More on XO

I remain skeptical that XO in milk is a hazard and was kindly sent the following:

From a correspondent:

XO is not 'released from mammary cells present in the milk', but was
put into the milk by the mammary cells for the calf's health, and
humans also use this strategy

Homogenization does not change the amount of enzyme exposed to the
bowel. Further, it is all digested in the bowel, or excreted, and
none will enter the body.

There is, however, some interesting developments on the 'immune
booster' front that involve XO. Specifically, it is now believed that
the immune system may accidentally cause a great deal of cancers
through inflammation action. It turns out that cytokines involved in
inflammation response trigger XO in human cells to produce oxide ion,
which kills pathogen, but can cause cancer in the long run. Many
herbal 'immune boosters' act by mimicing cytokines, and therefore may
be carcinogens in the long run through enzymatic interactions such as
those with XO.

I've seen this reference before:

Lancet 2000 Sep 2;356(9232):829-830 Antibacterial properties of
xanthine oxidase in human milk. Stevens CR, Millar TM, Clinch JG,
Kanczler JM, Bodamyali T, Blake DR.

Formula-fed babies contract gastroenteritis more than breast-fed
babies, which is of concern to mothers who cannot breastfeed or, as
with HIV-infected mothers, are discouraged from breastfeeding. The
ability of endogenous breastmilk xanthine oxidase to generate the
antimicrobial radical nitric oxide has been measured and its
influence on the growth of Escherichia coli and Salmonella
enteritides examined. Breastmilk, but not formula feed, generated
nitric oxide. Xanthine oxidase activity substantially inhibited the
growth of both bacteria. An important natural antibiotic system is
missing in formula feeds; the addition of xanthine oxidase may
improve formula for use when breastfeeding is not a safe option.

--John