Hepatic fatty acid and cholesterol metabolism in nephrotic syndrome.

Heavy proteinuria (nephrotic syndrome) is associated with hypercholesterolemia, hypertriglyceridemia and a high risk of atherosclerosis. Hypertriglyceridemia in nephrotic syndrome (NS) is partly due to increased TG and TG-rich lipoprotein production. However, data on the effect of NS on fatty acid production and catabolic machinery are limited. NS was induced in male Sprague Dawley rats by IP injection of puromycin aminonucleoside. Six weeks after the second injection the animals were euthanized, liver was harvested and processed. The NS group exhibited heavy proteinuria, hypercholesterolemia, hypertriglyceridemia, activation of SREBP-1 and LXR α/ß, up-regulation of FAS, ACC and HMG CoA reductase. In contrast hepatic tissue ChREBP activity was reduced in NS excluding its role in upregulation of FA synthetic pathway. Despite increased expression and nuclear translocation of PPARα, expression of ACO and abundance of CPT and L-FABP, were decreased in the liver of nephrotic animals. Therefore, NS results in upregulation of FA production machinery. Increased hepatic fatty acid production capacity in NS is compounded by reduced FA catabolism, events that contribute to the associated hypertiglyceridemia.

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.

Nephrotic syndrome causes upregulation of HDL endocytic receptor and PDZK-1-dependent downregulation of HDL docking receptor.

BACKGROUND: Nephrotic syndrome (NS) is associated with dysregulation of lipid/lipoprotein metabolism and impaired high-density lipoprotein (HDL)-mediated reverse cholesterol transport and atherosclerosis. HDL serves as vehicle for transport of surplus lipids from the peripheral tissues for disposal in the liver via two receptors: (i) scavenger receptor class B type I (SR-BI) which serves as a docking receptor, enabling HDL to unload its lipid cargo and return to circulation to repeat the cycle, and (ii) beta chain ATP synthase which serves as the endocytic receptor mediating removal and catabolism of lipid-poor HDL. SR-BI abundance is regulated by PDZ-containing kidney protein 1 (PDZK1), a multifunctional protein, which prevents SRB-1 degradation at the post-translational level. This study explored the effect of NS on hepatic expression of these important molecules. METHODS: Gene expression, protein abundance and immunohistological appearance of the above proteins were measured in the liver of rats with puromycin-induced NS and control rats. RESULTS: The nephrotic animals exhibited severe proteinuria, hypoalbuminemia, hypercholesterolemia, hypertriglyceridemia, reduced HDL/total cholesterol ratio, normal glomerular filtration rate, significant upregulation of the endocytic HDL receptor messenger RNA (mRNA) and protein (P < 0.005) and significant reduction of SR-BI protein (P < 0.002) despite its normal mRNA abundance. The reduction in SR-BI protein abundance in NS animals was accompanied by parallel reductions in PDZK1 mRNA (P = 0.02) and protein abundance (P = 0.012). CONCLUSIONS: NS results in elevation of hepatic HDL endocytic receptor and deficiency of HDL docking receptor. The latter is associated with and, in part, mediated by downregulation of PDZK1. Together, these abnormalities can increase catabolism and diminish recycling of HDL and contribute to the defective reverse cholesterol/lipid transport in NS.

Effect of nephrotic syndrome on homocysteine metabolism.

BACKGROUND: Proteinuria and hyperhomocysteinaemia are independently associated with increased risk of atherosclerosis and cardiovascular disease. The available data on plasma homocysteine (Hcy) level in patients with nephrotic syndrome (NS) are contradictory with increased, decreased and unchanged values reported by different investigators. The majority of Hcy in the plasma is bound to albumin whose urinary losses and diminished plasma concentration are the defining features of NS. The present study was designed to explore the effect of NS on plasma concentration and urinary excretion of Hcy and hepatic expression of methylenetetrahydrofolate reductase (MTHFR) and cystathionine-ß-synthase (CBS), the key enzymes in re-methylation and trans-sulphuration of Hcy, respectively. METHODS: Sprague-Dawley rats were rendered nephrotic by IP injection of puromycin aminonucleoside. Urine and plasma were used for measurement of Hcy, and the liver was processed for assessment of MTHFR and CBS protein expression. RESULTS: Compared with the controls, nephrotic rats showed heavy proteinuria, hypoalbuminaemia, hypercholesterolaemia, normal plasma creatinine and creatinine clearance, reduced plasma Hcy, increased urinary Hcy, and downregulation of CBS but not MTHFR expression. Plasma Hcy correlated directly with plasma albumin and inversely with urinary protein excretion. The urinary Hcy excretion correlated directly with urine protein excretion. CONCLUSIONS: NS results in significant reduction in plasma total Hcy concentration which is due to the reduction in albumin-bound Hcy as opposed to the free Hcy fraction. This is coupled with increased urinary excretion of albumin-bound Hcy. In addition, NS results in down-regulation of CBS which can curtail conversion of Hcy to cysteine and reduce production of H(2)S which is an important endogenous signalling molecule.

Effect of chronic kidney disease on the expression of thiamin and folic acid transporters.

BACKGROUND: Chronic kidney disease (CKD) is associated with significant cardiovascular, neurological and metabolic complications. Thiamin and folate are essential for growth, development and normal cellular function, and their uptake is mediated by regulated transport systems. While plasma folate and thiamin levels are generally normal in patients with CKD, they commonly exhibit features resembling vitamin deficiency states. Earlier studies have documented impaired intestinal absorption of several B vitamins in experimental CKD. In this study, we explored the effect of CKD on expression of folate and thiamin transporters in the key organs and tissues. METHODS: Sprague-Dawley rats were randomized to undergo 5/6 nephrectomy or sham operation and observed for 12 weeks. Plasma folate and thiamin concentrations and gene expression of folate (RFC, PCFT) and thiamin transporters (THTR-1 and THTR-2) were determined in the liver, brain, heart and intestinal tissues using real-time PCR. Hepatic protein abundance of these transporters was determined using western blot analysis. RESULTS: Plasma folate and thiamin levels were similar between the CKD and the control groups. However, expressions of both folate (RFC and PCFT) and thiamin (THTR-1, THTR-2) transporters were markedly reduced in the small intestine, heart, liver and brain of the CKD animals. Liver protein abundance of folate and thiamin transporters was significantly reduced in the CKD animals when compared with the sham-operated controls. Furthermore, we found a significant reduction in mitochondrial folate and thiamin transporters in the CKD animals. CONCLUSIONS: CKD results in marked down-regulation in the expression of folate and thiamin transporters in the intestine, heart, liver and brain. These events can lead to reduced intestinal absorption and impaired cellular homeostasis of these essential micronutrients despite their normal plasma levels.

Effects of end-stage renal disease and haemodialysis on dendritic cell subsets and basal and LPS-stimulated cytokine production.

BACKGROUND: Although bacterial infections have dramatically declined as a cause of death in the general population, they remain a major cause of mortality in patients with end-stage renal disease (ESRD). Moreover, the response to vaccination is profoundly impaired in this population. Dendritic cells (DC) are the major antigen-presenting cells that bridge the innate and adaptive immune responses. Activation of DC by pathogens results in secretion of inflammatory cytokines and up-regulation of co-stimulatory molecules. The activated DC prime naïve T and B cells to the captured antigens. METHODS: Using flow cytometry, the number and phenotype of circulating DC [myeloid DC (mDC) and plasmacytoid DC (pDC)] were quantified in pre- and post-dialysis blood samples from 20 ESRD patients maintained on haemodialysis. Ten normal individuals served as controls. In addition, the level of DC activation and their response to lipopolysaccharide (LPS) stimulation were determined by assessing expression of co-stimulatory molecule, CD86, and antigen-presenting molecule, HLA-DR, as well as production of TNFalpha, IFNalpha and IL-6. RESULTS: Compared to the control group, the circulating dendritic cell count was significantly reduced in the ESRD patients before dialysis and declined further after dialysis. The reduction in pDC numbers was more striking than mDC. The magnitude of the LPS-induced up-regulation of CD86 was comparable among the study groups as well as pre- and post-dialysis samples. However, LPS-induced TNFalpha production was significantly reduced in the post-dialysis samples with no significant difference in IL-6 and IFNalpha productions among the study groups and in pre- and post-dialysis samples. CONCLUSIONS: ESRD results in significant DC depletion which is largely due to diminished plasmacytoid DC subset. Haemodialysis procedure intensifies DC depletion and impairs LPS-induced TNFalpha production.

Effect of end-stage renal disease on B-lymphocyte subpopulations, IL-7, BAFF and BAFF receptor expression.

BACKGROUND: End-stage renal disease (ESRD) results in increased susceptibility to infections, impaired response to vaccination and diffuse B-cell lymphopenia. However, the precise nature and mechanism of ESRD-induced B-cell lymphopenia remains unclear. Therefore, we studied the distribution of major B-cell subsets, B-cell growth, differentiation and survival factors, IL-7 and BAFF, and their receptors in 21 haemodialysis patients and 21 controls. METHODS: Innate B1 cells (CD19+, CD5+), conventional B2 cells (CD19+, CD5-), newly formed transitional B cells (CD19+, CD10+, CD27-), naïve B cells (CD19+, CD27-) and memory B cells (CD19+, CD27+) and BAFF receptor were quantified by flow cytometry. Plasma IL-7, BAFF, IL-6, TNF-alpha and IL-10 were measured by ELISA. RESULTS: The ESRD group exhibited significant reductions of all B-cell subpopulations except for transitional B cells that were less severely affected. No significant difference was found in B-cell apoptosis between the ESRD and control groups. Moreover, plasma IL-7 and BAFF levels were elevated in ESRD patients, therefore excluding their deficiencies as a possible culprit. However, BAFF receptor expression was significantly reduced in transitional but not mature B cells in the ESRD group. Interestingly, B-cell activation with the TLR9 agonist resulted in significantly greater production of IL-6 and TNF alpha but not IL-10 in the ESRD group. CONCLUSIONS: Thus, despite elevation of B-cell growth, differentiation and survival factors, ESRD patients exhibited diffuse reduction of B-cell subpopulations. This was associated with the down-regulation of BAFF receptor in transitional B cells. The latter can, in part, contribute to B-cell lymphopenia by promoting resistance to the biological actions of BAFF that is a potent B-cell differentiation and survival factor.