Carnosine Prevents Aβ-Induced Oxidative Stress and Inflammation in Microglial Cells: A Key Role of TGF-β1

Abstract

Carnosine (β-alanyl-L-histidine), a dipeptide, is an endogenous antioxidant widely distributed in excitable tissues like muscles and the brain. Carnosine is involved in cellular defense mechanisms against oxidative stress, including the inhibition of amyloid-beta (Aβ) aggregation and the scavenging of reactive species. Microglia play a central role in the pathogenesis of Alzheimer’s disease, promoting neuroinflammation through the secretion of inflammatory mediators and free radicals. However, the effects of carnosine on microglial cells and neuroinflammation are not well understood. In the present work, carnosine was tested for its ability to protect BV-2 microglial cells against oligomeric Aβ1-42-induced oxidative stress and inflammation. Carnosine prevented cell death in BV-2 cells challenged with Aβ oligomers through multiple mechanisms. Specifically, carnosine lowered the oxidative stress by decreasing NO and O2−• intracellular levels as well as the expression of iNOS and Nox enzymes. Carnosine also decreased the secretion of pro-inflammatory cytokines such as IL-1β, simultaneously rescuing IL-10 levels and increasing the expression and the release of TGF-β1. Carnosine also prevented Aβ-induced neurodegeneration in mixed neuronal cultures challenged with Aβ oligomers, and these neuroprotective effects were completely abolished by SB431542, a selective inhibitor of the type-1 TGF-β receptor. Our data suggest a multimodal mechanism of action of carnosine underlying its protective effects on microglial cells against Aβ toxicity with a key role of TGF-β1 in mediating these protective effects.

Modulation of Pro-Oxidant and Pro-Inflammatory Activities of M1 Macrophages by the Natural Dipeptide Carnosine

“…Furthermore, strong evidence that carnosine protects against pathologies characterized by oxidative stress and/or inflammation such as diabetes [29], depression [30], cerebral ischemia [31] and Alzheimer's disease (AD) [32] has been proved. In previous studies, we showed that 20 mM carnosine is highly effective to positively regulating macrophage and microglial functions [23,33]. In particular, we found that carnosine, in macrophages challenged with LPS + IFN-γ, increases the rate of NO transformation into its stable end-product nitrite, modulates the composition of macrophage sub-populations and decreases the release of pro-inflammatory cytokines into the cell medium.…”

“…Additionally, a significant deficit of TGF-β1, paralleling memory deficits and depressive-like phenotype, has been found in the hippocampus of Aβ-injected mice [89]. Very recently, the ability of carnosine to protect brain macrophages and neurons against Aβ-induced cell toxicity by increasing TGF-β1 expression and secretion has been proposed [23].…”

“…The concentration of total RNA, recovered from 4.5 × 10 5 control cells or cells treated with LPS + IFN-γ, without or with 1 h pre-treatment with carnosine for 6 or 24 h, was determined by measuring the absorbance at 260 nm with a NanoDrop ® ND-1000 (Thermo Fisher Scientific, Waltham, MA, USA). The protocol employed for reverse transcription, sample amplification, fluorescence data collection, and sample quantification is the same previously described by us [23], with slight modifications. Briefly, the mRNA extracted (RNeasy Mini Kit) from each sample (1 µg) was retrotranscripted (SuperScript III First-Strand Synthesis SuperMix kit) and the resultant cDNAs, loaded on a 384-well plate, were amplified by using specific, genomewide, bioinformatically validated primer sets.…”

A Path Toward Precision Medicine for Neuroinflammatory Mechanisms in Alzheimer's Disease

“…Aβ, amyloid beta; Aβ 1−42 , 42-amino acid-long amyloid beta peptide; BDNF, brain-derived neurotrophic factor; IL-1β, interleukin-1 beta; MMP-9, metalloprotease-9; NGF, nerve growth factor; mNGF, mature nerve growth factor; proNGF, precursor of the nerve growth factor; RNS, reactive nitrogen species; ROS, reactive oxygen species; TGF-β, transforming growth factor-beta; TNF-α, tumor necrosis factor-alpha. produce and release proinflammatory cytokines (14,68) and also by interfering with the synthesis of anti-inflammatory cytokines, for instance the transforming growth factor-beta 1 (TGF-β1) ( Figure 2) (69)(70)(71). This early proinflammatory process is characterized by neuronal and microglia-derived cytokines and chemokines as well as by mobilization of microglia toward Aβ-burdened neurons (Figure 2) (19,72).…”

Carnosine as a Possible Drug for Zinc-Induced Neurotoxicity and Vascular Dementia

“…Corona et al have demonstrated that carnosine supplementation inhibited AβP deposition and improved learning abilities of AD model mice [90]. Carnosine prevents the oxidative stress and inflammation induced by AβP [91]. We showed that carnosine attenuated the neuronal death induced by prion protein fragment peptide (PrP106-126) by changing its conformation [92].…”