Heme oxygenase-1 induction by cobalt protoporphyrin enhances fever and inhibits pyrogenic tolerance to lipopolysaccharide

Activation of Heme Oxygenase Expression by Cobalt Protoporphyrin Treatment Prevents Pneumonic Plague Caused by Inhalation of Yersinia pestis

Pneumonic plague, caused by the Gram-negative bacteria Yersinia pestis, is an invasive, rapidly progressing disease with poor survival rates. Following inhalation of Y. pestis, bacterial invasion of the lungs and a tissue-damaging inflammatory response allows vascular spread of the infection. Consequently, primary pneumonic plague is a multiorgan disease involving sepsis and necrosis of immune tissues and the liver, as well as bronchopneumonia and rampant bacterial growth. Given the likely role of the hyperinflammatory response in accelerating the destruction of tissue, in this work we evaluated the therapeutic potential of the inducible cytoprotective enzyme heme oxygenase 1 (HO-1) against primary pneumonic plague. On its own, the HO-1 inducer cobalt protoporphyrin IX (CoPP) provided mice protection from lethal challenge with Y. pestis CO92 with improved pulmonary bacterial clearance and a dampened inflammatory response compared to vehicle-treated mice. Furthermore, CoPP treatment combined with doxycycline strongly enhanced protection in a rat aerosol challenge model. Compared to doxycycline alone, CoPP treatment increased survival, with a 3-log decrease in median bacterial titer recovered from the lungs and the general absence of a systemic hyperinflammatory response. In contrast, treatment with the HO-1 inhibitor SnPP had no detectable impact on doxycycline efficacy. The combined data indicate that countering inflammatory toxicity by therapeutically inducing HO-1 is effective in reducing the rampant growth of Y. pestis and preventing pneumonic plague.

High mobility group box 1 protein released in the course of aseptic necrosis of tissues sensitizes rats to pyrogenic effects of lipopolysaccharide

It is still an open question as to whether or not aseptic injuries affect the generation of fever due to exogenous pyrogens including bacterial products. Therefore, in the present paper we have investigated the course of endotoxin fever in rats induced with lipopolysaccharide (LPS; given intraperitoneally in a dose of 50 μg/kg) 48 h after subcutaneous administration of turpentine oil (TRP; 0.1 mL per rat) that causes aseptic necrosis of tissues. We found that febrile response was significantly augmented in the animals pre-treated with turpentine compared to control rats (pre-treated with saline), and that observed excessive elevation of body temperature (Tb) was accompanied by enhanced release of fever mediators: interleukin-6 (IL-6) and prostaglandin E₂ (PGE₂) into plasma. Moreover, we found that sensitization to pyrogenic effects of lipopolysaccharide was associated with the increase in plasma level of high mobility group box 1 protein (HMGB1), one of the best-known damage-associated molecular patterns (DAMP), which was recently discovered as inflammatory mediator. Since the injection of anti-HMGB1 antibodies weakened observed hyperpyrexia in the animals pre-treated with turpentine, we conclude that HMGB1 is a plasma-derived factor released in the course of aseptic injury that enhances pyrogenic effects of LPS.

Extract from Coriolus versicolor fungus partially prevents endotoxin tolerance development by maintaining febrile response and increasing IL-6 generation

Endotoxin tolerance is defined as a reduced endotoxin-induced fever following repeated injections of lipopolysaccharide (LPS). Clinical examples of endotoxin tolerance include sepsis or cystic fibrosis. This state is characterized by inhibition of pro-inflammatory cytokines production and decrease in nuclear factor-kappa B (NF-κB) activation. Extract from Coriolus versicolor (CV) fungus is classified as a biological response modifier, which exhibits various biological activities, including immunopotentiating properties. The aim of study was to examine the effect of CV extract injection on body core temperature of Wistar rats during LPS-induced endotoxin tolerance. Body temperature was measured using biotelemetry. CV extract was injected intraperitoneally (100 mg kg^-1) 2 h prior to the first LPS peritoneal administration (50 μg/kg). Endotoxin tolerance was induced by three consecutive daily injections of LPS at the same dose. We also investigated the influence of CV extract pre-injection on the properties of peripheral blood mononuclear cells (PBMCs) isolated from LPS-treated rats in response to LPS stimulation ex vivo. PBMCs were isolated 2 h after the first LPS injection. After 24 h pre-incubation, the cells were stimulated with LPS (1 μg ml^-1) for 4 h. Our results revealed that CV extract partially prevents endotoxin tolerance through maintaining febrile response in rats following consecutive exposure to LPS. This state was accompanied by the ability of PBMCs isolated from rats injected with CV extract and LPS to release larger amounts of interleukin 6 and greater NF-κB activation in response to LPS stimulation ex vivo compared with the cells derived from rats injected only with LPS. Data also showed that CV extract augmented mitogenic effect of LPS on PBMCs and caused increase in reactive oxygen species generation. We concluded that CV extract, by a modifying effect on body temperature during endotoxin tolerance, can be consider as the immunostimulating agent, which prevents the non-specific refractoriness described in patients with sepsis or ischemia.

The weakening effect of soluble epoxide hydrolase inhibitor AUDA on febrile response to lipopolysaccharide and turpentine in rat

A still growing body of evidence suggests the importance of epoxyeicosatrienoic acids (EETs) in the regulation of inflammatory response; therefore, drugs that stabilize their levels by targeting the soluble epoxide hydrolase (sEH), an enzyme responsible for their metabolism, are currently under investigation. The effect of sEH inhibitors on molecular components of fever mechanism, i.e., on synthesis of pro-inflammatory cytokines or prostaglandins, has been repeatedly proven; however, the hypothesis that sEH inhibitors affect febrile response has never been tested. The aim of this study was to examine if sEH inhibition affects core body temperature (Tb) as well as Tb changes during febrile response to infectious (lipopolysaccharide; LPS) or non-infectious (turpentine; TRP) stimuli. Male Wistar rats were implanted intra-abdominally with miniature biotelemeters to monitor Tb. A potent sEH inhibitor 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA) was suspended in olive oil and administrated into animals in the intraperitoneal (i.p.) dose of 15 mg/kg, which, as we showed, has no significant influence on normal Tb. We have found that AUDA injected 3 h after LPS (50 μg/kg i.p.) significantly weakened febrile rise of Tb. Moreover, injection of sEH inhibitor 7 h after turpentine (administrated subcutaneously in a dose of 100 μL/rat) markedly reduced the peak period of aseptic fever. Obtained results provide first experimental evidence that sEH inhibitors possess anti-pyretic properties. Therefore, medicines targeting sEH enzymatic activity should be considered as a complement to the arsenal of topical medications used to treat fever especially in clinical situations when non-steroidal anti-inflammatory drugs are ineffective.

In vivo response of heme-oxygenase-1 to metal ions released from metal-on-metal hip prostheses

Metal ion release and accumulation is considered to be a factor responsible for the high failure rates of metal-on-metal (MoM) hip implants. Numerous studies have associated the presence of these ions, besides other factors, including a hypoxia‑like response and changes in pH due to metal corrosion leading to the induction of the oxidative stress response. The aim of the present study was to verify whether, in patients with a MoM hip prosthesis, mRNA and protein expression of HMOX‑1 was modulated by the presence of metal ions and whether patients without prostheses exhibit a different expression pattern of this enzyme. The study was conducted on 22 matched pairs of patients with and without prostheses, for a total of 44 samples. Ion dosage was determined using inductively coupled plasma mass spectrometry equipped with dynamic cell reaction. HMOX‑1 gene expression was quantified by reverse transcription-quantitative polymerase chain reaction and HMOX‑1 protein expression was analyzed using an enzyme-linked immunosorbent assay. The results demonstrated that although there were significant differences in the metallic ion concentrations amongst the two groups of patients, there was no correlation between circulating levels of cobalt (Co) and chromium (Cr), and HMOX‑1 gene and protein expression. Additionally, there was no significant difference in the protein expression levels of HMOX‑1 between the two groups. In conclusion, it was demonstrated that circulating Co and Cr ions released by articular prosthetics do not induce an increase in HMOX‑1 mRNA and protein expression at least 3.5 years after the implant insertion. The present study suggests that involvement of HMOX‑1 may be excluded from future studies and suggests that other antioxidant enzymes, including superoxide dismutase, glutathione peroxidase and reductase should be investigated.