Subtenon lidocaine vs topical proparacaine in adult strabismus surgery

Proparacaine induces cytotoxicity and mitochondria-dependent apoptosis in corneal stromal cells both in vitro and in vivo

Proparacaine (PPC) is a widely used topical anaesthetic in the eye clinic; its abuse may damage the cornea and result in impairment of vision. Although PPC has been reported to be cytotoxic to human keratocytes, there is no scientific report about its toxic mechanisms in human corneal stroma. Here, we evaluated the cytotoxicity of PPC to corneal stroma in an in vitro model of human corneal stromal (HCS) cells and an in vivo model of cat corneas. To postulate the cellular and molecular mechanisms involved in PPC toxicity, changes in the hallmarks of apoptosis as well as in pro-apoptotic signaling pathways were investigated. Our results showed that PPC at concentrations varying from 5.0 to 0.15625 g L^-1 induced dose- and time-dependent cell atrophy, vacuolation, cytopathic effects, and viability decline in vitro. Moreover, PPC induced G₁ phase arrest, plasma membrane permeability elevation, phosphatidylserine externalization, DNA fragmentation, chromatin condensation, and apoptotic body formation of HCS cells. Furthermore, PPC could induce caspase-2, -3 and -9 activation, and mitochondrial transmembrane potential disruption. Expression of Bcl-xL and Bax were downregulated and upregulated, respectively, and cytoplasmic cytochrome c and apoptosis inducing factor were upregulated remarkably after PPC treatment. The cytotoxicity and pro-apoptotic effects of PPC were also proven by induced corneal edema, apoptotic-like ultrastructural alterations and DNA fragmentation of keratocytes in cat corneas in vivo. These results suggest that PPC above 1/32 of its clinical dosage has remarkable cytotoxicity to corneal stromal cells, which is achieved by inducing death receptor-mediated mitochondria-dependent apoptosis of HCS cells.

Local anesthetic lidocaine induces apoptosis in human corneal stromal cells in vitro

AIM

To demonstrate the apoptosis-inducing effect of lidocaine on human corneal stromal (HCS) cells in vitro, and provide experimental basis for safety anesthetic usage in clinic of ophthalmology.

METHODS

In vitro cultured HCS cells were treated with lidocaine at different doses and times, and their morphology was monitored successively with inverted phase contrast microscopy. The membrane permeability of them was detected by acridine orange/ethidium bromide (AO/EB) double staining. The DNA fragmentation of them was examined by agarose gel electrophoresis, and their ultrastructure was observed by transmission electron microscopy (TEM), respectively.

RESULTS

Exposure to lidocaine at doses from 0.3125g/L to 20g/L induced morphological changes of HCS cells such as cytoplasmic vacuolation, cellular shrinkage, and turning round, and elevated membrane permeability of these cells in AO/EB staining. The change of morphology and membrane permeability was dose- and time-dependent, while lidocaine at dose below 0.15625g/L could not induce these changes. Furthermore, lidocaine induced DNA fragmentation and ultrastructural changes such as cytoplasmic vacuolation, structural disorganization, chromatin condensation, and apoptotic body appearance of the cells.

CONCLUSION

Lidocaine has significant cytotoxicity on human corneal stromal cells in vitro in a dose- and time-dependent manner by inducing apoptosis of these cells. The established experimental model and findings based on this model here help provide new insight into the apoptosis-inducing effect of local anesthetics in eye clinic.

A randomised comparison of lidocaine 2% gel and proparacaine 0.5% eye drops in paediatric squint surgery

We conducted a randomised trial comparing lidocaine 2% gel with proparacaine 0.5% eye drops in children having elective squint surgery. One hundred and forty children aged between 3 and 14 years were recruited. The requirement for intra-operative fentanyl and postoperative ibuprofen was significantly less in the lidocaine group compared with the proparacaine group (1 (1.7%) vs 12 (18.5%), p=0.002 and 16 (27.6%) 38 (58.5%), p=0.001, respectively). The incidence of postoperative nausea and vomiting was significantly less in the lidocaine group compared with the proparacaine group (6 (10.3%) vs 16 (24.6%), p=0.04). There were no differences between the groups in terms of incidence and severity of the oculocardiac reflex. We conclude that, compared with proparacaine 0.5% eye drops, a single application of lidocaine 2% gel improves peri-operative analgesia and reduces the incidence of postoperative nausea and vomiting in elective paediatric squint surgery.