HDL metabolism and activity in chronic kidney disease

APOL1 localization in normal kidney and nondiabetic kidney disease

In patients of African ancestry, genetic variants in APOL1, which encodes apolipoprotein L1, associate with the nondiabetic kidney diseases, focal segmental glomerulosclerosis (FSGS), HIV-associated nephropathy (HIVAN), and hypertensive nephropathy. Understanding the renal localization of APOL1 may provide clues that will ultimately help elucidate the mechanisms by which APOL1 variants promote nephropathy. Here, we used immunohistology to examine APOL1 localization in normal human kidney sections and in biopsies demonstrating either FSGS (n = 8) or HIVAN (n = 2). Within normal glomeruli, APOL1 only localized to podocytes. Compared with normal glomeruli, fewer cells stained for APOL1 in FSGS and HIVAN glomeruli, even when expression of the podocyte markers GLEPP1 and synaptopodin appeared normal. APOL1 localized to proximal tubular epithelia in normal kidneys, FSGS, and HIVAN. We detected APOL1 in the arteriolar endothelium of normal and diseased kidney sections. Unexpectedly, in both FSGS and HIVAN but not normal kidneys, the media of medium artery and arterioles contained a subset of α-smooth muscle actin-positive cells that stained for APOL1. Comparing the renal distribution of APOL1 in nondiabetic kidney disease to normal kidney suggests that a previously unrecognized arteriopathy may contribute to disease pathogenesis in patients of African ancestry.

The imbalance of Th17/Th1/Tregs in patients with type 2 diabetes: relationship with metabolic factors and complications

Immune disorders are linked to the development of type 2 diabetes (T2D) and its complications. The relationship of CD4(+)CD25(hi) T regulatory cells (Treg) and pro-inflammatory Th17 and Th1 subsets in T2D patients with metabolic disorders and complications need to be determined. The ratios of CD4(+)CD25(hi) Treg/Th17 cells and CD4(+)CD25(hi) Treg/Th1 cells, but not Th17/Th1 cells, were significantly decreased in T2D patients. The thymic output CD4(+)Foxp3(+)Helios(+) Tregs were normal but peripheral induced CD4(+)Foxp3(+)Helios(-) Tregs were decreased in T2D patients. The Bcl-2/Bax ratio decreased in CD4(+)CD25(hi) Tregs in T2D patients, supporting the increased sensitivity to cell death of these cells in T2D. CD4(+)CD25(hi)CD127(-) Tregs in T2D patients with microvascular complications were significantly less than T2D patients with macrovascular complications. Importantly, CD4(+)CD25(hi)CD127(-) Tregs were positively correlated with plasma IL-6, whereas IL-17(+)CD4(+)cells were negatively related to high-density lipoprotein (HDL). Our data offered evidence for the skewed balance of anti- and pro-inflammatory T cell subsets in T2D patients and identified that HDL closely modulate T cell polarization. These results opened an alternative explanation for the substantial activation of immune cells as well as the development of T2D and complications, which may have significant impacts on the prevention and treatment of T2D patients.

Salutary effects of hemodialysis on low-density lipoprotein proinflammatory and high-density lipoprotein anti-inflammatory properties in patient with end-stage renal disease

End-stage renal disease (ESRD) causes oxidative stress, inflammation, low-density lipoprotein (LDL) oxidation, high-density lipoprotein (HDL) deficiency and accelerated atherosclerosis. Uptake of oxidized LDL by macrophages results in foam cell and plaque formation. HDL mitigates atherosclerosis via reverse cholesterol transport and inhibition of LDL oxidation. ESRD heightens LDL inflammatory activity and suppresses HDL anti-inflammatory activity. The effect of hemodialysis on the LDL and HDL inflammatory properties is unknown. By removing the potential pro-oxidant/proinflammatory uremic toxins, dialysis may attenuate LDL inflammatory and HDL anti-inflammatory properties. Conversely, exposure to dialyzer membrane and tubing and influx of impurities from dialysate can intensify LDL and HDL inflammatory activities. This study examined the effect of hemodialysis on LDL and HDL inflammatory activities. Plasma samples were obtained from 12 normal control and 26 ESRD patients before and after hemodialysis with (16 patients) or without (10 patients) heparinization. HDL and LDL were isolated and tested for monocyte chemotactic activity in cultured endothelial cells. ESRD patients had increased LDL chemotactic activity, reduced HDL anti-inflammatory activity, paraoxonase and glutathione peroxidase levels, and elevated plasma IL-6 before dialysis. Hemodialysis partially improved LDL inflammatory and HDL anti-inflammatory activities and enhanced patients' HDL ability to suppress their LDL inflammatory activity. The salutary effect on LDL inflammatory activity was significantly greater in patients dialyzed with than those without heparin. ESRD heightens LDL inflammatory and impairs HDL anti-inflammatory activities. Hemodialysis partially improves LDL and HDL inflammatory activities. The salutary effects of hemodialysis are in part mediated by heparin, which is known to possess lipolytic and antioxidant properties.

Adverse effects of simulated hyper- and hypo-phosphatemia on endothelial cell function and viability

Background

Dysregulaiton of phosphate homeostasis as occurs in chronic kidney disease is associated with cardiovascular complications. It has been suggested that both hyperphosphatemia and hypophosphatemia can cause cardiovascular disease. The molecular mechanisms by which high or low serum phosphate levels adversely affect cardiovascular function are poorly understood. The purpose of this study was to explore the mechanisms of endothelial dysfunction in the presence of non-physiologic phosphate levels.

Methodology/Principal Findings

We studied the effects of simulated hyper- and hypophosphatemia in human umbilical vein endothelial cells in vitro. We found both simulated hyperphosphatemia and hypophosphatemia decrease eNOS expression and NO production. This was associated with reduced intracellular calcium, increased protein kinase C β2 (PKCβ2), reduced cell viability, and increased apoptosis. While simulated hyperphosphatemia was associated with decreased Akt/p-Akt, Bcl-xl/Bax ratios, NFkB-p65 and p-Erk abundance, simulated hypophosphatemia was associated with increased Akt/p-Akt and Bcl-xl/Bax ratios and p-Mek, p38, and p-p38 abundance.

Conclusions/Significance

This is the first demonstration of endothelial dysfunction with hypophosphatemia. Our data suggests that both hyperphosphatemia and hypophosphatemia decrease eNOS activity via reduced intracellular calcium and increased PKCβ2. Hyperphosphatemia also appears to reduce eNOS transcription via reduced signaling through PI3K/Akt/NF-kB and MAPK/NF-kB pathways. On the other hand, hypophosphatemia appears to activate these pathways. Our data provides the basis for further studies to elucidate the relationship between altered phosphate homeostasis and cardiovascular disease. As a corollary, our data suggests that the level of phosphate in the culture media, if not in the physiologic range, may inadvertently affect experimental results.

Inflammation, high-density lipoprotein and cardiovascular dysfunction

PURPOSE OF REVIEW

This review describes the evidence that supports the hypothesis that high-density lipoprotein (HDL) is atheroprotective due to its antiinflammatory effects and benefits on vascular health.

RECENT FINDINGS

Recent investigations have shown that HDL may inhibit atherosclerosis by promoting healthy endothelial function and by limiting or inhibiting the activation of macrophage and other immune cells. Receptors for HDL clearly regulate immune system function as well as cellular stress. Recent studies also suggest that participation of HDL in the process of reverse cholesterol transport may inhibit growth factor and cytokine receptor signaling by depleting cholesterol from lipid rafts. However, inflammation can also be associated with circulating dysfunctional HDL, which often possesses both prooxidative and proinflammatory properties.

SUMMARY

These studies suggest that HDL-based therapeutics have potential in treating both acute and chronic conditions associated with inflammation. These studies also reveal several other pathways that may be targeted for therapeutic drug development.

Uremia alters HDL composition and function

Functional impairment of HDL may contribute to the excess cardiovascular mortality experienced by patients with renal disease, but the effect of advanced renal disease on the composition and function of HDL is not well understood. Here, we used mass spectrometry and biochemical analyses to study alterations in the proteome and lipid composition of HDL isolated from patients on maintenance hemodialysis. We identified a significant increase in the amount of acute phase protein serum amyloid A1, albumin, lipoprotein-associated phospholipase A2, and apoC-III composing uremic HDL. Furthermore, uremic HDL contained reduced phospholipid and increased triglyceride and lysophospholipid. With regard to function, these changes impaired the ability of uremic HDL to promote cholesterol efflux from macrophages. In summary, the altered composition of HDL in renal disease seems to inhibit its cardioprotective properties. Assessing HDL composition and function in renal disease may help identify patients at increased risk for cardiovascular disease.

The effect of prolonged oral exposure of cockerels to disinfectant (Iodosteryl(®)) on induction of oxidative stress and liver damage

This study was designed to investigate the effect of prolonged oral exposure of cockerels to disinfectant (Iodosteryl(®)) present in drinking water and its ability to induce liver damage and oxidative stress. Thirty-two healthy birds were used for this study. They were grouped into four groups of eight per group. Group I received 10 ml/kg body weight of physiological saline. Groups II, III and IV received 1 part per million, 2 part per million and 4 part per million of Iodosteryl(®) in their drinking water for six weeks. The results revealed significant (P<0.05) increase in alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase activities in a dose-dependent manner in birds administered with Iodosteryl(®) when compared with control. Significant (P<0.05) increase in sodium and potassium ions was obtained from birds that received Iodosteryl(®) (4 part per million) compared with control. Also, there was significant (P<0.05) increase in total cholesterol, triglycerides, high density lipoprotein and low density lipoprotein levels in all treatment groups (1, 2 and 4 part per million) compared with control. Serum blood urea nitrogen levels increased significantly (P<0.05) in a dose-dependent manner. Biologic markers of oxidative stress (malondialdehyde and hydrogen peroxide generation) increased significantly with concomitant significant (P<0.05) decrease in serum glutathione level in a dose-dependent manner when compared with control. Histological sections revealed hepatic congestion, vacuolation and fibrosis at varying concentration of Iodosteryl(®). Overall, Iodosteryl(®) induced hepatic damage, increased oxidative stress and decreased antioxidant defense system; hence exposure of both animals and humans to prolonged iodine disinfectant is potentially harmful.

Estimated glomerular filtration rate and albuminuria are independent predictors of cardiovascular events and death in type 2 diabetes mellitus: the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study

AIMS/HYPOTHESIS

We investigated effects of renal function and albuminuria on cardiovascular outcomes in 9,795 low-risk patients with diabetes in the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) study.

METHODS

Baseline and year 2 renal status were examined in relation to clinical and biochemical characteristics. Outcomes included total cardiovascular disease (CVD), cardiac and non-cardiac death over 5 years.

RESULTS

Lower estimated GFR (eGFR) vs eGFR ≥90 ml min⁻¹ 1.73 m⁻² was a risk factor for total CVD events: (HR [95% CI] 1.14 [1.01-1.29] for eGFR 60-89 ml min⁻¹ 1.73 m⁻²; 1.59 [1.28-1.98] for eGFR 30-59 ml min⁻¹ 1.73 m⁻²; p < 0.001; adjusted for other characteristics). Albuminuria increased CVD risk, with microalbuminuria and macroalbuminuria increasing total CVD (HR 1.25 [1.01-1.54] and 1.19 [0.76-1.85], respectively; p = 0.001 for trend) when eGFR ≥90 ml min⁻¹ 1.73 m⁻². CVD risk was further modified by renal status changes over the first 2 years. In multivariable analysis, 77% of the effect of eGFR and 81% of the effect of albumin:creatinine ratio were accounted for by other variables, principally low HDL-cholesterol and elevated blood pressure.

CONCLUSIONS/INTERPRETATION

Reduced eGFR and albuminuria are independent risk factors for cardiovascular events and mortality rates in a low-risk population of mainly European ancestry. While their independent contributions to CVD risk appear small when other risk factors are considered, they remain excellent surrogate markers in clinical practice because they capture risk related to a number of other characteristics. Therefore, both should be considered when assessing prognosis and treatment strategies in patients with diabetes, and both should be included in risk models.

Height constitutes an important predictor of mortality in end-stage renal disease

Aim. Height is an important determinant of augmentation index (AI) that anticipates cardiovascular prognosis. There is a scanty of the data whether short height predicts survival in patients with end-stage renal diseases, a high risk population. Methods. Fifty two hypertensive patients with type 2 diabetic nephropathy receiving hemodialysis and 52 patients with nondiabetic nephropathy were enrolled. In addition to AI estimated with radial artery tonometry, classical cardiovascular risk factors were considered. Patients were followed for 2 years to assess cardiovascular prognosis. Results. Cox hazards regression revealed that both smoking and shortness in height independently contributed to total mortality and indicated that smoking as well as the presence of left ventricular hypertrophy predicted cardiovascular mortality. Our findings implicated that high AI, the presence of diabetes, and low high-density lipoprotein cholesterol were significant contributors to cardiovascular events. Conclusions. Our findings provide new evidence that shortness in height independently contributes to total mortality in hemodialysis patients.