Pharmacokinetics of reduced D-penicillamine in patients with rheumatoid arthritis

Bis-choline tetrathiomolybdate prevents copper-induced blood-brain barrier damage

The blood–brain barrier endothelial cell monolayer becomes permeable to elevated copper loosely bound to albumin, which can be avoided by a high-affinity copper chelator but not by D-penicillamine.

In Wilson disease, excessive copper accumulates in patients’ livers and may, upon serum leakage, severely affect the brain according to current viewpoints. Present remedies aim at avoiding copper toxicity by chelation, for example, by D-penicillamine (DPA) or bis-choline tetrathiomolybdate (ALXN1840), the latter with a very high copper affinity. Hence, ALXN1840 may potentially avoid neurological deterioration that frequently occurs upon DPA treatment. As the etiology of such worsening is unclear, we reasoned that copper loosely bound to albumin, that is, mimicking a potential liver copper leakage into blood, may damage cells that constitute the blood-brain barrier, which was found to be the case in an in vitro model using primary porcine brain capillary endothelial cells. Such blood–brain barrier damage was avoided by ALXN1840, plausibly due to firm protein embedding of the chelator bound copper, but not by DPA. Mitochondrial protection was observed, a prerequisite for blood–brain barrier integrity. Thus, high-affinity copper chelators may minimize such deterioration in the treatment of neurologic Wilson disease.

D-penicillamine-induced autoimmunity: relationship to macrophage activation

Idiosyncratic drug reactions represent a serious health problem, and they remain unpredictable largely due to our limited understanding of the mechanisms involved. Penicillamine-induced autoimmunity in Brown Norway (BN) rats represents one model of an idiosyncratic reaction, and this drug can also cause autoimmune reactions in humans. We previously demonstrated that penicillamine binds to aldehydes on the surface of macrophages. There is evidence that an imine bond formed by aldehyde groups on macrophages and amine groups on T cells is one type of interaction between these two cells that is involved in the induction of an immune response. We proposed that the binding of penicillamine with aldehyde groups on macrophages could lead to their activation and in some patients could lead to autoimmunity. In this study, the transcriptome profile of spleen macrophages 6 h after penicillamine treatment was used to detect effects of penicillamine on macrophages with a focus on 20 genes known to be macrophage activation biomarkers. One biological consequence of macrophage activation was investigated by determining mRNA levels for IL-15 and IL-1 beta which are crucial for NK cell activation, as well as levels of mRNA for selected cytokines in spleen NK cells. Up-regulation of the macrophage activating cytokines, IFN-gamma and GM-CSF, and down-regulation of IL-13 indicated activation of NK cells, which suggests a positive feedback loop between macrophages and NK cells. Furthermore, treatment of a murine macrophage cell line, RAW264.7, with penicillamine increased the production of TNF-alpha, IL-6, and IL-23, providing additional evidence that penicillamine activates macrophages. Hydralazine and isoniazid cause a lupus-like syndrome in humans and also bind to aldehyde groups. These drugs were also found to activate RAW264.7 macrophages. Together, these data support the hypothesis that drugs that bind irreversibly with aldehydes lead to macrophage activation, which in some patients can lead to an autoimmune syndrome.

A western blot approach to detection of human plasma protein conjugates derived from D-penicillamine

OBJECTIVES

To develop and apply an immunochemical approach to the study of drug-plasma protein conjugates derived from the anti-arthritic drug D-penicillamine (DP).

METHODS

An antiserum with specificity for protein-conjugated DP was raised in a rabbit. Plasma samples from patients receiving DP or from incubations of isolated normal plasma with DP were analysed for DP-derived conjugates by Western blotting using the anti-drug antibody.

RESULTS

A single DP-positive protein band was detected in plasma samples from 15/16 patients with rheumatoid arthritis receiving DP but in none of 20 patients of similar disease status who had not taken DP. The positive band appeared in patients' plasma during the course of treatment with DP. It was seen under nonreducing but not reducing conditions indicating that the drug is disulphide linked to the protein. The drug-modified protein migrated to a position intermediate between the trailing edge of albumin and the leading edge of transferrin (both non-reduced) suggesting a molecular weight of between 66 and 77 kDa. Incubations of normal human plasma, but not purified albumin or transferrin, with low concentrations of DP generated the same distinct band plus several less intense DP-positive bands.

CONCLUSIONS

Drug-plasma protein conjugates derived from DP in vivo and in vitro can be detected immunochemically by the Western blot method. Theories of DP immunotoxicity have implicated antigenicity of the drug, but this is the first immunochemical demonstration of a potential DP-derived antigen in human plasma. The method we describe may have application to studies of the relationship between DP antigenicity and toxicity.

Pharmacokinetics of oral tiopronin

Ten healthy subjects were given 500 mg (3064 mumol) tiopronin, or 2-mercaptopropionylglycine (2-MPG) by mouth. Cmax was reached after 3-6 h, and after a shorter beta-phase a long terminal half-life of 53 h of total tiopronin was found. Tiopronin measured as unbound (non-protein-bound) drug disappeared more rapidly from plasma, with a calculated t1/2 of 1.8 h. Mean residence time was higher (58 h) when calculated as total tiopronin than as unbound tiopronin (6 h), and this was also the case for the volume of distribution (V lambda = 455 l vs V lambda,u = 41 l). The results indicate extensive protein binding in plasma and a deep pool of tissue bound tiopronin after the first absorption and distribution phases. Absolute bioavailability (f) was 63%, and bioavailability calculated from urinary excretion was 47%, which are well correlated with each other. Urinary excretion was mainly confined to the first 6 h (74%) and was almost complete (98%) within 12 h. We conclude that the maximal absorption of the tiopronin was late, protein and tissue binding of the drug were high and its bioavailability varied. The renal excretion of low molecular weight tiopronin occurred early, which implies that the drug should be given in divided doses, at least twice daily, for optimal efficiency in the treatment of cystinuria.

Pharmacokinetics and bioavailability of 2-mercaptopropionylglycine administered intravenously and orally in dogs

The pharmacokinetic disposition of 2-mercaptopropionylglycine (2-MPG) given as a single intravenous injection and/or as a single oral dose was studied in 9 normal and 13 cystinuric dogs. After intravenous injection of approximately 10 or 20 mg/kg body weight the pharmacokinetics were best described by a three-exponential function. The first phase involved a distribution process apparently including establishment of drug-plasma protein and drug-tissue binding. The second phase involved rapid renal elimination and 60% of the drug was excreted within 3 h of administration. There was also a slow terminal third phase with a long half-life after both intravenous (t1/2 = 23 h) and oral (t1/2 = 22 h) administration. No dose dependency was observed. A deep pool of reversibly tissue-bound 2-MPG was indicated by a Vss of 3.3 +/- 0.9 l/kg body weight and the long terminal elimination phase. Total clearance was estimated as 4.1 +/- 0.9 ml/min/kg body weight. 2-MPG was eliminated mainly by renal excretion, but there was a difference in recovery of dose between normal and cystinuric dogs. During the first 24 h after intravenous and oral administration, 69% and 54%, respectively, of the drug was recovered in the urine of normal dogs. The corresponding figures in cystinuric dogs were 44% and 29%, respectively. The absolute bioavailability (FAUC) was 88 +/- 20% in normal dogs.

In vitro effects of two gold compounds, and D-penicillamine on the production of interferon gamma

There are contradictory reports on Interferon Gamma (IFN gamma) production by peripheral blood mononuclear cells (PBMC) in rheumatoid arthritis (RA). Since many patients previously studied were on Gold Sodium Thiomalate (GST), Auranofin (Auf), or D-Penicillamine (D-Pen) we have investigated the effects of these drugs on IFN gamma production using PBMC from normal controls (NC), and RA patients off GST, Auf, and D-Pen. Auf in low concentrations enhanced IFN gamma production by PBMC from NC but not RA; GST, and D-Pen had no effect. In other experiments PBMC were stimulated with concanavalin A (CONA A), or phytohemagglutinin (PHA). Auf, and GST inhibited IFN gamma production by CON A - stimulated NC and RA cells; D-Pen had no effect. Auf in low concentrations enhanced IFN gamma production by PHA - stimulated NC cells, but this effect was not seen with RA cells; GST inhibited both RA and NC cell production of IFN gamma, and D-Pen had no effect. Auf has a biphasic effect on IFN gamma production by NC cells with low concentrations being stimulatory or co-stimulatory, possibly by acting on T helper cells. Higher concentrations of Auf and GST, equivalent to those achieved in vivo in the course of therapy, inhibit IFN gamma production. These results suggest that gold therapy may affect IFN gamma production in RA, and could explain discrepancies noted in previous studies.

Determination of homocysteine, penicillamine, and their symmetrical and mixed disulfides by liquid chromatography with electrochemical detection

A method for the determination of D-penicillamine, homocysteine, homocystine, penicillamine-homocysteine mixed disulfide, and penicillamine disulfide in human plasma and urine is described. The method involves separation of the various thiols and disulfides by high-performance liquid chromatography with detection by a dual Hg/Au amalgam electrochemical detector. D-Penicillamine and homocysteine are detected at the downstream electrode; the disulfides are first reduced to thiols at the upstream electrode and then the thiols are detected at the downstream electrode. Hydrodynamic voltammograms were measured for the various thiols and disulfides to determine optimum settings for the electrochemical detector, and the effect of mobile phase parameters on retention times was studied to optimize the separation. A convenient method for the preparation of calibration solutions of penicillamine-homocysteine mixed disulfide by thiol/disulfide exchange with standardization of the solution by H NMR spectroscopy is described. Detection limits are below the concentrations of homocystine and penicillamine-homocysteine mixed disulfide reported to be present in the plasma and urine, respectively, of homocystinuric patients under treatment with D-penicillamine.

Determination of penicillamine, penicillamine disulfide and penicillamine-glutathione mixed disulfide by high-performance liquid chromatography with electrochemical detection

Methodology is described for the simultaneous determination of D-penicillamine, penicillamine disulfide and the penicillamine-glutathione mixed disulfide, as well as glutathione and glutathione disulfide, in human plasma, erythrocytes and urine. The various thiols and disulfides are separated by reversed-phase ion-pairing liquid chromatography with detection by an electrochemical detector with dual gold/mercury amalgam electrodes in series. The thiols are detected at the downstream electrode; the disulfides are reduced at the upstream electrode and then detected as the thiols at the downstream electrode. Detection limits (at a signal-to-noise ratio of 2.0) are in the picomole range for 20 microliters of injected solution for all compounds except penicillamine disulfide, which has a detection limit of 600 pmol in 20 microliters. A convenient method is described for preparation of the penicillamine-glutathione mixed disulfide by thiol/disulfide exchange with standardization of the solution by 1H NMR spectroscopy.

Stimulatory effects of anti-rheumatic drugs on human neutrophil functions

Auranofin (AF), D-penicillamine (D-pen) and thiola are prescribed as disease-modifying drugs in the treatment of rheumatoid arthritis (RA). We have shown here that auranofin, 10(-8) to 10(-6) M, D-penicillamine, 10(-6) to 10(-3) M, thiola, 10(-7) to 10(-3) M, and the tripeptide thiol, glutathione, 10(-6) to 10(-3) M, enhanced f-met-leu-phe-induced lysosomal enzyme release and the phagocytic uptake of bacteria by up to 40%. The previously reported inhibitory effects of AF were only observed at concentrations in excess of those likely to be available to effector cells in vivo. The stimulatory effects of thiola and D-pen occurred at concentrations likely to be available to effector cells in vivo and, therefore, may be of greater clinical relevance. There is evidence that the drugs used in this study exert their effects via a thiol moiety and their therapeutic effect is preceded by an elevation of intracellular thiol levels.

Effects of D-penicillamine on mononuclear cells in vitro

D-penicillamine (D-pen) inhibited pokeweed mitogen-induced plaque-forming cell (PFC) response in a dose-dependent manner. This inhibition was irreversible as preincubation for a few hours with the drug followed by washes still caused suppression of the PFC response. Pretreatment of the different mononuclear cell populations with D-pen for short periods (2-24 h) showed that both macrophages (Mo) and B lymphocytes were affected by the drug. By contrast T cells were resistant. Mo appears to be more susceptible to D-pen than B cells, and in the case of drug-treated Mo, the response was restored completely with the addition of 20% fresh Mo. Our results show that D-pen, without exogenous Cu2+, inhibits the polyclonal immunoglobulin secretion by human mononuclear cells in vitro due to a strong effect on both Mo and B cells. This may explain the decrease in serum immunoglobulin levels seen in patients with rheumatoid arthritis undergoing this therapy.

Identification of factors limiting the accurate measurement of plasma D-penicillamine in rheumatoid arthritis patients

Free and total reduced concentrations of D-penicillamine have been measured in the plasma of rheumatoid arthritis patients by HPLC and electro-chemical detection. A reverse-phase ion-pair separation in conjunction with a dual porous graphite electrode satisfied the requirements of robustness, sensitivity, selectivity and suitable retention time. Plasma levels measured between 1.5 and 3 h after an oral dose, were less than 0.3 to 57.6 mumol/L and 0.6 to 85.0 mumol/L (n = 26) for free and total reduced drug concentrations, respectively. Sources of error in the accurate measurement of peak plasma D-penicillamine levels were identified as oxidative loss and alteration in the free to protein-bound ratio in the period following sample collection.

Interactions of vitamin E and penicillamine in the treatment of hereditary avian muscular dystrophy

Our prior work demonstrated that penicillamine treatment of dystrophic chickens delayed the onset of symptoms, partially alleviated contractures, improved muscle function, and lowered serum creatine kinase. Penicillamine, a sulfhydryl compound with reducing properties, also prevented inactivation of glycolytic enzymes by protecting thiol groups. The present study shows that vitamin E enhances the therapeutic effects of penicillamine. Interaction of these two reductants is dose related. With vitamin E as adjunct therapy, the dosage level of penicillamine could be lowered by 50%, thereby minimizing side effects. The therapeutic rationale for two antioxidants is that penicillamine may act primarily in the cytoplasm to prevent oxidative damage, whereas the more hydrophobic vitamin E may protect membrane bilayers. Additionally, penicillamine may prevent collagen cross-linking and, deposition of insoluble collagen in muscle and thus decrease contracture formation. General applications of combined penicillamine and vitamin E therapy are discussed regarding prevention of free radical and oxidative damage in Duchenne dystrophy and a wide range of human diseases.

Enterocyte function in progressive systemic sclerosis as estimated by the deconjugation of pteroyltriglutamate to folic acid

As a measure of enterocyte function, the deconjugation of pteroyl-L-glutamyl-gamma-L-glutamyl-gamma-L-glutamic acid to folic acid and subsequent active absorption was measured in 19 patients with progressive systemic sclerosis and compared with 14 controls. The absorption step of folic acid was identical in the two groups, while deconjugation of pteroyl-L-glutamyl-gamma-L-glutamyl-gamma-L-glutamic acid was significantly decreased in the patients with progressive systemic sclerosis. This observation suggests a primary epithelial defect of the small intestine in patients with progressive systemic sclerosis.

Inhibition of T cell-dependent antibody production by D-penicillamine. Different requirements for Cu2+ in suppression of polyclonal and antigen-specific B cell responses

The effects of D-penicillamine (D-Pen) on the production of immunoglobulins (Ig) and anti-microbial antibodies (Ab) by human mononuclear cells (MNC) cultured in vitro were analysed by haemolytic plaque forming cell (PFC) assays. Polyclonal Ig and Ab production, induced by pokeweed mitogen (PWM), was not affected by D-Pen in pharmacologically relevant concentrations, unless Cu2+ was added. Likewise, D-Pen + Cu2+, but not D-Pen alone, affected polyclonal Ig production induced by Epstein-Barr virus. The production of interleukin-2 and B cell growth factor by phytohaemagglutinin-stimulated T cells was not inhibited by D-Pen; again D-Pen + Cu2+ markedly reduced the production of these cytokines. By contrast, D-Pen significantly reduced the antigen-induced antibody production without requirement of additional Cu2+. Addition of cytokine-containing supernatant to MNC treated with D-Pen + Cu2+ tended to increase the PWM-induced Ig responses, but had no effect on the antigen-induced Ab production of MNC cultured with D-Pen. Thus, the mechanisms by which D-Pen suppresses polyclonal and antigen-induced B lymphocyte responses are different.

Bioavailability of D-penicillamine in relation to gastrointestinal involvement of generalized scleroderma

The bioavailability of D-penicillamine was measured in 24 patients with generalized scleroderma (Progressive Systemic Sclerosis, PSS). Esophageal changes characteristic of generalized scleroderma were present in 15 of the patients, and 3 of those patients had duodenal involvements as well. The plasma concentrations of D-penicillamine were measured at 0 h, 1 h, 2 h, and 4 h after an oral dose of 300 mg D-penicillamine. Patients with duodenal and/or esophageal changes specific for scleroderma had significantly lower bioavailability of D-penicillamine than scleroderma patients without gastrointestinal manifestations. The decreased plasma D-penicillamine in scleroderma patients with involvement of the gastrointestinal tract may be due to an increased degradation of D-penicillamine in the gastrointestinal tract and/or an impaired absorption of the drug. Since the plasma level of D-penicillamine is so sensitive to pathological changes of the gastrointestinal tract, it may be advisable to adjust the dose of D-penicillamine on the basis of measurements of the plasma concentration of D-penicillamine.

Increased binding of D-penicillamine to monocytes in rheumatoid arthritis

Long-term therapy of D-penicillamine (D-Pen) for rheumatoid arthritis (RA) is associated with a fall in rheumatoid factor, but many patients develop autoantibodies. In vitro binding of D-Pen to human peripheral blood monocytes was examined in 37 patients with RA and 75 healthy subjects. Mononuclear cells were reacted with D-Pen coupled to a fluorescein isothiocyanate-bovine serum albumin (BSA) conjugate in the presence of sodium azide and BSA, and analyzed by flow cytometry. Patients showed significantly higher D-Pen binding to monocytes than did healthy subjects. The proportion of monocytes binding D-Pen increased with age in the patients but not in healthy subjects. None of 6 patients who had D-Pen-induced autoimmune side effects was associated with increased D-Pen binding though patients with therapeutic responses showed high D-Pen binding. These results suggest that D-Pen binding to monocytes may be important in mediating therapy and inducing autoimmune side effects.

Measurement of penicillamine and N-acetylcysteine in human blood by high-performance liquid chromatography and electrochemical detection

A rapid and precise high-performance liquid chromatographic assay for both N-acetylcysteine and penicillamine in blood samples is described using selective reductive electrochemical detection and a high-efficiency C18 reversed-phase column. The use of an internal standard compensated for changes in detector responses during a run and for variable sample recovery. The detection limits for N-acetylcysteine and penicillamine were 25 and 10 ng/ml, respectively, using 500-microliters blood samples. Reproducibility of measurement for both thiols was excellent. This method allows routine monitoring of blood levels and pharmacokinetic studies with N-acetylcysteine and penicillamine.

Bioavailability of D-penicillamine in a patient with gastrointestinal progressive systemic sclerosis

D-penicillamine pharmacokinetics were studied in a patient with gastrointestinal progressive systemic sclerosis possibly complicated by malabsorption. D-penicillamine bioavailability was examined after oral, duodenal, intravenous and rectal administration. No D-penicillamine was detectable in plasma after administration to the gastrointestinal tract. The pharmacokinetics after intravenous administration agreed closely with the corresponding situation in healthy volunteers.

In vitro production and scavenging of hydrogen peroxide by D-penicillamine. Relationship to copper availability

The capacity of D-penicillamine (DP) to produce or scavenge hydrogen peroxide was investigated. DP added to copper produced H2O2. Greater production was observed with copper sulfate than with copper bound to ceruloplasmin. In contrast, DP in the absence of copper scavenged H2O2, as measured in a direct assay. Furthermore, DP or D-cysteine alone reversed H2O2-mediated inhibition of concanavalin A-stimulated mononuclear cell proliferation. These opposing immunomodulating properties of DP may be relevant to its toxic or therapeutic actions in rheumatoid arthritis.

D-penicillamine in patients with rheumatoid arthritis. Serum levels, pharmacokinetic aspects, and correlation with clinical course and side effects

After administration of D-penicillamine to patients with rheumatoid arthritis, measurements of serum level and urinary excretion showed half-life times of 1.6 hours in the rapid phase and 4-6 days in the slow phase. The latter evidence suggests that tissue pooling occurs. With a dosage of 750 mg/day, basic serum levels of 100 microM are gradually reached. Serum D-penicillamine levels were shown to be the same for patients who responded well to treatment, those who did not respond, and for patients who had adverse side effects as well as those who had none. Intestinal resorption decreased when D-penicillamine was taken close to meals and was greatly reduced by iron preparations.

Free thiomalate levels in patients with rheumatoid arthritis treated with disodium aurothiomalate: relationship to clinical outcome of therapy

Sixteen patients with seropositive rheumatoid arthritis were treated with 20 mg disodium aurothiomalate (Myocrisin) weekly for six months. Disease activity was assessed before and after treatment. Plasma profiles and urinary excretion of free thiomalate were measured in all patients after the initial injection and again at six months in the 12 patients remaining on therapy. No difference was found in plasma levels or urinary excretion of free thiomalate between patients who responded to treatment or who developed toxic reactions and those who did not.

Cytokine modulation of chondrocyte proteinase release

Nonenzymatic, trypsin sensitive cytokines derived from lectin stimulated normal human mononuclear cells have been shown to induce release of proteoglycan and collagen degrading proteinase activity from chondrocytes in cartilage organ and isolated suspension culture systems. Active chondrocyte protein and RNA synthesis were required to induce activity. Cytokines responsible were of both monocyte and T cell origin. Direct monokine catabolic induction and monokine/lectin-triggered lymphokine inducing activity could be demonstrated. Cyclooxygenase inhibitors and direct or indirect modulation of mononuclear cell or chondrocyte cAMP levels had no effect on factor synthesis or activity. Hydrocortisone abrogated the effect. Cytokines responsible were heat labile, unaffected by reduction/alkylation or neuraminidase exposure, and stable over a pH range of 3-10.

Conversion in vitro of urinary (+)-penicillamine to its major metabolites, PSSP and PSSC

To investigate the discrepancy between the apparent pharmacokinetic disposition of (+)-penicillamine in plasma and urine, the spontaneous degradation of (+)-penicillamine was studied in acidified and non-acidified urine. Degradation was prevented by acidification. The oxidized metabolites were converted to reduced (+)-penicillamine by electrolysis.