DM is a metabolic disease characterized by the permanent destruction of pancreatic beta cells. This destruction causes degranulation and a decrease in insulin secretion . This study aimed to evaluate the antioxidant and anti-inflammatory properties of moss and quercetin administered orally for treatment, and the effects on the liver under light microscopy in rats with diabetes induced by STZ, including the changes in histopathological and biochemical parameters in the literature. In addition, the aim was to provide a different perspective on diabetes with the combined treatment option and to reveal alternative herbal products that will be more effective and have nutritional and medicinal properties that will enrich the quality of life of diabetes patients. There is no study investigating the histological and biochemical effects of STZ on the liver in rats with diabetes previously induced. This study showed that high blood glucose levels, dyslipidemia, inflammation in the liver, and apoptosis could be prevented. The effects of diabetes on the liver include ultrastructural changes such as hypertrophy of hepatocytes and the appearance of autophagic vacuoles. The hepatocyte nucleus is usually enlarged, sometimes with irregular contours and an appearance containing intranuclear inclusions. In the diabetic group, cytoplasmic changes are observed as decreased glycogen granules and an underdeveloped rough endoplasmic reticulum . In our study, diffuse degeneration due to vacuolization and necrosis was observed in hepatocytes of diabetic rats under light microscopy. No increase in perisinusoidal fibrous and collagenous material was observed in any group. In a previous study, it was reported that fibrosis was observed in the diabetic liver. However, some authors claimed that fibrosis in the diabetic liver is not directly related to diabetes but due to liver vascular anomalies and genetic predisposition in the studied rat lineage . Fibrosis was not observed in the liver findings in our study. When the degenerative picture in which cytoplasmic vacuolization became widespread is examined, it was in parallel with the results reported in other studies.
In the present study, diabetic rats exhibited a significant increase in blood glucose with a substantial decrease in serum levels of C-peptide. The combination of moss and quercetin returned these parameters to average values, reflecting its potential effect on glucose homeostasis. The administration of moss alone caused a significant decrease in glucose level, while the C-peptide level significantly increased. When quercetin was given alone, it produced a considerable effect, as shown by the reduction in glucose level and the increase in serum levels of C-peptide . Quercetin also increases blood glucose uptake by hepatic cells by activating hexokinase and adenosine monophosphate-activated protein kinase . In addition, quercetin was reported to lower blood sugar by increasing the proliferation of pancreatic β-cells in STZ-induced diabetic rats .
This study showed that quercetin and moss extract, which are plant-derived compounds, have a synergistic antidiabetic effect in diabetes by improving glucose metabolism enzymes. Therefore, we used this model to develop DM in Wistar rats. To overcome the hyperglycemic effect in rats, they were treated with 50 mg/kg Q and 100 mg/kg HS doses. The treatment doses were determined based on body mass index and the available literature about both compounds. The compounds were therapeutically effective at reducing the hyperglycemic effect in STZ-induced diabetic rats. Mukhopadhyay and Prajapati noted that quercetin could reduce hyperglycemia of pancreatic islets to release enough insulin. It is known to strengthen the pancreatic islets of Langerhans to produce flavonoids, insulin, and glucagon and secrete them into the bloodstream .
The liver is a central metabolic organ and is exposed to reactive oxygen species formed due to oxidative damage caused by diabetes. For this reason, it was suggested that apoptosis occurs in hepatocytes and endothelial cells . In diabetes studies using STZ, necrosis in hepatocytes, inflammatory cell infiltration, lipidosis, dilatation in sinusoids , and disorders in portal spaces are reported findings. In the present study, similar results were observed in rats in the diabetes group. These findings significantly reduced with treatment using moss and quercetin.
In a study administering quercetin to male rats with experimental diabetes mellitus induced with STZ, quercetin played a stabilizing role in blood sugar control . In another study examining the effect of quercetin on protein and lipid damage in experimental diabetic rats, quercetin did not have a practical protective feature against protein damage caused by DM but had a protective role against lipid peroxidation. In a study administering quercetin to rats, it prevented the formation of free oxygen radicals in cells and protected against lipid peroxidation . In addition to studies that reporting that quercetin administration inhibited lipid peroxidation, there are also studies reporting it reduced lipid peroxidation in human lymphocytes .
Studies showed that low-grade inflammation is associated with an increased risk of developing type 2 diabetes mellitus. In addition, chronic subclinical inflammation is a factor in the development of insulin resistance, a vital feature of metabolic syndrome [3, 4]. Throughout a trial, Wong et al. studied the effect on the regulation of glucose metabolism and body weight by feeding IFN-γ-deficient mice with standard low-fat mouse chow and observed reduced body weight was associated with negative energy balance, glucose tolerance, and hepatic insulin sensitivity in mice. The researchers stated that IFN-γ plays a vital role in regulating glucose metabolism and weight gain . Obese IFN-γ-knockout mice were found to exhibit milder insulin resistance, reduced adipocyte size, and M2-related cytokine expression in adipose tissue compared to healthy mice, and IFN-γ was associated with glucose homeostasis, adipogenesis, and cytokine expression in adipose tissue . These studies show that the IFN-γ level, which is essential in terms of glucose tolerance and hepatic insulin sensitivity, was significantly different between the diabetic group in our research and the treatment groups. IFN-γ, which was highest in the diabetes group, decreased in the HS + Q group. The survey conducted by Pradhan et al. showed that increased inflammatory biomarkers are associated with the development of type 2 diabetes and insulin resistance . Although the mechanism by which chronic inflammation stimulates the development of type 2 diabetes mellitus is not fully understood, it was shown that adipose tissue can synthesize tumor necrosis factors, major proinflammatory cytokines such as interleukin-1, and interleukin-6 and that the inflammatory process is associated with biomarkers for body fat mass. This suggests that activated innate immunity and inflammation are essential biological factors in the pathogenesis of diabetes mellitus and complications of type 2 diabetes mellitus . Pitsavos et al. recruited 3042 subjects (1514 men and 1528 women) in a randomized controlled trial to investigate the survival impact of type 2 diabetes inflammatory biomarkers. The authors reported an association between low-grade markers of inflammation and glycemic control parameters, independent of demographic, clinical, and lifestyle indices such as dietary factors.
Studies by Tanaka et al. on the level of 8-hydroxy-deoxyguanosine-modified proteins in GK-rats and Tucker diabetic rats, respectively, showed that hyperglycemia was the main potential factor for oxidative stress in pancreatic beta cells, and glucose-induced oxidative stress explained the mechanism behind glucotoxicity . In our study, hyperglycemia was observed in diabetic rats. It manifested itself with an almost 4-fold significant increase in serum blood glucose level compared to the control group. The treatment groups with daily HS and Q had significantly lowered serum glucose levels. Co-administration of both agents significantly normalized the serum glucose level compared to the diabetic group. In addition, STZ-induced animals showed a significant decrease in serum C-peptide level compared to the control group. Serum C-peptide level significantly increased with HS and Q administration and there was a considerable increase compared to the diabetic and normal groups. Meanwhile, daily co-administration of sitagliptin with quercetin normalized the serum C-peptide level.
As can be seen, much experimental evidence highlights a direct link between oxidative stress and diabetes through the measurement of oxidative stress biomarkers in both diabetic patients and rodents. In our study too, diabetic animals exhibited a significant increase in serum MDA level, which reached almost twice that of normal rats. After daily treatment with HS and Q, serum MDA level was significantly lower than in the diabetic group. When MDA level was compared with the diabetic group, it approached normal when both agents were administered together. Catalase enzyme activity in the liver tissue of untreated diabetic rats was lower than in normal rats. Catalase levels increased significantly in all treatment groups compared to normal and untreated diabetic rats, showing the highest levels in the DHSQ group. Diabetic animals exhibited a significant reduction in SOD activity compared to controls. In diabetic animals treated with HS and Q, SOD activity showed a dose-dependent increase. The highest increase was observed in the HS + Q group.
Our study showed that taking moss extract together with an agent with known antioxidant properties such as quercetin can prevent liver damage. These results may shed light on the prevention of the third leading indication for liver transplantation in the USA of cryptogenic cirrhosis, the most common cause of which is diabetes.
A study on the relationship between inflammation, oxidative stress, and type 2 diabetes suggested that controlling inflammation and oxidative stress is necessary to accelerate the treatment process and prevent diabetic complications . Again, Navarro and Mora  were more precise about the type of evolution of diabetes. Specifically, the authors reported conversion from a metabolic disorder to an inflammatory state. These studies show that blood glucose levels, oxidative stress, and inflammatory cytokines play a significant role in type 2 diabetes and liver damage diabetes. As can be understood from all these studies, hyperglycemia increases the production of free radicals resulting in oxidative stress. Increases in oxidative stress are known to contribute to the development and progression of hepatic complications in diabetes. Evidence supporting the role of inflammation in type-2 diabetes is increasingly being found in studies. Inflammatory cells and cytokines are involved in the pathogenesis of diabetic complications through increased vascular inflammation and fibrosis. Although the causes of increased inflammation in diabetes are still being investigated, reactive oxygen species were shown to be primary candidates. Therefore, we believe that targeting oxidative stress and inflammatory cytokine signaling may improve therapeutic options for diabetes and diabetic complications.