Is there NO help for leptin?

Causal association of adipokines with osteoarthritis: a Mendelian randomization study

OBJECTIVE

This two-sample Mendelian randomization study aimed to delve into the effects of genetically predicted adipokine levels on OA.

METHODS

Summary statistic data for OA originated from a meta-analysis of a genome-wide association study with an overall 50 508 subjects of European ancestry. Publicly available summary data from four genome-wide association studies were exploited to respectively identify instrumental variables of adiponectin, leptin, resistin, chemerin and retinol-blinding protein 4. Subsequently, Mendelian randomization analyses were conducted with inverse variance weighted (IVW), weighted median and Mendelian randomization-Egger regression. Furthermore, sensitivity analyses were then conducted to assess the robustness of our results.

RESULTS

The positive causality between genetically predicted leptin level and risk of total OA was indicated by IVW [odds ratio (OR): 2.40, 95% CI: 1.13-5.09] and weighted median (OR: 2.94, 95% CI: 1.23-6.99). In subgroup analyses, evidence of potential harmful effects of higher level of adiponectin (OR: 1.28, 95% CI: 1.01-1.61 using IVW), leptin (OR: 3.44, 95% CI: 1.18-10.03 using IVW) and resistin (OR: 1.18, 95% CI: 1.03-1.36 using IVW) on risk of knee OA were acquired. However, the mentioned effects on risk of hip OA were not statistically significant. Slight evidence was identified supporting causality of chemerin and retinol-blinding protein 4 for OA. The findings of this study were verified by the results from sensitivity analysis.

CONCLUSIONS

An association between genetically predicted leptin level and risk of total OA was identified. Furthermore, association of genetically predicted levels of adiponectin, leptin and resistin with risk of knee OA were reported.

Influences of maternal nutrient restriction and arginine supplementation on visceral metabolism and hypothalamic circuitry of offspring

Maternal nutrient restriction during gestation can exert long-term negative effects on offspring health and performance. Arginine supplementation may rescue some of the negative effects elicited by maternal nutrient restriction. We tested the hypothesis that maternal arginine supplementation during gestation would rescue deleterious effects of nutrient restriction on in vitro O₂ consumption in the liver and jejunum and hypothalamic protein expression of proopiomelanocortin (POMC), neuropeptide Y (NPY), agouti-related peptide (AgRP), and neuronal nitric oxide synthase (nNOS), and the colocalization of nNOS and active phosphor-signal transducer and activator of transcription 3 (pSTAT3) in female offspring. Multiparous ewes were assigned to dietary treatment at 54 d of gestation: 100% of requirements (Con), 60% of control (Res), or Res plus rumen-protected arginine (Res-Arg; 180 mg/kg). At parturition, offspring were immediately removed from their dam and placed on a common diet. At 54 ± 4 d of age, female lambs (n = 6 per treatment) were weighed, the liver and jejunum were weighed, and samples were collected for in vitro measurement of O₂ consumption. The hypothalamus was collected to determine protein expression of POMC, NPY, AgRP, and nNOS, and the colocalization of nNOS and pSTAT3 (n = 3, 4, and 4 for Con, Res, and Res-Arg, respectively). Hepatic consumption of O₂ in vitro (mol/min/liver) was decreased (P = 0.04) in the Res and Res-Arg group compared with Con. Intensity of staining for NPY-containing fibers tended to decrease (P = 0.10) in Res and Res-Arg compared with Con. Number of POMC neuronal cells in the arcuate nucleus (ARC) of the hypothalamus decreased (P ≤ 0.03) in the Res group compared with Res-Arg. These observations demonstrate that maternal nutrient restriction decreases energy utilization in the liver and number of POMC cells in the ARC of offspring. Supplementation of arginine to the gestating ewe failed to influence hepatic use of energy in lambs from Res ewes. Numbers of POMC-containing cells were increased in the ARC in lambs from ewes restricted to 60% of nutritional requirements and supplemented with rumen-protected arginine, potentially influencing feeding behavior and hepatic energy metabolism.

Circulating levels of proinflammatory mediators as potential biomarkers of post-traumatic knee osteoarthritis development

Background

The identification of biomarkers of post-traumatic osteoarthritis (PTOA) progression is of clinical importance. The aims of this study were: (1) to assess the abilities of various soluble proinflammatory mediators in plasma to distinguish patients with knee PTOA from controls; (2) to determine the correlations between the mediators in plasma and those mediators in synovial fluid (SF); and (3) to explore the associations of the mediators with radiographic PTOA severity.

Materials and methods

The concentrations of IL-1β, IL-6, IL-18, TNFα, and leptin were measured using ELISA. Nitric oxide was determined as nitrite/nitrate (NO_x) using the Griess reaction.

Results

We included 171 subjects (134 PTOA patients and 37 controls) and excluded patients with rheumatoid arthritis or gout. The ROC curve of plasma NO_x had the highest AUC, a specificity of 100%, and a sensitivity of 84.4%. The combination of IL-6 and leptin proved to be the most discriminatory, with an AUC value of 0.933, a specificity of 96.7%, and a sensitivity of 85.7%. The levels of NO_x, IL-6, IL-18, and leptin in plasma were significantly correlated with their levels in SF. Leptin levels in both plasma (p = 0.036) and SF (p = 0.041) and the synovial IL-18 level (p = 0.045) were correlated with the Kellgren–Lawrence (KL) grade. Early-stage PTOA (KL 1–2) was associated with a high concentration of IL-1β in plasma before and after (OR 6.235, 95% CI 1.362 to 28.552, p = 0.018) adjusting for age, gender, and BMI.

Conclusions

Circulating NO_x level and a combination of IL-6 and leptin permitted the strongest discrimination of patients with PTOA from controls. PTOA severity was correlated with leptin levels in plasma and SF and with the synovial IL-18 level. Early PTOA was associated with the circulating level of IL-1β.

Level of evidence

III (case–control study).

Ghrelin enhances food intake and carbohydrate oxidation in a nitric oxide dependent manner

In the present study we sought to investigate interactions between hypothalamic nitric oxide (NO) and ghrelin signaling on food intake and energy substrate utilization as measured by the respiratory exchange ratio (RER). Guide cannulae were unilaterally implanted in either the arcuate (ArcN) or paraventricular (PVN) nuclei of male Sprague-Dawley rats. Animals were pretreated with subcutaneous (2.5-10mg/kg/ml) or central (0-100pmol) N-nitro-l-Arginine methyl ester (l-NAME) followed by 50pmol of ghrelin administered into either the ArcN or PVN. Both l-NAME and ghrelin were microinjected at the onset of the active cycle and food intake and RER were assessed 2h postinjection. RER was measured as the ratio of the volume of carbon dioxide expelled relative to the volume of oxygen consumed (VCO₂/VO₂) using an open-circuit indirect calorimeter. Our results demonstrated that peripheral and central l-NAME pretreatment dose-dependently attenuated ghrelin induced increases in food intake and RER in either the ArcN or PVN. In fact the 100pmol dose largely reversed the metabolic effects of ghrelin in both anatomical regions. These findings suggest that ghrelin enhancement of food intake and carbohydrate oxidation in the rat ArcN and PVN is NO-dependent.

Demethylation of an NF-κB enhancer element orchestrates iNOS induction in osteoarthritis and is associated with altered chondrocyte cell cycle

OBJECTIVE

To examine the methylation profile of the nuclear factor (NF)-κB enhancer region at -5.8 kb of inducible nitric oxide synthase (iNOS) and the subsequent role in the induction of osteoarthritis (OA) via cell cycle regulation.

METHODS

Percentage methylation was determined by pyrosequencing, gene expression by qRT-PCR and cell proliferation was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Transient transfections were induced to determine the effect of the NF-κB enhancer region on cell proliferation and the influence of DNA methylation.

RESULTS

In vitro de-methylation with 5-aza-dC showed decreased levels of DNA methylation at CpG sites localised at -5.8 kb, which correlated with higher levels of iNOS expression. In vitro methylation of the NF-κB enhancer region at -5.8 kb increased the percentage of cells at G0/G1 cell cycle phase. Loss of methylation within this region correlated with, enhanced proliferation and increased number of cells at G2/M phase. OA chondrocytes demonstrated up-regulation of the G0/G1 cell cycle progression markers Cyclin D1 and CDK6 in contrast to control cells. We demonstrate the loss of methylation that occurs at specific CpG sites localised at the -5.8 kb NF-κB enhancer region of the iNOS gene in OA chondrocytes permits the binding of this transcription factor activating the expression of iNOS. This results in subsequent altered cell cycle regulation, altered proliferative phenotype and transmission of the pathogenic phenotype to daughter cells.

CONCLUSIONS

This study indicates that inhibition of cell cycle progression by iNOS enhancer hypermethylation is capable of reducing pro-inflammatory responses via down-regulation of NF-κB with important therapeutic implications in OA.

Leptin and maintenance of gastrointestinal function

Leptin is a protein hormone encoded by the obese (Ob) gene, exerting an important biological role in the life. Initially, leptin is believed to play a major role in regulating appetite control and energy metabolism, including adjusting the energy metabolism. However, recent data suggest that leptin also plays an important part in regulating the function of the gastrointestinal tract, immune and inflammation response, injury repair, and tumor angiogenesis. This article reviews the protective effects of leptin on the function of the gastrointestinal tract.

Citrulline reduces glyceroneogenesis and induces fatty acid release in visceral adipose tissue from overweight rats

SCOPE

High-fat diet (HFD) increases visceral adipose tissue (AT). Our aim was to evaluate whether citrulline (CIT) affected nonesterified fatty acid (NEFA) metabolism in AT from HFD-fed rats.

METHODS AND RESULTS

Rats were fed for 8 weeks with either a control diet (CD) or HFD. Retroperitoneal AT explants were exposed to 2.5 mmol/L CIT for 24 h. We analyzed lipolysis, beta-oxidation, glyceroneogenesis, and the expression of the key associated enzymes. CIT doubled NEFA release selectively in HFD AT. Phosphorylation of hormone-sensitive lipase was upregulated 50 and 100% by CIT in CD and HFD AT, respectively. Under CIT, beta-oxidation increased similarly whatever the diet, whereas glyceroneogenesis, which permits NEFA re-esterification, was downregulated 50 and 80% in CD and HFD AT, respectively. In the latter, the important decrease in re-esterification probably explains the rise of NEFA release. A pretreatment with the nitric oxide synthase inhibitor N ω-nitro-l-arginine methyl ester abolished CIT effects.

CONCLUSION

These results demonstrate direct lipolytic and antiglyceroneogenic effects of CIT on CD and HFD AT. The selective CIT-mediated NEFA release from HFD AT was probably the consequence of the drastic decrease in glyceroneogenesis and nitric oxide was a mediator of CIT effects. These results provide evidence for a direct action of CIT on AT to reduce overweight.

Nitric oxide and energy metabolism in mammals

Nitric oxide (NO) is a signaling molecule synthesized from L-arginine by NO synthase in animals. Increasing evidence shows that NO regulates the mammalian metabolism of energy substrates and that these effects of NO critically depend on its concentrations at the reaction site and the period of exposure. High concentrations of NO (in the micromolar range) irreversibly inhibit complexes I, II, III, IV, and V in the mitochondrial respiratory chain, whereas physiological levels of NO (in the nanomolar range) reversibly reduce cytochomrome oxidase. Thus, NO reduces oxygen consumption by isolated mitochondria to various extents. In intact cells, through cGMP and AMP-activated protein kinase signaling, physiological levels of NO acutely stimulate uptake and oxidation of glucose and fatty acids by skeletal muscle, heart, liver, and adipose tissue, while inhibiting the synthesis of glucose, glycogen and fat in the insulin-sensitive tissues, and enhancing lipolysis in white adipocytes. Chronic effects of physiological levels of NO in vivo include stimulation of angiogenesis, blood flow, mitochondrial biogenesis, and brown adipocyte development. Modulation of NO-mediated pathways through dietary supplementation with L-arginine or its precursor L-citrulline may provide an effective, practical strategy to prevent and treat metabolic syndrome, including obesity, diabetes, and dyslipidemia in mammals, including humans.