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Biomedical subjects

David C Wheeler

Publications and source records attributed to David C Wheeler.

16 recordsLinked to original sources
PubMed2006

Mechanisms of dysregulation of low-density lipoprotein receptor expression in vascular smooth muscle cells by inflammatory cytokines.

OBJECTIVE: Although inflammation is a recognized feature of atherosclerosis, the impact of inflammation on cellular cholesterol homeostasis is unclear. This study focuses on the molecular mechanisms by which inflammatory cytokines disrupt low-density lipoprotein (LDL) receptor regulation. METHODS AND RESULTS: IL-1beta enhanced transformation of vascular smooth muscle cells into foam cells by increasing uptake of unmodified LDL via LDL receptors and by enhancing cholesterol esterification as demonstrated by Oil Red O staining and direct assay of intracellular cholesterol concentrations. In the absence of IL-1beta, a high concentration of LDL decreased LDL receptor promoter activity, mRNA synthesis and protein expression. However, IL-1beta enhanced LDL receptor expression, overriding the suppression usually induced by a high concentration of LDL and inappropriately increasing LDL uptake. Exposure to IL-1beta also caused overexpression of the sterol regulatory element binding protein (SREBP) cleavage-activating protein (SCAP), and enhanced its translocation from the endoplasmic reticulum to the Golgi, where it is known to cleave SREBP, thereby enhancing LDL receptor gene expression. CONCLUSIONS: These observations demonstrate that IL-1beta disrupts cholesterol-mediated LDL receptor feedback regulation, permitting intracellular accumulation of unmodified LDL and causing foam cell formation. The implication of these findings is that inflammatory cytokines may contribute to intracellular LDL accumulation without previous modification of the lipoprotein.

Cells, Cultured↗
PubMed2006

The second United Kingdom Heart and Renal Protection (UK-HARP-II) Study: a randomized controlled study of the biochemical safety and efficacy of adding ezetimibe to simvastatin as initial therapy among patients with CKD.

BACKGROUND: Evaluating the effects of decreasing low-density lipoprotein (LDL) cholesterol levels requires large randomized trials. In preparation for such a trial, we assessed the biochemical efficacy, safety, and tolerability of adding ezetimibe, 10 mg/d, to simvastatin, 20 mg/d, as initial therapy for such patients. METHODS: Two hundred three patients (152 predialysis patients with creatinine levels > or = 1.7 mg/dL [> or = 150 micromol/L], 18 patients on peritoneal dialysis therapy, and 33 patients on hemodialysis therapy) were randomly assigned to the administration of simvastatin, 20 mg/d, plus ezetimibe, 10 mg/d; or simvastatin, 20 mg, plus placebo ezetimibe daily. RESULTS: After 6 months, allocation to simvastatin monotherapy was associated with a 31-mg/dL (0.8-mmol/L) decrease in nonfasting LDL cholesterol levels compared with baseline. Allocation to simvastatin plus ezetimibe produced an additional 18-mg/dL (0.47-mmol/L) decrease in LDL cholesterol level, representing an incremental 21% reduction over that achieved with simvastatin monotherapy (P < 0.0001). There were no statistically significant effects of the addition of ezetimibe to simvastatin on triglyceride or high-density lipoprotein cholesterol levels. Ezetimibe was not associated with an excess risk of abnormal liver function test results or of elevated creatine kinase levels and did not impair absorption of fat-soluble vitamins. There were no serious adverse events caused by study treatment. CONCLUSION: This 6-month study shows that the addition of ezetimibe to simvastatin, 20 mg/d, as initial therapy for patients with chronic kidney disease was well tolerated and produced an additional 21% decrease in LDL cholesterol levels. The clinical efficacy and safety of combination therapy in this population are now being assessed in a large randomized trial.

Anticholesteremic Agents↗
PubMed2005

First United Kingdom Heart and Renal Protection (UK-HARP-I) study: biochemical efficacy and safety of simvastatin and safety of low-dose aspirin in chronic kidney disease.

BACKGROUND: Patients with chronic kidney disease are at increased risk for cardiovascular disease, but the efficacy and safety of simvastatin and aspirin are unknown in this patient group. METHODS: Patients were randomly assigned in a 2 x 2 factorial design to the administration of: (1) 20 mg of simvastatin daily versus matching placebo, and (2) 100 mg of modified-release aspirin daily versus matching placebo. RESULTS: Overall, 448 patients with chronic kidney disease were randomly assigned (242 predialysis patients with a creatinine level > or = 1.7 mg/dL [> or =150 micromol/L], 73 patients on dialysis therapy, and 133 patients with a functioning transplant). Compliance with study treatments was 80% at 12 months. Allocation to treatment with 100 mg of aspirin daily was not associated with an excess of major bleeds (aspirin, 4 of 225 patients [2%] versus placebo, 6 of 223 patients [3%]; P = not significant [NS]), although there was a 3-fold excess of minor bleeds (34 of 225 [15%] versus 12 of 223 patients [5%]; P = 0.001). Among those with predialysis renal failure or a functioning transplant at baseline, aspirin did not increase the number of patients who progressed to dialysis therapy (7 of 187 [4%] versus 6 of 188 patients [3%]; P = NS) or experienced a greater than 20% increase in creatinine level (63 of 187 patients [34%] versus 56 of 188 patients [30%]; P = NS). After 12 months of follow-up, allocation to 20 mg of simvastatin daily reduced nonfasting total cholesterol levels by 18% (simvastatin, 163 mg/dL [4.22 mmol/L] versus placebo, 196 mg/dL [5.08 mmol/L]; P < 0.0001), directly measured low-density lipoprotein cholesterol levels by 24% (89 mg/dL [2.31 mmol/L] versus 114 mg/dL [2.96 mmol/L]; P < 0.0001), and triglyceride levels by 13% (166 mg/dL [1.87 mmol/L] versus 186 mg/dL [2.10 mmol/L]; P < 0.01), but there was no significant effect on high-density lipoprotein cholesterol levels (2% increase; P = NS). Allocation to simvastatin therapy was not associated with excess risk for abnormal liver function test results or elevated creatine kinase levels. CONCLUSION: During a 1-year treatment period, simvastatin, 20 mg/d, produced a sustained reduction of approximately one quarter in low-density lipoprotein cholesterol levels, with no evidence of toxicity, and aspirin, 100 mg/d, did not substantially increase the risk for a major bleeding episode. Much larger trials are now needed to assess whether these treatments can prevent vascular events.

Adult↗
PubMed2005

EPA and DHA reduce LPS-induced inflammation responses in HK-2 cells: evidence for a PPAR-gamma-dependent mechanism.

BACKGROUND: Recent studies have shown that fish oil, containing omega-3 polyunsaturated fatty acids (omega-3 PUFAs) eicosapentaenoic acid (EPA) (C20:5 omega 3), and docosahexaenoic acid (DHA) (C22:6 omega 3) retard the progression of renal disease, especially in IgA nephropathy (IgAN). Despite increasing knowledge of the beneficial effects of fish oils, little is known about the mechanisms of action of omega-3 PUFAs. It has been reported that activation of peroxisome proliferator-activated receptors (PPARs) inhibits production of proinflammatory cytokines. Both EPA and DHA have been shown to activate PPARs. The aim of this study was to examine if omega-3 PUFAs have anti-inflammatory effects via activation of PPARs in human renal tubular cells. METHODS: An immortalized human proximal tubular cell line [human kidney-2 (HK-2) cells] was used in all experiments. Conditioned media was collected from omega-3 PUFAs- treated cells and subjected to enzyme-linked immunosorbent assay (ELISA). Total cellular RNA was isolated from the above cells for real-time quantitative polymerase chain reaction (PCR). Nuclear Extracts were prepared from the HK-2 cells for transcription factor activation assay. RESULTS: Both EPA and DHA at 10 micromol/L and 100 micromol/L concentrations effectively decreased lipopolysaccharide (LPS)-induced nuclear factor-kappaB (NF-kappaB) activation and monocyte chemoattractant protein-1 (MCP-1) expression. EPA and DHA also increased both PPAR-gamma mRNA and protein activity (two- to threefold) in HK-2 cells. A dose of 100 micromol/L bisphenol A diglycidyl ether (BADGE) abolished the PPAR-gamma activation induced by both EPA and DHA and removed the inhibitory effect of EPA and DHA on LPS-induced NF-kappaB activation in HK-2 cells. Overexpression of PPAR-gamma further inhibited NF-kappaB activation compared to the control cells in the presence of EPA and DHA. CONCLUSION: Our data demonstrate that both EPA and DHA down-regulate LPS-induced activation of NF-kappaB via a PPAR-gamma-dependent pathway in HK-2 cells. These results suggest that PPAR-gamma activation by EPA and DHA may be one of the underlying mechanisms for the beneficial effects of fish oil.

Benzhydryl Compounds↗
PubMed2004

Inflammation, endothelial dysfunction, and platelet activation in patients with chronic kidney disease: the chronic renal impairment in Birmingham (CRIB) study.

BACKGROUND: Studies in the general population suggest that low-grade inflammation, endothelial dysfunction, and platelet activation are associated with an increased risk of cardiovascular events. METHODS: Markers of inflammation, endothelial dysfunction, and platelet activation were measured in 334 patients with chronic kidney disease (serum creatinine >1.47 mg/dL [>130 micromol/L] at screening) and compared with 2 age- and sex-matched control groups, 1 comprising 92 patients with coronary artery disease and the other comprising 96 apparently healthy individuals with no history of cardiovascular or kidney disease. RESULTS: There was evidence of low-grade inflammation in the chronic renal impairment group compared with healthy controls, with higher concentrations of C-reactive protein (3.70 versus 2.18 mg/L, P < 0.01) and fibrinogen (3.48 versus 2.67 g/L, P < 0.001) and lower serum albumin concentration (41.8 versus 44.0 g/dL [418 versus 440 g/L], P < 0.001). More severe renal impairment was associated with a trend towards higher fibrinogen and lower albumin concentrations (both P < 0.001), although there was no association with higher C-reactive protein level. As compared to healthy controls, plasma von Willebrand factor (142 versus 108 IU/dL, P < 0.001) and soluble P-selectin concentrations (57.0 versus 43.3 ng/mL, P < 0.001) were also higher in the chronic renal impairment group. More severe renal impairment was associated with a trend towards higher levels of von Willebrand factor (P < 0.001) and of soluble P selectin (P < 0.05). CONCLUSION: This cross-sectional analysis demonstrates that chronic kidney disease is associated with low-grade inflammation, endothelial dysfunction, and platelet activation, even among patients with moderate renal impairment.

Adult↗
PubMed2004

Transjugular kidney biopsy.

BACKGROUND: Most previous studies demonstrating the feasibility of transjugular kidney biopsy have used a modified Colapinto aspiration biopsy needle. We present 25 high-risk patients, with contraindications to percutaneous renal biopsy, who underwent transjugular kidney biopsy using a transvenous side-cut needle. This technique is easier to learn and can be performed by an interventional radiologist with transjugular liver biopsy experience and equipment. The needle is designed for optimal cortical sampling but has a high incidence of capsular perforation. Elective coil embolization was used in selected patients to reduce the risk of bleeding. METHODS: We retrospectively reviewed the indications for obtaining renal histology, based on clinical presentation, and the specific indications for transjugular biopsy. Transjugular kidney biopsy was assessed for sampling effectiveness and adequacy, the impact of histology on patient management, and technique complication rates. RESULTS: Renal tissue was obtained in 23 cases, with diagnostic biopsies in 21 of 23 (91.3%). A mean of 3.5 cores were obtained with 9.9 glomeruli per procedure for light microscopy (range, 0 to 32), 2.2 (range, 1 to 7) for electron microscopy, and adequate tissue for immunoflorescence available in 11 of 23 biopsies. Histology influenced patient management in all 23 cases. Capsular perforation was recorded in 73.9% (17 of 23) of cases with 6 undergoing elective coil embolization. Two major complications occurred, both in patients with multiple risk factors for bleeding. One required coil embolization of an arterio-calyseal system fistula. A further patient developed renal vein thrombosis 6 days after a failed transjugular kidney biopsy. CONCLUSION: Transjugular kidney biopsy provides a histological diagnosis in high-risk patients, making an important contribution to patient management.

Adult↗
PubMed2003

Monocyte adhesion to mesangial matrix modulates cytokine and metalloproteinase production.

BACKGROUND: Monocytes migrate into the glomerular mesangium during acute inflammatory renal disease, differentiate into macrophages, and may play a key role in the development and progression of glomerular scarring. Treatment strategies that inhibit monocyte infiltration ameliorate glomerular injury in animal models. Mesangial matrix contains several potential monocyte-binding domains that may contribute to monocyte entrapment and modulate cell activation. METHODS: Adhesion of peripheral blood-derived monocytes to matrix synthesized by human mesangial cells and to individual matrix proteins was assessed by colorimetry of nuclear staining with crystal violet. Monoclonal antibodies were used to identify the cell-surface integrins and matrix ligands involved. Monocyte proliferation was assessed by 3H-thymidine incorporation and cytokine production using enzyme-linked immunosorbent assay (ELISA). Secretion of metalloproteinases and their inhibitors was determined by zymography and ELISA, respectively. RESULTS: Monocytes bound to matrix synthesized by mesangial cells. Prestimulation of mesangial cells with tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) enhanced matrix fibronectin content (P < 0.001) and monocyte binding (P < 0.001). Blocking antibodies to fibronectin, as well as to the integrins very late antigen-4 (VLA-4) and VLA-5, reduced monocyte adhesion to mesangial matrix by approximately 50%. Incubation of monocytes with matrix, fibronectin, laminin and collagen IV enhanced production of interleukin-1beta (IL-1beta), interleukin-6 (IL-6), TNF-alpha and metalloproteinase-9 (MMP-9) when compared to cells incubated in plastic wells. However, there was no apparent difference in proliferation rate and no change in production of metalloproteinase inhibitors. CONCLUSION: Monocyte activation within the glomerulus may be mediated by binding to mesangial matrix components, particularly fibronectin. Matrix-mediated activation enhances production of inflammatory cytokines and matrix-degrading enzymes.

Cell Adhesion↗
PubMed2003

Cardiovascular risk factors in predialysis patients: baseline data from the Chronic Renal Impairment in Birmingham (CRIB) study.

BACKGROUND: Patients with end-stage kidney failure have a greatly increased risk of developing premature cardiac and vascular disease. However, little is known about the evolution of cardiovascular diseases in individuals with less severely impaired kidney function. METHODS: The prevalence of cardiovascular diseases and of suspected cardiovascular risk factors was studied in a group of 369 individuals (median age, 63 years, 67% male) with various degrees of impaired kidney function (calculated creatinine clearances 6 to 105 mL/min), in 103 patients with angiographically proven coronary artery disease, and in 103 apparently healthy individuals. These patients are being followed prospectively. RESULTS: Of those patients with kidney disease, 34% had a history of vascular disease and 21% had left ventricular hypertrophy on electrocardiogram at baseline. Traditional risk factors were prevalent, with a history of hypertension in 76% of kidney disease patients, diabetes in 15%, and dyslipidemia with reduced low-density lipoprotein (LDL) cholesterol, elevated serum triglycerides, and decreased high-density lipoprotein (HDL) levels. Other possible cardiovascular risk factors include elevated concentrations of plasma homocysteine, as well as low serum albumin and hemoglobin levels. Patients with more severely impaired renal function had lower diastolic blood pressures, lower LDL and HDL cholesterol levels, were more anemic, and had higher plasma homocysteine concentrations. CONCLUSIONS: Vascular disease and left ventricular hypertrophy are prevalent among patients with chronic kidney disease not requiring dialysis. In addition to traditional risk factors, other features of the uremic syndrome such as anemia, hyperhomocysteinemia, and inflammation (suggested by hypoalbuminemia) may contribute.

Creatinine↗
PubMed2003

PPAR agonists protect mesangial cells from interleukin 1beta-induced intracellular lipid accumulation by activating the ABCA1 cholesterol efflux pathway.

Previous studies have demonstrated that inflammatory cytokines such as interleukin-1beta (IL-1beta) promote lipid accumulation in human mesangial cells (HMC) by dysregulating the expression of lipoprotein receptors. Intracellular lipid accumulation is governed by both influx and efflux; therefore, the effect of IL-1beta on the efflux of lipid from HMC was investigated. IL-1beta was shown to inhibit (3)H-cholesterol efflux from HMC and increase total intracellular cholesterol concentration, probably as a result of reduced expression of the adenosine triphosphate (ATP) binding cassette A1 (ABCA1), a transporter protein involved in apolipoprotein-A1 (apo-A1)-mediated lipid efflux. To ascertain the molecular mechanisms involved, expression of peroxisome proliferator-activated receptors (PPAR) and liver X receptoralpha (LXRalpha) were examined. IL-1beta (5 ng/ml) reduced PPARalpha, PPARgamma, and LXRalpha mRNA expression. Activation of PPARgamma with the agonist prostaglandin J2 (10 micro M) and of PPARalpha with either bezafibrate (100 micro M) or Wy14643 (100 micro M) both increased LXRalpha and ABCA1 gene expression also and enhanced apoA1-mediated cholesterol efflux from lipid-loaded cells, even in the presence of IL-1beta. A natural ligand of LXRalpha, 25-hydroxycholesterol (25-OHC), had similar effects; when used together with PPAR agonists, an additive effect was observed, indicating co-operation between PPAR and LXRalpha in regulating ABCA1 gene expression. This was supported by the observation that overexpression of either PPARalpha or PPARgamma by transfection enhanced LXRalpha and ABCA1 gene induction by PPAR agonists. Taken together with previous data, it appears that, in addition to increasing lipid uptake, inflammatory cytokines promote intracellular lipid accumulation by inhibiting cholesterol efflux through the PPAR-LXRalpha-ABCA1 pathway. These results suggest potential mechanisms whereby inflammation may exacerbate lipid-mediated cellular injury in the glomerulus and in other tissues and indicate that PPAR agonists may have a protective effect.

ATP-Binding Cassette Transporters↗
PubMed2002

A placebo-controlled trial examining atorvastatin in dyslipidemic patients undergoing CAPD.

BACKGROUND: Individuals with chronic renal disease are at high risk of cardiovascular morbidity and mortality, and therefore the management of dyslipidemia is particularly important in this patient population. This double-blind randomized study investigated the efficacy and safety of the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, atorvastatin, in continuous ambulatory peritoneal dialysis (CAPD) patients with dyslipidemia. METHODS: Following a two- to four-week baseline period, patients with low-density lipoprotein (LDL)-cholesterol > or =3.5 mmol/L (135 mg/dL) were randomized to receive either atorvastatin 10 mg (N = 82) or placebo (N = 95) for 16 weeks. If LDL-cholesterol remained > or =3.5 mmol/L, the dose of atorvastatin was titrated to 20 mg and 40 mg after four and eight weeks, respectively. RESULTS: After four weeks a significantly greater proportion of patients receiving atorvastatin 10 mg had achieved the LDL-cholesterol goal < or =3.5 mmol/L compared with patients receiving placebo (85.4% vs. 16.0%; P < or = 0.001). The statistically significant difference between the two groups was maintained at week 8 and week 16 (P < or = 0.001 at both time points). At week 16, patients receiving atorvastatin had significantly greater reductions from baseline in LDL-cholesterol, total cholesterol, triglycerides and total cholesterol:HDL-cholesterol ratio (all P = 0.0001), and a significantly greater increase from baseline in HDL-cholesterol (P = 0.001) than patients receiving placebo. The overall adverse event profile for atorvastatin was similar to that observed with placebo. CONCLUSIONS: Atorvastatin was effective in achieving target LDL-cholesterol levels in a high proportion of the dyslipidemic CAPD patients studied at doses that are well tolerated.

Adult↗
PubMed2002

Synthesis of 1,25-dihydroxyvitamin D(3) by human endothelial cells is regulated by inflammatory cytokines: a novel autocrine determinant of vascular cell adhesion.

In addition to its calciotropic function, the secosteroid 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) has potent nonclassical effects. In particular, local production of 1,25D(3) catalyzed by the enzyme 1alpha-hydroxylase (1alpha-OHase) may act as an autocrine/paracrine immunomodulatory mechanism. To investigate the significance of this in vascular tissue the expression and function of 1alpha-OHase in human endothelial cells was characterized. Immunohistochemical and in situ hybridization analyses show, for the first time, the presence of 1alpha-OHase mRNA and protein in endothelial cells from human renal arteries as well as postcapillary venules from lymphoid tissue. Reverse transcription-PCR and Western blot analyses confirmed the presence of 1alpha-OHase in primary cultures of human umbilical vein endothelial cells (HUVEC). Enzyme activity in HUVEC (318 +/- 56 fmoles 1,25(OH)(2)D(3)/hr/mg protein) increased after treatment with tumor necrosis factor-alpha (1054 +/- 166, P < 0.01), lipopolysaccharide (1381 +/- 88, P < 0.01), or forskolin (554 +/- 56, P < 0.05). Functional studies showed that exogenously added 1,25(OH)(2)D(3) or its precursor, 25-hydroxyvitamin D(3) (25(OH)D(3)), significantly decreased HUVEC proliferation after 72 h of treatment (33% and 11%, respectively). In addition, after 24 h treatment, both 1,25(OH)(2)D(3) and 25(OH)D(3) increased the adhesion of monocytic U937 cells to HUVEC (159% and 153%, respectively). These data indicate that human endothelia are able to produce active vitamin D. The rapid induction of endothelial 1alpha-OHase activity by inflammatory cytokines suggests a novel autocrine/paracrine role for the enzyme, possibly as a modulator of endothelial cell adhesion.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗