Clinical Chemistry Chapter 3 Carbohydrates Dr Atef Masad PhD Biomedicine UK

1. Clinical Chemistry Chapter 3 Carbohydrates Dr Atef MasadPhD Biomedicine UK Dr Atef Masad Carbohydrates

2. Carbohydrates • Living systems depend on the oxidation of complex organic compounds to obtain energy. • Three types of organic compoundsare used as a source of energy, Carbohydrates, Amino Acids, and Lipids • Carbohydrates are the primary source of energy for brain, erythrocytes, and retinal cells. • Carbohydrates are stored in liver and muscle as glycogen. • Polysaccharides are formed by the linkage of many monosaccharide units. • On hydrolysis, Polysaccharides yield more than ten monosaccharides. • The most common Polysaccharides are starch and glycogen.

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4. Glucose Metabolism • Glucose is the primary source of energy for humans. • The nervous system, including the brain, totally dependant on glucose from the surrounding extracellular fluid "ECF" for energy. • Nervous tissue cannot concentrate carbohydrates nor store it. • Therefore, it is critical to maintain a steady supply of glucose to the tissues. • When the concentration of glucose falls below a certain level, the nervous tissues lose their primary energy source and are incapable of maintaining normal function.

5. Major energy pathways involved either directly or indirectly with glucose metabolism 1- Glycolysis • Breakdown of glucose for energy production 2- Glycogenesis • Excess glucose is converted and stored as glycogen • High concentrations of glycogen in liver and skeletal muscle 3- Glycogenolysis • Breakdown of glycogen into glucose • Glycogenolysis occurs when plasma glucose is decreased Dr Atef Masad Carbohydrates

6. Gluconeogenesis • Conversion of non-carbohydrate carbon substrates to glucose, takes place, mainly in the liver • Lipogenesis • Conversion of carbohydrates into fatty acids • Fat is another energy storage form, but not as quickly accessible as glycogen • Lipolysis • Decomposition of fat Dr Atef Masad Carbohydrates

7. Destiny of Glucose • Salivary and Pancreatic amylase digests dietary starch and glycogen into dextrins and disaccharides. • Maltase, sucrase and lactase hydrolyze them to monosaccarides. • Maltase is an enzyme released by intestinal mucosa that hydrolze maltose to two glucose units • Sucrase hydrolyze sucrose to glucose & fructose • Lactase: hydrolyze lactose to glucose & galatose. • Monosaccarides are absorbed by the gut and transported to the liver by the hepatic portal venous blood supply. • All sugars must be converted into glucose which enters the cell. Dr Atef Masad Carbohydrates

8. The ultimate goal of the cell is to convert glucose into carbon dioxide and water. • Glucose is converted into G-6-P using ATP and hexokinase. • G-6-P can enter glycolysis or HMS (hexose monophosphate shunt) pathways or can be converted into glycogen. Glycolysis and HMS generate energy. Dr Atef Masad Carbohydrates

9. Scheme of glycogen synthesis and degradation Dr Atef Masad Carbohydrates

10. Regulation of Carbohydrate Metabolism • The liver, Pancreas, and other endocrine glands are all involved in the controlling of blood glucose concentrations. • During a brief fast, glucose is supplied to the ECF from the liver through glycogenolysis. • When the fasting period is longer than 1 day, glucose is synthesized from other sources through gluconeogenesis. Dr Atef Masad Carbohydrates

11. Glycogenolysis in skeletal muscle and liver. Glycogen stores serve different functions in muscle cells and liver. In the muscle and most other cell types, glycogen stores serve as a fuel source for the generation of ATP. In the liver, glycogen stores serve as asource of blood glucose. Dr Atef Masad Carbohydrates

12. Sources of blood glucose in the fed, fasting, and starved states. Dr Atef Masad Carbohydrates

13. Insulin and glucagon control blood glucose. • Insulin is released when glucose levels are high and is not released when glucose levels are decreased. • It decreases blood glucose by increasing the transport entry of glucose in muscle and adipose tissue by way of nonspecific receptors. • Insulin is referred to as a hypoglycemic agent. • Glucagon is the primary hormone responsible for increasing glucose levels, it is released during stress and fasting from panc α-cells. • It is a hyperglycemic agent Dr Atef Masad Carbohydrates

14. Hyperglycemia • Hyperglycemia or increased plasma glucose, is caused by an imbalance of hormones. Dr Atef Masad Carbohydrates

15. Epinephrine increases plasma glucose • Stimulates conversion of hepatic glycogen to gluocose(glycogenolysis ) and promoting lipolysis. • Glucocorticoids e.g cortisol, are released from adrenal cortex increases blood glucose • Glucocorticoidsstimulates formation of glucose from non-carbohydrate sources (gluconeogenesis). • Growth hormone "GH" and ACTH promote increased plasma glucose. • GH increases plasma glucose by decreasing the entry of glucose into the cells and by decreasing glycolysis. Dr Atef Masad Carbohydrates

16. Decreased levels of cortisol stimulate the anterior pituitary to release ACTH • ACTH then stimulates the adrenal cortex to release cortisol and increases plasma glucose levels by converting liver glycogen to glucose, and by promoting gluconeogenesis. • Thyroxine increases blood glucose by increasing glycogenolysis, gluconeogenesis and intestinal absorption of glucose. • Somatostatin which is produced by D cells of the islets of langerhans of the pancreas increases plasma glucose levels by the inhibition of insulin. Dr Atef Masad Carbohydrates

17. Islets of Langerhans and insulin secretion • The islets of Langerhans secrete hormones directly into the blood flow by (at least) five different types of cells:- • α-cells, producing glucagon (15-20% of total islet cells) • β-cells, producing insulin and amylin (65-80% of total islet cells) • δ-cells, producing somatostatin (3-10% of total islet cells) • PP cells, producing pancreatic polypeptide (3-5% of total islet cells) • ε-cells, producing *Ghrelin (<1% of total islet cells) Dr Atef Masad Carbohydrates

18. Insulin acts through chemical responses to receptors on the cells of target tissues. • In the muscle, insulin stimulates glucose uptake into cells and enhances glycogenesis. • In adipose tissue, insulin stimulates glucose uptake into cells and enhances lipogenesis. • In the liver, insulin has a negative effect, inhibiting gluconeogenesis and glycogenolysis. Dr Atef Masad Carbohydrates

19. Types of diabetes mellitus. Dr Atef Masad Carbohydrates

20. Type 1 diabetes • Is characterized by lack of insulin production and secretion by the beta cells of the pancreas. • One cause of the hyperglycemia of type 1 diabetes mellitus is an autoimmune destruction of the beta cells of the pancreas. • The cell mediated response causes infiltration of the pancreas and reduction in the volume of beta cells. Dr Atef Masad Carbohydrates

21. Autoantibodies are present in the circulation of many individuals with type 1 diabetes. • There appears to be a genetic susceptibility to development of autoantibodies, with certain histocompatibility antigens predominant in the type 1 diabetes population. • The development of disease is complex; triggering factors, such as rubella, mumps, and other viral infection, and chemical contact may be necessary for progression of disease. Dr Atef Masad Carbohydrates

22. Type 2 diabetes • The most common form of diabetes is type 2 diabetes. About 90 to 95 % of people with diabetes have type 2. • This form of diabetes is associated with older age, obesity, family history of diabetes, previous history of gestational diabetes, physical inactivity, and ethnicity. • About 80 % of people with type 2 diabetes are overweight. Type 2 diabetes is increasingly being diagnosed in children and adolescents. Dr Atef Masad Carbohydrates

23. When type T2DM is diagnosed, the pancreas is usually producing enough insulin, but for unknown reasons, the body cannot use the insulin effectively, a condition called insulin resistance. • After several years, insulin production decreases. The result is the same as for type 1 diabetes - glucose builds up in the blood and the body cannot make efficient use of its main source of fuel. • T2DM is a major risk factor for cardiovascular disease, from which 60–80% of the patients die at a relatively young age Dr Atef Masad Carbohydrates

24. Its prevalence and incidence continue to rise in most, if not all countries. • The global figure of people with diabetes is set to rise from about 118 million in 1995 to 220 million in 2010 and 300 million in 2025. • Between 1995 and 2010, the global prevalence of diabetes will rise by 55% from 2.1 to 3.2% Dr Atef Masad Carbohydrates

25. Type 2 diabetes • Is characterized by decline in insulin action due to the resistance of tissue cells to the action of insulin. • The problem is increased by the inability of the beta cells of the pancreas to produce enough insulin to counteract the resistance. • Type 2 D. M. constitutes the majority of the diabetes cases, most patients are obese, it is associated with genetic predisposition • Type 2 diabetes is a disorder of both insulin resistance and relative deficiency of insulin. Dr Atef Masad Carbohydrates

26. Insulin resistance syndrome, also known as metabolic syndrome and syndrome X, affects the metabolism of many nutrients, including glucose, triglycerides, and high-density lipoprotein (HDL) cholesterol. • Individuals who are diagnosed with metabolic syndrome may show abdominal obesity and high blood pressure. • Such individuals are at increased risk for cardiovascular disease. Dr Atef Masad Carbohydrates

27. Gestational diabetes • is similar in etiology to type 2 diabetes; • it is defined as diabetes that is diagnosed in pregnancy. • Pregnancy is associated with increased tissue cell resistance to insulin. • The hyperglycemia of gestational diabetes diminishes after delivery; however, the individual who has developed gestational diabetes is at higher risk for the development of type 2 diabetes thereafter. Dr Atef Masad Carbohydrates

28. Signs and symptoms include • Polydipsia "excessive thirst". • Polyphagia "increased food intake". • Polyuria "excessive urine production". • Rapid weight loss. • Weight loss despite polyphagia • Blurred vision • Growth impairment • Susceptibility to infections. Dr Atef Masad Carbohydrates

29. Mental confusion and possible loss of consceiousness due to increased glucose to brain. • Complications include microvascular problems such as nephropathy, neuropathy, retinopaty, increased heart disease. Dr Atef Masad Carbohydrates

30. DIABETES MELLITUS Complications • K etosis, coma • A theroma swelling in artery walls - CVD, Strokes • N europathy : Peripheral & Autonomic • G angrene: neuropathy, atheroma, infection • I nfection: increased susceptibility • R enal: nephropathy, UTI • O phthalmic: retinopathy, cataracts • O bstetric: recurrent poor obstetric history Dr Atef Masad Carbohydrates

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32. Pathophysiology of D. M • Glucosuria happens when the glucose concentration of plasma exceeds roughly 180 mg/dl in an individual with normal renal function and urine output. • If the hepatic glucose overproduction continues, the plasma glucose concentration reaches a plateau around 300 mg/dl to 500 mg/dl. • This leads to polyuria (an osmotic diuresis), which, in turn, leads to volume depletion and hemoconcentration that causes a further increase in blood glucose level. Dr Atef Masad Carbohydrates

33. In type 1 there is an absence of insulin with an excess of glucagon, this permits gluconeogenesis and lipolysis to occur. • If type 2 insulin is present therefore glucagon is attenuated, fatty acid oxidation is inhibited. • Individuals with type 1 have tendency to produce ketones while type 2 patients have greater tendency to develop hyperosmolar nonketotic states (diabetic coma). • Diabetic patient with ketoacidosis tend to reflect dehydration, electrolyte disturbances and acidosis. Dr Atef Masad Carbohydrates

34. Acetoacetate, -hydroxybutyrate, acetone are produced from the oxidation of fatty acids. • Serum osmolality is high due to hyperglycemia. • Sodium concentration tends to be low because of the losses "polyuria" and the shift of water from cells due to hyperglycemia. Hyperkalemia is present due to the displacement of potassium from cells in acidosis. • The Na-K ATPase ion pump moves 3 Na ions out of the cell in exchange for 2 K ions moving into the cell as ATP is Converted into ADP. buy Dr Atef Masad Carbohydrates

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36. Islet amyloid and T2DM • Amyloid fibrils are insoluble protein depositswhichare a common link between many apparently unrelated diseases. • Associated with considerable damage to tissues. • Could be due to generation of free radicals and reactive oxygen species (ROS) by aggregating proteins. • Amyloid deposits derived from a peptide called ‘amylin’ are found in the pancreas in the vast majority of cases of T2DM. • CRITICAL THINKING..WAT is amyloidoses? Dr Atef Masad Carbohydrates

37. Islet amyloid and β-cell toxicity • Loss of β-cell mass contributes to progressive β-cell failure in T2DM. • Islet amyloid could play an important role in loss of islet cells and decline in insulin secretion. • Increased production of amylin, associated with increased demand for insulin, results in accumulation and aggregation of amylin. • hA (but not rA) aggregates to form fibrils that are toxic to islet β-cells in culture. Dr Atef Masad Carbohydrates 37

38. Criteria for the diagnosis of D. M. • All adults older than age 45 years should have a measurement of fasting blood glucose every 3 years. Testing should be carried out at an earlier age or more frequently in individuals who display: • Obesity • Family history of D. M • History of gestational D. M • Hypertension • Elevated triglycerides • Low HDL Dr Atef Masad Carbohydrates

39. Diagnostic criteria for DM • Random plasma glucose  200 mg/dL "11.1 mmol/L". • Plus symptoms of diabetes • Fasting plasma glucose  126 mg/dL "7.0 mmol/L". • 2 hours plasma glucose  200 mg/dL "11.1 mmol/L". • during an oral glucose tolerance test. • N:B any of the three criteria must be confirmed on a subsequent day by any of the three methods. Dr Atef Masad Carbohydrates

40. Categories of Fasting Plasma Glucose • Normal fasting glucose < 110 mg/dL • Impaired fasting glucose  110 mg/dL and 126 mg/dL • Provisional diabetes diagnosis  126 mg/dL • Categories of oral glucose Tolerance • Normal glucose tolerance 2 h< 140 mg/dL • Impaired glucose tolerance 2 h  140 mg/dL and 200 mg/dL • Provisional diabetes diagnosis  200 mg/dL Dr Atef Masad Carbohydrates

41. Hypoglycemia •  Hypoglycemia involves decreased plasma glucose levels. • Signs of hypoglycemia are related to the CNS. • Epinephrine act with glucagon to increase plasma glucose. • In addition cortisol and GH are released which increased glucose metabolism. • Hypoglycemia can be classified as: • 1- Postabsorptive "fasting", an individual has a loss of glycemic control during fasting state. • -Healthy individuals rely on gluconeogenesis to maintain the extracellular glucose concentration. Dr Atef Masad Carbohydrates

42. -Glucose must be given to the patient to relieve symptoms. • -In -cell tumors "insulinoma" there is elevated insulin levels. • 2- Postprandial "reactive" hypoglycemia • Not serious • -Excess insulin results in decrease glucose levels below normal fasting level. • -Spontaneous recovery of glucose level as insulin levels return to normal. Dr Atef Masad Carbohydrates

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44. Genetic Defects in CarbohydrateMetabolism • Glycogen storage disease • result from enzyme defects that affect the processing of glycogen synthesis or breakdown within muscles, liver, and other cell types • Nine distinct diseases considered to be glycogen storage diseases • Glucose – 6 – phasphatase deficiency type 1. "Glycogenolysis is inhibited". • An autosomal recessive disease. • Characterized by severe hypoglycemia match with metabolic acidosis, ketonemia, and elevated lactate and alanine. Dr Atef Masad Carbohydrates

45. Galactosemia • Congenital deficiency in one of three enzymes involved in galactose metabolism resulting in increased plasma galactose. • 1-Galactose-1-phosphate uridyl transferase • 2-Galactokinase • 3-UDP galactose epimerase • Galactose must be removed from diet. • If untreated, patient may develop mental retardation and cataract. Dr Atef Masad Carbohydrates

46. leading to toxic levels of galactose to build up in the blood, resulting in hepatomegaly (an enlarged liver), cirrhosis, renal failure, cataracts, brain damage, and ovarian failure. • Without treatment, mortality in infants with galactosemia is about 75%. • Symptoms may include hypoglycemia. Dr Atef Masad Carbohydrates

47. Methods of glucose Measurement • Glucose oxidase or hexokinase are the most used methods of glucose analysis • Glucose oxidase is specificly reacts with -D-glucose and converts it to gluconic acid. • O2 is consumed and H2O2 is produced. • The reaction can be monitored either by measuring the rate of disappearance of oxygen using an oxygen electrode or by consuming H2O2 in a side reaction. • Horseradish peroxidase is used to catalyze the second reaction and H2O2 is used to oxidize a dye compound. Dr Atef Masad Carbohydrates

48. 1- Glucose oxidase specific for beta-D-glucose May be coupled with a peroxidase indicator reaction or may be assessed by measuring oxygen consumption, using an oxygen electrode. Dr Atef Masad Carbohydrates

49. The hexokinase method • the reference method for glucose determination • considered more accurate than glucose oxidase methods because the coupling reaction using G-6-PD is highly specific. • The increase in absorbance of NADPH at 340 nm is measured as directly proportional to glucose. • The hexokinase reaction may also be coupled to an indicator reaction and measured through the development of a colored product. Dr Atef Masad Carbohydrates

50. 2- Hexokinase 3- Glucose dehydrogenase involves the measurement of NADH production: Dr Atef Masad Carbohydrates