Notes in CARBOHYDRATES, LIPIDS, PROTEINS, AND NPNs

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• Carbohydrates are the primary energy source stored primarily as glycogen in the muscle and liver.

• Disease states involved hyperglycemia (INCREASE GLUCOSE LEVEL) and hypoglycemia (DECREASE PLASMA GLUCOSE).

• Carbohydrates are hydrates of aldehydes or ketones and contain C, H, and O.

• Classification of carbohydrates is based on the size of the base carbon chain, location of the carbonyl functional group, stereochemistry of the compound, and number of sugar units.

• Monosaccharides are the simplest form of sugar and include fructose, glucose, and galactose.

• Disaccharides are formed by the interaction of two monosaccharides and include maltose, lactose, and sucrose.

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• Polysaccharides are formed by the linkage of many monosaccharide units and include starch, glycogen, cellulose, and oligosaccharides.

• Carbohydrate models include Fischer projection and Haworth projection.

• Glucose metabolism involves the digestion of complex sugars in the small intestine, absorption into the bloodstream, and circulation to different cells or tissues.

• Insulin is the hormone responsible for lowering plasma glucose levels and promoting cell uptake of glucose, glycolysis, glycogenesis, and lipogenesis.

• Glucose metabolism also involves glycolysis, gluconeogenesis, glycogenolysis, lipogenesis, and lipolysis.

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• Glycolysis is the metabolism of glucose to lactate or pyruvate for energy production.

• Gluconeogenesis is the formation of glucose-6-phosphate from non-carbohydrate sources such as fats and proteins.

• Glycogenesis is the conversion of glucose to glycogen for storage in the liver and muscles.

• Glycogenolysis is the breakdown of glycogen to glucose-6-phosphate.

• Lipogenesis is the conversion of carbohydrates to fatty acids.

• Lipolysis is the decomposition of fat.

• Glucose metabolism is regulated by hormones, with insulin being the primary hormone responsible for decreasing blood glucose levels.

Regulation of Glucose Metabolism:

• Glucose metabolism is controlled by hormones.

• Insulin is the primary hormone responsible for decreasing blood glucose levels.

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• Hormones involved in glucose regulation:

  • Insulin:

    • Synthesized by the β-cells of the islets of Langerhans in the pancreas.

    • Regulates blood glucose by increasing glycogenesis, glycolysis, and lipogenesis.

    • Can be synthesized or produced outside the body and injected to a person with insulin deficiency.

  • Glucagon:

    • Synthesized by the alpha cells of the islets of Langerhans in the pancreas.

    • Primary hormone responsible for increasing blood glucose.

    • Regulates blood glucose by increasing glycogenolysis and gluconeogenesis.

  • Epinephrine:

    • Produced by the adrenal cortex in response to ACTH.

    • Increases plasma glucose by decreasing intestinal entry of glucose into the cell and increasing gluconeogenesis, glycogenolysis, and lipolysis.

    • Associated with stress and promotes the inhibition and secretion of insulin.

  • Cortisol (Glucocorticoids):

    • Produced by the adrenal cortex in response to ACTH.

    • Increases plasma glucose by lowering interstitial entry of glucose into the cell and promoting gluconeogenesis, glycogenolysis, and lipolysis.

  • Growth hormone:

    • Produced by the anterior pituitary gland.

    • Increases plasma glucose by decreasing glucose entry to cells and increasing glycolysis.

  • Thyroxine (T4):

    • Produced by the thyroid gland.

    • Increases plasma glucose by promoting glycogenolysis, gluconeogenesis, and glucose intestinal absorption.

  • Somatostatin:

    • Produced by the Delta cells of the islets of Langerhans in the pancreas and hypothalamus.

    • Affects glucagon and growth hormone.

    • Increases plasma glucose by inhibiting insulin, glucagon, and growth hormone.

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• Hyperglycemia:

  • Elevated plasma glucose; increase in blood glucose levels.

  • Can be seen in physiologic and pathologic conditions.

  • Causes include stress, severe infection, dehydration, pregnancy, pancreatectomy, hemochromatosis, insulin deficiency or abnormal insulin receptor.

  • Fasting blood sugar levels:

    • Normal: 70-110 mg/dL.

    • Impaired fasting glucose/borderline fasting glucose: 111-125 mg/dL.

    • Diabetes mellitus: FBS levels ≥126 mg/dL.

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• Diabetes Mellitus:

  • Metabolic disease characterized by hyperglycemia resulting from defects in insulin secretion, insulin or both.

  • Types of DM: Type 1 (insulin-dependent), Type 2 (non-insulin dependent), Gestational.

  • Type 3 DM is a proposed type associated with the development of Alzheimer's disease.

• Pathogenesis of Type 1 DM:

  • β-Cell destruction and absolute insulin deficiency linked to autoimmune disorder caused by genetic defect.

  • Autoantibodies involved: Islet cell autoantibodies, Insulin autoantibodies, Glutamic acid decarboxylase autoantibodies, Tyrosine phosphatase IA-2 & IA-2B autoantibodies.

• Pathogenesis of Type 2 DM:

  • Insulin resistance with insulin secretory defect.

  • Increased with age, obesity, and lack of exercise.

• Gestational Diabetes Mellitus:

  • Due to metabolic and hormonal changes during pregnancy.

  • High risk for respiratory distress syndrome, hypocalcemia, and hyperbilirubinemia.

  • Mothers with GDM after pregnancy can develop type 2 DM.

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• Characteristics of Type 1 DM:

  • Abrupt onset, insulin dependence, ketosis tendency.

  • Sign and Symptoms: Polydipsia, Polyphagia, Polyuria.

• Characteristics of Type 2 DM:

  • Non-insulin dependent, milder symptoms than Type 1.

  • Sign and Symptoms: Polydipsia, Polyphagia, Polyuria.

• Other associated conditions with diabetes: Genetic defects of β-cell function, pancreatic disease, endocrine disease, drug or chemical-induced, insulin receptor abnormalities, other genetic syndromes.

• Laboratory findings in diabetes: Elevated urine specific gravity, ketones in serum and urine, decreased blood and urine pH, electrolyte imbalance.

• Categories of fasting plasma glucose: Normal fasting glucose (FBG ≤110 mg/dL), Impaired fasting glucose (FBG 111-125 mg/dL), Provisional diabetes diagnosis (FBG >126 mg/dL).

• Categories of oral glucose tolerance: Normal, Impaired glucose tolerance, Diabetes mellitus.

• Diagnostic criteria for diabetes mellitus: Random plasma glucose ≥200mg/dL with symptoms, Fasting plasma glucose ≥126 mg/dL, 2-h plasma glucose ≥200 mg/dL during an OGTT.

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• Normal glucose tolerance:

  • 2-h PG <140 mg/dL

• Impaired glucose tolerance:

  • 2-h PG 14-199 mg/dL

• Provisional diabetes diagnosis:

  • 2-h PG ≥200 mg/dL

• Glucose load for different groups:

  • Non-pregnant female and male: 75g

  • Kids: 1.75g per kg body weight

  • Pregnant: 100g

• Hypoglycemia:

  • Low/decreased plasma glucose level

  • Imbalance between glucose utilization and production

  • Symptoms:

    • Neurogenetic symptoms: tremors, palpitations, anxiety, diaphoresis

    • Neuroglycopenic symptoms: dizziness, tingling sensation, blurred vision, confusion, behavioral changes

  • Causes of hypoglycemia:

    • Patient appears healthy with no coexisting disease

    • Drugs

    • Insulinoma, Islet hyperplasia/Nesidioblastosis

    • Factitial hypoglycemia from insulin/sulfonylurea

    • Severe exercise, Ketotic hypoglycemia

• Diagnostic criteria for gestational diabetes mellitus:

  • 1-h plasma glucose ≥140 mg/dL during an OGTT + symptoms of gestational diabetes (100 grams glucose load)

  • 3-h plasma glucose:

    • Fasting (8-14 hrs) – >95 mg/dL

    • 1 hr – ≥180 mg/dL

    • 2 hrs – ≥155 mg/dL

    • 3 hrs – ≥140 mg/dL

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• Compensated coexistent:

  • Drugs/disease

• Laboratory findings:

  • Decreased glucose in plasma

  • Increased in patients with pancreatic βcells tumors (insulinoma) – high insulin levels

• Inborn errors of metabolism:

  • Galactosemia:

    • Congenital deficiency of enzymes involved in galactose metabolism

    • Laboratory feature: elevated blood and urine galactose

    • Clinical features: jaundice, hepatomegaly, easy bruisability, galactosuria, E.coli, sepsis, cataract, hypotonia, sensory neural deafness

    • Diagnostic test: erythrocyte galactose-1-phosphate uridyl transferase activity

  • Essential fructosuria:

    • Autosomal recessive disorder characterized by fructokinase deficiency

    • Fructokinase catalyzes the conversion of fructose to glucose 1-phosphate

    • Diagnostic indicator: presence of fructose in urine

  • Hereditary fructose deficiency:

    • Defect of fructose 1-6-biphosphate aldolase B activity in the liver, kidney, and intestine

    • Inability to convert fructose-1-phosphate and fructose1-6-biphosphate into dihydroxyacetone phosphate, glyceraldehydes-3-phosphate, and glyceraldehydes

    • Clinical features: [no details provided]

  • Fructose 1-6-biphosphate deficiency:

    • Defect in fructose-1-6 biphosphate results in failure of hepatic glucose generation by gluconeogenic precursors such as lactate and glycerol

    • Clinical features: hypoglycemia, lactic acidosis, convulsions, and coma

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• Glycogen storage disease:

  • Deficiency of specific enzymes involved in the metabolism of glycogen

  • Inherited autosomal recessive trait

  • Von-Gierke disease:

    • Most common glycogen storage disease (type 1A)

    • Affects liver and muscle

    • Clinical features: liver damage, muscular defect

    • Other GSD's: deficiencies of LDH, PK, phosphoglycerate kinase, and mutase

• Types of GSD:

  • Ia (Von Gierke): Glucose 6-phosphatase deficiency (liver)

    • Clinical features: hepatomegaly, retarded growth, seizures

  • Ib: Same as Ia; recurrent bacterial infections

  • II (Pompe): Glucose-6-phosphatase translocase deficiency

    • Clinical features: cardiomegaly, infantile death

  • IIIa (Cori Forbes): De Brancher deficiency (liver and muscle)

    • Clinical features: hepatomegaly, muscle weakness, retarded growth, cardiomyopathy

  • IIIb: De Brancher deficiency (liver)

    • Clinical features: same as IIIa except muscle weakness

  • IV (Andersen): Brancher deficiency

    • Clinical features: cirrhosis, esophageal varices, ascites

  • V (McAndle): Muscle phosphorylase deficiency

    • Clinical features: myoglobinuria, muscle cramps

  • VI (Hers): Liver phosphorylase deficiency

    • Clinical features: hepatomegaly, hypoglycemia

  • VII (Tarui): Phosphofructokinase deficiency

    • Clinical features: pain and stiffness on exertion

  • VIII (Adenyl kinase): Urinary excretion of catecholamines

  • IXa: Phosphorylase kinase deficiency (liver)

    • Clinical features: hepatomegaly, hypoglycemia, delay in motor development

  • IXb: Phosphorylase deficiency (liver and muscle)

    • Clinical features: hepatomegaly, retarded growth, muscle hypotonia

  • X: Cyclic AMP-dependent

    • Clinical features: hepatomegaly

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• Fanconi-Bickel

  • Glucose transporter-2

  • Hepatomegaly, rickets

  • Glycogen synthase

  • No Hepatomegaly; hypoglycemic symptoms in morning; mild growth delay

• CSF GLUCOSE

  • Lag phase

  • About 40-60% of the blood plasma glucose level

  • Affected or decreased whenever there is infection in the CNS; bacterial meningitis

  • Any changes in blood sugar are reflected in the CSF approximately one hour later because of the lag in CSF glucose equilibrium time

  • For comparison, a blood glucose specimen should be collected before the lumbar puncture

  • Markedly decreased CSF glucose (<40 mg/dL) and increased WBC count (neutrophil)

    • Increased levels: diabetes

    • Decreased levels: bacterial meningitis, tuberculosis, fungal and amebic meningitis, subarachnoid hemorrhage, systemic hypoglycemia

  • Viral meningitis: CSF Glucose is unaffected because viruses do not utilize glucose. It needs a living host

    • Reference values: 40-70 mg/dL (adult)

    • 60-80 mg/dL (child)

    • Normal CSF-to-glucose ratio: <0.5

• C-PEPTIDE TEST

  • Formed during the conversion of pro-insulin (pre cursor molecule for the synthesis of insulin in the β -cells) to insulin

  • Level of insulin is directly proportional to the c-peptide formed

  • The amount of circulating C-peptide provides reliable indicators for pancreatic and insulin secretion (B-cell function)

  • Can be used to monitor individual responses to pancreatic surgery

  • This test mainly evaluates hypoglycemia and continues assessment of B-cell function

    • Specimen: fasting blood

    • Method for testing: Immunometric assay (anti-C peptide is the antibody reagent – react with the c-peptide)

    • Increased: insulinoma, type 2 DM, ingestion of hypoglycemia drugs

    • Decreased: type 1 DM

    • Reference values: 0.90-4.3 mg/mL (CF: 0.333)

• DIAGNOSIS OF PATIENTS WITH GLUCOSE METABOLIC ALTERATIONS

  • WB glucose concentration 11% lower than plasma - To prevent false decrease

  • Serum or plasma must be refrigerated and separated from the cells within 1hr

  • Sodium fluoride (gray-top) can be used to inhibit glycolytic enzymes – if not inhibited, it could lead to false decrease

  • FBG should be obtained in the morning after 6 to 8 hours fasting (not longer than 16 hours)

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• NON-ENZYMATIC METHODS OF GLUCOSE MEASUREMENT

  • Nelson Somogyi

    • Copper reduction method (uses BaSO4 to remove saccharoids)

    • Glucose + arsenomolybdic acid à arsenomolybdenum blue

    • Utilizes direct colorimetric method (measured colorimetrically); increased absorbance

  • Hagedorn Jensen

    • Ferric reduction method (inverse colorimetry)

    • Glucose + Ferricyanide (yellow) à Ferrocyanide (colorless)

    • Color reactant is reduced to colorless; decreased absorbance

  • Ortho-toluidine (Dubowski)

    • Condensation of carbohydrates with aromatic amines producing Schiff bases (green)

    • Utilizes direct colorimetric method (measured colorimetrically); increased absorbance

• ENZYMATIC METHODS OF GLUCOSE MEASUREMENT

  • Glucose oxidase (Saifer Gernstenfield)

    • B-D-glucose + H2O – glucose oxidase à gluconic acid + H2O2

    • H2O2 + reduce chromogen- peroxidase à oxidized chromogen + H2O

    • Couple reaction is known Trinder’s reaction

    • False low results due to ↑ uric acid, bilirubin, and ascorbic acid

    • O2 consumption electrode (polarographic glucose analyzers) can also measure oxygen depletion

    • Main enzyme: glucose oxidase

    • Measured: oxidized something

  • Hexokinase (reference method)

    • Glucose + ATP -hexokinase à glucose 6-PO4 + ADP

    • Glucose 6-PO4 + NADP+ ―G-6-PD à NADPH + H+ 6-phosphogluconate

    • ↑ in absorbance is measured at 340 nm

    • False low results due to gross hemolysis and ↑↑↑ bilirubin

    • Main enzyme: hexokinase

    • Secondary enzyme/coupling: G6PD

    • NADP- oxidized form

    • NADPH- reduced form

  • Clinitest

    • Reducing substance + Cu+2 à Cu+1O

• SELF MONITORING OF BLOOD GLUCOSE

  • Type 1 diabetes – 3 to 4 times/day

• ORAL GLUCOSE TOLERANCE TEST

  • A solution containing 75g (adults) or 1.75g/kg (children) of glucose is administered, and a 2-Hour Postprandial Tests specimen is drawn 2 hrs later

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• HBA1C

  • Index for long term plasma glucose control (2-3 months period), indicating compliance and efficacy of DM therapy.

  • Formed by the attachment of glucose to Hb to form a ketoamine

  • Specimen requirement is EDTA WB sample

  • Normal value: 4.5 to 8.0%

  • Normal: px complies/ medication is effective (for px diagnosed with diabetes)

  • High hba1c: px do not follow/medication is not effective

• METHODS OF HBA1C MEASUREMENT BASED ON STRUCTURAL DIFFERENCES

  • IMMUNOASSAYS

    • Polyclonal or monoclonal antibodies toward the glycated N- terminal group of the B chain of Hb

  • AFFINITY

    • Separated based on chemical structure using boronate group to bind glycosylated proteins

  • CATION-EXCHANGE CHROMATOGRAPHY

    • Positive-charge resin bed attaches to negatively charged hemoglobin

  • ELECTROPHORESIS

    • Separation is based on differences in charge

  • ISOELECTRIC FOCUSING

    • Type of electrophoresis using isoelectric point to separate

• KETONE

  • Produced by the liver through metabolism of stored lipids

  • Increased in type 1 DM

  • 3 ketone bodies:

    • Acetone (2%)

    • Acetoacetic acid (20%) – most commonly tested

    • 3-B-hydroxybutyric acid (78%)

  • Ketonemia

    • Accumulation of ketones in blood

  • Ketonuria

    • Accumulation of ketones in urine

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• METHODS OF KETONE MEASUREMENT

  • Gerhardt’s Test

    • Acetoacetic acid + Ferric chloride à Red color

  • Nitroprusside

    • Acetoacetic acid + nitroprusside –alkaline pHà Purple color

  • Enzymatic

    • NADH + H+ + acetoacetic acid –β-HBDà NAD + βhydroxybutyric acid

• METHODS OF HbA1C MEASUREMENT BASED ON CHARGE DIFFERENCES

  • Cation-exchange Chromatography

    • Positive-charge resin bed attaches to negatively charged hemoglobin

  • Electrophoresis

    • Separation is based on differences in charge

  • Isoelectric focusing

    • Type of electrophoresis using isoelectric point to separate

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• HPLC (High-Performance Liquid Chromatography)

  • A form of ion-exchange chromatography

  • Used to separate all forms of HbA1C (A1a, A1b, A1c)

• MICROALBUMINURIA

  • Diagnosis at an early-stage diabetic renal nephropathy and before the development of proteinuria

  • Persistent albuminuria in the range of 30-299 mg/24 hr or albumin creatinine ratio of 30 to 300 µg/mg

  • Normally reabsorbed.