Comparative study on pharmacokinetics and toxicity of intravitreal and sub-Tenon injection of triamcinolone acetonide in ocular tissues.

AIM: To compare the differences in kinetics, distribution, and toxicity of triamcinolone acetonide (TA) between the injection methods, sub-Tenon and intravitreal injections in rabbit ocular tissues. METHODS: TA was injected into the vitreous or the sub-Tenon in rabbits. For pharmacokinetic study, rabbits were sacrificed periodically and then TA in blood and ocular tissues (retina/choroids, vitreous, and aqueous humor) were measured over 91d. For toxicological study, clinical signs, slit-lamp microscopic examination, ophthalmological test were performed. The eyeballs and surrounding tissues were collected and fixed with glutaraldehyde-formalin solution, and then paraffin embedded for histological investigation. RESULTS: Higher levels of TA were distributed in the intraocular tissues when injected into the vitreous compared to the sub-Tenon. Conversely, TA level was remarkably lower in the rabbits which received intravitreal TA injections than those treated with sub-Tenon injection throughout the study period in plasma. Optical discharge probably caused by systemic circulation of TA was observed by receiving sub-Tenon TA injection. Meanwhile, technic-associated toxicological ocular symptoms and findings were more frequently observed in intravitreal injection than in sub-Tenon injection. CONCLUSION: There are significant differences in kinetics and distribution of TA in vitreous body, aqueous humor and plasma, between the two injection methods. Although further study is needed to explain the species difference between human and rabbit, it is assumed that the difference in the frequency of intraocular pressure elevation and cataract formation by TA between the two injection methods are directly related to the TA concentrations in aqueous humor and vitreous body in each injection methods. Systemic toxicity and technic-associated toxicity are also closely related to kinetics of TA in plasma and each injection method itself, respectively.

The carboxyl-terminal region of Crtac1B/LOTUS acts as a functional domain in endogenous antagonism to Nogo receptor-1.

Myelin-derived axon growth inhibitors, such as Nogo, bind to Nogo receptor-1 (NgR1) and thereby limit the action of axonal regeneration after injury in the adult central nervous system. Recently, we have found that cartilage acidic protein-1B (Crtac1B)/lateral olfactory tract usher substance (LOTUS) binds to NgR1 and functions as an endogenous NgR1 antagonist. To examine the functional domain of LOTUS in the antagonism to NgR1, analysis using the deletion mutants of LOTUS was performed and revealed that the carboxyl-terminal region (UA/EC domain) of LOTUS bound to NgR1. The UA/EC fragment of LOTUS overexpressed together with NgR1 in COS7 cells abolished the binding of Nogo66 to NgR1. Overexpression of the UA/EC fragment in cultured chick dorsal root ganglion neurons suppressed Nogo66-induced growth cone collapse. These findings suggest that the UA/EC region is a functional domain of LOTUS serving for an antagonistic action to NgR1.

Cartilage acidic protein-1B (LOTUS), an endogenous Nogo receptor antagonist for axon tract formation.

Neural circuitry formation depends on the molecular control of axonal projection during development. By screening with fluorophore-assisted light inactivation in the developing mouse brain, we identified cartilage acidic protein-1B as a key molecule for lateral olfactory tract (LOT) formation and named it LOT usher substance (LOTUS). We further identified Nogo receptor-1 (NgR1) as a LOTUS-binding protein. NgR1 is a receptor of myelin-derived axon growth inhibitors, such as Nogo, which prevent neural regeneration in the adult. LOTUS suppressed Nogo-NgR1 binding and Nogo-induced growth cone collapse. A defasciculated LOT was present in lotus-deficient mice but not in mice lacking both lotus- and ngr1. These findings suggest that endogenous antagonism of NgR1 by LOTUS is crucial for normal LOT formation.

Developmental changes in the regulation of calcium-dependent neurite outgrowth.

Intracellular calcium ions (Ca(2+)) have an essential role in the regulation of neurite outgrowth, but how outgrowth is controlled remains largely unknown. In this study, we examined how the mechanisms of neurite outgrowth change during development in chick and mouse dorsal root ganglion neurons. 2APB, a potent inhibitor of inositol 1,4,5-trisphosphate (IP(3)) receptors (IP(3)R), inhibited neurite outgrowth at early developmental stages, but not at later stages. In contrast, pharmacological inhibition with Ni(2+), Cd(2+), or dantrolene revealed that ryanodine receptor (RyR)-mediated Ca(2+)-induced Ca(2+) release (CICR) was involved in neurite outgrowth at later stage, but not at early stages. The distribution of IP(3)R and RyR in growth cones also changed during development. Furthermore, pharmacological inhibition of the Ca(2+)-calmodulin-dependent phosphatase calcineurin with FK506 reduced neurite outgrowth only at early stages. These data suggest that the calcium signaling that regulates neurite outgrowth may change during development from an IP(3)R-mediated pathway to a RyR-mediated pathway.