Success Chemistry

Improve who you are | Become unforgettable

Biochemistry

Choline

Biochemistry, GlossarySuccess Chemistry Staff

Choline is a essential nutrient for humans it is consumed

in many foods.

It is a constituent of all cell membranes

and is necessary for growth and development. Also, as

the major precursor of betaine, it is used by the kidney

to maintain water balance and by the liver as a source of

methyl groups for the removal of homocysteine in methionine

formation. Finally, choline is used to produce the

important neurotransmitter (nerve messenger chemical)

acetylcholine, which is involved in memory and other

nervous system functions (Fig. 1). Maternal diets deficient

in choline during the second half of pregnancy in

rodents caused decreased neurogenesis and increased

neuronal apoptosis in fetal hippocampus (the memory

center), resulting in permanent behavioral (memory)

modifications in the offspring. Dietary deficiency of

choline in rodents causes development of liver cancer in

the absence of any known carcinogen. In humans, dietary

deficiency of choline is associated with fatty liver and liver

damage.

The dietary requirement for choline is influenced

by gender as well as by genetic polymorphisms.

 

Using a comprehensive database of the choline content of foods, a

number of epidemiological studies identified associations

between dietary choline intake and plasma homocysteine

levels (risk factor for cardiovascular disease), cancer, and

birth defects.

BIOCHEMISTRY AND RELATIONSHIPS

WITH OTHER NUTRIENTS

Choline is needed for synthesis of several major phospholipids

(phosphatidylcholine and sphingomyelin) in cell

membranes and is also involved in methyl metabolism,

cholinergic neurotransmission, transmembrane signaling,

and lipid–cholesterol transport and metabolism (1)

(Fig. 2). Choline can be acetylated, phosphorylated, oxidized,

or hydrolyzed. There are several comprehensive

reviews of the metabolism and functions of choline (1).

Cells absolutely require choline and die by apoptosis

when deprived of this nutrient (2,3). Humans derive

choline from foods, as well as from the de novo biosynthesis

of the choline moiety via the methylation of phosphatidylethanolamine

using (S)-adenosylmethionine as

the methyl donor (most active in the liver). This ability

to form choline means that some of the demand for

choline can, in part, be met by using methyl groups derived

from one carbon metabolism (via methyl-folate and

methionine). Several vitamins (folate, vitamin B12, vitamin

B6, and riboflavin) and the amino acid methionine interact

with choline in 1-carbon metabolism. There has been

renewed interest in these pathways during the past several

years, engendered by recent insights that indicate that

modest dietary inadequacies of the above-mentioned nutrients,

of a degree insufficient to cause classical deficiency

syndromes, can still contribute to important diseases

such as neural tube defects, cardiovascular disease, and

cancer (4).

Perturbing the metabolism of one of these pathways

results in compensatory changes in the others (1).

For example, methionine can be formed from homocysteine

using methyl groups from methyl-tetrahydrofolate

(THF), or using methyl groups from betaine that are

derived from choline. Similarly, methyl-THF can be

formed fromone-carbon units derived fromserine or from

the methyl groups of choline via dimethylglycine, and

choline can be synthesized de novo using methyl groups

derived from methionine [via (S)-adenosylmethionine].

 

Pathways of choline metabolism

Choline can be a methyl-group donor and interacts with methionine

and folate metabolism. It can be acetylated to form the neurotransmitter

acetylcholine, and it can be phosphorylated to form

membrane phospholipids such as phosphatidylcholine (lecithin)

and sphingomyelin. Choline can be formed via the methylation of

phosphatidylethanolamine (forming phosphatidylcholine, which

can be hydrolyzed to make choline).

use more methyl-THF to remethylate homocysteine in the

liver and increase dietary folate requirements. Conversely,

when they are deprived of folate, they use more methyl

groups from choline, increasing the dietary requirement

for choline (5). The availability of transgenic and knockout

mice has made possible additional studies that demonstrate

the interrelationship of these methyl sources (6).

When considering dietary requirements it is important to

realize that methionine, methyl-THF, and choline can be

fungible sources of methyl groups.

Choline is found in foods as free choline and as

esterified forms such as phosphocholine, glycerophosphocholine,

sphingomyelin, and phosphatidylcholine

(7). Lecithin is a term often used interchangeably

with phosphatidylcholine, whereas the compound is a

phosphatidylcholine-rich mixture added as an emulsifying

agent in the food industry. Pancreatic enzymes can liberate

choline from dietary phosphocholine, glycerophosphocholine,

and phosphatidylcholine. Before choline can

be absorbed in the gut, some is metabolized by bacteria

to form betaine and methylamines (which are not methyl

donors).

There is no estimate for percentage absorption of the

various forms of choline in humans. The water-soluble

choline-derived compounds (choline, phosphocholine,

and glycerophosphocholine) are absorbed via the portal

circulation, whereas the lipid-soluble compounds

(phosphatidylcholine and sphingomyelin) are absorbed

as chylomicrons. Lecithin is the most abundant choline containing

compound in the diet. About half of the lecithin

ingested enters the thoracic duct, and the remaining is metabolized

to glycerophosphocholine in the intestinal mucosa

and then to choline in the liver. The liver takes up

the majority of choline and stores it in the form of phosphatidylcholine

and sphingomyelin. The kidney and the

brain also accumulate choline. Although some free choline

is excreted with urine, most is oxidized in the kidney to

form betaine, which is responsible for maintaining the osmolarity

in the kidney. A specific carrier is needed for the

transport of free choline across the blood–brain barrier;

the capacity is especially high in neonates.

 

Choline and Epigenetics

Choline and other methyl donors are important dietary

modulators of epigenetic marks on genes. The term “epigenetics”

defines heritable changes in gene expression

that are not coded in the DNA sequence itself. Epigenetic

mechanisms include DNA methylation and histone modification.

DNA methylation occurs predominantly at the

cytosine bases followed by a guanosine (CpGs). When it

occurs in promoter regions that regulate DNA transcription,

the expression of the associated gene is altered (8,9).

Although there are exceptions, increased methylation is

usually associated with gene silencing, whereas decreased

methylation with induced gene expression. Another epigenetic

mechanism is histone modification (10). Histones

are proteins around which DNA is tightly wound, forming

the dynamic structure called chromatin. Chromatin can be

either an inactive state or an active state at which transcription

factors can pass through. Histone acetylation predominantly

promotes active chromatin, whereas histone

methylation can be associated with both transcriptionally

active and inactive chromatin. Furthermore, the degree of

methylation (mono-, di-, or tri-) results in distinct effects

on chromatin state (11). Methylation of DNA and histone

requires (S)-adenosylmethionine to methylate cytosines

in DNA and lysine and arginine residues in histones, respectively.

The availability of (S)-adenosylmethionine is

directly influenced by dietary choline and other methyl

donors.

Examples of epigenetic effects of choline and other

methyl donors include experiments in rodents in which

pregnant dams were fed diets that were choline deficient

versus normal, and DNA methylation in fetal brain was

modified, resulting in over expression of genes that inhibit

cell cycling in neural progenitor cells of developing brain

(12,13). Gestational choline availability also affects histone

methylation in the developing embryo, resulting in

changes in expression of genes that regulate methylation

and neuronal cell differentiation (14). Feeding pregnant

Pseudoagouti Avy/a mouse dams a choline and methylsupplemented

diet altered epigenetic regulation of agouti

expression in their offspring, as indicated by increased

agouti/black mottling of their coats and by lean body

phenotype (15,16). In another example, choline and

methyl donor supplementation to dams increased DNA

methylation of the fetal gene Axin fused [Axin(Fu)] and

reduced incidence of tail kinking in Axin(Fu)/+ offspring

by 50% (17). Thus, dietary manipulation of choline and

methyl donors (either deficiency or supplementation) can

have a profound impact upon gene expression.

138 Zeisel

 

HUMAN REQUIREMENT FOR CHOLINE

In one of the first clinical nutrigenomics studies, humans

were phenotyped with respect to their susceptibility

to developing organ dysfunction when fed a low choline

diet (18–21). Adult men and women (pre- and

postmenopausal) aged 18 to 70 years were fed a standard

diet containing a known amount of choline (550 mg/

70 kg/day; baseline) for 10 days. On day 11 subjects were

placed on a diet containing less than 50 mg choline/day

for up to 42 days. Blood and urine were collected to measure

various experimental parameters of dietary choline

status, and markers of organ dysfunction and liver fat

were assessed. If at some point during the depletion period,

functional markers indicated organ dysfunction associated

with choline deficiency, subjects were switched

to a diet containing choline until replete.

Most men and postmenopausal women fed the low choline

diets developed reversible fatty liver (measure by

mass resonance spectroscopy) as well as liver and muscle

damage, whereas 56% of premenopausal women were

resistant to developing choline deficiency (21). The fatty

liver occurred due to lack of phosphatidylcholine synthesis

in liver, which is required for very low density lipoprotein

(VLDL) synthesis needed for export of excess triacylglycerol

from liver (22). Choline deficiency liver damage

was characterized by elevated serum aminotransferase

(23) and muscle damage was characterized by elevated

plasma serum creatine phosphokinase (19): both were due

to increased rates of apoptosis in these tissues (also occurred

in peripheral lymphocytes (24)). Choline-deficient

subjects also had impaired ability to handle a methionine

load, resulting in elevated plasma homocysteine concentrations

(20,25).

Only 44% of premenopausal women develop

signs of choline deficiency when deprived of dietary

choline as compared with most adult men and postmenopausal

women, suggesting their higher resistance

to choline deficiency (19,20). Premenopausal women required

less dietary choline because estrogen induces the

phosphatidylethanolamine-N-methyltransferase (PEMT)

gene to enhance the de novo biosynthesis of choline moiety

(26). Estrogen binds to its receptors, and this complex

interacts with estrogen response elements (EREs) in the

promoter of the PEMT gene, resulting in an upregulation

in PEMT mRNA expression and in hepatic enzyme activity

(26). Estrogen as the mediator of increasing PEMT activity

in women is important, especially during pregnancy

when fetal development uses a great deal of choline. Estradiol

concentration rises from 1 to 60 nMduring pregnancy

(27,28), suggesting that the capacity for endogenous synthesis

of choline should be highest when choline is needed

most. Pregnancy and lactation are stages of life that demand

high dietary choline intake and leave mothers extremely

vulnerable to choline deficiency (29). In utero,

the fetus is exposed to very high choline concentrations,

with a progressive decline in blood choline concentration

until adult levels of choline concentration are achieved

after the first weeks of life (30). Plasma or serum choline

concentrations are 6–7°ø higher in the fetus and newborn

than those in adults (31,32). High circulating choline in

the fetus and neonate ensures the availability of choline to

tissues.

Less than 15% of pregnant women consume the recommended

adequate intake for choline (33), and in casecontrol

studies in California, women eating diets in the

lowest quartile for choline were at fourfold increased risk

for having a baby with a neural tube defect and at almost

twofold increased risk for having a baby with a cleft

palate; these risks were calculated after controlling for folate

intake (34,35).

 

Genetics of Choline Requirements

Although premenopausal women are more resistant to

choline deficiency, a significant portion of them (44%) still

develops organ dysfunction when deprived of choline,

suggesting individual differences in susceptibility to

choline deficiency. In fact, some men and women require

more than 850 mg/70 kg/day choline in their diet,

whereas others require less than 550 mg/kg/day (21).

Genetic variation likely underlies the differences in these

dietary requirements. A single-nucleotide polymorphism

(SNP) is a genetic variation occurring when a single nucleotide

(A, T, C, or G) in the genome sequence is altered.

These variations may affect metabolism. Only a few

reports investigate whether SNPs in the genes involved

in one carbon metabolism have roles in choline requirements

(36,37). Premenopausal women with a SNP in 5,10-

methylenetetrahydrofolate dehydrogenase (MTHFD1

rs2236225) were 15°ø more susceptible to choline deficiency

than did noncarriers. This variant increased the

use of choline perhaps by limiting the availability of

methyl-folate for Hcy remethylation and increasing the

demand for choline as a methyl-group donor. In addition,

individuals with a SNP in PEMT (rs12325817) were more

susceptible to choline deficiency, and women harboring

this SNP were more affected than did men. SNPs in

the PEMT gene alter endogenous synthesis of choline,

thereby increasing the dietary requirement for choline.

Dietary Recommendations

In 1998, the Institute of Medicine (IOM) made recommendations

for choline intake in the diet (4). At the time, there

were insufficient data with which to derive an estimated

average requirement for choline, thus only an adequate intake

(AI) could be estimated. The IOM report cautioned,

“this amount will be influenced by the availability of methionine

and methyl-folate in the diet. Itmaybe influenced

by gender, and it may be influenced by pregnancy, lactation,

and stage of development. Although AIs are set for

choline, it may be that the choline requirement can be met

by endogenous synthesis at some of these stages.”

 

Food Sources

In foods, there are multiple choline compounds that contribute

to total choline content (choline, glycerophosphocholine,

phosphocholine, phosphatidylcholine, and

sphingomyelin) (7). The U.S. Department of Agriculture

(USDA) maintains a database of choline content in

foods (38). Excellent sources of dietary choline are foods

that contain membranes, such as eggs and liver. Average

dietary choline intake on ad libitum diets for males and

females are 8.4 and 6.7 mg/kg choline per day.

Human milk is rich in choline. Choline is routinely added to

commercially available infant formulas. Until recently

some infant formulas had inadequate choline content (especially

soy-derived infant formulas), but in 2007–2008,

many infant formula companies increased the choline content

of their formulas so that they matched mature breast

milk. These formulas still have different mixtures of the

esters of choline than are present in human milk, perhaps

resulting in different bioavailability as compared to human

milk (41).

Adverse Effects

High doses of choline (>6 g) have been associated with excessive

cholinergic stimulation, such as vomiting, salivation,

sweating, and gastrointestinal effects (4). In addition,

fishy body odor results from the excretion of trimethylamine,

a choline metabolite from bacterial action (24). The

tolerable upper limit for choline has been set at 3 g/day (4).

Assessing Choline Status

Measurement of choline and choline metabolites is useful

in estimating choline status, but the measure is not definitive.

Plasma choline concentration varies in response to

diet and can rise as much as twofold after a two-egg

meal. Fasting plasma choline concentrations vary from7 to

15 M, with most subjects having concentrations of

10 M. Individuals that have starved for up to seven

days have diminished plasma choline, but levels never

drop below 50% of normal, probably because tissue phospholipids

are “cannibalized” to prevent concentrations

of choline from falling further (42). Note that children

during the first year of life have normal plasma choline

concentrations that are higher than 10 to 15 M (43).

Plasma phosphatidylcholine concentration also decreases

in choline deficiency (44), but these values are also influenced

by factors that change plasma lipoprotein levels.

Fasting plasma phosphatidylcholine concentrations

are approximately 1 to 1.5 mM. Thus, measurements of

choline or phosphatidylcholine in blood identify subjects

with low dietary choline intake, but provide little help in

differentiating the degree of deficiency.

 

CHOLINE AND CARDIOVASCULAR DISEASE

Choline and betaine may benefit heart health by lowering

blood pressure, altering blood lipid profiling, and reducing

plasma Hcy, a risk factor for cardiovascular disease

(CVD) (45). Dietary choline intake was found to have a statistically

significant inverse relationship to circulating Hcy

concentrations in the Framingham Heart Study (46) and in

the Nurse’s Health Study (25), suggesting a protective effect

of choline intake. However, when looking at the association

between dietary choline intake and CVDincidence,

no association was found (14) in the European Prospective

Investigation into Cancer and Nutrition (EPIC) study

(47), and a marginal positive association was found in the

Atherosclerosis Risk in Communities (ARIC) study (48).

It is important to note that in the ARIC study, most individuals

in the cohort had choline intake below AI (49).

Hence, the effects of choline supplementation on CVD

risk remain unknown. Some human studies suggested

that high betaine supplementation increases plasma lowdensity

lipoprotein (LDL) cholesterol and triacylglycerol

concentrations (50–52), effects that might counterbalance

its Hcy lowering effects. However, the changes in serum

lipid concentrations were not associated with higher risk

of CVD. Moreover, the rise in LDL concentration may

be an artifact of increasing VLDL and triacylglycerol

excretion from fatty liver to plasma, which is not an adverse

outcome (for critical review see Ref. 53). The relationship

between choline and heart health warrants more

study.

The choline-containing phospholipid phosphatidylcholine

has been used as a treatment to lower the

cholesterol concentrations because lecithin-cholesterol

acyltransferase has an important role in the removal of

cholesterol from tissue. Betaine, the oxidized product

of choline, has been used to normalize the plasma

homocysteine and methionine levels in patients with

homocystinuria, a genetic disease caused by 5,10-

methylenetetrahydrofolate reductase deficiency. Therefore,

dietary choline intake might be correlated with

cardiovascular disease risk. Many epidemiologic studies

have examined the relationship between dietary folic acid

and cancer or heart disease. It may be helpful to also consider

choline intake as a confounding factor because folate

and choline methyl donation can be interchangeable (7).

 

CHOLINE DEFICIENCY AND CANCER

An interesting effect of dietary choline deficiency in rats

and mice has never been studied in humans. Dietary

deficiency of choline in rodents causes development of

hepatocarcinome in the absence of any known carcinogen

(54). Choline is the only single nutrient for which

this is true. It is interesting that choline-deficient rats not

only have a higher incidence of spontaneous hepatocarcinoma

but also are markedly sensitized to the effects of

administered carcinogens. Several mechanisms are suggested

for the cancer-promoting effect of a choline-free

diet. These include increased cell proliferation related to

regeneration after parenchymal cell death occurs in the

choline-deficient liver; hypomethylation of DNA (alters

expression of genes); reactive oxygen species leakage from

mitochondria with increased lipid peroxidation in liver;

activation of protein kinase C signaling due to accumulation

of diacylglycerol in liver; mutation of the fragile

histidine triad (FHIT) gene, which is a tumor suppressor

gene; and defective cell-suicide (apoptosis) mechanisms

140 Zeisel

(54). Loss of PEMT function may also contribute to malignant

transformation of hepatocytes (55).

Only a handful of epidemiologic studies explore

how choline and betaine intakes alter cancer risk in populations.

This was perhaps due to the absence of food composition

data, which has not been developed until recently

(7). The Long Island Breast Cancer Study found that high

choline consumption was associated with reduced breast

cancer risk (56), and high choline and betaine consumption

was associated with reduced breast cancer mortality

(57). Moreover, individuals with PEMT rs12325817 and

CHDH rs12676 SNPs had lower risk of developing breast

cancer, whereas BHMT rs3733890 had lower breast cancer

mortality. These data suggest the importance of nutrients

and genetic interactions in the etiology of cancer. Alternatively,

the Nurse’s Health Study II found no association

between choline intake and breast cancer risk (58), but a

positive association between choline intake and colorectal

cancer risk (59), suggesting different etiologies between

breast and colorectal cancer. More research is warranted.

 

CHOLINE AND BRAIN

Choline and Brain Development

In rodents, maternal dietary choline intake during late

pregnancy modulated mitosis and apoptosis in progenitor

(stem) cells of the fetal hippocampus and septum

and altered the differentiation of neurons in fetal hippocampus

(60). Variations in maternal dietary choline

intake (choline supplementation or choline deficiency)

during late pregnancy were also associated with significant

and irreversible changes in hippocampal function in

the adult animal, including altered long-term potentiation

(LTP) and altered memory (61). More choline (about 4°ø

dietary levels) during days 11–17 of gestation in the rodent

increased hippocampal progenitor cell proliferation,

decreased apoptosis in these cells, enhanced LTP in the

offspring when they were adult animals, and enhanced

visuospatial and auditory memory by as much as 30%

in the adult animals throughout their lifetimes (61). The

enhanced maze performance appears to be due to cholineinduced

improvements in memory capacity. Indeed, adult

rodents decrement in memory as they age, and offspring

exposed to extra choline in utero do not show this

“senility” (62). In contrast, mothers fed choline-deficient

diets during late pregnancy have offspring with diminished

progenitor cell proliferation and increased apoptosis

in fetal hippocampus, insensitivity to LTP when they

were adult animals, and decremented visuospatial and

auditory memory (61).

Early postnatal choline supplementation significantly

attenuated the effects of prenatal alcohol on a learning

task, suggesting that early dietary interventions may

also influence brain development (63). The mechanisms

for these developmental effects of choline are not yet clear.

Fetal alcohol syndrome (FAS) is an important concern of

pediatricians, with 1 in every 750 infants born with FAS

each year in the United States. Rats exposed to alcohol during

the perinatal period had poor performance on memory

tasks, which were improved by either prenatal or postnatal

choline supplementation (64,65). Rett syndrome (RTT),

a neurodevelopmental disorder associated with mutations

in the methyl-CpG-binding protein 2 (MeCP2) gene, is the

second leading cause of mental retardation in girls. RTT

girls experience a variety of deficits in cognitive, motor,

and social functions. In mouse models of RTT, enhancing

maternal or postnatal choline supplementation attenuates

motor coordination deficits and improves neuronal

integrity, proliferation, and survival (66,67). Choline supplementation

also ameliorates the symptoms in rodent

models of traumatic brain injury (68), status epilepticus

(69–71), and schizophrenia (72).

Are these findings in animals likely to be true in humans?

We do not know. Human and rat brains share many

elements of brain development but they mature at different

rates. In terms of hippocampal development, the embryonic

days 12–18 in the rat correspond to approximately

the last trimester in humans. Rat brain is comparatively

more mature at birth than is the human brain, but human

hippocampal development may continue for months or

years after birth.

 

Choline and Adult Brain

Acetylcholine is one of the most important neurotransmitters

used by neurons in the memory centers of brain

(hippocampus and septum). Choline accelerates the synthesis

and release of acetylcholine in nerve cells. Choline

used by brain neurons is largely derived from membrane

lecithin, or fromdietary intake of choline and lecithin. Free

choline is transported across the blood–brain barrier at a

rate that is proportional to serum choline level; lecithin

may be carried into neurons as part of an ApoE lipoprotein.

Choline derived from lecithin may be especially important

when extracellular choline is in short supply, as

might be expected to occur in advanced age because of

decreased brain choline uptake (73).

Results from studies using choline or phosphatidylcholine

to treat adults with brain disorders have been

very variable. Single doses of choline or lecithin in adult

humans may enhance memory performance in healthy

individuals, perhaps with greatest effect in individuals

with the poorest memory performance. Studies in students

showed that lecithin or choline treatment improved

memory transiently for hours after administration (74). In

humans with Alzheimer-type dementia, some studies report

enhanced memory performance after treatment with

lecithin (75), whereas other studies did not observe this.

Buchman et al. recently reported that humans on longterm

total parenteral nutrition may have verbal and visual

memory impairment, which may be improved with

choline supplementation (76). If lecithin is effective, it is in

a special subpopulation in the early stages of the disease.

Choline and lecithin have also been effectively used to

treat tardive dyskinesia, presumably working by increasing

cholinergic neurotransmission (77).

 

CONCLUSION

Choline in the diet is important for many reasons. Humans

deprived of it develop liver and muscle dysfunction, and

parenterally nourished patients need a source of choline.

As our understanding of the importance of folate and homocysteine

nutrition increases, there should be increased

interest in how choline interacts with these compounds.

Recent findings about choline in brain development in

animals should stimulate comparable studies in humans.

The availability of food composition data now makes it

possible to examine interactions between choline, folate,

and methionine when considering epidemiological data.

ACKNOWLEDGMENTS

This work was supported by grants from the National

Institutes of Health (AG09525, DK55865). Support for this

work was also provided by grants from the NIH to the

UNC Clinical Nutrition Research Unit (DK56350).

 

REFERENCES

1. Zeisel, SH. Choline: Critical role during fetal development

and dietary requirements in adults. Annu Rev Nutr 2006;

26:229–250.

2. Albright CD, Lui R, Bethea TC, et al. Choline deficiency induces

apoptosis in SV40-immortalized CWSV-1 rat hepatocytes

in culture. FASEB J 1996; 10:510–516.

3. Albright CD, Salganik RI, Kaufmann WK, et al. A p53-

dependent G1 checkpoint function is not required for induction

of apoptosis by acute choline deficiency in immortalized

rat hepatocytes in culture. J Nutr Biochem 1998; 9:476–

481.

4. Institute of Medicine, and National Academy of Sciences

USA. Choline. In: Dietary reference intakes for folate, thiamin,

riboflavin, niacin, vitamin B12, panthothenic acid,

biotin, and choline. Vol. 1. Washington, D.C.: National

Academy Press, 1998:390–422.

5. Kim YI, MillerJW, da Costa KA, et al. Folate deficiency causes

secondary depletion of choline and phosphocholine in liver.

J Nutr 1995; 124:2197–2203.

6. Waite KA, Cabilio NR, Vance DE. Choline deficiencyinduced

liver damage is reversible in Pemt(–/–) mice. J Nutr

2002; 132:68–71.

7. Zeisel SH, Mar MH, Howe JC, et al. Concentrations of

choline-containing compounds and betaine in common

foods. J Nutr 2003; 133:1302–1307.

8. Jeltsch A. Beyond Watson and Crick: DNA methylation and

molecular enzymology of DNA methyltransferases. Chembiochem

2002; 3:382.

9. Bird AP. CpG-rich islands and the function of DNA methylation.

Nature 1986; 321:209–213.

10. Kim JK, Samaranayake M, Pradhan S. Epigenetic mechanisms

in mammals. Cell Mol Life Sci 2009; 66:596–612.

11. Rice JC, Briggs SD, Ueberheide B, et al. Histone methyltransferases

direct different degrees of methylation to define distinct

chromatin domains. Mol Cell 2003; 12:1591–1598.

12. Niculescu MD, Craciunescu CN, Zeisel SH. Gene expression

profiling of choline-deprived neural precursor cells isolated

from mouse brain. Brain Res Mol Brain Res 2005; 134:309–

322.

13. Niculescu MD, Yamamuro Y, Zeisel SH. Choline availability

modulates human neuroblastoma cell proliferation

and alters the methylation of the promoter region of the

cyclin-dependent kinase inhibitor 3 gene. J Neurochem 2004;

89:1252–1259.

14. Davison JM, Mellott TJ, Kovacheva VP, et al. Gestational

choline supply regulates methylation of histone H3, expression

of histone methyltransferases G9 a (Kmt1 c) and

Suv39h1 (Kmt1 a), and DNA methylation of their genes

in rat fetal liver and brain. J Biol Chem 2009; 284:1982–

1989.

15. Cooney CA, Dave AA, Wolff GL. Maternal methyl supplements

in mice affect epigenetic variation and DNA methylation

of offspring. J Nutr 2002; 132:2393S–2400S.

16. Wolff GL, Kodell RL, Moore SR, et al. Maternal epigenetics

and methyl supplements affect agouti gene expression in

Avy/a mice. FASEB J 1998; 12:949–957.

17. Waterland RA, Dolinoy DC, Lin JR, et al. Maternal methyl

supplements increase offspring DNA methylation at Axin

fused. Genesis 2006; 44:401–406.

18. Busby MG, Fischer L, Da Costa KA, et al. Choline- and

betaine-defined diets for use in clinical research and for the

management of trimethylaminuria. J Am Diet Assoc 2004;

104:1836–1845.

19. da Costa KA, Badea M, Fischer LM, et al. Elevated serum

creatine phosphokinase in choline-deficient humans: Mechanistic

studies in C2C12 mouse myoblasts. Am J Clin Nutr

2004; 80:163–170.

20. da Costa KA, Gaffney CE, Fischer LM, et al. Choline deficiency

in mice and humans is associated with increased

plasma homocysteine concentration after a methionine load.

Am J Clin Nutr 2005; 81:440–444.

21. Fischer LM, da Costa K, Kwock L, et al. Sex and menopausal

status influence human dietary requirements for the nutrient

choline. Am J Clin Nutr 2007; 85:1275–1285.

22. Yao ZM, Vance DE. The active synthesis of phosphatidylcholine

is required for very low density lipoprotein secretion

from rat hepatocytes. J Biol Chem 1988; 263:2998–

3004.

23. Zeisel SH. Choline: An essential nutrient for humans. Nutrition

2000; 16:669–671.

24. da Costa KA, Niculescu MD, Craciunescu CN, et al. Choline

deficiency increases lymphocyte apoptosis and DNA damage

in humans. Am J Clin Nutr 2006; 84:88–94.

25. Chiuve SE, Giovannucci EL, Hankinson SE, et al. The association

between betaine and choline intakes and the plasma

concentrations of homocysteine in women. Am J Clin Nutr

2007; 86:1073–1081.

26. Resseguie M, Song J, Niculescu MD, et al. Phosphatidylethanolamine

N-methyltransferase (PEMT) gene expression

is induced by estrogen in human and mouse primary

hepatocytes. FASEB J 2007; 21:2622–2632.

27. Adeyemo O, Jeyakumar H. Plasma progesterone, estradiol-

17 beta and testosterone in maternal and cord blood, and

maternal human chorionic gonadotropin at parturition. Afr

J Med Med Sci 1993; 22:55–60.

28. Sarda IR, Gorwill RH. Hormonal studies in pregnancy. I.

Total unconjugated estrogens in maternal peripheral vein,

cord vein, and cord artery serum at delivery. Am J Obstet

Gynecol 1976; 124:234–238.

29. Zeisel SH, Mar MH, Zhou ZW, et al. Pregnancy and lactation

are associated with diminished concentrations of

choline and its metabolites in rat liver. J Nutr 1995; 125:

3049–3054.

30. McMahon KE, Farrell PM. Measurement of free choline concentrations

in maternal and neonatal blood by micropyrolysis

gas chromatography. Clin Chim Acta 1985; 149:

1–12.

31. Ozarda Ilcol Y, Uncu G, Ulus IH. Free and phospholipidbound

choline concentrations in serum during pregnancy,

after delivery and in newborns. Arch Physiol Biochem 2002;

110:393–399.

32. Zeisel SH,Wurtman RJ. Developmental changes in rat blood

choline concentration. Biochem J 1981; 198:565–570.

33. JensenHH,Batres-Marquez SP, Carriquiry A, et al. Choline in

the diets of the US population: NHANES, 2003–2004. FASEB

J 2007; 21:lb219.

34. Shaw GM, Carmichael SL, Laurent C, et al. Maternal nutrient

intakes and risk of orofacial clefts. Epidemiology 2006;

17:285–291.

142 Zeisel

35. Shaw GM, Carmichael SL, Yang W, et al. Periconceptional

dietary intake of choline and betaine and neural tube defects

in offspring. Am J Epidemiol 2004; 160:102–109.

36. da Costa KA, Kozyreva OG, Song J, et al. Common genetic

polymorphisms affect the human requirement for the nutrient

choline. FASEB J 2006; 20:1336–1344.

37. Kohlmeier M, da Costa KA, Fischer LM, et al. Genetic variation

of folate-mediated one-carbon transfer pathway predicts

susceptibility to choline deficiency in humans. Proc Natl

Acad Sci U S A 2005; 102:16025–16030.

38. USDA Database for the Choline Context of Common Foods

2004. http://www.nal.usda.gov/fnic/foodcomp/Data/

Choline/Choline.html. Accessed April 5, 2010.

39. Fischer LM, Scearce JA, Mar MH, et al. Ad libitum choline

intake in healthy individuals meets or exceeds the proposed

adequate intake level. J Nutr 2005; 135:826–829.

40. Zeisel SH, Mar MH, Howe JC, et al. Erratum: Concentrations

of choline-containing compounds and betaine in common

foods. J Nutr 2003; 133:1302–1307.

41. Holmes-McNary M, Cheng WL, Mar MH, et al. Choline and

choline esters in human and rat milk and infant formulas.

Am J Clin Nutr 1996; 64:572–576.

42. Savendahl L, Mar MH, Underwood L, et al. Prolonged fasting

results in diminished plasma choline concentration but

does not cause liver dysfunction. Am J Clin Nutr 1997;

66:622–625.

43. Ilcol YO, Ozbek R, Hamurtekin E, et al. Choline status in

newborns, infants, children, breast-feeding women, breastfed

infants and human breast milk. J Nutr Biochem 2005;

16:489–499.

44. Zeisel SH, da Costa KA, Franklin PD, et al. Choline,

an essential nutrient for humans. FASEB J 1991; 5:2093–

2098.

45. Zeisel SH. Dietary choline: Biochemistry, physiology, and

pharmacology. Ann Rev Nutr 1981; 1:95–121.

46. Cho E, Zeisel SH, Jacques P, et al. Dietary choline and

betaine assessed by food-frequency questionnaire in relation

to plasma total homocysteine concentration in the

Framingham Offspring Study. Am J Clin Nutr 2006; 83:

905–911.

47. DalmeijerGW, Olthof MR, Verhoef P, et al. Prospective study

on dietary intakes of folate, betaine, and choline and cardiovascular

disease risk in women. Eur J Clin Nutr 2008;

62:386–394.

48. Bidulescu A, Chambless LE, Siega-Riz AM, et al. Usual

choline and betaine dietary intake and incident coronary

heart disease: The Atherosclerosis Risk in Communities

(ARIC) study. BMC Cardiovasc Disord 2007; 7:20.

49. Bidulescu A, Chambless LE, Siega-Riz AM, et al. Repeatability

and measurement error in the assessment of choline and

betaine dietary intake: The Atherosclerosis Risk in Communities

(ARIC) study. Nutr J 2009; 8:14.

50. Olthof MR, van Vliet T, Verhoef P, et al. Effect of

homocysteine-lowering nutrients on blood lipids: Results

from four randomised, placebo-controlled studies in healthy

humans. PLoS Med 2005; 2:e135.

51. Schwab U, Torronen A, Toppinen L, et al. Betaine supplementation

decreases plasma homocysteine concentrations

but does not affect body weight, body composition, or resting

energy expenditure in human subjects. Am J Clin Nutr

2002; 76:961–967.

52. McGregor DO, Dellow WJ, Robson RA, et al. Betaine supplementation

decreases post-methionine hyperhomocysteinemia

in chronic renal failure. Kidney Int 2002; 61:1040–

1046.

53. Zeisel SH. Betaine supplementation and blood lipids: Fact or

artifact? Nutr Rev 2006; 64:77–79.

54. Zeisel SH, Albright CD, Shin OK, et al. Choline deficiency selects

for resistance to p53-independent apoptosis and causes

tumorigenic transformation of rat hepatocytes. Carcinogenesis

1997; 18:731–738.

55. Zou W, Li ZY, Li YL, et al. Overexpression of PEMT2 downregulates

the PI3 K/Akt signaling pathway in rat hepatoma

cells. Biochim Biophys Acta 2002; 1581:49–56.

56. Xu X, Gammon MD, Zeisel SH, et al. Choline metabolism

and risk of breast cancer in a population-based study. FASEB

J 2008; 22:2045–2052.

57. Xu X, Gammon MD, Zeisel SH, et al. High intakes of choline

and betaine reduce breast cancer mortality in a populationbased

study. FASEB J 2009; 23(11):4022–4028.

58. Cho E, Holmes M, Hankinson SE, et al. Nutrients involved

in one-carbon metabolism and risk of breast cancer among

premenopausal women. Cancer Epidemiol Biomarkers Prev

2007; 16:2787–2790.

59. Cho E, Willett WC, Colditz GA, et al. Dietary choline and

betaine and the risk of distal colorectal adenoma in women.

J Natl Cancer Inst 2007; 99:1224–1231.

60. Albright CD, Mar MH, Friedrich CB, et al. Maternal

choline availability alters the localization of p15Ink4B and

p27Kip1 cyclin-dependent kinase inhibitors in the developing

fetal rat brain hippocampus. Dev Neurosci 2001; 23:

100–106.

61. Meck WH, Williams CL. Choline supplementation during

prenatal development reduces proactive interference

in spatial memory. Brain Res Dev Brain Res 1999; 118:

51–59.

62. Meck WH, Williams CL. Metabolic imprinting of choline

by its availability during gestation: Implications for memory

and attentional processing across the lifespan. Neurosci

Biobehav Rev 2003; 27:385–399.

63. Thomas JD, La Fiette MH, Quinn VR, et al. Neonatal choline

supplementation ameliorates the effects of prenatal alcohol

exposure on a discrimination learning task in rats. Neurotoxicol

Teratol 2000; 22:703–711.

64. Thomas JD, Garrison M, O’Neill TM. Perinatal choline supplementation

attenuates behavioral alterations associated

with neonatal alcohol exposure in rats. Neurotoxicol Teratol

2004; 26:35–45.

65. Thomas JD, Abou EJ, Dominguez HD. Prenatal choline supplementation

mitigates the adverse effects of prenatal alcohol

exposure on development in rats. Neurotoxicol Teratol 2009;

31(5):303–311.

66. Nag N, Mellott TJ, Berger-Sweeney JE. Effects of postnatal

dietary choline supplementation on motor regional brain

volume and growth factor expression in a mouse model of

Rett syndrome. Brain Res 2008; 1237:101–109.

67. Ward BC, Kolodny NH, Nag N, et al. Neurochemical changes

in a mouse model of Rett syndrome: Changes over time and

in response to perinatal choline nutritional supplementation.

J Neurochem 2009; 108:361–371.

68. Guseva MV, Hopkins DM, Scheff SW, et al. Dietary choline

supplementation improves behavioral, histological, and

neurochemical outcomes in a rat model of traumatic brain

injury. J Neurotrauma 2008; 25:975–983.

69. Wong-Goodrich SJ, Mellott TJ, Glenn MJ, et al. Prenatal

choline supplementation attenuates neuropathological response

to status epilepticus in the adult rat hippocampus.

Neurobiol Dis 2008; 30:255–269.

70. Holmes GL, Yang Y, Liu Z, et al. Seizure-induced memory

impairment is reduced by choline supplementation before

or after status epilepticus. Epilepsy Res 2002; 48:3–13.

71. Yang Y, Liu Z, Cermak JM, et al. Protective effects of prenatal

choline supplementation on seizure-induced memory

impairment. J Neurosci 2000; 20:RC109.

72. Stevens KE, Adams CE, Yonchek J, et al. Permanent improvement

in deficient sensory inhibition in DBA/2 mice with increased

perinatal choline. Psychopharmacology (Berl) 2008;

198:413–420.

Choline 143

73. Cohen BM, Renshaw PF, Stoll AL, et al. Decreased brain

choline uptake in older adults. An in vivo proton magnetic

resonance spectroscopy study. JAMA 1995; 274:902–

907.

74. Sitaram N,Weingartner H, Caine ED, et al. Choline: Selective

enhancement of serial learning and encoding of low imagery

words in man. Life Sci 1978; 22:1555–1560.

75. Little A, Levy R, Chuaqui-Kidd P, et al. A double-blind,

placebo controlled trial of high-dose lecithin in Alzheimer’s

disease. J Neurol Neurosurg Psychiatry 1985; 48:736–

742.

76. Buchman AL, Sohel M, Brown M, et al. Verbal and visual

memory improve after choline supplementation in longterm

total parenteral nutrition:Apilot study. JPEN J Parenter

Enteral Nutr 2001; 25:30–35.

77. Growdon JH, Gelenberg AJ. Choline and lecithin administration

to patients with tardive dyskinesia. Trans Am Neurol

Assoc 1978; 103:95–99.

Biochemistry

BiochemistrySuccess Chemistry Staff

Biochemistry describes and explores the molecular basis of living nature. Thematic and methodological overlaps exist with other disciplines, such as physiological chemistry, food chemistry, biotechnology, pharmacology, natural products chemistry or toxicology. For example, the collective field of molecular life sciences has established itself as the collective term for Molecular Life Sciences.

Biochemistry has made rapid progress in recent decades. More and more causes of disease and their molecular basis are understood. Methods and insights in biochemistry and molecular biology determine new developments in medicine, biotechnology, plant breeding & nutrition research. The structural understanding of biomolecules at the atomic level plays an increasingly important role.

Biochemists ask how living things or cells build or break down carbohydrates, fats, amino acids or hereditary molecules, and what amounts of energy are gained or consumed. They explore the structure and chemical composition of nucleic acids and the process of translating genetic information into physiological functions in a body cell.

They study how cell signaling works, which regulates the many metabolic pathways involved in breaking down and degrading, or how a fertilized egg can be used to create a complex organism with hundreds of different cell types. How does cancer develop? What causes death? How does our brain work? These are exciting questions whose answers biochemistry seeks on the molecular level.

Chemical knowledge and experimental competence play a key role here. Bioanalytics are refining modern separation and analysis methods, and technologies are increasingly penetrating into the single-molecule analysis. Tailored proteins are playing an increasingly important role in drug development alongside traditional substance libraries. Based on findings such as enzyme research, biochemists have the task of designing and synthesizing new biological agents with tailor-made properties.

 

Training in biochemistry

Is possible in several ways. In-Depth knowledge acquisition in biochemistry in the context of chemistry, biology or biotechnology studies can also be an alternative.

When taking up a bachelor's degree in chemistry with profiling in biochemistry, it is advisable to take additional biological basic lectures and internships as well as an introductory lecture in biochemistry. To specialize, you enroll in a bachelor's degree for a master's degree in biochemistry, attend biochemistry lectures and complete biochemical internships.

It is advisable, after detailed consultation, to additionally attend lectures and internships, especially in molecular biology, biophysical chemistry, and biophysics, genetics, cell biology, microbiology, biomedicine or related subjects. Solid knowledge in bioinformatics is also increasingly important. The required and offered study content and its scope vary from university to university.

At a number of universities, training as a molecular biologist or biochemist in biology studies is possible, with specialization in the master's program. Here conversely, in addition to lectures and courses in molecular biology and biochemistry, in particular knowledge in the branches of chemistry and biophysics should be made up and deepened.

An increasing number of universities offer their own biochemistry degree program. The program offers a cross-section between a chemical, biological, and some medical education and concludes - via the Bachelor - with the Master, mostly followed by a doctorate. An overview of the universities with the program Biochemistry is available in our university finder.

Some universities also offer additional special courses, in particular in the field of molecular biotechnology, molecular medicine, and medicinal chemistry. Despite medical references, these programs are usually affiliated with natural science faculties and lead to a master's degree, which is usually followed by a scientific doctorate.

In general, life sciences, with their strong interdisciplinary implications, are not always clearly defined in the curriculum. Anyone who has chosen this area as a career choice can also successfully enter biochemical research through training in organic chemistry, pharmacology, toxicology, pharmacy, physics or food chemistry. A suitable mix of appropriately trained professionals is increasingly being sought in the most strongly interdisciplinary research teams in science and industry. 

 

Biochemistry as a career

The career opportunities in the field of biochemistry are diverse. If you want to stay in basic research, you can find a job at universities and research institutes. Especially in the border area to medicine, there is an increasing need for research. Biochemists are increasingly in demand in the clinical area.

In the industry, there are companies in the pharmaceutical and biotech industries that have a need for biochemistry graduates for applications in "red" biotechnology. "White" biotechnology is also on the upswing, with which chemical companies produce plastics and everyday chemicals with environmentally friendly processes or from renewable raw materials, creating many new jobs.

As biocatalytic processes are increasingly used in industrial applications, protein biochemists are increasingly needed who have learned how to deal with enzymes, antibodies or other proteins. There are also interesting opportunities in the areas of crop protection, nutrition and in consumer-related sectors such as the food and cosmetics industry.

Interesting perspectives arise in addition to the production of active ingredients in product development and marketing. The area of public relations and administration in public authorities, associations and research institutes is also playing an increasingly important role. In addition, leadership positions in the chemical and pharmaceutical industries, as well as in management consultancy and finance companies are being filled by life scientists.