Full Text: 1 Introduction Diabetes is a metabolic disorder that is arising due to abnormal carbohydrate metabolism, insulin deficiency, and/or insulin resistance. The global prevalence of diabetes increases day by day and now it is an alarming situation for developing countries (ADA, 2007; IDF, 2017). As per the forecast of IDF (2017), worldwide the number of diabetic persons will reach 629 million by 2045 is noticed. A report of WHO (2016) revealed that the prevalence of diabetes in Burkina Faso was 4.2% in 2014. Among reported diabetes, 90% are suffering from type II diabetes. The treatment of diabetes is based on parenteral insulin and oral antidiabetic drugs. The most common conventional oral antidiabetic agents such as glibenclamide, chlorpropamide, tolbutamide, acarbose, rosiglitazone, sitagliptin, vildagliptin, saxagliptin, etc, are widely used for the management of diabetes (Surya et al., 2014). Although these hypoglycemic drugs are effective in managing blood sugar level, these are quite expensive and have serious side effects and deleterious contraindications, such as hypoglycemia, weight gain, diarrhea, abdominal cramping, flatulence, hepatotoxicity, hypersensitivity, and skin ulceration (Nasri et al., 2015; IDF, 2017). Some most common alternative diabetes management strategies are stimulation of insulin production and release, inhibition of dipeptidyl peptidase-4, lens aldose reductase, oxidative stress protection and inhibition of advanced glycation (Alam et al., 2018). Among the available alternate diabetes management strategies, the management of α-amylase and α-glucosidase end products formation, inhibition of aldose reductase, lowering plasma glucose levels, altering enzyme activity of hexokinases and glucose-6-phosphate, stimulation of GLUT-4 (Glucose Transporters), lowering the level of skeletal hexokinases, Glucagon-like Peptide-1(GLP-1) analogs and inhibition of Sodium-Glucose co-Transporters 2 (SGLT2) (Kim et al.,2000; Tadera et al., 2006; Alam et al., 2018). Enzymes is also the most common and effective one. Reduced the risk of postprandial glycemia by retarding glucose uptake through the inhibition of carbohydrate hydrolyzing enzymes, such as α-Glucosidase and β-Galactosidase, is the most recent and interesting approach (Read et al., 1986; Tadera et al., 2006; Alam et al., 2018).  Further, complications arising with diabetes are closely related to the free radical associated oxidative stress. Hence the use of antioxidants and effective management of α-amylase are two effective measures for managing diabetes-related complications (Tiwari, 2001). Traditional medicine plants could serve as an alternative source of antidiabetic agents because these owe a wide variety of secondary metabolites. Previous literature revealed that plant secondary metabolites such as alkaloids, tannins, polyphenols, etc, could act as potentials sources of antidiabetic, antihyperglycemic, and hypoglycemic activities as well as an α-amylase inhibitor and antioxidant (Tiwari, 2001; Dal & Sigrist, 2016). Tamarindus (T.) indica  is widely distributed throughout the tropical belt, from Africa to South Asia, Northern Australia, Southeast Asia, Taiwan, and China (Arbonnier, 2002). In Burkina Faso, this is commonly distributed in Northern Sudan, the sub-Sahel and Southern Sudan phytogeographical areas (Bonde, 2019). Mitragyna (M.) inermis is a small bushy tree or shrub which spread from the Sahel to the humid forest of the tropics. In African continents, it is widely distributed in the Côte d’Ivoire, Togo, Senegal, Sudan, and seashore of Benin. While in Burkina Faso, it is frequently reported in all regions (Arbonnier, 2002). Ethnobotanical studies have revealed the uses of M. inermis in traditional medicine, all plant parts such as bark, leaves, and root are used to cure various human diseases. Further bark is used in the treatment of fever, diabetes, hypertension, epilepsy, and infertility. Similarly, leaves are used in the treatment of diabetes, debility, asthenia, malaria while roots are used in the treatment of edema, leprosy, anorexia, constipation and mental illness (Nacoulma, 1996; Arbonnier, 2002; Zerbo et al., 2011; Zizka et al., 2015; Kinda et al., 2017). Like M. inermis, T. indica also hasan important place in African traditional medicines, the leaves of the tree are used in the treatment of biliary affections, liver abscess, sudden malaise, diabetes, biliary fevers, etc. Also, the barks are used in the treatment of urinary inflammations, diabetes, and digestive disorders. Similarly, roots and fruit pulp are commonly used for curing diabetes, hypoglycemic, hypertension and vasodilator (Nacoulma, 1996; Arbonnier, 2002; Konkon et al., 2006; Thiombiano et al., 2012; Olivier et al., 2013; Kinda et al., 2017). Phytochemical studies of M. inermis showed that the leaves aqueous extracts of the tree contain sterols, triterpenes, polyphenols, flavonoids, catechic tannins, saponins, quinones, and alkaloids (Konkon et al., 2006; Konkon et al., 2008; Pahaye et al., 2017). Similarly, phytochemical investigation of T. indica leaves showed the presence of tannins, saponins, sesquiterpenes, alkaloids, and phlobatanins (Doughari, 2006; Choudhary & Swarnkar, 2011; Raghavendra et al., 2013).The antioxidant properties of these trees are well reported by Raghavendra et al. (2013) and Pahaye et al. (2017). In the current study, the α-amylase inhibitory and antioxidant potential of M. inermis and T. indica leaves extracts were in vitro investigated. 2 Materials and Methods 2.1 Plant materials Leaves of T. indica and M. inermis were collected from the forest of Dinderesso (15 km from the Bobo-Dioulasso) in mid of October 2019. Collected plant samples were identified and authenticated by the renowned botanist of Université Nazi BONI, Burkina Faso. Collected leaves samples were shade dried under laboratory conditions and converted into powder with the help of mortar and pestle, this prepared powder was stored in plastic zip bags. The moisture content of the powder was measure by KERN (MLS 50-3C, Germany) and used for maceration in the distilled water (40g leaves powder in 400 ml distilled water) in a ratio of 1 : 10 (W/V) for 48 h at room temperature at magnetic shaker (Souhila et al., 2013). Then, the mixture was filtered using cotton followed by Whatman filter paper N^o1 (GE Healthcare companies, UK). The extraction was repeated three times for getting the average yield and this was reported as 12.27±2.06% for T. indica and 10.93±1.26% for M. inermis. Each obtained extract was stored under the refrigerator to determine the in vitro antioxidant and α-amylase inhibitory activity. Seeds of Sorghum bicolor were purchased from the local market and used for the α-amylase extraction as per the standard protocol described by Adefila et al. (2012). The activity of α-amylase was quantified by using glucose (Scharlau Chemie S.A, Spain) as the standard as described by Miller (1959). The specific activity was expressed in µg of glucose released per min (U) and per mg of protein. Further, the protein concentration of extracts was measured with the Bicinchoninic Acid (BCA) Protein Assay Kit (Pierce, Rockford, IL) using BSA (Bovine Serum Albumin) as standard (Sigma-Aldrich, LLC, USA). The protein concentration of the extracts was 5.03 mg/mL and has a specific activity of 3.32 U/mg protein. 2.1 Estimation of phenolic compounds 2.1.1 Determination of total polyphenols Estimation of polyphenols content of two leaf extracts was evaluated by using a Folin Ciocalteu reagent method with some modification (Meda et al., 2010). The prepared stock solution of each sample         (10 mg/mL) was diluted with the help of distilled water (1/100); from this 125 μL of each extract was mixed with 625 μL of 0.2 N Folin Ciocalteu reagent (MP Biomedicals, LLC, USA). The mixture was kept in dark for 5 minutes, followed by the addition of 500 µL sodium carbonate solution (75 mg/mL, CARLO ERBA Reagents S.A.S, France). Again the mixture was kept in the dark place for 2 h and the absorbances of the mixture were measured at 760 nm using a spectrophotometer (GENESYS 30 Visible Spectrophotometer). The standard calibration curve was plotted using gallic acid (Sigma–Aldrich Chemie, Steinheim, China) (0-200 mg/L) (y=4.668?.10?^(-3) x-0.034; R^2=0.9991). The average of three optical densities (OD) was used and the results expressed in mg Gallic Acid Equivalents (GAE)/100 mg extract. 2.1.2 Determination of total flavonoids The total flavonoids content of both aqueous leaf extracts was determined by modifying AlCl₃ method, as reported by Meda et al. (2010). The same dilution of both the extracts, as mentioned above was prepared with methanol (Fisher Scientific, UK). From this, 625 μL of each extract (0.1 mg/mL) was mixed with 625 μL of aluminum trichloride (AlCl₃) (Lab-honeywell, Germany) in 625 μL of methanol (2%). The mixture was kept in a dark for 10 minutes and the absorbances of each sample were recorded at 415 nm using a UV-visible spectrophotometer. Quercetin (0-50 mg/L) (Sigma– Aldrich Chemie, Steinheim, China) was used as a reference compound to produce the calibration curve (y=1.259?.10?^(-2) x; R^2=0.9990) and determine total flavonoid content. The average of three OD was used as a result and expressed in mg Quercetin Equivalent (QE) / 100 mg extract (Meda et al., 2010). 2.3 Estimating of antioxidant activity 2.2.1 Radical 2,2’-azinobis-3-ethylbenzothiazoline-6-sulphonate (ABTS) decoloration assay The antioxidant capacity of both extracts was estimated by the method given by Meda et al. (2010). For this, methanolic dilution at 1/100 was prepared from both the extracts (10 mg/mL), and from this, 10 μL of diluted extract (0.1 mg.mL^-1) were reacted with 990 μL of fresh ABTS•+ (Meridian Rd, Rockford, U.S.A) solution and incubated in the dark. The absorbance of the ABTS•+ solution was measured at 734 nm. Ascorbic acid (0-10 µg/mL) (Sigma – Aldrich Chemie, Steinheim, China) was used as standard (y=-7.874?.10?^(-4)x+0.709 ; R^2=0.9993)  while Quercetin was taken as the reference-free radical scavenger. Free radical scavenging capacity of extracts was expressed in µmol Ascorbic Acid Equivalent (AAE)/g extract (Meda et al.,2010). 2.3.2 Radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging test The methanol dilution of the used extracts was prepared as described above. Then 375 µL of each extract was mixed with 750 µL of DPPH solution (0.02 mg/mL methanol) (Acros Organics, Spain). After incubation for 15 min at room temperature, the OD of the mixture was recorded against the blank at 517 nm. The test was performed in triplicate andthe standard calibration curve was plotted using ascorbic acid (0-10 µg/mL) (Sigma– Aldrich Chemie, Steinheim, China) (y=-2.224?.10?^(-2)x+0.348 ;R^2=0.9966 ) (Meda et al., 2005). 2.3.3 Ferric reducing antioxidant power (FRAP) assay The antioxidant capacity of the T. indica and M. inermis was estimated spectrophotometrically by FRAP assay. For FRAP assay, an aqueous solution (10 mg/mL) of the two extracts was used. For this, 0.5 mL of each extract (100 μg.mL^-1) was mixed with 1.25 mL phosphate buffer (0.2 M, pH 6.6) (Carlo Erba Reagents, France) and 1.25 mL potassium hexacyanoferrate [K₃Fe(CN)₆] aqueous solution (1%) (Fisher Chemical, UK). After 30 min of incubation at 50°C, 1.25 mL trichloroacetic acid (10%) (ACS, Reagent Ph Eur, Germany) was added to the mixture and centrifuged at 3000 rpm for 10 min. Subsequently, 0.625 mL of the supernatant was mixed with 0.625 mL distilled water and 0.125 mL of a freshly prepared FeCl₃ solution (0.1%) (Chem-Lab NV, Belgium), and the absorbance at 700 nm was recorded against a reagent blank after 30 min incubation (y=3.270?.10?^(-3)x ; R^2=0.9990 ). All the determinations were performed in triplicates and Quercetin was taken as the reference reducer. The determination of Fe³⁺ reducing activity was performed in triplicate and expressed as µmol Ascorbic Acid Equivalent (AAE)/g extract (Meda et al., 2010). 2.4 Evaluation of α-amylase inhibitory activity In vitro α-amylase, an inhibitory assay of T. indica and M. inermis leaves extracts were performed according to Adewale et al. (2006); Adewale & Oladejo (2009) with some modifications. The test was conducted with two concentrations, viz., 10, and 0.005 mg/mL of plant extract.The 500 µL of plant extract was mixed in 1750 µL of 1% starch solution (Carlo Erba Reagents S.A, Frence), 727 µL of the buffer, 23 µL of α-amylase aliquot and incubated at 37°C for 60 min. To stop the reaction, 100 µL of 3,5 dinitrosalicylic acid colour reagent was added to the test tube and the test tubes were incubated in a water bath at 85°C for 5 min. The reaction mixture was then diluted after adding 750 ml distilled water and absorbance was measured at 540 nm in a spectrophotometer. Different blanks were prepared by replaced an aliquot of the enzyme with a buffer for correcting the background absorbance.Readings were taken in triplicates. The specific activity was measured by reference to the glucose calibration curve. One unit of the amylase activity was defined as the amount of enzyme which liberated reducing sugar equivalent to 1 µg of D-glucose per minute from soluble starch at 25°C. α-Amylase inhibition percentage (%I) was calculated as follows: 2.5 Statistical analysis Statistical analysis was performed with R 3.5.1. The results are presented as means ± standard deviations. Student t-test was used to compare the means of activities between the two plant extracts and between each extract to quercetin as standard.P-values (p) < 0.05 were considered significant. 3 Results and discussion 3.1 Total polyphenol, flavonoid and Antioxidant contents of plant extracts The selection of a good extraction method is a crucial step in getting extracts with an acceptable yield of antioxidant compounds. The presence of phenolic and flavonoid compounds are important constituents of plant extracts responsible for antioxidant activity. Total polyphenol and flavonoid contents were quantified in the aqueous extract of M. inermis and T. indica and the results of total polyphenol were derived from a calibration curve (y=4.668?.10?^(-3) x-0.034; R^2=0.9991) of gallic acid and expressed in gallic acid equivalents (GAE) per 100 mg extract weight. While the results of flavonoid contents were derived from the calibration curve (y=1.259?.10?^(-2) x; R^2=0.9990) of quercetin and expressed in quercetin equivalents (QE) per 100 mg dry extract weight.Results of the study revealed that both aqueous extracts have almost equal polyphenol content and it was reported 20.24 mg GAE/ 100 mg and 24.42 mg GAE/ 100 mg for T.indica and M. inermis respectively (Table 1). While in the case of flavonoid content, a significant difference was reported between T.indica (9.90 mg QE/100 mg extract) and M. inermis (0.95 mg QE/100 mg extract). The extracts rich with phenolic compounds could be a good antioxidant source that would help increase the overall antioxidant capacity of an organism and guard it against diabetes. Antioxidant activity of T. indica and M. inermis leaves aqueous was related to the available concentration of total phenols and flavonoids which are responsible for deactivating free radicals based on their ability to donate hydrogen atoms to free radicals. The results of the study revealed that the tested extracts had different levels of antioxidants (Table 2). The ABTS and DPPH tests have significantly lower antioxidant levels than quercetin (p?0.01). As for the Fe³⁺ reduction test, the aqueous extracts of T. indica (677.26 µmol AAE/g extract) and M. inermis (329.95±49.11 µmol AAE/g extract) showed very low levels of reduction as compared to the reference ferric reducer (p?0.001).These plant phenolic compounds and flavonoid content are responsible for significantantioxidant activities (Lamien-Meda et al., 2008; Choudhary & Swarnkar, 2011; Raghavendra et al., 2013; Nyambe-Silavwe et al., 2015). Antioxidant compounds counter with free radicals mediate oxidative stress in the cell and prevent chronic illness such as diabetes (Lamien-Meda et al., 2008; Pahaye et al., 2017). Mostly plant antioxidants act as hydrogen/electron donors or redical scavenger; in this either they donate one electron/hydrogen to the free radical present in a biological system or suppress chain initiation and/or break the chain propagation reactions by scavenging the active radicals (Rolland, 2004). The antioxidants present in the aqueous extracts of T. indica and M. inermis leaves trapped the radicals DPPH, ABTS and reduced Fe(III) which help in preventing antioxidants. The result of the study revealed that both extracts have the potential to overcome oxidative stress and could serve as therapeutic agents for treating radical related pathological damage associated with diabetes but some further detailed study is required to get more molecular details. 3.2 α-amylase Inhibitory activity of plant extracts In this study, the α-amylase inhibitory activity of T. indica and M. inermis leaves extracts was investigated (Table 3). The percentage inhibition of α-amylase by both the extracts was studied at two concentrations viz., 0.005 mg/ml, and 10 mg/ml. At the lowest concentration (0.005 mg/mL), 36.49 and 26.28% α-amylase inhibition was reported for T. indica and M. inermis leaves extracts respectively. While this inhibition reached 89.55 and 75.65% for T. indica and M. inermis extracts respectively at higher concentrations (10 mg/mL). The percentage inhibition of both the extracts was dose-dependent. It has been reported that plant phenolic compounds modulate the enzymatic breakdown of carbohydrates by inhibiting α-amylase enzymes (Kim et al., 2000; Tadera et al., 2006). Various studies suggested that leaves of T. indica contain various polyphenols such as 8-C-glycosyl-apigénin, 6-C-glycosyl-apigénin, 8-C-glycosyl-lutéolin, 6-C-glycosyl-lutéolin,7-o-glucosideluteolin, vitexin, isovitexin, orientin, and iso-orientin which could justify the α-amylase inhibitory activities of this tree (Bhatia et al., 1966; Nacoulma, 1996; Escalona-Arranz et al., 2010).This α-amylase inhibitory activity of this plant extracts could justify the antidiabetic property and traditional use of these plants in diabetes treatment (Tadera et al., 2006; Alam et al., 2018). Similarly, Mentreddy (2007) and Alam et al. (2018) associated the antihyperglycemic properties of this plant with the presence of various secondary metabolites, such as polyphenols, alkaloids, terpene compounds, glucosides, and saponosides. However, phytochemical investigations of the M. inermi sleaves extracts have identified the presence of many alkaloids such as uncarin D, rhynchophyllin, isorhynchophyllin, rotundifolin, isorotundifolin, ciliaphyllin, speciogynin, pteropodin, uncarin F, mitraphyllin, isomitraphyllin and mitraciliantin (Shellard & Sarpong, 1969;  Shellard & Sarpong, 1970; Phillipson, 1973; Toure et al., 1996; Fiot et al., 2005). Thus, the result of the study suggested that the antidiabetics activities of a plant is not only associated with the phenolic compounds alone but it is a combined effect of various biomolecules such as polyphenols, flavonoids, alkaloids, etc. (Feknous et al., 2014). The results of α-amylase inhibitory properties of M. inermis were also confirmed by the findings of previous researchers (Narkhede, 2012). Conclusion Hence the above results suggest that the leaf extracts of T. indica and M. inermis could be greatly beneficial in reducing the absorption of starch into the body also justify the use of these plants in traditional herbal medicines. The extent of antioxidant and α-amylase inhibition by these extracts is dependent on the available active ingredients polyphenols and flavonoids. Thus this study confirms that the leaves of T. indica and M. inermiscan mitigate postprandial hyperglycemia and oxidative stress and therefore assist in combating diabetic complications but the crude extract contains several bioactive compounds; therefore, further deep investigations are required to characterize the active molecule, which may be a potent antioxidant and enzyme inhibitor. Acknowledgement We are thankful to Herbalists of Bobo-Dioulasso city for having shared theirs recipes. Conflict of interest The authors declare no interest conflicts inthis manuscript.