NCT Acute Studies Bromobenzene 1 2 Dichlorobenzene 1

NCT Acute Studies • • Bromobenzene 1, 2 - Dichlorobenzene 1, 4 - Dichlorobenzene N-Nitrosomorpholine Diquat Monocrotaline Thioacetamide Galatosamine Herbert Cesta Boorman Turnier Nyska Hailey Boorman

Today’s Overview • Chemical Mechanism - Rick Irwin • Morphology - Gary Boorman

Bromobenzene

Bromobenzene • CYP P 450 catalyzed formation of reactive epoxide metabolite – CYP expression predominates around the central vein • quinone metabolites also formed • metabolites react with cellular proteins • detoxification by reaction with GSH • cytosolic GSH depletion • mitochondrial damage

Bromobenzene • Acute centrilobular necrosis • Rim of hepatocytes immediately adjacent to terminal hepatic venule • Minimal inflammatory infiltrate • Fairly uniform between animals/lobes • Bromobenzene and 1, 2 -dichlorobenzene appear similar; 1, 4 -DCB - no lesions

Bromobenzene 24 -hour Sac • Example of centrilobular hepatocyte degeneration at 75 mg/kg; degenerative hepatocytes are swollen and have pale (rarefied) cytoplasm; note that there is also centrilobular glycogen depletion

Bromobenzene 24 -hour Sac • Example of centrilobular hepatocyte necrosis at 250 mg/kg; necrosis is massive coagulative and hemorrhagic effacing large areas of the hepatic parenchyma

N-Nitrosomorpholine • CYP catalyzed hydroxylation at 2’ and 3’ position on morpholine ring • protein and DNA adducts

Hepatotoxicity • an initial wave of apoptosis which peaks at 12 hours but involves only 3 -6% of hepatocytes • followed by hepatocellular necrosis which is prominent by 24 hours • no depeltion of GSH

N-Nitrosomorpholine, 300 mg/kg @ 24 hours, Rat # 34

PP Necrosis Hemorrhage THV N-Nitrosomorpholine 300 mg/kg at 24 hours, Rat # 34

N-Nitrosomorpholine • • • Acute centrilobular necrosis Mononuclear inflammatory infiltrate Fairly uniform between animals/lobes Prominent karyorrhexis of hepatocytes Prominent hemorrhage

Diquat (dibromide) • widely used bipyridinium herbicide • under goes one electron redox reaction catalyzed by NADPH cytochrome c reductase to produce high levels of ROS • primary lesion reported to be centrilobular necrosis • initial injury not associated with depletion of GSH • characterized by formation of reactive protein carbonyls aldehydes and ketones

Diquat 30 mg/kg at 24 hours, Rat # 7

Diquat • Acute centrilobular necrosis • At early times clearly demarcated zone of pale hepatocytes • Rim of hemorrhage at margin of lesions • Necrosis secondary to vascular damage and ischemia?

Monocrotaline • requires bioactivation by CYP’s to reactive dehydro-MCT • targets endothelial cells in the sinusoids and central vein • hepatotoxicity characterized by hemorrhage and activation of coagulation system. • may progress to hepatic veno-occlusive disease (HVOD); used as a model for similar human disease • produces caspase dependent apoptosis

Monocrotaline 300 mg/kg at 24 hrs

Monocrotaline 300 mg/kg at 24 hrs

Monocrotaline • • Acute Centrilobular Necrosis Prominent Hemorrhage Primary Endothelial Injury? Hepatocellular Injury Secondary to Ischemia? • Diquat and Riddelliine may have similar mechanisms

Thioacetamide • fungicide • CYP 2 E 1 bioactivation to reactive metabolites • hepatocytes primary target resulting in necrosis

Thioacetamide 150 mg/kg @ 4 x

Thioacetamide 150 mg/kg @10 x

Thioacetamide • • Acute centrilobular necrosis Apoptosis? Mononuclear Cell Inflammatory Infiltrate Fairly uniform between animals/lobes

Galactosamine • metabolized to UDP-hexoseamines and UDP-N-acetylhexosamines in hepatocytes and depletion of UTP • causes a transient block in transcription and protein synthesis associated with UTP depletion • accumulation of metabolites inhibit the synthesis of certain critical membrane proteins • increases permeability of gut and potentially absorption of endotoxin • produces oncotic necrosis, caspase dependent apoptosis, and induces oval cell proliferation

Galactosamine, 1500 mg/kg at 24 hours, Rat # 17

THV PP Galactosamine 1500 mg/kg at 24 hours, Rat # 17

Galactosamine • Patchy to Peripotal necrosis • Granulocytes and Mononuclear Cell Infiltrates • Hemorrhage is not prominent

NCT Acute Studies • Very Rich Morphological Data Base • Both Similarities and Differences with chemicals • Bromobenzene and 1, 2 -dichlorobenzene appear similar; 1, 4 -DCB - Comparison • Diquat, Monocrotaline and Riddelliine Comparison