Lipid metabolism disorders / Questions and case reports

Questions

1. Which of the following statements about LDL is true?
   • A – is involved in the supply of triacylglycerols to peripheral tissues
   • B – the main component of the surface part are cholesterol esters
   • C – apolipoprotein C is needed for its function
   • D – this particle is removed from the circulation by receptor-mediated endocytosis
2. Which of the following does not participate in esterification in the centripetal transport of cholesterol?
   • A – lecithin-cholesterol acyltransferase (LCAT)
   • B – phosphatidylcholine
   • C – apolipoprotein A
   • D – apolipoprotein B
3. Squalene is an intermediate metabolite in biosynthesis:
   • A – cholesterol
   • B – β-hydroxybutyrate
   • C – unsaturated fatty acid
   • D – sphingomyelin
   • E – acylcarnitine
4. The following does not apply to triacylglycerol hormone-sensitive lipases:
   • A – catalyzes the degradation of triacylglycerols, which are transported in the nucleus of VLDL particles
   • B – is induced by insulin
   • C – is regulated by phosphorylation and dephosphorylation
   • D – is an integral part of HDL
5. What results in the complete absence of apolipoprotein B-48??
   • A – VLDL cannot be formed
   • B – chylomicrons cannot be formed
   • C – LDL particles cannot be formed
   • D – cholesterol synthesis in the liver is impaired
6. Fatty acids released from adipose tissue are transported by circulation::
   • A – in relation to albumin
   • B – as chylomicron-transferred triacylglycerols
   • C – as lecithin on the surface of HDL particles
   • D – none of the above mechanisms
7. Fatty acid catabolism stimulates gluconeogenesis in all of the following ways except:
   • A – by contributing to the production of NADH
   • B – by providing carbons for the glucose skeleton
   • C – by activating pyruvate carboxylase
   • D –by contributing to the production of ATP
8. Fatty acid serves as a source of energy for (list all):
   • A – liver
   • B – brain
   • C – muscles
   • D – red blood cells
9. Which statement about HDL is correct?
   • A – has an antiatherogenic effect
   • B – arise in adipose tissue
   • C –transfer triacylglycerols in their nucleus
   • D – enable centripetal transport of cholesterol
   • E – in the circulation, they transmit apolipoprotein E and C to chylomicrons
10. Multiplication of LDL particles is more dangerous in terms of atherogenicity than a multiplication of chylomicrons or VLDL because:
    • A – LDL particles are smaller than VLDL or chylomicron, so they penetrate the pores of the blood capillary wall and reach the target cells to which they supply cholesterol.
    • B – contain lecithin-cholesterol acyltransferase, which esterifies cholesterol to non-polar cholesteryl esters.
    • C – are taken up by target cells by endocytosis driven by specific receptors
    • D – their increased amount in the circulation stimulates endogenous cholesterol production in the endothelium of vascular capillaries
11. Why are VLDL particles increased in alcoholics?
12. Which lipoprotein particles are elevated in the absence of lipoprotein lipase?

Answers

Question 1. A - poorly - the supply of triacylglycerol to peripheral tissues takes place via VLDL or chylomicrons; LDL is the major transport particle for cholesterol B - false - cholesterol esters are hydrophobic and are therefore located not on the surface, but in the core of lipoprotein particles C - false - apolipoprotein C is a cofactor of lipoprotein lipase D – correct - LDL passes through the pores of the endothelial wall of the capillary, is taken up by target cells through specific receptors that bind apolipoprotein B; the resulting complex is enveloped by entrapment of a part of the cell membrane (endocytosis); this creates a vesicle that combines with the lysosomes; Their hydrolytic enzymes degrade the CDL particle; the released cholesterol is used to build cell membranes or is (if there is an excess) transported back to the liver (centripetal transport) by HDL particles. Question 2. A – false - LCAT is involved; catalyzes the esterification of cholesterol B - poor - phosphatidylcholine participates as a fatty acid donor after esterification C - poor - apolipoprotein A is a cofactor of LCAT D – correct - apolipoprotein B is not important for the centripetal cholesterol transport system; its role is in the metabolism of VLDL particles (mediates their secretion from hepatocytes) and LDL particles (is a binding protein for receptor-mediated endocytosis)) E – wrong - esterification with LCAT and phosphatidylcholine takes place on HDL particles after cholesterol uptake from the cell membrane Question 3. A – correct - squalene is formed from 6 isoprene units (isopentenyl pyrophosphate); it is then cyclized to lanosterol B – bad - β-hydroxybutyrate is a ketone substance that is formed from acetoacetate during ketogenesis; this takes place in the mitochondria and not in the cytoplasm (unlike cholesterol biosynthesis) C - poorly - unsaturated fatty acids do not have the precursor squalene D - bad - sphingomyelin is formed from serine and palmityl-CoA, which give sphingosine, which is converted to ceramide by the addition of another fatty acid; sphingomyelin is formed by reaction with cytidine diphosphate choline E - poor - acylcarnitine is involved in the transport of fatty acids through the mitochondrial membrane Question 4. A – bad - catalyzes the degradation of triacylglycerols, which are transported in the nucleus of VLDL particles B - bad - is induced by insulin C - wrong - is regulated by phosphorylation and dephosphorylation D – correct - is an integral part of HDL Question 5. A – wrong - VLDL particles contain apolipoprotein B-100, which allows them to be secreted from the hepatocyte B – correct - chylomicrons that form in the intestinal mucosa need the presence of apolipoprotein B-48 for secretion into the lymphatic circulation C – poor - LDL particles contain apolipoprotein B-100, which functions as a binding protein for receptor-mediated endocytosis D – poor - cholesterol synthesis in the liver is not affected by the presence of apolipoprotein B-48 Question 6. A – correct - fatty acids after release by lipolysis in adipose tissue are transported in the circulation in binding to albumin B – wrong - like triacylglycerols inside chylomicrons, fatty acids are transported from the intestine to adipose tissue or muscle C - bad - lecithin on the surface of HDL particles provides a fatty acid for cholesterol esterification D - wrong Question 7. A – poorly - the breakdown of fatty acids leads to the production of NADH, which is needed for gluconeogenesis, but it is necessary that NADH is transferred from mitochondria (the mitochondrial membrane is not permeable to NADH) into the cytoplasm by so-called malate or glycerol phosphate "shuttle" B – correct - Fatty acid catabolism by Đ-oxidation does not provide carbon atoms for the glucose skeleton. Fatty acids are broken down into acetyl-CoA and acetoacetate, which is used to form ketone bodies. Most carbon atoms are provided for gluconeogenesis from the carbon skeleton of amino acids. Some amino acids are catabolized to pyruvate and thus enter the gluconeogenic pathway via the pyruvate carboxylase reaction. Others are converted to 4- to 5-carbon intermediates of the citric acid cycle and thus increase the content of oxaloacetate and malate in mitochondria. Only leucine is completely degraded to acetyl CoA and is therefore only ketogenic. Other amino acids are glucogenic or both. C – poor - fatty acid catabolism increases the content of acetyl CoA, which promotes (allosteric activation) pyruvate carboxylase D – wrong - most of the energy for gluconeogenesis is supplied by fatty acid catabolism Question 8. A – yes - fatty acids are catabolized in the liver, which provides complete oxidation of palmitate to CO 2, ie β-oxidation + degradation of acetyl-CoA in the citric acid cycle, 129 ATP molecules, ie 8.1 ATP / 1 C atom B – no - the brain is dependent on glucose energy consumption C – yes - skeletal muscle and myocardium use fatty acids as a source of energy D – no - red blood cells cannot use fatty acids as a source of energy because they do not have mitochondria Question 9. A – yes - HDL has an antiatherogenic effect because it deprives cells of excess cholesterol, converts it into cholesterol esters and in this form transfers it to the liver, where cholesterol is metabolized B – no - HDL is formed in the liver, part is formed during the conversion of chylomicrons to chylomicron residues C – no - HDL transport cholesterol esters in their nucleus D – yes - HDL mediates centripetal (reverse) transport of cholesterol from peripheral tissues to the liver E – yes - HDL in the circulation passes apolipoproteins E and C to newly formed chylomicrons Question 10. A – correct - the smaller size of the LDL particles allows the pores of the vascular wall of the capillaries to penetrate and thus get out of the circulation; this is not possible with VLDL and chylomicron B – bad - LDL do not contain LCAT enzyme; HDL particles have this C – correct - specific receptor - driven endocytosis or a defect in the synthesis of these receptors results in hyper-LDL-lipoproteinemia, which is the cause of so-called familial hypercholesterolemia D – correct - an increase in circulating LDL reduces the synthesis of a specific LDL receptor and thus reduces the possibility of endocytosis of LDL particles; this leads to stimulation of endogenous cholesterol production in the cells Question 11. Alcohol oxidation in the liver shifts the NAD + / NADH ratio in favour of NADH. Increased NADH inhibits the oxidation of fatty acids, which re-esterify in the liver to triacylglycerols and are incorporated into VLDL particles and secreted into the circulation. Question 12. Chylomicrons and VLDL. Lipoprotein lipase anchored on the vascular endothelial membrane hydrolyzes triacylglycerols from chylomicrons and VLDL, which then turn into so-called "remnants" ev. other particles. When LPL or its cofactor (Apo CII) is deficient, the cleavage of triacylglycerols is deficient and chylomicrons and VLDL accumulate in the circulation.

Case reports

Patient with hypertension and ischemic heart disease

A 52-year-old woman with hypertension (drug-controlled), coronary heart disease was examined for a lipid profile. The finding showed an increase in LDL-cholesterol (4.62 mmol / l), a decrease in HDL-cholesterol (0.90 mmol / l) and an increase in triacylglycerols (2.85 mmol / l). Her brother had mild hypercholesterolemia but a significant reduction in HDL cholesterol and normotriacylglycelemia, and her sister had severe triacylglycerolemia.

Questions:

1. What are the main risk factors for coronary heart disease?
2. What adverse effects can poorly treated diabetes have on lipoprotein metabolism?
3. What induces oxidized LDL particles?

Answers

Age over 45 years, history of coronary heart disease in the family, cigarette smoking (over 15 per day) hypertension, obesity, little exercise, diabetes mellitus, hyperlipoproteinemia. Poorly treated diabetes with more persistent attacks of hyperglycemia leads to glycation of proteins as well as LDL-receptor protein and Apo B100. Such altered proteins are not normally metabolized, there is an accumulation of LDL particles in the circulation. Arterial wall endothelium can be damaged in various ways (mechanically, cytotoxically, also by oxidized LDL particles). The damaged area attracts monocytes, which turn into macrophages. These captures oxidized LDL and turn into foam cells. Damaged endothelium begins to produce thromboxane A2, which induces platelet aggregation.

Patient after acute IM

A 53-year-old man who had an acute myocardial infarction was monitored by a attending physician. Triacylglycerol level: 1.6 mmol / l, HDL-cholesterol: 0.89 mmol / l, cholesterol: 9.5 mmol / l, calculated LDL-cholesterol also significantly increased. A "high cholesterol" has been reported in his younger brother's family history.

Questions:

1. What is the most likely form of hyperlipoproteinemia in this patient?
2. What is the mechanism of action of cholestyramine (bile acid sequestrant) and statins

Answers

Familial hypercholesterolemia (type Iia according to Fredrickson). Cholestyramine-type preparations (eg Colestipol) bind bile acids in the intestine and thus prevent their re-absorption (block entero-hepatic circulation). This leads to increased metabolism of cholesterol in the liver to bile acids. Statins are inhibitors of a key enzyme in cholesterol biosynthesis in cells - hydroxymethyl-glutaryl-CoA reductase.

Patient with hyperlipidemia

In a 65-year-old man, hyperlipidemia was detected at the routine examination: cholesterol: 8.8 mmol / l, triacylglycerols: 2.4 mmol / l. The patient had periorbital edema, dry skin and hair, had no family history of cardiovascular disease.

Questions:

1. What can be the causes of combined hyperlipoproteinemia?
2. What other tests do you recommend for differential diagnosis?

Answers

Primary: Familial combined hyperlipoproteinemia (Fredrickson type IIb), familial dysbetalipoproteinemia (type II), unclassified, Secondary: type 2 diabetes mellitus, hypothyroidism, nephropathy, immunoglobulinopathy, cholestasis, hepatopathy, systemic lupus erythematosus, Tests for examination of the thyroid gland, liver, kidneys, protein electrophoresis. Results: aminotransferases normal, GMT normal, bilirubin and ALP not elevated, chemical examination of urine and urinary sediment within the norm, TSH – 43 U/l (standard below 5,5), thyroxine – 12 nmol/l (standard: 60–160).

What is the diagnosis now?

Hypothyroidism, secondary hyperlipoproteinemia.

Note: thyroid disorder should be treated primarily, hyperlipoproteinemia usually resolves.

Patient with xanthomas and hypercholesterolemia

A 55-year-old obese woman came to the GP with nodules about 2 cm in diameter on her forearms. She had yellowish streaks (palmar striae) on her palms.

Laboratory examination:

• cholesterol: 11,9 mmol/l
• triacylglycerides: 8,7 mmol/l
• Lipoprotein ELFO: broad β fraction

Questions:

1. What type of hyperlipoproteinemia is it?

Answers

It is a familial dysbetalipoproteinemia (type III according to Fredrickson). It is accompanied by the apoprotein 2/2 phenotype. It is caused by insufficient degradation of VLDL, which accumulates in the circulation (defect in the ligand of VLDL-residues for the apoE / apoB-receptor in the liver).

46-year-old manager on a preventive check-up

He had a father's history of acute myocardial infarction at the age of 57 but lived to the age of 79. The patient is obese (104 kg, 175 cm), blood pressure 170/100 mmHg.

Laboratory examination:

• cholesterol: 6,5 mmol/l
• triacylglycerols: 2,9 mmol/l
• HDL cholesterol: 0,84 mmol/l

Question:

1. What are the health risks of this patient?

Answer

Ischemic heart disease: hypertension, mild hypercholesterolemia, triacylglycerolemia, decreased HDL-cholesterol, obesity, lack of exercise, stressful employment.

Links

Related articles

• Cholesterol
• Other chapters from the book MASOPUST, J., PRŮŠA, R .: Pathobiochemistry of metabolic pathways

Source

• MASOPUST, Jaroslav and Richard PRŮŠA. Pathobiochemistry of metabolic pathways. 1st edition. Prague: Charles University, 1999. 182 pp. 80-85. ISBN 80-238-4589-6 .

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