Iron scavenging and suppression of collagen cross-linking underlie antifibrotic effects of carnosine in the heart with obesity

Oral consumption of histidyl dipeptides such as l-carnosine has been suggested to promote cardiometabolic health, although therapeutic mechanisms remain incompletely understood. We recently reported that oral consumption of a carnosine analog suppressed markers of fibrosis in liver of obese mice, but whether antifibrotic effects of carnosine extend to the heart is not known, nor are the mechanisms by which carnosine is acting. Here, we investigated whether oral carnosine was able to mitigate the adverse cardiac remodeling associated with diet induced obesity in a mouse model of enhanced lipid peroxidation (i.e., glutathione peroxidase 4 deficient mice, GPx4+/-), a model which mimics many of the pathophysiological aspects of metabolic syndrome and T2 diabetes in humans. Wild-type (WT) and GPx4+/-male mice were randomly fed a standard (CNTL) or high fat high sucrose diet (HFHS) for 16 weeks. Seven weeks after starting the diet, a subset of the HFHS mice received carnosine (80 mM) in their drinking water for duration of the study. Carnosine treatment led to a moderate improvement in glycemic control in WT and GPx4+/-mice on HFHS diet, although insulin sensitivity was not significantly affected. Interestingly, while our transcriptomic analysis revealed that carnosine therapy had only modest impact on global gene expression in the heart, carnosine substantially upregulated cardiac GPx4 expression in both WT and GPx4+/-mice on HFHS diet. Carnosine also significantly reduced protein carbonyls and iron levels in myocardial tissue from both genotypes on HFHS diet. Importantly, we observed a robust antifibrotic effect of carnosine therapy in hearts from mice on HFHS diet, which further in vitro experiments suggest is due to carnosine's ability to suppress collagen-cross-linking. Collectively, this study reveals antifibrotic potential of carnosine in the heart with obesity and illustrates key mechanisms by which it may be acting.

A Catecholaldehyde Metabolite of Norepinephrine Induces Myofibroblast Activation and Toxicity via the Receptor for Advanced Glycation Endproducts: Mitigating Role of l-Carnosine

Monoamine oxidase (MAO) is rapidly gaining appreciation for its pathophysiologic role in cardiac injury and failure. Oxidative deamination of norepinephrine by MAO generates H₂O₂ and the catecholaldehyde 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL), the latter of which is a highly potent and reactive electrophile that has been linked to cardiotoxicity. However, many questions remain as to whether catecholaldehydes regulate basic physiological processes in the myocardium and the pathways involved. Here, we examined the role of MAO-derived oxidative metabolites in mediating the activation of cardiac fibroblasts in response to norepinephrine. In neonatal murine cardiac fibroblasts, norepinephrine increased reactive oxygen species (ROS), accumulation of catechol-modified protein adducts, expression and secretion of collagens I/III, and other markers of profibrotic activation including STAT3 phosphorylation. These effects were attenuated with MAO inhibitors, the aldehyde-scavenging dipeptide l-carnosine, and FPS-ZM1, an antagonist for the receptor for advanced glycation endproducts (RAGE). Interestingly, treatment of cardiac fibroblasts with a low dose (1 μM) of DOPEGAL-modified albumin phenocopied many of the effects of norepinephrine and also induced an increase in RAGE expression. Higher doses (>10 μM) of DOPEGAL-modified albumin were determined to be toxic to cardiac fibroblasts in a RAGE-dependent manner, which was mitigated by l-carnosine. Collectively, these findings suggest that norepinephrine may influence extracellular matrix remodeling via an adrenergic-independent redox pathway in cardiac fibroblasts involving the MAO-mediated generation of ROS, catecholaldehydes, and RAGE. Furthermore, since elevations in the catecholaminergic tone and oxidative stress in heart disease are linked with cardiac fibrosis, this study illustrates novel drug targets that could potentially mitigate this serious disorder.

Characterization of Catecholaldehyde Adducts with Carnosine and l-Cysteine Reveals Their Potential as Biomarkers of Catecholaminergic Stress

Monoamine oxidase (MAO) catalyzes the oxidative deamination of dopamine and norepinephrine to produce 3,4-dihydroxyphenylacetaldehyde (DOPAL) and 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL), respectively. Both of these aldehydes are potently cytotoxic and have been implicated in pathogenesis of neurodegenerative and cardiometabolic disorders. Previous work has demonstrated that both the catechol and aldehyde moieties of DOPAL are reactive and cytotoxic via their propensity to cause macromolecular cross-linking. With certain amines, DOPAL likely reacts via a Schiff base before oxidative activation of the catechol and rearrangement to a stable indole product. Our current work expands on this reactivity and includes the less-studied DOPEGAL. Although we confirmed that antioxidants mediated DOPAL’s reactivity with carnosine and N-acetyl-l-lysine, antioxidants had no effect on reactivity with l-cysteine. Therefore, we propose a non-oxidative mechanism where, following Schiff base formation, the thiol of l-cysteine reacts to form a thiazolidine. Similarly, we demonstrate that DOPEGAL forms a putative thiazolidine conjugate with l-cysteine. We identified and characterized both l-cysteine conjugates via HPLC-MS and additionally identified a DOPEGAL adduct with carnosine, which is likely an Amadori product. Furthermore, we were able to demonstrate that these conjugates are produced in biological systems via MAO after treatment of the cell lysate with norepinephrine or dopamine along with the corresponding nucleophiles (i.e., l-cysteine and carnosine). As it has been established that metabolic and oxidative stress leads to increased MAO activity and accumulation of DOPAL and DOPEGAL, it is conceivable that conjugation of these aldehydes to carnosine or l-cysteine is a newly identified detoxification pathway. Furthermore, the ability to characterize these adducts via analytical techniques reveals their potential for use as biomarkers of dopamine or norepinephrine metabolic disruption.

Enhanced Catecholamine Flux and Impaired Carbonyl Metabolism Disrupt Cardiac Mitochondrial Oxidative Phosphorylation in Diabetes Patients

Aims: Catecholamine metabolism via monoamine oxidase (MAO) contributes to cardiac injury in models of ischemia and diabetes, but the pathogenic mechanisms involved are unclear. MAO deaminates norepinephrine (NE) and dopamine to produce H₂O₂ and highly reactive "catecholaldehydes," which may be toxic to mitochondria due to the localization of MAO to the outer mitochondrial membrane. We performed a comprehensive analysis of catecholamine metabolism and its impact on mitochondrial energetics in atrial myocardium obtained from patients with and without type 2 diabetes. Results: Content and maximal activity of MAO-A and MAO-B were higher in the myocardium of patients with diabetes and they were associated with body mass index. Metabolomic analysis of atrial tissue from these patients showed decreased catecholamine levels in the myocardium, supporting an increased flux through MAOs. Catecholaldehyde-modified protein adducts were more abundant in myocardial tissue extracts from patients with diabetes and were confirmed to be MAO dependent. NE treatment suppressed mitochondrial ATP production in permeabilized myofibers from patients with diabetes in an MAO-dependent manner. Aldehyde dehydrogenase (ALDH) activity was substantially decreased in atrial myocardium from these patients, and metabolomics confirmed lower levels of ALDH-catalyzed catecholamine metabolites. Proteomic analysis of catechol-modified proteins in isolated cardiac mitochondria from these patients identified >300 mitochondrial proteins to be potential targets of these unique carbonyls. Innovation and Conclusion: These findings illustrate a unique form of carbonyl toxicity driven by MAO-mediated metabolism of catecholamines, and they reveal pathogenic factors underlying cardiometabolic disease. Importantly, they suggest that pharmacotherapies targeting aldehyde stress and catecholamine metabolism in heart may be beneficial in patients with diabetes and cardiac disease. Antioxid. Redox Signal. 35, 235-251.

Mechanical cues protect against silica nanoparticle exposure in SH-SY5Y neuroblastoma

The increasing appearance of engineered nanomaterials in broad biomedical and industrial sectors poses an escalating health concern from unintended exposure with unknown consequences. Routine in vitro assessments of nanomaterial toxicity are a vital component to addressing these mounting health concerns; however, despite the known role of cell-cell and cell-matrix contacts in governing cell survival, these physical interactions are generally ignored. Herein, we demonstrate that exposure to amorphous silica particles destabilizes mitochondrial membrane potential, stimulates reactive oxygen species (ROS) production and promotes cytotoxicity in SH-SY5Y human neuroblastoma through mechanisms that are potently matrix dependent, with SH-SY5Y cells plated on the softest matrix displaying a near complete recovery in viability compared to dose-matched cells plated on tissue-culture plastic. Cells on the softest matrix (3 kPa) further displayed a 50% reduction in ROS production and preserved mitochondrial membrane potential. The actin cytoskeleton is mechanosensitive and closely related to ROS production. SH-SY5Y cells exposed to a 100 μg/mL dose of 50 nm silica particles displayed distinct cytoskeletal aberrations and a 70% increase in cell stiffness. Overall, this study establishes that the mechanical environment can significantly impact silica nanoparticle toxicity in SH-SY5Y cells. The mechanobiochemical mechanisms behind this regulation, which are initiated at the cell-matrix interface to adjust cytoskeletal structure and intracellular tension, demand specific attention for a comprehensive understanding of nanotoxicity.

A Highly Sensitive, Reproducible Assay for Determining 4-hydroxynonenal Protein Adducts in Biological Material

Oxidative stress is associated with numerous diseases, and markers of oxidative stress in biological material are becoming a mainstay of both experimental and clinical/epidemiological research. Lipid peroxidation is a major form of oxidative stress, but due to their rapid degradation and instability, lipid peroxides are notoriously difficult to measure, particularly in biological specimens where their production and removal are continuously occuring. Thus, a commonly used surrogate marker of lipid peroxidation is protein adducts of 4-Hydroxynonenal (HNE), an α, β-unsaturated hydroxyalkenal (i.e., a reactive aldehyde) formed via degradation of oxidized polyunsaturated fatty acids (PUFAs). HNE adducts can be measured via commercially-available immunosorbent assays, but these have their limitations due to excessive costs, and reproducibility among laboratories is challenging due to variability in assay sensitivity, procedure, and reagents. Here we present a reproducible, facile, and economically conservative protocol for quantifying HNE protein adducts. The key to this protocol is to generate HNE-adduct standards by incubating bovine serum albumin (BSA) with HNE. These standards are then adsorbed to immunsorbent plastic in a multi-well plate format alongside biological samples. An enzyme-linked immunosorbent assay (ELISA) is then performed on the multi-well plate using commercially-available primary and secondary antibodies, and a peroxide-based fluorescent developing reagent. This protocol is highly sensitive and offers advantages to commercial sources in that it allows for reproducible, high-throughput quantitation of HNE adducts in a large number of samples. As such, it may be useful as a biomarker of chronic oxidative stress for experimental and clinical studies.

A carnosine analog mitigates metabolic disorders of obesity by reducing carbonyl stress

Sugar- and lipid-derived aldehydes are reactive carbonyl species (RCS) frequently used as surrogate markers of oxidative stress in obesity. A pathogenic role for RCS in metabolic diseases of obesity remains controversial, however, partly because of their highly diffuse and broad reactivity and the lack of specific RCS-scavenging therapies. Naturally occurring histidine dipeptides (e.g., anserine and carnosine) show RCS reactivity, but their therapeutic potential in humans is limited by serum carnosinases. Here, we present the rational design, characterization, and pharmacological evaluation of carnosinol, i.e., (2S)-2-(3-amino propanoylamino)-3-(1H-imidazol-5-yl)propanol, a derivative of carnosine with high oral bioavailability that is resistant to carnosinases. Carnosinol displayed a suitable ADMET (absorption, distribution, metabolism, excretion, and toxicity) profile and was determined to have the greatest potency and selectivity toward α,β-unsaturated aldehydes (e.g., 4-hydroxynonenal, HNE, ACR) among all others reported thus far. In rodent models of diet-induced obesity and metabolic syndrome, carnosinol dose-dependently attenuated HNE adduct formation in liver and skeletal muscle, while simultaneously mitigating inflammation, dyslipidemia, insulin resistance, and steatohepatitis. These improvements in metabolic parameters with carnosinol were not due to changes in energy expenditure, physical activity, adiposity, or body weight. Collectively, our findings illustrate a pathogenic role for RCS in obesity-related metabolic disorders and provide validation for a promising new class of carbonyl-scavenging therapeutic compounds rationally derived from carnosine.