Molecular docking analysis and anti-hyperglycaemic activity of Synacinn™ in streptozotocin-induced rats

Abstract

Synacinn™ is a standardized polyherbal supplement formulated from Cinnamomum zeylanicum Blume, Curcuma zanthorrhiza Roxb., Syzygium polyanthum (Wight) Walp., Orthosiphon stamineus Benth. and Andrographis paniculata (Burm.f.) Nees. It is designed for the synergistic treatment of diabetes mellitus and its complications. Although the beneficial effects are yet to be verified scientifically, it is traditionally used to improve general health in patients with diabetes. This study aimed to evaluate the anti-hyperglycemic effects of Synacinn™ in a streptozotocin-induced type 1 diabetes rat model. Initially, Synacinn™ was used for in vivo acute oral toxicity tests and 14 day repeated dose toxicity tests to determine the toxicity levels. An efficacy study of Synacinn™ was carried out via the oral administration of 10, 50, 100, 250, and 250 (b.i.d.) mg kg^-1 doses to streptozotocin-induced diabetic rats. After 28 days, blood serum was collected to measure the fasting blood glucose, triglyceride, cholesterol, alanine aminotransferase, alkaline phosphatase, creatinine, and uric acid levels. The liver, kidney, and pancreas structures were histopathologically analyzed. In silico binding interaction studies of five phytochemicals in Synacinn™ identified via HPLC with glucokinase were performed using molecular docking analysis. The results showed that although no mortality was observed during the acute oral toxicity tests, notable damage to the liver and kidney occurred during the 14 day repeated dose testing at Synacinn™ levels of 600 mg kg^-1 and 2000 mg kg^-1. Treatment with 250 mg kg^-1 (b.i.d.) Synacinn™ of the streptozotocin-induced type 1 diabetic rats significantly (p < 0.05) improved the fasting blood glucose (59%), triglyceride (58%), cholesterol (47%), alanine aminotransferase (60%), alkaline phosphatase (90%), and creatinine (32%) levels. Synacinn™ also improved the relative weights of liver (35%), kidney (36%), and pancreatic (36%) tissue. Histological analysis showed improvements in the conditions of the central vein of the liver, the kidney Bowman's capsule and glomerulus, and the pancreatic islets of Langerhans. HPLC analysis of a standardized extract identified five active phytochemicals: andrographolide (17.36 mg g^-1), gallic acid (11.5 mg g^-1), curcumin (2.75 mg g^-1), catechin (3.9 mg g^-1), and rosmarinic acid (5.54 mg g^-1). Molecular docking studies with glucokinase showed that andrographolide yields the highest binding energy (-12.1 kcal mol^-1), followed by catechin (-10.2 kcal mol^-1), rosmarinic acid (-8.6 kcal mol^-1), curcumin (-7.8 kcal mol^-1), and gallic acid (-5.6 kcal mol^-1). These current findings suggest that Synacinn™ at a dose of 250 mg kg^-1 was non-toxic to rats. A twice-daily 250 mg kg^-1 dose of Synacinn™ is an effective anti-hyperglycemic agent, lowering blood glucose, triglyceride, and cholesterol levels, and assisting the recovery of organ impairment caused by streptozotocin in type 1 diabetic rats.

Fig. 1. The effect of Synacinn™ on the body weights of rats. Values are mean ± SEM, with n = 6 rats per group in the 14 days of repeated dosing and n = 3 in the recovery period.

Fig. 2. The effects of Synacinn™ on (A) food consumption and (B) water intake. Values are means ± SEM; n = 3 rats per group; *: p < 0.05 compared to the control group; one-way ANOVA followed by Dunnett's test for post-hoc analysis.

Fig. 3. The effects of Synacinn™ on the relative organ weights of rats: (A) relative liver weights; (B) relative kidneys weights. Values are means ± SEM; n = 3 rats per group; *: p < 0.05 compared to the control group; one-way ANOVA followed by Dunnett's test for post-hoc analysis.

Fig. 4. Histopathological analysis of rat liver samples: (A) control after 14 days of repeated doses; (B) 250 mg kg⁻¹ Synacinn™ after 14 days of repeated doses; (C) 600 mg kg⁻¹ Synacinn™ after 14 days of repeated doses; (D) 2000 mg kg⁻¹ Synacinn™ after 14 days of repeated doses; (E) control after a 14 day recovery period; (F) 250 mg kg⁻¹ Synacinn™ after a 14 day recovery period; (G) 600 mg kg⁻¹ Synacinn™ after a 14 day recovery period; and (H) 2000 mg kg⁻¹ Synacinn™ after a 14 day recovery period. CV = central vein; H = hepatocytes; S = sinusoidal spaces.

Fig. 5. Histopathological analysis of rat kidney samples: (A) control after 14 days of repeated doses; (B) 250 mg kg⁻¹ Synacinn™ after 14 days of repeated doses; (C) 600 mg kg⁻¹ Synacinn™ after 14 days of repeated doses; (D) 2000 mg kg⁻¹ Synacinn™ after 14 days of repeated doses; (E) control after a 14 day recovery period; (F) 250 mg kg⁻¹ Synacinn™ after a 14 day recovery period; (G) 600 mg kg⁻¹ Synacinn™ after a 14 day recovery period; and (H) 2000 mg kg⁻¹ Synacinn™ after a 14 day recovery period. G = glomerulus; BC = Bowman's capsule; PCT = proximal convoluted tubule; DCT = distal convoluted tubule.

Fig. 6. The effects of Synacinn™ on (A) food consumption and (B) water intake by normal and diabetic rats. Values are mean ± SEM; n = 6 rats per group; °: p < 0.05 compared to the normal control; *: p < 0.05 compared with the diabetic control group; one-way ANOVA followed by Tukey's test for post-hoc analysis. D = diabetic induced; GBC = glibenclamide.

Fig. 7. Histological structures of liver samples after 28 days of treatment (H&E, 40×). CV = central vein, H = hepatocytes, S = sinusoidal spaces.

Fig. 8. Histological structures of kidney samples after 28 days of treatment (H&E, 40×). G = glomerulus, BC = Bowman's capsule, PCT = proximal convoluted tubule, DCT = distal convoluted tubule.

Fig. 9. Histological structures of pancreas samples after 28 days of treatment (H&E, 40×). IL = islets of Langerhans, A = acinar cells, BC = blood capillary.

Fig. 10. The effects of Synacinn™ on the islet areas. Values are mean ± SEM; n = 6 rats per group; °: p < 0.05 as compared to the normal control; *: p < 0.05 compared with the diabetic control group; one-way ANOVA followed by Dunnett's test for post-hoc analysis. D = diabetic rats, GBC = glibenclamide.

Fig. 11. The effects of Synacinn™ on (A) liver ALT, (B) liver ALP, (C) creatinine, and (D) uric acid levels. Values are mean ± SEM; n = 6 rats per group; °: p < 0.05 compared to the normal control; *: p < 0.05 compared with the diabetic control group; one-way ANOVA followed by Dunnett's test for post-hoc analysis. GBC = glibenclamide.

Fig. 12. HPLC chromatograms of andrographolide, catechin, curcumin, gallic acid, and rosmarinic acid.

Fig. 13. The molecular docking of andrographolide (magenta), catechin (brown), curcumin (green), gallic acid (blue), and rosmarinic acid (red) with 1V4S.

Fig. 14. Hydrogen bond interactions of (a) curcumin, (b) gallic acid, (c) rosmarinic acid, (d) andrographolide, and (e) catechin with 1V4S.

Fig. 15. The hydrophobic contacts of (a) gallic acid and (b) andrographolide with 1V4S.