Cardiovascular Journal of Africa: Vol 28 No 6 (November/December 2017)

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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 28, No 6, November/December 2017 394 AFRICA
Table 4 summarises NO changes in the heart, liver and
kidney tissue supernatants of rats administered ILO and SIL
in myocardial ischaemia–reperfusion. There was a negative
correlation between serum NO (r = –0.73; p < 0.005) and serum
irisin levels (r = –0.52; p < 0.005) of the groups, and positive
correlations between the serum and tissue NO levels (r = 0.64; p <
0.005) and myocardial infarct markers [CK (r = 0.49; p < 0.005),
CKMB (r = 0.56; p < 0.005) and troponin I (r = 0.66; p < 0.005)].
These correlations either disappeared or were reversed with the
administration of ILO and SIL.
Discussion
Disruption of the arterial or venous blood flow in biological
systems (hypoxia) causes inadequate perfusion of the organ
or tissues, resulting in generalised cell injury or cell death.5
Ischaemia–reperfusion injury in the heart tissue causesmyocardial
stunning, reperfusion arrhythmias, necrosis in the myocytes, as
well as coronary endothelial and microvascular dysfunction.29
Ischaemia–reperfusion injury in the heart also affects the
renal tissues,20 and the hepatic tissues where gluconeogenesis
takes place.21 In this study, ischaemia was induced by left
coronary artery ligation, and the roles of ILO and SIL in tissue
reperfusion, and their effect on the fate of irisin, which functions
in heat regulation, were examined.
The induction of ischaemia by left coronary artery ligation
was confirmed by Masson’s trichrome staining of the heart
tissue. Light microscopy of the cells showed that the control
heart tissues had a normal appearance, while the MI group was
characterised by an increase in inflammatory cells, congestion,
impairment of tissue integrity and oedema. This resulted from the
interruption of ATP production. However, since ATP catabolism
continues, AMP and adenosine were formed from ATP. The
depletion of cellular energy reserves and the accumulation
of toxic metabolites due to ischaemia led to an increase in
inflammatory cells, congestion, and finally cell death.35 The
presence of ischaemia was also confirmed by the levels of CK,
CKMB and troponin I, which increased dramatically during
myocardial ischaemia, compared to the control levels. The levels
of CK, CKMB and troponin I in our study were similar to those
found in previous animal studies, where myocardial ischaemia
was induced with isoproterenol.35
When irisin levels in the ischaemic groups were compared to
those in the control group, irisin was statistically significantly
lower in the serum, and individual or combined administration
of ILO and SIL restored irisin serum concentrations. The
ischaemia-associated decrease in irisin concentrations in
biological systems may be attributed to increased demand for
ATP in the tissues, as irisin elevates the levels of uncoupling
proteins, which in turn causes increased heat production in the
cells, rather than increased ATP production.18,19,36
However, there is a need for much greater amounts of ATP
to reduce the amount of cell injury and death resulting from
hypoxia.17 Therefore the heart, liver and kidney tissues may have
limited their irisin production for the purposes of encouraging
cells to produce ATP instead of heat. The decrease in ATP levels
during this period indicates that the increase in inflammatory
cells, congestion, impairment of tissue integrity and oedema
provoked the development of rigor-type contracture.35 In the
case of ischaemia-associated coronary endothelial dysfunction,
the vasodilator response is reduced because the increase in
endothelin-1 level, a potent vasoconstrictor, which is formed in
the process, causes vasoconstriction and leads to a decrease in
blood flow.37
In this context, administration of ILO and SIL to the rats
individually or in combination enhanced the blood flow by
vasodilatation, ensuring re-oxygenation of the cells, and hence
increased irisin synthesis. Energy production of the cells during
re-oxygenation is probably kept under strict control by irisin
(considered as the decisive molecule at the stage of heat or ATP
production) via regulation of the flow of oxygen in the electron
transport chain in the mitochondrial organ, depending on the
need for ATP. Otherwise, the entry of high doses of molecular
oxygen into the cell would increase free oxygen radical (FOR)
derivatives and cause reperfusion damage.38 This is because
about 1–4% of the oxygen intake is used for superoxide anion
production and about 20% of the produced superoxide anions is
channelled to the cells. This is believed to be directly related to
the production of energy molecules or ATP by the cells.
Limited irisin production in biological tissues causes a
reduction in serum irisin levels. Given that the source of serum
irisin is biological tissue, the decrease in irisin synthesis by the
tissues is reflected in serum irisin levels. These data not only
support the finding of reduced irisin levels in MI induced by
ISO,35 but also are consistent with the MI results provided by
Aydin et al. in saliva, and by Emanuele et al.39,40
In our study, ischaemia induced by left coronary artery
ligation caused ischaemia–reperfusion injury, not only in the
heart, but also in the liver and kidneys. Ischaemic damage
inflicted on the liver and kidneys, as in damage to the heart
tissue, was reduced by the administration of ILO or SIL, or their
combination, relative to the group not administered any drug,
and the administration of these drugs also elevated the irisin
levels in these tissues. ILO is thought to restore ischaemic injury
in the liver and kidneys via its anti-platelet, cytoprotective and
fibrinolytic action, and vasodilator effect, while SIL, a specific
phosphodiesterase type 5 (PDE 5) inhibitor, is believed to reduce
ischaemic injury via its vasodilator effect mediated by NO.41
Administration of SIL alone was found to be more effective in
reducing ischaemic injury than ILO alone or the combination of
both agents. The possible mechanism underlying the potency of
SIL is that since it uses NO, the NO produced during ischaemia
is reduced in the presence of SIL. Had NO not been depleted or
reduced, it would have combined with the superoxide (O2
-) radical
produced during reperfusion to form peroxynitrite (ONOO-), a
toxic oxygen metabolite, and the resulting ONOO- could have
caused damage to the tissues.15,16 Therefore, a possible reason why
Table 4. Nitric oxide (μmol/g wet weight) changes in the heart, hepatic
and kidney tissue supernatants of rats administered iloprost (ILO)
and sildenafil (SIL) in myocardial ischaemia–reperfusion (MI)
Heart Liver Kidney
Control 76 ± 17 54 ± 11 24 ± 7
ILO 85 ± 16 61 ± 13 32 ± 8
SIL 69 ± 14 48 ± 9 19 ± 6
ILO + SIL 71 ± 12 56 ± 10 22 ± 5
MI 248 ± 46a 125 ± 29a 106 ± 19a
MI + ILO 186 ± 32b 82 ± 18b 73 ± 18b
MI + SIL 106 ± 18b 64 ± 17b 41 ± 9 b
MI + ILO + SIL 119 ± 21b 77 ± 17b 59 ± 10b
aIn comparison with the control group, bin comparison with the MI group, p < 0.05.