Rita S. Patarrão

Effects of CPAP on nitrate and norepinephrine levels in severe and mild-moderate sleep apnea

BackgroundReduced plasma nitrate (NOx) levels and increased urinary norepinephrine (U-NE) levels have been described in severe obstructive sleep apnea (OSA), and are reverted by continuous positive airway pressure (CPAP). The effect of CPAP on these biomarkers in mild-moderate OSA is not well understood.The aim of this study was to compare NOx and U-NE levels and blood pressure (BP) between male patients with mild-moderate and severe OSA and determine the impact of 1 month of CPAP therapy on these parameters.MethodsWe undertook a prospective study of 67 consecutive OSA patients (36 mild-moderate, 31 severe). Measurements of plasma NOx at 11 pm, 4 am and 7 am, 24-h U-NE and ambulatory BP were obtained at baseline and after 1 month of CPAP.ResultsAt baseline, NOx levels showed a significant decrease during the night in both groups (p < 0.001). U-NE level and BP were significantly higher in the severe OSA group. After 1 month of CPAP, there was a significant increase in NOx levels and a reduction in U-NE level and BP only in patients with severe OSA.ConclusionsOne month of CPAP results in significant improvements in NOx levels, 24-h U-NE level and BP in patients with severe OSA, but not in patients with mild-moderate OSA.Trial registrationClinicalTrials.gov: http://NCT01769807

How Inflammation Impinges on NAFLD: A Role for Kupffer Cells

Nonalcoholic fatty liver disease (NAFLD) is rapidly becoming the most prevalent cause of liver disease worldwide and afflicts adults and children as currently associated with obesity and insulin resistance. Even though lately some advances have been made to elucidate the mechanism and causes of the disease much remains unknown about NAFLD. The aim of this paper is to discuss the present knowledge regarding the pathogenesis of the disease aiming at the initial steps of NAFLD development, when inflammation impinges on fat liver deposition. At this stage, the Kupffer cells attain a prominent role. This knowledge becomes subsequently relevant for the development of future diagnostic, prevention, and therapeutic options for the management of NAFLD.

Understanding Postprandial Glucose Clearance by Peripheral Organs: The Role of the Hepatic Parasympathetic System

The hepatic parasympathetic system is one of the major contributors for preserving insulin sensitivity in the postprandial state. Postprandial hepatic vagal control of whole‐body glucose clearance and its effect on specific organs remains unknown. Our hypothesis is that, in the postprandial state, the hepatic parasympathetic nerves (HPN) are responsible for a considerable part of extra‐hepatic tissue glucose clearance. Two groups of 9‐week‐old Sprague–Dawley rats were studied, comparing sham‐operated versus hepatic parasympathetic denervated animals. Insulin sensitivity was evaluated in the postprandial state by the rapid insulin sensitivity test (RIST). [3H]2‐deoxy‐d‐glucose was administered during the RIST. Plasma glucose rate of the disappearance and clearance by skeletal muscle, adipose tissue, liver, pancreas, heart and kidney of this radioisotope was measured. The postprandial denervated group showed a decrease insulin sensitivity of 41.4 ± 5.2%. This group of animals showed a decrease in the rate of plasma [3H]2‐deoxy‐d‐glucose disappearance and skeletal muscle, heart and kidney glucose clearance by 45%, 35% and 67%, respectively. These studies show that the major contributor of postprandial whole‐body glucose clearance was skeletal muscle; in the range 69–38%, depending on HPN integrity. The results obtained in the present study indicate that HPN are crucial for postprandial action of insulin through a mechanism that is essential for maintenance of skeletal muscle, heart and kidney glucose clearance. These results suggest that hepatic parasympathetic dysfunction could lie at the genesis of type 2 diabetes complications, namely insulin resistance, nephropathy and cardiomyopathy.

Risk of postprandial insulin resistance: the liver/vagus rapport.

Ingestion of a meal is the greatest challenge faced by glucose homeostasis. The surge of nutrients has to be disposed quickly, as high concentrations in the bloodstream may have pathophysiological effects, and also properly, as misplaced reserves may induce problems in affected tissues. Thus, loss of the ability to adequately dispose of ingested nutrients can be expected to lead to glucose intolerance, and favor the development of pathologies. Achieving interplay of several organs is of upmost importance to maintain effectively postprandial glucose clearance, with the liver being responsible of orchestrating global glycemic control. This dogmatic role of the liver in postprandial insulin sensitivity is tightly associated with the vagus nerve. Herein, we uncover the behaviour of metabolic pathways determined by hepatic parasympathetic function status, in physiology and in pathophysiology. Likewise, the inquiry expands to address the impact of a modern lifestyle, especially one’s feeding habits, on the hepatic parasympathetic nerve control of glucose metabolism.

Postprandial insulin resistance in Zucker diabetic fatty rats is associated with parasympathetic-nitric oxide axis deficiencies.

The Zucker diabetic fatty (ZDF) rat is an obesity and type 2 diabetes model. Progression to diabetes is well characterised in ZDF rats, but only in the fasted state. We evaluated the mechanisms underlying postprandial insulin resistance in young ZDF rats. We tested the hypothesis that the overall postprandial action of insulin is affected in ZDF rats as a result of impairment of the hepatic parasympathetic‐nitric oxide (PSN‐NO) axis and/or glutathione (GSH), resulting in decreased indirect (PSN‐NO axis) and direct actions of insulin. Nine‐week‐old male ZDF rats and lean Zucker rats (LZR, controls) were used. The action of insulin was assessed in the fed state before and after parasympathetic antagonism atropine. Basal hepatic NO and GSH were measured, as well as NO synthase (NOS) and γ‐glutamyl‐cysteine synthethase (GCS) activity and expression. ZDF rats presented postprandial hyperglycaemia (ZDF, 201.4 ± 12.9 mg/dl; LZR, 107.7 ± 4.3 mg/dl), but not insulinopaenia (ZDF, 5.9 ± 0.8 ng/ml; LZR, 1.5 ± 0.3 ng/ml). Total postprandial insulin resistance was observed (ZDF, 78.6 ± 7.5 mg glucose/kg; LZR, 289.2 ± 24.7 mg glucose/kg), with a decrease in both the direct action of insulin (ZDF, 54.8 ± 7.0 mg glucose/kg; LZR, 173.3 ± 20.5 mg glucose/kg) and the PSN‐NO axis (ZDF, 24.5 ± 3.9 mg glucose/kg; LZR, 115.9 ± 19.4 mg glucose/kg). Hepatic NO (ZDF, 117.2 ± 11.4 μmol/g tissue; LZR, 164.6 ± 4.9 μmol/g tissue) and GSH (ZDF, 4.9 ± 0.3 μmol/g; LZR, 5.9 ± 0.2 μmol/g) were also compromised as a result of decreased NOS and GCS activity, respectively. These results suggest a compromise of the mechanism responsible for potentiating insulin action after a meal in ZDF rats. We show that defective PSN‐NO axis and GSH synthesis, together with an impaired direct action of insulin, appears to contribute to postprandial insulin resistance in this model.

Acute Glucagon Induces Postprandial Peripheral Insulin Resistance

Glucagon levels are often moderately elevated in diabetes. It is known that glucagon leads to a decrease in hepatic glutathione (GSH) synthesis that in turn is associated with decreased postprandial insulin sensitivity. Given that cAMP pathway controls GSH levels we tested whether insulin sensitivity decreases after intraportal (ipv) administration of a cAMP analog (DBcAMP), and investigated whether glucagon promotes insulin resistance through decreasing hepatic GSH levels.Insulin sensitivity was determined in fed male Sprague-Dawley rats using a modified euglycemic hyperinsulinemic clamp in the postprandial state upon ipv administration of DBcAMP as well as glucagon infusion. Glucagon effects on insulin sensitivity was assessed in the presence or absence of postprandial insulin sensitivity inhibition by administration of L-NMMA. Hepatic GSH and NO content and plasma levels of NO were measured after acute ipv glucagon infusion. Insulin sensitivity was assessed in the fed state and after ipv glucagon infusion in the presence of GSH-E. We founf that DBcAMP and glucagon produce a decrease of insulin sensitivity, in a dose-dependent manner. Glucagon-induced decrease of postprandial insulin sensitivity correlated with decreased hepatic GSH content and was restored by administration of GSH-E. Furthermore, inhibition of postprandial decrease of insulin sensitivity L-NMMA was not overcome by glucagon, but glucagon did not affect hepatic and plasma levels of NO. These results show that glucagon decreases postprandial insulin sensitivity through reducing hepatic GSH levels, an effect that is mimicked by increasing cAMP hepatic levels and requires physiological NO levels. These observations support the hypothesis that glucagon acts via adenylate cyclase to decrease hepatic GSH levels and induce insulin resistance. We suggest that the glucagon-cAMP-GSH axis is a potential therapeutic target to address insulin resistance in pathological conditions.

In vitro nitrosation of insulin A- and B-chains

The physiological roles of insulin and nitric oxide (NO) have recently been recognized by several studies. A diversity of chemical modifications of insulin is reported both in vivo and in vitro. S-nitrosation, the covalent linkage of NO to cysteine-free thiol, is recognized as an important post-translational regulation in many proteins. Here, we report the in vitro synthesis of a S-nitrosothiol of bovine insulin A- and B-chains. These compounds were characterized by their HPLC chromatographic behavior, monitored by UV visible spectroscopy and electron spray ionization mass spectrometry. The experimental results indicate that each A- and B-chain were S-nitrosated with only one NO group. Stability and solubility of these synthesized derivatives is described for physiological purposes. In this work, nitroso A- and B-chains of insulin were synthesized in vitro in order to better understand the possible interactions between insulin and NO that may be involved in the etiology of insulin resistance.