Background
Diabetes mellitus is one of the most common metabolic diseases caused by high blood glucose and lack of insulin production or sensitivity, which influence body system functions [
1]. Insulin resistance syndrome is one of the metabolic dysfunctions that play a crucial role in the pathogenesis of type 2 diabetes mellitus [
2,
3]. Obesity and high triglyceride (TG) levels are dependent risk factors for insulin resistance syndrome [
4,
5]. The increase in the number of people afflicted with diabetes over the past two decades can be due to lessened physical activity, poor dietary habits, overweight or obesity, and psychological stress [
6,
7]. Diabetes is an epidemic disease, and over 5 % of the total population or an estimated 135 million people are infected. Hence, the World Health Organization estimated a rising prevalence of this silent disease. Approximately 285 million people worldwide were infected in 2010 [
8], and this number would likely reach about 380 million by 2025 [
7], and 439 million by 2035 (7.7 %) [
9‐
11]. These predictions estimate a growing burden of diabetes particularly in developing countries [
10]. This silent disease will become the strongest and deadliest leading cause of death in humans worldwide in the next 25 years [
6]. Diabetes in populated countries such as India, China, and United States is rapidly increasing. In India, 30 million people were diagnosed as diabetics in 1995, and by 2025, this number is estimated to reach 70 million [
11,
12].
Medicinal plants have been identified globally as biological source and have been investigated extensively as crude material for treating various disease conditions because of their effectiveness and economic values. Plant-derived medicines are safer to use than their synthetic alternatives, offering profound therapeutic benefits and affordable treatments. Currently, more than 30 % of medicines derived from natural sources are used in hospitals and clinics [
13‐
15]. Despite their useful roles, most of the chemical medicines used in diabetes have damaging side effects [
14,
16]; therefore, practitioners have considered changing to alternative natural plant therapy [
17,
18].
Urtica dioica (UD) is one of natural plants used in traditional medicine [
19,
20]. It has been used for homeopathy allergies, anemia, internal bleeding, kidney stones, burns, and diabetes [
21]. Aside from its antihyperglycemic, anti-proliferative [
22], anti-oxidant [
23], and anti-dandruff [
24] properties, it has anti-inflammatory or antimicrobial activity and has been proven to cure infectious diseases [
25]. Furthermore The effects of UD on glucose transporter-4 (GLUT4) translocation on L6 muscle cells show that this plant stimulates GLUT4 transport to plasma membrane and glucose uptake into skeletal muscle [
26].
The chemical compounds of this plant are lectin, lecithin, potassium, calcium, acetophenone, acetylcholine, quercetin, quinic acid, chlorogenic acid, butyric acid, caffeic acid, carbonic acid, coumaric acid, formic acid, histamine, succinic acid, pantothenic acid, linolenic acids, palmitic acid, serotonin, stigmasterol, terpenes, choline, agglutinin, alkaloids, xanthophyll, chlorophyll, kaempferol, coproporphyrin, lignan, linoleic, and violaxanthin. UD also contains protein, fatty substance, albumins, carotene, vitamin C, oxalate, fixed oil in its seeds, provitamin A, vitamin B1, K, xanthophylls, silicium, ferric oxide, and sistosterin in its leaves [
27‐
29]. Among the many different types of this plant, two-basis nettle (Urtica dioica L) has been known as a traditional medicine in the world [
27]. Other positive effects of this plant are joint pain reduction, bone inflammation treatment [
30], cure for urinary tract infectious diseases, coronary heart disease, diabetes, cancer, inflammation, psychotic disorders, liver inflammation, and viral and parasitic diseases [
31,
32], as well as influences on physiological brain function with exercise [
33].
Aerobic activity is one of the useful ways to cure or prevent diabetes [
5,
7,
34]. Physical activity has associated effects on glycemic and lipid profiles as well as metabolic risk factors for cardiovascular diseases, such as reduction of insulin resistance, atherogenic lipid abnormalities, high blood pressure, and improvement of metabolic status [
34,
35]. The effect of regular exercise on improving glucose metabolism is well known in type 2 diabetes [
35,
36], which may be due, in part, to the muscle contraction with insulin-like action as well as training-induced adaptations [
37,
38]. Both physical activity and UD extract consumption approaches result in hypoglycemia and hypolipidemia. Nevertheless, data on the effect of the combination of these two beneficial variables on diabetes are unavailable. To fill this research gap, the present study aims to investigate in vivo and in vitro evaluation of Urtica dioica effects and swimming activity on diabetic factors and pancreatic beta cells on streptozotocin diabetic with the use of synthetic metformin medicine and normal rats.
Induction of experimental diabetes
To induce diabetes in rats, Streptozotocin (STZ, Enzo Life Sciences) was used by intraperitoneal injection (50 mg/kg). Distilled normal physiologic saline was used to prepare the injection solution. Rats were fasted 14 h before injection. The control group received normal saline. Blood sample for glucose measurements was collected from tail vein. A glucometer (Bionine-GM300) was used to measure blood glucose. Hyperglycemic animals with fasting blood glucose of more than 250 mg/dl were considered as diabetic.
Insulin resistance was calculated by following formula [
43]:
$$ \mathrm{Insulin}\ \mathrm{resistance} = \mathrm{fasting}\ \mathrm{insulin}\left(\upmu \mathrm{U}/\mathrm{mL}\right) \times \mathrm{fasting}\ \mathrm{glucose}\ \left(\mathrm{mg}/\mathrm{dl}\right)/405 $$
Serum insulin level was evaluated by ultra-sensitive rat insulin ELISA Kit (Alpco-US). Insulin sensitivity was calculated by following formula [
44]:
$$ 1/\left[ \log\ \mathrm{fasting}\ \mathrm{insulin}\ \left(\mathrm{mU}/\mathrm{L}\right) + \log\ \mathrm{fasting}\ \mathrm{glucose}\ \left(\mathrm{mg}/\mathrm{dL}\right)\right] $$
The Friedewald equation method was used to measure low-density lipoprotein (LDL) cholesterol concentration [
45]. All data analyses were conducted in triplicate.
Swimming protocol instructions
A swimming program was considered an exercise activity model in this study. Swimming was conducted in a clear plastic tank (70 cm × 90 cm × 150 cm) containing 30 cm of water (28 ± 0.5 °C). Before the exercise program, the swimming groups were familiarized to swimming (5 min/day in the first 3 days and 10 min/day in the second 3 days) to reduce stress. The exercise program consisted of swimming five times per week with gradual increases up to 4 weeks. The first week was for 15 min to 20 min at a depth of 20 cm; the second week was for 20 min to 30 min at a depth of 30 cm; the third week was for 30 min to 40 min at a depth of 40 cm; and the fourth week was for 45 min at a depth of 50 cm. the intensity of the exercise was monitored by increasing time and depth of water in plastic tank [
39].
Histological experiment sample preparation
After 4 weeks of tests, the hearts of the animals were punctured, and their pancreas tissues were exposed for histological experiment. The tissue was cleaned, fixed in 10 % formalin, and then paraffin embedded for microscopic procedures. Histopathology test was performed in hematoxylin and eosin stained at 5 μm thickness (Leitz 1512, Germany). The cellularity evaluation of Langerhans islets was conducted by light microscope (BX41 Olympus).
Statistical analysis
All data values were mean ± standard deviation. The obtained data in this study were analyzed using SPSS version 17 and described in terms of central tendency and dispersion. Analysis of variance was used to evaluate the differences between the mean values. Kolmogorov–Smirinov test showed that the data were normally distributed. p value less than 0.05 was considered statistically significant.
Discussion
Our in vivo study results revealed that the 4-week administration of different doses of UD with exercises on diabetic rats caused significant decrease in diabetes markers, such as insulin resistance reduction, increased insulin sensitivity, lower TG and cholesterol, and improved function of the pancreatic beta cells compared with the diabetic group. Improved weight gain was noticed in the treatment groups. This positive change was more pronounced in the group that had swimming activity and consumed 1.25 g/kg UD. Increasing the enzyme hormone-sensitive lipase activity and stored triglycerides hydrolysis can release large amounts of fatty acids and glycerol into the blood circulation of patients with insulin deficient activity [
46]. Thus, medications such as metformin that reduce blood triglycerides and cholesterol did not significantly change the lipid profiles, as observed in the present study. The data from the in vitro study indicated that UD extract increased insulin secretion through RIN-5F and glucose uptake by the L6 myotube cells.
The effects of UD on hypoglycemic, hypolipidemic, protection, and beta cell regeneration have been proven [
15,
47] in several studies. Whereas Other studies have indicated that UD consumption has no effect on blood glucose and beta cell regeneration in diabetic rats [
48]. By contrast, UD leaf extracts have been reported to have a protective role in increasing blood glucose and destroying pancreatic beta cells [
19,
49]. Domola et al. [
50] concluded that the compound Gazlin from UD extract has insulin-like effect in lowering blood glucose in diabetic patients. These differences in results may be caused by differences in regions, cities, and parts of UD (stalk, root, and leaves) used.
Our result supports the findings of Silevera et al. (2008), that is, blood sugar is reduced and weight is induced in diabetic rats with swimming activity [
51]. The present data were consistent with the findings of Zinman et al. (2004) and confirmed the effect of exercise on blood sugar and insulin resistance [
52]. Tjønna et al. [
53] compared the effects of 90 % and 70 % aerobic exercise intensity on metabolic factors and insulin sensitivity in metabolic syndrome patients. Their data showed no significant differences in the weights of both exercise groups. Although insulin was increased, pancreatic beta-cell function had been observed by TG reduction and increased oxidation of free fatty acids. Nevertheless, pancreatic beta-cell function was significantly pronounced with exercise intensity. In this regard, aerobic capacity improvement, mitochondrial oxidation, and higher quality of life for individuals at high risk of diabetes were more pronounced in the periodic training group than in the continuous training group [
54]. Although this study was conducted on humans, the results were consistent with the present study in terms of increase in insulin sensitivity, beta cell function, TG reduction, and fat metabolism.
Several studies have proven that moderate intensity exercise had no desirable effect on blood lipids, glucose, insulin, and insulin resistance [
3,
5] The present study corroborates these findings. Aerobic activity has no significant effect on LDL and HDL but has a significant effect on blood glucose, cholesterol, TG reduction, insulin resistance, and insulin sensitivity.
A study conducted on diabetic rats by STZ and oral administration of aqueous extract of UD concluded that the aqueous extract of UD could have antihyperlipidemic and antihyperglycemic effects. Moreover, the aqueous extract of UD could decrease and increase glycemic markers and lipid levels [
46], similar to the findings of this study. By contrast, Swanston Flatt showed that UD had no significant effect on blood glucose reduction in diabetic mice [
19]. The effect of five natural plant extracts, including UD, on serum lipoprotein was investigated by Avci et al. They reported that the administration of UD on rats with full cholesterol consumption was closely associated with HDL enhancement and LDL abatement [
55]. Furthermore, nettle seeds of Pilulifera reduced blood sugar and increased the number of Langerhans beta cells in diabetic rats [
30].
The present study showed that the combination of aerobic exercises along with UD extract consumption could decrease blood sugar and insulin resistance, increase sensitivity of tissue to insulin, decrease fat serum, as well as improve the function and proliferation of Langerhans islets Beta cells, which were more pronounced in the group of UD consumption with swimming activities. As has been reported, UD extract can form a substance peptide loop (an amino acids chain) called Gazlin. Experiments conducted in this area have revealed that the attachment of 10 Gazlin molecules caused the formation of small tunnels on target tissues via cell membrane adhesion; this phenomenon made glucose to trickle into the cell, thereby reducing blood sugar [
50]. It was also reported that the water extract of UD increased lipoprotein lipase (LPL) activity [
46]. Thus, consumption of UD water extract and sport activities may decline the severity of diabetes. However, more studies are warranted to investigate the mechanisms of this plant.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
MAA, FD, and AR conceived the idea, drafted the proposal and involved in all implementation stages of the project and write up. MAA, FD, AY, and AR have performed the experiments and analysis. MAA, FD, and AR critically evaluated the paper and provided the final manuscript. AY, MYI, SA, BT, PF, AHM and RH reviewed the proposal, and involved in all implementation stages of the project and write up. All authors reviewed the proposal and the final manuscript. All authors read and approved final version of the manuscript.