Endothelial cell dysfunction in homocystinuria

Abstract

This report describes the isolation and culture of venous endothelial cells from the umbilical cord of an obligate heterozygote for homocystinuria. The effect of different sulphur-containing amino acids on the viability and function of these cells was studied and compared with cultured normal endothelial cells. When endothelial cells were cultured in the presence of methionine (10 mmol/l) or homocystine (10 mmol/l), differences occurred between the viability and function of the heterozygote and normal cells in terms of 51Cr release and ability to prevent platelet adherence. The Cr release corrected for spontaneous release increases for the heterozygote cells after incubation/for 21 h in the presence of methionine to 81.3% (control cells, range: 0-23.3%, n = 5) and in the presence of homocystine to 141% (control cells, range: 13.5-55.2%, n = 5). The total number of platelets that adhere to confluent monolayers increases for heterozygote cells cultured in the presence of methionine to 0.98 X 10(7) platelets cm-2 (normal cells, range: 0.56-0.72 X 10(7) platelets cm-2) and in the presence of homocystine to 1.41 X 10(7) platelets cm-2 (normal cells, range: 0.94-1.06 X 10(7) platelets cm-2). Both normal and control cells were sensitive to homocysteine. This study/indicates for the first time what vascular endothelial cells, derived from an obligate heterozygote, are (partly) deficient in cysthathionine synthase and are more susceptible to methionine- and homocystine-mediated injury than normal endothelial cells. Consequently, in homocystinuria, due to dysfunction of the endothelial cells, toxic sulphur-containing amino acids may accumulate in these cells, causing injury of these cells.

Homocysteine Induces Programmed Cell Death in Human Vascular Endothelial Cells through Activation of the Unfolded Protein Response

“…This suggests that intracellular enzyme activities such as cystathionine ␤-synthase or 5,10-methylenetetrahydrofolate reductase are critical in regulating the intracellular homocysteine concentration. Indeed, endothelial cells possess very little cystathionine ␤-synthase activity (48), and cells heterozygous for this enzyme deficiency are more sensitive to homocysteine than normal cells (49). Thus, homocysteine-induced cell death mediated through ER stress might occur in a patient with severe hyperhomocysteinemia due to homozygous enzyme deficiency where the total plasma concentration of homocysteine increases up to 40-fold (1,18).…”

Nutritional aspects and possible pathological mechanisms of hyperhomocysteinaemia: an independent risk factor for vascular disease

“…Studies have shown that homocysteine is directly toxic to endothelial cells in a dose-dependent manner (Wall et al (1981) renal transplant recipients Brattstrom et al (1988) healthy subjects Brattstrom et al (1990) occlusive arterial disease Arnadottir et al (1993) dialysis patients Ubbink et al (1994) hyperhomocysteinaemic men Bostom et al (1997a) renal transplant recipients Dierkes et al (1998) healthy young women Lakshmi & Ramalakshmi (1998) clinical and biochemical vitamin B 6 deficiency Mansoor et al (1999) healthy subjects Groot et al 1983;Blann, 1992;Dudman 1999) and that this damage can be prevented by catalase, which indicates that the generation of H 2 O 2 possibly from homocysteine auto-oxidation, is important in the pathological process (Starkebaum & Harlan, 1986;Dudman et al 1991;Emsley et al 1999). Studies also indicate that elevated homocysteine is associated with a reduced ability to produce endothelium-derived relaxing factor (NO; Stamler et al 1993;Loscalzo, 1996;Welch et al 1997).…”

Hyperhomocysteinaemia and endothelial dysfunction in young patients with peripheral arterial occlusive disease

“…Homocysteine, a highly reactive sulphur-containing amino acid, is thought to damage endothelial cells by several mechanisms, e.g. generation of hydrogen peroxide [7] and depletion of nitric oxide-mediated detoxification of homocysteine [9], In addition, as hyperhomocysteinaemia is often due to genetic defects in the enzymes that regulate homocysteine metabolism [1,2,4,22], and because these defects are also present in endothelial cells [8], the endothelium of these individuals may be particu larly vulnerable to homocysteine toxicity [6]. Endothelial dysfunction is a central feature of current models of atherogenesis [24].…”

“…The effect on fasting and post-load homocysteine levels was studied after 6 weeks and, in patients in whom the post-load plasma concentra tion at 6 weeks was not in the normal range, again 6 weeks later. Parameters of endothelial function, and the effect of treatment on these parameters, were investigated in all patients who, in June 1993, had completed at least 1 year of treatment (n -18).…”

“…Studies in animals and in vitro indicate that high plasma concentrations of homocysteine, derived from demethylation of dietary methionine, may pre dispose to atherosclerosis by injuring the vascular endothelium, which results in endothelial dysfunc tion [5][6][7][8][9]. Pyridoxine and/or folic acid supplementa tion have been shown to reduce plasma homocysteine concentrations in mildly hyperhomocystcinaemic patients with peripheral occlusive disease [10], but it is not known to what extent such treatment nor malizes homocysteine metabolism as estimated by plasma homocysteine concentrations in the fasting state and after an oral methionine load.…”