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Cholesterol. Steran skeleton. Characteristics of steran-derived compound. Angular methyl group: AB,CD Substituent of C3 : R1 Double bounds: 4/5 C 5/6 C C17: R2 -OH =O Carbonic atom containing side chains ríng In position of C11, C12 -OH =O „A” ring - aromatic

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characteristics of steran derived compound
Characteristics of steran-derived compound
  • Angular methyl group: AB,CD
  • Substituent of C3 : R1
  • Double bounds:
    • 4/5 C
    • 5/6 C
    • C17: R2
    • -OH
    • =O
    • Carbonic atom containing side chains
    • ríng
  • In position of C11, C12
    • -OH
    • =O
  • „A” ring - aromatic
    • no C19 angular CH3
cholesterol1
Cholesterol
  • 8 chiral carbon atoms: 256 possible stereoisomer
  • C19 – angular methylgroup
  • C13, C17 – cis
  • C3 –OH cis
  • Reduction of cholesterol results in two different compounds
biosynthesis of cholesterol
Biosynthesis of cholesterol

I.

Ac-CoA - Mevalonate

acetyl coa hmg coa mevalonate
Acetyl-CoA – HMG-CoA - Mevalonate
  • Ac-CoA – Acetoacetyl - CoA
    • Ketone body formation in mitochondria
    • Biosynthesis of cholesterol is extramitochondrial
    • Diffusion of excess acetoacetate into citosol
    • Acetoacetate is activated by Acetyl-CoA synthase -- acetoacetyl-CoA
      • ATP, CoA
acetyl coa hmg coa mevalonate1
Acetyl-CoA – HMG-CoA - Mevalonate
  • Acetoacetyl-CoA – HMG-CoA
    • Acetoacetyl-CoA + acetyl-CoA
acetyl coa hmg coa mevalonate2
Acetyl-CoA – HMG-CoA - Mevalonate
  • HMG-CoA – Mevalonate
    • Two stage reduction
      • NADPH
    • Microsomal enzyme
    • The rate limiting step of cholesterol biosynthesis Statins
mechanism of actions of statins
Mechanism of actions of Statins
  • Fig. 1.Inhibition of HMG CoA reductase reduces intracellular cholesterol levels; this activates a protease, which in turn cleaves sterol regulatory element-binding proteins (SREBP\'s) from the endoplasmic reticulum. The SREBP\'s translocate to the nucleus where they upregulate expression of the LDL receptor gene. Enhanced LDL receptor expression increases receptor-mediated endocytosis of LDL and thus lowers serum LDL. Inhibition of HMG CoA reductase also reduces intracellular levels of isoprenoids, which are intermediates in cholesterol biosynthesis. (From the American College of Cardiology. Vaughan, CJ, Gotto, AM, Basson, CT. J Am Coll Cardiol 2000; 35:1).
biosynthesis of cholesterol1
Biosynthesis of cholesterol

II.

Active isoprenoid units

mevalonate active isoprenoid units
Mevalonate – active isoprenoid units
  • Phosphorylation of ATP
  • Intermediers
biosynthesis of cholesterol2
Biosynthesis of cholesterol

6 izoprenoid units

squalene

III.

synthesis of squalene
Synthesis of Squalene
  • Geranyl-PP
  • Farnesyl-PP
  • 2 Farnesyl-PP
  • Squalene
biosynthesis of cholesterol3
Biosynthesis of cholesterol

Squalene - Lanosterol

IV.

squalene lanosterol talakul s
Squalene – lanosterol átalakulás

ER

Mixed function

oxygenase:

Squalene epoxydase

biosynthesis of cholesterol4
Biosynthesis of cholesterol

Lanosterol - cholesterol

V.

squalene lanosterol conversion
Squalene – lanosterol conversion

ER

Squalene &

Sterol carrier

protein

bile acids
Bile acids

Tauro ~

Glyko ~

Tauro ~

Glyko ~

Cholesterol

Chenodeoxycholic acid

Litocholic acid

Cholic acid

Primary bile acids

Deoxycholic acid

Secondary bile acids

compartmentalisation of bile acid synthesis
Compartmentalisation of bile acid synthesis

7a-hydroxylase

Monooxygenase, NADPH, Cit P450

Conjugation of

Taurin &

Glycine + Bile acids

Side chain -”cleavage”

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