Galactose

Galactose (Gal)

• GalactoseGalactose• Type of sugar foundType of sugar found

– In dairy productsIn dairy products– Sugar beetsSugar beets– MucilagesMucilages

• It can be found in the It can be found in the bodybody– GlycolipidsGlycolipids– GlycoproteinsGlycoproteins

• sweetenersweetener

• Disaccharide lactoseDisaccharide lactose– Galactose Galactose – GlucoseGlucose

• Hydrolysis of lactose to Hydrolysis of lactose to glucose and galactose glucose and galactose – LactaseLactase

• In the human body, In the human body, glucose is changed into glucose is changed into galactose in order to galactose in order to enable the mammary enable the mammary glands to secrete glands to secrete lactose.lactose.

Galactose (Gal)Galactose (Gal)

• Blindness is due to Blindness is due to the conversion of the conversion of circulating circulating galactose to the galactose to the sugar alcohol sugar alcohol galacitol, by an galacitol, by an NADPH-dependent NADPH-dependent galactose reductasegalactose reductase that is present in that is present in neural tissue and in neural tissue and in the lens of the eye.the lens of the eye.

Galactose (Gal)Galactose (Gal)

Absorption of glucose, galAbsorption of glucose, galaactose – Nactose – Na++ cotransportcotransport

LumenCapillary

SGLTGlu, Gal

Na+

ADP + Pi

ATP

K+,Na+-ATP-ase

GluT2

Fructose

GluT5

Gyors cukor pótlás Gyors cukor pótlás Só – víz pótlásSó – víz pótlás

Fructose

Glu, Gal

Na+ Na+

Intestinal epithel cells

SGLT – sodium-glucose transporter

Lactose intolerance

• the inability to metabolize lactose, a sugar found in milk and other dairy products

• 75% of adults worldwide show some decrease in lactase activity during adulthood

• The frequency of decreased lactase activity ranges from as little as 5% in northern Europe, up to 71% for Southern Europe, to more than 90% in some African and Asian countries

Lactose intolerance

• Disaccharides cannot be absorbed through the wall of the small intestine

• lactose present in ingested dairy products remains uncleaved and passes intact into the colon.

• enteric bacteria – in vivo fermentation produces copious

amounts of gas (a mixture of hydrogen, carbon dioxide, and methane).

Primary lactose intolerance.

• Environmentally induced when weaning a child in non-dairy consuming societies

• This is found in many Asian and African cultures, where industrialized and commercial dairy products are uncommon.

Secondary lactose intolerance.

• resulting from certain gastrointestinal diseases• including exposure to intestinal parasites such

as giardia• such cases the production of lactase may be

permanently disrupted• A very common cause of temporary lactose

intolerance is gastroenteritis, particularly when the gastroenteritis is caused by rotavirus.

• Another form of temporary lactose intolerance is lactose overload in infants.

Congenital lactase deficiency.

• A genetic disorder which prevents enzymatic production of lactase.

• Present at birth, and diagnosed in early infancy.

Lactase activity

• The normal mammalian condition is for the young of a species to experience reduced lactase production at the end of the weaning period – (a species-specific length of time).

• In non dairy consuming societies, lactase production usually drops about 90% during the first four years of life, although the exact drop over time varies widely.

Lactase activity

• a mutation on chromosome 2 which eliminates the shutdown in lactase production,

• making it possible for members of these populations to continue consumption of fresh milk and other dairy products throughout their lives without difficulty.

Lactase activity

• This appears to be an evolutionarily recent adaptation to dairy consumption, and has occurred independently in both northern Europe and east Africa in populations with a historically pastoral lifestyle.

• Lactase persistence, allowing lactose digestion to continue into adulthood, is a dominant allele, making lactose intolerance a recessive genetic trait.

Glucose-galactose malabsorption

• generally becomes apparent in the first few weeks of a baby's life.

• Affected infants experience severe diarrhea resulting in– life-threatening dehydration, – increased acidity of the blood and tissues

(acidosis), – weight loss when fed breast milk or regular

infant formulas.

Glucose-galactose malabsorption

• However, they are able to digest fructose-based formulas that do not contain glucose or galactose.

• Some affected children are better able to tolerate glucose and galactose as they get older.

Glucose-galactose malabsorption

• is a rare disorder; • only a few hundred cases have been identified

worldwide. • 10 percent of the population may have a

somewhat reduced capacity for glucose absorption without associated health problems.

• This condition may be a milder variation of glucose-galactose malabsorption.

• This condition is inherited in an autosomal recessive pattern

galactokinase (GALK)

galactose-1-phosphate uridyltransferase (GALT)

uridine diphosphate galactose 4'-epimerase (GALE)

Clinical Significances of Galactose Metabolism

• Three inherited disorders of Three inherited disorders of galactose metabolism have galactose metabolism have been delineated. been delineated. – loss of the enzyme loss of the enzyme galactose-1-galactose-1-

phosphate uridyl transferasephosphate uridyl transferase– loss of the enzyme loss of the enzyme

galactokinasegalactokinase• Vomiting and diarrhea occur Vomiting and diarrhea occur

following ingestion of milk, following ingestion of milk, hence individuals are termed hence individuals are termed lactose intolerant. lactose intolerant.

• impaired liver function (severe impaired liver function (severe cirrhosis), cirrhosis),

• elevated blood galactose, elevated blood galactose, • hypergalactosemia, hypergalactosemia, • hyperchloremic metabolic hyperchloremic metabolic

acidosis, acidosis, • urinary galactitol excretion urinary galactitol excretion • hyperaminoaciduria. hyperaminoaciduria.

Clinical Significances of Galactose Metabolism

• Unless controlled by Unless controlled by exclusion of exclusion of galactose from the galactose from the diet, these diet, these galactosemias can galactosemias can go on to produce go on to produce blindness and fatal blindness and fatal liver damage.liver damage.

Clinical Significances of Galactose Metabolism

• The third disorder of The third disorder of galactose metabolism result galactose metabolism result from a deficiency of from a deficiency of UDP-UDP-galactose-4-epimerasegalactose-4-epimerase. .

• Two different forms of this Two different forms of this deficiency have been found. deficiency have been found. – One is benign affecting only One is benign affecting only

red and white blood cells. red and white blood cells. – The other affects multiple The other affects multiple

tissues and manifests tissues and manifests symptoms similar to the symptoms similar to the transferase deficiency. transferase deficiency.

• Treatment involves Treatment involves restriction of dietary restriction of dietary galactose. galactose.

Lactose Synthesis