Plasma metabolite profiles, cellular cholesterol efflux, and non-traditional cardiovascular risk in patients with CKD.

BACKGROUND: Patients with chronic kidney disease (CKD) experience high rates of atherosclerotic cardiovascular disease and death that are not fully explained by traditional risk factors. In animal studies, defective cellular cholesterol efflux pathways which are mediated by the ATP binding cassette transporters ABCA1 and ABCG1 are associated with accelerated atherosclerosis. We hypothesized that cholesterol efflux in humans would vary in terms of cellular components, with potential implications for cardiovascular disease. METHODS: We recruited 120 CKD patients (eGFR<30mL/min/1.73m2) and 120 control subjects (eGFR ≥60mL/min/1.73m2) in order to measure cholesterol efflux using either patients' HDL and THP-1 macrophages or patients' monocytes and a flow cytometry based cholesterol efflux assay. We also measured cell-surface levels of the common ß subunit of the IL-3/GM-CSF receptor (IL-3Rß) which has been linked to defective cholesterol homeostasis and may promote monocytosis. In addition, we measured plasma inflammatory cytokines and plasma metabolite profiles. RESULTS: There was a strong positive correlation between cell-surface IL-3Rß levels and monocyte counts in CKD (P<0.001). ABCA1 mRNA was reduced in CKD vs. control monocytes (P<0.05), across various etiologies of CKD. Cholesterol efflux to apolipoprotein A1 was impaired in monocytes from CKD patients with diabetic nephropathy (P<0.05), but we found no evidence for a circulating HDL-mediated defect in cholesterol efflux in CKD. Profiling of plasma metabolites showed that medium-chain acylcarnitines were both independently associated with lower levels of cholesterol transporter mRNA in CKD monocytes at baseline (P<0.05), and with cardiovascular events in CKD patients after median 2.6years of follow-up. CONCLUSIONS: Cholesterol efflux in humans varies in terms of cellular components. We report a cellular defect in ABCA1-mediated cholesterol efflux in monocytes from CKD patients with diabetic nephropathy. Unlike several traditional risk factors for atherosclerotic cardiovascular disease, plasma metabolites inversely associated with endogenous cholesterol transporters predicted cardiovascular events in CKD patients. (Funded by the National Institute of Diabetes and Digestive and Kidney DiseasesK23DK097288 and others.).

Chronic kidney disease and end-stage renal disease in disadvantaged communities of North America: an investigational challenge to limit disease progression and cardiovascular risk.

Chronic kidney disease (CKD) and end-stage renal disease (ESRD) are growing public health issues associated with significant morbidity and mortality around the world. In the United States, Black and Hispanic minorities suffer higher rates of CKD and ESRD, mostly attributed to Diabetic Kidney Disease (DKD). DKD is the leading cause of both CKD and ESRD in the developed world and disproportionately affects minority populations such as African Americans, Hispanic Americans, and Aboriginal Americans in comparison with Whites. This review will discuss the incidence, prevalence, and etiology of renal disease in disadvantaged minorities in the U.S. and will take a closer look at diabetic kidney disease as it is the primary cause of kidney disease in these populations.

Inhibition of miR-33a/b in non-human primates raises plasma HDL and lowers VLDL triglycerides.

Cardiovascular disease remains the leading cause of mortality in westernized countries, despite optimum medical therapy to reduce the levels of low-density lipoprotein (LDL)-associated cholesterol. The pursuit of novel therapies to target the residual risk has focused on raising the levels of high-density lipoprotein (HDL)-associated cholesterol in order to exploit its atheroprotective effects. MicroRNAs (miRNAs) have emerged as important post-transcriptional regulators of lipid metabolism and are thus a new class of target for therapeutic intervention. MicroRNA-33a and microRNA-33b (miR-33a/b) are intronic miRNAs whose encoding regions are embedded in the sterol-response-element-binding protein genes SREBF2 and SREBF1 (refs 3-5), respectively. These miRNAs repress expression of the cholesterol transporter ABCA1, which is a key regulator of HDL biogenesis. Recent studies in mice suggest that antagonizing miR-33a may be an effective strategy for raising plasma HDL levels and providing protection against atherosclerosis; however, extrapolating these findings to humans is complicated by the fact that mice lack miR-33b, which is present only in the SREBF1 gene of medium and large mammals. Here we show in African green monkeys that systemic delivery of an anti-miRNA oligonucleotide that targets both miR-33a and miR-33b increased hepatic expression of ABCA1 and induced a sustained increase in plasma HDL levels over 12 weeks. Notably, miR-33 antagonism in this non-human primate model also increased the expression of miR-33 target genes involved in fatty acid oxidation (CROT, CPT1A, HADHB and PRKAA1) and reduced the expression of genes involved in fatty acid synthesis (SREBF1, FASN, ACLY and ACACA), resulting in a marked suppression of the plasma levels of very-low-density lipoprotein (VLDL)-associated triglycerides, a finding that has not previously been observed in mice. These data establish, in a model that is highly relevant to humans, that pharmacological inhibition of miR-33a and miR-33b is a promising therapeutic strategy to raise plasma HDL and lower VLDL triglyceride levels for the treatment of dyslipidaemias that increase cardiovascular disease risk.

Antagonism of miR-33 in mice promotes reverse cholesterol transport and regression of atherosclerosis.

Plasma HDL levels have a protective role in atherosclerosis, yet clinical therapies to raise HDL levels have remained elusive. Recent advances in the understanding of lipid metabolism have revealed that miR-33, an intronic microRNA located within the SREBF2 gene, suppresses expression of the cholesterol transporter ABC transporter A1 (ABCA1) and lowers HDL levels. Conversely, mechanisms that inhibit miR-33 increase ABCA1 and circulating HDL levels, suggesting that antagonism of miR-33 may be atheroprotective. As the regression of atherosclerosis is clinically desirable, we assessed the impact of miR-33 inhibition in mice deficient for the LDL receptor (Ldlr-/- mice), with established atherosclerotic plaques. Mice treated with anti-miR33 for 4 weeks showed an increase in circulating HDL levels and enhanced reverse cholesterol transport to the plasma, liver, and feces. Consistent with this, anti-miR33-treated mice showed reductions in plaque size and lipid content, increased markers of plaque stability, and decreased inflammatory gene expression. Notably, in addition to raising ABCA1 levels in the liver, anti-miR33 oligonucleotides directly targeted the plaque macrophages, in which they enhanced ABCA1 expression and cholesterol removal. These studies establish that raising HDL levels by anti-miR33 oligonucleotide treatment promotes reverse cholesterol transport and atherosclerosis regression and suggest that it may be a promising strategy to treat atherosclerotic vascular disease.

Inhibiting proteasomal degradation of microsomal triglyceride transfer protein prevents CCl4-induced steatosis.

Carbon tetrachloride (CCl(4)) interferes with triglyceride secretion and causes steatosis, fibrosis, and necrosis. In mice, CCl(4) decreased plasma triglyceride-rich lipoproteins, increased cellular lipids, and reduced microsomal triglyceride transfer protein (MTP) without diminishing mRNA levels. Similarly, CCl(4) decreased apoB-lipoprotein production and MTP activity but had no effect on mRNA levels in primary enterocytes and colon carcinoma and hepatoma cells. CCl(4) did not affect MTP synthesis but induced post-translational degradation involving ubiquitinylation and proteasomes in McA-RH7777 cells. By contrast, MTP inhibitor increased cellular lipids without affecting MTP protein. MTP was covalently modified when cells were incubated with (14)CCl(4). This modification was prevented by the inhibition of P450 oxygenases, indicating that CCl(3)(.) generated by these enzymes targets MTP for degradation. To determine whether inhibition of proteolysis could prevent CCl(4) toxicity, mice were fed with CCl(4) with or without lactacystin. Lactacystin increased ubiquitinylated MTP and prevented lipid accumulation in tissues. Thus, CCl(4) induces post-translational degradation without affecting lipid transfer activity, whereas MTP antagonist inhibits lipid transfer activity without causing its destruction. These studies identify MTP as a major target of CCl(4) and its degradation as a novel mechanism involved in the onset of steatosis, suggesting that inhibition of proteolysis may prevent some forms of steatosis.