Phosphatidylcholine and lysophosphatidylcholine excretion is increased in children with cystic fibrosis and is associated with plasma homocysteine, S-adenosylhomocysteine, and S-adenosylmethionine

Evidence and Perspectives for Choline Supplementation during Parenteral Nutrition-A Narrative Review

Choline is an essential nutrient, with high requirements during fetal and postnatal growth. Tissue concentrations of total choline are tightly regulated, requiring an increase in its pool size proportional to growth. Phosphatidylcholine and sphingomyelin, containing a choline headgroup, are constitutive membrane phospholipids, accounting for >85% of total choline, indicating that choline requirements are particularly high during growth. Daily phosphatidylcholine secretion via bile for lipid digestion and very low-density lipoproteins for plasma transport of arachidonic and docosahexaenoic acid to other organs exceed 50% of its hepatic pool. Moreover, phosphatidylcholine is required for converting pro-apoptotic ceramides to sphingomyelin, while choline is the source of betaine as a methyl donor for creatine synthesis, DNA methylation/repair and kidney function. Interrupted choline supply, as during current total parenteral nutrition (TPN), causes a rapid drop in plasma choline concentration and accumulating deficit. The American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.) defined choline as critical to all infants requiring TPN, claiming its inclusion in parenteral feeding regimes. We performed a systematic literature search in Pubmed with the terms "choline" and "parenteral nutrition", resulting in 47 relevant publications. Their results, together with cross-references, are discussed. While studies on parenteral choline administration in neonates and older children are lacking, preclinical and observational studies, as well as small randomized controlled trials in adults, suggest choline deficiency as a major contributor to acute and chronic TPN-associated liver disease, and the safety and efficacy of parenteral choline administration for its prevention. Hence, we call for choline formulations suitable to be added to TPN solutions and clinical trials to study their efficacy, particularly in growing children including preterm infants.

Different choline supplement metabolism in adults using deuterium labelling

BACKGROUND

Choline deficiency leads to pathologies particularly of the liver, brain and lung. Adequate supply is important for preterm infants and patients with cystic fibrosis. We analysed the assimilation of four different enterally administered deuterium-labelled (D9-) choline supplements in adults.

METHODS

Prospective randomised cross-over study (11/2020-1/2022) in six healthy men, receiving four single doses of 2.7 mg/kg D9-choline equivalent each in the form of D9-choline chloride, D9-phosphorylcholine, D9-alpha-glycerophosphocholine (D9-GPC) or D9-1-palmitoyl-2-oleoyl-glycero-3-phosphoryl-choline (D9-POPC), in randomised order 6 weeks apart. Plasma was obtained at baseline (t = - 0.1 h) and at 0.5 h to 7d after intake. Concentrations of D9-choline and its D9-labelled metabolites were analysed by tandem mass spectrometry. Results are shown as median and interquartile range.

RESULTS

Maximum D9-choline and D9-betaine concentrations were reached latest after D9-POPC administration versus other components. D9-POPC and D9-phosphorylcholine resulted in lower D9-trimethylamine (D9-TMAO) formation. The AUCs (0-7d) of plasma D9-PC concentration showed highest values after administration of D9-POPC. D9-POPC appeared in plasma after fatty acid remodelling, predominantly as D9-1-palmitoyl-2-linoleyl-PC (D9-PLPC), confirming cleavage to 1-palmitoyl-lyso-D9-PC and re-acylation with linoleic acid as the most prominent alimentary unsaturated fatty acid.

CONCLUSION

There was a delayed increase in plasma D9-choline and D9-betaine after D9-POPC administration, with no differences in AUC over time. D9-POPC resulted in a higher AUC of D9-PC and virtually absent D9-TMAO levels. D9-POPC is remodelled according to enterocytic fatty acid availability. D9-POPC seems best suited as choline supplement to increase plasma PC concentrations, with PC as a carrier of choline and targeted fatty acid supply as required by organs. This study was registered at Deutsches Register Klinischer Studien (DRKS) (German Register for Clinical Studies), DRKS00020498, 22.01.2020.

STUDY REGISTRATION

This study was registered at Deutsches Register Klinischer Studien (DRKS) (German Register for Clinical Studies), DRKS00020498.

The fatty acid imbalance of cystic fibrosis exists at birth independent of feeding in pig and ferret models

Persons with cystic fibrosis (CF) exhibit a unique alteration of fatty acid composition, marked especially among polyunsaturates by relative deficiency of linoleic acid and excess of Mead acid. Relative deficiency of docosahexaenoic acid is variably found. However, the initial development of these abnormalities is not understood. We examined fatty acid composition in young CF ferrets and pigs, finding abnormalities from the day of birth onward including relative deficiency of linoleic acid in both species. Fatty acid composition abnormalities were present in both liver and serum phospholipids of newborn CF piglets even prior to feeding, including reduced linoleic acid and increased Mead acid. Serum fatty acid composition evolved over the first weeks of life in both non-CF and CF ferrets, though differences between CF and non-CF persisted. Although red blood cell phospholipid fatty acid composition was normal in newborn animals, it became perturbed in juvenile CF ferrets including relative deficiencies of linoleic and docosahexaenoic acids and excess of Mead acid. In summary, fatty acid composition abnormalities in CF pigs and ferrets exist from a young age including at birth independent of feeding and overlap extensively with the abnormalities found in humans with CF. That the abnormalities exist prior to feeding implies that dietary measures alone will not address the mechanisms of imbalance.

Cystic fibrosis-related liver disease: Clinical presentations, diagnostic and monitoring approaches in the era of CFTR modulator therapies

Cystic fibrosis (CF) is the most common autosomal recessive disease in the Caucasian population. Cystic fibrosis-related liver disease (CFLD) is defined as the pathogenesis related to the underlying CFTR defect in biliary epithelial cells. CFLD needs to be distinguished from other liver manifestations that may not have any pathological significance. The clinical/histological presentation and severity of CFLD vary. The main histological presentation of CFLD is focal biliary fibrosis, which is usually asymptomatic. Portal hypertension develops in a minority of cases (about 10%) and may require specific management including liver transplantation for end-stage liver disease. Portal hypertension is usually the result of the progression of focal biliary fibrosis to multilobular cirrhosis during childhood. Nevertheless, non-cirrhotic portal hypertension as a result of porto-sinusoidal vascular disease is now identified increasingly more frequently, mainly in young adults. To evaluate the effect of new CFTR modulator therapies on the liver, the spectrum of hepatobiliary involvement must first be precisely classified. This paper discusses the phenotypic features of CFLD, its underlying physiopathology and relevant diagnostic and follow-up approaches, with a special focus on imaging.

Differential metabolism of choline supplements in adult volunteers

BACKGROUND

Adequate intake of choline is essential for growth and homeostasis, but its supply does often not meet requirements. Choline deficiency decreases phosphatidylcholine (PC) and betaine synthesis, resulting in organ pathology, especially of liver, lung, and brain. This is of particular clinical importance in preterm infants and cystic fibrosis patients. We compared four different choline supplements for their impact on plasma concentration and kinetics of choline, betaine as a methyl donor and trimethylamine oxide (TMAO) as a marker of bacterial degradation prior to absorption.

METHODS

Prospective randomized cross-over study (1/2020-4/2020) in six healthy adult men. Participants received a single dose of 550 mg/d choline equivalent in the form of choline chloride, choline bitartrate, α-glycerophosphocholine (GPC), and egg-PC in randomized sequence at least 1 week apart. Blood was taken from t = - 0.1-6 h after supplement intake. Choline, betaine, TMAO, and total PC concentrations were analyzed by tandem mass spectrometry. Results are shown as medians and interquartile range.

RESULTS

There was no difference in the AUC of choline plasma concentrations after intake of the different supplements. Individual plasma kinetics of choline and betaine differed and concentrations peaked latest for PC (at ≈3 h). All supplements similarly increased plasma betaine. All water-soluble supplements rapidly increased TMAO, whereas egg-PC did not.

CONCLUSION

All supplements tested rapidly increased choline and betaine levels to a similar extent, with egg-PC showing the latest peak. Assuming that TMAO may have undesirable effects, egg-PC might be best suited for choline supplementation in adults.

STUDY REGISTRATION

This study was registered at "Deutsches Register Klinischer Studien" (DRKS) (German Register for Clinical Studies), 17.01.2020, DRKS00020454.

Resolution of severe hepatosteatosis in a cystic fibrosis patient with multifactorial choline deficiency: A case report

In cystic fibrosis (CF), 85% to 90% of patients develop exocrine pancreatic insufficiency. Despite enzyme substitution, low pancreatic phospholipase A2 (sPLaseA2-IB) activity causes fecal loss of bile phosphatidylcholine and choline deficiency. We report on a female patient who has CF and progressive hepatosteatosis from 4.5 y onward. At 22.3 y, the liver comprised 27% fat (2385 mL volume) and transaminases were strongly increased. Plasma choline was 1.9 µmol/L (normal: 8-12 mol/L). Supplementation with 3 ×  1g/d choline chloride decreased liver fat and volume (3 mo: 8.2%; 1912 mL) and normalized transaminases. Plasma choline increased to only 5.6 µmol/L upon supplementation, with high trimethylamine oxide levels (12-35 µmol/L; normal: 3 ± 1 mol/L) proving intestinal microbial choline degradation. The patient was homozygous for rs12325817, a frequent single-nucleotide polymorphism in the PEMT gene, associated with severe hepatosteatosis in response to choline deficiency. Resolution of steatosis required 2 y (4.5% fat). Discontinuation/resumption of choline supplementation resulted in rapid relapse/resolution of steatosis, increased transaminases, and abdominal pain.

Distinctive lipid signatures of bronchial epithelial cells associated with cystic fibrosis drugs, including Trikafta

In recent years, a number of drugs have been approved for the treatment of cystic fibrosis (CF). Among them, newly released Trikafta, a combination of 3 drugs (VX-661/VX-445/VX-770), holds great promise to radically improve the quality of life for a large portion of patients with CF carrying 1 copy of F508del, the most frequent CF transmembrane conductance regulator (CFTR) mutation. Currently available disease-modifying CF drugs work by rescuing the function of the mutated CFTR anion channel. Recent research has shown that membrane lipids, and the cell lipidome in general, play a significant role in the mechanism of CFTR-defective trafficking and, on the other hand, its rescue. In this paper, by using untargeted lipidomics on CFBE41o- cells, we identified distinctive changes in the bronchial epithelial cell lipidome associated with treatment with Trikafta and other CF drugs. Particularly interesting was the reduction of levels of ceramide, a known molecular player in the induction of apoptosis, which appeared to be associated with a decrease in the susceptibility of cells to undergo apoptosis. This evidence could account for additional beneficial roles of the triple combination of drugs on CF phenotypes.

Choline in cystic fibrosis: relations to pancreas insufficiency, enterohepatic cycle, PEMT and intestinal microbiota

BACKGROUND

Cystic Fibrosis (CF) is an autosomal recessive disorder with life-threatening organ manifestations. 87% of CF patients develop exocrine pancreas insufficiency, frequently starting in utero and requiring lifelong pancreatic enzyme substitution. 99% develop progressive lung disease, and 20-60% CF-related liver disease, from mild steatosis to cirrhosis. Characteristically, pancreas, liver and lung are linked by choline metabolism, a critical nutrient in CF. Choline is a tightly regulated tissue component in the form of phosphatidylcholine (Ptd'Cho) and sphingomyelin (SPH) in all membranes and many secretions, particularly of liver (bile, lipoproteins) and lung (surfactant, lipoproteins). Via its downstream metabolites, betaine, dimethylglycine and sarcosine, choline is the major one-carbon donor for methionine regeneration from homocysteine. Methionine is primarily used for essential methylation processes via S-adenosyl-methionine.

CLINICAL IMPACT

CF patients with exocrine pancreas insufficiency frequently develop choline deficiency, due to loss of bile Ptd'Cho via feces. ~ 50% (11-12 g) of hepatic Ptd'Cho is daily secreted into the duodenum. Its re-uptake requires cleavage to lyso-Ptd'Cho by pancreatic and small intestinal phospholipases requiring alkaline environment. Impaired CFTR-dependent bicarbonate secretion, however, results in low duodenal pH, impaired phospholipase activity, fecal Ptd'Cho loss and choline deficiency. Low plasma choline causes decreased availability for parenchymal Ptd'Cho metabolism, impacting on organ functions. Choline deficiency results in hepatic choline/Ptd'Cho accretion from lung tissue via high density lipoproteins, explaining the link between choline deficiency and lung function. Hepatic Ptd'Cho synthesis from phosphatidylethanolamine by phosphatidylethanolamine-N-methyltransferase (PEMT) partly compensates for choline deficiency, but frequent single nucleotide polymorphisms enhance choline requirement. Additionally, small intestinal bacterial overgrowth (SIBO) frequently causes intraluminal choline degradation in CF patients prior to its absorption. As adequate choline supplementation was clinically effective and adult as well as pediatric CF patients suffer from choline deficiency, choline supplementation in CF patients of all ages should be evaluated.

Homocysteine and Hyperhomocysteinaemia

Homocysteine (Hcy) is a thiol group containing the amino acid, which naturally occurs in all humans. Hcy is degraded in the body through two metabolic pathways, while a minor part is excreted through kidneys. The chemical reactions that are necessary for degradation of Hcy require the presence of folic acid, vitamins B6 and B12. Consequently, the level of the total Hcy in the serum is influenced by the presence or absence of these vitamins. An elevated level of the Hcy, hyperhomocysteinemia (HHcy) and homocystinuria is connected with occlusive artery disease, especially in the brain, the heart, and the kidney, in addition to venous thrombosis, chronic renal failure, megaloblastic anemia, osteoporosis, depression, Alzheimer's disease, pregnancy problems, and others. Elevated Hcy levels are connected with various pathologies both in adult and child population. Causes of HHcy include genetic mutations and enzyme deficiencies in 5, 10-methylenetetrahydrofolate reductase (MTHFR) methionine synthase (MS), and cystathionine β-synthase (CβS). HHcy can be caused by deficiencies in the folate, vitamin B12 and to a lesser extent, deficiency in B6 vitamin what influences methionine metabolism. Additionally, HHcy can be caused by the rich diet and renal impairment. This review presents literature data from recent research related to Hcy metabolism and the etiology of the Hcy blood level disorder. In addition, we also described various pathological mechanisms induced by hereditary disturbances or nutritional influences and their association with HHcy induced pathology in adults and children and treatment of these metabolic disorders.

The emerging burden of liver disease in cystic fibrosis patients: A UK nationwide study

Objective

Cystic fibrosis associated liver disease (CFLD) is the third largest cause of mortality in CF. Our aim was to define the burden of CFLD in the UK using national registry data and identify risk factors for progressive disease.

Methods

A longitudinal population-based cohort study was conducted. Cases were defined as all patients with CFLD identified from the UK CF Registry, 2008–2013 (n = 3417). Denominator data were derived from the entire UK CF Registry. The burden of CFLD was characterised. Regression analysis was undertaken to identify risk factors for cirrhosis and progression.

Results

Prevalence of CFLD increased from 203.4 to 228.3 per 1000 patients during 2008–2013. Mortality in CF patients with CFLD was more than double those without; cirrhotic patients had higher all-cause mortality (HR 1.54, 95% CI 1.09 to 2.18, p = 0.015). Median recorded age of cirrhosis diagnosis was 19 (range 5–53) years. Male sex, Pseudomonas airway infection and CF related diabetes were independent risk factors for cirrhosis. Ursodeoxycholic acid use was associated with prolonged survival in patients without cirrhosis.

Conclusions

This study highlights an important changing disease burden of CFLD. The prevalence is slowly increasing and, importantly, the disease is not just being diagnosed in childhood. Although the role of ursodeoxycholic acid remains controversial, this study identified a positive association with survival.

Choline Supplementation in Cystic Fibrosis-The Metabolic and Clinical Impact

Background: Choline is essential for the synthesis of liver phosphatidylcholine (PC), parenchymal maintenance, bile formation, and lipoprotein assembly to secrete triglycerides. In choline deficiency, the liver accretes choline/PC at the expense of lung tissue, thereby impairing pulmonary PC homoeostasis. In cystic fibrosis (CF), exocrine pancreas insufficiency results in impaired cleavage of bile PC and subsequent fecal choline loss. In these patients, the plasma choline concentration is low and correlates with lung function. We therefore investigated the effect of choline supplementation on plasma choline/PC concentration and metabolism, lung function, and liver fat. Methods: 10 adult male CF patients were recruited (11/2014–1/2016), and orally supplemented with 3 × 1 g choline chloride for 84 (84–91) days. Pre-/post-supplementation, patients were spiked with 3.6 mg/kg [methyl-D₉]choline chloride to assess choline/PC metabolism. Mass spectrometry, spirometry, and hepatic nuclear resonance spectrometry served for analysis. Results: Supplementation increased plasma choline from 4.8 (4.1–6.2) µmol/L to 10.5 (8.5–15.5) µmol/L at d84 (p < 0.01). Whereas plasma PC concentration remained unchanged, D₉-labeled PC was decreased (12.2 [10.5–18.3] µmol/L vs. 17.7 [15.5–22.4] µmol/L, p < 0.01), indicating D₉-tracer dilution due to higher choline pools. Supplementation increased Forced Expiratory Volume in 1 second percent of predicted (ppFEV1) from 70.0 (50.9–74.8)% to 78.3 (60.1–83.9)% (p < 0.05), and decreased liver fat from 1.58 (0.37–8.82)% to 0.84 (0.56–1.17)% (p < 0.01). Plasma choline returned to baseline concentration within 60 h. Conclusions: Choline supplementation normalized plasma choline concentration and increased choline-containing PC precursor pools in adult CF patients. Improved lung function and decreased liver fat suggest that in CF correcting choline deficiency is clinically important. Choline supplementation of CF patients should be further investigated in randomized, placebo-controlled trials.

Gut microbiota signatures in cystic fibrosis: Loss of host CFTR function drives the microbiota enterophenotype

Background

Cystic fibrosis (CF) is a disorder affecting the respiratory, digestive, reproductive systems and sweat glands. This lethal hereditary disease has known or suspected links to the dysbiosis gut microbiota. High-throughput meta-omics-based approaches may assist in unveiling this complex network of symbiosis modifications.

Objectives

The aim of this study was to provide a predictive and functional model of the gut microbiota enterophenotype of pediatric patients affected by CF under clinical stability.

Methods

Thirty-one fecal samples were collected from CF patients and healthy children (HC) (age range, 1–6 years) and analysed using targeted-metagenomics and metabolomics to characterize the ecology and metabolism of CF-linked gut microbiota. The multidimensional data were low fused and processed by chemometric classification analysis.

Results

The fused metagenomics and metabolomics based gut microbiota profile was characterized by a high abundance of Propionibacterium, Staphylococcus and Clostridiaceae, including Clostridium difficile, and a low abundance of Eggerthella, Eubacterium, Ruminococcus, Dorea, Faecalibacterium prausnitzii, and Lachnospiraceae, associated with overexpression of 4-aminobutyrate (GABA), choline, ethanol, propylbutyrate, and pyridine and low levels of sarcosine, 4-methylphenol, uracil, glucose, acetate, phenol, benzaldehyde, and methylacetate. The CF gut microbiota pattern revealed an enterophenotype intrinsically linked to disease, regardless of age, and with dysbiosis uninduced by reduced pancreatic function and only partially related to oral antibiotic administration or lung colonization/infection.

Conclusions

All together, the results obtained suggest that the gut microbiota enterophenotypes of CF, together with endogenous and bacterial CF biomarkers, are direct expression of functional alterations at the intestinal level. Hence, it’s possible to infer that CFTR impairment causes the gut ecosystem imbalance.This new understanding of CF host-gut microbiota interactions may be helpful to rationalize novel clinical interventions to improve the affected children’s nutritional status and intestinal function.

Choline and choline-related nutrients in regular and preterm infant growth

BACKGROUND

Choline is an essential nutrient, with increased requirements during development. It forms the headgroup of phosphatidylcholine and sphingomyelin in all membranes and many secretions. Phosphatidylcholine is linked to cell signaling as a phosphocholine donor to synthesize sphingomyelin from ceramide, a trigger of apoptosis, and is the major carrier of arachidonic and docosahexaenoic acid in plasma. Acetylcholine is important for neurodevelopment and the placental storage form for fetal choline supply. Betaine, a choline metabolite, functions as osmolyte and methyl donor. Their concentrations are all tightly regulated in tissues.

CLINCAL IMPACT

During the fetal growth spurt at 24-34-week postmenstrual age, plasma choline is higher than beyond 34 weeks, and threefold higher than in pregnant women [45 (36-60) µmol/L vs. 14 (10-17) µmol/L]. The rapid decrease in plasma choline after premature birth suggests an untimely reduction in choline supply, as cellular uptake is proportional to plasma concentration. Supply via breast milk, with phosphocholine and α-glycerophosphocholine as its major choline components, does not prevent such postnatal decrease. Moreover, high amounts of liver PC are secreted via bile, causing rapid hepatic choline turnover via the enterohepatic cycle, and deficiency in case of pancreatic phospholipase A2 deficiency or intestinal resection. Choline deficiency causes hepatic damage and choline accretion at the expense of the lungs and other tissues.

CONCLUSION

Choline deficiency may contribute to the impaired lean body mass growth and pulmonary and neurocognitive development of preterm infants despite adequate macronutrient supply and weight gain. In this context, a reconsideration of current recommendations for choline supply to preterm infants is required.

Acute retinal vein occlusion and cystic fibrosis

Background

The ocular manifestations of cystic fibrosis typically present with surface irritation or nyctalopia due to Vitamin A deficiency, however, there have been two previous reports of patients with cystic fibrosis that developed retinal vein occlusions. These reports hypothesized that either elevated fibrinogen levels due to chronic infections or elevated homocysteine levels have predisposed patients with cystic fibrosis to develop retinal vein occlusions.

Case presentation

We present a case of a 35-year-old male with cystic fibrosis complicated by chronic sinusitis with no history of organ transplantation or chronic pulmonary infections who presented with an acute branch retinal vein occlusion in his left eye with associated macular edema. Evaluation revealed an elevated fibrinogen level, while the rest of his workup was relatively unremarkable including a normal homocysteine level. His vision remained 20/20 throughout his care and he did not require treatment of his macular edema.

Conclusions

Patients with cystic fibrosis are at an increased risk of developing retinal vein occlusions likely due to a variety of systemic thrombogenic factors rather than a single risk factor which had been reported previously. Elevated fibrinogen levels in these patients may not be due to chronic infections, but inherent to the cystic fibrosis.

Complex Relation Between Diet and Phospholipid Fatty Acids in Children With Cystic Fibrosis

OBJECTIVES

Altered total plasma n-6 and n-3 fatty acids are common in cystic fibrosis (CF). Whether alterations extend to plasma phosphatidylcholine (PC) and phosphatidylethanolamine (PE) and are explained by diet is unclear. The present study was to describe the dietary intake of a large group of children with CF and to determine whether dietary fat composition explains differences in plasma PC and PE fatty acids between children with and without CF.

METHODS

Dietary intake was assessed using a food frequency questionnaire. Venous blood was collected. Plasma PC and PE were separately analyzed for fatty acids.

RESULTS

Children with CF, n = 74, consumed more calories and fat (g/day and % energy), with significantly more saturates mainly from dairy foods and less polyunsaturates including linoleic acid (LA), arachidonic acid (ARA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) (% fat) than reference children, n = 71. A subset of children with CF, not differing in dietary intake from the larger group, had significantly lower LA and DHA, but higher EPA in plasma PC and had higher LA and lower ARA and DHA in plasma PE, compared to a subset of reference children. In both groups, LA intake and LA in plasma PC and PE were not associated. EPA and DHA intakes were positively associated with EPA and DHA, respectively, in plasma PC, but not PE, in reference children only.

CONCLUSIONS

The fatty acid composition of plasma PC and PE is altered in CF. Fatty acid differences between children with and without CF are inconsistent between PC and PE and are not explained by dietary fat.

Choline Deficiency Is Associated With Increased Risk for Venous Catheter Thrombosis

BACKGROUND

Patients with intestinal failure who require long-term parenteral nutrition (PN) develop catheter thrombosis as a complication. This patient group may also develop choline deficiency because of a defect in the hepatic transsulfuration pathway in the setting of malabsorption. This study was undertaken to determine whether choline deficiency is a risk factor for development of catheter thrombosis.

METHODS

Plasma free and phospholipid-bound choline concentrations were measured in a group of 41 patients that required long-term PN. Episodes of catheter thrombosis from onset of PN to the time of blood testing were recorded.

RESULTS

Sixteen (39%) patients developed catheter thrombosis, and 5 of these had recurrent catheter thrombosis. Plasma free choline was 7.7 +/- 2.7 nmol/mL in patients with no history of catheter thrombosis and 6.2 +/- 1.7 nmol/mL in patients with previous catheter thrombosis (p = .076 by Wilcoxon rank-sum test). The partial correlation between plasma free choline concentration and the frequency of clots after controlling for catheter duration was r = -0.33 (p = .038). The relative risk for catheter thrombosis in subjects with a plasma free choline concentration <8 nmol/mL was 10.0, 95% confidence interval (1.134-88.167). Plasma phospholipid-bound choline concentration was 2191.7 +/- 679.0 nmol/mL in patients with previous catheter thrombosis and 2103.3 +/- 531.2 nmol/mL in patients without history of catheter thrombosis (p = NS).

CONCLUSION

Choline deficiency is a significant risk factor for development of catheter thrombosis in patients with intestinal failure who require PN.

Choline Supplementation With a Structured Lipid in Children With Cystic Fibrosis: A Randomized Placebo-Controlled Trial

BACKGROUND

Choline depletion is seen in cystic fibrosis (CF) and pancreatic insufficiency in spite of enzyme treatment and may result in liver, fatty acid, and muscle abnormalities. This study evaluated the efficacy and safety of an easily absorbed choline-rich structured lipid (LYM-X-SORB™ [LXS]) to improve choline status.

METHODS

Children with CF and pancreatic insufficiency were randomized to LXS or placebo in a 12-month double blind trial. Dietary choline intake, plasma cholines, plasma and fecal phospholipids, coefficient of fat absorption, pulmonary function, growth status, body composition, and safety measures were assessed. Magnetic resonance spectroscopy for calf muscle choline and liver fat were assessed in a subgroup and compared with a healthy comparison group matched for age, sex, and body size.

RESULTS

A total of 110 subjects were enrolled (age 10.4 ± 3.0 years). Baseline dietary choline, 88% recommended, increased 3-fold in the LXS group. Plasma choline, betaine, and dimethylglycine increased in the LXS but not placebo (P = 0.007). Plasma lysophosphatidylcholine and phosphatidylcholine increased, and fecal phosphatidylcholine/phosphatidylethanolamine ratio decreased (P ≤ 0.05) in LXS only, accompanied by a 6% coefficient of fat absorption increase (P = 0.001). Children with CF had higher liver fat than healthy children and depleted calf muscle choline at baseline. Muscle choline concentration increased in LXS and was associated with improvement in plasma choline status. No relevant changes in safety measures were evident.

CONCLUSIONS

LXS had improved choline intake, plasma choline status, and muscle choline stores compared with placebo group. The choline-rich supplement was safe, accepted by participants, and improved choline status in children with CF.

Sequential bilateral central retinal vein occlusions in a cystic fibrosis patient with hyperhomocysteinemia and hypergamma-globulinemia

PURPOSE

To report a case of sequential bilateral central retinal vein occlusions in a cystic fibrosis patient with hyperhomocysteinemia and hypergamma-globulinemia over 6 years of follow up.

METHODS

Observational case report of one patient.

RESULTS

A 31 year-old male with a history of cystic fibrosis presented with a central retinal vein occlusion (CRVO) in his left eye, followed by a CRVO in his right eye 4 years later. His medical workup was significant for elevated levels of homocysteine and gamma-globulins, which coincided with initiation of intravenous immunoglobulin (IVIG) proceeding his second CRVO.

CONCLUSIONS

We describe a case of sequential bilateral central retinal vein occlusions in a cystic fibrosis patient with hyperhomocysteinemia and hypergamma-globulinemia over 6 years of follow up and discuss the important role of these risk factors in retinal venous occlusive disease.

Metabolomic analyses of faeces reveals malabsorption in cirrhotic patients

BACKGROUND

The study of faeces offers a unique opportunity to observe cooperation between the microbiome and the metabolism of mammalian hosts, an essential element in the study of the human metabolome. In the present study, a global metabolomics approach was used to identify metabolites differentially excreted in the faeces of cirrhotic patients compared to controls.

METHODS

Seventeen cirrhotic patients and 24 healthy individuals were recruited. Faecal metabolites were detected through non-targeted reversed-phase ultra-performance liquid chromatography coupled to electrospray ionization quadrupole time-of-flight mass spectrometry.

RESULTS

A total of 9215 peaks were detected. Using unequal variance t-tests, 2393 peaks were observed with P≤0.05, approximately 74.0% of which were due to decreased faecal metabolite concentrations in liver cirrhosis vs. healthy controls. Integrating multivariate data analyses, we identified six major groups of metabolites. Relative levels of identified metabolites were as follows: strong increase in lysophosphatidylcholines, aromatic amino acids, fatty acids, and acylcarnitines, and a dramatic decrease in bile acids and bile pigments.

CONCLUSION

With severe hepatic injury in patients with liver cirrhosis, malabsorption occurs along with disorders of fatty acid metabolism, potentially due to changes in gut microflora.

Relation between dietary fat intake type and serum fatty acid status in children with cystic fibrosis

BACKGROUND AND OBJECTIVE

Children with cystic fibrosis (CF) and pancreatic insufficiency (PI) are at risk for fatty acid (FA) abnormalities and essential FA deficiency, with low linoleic acid (LA) and docosahexaenoic acid (DHA) concentrations and abnormal triene:tetraene (T:T) and arachidonic acid (AA):DHA ratios. The aim of the article was to determine whether type of dietary fat predicted serum LA, DHA, T:T, and AA:DHA ratios in subjects with CF and PI as compared to an unaffected comparison group.

METHODS

Serum FA concentrations were assessed by capillary gas-liquid chromatography (mol%) and dietary intake by 7-day weighed food records; the 3-day coefficient of fat absorption was calculated. Total energy intake was expressed in kilocalories.

RESULTS

A total of 65 subjects with CF and PI (8.4 ± 1.0 years, 32 girls) and 22 controls (8.5 ± 1.1 years, 13 girls) were included. Despite greater energy, saturated fat, and LA intake, the subjects with CF had lower serum LA and DHA and higher T:T and AA:DHA than those in the comparison group. Dietary total fat, monounsaturated fatty acid (MUFA), polyunsaturated fatty acid (PUFA), LA, total ω 6 polyunsaturated fatty acid (Tω6PUFA), and α-linolenic acid (ALA) intake positively predicted serum LA concentration. MUFA, total ω 3 polyunsaturated fatty acid (Tω3PUFA), and ALA intake positively predicted serum DHA concentration. Total dietary fat, MUFA, PUFA, Tω3PUFA, LA, and ALA intake negatively predicted serum T:T. ALA and Tω3PUFA intake negatively predicted serum AA:DHA.

CONCLUSIONS

Dietary fat patterns influenced serum LA, DHA, T:T, and AA:DHA in children with CF and PI. These data suggest that changes in dietary practices may result in FA profiles associated with improved clinical outcomes.

Non-invasive evaluation of cystic fibrosis related liver disease in adults with ARFI, transient elastography and different fibrosis scores

Background

Cystic fibrosis-related liver disease (CFLD) is present in up to 30% of cystic fibrosis patients and can result in progressive liver failure. Diagnosis of CFLD is challenging. Non-invasive methods for staging of liver fibrosis display an interesting diagnostic approach for CFLD detection.

Aim

We evaluated transient elastography (TE), acoustic radiation force impulse imaging (ARFI), and fibrosis indices for CFLD detection.

Methods

TE and ARFI were performed in 55 adult CF patients. In addition, AST/Platelets-Ratio-Index (APRI), and Forns' score were calculated. Healthy probands and patients with alcoholic liver cirrhosis served as controls.

Results

Fourteen CF patients met CFLD criteria, six had liver cirrhosis. Elastography acquisition was successful in >89% of cases. Non-cirrhotic CFLD individuals showed elastography values similar to CF patients without liver involvement. Cases with liver cirrhosis differed significantly from other CFLD patients (ARFI: 1.49 vs. 1.13 m/s; p = 0.031; TE: 7.95 vs. 4.16 kPa; p = 0.020) and had significantly lower results than individuals with alcoholic liver cirrhosis (ARFI: 1.49 vs. 2.99 m/s; p = 0.002). APRI showed the best diagnostic performance for CFLD detection (AUROC 0.815; sensitivity 85.7%, specificity 70.7%).

Conclusions

ARFI, TE, and laboratory based fibrosis indices correlate with each other and reliably detect CFLD related liver cirrhosis in adult CF patients. CF specific cut-off values for cirrhosis in adults are lower than in alcoholic cirrhosis.

Best practice guidance for the diagnosis and management of cystic fibrosis-associated liver disease

Approximately 5-10% of cystic fibrosis (CF) patients develop multilobular cirrhosis during the first decade of life. Most CF patients later develop signs of portal hypertension with complications, mainly variceal bleeding. Liver failure usually occurs later, after the paediatric age. Annual screening for liver disease is recommended to detect pre-symptomatic signs and initiate ursodeoxycholic acid therapy, which might halt disease progression. Liver disease should be considered if at least two of the following variables are present: abnormal physical examination, persistently abnormal liver function tests and pathological ultrasonography. If there is diagnostic doubt, a liver biopsy is indicated. All CF patients with liver disease need annual follow-up to evaluate the development of cirrhosis, portal hypertension or liver failure. Management should focus on nutrition, prevention of bleeding and variceal decompression. Deterioration of pulmonary function is an important consideration for liver transplantation, particularly in children with hepatic dysfunction or advanced portal hypertension.

Comparison of lysophospholipid levels in rat feces with those in a standard chow

Although lysophospholipids have attracted much attention due to their diverse physiological activities through their specific receptors, little is known about their metabolic fates in mammalian digestive systems after their ingestion as a minor food component. In this study, we analyzed five lysophospholipids in lipid extracts of a standard rat chow and feces of rats fed the chow by two-dimensional thin layer chromatography and liquid chromatography-tandem mass spectrometry. The most abundant lysophospholipid in the rat chow was lysophosphatidylcholine followed by lysophosphatidylethanolamine, lysophosphatidic acid (LPA), lysophosphatidylinositol and lysophosphatidylserine (LPS) in an increasing order, but their concentrations were very low in rat feces. Among the molecular species of LPS in the chow, only saturated species were detected in the feces in significant amounts. In addition, several molecular species of LPA remained in the feces in variable portions (saturated > monounsaturated > polyunsaturated). These results suggest that a portion of ingested LPA and LPS reach the rat large intestine, affecting physiological colon functions.

Oral choline supplementation in children with intestinal failure

Choline deficiency leads to steatohepatitis, elevated transaminases, susceptibility to septic shock, and an increased risk of central catheter thrombosis. Children with intestinal failure (IF) are at risk for choline deficiency. In an unblinded, open-label study, we studied 7 children with IF on parenteral nutrition, measured their plasma free choline level, and, if low, supplemented enterally with adequate intake (AI) doses of choline. Four to 6 weeks later we remeasured their plasma free choline. Unlike adults, infants did not respond to oral choline supplementation at AI doses. Additionally, we have calculated plasma free choline percentiles versus age for normal children.

Plasma choline depletion is associated with decreased peripheral blood leukocyte acetylcholine in children with cystic fibrosis

BACKGROUND

Choline is an important constituent of acetylcholine. Choline is needed for acetylcholine in the nonneuronal acetylcholine system that includes epithelial cells of the lung and intestine, endothelial cells, and immune cells. Plasma free choline concentrations are low in children with cystic fibrosis (CF), but the implications for acetylcholine are unknown.

OBJECTIVE

We determined the relation between plasma free choline and related metabolites and leukocyte acetylcholine in children with CF and in a control group of healthy children without CF.

DESIGN

This was a cross-sectional study in 34 children with CF who were pancreatic insufficient and taking pancreatic enzyme-replacement therapy and in 16 healthy children. Plasma free choline, betaine, dimethylglycine, methionine, homocysteine, and leukocyte acetylcholine concentrations were quantified by using isotope-dilution HPLC-tandem mass spectrometry.

RESULTS

Mean (±SE) plasma free choline was 9.30 ± 0.37 and 6.54 ± 0.38 μmol/L (P < 0.05) and leukocyte acetylcholine was 1.21 ± 0.016 and 0.077 ± 0.011 pmol leukocyte acetylcholine/10(6) cells (P < 0.05) in control children and children with CF, respectively. Leukocyte acetylcholine was positively correlated with plasma free choline concentration in children with CF (r = 0.412, P < 0.05) but not in control children. Plasma betaine, dimethylglycine, and methionine concentrations were also lower in children with CF than in control children (P < 0.05).

CONCLUSIONS

A low free choline and methyl status in children with CF is associated with reduced acetylcholine in leukocytes. Whether these changes are explained by a mutation in the CF transmembrane conductance regulator or disturbances in choline metabolism and the implications for immune cell dysfunction in CF are unknown. This trial was registered at clinicaltrials.gov as NCT01150136.

A novel lipidomic strategy reveals plasma phospholipid signatures associated with respiratory disease severity in cystic fibrosis patients

The aim of this study was to search for lipid signatures in blood plasma from cystic fibrosis (CF) patients using a novel MALDI-TOF-ClinProTools strategy, initially developed for protein analysis, and thin layer chromatography coupled to MALDI-TOF (TLC-MALDI). Samples from 33 CF patients and 18 healthy children were subjected to organic extraction and column chromatography separation of lipid classes. Extracts were analyzed by MALDI-TOF, ion signatures were compared by the ClinProTools software and by parallel statistical analyses. Relevant peaks were identified by LC-MSn. The ensemble of analyses provided 11 and 4 peaks differentially displayed in CF vs healthy and in mild vs severe patients respectively. Ten ions were significantly decreased in all patients, corresponding to 4 lysophosphatidylcholine (18:0, 18:2, 20:3, and 20:5) and 6 phosphatidylcholine (36:5, O-38:0, 38:4, 38:5, 38:6, and P-40:1) species. One sphingolipid, SM(d18:0), was significantly increased in all patients. Four PC forms (36:3, 36:5, 38:5, and 38:6) were consistently downregulated in severe vs mild patients. These observations were confirmed by TLC-MALDI. These results suggest that plasma phospholipid signatures may be able to discriminate mild and severe forms of CF, and show for the first time MALDI-TOF-ClinProTools as a suitable methodology for the search of lipid markers in CF.

Nutrition management of pediatric patients who have cystic fibrosis

Since the identification of cystic fibrosis (CF) in the 1940s, nutrition care of patients who have CF has been a challenge. Through optimal caloric intake and careful management of malabsorption, patients are expected to meet genetic potential for growth. Yet factors beyond malabsorption, including nutrient activity at the cellular level, may influence growth and health. This article reviews nutrition topics frequently discussed in relationship to CF and presents intriguing new information describing nutrients currently being studied for their impact on overall health of patients who have CF.

Hepatobiliary disease in patients with cystic fibrosis

PURPOSE OF REVIEW

This review explores the recent advances in knowledge regarding hepatobiliary disease in patients with cystic fibrosis.

RECENT FINDINGS

Hepatobiliary abnormalities associated with cystic fibrosis are varied in nature and range from defects attributable to the underlying genetic defect to those related to systemic disease and malnutrition. Novel research into the underlying pathogenesis of cystic fibrosis liver disease and the primary role of cystic fibrosis transmembrane conductance regulator in biliary secretory epithelium is presented. This work has been fostered by the development of new animal models of cystic fibrosis transmembrane conductance regulator dysfunction. Of the wide range of hepatobiliary complications associated with cystic fibrosis the most clinically relevant problem is progression of focal biliary cirrhosis to multilobular cirrhosis with its attendant complications of portal hypertension and potentially end-stage liver disease. However, recent studies suggest that liver transplantation may not improve survival in patients with cystic fibrosis and significant portal hypertension.

SUMMARY

Hepatobiliary disease is a common finding in patients with cystic fibrosis; the pathogenesis is multifactorial in nature. As new therapeutic strategies emerge, life expectancy will continue to increase as will the impact of liver disease on quality of life and survival of patients with cystic fibrosis. This review will discuss novel insights into pathogenesis as well as diagnostic and management options.

Abrogation of the resistance of choline-induced Pseudomonas aeruginosa virulence to sub-MIC erythromycin by ethanol

Despite Pseudomonas aeruginosa antibiotic resistance, erythromycin (ERM, a macrolide) at subinhibitory concentration (sub-MIC) reduces its pathogenicity. We assessed ERM effects on P. aeruginosa in cultures containing choline (Ch) without and with 1% ethanol (Et) addition. Ch, as an osmoprotectant, increases the following virulence factors (VIFs): lectins (haemagglutination); proteases (casein and elastin lysis); haemolytic phospholipase C (PLC-H; haemolysis); pyocyanin (pigment o.d.) and autoinducers (violacein bioassay). Ethanol also increases lectins, proteases, pyocyanin, autoinducers and rhamnolipid (RHAL; haemolysis) formation, but reduces Ch-induced PLC and protease (elastase) activities. ERM has been shown to totally suppress the Et-induced VIFs, whereas partially reducing the Ch-induced ones. Unexpectedly, ERM combination with 1% Et dramatically annuls the Ch-induced factors. Et contribution might be attributed to its effect on cell membrane, displaying synergism with ERM, whereas antagonizing Ch osmoprotective potential and shifting gene expression. This information is worth further molecular investigation and clinical consideration for skin infection therapy.

Cystic Fibrosis and Nutrition: Linking Phospholipids and Essential Fatty Acids with Thiol Metabolism

Cystic fibrosis (CF) is the most common lethal inherited disorder among Caucasians and results from mutation in the gene encoding the CF transmembrane conductance regulator. In addition to its multisystem clinical effects, the disease is characterized by increased proinflammatory mediators and oxidant stress, and systemic redox imbalance with reduced glutathione (GSH), together with alterations in circulating and tissue (n-6) and (n-3) fatty acids, particularly a decrease in docosahexaenoic acid. The metabolism of phospholipids and fatty acids is closely related to GSH through the methionine-homocysteine cycle, in which choline via betaine provides methyl groups to regenerate S-adenosylmethionine, important in generating phosphatidylcholine and amino acid precursors for GSH. Current research focuses both on fatty acid supplementations to normalize altered (n-6) to (n-3) fatty acid balance and decrease generation of (n-6) fatty acid-derived inflammatory mediators, and strategies to improve oxidant defenses and redox balance. However, further research is needed before such strategies can be included in clinical care of individuals with CF.

Liver disease in cystic fibrosis

PURPOSE OF REVIEW

This review highlights recent developments in liver disease associated with cystic fibrosis.

RECENT FINDINGS

The broad spectrum of hepatobiliary problems in cystic fibrosis includes specific alterations ascribable to the underlying defect as well as lesions of iatrogenic origin or that reflect the effects of a disease process occurring outside the liver. Focal biliary cirrhosis, resulting from biliary obstruction and progressive periportal fibrosis, is the most clinically relevant problem, because extension of the initially focal fibrogenic process may lead to multilobular biliary cirrhosis, portal hypertension and eventually liver failure. Cystic fibrosis associated liver disease is presently classified among genetic cholangiopathies and results from lack or dysfunction of the cystic fibrosis transmembrane regulator at the apical membrane of bile duct cells. Major advances have been achieved regarding characterization of natural history, risk factors, diagnostic modalities and treatment options.

SUMMARY

Liver disease is a relatively frequent and early complication of cystic fibrosis. The pathogenesis is apparently multifactorial, with contributions from environmental and genetic determinants. Its impact on quality of life and survival will increase in future years, and its early detection and treatment will become increasingly important issues. Ursodeoxycholic acid is the only treatment currently available, but novel therapeutic options are being evaluated.

Choline-related supplements improve abnormal plasma methionine-homocysteine metabolites and glutathione status in children with cystic fibrosis

BACKGROUND

Liver triacylglycerol accumulation and oxidative stress are common in cystic fibrosis (CF) and also occur in choline deficiency. Previously, we showed an association between elevated plasma homocysteine, reduced ratios of S-adenosylmethionine to S-adenosylhomocysteine (SAM:SAH) and of phosphatidylcholine to phosphatidylethanolamine, and phospholipid malabsorption in children with CF.

OBJECTIVE

The objective was to address a possible relation between altered methionine-homocysteine metabolism and choline metabolism in children with CF.

DESIGN

Children with CF were assigned without bias to supplementation with 2 g lecithin/d (n = 13), 2 g choline/d (n = 12), or 3 g betaine/d (n = 10) for 14 d. Plasma concentrations of methionine, adenosine, cysteine, cysteinyl-glycine, glutathione, glutathione disulfide (GSSG), and fatty acids; SAM:SAH; and red blood cell phospholipids were measured within each group of children with CF before and after supplementation. Plasma from healthy children without CF (n = 15) was analyzed to obtain reference data.

RESULTS

Children with CF had higher plasma homocysteine, SAH, and adenosine and lower methionine, SAM:SAH, and glutathione:GSSG than did children without CF. Supplementation with lecithin, choline, or betaine resulted in a significant increase in plasma methionine, SAM, SAM:SAH, and glutathione:GSSG and a decrease in SAH (n = 35). Supplementation with choline or betaine was associated with a significant decrease in plasma SAH and an increase in SAM:SAH, methionine, and glutathione:GSSG. Supplementation with lecithin or choline also increased plasma methionine and SAM.

CONCLUSION

We showed that dietary supplementation with choline-related compounds improves the low SAM:SAH and glutathione redox balance in children with CF.

Ethanol Effects on Pseudomonas aeruginosa Lectin, Protease, Hemolysin, Pyocyanin, Autoinducer, and Phosphatase Levels Depending on Medium Composition and Choline Presence

Pseudomonas aeruginosa is a serious pathogen involved in nosocomial infections. Its pathogenicity is owed to rich production of virulence factors (VIFs) regulated by several complex hierarchical signal systems depending on environmental conditions, medium composition, and the presence of certain active compounds in it. Choline (Ch), which exists in patient tissues, and ethanol (Et), whose consumption aggravates infections, were reported to augment this microbe virulence. The goal of the present study was to show the effect of Et addition to P. aeruginosa cultures in two media (minimal culture medium [MM] and Eagon-Grelet medium [EGM]) in the absence or presence of Ch on its VIF levels. In MM, Et sharply repressed the basal and Ch-induced levels of the P. aeruginosa lectins PA-IL (galactose-specific) and PA-IIL (fucose/mannose-binding) and proteolytic activities, while increasing C(6)-HSL (autoinducer), hemolytic phospholipase C (PLC-H), and phosphatase levels. In EGM, it profoundly increased lectin, protease, pyocyanin, rhamnolipid (RhaL), autoinducer, and slightly phosphatase levels, but reduced Ch-induced protease, PLC-H, and acid phosphatase activities, except the short-chain HSL levels, which were increased by Et in combination with Ch. The presented results enlighten part of the complex molecular basis of Et-induced aggravation of P. aeruginosa infections due to increasing the bacterium virulence, which runs in parallel to suppression of the patient's immunity.

Evidence of choline depletion and reduced betaine and dimethylglycine with increased homocysteine in plasma of children with cystic fibrosis

Cystic fibrosis (CF) is associated with many clinical complications including steatosis for which the relation to defective CF transmembrane conductance regulator protein is unclear. Choline deficiency results in hepatic steatosis. Choline is the precursor of betaine, which donates methyl groups for remethylation of homocysteine to methionine and dimethylglycine. Previously, we have shown phospholipid malabsorption and increased plasma homocysteine in children with CF. In these studies we used normal phase HPLC with tandem mass spectrometry to determine plasma choline, betaine, and dimethylglycine in children with CF (n = 34) and healthy control children without CF (n = 15). Plasma choline, betaine, and dimethylglycine were significantly lower in children with CF (means +/- SEM, 6.48 +/- 0.35, 23.8 +/- 1.49, 1.49 +/- 0.13 mumol/L, respectively) than in children without CF (8.98 +/- 0.46, 37.3 +/- 1.84, 3.01 +/- 0.17 mumol/L, respectively). Plasma choline (r = 0.373, P = 0.007) and betaine (r = 0.399, P = 0.005) were positively related to methionine, and choline was inversely related to homocysteine (r = -0.316, P = 0.03). Choline, betaine, and dimethylglycine were all significantly and positively related to the plasma S-adenosylmethionine:S-adenosylhomocysteine (SAM:SAH) ratio (r = 0.294, r = 0.377, r = 0.442, respectively; P < 0.05). The plasma choline:betaine and betaine:dimethylglycine ratios did not differ between the children with CF and the control children, suggesting no increase in betaine synthesis, or betaine-dependent remethylation of homocysteine. These studies suggest that choline depletion may contribute to increased homocysteine in children with CF. Choline depletion and altered thiol metabolism may contribute to the clinical complications associated with CF.

Is it time to reevaluate methyl balance in humans?

S-Adenosylmethionine (AdoMet) is the major biological methyl donor. AdoMet's methyl group arises both from the diet (eg, methionine, choline, and betaine) and from de novo synthesis by the process of methylneogenesis. At least 50 AdoMet-dependent methylation reactions have been identified in mammals, and genomic analyses suggest that the final number will be much higher. Such methylation reactions play major roles in biosynthesis, regulation, and detoxification. Creatine synthesis is thought to account for the use of >70% of AdoMet-derived methyl groups in humans. This is not consistent with recent studies in mice, in which the phosphatidylethanolamine methyltransferase gene was deleted (PEMT-/-). Loss of this hepatic enzyme resulted in a 50% decrease in plasma homocysteine, which suggests that it accounts for a major component of whole-body AdoMet utilization. A reexamination of human creatine metabolism showed that dietary creatine can account for as much as 50% of daily creatine requirements in nonvegetarians and, therefore, that estimates of creatine synthesis need to be reduced. We suggest that creatine synthesis is responsible for a smaller proportion of AdoMet-derived methyl groups than has been suggested and that phosphatidylcholine synthesis via phosphatidylethanolamine methyltransferase is a major consumer of these methyl groups.