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Disorders of lipid metabolism & atherosclerosis
Lectures from molecular medicineschool year 2009/2010Oliver RáczInstitite of Pathological PhysiologyMedical School, UPJŠ Košice
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Introduction
Atherosclerosis is a medical problem only from the XIXth centuryShort lifespan due to other diseasesNo clinical biochemistry
Rokitansky (Vienna, 1852) incrustation [thrombogen] theoryVirchow (Berlin, 1855) infiltration [lipid] theoryFramingham study (1948)2000 ≈ 25 theories and numeral epidemiological studies
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Overview
General pathological physiologyBlood lipids and lipoproteins (function & metabolism)Lipids & atherosclerosis (epidemiological &experimental proofs)Other factors of atherosclerosis developmentComments on diagnosticsClassification of dyslipoproteinemiasGenetic background of lipid metabolism disorders and atherosclerosis
Special pathological physiology – tissue and organ level, CHD, stroke
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Cholesterol,free and esters with fatty acids*
275 mmol in the body50 mmol LP, GIT, liver 25 mmol fat tissue90 mmol muscles & vessel wall110 mmol nervous system
3 mmol/d exchange
double lipid !
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Catch 22
CholesterolIn: food and synthesis in cells (from CoA*)Breakdown: noOut: bile (enterohepatal circuit); stool
LDL cholesterolThe normal level (3,1 – 3,9 mmol/l) is not normal for the endothelNewborns & atherosclerosis resistant animals only ≈ 0,8 mmol/l
*HMG-CoA reductase
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Triacylglycerols & fatty acidsTAG & FFA
15 kg in nonobese subjects570 000 kJ; enough for 3 monthsThermal isolation, fertility, body shapeIntake & synthesis: 80 – 170 mmol/dDifferent fatty acids – saturated, unsaturated, polyunsaturated (eikosanoids), shorter and longer chainRapid turnover dependent on diet and alcohol intake, breakdown through physical activity(FFA – minutes)
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3 lipoprotein families (LP)spherical or discoid particles synthesised in guts or liverHydrophilic surface (phospholipids, cholesterol estersand apoproteins)Hydrophobic inner part (TAG, CH)Dynamic interaction with vessel wall and each other
Chylomicrons ⇒ chylomicron remnantsVLDL ⇒ IDL ⇒ LDL (heterogenous group*)HDL nascent ⇒ HDL3 ⇔ HDL2
*including “black sheep” Lp(a)
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Apoproteins
APOPROTEIN, FUNCTION LOCATION OF THE
GENE
MAIN OCCURENCE
A 1 – ACTIVATOR OF LCAT 11q23-qter HDL, CHYA 2 – ACTIVATOR OF LIVER LIPASE,INHIBITOR OF LCAT
11q21-q23 HDL, CHY
A 4 – LCAT ACTIVATION 11q23-qter HDL, CHYB 100 LIGAND OF LDL RECEPTOR 2p23-24 LDL, IDL, VLDLB 48 SHORT FORM OF B 100 ib. CHYC 1 – LCAT COFACTOR 19q12-q13.2 CHY, VLDLC 2 – LPL ACTIVATOR (LIPOPROTEIN LIPASE) 19q12-q13.2 CHY, VLDL, HDLC 3 – LPL & LIVER LIPASE INHIBITOR 11q23-qter CHY, VLDL, IDLD – CHOLESTEROL ESTER TRANSFER REGULATION 3q14.2-qter HDLE – RECEPTOR LIGAND 19q12-q13.2 CHY, VLDL, IDL
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And other genes...P r o te in L o c a t io n o f th e g e n eL D L r e c e p to r 1 9 p 1 3 .2H D L r e c e p to rL ip o p r o te in l i p a s e 8 p 2 2H e p a t i c T G l i p a s e 1 5 q 2 1L C A T 1 6 q 1 2 - q 2 1C E T P 1 6 q 1 2 - q 2 1A p o ( a ) f o r L P ( a ) 6 q 2 6 - q 2 7
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ChylomicronsEnterocytesapoB48, others from HDLTAG into fat and other tissues, LPLCH into liver (from bile and food)Peak 3 – 6 h after meal, t1/2 30 min, after 9 h ØRemnants into liver through receptor cytotoxic and atherogenic
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VLDL – LDL family
Liver, endogeneous TAG, CHB100 and othersfunctions and metabolism similar to CHYVLDL t1/2 2 – 4 hod, transformation to IDL, LDLLDL has a slow turnover, can be modified – oxidation, glycation
small dense LDL
Receptor and scavenger receptor
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The reality is different
B = binding site to LDL receptor
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Without apoBWithout apoBthethe synthesissynthesisofof LDL a LDL a CHY CHY is not possibleis not possible!!
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1500
1500
1500
1500
750
750
750
750
750
750
750
750
Cholesterol = 6000
ApoB100 = 4
Cholesterol = 6000
ApoB100 = 8
Same cholesterol concentration
Different ApoB – higher in the case ofsmall dense particles
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LDL classes
9< 21,8> 1,048V
2224,2 – 21,81,048IV
5025,5 – 24,2 1,034III
1626,0 – 25,51,028II
327,5 – 26,01,025I
% of LDLdiameter, nm
density, g/ml
LDL class
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Reverse transport of cholesterol by HDL
Liver, enterocytes and fromCHY as nascent „disc“Lot of apoproteinsLCAT and CEPT
lecitin-cholesterol acyltransferase, esterifies CHcholesterol ester transfer protein transprots CH-E from HDL into other LPs
Takes out cholesterol from tissues, disc is filled to HDL3Exchanges CH-E for TAG with other LPs transforms to HDL2Binds through AI to specific receptor in liver
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What is the essence of the association of lipids and atherosclerosis ???
„Bad and good“ lipids, lipoproteinsEpidemiological studies – onlzy statistics: they are true but do not answer the basic question „why?“
Atherosclerosis is the consequence of endothel dysfunction – inapproproate response to chronic injuryNot only lipids
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Endothel
Intelligent interface between blood and vessel wall/tissues1500 g, football field (1000 m2)Endocrine, paracrine and autocrine functionsvessel tonus, coagulation, adhesion, cell replication
Organ specificity, differences in arteries, capillaries a venesDysfunction in hypertension, diabetes, dyslipidemia...
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Risk factors (CHD, IM)Basic biological
age, gender, family history (= genes)
Biochemical, classicalcholesterol (§ 22), LDL-CH, TAG, ↓ HDL-CH, apoproteins, Lp(a), indexes
Biochemical, newfibrinogen, homocysteine, ferritin (Popeye)small dense LDL, oxidized LDL
Nutrition and life styletoo much fat, (?) sugar, antioxidant and fiber deficiencySMOKING, SEDENTARY LIFE STYLE
Diseasesobesity, diabetes (IR!), hypertension, kidney failure
Genetic RF LDL receptor (FH), apo E variants and many others
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Comments on Clinical Chemistry
Total cholesterol – also after mealTAG – after 12h fastingHDL cholesterol – basic parameterLDL cholesterol – calculated ???LDL cholesterol direct !apoproteins, Lp(a) & other special assaysindexes
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Biochemical diagnosis od dyslipoproteinemias
High number of CH a TAG assaysTotal cholesterol in healthy adults every 5 yearsBasic panel: TCH, HDL-CH, TAG LDL calculated = TCH – (HDL-CH + TAG/2,2)not possible if TAG > 4,5 mmol/l
Direct LDL assay
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Normal (desired) values
T-CH < 5,0 mmol/l 4,55 – 5,45HDL-CH > 1,0 mmol/l 0,87 – 1,13LDL-CH < 3,0 mmol/l 2,65 – 3,35TAG < 2,0 mmol/l 1,70 – 2,30INDEXES
T-CH/HDL-CH < 5,0NONHDL-CH < 3,8LDL-CH/HDL-CH < 3,0Klimov (T-CH – HDL-CH)/HDL-CH < 4,2APO AI/APO B > 1,3
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Other laboratory methods
SpecialApo B, Apo AI, Lp(a)homocysteine, coagulation and fibrinolytic factors.
Very specialLDL receptorsApo C, E, LPL, CETP, LCATclasses of LDL, HDL
Yesterdaytotal lipids, phospholipids, fatty acid esterselektrophoresis
Tomorrow - genomics
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Classifications
Fredrickson 1967, WHO 1970I, IIa, IIb, III, IV, V, VI - partly history
Therapeutical 1992, European task forceCH, TAG, both
Etiological – futureprimary and secondary DLP is not sufficient! most primary DLP are not exactly characterized
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“Secondary DLP”Nutrition and lifestyle
including smoking, alcohol and micronutrient deficiency
ObesityDiabetes mellitus
type 2 usually, decompensated type 1 (BG 20 – extreme TAG)
Kidney failureLiver diseaseEndocrine diseases – ⇓ thyroid functionDrugsHormones – anticonception, gravidity, postmenopausal, anabolics
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“Primary DLP”
�Familiar hypercholesterolemia (LDL rec.)
�Familiar defect of ApoB100 (FDB)? Polygenous hypercholesterolemia? Polygeneous hypertriglcyceridemia? Dysbetalipoproteinemia (IDL)? Familiar type V hyperlipidemia
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E apoprotein genes and types
Genotype Occurence, % e2/e2 < 2 e3/e3 60 e4/e4 < 1 e2/e3 23 e2/e4 < 2 e3/e4 12
E3 = 112 Cys, 158 ArgE2 = 112 Arg, 158 ArgE4 = 112 Cys, 158 Cys