Pro-healing potential of hemin: an inducer of heme oxygenase-1

Multifunctional Self-Healing Carbon Dot-Gelatin Bioadhesive: Improved Tissue Adhesion with Simultaneous Drug Delivery, Optical Tracking, and Photoactivated Sterilization

Bioadhesives with all-inclusive properties for simultaneous strong and robust adhesion, cohesion, tracking, drug delivery, self-sterilization, and nontoxicity are still farfetched. Herein, a carbon dot (CD) is made to infuse each of the above-desired aspects with gelatin, an inexpensive edible protein. The CD derived through controlled hydrothermal pyrolysis of dopamine and terephthaldehyde retained -NH2, -OH, -COOH, and, most importantly, -CHO functionality on the CD surface for efficient skin adhesion and cross-linking. Facile fabrication of CD-gelatin bioadhesive through covalent conjugation of -CHO of the CD with -NH2 of gelatin through Schiff base formation was accomplished. This imparts remarkable self-healing attributes as well as excellent adhesion and cohesion evident from physicomechanical analysis in a porcine skin model. Improved porosity of the bioadhesive allows loading hemin as a model drug whose disembarkment is tracked with intrinsic CD photoluminescence. In a significant achievement, antibiotic-free self-sterilization of bioadhesive is demonstrated through visible light (white LED, 23 W)-irradiated photosensitization of the CD to produce reactive oxygen species for annihilation of both Gram-positive and Gram-negative bacteria with exceptional efficacy (99.9%). Thus, a comprehensive CD-gelatin bioadhesive for superficial and localized wound management is reported as a promising step for the transformation of the bioadhesive domain through controlled nanotization for futuristic clinical translations.

Iron metabolism in the cell as a target in the development of potential antimicrobial and antiviral agents

The search and creation of innovative antimicrobial drugs, acting against resistant and multiresistant strains of bacteria and fungi, are one of the most important tasks of modern bioorganic chemistry and pharmaceuticals. Since iron is essential for the vital activity of almost all organisms, including mammals and bacteria, the proteins involved in its metabolism can serve as potential targets in the development of new promising antimicrobial agents. Such targets include endogenous mammalian biomolecules, heme oxygenases, siderophores, protein 24p3, as well as bacterial heme oxygenases and siderophores. Other proteins that are responsible for the delivery of iron to cells and its balance between bacteria and the host organism also attract certain particular interest. The review summarizes data on the development of inhibitors and inducers (activators) of heme oxygenases, selective for mammals and bacteria, and considers the characteristic features of their mechanisms of action and structure. Based on the reviewed literature data, it was concluded that the use of hemin, the most powerful hemooxygenase inducer, and its derivatives as potential antimicrobial and antiviral agents, in particular against COVID-19 and other dangerous infections, would be a promising approach. In this case, an important role is attributed to the products of hemin degradation formed by heme oxygenases in vitro and in vivo. Certain attention has been paid to the data on the antimicrobial action of iron-free protoporphyrinates, namely complexes with Co, Ga, Zn, Mn, their advantages and disadvantages compared to hemin. Modification of the well-known antibiotic ceftazidime with a siderophore molecule increased its effectiveness against resistant bacteria.

Heme Oxygenase-1 as Therapeutic Target for Diabetic Foot Ulcers

A diabetic foot ulcer (DFU) is one of the major complications of diabetes. Wound healing under diabetic conditions is often impaired. This is in part due to the excessive oxidative stress, prolonged inflammation, immune cell dysfunction, delayed re-epithelialization, and decreased angiogenesis present at the wound site. As a result of these multifactorial impaired healing pathways, it has been difficult to develop effective therapeutic strategies for DFU. Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in heme degradation generating carbon monoxide (CO), biliverdin (BV) which is converted into bilirubin (BR), and iron. HO-1 is a potent antioxidant. It can act as an anti-inflammatory, proliferative, angiogenic and cytoprotective enzyme. Due to its biological functions, HO-1 plays a very important role in wound healing, in part mediated through the biologically active end products generated by its enzymatic activity, particularly CO, BV, and BR. Therapeutic strategies involving the activation of HO-1, or the topical application of its biologically active end products are important in diabetic wound healing. Therefore, HO-1 is an attractive therapeutic target for DFU treatment. This review will provide an overview and discussion of the importance of HO-1 as a therapeutic target for diabetic wound healing.

Stereological and molecular studies on the effects of Ferula persica extract on wound healing in rats

BACKGROUND

Ferula persica is one of the most important traditional medicinal plants that is used to treat various diseases such as diabetes, backache and rheumatism. The aim of the present study was to evaluate the anti-inflammatory and wound healing potential of F. persica using stereological and molecular methods in experimental models.

METHODS

In the present study, two wound models (circular excision and linear incision) were used. Male Wistar rats were divided into four groups (n = 16), including control, vehicle treated, treated with F. persica extract ointment (5% w/w) and treated with the reference drug (Madecassol). All the animals were treated topically once a day. The circular and linear wounds were treated for 9 and 17 days, respectively. At the end of the study, samples from wounds area were harvested for histology, stereology, immunohistochemistry and molecular assessments to determine the in vivo healing potential and anti-inflammatory activity.

RESULTS

We observed significant recovery in macroscopic evaluation of wound healing in the F. persica extract treated group compared with the control and vehicle treated groups (p < 0.05). Histological and stereological assessments showed complete repair of the epidermal layer, increasing fibroblast cells and collagen density, decreasing inflammatory cells and a remarkable degree of neovascularization by determining length density of blood vessels in the extract group, which were significant as compared to the control and vehicle treated groups (p < 0.05). Expressions of TNF-α and TGF-β were found to be decreased and increased (p > 0.05, p < 0.05, respectively), in the extract treated group as compared to the control and vehicle treated groups. Also, greater COX-2 expression could be detected in the control and vehicle treated groups, which was significantly attenuated in the extract group.

CONCLUSION

Our results confirm that the F. persica extract is a valuable source of antioxidant and anti-inflammatory activity and can allow damaged tissue in wounds to recover markedly.

Hemin attenuated oxidative stress and inflammation to improve wound healing in diabetic rats

Oxidative stress and persistent inflammation play crucial role in the progression of diabetic wound complications. Hemeoxgenase-1 (HO-1) by degrading hemin has been shown to display anti-oxidant and anti-inflammatory effects. Further, hemin is a potent HO-1 inducer. Thus, the current study was aimed to evaluate the effect of topical application of hemin on diabetic wound in rats. Four hundred square millimeter open excision wound were created 2 weeks after induction of diabetes with single intraperitoneal injection of streptozotocin (60 mg/kg), and the diabetic rats were divided into three groups namely diabetic control, hemin, and tin protoporphyrin (SnPPIX). Ointment base, hemin (0.5% in ointment base), and SnPPIX (0.5% in ointment base) were applied topically to wounded area in diabetic control, hemin, and SnPPIX group rats, respectively, twice daily for 19 days. Hemin significantly increased the wound contraction in comparison to control and SnPPIX-treated rats. Time-dependent analysis revealed significant increase in anti-oxidants with concomitant decrease in oxidants in hemin-treated rats as compared to diabetic control rats. Further, mRNA expression decreased for inflammatory cytokine and increased for anti-inflammatory cytokine in hemin group as compared to diabetic control rats. Expression of HO-1 also increased in hemin group as compared to diabetic control rats. However, SnPPIX group results were in disagreement with results of hemin which is clearly reflected in histopathology. Results indicate the ability of hemin to accelerate wound healing in diabetic rats by combating inflammation and oxidative stress probably via HO-1.

Low concentrations of clarithromycin upregulate cellular antioxidant enzymes and phosphorylation of extracellular signal-regulated kinase in human small airway epithelial cells

BACKGROUND

It is well known that low-dose, long-term macrolide therapy is effective against chronic inflammatory airway diseases. Oxidative stress is considered to be a key pathogenesis factor in those diseases. However, the mechanism of action of low-dose, long-term macrolide therapy remains unclear. We have reported that clarithromycin (CAM), which is a representative macrolide antibiotic, could inhibit hydrogen peroxide (H2O2)-induced reduction of the glutathione (GSH)/glutathione disulfide (GSSG) ratio in human small airway epithelial cells (SAECs), via the maintenance of GSH levels through an effect on γ-glutamylcysteine synthetase (γ-GCS) expression. In this study, we examined the influence of CAM against H2O2-induced activities of cellular antioxidant enzymes and phosphorylated extracellular signal regulatory kinase (p-ERK) using SAECs, the main cells involved in chronic airway inflammatory diseases.

METHODS

SAECs were pretreated with CAM (1, 5, and 10 μM) for 72 h, and subsequently exposed to H2O2 (100 μM) for 0.5-2 h. Levels of GSH and GSSG, and activities of glutathione peroxidase (GPx)-1, glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), heme oxygenase (HO)-1 and p-ERK were assayed. mRNA expressions of GPx-1 and HO-1 were measured using the real-time reverse transcription polymerase chain reaction (RT-PCR). Tukey's multiple comparison test was used for analysis of statistical significance.

RESULTS

Pretreatment with low-dose (1 and 5 μM) CAM for 72 h inhibited H2O2-induced reductions of GPx-1, GR, SOD, CAT and HO-1 activities, and mRNA expressions of GPx-1 and HO-1, and improved the GSH/GSSG ratio. However, these alterations were not observed after pretreatment with high-dose (10 μM) CAM, which suppressed phosphorylation of cell proliferation-associated ERK to cause a significant (p < 0.01) decrease in cell viability.

CONCLUSIONS

CAM is efficacious against deterioration of cellular antioxidant enzyme activity caused by oxidative stress under low-dose, long-term treatment conditions. On the other hand, pretreatment with high-dose CAM suppressed phosphorylation of cell proliferation-associated ERK and decreased cell viability. The present study may provide additional evidence as to why low-dose, long-term administration of macrolides is effective for treating chronic inflammatory airway diseases.

The Role of Macrophages in Acute and Chronic Wound Healing and Interventions to Promote Pro-wound Healing Phenotypes

Macrophages play key roles in all phases of adult wound healing, which are inflammation, proliferation, and remodeling. As wounds heal, the local macrophage population transitions from predominantly pro-inflammatory (M1-like phenotypes) to anti-inflammatory (M2-like phenotypes). Non-healing chronic wounds, such as pressure, arterial, venous, and diabetic ulcers indefinitely remain in inflammation—the first stage of wound healing. Thus, local macrophages retain pro-inflammatory characteristics. This review discusses the physiology of monocytes and macrophages in acute wound healing and the different phenotypes described in the literature for both in vitro and in vivo models. We also discuss aberrations that occur in macrophage populations in chronic wounds, and attempts to restore macrophage function by therapeutic approaches. These include endogenous M1 attenuation, exogenous M2 supplementation and endogenous macrophage modulation/M2 promotion via mesenchymal stem cells, growth factors, biomaterials, heme oxygenase-1 (HO-1) expression, and oxygen therapy. We recognize the challenges and controversies that exist in this field, such as standardization of macrophage phenotype nomenclature, definition of their distinct roles and understanding which phenotype is optimal in order to promote healing in chronic wounds.

Hypoglycemic, Hypolipidemic, and Wound Healing Potential of Quercetin in Streptozotocin-Induced Diabetic Rats

BACKGROUND

Among the dietary polyphenolic, quercetin is the most common compound available in vegetables and fruits. The phytochemicals are used to treat diabetic wounds and diabetes, and specifically dietary polyphenols are being extensively studied for their anti-inflammatory and antioxidant abilities.

OBJECTIVE

The objective of the study was to assess the hypoglycemic, hypolipidemic, and wound healing potential of quercetin in streptozotocin (STZ)-induced diabetic Wistar rats.

MATERIALS AND METHODS

Induction of diabetes was done by intraperitoneally administration of STZ at the dose of 55 mg/kg in Wistar rats. An excision wound was created in diabetic rats that were treated with quercetin (100 mg/kg) orally and quercetin ointment topically to evaluate the antidiabetic and wound healing potential of quercetin.

RESULTS

Repeated oral administration of quercetin along with topical application of quercetin ointment in diabetic rats normalized the altered blood glucose, hydroxyproline, and glucosamine levels. Topical application of quercetin ointment alone on the excised wound was sufficient enough to heal the wound area in diabetic rats.

CONCLUSIONS

The result of the present study indicates that quercetin produces hypoglycemic effect in STZ-induced diabetic rats and normalized plasma lipids and protein profiles. Besides, this quercetin also has an excellent wound healing property when applied topically on the wound area in diabetic rats.

SUMMARY

Quercetin has hypoglycaemic and hypolipidemic potential in streptozotocin induced diabetes in wistar ratsDermal application along with oral administrations of quercetin has more effective in wound healing in diabetic animalsHistopathological studies of pancreas, skin and liver shows significant reduction in archaeological alterations on quercetin administrations in diabetic rats. Abbreviation used: STZ: Streptozotocin; CMC: Carboxy methyl cellulose; HDL: High density lipoproteins; LDL: low density lipoproteins.

Skin Wound Healing Potential and Mechanisms of the Hydroalcoholic Extract of Leaves and Oleoresin of Copaifera langsdorffii Desf. Kuntze in Rats

The wound healing is a complex process which, sometimes, can be a problem in public health because of the possibility of physical disability or even death. Due to the lack of a gold standard drug in skin wound treatment and aiming at the discovery of new treatments in skin repair and the mechanisms involved in the process, we used oleoresin (OR) from Copaifera langsdorffii and hydroalcoholic extract of the leaves (EH) to treat rat skin wounds. For that, male Wistar rats were divided into groups (n = 8): Lanette, Collagenase, 10% EH, or 10% OR and, after anesthesia, one wound of 2 cm was made in the back of animals. The wounds were treated once a day for 3, 7, or 14 days and the wound areas were measured. The rats were euthanized and skin samples destined to biochemical, molecular, and immunohistochemical analysis. The results showed a macroscopic retraction of the wounds of 10% EH and 10% OR creams and both treatments showed anti-inflammatory activity. Molecular and immunohistochemical results demonstrated the activity of Copaifera langsdorffii creams in angiogenesis, reepithelialization, wound retraction, and remodeling mechanisms.

Effects of Remote Ischemic Preconditioning on Heme Oxygenase-1 Expression and Cutaneous Wound Repair

Skin wounds may lead to scar formation and impaired functionality. Remote ischemic preconditioning (RIPC) can induce the anti-inflammatory enzyme heme oxygenase-1 (HO-1) and protect against tissue injury. We aim to improve cutaneous wound repair by RIPC treatment via induction of HO-1. RIPC was applied to HO-1-luc transgenic mice and HO-1 promoter activity and mRNA expression in skin and several other organs were determined in real-time. In parallel, RIPC was applied directly or 24h prior to excisional wounding in mice to investigate the early and late protective effects of RIPC on cutaneous wound repair, respectively. HO-1 promoter activity was significantly induced on the dorsal side and locally in the kidneys following RIPC treatment. Next, we investigated the origin of this RIPC-induced HO-1 promoter activity and demonstrated increased mRNA in the ligated muscle, heart and kidneys, but not in the skin. RIPC did not change HO-1 mRNA and protein levels in the wound 7 days after cutaneous injury. Both early and late RIPC did not accelerate wound closure nor affect collagen deposition. RIPC induces HO-1 expression in several organs, but not the skin, and did not improve excisional wound repair, suggesting that the skin is insensitive to RIPC-mediated protection.

N-acetyl cysteine inhibits H2O2-mediated reduction in the mineralization of MC3T3-E1 cells by down-regulating Nrf2/HO-1 pathway

There are controversial findings regarding the roles of nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway on bone metabolism under oxidative stress. We investigated how Nrf2/HO-1 pathway affects osteoblast differentiation of MC3T3-E1 cells in response to hydrogen peroxide (H₂O₂), N-acetyl cysteine (NAC), or both. Exposing the cells to H₂O₂ decreased the alkaline phosphatase activity, calcium accumulation, and expression of osteoblast markers, such as osteocalcin and runt-related transcription factor-2. In contrast, H₂O₂ treatment increased the expression of Nrf2 and HO-1 in the cells. Treatment with hemin, a chemical HO-1 inducer, mimicked the inhibitory effect of H₂O₂ on osteoblast differentiation by increasing the HO-1 expression and decreasing the osteogenic marker genes. Pretreatment with NAC restored all changes induced by H₂O₂ to near normal levels in the cells. Collectively, our findings suggest that H₂O₂-mediated activation of Nrf2/HO-1 pathway negatively regulates the osteoblast differentiation, which is inhibited by NAC. [BMB Reports 2015; 48(11): 636-641]

Mechanical Stress Changes the Complex Interplay Between HO-1, Inflammation and Fibrosis, During Excisional Wound Repair

Mechanical stress following surgery or injury can promote pathological wound healing and fibrosis, and lead to functional loss and esthetic problems. Splinted excisional wounds can be used as a model for inducing mechanical stress. The cytoprotective enzyme heme oxygenase-1 (HO-1) is thought to orchestrate the defense against inflammatory and oxidative insults that drive fibrosis. Here, we investigated the activation of the HO-1 system in a splinted and non-splinted full-thickness excisional wound model using HO-1-luc transgenic mice. Effects of splinting on wound closure, HO-1 promoter activity, and markers of inflammation and fibrosis were assessed. After seven days, splinted wounds were more than three times larger than non-splinted wounds, demonstrating a delay in wound closure. HO-1 promoter activity rapidly decreased following removal of the (epi)dermis, but was induced in both splinted and non-splinted wounds during skin repair. Splinting induced more HO-1 gene expression in 7-day wounds; however, HO-1 protein expression remained lower in the epidermis, likely due to lower numbers of keratinocytes in the re-epithelialization tissue. Higher numbers of F4/80-positive macrophages, αSMA-positive myofibroblasts, and increased levels of the inflammatory genes IL-1β, TNF-α, and COX-2 were present in 7-day splinted wounds. Surprisingly, mRNA expression of newly formed collagen (type III) was lower in 7-day wounds after splinting, whereas, VEGF and MMP-9 were increased. In summary, these data demonstrate that splinting delays cutaneous wound closure and HO-1 protein induction. The pro-inflammatory environment following splinting may facilitate higher myofibroblast numbers and increase the risk of fibrosis and scar formation. Therefore, inducing HO-1 activity against mechanical stress-induced inflammation and fibrosis may be an interesting strategy to prevent negative effects of surgery on growth and function in patients with orofacial clefts or in patients with burns.

Irradiation inhibits the maturation and mineralization of osteoblasts via the activation of Nrf2/HO-1 pathway

Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) regulates the induction of antioxidant gene expression and protects cells against oxidative injury. However, there are controversial findings regarding the roles of Nrf2 on bone metabolism under oxidative stress. The role of Nrf2 on the differentiation of radiation-exposed osteoblasts is also unclear. We investigated whether Nrf2 negatively or positively affects osteoblast differentiation in response to irradiation. Irradiation inhibited osteoblast differentiation of MC3T3-E1 cells in a dose-dependent manner. This inhibition was evidenced by the irradiation-mediated decreases in bone-like nodule formation, alkaline phosphatase (ALP) activity, calcium accumulation, and expression of osteoblast markers, such as ALP, osteocalcin, osteopontin, bone sialoprotein, osterix, and Runx2. These reductions were accompanied by increased induction of Nrf2 and heme oxygenase-1 (HO-1), accumulation of cellular oxidants, and depletion of antioxidant defense enzymes. siRNA-mediated silencing of Nrf2 markedly reversed the negative effect of irradiation on osteoblast differentiation of the cells, leading to a decrease in HO-1 and an increase in Runx2 levels. Irradiation-mediated decreases in the levels of Runx2 and osteocalcin mRNA, but not of Nrf2 protein, were also significantly inhibited by HO-1 inhibitor, zinc protoporphyrin IX. Furthermore, N-acetyl cysteine restored all of the changes induced by irradiation to near-normal levels in the cells. These results demonstrate that irradiation inhibits osteoblast differentiation and mineralization of MC3T3-E1 cells through the oxidative stress-mediated activation of Nrf2/HO-1 pathway.

Delayed cutaneous wound closure in HO-2 deficient mice despite normal HO-1 expression

Impaired wound healing can lead to scarring, and aesthetical and functional problems. The cytoprotective haem oxygenase (HO) enzymes degrade haem into iron, biliverdin and carbon monoxide. HO-1 deficient mice suffer from chronic inflammatory stress and delayed cutaneous wound healing, while corneal wound healing in HO-2 deficient mice is impaired with exorbitant inflammation and absence of HO-1 expression. This study addresses the role of HO-2 in cutaneous excisional wound healing using HO-2 knockout (KO) mice. Here, we show that HO-2 deficiency also delays cutaneous wound closure compared to WT controls. In addition, we detected reduced collagen deposition and vessel density in the wounds of HO-2 KO mice compared to WT controls. Surprisingly, wound closure in HO-2 KO mice was accompanied by an inflammatory response comparable to WT mice. HO-1 induction in HO-2 deficient skin was also similar to WT controls and may explain this protection against exaggerated cutaneous inflammation but not the delayed wound closure. Proliferation and myofibroblast differentiation were similar in both two genotypes. Next, we screened for candidate genes to explain the observed delayed wound closure, and detected delayed gene and protein expression profiles of the chemokine (C-X-C) ligand-11 (CXCL-11) in wounds of HO-2 KO mice. Abnormal regulation of CXCL-11 has been linked to delayed wound healing and disturbed angiogenesis. However, whether aberrant CXCL-11 expression in HO-2 KO mice is caused by or is causing delayed wound healing needs to be further investigated.

Pro-healing effects of bilirubin in open excision wound model in rats

Bilirubin, a by-product of heme degradation, has an important role in cellular protection. Therefore, we speculated that bilirubin could be of potential therapeutic value in wound healing. To validate the hypothesis, we used a full-thickness cutaneous wound model in rats. Bilirubin (30 mg/kg) was administered intraperitoneally every day for 9 days. The surface area of the wound was measured on days 0, 2, 4, 7 and 10 after the creation of the wound. The granulation tissue was collected on day 10 post-wounding for analysing various parameters of wound healing. Bilirubin treatment accelerated wound contraction and increased hydroxyproline and glucosamine contents. mRNA expression of pro-inflammatory factors such as intercellular cell adhesion molecule-1 (ICAM-1) and tumour necrosis factor-α (TNF-α) were down-regulated and that of anti-inflammatory cytokine interleukin-10 (IL-10) was up-regulated. The findings suggest that bilirubin could be a new agent for enhancing cutaneous wound healing.

Topical application of Acalypha indica accelerates rat cutaneous wound healing by up-regulating the expression of Type I and III collagen

ETHNOPHARMACOLOGICAL RELEVANCE

Acalypha indica Linn. (Acalypha indica) vernacularly called Kuppaimeni in Tamil, has been used as a folklore medicine since ages for the treatment of wounds by tribal people of Tamil Nadu, Southern India. The present study investigates the biochemical and molecular rationale behind the healing potential of Acalypha indica on dermal wounds in rats.

MATERIAL AND METHODS

Acalypha indica extract (40 mg/kg body weight) was applied topically once a day on full-thickness excision wounds created on rats. The wound tissue was removed and used for estimation of various biochemical and biophysical analyses and to observe histopathological changes with and with-out extract treatment. The serum levels of pro-inflammatory cytokine tumor necrosis factor (TNF-α) was measured at 12 h, 24 h, 48 h and 72 h post-wounding using ELISA. Reverse transcription-polymerase chain reaction (RT-PCR) analysis was performed to study the expression pattern of transforming growth factor [TGF-β1], collagen 1 α (I) [Col 1 α (I)] and collagen 3 α (I) [Col 3 α (I)]. Likewise, linear incision wounds were created and treated with the extract and used for tensile strength measurements.

RESULTS

Wound healing in control rats was characterized by less inflammatory cell infiltration, lack of granulation tissue formation, deficit of collagen and significant decrease in biomechanical strength of wounds. Acalypha indica treatment mitigated the oxidative stress and decreased lipid peroxidation with concomitant increase in ascorbic acid levels. It also improved cellular proliferation, increased TNF-α levels during early stages of wound healing, up-regulated TGF-β1 and elevated collagen synthesis by markedly increasing the expression of Col 1 α (I) and Col 3 α (I). Increased rates of wound contraction, epithelialization, enhanced shrinkage temperature and high tensile strength were observed in the extract treated rats.

CONCLUSION

Acalypha indica extract was shown to augment the process of dermal wound healing by its ability to increase collagen synthesis through up-regulation of key players in different phases of wound healing and by its antioxidative potential.

Heme oxygenase, inflammation, and fibrosis: the good, the bad, and the ugly?

Upon injury, prolonged inflammation and oxidative stress may cause pathological wound healing and fibrosis, leading to formation of excessive scar tissue. Fibrogenesis can occur in most organs and tissues and may ultimately lead to organ dysfunction and failure. The underlying mechanisms of pathological wound healing still remain unclear, and are considered to be multifactorial, but so far, no efficient anti-fibrotic therapies exist. Extra- and intracellular levels of free heme may be increased in a variety of pathological conditions due to release from hemoproteins. Free heme possesses pro-inflammatory and oxidative properties, and may act as a danger signal. Effects of free heme may be counteracted by heme-binding proteins or by heme degradation. Heme is degraded by heme oxygenase (HO) that exists as two isoforms: inducible HO-1 and constitutively expressed HO-2. HO generates the effector molecules biliverdin/bilirubin, carbon monoxide, and free iron/ferritin. HO deficiency in mouse and man leads to exaggerated inflammation following mild insults, and accumulating epidemiological and preclinical studies support the widely recognized notion of the cytoprotective, anti-oxidative, and anti-inflammatory effects of the activity of the HO system and its effector molecules. In this review, we address the potential effects of targeted HO-1 induction or administration of HO-effector molecules as therapeutic targets in fibrotic conditions to counteract inflammatory and oxidative insults. This is exemplified by various clinically relevant conditions, such as hypertrophic scarring, chronic inflammatory liver disease, chronic pancreatitis, and chronic graft rejection in transplantation.

Heme oxygenase-1 is associated with wheat salinity acclimation by modulating reactive oxygen species homeostasis

Heme oxygenase-1 (HO-1) has been recently identified as an endogenous signaling system in animals. In this study, HO-1 upregulation and its role in acquired salt tolerance (salinity acclimation) were investigated in wheat plants. We discovered that pretreatment with a low concentration of NaCl (25 mmol/L) not only led to the induction of HO-1 protein and gene expression, as well as enhanced HO activity, but also to a salinity acclimatory response thereafter. The effect is specific for HO-1, since the potent HO-1 inhibitor zinc protoporphyrin IX blocks the above cytoprotective actions, and the cytotoxic responses conferred by 200 mmol/L NaCl are reversed partially when HO-1 inducer hemin is added. Heme oxygenase catalytic product, carbon monoxide (CO) aqueous solution pretreatment, mimicked the salinity acclimatory responses. Meanwhile, the CO-triggered re-establishment of reactive oxygen species (ROS) homeostasis was mainly guaranteed by the induction of total and isozymatic activities, or corresponding transcripts of superoxide dismutase, ascorbate peroxidase, and cytosolic peroxidase (POD), as well as the downregulation of NADPH oxidase expression and cell-wall POD activity. A requirement of hydrogen peroxide homeostasis for HO-1-mediated salinity acclimation was also discovered. Taken together, the above results suggest that the upregulation of HO-1 expression was responsible for the observed salinity acclimation through the regulation of ROS homeostasis.