Evaluating retinal toxicity of intravitreal caspofungin in the mouse eye.

PURPOSE: Caspofungin is a synthetic echinocandin antifungal agent that inhibits the synthesis of ß(1,3)-D-glucan, an essential component of the cell wall of susceptible Aspergillus and Candida species. In this study, retinal toxicity was determined after intravitreal injection of caspofungin in a mouse model to assess its safety profile for the treatment of fungal endophthalmitis. METHODS: Caspofungin acetate was injected intravitreally in the left eyes of male C57BL/6 mice, with final vitreal concentrations corresponding to 0.41, 1.2, 2.5, 4.1, and 41 µM (five mice per cohort). A total of 25 age-matched male C57BL/6 mice injected with balanced salt solution were used as control subjects (five for each of the five different caspofungin acetate concentrations). Electroretinograms (ERGs) were recorded 7 weeks after the injections, and the injected eyes were examined histologically. RESULTS: Mice injected with caspofungin at vitreal concentrations from 0.41 to 4.1 µM did not have significant alterations in their ERG waveforms, and their retinas had no detectable morphologic changes or loss of cells. At the vitreal concentration of 41 µM, caspofungin reduced the amplitudes of the a-waves, b-waves, and scotopic threshold responses of the ERG and also produced a decrease in the number of cells in the ganglion cell layer. CONCLUSIONS: Caspofungin is a safe antifungal agent at vitreal concentrations of 0.41 to 4.1 µM in mice and consequently shows promise for the treatment of fungal endophthalmitis in humans. Much higher doses produce toxicity and should not be used.

Voltage-gated sodium channel alpha-subunits Na(v)1.1, Na(v)1.2, and Na(v)1.6 in the distal mammalian retina.

PURPOSE: Recent studies indicate the presence of functional voltage-gated sodium channels (Na(v) channels) in the distal retina in several species. This study examined the distribution of Na(v) channels in the outer plexiform layer (OPL) of rat, mouse, and rabbit retinas. METHODS: Immunohistochemical and electroretinographic approaches were used. RESULTS: Antibodies specific for Na(v)1 alpha-subunits appropriately labeled retinal ganglion cells, their axons, and amacrine cells that are known to have tetrodotoxin (TTX)-sensitive Na(v) channels. Pan-Na(v), Na(v)1.2, and Na(v)1.6 labeling was found in horizontal cells and processes in all three species. Weaker Na(v)1.1 labeling was observed in rodent horizontal cells, but some rabbit horizontal cells and processes were prominently labeled. Additional labeling for Na(v)1.1, Na(v)1.2, and Na(v)1.6 that was not attributable to horizontal cells was also present in the OPL. Much of this labeling was diffusely distributed. Some of the additional Na(v)1.1 labeling was associated with photoreceptor terminals. By exclusion using photoreceptor and horizontal cell markers, some of this labeling could have been associated with bipolar cell dendrites, although colocalization was not directly established due to the diffuse nature of the labeling and limits on anatomical resolution. No Na(v)1 alpha-subunit labeling was observed in bipolar cell bodies. Testing for functional Na(v) channels was performed by recording full field flash electroretinograms from dark-adapted rats before and after intravitreal injections of TTX, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), or TTX+CNQX. TTX and CNQX+TTX, but not CNQX alone, greatly attenuated the dark-adapted cone-driven b-waves. CONCLUSIONS: Horizontal cells from three different mammalian retinas showed prominent labeling for Na(v)1 alpha-subunits. Some additional diffuse Na(v)1 alpha-subunit labeling in the OPL was associated with photoreceptor terminals. Na(v)1 alpha-subunit labeling also may have been present on bipolar cell dendrites, although it was not possible to establish this localization unequivocally by immunostaining. However, cone-driven b-waves in rats were reduced in maximum amplitude by TTX in the presence of CNQX which blocks synaptic input to horizontal, amacrine, and ganglion cells. This finding is consistent with TTX effects on the b-wave being due to blockade of Na(v) channels in cone bipolar cell dendrites in the OPL. The role of Na(v) channels in horizontal cells remains to be determined.