Differential induction of peroxisomal and microsomal fatty‐acid‐oxidising enzymes by peroxisome proliferators in rat liver and kidney

Abstract

The induction of renal fatty-acid-oxidising enzymes has been investigated following short-term exposure to a group of structurally diverse peroxisome proliferators and compared to the more extensively documented hepatic responses in the rat. There was a marked compound dependence on induction of both cytochrome P-450-IVA1-dependent w-hydroxylation of lauric acid and enzymes of the peroxisomal fatty acid B-oxidation pathway (measured as cyanide-insensitive palmitoyl-CoA oxidation and enoyl-CoA hydratase).Cytochrome P-450 IVAl (or a very closely related isoenzyme in the same gene family) was a major constitutive haemoprotein in rat kidney microsomes and actively supported the o-hydroxylation of lauric acid. This activity was induced 2 -%fold by peroxisome proliferators such as clofibrate, di-(2-ethylhexyl)phthalate, bezafibrate and nafenopin. By using a cDNA probe to the cytochrome P-450 IVAl gene in Northern blot analysis, we have shown that increased renal and hepatic w-hydroxylation of lauric acid, after treatment with peroxisome proliferators is a consequences of a substantial increase in the mRNA coding for this haemoprotein. In addition, programming of an in vitro rabbit reticulocyte translation system with both renal and hepatic RNA resulted in the synthesis of similar (if not identical) cytochrome-P-450-IVAl-related polypeptides. Furthermore, we have provided Western blot evidence that both rat liver and kidney microsomes contain two closely related cytochrome P-450 lVAl polypeptides, the major one characterised by a monomeric molecular mass of 51.5 kDa (identical to authentic, purified hepatic cytochrome P-450 IVA1) and a minor one of 52 kDa. The kidney-supported fatty acid w-hydroxylase activity was refractory to inhibition by a polyclonal antibody to liver cytochrome P -450 IVAl , which may be related to the existence of two closely related (but immunochemically distinct) fatty acid hydroxylases in this tissue.Our studies have also demonstrated that certain of the compounds tested (including clofibrate, bezafibrate and nafenopin) induced renal fatty acid j-oxidation, mirroring the increased w-hydroxylase activity in the endoplasmic reticulum. Our studies have also indicated that the kidney was more refractory to induction of the endoplasmic reticulum and peroxisomal fatty-acid-oxidising enzymes than the liver. Taken collectively, our data is strongly suggestive of a possible linkage of the renal fatty acid oxidative enzymes in these two organelles, a situation that also occurs in the liver. In addition, our studies have provided a possible conceptual framework that may rationalise the decreased susceptibility of the kidney to the toxicity of peroxisome proliferators.The effects of hypolipidaemic agents on rat liver have been extensively studied both in terms of the endoplasmic reticulum changes [l -61 and the associated morphometric and biochemical responses in peroxisomes [7 -91. A recent study has postulated that these adaptive responses are based on a mechanistic interrelationship, whereby chemical c...

Clofibrate prevents the development of hypertension in Dahl salt-sensitive rats.

“…On the other hand, some evidence indicates that the induction of P-450 w-hydroxylase activity may be secondary to the antilipidemic actions of clofibrate and the subsequent increase in the intracellular turnover of fatty acids. 15 If this is true, other antilipidemic agents might also induce renal P-450 w-hydroxylase activity and lower arterial pressure in Dahl SS/Jr rats. In this regard, lovastatin has been reported to lower arterial pressure in Dahl SS/Jr rats.…”

Protective effect of 20-hydroxyeicosatetraenoic acid (20-HETE) on glomerular protein permeability barrier

“…Clofibrate is known to induce CYP450 4A, the major source of 20-HETE, in kidney tissue [7][8][9][10]. Glomeruli were isolated from rats pretreated with clofibrate for 3 days, then incubated with PAN (5 lg/mL) for 15 minutes.…”

“…The mainstays of treatment of nephrotic syndrome include corticosteroids, cyclosporine A, and angiotensin-converting enzyme (ACE) inhibitors, as well as lipid-lowering agents such as fibrates, and maneuvers such as low salt diet [1]. Each of these interventions has been shown in animal models to increase renal expression and/or activity of cytochrome P450 4A (CYP450 4A), an enzyme that metabolizes arachidonic acid and other lipid mediators, and whose primary product is 20-hydroxyeicosatetraenoic acid (20-HETE) [2][3][4][5][6][7][8][9][10][11]. These observations lead us to hypothesize that 20-HETE plays an important role in the maintenance of the glomerular protein permeability barrier, and that 20-HETE is protective against agents and/or conditions that result in increased glomerular leak of protein.…”

Effects of the plasticiser DEHP on lung of newborn rats: catalase immunocytochemistry and morphometric analysis

“…Adult rats treated for 3-14 days with 1,000-2,500 mg/kg per day, showed peroxisomal proliferation and increases in activities of several enzymes, especially in the liver and, to a lesser extent, in the kidney (Osumi and Hashimoto 1978;Lake et al 1984;Sharma et al 1989;Reubsaet et al 1990). Suckling animals appeared more sensitive to lethal and growth retardation effects, while at lower doses, biochemical and morphological alterations were substantially similar to those found in adult animals (Dostal et al 1987;Cimini et al 1994;Stefanini et al 1995).…”