Effect of HDL and atherogenic lipoproteins on formation of O2- and renin release in juxtaglomerular cells

Serum lipoprotein(a) levels and diabetic nephropathy among Japanese patients with type 2 diabetes mellitus

AIMS

We aimed to evaluate the association between serum lipoprotein(a) [Lp(a)] levels and diabetic nephropathy among Japanese patients with type 2 diabetes mellitus.

METHODS

This study included 581 patients with type 2 diabetes mellitus. Serum Lp(a) levels were divided into four groups; the cut-off points were at the 30th, 60th, and 90th percentile values on the basis of the distribution for all subjects. Diabetic nephropathy was defined as present when the urinary albumin-creatinine ratio was ≥33.9mg/mmol creatinine and/or the estimated glomerular filtration rate was <30ml/min/1.72m(2). Adjustment was made for age, sex, body mass index, hemoglobin A1c, duration of diabetes mellitus, current drinking, current smoking, hypertension, dyslipidemia, coronary heart disease, and stroke.

RESULTS

Higher serum Lp(a) levels were significantly associated with a higher prevalence of diabetic nephropathy: the adjusted odds ratios (95% confidence intervals) for diabetic nephropathy in relation to serum Lp(a) levels of ≤6, 7-15, 16-38, and ≥39mg/dl were 1.00 (reference), 2.74 (1.08-7.00), 3.31 (1.28-8.54), and 4.80 (1.57-14.60), respectively (P for trend=0.004).

CONCLUSIONS

The results suggest that serum Lp(a) levels may be positively associated with diabetic nephropathy among Japanese patients with type 2 diabetes mellitus.

Hydrogen sulphide and tempol treatments improve the blood pressure and renal excretory responses in spontaneously hypertensive rats

Oxidative stress and suppressed H2S production lead to increased renal vascular resistance, disturbed glomerular hemodynamics, and abnormal renal sodium and water handling, contribute to the pathogenesis and maintenance of essential hypertension in man and the spontaneously hypertensive rat. This study investigated the impact of H2S and tempol alone and in combination on blood pressure and renal hemodynamics and excretory functions in the SHR. Groups of WKY rats or SHR (n=6) were treated for 4 weeks either as controls or received NaHS (SHR+NaHS), tempol (SHR+Tempol), or NaHS plus tempol (SHR+NaHS +Tempol). Metabolic studies were performed on days 0, 14, and 28, thereafter animals were anaesthetized to measure renal hemodynamics and plasma oxidative and antioxidant markers. SHR control rats had higher mean arterial blood pressure (140.0 ± 2 vs. 100.0 ± 3 mmHg), lower plasma and urinary H2S, creatinine clearance, urine flow rate and urinary sodium excretion, and oxidative stress compared to WKY (all p<0.05). Treatment either with NaHS or with tempol alone decreased blood pressure and oxidative stress and improved renal hemodynamic and excretory function compared to untreated SHR. Combined NaHS and tempol therapy in SHRs caused larger decreases in blood pressure (∼20-22% vs. ∼11-15% and ∼10-14%), increases in creatinine clearance, urinary sodium excretion and fractional sodium excretion and up-regulated the antioxidant status compared to each agent alone (all p<0.05). These findings demonstrated that H2S and tempol together resulted in greater reductions in blood pressure and normalization of kidney function compared with either compound alone.

Differential dyslipidemia associated with albuminuria in type 2 diabetic patients in Taiwan

BACKGROUND

This study evaluated the lipid abnormalities associated with different stages of albuminuria in type 2 diabetic patients.

METHODS AND RESULTS

A total of 549 patients (245 men and 304 women) with mean age of 63.4 were studied. Normoalbuminuria (n=251), microalbuminuria (n=242) and macroalbuminuria (n=56) were defined as albumin-to-creatinine ratio of < 30, 30-299 and > or = 300 microg/mg, respectively. Lipid parameters included total cholesterol, triglyceride (TG), high- and low-density lipoprotein (LDL) cholesterol, apolipoproteins A1 and B (ApoB), and lipoprotein(a) [Lp(a)]. Results showed that ApoB differed significantly (p<0.05) between normoalbuminuria and microalbuminuria/macroalbuminuria and Ln[Lp(a)] differed between normoalbuminuria/microalbuminuria and macroalbuminuria. Ln(TG) increased progressively with increasing albuminuria. In multivariate logistic regression analyses, only ApoB showed significant odds ratio (95% confidence interval) for microalbuminuria: 1.013 (1.004-1.022); and both ln(TG) and ln[Lp(a)] were significant for macroalbuminuria [respective odds ratios: 1.995 (1.010-3.938) and 1.708 (1.200-2.430)].

CONCLUSIONS

A differential dyslipidemia is observed for microalbuminuria and macroalbuminuria. Apo(B) and Lp(a) increase at the stages of microalbuminuria and macroalbuminuria, respectively. However, TG increases significantly throughout the three stages of albuminuria.

Impact of oxidized low density lipoprotein on vascular cells

Oxidized LDL (OxLDL) is a proatherogenic lipoprotein, accumulating in the vascular wall and contributing to the pathogenesis of vascular dysfunction early in the development of atherosclerosis. Enhanced serum levels of OxLDL, as well as antibodies against its epitopes, are predictive for endothelial dysfunction and coronary heart disease. While enhanced oxidative stress is one factor triggering formation of OxLDL, OxLDL itself has been identified as a potent stimulus for vascular oxygen radical formation, causing a vicious circle. OxLDL-induced O(2)(-) formation, largely through activation of NADPH oxidase, but also through uncoupling of endothelial NO-synthase and through direct O(2)(-) release, leads to endothelial dysfunction. Furthermore, OxLDL-induced O(2)(-) formation has a strong impact on tissue remodeling, resulting in either cell growth - proliferation or hyperplasia - or apoptotic cell death. The effect of OxLDL on cell cycle regulation is mediated by activation of the small GTPase RhoA and consequent regulation of p27(KIP1), a key enzyme of the cell cycle. In addition, OxLDL-induced activation of RhoA sensitizes the contractile apparatus of the vessel wall, enhancing the contractile tonus and favoring vasospasm. Thus, through a variety of mechanisms, OxLDL importantly contributes to vascular dysfunction and remodeling.

Antihypertensive response to prolonged tempol in the spontaneously hypertensive rat

INTRODUCTION

Tempol is a permeant nitroxide superoxide dismutase (SOD) mimetic that lowers mean arterial pressure (MAP) in spontaneously hypertensive rats (SHRs). We investigated the hypothesis that the antihypertensive response entails a negative salt balance, blunting of plasma renin activity (PRA), endothelin-1 (ET-1), or catecholamines or correction of oxidative stress as indexed by 8-isoprostane prostaglandin F(2alpha) (PGF(2alpha)) (8-Iso).

METHODS

Groups (N= 6 to 8) of SHRs were infused for 2 weeks with vehicle or tempol (200 nmol/kg/min) or given tempol (2 mmol/L) in drinking water.

RESULTS

Tempol infusion reduced the MAP of anesthetized SHRs (150 +/- 5 vs. 126 +/- 6 mm Hg) (P < 0.005). Oral tempol did not change the heart rate but reduced the MAP of conscious SHRs (-23 +/- 6 mm Hg) (P < 0.01) but not Wistar-Kyoto (WKY) rats. Tempol infusion increased the PRA (2.2 +/- 0.2 vs. 5.0 +/- 0.9 ng/mL/hour) (P < 0.005), did not change excretion of nitric oxide (NO) [NO(2)+ NO(3) (NOx)], ET-1, or catecholamines but reduced excretion of 8-Iso (13.2 +/- 1.4 vs. 9.6 +/- 0.9 ng/24 hours; P < 0.01). Cumulative Na(+) balance and gain in body weight were unaltered by tempol infusion. Tempol prevented a rise in MAP with high salt intake.

CONCLUSION

Tempol corrects hypertension without a compensatory sympathoadrenal activation or salt retention. The response is independent of nitric oxide, endothelin, or catecholamines and occurs despite increased PRA. It is accompanied by a reduction in oxidative stress and is maintained during increased salt intake.

Lipid abnormalities and renal disease: is dyslipidemia a predictor of progression of renal disease?

Dyslipidemia is a cardiovascular disease (CVD) risk factor that is associated with enhanced atherosclerosis and plaque instability. Renal insufficiency is associated with abnormalities in lipoprotein metabolism in both the early and the advanced stages of chronic renal failure. These include alterations in apolipoprotein A (apo A)- and B- containing lipoproteins, high-density lipoproteins, and triglycerides. In animal models, these alterations in lipid metabolism and action lead to macrophage activation and infiltration in the kidney with resultant tubulointerstitial and endothelial cell injury. Limited data in humans suggest that, in addition to contributing to CVD, dyslipidemia may be a risk factor for the progression of renal disease. The effects of dyslipidemia on the kidney are mainly observed in those with other risk factors for renal disease progression such as hypertension, diabetes, and proteinuria. Renal disease is a strong risk factor for CVD and African Americans have high rates of renal disease. Therefore, examining the effects of dyslipidemia on the development or progression or renal disease will be an important question for the Jackson Heart Study and is the topic of this review.

Oxidative modification of low-density lipoproteins and the outcome of renal allografts at 1 1/2 years

BACKGROUND

Previous studies reported a significant association between hyperlipidemia of the recipient and chronic allograft nephropathy (CAN). However, the nature and the pathogenic mechanism of circulating lipid abnormalities in CAN remain unclear.

METHODS

In a prospective study of 50 consecutive adult recipients of a cadaveric renal allograft, we investigated the impact of lipid abnormalities on the outcome of the graft at 1 1/2 years. Besides morphometric analysis of implantation and protocol biopsies, clinical and biochemical variables were studied at three-month intervals. Plasma concentrations of oxidized low-density lipoprotein (OxLDL) were determined by means of enzyme-linked immunosorbent assay. Immunohistochemical staining for OxLDL and macrophages was performed on paired renal biopsies. Study end points were the fractional interstitial volume and the 24-hour creatinine clearance at 11/2 years.

RESULTS

High-density lipoprotein (HDL) cholesterol of the recipient < or =47 mg/dL was a risk factor for the functional (RR = 1.56; 95% CI, 0.978 to 2.497) and the morphological (RR = 2.75; 95% CI, 1.075 to 7.037) outcome of the graft, mainly in patients without acute rejection (RR = 2.03; 95% CI, 1.13 to 3.65, and RR = 4.67; 95% CI, 1.172 to 18.582, respectively). Interstitial accumulation of OxLDL was inversely associated with HDL cholesterol (R = -0.476, P = 0.019), and was associated with a higher density of tubulointerstitial macrophages (R = 0.656, P = 0.001) and a higher fractional interstitial volume at 11/2 years (P = 0.049).

CONCLUSION

Decreased HDL cholesterol levels of the recipient adversely affect the outcome of renal allografts through the accumulation of OxLDL in the renal interstitium of the graft. Interstitial accumulation of OxLDL was associated with the presence of macrophages and the development of interstitial fibrosis.

Oxidized LDL suppresses NF-kappaB and overcomes protection from apoptosis in activated endothelial cells

Atherosclerosis is a chronic inflammatory disease associated with enhanced apoptotic cell death in vascular cells, partly induced by oxidized low-density lipoprotein (OxLDL). However, proinflammatory stimuli such as lipopolysaccharide (LPS) or tumor necrosis factor-alpha (TNF-alpha) activate endothelial cells (EC) and inhibit apoptosis through induction of nuclear factor kappaB (NF-kappaB)-dependent genes. This study therefore investigated whether OxLDL or its component, lysophosphatidylcholine (LPC), interacts with the effect of LPS or TNF-alpha on cell survival. Human EC were incubated with LPS, TNF-alpha, OxLDL, or LPC alone or in combinations. OxLDL (100 to 200 microg/ml) and LPC (100 to 300 microM) induced apoptosis dose-dependently. LPS and TNF-alpha had no effect on cell survival in the presence or absence of OxLDL or LPC. LPS and TNF-alpha both induced the antiapoptotic gene A20, whereas OxLDL and LPC suppressed its induction. Expression of A20 is regulated by NF-kappaB. OxLDL and LPC dose-dependently suppressed NF-kappaB activity. For functional analysis, bovine EC were transfected with A20 encoding expression constructs in sense and antisense orientation. Bovine EC that overexpressed A20 were protected against OxLDL-induced apoptosis, whereas expression of antisense A20 rendered cells more sensitive to OxLDL. These results suggest that OxLDL not only induces cell death, as has been shown before, but also compromises antiapoptotic protection of activated EC. OxLDL sensitizes EC to apoptotic triggers by interfering with the induction of A20 during the inflammatory response seen in atherosclerotic lesions. This inhibition is based on repression of NF-kappaB activation. The effect may be caused by the OxLDL component LPC.

Oxidant stress in hemodialysis: prevention and treatment strategies

Oxidant stress has been implicated in a number of pathologies associated with uremia and hemodialysis. These patients have an increased incidence of cardiovascular disease, amyloidosis associated with protein modification, and notable changes in both function and structure of many cellular components. Oxidative reactions most frequently involving free radical intermediates play an important role in these processes and participate both directly and indirectly by further amplification of the inflammatory responses or in activation of signaling cascades mediating proliferation, differentiation, and cell death. Proteins and lipids are susceptible to oxidative degradation. These changes can ultimately alter important structural and functional characteristics and lead to pathological changes. This article addresses some of the diverse mechanisms and pathways involved in these changes, and suggests new therapeutic strategies in preventing oxidative damage.

CyA and OxLDL cause endothelial dysfunction in isolated arteries through endothelin-mediated stimulation of O(2)(-) formation

BACKGROUND

Cyclosporin A (CyA) and oxidized low-density lipoprotein (OxLDL) cause endothelial dysfunction, partly through stimulation of O(2)(-) formation (which can inactivate nitric oxide). We investigated whether CyA and OxLDL potentiate their influence on oxidative stress, whether endothelin (ET) is a mediator of CyA- and OxLDL-induced O(2)(-) formation, and whether enhanced oxidative stress results in further attenuation of endothelium-dependent vasodilation.

METHODS AND RESULTS

Human LDL was oxidized by Cu(++). O(2)(-) formation of isolated rat aortic rings was measured using a chemiluminescence assay. Incubation (60 min) of aortic rings with CyA (10 ng-10 microg/ml) or with OxLDL (300 microg/ml) caused a significant, dosedependent increase of the basal O(2)(-) formation. Pretreatment of the aortic rings with CyA (10 ng/ml) further enhanced the OxLDL-induced O(2)(-) formation by factor 1.9. The enhancement of the OxLDL-induced stimulation of O(2)(-) formation by CyA could be completely blocked by BQ123, a selective endothelin-1 (ET-1) receptor antagonist. Likewise, exogenously applied ET-1 (1 nM) potentiated the OxLDL-induced O(2)(-) formation by factor 1.8. Endothelium-dependent dilation was measured in isolated rings of rabbit aorta superfused with physiological salt solution in an organ bath. Incubation of the aortic rings with CyA (10 microg/ml, 60 min) or with OxLDL (300 microg/ml, 60 min) alone did not attenuate endothelium-dependent dilations. However, coincubation of the aortic rings with CyA+OxLDL in the presence of diethyl-dithio-carbamate, an inhibitor of the endogenous superoxide dismutase, caused a 60% inhibition of acetylcholine-induced dilator responses.

CONCLUSIONS

Coincubation of isolated aortic rings with CyA and OxLDL causes a potent enhancement of vascular O(2)(-) formation. ET-1 seems to be mediator of the CyA-induced O(2)(-) formation. Enhanced oxidative stress results in further attenuation of endothelium dependent vasodilation.

Studies of renal injury III: lipid-induced nephropathy in type II diabetes

Studies of renal injury III: Lipid-induced nephropathy in type II diabetes.

BACKGROUND

Nephrotoxicity from elevated circulating lipids occurs in experimental and clinical situations. We tested the hypothesis that lipid-induced nephropathy causes advanced renal failure in rats with type II diabetes and dyslipidemia.

METHODS

First generation (F1) hybrid rats derived from the spontaneous hypertensive heart failure rat (SHHF/Gmi-fa) and the LA/NIH-corpulent rat (LA/N-fa) were studied for 41 weeks while being on specific diets. Group 1 (14 rats) ingested 11.5% protein, 47.9% fat, and 40.6% carbohydrate. Group 2 (8 rats) ingested 26.9% protein, 16.7% animal fat, and 56.4% carbohydrate, and group 3 (20 rats) ingested 20.2% protein, 40.4% soy and coconut oil, and 39.4% carbohydrate.

RESULTS

Hyperglycemia was more severe in rat groups 1 and 2 than in group 3. In contrast, circulating cholesterol and hydroperoxide levels were highest in group 3, intermediate in group 2, and lowest in group 1. Group 3 had severe renal failure secondary to glomerulosclerosis and tubulointerstitial disease, with striking deposition of the lipid peroxidation stress biomarker 4-hydroxynonenal in glomeruli and renal microvessels. Moreover, in group 3, increased arterial wall thickness also connoted vascular injury. In contrast, the glycoxidation stress biomarkers pentosidine and carboxymethyl-lysine were preferentially localized to renal tubules of hyperglycemic rats in groups 1 and 2 and did not segregate with the most severe renal injury. Glomerular and interstitial fibrosis was accompanied by proportional increases in renal transforming growth factor-beta1 levels, which were threefold higher in the hypercholesterolemic rats of group 3 than in the hyperglycemic rats of group 1.

CONCLUSIONS

Acquisition of non-nodular glomerular sclerosis and tubulointerstitial disease is dependent on lipoxidation stress in rats with type II diabetes. On the other hand, in the absence of hypercholesterolemia, prolonged glycoxidation stress does not appear to be uniquely nephrotoxic.

Atherogenic lipoproteins, oxidative stress, and cell death

BACKGROUND

Glomerulosclerosis and atherosclerosis are chronic inflammatory processes that may be influenced by oxidized lipoproteins, oxidized low-density lipoproteins (oxLDL), and oxidized lipoprotein(a) [oxLp(a)]. We hypothesize that these lipoproteins contribute to the development of glomerulosclerosis and atherosclerosis through the induction of oxidative stress, which influences cell viability. We therefore determined the impact of oxLDL and oxLp(a) on O2- formation and on necrotic and apoptotic cell death in vascular and glomerular cells.

METHODS

The impact of human LDL and Lp(a) (oxidized with CuSO4) on O2- formation (detected with a chemiluminescence method), apoptosis, and necrosis (determined with the annexin assay) was studied in cultured human umbilical vein endothelial cells (ECs) and in cultured human mesangial cells (MCs).

RESULTS

O2- formation was increased by 10 micrograms/ml oxLDL (by factor 2.5 in ECs) and by 5 micrograms/ml oxLp(a) (by factor 3.5 in ECs). OxLDL and oxLp(a) both significantly and dose-dependently increased the rate of apoptotic cell death in ECs and in MCs, with oxLp(a) being the more potent stimulus that also caused necrosis. The induction of apoptosis by oxLDL and oxLp(a) in ECs and MCs was enhanced by inhibition of the endogenous superoxide dismutase (SOD) with diethyl-dithio-carbamate and was blunted by the antioxidants N-acetylcysteine, vitamin C + E, SOD, and catalase, suggesting that oxidative stress was the stimulus for apoptosis.

CONCLUSIONS

These data suggest that oxLDL and oxLp(a) contribute to inflammation by stimulating O2- formation, leading to apoptotic cell death in the vascular wall and in the glomerulus. The oxidized lipoproteins may thereby influence the pathogenesis of atherosclerosis and glomerulosclerosis.

Lp(a) and LDL induce apoptosis in human endothelial cells and in rabbit aorta: role of oxidative stress

BACKGROUND

Atherogenic lipoproteins cause injury to the vascular wall in the early phase of atherogenesis. We assessed the effects of native (nLDL) and oxidized (oxLDL) low-density lipoprotein (LDL) and lipoprotein (a) [Lp(a)] on O2- formation and cell death in cultured human umbilical vein endothelial cells (HUVECs) and rabbit aorta (RA).

METHODS AND RESULTS

O2- formation of HUVECs and RA segments was not influenced by nLDL, but was dose dependently increased by oxLDL and was moderately increased by nLp(a). oxLp(a) was the most potent stimulus for O2- formation, increasing it in HUVECs by 356% at 5 micrograms/ml and in RA by 294% at 100 micrograms/ml. Apoptosis was detected by DNA fragmentation and Annexin assay in HUVECs and by TUNEL staining in RA. Incubation of HUVECs and RA with oxLDL, but not nLDL, dose and time dependently induced apoptosis with only a minimal effect on necrosis. nLp(a) elicited a small but significant effect on apoptosis, whereas oxLp(a) induced apoptosis more potently than oxLDL in HUVECs and RA and caused necrotic cell death in HUVECs. Induction of apoptosis by oxLDL and oxLp(a) in RA was enhanced by the superoxide dismutase (SOD) inhibitor, diethyl-dithio-carbamate, and was blunted by SOD and catalase in HUVECs and RA, suggesting that O2- formation was involved. The concentration of lysophosphatidylcholine, a lipoprotein oxidation product and stimulus for O2- formation, was significantly enhanced by factor 5 in oxLDL and by factor 7 in oxLp(a) compared with native lipoproteins.

CONCLUSION

Atherogenic lipoproteins stimulate O2- formation and induction of apoptosis in HUVECs and RA, and may thereby influence the pathogenesis of atherosclerosis.

Glyc-oxidized LDL impair endothelial function more potently than oxidized LDL: role of enhanced oxidative stress

Hypercholesterolemia is associated with impairment of endothelial function due to increased levels of LDL. In diabetic patients, however, attenuation of endothelial function occurs even under normocholesterolemic conditions. Here we assessed whether glycation of LDL potentiates their influence on endothelial function, with particular emphasis on the oxidizability of LDL and the role of O2-. Human LDL was glycated by dialyzation for 7 days against buffer containing 200 mmol/l glucose, or sham-treated without glucose, and oxidized by incubation with Cu2+. Glycation significantly enhanced the oxidizability of LDL, as detected by diene formation and by electrophoretic mobility (27.5 mm for oxidized LDL vs. 34 mm for oxidized glycated LDL at 20 h of oxidation). Isolated rings of rabbit aorta were superfused with physiological salt solution, and isometric tension was recorded. Incubation of the aortic rings with sham-treated or with glycated LDL, not oxidized, had no influence on acetylcholine-induced, endothelium-dependent relaxation. Exposure of the aortic rings to oxidized non-glycated LDL caused a significant inhibition (30% at 1 microM acetylcholine) of the endothelium-dependent relaxation only in the presence of diethyl-dithiocarbamate (DDC), an inhibitor of the endogenous superoxide dismutase (SOD). Incubation of aortic rings with oxidized glycated LDL attenuated endothelium-dependent relaxation even in the absence of DDC (by 31% at 1 microM acetylcholine). The presence of DDC potentiated the inhibition of relaxation (65% inhibition at 1 microM acetylcholine), and co-incubation with exogenous SOD and catalase prevented the inhibition of relaxation, indicating a mediator role of O2-. Endothelium-independent relaxation induced by forskolin was unaffected by any of the lipoproteins. Using a chemiluminescence assay, significantly increased O2- production of aortic rings pretreated with oxidized glycated LDL (4101 +/- 360 counts/s) in comparison to control rings (753 +/- 81 counts/s) or arteries pretreated with oxidized non-glycated LDL (2358 +/- 169 counts/s) could be detected, suggesting that enhanced NO-inactivation by O2- could be the underlying mechanism for the stronger impairment of endothelium-dependent dilations by oxidized glycated LDL. Glycation increases the oxidizability of LDL and potentiates its endothelium-damaging influence. The likely mechanism for attenuation of endothelium-dependent dilations is increased formation of O2-, resulting in inactivation of nitric oxide. This mechanism may play an important role in diabetic patients and may contribute to disturbed organ perfusion.

Serum lipoprotein (a) concentration in patients with nephrotic syndrome and its clinical implication

Serum lipoprotein(a) [Lp(a)] concentration was determined in 42 patients with primary nephrotic syndrome (NS) and the relationships between Lp (a) and plasma lipids, apolipoproteins, serum creatinine (Scr), albumin, urinary proteins (Upro) were also analyzed. The results showed that: (1) serum Lp(a) concentrations in the patients with NS were higher than those in healthy controls; (2) the levels of serum Lp(a) were correlated positively with total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), very low density lipoprotein cholesterol (VLDL-C), apolipoprotein B (Apo-B), Upros (Upro). It is concluded that the NS patients had the potential risk of suffering from coronary artery disease, glomerular sclerosis and thrombosis. The remission of NS may partially decrease the serum Lp(a) levels. Further studies are needed to explore the prevention and treatment of dislipedemia in patients with NS.