The intestines of healthy persons are colonized by a diverse array of bacteria, with Firmicutes and Bacteroides accounting for the majority of the intestinal flora (16). The intestinal microbial ecology is involved in the digestion and absorption of nutrients, energy metabolism, immunological control, and a variety of other physiological functions (17–19). According to studies, the occurrence and progression of diseases alters the gut flora.
There is mounting evidence that DKD patients' gut bacteria are changed (20, 21). Our findings indicated that the DKD and HC groups had significantly different microbial counts and relative abundances. Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria, and Actinobacteria accounted for the majority of the microbial content in all samples in this investigation, which was consistent with earlier findings. Firmicutes and Bacteroidetes are the two major bacterial groupings found in healthy humans, together accounting for around 90% of the phylum level (22). Interestingly, we discovered that the DKD group possessed a larger relative abundance of Proteobacteria, Acidobacteria, and Actinobacteria, but lacked Firmicutes and Bacteroidetes. Nosratola D.Vaziri found that Actinobacteria, Firmicutes, and Proteobacteria were abundant in patients with ESRD than healthy controls (23). Numerous studies have demonstrated that the number of proteobacteria increases at the phylum level in obese and diabetic patients, while the Bacteroidetes phylum decreases (24, 25). Proteobacteria rise promotes the formation of Lipopolysaccharides (LPS), which results in an increase in pro-inflammatory factors and an inflammatory response (26).
Meanwhile, we detected a considerable decrease in the relative abundance of Lactobacillus at the genus level in the DKD, while Escherichia-Shigella increased. Lactobacillus is high in probiotics, which aid in the maintenance of the intestinal functional barrier's integrity. Tae-Hee Lee et al. confirmed that BP121 boosted the number of good intestinal flora Lactobacillus and decreased kidney inflammation, oxidative stress, and uremic toxins (27). Lactobacillus may create the helpful organic acid lactate, which is metabolized in the colon to butyric acid (28). As a result, we hypothesized that reducing Lactobacillus would potentially result in an increased inflammatory response. Additionally, butyrate contributes to the reduction of the pro-inflammatory effects of LPS activation. Escherichia-Shigella was shown to be abundant in stool samples of patients with DKD and reduced renal function after crossing the intestinal epithelial barrier, according to a study (29). Escherichia coli may create more indoxyl sulfate (IS) in people with advanced chronic kidney disease (30).
More and more data from trials in mice and humans suggests that metabolites produced by the gut microbiota play a critical role in the development and progression of renal disorders. Numerous studies have demonstrated that trimethylamine-oxide (TMAO), short-chain fatty acids (SCFAs), protein-bound uremic toxins (PBUTs), bile acids (BAs), tryptophan-derived metabolites, and branched-chain amino acids (BCAAs) were abundant in DKD patients, all of which play a significant role in the progression of DKD. We observed an increasing rise in several organic nitrogen compounds, including TMPO, L-Carnitine, and Choline, in serum samples from DKD patients. Trimethylamine (TMA) is primarily generated from choline, phosphatidylcholine, and L-carnitine by intestinal bacteria and is subsequently oxidized to TMAO in the liver by monooxygenase 3 enzymes before being distributed to various tissues or eliminated via the kidney (31). The TMAO pathway was the first to establish a relationship between gut microbe-produced compounds and the risk of cardiovascular and renal illness (32). High TMAO levels were reported to worsen DKD in animal models, and supplementation with TMAO inhibitors (3,3-dimethyl-1-butanol) was found to mitigate the exacerbation of DKD symptoms (20, 33). Posada-Ayala et al. detected seven distinct metabolites in s from 16 chronic kidney disease patients and 15 healthy controls, with chronic kidney disease patients having higher plasma TMAO levels, consistent with our finding (34).
Numerous PBUTs (for example, indoxyl sulfate, phenyl sulfate, and phenylacetylglutamine) are derived from the results of microbial metabolism of food chemicals in the intestine, including aromatic amino acids, tyrosine, phenylalanine, and tryptophan (35). Barrios et al. established that indoxyl-sulfate, p-cresyl-sulfate, and phenylacetylglutamine were all early indicators of renal function decrease (36). Numerous investigations have demonstrated that phenyl sulfate may impair the barrier function of the glomerular basement membrane, resulting in increased urine protein levels (37). Increased serum phenylacetylglutamine levels have been shown to be an independent risk factor for cardiovascular disease (38, 39), implying that DKD patients in this study may be at an increased risk of developing cardiovascular disease. Certain uremic toxins, such as Phenylacetylglutamine, N-acetyl-L-arginine, Methylguanidine, and Guanidinosuccinic acid, can be found as metabolites in patients with end-stage renal failure. They demonstrated an upward trend in DKD in our study, implying that it may advance to ESRD. These uremic solutes have the potential to impair endothelium repair following injury and to cause direct vascular damage, hence increasing the risk of cardiovascular problems.In our study, they showed an uptrend in the DKD, which suggested that it might progress to ESRD. These uremic solutes have the potential to impair endothelium repair following injury and to cause direct vascular damage, hence increasing the risk of cardiovascular problems.
We analyzed the KEGG database to gain a better understanding of the probable function of DKD intestinal flora. We discovered an enrichment in arginine and proline metabolism in serum samples from DKD patients. Citrulline, L-Arginine, D-Proline, Hydroxyproline, Guanidoacetic acid, Creatinine, 5-Guanidino-2-oxopentanoate, 4-Aminobutyraldehyde, and 5-Aminopentanoic acid were all constituents of this pathway. Arginine and its metabolites are involved in a variety of metabolic processes. In adults, glutamine and proline are metabolized to citrulline in the colon via pyrroline-5-carboxylate (P5C), and subsequently to arginine in the kidneys. L-arginine is a precursor to the formation of nitric oxide (NO), polyamines, and agmatine. These metabolites play a role in the progression of renal disease (40, 41). Additionally, NO metabolism is critical for endothelial dysfunction in DKD (42). Although animal models of kidney disease have demonstrated that supplementing with L-arginine is good for diabetic nephropathy, the mechanism by which it works is yet unknown (43). Numerous traditional Chinese remedies, including Cicada Cordyceps Polysaccharide, Tangshen Recipe, and Shenyankangfu Pian, have demonstrated that DKD can be treated by modifying the intestinal microbiota's composition or function.
Our research was not without flaws. The experiment used blood samples for differential metabolite analysis and did not include pee samples for comparison. We used the 16S RNA gene sequencing technique to determine bacterial taxa at a low resolution (genus) level in order to investigate the gut microbiota. As a result, the absence of comprehensive characterization of the entire microbiome precluded us from examining the taxonomic and functional potentials of species and subspecies.