In vitro UVB irradiation of bovine crystalline lens causes cell damage and reduction in leucine aminopeptidase activity in lens epithelium

Surfactant and UV-B-induced damage of the cultured bovine lens

PURPOSE

To evaluate in vitro methods for testing the toxicity of the surfactants, sodium dodecyl sulfate (SDS) and benzalkonium chloride (BAK), and Ultraviolet (UV)-B radiation to the bovine lens.

METHODS

Lenses were dissected from bovine eyes--obtained from a local abattoir--and incubated in M199 culture medium at 37 degrees C, with 4% CO(2) and 96% air atmosphere. For the SDS and BAK experiments, the lenses (n = 153) were exposed directly to 0.001%, 0.01%, 0.1%, and 1.0% solutions for 15 min. These lenses were then rinsed five times each with saline and medium. Another group of lenses (n = 36) was irradiated with broadband UV-B at energy levels of 1.0 and 2.0 J/cm(2) (0.445 and 0.89 J/cm(2) in the biologically effective energy levels). For all of the above experiments, lens optical quality and cellular viability of lens epithelial cells were evaluated.

RESULTS

The analysis of optical quality, using a scanning laser in vitro assay system, of exposed lenses treated with SDS and BAK at concentrations of 0.01%, 0.1%, and 1.0%, and with UV-B at energy levels of 0.445 and 0.89 J/cm(2) showed a dose- and time-dependent increase in back vertex distance (BVD) variability, indicating loss of sharp focus in comparison with control lenses. Both 0.001% SDS and 0.001% BAK-treated lenses did not show any optical damage until 8-days after exposure. Lenses treated with 0.01% SDS showed recovery from optical damage 6-days later after exposure. Optical damage was not shown immediately for UV-B-exposed lenses. The Alamar Blue assay data for SDS, BAK and UV-B-exposed lenses, except the 0.001% SDS treated lens group, showed also dose- and time-dependent decreases in cellular viability in comparison with the control lenses, and there was no cellular recovery during the entire culture period. Lenses treated with 0.001% SDS did not show biological damage until 8-days after exposure. It appears that cellular changes appeared earlier than optical changes.

CONCLUSIONS

The findings suggest that cultured bovine lenses can be evaluated by assays that probe optical properties and cellular function after exposure to surfactants and UV-B irradiation, and that the optical and biological assay methods are valuable for in vitro mild ocular toxicity research.

Evaluation of a porcine lens and fluorescence assay approach for in vitro ocular toxicological investigations

Cell biology, as monitored with the fluorescent indicator dyes Alamar Blue and 5-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM), and lens optical quality, as measured with an in vitro scanning laser system, have been used to evaluate in vitro the condition of porcine lenses after being placed in a culture medium. The measurements, beginning from week one of culture, were compared statistically. Optical quality and cellular viability, as measured with either dye, were unchanged in lenses that had been maintained for 6 weeks in modified M199 medium. Some lenses were treated with 0.152J/cm(2) UVB radiation, and a decline was observed after 48 hours in both optical and metabolic capabilities, as indicated by a decreased capacity of the lenses to reduce Alamar Blue. The measurements with CFDA-AM did not show complete concordance with the other indicators of lens health after UV treatment, making this dye less reliable as applied currently to lens cultures. Overall, the findings suggest that porcine lenses can be maintained for weeks in culture, and that their condition can be evaluated quantitatively by assays that probe cellular functions and optical properties. Such a system should prove valuable for in vitro ocular pharmacotoxicological research.

The induction of tomato leucine aminopeptidase genes (LapA) after Pseudomonas syringae pv. tomato infection is primarily a wound response triggered by coronatine

Tomato plants constitutively express a neutral leucine aminopeptidase (LAP-N) and an acidic LAP (LAP-A) during floral development and in leaves in response to insect infestation, wounding, and Pseudomonas syringae pv. tomato infection. To assess the physiological roles of LAP-A, a LapA-antisense construct (35S:asLapA1) was introduced into tomato. The 35S:asLapA1 plants had greatly reduced or showed undetectable levels of LAP-A and LAP-N proteins in healthy and wounded leaves and during floral development. Despite the loss of these aminopeptidases, no global changes in protein profiles were noted. The 35S:asLapA1 plants also exhibited no significant alteration in floral development and did not impact the growth and development of Manduca sexta and P. syringae pv. tomato growth rates during compatible or incompatible infections. To investigate the mechanism underlying the strong induction of LapA upon P. syringae pv. tomato infection, LapA expression was monitored after infection with coronatine-producing and -deficient P. syringae pv. tomato strains. LapA RNA and activity were detected only with the coronatine-producing P. syringae pv. tomato strain. Coronatine treatment of excised shoots caused increases in RNAs for jasmonic acid (JA)-regulated wound-response genes (LapA and pin2) but did not influence expression of a JA-regulated pathogenesis-related protein gene (PR-1). These results indicated that coronatine mimicked the wound response but was insufficient to activate JA-regulated PR genes.

Specificity of the wound-induced leucine aminopeptidase (LAP-A) of tomato activity on dipeptide and tripeptide substrates

Wounding of tomato leaves results in the accumulation of an exoprotease called leucine aminopeptidase (LAP-A) that preferentially hydrolyzes amino acid-p-nitroanilide and -beta-naphthylamide substrates with N-terminal Leu, Met and Arg residues. To determine the substrate specificity of LAP-A on more natural substrates, the rates of hydrolysis of 60 dipeptide and seven tripeptide substrates were determined. For comparison, the specificities of the porcine and Escherichia coli LAPs were evaluated in parallel. Several marked differences in substrate specificities for the animal, plant and prokaryotic LAP enzymes were observed. Substrates with variable N-terminal (P1) residues (Xaa) were evaluated; these substrates had Leu or Gly in the penultimate (P1') position. The plant, animal, and prokaryotic LAPs hydrolyzed dipeptides with N-terminal nonpolar aliphatic (Leu, Val, Ile, and Ala), basic (Arg), and sulfur-containing (Met) residues rapidly, while P1 Asp or Gly were cleaved inefficiently from peptides. Significant differences in the cleavage of dipeptides with P1 aromatic residues (Phe, Tyr, and Trp) were noted. To systematically evaluate the impact of the P1' residue on cleavage of dipeptides, three series of dipeptides (Leu-Xaa, Gly-Xaa, and Arg-Xaa) were evaluated. The P1' residue strongly influenced hydrolysis of dipeptides and the magnitude of its effect was dependent on the P1 residue. P1' Pro, Asp, Lys and Gly slowed the hydrolysis rates of the tomato LAP-A, porcine LAP, and E. coli PepA markedly. Analysis six Arg-Gly-Xaa tripeptides showed that more diversity was tolerated in the P2' position. P2' Arg inhibited tripeptide cleavage by all three enzymes, while P2' Asp enhanced hydrolysis rates for the porcine and prokaryotic LAPs.