The source of heme for vascular heme oxygenase II: de novo heme biosynthesis in rat aorta

Abstract

Heme is an essential prosthetic group or substrate for many proteins, including hemoglobin, and hemo enzymes such as nitric oxide synthase, soluble guanylyl cyclase, and heme oxygenase (HO). HO is responsible for the breakdown of heme into equimolar amounts of biliverdin, iron, and carbon monoxide, the latter of which is thought to play a role in the regulation of vascular tone. It is not clear whether the source of heme for cardiovascular functions is derived from uptake from the extracellular milieu or synthesis. In this study, we tested the hypothesis that blood vessels obtain their supply of heme for HO through de novo synthesis. Adult male Sprague-Dawley rat aorta was incubated at 37 degrees C in Krebs' solution with 1 micro M [14C]delta-aminolevulinic acid (ALA). [14C]ALA uptake was linear for about 30 min and reached a plateau at approximately 100 min. The radioactivity was incorporated into porphyrins and heme as determined by esterification of 14C-labelled metabolites and thin-layer chromatography. The first and rate-limiting step of heme biosynthesis is catalyzed by ALA synthase (ALA-S), the activity of which was determined in rat aorta using a radiometric assay, approximately 250 nmol x (g wet mass)(-1) x h(-1). Inducing HO-1 in rat aorta with S-nitroso-N-acetylpenicillamine (500 micro M) did not increase ALA-S activity as compared with basal activity levels of the enzyme. It appears that there is a sufficient amount of heme available under basal ALA-S activity conditions to meet the increased demand for heme resulting from HO-1 induction. These observations indicate that the complete enzymatic pathway for de novo heme biosynthesis resides in rat aorta and furthermore indicate that de novo heme synthesis is capable of supplying a substantial portion of the heme substrate for HO in the aorta.

Vascular gene expression in mice overexpressing human endothelin-1 targeted to the endothelium

“…Alas2 encodes a rate-limiting enzyme that catalyzes the first step of the heme biosynthetic pathway (18). Heme is a constituent of NO synthase, soluble guanylyl cyclase (sGC), and heme oxygenase (HO), all important in the regulation of vascular tone (21). Ddah1 contributes to catabolize asymmetric dimethylarginine (ADMA) and NG-monomethyl-L-arginine (MMA), which are inhibitors of NO synthase and Ingenuity Pathway Analysis top networks, functions and pathways were generated for lists of differentially expressed genes in mesenteric arteries of transgenic mice with endothelium-restricted human preproendothelin-1 overexpression and compared to wild-type littermate mice using microarrays analyzed using two statistical tests, 2-sample Bayes T and cyber-T (Baldi and Long), as described in Methods.…”

Cerebroprotective Functions of HO-2

“…In the brain, endogenous heme level is comparable with that of liver (1.3 nmol/mg protein [51]). ALAS1-mediated formation of endogenous heme is required for synthesis and catabolism of hemoproteins, such as nitric oxide synthase, cyclooxygenase, and mitochondrial cytochromes, essential in brain development and functions [51,64,[70][71][72]. Moreover, HO-catalyzed degradation of endogenous heme produces vasodilator, neuromediator, antioxidant and cytoprotective compounds critical for brain functioning.…”

Effects of carbon monoxide and heme oxygenase inhibitors in cerebral vessels of rats and mice

“…For instance, rat gracilis arterioles dilate to exogenous CO as well as to the heme precursor ␦-ALA (20). Formation of ␦-ALA is the major regulatory step in the heme biosynthetic pathway, and exogenous ␦-ALA stimulates heme production and the subsequent synthesis of CO by HO (19,26,37). In the present study, administration of ␦-ALA did not dilate either rat or mouse MCAs, a result consistent with the insensitivity to exogenous CO.…”