C13 pt 2 Flashcards
why is the liver prone to toxic damage?
what can increase toxicity?
The liver is very prone to toxic damage because it sees everything that is ingested, and is a major site of metabolism of xenobiotics (ingested foreign chemicals)
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* Metabolism often occurs in multiple stages, and sometimes the toxicity of a substance can be higher at an intermediate stage
o Substances can compete for the same metabolic pathway, increasing risk of toxicity of any of the competing substances
what liver zone most prone to toxic injury by metabolites? what about direct toxicity?
- Recall centrilobular (zone 3) hepatocytes are most prone to toxic injury by metabolites because they are most metabolically active
<><><><> - Periportal (zone 1) on the other hand, are prone to immediately toxic substances because they are closest to incoming portal blood
- Different species have different detoxification enzyme activity levels
- what is the issue with cats and acetaminophen?
- Cats have reduced uridine diphosphate-glucuronosyl transferase
o Reduced metabolism of acetaminophen leads to accumulation of its toxic
metabolite, NAPQI (more sensitive than dogs)
o This causes cell death and methemoglobinaemia
- Mechanisms of toxic hepatic injury
o Binding cell proteins and causing cellular dysfunction
o Disruption of canalicular bile transport (cholestasis)
o Inhibition of cell enzyme pathways
o Binding cellular proteins and prompting immune cell attack
o Activation of programmed cell death
o Inhibition of mitochondrial function
Classifications of hepatotoxin and their properties
Intrinsic:
- Dose-related, predictable, reproducible
- Usually involves conversion to reactive metabolites
- Ex: acetaminophen in cats and dogs
> In toxic metabolite dependent reactions, there is either excess metabolite
generated or an unusual toxic metabolite is formed
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Idiosyncratic:
- Less dose-related, unpredictable
- Occur in a small proportion of animals (related to individual susceptibility)
- Mechanisms often unknown, suspected genetic component
- Hypersensitivity related (drug allergy) or toxic metabolite dependent
> Drug ‘allergy’ has a latent period before toxicity and is often due to protein binding
liver toxic diseases - cytotoxic injury lesions, when we see them
hepatocyte degeneration, zonal necrosis, apoptosis, lipidosis
o Lipidosis and centrilobular necrosis especially common in acute toxic injury
Clinical and gross presentation of acute toxicity
- can we tell the cause by the signs?
- Clinical and gross presentation of acute toxicity is usually consistent across causes
o Encephalopathy, zonal pattern, hemorrhages
Clinical and gross presentation of chronic toxicity
- can we tell the cause by the signs?
- Chronic toxicity is more variable (more helpful to differentiate causes)
o Often a combination of lesions, clinical signs due to inadequate detoxification
what can cause hepatotoxicity? what determines if it is acute or chronic?
- Pretty much everything can cause hepatotoxicity (metals, drugs, plants, fungi, bacterial toxins, etc…)
o Dose rate determines whether toxicity is acute or chronic
- Adverse drug reactions: cause drug-induced liver injury (DILI)
- definition
o ‘An injurious or unintended response that occurs at a normal dose’
Drugs with known liver ADR
TMS - Massive to submassive necrosis and cholestasis (dog)
Diazepam - Repeated administration: lobular to massive necrosis (cat)
Xylitol - Acute severe hepatic necrosis (dog)
Carprofen - Vacuolar degeneration, bridging necrosis (dog)
Phenobarbital - Cirrhosis (uncommon), hepatocutaneous syndrome (dog)
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- Others: SQ injection of intranasal Bordetella vaccine in dogs, halothane
Cyanobacteria (blue-green algae)
- effects on liver?
- where its found
- species
- effects
Cyanobacteria (blue-green algae): primarily Microcystis aeruginosa
o Seasonal blooms in water bodies contaminated with agricultural runoff
o Microcystin-LR toxin disrupts the cytoskeleton and causes necrosis
o Most common in ruminants but all species at risk
o Other toxins can cause rapid death by interfering with nervous function
Fungi that are hepatoxic
o Amanita sp. mushrooms: toxin interferes with protein synthesis (necrosis)
o Aflatoxin: Aspergillus sp., chronic exposure is carcinogenic
§ Midzonal necrosis
o Fumonisin: Fusarium sp. on mouldy corn (pigs and horses)
o Sporidesmin: Pithomyces chartarum on ryegrass (ruminants, causes
photosensitization and liver fibrosis)
plant hepatotoxin? most common when? histo sign?
- Plant toxicity is most common when animals are grazing poor pastures
- Pyrrolizidine alkaloids: Senecio sp., Crotalaria sp., heliotrope, others
o Damage cell proteins, antimitotic (DNA replicates but nuclei can’t divide)
o Huge nuclei form (megalocytes)
hepatotoxic metals?
- how?
- risks?
- pathogenesis
- Iron can cause hepatotoxicity in young pigs if accidentally overdosed
<><><><> - Copper: sheep are very sensitive to copper toxicity (low biliary excretion)
o Vitamin E or molybdenum deficiency increases risk of copper toxicity
o Toxicity is usually chronic (levels build up in liver over time)
o Eventually the liver can’t cope and plasma copper quickly rises to levels that
damage red blood cells (intravascular haemolysis) > Mix of hemoglobin and methemoglobin
o Anemia makes hepatocyte necrosis worse, so more copper is released
o Can be precipitated by stress, death occurs within a few hours
species with bile duct separate from exocrine pancreas
cattle
pig
dos
species with bile duct combined with exocrine pancreas
horse
sheep
goat
cat
what tissue makes up the pancreas? what regulates it?
- 98-99% is exocrine tissue, but it is still regulated by the endocrine part
o Insulin and pancreatic polypeptide are stimulatory
o Somatostatin and glucagon are inhibitory
pancreas size and secretory activity are altered based on:
Organ size and secretory activity are altered based on diet
o Hypertrophy with rich protein/energy, atrophy if insufficient
pancreatic autolysis character
Autolysis is rapid due to release and activation of enzymes, and can look hemorrhagic even in postmortem change
pancreas regenerative and anti-injury capabilities
- All cells within the pancreas can regenerate, and exocrine acini are repaired rapidly
<><><><> - Resident stellate cells mediate fibrosis in persistent injury
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similar to liver….
pancreatic atrophy
- common when?
- how fast
- extent
- mechanisms
o Common in animals with insufficient nutrition of any cause, especially fast-growing
o Rapid reduction in mass (>75% within 4 days) by protein catabolism without cell death o Can decrease to <10% normal mass in prolonged starvation
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* Two mechanisms involved
o Inability to synthesize proteins (normally a high number are produced)
o Lack of stimulation from the GI tract
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* Ductal obstruction can also cause rapid atrophy
o Look for dilation above the obstruction
Developmental anomalies of the pancreas
- how common
- appearance
Uncommon and largely incidental
o Ectopic tissue in GI wall or spleen
o Formation of a ring around the duodenum in dogs, pigs (may cause stenosis)
o Cysts in lambs, associated with PKD in cats, pigs, goats
exocrine pancreas main job, output?
other roles?
generates what that can cause injury?
- The exocrine pancreas’ main job is producing and secreting digestive enzymes o Highest protein production by weight of any tissue
o Proenzymes (activated in gut) ex. trypsin, phospholipase
o Active enzymes ex. amylase, lipase
<><><><> - Other roles
o Intrinsic factor allows absorption of vitamin B12 (cobalamin)
o Secretions inhibit bacterial proliferation
<><><><> - Lots of free radicals are generated via normal metabolism, so exogenous free radicals can cause injury
Exocrine pancreatic insufficiency
- etiology
- when do clinical signs show
- common cause in dogs, demographics
- occurence in cats
- Dx
- Congenital or acquired loss of exocrine tissue activity
o Must lose at least 90% of secretory ability to show clinical signs
o Acquired loss can be due to anything that destroys tissue or interferes with signals
<><><><> - Dogs: most commonly due to juvenile pancreatic atrophy
o Second most common demographic is older females (probably necrosis?)
<><><><> - Less common in cats, not strongly linked to chronic pancreatitis
<><><><> - Confirm via reduced trypsin-like immunoreactivity in serum
Exocrine pancreatic insufficiency
- consequences
- clinical signs
- Reduced enzymes cause maldigestion and malabsorption
o Also reduced cleavage of proenzymes – makes maldigestion worse
o Antigenic proteins are not broken down – prone to dietary sensitivity
<><><><> - Risk of small intestinal bacterial overgrowth (SIBO)
o Carbohydrate fermentation leads to osmotic diarrhea
o Hard to prove due to overlap with normal flora
<><><><> - Clinical signs
o Pot belly due to bulky GI contents
o May develop hepatic lipidosis
o Dogs more prone to mesenteric torsion
o Cats may have greasy fecal soiling of hind end
Juvenile pancreatic atrophy
- disease course, precipitation
- early stage
- late stage
- clinical signs, anatomic signs
- Most are normal until 6-12 months old, often precipitated by GI illness or a change to diet or environment
- Early stages: T cell infiltrate without fibrosis (autoimmune?)
- Late stage (clinical signs): advanced atrophy with no inflammation, normal islets
<><><><> - Weight loss despite normal to voracious appetite
- Poor hair coat, muscle atrophy
- Pale (often greyish), soft, voluminous, malodourous feces
- Minimal abdominal fat
- Small pancreatic remnants surround normal ducts
<><><><> - familial or sporadic
Acute pancreatic necrosis
- is it pancreatitis? why?
- associations, causes
- risk factors, predispositions
- Clinically called ‘pancreatitis’ but different pathogenesis than true pancreatitis
o Inflammation is not the primary issue
<><><><> - Associated with high fat, low protein diets but the inciting cause is often unclear
o May develop after hypotension, abdominal surgery, GDV, trauma, some drugs
o Middle aged to older, overweight, female dogs at higher risk
o Miniature schnauzers with idiopathic hyperlipidemia especially at risk
o Hyperadrenocorticism, hypothyroidism, uremia, hypercalcemia predispose
Acute pancreatic necrosis
- disease course
- mortality, prognosis
- consequences
- Acute, life threatening condition or intermittent relapsing disease
o Either can progress to exocrine pancreatic insufficiency and/or diabetes
o Mortality reported at 27-42%, though most mild cases recover within days
o Can cause systemic problems, ex. cytokine storm and SIRS, endothelial damage and DIC
o Some dogs develop multifocal necrotizing panniculitis (systemic enzyme release?)
Acute pancreatic necrosis
- pathogenesis
Pathogenesis incompletely understood
o Acinar necrosis leads to increased calcium
o Sustained increase in calcium leads to fusion of lysosomes and zymogen granules
o Protective zymogen degradation mechanisms are overwhelmed
o Enzymes are activated, leak, and damage nearby tissue including vessels and adipose
o Damaged cells attract leukocytes, which worsen the enzymatic damage
o Vessel damage leads to hemorrhage
Acute pancreatic necrosis in dogs
- early lesions
- chronic appearance
- resolution?
- consequences
- The earliest lesion is peripancreatic adipose saponification (yellow flecks) accompanied by swelling and edema, hemorrhages in and around the pancreas, fibrin
- In chronic cases, the pancreas is irregular to shrunken
- Complete resolution is unlikely
o Necrosis continues slowly and asymptomatically until the entire pancreas is destroyed
o Common cause of diabetes in dogs
Acute pancreatic necrosis in cats
- appearance
- signalment
- consequences
- In cats, acute necrosis looks like chronic pancreatitis
o Older DSH, no sex predilection
o Consequences similar to dogs but often also develop severe hepatic lipidosis
toxic causes of pancreatic necrosis
- toxins
- susceptibility
- early lesions
- late lesions
o Several mycotoxins, selenium toxicity
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Zinc toxicity:
o Susceptible due to role in zinc excretion
o Early lesions: enlarged, pale, with interstitial edema, diffuse
microvesicular degeneration of acini
o Later: shrunken, nodular, with interstitial fibrosis, acinar atrophy
acute pancreatitis
- similarities to acute necrosis
- species
- cause in dogs?
Acute
o More intense hemorrhage but otherwise similar to acute necrosis
o Occasionally seen in cats, horses
o In dogs, cause unclear but may be due to reflux of duodenal contents during
increased abdominal pressure (ex. vomiting)
chronic pancreatitis
- species
- anatomical extent
- signalment, causes
o The most common pattern of pancreatic injury in species other than dogs
o Usually extends from the ducts into the acini
o Most common in adult cats (triaditis, FIP, toxoplasmosis)
o Occasional in horses (ascending bacteria, strongyle migration), rare in others
Hyperplasia and neoplasia of the pancreas
- types
- species
- number
- size
- demarcation
- compression
- notes
Exocrine hyperplasia
- Older dogs, cats, cattle
- multiple
- variable size
- discrete demarcation
- no compression
- Very common, grey-white and firm, usually incidental
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Exocrine adenoma
- single
- large
- discrete demarcation
- compression
- Rare, usually incidental, unlikely to progress to carcinoma
- Look more like normal parenchyma than nodular hyperplasia
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Exocrine adenocarcinoma
- Older dogs, cats
- Single or multiple
- Large
- poor demarcation
- invasive
- Rare in all species, female > male
- May be scirrhous, often contain necrosis
- Poor prognosis – metastasize quickly and everywhere
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- Round cell tumours may metastasize to the pancreas, and liver and GI tumours may locally invade pancreatic tissue
Exocrine adenocarcinoma of the pancreas
- predispositions
- when diagnosed?
- consequences
- possible sequelae
- rare presentation in cats
o Nitrosamines, concurrent pancreatic disease, and chronic pancreatitis predispose
o Usually diagnosed late in disease course, nonspecific signs (anorexia, vomiting, etc)
o Destruction of normal tissue can lead to EPI
o Often invade duodenum, may block pancreatic and biliary ducts
o Like pancreatic necrosis, can cause panniculitis in dogs
o Rarely causes paraneoplastic alopecia in cats – characteristic shiny skin
