Blood glucose lowering and effect of oyster (Pleurotus ostreatus)‐ and shiitake (Lentinus subnudus)‐supplemented diet on key enzymes linked diabetes and hypertension in streptozotocin‐induced diabetic in rats

Abstract

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.

INTRODUCTION

Diabetes mellitus (DM) is heterogeneous group of disorders that occur due to impairment in insulin secretion and resistance or in some cases, manifestation of both (Elangovan et al., 2019). DM is a metabolic disorder of carbohydrate metabolism and it often enhances oxidative stress-related diseases (Konda et al., 2019). Globally, DM is among the foremost cause of mortality in the world with a projected prevalence of DM in adult to be 462 million by 2045 (WHO, 2017). Interestingly, the two types of diabetes have different underlying mechanisms, but in both types, hyperglycemia and hypertension are common. However, major practical approach adopts toward achieving reduced postprandial hyperglycemia in diabetes is to slow down the progression of carbohydrate metabolism by inhibiting the activity of relevant enzymes such as α-amylase and α-glucosidase involved in carbohydrate metabolism so as to reduce glucose availability absorption (Oboh, Ademiluyi, Agunloye, et al., 2018). Pancreatic α-amylase is a hydrolytic enzyme involved in the breaking down of dietary carbohydrate (starchy food) into smaller units (disaccharides). These disaccharide compounds are further degraded by another hydrolytic enzyme called α-glucosidase that hydrolyzed the disaccharides to glucose residues, the form in which carbohydrate meals could be accessed by the body. However, inhibiting activity of α-amylase and α-glucosidase would delay or slow down rate of metabolism of carbohydrate meal and minimized liberation of glucose (Kajaria et al., 2013). Meanwhile, antidiabetic drugs (acarbose, voglibose, and miglitol) have an inhibitory effect against activity of these enzymes in practice but they often have some undesirable side effects (Derosa & Maffioli, 2012). Interestingly, in diabetes, hyperglycemia cause elevation of blood pressure as well as generation of free radicals, adjudged by a decline in enzymic and nonenzymic antioxidant potentials (Evans et al., 2002; ). The oxidative damage caused by ROSis validated by an incessant upsurge of malondialdehyde (MDA) concentration in various tissues of diabetic animal (Matough et al., 2012).

Mushrooms are common foods consumed in many parts of the world. They have abundant insoluble carbohydrate, phenolic acid, flavonoids, and alkaloids protein, chitin (Agunloye et al., 2020). Mushrooms generally have been used in the management of nutrition deficiency in the developing countries (Pedneault et al., 2006), whereas various research outputs have shown that mushrooms exhibit antitumor activity (Elmastas et al., 2007), antifungal activity (Jose & Janardhanan, 2000), antimicrobial activity (Turkoglu et al., 2007), and neuroprotective property (Agunloye et al., 2020). Oyster mushroom and shiitake mushroom are among most commonly consumed mushrooms in southwestern Nigeria. Oyster mushroom and shiitake mushroom are a cheap source of bioactive compounds to the rural dwellers in Nigeria. Oyster mushroom and shiitake mushroom grow naturally in southwestern Nigeria during raining season in the forests, grasslands, and damp rotten logs. In this study, we aim to evaluate the blood glucose lowering property and their underling mechanisms vis-à-vis effect on the activity of α-amylase, α-glucosidase, ACE, and arginase in diabetic rats.

MATERIAL AND METHODS

Oyster mushroom and shiitake mushroom were purchased locally from farm settlement at Ibule-soro, Ondo state, and were identified at Herbarium, Federal University of Technology, Akure, Nigeria. The samples were oven dried and diet supplementations were done as previously reported by Adefegha et al. (2014). Meanwhile, chemicals such as streptozotocin (STZ), arginine, hippuryl-histidyl-leucine, and other reagents were of analytical standard.

Induction and experimental design

Experimental animals (adult male Wistar albino rats; 180–200 g, age 11–12 weeks) were used for this study. Before the commencement of the research, approval for the use of experimental animals was granted and selected animals were handled in accord to the approval of the Animal Ethics Committee of our institution. The rats were acclimatized for 14 days and were nurtured with commercial rat's feed and free access to water. Induction was done via administration of STZ (50 mg/body weight, single-dose i.p.) (Parveen et al., 2011). Hyperglycemia was confirmed by determining the fasting blood glucose (FBG) level of STZ-administered rat after 72 h postadministration. Rats with FBG greater than 250 mg/dl were chosen for further study and tagged diabetic rats.

Groups and experimental design

Experimental rats were randomly distributed into seven groups of six rats each. Group 1: the control group (nondiabetic); group 2: untreated diabetic (DM) rat (negative control); group 3: DM rats (positive control) placed on acarbose (25 mg/body weight per day). It should be noted that rats in groups 1–3 were placed on the basal diet throughout the diet regime. Groups 4 and 5: DM rats fed with diet containing 10% and 20% oyster mushroom inclusion; groups 6 and 7: DM rats placed on diet containing 10% and 20% inclusion of shiitake mushroom. It should be noted that the rats were caged individual to ascertained daily feed intake and proper monitoring. Treatment lasted for 14 days, during this period, the FBG was measured at 0, 7th, and 14th day. The rats were made to fast overnight on the last day of the experiment and sacrificed. Then blood was drawn via cardiac puncture, liver, and pancreas, and intestine was harvested and homogenized. The homogenates were prepared to obtain clear supernatants that were later use for various biochemical assays (Belle et al., 2004).

Biochemical assays Fasting blood glucose determination

FBG was measured using glucometer (Accu check Active) according to manufacturer instruction.

Determination of α-amylase activity

Pancreatic α-amylase activity was evaluated as previously reported by Worthington (1993). Briefly, 500 μL of 20 mM sodium phosphate buffer (pH 6.9 with 6 mM NaCl) and 100 L pancreatic homogenate (α-amylase source) were incubated at 25°C for 10 min, and then followed by addition of 1000 μL of dinitrosalicylic acid (DNSA) solution. The mixture was incubated at 100°C for 5 min so as to stop the reaction, and then cooled at room temperature. The mixture was diluted by adding 10 mL of distilled water. The absorbance was read at 540 nm using spectrophotometer and α-amylase activity was finally calculated.

Determination of α-glucosidase activity

Activity of α-glucosidase in diabetic rats was assessed according to the method of Apostolidis et al. (2007). Briefly, the reaction mixture consists of homogenate from small intestine, 100 μL of small intestinal homogenate (α-glucosidase source), and phosphate buffer (0.1 M, pH 6.9), and the mixture was incubated at room temperature for 10 min. Then, p-nitrophenyl-d-glucopyranoside solution (5 mM) was added and incubated at 25°C for 5 min. The absorbance was then read at 405 nm and α-glucosidase activity was calculated.

Determination of ACE activity

The lung ACE activity was estimated as previous reported by Cushman and Cheung (1971). Briefly, the reaction mixture consists of lung homogenate that was preincubated 125 mM Tris-HCl at room temperature for 10 min. Subsequently, 50 μL of 8.3 mM hip-his-leu (HHL) (ACE substrate) was introduced to the mixture, incubated at room temperature for 30 min. The rate of HHL hydrolysis reaction was terminated by adding of HCl (1.0 M), whereas the resulting hippuric acid generated was obtained using 1.5 ml of ethyl acetate. Then, the mixture was separated via centrifugation and clear upper layer was carefully removed into another clean test tube and was then evaporated to dryness. Finally, the extracted hippuric acid was recovered by addition of 1.0 ml of distilled water in the test tube and the absorbance was measured at 228 nm using a Jenway UV–vis spectrophotometer. The specific activity of the enzyme was subsequently calculated. The ACE activity was expressed as mmol/min/mg protein.

Determination of arginase activity

Arginase activity was evaluated as previously described by Kaysen and Strecker (1973). Briefly, the reaction mixture consists of clear heart homogenate, Tris-HCl (50 mmol/L, pH 7.5), and was preincubated at room temperature for 10 min for enzyme activation. Thereafter, l-arginine solution was added to the activated enzyme incubated at room temperature for 1 h. Finally, acid mixture containing [H₂SO₄/H₃PO₄/H₂O = 1:3:7 (v/v/v)] was added to stop to halt the rate of the reaction. The arginase activity was expressed as μmol urea produced/min/mg protein.

Determination of NOx level

Tissue nitric oxide (NOx) content was determined using the method (Miranda et al., 2001). NOx content (pancreas and heart) was assessed in a medium containing 150 μL of each of tissue homogenate and Griess reagent. Thereafter, the mixture was incubated at room temperature for 60 min nitrite. The nitrate level was measured spectrophotometrically at 540 nm and nitrite plus nitrate levels were expressed as micromole of NOx/mg protein.

Superoxide dismutase determination

Super oxide dismutase activity was evaluated according to the method of Misra and Fridovich (1972). The reaction mixture consists of 500 μL either plasma or tissue homogenate, carbonate solution (50 mM), and 17 μL adrenaline. The adrenaline was oxidized to adrenochrome, a colored product that was detected at 480 nm. The rate at which adrenaline was inhibited in the samples was monitored for 180 s. The enzymatic activity was expressed in units/mg protein.

Catalase activity determination

Catalase activity was determined according to the method of Nelson and Kiesow (1972). Briefly, the reaction mixture consists of 1000 μL of 10 mM phosphate buffer (pH 7.4), 100 μL of either plasma or tissue homogenate, 400 μL of hydrogen peroxide (H₂O₂), and 1000 μL of dichromate and acetic acid solution (1:3 w/v). Thereafter, the mixture was incubated and the rate of hydrogen peroxide reaction was monitored at 240 nm for 2 min at room temperature. Catalase activity was expressed as mole H₂O₂ consumed/min/mg protein.

Malondiadehyde quantification

MDA level was quantify according to the method of Ohkawa et al. (1979). The reaction mixture composed of 200 μL plasma or tissue homogenate and sodium dodecylsulfate (SDS) and 750 μL of acetic acid and thiobarbituric acid (TBA). The mixture was incubated at 95°C for 1 h and 30 min. The absorbance was measured at 532 nm and MDA tissue level was expressed as μmol MDA/mg protein.

Data analysis

Data were presented as mean ± standard deviation (SD). Difference in means was analyzed using one-way ANOVAfollowed by Turkey post-hoc multiple test as the level p < .05 using graph pad 5.0.

RESULTS

The mean body weight of normal, STZ-induced diabetic, acarbose treated diabetic rat, as well as diabetic rats placed on diets supplemented with oyster mushroom and shiitake mushroom was presented in Table 1. STZ administration caused a decline in the mean body weight of untreated diabetic rats when compared with normal nondiabetic rats. Meanwhile, diabetic rats administered with acarbose (25 mg/BW) and those place on diets supplemented with 10% and 20% of oyster mushroom and shiitake mushroom, respectively, had an improved weight gain when compared with untreated diabetic rats.

TABLE 1 Effect of acarbose, oyster mushroom (Pleurotus ostreatus), and shiitake mushroom (Lentinus subnudus) supplemented diet on body weight (g) of STZ-induced diabetes in rats

	Initial weight before STZ administration	After STZ administration	After treatment
Control	210 ± 4.73	218 ± 2.44	230 ± 4.89
Diabetic (DB)	222 ± 3.47	211 ± 4.38	187 ± 1.67
DB + acarbose (25 mg/BW)	226 ± 5.09	214 ± 3.16	226 ± 3.74
DB + 10% P. ostreatus	222 ± 4.78	202 ± 4.00	218 ± 3.89
DB + 20% P. ostreatus	220±3.89	206±3.16	219±4.47
DB + 10% L. subnudus	227 ± 4.70	212 ± 1.60	229 ± 2.74
DB + 20% L.subnudus	227 ± 3.44	214 ± 4.00	231 ± 2.44

Values are mean ± SD from six rats in each group.

Figure 1 illustrates the effect of oyster-mushroom- and shiitake-mushroom-supplemented diets on FBG of diabetic rats. The FBG of diabetic rats was observed significantly (p < .05) higher in untreated diabetic rats when compared with FBG level of normal rats (nondiabetic rats). However, FBG of diabetic rats administered with acarbose (a standard antidiabetic drug) as well as those placed on diets supplemented with oyster mushroom and shiitake mushroom (10% and 20% inclusion) was significantly reduced progressively during the period of the study. Nevertheless, shiitake-mushroom-supplemented diets had better FBG lowering ability than oyster mushroom inclusion diet. Effect of oyster mushroom and shiitake mushroom inclusion diets on the activity of α-amylase in diabetic rats was shown in Figure 2. The obtained results showed a significant (p < .05) increase in the pancreatic α-amylase activity of untreated diabetic rats in comparison with the nondiabetic rats. Nevertheless, diabetic rats administered with acarbose (25 mg/kgbody weight), fed with supplemented diets (oyster and shiitake mushrooms), showed a significant (p < .05) reduction in the activity of pancreatic α-amylase in comparison with untreated diabetic rats. Comparatively, diabetic rats treated with acarbose exhibited significantly (p < .05) lower α-amylase activity than those fed with diets supplemented with 10% inclusion of oyster mushroom and shiitake mushroom, whereas a nonsignificant difference was observed when the effect of acarbose on α-amylase activity was compared with those (diabetic rats) placed on diets supplemented with 20% oyster mushroom and shiitake mushroom inclusion. Nevertheless, shiitake-mushroom-supplemented diets lower α-amylase activity less than oyster-mushroom-supplemented diets when their effects were compared. However, oyster mushroom at 20% percentage inclusion in diet significantly (p < .05) reduced α-amylase activity than 10% oyster mushroom inclusion. Meanwhile, there is no significant difference in the effect of shiitake mushroom supplemented on α-amylase activity when their effects were compared.

Also, Figure 3 revealed the activity of intestinal α-glucosidase in STZ-induced diabetic rats fed with diets supplemented with oyster mushroom and shiitake mushroom. The results disclosed that STZ caused a significant (p < .05) increase in the intestinal α-glucosidase activity in induced rats when compared with the nondiabetic rats. Interestingly, diabetic rats treated with acarbose (25 mg/kgbody weight) exhibited significantly (p < .05) lower α-glucosidase activity than those fed with diets supplemented with 10% inclusion of oyster mushroom and shiitake mushroom, whereas a nonsignificant difference was observed when the effect of acarbose on α-glucosidase activity was compared with those (diabetic rats) placed on diets supplemented with 20% oyster mushroom and shiitake mushroom inclusion. Nevertheless, diabetic rats placed on oyster mushroom and shiitake mushroom inclusion diet (10% and 20%, respectively) showed a significant (p < .05) reduction in α-glucosidase activity when compared diabetic rats (untreated rats). However, activity of intestinal α-glucosidase in diabetic rats fed with diets supplemented with 20% shiitake mushroom and oyster mushroom was significantly (p < .05) lower than those fed with 10% shiitake mushroom and oyster mushroom inclusion. Figure 4 depicts activity of angiotensin-converting enzyme (ACE) in the lung of diabetic rats fed with oyster mushroom and shiitake mushroom inclusion diets. The results disclosed a significant (p < .05) increase in the lung ACE activity of diabetic rats in comparison with nondiabetic rats. Nevertheless, oyster mushroom and shiitake mushroom inclusion diets produced a significant (p < .05) reduction in lung ACE activity in diabetic rats fed with the supplemented diets in comparison with the ACE activity of untreated diabetic rats as shown in Figure 4. Although diet with 20% inclusion of shiitake and oyster mushroom significantly (p < .05) lower lung ACE activity than diet supplemented with 10% oyster mushroom and shiitake mushroom. Similarly, results from this study also revealed that STZ-induced diabetic (untreated) rats exhibited a significant (p < .05) higher plasma and heart arginase activity than control rats, the nondiabetic rats as presented in Figure 5(a, b). Nevertheless, oyster mushroom and shiitake mushroom inclusion diets (10% and 20% inclusion) significantly (p < .05) decline plasma and heart arginase activity in comparison with untreated diabetic rats. Comparatively, shiitake mushroom at 20% inclusion significantly (p < .05) lower arginase activity in heart of diabetic rats than diet containing 10% shiitake mushroom, whereas a nonsignificant difference was observed in diabetic rats fed with oyster-mushroom-supplemented diets. Figure 6 depicts the effect of oyster and shiitake-mushrooms-supplemented diet on pancreas and heart NO level. The results showed that untreated diabetic rats exhibited significantly (p < .05) lower pancreatic and heart NO level in comparison with the nondiabetic rats. However, oyster mushroom and shiitake mushroom inclusion diets (10% and 20%) significantly (p < .05) enhanced NO level in pancreatic and heart of diabetic rat after feeding diabetic rats with the supplemented diets for 14 days in comparison with the untreated diabetic rats. Meanwhile, diabetic rats fed with diets supplemented with 20% of oyster mushroom and shiitake mushroom, respectively, enhanced NO level significantly (p < .05) than 10% inclusion diets when their effect on NO level were compared as shown in Figure 6.

Also, Figure 7 illustrates the effect of oyster mushroom and shiitake mushroom 10% and 20% inclusion diets on the activity superoxide dismutase (SOD) in the liver and pancreas of diabetic rat. The obtained results showed that pancreas and liver SOD activity was observed significantly (p < .05) less in untreated diabetic rats when compared with nondiabetic rats. Nevertheless, oyster mushroom and shiitake mushroom 10% and 20% inclusion diets significantly (p < .05) enhanced higher SOD activity in diabetic rats in comparison with the untreated diabetic rats. Nevertheless, shiitake mushroom supplementation enhanced SOD activity higher than oyster-mushroom-supplemented diet in diabetic rats. Meanwhile, diabetic rats fed with diet supplemented with 20% shiitake mushroom significantly increase SOD activity in diabetic rats than 10% supplemented diet, whereas a nonsignificant was observed in SOD activity of diabetic rats fed with diet supplemented with 10% and 20% oyster mushroom as presented in Figure 7. Likewise, liver and pancreas catalase activity was significantly reduced in untreated diabetic rats when compared with the nondiabetic rats as presented in Figure 8. Meanwhile, shiitake and oyster mushroom inclusion diets improved liver and pancreatic catalase activity significantly after placing the diabetic rat on the supplemented diets for 14 days when compared with untreated diabetic rats. However, shiitake mushroom inclusion diets enhanced catalase activity higher than oyster-mushroom-supplemented diets in diabetic rats. Diets supplemented with 20% shiitake and oyster mushroom significantly enhanced catalase activity than 10 shiitake and oyster mushroom in the pancreas diabetic rats. Conversely, it was shiitake mushroom at 20% inclusion that caused significant increase in catalase activity in diabetic rats, while a nonsignificant difference was observed in diabetic rats fed with diet supplemented with oyster mushroom.

Also, Figure 9a–c depicts MDA equivalent compounds in the pancreas, liver, and heart of diabetic rats placed on shiitake mushroom and oyster mushroom inclusion diets. The obtained results revealed that MDA level in the pancreas, liver, and heart untreated diabetic was significantly (p < .05) higher when compared with nondiabetic rats, as shown in Figure 9a–c. However, diabetic rats placed on supplemented diets exhibited significant less MDA level when compared to the untreated diabetic rats. Nevertheless, shiitake mushroom inclusion diets reduced MDA level than oyster mushroom-diet-treated diabetic rats.

DISCUSSION

Diabetes and its complications are among the major public health challenges in the world. It causes prolong damage, dysfunction, and organ failure in diabetic individual (Asrafuzzaman et al., 2018). However, holistic approach toward prevention of diabetes as well as to reduce long-term complications of diabetes central on controlling and monitoring of glycemic level that could be achieved through the use of antidiabetes drugs that often have some side effects as well as through the use of medicinal foods (Oboh, Agunloye, Adefegha, et al., 2015). Meanwhile, there is a continuous search for a better therapeutic advance toward the management of diabetes. Hyperglycemia usually typified by an increase postprandial blood glucose and this occurrence has been adjudged as an onset to the development of diabetes and associated complications (hypertension) (Boustany et al., 2004), as well as oxidative stress-imbalanced implicated in vascular complications (Kushiro et al., 2017; Muniyappa & Quon, 2007). Therefore, management of hyperglycemic state in diabetes is considered as a better strategy in diabetes management as well as its related complications such as hypertension. To achieve this feat, the activities of vital enzymes prominent in carbohydrate metabolism as well as activity of ACE and arginase implicated in the progression of hypertension must be checked and downregulated. Hence, the antidiabetic effect of the oyster-mushroom- and shiitake-mushroom-supplemented diets were evaluated with the main aim focusing on their effect on fasting blood–glucose level, activity of carbohydrate enzymes, ACE, arginase, and NO level in STZ-induced diabetes rats.

Owing to the reduction in the FBG of diabetic rats fed with oyster-mushroom- and shiitake-mushroom-supplemented diets as presented in Figure 1, this observation suggests the antihyperglycemic property of the selected mushrooms. Interestingly, the antihyperglycemic effect of the seleted mushrooms could as a results of reduction in the activity of α-amylase and α-glucosidase in diabetic rats by bioactive compounds present in the oyster mushroom and shiitake mushroom as presented in Figures 2 and 3, respectively. These will lead to a reduction in the rate of glucose liberation and absorption into the blood circulation (Oboh, Ademiluyi, Agunloye, et al., 2015; Oboh, Ademiluyi, Agunloye, et al., 2018). As observed in this study, an increase in the activity of carbohydrate hydrolyzing enzymes in untreated diabetic (control) rats plays a major role in the elevated glucose level recorded as presented in Figure 1. These observations agreed with earlier finding on the elevated level of the α-amylase and α-glucosidase activities in a diabetic state (Martı´nez et al., 2003; Tormo et al., 2006). An increase in the activity of carbohydrate hydrolyzing enzymes is responsible for elevated postprandial hyperglycemia peaks, whereas prompt reduction in their enzymatic activities will help in the management of hyperglycemic state as well as to prevent the onset of hypertension and manifestation of free radical. Interestingly, diabetic rats fed with diet containing oyster mushroom and shiitake mushroom, respectively, exhibited a steady decline in the FBG level. These findings could be linked to the therapeutic effect of diverse phytochemicals bestow in the studied mushrooms on the activity of carbohydrate hydrolyzing enzymes, as shown in Figures 1–3, respectively. Studies have established that bioactive compounds could modulate the expression of the gene coding for α-amylase and intestinal α-glucosidase (Piras et al., 2010; Pouyamanesh et al., 2016).

Diabetes has been adjudged as a predisposing factor for the manifestation of hypertension (Nazar, 2014). The hallmark event leads to the pathogenesis of hypertension in diabetes central on ACE activity that has been linked to the production of vasoconstrictive biomolecule (angiotensin II) (Oboh, Ademiluyi, Agunloye, et al., 2018). Likewise, arginase activity contributes to the hypertensive effect by decreasing the availability of l-arginine for NO production via endothelial NO synthase (eNOS) (Agunloye & Oboh, 2018). NO has been known as a potent vasodilator but its availability has been limited as a result of competition for the same substrate by both arginase and eNOS (Agunloye & Oboh, 2018). In the same vein, the hydrolytic product of arginase activity has been reported in smooth muscle stiffness (Agunloye et al., 2019). Interestingly, oyster-mushroom- and shiitake-mushroom-supplemented diet reduced ACE and arginase activities in diabetic rats, whereas NO level was enhanced. Research findings have shown that mushroom supplements ameliorated blood pressure elevation (systolic and diastolic blood pressure) via their modulatory effects on the renin–angiotensin system (Preuss et al., 2010; Talpur et al., 2002). These observed effects could be linked to the bioactive compound present in oyster and shiitake mushroom, respectively.

Oxidative stress often accompanied chronic hyperglycemic and this occurrence compromised the antioxidant defense mechanisms in the diabetic state (Irondi et al., 2015). The manifestation of reactive oxygen species in diabetes could be linked to free radicals emanating from glucose autooxidation and glycation of proteins. These promote and initiate various free radical damages quantify as MDA content. Also, hyperglycemia-induced production of free radical has been identified as one of the major events that disrupt the endogenous antioxidant defense system in diabetes. Thus, it is obvious that diabetes caused depletion in antioxidant defense system (Irondi et al., 2015). Nevertheless, restitution of antioxidant defense prowess by the oyster mushroom and shiitake mushroom inclusion diets as shown in Figures 7 and 8 gave credence to the oyster mushroom and shiitake mushroom antioxidant prowess in diabetes rats. The first lines of defense (antioxidant enzymes) against ROS in the cell offer a protective role for cell membranes owning to their radical mopping ability and prevent oxidation of lipid (Matough et al., 2012). As shown in this study, a decline in the activity of enzymic antioxidant, as well as elevated lipid oxidation (elevated MDA level) in untreated diabetic rats, could be linked to the limitation in their capacity to detoxify emanating free radicals (Matough et al., 2012). We investigated the modulatory effect of oyster-mushroom- and shiitake-mushroom-supplemented diets on activity of antioxidant enzymes that offer protective defense against oxidative stress assault and prevent lipid peroxidation in diets-treated rats (diabetic). Interestingly, diabetic rats fed withsupplemented diets exhibited significantly higher antioxidant enzymes activities, whereas MDA level was significantly reduced. Studies have shown that mushroom bioactive compounds such as β-glucan, phenolic acids, peptide, and alkaloids exhibited strong antioxidant and hypoglycemic properties (Agunloye et al., 2020; Irondi et al., 2015; Jayakumar & Ramesh, 2006; Yang et al., 2005).

In summary, the antidiabetic properties of oyster and shiitake have been elucidated and it is central on lowering of blood glucose, reducing the activity of carbohydrate hydrolysis enzymes as well as relevant enzymes linked to hypertension. Also, oyster and shiitake offer a protective shield against hyperglycemic-induced ROS in diabetes. This research suggested that human consumption of oyster and shiitake could offer a therapeutic effect against the progression of diabetes and its complications. Meanwhile, shiitake seems better than oyster when the overall effects were compared in diabetic rats.

COMPLIANCE WITH ETHICAL STANDARDS

Before the commencement of the research, approval for the use of experimental animal was granted and selected animals were handled in accord to the approval of the Animal Ethics Committee of our institution.

COMPETING INTERESTS

The authors have nothing to declare.