The Effect of D-Penicillamine on Protein-Bound Homocyst(e)ine in Homocystinurics

Abstract

SummaryThere is considerable evidence that homocystine has a direct damaging effect on vascular endothelium and other tissues. The demonstration of the existance of protein-bound homocyst(e)ine has strengthened this hypothesis. In an attempt to remove bound homocyst(e)ine, mpenicillamine was given to three patients with pyridoxine-nonresponsive homocystinuria. Before the clinical trial, it had been demonstrated that 0.1 v o l e per ml concentration of ~penicillamine or cysteamine released approximately 50% of the homocyst(e)ine bound to plasma proteins in vitro. Oral mpenicillamine effectively reduced both free and plasma protein-bound homocyst(e)ine in homocystinurics from the second day of treatment. The homocystine excreted in the urine was mainly in the form of homocysteine-penicillamine disulfide. No mixed disulfide was detectable in the plasma, indicating an extremely high renal clearance. These observations suggested that oral wpenicillamine removed a considerable quantity of the bound homocyst(e)ine accumulated in the tissue proteins. Speculation D-Penicillamine treatment may be used on an experimental basis in pyridoxine-nonresponsive homocystinuric patients when dietary treatment is not practical. It may also be used in pyridoxine-responsive patients when control with pyridoxine is unsatisfactory. In addition, determination of protein-bound homocyst(e)ine should be used for the assessment of the effectiveness of therapy.Homocystinuria may be due to a metabolic block in the synthesis of cystathionine from homocysteine and serine, or due to defects in the remethylation of homocysteine to methionine, resulting in an accumulation of homocystine in the plasma and urine (1, 3, 8, 13-15, 17, 20); however, homocystine is not found in tissue fluids of normal subjects when conventional methods are used for detection.Recently, using a new method, we demonstrated the presence of protein-bound homocyst(e)ine in the plasma of both normal and homocystinuric subjects (10). Furthermore, we were able to demonstrate a significantly elevated concentration of proteinbound homocyst(e)ine (7-10-fold of normal value) in pyridoxine responsive patients when free homocystine was undetectable in the plasma. A large amount of protein-bound homocyst(e)ine was also demonstrated in the brain, liver and kidney of homocystinuric patients. These observations might account for the findings that some clinical abnormalities such as ectopia lentis and abnormal morphology in the hepatocytes persisted or developed in pyridoxine responsive homocystinuric patients despite the absence of free homocystine in their tissue fluids (4, 5, 7). We postulated that the formation of protein-bound homocyst(e)ine might be responsible for the direct damaging effect of homocystine on the vascular endothelium and other tissues. We therefore attempted to dissociate and remove protein-bound homocyst(e)ine.The studies in this paper provide evidence that oral D-penicillamine produces a significant reduction of free and plasma protein-bound homocyst(e)ine in patien...

Plasma d-penicillamine redox state evaluation by capillary electrophoresis with laser-induced fluorescence

“…Concentration of total d-Pen was 15.69 mol/l and, as previously reported [34], the predominant form of d-Pen was bound to plasma protein (14.98 mol/l) while concentrations of free oxidized and reduced forms were very low (0.532 and 0.128 mol/l) probably because reduced penicillamine was extremely reactive and free disulphides are rapidly excreted in the urine, causing a rapid loss of this fractions [30]. Moreover, as reported by other authors [17,18,35], we observe that Wilson's disease patient treated with d-Pen has lower levels of total homocysteine and cysteine (3.8 and 145 mol/l, respectively) when compared with normal subjects (10.6 and 247 mol/l) and lower concentration of protein-bound form of homocysteine and cysteine (2.64 and 57 mol/l) versus 8.4 and 142 mol/l of healthy subjects (data not shown). These finding suggest that d-Pen treatment removes a considerable quantity of homocysteine and cysteine principally from the protein-bound fraction.…”

“…For example, in cystinuria, d-Pen-cysteine disulfide formation, which is a dimer more soluble than cystine, prevents the clinical manifestation of the pathology [16]. This suggests that it may also represent a potential drug for the hyperhomocyst(e)inemia and hypercyst(e)inemia treatment, two independent risk factors for atherosclerosis and cardiovascular disease [17,18]. According to us, it is not sufficient to measure only one form or another of d-Pen (i.e., total or free) in order to evaluate the extent of disulphide interchange reactions and its therapeutic effectiveness and to accomplish more accurate pharmacokinetic studies.…”

Hydrolysis of homocysteine thiolactone results in the formation of Protein‐Cys‐S‐S‐homocysteinylation

“…A majority of homocysteine (~70-80%) exists in the protein bound form through disulfide (-S-S-) linkage. Protein-bound homocysteine is also a predominant form of homocysteine in homocystinuria [8][9][10][11][12] and various other conditions such as end stage renal disease [13][14][15] peripheral vascular disease, 16 stroke, 17 cobalamin deficiency, 18 coronary artery disease, 19 etc. In addition, it is generally believed that a small fraction of homocysteine is metabolically converted to homocysteine thiolactone (HTL), a cyclic form of homocysteine, by methionine t-RNA synthetase.…”

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

“…Drugs associated with an increase in homocysteine levels include: methotrexate, a folate antagonist, which inhibits the enzyme dihydrofolate reductase (Refsum et al 1986, Refsum & Ueland, 1990Quinn et al 1998;Morgan et al 1998); N 2 O, which inactivates vitamin B 12 (Ermens et al 1991;Christensen et al 1993;Badner et al 1998); 6-azauridine triacetate, which is a vitamin B 6 antagonist (Slavik et al 1969(Slavik et al , 1982; and anticonvulsant therapy which alters folate metabolism by mechanisms which are not clearly understood Schwaninger et al 1999). Other drugs associated with a reduction in homocysteine levels include aminothiols such as penicillamine and acetylcysteine (Kang et al 1982(Kang et al , 1986bWiklund et al 1996), and oral contraceptives and hormone therapy (Brattstrom et al 1992a;van der Mooren et al 1994;Anker et al 1995).…”