Histone deacetylase III as a potential therapeutic target for the treatment of lethal sepsis

An Fgr kinase inhibitor attenuates sepsis-associated encephalopathy by ameliorating mitochondrial dysfunction, oxidative stress, and neuroinflammation via the SIRT1/PGC-1α signaling pathway

BACKGROUND

Sepsis-associated encephalopathy (SAE) is characterized by diffuse brain dysfunction, long-term cognitive impairment, and increased morbidity and mortality. The current treatment for SAE is mainly symptomatic; the lack of specific treatment options and a poor understanding of the underlying mechanism of disease are responsible for poor patient outcomes. Fgr is a member of the Src family of tyrosine kinases and is involved in the innate immune response, hematologic cancer, diet-induced obesity, and hemorrhage-induced thalamic pain. This study investigated the protection provided by an Fgr kinase inhibitor in SAE and the underlying mechanism(s) of action.

METHODS

A cecal ligation and puncture (CLP)-induced mouse sepsis model was established. Mice were treated with or without an Fgr inhibitor and a PGC-1α inhibitor/activator. An open field test, a novel object recognition test, and an elevated plus maze were used to assess neurobehavioral changes in the mice. Western blotting and immunofluorescence were used to measure protein expression, and mRNA levels were measured using quantitative PCR (qPCR). An enzyme-linked immunosorbent assay was performed to quantify inflammatory cytokines. Mitochondrial membrane potential and morphology were measured by JC-1, electron microscopy, and the MitoTracker Deep Red probe. Oxidative stress and mitochondrial dysfunction were analyzed. In addition, the regulatory effect of Fgr on sirtuin 1 (SIRT1) was assessed.

RESULTS

CLP-induced sepsis increased the expression of Fgr in the hippocampal neurons. Pharmacological inhibition of Fgr attenuated CLP-induced neuroinflammation, the survival rate, cognitive and emotional dysfunction, oxidative stress, and mitochondrial dysfunction. Moreover, Fgr interacted with SIRT1 and reduced its activity and expression. In addition, activation of SIRT1/PGC-1α promoted the protective effects of the Fgr inhibitor on CLP-induced brain dysfunction, while inactivation of SIRT1/PGC-1α counteracted the benefits of the Fgr inhibitor.

CONCLUSIONS

To our knowledge, this is the first report of Fgr kinase inhibition markedly ameliorating SAE through activation of the SIRT1/PGC-1α pathway, and this may be a promising therapeutic target for SAE.

Epigenetic mechanisms of Immune remodeling in sepsis: targeting histone modification

Sepsis is a life-threatening disorder disease defined as infection-induced dysregulated immune responses and multiple organ dysfunction. The imbalance between hyperinflammation and immunosuppression is a crucial feature of sepsis immunity. Epigenetic modifications, including histone modifications, DNA methylation, chromatin remodeling, and non-coding RNA, play essential roles in regulating sepsis immunity through epi-information independent of the DNA sequence. In recent years, the mechanisms of histone modification in sepsis have received increasing attention, with ongoing discoveries of novel types of histone modifications. Due to the capacity for prolonged effects on immune cells, histone modifications can induce immune cell reprogramming and participate in the long-term immunosuppressed state of sepsis. Herein, we systematically review current mechanisms of histone modifications involved in the regulation of sepsis, summarize their role in sepsis from an immune perspective and provide potential therapeutic opportunities targeting histone modifications in sepsis treatment.

HDAC inhibition as neuroprotection in COVID-19 infection

The SARS-CoV-2 virus is responsible of COVID-19 affecting millions of humans around the world. COVID-19 shows diverse clinical symptoms (fever, cough, fatigue, diarrhea, body aches, headaches, anosmia and hyposmia). Approximately 30% of the patients with COVID-19 showed neurological symptoms, these going from mild to severe manifestations including headache, dizziness, impaired consciousness, encephalopathy, anosmia, hypogeusia, hyposmia, psychology and psychiatry among others. The neurotropism of SARS-CoV-2 virus explains its neuroinvasion provoking neurological damage as acute demyelination, neuroinflammation etc. At molecular level, the COVID-19 patients had higher levels of cytokines and chemokines known as cytokines storms which disrupt the blood brain barrier allowing the entrance of monocytes and lymphocytes causing neuroinflammation, neurodegeneration and demyelination. In addition, ischemic, hemorrhagic strokes, seizures and encephalopathy have been observed due to the proinflammatory cytokines. In this sense, to avoid or decrease neurological damage due to SARS-CoV-2 infection, an early neuroprotective management should be adopted. Several approaches can be used; one of them includes the use of HDAC inhibitors (HDACi) due to their neuroprotective effects. Also, the HDACi down regulates the pro-inflammatory cytokines (IL-6 and TNF- decreasing the neurotoxicity. HDACi can also avoid and prevent the entrance of the virus into the Central nervous System (CNS) as well as decrease the virus replication by downregulating the virus receptors. Here we review the mechanisms that could explain how the SARS-CoV-2 virus could reach the CNS, induce the neurological damage and symptoms, as well as the possibility to use HDACi as neuroprotective therapy.

Lactylated Histone H3K18 as a Potential Biomarker for the Diagnosis and Predicting the Severity of Septic Shock

Objective

To date, there are no studies regarding the lactylation profile and its role in critically ill patients. Thus, we aimed to examine expression of histone H3 lysine 18 (H3K18) lactylation and its role in patients with septic shock.

Methods

Thirteen healthy volunteers and 35 critically ill patients from the Department of Surgical Intensive Care Medicine, Beijing Hospital were enrolled in our study. Baseline information and clinical outcomes were obtained prospectively. Lactylation levels of all proteins and H3K18 from peripheral blood mononuclear (PBMC) were determined by western blotting and serum levels of inflammatory cytokines by flow cytometry. Arginase-1 (Arg1) and Krüppel-like factor-4 (Klf4) mRNA expression was evaluated by quantitative real-time PCR (qRT-PCR).

Results

Lactylation was found to be an all-protein post-translational modification and was detected in PBMCs from both healthy volunteers and critically ill patients, with a significantly higher relative density in shock patients (t=2.172, P=0.045). H3K18la was expressed in all subjects, including healthy volunteers, with the highest level in septic shock patients (compared with non-septic shock patients, critically ill without shock patients and healthy volunteers P=0.033, 0.000 and 0.000, respectively). Furthermore, H3K18la protein expression correlated positively with APACHE II scores, SOFA scores on day 1, ICU stay, mechanical ventilation time and serum lactate (ρ=0.42, 0.63, 0.39, 0.51 and 0.48, respectively, ρ=0.012, 0.000, 0.019, 0.003 and 0.003, respectively). When we matched patients with septic shock and with non-septic shock according to severity, we found higher H3K18la levels in the former group (t=-2.208, P =0.040). Moreover, H3K18la exhibited a close correlation with procalcitonin levels (ρ=0.71, P=0.010). Patients with high H3K18la expression showed higher IL-2, IL-5, IL-6, IL-8, IL-10, IL-17, IFN-α levels (ρ=0.33, 0.37, 0.62, 0.55, 0.65, 0.49 and 0.374 respectively, P=0.024, 0.011, 0.000, 0.000, 0.000 and 0.000 respectively). H3K18la expression also displayed a positive correlation with the level of Arg1 mRNA (ρ=0.561, P=0.005).

Conclusions

Lactylation is an all-protein post-translational modification occurring in both healthy subjects and critically ill patients. H3K18la may reflect the severity of critical illness and the presence of infection. H3K18la might mediate inflammatory cytokine expression and Arg1 overexpression and stimulate the anti-inflammatory function of macrophages in sepsis.

Histone Deacetylase Inhibitors: A Novel Strategy in Trauma and Sepsis

Trauma remains a leading cause of morbidity and mortality among all age groups in the United States. Hemorrhagic shock and traumatic brain injury (TBI) are major causes of preventable death in trauma. Initial treatment involves fluid resuscitation to improve the intravascular volume. Although crystalloids may provide volume expansion, they do not have any pro-survival properties. Furthermore, aggressive fluid resuscitation can provoke a severe inflammatory response and worsen clinical outcomes. Due to logistical constraints, however, definitive resuscitation with blood products is often not feasible in the prehospital setting-highlighting the importance of adjunctive therapies. In recent years, histone deacetylase inhibitors (HDACis) have shown promise as pharmacologic agents for use in both trauma and sepsis. In this review, we discuss the role of histone deacetylases (HDACs) and pharmacologic agents that inhibit them (HDACis). We also highlight the therapeutic effects and mechanisms of action of HDACis in hemorrhagic shock, TBI, polytrauma, and sepsis. With further investigation and translation, HDACis have the potential to be a high-impact adjunctive therapy to traditional resuscitation.

Inhibition of SIRT1 promotes taste bud stem cell survival and mitigates radiation-induced oral mucositis in mice

Taste loss is one of the debilitating complications in radiation-induced oral mucositis (RIOM), as occurs in head and neck cancer patients undergoing radiotherapy. We report here a radio-mitigation effect of Sirtuin 1 (SIRT1) inhibitors in taste bud organoids and a mouse model of radiation-induced taste bud injury. The organoids, developed from circumvallate (CV) papilla, were irradiated with single dose of X-rays and inhibitors of SIRT1 or SIRT2 were added 24 h later. The survival was evaluated by measuring the number and size of regenerated organoids after irradiation (IR). Oral mucositis (OM) was induced by IR of the oral region of Lgr5-lacZ transgenic mice. The surviving Lgr5+ taste bud stem cells were identified after lacZ-staining and the mucosal ulceration on tongue dorsal surface was determined by histological methods. Results showed that SIRT1 inhibitors (nicotinamide, EX527, salermide and sirtinol), but not SIRT2 inhibitors, significantly improve taste bud organoid survival after IR. Remarkably, administration of nicotinamide (NAM), a recognized inhibitor of SIRT1 to mice 24 h after IR promotes the survival of Lgr5+ taste bud stem cells, resulting in alleviated tongue mucositis. In conclusion, SIRT1 inhibitors promote Lgr5+ taste bud stem cell survival and mitigate RIOM in mice. These observations have important implications for efforts to develop therapeutic strategies against taste dysfunction and mucosal ulceration in RIOM.

Metabolic Resuscitation Strategies to Prevent Organ Dysfunction in Sepsis

Significance: Sepsis is the main cause of death among patients admitted to the intensive care unit. As current treatment is limited to antimicrobial therapy and supportive care, mortality remains high, which warrants efforts to find novel therapies. Recent Advances: Mitochondrial dysfunction is emerging as a key process in the induction of organ dysfunction during sepsis, and metabolic resuscitation might reveal to be a novel cornerstone in the treatment of sepsis. Critical Issues: Here, we review novel strategies to maintain organ function in sepsis by precluding mitochondrial dysfunction by lowering energetic demand to allow preservation of adenosine triphosphate-levels, while reducing free radical generation. As the most common strategy to suppress metabolism, that is, cooling, does not reveal unequivocal beneficial effects and may even increase mortality, caloric restriction or modulation of energy-sensing pathways (i.e., sirtuins and AMP-activated protein kinase) may offer safe alternatives. Similar effects may be offered when mimicking hibernation by hydrogen sulfide (H₂S). In addition H₂S may also confer beneficial effects through upregulation of antioxidant mechanisms, similar to the other gasotransmitters nitric oxide and carbon monoxide, which display antioxidant and anti-inflammatory effects in sepsis. In addition, oxidative stress may be averted by systemic or mitochondria-targeted antioxidants, of which a wide range are able to lower inflammation, as well as reduce organ dysfunction and mortality from sepsis. Future Directions: Mitochondrial dysfunction plays a key role in the pathophysiology of sepsis. As a consequence, metabolic resuscitation might reveal to be a novel cornerstone in the treatment of sepsis.

Epigenetics in Sepsis: Understanding Its Role in Endothelial Dysfunction, Immunosuppression, and Potential Therapeutics

Sepsis has a complex pathophysiology in which both excessive and refractory inflammatory responses are hallmark features. Pro-inflammatory cytokine responses during the early stages are responsible for significant endothelial dysfunction, loss of endothelial integrity, and organ failure. In addition, it is now well-established that a substantial number of sepsis survivors experience ongoing immunological derangement and immunosuppression following a septic episode. The underpinning mechanisms of these phenomena are incompletely understood yet they contribute to a significant proportion of sepsis-associated mortality. Epigenetic mechanisms including DNA methylation, histone modifications, and non-coding RNAs, have an increasingly clear role in modulating inflammatory and other immunological processes. Recent evidence suggests epigenetic mechanisms are extensively perturbed as sepsis progresses, and particularly play a role in endothelial dysfunction and immunosuppression. Whilst therapeutic modulation of the epigenome is still in its infancy, there is substantial evidence from animal models that this approach could reap benefits. In this review, we summarize research elucidating the role of these mechanisms in several aspects of sepsis pathophysiology including tissue injury and immunosuppression. We also evaluate pre-clinical evidence for the use of "epi-therapies" in the treatment of poly-microbial sepsis.

Histone Deacetylation Inhibitors as Therapy Concept in Sepsis

Sepsis is characterized by dysregulated gene expression, provoking a hyper-inflammatory response occurring in parallel to a hypo-inflammatory reaction. This is often associated with multi-organ failure, leading to the patient’s death. Therefore, reprogramming of these pro- and anti-inflammatory, as well as immune-response genes which are involved in acute systemic inflammation, is a therapy approach to prevent organ failure and to improve sepsis outcomes. Considering epigenetic, i.e., reversible, modifications of chromatin, not altering the DNA sequence as one tool to adapt the expression profile, inhibition of factors mediating these changes is important. Acetylation of histones by histone acetyltransferases (HATs) and initiating an open-chromatin structure leading to its active transcription is counteracted by histone deacetylases (HDACs). Histone deacetylation triggers a compact nucleosome structure preventing active transcription. Hence, inhibiting the activity of HDACs by specific inhibitors can be used to restore the expression profile of the cells. It can be assumed that HDAC inhibitors will reduce the expression of pro-, as well as anti-inflammatory mediators, which blocks sepsis progression. However, decreased cytokine expression might also be unfavorable, because it can be associated with decreased bacterial clearance.

Emerging Evidence concerning the Role of Sirtuins in Sepsis

Sepsis, a dysregulated host response to infection, is a major public health concern. Though experimental and clinical studies relating to sepsis are increasing, the mechanism of sepsis is not completely understood. To date, numerous studies have shown that sirtuins (silent mating type information regulation 2 homolog), which belong to the class III histone deacetylases, may have a varied, or even opposite, effect in the pathogenesis of sepsis. Notably, downstream mechanisms of sirtuins are not fully understood. The sirtuin family consists of sirtuins 1-7; among them, sirtuin 1 (SIRT1) is the most studied one, during the development of sepsis. Furthermore, other sirtuin members are also confirmed to be involved in the regulation of inflammatory or metabolic signaling following sepsis. In addition, sirtuins may interact with each other to form a precise regulatory mechanism in different phases of sepsis. Therefore, in this review, by accumulating data from PubMed, we intend to explain the role of sirtuin in sepsis, which we hope will pave the way for further experimental study and the potential future clinical applications of sirtuins.

Histone deacetylase inhibitors: Isoform selectivity improves survival in a hemorrhagic shock model

BACKGROUND

Hemorrhage is a leading preventable cause of death. Nonselective histone deacetylase inhibitors (HDACIs), such as valproic acid (VPA), have been shown to improve outcomes in hemorrhagic shock (HS). The HDACs can be divided into four functional classes (I, IIa/IIb, III, and IV). Classes I, IIa/IIb, and III have previously been implicated in the pathophysiology of HS. This study aimed to determine which HDAC class, or classes, are responsible for the survival benefit observed with nonselective HDACIs.

METHODS

Survival study: Sprague-Dawley rats were subjected to lethal HS (50% hemorrhage) and randomized to the following groups (n = 8): (1) no treatment, (2) normal saline vehicle, (3) cyclodextrin vehicle, (4) MS275 (class I HDACI), (5) VPA (class I/IIa HDACI), (6) MC1568 (class IIa HDACI), (7) ACY1083 (class IIb HDACI), and (8) EX527 (class III HDACI). Survival was monitored for 24 hours. Mechanistic study: Sprague-Dawley rats were subjected to sublethal HS (40% hemorrhage) and randomized to the same groups (n = 3), excluding EX527, based on results of the survival study. Tissues were harvested at 3 hours posttreatment, and expression of phosphorylated-AKT, β-catenin, acetylated histones H3 and H4, and acetylated α-tubulin were analyzed in myocardial tissue.

RESULTS

Survival rate was 12.5% in the untreated group, and did not improve with vehicle or MS275 treatment. EX527 improved survival to 50%, although this did not achieve statistical significance (p = 0.082). However, treatment with VPA, MC1568, and ACY1083 improved survival rates to 87.5%, 75%, and 75%, respectively (p < 0.05). The VPA-induced acetylation of both histones H3 and H4, while MC1568 and ACY1083 increased acetylation of histone H4. ACY1083 also induced acetylation of α-tubulin. All treatment groups, except MS275, increased phosphorylated-AKT, and β-catenin.

CONCLUSION

Inhibition of HDAC classes IIa or IIb, but not class I, activates prosurvival pathways, which may be responsible for the improved outcomes in rodent models of HS.

Targeting macrophage immunometabolism: Dawn in the darkness of sepsis

Sepsis is known since the time (470 BC) of great Greek physician, Hippocrates. Advancement in modern medicine and establishment of separate branches of medical science dealing with sepsis research have improved its outcome. However, mortality associated with sepsis still remains higher (25-30%) that further increases to 40-50% in the presence of septic shock. For example, sepsis-associated deaths account more in comparison to deaths-associated with myocardial-infarction and certain cancers (i.e. breast and colorectal cancer). However, it is now well established that profound activation of innate immune cells including macrophages play a very important role in the immunopathogenesis of sepsis. Macrophages are sentinel cells of the innate immune system with their location varying from peripheral blood to various target organs including lungs, liver, brain, kidneys, skin, testes, vascular endothelium etc. Thus, profound and dysregulated activation of these cells during sepsis can directly impact the outcome of sepsis. However, the emergence of the concept of immunometabolism as a major controller of immune response has raised a new hope for identifying new targets for immunomodulatory therapeutic approaches. Thus this present review starts with an introduction of sepsis as a major medical problem worldwide and signifies the role of dysregulated innate immune response including macrophages in its immunopathogenesis. Thereafter, subsequent sections describe changes in immunometabolic stage of macrophages (both M1 and M2) during sepsis. The article ends with the discussion of novel macrophage-specific therapeutic targets targeting their immunometabolism during sepsis and epigenetic regulation of macrophage immunometabolism and vice versa.

The SIRT1 inhibitor EX-527 suppresses mTOR activation and alleviates acute lung injury in mice with endotoxiemia

It is generally regarded that Sirtuin 1 (SIRT1), a longevity factor in mammals, acts as a negative regulator of inflammation. However, recent studies also found that SIRT1 might be a detrimental factor under certain inflammatory circumstance. In this study, the potential pathophysiological roles and the underlying mechanisms of SIRT1 in a mouse model with endotoxemia-associated acute lung injury were investigated. The results indicated that treatment with the selective SIRT1 inhibitor EX-527 suppressed LPS-induced elevation of TNF-α and IL-6 in plasma. Treatment with EX-527 attenuated LPS-induced histological abnormalities in lung tissue, which was accompanied with decreased myeloperoxidase level and suppressed induction of tissue factor and plasminogen activator inhibitor-1. Treatment with EX-527 also suppressed LPS-induced phosphorylation of eukaryotic translation initiation factor-binding protein 1 (4E-BP1). Co-administration of a mammalian target of rapamycin (mTOR) activator 3-benzyl-5-[(2-nitrophenoxy) methyl]-dihydrofuran-2 (3H)-one (3BDO) abolished the inhibitory effects of EX-527 on 4E-BP1 phosphorylation. Meanwhile, the inhibitory effects of EX-527 on IL-6 induction and the beneficial effects of EX-527 on lung injury were partially reversed by 3BDO. This study suggests that selective inhibition of SIRT1 by EX-527 might alleviate endotoxemia-associated acute lung injury partially via suppression of mTOR, which implies that SIRT1 selective inhibitors might have potential value for the pharmacological intervention of inflammatory lung injury.

Protective effect of Cl-amidine against CLP-induced lethal septic shock in mice

Production of innate and adaptive immune cells from hematopoietic stem cells, and maturation of T lymphocytes are effective immune responses to fight severe microbial infection. In sepsis, this emergency myelopoiesis is damaged, leading to failure of bacterial clearance, and excessive stress-induced steroids cause immature T-lymphocyte apoptosis in thymus. We recently found that Cl-amidine, a peptidylarginine deiminase (PAD) inhibitor, improves survival in a mouse model of cecal ligation and puncture (CLP)-induced septic shock. In the present study we investigated how Cl-amidine promotes survival, focusing on protective effects of Cl-amidine on immune response. We confirmed survival-improving effect of Cl-amidine and are the first to explore the role of Cl-amidine in immune response. CLP caused bone marrow (BM) and thymus atrophy, decreased innate immune cells in BM. CLP increased levels of cytokines (IL-1β, IL-6, and TNF-α) and bacteria load in blood/liver. In primary splenocyte culture, lipopolysaccharide increased TNF-α production. In contrast, Cl-amidine attenuated these CLP and lipopolysaccharide-induced alterations. Moreover, Cl-amidine increased circulating monocytes. Collectively, our results demonstrate Cl-amidine plays protective roles by significantly decreasing BM and thymus atrophy, restoring innate immune cells in BM, increasing blood monocytes and blood/liver bacteria clearance, and attenuating pro-inflammatory cytokine production in a murine model of lethal sepsis.

Selective Inhibition of SIRT2 Improves Outcomes in a Lethal Septic Model

BACKGROUND

Seven isoforms of histone deacetylase Class III have been reported - Sirtuin (SIRT) 1-7. We recently demonstrated that EX-527, an inhibitor of SIRT1, reduces mortality in a mouse model of lethal-cecal-ligationand- puncture (CLP)-induced septic shock. Our present study was aimed at determining whether selective inhibition of SIRT2, with AGK2, would decrease animal death and attenuate the inflammatory response in a septic model.

METHODS

Experiment I: C57BL/6J mice were intraperitoneally given either AGK2 (82 mg/kg) in dimethyl sulfoxide (DMSO) or DMSO alone, and 2 h later subjected to CLP. Survival was monitored for 240 hours. Experiment II: mice treated the same way as Experiment I, were grouped into (i) DMSO vehicle, and (ii) AGK2, with sham mice (operating but without any treatment) serving as controls. Peritoneal fluid and peripheral blood were examined at 24 and 48 hours for cytokine production. Samples of blood at 48 h were also allocated to assess coagulability using Thrombelastography (TEG). Morphological changes of bone marrow were evaluated from long bones (femurs and tibias) with hematoxylin and eosin (H&E) staining. Bone marrow atrophy was quantified by a blinded pathologist. Experiment III: cytokines in supernatant of the cultured normal primary splenocytes were measured after the cells were stimulated by lipopolysaccharide and treated with or without AGK2 (10 µM) for 6 hours.

RESULTS

AGK2 significantly reduced mortality and decreased levels of cytokines in blood (TNF-α: 298.3±24.6 vs 26.8±2.8 pg/ml, p=0.0034; IL-6: 633.4±82.8 vs 232.6±133.0 pg/ml, p=0.0344) and peritoneal fluid (IL-6: 704.8±67.7 vs 391.4±98.5 pg/ml, p=0.033) compared to vehicle control. Also, AGK2 suppressed the TNF-α and IL-6 production in the cultured splenocytes (TNF-α: 68.1±6.4 vs 23.9±2.8 pg/ml, p=0.0009; IL-6: 73.1±4.2 vs 49.6±3.0 pg/ml; p=0.0051). The TEG data showed that the mice subjected to CLP displayed prolonged fibrin formation and fibrin cross-linkage time, slower clot formation, decreased platelet function, and clot rigidity. AGK2 treatment was associated with dramatic improvements in fibrin cross-linkage and clot formation times, without a significant impact on the clot initiation parameters or platelet function. Additionally, AGK2 significantly attenuated the bone marrow atrophy (58.3±6.5 vs 30.0±8.2%, p=0.0262).

CONCLUSION

Selective inhibition of SIRT2 significantly improves survival, and attenuates sepsis-associated "cytokine storm", coagulopathy, and bone marrow atrophy in a mouse model of lethal septic shock.

Propagation of errors in citation networks: a study involving the entire citation network of a widely cited paper published in, and later retracted from, the journal Nature

BACKGROUND

In about one in 10,000 cases, a published article is retracted. This very often means that the results it reports are flawed. Several authors have voiced concerns about the presence of retracted research in the memory of science. In particular, a retracted result is propagated by citing it. In the published literature, many instances are given of retracted articles that are cited both before and after their retraction. Even worse is the possibility that these articles in turn are cited in such a way that the retracted result is propagated further.

METHODS

We have conducted a case study to find out how a retracted article is cited and whether retracted results are propagated through indirect citations. We have constructed the entire citation network for this case.

RESULTS

We show that directly citing articles is an important source of propagation of retracted research results. In contrast, in our case study, indirect citations do not contribute to the propagation of the retracted result.

CONCLUSIONS

While admitting the limitations of a study involving a single case, we think there are reasons for the non-contribution of indirect citations that hold beyond our case study.

Creating a "Prosurvival Phenotype" Through Histone Deacetylase Inhibition: Past, Present, and Future

Traumatic injuries and their sequelae represent a major source of mortality in the United States and globally. Initial treatment for shock, traumatic brain injury, and polytrauma is limited to resuscitation fluids to replace lost volume. To date, there are no treatments with inherent prosurvival properties. Our laboratory has investigated the use of histone deacetylase inhibitors (HDACIs) as pharmacological agents to improve survival. This class of drugs acts through posttranslational protein modifications and is a direct regulator of chromatin structure and function, as well as the function of numerous cytoplasmic proteins. In models of hemorrhagic shock and polytrauma, administration of HDACIs offers a significant survival advantage, even in the absence of fluid resuscitation. Positive results have also been shown in two-hit models of hemorrhage and sepsis and in hemorrhagic shock combined with traumatic brain injury. Accumulating data generated by our group and others continue to support the use of HDACIs for the creation of a prosurvival phenotype. With further research and clinical trials, HDACIs have the potential to be an integral tool in the treatment of trauma, especially in the prehospital phase.

Histone deactylase gene expression profiles are associated with outcomes in blunt trauma patients

BACKGROUND

Treatment with histone deacetylase (HDAC) inhibitors, such as valproic acid, increases survival in animal models of trauma and sepsis. Valproic acid is a pan-inhibitor that blocks most of the known HDAC isoforms. Targeting individual HDAC isoforms may increase survival and reduce complications, but little is known of the natural history of HDAC gene expression following trauma. We hypothesized that distinct HDAC isoform gene expression patterns would be associated with differences in outcomes following trauma.

METHODS

Twenty-eight-day longitudinal HDAC leukocyte gene expression profiles in 172 blunt trauma patients were extracted from the Inflammation and the Host Response to Injury (Glue Grant) data set. Outcome was classified as complicated (death or no recovery by Day 28, n = 51) or uncomplicated (n = 121). Mixed modeling was used to compare the HDAC expression trajectories between the groups, corrected for Injury Severity Score (ISS), base deficit, and volume of blood products transfused during the initial 12 hours following admission. Weighted gene correlation network analysis identified modules of genes with significant coexpression, and HDAC genes were mapped to these modules. Biologic function of these modules was investigated using the Gene Ontology database.

RESULTS

Elevated longitudinal HDAC expression trajectories for HDAC1, HDAC3, HDAC6, and HDAC11 were associated with complicated outcomes. In contrast, suppressed expression of Sirtuin 3 (SIRT3) was associated with adverse outcome (p < 0.01). Weighted gene correlation network analysis identified significant coexpression of HDAC and SIRT genes with genes involved in ribosomal function and down-regulation of protein translation in response to stress (HDAC1), T-cell signaling, and T-cell selection (HDAC3) as well as coagulation and hemostasis (SIRT3). No coexpression of HDAC11 was identified.

CONCLUSION

Expression trajectories of HDAC1, HDAC3, HDAC6, HDAC11, and SIRT3 correlate with outcomes following trauma and may potentially serve as biomarkers. They may also be promising targets for pharmacologic intervention. The effects of HDAC and SIRT gene expression in trauma may be mediated through pathways involved in ribosomal and T-cell function as well as coagulation and hemostasis.

LEVEL OF EVIDENCE

Prognostic study, level III.

Inhibition of histone deacetylase 6 restores innate immune cells in the bone marrow in a lethal septic model

BACKGROUND

We have previously demonstrated that Tubastatin A, a selective inhibitor of histone deacetylase 6 (HDAC6), improves survival and increases circulating monocyte count and bacterial clearance in a lethal model of cecal ligation and puncture (CLP) in mice. The aim of the present study was to characterize the effects of inhibition of HDAC6 on the bone marrow cell population.

METHODS

C57BL/6J mice were subjected to CLP and, 1 hour later, given an intraperitoneal injection of either Tubastatin A (70 mg/kg) dissolved in DMSO or DMSO alone (n = 9 per group). Sham-operated animals were treated in an identical fashion, without CLP. Forty-eight hours later, bone marrow cells were flushed out from the femurs and tibias. Erythrocytes were lysed, and a single-cell suspension was made for analysis. Cells were washed; blocked with antimouse CD16/32; stained with antimouse B220 PE-Cy7, CD3 APC-eFluor 780, CD11b FITC, Gr-1 PerCP-Cy5.5, and F4/80 Antigen APC; and subjected to flow cytometry. Data were acquired on an LSRII Flow Cytometer (BD Biosciences, San Jose, CA) and analyzed with FlowJo (Flowjo, LLC, Ashland, OR).

RESULTS

In comparison with the sham group, CLP animals showed decreased percentage of innate immune cells (CD11b, 62.1% ± 3.1% vs. 32.9% ± 4.9%, p = 0.0025) and macrophages (CD11bF4/80, 44.6% ± 3.4% vs. 19.8% ± 2.6%, p = 0.0002) as well as increased percentage of T lymphocytes (CD3, 1.1% ± 0.2% vs. 3.3% ± 0.4%, p = 0.0082) in the bone marrow 48 hours after CLP. Treatment with Tubastatin A restored the innate immune cells (32.9% ± 4.9% vs. 54.0% ± 4.1%, p = 0.0112) and macrophages (19.8% ± 2.6% vs. 47.1% ± 4.6%, p = 0.0001) and increased the percentage of neutrophils (CD11bGr-1, 28.4% ± 3.9% vs. 48.0% ± 4.0%, p = 0.0075). The percentages of B (B220) and T lymphocytes were not significantly altered by Tubastatin A, compared with the vehicle-treated CLP animals.

CONCLUSION

Selective inhibition of HDAC6 in this lethal septic model restored the innate immune cell and macrophage populations and increased the neutrophil composition in the bone marrow. These results may explain the previously reported beneficial effects of Tubastatin A treatment in a septic model.

Inhibition of histone deacetylase 6 improves long-term survival in a lethal septic model

BACKGROUND

We recently demonstrated that suberoylanilide hydroxamic acid, a broad-spectrum histone deacetylase (HDAC) inhibitor that inhibits HDACs 1, 2, 3, and 6, improves survival in a mouse model of cecal ligation and puncture (CLP)-induced lethal sepsis. The current study was undertaken to determine the effect of selective inhibition of HDAC isoform on survival, key cytokine production, organ injury, bacteria clearance, and cell apoptosis.

METHODS

In Experiment 1, C57BL/6J mice were subjected to CLP and, 1 hour later, given intraperitoneal injections of (1) Tubastatin A (inhibitor of HDAC6) dissolved in dimethyl sulfoxide (DMSO), (2) MS-275 (inhibitor of HDACs 1, 2, and 3) in DMSO, and (3) DMSO only. Survival was monitored for 10 days. In Experiment 2, 1 hour after CLP, animals were treated with DMSO vehicle or Tubastatin A. Sham-operated animals served as control. Peritoneal fluid and blood samples were collected for measurement of cytokines at 24 hours or 48 hours. Blood at 48 hours was also used to determine bacteria load. Liver was harvested to evaluate acute liver injury. In Experiment 3, Primary splenocytes were used to assess cytokine responses and phagocytosis. Macrophages were cultured and harvested 3 hours and 6 hours after lipopolysaccharide stimulation in the absence or presence of Tubastatin A to analyze cell apoptosis.

RESULTS

Animals treated with Tubastatin A, but not MS-275, displayed a significant improvement in survival. Moreover, Tubastatin A significantly inhibited cytokine production in peritoneal fluid and plasma as well as in supernatant from splenocytes stimulated with lipopolysaccharide. Tubastatin A significantly attenuated acute liver injury, increased blood bacteria clearance and splenocyte phagocytosis, and decreased macrophage apoptosis.

CONCLUSION

HDAC6 inhibition significantly improves survival, reduces "cytokine storm," attenuates acute livery injury, increases bacteria clearance and immune cell phagocytosis, and inhibits macrophage apoptosis in a lethal mouse CLP model.

Selective histone deacetylase 6 inhibition prolongs survival in a lethal two-hit model

BACKGROUND

Hemorrhagic shock (HS) followed by a subsequent insult ("second hit") often initiates an exaggerated systemic inflammatory response and multiple organ failure. We have previously demonstrated that valproic acid, a pan histone deacetylase inhibitor, could improve survival in a rodent "two-hit" model. In the present study, our goal was to determine whether selective inhibition of histone deacetylase 6 with Tubastatin A (Tub-A) could prolong survival in a two-hit model where HS was followed by sepsis from cecal ligation and puncture (CLP).

METHODS

C57Bl/6J mice were subjected to sublethal HS (30% blood loss) and then randomly divided into two groups (n = 13 per group) such as Tub-A group (treatment) and vehicle (VEH) group (control). The Tub-A group was given an intraperitoneal injection of Tub-A (70 mg/kg) dissolved in dimethyl sulfoxide (DMSO). The VEH group was injected with DMSO (1 μl/g body weight). After 24 h, all mice were subjected CLP followed immediately by another dose of Tub-A or DMSO. Survival was monitored for 10 d. In a parallel study, peritoneal irrigation fluid and liver tissue from Tub-A- or DMSO-treated mice were collected 3 h after CLP. Enzyme-linked immunosorbent assay was performed to quantify activity of the myeloperoxidase and concentrations of tumor necrosis factor-alpha (TNF-α) and interleukin 6 (IL-6) in the peritoneal irrigation fluid. RNA was isolated from the liver tissue, and real-time polymerase chain reaction was performed to measure relative messenger RNA levels of TNF-α and IL-6.

RESULTS

Treatment with Tub-A significantly improved survival compared with that of the control (69.2% versus 15.4%). In addition, Tub-A significantly suppressed myeloperoxidase activity (169.9 ± 8.4 ng/mL versus 70.4 ± 17.4 ng/mL; P < 0.01) and reduced levels of cytokines TNF-α and IL-6 in the peritoneal fluid (TNF-α: 105.7 ± 4.7 versus 7.4 ± 2.4 pg/mL; IL-6: 907.4 ± 2.3 versus 483.6 ± 1.6 pg/mL; P < 0.01) compared with those in the VEH control. Gene expression measured by real-time polymerase chain reaction confirmed that Tub-A inhibits transcription of TNF-α and IL-6.

CONCLUSIONS

Tub-A treatment significantly improves survival, attenuates inflammation, and downregulates TNF-α and IL-6 gene expression in a rodent two-hit model.

Hypothermia and valproic acid activate prosurvival pathways after hemorrhage

BACKGROUND

Therapeutic hypothermia (hypo) and valproic acid (VPA, a histone deacetylase inhibitor) have independently been shown to be protective in models of trauma and hemorrhagic shock but require logistically challenging doses to be effective. Theoretically, combined treatment may further enhance effectiveness, allowing us to use lower doses of each modality. The aim of this study was to determine whether a combination of mild hypo and VPA treatments would offer better cytoprotection compared with that of individual treatments in a hemorrhage model.

MATERIALS AND METHODS

Male Sprague-Dawley rats were subjected to 40% volume-controlled hemorrhage, kept in shock for 30 min, and assigned to one of the following treatment groups: normothermia (36°C-37°C), hypo (30 ± 2°C), normothermia + VPA (300 mg/kg), and hypo + VPA (n = 5 per group). After 3 h of observation, the animals were sacrificed, liver tissue was harvested and subjected to whole cell lysis, and levels of key proteins in the prosurvival Akt pathway were measured using Western blot.

RESULTS

Activation of the proapoptotic protein cleaved caspase-3 was significantly lower in the combined treatment group relative to normothermia (P < 0.05). Levels of the prosurvival Bcl-2 was significantly higher in the combined treatment group relative to sham, normothermia, and normothermia + VPA groups (P < 0.005). The downstream prosurvival protein phospho-GSK-3β was significantly higher in the sham, hypo, and combined treatment groups compared with that in normothermia groups with or without VPA (P < 0.05). Levels of the prosurvival β-catenin were significantly higher in the combined treatment group relative to normothermia (P < 0.01).

CONCLUSIONS

This is the first in vivo study to demonstrate that combined treatment with VPA and hypo offers better cytoprotection than these treatments given independently.