The investigation of the interaction between Tropicamide and bovine serum albumin by spectroscopic methods.

The fluorescence and ultraviolet-visible (UV-Vis) spectroscopy were explored to study the interaction between Tropicamide (TA) and bovine serum albumin (BSA) at three different temperatures (292, 301 and 310K) under imitated physiological conditions. The experimental results showed that the fluorescence quenching mechanism between TA and BSA was static quenching procedure. The binding constant (Ka), binding sites (n) were obtained. The corresponding thermodynamic parameters (ΔH, ΔS and ΔG) of the interaction system were calculated at different temperatures. The results revealed that the binding process is spontaneous, hydrogen binds and vander Waals were the main force to stabilize the complex. According to Förster non-radiation energy transfer theory, the binding distance between TA and BSA was calculated to be 4.90 nm. Synchronous fluorescence spectroscopy indicated the conformation of BSA changed in the presence of TA. Furthermore, the effect of some common metal ions (Mg(2+), Ca(2+), Cu(2+), and Ni(2+)) on the binding constants between TA and BSA were examined.

Evaluation of tropicamide-loaded tamarind seed xyloglucan nanoaggregates for ophthalmic delivery.

The present study was aimed to prepare tamarind seed nanoaggregates and its evaluation for ophthalmic delivery. The preparation of tropicamide-loaded tamarind seed xyloglucan nanoaggregates was optimized using face centred central composite experimental design, employing the concentrations of tamarind seed xyloglucan and Poloxamer-407, as independent variables. The results revealed that concentration of TSX has a significant antagonistic effect on particle size, while poloxamer displayed a significant synergistic effect on encapsulation efficiency. The optimal concentrations of TSX and poloxamer were found to be 0.45% (w/v) and 0.5% (w/v) respectively. The optimized formulation of tropicamide-loaded TSX nanoaggregates showed a significantly higher corneal permeation of tropicamide across the isolated goat cornea compared to commercial conventional aqueous formulation. The results revealed excellent mucoadhesive properties of TSX nanoaggregates. Further, the tropicamide-loaded TSX nanoaggregates formulation showed excellent ocular tolerance and biocompatibility as determined by hen's egg test chorioallantoic membrane and resazurin assay on Vero cell lines.

Autoradiographic localisation of muscarinic cholinergic receptor subtypes in human placenta.

The localisation of M1-M4 muscarinic cholinergic receptor subtypes was investigated in sections of normal human term placenta by light microscope autoradiography. Muscarinic cholinergic receptor subtypes were found almost exclusively in syncytiotrophoblast. Neither other cellular components of placenta, nor blood vessels were labelled. Quantitative analysis of the density of silver grains developed in sections incubated with the different protocols for labelling M1-M4 receptor subtypes, revealed that syncytiotrophoblast expresses all subtypes of muscarinic cholinergic receptor investigated. A higher density of binding sites was found in the apical than in the basal portion of syncytiotrophoblast. The demonstration of muscarinic cholinergic receptors in syncytiotrophoblast suggests that a cholinergic system may have a role in regulating transport of compounds from maternal to foetal interface.

Pharmacokinetics of topically applied cyclopentolate HCl and tropicamide.

The time course of accommodative loss after the topical application of 0.5% and 1.0% concentrations of cyclopentolate HCl and tropicamide was measured over a 20-min interval in 50 age- and sex-matched subjects between 20 and 30 years of age. Computer-assisted measures of residual accommodation provided detailed data on the temporal aspects of the cycloplegia induced by these commonly utilized drugs when used alone or with the topical anesthetic proparacaine HCl. The pattern of recovery of ocular accommodation from cycloplegia was also measured over a 5-h period, starting 2 h after drug application. The results show that latency, depth of cycloplegia, and rate of accommodative loss are regulated to drug type and concentration, and are influenced by the iris coloration of the test eye. The rate of onset of cycloplegia was not accelerated in blue or brown irides by the preadministration of proparacaine. Regardless of iris pigmentation, recovery from tropicamide cycloplegia was much faster than recovery from cyclopentolate cycloplegia. In contrast, the depth of cyclopentolate cycloplegia present in brown irides during the recovery phase was much greater than in blue irides. Mechanisms to explain these observations are proposed and clinical implications of these findings are presented.

Methods for increasing bioavailability of cycloplegics.

Since it has been shown that (1) fluid instilled in the pouch created by pulling the lower lid away from the eyeball is entrapped, (2) no fluids move into the lacrimal sac when the eyelids are shut and (3) gravity is important in tear-flow dynamics, we reasoned that an instillation technique for topical ocular drugs could be devised which would increase the drug effect for a given amount of drug. To test this hypothesis we administered one drop of 0.5% tropicamide to the right eyes of 12 young adults using an experimental method of instillation and to the left eyes using the conventional technique. The experimental technique produced a significantly greater loss of accommodation than the conventional technique. Wtih this experimental or similar technique, it may be possible to use lower concentrations of a drug to produce the same ocular effects produced by a higher concentration instilled in the conventional manner.