PKR inhibitor imoxin prevents hypertension, endothelial dysfunction and cardiac and vascular remodelling in L-NAME-treated rats

Activation of protein kinase receptor (PKR) plays a pro-viral role in mammarenavirus-infected cells

Many viruses, including mammarenaviruses, have evolved mechanisms to counteract different components of the host cell innate immunity, which is required to facilitate robust virus multiplication. The double-stranded RNA (dsRNA) sensor protein kinase receptor (PKR) pathway plays a critical role in the cell anti-viral response. Whether PKR can restrict the multiplication of the Old World mammarenavirus lymphocytic choriomeningitis virus (LCMV) and the mechanisms by which LCMV may counteract the anti-viral functions of PKR have not yet been investigated. Here we present evidence that LCMV infection results in very limited levels of PKR activation, but LCMV multiplication is enhanced in the absence of PKR. In contrast, infection with a recombinant LCMV with a mutation affecting the 3'-5' exonuclease (ExoN) activity of the viral nucleoprotein resulted in robust PKR activation in the absence of detectable levels of dsRNA, which was associated with severely restricted virus multiplication that was alleviated in the absence of PKR. However, pharmacological inhibition of PKR activation resulted in reduced levels of LCMV multiplication. These findings uncovered a complex role of the PKR pathway in LCMV-infected cells involving both pro- and anti-viral activities.IMPORTANCEAs with many other viruses, the prototypic Old World mammarenavirus LCMV can interfere with the host cell innate immune response to infection, which includes the dsRNA sensor PKR pathway. A detailed understanding of LCMV-PKR interactions can provide novel insights about mammarenavirus-host cell interactions and facilitate the development of effective anti-viral strategies against human pathogenic mammarenaviruses. In the present work, we present evidence that LCMV multiplication is enhanced in PKR-deficient cells, but pharmacological inhibition of PKR activation unexpectedly resulted in severely restricted propagation of LCMV. Likewise, we document a robust PKR activation in LCMV-infected cells in the absence of detectable levels of dsRNA. Our findings have revealed a complex role of the PKR pathway during LCMV infection and uncovered the activation of PKR as a druggable target for the development of anti-viral drugs against human pathogenic mammarenaviruses.

Refractory IgA Nephropathy: A Challenge for Future Nephrologists

IgA nephropathy (IgAN) represents the most prevalent form of primary glomerulonephritis, and, on a global scale, it ranks among the leading culprits behind end-stage kidney disease (ESKD). Presently, the primary strategy for managing IgAN revolves around optimizing blood pressure and mitigating proteinuria. This is achieved through the utilization of renin-angiotensin system (RAS) inhibitors, namely, angiotensin-converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARBs). As outlined by the KDIGO guidelines, individuals who continue to show a persistent high risk of progressive ESKD, even with comprehensive supportive care, are candidates for glucocorticoid therapy. Despite these therapies, some patients have a disease refractory to treatment, defined as individuals that present a 24 h urinary protein persistently >1 g after at least two rounds of regular steroids (methylprednisolone or prednisone) and/or immunosuppressant therapy (e.g., mycophenolate mofetil), or who do not tolerate regular steroids and/or immunosuppressant therapy. The aim of this Systematic Review is to revise the current literature, using the biomedical database PubMed, to investigate possible therapeutic strategies, including SGLT2 inhibitors, endothelin receptor blockers, targeted-release budesonide, B cell proliferation and differentiation inhibitors, fecal microbiota transplantation, as well as blockade of complement components.

Elevated levels of IL-6 in IgA nephropathy patients are induced by an epigenetically driven mechanism modulated by viral and bacterial RNA

BACKGROUND

Immunoglobulin A nephropathy (IgAN) is the most frequent primary glomerulonephritis and the role of IL-6 in pathogenesis is becoming increasingly important. A recent whole genome DNA methylation screening in IgAN patients identified a hypermethylated region comprising the non-coding RNA Vault RNA 2-1 (VTRNA2-1) that could explain the high IL-6 levels.

METHODS

The pathway leading to IL-6 secretion controlled by VTRNA2-1, PKR, and CREB was analyzed in peripheral blood mononuclear cells (PBMCs) isolated from healthy subjects (HS), IgAN patients, transplanted patients with or without IgAN. The role of double and single-strand RNA in controlling the pathway was investigated.

RESULTS

VTRNA2-1 was downregulated in IgAN compared to HS and in transplanted IgAN patients (TP-IgAN) compared to non-IgAN transplanted (TP). The loss of the VTRNA2-1 natural restrain in IgAN patients caused PKR hyperphosphorylation, and consequently the activation of CREB by PKR, which, in turn, led to high IL-6 production, both in IgAN and in TP-IgAN patients. IL-6 levels could be decreased by the PKR inhibitor imoxin. In addition, PKR is normally activated by bacterial and viral RNA, and we found that both the RNA poly(I:C), and the COVID-19 RNA-vaccine stimulation significantly increased the IL-6 levels in PBMCs from HS but had an opposite effect in those from IgAN patients.

CONCLUSION

The discovery of the upregulated VTRNA2-1/PKR/CREB/IL-6 pathway in IgAN patients may provide a novel approach to treating the disease and may be useful for the development of precision nephrology and personalized therapy by checking the VTRNA2-1 methylation level in IgAN patients.

1,8-Cineole ameliorates endothelial injury and hypertension induced by L-NAME through regulation of autophagy via PI3K/mTOR signaling pathway

Our previous data confirmed that 1,8-Cineole had an antihypertensive effect in animal models. However, it is unclear whether antihypertension is dependent on the protective effect of 1,8-Cinceole on endothelial function and structure. At present, the purpose was to investigate the protective effects of 1,8-Cineole on vascular endothelial tissue in hypertensive rats and human umbilical vein endothelial cells (HUVECs). Our results showed that 1,8-Cineole significantly reduced the blood pressure and improved the vascular endothelial lesion, attenuated vascular oxidative stress and inflammation induced by L-nitroarginine methyl ester hydrochloride (L-NAME) in rats. Pretreatment with 1,8-Cineole was able to inhibit the increase in malondialdehyde (MDA) and reactive oxygen species (ROS) induced by L-NAME, and increased the release and expression of superoxide dismutase (SOD) and nitric oxide (NO). In addition, 1,8-Cineole also reversed the increase of autophagy-associated protein LC3Ⅱ/LC3Ⅰ and the decrease of P62 in vivo and in vitro respectively. There was a synergistic effect between PI3K agonists and drugs, while PI3K inhibitors blocked the efficacy of 1,8-Cineole. The addition of autophagy inhibitor CQ increases the expression of eNOS. Taken together, our results indicate that 1,8-Cineole has potential beneficial promising antihypertension depending on the integrity of vascular endothelial structure and function induced by L-NAME, and the mechanism involves ameliorating autophagy by regulatiing of PI3K/mTOR.

The antihypertensive and diuretic effect of crude root extract and saponins from Solanum sisymbriifolium Lam., in L-NAME-induced hypertension in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Solanum sisymbriifolium Lam., is used in Paraguayan folk medicine claiming antihypertensive and diuretic properties.

AIM OF THE STUDY

This study aimed to determine the influence of chronic oral administration of the crude root extract and saponins obtained from S. sisymbriifolium Lam., on the blood pressure of male and female rats with hypertension induced by L-NAME, and its consequences on diuresis, the body weight, blood glucose, and level of serum parameters of liver and kidney functionality.

MATERIALS AND METHODS

Wistar rats were randomly divided into seven male, and seven female groups (8 animals each), which received as 6-week pretreatment, 0.9% saline solution (two groups; 0.1mL/10 g of b.w.), L-arginine (100.0 mg/kg/day), enalapril (15.0 mg/kg/day), crude extract (CESs 100.0 mg/kg/day), and saponin purified fraction (1.0, and 10.0 mg/kg/day), and treated with L-NAME (20 mg/kg/day/i.p.) twice, 1, and 6 h after pre-treatment. The animals' body weight, glycemia, and blood pressure were recorded weekly, while serum, hepatic, renal, and histological parameters were analyzed at the end of 6-week of treatment.

RESULTS

A protective effect of CESs (100.0 mg/kg/day), and saponins (1.0, and 10.0 mg/kg/day) against hypertension induced by L-NAME was verified in the systolic, diastolic, and mean blood pressure values, which were significantly lower than the positive L-NAME-hypertensive control group (male and female) at the end of the 6-week treatment. Also, pretreatment with enalapril (15.0 mg/kg/day) induced an efficient protective activity, which validates the method used. Likewise, the volume of urine, creatinine, uric acid, urea, and electrolyte excretion was enhanced at the end of 6-week of treatment in concordance with the reduction in serum level of the same parameters, compatible with the improvement of the diuretic activity. The glycemia, body weight, heart rate, and functional hepato-renal parameters were not modified after a 6-week of treatment, in comparison to the control group, indicating relatively acceptable harmless properties of CESs and saponins. Interestingly, the HDL level in females was increased in contrast to male rats by chronic saponins treatment when compared with the negative control group.

CONCLUSIONS

It can be concluded that either the increment in blood pressure (systolic, diastolic, and median) or cardiorenal remodeling effects in male and female rats submitted to L-NAME-induced hypertensive condition, were prevented and well-preserved without a significant variation during a period of 6-week of pretreatment with CESs and saponins pretreatments. Likewise, an important diuretic effect was revealed after this period of treatment.

Daily consumption of wild olive (acebuche) oil reduces blood pressure and ameliorates endothelial dysfunction and vascular remodelling in rats with NG-nitro-L-arginine methyl ester-induced hypertension

Despite numerous reports on the beneficial effects of olive oil in the cardiovascular context, very little is known about the olive tree's wild counterpart (Olea europaea, L. var. sylvestris), commonly known as acebuche (ACE) in Spain. The aim of this study was to analyse the possible beneficial effects of an extra virgin ACE oil on vascular function in a rodent model of arterial hypertension (AH) induced by NG-nitro-l-arginine methyl ester (L-NAME). Four experimental groups of male Wistar rats were studied: (1) normotensive rats (Control group); (2) normotensive rats fed a commercial diet supplemented with 15 % (w/w) ACE oil (Acebuche group); (3) rats made hypertensive following administration of L-NAME (L-NAME group); and (4) rats treated with L-NAME and simultaneously supplemented with 15 % ACE oil (LN + ACE group). All treatments were maintained for 12 weeks. Besides a significant blood pressure (BP)-lowering effect, the ACE oil-enriched diet counteracted the alterations found in aortas from hypertensive rats in terms of morphology and responsiveness to vasoactive mediators. In addition, a decrease in hypertension-related fibrotic and oxidative stress processes was observed in L-NAME-treated rats subjected to ACE oil supplement. Therefore, using a model of AH via nitric oxide depletion, here we demonstrate the beneficial effects of a wild olive oil based upon its vasodilator, antihypertensive, antioxidant, antihypertrophic and antifibrotic properties. We postulate that regular inclusion of ACE oil in the diet can alleviate the vascular remodelling and endothelial dysfunction processes typically found in AH, thus resulting in a significant reduction of BP.

The double-stranded RNA-dependent protein kinase inhibitor alleviates endoplasmic reticulum stress and alleviates sepsis-induced renal injury

The double-stranded RNA-dependent protein kinase (PKR) is involved in inflammatory cytokine expression and disease pathogenesis in many conditions. The aim of this study was to explore the role of PKR in sepsis-induced renal tissue injury. Six-week-old C57BL/6J mice received PKR inhibitor (imoxin) and Endoplasmic reticulum (ER) inducer (tunicamycin) 2 hr prior to induction of inflammation via cecal ligation and puncture (CLP). Renal tissues were collected 24 hr after the CLP treatment and protein expression were assessed. The expression of creatinine (Cre) and blood urea nitrogen (BUN) in serum and inflammation factor in tissues was detected by ELISA, and the apoptosis of renal tissue was detected by TUNEL staining. PKR inhibitors reduce the expression of sepsis-induced ER stress in renal tissue, as well as the pathological changes and renal impairment in renal tissue. PKR inhibitors reduce the expression of sepsis-induced inflammatory response and sepsis-induced apoptosis in renal tissue by ER stress. In conclusion, PKR inhibitor alleviates ER stress and alleviates sepsis-induced renal injury.

Protein Kinase R in Bacterial Infections: Friend or Foe?

The global antimicrobial resistance crisis poses a significant threat to humankind in the coming decades. Challenges associated with the development of novel antibiotics underscore the urgent need to develop alternative treatment strategies to combat bacterial infections. Host-directed therapy is a promising new therapeutic strategy that aims to boost the host immune response to bacteria rather than target the pathogen itself, thereby circumventing the development of antibiotic resistance. However, host-directed therapy depends on the identification of druggable host targets or proteins with key functions in antibacterial defense. Protein Kinase R (PKR) is a well-characterized human kinase with established roles in cancer, metabolic disorders, neurodegeneration, and antiviral defense. However, its role in antibacterial defense has been surprisingly underappreciated. Although the canonical role of PKR is to inhibit protein translation during viral infection, this kinase senses and responds to multiple types of cellular stress by regulating cell-signaling pathways involved in inflammation, cell death, and autophagy – mechanisms that are all critical for a protective host response against bacterial pathogens. Indeed, there is accumulating evidence to demonstrate that PKR contributes significantly to the immune response to a variety of bacterial pathogens. Importantly, there are existing pharmacological modulators of PKR that are well-tolerated in animals, indicating that PKR is a feasible target for host-directed therapy. In this review, we provide an overview of immune cell functions regulated by PKR and summarize the current knowledge on the role and functions of PKR in bacterial infections. We also review the non-canonical activators of PKR and speculate on the potential mechanisms that trigger activation of PKR during bacterial infection. Finally, we provide an overview of existing pharmacological modulators of PKR that could be explored as novel treatment strategies for bacterial infections.

Preclinical rodent models of cardiac fibrosis

Cardiac fibrosis (scarring), characterised by an increased deposition of extracellular matrix (ECM) proteins, is a hallmark of most types of cardiovascular disease and plays an essential role in heart failure progression. Inhibition of cardiac fibrosis could improve outcomes in patients with cardiovascular diseases and particularly heart failure. However, pharmacological treatment of the ECM build-up is still lacking. In this context, preclinical models of heart disease are important tools for understanding the complex pathogenesis involved in the development of cardiac fibrosis which in turn could identify new therapeutic targets and the facilitation of antifibrotic drug discovery. Many preclinical models have been used to study cardiac fibrosis and each model provides mechanistic insights into the many factors that contribute to cardiac fibrosis. This review discusses the most frequently used rodent models of cardiac fibrosis and also provides context for the use of particular models of heart failure.

COVID-19 and hypertension: Is there a role for dsRNA and activation of Toll-like receptor 3?

The virus responsible for the coronavirus disease of 2019 (COVID-19) is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Evidences suggest that COVID-19 could trigger cardiovascular complications in apparently healthy patients. Coronaviruses are enveloped positive-strand RNA viruses acting as a pathogen-associated molecular pattern (PAMP)/ danger-associated molecular patterns (DAMP). Interestingly, Toll-like receptor (TLR) 3 recognize both PAMPs DAMPs and is activated by viral double-stranded RNA (dsRNA) leading to activation of TIR receptor domain-containing adaptor inducing IFN-β (TRIF) dependent pathway. New evidence has shown a link between virus dsRNA and increased BP. Hence, we hypothesize that COVID-19 infection may be over activating the TLR3 through dsRNA, evoking further damage to the patients, leading to vascular inflammation and increased blood pressure, favoring the development of several cardiovascular complications, including hypertension.

Up-regulation of PKR pathway contributes to L-NAME induced hypertension and renal damage

Objective

Hypertension induced kidney damage is often associated with fibrosis and tubular apoptosis. Double-stranded protein kinase (PKR) is a well recognized inducer of inflammation and apoptosis. However, role of PKR in hypertension coupled renal damage is still not explored. Therefore here we sought to investigate the role of PKR in the pathogenesis of L-NAME induced hypertension and renal damage in Wistar rats and the underneath molecular mechanism.

Methods

L-NAME (40 mg/kg, p.o) and imoxin (0.5 mg/kg, i.p) was given to Wistar rats for 4 weeks. Increased eNOS expression, serum creatinine, BUN and changes in mean arterial pressure confirmed for hypertensive renal damage. Western blot and immunohistochemistry was carried out for PKR and markers for fibrosis and apoptosis. Morphological alterations were assessed by H&E staining. Sirius red and Masson's Trichrome staining was performed for collagen and fibrosis. TUNEL assay was done for tubular cell death and apoptosis.

Results

Increased expression of PKR and its downstream markers were reported in L-NAME rats, attenuation was observed with imoxin treatment. L-NAME treated rats showed a significant increase in MAP, serum calcium, creatinine and BUN along with the significant morphological changes, attenuation was reported with the imoxin treatment.

Conclusion

PKR is a core contributor in the pathogenesis of L-NAME induced renal damage and tubular apoptosis. Therapeutically targeting of PKR could be an attractive approach to treat the renal complications associated with hypertension.