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CMBM Exam 2 > Lipoproteins > Flashcards

Lipoproteins Flashcards

1
Q

4 types of lipoproteins

A
  • chylomicrons
  • VLDL
  • HDL
  • LDL
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2
Q

Which lipoproteins predominantly transfer cholesterol

A
  • HDL

- LDL

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3
Q

Which lipoproteins predominantly transfer triacylglycerol

A
  • Chylomicrons

- VLDL

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4
Q

During low energy circumstances TG is mobilized from adipose tissue as fatty acids and transported on

A
  • Albumin
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5
Q

Do medium and short chain fatty acids need to be carried on lipoproteins?

A
  • No
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6
Q

Chylomicrons

A
  • largest and the most bouyant of the lipoproteins, due to the large amount of triacylglycerol present in the non-polar core of the lipoprotein
  • come from dietary sources
  • contain ApoB48 apoproteins, which are synthesized and packaged with nascent chylomicrons in the intestinal epithelial cells
  • acquire apoproteins ApoCII and ApoE from HDL
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7
Q

VLDL

A
  • 2nd largest lipoprotein
  • contains a large amount of TG, but not as much TG as Chylomicrons
  • contain ApoB100 apoproteins, which are synthesized and packaged with nascent VLDL in liver cells
  • acquire ApoCII and ApoE from HDL
  • liver synthesizes fatty acids from glucose and packages them as triglycerides in VLDL
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8
Q

LDL

A
  • smaller and less dense, having the least amount of TG and the largest amount of cholesterol esters
  • derived from VLDL
    • after VLDL releases the majority of their TG, they become Intermediate density lipoproteins (IDL), and with further loss of TG, the IDL become LDL
  • contains ApoB100, but they transfer back ApoCII and ApoE to the HDL lipoproteins
  • deliver cholesterol to tissues
  • LDL that is delivered to tissues does not pose a threat of atherosclerosis, but increased LDL remaining in the bloodstream is the basis of coronary artery disease
  • All cells in the body can take up LDL through specialized LDL receptors
    • recognize ApoB-100 and uptake by receptor-mediated endocytosis
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9
Q

HDL

A
  • very small, highly dense lipoproteins, having few TG and large amounts of cholesterol esters and protein, depending on their life cycle
  • contain ApoA apoproteins as well as other apoproteins, such as ApoCII and ApoE
  • two major functions:
    • carry cholesterol away from the tissues to the liver
    • carry and distribute apoproteins to other lipoproteins for their function
  • newly secreted HDL particles acquire additional cholesterol and phospholipids via ABCA-1 on peripheral tissue
  • also carries:
    • Phosphatidyl choline:Cholesterol Acyl-Transferase (PCAT)
    • Cholesterol Ester Transfer Protein (CETP)
    • Phospholipid Transfer Protein (PLTP)
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10
Q

Apolipoproteins

A
  • proteins that combine with lipoproteins either during packaging or are acquired later
  • Apoproteins destined to be packaged with lipoproteins are synthesized on the rough ER and are packaged with lipids,
    cholesterol, and fat-soluble vitamins in the Golgi apparatus
  • some apoproteins function as cofactors for enzymatic activity or are themselves enzymes, others assist in transferring lipids among various lipoproteins, and still others are
    recognized by cellular receptors to allow the lipoprotein to dock and be taken up by the cell
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11
Q

ApoA-1

A 
Lipoprotein expressed on:
- HDL
- chylomicrons 
Function 
- activates LCAT; ligand for HDL receptor
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12
Q

ApoB-100

A 
Lipoprotein expressed on: 
- LDL
- VLDL
- IDL 
Function: 
- LDL receptor ligand
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13
Q

ApoB-48

A 
Lipoprotein expressed on:
- chylomicrons
- chylo remnants 
Function: 
- Chylo assembly and secretion; dietary lipids
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14
Q

ApoC-II

A

Lipoprotein expressed on:

  • VLDL
  • HDL
  • Chylomicrons

Function:
- activates LPL, transfers b/w HDL and VLDL/chylomicrons

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15
Q

ApoE

A

Lipoprotein expressed on:

  • VLDL
  • HDL
  • Chylomicrons
  • chylo remnants
  • LDL

Function:
- Hepatic receptor ligand for chylomicron, LDL; is recycled b/w HDL and VLDL/chylomicrons

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16
Q

Lipoprotein Lipase (LPL)

A
  • an enzyme located on the
    inner leaflet of the endothelial cells lining the bloodstream
  • breaks down the TG into three fatty acids plus glycerol
  • LPL isozymes are regulated differently depending on the tissue
    • insulin activates LPL in adipocytes and in the capillary endothelium
    • By contrast, insulin has been shown to decrease expression of muscle LPL
    • Muscle and myocardial LPL is instead activated by glucagon and adrenaline
17
Q

chylomicron remnants

A
  • chylomicrons that have lost most of their triglycerides
18
Q

Acyl CoA:Cholesterol Acyltransferase (ACAT)

A
  • converts excess cellular cholesterol to cholesterol esters for storage
  • attaches a fatty acid from fatty acyl-CoA to the free hydroxyl of cholesterol to form cholesterol ester, the non-polar storage form
19
Q

Regulatory functions of cholesterol:

A
  • ↑ cholesterol inhibits HMG CoA Reductase enzyme
  • ↑ cholesterol inhibits LDL receptor biosynthesis
  • ↑ cholesterol activates ACAT (acyl CoA cholesterol acyltransferase)
20
Q

ATP-binding cassette-A-1 (ABCA-1)

A
  • one of a large family of transfer proteins that use energy in the form of ATP in the transfer of bile, cholesterol, ions, and many drugs across membranes
  • ABCA-1 was the first discovered member of this family, and its function is to provide cholesterol to HDL
21
Q

Phosphatidyl choline:Cholesterol Acyl-Transferase (PCAT)

A
  • carried by HDL
  • converts cholesterol to cholesterol ester by transferring a fatty acyl group from the phospholipid phosphatidyl choline to cholesterol to form cholesterol ester
22
Q

Cholesterol Ester Transfer Protein (CETP)

A
  • carried on HDL
  • synthesized by many tissues,
    including liver and adipose
  • exchanges cholesterol ester on HDL for triglyceride on VLDL
  • pro- and anti-atherogenic functions
  • Deficiency in CETP is associated with increased HDL levels
23
Q

Phospholipid Transfer Protein (PLTP)

A
  • exchanges triglyceride on HDL for phospholipids on VLDL
  • ApoE may be essential for stabilizing
  • involved in HDL and VLDL remodeling, including conversion of HDL to large HDL2 and small lipid-poor HDL particles
  • pro- and anti-atherogenic functions
  • Deficiency is associated with decreased HDL and ApoA-1 levels.
24
Q

Cholesterol

A
  • LDL delivers its cholesterol to the peripheral tissues, including a major user, the adrenal gland
    • converted to various cholesterol-derived hormones

Synthesized from acetyl CoA:

  • first reaction forms hydroxyl-methyl-glutaryl-CoA (HMG-CoA)
  • next step—converting HMG-CoA to mevalonic acid—is catalyzed by the enzyme HMG-CoA reductase
    • This is the committed step toward cholesterol synthesis and the regulated, rate-limiting step
  • HMG-CoA reductase is inhibited by its ultimate product, cholesterol
    • This enzyme is the target of the statin drugs
  • A series of cycling reactions results in Lanosterol, and finally Cholesterol
25
Q

Atherosclerosis

A
  • Atherosclerosis, coronary heart disease (CHD), and coronary artery disease (CAD)
  • hallmark of CHD is the presence of excess LDL in circulation
26
Q

Familial Hypercholesterolemia

A
  • genetic abnormality will result in increased circulating LDL
  • affects the synthesis and/or expression of LDL receptors on cell surfaces
    • Without these receptors, LDL levels and therefore cholesterol levels rise in the bloodstream
27
Q

Plasma LDL profile is characterization

A

characterized on the basis of size and density into two patterns:

  • large, buoyant LDL (pattern A)
  • small, dense LDL (pattern B)
    • Small, dense LDL (sd-LDL) penetrates more readily into the subintimal spaces, binds more tightly to proteoglycans in the ECM, therefore remaining longer in the ECM, and these types LDL are oxidized more rapidly than the larger LDL particles
28
Q

Genetic causes of hyperlipidemia

A
  • Familial LPL deficiency (A type I hyperlipidemia)
  • PCAT deficiency (“Fish Eye Dz”) (A type II hyperlipidemia) HDL)
  • Familial ApoCII Deficiency (A type V hyperlipidemia)
  • Familial Defective ApoB100 (A type IIa hyperlipidemia)
  • Familial Hypercholesterolemia (A type IIa hyperlipidemia)
  • Polygenic Hypercholesterolemia
29
Q

Familial LPL deficiency

A
  • defect in lipoprotein lipase
    • results in hypertriglyceridemia
    • Yields elevated chylomicrons
    • Autosomal recessive
    • Causes infantile pancreatitis, eruptive xanthomas, hepatomegaly, lipemia retinalis
30
Q

PCAT deficiency (“Fish Eye Dz”)

A

defect in PCAT

  • PCAT converts amphipathic cholesterol to non-polar cholesterol esters, thereby changing the shape of nascent HDL from pancake to spherical
  • Results in hypercholesterolemia (w/ unrecyclable HDL)
  • Yields elevated VLDL and total cholesterol
  • Causes corneal opacities, renal failure, vascular disease
31
Q

Familial ApoCII Deficiency

A

Deficient ApoCII

  • Autosomal recessive (RARE)
  • Yields severe hypertriglyceridemia, w/ ⇧ VLDL, chylo
  • Causes pancreatitis
32
Q

Familial Defective ApoB100

A

deficiency of ApoB100

  • Autosomal Dominant
  • Results in hypercholesterolemia
  • Yields elevated plasma LDL
  • Causes vascular disease (atherosclerosis)
33
Q

Familial Hypercholesterolemia

A

deficiency of LDL receptors

  • Autosomal Dominant
  • Results in hypercholesterolemia
  • Yields elevated plasma LDL
  • Causes early SEVERE vascular disease
  • xanthomas
34
Q

Polygenic Hypercholesterolemia

A

The number one cause for hypercholesterolemia

multiple genetic influences in combination environmental and other causes from underlying disorders

  • Yields elevated LDL +/- other anomalies
  • Causes vascular disease
35
Q

Cholesterol Screening

A
  • cholesterol is ≥ 200 mg/dL, then HDL and TG should be checked
  • LDL is calculated from these values using the following formula:
    • Total cholesterol = LDL + TG/5 + HDL
36
Q

CHD Risk factors

A
  • age
    • Male- 45yr.
    • Female- 55yr., premature menopause
  • family history of premature CHD
  • smoking
  • hypertension
  • HDL-cholesterol <35mg/dL
  • diabetes
  • obesity

CMBM Exam 2 (13 decks)

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