Background: Chlorogenic acid is a major phenolic compound that forms a substantial part of plant foods and is an ester of caffeic acid and quinic acid. However, the effect of the structures of both chlorogenic and caffeic acids on their antioxidant and antidiabetic potentials have not been fully understood. Thus, this study sought to investigate and compare the interaction of caffeic acid and chlorogenic acid with α-amylase and α-glucosidase (key enzymes linked to type 2 diabetes) activities in vitro. Methods: The inhibitory effect of the phenolic acids on α-amylase and α-glucosidase activities was evaluated. Thereafter, their antioxidant activities as typified by their 1,1-diphenyl-2 picrylhydrazyl radical scavenging ability and ferric reducing antioxidant properties were determined. Results: The results revealed that both phenolic acids inhibited α-amylase and α-glucosidase activities in a dose-dependent manner (2–8 μg/mL). However, caffeic acid had a significantly (p<0.05) higher inhibitory effect on α-amylase [IC ₅₀ (concentration of sample causing 50% enzyme inhibition)=3.68 μg/mL] and α-glucosidase (IC ₅₀ =4.98 μg/mL) activities than chlorogenic acid (α-amylase IC ₅₀ =9.10 μg/mL and α-glucosidase IC ₅₀ =9.24 μg/mL). Furthermore, both phenolic acids exhibited high antioxidant properties, with caffeic acid showing higher effects. Conclusions: The esterification of caffeic acid with quinic acid, producing chlorogenic acid, reduces their ability to inhibit α-amylase and α-glucosidase activities. Thus, the inhibition of α-amylase and α-glucosidase activities by the phenolic acids could be part of the possible mechanism by which the phenolic acids exert their antidiabetic effects.

Caffeic acid (CAA) and chlorogenic acid (CHA) are important members of hydroxycinnamic acid with natural antioxidant and cardio-protective properties. The present study aimed to determine the effect of CAA and CHA on systolic blood pressure, heart rates (HR) as well as on the activity of the angiotensin-1-converting enzyme (ACE), acetylcholinesterase (AChE), butrylcholinesterase (BChE) and arginase in cyclosporine-induced hypertensive rats. Experimental rats were distributed into 7 groups (n = 6): normotensive control rats; hypertensive rats (induced rats) as well as hypertensive- treated groups with captopril (10 mg/kg/day), CAA (10 and 15 mg/kg/day) and CHA (10 and 15 mg/kg/day), respectively. The experiment lasted for 7 days and the systolic blood pressure (SBP) and heart rates were recorded using tail-cuff method. Oral administration of captopril, caffeic acid and chlorogenic acid normalized hypertensive effect caused by cyclosporine administration. CAA and CHA significantly (P < 0.05) reduced SBP and HR, activity of ACE, AChE, BChE and arginase in the treated hypertensive rats compared with cyclosporine induced-hypertensive rats. Likewise, CAA and CHA improved nitric oxide (NO) bioavailability, increased catalase activity and reduced glutathione content while malondialdehyde (MDA) level was reduced compared with cyclosporine hypertensive rats. Findings from this study shows that CAA and CHA exhibited blood pressure lowering properties and reduced activities of key enzymes linked to the pathogenesis of hypertension in cyclosporine-induced rats. These might be some of the possible mechanisms of action by which their cardio-protective properties are exhibited.

Spices are used in soup preparation in many homes and serve as ingredients in the preparation of several traditional delicacies endowed with natural antioxidants such as polyphenols. The aim of this study is to evaluate the effect of aqueous extract of garlic, white onion, and purple onion on angiotensin-converting enzyme, α-amylase, and α-glucosidase activity in vitro and determine their antioxidant properties via various antioxidant assays such as OH^*, Fe²⁺ chelation, and 2, 2′-azino-bis 3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical-scavenging assays. The results reveal that aqueous extract of garlic, purple onion, and white onion inhibited angiotensin-converting enzyme, α-amylase, and α-glucosidase in a concentration-dependent manner (0–4 mg/ml). However, purple onion (IC₅₀ = 0.59 mg/ml) had higher inhibitory effect on angiotensin-converting enzyme than white onion (IC₅₀ = 0.66 mg/ml) and purple onion (IC₅₀ = 0.96 mg/ml). Furthermore, white onion had significantly (p < .05) stronger inhibitory effect on α-amylase (IC₅₀ = 3.93 mg/mL) than garlic (IC₅₀ = 8.19 mg/ml) and purple onion (IC₅₀ = 8.27 mg/ml). Conversely, garlic (IC₅₀ = 4.50 mg/ml) had no significantly higher inhibitory effect on α-glucosidase activity than white onion and purple onion. In addition, the aqueous extracts were able to scavenge 2,2- diphenyl-1-picrylhydrazyl (DPPH^*) free radical and reduce Fe³⁺ to Fe²⁺ in a dose-dependent manner. Therefore, a possible mechanism by which garlic, white onion, and purple onion exert antidiabetes and antihypertensive properties could be through the inhibitory effect on ACE, α-amylase, and α-glucosidase coupled with their ability to prevent lipid peroxidation in the pancreas and heart, which justify their strong antioxidant properties.

Diabetes is a global pandemic typified by impaired carbohydrate metabolism. In folklore, mushrooms consumption has been linked to diabetes management. However, this study aims to unravel the blood‐glucose‐lowering mechanisms of oyster mushroom (Pleurotus ostreatus) and shiitake mushroom (Lentinus subnudus) in streptozotocin induced‐diabetic rats. Forty two adult Wistar rats were randomly divided into seven groups: the control (C), untreated diabetic rats (group 2), diabetic rats treated with acarbose (25 mg/bodyweight) (group 3), and diabetic rats placed on diet supplemented with 10% and 20% oyster mushroom and shiitake mushroom designated as groups 4–7, respectively. The experiment lasted for 14 days. However, the fasting blood glucose (FBG), activity of α‐amylase, α‐glucosidase, angiotensin‐1 converting enzyme (ACE), arginase, lipid peroxidation, and antioxidant status in rat's pancreas and heart were evaluated. The FBG level, activity of α‐amylase, α‐glucosidase, ACE, and arginase were all reduced significantly (p < .05) in normal rats and in diabetic rat placed on oyster mushroom and shiitake mushroom inclusion diets when compared with untreated diabetic rats. Similarly, activity of superoxide dismutase and catalase was significantly (p < .05) elevated in diets‐treated diabetic rats when compared with an untreated diabetic rat. Also, elevated malondialdehyde equivalent compounds in untreated diabetic rats were significantly reduced in diabetic rats fed with the supplemented diets. Nevertheless, oyster‐mushroom‐ and shiitake‐mushroom‐supplemented diets exhibited FBG lowering ability, reduced activity of α‐amylase, α‐glucosidase, ACE, and improved diabetic rats antioxidant status. Nevertheless, shiitake‐mushroom‐supplemented diets exhibited better effects than oyster‐mushroom‐supplemented diets in treated diabetic rats.