The protective effect of gamma aminobutyric acid B receptor activation on sympathetic nerve remodeling via the regulation of M2 macrophage polarization after myocardial infarction

INTRODUCTION & OBJECTIVES

Acute myocardial infarction (AMI) in coronary heart disease is a leading cause of sudden death primarily due to malignant ventricular arrhythmias (VAs). Inflammatory cell infiltration and inflammation-induced overactivation of sympathetic nerves are the major cause of VAs in AMI pathophysiological processes. Type 2 macrophages play an anti-inflammatory role in AMI. Targeting macrophages may be a therapeutic strategy to prevent VAs post AMI. We found that gamma aminobutyric acid (GABA) promotes macrophages polarized to M2 and hypothesized that GABA might exert anti-inflammatory effects by promoting type 2 macrophage polarization in AMI. We aim to characterized GABA_B receptor distribution, function, and mechanisms in M2 macrophage polarization and explored the functional aspect of GABA_B receptor activation in sympathetic remodeling.

RESULTS

Gamma aminobutyric acid B receptors were expressed on macrophage surface both in vitro and in vivo. GABA_B receptor agonist baclofen, GABA promoted macrophage switch to M2. While GABA_B receptor antagonist CGP52432 blocked a baclofen induced switch to M2 polarization. GABA and baclofen increased M2 macrophage percentage and CGP52432 blocked this process in vivo. Also, IL-10 and TGF-β1 released by M2 were increased in both AMI and baclofen/AMI group; Serum NE levels were decreased by baclofen. All the above effects were reversed by CGP52432 treatment. Baclofen decreased TH and GAP-43 staining while CGP52432 enhanced their expression post AMI indicating GABA_B receptor activation inhibited sympathetic nerve sprouting and activity by reducing NE release.

CONCLUSIONS

Gamma aminobutyric acid B receptor activation promoted M2 polarization and protested AMI heart by regulating sympathetic nerve remodeling.

The Interaction of Central Nervous System and Acute Kidney Injury: Pathophysiology and Clinical Perspectives

Acute kidney injury (AKI) is a common disorder in critically ill hospitalized patients. Its main pathological feature is the activation of the sympathetic nervous system and the renin-angiotensin system (RAS). This disease shows a high fatality rate. The reason is that only renal replacement therapy and supportive care can reduce the impact of the disease, but those measures cannot significantly improve the mortality. This review focused on a generalization of the interaction between acute kidney injury and the central nervous system (CNS). It was found that the CNS further contributes to kidney injury by regulating sympathetic outflow and oxidative stress in response to activation of the RAS and increased pro-inflammatory factors. Experimental studies suggested that inhibiting sympathetic activity and RAS activation in the CNS and blocking oxidative stress could effectively reduce the damage caused by AKI. Therefore, it is of significant interest to specify the mechanism on how the CNS affects AKI, as we could use such mechanism as a target for clinical interventions to further reduce the mortality and improve the complications of AKI.

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The sympathetic nervous system in acute kidney injury

Acute kidney injury (AKI) is frequently accompanied by activation of the sympathetic nervous system (SNS). This may result from pre-exisiting chronic diseases associated with sympathetic activation prior to AKI or it may be induced by stressors that ultimately lead to AKI such as endotoxins and arterial hypotension in circulatory shock. Conversely, sympathetic activation may also result from acute renal injury. Focusing on studies in experimental renal ischaemia and reperfusion (IR), this review summarizes the current knowledge on how the SNS is activated in IR-induced AKI and on the consequences of sympathetic activation for the development of acute renal damage. Experimental studies show beneficial effects of sympathoinhibitory interventions on renal structure and function in response to IR. However, few clinical trials obtained in scenarios that correspond to experimental IR, namely major elective surgery, showed that peri-operative treatment with centrally acting sympatholytics reduced the incidence of AKI. Apparently, discrepant findings on how sympathetic activation influences renal responses to acute IR-induced injury are discussed and future areas of research in this field are identified.

The Roles of GABA in Ischemia-Reperfusion Injury in the Central Nervous System and Peripheral Organs

Ischemia-reperfusion (I/R) injury is a common pathological process, which may lead to dysfunctions and failures of multiple organs. A flawless medical way of endogenous therapeutic target can illuminate accurate clinical applications. γ-Aminobutyric acid (GABA) has been known as a marker in I/R injury of the central nervous system (mainly in the brain) for a long time, and it may play a vital role in the occurrence of I/R injury. It has been observed that throughout cerebral I/R, levels, syntheses, releases, metabolisms, receptors, and transmissions of GABA undergo complex pathological variations. Scientists have investigated the GABAergic enhancers for attenuating cerebral I/R injury; however, discussions on existing problems and mechanisms of available drugs were seldom carried out so far. Therefore, this review would summarize the process of pathological variations in the GABA system under cerebral I/R injury and will cover corresponding probable issues and mechanisms in using GABA-related drugs to illuminate the concern about clinical illness for accurately preventing cerebral I/R injury. In addition, the study will summarize the increasing GABA signals that can prevent I/R injuries occurring in peripheral organs, and the roles of GABA were also discussed correspondingly.

The Role of Gamma Amino Butyric Acid in Cisplatin-induced Nephrotoxicity in Streptozotocin-induced Diabetic Rats

Background:

Diabetes mellitus can change the risk of developing cancer. Cisplatin (CP) is a common antineoplastic drug. The major side effect of CP is nephrotoxicity. Gamma amino butyric acid (GABA) is an antioxidant agent that may have a protective role against CP-induced nephrotoxicity. The aim of the present study was to investigate the role of GABA in CP-induced nephrotoxicity in hyperglycemic male and female rats.

Materials and Methods:

Sixty male and female Wistar diabetic rats were used in ten experimental groups. GABA alone groups received GABA (50 μmol/kg/d i.p.) for 12 days. CP alone groups received CP (2.5 mg/kg/d i.p.) for 6 days. Other groups received GABA in the form of therapy (T) + CP, prophylaxis (P) + CP, and prophylaxis-treatment (PT) + CP. Finally, blood samples were obtained, and animals were killed for kidney tissue investigation.

Results:

In female rats, the serum levels of creatinine (Cr) did not change by GABA rather than CP and also there were no significant changes in blood urea nitrogen to creatinine ratio (BUN/Cr). In male rats, plasma Cr level increased by GABA (P) and (T). Body weight loss was significantly different among groups (P < 0.05). BUN/Cr ratio significantly increased in CP and GABA (PT) + CP groups. In two genders, plasma Cr level significantly decreased in CP groups (P < 0.05). The kidney levels of malondialdehyde enhanced significantly in CP groups.

Conclusion:

Hyperglycemia has protective effect against CP-induced nephrotoxicity. GABA did not change this effect in female, but in male in the form of PT, GABA maintained it.