Hepatic changes produced by 30-day administration of a novel aminocyclitol antibiotic, trospectomycin sulfate, to laboratory animals

Potential to induce lamellar bodies and acute cytotoxicity of 6'-alkyl analogues of spectinomycin in primary cultures of rat hepatocytes

A study was undertaken to investigate the potential of 6'-alkyl analogues of spectinomycin (SPE) to induce cytotoxicity and the formation of lamellar bodies in rat hepatocytes in culture. The cultured hepatocytes were treated with SPE, 6'-propylspectinomycin (trospectomycin sulphate; TRO), 6'-pentylspectinomycin (PES) or 6'-ocytlspectinomycin (OCS) in increasing concentrations up to 2.5 mm in the tissue-culture medium for 24 hr. Assay of lactate dehydrogenase (LDH) release into the medium was used to assess cytotoxicity, and the formation of lamellar bodies was assessed by transmission electron microscopy (TEM). Acid phosphatase cytochemistry was used in conjunction with TEM to determine the relationship of lamellar bodies to the lysosome. Neither SPE nor TRO produced significant cytotoxicity at the concentrations tested. Cytotoxicity was observed with PES at all concentrations >/=0.5 mm, and with OCS at all concentrations >/=0.1 mm. The number of lamellar bodies per cell section was correlated with the length of the 6'-alkyl side chain, and the capacity of the compounds to induce lamellar bodies was ranked in the order OCS > PES > TRO. Lamellar bodies were not observed above control levels in SPE-treated hepatocytes. Lamellar bodies were observed to stain positive for acid phosphatase activity, indicating that they were lysosomal. We conclude that the length of the 6'-alkyl side chain of spectinomycin analogues is correlated with acute cytotoxicity and the induction of lamellar bodies.

Drug-induced phospholipidosis: issues and future directions

Numerous drugs containing a cationic amphiphilic structure are capable of inducing phospholipidosis in cells under conditions of in vivo administration or ex vivo incubation. The principal characteristics of this condition include the reversible accumulation of polar phospholipids in association with the development of unicentric or multicentric lamellated bodies within cells. There is an abundance of data providing an understanding of potential mechanisms for the induction of phospholipidosis; however, the process is likely to be complex and may differ from one drug to another. The functional consequences of the presence of this condition on cellular or tissue function are not well understood. The general consensus is that the condition is an adaptive response rather than a toxicological manifestation; however, additional studies to examine this question are needed. Until this issue is resolved, concerns about phospholipidosis will continue to exist at regulatory agencies. Procedures for the screening of potential phospholipogenic candidate compounds are available. In contrast, a clear need exists for the identification of valid biomarkers to assess the development of phospholipidosis in preclinical and clinical studies.

Cultured hepatocytes as investigational models for hepatic toxicity: practical applications in drug discovery and development

Drugs can fail at any phase during discovery, preclinical or clinical development due to unacceptable levels of toxicity, and liver is commonly the principle target organ. Investigational toxicology methods, using appropriate models and hypotheses, can often resolve problems, identify toxic chemical substituents and salvage therapeutic discovery programs. While in vivo models are used to investigate hepatic drug effects in the context of toxicokinetics and systemic influences, cell culture models provide in vitro systems for investigating specific mechanisms in a precisely controlled environment. Using primary hepatocytes isolated from laboratory animals, we have explored several drug-induced hepatic disorders that surfaced during different phases of drug discovery and development. Additionally, the use of human hepatocytes has allowed us to address concerns for human exposure, examine human relevance of animal data, and provide perspective on problems encountered in clinical trials.

Pharmacokinetics of trospectomycin sulphate in healthy subjects after single intravenous and intramuscular doses

The pharmacokinetics of trospectomycin (75-1000 mg free base equivalents) were studied in 128 healthy males (eight per dose group), after a 20 min intravenous (i.v.) infusion and intramuscular (i.m.) injection of trospectomycin sulphate. The concentrations of trospectomycin in serum were described by bi- or tri-exponential disposition functions indicating an initial half-life of 1.1-1.4 h for the i.v. dose and 1.6-2.1 h for the i.m. dose and terminal half-lives of over 15 h. Most of the drug was eliminated rapidly (mean residence time 5-12 h). The distribution volume was 59-112% of body weight and clearance was 112-152 ml min-1. The absorption into blood after i.m. dosing was rapid. The area under the concentration-time curve and maximum concentration values were linearly related to dose. Serum drug concentrations fell below the minimum inhibitory concentration values for a variety of organisms by 8-12 h, which indicates that two or three times daily dosing would be appropriate. However, the long terminal half-life suggests that significant accumulation is likely in some tissues with an 8 h dose interval and this may prolong the action of trospectomycin.