Page 442 - Small Animal Clinical Nutrition 5th Edition

456 Small Animal Clinical Nutrition

become a concern in patients experiencing excessive urinary loss Omega-3 Fatty Acids
VetBooks.ir of those minerals due to intensive diuretic therapy. Most pet The effect of dietary fatty acids on the immune system
depends on which fatty acid is fed and what specific aspects
foods contain adequate amounts of these nutrients, thus defi-
ciency should not be of concern if the repleted patient continues
of the immune system are evaluated. Dietary fatty acids are
eating enough food to meet its RER. Calcium and magnesium thought to affect the immune system by three mechanisms: 1)
are not added to parenteral nutrition solutions due to insolubil- altered eicosanoid synthesis, 2) changes in cell membranes
ity problems; however, phosphorus, sodium and potassium can that affect membrane-associated protein and receptor func-
be added to parenteral nutrition solutions at maintenance con- tion and 3) changes in intracellular nonesterified fatty acid
centrations or for repletion if needed. pools that affect cytokine production. Generally, omega-3 (n-
3) fatty acids produce fewer inflammatory cytokines, whereas
Nucleotides omega-6 (n-6) fatty acids produce more proinflammatory
Nucleotides are precursors of DNA and RNA, but they also cytokines (Lands, 1992).
participate in a number of metabolic reactions fundamental to The capacity of tissues and WBC to produce pro- or anti-
cellular activity. Dietary nucleotides appear to be important inflammatory prostaglandins and lipoxygenase products is
for maintenance of normal cellular immunity and are vital to largely determined by the amount and type of fatty acids pres-
maintain host defenses against bacterial and fungal ent, which is mostly determined by concentration of dietary
pathogens. Dietary nucleotides appear essential to the normal fatty acids. Omega-3 fatty acids, once incorporated into the
maturation of lymphocytes (Hall et al, 1998). In vitro mixed plasma membrane, affect immune cell function by altering
lymphocyte culture response and mitogen stimulation are membrane fluidity and second messenger function, and by
suppressed in patients supported on a casein-based laborato- increasing production of dienoic prostaglandins, the 3-series
ry food. Such foods are nucleotide free. Mice maintained on prostaglandins and 5-series leukotrienes. These changes may
nucleotide-free foods are much more susceptible to lethal be responsible for alterations in such cell functions as phago-
infections caused by Candida albicans and Staphylococcus aureus cytosis, production of interleukins and production of superox-
and exhibit depressed macrophage bactericidal activity com- ides. A significant reduction in dietary omega-6 polyunsatu-
pared to nucleotide-fed counterparts. Similarly, animals fed a rated fatty acids will lower production of proinflammatory
nucleotide-free food for six weeks had significant immuno- eicosanoids and appears to be a prudent approach in nutri-
suppression as demonstrated by enhanced cardiac allografts tional support of immunocompromised, traumatized, postop-
and diminished ability to survive a fungal challenge. These erative or infected patients. Conversely, the inclusion of
findings are significant because all commercially available par- omega-3 fatty acids in such foods would seem to be beneficial
enteral and nearly all enteral human products are devoid of in increasing antiinflammatory eicosanoid production.
nucleotides. Findings suggest that marked improvement can be made in
The clinical value of nucleotides was evaluated in two sep- foods by adjusting the omega-6 and omega-3 components to
arate studies that investigated the effects of a human enteral ensure optimal immune function.
product enriched with arginine, nucleotides and omega-3 Clinical evidence suggests that dietary omega-3 fatty acids
a
fatty acids (Impact ). In one study, researchers investigated may benefit the management of severe inflammatory and
the effects of this enriched enteral product on immune autoimmune disorders in rodents and people. These less
parameters of patients undergoing major abdominal surgery. inflammatory metabolites alter immune function and may
In general, patients receiving the enriched product had improve survival in patients in which the inflammatory
enhanced immunocompetence and fewer infectious compli- process threatens to cause irreversible damage, as in septic
cations than patients in other groups. In the other study, a shock or endotoxemia. Omega-3 fatty acids shift the response
subset of patients with sepsis who were fed the enriched away from intense inflammation. In other studies, fish oil pro-
enteral product (Impact) had shorter hospital stays and a tected guinea pigs from endotoxic shock and lactic acidosis,
major reduction in the frequency of acquired infections vs. providing them with a survival advantage (Fritsche and
other groups (Bower et al, 1995). Though clinical gain was McGuire, 1996).
evident from the nucleotide-enriched food, it is not clear if Timing of dietary omega-6 and omega-3 fatty acid
the benefit was from nucleotides alone or from the combina- manipulation is critical to influencing patient inflammatory
tion of special nutrients provided in the food. There are no response. The literature varies when reporting dosing route,
reported studies evaluating the clinical value of nucleotide- concentration and species. Nonesterified fatty acids in tis-
enriched foods for critical care veterinary patients, likely sues have been effectively altered within hours of oral dos-
because pet foods that use meats and cereal grains as ingre- ing with omega-3 fatty acids. In cats, concentrations of spe-
dients should provide adequate levels of dietary nucleotides. cific fatty acids were altered in immune cell membranes
Despite the limiting data substantiating their clinical value in within 28 days of enteral feeding (Saker, 2002); whereas in
veterinary patients, dietary nucleotides are a vital component pigs, plasma phospholipid profiles differed significantly
of regimens to maintain or restore immune function and host within eight days (Murray et al, 1991). Intestinal mucosa
defense and, therefore, should be considered when choosing and plasma had an altered fatty acid profile within four
a critical-care food. weeks, whereas an alteration in the fatty acid profile of skin