Telmisartan Protects a Microglia Cell Line from LPS Injury Beyond AT1 Receptor Blockade or PPARγ Activation

Amorfrutin B Compromises Hypoxia/Ischemia-induced Activation of Human Microglia in a PPARγ-dependent Manner: Effects on Inflammation, Proliferation Potential, and Mitochondrial Status

Amorfrutin B is a selective PPARγ modulator that we demonstrated to be a promising neuroprotective compound in cellular models of stroke and perinatal asphyxia. Although neuronal mechanisms of amorfrutin B-evoked neuroprotection have been identified, none of them reflects the actions of the compound on microglia, which play a pivotal role in brain response to hypoxia/ischemia. Here, we provide evidence for amorfrutin B-induced effects on human microglia subjected to hypoxia/ischemia; the compound counteracts inflammation, and influences mitochondrial status and proliferation potential in a PPARγ-dependent manner. Post-treatment with amorfrutin B decreased the IBA1 fluorescence intensity, reduced caspase-1 activity, and downregulated IL1B/IL-1β and TNFA but not IL10/IL-10 expression, which was upregulated. Amorfrutin B also stimulated PPARγ signaling, as evidenced by increased mRNA and/or protein levels of PPARγ and PGC1α. In addition, amorfrutin B reversed the hypoxia/ischemia-evoked effects on mitochondria-related parameters, such as mitochondrial membrane potential, BCL2/BCL2 expression and metabolic activity, which were correlated with diminished proliferation potential of microglia. Interestingly, the inhibitory effect of amorfrutin B on the proliferation potential and mitochondrial function of microglia is opposite to the stimulatory effect of amorfrutin B on mouse neuronal survival, as evidenced by increased neuronal viability and reduced neurodegeneration. In summary, this study showed for the first time that amorfrutin B compromises hypoxia/ischemia-induced activation of human microglia in a PPARγ-dependent manner, which involves inhibiting inflammation, normalizing mitochondrial status, and controlling proliferation potential. These data extend the protective potential of amorfrutin B in the pharmacotherapy of hypoxic/ischemic brain injury, targeting not only neurons but also activated microglia.

Telmisartan inhibits microglia-induced neurotoxic A1 astrocyte conversion via PPARγ-mediated NF-κB/p65 degradation

Astrocytes are crucially involved in neuroinflammation. Activated astrocytes exhibit at least two phenotypes, A1 (neurotoxic) and A2 (neuroprotective). The A1 phenotype is the major reactive astrocyte phenotype involved in aging and neurodegenerative diseases. Telmisartan, which is an antihypertensive agent, is a promising neuroprotective agent. This study aimed to investigate the effects of telmisartan on the phenotype of reactive astrocytes. Astrocytes were activated by culturing with the conditioned medium derived from lipopolysaccharide-stimulated microglia. This conditioned medium induced early, transient A2 astrocyte conversion (within 24 h) and late, sustained A1 conversion (beginning at 24 h and lasting up to 7 days), with a concomitant increase in the production of pro-inflammatory cytokines (interleukin [IL]-1β, tumor necrosis factor [TNF]α, and IL-6) and phosphorylation of nuclear factor-κB (NF-κB)/p65. Telmisartan treatment promoted and inhibited A2 and A1 conversion, respectively. Telmisartan reduced total and phosphorylated p65 protein levels. Losartan, a specific angiotensin II type-1 receptor (AT1R) blocker, did not influence the reactive state of astrocytes. Additionally, AT1R activation by angiotensin II did not induce the expression of pro-inflammatory cytokines and A1/A2 markers, indicating that the AT1R signaling pathway is not involved in the astrocyte-mediated inflammatory response. A peroxisome proliferator-activated receptor γ (PPARγ) antagonist reversed the effects of telmisartan. Moreover, telmisartan-induced p65 downregulation was reversed by the proteasome inhibitor MG132. These results indicate that telmisartan suppresses activated microglia-induced neurotoxic A1 astrocyte conversion through p65 degradation. Our findings contribute towards the elucidation of the anti-inflammatory activity of telmisartan in brain disorders.

Anti-inflammatory and analgesic effects of Streblus indicus

The bark of Streblus indicus, a Dai medicine in China, has been listed in the Chinese Materia Medica as possessing hemostatic and analgesic properties. Ethnic medicine books record that its bark or leaves for the treatment of mumps and lymphoma. However, according to the literature survey, anti-inflammatory and analgesic studies available for leaves and branches of S. indicus have been seldom reported so far. The current study focuses on the metabolites of S. indicus bark and leaves responsible for anti-inflammatory and analgesic effects on the basis of bioactive-included acetic acid writhing, hot-plate, and xylene-induced ear swelling. The secretion of inflammatory mediators, TNF-α, IL-6, IL-1β, IL-4, and IL-10, were evaluated for their anti-inflammatory by xylene-induced in mouse ear cells. Histological examination was used to assess the anti-inflammatory and analgesic effects of the branches and leaves of S. indicus, and Western blot analysis determined the mechanism of the methanolic extract of branches and leaves. Different metabolites of S. indicus significantly alleviated analgesic and anti-inflammatory effects, with no discernable differences among them. All metabolites decreased the levels of TNF-α, IL-1β, and IL-6 and increased the levels of IL-4 and IL-10. The analgesic and anti-inflammatory mechanism of the methanolic extract was related to the NF-kB signaling pathway. These results not only would account for scientific knowledge for the traditional application of S. indicus, but also provide a credible theoretical foundation for the further development of anti-inflammatory and analgesic agents.

Therapeutic Implications of Renin-Angiotensin System Modulators in Alzheimer's Dementia

The Renin-Angiotensin System (RAS) has attracted considerable interest beyond its traditional cardiovascular role due to emerging data indicating its potential involvement in neurodegenerative diseases, including Alzheimer's dementia (AD). This review investigates the therapeutic implications of RAS modulators, specifically focusing on angiotensin-converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), and renin inhibitors in AD. ACEIs, commonly used for hypertension, show promise in AD by reducing angiotensin (Ang) II levels. This reduction is significant as Ang II contributes to neuroinflammation, oxidative stress, and β-amyloid (Aβ) accumulation, all implicated in AD pathogenesis. ARBs, known for vasodilation, exhibit neuroprotection by blocking Ang II receptors, improving cerebral blood flow and cognitive decline in AD models. Renin inhibitors offer a novel approach by targeting the initial RAS step, displaying anti-inflammatory and antioxidant effects that mitigate AD degeneration. Preclinical studies demonstrate RAS regulation's favorable impact on neuroinflammation, neuronal damage, cognitive function, and Aβ metabolism. Clinical trials on RAS modulators in AD are limited, but with promising results, ARBs being more effective that ACEIs in reducing cognitive decline. The varied roles of ACEIs, ARBs, and renin inhibitors in RAS modulation present a promising avenue for AD therapeutic intervention, requiring further research to potentially transform AD treatment strategies.

Serelaxin Inhibits Lipopolysaccharide-induced Inflammatory Response in Cardiac Fibroblasts by Activating Peroxisome Proliferator-activated Receptor-γ and Suppressing the Nuclear Factor-Kappa B Signaling Pathway

ABSTRACT

Serelaxin (sRLX) has an inhibitory effect on fibrosis. However, whether the antifibrotic effects of sRLX are achieved by inhibiting the inflammatory response has not been clarified. This study aimed to investigate the role of sRLX in lipopolysaccharide (LPS)-induced inflammation in cardiac fibroblasts and elucidate the underlying mechanisms. Cardiac fibroblasts were isolated from adult rat hearts. The effect of sRLX on the inhibition of the inflammatory response after LPS induction was examined. Cell viability was measured by MMT assay. Cell proliferation was determined using the Cell Counting Kit-8. The levels of inflammatory cytokines IL-1β, IL-6, TNF-α, and IL-10 were measured using an enzyme-linked immunosorbent assay. The mRNA levels of α-smooth muscle actin (α-SMA), collagen I/III, MMP-2, MMP-9, IL-1β, IL-6, TNF-α, IL-10, IκBα, p-IκBα, p65 subunit of nuclear factor-kappa B (NF-κB), and peroxisome proliferator-activated receptor-γ (PPAR-γ) were assessed by real-time quantitative PCR. The protein levels of α-SMA, collagen I/III, MMP-2, MMP-9, IκBα, p-IκBα, p65, p-p65, and PPAR-γ were examined by western blotting. sRLX inhibited LPS-induced IL-1β, IL-6, TNF-α, α-SMA, and collagen I/III, and elevated the expression of IL-10, MMP-2, and MMP-9. Moreover, LPS-induced activation of NF-κB pathway was suppressed by sRLX treatment. Further studies showed that sRLX did not significantly increase the expression of PPAR-γ mRNA and protein, but activated PPAR-γ activity, and the PPAR-γ inhibitor GW9662 reversed the inhibitory effect of sRLX on IL-1β, IL-6, and TNF-α production. These results suggest that sRLX alleviates cardiac fibrosis by stimulating PPAR-γ through a ligand-independent mechanism that subsequently abolish the expression of NF-κB signaling pathway.

Telmisartan Alleviates Alzheimer's Disease-Related Neuropathologies and Cognitive Impairments

BACKGROUND

Alzheimer's disease (AD) is the most common type of neurodegenerative disorder. There are few effective medications for halting the progression of AD. Telmisartan (TEL) is a widely used anti-hypertensive drug approved by FDA. Aside from treating hypertension, TEL has been revealed to provide protection against AD. However, the underlying mechanisms remain unclear.

OBJECTIVE

To investigate the mechanisms underlying the beneficial effects of TEL against AD.

METHODS

Eight-month-old APP/PS1 mice were administered with 5 mg/kg TEL once per day for 4 successive months. Nesting test, Y-maze test, and Morris water maze test were employed to assess the cognitive and executive functions. Neuronal and synaptic markers, Aβ pathology, neuroinflammation, and oxidative stress in the brains were measured. Specifically, components involved in amyloid-β (Aβ) production and degradation pathway were analyzed to explore the mechanisms underlying the therapeutic effect of TEL against Aβ pathology. The primary microglia were used to uncover the mechanisms underlying the anti-inflammatory effects of TEL in AD. Additionally, the preventive effect of TEL against AD were investigated using 4-month-old APP/PS1 mice.

RESULTS

TEL treatment ameliorated cognitive and executive impairments, neuronal and synaptic injury, Aβ pathology, neuroinflammation, and oxidative stress in APP/PS1 mice. The favorable effects of TEL on Aβ pathology were achieved by inhibiting enzymatic Aβ production and facilitating enzymatic and autophagic Aβ degradation. Meanwhile, the anti-inflammatory effects of TEL were accomplished via microglial PPARγ/NLRP3 pathway. The administration of TEL prior to symptom onset prevented AD-related cognitive decline and neuropathologies.

CONCLUSION

TEL represents a promising agent for AD prevention and treatment.

Knockdown of SEMA7A alleviates MPP+ -induced apoptosis and inflammation in BV2 microglia via PPAR-γ activation and MAPK inactivation

INTRODUCTION

The inflammation mediated by microglial cells plays an important role in the process of neurodegenerative diseases. Recent evidence indicates that semaphorin 7A (SEMA7A) is implicated in various neurodegenerative diseases, but whether it plays a role in Parkinson's disease (PD) remains unclear.

METHODS

In this study, 1.0 mmol/L 1-methyl-4-phenylpyridinium (MPP+ )-stimulated mouse microglia (BV2) cells were used as an in vitro model of PD. The expression of SEMA7A was detected by quantitative polymerase chain reaction. Cell Counting Kit-8 and apoptosis kits were used to analyze the viability and apoptosis of BV-2 cells. The content of IL-6, IL-β, and tumor necrosis factor-α was determined by ELISA (enzyme-linked immunosorbent assay) kit. Western blot was used to detect the protein expression level of the inducible NO synthase and cyclooxygenase-2.

RESULTS

Our findings indicated that SEMA7A expression in BV2 cells was upregulated after MPP+ stimulation. Knockdown of SEMA7A promoted cell viability while it inhibited apoptosis and the expression of proinflammatory enzymes and proinflammatory cytokines. Silencing SEMA7A-induced peroxisome proliferator-activated receptor-gamma (PPAR-γ) activation and mitogen-activated protein kinase (MAPK) signaling pathway inactivation. Furthermore, a PPAR-γ inhibitor and an MAPK activator promoted the effect of MPP+ on cell viability, apoptosis, and inflammation of BV2 cells; what is more, the PPAR-γ inhibitor and MAPK activator blocked the inhibitory effect of SEMA7A downregulation on MPP+ -induced injury.

CONCLUSION

In general, knockdown of SEMA7A inhibits MPP+ -induced BV2 cell apoptosis and inflammation via PPAR-γ activation and MAPK inactivation, which may provide a new therapy target for PD.

Sacubitril/valsartan alleviates sepsis-induced acute lung injury via inhibiting GSDMD-dependent macrophage pyroptosis in mice

Sepsis-induced acute lung injury (ALI) is a life-threatening disorder with intricate pathogenesis. Macrophage pyroptosis reportedly plays a vital role in ALI. Although it has been established that angiotensin receptor blockers (ARBs) can reduce sepsis-induced organ injury, the efficacy of sacubitril/valsartan (SV) for sepsis has been largely understudied. Here, we aimed to investigate the role of SV in sepsis-induced ALI. Caecal ligation and puncture (CLP) were used to induce polymicrobial sepsis and related ALI. The therapeutic effects of SV in CLP mice were subsequently assessed. Gasdermin D (GSDMD)^-/- mice were used to validate the signalling pathways affected by SV. In vitro, mouse bone marrow-derived macrophages (BMDMs) and Raw264.7 cells were treated with SV following exposure to lipopolysaccharide and adenosine triphosphate. Finally, the serum obtained from 42 septic patients was used for biochemical analysis. Compared to the other ARBs, SV yielded more pronounced anti-inflammatory effects on macrophages. In vivo, SV decreased mortality rates, significantly reduced lung damage and prevented the inflammatory response in CLP mice. In addition, SV suppressed GSDMD-mediated macrophage pyroptosis in mice. In BMDMs and Raw264.7 cells, the anti-inflammatory and anti-pyroptosis properties of SV were verified. SV treatment effectively inhibited NLRP3 inflammasome activation and prevented macrophage pyroptosis in a GSDMD-dependent manner. Furthermore, we found that septic individuals had considerably higher serum angiotensin II levels. Overall, we found that SV might prevent ALI in CLP mice by inhibiting GSDMD-mediated pyroptosis of macrophages. Thus, SV might be a viable drug for sepsis-induced ALI.

Asperosaponin VI ameliorates the CMS-induced depressive-like behaviors by inducing a neuroprotective microglial phenotype in hippocampus via PPAR-γ pathway

Background

The natural compound asperosaponin VI has shown potential as an antidepressant, but how it works is unclear. Here, we explored its effects on mice exposed to chronic mild stress (CMS) and the underlying molecular pathways.

Methods

Mice were exposed to CMS for 3 weeks followed by asperosaponin VI (40 mg/kg) or imipramine (20 mg/kg) for another 3 weeks. Depression-like behaviors were assessed in the forced swimming test (FST), sucrose preference test (SPT), tail suspension test (TST). Microglial phenotypes were evaluated using immunofluorescence staining, real-time quantitative PCR and enzyme-linked immunosorbent assays in hippocampus of mice. In some experiments, stressed animals were treated with the PPAR-γ antagonist GW9662 to examine its involvement in the effects of asperosaponin VI. Blockade of PPAR-γ in asperosaponin VI-treated primary microglia in the presence of lipopolysaccharide (LPS) was executed synchronously. The nuclear transfer of PPAR-γ in microglia was detected by immunofluorescence staining in vitro and in vivo. A co-cultured model of neuron and microglia was used for evaluating the regulation of ASA VI on the microglia–neuron crosstalk molecules.

Results

Asperosaponin VI ameliorated depression-like behaviors of CMS mice based on SPT, TST and FST, and this was associated with a switch of hippocampal microglia from a pro-inflammatory (iNOS⁺-Iba1⁺) to neuroprotective (Arg-1⁺-Iba1⁺) phenotype. CMS reduced the expression levels of PPAR-γ and phosphorylated PPAR-γ in hippocampus, which asperosaponin VI partially reversed. GW9662 treatment prevented the nuclear transfer of PPAR-γ in asperosaponin VI-treated microglia and inhibited the induction of Arg-1⁺ microglia. Blockade of PPAR-γ signaling also abolished the ability of asperosaponin VI to suppress pro-inflammatory cytokines while elevating anti-inflammatory cytokines in the hippocampus of CMS mice. The asperosaponin VI also promoted interactions between hippocampal microglia and neurons by enhancing CX3CL1/CX3CR1 and CD200/CD200R, and preserved synaptic function based on PSD95, CamKII β and GluA levels, but not in the presence of GW9662. Blockade of PPAR-γ signaling also abolished the antidepressant effects of asperosaponin VI in the SPT, TST and FST.

Conclusion

CMS in mice induces a pro-inflammatory microglial phenotype that causes reduced crosstalk between microglia and neuron, inflammation and synaptic dysfunction in the hippocampus, ultimately leading to depression-like behaviors. Asperosaponin VI may ameliorate the effects of CMS by inducing microglia to adopt a PPAR-γ-dependent neuroprotective phenotype.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02478-y.

Addressing Peroxisome Proliferator-Activated Receptor-gamma in 3-Nitropropionic Acid-Induced Striatal Neurotoxicity in Rats

Telmisartan (TEL) is an angiotensin II type 1 receptor blocker and a partial activator of peroxisome proliferator-activated receptor-gamma (PPARγ), which regulates inflammatory and apoptotic pathways. Increasing evidence has demonstrated the PPARγ agonistic property of TEL in several brain disorders. This study aims to explore the neuroprotective impact of TEL in 3-nitropropionic acid (3-NP)-induced neurotoxicity in rats. The PPARγ effect of TEL was affirmed by using the PPARγ agonist pioglitazone (PIO), and the antagonist GW9662. 3-NP led to a significant reduction in body weight alongside motor and cognitive functioning. The striata of the 3-NP-treated rats showed energy-deficit, microglia-mediated inflammatory reactions, apoptotic damage as well as histopathological lesions. PIO and TEL improved motor and cognitive perturbations induced by 3-NP, as confirmed by striatal histopathological examination, energy restoration, and neuronal preservation. Both drugs improved mitochondrial biogenesis evidenced by elevated mRNA expression of PPARγ, PGC-1α, and TFAM, alongside increased striatal ATP and SDH. The mitochondrial effect of TEL was beyond PPARγ activation. As well, their anti-inflammatory effect was attributed to suppression of microglial activation, and protein expression of pS536 p65 NF-κB with marked attenuation of striatal inflammatory mediator's release. Anti-inflammatory cytokine IL-10 expression was concurrently increased. TEL effectively participated in neuronal survival as it promoted phosphorylation of Akt/GSK-3β, further increased Bcl-2 expression, and inhibited cleavage of caspase-3. Interestingly, co-treatment with GW9662 partially revoked the beneficial effects of TEL. These findings recommend that TEL improves motor and cognitive performance, while reducing neuronal inflammation and apoptosis in 3-NP-induced neurotoxicity via a PPARγ-dependent mechanism.

Telmisartan ameliorates LPS-induced pneumonia in rats through regulation of the PPARγ/NF-κB pathway

Pneumonia is a common disorder of the respiratory system associated with inflammation. Telmisartan (TEL) has been reported to treat inflammatory-related diseases. The current study is aimed to make investigations for the possible role and action mechanism of TEL on lipopolysaccharide (LPS)-induced pneumonia rats. Forty male Sprague Dawley (SD) rats aged 8 weeks were assigned into four groups ad libitum: a control group received saline only, an experimental group received LPS, a group received TEL (5 mg/kg), followed by LPS treatment, and a group received TEL (10 mg/kg), followed by LPS treatment. LPS (2 mg/kg) and equal saline were administered intratracheally. TEL was orally administrated 5 days before LPS. After LPS treatment for 24 h, bronchoalveolar lavage fluid (BALF) and serum were collected for the analysis of cell counts and/or cytokines. Lung tissues were used to perform histological examination, assess oxidative stress levels, and determine the levels of PPARγ/NF-κB pathway-related proteins. Rats received LPS treatment exhibited high levels of lung wet/dry ratio, ALP, LDH, BALF polymorphonuclear leukocytes count, inflammatory cytokines, and oxidative stress. Meanwhile, LPS also resulted in severe interstitial edema and inflammatory cells infiltration. Interestingly, TEL by oral administration remarkably ameliorated the adverse effects on pneumonia rats caused by LPS. In addition, western blotting further revealed that TEL could activate PPARγ and repress NF-κB (p65). TEL is protective against pneumonia through inhibition of the inflammation and oxidative stress via the PPARγ/NF-κB pathway. This article is protected by copyright. All rights reserved.

The Antihypertensive Drug Telmisartan Protects Oligodendrocytes from Cholesterol Accumulation and Promotes Differentiation by a PPAR-γ-Mediated Mechanism

Our previous studies have demonstrated that specific peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists play a fundamental role in oligodendrocyte progenitor (OP) differentiation, protecting them against oxidative and inflammatory damage. The antihypertensive drug Telmisartan (TLM) was shown to act as a PPAR-γ modulator. This study investigates the TLM effect on OP differentiation and validates its capability to restore damage in a pharmacological model of Niemann-Pick type C (NPC) disease through a PPAR-γ-mediated mechanism. For the first time in purified OPs, we demonstrate that TLM-induced PPAR-γ activation downregulates the type 1 angiotensin II receptor (AT1), the level of which naturally decreases during differentiation. Like other PPAR-γ agonists, we show that TLM promotes peroxisomal proliferation and promotes OP differentiation. Furthermore, TLM can offset the OP maturation arrest induced by a lysosomal cholesterol transport inhibitor (U18666A), which reproduces an NPC1-like phenotype. In the NPC1 model, TLM also reduces cholesterol accumulation within peroxisomal and lysosomal compartments and the contacts between lysosomes and peroxisomes, revealing that TLM can regulate intracellular cholesterol transport, crucial for myelin formation. Altogether, these data indicate a new potential use of TLM in hypomyelination pathologies such as NPC1, underlining the possible repositioning of the drug already used in other pathologies.

Microglial TREM2 Mitigates Inflammatory Responses and Neuronal Apoptosis in Angiotensin II-Induced Hypertension in Middle-Aged Mice

Growing evidence suggests that hypertension and aging are prominent risk factors for the development of late-onset Alzheimer's disease (LOAD) by inducement of neuroinflammation. Recent study showed that neuroinflammation via activated microglia induces reactive astrocytes, termed A1 astrocytes, that highly upregulate numerous classical complement cascade genes that are destructive to neurons in neurodegeneration diseases. Moreover, triggering receptor expressed on myeloid cells 2 (TREM2) is considered as one of the strongest single-allele genetic risk factors and plays important roles in neuroinflammation for LOAD. However, the mechanisms of microglia in the regulation of A1 astrocytic activation are still not clear. We introduced angiotensin II-induced hypertension in middle-aged mice and found that hypertension-upregulated TREM2 expression and A1 astrocytic activation were involved in neuroinflammation in the animal models used in this study. The in vitro results revealed that overexpression of microglial TREM2 not only mitigated microglial inflammatory response but also had salutary effects on reverse A1 astrocytic activation and neuronal toxicity.

Angiotensin Receptor Blockers Are Not Just for Hypertension Anymore

Beyond blood pressure control, angiotensin receptor blockers reduce common injury mechanisms, decreasing excessive inflammation and protecting endothelial and mitochondrial function, insulin sensitivity, the coagulation cascade, immune responses, cerebrovascular flow, and cognition, properties useful to treat inflammatory, age-related, neurodegenerative, and metabolic disorders of many organs including brain and lung.

Losartan Treatment Could Improve the Outcome of TBI Mice

Traumatic brain injury frequently leads to serious mortality and physical disability, yet effective treatments remains insufficient. TBI always leads to a series of secondary brain injuries including neuronal apoptosis, continuous inflammation, endoplasmic reticulum stress, and disruption of the blood-brain barrier. Sartans that block angiotensin II type 1 receptors are strongly neuroprotective, neurorestorative and anti-inflammatory. However, whether losartan, a FDA-approved and widely used drug for regulating blood pressure, is beneficial for improving the prognosis of TBI need more evidence. Through a controlled cortical impact injury mice model, we confirmed that losartan treatment could ameliorate CCI-induced secondary brain injury. We found that losartan treatment decreased brain lesion volume, neuronal apoptosis and ER stress protein ATF4 and eIF2α. Moreover, our results showed that losartan also improved neurological and motor function. It is worth pointing out that losartan increased the expression of tight junction proteins ZO-1 and alleviated brain edema and blood brain barrier leakage. Additionally, losartan inhibited pro-inflammatory factor TNF-α and improve anti-inflammatory factor IL-10. Taken together, our data demonstrated that losartan could improve the prognosis of TBI and may be a promising therapeutic method for mitigating TBI.

The role of the brain renin-angiotensin system (RAS) in mild traumatic brain injury (TBI)

There is considerable interest in traumatic brain injury (TBI) induced by repeated concussions suffered by athletes in sports, military personnel from combat-and non-combat related activities, and civilian populations who suffer head injuries from accidents and domestic violence. Although the renin-angiotensin system (RAS) is primarily a systemic cardiovascular regulatory system that, when dysregulated, causes hypertension and cardiovascular pathology, the brain contains a local RAS that plays a critical role in the pathophysiology of several neurodegenerative diseases. This local RAS includes receptors for angiotensin (Ang) II within the brain parenchyma, as well as on circumventricular organs outside the blood-brain-barrier. The brain RAS acts primarily via the type 1 Ang II receptor (AT₁R), exacerbating insults and pathology. With TBI, the brain RAS may contribute to permanent brain damage, especially when a second TBI occurs before the brain recovers from an initial injury. Agents are needed that minimize the extent of injury from an acute TBI, reducing TBI-mediated permanent brain damage. This review discusses how activation of the brain RAS following TBI contributes to this damage, and how drugs that counteract activation of the AT₁R including AT₁R blockers (ARBs), renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, and agonists at type 2 Ang II receptors (AT₂) and at Ang (1-7) receptors (Mas) can potentially ameliorate TBI-induced brain damage.

Telmisartan Inhibits TNFα-Induced Leukocyte Adhesion by Blocking ICAM-1 Expression in Astroglial Cells but Not in Endothelial Cells

Telmisartan is an angiotensin-II receptor blocker and acts as a selective modulator of peroxisome proliferator-activated receptor gamma (PPARγ). Several studies have demonstrated that telmisartan ameliorates depression and memory dysfunction and reduces brain inflammation. We hypothesized that the beneficial effects of telmisartan on brain could be due to modulation of the blood-brain barrier (BBB) function. Here, we examined the effect of telmisartan on tumor necrosis factor alpha (TNF-α)-induced expression of intercellular adhesion molecule 1 (ICAM-1) which plays an important role in leukocyte transcytosis through the BBB. Telmisartan blocked TNF-α-induced ICAM-1 expression and leukocyte adhesion in U87MG human glioma cells but showed no effect on human brain microvascular endothelial cells. In U87MG cells, a PPAR antagonist, GW9662 did not block the effect of telmisartan on ICAM1 expression but rather potentiated. Moreover, GW9662 caused no change in TNF-α-induced ICAM-1 expression, suggesting no implication of PPARγ in the telmisartan effect. Further studies showed that telmisartan blocked TNF-α- induced activation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and nuclear factorkappa B (NF-κB). In contrast, inhibitors of JNK, ERK1/2 and NF-κB but not p38, blocked ICAM-1 expression induced by TNF-α. Thus, our findings suggest that the beneficial effect of telmisartan is likely due to the reduction of astrocytic ICAM1 expression and leukocytes adhesion to astrocytes, and that this response was mediated by the inhibition of JNK/ERK1/2/NF-κB activation and in the PPAR-independent manner. In conclusion, this study enhances our understanding of the mechanism by which telmisartan exerts the beneficial brain function.

Candesartan Neuroprotection in Rat Primary Neurons Negatively Correlates with Aging and Senescence: a Transcriptomic Analysis

Preclinical experiments and clinical trials demonstrated that angiotensin II AT₁ receptor overactivity associates with aging and cellular senescence and that AT₁ receptor blockers (ARBs) protect from age-related brain disorders. In a primary neuronal culture submitted to glutamate excitotoxicity, gene set enrichment analysis (GSEA) revealed expression of several hundred genes altered by glutamate and normalized by candesartan correlated with changes in expression in Alzheimer's patient's hippocampus. To further establish whether our data correlated with gene expression alterations associated with aging and senescence, we compared our global transcriptional data with additional published datasets, including alterations in gene expression in the neocortex and cerebellum of old mice, human frontal cortex after age of 40, gene alterations in the Werner syndrome, rodent caloric restriction, Ras and oncogene-induced senescence in fibroblasts, and to tissues besides the brain such as the muscle and kidney. The most significant and enriched pathways associated with aging and senescence were positively correlated with alterations in gene expression in glutamate-injured neurons and, conversely, negatively correlated when the injured neurons were treated with candesartan. Our results involve multiple genes and pathways, including CAV1, CCND1, CDKN1A, CHEK1, ICAM1, IL-1B, IL-6, MAPK14, PTGS2, SERPINE1, and TP53, encoding proteins associated with aging and senescence hallmarks, such as inflammation, oxidative stress, cell cycle and mitochondrial function alterations, insulin resistance, genomic instability including telomere shortening and DNA damage, and the senescent-associated secretory phenotype. Our results demonstrate that AT₁ receptor blockade ameliorates central mechanisms of aging and senescence. Using ARBs for prevention and treatment of age-related disorders has important translational value.