Beneficial effects of cinnamon proanthocyanidins on the formation of specific advanced glycation endproducts and methylglyoxal-induced impairment on glucose consumption

Advanced Glycation End-Products and Diabetic Neuropathy of the Retina

Diabetic retinopathy is a tissue-specific neurovascular impairment of the retina in patients with both type 1 and type 2 diabetes. Several pathological factors are involved in the progressive impairment of the interdependence between cells that consist of the neurovascular units (NVUs). The advanced glycation end-products (AGEs) are one of the major pathological factors that cause the impairments of neurovascular coupling in diabetic retinopathy. Although the exact mechanisms for the toxicities of the AGEs in diabetic retinopathy have not been definitively determined, the AGE-receptor of the AGE (RAGE) axis, production of reactive oxygen species, inflammatory reactions, and the activation of the cell death pathways are associated with the impairment of the NVUs in diabetic retinopathy. More specifically, neuronal cell death is an irreversible change that is directly associated with vision reduction in diabetic patients. Thus, neuroprotective therapies must be established for diabetic retinopathy. The AGEs are one of the therapeutic targets to examine to ameliorate the pathological changes in the NVUs in diabetic retinopathy. This review focuses on the basic and pathological findings of AGE-induced neurovascular abnormalities and the potential therapeutic approaches, including the use of anti-glycated drugs to protect the AGE-induced impairments of the NVUs in diabetic retinopathy.

Comparative Metabolite Profiling and Fingerprinting of Medicinal Cinnamon Bark and Its Commercial Preparations via a Multiplex Approach of GC–MS, UV, and NMR Techniques

Various species of cinnamon (Cinnamomum sp.) are consumed as traditional medicine and popular spice worldwide. The current research aimed to provide the first comparative metabolomics study in nine cinnamon drugs and their different commercial preparations based on three analytical platforms, i.e., solid-phase microextraction coupled to gas chromatography–mass spectrometry method (SPME/GC–MS), nuclear magnetic resonance (NMR), and ultraviolet-visible spectrophotometry (UV/Vis) targeting its metabolome. SPME/GC–MS of cinnamon aroma compounds showed a total of 126 peaks, where (E)-cinnamaldehyde was the major volatile detected at 4.2–60.9% and 6.3–64.5% in authenticated and commercial preparations, respectively. Asides, modeling of the GC/MS dataset could relate the commercial products CP-1 and CP-3 to C. cassia attributed to their higher coumarin and low (E)-cinnamaldehyde content. In contrast, NMR fingerprinting identified (E)-methoxy cinnamaldehyde and coumarin as alternative markers for C. verum and C. iners, respectively. Additionally, quantitative NMR (qNMR) standardized cinnamon extracts based on major metabolites. UV/Vis showed to be of low discrimination power, but its orthogonal projections to latent structures discriminant analysis (OPLS-DA) S-plot showed that C. iners was more abundant in cinnamic acid compared to other samples. Results of this study provide potential insights into cinnamon drugs QC analysis and identify alternative markers for their discrimination.

Nɛ-(carboxymethyl)lysine, Available Lysine, and Volatile Compound Profile of Biscuits Enriched with Grape by-Product During Storage

We investigated the changes in Nɛ-(carboxymethyl)lysine (CML) and available lysine content, antioxidant properties, volatiles, and oxidation products of biscuits enriched with grape by-product (GP), stored for six months under a modified atmosphere of 0%/30%/70% O₂/CO₂/N₂ and in air. Fresh GP-formulated biscuits showed lower concentrations of CML (89%), available lysine (40%), and pyrazines (75%), but higher antioxidant capacities (~ sixfold), furans (12-fold), and lipid-derived compounds (three-fold) than the control. Although ~ 15% higher losses of Maillard-type volatiles were identified in the air atmosphere during storage, lipid oxidation was ~ 30% less pronounced in the modified atmosphere. A significant correlation of 0.994 between the reduction in CML and the available lysine suggest further CML reactions with the ɛ-NH₂ group of amino acids. Significant correlations (of -0.550 to -0.980) between oxidation products, antioxidant capacities, and changes in CML content during storage suggest that these parameters might be involved in the CML elimination mechanism.

Assessing the In Vitro Inhibitory Effects on Key Enzymes Linked to Type-2 Diabetes and Obesity and Protein Glycation by Phenolic Compounds of Lauraceae Plant Species Endemic to the Laurisilva Forest

Methanolic leaf extracts of four Lauraceae species endemic to Laurisilva forest (Apollonias barbujana, Laurus novocanariensis, Ocotea foetens and Persea indica) were investigated for the first time for their potential to inhibit key enzymes linked to type-2 diabetes (α-amylase, α-glucosidase, aldose reductase) and obesity (pancreatic lipase), and protein glycation. Lauraceae extracts revealed significant inhibitory activities in all assays, altough with different ability between species. In general, P. indica showed the most promissing results. In the protein glycation assay, all analysed extracts displayed a stronger effect than a reference compound: aminoguanidine (AMG). The in vitro anti-diabetic, anti-obesity and anti-glycation activities of analysed extracts showed correlation with their flavonols and flavan-3-ols (in particular, proanthocyanins) contents. These Lauraceae species have the capacity to assist in adjuvant therapy of type-2 diabetes and associated complications, through modulation of the activity of key metabolic enzymes and prevention of advanced glycation end-products (AGEs) formation.

Air frying combined with grape seed extract inhibits Nε-carboxymethyllysine and Nε-carboxyethyllysine by controlling oxidation and glycosylation

Advanced glycation end products (AGE), compounds formed in meat at the advanced stage of Maillard reaction, are easily exposed to thermal processing. Improving cooking condition and adding antioxidants are 2 common ways for AGE reduction. The present work compared the inhibition of grape seed extract (GSE) on levels of free and protein-bound N^ε-carboxymethyllysine (CML) and N^ε-carboxyethyllysine (CEL) in chicken breast under deep-frying and air-frying conditions. Efficiency of 5 concentrations of GSE (0.0, 0.2, 0.5, 0.8, and 1.0 g/kg) in retarding oxidation, glyoxal (GO), methylglyoxal (MGO), lysine (Lys), Maillard reaction degree (A₂₉₄, A₄₂₀), and Shiff's base were tested. Results showed that 0.5 g/kg GSE before heating significantly (P < 0.05) reduced AGE in fried breast chicken, whereas excessive supplementation of GSE (0.8 and 1 g/kg) was reverse. Air frying was found significantly (P < 0.05) better than deep frying to reduce the precursor substances (GO, MGO, and Lys) of AGE. In conclusion, GSE-derived polyphenols exhibited different inhibitory effects on oxidation and glycosylation at different concentrations. We found that 0.5 g/kg of GSE combined with air frying was the best recommendation for inhibiting CML and CEL.

In vitro anti-diabetic effects and phytochemical profiling of novel varieties of Cinnamomum zeylanicum (L.) extracts

BACKGROUND

Diabetes mellitus type 2 (DMT2) is a leading metabolic disorder in the world. Anti-diabetic actions of phytochemicals from various medicinal herbs have been explored as an alternative therapy in the management of DMT2 due to adverse effects of synthetic drugs used in allopathic medicine. α-amylase and α-glucosidase inhibitory potential and phytochemical profiling were investigated in aqueous extracts of two new Cinnamomum zeylanicum accessions, namely C. zeylanicum Sri Wijaya (SW), C. zeylanicum Sri Gemunu (SG) and commercially available C. zeylanicum (CC).

METHODS

Microwave Digestion (MD), Pressurized Water Extraction (PWE), Steam Distillation (SD), Solvent Extraction (SE), Decoction Water Extraction (DWE) and Infusion Water Extraction (IWE) methods were used to prepare Cinnamon quill extracts. Total phenolic content (TPC, Folin-Ciocalteu method) and Proanthocyanidin content (PC, vanillin assay), α-amylase and α-glucosidase inhibition of Cinnamon extracts were determined spectrophotometrically. The α-amylase and α-glucosidase inhibition were reported in terms of IC50 value. The phytochemical profiling was accomplished by GC-MS technique.

RESULTS AND DISCUSSION

Lowest IC50 values were observed in PWE and DWE of SW. The highest PC and TPC were also observed in PWE and DWE of SW. Pressured water and decoctions are promising methods for the extraction of antidiabetic constituents from cinnamon. Benzoic acid, cinnamyl alcohol, benzyl alcohol, and 4-Allyl-2,6-dimethoxyphenol were identified as major compounds in SW extracts. These compounds are believed to be responsible for strong enzyme inhibitory activity of the extracts.

CONCLUSIONS

This is the first study to explore the use of pressured and decoctions water to extract anti-diabetic phytochemicals from cinnamon. The extensive metabolite profiling of novel SW and SG extracts and comparison of that with commercially available CC are reported for the first time in this study. The C. zeylanicum, SW accession holds some promise in the management of diabetes.

Healthy eating recommendations: good for reducing dietary contribution to the body's advanced glycation/lipoxidation end products pool?

The present review aims to give dietary recommendations to reduce the occurrence of the Maillard reaction in foods and in vivo to reduce the body's advanced glycation/lipoxidation end products (AGE/ALE) pool. A healthy diet, food reformulation and good culinary practices may be feasible for achieving the goal. A varied diet rich in fresh vegetables and fruits, non-added sugar beverages containing inhibitors of the Maillard reaction, and foods prepared by steaming and poaching as culinary techniques is recommended. Intake of supplements and novel foods with low sugars, low fats, enriched in bioactive compounds from food and waste able to modulate carbohydrate metabolism and reduce body's AGE/ALE pool is also recommended. In conclusion, the recommendations made for healthy eating by the Spanish Society of Community Nutrition (SENC) and Harvard University seem to be adequate to reduce dietary AGE/ALE, the body's AGE/ALE pool and to achieve sustainable nutrition and health.

Antioxidant and Glycemic Regulatory Properties Potential of Different Maturity Stages of Leaf of Ceylon Cinnamon (Cinnamomum zeylanicum Blume) In Vitro

Dichloromethane:methanol (1:1, v/v) extracts of different maturity stages (immature, partly mature, and mature) of authenticated leaves of Ceylon cinnamon (CC) were used in this study. Antioxidant properties [total polyphenolic content (TPC) and total flavonoid content (TFC), 1, 1-diphenyl-2-picryl-hydrazyl (DPPH), 2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS)), oxygen radical absorbance capacity (ORAC), and ferric reducing antioxidant power (FRAP)] and glycemic regulatory properties [antiamylase (AA); antiglucosidase (AG)] were evaluated using 96-well microplate based bio assays in vitro (TPC, TFC, DPPH, ABTS, ORAC n=4 each; FRAP, AA, AG n=3 each). Results clearly revealed significant differences (p<0.05) among different maturity stages of leaf of CC for both antioxidant and glycemic regulatory properties (except AG activity). The mean antioxidant and glycemic regulatory activities of immature, partly mature, and mature leaves ranged from TPC: 0.68 ± 0.02-22.35 ± 0.21 mg gallic acid equivalents/g of sample (GS); TFC: 0.85 ± 0.01-4.68 ± 0.06 mg quercetin equivalents/GS; DPPH: 0.42 ± 0.01-27.09 ± 0.65 mg Trolox equivalents (TE)/GS; ABTS: 3.57 ± 0.10-43.91 ± 1.46 TE/GS; ORAC: 0.71 ± 0.01-18.70 ± 0.26 TE/G, FRAP: 0.31 ± 0.02-69.16 ± 0.52 TE/GS; and AA: 18.05 ± 0.24-36.62 ± 4.00% inhibition at 2.5 mg/mL. Mature leaf had the highest antioxidant and AA activities for all the assays investigated. In contrast, immature leaf had the lowest. The order of potency for antioxidant and AA activities was mature leaf > partly mature leaf > immature leaf. This is the first study to report on antioxidant and glycemic regulatory properties of different maturity stages of leaf of Ceylon cinnamon and highlights its potential use in management of oxidative stress-associated chronic diseases including diabetes mellitus.

Developments in Taste-Masking Techniques for Traditional Chinese Medicines

A variety of pharmacologically active substances, including chemotherapeutic drugs and the substances from traditional Chinese medicine (TCM), always exhibit potent bioactivities after oral administration. However, their unpleasant taste (such as bitterness) and/or odor always decrease patient compliance and thus compromise their curative efficacies in clinical application. Therefore, the developments of taste-masking techniques are of great significance in improving their organoleptic properties. However, though a variety of taste-masking techniques have been successfully used to mask the unpalatable taste of chemotherapeutic drugs, their suitability for TCM substances is relatively limited. This is mainly due to the fact that the bitter ingredients existing in multicomponent TCM systems (i.e., effective fractions, single Chinese herbs, and compound preparations) are always unclear, and thus, there is lack of tailor-made taste-masking techniques to be utilized to conceal their unpleasant taste. The relevant studies are also relatively limited. As a whole, three types of taste-masking techniques are generally applied to TCM, including (i) functional masking via sweeteners, bitter blockers, and taste modifiers; (ii) physical masking via polymer film-coating or lipid barrier systems; and (iii) biochemical masking via intermolecular interaction, β-cyclodextrin inclusion, or ion-exchange resins. This review fully summarizes the results reported in this field with the purpose of providing an informative reference for relevant readers.

Cinnamon, a promising prospect towards Alzheimer's disease

Over the last decades, an exponential increase of efforts concerning the treatment of Alzheimer's disease (AD) has been practiced. Phytochemicals preparations have a millenary background to combat various pathological conditions. Various cinnamon species and their biologically active ingredients have renewed the interest towards the treatment of patients with mild-to-moderate AD through the inhibition of tau protein aggregation and prevention of the formation and accumulation of amyloid-β peptides into the neurotoxic oligomeric inclusions, both of which are considered to be the AD trademarks. In this review, we presented comprehensive data on the interactions of a number of cinnamon polyphenols (PPs) with oxidative stress and pro-inflammatory signaling pathways in the brain. In addition, we discussed the potential association between AD and diabetes mellitus (DM), vis-à-vis the effluence of cinnamon PPs. Further, an upcoming prospect of AD epigenetic pathophysiological conditions and cinnamon has been sighted. Data was retrieved from the scientific databases such as PubMed database of the National Library of Medicine, Scopus and Google Scholar without any time limitation. The extract of cinnamon efficiently inhibits tau accumulations, Aβ aggregation and toxicity in vivo and in vitro models. Indeed, cinnamon possesses neuroprotective effects interfering multiple oxidative stress and pro-inflammatory pathways. Besides, cinnamon modulates endothelial functions and attenuates the vascular cell adhesion molecules. Cinnamon PPs may induce AD epigenetic modifications. Cinnamon and in particular, cinnamaldehyde seem to be effective and safe approaches for treatment and prevention of AD onset and/or progression. However, further molecular and translational research studies as well as prolonged clinical trials are required to establish the therapeutic safety and efficacy in different cinnamon spp.

Functional food supplements to ameliorate the secondary complications in high fructose fed diabetic rats

Poly-herbal functional food supplements inhibited high fructose induced glycation in diabetic rats and showed promise for effective management of secondary complications of diabetes such as improved lipid profile, kidney function and reduction of oxidative stress.

The inhibitory effect of selenium nanoparticles on protein glycation in vitro

Selenium nanoparticles (Se NPs) possess well-known excellent biological activities and low toxicity, and have been employed for numerous applications except as inhibitors to protein glycation. Herein, the present study is carried out to investigate the inhibitory effect of Se NPs on protein glycation in a bovine serum albumin (BSA)/glucose system. By measuring the amount of glucose covalently bound onto BSA, the formation of fructosamine and fluorescent products, it is found that Se NPs can hinder the development of protein glycation in a dose-dependent but time-independent manner under the selected reaction conditions (55 °C, 40 h). And after comparing the increase of inhibitory rate in different stages, it is observed that Se NPs show the greatest inhibitory effect in the early stage, then in the advanced stage, but no effect in the intermediate stage. Fourier transform infrared spectroscopy characterization of Se NPs collected after glycation and determination of ·OH influence and glyoxal formation show that the mechanism for the inhibitory efficacy of Se NPs is related to their strong competitive activity against available amino groups in proteins, their great scavenging activity on reactive oxygen species and their inhibitory effect on α-dicarbonyl compounds' formation. In addition, it is proved that Se NPs protect proteins from structural modifications in the system and they do not exhibit significant cytotoxicity towards BV-2 and BRL-3A cells at low concentrations (10 and 50 μg mL(-1)). Consequently, Se NPs may be suitable for further in vivo studies as novel anti-glycation agents.

Recent development of plant products with anti-glycation activity: a review

This review article summarizes the plant natural products that inhibit glycation at different stages leading to the AGEs formation.

Cinnamon: a multifaceted medicinal plant

Cinnamon (Cinnamomum zeylanicum, and Cinnamon cassia), the eternal tree of tropical medicine, belongs to the Lauraceae family. Cinnamon is one of the most important spices used daily by people all over the world. Cinnamon primarily contains vital oils and other derivatives, such as cinnamaldehyde, cinnamic acid, and cinnamate. In addition to being an antioxidant, anti-inflammatory, antidiabetic, antimicrobial, anticancer, lipid-lowering, and cardiovascular-disease-lowering compound, cinnamon has also been reported to have activities against neurological disorders, such as Parkinson's and Alzheimer's diseases. This review illustrates the pharmacological prospective of cinnamon and its use in daily life.

Hypoglycemic Activity and Antioxidative Stress of Extracts and Corymbiferin from Swertia bimaculata In Vitro and In Vivo

The present study was to investigate the anti-diabetic activities of Swertia bimaculata. Based on the glucose consumption of S. bimaculata extractsand different fractions (petroleum, dichloromethane, ethyl acetate, n-butanol and water extracts) in 3T3-L1 adipocyte assay, ethanol (ETH) and dichloromethane (DTH) extracts had the most effective potency. Furthermore, ETH, DTH and corymbiferin (the most abundant component of DTH) were evaluated for anti-diabetic effects in high fat and sucrose fed combined with low dose streptozocin induced diabetic rats. DTH and corymbiferin displayed remarkable anti-diabetic activities. The fasting blood glucose levels were significantly decreased, while the serum insulin levels were obviously increased. The oral glucose tolerance was also improved. The lowed serum total cholesterol, low density lipoprotein (LDL) and triglyceride levels and increased ratio of HDL (high density lipoprotein)/LDL were observed. The insulin sensitivity was improved on the basis of increased expressions of insulin-receptor substrate-2, phosphatidylinositol 3-kinase and Ser/Thr kinase AKT2. And also DTH and corymbiferin improved antioxidant capacity and carbohydrate metabolism in diabetic rats, along with the improvement of histopathology of livers and pancreatic β cells. Corymbiferin was one of active constituents, responsible for anti-diabetic properties. Therefore, S. bimaculata could be considered as an alternative agent against diabetes mellitus.

The role of polyphenols in the modulation of sirtuins and other pathways involved in Alzheimer's disease

Alzheimer's disease (AD) is characterised by extracellular amyloid deposits, neurofibrillary tangles, synaptic loss, inflammation and extensive oxidative stress. Polyphenols, which include resveratrol, epigallocatechin gallate and curcumin, have gained considerable interest for their ability to reduce these hallmarks of disease and their potential to slow down cognitive decline. Although their antioxidant and free radical scavenging properties are well established, more recently polyphenols have been shown to produce other important effects including anti-amyloidogenic activity, cell signalling modulation, effects on telomere length and modulation of the sirtuin proteins. Brain accessible polyphenols with multiple effects on pathways involved in neurodegeneration and ageing may therefore prove efficacious in the treatment of age-related diseases such as AD, although the evidence for this so far is limited. This review aims to explore the known effects of polyphenols from various natural and synthetic sources on brain ageing and neurodegeneration, and to examine their multiple mechanisms of action, with an emphasis on the role that the sirtuin pathway may play and the implications this may have for the treatment of AD.

Dietary Chinese quince polyphenols suppress generation of α-dicarbonyl compounds in diabetic KK-A(y) mice

Many dietary polyphenols can provide health benefits, such as antioxidant and antidiabetic effects, and can down-regulate the progression of glycation (one cause of diabetic complications). Chinese quince (CQ) is rich in polyphenols, especially procyanidins. A few studies have indicated that CQ has an effect on diabetes. In this study, a procyanidin-rich extract was prepared from Chinese quince fruit (CQE), and its effects were investigated and compared with those of green tea extract (GTE) in type 2 diabetes model KK-A(y) mice. Mice were provided one of two high-fat (HF) diets for 4 weeks: a HF diet containing 0.5% CQE or a HF diet containing 0.5% GTE. Blood glucose was suppressed in mice fed CQE and GTE during the experimental period (p < 0.05), although the effect of CQE was weaker than that of GTE. Intake of CQE had no effect on the blood insulin level, whereas GTE decreased the insulin level. Body weight gain was suppressed in mice fed CQE similarly to mice fed GTE (p < 0.05). Hepatic lipid content and α-dicarbonyl compounds in the kidney were reduced in mice fed CQE and GTE (p < 0.05). These results suggest that intake of CQE could moderate type 2 diabetes and diabetic complications.

Medicago glucosyltransferase UGT72L1: potential roles in proanthocyanidin biosynthesis

In the first reaction specific for proanthocyanidin (PA) biosynthesis in Arabidopsis thaliana and Medicago truncatula, anthocyanidin reductase (ANR) converts cyanidin to (-)-epicatechin. The glucosyltransferase UGT72L1 catalyzes formation of epicatechin 3'-O-glucoside (E3'OG), the preferred substrate for MATE transporters implicated in PA biosynthesis in both species. The mechanism of PA polymerization is still unclear, but may involve the laccase-like polyphenol oxidase TRANSPARENT TESTA 10 (TT10). We have employed a combination of cell biological, biochemical and genetic approaches to evaluate this PA pathway model. The promoter regions of UGT72L1 and MtANR share common cis-acting elements and direct overlapping, but partially distinct, expression patterns. UGT72L1 and MtANR are localized in the cytosol, whereas TT10 is localized to the vacuole. Over-expression of UGT72L1 in M. truncatula hairy roots results in increased accumulation of PA-like compounds, and loss of function of UGT72L1 partially reduces epicatechin, E3'OG and extractable PA levels in M. truncatula seeds. Expression of UGT72L1 in A. thaliana leads to a massive increase in E3'OG in immature seed, but reduced levels of extractable PAs. However, when UGT72L1 was expressed in the Arabidopsis tt10 mutant, extractable PA levels increased and seed coat browning was delayed. Our results suggest that glycosylation of epicatechin is important for both PA precursor transport and assembly, but that additional redundant pathways may exist.

Molecular strategies to prevent, inhibit, and degrade advanced glycoxidation and advanced lipoxidation end products

The advanced glycoxidation end products (AGEs) and lipoxidation end products (ALEs) contribute to the development of diabetic complications and of other pathologies. The review discusses the possibilities of counteracting the formation and stimulating the degradation of these species by pharmaceuticals and natural compounds. The review discusses inhibitors of ALE and AGE formation, cross-link breakers, ALE/AGE elimination by enzymes and proteolytic systems, receptors for advanced glycation end products (RAGEs) and blockade of the ligand-RAGE axis.

Anti-diabetic activities of Gegen Qinlian Decoction in high-fat diet combined with streptozotocin-induced diabetic rats and in 3T3-L1 adipocytes

Gegen Qinlian Decoction (GGQLD) is one of the well-known traditional Chinese medicines. Recently, it was reported that GGQLD had good clinical effects on type 2 diabetes mellitus. However, few studies have confirmed in detail the anti-diabetic activities of GGQLD in vivo and in vitro. In the present study, we investigated the anti-diabetic effects of GGQLD in high-fat diet combined with streptozotocin-induced diabetic rats and in 3T3-L1 adipocytes. The present results suggested GGQLD (4.95, 11.55 and 18.15 g/kg) decreased significantly fasting blood glucose, glycosylated serum protein, and glycosylated hemoglobin of diabetic rats (p<0.05), and GGQLD (4.95 and 18.15 g/kg) decreased significantly fasting serum insulin levels of diabetic rats (p<0.05); in 3T3-L1 adipocytes, Gegen Qinlian Decoction-containing serum (GGQLD-CS) (4%, 8% and 16%) enhanced glucose consumption, triglyceride (TG) content, adiponectin protein concentration and the mRNA expression of adiponectin. Adiponectin contributes to the regulation of lipid and glucose metabolism, and can play a critical role in the development of diabetes mellitus; the mechanisms of action of GGQLD might be related to augmentation of adiponectin protein concentration and up-regulation of the mRNA expression of adiponectin. However, the multi-target mechanisms of action of GGQLD need to be clarified further. The present study further validated the beneficial effects of GGQLD as an anti-diabetic agent. These findings provide a new insight into the anti-diabetic application for GGQLD in clinic and display the potential of GGQLD as a new drug candidate for the treatment of diabetes mellitus.

Efficacy and safety of 'true' cinnamon (Cinnamomum zeylanicum) as a pharmaceutical agent in diabetes: a systematic review and meta-analysis

AIMS

Diabetes is a leading cause of morbidity and mortality worldwide. Studies have frequently looked at dietary components beneficial in treatment and prevention. We aim to systematically evaluate the literature on the safety and efficacy of Cinnamomum zeylanicum on diabetes.

METHODS

A comprehensive search of the literature was conducted in the following databases; PubMed, Web of Science, Biological Abstracts, SciVerse Scopus, SciVerse ScienceDierect, CINAHL and The Cochrane Library. A meta-analysis of studies examining the effect of C. zeylanicum extracts on clinical and biochemical parameters was conducted. Data were analysed using RevMan v5.1.2.

RESULTS

The literature search identified 16 studies on C. zeylanicum (five in-vitro, six in-vivo and five in-vivo/in-vitro). However, there were no human studies. In-vitro C. zeylanicum demonstrated a potential for reducing post-prandial intestinal glucose absorption by inhibiting pancreatic α-amylase and α-glucosidase, stimulating cellular glucose uptake by membrane translocation of glucose transporter-4, stimulating glucose metabolism and glycogen synthesis, inhibiting gluconeogenesis and stimulating insulin release and potentiating insulin receptor activity. The beneficial effects of C. zeylanicum in animals include attenuation of diabetes associated weight loss, reduction of fasting blood glucose, LDL and HbA(1c) , increasing HDL cholesterol and increasing circulating insulin levels. Cinnamomum zeylanicum also significantly improved metabolic derangements associated with insulin resistance. It also showed beneficial effects against diabetic neuropathy and nephropathy, with no significant toxic effects on liver and kidney and a significantly high therapeutic window.

CONCLUSION

Cinnamomum zeylanicum demonstrates numerous beneficial effects both in vitro and in vivo as a potential therapeutic agent for diabetes. However, further randomized clinical trials are required to establish therapeutic safety and efficacy.

Diverse mechanisms of antidiabetic effects of the different procyanidin oligomer types of two different cinnamon species on db/db mice

The procyanidin oligomers are thought to be responsible for the antidiabetic activity of cinnamon. To investigate the hypoglycemic effects of different procyanidin oligomer types, the procyanidin oligomer-rich extracts were prepared from two different cinnamon species. Using high-performance liquid chromatography with purified procyanidin oligomers as reference compounds, we found that the Cinnamomum cassia extract (CC-E) and Cinnamomum tamala extract (CT-E) were rich in B- and A-type procyanidin oligomers, respectively. In the experiment, 8-week-old diabetic (db/db) mice were gavaged with CC-E and CT-E (both 200 mg/kg per day) for 4 weeks. Both CC-E and CT-E exhibited antidiabetic effects. Moreover, histopathological studies of the pancreas, liver, and adipose tissue showed that CC-E promoted lipid accumulation in the adipose tissue and liver, whereas CT-E mainly improved the insulin concentration in the blood and pancreas.

Trapping of methylglyoxal by curcumin in cell-free systems and in human umbilical vein endothelial cells

Curcumin, the most active compound of curcuminoids, has been shown to inhibit formation of advanced glycation end products (AGEs) in streptozotocin-induced diabetic rats. However, little is known on whether curcumin may trap methylglyoxal (MGO), a major reactive dicarbonyl compound, to inhibit AGE formation. We found that one molecule of curcumin effectively trapped one molecule of MGO at a 1:3 ratio at 24 h of incubation under physiological conditions (pH 7.4, 37 °C). Curcumin decreased N(ε)-(carboxymethyl)lysine (CML) expression in human umbilical vein endothelial cells. We further used two curcumin analogues, dimethoxycurcumin (DIMC) and ferulic acid, to investigate the possible MGO-trapping mechanism of curcumin. Results reveal that DIMC, but not ferulic acid, exhibited MGO-trapping capacity, indicating curcumin traps MGO at the electron-dense carbon atom (C10) between the two keto carbon groups. Thus, curcumin may prevent MGO-induced endothelial dysfunction by directly trapping MGO.

Flavour chemistry of methylglyoxal and glyoxal

Methylglyoxal (MGO) and glyoxal (GO), known as reactive carbonyl species, can be generated endogenously and exogenously (human body and food system). They are attracting increased attention because of their relationship with diabetes and flavour generation. In this review, their characteristics relating to flavour chemistry are discussed. MGO and GO can be detected in food systems by GC and HPLC after derivatization. MGO and GO formed in the Maillard reaction play important roles as precursors of aroma and colour compounds, especially in Strecker degradation, a major flavour generation reaction. When combined with amino acids they undergo Schiff base formation, decarboxylation and α-aminoketone condensation leading to heterocyclic aroma compounds such as pyrazines, pyrroles and pyridines. They attack amine groups in amino acids, peptides and proteins to form advanced glycation end products (AGEs) and cause carbonyl stress followed by oxidative stress and tissue damage. Therefore, many studies about scavengers of MGO and GO are seen. The influence of these scavengers on flavour generation is also discussed.

Cinnamic acid and its derivatives inhibit fructose-mediated protein glycation

Cinnamic acid and its derivatives have shown a variety of pharmacologic properties. However, little is known about the antiglycation properties of cinnamic acid and its derivatives. The present study sought to characterize the protein glycation inhibitory activity of cinnamic acid and its derivatives in a bovine serum albumin (BSA)/fructose system. The results demonstrated that cinnamic acid and its derivatives significantly inhibited the formation of advanced glycation end products (AGEs) by approximately 11.96–63.36% at a concentration of 1 mM. The strongest inhibitory activity against the formation of AGEs was shown by cinnamic acid. Furthermore, cinnamic acid and its derivatives reduced the level of fructosamine, the formation of N^ɛ-(carboxymethyl) lysine (CML), and the level of amyloid cross β-structure. Cinnamic acid and its derivatives also prevented oxidative protein damages, including effects on protein carbonyl formation and thiol oxidation of BSA. Our findings may lead to the possibility of using cinnamic acid and its derivatives for preventing AGE-mediated diabetic complications.

Apple Procyanidins Suppress Amyloid β-Protein Aggregation

Procyanidins (PCs) are major components of the apple polyphenols (APs). We previously reported that treatment with PC extended the mean lifespan of Caenorhabditis elegans (Sunagawa et al., 2011). In order to estimate the neuroprotective effects of PC, we investigated the antiaggregative activity of PC on amyloid β-protein (Aβ) aggregation, which is a pathological hallmark of Alzheimer's disease. We herein report that PC significantly suppressed Aβ42 aggregation and dissociated Aβ42 aggregates in a dose-dependent manner, indicating that PC is a potent suppressor of Aβ aggregation. Furthermore, PC significantly inhibited Aβ42 neurotoxicity and stimulated proliferation in PC-12 cells. These results suggested that the PC and AP acted as neuroprotective factors against toxic Aβ aggregates.