Patterns of plasma leptin and insulin concentrations in hospitalized patients after the initiation of total parenteral nutrition

The Impact of Glucose-Based or Lipid-Based Total Parenteral Nutrition on the Free Fatty Acids Profile in Critically Ill Patients

Introduction: Our study aim was to assess how the macronutrient intake during total parenteral nutrition (TPN) modulates plasma total free fatty acids (FFAs) levels and individual fatty acids in critically ill patients. Method: Adult patients aged 18–80, admitted to the intensive care unit (ICU), who were indicated for TPN, with an expected duration of more than three days, were included in the study. Isoenergetic and isonitrogenous TPN solutions were given with a major non-protein energy source, which was glucose (group G) or glucose and lipid emulsions (Smof lipid; group L). Blood samples were collected on days 0, 1, 3, 6, 9, 14, and 28. Results: A significant decrease (p < 0.001) in total FFAs occurred in both groups with a bigger decrease in group G (p < 0.001) from day 0 (0.41 ± 0.19 mmol∙L⁻¹) to day 28 (0.10 ± 0.07 mmol∙L⁻¹). Increased palmitooleic acid and decreased linoleic and docosahexaenoic acids, with a trend of increased mead acid to arachidonic acid ratio, on day 28 were observed in group G in comparison with group L. Group G had an insignificant increase in leptin with no differences in the concentrations of vitamin E, triacylglycerides, and plasminogen activator inhibitor-1. Conclusion: Decreased plasma FFA in critically ill patients who receive TPN may result from increased insulin sensitivity with a better effect in group G, owing to higher insulin and glucose dosing and no lipid emulsions. It is advisable to include a lipid emulsion at the latest from three weeks of TPN to prevent essential fatty acid deficiency.

Association between adipokines and critical illness outcomes

BACKGROUND

Adipose tissue is an endocrine organ that plays a critical role in immunity and metabolism by virtue of a large number of hormones and cytokines, collectively termed adipokines. Dysregulation of adipokines has been linked to the pathogenesis of multiple diseases, but some questions have arisen concerning the value of adipokines in critical illness setting. The objective of this review was to evaluate the associations between blood adipokines and critical illness outcomes.

METHODS

PubMed, CINAHL, Scopus, and the Cochrane Library databases were searched from inception through July 2016 without language restriction. Studies reporting the associations of adipokines, leptin, adiponectin, resistin, and/or visfatin with critical illness outcomes mortality, organ dysfunction, and/or inflammation were included.

RESULTS

A total of 38 articles were selected according to the inclusion/exclusion criteria of the study. Significant alterations of circulating adipokines have been reported in critically ill patients, some of which were indicative of patient outcomes. The associations of leptin and adiponectin with critical illness outcomes were not conclusive in that blood levels of both adipokines did not always correlate with the illness severity scores or risks of organ failure and mortality. By contrast, studies consistently reported striking increase of blood resistin and visfatin, independently of the critical illness etiology. More interestingly, increased levels of these adipokines were systematically associated with severe inflammation, and high incidence of organ failure and mortality.

CONCLUSIONS

There is strong evidence to indicate that increased levels of blood resistin and visfatin are associated with poor outcomes of critically ill patients, including higher inflammation, and greater risk of organ dysfunction and mortality.

LEVEL OF EVIDENCE

Systematic review, level III.

Insulin receptor-insulin interaction kinetics using multiplex surface plasmon resonance

Type 2 diabetes affects millions of people worldwide, and measuring the kinetics of insulin receptor-insulin interactions is critical to improving our understanding of this disease. In this paper, we describe, for the first time, a rapid, real-time, multiplex surface plasmon resonance (SPR) assay for studying the interaction between insulin and the insulin receptor ectodomain, isoform A (eIR-A). We used a scaffold approach in which anti-insulin receptor monoclonal antibody 83-7 (Abcam, Cambridge, UK) was first immobilized on the SPR sensorchip by amine coupling, followed by eIR-A capture. The multiplex SPR system (ProteOn XPR36™, Bio-Rad Laboratories, Hercules, CA) enabled measurement of replicate interactions with a single, parallel set of analyte injections, whereas repeated regeneration of the scaffold between measurements caused variable loss of antibody activity. Interactions between recombinant human insulin followed a two-site binding pattern, consistent with the literature, with a high-affinity site (dissociation constant K(D1)  = 38.1 ± 0.9 nM) and a low-affinity site (K(D2)  = 166.3 ± 7.3 nM). The predominantly monomeric insulin analogue Lispro had corresponding dissociation constants K(D1)  = 73.2 ± 1.8 nM and K(D2)  = 148.9 ± 6.1 nM, but the fit to kinetic data was improved when we included a conformational change factor in which the high-affinity site was converted to the low-affinity site. The new SPR assay enables insulin-eIR-A interactions to be followed in real time and could potentially be extended to study the effects of humoral factors on the interaction, without the need for insulin labeling.

Endocrine, metabolic, and morphologic alterations of adipose tissue during critical illness

OBJECTIVE

Observational studies report lower mortality in obese than in lean critically ill patients, an association referred to as the "obesity paradox." This may suggest a possible protective role for adipose tissue during severe illness.

DATA SOURCES

Relevant publications were identified based on searches in PubMed and on secondary searches of their bibliographies.

DATA SYNTHESIS

The endocrine functions of adipose tissue might play a role in the adaptation to critical illness. In the acute phase of illness, the anti-inflammatory adiponectin is reduced, whereas proinflammatory cytokine expression in adipose tissue is up-regulated. In the prolonged phase of critical illness, both adiponectin and anti-inflammatory cytokine production are increasing. Studies on the proinflammatory adipokine leptin during critical illness are inconsistent, possibly due to confounders such as gender, body mass index, and feeding. Morphologically, adipose tissue of critically ill patients reveals an increased number of newly differentiated, smaller adipocytes. Accentuated macrophage accumulation showing a phenotypic switch to M2-type suggests an adaptive response to the microenvironment of severe illness. Functionally, adipose tissue of critically ill patients develops an increased ability to store glucose and triglycerides.

CONCLUSIONS

Endocrine, metabolic, and morphologic properties of adipose tissue change during critical illness. These alterations may suggest a possible adaptive, protective role in optimizing chances of survival. More research is needed to understand the exact role of adipose tissue in lean vs. obese critically ill patients, in order to understand how illness-associated alterations contribute to the obesity paradox.

Insulin-stimulated increase in serum leptin levels precedes and correlates with weight gain during insulin therapy in type 2 diabetes

CONTEXT

Infusion of insulin acutely stimulates leptin production and chronic insulin treatment is associated with elevated serum leptin levels and body weight in subjects with type 2 diabetes.

OBJECTIVE

The objective of the study was to investigate the relationship between insulin administration, leptin levels, and weight gain in subjects with type 2 diabetes.

DESIGN

This was a post hoc analysis of two randomized, controlled trials.

SETTING

The study was conducted at an outpatient clinic.

SUBJECTS

Subjects included 35 (study 1) and 32 (study 2) poorly controlled oral hypoglycemic agent (OHA)-treated type 2 diabetic subjects.

INTERVENTION

Study 1: subjects were investigated during a hyperinsulinemic, euglycemic glucose clamp and 12 months after being randomly allocated to start insulin or continue on OHAs. Study 2: 1 yr treatment with either OHAs and lifestyle intervention or insulin with or without concomitant lifestyle intervention.

MAIN OUTCOME MEASURE

Changes in serum leptin levels during clamp and during 1 yr of treatment in relationship to changes in body weight.

RESULTS

Study 1: during acute insulin infusion leptin levels increased by 10% (P < 0.001). During 1 yr of insulin therapy, mean body weight increased by 6%, whereas the fasting leptin levels increased by 108% (both P < 0.001). The weight gain observed at 1 yr correlated with the increase in leptin levels observed during the clamp (r = 0.62, P = 0.003). Study 2: mean body weight increased by 4% (P < 0.01), whereas leptin levels increased by 56% (P < 0.001) during 1 yr of insulin treatment and the increase in leptin preceded the increase in body weight.

CONCLUSIONS

Significant correlations were observed between insulin's effect on serum leptin levels and the increase in weight that accompanied insulin therapy.

Acute effects of hyperglycemia and hyperinsulinemia on hepatic oxidative stress and the systemic inflammatory response in rats

OBJECTIVES

Intensive blood glucose control to a target value of 80-110 mg/dL has been shown to reduce morbidity and mortality in surgical intensive care unit patients. This was attributed predominantly to correction of hyperglycemia, based on multivariate regression analysis. However, the effects of glucose and insulin have not been independently evaluated. This study investigated the development of hepatic oxidative processes and systemic inflammatory response in rats with different levels of induced hyperglycemia and hyperinsulinemia. The effects of a modest increase in blood glucose following glucose infusion at a level adequate to meet energy requirements, hyperinsulinemia induced by a hyperinsulinemic euglycemic clamp with administered glucose in similar amounts, and marked hyperglycemia and hyperinsulinemia secondary to glucose infusion on hepatic oxidative stress and systemic inflammatory response in vivo were examined.

DESIGN

Controlled laboratory study.

SETTING

Medical school laboratory.

SUBJECTS

Specific pathogen-free male Sprague-Dawley rats.

INTERVENTIONS

Blood glucose was monitored over 3 hrs. At the end of study, the serum concentrations of insulin, tumor necrosis factor-alpha, interleukin-1, and alpha1 acid glycoprotein were determined. Malondialdehyde and total glutathione content were measured in the liver.

MEASUREMENTS AND MAIN RESULTS

Glucose infusion adequate to provide energy requirements resulted in a modest increase in blood glucose (143+/-8 mg/dL) and hyperinsulinemia (45 microU/mL) and did not induce measurable hepatic oxidative stress or systemic inflammation. A hyperinsulinemic euglycemic clamp (insulin 112+/-9 microU/mL) resulted in evidence of increased oxidative processes in the liver but no change in hepatic antioxidant capacity or evidence of systemic inflammation. When hyperglycemia (approximately 350 mg/dL) and hyperinsulinemia (167+/-9 microU/mL) were induced by excess glucose infusion, rats manifested hepatic oxidative stress, antioxidant depletion, and a mild systemic inflammatory response.

CONCLUSIONS

Hyperglycemia is a major cause of the systemic inflammatory response. Maintaining normal blood glucose, by avoiding overfeeding and providing insulin therapy when necessary, appears key to minimizing oxidative stress and systemic inflammation when intravenous nutrition is provided.

Leptin and insulin response to long-term total parenteral nutrition depends on body fat mass

BACKGROUND & AIMS

Circulating leptin and insulin concentrations are physiologically representing energy homeostasis. However, the artificial situation of long-term total parenteral nutrition (TPN) and its effects on serum leptin and insulin is not fully understood.

METHODS

We studied 42 gastroenterological patients who received TPN for 19+/-11 days. Serum leptin and insulin levels as well as body composition assessed by bioelectrical impedance analysis were evaluated on days 0, 7 and 14. Insulin sensitivity was estimated by calculating the QUICKI.

RESULTS

Before the start of TPN, leptin correlated positively with female gender (P<0.03), BMI (P<0.02), fat mass (P<0.02), insulin levels (P<0.001) and QUICKI (P<0.001). Within the first week of TPN, an increase of leptin levels was found only in patients with a body fat mass of >30% (P<0.02). As these were predominantly women, their leptin levels increased likewise (P<0.003). In regression analysis, fat mass (P<0.001), female gender (P<0.04), insulin levels (P<0.03), and i.v. glucose supply rates (P<0.05) were independently associated to leptin levels.

CONCLUSIONS

TPN-especially glucose-induces a neurohumoral response as shown here for leptin and insulin that is mainly depending on the fat mass. Better understanding of this regulatory mechanism during artificial nutrition could offer a new approach to improve its therapeutic effects.

Insulin resistance and hyperglycemia in critical illness: role of insulin in glycemic control

Alterations in glucose metabolism, including hyperglycemia associated with insulin resistance, occur in critical illness. Acutely, such alterations result from normal, adaptive activation of endocrine responses, including increased release of catecholamines, cortisol, and glucagon and a reduced glucose uptake capacity. In prolonged critical illness, neuroendocrine changes lead to more extensive metabolic changes that may be associated with development of complications and poor prognosis. Until recently, hyperglycemia was not routinely controlled in intensive care units, except among patients with known diabetes mellitus. Studies have demonstrated that glycemic management in postmyocardial infarction in patients with diabetes is an effective practice. Recent investigation has extended this to demonstrate reduced morbidity and mortality in a surgical critically ill population with and without diabetes mellitus in later phases of critical illness. Although the mechanisms for improved patient outcomes need to be established, this novel approach to management of hyperglycemia in critical illness is a new and important concept for those working in critical care. This article reviews alterations in glucose metabolism which occur in critically ill patients and discusses potential mechanisms and mediators (e.g., hormones, cytokines) that may play a key role in hyperglycemia and insulin resistance during acute and prolonged phases of severe illness. The article addresses the application of insulin protocols and exogenous regulation of glucose concentration in critical illness based on a review of recent intervention studies.