Streptozotocin-induced inhibiting the EL, PEI, ML and IL

Streptozotocin-induced diabetes in rodents appears to be the most
suitable animal model because it reflects the symptoms of diabetes in human (King, 2012) and it is
characterized by severe loss in body weight (Al-Roujeaie et al., 2016), and
this is also reflected in the present study. The decreases in body and testis
weight in diabetic rats showed the loss or degradation of structural proteins
due to diabetes and a significant reduction in the serum levels of
the main androgenic hormone, testosterone (Roy
et al., 2014). NG treatment enhanced the testicular weight.
Recently, Al-Roujeaie and his colleagues (2016) reported
that, rutin a phenolic compound enhanced the testicular weight of STZ-induced
diabetic rats and enhanced the sexual behavioral activity. This may consider
that phenolic compounds have ability to enhance the testicular weight which
further justified with present results.

 

Epidemiological studies showed the higher prevalence of severe ED
in diabetic men compared to normal healthy males (Maiorino et al., 2014; Saenz
et al., 2005). Experimentally-induced diabetic models are well-established to
elaborate the mechanism of diabetic-induced ED and also a recommended model for
establishing the beneficial effect of any new compound against diabetes ED
(Hirata et al., 2009; Li et al., 2016). In present study, sever sexual
impairment was found in STZ-induced diabetic rat by inhibiting the EL, PEI, ML
and IL latencies and increasing the MF and IF frequencies.  Our observations are in agreement with
earlier reports showed fewer in sexual behaviors of diabetic animals compared
controls (Scarano et al., 2006; De et al., 2016). In NG supplemented diabetic
rats, we found improvement in all the behavioral parameters that suggests the
drug produces beneficial effect in one of the diabetic-induced complication. It
is well established that the testosterone levels decreases in diabetic
conditions. However, this factor alone does not appear responsible for changes
in mating behavior as testosterone replacement did not reverse the adverse
effects of diabetes on sexual behavior. While STZ-induced sexual dysfunction
might be due to reduced testosterone responsiveness, it seems likely that ED in
the diabetic state results from direct or indirect action of insulin and/or
glucose on the adrenergic complex (Kniel et al., 1986). Our results also showed
significant decrease in serum testosterone levels compared to controls.

 

It is well known that penile erection depends on decreased penile
vascular resistance, which subsequently results in increased penile blood flow.
The action consists of the relaxation of the penile helicine arteries and the
cavernous smooth muscle that lines the cavernosal spaces (Andersson and Wagner,
1995). It has demonstrated that reduced vasorelaxation or increased
vasoconstriction under diabetic conditions accounts for the development of ED. As previously reported, the rats showed evidence of declining
erectile function following the STZ injection (Choi et al., 2012; Ari et al.,
1999; Italiano et al., 1993). When Choi and his colleagues (2012) compared to
the age-matched controls, the diabetic rats showed a significant decrease in
the ICP/MAP and AUC at the eight and twelve week assessments after the STZ
injection, respectively. Present results also showed similar decline in ICP/MAP
ratio in diabetic rats compared to normal healthy animals. The NG treatment
markedly improved in ICP/MAP ratio compared to untreated diabetic rats.   Furthermore, our results are more consistent
with those from Melman et al, (2009) which have reported significant changes in
ICP/MAP in as early as 1 month after STZ injection. The necessity for other
indices in addition to the ICP/MAP has been suggested by others. Earlier, Zhang
and his colleagues (2011) studied such phenolic compound QT on intracavernous
pressure (ICP) of STZ-induced diabetic rats and clearly documented the potential
effect of QT against ED.

 

It
is well established that the testosterone levels decreases in diabetic
conditions. Hyperglycemia-induced sexual dysfunction might be due to the
inhibition of testosterone, in diabetic state results from direct or indirect action
of insulin and/or glucose on the adrenergic complex (Kniel et al., 1986). Present results also showed
significant decrease in serum testosterone levels compared to controls. The NG
treatment markedly increased the inhibited testosterone levels in our diabetic
rats which showed potentials of NG against diabetic-induced ED. Earlier reports
documented that, diabetes causes inhibition in sperm count, motility and
viability (Scarano et
al., 2006), similar changes have noted in present study. The decreased
values of sperm numbers, motility and viability were significantly enhanced by
the NG treatment. It supports the beneficial effect of NG against
diabetic-induced ED.

 

The pathophysiologic mechanism of diabetic-induced ED
includes both the functional and structural impairment. Endothelial
dysfunction, coordination disorder of the relaxation and contraction of
corporal smooth muscles via the NO/cGMP pathway and the RhoA/Rho-kinase (ROCK)
pathway, autonomic neuropathy and apoptosis in corporal smooth muscles were
simultaneously happened. These processes do not work independently; diverse
combinations of each pathologic mechanism may manifest as DM progresses (Maiorino et al., 2014; Hadi and Suwaidi, 2007; Park et al., 2011;
Cho et al., 2011). Therefore, to prevent and
reinstate the endothelial function of the corpus cavernosum before progression
of the irreversible changes is the best treatment option to overcome diabetic-induced
erectile dysfunction. Indeed, the role of oxidative impairments in
the male reproductive system has been suggested in several experimental studies
(Agbaje et al., 2007; Shrilatha, and Muralidhara, 2007; Amaral
et al., 2006). Induction of lipid peroxidation
process and elevation of its biomarker like TBARS in the testicular tissues was
shown to have fundamental implications on testicular physiology and sperm
function (Agarwal and Said, 2005). Diabetes
mellitus is well known to be strongly correlated with oxidative stress leading
to production of free radicals and act as intercellular second messengers that
can induce activation downstream signaling of many molecules, including
transcription factors like nuclear factor kappa B (NF-?B). These NF-?B and
other transcription factors mediate vascular smooth muscle cell growth and
migration as well as the expression of pro-in?ammatory cytokines such as TNF-?,
IL-1?, and IL-6 (Touyz, 2004). These elevated pro-in?ammatory mediators
antagonize insulin action because of their ability to augment insulin receptor
substrate phosphorylation, leading to insulin resistance (Emanuelli et al., 2000; Senn et al., 2003). Therefore, attenuation of free radical
induced NF-?B translocation and ameliorating oxidative stress in diabetic rats
explains an associative relationship between the in?ammatory cytokines and DM.
In the present study, also found an elevation in the levels of pro-inflammatory
and oxidative stress biomarkers. Such as TNF-?, IL-1? and IL-6 were markedly
elevated in the diabetic group of animals. NG treatment to diabetic rats found
markedly inhibited the pro-inflammatory biomarkers. These findings show the
anti-inflammatory potential of NG which earlier, Lin
and Lin, (2011), reported the anti-inflammatory effect NG was
in primary mouse splenocytes in the absence or presence of lipopolysaccharide
(LPS) and it showed strong anti-inflammatory activity. In
addition, a beneficial systemic effect of NG on diabetic rats observed by
lowering fasting glucose and enhanced insulin levels in the serum of diabetic
rats. Similar systemic effects of NG on experimentally induced diabetes were
reported in earlier studies also (Hasanein and Fazeli, 2014; Annadurai et al.,
2012; Al-rejaie et al., 2015).

 

In
present study, cGMP levels in penile tissues of diabetic rats were
significantly inhibited. Similar cGMP inhibition was seen earlier in experimentally-induced
diabetic animal’s penile tissue (Yang et al., 2013; Yang et al., 2008). Indeed,
the role of oxidative impairments in the male reproductive
system has been suggested in several experimental studies (Agbaje et al., 2007; Amaral et al., 2006; Shrilatha
and Muralidhara, 2007). It is known that hyperglycemia induced increases in the production
of glycation end-products, reactive oxygen and nitrogen species impair nitric
oxide bioavailability and affect penile tissue, leading to changes in
endothelium-dependent vasorelaxation mechanisms (Newsholme et al., 2007;
Agarwal et al., 2006). Adenoviral
gene transfer of EC-SOD in vivo can reduce corporal superoxide anion levels and
raise cavernosal cGMP levels by increasing NO bioavailability thus restoring
erectile function in the STZ-diabetic rat (Bivalacqua et al., 2005b). The
present study determined TBARS and GSH levels and SOD, CAT, GST and GPx
activities as a marker for oxidative stress in testicular cells. Decreased GSH
levels, SOD, CAT, GST and GPx activities and elevated levels of TBARS were
found in STZ-diabetic rats compared with that in normal controls. In addition,
this abnormality in diabetic rats was significantly restored by NG treatment in
dose dependent manner. Earlier reports revealed that NG has
antioxidant potentials (Jagetia and
Reddy, 2002; Al-Rejaie et al., 2015). This suggests that NG treatment could
improve ED in diabetic rats partly by restoring the enzymatic activities and
inhibiting oxidative stress in testicular cells.

 

In
summary, we found that diabetic rats exhibited decreased sexual performance,
ICP levels and ICP/MAP ratio, sperm count inhibition with low motility,
viability, reduced levels of enzymatic activities including SOD, CAT, GST and
GPx, as well as elevated levels of TBARS and inhibited GSH levels in testicular
cells. Treatment with NG markedly corrected these diabetic-induced changes in
mostly dose dependent manner. Finally, could conclude that NG supplementation
may improve the diabetic-induced testicular oxidative stress, inflammation and
that can make improvement in sexual performance. Further preclinical research
into the utility of NG treatment may indicate its usefulness as a valuable
therapeutic approach in ED.