Effects of Thymus Vulgaris L. and Thymbra Spicata L. on diabetes mellitus associated cognitive impairment and neuropathy: Thymus Vulgaris and Cognitive Function Improvements

Received: 16 Jun 2014, Revised 24 Jun 2014, Accepted 24 Jun 2014, Available Online 30 Jun 2014 Celal Bayar University, School of Medicine, Department of Biophysics, Manisa-Turkey Yuzuncu Yil University, School of Medicine, Department of Pharmacology, Van-Turkey Dicle University, School of Medicine, Department of Family Medicine, Diyarbakir-Turkey *Corresponding Author: Zafer Akan, zafer.akan@cbu.edu.tr Effects of Thymus Vulgaris L. and Thymbra Spicata L. on diabetes mellitus associated cognitive impairment and neuropathy: Thymus Vulgaris and Cognitive Function Improvements


Introduction
Diabetes mellitus (DM) is the common metabolic disease referring to hyperglycemia due to the corruption of insulin secretion, insufficient insulin sensitivity, or both. DM can affect almost every organ system in the body, and the level of the damage is particularly related to the severity and duration of the disease [1,2]. Type 1 DM (T1D) is an autoimmune disease characterized by the destruction of pancreatic ß-cells. Exposure of environmental harmful substances during neonatal period is accused of leading to initiation of immune process underlying the destruction of ßcells and the development of disorder [3]. Patients with Type 1 Diabetes (T1D) are presented with absolute insulin deficiency, and multiple types of insulin formulations have been developed for the treatment of T1D in the last three decades [4]. Type 2 Diabetes (T2D), non-insulin-dependent type of DM, is mainly an adult disease and associated with insulin resistance. The incidences of T2D rapidly increase due to the decrease in physical activity, sedentary lifestyle, and aging population. 17 T2D is characterized by insulin insensitivity as a result of insulin resistance, decreased insulin production, and finally pancreatic ß-cell failure. Patients with T2D should receive lifestyle alteration recommendations and diet modification.
Although novel drugs are being developed, no cure is currently available for DM related diseases [5,6]. DM may lead to the microstructural complications, such as neuropathy, retinopathy. Diabetic neuropathy is characterized by distal symmetric polyneuropathy. The most common symptoms and findings are fatigue, paresthesia, plantar burning, loss of sense and pain. As a result, some pathology, such as diabetic foot and a morbid condition, may occur due to diabetic neuropathy [7]. Thymus vulgaris L. (Local name: Izmir Kekigi) (TVL) is a species of flowering plant in the mint family Lamiaceae and native to the west of Turkey. Thymbra Spicata L (Local name: Karabas Kekik or Zahter) (TSL) is also a member of the Lamiaceae family, and the leaves of this plant have recently gained much popularity as a remedy to combat hypercholesterolaemia [8]. TVL and TSL have been arbitrarily and widely used in the west region of Turkey for the treatment of various diseases, such as diabetes mellitus, diabetes dependent retinopathy, neuropathy, urinary system disorders, and cardiovascular diseases, in folk medicine. However, no previous scientific report is available regarding the influences of TVL and TSL on DM related damage and impairment in cognitive systems. Therefore, the present study was created to examine the possible effects of TVL and TSL on the DM associated neuropathy and cognitive improvements. CRs/versus P value DRs *** *** *** *** *** DRs+Gli *** *** *** ** ** DRs+TVL100 *** *** ** * * DRs+TVL200 *** *** ** P>0.05 P>0.05 DRs+TSL100 *** *** *** *** *** DRs+TSL200 *** *** *** *** **

The assessment of TVL and TSL treatment on spatial learning of diabetic rats by Morris water maze test:
The Morris water maze (MWM) is a test for spatial learning examination for rodents that relies on distal cues to navigate from start locations around the perimeter of an open swimming arena to locate a submerged escape platform [9]. We tested spatial learning of control, diabetic, and Glibenclamide/TVL/TSL treated rats.
Present protocols for performing variants of the MWM test, from which results can be obtained from individual animals in as few as 4 days end of the study. All tissue and blood samples were collected to search for different tissue involvements under anesthetic conditions (200 U/kg Ketalar).

Statistical Methods
For spatial learning tests; a total of 56 rats including 8 rats in each group were subjected to the study. Each experiment was repeated at least 3 times, and the results of a representative experiment were shown. One-way Analysis of Variance (ANOVA) and Tukey-Kramer Multiple Comparisons tests were applied to the variables, and each result was reported as mean ± S.E.M. and a, p value less than 0.05 was accepted as statistically significant. (*P<0.05, **P<0.01 and ***P<0.001)

Results
Control group blood glucose levels were measured in an average of 86.7 mg/dl. BGL were chronically elevated to the average of 422.3 mg/dl by the single (Acute) dose STZ (50 mg/kg) administration. BGL remained stable in both Control and STZ groups for 5 weeks. TVL improved the maze navigation in dose manner both 100 mg/ml and 200 mg/ml concentrations (P < 0.01). Each point represents data (mean ± SEM) 20 BGL were slightly decreased by the Glibenclamide treatment in the Glibenclamide group. The most significant results over the increased BGL were obtained with TVL100 mg/kg and TVL 200 mg/kg treatments (p<0.01) ( Table 1). The mean body weight was 305.2 gr, and it was decreased to 208.3 gr by the administration of STZ at the end of 5th week. TVL treatment reduced body weight loss in STZ administrated diabetic rats (p < 0.01). As to spatial learning MWM test results; figure 1 and table 2 showed that the escape latency to locate the hidden platform was statistically significantly shorter in the groups of control, TVL 100 and 200 mg/kg treated diabetic rats compared with the diabetic vice/versa glibenclamide, TSL100 and 200 mg/kg treated groups (*p < 0.05, **p < 0.01). The performance at fourth day of the control, TVL 100 and 200 mg/kg groups was not statistically different (p > 0.05). Spatial learning performances of diabetic rats were improved by the TVL 100 and 200 mg/kg treatments (Figure 1)

Discussion
TVL and TSL are known with their antimicrobial and antiviral effects, thus the use is common among the population for the treatment of DM and various diseases. They are characterized by the large scale component of free radical scavenger essential oils such as thymol, carvacrol, 8terpinene, p-ceymene and α-pinene. In addition, the chemical composition of TVL and TSL essential oils varies in a wide range. Carvacrol and thymol are the main components of the mint family Lamiaceae plants. The rate of these components is due to the environment and ecology [8]. The aim of the present study was to analyze the impact of TVL and TSL in terms of blood glucose, vascular, renal and cognitive systems in diabetic rats. Streptozotocin is particularly toxic to the insulin-producing beta cells of the pancreas in mammals. It is used in medical research to produce an animal model for Type 1 DM in single large dose as well as Type 2 DM with multiple low doses. In a long period of time, diabetic rats are characterized by high blood glucose and body weight loss. In our study, we produced Type 1 DM by a single large dose of STZ administration (50 mg/kg) in the Wistar albino rats. The diabetic rats were treated by glibenclamide, TVL and TSL aqueous extracts. It was seen that TVL was significantly effective in the avoidance of the increase in blood glucose, weight loss, the decline in cognitive functions, and also in the improvement of them. DM is associated with slowly progressive end-organ damage in the brain. Mild to moderate deteriorations of cognitive functions have been declared in patients with both type 1 and in type 2 DM [10]. Many of DM related clinical complications are commonly caused by the vessel disorders. The peripheral microvascular complications of DM occurring outside the brain seem to be associated with corresponding microvascular changes in the brain. For instance, diabetic retinal microvascular abnormalities were associated with various MRI findings including small focal white matter hyper intensities and lesions [11]. In the present study, it was determined that a significant improvement in cognitive functions of diabetic rats was provided by the TVL treatment. It was supposed that this positive impact of TVL on the cognitive function was due to its positive effects on blood glucose level and microvascular system. In conclusion, it was supposed that both TVL and TSL had dose dependent protecting and healing effects against the damaging effects of DM in terms of blood glucose cognitive systems moreover, diabetic neuropathy. Our finding strongly recommends the usage of TVL treatments for DM control by the DM patients