six participants in KOA_VDD, KOA, VDD and Normal (NVD) groups respectively (Table 2). These participants were predominantly rural or semi-urban dwellers belonging to middle- to lower-middle socioeconomic status. None of them were on Vitamin D supplementation and they did not consume milk. They had no other co-morbidities. The mean BMI was > 30 with the highest BMI 28.9 ± 2.6 (mean ± SD) in VDD group and the lowest BMI 22.9 ± 2.5 (mean ± SD) in the Normal group. Normal group was significantly different (p < 0.05) from all the three-study group, however, BMI among the three-study groups was not different. Their hemoglobin levels were 13 ± 1.7 (mean ± SD) gm/dl and none of them were on any treatment. KOA and KOA_VDD groups had a chronic history of pain ranging from 4 weeks to 3 years and they performed only mild to moderate physical activity, and had an WOMAC score of 57.6 ± 15.1 and 54.3 ± 10.7 (mean ± SD) respectively. All participants in study groups KOA_VDD, KOA, and VDD had occupation that kept them indoors.
Table 2
Participant Demographics and clinical characteristics.
Characteristics
|
KOA_VDD (n = 7)
|
KOA (n = 4)
|
VDD (n = 7)
|
Normal (NVD) (n = 6)
|
Age (Years ± SD)
|
52 ± 7.2
|
50 ± 9.70
|
44 ± 8.1
|
37.7 ± 12.7
|
Gender (Male/ Female)
|
1/6
|
1/3
|
7/0
|
7/0
|
Clinical Presentation:
Painful Knee
WOMAC Score (Score ± SD)
Kellgren-Lawrence grade (Grade ± SD)
|
++
57.6 ± 7.2
2.3 ± 0.9
|
++
54.3 ± 10.7
3.5 ± 0.6
|
NA
90 ± 2.2
NA
|
NA
93 ± 0.4
NA
|
Demography:
Vitamin D ng/ml (Levels ± SD)
Hemoglobin g/dl (levels ± SD
BMI
Physical activity
Socio-economic score (Score ± SD)
|
21.2 ± 3.5
12.8 ± 1.7
28.2 ± 2.7
Mild
13.7 ± 4.7
|
35.8 ± 4.2
12.7 ± 1.9
27.5 ± 2.8
Mild to
12 ± 2.4
|
19.1 ± 4.3
13.1 ± 2.1
28.9 ± 2.6
Moderate
20 ± 5.2
|
42 ± 9.8
13.1 ± 1.8
22.9 ± 2.6
Active
14.1 ± 2.1
|
Gut microbiome profile: We determined the gut microbiome composition, through the analysis of faecal microbiome. For the identification of bacterial taxa, we sequenced the V3-V4 hypervariable regions of the bacterial 16S rRNA gene using an Illumina MiSeq system. After quality control and filtering, ~ 3,401,904 high-quality sequences with an average length of 600 bp were recovered for further analysis, with an average of ~ 141,746 reads per sample (ranging from 68,540 to 250,424 reads) (Supplementary Information table S1). The rarefaction curves obtained for each sample reached a plateau indicating that there was sufficient sequencing coverage depth (data not shown). The mapping of the 16S rDNA sequencing reads against the Silva 16S sequence database (v128) using RDP classifier lead to identification of 447 distinct OTUs. The gut microbiome composition of 24 participants were then schematically presented the Fig. 1A. At phylum level, the dominant phyla were Firmicutes (59.4%) and Proteobacteria (18.6%), followed by Tenericutes (11%) and Actinobacteria (6.5%) and Bacteroidetes (2.7%). Using Venn diagram, we observed that all 4 groups shared 217 OTUs, whereas 32, 39,33 and 23 OTUs were specific to the KOA, KOA_VDD, VDD and NVD groups, respectively (Supplementary Information Figure S1). However, when OTUs with counts less than 50 were removed, all 4 groups shared only 4 OTUs, whereas 14, 2,1 and 0 OTUs were specific to the KOA, KOA_VDD, VDD and normal groups respectively (Fig. 1B). We also evaluated the overall differences in beta diversity between faecal microbiome of KOA_VDD, KOA, VDD and Normal Participants using canonical correspondence analysis (CCA), based on Bray-Curtis distances (Fig. 1C). All study groups emerge to cluster differently although the ADONIS test does not explain statistically this difference (p = 0.12).
Knee osteoarthritis-associated dysbiosis: To assess the effect of the Knee osteoarthritis disease on the gut microbiome, we compared the gut microbiome composition of individuals with normal vitamin D status, diagnosed with Knee osteoarthritis disease (KOA), and those considered as “healthy” (NVD). We first evaluated the overall differences in beta diversity between faecal microbiome samples of both groups using canonical correspondence analysis (CCA), based on Bray-Curtis distances (Fig. 2A). The two groups appear to cluster differently although the ADONIS test does not explain statistically this difference (p = 0.13).
We estimated α-diversity using the observed OTU and Shannon index (using the Shannon index measuring how evenly OTUs are distributed in a sample) in both groups (Fig. 2B). KOA samples had overall higher bacterial diversity compared to those of healthy participants (observed OTU index, 174.2 ± 14.8 vs. 145.7 ± 26.2; and Shannon index, 3.2 ± 0.19 vs. 2.7 ± 0.6), although these differences are not statistically significant.
To investigate differentially abundant taxa between both groups, we then performed LEfSe analysis to compare the abundance of bacterial taxa in KOA patients and healthy subjects. A histogram of the Linear Discriminate Analysis scores was computed for features that showed differential abundance between healthy (NVD) subjects and KOA patients (Fig. 2C). The LDA scores indicated that the relative abundances of Peptococcus, Shimwellia, Propionibacterium, Intestinimonas, and Pavimonas were enriched in patients with KOA patients than in healthy (NVD) subjects. The most differentially abundant bacterial taxon in patients with KOA was Peptococcus and for the NVD group, it was Anaerofilum with a 3-fold difference in LDA score.
Knee osteoarthritis-associated dysbiosis in patients with vitamin D deficiency: To assess the effect of Vitamin D deficiency on the Knee osteoarthritis disease on the gut microbiome, we compared the gut microbiome composition of individuals with Knee osteoarthritis patient with vitamin D deficiency (KOA_VDD) and those with vitamin D deficient (VDD). We first evaluated the overall differences in beta diversity between faecal microbiome samples of both groups using canonical correspondence analysis (CCA), based on Bray-Curtis distances (Fig. 3A). The two groups appear to cluster differently although the ADONIS test does not explain statistically this difference (p = 0.19).
We estimated α-diversity using the observed OTU and Shannon index (using the Shannon index measuring how evenly OTUs are distributed in a sample) in both groups (Fig. 3B) and they were not statistically significant (observed OTU index, P = 0.7; and Shannon index, P = 0.42).
However, when LEfSe analysis was performed between KOA_VDD and VDD, the gut microbiome of KOA_VDD was found enriched with Phascolarctobacterium, Gordonibacter, Delftia, Parabacteroides, Candidatus-saccharimoanas, Butyricimonas while the gut microbiome in VDD were formed predominantly by Alloprevotella, Odoribacter, and Oribacterium (Fig. 3C).
Vitamin D deficiency impacts Knee osteoarthritis-associated dysbiosis: We assessed the effect of the Vitamin D deficiency on the gut microbiome of KOA patients, by comparing the gut microbiome of KOA patients with and without Vitamin D deficiency (KOA vs KOA_VDD). Although the CCA analysis presents two distinct clusters representing the KOA and KOA_VDD groups, this difference is not significantly different (Adonis, p = 0.055) (Fig. 4A). We observed also a decreased alpha diversity in the KOA_VDD group compared to the KOA (observed OTU index, 158.3 ± 28.4 vs. 174.2 ± 14.8; and Shannon index, 3.0 ± 0.5 vs. 3.2 ± 0.19), but this difference was not statistically different (Fig. 4B). However, as revealed by the LEfSe analysis, the gut microbiome of KOA_VDD are enriched by bacterial taxa, including Bacteroides, Parabacteroides, Pseudobutyrivibrio, Odoribacter, and Butyricimonas. On the other hand, the KOA microbiome was characterized by OTUs including Sphingomonas, Hydrogenoanaerobacterium, Rickenellaceae, Luteimonas, Selenomonas, Oxalobacteraceae, Ruminococcaceae, and Neisseriaceae (Fig. 4C).
Vitamin D deficiency affects the gut bacterial communities: To investigate the effect of the Vitamin D deficiency on the gut microbiome composition, we analyzed the gut microbiome composition of participants with levels of Vitamin D considered as deficient (< 30 ng/ml, VDD group) and normal (> 30 ng/ml, NVD group). Globally, as shown, the CCA analyzed (Fig. 5A) the VDD and NVD groups clustered separately, displaying an effect of the Vitamin D deficiency on the gut microbiome, although the ADONIS test did not confirm it (ADONIS, p = 0.43). We observed that the Vitamin D deficiency tended to increase the alpha diversity (Fig. 5B) (observed OTU index, 153.4 ± 24.2 vs. 145.7 ± 26.2; and Shannon index, 2.8 ± 0.3 vs. 2.7 ± 0.6), although it is not statistically significant. Nevertheless, Vitamin D deficiency affects significantly the abundance of some taxa, as the LEfSe analysis shows (Fig. 5C). The deficiency of Vitamin D was associated with a decreased abundance of five OTUs (LDA score [log10] > 4), including Megasphaera (Genus level), Bacteroides (Genus level), Subdologranulum (Genus level), Paradoxostoma variabile (Species-level), Clostridia (Class level).
On the other hand, when LEfSe Analysis was performed on all four study groups, the distinct gut microbiome patterns for each of the groups were identified. The distinct OTUs for KOA were Peptococcus, Delftia, and Oribacterium while it was Gordonibacter, Butyricimonas, and Parabacteroides for KOA_VDD (supplementary information Figure S4). While Pseudobutyrivibrio and Odoribacter are specific for VDD and Normal group (NVD) was enriched with Faecalibacterium and Anaerofilum. These distinctions are significant and show a strong association between Vitamin D status, microbiome, and KOA.