Fructose and Galactose Metabolism Almoeiz Yousif Sunday June
Fructose and Galactose Metabolism Almoeiz Yousif Sunday, June 6, 2021 1
Fructose Metabolism • Fructose can be metabolized by the liver, muscle and sperm cells Fructose Metabolism Muscle Sunday, June 6, 2021 Liver 2
Fructose Metabolism in Muscle Sunday, June 6, 2021 3
Fructose Metabolism in liver Sunday, June 6, 2021 4
Fructose Metabolism in Sperm Cells Fructose is the major energy source for sperm cells and is formed from glucose in the seminal vesicle. Sunday, June 6, 2021 5
Fructose and Sorbitol • Fructose can be synthesized from glucose via reduction it to sorbitol, and then oxidation to fructose. • NADPH and NAD+ are used as coenzymes Sunday, June 6, 2021 6
The sperm gets its fructose through this pathway. Sunday, June 6, 2021 7
Diseases associated to fructose metabolism 1. Fructosuria 2. Hereditary fructose intolorence Sunday, June 6, 2021 8
1. Fructosuria • Rare, not dangerous, genetic disorder caused by a deficiency in fructokinase • Why is this disease not dangerous? • Answer: no toxic fructose intermediates accumulate, most is excreted harmlessly in the urine Sunday, June 6, 2021 9
2. Hereditary Fructose Intolerance (Deficiency in aldolase B in the livre) Sunday, June 6, 2021 10
Hereditary Fructose Intolerance Genetic Disease Too much fructose-1 -phosphate accumulates in liver – Decreases PO 4 available in liver cells – So reduces ATP synthesis Sunday, June 6, 2021 11
Clinical Manifestations of HFI • Fructose-1 -Phosphate accumulates in hepatocytes = progressive liver disease - Seen primarily in children, symptoms include diarrhea, vomiting, failure to thrive and effects of hypoglycemia. - Untreated, can result in hepatic and/or renal failure Sunday, June 6, 2021 12
Treatment of HFI: Diet Control – Eliminate fructose and sucrose from the diet – Early recognition and treatment of the disease is important to avoid damage to the liver and kidneys Sunday, June 6, 2021 13
Cataract in Diabetic Patients • In the eye, sorbitol production can be a problem in the formation of cataracts, especially in patients with diabetes mellitus. • The increased fructose and sorbitol levels create a high osmotic pressure in the lens. Sunday, June 6, 2021 14
• This may be a cause development of the lens cataracts and the neural dysfunction that occur. Sunday, June 6, 2021 15
SORBITOL METABOLISM IN DIABETES The formation of sorbitol from glucose proceeds rapidly in the lens of the eye and in the Schwann cells of the nervous system. Sunday, June 6, 2021 16
Sorbitol cannot pass through the cell membrane, and in people with diabetes, sorbitol levels build up in these cells because the rate of oxidation of sorbitol to fructose is decreased. Sunday, June 6, 2021 17
METABOLISM OF GALACTOSE Sunday, June 6, 2021 18
Galactosemia • One of the most common genetic diseases, and frequently screened in newborns • Result from defects 1. in galactokinase (a milder, rarer form) 2. or galactose 1 -phosphate uridyltransferase Sunday, June 6, 2021 19
1. Galactokinase Deficiency • a milder, rarer form • Lead Cataract forms Sunday, June 6, 2021 20
Galactokinase deficiency • leads to an accumulation of galactose in blood and tissues. • In the lens of the eye, galactose is reduced by aldose reductase to galactitol, which cannot escape from the cells. • This causes an osmotic imbalance, which leads to formation of cataracts. Sunday, June 6, 2021 21
2. Classic Galactosemia • Galactose-l-phosphate uridyl transferase deficiency • Leads to accumulation of galactose-1 -P in tissues, blood and urine • Depletes liver of PO 4, • and can lead to liver failure and mental retardation. • Also Cataract forms Sunday, June 6, 2021 22
Metabolism of Galactose Sunday, June 6, 2021 23
Biosynthesis of Lactose 1. In humans, this occurs only in the mammary glands. 2. Lactose is formed from UDP-galactose and glucose in a reaction catalyzed by galactosyl transferase. Sunday, June 6, 2021 24
This is the end of our course Good luck Almoeiz , , ,
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