16. Toxicity: Integument, Bones, & Teeth

severe dermatitis that results from a heightened reactivity of skin cells and associated dermal tissues upon their exposure to sunlight, following ingestion or contact with plant pigments or secondary products that are UV or light reactive

photosensitization

True or false: Photocytotoxic photosensitization can show highly variable onset. It can occur within minutes of exposure to the toxic substance by direct contact, within hours (via contact or ingestion) of deposition of the primary photosensitizing agent, or days after exposure due to activation of secondary photosensitizers (following liver damage and deposition of phytoporphyrin into skin).

true

True or false: Photosensitization is not equivalent to sunburn although its appearance can be superficially very similar.

true

What type of animals will also be more affected by photosensitization?

animals with light-colored or thin coat or fleece covering will also be more affected than their pigmented or thick-coated counterparts

In domestic livestock, where is photosensitization most often observed?

areas of skin that remain hairless, such as the skin around the eyes, ears, face, muzzle, mammary gland, tail and the area directly adjacent to the hoof wall

True or false: The outer-most layer of epidermis, the stratum corneum (SC), consists of dead keratinized cells that are constantly abraded from the skin’s surface and replenished by mitotically active cells of the underlying stratum basale (SB).

true

True or false: The deeper layers of integument, the dermis and hypodermis, offer limited or no protection from penetrating substances or light. Darker skin containing melanin or pigment also serves as protection to prevent additional photosensitization.

true

True or false: The presence of light reactive compounds produced by higher plants can result in considerable damage to sensitive dermal tissues, causing irritation, tissue abrasion, secondary skin infection, and even death due to associated trauma.

true

What amino acids in animal skin are particularly susceptible to light-mediated oxidation and eventually invoke significant inflammatory responses in affected tissues and blood vessels that can lead to animal tissue necrosis?

tryptophan, tyrosine, and histidine

type of photosensitization that occurs when phototoxic plant-produced compounds or their metabolites become bioavailable within the animal after ingestion, or become localized in the cellular layers of the skin

primary photosensitization

What agents cause type I primary photosensitization? What else have been reported to also be agents?

hypericin (from St. John’s Wort) and fagopyrin (from buckwheat); coal tar derivatives such as polycyclic aromatic hydrocarbons, tetracyclines, and some sulfonamides

What is an example of type II primary photosensitization?

endogenous pigments that arise from inherited or acquired defective functions of enzymes involved in haem synthesis

results from the accumulation of the photodynamic compound phytoporphyrin

secondary hepatogenic photosensitization

microbially-produced metabolite of chlorophyll

phytoporphyrin

Secondary photosensitization may occur as a result of what?

acute or chronic liver damage in the affected animal when porphyrin and derivatives are not cleared by the damaged liver

What is involved in type III secondary photosensitization?

lack of ability to complete the excretion of phylloerythrin (PE) due to liver dysfunction of bile duct lesions increases the amount of it in general circulation

derived from the breakdown of chlorophyll by microorganisms in the GI tract

phylloerythrin (PE)

True or false: Phylloerythrin (PE), but not chlorophyll, is normally absorbed into the circulation and is effectively excreted by the liver in the bile fluid.

true

this large perennial presents a significant human and animal health issue as direct contact with the photosensitizing compounds causes severe-burn-like lesions on exposed skin, sometimes leading to amputation or loss of use, in which lesions are caused by exposure to both live and cut or harvested plant material

giant hogweed

What toxic agent is found in the sap of giant hogweed?

furanocoumarins

What is the bioactive compound identified to be the casual agent of photosensitivity in St. John’s Wort?

hypericin

What is the chemical found in buckwheat?

fagopyrin

What part of the buckwheat plant has the highest amounts of fagopyrin?

the leaves

Kangaroos present with liver histopathology showing abnormal bile duct structure, onion skin appearance, multiple cellular layers, and refractive crystalline inclusions. They were congregating in shady urban areas and were reluctant to move. What is your top DDX?

pancium grass (switchgrass)

What can be seen in sheep foraging in old turnips or rutabaga fields? What is significant in cattle?

1 deg photosensitization; it is a 2nd deg sensitization

What is the primary agent responsible for the severe jaundice and photosensitization seen within 1-2 days following the consumption of lantana camara?

triterpenes

What toxic heavy metals commonly affect animals?

A
L
C
C
N

• aresenic

• lead

• cadmium

• chromium

• nickel

What are examples of moderately toxic metals?

I
Z
S
M
C

• iron

• zinc

• selenium

• mercury

• copper

What metals act directly or indirectly on intracellular proteins in the skin?

C
C
N

• cadmium

• chromium

• nickel

Forage crops grown on seleniferous soils contain significant amounts of what to cause poisoning in domestic animals, as well as risk from incorrectly formulated supplements?

selenium

What plant species accumulates selenium in toxic amounts and can cause problems in animals which consume them?

astragalus genus (locoweeds and milk vetches)

What are clinical signs associated with chronic selenium poisoning in cattle, sheep, and horses?

L
D
S

• loss of hair/wool

• deformation

• sloughing of the hoof

occurs when animals ingest water-soluble selenium compounds naturally found in accumulator plants

blind staggers

toxicity from eating plants or grain with protein-bound, insoluble selenium

alkali disease

What drug has shown to cause increased apoptosis of canine tendon cells and chrondrocytes in a dose and time-dependent manner?

flouroquinolones

What drug can bind calcium during enamel formation and turn teeth brown, and is commonly often used to treat tendon contracture in foals?

tetracyclines