GIT, Hepatobiliary, Pancreatic Flashcards
Zones in the liver & implications?
Zone 1: periportal - most prone to toxic injury. Site mainly affected by SECONDARY causes of Cu accumulation.
Zone 2:
Zone 3: centrilobular - most prone to hypoxic injury. Site mainly affected with PRIMARY defects in Cu accumulation.
Breeds predisposed to copper storage hepatopathy?
Pure + mixed breeds.
Bedlington terriers, Labs, WHWT, Dobermans, Skye terrier, Dalmatians.
Copper storage hepatopathy in Bedlington terriers - gene mutation, clinical characteristics?
Autosomal recessive disorder.
Deletion of exon 2 of copper metabolism domain containing 1 (COMMD1) gene –> complete absence of protein that normally regulates copper metabolism & homeostasis –> affects biliary copper excretion pathway –> copper accumulation in hepatocellular lysosomes.
Acute form - 2-6yo, hepatomegaly, jaundice, hemolytic anemia. Elevated ALT.
Chronic form - middle-aged and older dogs. Less severe CSx, progressive liver damage.
Dx - liver bx. BUT liver [Cu] does not always correlate with the extent of liver damage & dz progression, also may not ID substantial Cu accumulation in hepatocytes in early dz.
Copper metabolism pathway and transporter genes involved?
Copper homeostasis relies on regulation of uptake of copper in
the small intestine, cellular metabolism executed by a variety of copper transporters and chaperones, as well as excretion of excessive copper via the biliary tract.
The P-type copper-transporting ATPases, ATP7A and ATP7B are crucial for the regulation of copper homeostasis.
- ATP7A mainly resides at the basal membrane of enterocytes and facilitates copper transport into the portal circulation.
- ATP7B is located at the Golgi complex in hepatocytes and moves to the endo-lysosomal cellular compartments upon copper overload. ATP7B has a dual function. In terms of its biosynthetic role, ATP7B facilitates incorporation of copper into apo-ceruloplasmin within the trans-Golgi network to form ceruloplasmin. Furthermore, ATP7B facilitates excretion of copper into the bile via the apical membrane of hepatocytes.
Cu associated hepatitis in Labs - causative gene mutation?
Mutations in ATP7A & ATP7B genes leading to amino acid substitutions.
WSAVA classification of feline inflammatory liver diseases?
3 histopath groups:
1) Neutrophilic (acute & chronic)
2) Lymphocytic
3) Chronic cholangitis 2’ to liver flukes (Platynosomum spp. and Amphimerus pseudofelineus)
Liver fluke cholangitis in cats - pathogenesis?
Endemic - ‘lizard poisoning’ - eating
infected lizards found in the tropics and subtropics. Fluke resides in the GB & biliary ducts of infected cats, creating inflammation within bile ducts & portal areas.
High burden –> chronic mucoid D+ & icterus. Non-specific signs when chronic (adult flukes persist).
Hepatocutaneous syndrome - signalment, skin lesion appearance & locations?
Signalment: small-med sized dogs, males > females, median onset 10yo. Breeds reported - Shetland, Cockers, WHWT.
Skin: crusting, ulcerative, painful dermatosis
that affects the mucocutaneous junctions, pressure
points, and footpads with classic histologic features of superficial necrolytic dermatitis
What do the CCECAI and CIBDAI systems stand for (differences) and what is their clinical utility?
Both systems used for scoring dogs with IBD. CIBDAI has also been utilised to assess dogs with acute pancreatitis.
CIBDAI = canine IBD activity index.
= 6 components, attitude/activity, appetite, vomiting, stool consistency, stool frequency, weight loss (see table)
CCECAI = canine chronic enteropathy clinical activity index.
= CIBDAI components + serum [albumin], peripheral oedema & ascites, severity of pruritus.
allows better assessment of therapeutic success
Describe the technique of contrast-enhanced ultrasound & its indications.
Salavati JVIM 2020
CEUS uses gas-filled microbubbles (usually sulfur hexafluoride) as a tracer to assess tissue perfusion. The microbubbles remain entirely within the intravascular space & have rheology (flow & deformation) similar to RBCS. Excess sulfur hexafluoride is exhaled, and the phospholipid microbubble shell enters the endogenous phospholipid metabolic pathway. The microbubbles have an elimination half-life of ~6mins; >80% of the administered gas is exhaled via the lungs after 11 mins.
Indications:
Humans - assess mucosal healing with IBD
Dogs - evaluate perfusion abnormalities in several organs (focal splenic lesions, adrenal tumors, prostatic disease); assessment of GIT in healthy dogs & cats, assess duodenal perfusion in dogs with CIE & intestinal LSA.
a) DGGR lipase vs traditional lipase assay components?
b) Agreement of DGGR lipase with current gold standard tests for diagnosis of pancreatitis?
a) DGGR lipase assay = 1,2-O-dilauryl-rac-glycero glutaric acid-(60-methylresorufin) ester (DGGR) substrate. Traditional lipase = 1,2-diglyceride (1,2 DiG) substrate.
b) High level of agreement between DGGR & spec CPL, similar sensitivity. DGGR is cheaper with more rapid turnaround time, used as screening biomarker in routine biochemistry panels.
Normal hepatic [copper] in dogs?
150-400 μg/g dry weight (parts per million/ppm).
Cut-off hepatic Cu level for differentiating primary vs secondary copper hepatopathy?
<800ppm likely secondary
>800ppm likely primary
What is the current best indicator of cobalamin (Cbl) status in cats & dogs?
What is the role of this indicator in B12 metabolism?
Measurement of methylmalonic acid (MMA) concentrations - indicator of Cbl cellular stores.
Adenosyl-Cbl = cofactor for a) conversion of methylmalonyl-CoA to succinyl-CoA via methylmalonyl-CoA mutase, and b) re-methylation of homocysteine via methionine synthase.
B12 deficiency –> decreased methylmalonyl-CoA mutase activity –> increased serum [MMA].
NB: cats don’t have increased [homocysteine].
Roles of bile acids?
- Aid in digestion & absorption of lipids in the GIT
- Signalling molecules
- Primary BA converted to secondary BA by bacteria with 7α-dehydroxylation capabilities.
- Secondary BAs inhibit growth & germination of C. difficile (in people, possibly in dogs).
1) Which bacteria is involved in bile acid metabolism?
2) Significance in dogs/cats with CE?
3) Diagnostic test available?
1) Clostridium hiranonis
Main BA converting bacteria spp in dogs - convert primary BAs to secondary BAs by 7a-dehydroxylation
2) Depleted in CE (also by abx use) –> decreased proportion of secondary BA in colon in these dogs. Can be partially restored with FMT.
3) Included as 1 of 7 bacteria spp. quantified with the faecal dysbiosis index (DI).
List primary & secondary bile acids, and their roles.
Primary BA:
- Cholic acid, chenodeoxycholic acid
- In the duodenum: solubilise dietary lipids to aid digestion post-prandium
Secondary BA:
- Deoxycholic acid, lithocholic acid
- Bind to transmembrane G protein-coupled bile acid receptor GPBAR-1 (AKA TGR5 as signaling molecules)
- Anti-inflammatory properties.
- Lower glucose concentrations by binding to the farnesoid X receptor.
Differences in bile acid conjugation between cats & dogs?
- Cats: BA exclusively conjugated with taurine (essential AA) - so prone to rapidly developing taurine deficiency with hepatic disease
- Dogs: taurine or glycine
Risk factors for PPDH in dogs & cats?
Dogs - Weimaraners
Cats - DMH, DLH (Himalayans, Persians)
Ductal plate malformations:
1. Define
2. Phenotypes
3. Complications/consequences
- DPMs = embryonic abnormalities secondary to dysfunction of the primary cilia that result in defective tubulogenesis & affect the formation of bile ducts. (Primary cilia are present in the liver on only
cholangiocytes, not hepatocytes). - Caroli DPM (malformative medium-to-large bile ducts with irregularly distended or variably sacculated silhouettes, evaginating diverticular buds, and occasional scattered circumferential satellite bile duct profiles, similar to the embryologic ductal plate) or proliferative-like DPM. 1st r/o mechanical cholestasis before diagnosis.
Expansive cystadenoma DPM - cats > dogs - Pre-sinusoidal hypertension develops due to non-compliant portal fibrosis. Congenital hepatic fibrosis –> variable clinical progression but can lead to acquired PSS & ascites.
Which immunohistochemical stains are used to diagnosed copper storage hepatopathy?
Rhodanine stain - highlights copper granules as bright orange-red cytosolic inclusions. Limitation - stain fades over time esp with light exposure (overcome by digitally staining fresh slides).
Copper storage hepatopathy
- Breeds
- Causal gene mutation?
- Pathogenesis
- Bedlington Terriers, Dobers, Labs
- COMMD1 - homozygous deletion of exon 2 (Bedlington)
- SNP (all 3 above)
Complete absence/dysfunction of ATP7β (Cu transporter protein responsible for Cu transport into plasma protein ceruloplasmin & Cu bile elimination)
Describe how copper accumulation causes liver injury.
Cu exists in an oxidized (cupric [Cu2+]) or reduced (cuprous [Cu1+]) state - so functions as electron acceptor or donor. Allows Cu to participate in redox cycling reactions that promote generation of ROS.
Haber-Weiss/Fenton reaction: generates superoxide (O2−), hydroxyl (OH) radicals & other ROS from H2O2. Effects of ROS: break DNA strands, ER stress & oxidative injury to cell & mitochondrial membranes, impair protein synthesis + promote cell death pathways. Oxidative injury –> consumptive depletion of hepatocytes & mitochondiral antioxidants (glutathione & a-tocopherol) –> perpetuates oxidative injury.
Decreased hepatic & plasma gluthathione & vit E [ ]
Can also exacerbate oxidative injury caused by concurrent extra-hepatic illness (due to glutathione depletion)
Describe histopath findings encountered with copper storage hepatopathy.
- Accumulation of refractile eosinophilic cytosolic granules in centrilobular (rather than periportal) hepatocytes. Often colocalize with lipofuscin (tan-colored product derived from oxidized membrane lipids).
- Copper pigment granulomas - cellular response to dead/dying hepatocytes; populated by macrophages (containing phagocytized hemosiderin, copper, and lipofuscin-laden debris) > fewer lymphocytes, occ Np. Can extend to all zones with progressive disease
- Lymphohistiocytic infiltrates
- Hepatocyte microvesicular lipid vacuolation - result of mitochondrial & ER injury, seen in severe disease
- Mp may sequester iron (phagocytosis of heme-rich cell debris)
- Progressive disease - parenchymal remodelling & fibrosis, see regenerative nodules.
- Advanced disease - loss of acinar structures & parenchymal distinction. Grossly small pale firm liver with many nodules.
- With cirrhosis, Cu accumulates in areas of inflammatory infiltrates or at the margins of regenerative nodules
What are indications for initiating copper chelation therapy in dogs?
> 1500 mcg/g dry weight regardless of distribution
750 mcg/g dry weight if there is centrilobular accumulation esp in predisposed breeds
Center JAVMA 2021 update: >/=600mcg/g DW if histologic lesions seen with hepatocyte Cu accumulation or if fluctuating ALT activities are seen with no alternative identifiable cause. (as low as 600mcg/g has been associated with copper storage hepatopathy).
What are 2 rare complications of severe copper storage hepatopathy in dogs?
- Acute, severe panlobular hepatic necrosis - associated with massive Cu release from damaged hepatocytes –> may cause markedly increased circulating [Cu] & haemolysis. Grossly liver appears normal/plump or has soft pale-yellow necrotic foci.
- Acquired Fanconi syndrome (euglycemic glucosuria > acute proximal tubular injury). Can visualise Cu accumulation in PT epithelium of renal biopsies with Rhodanine staining. Clinical recovery possible with intensive supportive care.
Liver copper accumulation in cats - causes & differences with dogs?
Cats with slowly progressive cholangitis –> cholestasis –> periportal Cu accumulation.
Vs dogs - pathological hepatic Cu accumulation is centrilobular, cholestasis is an uncommon cause for significant Cu accumulation (even with EHBDO)
What are the key GI bacterial phyla in dogs and cats?
Firmicutes, Bacteroidetes, Proteobacteria, Fusobacteria, Actinobacteria
What RBC abnormalities are more common in dogs with GI lymphoma vs chronic enteropathy?
Parachini-Winter JAVMA 2019
Anaemia
3+ RBC anomalies, (Sn 71%, Sp 70%)
Particularly presence of eccentrocytes (29% LSA vs 4% CIE)
Eccentrocytes reflect oxidative injury.
Differences in oesophagus musculature between dogs & cats? Implications for treatments?
Dogs - striated muscle throughout oesophagus
Cats - upper 80% striated, distal 20% smooth muscle
Smooth muscle agents (metoclopramide & cisapride) don’t work to increase oesophageal motility in dogs, but may work to increase distal oesophageal motility in cats.
What are the 2 types of cricopharyngeal dysphagia?
- Achalasia = a primary esophageal motility disorder; results from a selective loss of inhibitory myenteric neurons leading to failure of the LES to relax in response to a pharyngeal swallow and impaired esophageal peristalsis.
- Assynchrony = lack of coordination between UES relaxation & pharyngeal contraction.
Clinical signs are indistinguishable.
Which drugs may be associated with GB mucocoele formation?
Thyroxine, trilostane, imidocloprid (esp in Shetland sheepdogs)
Nutritional deficiency in …… is of potential concern in dogs with GBM, due to ……
Lipid-soluble substances
EHBDO
Liver of dog - most likely ddx? Common concurrent clinical manifestation?
Hepatocutaneous syndrome. Honeycomb appearance (hypoechoci nodules with hyperechoic liver parenchyma)
Superficial necrolytic dermatitis - pedal skin lesions
