Vitamin D , endocrine system , evolution , pleiotropic effect , mortality ,cancer , cardiovascular , immunomodulator effect , Blood pressure , RAAS

1. VITAMIN D ENDOCRINE SYSTEM
FROM EVOLUTION TO REVOLUTION
By
AHMED MOSTAFA TAHA MOHAMED
Borham_ahmad@yahoo.com

2. WHY EVOLUTION OF VIT D IS IMPORTANT?
Vitamin D as a unique ancient molecule and its related system , exposed to a lot of
modifications through its journey in Biological history .
Also this functional and structural evolution helped us to understand the complexity
of vit D system , up to considering it , An Endocrine System , Not just a simple
Vitamin !!
It attracted to researchers all over world to uncover more and more of its mystery
which reached new places that never crossed our imagination to be Vit D related !
I hope You will find this scientific Time journey with this Endocrine System is very
interesting as giving you a new look to this important topic.
Special Thanks to Prof. Sandro Mazzaferro and Prof.Marzia Pasquali who inspired me
this presentation

3. Unstable Molecule

4. 750 MILLION YEARS AGO
We can find the precursor of vitamin D3, 7-deydrocholesterol or pro-vitamin D3, in very old
living organisms, such as plankton.
The synthetic pathway of this precursor is much conserved, starting from cholesterol. Just
2 hydrogen atoms removed. This resemblance allows us to hypothesize that in unicellular
organisms, vitamin D3 was a component of the plasma membrane just like Cholesterol and
synthesized from it. However ,a specific feature characterizes this pro-vitamin D3: the
capacity of absorbing UV-B rays in the same wavelength of DNA. For this reason, the
biological role of pro-vitamin D3 in ancient organisms could have been that of protecting
DNA from the toxic effects of UV-B rays, rather than regulating Ca metabolism
Holick MF. Vitamin D: evolutionary, physiological
and health perspectives.Curr Drug Targets 2011

5. PLANKTON

6. After UV-B ray absorption, pro-vitamin D3 is transformed into the thermodynamically
unstable pre-vitamin D3, which requires a final transformation into the more stable
cholecalciferol or vitamin D3 .As such, this new molecule could be regarded as an
inactivated end-product.
However, in very old organisms like algae, it is capable of promoting growth activity,
which points to the persistence of some biological effect.
Algae under
microscope
ALgae

7. the specific enzymes capable of producing hydroxylated metabolites appear early in
evolution, in yeasts and old plants that have no calcified structure.
A role for vitamin D in the process of mineralization can be seen some 550 MYA in snails
and crustaceans, in which 25-hydroxyvitamin D (25OHD3) and 1,25-dihydroxyvitamin D
could have some implication in the mineralization processes
550 MILLION YEARS AGO
Marine Snails

8. 450 MILLION YEARS AGO
jawless fishes that possess a type of vitamin D receptor (VDR), the complexity of the vitamin D
system increases slightly. In these cartilaginous (non-calcified) fishes, however, this ancestral
receptor is involved in xenobiotic detoxification which is considered as a type of immune
response and not with calcification
Agnatha
Whitfield GK, Dang HT, Schluter SF et al. Cloning of a functional vitamin D receptor from the lamprey (Petromyzon marinus), an ancient
vertebrate lacking a calcified skeleton and teeth. Endocrinology 2003

9. 375 MLLION YEAR AGO
It is in teleosts (complete bone fishes) with cellular and remodelling bone that VDR
activation, for the first time, is involved with calcium and phosphate absorption and
bone mineralization

10. 200-300 MILLION YEARS AGO
It is subsequently in terrestrial animals that the VDR becomes functionally divergent from
that of aquatic animals by acquiring more definite ‘calcium-phosphate-oriented’ effects
Along with the VDR, in vertebrates a specific vitamin D binding protein (DBP) also appears
seemingly functional to the need of systemic transportation of the hydrophobic vitamin.
This protein has a specific ligand binding domain (LBD) for vitamin D metabolites and
circulates in excess amounts compared with ligands, thus representing a storage
compartment. Further, it has different affinity for each of the vitamin D metabolites [e.g. 600
times higher for 25OHD3 than for 1,25(OH)2D3] and in this way regulates circulating levels
of the free fractions of each metabolite
Howarth D, Law SHW, Barnes B et al. Paralogous vitamin D
receptors in
teleosts: transition of nuclear receptor function. Endocrinology 2008

12. WHY EARLY LIFE LACKED BONE ?
We can notice this easily as life continued about 300 Million years without bone , and
it started only when evolution is directed more toward the land surface .
The fact is plenty of calcium has been available in seawater (some 40 mg/dL) which is
4 times what present in human circulation as example showing no need for storing Ca
in Bone , and lack of any need to Vit D calcium enhancing absorption , this metabolic
view of our Bones can give us a new view .
Accordingly, defensive or detoxifying roles are the most probable functions of vitamin
D in more simple life species in the sea.

13. FGF23/KLOTHO SYSTEM
FGF23 is the most famous phosphatonin , which is a group of proteins secreted to control
phosphorus level through its phosphaturic effect with help of Klotho , also it downregulate
Vit D which has a stimulatory effect on FGF gene , so there is regulatory effect between the
two linked systems .
The complete biological relevance of the FGF23/Klotho system is still not settled and could
possibly go beyond mineral metabolism, since direct cardiac effects have been demonstrated
for both FGF23 and Klotho.
Further, by regulating renal tubular Na-Cl cotransporters, FGF23 may influence blood
volume and pressure , it started in bone vertebrates.

14. OSTEOCALCIN
OC has been considered a bone protein involved with mineralization processes. However,
OC null mice show increased bone mass without mineralization defects in front of a clear
phenotype of diabetes-obesity.
we now know that a metabolite of OC, undercarboxylated OC, which is mainly produced
during bone resorption, stimulates insulin secretion by the pancreatic β-cells and promotes
insulin sensitivity in peripheral organs while also modulating adipocyte activity .
Importantly, by stimulating its own receptor on osteoblasts, insulin inhibits the synthesis
of osteoprotegerin in these cells, thus increasing osteoclast recruitment, bone resorption
and further OC production (Positive feedback). Vitamin D, which regulates bone cells in
general and can either stimulate transcription or reduce circulating levels of OC , is thus
involved with energy metabolism

15. VITAMIN D AND MUSCULOSKELETAL SYSTEM
Migration of life from sea to land carried some challenges like more need for calcium
and minerals regulation in more tight way with storage urgency , and Bone solved this
with help of Vit D
Second challenge was the need for more free movements and that happened with
cooperation of the musculoskeletal system which is high energy consuming organ , as
we can see the role of Vit D in regulation of such energy metabolism with mineral
availability needed for Muscle contraction physiology.

16. VITAMIN D PLEIOTROPIC EFFECTS
From all what we studied through our Time journey with Vit D evolution , we can now
have Idea , why Vitamin D only was the topic of more than 4000 paper in 2014 only ,
and why scientist was directed to new aspects of research which is slightly far from
simple mineralization process to more wide systemic effects of Vitamin D endocrine
system .
Vit D role in aspects like , immune modulation , cell proliferation and growth with its
relation to cancer,apoptotic and antifibrotic studies , cardiovascular system and its
role in Mortality , energy metabolism and DM, renoprotective roles ….. Etc are almost
inspired form the thorough study of Vit D Evolution.

17. VITAMIN D RENAL PROTECTION
Several studies have shown that the administration of vitamin D analogues attenuates the
renal damage in various experimental models of uraemia .
nephrectomized rats treated with 1,25-(OH)2D3 and found that vitamin D reduces renal
cell proliferation and glomerular growth as well as glomerulosclerosis andalbuminuria
as indicators of progressive glomerular damage. With a similar subtotally nephrectomized
rat model.
Vit D and its analogs can suppress macrophage infiltration, monocyte chemoattractant
protein-1 (MCP-1) production, transforming growth factor-beta-1 (TGF-β1) mRNA and
protein expression, and phosphorylation of Smad2, and these effects are amplified when
blood pressure is controlled via renin–angiotensin system blockade.

18. The use of vitamin D analogues in chronic kidney diseases: possible mechanisms beyond
bone and mineral metabolism NDT Plus (2009) 2: 205–212

19. CONTINUED
It is found that treatment with 1,25-(OH)2D3 abrogated podocytes injury, detected as
desmin expression, and loss of nephrin and zonula occludens-1 (two slit diaphragm
associated proteins) and glomerular polyanion staining, suggesting that vitamin D may
revert proteinuria by counteracting glomerular podocyte injury. On the other hand, in a
study of experimental obstructive nephropathy, a model that is characterized by
predominant tubulointerstitial lesions, Tan et al. showed that paricalcitol significantly
attenuated renal interstitial fibrosis, as demonstrated by a reduced interstitial volume,
decreased collagen deposition and repressed mRNA expression of fibronectin and type I
and type III collagens. Paricalcitol also preserved E-cadherin and reduced alpha-smooth
muscle actin expression in vivo.
In addition, paricalcitol suppressed renal TGF-β1 and its type I receptor expression

20. MORTALITY IN CKD AND DIALYSIS
PATIENTS
The use of vitamin D analogues in chronic kidney diseases: possible mechanisms beyond
bone and mineral metabolism NDT Plus (2009) 2: 205–212

21. DIABETIC NEPHROPATHY
Diabetic nephropathy needs special considerations because it is the leading cause of
dialysis-dependent end-stage renal disease, and the renin– angiotensin system (RAS) is a
major mediator of progressive renal injury in diabetic nephropathy. As discussed above,
vitamin D negatively regulates the RAS, and the renal protective role of vitamin D in
diabetic nephropathy has been specifically studied . Diabetic VDR knockout mice developed
more severe albuminuria and glomerulosclerosis due to increased glomerular basement
membrane thickening and podocyte effacement . More fibronectin and less nephrin were
expressed in the VDR knockout mice compared to diabetic wild-type mice. In receptor
knockout mice, increased renin, angiotensinogen, TGF-β and connective tissue growth factor
accompanied the more severe renal injury.

22. RAAS BLOCK
Combined treatment with an ARB and a vitamin D analogue markedly ameliorated renal
injury in the streptozotocin induced diabetes model due to the blockade of the compensatory
renin rise by the vitamin D analogue, leading to more effective inhibition of the renin–
angiotensin system . The combined treatment suppressed the induction of fibronection, TGF-β
and MCP-1 and reversed the decline of slit diaphragm proteins nephrin, zonula occludens-1
and alpha-actinin-4. These were accompanied by blockade of intrarenal renin and angiotensin

23. BLOOD PRESSURE
In the last two decades, epidemiological studies have revealed an inverse relationship
between the plasma 1,25-(OH)2D3 concentration and the blood pressure or the plasma renin
activity in both normotensive men and patients with essential hypertension.
Furthermore, it has been reported that vitamin D3 supplementation reduces blood pressure
in patients with essential hypertension , and 1,25-(OH)2D3 treatment reduces blood pressure,
plasma renin activity and Ang II levels in hyperparathyroidism patients.
The effect of a vitamin D analogue on the renin– angiotensin system, however, may not be
directed on renin alone .
showed that paricalcitol decreases angiotensinogen, renin, renin receptor and vascular
endothelial growth factor mRNA levels in the remnant kidney by 30–50% as compared to
untreated animals. Similarly, the protein expression of renin, renin receptor, the angiotensin
type 1 receptor and vascular endothelial growth factor were all significantly decreased.

24. MYOCARDIUM EFFECTS
Vitamin D has a direct effect on myocardium, independent of its suppressive effect on the
renin–angiotensin system. It directly suppresses myocardial hypertrophy and could improve
cardiac performance.
The uptake of calcium by cardiac muscle cells is in part regulated by vitamin D.
O’Connell et al. showed that 1,25-(OH)2D3 reduces proliferation rate, PCNA levels and c-
Myc levels of myocytes in culture through decreased entry into the S phase. Vitamin D
deficiency also results in a shift in the tissue distribution of V1 and V3 myosin chains,
favouring the V1 isotype . Shifts in myosin isotypes have been shown to alter myocyte
contractility . In addition, vitamin D has a biphasic action on vascular smooth muscle cell
and prevents its proliferation
Active vitamin D also suppresses the stimulatory effect of epidermal growth factor on
vascular smooth muscle cell proliferation.
At low dose, vitamin D may also stimulate the production of inhibitors of arterial
calcification and have an anti-thrombotic effect . In contrast, active form of vitamin D
applied in supraphysiological concentration is a mitogenic factor for aortal smooth muscle
cell

25. METABOLIC EFFECTS
Vitamin D has also been reported to enhance insulin sensitivity and induce a favourable
plasma lipid profile.
Chiu et al. found an independent correlation between serum 25(OH)D concentration and
insulin sensitivity index, and an independent negative relationship of 25(OH)D
concentration with plasma glucose concentration at fasting, 60, 90 and 120 min during
the oral glucose tolerance test. In this study, subjects with hypovitaminosis D (below 20
ng/mL) had a greater prevalence of components of metabolic syndrome than did subjects
without hypovitaminosis D. Vitamin D has also been reported to increase apolipoprotein
A-I and high-density lipoprotein (HDL) cholesterol, resulting in a favourable plasma lipid
profile

26. IMMUNOMODULATING EFFECTS
A vitamin D analogue is also a potent regulator of the immune system, in particular, on T cell-
mediated immunity . Vitamin D receptor is found in significant concentrations in the T
lymphocyte and macrophage populations However, its highest concentration is in the
immature immune cells of the thymus and the mature CD8 T lymphocytes The significant role
of vitamin D compounds as selective immunosuppressants is illustrated by their ability to
either prevent or markedly suppress animal models of autoimmune disease. Results show that
1,25-(OH)2D3 can either prevent or markedly suppress experimental autoimmune
encephalomyelitis, rheumatoid arthritis, systemic lupus erythematosus, type I diabetes and
inflammatory bowel disease . Vitamin D hormone stimulates interleukin 4 (IL-4) production,
which in turn suppresses inflammatory T cell activity . Calcitriol attenuates the expression of
experimental murine lupus . In the kidney , 1,25(OH)2D3 also regulates mesangial cell smooth
muscle phenotypes in a TGF-β1-mediated manner and ameliorates glomerular injury in rats
with experimental glomerulonephritis

27. Vitamin D: a pleiotropic hormone Kidney international Vol 78, issue 2, 2 July
2010

28. CANCER
Several large-scale epidemiological studies have shown an inverse correlation between
exposure to sunlight (the major source of vitamin D) or vitamin D intake and risk of colorectal,
breast, and prostate cancer.
Worldwide research has focused on the development of structural analogs of 1,25(OH)2D3 with
a clear dissociation between antiproliferative and calcemic effects. One of these analogs, TX
522 (Inecalcitol;) is currently in phase II in patients with hormone-refractory prostate cancer.
Preliminary results showed that 27 of the 31 patients treated with Inecalcitol (at different
doses up to 600 mg per day) and Taxotere during 18 weeks showed a decrease in prostate-
specific antigen levels of more than 30% within 3 months of initiation of treatment without any
changes in calcium parameters

29. A recent meta-analysis of the association between serum 25(OH)D3 and colorectal
cancer risk supports the conclusion that lower serum 25(OH)D3 levels are inversely
associated with colorectal cancer.
The association between breast cancer risk and 25(OH)D3 status has been studied
among others in the United States as well as in Europe. The UK study showed that
women with 25(OH)D3 levels o50nmol/l have an odds ratio of 3.54 for breast cancer
risk compared with women with levels 450 nmol/l.
From these studies, it became clear that not one single gene or one single pathway
mediates the antiproliferative effects of 1,25(OH)2D3 but that multiple pathways are
involved, among which epidermal growth factor,insulin-like growth factor,
transforming growth factor, and prostaglandins signaling cascades.

30. BONE AND CALCIUM HOMEOSTASIS
1a,25-Dihydroxyvitamin D3 (1,25(OH)2D3) is a major calcitropic hormone with as primary
purpose to keep the plasma Ca concentration within narrow limits. The renal production of
1,25(OH)2D3 is therefore tightly regulated by two hormones. First, hypocalcemia induces the
secretion of parathyroid hormone (PTH) by the parathyroid gland PTH targets the kidney to
decrease Ca excretion, inhibit phosphate reabsorption, and stimulate 1,25(OH)2D3
production. 1,25(OH)2D3 will then increase active Ca and phosphate transport in the small
intestine and stimulate Ca reabsorption in the kidney. In concert with the effects of PTH on
bone, 1,25(OH)2D3 action also enhances Ca exchange from bone and the cooperation of these
pathways restores serum Ca levels to normal. Second, 1,25(OH)2D3 stimulates the secretion
of FGF23 by the osteocytes. FGF23 is the major phosphaturic hormone inhibiting renal
phosphate reabsorption (by the specific transporter NaPiT2a) and decreasing the renal
production of 1,25(OH)2D3. In addition, 1,25(OH)2D3 and phosphate stimulate and FGF23
inhibits PTH production creating a true phosphate feedback loop.