Determination of body fat distribution by dual-energy X-ray absorptiometry and attenuation of visceral fat vasoconstriction by enalapril

A Long-Term Pilot Study on Sex and Spinal Cord Injury Shows Sexual Dimorphism in Functional Recovery and Cardio-Metabolic Responses

More than a quarter of a million individuals in the US live with spinal cord injury (SCI). SCI disrupts neural circuitry to vital organs in the body. Despite severe incidences of long-term peripheral complications from SCI, the cardio-metabolic consequences and divergences in sex-related responses are not well described. We examined the effects of SCI on functional recovery, cardiac structure and function, body composition, and glucose metabolism on adult female and male Sprague Dawley (SD) rats. SCI was induced at T10 via contusion. Measured outcomes include behavioral assessment, body weight, dual-energy X-ray absorptiometry (DEXA) for body composition, echocardiography for cardiac structure and function, intraperitoneal glucose tolerance test (IPGTT) for glucose metabolism, insulin tolerance test (ITT), and histology of cardiac structure at the endpoint. There was a decrease in body fat percentage in both sexes, with SCI females disproportionately affected in percent body fat change. Left ventricular internal diameter during systole (LVIDs) was decreased in SCI females more than in SCI males. No significant differences in glucose metabolism were observed up to 20 weeks post-injury (PI). These data show significant cardio-metabolic differences as a consequence of SCI and, furthermore, that sex is an underlying factor in these differences.

Capsaicin as an anti-obesity drug

Laboratory studies support a role of capsaicin as an anti-obesity agent. Intestinal mucosal afferent nerves appear to play a role in controlling adipose tissue distribution between visceral and subcutaneous sites. Activation of the transient receptor potential vanilloid-1 channels by capsaicin prevents adipogenesis. A neurogenic mechanism modulates the regulation of fat metabolism by transient receptor potential vanilloid-1-sensitive sensory nerves. A neural pathway enables the selective activation of the central network that regulates brown adipose tissue sympathetic nerve activity in response to a specific stimulation of gastrointestinal transient receptor potential channels. Dietary capsaicin reduces metabolic dysregulation in obese/diabetic mice by enhancing expression of adiponectin and its receptor. The effects of capsaicin in adipose tissue and liver are related to its dual action on peroxisome proliferator-activated receptor alpha and transient receptor potential vanilloid-1 expression/activation. Local desensitization of the abdominal capsaicin-sensitive fibers attenuates the hypometabolic adaptation to food deprivation. Truncal vagotomy leads to significant reductions in both diet-induced weight gain and visceral abdominal fat deposition. Vagal de-afferentation leads to a more modest, but clinically and statistically significant, reduction in visceral abdominal fat. Thermogenesis and lipid metabolism-related proteins are altered upon capsaicin treatment in white adipose tissue. Capsaicin induces apoptosis and inhibits adipogenesis in preadipocytes and adipocytes. Epidemiologic data show that consumption of foods containing capsaicin is associated with a lower prevalence of obesity. Clinical evidence supports a role of capsaicin as an anti-obesity agent. Both oral and gastrointestinal exposure to capsaicin increase satiety and reduce energy and fat intake; the stronger reduction with oral exposure suggests a sensory effect of capsaicin. Bioactive components containing capsaicin may support weight maintenance after a hypocaloric diet. Capsaicin consumption 1 h before low intensity exercise is a valuable supplement for the treatment of individuals with hyperlipidemia and/or obesity because it improves lipolysis. Capsinoid ingestion increases energy expenditure through the activation of brown adipose tissue in humans. Capsinoid ingestion is associated with an increase in fat oxidation that is nearly significant; and two common genetic variants may be predictors of response. Further clinical research to develop convenient approaches for obese individuals to take advantage of this common dietary ingredient to prevent the onset or curtail the progression of obesity will be instructive and clinically relevant.

Abdominal fat analyzed by DEXA scan reflects visceral body fat and improves the phenotype description and the assessment of metabolic risk in mice

Clinical studies have demonstrated a strong relationship between visceral fat content and metabolic diseases, such as type 2 diabetes and liver steatosis. Obese mouse models are an excellent tool to study metabolic diseases; however, there are limited methods for the noninvasive measurement of fat distribution in mice. Although micromagnetic resonance imaging and microcomputed tomography are the "gold standards" in the measurement of fat distribution, more economical and accessible methods are required. Dual energy X-ray absorptiometry (DEXA) is an effective method in characterizing fat content; however, it cannot discriminate between visceral and subcutaneous fat depots. We demonstrate that an evaluation of abdominal fat content measured by DEXA through the selection of one localized abdominal area strongly correlates with visceral fat content in C57BL/6J mice. We found that DEXA is able to measure fat pad volume ex vivo with high accuracy; however, the measurement of visceral fat in vivo shows an overestimation caused by subcutaneous tissue interference. The overestimation is almost constant for a wide range of values, and thus it is possible to correct the data for a more accurate estimation of visceral fat content. We demonstrate the utility of this technique in characterizing phenotypes of several obese mouse models (ob/ob, db/db, MC4R-KO, and DIO) and evaluating the effect of treatments on visceral fat content in longitudinal studies. Additionally, we also establish abdominal obesity as a potential biomarker for metabolic abnormalities (liver fat accumulation, insulin resistance/diabetes) in mice, similar to that described in humans.

Visceral fat mass determination in rodent: validation of dual-energy X-ray absorptiometry and anthropometric techniques in fat and lean rats

Background

Because abdominal obesity is predisposed to various metabolic disorders, it is of major importance to assess and track the changes with time of this specific fat mass. The main issue for clinicians or researchers is to use techniques for assessing abdominal fat deposition and its accumulation or changes over time, without sacrificing of experimental subjects. In the rat, techniques to investigate in-vivo visceral fat mass are lacking. The purpose of the study was to validate indirect Dual-energy X-ray Absorptiometry technique and abdominal circumference measurement as tools to predict visceral adipose tissue in rats.

Forty-three Wistar male rats from different body weight, fat mass and ages were included in the study. Visceral fat mass was assessed by weighing the total perirenal and peri-epididymal adipose tissues after dissection. Statistical methods were used to discriminate the best region of interest allowing the in-vivo measure of Central Fat Mass by DXA. Abdominal circumference was measured at the same time as the DXA scan.

Results

A region of interest including Central Fat Mass from the whole body DXA scan (extending from L2 to L5 vertebrae), correlated strongly with ex-vivo Fat Mass (r = 0.94, p < 0.001). Abdominal circumference correlated significantly with ex-vivo Fat Mass (r = 0.82, p < 0.001) and Central Fat Mass (0.90, p < 0.001) in the whole group of rats. When dividing the whole group into lean and fat rats, correlations remained significant between Central Fat Mass and ex-vivo Fat Mass but disappeared for the lean group between abdominal circumference and ex-vivo Fat Mass.

Conclusions

This study validates the Central Fat Mass determined by DXA as a non-sacrificial technique to assess visceral fat for in-vivo investigations in rats. The abdominal circumference measure appears useful in studying overweight or obese rats. These two techniques could be convenient tools in follow-up and longitudinal studies.

Interaction between age and obesity on cardiomyocyte contractile function: role of leptin and stress signaling

Objectives

This study was designed to evaluate the interaction between aging and obesity on cardiac contractile and intracellular Ca²⁺ properties.

Methods

Cardiomyocytes from young (4-mo) and aging (12- and 18-mo) male lean and the leptin deficient ob/ob obese mice were treated with leptin (0.5, 1.0 and 50 nM) for 4 hrs in vitro. High fat diet (45% calorie from fat) and the leptin receptor mutant db/db obesity models at young and older age were used for comparison. Cardiomyocyte contractile and intracellular Ca²⁺ properties were evaluated including peak shortening (PS), maximal velocity of shortening/relengthening (± dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR₉₀), intracellular Ca²⁺ levels and decay. O₂⁻ levels were measured by dihydroethidium fluorescence.

Results

Our results revealed reduced survival in ob/ob mice. Aging and obesity reduced PS, ± dL/dt, intracellular Ca²⁺ rise, prolonged TR₉₀ and intracellular Ca²⁺ decay, enhanced O₂⁻ production and p^47phox expression without an additive effect of the two, with the exception of intracellular Ca²⁺ rise. Western blot analysis exhibited reduced Ob-R expression and STAT-3 phosphorylation in both young and aging ob/ob mice, which was restored by leptin. Aging and obesity reduced phosphorylation of Akt, eNOS and p38 while promoting pJNK and pIκB. Low levels of leptin reconciled contractile, intracellular Ca²⁺ and cell signaling defects as well as O₂⁻ production and p^47phox upregulation in young but not aging ob/ob mice. High level of leptin (50 nM) compromised contractile and intracellular Ca²⁺ response as well as O₂⁻ production and stress signaling in all groups. High fat diet-induced and db/db obesity displayed somewhat comparable aging-induced mechanical but not leptin response.

Conclusions

Taken together, our data suggest that aging and obesity compromise cardiac contractile function possibly via phosphorylation of Akt, eNOS and stress signaling-associated O₂⁻ release.