Increased levels of circulating arginase I in overweight compared to normal weight adolescents

Pathophysiological correlation of arginase-1 in development of type 2 diabetes from obesity in adolescents

BACKGROUND

There is great interest to understand causal pathophysiological correlation between obesity and diabetes mellitus (DM). Vascular endothelial dysfunction is crucially involved in pathogenesis of vascular complications in DM. Recently, increased arginase expression and activity have been described as underlying mechanisms of endothelial dysfunction in DM and vascular inflammation in obesity. By limiting L-arginine bioavailability to endothelial nitric oxide synthase (NOS III), nitric oxide production is potentially impaired.

METHODS

We investigated the impact of plasma from diabetic and obese adolescents on arginase and NOS III expression in cultured human endothelial cells (ECs). A total of 148 male adolescents participated in this study including 18 obese, 28 type 1-, 28 type 2-DM patients, and 74 age-matched healthy volunteers.

RESULTS

A concurrent increase in arginase-1 (1.97-fold) and decrease in NOS III expression (1.45-fold) was observed in ECs exposed to type 2 diabetic plasma compared to control subjects. ECs incubated with type 1 DM plasma had a diminished NOS III level without impact on arginase-1 expression. Urea-assay featured an increased arginase activity in treated ECs with type 1- or 2-DM plasma. Despite increased pro-inflammatory cytokines and chemokines in obese plasma, arginase-1 expression/activity did not change in treated ECs. However, NOS III expression was significantly reduced. Pearson analysis revealed positive correlation between arginase-1, but not NOS III, expression with FBS in ECs treated with type 2-DM plasma.

CONCLUSIONS

Our data demonstrate that increased arginase-1 expression/activity in ECs, as critical pathogenic factor is correlated with development of obesity-related type 2-DM and linked vascular disease.

Obesity-Associated Myeloid Immunosuppressive Cells, Key Players in Cancer Risk and Response to Immunotherapy

Obesity is a risk factor for developing several cancers. The dysfunctional metabolism and chronic activation of inflammatory pathways in obesity create a milieu that supports tumor initiation, progression, and metastasis. Obesity-associated metabolic, endocrine, and inflammatory mediators, besides interacting with cells leading to a malignant transformation, also modify the intrinsic metabolic and functional characteristics of immune myeloid cells. Here, the evidence supporting the hypothesis that obesity metabolically primes and promotes the expansion of myeloid cells with immunosuppressive and pro-oncogenic properties is discussed. In consequence, the accumulation of these cells, such as myeloid-derived suppressor cells and some subtypes of adipose-tissue macrophages, creates a microenvironment conducive to tumor development. In this review, the role of lipids, insulin, and leptin, which are dysregulated in obesity, is emphasized, as well as dietary nutrients in metabolic reprogramming of these myeloid cells. Moreover, emerging evidence indicating that obesity enhances immunotherapy response and hypothesized mechanisms are summarized. Priorities in deeper exploration involving the mechanisms of cross talk between metabolic disorders and myeloid cells related to cancer risk in patients with obesity are highlighted.

Possible contribution of hepatocyte secretion to the elevation of plasma exosomal arginase-1 in high-fat diet-fed mice

AIMS

The elevation of arginase in vascular tissues decreases nitric oxide production, which is considered as an early step of atherosclerosis in obesity. Previously, we found that arginase-1, one of arginase isozymes, was elevated in the blood plasma of obese adults. The purpose of this study is to elucidate the mechanism by which obesity increases arginase-1 levels in the blood.

MAIN METHODS

C57/BL6J male mice fed a high-fat diet (HFD) for 12 weeks were analyzed for factors related to nitric oxide/arginine metabolism and plasma exosomes. To explore the arginase secretory organs, the protein expression levels were analyzed in several organs. To further investigate the relationship between exosomal arginase-1 in plasma, blood glucose levels and arginase-1 in the liver, HepG2 (the human hepatoma cell line) was analyzed after treatment with high glucose.

KEY FINDINGS

The increase in arginase activity in the plasma of HFD-fed mice was positively corelated with blood glucose levels and was accompanied by an increase in exosomal arginase-1 levels. Among the organs that highly express arginase, the liver of HFD-fed mice showed a significant increase in arginase-1. The expression of arginase-1 in exosomes and total lysates of HepG2 cells were increased by high glucose exposure.

SIGNIFICANCE

Increased exosomal arginase-1 in plasma contributes to increased plasma arginase activity in obesity. The liver is a candidate organ for the secretion of exosomal arginase-1 into plasma, and the p38 pathway induced by high glucose levels may be involved.

Targeting arginase and nitric oxide metabolism in chronic airway diseases and their co-morbidities

In the airways, arginase and NOS compete for the common substrate l-arginine. In chronic airway diseases, such as asthma and COPD, elevated arginase expression contributes to airway contractility, hyperresponsiveness, inflammation and remodeling. The disrupted l-arginine homeostasis, through changes in arginase and NOS expression and activity, does not only play a central role in the development of various airways diseases such as asthma or COPD. It possibly also affects l-arginine homeostasis throughout the body contributing to the emergence of co-morbidities. This review focusses on the role of arginase, NOS and ADMA in co-morbidities of asthma and COPD and speculates on their possible connection.

Arginase inhibition prevents the development of hypertension and improves insulin resistance in obese rats

This study investigated the temporal activation of arginase in obese Zucker rats (ZR) and determined if arginase inhibition prevents the development of hypertension and improves insulin resistance in these animals. Arginase activity, plasma arginine and nitric oxide (NO) concentration, blood pressure, and insulin resistance were measured in lean and obese animals. There was a chronological increase in vascular and plasma arginase activity in obese ZR beginning at 8 weeks of age. The increase in arginase activity in obese animals was associated with a decrease in insulin sensitivity and circulating levels of arginine and NO. The rise in arginase activity also preceded the increase in blood pressure in obese ZR detected at 12 weeks of age. Chronic treatment of 8-week-old obese animals with an arginase inhibitor or L-arginine for 4 weeks prevented the development of hypertension and improved plasma concentrations of arginine and NO. Arginase inhibition also improved insulin sensitivity in obese ZR while L-arginine supplementation had no effect. In conclusion, arginase inhibition prevents the development of hypertension and improves insulin sensitivity while L-arginine administration only mitigates hypertension in obese animals. Arginase represents a promising therapeutic target in ameliorating obesity-associated vascular and metabolic dysfunction.

Obesity-induced vascular dysfunction and arterial stiffening requires endothelial cell arginase 1

AIMS

Elevation of arginase activity has been linked to vascular dysfunction in diabetes and hypertension by a mechanism involving decreased nitric oxide (NO) bioavailability due to L-arginine depletion. Excessive arginase activity also can drive L-arginine metabolism towards the production of ornithine, polyamines, and proline, promoting proliferation of vascular smooth muscle cells and collagen formation, leading to perivascular fibrosis. We hypothesized that there is a specific involvement of arginase 1 expression within the vascular endothelial cells in this pathology.

METHODS AND RESULTS

To test this proposition, we used models of type 2 diabetes and metabolic syndrome. Studies were performed using wild type (WT), endothelial-specific arginase 1 knockout (EC-A1-/-) and littermate controls(A1con) mice fed high fat-high sucrose (HFHS) or normal diet (ND) for 6 months and isolated vessels exposed to palmitate-high glucose (PA/HG) media. Some WT mice or isolated vessels were treated with an arginase inhibitor, ABH [2-(S)-amino-6-boronohexanoic acid. In WT mice, the HFHS diet promoted increases in body weight, fasting blood glucose, and post-prandial insulin levels along with arterial stiffening and fibrosis, elevated blood pressure, decreased plasma levels of L-arginine, and elevated L-ornithine. The HFHS diet or PA/HG treatment also induced increases in vascular arginase activity along with oxidative stress, reduced vascular NO levels, and impaired endothelial-dependent vasorelaxation. All of these effects except obesity and hypercholesterolemia were prevented or significantly reduced by endothelial-specific deletion of arginase 1 or ABH treatment.

CONCLUSION

Vascular dysfunctions in diet-induced obesity are prevented by deletion of arginase 1 in vascular endothelial cells or arginase inhibition. These findings indicate that upregulation of arginase 1 expression/activity in vascular endothelial cells has an integral role in diet-induced cardiovascular dysfunction and metabolic syndrome.

Characterisation of betatrophin concentrations in childhood and adolescent obesity and insulin resistance

BACKGROUND AND OBJECTIVE

Betatrophin, a novel hormone, is correlated with insulin resistance and promotes pancreatic β-cell growth in mice. The aim of this study was to determine circulating betatrophin levels in overweight or obese children and adolescents.

METHODS

The following pairs of subjects were included: (i) normal-weight healthy (n = 27) and overweight or obese (n = 28); (ii) non-insulin-resistant overweight or obese (n = 25) and insulin-resistant obese (n = 15); (iii) normal-weight males (n = 18) and females (n = 20); (4) 5 to 8 yr olds (n = 20) and 8 to 14 yr olds (n = 18). Circulating betatrophin levels were measured using enzyme-linked immunosorbent assay (ELISA). In addition, clinical data were recorded and anthropometrical measurements were performed.

RESULTS

Circulating betatrophin levels were increased significantly in obese children and adolescents with insulin resistance (365.77 ± 30.86 pg/mL) compared with overweight or obese subjects without insulin resistance (274.25 ± 26.52 pg/mL; p < 0.05). However, no differences in betatrophin levels were seen between lean and overweight or obese children (323.18 ± 25.91 vs. 348.27 ± 18.91 pg/mL, respectively; p > 0.05). In the normal-weight cohort, males had higher serum betatrophin level than did females, and subjects <8 yr old had lower serum betatrophin levels compared with those >8 yr. Surprisingly, betatrophin concentrations were correlated negatively with body mass index (BMI), but not with the BMI Z-score, in non-insulin-resistant children and adolescents.

CONCLUSIONS

These results demonstrated that circulating betatrophin levels were increased in insulin-resistant obese children or adolescents and might act as a potential biomarker of insulin resistance in these populations. Furthermore, serum betatrophin concentrations might vary during the development of children and adolescents, as well as between genders.

Arginase as a Critical Prooxidant Mediator in the Binomial Endothelial Dysfunction-Atherosclerosis

Arginase is a metalloenzyme which hydrolyzes L-arginine to L-ornithine and urea. Since its discovery, in the early 1900s, this enzyme has gained increasing attention, as literature reports have progressively pointed to its critical participation in regulating nitric oxide bioavailability. Indeed, accumulating evidence in the following years would picture arginase as a key player in vascular health. Recent studies have highlighted the arginase regulatory role in the progression of atherosclerosis, the latter an essentially prooxidant state. Apart from the fact that arginase has been proven to impair different metabolic pathways, and also as a consequence of this, the repercussions of the actions of such enzyme go further than first thought. In fact, such metalloenzyme exhibits direct implications in multiple cardiometabolic diseases, among which are hypertension, type 2 diabetes, and hypercholesterolemia. Considering the epidemiological repercussions of these clinical conditions, arginase is currently seen under the spotlights of the search for developing specific inhibitors, in order to mitigate its deleterious effects. That said, the present review focuses on the role of arginase in endothelial function and its participation in the establishment of atherosclerotic lesions, discussing the main regulatory mechanisms of the enzyme, also highlighting the potential development of pharmacological strategies in related cardiovascular diseases.

Serum fetuin-A and arginase-1 in human obesity model: Is there any interaction between inflammatory status and arginine metabolism?

Obesity is a major risk factor for many chronic metabolic diseases such as inflammation, insulin resistance (IR) and fatty liver injury. It was reported that obesity causes some variations on the serum levels of fetuin-A and is associated with arginine metabolism, especially arginase-1 levels. The aim of our study was to evaluate, the interaction and possible changes of these liver over produced proteins, fetuin-A and arginase-1 levels in obesity-related inflammatory status. Study groups were composed of individuals aged between 19 and 63 (n = 62). The control group included healthy subjects with BMI < 25, obese group included obese patients with BMI > 30 and with no other chronic disease. Biochemical markers were determined by an auto-analyzer. Adiponectin, fetuin-A, arginase-1, asymmetric dimethylarginine (ADMA), arginine, Hexanoyl-lysine (HEL) and leptin levels were measured with commercial ELISA immunoassay kits. Nitrite and nitrate were determined with colorimetric assay kit in serum samples. High sensitive C-reactive protein (hsCRP) levels and liver function enzymes activities were higher in the obese group in respect to the control group. Serum fetuin-A, arginase-1 and leptin levels were increased but adiponectin levels were decreased in obese subjects. Fetuin-A levels showed significant correlations with arginase-1 and HOMA-IR. Consequently, we carried out an investigation about higher serum fetuin-A and arginase-1 levels may have an important role in obesity and obesity-related liver damage.

Arginase promotes endothelial dysfunction and hypertension in obese rats

OBJECTIVE

This study investigated whether arginase contributes to endothelial dysfunction and hypertension in obese rats.

METHODS

Endothelial function and arginase expression were examined in skeletal muscle arterioles from lean and obese Zucker rats (ZRs). Arginase activity, arginine bioavailability, and blood pressure were measured in lean and obese animals.

RESULTS

Arginase activity and expression was increased while global arginine bioavailability decreased in obese ZRs. Acetylcholine or luminal flow caused dilation of isolated skeletal muscle arterioles, but this was reduced or absent in vessels from obese ZRs. Treatment of arterioles with a nitric oxide synthase inhibitor blocked dilation in lean arterioles and eliminated differences among lean and obese vessels. In contrast, arginase inhibitors or l-arginine enhanced vasodilation in obese ZRs and abolished differences between lean and obese animals, while d-arginine had no effect. Finally, mean arterial blood pressure was significantly increased in obese ZRs. However, administration of l-arginine or arginase inhibitors lowered blood pressure in obese but not lean animals, and this was associated with an improvement in systemic arginine bioavailability.

CONCLUSIONS

Arginase promotes endothelial dysfunction and hypertension in obesity by reducing arginine bioavailability. Therapeutic approaches targeting arginase represent a promising approach in treating obesity-related vascular disease.