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Xu Q, Cao S, Rajapakse S, Matsubara JA. Understanding AMD by analogy: systematic review of lipid-related common pathogenic mechanisms in AMD, AD, AS and GN. Lipids Health Dis 2018; 17:3. [PMID: 29301530 PMCID: PMC5755337 DOI: 10.1186/s12944-017-0647-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Accepted: 12/17/2017] [Indexed: 12/15/2022] Open
Abstract
RATIONALE Age-related macular degeneration (AMD) is one of the leading causes of blindness among the elderly. Due to its complex etiology, current treatments have been insufficient. Previous studies reveal three systems closely involved in AMD pathogenesis: lipid metabolism, oxidation and inflammation. These systems are also involved in Alzheimer's disease, atherosclerosis and glomerulonephritis. Understanding commonalities of these four diseases may provide insight into AMD etiology. OBJECTIVES To understand AMD pathogenesis by analogy and suggest ideas for future research, this study summarizes main commonalities in disease pathogenesis of AMD, Alzheimer's disease, atherosclerosis and glomerulonephritis. METHODS Articles were identified through PubMed, Ovid Medline and Google Scholar. We summarized the common findings and synthesized critical differences. RESULTS Oxidation, lipid deposition, complement activation, and macrophage recruitment are involved in all four diseases shown by genetic, molecular, animal and human studies. Shared genetic variations further strengthen their connection. Potential areas for future research are suggested throughout the review. CONCLUSIONS The four diseases share many steps of an overall framework of pathogenesis. Various oxidative sources cause oxidative stress. Oxidized lipids and related molecules accumulate and lead to complement activation, macrophage recruitment and pathology. Investigations that arise under this structure may aid us to better understand AMD pathology.
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Affiliation(s)
- Qinyuan Xu
- Department of Ophthalmology and Visual Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 3N9 Canada
| | - Sijia Cao
- Department of Ophthalmology and Visual Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 3N9 Canada
| | - Sanjeeva Rajapakse
- Department of Ophthalmology and Visual Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 3N9 Canada
| | - Joanne A. Matsubara
- Department of Ophthalmology and Visual Sciences, Faculty of Medicine, University of British Columbia, Vancouver, BC V5Z 3N9 Canada
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Pei Z, Okura T, Nagao T, Enomoto D, Kukida M, Tanino A, Miyoshi KI, Kurata M, Higaki J. Osteopontin deficiency reduces kidney damage from hypercholesterolemia in Apolipoprotein E-deficient mice. Sci Rep 2016; 6:28882. [PMID: 27353458 PMCID: PMC4926090 DOI: 10.1038/srep28882] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Accepted: 05/17/2016] [Indexed: 02/06/2023] Open
Abstract
Hypercholesterolemia is a well-established risk factor for kidney injury, which can lead to chronic kidney disease (CKD). Osteopontin (OPN) has been implicated in the pathology of several renal conditions. This study was to evaluate the effects of OPN on hypercholesterolemia induced renal dysfunction. Eight-week-old male mice were divided into 4 groups: apolipoprotein E knockout (ApoE−/−) and ApoE/OPN knockout (ApoE−/−/OPN−/−) mice fed a normal diet (ND) or high cholesterol diet (HD). After 4 weeks, Periodic acid-Schiff (PAS) and oil red O staining revealed excessive lipid deposition in the glomeruli of ApoE−/−HD mice, however, significantly suppressed in ApoE−/−/OPN−/−HD mice. Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) expression was lower in the glomeruli of ApoE−/−/OPN−/−HD mice than ApoE−/−HD mice. In vitro study, primary mesangial cells were incubated with recombinant mouse OPN (rmOPN). RmOPN induced LOX-1 mRNA and protein expression in primary mesangial cells. Pre-treatment with an ERK inhibitor suppressed the LOX-1 gene expression induced by rmOPN. These results indicate that OPN contributes to kidney damage in hypercholesterolemia and suggest that inhibition of OPN may provide a potential therapeutic target for the prevention of hypercholesterolemia.
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Affiliation(s)
- Zouwei Pei
- Department of Cardiology, Pulmonology, Hypertension and Nephrology, Ehime University Graduate School of Medicine, Ehime, Japan
| | - Takafumi Okura
- Department of Cardiology, Pulmonology, Hypertension and Nephrology, Ehime University Graduate School of Medicine, Ehime, Japan
| | - Tomoaki Nagao
- Department of Cardiology, Pulmonology, Hypertension and Nephrology, Ehime University Graduate School of Medicine, Ehime, Japan
| | - Daijiro Enomoto
- Department of Cardiology, Pulmonology, Hypertension and Nephrology, Ehime University Graduate School of Medicine, Ehime, Japan
| | - Masayoshi Kukida
- Department of Cardiology, Pulmonology, Hypertension and Nephrology, Ehime University Graduate School of Medicine, Ehime, Japan
| | - Akiko Tanino
- Department of Cardiology, Pulmonology, Hypertension and Nephrology, Ehime University Graduate School of Medicine, Ehime, Japan
| | - Ken-Ichi Miyoshi
- Department of Cardiology, Pulmonology, Hypertension and Nephrology, Ehime University Graduate School of Medicine, Ehime, Japan
| | - Mie Kurata
- Department of Pathology, Ehime University Proteo-Science Center and Graduate School of Medicine, Ehime, Japan
| | - Jitsuo Higaki
- Department of Cardiology, Pulmonology, Hypertension and Nephrology, Ehime University Graduate School of Medicine, Ehime, Japan
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Rashid Khan M, Ahsan H, Siddiqui S, Siddiqui WA. Tocotrienols have a nephroprotective action against lipid-induced chronic renal dysfunction in rats. Ren Fail 2014; 37:136-43. [DOI: 10.3109/0886022x.2014.959433] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Bianchi S, Bigazzi R, Campese VM. Intensive Versus Conventional Therapy to Slow the Progression of Idiopathic Glomerular Diseases. Am J Kidney Dis 2010; 55:671-81. [DOI: 10.1053/j.ajkd.2009.11.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Accepted: 11/03/2009] [Indexed: 12/30/2022]
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6
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Kassimatis TI, Konstantinopoulos PA. The role of statins in chronic kidney disease (CKD): Friend or foe? Pharmacol Ther 2009; 122:312-23. [DOI: 10.1016/j.pharmthera.2009.03.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2009] [Accepted: 03/20/2009] [Indexed: 01/11/2023]
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7
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Effects of HMG-CoA reductase inhibitors (statins) on progression of kidney disease. Kidney Int 2008; 74:571-6. [DOI: 10.1038/ki.2008.231] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Fujita H, Koshimura J, Sato T, Miura T, Sasaki H, Morii T, Narita T, Kakei M, Ito S, Yamada Y. Effects of long-term pravastatin treatment on serum and urinary monocyte chemoattractant protein-1 levels and renal function in type 2 diabetic patients with normoalbuminuria. Ren Fail 2008; 29:791-6. [PMID: 17994445 DOI: 10.1080/08860220701543056] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
To explore the renoprotective and anti-inflammatory effects of pravastatin, we analyzed the changes in renal function and urinary monocyte chemoattractant protein-1 (MCP-1) level as a renal tubulointerstitial inflammatory biomarker and serum MCP-1 level as a systemic inflammatory biomarker following the introduction of treatment with 10 mg/day of pravastatin in 10 hyperlipidemic type 2 diabetic patients with normoalbuminuria. Twelve months of the pravastatin treatment did not affect urinary levels of albumin, transferrin, N-acetylglucosaminidase, or MCP-1 in the hyperlipidemic diabetic patients, whereas the treatment significantly reduced serum levels of MCP-1 in the patients. The pravastatin treatment effectively lowered low-density lipoprotein cholesterol (LDL-C) levels in the hyperlipidemic diabetic patients to levels nearly to those in 11 non-hyperlipidemic type 2 diabetic patients with normoalbuminuria. Interestingly, serum MCP-1 levels were significantly lower in the hyperlipidemic patients treated with pravastatin than in the non-hyperlipidemic patients. No significant correlation was observed between serum LDL-C and MCP-1 levels in all the data in the hyperlipidemic patients before and after the pravastatin treatment and in the non-hyperlipidemic patients. These results collectively indicate that pravastatin may ameliorate systemic vascular inflammation rather than local renal inflammation in hyperlipidemic type 2 diabetic patients with normoalbuminuria, independent of its cholesterol-lowering effects.
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Affiliation(s)
- Hiroki Fujita
- Division of Endocrinology, Metabolism and Geriatric Medicine, Department of Internal Medicine, Akita University School of Medicine, Akita, Japan.
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Stephany BR, Alao B, Budev M, Boumitri M, Poggio ED. Hyperlipidemia is associated with accelerated chronic kidney disease progression after lung transplantation. Am J Transplant 2007; 7:2553-60. [PMID: 17868063 DOI: 10.1111/j.1600-6143.2007.01968.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Hyperlipidemia is associated with faster progression of chronic kidney disease (CKD) in the general public. We sought to investigate this association after lung transplantation. Data was retrospectively collected on 230 lung recipients transplanted between January 1997 and December 2003. Estimated glomerular filtration rates (eGFR) and lipid levels were recorded at regular intervals posttransplant. Independent associations between lipid levels early posttransplant and pertinent renal endpoints were investigated. Baseline LDL was 110 +/- 35 mg/dL and remained unchanged at 6 months. A faster decline in eGFR was seen in those with 6 month LDLs > versus < the mean level of 110 mg/dL (p = 0.05). By 6 months posttransplant eGFRs were lower in the 6 month LDL > versus < 110 mg/dL group (53 +/- 23 vs. 62 +/- 29 mL/min/1.73 m2, p = 0.01), a difference that persisted at 60 months (39 +/- 24 vs. 73 +/- 57 mL/min/1.73 m2, p = 0.05). On univariate analysis, a 6 month LDL in the highest quartile, i.e. >140 mg/dL, predicted faster progression to CKD, defined as declining to an eGFR < 30 mL/min/1.73 m2 (HR 1.5, p = 0.01). This finding persisted in the multivariate Cox-proportional model (HR 1.4, p = 0.02). Hyperlipidemia predicts faster decline in renal function after lung transplant. Prospective trials are needed to confirm this finding.
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Affiliation(s)
- B R Stephany
- Department of Nephrology and Hypertension, Cleveland Clinic, Cleveland, OH, USA.
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Vaziri ND. Dyslipidemia of chronic renal failure: the nature, mechanisms, and potential consequences. Am J Physiol Renal Physiol 2006; 290:F262-72. [PMID: 16403839 DOI: 10.1152/ajprenal.00099.2005] [Citation(s) in RCA: 307] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Chronic renal failure (CRF) results in profound lipid disorders, which stem largely from dysregulation of high-density lipoprotein (HDL) and triglyceride-rich lipoprotein metabolism. Specifically, maturation of HDL is impaired and its composition is altered in CRF. In addition, clearance of triglyceride-rich lipoproteins and their atherogenic remnants is impaired, their composition is altered, and their plasma concentrations are elevated in CRF. Impaired maturation of HDL in CRF is primarily due to downregulation of lecithin-cholesterol acyltransferase (LCAT) and, to a lesser extent, increased plasma cholesteryl ester transfer protein (CETP). Triglyceride enrichment of HDL in CRF is primarily due to hepatic lipase deficiency and elevated CETP activity. The CRF-induced hypertriglyceridemia, abnormal composition, and impaired clearance of triglyceride-rich lipoproteins and their remnants are primarily due to downregulation of lipoprotein lipase, hepatic lipase, and the very-low-density lipoprotein receptor, as well as, upregulation of hepatic acyl-CoA cholesterol acyltransferase (ACAT). In addition, impaired HDL metabolism contributes to the disturbances of triglyceride-rich lipoprotein metabolism. These abnormalities are compounded by downregulation of apolipoproteins apoA-I, apoA-II, and apoC-II in CRF. Together, these abnormalities may contribute to the risk of arteriosclerotic cardiovascular disease and may adversely affect progression of renal disease and energy metabolism in CRF.
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Affiliation(s)
- N D Vaziri
- Division of Nephrology and Hypertension, UCI Medical Center, Orange, CA 92868, USA.
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Epstein M, Campese VM. Pleiotropic effects of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitors on renal function. Am J Kidney Dis 2005; 45:2-14. [PMID: 15696439 DOI: 10.1053/j.ajkd.2004.08.040] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Pleiotropic, or non-lipid-dependent, effects mediated by 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) have important clinical implications for the cardiovascular (CV) system. Atherosclerosis is an inflammatory process accompanied by increases in levels of plasma inflammatory markers and accumulation of immune cells within atherosclerotic plaques. Statins not only decrease serum lipid levels, but also inhibit signaling molecules at several points in inflammatory pathways. The anti-inflammatory effects and improved endothelial function associated with statin therapy are thought to be partly responsible for the reduction in CV morbidity and mortality. In analogy, patients with chronic kidney disease administered statins for CV risk reduction show evidence of improved renal function. However, whether statins confer similar protective benefits on the kidney has not been established. Several lines of evidence suggest that similar etiologic and pathological processes may be involved in CV and chronic kidney diseases. If inflammation and functional changes in the renovascular endothelium contribute to the progression of kidney disease, statins are likely to be effective in the treatment of renal disease. In this review, we critically consider emerging data indicating that statins may modulate renal function by altering the inflammatory response of the kidney and renal vasculature to dyslipidemia. Whether the amelioration of renal function by statins is separable from the lipid-lowering effects of these drugs still remains to be delineated. Other questions that remain to be addressed and issues that should be investigated also are presented.
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Affiliation(s)
- Murray Epstein
- Department of Medicine, Division of Nephrology and Hypertension, University of Miami, Miami, FL, USA.
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Raj DSC, Lim G, Levi M, Qualls C, Jain SK. Advanced glycation end products and oxidative stress are increased in chronic allograft nephropathy. Am J Kidney Dis 2004; 43:154-60. [PMID: 14712439 DOI: 10.1053/j.ajkd.2003.09.021] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
BACKGROUND The histologic picture of chronic allograft nephropathy (CAN) resembles early arteriosclerotic lesion. Oxidative stress and advanced glycation end products (AGES) have been implicated in the pathogenesis of atherosclerosis and progression of renal disease. METHODS The authors serially measured the plasma malonyldialdehyde (MDA), carbonyl protein (CP), pentosidine, and argpyramidine levels in 11 postrenal transplant patients with normal renal function (KPT) and 10 patients with biopsy proven CAN at 1, 3, 6, 9 through 12, and 18 through 24 months posttransplant. Data were also obtained in 16 controls and 13 patients with chronic renal failure (CRF). RESULTS Although serum creatinine, MDA, CP, pentosidine, and argpyrimidine levels decreased during follow-up in KPT, it progressively increased in patients with CAN. The mean serum creatinine level was higher in patients with CRF (3.3 +/- 0.8 mg/dL [291.7 +/- 70.7 micromol/L]) and CAN (2.4 +/- 1.1 mg/dL [212.1 +/- 96.6 micromol/L]) than in controls (1.2 +/- 0.3 mg/dL [105.8 +/- 26.7 micromol/L]) and KPT patients (1.2 +/- 0.2 mg/dL [109.7 +/- 17.7 micromol/L]; P < 0.001). Markers of oxidative stress and AGEs measured at 18 to 24 months posttransplant in patients with CAN were higher than in KPT, controls, and CRF patients. MDA (nmol/mL) was significantly higher in patients with CAN (1.30 +/- 0.30) compared with controls (0.53 +/- 0.12), KPT (0.52 +/- 0.15), and CRF (0.74 +/- 0.27) groups (P < 0.001). Plasma CP (nmol/mg protein) in patients with CAN (4.3 +/- 1.00) was higher than in controls (1.90 +/- 0.69) and KPT (2.62 +/- 1.00) groups at the same time-point (P < 0.001), but comparable with CRF (2.69 +/- 1.20). Plasma pentosidine (pmol/micromol protein) level in patients with CAN (19.69 +/- 5.05) was higher compared with controls (2.49 +/- 0.86), CRF (13.10 +/- 3.68), and KPT (14.32 +/- 6.28) groups (P < 0.001). Plasma argpyrimidine (pmol/10 micromol protein) was higher in patients with CAN (123.8 +/- 17.9) compared with controls (4.81 +/- 1.91), CRF (56.92 +/- 29.67), and KPT (31.1 +/- 11.1; P < 0.001) groups. CONCLUSION Oxidative stress and AGEs are increased in patients with CAN, which cannot be explained by the decline in renal function alone. Oxidative stress and AGEs may be one among the nonimmune mediators of CAN.
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Affiliation(s)
- Dominic S C Raj
- Division of Nephrology, University of New Mexico, Albuquerque, NM, USA.
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Bianchi S, Bigazzi R, Caiazza A, Campese VM. A controlled, prospective study of the effects of atorvastatin on proteinuria and progression of kidney disease. Am J Kidney Dis 2003; 41:565-70. [PMID: 12612979 DOI: 10.1053/ajkd.2003.50140] [Citation(s) in RCA: 253] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
BACKGROUND Chronic kidney diseases, particularly if presenting with significant proteinuria, are commonly associated with substantial alteration of serum lipid levels. Experimental evidence suggests that lipid abnormalities may contribute to the progression of kidney disease. However, studies in humans on the subject are scarce. METHODS In a prospective, controlled open-label study, the authors have evaluated the effects of one-year treatment with atorvastatin, a 3-hydroxy-3-methyglutaryl coenzyme A (HMG-CoA) reductase inhibitor, versus no treatment on proteinuria and progression of kidney disease in 56 patients with chronic kidney disease. Before randomization, all patients had already been treated for one year with angiotensin-converting enzyme (ACE) inhibitors or angiotensin AT1 receptor antagonists (ARBs) and other antihypertensive drugs. RESULTS By the end of one-year treatment, urine protein excretion decreased from 2.2 +/- 0.1 to 1.2 +/- 1.0 g every 24 hours (P < 0.01) in patients treated with atorvastatin in addition to ACE inhibitor and ARBs. By contrast, urinary protein excretion decreased only from 2.0 +/- 0.1 to 1.8 +/- 0.1 g every 24 hours (P value not significant) in patients who did not receive atorvastatin in addition to ACE inhibitor or ARBs. During this time, creatinine clearance decreased only slightly and not significantly (from 51 +/- 1.8 to 49.8 +/- 1.7) in patients treated with atorvastatin. By contrast, during the same period of observation, creatinine clearance decreased from 50 +/- 1.9 to 44.2 +/- 1.6 mL/min (P < 0.01) in patients who did not receive atorvastatin. CONCLUSIONS This study has shown that treatment with atorvastatin in addition to a regimen with ACE inhibitors or ARBs may reduce proteinuria and the rate of progression of kidney disease in patients with chronic kidney disease, proteinuria, and hypercholesterolemia. The benefits appear to occur in addition to those of treatment with ACE inhibitor and ARBs.
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Affiliation(s)
- Stefano Bianchi
- Unitá Operativa Nefrologia, Spedali Riuniti di Livorno, Livorno, Italy
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Fried LF, Forrest KY, Ellis D, Chang Y, Silvers N, Orchard TJ. Lipid modulation in insulin-dependent diabetes mellitus: effect on microvascular outcomes. J Diabetes Complications 2001; 15:113-9. [PMID: 11358679 DOI: 10.1016/s1056-8727(01)00140-4] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Although hyperlipidemia is associated with the development of diabetes complications, the effect of lipid reduction on microvascular complications is unknown. We initiated a 2-year, randomized, double-blinded placebo-controlled pilot trial of simvastatin/diet vs. diet alone in Type 1 diabetic patients without overt nephropathy. Thirty-nine patients with LDL cholesterol 100-160 mg/dl, >10 year duration of diabetes and an albumin excretion rate (AER) <200 microg/min were recruited for study. The primary end-point was change in AER. Secondary end-points were change in ankle-brachial index, progression of retinopathy status, change in vibratory threshold, and development of new clinical neuropathy. Nineteen patients were treated with simvastatin and twenty with placebo. However, because of the lowering of drug initiation levels by the American Diabetes Association, the trial was terminated early with 2 subjects reaching 2 years, 17 reaching 18 months, 36 reaching 1 year, and all 6 months. Simvastatin significantly reduced total cholesterol (mean on treatment 173.4 vs. 191.4, P=.020) and LDL cholesterol (mean on treatment 105.0 vs. 127.7, P<.001). Simvastatin therapy was associated with a slower rise in AER compared to placebo, though the result was not statistically significant (median rate of change/month 0.004 vs. 0.029). There was a trend towards slower progression of neuropathy as measured by vibratory threshold (median change at 1 year 0.03 simvastatin vs. 0.94, P=.07). There was no difference in change in ankle-brachial index, clinical neuropathy status, or retinopathy status. In conclusion, treatment with simvastatin may have a beneficial effect on early nephropathy and diabetic neuropathy, justifying a fully powered trial. However, this would be difficult under current treatment guidelines.
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Affiliation(s)
- L F Fried
- Renal-Electrolyte Division, University of Pittsburgh School of Medicine, 938 Scaife Hall, 3550 Terrace Street, Pittsburgh, PA 15213, USA. lff9+@pitt.edu
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Boyd AC, Abdel-Wahab YH, McKillop AM, McNulty H, Barnett CR, O'Harte FP, Flatt PR. Impaired ability of glycated insulin to regulate plasma glucose and stimulate glucose transport and metabolism in mouse abdominal muscle. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1523:128-34. [PMID: 11099867 DOI: 10.1016/s0304-4165(00)00113-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Previous studies have shown that glycated insulin is secreted from pancreatic beta-cells under conditions of hyperglycaemia. This study has investigated the effects of monoglycated insulin on plasma glucose homeostasis and in vitro cellular glucose transport and metabolism by isolated abdominal muscle of mice. Monoglycated insulin was prepared under hyperglycaemic reducing conditions, purified by RP-HPLC and identified by electrospray ionisation mass spectrometry (5971.1 Da). When administered to mice at an intraperitoneal dose of 7 nmoles/kg body weight, insulin (non-glycated) decreased plasma glucose concentrations and substantially reduced the glycaemic excursion induced by conjoint intraperitoneal injection of 2 g glucose/kg body weight. In comparison, the same dose of monoglycated insulin decreased plasma glucose concentrations to a lesser extent (P < 0.05), corresponding to an approx. 20% reduction of glucose lowering potency. Using isolated abdominal muscle, insulin (10(-9)-10(-7) M) stimulated dose-dependent increases in cellular 2-deoxy-D-[1-3H]glucose uptake, D-[U-14C]glucose oxidation and glycogen production. Monoglycated insulin was approx. 20% less effective than native insulin in stimulating glucose uptake and both indices of metabolism, generally requiring 10-fold greater concentrations to achieve significant stimulatory effects. These data indicate that the impaired biological activity of glycated insulin may contribute to glucose intolerance of diabetes.
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Affiliation(s)
- A C Boyd
- School of Biomedical Sciences, University of Ulster, Coleraine, UK
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Kohno M, Yasunari K, Maeda K, Kano H, Minami M, Hanehira T, Yoshikawa J. Effects of cardiac natriuretic peptides on oxidized low-density lipoprotein- and lysophosphatidylcholine-induced human mesangial cell migration. Hypertension 2000; 35:971-7. [PMID: 10775571 DOI: 10.1161/01.hyp.35.4.971] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The objectives of the present study were (1) to determine whether oxidized LDL and lysophosphatidylcholine (lyso-PtdCho), a major phospholipid component of oxidized LDL, stimulate the migration of cultured human mesangial cells and (2) to investigate the possible effects on mesangial cell migration of the cardiac natriuretic peptides atrial and brain natriuretic peptide (ANP and BNP). Oxidized LDL (10 and 100 microg/mL) and lyso-PtdCho (10(-7) to 10(-5) mol/L) stimulated migration in a concentration-dependent manner. In contrast, the effects of native LDL and phosphatidylcholine were modest or nonexistent. Protein kinase C (PKC) inhibitor and downregulation of PKC activity by phorbol ester inhibited oxidized LDL- and lyso-PtdCho-induced migration. Human ANP(1-28) and human BNP-32 significantly inhibited oxidized LDL- and lyso-PtdCho-induced migration in a concentration-dependent manner. C-ANF (des-[Glu(18),Ser(19),Gly(20),Leu(21),Gly(22)]ANP(4-23)), a specific ligand for ANP clearance receptors, could not inhibit oxidized LDL- and lyso-PtdCho-induced migration. Inhibition by ANP and BNP of lyso-PtdCho-induced migration was paralleled by an increase in the cellular level of GMP. Oxidized LDL- and lyso-PtdCho-induced migrations were inhibited by 8-bromo-cGMP. The results suggest that oxidized LDL and lyso-PtdCho stimulate the migration of human mesangial cells, at least in part, through a PKC-dependent process and that ANP and BNP inhibit this stimulated migration, probably through a cGMP-dependent process.
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Affiliation(s)
- M Kohno
- First Department of Internal Medicine, Osaka City University Medical School, Abeno-ku, Osaka, Japan
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Raj DS, Choudhury D, Welbourne TC, Levi M. Advanced glycation end products: a Nephrologist's perspective. Am J Kidney Dis 2000; 35:365-80. [PMID: 10692262 DOI: 10.1016/s0272-6386(00)70189-2] [Citation(s) in RCA: 227] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Advanced glycation end products (AGEs) are a heterogeneous group of molecules that accumulate in plasma and tissues with advancing age, diabetes, and renal failure. There is emerging evidence that AGEs are potential uremic toxins and may have a role in the pathogenesis of vascular and renal complications associated with diabetes and aging. AGEs are formed when a carbonyl of a reducing sugar condenses with a reactive amino group in target protein. These toxic molecules interact with specific receptors and elicit pleiotropic responses. AGEs accelerate atherosclerosis through cross-linking of proteins, modification of matrix components, platelet aggregation, defective vascular relaxation, and abnormal lipoprotein metabolism. In vivo and in vitro studies indicate that AGEs have a vital role in the pathogenesis of diabetic nephropathy and the progression of renal failure. The complications of normal aging, such as loss of renal function, Alzheimer's disease, skin changes, and cataracts, may also be mediated by progressive glycation of long-lived proteins. AGEs accumulate in renal failure as a result of decreased excretion and increased generation resulting from oxidative and carbonyl stress of uremia. AGE-modified beta(2)-microglobulin is the principal pathogenic component of dialysis-related amyloidosis in patients undergoing dialysis. Available dialytic modalities are not capable of normalizing AGE levels in patients with end-stage renal disease. A number of reports indicated that restoration of euglycemia with islet-cell transplantation normalized and prevented further glycosylation of proteins. Aminoguanidine (AGN), a nucleophilic compound, not only decreases the formation of AGEs but also inhibits their action. A number of studies have shown that treatment with AGN improves neuropathy and delays the onset of retinopathy and nephropathy. N-Phenacylthiazolium bromide is a prototype AGE cross-link breaker that reacts with and can cleave covalent AGE-derived protein cross-links. Thus, there is an exciting possibility that the complications of diabetes, uremia, and aging may be prevented with these novel agents.
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Affiliation(s)
- D S Raj
- Department of Medicine, Lousiana State University Medical Center, Shreveport, LA,USA
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18
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Mondorf UF, Piiper A, Herrero M, Olbrich HG, Bender M, Gross W, Scheuermann E, Geiger H. Lipoprotein(a) stimulates growth of human mesangial cells and induces activation of phospholipase C via pertussis toxin-sensitive G proteins. Kidney Int 1999; 55:1359-66. [PMID: 10201000 DOI: 10.1046/j.1523-1755.1999.00367.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Renal disease is commonly associated with hyperlipidemia and correlates with glomerular accumulation of atherogenic lipoproteins, for example, lipoprotein(a) [Lp(a)], and mesangial hypercellularity. Specific binding of Lp(a) to mesangial cells and induction of c-myc and c-fos expression has been demonstrated. Therefore, in this study, we investigated a possible growth stimulatory effect and mode of action of Lp(a) in human mesangial cells. METHODS Lp(a) was purified from the regenerate fluid of a dextran sulfate column-based low-density lipoprotein apheresis system. Human mesangial cells were isolated by a sequential sieving technique from patients undergoing tumor nephrectomy. DNA synthesis was measured by [3H]-thymidine incorporation. The intracellular calcium concentration ([Ca2+]i) was determined by Fura 2-fluorescence, and inositol 1,4,5-trisphosphate (1,4,5-IP3) concentration was measured by a radioreceptor assay. RESULTS The data show that Lp(a) bound to the cells with a Kd of 17.0 micrograms/ml and increased DNA synthesis and cell proliferation. Lp(a) caused a rapid increase in 1,4,5-IP3 and [Ca2+]i via a pertussis toxin-sensitive mechanism. The phospholipase C (PLC) inhibitor U73122 abolished Lp(a)-induced cell proliferation. In contrast, vasopressin-induced increase in 1,4,5-IP3 and [Ca2+]i was pertussis toxin insensitive. CONCLUSION This study revealed that Lp(a) stimulates growth of human mesangial cells. Lp(a)-induced signaling involves binding to a receptor and stimulation of PLC via Gi proteins. Stimulation of PLC appears to be essential for the growth stimulatory effect of Lp(a). Whether these effects of Lp(a) contribute to the pathophysiology of renal disease needs to be determined.
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Affiliation(s)
- U F Mondorf
- Department of Thoracic Surgery, Johann Wolfgang Goethe-University, Frankfurt, Germany.
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19
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Iseki K, Ikemiya Y, Fukiyama K. Serum cholesterol and risk of end-stage renal disease in a cohort of mass screening. Clin Exp Nephrol 1998. [DOI: 10.1007/bf02480619] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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20
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Affiliation(s)
- M A Smith
- Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106, USA
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21
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Lynn EG, O K. Role of lipoprotein-X in foam cell formation and rat mesangial cell proliferation. Clin Exp Pharmacol Physiol 1997; 24:973-5. [PMID: 9406668 DOI: 10.1111/j.1440-1681.1997.tb02731.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
1. In the present study, the effect of reconstituted lipoprotein-X (rLp-X) on lipid accumulation and foam cell formation in rat peritoneal macrophages was evaluated. Furthermore, the combined effect of rLp-X and macrophages on mesangial cell proliferation was examined. 2. Incubation of macrophages with rLp-X (177 and 387 nmol unesterified cholesterol (FC)/mL) resulted in an increase of cellular cholesterol (162%) and cholesteryl esters (223 to 245%) relative to control. 3. Oil Red O staining of macrophages treated with rLp-X revealed the presence of foam cells. 4. In conclusion, rLp-X had no effect on the proliferation of mesangial cells incubated in macrophage-conditioned medium.
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Affiliation(s)
- E G Lynn
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, Canada
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22
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Lynn EG, Choy PC, Magil A, O K. Uptake and metabolism of lipoprotein-X in mesangial cells. Mol Cell Biochem 1997; 175:187-94. [PMID: 9350051 DOI: 10.1023/a:1006865420286] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Progressive glomerulosclerosis is a major complication in patients with familial lecithin:cholesterol acyltransferase (LCAT) deficiency. The lack of LCAT activity results in the accumulation of an abnormal lipoprotein, lipoprotein-X (Lp-X), in the plasma of these patients. Lipoprotein-X contains high levels of unesterified cholesterol and phosphatidylcholine. Lp-X may play a role in the accumulation of lipids in the kidney, which in turn may lead to glomerulosclerosis. The objective of this study is to examine the uptake and metabolism of Lp-X by rat mesangial cells. Our results suggest that Lp-X is taken up by mesangial cells and that the lipids in Lp-X are metabolized. Lysosomes containing unesterified cholesterol and phosphatidylcholine, in a molar ratio similar to Lp-X, were synthesized to investigate the roles individual apolipoproteins (apo CI, II, III and E) play in the uptake of Lp-X. Both apo CI and CIII inhibited its uptake while apo CII (1.5 fold) and E (4 fold) stimulated the uptake of Lp-X. Very low density lipoprotein (VLDL) and low density lipoprotein (LDL) inhibited Lp-X uptake by mesangial cells. However, at higher concentrations of high density lipoprotein (HDL), the uptake of Lp-X was stimulated. Proteoglycans have an important role in regulating the uptake of Lp-X, while cytoskeleton-dependent phagocytosis and the scavenger receptor do not appear to be involved.
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Affiliation(s)
- E G Lynn
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, Canada
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23
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Tan MS, Lee YJ, Shin SJ, Tsai JH. Oxidized low-density lipoprotein stimulates endothelin-1 release and mRNA expression from rat mesangial cells. THE JOURNAL OF LABORATORY AND CLINICAL MEDICINE 1997; 129:224-30. [PMID: 9016859 DOI: 10.1016/s0022-2143(97)90143-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Evidence indicates that the glomerular injuries and renal hemodynamic abnormalities in hyperlipidemia are caused by the interaction of low-density lipoprotein (LDL) and oxidized LDL (Ox-LDL) with mesangial cells. Experiments were designed to investigate whether the synthesis of mesangial cell endothelin-1 (ET-1), a potent renal vasoconstrictor and mitogen for mesangial cells, is modulated by LDL and Ox-LDL. Using competitive semi-quantitative reverse transcription polymerase chain reaction (PCR), we report that the expression of cultured rat mesangial cell ET-1 mRNA was increased after treatment with Ox-LDL but not native LDL. Ox-LDL stimulated the release of ET-1 peptide into the culture medium in a time- and concentration-dependent manner. The maximal effect was observed at a concentration of 100 microg/ml, and a higher dose of Ox-LDL was found to be cytotoxic to the mesangial cells. Our results suggest that ET-1 released by Ox-LDL stimulation may be an important pathogenetic factor contributing to the renal hemodynamic alterations and progressive chronic renal diseases induced by hypercholesterolemia.
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Affiliation(s)
- M S Tan
- Graduate Institute of Medicine, Kaohsiung Medical College, Taiwan, Republic of China
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24
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Sharma P, Reddy K, Franki N, Sanwal V, Sankaran R, Ahuja TS, Gibbons N, Mattana J, Singhal PC. Native and oxidized low density lipoproteins modulate mesangial cell apoptosis. Kidney Int 1996; 50:1604-11. [PMID: 8914027 DOI: 10.1038/ki.1996.476] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Hyperlipidemia has been demonstrated to contribute to hypercellularity of the mesangium in experimental animal models of glomerulosclerosis. We studied whether it also has the potential to convert a hypercellular mesangium into a hypocellular one by inducing mesangial cell (MC) apoptosis. Low density lipoprotein (LDL) enhanced (P < 0.001) mouse mesangial cell (MMC) proliferation at lower concentrations (control, 10.3 +/- 0.3 vs. LDL 100 micrograms/ml, 24.2 +/- 0.3 x 10(4) cells/ml) but augmented (P < 0.001) apoptosis at higher concentrations (control, 5.6 +/- 0.5% vs. LDL, 500 micrograms/ml 26.2 +/- 3.4% apoptotic cells/field). Oxidized (OX) LDL enhanced MMC apoptosis in concentrations of 50 to 200 micrograms/dl. There was a direct relationship between MMC apoptosis and oxidation of LDL as judged by measuring thiobarbituric acid reactive species (TBARS). Since superoxide dismutase (SOD) attenuated (P < 0.001) LDL-induced MMC apoptosis, it seems to be mediated through the generation of free radicals by mesangial cells (control, 4.3 +/- 1.5%; LDL, 200 micrograms/ml, 19.4 +/- 0.5%; LDL + SOD, 8.1 +/- 1.3% apoptotic cells/field). LDL also induced a similar effect on human mesangial cells. These studies were further confirmed by DNA fragment assays and ELISA for programmed cell death. LDL treated cells also showed enhanced mRNA expression for RSG-2, a marker for active cell death. These in vitro results provide a basis for the speculation that LDL has the potential to cause an initial hypercellular and subsequent hypocellular mesangium in the course of the development of glomerulosclerosis.
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Affiliation(s)
- P Sharma
- Department of Medicine, Long Island Jewish Medical Center, New Hyde Park, New York, USA
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25
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Peruzzi L, Trusolino L, Amore A, Gianoglio B, Cirina P, Basso G, Emancipator SN, Marchisio PC, Coppo R. Tubulointerstitial responses in the progression of glomerular diseases: albuminuria modulates alpha v beta 5 integrin. Kidney Int 1996; 50:1310-20. [PMID: 8887293 DOI: 10.1038/ki.1996.443] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Proteinuria represents one of the most unfavorable prognostic factors in the progression of nephropathies. Several lines of evidence support a role for proteinuria per se in the development of interstitial fibrosis, albeit the molecular mechanisms are still unknown. We investigated the potential role of integrins expressed on tubular cells in regulating the synthesis and organization of interstitial matrix or as mediators of tubulointerstitial damage in conditions mimicking the nephrotic milieu. Under basal conditions, cultured tubular cells highly expressed alpha 3 beta 1 and, at focal contacts, alpha v beta 3. In contrast, alpha v beta 5 was weakly and diffusely distributed all over the plasma membrane. Cultures on a variety of matrix substrates (fibronectin, laminin, collagen types I and IV, vitronectin, von Willebrand factor, fibrinogen) did not induce any phenotypic change in integrin expression by tubular cells. Conversely, the addition of albumin resulted in a highly increased membrane expression of beta 5, which was organized in typical focal contacts and was related to the dose of albumin added. Immunofluorescence, flow cytometry, immunoprecipitation and RT-PCR experiments argue for a complex mechanism that includes increased post-transcriptionally regulated protein synthesis, accelerated conversion of precursors to mature forms, and increased surface delivery to discrete adhesive structures. Up-regulation of the beta 5 chain in tubular cells was confirmed in 9 out of 11 kidney biopsies from proteinuric glomerulonephritides including membranous and focal sclerosing glomerulonephritis, while it was not expressed in nonproteinuric kidneys including five biopsy specimens. This is the first report indicating that proteinuria up-regulates the surface expression and distribution of a specific integrin chain on tubular cells. These observations suggest the participation of integrins in a hitherto unexplored mechanism of tubulo-interstitial responses to glomerular injury.
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Affiliation(s)
- L Peruzzi
- Division of Nephrology and Dialysis, University of Torino, Regina Margherita Children's Hospital, Italy
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26
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Guijarro C, Kasiske BL, Kim Y, O'Donnell MP, Lee HS, Keane WF. Early glomerular changes in rats with dietary-induced hypercholesterolemia. Am J Kidney Dis 1995; 26:152-61. [PMID: 7611247 DOI: 10.1016/0272-6386(95)90169-8] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Increasing evidence suggests that lipids may be important modulators of progressive glomerular injury. We previously reported the long-term glomerular changes in rats with dietary-induced hypercholesterolemia. In this work, we evaluated the early glomerular changes induced by hypercholesterolemia that precede the development of glomerulosclerosis. In cholesterol-fed rats, an early macrophage influx was observed. This was associated with an increase in glomerular size, mesangial matrix expansion, lipid deposits, and foam cell formation. Immunohistochemical techniques showed that type IV collagen, fibronectin, and laminin were increased in cholesterol-fed rats. The mRNA expression for the alpha 1 chain of type IV collagen and an inhibitor of type IV collagenase were increased, suggesting that both increased synthesis and reduced degradation may be involved in cholesterol-induced mesangial matrix accumulation. The glomerular mRNA expression of transforming growth factor-beta 1 was also upregulated, suggesting that transforming growth factor-beta 1 could be an important mediator for mesangial matrix accumulation in hypercholesterolemic states. The early cholesterol-induced changes in the glomerulus are reminiscent in many respects to the process leading to glomerulosclerosis in the vessel wall.
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Affiliation(s)
- C Guijarro
- Department of Medicine, University of Minnesota Medical School, Hennepin County Medical Center, Minneapolis 55439, USA
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27
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Nishikawa T, Kobori S, Takeda H, Higashi T, Sato Y, Sasahara T, Yano T, Kasho M, Anami Y, Shichiri M. Beta-migrating very low density lipoproteins induce foam cell formation in mouse mesangial cells. Atherosclerosis 1995; 114:123-32. [PMID: 7605371 DOI: 10.1016/0021-9150(94)05476-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
To elucidate whether beta-migrating very low density lipoproteins (beta-VLDL) induce foam cell formation in mesangial cells or not, surface binding and foam cell formation with beta-VLDL were studied in mouse mesangial cells. Specific binding kinetics for beta-VLDL and low density lipoproteins (LDL) on the mesangial cells were observed with Kd = 3.8 and 13.7 micrograms/ml, and Bmax = 65.9 and 71.9 ng/ml cell protein at 4 degrees C, respectively. The binding of beta-VLDL was inhibited by excess amounts of LDL or beta-VLDL, but not by acetyl-low density lipoproteins. Ligand blotting using beta-VLDL or LDL and immunoblotting using anti-human LDL receptor monoclonal antibody detected the same apparent single protein (approx. 130 kDa). Incorporation of [14C]oleate into cholesteryl ester in mouse mesangial cells was enhanced by beta-VLDL to 3-fold higher than that by LDL, and it was inhibited by chloroquine or anti-human LDL receptor monoclonal antibody. The light microscopic findings also demonstrated that cholesteryl ester deposition increased in these cells incubated with beta-VLDL, but not with LDL. In conclusion, beta-VLDL was specifically taken up by receptor-mediated endocytosis in mouse mesangial cells through LDL receptors, resulting in foam cell formation.
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Affiliation(s)
- T Nishikawa
- Department of Metabolic Medicine, Kumamoto University School of Medicine, Japan
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28
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Affiliation(s)
- W F Keane
- Hennepin County Medical Center, Minneapolis, Minnesota
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29
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King GL, Shiba T, Oliver J, Inoguchi T, Bursell SE. Cellular and molecular abnormalities in the vascular endothelium of diabetes mellitus. Annu Rev Med 1994; 45:179-88. [PMID: 8198375 DOI: 10.1146/annurev.med.45.1.179] [Citation(s) in RCA: 87] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Diabetic vascular complications affect both micro- and macrovasculature, primarily in the retina, renal glomeruli, and multiple sites in the macrovessels. This review presents a summary of the abnormal function found in vivo and in cultured vascular cells exposed to elevated levels of glucose. We also discuss the various biochemical hypotheses that have been proposed to explain the adverse effects of hyperglycemia on vascular cells.
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Affiliation(s)
- G L King
- Joslin Diabetes Center, Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts
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30
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Abstract
Hyperlipidemias may play a role in the progression of various renal diseases, including diabetes mellitus. We therefore examined the characteristics of low-density lipoprotein (LDL) binding and uptake in cultured rat mesangial cells. Mesangial cells bound and took up LDL in a manner consistent with specific receptor mediation. Furthermore, exposure of mesangial cells to LDL enhanced intracellular cholesteryl esterification and decreased de novo cholesterol synthesis. Mesangial cells expressed mRNA for LDL receptor and their expression was downregulated after preloading of cells with LDL. These results are consistent with regulation of cholesterol uptake and metabolism by a specific LDL receptor mechanism. During diabetes the apolipoprotein B of LDL undergoes nonenzymatic glycation, which may alter its affinity for the LDL receptor. Glycation of LDL reduced its affinity for binding to the receptor sites and decreased its uptake by mesangial cells. Thus, during diabetes less LDL may be taken up and more remain extracellularly, where it can be trapped in the matrix. Oxidation of LDL bound to extracellular matrix is believed to be a major factor in the pathobiology of hyperlipidemias. Specific scavenger receptors for oxidized LDL have been described and cloned. We therefore examined whether rat mesangial cells bound and took up oxidized LDL. We demonstrated low-affinity but high-capacity binding sites for oxidized LDL on mesangial cells. In contrast to LDL, which supported mesangial cell proliferation, oxidized LDL was cytotoxic for the cells and resulted in stimulation of mesangial cell prostaglandin E2 production. Trapping of LDL in the extracellular matrix is considered an initial event in LDL-induced vascular pathology. We therefore evaluated binding of LDL and modified LDL to extracellular matrix produced by cultured mesangial cells. Mesangial matrix had a high capacity to bind LDL and modified LDL (glycated or oxidized) in a nonsaturable manner. These results obtained with cultured mesangial cells and their matrix allow the formulation of a working hypothesis. Under normal eulipemic conditions mesangial cells handle LDL in a regulated manner. During hyperlipidemia or expansion of extracellular matrix LDL accumulates in the matrix. There LDL would be subject to oxidative modifications, especially under conditions of mesangial cell stress, such as inflammatory, mechanical, or ischemic injury. Part of the oxidized LDL could be taken up by scavenger receptors on mesangial cells and monocyte-macrophages, resulting in foam cell formation. Excess oxidized LDL, and specifically the lipid peroxides and lysolipids of oxidized LDL, would act as cytotoxic agents on mesangial, epithelial, and endothelial cells, thereby contributing to a vicious cycle of cell damage and sclerosis.
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Affiliation(s)
- D Schlondorff
- Renal Division, Albert Einstein College of Medicine, Bronx, NY 10461
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