Blood lipids affect rat islet blood flow regulation through β₃-adrenoceptors

Diabetes and COVID-19: Role of insulin resistance as a risk factor for COVID-19 severity

Patients with diabetes are more susceptible to coronavirus disease 2019 (COVID-19), and as a consequence, develop more severe form of disease. This is partly due to a systemic inflammatory state and pro thrombotic milieu seen in metabolic syndrome. In this review, we attempt to explore the pathogenetic links between insulin resistance and COVID-19 disease severity. Insulin resistance is an underlying condition for metabolic syndromes, including type 2 diabetes, which impairs insulin signaling pathways affecting metabolic and cardiovascular homeostasis. A high concentration of circulating insulin shifts the balance to mitogen activated protein kinase (MAPK)-dependent signaling and causes endothelial cell damage. The phosphatidylinositol 3 kinase and MAPK dependent signaling pathways maintain a balance between nitric oxide-dependent vasodilator and endothelin-1 dependent vasoconstriction actions of insulin. Vascular smooth muscle cell dysfunction is responsible for inflammation and blood coagulation leading to microvascular and macrovascular complications in diabetes. Hyperactivity in renin-angiotensin system is implicated in development of islet oxidative stress and subsequent β-cell dysfunction, as it alters the islet blood flow. These deleterious effects of insulin resistance involving altered blood pressure, vascular dysfunction, and inflammation could be associated with increased severity in COVID-19 patients. We conclude that clinical and/or biochemical markers of insulin resistance should be included as prognostic markers in assessment of acute COVID-19 disease.

The effect of mirabegron on energy expenditure and brown adipose tissue in healthy lean South Asian and Europid men

AIM

To compare the effects of cold exposure and the β3-adrenergic receptor agonist mirabegron on plasma lipids, energy expenditure and brown adipose tissue (BAT) activity in South Asians versus Europids.

MATERIALS AND METHODS

Ten lean Dutch South Asian (aged 18-30 years; body mass index [BMI] 18-25 kg/m² ) and 10 age- and BMI-matched Europid men participated in a randomized, double-blinded, cross-over study consisting of three interventions: short-term (~ 2 hours) cold exposure, mirabegron (200 mg one dose p.o.) and placebo. Before and after each intervention, we performed lipidomic analysis in serum, assessed resting energy expenditure (REE) and skin temperature, and measured BAT fat fraction by magnetic resonance imaging.

RESULTS

In both ethnicities, cold exposure increased the levels of several serum lipid species, whereas mirabegron only increased free fatty acids. Cold exposure increased lipid oxidation in both ethnicities, while mirabegron increased lipid oxidation in Europids only. Cold exposure and mirabegron enhanced supraclavicular skin temperature in both ethnicities. Cold exposure decreased BAT fat fraction in both ethnicities. After the combination of data from both ethnicities, mirabegron decreased BAT fat fraction compared with placebo.

CONCLUSIONS

In South Asians and Europids, cold exposure and mirabegron induced beneficial metabolic effects. When combining both ethnicities, cold exposure and mirabegron increased REE and lipid oxidation, coinciding with a higher supraclavicular skin temperature and lower BAT fat fraction.

Pancreatic Blood Flow with Special Emphasis on Blood Perfusion of the Islets of Langerhans

The pancreatic islets are more richly vascularized than the exocrine pancreas, and possess a 5- to 10-fold higher basal and stimulated blood flow, which is separately regulated. This is reflected in the vascular anatomy of the pancreas where islets have separate arterioles. There is also an insulo-acinar portal system, where numerous venules connect each islet to the acinar capillaries. Both islets and acini possess strong metabolic regulation of their blood perfusion. Of particular importance, especially in the islets, is adenosine and ATP/ADP. Basal and stimulated blood flow is modified by local endothelial mediators, the nervous system as well as gastrointestinal hormones. Normally the responses to the nervous system, especially the parasympathetic and sympathetic nerves, are fairly similar in endocrine and exocrine parts. The islets seem to be more sensitive to the effects of endothelial mediators, especially nitric oxide, which is a permissive factor to maintain the high basal islet blood flow. The gastrointestinal hormones with pancreatic effects mainly influence the exocrine pancreatic blood flow, whereas islets are less affected. A notable exception is incretin hormones and adipokines, which preferentially affect islet vasculature. Islet hormones can influence both exocrine and endocrine blood vessels, and these complex effects are discussed. Secondary changes in pancreatic and islet blood flow occur during several conditions. To what extent changes in blood perfusion may affect the pathogenesis of pancreatic diseases is discussed. Both type 2 diabetes mellitus and acute pancreatitis are conditions where we think there is evidence that blood flow may contribute to disease manifestations. © 2019 American Physiological Society. Compr Physiol 9:799-837, 2019.

Blocking fatty acid-fueled mROS production within macrophages alleviates acute gouty inflammation

Gout is the most common inflammatory arthritis affecting men. Acute gouty inflammation is triggered by monosodium urate (MSU) crystal deposition in and around joints that activates macrophages into a proinflammatory state, resulting in neutrophil recruitment. A complete understanding of how MSU crystals activate macrophages in vivo has been difficult because of limitations of live imaging this process in traditional animal models. By live imaging the macrophage and neutrophil response to MSU crystals within an intact host (larval zebrafish), we reveal that macrophage activation requires mitochondrial ROS (mROS) generated through fatty acid oxidation. This mitochondrial source of ROS contributes to NF-κB-driven production of IL-1β and TNF-α, which promote neutrophil recruitment. We demonstrate the therapeutic utility of this discovery by showing that this mechanism is conserved in human macrophages and, via pharmacologic blockade, that it contributes to neutrophil recruitment in a mouse model of acute gouty inflammation. To our knowledge, this study is the first to uncover an immunometabolic mechanism of macrophage activation that operates during acute gouty inflammation. Targeting this pathway holds promise in the management of gout and, potentially, other macrophage-driven diseases.

Autonomic nervous system and pancreatic islet blood flow

Vascularization and innervation of the islet of Langerhans are highly interconnected and are critical for intercellular and intertissular communication. They are both involved in the control of islet blood flow which has been shown to have an important role in the control of endocine secretion. Both parameters are disturbed during the course of metabolic pathologies and particularly diabetes. A better understanding of these mechanisms has and will greatly benefit from the rapidly-emerging technologies particularly in vivo imaging enabling to study both anatomy and functions of the islet.

Plasma HDL-cholesterol and triglycerides, but not LDL-cholesterol, are associated with insulin secretion in non-diabetic subjects

OBJECTIVE

Experimental data support the notion that lipoproteins might directly affect beta cell function, however clinical data are sparse and inconsistent. We aimed at verifying whether, independently of major confounders, serum lipids are associated with alterations in insulin secretion or clearance non-diabetic subjects.

METHODS

Cross sectional and observational prospective (3.5yrs), multicentre study in which 1016 non-diabetic volunteers aged 30-60yrs. and with a wide range of BMI (20.0-39.9kg/m²) were recruited in a setting of University hospital ambulatory care (RISC study).

MAIN OUTCOME MEASURES

baseline fasting lipids, fasting and OGTT-induced insulin secretion and clearance (measured by glucose and C-peptide modeling), peripheral insulin sensitivity (by the euglycemic clamp). Lipids and OGTT were repeated in 980 subjects after 3.5years.

RESULTS

LDL-cholesterol did not show independent associations with fasting or stimulated insulin secretion or clearance. After accounting for potential confounders, HDL-cholesterol displayed negative and triglycerides positive independent associations with fasting and OGTT insulin secretion; neither with insulin clearance. Low HDL-cholesterol and high triglycerides were associated with an increase in glucose-dependent and a decrease in non-glucose-dependent insulin secretion. Over 3.5years both an HDL-cholesterol decline and a triglycerides rise were associated with an increase in fasting insulin secretion independent of changes in body weight or plasma glucose.

CONCLUSIONS

LDL-cholesterol does not seem to influence any major determinant of insulin bioavailability while low HDL-cholesterol and high triglycerides might contribute to sustain the abnormalities in insulin secretion that characterize the pre-diabetic state.

Elevated nocturnal NEFA are an early signal for hyperinsulinaemic compensation during diet-induced insulin resistance in dogs

AIMS/HYPOTHESIS

A normal consequence of increased energy intake and insulin resistance is compensatory hyperinsulinaemia through increased insulin secretion and/or reduced insulin clearance. Failure of compensatory mechanisms plays a central role in the pathogenesis of type 2 diabetes mellitus; consequently, it is critical to identify in vivo signal(s) involved in hyperinsulinaemic compensation. We have previously reported that high-fat feeding leads to an increase in nocturnal NEFA concentration. We therefore designed this study to test the hypothesis that elevated nocturnal NEFA are an early signal for hyperinsulinaemic compensation for insulin resistance.

METHODS

Blood sampling was conducted in male dogs to determine 24 h profiles of NEFA at baseline and during high-fat feeding with and without acute nocturnal NEFA suppression using a partial A1 adenosine receptor agonist.

RESULTS

High-fat feeding increased nocturnal NEFA and reduced insulin sensitivity, effects countered by an increase in acute insulin response to glucose (AIR(g)). Pharmacological NEFA inhibition after 8 weeks of high-fat feeding lowered NEFA to baseline levels and reduced AIR(g) with no effect on insulin sensitivity. A significant relationship emerged between nocturnal NEFA levels and AIR(g). This relationship indicates that the hyperinsulinaemic compensation induced in response to high-fat feeding was prevented when the nocturnal NEFA pattern was returned to baseline.

CONCLUSIONS/INTERPRETATION

Elevated nocturnal NEFA are an important signal for hyperinsulinaemic compensation during diet-induced insulin resistance.