7. cholecalciferol, vitamin D3
origin from 7-dehydrocholesterol
(skin, UV radiation)
open B ring („seco-“ compound)
systeme of conjugated double bonds
(the first in the position 5,
like as in cholesterol)
7
8. Brassinosteroid (→ steroid hormones of plants) :
HO OH
HO
HO
O
O
● regulate the growth and development in plants
(no influence on sexuality in plants !)
● skeletone similar to cholesterol
(here is next carbon atom in the side chain,
the structure of B ring is a lactone, i.e. cyclic ester)
8
9. ergostane C28 :
28
C28 - basic steroid hydrocarbon in plants (fytosterol)
(the 28th carbon of skelet is in this position marked right as „241“ ) 9
10. Steroids numbering :
IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN) (1989)
The nomenclature of steroids. Recommendations 1989. Eur. J. Biochem. 186, 429-458.
10
13. Change of vitamin to hormone
„calcitriol“: 25 - OH in the liver
1 - OH in the kidneys
(influence of parathormone)
OH
1
25
HO
Calcitriol expression of CBP gene (calcium binding protein)
synthesis of protein rich in –COOH groups in side chains
OH
binding of Ca2+ 13
14. the liver 1-hydroxylase :
• mitochondrial enzyme in the proximal
tubule of kidneys
• hydroxylate 25-hydroxy-vit.D3 (from the
liver)
• it is inhibited by higher concentration of
calcitriol (feedback),
by higher concentration of Ca2+ and
phosphates in plasma
• stimulated by parathormone and by
decrease of concentration of phosphate
in plasma
• at its inhibition is formed the inactive
24,25- dihydroxy-vit.D3 (proceeds
„alternative“ 24-hydroxylation in
substitution of „common“ hydroxylation
at the C-1 )
• megalin/cubilin mediated reabsorption of „vitamin D binding protein“ is responsible
14
for the renal conversion of 25(OH)D3 to 1,25(OH)2D3 in the proximal tubule
16. Binding proteins of steroids (1):
SHBG (= TEBG) sex hormone binding globulin,
testosterone/estrogens binding globulin
• 1-globulin of blood plasma, transport protein,
synthetized in the liver
• testosteron has conspicuously higher affinity to SHBG than estradiol
(approximately 5times)
• estrogens increase the SHBG concentration (woman has app. twice higher
SHBG),
testosterone reversely decreases the concentration SHBG in plasma
• only free hormones can be bonded on proteins,
conjugated proteins cannot be bonded (glucosiduronates, sulfates)
• steroid, bonded on the protein SHBG, is in this form transported into the
cell (i.e. complex: steroid-protein)
• increase of SHBG in man „estrogenization“
(= result of increase of E2 transported into cell – i.e. increase on SHBG
bonded E2 ! ) 16
17. Binding proteins of steroids (2):
BLOOD PLASMA:
SHBG (= TEBG) sex hormones binding globulin
testosterone/estrogen binding globulin
transfer: testosterone
estrogenes (this hormones do not have the side chain on C-17)
CBG = corticosteroids/cortisol binding globulin
(transcortin)
transfer: progesterone
cortisol (they have two carbon side chain on the C-17, total C21 )
Gc-globulin = vitamin D binding globulin
transfer: vitamin D and its derivatives
(they have voluminous C8 to C9 side chain on C-17, total C27 to C28 )
17
18. Regulating effect of hormones in the males / females :
1/ steroid hormone stimulates / inhibits the synthesis of its
transport (binding) protein
2/ steroid hormones have different affinity for binding proteins
3/ testosterone (TST) is a prohormone, little effective only.
(The effective hormone itself is 5α-dihydrotestosterone)
18
19. SHBG in woman :
testosterone (TST) estradiol (E2)
5times
higher
affinity
SHBG
the increase of concentration
of binding globulin (supported
by estrogens)
the woman
estrogens can be bonded has twice
in greater extent concentration
of SHBG
At the sufficient concentration of SHBG is bonded on the protein
both TST and E2. - SHBG allows the transport of hormons to the
19
cell, because it is a ligand for megalin.
20. SHBG in man :
testosterone (TST) estradiol (E2)
5times
higher
affinity
SHBG
the decrease of concentration
of binding globulin
(supported by testosterone)
the man has
half SHBG
estrogens cannot be
concentration
bonded in greater extent
At the lower concentration of SHBG on the protein is bonded in effect TST only.
TST with higher affinity to SHBG takes nearly all binding places.
So SHBG (ligand for megalin) allowes the transport of TST nearly exclusively.
20
21. Transformations of testosterone :
In woman goes into cell both TST and E2 together with SHBG.
TST (as a prohormone is little effective only !!) is transformated to E2 by aromatase.
OH
testosterone (TST)
O prohormone !!
aromatase 5-reduktase
( WOMAN ) ( MAN )
OH OH
estradiol (E2) 5-dihydroTST
HO O 21
22. Principle of effect of steroid hormones :
steroid - enters the cell, bonded on SHBG (transport: megalin)
lysosom - steroid hydrolytic is released from the bond on SHBG
receptor protein for steroids in cytoplasm by bonding of steroid the transcription factor is
created - different types of protein for different
steroids, the structure of „zinc “ finger
enter the nucleus
enhancer / steroid responsive element bonding of steroid receptor.
On the SRE are bonded 2 identical structures
(homodimer)
activation of promotor
transcription
proteosynthesis
22
23. Remark:
Everybody has all existing sex hormones
( his „own“ hormones and the „opposite“ hormones )
1/ the man stays man because:
in foetus is influence of antiMüller hormone (from Sertoli cells)
created estradiol act locally only (not endocrinely ! - it may act on nearby
cells only)
strong affinity of testosterone to SHBG
occupation nearly all binding places of SHBG by testosterone
testosterone is so (in complex with SHBG) „preferentially“ transported
to the cells
under influence of testosterone is synthesis of SHBG considerably limited
„do not remain“ free binding places for estradiol (estradiol „cannot go“
to the cells)
23
24. Remark:
Everybody has all existing sex hormones
( his „own“ hormones and the „opposite“ hormones )
2/ the woman stays woman because:
testosteron is nearly present as an intermediate product for synthesis of
estrogens
( aromatase)
testosterone alone is little effective (it is prohormone !!)
SHBG with strong affinity to testosterone allowes sufficient transport of
testosterone into cells
sufficiency of testosterone as a substrate for transformation to estradiol
under influence of estrogene is the synthesis of SHBG markedly increased
sufficiency of binding capacity for estrogens
by binding of E2 on SHBG is allowed transport estrogens into the cells
SHBG = sex hormone binding globulin = TEBG = testosterone / estrogen binding globulin
24
25. Estradiol (E2) in man :
no endocrine effect !!
(man´s body is not under paracrine and autocrine effect
„flood“ of E2) (effect of E2 near the place of origin)
The lack of aromatase (and so estrogens!) can evoke infertility in man
25
and failures of maturation in bones !! Estrogens regulate spermatogenesis in mammals.
27. In man and in woman are identical control mechanisms :
GnRH feedback by sex
hypothalamus
(gonadotropin releasing hormone) hormones in blood
one hypothalamic hormone
controls both hormones
LH of hypophysis FSH
(luteinizing hormone) (follicle stimulating hormone) anterior lobe of pituitary
t1/2 = cca 50 min t1/2 = 4 h (adenohypophysis)
effect of both hypophysary
hormones is mediated by cAMP
in target tissues
corpus luteum Leydig cells follicular cells. Sertoli cells target tissues
ovaries testes ovaries testes (ovaries, testes)
(progesterone) (testosterone) (estrogens)
27
29. 27-hydroxycholesterol : ( 2007 )
HO 27
OH
bonds on the same receptors in heart vessels as estrogens
inhibits so the production of nitric oxide, which produces
vasodilatation
unfavourable circumstances: menopause, hypercholesterolemia
29
31. Neurosteroids :
● specifically progesterone (PROG) and some of its
metabolites (allopregnanolone) are neuroprotective in some
brain injuries (traumatic, hypoxic, ischemic stroke, …)
● effects are systemic and not limited to CNS injury itself
● multiple beneficial effects cannot be atributed solely to the
PROG intranuclear receptor
● actions are result of hormone´s effects on maitenance of
mitochondrial functions
● vitamin D deficiency reduces the benefits of PROG treatment
neurosteroids e.g. ● protect neurons from ischemic injury
● decrease the size of a lesion
● reduce inflammatory reactions, apoptosis
and reactive oxygen species
● stimulate myelin synthesis (remyelination)
● …… 31
33. Metabolism of steroids → inactivation
and increasing solubility in water :
1/ the reduction of double bonds (including
the oxo-groups)
2/ conjugation to the glucosiduronates and sulfates
3/ the main location: liver, however kidneys too
- the main place of excretion
exception: testosterone 5-dihydrotestosterone
(effective metabolite !!)
33
34. Origin of UDP-Glc : OH
CH2OH N
O
O N
O P P P P O CH2
O
Glc-1-P UTP
OH
CH2OH
N
O
O N P P
O P P O CH2
O
anhydrid bond
UDP-Glc anhydrid bond
34
35. Conjugation with glucuronic acid
(„GlcUA“) :
CH2OH COOH
O O
O O
UDP-Glc UDP-GlcUA
COOH
O steroid-3-glucosiduronate
(schematicly)
O
35
36. The most common transformation of steroids :
O
reduction
HO
conjugation
COOH
O
( steroid-3-glucosiduronate )
O
excretion
(urine, bile)
36
37. Steroid skeleton cannot be degraded :
O
inactivation of hormone by reduction of double bonds
COOH
OH
O
conjugation
20 O
( pregnandiole-20-glucosiduronate )
HO
excretion
37
38. Glucosiduronates :
• C-3-glucosiduronates are the most frequent
(however the pregnandiol-20-glucosiduronate is the main
metabolite of progesterone excreted in urine)
• glucosiduronates are present as sodium salts
• glucosiduronates are formed in the reaction with glucuronic acid
(GlcUA) which is activated by the bond on uridindiphosphate
(UDP-GlcUA)
COOH
O
COOH
O
20 O
O
HO
38
39. „PAPS“ :
NH2
N N OH O
N N CH2 O P O S O-
O
O O
OH
O
HO P OH
O
anhydrid
bond
= 3´- phosphoadenosin - 5´- phosphosulfate = „active sulfate“
39
40. Conjugation with sulfuric acid :
O
HO S O
O
Schematicly is depicted alkylsulfate i.e. ester of sulfuric acid and 3-OH steroid.
This type of conjugates is less frequent in steroids than glucosiduronate .
40
42. Megalin :
● megalin = transmembrane glycoprotein
Mr ~ 600.000, multiligand transport protein
(the member of the LDL-receptors family)
● megalin allowes the way to cell uptake of androgenes a estrogenes
bonded on SHBG
● megalin-deficient mice (megalin-knockout) have development disorders
of sexual organs from lack of androgenes/estrogenes
● probably exist (less important !!) transport of steroids independent on megalin/cubilin,
(in experiment elimination of megalin is not fully identical to the picture after
blockade of steroid receptors)
42
43. Cubilin :
● Mr = 456.000, glycoprotein, many repeating sequences („CUB“ domains,
from their abbreviation the name - acronymus)
● periferal membrane protein (= on the surface of cells)
● has not the signal sequence for endocytosis
● internalization of cubilin (with bonded ligands) allowes megalin
(presence of Ca2+ ionts on the bond)
● identical to receptor for the complex intrinsic factor with vitamin B12 +)
+) uptake of vit. B is facilitated by the cobalamin-binder (gastric)
12
„intrinsic factor“.
Vit. B12 and intrinsic factor create complex.
Intrinsic factor recognises a receptor cubilin, present in epithelium
of intestine and kidney.
43
46. Transport of steroid hormone into cells
– yesterday, today and tomorrow ?
● yesterday: transport (plasma) globulin binds a steroid
hormone. At the target cell the hormone detaches
from its transport protein. A free hormone as a nonpolar
substance passes (also) nonpolar cell membrane.
A free (unbound) hormone entering the cell becomes
biologically active (according to this idea)
● today: transport (plasma) globulin is a ligand for the receptor
megalin/cubilin. Only the hormone bound to plasma
globulin enters the cell. A bonded hormone entering
the cell becomes biologically active.
● tomorrow ? a posssibility of blocking megalin/cubilin
receptor → impact on malignant processes ?
46
47. Megalin and cubilin
– multiligand receptors, schematicly :
cubilin is a periferal (surface)
membrane glycoprotein
cubilin
megalin
cell membrane
megalin is a transmembrane glycoprotein
47
48. Megalin and cubilin (2) :
ligands
hormones (●) bonding on their transport proteins ()
cubilin
megalin
cell membrane
both receptors are able to bond large amount+) of different ligands,
which are mainly proteins (transport proteins of unpolar hormones too)
+) μεγαλος = large, huge → „megalin“ ?
48
49. Megalin and cubilin (3) :
hormones (●) bonding on their transport proteins ()
cubilin
megalin
cell membrane
the internalization of cubilin bonded ligands
is allowed by colaboration of cubilin with
megalin – only megalin is transmebrane protein !
internalization (hormone including a protein)
49
50. Megalin and cubilin (4) :
hormones (●) bonding on their transport proteins ()
cubilin
megalin
cell membrane
internalization (hormone including a protein)
lysosome 50
(releasing hormone from the bond on a protein)
51. Impact on tumor cells ?
LHRH = GnRH (see the remark)
α- = negation, anti- :
REMARK :
α-estrogenes = antiestrogenes
GnRH = gonadotrop(h)in releasing hormone
LHRH = LHRF = luteinizing hormone releasing hormone / factor α-androgenes = antiandrogenes
- all the names are of the same significance, however the GnRH shoud
be prefered !!!!!
51
52. Possibility of blockade of megalin receptor ?
blue: active receptor megalin white: blockade receptor megalin
„up-regulation“ → carcinoma mammae (estradiol)
→ carcinoma prostatae (testosteron)
52
