L-homoarginine administration reduces neointimal hyperplasia in balloon-injured rat carotids

Microarray analysis identifies human apoA-IMilano and apoA-II as determinants of the liver gene expression related to lipid and energy metabolism

The phenotype of individuals carrying the apolipoprotein A-IMilano (apoA-IM), the mutant form of human apoA-I (apoA-I), is characterized by very low concentrations of HDL and apoA-I, and hypertriglyceridemia. Paradoxically, these subjects are not found to be at increased risk of premature cardiovascular disease compared to controls. Besides, various in vitro and in vivo studies have demonstrated that apoA-IM possesses greater anti-atherosclerotic activity compared to apoA-I. The molecular mechanisms explaining the apoA-IM carrier's phenotype and the apoA-IM higher efficacy are still not fully elucidated. To investigate such mechanisms, we crossed previously generated apoA-I (A-I k-in) or apoA-IM knock-in mice (A-IM k-in) with transgenic mice expressing human apoA-II but lacking murine apoA-I (hA-II) to generate hA-II/A-I k-in, and hA-II/A-IM k-in, respectively. These genetically modified mice completely reproduced the apoA-IM carrier's phenotype, including hypoalphalipoproteinemia and hypertriglyceridemia. Furthermore, by using the microarray methodology, we investigated the intrinsic differences in hepatic gene expression among these k-in mouse lines. The expression of 871, 1,018, 1129 and 764 genes was significantly altered between 1) hA-II/A-I and hA-II/A-IM k-in; 2) A-IM and hA-II/A-IM k-in; 3) A-I and A-IM; 4) A-I and hA-II/A-I k-in liver samples, respectively. Bioinformatics analysis highlighted that the hepatic expression of two genes, Elovl6 and Gatm, related to fatty acid/lipid and energy metabolism, respectively, is influenced by the presence of the apoA-IM natural variant and/or apoA-II.

The Amino Acid Homoarginine Inhibits Atherogenesis by Modulating T-Cell Function

BACKGROUND

Amino acid metabolism is crucial for inflammatory processes during atherogenesis. The endogenous amino acid homoarginine is a robust biomarker for cardiovascular outcome and mortality with high levels being protective. However, the underlying mechanisms remain elusive. We investigated the effect of homoarginine supplementation on atherosclerotic plaque development with a particular focus on inflammation.

METHODS

Female ApoE-deficient mice were supplemented with homoarginine (14 mg/L) in drinking water starting 2 weeks before and continuing throughout a 6-week period of Western-type diet feeding. Control mice received normal drinking water. Immunohistochemistry and flow cytometry were used for plaque- and immunological phenotyping. T cells were characterized using mass spectrometry-based proteomics, by functional in vitro approaches, for example, proliferation and migration/chemotaxis assays as well as by super-resolution microscopy.

RESULTS

Homoarginine supplementation led to a 2-fold increase in circulating homoarginine concentrations. Homoarginine-treated mice exhibited reduced atherosclerosis in the aortic root and brachiocephalic trunk. A substantial decrease in CD3⁺ T cells in the atherosclerotic lesions suggested a T-cell-related effect of homoarginine supplementation, which was mainly attributed to CD4⁺ T cells. Macrophages, dendritic cells, and B cells were not affected. CD4⁺ T-cell proteomics and subsequent pathway analysis together with in vitro studies demonstrated that homoarginine profoundly modulated the spatial organization of the T-cell actin cytoskeleton and increased filopodia formation via inhibition of Myh9 (myosin heavy chain 9). Further mechanistic studies revealed an inhibition of T-cell proliferation as well as a striking impairment of the migratory capacities of T cells in response to relevant chemokines by homoarginine, all of which likely contribute to its atheroprotective effects.

CONCLUSIONS

Our study unravels a novel mechanism by which the amino acid homoarginine reduces atherosclerosis, establishing that homoarginine modulates the T-cell cytoskeleton and thereby mitigates T-cell functions important during atherogenesis. These findings provide a molecular explanation for the beneficial effects of homoarginine in atherosclerotic cardiovascular disease.

An Optimized MRM-Based Workflow of the l-Arginine/Nitric Oxide Pathway Metabolites Revealed Disease- and Sex-Related Differences in the Cardiovascular Field

Clinical data indicate that low circulating l-homoarginine (HArg) concentrations are associated with cardiovascular (CV) disease, CV mortality, and all-cause mortality. A high number of LC-based analytical methods for the quantification of HArg, in combination with the l-arginine (Arg)-related pathway metabolites, have been reported. However, these methods usually consider a limited panel of analytes. Thus, in order to achieve a comprehensive picture of the Arg metabolism, we described an improved targeted metabolomic approach based on a multiple reaction monitoring (MRM) mass spectrometry method for the simultaneous quantification of the Arg/nitric oxide (NO) pathway metabolites. This methodology was then employed to quantify the plasma concentrations of these analytes in a cohort of individuals with different grades/types of coronary artery disease (CAD) in order to increase knowledge about the role of HArg and its associated metabolites in the CV field. Our results showed that the MRM method here implemented is suitable for the simultaneous assessment of a wide panel of amino acids involved in the Arg/NO metabolic pathway in plasma samples from patients with CV disease. Further, our findings highlighted an impairment of the Arg/NO metabolic pathway, and suggest a sex-dependent regulation of this metabolic route.

L-homoarginine is associated with decreased cardiovascular- and all-cause mortality

BACKGROUND

Increasing evidence suggests that L-homoarginine, an endogenous analogue of the amino acid L-arginine, may have beneficial effects on vascular homeostasis. We examined whether L-homoarginine is associated with 10-year risk of all-cause and cardiovascular mortality in a black South African population.

METHODS

We included 669 black South African participants (mean age 59.5 years), 143 of whom died during the 10-year follow-up period. Mortality data were acquired via verbal autopsy. Plasma L-homoarginine (and other related markers) were analysed with liquid chromatography-tandem mass spectrometry.

RESULTS

Survivors had higher L-homoarginine levels compared with nonsurvivors (1.25 µM vs. 0.89 µM; P < .001). Multivariable Cox regression analyses revealed that higher plasma L-homoarginine predicted a reduction in 10-year cardiovascular (hazard ratio [HR] per SD increment, 0.61; 95% CI 0.50 to 0.75) and all-cause (hazard ratio [HR] per SD increment, 0.59; 95% CI 0.41 to 0.84) mortality risk.

CONCLUSION

Higher L-homoarginine levels are associated with reduced risk of 10-year cardiovascular and all-cause mortality. Regulation of L-homoarginine levels as a therapeutic target in the management of cardiovascular disease should be investigated.

NO Synthesis Markers are Not Significantly Associated with Blood Pressure and Endothelial Dysfunction in Patients with Arterial Hypertension: A Cross-Sectional Study

Nitric oxide (NO) synthesis markers, comprising L-homoarginine, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), are significantly associated with cardiovascular events and mortality. Being involved in NO pathways, they may be of high importance regulating vascular tone and arterial hypertension, but data on this topic are sparse and controversial. In this study, we evaluated whether these NO synthesis markers are associated with blood pressure values and pulse wave velocity (PWV). This analysis was based on the data of the Styrian Vitamin D Hypertension Trial, which included adults with arterial hypertension. We analyzed correlations of NO synthesis markers with 24 h ambulatory blood pressure values and PWV (primary outcomes), as well as with anthropometric and laboratory data. A total of 509 patients were included in the present analysis. The mean age was 61.2 ± 10.5 years, mean PWV was 8.6 ± 2.4 m/s, mean 24 h systolic blood pressure was 127.5 ± 13.8 mmHg and mean 24 h diastolic blood pressure was 76.4 ± 9.5 mmHg. In bivariate analyses, there was a significant positive correlation between homoarginine and 24 h diastolic blood pressure (r = 0.1; p = 0.02), which was revealed to be no longer significant after adjustment for age, gender and glomerular filtration rate (GFR) in multivariate regression analysis. No other significant correlations of any NO synthesis markers with blood pressure or PWV were observed. In line with previous studies, there were inverse associations between homoarginine and age and between ADMA or SDMA and GFR (p < 0.05 for all). This study did not reveal a significant association between homoarginine, ADMA or SDMA and blood pressure or PWV in hypertensive adults. These results suggested that the associations of these parameters with adverse outcome may not be mediated by hypertension and/or endothelial dysfunction.

Marine n-3 polyunsaturated fatty acids: Efficacy on inflammatory-based disorders

Inflammation is a physiological response to injury, stimulating tissue repair and regeneration. However, the presence of peculiar individual conditions can negatively perturb the resolution phase eventually leading to a state of low-grade systemic chronic inflammation, characterized by tissue and organ damages and increased susceptibility to non-communicable disease. Marine n-3 polyunsaturated fatty acids (n-3 PUFAs), mainly eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), are able to influence many aspects of this process. Experiments performed in various animal models of obesity, Alzheimer's disease and multiple sclerosis have demonstrated that n-3 PUFAs can modulate the basic mechanisms as well as the disease progression. This review describes the available data from experimental studies to the clinical trials.

Atherosclerosis Linked to Aberrant Amino Acid Metabolism and Immunosuppressive Amino Acid Catabolizing Enzymes

Cardiovascular disease is the leading global health concern and responsible for more deaths worldwide than any other type of disorder. Atherosclerosis is a chronic inflammatory disease in the arterial wall, which underpins several types of cardiovascular disease. It has emerged that a strong relationship exists between alterations in amino acid (AA) metabolism and the development of atherosclerosis. Recent studies have reported positive correlations between levels of branched-chain amino acids (BCAAs) such as leucine, valine, and isoleucine in plasma and the occurrence of metabolic disturbances. Elevated serum levels of BCAAs indicate a high cardiometabolic risk. Thus, BCAAs may also impact atherosclerosis prevention and offer a novel therapeutic strategy for specific individuals at risk of coronary events. The metabolism of AAs, such as L-arginine, homoarginine, and L-tryptophan, is recognized as a critical regulator of vascular homeostasis. Dietary intake of homoarginine, taurine, and glycine can improve atherosclerosis by endothelium remodeling. Available data also suggest that the regulation of AA metabolism by indoleamine 2,3-dioxygenase (IDO) and arginases 1 and 2 are mediated through various immunological signals and that immunosuppressive AA metabolizing enzymes are promising therapeutic targets against atherosclerosis. Further clinical studies and basic studies that make use of animal models are required. Here we review recent data examining links between AA metabolism and the development of atherosclerosis.

Biotechnology Approaches for the Treatment of Dyslipidemia

BACKGROUND

Despite advances in the development of lipid-lowering therapies, clinical trials have shown that a significant residual risk of cardiovascular disease persists. Specifically, new drugs are needed for non-responding or statin-intolerant subjects or patients considered at very high risk for cardiovascular events even though are already on treatment with the best standard of care.

RESULTS AND CONCLUSIONS

Besides, genetic and epidemiological studies and Mendelian randomization analyses have strengthened the linear correlation between the concentration of low-density lipoprotein cholesterol (LDL-C) and the incidence of cardiovascular events and highlighted various novel therapeutic targets. This review describes the novel strategies to reduce the levels of LDL-C, non-HDL-C, triglyceride, apolipoprotein B, and Lp(a), focusing on those developed using biotechnology-based strategies.

Kidney and liver are the main organs of expression of a key metabolic enzyme alanine:glyoxylate aminotransferase 2 in humans

BACKGROUND

The metabolic syndrome is a cluster of cardiovascular risk factors and is highly predictive for development of cardiovascular diseases. An association between elevated plasma levels of the endogenous inhibitor of nitric oxide synthases asymmetric dimethylarginine (ADMA) and risk of cardiovascular diseases has been demonstrated in numerous epidemiological studies. ADMA can be catabolized by dimethylarginine dimethylaminohydrolase (DDAH) or metabolized through a much less understood alternative pathway by alanine:glyoxylate aminotransferase 2 (AGXT2) with the formation of α-keto-δ-(N,N-dimethylguanidino)valeric acid (ADGV). Previous RT-PCR and Western Blot studies suggested that Agxt2 is expressed in the mouse kidney and liver at comparable levels, while Northern Blot and in-situ RNA-hybridisation experiments demonstrated that the kidney is the main organ of Agxt2 expression in rats. Given this discrepancy, the goal of the current study was to analyse the expression of AGXT2 in human tissues.

MATERIAL AND METHODS

We analyzed AGXT2 expression in human tissues from a normal tissue bank by RT-PCR and further validated the results by Western Blot. We also performed immunohistochemical staining for AGXT2 and double fluorescent staining with an anti-AGXT2 antibody and a monoclonal anti-mitochondrial antibody.

RESULTS

We saw the strongest expression of AGXT2 in the kidney and liver and confirmed this results on protein level. By IHC staining we were able to show that AGXT2 is present in the convoluted tubule in the kidney and in the liver hepatocytes. The double fluorescent staining revealed mitochondrial localization of AGXT2.

CONCLUSIONS

Our current data suggest that both hepatocytes and kidney tubular epithelial cells are the major sources of AGXT2 in humans. We also demonstrated the mitochondrial localization of human AGXT2 enzyme.

Homoarginine- and Creatine-Dependent Gene Regulation in Murine Brains with l-Arginine:Glycine Amidinotransferase Deficiency

l-arginine:glycine amidinotransferase (AGAT) and its metabolites homoarginine (hArg) and creatine have been linked to stroke pathology in both human and mouse studies. However, a comprehensive understanding of the underlying molecular mechanism is lacking. To investigate transcriptional changes in cerebral AGAT metabolism, we applied a transcriptome analysis in brains of wild-type (WT) mice compared to untreated AGAT-deficient (AGAT^−/−) mice and AGAT^−/− mice with creatine or hArg supplementation. We identified significantly regulated genes between AGAT^−/− and WT mice in two independent cohorts of mice which can be linked to amino acid metabolism (Ivd, Lcmt2), creatine metabolism (Slc6a8), cerebral myelination (Bcas1) and neuronal excitability (Kcnip3). While Ivd and Kcnip3 showed regulation by hArg supplementation, Bcas1 and Slc6a8 were creatine dependent. Additional regulated genes such as Pla2g4e and Exd1 need further evaluation of their influence on cerebral function. Experimental stroke models showed a significant regulation of Bcas1 and Slc6a8. Together, these results reveal that AGAT deficiency, hArg and creatine regulate gene expression in the brain, which may be critical in stroke pathology.

Arginine Derivatives in Cerebrovascular Diseases: Mechanisms and Clinical Implications

The amino acid L-arginine serves as substrate for the nitric oxide synthase which is crucial in vascular function and disease. Derivatives of arginine, such as asymmetric (ADMA) and symmetric dimethylarginine (SDMA), are regarded as markers of endothelial dysfunction and have been implicated in vascular disorders. While there is a variety of studies consolidating ADMA as biomarker of cerebrovascular risk, morbidity and mortality, SDMA is currently emerging as an interesting metabolite with distinct characteristics in ischemic stroke. In contrast to dimethylarginines, homoarginine is inversely associated with adverse events and mortality in cerebrovascular diseases and might constitute a modifiable protective risk factor. This review aims to provide an overview of the current evidence for the pathophysiological role of arginine derivatives in cerebrovascular ischemic diseases. We discuss the complex mechanisms of arginine metabolism in health and disease and its potential clinical implications in diverse aspects of ischemic stroke.

Is Homoarginine a Protective Cardiovascular Risk Factor?

A series of recent epidemiological studies have implicated the endogenous nonproteinogenic amino acid l-homoarginine as a novel candidate cardiovascular risk factor. The association between homoarginine levels and the risk of adverse cardiovascular outcomes is inverse (ie, high cardiovascular risk is predicted by low rather than high homoarginine levels), which makes it plausible to normalize systemic homoarginine levels via oral supplementation. The emergence of homoarginine as a potentially treatable protective cardiovascular risk factor has generated a wave of hope in the field of cardiovascular prevention. Herein, we review the biochemistry, physiology, and metabolism of homoarginine, summarize the strengths and weaknesses of the epidemiological evidence linking homoarginine to cardiovascular disease and its potential protective cardiovascular effects, and identify priorities for future research needed to define the clinical utility of homoarginine as a prognostic factor and therapeutic target in cardiovascular disease.

The Gut Microbiota Affects Host Pathophysiology as an Endocrine Organ: A Focus on Cardiovascular Disease

It is widely recognized that the microorganisms inhabiting our gastrointestinal tract-the gut microbiota-deeply affect the pathophysiology of the host. Gut microbiota composition is mostly modulated by diet, and gut microorganisms communicate with the different organs and tissues of the human host by synthesizing hormones and regulating their release. Herein, we will provide an updated review on the most important classes of gut microbiota-derived hormones and their sensing by host receptors, critically discussing their impact on host physiology. Additionally, the debated interplay between microbial hormones and the development of cardiovascular disease will be thoroughly analysed and discussed.

Effects of Fish n-3 PUFAs on Intestinal Microbiota and Immune System

Studies over several decades have documented the beneficial actions of n-3 polyunsaturated fatty acids (PUFAs), which are plentiful in fish oil, in different disease states. Mechanisms responsible for the efficacy of n-3 PUFAs include: (1) Reduction of triglyceride levels; (2) anti-arrhythmic and antithrombotic effects, and (3) resolution of inflammatory processes. The human microbiota project and subsequent studies using next-generation sequencing technology have highlighted that thousands of different microbial species are present in the human gut, and that there has been a significant variability of taxa in the microbiota composition among people. Several factors (gestational age, mode of delivery, diet, sanitation and antibiotic treatment) influence the bacterial community in the human gastrointestinal tract, and among these diet habits play a crucial role. The disturbances in the gut microbiota composition, i.e., gut dysbiosis, have been associated with diseases ranging from localized gastrointestinal disorders to neurologic, respiratory, metabolic, ocular, and cardiovascular illnesses. Many studies have been published about the effects of probiotics and prebiotics on the gut microbiota/microbioma. On the contrary, PUFAs in the gut microbiota have been less well defined. However, experimental studies suggested that gut microbiota, n-3 PUFAs, and host immune cells work together to ensure the intestinal wall integrity. This review discussed current evidence concerning the links among gut microbiota, n-3 PUFAs intake, and human inflammatory disease.

Amino Acids and Their Metabolism in Atherosclerosis

As a leading cause of death worldwide, cardiovascular disease is a global health concern. The development and progression of atherosclerosis, which ultimately gives rise to cardiovascular disease, has been causally linked to hypercholesterolemia. Mechanistically, the interplay between lipids and the immune system during plaque progression significantly contributes to the chronic inflammation seen in the arterial wall during atherosclerosis. Localized inflammation and increased cell-to-cell interactions may influence polarization and proliferation of immune cells via changes in amino acid metabolism. Specifically, the amino acids l -arginine (Arg), l -homoarginine (hArg) and l -tryptophan (Trp) have been widely studied in the context of cardiovascular disease, and their metabolism has been established as key regulators of vascular homeostasis, as well as immune cell function. Cyclic effects between endothelial cells, innate, and adaptive immune cells exist during Arg and hArg, as well as Trp metabolism, that may have distinct effects on the development of atherosclerosis. In this review, we describe the current knowledge surrounding the metabolism, biological function, and clinical perspective of Arg, hArg, and Trp in the context of atherosclerosis.

Effects of Vegetable Proteins on Hypercholesterolemia and Gut Microbiota Modulation

Risk assessment tools, i.e., validated risk prediction algorithms, to estimate the patient's 10-year risk of developing cardiovascular disease (CVD) should be used to identify high-risk people for primary prevention. Current evidence confirms that appropriate monitoring and control of risk factors either reduces the likelihood of CVD or slows down its progression. It is thus crucial that all health professionals make appropriate use of all the available intervention strategies to control risk factors: from dietary improvement and adequate physical activity to the use of functional foods, food supplements, and drugs. The gut microbiota, which encompasses 1 × 1014 resident microorganisms, has been recently recognized as a contributing factor in the development of human disease. This review examines the effect of both some vegetable food components belong to the "protein food group" and the underexploited protein-rich hempseed on cholesterolemia and gut microbiota composition.

Homoarginine and all-cause mortality: A systematic review and meta-analysis

BACKGROUND

Homoarginine, a basic amino acid and analogue of L-arginine, has been shown to exert salutary effects on vascular homoeostasis, possibly through interaction with the enzymes nitric oxide synthase and arginase. This might translate into improved survival outcomes, particularly in subjects with moderate-high cardiovascular risk. We conducted a systematic review and meta-analysis to investigate the association between circulating homoarginine concentrations and all-cause mortality in observational studies of human cohorts.

MATERIALS AND METHODS

Studies reporting baseline circulating homoarginine concentrations and all-cause mortality as outcome were searched using the MEDLINE, Scopus and Cochrane databases until January 2018. Hazard ratios (HRs) with 95% confidence intervals (CIs) derived from multivariate Cox's proportional-hazards analysis were extracted from individual studies.

RESULTS

A total of 13 studies in 11 964 participants were included in the final analysis. Homoarginine concentrations were inversely associated with all-cause mortality (HR 0.64, 95% CI 0.57-0.73). This association remained significant in participant sub-groups with predominant cardiovascular disease (HR 0.64, 95% CI 0.55-0.76) and renal disease (HR 0.60, 95% CI 0.46-0.68).

CONCLUSIONS

This meta-analysis of observational studies showed an inverse association between circulating homoarginine concentrations and all-cause mortality. Further research is warranted to investigate the direct effects of homoarginine on cardiovascular homoeostasis, the associations between homoarginine and all-cause mortality in other population groups, and the effects of interventions on homoarginine concentrations on clinical outcomes.

Effect of Dietary Components from Antarctic Krill on Atherosclerosis in apoE-Deficient Mice

SCOPE

Antarctic krill is a great source of n-3 fatty acids and high-quality proteins. Aim of the study was to evaluate the effect of Antarctic krill components on plasma lipids and atherosclerosis development.

METHODS AND RESULTS

Sixty apoEKO mice were divided into four groups and fed Western diet (CONTROL) or Western-like diets, differing for protein or fat content. Specifically, casein or fat in CONTROL was partially replaced by krill proteins (PRO), krill oil (KRILL OIL), or both (KRILL OIL+PRO). In KRILL OIL+PRO and KRILL OIL, cholesterol levels were significantly lower than in CONTROL group. Atherosclerosis in aorta of PRO, KRILL OIL and KRILL OIL+PRO was lower than in CONTROL, whereas, at the aortic sinus, atherosclerosis reduction was only observed in KRILL OIL. Liver steatosis, commonly present in CONTROL and PRO animals, was sporadic in KRILL OIL+PRO and KRILL OIL mice. Krill oil containing diets affected the expression of genes involved in cholesterol metabolism, mainly HMG-CoA reductase. No reduced systemic inflammation was found in all groups.

CONCLUSION

Krill oil containing diets were able to reduce cholesterol levels, inhibit plaque development and prevent liver damage. Krill proteins also reduced atherosclerosis development through mechanisms not involving lipid metabolism.

The biomarker and causal roles of homoarginine in the development of cardiometabolic diseases: an observational and Mendelian randomization analysis

High L-homoarginine (hArg) levels are directly associated with several risk factors for cardiometabolic diseases whereas low levels predict increased mortality in prospective studies. The biomarker role of hArg in young adults remains unknown. To study the predictive value of hArg in the development of cardiometabolic risk factors and diseases, we utilized data on high-pressure liquid chromatography-measured hArg, cardiovascular risk factors, ultrasound markers of preclinical atherosclerosis and type 2 diabetes from the population-based Young Finns Study involving 2,106 young adults (54.6% females, aged 24–39). We used a Mendelian randomization approach involving tens to hundreds of thousands of individuals to test causal associations. In our 10-year follow-up analysis, hArg served as an independent predictor for future hyperglycaemia (OR 1.31, 95% CI 1.06–1.63) and abdominal obesity (OR 1.60, 95% 1.14–2.30) in men and type 2 diabetes in women (OR 1.55, 95% CI 1.02–2.41). The MR analysis revealed no evidence of causal associations between serum hArg and any of the studied cardiometabolic outcomes. In conclusion, lifetime exposure to higher levels of circulating hArg does not seem to alter cardiometabolic disease risk. Whether hArg could be used as a biomarker for identification of individuals at risk developing cardiometabolic abnormalities merits further investigation.