[Show abstract][Hide abstract] ABSTRACT: Current thinking, which is based mainly on rodent studies, is that physiologic doses of folic acid (pterylmonoglutamic acid), such as dietary vitamin folates, are biotransformed in the intestinal mucosa and transferred to the portal vein as the natural circulating plasma folate, 5-methyltetrahydrofolic acid (5-MTHF) before entering the liver and the wider systemic blood supply.OBJECTIVE: We tested the assumption that, in humans, folic acid is biotransformed (reduced and methylated) to 5-MTHF in the intestinal mucosa.DESIGN: We conducted a crossover study in which we sampled portal and peripheral veins for labeled folate concentrations after oral ingestion with physiologic doses of stable-isotope-labeled folic acid or the reduced folate 5-formyltetrahydrofolic acid (5-FormylTHF) in 6 subjects with a transjugular intrahepatic porto systemic shunt (TIPSS) in situ. The TIPSS allowed blood samples to be taken from the portal vein.RESULTS: Fifteen minutes after a dose of folic acid, 80 ± 12% of labeled folate in the hepatic portal vein was unmodified folic acid. In contrast, after a dose of labeled 5-FormylTHF, only 4 ± 18% of labeled folate in the portal vein was unmodified 5-FormylTHF, and the rest had been converted to 5-MTHF after 15 min (postdose).Conclusions: The human gut appears to have a very efficient capacity to convert reduced dietary folates to 5-MTHF but limited ability to reduce folic acid. Therefore, large amounts of unmodified folic acid in the portal vein are probably attributable to an extremely limited mucosal cell dihydrofolate reductase (DHFR) capacity that is necessary to produce tetrahydrofolic acid before sequential methylation to 5-MTHF. This process would suggest that humans are reliant on the liver for folic acid reduction even though it has a low and highly variable DHFR activity. Therefore, chronic liver exposure to folic acid in humans may induce saturation, which would possibly explain reports of systemic circulation of unmetabolized folic acid. This trial was registered at clinicaltrials.gov as NCT02135393.
American Journal of Clinical Nutrition 06/2014; · 6.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We genotyped 2,861 cases of primary biliary cirrhosis (PBC) from the UK PBC Consortium and 8,514 UK population controls across 196,524 variants within 186 known autoimmune risk loci. We identified 3 loci newly associated with PBC (at P < 5 × 10(-8)), increasing the number of known susceptibility loci to 25. The most associated variant at 19p12 is a low-frequency nonsynonymous SNP in TYK2, further implicating JAK-STAT and cytokine signaling in disease pathogenesis. An additional five loci contained nonsynonymous variants in high linkage disequilibrium (LD; r(2) > 0.8) with the most associated variant at the locus. We found multiple independent common, low-frequency and rare variant association signals at five loci. Of the 26 independent non-human leukocyte antigen (HLA) signals tagged on the Immunochip, 15 have SNPs in B-lymphoblastoid open chromatin regions in high LD (r(2) > 0.8) with the most associated variant. This study shows how data from dense fine-mapping arrays coupled with functional genomic data can be used to identify candidate causal variants for functional follow-up.
[Show abstract][Hide abstract] ABSTRACT: We explored patients' experiences of receiving a diagnosis of the liver disease primary biliary cirrhosis (PBC) through qualitative interviews. Findings were used to develop a patient information DVD with expert clinicians describing PBC and patients talking about their experiences. The DVD was premièred to an audience of PBC, patients who provided positive feedback. This research identified areas leading to a positive diagnosis experience, such as knowledge, information, consistency, a positive approach, simplification and repetition. We believe that introducing such a DVD into clinical practice, following diagnosis, will make a real difference to the quality of life of newly-diagnosed PBC patients.
Journal of Visual Communication in Medicine 03/2011; 34(1):4-13.
[Show abstract][Hide abstract] ABSTRACT: In addition to the HLA locus, six genetic risk factors for primary biliary cirrhosis (PBC) have been identified in recent genome-wide association studies (GWAS). To identify additional loci, we carried out a GWAS using 1,840 cases from the UK PBC Consortium and 5,163 UK population controls as part of the Wellcome Trust Case Control Consortium 3 (WTCCC3). We followed up 28 loci in an additional UK cohort of 620 PBC cases and 2,514 population controls. We identified 12 new susceptibility loci (at a genome-wide significance level of P < 5 × 10⁻⁸) and replicated all previously associated loci. We identified three further new loci in a meta-analysis of data from our study and previously published GWAS results. New candidate genes include STAT4, DENND1B, CD80, IL7R, CXCR5, TNFRSF1A, CLEC16A and NFKB1. This study has considerably expanded our knowledge of the genetic architecture of PBC.
[Show abstract][Hide abstract] ABSTRACT: Primary biliary cirrhosis (PBC) is associated with fatigue, memory impairment, and sleep disturbances. These symptoms suggest the possibility of underlying central nervous system (CNS) dysfunction. During exercise, fatigue develops due to muscular processes (peripheral fatigue) and decreased neurological activation of the muscle (central fatigue). In this study we objectively quantify central and peripheral fatigue in PBC and investigate the integrity of cortical inhibitory and excitatory circuits. Finally, we determine the relationship of these indices to the symptoms of PBC.
16 early-stage PBC patients, 8 post-liver transplant PBC patients, and 12 age-matched controls were studied at the Specialist PBC clinic and neuroscience research unit. In these patients, twitch interpolation was used to measure peripheral and central fatigue. Paired-pulse trans-cranial magnetic stimulation was used to assess intra-cortical inhibition (ICI) and facilitation (ICF).
PBC patients had a significantly lower central activation before fatiguing exercise (mean 86.6.8% (±12.75) vs. 95.2% (±7.4); p<0.05) and a greater response variability than controls. The decline in central activation during exercise and peripheral fatigue were normal. ICI was significantly reduced in PBC patients and daytime somnolence was greater in patients where net inhibition exceeded facilitation. Transplanted and non-transplanted patients had similar central activation, ICI, and ICF.
PBC patients have impaired central activation and abnormal ICI, suggesting CNS abnormalities beyond voluntary control. Transplanted and non-transplanted patients show similar abnormalities raising interesting questions about the mechanisms underpinning these changes and the permanence of neurological dysfunction in PBC. ICI and ICF and the balance between them are related to daytime somnolence (an important symptom in PBC).
Journal of Hepatology 12/2010; 53(6):1095-100. · 9.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Long-term outcome in primary biliary cirrhosis (PBC) remains unclear. Whilst response to ursodeoxycholic acid (UDCA) is associated with good outcome, this effect is not universal. Early data from our group have suggested that one factor associated with a poorer outcome in PBC is fatigue. The aim of this study was to explore the inter-relationship between UDCA use, response, and fatigue in determining outcome over 9 years in a unique, comprehensive patient cohort.
Longitudinal prospective study of a geographically-defined complete cohort of PBC patients in North-East England and matched community controls.
Survival to death or transplant was significantly lower in PBC patients than in the case-control population (88/136 (65%) v 114/136 84% (p<0.001 by log-rank test), with better survival in UDCA responders (defined using the Paris criteria) than in patients not treated with UDCA at study outset. Compared to the whole control group survival was reduced in PBC patients fatigued at study outset but not in those without fatigue (p<0.0001); an effect independent of the beneficial effect of UDCA response and of conventional parameters of liver disease severity. UDCA responders without fatigue at the study outset had a 9 year survival which was identical to controls. Patients without fatigue at the study outset who developed fatigue during follow-up had significantly worse survival than patients who remained without fatigue throughout (p<0.05). Fatigued controls had worse survival than non-fatigued controls (p = 0.05).
Survival in a comprehensive cohort of PBC patients is substantially reduced compared with case-matched community controls. Development of fatigue and non-treatment with UDCA were specifically (and independently) associated with increased risk of death in PBC.
Journal of Hepatology 11/2010; 53(5):911-7. · 9.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To determine whether the magnetization transfer ratio (MTR) of the globus pallidus (GP) in patients with primary biliary cirrhosis (PBC) correlates with age, disease stage, and fatigue, using T(1) and T(2) mapping to determine whether the mechanism of change is consistent with manganese deposition in the GP as suggested by previous reports.
In all, 30 early-stage PBC patients, four end-stage PBC patients, and 14 female controls were recruited to age-matched groups. MTR, T(1) and T(2) measurements were performed. A bilateral region of interest (ROI)-based analysis was used to calculate GP MTR, T(1), and T(2) values. These were correlated with age, disease status, and fatigue.
MTR measurements showed a significant, negative correlation with age for controls and early-stage PBC patients, a positive correlation with T(2), and no correlation with T(1). Only GP T(2) is significantly lower in early-stage PBC patients than controls, while end-stage patients demonstrated a simultaneous reduction in T(1) and MTR, consistent with GP manganese deposition.
MTR measurements correlate with age in both early-stage patient and control groups, but are not associated with manganese deposition or fatigue severity: only the end-stage disease group shows changes in MTR, T(1), T(2) that are consistent with manganese deposition.
Journal of Magnetic Resonance Imaging 05/2009; 29(4):780-4. · 2.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Lipoylated enzymes such as the E2 component of pyruvate dehydrogenase complex (PDC-E2) are targets for autoreactive immune responses in primary biliary cirrhosis, with lipoic acid itself forming a component of the dominant auto-epitopes. A candidate mechanism for the initiation of tolerance breakdown in this disease is immune recognition of neo-antigens formed by xenobiotic substitution of normal proteins. Importantly, sensitization with proteins artificially substituted with the lipoic acid analogue xenobiotic 6-bromohexanoic acid (6BH) can induce an immune response that cross-reacts with PDC-E2. This study investigated the potential of recombinant lipoylation enzymes lipoate activating enzyme and lipoyl-AMP(GMP):N-lysine lipoyl transferase to aberrantly incorporate xenobiotics into PDC-E2. It was found that these enzymes could incorporate lipoic acid analogues including octanoic and hexanoic acids and the xenobiotic 6BH into PDC-E2. The efficiency of incorporation of these analogues showed a variable dependence on activation by adenosine triphosphate (ATP) or guanosine triphosphate (GTP), with ATP favoring the incorporation of hexanoic acid and 6BH whereas GTP enhanced substitution by octanoic acid. Importantly, competition studies showed that the relative incorporation of both 6BH and lipoic acid could be regulated by the balance between ATP and GTP, with the formation of 6BH-substituted PDC-E2 predominating in an ATP-rich environment. Conclusion: Using a well-defined system in vitro we have shown that an important xenobiotic can be incorporated into PDC in place of lipoic acid by the exogenous lipoylation system; the relative levels of lipoic acid and xenobiotic incorporation may be determined by the balance between ATP and GTP. These observations suggest a clear mechanism for the generation of an auto-immunogenic neo-antigen of relevance for the pathogenesis of primary biliary cirrhosis.
[Show abstract][Hide abstract] ABSTRACT: Autoantibodies to the pyruvate dehydrogenase complex (PDC) are present in the serum of more than 95% of patients with primary biliary cirrhosis (PBC), the major epitope being the inner lipoyl domain of the E2 component. Immunoblotting suggests a similar prevalence of antibodies to a tightly associated lipoic acid–containing protein, E3 binding protein (;E3BP). Attempts to resolve E3BP from E2 have been unsuccessful, restricting study of the nature and significance of antibody responses to the individual proteins. In particular, it is unclear (;1) whether there is true cross-reactivity between E3BP and E2 and, if so, which is the originating response and (;2) whether autoantibodies preferentially bind a lipoylated epitope on E3BP as is the case with PDC-E2. In this study, complementary DNAs encoding rE2, full-length rE3BP, its single lipoyl domain (;rLip), and core domain (;rE3BPCore) were cloned, and the proteins were expressed in Escherichia coli. Sera from 47 PBC patients were studied by immunoblotting and enzyme-linked immunosorbent assay (;ELISA) against rE2, rE3BP, rE3BPCore, and both unlipoylated (;U) and lipoylated (;L) rLip. All sera were reactive by ELISA to some degree with all recombinant proteins except rE3BPCore, to which only 6 of 47 showed any reactivity. Significant correlations (;P < .0001) were observed when comparing absorbance values for rE3BP with both rLip (;U) (;r = 0.793) and (;L) (;r = 0.963). The mean absorbance for rLip (;U, 0.26 ± 0.05) was, however, significantly lower than the absorbance for rLip (;L) (;0.78 ± 0.12; P < .0001). After probing by immunoblotting and elution of antibodies from rE2 and rE3BP, subsequent reprobing against the components in whole PDC revealed true cross-reactivity. In summary, the response to E3BP is primarily directed against the lipoylated domain of the protein. It still remains unclear, however, whether the initial breakdown of tolerance is to E2 or E3BP.