Effect of leptin and insulin resistance on properties of human monocytes in lean and obese healthy participants

Regulation of cardiovascular health and disease by visceral adipose tissue-derived metabolic hormones

Visceral adipose tissue (VAT) is a metabolic organ known to regulate fat mass, and glucose and nutrient homeostasis. VAT is an active endocrine gland that synthesizes and secretes numerous bioactive mediators called 'adipocytokines/adipokines' into systemic circulation. These adipocytokines act on organs of metabolic importance like the liver and skeletal muscle. Multiple preclinical and in vitro studies showed strong evidence of the roles of adipocytokines in the regulation of metabolic disorders like diabetes, obesity and insulin resistance. Adipocytokines, such as adiponectin and omentin, are anti-inflammatory and have been shown to prevent atherogenesis by increasing nitric oxide (NO) production by the endothelium, suppressing endothelium-derived inflammation and decreasing foam cell formation. By inhibiting differentiation of vascular smooth muscle cells (VSMC) into osteoblasts, adiponectin and omentin prevent vascular calcification. On the other hand, adipocytokines like leptin and resistin induce inflammation and endothelial dysfunction that leads to vasoconstriction. By promoting VSMC migration and proliferation, extracellular matrix degradation and inflammatory polarization of macrophages, leptin and resistin increase the risk of atherosclerotic plaque vulnerability and rupture. Additionally, the plasma concentrations of these adipocytokines alter in ageing, rendering older humans vulnerable to cardiovascular disease. The disturbances in the normal physiological concentrations of these adipocytokines secreted by VAT under pathological conditions impede the normal functions of various organs and affect cardiovascular health. These adipokines could be used for both diagnostic and therapeutic purposes in cardiovascular disease.

The regulatory role of insulin in energy metabolism and leukocyte functions

Insulin is the hormone responsible for maintaining glucose homeostasis in the body, in addition to participating in lipid metabolism, protein synthesis, and the inhibition of gluconeogenesis. These functions are well characterized in the classic organ target cells that are responsible for general energy regulation: the liver, skeletal muscle, and adipose tissue. However, these actions are not restricted to these tissues because insulin has been shown to affect most cells in the body. This review describes the role of insulin in leukocyte signaling pathways, metabolism and functions, and how insulin resistance could affect this signaling and deteriorate leukocyte metabolism and function, in addition to showing evidence that suggests leukocytes may substantially contribute to the development of systemic insulin resistance.

Predictors of Subclinical Inflammatory Obesity: Plasma Levels of Leptin, Very Low-Density Lipoprotein Cholesterol and CD14 Expression of CD16+ Monocytes

OBJECTIVE

Predictors of subclinical inflammatory obesity (SIO) can be important tools for early therapeutic interventions in obesity-related comorbidities. Waist circumference (WC) and BMI have different SIO sensitivity. We aimed to i) identify SIO predictors and ii) investigate whether CD16+ monocytes are associated with BMI- (generally) or WC-defined (centrally) obesity.

METHODS

Anthropometric and metabolic/endocrine (namely catecholamines, adrenaline and noradrenaline) parameters were evaluated, and CD16+ monocytes were studied by flow cytometry in the peripheral blood from 63 blood donors, and compared and correlated to each other. Multiple linear regression analysis was performed to identify variables that best predict SIO.

RESULTS

CD16+ monocyte counts were similar in BMI and WC groups. CD16+ monocytes from centrally obese (CO) showed a more inflammatory pattern, as compared to non-CO subjects. WC was sensitive to lipidemia and, in CO subjects, lipidemia was associated with a more inflammatory phenotype of CD16+ monocytes. These differences were not noticed between BMI groups. Adrenaline was correlated with CD16+ monocyte expansion with a lower inflammatory pattern. Leptin, very low-density lipoprotein cholesterol (VLDL-C), and CD14 expression of CD16+ monocytes were found to be CO predictors.

CONCLUSIONS

WC-, but not BMI-defined obesity, was associated with a more inflammatory pattern of CD16+ monocytes, without monocyte expansion, suggesting that a monocyte maturation process rather than an independent arise of CD16+ monocytes occurs in CO. Thus, in a population with low cardiovascular risk, leptin, VLDL-C, and CD14 expression of CD16+ monocytes predict CO, constituting a putative tool for screening of SIO.

Serum levels of appetite-regulating hormones and pro-inflammatory cytokines are ameliorated by a CLA diet and endurance exercise in rats fed a high-fat diet

PURPOSE

This study examined whether conjugated linoleic acid (CLA) supplementation and endurance exercise affect appetite-regulating hormones and pro-inflammatory cytokines in rats.

METHODS

Seven-week-old male Sprague-Dawley rats were divided randomly into the high-fat diet sedentary group (HS, n=8), the 1.0% CLA supplemented high-fat diet sedentary group (CS, n=8), and the 1.0% CLA supplemented high-fat diet exercise group (CE, n=8). Rats in the CE group swam 60 min/day, 5 days/week for 4 weeks.

RESULTS

Leptin and insulin levels in the CS and CE groups were significantly lower than those in the HS group (p<0.001), whereas leptin (p<0.01) and insulin (p<0.05) levels decreased significantly in the CE compared to those in the CS group. Interleukin (IL)-1β (p<0.001) and IL-6 (p<0.01) levels in the CS and CE groups decreased significantly compared to those in the HS group. Leptin (IL-1β: r=0.835, p<0.001), IL-6 (r=0.607, p<0.05), insulin (IL-1β: r=0.797, p<0.01), and IL-6 (r=0.827, p<0.01) levels were positively related with pro-inflammatory cytokine levels.

CONCLUSION

Endurance exercise may play an important role during CLA supplementation of rats on a high-fat diet.

Effects of exercise on brain functions in diabetic animal models

Human life span has dramatically increased over several decades, and the quality of life has been considered to be equally important. However, diabetes mellitus (DM) characterized by problems related to insulin secretion and recognition has become a serious health problem in recent years that threatens human health by causing decline in brain functions and finally leading to neurodegenerative diseases. Exercise is recognized as an effective therapy for DM without medication administration. Exercise studies using experimental animals are a suitable option to overcome this drawback, and animal studies have improved continuously according to the needs of the experimenters. Since brain health is the most significant factor in human life, it is very important to assess brain functions according to the different exercise conditions using experimental animal models. Generally, there are two types of DM; insulin-dependent type 1 DM and an insulin-independent type 2 DM (T2DM); however, the author will mostly discuss brain functions in T2DM animal models in this review. Additionally, many physiopathologic alterations are caused in the brain by DM such as increased adiposity, inflammation, hormonal dysregulation, uncontrolled hyperphagia, insulin and leptin resistance, and dysregulation of neurotransmitters and declined neurogenesis in the hippocampus and we describe how exercise corrects these alterations in animal models. The results of changes in the brain environment differ according to voluntary, involuntary running exercises and resistance exercise, and gender in the animal studies. These factors have been mentioned in this review, and this review will be a good reference for studying how exercise can be used with therapy for treating DM.

Ghrelin-leptin network influences serum chitinase 3-like protein 1 (YKL-40) levels in obese prepubertal children

OBJECTIVE

This study aimed to investigate any possible interactions between hormonal regulators of weight gain and markers of subclinical inflammation in childhood obesity. Forty-one obese prepubertal children and 41 age- and gender-matched lean controls were included. Children were classified as obese or non-obese according to international age- and gender-specific body mass index (BMI) cutoff points defined by the International Obesity Task Force to define childhood obesity. Anthropometric measurements, serum insulin, chitinase 3-like protein (YKL-40), ghrelin and leptin levels as well as plasma glucose in the fasting state were determined.

RESULTS

Obese children as compared with controls had higher YKL-40 (50.7±15.2 vs 41.0±10.5 ng/ml, p=0.003), higher leptin (33.8±16.0 vs 9.7±7.5 ng/ml, p<0.001) and lower ghrelin serum levels (871.4±368.0 vs 1417.6±387.3 pg/ml, p<0.001). The obese children with ghrelin levels above median (43.8±10.2 ng/ml) as compared to those with ghrelin below median (57.2±16.6 ng/ml) presented lower serum YKL-40 levels (p=0.009), indicating more severe inflammation with lower levels of ghrelin. By contrast, although the obese children with leptin levels above median (49.7±16.3 ng/ml) presented lower serum YKL-40 levels as compared to those with leptin levels below median (51.6±14.6 ng/ml), this difference did not reach the level of statistical significance (p=0.726). Moreover, serum YKL-40 levels were significantly correlated with ghrelin (r=-0.359, p=0.014) but not with leptin levels (r=0.169, p=0.261). A significant negative correlation between ghrelin and leptin levels was also found (r=-0.276, p=0.041). These findings remained unchanged for obese, when analyses were done separately, whereas the significance of correlations was lost for non-obese subjects.

CONCLUSIONS

Ghrelin-leptin network had an impact on serum YKL-40 levels in obese prepubertal children; upregulation of YKL-40 secretion seems to be a consequence of reduced ghrelin rather than elevated leptin concentrations.

Insulin resistance: a significant risk factor of endometrial cancer

OBJECTIVE

To review the role played by insulin resistance in the development of endometrial cancer.

METHODS

Relevant manuscripts and studies were searched on Medline using the terms endometrial cancer, insulin resistance, obesity, adipokine, C-peptide, leptin, adiponectin, plasminogen activator inhibitor-1, insulin, PI3K/Akt, Ras/MAPK and metformin alone or in combination.

RESULTS

Epidemiological studies have shown that insulin resistance is an important potential risk factor of endometrial cancer, and several research studies have been undertaken to determine the mechanism underlying its link to this malignant disease. Risk factors of insulin resistance, such as the inflammatory mediators, adipokines adiponectin, leptin and plasminogen activator inhibitor-1 and excessive androgen are also risk factors of endometrial cancer. High levels of insulin induced by insulin resistance have been found to exert direct and indirect effects that contribute to the development of endometrial cancer. Insulin directly promotes cell proliferation and survival through the PI3K/Akt and Ras/MAPK pathways. Moreover, the network among insulin, estrogen and insulin-like growth factor-1 also contributes to the development of endometrial cancer. Indirectly, insulin leads to changes in sex hormone levels, including increases in the levels of estrogen. Additionally, a small number of studies suggested that metformin, an insulin-sensitizing agent, has therapeutic potential for endometrial cancer.

CONCLUSIONS

This evidence suggests that insulin resistance plays a central role in endometrial cancer development. Understanding the relationship between insulin resistance and endometrial cancer may supply new ideas to fight this malignancy. Furthermore, combating insulin resistance may be a useful preventive and therapeutic strategy for endometrial cancer.

Endurance exercise is a leptin signaling mimetic in hypothalamus of Wistar rats

BACKGROUND

Endurance exercise is known to promote a substantial effect on the energy balance in rats and humans. However, little is known about the exact mechanisms for the appetite-suppressive effects of endurance exercise. We hypothesized that endurance training might activate signaling cascades in the hypothalamus known to be involved in leptin signaling.

METHODS

16 male Wistar rats were randomly assigned to two groups: sedentary (n = 8) and exercise groups (n = 8). Animals in the exercise group started treadmill running at 30 m/min, 0% grade, for 1 min/bout. Running time was gradually increased by 2 min/bout every day. The training plan was one bout per day during initial two weeks, and two bouts per day during 3rd-9th week. At the end of nine-week experiment, blood was analyzed for low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), total cholesterol (TC), free fatty acid (FFA), interleukin (IL)-6, and leptin in both groups. Activations of janus kinase 2-signaling transducer and activator of transcription 3 (JAK2-STAT3), protein kinase B (Akt), extracellular regulated kninase (ERKs), and suppressor of cytokine signaling 3 (SOCS3) in hypothalamus were measured in the end of nine weeks of exercise protocol.

RESULTS

Nine-week endurance exercise induced lower concentrations of LDL-C, TG, TC, FFA, and leptin in rats (P < 0.05 or P < 0.01). Nine-week endurance exercise significantly increased the circulating IL-6 concentration compared with sedentary group (239.6 ± 37.2 pg/ml vs. 151.8 ± 31.5 pg/ml, P < 0.01). Exercise rats showed significant increases in JAK2, STAT3, Akt, ERKs, and SOCS3 phosphorylations compared with sedentary rats (P < 0.01).

CONCLUSION

The data suggest that endurance exercise is a leptin signaling mimetic in hypothalamus of Wistar rats.

Effect of volatile oil from Cinnamomi Cortex on blood glucose and lipid metabolism in insulin-resistant mice

AIM: To investigate the effect of volatile oil from Cinnamomi Cortex (VOCC) on blood glucose and lipid metabolism in insulin-resistant mice and to investigate the possible mechanisms involved.

METHODS: Insulin resistance was induced by feeding a high-fat diet. After insulin-resistant mice were treated orally with VOCC, oral glucose tolerance test and insulin tolerance test were performed. The body weight, blood glucose, serum insulin, total cholesterol, triglyceride, leptin, resistin, and adiponectin were determined using biochemical methods.

RESULTS: VOCC administration decreased body weight gain (30.3 ± 3.6 vs 34.6 ± 3.1, P < 0.05), blood glucose (7.6 ± 2.2 vs 9.2 ± 1.3, P < 0.05), serum insulin (1.3 ± 0.1 vs 1.7 ± 0.2, P < 0.05), total cholesterol (70.1 ± 10.9 vs 65.4 ± 19.5, P < 0.05), triglyceride (93.2 ± 13.8 vs 102.3 ± 21.5, P < 0.05), leptin, and resistin levels. Treatment with VOCC also decreased insulin resistance by improving oral glucose tolerance and insulin tolerance.

CONCLUSION: VOCC improved blood glucose and lipid metabolism by reducing serum leptin and resistin in insulin-resistant mice, thereby enhancing insulin sensitivity.

Involvement of signaling molecules on na/h exchanger-1 activity in human monocytes

Background:

Sodium/hydrogen exchanger-1 (NHE-1) contributes to maintaining intracellular pH (pHi). We assessed the effect of glucose, insulin, leptin and adrenaline on NHE-1 activity in human monocytes in vitro. These cells play a role in atherogenesis and disturbances in the hormones evaluated are associated with obesity and diabetes.

Methods and Results:

Monocytes were isolated from 16 healthy obese and 10 lean healthy subjects. NHE-1 activity was estimated by measuring pHi with a fluorescent dye. pHi was assessed pre- and post-incubation with glucose, insulin, leptin and adrenaline. Experiments were repeated after adding a NHE-1 inhibitor (cariporide) or an inhibitor of protein kinase C (PKC), nitric oxide synthase (NOS), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, phosphoinositide 3-kinases (PI3K) or actin polymerization. Within the whole study population, glucose enhanced NHE-1 activity by a processes involving PKC, NOS, PI3K and actin polymerization (p = 0.0006 to 0.01). Insulin-mediated activation of NHE-1 (p = <0.0001 to 0.02) required the classical isoforms of PKC, NOS, NADPH oxidase and PI3K. Leptin increased NHE-1 activity (p = 0.0004 to 0.04) through the involvement of PKC and actin polymerization. Adrenaline activated NHE-1 (p = <0.0001 to 0.01) by a process involving the classical isoforms of PKC, NOS and actin polymerization. There were also some differences in responses when lean and obese subjects were compared. Incubation with cariporide attenuated the observed increase in NHE-1 activity.

Conclusions:

Selective inhibition of NHE-1 in monocytes could become a target for drug action in atherosclerotic vascular disease.