Adipose stress-sensing kinases: linking obesity to malfunction.

Obesity has been proposed to inflict a variety of stresses on adipose tissue, including inflammatory, metabolic, oxidative and endoplasmic reticulum stress. Through the activation of 'stress-sensing pathways', metabolic and endocrine alterations are produced, which probably contribute to the co-morbidities associated with obesity. Here, we review the evidence supporting the development of various obesity-related stresses and the activation of several stress-sensing pathways, specifically in adipocytes and/or adipose tissue, which manifest metabolic and endocrine dysfunction frequently in obesity. As the central role of adipose tissue in regulating whole-body metabolism is elucidated, understanding adipose tissue stress-sensing pathways might provide potential new therapeutic targets to attenuate obesity-related morbidity.     

Indinavir uncovers different contributions of GLUT4 and GLUT1 towards glucose uptake in muscle and fat cells and tissues

AIMS/HYPOTHESIS: Insulin-dependent glucose influx in skeletal muscle and adipocytes is believed to rely largely on GLUT4, but this has not been confirmed directly. We assessed the relative functional contribution of GLUT4 in experimental models of skeletal muscle and adipocytes using the HIV-1 protease inhibitor indinavir. METHODS: Indinavir (up to 100 micro mol/l) was added to the glucose transport solution after insulin stimulation of wild-type L6 muscle cells, L6 cells over-expressing either GLUT4myc or GLUT1myc, 3T3-L1 adipocytes, isolated mouse brown or white adipocytes, and isolated mouse muscle preparations. RESULTS: 100 micro mol/l indinavir inhibited 80% of both basal and insulin-stimulated 2-deoxyglucose uptake in L6GLUT4myc myotubes and myoblasts, but only 25% in L6GLUT1myc cells. Cell-surface density of glucose transporters was not affected. In isolated soleus and extensor digitorum longus muscles, primary white and brown adipocytes, insulin-stimulated glucose uptake was inhibited 70 to 80% by indinavir. The effect of indinavir on glucose uptake was variable in 3T3-L1 adipocytes, averaging 45% and 67% inhibition of basal and maximally insulin-stimulated glucose uptake, respectively. In this cell, fractional inhibition of glucose uptake by indinavir correlated positively with the fold-stimulation of glucose uptake by insulin, and was higher with sub-maximal insulin concentrations. The latter finding coincided with an increase only in GLUT4, but not GLUT1, in plasma membrane lawns. CONCLUSION/INTERPRETATION: Indinavir is a useful tool to assess different functional contributions of GLUT4 to glucose uptake in common models of skeletal muscle and adipocytes.     

Agranulocytosis associated with parvovirus B19 infection in otherwise healthy patients

In the course of 6 years, 23 otherwise healthy patients with acute febrile illness and leukopenia were diagnosed as having acute parvovirus B19 infection. Five of these patients had agranulocytosis associated with acute parvovirus B19 infection and one had chronic agranulocytosis due to persistent parvovirus B19 infection. The diagnosis was made after positive anti-parvovirus B19 IgM antibodies were found in all of the patients and viral DNA was detected by PCR in four patients. Neutropenia and agranulocytosis appear to be much more frequently associated with parvovirus B19 infection than previously reported.     

IRS1 degradation and increased serine phosphorylation cannot predict the degree of metabolic insulin resistance induced by oxidative stress

AIM/HYPOTHESIS: Oxidative stress was shown to selectively induce impaired metabolic response to insulin, raising the possible involvement of alterations in Insulin-Receptor-Substrate (IRS) proteins. This study was conducted to assess whether oxidative stress induced IRS protein degradation and enhanced serine phosphorylation, and to assess their functional importance. METHODS: 3T3-L1 adipocytes and rat hepatoma cells (FAO) were exposed to micro-molar H(2)O(2) by adding glucose oxidase to the culture medium, and IRS1 content, its serine phosphorylation and downstream metabolic insulin effects were measured. RESULTS: Cells exposed to oxidative stress exhibited decreased IRS1 (but not IRS2) content, and increased serine phosphorylation of both proteins. Total protein ubiquitination was increased in oxidized cells, but not in cells exposed to prolonged insulin treatment. Yet, lactacystin and MG132, two unrelated proteasome inhibitors, prevented IRS1 degradation induced by prolonged insulin but not by oxidative stress. The PI 3-kinase inhibitor LY294002 and the mTOR inhibitor rapamycin, but not the MEK1 inhibitor PD98059, could prevent IRS1 changes in oxidized cells. Rapamycin, which protected against IRS1 degradation and serine phosphorylation was not associated with improved response to acute insulin stimulation. Moreover, the antioxidant alpha lipoic acid, while protecting against oxidative stress-induced insulin resistance in 3T3-L1 adipocytes, could not prevent IRS1 degradation and serine phosphorylation. CONCLUSION/INTERPRETATION: Oxidative stress induces serine phosphorylation of IRS1 and increases its degradation by a proteasome-independent pathway; yet, these changes do not correlate with the induction of impaired metabolic response to insulin.     

Inverse correlation between coronary and retinal blood flows in patients with normal coronary arteries and slow coronary blood flow

Background

The “Slow Coronary Flow” (SCF) phenomenon in the presence of angiographically normal coronaries is attributed to microvascular and endothelial dysfunction. The microcirculation can be non-invasively assessed by measuring retinal blood flow velocity.The aim of the present study was to evaluate the efficacy of the “Retinal Functional Imager” (RFI) device as a noninvasive method of diagnosing patients with slow coronary flow.

Methods

Coronary blood flow velocity assessed by corrected TIMI Frame Count and retinal arterioles blood flow assessed by RFI were measured in 28 consecutive patients with normal coronary arteries. The patients were divided into 2 groups: a slow coronary flow (SCF) and a normal coronary flow (NCF) groups.

Results

Inverse correlation was found between retinal and coronary blood flows so that higher retinal arterial flow velocity was observed in the SCF group (3.8 ± 1.1 mm/s vs. 2.9 ± 0.61 mm/s, respectively, p = 0.022). RFI provided 73% sensitivity and 77% specificity for diagnosing SCF using ROC analysis. Additionally, patients with SCF had higher values of serum LDL cholesterol (104.7 ± 18.93 mg/dl vs. 81.55 ± 14.62 mg/dl in NCF, p = 0.005), Glucose (96.9 ± 23.0 mg/dl vs. 83.55 ± 9.7 mg/dl in NCF, p = 0.024), and lower percentage of statin consumption (40.0% vs. 76.9% in NCF, p = 0.049).

Conclusions

Slow coronary blood flow can be non-invasively diagnosed with Retinal Functional Imager. Patients with normal coronary arteries and slow coronary blood flow have high retinal arteriolar blood flow. Early non-invasive diagnosis of SCF might help detect individuals who are at higher risk to develop coronary atherosclerosis, and to provide them with early preventive measures.     

Echo Decorrelation Imaging of Rabbit Liver and VX2 Tumor during In Vivo Ultrasound Ablation

In open surgical procedures, image-ablate ultrasound arrays performed thermal ablation and imaging on rabbit liver lobes with implanted VX2 tumor. Treatments included unfocused (bulk ultrasound ablation, N = 10) and focused (high-intensity focused ultrasound ablation, N = 13) exposure conditions. Echo decorrelation and integrated backscatter images were formed from pulse-echo data recorded during rest periods after each therapy pulse. Echo decorrelation images were corrected for artifacts using decorrelation measured prior to ablation. Ablation prediction performance was assessed using receiver operating characteristic curves. Results revealed significantly increased echo decorrelation and integrated backscatter in both ablated liver and ablated tumor relative to unablated tissue, with larger differences observed in liver than in tumor. For receiver operating characteristic curves computed from all ablation exposures, both echo decorrelation and integrated backscatter predicted liver and tumor ablation with statistically significant success, and echo decorrelation was significantly better as a predictor of liver ablation. These results indicate echo decorrelation imaging is a successful predictor of local thermal ablation in both normal liver and tumor tissue, with potential for real-time therapy monitoring.