Diabetes type-2 accounts for almost 90% of the diabetes cases worldwide and among its complications is bladder dysfunction. We have previously shown that in a diabetes type-2 rat model of 14 days experimental period, antioxidants may be of value as an adjunct therapy [1]. In the present study we created a diabetes type-2 model in order to investigate oxidative stress-related alterations in the bladder in a period of 8 weeks. Additionally, the effects of antioxidants (taurine or resveratrol) or Rho kinase inhibitor (fasudil) treatment were examined in the diabetes-induced alterations in the bladder.

The diabetes mellitus type-2 that we created was a combination of a single dose of streptozotocin (STZ) with high fat diet. We used adult male rats at the age of 8 weeks old. Initially the animals were exposed to 12 h of fasting and subsequently they were injected STZ (40mg/kg) intraperitoneally (i.p.) once. Two days after the STZ injection and being subjected to 12h of fasting, the animals were tested for the induction of diabetes. Diabetes was induced to all animals. The next day, the animals were randomly separated into 4 groups and for 8 weeks they followed a high fat diet. One group received no treatment (DM group), another group received resveratrol i.p. (10mg/Kg; Resv group), the third one received taurine i.p. (1g/Kg; Tau group) and the fourth received fasudil i.p. (10mg/kg; Fas group). Age matched control animals were used and were fed with normal diet (Control group). Eight weeks later animals were sacrificed and bladders were processed for histological evaluation. The levels of glucose were measured and immunohistochemistry (IHC) was performed for oxidative stress markers and nerve growth factor (NGF), a key protein for bladder function.

The four diabetic groups had significantly lower body weight compared to the Control. The bladder weight was significantly higher in all diabetic groups compared to the Control group. DM group demonstrated significantly higher ratio of bladder weight to body weight compared to the Control, as well as the other three diabetic groups with treatment. The animals in Tau and Fas groups demonstrated significantly lower ratio bladder weight to body weight compared to the DM group. The blood glucose levels were significantly higher in all diabetic groups compared to the Control. Treatment with resveratrol, taurine or fasudil slightly decreased the blood glucose levels of the treatment groups but it did not reach a level of statistical significance compared to the DM group. The histological evaluation revealed a severe damage in the bladder tissue in the DM group such as atrophy of urothelial cells, increased collagen fibers in the smooth muscle area, abruption of the mucosa from the muscularis as well as edema in the transitional epithelium. Treatment with resveratrol, taurine or fasudil protected the bladder tissue and these alterations were recovered. In the DM group we observed moderate to strong expression of oxidative stress markers: a) malondialdehyde (MDA), b) 4-Hydroxynonenal (4-HNE) and c) DNA oxidative stress marker 8-deoxyguanosine (8-OHdG) as the IHC results indicated compared with the other four groups. Additionally, NGF was strongly expressed in the bladder tissue of the DM, group compared to the Control. Treatment with resveratrol, taurine or fasudil did not significantly alter this parameter.

Diabetes at a period of 2 months appears to significantly affect the bladder tissue by inducing a severe damage. Additionally, the diabetes-induced oxidative stress at this stage is highly expressed and present in the bladder. Treatment with antioxidants or Rho kinase inhibitor in the onset of diabetes appears to be of benefit for the bladder. Treatment with resveratrol, taurine or fasudil could significantly alter the histological damage. The decrease of oxidative stress in the bladder by the treatment is reflected also in the histology of the bladder which is profoundly improved compared to the no-treatment DM group. The elevation of oxidative stress which is induced by the diabetes has a direct and harmful effect in the bladder histology. Resveratrol has both anti-oxidant and anti-inflammatory effects among others and by enhancing the anti-oxidant capacity of the cells in the bladder could decrease the oxidative stress. In the same fashion, taurine has been proved to provide cytoprotection through its ability to inhibit MDA and advanced glycation end products. Additionally, taurine could amplify the antioxidant mechanisms of the bladder and by inhibiting lipid peroxidation could protect the bladder tissue. Fasudil has also been proved to have some antioxidant role by elevating the antioxidant enzymes activities [2] and by this way it could protect the bladder from the elevated oxidative stress induced by the diabetes. Adding all the above, we may say that it is possible to reverse the damage in the bladder tissue in diabetic animal models once the treatment is appropriate and on time. Our results indicate that all three treatments had a beneficial effect in the histological changes induced by the diabetes; hence a treatment with antioxidant properties may be of value for diabetic patients. Additionally, the expression and localization of lipid peroxidation and DNA oxidative damage in the bladder were significantly decreased by the resveratrol, taurine or Fasudil treatment compared to the no treated DM group. This further gives evidence that the diabetes-induced oxidative stress in the bladder is highly connected to the alterations in the bladder histology. Consequently, downregulation of oxidative stress levels can result in the improvement of bladder histology. Antioxidants did not have a significant effect on hyperglycemia, which implies that antioxidants cannot substitute the anti-diabetic medication, but mostly they could function as an additional treatment for diabetes-induced bladder dysfunction.

The results of the present study indicate that treatment with antioxidants may be of value as a supplementary therapy, for the histological changes in the bladder and as an inhibitor of diabetes-induced oxidative stress-related changes in the diabetes.

Tsounapi et al., In Vivo. 2019 Nov-Dec;33(6):1819-1826.
Ma et al., Clin. Exp. Pharmacol. Physiol., 2011; 38: 688-694