An in vitro study of the effect of picolinic acid on metal translocation across lipid bilayers

A review on α-glucosidase inhibitory activity of first row transition metal complexes: a futuristic strategy for treatment of type 2 diabetes

Type 2 diabetes mellitus (T2DM) is characterized by high blood glucose levels and has emerged as a controversial public health issue worldwide. The increasing number of patients with T2DM on one hand, and serious long-term complications of the disease such as obesity, neuropathy, and vascular disorders on the other hand, have induced a huge economic impact on society globally. In this regard, inhibition of α-glucosidase, the enzyme responsible for the hydrolysis of carbohydrates in the body has been the main therapeutic approach to the treatment of T2DM. As α-glucosidase inhibitors (α-GIs) have occupied a special position in the current research and prescription drugs are generally α-GIs, researchers have been encouraged to design and synthesize novel and efficient inhibitors. Previously, the presence of a sugar moiety seemed to be crucial for designing α-GIs since they can attach to the carbohydrate binding site of the enzyme mimicking the structure of disaccharides or oligosaccharides. However, inhibitors lacking glycosyl structures have also shown potent inhibitory activity and development of non-sugar based inhibitors is accelerating. In this respect, in vitro anti-α-glucosidase activity of metal complexes has attracted lots of attention and this paper has reviewed the inhibitory activity of first-row transition metal complexes toward α-glucosidase and discussed their probable mechanisms of action.

Role of Kynurenine Pathway in Oxidative Stress during Neurodegenerative Disorders

Neurodegenerative disorders are chronic and life-threatening conditions negatively affecting the quality of patients’ lives. They often have a genetic background, but oxidative stress and mitochondrial damage seem to be at least partly responsible for their development. Recent reports indicate that the activation of the kynurenine pathway (KP), caused by an activation of proinflammatory factors accompanying neurodegenerative processes, leads to the accumulation of its neuroactive and pro-oxidative metabolites. This leads to an increase in the oxidative stress level, which increases mitochondrial damage, and disrupts the cellular energy metabolism. This significantly reduces viability and impairs the proper functioning of central nervous system cells and may aggravate symptoms of many psychiatric and neurodegenerative disorders. This suggests that the modulation of KP activity could be effective in alleviating these symptoms. Numerous reports indicate that tryptophan supplementation, inhibition of KP enzymes, and administration or analogs of KP metabolites show promising results in the management of neurodegenerative disorders in animal models. This review gathers and systematizes the knowledge concerning the role of metabolites and enzymes of the KP in the development of oxidative damage within brain cells during neurodegenerative disorders and potential strategies that could reduce the severity of this process.

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.

Application of Protocols Devised to Study Bi(III) Complex Formation by Voltammetry: The Bi(III)-Picolinic Acid System

Bi(III) coordination chemistry has been largely neglected due to the difficulties faced when studying these systems even though Bi(III) is used in various medicinal applications. This study of the Bi(III)-picolinic acid system by voltammetry applies the rigorous methodologies already developed to enable the study of Bi(III) systems starting in very acidic solutions to prevent precipitation. This includes calibrating the glass electrode accurately at these low pHs, compensating for the diffusion junction potential below pH 2 and determining the reduction potential of uncomplexed Bi(III) which cannot be directly measured. The importance of including nitrate from the background electrolyte as a competing species is highlighted, especially for data acquired below pH ∼ 2. From analysis of the voltammetric data, it was not clear whether a ML₃OH species formed in solution or whether it was a combination of ML₄ and ML₄OH. Information from crystal structures and electrospray ionization-mass spectrometry measurements was thus used to propose the most probable species model. The log β values determined were 7.77 ± 0.07 for ML, 13.89 ± 0.07 for ML₂, 18.61 ± 0.01 for ML₃, 22.7 ± 0.2 for ML₄, and 31.4 ± 0.2 for ML₄OH. Application of these methodologies thus opens the door to broaden our understanding of Bi(III) complexation.

Changing the face of kynurenines and neurotoxicity: therapeutic considerations

Kynurenines are the products of tryptophan metabolism. Among them, kynurenine and kynurenic acid are generally thought to have neuroprotective properties, while 3-hydroxykynurenine, 3-hydroxyanthranilic acid and quinolinic acid are considered neurotoxic. They participate in immunoregulation and inflammation and possess pro- or anti-excitotoxic properties, and their involvement in oxidative stress has also been suggested. Consequently, it is not surprising that kynurenines have been closely related to neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and multiple sclerosis. More information about the less-known metabolites, picolinic and cinnabarinic acid, evaluation of new receptorial targets, such as aryl-hydrocarbon receptors, and intensive research on the field of the immunomodulatory function of kynurenines delineated the high importance of this pathway in general homeostasis. Emerging knowledge about the kynurenine pathway provides new target points for the development of therapeutical solutions against neurodegenerative diseases.

Kynurenines with neuroactive and redox properties: relevance to aging and brain diseases

The kynurenine pathway (KP) is the main route of tryptophan degradation whose final product is NAD(+). The metabolism of tryptophan can be altered in ageing and with neurodegenerative process, leading to decreased biosynthesis of nicotinamide. This fact is very relevant considering that tryptophan is the major source of body stores of the nicotinamide-containing NAD(+) coenzymes, which is involved in almost all the bioenergetic and biosynthetic metabolism. Recently, it has been proposed that endogenous tryptophan and its metabolites can interact and/or produce reactive oxygen species in tissues and cells. This subject is of great importance due to the fact that oxidative stress, alterations in KP metabolites, energetic deficit, cell death, and inflammatory events may converge each other to enter into a feedback cycle where each one depends on the other to exert synergistic actions among them. It is worth mentioning that all these factors have been described in aging and in neurodegenerative processes; however, has so far no one established any direct link between alterations in KP and these factors. In this review, we describe each kynurenine remarking their redox properties, their effects in experimental models, their alterations in the aging process.

Pesticide exposure and depression among agricultural workers in France

Pesticides are ubiquitous neurotoxicants, and several lines of evidence suggest that exposure may be associated with depression. Epidemiologic evidence has focused largely on organophosphate exposures, while research on other pesticides is limited. We collected detailed pesticide use history from farmers recruited in 1998-2000 in France. Among 567 farmers aged 37-78 years, 83 (14.6%) self-reported treatment or hospitalization for depression. On the basis of the reported age at the first such instance, we used adjusted Cox proportional hazards models to estimate hazard ratios and 95% confidence intervals for depression (first treatment or hospitalization) by exposure to different pesticides. The hazard ratio for depression among those who used herbicides was 1.93 (95% confidence interval (CI): 0.95, 3.91); there was no association with insecticides or fungicides. Compared with nonusers, those who used herbicides for <19 years and ≥19 years (median for all herbicide users, 19 years) had hazard ratios of 1.51 (95% CI: 0.62, 3.67) and 2.31 (95% CI: 1.05, 5.10), respectively. Similar results were found for total hours of use. Results were stronger when adjusted for insecticides and fungicides. There is widespread use of herbicides by the general public, although likely at lower levels than in agriculture. Thus, determining whether similar associations are seen at lower levels of exposure should be explored.

The physiological action of picolinic Acid in the human brain

Picolinic Acid is an endogenous metabolite of L-tryptophan (TRP) that has been reported to possess a wide range of neuroprotective, immunological, and anti-proliferative affects within the body. However the salient physiological function of this molecule is yet to be established. The synthesis of picolinic acid as a product of the kynurenine pathway (KP) suggests that, similar to other KP metabolites, picolinic acid may play a role in the pathogenesis of inflammatory disorders within the CNS and possibly other organs.

In this paper we review the limited body of literature dealing with the physiological actions of picolinic acid in the CNS and its associated synthesis via the kynurenine pathway in health and disease. Discrepancies and gaps in our current knowledge of picolinic acid are identified highlighting areas of research to promote a more complete understanding of its endogenous function in the brain.

Copper complexes of pyridine derivatives with superoxide scavenging and antimicrobial activities

Superoxide anions are reactive oxygen species that can attack biomolecules such as DNA, lipids and proteins to cause many serious diseases. This study reports the synthesis of copper complexes of nicotinic acid with related pyridine derivatives. The copper complexes were shown to possess superoxide dismutase (SOD) and antimicrobial activities. The copper complexes exerted SOD activity in range of 49.07-130.23 microM. Particularly, copper complex of nicotinic acid with 2-hydroxypyridine was the most potent SOD mimic with an IC(50) of 49.07 microM. In addition, the complexes exhibited antimicrobial activity against Bacillus subtilis ATCC 6633 and Candida albicans ATCC 90028 with MIC range of 128-256 microg/mL. The SOD activities were well correlated with the theoretical parameters as calculated by density functional theory at the B3LYP/LANL2DZ level of theory. Interestingly, the SOD activity of the copper complexes was demonstrated to be inversely correlated with the electron affinity, but was well correlated with both HOMO and LUMO energies. The vitamin-metal complexes described in this report are great examples of the value-added benefits of vitamins for medicinal applications.

Kynurenine pathway metabolism in human blood-brain-barrier cells: implications for immune tolerance and neurotoxicity

The catabolic pathway of l-tryptophan (l-trp), known as the kynurenine pathway (KP), has been implicated in the pathogenesis of a wide range of brain diseases through its ability to lead to immune tolerance and neurotoxicity. As endothelial cells (ECs) and pericytes of the blood-brain-barrier (BBB) are among the first brain-associated cells that a blood-borne pathogen would encounter, we sought to determine their expression of the KP. Using RT-PCR and HPLC/GC-MS, we show that BBB ECs and pericytes constitutively express components of the KP. BBB ECs constitutively synthesized kynurenic acid, and after immune activation, kynurenine (KYN), which is secreted basolaterally. BBB pericytes produced small amounts of picolinic acid and after immune activation, KYN. These results have significant implications for the pathogenesis of inflammatory brain diseases in general, particularly human immunodeficiency virus (HIV)-related brain disease. Kynurenine pathway activation at the BBB results in local immune tolerance and neurotoxicity: the basolateral secretion of excess KYN can be further metabolized by perivascular macrophages and microglia with synthesis of quinolinic acid. The results point to a mechanism whereby a systemic inflammatory signal can be transduced across an intact BBB to cause local neurotoxicity.

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.

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.