Dual Effect of Curcumin-Zinc Complex in Controlling Diabetes Mellitus in Experimentally Induced Diabetic Rats

Food Polyphenols and Type II Diabetes Mellitus: Pharmacology and Mechanisms

Type II diabetes mellitus and its related complications are growing public health problems. Many natural products present in our diet, including polyphenols, can be used in treating and managing type II diabetes mellitus and different diseases, owing to their numerous biological properties. Anthocyanins, flavonols, stilbenes, curcuminoids, hesperidin, hesperetin, naringenin, and phenolic acids are common polyphenols found in blueberries, chokeberries, sea-buckthorn, mulberries, turmeric, citrus fruits, and cereals. These compounds exhibit antidiabetic effects through different pathways. Accordingly, this review presents an overview of the most recent developments in using food polyphenols for managing and treating type II diabetes mellitus, along with various mechanisms. In addition, the present work summarizes the literature about the anti-diabetic effect of food polyphenols and evaluates their potential as complementary or alternative medicines to treat type II diabetes mellitus. Results obtained from this survey show that anthocyanins, flavonols, stilbenes, curcuminoids, and phenolic acids can manage diabetes mellitus by protecting pancreatic β-cells against glucose toxicity, promoting β-cell proliferation, reducing β-cell apoptosis, and inhibiting α-glucosidases or α-amylase. In addition, these phenolic compounds exhibit antioxidant anti-inflammatory activities, modulate carbohydrate and lipid metabolism, optimize oxidative stress, reduce insulin resistance, and stimulate the pancreas to secrete insulin. They also activate insulin signaling and inhibit digestive enzymes, regulate intestinal microbiota, improve adipose tissue metabolism, inhibit glucose absorption, and inhibit the formation of advanced glycation end products. However, insufficient data are available on the effective mechanisms necessary to manage diabetes.

The dual therapeutic effect of metformin nuclei‐based drugs modified with one of Tulbaghia violacea extract compounds

Novel Schiff base was synthesized from the condensation reaction of metformin with [4‐(Diethylamino) benzaldehyde (NBM). Different metal complexes were prepared using Pd (II), Pt (II), Cu (II), and V (IV) metal ions. All complexes showed the nonelectrolytic behavior. So, the expected molecular formulas for complexes were [Pd (NBM)Cl2], [Pt (NBM)Cl2], [Cu (NBM)2Cl2] and [VO (NBM)2]. The cytotoxicity of (NBM) Schiff base and its metal complexes on human cancer cell line, MCF‐7, was investigated. V (IV) and Cu (II) complexes showed potential blood glucose lowering effect higher than the commercial metformin drug. VO (II) complex has superior antioxidant activity more than the other synthesized compounds and the standard ascorbic acid. Molecular docking investigation proved the presence of interesting interactions between all synthesized compounds with the active site amino acids of EGFR tyrosine kinase (anticancer activity). The molecular docking of metal complexes has observed effective inhibition for the specific mTOR protein that is expected to aid the growth of the COVID‐19 virus.

Zinc-curcumin based complexes in health and diseases: An approach in chemopreventive and therapeutic improvement

Curcumin, a polyphenolic compound isolated from turmeric rhizome, displays antioxidant, anti-inflammatory, anticancer, anti-microbial, antiviral, antidiabetic, neuroprotective, immune boosting and other chemopreventive and therapeutic properties. However, the efficacy of curcumin is confined due to its aqueous insolubility, instability, low intestinal absorption, poor bioavailability, and systemic elimination. Therefore, to overcome these issues and enhance pharmacological activities of curcumin, a complex of curcumin with metals such as zinc have been synthesized. Curcumin acts as a ligand and forms a stable complex with zinc. In this review, the improved protective, and therapeutic activities of zinc-curcumin complexes are discussed. Zinc-curcumin conjugates have exhibited enhanced antioxidant, anti-inflammatory, anticancer, antimicrobial and antidiabetic properties. Zinc-curcumin complexes have also displayed hepatoprotective, gastroprotective, neuroprotective, cardioprotective and osteogenesis efficacy. These protective and therapeutic efficacies of zinc-curcumin conjugates were associated with modulation of multiple molecular mechanisms including decreased inflammatory cytokines, increased antioxidant enzymes, quenched free radicals, decreased blood glucose levels, decreased insulin resistance, induced apoptosis markers, and restored function of tumor suppressor protein p53 in cancer cells. Overall, applications of zinc-curcumin complex could be a new approach against various diseases and could also be helpful in improvement of health.

Effects of turmeric (Curcuma longa) and its constituent (curcumin) on the metabolic syndrome: An updated review

Metabolic syndrome (MS) involves people with the following risk factors: obesity, hypertension, high glucose level and hyperlipidemia. It can increase the risk of heart disease, stroke and type 2 diabetes mellitus. The prevalence of MS in the world's adult population is about 20%-25%. Today, there is much care to use medicinal plants. Turmeric (Curcuma longa) as well as curcumin which is derived from the rhizome of the plant, has been shown beneficial effects on different components of MS. Thus, the purpose of this manuscript was to introduce different in vitro, in vivo and human studies regarding the effect of turmeric and its constituent on MS. Moreover, different mechanisms of action by which this plant overcomes MS have been introduced. Based on studies, turmeric and its bioactive component, curcumin, due to their anti-inflammatory and antioxidant properties, have antidiabetic effects through increasing insulin release, antihyperlipidemic effects by increasing fatty acid uptake, anti-obesity effects by decreasing lipogenesis, and antihypertensive effects by increasing nitric oxide. According to several in vivo, in vitro and human studies, it can be concluded that turmeric or curcumin has important values as a complementary therapy in MS. However, more clinical trials should be done to confirm these effects.

A review of the berberine natural polysaccharide nanostructures as potential anticancer and antibacterial agents

Despite the promising medicinal properties, berberine (BBR), due to its relatively poor solubility in plasma, low bio-stability and limited bioavailability is not used broadly in clinical stages. Due to these drawbacks, drug delivery systems (DDSs) based on nanoscale natural polysaccharides, are applied to address these concerns. Natural polymers are biodegradable, non-immunogenic, biocompatible, and non-toxic agents that are capable of trapping large amounts of hydrophobic compounds in relatively small volumes. The use of nanoscale natural polysaccharide improves the stability and pharmacokinetics of the small molecules and, consequently, increases the therapeutic effects and reduces the side effects of the small molecules. Therefore, this paper presents an overview of the different methods used for increasing the BBR solubility and bioavailability. Afterwards, the pharmacodynamic and pharmacokinetic of BBR nanostructures were discussed followed by the introduction of natural polysaccharides of plant (cyclodextrines, glucomannan), the shells of crustaceans (chitosan), and the cell wall of brown marine algae (alginate)-based origins used to improve the dissolution rate of poorly soluble BBR and their anticancer and antibacterial properties. Finally, the anticancer and antibacterial mechanisms of free BBR and BBR nanostructures were surveyed. In conclusion, this review may pave the way for providing some useful data in the development of BBR-based platforms for clinical applications.

A Family of [Zn6] Complexes from the Carboxylate-Bridge-Supported Assembly of [Zn2] Building Units: Synthetic, Structural, Spectroscopic, and Systematic Biological Studies

The three discrete [Zn₆] complexes [Na₃Zn₆(cpdp)₃(μ-Bz)₃(CH₃OH)₆][ZnCl₄][ZnCl₃(H₂O)]·3CH₃OH·1.5H₂O (1), [Na₃Zn₆(cpdp)₃(μ-p-OBz)₃(CH₃OH)₆]·2H₂O (2), and [Na₃Zn₆(cpdp)₃(μ-p-NO₂Bz)₃(CH₃OH)₆]Cl₃·2H₂O (3), supported by the carboxylate-based multidentate ligand N,N'-bis[2-carboxybenzomethyl]-N,N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol (H₃cpdp), have been successfully synthesized and fully characterized (Bz = benzoate; p-OBz = dianion of p-hydroxybenzoic acid; p-NO₂Bz = p-nitrobenzoate). The complexes have been characterized by elemental analysis, FTIR, UV-vis, NMR spectroscopy, PXRD, and thermal analysis, including single-crystal X-ray crystallography of 1 and 2. The molecular architectures of 1-3 are built from the self-assembly of their corresponding [Zn₂] units, which are interconnected to the central [Na₃(CH₃OH)₆]³⁺ core by six endogenous benzoate groups, with each linking one Zn(II) and one Na(I) ion in a μ₂:η¹:η¹-syn-anti bidentate fashion. The composition of the (cpdp^3-)₃/(Zn²⁺)₆ complexes in 1-3 has been observed to be 1:2, on the basis of the UV-vis titration and NMR spectroscopic results, which is further supported by X-ray crystallography. Systematic biological studies performed with a mice model suggested possible antidiabetic efficacy as well as anticancer activities of the complexes. When complexes 1-3 were administered intraperitoneally in mice, 1 showed a lowering in the blood glucose level, overall maintenance of the pancreatic tissue mass, restriction of DNA damage in pancreatic cells, and retention of lipid droplet (LD) frequency, whereas 2 and 3 showed hepatic tissue mass consistency by inhibiting the DNA damage in hepatic cells, prior to the exposure to a potent diabetic inducer, alloxan (ALX). Similar trends of results were observed in inhibiting the generation of reactive oxygen species (ROS) in the pancreatic and hepatic cells, as examined by spectrofluorometric methods. Thus, 1 seems to be a better compound for overall diabetic management and control, whereas 2 and 3 seem to be promising compounds for designing chemopreventive drugs against hepatic carcinoma.

Ameliorative effect of curcumin and zinc oxide nanoparticles on multiple mechanisms in obese rats with induced type 2 diabetes

The present study was carried out to investigate the therapeutic effect of synthesized naturally compounds, curcumin nanoparticles (CurNPs) and metal oxide, zinc oxide nanoparticles (ZnONPs) on a high-fat diet (HFD)/streptozotocin (STZ)-induced hepatic and pancreatic pathophysiology in type 2 diabetes mellitus (T2DM) via measuring AKT pathway and MAPK pathway. T2DM rats were intraperitoneally injected with a low dose of 35 mg/kg STZ after being fed by HFD for 8 weeks. Then the rats have orally received treatments for 6 weeks. HFD/STZ-induced hepatic inflammation, reflected by increased phosphorylation of p38-MAPK pathway's molecules, was significantly decreased after nanoparticle supplementation. In addition, both nanoparticles significantly alleviated the decreased phosphorylation of AKT pathway. Further, administration of ZnONPs, CurNPs, conventional curcumin, and ZnSO₄ (zinc sulfate), as well as metformin, effectively counteracted diabetes-induced oxidative stress and inflammation in the internal hepatic and pancreatic tissues. Based on the results of the current study, ZnONPs and CurNPs could be explored as a therapeutic adjuvant against complications associated with T2DM. Both nanoparticles could effectively delay the progression of several complications by activating AKT pathway and down-regulating MAPK pathway. Our findings may provide an experimental basis for the application of nanoparticles in the treatment of T2DM with low toxicity.

Metal-Curcumin Complexes in Therapeutics: An Approach to Enhance Pharmacological Effects of Curcumin

Curcumin, an active component of the rhizome turmeric, has gained much attention as a plant-based compound with pleiotropic pharmacological properties. It possesses anti-inflammatory, antioxidant, hypoglycemic, antimicrobial, neuroprotective, and immunomodulatory activities. However, the health-promoting utility of curcumin is constrained due to its hydrophobic nature, water insolubility, poor bioavailability, rapid metabolism, and systemic elimination. Therefore, an innovative stride was taken, and complexes of metals with curcumin have been synthesized. Curcumin usually reacts with metals through the β-diketone moiety to generate metal–curcumin complexes. It is well established that curcumin strongly chelates several metal ions, including boron, cobalt, copper, gallium, gadolinium, gold, lanthanum, manganese, nickel, iron, palladium, platinum, ruthenium, silver, vanadium, and zinc. In this review, the pharmacological, chemopreventive, and therapeutic activities of metal–curcumin complexes are discussed. Metal–curcumin complexes increase the solubility, cellular uptake, and bioavailability and improve the antioxidant, anti-inflammatory, antimicrobial, and antiviral effects of curcumin. Metal–curcumin complexes have also demonstrated efficacy against various chronic diseases, including cancer, arthritis, osteoporosis, and neurological disorders such as Alzheimer’s disease. These biological activities of metal–curcumin complexes were associated with the modulation of inflammatory mediators, transcription factors, protein kinases, antiapoptotic proteins, lipid peroxidation, and antioxidant enzymes. In addition, metal–curcumin complexes have shown usefulness in biological imaging and radioimaging. The future use of metal–curcumin complexes may represent a new approach in the prevention and treatment of chronic diseases.

Effect of eight-week curcumin supplementation with endurance training on glycemic indexes in middle age women with type 2 diabetes in Iran, A preliminary study

BACKGROUND AND AIMS

The purpose of this study was to determine the effects of curcumin supplementation & endurance training on glycemic indexes in middle-aged women with type 2 diabetes.

METHODS

40 middle-aged women with type 2 diabetes were randomly divided into four groups (control, curcumin, training & curcumin + training). Endurance training protocol included running on treadmill for eight weeks, three sessions per week and each session for 45-60 min, with a maximum intensity of 50-70% of MHR. The experimental groups received a supplementation of curcumin as a daily dose of 80 mg curcumin soft gel for 8 weeks while the control group was subjected to no supplementation or exercise during this period. One day before and one day after the eight-week experimental period, blood samples were taken from the subjects to measure the glycemic indexes, including fasting blood glucose, glycosylated hemoglobin, and serum insulin levels. T-test and two-way covariance analysis tests were used for analyzing the findings at a significant level of less than 0.05.

RESULTS

Eight weeks of curcumin supplementation and endurance training, whether done separately or simultaneously, significantly reduced fasting blood glucose, glycosylated hemoglobin and serum insulin levels (P < 0.05). The combination of curcumin supplementation and endurance training compared to the other two interventions caused a significant further decrease in these glycemic indexes (P < 0.05).

CONCLUSION

The findings of this study showed that eight weeks of curcumin supplementation and endurance training helped each other in improving the glycemic indexes of women with type 2 diabetes.

Medicinal Plants and Bioactive Compounds for Diabetes Management: Important Advances in Drug Discovery

BACKGROUND

Diabetes is a major public health problem in the world. It affects each and every part of the human body and also leads to organ failure. Hence, great progress is made in the field of herbal medicine and diabetic research.

OBJECTIVES

Our review will focus on the effect of bioactive compounds of medicinal plants which are used to treat diabetes in India and other countries.

METHODS

Information regarding diabetes, oxidative stress, medicinal plants and bioactive compounds was collected from different search engines like Science direct, Springer, Wiley online library, Taylor and francis, Bentham Science, Pubmed and Google scholar. Data was analyzed and summarized in the review.

RESULTS

Anti-diabetic drugs that are in use have many side effects on vital organs like heart, liver, kidney and brain. There is an urgent need for alternative medicine to treat diabetes and their disorders. In India and other countries, herbal medicine was used to treat diabetes. Many herbal plants have antidiabetic effects. The plants like ginger, phyllanthus, gymnea, aswagandha, aloe, hibiscus and curcuma showed significant anti-hyperglycemic activities in experimental models and humans. The bioactive compounds like Allicin, azadirachtin, cajanin, curcumin, querceitin, gingerol possess anti-diabetic, antioxidant and other pharmacological properties. This review focuses on the role of bioactive compounds of medicinal plants in the prevention and management of diabetes.

CONCLUSION

Moreover, our review suggests that bioactive compounds have the therapeutic potential against diabetes. However, further in vitro and in vivo studies are needed to validate these findings.

Zinc(II) complexes in diabetes management: Plant-derived phenolics as understudied promising ligands

Zinc mineral has been known as a supplement for diabetics due to its deficiency in diabetics. Its glycemic control and insulin mimetic properties have been reported. Thus, it has been complexed with numerous types of ligands to improve the glycemic control property of the ligands. Unfortunately, mostly synthetic ligands with little or no bioactive properties and toxicity concerns have been complexed with Zn, while plant-derived dietary phenolics have rarely been explored as ligand for Zn complexation, despite their medicinal credence and minimal toxicity concern. In this letter, plant-derived phenolics have been presented as promising ligands for Zn(II) in developing potent antidiabetic and antioxidative nutraceutical complexes with improved and multi-facet bioactivity profile, as well as minimal toxicity concerns. Thus, fostering the paradigm shift from synthetic medicine toward dietary and functional medicine. PRACTICAL APPLICATIONS: Potentially, complexing Zn(II) with bioactive plant-derived dietary phenolics could result in novel nutraceuticals and/or supplements with improved and multi-facet bioactivity profile, as well as minimal toxicity concerns.

Synthesis, characterization, antidiabetic and antioxidative evaluation of a novel Zn(II)-gallic acid complex with multi-facet activity

Objectives

This study was done to synthesize a novel Zn(II)-gallic acid complex with improved antidiabetic and antioxidative properties.

Methods

The complex was synthesized and characterized using Fourier Transform Infrared (FT-IR) and 1H NMR. Cytotoxicity was evaluated using Chang liver cells and L6 myotubes. Radical scavenging and Fe3+-reducing, as well as α-glucosidase, α-amylase and glycation inhibitory properties were measured. Glucose uptake was measured in L6 myotubes, while the complex was docked against glucose transporter type 4 (GLUT-4) and protein kinase B (PKB).

Key findings

Analysis showed that complexation occurred through a Zn(O4) coordination; thus, the complex acquired two moieties of gallic acid, which suggests why complexation increased the DPPH (IC50 = 48.2 µm) and ABTS (IC50 = 12.7 µm) scavenging and α-glucosidase inhibitory (IC50 = 58.5 µm) properties of gallic acid by several folds (5.5, 3.6 and 2.7 folds; IC50 = 8.79, 3.51 and 21.5 µm, respectively). Zn(II) conferred a potent dose-dependent glucose uptake activity (EC50 = 9.17 µm) on gallic acid, without reducing the viability of L6 myotubes and hepatocytes. Docking analysis showed the complex had stronger interaction with insulin signalling proteins (GLUT-4 and PKB) than its precursor.

Conclusions

Data suggest that complexation of Zn(II) with gallic acid resulted in a complex with improved and multi-facet antioxidative and glycaemic control properties.

A comprehensive review on zinc(II) complexes as anti-diabetic agents: The advances, scientific gaps and prospects

Zinc has gained notable attention in the development of potent anti-diabetic agents, due to its role in insulin storage and secretion, as well as its reported insulin mimetic properties. Consequently, zinc(II) has been complexed with numerous organic ligands as an adjuvant to develop anti-diabetic agents with improved and/or broader scope of pharmacological properties. This review focuses on the research advances thus far to identify the major scientific gaps and prospects. Peer-reviewed published data on the anti-diabetic effects of zinc(II) complexes were sourced from different scientific search engines, including, but not limited to "PubMed", "Google Scholar", "Scopus" and ScienceDirect to identify potent anti-diabetic zinc(II) complexes. The complexes were subcategorized according to their precursor ligands. A critical analysis of the outcomes from published studies shows promising leads, with Zn(II) complexes having a "tri-facet" mode of exerting pharmacological effects. However, the promising leads have been flawed by some major scientific gaps. While zinc(II) complexes of synthetic ligands with little or no anti-diabetic pharmacological history remain the most studied (about 72 %), their toxicity profile was not reported, which raises safety concerns for clinical relevance. The zinc(II) complexes of plant polyphenols; natural ligands, such as maltol and hinokitiol; and supplements, such as ascorbic acid (a natural antioxidant), l-threonine and l-carnitine, showed promising insulin mimetic and glycemic control properties but remain understudied and lack clinical validation, in spite of their minimal safety concerns and health benefits. A paradigm shift toward probing (including clinical studies) supplements, plant polyphenol and natural ligands as anti-diabetic zinc(II) complex is, therefore, recommended. Also, promising anti-diabetic Zn(II) complexes of synthetic ligands should undergo critical toxicity evaluation to address possible safety concerns.

Effects of Turmeric (Curcuma longa) Extract in streptozocin-induced diabetic model

Herbal remedies have been used for centuries to ameliorate complications of diabetes mellitus (DM). The aim of this study is to compare the effects of the oral curcumin supplement versus parenteral administration of turmeric extract on diabetic complications in a streptozocin (STZ) diabetic model. STZ DM rats received low and high doses turmeric extract intraperitoneally as well as oral curcumin. Curcumin and turmeric extracts significantly reduced blood glucose and creatinine levels, but not urea, and caused an increase in uric acid. Low dose improved liver enzymes, while higher dose and oral administration caused an increase in the ALT and AST. All groups showed an improvement in the serum cholesterol, while the triglycerides were not improved in the high and oral treatment. Histological evaluation showed islet cell protection. High-dose injection showed almost intact renal corpuscles as well as tubular structures with minimal degeneration. Treatment showed limited protection of Liver tissue. PRACTICAL APPLICATION: Curcumin has been heavily marketed as a protective agent. The current study shows some potential risk of curcumin use. Oral and injectable curcumin should be used with caution. Turmeric extract and oral curcumin supplement showed protective effects on pancreatic, and renal structure and function. Although both did show some improvement in liver function, higher doses caused disturbance in liver enzymes and did not show histological evidence of liver tissue protection.

Zn(II) Curcuminate Complexes with 2,2'-bipyridine and Carboxylates

Two novel zinc(II) compounds with curcuminate (abbreviated as cur-), [Zn(CH3COO)(cur)(bpy)](1)·CH3OH·2H2O (bpy = 2,2'-bipyridine) and [Zn(PhCOO)(cur)(bpy)] (2)·CH3OH, have been synthesized and characterized. Their composition has been determined by single-crystal X-ray structure analysis. Complexes 1 and 2 are similar: in both a five-fold coordination environment of zinc(II) consists of a monodentate carboxylate, a chelating bidentate 2,2'-bipyridine, and curcuminate, which is bound via a deprotonated 1,3-dione moiety. In 1, 2,2'-bipyridine nitrogen atoms and curcuminate oxygen atoms form the base of a square pyramid, whereas the acetate oxygen occupies its apex. The O3N2 donor set in 2 defines a polyhedron which more closely resembles a trigonal bipyramid. The packing in the crystal lattices of both compounds is governed by hydrogen-bonds. Complexes 1 and 2 display higher stability than curcumin in buffered media at pH = 7.0, however, the degradation of coordinated cur- is comparable to that of yellow pigment curcumin (curH) when the pH is raised to 7.2. Both complexes 1 and 2 in DMSO exhibit fluorescence with Stokes shifts of 5367 and 4634 cm-1, respectively.

The progresses in curcuminoids-based metal complexes: especially in cancer therapy

Curcuminoids (CURs), a series of derivatives in turmeric (Curcuma longa), are commonly discovered to control the deterioration of cancers. However, the physiochemical properties and the original side effects of many CURs complexes put barriers in their medical applications. To address them, the investigation of metal-based complexes with CURs is in progress. The complexes were summarized according to articles in recent years. The results showed that the complexes improved the physicochemical properties or therapeutic performances compared with pure CURs. Further, it is possible for the novel complexes to be applied in chemical detecting, paramagnetic-luminescent and bio-imaging fields. Therefore, the formation of the metal-based CURs complexes (MBCCs) is beneficial for the development of CURs especially in medical fields.

Biological properties of metal complexes of curcumin

Curcumin, a naturally occurring phenolic compound isolated from Curcuma longa, has different pharmacological effects, including antiinflammatory, antimicrobial, antioxidant, and anticancer properties. However, curcumin has been found to have a limited bioavailability because of its hydrophobic nature, low-intestinal absorption, and rapid metabolism. Therefore, there is a need for enhancing the bioavailability and its solubility in water in order to increase the pharmacological effects of this bioactive compound. One strategy is curcumin complexation with transition metals to circumvent the abovementioned problems. Curcumin can undergo chelation with various metal ions to form metallo-complexes of curcumin, which may show greater effects as compared with curcumin alone. Promising results with metal curcumin complexes have been observed with regard to antioxidant, anticancer, and antimicrobial activity, as well as in treatment of Alzheimer's disease. The present review provides a concise summary of the characterization and biological properties of curcumin-metal complexes. © 2019 BioFactors, 45(3):304-317, 2019.

Effect of Red Ginseng Extract on the Pharmacokinetics and Efficacy of Metformin in Streptozotocin-Induced Diabetic Rats

The purpose of this study was to investigate the effect of red ginseng extract on the pharmacokinetics (PK) and efficacy of metformin in streptozotocin-induced diabetic rats. The diabetes mellitus rat model was established by intraperitoneally administering multiple doses of streptozotocin (30 mg/kg, twice on day 1 and 8), and diabetic rats received metformin 50 mg/kg with or without single or multiple administration of Korean red ginseng extract (RGE, 2 g/kg/day, once or for 1 week). RGE administration did not affect the plasma concentration and renal excretion of metformin. Further, diabetic rats were administered metformin (50 mg/kg) and RGE (2 g/kg) alone or concomitantly for 5 weeks, and both regimens decreased the fasting blood glucose and glycated hemoglobin (Hb-A1c) levels. Furthermore, fasting blood glucose levels were reduced by metformin or RGE administered alone but recovered to the control level following co-administration, suggesting that the effect was additive. However, triglyceride and free fatty acid levels were not different with metformin and RGE treatment alone or in combination. Biochemical parameters such as alanine aminotransferase (ALT), aspartate aminotransferase (AST), triglycerides, total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol levels were not different among the three treatment groups. In conclusion, RGE and metformin showed an additive effect in glycemic control. However, the co-administration of RGE and metformin did not cause PK interactions or affect biochemical parameters including the free fatty acid, triglyceride, AST, ALT, or cholesterol levels.

Investigation of Biodistribution and Speciation Changes of Orally Administered Dual Radiolabeled Complex, Bis(5-chloro-7-[131I]iodo-8-quinolinolato)[65Zn]zinc

Many zinc (Zn) complexes have been developed as promising oral antidiabetic agents. In vitro assays using adipocytes have demonstrated that the coordination structures of Zn complexes affect the uptake of Zn into cells and have insulinomimetic activities, for which moderate stability of Zn complexes is vital. The complexation of Zn plays a major role improving its bioavailability. However, investigation of the speciation changes of Zn complexes after oral administration is lacking. A dual radiolabeling approach was applied in order to investigate the speciation of bis(5-chloro-7-iodo-8-quinolinolato)zinc complex [Zn(Cq)₂], which exhibits the antidiabetic activity in diabetic mice. In the present study, ⁶⁵Zn- and ¹³¹I-labeled [Zn(Cq)₂] were synthesized, and their biodistribution were analyzed after an oral administration using both invasive conventional assays and noninvasive gamma-ray emission imaging (GREI), a novel nuclear medicine imaging modality that enables analysis of multiple radionuclides simultaneously. The GREI experiments visualized the behavior of ⁶⁵Zn and [¹³¹I]Cq from the stomach to large intestine and through the small intestine; most of the administered Zn was transported together with clioquinol (5-chloro-7-iodo-8-quinolinol) (Cq). Higher accumulation of ⁶⁵Zn for [Zn(Cq)₂] than ZnCl₂ suggests that the Zn associated with Cq was highly absorbed by the intestinal tract. In particular, the molar ratio of administered iodine to Zn decreased during the distribution processes, indicating the dissociation of most [Zn(Cq)₂] complexes. In conclusion, the present study successfully evaluated the speciation changes of orally administered [Zn(Cq)₂] using the dual radiolabeling method.