Neopterin negatively regulates expression of ABCA1 and ABCG1 by the LXRα signaling pathway in THP-1 macrophage-derived foam cells

Brain-specific loss of Abcg1 disturbs cholesterol metabolism and aggravates pyroptosis and neurological deficits after traumatic brain injury

Based on accumulating evidence, cholesterol metabolism dysfunction has been suggested to contribute to the pathophysiological process of traumatic brain injury (TBI) and lead to neurological deficits. As a key transporter of cholesterol that efflux from cells, the ATP-binding cassette (ABC) transporter family exerts many beneficial effects on central nervous system (CNS) diseases. However, there is no study regarding the effects and mechanisms of ABCG1 on TBI. As expected, TBI resulted in the different time-course changes of cholesterol metabolism-related molecules in the injured cortex. Considering ABCG1 is expressed in neuron and glia post-TBI, we generated nestin-specific Abcg1 knockout (Abcg1-KO) mice using the Cre/loxP recombination system. These Abcg1-KO mice showed reduced plasma high-density lipoprotein cholesterol levels and increased plasma lower-density lipoprotein cholesterol levels under the base condition. After TBI, these Abcg1-KO mice were susceptible to cholesterol metabolism turbulence. Moreover, Abcg1-KO exacerbated TBI-induced pyroptosis, apoptosis, neuronal cell insult, brain edema, neurological deficits, and brain lesion volume. Importantly, we found that treating with retinoid X receptor (RXR, the upstream molecule of ABCG1) agonist, bexarotene, in Abcg1-KO mice partly rescued TBI-induced neuronal damages mentioned above and improved functional deficits versus vehicle-treated group. These data show that, in addition to regulating brain cholesterol metabolism, Abcg1 improves neurological deficits through inhibiting pyroptosis, apoptosis, neuronal cell insult, and brain edema. Moreover, our findings demonstrate that the cerebroprotection of Abcg1 on TBI partly relies on the activation of the RXRalpha/PPARgamma pathway, which provides a potential therapeutic target for treating TBI.

The potential role of neopterin in Covid-19: a new perspective

Neopterin (NPT) is a member of pteridines group, synthesized by macrophages when stimulated by interferon gamma (INF-γ). NPT is regarded as a macrophage stimulation indicator, marker of cellular immune activation and T helper 1 (Th1) type 1 immune response. Here, we aimed to provide a view point on the NPT features and role in Covid-19. Serum NPT level is regarded as an independent prognostic factor for Covid-19 severity, with levels starting to increase from the 3rd day of SARS-CoV-2 infection, being associated with severe dyspnea, longer hospitalization period and complications. Also, early raise of NPT reflects monocytes/macrophages activation before antibody immune response, despite the NPT level may also remain high in Covid-19 patients or at the end of incubation period before the onset of clinical symptoms. On the other hand, NPT attenuates the activity of macrophage foam cells and is linked to endothelial inflammation through inhibition of adhesion molecules and monocytes migration. However, NPT also exerts anti-inflammatory and antioxidant effects by suppressing NF-κB signaling and NLRP3 inflammasomes. NPT can be viewed as a protective compensatory mechanism to counterpoise hyper-inflammation, oxidative stress, and associated organ damage.

Neopterin derivatives - a novel therapeutic target rather than biomarker for atherosclerosis and related diseases

This review provides an updated overview of the emerging roles of neopterin derivatives in atherosclerosis. Neopterin, a metabolite of guanosine triphosphate, is produced by interferon-γ-activated macrophages and is expressed at high levels in atheromatous plaques within the human carotid and coronary arteries as well as in the aorta. Plasma concentrations of neopterin are higher in patients with carotid, cerebral, and coronary artery diseases as well as aortic aneurysm. The concentration of neopterin is positively correlated with the severity of coronary artery disease. However, a prospective cohort study showed that neopterin contributes to protection against plaque formation in carotid arteries in patients with atherosclerosis. Moreover, using both in vitro and in vivo experiments, a recent study has shown the atheroprotective effects of neopterin. Neopterin suppresses the expression of monocyte chemotactic protein-1, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1 in endothelial cells, and thereby suppresses the adhesion of monocytes to endothelial cells. It also suppresses the inflammatory phenotype of monocyte-derived macrophages. In addition, neopterin suppresses oxidized low-density lipoprotein-induced foam cell formation in macrophages and the migration and proliferation of vascular smooth muscle cells. Neopterin injection into apolipoprotein E-deficient (Apoe^-/-) mice suppresses the development of atherosclerotic lesions. A neopterin derivative tetrahydroneopterin (BH4), also known as a cofactor for nitric oxide (NO) synthases, suppresses atherosclerosis and vascular injury-induced neointimal hyperplasia in Apoe^-/- mice. BH4 administration improves endothelial dysfunction in patients with coronary artery disease. These findings suggest that neopterin production may increase to counteract the progression of atherosclerosis, as neopterin contributes to atheroprotection. Otherwise, the increased neopterin levels in atherosclerosis may reflect a compensatory mechanism associated with inducible NO synthase upregulation in macrophages to supply BH4 for high output NO production caused by decreased endothelial NO synthase in atherosclerosis. Therefore, neopterin derivatives are a novel therapeutic target for atherosclerosis and related diseases.

Analysis of Low Molecular Weight Substances and Related Processes Influencing Cellular Cholesterol Efflux

Cholesterol efflux is the key process protecting the vascular system from the development of atherosclerotic lesions. Various extracellular and intracellular events affect the ability of the cell to efflux excess cholesterol. To explore the possible pathways and processes that promote or inhibit cholesterol efflux, we applied a combined cheminformatic and bioinformatic approach. We performed a comprehensive analysis of published data on the various substances influencing cholesterol efflux and found 153 low molecular weight substances that are included in the Chemical Entities of Biological Interest (ChEBI) database. Pathway enrichment was performed for substances identified within the Reactome database, and 45 substances were selected in 93 significant pathways. The most common pathways included the energy-dependent processes related to active cholesterol transport from the cell, lipoprotein metabolism and lipid transport, and signaling pathways. The activators and inhibitors of cholesterol efflux were non-uniformly distributed among the different pathways: the substances influencing ‘biological oxidations’ activate cholesterol efflux and the substances influencing ‘Signaling by GPCR and PTK6’ inhibit efflux. This analysis may be used in the search and design of efflux effectors for therapies targeting structural and functional high-density lipoprotein deficiency.

Neopterin Counters Vascular Inflammation and Atherosclerosis

BACKGROUND

Neopterin, a metabolite of GTP, is produced by activated macrophages and is abundantly expressed within atherosclerotic lesions in human aorta and carotid and coronary arteries. We aimed to clarify the influence of neopterin on both vascular inflammation and atherosclerosis, as neither effect had been fully assessed.

METHODS AND RESULTS

We investigated neopterin expression in coronary artery lesions and plasma from patients with coronary artery disease. We assessed the atheroprotective effects of neopterin in vitro using human aortic endothelial cells, human monocyte-derived macrophages, and human aortic smooth muscle cells. In vivo experiments included a study of aortic lesions in apolipoprotein E-deficient mice. Neopterin expression in coronary artery lesions and plasma was markedly increased in patients with versus without coronary artery disease. In human aortic endothelial cells, neopterin reduced proliferation and TNF-α (tumor necrosis factor α)-induced upregulation of MCP-1 (monocyte chemotactic protein 1), ICAM-1 (intercellular adhesion molecule 1), and VCAM-1 (vascular cell adhesion molecule 1). Neopterin attenuated TNF-α-induced monocyte adhesion to human aortic endothelial cells and the inflammatory macrophage phenotype via NF-κB (nuclear factor-κB) downregulation. Neopterin suppressed oxidized low-density lipoprotein-induced foam cell formation associated with CD36 downregulation and upregulation of ATP-binding cassette transporters A1 and G1 in human monocyte-derived macrophages. In human aortic smooth muscle cells, neopterin suppressed angiotensin II-induced migration and proliferation via c-Src/Raf-1/ERK1/2 downregulation without inducing apoptosis. Exogenous neopterin administration and endogenous neopterin attenuation with its neutralizing antibody for 4 weeks retarded and promoted, respectively, the development of aortic atherosclerotic lesions in apolipoprotein E-deficient mice.

CONCLUSIONS

Our results indicate that neopterin prevents both vascular inflammation and atherosclerosis and may be induced to counteract the progression of atherosclerotic lesions. Consequently, neopterin could be of use as a novel therapeutic target for atherosclerotic cardiovascular diseases.

Mildly compromised tetrahydrobiopterin cofactor biosynthesis due to Pts variants leads to unusual body fat distribution and abdominal obesity in mice

Tetrahydrobiopterin (BH4) is an essential cofactor for the aromatic amino acid hydroxylases, alkylglycerol monooxygenase, and nitric oxide synthases (NOS). Inborn errors of BH4 metabolism lead to severe insufficiency of brain monoamine neurotransmitters while augmentation of BH4 by supplementation or stimulation of its biosynthesis is thought to ameliorate endothelial NOS (eNOS) dysfunction, to protect from (cardio-) vascular disease and/or prevent obesity and development of the metabolic syndrome. We have previously reported that homozygous knock-out mice for the 6-pyruvolytetrahydropterin synthase (PTPS; Pts-ko/ko) mice with no BH4 biosynthesis die after birth. Here we generated a Pts-knock-in (Pts-ki) allele expressing the murine PTPS-p.Arg15Cys with low residual activity (15% of wild-type in vitro) and investigated homozygous (Pts-ki/ki) and compound heterozygous (Pts-ki/ko) mutants. All mice showed normal viability and depending on the severity of the Pts alleles exhibited up to 90% reduction of PTPS activity concomitant with neopterin elevation and mild reduction of total biopterin while blood L-phenylalanine and brain monoamine neurotransmitters were unaffected. Yet, adult mutant mice with compromised PTPS activity (i.e., Pts-ki/ko, Pts-ki/ki or Pts-ko/wt) had increased body weight and elevated intra-abdominal fat. Comprehensive phenotyping of Pts-ki/ki mice revealed alterations in energy metabolism with proportionally higher fat content but lower lean mass, and increased blood glucose and cholesterol. Transcriptome analysis indicated changes in glucose and lipid metabolism. Furthermore, differentially expressed genes associated with obesity, weight loss, hepatic steatosis, and insulin sensitivity were consistent with the observed phenotypic alterations. We conclude that reduced PTPS activity concomitant with mildly compromised BH4-biosynthesis leads to abnormal body fat distribution and abdominal obesity at least in mice. This study associates a novel single gene mutation with monogenic forms of obesity.

Effects of pomegranate peel polyphenols on lipid accumulation and cholesterol metabolic transformation in L-02 human hepatic cells via the PPARγ-ABCA1/CYP7A1 pathway

PPPs, PC and PEA in different concentrations were found to decrease the total cholesterol (TC) content and increase the total bile acid (TBA) content of a human hepatic cell model, and so possess a lipid-lowering effect.

Neopterin as a Predictor of Functional Outcome and Mortality in Chinese Patients with Acute Ischemic Stroke

Immune responses and inflammation play an important role in the pathogenesis of ischemic stroke. We therefore evaluated the 6-month prognostic value of early measurement of serum neopterin levels, a marker of inflammation and immune system activation, in Chinese patients with acute ischemic stroke (AIS). Consecutive AIS patients admitted to the emergency department were identified. Clinical information was collected. Serum concentration of neopterin and NIH stroke scale (NIHSS) were measured at the time of admission. Functional outcome was measured by modified Rankin scale (mRS) 6 months after admission. Multivariate analyses were performed using logistic regression models. During the inclusion period, 312 patients with first-ever AIS were included and 290 completed follow-up. The results indicated that the serum neopterin levels were significantly (P < 0.0001) higher in acutely ischemic stroke patients as compared to normal controls. Neopterin was an independent prognostic marker of 6-month functional outcome and death [odds ratio (OR) 4.33 (1.83-10.32) and 6.68 (2.44-12.13), respectively, P < 0.0001 for both, adjusted for NIHSS, other predictors and vascular risk factors] in patients with AIS. Neopterin improved the area under the receiver operating characteristic curve of the NHISS score for functional outcome from 0.75 (95 % CI 0.69-0.83) to 0.85 (95 % CI 0.79-0.91; P < 0.001) and for mortality from 0.76 (95 % CI 0.68-0.85) to 0.87 (95 % CI 0.81-0.94; P < 0.001). Serum neopterin is a useful, independent tool to predict functional outcome and mortality 6 months after stroke.

22(R)-hydroxycholesterol and pioglitazone synergistically decrease cholesterol ester via the PPARγ-LXRα-ABCA1 pathway in cholesterosis of the gallbladder

Cholesterosis is a disease of cholesterol metabolism characterized by the presence of excessive lipid droplets in the cytoplasm. These lipid droplets are mainly composed of cholesterol esters derived from free cholesterol. The removal of excess cholesterol from gallbladder epithelial cells (GBECs) is very important for the maintenance of intracellular cholesterol homeostasis and the preservation of gallbladder function. Several lines of evidence have indicated that the activation of either peroxisome proliferator-activated receptor gamma (PPARγ) or liver X receptor α (LXRα) relates to cholesterol efflux. While pioglitazone can regulate the activation of PPARγ, 22(R)-hydroxycholesterol can activate LXRα and is a metabolic intermediate in the biosynthesis of steroid hormones. However, the effect of 22(R)-hydroxycholesterol in combination with pioglitazone on cholesterosis of the gallbladder is unclear. GBECs were treated with pioglitazone, 22(R)-hydroxycholesterol or PPARγ siRNA followed by Western blot analysis for ATP-binding cassette transporter A1 (ABCA1), PPARγ and LXRα. Cholesterol efflux to apoA-I was determined, and Oil Red O staining was performed to monitor variations in lipid levels in treated GBECs. Our data showed that 22(R)-hydroxycholesterol can modestly up-regulate LXRα while simultaneously increasing ABCA1 by 56%. The combination of 22(R)-hydroxycholesterol and pioglitazone resulted in a 3.64-fold increase in ABCA1 expression and a high rate of cholesterol efflux. Oil Red O staining showed an obvious reduction in the lipid droplets associated with cholesterosis in GBECs. In conclusion, the present findings indicate that the anti-lipid deposition action of 22(R)-hydroxycholesterol combined with pioglitazone involves the activation of the PPARγ-LXRα-ABCA1 pathway, increased ABCA1 expression and the efflux of cholesterol from GBECs. Thus, 22(R)-hydroxycholesterol synergistically combined with pioglitazone to produce a remarkable effect on lipid deposition in cholesterosis GBECs.