This is the first investigation on gut microbiota and associated factors in CCS patients undergoing coronary angiography in Thailand. In this study, the gut microbiome differed among the three groups. There was a reduction in diversity in dyslipidemia patients’ group and CCS patients’ group, which correlated with other studies 18–20. This finding is in consistent with other studies that patients suffering with varies diseases have also reduced bacterial diversity, for instance, hypertension 21, Crohn’s disease 22, psoriatic arthritis 23, metabolic syndrome24, diabetes mellitus and obesity 25.
In this study, the composition pattern of the bacterial microbiota differed significantly between the group of CCS patients and healthy volunteers. The most prevalent bacterial phyla were Firmicutes, Bacteroidetes, Proteobacteria and Actinobacteria, which correlated with other studies 26. Alterations in the ratio of the major phyla Firmicutes to Bacteroidetes have been proposed as a potential CAD risk factor, suggesting that changes in the microbiome's composition may also contribute to the onset and progression of atherosclerosis and CAD 27–29. Furthermore, it was established that a greater Firmicutes/Bacteroidetes ratio (F/B ratio) plays a significant impact in CAD patients 29. F/B ratio is used to diagnose gut dysbiosis and the relationship between this ratio and numerous well-known cardiovascular risk factors, including age, sex, food, and BMI, has been demonstrated 28,30–32. However, in this study, dyslipidemia patients’ group had the greatest F/B ratio whereas the CCS patients’ group did not.
Numerous pathogenic genera, including Escherichia, Salmonella, Vibrio, Yersinia, and Legionella, are members of the phylum Proteobacteria. In our study, the relative abundance proportion of Proteobacteria was the highest in CCS patients’ group. According to Shin et al. study, a higher relative abundance of Proteobacteria is associated with gut dysbiosis and many diseases (obesity, T2DM, and cancers) in human 33. Mainly Proteobacteria, particularly by Enterobacteriaceae and some Firmicutes is the abundance of bacteria producing TMAO precursor 34.
Fusobacteria proportion was increased in the group of CCS patients, however, Actinobacteria and Verrucomicrobia exhibited the lowest relative abundances proportion in CCS patients in comparison with others. This finding is consistent with the study by Zhang et al 35 and Cui et al 29. Fusobacterium nucleatum may initially cause periodontal disease, which then cause CAD due to atherosclerosis via inflammation and lipid metabolism 36. However, no research on the association between Fusobacterium and CAD has been published.
In addition, Streptococcus, Veillonella and Prevotella genera were more common abundance than other groups in the group of CCS patients, with statistical significance following from the Bacteroides genus. Previous studies have reported that Prevotella and Streptococcus genera had a close relationship with metabolic syndrome, atherosclerosis and CAD 37–40. It suggested that the changes in the abundance of Streptococcus, Veillonella, Prevotella was the characteristics of the bacterial microbiota of the CCS patients. The greatest associations were found for Streptococcus anginosus and Streptococcus oralis, according to Sayols-Baixeras et al.'s study of the correlation between Streptococcus spp. and subclinical coronary atherosclerosis 41. The prevalence of various LPS-producing gram-negative bacteria, including Escherichia, Shigella, Veillonella, Klebsiella and Haemophilus increased with the severity of the CAD, according to a study by Liu H. et al 14. High blood LPS level were associated with a threefold increased risk of incident atherosclerosis 42. Veillonella could be found in atherosclerosis plaque and associated with cholesterol levels 43. In addition, Veillonella is high relative abundance in CAD patients 35,44. These findings suggested that the differences in bacterial abundance between the three groups may be linked to the progression of CAD and lipid metabolism in dyslipidemia patients.
The role of Prevotella in human health is controversial. Prevotella is a beneficial microbe, however it is associated to chronic inflammation. Prevotella is linked to high in complex carbohydrates diets from plants, fruits and vegetables, whereas Bacteroides is connected to fat and protein diets 45. Prevotella can be found in healthy human and is considered as commensal bacteria. According to De Filippis et al.'s research, vegetarians had the Mediterranean diet at a high level, that was connected with this bacteria strains and higher levels of SCFAs 46. According to Emoto et, Lactobacillus, Streptococcus, and Enterococcus increased in the gut microbiota of CAD patients whereas Bacteroides and Prevotella was decreased 28.
Prevotella strains' genetic diversity may help to explain the variations in how it reacts to dietary and health conditions in different patients 47. For example, in the study of Italian people’s gut microbiome showed that varying dietary choices could be responsible for P. copri strains with different functions, which resulted in different way for human health 48. P. copri increases the prevalence in non-Westernized people. They typically consume diets rich in fresh vegetables and fruits 49.
However, recent studies have connected increasing Prevotella abundance and certain strains to metabolic syndrome, obesity, hypertension, insulin resistance, non-alcoholic fatty liver disease (NAFLD) and low-grade systemic inflammation 37,50,51 due to augmentation mucosal helper T-cell (Th17) immune responses and stimulation epithelial cells to produce interleukin-1 (IL-1), IL-8, IL-6 and IL-23 52.
P. copri was higher in CCS patients than healthy volunteers in our study, which is correlated with many studies. Numerous diseases are linked with this microorganism to chronic inflammatory process; for example, rheumatoid arthritis, periodontitis, HIV infection, metabolic syndrome, inflammatory bowel disease, CAD and cardiac valve calcification. This bacterium has a role in the development of rheumatoid arthritis (RA) and is immune-relevant 53. In RA patients, gut dysbiosis may have a role in the early stage of RA as shown by the enrichment of P. copri 54. Moreover, P. copri showed a high degree of genetic and functional diversity depending on the lifestyle of the patients and associated with worse arthritis in these patients 55. In CVD patients, P. copri may be a major risk factor, particularly in cardiac valve calcification patients. This microorganism and LDL-C have a positive correlation, which likely supports its pro-inflammatory effects. It is a potential key pathogen implicated in CVDs because of its roles in immunity and inflammation 56. Moreover, P. intermedia, P. nigrescens were periodontopathic bacteria in atherosclerotic plaques 57.
In this investigation, Faecalibacterium genera were lower in CSS patients’ group than in the others. This finding is correlated with Zhu et al, Faecalibacterium, Subdoligranulum, Roseburia, and Eubacterium rectale were decreased 58. There is a significant anti-inflammatory property of Faecalibacterium 59.
The Bacteroides genus had the highest relative abundance when we compared the healthy volunteers' group to the other groups, and the relative abundance of the Roseburia genus was higher in the healthy volunteers' group than in the other groups in our study. Due to their ability to produce SCFAs, prior research indicated that Bacteroides and Bifidobacterium have a certain protective effect on metabolism and are primarily protective bacteria for CCS 60–62. In addition, Roseburia has been linked to improved glucose intolerance and weight loss in mice and in patients with atherosclerosis comparatively high amounts of Collinsella, whereas the normal control group has a substantially larger abundance of Roseburia and Eubacterium 14,63. A study by Liu H. et al. revealed that the prevalence of bacteria that produced butyric acid, such as Lachnospiraceae and Ruminococcaceae, decreased with the progression of CAD 14, this findings is correlated with our study that Lachnospiraceae and Ruminococcacea families were less proportion in CCS patients when compare to others.
SCFAs are metabolites of the fermentation of complex carbohydrates. Members of phylum Bacteroidetes can produce butyrate and acetate, whereas phylum Firmicutes can produce butyrate. SCFAs have a favorable correlation with Roseburia, Bacteroides spp., and Eubacterium rectale. They have been proposed as a protective effect of CCS patients and SCFAs producers have decreased in some CCS patients. Additionally, they improve health by boosting the immunological response of the host, preserving the integrity of the intestinal barrier by controlling the expression of tight junction proteins, and reducing blood lipid levels by preventing the production of cholesterol 64–66. SCFAs plays a protective role in atherosclerosis, while LPS stimulates body inflammation and accelerates the formation of atherosclerosis 67.
When butyrate-producing bacteria disappear, the gut barrier may become damaged, making it easier for microbial toxins like LPS to leak and cause inflammation by binding to Toll-like receptors. Patients with CAD have been found to have a higher LPS biosynthesis in the microbiome, which has connected to insulin resistance and abdominal obesity 68,69.
The synthesis of TMAO, a strong risk factor for the development of CAD, involves dietary choline, betaine, phosphatidylcholine, L-carnitine and lecithin which are obtained from a variety of sources, including egg, fish, red meat, soybean, peanuts 58,70. By producing choline and the intermediary molecule trimethy-lamine (TMA), the gut bacteria also contribute to the synthesis of TMAO. The capacity of the gut microbiota to synthesise choline via the phospholipase D (PLD) enzyme has just recently been discovered. The flavin-containing monooxygenase (FMO) enzyme metabolizes the microbiome-derived TMA molecule into TMAO in hepatocytes 71. Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes are the TMA producers. The production of foam cells is stimulated by the impairment of cholesterol metabolism in macrophages caused by TMAO-dependent activation of macrophage scavenger receptors and CD36 expression. The higher TMAO production, the higher CAD risk 72. In the context of increased intestinal permeability, TMAO is also linked to C-reactive protein (CRP), endothelial dysfunction, and elevated blood level of the LPS endotoxin. It can also cause platelet hyperreactivity, which have an impact on CAD progression 73.
The LDL-C level was lowest in CCS patients. The reasons for the differences in LDL-C levels was that the majority of patients (96.67%) were treated with statins. The treatment with statins is associated with lower prevalence of gut microbiota dysbiosis 74. In mice study, statins could moderate gut microbiota by increasing the abundance of Bacteroides, Butyricimonas and Mucispirillum 75. Moreover, the clinical response to statin therapy in individuals with CAD is associated with the gut microbiota. For instance, poor statin response is associated with a significant reduction in the number of beneficial bacteria (Akkermansia muciniphila and Lactobacillus) and an increase in the number of bacteria (Holdemanella and Facecallibacterium) 76. Statins have also been linked to anti-inflammatory and immunomodulatory properties 77.
The genus Megasphaera was strongly positively correlated with TG level and negatively correlated with HDL-C. Lopez-Montoya et al. investigation confirmed our results, showing Megasphaera and Escherichia-Shigella were highly associated with atherogenic dyslipidemia patients, defined as both hypertriglyceridemia and low HDL-C 78. Moreover, one study has shown that patients with symptomatic stroke had an altered gut microbiota and defined Megasphaera as opportunistic pathogens 79. In obesity and overweight patients, Megasphaera was significantly increased relative abundance and correlated with low physical activity 80. Megasphaera is involved in a mechanism that generates ammonia, which has negative consequences 81.
Hs-CRP can help in identifying chronic inflammation. Periodontal disease was linked to CAD and low grade inflammation, increased CRP and fibrinogen, according to de Oliveira et al.’s research 82. There is correlation between hs-CRP and CAD severity in CCS patients 83. Patients with myocardial infarction with elevated hs-CRP level (≥ 2 mg/L) were at higher risk of major adverse cardiovascular events and death 84. In CCS patients of our study, the Lachnospiraceae, Peptostreptococcaceae families and Pediococcus genus was positively correlated with hs-CRP, a finding that has not been reported before. There are some limitations in our study, the specific function and the metabolites of the gut microbiota were not examined.
In conclusion, this study demonstrated a significant difference in the composition of gut microbiota between CCS patients, dyslipidemia patients and healthy volunteers. The alpha diversity was lower in CCS and dyslipidemia patients than in healthy volunteers. The relative abundance of Proteobacteria, Fusobacteria, Prevotella and Streptococcus were significantly increased while Roseburia, Ruminococcus and Faecalibacterium were lower in CCS patients. In dyslipidemia patients, Megasphaera was strongly positively correlated with TG level and negatively correlated with HDL-C. Modification of gut microbiota is associated with changes in clinical parameters involved in development of CAD in CCS patients.