Page 101 - Small Animal Clinical Nutrition 5th Edition

Macronutrients 101

and platelet aggregation (MacDonald et al, 1984b, 1984c). mentation. One group of investigators concluded that cats
VetBooks.ir Because dogs can convert linoleic acid (18:2n-6) to arachidon- cannot convert linoleic acid to arachidonic acid in sufficient
quantities for platelet aggregation and prevention of mild
ic acid (20:4n6), linoleic acid is usually listed as an EFA for
mineralization of the kidneys (McDonald et al, 1984b).
dogs. A concentration of 1% of the food DM as linoleic acid is
a safe and effective concentration for dogs (Wiese et al, 1962, Arachidonic acid supplementation allows normal reproduc-
1965, 1966). tion in female cats (McDonald et al, 1984c). Male reproduc-
Because linoleic acid corrected many clinical signs of fatty tion (spermatogenesis), unlike female reproduction, does not
acid deficiency in cats, it also is listed as an EFA for cats require dietary arachidonate because of the testes’ ability to
(McDonald et al, 1984a). Some of the signs of EFA deficien- elongate and desaturate linoleate (McDonald et al, 1984c).
cy in cats, however, were not ameliorated by linoleic acid but These studies indicate that arachidonate is an EFA for cats.
rather improvement depended on arachidonic acid supple- Foods for cats should contain at least 0.5% DM linoleic acid

Box 5-13. What’s New in Fatty Acids: Resolvins, Protectins and
Omega-3-Derived Mediators.

INTRODUCTION Both the D and E classes of resolvins appear as biosynthetic prod-
ucts involving cell-to-cell interaction with vascular endothelial cells
Beneficial actions of polyunsaturated fatty acids were noted many and are potent regulators of leukocyte infiltration. Specifically,
years ago but the underlying mechanisms for these effects are resolvin E1 (RvE1) dramatically reduces dermal inflammation, peri-
poorly understood. It is clear that arachidonic acid is transformed tonitis, colitis, periodontitis, dendritic cell migration and interleukin
into many potent bioactive compounds such as prostaglandins, (IL)-12 production. Resolvins of the D series block tumor necrosis
leukotrienes and lipoxins. The departure of fatty acids from simply factor-alpha activity and act as potent regulators to limit leukocyte
playing structural roles in cell membranes and/or as energy stores infiltration into inflamed brain, skin and peritoneum.
came largely from the recognition of the rapid transformation of Among the essential fatty acids, DHA is concentrated in the
arachidonic acid to these potent eicosanoids by both cyclooxyge- central nervous system, neurons and retina where it is thought to
nase and lipoxygenase mechanisms. Many of the classic regulate membrane fluidity and ion fluxes. The term docosanoids
prostaglandins and leukotriene mediators are pro-inflammatory has been proposed to describe products generated from DHA.
and play a decisive role in inflammation and/or in systems in which DHA-derived docosatrienes have neuroprotective action in retinal
prostaglandins are key physiologic regulators. Inflammation is a cells and can improve the sequelae associated with stroke and
vital reaction but it also plays a central role in many prevalent dementia. The terms protectin or neuroprotectin describe these
chronic diseases such as osteoarthritis, periodontal disease, compounds, which are rapidly generated from DHA and released
inflammatory bowel disease, cancer, brain aging/dementia, aller- locally into tissues. There is emerging evidence that resolvins and
gic dermatitis and lower urinary tract disease. docosanoid compounds may also have immunoregulatory actions
In sharp contrast, it has become clear in recent years that by influencing antigen-presenting cells and T-cell traffic.
counter-regulatory substances such as lipoxins are generated dur-
ing resolution of acute inflammation, and that these serve as ago- CONCLUSION AND CLINICAL
nists for endogenous antiinflammatory mechanisms. This consti- IMPLICATIONS
tutes the first evidence that the resolution of inflammation, which
was once thought to be a passive process, is actually an active Fatty acid supplementation has been used for many years to
process that involves up-regulating specific pro-resolution circuits. help manage patients with a variety of inflammatory diseases.
Thus, resolution of inflammation is an active endogenous process The underlying mechanisms for the beneficial effects of fatty
aimed at protecting the host from exacerbated inflammation. acid supplementation have been poorly understood. Recent
research has identified novel oxygenated compounds termed
THE OMEGA-3 FATTY ACID CONNECTION resolvins and protectins, which are generated from EPA and
DHA. These endogenous lipid/chemical mediators are “switched-
The molecular mechanisms underlying the beneficial actions of on” in the resolution phase of an inflammatory response, thus
polyunsaturated fatty acids remain an area of active research. acting as “braking-signals” in inflammation and reducing leuko-
Investigators have recently identified novel oxygenated products cyte-mediated injury in several different tissues. The discovery of
generated by enzymatic processes from the precursor omega-3 resolvins and protectins offers molecular mechanisms that could
fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid underlie some of the beneficial actions of dietary fatty acid sup-
(DHA). These new compounds possess potent actions in the reso- plementation observed in many clinical settings.
lution of inflammation and may also have neuroprotective proper-
ties. The term resolvin (resolution phase interaction products) has
been proposed for some of these compounds because they dis- Philip Roudebush, DVM, Dipl. ACVIM
play potent antiinflammatory and immunoregulatory properties, (Small Animal Internal Medicine)
reducing neutrophil traffic and the magnitude of the inflammatory Hill’s Scientific Affairs
response. The term protectin (or neuroprotectin) has been pro- Hill’s Pet Nutrition, Topeka, KS, USA
posed given the protective actions of some of these compounds in
neural and retinal tissues. The Bibliography for Box 5-13 can be found can be found at
Resolvins are derived from EPA (E series) and DHA (D series). www.markmorris.org.