Ferric heme b in aqueous micellar and vesicular systems: state-of-the-art and challenges.

Ferric heme b (= ferric protoporphyrin IX = hemin) is an important prosthetic group of different types of enzymes, including the intensively investigated and widely applied horseradish peroxidase (HRP). In HRP, hemin is present in monomeric form in a hydrophobic pocket containing among other amino acid side chains the two imidazoyl groups of His170 and His42. Both amino acids are important for the peroxidase activity of HRP as an axial ligand of hemin (proximal His170) and as an acid/base catalyst (distal His42). A key feature of the peroxidase mechanism of HRP is the initial formation of compound I under heterolytic cleavage of added hydrogen peroxide as a terminal oxidant. Investigations of free hemin dispersed in aqueous solution showed that different types of hemin dimers can form, depending on the experimental conditions, possibly resulting in hemin crystallization. Although it has been recognized already in the 1970s that hemin aggregation can be prevented in aqueous solution by using micelle-forming amphiphiles, it remains a challenge to prepare hemin-containing micellar and vesicular systems with peroxidase-like activities. Such systems are of interest as cheap HRP-mimicking catalysts for analytical and synthetic applications. Some of the key concepts on which research in this fascinating and interdisciplinary field is based are summarized, along with major accomplishments and possible directions for further improvement. A systematic analysis of the physico-chemical properties of hemin in aqueous micellar solutions and vesicular dispersions must be combined with a reliable evaluation of its catalytic activity. Future studies should show how well the molecular complexity around hemin in HRP can be mimicked by using micelles or vesicles. Because of the importance of heme b in virtually all biological systems and the fact that porphyrins and hemes can be obtained under potentially prebiotic conditions, ideas exist about the possible role of heme-containing micellar and vesicular systems in prebiotic times.

Hemin-induced reactive oxygen species triggers autophagy-dependent macrophage differentiation and pro-inflammatory responses in THP-1 cells.

The toxic effect of oxidized-heme, also known as hemin, is implicated in developing adverse clinical outcome in various hematolytic diseases. To simulate and reconstruct the molecular events associated with hemin exposure on circulating monocytes, we employed a THP-1 cell line based in vitro model. Flow cytometry and Western blot analyses were subsequently applied. Hemin-treated THP-1 produced ROS in a dose-dependent manner which resulted in 10-30 % of cell death primarily through apoptosis. Surviving cells induced autophagy which too was ROS-dependent, as revealed by application of N-acetyl-L-cysteine. Hemin-mediated autophagy promoted differentiation of CD14+ THP-1 cells into CD11b+ macrophages. Application of 3-methyladenine, reinforced that differentiation of THP-1 was an autophagy-dependent process. It was revealed that despite a higher polarization towards M2-macrophage, synthesis of pro-inflammatory cytokines namely TNF-α, IL-1A, IL-2, IL-8 and IL-17A predominated. IL-6, a pleiotropic cytokine, was also elevated. It may thus be surmised that hemin-induced pro-inflammatory response in THP-1 is downstream to ROS-dependent autophagy and monocyte differentiation. This finding is translationally meaningful as hemin is already approved by FDA for amelioration of acute porphyria and is actively considered as a therapeutic agent for other diseases. This study underscores the need of further research untangling the reciprocal regulation of inflammatory signaling and autophagy under oxidative stress.

Crystal structure of the Ate1 arginyl-tRNA-protein transferase and arginylation of N-degron substrates.

N-degron pathways are proteolytic systems that target proteins bearing N-terminal (Nt) degradation signals (degrons) called N-degrons. Nt-Arg of a protein is among Nt-residues that can be recognized as destabilizing ones by the Arg/N-degron pathway. A proteolytic cleavage of a protein can generate Arg at the N terminus of a resulting C-terminal (Ct) fragment either directly or after Nt-arginylation of that Ct-fragment by the Ate1 arginyl-tRNA-protein transferase (R-transferase), which uses Arg-tRNAArg as a cosubstrate. Ate1 can Nt-arginylate Nt-Asp, Nt-Glu, and oxidized Nt-Cys* (Cys-sulfinate or Cys-sulfonate) of proteins or short peptides. Ate1 genes of fungi, animals, and plants have been cloned decades ago, but a three-dimensional structure of Ate1 remained unknown. A detailed mechanism of arginylation is unknown as well. We describe here the crystal structure of the Ate1 R-transferase from the budding yeast Kluyveromyces lactis. The 58-kDa R-transferase comprises two domains that recognize, together, an acidic Nt-residue of an acceptor substrate, the Arg residue of Arg-tRNAArg, and a 3'-proximal segment of the tRNAArg moiety. The enzyme's active site is located, at least in part, between the two domains. In vitro and in vivo arginylation assays with site-directed Ate1 mutants that were suggested by structural results yielded inferences about specific binding sites of Ate1. We also analyzed the inhibition of Nt-arginylation activity of Ate1 by hemin (Fe3+-heme), and found that hemin induced the previously undescribed disulfide-mediated oligomerization of Ate1. Together, these results advance the understanding of R-transferase and the Arg/N-degron pathway.

The subtilisin-like protease furin regulates hemin-induced CD63 surface expression on platelets.

Accumulation of free heme B in the plasma can be the result of severe hemolytic events, when the scavenger system for free hemoglobin and heme B is overwhelmed. Free heme B can be oxidized into toxic hemin, which has been proven to activate platelet degranulation and aggregation and promote thrombosis. In the present study we analyzed the effect of hemin on the activation-mediated lysosomal degranulation and CD63 surface expression on platelets using classic flow cytometry and fluorescence microscopy techniques. Classical platelet activators were used as control to distinguish the novel effects of hemin from known activation pathways. CD63 is a tetraspanin protein, also known as lysosomal-associated membrane protein 3 or LAMP-3. In resting platelets CD63 is located within the membrane of delta granules and lysosomes of platelet, from where it is integrated into the platelet outer membrane upon stimulation. We were able to show that hemin like the endogenous platelet activators ADP, collagen or thrombin does provoke CD63 re-localization. Interestingly, only hemin-induced CD63 externalization is dependent on the subtilisin-like pro-protein convertase furin as shown by inhibitor experiments. Furthermore, we were able to demonstrate that hemin induces lysosome secretion, a source of the hemin-mediated CD63 presentation. Again, only the hemin-induced lysosome degranulation is furin dependent. In summary we have shown that the pro-protein convertase furin plays an important role in hemin-mediated lysosomal degranulation and CD63 externalization.

In vitro Production of Hemin-Based Artificial Metalloenzymes.

Developing enzyme alternatives is pivotal to improving and enabling new processes in biotechnology and industry. Artificial metalloenzymes (ArMs) are combinations of protein scaffolds with metal elements, such as metal nanoclusters or metal-containing molecules with specific catalytic properties, which can be customized. Here, we engineered an ArM based on the consensus tetratricopeptide repeat (CTPR) scaffold by introducing a unique histidine residue to coordinate the hemin cofactor. Our results show that this engineered system exhibits robust peroxidase-like catalytic activity driven by the hemin. The expression of the scaffold and subsequent coordination of hemin was achieved by recombinant expression in bulk and through in vitro transcription and translation systems in water-in-oil drops. The ability to synthesize this system in emulsio paves the way to improve its properties by means of droplet microfluidic screenings, facilitating the exploration of the protein combinatorial space to discover improved or novel catalytic activities.

Hemin competitively inhibits HSPA8 ATPase activity mitigating its foldase function.

Hemolysis in red blood cells followed by hemoglobin degradation results in high hemin levels in the systemic circulation. Such a level of hemin is disastrous for cells and tissues and is considerably responsible for the pathologies of diseases like severe malaria. Hemin's hydrophobic chemical nature and structure allow it to bind several proteins leading to their functional modification. Such modifications in physiologically relevant proteins can have a high impact on various cellular processes. HSPA8 is a chaperone that has a protective role in oxidative stress by aiding protein refolding. Through ATPase activity assays we found that hemin can competitively inhibit ATP hydrolysis by the chaperone HSPA8. Hemin as such does not affect the structural integrity of the protein which is inferred from CD spectroscopy and Gel filtration but it hinders the ATP-dependent foldase function of the chaperone. HSPA8 was not able to cause the refolding of the model protein lysozyme in the presence of hemin. The loss in HSPA8 function was due to competition between hemin and ATP as the chaperone was able to regain the foldase function when the concentration of ATP was gradually increased with hemin present at the inhibitory concentration. In-silico studies to establish the competition for the specific binding site revealed that ATP was unable to replace hemin from the ATP binding pocket of HSPA8 and was forced to form a non-specific and unstable complex. In-vitro isothermal calorimetry revealed that the affinity of ATP for binding to HSPA8 was reduced 22 folds in the presence of hemin. The prevention of HSPA8's cytoprotective function by hemin can be a major factor contributing to the overall cellular damage during hemin accumulation in the case of severe malaria and other hemolytic diseases.

Interaction analysis of RNA G-quadruplex with ligands and in situ imaging application.

RNA G4, as an integral branch of G4 structure, possesses distinct interactions with ligands compared to the common DNA G4, thus the investigation of RNA G4/ligand interactions might be considered as a fresh breakthrough to improve the biosensing performance of G4/ligand system. In this study, we comparatively explored the structural and functional mechanisms of RNA G4 and DNA G4 in the interaction with ligands, hemin and thioflavin T (ThT), utilizing the classical PS2.M sequence as a model. We found that although the catalytic performance of RNA G4/hemin system was lower than DNA G4/hemin, RNA G4/ThT fluorescence system exhibited a significant improvement (2∼3-fold) compared to DNA G4/ThT, and adenine modification could further enhance the signaling. Further, by exploring the interaction between RNA G4 and ThT, we deemed that RNA G4 and ThT were stacked in a bimolecular mode compared to single-molecule binding of DNA G4/ThT, thus more strongly limiting the structural spin in ThT excited state. Further, RNA G4/ThT displayed higher environmental tolerance and lower ion dependence than DNA G4/ThT. Finally, we employed RNA G4/ThT as a highly sensitive label-free fluorescent signal output system for in situ imaging of isoforms BCR-ABL e13a2 and e14a2. Overall, this study successfully screened a high-performance RNA G4 biosensing system through systematic RNA G4/ligands interaction studies, which was expected to provide a promising reference for subsequent G4/ligand research.

A simple and sensitive colorimetric approach for mecA gene analysis via exonuclease-III catalyzed signal cascade.

Analysis of mecA gene in Staphylococcus aureus (S. aureus) is essential for controlling infections in intensive care units (ICU) and preventing the use of ineffectual empirical treatments. However, quantitative determination of the mecA gene remains difficult. Herein, we propose a simple and sensitive colorimetric approach by integrating exonuclease-III (Exo-III) assisted signal cascade and G-quadruplex/hemin DNAzymes (G4 DNAzymes) catalyzed 2,2'-azino-bis (3-ethylben-zothiazoline-6-sulfonic acid) (ABTS) based color reaction. In this method, signal amplification does not necessitate the use of complex experimental components, such as multiple enzymes and primer design, while still maintaining a high signal amplifying efficiency. Therefore, the method has a broad mecA gene detection range from 10 fM to 1 nM and a low limit of detection down to 3.4 fM level. Taking the merit of simplicity and high sensitivity, the approach is promising in analyzing mecA gene in S. aureus and diagnosing infections.

Intravenous Hemin, a potential heme oxygenase-1 activator, does not protect from post-ERCP acute pancreatitis in humans: Results of a randomized multicentric multinational placebo-controlled trial.

OBJECTIVE: Hemin, a heme oxygenase 1 activator has shown efficacy in the prevention and treatment of acute pancreatitis in mouse models. We conducted a randomized controlled trial (RCT) to assess the protective effect of Hemin administration to prevent post-endoscopic retrograde cholangiopancreatography (ERCP) pancreatitis (PEP) in patients at risk. METHODS: In this multicenter, multinational, placebo-controlled, double-blind RCT, we assigned patients at risk for PEP to receive a single intravenous dose of Hemin (4 mg/kg) or placebo immediately after ERCP. Patients were considered to be at risk on the basis of validated patient- and/or procedure-related risk factors. Neither rectal NSAIDs nor pancreatic stent insertion were allowed in randomized patients. The primary outcome was the incidence of PEP. Secondary outcomes included lipase elevation, mortality, safety, and length of stay. RESULTS: A total of 282 of the 294 randomized patients had complete follow-up. Groups were similar in terms of clinical, laboratory, and technical risk factors for PEP. PEP occurred in 16 of 142 patients (11.3%) in the Hemin group and in 20 of 140 patients (14.3%) in the placebo group (p = 0.48). Incidence of severe PEP reached 0.7% and 4.3% in the Hemin and placebo groups, respectively (p = 0.07). Significant lipase elevation after ERCP did not differ between groups. Length of hospital stay, mortality and severe adverse events rates were similar between groups. CONCLUSION: We failed to detect large improvements in PEP rate among participants at risk for PEP who received IV hemin immediately after the procedure compared to placebo. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov number, NCT01855841).

Both hemoglobin and hemin cause damage to retinal pigment epithelium through the iron ion accumulation.

Subretinal hemorrhages result in poor vision and visual field defects. During hemorrhage, several potentially toxic substances are released from iron-based hemoglobin and hemin, inducing cellular damage, the detailed mechanisms of which remain unknown. We examined the effects of excess intracellular iron on retinal pigment epithelial (RPE) cells. A Fe2+ probe, SiRhoNox-1 was used to investigate Fe2+ accumulation after treatment with hemoglobin or hemin in the human RPE cell line ARPE-19. We also evaluated the production of reactive oxygen species (ROS) and lipid peroxidation. Furthermore, the protective effect of-an iron chelator, 2,2'-bipyridyl (BP), and ferrostatin-1 (Fer-1) on the cell damage, was evaluated. Fe2+ accumulation increased in the hemoglobin- or hemin-treated groups, as well as intracellular ROS production and lipid peroxidation. In contrast, BP treatment suppressed RPE cell death, ROS production, and lipid peroxidation. Pretreatment with Fer-1 ameliorated cell death in a concentration-dependent manner and suppressed ROS production and lipid peroxidation. Taken together, these findings indicate that hemoglobin and hemin, as well as subretinal hemorrhage, may induce RPE cell damage and visual dysfunction via intracellular iron accumulation.

A Fluorescence Biosensor Based on Carbon Quantum Dots Prepared from Pomegranate Peel and T-Hg2+-T Mismatch for Hg2+ Detection.

Mercury ions (Hg2+) can cause damage to human health, and thus, the study of the detection of Hg2+ is extraordinarily important in daily life. This work reported a fluorescence biosensor for the detection of Hg2+. The key point of this strategy was that the fluorescence of carbon quantum dots made from pomegranate peel (P-CQDs) was quenched by hemin, and restored after G-quadruplex binding with hemin. The presence of Hg2+ caused thymine (T)-rich DNA fragments to form T-Hg2+-T mismatches, and this change allowed the release of G-quadruplex. G-quadruplex could change the fluorescence of hemin/P-CQDs. P-CQDs exhibited excellent properties through characterization analysis, such as transmission electron microscope, X-ray photoelectron spectroscopy and Fourier transform infrared. This proposed fluorescence detection strategy established the linear ranges of Hg2+ from 1 nM to 50 nM. In conclusion, this simple biosensor had the advantages of strong sensitivity, high selectivity, and low cost for Hg2+ detection in environmental water samples.

Hemin regulates platelet clearance in hemolytic disease by binding to GPIbα.

Hemolysis is associated with thrombosis and vascular dysfunction, which are the pathological components of many diseases. Hemolytic products, including hemoglobin and hemin, activate platelets (PLT). Despite its activation, the effect of hemolysis on platelet clearance remains unclear, It is critical to maintain a normal platelet count and ensure that circulating platelets are functionally viable. In this study, we used hemin, a degradation product of hemoglobin, as a potent agonist to treat platelets and simulate changes in vivo in mice. Hemin treatment induced activation and morphological changes in platelets, including an increase in intracellular Ca2+ levels, phosphatidylserine (PS) exposure, and cytoskeletal rearrangement. Fewer hemin-treated platelets were cleared by macrophages in the liver after transfusion than untreated platelets. Hemin bound to glycoprotein Ibα (GPIbα), the surface receptor in hemin-induced platelet activation and aggregation. Furthermore, hemin decreased GPIbα desialylation, as evidenced by reduced Ricinus communis agglutinin I (RCA- I) binding, which likely extended the lifetime of such platelets in vivo. These data provided new insight into the mechanisms of GPIbα-mediated platelet activation and clearance in hemolytic disease.

What is the context? Hemolysis is a primary hematological disease. Hemolysis is a pathological complication of several diseases.Hemin, a degradation product of cell-free hemoglobin, has been proven to be a more potent agonist than hemoglobin for directly activating platelets.Platelet membrane glycoproteins (GP), including GPIb-IX and GPIIb/IIIa complexes, play crucial roles in platelet hemostasis.Desialylation (loss of sialic acid residues) of GPIbα, is believed to regulate physiological platelet clearance through liver macrophages and hepatocytes.What is new? In this study, we evaluated the effects of hemolysis on platelet clearance. We first analyzed the influence of hemin at 0-50 µM on platelets in vitro before exploring the mechanism underlying hemin-induced platelet activation and its role in platelet clearance in vitro and in vivo.Our analyses suggest that: Hemin bound to GPIbα on the platelet surface with high affinity.Platelet clearance occurred slowly in the liver and spleen after hemin treatment.Platelets exhibited significant significantly reduced GPIbα surface expression and desialylation after hemin treatment.Platelets exhibited significant significantly reduced GPIbα surface expression and desialylation after hemin treatment.What is the impact? This study provides new insights into the role of hemin in the mechanisms of GPIbα-mediated platelets activation and clearance in diseases associated with hemolysis.

Anticancer Effect of Hemin through ANO1 Inhibition in Human Prostate Cancer Cells.

Anoctamin1 (ANO1), a calcium-activated chloride channel, is overexpressed in a variety of cancer cells, including prostate cancer, and is involved in cancer cell proliferation, migration, and invasion. Inhibition of ANO1 in these cancer cells exhibits anticancer effects. In this study, we conducted a screening to identify novel ANO1 inhibitors with anticancer effects using PC-3 human prostate carcinoma cells. Screening of 2978 approved and investigational drugs revealed that hemin is a novel ANO1 inhibitor with an IC50 value of 0.45 µM. Notably, hemin had no significant effect on intracellular calcium signaling and cystic fibrosis transmembrane conductance regulator (CFTR), a cyclic AMP (cAMP)-regulated chloride channel, and it showed a weak inhibitory effect on ANO2 at 3 µM, a concentration that completely inhibits ANO1. Interestingly, hemin also significantly decreased ANO1 protein levels and strongly inhibited the cell proliferation and migration of PC-3 cells in an ANO1-dependent manner. Furthermore, it strongly induced caspase-3 activation, PARP degradation, and apoptosis in PC-3 cells. These findings suggest that hemin possesses anticancer properties via ANO1 inhibition and could be considered for development as a novel treatment for prostate cancer.

Selective Hemin Binding by a Non-G-quadruplex Aptamer with Higher Affinity and Better Peroxidase-like Activity.

Previous aptamers for porphyrins and metalloporphyrins were all guanine-rich sequences that can fold in G-quadruplex structures. Due to stacking-based binding, these aptamers can hardly tell different porphyrins apart, and they can also bind other planar molecules, hindering their practical applications. In this work, we used the capture selection method to obtain aptamers for hemin and protoporphyrin IX (PPIX). The hemin aptamer (Hem1) features two highly conserved repeating binding loops, and it cannot form a G-quadruplex, which was supported by its Mg2+ -dependent but K+ -independent hemin binding and CD spectroscopy. Isothermal titration calorimetry revealed much higher enthalpy change for the new aptamer, and the best aptamer showed a Kd of 43 nM hemin. Hem1 can also enhance the peroxidase-like activity of hemin. This work demonstrates that aptamers have alternative ways to bind porphyrins allowing selective recognition of different porphyrins.

Regulatory effects of Hemin on prevention and rescue of salt stress in rapeseed (Brassica napus L.) seedlings.

BACKGROUND: Salt stress severely restricts rapeseed growth and productivity. Hemin can effectively alleviate salt stress in plants. However, the regulatory effect of Hemin on rapeseed in salt stress is unclear. Here, we analyzed the response and remediation mechanism of Hemin application to rapeseed before and after 0.6% (m salt: m soil) NaCl stress. Experiment using two Brassica napus (AACC, 2n = 38) rapeseed varieties Huayouza 158R (moderately salt-tolerant) and Huayouza 62 (strongly salt-tolerant). To explore the best optional ways to improve salt stress resistance in rapeseed. RESULTS: Our findings revealed that exogenous application of Hemin enhanced morph-physiological traits of rapeseed and significantly attenuate the inhibition of NaCl stress. Compared to Hemin (SH) treatment, Hemin (HS) significantly improved seedlings root length, seedlings height, stem diameter and accumulated more dry matter biomass under NaCl stress. Moreover, Hemin (HS) significantly improved photosynthetic efficiency, activities of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and decreased electrolyte leakage (EL) and malondialdehyde (MDA) content, thus resulting in the alleviation of oxidative membrane damage. Hemin (HS) showed better performance than Hemin (SH) under NaCl stress. CONCLUSION: Hemin could effectively mitigate the adverse impacts of salt stress by regulating the morph-physiological, photosynthetic and antioxidants traits of rapeseed. This study may provide a basis for Hemin to regulate cultivated rapeseed salt tolerance and explore a better way to alleviate salt stress.

Specific Chemiluminescence Imaging and Enhanced Photodynamic Therapy of Bacterial Infections by Hemin-Modified Carbon Dots.

Antibacterial photodynamic therapy (aPDT) is a promising antibiotics-alternative strategy for bacterial infectious diseases, which features broad-spectrum antibacterial activity with a low risk of inducing bacterial resistance. However, clinical applications of aPDT are still hindered by the hydrophobicity-caused inadequate photodynamic activity of conventional photosensitizers and the hypoxic microenvironment of bacterial infections. To address these problems, herein, a promising strategy is developed to achieve specific chemiluminescence (CL) imaging and enhanced PDT of bacterial infections using hemin-modified carbon dots (H-CDs). The H-CDs can be facilely prepared and exhibit favorable water solubility, augmented photodynamic activity, and unique peroxidase-mimicking capacity. Compared with the free CDs, the photodynamic efficacy of H-CDs is significantly augmented due to the increased electron-hole separation efficiency. Moreover, the peroxidase catalytic performance of H-CDs enables not only infection identification via bacterial infection microenvironment-responsive CL imaging but also oxygen self-supplied aPDT with hypoxia-relief-enhanced bacteria inactivation effects. Finally, the enhanced aPDT efficiencies of H-CDs are validated in both in vivo abscess and infected wound models. This work may provide an effective antibacterial platform for the selective imaging-guided treatment of bacterial infections.

Nitrite decreases sickle hemoglobin polymerization in vitro independently of methemoglobin formation.

The root cause of sickle cell disease (SCD) is the polymerization of sickle hemoglobin (HbS) leading to sickling of red blood cells (RBC). Earlier studies showed that in patients with SCD, high-dose nitrite inhibited sickling, an effect originally attributed to HbS oxidation to methemoglobin-S even though the anti-sickling effect did not correlate with methemoglobin-S levels. Here, we examined the effects of nitrite on HbS polymerization and on methemoglobin formation in a SCD mouse model. In vitro, at concentrations higher than physiologic (>1 µM), nitrite increased the delay time for polymerization of deoxygenated HbS independently of methemoglobin-S formation, which only occurred at much higher concentrations (>300 µM). In vitro, higher nitrite concentrations oxidized 100% of normal hemoglobin A (HbA), but only 70% of HbS. Dimethyl adipimidate, an anti-polymerization agent, increased the fraction of HbS oxidized by nitrite to 82%, suggesting that polymerized HbS partially contributed to the oxidation-resistant fraction of HbS. At low concentrations (10 µM-1 mM), nitrite did not increase the formation of reactive oxygen species but at high concentrations (10 mM) it decreased sickle RBC viability. In SCD mice, 4-week administration of nitrite yielded no significant changes in methemoglobin or nitrite levels in plasma and RBC, however, it further increased leukocytosis. Overall, these data suggest that nitrite at supra-physiologic concentrations has anti-polymerization properties in vitro and that leukocytosis is a potential nitrite toxicity in vivo. Therefore, to determine whether the anti-polymerization effect of nitrite observed in vitro underlies the decreases in sickling observed in patients with SCD, administration of higher nitrite doses is required.

Heme oxygenase-1 therapy attenuates muscle atrophy following global brachial plexus avulsion in juvenile rats.

INTRODUCTION/AIMS: Brachial plexus injury can seriously affect distal target muscle function, and long-term denervation leads to irreversible structural damage. In the present study, we examined the effect of hemin, a heme oxygenase-1 (HO-1) inducer, on intrinsic forepaw muscle atrophy induced by pan-plexus injury in juvenile rats, as well as its underlying mechanism. METHODS: A global brachial plexus avulsion (GBPA) model of rat was established, and thirty 6-wk-old male rats were randomly divided into five groups: control, GBPA plus scramble small intering RNA (siRNA), GBPA plus scramble siRNA plus hemin, GBPA plus HO-1 siRNA, and GBPA plus HO-1 siRNA plus hemin. Hemin (50 mg/kg) was administered intraperitoneally once daily and the siRNA (5 µg) was injected intramuscularly twice a week. Intrinsic forepaw muscles were used for analysis. Myofiber cross-sectional area (CSA), capillary-to-fiber ratio (C/F), and fiber-type composition were assessed. The levels of inflammatory factors, ubiquitin-protein ligases, and autophagy-related proteins were also measured. RESULTS: We found that hemin treatment could effectively ameliorate denervated intrinsic forepaw muscle atrophy and suppress type I to II myofiber-type conversion. Hemin treatment failed to prevent muscle capillary loss after denervation. The levels of inflammatory factors (tumor necrosis factor alpha [TNFα] and interleukin 6 [IL-6]), ubiquitin-protein ligases (MuRF-1 and MAFbx), and autophagy-related proteins (BNIP3 and LC3B-II/I ratio) were increased by denervation and HO-1 therapy attenuated the increment. DISCUSSION: Upregulation of HO-1 might potentially be an effective strategy to alleviate denervation-related muscle atrophy and might be a promising adjunctive treatment to improve hand function in children with pan-plexus injury.

Peptide nanotube/hemin composite with enhanced peroxidase activity for the detection of dopamine in food and drug samples.

Inspired by natural enzymes, artificial enzymes have been widely studied due to their ease of mass production, robustness to harsh environments and high stability. In this work, a peptide nanotube/hemin composite (KL@hemin) as an artificial enzyme was prepared by immobilizing hemin onto self-assembled peptide nanotubes (PNTs). The successful loading of hemin was determined by a series of characterizations. The multiple noncovalent interactions between the PNTs and hemin endow KL@hemin with strong stability. Subsequent enzyme activity tests showed that the prepared KL@hemin exhibited enhanced peroxidase activity. Further experiments indicate that PNTs as carriers can not only protect hemin from dimerization to maintainenzyme activity but also increase the affinity of hemin to the substrate for faster binding and accelerate mass transfer, thus promoting the whole catalytic process. Coupled with a peroxidase-catalyzed chromogenic system, a colorimetric method for dopamine detection was constructed based on KL@hemin. The strategy shows high sensitivity and selectivity and has been applied to the determination of dopamine in dopamine injection and meat samples.

Hemin enhances radiosensitivity of lung cancer cells through ferroptosis.

The principle underlying radiotherapy is to kill cancer cells while minimizing the harmful effects on non-cancer cells, which has still remained as a major challenge. In relation, ferroptosis has recently been proposed as a novel mechanism of radiation-induced cell death. In this study, we investigated and demonstrated the role of Hemin as an iron overloading agent in the generation of reactive oxygen species (ROS) induced by ionizing radiation in lung cancer and non-cancer cells. It was found that the presence of Hemin in irradiated lung cancer cells enhanced the productivity of initial ROS, resulting in lipid peroxidation and subsequent ferroptosis. We observed that application of Hemin as a co-treatment increased the activity of GPx4 degradation in both cancer and normal lung cells. Furthermore, Hemin protected normal lung cells against radiation-induced cell death, in that it suppressed ROS after radiation, and boosted the production of bilirubin which was a lipophilic ROS antioxidant. In addition, we demonstrated significant FTH1 expression in normal lung cells when compared to lung cancer cells, which prevented iron from playing a role in increasing IR-induced cell death. Our findings demonstrated that Hemin had a dual function in enhancing the radiosensitivity of ferroptosis in lung cancer cells while promoting cell survival in normal lung cells.