Ronald D. Parker

Evaluation of Seven in Vitro Alternatives for Ocular Safety Testing

Seven in vitro assays were evaluated to determine if any were useful as screening procedures in ocular safety assessment. Seventeen test materials (chemicals, household cleaners, hand soaps, dishwashing liquids, shampoos, and liquid laundry detergents) were tested in each assay. In vivo ocular irritation scores for the materials were obtained from existing rabbit low volume eye test (LVET) data. The seven assays evaluated included the silicon microphysiometer (SM), luminescent bacteria toxicity test (LBT), neutral red assay (NR), total protein assay (TP), Tetrahymena thermophila motility assay (TTMA), bovine eye/chorioallantoic membrane assay (BE/CAM), and the EYTEX system (ETS). For the seventeen materials used in this study there was a significant correlation between the in vivo irritant potential and in vitro data for all the tests except the EYTEX System (SM, r = -0.87; LBT, r = -0.91; NR, r = -0.85; TTMA, r = 0.78; TP, r = -0.86; ETS, r = 0.29). The irritation classifications provided by the BE/CAM also did not correspond with the actual in vivo irritancy potential of the test materials. The result of this study suggested it may be possible to classify materials into broad irritancy categories with some of the assays. This would allow their use as screens prior to limited in vivo confirmation in the ocular safety assessment process.

Ocular Irritation: Microscopic Changes Occurring Over Time in the Rat with Surfactants of Known Irritancy

The pathology of surfactant-induced ocular irritation, especially in the context of accidental human exposures and animal tests used to assess a surfactants potential ocular irritation, is not well understood. The purpose of this study was to characterize the microscopic changes in rats at 3 hr and on days 1, 2, 3, 4, 7, 14, and 35 following treatment with anionic, cationic, and nonionic surfactants of differing irritancy. The right eye of each rat was treated by placing 10 μl of a surfactant directly on the cornea. Untreated left eyes served as the controls. At each time point, eyes and eyelids were macroscopically examined and collected for microscopic examination. Macroscopically, the differing levels of irritation were characterized by differences in incidence and magnitude of scores, reflecting involvement of the cornea, conjunctiva, and iris, as well as by the incidence of neovascularization and time to recovery. Microscopically, differences in the area and depth of injury paralleled the differences seen grossly and the relative irritancies of the various surfactants. All surfactants affected the corneal and conjunctival epithelium. All surfactants, except the slightly irritating anionic surfactant, caused corneal stromal changes, with this involvement being proportional to their overall level of irritation. Corneal endothelial cell effects principally occurred with only the severely irritating cationic surfactant. Over time, responses to surfactants of differing irritancy were qualitatively and quantitatively different, and these differences correlated with the extent of initial injury. Qualitative differences in response included presence of keratocyte regeneration, corneal neovascularization, and conjunctivalization of the corneal epithelium with all of the surfactants except the slight irritant. Quantitative differences in response occurred in the extent of epithelial regeneration, edema, and inflammation for surfactants of slight to severe irritancy, and with neovascularization, keratocyte regeneration, and conjunctivalization for surfactants of mild to severe irritancy. These results suggest that by defining initial area and depth of injury associated with an ocular irritant, it may be possible to predict the subsequent response and final outcome. Such an approach would be applicable to the development of mechanistically based in vitro assays.

Increased hyaline droplet formation in male rats exposed to decalin is dependent on the presence of α2u-globulin

A peculiar decalin-induced male rat nephropathy associated with the altered renal handling of filtered protein appears limited to the accumulation of the protein, alpha 2u-globulin. Several strains of male rats that produce alpha 2u-globulin (Fischer-344, Sprague-Dawley, Buffalo, and Norway Brown) demonstrate spontaneous renal cortical hyaline droplets which are exacerbated after exposure to decalin. In all cases, a close correlation exists between hyaline droplet formation observed histologically and alpha 2u-globulin accumulation measured biochemically. In stark contrast, the NCI-Black-Reiter strain, which does not produce measurable quantities of alpha 2u-globulin, neither forms hyaline droplets nor accumulates any filtered protein in its kidney cortex either spontaneously or after exposure to decalin. Also, female rats injected ip with male rat alpha 2u-globulin exhibit increased hyaline droplet formation and alpha 2u-globulin accumulation when treated with decalin. These data provide evidence that the presence of alpha 2u-globulin is key in understanding why this nephropathy appears unique to the male rat.

Development of an Acute Model for the Study of Chloromethanediphosphonate Nephrotoxicity

Chloromethanediphosphonate (Cl2MDP), a cation chelator, is used as a therapeutic for hypercalcemia of malignancy. Cl2MDP exhibits nephrotoxic potential. Thus, a useful model has been developed to study the mechanism of injury. Intraperitoneal administration of highly exaggerated dosages, specifically 200 mg/kg b.i.d., resulted in a consistent mild to moderate extent of kidney damage after the third day of treatment in rats. Proteinuria and lowered serum phosphorus levels occur prior to onset of histopathologic changes. Injury was characterized as necrosis of proximal tubular epithelium with predilection for pars recta. Unlike many renal toxicity models, the necrosis occurs as cell lysis only after 24 to 48 hours of treatment. However, this model significantly reduces the time required to induce renal toxicity observed in routine toxicity studies from months of treatment to less than 1 week and will, thus, serve as a baseline for subsequent pathogenetic studies.

Reducing the number of rabbits in the low-volume eye test

Although the Draize eye irritation test has provided important and useful information for eye safety assessments, considerable effort has been directed toward refining the assay procedure, reducing the number of animals used, and replacing this assay with alternative methods. The low-volume eye test (LVET) is a refinement of the Draize eye irritation test that uses 1/10 the volume of test substance placed directly on the cornea. The level and duration of eye irritation in the LVET are less than those in the Draize procedure, which means that it is a less stressful test. Furthermore, LVETs are more predictive of human response. Statistical studies have been conducted to determine the effects of reducing the number of animals used in the Draize test. These results suggested that a three-animal test would provide essentially the same information as the six-animal test. A similar analysis has not been performed on results from the LVET. Accordingly, the present study was undertaken to evaluate previously existing LVET data to determine if the number of animals used in a LVET can be decreased as has been shown for the Draize test. The results of the analysis are consistent with the findings of earlier evaluations of classical Draize data. Three-animal subsets from 119 six-animal LVETs provided the correct classification greater than 92% of the time for three different classification schemes. Furthermore, the discrepancies between the three-animal subsets and the six-animal maximum average score tended to be smaller than those observed for the Draize test.(ABSTRACT TRUNCATED AT 250 WORDS)

Microscopic Changes with Acetic Acid and Sodium Hydroxide in the Rabbit Low-Volume Eye Test

Differences in ocular irritancy have been hypothesized to reflect differences in the extent of initial injury. Although differences in the processes leading to tissue damage may exist, extent of injury is believed to be the principal factor determining final outcome of ocular irritation. Previous studies characterizing the pathology of surfactant-induced ocular irritation support this premise. The purpose of this study was to begin to determine the applicability of this premise in terms of nonsurfactants; we planned to accomplish this by assessing the ocular irritancy of different concentrations of an acid and an alkali. Ten microliters of 3 or 10% acetic acid (C2H4O2) or 2 or 8% sodium hydroxide (NaOH) were directly applied to the cornea of the right eye of each test rabbit. Untreated left eyes served as the controls. Eyes and eyelids were macroscopically examined for signs of irritation beginning 3 hours after dosing and periodically until recovery or day 35. Eyes and eyelids from animals in each group were collected for microscopic examination after 3 hours and on days 1, 3, and 35. The macroscopic and microscopic changes were consistent with slight (3% C2H4O2), mild (2% NaOH, 10% C2H4O2), and severe (8% NaOH) irritancy. The spectra of changes were similar to those previously reported for surfactants of differing types and irritancies. As with surfactants, as the extent of initial injury increased, the intensity and duration of the subsequent responses increased. These results indicate that our hypothesis also applies to nonsurfactants. The results also support our belief that the initial extent of injury associated with ocular irritation may be used to predict the subsequent responses and final outcome. Finally, our results further indicate that such an approach may be applicable to the development of alternative assays that are based on either injury to ex vivo eyes or injury to an in vitro corneal equivalent system.

Ocular Irritation: Pathological Changes Occurring in the Rat with Surfactants of Unknown Irritancy

We believe the development and validation of in vitro alternatives to eliminate the need to use animals in ocular irritation testing must be based on a thorough understanding of the mechanisms of ocular irritation. We have recently undertaken the task of developing such an understanding for a panel of surfactants. The purpose of this study was to expand our current panel of surfactants for which the microscopic changes occurring over time have been characterized. Macroscopic and microscopic findings regarding the ocular irritation of 6 surfactants of relatively unknown irritancy were compared to those of 6 surfactants of known irritancy. The right eye of each rat was treated by placing 10 μl of a surfactant directly on the cornea. Untreated left eyes served as the controls. At 3 hr and on days 1, 3, and 35, eyes and eyelids were collected for microscopic examination. Collectively, the macroscopic and microscopic findings revealed 3 surfactants to be similar to the mildly irritating surfactants previously studied, and 3 surfactants to be similar to the moderately irritating surfactant previously studied. Information such as this will be important to develop mechanistically based in vitro alternatives to replace the use of animals for ocular irritation testing.

Use of the occlusive patch to evaluate the photosensitive properties of chemicals in guinea-pigs

Guinea-pig tests were conducted on a known photocontact allergen, tetrachlorosalicylanilide (TCSA), a known phototoxin, 8-methoxypsoralen, two reportedly weak photoallergens, musk ambrette and 6-methylcoumarin, and a negative control, octylphenoxy polyethoxyethanol (Triton X-15). The data show that under the test conditions used, photosensitivity responses can be produced, and combinations of these as well as the other biological responses can be readily defined. The results indicate that musk ambrette is photoallergenic, that 8-methoxypsoralen is phototoxic and that Triton X-15 is only a slight irritant. On the other hand, results with TCSA suggest that it is a strong contact allergen and photoallergen, while 6-methylcoumarin would be considered to be a weak contact allergen with weak phototoxic properties. Previous reports that barrier destruction or adjuvanticity is necessary to produce photoallergy to musk ambrette were not confirmed; by ensuring occlusion using standard methods, the photoallergic nature of the response to this material was clearly demonstrated. A device described elsewhere (Newmann & Parker, Fd Chem. Toxic. 1985, 23, 683) has made it possible to develop methods that can be used to differentiate clearly among the possible biological responses that can occur in guinea-pigs when photoreactive materials are applied to their skin and irradiated. The probable biological responses that need to be defined, under the above conditions, are primary irritation, delayed contact hypersensitivity, phototoxicity and/or photoallergenicity.

Differences in Corneal Cytokine Levels with Surfactant-Induced Ocular Irritation in Rats

Abstract Previously, we have characterized pathological differences in corneal injury caused by surfactants known to have differing irritation potentials. The purposes of this study were to determine if differences in corneal cytokine levels occur following surfactant-induced corneal injury, and if these differences might relate to extent of corneal injury. Ten μ1 of a slightly, moderately, or severely irritating surfactant was placed directly on the corneas of rats. After 15 min, the rats were sacrificed and the corneas were removed. Corneas were cultured for 1, 3, 5, or 24 h. Supernatants and corneal lysates were collected at these time points and levels of interleukin (IL)-1α, IL-1β IL-6, and tumor necrosis factor (TNF)α were determined using enzyme-linked immunoassays. For these time points but for separate sets of corneas, light microscopic examinations were performed. On microscopic examination, the slight irritant damaged the superficial epithelium, the moderate irritant principally damaged the epithelium and stroma, and the severe irritant damaged the epithelium, stroma, and endothelium. Differences in the levels of lysate and supernatant IL-loc and supernatant IL-1β and IL-6 were observed, but differences in the levels of TNFα were not detected. The

Delayed contact hypersensitivity in the vagina and skin of the guinea pig

A new method was developed to permit the contact of haptens exclusively with the vaginal mucosal surfaces of the guinea pig. The method described has some unique characteristics that make it potentially useful, not only for studies of the immune response but also for other areas of toxicologic concern. Utilizing this approach it was demonstrated that delayed contact hypersensitivity was as readily produced in the vagina as it was in the skin. Grossly, the vaginas of sensitized animals appeared normal when challenged with a non-irritating concentration of hapten but, histologically, a perivascular lymphocytic cuffing, that is the hallmark of the delayed hypersensitivity response, was demonstrated.