Metabolic Turnover, Inflammation, and Redistribution: Impact on Nutrient Requirements: Vitamin B6 Example Jesse F. Gregory, PhD Food Science & Human Nutrition Dept. University of Florida Gainesville, FL
Current Assessment of Vitamin B6 Status Generally adequate dietary vitamin B6 intake in most developed countries. In healthy individuals, B6 status is generally a function of food selection patterns and use of dietary supplements. Below current cutoff (plasma PLP<20nmol/L) is rare. ~10% of US population in NHANES (Pfeiffer et al. J Nutr 2013; 143: 938S-47S.). Current RDAs for B6 are based on a cut-off of plasma PLP of 20 nmol/l. We observed 13% of healthy women having PLP <30nmol/L. (Rios-Avila et al., AJCN 2015; 102: 616-25). Current (1998) RDAs for B6: 19-50yr 50-70yr >70yr Men 1.3mg 1.3mg 1.7mg Women 1.3mg 1.3mg 1.5mg
Plasma PLP as a nutritional status biomarker Most common direct biomarker is plasma pyridoxal phosphate (PLP). - Widely used B6 status assessment tool. - Readily automated, high throughput. - Parallels B6 intake in healthy people. - Parallels liver PLP content.
Functions of PLP Coenzyme in ~160 enzymatic reactions, including: Transamination (aminotransferases) Decarboxylation (DOPA decarboxylase) Dehydration (serine dehydratase) Gluconeogenesis and glycogenolysis Serine-glycine interconversion and 1C transfer (serine hydroxymethyltransferases) Glycine catabolism and 1C transfer (mitochondrial glycine cleavage system P-protein = GDC system) Transsulfuration (catabolism of homocysteine, cysteine & H 2 S synthesis (cystathionine β-synthase and cystathionine-γ-lyase) Tryptophan catabolism & niacin synthesis Sphingolipid synthesis; effects on PUFA metabolism? Hierarchy of deficiency effects is unclear.
Disease Relationships of B6 Risk of cardiovascular disease, venous thrombosis & stroke is increased when plasma PLP is low (either <20 or <30 nmol/l used in epidemiological studies). Low B6 intake also is a CVD risk factor (Rimm et al., JAMA 1998) C-reactive protein, a marker of systemic inflammation, which is often associated with vascular disease risk also is associated low plasma PLP. In inflammatory bowel disease (IBD) and rheumatoid arthritis (RA), the disease severity is inversely associated with plasma PLP. (but normal erythrocyte PLP, however).
Plasma PLP is inversely associated with many biomarkers of systemic inflammation.
Sakakeeny et al. IS = sum of Z-scores of CRP, fibrinogen, IL-6, TNFa, TNFR-2, osteoprotegerin, P-selectin, CD40L, ICAM-1, MCP-1, myeloperoxidase, LPLPA2 mass, LPLP-A2 activity, and isoprostanes.
Conclusion: Even at adequate B6 intake of >2mg/d, there is a misleadingly high frequency of PLP<20nmol/L in people with a high level of systemic inflammation.
Why is plasma PLP lower in inflammation? Hypotheses: Possible relocation of PLP from liver to sites of inflammation because immune/inflammatory response requires PLP-dependent processes. Sphingolipid, sphingosine metabolism Tryptophan catabolism, other amino acids. Support of 1-carbon metabolism for cell synthesis and replication. Support of transsulfuration cysteine, glutathone, H 2 S Anapleurotic effects to support TCA cycle.??? Potentially greater catabolism to PA or B6 excretion in inflammation? Little evidence for greater urinary excretion of PA or other B6 forms. However, greater circulating PA, suggestive of an increase in B6 catabolism. The pyridoxic acid ratio PA/(PL+PLP) is a good indicator of inflammation.
Body pools of vitamin B6 Whole body pool ~1000 µmol, which is ~170 mg B6 equivalents. (Coburn studies). Muscle is the major pool of B6, mainly as PLP bound to glycogen phosphorylase. Liver and other organs comprise ~20-30% of total B6. These pools readily decline in deficiency and/or inflammation. The labile pools of B6 are available to redistribution to sites of inflammation. Body B6 Pools a Muscle Liver, other organs Very slow turnover Variable turnover kinetics Total 1000 170 µmol mg B6 Kinetics 700-800 120-135 Little change in B6 deficiency or supplementation 200-300 35-50 Prone to depletion, faster kinetics
Alternative vitamin B6 biomarkers Erythrocyte transaminase stimulation. -poor for high throughput studies. Erythrocyte PLP. -Not prone to inflammation or other confounders, but awkward methodology not well standardized. Urinary PA. -largely assesses recent B6 intake. Influenced by renal insufficiency. Plasma PA influenced by inflammation. Plasma cystathionine. -sensitive biomarker of B6 insufficiency, but influenced by B12 or folate insufficiency. Plasma kynurenines. -Good for high throughput studies. HK/XA, HK/KA and HK/HAA promising but not well standardized.
Mice treated with dextran sodium sulfate to induce colitis. Improved clinical outcome if B6 deficient. increased survival, weight maintenance, and reduced disease scores Low B6 suppressed transsulfuration in methionine metabolism.
Ratios HK:XA, HK:HAA, and HK:KA showed markedly stronger negative correlations with PLP than did HK alone
Further applications of alternative biomarkers for B6 status assessment da Silva et al. J. Nutr. 2013; 143: 1719-2013. N=23 healthy men and women (no OC) before and after 28-day B6 restriction. Fasting samples. Plasma B6 biomarkers Adequate (baseline) B6 Restricted PLP, nmol/l 52 ± 14 21 ± 5 P<0.05 HK nmol/l 24.5 ± 9.46 32.4 ± 11.0 P<0.05 HK/XA 3.36 ± 1.92 5.20 ± 3.10 P<0.05 HK/HAA 1.32 ± 0.52 1.95 ± 0.84 P<0.05 *HK/XA and HK/HAA ratios calculated from published data.
Elevated cystathionine has been reported to be associated with CVD risk in the WECAC study. To evaluate metabolic and nutritional factors associated with cystathionine elevation, we conducted targeted metabolite profile analysis and untargeted metabolomic analysis by NMR and LC-MS/MS.
Metabolomic evaluation of the consequences of plasma cystathionine elevation in subjects with angina pectoris Targeted metabolites Variable Low Cystathionine Group (n=40) Methionine, homocysteine and transsulfuration metabolites High Cystathionine Group (n=40) P-value controlled for false discovery rate 2 Methionine, µmol/l 15.9 ± 3.65 21.2 ± 5.78* 0.003 Total Homocysteine, 9.32 ± 2.22 13.1 ± 4.54* 0.003 µmol/l Serine, µmol/l 125 ± 19.2 117 ± 30.6 0.472 Cystathionine, µmol/l 0.137 ± 0.011 1.32 ± 0.60* 0.003 Cysteine, µmol/l 248 ± 34.4 267 ± 39.1* 0.039 Glutathione, µmol/l 5.37± 2.21 3.49 ± 1.68* 0.003 Lanthionine, µmol/l 0.0317 ± 0.0133 0.121 ± 0.0437* 0.003 Homolanthionine, µmol/l 0.243 ± 0.116 0.257 ± 0.0892 0.472 Choline, glycine and choline oxidation metabolites DeRatt et al. 2017 J. Nutr. Choline, µmol/l 8.48 ± 1.85 10.8 ± 2.45* 0.003 Glycine, µmol/l 214 ± 66.0 202 ± 50.1 0.470 Betaine, µmol/l 46.0 ± 30.4 42.0 ± 18.0 0.544 Dimethylglycine, µmol/l 3.86 ± 1.61 5.10 ± 2.01* 0.007 B vitamins, metabolites and biomarkers Serum Folate, nmol/l 16.8 ± 10.9 12.0 ± 6.46* 0.039 Serum Cobalamin, pmol/l 349 ± 144 329 ± 154 0.760 Methylmalonic Acid, µmol/l 0.142 ± 0.0516 0.211 ± 0.0957* 0.003
Metabolomic evaluation of the consequences of plasma cystathionine elevation in subjects with angina pectoris Low cysta High cysta P Pyridoxal 5 phosphate, 60.1 ± 56.1 39.0 ± 20.9 0.057 nmol/l Pyridoxal, nmol/l 12.5 ± 10.7 9.97 ± 3.36 0.241 Pyridoxic acid, nmol/l 26.0 ± 14.3 29.8 ± 13.4 0.303 PAr Index 0.448 ± 0.205 0.692 ± 0.343* 0.003 Riboflavin, nmol/l 14.7 ± 17.7 14.9 ± 11.0 0.940 Tryptophan and tryptophan catabolites Tryptophan, µmol/l 54.3 ± 10.5 72.4 ± 16.9* 0.003 Kynurenine, µmol/l 1.04 ± 0.236 1.92 ± 0.574* 0.003 Kynurenine: Tryptophan 1.97 ± 0.551 2.76 ± 1.05* 0.003 Hydroxykynurenine, nmol/l 18.3 ± 6.33 48.0 ± 31.8* 0.003 Kynurenic Acid, nmol/l 32.1 ± 9.97 64.3 ± 23.4* 0.003 Xanthurenic Acid, nmol/l 8.45 ± 2.90 19.0 ± 8.51* 0.003 Anthranilic Acid, nmol/l 11.9 ± 4.30 16.1 ± 6.73* 0.003 3-hydroxyanthranilic Acid, 19.3 ± 7.61 44.0 ± 17.9* 0.003 nmol/l HK/XA 0.607 ± 0.252 0.776 ± 0.479 0.061 Glucose, TMAO, assorted metabolites, and inflammatory markers Glucose, mmol/l 5.51 ± 1.40 7.25 ± 3.09* 0.014 Trimethylamine N-oxide, 5.22 ± 6.58 11.5 ± 8.41* 0.003 µmol/l C-reactive Protein, mg/l 3.45 ± 5.80 7.30 ±13.8 0.165 Hemoglobin A1 C, % 6.27 ± 1.62 5.98 ± 1.31 0.115 Palmitoylcarnitine, pmol/l 80.8 ± 26.3 85.8 ± 40.1 0.565 1 Data are presented as mean ± SD (n=80). DeRatt et al. 2017 submitted
Metabolomic evaluation of the consequences of plasma cystathionine elevation in subjects with angina pectoris Targeted metabolite profile (vitamins, 1C and trp metabolites: PLS-DA n=40/group Scores plot high versus low cystathionine groups R 2 =0.86 Q 2 =0.79 DeRatt et al. 2017 submitted
Metabolomic evaluation of the consequences of plasma cystathionine elevation in subjects with angina pectoris Targeted metabolite profile including clinical variables: PLS-DA n=40 per group DeRatt et al. 2017 submitted
Summary Plasma PLP is a good biomarker of B6 status in healthy people. Implication on use of PLP as basis of RDA. Localized insufficiency (tissue or cell) more plausible than whole-body deficiency. Inflammation suppresses PLP, overestimating B6 insufficiency in inflammatory conditions. Redistribution of PLP to inflammatory tissues is a plausible mechanism. Ratios of tryptophan catabolites may be suitable B6 biomarkers, but need further validated. Unknown whether inflammation induces localized or cellular insufficiency. (e.g. intestinal mucosa, endothelial cell, immune cells). Major research priority.
Folic Acid, Vitamin B12, and One-Carbon Metabolism Chaired by Ralph Green and Jess Gregory July 29 to August 3, 2018 Atlantica Oak Island Resort & Conference Center Western Shore, Nova Scotia, Canada For more information please visit www.faseb.org/src