Experimental evidence that ornithine and homocitrulline disrupt energy metabolism in brain of young rats.
Tissue accumulation of ornithine (Orn), homocitrulline (Hcit), ammonia and orotic acid (Oro) is the biochemical hallmark of patients affected by hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome, a disorder clinically characterized by neurological symptoms, whose pathophysiology is practically unknown. In the present study, we investigated the in vitro effect of Orn, Hcit and Oro on important parameters of energy metabolism in brain of 30-day-old Wistar rats since mitochondrial abnormalities have been observed in the affected patients. We first verified that Orn and Hcit significantly inhibited the citric acid cycle (inhibition of CO(2) synthesis from [1-(14)C] acetate, as well as aconitase and alpha-ketoglutarate dehydrogenase activities), the aerobic glycolytic pathway (reduced CO(2) production from [U-(14)C] glucose) and moderately the electron transfer flow (inhibitory effect on complex I-III). Hcit, but not Orn, was also able to significantly inhibit the mitochondrial creatine kinase activity. Furthermore, this inhibition was prevented by GSH, suggesting a possible role of reactive species oxidizing critical thiol groups of the enzyme. In contrast, the other enzyme activities of the citric acid cycle and of the electron transfer chain, as well as synaptic Na(+),K(+)-ATPase were not altered by either Orn or Hcit at concentrations as high as 5.0 mM. Similarly, Oro did not interfere with any of the tested parameters. Taken together, these data strongly indicate that Orn and Hcit compromise brain energy metabolism homeostasis and Hcit also interferes with cellular ATP transfer and buffering. It is therefore suggested that Orn and especially Hcit may be involved in the neurological damage found in patients affected by HHH syndrome.
Viegas
Carolina Maso
CM
Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, UFRGS, Porto Alegre, RS, Brazil.
Zanatta
Angela
A
Knebel
Lisiane Aurélio
LA
Schuck
Patrícia Fernanda
PF
Tonin
Anelise Miotti
AM
Ferreira
Gustavo da Costa
Gda C
Amaral
Alexandre Umpierrez
AU
Dutra Filho
Carlos Severo
CS
Wannmacher
Clovis Milton Duval
CM
Wajner
Moacir
M
D000704:Analysis of Variance; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D002952:Citric Acid Cycle / Q000187:drug effects / Q000502:physiology; D002956:Citrulline / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D003402:Creatine Kinase / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D045222:Electron Transport Chain Complex Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009952:Ornithine / Q000378:metabolism* / Q000494:pharmacology; D009963:Orotic Acid / Q000378:metabolism / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013053:Spectrophotometry; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism
D045222:Electron Transport Chain Complex Proteins; C001352:homocitrulline; D002956:Citrulline; D009963:Orotic Acid; D009952:Ornithine; D003402:Creatine Kinase; D000254:Sodium-Potassium-Exchanging ATPase