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[A1CR]

[posted on behalf of CRON4healthyfuture; 2003-07-03]

Free radicals protect neurons; Antioxidants abolish effect

Wake Forest University School of Medicine has produced an interesting
little study.

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"Additionally, generation of reactive oxygen species was observed in
response to diazoxide, assessed using the oxidation-sensitive dye
hydroethidine, and this effect was abolished by antioxidants, catalase, and
a superoxide dismutase mimetic, M40401."

"Our findings demonstrate that opening of mK(ATP) by diazoxide identifies a
delayed preconditioning effect that is protective against two types of
injury in astrocytes and that diazoxide may deliver protection via
mitochondrial depolarization, free radical production, and PKC activation."

=-=-=-=-=-=-=-=-=-=-=--

J Neurosci Res. 2003 Jul 15;73(2):206-214. Related Articles, Links

Diazoxide pretreatment induces delayed preconditioning in astrocytes
against oxygen glucose deprivation and hydrogen peroxide-induced toxicity.

Rajapakse N, Kis B, Horiguchi T, Snipes J, Busija D.

Department of Physiology and Pharmacology, Wake Forest University School of
Medicine, Winston-Salem, North Carolina.

Recent studies suggest that activation of mitochondrial ATP-sensitive
potassium channels (mK(ATP)) with diazoxide can protect neurons against
ischemic stress. However, it is not yet known whether astrocytes, which are
more resilient against ischemia, respond similarly to diazoxide. We exposed
cultured astrocytes to oxygen-glucose deprivation (OGD) or hydrogen
peroxide (H(2)O(2)) with or without pretreatment with the mK(ATP) opener
diazoxide. Marked decreases in astrocyte viability were evident after 9 and
12 hr of OGD [76% +/- 3% (n = 50) and 60% +/- 1% (n = 50)] and 400 and 600
&mgr;M H(2)O(2) [40% +/- 2% (n = 16) and 25% +/- 2% (n = 16)],
respectively, compared with no treatment (100% +/- 1%). Diazoxide treatment
(3 days of sequential application) dramatically reversed the negative
effects of OGD and H(2)O(2), resulting in complete blockade of astrocyte
cell death. Effects of diazoxide were blocked by the mK(ATP) blocker 5-
hydroxydecanoic acid (5-HD). Furthermore, incubation of astrocytes with
diazoxide resulted in loss of mitochondrial membrane potential monitored by
tetramethylrhodamineethylester fluorescence. Additionally, generation of
reactive oxygen species was observed in response to diazoxide, assessed
using the oxidation-sensitive dye hydroethidine, and this effect was
abolished by antioxidants, catalase, and a superoxide dismutase mimetic,
M40401. Finally, diazoxide increased the protein level of phosphorylated
protein kinase C (PKC) revealed by immunoblot analysis. Our findings
demonstrate that opening of mK(ATP) by diazoxide identifies a delayed
preconditioning effect that is protective against two types of injury in
astrocytes and that diazoxide may deliver protection via mitochondrial
depolarization, free radical production, and PKC activation. Copyright 2003
Wiley-Liss, Inc.

PMID: 12836163 [PubMed - as supplied by publisher]

[MR]

CRON4healthyfuture, what justification do you have for your subject line, above?
Let's look at this. The abstract says that "recent studies suggest that
activation of mitochondrial ATP-sensitive potassium channels (mK(ATP))
with diazoxide can protect neurons against ischemic stress"; it
confirms this with the finding that the protective "Effects of
diazoxide were blocked by the mK(ATP) blocker". And, yes, it ALSO found
that " Additionally, generation of reactive oxygen species was observed
in response to diazoxide" -- but it does not assert that this ROS
induction is itself the cause of diazoxide's protective effect. And
while it found that "this effect [ie, 'generation of reactive oxygen
species was observed in response to diazoxide'] was abolished by
antioxidants", it doesn't connect this to any loss of neuroprotection.

Now, I wouldn't be surprised if they were to find this, as they are,
after all, asserting delayed preconditioning. But surely we can't take
the subject heading as an accurate summary of the abstract.

And, of course, even if they DID find this, it would hardly justify the
subject line -- since (after all) the very thing against which the drug
is here shown to protect is ROS damage. Further, "incubation of
astrocytes with diazoxide resulted in loss of mitochondrial membrane
potential"; surely you aren't suggesting that this (or something like
it) is something in which we should be interested as an intervention?


A CRONie wrote:
> >
>> > > CRON4healthyfuture, the paper cites SOD and CAT mimetics. Do you know such
>> > > substances?
> >
> > I don't know of any.

But the paper mentions the one used by name: "a superoxide dismutase
mimetic, M40401". This is MetaPhore's mimetic; the Buck Institute is
experimenting with another family of SOD/CAT mimetics, the EUK
compounds. Plenty of info on PubMed, and some in th eArchives or on sci.l-e.

> > Maybe some of those "spin-trap" reagents

But if they were spin traps, they wouldn't be SOD/CAT mimetics, would
they?

> > that still
> > haven't extended the life of organisms with any substantive degree of
> > complexity?

Um, there are at least 2 reports of spin traps extending the lives of
lab rodents. What there AREN'T, however, are demonstrations of a robust,
CR-like retardation of aging & consequent extension of MAX LS -- as one
would predict from, say, MiFRA, were one familiar therewith.

-MR

> > J Neurosci Res. 2003 Jul 15;73(2):206-214. Related Articles, Links
> >
> > Diazoxide pretreatment induces delayed preconditioning in astrocytes
> > against oxygen glucose deprivation and hydrogen peroxide-induced toxicity.
> >
> > Rajapakse N, Kis B, Horiguchi T, Snipes J, Busija D.
> >
> > Department of Physiology and Pharmacology, Wake Forest University School of
> > Medicine, Winston-Salem, North Carolina.
> >
> > Recent studies suggest that activation of mitochondrial ATP-sensitive
> > potassium channels (mK(ATP)) with diazoxide can protect neurons against
> > ischemic stress. However, it is not yet known whether astrocytes, which are
> > more resilient against ischemia, respond similarly to diazoxide. We exposed
> > cultured astrocytes to oxygen-glucose deprivation (OGD) or hydrogen
> > peroxide (H(2)O(2)) with or without pretreatment with the mK(ATP) opener
> > diazoxide. Marked decreases in astrocyte viability were evident after 9 and
> > 12 hr of OGD [76% +/- 3% (n = 50) and 60% +/- 1% (n = 50)] and 400 and 600
> > &mgr;M H(2)O(2) [40% +/- 2% (n = 16) and 25% +/- 2% (n = 16)],
> > respectively, compared with no treatment (100% +/- 1%). Diazoxide treatment
> > (3 days of sequential application) dramatically reversed the negative
> > effects of OGD and H(2)O(2), resulting in complete blockade of astrocyte
> > cell death. Effects of diazoxide were blocked by the mK(ATP) blocker 5-
> > hydroxydecanoic acid (5-HD). Furthermore, incubation of astrocytes with
> > diazoxide resulted in loss of mitochondrial membrane potential monitored by
> > tetramethylrhodamineethylester fluorescence. Additionally, generation of
> > reactive oxygen species was observed in response to diazoxide, assessed
> > using the oxidation-sensitive dye hydroethidine, and this effect was
> > abolished by antioxidants, catalase, and a superoxide dismutase mimetic,
> > M40401. Finally, diazoxide increased the protein level of phosphorylated
> > protein kinase C (PKC) revealed by immunoblot analysis. Our findings
> > demonstrate that opening of mK(ATP) by diazoxide identifies a delayed
> > preconditioning effect that is protective against two types of injury in
> > astrocytes and that diazoxide may deliver protection via mitochondrial
> > depolarization, free radical production, and PKC activation. Copyright 2003
> > Wiley-Liss, Inc.
> >
> > PMID: 12836163 [PubMed - as supplied by publisher]
> >
> > =-=-=-=-=-=--=