synthesis of vitamin d - hot topic..



Vitamin D generated by sunlight may help protect the
skin from cellular damage, including damage caused by
sunlight itself, suggests a new study published in
this week's Nature Immunology. The researchers found
that dendritic cells can convert vitamin D3 --
generated under the skin by sunlight -- into its
active hormonal form, and induce T cells to migrate to
the skin. 

"It's a new action for a chemical we've known to be
present for a long time," said Clay Cockerell, a
dermatologist at the University of Texas Southwestern
Medical Center at Dallas, who was not involved in the
study. "We may eventually find that [the T cell
response] is protective in some way against skin
cancer." 

However, this does not mean that more time in the sun
is good for the skin, Cockerell stressed. On the
contrary, he said, the study implies that excessive
sun exposure could trigger a cutaneous inflammation --
providing yet another reason to stay out of the sun. 

Previous studies found that vitamin D3 generated under
the skin by the sun's ultraviolet rays can be
converted into its active form, calcitriol (1,25
dihydroxy-vitamin D3), by enzymes in the liver and
kidneys. The new study shows that human dendritic
cells could accomplish the same conversion without
involving the endocrine system at all. "We propose
that the whole thing could be happening in the skin
itself," first author Hekla Sigmundsdottir of the
Stanford University School of Medicine told The
Scientist. 

In 2004, research showed that vitamin A could induce T
cells to move to the gut. Since the receptors for
vitamins A and D are very similar in structure, and
the chemokines expressed by epithelial cells in the
gut and skin are also closely related, Sigmundsdottir
and her colleagues hypothesized a similar T cell
homing function for vitamin D, but with the skin as
the target. 

Using a chemotaxis assay on a co-culture of T and
dendritic cells, they showed that vitamin D did
attract T cells towards CCL27, a chemokine expressed
by skin cells. Indeed, vitamin D not only activated
the T cells' skin-homing receptor CCR10, it suppressed
the corresponding gut-homing receptor CCR9 that
vitamin A activates. "The two vitamins seem to compete
with each other," Sigmundsdottir noted. 

Vitamin D2, the primary nutritional form of the
prohormone, was much less effective in inducing CCR10
expression in T cells than vitamin D3, the sun-induced
version. "A little sunshine may be good for your
immune system," Sigmundsdottir concluded. "This is
what attracts T cells to the skin." 

This study adds to a long-standing debate between two
research groups: Vitamin D experts, some of whom who
argue some sun exposure may be beneficial, and
dermatologists (such as Cockerell) who generally
advise against any sun exposure, and recommend
supplements to meet the body's vitamin D requirements.
The new study determined, however, that the levels of
vitamin D needed to initiate a T cell response exceed
those found in normal serum, even when taking
supplements. "This suggests that UV production --
leading to the high local vitamin D levels -- is
necessary," said James Fleet of Purdue University in
West Lafayette, Ind., who studies nutrition and
vitamin D, but was not involved in the study. 

Fleet offered a possible compromise -- a topical
application of vitamin D, which would protect the skin
without putting it at risk from sunlight exposure.
(Fleet said he has no financial ties to companies
marketing topical vitamin D products.) Sigmundsdottir
acknowledged that topical vitamin D -- just like its
sun-induced counterpart -- might also be able to draw
T cells to the skin. That could perhaps explain why
topical vitamin D is effective against psoriasis and
other skin conditions, she added. 

Chandra Shekhar 


http://www.the-scientist.com/news/home/44290/


--- elan lior <[log in to unmask]> wrote:

> Dear Colleagues/ Friends,
>    
>   I am seeking examples and information on instances
> in nature where light affects matter, for a course
> in artifact design.
>    
>   These could be cases like the sunflower, or any
> other case where reciprocal relations between light
> and matter are evident, be it flora or fauna.
>    
>    
>   Any such or related Information would be greatly
> appreciated!
>   Thanks and Best wishes
>    
>   Elan
>    
> 
>        
> ---------------------------------
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