Dietary fatty acid modulates glomerular atrial natriuretic peptide receptor

Perinatal nutrient restriction reduces nephron endowment increasing renal morbidity in adulthood: a review

Perinatal malnutrition has been included among the causes of renal disease in adulthood. Here, we consider the relationships between early supply of specific nutrients (such as protein, fat, vitamins and electrolytes) and renal endowment. Prenatal and postnatal nutrition mismatch is also discussed. In addition, this article presents the role of nutrition of both mothers and pre-term infants on nephron endowment, with final practical considerations.

Eicosapentaenoic acid inhibits PDGF-induced mitogenesis and cyclin D1 expression via TGF-beta in mesangial cells

Eicosapentaenoic acid (EPA), an omega-3 polyunsaturated fatty acid derived from fish oil, is efficacious in glomerular diseases where mesangial proliferation is a key event. We examined the mechanisms of action of EPA on platelet-derived growth factor (PDGF)-stimulated rat mesangial cell mitogenesis. EPA dose-dependently inhibited PDGF-stimulated [(3)H]-thymidine incorporation. PDGF-induced PDGF receptor autophosphorylation, an initial event for PDGF signaling, was not affected by 2 micro g/ml EPA. Similarly, PDGF-stimulated activation of extracellular signal-regulated kinase (ERK) was not altered. On the other hand, EPA inhibited cyclin-dependent kinase 4 (CDK4) activation and cyclin D1 protein induction, a critical step for G1/S progression. TGF-beta secretion assessed by ELISA and bioassay was increased by EPA at 18 h. Coincubation with anti-TGF-beta antibody inhibited the EPA-induced suppression of [(3)H]-thymidine incorporation and cyclin D1 expression. SB203580, an inhibitor of p38, a downstream kinase of TGF-beta, did not affect EPA's growth inhibitory effect. These results demonstrate that EPA inhibits PDGF-stimulated mesangial cell mitogenesis and cyclin D1 expression via TGF-beta.

Omega-3 fatty acids enhance ligament fibroblast collagen formation in association with changes in interleukin-6 production

Altering dietary ratios of n-3 and n-6 polyunsaturated fatty acids (PUFA) represents an effective nonpharmaceutical means to improve systemic inflammatory conditions. An effect of PUFA on cartilage and bone formation has been demonstrated, and the purpose of this study was to determine the potential of PUFA modulation to improve ligament healing. The effects of n-3 and n-6 PUFA on the in vitro healing response of medial collateral ligament (MCL) fibroblasts were investigated by studying the cellular coverage of an in vitro wound and the production of collagen, PGE2, IL-1, IL-6, and TNF. Cells were exposed to a bovine serum albumin (BSA) control or either eicosapentaenoic acid (EPA, 20:5n-3) or arachidonic acid (AA, 20:4n-6) in the form of soaps loaded onto BSA for 4 days and wounded on Day 5. AA and EPA improved the healing of an in vitro wound over 72 hr. EPA increased collagen synthesis and the overall percentage of collagen produced, but AA reduced collagen production and total protein. PGE2 production was increased in the AA-treated group and decreased in the EPA-treated group, but was not affected by wounding. IL-1 was not produced at the time point evaluated, but TNF and IL-6 were both produced, and their levels varied relative to the PUFA or wounding treatment. There was a significant linear correlation (r2 = 0.57, P = 0.0045) between IL-6 level and collagen production. These results demonstrate that n-3 PUFA (represented by EPA in this study) positively affect the healing characteristics of MCL cells and therefore may represent a possible noninvasive treatment to improve ligament healing. Additionally, these results show that MCL fibroblasts produce PGE2, IL-6, and TNF and that IL-6 production is related to MCL collagen synthesis.

Mechanisms of mitogen-activated protein kinase activation in experimental diabetes

Various growth factors and vasoactive substances are implicated in the pathogenesis of renal growth seen in early diabetes mellitus (DM). Mitogen-activated protein kinase (MAPK) is an important mediator of these extracellular stimuli. Protein kinase C (PKC), an enzyme known to be stimulated in DM, also activates MAPK. Thus, MAPK activity was examined in glomeruli from streptozotocin-induced DM rats. MAPK activity, measured as myelin basic protein kinase, was elevated by approximately 50% in DM versus controls (CON). Increased protein contents of p42mapk and p44mapk, as well as increased tyrosine phosphorylation and mobility shift of p42mapk, were also observed in DM. Tyrosine dephosphorylation of pp42mapk, on the other hand, assessed by incubating glomerular membrane with or without sodium orthovanadate (vanadate), was significantly diminished in DM. Protein expression of MAPK phosphatase-1 (MKP-1), a dual specificity phosphatase that inactivates MAPK, was approximately 60% of CON. Reduction in MKP-1 was reproduced in cultured mesangial cells grown under high glucose (30 mM; HG). The suppression of MKP-1 was PKC-dependent since incubation of HG cells with phorbol 12-myristate 13-acetate for 24 h abolished it. Furthermore, calcium ionophore A23187 reversed the suppression, suggesting that blunted Ca2+ signalling, characteristic of HG cells secondary to PKC stimulation, may be the cause. These results demonstrate that glomerular MAPK is activated in DM by multiple mechanisms i.e., increases in protein contents, increased phosphorylation, and decreased dephosphorylation of the enzyme due to suppression of MKP-1. These alterations may have an implication in the pathogenesis of diabetic nephropathy.

Inhibition of platelet-derived growth factor receptor tyrosine kinase by atrial natriuretic peptide

Atrial natriuretic peptide (ANP) is known to suppress platelet-derived growth factor (PDGF)-stimulated proliferation of rat cultured vascular smooth muscle cells. The present study examined whether ANP inhibits the PDGF receptor (PDGFR) tyrosine kinase activation, an initial event for PDGF cellular signaling. ANP reduced the in vivo tyrosine phosphorylation of PDGFR stimulated by PDGF in a dose-dependent manner. This effect was not due to the reduction in PDGFR protein as detected by immunoblot analysis. 8-Bromo-cyclic GMP, a membrane-permeable 3',5'-cyclic monophosphate (cGMP) derivative, mimicked the action of ANP. HS-142-1, an antagonist for guanylate cyclase A (GC-A) and B, co-incubated with ANP, restored the PDGF-induced PDGFR autophosphorylation. The effect of ANP was also observed in the presence of a protein tyrosine phosphatase inhibitor, sodium orthovanadate. To confirm that ANP exerts its action by inhibiting protein tyrosine kinase (PTK), an in vitro kinase assay was performed. Cyclic GMP inhibited PTK activity of PDGFR partially purified by lectin affinity chromatography. In contrast, PTK activity in immobilized PDGFR immunocomplexes was not inhibited by cGMP. However, exogenous cGMP dependent protein kinase (PKG) reduced the PTK activity in the presence of cGMP. These results demonstrate that ANP suppresses PDGFR PTK through GC-A probably by activating PKG. This may be an important mechanism by which ANP exerts its anti-proliferative action antagonizing PDGF.

Changes in renal hemodynamics and physiology after normothermic ischemia in animals supplemented with eicosapentaenoic acid

In order to determine whether treatment of animals with an n-3 fatty acid, eicosapentaenoic acid (EPA), could modify renal hemodynamics and physiology after normothermic ischemia, we studied 42 Spraque Dawley rats orally supplemented with either olive oil or a purified lysine salt of EPA for 4 weeks. Four experimental groups were established. Three groups were treated with increasing doses of EPA: 20 mg/kg per day (EPA 20), 40 mg/kg per day (EPA 40) and 80 mg/kg per day (EPA 80), and one group was supplemented with isovolumetric olive oil (OLI). A control group that received neither EPA nor ischemia was also studied. On day 28, right nephrectomy was performed, followed by 30 min of left renal warm ischemia. Basal arterial pressure and renal blood flow (RBF) were monitored in two kidneys before arterial occlusion and continuously thereafter throughout the experiment in one kidney using an electronic transducer and a flowmeter. From 60 to 120 min after the end of ischemia, urine output (microliter/min), glomerular filtration rate (GFR, microliter/min), measured by inulin clearance, and fractional reabsortion of sodium (FRNa) were determined every 20 min. Renal plasma flow (RPF, ml/min) and renal vascular resistance (VR, mm Hg/ml per min) were calculated. RPF was estimated as RBF (1-hematocrit). Before ischemia, the mean RPF and RBF were higher in EPA-fed than in olive oil-fed animals and after ischemia showed a significantly greater increase in EPA-fed animals than in olive oil-fed animals. Mean VR was lower in EPA-fed animals than in olive oil-fed animals, both before arterial occlusion and after ischemia. Mean urine output was similar in the OLI and EPA 20 groups, and significantly higher in the EPA 40 and EPA 80 groups than in the control group. GFR was significantly lower in the OLI and EPA 20 groups than in the control group. Finally, the EPA 40 group showed a similar and the EPA 80 group a slightly higher GFR than the control group. We conclude that EPA supplementation provides protection from renal ischemic-reperfusion injury, and this effect is more evident at higher EPA doses.