Evaluation of miR-216a and miR-217 as Potential Biomarkers of Acute Exocrine Pancreatic Toxicity in Rats

Detecting and monitoring exocrine pancreatic damage during nonclinical and clinical testing is challenging because classical biomarkers amylase and lipase have limited sensitivity and specificity. Novel biomarkers for drug-induced pancreatic injury are needed to improve safety assessment and reduce late-stage attrition rates. In a series of studies, miR-216a and miR-217 were evaluated as potential biomarkers of acute exocrine pancreatic toxicity in rats. Our results revealed that miR-216a and miR-217 were almost exclusively expressed in rat pancreas and that circulating miR-216a and miR-217 were significantly increased in rats following administration of established exocrine pancreatic toxicants caerulein (CL) and 1-cyano-2-hydroxy-3-butene (CHB) as well as in rats administered a proprietary molecule known to primarily affect the exocrine pancreas. Conversely, neither microRNA was increased in rats administered a proprietary molecule known to cause a lesion at the pancreatic endocrine–exocrine interface (EEI) or in rats administered an established renal toxicant. Compared with amylase and lipase, increases in miR-216a and miR-217 were of greater magnitude, persisted longer, and/or correlated better with microscopic findings within the exocrine pancreas. Our findings demonstrate that in rats, miR-216a and miR-217 are sensitive and specific biomarkers of acute exocrine pancreatic toxicity that may add value to the measurement of classical pancreatic biomarkers.

Abstract 69: Characterization of the Role of Glycerol-3-phosphate Acyltransferase-3 in Intestinal Lipid Absorption

Glycerol-3-phosphate acyltransferases (GPAT) catalyze the first step in the synthesis of glycerolipids and glycerophospholipids. Microsomal GPAT, the major GPAT activity, is encoded by at least two closely related genes, GPAT3 and GPAT4 (also known as AGPAT9 and 8, respectively). The physiological role of GPAT3 is poorly understood. GPAT3 mRNA was found to be abundantly expressed in small intestine which was confirmed by immunohistochemistry. The GPAT3 protein was highly enriched in enterocytes suggesting a potential role in intestinal lipid absorption. To further investigate this possibility, we generated Gpat3-deficient mice (Gpat3-/-). The Gpat3-/- mice were viable and fertile, and exhibited no obvious metabolic abnormalities on standard laboratory chow. As expected, Gpat3-/- mice had reduced intestinal GPAT activity compared to wild-type animals and when challenged with an oral lipid bolus, Gpat3-/- mice displayed attenuated plasma triglyceride excursion. Histological and biochemical analysis of the small intestine revealed dramatically increased lipid deposition in the intestinal mucosa of Gpat3-/- mice. Long chain acylcarnitine levels were elevated in the jejunum of Gpat3-/- suggesting a compensatory increase in mitochondrial fatty acid oxidation. Lipid flux studies performed in primary cultures of enterocytes derived from wild-type and Gpat3-/- mice reveal a defect in triacylglycerol trafficking suggesting a role for GPAT3 in the post-prandial secretion of lipid in the intestine. Finally, gene expression analysis revealed dysregulation of multiple genes involved in lipid absorption, chylomicron assembly, and secretion. Taken together, our results demonstrate a hitherto unappreciated role for GPAT3 in lipid absorption.

Porcine brain microvessel endothelial cells as an in vitro model to predict in vivo blood-brain barrier permeability

The objective of the study was to establish primary cultured porcine brain microvessel endothelial cells (PBMECs) as an in vitro model to predict the blood-brain barrier (BBB) permeability in vivo. The intercellular tight junction formation of PBMECs was examined by electron microscopy and measured by transendothelial electrical resistance (TEER). The mRNA expression of several BBB transporters in PBMECs was determined by reverse transcriptionpolymerase chain reaction analysis. The in vitro permeability of 16 structurally diverse compounds, representing a range of passive diffusion and transporter-mediated mechanisms of brain penetration, was determined in PBMECs. Except for the perfusion flow rate marker diazepam, the BBB permeability of these compounds was determined either in our laboratory or as reported in literature using in situ brain perfusion technique in rats. Results in the present study showed that PBMECs had a high endothelium homogeneity, an mRNA expression of several BBB transporters, and high TEER values. Culturing with rat astrocyte-conditioned medium increased the TEER of PBMECs, but had no effect on the permeability of sucrose, a paracellular diffusion marker. The PBMEC permeability of lipophilic compounds measured under stirred conditions was greatly increased compared with that measured under unstirred conditions. The PBMEC permeability of the 15 test compounds, determined under the optimized study conditions, correlated with the in situ BBB permeability with an r2 of 0.60. Removal of the three system L substrates increased the r2 to 0.89. In conclusion, the present PBMEC model may be used to predict or rank the in vivo BBB permeability of new chemical entities in a drug discovery setting.

A stepwise method for the isolation of endothelial cells and smooth muscle cells from individual canine coronary arteries

Methods for the stepwise isolation of endothelial cells and smooth muscle cells from individual canine coronary arteries are described. Both cell types can be isolated in pure culture with high yields. Dogs are a common species used in the study of atherosclerosis and coronary artery disease. Capacity to isolate endothelial cells and smooth muscle cells from individual canine coronary arteries should prove useful in the study of coronary artery disease.

Malignant intracranial teratoma in a juvenile Wistar rat

An intracranial malignant teratoma was identified in a 91-day-old male Wistar rat manifesting central nervous system-related clinical signs. This tumor occupied the right midbrain and portions of the right caudal cerebrum and cranioventral cerebellum. Microscopically, the tumor contained intermingled cartilage, bone (with medullary hematopoietic tissue), fibrous connective tissue, skeletal muscle, fat, pseudostratified ciliated epithelium, stratified squamous epithelium, serous and mucoserous glands, and neural tissue with ependymal and choroid plexus epithelia. Poorly differentiated cells with primitive cartilaginous matrix were present throughout the lining of lateral ventricles, in the aqueduct of Sylvius, and in meninges overlying normal cerebellar tissue indicating tumor metastasis occurred via cerebrospinal fluid. This neoplasm was not identified in extracranial sites and hence was considered a primary intracranial malignant teratoma with metastases via cerebrospinal fluid.

Elemental profiles in cryosections and frozen-dried bulk specimens of the normal lens

Energy-dispersive X-ray analysis was used to obtain distribution profiles of Na, K, Cl, P and S in rapidly frozen-dried bulk specimens, and in cryosections of the normal rat lens. Na and Cl are highly concentrated in the capsule, and K and P, in the epithelial cells. Profiles of the entire radius of a lens show relatively high concentrations of K and P in the outermost cells of the lens, with decreasing concentrations through the cortex, and a minimum throughout the nuclear region. S, on the other hand, shows increasing concentrations at deeper locations, with maximum values throughout the nuclear region.