Basic Biochemistry:Purines in Food

Dr Liz Carrey

UCL Institute of Child Health

Gout• Primary gout: excess

uric acid in circulation, from purines taken in the diet

Nucleic acids

DNA: genetic information

RNA: many roles

A mammalian cell

Mitochondria

Purines in the diet 1

• DNA and RNA are highest in cells that are multiplying, tissues that are regenerating

• Mitochondria are most numerous in energy-producing cells (e.g. muscle)

• Mitochondria contain ATP and DNA

NN

NN

NH2

O O (phosphate)3

OH OH

ATP

• energy

• purinergic signalling

• RNA, DNA

• cofactors (NAD etc)

• cAMP and AMP

• phosphate donor

O O phosphate

OH OH

NN

NN

OIMP

umami

Purines in the diet 2

• DNA, RNA, nucleotides and bases are digested in the gut

• No purines are absorbed from the diet

• Uric acid is excreted directly from the gut (1/3) or via kidneys, in the urine (2/3)

Purines

uric acid

allantoin

N N

NH

N

NH2

N

NN

O

H

H

H

O

O

H N

NH

O

N

NH

H

OHN

O

H

X

uric acid

N

NN

O

H

H

H

O

O

H N

xanthine N N

NHNO

O

Less soluble at acid pH

Forms kidney stones if not excreted

Excess may be deposited in joints and under the skin

uric acid

allantoin

N

NN

O

H

H

H

O

O

H N

NH

O

N

NH

H

OHN

O

H

xanthine N N

NHNO

O

ALLOPURINOL

URICASE

High-purine foods

• Red meat (mitochondria, ATP)

• Organ meats (regenerating tissue: DNA)

• Sea food (energy, growth)

• Beer (yeast, rapidly multiplying: DNA)

• Asparagus, cauliflower (multiplying: DNA)

• Wheat germ, cereals, seeds (DNA)

Purine-rich meat, seafood and beer increase the risk of gout in men

Choi et al, 2004: NEJM & Lancet

• Prospective 12-yr study of men aged 40 – 75, health professionals in USA

• 5.6% already had gout symptoms

• Of remaining 47,150 gout developed in 730, incidence of 1:1000 per year

The risk of gout in men

• Relative risk for meat-eaters 1.41; for high seafood consumption 1.51

• Beer: RR 1.49 per 12oz/day

• No relationship to high-purine vegetables?

• Highest dairy intake, RR 0.56

Low-purine foods

• White bread

• Dairy products (milk, cheese, yogurt)

• Sugar and confectionery

• Most fruit and salad vegetables

• Fruit juices

• Water

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Giles Coren’s dinnerat Bond’s, 5 Threadneedle Street

Salad of smoked eel

Rooster’s testicles on a bed of sweetbreads and kidney

Sea bass with frog leg aïoli and 2 fritters of bone marrowVegetables?

Dessert?

£100 for two without wine

Purines in the diet 3• Lower proportion of high-purine foods

• More dairy products (low fat!)

• Less fruit juice and fructose

• Smaller portion sizes

• More water – to dilute the urine