Coordination ability of bradykinin with ZnII- and AgI-metal ions – Experimental and theoretical study

Metal-dependent hormone function: the emerging interdisciplinary field of metalloendocrinology

For over 100 years, there has been an incredible amount of knowledge amassed concerning hormones in the endocrine system and their central role in human health. Hormones represent a diverse group of biomolecules that are released by glands, communicate signals to their target tissue, and are regulated by feedback loops to maintain organism health. Many disease states, such as diabetes and reproductive disorders, stem from misregulation or dysfunction of hormones. Increasing research is illuminating the intricate roles of metal ions in the endocrine system where they may act advantageously in concert with hormones or deleteriously catalyze hormone-associated disease states. As the critical role of metal ions in the endocrine system becomes more apparent, it is increasingly important to untangle the complex mechanisms underlying the connections between inorganic biochemistry and hormone function to understand and control endocrinological phenomena. This tutorial review harmonizes the interdisciplinary fields of endocrinology and inorganic chemistry in the newly-termed field of "metalloendocrinology". We describe examples linking metals to both normal and aberrant hormone function with a focus on highlighting insight to molecular mechanisms. Hormone activities related to both essential metal micronutrients, such as copper, iron, zinc, and calcium, and disruptive nonessential metals, such as lead and cadmium are discussed.

Binding of Cu+ and Cu2+ with peptides: Peptides = oxytocin, Arg8 -vasopressin, bradykinin, angiotensin-I, substance-P, somatostatin, and neurotensin

The intrinsic binding ability of 7 natural peptides (oxytocin, arg⁸ -vasopressin, bradykinin, angiotensin-I, substance-P, somatostatin, and neurotensin) with copper in 2 different oxidation states (Cu^I/II ) derived from different Cu^+/2+ precursor sources have been investigated for their charge-dependent binding characteristics. The peptide-Cu^I/II complexes, [M - (n-1)H + nCu^I ] and [M - (2n-1)H + nCu^II ], are prepared/generated by the reaction of peptides with CuI solution/Cu-target and CuSO₄ solution and are analyzed by using matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. The MALDI mass spectra of both [M - (n-1)H + nCu^I ] and [M - (2n-1)H + nCu^II ] complexes show no mass shift due to the loss of ─H atoms in the main chain ─NH of these peptides by Cu⁺ and Cu²⁺ deprotonation. The measured m/z value indicates the reduction of Cu^I/II oxidation state into Cu⁰ during MALDI processes. The number and relative abundance of Cu⁺ bound to the peptides are greater compared with the Cu²⁺ bound peptides. Oxytocin, arg⁸ -vasopressin, bradykinin, substance-P, and somatostatin show the binding of 5Cu⁺ , and angiotensin-I and neurotensin show the binding of 7Cu⁺ from both CuI and Cu targets, while bradykinin shows the binding of 2Cu²⁺ , oxytocin, arg⁸ -vasopressin, angiotensin-I, and substance-P; somatostatin shows the binding of 3Cu²⁺ ; and neurotensin shows 4Cu²⁺ binding. The binding of more Cu⁺ with these small peptides signifies that the bonding characteristics of both Cu⁺ and Cu²⁺ are different. The amino acid residues responsible for the binding of both Cu⁺ and Cu²⁺ in these peptides have been identified based on the density functional theory computed binding energy values of Cu⁺ and the fragment transformation method predicted binding preference of Cu²⁺ for individual amino acids.

Copper, differently from zinc, affects the conformation, oligomerization state and activity of bradykinin

The sole role of bradykinin (BK) as an inflammatory mediator is controversial, as recent data also support an anti-inflammatory role for BK in Alzheimer's disease (AD). The involvement of two different receptors (B1R and B2R) could be a key to understand this issue. However, although copper and zinc dyshomeostasis has been demonstrated to be largely involved in the development of AD, a detailed study of the interaction of BK with these two metal ions has never been addressed. In this work, we have applied mass spectrometry, circular dichroism as well as computational methods in order to assess if copper and zinc have the ability to modulate the conformation and oligomerization of BK. In addition, we have correlated the chemical data with the effect of metals on the activity of BK analyzed in cell cultures by biochemical procedures. The biochemical analyses on monocyte/macrophage cell culture (THP-1 Cell Line human) in line with the effect of metals on the conformation of BK showed that the presence of copper can affect the signaling cascade mediated by the BK receptors. The results obtained show a further role of metal ions, particularly copper, in the development and outcome of neuroinflammatory diseases. The possible implications in AD are discussed.

Metal-Containing Poly(ionic liquid) Membranes for Antibacterial Applications

Imidazolium-type metal-containing ionic liquid (IL) monomers and their corresponding poly(ionic liquid) (PIL) membranes coordinated with CuCl₂ (PILM-Cu), FeCl₃ (PILM-Fe), or ZnCl₂ (PILM-Zn) were synthesized. The effect of metal ions on the antimicrobial activities against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was investigated. Compared with pristine PILM-Br membrane, PILM-Cu, PILM-Fe, and PILM-Zn membranes exhibit enhanced antibacterial activities due to the attributes of both imidazolium cations and metal-containing anions. Furthermore, all of the metal-containing PIL membranes present low hemolysis toward human red blood cell and high long-term antibacterial stability, even after immersion in water for 90 days, demonstrating clinical feasibility in topical applications.

Analysis of argentinated peptide complexes using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: Peptide = oxytocin, arg(8) -vasopressin, bradykinin, bombesin, somatostatin, neurotensin

RATIONALE

The increased use of silver nanoparticles (AgNPs) for various biological applications, and over-expression of various peptide receptors in different tumors/cancer cells, necessitate the need for dedicated investigations on the intrinsic binding ability of Ag with various biologically important peptides for better understanding of AgNPs-peptide interactions and for the future development of contrasting agents as well as drugs for imaging/biomedical applications.

METHODS

The [M+(Ag)n ](+) complexes are prepared and characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS).

RESULTS

Silver complexes of the peptides [M+(Ag)n ](+) , where M = oxytocin, arg(8) -vasopressin, bradykinin, bombesin, somatostatin, and neurotensin, have been investigated for their intrinsic Ag(+) -binding ability. Unusual binding of up to seven Ag(+) with these small peptides is observed. The mass spectra show n = 1-5 for bombesin and somatostatin, n = 1-6 for bradykinin and arg(8) -vasopressin, and n = 1-7 for oxytocin and neurotensin. In addition, oxytocin and arg(8) -vasopressin show the formation of dimers and their complexes [M2 +(Ag)n ](+) with n = 1-8 and n = 1-5, respectively. The possible amino acid residues responsible for Ag(+) binding in each peptide have been identified on the basis of density functional theory (DFT)-calculated binding energy values of Ag(+) towards individual amino acids.

CONCLUSIONS

Mass spectrometric evidence indicates that the peptides, viz., oxytocin, arg(8) -vasopressin, bradykinin, bombesin, somatostatin, and neurotensin, show greater affinity for Ag(+) . Hence, they may be used as carriers for AgNPs in targeted drug delivery as well as an alternative for iodinated contrasting agents in dual energy X-ray imaging techniques. Radio-labeled Ag with these peptides can also be used in radio-pharmaceuticals for diagnostic and therapeutic applications. Copyright © 2016 John Wiley & Sons, Ltd.