heme-arginate and Fibrosis

Givosiran is a novel approach to treat patients with acute intermittent porphyrias (AIP) by silencing of ∂-ALA-synthase 1, the first enzyme of heme biosynthesis in the liver. We included two patients in the Envision study who responded clinically well to this treatment. However, in both patients, therapy had to be discontinued because of severe adverse effects: One patient (A) developed local injection reactions which continued to spread all over her body with increasing number of injections and eventually caused a severe systemic allergic reaction. Patient B was hospitalized because of a fulminant pancreatitis. Searching for possible causes, we also measured the patients plasma homocysteine (Hcy) levels in fluoride-containing collection tubes: by LC-MS/MS unexpectedly, plasma Hcy levels were 100 and 200 in patient A and between 100 and 400 μmol/l in patient B. Searching for germline mutations in 10 genes that are relevant for homocysteine metabolism only revealed hetero- and homozygous polymorphisms in the MTHFR gene. Alternatively, an acquired inhibition of cystathionine-beta-synthase which is important for homocysteine metabolism could explain the plasma homocysteine increase. This enzyme is heme-dependent: when we gave heme arginate to our patients, Hcy levels rapidly dropped. Hence, we conclude that inhibition of ∂-ALA-synthase 1 by givosiran causes a drop of free heme in the hepatocyte and therefore the excessive increase of plasma homocysteine. Hyperhomocysteinemia may contribute to the adverse effects seen in givosiran-treated patients which may be due to protein-N-homocysteinylation.

Topics: 5-Aminolevulinate Synthetase; Acetylgalactosamine; Adult; Arginine; Colitis; Colon, Sigmoid; Controlled Clinical Trials as Topic; Drug Hypersensitivity; Female; Fibrosis; Heme; Hepatocytes; High-Throughput Nucleotide Sequencing; Homocysteine; Humans; Hydroxymethylbilane Synthase; Hyperhomocysteinemia; Male; Models, Biological; Pancreatitis; Porphyria, Acute Intermittent; Pyrrolidines

Although heme-oxygenase (HO) is cytoprotective, its effects on podocyte regulators like podocalyxin, podocin, CD2-associated protein (CD2AP) in renal dysfunction in N (ω)-nitro-l-arginine-methyl ester (l-NAME) hypertension are largely unclear.. Hypertension was induced in normotensive Sprague Dawley rats by administering l-NAME for 4 weeks. Enzyme immunoassay, enzyme-linked immunosorbent, histology/morphology, spectrophotometry, and western immunoblotting were used. HO was enhanced with heme-arginate (HA) or inhibited with chromium mesoporphyrin (CrMP).. Treatment with heme-arginate reduced several renal histo-pathological lesions including renal arteriolar thickening, glomerular abnormalities, tubular cast, tubular atrophy/fibrosis, and mononuclear cell infiltration in l-NAME-hypertensive rats. Similarly, HA abated the elevated levels of renal extracellular matrix/profibrotic proteins like collagen and fibronectin that deplete nephrin, a fundamental transmembrane protein that forms the scaffoldings of the podocyte slit diaphragm permitting small ions to filter, but not massive excretion of proteins, hence proteinuria. Correspondingly, HA enhanced the aberrant expression of nephrin alongside other important regulators of podocyte like podocalyxin, podocin, and CD2AP, and improved renal function by reducing albuminuria/proteinuria, while increasing creatinine clearance. The renoprotection by HA were accompanied by significant reduction of inflammatory/oxidative mediators including nuclear factor-kappaB, macrophage inflammatory protein-1-alpha, macrophage chemoattractant protein-1, tumor necrosis factor-alpha, interleukin (IL)-6, IL1β, 8-isoprostane, endothelin-1, and aldosterone. These were associated with increased levels of adiponectin, HO-1, HO activity, cyclic guanosine monophosphate, and atrial natriuretic peptide (ANP), whereas the HO inhibitor, CrMP annulled the renoprotection and exacerbated renal dysfunction.. HA improves renal function by attenuating histopathological lesions, suppressing inflammatory/oxidative mediators, abating profibrotic/extracellular matrix proteins, and reducing albuminuria/proteinuria, while concomitantly potentiating the HO-adiponectin-ANP axis, enhancing nephrin, podocin, podocalyxin, CD2AP and increasing creatinine clearance. Our study underscores the benefit of potentiating the HO-adiponectin-ANP against nephropathy.

Topics: Animals; Arginine; Biomarkers; Cytoprotection; Disease Models, Animal; Enzyme Induction; Enzyme Inhibitors; Extracellular Matrix Proteins; Fibrosis; Heme; Heme Oxygenase (Decyclizing); Hypertension; Inflammation Mediators; Kidney; Male; Mesoporphyrins; NG-Nitroarginine Methyl Ester; Oxidative Stress; Podocytes; Rats, Sprague-Dawley; Signal Transduction