Peroxynitrite scavenger FeTPPS binds with hCT to effectively inhibit its amyloid aggregation

Human calcitonin (hCT) is an endogenous polypeptide commonly employed in treating bone resorption-related illnesses, but its clinical application is limited due to its high aggregation tendency. Metalloporphyrins are effective in suppressing amyloid fibrillation, positioning them as potential drug candidates for amyloidogenic disorders like Alzheimer's and type 2 diabetes. In this work, we investigated the effects of Fe(III) meso-tetra(4-sulfonatophenyl)porphine chloride (FeTPPS), a highly efficient ONOO- decomposition catalyst, on hCT aggregation. Our findings reveal that FeTPPS effectively precludes hCT fibrillation by stabilizing the monomers and delaying the structural transition from α-helix bundles to β-sheet-rich aggregates. The macrocyclic ring of FeTPPS plays a significant role in disrupting hCT self-associations. Among various porphyrin analogs, those with an iron center and negatively charged peripheral substituents exhibit a stronger inhibitory effect on hCT aggregation. Spectroscopic analyses and computational simulations indicate that FeTPPS binds to hCT's core aggregation region via complexation with His20 in a 1 : 1 molar ratio. Hydrophobic interaction, hydrogen bonding, and π-π stacking with the residues involving Tyr12, Phe19, and Ala26 also contribute to the interactions. Collectively, our study provides a promising approach for developing novel hCT drug formulations and offers theoretical guidance for designing metalloporphyrin-based inhibitors for various amyloidosis conditions.

Tyrosine nitration of glucagon impairs its function: Extending the role of heme in T2D pathogenesis

New studies raise the possibility that the higher glucagon (GCG) level present in type 2 diabetes (T2D) is a compensatory mechanism to enhance β-cell function, rather than induce dysregulated glucose homeostasis, due to an important role for GCG that acts directly within the pancreas on insulin secretion by intra-islet GCG signaling. However, in states of poorly controlled T2D, pancreatic α cell mass increases (overproduced GCG) in response to insufficient insulin secretion, indicating decreased local GCG activity. The reason for this decrease is not clear. Recent evidence has uncovered a new role of heme in cellular signal transduction, and its mechanism involves reversible binding of heme to proteins. Considering that protein tyrosine nitration in diabetic islets increases and glucose-stimulated insulin secretion (GSIS) decreases, we speculated that heme modulates GSIS by transient interaction with GCG and catalyzing its tyrosine nitration, and the tyrosine nitration may impair GCG activity, leading to loss of intra-islet GCG signaling and markedly impaired insulin secretion. Data presented here elucidate a novel role for heme in disrupting local GCG signaling in diabetes. Heme bound to GCG and induced GCG tyrosine nitration. Two tyrosine residues in GCG were both sensitive to the nitrating species. Further, GCG was also demonstrated to be a preferred target peptide for tyrosine nitration by co-incubation with BSA. Tyrosine nitration impaired GCG stimulated cAMP-dependent signaling in islet β cells and decreased insulin release. Our results provided a new role of heme for impaired GSIS in the pathological process of diabetes.

Heme and Cu2+-induced vasoactive intestinal peptide (VIP) tyrosine nitration: A possible molecular mechanism for the attenuated anti-inflammatory effect of VIP in inflammatory diseases

Vasoactive intestinal peptide (VIP) is a neuropeptide that play an important role in immunoregulation and anti-inflammation. Numerous inflammatory/autoimmune disorders are associated with decreased VIP binding ability to receptors and diminished VIP activation of cAMP generation in immune cells. However, the mechanisms linking oxidative/nitrative stress to VIP immune dysfunction remain unknown. It has been reported that the elevated heme or Cu2+ in inflammatory diseases can cause oxidative and nitrative damage to nearby biological targets under high oxidative stress conditions, which affects the structure and activity of linked peptides or proteins. Thus, the VIP down-regulated immune response may be interfered by redox metal catalyzed VIP tyrosine nitration. To explore this, we systematically investigated the possibility of heme or Cu2+ to catalyze VIP tyrosine nitration. The results showed that Tyr10 and Tyr22 of VIP can both be nitrated in heme/H2O2/NO2- system as well as in Cu2+/H2O2/NO2- system. Then, we used synthetic mutant VIPs with tyrosine residues substituted by 3-nitrotyrosine to study the impact of tyrosine nitration on VIP activity in SHSY-5Y cells. Our findings demonstrated that VIP nitration dramatically decreased the content of its α-helix and random coil, suggesting that VIP nitration might reduce its affinity to the receptor. This was further confirmed in the cAMP assay. The results showed that 10 nM of these tyrosine nitrated VIPs could significantly (p < 0.01) decrease cAMP secretion compared to the wild type VIP. Our data reveal that the attenuation of the neuroprotective effect of VIP in inflammation-related diseases might be attributed to metal-catalyzed VIP tyrosine nitration.

Structure effect of water-soluble iron porphyrins on catalyzing protein tyrosine nitration in the presence of nitrite and hydrogen peroxide

Water-soluble iron porphyrins, such as FeTPPS (5,10,15,20-tetrakis (4-sulfonatophenyl) porphyrinato iron (III)), FeTMPyP (5,10,15,20-tetrakis (N-methyl-4'-pyridyl) porphyrinato iron (III) chloride) and FeTBAP (5,10,15,20-tetrakis (4-benzoic acid) porphyrinato iron (III)), are highly active catalysts for peroxynitrite decomposition and thereby have been suggested as therapeutic agent for inflammatory diseases that implicate the involvement of nitrotyrosine formation. Here, we systemically investigated catalytic properties of FeTPPS, FeTMPyP and FeTBAP on protein nitration in the presence of hydrogen peroxide and nitrite. We showed that FeTPPS, FeTBAP and FeTMPyP all exhibited higher peroxidase activity in compared with hemin. As to protein nitration, the catalytic effect of FeTPPS and FeTBAP are effective in the presence of hydrogen peroxide and nitrite, while negligible BSA nitration was observed in the case of FeTMPyP. Moreover, the underlying mechanism of the oxidation of FeTPPS, FeTBAP and FeTMPyP was further studied. Collectively, our results suggest that, compound I and II species are involved in as the key intermediates in FeTMPyP/H₂O₂ system as similar as those in FeTPPS/H₂O₂ and FeTBAP/H₂O₂ system. As compared to weak antioxidants, TPPS and TBAP, however, TMPyP scavenges oxo-Fe (IV) intermediates of FeTMPyP at a faster rate by significant self-degradation; results in the shortest lifetimes of OFe^IV-TMPyP and the lowest catalytic activity on oxidizing tyrosine and nitrite; and therefore, attributes to inactivation of FeTMPyP in protein nitration. In addition, association of FeTMPyP to BSA was found weak, while strong binding of FeTPPS and FeTBAP were observed. The weak binding keeps away of target residue of BSA from the center of FeTMPyP where the RNS is generated, which might be attributed as additional factors to the inactivation of FeTMPyP in protein nitration.

Heme prevents highly amyloidogenic human calcitonin (hCT) aggregation: A potential new strategy for the clinical reuse of hCT

Irreversible aggregation can extremely limit the bioavailability and therapeutic activity of peptide-based drugs. Thus, peptide fibrillation is an excellent challenge for biotechnological drug development. Human calcitonin (hCT) is such a peptide hormone known for its hypocalcaemic effect but has limited pharmaceutical potential due to a high tendency to aggregate. hCT is therefore not widely used preparation in clinical practice. Nonetheless, hCT seems to be still an ideal target for clinical therapy when fibrillation is effectively inhibited, because the alternatives of hCT can stimulate undesirable immune responses in patients and cause side effects. Interestingly, heme is an essential component for many livings and has been shown a strong inhibitory effect on some amyloidogenic peptides aggregation. Here we demonstrate that it may be a most suitable, safe, biocompatible small molecule inhibitor on hCT aggregation, and thereby improving its activity when guiding the drug peptide in clinical therapeutics. In this work, we found that heme was able to reversibly bind with hCT to form a heme-hCT complex with a moderate binding constant (9.17 × 10⁶ M^-1) and significantly suppress the aggregation of hCT probably accomplished by heme binding to it, blocking the β-sheet structure assembly which is essential in hCT fibril aggregation. Meanwhile, the heme-hCT complexes showed enhanced bioactivity compared to hCT itself after a 24 h incubation time in reducing blood calcium levels in mice. This study may develop a new strategy to reuse the wild-type hCT in clinical therapeutics.

The effect of peptide tyrosine tyrosine (PYY3–36), a selective Y2 receptor agonist on streptozotocin-induced diabetes in albino rats

Objective. The aim of the present study was to assess the effect of the PYY3–36, as a potential therapy for the type 2 diabetes mellitus (T2DM), induced by high fat diet (HFD) and an intraperitoneal (i.p.) administration of streptozotocin (STZ) in albino rats.

Methods. Forty adult male albino Wistar rats were divided into: 1) control group (C, in which the rats were fed with a standard diet and received vehicle; 2) diabetic group (D, in which T2DM was induced by feeding the rats with HFD for four weeks followed by a single i.p. injection of 35 mg/kg STZ, this group was also allowed to have HFD till the end of the study; and 3) D+PYY3–36 group (in which the diabetic rats were treated with 50 µg/kg i.p. PYY3–36 twice a day for one week). Food intake, water intake, body weight (b.w.), visceral fat weight (VFW), liver glycogen content, serum levels of glucose, insulin, and interleukin-6 (IL-6), were measured. Homeostatic-model assessment of insulin resistance (HOMA-IR) was estimated. The gene expression of the hypothalamic neuropeptide Y (NPY) and visceral nuclear factor kappa B (NF-κB) were assessed by a reverse transcription polymerase chain reaction (RT-PCR).

Results. The PYY3–36 administration to the diabetic group of rats significantly increased the serum insulin levels and liver glycogen content, decreased the body weight, VFW, food intake, water intake, serum levels of the glucose, IL-6, and HOMA-IR. It also decreased the expression of both the hypothalamic NPY and the visceral fat NF-κB.

Conclusion. With respect to the fact of improved insulin release and enhanced insulin sensitivity (an effect that may be mediated via suppressing accumulation of visceral fat and inflammatory markers), in the rats treated with PYY3–36, the PYY3–36 might be considered for the future as a promising therapeutic tool in T2DM.

Copper Binding Induces Nitration of NPY under Nitrative Stress: Complicating the Role of NPY in Alzheimer's Disease

Neuropeptide Y (NPY) is a 36 amino acid peptide that regulates a multitude of physiological functions in the central nervous system and has been shown to be involved in Alzheimer's disease (AD). A change in copper homeostasis is a remarkable feature of AD, and the dysregulation may contribute to toxicity in neural cells. Moreover, it has been shown that copper could interact with many neuropeptides and result in catalyzing the production of reactive oxygen species, which may lead to peptide oxidation. Besides, copper could also catalyze protein tyrosine nitration under oxidative stress, and there are two tyrosine residues playing an important role in NPY. Therefore, it is also likely that copper has an action on NPY and potentially influences its functions through tyrosine nitration. In this paper, the studies of the interaction of copper with NPY and the copper-catalyzed NPY nitration were performed. The electrochemical techniques, UV-vis spectroscopy, mass spectrometry, and fluorescence titration, have been applied to show that copper can interact with NPY to form a Cu-NPY complex with a conditional dissociation constant of 0.021 μmol/L, and the binding promotes the generation of •OH. Dot blotting results reveal that NPY can be nitrated upon binding with copper under nitrative stress. Furthermore, liquid chromatography-mass spectrometry (LC-MS) identify that the tyrosine residues in NPY are all nitrated during the nitration process, which will cause the inactivation of NPY shown by our previous study. This study supports the hypothesis that copper has a close correlation with NPY and implicates the peptide in AD. These data may provide a new insight into understanding the pathology and pathogenesis of AD.