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Department of Paediatrics, University of British Columbia, Vancouver, Canada V5Z 4H4
2To whom correspondence should be addressed.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • monounsaturated fatty acids • canola oil • infant formula • platelets • piglets
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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- linolenic acid [18:3(n-3)], and low levels of saturated
fatty acids. The positive health benefits afforded to canola oil have
been derived in part from epidemiological studies that show the
prevalence of coronary heart disease is lower among populations
following a Mediterranean diet high in monounsaturated fatty acids,
specifically oleic acid [18:1(n-9)], and clinical studies that show
diets with olive oil have beneficial effects on plasma lipoproteins and
cholesterol (Dreon et al. 1990
, Keys et al. 1986
, Mensink and Katan 1989
, Sitori et
al. 1986
). The traditional source of monounsaturated fatty
acids in the Mediterranean diet is olive oil, which unlike canola oil
is low in 18:3(n-3). Canola and olive oil also differ in several other
aspects, including the distribution of the fatty acids in the
triglycerides and the composition of the sterols. Clinical studies,
however, have shown that, within the context of a lipid lowering diet,
canola oil is efficacious in lowering serum cholesterol
(Gustafsson et al. 1994
).
Diets high in (n-3) fatty acids are also associated with a lower risk
of morbidity and mortality from several chronic diseases. A high intake
of (n-3) fatty acids, particularly eicosapentaenoic acid [20:5(n-3)],
is considered to have favorable effects on plasma lipids, platelet
aggregation and bleeding time with respect to risk of coronary heart
disease and thrombotic disease (Dyerberg and Bang 1979
,
Harris 1989
, Kinsella et al. 1990
).
Increased intakes of oils providing relatively high amounts of
18:3(n-3) may increase blood lipid levels of 20:5(n-3) (Chan et al. 1993
; Gustafson et al. 1994
). Furthermore
low dietary intakes of (n-3) fatty acids is of concern because of the
important role of 22:6(n-3), formed by desaturation and elongation of
18:3(n-3), in visual and neural function (Innis 1991
).
The high levels of both 18:1 and 18:3(n-3) in canola oil, thus,
supports canola oil as an attractive oil for many dietary applications,
including infant formulas.
At the present time, canola oil containing no more than 2% fatty
acids as 22:1(n-9) is permitted in foods for adults and children, but
not in infant formulas (Federal Register 1985
). The use
of canola oil in infant formulas is not permitted because infants fed
formula might consume higher amounts of 22:1(n-9) than would be
provided in usual mixed diets and because of the lack of data about
infants fed diets containing canola oil. Studies from this
laboratory have reported lower platelet counts and higher platelet
volumes in piglets fed formula containing canola and high oleic
sunflower or safflower oil blended with medium chain triglycerides
(MCT)3
or coconut oil rather than a similar formula with palm oil
(Innis et al. 1993
). Others have reported lower platelet
counts in piglets fed a milk replacer with canola oil rather than
soybean oil (Kramer et al. 1994
). Diets containing
canola oil also have adverse effects on homeostatic parameters in
stroke-prone, spontaneously hypertensive (SHR-SP) rats, in which
the major cause of death is cerebral bleeding. A series of studies have
reported shorter life span in SHR-SP rats (maintained with 10 g/L
sodium chloride as drinking water) fed low erucic acid rapeseed rather
than soybean oil (Huang et al. 1996 and 1997
).
Although many studies have shown that both the quantity and quality of
dietary fat can influence platelet characteristics and function in
humans, most of the emphasis was with respect to benefits associated
with reducing the risk of thrombotic disease (Dyerberg and Bang 1979
, Goodnight et al. 1981
, Hay et al. 1982
, Lorenz et al. 1983
, McGregor et al. 1980
, Malle et al. 1991
, Nelson et al. 1991
, Siess et al. 1980
, Von Schacky et al. 1985
) rather than on the adverse effects relevant to
hemorrhagic disease. Furthermore, whether canola oil has specific
effects on platelet characteristics that differ from those of other
unsaturated vegetable oils is not clear. However, human (and pig) milk
typically contain 35–40% fatty acids as 18:1 (Innis 1992
), and oil(s) high in 18:1 may be included in infant
formula to achieve a pattern of saturated, monounsaturated and
polyunsaturated fatty acids that resembles milk. The primary objective
of the study, therefore, was to determine whether canola oil has any
effect on hematological parameters or blood lipids in piglets fed
formula, either as the only source of fat or blended with
saturated fats to more closely resemble the usual fatty acid
composition of pig and human milk and some currently available
infant formulas. Formulas with soybean oil were used for comparison
because soybean oil is currently used as a source of unsaturated fatty
acids in many formulas and has a different pattern of C18 unsaturated
fatty acids than canola oil. The study also included comparison of
formula with canola oil to formula with a blend of oils designed to
mimic the levels of carbon chain (C) 16 and 18 saturated and
unsaturated fatty acids, without 22:1(n-9) or the sterols components of
canola oil.
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Five fat blends were prepared using (g/100g) 100% canola oil; 100%
soybean oil; a mixture (% fat by volume) of 29% soybean, 59% high
oleic acid sunflower, and 12% flax oil (canola oil mimic); 26%
canola, 42% palm, 4% high oleic acid sunflower, 16% sunflower, and
12% coconut oil (canola oil blend); or 26% soybean, 48% palm, 14%
high oleic acid sunflower, and 12% coconut oil (soybean oil blend)
(Table 1). The formulas with 26% canola or soybean oil and palm, high
oleic sunflower and coconut oil were designed to resemble formula for
healthy, term-gestation infants, which include levels of 16:0 and
18:1 similar to those in human milk (Innis 1992
). The
formulas with 100 or 26% canola oil or soybean oil addressed the
primary objectives, which were to determine the effect on hematological
parameters of canola oil alone or when blended with saturated fatty
acids in a formula similar to that of some term infant formulas. The
canola oil mimic was designed to give a composition of 16:0, 18:1,
18:2(n-6) and 18:3(n-3) as similar as possible to that in canola oil,
without 20:1(n-9) and 22:1(n-9). The comparison of formula with 100%
canola oil and the canola oil mimic addressed the secondary objectives
of whether unique aspects of canola oil not found in other vegetable
oils, i.e., sterol components or triglyceride structure, may explain
any effects of canola on hematological variables in young piglets. All
the diets were prepared as complete, liquid, ready-to-feed formulas by
using procedures similar to those used by Ross Laboratories, Columbus,
OH, in the manufacture of infant formula. A group of piglets left with
the sow from birth were studied to provide laboratory reference data.
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All of the procedures involving the piglets were approved by the Animal Care Committee of the University of British Columbia and conformed to the guidelines of the Canadian Council on Animal Care.
Blood sampling and measurements.
The piglets were anesthetized with ketamine:rompun (37.5:3.75 mg/kg, MTC pharmaceuticals and Chemagro, Etobicoke, Ontario, respectively), by intramuscular injection at 5, 10 and 18 d of age, and blood was drawn from the vena cava into vacutainer tubes containing 150 mg EDTA/L in 9 g NaCl/L. Whole blood for complete blood counts was taken immediately for analysis. Measurements of platelet count, volume, platelet distribution width (PDW, a measure of the variation in platelet width), hemoglobin and red blood cell characteristics were done by routine procedures in the Haematopathology Laboratory of the British Columbia Children's Hospital by using an automated multiparameter blood counter TAO Sysinex NE-8000, NE 5500 (Canlab, Vancouver, B.C.). Plasma for lipid analysis was prepared by centrifugation of whole blood for 15 min at 3000 rpm and frozen at -80°C.
Plasma total lipids were extracted according to Folch et al. (1959)
,
and the triglycerides, phospholipids and cholesteryl esters separated
by TLC using petroleum ether-diethyl ether-acetic acid (85/15/3,
v/v/v) as the solvent system (Hrboticky et al. 1990
). Known amounts of 1,2
dipentadecanoyl-sn-glycero-3 phosphocholine,
triheptadecanoin and cholesteryl nonadecanoate were added to the plasma
lipid extracts, as standards, prior to TLC. The separated lipid
fractions were recovered; the fatty acid components were converted to
their respective methyl esters, then separated and quantitated using a
Varian 3400 gas liquid chromatograph equipped for analysis with SP 2330
capillary columns, 30 m x 0.25 mm inside diameter and a
Varian Star data system (Varian Canada, Georgetown, Ontario)
(Innis et al. 1997
). To consider whether the
formula triglyceride fatty acid distribution might influence the
distribution, as well as composition, of fatty acids in plasma
phospholipids, we did exploratory analysis by using phospholipase
A2 hydrolysis of plasma phospholipid, followed by analysis
of the free fatty acid products (Innis et al. 1997a
and 1997b
). Similarly, the
possible effects of unusual sterol components was considered by
analyzing the plasma sterols by gas chromatography/mass
spectrometry, as described by Dyer et al. (1995)
, with
derivatisation to trimethylsilyl ethers by using 50µL
1-methylimidazole to 1 mL N-methyl-N
(trimethylsilyl)-hepta-flurobutyramide.
Statistical Analyses.
Results were compared between the groups of formula-fed piglets by using two-way ANOVA for piglets fed the formula with canola or soybean oil alone or blended with other oils. Formal tests for significant difference were made using Fisher's least significant difference and were performed only for ANOVA results with P < 0.05. These analyses, therefore, considered the amount of canola or soybean oil and the addition of saturated fatty acids to the formula as the two main variables. Where a statistically significant effect was found, preplanned comparisons were made to determine the effect of feeding the 100% canola oil compared to 100% soybean oil and the effect of feeding 100% canola oil compared to a blend with 26% canola and a blend with 26% soybean oil compared to 100% soybean oil. One-way ANOVA was used to compare the effects of feeding the formula with canola oil alone to the effects of feeding the canola oil mimic. Values are means ± SEM.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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The formulas were designed to study whether the low levels of 16:0,
proportions of 18:1(n-6) and 18:3(n-3), small amounts of 20:1 and 22:1
or some other component of canola oil compared to other vegetable oils
alters growth, blood lipids or platelet characteristics in young
piglets. The formula with canola oil as the only fat was characterized
by low levels of 16:0, high 18:1 and 18:3(n-3), and a
18:2(n-6)/18:3(n-3) ratio of ~2:1 (Table 1)
. Soybean oil, by
comparison, had similarly high levels of 18:3(n-3), but higher
18:2(n-6) and a 18:2(n-6)/18:3(n-3) ratio of ~7:1. The formulas with
canola or soybean oil blended with palm and coconut oil had a similar
composition of C16 and 18 fatty acids, with higher levels of 16:0
(21–24% fatty acids) and lower 18:3(n-3) than the 100% canola or
soybean oil, which had 18:2(n-6)/18:3(n-3) ratios of 8:1 and 9:1,
respectively. The canola oil mimic provided a formula with the same
proportions of 16:0, 18:1, 18:2(n-6), and 18:3(n-3) to canola oil, but
without 22:1 and with a trace (0.1%) of 20:1, allowing for
consideration of specific effects of canola oil in the rapidly growing
formula-fed piglet.
Growth.
There were no significant differences in body weight, weight gain, liver weight or formula intake at any age among the groups of piglets fed the formula with 100% or blended canola oil or soybean oil, or the canola oil mimic (data not shown). The body weight at 18 d was 6.19 ± 0.26, 6.30 ± 0.30, 5.94 ± 0.13, 6.08 ± 0.23 and 5.77 ± 0.18 kg, and weight gain for the 18-d feeding period was 4.68 ± 0.20, 4.92 ± 0.22, 4.58 ± 0.12, 4.67 ± 0.15 and 4.41 ± 0.16 kg for groups fed formula with 100% canola or soybean oil, the canola or soybean oil blend, or the canola oil mimic, respectively. The heart weight and heart weight/kg body weight was also not different between piglets fed the formulas with canola oil and those with soybean oil at 10 or 18 d. The heart weight of 18-d-old, but not 10-d-old piglets, fed the canola oil mimic was significantly lower than that of piglets fed the 100% canola oil, 33.7 ± 1.2g and 37.9 ± 1.5, respectively. Because the heart/body weight ratio at 18 d was not different between piglets fed 100% canola oil and those fed the canola oil mimic (6.0 ± 0.2 and 5.8 ± 0.1 g/kg, respectively), it seems reasonable that the lower heart weight of piglets fed the canola oil mimic was related to the lower, although not significantly, weight of piglets in this group.
Platelet characteristics.
The measures of platelet count, volume and distribution width
(a measure of the variability in platelet width) showed that the fat
composition of formula fed to piglets during the first 18 d after
birth had a significant effect on platelet characteristics (Fig. 1
). Piglets fed the formulas with canola oil (100% or blended) had
significantly lower platelet counts than piglets fed the formulas with
soybean oil (Fig. 1)
. At 10 d of age, the platelet count of
piglets fed the formula with 100% canola oil was significantly lower
than that of piglets fed the formula with 100% soybean oil. This
difference was explained by a failure to increase the platelet count
during the first 10 d after birth in the group fed 100% canola
oil (Fig. 1)
. Piglets fed the canola oil mimic also had significantly
higher platelet counts at 10, but not 5 or 18, d of age than did
piglets fed the 100% the canola oil formula. Piglets fed the formula
with only canola or soybean oil also had significantly lower platelet
counts, but higher PDW and platelet volumes than piglets fed the
formula with blended canola or soybean oil (P < 0.05).
The differences in platelet count between the groups fed the 100%
compared to the blended oils were significance at 10, but not 5 or 18,
d of age (Fig. 1)
. Similarly, piglets fed the formula with 100% canola
oil had a significantly higher PDW than piglets fed blended canola oil
at 10 d of age. The higher PDW of the piglets fed the 100% canola
oil, at 5 and 18 d of age, or the 100% soybean oil, at 5, 10 and
18 d of age, compared to their respective oil blends, however, was
not significant.
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The fat composition of the formula also had a significant effect on the characteristics of red blood cells. Piglets fed the formulas with 100% canola oil or the canola oil blend had a significantly higher red blood cell count (4.10 ± 0.18 and 4.16 ± 0.15 x 109/L, respectively) and hematocrit (0.316 ± 0.011 and 0.314 ± 0.010, respectively) at 5 d of age than did piglets fed the formula with 100% soybean oil (RBC: 3.64 ± 0.17 x 109/L, hematocrit: 0.276 ± 0.008) or the soybean oil blend (RBC: 3.48 ± 0.17 x 109/L, hematocrit: 0.266 ± 0.008). At 18 d of age, however, the red blood cell count was lower in the group fed 100% canola oil than in those fed 100% soybean oil (4.79 ± 0.09 and 5.10 ± 0.16 x 109/L, respectively). No differences were found in the red cell distribution width, mean corpuscular width, or mean corpuscular hemoglobin concentration among the groups fed the different formulas at 5, 10 or 18 d. And no differences were found between piglets, with the exception that, at 10 d, the mean corpuscular hemoglobin concentration was lower in the group fed 100% canola oil compared to the group fed the canola oil mimic (26.5 ± 0.3 and 27.4 ± 0.2 g/L, respectively).
Blood lipids and fatty acids.
The formula oil composition also had a significant effect on the plasma
lipids of the piglets (Table 2). Piglets fed the formula with canola or soybean oil blended with
other oils (thus increasing the dietary 16:0 and reducing unsaturated
fatty acids) had significantly higher plasma cholesterol levels at 10
and 18 d of age, higher HDL cholesterol at 10 d and higher
triglycerides at 18 d than did the piglets fed the formulas with
100% canola or soybean oil (Table 2)
. Although there were no
significant differences in total or HDL cholesterol or phospholipid
between piglets fed canola oil compared to soybean oil, the levels of
free cholesterol were significantly higher in piglets fed the formula
with 100% canola oil than in those fed 100% soybean oil at both 10
and 18 d of age. The differences in plasma free (cholesterol) were
accompanied by differences in the cholesterol ester levels of 18:1 and
18:2(n-6). The percentage of 18:1 was ~100% higher (in total fatty
acids, 34.9 ± 0.9 versus 15.1 ± 0.5%, P < 0.05) and of 18:2(n-6) was significantly lower (41.3 ± 1.8 versus
61.8 ± 0.7%, P < 0.05) in piglets fed the
formula with 100% canola oil than in piglets fed the formula with
100% soybean oil. In contrast, the plasma cholesterol ester percentage
18:1 (28.4 ± 0.8 versus 30.5 ± 0.9%) and 18:2(n-6) (47.9
± 0.8 versus 46.4 ± 0.8%) were not different between
piglets fed the canola oil and soybean oil blends, but 18:1 was higher
and 18:2(n-6) was lower in piglets fed the soybean oil blend compared
to the 100% soybean oil formula (P < 0.05). The
plasma levels of cholesterol, phospholipid and triglyceride were not
different between piglets fed the formula with 100% canola oil and
those fed the canola oil mimic (Table 2)
. Similarly, there were no
significant differences in the plasma cholesterol ester percentage of
18:2(n-6), although the percentage of 18:1 was significantly lower in
piglets fed the canola oil mimic than in piglets fed the 100%
canola oil formula (data not shown).
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) levels of C16 and 18 fatty acids among piglets fed the formulas
reflected the differences in 16:0, 18:1, 18:2(n-6) and 18:3(n-3) among
the formulas. Piglets fed the formula with 100% canola or soybean oil
had a significantly lower percentage of 16:0 and higher percentage of
18:3(n-3) in their plasma phospholipids and triglycerides than piglets
fed the formulas with the canola oil and soybean oil blends. Similarly,
piglets fed the formula with 100% canola oil had significantly higher
plasma phospholipid and triglyceride levels of 18:1 and lower
triglyceride levels of 18:2(n-6) than piglets fed the canola oil blend.
Piglets fed the formula with 100% soybean oil, on the other hand, had
a significantly higher percentage of 18:1 and lower percent 18:2(n-6)
in plasma phospholipids and triglycerides than piglets fed the soybean
oil blend. Of note, the plasma phospholipid percentages of 20:4(n-6)
and 22:6(n-3) were higher in piglets fed the formula with the canola or
soybean oil blend, providing 9.6 and 7.7% fatty acids as 18:3(n-3),
respectively, than in piglets fed the 100% canola or soybean oil
formula, respectively. Piglets fed the formula with the canola oil
mimic had significantly higher 18:0 and lower 18:1, 20:1 and 22:1 in
plasma phospholipids, and lower 16:0 and 22:1, but higher 18:2(n-6), in
plasma triglycerides than piglets fed the formula with 100% canola
oil.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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The study reported here shows that the type of oil, canola, soybean, or
a blend of canola or soybean oil, in formula influences the
developmental changes in platelet characteristics that occur in piglets
fed formula during the first 18 d after birth. The fat composition
of the formula, however, had no significant effect on the body weight
or weight gain of the piglets. One recent study reported lower weight
at 120 d of age in infants fed a formula with ~3.2% fatty acids
as 18:3(n-3) and a 18:2(n-6)/18:3(n-3) ratio of 4.8:1 (n
= 13) than in infants fed formula with 0.4% 18:3(n-3) and a
18:2(n-6)/18:3(n-3) ratio of 44:1 (n = 17)
(Jensen et al. 1997
). Other studies have not found
differences in growth among infants fed formulas with 4.7% 18:3(n-3),
18:2(n-6)/18:3(n-3) of 7.3:1 compared to 2% 18:3(n-3),
18:2(n-6)/18:3(n-3) of 9.5:1 (Innis et al. 1997a
and 1997b
), or formulas with 4.8% 18:3(n-3),
18:2(n-6)/18:3(n-3) of 7:1 compared to 0.8% 18:3(n-3),
18:2(n-6)/18:3(n-3) of 39:1 (Ponder et al. 1992
). The
formulas fed to piglets here had 2–9.6% 18:3(n-3) with
18:2(n-6)/18:3(n-3) ratios of about 2:1, 7:1, 8:1 and 9:1. The present
study suggests that intakes of 
9.6% 18:3(n-3) with
18:2(n-6)/18:3(n-3) ratios of 2:1 have no adverse effect on growth in
piglets. The limited published information on the possible adverse
effects of high intakes of 18:3(n-3) with low 18:2(n-6) on growth of
infants does not support a possible species differences
concerning 18:3(n-3) and growth.
Blood lipids and fatty acids.
The effects of the dietary fat composition on the plasma lipids
and fatty acids in the present study are consistent with others that
compared highly monounsaturated, 18:2(n-6)-rich, and saturated fats and
oils (Dreon et al. 1990
, Gustafsson et al. 1994
, Mensink and Katan 1989
, Sirtori et al. 1986
). Feeding soybean oil, which is high in 18:2(n-6),
was associated with lower HDL cholesterol, unesterified cholesterol,
and cholesterol ester 18:1 and higher cholesterol ester 18:2(n-6) in
piglet plasma than was canola oil, which is high in 18:1. Blending the
soybean oil to increase the intake of 16:0 and 18:1 and reduce
18:2(n-6) resulted in higher plasma HDL cholesterol and free
cholesterol and lower cholesterol ester levels of 18:2(n-6). It should
be noted, however, that the plasma total and HDL cholesterol levels in
the formula-fed piglets were lower than in milk-fed
piglets (plasma total cholesterol and HDL cholesterol 4.2
± 0.2 and 1.7 ± 0.4 mmol/L, respectively, at 18 d of
age). The physiological significance of differences in plasma
cholesterol between piglets or infants fed formula varying in fat
composition, or which result from breast-feeding compared to
bottle-feeding, is not yet known.
The study reported here also provides information on the effects of the dietary 18:2(n-6) and 18:3(n-3) and 18:2(n-6)/18:3(n-3) ratio on plasma phospholipid 20:4(n-6) and 22:6(n-3). As in currently available infant formulas in North America, the formulas fed to the piglets in this study had no 20:4(n-6) or 22:6(n-3). Thus, after 18 d feeding with considerable growth having occurred, differences in the plasma phospholipid 20:4(n-6), 20:5(n-3) and 22:6(n-3) probably reflect the effects of the fatty acid intake on 20:4(n-6), 20:5(n-3) and 22:6(n-3) synthesis and phospholipid acylation. The formulas with 100% canola oil, the canola oil mimic, and the canola oil and soybean oil blends all contained 20–22% fatty acids as 18:2(n-6). However, whereas canola oil and the canola oil mimic had 8.6–9.6% fatty acids as 18:3(n-3) with 18:2(n-6)/18:3(n-3) ratios of ~2:1, the canola oil and soybean oil blends has 2.2–2.8% 18:3(n-3) with 18:2(n-6)/18:3(n-3) ratios of 8:1 and 9:1, respectively. Soybean oil had high 18:3(n-3) (7.7% fatty acids), but a similar 18:2(n-6)/18:3(n-3) ratio of ~7:1. The higher plasma phospholipid 20:4(n-6) levels in piglets fed the formulas with the canola oil or soybean oil blends (10.6 ± 0.7 and 11.1 ± 0.6 fatty acids at 18 d, respectively) than in piglets fed 100% canola or soybean oil or the canola oil mimic (7.2 ± 0.3, 9.7 ± 0.4, and 8.2 ± 0.3% fatty acids at 18 d, respectively) suggests the dietary intake of 18:3(n-3) is a more important determinant of 18:2(n-6) desaturation than the 18:2(n-6)/18:3(n-3) ratio. This is consistent with inhibition of 18:2(n-6) desaturation by 18:3(n-3). In contrast, the four to fivefold higher plasma phospholipid levels of 20:5(n-3) in piglets fed the formula with 100% canola oil or the canola oil mimic (0.8 ± 0.0 and 1.0 ± 0.1%, respectively) than in piglets fed 100% soybean oil or the canola or soybean oil blends (0.2 ± 0.0, 0.2 ± 0.0, and 0.3 ± 0.0%, respectively) suggests the dietary 18:2(n-6)/18:3(n-3) ratio is a more important determinant of 18:3(n-3) desaturation and/or 20:5(n-3) acylation into phospholipids than the intake of 18:3(n-3).
Platelet characteristics.
The results of this study provide clear evidence that the oil
composition of formula has a significant effect on platelet count and
size in formula-fed piglets. The inclusion of canola oil in the
formula was associated with lower platelet counts than that found with
soybean oil. Further, feeding a formula containing a single, highly
monounsaturated (canola) or polyunsaturated (soybean) oil was
associated with lower platelet counts and higher platelet volumes and
PDW (a measure of the range of size) than when the respective oil was
blended with saturated vegetable oils. These findings are consistent
with previous studies from this laboratory that show lower platelet
counts and higher platelet volumes and PDW in piglets fed from birth to
18 d with formulas containing canola oil with high oleic acid
safflower or sunflower oil with MCT or coconut oil than in piglets fed
canola oil blended with palm oil (Innis et al. 1993
).
The consistently lower platelet counts in piglets fed the formula with
100% canola and the canola oil blend compared to the 100% soybean and
the soybean oil blend or the canola oil mimic suggests that some
property of canola oil, other than the levels of C16 and 18 fatty
acids, influences platelet characteristics. The prospective measures in
this study suggest dietary canola oil suppresses the normal increase in
platelet count in piglets during the first 10 d after birth. Thus,
the platelet count was not different at 5, 10 and 18 d of age in
piglets fed the formula with 100% canola oil (497 ± 38, 487
± 37 and 514 ± 59x109/L,
respectively, P > 0.5), but increased between 5 and
10 d of age in the groups fed the other formulas. Consistent with
this, Kramer et al. (1994)
reported lower platelet counts at 7 and 14,
but not 21, d of age in piglets fed a milk replacer with canola oil
than that found in piglets fed a milk replacer with soybean oil.
Bleeding time depends on both platelet count and volume, and that
platelet count and volume usually change inversely (Martin et al. 1983
). Future studies should establish whether canola oil
reduces platelet synthesis or reactivity and the relevance of the
findings of this and other studies with piglets(Innis et al. 1993
, Kramer et al. 1994
) to human nutrition
products, which contain canola and other highly monounsaturated
vegetable oils. Because the effects of canola oil in piglets appear to
involve suppression of the normal developmental increase in platelet
count, it is possible that any effects of canola oil are more important
in early infancy or following thrombocytopenia, and in conditions
associated with increased bleeding, rather than thrombus formation. In
this regard, studies with SHR-SP rats, in which the major cause of
death is cerebral bleeding, have found that feeding canola oil compared
to soybean oil results in significant shortening of the life span
(Huang et al. 1996 and 1997
). Shortening of the
life-span in SHR-SP rats, however, also occurs with other
highly monounsaturated vegetable oils, unesterified fatty acids from
canola oil, and hydrogenated soybean oil (Huang et al. 1996 and 1997
, Miyazaki et al. 1998
).
Numerous studies have shown that postprandial lipemia, as well as the
dietary fat content and composition, alter platelet characteristics
(Burri et al. 1991
, Goodnight et al. 1981
, Jakubowski and Ardlie 1978
, Kwon et al. 1991
, Markmann et al. 1990
, Miller et al. 1991
, Nimpf et al. 1989
, Renaud et al. 1986
, Silveira et al. 1994
, Sirtori et al. 1986
). Despite this and the knowledge that platelets
play an important role in arterial thrombosis and atherosclerosis, the
relation of diet-induced changes in platelet count and size to
platelet function are not well understood. Changes in platelet number,
volume and function following dietary modification to increase the
intake of long-chain (n-3) fatty acids, particularly 20:5(n-3),
have been widely reported (Goodnight et al. 1981
,
Hay et al. 1982
, Lorenz et al. 1983
Malle et al. 1991
, Nelson et al. 1991
,
Siess et al. 1980
, Von Schacky et al. 1985
). An increased intake of 20:5(n-3) is accompanied by
increased 20:5(n-3) and decreased 20:4(n-6) in plasma and platelet
phospholipids. When released from phospholipids, 20:5(n-3) competes
with 20:4(n-6) for cyclo-oxygenase, thus reducing synthesis of
thromboxane A2 from 20:4(n-6) and increasing
synthesis of thromboxane A3 which, is a poor
agonist for platelet aggregation (Carega-Houck and Sprecher 1989
, Sprecher 1986
). The study presented here
found no relations between the plasma phospholipid 20:4(n-6) or the
20:4(n-6)/20:5(n-3) ratio and platelet count, within or among the
piglet groups at any age (P > 0.05). Although the
composition of platelet phospholipid fatty acids was not determined,
platelets lack 
-6 desaturase and obtain their fatty acids,
at least in part, from plasma. These results suggest that canola oil
may alter platelet count by a mechanism unrelated to 20:4(n-6) and
20:5(n-3). Similarly, increasing 18:2(n-6) or 18:1 compared to
saturated fat appears to reduce the ability of platelets to aggregate
in humans by a mechanism unrelated to changes in (n-3) fatty acids or
20:4(n-6) (Burri et al. 1991
, Kwon et al. 1991
).
The lower platelet counts in piglets fed the formulas with canola
oil rather than soybean oil or the canola oil mimic suggests the
effects of canola oil on platelet counts are not caused by a low intake
of 16:0, a high intake of 18:1 or 18:3(n-3), or a low dietary
18:2(n-6)/18:3(n-3) ratio. The higher platelet count in piglets fed the
formulas with blended soybean or canola rather than soybean or canola
oil alone, however, does show the intake of saturated fatty acids is an
important determinant of platelet characteristics. In this regard,
several studies have shown that dietary saturated fat is associated
with more responsive platelets than are diets containing unsaturated
fat (Jakubowski and Ardlie 1978
, Markmann et al. 1990
, Renaud et al. 1986
). Furthermore, several
studies have provided evidence that monounsaturated (18:1) and
polyunsaturated- [18:2(n-6)] rich oils may have different effects on
platelet function (Burri et al. 1991
, Kwon et al. 1991
, Renaud et al. 1986
). Burri et al. (1991)
reported that thresholds of ADP- and collagen-induced platelet
aggregation were significantly higher in adults following a diet high
in 18:2(n-6) from safflower oil rather than a diet high in 18:1 from
high oleic acid safflower oil. Kwon et al. (1991)
, on the other hand,
reported that although diets high in 18:1 from canola oil and in
18:2(n-6) from safflower oil, when compared to a saturated fat, both
reduced platelet aggregation, canola oil, but not safflower oil, was
associated with lower ATP secretion in response to collagen-induced
platelet aggregation. Studies by McDonald et al. (1989)
noted a
significant increase in bleeding time and in production of
6-keto-PGF1 in men after 18d with a canola,
but not sunflower, oil diet when compared to a mixed-fat diet.
Diet-induced changes in the platelet membrane phospholipid fatty acids
could lead to changes in platelet membrane fluidity, and consequently
membrane-associated functions. Some studies with human platelets,
however, have not found alterations in membrane fluidity, despite
changes in platelet fatty acid composition, count and volume
(Malle et al. 1991
, Vognild et al. 1998
).
Another possible explanation for the effects of canola oil on platelet
count may relate to the composition or distribution of fatty acids in
the canola triglycerides or on the effects of brassica or other sterols
in the oils. The positional distribution of fatty acids in canola oil
differs from other unsaturated vegetable oils, in that ~25% of the
triglycerides are triolein (Eskin et al. 1996
).
Furthermore, ~65 and 70% of fatty acids at the glycerol positions 1
and 3, respectively, are 18:1 (Eskin et al. 1996
). This
unusual fatty acid distribution was not achieved by the soybean, high
oleic acid sunflower and flax oil blend in the canola oil mimic.
Studies in this and other laboratories have shown that the dietary
triglyceride fatty acid distribution influences the distribution of
fatty acids in plasma lipids (Innis et al. 1994
and
1997
, Ruiz-Gutiérrez et al. 1998
).
However, the present study found no evidence to suggest that changes in
the plasma phospholipid sn-2 position 20:4(n-6) and
20:5(n-3) were involved in the effects of canola oil on the platelet
counts of formula-fed piglets.
Recent studies have shown that several platelet proteins contain
thioester-linked fatty acids and that an important part of platelet
activation by thrombin is the incorporation of fatty acid-linked
proteins into the cell cytoskeleton (Laposata and Muszbek 1996
, Muszbek and Laposata 1989
). Covalent
modification of platelet proteins by thioester-linked fatty acids
demonstrates relaxed specificity for several fatty acids, including
14:0, 16:0, 18:0, 20:4(n-6) and 20:5(n-3), and is not dependent on
protein synthesis (Laposata and Muszbek 1996
, Van
Cott et al. 1997
). Furthermore, inverse associations between
16:0 and 18:0 in platelet phospholipids and platelet aggregation
(Kwon et al. 1991
), and between dietary saturated fat
intake and platelet clotting activity, (Renaud et al. 1986
) were noted. Whether or not the composition of fatty acids
or monoglycerides released during chylomicron triglyceride hydrolysis
by lipoprotein lipase can influence the composition of
thioester-linked fatty acids on the platelet surface is not known.
A more rigorous investigation with randomized canola oil
feeding is needed before definitive conclusions on the
possible effects of the triglyceride fatty acid distribution on
platelet count can be made.
Canola oil contains relatively high amounts of phytosterols, ~890
mg/100g compared to ~440 mg/100g in soybean oil (Eskin et al. 1996
). Furthermore, canola oil, unlike other common dietary
oils, contains brassicasterol. The plasma brassica, as well as total
sterol levels, were significantly higher in piglets fed the formula
with canola oil than in those fed soybean oil or the canola oil mimic.
It will be important for future studies to consider if these sterols
are incorporated into the platelet membrane or contribute to changes in
platelet count or function following diets high in canola oil.
|
FOOTNOTES |
|---|
3 Abbreviations used: C, carbon chain length; MCT,
medium chain triglycerides; PDW, platelet distribution width;
SHR-SP, stroke-prone spontaneously hypertensive.
Manuscript received October 5, 1998. Initial review completed November 2, 1998. Revision accepted March 23, 1999.
|
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