90 6 ART for Antiaging
6.2.2.8 Covalent ART-Heme Conjugation and Synchronous COX
Induction
Until currently, no direct evidence informs how CR elicits ROS and induces
antioxidant enzymes. Considering the previous results demonstrating that ART
can alkylate the heme moiety and hence inactivate heme-harboring proteins, we
proposed that ART may covalently conjugate COX and permanently inhibit its
activity, which in turn induces COX and increases its activity. Indeed, we found
that ART really increases yeast COX activity in different concentrations and incu-
bated for a varying duration. This finding might be well interpreted by an induc-
tion of Cox after ART conjugation to COX.
As our finding, both heme and ART-heme adducts increase after treatment for
3 h with low-dose ART, but both decrease by high-dose ART. The increase of
A 415 (heme) and A 476 (ART-heme adducts) readings following exposure of yeast
to low-dose ART for 3 h means de novo hemoprotein biosynthesis, and the sub-
sequent decline of both A 415 and A 476 under a low-does ART indicates hemopro-
tein degradation. In high-dose ART groups, neither heme induction nor ART-heme
conjugation were observed, probably because yeast cells are killed by an overdose
of ART (Wang et al. 2015a).
Upon the inhibition of COX activity, it should be expected to detect the
increase of ART-induced Cox1 expression during the initial phase. The microarray
data indicated that all COX components become downregulated after exposure to
ART for only 1 h. Accordingly, mitochondrial respiratory chain genes responsi-
ble for oxidative phosphorylation were also found to be globally downregulated.
Therefore, ART can functionally mimic CR-triggered NO to enhance ROS pro-
duction and induce antioxidant responses, which may be the consequence of mito-
chondrial biogenesis or compensatory enhancement of mitochondrial function.
Accelerated ROS generation may be attributed to COX inhibition by NO as well
as ART, whereas reduced ROS emission can be the result of antioxidant induction
upon mitochondrial enhancement.
6.3.3 Discussion
CR is convinced in delaying aging/prolonging lifespan among examined eukary-
otes, either in yeast (Skinner and Lin 2010 ) or in mice (Nisoli et al. 2003 ). At
present, how can CR exert beneficial effects on health and lifespan remains
debating, and some conclusions about the mechanism underlying CR-driven lon-
gevity are apparently controversial (Piper et al. 2011 ). An implication of mito-
chondrial biogenesis in CR-mediated lifespan extension was suggested in last
decade (Nisoli et al. 2003 ), but challenges to it are frequently raised (Hancock
et al. 2011 ; Lanza et al. 2012 ; Miller et al. 2012 ). Mitochondrial biogenesis
is characterized by an enhanced respiratory activity, which means more glu-
cose should be consumed and much ATP produced for compensating energy