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chem path > lipoprotein metabolism > Flashcards

lipoprotein metabolism Flashcards

1
Q

what determines whether the cholesterol is beneficial or noxious

A

the type of lipoprotein carrying it

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2
Q

how are fats absorbed

A

-dietary lipids emulsified by bile salts in intestine
-pancreatic lipase breaks down triglycerides into fatty acids + monoglycerides
-absorbed by enterocytes & converted back to triglycerides

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3
Q

how are chylomicrons formed

A

-triglycerides are packed with cholesterol, phospholipids & proteins to form chylomicrons in enterocytes
-apolipoproteins are incorporated within chylomicrons

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4
Q

how do chylomicrons go to tissues & give energy

A

-in the circulation, chylomicrons deliver triglycerides to peripheral tissues
-chylomicrons acquire ApoC2 in circulation which activates LPL (lipoprotein lipase)
-LPL breaks down triglycerides into fatty acids & glycerol allowing uptake into tissues for energy

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5
Q

what happens to the chylomicrons after hydrolysis by LPL

A

-chylomicrons decrease in size and become remnants
-chylomicron remnants taken up by hepatocytes using ApoE (which facilitates reUptake into hepatocytes)

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6
Q

how is cholesterol synthesized de novo in the liver

A

-HMG-CoA is reduced to mevalonate through enzyme HMG-CoA reductase (rate limiting step)
-mevalonate converted to cholesterol

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7
Q

what happens to excess cholesterol & triglycerides in liver

A

-excess cholesterol and triglycerides are packaged into VLDL (very low density lipoprotein) which contains ApoB100
-in circulation VLDL is hydrolysed by LPL to remove most of triglycerides and becomes LDL (low density lipoprotein)

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8
Q

what does LDL do?

A

-carried cholesterol to peripheral tissues

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9
Q

what does PSCK9 do?

A

enzyme that regulated LDL receptors on hepatocyte surface
-more PSCK9 binding to LDL receptors, less clearance of LDL from circulation

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10
Q

how does reverse cholesterol transport work?

A

-HDL collects excess cholesterol from tissues and transports it back to liver to be recycled

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11
Q

what does excess cholesterol /LDLs lead do?

A

atheromas

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12
Q

how is most of cholesterol made

A

de novo synthesis in liver

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13
Q

which genes are involved in familial hypercholesteraemia? (familial type II)

A

-LDLR (reduced clearance of LDL)
-apoB (affects binding of LDL to receptor & thus clearance)
-PCSK9: increased degradation of LDL receptors (gain of function)

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14
Q

what genes involved in polygenic hypercholesteraemia?

A

multiple polymorphisms (eg. LDLR, ApoB)

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15
Q

what happens in familial hyperα-lipoproteinaemia?

A

CETP deficiency causes high HDL (good mutation - longevity)

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16
Q

what is involved in phytosterolaemia?

A

-ABCG5 & ABCG8 (which usually prevent jejunal cholesterol absorption) are mutated meaning too much is absorbed (too much plant sterols)
-early atherosclerosis

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17
Q

mutations in type I familial hypertriglyceridaemia?

A

LPL (lipoprotein lipase) or ApoC2 (prevents lipolysis increasing chylomicrons)

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18
Q

what happens in familial dysβlipoproteinaemia (type III) + feature

A

-aberrant ApoE
-assocaited with alzheimers
-yellow palmar crease

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19
Q

what is most common cause of hypolipidaemia?

A

αβ - lipoproteinaemia
-MTP deficiency (packages chylomicrons) causing very low cholesterol

20
Q

mnemonic to remember familial dyslipidaemias?

A

1 LP, 2 LD, b adds V, 3 is E, 4 gets more

type 1: LPL deficiency
type 2: LDL receptor deficiency
type 2b: same as 2 but adds VLDL
type 3: ApoE deficiency
type 4: excess TG & VLDL
type 5: type 1+ 4 = 5

type 2 affects pairs (2)- 2 eyes 2 ankles - corneal arcus & achilles tendon xanthomas

21
Q

which is the most common ApoE isoform?

A

APOE3

22
Q

which APoE is associated with alzheimers risk

A

APOE4

23
Q

which APOE isoform offers protection against alzheimers

A

APOE2

24
Q

what is a feature of familial type 3 (apoE deficiency)?

A

palmar crease xanthomas
(3 palmar creases!)

25
Q

what do familial hypertriglyceridaemias cause?

A

eruptive xanthomas (eg. butt)

26
Q

features of lipoproteinaemia?

A

decreased fat absorption so steatorrhea & decreased fat soluble vitamins (A & E)

27
Q

put lipoproteins in order of density (lowest to highest)

A

chylomicron
FFA
VLDL
LDL
IDL
HDL

28
Q

what does PCSK9 do?

A

binds LDLR and promotes its degradation so less LDL absopriton back into liver (more LDL in blood)

29
Q

how can PCSK9 be targeted

A

PCSK9 inhibitor (evolocumab) - reduces incidents to EVents (not mortality)

30
Q

when can evolocumab be used

A

statin-intolerant or uncontrolled lipids

31
Q

how do you treat lipoprotein(a)

A

-CVD risk factor
-nicotinic acid

32
Q

what is tangiers disease + features?

A

-hypolipidaemia
-orange tonsils (TANGerine)
-ABCA1 gene
-prevents release of cholesterol from cells so they accumulate in tissues - hepatomegaly, splenomegaly, orange tonsils in kids
-low HDL levels in blood. soCVD risk

33
Q

what does prednisolone do to LDL

A

increases circulating LDL levels

34
Q

how do you manage hyperlipidaemia

A

1) dietary modification + exercise (despite poor dietary correlation)
2)statin (HMG-CoA reductase inhibitor) - reduces intrinsic synthesis of cholesterol
3) other - ezetimibe (cholesterol abs blocker)

35
Q

side effect of statin

A

myopathy/rhabdo, fatigue

36
Q

how to reduce triglicerides?

A

fibrates (gemfibrozil)

37
Q

how to reduce lipoprotein a?

A

nicotinic acid (not used now cos side effect profile)

38
Q

what does lomitamibe do?

A

used in FH
-inhibits MTP -(loMiTamibe) to block release of VLDL

39
Q

what does cholestyramine do?

A

resin that binds to bile acids reducing their absorption in terminal ileum (more cholesterol used to make more bile acids - lowers cholesterol)

40
Q

what is the best way of determining obesity clinically

A

waist: hip ratio (predicts adiposity & CVD risk)

41
Q

obesity BMI definition + obesity BMI definition in south asians?

A

BMI >30
south asians 27.5 (always 2.5 below )

42
Q

management of obesity?

A

-conservative
-medical: orlistat (lipase inhibitor)
-surgery: bariatric surgery if BMI >40 or >35 + comorbidity

43
Q

side effects of orlistat?

A

flatus, diarrhoea, steatorrhea

43
Q

indications for bariatric surgery

A

BMI >40
BMI >35 + comorbidity

44
Q

types of bariatric surgery?

A

-gastric band –> smaller stomach, fuller after meals
-sleeve gastrectomy
-roux-en-Y bypass (distal jejunum anastamosed to stomach)

chem path (20 decks)

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