Thromboxane in the pathogenesis of glomerular injury in diabetes

L-methionine protects against nephrotoxicity induced by methotrexate through modulation of redox status and inflammation

Objective: Methotrexate (MTX) is a drug used in the treatment of cancer and autoimmune disorders; however, its clinical use is limited because of serious side effects including renal toxicity. This study aimed to investigate the protective effect of Lmethionine (L-Met) on MTX toxicity in the kidneys of rats.Methods: Thirty male rats were divided equally into five groups: control (saline), Met400 (400 mg/kg L-Met), MTX (20 mg/kg MTX), MTX-Met300 (300 mg/kg L-Met and 20 mg/kg MTX), and MTX-Met400 (400 mg/kg L-Met and 20 mg/kg MTX). Rats were euthanized one day after the last dose administration (day 16) and serum and renal tissue samples were collected. Renal function and injury indices, oxidative stress/antioxidant indices and proinflammatory cytokines were evaluated.Results: The results showed that L-Met could effectively counteract the nephrotoxic effects of MTX, in a dose-related manner, by improving most of the tested parameters. Furthermore, the higher dose of L-Met was able to restore several parameters to normal levels. In addition, investigation of MTX-induced hematological changes revealed a corrective potential of L-Met.Conclusion: L-Met can be an effective adjuvant therapy to modulate renal toxicity associated with MTX because of its antioxidant and antiinflammatory effects.

Inhibition of notch signalling and mesangial expansion by combined glucagon like peptide-1 agonist and crocin therapy in animal model of diabetic nephropathy

Diabetic nephropathy (DN) is one of the devastating complications in diabetes mellitus (DM). Glucagon-like peptide-1 (GLP-1) is one of the incretins secreted from L cells in the intestine. Crocin (a carotenoid component of saffron) has antioxidants properties. We investigated the renal effects of Exendin-4 as a GLP-1 agonist and Crocin in DN.Thirty male rats were divided into five groups: control, type II DM, type II DM + Exendin-4, type II DM + Crocin ‏ and type II DM + Exendine-4 + Crocin. At the end of the experimental period, systolic and diastolic blood pressures were measured, and GFR was calculated. Blood and urine samples were collected for biochemical analysis. Tissue samples were collected from the kidney for histological examination and biochemical measurements of protein expression.Treatment with GLP-1 agonist or Crocin caused a significant improvement in renal function. Better results were achieved with simultaneous administration of both drugs with inhibition of notch signalling pathway and the related proteins.

Protective effects of Saraca indica L. leaves extract (family Fabaceae) against gamma irradiation induced injury in the kidney of female albino rats

This work was designed to estimate the protective effect of Saraca indica L. leaves ethanolic exract against γ-irradiation induced renal damage in rats. Phytochemical examinations of S. indica L. leaves extract resulted in the separation of three flavanone glycosides: Astilibin (1), Neoastilbin (2), and Eriodictyol-7-O-α-l-rhamnopyranoside (3); two flavonols: Quercetin (4) and Quercetin-3-O-α-l-arabinopyranosyl-(1'''-6'')-O-β-D-galactopyranoside (5) in addition of Gallic acid (6) and methyl gallate (7). Their structures elucidated by chemical evidences and spectroscopic analysis (1 and 2D-NMR, -ESI-MS, UV). Female rats were used and classified into: control, Ext (200 mg/kg body wt/day orally for 7 days), IRR (8Gy), Ext + IRR, and Sily+IRR groups (received silymarin 50 mg/kg b.wt orally as reference drug). Results showed that S. indica L. leaves extract ameliorated the kidney function tests, hs-CRP, IL-1β, ACE, TNF-α, GSH, and MDA as well as, decreased the histopathological changes of kidney. In conclusion, S. indica L. leaves extract had a renoprotective activity against irradiation induced renal injury due to its flavononid contents.

Effects of Curcumin on the Renal Toxicity Induced by Ochratoxin A in Rats

Ochratoxin A (OTA) is a powerful nephrotoxin and the severity of its damage to kidneys depends on both the dose and duration of exposure. According to the scientific data currently available, the mechanism of action still is not completely clarified, but it is supposed that oxidative stress is responsible for OTA-induced nephrotoxicity. Bioactive compound use has emerged as a potential approach to reduce chronic renal failure. Therefore, curcumin (CURC), due to its therapeutic effects, has been chosen for our study to reduce the toxic renal effects induced by OTA. CURC effects are examined in Sprague Dawley rats treated with CURC (100 mg/kg), alone or in combination with OTA (0.5 mg/kg), by gavage daily for 14 days. The end result of the experiment finds rats treated with OTA show alterations in biochemical and oxidative stress parameters in the kidney, related to a decrease in the Glomerular Filtration Rate (GFR). Conversely, the administration of CURC attenuates oxidative stress and prevents glomerular hyperfiltration versus the OTA group. Furthermore, kidney histological tests show a reduction in glomerular and tubular damage, inflammation and tubulointerstitial fibrosis. This study shows that CURC can mitigate OTA-induced oxidative damage in the kidneys of rats.

Flavonoid rich fraction of Punica granatum improves early diabetic nephropathy by ameliorating proteinuria and disturbed glucose homeostasis in experimental animals

CONTEXT

Different parts of Punica granatum Linn. (Punicaceae) are traditionally used as renal protective agents in the Indian system of medicine. However, there is paucity of information regarding its role in diabetic nephropathy.

OBJECTIVE

The present study investigates the nephroprotective potential of flavonoid-rich fraction of P. granatum leaves in streptozotocin (STZ)-induced early diabetic nephropathy in experimental animals.

MATERIALS AND METHODS

Experimental diabetic nephropathy was induced in Wistar rats by single intraperitonial injection of STZ (65 mg/kg) dissolved in ice cold citrophosphate buffer (pH 4.3). After induction rats were divided into five groups (6 normal; 24 diabetic) and administered with glibenclamide (5 mg/kg) and three dose levels of flavonoid-rich fraction of P. granatum leaves (PGFF), i.e. 50, 100, and 200 mg/kg body weight/day for 28 d. Fasting blood glucose, lipid profile, serum albumin, serum total protein, serum creatinine, blood urea nitrogen (BUN) glycosylated hemoglobin, and biomarkers of kidney oxidative stress were assessed at the end of the treatment period. Urine was analyzed for the measurement of total protein, albumin, and creatinine clearance. Kidney sections were subjected to histopathological study.

RESULTS

Daily oral administration of variable dose levels of PGFF for 28 d normalized various biochemical, metabolic, and histopathological changes in the diabetic rats. PGFF significantly (p < 0.01 and p < 0.05) improved the glycemic status and renal function in diabetic rats as compared with diabetic control rats.

DISCUSSION AND CONCLUSION

The results of our study thus prove the protective effect of PGFF in early diabetic nephropathy by ameliorating proteinuria and disturbed glucose homeostasis in experimental animals.

Oleanolic acid prevents progression of streptozotocin induced diabetic nephropathy and protects renal microstructures in Sprague Dawley rats

Objective:

To study the effect of oleanolic acid (OA) on streptozotocin induced diabetic nephropathy in Sprague Dawley rats.

Materials and Methods:

Four weeks after intra-peritoneal injection of streptozotocin (STZ; 55 mg/kg), the rats with proteinuria were grouped as: Control (non-diabetic, treated orally with vehicle), diabetic control (treated orally with vehicle) and three diabetic groups receiving 20, 40 and 60 mg/kg/day oral doses of OA. At the end of 8 weeks, urine and serum samples from the rats were processed for determination of creatinine, BUN and GFR. The kidney samples were processed for determination of weight changes, oxidative stress related parameters like catalase, superoxide dismutase and reduced glutathione levels. A part of one kidney from each rat was used for transmission electron microscopy (TEM).

Result:

As evident in TEM, OA inhibited the nephropathy induced alterations in podocyte integrity, basement membrane thickness and spacing between the podocytes at 60 mg/kg dose. It increased GFR and reduced oxidative stress in the kidneys in a dose dependent manner. These findings conclusively demonstrate the efficacy of OA in diabetic nephropathy. Significant decrease in the oxidative stress in kidneys indicates the role of anti-oxidant mechanisms in the effects of OA. However, OA is known to act through multiple mechanisms like inhibition of the generation of advanced glycation end products and improving the insulin secretion. These mechanisms might have contributed to its efficacy.

Conclusion:

These results conclusively demonstrate the efficacy of OA in diabetic nephropathy through its possible antioxidant activity.

Synthesis and biological evaluation of sulfonylurea and thiourea derivatives substituted with benzenesulfonamide groups as potential hypoglycemic agents

A novel class of sulfonylurea and thiourea derivatives substituted with benzenesulfonamide groups were designed and synthesized. The target compounds were assayed for the effects on the insulin release of isolated rat pancreatic islets and the glucose transport in adipocytes of rats. Some of them exhibited high potency. Compound 10 also had potent antiplatelet activity and showed an excellent property to protect collagen-epinephrine-induced mice mortality as well as plasma glucose-lowering activity in vivo. The preliminary pharmacological profile of compound 10 showed that it might be useful in the treatment of diabetics with cardiovascular and nephropathy complications.

Attenuation of diabetic nephropathy by tocotrienol: involvement of NFkB signaling pathway

AIM

Diabetic nephropathy is a serious complication for patients with diabetes mellitus. Approximately 30-40% of patients with type I and 15% with type II diabetes mellitus develop end stage renal disease. The study was designed to evaluate the impact of tocotrienol on renal function and reno-inflammatory cascade in streptozotocin-induced diabetes.

MAIN METHODS

Streptozotocin (STZ)-induced diabetic rats were treated with tocotrienol (25, 50 and 100 mg/kg), alpha-tocopherol (100 mg/kg) or with vehicle form 5th to 8th weeks. After 8 weeks, urine albumin excretion, urine output, serum creatinine, blood urea nitrogen, creatinine and urea clearance were measured. Cytoplasmic and nuclear fractions of kidney was prepared for the quantification of oxidative-nitrosative stress (lipid peroxidation, superoxide dismutase, catalase, non protein thiols, total nitric oxide), tumor necrosis factor-alpha (TNF-alpha), tissue growth factor-1beta (TGF-beta1), p65 subunit of NFkappabeta and caspase-3.

KEY FINDINGS

After 8 weeks of STZ injection, the rats produced significant alteration in renal function, increased oxidative-nitrosative stress, TNF-alpha, TGF-beta1, caspase-3 activity in cytoplasmic lysate and active p65 subunit of NFkappabeta in nuclear lysate of kidney of diabetic rats. Interestingly, co-administration of tocotrienol significantly and dose-dependently prevented biochemical and molecular changes associated with diabetes. Tocotrienol (100 mg/kg) was demonstrated to be more effective than alpha-tocopherol (100 mg/kg). Moreover, diabetic rats treated with insulin-tocotrienol combination produced more pronounced effect on molecular parameters as compared to their respective groups.

SIGNIFICANCE

Taken together, the data reveal that tocotrienol modulates the release of profibrotic cytokines, oxidative stress, ongoing chronic inflammation and apoptosis and thus exerts a marked renoprotective effect.

Altered TP receptor function in isolated, perfused kidneys of nondiabetic and diabetic ApoE-deficient mice

Early manifestations of kidney disease occur in atherosclerosis and activation of TP (thromboxane A2) receptors is implicated in atherosclerotic, diabetes, and renal diseases. The purpose of the present study was to analyze, in isolated, perfused mouse kidneys, the participation of TP receptors in renal vasoconstrictions and vasodilatations. In kidneys, taken from wild-type C57BL6, apolipoprotein E-deficient (ApoE-KO) and diabetic ApoE-KO mice, changes in perfusion pressure were recorded. Constrictions to TP receptor ligands U 46619, arachidonic acid, PGH2, and 8-iso-PGF2α, but not those to angiotensin II, endothelin, or norepinephrine, were inhibited by the selective TP receptor antagonist Triplion (S 18886; 10 nM). Acetylcholine and prostacyclin evoked biphasic responses during methoxamine constrictions; the constrictor part was blocked by Triplion. In ApoE-KO mouse kidneys, compared with C57BL6, a specific decrease in norepinephrine response and no modification in dilator responses were observed. In diabetic ApoE-KO mouse kidneys, constrictions to U 46619 and those to 8-iso-PGF2α were significantly and selectively augmented, without modification in the expression of the TP receptor, and again without any significant change in vasodilator activity. Thus TP receptors are functional, and their activation is not involved in norepinephrine, endothelin, and angiotensin II vasoconstrictions but is implicated in the unusual vasoconstrictions to acetylcholine and prostacyclin. Increased responsiveness of TP receptors occurs in diabetic ApoE-KO mouse kidneys. Thus early changes in TP receptor-mediated vasoconstrictor activity may participate in the development of kidney disease in atherosclerosis and diabetes.

Renal effects of S18886 (Terutroban), a TP receptor antagonist, in an experimental model of type 2 diabetes

Thromboxane A(2) (TxA(2)) is assumed to contribute to the development of diabetes complications, including nephropathy. We investigated whether the selective thromboxane-prostanoid endoperoxide receptor antagonist, S18886, ameliorates renal damage in uninephrectomized (UNX) obese Zucker rats (OZR). S18886, at doses of 10 (S18886-10) and 30 (S18886-30) mg x kg(-1) x day(-1), was administered to UNX-OZR by gavage over 8 weeks (n = 8 each group). UNX lean rats (n = 12) and OZR rats that received placebo (OZR-PLAC, n = 8) served as controls. As compared with the OZR-PLAC, S18886 had no significant effect on the elevated blood pressure and the enhanced creatinine clearance, while augmented proteinuria was partially prevented (-12 and -37%, low and high dose, respectively; NS). The increased excretion of transforming growth factor beta(1) (TGF-beta(1)) and of the thromboxane metabolite 2,3-dinor thromboxane B(2) (TxB(2)) was lowered (P < 0.05). S18886 prevented both the enhanced mesangiolysis (P < 0.01) in the OZR-PLAC as well as enlargement and degeneration of podocytes. In the blood, S18886-30 augmented the antioxidant enzymes (P < 0.01) and lessened the increase of plasma advanced oxidation protein products (-25%, NS). Body weight, hyperglycemia, and dyslipidemia remained uninfluenced under both doses of treatment. S18886 has renoprotective properties in the model of UNX-OZR. It prevents mesangiolysis, reduces urinary TGF-beta(1) and 2,3-dinor-TxB(2) excretion, and enhances the antioxidative defense.

Curcumin, the active principle of turmeric (Curcuma longa), ameliorates diabetic nephropathy in rats

Chronic hyperglycaemia in diabetes leads to the overproduction of free radicals and evidence is increasing that these contribute to the development of diabetic nephropathy. Among the spices, turmeric (Curcuma longa) is used as a flavouring and colouring agent in the indian diet every day and is known to possess anti-oxidant properties. The present study was designed to examine the effect of curcumin, a yellow pigment of turmeric, on renal function and oxidative stress in streptozotocin (STZ)-induced diabetic rats. Diabetes was induced by a single intraperitoneal injection of STZ (65 mg/kg) in rats. Four weeks after STZ injection, rats were divided into four groups, namely control rats, diabetic rats and diabetic rats treated with curcumin (15 and 30 mg/kg, p.o.) for 2 weeks. Renal function was assessed by creatinine, blood urea nitrogen, creatinine and urea clearance and urine albumin excretion. Oxidative stress was measured by renal malonaldehyde, reduced glutathione and the anti-oxidant enzymes superoxide dismutase and catalase. Streptozotocin-injected rats showed significant increases in blood glucose, polyuria and a decrease in bodyweight compared with age-matched control rats. After 6 weeks, diabetic rats also exhibited renal dysfunction, as evidenced by reduced creatinine and urea clearance and proteinuria, along with a marked increase in oxidative stress, as determined by lipid peroxidation and activities of key anti-oxidant enzymes. Chronic treatment with curcumin significantly attenuated both renal dysfunction and oxidative stress in diabetic rats. These results provide confirmatory evidence of oxidative stress in diabetic nephropathy and point towards the possible anti-oxidative mechanism being responsible for the nephroprotective action of curcumin.

Renal prostaglandin E2 receptor (EP) expression profile is altered in streptozotocin and B6-Ins2Akita type I diabetic mice

The homeostatic function of prostaglandin E(2) (PGE(2)) is dependent on a balance of EP receptor-mediated events. A disruption in this balance may contribute to the progression of renal injury. Although PGE(2) excretion is elevated in diabetes, the expression of specific EP receptor subtypes has not been studied in the diabetic kidney. Therefore, the purpose of this study was to characterize the expression profile of four EP receptor subtypes (EP(1-4)) in 16-wk streptozotocin (STZ) and B6-Ins2(Akita) type I diabetic mice. In diabetic mice, the ratio of kidney weight to body weight was increased twofold compared with controls, blood glucose was elevated, but urine albumin was only increased in B6-Ins2(Akita) mice. The excretion of PGE(2) and its metabolite was augmented two- to fourfold as determined by enzyme immunoassay. Accordingly, renal cyclooxygenases were also increased in diabetic mice, with isoform-specific and regional differences in each model. Finally, there was altered EP(1-4) receptor expression in diabetic kidneys, with significant differences between STZ and B6-Ins2(Akita) mice (fold-control). In STZ mice, cortical EP(1) increased by 1.6, EP(3) increased by 2.3, and EP(4) decreased by 0.63; yet in B6-Ins2(Akita) mice, cortical EP(1) increased by 2.4, but there was a general decrease in the remaining subtypes. Similarly, in the STZ medulla EP(3) increased by 3.6, but both EP(1) and EP(3) increased by 5.5 and 1.95, respectively, in B6-Ins2(Akita) mice. Therefore, knowing the pattern of change in relative EP receptor expression in the kidney could be useful in identifying specific EP targets for the prevention of various components of diabetic kidney disease.

Resveratrol, a Polyphenolic Phytoalexin, Attenuates Diabetic Nephropathy in Rats

Diabetic nephropathy is a serious microvascular complication and one of the main causes of end-stage renal disease. Various studies have revealed that increased oxidative stress is a major pathophysiological mechanism which is involved in the etiology of diabetic nephropathy. Resveratrol, a polyphenolic phytoalexin present in red wine, is known to possess potent antioxidant properties and thus we aimed to examine its effect on renal function and oxidative stress in streptozotocin (STZ)-induced diabetic rats. Diabetes was induced by a single intraperitoneal injection of STZ (65 mg/kg) in rats. After 4 weeks of STZ injection, rats were divided into four groups: the control rats, diabetic rats and diabetic rats treated with resveratrol (5 and 10 mg/kg, orally) respectively from week 4 up till week 6. At the termination of the experiments, urine albumin excretion, urine output, serum creatinine, blood urea nitrogen, creatinine and urea clearance were measured. The levels of the renal oxidative stress markers malonaldehyde and glutathione and the antioxidant enzymes superoxide dismutase and catalase were measured in kidney homogenate. STZ-injected rats showed significant increases in blood glucose, polyuria, proteinuria and a decrease in body weight compared with age-matched control rats. After 6 weeks, diabetic rats exhibited renal dysfunction, as evidenced by reduced creatinine and urea clearance, and proteinuria along with a marked increase in oxidative stress, as determined by lipid peroxidation and activities of key antioxidant enzymes. Treatment with resveratrol significantly attenuated renal dysfunction and oxidative stress in diabetic rats. The present study reinforces the important role of oxidative stress in diabetic kidney and points towards the possible antioxidative mechanism being responsible for the renoprotective action of resveratrol.

Quercetin, an anti-oxidant bioflavonoid, attenuates diabetic nephropathy in rats

1. Diabetic nephropathy is an important microvascular complication and one of the main causes of end-stage renal disease. Many in vivo and in vitro studies have indicated that oxidative stress is one of the major pathophysiological mechanisms involved in the development of diabetic nephropathy. In the present study, we examined the effect of an anti-oxidant bioflavonoid quercetin on renal function and oxidative stress in streptozotocin (STZ)-induced diabetic rats. 2. Diabetes was induced in Sprague-Dawley rats with a single intravenous injection of STZ (45 mg/kg). Four weeks after STZ injection, quercetin (10 mg/kg per day) was given orally for 4 weeks in both control and diabetic rats. Plasma glucose levels and bodyweights were measured at 4 and 8 weeks after the STZ injection. At the termination of the experiments, urine albumin excretion, urine output, serum creatinine, blood urea nitrogen, creatinine and urea clearance were measured. The renal oxidative stress marker malonaldehyde, glutathione levels and the anti-oxidant enzymes superoxide dismutase and catalase were measured in kidney homogenate. 3. Streptozotocin-injected rats showed significant increases in blood glucose, polyuria, proteinuria and a decrease in bodyweight compared with age-matched control rats. After 8 weeks, diabetic rats exhibited renal dysfunction, as evidenced by reduced creatinine and urea clearance, and proteinuria along with a marked increase in oxidative stress, as determined by lipid peroxidation and activities of key anti-oxidant enzymes. Treatment with quercetin significantly attenuated renal dysfunction and oxidative stress in diabetic rats. 4. These results confirm the role of oxidative stress in the development of diabetic nephropathy and point to the possible anti-oxidative mechanism being responsible for the nephroprotective action of quercetin.

Effect of irbesartan on the antioxidant defence system and nitric oxide release in diabetic rat kidney

BACKGROUND/AIMS

Increased oxidative stress is involved in the aetiology of diabetic nephropathy, and angiotensin II is reported to play a considerable role in the development of renal damage in diabetic kidney. Angiotensin antagonism can slow the progression of renal impairment in diabetes. The present study was thus designed to examine the effect of an angiotensin II type 1 (AT1) receptor antagonist, irbesartan on renal function, oxidative stress and nitric oxide (NO) release in streptozotocin (STZ)-induced diabetic rats.

METHODS

Diabetes was induced by a single intraperitoneal injection of streptozotocin (65 mg/kg) in rats. After 4 weeks of STZ injection, rats were divided into four groups: the control rats, diabetic rats and diabetic rats treated with irbesartan (25 and 50 mg/kg, orally) respectively till 8 weeks starting from 4 weeks after STZ injection. Renal function was assessed by creatinine, blood urea nitrogen, creatinine clearance and urea clearance. Oxidative stress was measured by renal malondialdehyde (MDA), reduced glutathione (GSH), superoxide dismutase (SOD) and catalase. We also measured renal nitrite levels.

RESULTS

At the end of the 8th week, diabetic rats exhibited renal dysfunction as evidenced by reduced creatinine and urea clearance along with enhanced albumin excretion rate as compared with control rats. Biochemical analysis of kidneys revealed a marked increase in oxidative stress demonstrated by increased lipid peroxidation and decreased activities of key antioxidant enzymes, GSH, SOD and catalase in diabetic rats. NO release was also significantly higher in diabetic rats than controls. Chronic treatment with irbesartan in diabetic rats significantly attenuated both renal dysfunction and oxidative stress along with increased NO levels as compared with untreated diabetic rats. The kidneys of diabetic rats showed morphological changes such as hyaline casts, glomerular thickening and moderate interstitial fibrosis and arteriolopathy, whereas irbesartan administration markedly prevented diabetic-induced renal morphological alterations.

CONCLUSIONS

The present study suggests that oxidative stress/nitrosative stress is increased in the diabetic kidney and AT1 receptor blockade can prevent these changes. The results also suggest that in STZ-induced diabetic rats, the protective action of irbesartan might be mediated, at least in part, by its effect on tissue oxidant/antioxidant status.

Reduced IP receptors in STZ-induced diabetic rat kidneys and high-glucose-treated mesangial cells

Mesangial cells (MG) are an important source of renal PGE2 and PGI2. The purpose of this study was to examine the effects of cicaprost (CCP; PGI2 analog) on MG function and the expression of IP receptors in streptozotocin (STZ)-diabetic rats and glucose-treated MG cells. CCP increased cellular cAMP in immortalized rat MG cells. Both glucose and anisomycin attenuated CCP-cAMP, but not PMA, angiotensin II, or transforming growth factor-beta. Also, IP receptor protein was reduced in response to glucose. While CCP decreased the levels of the cell cycle inhibitor p27, it did not alter thymidine or leucine incorporation. However, CCP reduced fibronectin levels by 40% and increased matrix metalloproteinase-2 levels threefold, a key enzyme in matrix degradation. Finally, IP receptors were significantly reduced in the outer medulla of 4- and 12-wk STZ-diabetic rats and in the cortex, outer, and inner medullary regions in 6-mo uninephrectomized STZ-diabetic rats. The changes in the CCP/IP system observed in this study suggest that IP may serve as an alternate therapeutic target in diabetes.

Attenuation of renal injury in db/db mice overexpressing superoxide dismutase: evidence for reduced superoxide-nitric oxide interaction

The effects of overexpression of Cu(2+)/Zn(2+) superoxide dismutase-1 (SOD-1) on indexes of renal injury were compared in 5-month-old nontransgenic (NTg) db/db mice and db/db mice hemizygous for the human SOD-1 transgene (SOD-Tg). Both diabetic groups exhibited similar hyperglycemia and weight gain. However, in NTg-db/db mice, albuminuria, glomerular accumulation of immunoreactive transforming growth factor-beta, collagen alpha1(IV), nitrotyrosine, and mesangial matrix were all significantly increased compared with either nondiabetic mice or SOD-Tg-db/db. SOD-1 activity and reduced glutathione levels were higher, whereas malondialdehyde content was lower, in the renal cortex of SOD-Tg-db/db compared with NTg-db/db mice, consistent with a renal antioxidant effect in the transgenic mice. Inulin clearance (C(IN)) and urinary excretion of guanosine 3',5'-cyclic monophosphate (U(cGMP)) were increased in SOD-Tg-db/db mice compared with corresponding values in nondiabetic mice or NTg-db/db mice. C(IN) and U(cGMP) were suppressed by Nomega-nitro-L-arginine methyl ester in SOD-Tg-db/db but not in NTg-db/db mice, implying nitric oxide (NO) dependence of these increases and enhanced renal NO bioactivity in SOD-Tg-db/db. Studies of NO-responsive cGMP in isolated glomeruli supported greater quenching of NO in glomeruli from NTg-db/db compared with SOD-Tg-db/db mice. Evidence of increased NO responsiveness and the suppression of glomerular nitrotyrosine may both reflect reduced NO-superoxide interaction in SOD-Tg-db/db mice. The results implicate superoxide in the pathogenesis of diabetic nephropathy.

Role for thromboxane A2 from glomerular thrombi in nephropathy with type 2 diabetic rats

We used rats (the Otsuka Long-Evans Tokushima Fatty strain) as a model of type 2 diabetes to find whether thromboxane (TX) A2 is involved in diabetic nephropathy, and if so, to identify where it is synthesized. We measured urinary excretion of TXB2 and 2,3-dinor-TXB2 in rats up to 60 weeks of age as markers of renal and platelet synthesis of TXA2, respectively. Some diabetic rats were given daily oral doses of OKY-046 (100 mg/kg), a TXA2 synthase inhibitor, starting when they were 10 weeks of age. Healthy Long-Evans Tokushima Otsuka rats served as the controls. Urinary excretion of protein was greater in diabetic rats at 26 weeks than in controls, and the difference increased with age. Urinary excretion of TXB2 by diabetic rats was about 150% that of controls at 14 weeks, and remained at that level. In diabetic rats, urinary excretion of 2,3-dinor-TXB2 increased with age in parallel to increases in proteinuria, but in controls, excretion of these metabolites did not change with age. In diabetic rats, OKY-046 prevented the increase in urinary excretion of both metabolites, and decreased the proteinuria. Histologic examination at 60 weeks showed intraglomerular thrombi in diabetic rats but not in controls. OKY-046 reduced intraglomerular thrombi formation and the score for glomerulosclerosis. When platelet aggregation began, more TXA2 than before was released from the thrombi that formed, and the TXA2 contributed to the progress of nephropathy in this rat model of type 2 diabetes.

Alpha-lipoic acid attenuates hyperglycemia and prevents glomerular mesangial matrix expansion in diabetes

Previous studies demonstrated that 2 mo of dietary supplementation with alpha-lipoic acid (LA) prevented early glomerular injury in non-insulin-treated streptozotocin diabetic rats (D). The present study examined the effects of chronic LA supplementation (30 mg/kg body wt per d) on nephropathy in D after 7 mo of diabetes. Compared with control rats, D developed increased urinary excretion of albumin and transforming growth factor beta, renal insufficiency, glomerular mesangial matrix expansion, and glomerulosclerosis in association with depletion of glutathione and accumulation of malondialdehyde in renal cortex. LA prevented or ameliorated all of these changes in D. Because chronic LA supplementation also attenuated hyperglycemia in D after 3 mo, its effects on renal injury were compared with treatment of rats with sufficient insulin to maintain a level of glycemic control for the entire 7-mo period (D-INS) equivalent to that observed with LA during the final 4 mo. Despite superior longitudinal glycemic control in D-INS, urinary excretion of albumin and transforming growth factor beta, glomerular mesangial matrix expansion, the extent of glomerulosclerosis, and renal cortical malondialdehyde content were all significantly greater, whereas cortical glutathione content was lower than corresponding values in D given LA. Thus, the renoprotective effects of LA in D were not attributable to improved glycemic control alone but also likely reflected its antioxidant activity. The combined antioxidant and hypoglycemic actions of LA both may contribute to its utility in preventing renal injury and other complications of diabetes.

Overexpression of Cu2+/Zn2+ superoxide dismutase protects against early diabetic glomerular injury in transgenic mice

Ex vivo and in vitro observations implicate superoxide as a mediator of cell injury in diabetes, but in vivo evidence is lacking. In the current studies, parameters of glomerular injury were examined in hemizygous nondiabetic transgenic mice (SOD) and streptozotocin-diabetic (D) transgenic mice (D-SOD), which overexpress human cytoplasmic Cu2+/Zn2+ superoxide dismutase (SOD-1), and in corresponding wild-type littermates (WT, D-WT) after 4 months of diabetes. In both SOD and D-SOD mice, renal cortical SOD-1 activity was twofold higher than values in the WT mice; blood glucose and glycosylated hemoglobin (GHb) levels did not differ in the two diabetic groups. Urinary albumin excretion, fractional albumin clearance, urinary transforming growth factor-beta (TGF-beta) excretion, glomerular volume, glomerular content of immunoreactive TGF-beta, and collagen alpha1 (IV) and renal cortical malondialdehyde (MDA) levels were significantly higher in D-WT mice compared with corresponding values in D-SOD mice. Glomerular volume, glomerular content of TGF-beta and collagen IV, renal cortical MDA, and urinary excretion of TGF-beta in D-SOD mice did not differ significantly from corresponding values in either the nondiabetic SOD or WT mice. In separate groups of mice studied after 8 months of diabetes, mesangial matrix area, calculated as a fraction of total glomerular tuft area, and plasma creatinine were significantly higher in D-WT but not in D-SOD mice, compared with corresponding values in the nondiabetic mice. In vitro infection of mesangial cells (MC) with a recombinant adenovirus encoding human SOD-1 increased SOD-1 activity threefold over control cells and prevented the reduction of aconitase activity, an index of cellular superoxide, and the increase in collagen synthesis that otherwise occurred in control MC in response to culture with 300 or 500 mg/dl glucose. Thus, increases in cellular SOD-1 activity attenuate diabetic renal injury in vivo and also prevent stimulation of MC matrix protein synthesis induced in vitro by high glucose.

Immunohistochemical and functional correlations of renal cyclooxygenase-2 in experimental diabetes

Prostaglandins (PGs) generated by the enzyme cyclooxygenase (COX) have been implicated in the pathological renal hemodynamics and structural alterations in diabetes mellitus, but the role of individual COX isoenzymes in diabetic nephropathy remains unknown. We explored COX-1 and COX-2 expression and hemodynamic responses to the COX-1 inhibitor valeryl salicylate (VS) or the COX-2 inhibitor NS398 in moderately hyperglycemic, streptozotocin-diabetic (D) and control (C) rats. Immunoreactive COX-2 was increased in D rats compared with C rats and normalized by improved glycemic control. Acute systemic administration of NS398 induced no significant changes in mean arterial pressure and renal plasma flow in either C or D rats but reduced glomerular filtration rate in D rats, resulting in a decrease in filtration fraction. VS had no effect on renal hemodynamics in D rats. Both inhibitors decreased urinary excretion of PGE(2). However, only NS398 reduced excretion of thromboxane A(2). In conclusion, we documented an increase in renal cortical COX-2 protein expression associated with a different renal hemodynamic response to selective systemic COX-2 inhibition in D as compared with C animals, indicating a role of COX-2-derived PG in pathological renal hemodynamic changes in diabetes.

Effects of dietary supplementation of alpha-lipoic acid on early glomerular injury in diabetes mellitus

Antioxidants, in particular vitamin E (VE), have been reported to protect against diabetic renal injury. alpha-Lipoic acid (LA) has been found to attenuate diabetic peripheral neuropathy, but its effects on nephropathy have not been examined. In the present study, parameters of glomerular injury were examined in streptozotocin diabetic rats after 2 mo on unsupplemented diets and in diabetic rats that received the lowest daily dose of dietary LA (30 mg/kg body wt), VE (100 IU/kg body wt), or vitamin C (VC; 1 g/kg body wt), which detectably increased the renal cortical content of each antioxidant. Blood glucose values did not differ among the diabetic groups. At 2 mo, inulin clearance, urinary albumin excretion, fractional albumin clearance, glomerular volume, and glomerular content of immunoreactive transforming growth factor-beta (TGF-beta) and collagen alpha1 (IV) all were significantly increased in unsupplemented D compared with age-matched nondiabetic controls. With the exception of inulin clearance, LA prevented or significantly attenuated the increase in all of these glomerular parameters in D, as well as the increases in renal tubular cell TGF-beta seen in D. At the dose used, VE reduced inulin clearance in D to control levels but failed to alter any of the other indices of glomerular injury or to suppress renal tubular cell TGF-beta in D. VC suppressed urinary albumin excretion, fractional albumin clearance, and glomerular volume but not glomerular or tubular TGF-beta or glomerular collagen alpha1 (IV) content. LA but not VE or VC significantly increased renal cortical glutathione content in D. These data indicate that LA is effective in the prevention of early diabetic glomerular injury and suggest that this agent may have advantages over high doses of either VE or VC.

Renal production of thromboxane and prostaglandins in a rat model of type 2 diabetes

In an investigation of the involvement of prostanoids in the pathogenesis of nephropathy in type 2 diabetes, we repeatedly measured the urinary excretion of prostanoids in both diabetic and healthy rats as the rats aged. Seven rats of the Otsuka Long-Evans Tokushima Fatty strain were used as rats with a model of type 2 diabetes and seven rats of the Long-Evans Tokushima Otsuka strain were used as rats without diabetes. Thromboxane (TX) B2 and 6-keto-prostaglandin (PG) F1alpha, the amounts of which reflect renal production of TXA2 and PGI2, respectively, and PGE2 in urine collected in metabolic cages were assayed when rats were 14, 30, 46, and 54 weeks old. Plasma glucose and urinary protein excretion also were measured periodically. The mean plasma glucose concentration of the diabetic rats was higher than that of the healthy rats throughout the study. At 30 weeks and later, urinary protein excretion by the diabetic rats was greater than that of the healthy rats, and it increased with age. Urinary excretion of TXB2 by the diabetic rats was higher than that of the healthy rats at 14 weeks (52.4+/-23.5 vs. 27.0+/-2.6 ng/day; mean +/- SD, P = .015) and the difference continued to the end of the experiment. Urinary excretion of 6-keto-PGF1alpha by the diabetic rats was high at 14 weeks (52.3+/-12.8 vs. 26.9+/-4.6 ng/day; mean +/- SD, P<.001) but decreased with age and was the same as that of the healthy rats at 54 weeks. The urinary excretion of PGE2 by the two groups of rats was not significantly different. These results suggest that altered renal production of TXA2 and PGI2 is involved in the pathogenesis of diabetic nephropathy in rats with type 2 diabetes.

Characterization of prostanoid receptors in podocytes

Prostaglandins participate in the regulation of important glomerular functions and are involved in the pathogenesis of glomerular diseases. This study investigates the influence of prostaglandins on membrane voltage, ion conductances, cAMP accumulation, and cytosolic calcium activity ([Ca2+]i) in differentiated podocytes. Prostaglandin E2 (PGE2) caused a concentration-dependent depolarization and an increase of the whole cell conductance in podocytes (EC50 approximately 50 nM). Compared with PGE2, the EP2/EP3/EP4 receptor agonist 11-deoxy-PGE1 caused an equipotent depolarization, whereas the DP receptor agonist BW 245 C, the EP1/EP3 receptor agonist sulprostone, and the IP receptor agonist iloprost were at least 100 to 1000 times less potent than PGE2. The EP2 receptor agonist butaprost did not change membrane voltage of podocytes. The depolarizing effect of PGE2 was increased in an extracellular solution with a reduced Cl- concentration (from 145 to 32 mM). PGE2 and the prostaglandin agonists, but not the IP receptor agonist iloprost and the EP2 receptor agonist butaprost, induced a time- and concentration-dependent cAMP accumulation in podocytes. In fura-2 fluorescence experiments, PGE2, sulprostone, PGF2alpha, fluprostenol (a potent FP agonist), and U-46619 (a selective thromboxane A2 agonist) induced a biphasic increase of [Ca2+]i in 60 to 80% of podocytes. In reverse transcription-PCR studies, podocyte mRNA for the EP1, EP4, FP, and TP receptor could be amplified. These data indicate that in podocytes, PGE2 regulates distinct cellular functions via the EP1 and EP4 receptor, thereby increasing [Ca2+]i and cAMP, respectively. Furthermore, PGF1alpha and U-46619 increase [Ca2+]i via their specific receptors.

Effect of acute thromboxane A2 inhibition on the renal hemodynamics in a spontaneously non-insulin-dependent diabetic rat, Otsuka Long-Evans Tokushima Fatty rat

Thromboxane (TX) A2 plays important roles on renal injuries in streptozotocin (STZ)-induced diabetic rats, whereas its role on the renal injuries in non-insulin-dependent diabetic (NIDDM) rats remains unknown. We evaluated the effects of an intravenous infusion of TXA2 synthetase inhibitor (OKY-046, 6 mg/kg/h) on the clearances on inulin and para-aminohippurate (Cin, C(PAH)) in a spontaneously NIDDM rats, Otsuka Long-Evans Tokushima Fatty (OLETF) rats (n = 8), and Long-Evans Tokushima Otsuka (LETO) rats (n = 7), served as control rats, at the age of 40-44 weeks. OLETF rats showed obesity, moderate hyperglycemia, and hyperinsulinemia. Urinary excretion of TXB2 was slightly higher and the ratio of TXB2 to 6-keto prostaglandin F1alpha (6-kPG) was significantly higher in OLETF rats (TXB2/6-kPG: 0.22 +/- 0.04 versus 0.12 +/- 0.02, P < 0.05). Both Cin and C(PAH) were significantly higher in OLETF rats than in LETO rats (Cin: 1.1 +/- 0.1 versus 0.7 +/- 0.1 mL/min/100 g BW, C(PAH): 3.1 +/- 0.2 versus 2.3 +/- 0.3 mL/min/100gBW, P < 0.01). OKY-046 did not restore Cin and C(PAH) in OLETF rats although it significantly decreased urinary excretion of TXB2, and thus ameliorated TXB2/6-kPG in OLETF rats. These data suggested that TXA2 was not involved in the renal hyperfiltration in OLETF rats at the age of 40-44 weeks, and that TXA2 might contribute to renal injuries in OLETF rats through mechanisms other than hemodynamic injury.

Coagulation defects and altered hemodynamic responses in mice lacking receptors for thromboxane A2

Thromboxane A2 (TXA2) is a labile metabolite of arachidonic acid that has potent biological effects. Its actions are mediated by G protein-coupled thromboxane-prostanoid (TP) receptors. TP receptors have been implicated in the pathogenesis of cardiovascular diseases. To investigate the physiological functions of TP receptors, we generated TP receptor-deficient mice by gene targeting. Tp-/- animals reproduce and survive in expected numbers, and their major organ systems are normal. Thromboxane agonist binding cannot be detected in tissues from Tp-/- mice. Bleeding times are prolonged in Tp-/- mice and their platelets do not aggregate after exposure to TXA2 agonists. Aggregation responses after collagen stimulation are also delayed, although ADP-stimulated aggregation is normal. Infusion of the TP receptor agonist U-46619 causes transient increases in blood pressure followed by cardiovascular collapse in wild-type mice, but U-46619 caused no hemodynamic effect in Tp-/- mice. Tp-/- mice are also resistant to arachidonic acid-induced shock, although arachidonic acid signifi-cantly reduced blood pressure in Tp-/- mice. In summary, Tp-/- mice have a mild bleeding disorder and altered vascular responses to TXA2 and arachidonic acid. Our studies suggest that most of the recognized functions of TXA2 are mediated by the single known Tp gene locus.

Effect of selenium and vitamin E supplements on tissue lipids, peroxides, and fatty acid distribution in experimental diabetes

The protective role of selenium (Se), given as a Se-rich yeast, selenomethionine or selenomethionine + vitamin E supplement, toward changes in lipid, peroxide, and fatty acid distribution in tissues of streptozotocin-induced diabetic rats, was investigated, after 24 wk of disease. Diabetes increased liver thiobarbituric acid-reactive substances and conjugated dienes; Se supplement completely corrected these changes. In kidney, as in heart, the peroxide levels were not significantly changed by diabetes. In diabetic rat liver, a significant drop in triglycerides and phospholipids (P < 0.05) was observed; this was modulated by Se + vitamin E supplementation. Se + vitamin E supplementation also inhibited the decrease in 18:2n-6 and the increase in 22:6n-3 observed in liver of diabetic rats, changes which reflect altered glycemic control. In kidney, heart, and aorta, diabetes produced some changes in lipid content and fatty acid distribution, especially an increase in heart triglycerides which was also corrected by the Se supplement. Se supplementation to diabetic rats also increased 18:0 ether-linked alcohol, 20:4 n-6, and 22:5 n-3 in cardiac lipids. In aorta, Se + vitamin E significantly increased 20:5 n-3. These polyunsaturated fatty acids are precursors, in situ, of prostaglandin I2 (PGI2) and PGI3 which may protect against cardiovascular dysfunction. In kidney, conversely, Se decreased 20:4 n-6, the precursor of thromboxane A2 implicated in diabetic glomerular injury. Thus Se, and more efficiently Se + Vitamin E supplementation, in experimental diabetes could play a role in controlling oxidative status and altered lipid metabolism in liver, thereby maintaining favorable fatty acid distribution in the major tissues affected by diabetic complications.

Decreased activity of arachidonate 12-lipoxygenase in platelets of Japanese patients with non-insulin-dependent diabetes mellitus

To study the metabolism of the platelet 12-lipoxygenase pathway in diabetes, we evaluated the correlation between the activity and amount of arachidonate 12-lipoxygenase in the platelets of patients with non-insulin-dependent-diabetes mellitus (NIDDM). There were four parts in this investigation: (1) examination of abnormalities in platelet 12-lipoxygenase in patients with NIDDM recruited from the Hospital of Juntendo University School of Medicine; (2) comparison of 12-lipoxygenase in the platelets of non-obese NIDDM patients without angiopathy versus normal subjects matched for age, sex, and body mass index (BMI); (3) evaluation of gender differences; and (4) assessment of the potential influence of glycemic control. The activity of 12-lipoxygenase was assayed by incubation of [1-14C]arachidonic acid with the platelet cytosol. The reaction mixture was extracted and separated by thin-layer chromatography, and the radioactive end products were detected. The activity of 12-lipoxygenase in the platelets of patients with NIDDM was significantly less than in normal subjects (P < .003), whereas the amount of 12-lipoxygenase protein did not differ between the two groups. Thus, the specific activity of 12-lipoxygenase in diabetic patients was significantly less than that of normal subjects (P < .001). The enzyme activity and the specific enzyme activity of 12-lipoxygenase in non-obese NIDDM patients without angiopathy were significantly lower than the values in normal subjects matched for gender, age, and BMI (P < .006 and P < .0007, respectively). No significant difference in the activity or amount of platelet 12-lipoxygenase was observed between males and females matched for age, BMI, and disease. In addition, no relationship was observed between 12-lipoxygenase activity and blood glucose levels measured at the time of specimen collection. However, slight negative correlations were noted between 12-lipoxygenase activity and 1,5-anhydroglucitol, hemoglobin A1c (HbA1c), and fructosamine (r = .369, -.354, and -.279, respectively). When recombinant 12-lipoxygenase was incubated with varying concentrations of glucose or fructose, enzyme inactivation was related to the length of incubation, and was unaffected by glucose or fructose. These observations suggest that the activity of 12-lipoxygenase in the platelets of patients with NIDDM is decreased by prolonged hyperglycemia. The mechanism involved requires further investigation.

A central role for protein kinase C overactivity in diabetic glomerulosclerosis: implications for prevention with antioxidants, fish oil, and ACE inhibitors

The primary etiologic factor in diabetic glomerulosclerosis appears to be an overproduction of transforming growth factor-beta by mesangial cells, which in turn reflects a hyperglycemically mediated overactivation of protein kinase C (PKC) throughout the glomerulus. Membrane-active antioxidants, fish oil, and angiotensin-converting enzyme inhibitors can act to down-regulate glomerular PKC activity, via a variety of mechanisms that may include activation of diacylglycerol kinase and suppression of phosphatidate phosphohydrolase, support of endothelial nitric oxide and heparan sulfate production, inhibition of thromboxane and angiotensin synthesis/activity, and correction of glomerular hypertension. The beneficial impact of these measures on vascular endothelial function may be of more general utility in the prevention of diabetic complications such as retinopathy, neuropathy, and atherosclerosis. Adjunctive use of gamma-linolenic acid is indicated for prevention of neuropathy, and it is conceivable that bioactive chromium will have protective activity not solely attributable to improved glycemic control. Re-establishing euglycemia must clearly remain the core strategy for preventing diabetic complications, but when glycemic control remains suboptimal, practical, safe measures are at hand for decreasing risk.

Studies on the impact of dietary fat composition on proteinuria in diabetic rats

Rats with streptozotocin diabetes were pair-fed diets containing 20% beef tallow (BT), fish oil (FO), or safflower oil (SO) for up to six months. After one month, differences in glucose control were not observed but rats fed FO had more renal hypertrophy. FO reduced glomerular prostaglandin E2 and 6-keto F1 alpha, and BT increased thromboxane B2 production, but there were no differences in glomerular filtration rate (GFR) or renal plasma flow (RPF). Animals fed BT needed more insulin after two months than rats fed FO followed by SO. After six months, diabetic rats fed FO had larger relative kidney weights than SO or BT, but a similar pattern was present in non-diabetic controls fed the same diets. Diabetic rats fed BT had more proteinuria than diabetic rats fed SO but not FO. However, FO-fed controls had more proteinuria than controls fed SO and similar levels of proteinuria as diabetic rats fed FO. The composition of dietary fat alters glucose tolerance in diabetic rats after two months. BT increases glomerular thromboxane production and hastens proteinuria compared to SO. FO enhances renal growth and proteinuria, but this effect is independent of the diabetic condition.

The cardiovascular protective role of docosahexaenoic acid

Dietary fish oils rich in n-3 polyunsaturated fatty acids can modulate a diverse range of factors contributing to cardiovascular disease. This study examined the relative roles of eicosapentaenoic acid (20:5 n-3; EPA) and docosahexaenoic acid (22:6 n-3; DHA) which are the principal n-3 polyunsaturated fatty acids regarded as candidates for cardioprotective actions. At low dietary intakes (0.4-1.1% of energy (%en)), docosahexaenoic acid but not eicosapentaenoic acid inhibited ischaemia-induced cardiac arrhythmias. At intakes of 3.9-10.0%en, docosahexaenoic acid was more effective than eicosapentaenoic acid at retarding hypertension development in spontaneously hypertensive rats (SHR) and inhibiting thromboxane-like vasoconstrictor responses in aortas from SHR. In stroke-prone SHR with established hypertension, docosahexaenoic acid (3.9-10.0%en) retarded the development of salt-loading induced proteinuria but eicosapentaenoic acid alone was ineffective. The results demonstrate that purified n-3 polyunsaturated fatty acids mimic the cardiovascular actions of fish oils and imply that docosahexaenoic acid may be the principal active component conferring cardiovascular protection.

Protein kinase C in diabetic nephropathy

Protein kinase C is activated in numerous tissues obtained from diabetic animals and in several cultured cell systems exposed to high media glucose in vitro including glomerular mesangial cells. Several activators of protein kinase C, such as high media glucose, angiotensin II, phorbol ester, low density lipoprotein, and the thromboxane analogue U-46619, increase TGF beta bioactivity or mRNA expression and increase the synthesis of extracellular matrix proteins by mesangial cells in culture. The studies described in the present report support the hypothesis that activation of protein kinase C by thromboxane, an eicosanoid whose production is known to be elevated in diabetes, increases TGF beta production by mesangial cells in culture. TGF beta then acts to increase extracellular matrix protein synthesis through a mechanism that does not require active protein kinase C. Thus, activation of protein kinase C in the glomerulus in diabetes could contribute to mesangial expansion by stimulating active TGF beta production.

Protein kinase C signals thromboxane induced increases in fibronectin synthesis and TGF-beta bioactivity in mesangial cells

Previous studies have demonstrated that thromboxane (TX) stimulates matrix protein synthesis in mesangial cells (MC), and that this action is signalled by receptor mediated activation of protein kinase C (PKC). In the present study, we examined the hypothesis that activation of PKC by TX signals increases in transforming growth factor beta (TGF-beta) bioactivity, which in turn induces enhanced matrix protein synthesis. In cultured rat MC, the TXA2/prostaglandin endoperoxide analogue U-46619, but not exogenous human platelet TGF-beta 1, activated PKC as reflected by enhanced in situ phosphorylation of MARCKS protein, an endogenous substrate of PKC. U-46619 and TGF-beta 1 stimulated fibronectin (Fn) synthesis in MC, as shown by [35S]methionine incorporation into immunoprecipitable Fn. Pan-specific rabbit anti-TGF-beta antibody blocked the increases in Fn synthesis induced by exogenous TGF-beta and those induced by U-46619 at 24 to 72 hours after addition. Anti-TGF-beta antibody did not block the small increases in FN synthesis observed six hours after addition of U-46619, suggesting that this acute response was not dependent on TGF-beta. Anti-TGF-beta antibody also failed to block activation of PKC by U-46619. U-46619 and 50 nM of the PKC agonist phorbol dibutyrate (PDBu) significantly increased both the active fraction and total (latent plus active) TGF-beta in MC culture media, as assayed with the mink lung epithelial cell bioassay system.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term effect of eicosapentaenoic acid ethyl (EPA-E) on albuminuria of non-insulin dependent diabetic patients

Dietary cod-liver oil containing eicosapentaenoic acid is effective on microvascular albumin leakage in diabetic patients with albuminuria. We determined the long-term effects of oral pure eicosapentaenoic acid ethyl (EPA-E: 900 mg/day) administration on diabetic nephropathy in non-insulin dependent diabetic (NIDDM) patients. The effects of EPA-E were determined by observing the changes of the index of urine albumin excretion level/urine creatinine (Cr) excretion level (UAI), the ratio of beta 2-microglobulin excretion level/urine Cr excretion level (beta 2-MG/Cr) and the ratio of N-acetyl-D-glucosaminidase excretion level/urine Cr excretion level (NAG/Cr) at 3, 6 and 12 months after the start of the treatment. Oral EPA-E administration immediately improved the increased UAI at 3 months after the start of treatment. A significant improvement of the UAI by EPA-E was sustained 12 months later. EPA E administration also tended to decrease the urine beta 2-MG/Cr ratio from 6 months, but the difference was statistically not significant. However, the urine NAG/Cr ratio was not changed by EPA-E administration. EPA-E administration did not affect blood pressure levels, glycemic control and lipid metabolism in these patients. The present data indicated that EPA-E administration improved increased albumin excretion in NIDDM patients with nephropathy and its effects on albuminuria sustained for at least 12 months after the start of treatment. However, tubular factors were not influenced by EPA-E administration.

The effect of a thromboxane A2 synthase inhibitor on the dyslipoproteinemia of an inbred rat strain with spontaneous age-related nephrotic syndrome

We have previously shown that the administration of a thromboxane A2 (TXA2) synthase inhibitor (FCE 22178) reduced the progression of glomerular lesions and proteinuria in MNS rats, an inbred strain which develops an age-related nephrotic syndrome. In the present study we investigated the effect of FCE 22178 on the plasma lipoproteins of MNS rats at 28 weeks of age (with mild proteinuria and moderate dyslipoproteinemia) and at 48 weeks of age (with heavy proteinuria and severe dyslipoproteinemia). Drug treatment reduced proteinuria (by 70% and 36% at 28 and 48 weeks of age, respectively) plasma cholesterol (by 36% and 27% at 28 and 48 weeks of age, respectively) and prevented the decrease of plasma albumin observed in untreated rats (C-MNS) 48 weeks old. In treated rats (T-MNS), the decrease of proteinuria was positively correlated with that of plasma cholesterol. FCE 22178 reduced the elevation in plasma HDL1 (by 17.4%) and HDL2 levels (by 30%), a key feature of nephrotic dyslipoproteinemia in the rat. From 28 to 48 weeks of age plasma apo A-I and apo E increased 217% and 128%, respectively, in C-MNS rats and 191% and 121%, respectively, in T-MNS rats. A significant increase of apo A-I/apo E ratio was found in C-MNS rats from 28 (2.28 +/- 0.36) to 48 weeks of age (3.84 +/- 0.9) but not in T-MNS rats. FCE 22178 altered the lipid composition of VLDL and HDL2 by reducing the content of cholesteryl esters and increasing that of free cholesterol and phospholipids. These findings suggest that the beneficial effect of FCE 22178 on the dyslipoproteinemia of nephrotic MNS rats is secondary to the amelioration in kidney function and to the reduction of proteinuria produced by this drug.

Thromboxane stimulation of mesangial cell fibronectin synthesis is signalled by protein kinase C and modulated by cGMP

Thromboxane (TX) has been implicated in the pathogenesis of glomerulosclerosis in several models of glomerular injury. In the present study, we examined the role of the protein kinase C (PKC) signalling system in expression of the action of the TXA2/PGH2 analogue U-46619 to stimulate fibronectin (Fn) synthesis in cultured rat mesangial cells (MC), and the influence of cGMP on this MC response. U-46619 activated PKC and enhanced Fn synthesis in MC in a time and concentration dependent fashion. Both responses to U-46619 were blocked by GF 109203X, a selective inhibitor of PKC activity, as well as by calphostin C and staurosporine, PKC inhibitors structurally distinct from GFX. Down-regulation of PKC by prior sustained exposure of MC to 0.5 microM phorbol myristate acetate similarly blocked increases in Fn synthesis induced by U-46619. The TXA2/PGH2 receptor antagonist Sq-29548 also prevented activation of PKC and stimulation of Fn synthesis by U-46619, consistent with transduction of these responses via specific high affinity TXA2/PGH2 receptors on MC. Addition of exogenous 8-Br-cGMP or stimulation of endogenous cGMP generation with atrial natriuretic peptide (ANP) suppressed both U-46619 activation of PKC and stimulation of Fn synthesis. cGMP did not alter TXA2/PGH2 receptor number of affinity in MC, but significantly suppressed phorbol ester activation of PKC. Thus, cGMP inhibition of U-46619 actions is expressed at steps distal to TX receptor binding and may involve effects at and proximal to activation of PKC. Interactions between the PKC and cGMP cellular signalling systems may be important determinants of MC matrix protein production in response to TX.

n-3 fatty acids and renal diseases

There are numerous biologic rationales for the use of n-3 fatty acids in renal diseases, including a possible increase in the renal vasodilatory capacity by a rearrangement of renal prostanoid production, a reduction in the production of proinflammatory leukotrienes, a reduction in the transcapillary escape rate of albumin, and actions limiting cyclosporine-related nephrotoxicity. Studies of animal models of renal disease, mostly of immune-renal disease, support the idea of the possible usefulness of these compounds. The most promising areas of clinical investigation include the reduction of proteinuria in some chronic glomerular diseases, the treatment of immunoglobulin A nephropathy, and the prevention of cyclosporine-induced nephrotoxicity. However, the results of larger clinical studies, some of which are ongoing, are necessary to support the use of n-3 fatty acids in human renal diseases.

Acute and chronic effects of thromboxane A2 inhibition on the renal hemodynamics in streptozotocin-induced diabetic rats

We examined acute and chronic effects of thromboxane (TX) A2 inhibition on the renal hemodynamics at early and late stage of untreated streptozotocin (STZ)-induced diabetic rats. Two weeks and 28 weeks after the induction of diabetes, renal blood flow (RBF) under anesthesia was measured with an electromagnetic flowmeter before and after TXA2 inhibition. In two-week-old diabetic rats, a specific TXA2 synthetase inhibitor, OKY-046, or a specific TXA2 receptor antagonist, Sulotroban, increased renal vascular resistance (RVR) and ameliorated the hyperperfusion. The renal vasoconstrictive effect of OKY-046 was blunted by an angiotensin converting enzyme (ACE) inhibitor, MK422, or an angiotensin II receptor antagonist, Saralasin. On the contrary, OKY-046 ameliorated the renal hypoperfusion by decreasing RVR in 28-week-old diabetic rats. Chronic oral administration of OKY-046 ameliorated not only the renal hyperperfusion but increased urinary albumin excretion (UAE) at two weeks, but also the renal hypoperfusion, filtration fraction and UAE at 24 weeks. It is suggested that TXA2 might, at least in part, play important roles in the hyperperfusion by modulating activity of the renin-angiotensin system at an early stage of untreated diabetic rats and in the hypoperfusion at the late stage of untreated diabetic rats, and that TXA2 is also involved in the increase of UAE. These results support roles for TXA2 in the progression of renal injury in STZ-induced diabetic rats.

Impaired nitric oxide-dependent cyclic guanosine monophosphate generation in glomeruli from diabetic rats. Evidence for protein kinase C-mediated suppression of the cholinergic response

Nitric oxide (NO)-dependent cyclic guanosine monophosphate (cGMP) generation was examined in glomeruli isolated from 1-2-wk and 2-mo streptozotocin diabetic (D) and control (C) rats. After 1-2 wk of diabetes, ex vivo basal cGMP generation and cGMP responses to carbamylcholine (CCh) were significantly suppressed in glomeruli from D compared with those from C, whereas cGMP responses to the calcium ionophore A23187 and nitroprusside (NP) did not differ in glomeruli from D vs. those from C. After 2 mo, glomeruli from D did not respond to CCh, and responses to A23187 and NP were suppressed compared with those from C. Differences in basal, CCh, and A23187-responsive cGMP between D and C were abolished by the NO synthetase inhibitor NG-monomethyl-L-arginine. Soluble glomerular guanylate cyclase prepared from either D or C responded indistinguishably to NP, suggesting a role for NO quenching in the suppression of cGMP in intact glomeruli from D. Compared with those from C, glomeruli isolated from D demonstrated increased generation of thromboxane A2 (TXA2) and activation of protein kinase C (PKC). Both the TXA2/endoperoxide receptor antagonist Bay U3405 and inhibitors of PKC activity restored a cGMP response to CCh in glomeruli from D. Conversely, in glomeruli from C, the TXA2/endoperoxide analogue U46619 activated PKC and suppressed the cGMP response to CCh. Both of those actions were blocked by inhibitors of PKC. The results indicate a progressive impairment of NO-dependent cGMP generation in glomeruli from D which may be mediated in part by TXA2 and activation of PKC. This impairment may participate in glomerular injury in diabetes.

Effects of KW-3635, a specific thromboxane A2-receptor antagonist, on the development of lupus nephritis in NZB x NZW F1 mice

We examined the effect of KW-3635, a specific thromboxane A2 (TXA2)-receptor antagonist, on the development of lupus nephritis in NZB x NZW F1 mice. KW-3635 was orally given once a day for 33 weeks beginning at eight weeks of age. In the control group, the mice began to die at 39 weeks of age, showing severe proteinuria and histopathologic abnormality in the renal glomeruli. Administration of KW-3635 (30 mg/kg/day) significantly reduced urinary protein excretion (1.7 +/- 0.9 vs. 8.5 +/- 2.4 mg/6 hr/mouse, P < 0.01), mortality (1/18 vs. 6/19, P < 0.05) and the histopathologic score of the kidney examined at 41 weeks of age. Thus, chronic administration of KW-3635 markedly attenuated the renal disease in NZB x NZW F1 mice, suggesting that TXA2 is an important mediator of the pathogenesis in this murine model of lupus nephritis.

Eicosanoids in the pathogenesis of the functional and structural alterations of the kidney in diabetes

Diabetes mellitus alters the cellular production of eicosanoids in a number of tissues, including the kidney, and these agents have in turn been implicated in the pathogenesis of diabetic nephropathy. As delineated in the streptozotocin diabetic rat (SDR) model, a preferential enhancement of glomerular synthesis of the vasodilatory prostaglandins (PGs) PGE2 and PGI2 with concurrent smaller increases in thromboxane (TX)A2 occurs within 1 week after induction of diabetes. This early alteration in glomerular synthesis of eicosanoids in the SDR has been linked to glucose-induced activation of the glomerular protein kinase C signalling system that enhances phospholipase A2 activity and, therefore, release of membrane-bound arachidonic acid for oxygenation. The preferential increase in glomerular production of vasodilatory PGs may contribute to the glomerular hyperfiltration that is characteristic of early diabetes. After more prolonged (months) diabetes in the SDR, glomerular generation and urinary excretion of thromboxane (TX) are preferentially enhanced. Studies with selective inhibitors of TX synthesis in the SDR have implicated this eicosanoid in the pathogenesis of both albuminuria and glomerular structural changes (basement membrane thickening and mesangial matrix expansion). Direct stimulation of matrix protein production has been demonstrated in cultured mesangial cells in response to both TX and high ambient concentrations of glucose. The actions of TX and glucose on mesangial cell matrix production appear to be interactive, with each signalled through distinct pathways of protein kinase C activation.