Studies on the formation of the penicillin antigen. II. Some reactions of d-benzylpenicillenic acid in aqueous solution at pH 7.5

Stabilizing photo-sensitive colchicine through rebalancing electron distribution of the reactive tropolone ring

Photo-sensitive tropolone was stabilized by rebalancing the electron distribution of the reactive system.

Continued need of appropriate betalactam-derived skin test reagents for the management of allergy to betalactams

Immediate allergic reactions to betalactams (BLs) are due to IgE antibodies that recognize the ring-derived penicilloyl determinant or side-chain structures of common BLs. The presence of specific IgE antibodies can be demonstrated by skin testing, the determination of specific IgE antibodies in sera or their binding to basophils with subsequent activation upon contact with penicillins in vitro. Skin tests are still the most sensitive technique followed by in vitro tests, which may sometimes yield useful complementary information. The diversity of the response to BLs has meant that in some instances, in addition to benzylpenicillin-derived determinants, testing for amoxycillin, cephalosporins or other BLs may also be required to establish the diagnosis. The recent withdrawal from the market of BL-derived materials for skin testing will have a serious effect on public health, resulting in a return to the pre-1960 era before these reagents became available. Because of their greater sensitivity, these skin tests cannot yet be replaced by in vitro tests. Furthermore, skin tests are the most readily available form of allergy testing for physicians. This paper reviews the results of skin tests in BL allergy and provides evidence for their continued need.

Studies on the dimensions of the rabbit antibenzylpenicilloyl antibody-combing sites

Rabbit antisera prepared against conjugates of the benzylpenicilloyl (BPO) bifunctional haptenic group were analyzed to determine whether the antibodies are adapted to only a portion of the large BPO molecule, or to the entire molecule, and whether specificity extends to the lysine side chain and adjoining structures of the immunizing carrier protein. No antibodies adapted to the phenylacetylamine portion of the BPO group could be detected in a pooled rabbit anti-BPO serum globulin fraction by PCA and quantitative precipitin analysis using several phenylacetylamine-protein conjugates as antigens. No antibodies adapted only to the thiazolidine carboxylic acid portion of the BPO molecule were detected in the anti-BPO globulin fraction using quantitative precipitin and hapten inhibition methods. At least the bulk of the anti-BPO antibodies was found to be adapted to the entire BPO haptenic group. By quantitative hapten inhibition of precipitation of the anti-BPO globulin fraction, the anti-BPO antibodies were found to show specificity for a 6 carbon amide side chain corresponding to the lysine side chain through which BPO groups are bound predominantly to protein. The contribution of this 6 carbon chain to antibody-hapten binding was small; (-DeltaF degrees ) was calculated to be 460 calories per mole (average). Rabbit anti-BPO antibodies prepared against BPO-rabbit serum albumin conjugates showed specificity also toward structures of the immunizing carrier protein, and possibly toward secondary or tertiary structural configurations. Penicilloyl conjugates of rabbit serum albumin precipitated from 3 individual rabbit antisera more anti-BPO antibodies than did penicilloyl conjugates of heterologous carriers (poly-L-lysine, human serum albumin, and human gamma-globulin). Anti-BPO antibodies demonstrated heterogeneity with regard to closeness of fit to the haptenic group, or with regard to the dimensions of the combining sites, or both. It was concluded that at least a large part of anti-BPO antibodies are specifically adapted to a large antigenic unit comprised of the entire BPO group, the lysine side chain, and structural configurations of the immunizing carrier protein.

Studies on the mechanism of the formation of the penicillin antigen. III. The N-(D-alpha-benzylpenicilloyl) group as an antigenic determinant responsible for hypersensitivity to penicillin G

An excess of D-benzylpenicillenic acid (BPE) was reacted with human γ-globulin, human serum albumin, gelatin, and poly-L-lysine in aqueous solution buffered at pH 7.5–8.0. Under these conditions, BPE reacted predominantly with lysine ε-amino groups of the proteins to form the mixture of diastereomers of ε-N-(D-α-benzylpenicilloyl)-lysine groups (Di-BPO-Lys). BPE reacted also, but to a considerably smaller extent, with cystine disulfide linkages of human γ-globulin and human serum albumin to form D-benzylpenicillenic acid-cysteine mixed disulfide groups (BPE-SS-Cys). Conjugates containing large numbers of BPE or D-penicillamine mixed disulfide groups were prepared by reaction of BPE or D-penicillamine with thiolated human γ-globulin under mild oxidizing conditions. Anti-penicillin antibodies were produced in rabbits by immunization with either potassium penicillin G (PG) or a preincubated mixture of PG with normal rabbit serum (PG-NRS) in complete Freund's adjuvant. Specific precipitation analyses in aqueous and gel media (Ouchterlony), PCA analyses, and specific inhibition of these reactions with haptens were carried out on the rabbit anti-PG and anti-(PG-NRS) sera, using the above conjugates as antigens. The anti-penicillin antibodies were found to be directed against the diastereomeric mixture of N-(D-α-benzylpenicilloyl) groups, predominantly the Di-BPO-Lys groups. By these techniques, no antibodies directed against the BPE-mixed disulfide or the D-penicillamine mixed disulfide groups were detected. Three out of six patients with histories of allergic reactions to PG responded with wheal-and-erythema reactions to the N-(D-α-benzylpenicilloyl) (BPO) groups contained in BPE-human gamma globulin conjugate. Another such patient exhibited serum antibodies specific for the BPO group. One patient being treated with 25 gm per day of PG showed the presence of non-dialyzable antigenic BPO-conjugates in his serum. These results demonstrate that the diastereomeric BPO groups (predominantly Di-BPO-Lys groups) are major antigenic determinant groups responsible for PG hypersensitivity in rabbits and human beings. The possible clinical usefulness of multivalent Di-BPO conjugates and univalent Di-BPO haptens is discussed.

The preparation and some properties of penicillenic acid derivatives relevant to penicillin hypersensitivity

A number of penicillenate and penicilloyl derivatives potentially useful in the study of penicillin hypersensitivity have been prepared and some of their properties described.

Drug-protein conjugates--XVII. The effect of storage on the antigenicity and immunogenicity of benzylpenicillin in the rat

The disposition and immunogenicity of freshly prepared and stored solutions of benzylpenicillin (BP) and benzylpenicillenic acid (BPE), a degradation product of BP, were studied. No IgG anti-benzylpenicilloyl (BPO) antibodies were detected by enzyme-linked immunosorbent assay (ELISA) following daily i.p. or i.m. administration to male Wistar rats of BP (2.7 mmol/kg) freshly dissolved in 0.5% glucose, for 4 consecutive days at 4-week intervals. In contrast, IgG anti-BPO antibodies were detected following both chronic i.p. and i.m. administration of BP (2.7 mmol/kg) stored for 24 hr at room temperature in 0.5% glucose. An IgG anti-BPO response was obtained only after the high dose, following daily i.m. administration of BPE (27 mumol/kg, 2.7 mumol/kg, 0.24 mumol/kg). The specificity of the IgG antibody for the BPO-determinant was confirmed by ELISA inhibition with BPO-amino-caproate. Circulating BPO plasma-protein antigens were detected by a modified ELISA following i.p. and i.m. administration of both stored and fresh BP. Significantly lower BPO-antigen levels were detected in serum following BPE administration. Irreversible binding of BP to 75% rat plasma proteins was of the same magnitude when freshly dissolved in phosphate buffer or in 0.5% glucose (2.63 +/- 0.32% and 2.55 +/- 0.25% bound, respectively after 3 hr incubation at 37 degrees). Irreversible binding was significantly greater (P less than 0.05) when the BP was stored prior to incubation with the protein (3.81 +/- 0.27%). The major degradation product of stored BP was benzylpenicilloic acid; a small amount of BPE (0.2% of incubated BP) was detected in stored but not fresh BP. Thus, the increased immunogenicity of BP stored for 24 hr at room temperature may be due to the formation of reactive degradation products such as BPE in vitro, which can then form immunogenic drug-protein conjugates in vivo. These experiments also show that although BP and BPE form drug-protein conjugates in vivo, circulating levels of antigen do not relate to the immunogenicity of either of the compounds.

Epimerization of benzylpenicilloic acid in alkaline media

5R,6R-Benzylpenicilloic acid was found to epimerize slowly in alkaline media to 5S,6R-benzylpenicilloic acid until equilibrium was established. Epimerization proceeded via the imine tautomer of penamaldic acid rather than the enamine form and was found to favor the 5S,6R-epimer at equilibrium. The conversion process was monitored using both reverse-phase high-performance liquid chromatography and NMR spectroscopy.

Demonstration of penicillamine as a product in benzylpenicillenic acid degradation in neutral media using differential pulse polarography

During the study of the temporal changes of benzylpenicillenic acid in aqueous buffers using differential pulse polarography, penicillamine was found to be a degradation product at neutral pH. Since this result was not previously reported, the effects of pH and buffer concentration on penicillamine formation were investigated. The amount of penicillamine produced was greatest under conditions producing maximum benzylpenicillenic acid stability. Penicillamine was not obtained from benzylpenicilloic acid, the reported degradation product of benzylpenicillenic acid at neutral pH. Penicillamine also was detected in penicillin G solutions of neutral pH. Therefore, it is suggested that penicillamine found in penicillin G solutions arises from benzylpenicillenic acid degradation which, in turn, is produced from penicillin G isomerization. A pathway is proposed to show that penicillamine originates from the UV-absorbing isomer of benzylpenicillenic acid.

Physicochemical properties of beta-lactam antibacterials: deuterium solvent isotope effect on penicillin G degradation rate

To obtain kinetic evidence on the degradation mechanism of penicillin in aqueous solution, degradation rates of penicillin G in water and deuterium oxide were measured in the pH (pD) range of 4-10. The solvent isotope effect (kH2O/kD2O) of 1.53 below pH (pD) 6 supports the mechanism of water-catalyzed rearrangement of undissociated penicillin G to benzylpenicillenic acid. The spontaneous degradation at neutral pH (pD) and the hydroxide-ion-catalyzed degradation in the alkaline pH (pD) range progress with a deuterium solvent isotope effect (kH2O/kD2O) of 4.5 and 0.59, respectively. This finding indicates the mechanisms of general base-catalyzed hydrolysis by water in the neutral pH range and of nucleophilic attack of the hydroxide ion on the beta-lactam in the alkaline pH range. No significant side-chain dependency was observed in the reaction of penicillins with bases. The solvent isotope studies led to the conclusion that penicillin degradation is catalyzed by a series of bases via general base-catalyzed and nucleophilic mechanisms, depending on their basicity.

High-performance liquid chromatographic analysis of ampicillin

A high-pressure liquid chromatographic method for the analysis of ampicillin is described. The method uses a 1-m long stainless steel column packed with anionic exchange resin, with a mobile phase of 0.02 M NaNO3 in 0.01 M pH 9.15 borate buffer at a flow rate of 0.45 ml/min. The degradation products of ampicillin, penicillenic and penicilloic acids of ampicillin, can be separated and quantitated in less than 12 min of chromatographic time. The relative standard deviation for the analysis of ampicillin is less than 1%, and the method is sensitive to approximately 20 ng of ampicillin/sample injected. The method was applied to the analysis of various pharmaceutical preparations of ampicillin. It is also applicable, with a slight modification, for the analysis of penicillins G and V.

Studies on the mechanism of penicillin-induced fever

Rabbits immunized to benzylpenicillin G responded with fever when challenged with a penicillin-serum protein conjugate, but not with penicillin itself. After one or two challenges with conjugate, the rabbits became unresponsive (tolerant) to further injections. This form of hypersensitivity was transferable with plasma of immunized donors to normal rabbits. Blood leukocytes of immunized rabbits incubated with penicillin-protein conjugate and hypersensitive serum released endogenous pyrogen in vitro. Spleen cells from the same animals, on the other hand, were inactive when incubated with this antigen in vitro. These experiments appear to be the first to demonstrate in vitro a possible mechanism of drug-induced fever.