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.).

Disruption of mammalian target of rapamycin complex 1 in macrophages decreases chemokine gene expression and atherosclerosis.

RATIONALE: The mammalian target of rapamycin complex 1 inhibitor, rapamycin, has been shown to decrease atherosclerosis, even while increasing plasma low-density lipoprotein levels. This suggests an antiatherogenic effect possibly mediated by the modulation of inflammatory responses in atherosclerotic plaques. OBJECTIVE: Our aim was to assess the role of macrophage mammalian target of rapamycin complex 1 in atherogenesis. METHODS AND RESULTS: We transplanted bone marrow from mice in which a key mammalian target of rapamycin complex 1 adaptor, regulatory-associated protein of mTOR, was deleted in macrophages by Cre/loxP recombination (Mac-Rap(KO) mice) into Ldlr(-/-) mice and then fed them the Western-type diet. Atherosclerotic lesions from Mac-Rap(KO) mice showed decreased infiltration of macrophages, lesion size, and chemokine gene expression compared with control mice. Treatment of macrophages with minimally modified low-density lipoprotein resulted in increased levels of chemokine mRNAs and signal transducer and activator of transcription (STAT) 3 phosphorylation; these effects were reduced in Mac-Rap(KO) macrophages. Although wild-type and Mac-Rap(KO) macrophages showed similar STAT3 phosphorylation on Tyr705, Mac-Rap(KO) macrophages showed decreased STAT3Ser727 phosphorylation in response to minimally modified low-density lipoprotein treatment and decreased Ccl2 promoter binding of STAT3. CONCLUSIONS: The results demonstrate cross-talk between nutritionally induced mammalian target of rapamycin complex 1 signaling and minimally modified low-density lipoprotein-mediated inflammatory signaling via combinatorial phosphorylation of STAT3 in macrophages, leading to increased STAT3 activity on the chemokine (C-C motif) ligand 2 (monocyte chemoattractant protein 1) promoter with proatherogenic consequences.

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.

Mild renal dysfunction and metabolites tied to low HDL cholesterol are associated with monocytosis and atherosclerosis.

BACKGROUND: The number of circulating blood monocytes impacts atherosclerotic lesion size, and in mouse models, elevated levels of high-density lipoprotein cholesterol suppress blood monocyte counts and atherosclerosis. We hypothesized that individuals with mild renal dysfunction at increased cardiovascular risk would have reduced high-density lipoprotein levels, high blood monocyte counts, and accelerated atherosclerosis. METHODS AND RESULTS: To test whether mild renal dysfunction is associated with an increase in a leukocyte subpopulation rich in monocytes that has a known association with future coronary events, we divided individuals from the Malmö Diet and Cancer study (MDC) into baseline cystatin C quintiles (n=4757). Lower levels of renal function were accompanied by higher monocyte counts, and monocytes were independently associated with carotid bulb intima-media thickness cross-sectionally (P=0.02). Cystatin C levels were positively and plasma high-density lipoprotein cholesterol levels negatively associated with monocyte counts at baseline, after adjustment for traditional risk factors. Several amino acid metabolites tied to low levels of high-density lipoprotein cholesterol and insulin resistance measured in a subset of individuals (n=752) by use of liquid chromatography-mass spectrometry were independently associated with a 22% to 34% increased risk of being in the top quartile of monocytes (P<0.05). CONCLUSIONS: A low high-density lipoprotein cholesterol, insulin resistance phenotype occurs in subjects with mild renal dysfunction and is associated with elevated monocytes and atherosclerosis. High blood monocyte counts may represent a previously unrecognized mechanism underlying the strong relationship between cystatin C and cardiovascular risk.

Inflammatory activation: cardiac, renal, and cardio-renal interactions in patients with the cardiorenal syndrome.

Although inflammation is a physiologic response designed to protect us from infection, when unchecked and ongoing it may cause substantial harm. Both chronic heart failure (CHF) and chronic kidney disease (CKD) are known to cause elaboration of several pro-inflammatory mediators that can be detected at high concentrations in the tissues and blood stream. The biologic sources driving this chronic inflammatory state in CHF and CKD are not fully established. Traditional sources of inflammation include the heart and the kidneys which produce a wide range of pro-inflammatory cytokines in response to neurohormones and sympathetic activation. However, growing evidence suggests that non-traditional biomechanical mechanisms such as venous and tissue congestion due to volume overload are also important as they stimulate endotoxin absorption from the bowel and peripheral synthesis and release of pro-inflammatory mediators. Both during the chronic phase and, more rapidly, during acute exacerbations of CHF and CKD, inflammation and congestion appear to amplify each other resulting in a downward spiral of worsening cardiac, vascular, and renal functions that may negatively impact patients' outcome. Anti-inflammatory treatment strategies aimed at attenuating end organ damage and improving clinical prognosis in the cardiorenal syndrome have been disappointing to date. A new therapeutic paradigm may be needed, which involves different anti-inflammatory strategies for individual etiologies and stages of CHF and CKD. It may also include specific (short-term) anti-inflammatory treatments that counteract inflammation during the unsettled phases of clinical decompensation. Finally, it will require greater focus on volume overload as an increasingly significant source of systemic inflammation in the cardiorenal syndrome.

Echocardiographic changes following hemodialysis initiation in patients with advanced chronic kidney disease and symptomatic heart failure with reduced ejection fraction.

BACKGROUND: In patients without overt cardiac disease, the degree of left ventricular hypertrophy (LVH) gets worse following hemodialysis (HD) initiation; however, in patients with both advanced chronic kidney disease (CKD) and symptomatic heart failure (HF) with reduced ejection fraction (EF), the short-term effect of HD on LVH and LV geometry has not been examined. We hypothesized that left ventricular mass index (LVMI) would decrease following HD initiation in CKD patients with symptomatic HF. METHODS: We retrospectively evaluated changes in LVMI, LV geometry, and LV fractional shortening (LVFS), assessed by 2D transthoracic echocardiography (TTE), in 41 patients with HF initiating HD while hospitalized from 1995 to 2006. HF was defined by LVEF ≤ 45% or dyspnea plus two of the following: raised jugular venous pressure, bibasilar crackles, pulmonary venous hypertension, interstitial edema on chest X-ray, or both. TTE was performed within 3 months prior to first HD and repeated 8.6 ± 5.2 months after start of HD. TTE recordings were obtained from storage and analyzed by a cardiologist blinded to patient clinical characteristics. RESULTS: Before initiation of HD, LVMI in 39 patients was 167.9 ± 53.1 g/m2 and it decreased by -24.3 ± 35.4 g/m2 by follow-up, p < 0.001. 26% of patients with concentric LVH at baseline had concentric remodeling or eccentric LVH at follow-up. LVFS did not significantly change over time in all 41 patients with HF (25.7 ± 8.7% vs. 26.4 ± 8.7%, p = 0.66). However, in an expanded analysis of all 69 patients with serial TTEs, a 1% increase in LVFS after starting HD was associated with a 16% reduction in risk of cardiovascular hospitalization at follow-up (HR 0.84, 95% CI 0.73 - 0.96, p = 0.01). CONCLUSIONS: LVMI decreases following HD initiation in CKD patients with symptomatic HF and reduced LVEF, possibly due to relief of venous congestion. Increase in LVFS following HD initiation predicts improved cardiac outcome.

Venous congestion and endothelial cell activation in acute decompensated heart failure.

Despite accumulating clinical evidence supporting a key role for venous congestion in the development of acute decompensated heart failure (ADHF), there remain several gaps in our knowledge of the pathophysiology of ADHF. Specifically, the biomechanically driven effects of venous congestion on the vascular endothelium (the largest endocrine/paracrine organ of the body), on neurohormonal activation, and on renal and cardiac dysfunction remain largely unexplored. We propose that venous congestion is a fundamental, hemodynamic stimulus for vascular inflammation, which plays a key role in the development and possibly the resolution of ADHF through vascular, humoral, renal, and cardiac mechanisms. A better understanding of the role of venous congestion and endothelial activation in the pathophysiology of ADHF may provide a strong rationale for near-future testing of treatment strategies that target biomechanically driven inflammation. Targeting vascular and systemic inflammation before symptoms arise may prevent progression to overt clinical decompensation in the ADHF syndrome.

Cholesterol Accumulation in Dendritic Cells Links the Inflammasome to Acquired Immunity.

Autoimmune diseases such as systemic lupus erythematosus (SLE) are associated with increased cardiovascular disease and reduced plasma high-density lipoprotein (HDL) levels. HDL mediates cholesterol efflux from immune cells via the ATP binding cassette transporters A1 and G1 (ABCA1/G1). The significance of impaired cholesterol efflux pathways in autoimmunity is unknown. We observed that Abca1/g1-deficient mice develop enlarged lymph nodes (LNs) and glomerulonephritis suggestive of SLE. This lupus-like phenotype was recapitulated in mice with knockouts of Abca1/g1 in dendritic cells (DCs), but not in macrophages or T cells. DC-Abca1/g1 deficiency increased LN and splenic CD11b+ DCs, which displayed cholesterol accumulation and inflammasome activation, increased cell surface levels of the granulocyte macrophage-colony stimulating factor receptor, and enhanced inflammatory cytokine secretion. Consequently, DC-Abca1/g1 deficiency enhanced T cell activation and Th1 and Th17 cell polarization. Nlrp3 inflammasome deficiency diminished the enlarged LNs and enhanced Th1 cell polarization. These findings identify an essential role of DC cholesterol efflux pathways in maintaining immune tolerance.

Regulation of hepatic LDL receptors by mTORC1 and PCSK9 in mice.

Individuals with type 2 diabetes have an increased risk of atherosclerosis. One factor underlying this is dyslipidemia, which in hyperinsulinemic subjects with early type 2 diabetes is typically characterized by increased VLDL secretion but normal LDL cholesterol levels, possibly reflecting enhanced catabolism of LDL via hepatic LDLRs. Recent studies have also suggested that hepatic insulin signaling sustains LDLR levels. We therefore sought to elucidate the mechanisms linking hepatic insulin signaling to regulation of LDLR levels. In WT mice, insulin receptor knockdown by shRNA resulted in decreased hepatic mTORC1 signaling and LDLR protein levels. It also led to increased expression of PCSK9, a known post-transcriptional regulator of LDLR expression. Administration of the mTORC1 inhibitor rapamycin caused increased expression of PCSK9, decreased levels of hepatic LDLR protein, and increased levels of VLDL/LDL cholesterol in WT but not Pcsk9-/- mice. Conversely, mice with increased hepatic mTORC1 activity exhibited decreased expression of PCSK9 and increased levels of hepatic LDLR protein levels. Pcsk9 is regulated by the transcription factor HNF1α, and our further detailed analyses suggest that increased mTORC1 activity leads to activation of PKCδ, reduced activity of HNF4α and HNF1α, decreased PCSK9 expression, and ultimately increased hepatic LDLR protein levels, which result in decreased circulating LDL levels. We therefore suggest that PCSK9 inhibition could be an effective way to reduce the adverse side effect of increased LDL levels that is observed in transplant patients taking rapamycin as immunosuppressive therapy.

Inflammatory stress in primary venous and aortic endothelial cells of type 1 diabetic mice.

OBJECTIVE: The progression of diabetes is associated with profound endothelial dysfunction. We tested the hypothesis that cellular stress would be detectable in ECs retrieved from arterial and venous vessels of diabetic mice. METHOD: We describe a method for direct isolation of well-characterised aortic and venous ECs from mice in which cells are not subjected to propagation in culture. RESULTS: Gene expression profiling, confirmed by real-time PCR, revealed a progressive increase in markers of injury within two main gene families, EC activation and EC apoptosis, in aortic and venous ECs recovered from diabetic versus non-diabetic mice. In short-term diabetes, Il1b mRNA transcripts were higher in aortic and venous ECs of diabetic mice versus controls. In long-term diabetes, casp-1 mRNA transcripts were higher in aortic and venous ECs of diabetic mice versus controls. CONCLUSION: These data suggest that diabetes imparts diffuse endothelial perturbation in the arterial and venous endothelium.