Philipp Eller

Potential role of regulatory T cells in reversing obesity-linked insulin resistance and diabetic nephropathy

OBJECTIVE To assess the potential role of FoxP3-expressing regulatory T cells (Tregs) in reversing obesity-linked insulin resistance and diabetic nephropathy in rodent models and humans. RESEARCH DESIGN AND METHODS To characterize the role of Tregs in insulin resistance, human visceral adipose tissue was first evaluated for Treg infiltration and second, the db/db mouse model was evaluated. RESULTS Obese patients with insulin resistance displayed significantly decreased natural Tregs but an increase in adaptive Tregs in their visceral adipose tissue as compared with lean control subjects. To further evaluate the pathogenic role of Tregs in insulin resistance, the db/db mouse model was used. Treg depletion using an anti-CD25 monoclonal antibody enhanced insulin resistance as shown by increased fasting blood glucose levels as well as an impaired insulin sensitivity. Moreover, Treg-depleted db/db mice developed increased signs of diabetic nephropathy, such as albuminuria and glomerular hyperfiltration. This was paralleled by a proinflammatory milieu in both murine visceral adipose tissue and the kidney. Conversely, adoptive transfer of CD4+FoxP3+ Tregs significantly improved insulin sensitivity and diabetic nephropathy. Accordingly, there was increased mRNA expression of FoxP3 as well as less abundant proinflammatory CD8+CD69+ T cells in visceral adipose tissue and kidneys of Treg-treated animals. CONCLUSIONS Data suggest a potential therapeutic value of Tregs to improve insulin resistance and end organ damage in type 2 diabetes by limiting the proinflammatory milieu.

Serum Amyloid A in Uremic HDL Promotes Inflammation

Uremia impairs the atheroprotective properties of HDL, but the mechanisms underlying why this occurs are unknown. Here, we observed that HDL isolated from healthy individuals inhibited the production of inflammatory cytokines by peripheral monocytes stimulated with a Toll-like receptor 2 agonist. In contrast, HDL isolated from the majority of patients with ESRD did not show this anti-inflammatory property; many HDL samples even promoted the production of inflammatory cytokines. To investigate this difference, we used shotgun proteomics to identify 49 HDL-associated proteins in a uremia-specific pattern. Proteins enriched in HDL from patients with ESRD (ESRD-HDL) included surfactant protein B (SP-B), apolipoprotein C-II, serum amyloid A (SAA), and α-1-microglobulin/bikunin precursor. In addition, we detected some ESRD-enriched proteins in earlier stages of CKD. We did not detect a difference in oxidation status between HDL isolated from uremic and healthy patients. Regarding function of these uremia-specific proteins, only SAA mimicked ESRD-HDL by promoting inflammatory cytokine production. Furthermore, SAA levels in ESRD-HDL inversely correlated with its anti-inflammatory potency. In conclusion, HDL has anti-inflammatory activities that are defective in uremic patients as a result of specific changes in its molecular composition. These data suggest a potential link between the high levels of inflammation and cardiovascular mortality in uremia.

Cholesteryl Ester Transfer Protein and Mortality in Patients Undergoing Coronary Angiography The Ludwigshafen Risk and Cardiovascular Health Study

Background— The role of cholesteryl ester transfer protein (CETP) in the development of atherosclerosis is still open to debate. In the Investigation of Lipid Level Management to Understand its Impact in Atherosclerotic Events (ILLUMINATE) trial, inhibition of CETP in patients with high cardiovascular risk was associated with increased high-density lipoprotein levels but increased risk of cardiovascular morbidity and mortality. In this report, we present a prospective observational study of patients referred to coronary angiography in which CETP was examined in relation to morbidity and mortality. Methods and Results— CETP concentration was determined in 3256 participants of the Ludwigshafen Risk and Cardiovascular Health (LURIC) study who were referred to coronary angiography at baseline between 1997 and 2000. Median follow-up time was 7.75 years. Primary and secondary end points were cardiovascular and all-cause mortality, respectively. CETP levels were higher in women and lower in smokers, in diabetic patients, and in patients with unstable coronary artery disease, respectively. In addition, CETP levels were correlated negatively with high-sensitivity C-reactive protein and interleukin-6. After adjustment for age, sex, medication, coronary artery disease status, cardiovascular risk factors, and diabetes mellitus, the hazard ratio for death in the lowest CETP quartile was 1.33 (1.07 to 1.65; P=0.011) compared with patients in the highest CETP quartile. Corresponding hazard ratios for death in the second and third CETP quartiles were 1.17 (0.92 to 1.48; P=0.19) and 1.10 (0.86 to 1.39; P=0.46), respectively. Conclusions— We interpret our data to suggest that low endogenous CETP plasma levels per se are associated with increased cardiovascular and all-cause mortality, challenging the rationale of pharmacological CETP inhibition.

The Liver-Selective Thyromimetic T-0681 Influences Reverse Cholesterol Transport and Atherosclerosis Development in Mice

Background Liver-selective thyromimetics have been reported to efficiently reduce plasma cholesterol through the hepatic induction of both, the low-density lipoprotein receptor (LDLr) and the high-density lipoprotein (HDL) receptor; the scavenger receptor class B type I (SR-BI). Here, we investigated the effect of the thyromimetic T-0681 on reverse cholesterol transport (RCT) and atherosclerosis, and studied the underlying mechanisms using different mouse models, including mice lacking LDLr, SR-BI, and apoE, as well as CETP transgenic mice. Methodology/Principal Findings T-0681 treatment promoted bile acid production and biliary sterol secretion consistently in the majority of the studied mouse models, which was associated with a marked reduction of plasma cholesterol. Using an assay of macrophage RCT in mice, we found T-0681 to significantly increase fecal excretion of macrophage-derived neutral and acidic sterols. No positive effect on RCT was found in CETP transgenic mice, most likely due to the observed decrease in plasma CETP mass. Studies in SR-BI KO and LDLr KO mice suggested hepatic LDLr to be necessary for the action of T-0681 on lipid metabolism, as the compound did not have any influence on plasma cholesterol levels in mice lacking this receptor. Finally, prolonged treatment with T-0681 reduced the development of atherosclerosis by 60% in apoE KOs on Western type diet. In contrast, at an earlier time-point T-0681 slightly increased small fatty streak lesions, in part due to an impaired macrophage cholesterol efflux capacity, when compared to controls. Conclusions/Significance The present results show that liver-selective thyromimetics can promote RCT and that such compounds may protect from atherosclerosis partly through induction of bile acid metabolism and biliary sterol secretion. On-going clinical trials will show whether selective thyromimetics do prevent atherosclerosis also in humans.

Cholesteryl ester transfer protein in patients with coronary heart disease

Eur J Clin Invest 2010; 40 (7): 616–622

Atorvastatin attenuates murine anti-glomerular basement membrane glomerulonephritis

Statins mediate many of their protective effects by lowering lipids as well as by modulating inflammation. Here, we studied their potential immunomodulatory role in renal inflammation using an autoimmune mouse model of anti-glomerular basement membrane glomerulonephritis. Oral treatment with Atorvastatin dramatically reduced albuminuria and histological changes in the kidneys as compared to vehicle-treated control animals. There was a significant decrease in the Th1 and Th17 response in the regional lymph nodes draining the kidneys. This systemic effect was accompanied by decreased infiltration of the kidneys with inflammatory CD4(+) T and Th17 cells, macrophages, and neutrophils in statin-treated mice. Regulatory T cells were not altered in their number, FoxP3 expression, or suppressive capacity, but their interleukin-10 production was significantly increased by statin treatment. Hence, Atorvastatin systemically and locally decreased the Th1 and Th17 response, thereby protecting the mice against anti-glomerular basement membrane glomerulonephritis. Whether statins can be used to treat human autoimmune renal diseases will require more direct studies.

Hepatic lipase polymorphism and increased risk of peripheral arterial disease

Background.  Hepatic lipase plays a key role in the metabolism of pro‐atherogenic and anti‐atherogenic lipoproteins affecting their plasma level as well as their physico‐chemical properties. We hypothesized single nucleotide polymorphisms in the promoter region of the hepatic lipase gene to be associated with an increased risk for peripheral arterial disease (PAD).

Aspirin regulates expression and function of scavenger receptor-BI in macrophages: studies in primary human macrophages and in mice

Scavenger receptor class B type I (SR‐BI) has been shown to be expressed in human atherosclerotic plaque macrophages, where it is believed to reduce atherosclerosis by promoting cholesterol efflux. In this study we investigated the influence of aspirin and other NSAIDs on SR‐BI expression and function in cultured human macrophages as well as in different mouse strains. Incubation of human macrophages with 0.5 mmol/l aspirin resulted in increased SR‐BI protein expression and increased uptake of HDL‐associated [3H]cholesteryl oleate without changes of SR‐BI mRNA levels. In contrast, using 5 mmol/l of aspirin, SR‐BI expression and function were significantly decreased. Sodium salicylate exerted similar effects on SR‐BI expression, whereas no effects were observed using known COX1/2 inhibitors ibuprofen and naproxen, respectively. In in vivo studies low‐dose aspirin treatment (6 mg/kg·day) induced SR‐BI expression in wild‐type and PPAR‐α knockout mice, respectively, whereas the opposite effect was observed upon high‐dose aspirin treatment (60 mg/kg·day) in these animals. We could show that COX‐independent effects of aspirin were able to enhance expression of SR‐BI in macrophages in a post‐transcriptional, PPAR‐α independent way, suggesting a novel pharmacologic effect of aspirin.—Tancevski, I., Wehinger, A., Schgoer, W., Eller, P., Cuzzocrea, S., Foeger, B., Patsch, J. R., Ritsch, A. Aspirin regulates expression and function of scavenger receptor‐BI in macrophages: studies in primary human macrophages and in mice. FASEB J. 20, 1328–1335 (2006)

Increased plasma levels of LDL cholesterol in rabbits after adenoviral overexpression of human scavenger receptor class B type I

Scavenger receptor class B type I (SR-BI), a CD36 family member, plays a key role in high-density lipoprotein (HDL) metabolism, reverse cholesterol transport, and whole body cholesterol homeostasis, and is shown to be involved in the development of atherosclerosis in mice. In this report, we describe the effects of the adenoviral overexpression of human SR-BI (hSR-BI) in New Zealand White (NZW) rabbits, a wild-type animal model that expresses cholesteryl ester transfer protein (CETP) in plasma, displays a manlike lipoprotein profile, and is susceptible to atherosclerosis. A total of 1×1012 adenoviral particles containing either hSR-BI or lacZ complementary deoxyribonucleic acid (control) were infused into the ear vein of NZW rabbits. Transgene expression was ascertained by TaqMan Real Time polymerase chain reaction measurements. Rabbits infected with Ad/hSR-BI (adenoviral plasmids containing hSR-BI) showed a faster clearance of administered [3H]HDL cholesterol and significantly decreased apolipoprotein (apo) A-I levels when compared to control rabbits, respectively. Interestingly, we found markedly increased levels of low-density lipoprotein (LDL) cholesterol exclusively in SR-BI-overexpressing rabbits. These changes were not accompanied by alterations in LDL receptor expression but by increased levels of CE transfer in these animals. By lowering HDL cholesterol and increasing plasma apoB-containing lipoprotein levels, the overexpression of SR-BI leads to a lipoprotein pattern, which is believed to enhance the development of atherosclerosis. The role of SR-BI in lipoprotein metabolism and atherogenesis in rabbits—a CETP-expressing animal model displaying a manlike lipoprotein profile—may therefore be different from the one found in rodents.

Sobetirome: A Selective Thyromimetic for the Treatment of Dyslipidemia

Atherosclerosis and its clinical sequelae still represent the primary cause of death in Western societies. During the past 25 years, a novel drug class to treat dyslipidemia, a main risk factor for coronary artery disease, emerged: liver- and thyroid hormone receptor isoform β-selective analogs. The present review will discuss the recent patents applied for sobetirome (GC-1), which set the course for the establishment of a novel approach to lower plasma cholesterol and triglycerides. We will focus on the major mechanisms conferring sobetirome lipid-lowering properties, including the induction of hepatic LDL receptor, the promotion of the so-called reverse cholesterol transport, and finally the induction of bile acid production and biliary sterol secretion. In summary, thyromimetics such as sobetirome may represent a useful treatment for combined hyperlipidemia, which is associated with a major cardiovascular risk.