Article

Metabolic consequences of folate-induced reduction of hyperhomocysteinemia in uremia.

Institute of Biochemistry of Macromolecules, Department of Pediatrics, School of Medicine and Surgery, Second University of Naples, Italy.
Journal of the American Society of Nephrology (Impact Factor: 9.47). 01/1998; 8(12):1899-905.
Source: PubMed

ABSTRACT Plasma homocysteine, a well-recognized risk factor for cardiovascular disease, is elevated in uremic patients on hemodialysis. The authors have recently demonstrated that one consequence is the reduction in red cell membrane protein methylation levels, caused by a rise of intracellular adenosylhomocysteine, a potent inhibitor of methyltransferases. Protein methylation is involved in a repair mechanism of damaged membrane proteins, and an impairment in methylation leads to the accumulation of altered proteins. Therapy with folates, cofactors in the transformation of homocysteine to methionine, is effective in lowering plasma homocysteine. This article details a study on the metabolic effects of oral methyltetrahydrofolate, the active form of folic acid, on 14 uremic hemodialysis patients. Two months of therapy led to a significant reduction of plasma homocysteine levels, with a proportional response to pre-folate levels. In five of 13 patients with homocysteine levels above 20 microM, plasma homocysteine level was reduced to less than 15 microM. After treatment, levels of adenosylmethionine, the methyl donor in transmethylations, had significantly increased; levels of adenosylhomocysteine had increased to a smaller extent. Therefore, the ratio between the two compounds, an excellent indicator of the presence and the degree of methylation inhibition, was significantly ameliorated. Methionine plasma levels increased after treatment in all patients and were correlated with posttreatment adenosylmethionine levels. It was concluded that treatment with methyltetrahydrofolate brings the plasma homocysteine concentration back to an "acceptable" level, and the metabolic consequences are in the direction of an increase in the normal flow of transmethylations, as monitored by an increase in the [adenosylmethionine]/[adenosylhomocysteine] ratio.

Download full-text

Full-text

Available from: De Santo Natale Gaspare, Sep 12, 2014
0 Followers
 · 
89 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Diets high in methionine lead to elevation of plasma homocysteine levels which are possibly linked to neurodegenerative diseases and oxidative stress. In the present study, we investigated the effects of methionine-enriched diet on antioxidant defences, on rat spontaneous behaviour and on the ability to sustain long-term potentiation in the dentate gyrus (DG). Sprague-Dawley rats were fed either a standard laboratory diet or a methionine enriched-diet (1% or 5% methionine in drinking water) for 8 weeks. After the 8 weeks, the animals were tested for spontaneous motor activity and habituation in an open field maze, for anxiety-like behaviour in an elevated plus maze and for the ability to sustain long-term potentiation (LTP) induced in the dentate gyrus under urethane anaesthesia. The brains were then removed and histochemically stained for superoxide dismutase (SOD) activity. Rats fed on 5% methionine significantly reduced total distance travelled during the open field test and exhibited no habituation with respect to the other two groups. Rats fed on 5% methionine also showed a significant increase of the anxiety level. Moreover, in this group, the ability to induce LTP in DG was impaired. SOD activity was significantly increased in the cerebral cortex of the rats fed on 1% and 5% methionine with respect to the control group. In conclusion, 5% methionine in drinking water led to evident impairment of locomotor skills and of synaptic plasticity. SOD activity in the cortex was increased in both the groups fed on 1% and 5% methionine, thus suggesting that metabolic adjustments, triggered by the methionine-enriched diet, are likely mediated by reactive oxygen species.
    Brain research 07/2012; 1471:66-74. DOI:10.1016/j.brainres.2012.06.048 · 2.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 3-Deazaadenosin ist ein effektiver Hemmstoff der die Aktivität zellulärer Methyltransferasen regulierenden SAH-hydrolase. In vorangegangenen Arbeiten konnte gezeigt werden, dass c3Ado über seine antiinflammatorischen Wirkungen die Bildung atherosklerotischer Läsionen verhindern kann. In der hier vorliegenden Arbeit wurde der Einfluss von c3Ado auf die Funktion glatter Gefäßmuskelzellen und die Bildung einer Neointima in vivo untersucht, da diesen Vorgängen eine Schlüsselrolle in der Entstehung und bei Komplikationen vaskuloproliferativer Erkrankungen zukommt. Die Proliferation und Migration glatter Gefäßmuskelzellen in vitro wurde durch die Applikation von c3Ado dosisabhängig reduziert. Dies war begleitet von einer gesteigerten Expression der Zyklin- Kinase- Inhibitoren p21waf/cip1 und p27Kip1, einer verminderten Expression der G1/S-Phase Zykline und einer verminderten Phosphorylierung des Retinoblastom-Genproduktes. In Übereinstimmung mit diesen Ergebnissen zeigte sich in der FACS-Analyse propidiumjodidgefärbter Zellen ein Zellzyklusarrest in der G0/ G1-Phase des Zellzyklus. Diese Effekte waren weder durch eine gesteigerte Apoptoserate noch durch eine erhöhte Toxizität dieser Substanz bedingt. Weitergehende Untersuchungen zeigten, dass die Applikation von c3Ado über die Hemmung der SAH-hydrolase zu einer verminderten Aktivität der ICMT führt. Dies hemmt den letzten Schritt der posttranslationalen Modifikationen der Ras-Proteine, die Carboxylmethylierung. Die Translokalisation von Ras an die Plasmamembran und dessen nachfolgende Aktivierung ist somit nicht mehr möglich. Folge ist eine Hemmung der Ras-abhängigen Signaltransduktionswege. Entsprechend dieser Ergebnisse zeigten weitere Western Blot Analysen eine dosisabhängige Abnahme der FCS-induzierten ERK und Akt-Phosphorylierung. Durch die Überexpression einer konstitutiv aktiven Ras-Mutante konnte der Effekt von c3Ado auf die Proliferation glatter Gefäßmuskelzellen aufgehoben werden. Für die in vivo Versuche wurde die A. femoralis von C57BL/6 Mäusen dilatiert. Anschließend erhielten sie eine atherogene Diät ohne oder mit Zusatz von c3Ado. Die Fütterung mit 150 µg c3Ado verhinderte die durch Dilatation induzierte Ras-Aktivierung sowie die Phosphorylierung von Akt und ERK. Des Weiteren führte die orale Aufnahme von c3Ado über 21 Tage nach Dilatation zu einer signifikanten Reduktion der Anzahl proliferierender Zellen in Neointima und Media sowie der Fläche der Neointima im Vergleich zur Kontrollgruppe. Auch in vivo führte die Applikation von c3Ado nicht zu einer Steigerung der Apoptoserate. Die hier vorgelegten Ergebnisse zeigen, dass c3Ado in die Ras-Methylierung und Aktivierung eingreift und somit die mitogene Aktivierung von ERK und Akt hemmt. Dies resultiert in einer Hemmung des Zellzykluseintritts, einer verminderten Proliferation glatter Gefäßmuskelzellen und somit auch in einer reduzierten Neointimabildung nach Angioplastie. Somit könnte die Hemmung der SAH-hydrolase durch c3Ado einen neuen Ansatz zur Verhinderung vaskuloproliferativer Erkrankungen darstellen. 3-Deazaadenosine (c3Ado) is a potent inhibitor of S-adenosylhomocysteine (SAH)-hydrolase which regulates cellular methyltransferase activity. In the present study we sought to determine c3Ado’s effect on vascular smooth muscle cell (VSMC) function and neointima formation in vivo. C3Ado dose-dependently prevented the proliferation and migration of human coronary VSMC in vitro. This was accompanied by an increased expression of the cyclin-dependend kinase inhibitors p21WAF1/Cip1, p27Kip1, a decreased expression of G1/S-phase cyclins and a lack of retinoblastoma protein hyperphosphorylation. In accordance with these findings, FACS analysis of propidium iodide stained cells indicated a cell cycle arrest in the G0/G1 phase. Importantly, c3Ado did not affect the number of viable (trypan blue exclusion) or apoptotic cells (TUNEL). Mechanistically, c3Ado prevented FCS-induced Ras carboxyl methylation, membrane translocation and activity by inhibiting isoprenylcysteine carboxyl methyltransferase, and reduced FCS-induced ERK 1/2 and Akt phosphorylation in a dosedependent manner. Conversely, rescuing signal transduction by overexpression of a constitutive active Ras mutant abrogated c3Ado’s effect on proliferation. For in vivo studies, the femoral artery of C57BL/6 mice was dilated and mice were fed with a diet containing 150 µg c3Ado/day. c3Ado prevented dilation-induced Ras-activation as well as ERK 1/2 and Akt phosphorylation in vivo. At day 21, VSMC proliferation (7.9 ±0.7 % vs. 10.8 ± 0.8 % PCNA pos. cells, P < 0.05) as well as the neointima/media ratio (0.7 ± 0.2 vs. 1.6 ± 0.4; P < 0.05) were significantly reduced, without any changes in the number of apoptotic cells. Our data indicate that c3Ado interferes with Ras methylation and function and thereby with mitogenic activation of ERK 1/2 and Akt, preventing VSMC cell cycle entry and proliferation and neointima formation in vivo. Thus, therapeutic inhibition of SAH-hydrolase by c3Ado may represent a novel approach to prevent vascular proliferative disease.
  • American Journal of Kidney Diseases 12/1998; 32(5 Suppl 3):S172-83. DOI:10.1053/ajkd.1998.v32.pm9820474 · 5.76 Impact Factor