Lipid spectrum disorders Lipids ■ Esters of fatty acids and alcohols (e.g. glycerol, cholesterol, sfingosin) ■ Sometimes, they also contain other chemical groups - e.g. Phosphate, choline, inositol (phospholipids), monosaccharide (glycolipids) ■ In wider sense lipid involve generally small hydrophobic or amphiphilic molecule with hydrocarbon chain (which involves free cholesterol, free fatty acids, icosanoids, retinoids) Molecule of phosphatidylcholine Physiological functions of lipids Energy storage - 1 gram of triacylglycerol can produce 39 kJ. double compared to saccharides and proteins Structural - amphiphilic lipids (especially phospholipids. Structural - amphiphilic lipids (especially phospholipids, cholesterol) makes most of cellular membranes and intracellular membrane compartments, myelin in nervous system (esp. sphingolipids, cholesterol) ^^^^^V^ signal - lipids and their derivates are responsible for endocrine (steroids), paracrine (icosanoids) and intracellular signalization (phosphatidylinositol phosphates) Other - role in embryogenesis, vision (retinoids), antioxidants (vitamins A, E) \ __„ Transport of blood lipids Lipids are not soluble in water Part is transformed into soluble metabolites (ketone bodies) ^^^^■^^Hh y^^BlI Free fatty acids (FFA) are bound to albumin in blood ^^^3 Most lipids in circulation form compounds of lipoprotein particles Lipoproteins Specific particles present in blood plasma They consist of lipid and protein compounds Phospholipids Cholcsicnol Coro mm Liming iriiicylglyccruls iind diolcstcryl Apolipopjuteinu Lipid com^und Phospholipids Cholesterol Triacylglyceroles (TAG) Protein compound Apolipoproteins (Apo) A-M Apolipoproteins Are situated on the surface of A . A T Apolipoprotem A-I lipoproteins ^^^^^^^^^^^^ 1* ^ * ^ *1 * d d ^b^^r^^^^I^S^^^v^^^^^^^^^I induction/inhibition of enzymes and B^^^S'^^B^I Th d* h d b 1 A Ivt ^^^^Mj^B^^jj^^S^^^ Some apolipoproteins (A, C and E) ^^^^^^fctjSHBF can be exchanged between different ^^^Hk^ particles ^^^^^^^^^Mfc ApoA and ApoC are in fact groups of proteins with similar structure, distinguished by Roman numbers. They, together with ApoE, form a structural family ApoB occurs in two forms, ApoB-48 and ApoB-100, which are products of the same gene (by mRNA editing, stop-codon 9 be made, which leads into mRNA translation into shorter ApoB-48). Metabolism of lipoproteins ■ Different lipoprotein classes can exchange both apolipoproteins and lipid compound u ■ Depending on the composition ■ w 'WmSa of protein compound, Bj lipoprotein ensures a specific lipid transport between tissues. IB ■ Lipoprotein metabolism can be 1599 divided into three main pathways: B IB • Exogennous pathway I • Endogenous pathway "\ nffl • Reverse transport ___„ 81 Lipid transport between tissues ■fro Ethr BLOODSTREAM £h|^riilcrDii Ftnmpart CUR f*LupLoi Lipoproteins - exogenous pathway ■ Chylomicrons (CMs) are big particles formed in the small intenstine ■ They contain all main types of apolipoproteins (A, B, C, E), ApoB-48 is a specific apolipoprotein ■ Through lipoprotein lipase (LPL) on capilary endothelium, induced by ApoC-II and inhibited by ApoC-III, CMs get rid of TAG, newly formed FFA get out of capillaries into tissues. ■ Most apolipoproteins are, together with TAG, transfered to HDL ■ Thus, chylomicrone remnants are formed. Through their ApoE, they bind to LDL or LRP receptors in the liver, where they are internalized Lipoproteins - endogenous pathway ■ VLDL are similar to chylomicrons, but they are smaller and contain ApoB-100 instead of ApoB-48 ■ In peripheral capillaries, they undergo similar modification as chylomicrons. Their remants are called IDL ■ Through LPL and hepatic lipase (on the endothelium of hepatic capillaries), they get rid of the rest of lipids (with the exception of cholesterol) and of ApoE ■ As a result, LDL particles are formed. They contain only one apolipoprotein, ApoB-100, and dominating lipid compound is cholesterol and its esters ■ ApoB-100 binds only to LDL receptor, which is frequent both in liver and peripheral tissues. The process leads to the transport of cholesterol into periphery Clearance of LDL is relatively slow. In a consequence, they are prone to oxidation and other modifications LDL-receptor is degraded with the help of chaperon PCSK-9 TG : tri acyl glycerol s Chi : chol e sterol and cholesterol esters Pl_ : phospholipids FA : free fatty acids A : apo - A - I , apo - A - II and apo - A - IV B - 43 : apo - B - 48 C - II : apo - C - II E : apo - E CRR : chylomicron remnant receptor LDL - R : LDL receptor Copyright 1 99G , S. Ma rc he si n i Lipoproteins - reverse transport ■ HDL are formed as nascent particles in the liver (and intestine), protein compound -ApoA-I - is dominant ■ Using ABCA-I transporter, ApoA-I is capable of reverse transport of cholesterol out of peripheral tissues (by other mechanisms, also ApoA-II a ApoE). ■ Apolipoproteins (except of Apo-B), TAG (in exchange for cholesterol esters - CETP) and phospholipids are transferred from other lipoproteins ■ Larger, lipid-enriched forms of HDL are formed, using LCAT, cholesterol is esterified. ■ Thanks to binding of ApoA-I to SR-BI receptor in liver (and steroidogenic issues), HDL „unloads" cholesterol and gets back into .circulation. TAG and phospholipides are degraded by hepatic lipase ^^^^^^^^^^^^^h^^^^b^^^^^^^^^^^^^h If modified HDL contains ApoE, it can be internalized by binding its receptors Ap^-n^lApoA-II bind to their receptor in kidney and can be excreted, they can return into circulation by binding protein cubilin Gut and Liver Liver Atherogenic a antiatherogenic lipoproteins ■ Antiatherogenic ■ HDL (especially nascent) ■ Atherogenic ■ LDL - in subendothelial space and other tissues (gingiva) they undergo oxidative modification, oxLDL are not recognized by LDL-R, but by macrophage scavenger receptors. Formation of oxLDL is easier, when the diet is rich for oxidated lipids. Subgroup of „small dense LDL" is especially atherogenic ^g*^0^ ■ Chylomicron remnants and IDL - they bind scavenger receptors without modifications ^^^^A ■ Other atherogenic modifications ■ glycation, glucooxidation, carbamylation (urea), aggregation ■ Lipoprotein (a) ^---- ^ Aterogenic lipoprotein penetration They must be sufficiently small (i.e. not chylomicrons and nascent VLDL) Endothelium: transcellular transport (vesicles) and paracellular transport („leaky junctions") Scavenger receptors SR-B participate in transcellular transport (on the other hand, the binding to LDL-receptor supports lipoproteik internalization - role of previous atherogenic modifications) Paracellular Leak Lumen / Basal Membrane Puid-ptia» Trans cytos is Receptor-mediated TranECEdlular Ctiannsl mMmSk i \ * '■■> * I f I ; -— Blood vessel lumen Endothelial cell f / I ENDQCVTQ5I5 | Subendothelial space ...•«*T" 0/ °OonDoooaoaacc °&oOCooot>ooooo A. Caveoiae SR-B1 ==5t'^r>- TRANSCYTOSI5 | Retention in subendothelial space Vesicular transport through the endothelium goes both ways ^^^H^^ ■ i.e. lipoproteins are rapidly removed from the subendothelial space \ Binding to subendothelial glycosaminoglycans —> retention Further modification (oxidation / glycation / aggregation...) —> binding to macrophage scavenger receptors ("toxic lipoproteins") ■ Eariy lipoprotein retention ■ Lowering plasma apoB LPs and decreasing risk factors will readily promote removal of atherogenic components and prevent maladaptive responses and future disease PRE-TEENS 1 Pre "iesional susceptible area of the arterial watl with diffuse intimal thickening (DIT) ' Lowering plasma apoB LPs and decreasing risk factors will prevent future vascular disease Diffuse intmnal thickening (DIT) apoB-LPs in plasma Endothelium VSMCs in media Atherothrombotic vascular disease Fibrous Mast ^tr. Expanded intima, rich in retentive ^ proteoglycans , Plaque necrosis with cholesterol crystals Ü C • Early responses to LP retention, e.g., monocyte entry - Lowering plasma apoB LPs _l and decreasing risk factors will m readily promote removal of athero-m genie components and prevent Z further responses and future W disease * Future strategies to prevent LP retention are likely to be most feasible up to this stage v<5 Tcell Dying Ivty ■TWENTIES AND BEYOND ■ Advanced responses to LP retention, including maladaptive inflammation, death, and plaque necrosis ■ LP retention continues to accelerates - Lowering plasma apoB LPs and reducing risk factors can promote removal of atherogenic components and promote regression, but reversal is more difficult and prolonged, and vascular disease may still develop ■ Continued responses to LP retention, e.g^ M foam cell formation and SMC migration • LP retention starts to accelerate . Lowering plasma apoB LPs and other risk factors can still promote removal of atherogenic components, promote regression, and prevent further responses and future disease ■ Small particle containing ApoB-100 and Apo(a) ■ Its elevated concentration is usually inherited (different genetic substrate) ■ It is one of most frequent causes of infarctions in young age (<20 years) ■ Its physiological function is unclear, Apo(a) is similar to plasminogene and tPA and binds fibrin. Probably, it is used in a repair of damaged vessel wall. Dyslipidemias ■ Disorders of lipid metabolism ■ They are not necessarily connected with obesity (but often they are) ^^^^H^ ■ Typically |total cholesterol, |LDL-cholesterol, jHDL-cholesterol and |TAG ^^^É^B^^^H ^^^^ ■ Sometimes, only some components are present (isolated hypertriacylglycerolemia, isolated hypercholesterolemia) ■ Hyper-TAG is in 90% connected with jHDL-C (phospholipid and TAG transfer to HDL leads to rapid degradation). Isolated jHDL-C (hypoalfalipoproteinemia) is rare -^"^ ■ LDL concentration is sometimes not measured directly, but is estimated using Friewald formula: ^^^^0 LDL-C = total chol. - HDL-C - (TAG/2,2) Clinical manifestation of severe hyperchlesterolemia Xanthelasmas, xanthomas of tendons Arcus corneae Polyarthritis, tendinitis Accelerated aterosclerosis Cholesterol and cardiovascular risk (SCORE) ■ 15% and over lOyearrbfcof Tauf CVDki popLditkms et Consequences of elevated TAG Cardiovascular risk sharply increases up to approx. 4 mmol/1, but does not substantially change further (contrary to overall mortality) r-------------- Copenhagen City Heart Study ana Copenhagen General fopuiation study Myocardial infarction N=96,394 (Events=3,287) Median fotlow-up 6 years Ischemic (=coronary) heart disease N=93,410(Events=7>183) Median follow-up 6 years 88 176 264 352 440 528 616 Vniiliisliiii; Iriiili i't ;-ido> All-cause mortality N=98,515 (Events= 14,547) Median follow-up 6 years nrml/L mg/dL 1 2 3 4 3 fi 7 88 176 264 352 440 528 616 Nun tag ting irijjlyvt rides Ischemic stroke N=97,442 (Events=2,994) Median fellow-lip 6 years in mi) LL 176 264 352 440 528 616 imul'L 1 2 3 4 S 6 7 88 176 264 352 440 528 616 NuiifasliiiKlriKlyceriües nimoLL mg/dL In high levels of TAG the TAG-rich lipoprotein particles increases in size, but not in number ■ Large lipoproteins do not pass into vascular intima, but may obstruct the microcirculation - see further Other complications of hyperTAGemia Acute pancreatitis ■ During pancreatitis development in hyperTAGemia, cytotoxic damage of acinar cells by unesterified FFA takes place Lipemia retinalis, retinal vein thrombosis Xantelasmas— 9 Desired values of blood lipids Czech atherosclerosis society recommendations, 2007 Patients Without complications Risk factors (e.g. DM2, DM1 with mikroalbuminuria) Presence of atherosclerosis \ Lipid mm o 1/1 mmol/1 mmol/1 Cholesterol <5,0 <4,5 <4,0 LDL-C <3,0 <2,5 <2,0 HDL-C >1,0 (men), >1,2 (women) TAG <1,7 Highly above the optimal values, but realistically achievable Primary and secondary dyslipidemias Primary ■ More frequent ■ Usually multifactorial, polygenic heritability, usually as a component of „metabolic syndrome" (syndrom X, Reaven ^jyndrom) ~" ■ Rare monogenic forms -usually mutations of apolipoproteins or their receptors Secondary ■ They are a consequence of other disease ■ E.g. diabetic dyslipidemia\iephrotic syndrome \ ■ They also may be a component of metabolic syndroflie(the boundary between primary and secondary dyslipidemia is not sharp) Frederickson classification of primary dyslipidemia Based on dominating fraction Type I -1 chylomicrons Type Ha -1 LDL ^^^^Kd Type lib -1 LDL and VLDL Type III -1 chylomicron remnants and ID] Type IV -1 VLDL Type V -1 VLDL and chylomicrons Simple phenotypic classification: cholesterol predominance vs. mixed vs^JAG predominance Familial hyperlipoproteinemia type I Very rare (1/1000000), endemic in Quebec Hypertriacylglycerolemia with high concentration of circulating chylomicrons Defect of LPL (LPLD) or deficiency of ApoC-II of Aj in the TAG up to 50mmol/l, manifestation in the childhood, often through acute pancreatitis or retinal thrombosis In serious cases, there is a necessity of plasma transfusion [ Familial hypercholesterolemia (FH) Frequent, prevalence 1:500 It is caused by defects of LDL-receptor, more rarely ApoB-100 (different sites of genes) Phenotype IIa, TAG are not very much elevated (lipoproteins rich by TAG contain also ApoE, so they can use alternative ways of degradation, while LDL clearance is dependent on ApoB-100 and LDL receptor) More serious homozygous, less serious heterozygous form FH - complications ■ In heterozygotes MI in 3rd -5th decade, in homozygotes before 20 years of age ■ Treatment: plasmapheresis (extracorporal precipitation of LDL by heparin), in serious case, it is an indication for liver \ transplantation ^ \ Polygenic hypercholesterolemia (Ha) Combination of disadvantageous", cholesterol-raising common polymorfisms in genes for ApoB, ApoE, PCSK9, LCAT, CETP and other proteins together with environmental factors Out of environmental factors, namely high caloric intake, high amounts of saturated fats and cholesterol in diet, little physical activity Role of fetal programing and early postnata^*^^ development Clinically, there is also higher susceptibility for gallstones formation Combined hyperlipidemia (lib) It is usually caused by ApoB overproduction in the liver, often resistance elevated ApoC-III ApoB/ApoA-I ratio is one of the most important risk factors for heart and brain atherosclerosis Variable fenotype, usually together with insulin resistance Monogenic forms are usually caused by variants of the genes for ApoC-II, Apo-C-III or CETP s\ More frequent polygenic form is usually part of the metabolic syndrome, heritability cca 20-30% (which is quite low -„acquired combined hyperlipidemia"), enviromental risk factors are basically the same as in Dolygem^^^^P k hypercholesterolemia Familial hyperlipoproteinemia type III (familiar dysbetalipoproteinemia, FDBL) ■ ApoE occurs in 3 functionally different isoforms, E2, E3, E4, which are coded by three common alleles s2, s3 a s4 (in most European populations, their frequency is -5-10%, 70-80%, 10-20%) ■ Izoform E2 binds badly to LDL-receptor, however ApoE2-containing lipoproteins can be degraded by alternative pathways ■ In cca 5% of s2/s2 homozygotes, the degradation is impaired as a result of their independent genetic defect and/or metabolic disease (e.g. DM2) ApoE and FDBL This leads into the disease known as familial dysbetalipoproteinemia (FDBL, FH III) FDBL can be caused also by rare mutations of ApoE, in these cases, it is inherited in dominant fashion with high penetrancy Both TAG (more) and cholesterol (less) is present, clinically xanthomas and precocious atherosclerosis Most s2/s2 homozygotes are normo- to hypolipidemic, in its heterozygous form, the allele is protective against the onset of atherosclerosis and its development ^^^^\ Allele s4 mildly increases the risk (and it markedly increases the risk of late-onset neurodegenerative diseases; because of its preferential binding to large lipoproteins it is insufficient for transferring lipids into neurons during their repair. The transport of lipids in the nervous svstem use^jj«BPiDL-like Polygennic hypertriacylglycerolemia Common, phenotype IV Genetically heterogeneous disease Polygennic, causes include LPL deficiency, overproduction of VLDL, deficiency of ApoA-V (inhibits chylomicron and VLDL production) \^^^^^^ It often occurs together with diabetes and obesity, but it has probably different genetic background - however the manifestation of hyperTAGemia is much more serious in a coincidence with diabetes The onset is usually provoked by alcoholic or nutritional excess Clinically often manifestated by serious fo rms of pan< creatiti Familial hyperlipoproteinemia type V Basically intermediate type between 1 and 4 As well as in all hyperTAGemias, there is a susceptibility to acute pancreatitis (esp. in TAG>10mmol/l). Sometimes, chronic pancreatitis can occur Secondary dyslipidemia I cholesterol ■ mixed cholestasis Kidney disease Hypothyreosis Obesity (TAG predominance) t TAG diabetes mellitus Alcohol abuse Diabetic hypertriacylglycerolemia Lack of insulin and insulin resistance leads into enhanced lipolysis in adipocytes and FFA formation In the liver, FFA can be used for TAG synthesis. TAG become part of VLDL. \ Moreover, insulin directly stimulates the production of LPL (and maybe also hepatic lipase)^Ctivity of these enzymes is then lower in DM and that helps fVLDL (secondarily also |HDL) -— iNon-esterified FFA also induce cytolysis pancreatic (3-cells ^^^^^^^^m Kidney diseases and dyslipidemia Nephrotic syndrome ■ Loss of LPL activators (I ratio ApoC-II / ApoC-III) t TAG ■ I HDL-cholesterol / total cholesterol ■ LCAT loss —► impaired transport of cholesterol iníóHDL___ ■ t hepatic expression —► jLDL-R —► decreased clearance of LDL (mediated possibly by increased TNF-a from damaged podocytes) CHRI ■ tApo-CIII ■ replacement of ApoA-I in HDL for serum amyloid A ■ tPCSK-9 -^\small dense LDL ■ CHRI often follows diabetes - see abov^ Strategies of the treatment ■ Lifestyle adjustment, physical aktivity (HDL) ■ Lowering of caloric intake, low-lipid (in I cholesterol) and low-saccharide (in |TAG) diet -more efficient in secondary dyslipidemia ■ Pharmacotherapy (clinical efficiency in a range of years!) ■ statins (they inhibit cholesterol synthesis) ■ fibrates, niacin (they lower VLDL synthesis) ^^^^^ ■ resins, ezetimib (they lower intestinal absorption of lipids) ■ PCSK- inhibitors (they prevent internalization of hepatic LDL-R) In serious case aphaeresis, transfusion of blood plasma, exceptionally liver transplantation Most expensive cure of history Alipogene tiparvorec (Glybera) Adenoviral vector with a gene for LPL Indication: familial hyperlipoproteinemia type I (LPLD) EMA approval in r. 2012 after approx. 10 years of testing -historically first gene therapy \ Controversial expressions of EMA commitees (weak evidence about clinical efficiency with low power of a test in a rare disease) 60 i.m. injections per a therapy - total price 1 mil. USD First doses came to market in 2015 Several tens of patients during a period of testing, 1 following the ^ approval (2015-2017) 2017 the request for prolongation of EMA registration wal^ withdrawn by a company