An orthogonal methods assessment of topical drug concentrations in skin and the impact for risk assessment in the viable epidermis.

Systemic toxicity assessments for oral or parenteral drugs often utilize the concentration of drug in plasma to enable safety margin calculations for human risk assessment. For topical drugs, there is no standard method for measuring drug concentrations in the stratum basale of the viable epidermis. This is particularly important since the superficial part of the epidermis, the stratum corneum (SC), is nonviable and where most of a topically applied drug remains, never penetrating deeper into the skin. We investigated the relative concentrations of a prototype kinase inhibitor using punch biopsy, laser capture microdissection, and imaging mass spectrometry methods in the SC, stratum basale, and dermis of minipig skin following topical application as a cream formulation. The results highlight the value of laser capture microdissection and mass spectrometry imaging in quantifying the large difference in drug concentration across the skin and even within the epidermis, and supports use of these methods for threshold-based toxicity risk assessments in specific anatomic locations of the skin, like of the stratum basale.

An in vitro alveolar epithelial cell model recapitulates LRRK2 inhibitor-induced increases in lamellar body size observed in preclinical models.

Alveolar type II (ATII) epithelial cells contain lamellar bodies (LBs) which synthesize and store lung surfactants. In animals, the inhibition or knockout of leucine-rich repeat kinase 2 (LRRK2) causes abnormal enlargement of LBs in ATII cells. This effect of LRRK2 inhibition in lung is largely accepted as being mediated directly through blocking of the kinase function; however, downstream consequences in the lung remain unknown. In this work we established an in vitro alveolar epithelial cell (AEC) model that recapitulates the in vivo phenotype of ATII cells and developed an assay to quantify changes in LB size in response to LRRK2 inhibitors. Culture of primary human AECs at the air-liquid interface on matrigel and collagen-coated transwell inserts in the presence of growth factors promoted the LB formation and apical microvilli and induced expression of LRRK2 and ATII cell markers. Treatment with a selective LRRK2 inhibitor resulted in pharmacological reduction of phospho-LRRK2 and a significant increase in LB size; effects previously reported in lungs of non-human primates treated with LRRK2 inhibitor. In summary, our human in vitro AEC model recapitulates the abnormal lung findings observed in LRRK2-perturbed animals and holds the potential for expanding current understanding of LRRK2 function in the lung.

Lens cholesterol biosynthesis inhibition: A common mechanism of cataract formation in laboratory animals by pharmaceutical products.

CJ-12,918, a 5-lipoxygenase (5-LO) inhibitor, caused cataracts during a 1-month safety assessment studies in rats whereas the structurally similar ZD-2138 was without effect. For CJ-12,918 analogs, blocking different sites of metabolic liability reduced (CJ-13,454) and eliminated (CJ-13,610) cataract formation in both rats and dogs. Using this chemical series as a test set, models and mechanisms of toxicity were first explored by testing the utility of ex vivo rat lens explant cultures as a safety screen. This model overpredicted the cataractogenic potential of ZD-2138 due to appreciably high lens drug levels and was abandoned in favor of a mechanism-based screen. Perturbations in lens sterol content, from a decline in lathosterol content, preceded cataract formation suggesting CJ-12,918 inhibited lens cholesterol biosynthesis (LCB). A 2-day bioassay in rats using ex vivo LCB assessments showed that the level of LCB inhibition was correlated with incidence of cataract formation in animal studies by these 5-LO inhibitors. Thereafter, this 2-day bioassay was applied to other pharmaceutical programs (neuronal nitric oxide synthase, sorbitol dehydrogenase inhibitor, squalene synthetase inhibitor and stearoyl-CoA desaturase-1 inhibitors/D4 antagonists) that demonstrated cataract formation in either rats or dogs. LCB inhibition >40% was associated with a high incidence of cataract formation in both rats and dogs that was species specific. Bioassay sensitivity/specificity were further explored with positive (RGH-6201/ciglitazone/U18666A) and negative (tamoxifen/naphthalene/galactose) mechanistic controls. This body of work over two decades shows that LCB inhibition was a common mechanism of cataract formation by pharmaceutical agents and defined a level of inhibition >40% that was typically associated with causing cataracts in safety assessment studies typically ≥1 month.

1,2-naphthoquinone stimulates lipid peroxidation and cholesterol domain formation in model membranes.

PURPOSE: Naphthalene induces cataract formation through the accumulation of its reactive metabolite, 1,2-naphthoquinone (1,2-NQ), in the ocular lens. 1,2-NQ increases lens protein oxidation and disrupts fiber cell membrane function; however, the association of these effects with changes in membrane structure is not understood. The goal of this study was to determine the direct effects of 1,2-NQ on membrane lipid oxidation and structural organization. METHODS: Iodometric approaches were used to measure the effects of naphthalene and 1,2-NQ on lipid hydroperoxide (LOOH) formation in model membranes composed of cholesterol and dilinoleoylphosphatidylcholine. Membrane samples were prepared at various cholesterol-to-phospholipid mole ratios and subjected to autoxidation at 37°C for 48 hours in the absence or presence of either agent alone (0.1-5.0 µM) or in combination with vitamin E. Small-angle x-ray diffraction was used to measure the effects of naphthalene and 1,2-NQ on membrane structure before and after exposure to oxidative stress. RESULTS: 1,2-NQ increased LOOH formation by 250% (P < 0.001) and 350% (P < 0.001) at 1.0 and 5.0 µM, respectively, whereas naphthalene decreased LOOH levels by 25% (P < 0.01) and 10% (NS). The pro-oxidant effect of 1,2-NQ was inversely affected by membrane cholesterol enrichment and completely blocked by vitamin E. 1,2-NQ also increased cholesterol domain formation by 360% in membranes exposed to oxidative stress; however, no significant changes in membrane lipid organization were observed with naphthalene under the same conditions. CONCLUSIONS: These data suggest a novel mechanism for naphthalene-induced cataract, facilitated by the direct effects of 1,2-NQ on lipid peroxidation and cholesterol domain formation.

An underlying role for hepatobiliary dysfunction in cyclosporine A nephrotoxicity.

Renal-derived cysteinyl leukotrienes (cysLT), such as leukotrienes C(4) (LTC(4)) and D(4) (LTD(4)) are thought to mediate acute and chronic cyclosporine A (CSA) nephrotoxicity. However, whole-body cysLT elimination is regulated primarily by hepatobiliary excretion. Since CSA is known to alter hepatobiliary function, the effects of CSA on whole-body cysLT elimination were investigated in vivo, with respect to hepatobiliary and renal function. Male rats were anesthetized and cannulated (jugular vein, bile duct, and urinary bladder). A tracer dose of tritiated LTC(4) ((3)H-LTC(4)) was administered systemically (i.v.) immediately following vehicle and then 90 min later after vehicle or CSA. In vehicle/vehicle controls, hepatobiliary (3)H-cysLT elimination predominated over renal elimination without altering glomerular filtration rate (GFR), bile flow, and urine production. (3)H-cysLT elimination kinetics were comparable between each 90 min collection period. In vehicle/CSA-treated rats, an acutely nephrotoxic dose of CSA (20 mg/kg, i.v.) reduced urine flow 74+/-9% and caused a transient reduction in GFR, while total bile flow decreased 40+/-13%. Hepatobiliary and renal (3)H-cysLT elimination was also impaired 59+/-5 and 61+/-18%, respectively. In contrast, a non-nephrotoxic dose (2 mg/kg i.v.) increased renal (3)H-cysLT elimination due to impaired hepatobiliary elimination without affecting GFR, bile flow or urine production. Both doses caused (3)H-cysLT retention in hepatic and renal tissue. These findings demonstrate that CSA alters whole-body handling of cysLT by disrupting hepatobiliary cysLT elimination. This disruption leads to increased renal exposure to systemically derived cysLT and renal cysLT tissue retention. Renal exposure to and accumulation of systemically derived cysLT products may be underlying factors in CSA nephrotoxicity.

Ciglitazone-induced lenticular opacities in rats: in vivo and whole lens explant culture evaluation.

The cataractogenic potential of the thiazolidinedione ciglitazone (CIG) was investigated in vivo and in vitro. In the rat, CIG caused a dose-dependent (30-300 mg/kg/day) increase in incidence and severity of nuclear cataract formation during a 3-month nonclinical safety assessment study. Potential mechanisms of toxicity were surveyed using whole rat lens explants exposed to CIG with or without various inhibitors of cataract formation. In vitro, CIG caused a concentration-(0.375-30 muM) and time-dependent (3-24 h) change in biochemical [ATP content or mitochondrial reduction of the tetrazolium dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) and reduced glutathione (GSH) content] and morphometric (lens wet weight and clarity) markers of damage. Within 3 h of exposure, 7.5 muM CIG decreased lens ATP content 37 +/- 7% (percentage of difference from control, p < 0.05). After 24 h of exposure, lens ATP content, MTT reduction, and GSH content declined 57 +/- 5, 30 +/- 28, and 42 +/- 8%, respectively. Lens wet weight increased 17 +/- 4% with a concomitant decrement in lens clarity. Pretreating lenses with the mitochondrial calcium uniport inhibitor ruthenium red (RR) partially or fully protected lenses from toxicity. In contrast, the antioxidant dithiothreitol, aldose reductase inhibitor sorbinil, and selective cell-permeable calpain inhibitors [calpain II inhibitor and (2S,3S)-trans-epoxysuccinyl-l-leucylamido-3-methylbutane ethyl ester (E64d)] were ineffective in providing protection under the present testing conditions. Early and selective changes in lenticular ATP content and the partial or full protective effect of RR suggest that alterations in lens bioenergetics may play an important role in CIG-induced cataract formation. Lens explant cultures were successfully used to select two thiazolidinediones that lacked cataractogenic activity when evaluated in 3-month rat safety assessment studies.