Thymus linearis Extracts Ameliorate Indices of Metabolic Syndrome in Sprague Dawley Rats

Abstract

Materials and methods: The extract library (n-hexane (NH), ethyl acetate (EA), methanol (M), distilled water (DW), and combined extract (CE)) was standardized using in vitro phytochemical, antioxidant, and α-amylase inhibition assays, after which the protective effect of selected "hit," i.e., CE against metabolic syndrome, was determined in vivo, using rats fed a high-fat diet supplemented with additional cholesterol administration. CE was administered to Sprague Dawley rats in high dose as 100 mg/kg in carboxymethyl cellulose (CMC) (1 ml; 0.75% in DW) and low-dose group as 50 mg/kg in CMC (0.5 ml; 0.75% in DW). After 10 weeks, the effects of CE on insulin resistance, lipid metabolism, nonalcoholic fatty liver disease (NAFLD), oxidative stress, and genotoxicity were assessed through histological, biochemical, and hematological investigations.

Results: Phytochemical analysis including RP-HPLC analysis of the extracts showed that flavonoids and phenolics (myricetin, kaempferol, and apigenin), previously known to be effective against obesity and diabetes, are present in the extracts. Antioxidant studies revealed that the plant possesses a highly significant (p < 0.05) concentration of antioxidants. Satisfactory α-amylase inhibitory activity was also observed in in vitro experiments. In vivo studies showed that CE-administered animals had significantly (p < 0.05) lower weight gain and smaller adipocytes than the control group. Moreover, CE resisted any significant (p < 0.05) change in the organ weights. Analogous to findings from its traditional use, the plant extract had a positive modulatory effect on insulin resistance and hyperglycemia. The study also indicated that CE resisted high-fat diet-induced disturbance in lipid profile and countered any pathological changes in liver enzymes caused by fat-infused diet. Furthermore, a study on endogenous antioxidant levels indicated that CE was effective in maintaining catalase and peroxidase levels within the normal range and resisted the effects of lipid peroxidation of thiobarbituric acid reactive substances.

Conclusion: In principle, the current study's findings scientifically validate the implication of T. linearis in metabolic syndrome and recommend further studies on molecular insights of the observed therapeutic activity.

Figure 1

Graphical representation of TPC and TFC estimation of T. linearis extracts. Note: values are expressed as mean of triplicate ± standard deviation. TPC: total phenolic content; TFC: total flavonoid content.

Figure 2

(a) HPLC chromatogram of standard polyphenols. (b) HPLC chromatogram of ethyl acetate extract. (c) HPLC chromatogram of methanol extracts. (d) HPLC chromatogram of distilled water extract. Note: 1, vanillic acid; 2, plumbagin; 3, thymoquinone; 4, gallic acid; 5, catechin; 6, syringic acid; 7, coumaric acid; 8, emodin; 9, gentisic acid; 10, caffeic acid; 11, ferulic acid; 12, luteolin; 13, apigenin; 14, myricetin; 15, quercetin; 16, kaempferol.

Figure 3

Graphical representation of DPPH free radical scavenging activity, IC₅₀ estimation, TAC, and TRP analysis of T. linearis extracts. Note: values are presented as average of triplicate ± standard error. TAC: total antioxidant capacity; TRP: total reducing power.

Figure 4

Graphical representation of α-amylase inhibition and IC₅₀ values of T. linearis extracts. Note: acarbose is used as a standard with an IC₅₀ 33.73 μg/ml. Values are presented as mean ± standard deviation.

Figure 5

Effect of standard diet, high-fat diet, and T. linearis extract on body weight gain and adipocyte diameter and HOMA-IR over period of 10 weeks. Note: means with different superscript (A–D) letters in the column are significantly different from one another according to Tukey's multiple comparison at p < 0.05. HOMA-IR: determination of homeostasis model of insulin resistance.

Figure 6

Pictorial representation of adipose tissue: (a) STD-Cnt, (b) STD-Veh, (c) STD-CE, (d) HFD-Cnt, (e) HFD-CE-HD, (f) HFD-CE-LD, and (g) HFD-Pos. Note: STD: standard laboratory diet-control; Cnt: control; Veh: vehicle; CE: combined extract; HFD: high-fat diet; HD: high dose; LD: low dose; Pos: positive.

Figure 7

Glucose tolerance results of rats administered 25% glucose solution (400 mg/2 ml).

Figure 8

Pictorial representation of hepatic histology of (a) STD-Cnt and (b) HFD-Cnt. Note: STD: standard laboratory diet-control; Cnt: control; Veh: vehicle; CE: combined extract; HFD: high-fat diet; HD: high dose; LD: low dose; Pos: positive.

Figure 9

Graphical representation of effects of T. linearis extracts, standard diet, high-fat diet, and positive control on CAT, POD, SOD, and TBARS values. Note: means with different superscript (A–F) letters in the column are significantly different from one another according to Tukey's multiple comparison at p < 0.05. CAT: catalase; POD: peroxidase; SOD: superoxide dismutase; TBARS: thiobarbituric acid reactive substances.

Figure 10

Fluorescence photomicrograph of effects of T. linearis extracts on DNA integrity. (a) STD-Cnt-brain, (b) STD-Cnt-heart, (c) STD-Cnt-liver, (d) STD-Cnt-kidney, (e) STD-CE-brain, (f) STD-CE-heart, (g) STD-CE-liver, and (h) STD-CE-kidney. Note: STD: standard laboratory diet-control; Cnt: control; Veh: vehicle; CE: combined extract.