Hyperleptinemia, adiposity, and risk of metabolic syndrome in older adults

Obesity: An Impact with Cardiovascular and Cerebrovascular Diseases

The authors sought to correlate the complex sequel of obesity with various parameters known to develop metabolic syndrome viz. insulin resistance, dyslipidemia, hypertension etc., as these anomalies are linked to vascular atherosclerosis and outbreak of cardiovascular and cerebrovascular diseases.  A comprehensive online survey using MEDLINE, Scopus, PubMed and Google Scholar was conducted for relevant journals from 1970 till present time (2023) with key search terms like: 'obesity', 'leptin', type-2 diabetes', 'atherosclerosis', 'cardiovascular and cerebrovascular diseases'. The findings of the reports were compared and correlated. The information was then collated for developing this review. Reports showed that in human obesity, hyper-leptinemia could induce hyperglycemia, which in turn templates hypercholesterolemia. Persisting hypercholesterolemia over a period of time may en-route atherosclerosis in blood vessels. Thus obesity has been considered as a template for originating hyperglycemia, hypercholesterolemia and outbreak of vascular atherogenesis or in other words, obesity in long run can trigger atherosclerosis and its related disorders e.g. heart attack and stroke. Literature survey shows that primarily, co-morbidities of human obesity start with leptin and insulin resistance and then multiplies with metabolic irregularities to an extreme that results in pathogenesis of heart attack and stroke. Atherosclerosis associated cardiovascular and cerebrovascular events are independent risks of obese subjects and particularly in the cases of persisting obesity.

Obstructive Sleep Apnoea and Lipid Metabolism: The Summary of Evidence and Future Perspectives in the Pathophysiology of OSA-Associated Dyslipidaemia

Obstructive sleep apnoea (OSA) is associated with cardiovascular and metabolic comorbidities, including hypertension, dyslipidaemia, insulin resistance and atherosclerosis. Strong evidence suggests that OSA is associated with an altered lipid profile including elevated levels of triglyceride-rich lipoproteins and decreased levels of high-density lipoprotein (HDL). Intermittent hypoxia; sleep fragmentation; and consequential surges in the sympathetic activity, enhanced oxidative stress and systemic inflammation are the postulated mechanisms leading to metabolic alterations in OSA. Although the exact mechanisms of OSA-associated dyslipidaemia have not been fully elucidated, three main points have been found to be impaired: activated lipolysis in the adipose tissue, decreased lipid clearance from the circulation and accelerated de novo lipid synthesis. This is further complicated by the oxidisation of atherogenic lipoproteins, adipose tissue dysfunction, hormonal changes, and the reduced function of HDL particles in OSA. In this comprehensive review, we summarise and critically evaluate the current evidence about the possible mechanisms involved in OSA-associated dyslipidaemia.

Contribution of obesity as an effect regulator to an association between serum leptin and incident metabolic syndrome

BACKGROUND

We investigated whether serum leptin can be a predictor for incident cases of MetS in a population-based study.

METHODS

This is a prospective cohort study of 1590 adults aged between 40 and 70 years, who did not have MetS in 2005-2008 (at baseline) and 2008-2011 (follow-up). The baseline serum leptin concentrations were measured by radioimmunoassay.

RESULTS

During an average of 2.8 years of follow-up, 113 men (17.1%) and 148 women (15.9%) developed MetS. In multivariable adjusted models, the odds ratio of incident MetS when comparing the lowest to the highest quartiles of leptin levels was 3.17 in men and 2.79 in women; nevertheless, the significance disappeared after adjusting for the body mass index (BMI). In subsidiary analyses by BMI, logistic regression analysis showed that subjects with the highest tertile of serum leptin level were 3.04 and 2.12 times more likely to have MetS than those with the lowest tertile in lean subjects (OR 3.04; 95% CI 1.44-6.41; p = .004 in men vs. OR 2.12; 95% CI 1.06-4.25; p = .036 in women, respectively).

CONCLUSIONS

Obesity is an effect regulator, which can predict an association between increased serum leptin level and the incidence of MetS in lean subjects.

Role of Leptin in Obstructive Sleep Apnea

Leptin is a peptide hormone produced mainly in white adipose tissue. It is known to regulate energy homeostasis, inflammation, metabolism, and sympathetic nerve activity. Increasing evidence suggests it has a role in ventilatory function and upper airway obstruction. Leptin levels correlate positively with measurements of adiposity and can potentially provide important insights into the pathophysiology of diseases associated with obesity. Obesity is a strong risk factor for obstructive sleep apnea, a disease characterized by periodic upper airway occlusion during sleep. The neuromuscular activity that maintains upper airway patency during sleep and the anatomy of upper airway are key factors involved in its pathogenesis. Experimental studies using animal models of a low leptin state such as leptin deficiency have shown that leptin regulates sleep architecture, upper airway patency, ventilatory function, and hypercapnic ventilatory response. However, findings from human studies do not consistently support the data from the animal models. The effect of leptin on the pathophysiology of obstructive sleep apnea is being investigated, but the results of studies have been confounded by leptin's diurnal variation and the short-term effects of feeding, adiposity, age, and sex. Improved study design and methods of assessing functional leptin levels, specifically their central versus peripheral effects, will improve understanding of the role of leptin in sleep apnea.

The Synergism in Hormonal and Cellular Changes in Male Mice on Long Term High Fat Exposure

OBJECTIVE

To determine the hormonal changes that occur as a result of the long-term intake of a very-high-fat diet (VHFD) that leads to simultaneous changes in the islets of Langerhans and adipocyte cell size.

METHODS

Male mice were fed with a normal chow diet (ND, n = 15) and a VHFD (n = 30) for 2, 12, and 24 weeks. Body weight, food intake, caloric intake (fat [saturated and unsaturated], protein, and carbohydrate), hormone levels (leptin and insulin), and islet of Langerhans/adipocyte size were quantitatively recorded.

RESULTS

In VHFD-fed animals, body weight showed a significant percent increase within the first 12 weeks and then plateaued with time. VHFD-fed animals consumed significantly less food than ND at all time periods, indicating that it was the quality of food and not the quantity that caused this increase in body weight. Male mice on VHFD showed a significant increase in leptin and insulin levels, along with accompanying growth in islet and adipocyte size within the first 12 weeks, which plateaued as the mice aged. The increases in the islet and adipocyte size in VHFD-fed animals were similar to the analogous increases in hormonal levels (2 vs. 12 vs. 24 weeks). These results, therefore, suggest that in diet-induced obesity changes, shifts in hormonal levels works hand-in-hand with metabolic adjustments at the cellular level to combat the effect of fat.

CONCLUSION

Thus, mechanisms like hormonal resistance, changes in adiposity, islet size, and caloric intake with prolonged exposure to high fat are probably defensive mechanisms employed to protect against diabetes. In order to understand these complicated and nuanced effects of high fat and to comprehend the underlying mechanism associated with it, it is important to focus on long-term studies that emphasize the synergy between cellular and hormonal changes, in addition to an analysis of individual components.

Ratios of leptin to insulin and adiponectin to endothelin are sex-dependently associated with extent of coronary atherosclerosis

OBJECTIVE

Noninvasive diagnostics of early stages of coronary artery disease and discrimination between various extents of vascular lesions in patients is an important clinical problem especially considering wide spread use of cholesterol lowering drugs that affect lipid and lipoprotein profiling. The main goal of our study was to evaluate applicability of new combinations of noninvasive biomarkers such as leptin to insulin and adiponectin to endothelin ratios, for detection of early stages of coronary atherosclerosis versus later stages of the disease.

PATIENTS AND METHODS

A number of previously validated serum biomarkers were tested in a group of 500 patients with coronary artery disease and examined for their association with severity of coronary lesion according to Gensini score determined by coronary angiography.

RESULTS

Lowest extent of coronary lesions was associated with significant increase in apoA-I levels and with significantly increased ratios of adiponectin to endothelin and leptin to insulin. In male but not in female patients, adiponectin to endothelin ratio below 7.0 was associated with Gensini score representing early to high coronary lesions (p = 0.02). In female but not in male patients, leptin to insulin ratio below 3.5 was associated with Gensini score representing early to high coronary lesions (p = 0.013).

CONCLUSION

Leptin to insulin and adiponectin to endothelin ratios are novel derived biomarkers useful for noninvasive diagnostics of initial stages of coronary lesions in patients with coronary artery disease.

The Association of Serum Leptin with Mortality in Older Adults

Objective

Elevated levels of serum leptin are associated with increased adiposity and production of pro-inflammatory cytokines. Both cytokines and body adiposity have been shown to predict cardiovascular events and mortality. The primary objective of the present study is to explore the associations between serum leptin and all-cause mortality and mortality from cardiovascular disease (CVD) over a span of 10 years, controlling for body adiposity and proinflammatory cytokines.

Methods

The Health, Aging and Body Composition (Health ABC) study is a prospective cohort of 3,075 older adults aged 70 to 79 years. This analysis includes 2,919 men and women with complete serum leptin and vital status data. Data on all-cause mortality and incident cardiovascular events (including Coronary Heart Disease and Congestive Heart Failure) were collected over 10 years of follow-up (mean 8.4 years).

Results

Women with leptin in quartile 2 and 3 were at lower risk of all-cause mortality, and those with leptin in quartile 2 were at lower risk of mortality from CVD as compared to women with lowest leptin values when adjusted for age, race, site, years of education, alcohol use, smoking, and physical activity. When these associations were additionally adjusted for body fat, C-reactive protein and pro-inflammatory cytokines, women with leptin values in quartile 3 were at lower risk of all-cause mortality and women with leptin in quartile 2 and 3 were at lower risk of mortality from CVD than women with lowest leptin values. These associations were not significant among men after adjusting for body fat and cytokines.

Conclusions

The present study suggests that moderately elevated concentrations of serum leptin are independently associated with lower risk of all-cause mortality and CVD-related mortality among older women. Among men, serum leptin is not associated with reduced risk of all-cause and CVD mortality after controlling for body fat and cytokines.

Metabolic syndrome triggered by high-fructose diet favors choroidal neovascularization and impairs retinal light sensitivity in the rat

Diabetic retinopathy and age-related macular degeneration are the leading causes of blindness in Western populations. Although it is a matter of controversy, large-scale population-based studies have reported increased prevalence of age-related macular degeneration in patients with diabetes or diabetic retinopathy. We hypothesized that metabolic syndrome, one of the major risk factors for type 2 diabetes, would represent a favorable environment for the development of choroidal neovascularization, the main complication of age-related macular degeneration. The fructose-fed rat was used as a model for metabolic syndrome in which choroidal neovascularization was induced by laser photocoagulation. Male Brown Norway rats were fed for 1, 3, and 6 months with a standard equilibrated chow diet or a 60%-rich fructose diet (n = 24 per time point). The animals expectedly developed significant body adiposity (+17%), liver steatosis at 3 and 6 months, hyperleptinemia at 1 and 3 months (two-fold increase) and hyperinsulinemia at 3 and 6 months (up to two-fold increase), but remained normoglycemic and normolipemic. The fructose-fed animals exhibited partial loss of rod sensitivity to light stimulus and reduced amplitude of oscillatory potentials at 6 months. Fructose-fed rats developed significantly more choroidal neovascularization at 14 and 21 days post-laser photocoagulation after 1 and 3 months of diet compared to animals fed the control diet. These results were consistent with infiltration/activation of phagocytic cells and up-regulation of pro-angiogenic gene expression such as Vegf and Leptin in the retina. Our data therefore suggested that metabolic syndrome would exacerbate the development of choroidal neovascularization in our experimental model.