A single-dose of cobalt-protoporphyrin protects islet beta cells from glucocorticoid suppression

Sirt1 mediates the effect of the heme oxygenase inducer, cobalt protoporphyrin, on ameliorating liver metabolic damage caused by a high-fat diet

BACKGROUND & AIMS

Heme oxygenase 1 (HO-1)-mediated increases in adiponectin, ameliorate the deleterious effects of obesity and metabolic syndrome; however, the effect of HO-1 on hepatic lipid metabolism remains elusive. The aim of this study is to evaluate the role of HO-1 in hepatic lipid metabolism.

METHODS

Functional studies were performed using C57BL/6J (WT) mice and Sirt1 liver specific mutant (Sirt1-deficient) mice. The molecular mechanism was explored in primary hepatocytes and mouse liver.

RESULTS

Chronic exposure to high-fat diet (HFD) induced hepatic steatosis in WT mice. Treatment of WT mice on HFD with cobalt protoporphyrin (CoPP), an inducer of HO-1 activity, decreased body weight and visceral fat content, reduced intracellular hepatic triglyceride and serum total cholesterol concentrations, and decreased liver lipid droplet formation. Compared with WT mice, the administration of CoPP to Sirt1-deficient mice on HFD increased visceral fat content, and slightly promoted liver lipid droplet formation. CoPP improved glucose tolerance and insulin sensitivity in WT mice on HFD, but compromised insulin sensitivity in Sirt1-deficient mice on HFD. Furthermore, CoPP-induced Sirt1 expression and decreased sterol regulatory element binding protein 1c (SREBP-1c) expression in WT mice on HFD. However, CoPP promoted SREBP-1c expression in Sirt1-deficient hepatocytes, which was reversed by a protein tyrosine phosphatase 1b inhibitor. Additionally, while the administration of CoPP to WT mice on HFD improved antioxidant and anti-inflammatory states, these CoPP-mediated effects were abolished in Sirt1-deficient mice.

CONCLUSIONS

Sirt1 mediates the effect of CoPP on ameliorating liver metabolic damage caused by HFD.

Cobalt protoporphyrin induces HO-1 expression mediated partially by FOXO1 and reduces mitochondria-derived reactive oxygen species production

Background

Reactive oxygen species arise in the mitochondria as byproducts of respiration and oxidase activity and have important roles in many physiological and pathophysiological conditions. The level of reactive oxygen species is regulated by a number of enzymes and physiological antioxidants, including HO-1, Sod2, catalase and COX-2, etc. And HO-1 against oxidative stress requires an increase in stress-responsive genes, such as Sod2 and catalase. Especially for the activity of HO-1, cobalt protoporphyrin is known to be a potent and effective inducer in many tissues. The transcription factor, FOXO1 is resistant to oxidative stress through downregulating reactive oxygen species production. Previous study showed that FOXO1 induces HO-1 expression by binding to HO-1 promoter. The question whether cobalt protoporphyrin induces HO-1 expression mediated by FOXO1 and subsequently lessens reactive oxygen species production remains to be elucidated.

Results

Cobalt protoporphyrin enhances the expression of FOXO1 and facilitates FOXO1 binding to HO-1 promoter and increasing its transcriptional activity without influencing the FOXO1 protein stability. CoPP induces HO-1 and other oxidative stress-responsive genes expression, such as catalase, cytochrome c, Sod2, and COX-2, and decreases mitochondria-derived reactive oxygen species production, which are mediated partially by FOXO1.

Conclusions

Cobalt protoporphyrin induces HO-1 and other oxidative stress-responsive genes expression mediated partially by FOXO1, and has an important role in reducing cellular reactive oxygen species level. Cobalt protoporphyrin may be a more promising therapeutic agent to upregulate some antioxidantive genes.

Cytoprotection behind heme oxygenase-1 in renal diseases

Renal insults are considered a public health problem and are linked to increased rates of morbidity and mortality worldwide. The heme oxygenase (HO) system consists of evolutionary specialized machinery that degrades free heme and produces carbon monoxide, biliverdin and free iron. In this sense, the inducible isoform HO-1 seems to develop an important role and is widely studied. The reaction involved with the HO-1 molecule provides protection to injured tissue, directly by reducing the toxic heme molecule and indirectly by the release of its byproducts. The up regulation of HO-1 enzyme has largely been described as providing antioxidant, antiapoptotic, anti-inflammatory and immunomodulatory properties. Several works have explored the importance of HO-1 in renal diseases and they have provided consistent evidence that its overexpression has beneficial effects in such injuries. So, in this review we will focus on the role of HO-1 in kidney insults, exploring the protective effects of its up regulation and the enhanced deleterious effects of its inhibition or gene deletion.

Role of heme oxygenase in inflammation, insulin-signalling, diabetes and obesity

Diabetes and obesity are chronic conditions associated with elevated oxidative/inflammatory activities with a continuum of tissue insults leading to more severe cardiometabolic and renal complications including myocardial infarction and end-stage-renal damage. A common denominator of these chronic conditions is the enhanced the levels of cytokines like tumour necrosis factor-alpha (TNF-α), interleukin (IL-6), IL-1β and resistin, which in turn activates the c-Jun-N-terminal kinase (JNK) and NF-κB pathways, creating a vicious cycle that exacerbates insulin resistance, type-2 diabetes and related complications. Emerging evidence indicates that heme oxygenase (HO) inducers are endowed with potent anti-diabetic and insulin sensitizing effects besides their ability to suppress immune/inflammatory response. Importantly, the HO system abates inflammation through several mechanisms including the suppression of macrophage-infiltration and abrogation of oxidative/inflammatory transcription factors like NF-κB, JNK and activating protein-1. This review highlights the mechanisms by which the HO system potentiates insulin signalling, with particular emphasis on HO-mediated suppression of oxidative and inflammatory insults. The HO system could be explored in the search for novel remedies against cardiometabolic diseases and their complications.

Heme-oxygenase induction inhibits arteriolar thrombosis in vivo: effect of the non-substrate inducer cobalt protoporphyrin

Heme oxygenase-1 (HO) metabolizes heme to form the vasodilator carbon monoxide and antioxidant biliverdin. Upregulation of HO-1 by hemin, which is also a substrate attenuates thrombosis in rodent models, however, whether protection is due to HO-1 upregulation or to increased substrate availability is unknown. This study tested the hypothesis that treatment of mice with cobalt protoporphyrin (CoPP), a non-substrate HO-1 inducer, would protect the endothelium from laser injury. C57Bl/J6 mice were treated with vehicle, CoPP (20 mg/kg), CoPP plus the HO-1 inhibitor tin protoporphyrin (SnPP; 20 mg/kg) or SnPP alone for 18 h. Intravital microscopy was used to quantitate thrombus formation in cremaster arterioles in response to laser ablation of the endothelium. CoPP treatment inhibited thrombosis by 43% compared to vehicle (P<0.05). SnPP co-treatment negated the inhibitory effect of CoPP while SnPP alone potentiated thrombosis compared to vehicle. In CoPP-treated animals, cremaster HO-1 mRNA expression was increased 59+/-17-fold over vehicle (P<0.001). Co-treatment with CoPP+SnPP attenuated this effect by 36%, however the increase in HO-1 protein induced by CoPP was unaffected by SnPP. Induction of HO-1 by the non-substrate inducer CoPP protects against laser induced endothelial injury without the need for increased substrate. Small molecule, substrate-independent upregulation of HO-1 expression represents a feasible approach to ameliorate endothelial dysfunction in cardiovascular disease.

Role of Bach1 and Nrf2 in up-regulation of the heme oxygenase-1 gene by cobalt protoporphyrin

Heme oxygenase (HO) catalyzes the conversion of heme to biliverdin with the release of iron and carbon monoxide. HO-1 is highly inducible by a large number of physical and chemical factors. CoPP is known to be a potent and effective inducer of HO-1 activity in many tissues. Here we report that CoPP up-regulates HO-1 via Bach1 and Nrf2 in human liver cells. CoPP did not influence hepatic Bach1 or Nrf2 mRNA levels, but markedly reduced Bach1 protein levels by increasing degradation of Bach1 protein (t(1/2) from 19 h to 2.8 h), and increased Nrf2 by decreasing degradation of Nrf2 protein (t(1/2) from 2.5 h to 9 h). Silencing Bach1 by Bach1-siRNA significantly increased levels of HO-1 mRNA and protein, and addition of CoPP up-regulated HO-1 mRNA and protein further. However, silencing Nrf2 mRNA by Nrf2-siRNA did not significantly change baseline HO-1 mRNA or protein levels, but significantly decreased 5-10 microM CoPP-mediated up-regulation of HO-1 mRNA levels compared with CoPP alone. Transfection with equal amounts of non-Bach1 or non-Nrf2 related control siRNA did not reduce Bach1 or Nrf2 mRNA or protein, confirming the specificity of Bach1- and Nrf2-siRNA in Huh-7 cells. We conclude that the pathway of CoPP-mediated induction of HO-1 involves the repression of Bach1 and up-regulation of the Nrf2 protein by post-transcriptional site(s) of action. Because CoPP, unlike heme, is neither a prooxidant nor a substrate for HO-1, it might be considered as a potential therapeutic agent in situations where up-regulation of HO-1 is desired.