The Use of Explant Lens Culture to Assess Cataractogenic Potential

Abstract

Explanted cultures of crystalline lenses have been used to investigate mechanisms of xenobiotic‐induced cataract formation. However, very few studies have utilized mechanistic information to predict the cataractogenic potential of structurally diverse xenobiotics. The present investigation outlines how visual assessment of lens clarity, biochemical endpoints of toxicity, and mechanisms of lenticular opacity formation can be used to select compounds with a lower probability of causing cataract formation in vivo. The rat lens explant culture system has been used to screen thiazolidinediones against ciglitazone for their direct cataractogenic potential in vitro. The two compounds that were selected as development candidates (englitazone and darglitazone) did not produce cataracts in rats exposed daily for 3 months. The culture system has also been used to illustrate that the lens is capable of metabolizing compounds to reactive intermediates. In this example, the toxicity of S‐(1,2‐dichlorovinyl)‐L‐cysteine (DCVC), a model cataractogen, was attenuated by inhibiting lenticular cysteine conjugate β‐lyase metabolism using aminooxyacetic acid. Finally, this model was used retrospectively to investigate the cataractogenic potential of CJ‐12,918 and CJ‐13,454 in rats. These compounds showed differences in the incidence of cataract formation in vivo based on differences in hepatic metabolism and penetration of parent drug and metabolites into the lens. The rank order of cataractogenic potential in vitro correlated better with in vivo results when an induced S9 microsomal fraction was added to the culture media. However, the model did not correctly predict the cataractogenic potential of ZD2138, a structurally similar compound. These studies illustrate the use of explant culture to assess mechanisms of cataract formation and outline its use and limitations for predicting cataractogenic potential in vivo.

Optimization of Imidazole 5-Lipoxygenase Inhibitors and Selection and Synthesis of a Development Candidate

“…In rat toxicology studies, no overt ocular toxicity was observed. [21][22][23] There have been several reports of a role of not only LTD 4 but also LTB 4 in the antigen-induced pulmonary reaction. While CycLT 1 receptor antagonists, such as pranlukast, reduce the asthmatic response, protection is incomplete.…”

“…Furthermore, no overt ocular toxicity was observed with 6, and consequently 6 was advanced to clinical development. [21][22][23][24] As already discussed, the ocular toxicity was speculated due to metabolite(s), and one of the potential explanations was that even though the systemic exposure of 2 in rats was much higher than that of 1, the incident of cataract formation with 2 was much lower than that of 1.…”

A current practice for predicting ocular toxicity of systemically delivered drugs

“…Although the lens represents a large portion of the rodent eye, it is fairly easily harvested from the rat eye and used as an explant culture (55). However, the development of this technique requires repeated practice to be able to routinely harvest lenses that are not damaged as a result of the extraction procedure.…”

“…Lenses are typically cultured in Medium 199 (Sigma-Aldrich, St. Louis, MO, USA) with various supplements, and can remain clear for periods up to 10 days. The lens explant culture model may be used to rank order and select alternative drug candidates based on their potential to cause opacity formation in vitro (55,56) and to investigate mechanisms of cataract formation with various drug candidates, such as S-(1,2-dichlorovinyl)-L-cysteine (DCVC) (57) and ciglitazone (56).…”

“…The isolated rat lens is often used as an in vitro model to rank order compounds for cataract risk and to study mechanisms of cataractogenesis (55). The benefits of using the isolated lens when compared with whole animal models include the ability to control the extracellular milieu bathing the lens (e.g., drug or other treatment conditions) and the ability to quantitatively measure biochemical or molecular endpoints associated with mechanisms of cataract formation (e.g., cholesterol biosynthesis, intracellular ion content or transport, adenosine triphosphate [ATP] content, glutathione reduction-oxidation [redox] status, and calpain activation).…”