Jehyun Park

Catalase Deficiency Accelerates Diabetic Renal Injury Through Peroxisomal Dysfunction

Mitochondrial reactive oxygen species (ROS) play an important role in diabetes complications, including diabetic nephropathy (DN). Plasma free fatty acids (FFAs) as well as glucose are increased in diabetes, and peroxisomes and mitochondria participate in FFA oxidation in an interconnected fashion. Therefore, we investigated whether deficiency of catalase, a major peroxisomal antioxidant, accelerates DN through peroxisomal dysfunction and abnormal renal FFA metabolism. Diabetes was induced by multiple injections of low-dose streptozotocin into catalase knock-out (CKO) and wild-type (WT) C57BL/6 mice. Murine mesangial cells (MMCs) transfected with catalase small interfering RNA followed by catalase overexpression were used to further elucidate the role of endogenous catalase. Despite equivalent hyperglycemia, parameters of DN, along with markers of oxidative stress, were more accelerated in diabetic CKO mice than in diabetic WT mice up to 10 weeks of diabetes. CKO mice and MMCs showed impaired peroxisomal/mitochondrial biogenesis and FFA oxidation. Catalase deficiency increased mitochondrial ROS and fibronectin expression in response to FFAs, which were effectively restored by catalase overexpression or N-acetylcysteine. These data provide unprecedented evidence that FFA-induced peroxisomal dysfunction exacerbates DN and that endogenous catalase plays an important role in protecting the kidney from diabetic stress through maintaining peroxisomal and mitochondrial fitness.

Mycophenolic Acid Inhibits Platelet-Derived Growth Factor-Induced Reactive Oxygen Species and Mitogen-Activated Protein Kinase Activation in Rat Vascular Smooth Muscle Cells

Vascular smooth muscle cell (VSMC) proliferation is the major pathologic feature associated with chronic allograft nephropathy, and mycophenolic acid (MPA) inhibits VSMC proliferation. Since the role of inosine monophosphate dehydrogenase (IMPDH)‐dependent de novo guanosine synthesis is limited in VSMCs, we examined the effects of MPA on platelet‐derived growth factor (PDGF)‐induced cellular ROS and mitogen‐actived protein kinases (MAPK) activation in VSMCs. Primary cultured rat VSMCs were stimulated with PDGF‐BB in the presence or absence of MPA. Cell proliferation was assessed by [3H]‐thymidine incorporation, ROS by flow cytometry and MAPK activation by Western blot analysis. PDGF increased cell proliferation, cellular ROS and extracellular‐regulated protein kinase (ERK) 1/2 and p38 MAPK activation by 3.4‐, 1.6‐, 3.3‐ and 3.9‐fold, respectively. MPA at above 1 μM inhibited PDGF‐induced cellular ROS and ERK 1/2 and p38 MAPK activation, as well as proliferation. Structurally different anti‐oxidants and inhibitor of ERK or p38 MAPK blocked PDGF‐induced proliferation. Anti‐oxidants also inhibited ERK 1/2 and p38 MAPK activation. Exogenous guanosine partially recovered the inhibitory effect of MPA on VSMC proliferation. These results suggest that MPA may inhibit PDGF‐induced VSMC proliferation partially through inhibiting cellular ROS, and subsequent ERK 1/2 and p38 MAPK activation in addition to inhibiting IMPDH.

Positive Feedback Loop between Plasminogen Activator Inhibitor-1 and Transforming Growth Factor-Beta1 during Renal Fibrosis in Diabetes

Background/Aims: Plasminogen activator inhibitor (PAI)-1 is increasingly recognized as a profibrotic factor but the mechanisms are not entirely clear. The present study examined the profibrotic mechanism of PAI-1 focusing on its effect on transforming growth factor (TGF)-β1 in experimental diabetes. Methods: PAI-1 knockout (KO) mesangial cells cultured under high glucose (HG) in addition to streptozotocin-induced diabetic PAI-1 KO mice were used. Results: PAI-1 deficiency did not affect plasma glucose significantly but reduced the fractional mesangial area, fibronectin and collagen I expression in the renal cortex after 20 weeks of diabetes as well as in HG-stimulated mesangial cells along with suppression of TGF-β1 mRNA expression. PAI-1 deficiency also reduced HG-induced βig-h3, a TGF-β1-induced gene product, mRNA expression. All these losses-of-function in PAI-1 KO mesangial cells were effectively gained by recombinant PAI-1. Recombinant PAI-1-induced fibronectin and collagen I expression was abrogated by TGF-β1 receptor inhibitor or anti-TGF-β antibody suggesting that the effect of PAI-1 was mediated by TGF-β1. In a similar context, recombinant PAI-1 stimulated TGF-β1 promoter activity to the same extent as TGF-β1 itself. Conclusion: Since TGF-β1 is well known to stimulate the PAI-1 promoter, we suggest that TGF-β1 and PAI-1 together constitute a positive feedback loop in the development of renal fibrosis in diabetes.

FR167653 inhibits fibronectin expression and apoptosis in diabetic glomeruli and in high-glucose-stimulated mesangial cells

Previous in vitro studies suggest that the p38 MAPK pathway may be involved in the pathogenesis of diabetic nephropathy, but the consequences of the inhibition of the p38 MAPK pathway have not been well elucidated in diabetic (DM) glomeruli. This study was undertaken to investigate the effect of p38 MAPK inhibitor, FR167653, on fibronectin expression and apoptosis in DM glomeruli and in high-glucose-stimulated mesangial cells (MC). In vivo, 32 Sprague-Dawley rats were injected with diluent (control, N = 16) or streptozotocin intraperitoneally (DM, N = 16). Eight rats from each group were treated with FR167653 for 3 mo. In vitro, rat MC were exposed to medium containing 5.6 mM glucose or 30 mM glucose [high glucose (HG)] with or without 10(-6) M FR167653 for 24 h. Fibronectin mRNA and protein expression were determined by real-time PCR and Western blot, respectively. Western blot for apoptosis-related molecules, terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling assay, and Hoechst 33342 staining were performed to determine apoptosis. FR167653 ameliorated the increases in fibronectin-to-GAPDH mRNA ratio and protein expression in DM glomeruli by 89 and 79% and in HG-stimulated MC by 70 and 91%, respectively (P < 0.05). Under diabetic conditions, Bcl-2 protein expression was decreased, whereas cleaved caspase-3 protein expression was increased (P < 0.05), and these changes were inhibited by FR167653 treatment. Apoptotic cells were also significantly increased in DM glomeruli and in HG-stimulated MC (P < 0.05), and FR167653 ameliorated these increases in apoptotic cells, both in vivo and in vitro. In conclusion, these findings suggest that the inhibition of the p38 MAPK pathway has a beneficial effect on the development of diabetic nephropathy by inhibiting the increase in fibronectin expression and apoptosis.

Textural Properties of Gelling System of Low‐Methoxy Pectins Produced by Demethoxylating Reaction of Pectin Methyl Esterase

After deesterification of commercial pectins with a pectin methyl esterase (PME), their gelling properties were characterized using instrumental texture analysis. The final degree of esterification (DE) of the high- and low-methoxy pectins reached approximately 6% after the PME treatment, while deesterification of low-methoxy amidated pectin stopped at 18% DE. Furthermore, DE of high-methoxy pectin was tailored to be 40%, which is equivalent to the DE of commercial low-methoxy pectin. As a result, significant changes in molecular weight (Mw) distribution were observed in the PME-treated pectins. The texture profile analysis showed that PME modification drastically increased hardness, gumminess, and chewiness, while decreasing cohesiveness and adhesiveness of the pectin gels (P < 0.05). The pectin gel with relatively high peak molecular weight (Mp, 3.5 x 10(5)) and low DE (6), which was produced from high-methoxy pectin, exhibited the greatest hardness, gumminess, chewiness, and resilience. The hardness of low-methoxy amidated pectin increased over 300% after PME deesterification, suggesting that the effects of amide substitution could be reinforced when DE is even lower. The partial least square regression analysis indicated that the Mw and DE of the pectin molecule are the most crucial factors for hardness, chewiness, gumminess, and resilience of gel matrix.

Renoprotective antioxidant effect of alagebrium in experimental diabetes

BACKGROUND Despite the beneficial effects of alagebrium (ALA), a putative advanced glycation end-product (AGE) breaker, on diabetic nephropathy, its renoprotective mechanisms are incompletely understood. Since oxidative stress exacerbates diabetic renal injury through interaction with AGE, the present study examined the antioxidative property of ALA in db/db mice, mesangial cells cultured under high glucose or H(2)O(2) and a test tube. METHODS ALA (2 mg/kg/day) was administered intraperitoneally for 12 weeks to 8-week-old db/m and db/db (D(ALA)E) mice or for 4 weeks to 16-week-old db/db mice (D(ALA)L). Oxidative stress markers (nitrotyrosine accumulation, expression and translocation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, cellular DCF-DA fluorescence) together with urinary albumin excretion and histological changes including mesangial expansion were measured. The concentration of H(2)O(2) in the presence and absence of ALA was measured by iodometric analysis in a test tube. RESULTS ALA significantly reduced not only urinary albumin excretion and renal pathological changes but also accumulation of pentosidine and nitrotyrosine and expression of NADPH oxidase subunits in db/db mice regardless of treatment protocol. In mesangial cells, ALA effectively prevented not only high glucose- but also H(2)O(2)-induced membrane translocation of NADPH oxidase subunit (p47 phox, p67 phox and rac1) and protein kinase C isoform (α, βI and βII) and Nox4 messenger RNA expression concomitant with cellular reactive oxygen species. Furthermore, ALA directly decreased H(2)O(2) in a test tube. CONCLUSION ALA has both direct and indirect antioxidant effects that may play important roles in ALAs renoprotective effect in diabetic kidneys.

Plasminogen Activator Inhibitor-1 Antisense Oligodeoxynucleotides Abrogate Mesangial Fibronectin Accumulation

Excessive extracellular matrix (ECM) accumulation is the main feature of chronic renal disease including diabetic nephropathy. Plasminogen activator inhibitor (PAI)-1 is known to play an important role in renal ECM accumulation in part through suppression of plasmin generation and matrix metalloproteinase (MMP) activation. The present study examined the effect of PAI-1 antisense oligodeoxynucleotide (ODN) on fibronectin upregulation and plasmin/MMP suppression in primary mesangial cells cultured under high glucose (HG) or transforming growth factor (TGF)-β1, major mediators of diabetic renal ECM accumulation. Growth arrested and synchronized rat primary mesangial cells were transfected with 1 µM phosphorothioate-modified antisense or control mis-match ODN for 24 hours with cationic liposome and then stimulated with 30 mM D-glucose or 2 ng/ml TGF-β1. PAI-1 or fibronectin protein was measured by Western blot analysis. Plasmin activity was determined using a synthetic fluorometric plasmin substrate and MMP-2 activity analyzed using zymography. HG and TGF-β1 significantly increased PAI-1 and fibronectin protein expression as well as decreased plasmin and MMP-2 activity. Transient transfection of mesangial cells with PAI-1 antisense ODN, but not mis-match ODN, effectively reversed basal as well as HG- and TGF-β1-induced suppression of plasmin and MMP-2 activity. Both basal and upregulated fibronectin secretion were also inhibited by PAI-1 antisense ODN. These data confirm that PAI-1 plays an important role in ECM accumulation in diabetic mesangium through suppression of protease activity and suggest that PAI-1 antisense ODN would be an effective therapeutic strategy for prevention of renal fibrosis including diabetic nephropathy.

Effects of carvedilol alone and in the presence of cyclosporine A on the DNA synthesis of cultured vascular smooth muscle cells.

AbstractPurpose. There is still no reliable method of preventing or treating chronic rejection or transplant vascular sclerosis. A recent in vitro cell culture study showed that carvedilol significantly inhibited the proliferation of vascular smooth muscle cells (VSMCs); however, the effect of carvedilol in the presence of cyclosporine (CsA) has not yet been reported. Using in vitro cultured VSMCs, we measured the antiproliferative activity of carvedilol alone and in combination with CsA. Methods. Growth-arrested cultured VSMCs from the thoracic aorta of Sprague-Dawley rats were exposed to platelet-derived growth factor (PDGF)-BB, endothelin (ET)-I, and angiotensin (ANG)-II. Carvedilol (1 and 10 μM) and/or CsA (100 nM) were added as test drugs. DNA synthesis was assessed by measuring the incorporated [3H]thymidine activity, and the percentage of inhibition in the presence of the test drugs was determined. Results. Compared with the PDGF-stimulated control, DNA synthesis decreased significantly to 60.3% ± 10.4% and 18.3% ± 5.9% in the presence of 1 and 10 μM of carvedilol, respectively (P < 0.05, each). Carvedilol significantly inhibited the activity of VSMCs stimulated by ET-1 and ANG-II. The IC50 of carvedilol was 1–10 μM. CsA only inhibited VSMCs significantly in the PDGF-stimulated subgroup. The addition of CsA in the presence of carvedilol did not affect the inhibitory activity of carvedilol. The pattern of inhibition in the combined group was uniform and similar to that of the carvedilol alone group, regardless of the stimulator used. Conclusion. Carvedilol significantly inhibited the DNA synthesis of VSMCs regardless of the kind of stimulators examined, even in the presence of CsA. These results indicate that carvedilol has the unique potential to inhibit the development of transplant vascular sclerosis in hypertensive transplant recipients under CsA-based immunosuppression.

Mycophenolic acid inhibits oleic acid-induced vascular smooth muscle cell activation by inhibiting cellular reactive oxygen species.

Background. Vascular smooth muscle cell (VSMC) proliferation and matrix protein accumulation play important roles in the development and progression of chronic allograft vasculopathy. Mycophenolic acid (MPA) inhibits various types of mesenchymal cell proliferation and cellular reactive oxygen species (ROS) are involved in the anti-proliferative effect of MPA. In this study, we investigated the effects of MPA on oleic acid (OA)-induced VSMC proliferation and the role of ROS in this process. Methods. Primary VSMCs from Sprague-Dawley rats were stimulated with 100 &mgr;M OA, with or without MPA (0.1– 10 &mgr;M) or 5 mM N-acetylcysteine (NAC) for one hour prior to the addition of OA. Cell proliferation was measured by methylthiazoletetrazolium (MTT) assays, proliferating cell nuclear antigen (PCNA) expression, and fibronectin secretion by Western blot analysis, and dichlorofluorescein (DCF)-sensitive cellular ROS by fluorescence-activated cell scanning (FACS). Results. OA (100 &mgr;M) increased cell proliferation, as measured by MTT (by 1.6-fold), PCNA expression, fibronectin secretion, and cellular ROS (by 1.6-fold). Treatment with MPA dose-dependently inhibited OA-induced VSMC proliferation, fibronectin secretion, and cellular ROS. Treatment with 5 mM NAC also inhibited OA-induced rat VSMC activation. Conclusions. These results suggest that MPA inhibits OA-induced VSMC proliferation and matrix protein synthesis partially by inhibiting cellular ROS.