Re: Carotene [--Conversion--To-->] Vitamin A

[Guest guest]

> Does anyone know if the conversion of carotene to retinal/retinol

> occurs in any other tissues besides the intestine?

I don't know offhand, but have you tried scirus.com, the research

engine?

http://www.scirus.com/srsapp/

The first listing I got was a full text of this nasty rat study (nasty

because they got their SFA from hydrogenated soybean oil!). It seems

up your alley anyway, maybe not in this particular regard, I dunno.

No time to look to close now, sorry.

http://www.nutrition.org/cgi/content/full/128/10/1614

Deanna

[Guest guest]

On 9/30/05, yoginidd <hl@...> wrote:

>

> > Does anyone know if the conversion of carotene to retinal/retinol

> > occurs in any other tissues besides the intestine?

> The first listing I got was a full text of this nasty rat study (nasty

> because they got their SFA from hydrogenated soybean oil!). It seems

> up your alley anyway, maybe not in this particular regard, I dunno.

> No time to look to close now, sorry.

>

> http://www.nutrition.org/cgi/content/full/128/10/1614

Thanks, but that's not what I'm looking for. I'm looking for carotene

conversion in OTHER tissues, or even information on carotene storage.

I'm not asking anyone to do research. I'll look into it at some

point, but I wasn't sure if anyone had info offhand. I know Suze did

some carotene reading last year or the year before.

I think it will be difficult to find, since nearly everything indexed

will be about intestinal conversion, and you can't really enter a

keyword that will block those abstracts from popping up.

Chris

--

Statin Drugs Kill Your Brain

And Cause Transient Global Amnesia:

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[Guest guest]

Chris-

>Does anyone know if the conversion of carotene to retinal/retinol

>occurs in any other tissues besides the intestine?

I think the liver can perform the conversion too.

>>The dioxygenase activity has been found in several organs of rats. After

>>intestine, liver has the next highest activity (During et al. 1996). The

>>specific activity of the dioxygenase in liver was not enhanced by the

>>PUFA diet, whereas the total activity in the whole liver was enhanced by

>>the PUFA diet. This may be of no physiologic importance because -carotene

>>is not present at detectable level in liver unless rats are fed

>>pharmacologic levels of -carotene. However, if this response occurs in

>>humans, it might enhance the conversion of -carotene to vitamin A.

That's from http://www.nutrition.org/cgi/content/full/128/10/1614 which is

pretty interesting.

Ah, now I have confirmation. Very interesting.

>>The two objectives of this study were to investigate beta-carotene

>>15,15'-dioxygenase activity in human tissues and to determine the effect

>>of desferrioxamine on the dioxygenase activity. Two human in vitro models

>>were used: the TC7 clone of the intestinal cell line Caco-2 and small

>>intestinal mucosa preparations. beta-Carotene 15,15'-dioxygenase activity

>>in the small intestinal mucosa was (mean +/- SD) 97.4 +/- 39.8 pmol/h.mg

>>protein for five adults (44-89 y) and 20 pmol/h.mg for an infant (17

>>months). No activity was detected in adult stomach tissue. We report for

>>the first time the dioxygenase activity in human liver: 62 pmol/h.mg for

>>a normal adult liver and 7 pmol/h.mg for a liver exhibiting gross

>>pathology. The maximum capacity of beta-carotene cleavage in an adult was

>>estimated to be 12 mg/day (one fifth by small intestine and four fifths

>>by liver), assuming an optimal beta-carotene/retinal cleavage ratio of

>>1:2. The dioxygenase activity was decreased up to 80% with increasing

>>desferrioxamine concentrations in the two in vitro models.

>>Desferrioxamine was characterized as a noncompetitive inhibitor. In TC7

>>cells, the inhibitory effect of desferrioxamine was reversed by iron

>>addition, suggesting that this effect was related to the ability of

>>desferrioxamine to chelate iron, purported to be an obligate cofactor of

>>the enzyme. In conclusion, these data report the presence of

>>beta-carotene 15,15'-dioxygenase activity in human small intestine and

>>liver and demonstrate that desferrioxamine efficiently inhibits

>>intestinal beta-carotene cleavage in human tissues and cells.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve & db=PubMed & list_uids=1\

2031257 & dopt=Abstract

I'm actually pretty surprised to see the liver reported as the main

converter, since discussions of carotene conversion generally seem to focus

on the intestines. Admittedly it's not a subject I've researched heavily,

though, since I make sure to get plenty of preformed vitamin A in food.

-

[Guest guest]

,

> I'm actually pretty surprised to see the liver reported as the main

> converter, since discussions of carotene conversion generally seem to focus

> on the intestines. Admittedly it's not a subject I've researched heavily,

> though, since I make sure to get plenty of preformed vitamin A in food.

Isn't this why diabetics, especially can't convert beta carotene to A?

Don't remember particulars other than pancreatic insufficiency or

shutdown affects process through liver.

Wanita

[Guest guest]

Wanita-

>Isn't this why diabetics, especially can't convert beta carotene to A?

>Don't remember particulars other than pancreatic insufficiency or

>shutdown affects process through liver.

Actually, I don't know why diabetics have a harder time making the

conversion, and I just spent a little time searching the net and couldn't

find an explanation.

-

[Guest guest]

On 9/30/05, Idol <Idol@...> wrote:

> Wanita-

>

> >Isn't this why diabetics, especially can't convert beta carotene to A?

> >Don't remember particulars other than pancreatic insufficiency or

> >shutdown affects process through liver.

>

> Actually, I don't know why diabetics have a harder time making the

> conversion, and I just spent a little time searching the net and couldn't

> find an explanation.

>

> -

Not only diabetics

WHO Food Additives excerpt

http://www.inchem.org/documents/jecfa/jecmono/v06je15.htm

In man 30-90% of ingested beta-carotene is excreted in the faeces

and concomitant intake of fat does not improve absorption. Excessive

doses depress the Vitamin A activity of the absorbed fraction. Only

small amounts appear in the serum. Beta-carotene dissolved in oil is

much better absorbed, 10-41% for adults, 50-80% for children (Fraps &

Meinke, 1945).

Vitamin E is necessary to prevent enzymatic destruction and bile

acids are necessary for absorption (Wagner, 1962).

Other workers quote 11% absorption by adults and 2.6% by babies

of a dose of 20 mg carotene (Kübler, 1963).

The major fraction of absorbed beta-carotene passes unchanged

through the gut wall and reaches the liver via the portal system and

to a small extent via the lymphatics. Some beta-carotene is stored in

the liver but is never released as such, and some is converted to

Vitamin A in jejunum, liver, lung, muscle and serum and stored in the

liver as Vitamin A. Large doses lead to a rise in serum carotene and

subsequent deposition in organs and the horny layer of the skin

without necessarily raising the Vitamin A serum level (Zbinden &

Studer, 1958).

Gastrointestinal and liver and renal disease, diabetes mellitus

and phosphor poisoning reduce the conversion to Vitamin A and

myxoedema blocks conversion. Infants and small children have a smaller

capacity for this conversion (Wagner, 1962).

Beta-carotene is transmitted in milk. In infants a single

administration of 20 mg of beta-carotene in milk produces a rise in

the beta-carotene blood level, peaking in 24 hours and a rise in the

Vitamin A ester blood level but practically no change in the Vitamin A

alcohol blood level (Auckland, 1952).

Wanita

[Guest guest]

On 9/30/05, Wanita Sears <wanita.sears@...> wrote:

> Not only diabetics

>

> WHO Food Additives excerpt

> http://www.inchem.org/documents/jecfa/jecmono/v06je15.htm

Thanks! This looks like a really useful excerpt. (In spite of being

from the WHO!)

, interesting study, thanks... surprising to me as well. My

biochem book doesn't even mention a conversion other than the liver.

What I'm trying to figure out is how easily the body can convert

carotene to A as needed. The WHO extract looks like a really

promising lead for investigating this issue.

Chris

--

Statin Drugs Kill Your Brain

And Cause Transient Global Amnesia:

http://www.cholesterol-and-health.com/Statin-Drugs-Side-Effects.html

[Guest guest]

Chris-

>, interesting study, thanks... surprising to me as well. My

>biochem book doesn't even mention a conversion other than the liver.

Other than the liver, or other than the intestine? I generally see the

enzyme referred to as an intestinal enzyme.

>What I'm trying to figure out is how easily the body can convert

>carotene to A as needed. The WHO extract looks like a really

>promising lead for investigating this issue.

I'm guessing, particularly from Wanita's excellent post, that it's not a

very useful as-needed source of vitamin A at all.

-

[Guest guest]

On 10/3/05, Idol <Idol@...> wrote:

> Chris-

>

> >, interesting study, thanks... surprising to me as well. My

> >biochem book doesn't even mention a conversion other than the liver.

>

> Other than the liver, or other than the intestine? I generally see the

> enzyme referred to as an intestinal enzyme.

Oops... other than the intestine.

> >What I'm trying to figure out is how easily the body can convert

> >carotene to A as needed. The WHO extract looks like a really

> >promising lead for investigating this issue.

>

> I'm guessing, particularly from Wanita's excellent post, that it's not a

> very useful as-needed source of vitamin A at all.

Right. What they veggie-lovers say about carotenes is really what's

true about retinol. The body uses retinol to convert into the various

active forms as needed, not carotenes. There's as much mythology

about vitamin A as there is about cholesterol, I think.

Chris

--

Statin Drugs Kill Your Brain

And Cause Transient Global Amnesia:

http://www.cholesterol-and-health.com/Statin-Drugs-Side-Effects.html