(1/3) Complementary combining site contact residue mutations of the anti-digoxin Fab 26-10 permit high affinity wild-type binding.

Antibody 26-10, obtained in a secondary immune response, binds digoxin with high affinity (K(a) = 1.3 x 10(10) M(-1)) because of extensive shape complementarity. We demonstrated previously that mutations of the hapten contact residue HTrp-100 to Arg (where H refers to the heavy chain) resulted in increased specificity for digoxin analogs substituted at the cardenolide 16 position. However, mutagenesis of H:CDR1 did not result in such a specificity change despite the proximity of the H:CDR1 hapten contact residue Asn-35 to the cardenolide 16 position. Here we constructed a bacteriophage-displayed library containing randomized mutations at H chain residues 30-35 in a 26-10 mutant containing Arg-100 (26-10-RRALD). Phage were selected by panning against digoxin, gitoxin (16-OH), and 16-acetylgitoxin coupled to bovine serum albumin. Clones that retained wild-type Asn at position 35 showed preferred binding to gitoxin, like the 26-10-RRALD parent. In contrast, clones containing Val-35 selected mainly on digoxin-bovine serum albumin demonstrated a shift back to wild-type specificity. Several clones containing Val-35 bound digoxin with increased affinity, approaching that of the wild type in a few instances, in contrast to the mutation Val-35 in the wild-type 26-10 background, which reduces affinity for digoxin 90-fold. It has therefore proven possible to reorder the 26-10 binding site by mutations including two major contact residues on opposite sides of the site and yet to retain high affinity for binding for digoxin. Thus, even among antibodies that have undergone affinity maturation in vivo, different structural solutions to high affinity binding may be revealed.  (+info)

(2/3) The effect of dietary fiber on postprandial serum digoxin concentration in man.

The postprandial digoxin concentrations in serum were measured for 4 hr by radioimmunological assay in six healthy volunteers who had received 0.8 mg beta-acetyldigoxin by the oral route. Digoxin was given together with a formula diet containing as admixture, respectively, wheat bran, microcrystalline cellulose, pectin, carrageenan, and carob seed flour. The various additions did not reduce the mean digoxin concentrations in serum. After carob seed flour, the concentrations were significantly (P less than 5%) higher, as compared to the control. After microcrystalline cellulose, pectin, and wheat bran the mean peak concentrations were reached later than in the control state.  (+info)

(3/3) The effect of meloxicam on the pharmacokinetics of beta-acetyl-digoxin.

The influence of multiple-dose administration of meloxicam on the pharmacokinetics of oral beta-acetyl-digoxin was studied in 12 healthy male volunteers in a randomized double-blind two-way crossover study. The primary endpoint, Cminss, was within the accepted range for bioequivalence, as were Cmaxss and AUCss. The 90% confidence interval and the point estimator of 98.7 for Cminss were within the equivalence range of 0.8-1.25. MRT and tmax were also unchanged, while the elimination rate constant was decreased slightly by 12%, which is of no therapeutic relevance. It is concluded that co-treatment with meloxicam has no effect on the pharmacokinetics of oral digoxin.  (+info)