Featured article: induction of heme oxygenase with hemin improves pericardial adipocyte morphology and function in obese Zucker rats by enhancing proteins of regeneration

The relevance of the heme oxygenase system in alleviating diabetes-related hormonal and metabolic disorders

Heme oxygenase (HO) is an enzyme that catalyzes heme degradation. HO dysfunction is linked to various pathological conditions, including diabetes. Results of animal studies indicate that HO expression and activity are downregulated in experimentally induced diabetes. This is associated with severe hormonal and metabolic disturbances. However, these pathological changes have been shown to be reversed by therapy with HO activators. In animals with experimentally induced diabetes, HO was upregulated by genetic manipulation or by pharmacological activators such as hemin and cobalt protoporphyrin. Induction of HO alleviated elevated blood glucose levels and improved insulin action, among other effects. This effect resulted from beneficial changes in the main insulin-sensitive tissues, i.e., the skeletal muscle, the liver, and the adipose tissue. The action of HO activators was due to positive alterations in pivotal signaling molecules and regulatory enzymes. Furthermore, diabetes-related oxidative and inflammatory stress was reduced due to HO induction. HO upregulation was effective in various animal models of type 1 and type 2 diabetes. These data suggest the possibility of testing HO activators as a potential tool for alleviating hormonal and metabolic disorders in people with diabetes.

Effects of Dietary Ferroporphyrin Supplementation on Growth Performance, Antioxidant Capacity, Immune Response, and Oxygen-Carrying Capacity in Gibel Carp (Carassius auratus gibelio)

An eight-week experiment was conducted to study the effects of dietary ferroporphyrin (FPR) supplementation on growth performance, antioxidant capacity, immune response, and oxygen-carrying capacity in gibel carp. The results demonstrated that the addition of FPR increased the moisture content of the whole fish body. Supplementation with 0.01% FPR significantly increased the plasma albumin (ALB), total protein (TP), and total cholesterol (TC) contents. The addition of 0.03% and 0.04% FPR significantly increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, respectively, while the glucose (GLU), TC, and total triglyceride (TG) levels showed opposite trends. In terms of antioxidant capacity, the 0.03% and 0.04% dietary FPR supplementation increased malondialdehyde (MDA) levels. The activity of glutathione peroxidase (GPx) exhibited an opposite trend to MDA levels. The supplementation of 0.03% of FPR resulted in a notable reduction in mRNA expression levels of nrf2, keap1, cat, and gpx. Regarding immunity, 0.01% FPR supplementation down-regulated the expression levels of il-1β mRNA, while 0.02% FPR down-regulated il-6 and nf-κb expression levels. Furthermore, 0.02% FPR supplementation significantly up-regulated the il-10 mRNA expression levels. In terms of oxygen-carrying capacity, high levels of FPR (0.03% and 0.04%) were found to influence the epo and vegf mRNA expression. In conclusion, the incorporation of dietary 0.01-0.02% FPR improved the immune system of gibel carp without affecting their antioxidant and oxygen-carrying capacity. However, supplementation with higher levels of FPR (0.03-0.04%) led to decreased antioxidant and oxygen-carrying capacity.

The Pharmacological Effect of Hemin in Inflammatory-Related Diseases: A Systematic Review

BACKGROUND

Hemin is clinically used in acute attacks of porphyria; however, recent evidence has also highlighted its capability to stimulate the heme oxygenase enzyme, being associated with cytoprotective, antioxidant, and anti-inflammatory effects. Indeed, current preclinical evidence emphasizes the potential anti-inflammatory role of hemin through its use in animal models of disease. Nevertheless, there is no consensus about the underlying mechanism(s) and the most optimal therapeutic regimens. Therefore, this review aims to summarize, analyze, and discuss the current preclinical evidence concerning the pharmacological effect of hemin.

METHODS

Following the application of the search expression and the retrieval of the articles, only nonclinical studies in vivo written in English were considered, where the potential anti-inflammatory effect of hemin was evaluated.

RESULTS

Forty-nine articles were included according to the eligibility criteria established. The results obtained show the preference of using 30 to 50 mg/kg of hemin, administered intraperitoneally, in both acute and chronic contexts. This drug demonstrates significant anti-inflammatory and antioxidant activities considering its capacity for reducing the expression of proinflammatory and oxidative markers.

CONCLUSIONS

This review highlighted the significant anti-inflammatory and antioxidant effects of hemin, providing a clearer vision for the medical community about the use of this drug in several human diseases.

N-acetylcysteine Provides Cytoprotection in Murine Oligodendrocytes through Heme Oxygenase-1 Activity

Oligodendrocytic injury by oxidative stress can lead to demyelination, contributing to neurodegeneration. We investigated the mechanisms by which an antioxidant, N-acetylcysteine (NAC), reduces oxidative stress in murine oligodendrocytes. We used normal 158N and mutant 158JP cells with endogenously high reactive oxygen species (ROS) levels. Oxidative stress was induced in 158N cells using hydrogen peroxide (H₂O₂, 500 μM), and both cells were treated with NAC (50 µM to 500 µM). ROS production, total glutathione (GSH) and cell survival were measured 24 h after treatment. In normal cells, H₂O₂ treatment resulted in a ~5.5-fold increase in ROS and ~50% cell death. These deleterious effects of oxidative stress were attenuated by NAC, resulting in improved cell survival. Similarly, NAC treatment resulted in decreased ROS levels in 158JP cells. Characterization of mechanisms underlying cytoprotection in both cell lines revealed an increase in GSH levels by NAC, which was partially blocked by an inhibitor of GSH synthesis. Interestingly, we observed heme oxygenase-1 (HO-1), a cytoprotective enzyme, play a critical role in cytoprotection. Inhibition of HO-1 activity abolished the cytoprotective effect of NAC with a corresponding decrease in total antioxidant capacity. Our results indicate that NAC promotes oligodendrocyte survival in oxidative stress-related conditions through multiple pathways.

Inhibition of soluble epoxide hydrolase attenuates a high-fat diet-mediated renal injury by activating PAX2 and AMPK

A high-fat diet (HFD) causes obesity-associated morbidities involved in macroautophagy and chaperone-mediated autophagy (CMA). AMPK, the mediator of macroautophage, has been reported to be inactivated in HFD-caused renal injury. However, PAX2, the mediator for CMA, has not been reported in HFD-caused renal injury. Here we report that HFD-caused renal injury involved the inactivation of Pax2 and Ampk, and the activation of soluble epoxide hydrolase (sEH), in a murine model. Specifically, mice fed on an HFD for 2, 4, and 8 wk showed time-dependent renal injury, the significant decrease in renal Pax2 and Ampk at both mRNA and protein levels, and a significant increase in renal sEH at mRNA, protein, and molecular levels. Also, administration of an sEH inhibitor, 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl)urea, significantly attenuated the HFD-caused renal injury, decreased renal sEH consistently at mRNA and protein levels, modified the renal levels of sEH-mediated epoxyeicosatrienoic acids (EETs) and dihydroxyeicosatrienoic acids (DHETs) as expected, and increased renal Pax2 and Ampk at mRNA and/or protein levels. Furthermore, palmitic acid (PA) treatment caused significant increase in Mcp-1, and decrease in both Pax2 and Ampk in murine renal mesangial cells (mRMCs) time- and dose-dependently. Also, 14(15)-EET (a major substrate of sEH), but not its sEH-mediated metabolite 14,15-DHET, significantly reversed PA-induced increase in Mcp-1, and PA-induced decrease in Pax2 and Ampk. In addition, plasmid construction revealed that Pax2 may positively regulate Ampk transcriptionally in mRMCs. This study provides insights into and therapeutic target for the HFD-mediated renal injury.

Induction of heme-oxygenase-1 (HO-1) does not enhance adiponectin production in human adipocytes: Evidence against a direct HO-1 - Adiponectin axis

Adiponectin is a salutary adipokine and hypoadiponectinemia is implicated in the aetiology of obesity-related inflammation and cardiometabolic disease making therapeutic strategies to increase adiponectin attractive. Emerging evidence, predominantly from preclinical studies, suggests induction of heme-oxygenase-1 (HO-1) increases adiponectin production and reduces inflammatory tone. Here, we aimed to test whether induction of HO-1 enhanced adiponectin production from mature adipocytes. Treatment of human adipocytes with cobalt protoporphyrin (CoPP) or hemin for 24-48 h increased HO-1 expression and activity without affecting adiponectin expression and secretion. Treatment of adipocytes with TNFα reduced adiponectin secretion and increased expression and secretion of additional pro-inflammatory cytokines, IL-6 and MCP-1, as well as expression of sXBP-1, a marker of ER stress. HO-1 induction failed to reverse these effects. These results demonstrate that induction of HO-1 does not directly enhance adiponectin production or ameliorate the pro-inflammatory effects of TNFα and argue against a direct HO-1 - adiponectin axis.

Induction of heme oxygenase-1 with hemin reduces obesity-induced adipose tissue inflammation via adipose macrophage phenotype switching

Adipose macrophages with the anti-inflammatory M2 phenotype protect against obesity-induced inflammation and insulin resistance. Heme oxygenase-1 (HO-1), which elicits antioxidant and anti-inflammatory activity, modulates macrophage phenotypes and thus is implicated in various inflammatory diseases. Here, we demonstrate that the HO-1 inducer, hemin, protects against obesity-induced adipose inflammation by inducing macrophages to switch to the M2 phenotype. HO-1 induction by hemin reduced the production of proinflammatory cytokines (TNF-α and IL-6) from cocultured adipocytes and macrophages by inhibiting the activation of inflammatory signaling molecules (JNK and NF-κB) in both cell types. Hemin enhanced transcript levels of M2 macrophage marker genes (IL-4, Mrc1, and Clec10a) in the cocultures, while reducing transcripts of M1 macrophage markers (CD274 and TNF-α). The protective effects of hemin on adipose inflammation and macrophage phenotype switching were confirmed in mice fed a high-fat diet, and these were associated with PPARγ upregulation and STAT6 activation. These findings suggest that induction of HO-1 with hemin protects against obesity-induced adipose inflammation through M2 macrophage phenotype switching, which is induced by the PPARγ and STAT6 pathway. HO-1 inducers such as hemin may be useful for preventing obesity-induced adipose inflammation.