Metallokinetic Study of Zinc in the Blood of Normal Rats Given Insulinomimetic Zinc(II) Complexes and Improvement of Diabetes Mellitus in Type 2 Diabetic GK Rats by their Oral Administration

Four-week repeated oral dose toxicity study of zinc maltol in rats

Zinc (Zn) is one of the trace elements, and Zn deficiency causes many adverse effects. Zn complexes are used for Zn supplementation, but there are few toxicity reports. Zn maltol (ZM) was orally administered for 4 weeks to male rats at a dose of 0, 200, 600, or 1000 mg/kg to assess its toxicity. As a ligand group, maltol was administered at a dose of 800 mg/kg/day. General conditions, ophthalmology, hematology, blood biochemistry, urinalysis, organ weights, necropsy, histopathology, and plasma Zn concentration were investigated. Plasma Zn concentration increased with dose levels of ZM. The following toxicities were observed at 1000 mg/kg. Pancreatitis was observed with histopathological lesions and increases in white blood cell parameters and creatine kinase. Anemia was observed with changes in red blood cell parameters and extramedullary hematopoiesis in the spleen. Decreases in the trabecula and growth plate in the femur were observed. On the other hand, no toxicities were observed in the ligand group. In conclusion, these toxicities induced by ZM have been reported as Zn-related toxicities. It was considered that these results will be helpful for a creation and development of new Zn complexes as well as supplements.

Endogenous zinc nanoparticles in the rat olfactory epithelium are functionally significant

The role of zinc in neurobiology is rapidly expanding. Zinc is especially essential in olfactory neurobiology. Naturally occurring zinc nanoparticles were detected in olfactory and nasal respiratory epithelia and cilia in animals. The addition of these nanoparticles to a mixture of odorants, including ethyl butyrate, eugenol, and carvone, considerably increased the electrical responses of the olfactory sensory receptors. Studies of these nanoparticles by ransmission electron microscopy (TEM) and selected area electron diffraction revealed metal elemental crystalline zinc nanoparticles 2–4 nm in diameter. These particles did not contain oxidized zinc. The enhancement of the odorant responses induced by the endogenous zinc nanoparticles appears to be similar to the amplification produced by engineered zinc nanoparticles. Zinc nanoparticles produce no odor response but increase odor response if mixed with an odorant. These effects are dose-dependent and reversible. Some other metal nanoparticles, such as copper, silver, gold, and platinum, do not have the effects observed in the case of zinc nanoparticles. The olfactory enhancement was observed in young and mature mouse olfactory epithelium cultures, in the dissected olfactory epithelium of rodents, and in live conscious dogs. The physiological significance of the detected endogenous metal nanoparticles in an animal tissue has been demonstrated for the first time. Overall, our results may advance the understanding of the initial events in olfaction.

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.

Antioxidant, anti-inflammatory, and anti-apoptotic effects of zinc supplementation in testes of rats with experimentally induced diabetes

One of the major obstacles that males with diabetes may confront is subfertility or infertility. Thus, the present study investigated the effect of co-administration of metformin and zinc (Zn) on the testes of streptozotocin-induced diabetic rats. Male albino rats were randomly divided into 4 groups: control group; untreated diabetic group; diabetic + metformin group, in which diabetic rats were treated orally with metformin (250 mg/kg) once daily for 4 weeks; and diabetic + metformin + Zn group, in which diabetic rats were treated orally with metformin in combination with Zn (10 mg/kg) once daily for 4 weeks. Concomitant administration of metformin and Zn produced a significant decrease in serum levels of glucose and insulin and testicular levels of malondialdehyde and tumor necrosis factor α. Additionally, there was a significant increase in serum levels of Zn, testosterone, and follicle-stimulating hormone, as well as testicular total antioxidant capacity and anti-apoptotic protein Bcl-2, when compared with both the diabetic and metformin-treated diabetic groups. Moreover, co-administration of Zn and metformin significantly improved testicular histopathology, with a significant reduction in percent area of collagen fibers and nuclear factor kappa B (p65) immunoreactivity and a significant increase in seminiferous tubule diameter and connexin 43 immunoreactivity as compared with the diabetic and metformin-treated diabetic groups. In conclusion, the combination of Zn and metformin was an efficacious and safe alternative treatment, as it had superior antihyperglycemic efficacy and provided additional benefits over metformin alone in rats with type 2 diabetes.

In vitro structure-specific Zn(II)-induced adipogenesis and structure-function bioreactivity correlations

The advent of Zn(II) metallodrugs in metabolic syndrome pathologies generates a strong challenge toward synthetic endeavors targeting well-defined, atoxic and biologically active binary/ternary species of Zn(II). Proper formulation of that metal ion's coordination sphere sets the stage for construction of appropriately configured Schiff ligands based on tromethamine and variably modified vanillin core components. The arising Schiff ligands react with Zn(II) in a defined stoichiometry, thereby delivering new binary Zn(II)-L species with defined physicochemical properties. Analytical (elemental), spectroscopic (FT-IR, Thermogravimetric Analysis) and crystallographic techniques attest to the distinct nature of the derived binary-ternary materials, bearing defined Zn(II):L molecular stoichiometry, variable nuclearity, charge, bulk and balance mix of hydrophilicity-hydrophobicity, thereby providing the physicochemical profile based on which biological studies could ensue. The structurally based selection of species was applied onto in vitro 3T3-L1 cultures, essentially exploring toxicity, migration, morphology, cell differentiation and maturation. The systematic effort toward comparative work on appropriately defined Zn(II) species and insulin in inducing adipogenesis reveals the salient structural features in the Schiff family of ligands configuring Zn(II) so as to promote complex formation sufficient to engage biomolecular targets during the process of initiation and maturation. Molecular targets of importance in adipogenesis were examined under the influence of Zn(II) and their expression levels suggest the structural composition that a Zn(II) ion might have to optimally pursue cell differentiation. Thus, a well-defined selection of binary Zn(II)-L species is tightly associated with the incurred bioactivity, thereby setting the stage for the development of efficient Zn(II) metallodrugs to combat Diabetes mellitus II.

After oxidation, zinc nanoparticles lose their ability to enhance responses to odorants

Electrical responses of olfactory sensory neurons to odorants were examined in the presence of zinc nanoparticles of various sizes and degrees of oxidation. The zinc nanoparticles were prepared by the underwater electrical discharge method and analyzed by atomic force microscopy and X-ray photoelectron spectroscopy. Small (1.2 ± 0.3 nm) zinc nanoparticles significantly enhanced electrical responses of olfactory neurons to odorants. After oxidation, however, these small zinc nanoparticles were no longer capable of enhancing olfactory responses. Larger zinc oxide nanoparticles (15 nm and 70 nm) also did not modulate responses to odorants. Neither zinc nor zinc oxide nanoparticles produced olfactory responses when added without odorants. The enhancement of odorant responses by small zinc nanoparticles was explained by the creation of olfactory receptor dimers initiated by small zinc nanoparticles. The results of this work will clarify the mechanisms for the initial events in olfaction, as well as to provide new ways to alleviate anosmia related to the loss of olfactory receptors.

Structure-specific adipogenic capacity of novel, well-defined ternary Zn(II)-Schiff base materials. Biomolecular correlations in zinc-induced differentiation of 3T3-L1 pre-adipocytes to adipocytes

Among the various roles of zinc discovered to date, its exogenous activity as an insulin mimetic agent stands as a contemporary challenge currently under investigation and a goal to pursue in the form of a metallodrug against type 2 Diabetes Mellitus. Poised to investigate the adipogenic potential of Zn(II) and appropriately configure its coordination sphere into well-defined anti-diabetic forms, (a) a series of new well-defined ternary dinuclear Zn(II)-L (L=Schiff base ligands with a variable number of alcoholic moieties) compounds were synthesized and physicochemically characterized, (b) their cytotoxicity and migration effect(s) in both pre- and mature adipocytes were assessed, (c) their ability to effectively induce cell differentiation of 3T3-L1 pre-adipocytes into mature adipocytes was established, and (d) closely linked molecular targets involving or influenced by the specific Zn(II) forms were perused through molecular biological techniques, cumulatively delineating factors involved in Zn(II)-induced adipogenesis. Collectively, the results (a) reveal the significance of key structural features of Schiff ligands coordinated to Zn(II), thereby influencing its (a)toxicity behavior and insulin-like activity, (b) project molecular targets influenced by the specific forms of Zn(II) formulating its adipogenic potential, and (c) exemplify the interwoven relationship between Zn(II)-L structural speciation and insulin mimetic biological activity, thereby suggesting ways of fine tuning structure-specific zinc-induced adipogenicity in future efficient antidiabetic drugs.

The discovery of vanadyl and zinc complexes for treating diabetes and metabolic syndromes

The incidence of diabetes mellitus has increased over the decades because of lifestyle changes. The number of people with diabetes mellitus worldwide is expected to increase from 150 million to 220 million by 2010 and to 300 million by 2025. There are two main types of diabetes mellitus. Type 1 diabetes mellitus is due to the autoimmune-mediated destruction of pancreatic β cells, resulting in absolute insulin deficiency; the patients require exogenous insulin injections. Type 2 is characterized by insulin resistance and abnormal insulin secretion and the patients require exercise, diet control and/or oral hypoglycemics. However, each treatment has some adverse effects, including physical burden, formation of self-antibodies for insulin injections, the severe side effects of hypoglycemics and the discontinuation of insulin synthesis in the pancreas. To overcome these adverse effects and replace the use of these agents, the author attempted to develop new antidiabetic agents with novel structures and mechanisms. This review focuses on the authors' recent development of vanadium and zinc complexes for antidiabetic and antimetabolic syndromes.

Investigation of the insulin-like properties of zinc(II) complexes of 3-hydroxy-4-pyridinones: identification of a compound with glucose lowering effect in STZ-induced type I diabetic animals

Results from an investigation in an in vivo model of STZ-induced diabetic rats demonstrate that compound bis(1,2-dimethyl-3-hydroxy-4(1H)-pyridinonate)zinc(II), Zn(dmpp)(2), significantly lowers the blood glucose levels of individuals, thus showing evidence of glucose lowering activity. The compound was selected from a set of eight zinc(II) complexes of 3-hydroxy-4-pyridinones with diverse lipophilicity that were prepared and characterized in our laboratory. Assessment of insulin-like activity of the complexes was firstly performed in vitro by measuring the inhibition of FFA release in isolated rat adipocytes. The results indicate that compounds bis(2-methyl-3-hydroxy-4-pyridinonate)zinc(II), Zn(mpp)(2) and Zn(dmpp)(2) display significantly higher activity than that of the respective positive control thus suggesting its selection for in vivo tests. Safety evaluation of the active zinc(II) compounds was performed in freshly isolated rat hepatocytes. The results support that cell viability is not significantly different from the control set after 1 and 2h of incubation with both zinc(II) complexes.

Zinc and diabetes--clinical links and molecular mechanisms

Zinc is an essential trace element crucial for the function of more than 300 enzymes and it is important for cellular processes like cell division and apoptosis. Hence, the concentration of zinc in the human body is tightly regulated and disturbances of zinc homeostasis have been associated with several diseases including diabetes mellitus, a disease characterized by high blood glucose concentrations as a consequence of decreased secretion or action of insulin. Zinc supplementation of animals and humans has been shown to ameliorate glycemic control in type 1 and 2 diabetes, the two major forms of diabetes mellitus, but the underlying molecular mechanisms have only slowly been elucidated. Zinc seems to exert insulin-like effects by supporting the signal transduction of insulin and by reducing the production of cytokines, which lead to beta-cell death during the inflammatory process in the pancreas in the course of the disease. Furthermore, zinc might play a role in the development of diabetes, since genetic polymorphisms in the gene of zinc transporter 8 and in metallothionein (MT)-encoding genes could be demonstrated to be associated with type 2 diabetes mellitus. The fact that antibodies against this zinc transporter have been detected in type 1 diabetic patients offers new diagnostic possibilities. This article reviews the influence of zinc on the diabetic state including the molecular mechanisms, the role of the zinc transporter 8 and MT for diabetes development and the resulting diagnostic and therapeutic options.

Vitaminas e minerais com propriedades antioxidantes e risco cardiometabólico: controvérsias e perspectivas

No processo celular de obtenção de energia, são gerados compostos chamados espécies reativas de oxigênio (ERO) que, em excesso, podem causar danos celulares. Estresse oxidativo resulta do desequilíbrio no estado de óxido-redução a favor da oxidação. Dos mecanismos de defesa antioxidante, participam enzimas endógenas e algumas vitaminas e minerais. A vitamina E encontra-se no plasma e na partícula de LDL, protegendo lipídeos da oxidação. Estudos observacionais relataram associação inversa entre ingestão de vitamina E e risco cardiometabólico (RCM). Entretanto, ensaios clínicos não comprovaram a eficácia de sua suplementação nos desfechos cardiometabólicos. A vitamina C participa do sistema de regeneração da vitamina E, mantendo o potencial antioxidante plasmático. Dados sobre os benefícios de sua suplementação na redução do risco cardiometabólico são inconclusivos. A atividade antioxidante dos carotenoides é responsável, em parte, por seu papel protetor contra doenças cardiovasculares e cânceres. A suplementação desse nutriente também não trouxe resultados consistentes no que se refere à redução do RCM. A participação do zinco e do selênio na defesa antioxidante vem sendo estudada mais recentemente, mas a sua suplementação em indivíduos com níveis séricos normais e ingestão adequada na dieta desses minerais não parece ser necessária. De um modo geral, há muita controvérsia sobre o papel desses micronutrientes no RCM. Estudos epidemiológicos sugerem que o consumo de substâncias antioxidantes provenientes da dieta ou dietas ricas em frutas e hortaliças diminui o RCM. Mais estudos são necessários antes de se recomendar o uso de antioxidantes isolados na forma de suplementos para tal finalidade.

Prospective study of zinc intake and risk of type 2 diabetes in women

OBJECTIVE

The aim of this study is to investigate the intake of zinc in relation to risk of type 2 diabetes in U.S. women.

RESEARCH DESIGN AND METHODS

Dietary intakes of zinc and other nutrients were assessed and updated using a validated food frequency questionnaire from 1980 to 2002 among 82,297 women who were aged 33-60 years at baseline in 1980 and followed up to 2004 in the Nurses' Health Study.

RESULTS

During the 24 years of follow-up, 6,030 incident cases of type 2 diabetes were ascertained. After adjustment of lifestyle and dietary risk factors, the relative risks (RRs) (95% CI) of type 2 diabetes comparing the highest with the lowest quintiles were 0.90 (0.82-0.99) (P(trend) = 0.04) for total zinc intake and 0.92 (0.84-1.00) (P(trend) = 0.009) for dietary zinc intake from food sources, respectively. We further found an inverse association for dietary zinc to heme iron ratio. After multivariate adjustment of covariates, the RRs (95% CI) across quintiles of this ratio were 1.0 (reference), 0.93 (0.86-1.01), 0.86 (0.79-0.94), 0.82 (0.75-0.90), and 0.72 (0.66-0.80), respectively (P(trend) < 0.0001).

CONCLUSIONS

Higher zinc intake may be associated with a slightly lower risk of type 2 diabetes in women. More studies are warranted to confirm this association and to explore potential mechanisms.

Sepsis: links between pathogen sensing and organ damage

The host's inflammatory response to sepsis can be divided into two phases, the initial detection and response to the pathogen initiated by the innate immune response, and the persistent inflammatory state characterized by multiple organ dysfunction syndrome (MODS). New therapies aimed at pathogen recognition receptors (PRRs) particularly the TLRs and the NOD-like receptors offer hope to suppress the initial inflammatory response in early sepsis and to bolster this response in late sepsis. The persistence of MODS after the initial inflammatory surge can also be a determining factor to host survival. MODS is due to the cellular damage and death induced by sepsis. The mechanism of this cell death depends in part upon mitochondrial dysfunction. Damaged mitochondria have increased membrane permeability prompting their autophagic removal if few mitochondria are involved but apoptotic cell death may occur if the mitochondrial losses are more extensive. In addition. severe loss of mitochondria results in low cell energy stores, necrotic cell death, and increased inflammation driven by the release of cell components such as HMGB1. Therapies, which aim at improving cellular energy reserves such as the promotion of mitochondrial biogenesis by insulin, may have a role in future sepsis therapies. Finally, both the inflammatory responses and the susceptibility to organ failure may be modulated by nutritional status and micronutrients, such as zinc, Therapies aimed at micronutrient repletion may further augment approaches targeting PRR function and mitochondrial viability.

A [meso-tetrakis(4-sulfonatophenyl)porphyrinato]zinc(ii) complex as an oral therapeutic for the treatment of type 2 diabetic KKA(y) mice

We prepared and characterized [meso-tetrakis(4-sulfonatophenyl)porphyrinato]zinc(II) ([Zn(tpps)]), and investigated its in vitro insulin-mimetic activity and in vivo hypoglycemic effect in type 2 diabetic KKA(y) mice. The results were compared with those of previously proposed insulin-mimetic zinc(II) complexes and zinc sulfate (ZnSO(4)). The in vitro insulin-mimetic activity of [Zn(tpps)] was considerably better than that of bis(allixinato)zinc(II) ([Zn(alx)(2)]), bis(maltolato)zinc(II) ([Zn(mal)(2)]), bis(2-aminomethylpyridinato)zinc(II) ([Zn(2-ampy)(2)](2+)), and ZnSO(4). In particular, the order of in vitro insulin-mimetic activity of the complexes was determined to be: [Zn(tpps)]>[Zn(alx)(2)]>[Zn(mal)(2)]>[Zn(2-ampy)](2+)>ZnSO(4). [Zn(tpps)] normalized the hyperglycemia of KKA(y) mice within 21 days when administered orally at doses of 10-20 mg (0.15-0.31 mmol) Zn per kg body mass for 28 days. In addition, metabolic syndromes such as insulin resistance, the degree of renal disturbance, and the degree of liver disturbance were significantly improved in [Zn(tpps)]-treated KKA(y) mice relative to those administered with saline and ZnSO(4). The improvement in diabetes was validated by the results of oral glucose-tolerance tests and the decrease in the HbA(1c) level observed. In contrast, ZnSO(4) and the ligand H(2)tpps did not lower the elevated blood glucose level under the same experimental conditions. Based on these observations, [Zn(tpps)] is proposed to be the first orally active zinc(II)-porphyrin complex for the efficacious treatment of not only type 2 diabetes but also metabolic syndromes in animals.

Interactions of insulin-mimetic zinc(II) complexes with cell constituents: glutathione and ATP

Ternary complex formation of some potent insulin-mimetic zinc(II) complexes of bidentate ligands: maltol and 3-hydroxy-1,2-dimethyl-pyridinone with (O,O), 2-picolinic acid and 6-methylpicolinic acid with (N,O) and the tridentate 2,6-dipicolinic acid with (O,N,O) coordination modes was studied in aqueous solutions by pH-potentiometry and spectroscopic (UV, CD, ESI-MS) methods in the presence of critical cell constituents such as L-glutathione reduced (GSH) and adenosine 5'-triphosphate (ATP). Results showed that formation of the ternary complexes was hindered in the case of 2,6-dipicolinic acid, especially with ATP, while it was favoured with the bidentate ligands in the physiological pH range. Driving force of the formation of mixed-ligand species was found to be a more enhanced coordination of GSH and ATP as second ligands in the ternary complexes than in their binary ones due to steric and electrostatic reasons. The mitochondrial dehydrogenase activity of the zinc(II) complexes, as an indirect indicator for the glucose intake, was measured on Mono Mac and 3T3-L1 adipocyte cell lines. The activity of the complexes up to approximately 10-100 microM concentration was in the range of the effect of 0.75-1.5 microM insulin, while at higher concentration it was broken down due to the sensitivity of the cells to toxicity of the complexes.

Antidiabetic copper(II)-picolinate: impact of the first transition metal in the metallopicolinate complexes

In order to examine the effect of metallopicolinate complexes with first transition metals and develop complexes that are more active than an insulinomimetic leading compound such as oxovanadium(IV)-picolinate complex, VO(pa)2, 10 metallopicolinate complexes were prepared, and their in vitro insulinomimetic and in vivo antidiabetic activities were evaluated. The in vitro activity was estimated by determining the inhibitory effects of these complexes on free fatty acid release from isolated rat adipocytes treated with epinephrine. Among the complexes, Cu(pa)2, and Mn(pa)3 exhibited higher activity than their respective metal ions and better activity than VO(pa)2. Since Cu(pa)2 was non-toxic in the cultured rat hepatic M cells, this complex was given streptozotocin (STZ)-induced type 1-like diabetic mice by single intraperitoneal injection, and found that this complex exhibited a higher hypoglycemic effect than the VO(pa)2 complex. Based on these results, we propose that Cu(pa)2 may be a potent alternative antidiabetic agent.

Antidiabetic zinc(II)-N-acetyl-L-cysteine complex: evaluations of in vitro insulinomimetic and in vivo blood glucose-lowering activities

The diabetic state is known to induce oxidative stress in its mechanism, which in turn is responsible for the complications of diabetes mellitus (DM). Recently, we found that Zn(II) complexes have in vitro insulinomimetic and in vivo blood glucose-lowering activities. During our study on the development of new Zn(II) complexes with antioxidative ligands involving L-cysteine, L-cysteine-methylester, and N-acetyl-L-cysteine (nac), we found a new (N-acetyl-L-cysteinato)Zn(II) (Zn(nac)) complex by evaluating of both its in vitro insulinomimetic and in vivo potencies. The insulinomimetic activity of Zn(nac) with respect to the inhibition of free fatty acid release in isolated rat adipocytes treated with epinephrine was higher than that of a well-known insulinomimetic VOSO4, being equivalent to that of ZnSO4. The blood glucose level of hyperglycemic KK-Ay mice with type 2 DM was reduced by daily intraperitoneal injections of Zn(nac) for 28 days. Their serum insulin, HbA1c, TCHO, and UN levels were remarkably decreased, indicating that Zn(nac) improved the insulin resistance of the mice. The improvement of DM by Zn(nac) was also confirmed by the oral glucose tolerance test. In conclusion, Zn(nac) complex is proposed to attenuate both hyperglycemia and hyperinsulinemia in KK-Ay mice by decreasing serum insulin, HbA1c, UN, and TCHO levels.

Zinc, the pancreas, and diabetes: insights from rodent studies and future directions

Molecular and cellular studies have demonstrated several roles for zinc (Zn) in insulin production and the consequent actions of insulin on metabolism. Clinical and epidemiological studies suggest that reduced Zn status is associated with diabetes. Investigations of Zn in rodent models of diabetes have provided a valuable link for understanding the molecular, cellular, clinical and epidemiological observations in the context of inter-organ metabolism and the metabolic disturbances of diabetes. This review highlights some of the current knowledge and future research directions for the role of Zn in the pancreas and diabetes based on rodent studies and experimental manipulations of Zn. Overall, Zn supplementation is effective for preventing or ameliorating diabetes in several rodent models of Type 1 and Type 2 diabetes. Studies with chemically-induced Type 1 diabetes indicate that the protective effects of Zn involve antioxidant mechanisms whether it is Zn alone (as an antioxidant), Zn induction of metallothionein or Zn inhibition of redox-sensitive transcription factors. Further studies are needed to identify the mechanism(s) for Zn protection in Type 2 diabetes, including pancreatic and peripheral effects. Experimental manipulations of Zn status in rodent models of diabetes provide a valuable approach to explore mechanisms for the protective effects of Zn; however, long term clinical studies establishing safety (lack of toxicity) and efficacy are required before any recommendations can be made for people with diabetes.

A family of insulinomimetic zinc(II) complexes of amino ligands with Zn(Nn) (n=3 and 4) coordination modes

Several metal ions and their complexes have been known to mimic the action of insulin in in vitro and in vivo systems. We prepared a family of Zn(II) complexes derived from amino ligands with Zn(Nn) (n=3 and 4) coordination modes, the insulinomimetic activity being estimated by an inhibitory effect of free fatty acid release from isolated rat adipocytes treated with epinephrine. In comparison with the positive controls VOSO(4) and ZnSO(4), Zn(II)-amine complexes with stability constants (log beta) lower than 11.5 exhibited higher insulinomimetic activities. Among them, a bis(2-aminomethyl pyridinato)Zn(II) (Zn(2-ampy)(2)(2+)) complex with the highest insulinomimetic activity and a higher stability constant but lower than 11.5 was selected, and subjected to in vivo evaluation in KK-A(y) mice with a genetically type 2 diabetes mellitus. The high blood glucose level of the mice was lowered by daily intraperitoneal injections of Zn(2-ampy)(2)(2+) at a dose of 2 mg Zn/kg body weight for 14 days. Based on the results, Zn(2-ampy)(2)(2+) with Zn(N(4)) coordination mode was proposed to have both a high in vitro insulinomimetic activity and an in vivo blood glucose lowering effect.

A new insulin-mimetic bis(allixinato)zinc(II) complex: structure?activity relationship of zinc(II) complexes

During the investigation of the development of insulin-mimetic zinc(II) complexes with a blood glucose-lowering effect in experimental diabetic animals, we found a potent bis(maltolato)zinc(II) complex, Zn(ma)(2), exhibiting significant insulin-mimetic effects in a type 2 diabetic animal model. By using this Zn(ma)(2) as the leading compound, we examined the in vitro and in vivo structure-activity relationships of Zn(ma)(2) and its related complexes. The in vitro insulin-mimetic activity of these complexes was determined by the inhibition of free fatty acid release and the enhancement of glucose uptake in isolated rat adipocytes treated with epinephrine. A new Zn(II) complex with allixin isolated from garlic, Zn(alx)(2), exhibited the highest insulin-mimetic activity among the complexes analyzed. The insulin-mimetic activity of the Zn(II) complexes examined strongly correlated (correlation coefficient=0.96) with the partition coefficient (log P) of the ligand, indicating that the activity of Zn(ma)(2)-related complexes depends on the lipophilicity of the ligand. The blood glucose-lowering effects of Zn(alx)(2) and Zn(ma)(2) were then compared, and both complexes were found to normalize hyperglycemia in KK- A(y) mice after a 14-day course of daily intraperitoneal injections. However, Zn(alx)(2) improved glucose tolerance in KK- A(y) mice much more than did Zn(ma)(2), indicating that Zn(alx)(2) possesses greater in vivo anti-diabetic activity than Zn(ma)(2). In addition, Zn(alx)(2) improved leptin resistance and suppressed the progress of obesity in type 2 diabetic KK- A(y) mice. On the basis of these observations, we conclude that the Zn(alx)(2) complex is a novel potent candidate for the treatment of type 2 diabetes mellitus.

The action mechanism of zinc(II) complexes with insulinomimetic activity in rat adipocytes

Zinc (Zn), an essential trace element, and its complexes have recently been known to exhibit insulinomimetic activities. However, the action mechanism of Zn(II) has yet been obscure. The purpose of the present study was to estimate the action mechanism of the Zn(II) complexes. We found first that Zn given in the chemical forms such as Zn(maltolate)2 and Zn(threoninate)2 complexes is highly uptaken in the isolated rat adipocytes compared with that of Zn(picolinate)2. Then, the action mechanism for the insulinomimetic activities was examined in terms of free fatty acid release from the adipocytes. Four Zn(II) compounds, ZnSO4, Zn(picolinate)2, Zn(maltolate)2, and Zn(threoninate)2, inhibited the free fatty acid release from the adipocytes treated with epinephrine (adrenaline). By using several inhibitors for fatty acids and glucose metabolisms in the adipocytes, the following results were obtained. (1) Zn(picolinic acid)2 complex acts on the insulin receptor and PI3-k, which relate to the glucose uptake, as indicated by the experiments using hydroxy-2-naphthalenylmethyl phosphonic acid tris acetoxy methyl ester (HNMPA-(AM)3) and wortmannin, respectively. (2) ZnSO4, and Zn(maltolate)2 and Zn(threoninate)2 complexes affect a glucose transporter 4 (GLUT 4), which is involved in the glucose uptake as indicated by the results using cytochalasin B. (3) Four Zn(II) compounds affect the activation of the phosphodiesterase as indicated by the experiments using cilostamide. These results indicate that the Zn(II) compounds promote the glucose uptake into the adipocytes by affecting at least three sites in the adipocytes, which in turn normalize the blood glucose levels in the experimental diabetic animals.