Metabolic products of the intestinal microbiome and extremes of atherosclerosis

BACKGROUND AND AIMS

There is increasing awareness that the intestinal microbiome plays an important role in human health. We investigated its role in the burden of carotid atherosclerosis, measured by ultrasound as total plaque area.

METHODS

Multiple regression with traditional risk factors was used to identify three phenotypes among 316/3056 patients attending vascular prevention clinics. Residual score (RES; i.e. the distance off the regression line, similar to standard deviation) was used to identify the 5% of patients with much less plaque than predicted by their risk factors (Protected, RES <-2), the 90% with about as much plaque as predicted (Explained, RES -2 to 2), and the 5% with much more plaque than predicted (Unexplained RES >2). Metabolic products of the intestinal microbiome that accumulate in renal failure - gut-derived uremic toxins (GDUT) - were assayed in plasma by ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry.

RESULTS

Plasma levels of trimethylamine n-oxide (TMAO), p-cresyl sulfate, p-cresyl glucuronide, and phenylacetylglutamine were significantly lower among patients with the Protected phenotype, and higher in those with the Unexplained phenotype, despite no significant differences in renal function or in dietary intake of nutrient precursors of GDUT. In linear multiple regression with a broad panel of risk factors, TMAO (p = 0.011) and p-cresyl sulfate (p = 0.011) were significant independent predictors of carotid plaque burden.

CONCLUSIONS

The intestinal microbiome appears to play an important role in atherosclerosis. These findings raise the possibility of novel approaches to treatment of atherosclerosis such as fecal transplantation and probiotics.

Abstract WP404: Intestinal Microbiome and Carotid Atherosclerosis

Background: It is increasingly recognized that metabolic products of the intestinal microbiome may have important effects on cardiovascular disease.

Methods: We studied dietary intake of precursors and plasma levels of toxic metabolic products of the intestinal microbiome in patients at extremes of carotid plaque burden, defined by residual scores (Res) in multiple regression with coronary risk factors: Protected (Res <-2, n = 83), Explained (Res -2 to 2 n = 82) and Unexplained atherosclerosis (Res >2 n = 62). Diet was assessed by a Harvard Food Frequency Questionnaire, and metabolites were measured by ultra-performance liquid chromatography (UPLC) coupled to mass spectrometry (MS). Microbiota were studied by DNA extraction from stool samples; bacteria in each sample were identified and quantitated based upon amplification and sequencing of 16S rRNA variable regions.

Results: There were no significant differences in Mediterranean diet score, renal function, intake of protein, total choline, carnitine, phenylalanine or tyrosine or the fecal microbiota amongst the groups. However, plasma levels of trimethylamine n-oxide (TMAO), indoxylsulfate, p-cresylsulfate, and phenylacetylglutamine were significantly lower in Protected patients and higher in Unexplained patients (Table 1). Serum creatinine and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid ( a marker of renal function) were not different among the groups. In this small sample we did not detect differences in the fecal microbiota.

Discussion: Despite no difference in dietary precursors, renal function or the fecal microbiota, patients protected from atherosclerosis had lower levels and those with unexplained atherosclerosis had higher levels of toxic metabolites of the intestinal microbiome. This suggests their intestinal microbiota are responding differently to dietary intake of precursors from those of patients with explained atherosclerosis.

Conclusion: This finding raises the potential for manipulation of the intestinal microbiota function through probiotic or prebiotic intake, or replacement of intestinal bacteria, to reduce the risk of carotid atherosclerosis and stroke.

The lectin-like protein 1 in Lactobacillus rhamnosus GR-1 mediates tissue-specific adherence to vaginal epithelium and inhibits urogenital pathogens

The probiotic Lactobacillus rhamnosus GR-1 has been documented to survive implantation onto the vaginal epithelium and interfere with urogenital pathogens. However, the molecular mechanisms involved are largely unknown. Here, we report for the first time the construction of dedicated knock-out mutants in L. rhamnosus GR-1 to enable the study of gene functions. In a search for genes responsible for the adherence capacity of L. rhamnosus GR-1, a genomic region encoding a protein with homology to lectin-like proteins was identified. Phenotypic analyses of the knock-out mutant of L. rhamnosus GR-1 revealed a two-fold decreased adhesion to the vaginal and ectocervical epithelial cell lines compared to wild-type. In contrast, the adhesion to gastro-intestinal epithelial (Caco2) and endocervical cell lines (Hela and End1/E6E7) was not drastically affected by the mutation, suggesting that the LGR-1_Llp1 lectins mediates tissue tropism. The purified LGR-1_Llp1 protein also inhibited biofilm formation and adhesion of uropathogenic Escherichia coli. For the first time, an important role for a novel lectin-like protein in the adhesion capacity and host cell-specific interaction of a vaginal probiotic Lactobacillus strain has been discovered, with an additional role in pathogen inhibition.

Impact of technical sources of variation on the hand microbiome dynamics of healthcare workers

We assessed the dynamics of hand microbial community structure of 34 healthcare workers from a single surgical intensive care unit over a short (3 week) time period, whilst taking into account the technical sources of variability introduced by specimen collection, DNA extraction, and sequencing. Sample collection took place at 3 different time points. Only the sampling collection method appeared to have a significant impact on the observed hand microbial community structure among the healthcare workers. Analysis of samples collected using glove-juice showed a slightly more similar microbial composition within individual hand samples over time than between the hands of different individuals over time. This was not true for samples collected using a swab, where samples from a single individual were no more similar to each other over time than those among other individuals over time, suggesting they were essentially independent. DNA extraction techniques (lysozyme only versus enzyme cocktail) and sequencing (replicate set 1 versus 2) using Ion Torrent Personal Genome Machine, were not influential to the microbial community structures. Glove-juice sample collection may likely be the method of choice in hand hygiene studies in the healthcare setting.

The Hsp90 family of proteins in Arabidopsis thaliana

The 90-kDa heat shock protein (Hsp90) is an essential molecular chaperone in eukaryotic cells, with key roles in the folding and activation of proteins involved in signal transduction and control of the cell cycle. A search for Hsp90 sequences in the Arabidopsis thaliana genome revealed that this family includes 7 members. The AtHsp90-1 through AtHsp90-4 proteins constitute the cytoplasmic subfamily, whereas the AtHsp90-5, AtHsp90-6, and AtHsp90-7 proteins are predicted to be within the plastidial, mitochondrial, and endoplasmic reticulum compartments, respectively. The deduced amino acid sequences of each of the cytoplasmic proteins contains the highly conserved C-terminal pentapeptide MEEVD. All of the AtHsp90 sequences include a conserved adenosine triphosphate-binding domain, whereas only the cytoplasmic and endoplasmic reticulum-resident sequences include an adjacent charged linker domain that is common in mammalian and yeast sequences. The occurrence of multiple AtHsp90 proteins in the cytoplasm and of family members in other subcellular compartments suggests a range of specific functions and target polypeptides.

The bacteriophage Mu N gene encodes the 64-kDa virion protein which is injected with, and circularizes, infecting Mu DNA

Upon infection of Escherichia coli with bacteriophage Mu, a 64-kDa protein is injected into the host cell along with the phage DNA. This protein is involved in circularizing the infecting Mu DNA (Harshey, R. M., and Bukhari, A. I. (1983) J. Mol. Biol. 167, 427-441; Puspurs, A. H., Trun, N. J., and Reeve, J. N. (1983) EMBO J. 2, 345-352). Its possible role in the integration of infecting Mu DNA and in the infection process remains to be established. To identify the source of this protein we have prepared antiserum to the protein purified from viral particles. We have shown that the antiserum is specific for the Mu N gene product. The antiserum has been used to immunologically screen a Mu DNA library cloned into an expression vector. Four clones have been shown to produce a protein of 64 kDa that is specifically bound by the antiserum. The only Mu gene common to all four clones is the N gene, as demonstrated by physical and genetic mapping. We have also demonstrated by peptide mapping that the cloned N gene product is identical to the 64-kDa protein found complexed with the injected Mu DNA.

A truncated form of the bacteriophage Mu B protein promotes conservative integration, but not replicative transposition, of Mu DNA

The phage-encoded proteins required for conservative integration of infecting bacteriophage Mu DNA were investigated. Our findings show that functional gpA, an essential component of the phage transposition system, is required for integration. The Mu B protein, which greatly enhances replicative transposition of Mu DNA, is also required. Furthermore, a truncated form of gpB lacking 18 amino acids from the carboxy terminus is blocked in replicative transposition, but not conservative integration. Our results point to a more prominent role for gpB than simply a replication enhancer in Mu DNA transposition. The ability of a truncated form of B to function in conservative integration, but not replicative transposition, also suggests a key role for the carboxy-terminal domain of the protein in the replicative reaction. The existence of a shortened form of gpB, which uncouples conservative integration from replicative transposition, should be invaluable for future dissection of Mu DNA transposition.

Amplification and purification of the bacteriophage Mu encoded B transposition protein

The A and B proteins encoded by the temperate bacteriophage Mu are involved in the high efficiency DNA transposition reaction which is the distinguishing feature of this phage. The genes encoding these early proteins were cloned in an expression vector under the control of the bacteriophage lambda leftward promoter. Under optimal conditions gpB was overproduced to account for 15% of the total cellular protein. The protein was purified to near homogeneity as determined by silver staining. Sequence analysis of the N terminus confirmed the identity of the purified protein as gpB. Proteolytic processing of the B protein does not occur at the amino terminus; the terminal methionine residue is quantitatively deformylated. The protein, which was found to be basic and a general DNA binding protein, was insoluble at low ionic strength in the absence, but not in the presence, of DNA. The B protein also displayed a tendency to aggregate at high ionic strength where it was soluble in the absence of DNA. In addition, the protein was characterized as to its amino acid composition and extinction coefficient at 280 nm. The purified protein is active in a soluble in vitro transposition-replication system.

ATP(GTP)-dependent conversion of MVM parvovirus single-stranded DNA to its replicative form by a purified 10 S species of mouse DNA polymerase alpha

A species of DNA polymerase alpha that is active in the ATP(GTP)-dependent conversion of MVM parvovirus single-stranded linear DNA to the duplex replicative form has been purified 4300-fold from Ehrlich ascites mouse tumour cells. The single-stranded----replicative form activity is maintained throughout ammonium sulfate precipitation, DEAE-cellulose, phosphocellulose and hydroxyapatite column chromatography and glycerol gradient sedimentation. Polypeptides with Mr = 230 000, 220 000, 183 000, 157 000, 125 000, 70 000, 65 000, 62 000, 57 000, 53 000 and 48 000 copurify with the single-stranded----replicative form activity, which sediments at approx. 10 S. The Mr = 183 000, 157 000 and 125 000 polypeptides exhibit catalytic activity when assayed in situ following SDS-polyacrylamide gel electrophoresis. The 10 S form of DNA polymerase alpha is functionally distinguishable from an 8.4 S form of the enzyme obtained from the same cells on the basis of single-stranded----replicative form activity. The single-stranded----replicative form activity of the 10 S enzyme is stable at 22 degrees C for up to 3 h, but exhibits a half life of only 5 min at 45 degrees C.

Characterization of a metastable, partially replicated dimeric intermediate of minute virus of mice

Intracellular, replicative-form DNA of minute virus of mice was characterized by agarose gel electrophoresis, velocity sedimentation, electron microscopy, restriction endonuclease digestion, and sensitivity to the single-stranded nuclease S1. This analysis demonstrated the presence in murine cells infected with minute virus of mice of a 10.0-kilobase pair dimer replicative form, a 5-kilobase pair monomer replicative form, as well as a 5-kilobase viral single-stranded DNA species. Two additional viral DNA species that migrated in 0.5% agarose gels with apparent sizes of 8.0 and 5.5 kilobase pairs were also observed. Further investigation indicated that the 8.0-kilobase pair DNA represents a novel class of metastable, partially replicated, dimeric intermediates. This finding has important implications for the mechanism of parvovirus DNA replication.