Metabolism of Oak Leaf
Ellagitannins and Urolithin
Production in Beef Cattle
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Abstract
Oak leaves have a high concentration of ellagitannins.
These phytochemicals
can be beneficial or poisonous to animals. Beef cattle are often intoxicated
by oak leaf consumption, particularly after suffering feed restriction.
The severity of the poisoning has recently been associated with the
ruminal microbiota, as different bacterial populations were found
in animals that tolerated oak leaves and in those that showed clinical
and pathological signs of toxicity. Intoxication has previously been
linked to the production of phenolic metabolites, particularly catechol,
phloroglucinol, and resorcinol. This suggested that the microbial
metabolism of ellagitannins could also be associated with its tolerance
or intoxication in different animals. Therefore, it is essential to
understand the metabolism of ellagitannins in cattle. Here we show
that ellagitannins are metabolized in the cattle rumen to urolithins.
Different urolithins were detected in ruminal fluid, feces, urine,
and plasma. Oak leaf ellagitannins declined as they were converted
to urolithins, mainly isourolithin A and urolithin B, by the ruminal
and fecal microbiota. Urolithin aglycons were observed in rumen and
feces, and glucuronide and sulfate derivatives were detected in plasma
and urine. Sulfate derivatives were the main metabolites detected
in plasma, while glucuronide derivatives were the main ones in urine.
The main urolithins produced in cattle were isourolithin A and urolithin
B. This is a relevant difference from the monogastric mammals studied
previously in which urolithin A was the main metabolite produced.
Low molecular weight phenolics of the benzoic, phenylacetic, and phenylpropionic
groups and metabolites such as catechol, resorcinol, and related compounds
were also detected. There was a large variability in the kinetics
of production of these metabolites in individual animals, although
they produced similar metabolites in all cases. This large variability
could be associated with the large variability in the rumen and intestine
microbiota that has previously been observed. Further studies are
needed to demonstrate if the efficiency in the metabolism of ellagitannins
by the microbiota could explain the differences observed in susceptibility
to intoxication by the different animals