Role of preoperative anterior segment optical coherence tomography in identifying intraoperative posterior capsular dehiscence in posterior polar cataract.

INTRODUCTION: The presence of preoperative posterior capsular dehiscence in posterior polar cataracts (PPCs) increases the chances of intraoperative posterior capsular rent. Our study aims to demonstrate the efficacy of preoperative anterior segment optical coherence tomography (ASOCT) to predict intraoperative posterior capsular rupture (PCR) in PPC. MATERIALS AND METHODS: This was an observational study including patients within 25-75 years of age, having PPC, undergoing phacoemulsification. ASOCT was done for evaluating preoperative posterior capsular status and was graded as "intact" or "dehiscent, and eventually ,intraoperative-posterior capsular status was noted. STATISTICAL ANALYSIS: SPSS (version 27.0) was used, and P value of ≤ 0.05 was considered statistically significant. RESULTS: ASOCT of 44 eyes had 9 (20.5%) dehiscent posterior capsules and 35 (79.5%) intact. Out of these 9 eyes, 7 (77.8%) had intraoperative PCR and 2 (22.2%) did not. Out of these 35, 34 (97.1%) were actually intact intraoperatively and 1 (2.9%) had intraoperative PCR. The sensitivity and specificity of ASOCT for detecting dehiscence were 94.4% and 87.5%, respectively. The positive and negative predictive values were 97.1 and 77.8, respectively. The diagnostic accuracy of the test was 95.45% with a Chi-square value of 27.01 (P < 0.0001). The diagnostic validity of ASOCT grading for detecting preoperative dehiscence was confirmed. The association between intraoperative PCR and preoperative dehiscence was statistically significant (Chi-square test - P < 0.0001). Our objective was established. DISCUSSION AND CONCLUSION: The demographics and clinical parameters were comparable with other studies. Two eyes with preoperative dehiscence on ASOCT had intact posterior capsule during surgery. The cause can be a dense opacity with increased optical density causing an obscured a clear capsule view on ASOCT, an artifact defect, giving a false impression of dehiscence. One eye who had nondehiscent PC on ASOCT was found to have PCR on the table, which can be due to an extremely thin PC or tightly adherent polar opacity to the capsule. According to our study, the diagnostic accuracy of ASOCT for detecting preoperative dehiscence was 94.4% (sensitivity)and of nondehiscence was 87.5%(specificity). 97.1% of eyes with dehiscence on ASOCT, had actual posterior capsular rent (positive predictive value). To conclude, ASOCT can be used as a reliable diagnostic modality.

Modelling of p-tyramine transport across human intestinal epithelial cells predicts the presence of additional transporters.

p-Tyramine (TYR) is an endogenous trace amine, which can also be synthesized by intestinal microbiota, and is present in commonly consumed diets. TYR is an agonist for the intracellular trace amine-associated receptor 1, which has been implicated in psychiatric, metabolic, and immune-related disorders. We have previously demonstrated TYR readily diffuses across lipid bilayers, while transport across Caco-2 cell membranes involves Organic Cation Transporter 2 (OCT2) and a Na+-dependent active transporter. Here we developed mathematical models to determine whether known kinetics for these processes are sufficient to explain observed transcellular TYR passage. Ordinary differential equations were developed for known TYR transport processes to predict concentration-time relationships. Michaelis-Menten kinetics were assumed for all transporter-mediated processes and a one phase exponential function used for simple diffusion. Modelled concentration-time plots were compared to published experimental results. Additional transporter functions were sequentially added to models to improve consistency, and a least squares error minimization approach utilized to determine added transporter kinetics. Finally, possible TYR compartmentalization was also modelled. Following apical loading, transport across the apical, but not the basolateral, membrane was modelled without additional transporters, suggesting a basolateral transporter was missing. Consistent with this, models of basolateral compartment loading did not match experimental observations, indicating missing basolateral transporters were bidirectional. Addition of a transporter with the kinetic characteristics of OCT2 did not improve models. Varying the kinetic parameters of the added transporter improved models of basolateral, but worsened apical, loading models, suggesting the need for either a directional preference in transporters, or intracellular TYR compartmentalization. Experimental parameters were recapitulated by introducing asymmetry into the apical OCT2 (Kt_OCT2_apicaltocell = 110.4 nM, Kt_OCT2_celltoapical = 1,227.9 nM), and a symmetric basolateral facilitated diffusion transporter (Vmax = 6.0 nM/s, Kt = 628.3 nM). The apparent directionality of OCT2 may reflect altered TYR ionization due to known pH differences between compartments. Models for asymmetry and compartmentalization were compared by root mean square deviation from experimental data, and it was found that TYR compartmentalization could only partially replace the need for asymmetry of OCT2. In conclusion, modelling indicates that known TYR transport processes are insufficient to explain experimental concentration-time profiles and that asymmetry of the apical membrane OCT2 combined with additional, low affinity, basolateral membrane facilitated diffusion transporters are required.

Involvement of Organic Cation Transporter 2 and a Na+-dependent active transporter in p-tyramine transport across Caco-2 intestinal cells.

AIMS: We have previously demonstrated that p-tyramine (TYR), an endogenous trace amine-associated receptor 1 agonist, passage across neuronal membranes involves a transporter exhibiting the pharmacological profile of Organic Cation Transporter 2 (OCT2). Since TYR is also a constituent of foodstuffs and produced by the intestinal microbiota, here we have investigated whether similar processes are involved in the passage of 100 nM TYR across apical and basolateral membranes of the Caco-2 human intestinal epithelial cell line. MATERIALS AND METHODS: [3H]TYR transport across apical and basolateral membranes of Caco-2 cell monolayers was measured in the presence of inhibitors of TYR metabolizing enzymes. Cellular, apical, and basolateral compartments were collected at various timepoints, TYR concentrations calculated, and transport properties pharmacologically characterized. KEY FINDINGS: Apical transport resulted in equimolar accumulation of TYR within cells. Pentamidine (OCT1/OCT2 inhibitor) decreased apical transport (P = 0.001) while atropine (OCT1 inhibitor) had no effect, suggesting apical transport involved OCT2. In contrast, basolateral transport resulted in 500-1000 nM cellular concentrations (P < 0.0001) indicating the presence of an active transporter. Replacement of Na+ on an equimolar basis with choline resulted in loss of TYR transport (P = 0.017). Unexpectedly, this active transport was also atropine-sensitive (P = 0.020). Kinetic analysis of the active transporter revealed Vmax = 43.0 nM/s with a Kt = 33.1 nM. SIGNIFICANCE: We have demonstrated for the first time that TYR is transported across Caco-2 apical membranes via facilitated diffusion by OCT2, whereas transport across basolateral membranes is by a Na+-dependent, atropine-sensitive, active transporter.