Leptin-Induced Endothelium-Independent Vasoconstriction in Thoracic Aorta and Pulmonary Artery of Spontaneously Hypertensive Rats: Role of Calcium Channels and Stores

The ontogenies of endometrial and myometrial leptin and adiponectin receptors in pregnant rats: Their putative impact on uterine contractility

AIMS

Limited data are available about the functions and expressions of leptin and adiponectin receptors (LEPR, AdipoRs) in the uterus. Our aim was to investigate the effects of leptin and adiponectin on the contractions of intact and denuded nonpregnant and pregnant uteri, as well as the changes in mRNA and protein expressions of LEPR and AdipoRs during the gestational period.

MAIN METHODS

Contractions of nonpregnant and 5-, 15-, 18-, 20- or 22-day pregnant uterine rings were measured in an isolated organ bath system. The tissue contractions were stimulated with KCl and modified by cumulative concentrations of leptin or adiponectin. The mRNAs, protein expressions and localizations of LEPR and AdipoRs were determined by RT-PCR, Western blot and immunohistochemistry, respectively.

KEY FINDINGS

Both adipokines relaxed the nonpregnant intact uterus more effectively than the denuded myometrium. Leptin inhibited the contractions of endometrium-denuded uteri throughout pregnancy, while its action was weakened on intact uteri towards term. The changes in LEPR receptor densities were independent of the relaxing effect. Adiponectin inhibited contractions, but this effect ceased on pregnancy day 22, while a gradual decrease was detected towards term on denuded myometria. These modifications were in harmony with changes in the expressions of AdipoRs.

SIGNIFICANCE

Both leptin and adiponectin play a role in the relaxation of the pregnant uterus, but their efficacy significantly decreases towards the end of gestation. Their endometrial receptors may have a fine-tuning role in uterine contractions, predicting the importance of these adipokines in uterine contractions under altered adipokine level conditions.

Vascular Dysfunction in Diabetes and Obesity: Focus on TRP Channels

Transient receptor potential (TRP) superfamily consists of a diverse group of non-selective cation channels that has a wide tissue distribution and is involved in many physiological processes including sensory perception, secretion of hormones, vasoconstriction/vasorelaxation, and cell cycle modulation. In the blood vessels, TRP channels are present in endothelial cells, vascular smooth muscle cells, perivascular adipose tissue (PVAT) and perivascular sensory nerves, and these channels have been implicated in the regulation of vascular tone, vascular cell proliferation, vascular wall permeability and angiogenesis. Additionally, dysfunction of TRP channels is associated with cardiometabolic diseases, such as diabetes and obesity. Unfortunately, the prevalence of diabetes and obesity is rising worldwide, becoming an important public health problems. These conditions have been associated, highlighting that obesity is a risk factor for type 2 diabetes. As well, both cardiometabolic diseases have been linked to a common disorder, vascular dysfunction. In this review, we briefly consider general aspects of TRP channels, and we focus the attention on TRPC (canonical or classical), TRPV (vanilloid), TRPM (melastatin), and TRPML (mucolipin), which were shown to be involved in vascular alterations of diabetes and obesity or are potentially linked to vascular dysfunction. Therefore, elucidation of the functional and molecular mechanisms underlying the role of TRP channels in vascular dysfunction in diabetes and obesity is important for the prevention of vascular complications and end-organ damage, providing a further therapeutic target in the treatment of these metabolic diseases.

Epoprostenol up-regulates serum adiponectin level in patients with systemic sclerosis: therapeutic implications

INTRODUCTION

Adiponectin, resistin and leptin belong to adipokines, a group of molecules secreted mainly by the adipose tissue, which impaired expression may be a missing link between various manifestations of systemic sclerosis. Adiponectin, which is also released in small amounts by the endothelium, possesses anti-inflammatory, anti-fibrotic and protective against endothelial injury properties. Both leptin and resistin exhibit features which are contradictory to adiponectin, as they trigger inflammation and the activation of skin fibroblasts. Epoprostenol is a prostaglandin analogue with powerful vasodilator activity and inhibitory effect on platelet aggregation. The aim of the study was to evaluate whether epoprostenol may have an effect on serum adipokine levels in patients with systemic sclerosis.

METHODS

A total of 27 patients were included in the study and received epoprostenol intravenously (25 µg of per day for 3 consecutive days). Serum concentrations of total adiponectin, resistin and leptin were assessed with enzyme-linked immunosorbent essay (R&D Systems, Minneapolis, MN, USA).

RESULTS

In all SSc patients, the basal level of adiponectin was significantly lower compared to healthy controls (mean 6.00 [Formula: see text] 2.81 μg/ml vs. 8.8 [Formula: see text] 4.3 μg/ml, p = 0.02) and basal level of resistin (mean 11.12 [Formula: see text] 3.36 ng/ml vs. 8.54 [Formula: see text] 3.07 ng/ml p = 0.02) was significantly higher than in the control group. The serum concentration of adiponectin increased significantly after treatment with epoprostenol (6.00 [Formula: see text] 2.81 μg/ml vs 9.29 [Formula: see text] 6.05 μg/ml; P = 0.002). The level of resistin and leptin remained unchanged.

CONCLUSION

Epoprostenol infusions up-regulate the serum concentration of adiponectin in patients with systemic sclerosis. In our opinion, future studies on treatments in systemic sclerosis should address the issue of their effect on adipokine metabolism.

Leptin receptor stimulation in late pregnant mouse uterine tissue inhibits spontaneous contractions by increasing NO and cGMP

The adipokine, leptin exerts inhibitory effect on both spontaneous and oxytocin-induced contractions in myometrium. However, the mechanisms involved in leptin-induced effect are not clear. In the present study, we studied the altered characteristics of uterine contractions in the presence of leptin and the possible mechanisms of its effect in late pregnant (18.5 day) mouse uterus. We conducted functional, biochemical and molecular biology studies to demonstrate the mechanism of leptin-induced response. Leptin exerted an inhibitory response (E_max 40.5 ± 3.99%) on basal uterine contractions. The extent of inhibition was less than that obtained with known uterine relaxants, salbutamol (E_max103 ± 8.66%) and BRL-37344 (E_max 84.79 ± 8.12%). Leptin-induced uterine response was inhibited by leptin receptor antagonist SHLA and JAK-STAT pathway inhibitor, AG-490. The relaxant response was also subdued by NO-cGMP-PK-G pathway blockers L-NAME, 1400W, ODQ and KT-5823. Further, leptin enhanced the levels of NO and cGMP in uterine tissues. Also, SHLA, AG-490 and a combination of 1400 W and L-NAME prevented leptin-induced increase in NO. Similar effect was observed on cGMP levels in presence of leptin and SHLA. However, leptin did not influence CaCl₂-induced response in potassium-depolarized tissues. We also detected leptin receptor protein in late pregnant mouse uterus located in endometrial luminal epithelium and myometrial layers. Real-time PCR studies revealed significantly higher expression of short forms of the receptor (ObRa and ObRc) in comparison to the long form (ObRb). In conclusion, the results of the present study suggest that leptin inhibits mouse uterine contraction by stimulating short forms of the leptin receptors and activating NO pathway in a JAK-STAT-dependent manner.

Circulating leptin is associated with serum uric acid level and its tubular reabsorption in a sample of adult middle-aged men

PURPOSE

Leptin is associated with cardiovascular risk factors (e.g. hypertension, insulin resistance, kidney disease and excess body weight). Experimental studies showed that leptin might affect serum uric acid, by modulation of the uric acid excretion. However, there are few observational data on the relationship between leptin and uric acid in the general population. Therefore, the aim of the present study was to evaluate the relationship between leptin and uric acid and its excretion in a large middle-aged male general population.

METHODS

A sample of 930 adult male individuals (mean age: 52 years) without therapy for high uric acid was included in the analysis (the Olivetti Heart Study).

RESULTS

Uric acid was significantly and positively associated with blood pressure, BMI, waist circumference, insulin resistance, C-reactive protein and leptin (p < 0.01), while inversely with renal function (p = 0.01). The multivariate analysis confirmed the association between leptin and uric acid after adjustment for potential confounders (p < 0.01). After division for adiposity, this trend was confirmed separately for normal weight and excess body weight participants. Moreover, leptin was inversely associated with excretion of uric acid (p < 0.01), also in multivariate analysis (p = 0.03).

CONCLUSION

The results of this study indicate a positive association between circulating leptin levels and uric acid, independently of potential confounders, both in normal and excess body weight men. Furthermore, an inverse association between leptin and uric acid excretion was detected.

Vascular endothelial growth factor enhances profibrotic activities through modulation of calcium homeostasis in human atrial fibroblasts

Vascular endothelial growth factor (VEGF), a pivotal activator of angiogenesis and calcium (Ca²⁺) signaling in endothelial cells, was shown to increase collagen production in atrial fibroblasts. In this study, we evaluated whether VEGF may regulate Ca²⁺ homeostasis in atrial fibroblasts and contribute to its profibrogenesis. Migration, and proliferation analyses, patch-clamp assay, Ca²⁺ fluorescence imaging, and western blotting were performed using VEGF-treated (300 pg/mL or 1000 pg/mL) human atrial fibroblasts with or without coadministration of Ethylene glycol tetra-acetic acid (EGTA, 1 mmol/L), or KN93 (a Ca²⁺/calmodulin-dependent protein kinase II [CaMKII] inhibitor, 10 μmol/L). VEGF (1000 pg/mL) increased migration, myofibroblast differentiation, pro-collagen type I, pro-collagen type III production, and phosphorylated VEGF receptor 1 expression of fibroblasts. VEGF (1000 pg/mL) increased the nonselective cation current (I_NSC) of transient receptor potential (TRP) channels and potassium current of intermediate-conductance Ca²⁺-activated K⁺ (K_Ca3.1) channels thereby upregulating Ca²⁺ entry. VEGF upregulated phosphorylated ERK expression. An ERK inhibitor (PD98059, 50 μmol/L) attenuated VEGF-activated I_NSC of TRP channels. The presence of EGTA attenuated the profibrotic effects of VEGF on pro-collagen type I, pro-collagen type III production, myofibroblast differentiation, and migratory capabilities of fibroblasts. VEGF upregulated the expression of phosphorylated CaMKII in fibroblasts, which was attenuated by EGTA. In addition, KN93 reduced VEGF-increased pro-collagen type I, pro-collagen type III production, myofibroblast differentiation, and the migratory capabilities of fibroblasts. In conclusion, we found that VEGF increases atrial fibroblast activity through CaMKII signaling by enhancing Ca²⁺ entry. Our findings provide benchside evidence leading to a potential novel strategy targeting atrial myopathy and arrhythmofibrosis.

Circulating leptin levels predict the decline in renal function with age in a sample of adult men (The Olivetti Heart Study)

Leptin (LPT) is associated with a number of cardiovascular risk factors, such as high blood pressure (BP), insulin resistance and excess in body weight. Some studies find an unfavorable cross-sectional association between LPT and renal disease, in particular in patients with already known kidney dysfunction. There are few data on the relationship between LPT and changes in renal function over time in subjects without evidence of kidney dysfunction. Hence, the aim of this study is to estimate the predictive role of LPT on the decline in renal function occurring in an 8-year follow-up observation of a sample of adult apparently healthy men (The Olivetti Heart Study). The study includes 319 untreated normotensive and nondiabetic men without clinical evidence of renal dysfunction (creatinine clearance-CrCl > 60 mL/min/1.73 m²) at baseline. At baseline, LPT is significantly and positively associated with BMI, abdominal circumference, BP and Homa index, no relationship is found with CrCl. At the end of the 8-year follow-up, a significant association is detected between baseline LPT and changes occurring in BP. Moreover, an inverse correlation with changes in CrCl is found (r = - 0.12). This unfavorable relationship between baseline LPT and decline in renal function is also confirmed in the multivariate analyses, after adjustment for all potential confounders (R² = 0.42, p < 0.01). The results of this prospective investigation suggest a predictive role of circulating LPT levels on decline in renal function over time, independently of main potential confounders, in normotensive and nondiabetic men with normal renal function at baseline.

Pulmonary vascular dysfunction in metabolic syndrome

Metabolic syndrome is a critically important precursor to the onset of many diseases, such as cardiovascular disease, and cardiovascular disease is the leading cause of death worldwide. The primary risk factors of metabolic syndrome include hyperglycaemia, abdominal obesity, dyslipidaemia, and high blood pressure. It has been well documented that metabolic syndrome alters vascular endothelial and smooth muscle cell functions in the heart, brain, kidney and peripheral vessels. However, there is less information available regarding how metabolic syndrome can affect pulmonary vascular function and ultimately increase an individual's risk of developing various pulmonary vascular diseases, such as pulmonary hypertension. Here, we review in detail how metabolic syndrome affects pulmonary vascular function.

Leptin Modifies the Rat Heart Performance Associated with Mitochondrial Dysfunction Independently of Its Prohypertrophic Effects

BACKGROUND

Functional receptors for leptin were described on the surface of cardiomyocytes, and there was a prohypertrophic effect with high concentrations of the cytokine. Therefore, leptin could be a link between obesity and the prevalence of cardiovascular diseases. On the other hand, a deleterious effect of leptin on mitochondrial performance was described, which was also associated with the evolution of cardiac hypertrophy to heart failure. The goal of our study was to analyze the effect of the exposure of rat hearts to a high concentration of leptin on cardiac and mitochondrial function.

METHODS

Rat hearts were perfused continuously with or without 3.1 nM leptin for 1, 2, 3, or 4 hours. Homogenates and mitochondria were prepared by centrifugation and analyzed for cardiac actin, STAT3, and pSTAT3 by Western blotting, as well as for mitochondrial oxidative phosphorylation, membrane potential, swelling, calcium transport, and content of oxidized lipids.

RESULTS

In our results, leptin induced an increased rate-pressure product as a result of increased heart rate and contraction force, as well oxidative stress. In addition, mitochondrial dysfunction expressed as a loss of membrane potential, decreased ability for calcium transport and retention, faster swelling, and less respiratory control was observed.

CONCLUSIONS

Our results support the role of leptin as a deleterious factor for cardiac function and indicates that mitochondrial dysfunction could be a trigger for cardiac hypertrophy and failure.