Captopril Disulfide Research Articles

HPLC Profile of Captopril Disulfide That Undergoes Reversible cis-trans Conversion among Three Isomers

Peculiarly shaped chromatograms of some compounds that consist of two reversible isomers have been reported. Those of a compound that consists of three reversible isomers are described here. Because disulfide of captopril has two cis-trans convertible bonds, it exists in three forms of cis-cis, cis-trans and trans-trans isomers. The disulfide has produced various HPLC-UV profiles under various conditions, such as three split peaks, three peaks with bridging plateaus and one broad peak. The effect of the column temperature and the eluent flow rate on the profile was investigated and explained by interconversion among three isomers. A profile analysis could provide some kinetic constants of this reaction.

Modulation of neutrophil migration by captopril.

Because neutrophils might be involved in some of the therapeutic effects of captopril we studied the effect of captopril on neutrophil migration. Captopril strongly enhances migration by rabbit peritoneal neutrophils. Stimulation by captopril was maximal at a concentration of about 400 microM; at higher concentrations stimulation decreased again. The stimulatory effect is partly chemokinetic, and partly chemotactic. Captopril disulfide also stimulates migration, though the stimulating effect is less than that of captopril. Captopril-induced stimulation of migration was strongly inhibited by pretreatment of neutrophils with pertussis toxin, indicating that the stimulation is mediated by a pertussis toxin-sensitive G protein. Intact sulfhydryl groups on the cell surface are required for stimulation because inactivation of these groups with the non-penetrating sulfhydryl reagent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) completely abolishes the stimulating effect of captopril and of captopril disulfide. Both captopril and captopril disulfide cause an enhancement of cyclic GMP level in the neutrophil. The enhancement of both the cGMP level and that of migration is blocked by methylene blue and by LY-83583, suggesting that the stimulating effect of captopril is mediated by cGMP. Inhibitors of NO generation, such as NG-monomethyl-L-arginine, NG-nitro-L-arginine and canavanine have no effect on captopril-induced stimulation of migration, indicating that NO is not involved in the stimulating effect of captopril.

Stability of captopril in powder papers under three storage conditions

The stability of captopril in powder papers under three different storage conditions was determined. Captopril 12.5-mg tablets were triturated with lactose to a final concentration of 2 mg of captopril in 100 mg of powder. A total of 240 powder papers were prepared and stored in class "A" prescription vials (80 papers), 002G plastic zip-lock bags (80 papers), and Moisture Proof Barrier Bags (80 papers). Immediately after preparation and at 1, 2, 3, 4, 8, 12, and 24 weeks of storage at room temperature, powder papers under each storage condition were reweighed and the contents were assayed for captopril concentration by a stability-indicating high-performance liquid chromatographic method. More than 90% of the initial captopril concentration was retained under all storage conditions during the first 12 weeks of the study. Captopril disulfide, a degradation product, was detected in one sample stored in a plastic zip-lock bag at 24 weeks. Captopril was stable for the entire 24-week period in powder papers stored in either the class A prescription vial or the Moisture Proof Barrier Bag. Captopril in powder papers is stable for at least 12 weeks when stored at room temperature under all three storage conditions.

Nuclear magnetic resonance studies of thiol/disulfide chemistry: I. Kinetics and equilibria of the reduction of captopril disulfide and captopril-glutathione mixed disulfide by glutathione

The kinetics and equilibria of the reduction of captopril disulfide (CpSSCp) and captopril-glutathione mixed disulfide (GSSCp) by glutathione (GSH) have been studied by 1H and 13C NMR. Reduction takes place by thiol/disulfide exchange: GSH + CpSSCp ⇄ GSSCp + CpSH GSH + GSSCp ⇄ GSSG + CpSH . Equilibrium constants were determined as a function of pH for the two reactions; at physiological pH, the equilibrium constants for the first and second reactions are 1.46 and 0.300, respectively. The equilibrium constant for the overall reaction is 0.436, which corresponds to a difference in formal electrode potential for the two half reactions ( E GSSG GSH o′ - E CpSSCp CpSH o′ ) of 0.011 V; i.e., CpSH is more strongly reducing than GSH. Rate constants were determined as a function of pD for the forward and reverse reactions of both steps. The results indicate that, at physiological pH, the rate predicted for the in vivo reduction of CpSSCp by endogenous thiols is much slower than that oberved experimentally, which supports previous conclusions that reduction of CpSSCp to CpSH involves both enzymatic and nonenzymatic, i.e., thiol/disulfide exchange, processes.

Passive and Carrier-Mediated Intestinal Absorption Components of Captopril

The intestinal absorption mechanism of captopril was investigated in fasted rats using a single-pass perfusion method. Captopril and captopril disulfide were analyzed by HPLC. A modified boundary-layer solution was applied to determine the apparent intestinal wall permeabilities (Pw*). The results indicated that captopril is very permeable in the small intestine but not in the colon, and the permeability in the small intestine is both pH and concentration dependent. The estimated parameters for the carrier are: Km*6 mM; Jmax*, 12 mM; and Pc*2. There is also a significant passive component to captopril absorption in the small intestine. Furthermore, the intestinal permeability of captopril was significantly decreased by the withdrawal of sodium from the perfusate (3 times), and the addition of 85 mM of gly-gly (2.5 times), 15 mM of gly-pro (4 times), dipeptide mixture (4.5 times), 0.5 mM of 2,4-dinitrophenol (4 times), and 10 mM of cephradine (6 times). This is the first demonstration that an angiotensin converting enzyme (ACE) inhibitor is at least in part transported by a carrier-mediated process in the intestine via the peptide carrier system. In addition, the results showed that the peptide carrier system can transport a substrate without a “N” terminal nitrogen atom.

Pharmacokinetics of intravenous captopril in healthy men.

The pharmacokinetic characteristics of intravenously-administered captopril were investigated in 7 healthy men 20 to 33 years old. Capropril, labeled with 14C, was given by injection over a 1 min period at mean doses of 2.78 mg (13.8 microCi), 5.67 mg (28.2 microCi) and 11.4 mg (56.8 microCi). Concentrations of unchanged captopril, captopril disulfide, and other metabolites (collectively) were determined in body fluids. Pharmacokinetic parameters were calculated for unchanged captopril, and it was shown that the disposition of intravenously-administered drug was linear with respect to dose over the dosage range studied.

Reversibility of disulfide formation: Comparison of chemical and enzyme-mediated reduction of penicillamine and captopril disulfides

The reduction of penicillamine disulfide by reductants in aqueous solutions has been studied and compared with that for captopril disulfide. Whereas near quantitative reduction for captopril disulfide was achieved with tributyl phosphine (200 mM), no detectable penicillamine was formed from penicillamine disulfide. Thiol reductants (25 mM) were, however, partially able to reduce penicillamine disulfide with the most effective agent being glutathione (15% reduction) following by dithioerythritol (8%) and cysteine (5.1%). The reduction of penicillamine-cysteine disulfide by glutathione was 6-fold higher than for penicillamine disulfide. Kinetic analysis showed that the initial rate of reduction and equilibrium constant for the reduction of penicillamine disulfides by glutathione were 267- and 875-fold less than for captopril disulfide at pH 7.4. Biotransformation studies in the cytosol fraction of rat blood cells demonstrated that whereas 48% of the reduction of captopril disulfide was enzyme-mediated only 19% of the penicillamine formed was enzyme-mediated for penicillamine disulfide. Accumulation of disulfides of penicillamine in patients taking penicillamine may therefore be a problem during chronic therapy.

Kinetics and mechanism of captopril oxidation in aqueous solution under controlled oxygen partial pressure.

The stability of captopril in aqueous solution at 32 degrees C was studied in the pH range 6.6 to 8.0 under controlled oxygen partial pressure (90-760 mm Hg) with and without the addition of cupric ion. The oxidation product, captopril disulfide, was found to be the sole degradation product. A change in reaction rate from first order to zero order occurs as the captopril concentration decreases. The concentration at which this transition takes place is a function of the pH, oxygen partial pressure, and cupric ion concentration. The apparent first-order rate constants show a first-order dependency on both the oxygen partial pressure and the cupric ion concentration. However, the apparent zero-order rate constants show a first-order dependency on oxygen partial pressure and a second-order dependency on cupric ion concentration. As the pH increases from 6.6 to 8.0, the first-order process becomes more predominant. A mechanism which consists of cupric ion- and molecular oxygen-catalyzed oxidation is proposed to explain those observations.

Captopril disulfide conjugates may act as prodrugs: Disposition of the disulfide dimer of captopril in the rat

The absorption and metabolism of the disulfide dimer conjugate of captopril has been studied in the rat following both oral and intravenous dosing and compared with that of the active monomer, captopril. Metabolism of the dimer to captopril has been shown after both oral and intravenous administration of the dimer (10 mg/kg) with peak plasma levels of captopril (154 ng/ml) occurring at 1 hr post dose. By contrast the peak plasma level of captopril after oral administration of captopril (10 mg/kg) at the same dose was much higher at 678 ng/ml and also occurred at 1 hr post dose. Plasma captopril disulfide species were much higher than the plasma levels of captopril after the administration of either dimer or captopril and tended to persist for much longer than for monomeric captopril particularly after administration of the dimer. Both the dimer and its pharmacologically active product captopril were found in relatively large amounts in lung, kidney and liver following the oral administration of the dimer.

Combined gas chromatographicmass spectrometric procedure for the measurement of captopril and sulfur-conjugated metabolites of captopril in plasma and urine

A gas chromatographicmass spectrometric method is described for the simultaneous measurement of the novel anti-hypertensive drug captopril, and the following metabolites: captopril disulfide dimer, S-methyl captopril, and S-methyl captopril sulfone. With this method all derivatives can be chromatographed using conventional gas chromatography of hexafluoroisopropyl esters in one temperature-programmed run and these can then be quantitated using selected-ion monitoring techniques. Using urine or plasma, captopril, S-methyl captopril and the disulfide dimer of captopril in concentrations as low as 1 ng/ml, 10 ng/ml and 25 ng/ml, respectively can be detected. The reproducibility of the method is satisfactory both within-assay and inter-assay. This technique has demonstrated that the pattern of urinary excretion of these compounds in both man and rat was similar. Excretion of unchanged captopril, S-methyl captopril and the disulfide dimer over 6 h in man given captopril (50 or 100 mg) chronically was 18.3%, 0.97% and 3.06%, respectively. Corresponding excretion of these three compounds in the rat following a single 10 mg/kg dose was 18.3%, 2.69% and 1.8%, respectively. A possible sulfone oxidation product of S-methyl captopril was not detected in the urine of either man or rat.

Disposition of captopril in normal subjects.

The disposition of captopril, an angiotensin-converting enzyme inhibitor with antihypertensive properties, was studied in 10 normal male subjects after a single 100-mg tablet of 35S-labeled drug. Average absorption parameters for unchanged captopril in blood were Tmax 0.93 +/- 0.08 hr and Cmax 800 +/- 76 ng/ml. For total radioactivity in blood the values were Tmax 1.05 +/- 0.08 hr and Cmax 1,580 +/- 90 ng/ml (as captopril equivalents). Because of the curvilinearity of the semilogarithmic plots of blood concentrations of captopril:time, elimination half-life (t1/2) of unchanged drug could not be determined. At 1 hr unchanged captopril accounted for about 52% of total radioactivity in blood, and the dimeric disulfide metabolite of captopril accounted for about 10%. In the first 5 days after dosing, an average of about 68% of the radioactive dose was recovered in urine and 18% in feces. The distribution of radioactivity in the first 24-hr urine sample (66% of the dose) was 58% captopril (38% of dose), 2% captopril disulfide (1.5% of dose), and 40% unidentified polar metabolites (26% of dose).