Structural signatures of the complex formed between 3-nitro-4-hydroxybenzoate and the Zn(II)-substituted R(6) insulin hexamer

Integration of dietary nutrition and TRIB3 action into diabetes mellitus

Despite intensive studies for decades, the common mechanistic correlations among the underlying pathology of diabetes mellitus (DM), its complications, and effective clinical treatments remain poorly characterized. High-quality diets and nutrition therapy have played an indispensable role in the management of DM. More importantly, tribbles homolog 3 (TRIB3), a nutrient-sensing and glucose-responsive regulator, might be an important stress-regulatory switch, linking glucose homeostasis and insulin resistance. Therefore, this review aimed to introduce the latest research progress on the crosstalk between dietary nutrition intervention and TRIB3 in the development and treatment of DM. This study also summarized the possible mechanisms involved in the signaling pathways of TRIB3 action in DM, in order to gain an in-depth understanding of dietary nutrition intervention and TRIB3 in the pathogenesis of DM at the organism level.

Insulin polymorphism induced by two polyphenols: new crystal forms and advances in macromolecular powder diffraction

This study focuses on the polymorphism of human insulin (HI) upon the binding of the phenolic derivativesp-coumaric acid ortrans-resveratrol over a wide pH range. The determination of the structural behaviour of HI via X-ray powder diffraction (XRPD) and single-crystal X-ray diffraction (SCXRD) is reported. Four distinct polymorphs were identified, two of which have not been reported previously. The intermediate phase transitions are discussed. One of the novel monoclinic polymorphs displays the highest molecular packing among insulin polymorphs of the same space group to date; its structure was elucidated by SCXRD. XRPD data collection was performed using a variety of instrumental setups and a systematic comparison of the acquired data is presented. A laboratory diffractometer was used for screening prior to high-resolution XRPD data collection on the ID22 beamline at the European Synchrotron Radiation Facility. Additional measurements for the most representative samples were performed on the X04SA beamline at the Swiss Light Source (SLS) using the MYTHEN II detector, which allowed the detection of minor previously untraceable impurities and dramatically improved thed-spacing resolution even for poorly diffracting samples.

Insulin Formulation Characterization-the Thioflavin T Assays

The insulin molecule was discovered in 1921. Shortly thereafter, its propensity towards amyloid fibril formation, fibrillation, was observed and described in the literature as a "precipitate." In the past decades, the increased incidence of type 2 diabetes has reached global epidemic proportions. This has emphasized the demands for both insulin production and the development of modern insulin products for unmet medical needs. Bringing such new insulin drug products to the market for the benefit of patients requires that many CMC-related processes are understood, described, and controlled. One potential undesired process is insulin fibril formation. The compound thioflavin T (ThT) is known as a fluorescent probe for amyloid fibrils. As such, ThT is utilized in a versatile research assay in microtiter plate format, the ThT assay. This review will describe an experimental set-up using not only a ThT microtiter plate assay but also two orthogonal methods. The use of the ThT assay in research and characterization of insulin analogues, as well as formulations of insulin, is described by cases drawn from the scientific literature and patents. The ThT assay is compared to other physical stability tests and in conclusion the advantages and limitations of the assay are compared.

Zinc-ligand interactions modulate assembly and stability of the insulin hexamer -- a review

Zinc and calcium ions play important roles in the biosynthesis and storage of insulin. Insulin biosynthesis occurs within the beta-cells of the pancreas via preproinsulin and proinsulin precursors. In the golgi apparatus, proinsulin is sequestered within Zn(2+)- and Ca(2+)-rich storage/secretory vesicles and assembled into a Zn(2+) and Ca(2+) containing hexameric species, (Zn(2+))(2)(Ca(2+))(Proin)(6). In the vesicle, (Zn(2+))(2)(Ca(2+))(Proin)(6) is converted to the insulin hexamer, (Zn(2+))(2)(Ca(2+))(In)(6), by excision of the C-peptide through the action of proteolytic enzymes. The conversion of (Zn(2+))(2)(Ca(2+))(Proin)(6)to (Zn(2+))(2)(Ca(2+))(In)(6) significantly lowers the solubility of the hexamer, causing crystallization within the vesicle. The (Zn(2+))(2)(Ca(2+))(In)(6) hexamer is an allosteric protein that undergoes ligand-mediated interconversion among three global conformation states designated T(6), T(3)R(3) and R(6). Two classes of allosteric sites have been identified; hydrophobic pockets (3 in T(3)R(3) and 6 in R(6)) that bind phenolic ligands, and anion sites (1 in T(3)R(3) and 2 in R(6)) that bind monovalent anions. The allosteric states differ widely with respect to the physical and chemical stability of the insulin subunits. Fusion of the vesicle with the plasma membrane results in the expulsion of the insulin crystals into the intercellular fluid. Dissolution of the crystals, dissociation of the hexamers to monomer and transport of monomers to the liver and other tissues then occurs via the blood stream. Insulin action then follows binding to the insulin receptors. The role of Zn(2+) in the assembly, structure, allosteric properties, and dynamic behavior of the insulin hexamer will be discussed in relation to biological function.

The potential biological mechanisms of arsenic-induced diabetes mellitus

Although epidemiologic studies carried out in Taiwan, Bangladesh, and Sweden have demonstrated a diabetogenic effect of arsenic, the mechanisms remain unclear and require further investigation. This paper reviewed the potential biological mechanisms of arsenic-induced diabetes mellitus based on the current knowledge of the biochemical properties of arsenic. Arsenate can substitute phosphate in the formation of adenosine triphosphate (ATP) and other phosphate intermediates involved in glucose metabolism, which could theoretically slow down the normal metabolism of glucose, interrupt the production of energy, and interfere with the ATP-dependent insulin secretion. However, the concentration of arsenate required for such reaction is high and not physiologically relevant, and these effects may only happen in acute intoxication and may not be effective in subjects chronically exposed to low-dose arsenic. On the other hand, arsenite has high affinity for sulfhydryl groups and thus can form covalent bonds with the disulfide bridges in the molecules of insulin, insulin receptors, glucose transporters (GLUTs), and enzymes involved in glucose metabolism (e.g., pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase). As a result, the normal functions of these molecules can be hampered. However, a direct effect on these molecules caused by arsenite at physiologically relevant concentrations seems unlikely. Recent evidence has shown that treatment of arsenite at lower and physiologically relevant concentrations can stimulate glucose transport, in contrary to an inhibitory effect exerted by phenylarsine oxide (PAO) or by higher doses of arsenite. Induction of oxidative stress and interferences in signal transduction or gene expression by arsenic or by its methylated metabolites are the most possible causes to arsenic-induced diabetes mellitus through mechanisms of induction of insulin resistance and beta cell dysfunction. Recent studies have shown that, in subjects with chronic arsenic exposure, oxidative stress is increased and the expression of tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6) is upregulated. Both of these two cytokines have been well known for their effect on the induction of insulin resistance. Arsenite at physiologically relevant concentration also shows inhibitory effect on the expression of peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear hormone receptor important for activating insulin action. Oxidative stress has been suggested as a major pathogenic link to both insulin resistance and beta cell dysfunction through mechanisms involving activation of nuclear factor-kappaB (NF-kappaB), which is also activated by low levels of arsenic. Although without supportive data, superoxide production induced by arsenic exposure can theoretically impair insulin secretion by interaction with uncoupling protein 2 (UCP2), and oxidative stress can also cause amyloid formation in the pancreas, which could progressively destroy the insulin-secreting beta cells. Individual susceptibility with respect to genetics, nutritional status, health status, detoxification capability, interactions with other trace elements, and the existence of other well-recognized risk factors of diabetes mellitus can influence the toxicity of arsenic on organs involved in glucose metabolism and determine the progression of insulin resistance and impaired insulin secretion to a status of persistent hyperglycemia or diabetes mellitus. In conclusions, insulin resistance and beta cell dysfunction can be induced by chronic arsenic exposure. These defects may be responsible for arsenic-induced diabetes mellitus, but investigations are required to test this hypothesis.