The methanolic extract of Thymus praecox subsp. skorpilii var. skorpilii restores glucose homeostasis, ameliorates insulin resistance and improves pancreatic β-cell function on streptozotocin/nicotinamide-induced type 2 diabetic rats
Graphical abstract
Introduction
Diabetes mellitus (DM) is a metabolic disorder which occurs due to hyperglycemia resulting from insulin resistance and/or deficiency in insulin secretion (Alam et al., 2014). Several pathologic mechanisms have been implicated in diabetes. Dysregulation of hepatic glucose metabolism is a core defect in the development of insulin resistance and subsequently Type 2 Diabetes Mellitus (T2DM) (Petersen et al., 2017).
The rate limiting enzymes of several processes implicated in glucose metabolism become important in the view of T2DM. For instance, phosphoenolpyruvate carboxykinase (PEPCK), hexokinase (HK) and glycogen synthase are responsible for gluconeogenesis, glycolysis and glycogenesis, respectively (Bouskila et al., 2010, Kwon et al., 2017, Liu et al., 2014). The transport systems mediating glucose intake and utilization are classified into two groups: glucose transporter proteins (GLUTs) and sodium-dependent glucose transporter proteins (SGLTs) (Harada and Inagaki, 2012). According to the literature data, upregulation of these two transporters can cause hyperglycemia (Hansen et al., 2014, Peng et al., 2015).
The pharmacological agents, used currently for the treatment of T2DM include mainly oral anti-diabetic drugs, such as sulfonylureas, biguanides, thiazolidinediones, α-glucosidase inhibitors, and dipeptidyl peptidase-4 (DPP-4) inhibitors, have restricted usage due to their inefficacy at the progression of diabetic complications and undesired side effects including nausea, diarrhea, hypoglycemia, weight gain, liver and heart failure (Alhadramy, 2016, Chaudhury et al., 2017, Du et al., 2014).
In order to keep blood glucose levels under control in DM, about 1200 plants are used worldwide and approximately 30% of conventional antidiabetic plants are examined pharmacologically and chemically. Plants are attractive sources for the development of novel safe and effective medicines for DM owing to their effectiveness, minimal side effects in clinical experiences and also relatively low cost (Nasri et al., 2015).
The genus Thymus (Lamiaceae) comprises of about 928 species worldwide (Morales, 2002). The several major components in essential oil of the different Thymus spp. are thymol, carvacrol, linalool, geraniol, thujanol, p-cymene which are behind the therapeutic activities (Schmidt et al., 2012). They are commonly used as culinary herbs and flavouring agents. Due to their antimicrobial, spasmolytic and antioxidant effects, they have been used for medicinal purposes. Besides, anti-inflammatory, antinociceptive and antitumoral activities of Thymus spp. that may vary depending on the species and the amount of chemical compositions have been reported (Safaei-Ghomi et al., 2009).
As having different biological activities, Thymus spp. have been tested in diabetic conditions (Al-Mustafa and Al-Thunibat, 2008, Alamgeer et al., 2016, Hajializadeh et al., 2014a, Ozkol et al., 2013). Although antidiabetic activities of Thymus spp. are attributed to their antioxidant properties, the exact mechanisms have not been fully elucidated by now.
Thymus praecox subsp. skorpilii var. skorpilii (TPS) (syn. Thymus praecox subsp. jankae (Celak.) Jalas) is a plant with long±woody, creeping branches, non-flowering or with a terminal inflorescence, flowering stems are born in rows. Cauline leaves of plant lanceolate-obovate to ovate-elliptic or almost orbicular. Corolla mauve to purple, rarely whitish (Jalas, 1982).
The dried leaves of T. praecox subsp. skorpilii var. skorpilii is used in tea form for the purpose of antispasmolytic, softening the throat and shortness of breath in Eskişehir-Turkey in traditional medicine (Yucel et al., 2010). Besides, leaves and aerial parts of this plant are used for the treatment of diabetes in Amasya and Giresun provinces of Turkey (Ezer and Mumcu Arisan, 2006, Tuzlaci, 2016). Methanol and water extracts of the leaves of TPS has been reported to possess significant antioxidant effect, native to Thymus spp. In details, it has been found that water and methanol extracts of TPS possessed reducing power effect in a dose-dependent manner. In addition, the major components of essential oil of this species were identified as thymol, o-cymene, γ-terpinene and α-pinene using GC-MS technique (Ozen et al., 2011).
In our previous investigation, the phenolic characterization of the methanol extract from plant was performed by ESI-Q-TOF LC/MS technique. The phenolic compounds in methanol extract were identified as chlorogenic acid, luteolin-7-O- glucoside, 3-O-feruloylquinic acid, quercetin-3-O-hexoside, and apigenin-7-O-glucuronide (Ucman et al., 2017).
According to the recorded data, there is no study showing the mechanism of antidiabetic action of TPS. Shortly after, in our study, we firstly evaluated the antidiabetic effects of TPS in diabetic rats induced by streptozotocin (STZ)/nicotinamide (NA) and we clearly observed that TPS extract has remarkably decreased blood glucose levels (Cam et al., 2017).
By this way, in the present study, our aim was to uncover the mechanisms of action of TPS by monitoring the biochemical and histopathological parameters in diabetic condition induced by STZ/NA in rats.
Section snippets
Chemicals
STZ, NA, metformin, Gill's Hematoxylin Solution were purchased from Santa Cruz Biotechnology, Inc. (Dallas, TX, USA). Enzyme-linked immunosorbent assay (ELISA) kits were procured from Bioassay Technology Laborator, Korain Biotech Co., Ltd (Shanghai, China).
Plant material and extract preparation
The aerial parts of TPS were collected in 15 July 2016 from Uludag-Bursa, Turkey in blooming semester and identified by Assist. Prof. Dr. İsmail Şenkardeş, Marmara University, Faculty of Pharmacy, Pharmaceutical Botany Department. A voucher
Effects of TPSE on blood glucose levels
The rats were bled by orbital puncture under ether anesthesia for measuring blood glucose levels. Diabetic rats showed a significant increase (438.83 ± 17.83 mg/dL, p < 0.001) in blood glucose levels compared with the other groups at the end of three weeks (Table 1). Blood glucose levels of TPSE treated rats lowered considerably (205.67 ± 11.56 mg/dL) compared to diabetic rats after one week and these decreases continued for three weeks (132.17 ± 4.58 mg/dL). At the end of three weeks,
Discussion
Classical therapy for T2DM has some limitation and because of that there is a need to go beyond the current standard of care. In this regard, approximately 30% of diabetic patients utilize the complementary and alternative medicine (Shewamene et al., 2015). Therefore, many herbal extracts have been investigated on experimental models in the context of their anti-diabetic activity (Pang et al., 2015).
STZ/NA-induced rat model of T2DM is described one of the most appropriate experimental models to
Conclusion
As noted in this study, the antidiabetic effects of the methanolic extract of TPSE can restore glucose homeostasis, ameliorate insulin resistance and decrease pancreatic β-cell damage. These effects could be due to SGLT-1, SGLT-2, GLUT2, PEPCK, α-glucosidase inhibition and GLP-1 activation in STZ/NA-induced diabetic rats. In the light of these findings, we suggest that TPSE is beneficial in diabetes treatment and the effects may come from compounds of chlorogenic acid, luteolin-7-O- glucoside, 3
Acknowledgements
This study was supported by Marmara University, Scientific Research Projects Committee (MU-BAPKO; SAG-C-DRP-250416-0173).
Conflicts of interest
Authors all declare that there is no existing conflict of interest.
Author Contribution
Muhammet Emin Cam: 5 Ayse Nur Hazar-Yavuz: 13 Sila Yildiz: 14 Busra Ertas: 7 Betul Ayaz Adakul: 12 Turgut Taskin: 8 Levent Kabasakal: 10
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