Differential metabolic responses to tumor necrosis factor with increase in age

Reparative effects of interleukin-1 receptor antagonist in young and aged/co-morbid rodents after cerebral ischemia

Neuroprotective strategies for ischemic stroke have failed to translate from bench to bedside, possibly due to the lack of consideration of key clinical co-morbidities. Stroke and co-morbidities are associated with raised levels of the pro-inflammatory cytokine interleukin-1 (IL-1). Inhibition of IL-1 by the administration of interleukin-1 receptor antagonist (IL-1Ra) has shown to be neuroprotective after experimental cerebral ischemia. Stroke can also trigger a robust neuroreparative response following injury, yet many of these new born neurons fail to survive or integrate into pre-existing circuits. Thus, we explore here effects of IL-1Ra on post-stroke neurogenesis in young and aged/co-morbid rats. Aged lean, aged Corpulent (a model of atherosclerosis, obesity and insulin resistance) and young Wistar male rats were exposed to transient cerebral ischemia, received subcutaneous IL-1Ra 3 and 6h during reperfusion, and effects on stroke outcome and neurogenesis were analyzed. Our results show that administration of IL-1Ra improves stroke outcome in both young and aged/co-morbid rats. Furthermore, IL-1Ra not only increases stem cell proliferation, but also significantly enhances neuroblast migration and the number of newly born neurons after cerebral ischemia. Overall, our data demonstrate that systemic administration of IL-1Ra improves outcome and promotes neurogenesis after experimental stroke, further highlighting the therapeutic potential of this clinically approved drug.

Human aging is associated with altered TNF-alpha production during hyperglycemia and hyperinsulinemia

Changes in tumor necrosis factor-alpha (TNF-alpha) may provide a mechanism to explain impaired glucose metabolism with advancing age. Hyperglycemic clamps (180 min, 10 mM) were performed on seven older [67 +/- 2 yr; body mass index (BMI) 24.7 +/- 1.0 kg/m(2)] and seven younger (22 +/- 1 yr; BMI 21.8 +/- 1.3 kg/m(2)) healthy sedentary males with normal glucose tolerance. TNF-alpha production at basal and at the end of 180 min of hyperglycemia and hyperinsulinemia was measured ex vivo from lipopolysaccharide-stimulated (1 ng/ml) peripheral blood mononuclear cells. Plasma glucose, insulin, and C-peptide levels were similar in both groups at basal and during the last 30 min of the hyperglycemic clamp. Glucose infusion rates were lower (P < 0.004) in the older group compared with the young, indicating decreased insulin action among the older subjects. Basal TNF-alpha secretion was similar in older and younger subjects. TNF-alpha was suppressed (P < 0.02) in the younger group (230 +/- 46 vs. 126 +/- 49 pg/ml; basal vs. clamp) but not in the older group (153 +/- 37 vs. 182 +/- 42 pg/ml), with significant group differences in response (P < 0.05). A significant correlation was observed between the level of suppression in TNF-alpha production and insulin action (Kendall's rank, tau = 0.40, P < 0.05). Furthermore, the TNF-alpha response during the clamp was related to fat mass (r = 0.88, P < 0.001) and abdominal fat (r = 0.81, P < 0.003). In conclusion, these findings suggest a possible mechanism by which TNF-alpha may modulate glucose metabolism in younger people. Aging and modest increases in adiposity prevent the "normal" suppression of TNF-alpha production after a sustained postprandial-like hyperglycemic-hyperinsulinemic stimulus, which may contribute in part to the decline in insulin sensitivity in older men.

Challenge differentially affects cytokine production and metabolic status of growing and finishing swine

Growing (35 kg body weight) and finishing (85 kg body weight) swine challenged with endotoxin (Escherichia coli O55:B5) at a dose of either 2 or 20 microg/kg produced tumor necrosis factor (TNF)alpha in a dose-response relationship as measured by bioassay. Peak TNFalpha plasma levels were observed 1-2 hr post-challenge, returning to basal values 4 hr post-challenge. However, both an enzyme-linked immunosorbent assay specific for swine TNFalpha and total human TNFalpha demonstrated no dose-response relationship; peak plasma levels of immunoreactive TNFalpha were also observed 1-2 hr post-challenge. Maximal plasma interleukin-6 levels occurred 1-2 hr post-challenge and remained elevated through 8 hr post-challenge; there was no effect of lipopolysaccharide dose or metabolic status. Although the metabolic status of the animals also affected glucose levels, with growing animals exhibiting greater sensitivity compared with finishing animals, endotoxin-induced decreases in blood glucose levels were primarily dose-dependent. In contrast, changes in plasma urea nitrogen and free fatty acid (FFA) levels were strictly related to the metabolic status. Urea nitrogen levels were unchanged in growing swine, whereas they were increased in finishing swine and remained elevated 24 hr post-challenge. FFA levels in growing and finishing swine increased 3-6 hr post-challenge. FFA levels returned to basal values for finishing swine 24 hr post challenge, but in growing swine remained elevated 24 hr post-challenge. Plasma aspartate transaminase levels were increased through 24 hr post-challenge; animals given a dose of 20 microg/kg exhibited the greatest increase. Similarly, swine challenged with a dose of 20 microg/kg also exhibited the greatest increase in levels of conjugated bilirubin; there was no effect on unconjugated (free) bilirubin. These results demonstrate that endotoxin challenge of swine result in a pattern of changes that are dependent on both the dose of endotoxin used and the metabolic status of the animal examined.

Myocardial tumor necrosis factor-alpha secretion in hypertensive and heart failure-prone rats

Acute increases in blood pressure (BP) increase myocardial tumor necrosis factor (TNF)-alpha production, but it is not known whether chronic hypertensive stress elevates myocardial TNF-alpha production, possibly contributing to cardiac remodeling, decreased cardiac function, and faster progression to heart failure. BP, cardiac function, and size were evaluated in normotensive [Sprague-Dawley (SD)], spontaneously hypertensive (SHR), and spontaneously hypertensive heart failure-prone (SHHF) rats at 6, 12, 15, and 18 mo of age and in failing SHHF. Left ventricular tissues were evaluated for secretion of bioactive TNF-alpha and inhibition of TNF-alpha secretion by phosphodiesterase inhibitors. All ventricles secreted bioactive and immunoreactive TNF-alpha, but secretion decreased with age. SHR and SHHF rats secreted more TNF-alpha than SD rats at 6 mo of age, but only failing SHHF rats secreted significantly more TNF-alpha at 18 mo. Amrinone inhibited TNF-alpha secretion in all rats and was less potent but more efficacious than RO-201724 in all strains. TNF-alpha secretion correlated with BP and left ventricular mass in 6-mo-old rats, but this relationship disappeared with age. Results suggest that hypertension and/or cardiac remodeling is associated with elevated myocardial TNF-alpha, and, although hypertension, per se, did not maintain elevated cardiac TNF-alpha levels, SHHF rats increase TNF-alpha production during the end stages of failure.

Undernutrition in rheumatoid arthritis patients with disability

Clinical evaluation of nutritional status (NS) was performed in 75 rheumatoid arthritis patients. They were distributed according to functional class, radiological stage and other prognostic factors (rheumatoid factor, extraarticular disease, disease duration). Evaluation of the different anthropometrical measurements in this group of long-standing RA patients (average disease duration: 10 years) revealed a significant impairment of lean body mass (LBM), especially among those with greater disability (Functional Class III and IV). Patients in more severe radiological stages (Radiological Stage III and IV) or patients with extraarticular disease also presented a significant loss of LBM compared with a matched cohort of the general population and patients with a more benign-course disease. There was less impairment of the fat mass, according to our clinical evaluation. Serological parameters of undernutrition (albumin and transferrin) did not show significant differences among the groups of patients. Clinical evaluation of NS in RA patients is a useful procedure for recognising patients at high risk of related complications by means of their poor nutritional status.