Could nitrile derivatives of turnip (Brassica rapa) glucosinolates be hepato- or cholangiotoxic in cattle?

Authors: COLLETT, MARK - Massey University; Stegelmeier, Bryan; TAPPER, BRIAN - Agresearch

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2014
Publication Date: 7/30/2014
Publication URL: http://handle.nal.usda.gov/10113/4791519
Citation: Collett, M.G., Stegelmeier, B.L., Tapper, B.A. 2014. Could nitrile derivatives of turnip (Brassica rapa) glucosinolates be hepato- or cholangiotoxic in cattle? Journal of Agricultural and Food Chemistry. 62(30):7370-7375.

Interpretive Summary: Turnips and rape and other forages from the Brassica genus are regarded as “safe” feed for cattle during late summer and fall in the North Island of New Zealand. This is when other grasses may have mold that causes liver disease and photosensitivity known as facial eczema. Ocassionally severe cases liver disease and photosensitization also are associated with turnip ingestion. This liver disease is different than facial eczema and these difference are visible in liver cells. To date, the toxins causing liver damage in turnip photosensitization in cattle is unknown. Several hydrolysis products of the various turnip chemicals include nitriles and epithionitriles. Nitriles and epithionitriles can be toxic to the liver, kidney and pancreas of rats. It is possible that the rumen degrades turnip chemicals into toxic nitriles. This perspective explores the possibility of the preferential formation of such toxins, especially the epithionitriles, in acidic conditions in the bovine rumen, followed by absorption, hepatotoxicity, and secondary photosensitization are explored.

Technical Abstract: Turnip (Brassica rapa ssp. rapa) and rape (Brassica napus ssp. biennis) and other brassica forage crops are regarded as “safe” feed for cattle during late summer and fall in the North Island of New Zealand when high Pithomyces chartarum spore counts in pastures frequently lead to sporidesmin toxicity (facial eczema). Sporadic acute severe cases of turnip photosensitization in dairy cows characteristically exhibit high '-glutamyl transferase and glutamate dehydrogenase serum enzyme activities that mimic those seen in facial eczema. The two diseases can, however, be distinguished by histopathology of the liver, where lesions, in particular those affecting small bile ducts, differ. To date, the hepato-/cholangiotoxic phytochemical causing liver damage in turnip photosensitization in cattle is unknown. Of the hydrolysis products of the various glucosinolate secondary compounds found in high concentrations in turnip and rape, work has shown that nitriles and epithionitriles can be hepatotoxic (and nephro- or pancreatotoxic) in rats. These derivatives include ß-hydroxy-thiiranepropanenitrile and 3-hydroxy-4-pentenenitrile from progoitrin; thiiranepropanenitrile and 4-pentenenitrile from gluconapin; thiiranebutanenitrile and 5-hexenenitrile from glucobrassicanapin; phenyl-3-propanenitrile from gluconasturtiin; and indole-3-acetonitrile from glucobrassicin. This perspective explores the possibility of the preferential formation of such derivatives, especially the epithionitriles, in acidic conditions in the bovine rumen, followed by absorption, hepatotoxicity, and secondary photosensitization.