Dietary omega-6/omega-3 ratio is not associated with gut microbiota composition and disease severity in patients with nonalcoholic fatty liver disease.

In this cross-sectional study, we hypothesized that a high dietary ratio of omega-6 (n-6) to omega-3 (n-3) fatty acids could be associated with an altered gut bacterial composition and with the disease severity in patients with nonalcoholic fatty liver disease (NAFLD). A total of 101 NAFLD patients were included in the study, of which 63 underwent a liver biopsy. All 101 patients completed a 14-day food and activity record. Ebispro 2016 professional software was used to calculate individual macronutrients and micronutrients consumed. Patients were grouped into 3 quantiles (Q) according to a low (Q1: <6.1, n = 34), moderate (Q2: 6.1-7.8, n = 33), or high (Q3: >7.8, n = 34) dietary n-6/n-3 ratio. Stool samples were analyzed using 16S rRNA gene sequencing. Spearman correlation coefficients and principal coordinate analysis were used to detect differences in the bacterial composition of the gut microbiota. The median dietary n-6/n-3 ratio of all patients was 6.7 (range, 3.1-14.9). No significant associations between the dietary n-6/n-3 ratio and the gut microbiota composition or disease severity were observed. However, the abundance of specific bacteria such as Catenibacterium or Lactobacillus ruminis were found to be positively correlated and the abundance of Clostridium were negatively correlated with dietary n-6 fatty acid intake. The results indicate that a high dietary n-6/n-3 ratio is probably not a highly relevant factor in the pathogenesis of human NAFLD. Further studies are needed to clarify the importance of interactions between gut bacterial taxa and n-6 fatty acids in the pathophysiology of NAFLD.

Longitudinal variability in the urinary microbiota of healthy premenopausal women and the relation to neighboring microbial communities: A pilot study.

BACKGROUND: The understanding of longitudinal changes in the urinary microbiota of healthy women and its relation to intestinal microbiota is limited. METHODS: From a cohort of 15 premenopausal women without known urogenital disease or current symptoms, we collected catheter urine (CU), vaginal and periurethral swabs, and fecal samples on four visits over six months. Additionally, ten participants provided CU and midstream urine (MU) to assess comparability. Urine was subjected to expanded culture. 16S rRNA gene sequencing was performed on all urine, fecal, and selected vaginal and periurethral samples. Sequence reads were processed (DADA2 pipeline) and analyzed using QIIME 2 and R. RESULTS: Relative abundances of urinary microbiota were variable over 6-18 months. The degree of intraindividual variability of urinary microbiota was higher than that found in fecal samples. Still, nearly half of the observed beta diversity of all urine samples could be attributed to differences between volunteers (R2 = 0.48, p = 0.001). After stratification by volunteer, time since last sexual intercourse was shown to be a factor significantly contributing to beta diversity (R2 = 0.14, p = 0.001). We observed a close relatedness of urogenital microbial habitats and a clear distinction from intestinal microbiota in the overall betadiversity analysis. Microbiota compositions derived from MU differed only slightly from CU compositions. Within this analysis of low-biomass samples, we identified contaminating sequences potentially stemming from sequencing reagents. CONCLUSIONS: Results from our longitudinal cohort study confirmed the presence of a rather variable individual urinary microbiota in premenopausal women. These findings from catheter urine complement previous observations on temporal dynamics in voided urine. The higher intraindividual variability of urinary microbiota as compared to fecal microbiota will be a challenge for future studies investigating associations with urogenital diseases and aiming at identifying pathogenic microbiota signatures.

Combined analysis of gut microbiota, diet and PNPLA3 polymorphism in biopsy-proven non-alcoholic fatty liver disease.

BACKGROUND AND AIMS: Non-alcoholic fatty liver disease (NAFLD) is a global health burden. Risk factors for disease severity include older age, increased body mass index (BMI), diabetes, genetic variants, dietary factors and gut microbiota alterations. However, the interdependence of these factors and their individual impact on disease severity remain unknown. METHODS: In this cross-sectional study, we performed 16S gene sequencing using fecal samples, collected dietary intake, PNPLA3 gene variants and clinical and liver histology parameters in a well-described cohort of 180 NAFLD patients. Principal component analyses were used for dimensionality reduction of dietary and microbiota data. Simple and multiple stepwise ordinal regression analyses were performed. RESULTS: Complete data were available for 57 NAFLD patients. In the simple regression analysis, features associated with the metabolic syndrome had the highest importance regarding liver disease severity. In the multiple regression analysis, BMI was the most important factor associated with the fibrosis stage (OR per kg/m2 : 1.23, 95% CI 1.10-1.37, P < .001). The PNPLA3 risk allele had the strongest association with the histological grade of steatosis (OR 5.32, 95% CI 1.56-18.11, P = .007), followed by specific dietary patterns. Low abundances of Faecalibacterium, Bacteroides and Prevotella and high abundances of Gemmiger were associated with the degree of inflammation, ballooning and stages of fibrosis, even after taking other cofactors into account. CONCLUSIONS: BMI had the strongest association with histological fibrosis, but PNPLA3 gene variants, gut bacterial features and dietary factors were all associated with different histology features, which underscore the multifactorial pathogenesis of NAFLD.

Prediction of advanced fibrosis in non-alcoholic fatty liver disease using gut microbiota-based approaches compared with simple non-invasive tools.

Liver fibrosis is the major determinant of liver related complications in patients with non-alcoholic fatty liver disease (NAFLD). A gut microbiota signature has been explored to predict advanced fibrosis in NAFLD patients. The aim of this study was to validate and compare the diagnostic performance of gut microbiota-based approaches to simple non-invasive tools for the prediction of advanced fibrosis in NAFLD. 16S rRNA gene sequencing was performed in a cohort of 83 biopsy-proven NAFLD patients and 13 patients with non-invasively diagnosed NAFLD-cirrhosis. Random Forest models based on clinical data and sequencing results were compared with transient elastography, the NAFLD fibrosis score (NFS) and FIB-4 index. A Random Forest model containing clinical features and bacterial taxa achieved an area under the curve (AUC) of 0.87 which was only marginally superior to a model without microbiota features (AUC 0.85). The model that aimed to validate a published algorithm achieved an AUC of 0.71. AUC's for NFS and FIB-4 index were 0.86 and 0.85. Transient elastography performed best with an AUC of 0.93. Gut microbiota signatures might help to predict advanced fibrosis in NAFLD. However, transient elastography achieved the best diagnostic performance for the detection of NAFLD patients at risk for disease progression.

High Protein Intake Is Associated With Histological Disease Activity in Patients With NAFLD.

Overconsumption of carbohydrates and lipids are well known to cause nonalcoholic fatty liver disease (NAFLD), while the role of nutritional protein intake is less clear. In Western diet, meat and other animal products are the main protein source, with varying concentrations of specific amino acids. Whether the amount or composition of protein intake is associated with a higher risk for disease severity has not yet been examined. In this study, we investigated associations of dietary components with histological disease activity by analyzing detailed 14-day food records in a cohort of 61 patients with biopsy-proven NAFLD. Furthermore, we used 16S ribosomal RNA gene sequencing to detect associations with different abundances of the gut microbiota with dietary patterns. Patients with definite nonalcoholic steatohepatitis (NAFLD activity score of 5-8 on liver biopsy) had a significantly higher daily relative intake of protein compared with patients with a NAFLD activity score of 0-4 (18.0% vs. 15.8% of daily protein-based calories, P = 0.018). After adjustment for several potentially confounding factors, a higher protein intake (≥17.3% of daily protein-based calories) remained associated with definite nonalcoholic steatohepatitis, with an odds ratio of 5.09 (95% confidence interval 1.22-21.25, P = 0.026). This association was driven primarily by serine, glycine, arginine, proline, phenylalanine, and methionine. A higher protein intake correlated with a lower Bacteroides abundance and an altered abundance of several other bacterial taxa. Conclusion: A high protein intake was independently associated with more active and severe histological disease activity in patients with NAFLD. Further studies are needed to investigate the potential harmful role of dietary amino acids on NAFLD, with special attention to meat as their major source.

Phenotyping non-alcoholic fatty liver disease by the gut microbiota: Ready for prime time?

BACKGROUND AND AIM: Several studies observed alterations in the gut microbiota in patients with non-alcoholic fatty liver disease (NAFLD). However, analyzed patient populations and methods strongly differ among these studies. The aim of this study was to prove the reproducibility of published results and to provide a detailed overview of all findings in our NAFLD cohort using next generation sequencing methods. METHODS: The individual taxonomic microbiota composition of fecal samples from 90 NAFLD patients and 21 healthy controls was analyzed using 16S rRNA gene sequencing. Study participants were grouped according to their disease stage and compared regarding their gut microbiota composition. Studies were identified from PubMed listed publications, and the results were compared with the findings in our cohort. RESULTS: Results from 13 identified studies were compared with our data. A decreased abundance of the Bacteroidetes and Ruminococcaceae as well as an increased abundance of Lactobacillaceae and Veillonellaceae and Dorea were the most frequently reported changes among NAFLD patients in 4/13, 5/13, 4/13, 2/13, and 3/13 studies, respectively. Even though these alterations in the gut microbiota composition were also observed in our patient cohort, the majority of published differences could not be reproduced, neither in our own nor in other NAFLD cohort studies. CONCLUSION: Despite repeatedly reproduced abundance patterns of specific bacteria, the heterogeneous study results did not reveal a consistent disease specific gut microbiota signature. Further prospective studies with homogenous patient cohorts and standardized methods are necessary to phenotype NAFLD by the gut microbiota.

Increased homologous integration frequency in Yarrowia lipolytica strains defective in non-homologous end-joining.

The ascomycetous yeast Yarrowia lipolytica has been established as model system for studies of several research topics as well as for biotechnological processes in the last two decades. However, frequency of heterologous recombination is high in this yeast species, and so knockouts of genes are laborious to achieve. Therefore, the aim of this study was to check whether a reduction of non-homologous end-joining (NHEJ) of double strand breaks (DSB) results in a strong increase of proportion of homologous recombinants. The Ku70-Ku80 heterodimer is known as an essential protein complex of the NHEJ. We show that deletion of YlKU70 and/or YlKU80 results in an increase of the rate of transformants with homologous recombination (HR) up to 85 % in each case. However, it never reaches near 100 % of HR in any case as described for some other yeast. Furthermore, we demonstrated that growth of Δylku strains was similar to that of the wild-type strain. In addition, no differences were detected between the Δylku strains and the parent strain in respect to sensitivity to the mutagenic agent EMS as well as to the antibiotics hygromycin, bleomycin and nourseothricin. However, Δylku70 and Δylku80 strain showed a slightly higher sensitivity against UV rays. Thus, the new constructed Δylku strains are attractive recipient strains for homologous integration of DNA fragments and a valuable tool for directed knockouts of genes. Nevertheless, our data suggest the existence of another system of non-homologous recombination what may be subject of further investigation.

Overexpression of alpha-ketoglutarate dehydrogenase in Yarrowia lipolytica and its effect on production of organic acids.

The yeast Yarrowia lipolytica is one of the most intensively studied "non-conventional" yeast species. Its ability to secrete various organic acids, like pyruvic (PA), citric, isocitric, and alpha-ketoglutaric (KGA) acid, in large amounts is of interest for biotechnological applications. We have studied the effect of the alpha-ketoglutarate dehydrogenase (KGDH) complex on the production process of KGA. Being well studied in Saccharomyces cerevisiae this enzyme complex consists of three subunits: alpha-ketoglutarate dehydrogenase, dihydrolipoyl transsuccinylase, and lipoamide dehydrogenase. Here we report the effect of overexpression of these subunits encoding genes and resulting increase of specific KGDH activity on organic acid production under several conditions of growth limitation and an excess of carbon source in Y. lipolytica. The constructed strain containing multiple copies of all three KGDH genes showed a reduced production of KGA and an elevated production of PA under conditions of KGA production. However, an increased activity of the KGDH complex had no influence on organic acid production under citric acid production conditions.