Abstract
Diet is the main modifiable risk factor underlying the progression of Type 2 Diabetes mellitus (T2DM). The African olive (Canarium schweinfurthii Engl.) of the family Burseraceae and genus Canarium is a source of food and medicine. This review summarized information on the nutritional and chemical composition of the Canarium schweinfurthii Engl. fruit pulp and explored its potential application in the management of T2DM. The literature search covered scientific databases comprising of Science Direct, Springer, Multidisciplinary Digital Publishing Institute, Science Hub and Google Scholar, from April 2023 up to January 2024. The following keywords were used: “Canarium schweinfurthii Engl.”, “Canarium schweinfurthii Engl. fruit pulp”, “Canarium schweinfurthii Engl. nutrition value, chemical composition and bioactive compounds”, “Canarium schweinfurthii Engl. against T2DM”, and “Nutritional requirements for T2DM”. This review evaluates the current state of research of global literature from 1992 to 2022 (n = 450) on Canarium schweinfurthii Engl. and T2DM. Data and information from literature (n = 115) was included in the review. The results of different studies showed that Canarium schweinfurthii Engl. fruit was composed of a wide range of nutritional and chemical components such as minerals, amino acids, fatty acids and vitamins. In addition, the fruit contains bioactive compounds reported to be effective against T2DM. Canarium schweinfurthii Engl. contains phytochemicals such as saponins, phenolics, alkaloids and flavonoids that have positive effects on cardio-metabolic health. Although the T2DM therapeutic effects of Canarium schweinfurthii bark stem extracts and fruit pulp oil have been reported, the therapeutic potential of the whole fruit pulp is yet to be reported.
Graphical Abstract
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1 Introduction
Canarium schweinfurthii Engl. belongs to the family Burseraceae and genus Canarium L. The genus Canarium L. comprises 75 tropical and subtropical species growing naturally across tropical Asia, Africa and the Pacific [1]. The Burseraceae family comprises of three tribes: Burserae, Protieae, Canariceae [2]. Members of the Canariceae are widely utilized for food and medicine. Canarium indicum L., Canarium odontophyllum Miq. and Canarium album L., Canarium ovatum Engl., Canarium bengalense Roxb. and Canarium schweinfurthii Engl. are prominent members of Canariceae [2]. The species, Canarium schweinfurthii Engl., which is the main subject of the review, is commonly found in Western, Eastern and Central African equatorial forest regions. Canarium schweinfurthii Engl. is a multipurpose tree that serves not only as a source of food but also medicine [3]. The stem bark of Canarium indicum L. has been used to treat chest pain [4]. The bark of Canarium ovatum Engl. has been used in the management of fever and as an anti-rheumatic [5]. On the other hand, the leaf and root extracts of Canarium bengalense Roxb. have been used in the treatment of asthma, cough, bronchitis, jaundice and leprosy [6]. Canarium schweinfurthii Engl. has been reported to have anti-hyperglycemic activity [3]. The basis for the utilization of Canarium schweinfurthii Engl. in disease management is attributed to its numerous bioactive compounds categorized into three groups of phytochemicals, namely, terpenes and terpenoids, phenolic compounds (saponins, flavonoids, kaempferol, epicatechins, rutin, tannins glycosides, phytates and oxalates) and alkaloids [7,8,9,10]. Despite their food and medicinal values, the Canariceae are generally categorized as underutilized plants [3].
Type 2 Diabetes mellitus (T2DM) the most common form of diabetes is a chronic metabolic disorder characterized by the underutilization of glucose caused by either insufficient production or the lack of insulin response [11, 12]. It is a complex condition characterized by abnormal disorders of homeostatic control of energy balance due to insulin resistance and pancreatic β-cell dysfunction [13]. In the past three decades, the prevalence of T2DM has risen dramatically in all countries irrespective of income level [12]. A person with T2DM is about four times more likely to get cardiovascular disease (CVD) while 80% of diabetics will die from the disease [14]. Diabetes mellitus has been reported to lead to 2 million deaths each year globally [15]. In addition, about 2% of people with diabetes have been reported to become blind after 15 years [14]. A person with T2DM incurs two to five times higher medical costs than one without the disease. According to WHO, up to 15% of the annual health budgets of many countries in the world are spent on diabetes-related illnesses [14]. Conventional drugs that are used in the management of T2DM are costly and are not easily accessible in many developing countries, moreover, various side effects have been associated with their use [16]. The high cost of T2DM management drugs in low-income countries often forces millions of people to seek alternative forms of treatment such as the use of herbal remedies that are affordable and presumed to have lesser side effects. Diet is the primary modifiable factor leading to the incidence and progression of T2DM. Therefore, the purpose of this review is to summarize information on the composition of the Canarium schweinfurthii Engl. fruit pulp with the view of exploring its potential application in the management of T2DM.
2 Methodology
2.1 Literature search
The literature search was carried out using scientific databases including Science Direct, Multidisciplinary Digital Publishing Institute, PubMed, Science Hub and Google Scholar, from April 2023 up to January 2024. The following keywords were used: “Canarium schweinfurthii Engl.”, “Canarium schweinfurthii Engl. fruit pulp”, “Canarium schweinfurthii Engl. nutrition value and chemical composition”, “Bioactive compounds in Canarium schweinfurthii Engl.”, “Canarium schweinfurthii Engl. against T2DM”, “Nutritional requirements for T2DM”. All authors individually reviewed the internet sources. The search yielded 1205 articles. After the removal of duplicate and irrelevant literature, 450 articles were selected. Only 115 of the 450 articles with necessary information were cited in this review. Research was mainly from Europe, Africa, South America, and Asia.
2.2 Study selection
Studies published in English from 1992 and 2022 with data relevant to the composition and nutritional value of Canarium schweinfurthii Engl., information on T2DM and contribution of Canarium schweinfurthii Engl. against T2DM were included. All authors screened the identified studies according to the inclusion criteria to select the relevant ones. The titles and abstracts were inspected during the initial stage to detect randomized controlled trial (RCTs) that measure Canarium schweinfurthii Engl. effects in some way. In the second step, the abstracts were analyzed to determine if information is reported on the chemical and nutritional composition, bioactive compounds of Canarium schweinfurthii Engl., T2DM, Canarium schweinfurthii Engl. and T2DM, and nutritional requirements for T2DM. In the final stage, the complete text of the relevant literature was thoroughly reviewed so that final qualifying articles could be chosen. Literature that did not have appropriate information about Canarium schweinfurthii Engl. was rejected. Selected reviews and original articles were reviewed and interpreted accordingly.
3 Nutritional and chemical composition of Canarium schweinfurthii Engl. fruit pulp
3.1 Proximate composition
The proximate composition of foods is very important during product development, quality control, and for regulatory purposes. Data on the proximate composition of the fruit pulp of C. schweinfurthii reported by different researchers indicates that the fruit is rich in crude fat and protein. It is also rich in minerals as shown by the ash content, and is a good source of fiber. Different researchers [10, 17,18,19,20,21] reported 12.00–19.00% m/m, 17.00–20.00% m/m, 30–58% m/m and 0.70–11.00% m/m (Table 1) of protein, carbohydrates, fat content and crude fibre content, respectively. A diet is considered high in protein if it exceeds 0.80 g/kg BW or the habitual 15.00–16.00% of total energy [22].
3.2 Fatty acid profile of oil extracted from Canarium schweinfurthii Engl. fruit
The fatty acid profile of lipids influences the food and food products physicochemical properties. Different studies (Table 2) have reported different fatty acid compositions for C.schweinfurthii fruit pulp oil. They include saturated and unsaturated fatty acids. Saturated fatty acids (SFAs) reported in C.schweinfurthii fruit pulp oil include palmitic acid (PA; 16:0), stearic acid (18:0), heptacosanoic acid (27:0), caprylic acid (8:0), myristic acid (14:0) and behenic acid (22:0). Monounsaturated fatty acids (MUFAs) include oleic acid (18:1ω9), gadoleic acid (C 20:1ω11), gondoic acid (C 20:1ω9), hypogeic acid (16:1ω9), palmitoleic acid (C 16:1ω7), pentadecenoic acid (C 15:1ω5) and vaccenic acid (trans and cis). The polyunsaturated fatty acids (PUFAs) include arachidonic acid (20:4 ω6), linoleic acid (18:2ω6) and linolenic acid (18:3ω3).
To assess its dietary applicability and safety, the nutritional quality indices (Table 2) of C.schweinfurthii fruit pulp oil were evaluated based on the reported fatty acid composition. These included atherogenic index (AI), PUFA/SFA and linoleic acid/ α-linolenic acid (ω6/ω3) ratio. Atherogenic index shows the possibility of fatty acids to attach to epithelial cells and prevent plaque aggregation and coronary diseases [23]. Hence, lower values of this index are desirable as they are considered to be protective against cardiovascular disorders [24]. For AI, apart from results reported by [25], other calculated values were close to 0.50 as recommended by Food and Agricultural Organization/World Health Organization [26]. The PUFA/SFA and ω6/ω3 ratios are useful for determining fatty acid quality of food products.
3.3 Amino acid profile
Studies have reported different amino acid compositions for C.schweinfurthii fruit pulp (Table 3). Amino acids are units that make up proteins and are important for gene expression, cell signaling, reproduction, neurotransmission, metabolism, oxidative stress, pain control, inflammatory responses, and detoxification [33]. Protein breakdown or synthesis causes a change in amino acid composition. Protein metabolism provides for the eight amino acids that must primarily come from food [34]. The amino acid composition of a protein is important for its nutrition quality as well adequate intake of essential amino acids [35]. A protein that contains most or all of the essential amino acids (lysine, histidine, threonine, cysteine, valine, methionine, isoleucine, leucine and phenylalanine) is a high quality protein [36]. According to data (Table 3), C.schweinfurthii provides almost all the essential amino acids in the amounts required for human body metabolism. Therefore, the fruit pulp of C.schweinfurthii may be a supplementary source of essential amino acids in the diet.
3.4 Mineral composition
Canarium schweinfurthii Engl. fruit pulp contains different types of minerals including micro-elements potassium (K), sodium (Na), calcium (Ca), magnesium (Mg) and phosphorus (P), and trace elements copper (Cu), manganese (Mn), iron (Fe) and zinc (Zn) (Table 4). According to [17], the content of Fe and Zn is 5.60 mg/100 g and 6.30 mg/100 g, respectively. This means that a 100.00 g serving of C.schweinfurthii fruit can provide 50.00% of the Recommended Dietary Allowance (RDA) of 8.00 mg/day for Fe in all age groups of men and postmenopausal women; 8.00 mg/ day and 11.00 mg/day of Zn for women and men, respectively [38]. Hence, C.schweinfurthii fruit can be a good source of both elements.
The mineral ratios (Table 4) of C.schweinfurthii fruit pulp were calculated based on available data in literature. These ratios are often important than the individual mineral levels because they show interactions among specific minerals, which can affect metabolism [41]. Copper has a positive effect on Fe absorption within the recommended ratio. Low levels of copper result into iron deficiency. A high intake of Zn relative to Fe has a detrimental effect on the absorption of the latter and may result in Fe deficiency [42]. A high intake of Ca relative to Mg interferes with the latter uptake and may result in its deficiency. Similarly, high intakes of Mg relative to Ca interfere with Ca absorption and may result in hypocalcemia. Calcium metabolism depends on the ratio of Ca to P. A Ca/P ratio > 0.50 has been suggested to be ideal for Ca uptake. Diets with Ca/P ratios > 2 increase Ca uptake while diets with ratios less than 0.50 are considered poor [41].
3.5 Vitamin content
Canarium schweinfurthii Engl. fruit contains a number of vitamins especially vitamins A, C and E (Table 5). These dietary vitamins may act as important antioxidants, promoting glucose and fatty acid metabolism.
3.6 Bioactive compounds
Bioactive compounds are natural essential phytochemicals that are part of the food chain, and have the potential to regulate metabolic functions that lead to beneficial health effects [43]. Examples of bioactive compounds include flavonoids, polyphenols, carotenoids, choline, coenzyme Q, glucosinolates, and taurine [44]. Canarium schweinfurthii fruit contains three main groups of phytochemicals: terpenes and terpenoids, phenolic compounds and alkaloids (Table 6). Bioactive compounds have been linked to multiple beneficial effects including antioxidant and anti-inflammatory activity as well as modulatory properties of cardio metabolic risk associated biomarkers such as body weight, lipids and glucose levels, systolic blood pressure (SBP) and diastolic blood pressure (DBP) [45].
4 Nutritional uses and T2DM health benefits of Canarium schweinfurthii Engl. fruit pulp
4.1 Macronutrients
Dietary factors affect the management and prevention of T2DM. Diets with varying nutrient composition result in changes of metabolites and gut microbiome that are responsible for glucose metabolism in the whole body [47]. Minimizing carbohydrate intake is the main goal of managing diabetes before introducing insulin as a therapy. This is because, of all the macronutrients, carbohydrates have the greatest effect on blood glucose and insulin levels. Diets low in carbohydrates will provide about 60.00–130.00 g/day of carbohydrates (26.00–45.00% energy needs) whereas very low carbohydrate diets will yield approximately 20.00–50.00 g/day [48]. Carbohydrate foods with low glucose levels tend to promote metabolic control of diabetes and its complications. Such diets with slow digestion of carbohydrates lower the glucose and insulin responses throughout the day improving the capacity for fibrinolysis, which may be a potential therapy for T2DM [49]. The carbohydrate content of C.schweinfurthii fruit was reported to range from 17 to 20%m/m [17, 18], which puts the fruit under low carbohydrate sources. Therefore, C. schweinfurthii fruit may be effective in the metabolic control of diabetes by limiting carbohydrate intake to 20 to 50 g per day and promoting low but sustainable blood glucose levels.
Proteins are important in supplying essential amino acids to maintain protein synthesis and support cellular processes such as cell growth and development [50]. In addition, proteins have a beneficial effect on body weight management and tremendously improve insulin sensitivity [49]. According to the Diabetes Nutrition Study Group (DNSG), daily protein intake of 0.8–1.3 g/kg body weight is safe for T2DM patients below 65 years of age, and about 1.3 g/kg body weight for people older than 65 years [51]. The reported protein content of C.schweinfurthii fruit ranged from 12 to 19% m/m [17, 18]. Furthermore, according to [17], 54.39% of the total amino acids in C.schweinfurthii fruit pulp are essential amino acids meaning that the protein is of good quality. Therefore, C.schweinfurthii fruit may be useful as a supplementary source of proteins and essential amino acids in the diet of people with T2DM. Diets rich in proteins have been recommended for people with diabetes because such diets are lower in energy density and have greater satisfying effect with subsequent weight loss [51]. These diets also lower insulin needs, thereby reducing insulin-induced lipogenesis and improving blood lipid markers such as total cholesterol [51]. Additionally [52], reported a protein-rich diet has a great effect on reducing liver fat than a low-protein diet largely due to reductions in hepatic fat uptake and lipid biosynthesis. A 6-month high-protein diet (1.87 g protein/kg body weight per day) in healthy individuals caused elevated fasting glucose levels, impaired hepatic glucose output suppression by insulin, and enhanced gluconeogenesis [53]. High plant protein intake showed a negative association with the risk of developing T2DM [54]. Additionally, plant proteins are thought to be high in L-arginine, an amino acid that was found to exert beneficial effects on the clinical outcomes of diabetic patients [55]. Amino acids such as leucine, isoleucine, and valine are reported to be important in regulating homeostasis [49]. According to [56], increasing dietary levels of leucine, isoleucine, and valine reduces the progression of T2DM. These amino acids regulate the release of hormones, including leptin (LEP), glucagon–like peptide-1(GLP-1), and ghrelin, which improves glucose metabolism [57] by activating the mammalian target of rapamycin complex 1/protein kinase C (mTORC1/PKC) signaling pathway [58]. Amino acids are also considered as gene expression regulators such as C/EBP homologous protein (CHOP), which is important to glucose metabolism [50]. Furthermore, Amino acids such as activate the mechanistic target of rapamycin/ribosomal protein kinase 1 S6 (mTOR/S6K1) pathway which regulates protein synthesis and glucose metabolism [59], and its action inhibits phosphoinositide 3-kinase (PI3K) that results in improved insulin sensitivity [60].
Reported crude fiber content of C.schweinfurthii fruit pulp is between 0.7 and 11%m/m [8, 9, 18]. Dietary fibers, mainly found in cereals, fruits, vegetables, or legumes, showed close associations with T2DM. Increased fiber intake, especially soluble fiber, plays a beneficial role in improving glycemic control in patients with T2DM [61]. Higher intakes of dietary fiber in diabetes management have been associated with improved measures of glycemic control, blood lipids, body weight as well as a reduction in inflammation and premature mortality [62]. High consumption of foods rich in soluble fiber or soluble fiber supplements has been reported to be effective for the postprandial glycemic control as well as insulinemic response [49]. For example, data from studies revealed that 4 g of soluble β-glucan significantly reduced postprandial glucose and improved insulin responses in healthy individuals [63, 64]. Such fibers absorb water forming viscous gels hence reducing gastric emptying [65] and absorption of glucose [66]. In addition, fibers alter intestinal motility, slow starch digestion and reduce α-amylase accessibility leading to reduced postprandial glucose [67].
Fatty acids are the binding blocks of larger lipid compounds and also serve as substrates for bioactive molecules. They are constitute hydrocarbon chain with a methyl and a carboxyl group at either end. Fatty acids have been reported to affect a number of physiological pathways [68]. Therefore, health organisations recommend replacing SFAs with MUFAs or PUFAs because the latter have positive effects and may improve insulin sensivity [49]. For example, oleic acid elicits beneficial effects on insulin sensitivity [69]. Oleic acid (C18:1ω9) has been reported to be the main MUFA at 30.24% in C.schweinfurthii fruit pulp oil [25]. Also, palmitoleic acid (C16:1ω7) has been indicated as the major MUFA while linoleic acid (C18:2ω6) and linolenic acid (C18:3ω3) as the predominant PUFAs [20]. Therefore, C.schweinfurthii fruit may be useful as a supplementary source of MUFAs or PUFAs in diabetes diets. For the prevention and management of cardiometabolic diseases such as T2DM, it is recommended to eat diets rich in MUFAs and PUFAs [62]. In vitro experiments have indicated that MUFAs prevent insulin resistance [70]. The binding of PUFAs to G protein-coupled receptor (GPCR) is also thought to indirectly increase the expression of glucose transporter type 4 (GLUT-4) in adipocytes and muscle cells, which increases glucose uptake [62]. The PUFAs have also been associated with significant reductions of fasting blood glucose, lowered glycated haemoglobin (HbA1c), and improved insulin secretion capacity in patients with diabetes [71]. Postprandial hyperlipidemia, which is common in T2DM patients, may be reduced with ω-3 fatty acids [72].
4.2 Micronutrients
Micronutrients such as Na, K, Ca and Mg, and trace elements like Fe, Zn, boron (B), chromium (Cr), copper (Cu), selenium (Se) and molybdenum (Mo) enhance insulin action by activating insulin receptor sites [73]. Additionally, Ca and Mn are important for healthy bones, teeth, muscles, nerve functioning, blood pressure regulation and immune system health. Sodium and potassium are required for proper fluid balance, nerve transmission and muscle contraction. Iron is essential for haemoglobin formation, normal functioning of central nervous system (CNS) and in the metabolism of macronutrients [74]. Zinc is required for making protein and genetic material, wound healing and immune system. Trace elements such as Cu, Se, Zn, Fe, Mn, and Mo are enzyme co-factors that play important roles in numerous biochemical pathways [75, 76].
Calcium plays an important role in the proper regulation, secretion and action of insulin [77]. Research suggested that low calcium and vitamin D levels contribute to the development of T2DM. However, supplementation with these two nutrients is reported to enhance glucose metabolism in the body [78]. Magnesium is suggested to decrease the risk of cardiovascular diseases in T2DM patients. It is a cofactor required for carbohydrate metabolism and movement of glucose into cells [79].
Chromium is involved in the cellular activity of insulin and therefore improves the glucose levels in subjects with hypoglycemia, hyperglycemia and diabetes [80]. It enhances glucose metabolism by binding of insulin to the insulin receptor (INSR) [81]. A significant reduction in postprandial and fasting glucose levels was reported after a 4 months supplementation of Cr [25]. This may be partly attributed to the increase of glucose transporter 2 (GLUT2) expression and the activation of phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) pathway in skeletal muscle [82]. Iron contributes to glucose metabolism [83] while molybdenum plays an important role in insulin action by activating insulin receptor sites [84]. Selenium is required for redox reactions catalyzed by enzymes such as glutathione peroxidase and thioredoxin reductase in human body [85]. Adequate Se intake can act as an insulin mimetic to reduce the progression of diabetes through decreasing glucose and insulin tolerance, thus preventing hepatic insulin resistance [86]. Selenium is also essential for the synthesis of selenoproteins. Selenoproteins, for example SELENOF, regulate glycogenolysis and lipogenesis thereby preventing glucose metabolism disorder [87]. Selenium deficiency may result in oxidative damage leading to the onset of metabolic diseases such as T2DM. Zinc is also an important component of enzymes that play vital roles in regulating insulin sensitivity and glucose homeostasis. It is a cofactor responsible for the function of intracellular enzymes that may be involved in protein, lipid, and glucose metabolism [88]. It plays an important role in the appropriate processing, storage, secretion and action of insulin in mammalian pancreatic cells hence its role in the management of diabetes mellitus [89]. The low concentrations of Zn in plasma and tissues in patients with T2DM may be attributed to the fact that it acts as an antioxidant thus reducing the effect of reactive oxidative species (ROS) production in the body [49]. Therefore, its supplementation, for example through consuming C.schweinfurthii fruit, may be important both in ageing and protection against diabetes mellitus [90].
Sodium intake enhances its excretion in the urine via peroxisome proliferator activated receptor γ/renal sodium–glucose cotransporter 2 (PPARγ/SGLT2) pathway and as such, it regulates glucose metabolism of T2DM patients [91]. Therefore, C.schweinfurthii fruit may be a useful source of micronutrients in the diet of people with T2DM [7, 10, 17, 39].
4.3 Bioactive compounds
Canarium schweinfurthii fruit contains bioactive compounds: terpenes and terpenoids, phenolic compounds and alkaloids [7,8,9,10]. Bioactive compounds for example flavonoids and phenolic acids can attenuate the postprandial glycemic response, improve acute insulin secretion, and insulin sensitivity [49, 92]. The hydrolysis of starch to glucose is a biochemical process catalyzed by the enzymes α-amylase found in saliva and pancreatic juices, and α-glucosidase found in the epithelium of the small intestine [93]. Hence, compounds that inhibit α-amylase and α-glucosidase slow the digestion of starch in the small intestines, which decreases the amount of glucose entering the bloodstream leading to an improved insulin response [94]. Phenolic compounds have been reported to possess such a property [14, 95]. Polyphenols may also possess antidiabetic effects through reduction of plasma glucose levels and oxidative stress damage, restoring antioxidant enzymes, inhibiting α-amylase and α-glucosidase [96]. In addition, they may increase the expression of GLUT-4 and insulin sensitivity proteins, such as peroxisome proliferator activated receptor γ (PPARγ) as a result of activation of protein kinase B (AKT) resulting in an increased cellular glucose uptake [97].
Flavonoids may also possess antidiabetic effects [14]. In vitro studies carried out on quercetin-containing Vaccinium vitis-idaea resulted into increased glucose uptake in skeletal muscles by stimulating the insulin-independent AMP-activated protein kinase (AMPK) pathway, which also can be true of quercetin found in other plant extracts [98].
Alkaloids may lower blood glucose levels through offsetting glucose uptake by inhibiting protein tyrosine phosphatase-1B (PTP-1B) (a major negative regulator for insulin receptor signaling) [99,100,101]. Additionally, they may also alleviate H2O2-induced oxidative damage in β-cells which can be attributed to the radical scavenging capacity [100].
4.4 Vitamins
Antioxidant vitamins A, C and E have been found to decrease in diabetic subjects, possibly due to increased demand as they are used to control oxidative stress due to abnormalities in glucose metabolism [102]. Vitamins C and E are required in high amounts by people with T2DM due to the high levels of oxidative stress caused by hyperglycemia [103]. The fruit pulp of C.schweinfurthii Engl. may serve as a supplementary source of vitamins C and E in the diets of people with T2DM [6, 9, 10, 39]. Formation of reactive oxygen species (ROS) from membrane nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondria may lead to insulin resistance [49]. Therefore, vitamins C and E are required in high amounts by people with T2DM due to the high levels of oxidative stress caused by hyperglycemia [103]. Supplementation with these vitamins decreases blood glucose levels while increasing superoxide dismutase activity and glutathione levels [104, 105]. Superoxide dismutase is the first detoxification enzyme and most powerful antioxidant in the body cells [106]. In addition, vitamin C improves chronic periodontitis in people newly diagnosed with T2DM [107]. Vitamin E directly regulates gene expression such as PPARγ, which plays important roles in insulin sensitivity [108,109,110]. Research has shown that the vitamin A may be involved in hepatic lipid metabolism, adipogenesis and pancreatic β -cell function [102]. It is required in high amounts during T2DM condition because of the high levels of oxidative stress caused by hyperglycemia [103]. Vitamin A protein transporter (retinol binding protein) is reported to have an important effect on insulin sensitivity [111].
5 Canarium schweinfurthii Engl. and its anti—diabetic activity
Canarium schweinfurthii fruit oil was reported to possess anti-hyperglycemic activities at a dose as low as 5 ml in streptozotocin (STZ)-induced diabetic rats. Results from doubling the amount of oil to 10 ml and treatment with standard drug, glibenclamide, were comparable [112]. The anti-diabetic effects of the methanol/methylene chloride extract of C. schweinfurthii stem bark in STZ-induced diabetes rats has also been reported. After 2 days of inducing diabetes (60 mg/ml), the rats received 150 mg/kg and 300 mg/kg of extract daily for 14 days. At 300 mg/kg, the extract significantly showed at least 69.9% reduction in blood glucose level [113]. Furthermore, the antidiabetic and hypolipidemic effects of C.schweinfurthii hexane bark extract in STZ-diabetic rats were investigated. Daily treatment of diabetic rats with bark extract (38, 75 and 150 mg/kg) significantly decreased blood glucose levels by 72.17, 79.91 and 73.68%, respectively [114]. The reported anti-diabetic activity of C.schweinfurthii extracts may be due to insulin like effect through enhancing glucose uptake or metabolism. It may also be attributed to the regeneration process and revitalization of the remaining β-cells [115]. Furthermore, the blood-glucose-lowering effect of C.schweinfurthii may be enhanced by various phytochemicals, which include terpenoids, polyphenols and alkaloids. Such compounds have been reported to inhibit α-amylase and mucosal α-glucosidases slowing starch digestion in the small intestines thus reducing the amount of glucose entering the bloodstream and resulting into improved insulin response [94]. Various phytochemicals have been stated to exhibit antidiabetic properties through inhibiting α-amylase and mucosal α-glucosidase enzymes [14].
6 Conclusion
Studies done on the C.schweinfurthii fruit have concentrated on the proximate composition, minerals, fatty acid and amino acid profile. However, data on trace elements in C.schweinfurthii fruit is hard to find yet such have been reported to play a significant role in management of T2DM. Although, the T2DM therapeutic effects of C.schweinfurthii bark stem extracts and fruit pulp oil have been reported, the therapeutic potential of the whole fruit pulp is yet to be documented. Since other parts of C.schweinfurthii Engl. plant are reported to contain phytochemicals, its documented anti-diabetic properties may refer to these compounds, which have been shown to decrease blood glucose levels through, for example, an up-regulation of GLUT-4 and alpha amylase activity. In Africa, information on the cytotoxicity of C.schweinfurthii fruit pulp is hardly found. Hence, further studies are required to provide data on cytotoxicity of the fruit pulp and contributing factors to its anti-diabetic effects.
Data availability
This article does not contain any new data that was collected by any of the authors. All of the research and associated data in this review is based upon the information available in the peer-reviewed scientific publications and/or public domain that can be publicly accessed.
Code availability
Not applicable.
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The Africa-UniNet Research Cooperation Project (1st Call) supported this study. It was implemented under the project title ‘Indigenous Fruits and Nut Trees (IFNT) as market opportunities for small scale farmers in Namibia, Ethiopia and Uganda: cultivation, nutritional value and screening of secondary compounds for anti-diabetic properties’ (P042_Namibia_Ethiopia_Uganda).
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Tabula, A., Bamuwamye, M. & Nakyinsige, K. The potential contribution of Canarium schweinfurthii Engl. fruit pulp in the management of type 2 diabetes mellitus. Discov Sustain 5, 293 (2024). https://doi.org/10.1007/s43621-024-00476-z
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DOI: https://doi.org/10.1007/s43621-024-00476-z