<em>Morus</em> Plant Genus: Superb Antidiabetic Activity and Outstanding Source of Nutrients

Abdullatif Azab

doi:10.37871/jbres1739

ISSN: 2766-2276

Medicine Group . 2023 April 27;4(4):806-832. doi: 10.37871/jbres1739.

Subject area(s)

Pharmaceutica Analytica Acta

| | |

Review Article

Morus Plant Genus: Superb Antidiabetic Activity and Outstanding Source of Nutrients

Abdullatif Azab*

Eastern Plants Company, Box 868, Arara, Israel

*Corresponding author: Abdullatif Azab, Eastern Plants Company, Box 868, Arara, Israel E-mail:

Received: 17 April 2023 | Accepted: 25 April 2023 | Published: 27 April 2023

How to cite this article: Azab A. Morus Plant Genus: Superb Antidiabetic Activity and Outstanding Source of Nutrients. J Biomed Res Environ Sci. 2023 Apr 27; 4(4): 806-832. doi: 10.37871/jbres1739, Article ID: jbres1739

Keywords

Morus
Ethnomedicine
Antidiabetic
Insulin regulation
Oxyresveratrol
Moracins
1-Deoxynojirimycin
Future directions

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Abstract

The plant genus Morus (Mulberry) has been used by humans for many centuries. All parts of the trees are used, but the fruits have the highest nutritional values. Most of the species of this genus were studied for various medicinal and biological activities, as well as many other properties, including chemical composition. Two species, Morus albaand Morus nigra were very extensively investigated, and research reports about them continue to be published very frequently. The chemistry of this plant genus is fascinating. It includes numerous natural products with unique structures and structure-sub-units, making them excellent candidates as organic synthesis starting materials. Many review articles were published about the Morus genus and some of its species, but this article is the most comprehensive regarding antidiabetic activity and insulin regulation. Active natural products are responsible for these activities will be presented, as well as possible and proposed mechanisms of action. Ethnobotanical and ethnomedicinal information related to the antidiabetic activity will be briefly presented. In addition, a thorough discussion section will lead to conclusions, some future directions, and recommendations for research.

Abbreviations

AMPK: 5' Adenosine Monophosphate-Activated Protein; ATR-FTIR: Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy; BW: Body Weight; DNJ: 1-Deoxynojirimycin; FoxO1: Forkhead Box Protein O1; GC-MS: Gas Chromatography-Mass Spectrometry; GLUT4: Glucose Transporter Type 4; HPLC: High Performance Liquid Chromatography; HPLC-MS: High Performance Liquid Chromatography-Mass Spectrometry; IRS1: Insulin Receptor Substrate 1; NEFA: Non-Esterified Fatty Acids; PDX-1: Pancreatic and Duodenal Homeobox 1; PI3K/AKT: Phosphoinositide 3-Kinase/Protein Kinase; PTP1B: Protein Tyrosine Phosphatase 1B; RBP4: Retinol-Binding Protein 4; T2MD: Type II Diabetes Mellitus; UVC: Ultraviolet C (radiation)

Introduction

Humans have used trees of the plant genus Morus since very ancient times. The practical uses were nutrition; leaves were and still are used to feed silkworms (Bombux mori). One of the earliest archeological pieces of evidence of Morus use by humans was discovered in Belgium, and the species used is Morus nigra [1]. Morus trees were domesticated thousands of years ago, but new studies suggest they were domesticated in several locations, not just on the Himalayas slopes, as previously assumed [2]. Greek Hippocrates used a Morus albaextract combined with a Mandragora autumnalis as a general anesthetic [3].

The species number of this genus is a matter of debate, and it ranges from 10 to 35, but the most acceptable number is 23 [4]. These are M. alba, M. atropurpurea, M. australis, M. bombycis, M. cathayana, M. celtidifolia, M. ihou, M. indica, M. isingnis, M. japonica, M. laevigata, M. liboensis, M. macroura, M. mesozygia, M. mongolica, M. multicaulis, M. nigra, M. notabilis, M. papyrifera, M. rotunbiloba, M. rubra, M. serrata, M. trilobata, M. wittiorum, M. yunnanensis. While some species, like M. alba and M. nigra (Figure 1), were extensively studied, M. japonica, M. liboensis, M. serrata, and M. trilobata were never published for medicinal or related properties.

Diabetes-Related Ethnomedicine and Ethnobotany of Morus

Trees of the Morus played an essential role in the ethnomedicine and ethnobotany of many cultures. The primary use was and still is for food, but many other services were recorded and published, including treating diabetes-related health disorders. A summary of these ethnomedicinal uses is shown in table 1.

Table 1: Diabetes-related ethnomedicinal uses of Morus alba and Morus nigraa.
Species	Country/Region	Method of Use	References
M. alba	Bangladesh	All parts of the tree. Method NIb	[5]
	China	Fruits and leaves are eaten, roots are extracted	[6]
	India	Fruits, bark and/or leaves Method NI	[7,8]
	Iran	Aerial parts. Method NI Plant parts NI, method NI Fruits, method NI	[9] [10] [11]
	Morocco	Plant parts NI, method NI	[12]
	Pakistan	Leaves decoction	[13]
		Leaves infusion	[14]
		Plant parts NI, method NI	[15]
	Peru	In folk commercial products	[16]
	Trinidad & Tobago	Plant parts NI, method NI	[17]
	Turkey	Fruits are eaten	[18]
M. nigra	Brazil	Plant parts NI, method NI	[19]
	Iran	Leaves, stem. Method NI	[9]
		Fruits are eaten fresh, leaves and roots are prepared as decoction or infusion	[20]
	Italy	Leaves, Method NI	[21]
	Kosovo	Leaves infusion or infusion	[22,23]
	Pakistan	Leaves decoction or infusion	[13,14,24]
	Peru	In folk commercial products	[16]
	Turkey	Fruits are eaten	[18]
a: No published reports of this property for other species; b: NI, Not indicated

Antidiabetic Properties of Morus Mixtures

Medicinal properties of plants are often discovered by initial tests of mixtures that are isolated or prepared from these plants. With “mixtures” we mean extracts, essential oils, formulations based on these, and obviously, raw materials taken directly from the plants, such as edible parts, spices, and herbs. In short, we present these mixtures' antidiabetic properties, but not pure natural products isolated from the Morus genus trees.

In section 2, we presented the major traditional knowledge and uses of some species of this genus as antidiabetics. Modern science has extensively and methodically studied this property, and a summary of the most important published studies is presented in table 2.

Table 2: Published antidiabetic and related properties of Morus mixtures.
Morusa alba
Mixturea	Testing Methods and Results	References
R-B Ext/s	α-Glucosidase inhibition. Acetone extract had highest activity among total of 7 extracts.	[25]
L Ext	Flavonoids-rich increased carbohydrate in eels (Monopterus albus).	[26]
L Ext	Ethanolic: (100 mg/kg BWb 8 weeks) decreased insulin resistance in female rats.	[27]
L,F Pw	Leaves and fruits powders were added to honey and the formulation inhibited α-amylase.	[28]
L Ext	Aqueous: (20 mg/100 g BW) lowered blood glucose in diabetic rats.	[29]
L Ext	50% Aqueous ethanol: Reduced activity of disaccharides in rats and inhibited human lactase and trehalase.	[30]
L Ext	Aqueous: was consumed (1 g/day for a week), resulting decrease in blood glucose in humans with T2DM.	[31]
L Ext	Ethanolic: Powder was supplemented with sucrose to human subjects, lowered blood glucose and regulated insulin.	[32]
L Ext	Aqueous: Administered (100 mg/kg BW, 4 days/week, 4 weeks) to diabetic rats, resulted increase in activity of some enzymes and reduction of activity of some others.	[33]
L Ext	70% Aqueous ethanol: Supplemented (250 or 750 mg/kg BW, 11 days) to diabetic rats, with or without three pure natural products. Chlorogenic acid and rutin enhanced the activity, but not isoquercitrin.	[34]
L Ext	50% Aqueous ethanol: Incubation of rat adipocytes (15 µg/mL) increased glucose uptake and GLUT4 translocation.	[35]
L Ext	Ethanolic: Administered to diabetic (200 mg/kg BW, daily, 10 days) rabbits reduced blood glucosec.	[36]
L Ext	Ethanolic: Supplemented (1 g/kg BW, daily, 8 weeks) to rats, increased the activity of liver glucokinase.	[37]
F Ext	50% Aqueous ethanol: Anthocyanin-rich was administered to diabetic rats. Daily 250 mg/kg BW for 5 weeks lowered blood glucose but did not regulate insulin, and 125 mg/kg administration had an opposite effect.	[38]
L Ext	Ethanolic: Supplemented (600 mg/kg BW, daily, 30 days) improved blood histological parameters. A similar effect was observed when Olive leaf extract was used.	[39]
L Ext	Aqueous: with Jackfruit leaves extract, was orally administered (500 mg/kg BW, daily, 8 weeks) lowered blood glucose	[40]
L Ext	Hydroethanolic (ratio is not presented) inhibited CYP450 enzymes and had no adverse extract-drug interactions.	[41]
L Ext	Tea was orally supplemented (0.25-0.5%) to diabetic rats, resulting weak lowering of blood glucose.	[42]
F Ext	95% Hydroethanolic with 1% HCl yielded anthocyanin-rich extract. It was administered (50 or 125 mg/kg BW, daily, 8 weeks) to diabetic mice, resulting blood glucose lowering and insulin regulation by activation of PI3K/AKT pathways.	[43]
L Ext	Aqueous: was orally supplemented (600 mg/kg BW, daily, 28 days) to rats resulted lowering of blood glucose	[44]
L Ext	Ethanolic: extracts were prepared from female and male trees, from leaves and stems, and in different seasons. All extracts were tested for their α-amylase and α-glucosidase inhibition activity. All were active but the most active were extracts prepared from spring plant materials.	[45]
L Ext	Aqueous: Supplemented (60 mk/kg BW, daily, 5 days) to diabetic rats resulting improvement of several histological variables.	[46]
L Pw	Rats were fed (20% w/w of diets) resulting the reduction of blood glucose by inhibition of NEFA signaling and restored intestinal microbiota.	[47]
L Ext	90% Aqueous ethanol: Administered (100 mg/kg BW, daily, 16 weeks) to diabetic rats resulting insulin regulation.	[48]
Bra Ext	60% Aqueous ethanol: Supplemented (0.5 or 1 g/kg BW, daily, 22 days) to diabetic mice lowered blood glucose.	[49]
L Ext	Ethanolic and methanolic extracts were combined and extracted again with ethanol. The obtained extract was fed (125 mg/kg BW, daily, 21 days) to diabetic mice, resulting improvement in many histological variables.	[50]
L Ext	Aqueous: Supplemented (80 mg/kg BW, daily, 10 weeks) to diabetic mice resulted insulin regulation through prevention of inactivation of insulin receptor substrate.	[51]
L Ext	Aqueous: Administered (50, 100, 250 mg/kg BW, daily, 8 weeks) resulting in glucose uptake stimulation.	[52]
L Dec	Aqueous: was orally supplemented (20 g/L) in drinking water to diabetic rats, decreased blood glucose.	[53]
L Pw	Was orally fed (5% of diet) to diabetic rats resulting in lowering blood glucose.	[54]
L Dec	Identical to [53].	[55]
F Ext	Ethanolic and 95% methanolic combined extracts were fed (200 mg/kg BW, daily, 21 days) to diabetic rats resulted blood glucose.	[56]
Bra Ext	Methanolic: then fractionated with CH2Cl2, EtOAc, n-BuOH and water. The original extract and its fractions were tested for α-glucosidase inhibition and aqueous fraction was most active.	[57]
L Ext	Aqueous: Activated (4.28 mg/mL) AMPK of rat skeletal muscle.	[58]
L Ext	Successive extraction with water (cold/hot), methanol, isopropanol, acetone, methyl-t-butyl ether, and cyclohexane. The combined extracts had clear α-amylase inhibition.	[59]
L Ext	Aqueous ethanol in various concentrations (0-100). Most active was 60% which had 83.5% inhibition of α-glucosidase and 70.5% inhibition of α-amylase.	[60]
L Ext	Aqueous: among 6 foods extracts and their combination, this was the most active (0.2 mg/mL) enzyme inhibitor: intestinal maltase and intestinal sucrase. It had very weak pancreatic α-amylase inhibition activity.	[61]
L Ext	Polyphenol-rich aqueous ext. had higher α-glucosidase and α-amylase inhibition activities than polyphenol-rich 60% ethanolic extd.	[62]
F Ext	80% Aqueous methanol: anthocyanin-rich, fed to diabetic mice (0.5% w/w, 5 weeks), resulted blood glucose lowering and higher insulin sensitivity.	[63]
L Ext	50% Ethanolic: Standardized for DNJ content (see section 4) then orally supplemented to diabetic rats (480 mg/kg BW, daily, 21 days) and to humans (2 g/kg) after fasting. In both cases strong inhibition of α-glucosidase was recorded.	[64]
F Ext	Aqueous and 60% ethanolic were prepared from 9 varieties and were tested for α-amylase and α-glucosidase inhibition. For both enzymes, aqueous extract was more potent.	[65]
B Ext	70% Aqueous ethanol ext. of Mori cortex was supplemented (10 g/kg BW, daily, 16 weeks, intragastric gavage) to diabetic mice, resulted lowering blood glucose.	[66]
F Ext	Gradient CHCl₃/MeOH extraction yielded polyphenol rich extract, which was administered (100 or 200 mg/kg BW, daily, 14 days), resulted blood glucose lowering. The higher dose had stronger effect.	[67]
L Ext	65% Aqueous ethanol or acetone extracts were fed (10% of high fat diet, for 4 weeks) to diabetic rats, resulting regulation of hepatic Fe and Cu concentrations.	[68]
L Ext	Ethanolic and methanolic extracts were fed (100 mg/kg BW, daily, 21 days) to diabetic rats, resulted lowering of blood glucose.	[69]
L Ext	Aqueous: oligopeptides were isolated from 4 cultivars and tested for α-amylase inhibition, where all were active.	[70]
L Ext	Nonpolar ext. obtained with CH2Cl2 had in vitro (cell culture) glucose lowering and insulin regulation activities.	[71]
L Ext	Commercial aqueous ext. was supplemented (200 mg/day, 4 weeks) in combinations with different nutraceuticals to human patient. The combination with berberine was most active in terms of glucose uptake and insulin regulation.	[72]
L Ext	95% Ethanolic: was supplemented (as powder in food or as solution in drinking water, 6 weeks) to diabetic rats, resulted higher uptake of blood glucose and increase of insulin levels.	[73]
L Ext	60% Aqueous ethanolic: was in vitro tested for several activities and found active blood glucose lowering and improving insulin sensitivity^e.	[74]
L Pw	Standardized for DNJ content, supplemented (100-140 mg, daily, 12 weeks) to human patients. This resulted in prevention of T2DM progress via modulation of RBP4 and hepatoglobin.	[75]
L Ext	Aqueous: Inhibited free α-glucosidase and/or in Caco-2 model	[76,77]
L Ext	50% Aqueous ethanolic: Supplemented (1 g/kg BW., daily, 8 weeks) to diabetic rats, resulted blood glucose lowering as well as liver enzymes.	[78]
L Ext	90% Aqueous ethanolic: Supplemented (400 or 600 mg/kg BW., daily, 35) to diabetic rats, resulted blood glucose lowering by regeneration of β cells.	[79]
L Ext	Aqueous: Administered (100 mg/kg BW, daily, 6 weeks) to diabetic pregnant female rats, resulting hepatic protection of their pups.	[80]
L Ext	70% Aqueous methanolic: Standardized for 4 active compounds, was supplemented (30, 60 or 120 mg/kg BW, daily, 3 days) to diabetic rats with hyperuricemia, resulting inhibition of xanthine oxidase and insulin regulation.	[81]
L Ext	Aqueous: was administered (2 or 7 g/kg BW, daily, 4 weeks) to diabetic rats, resulted lowering of blood glucose and insulin resistance.	[82]
L Ext	Aqueous: Standardized for DNJ, was supplemented (1 or 6 mg per tablet) to healthy adults at different times. It was found that supplementation is more efficient in terms of blood glucose lowering when consume in the evening.	[83]
L Dec	Aqueous: was administered (200 or 400 mg/kg BW, daily, 3 weeks) to diabetic rats, resulting amelioration of diabetic nephropathy.	[84]
L Ext	Aqueous: was supplemented (250 mg/kg BW, daily, 4 weeks) to diabetic rats, resulted lowering of blood glucose and improvement of neurotransmitters functioning.	[85]
F Ext	Aqueous: Two polysaccharides-rich fractions were administered (400 mg/kg BW, daily, 7 weeks) to high fat diabetic rats, resulting blood glucose lowering and amelioration of insulin resistance.	[86]
F Ext	Aqueous: was supplemented (100 mg/kg BW, daily, 12 weeks) to diabetic rats, resulting lowering of blood glucose and increasing spermatogenesis.	[87]
F Ext	Aqueous: Optimization of extraction conditions (temperature and solute to solvent ratio) afforded highly flavonoid-rich extracts. These had very high α-amylase inhibition activity, with acarbose as a reference.	[88]
B Ext	30% Ethanolic: and further extraction with 80% CHCl₃ in n-BuOH. This extract inhibited α-glucosidase and sucrose.	[89]
B Ext	70% Aqueous ethanolic: was administered (400 mg/kg, daily, 21 days) to diabetic rats, resulted lowering blood glucose and increasing insulin concentrations.	[90]
F Ext	Aqueous: After removing pigments with 90% aqueous ethanol, polysaccharides ext. was obtained. This ext. increased glucose consumption and increased insulin release, in vitro.	[91]
L Ext	Aqueous: was further extracted with several solvents, was supplemented (200 mg/kg BW, single dose) to diabetic mice, resulted clear blood glucose lowering.	[92]
B Ext	70% Aqueous ethanol: was administered (600 mg/kg BW, daily, 10 days) to diabetic rats, reduced blood glucose and increased insulin concentration.	[93]
L Ext	90% Aqueous ethanolic: Supplemented (400 or 600 mg/kg BW, daily, 35 days) to diabetic rats, resulted lowering of blood glucose and improvement of other histological parameters.	[94]
L Ext, P	Both standardized for DNJ content. Aqueous extract: was administered in a single dose (3.75 g/kg BW) was supplemented to Goto-Kakizaki/Wistar rats, and powder was fed (100 g/kg diet) over 8 weeks to Goto-Kakizaki/Wistar rats. In both cases blood glucose was reduced but powder administration was more effective.	[95]
L Ext	Aqueous: was supplemented (3.3 g in 100 g jelly, single dose) to diabetic patients, resulted in suppression of increase of blood glucose and regulation of insulin.	[96]
L Ext	Methanolic: was fractioned with n-C₆H₁₄, CHCl₃, EtOAC, n-BuOH. Extract and fractions were administered (50, 100, 200 mg/kg BW) diabetic rabbits and diabetic parameters were tested after administration. All experiments showed blood glucose lowering, where crude extract and CHCl₃ were most active.	[97]
L Ext	Aqueous: was fed (600 mg/kg BW, daily, 28 days) to diabetic rats, resulting lowering blood glucose by approximately 18%.	[98]
L Ext	Aqueous: Standardized for DNJ, was fed to normal-blood-sugar humans, with different amounts of DNJ/Reducose. In all experiments glucose uptake and insulin levels increased.	[99]
L Ext	70% Ethanolic: that was chromatographed for alkaloids, flavonoids, and polysaccharides fractions. Crude extract and fractions (separately) were in vitro tested for α-glucosidase inhibition: all found very active (acarbose control) and polysaccharide fraction was highest. Testing effect on blood glucose of diabetic mice (300, 600, 1200 mg/kg BW, daily, 14 weeks), showed that high dose extract had clear lowering activity.	[100]
R, L, Bra, F Ext/s	70% Aqueous ethanolic ext. of each part was prepared, and extracts were analyzed for phenolics, where 52 compounds were identified. All extracts were separately supplemented (200 mg/kg BW, daily, 28 days) to diabetic mice, resulted clear decrease in blood glucose.	[101]
L Bra Ext	95% Ethanolic extracts were prepared and analyzed for their major hypoglycemic components. Both extracts had clear α-glucosidase activity, and when administered (200 mg/kg BW, daily, 4 weeks) to diabetic rats, it lowered blood glucose.	[102]
S Ext	Aqueous: was tested in vitro and found active α-glucosidase inhibitor. When supplemented (100, 400 mg/kg BW, daily, 15 days) to diabetic mice, it decreased blood glucose.	[103]
L Ext	Aqueous: had clear α-amylase inhibition activity, and when administered (250, 500 mg/kg BW, daily, 10 days) to diabetic rats, it had blood glucose lowering effect.	[104]
L Ext	Aqueous: Supplemented (150, 300, 600 mg/kg BW, daily, 12 days) to diabetic/normal rats, resulted blood glucose decrease in both groups. Pancreatic islets were larger.	[105]
L Ext	Aqueous: Standardized for DNJ and administered (150 mg/kg BW, daily, 29 days) to diabetic rats, in combination with other plants extracts. This resulted decrease in blood glucose, and authors suggest promotion of IRS1 phosphorylation as possible mechanism for insulin sensitivity restoration.	[106]
L Ext	Aqueous: In vitro significant α-amylase inhibitor.	[107]
L Ext	90% Aqueous ethanolic: in vitro active α-amylase inhibitor.	[108]
F Pw	5% of diet of diabetic rats decreased blood glucose, by synergetic action of the different components.	[109]
	Morus atropupurea
Mixture	Testing Methods and Results	References
L Ext	Leaves were fermented and water extracted. Monosaccharides were removed from extract, remaining with mainly DNJ and polyphenols. Ext. solution was administered (230 mg/kg BW, daily, 5 weeks) to diabetic rats. Blood glucose and insulin sensitivity increased, through activation of PI3K/AKT and AMPK.	[110]
	Morus indica
Mixture	Testing Methods and Results	References
L Pw	Supplemented (25% of diet, 8 weeks) to diabetic rats, reduced blood glucose by approximately 60-70%, compared with control diabetic rats.	[111-115]
L Pw	Supplemented (500 mg/kg BW, daily, 15 days) to diabetic rats, reduced blood glucose by approximately 66%, compared with control diabetic rats.	[116]
L Ext	90% Aqueous ethanolic: administered (400 mg/kg, daily, 28 days) to diabetic rats, resulted significant blood glucose lowering.	[117]
L, Ba Pw	Supplemented (10% of diet, 90 days) to diabetic humans, significantly reduced blood glucose compared with control diabetic humans. Leaves powder was more effective.	[118]
L Ext	Aqueous: had significant α-amylase inhibition activity	[119]
L Pw	Administered (6 g, daily, 8 weeks) as tablets containing the powder to human diabetics, resulting 48% blood glucose reduction and restoration of insulin sensitivity.	[120]
L Ext	Aqueous, donated, was supplemented (3 g/day, 2 weeks) to diabetic subjects, resulting clear lowering of blood glucose.	[121]
L Ext	80% Methanolic: had in vitro had strong antidiabetic activity by inhibition of advanced glycation end products.	[122]
L Pw	Supplemented (500 mg/kg BW, daily, 6s) to diabetic rats, reduced blood glucose by approximately 69%, compared with control diabetic rats.	[123]
L Ext	Aqueous: Administered (500 mg/kg BW, daily, 5 days) to diabetic rats, resulting 40% decrease of blood glucose compared with control diabetic rats.	[124]
L Pw	Administered (3 g, daily, 4 weeks) as tablets containing the powder to human diabetics, resulting 27% blood glucose reduction and restoration of insulin sensitivity.	[125]
L Pw	Administered (3 g, daily, 30 days) as tablets containing the powder to human diabetics, resulting significant decrease of blood glucose.	[126]
	Morus insignis
Mixture	Testing Methods and Results	References
L Ext	70% Aqueous ethanolic: Supplemented (100 mg/kg BW, twice a day, 10 days) to diabetic rats, resulted approximately 35% decrease of blood glucose.	[127]
	Morus multicaulis
Mixture	Testing Methods and Results	References
Bra Pw	10% of diet was administered to normal mice for two weeks, then diabetes was induced (and in some of the other control groups). Results showed that treatment almost prevented the occurrence of diabetes in the treatment group.	[128]
Bra Pw	10% of diet was administered to normal mice for two weeks, then diabetes was induced (and in some of the other control groups). Results showed that treatment significantly lowered blood glucose and regulated insulin through inactivation of FoxO1.	[129]
B Ext	Gradient (10-90%) aqueous ethanolic was tested in vitro and found active α-glucosidase inhibitor. It was supplemented (50, 100, 200 mg/kg BW, daily, 3 weeks) to diabetic mice, resulting blood glucose and insulin-resistance decrease.	[130]
	Morus nigra
Mixture	Testing Method and Results	References
L Ext	90% Aqueous ethanolic: in vitro active α-amylase inhibitor	[108]
F Pw	5% Of diet of diabetic rats decreased blood glucose, by synergetic action of the different components.	[109]
S Ext	Extracted successively with petroleum ether, EtOAc, EtOH and water. All extracts were tested separately for α-amylase and α-glucosidase, where ethanolic extract was most active.	[131]
L Ext	90% Ethanolic: Supplemented (200, 400 mg/kg BW, daily, 14 days) to diabetic rats, resulting significant reduction of blood glucose.	[132]
F	Fresh fruits were eaten (100 g/day, 30 days) by diabetic subjects, resulting approximately 15% reduction of blood glucose.	[133]
L Ext	Aqueous: was administered (400 mg/kg BW, daily, 20 days) to pregnant female diabetic rats, which had no influence on hyperglycemia caused by diabetes induction.	[134]
F, L Ext	Both materials were separately and successively extracted with 70% aqueous ethanol and water. Both extracts were supplemented (500 mg/kg BW, daily, 30 days) to diabetic rats, resulting clear decrease of blood glucose. Leaves extract had higher activity.	[135]
L Ext	80% Methanolic: were tested in vitro (several concentrations) for its effects on β-cells isolated from male mice, resulting increase of insulin secretion	[136]
F Ext	Aqueous ethanolic (no ratio reported) was administered (400, 800 mg/kg BW, daily, 8 weeks) to diabetic rats, resulting approximately 46% reduction of blood glucose.	[137]
L Ext	Ethanolic: Supplemented (250, 500 mg/kg BW, daily, 4 weeks) to diabetic rats, resulting notable decrease of blood glucose. It also showed very strong α-glucosidase inhibition activity. In both tests, higher dose was more active.	[138]
F Ext	50% Aqueous ethanolic: was tested (0.5, 1, 1.5%) for α-amylase (3 different sources) and α-glucosidase with acarbose as a reference. All concentrations had high inhibition activity. Hydrolysis and glycemic indexes were lower in cooked pasta the contained this extract, for the three concentrations.	[139]
L Ext	95% Aqueous ethanolic: Administered (100 mg/kg BW, every 2 days, 6 days) to diabetic rats, resulted approximately 35% reduction of blood glucose compared with control diabetic rats.	[140]
L Ext	80% Aqueous ethanolic: Supplemented (5, 10, 100, 200, 400, 600, 800, 1000 mg/kg BW, daily, one week) to diabetic rats. Then the treated groups of 400 and 600 mg/kg continued daily, for 2 months. The result was reduction of blood glucose of approximately 3% and 17%, respectively.	[141]
L Ext	95% Aqueous ethanolic: Administered (100 mg/kg BW, daily, 2 weeks, and in combination with Anredera cordifolia extract) to diabetic rats. Results showed blood glucose decrease of 34-45%	[142]
	Morus rubra
Mixture	Testing Methods and Results	References
L Ext	Aqueous: Supplemented (100, 200, 400 mg/kg BW, daily, 21 days) to diabetic rats. The highest dose inhibited reduced glycosylated hemoglobin (~22%) and increase of plasma insulin (~145%), compared with control diabetic rats.	[143]
L Ext	Aqueous: Administered (100, 200, 400 mg/kg BW, daily, 30 days) to diabetic rats, resulting blood glucose decrease (highest dose) of approximately 60%, compared with control diabetic rats.	[144]

Antidiabetic Properties of Compounds Isolated from Morus and Selected Derivatives

In the previous section, we listed most of the published literature on the antidiabetic activities of mixtures (extracts, powders, and decoctions) isolated from Morus trees. Such mixtures and others (essential oils, infusions, creams, etc.), were also published for other medicinal or nutritional activities and uses of these plants, like numerous other published studies of the most known species of the plant kingdom.

But in terms of drug discovery and development, the efficiency of these mixtures could be improved compared with their pure constituents. This is due to the nature of these mixtures, meaning many parameters influence changing compositions. So, the importance of isolation, characterization, and testing the active pure active compounds is a key step in understanding the mechanisms of action and drug development [145].

Based on that understanding, we present in table 3 the antidiabetic activity purely natural products that were isolated from Morus trees.

Table 3: Antidiabetic activities of compounds/derivatives from Morus species.
Compound(s)/Figure	Test(s) and Result(s)	References
Oxyresveratrol	Lowering blood glucose of diabetic mice	[49]
Kuwanon C, moracin M, dihydromorin, oxyresveratrol, norartocarpetin, kuwanon G (Figure 2*)	Inhibited α-glucosidase. Oxyresveratrol was most active	[57]
24 Compounds were isolated from M. alba (Figure 3)	Compounds 1-16 were tested for α-glucosidase inhibition. Compound 1 was most active	[67]
Oxyresveratrol	Lowering blood glucose diabetic rats and inhibited α-glucosidase	[102]
Two new compounds were isolated from M. alba, with 7 known (Figure 4)	Compound 2 had strong α-glucosidase activity, as well as some of the known compound	[146]
Mulberrofuran G (3) and albanol B (4) from M. alba (Figure 4)	Both compounds (and kuwanon G) inhibited PTP1B and reduced insulin resistance in HepG2 cells	[147]
1-Deoxynojirimycin (DNJ) was isolated from M. alba with 17 other iminosugars (Figure 5)	DNJ was tested for several antidiabetic-related activities and found very active, and most active among all iminosugars isolated from M. alba	[148]
Five new pyrrole alkaloids were isolated from M. alba, and 12 previously known, figure 6 (active compounds)	All alkaloids were tested for pancreatic lipase inhibition, but only two previously known were active	[149]
DNJ and 7 derivatives	Tested for α-glucosidase inhibition, including molecular docking and kinetic studies	[150]
Sanggenon C, sanggenon G, mulberrofuran C, kuwanon L, moracin O and moracin P	Inhibited PTP1B	[151]
New compounds, Morusalbins A-D albanin T, were isolated from M. alba (Figure 6)	Morusalbins A-D along with previously known compounds inhibited PTP1B and α-glucosidase	[152]
Rutin, isoquercetin, and quercetin, from M. alba	Recovered alloxan-damaged pancreatic islets of zebra fish (Dinio rerio)	[153]
DNJ from M. alba compared with aqueous leaves extract	Extract was more active α-glucosidase inhibitor	[154]
DNJ from M. alba	Concentration and activity of DNJ in aqueous-ethanolic extract depends on ethanol to water ration	[155]
Four new compounds, Mortatarins A-D (Figure 7), from M. alba, with 8 previously known	Mortatarin D and 2 known compounds inhibited α-glucosidase	[156]
Ten new compounds (Figure 8) from M. alba, with 4 previously known	Compounds 1-7 (and 2 known) inhibited α-glucosidase, while compounds 1, 9 (and 4 known) inhibited PTP1B	[157]
DNJ, cyanidin-3-glucoside, cyanidin-3-rutinoside, resveratrol and oxyresveratrol, from Morus ssp.	Comprehensive mechanistic, kinetic, and thermodynamic comparison of the inhibition of α-glucosidase by these compounds. Oxyresveratrol is most active	[158]
Morusin, kuwanon H, chalcomoracin A and chalcomoracin B from M. alba	These compounds were isolated fom the roots bark extract, most active among four extracts (roots bark, stem bark, leaves, and fruits). Compounds inhibited α-glucosidase where chalcomoracin was most active	[159]
Five compounds from M. alba, DNJ and three drivatives, and myo-inositol	Tested for inhibition of sucrase and maltase, where DNJ was most active, 1.8 and 10.3 µM, respectively	[160]
Apigenin from M. indica	Kinetic investigation and molecular docking of inhibition of aldose reductase by apigenin	[161]
Seventeen compounds from M. atropurpurea. Figure 9 (active inhibitors)	Chromatography of leaves extract afforded 17 compounds. Six were α-glucosidase inhibitors	[162]
Four known flavonoids from M. atropurpurea	Rutin, isoquercetin, kaempferol-3-O-rutinoside and astragalin inhibited α-glucosidase	[163]
N-Sugars from M. bombycis	Blood glucose reduction in diabetic mice by N-sugars (Figure 5)	[164]
Mulberroside A from M. bombycis	This compound is the diglucosyl of oxyresveratrol (see section 5: Discussion), and it had antidiabetic activities in diabetic rats	[165]
DNJ, fagomine and Gal-DNJ from M. australis	Kinetic study of α-glucosidase inhibition leaves powder of M. australis and each one of these compounds (1,2,3 in Figure 5)	[166]
DNJ from silkworms that were fed with M. alba leaves	Pure compound administered (100 mg/kg BW, daily, 16 weeks) to diabetic rats, lowered blood glucose and insulin resistance	[167]
Chalcone-1-DNJ, (Figure 9)	Synthetic derivative that was supplemented (5,10,20 mg/kg BW, daily, 3 weeks) with DNJ (10 mg) as a control. The result was that the high dose lowered blood glucose of diabetic rats, more than DNJ or acarbose	[168]
Three chrysin-1-DNJ compounds, (Figure 9)	These synthetic derivatives were tested for α-glucosidase inhibition, where compound 3 was most active	[169]
Fagomine with fish oil	Pure compound, administered (0.96 g/kg BW, daily, 24 weeks) to diabetic rats, resulted decrease of blood glucose and insulin resistance	[170]
¹⁵N-DNJ	This isotope labeled pure compound was isolated from Bacillus amyloliquefaciens and tested for safety of administration to diabetic rats. Safe.	[171]
DNJ with polysaccharide from M. multicaulis	Hybrid treatment of diabetic mice with DNJ and polysaccharide (18.8 kDa, 8 different monomers), resulted improvement of histological parameters, mainly activation of PDX-1/insulin-1	[172]
DNJ with polysaccharide from M. multicaulis	The combination of these compounds had blood glucose decreasing effect in diabetic mice, mechanically studies by ¹³C-labeled glucose	[173]
Eight morbilisins (A-H) from M. notabilis (Figure 10).	These compounds were isolated from leaves aqueous extract, that was fractionized with several solvents. Compounds 1,5,7,9 inhibited PTP1B	[174]
DNJ-enriched leaves extract of M. alba	The objective of this study is to investigate the synergism of α-glucosidase inhibition of various components of this extract. DNJ synergized with flavonoids and polysaccharides, but these had no synergism with each other	[175]
*Selected structures of the natural products listed in table 3 (above) are presented in figures 2-10, according to their appearance in table 3.

Discussion

Many cultures have used the Morus genus trees in “the old world” since ancient times. The traditional uses of these trees included all parts, but nutrition was and still the most important. In this review, we focused on antidiabetics and related activities, yet numerous publications reported many other traditional uses [176-178]. And as presented in section 1, the leading species in traditional antidiabetic activity are M. alba and M. nigra, so this is the general outcome in all aspects of traditional uses and modern medicinal research findings for this genus.

The nutritional value of the fruits and leaves of these trees is very high. Obviously, this value is strongly affected by many factors: species, ripening degree, and agricultural and environmental parameters. In table 4, we present the averaged values of nutritional components of three Morus species from two different publications.

Table 4: Nutritional components of three Morus species.
*Morus* ssp./Plant Part	*alba* F*	*nigra* F	*rubra* F	*alba* F	*alba* L
Protein (% DW)	1.55	0.96	1.2	11	24.3
Fat (%)	1.1	0.95	0.85	1.77	4.1
Fiber (%)	1.47	11.75	---	7.2	26.9
Ascorbic acid (mg/100 g)	22.4	21.8	19.4	129.6	150
Calcium (mg/100 g)	152	132	132	---	---
Magnesium (mg/100 g)	106	106	115	---	---
Potassium (mg/100 g)	1668	922	834	---	---
Iron (mg/100 g)	4.2	4.2	4.5	---	---
Total phenolics (mgQE-1 100 g FW)	181	1422	1035	---	---
Carbohydrate (%)	---	---	---	71	23.5
Fructose (g/100 g FW)	6269	5634	5407	---	---
Glucose (g/100 g FW)	6864	7748	6068	---	---
β-Carotene (%)	---	---	---	13.7	10.8
Reference	[179]			[180]
*DW: Dry Weight; F: Fruits; FW: Fresh Weight; L: Leaves; QE: Quercetin Equivalent

Morus is one of the most studied genera for antidiabetic and its related activities, which we have focused on in this review article. But it is very important to highlight the fact that some of its outstanding properties, such as antioxidant activity, have a direct and major effect on human health [181,182]. Moreover, our presentation showed the actual situation of antidiabetic activity of Morus products, where most of the published studies used mixtures (Table 2) prepared from these trees. Along with that, it is important to remember that some of the studies of these mixtures emphasized the rule of very well previously known active components of these mixtures, such as in the case of chlorogenic acid and rutin [34].

Most active antidiabetic natural products are polar or very polar, polyphenols or iminosugars. Despite this, in some cases, the detected antidiabetic compounds of Morus origins were isolated from non-polar extracts or fractions. Loliolide had in vitro (cell culture) glucose-lowering and insulin-increasing activities, and was extracted from leaves of M. alba with CH2Cl2 [71]. Also, the 2-arylbenzofuran, mulberrofuran U, is officially considered polyphenol and was extracted with EtOAc from leaves of M. insignis [127]. The structures of both compounds are shown in figure 11.

It is generally accepted that there is a clear correlation between total phenolic content and many medicinal properties of plant materials, especially antioxidant activity [183]. But polyphenols content, as well as other natural products in Morus trees, is very highly affected by many factors: growth location, seasonality, species or subspecies, soil quality, irrigation, and many others; and all this has a direct effect on antidiabetic activities, such as α-glucosidase inhibition [184,185]. Another one of the best examples of the content variation of an active compound with external factors is the antidiabetic agent mulberroside A [186], which changed with the seasonality and growth stage of three Morus species [187]. In this study, changes in oxyresveratrol and resveratrol concentrations are reported. Another study from China reported a direct relationship between the area of Morus and hypoglycemic (and antioxidant) properties [188]. An interesting report was published by the Indoestion group concerning the effect of Morus species and the maturity stage of the trees on two variables: qualitative content (natural products families) and DNJ content [189]. All four species contained the same compound families as young or mature trees. But the concentration of DNJ was significantly different in both categories as seen in table 5.

Table 5: DNJ concentration in leaves of four Morus young and mature species.
Species	Maturity Stage	DNJ Concentration (mg/g)
M. alba	Young leaves	0.085
M. alba	Mature leaves	0.31
M. bombycis	Young leaves	0.331
M. bombycis	Mature leaves	1.425
M. cathayana	Young leaves	0.995
M. cathayana	Mature leaves	3.185
M. multicaullis	Young leaves	0.086
M. multicaullis	Mature leaves	0.183

But the special attention that the typical Morus natural products have drawn in the context of antidiabetic activity emerges from well-based research results. For example, oxyresveratrol was the most active when comparing the α-glucosidase inhibition activity of five compounds [158]. For this reason, many analytical methods were developed to determine the content of these important compounds and other methods to increase their production.

Oxyresveratrol, an aglycon of mulberry side A [49], is not only one of the most active antidiabetic agents, but it was also reported for important activities: antibacterial [190,191], anti-inflammatory [192], anticancer [193], and many others. So, several studies were published about the determination of this natural product in its sources or after use [194,195], as well as its isolation [196,197]. Moreover, biosynthesis and laboratory syntheses were widely published and reviewed [198], and many studies investigated the enhancement of oxyresveratrol bioproduction [199,200]. In other but related studies, the enhanced production of mulberry side A was reported [201].

D-Fagomine or shortly, fagomine (compound 8 in figure 5), is an iminosugar found in several plants, including Morus trees. It is anti-diabetic but possesses other properties, such as antibacterial [202]. Its antidiabetic activity is mostly unrelated to Morus products since it can be isolated from other plant sources or commercially purchased [203,204]. Determination and isolation of fagomine were also published [205] as its synthesis [206].

DNJ, or 1-Deoxynojirimycin is one of Morus's most studied and published active natural products. Even though this genus's trees are not the sole source of this compound, they are the major ones [207]. It has been reported to have many activities and properties in addition to antidiabetic: antibiofilm [208], anti-obesity [209], neuroprotective [210], and others. Its concentrations in plant sources are relatively low (Table 4). Consequently, many determination and analysis methods were developed to detect its concentrations and a notable number of methods to enhance its production in sources. A summary of these methods is shown in table 6.

Table 6: DNJ analysis, isolation, and enhanced production methods.
Analysis or Production Method	References
Derivation with 9-fluorenylmethyl chloroformate and HPLC	[211]
Precolumn derivation (6-aminoquinoiyi-N-hydroxysuccinimidyl carbamate) and HPLC	[212]
Microwave-assisted extraction	[213]
Derivation with 9-fluorenylmethyl succinimidyl carbonate and HPLC	[214]
HPLC analysis of 146 species and subspecies (India)	[215]
Determination in Italian cultivars by HPLC-MS	[216]
Determination in antidiabetic Fu-Zhu-Jiang-Tang tablets by GC-MS	[217]
Determination in dietary supplements by ATR-FTIR	[218]
HPLC analysis of UVC-irradiated M. alba leaves that increased DNJ content 4-fold	[219]
Production enhancement by leaves fermentation with G. lucidum	[220]
Fermentation of leaves powder with four species of bacteria increased the concentration of DNJ by all of them, and W. anomalus was highest	[221]

Several publications proposed the biosynthesis of DNJ. One of these presented 11 biosynthetic steps starting from aspartic acid [222], while starting from D-glucose required only 6 steps, and the authors named it “am-aza-ing” [223]. See a short version of these biosynthetic paths in figure 12.

The insulin regulation mechanism was presented by several publications [43,224,225]. Here we present in figure 13 the mechanism introduced by T-G. Hu and his colleagues [225].

As mentioned earlier, the importance of Morus trees is very high, both medicinally and nutritionally. This review presented most of the published literature about antidiabetic and its related activities. But this is a very partial scope since the Morus genus possesses many other medicinal activities. Nutritionally, these trees are not very important to humans but also to their livestock: cattle [226], chicken [227], fish [228], sheep [229], pigs [230], and rabbits [231], and these are some of the recent and much selected examples.

Apart from Turkey [232], Morus trees were always a “neglected crop” in the Middle East region, even though they were never rare: black mulberry (M. nigra) is mostly named “Damascus mulberry.” Morus albaand Morus nigra are the most common species, but recently, there has been a growing private gardening and commercial agriculture in Morus macroura, the “Afghani” mulberry. Another major difference between the Middle East and East Asia Morus consumption for human nutrition is that Morus leaves are widely eaten in East Asia. At the same time, they are almost ignored as food in the Middle East. This is not clear because the nutritional advantages of Morus leaves are very notable, especially as antidiabetic with their oxyresveratrol and DNJ content.

Conclusion

Morus trees are excellent sources of nutrients and contain very active antidiabetic natural products. Unlike many crop trees, Morus leaves are edible and very healthy and can be consumed fresh, enabling them another advantage.

The enormous number of published studies about the health and medicinal potentials of Morus trees is just growing. In the future vision, Morus trees should be extensively grown all over the globe, and their products should be more common and accessible.