| Background and AimsWith the development of society and improvement of people’s living standard, people’s life style, diet structure, environmental factors have been changed. The prevalence of diabetes, obesity and other metabolic diseases has drastically increased over the past few decades. Metabolic diseases such as diabetes and obesity are becoming a social problem of utmost importance for all countries. The investigation of China Diabetes Association found that, the prevalence of T2DM has increased significantly in China. In2012, China diabetes incidence rate reaches as high as9.7%, the national diabetes patients reached1million. The social system can certainly not afford the corresponding expenses. Therefore, the disease is poorly treated and pathological complications are blooming.Diabetes mellitus (DM) is an incompletely understood chronic, progressive multifactorial disease with the absolute or relative insufficient of insulin secretion and reduction of target cell sensitivity to insulin. Diabetes mellitus is a group of syndrome characterized by hypoglycemia and associated with systemic metabolic disorder of fat, protein, water and electrolyte. The disease is a major cause of early mortality due to atherosclerosis and cardiovascular disease, and is the leading cause of blindness, leg amputations, and chronic renal disease. DM included type1diabetes and Type2 diabetes, accounting for all the medical records of5-10%and90%respectively. WHO diagnosis of diabetes is:fasting plasma glucose7.0mmol/1or oral glucose tolerance test(OGTT)2h plasma glucose11.1mmol/1. In addition to diagnosed diabetes, there are two kinds of abnormal blood sugar symptoms, namely impaired fasting glucose (IFG) and impaired glucose tolerance(IGT).The diagnostic criteria for IFG fasting plasma glucose between6.1-6.9mmol/1, OGTT<7.8mmol/1; IGT for fasting plasma glucose<7.0mmol/1, OGTT2h>7.8mmol/1and<11.lmmol/1. These two kinds circumstances also known as pre-diabetes state (Pre-diabetes) which is the early symptoms of diabetes. If we can control of plasma glucose in the stage, block to the development of diabetes, it will be important for patients and families and the whole society.In recent years, studies have found that the occurrence of type2diabetes with insulin resistance is given priority to with relatively insufficient insulin or is given priority to with insufficient insulin secretion associated with insulin resistance as the basic characteristics. IR is characterized by chronic systemic low inflammation, pro-inflammatory factor and oxidative stress play an important role in the process of the IR. Epidemiological studies have shown that about2.5%of individuals with IR, and prevalence rate of IR is more than80%in T2DM patients. IR is correlated with islet cells, liver, skeletal muscle, adipose tissue and intestinal, hypothalamus, and the immune system, and other tissue organs. Occurs mainly in the peripheral tissues (muscle, fat) and liver, in the former insulin promote skeletal muscle and adipose tissue glucose uptake and utilization or storage were decreased, the latter is characterized by insulin suppression of hepatic glycogen output. The study shows that adipose tissue may be the center site of inflammation system activation:fat cells can produce TNF-a, lead to IR; High lipid diet and obesity induce adipose tissue inflammation, and associated with inflammation regulated factors such as IL-6, monocyte chemotactic protein1(MCP-1), NF-KB, excited protein-1(API) and the growth response factors increased.Studies have shown that intestinal flora is closely related to digestion, nutrition, metabolism, immunity, etc, is the "environment" factors for enter human body, its status and role is equivalent to acquired an important "organs". Beside an increased energy harvest from the diet, further mechanisms linking gut flora to obesity have been subsequently proposed, including chronic low-grade endotoxinemia, regulation of tissutal biologically active fatty acid composition and modulation of gut-derived peptide secretion.The chronic inflammation of T2DM patients is caused by metabolic endotoxinemia, which is a state of low levels of inflammation. Lipopolysaccharide (LPS), an alternative name of endotoxin which is a component of the gram-negative bacterial cell walls, can trigger the inflammatory process by binding to the CD14toll-like receptor-4(TLR-4) complex at the surface of innate immune cells. Recent work has shown that gut bacteria can initiate the inflammatory state of obesity and IR through the activity of LPS. The relevance of the TLR-4pathways for metabolic disease was confirmed by the finding that the deletion of TLR-4prevented the high-fat diet induced insulin resistance.A series of studies elegantly demonstrated that after4weeks of high-fat feeding, mice exhibited an obese phenotype accompanied by a change in gut flora composition (the reduction of Bifidobacteria and Eubacteria spp.) and a two to threefold increase in circulating LPS levels, which they called "metabolic endtoxemia" since LPS plasma concentrations were much lower than those observed during septic shock. When metabolic endotoxemia was reproduced by subcutaneous infusion of LPS, animals developed the same metabolic abnormalities induced by the high-fat diet, while LPS receptor KO (CD14K0) mice were resistant to the effects of both high-fat diet and LPS infusion. Moreover, CD14KOmice were hypersensitive to insulin even when they were fed a normal diet, suggesting that CD14may modulate insulin sensitivity in physiological conditions. In a subsequent experiment, changes in gut flora composition induced by antibiotic treatment reduced metabolic endotoxemia and the cecal content of LPS, closely correlating with an improvement in the obese phenotype in both high-fat-fed and ob/ob mice.The role of LPS in triggering systemic inflammation was subsequently evaluated in healthy human subjects. Research found a similar grade endotoxemia increased adipose tumor necrosis factor (TNF)-a and interleukin (IL)-6concentrations and promoted IR, and a high-fat, high-carbohydrate meal induced a significant postprandial plasma LPS elevation, accompanied by an in-creased mononuclear cell expression of TLR-4, nuclear factor KB (NF-KB), and suppressor of cytokine signaling-3(SOCS-3), an adipokine involved in IR. These increases were totally absent after an American Heart Association (AHA) meal rich in fiber and fruit.These data support the concept that endotoxinemia may play a key role in the pathogenesis of obesity-associated inflammatory state. As obesity is an important risk factor for T2DM, researchers suspect that there may have certain relationship between gut flora and T2DM. In recent years, with the gradually thorough of research, close links have been revealed between of intestinal flora and diabetes. Recent researches showed, the type2diabetic patients or the model of type2diabetic animals compared to controls, the intestinal flora composition changed, which is probably the factor caused of insulin resistance and diabetes. Scientists also found in animal experiments, regulation of intestinal flora by changing the structure of dietary factors such as feed with high fat diet can lead to obesity, which increase the risk of diabetes. Intestinal flora closely related to the occurrence and the development of metabolic diseases, which have become a new research hotspot at home and abroad.With the deepening of the research, people found that diabetes and obesity is characterized by insulin resistance and low grade of inflammation, and the intestinal flora and the host exist a close contact between the regulations of energy balance, inflammation reaction. So people speculate that in addition to genes and the environmental associated factors such as diet structure and physical activity, the intestinal flora may be play an important role the onset of obesity, T2DM and other metabolic diseases,Based on the above research background, this study selected T2DM, Pre-diabetes and healthy volunteers as the research object. There are two aims of the study:first, to assess the differences among the composition of the intestinal flora in T2DM, Pre-diabetes and healthy persons, and secondly is to figure out the relationship between fast plasma glucose, lipids metabolism and gut flora, to explore the potential role of intestinal flora in the development of T2DM.MethodsThe study included55type2diabetic patients,10type2pre-diabetic patients and46healthy volunteers. Fecal samples were collected from all subjects. Total DNA was extracted from collected stool samples and submitted to real-time quantitative PCR (qpcr) with primers specifically targeting V3region of the16srRNA gene.Results1. Comparison of the bacteria among three groupFirstly there were significant difference between T2DM, Pre-DM and healthy persons by comparing the total bacteria, pre-diabetes was significant more than the other two groups(P=0.000). Compare with the healthy persons and T2DM, the amount of Escherichia coli was significant increased in Pre-DM (P=0.002), Clostridium coccoides subgroup, Prevotella spp, Lactobacillus were although higher, but the difference were not significant(P value0.179,0.186,0.239respectively). Among the three group, the amount of Clostridium leptum subgroup, Bifidobacterium, Enterococcus were statistically increased (P value0.011,0.012,0.000respectively) in T2DM, but Bacteroides was significantly decreased (P=0.006).Second the Bacteroides/Clostridium coccoides subgroup was significantly decreased in T2DM and Pre-DM (P=0.000). In type2diabtetes the proportions of Clostridium leptum subgroup, Bifidobacterium and Enterococcus were significantly increase than the other two groups (P value0.000,0.001,0.015respectively). The proportions of Prevotella spp as well as Escherichia coli in pre-diabetes group were higher than the others, in which Escherichia coli was statistical higher (P=0.015), but the Prevotella spp was not significant difference. Thirdly, the proportion of Lactobacillus was minimal among the three groups.2. The relationship between intestinal flora and fasting blood glucoseThe amount and the proportions of Enterococcus subgroup were correlated positively and significantly with plasma glucose concentration(R=0.221P=0.020,R=0.187P=0.050respectively), on the contrary the amount of Bacteroides and Bacteroides/Clostridium coccoides were correlate negatively and significantly with plasma glucose concentration(R=-0.251P=0.008, R=-0.206P=0.030respectively).3. The relationship between intestinal flora and lipids metabolismThe amount and the proportions of Enterococcus subgroup were correlated positively and significantly with plasma triglycerides(TG) concentration(R=0.227P=0.016, R=0.313P=0.001respectively), on the contrary the proportions of Enterococcus and Clostridium leptum subgroup were correlated negatively and significantly with plasmaglucose high-density lipoprotein cholesterol(HDL) concentration (R=-0.228P=0.018,R=-0.248P=0.010respectively).Conclusion1. The results of this study indicate that T2DM and Pre-DM in humans is associated with compositional changes in intestinal flora.2. The level of fast plasma glucose and lipids should be considered when linking intestinal flora with T2DM and Pre-DM diseases.3. The level of lipids should be considered when linking intestinal flora with T2DM and Pre-DM diseases. |
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