Long-‐life supplementation with atenolol…
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Docosahexahenoic acid (22:6n-‐3) has six double bonds and consequently has
five bis-‐allylic hydrogens per chain, and is 320-‐times more susceptible to ROS attack
than oleic acid (18:1n-‐9), which is consistent with the strong decrease in secondary
protein lipoperoxidation observed (lower MDAL and CML in AT-‐treated animals). In
our case, a most relevant factor that contributed to decrease the DBI and PI seems to
be the strong decrease in β-‐peroxisomal lipoxidation (estimated as the 22:6n-‐
3/24:6n-‐3 ratio) in the atenolol group. The main function of this process seems to be
the partial degradation of very-‐long chain fatty acids, producing chain-‐shortened
acyl-‐CoAs, acetyl-‐CoA and NADH, which may exit from peroxisomes via pores that
permit the influx of substrates and efflux of products of β-‐oxidation. These substrates
go back to the mitochondria to complete the fatty acid oxidation process (47).
The decrease in DBI and PI confers higher resistance of membranes to lipid
peroxidation and lowers lipoxidation-‐dependent damage to macromolecules, like
proteins, and (likely) mtDNA. The long-‐term atenolol treatment was able to very
strongly and significantly decrease protein oxidation (GSA and AASA), glycoxidation
(CEL and CML) and lipoxidation (CML and MDAL) markers in both tissues, except for
CEL in SKM which also showed a trend to decrease that did not reach statistical
significance. Aging is known to increase protein oxidation in association with a
functional decline of proteasome activity (48) whereas decreases in protein oxidation
and increases in the catabolism of modified proteins have been described in
experimental modifications that extend longevity, like dietary restriction (49) and
methionine restriction (50, 33) even when applied to old animals (51). The
decreased fatty acid unsaturation degree most likely leads to a lower lipid-‐derived
secondary free radical formation, decreased specific protein oxidation and damage to
other macromolecules (52) which was reflected, in our case, in the decrease in
protein oxidation, glycoxidation and lipoxidation, as well as, in the case of the heart,
mtDNA oxidative damage.
The molecular mechanism suggested to explain these changes could be the
following: binding of hormones and neurotransmitters to β-‐adrenergic receptors
activates adenylate cyclase (AC) increasing cyclic adenosine monophosphate (cAMP)
and then protein kinase A (PKA). PKA inhibits Raf-‐1, which, in turn, stimulates p-‐MEK
and p-‐ERK. p-‐ERK enters the nucleus, where it can modify gene expression through
the action of many different molecules. Because AC stimulates PKA, and PKA inhibits
Raf-‐1, an increase in the Raf/MEK/ERK pathway is expected when AC is lacking or β-‐
adrenergic receptors are blocked. In agreement with this, an increase in p-‐MEK and
p-‐ERK was observed in tissues of AC5KO mice, including the heart (1). The same
happens in our pharmacological model of β-‐adrenergic blockade by atenolol, in
which p-‐ERK levels were increased both at short-‐term in the mice heart (2), as well
as in the present study after long-‐life AT treatment in heart and SKM mitochondria.
This protein can enter the nucleus and activate different transcription factors,
