EXG-09487; No of Pages 6 Experimental Gerontology xxx (2014) xxx–xxx
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Experimental Gerontology journal homepage: www.elsevier.com/locate/expgero
High corn oil dietary intake improves health and longevity of aging mice
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Hongwei Si a,⁎, Longyun Zhang a, Siqin Liu a, Tanya LeRoith b, Carlos Virgous c
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a r t i c l e
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Article history: Received 15 July 2014 Received in revised form 29 August 2014 Accepted 2 September 2014 Available online xxxx
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Keywords: Corn oil Aging mice Longevity Health
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Department of Family and Consumer Sciences, Tennessee State University, Nashville, TN 37209, United States Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24061, United States Animal Care Facility, Meharry Medical College, Nashville, TN 37208, United States
a b s t r a c t
Corn oil has been recommended as a replacement for saturated fats because of its high levels of poly- and monounsaturated fatty acids. In the present study, we tested whether very high levels of corn oil (58.6% fat-derived calories, FDC) intake improve health and longevity of aging mice. Twelve month old male C57BL/6 mice were fed a normal diet (10% FDC of corn oil, N) or a high fat diet (58.6% FDC of corn oil, HF) for 13–15 months. Our results show that a HF diet significantly increased the longevity of the aged mice (at 25 months of age, 53.8% of mice died in the N group, whereas the mortality rate was only 23.2% in the HF group). High corn oil also reversed agingincreased blood lipids including triglyceride, total cholesterol and LDL. Similarly, high corn oil intake overturned aging-raised pro-inflammatory markers including IL-1β, IL-6, and monocyte chemotactic protein-1 (MCP-1) in the blood. In addition, corn oil intake reversed aging-damaged rotarod performance and liver function. Interestingly, the HF group was significantly heavier than the N group (53.6 g/mouse vs. 41.3 g/mouse); however, both HF and N groups had the same calorie intake (12.48 kcal/d/mouse vs. 12.24 kcal/d/mouse). Although, the HF group's food consumption was lower than that of the N group (2.4 g/d/mouse vs. 3.4 g/d/mouse). These results suggest that if total calorie consumption stays in the normal range, very high levels of corn oil intake improve health and longevity of aging mice. © 2014 Published by Elsevier Inc.
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1. Introduction
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High saturated fat diets are well associated with obesity prevalence and the increased risk of cardiovascular disease, diabetes and cancer. Reducing saturated fats from the diet is recommended to eliminate Western diet-induced health problems. The common alternatives of animal (saturated) fats for humans are plant oil, including soybean oil, peanut oil and corn oil because of the high percentage of unsaturated fat acids. Corn oil is composed mainly (99% of the refined or 96% of the crude oil) of acylglycerols (mono-, di- and primarily tri-), and has 59% polyunsaturated (PUFA), 24% monounsaturated (MUFA) and 13% saturated fatty acid (SFA). The PUFA to SFA ratio (P/S) is about 4.6. Corn oil has one of the highest PUFA levels after sunflower, safflower, walnut and wheat germ oil (Landers and Rathmann, 1981). The primary PUFA is linoleic acid (C18:2n− 6), with a small amount of linolenic acid (C18:3n −3)
48 49 50 51 52
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Section Editor: Holly M Brown-Borg
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Abbreviations: BW, body weight; EFAs, essential fatty acids; FDC, fat-derived calories; GSR, glutathione-disulfide reductase; GSH, glutathione; H&E, hematoxylin and eosin; HDL, high-density lipoprotein; HF, high corn oil diet; IFN-γ, interferon gamma; IL, interleukin; KC, keratinocyte chemoattractant; LDL, low-density lipoprotein; MCP-1, macrophage chemoattractant protein-1; MUFA, monounsaturated fatty acid; N, normal diet; PUFA, polyunsaturatedfatty acid; ROS,reactive oxygen species; SFA,saturatedfatty acid; SOD,superoxide dismutase; TNFα, tumor necrosis factor-α; YC, youth control. ⁎ Corresponding author. E-mail address: [email protected] (H. Si).
giving a n − 6/n−3 ratio of 83. Corn oil contains a significant amount of ubiquinone and high amounts of gamma-tocopherols (vitamin E) (Dupont et al., 1990). These high contents of PUFA and vitamin E may contribute to the health benefits of corn oil consumption. The beneficial effects of PUFA have been extensively investigated, however, there are very few studies investigating the effects on human health with long-term corn oil consumption, particularly on the older population. This is very important because corn oil is the second leading vegetable oil consumed in the United States (USDA, 2014). Since U.S. adults age 65 and older heavily consume this high fat oil, their population is rapidly increasing and is projected to reach 71 million by 2030. The objectives of the present study are to investigate the long-term health effect of high volume of corn oil consumption in aging mice and to understand the relevant mechanisms.
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2. Methods and Materials
67
2.1. Experimental Animals and Diets
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Twelve-month old male C57BL/6 mice were purchased from the National Cancer Institute (Bethesda, MD). Mice were housed in an environmentally-controlled (23 ± 2 °C; 12-h light: dark cycle) animal facility and they were given ad libitum access to food and water. To test the health effect of high corn oil intake, mice were randomly divided into two groups (n = 31) and given either a normal diet (N) or a high
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http://dx.doi.org/10.1016/j.exger.2014.09.001 0531-5565/© 2014 Published by Elsevier Inc.
Please cite this article as: Si, H., et al., High corn oil dietary intake improves health and longevity of aging mice, Exp. Gerontol. (2014), http:// dx.doi.org/10.1016/j.exger.2014.09.001
54 55 56 57 58 59 60 61 62 63 64 65 66
70 71 72 73 74
2.3. Pathological Analysis
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Fresh livers were fixed in 10% phosphate buffered neutral formalin, embedded in paraffin, cut at thicknesses of 5 μm, and then stained with hematoxylin and eosin (H&E) for histological examination of hepatic lesions. Three sections from each mouse were examined. The
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Table 1 Diet composition and energy distribution.
107 108 109 110 111 112 113 114
118 119
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C
105 106
E
98 99
R
96 97
R
94 95
O
92 93
C
90 91
N
88 89
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2.5. Statistical Analysis
Ingredient
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Casein
t1:5 t1:6 t1:7 t1:8 t1:9 t1:10 t1:11 t1:12 t1:13 t1:14
L-Cystine
Sucrose Corn starch Dyetrose Corn oil Cellulose Mineral mix #210050 Vitamin mix #310025 Choline bitartrate Total
Normal diet (N)
High fat diet (HF)
g/kg
g/kg
kcal/kg
kcal/kg
140 1.8
501.2 7.2
226.8 3
811.9 12.0
100 465.7 155 40 50 35 10 2.5 1000.00
400 1676.52 589 360 0 29.4 38.7 0 3602.02
100 75.7 155 340 50 35 10 2.5 1000.00
400 272.52 589 3060 0 30.8 38.7 0 5214.96
123 124
127 128 129 130 131 132 Q5 133 134
The longevity curves were plotted using the Kaplan–Meier method including all available mice at each time point (Baur et al., 2006), and the Logrank test was applied to compare the distributions of the different groups. The results from the pathological analysis of the liver were analyzed using the Kruskal–Wallis test, and significant differences between treatment groups were further analyzed using the Mann– Whitney-U test. All other data were analyzed with one-way ANOVA and significant differences between treatment groups were further analyzed using the t-test. P-values less than 0.05 were considered to be statistically significant (*, P b 0.05; **, P b 0.01).
135 136 137 138 139 140 141 142 143 144
3. Results
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3.1. Longevity
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At 25 months of age, 53.8% of mice had died in the N group, whereas the mortality rate was only 23.2% in the HF group (P = 0.02, Fig. 1). The median for the HF group was reached two months later at 27 months of age. While the sample size (n = 31/group) was relatively small for a typical longevity study, we think that the observed effects of high corn oil on the longevity of aging mice is a real action of this compound because such a large difference between the two groups was unlikely due to random variation.
147 148
3.2. Similar Energy Intake
155
149 150 151 152 153 154
Although the average BW in the HF group was significantly higher 156 than that in the N group as shown in Fig. 2A, the food consumption 157 in the HF group was significantly lower than that in the N group 158
120 100
U
86 87
Rotarod assay, a simple and accurate approach to examining agerelated changes in balance and motor coordination (Baur et al., 2006), was performed using the rotarod apparatus (Med Associates, St. Albans VT) at 14 and 25 month old mice to examine their ability to remain on an revolving rod (Coyle et al., 2008). Briefly, a mouse was briefly placed in a separate lane of a rotarod with an accelerating speed (2–20 rpm) until the mouse fell off the rod. The length of time and speed of the mouse which stayed on the rod were recorded.
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84 85
125
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Serum total cholesterol, HDL-cholesterol, and triglycerides in mice were measured using a PTS CardioChek Blood Analysis Meter (Maria Stein, OH) according to the manufacturer's instructions and our previous report (Si et al., 2011). LDL-cholesterol was calculated using the formula from the manual of the analysis meter: LDL-cholesterol = total cholesterol − HDL-cholesterol − triglyceride / 5. Serum cytokines and chemokines including interleukin (IL)-6, IL-1β, IL-10, tumor necrosis factor-α (TNFα), keratinocyte chemoattractant (KC), monocyte chemotactic protein 1(MCP-1) and interferon gamma (IFN-γ) were tested by a Luminex mouse cytokine array assay (Capital Biosciences, MD) as previously described (Si et al., 2011; Veenbergen et al., 2010). The activity of glutathione-disulfide reductase (GSR) in the liver was measured as we previously described (Si et al., 2011).
82 83
2.4. Rotarod Test
R O
103 104
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2.2. Measurements of Serum Biological Markers and Hepatic Antioxidants
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121 122
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102
77 78
pathological alterations in the liver were scored according to the levels of vacuolar changes (hydropic degeneration or lipidosis) in hepatocytes (1 = 0–10%, 2 = 10–30%, 3 = 30–50%, and 4 ≥ 50% of hepatocytes affected).
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100 101
corn oil diet (HF). Both diets are based on the AIN-93 produced by Dyets Inc. (Bethlehem, PA) with two exceptions: 1) soybean oil was replaced with corn oil and 2) the percentage of corn oil in each diet. The normal diet has 10% fat derived calories (FDC) and the HF diet has 58% fat derived calories (FDC) (Reeves et al., 1993). This dose of corn oil (58% FDC) was calculated based on previous studies using high fat diet (60% FDC, 6% from soybean oil and 54% from lard) (Sung et al., 2014). Detailed compositions of the diets are listed in Table 1. To ensure the stability of the corn oil, diets were stored at 4 °C and were kept away from light. The diets were replaced every week. Body weight (BW) and food consumption were monitored weekly. The general health and well-being of the mice were monitored daily. If a mouse was reported as or marked as sick, the criteria for euthanizing mice were independently assessed by a veterinarian adhering to the Institutional Animal Care and Use Committee guidelines. Mice with a BW less than 30% of their original BW and other critical conditions including severe ulcerative dermatitis, urinary obstruction and abdominal masses were euthanized by inhalation of CO2 and censored. When the median for the control group was reached, the remaining 14 mice from the control group and 12 mice from the HF group were fasted overnight and euthanized using CO2, and their blood and tissues were collected for biochemical and physiological analysis. The HF group continued until the median was reached. We also collected blood and tissues from youth control mice (12-month old, 12 mice, YC) to compare the changes of biochemical and physiological analysis with the other two groups. The animal protocol was approved by the Institutional Animal Care and Use Committee at Meharry Medical College.
Survival Rate (%)
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H. Si et al. / Experimental Gerontology xxx (2014) xxx–xxx
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80 60 40
N HF
20 0 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Age: month Fig. 1. Longevity curve in normal diet (N) and high corn oil diet (HF) mice for 13–15 months. There initially was 31 mice/group. *P b 0.05. Q1
Please cite this article as: Si, H., et al., High corn oil dietary intake improves health and longevity of aging mice, Exp. Gerontol. (2014), http:// dx.doi.org/10.1016/j.exger.2014.09.001
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A
Food intake (g/mouse/d)
H. Si et al. / Experimental Gerontology xxx (2014) xxx–xxx
*
Body weight (g)
50 40 30 N HF
20 10 0
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
4.0
B
3.0 2.0 1.0 0.0
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
F O
C
R O
8.0
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N HF
4.0
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
D
Energy intake (Kcal/mouse/d)
Age:month
12
0.0
*
N HF
Age:month 16
3
Age:month
159 160
164
3.3. Maintained Rotarod Performance
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Physical activity and locomotor function continuously diminishing with aging (Baur et al., 2006; Yankner et al., 2008) and although corn oil increased longevity, it is important to know whether the quality of life was maintained. We evaluated the ability to perform on a rotarod, a classic method of testing balance and motor coordination. While the time on the rod was significantly decreased as mice aged in the N group (decreased from 115 s at month 14 to 80 s at month 25), the
171
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R
150 120
N C O
169 170
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167 168
Time on rod(s)
161 162
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(Fig. 2B). This may be a result of the texture of the HF diet, which has the consistency of paste. Some days an oily liquid would form on the top of the rodent feeding jars, while the N diets were typical pellets. Interestingly, there was no significant difference in energy intake between these two groups (Fig. 2C).
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Fig. 2. Curves of body weight (A), food intake (B) and energy intake (C) in normal diet (N) and high corn oil diet (HF) mice for 13–15 months. There initially was 31 mice/group. *P b 0.05.
*
90 60 30 0
N HF Mo: 14
N HF Mo: 25
Fig. 3. Corn oil maintained rotarod performance in both normal diet (N) and high corn oil diet (HF) mice at 14 and 25 months of age. Data are means ± SE, n = 12 mice/group. *P b 0.05.
HF group maintained their motor skills until they were 25 months of 172 age (Fig. 3). 173 3.4. Improved Hepatic Pathology
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Histological examination of liver sections stained with hematoxylin and eosin revealed a loss of cellular integrity and the accumulation of large lipid droplets in the livers of the N group, but the HF group reduced the size of intracytoplasmic lipid vacuoles. Blinded scoring of the liver sections for overall pathology on a scale of 0–4 (with 4 being the most severe) gave mean values of 2.5 for the N group, 1.8 for the HF group and 0.8 for the YC group (Fig. 4).
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3.5. Lowered Serum Lipids
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Circulating lipid abnormalities are increasingly recognized as playing an important role in the aging process and age-related disorders such as diabetes and vascular dysfunction (Labinskyy et al., 2006). Compared to the YC group, serum triglyceride, total cholesterol and LDL-cholesterol were significantly increased in the N group; however, all these three serum lipids were reversed in the HF group as shown in Table 2.
183 184
3.6. Decreased Serum Inflammatory Cytokines
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Consistent with observations of the pathological alterations in the liver and remarkably shortened lifespan of mice in the N group, circulating levels of cytokines including IL-1β, IL-6, IFN-γ and MCP-1 were significantly elevated in the N group compared to those in the YC group (Table 3). However, dietary consumption of corn oil significantly reduced these pro-inflammatory markers (Table 3), indicating that corn oil may suppress chronic inflammation caused by aging. In addition, GSR activity in the livers of the N group was significantly decreased
191
Please cite this article as: Si, H., et al., High corn oil dietary intake improves health and longevity of aging mice, Exp. Gerontol. (2014), http:// dx.doi.org/10.1016/j.exger.2014.09.001
176 177 178 179 180 181
185 186 187 188 189
192 193 194 195 196 197 198
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1.0 0
YC
N
HF
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Fig. 4. Corn oil improved hepatic pathology in aging mice. Hematoxylin and eosin stained slides of liver (three sections from each mouse) from young control (YC), normal diet (N) and high corn oil diet (HF) mice were scored and the number of mice at relevant categories based on the levels of vacuolar change (hydropic degeneration or lipidosis for the liver) was reported. A set of representative images and bar graphs (means ± SE, n = 12–14/group) were shown. The arrows point to intracytoplasmic lipid vacuoles. 200× magnification. Scale bar = 50 um. *P b 0.05.
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2.0
*
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3.0
O
4.0
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HF
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Pathological alterations of liver ( arbitrary unit)
YC
compared to that in the YC group, whereas the activity of this enzyme was reversed in the HF group (data no shown).
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4. Discussion
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Aging is well-known as an inevitable process that is physiologically characterized as a progressive, generalized systematic dysfunction of almost or all organs, giving rise to the escalated vulnerability to environmental challenges and resulting in increased risks of disease and death. Indeed, aging is associated with a greatly increased metabolic and oxidative stress, elevated chronic, low-grade inflammation, and accumulated DNA mutations as well as increased levels of its DNA damages (Frisard and Ravussin, 2006; Heininger, 2000a,b). It is established that calorie restriction delays age-associated organ disorders and increases longevity as well as improves inflammation and oxidative stress in a wide range of species, suggesting that targeting nutrient-sensing and energy metabolism pathways may be an effective approach to delay the aging process and age-related diseases. In the present study, we found that high level of corn oil (58.6% FDC) intake improved health and longevity of aging mice, which may be associated with reversing aging-increased blood lipids and pro-inflammatory makers as well as aging-damaged rotarod performance test and liver function. To our
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Table 2 Blood lipid levels (mg/dL).
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208 209
N
206 207
U
204 205
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199 200
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Group
Triglyceride
Total cholesterol
LDL
HDL
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YC N HF
115 ± 9 142 ± 15 124 ± 12
197 ± 19 314 ± 26⁎ 171 ± 15
135 ± 22 240 ± 23⁎ 113 ± 11
39 ± 1 52 ± 7 40 ± 3
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Values are means ± SE (n = 12–14 per group). ⁎ P b 0.05.
knowledge, the present study is the first study that shows that if total calorie intake is kept in the normal range, long-term very high level of corn oil intake can improve health and increase longevity of aging mice. A large body of evidence indicates that increased generation of reactive oxygen species (ROS) which are chemically reactive molecules with most of them containing oxygen and unpaired electrons is one of the major triggers of aging. There is a strong correlation between chronological age and the levels of ROS generation and oxidative damage of tissues. ROS are primarily produced by mitochondria during energy production (about 2% of total oxygen consumption was funneled to ROS) (Chance et al., 1979). Extra amounts of ROS induces oxidation of fatty acids and proteins and causes oxidative damage of DNA that may lead to cellular senescence, functional alterations, and pathological conditions (Harman, 1972; Linnane et al., 1989). This extra amount of ROS is deactivated to water and oxygen by endogenous enzymes including superoxide dismutase (SOD), catalase or glutathione peroxidases (Chang et al., 2004). Endogenous antioxidant glutathione (GSH) and exogenous antioxidants including vitamins C and E are also important ROS scavengers. Reducing ROS is proposed as a leading strategy to delay aging and related degenerative diseases. Corn oil is one of the highest natural sources of vitamin E (62.01 mg/100 g oil) and is just a little less than cottonseed oil (62.37 mg/100 g oil). This high content of vitamin E may prevent aging-increased ROS and extend the lifespan of aging mice. This is supported by our results showing that a decreased GSR activity, a critical endogenous antioxidant enzyme, was reversed by corn oil intake (data not shown). Aging-induced ROS also contributes to low-grade chronic inflammation (Brod, 2000), a crucial player of the process of aging and agerelated diseases in older adults. Indeed, chronic pro-inflammatory markers including IL-6, MCP-1 and TNF-α are consistently elevated with age in the absence of acute infection or other physiological stress (Ferrucci et al., 2005). Consequently, the sustained increases of these
Please cite this article as: Si, H., et al., High corn oil dietary intake improves health and longevity of aging mice, Exp. Gerontol. (2014), http:// dx.doi.org/10.1016/j.exger.2014.09.001
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H. Si et al. / Experimental Gerontology xxx (2014) xxx–xxx Table 3 Serum inflammatory cytokines (pg/ml). IL-1β
IL-6
IL-10
IFNγ
TNFα
KC
MCP-1
26.3 ± 10.8 43.4 ± 15.9⁎ 26.2 ± 8.4
17.5 ± 6.7 57.7 ± 11.6⁎ 20.2 ± 9.6
1.9 ± 0.0 4.9 ± 1.0 13.1 ± 4.0
43.9 ± 10.2 110.0 ± 28.5⁎ 99.0 ± 24.7
9.1 ± 3.9 6.8 ± 2.2 6.4 ± 2.0
42.2 ± 16.2 43.5 ± 6.6 55.3 ± 3.3
62.2 ± 15.2 310.0 ± 27.5⁎ 198.0 ± 18.3
pro-inflammatory molecules impair the function and integrity of various tissues and organs and thus accelerate aging and aging-related chronic diseases, although this increase is still in the sub-acute range (Chung et al., 2006). Interestingly, calorie restriction significantly attenuates the increase of these pro-inflammatory markers while extending the lifespan (Chung et al., 2006; Zou et al., 2004), suggesting that anti-inflammatory agents may have the potential to extend a healthy lifespan. Results from the present study show that dietary intake of corn oil significantly reversed the increase of circulating proinflammatory markers including IL-1β, IL-6, IFN-γ and MCP-1 in aging mice and therefore increased longevity. Elevated LDL-cholesterol is well known as one of the major risks of cardiovascular disease and reducing blood LDL is recommended to lower cardiovascular disease as well as other aging-related chronic diseases (NCEP, 2002). Corn oil has been found to be highly effective in lowering blood cholesterol, particularly LDL-cholesterol (Ahrens et al., 1957; Hill et al., 1979). Our results are in line with these previous studies that corn oil lowers LDL-cholesterol, total cholesterol and triglyceride. This effect may be due to the high PUFA, which is supported by evidence that corn oil is more effective than olive oil in lowering LDL-cholesterol because corn oil has higher PUFA (58.7 g/100 g oil) than olive oil (8.4 g/100 g oil) (Dupont et al., 1990; Howell et al., 1998). Corn oil has a plant sterol content of 128 mg/1000 kcal vs. 66 mg/1000 kcal for olive oil, and these plant sterols can reduce cholesterol absorption from the gut which in turn lowers body pools and enhances synthesis rate through de-suppression of cellular hydroxymethylglutaryl-CoA reductase activity (Howell et al., 1998). A lower ratio of omega-6/omega-3 fatty acids (n−6/n−3) is recommended to reduce the risk of many highly prevalent chronic diseases in Western societies (ratio of n−6/n−3 in Western diets is 15/1–16.7/1 (Simopoulos, 2002). Mammalian cells cannot convert omega-6 to omega-3 fatty acids because they lack the converting enzyme, omega3 desaturase. These two classes of essential fatty acids (EFAs) are not interconvertible, are metabolically and functionally distinct and have opposing physiological functions. Therefore, too much omega-6 may be detrimental for cells. Corn oil is not a good source for EFAs because the ratio of omega-6/omega-3 fatty acids from corn oil is 83, which is much higher than the recommended ratio (1/1 to 4/1) (Simopoulos, 2002). However, the present study and other studies show that high corn oil intake improves health and longevity in mice and rats (10 mg/kg/d by oral gavage) (NTP, 1994). One explanation is that majority of omega-6 PUFA from corn oil is used for energy, and is not used to produce thrombi and atheromas, which are required for cardiovascular disease development. Moreover, high levels of vitamin E (majorly γ-tocopherol) (Elmadfa and Park, 1999) and plant sterols (0.77% by weight) (Ostlund et al., 2002) may counter the bad effects of omega-6 PUFA of corn oil. For example, γ-tocopherol, the major form of vitamin E in the corn oil, and its metabolite have more anti-inflammatory properties than α-tocopherol, the predominant form of vitamin E in the tissues and most supplements (Jiang and Ames, 2003). Taken together, if total calorie intake is kept in a normal range, long-term very high intake of corn oil (58.6% FDC) reverses agingincreased blood lipids and circulating pro-inflammatory cytokines as well as aging-damaged rotarod performance test and liver function, and thus increases longevity of aging mice. These health benefits of corn oil may result from the combinations of the high levels of PUFA,
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E
260 261
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N C O
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vitamin E and plant sterols. Therefore, corn oil, even at a high energy 307 percentage (58%), is a favorable replacement of animal fats in the 308 human diet if the total energy intake is controlled. 309
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Conflict of Interest
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Values are means ± SE (n = 12–14 per group). ⁎ P b 0.05.
The authors declare that there are no conflicts of interest associated 311 with this manuscript. 312 Acknowledgments
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We are grateful for the support of the National Institute of Food and 314 Agriculture of USDA, Evans-Allen program (TENX-1103-FS, to H. Si) for 315 this work. 316
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References
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NTP, 1994. NTP comparative toxicology studies of corn oil, safflower oil, and tricaprylin (CAS nos. 8001-30-7, 8001-23-8, and 538-23-8) in male F344/N rats as vehicles for gavage. Natl. Toxicol. Program Tech. Rep. Ser. 426, 1–314. Ostlund, R.E., Racette, S.B., Okeke, A., Stenson, W.F., 2002. Phytosterols that are naturally present in commercial corn oil significantly reduce cholesterol absorption in humans. Am. J. Clin. Nutr. 75, 1000–1004. Reeves, P.G., Nielsen, F.H., Fahey Jr., G.C., 1993. AIN-93 purified diets for laboratory rodents: final report of the American Institute of Nutrition ad hoc writing committee on the reformulation of the AIN-76A rodent diet. J. Nutr. 123, 1939–1951. Si, H., Fu, Z., Babu, P.V., Zhen, W., Leroith, T., Meaney, M.P., Voelker, K.A., Jia, Z., Grange, R.W., Liu, D., 2011. Dietary epicatechin promotes survival of obese diabetic mice and Drosophila melanogaster. J. Nutr. 141, 1095–1100. Simopoulos, A.P., 2002. The importance of the ratio of omega-6/omega-3 essential fatty acids. Biomed. Pharmacother. 56, 365–379.
Sung, Y.Y., Kim, D.S., Kim, H.K., 2014. Viola mandshurica ethanolic extract prevents highfat-diet-induced obesity in mice by activating AMP-activated protein kinase. Environ. Toxicol. Pharmacol. 38, 41–50. USDA, 2014. Corn: market outlook. http://www.agweb.com/crops/corn/default.aspx (accessed August 28, 2014). Veenbergen, S., Smeets, R.L., Bennink, M.B., Arntz, O.J., Joosten, L.A., van den Berg, W.B., van de Loo, F.A., 2010. The natural soluble form of IL-18 receptor {beta} exacerbates collagen-induced arthritis via modulation of T cell immune responses. Ann. Rheum. Dis. 69, 276–283. Yankner, B.A., Lu, T., Loerch, P., 2008. The aging brain. Annu. Rev. Pathol. 3, 41–66. Zou, Y., Jung, K.J., Kim, J.W., Yu, B.P., Chung, H.Y., 2004. Alteration of soluble adhesion molecules during aging and their modulation by calorie restriction. FASEB J. 18, 320–322.
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Contents lists available at ScienceDirect
Experimental Gerontology journal homepage: www.elsevier.com/locate/expgero
High corn oil dietary intake improves health and longevity of aging mice
2Q3
Hongwei Si a,⁎, Longyun Zhang a, Siqin Liu a, Tanya LeRoith b, Carlos Virgous c
3Q4 4 5
a
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a r t i c l e
7 8 9 10 11 12 13
Article history: Received 15 July 2014 Received in revised form 29 August 2014 Accepted 2 September 2014 Available online xxxx
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Keywords: Corn oil Aging mice Longevity Health
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i n f o
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Department of Family and Consumer Sciences, Tennessee State University, Nashville, TN 37209, United States Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24061, United States Animal Care Facility, Meharry Medical College, Nashville, TN 37208, United States
a b s t r a c t
Corn oil has been recommended as a replacement for saturated fats because of its high levels of poly- and monounsaturated fatty acids. In the present study, we tested whether very high levels of corn oil (58.6% fat-derived calories, FDC) intake improve health and longevity of aging mice. Twelve month old male C57BL/6 mice were fed a normal diet (10% FDC of corn oil, N) or a high fat diet (58.6% FDC of corn oil, HF) for 13–15 months. Our results show that a HF diet significantly increased the longevity of the aged mice (at 25 months of age, 53.8% of mice died in the N group, whereas the mortality rate was only 23.2% in the HF group). High corn oil also reversed agingincreased blood lipids including triglyceride, total cholesterol and LDL. Similarly, high corn oil intake overturned aging-raised pro-inflammatory markers including IL-1β, IL-6, and monocyte chemotactic protein-1 (MCP-1) in the blood. In addition, corn oil intake reversed aging-damaged rotarod performance and liver function. Interestingly, the HF group was significantly heavier than the N group (53.6 g/mouse vs. 41.3 g/mouse); however, both HF and N groups had the same calorie intake (12.48 kcal/d/mouse vs. 12.24 kcal/d/mouse). Although, the HF group's food consumption was lower than that of the N group (2.4 g/d/mouse vs. 3.4 g/d/mouse). These results suggest that if total calorie consumption stays in the normal range, very high levels of corn oil intake improve health and longevity of aging mice. © 2014 Published by Elsevier Inc.
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37 35 34
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36
1. Introduction
39
High saturated fat diets are well associated with obesity prevalence and the increased risk of cardiovascular disease, diabetes and cancer. Reducing saturated fats from the diet is recommended to eliminate Western diet-induced health problems. The common alternatives of animal (saturated) fats for humans are plant oil, including soybean oil, peanut oil and corn oil because of the high percentage of unsaturated fat acids. Corn oil is composed mainly (99% of the refined or 96% of the crude oil) of acylglycerols (mono-, di- and primarily tri-), and has 59% polyunsaturated (PUFA), 24% monounsaturated (MUFA) and 13% saturated fatty acid (SFA). The PUFA to SFA ratio (P/S) is about 4.6. Corn oil has one of the highest PUFA levels after sunflower, safflower, walnut and wheat germ oil (Landers and Rathmann, 1981). The primary PUFA is linoleic acid (C18:2n− 6), with a small amount of linolenic acid (C18:3n −3)
48 49 50 51 52
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N C O
46 47
U
44 45
R
38
42 43
19 20 21 22 23 24 25 26 27 28 29 30 31 32
C
T
E
D
Section Editor: Holly M Brown-Borg
33
40 41
F
1
Abbreviations: BW, body weight; EFAs, essential fatty acids; FDC, fat-derived calories; GSR, glutathione-disulfide reductase; GSH, glutathione; H&E, hematoxylin and eosin; HDL, high-density lipoprotein; HF, high corn oil diet; IFN-γ, interferon gamma; IL, interleukin; KC, keratinocyte chemoattractant; LDL, low-density lipoprotein; MCP-1, macrophage chemoattractant protein-1; MUFA, monounsaturated fatty acid; N, normal diet; PUFA, polyunsaturatedfatty acid; ROS,reactive oxygen species; SFA,saturatedfatty acid; SOD,superoxide dismutase; TNFα, tumor necrosis factor-α; YC, youth control. ⁎ Corresponding author. E-mail address: [email protected] (H. Si).
giving a n − 6/n−3 ratio of 83. Corn oil contains a significant amount of ubiquinone and high amounts of gamma-tocopherols (vitamin E) (Dupont et al., 1990). These high contents of PUFA and vitamin E may contribute to the health benefits of corn oil consumption. The beneficial effects of PUFA have been extensively investigated, however, there are very few studies investigating the effects on human health with long-term corn oil consumption, particularly on the older population. This is very important because corn oil is the second leading vegetable oil consumed in the United States (USDA, 2014). Since U.S. adults age 65 and older heavily consume this high fat oil, their population is rapidly increasing and is projected to reach 71 million by 2030. The objectives of the present study are to investigate the long-term health effect of high volume of corn oil consumption in aging mice and to understand the relevant mechanisms.
53
2. Methods and Materials
67
2.1. Experimental Animals and Diets
68
Twelve-month old male C57BL/6 mice were purchased from the National Cancer Institute (Bethesda, MD). Mice were housed in an environmentally-controlled (23 ± 2 °C; 12-h light: dark cycle) animal facility and they were given ad libitum access to food and water. To test the health effect of high corn oil intake, mice were randomly divided into two groups (n = 31) and given either a normal diet (N) or a high
69
http://dx.doi.org/10.1016/j.exger.2014.09.001 0531-5565/© 2014 Published by Elsevier Inc.
Please cite this article as: Si, H., et al., High corn oil dietary intake improves health and longevity of aging mice, Exp. Gerontol. (2014), http:// dx.doi.org/10.1016/j.exger.2014.09.001
54 55 56 57 58 59 60 61 62 63 64 65 66
70 71 72 73 74
2.3. Pathological Analysis
117
120
Fresh livers were fixed in 10% phosphate buffered neutral formalin, embedded in paraffin, cut at thicknesses of 5 μm, and then stained with hematoxylin and eosin (H&E) for histological examination of hepatic lesions. Three sections from each mouse were examined. The
t1:1 t1:2
Table 1 Diet composition and energy distribution.
107 108 109 110 111 112 113 114
118 119
t1:3
C
105 106
E
98 99
R
96 97
R
94 95
O
92 93
C
90 91
N
88 89
126
2.5. Statistical Analysis
Ingredient
t1:4
Casein
t1:5 t1:6 t1:7 t1:8 t1:9 t1:10 t1:11 t1:12 t1:13 t1:14
L-Cystine
Sucrose Corn starch Dyetrose Corn oil Cellulose Mineral mix #210050 Vitamin mix #310025 Choline bitartrate Total
Normal diet (N)
High fat diet (HF)
g/kg
g/kg
kcal/kg
kcal/kg
140 1.8
501.2 7.2
226.8 3
811.9 12.0
100 465.7 155 40 50 35 10 2.5 1000.00
400 1676.52 589 360 0 29.4 38.7 0 3602.02
100 75.7 155 340 50 35 10 2.5 1000.00
400 272.52 589 3060 0 30.8 38.7 0 5214.96
123 124
127 128 129 130 131 132 Q5 133 134
The longevity curves were plotted using the Kaplan–Meier method including all available mice at each time point (Baur et al., 2006), and the Logrank test was applied to compare the distributions of the different groups. The results from the pathological analysis of the liver were analyzed using the Kruskal–Wallis test, and significant differences between treatment groups were further analyzed using the Mann– Whitney-U test. All other data were analyzed with one-way ANOVA and significant differences between treatment groups were further analyzed using the t-test. P-values less than 0.05 were considered to be statistically significant (*, P b 0.05; **, P b 0.01).
135 136 137 138 139 140 141 142 143 144
3. Results
145
3.1. Longevity
146
At 25 months of age, 53.8% of mice had died in the N group, whereas the mortality rate was only 23.2% in the HF group (P = 0.02, Fig. 1). The median for the HF group was reached two months later at 27 months of age. While the sample size (n = 31/group) was relatively small for a typical longevity study, we think that the observed effects of high corn oil on the longevity of aging mice is a real action of this compound because such a large difference between the two groups was unlikely due to random variation.
147 148
3.2. Similar Energy Intake
155
149 150 151 152 153 154
Although the average BW in the HF group was significantly higher 156 than that in the N group as shown in Fig. 2A, the food consumption 157 in the HF group was significantly lower than that in the N group 158
120 100
U
86 87
Rotarod assay, a simple and accurate approach to examining agerelated changes in balance and motor coordination (Baur et al., 2006), was performed using the rotarod apparatus (Med Associates, St. Albans VT) at 14 and 25 month old mice to examine their ability to remain on an revolving rod (Coyle et al., 2008). Briefly, a mouse was briefly placed in a separate lane of a rotarod with an accelerating speed (2–20 rpm) until the mouse fell off the rod. The length of time and speed of the mouse which stayed on the rod were recorded.
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84 85
125
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Serum total cholesterol, HDL-cholesterol, and triglycerides in mice were measured using a PTS CardioChek Blood Analysis Meter (Maria Stein, OH) according to the manufacturer's instructions and our previous report (Si et al., 2011). LDL-cholesterol was calculated using the formula from the manual of the analysis meter: LDL-cholesterol = total cholesterol − HDL-cholesterol − triglyceride / 5. Serum cytokines and chemokines including interleukin (IL)-6, IL-1β, IL-10, tumor necrosis factor-α (TNFα), keratinocyte chemoattractant (KC), monocyte chemotactic protein 1(MCP-1) and interferon gamma (IFN-γ) were tested by a Luminex mouse cytokine array assay (Capital Biosciences, MD) as previously described (Si et al., 2011; Veenbergen et al., 2010). The activity of glutathione-disulfide reductase (GSR) in the liver was measured as we previously described (Si et al., 2011).
82 83
2.4. Rotarod Test
R O
103 104
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2.2. Measurements of Serum Biological Markers and Hepatic Antioxidants
79 80
121 122
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77 78
pathological alterations in the liver were scored according to the levels of vacuolar changes (hydropic degeneration or lipidosis) in hepatocytes (1 = 0–10%, 2 = 10–30%, 3 = 30–50%, and 4 ≥ 50% of hepatocytes affected).
T
100 101
corn oil diet (HF). Both diets are based on the AIN-93 produced by Dyets Inc. (Bethlehem, PA) with two exceptions: 1) soybean oil was replaced with corn oil and 2) the percentage of corn oil in each diet. The normal diet has 10% fat derived calories (FDC) and the HF diet has 58% fat derived calories (FDC) (Reeves et al., 1993). This dose of corn oil (58% FDC) was calculated based on previous studies using high fat diet (60% FDC, 6% from soybean oil and 54% from lard) (Sung et al., 2014). Detailed compositions of the diets are listed in Table 1. To ensure the stability of the corn oil, diets were stored at 4 °C and were kept away from light. The diets were replaced every week. Body weight (BW) and food consumption were monitored weekly. The general health and well-being of the mice were monitored daily. If a mouse was reported as or marked as sick, the criteria for euthanizing mice were independently assessed by a veterinarian adhering to the Institutional Animal Care and Use Committee guidelines. Mice with a BW less than 30% of their original BW and other critical conditions including severe ulcerative dermatitis, urinary obstruction and abdominal masses were euthanized by inhalation of CO2 and censored. When the median for the control group was reached, the remaining 14 mice from the control group and 12 mice from the HF group were fasted overnight and euthanized using CO2, and their blood and tissues were collected for biochemical and physiological analysis. The HF group continued until the median was reached. We also collected blood and tissues from youth control mice (12-month old, 12 mice, YC) to compare the changes of biochemical and physiological analysis with the other two groups. The animal protocol was approved by the Institutional Animal Care and Use Committee at Meharry Medical College.
Survival Rate (%)
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H. Si et al. / Experimental Gerontology xxx (2014) xxx–xxx
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*
80 60 40
N HF
20 0 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Age: month Fig. 1. Longevity curve in normal diet (N) and high corn oil diet (HF) mice for 13–15 months. There initially was 31 mice/group. *P b 0.05. Q1
Please cite this article as: Si, H., et al., High corn oil dietary intake improves health and longevity of aging mice, Exp. Gerontol. (2014), http:// dx.doi.org/10.1016/j.exger.2014.09.001
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A
Food intake (g/mouse/d)
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*
Body weight (g)
50 40 30 N HF
20 10 0
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
4.0
B
3.0 2.0 1.0 0.0
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
F O
C
R O
8.0
P
N HF
4.0
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
D
Energy intake (Kcal/mouse/d)
Age:month
12
0.0
*
N HF
Age:month 16
3
Age:month
159 160
164
3.3. Maintained Rotarod Performance
165 166
Physical activity and locomotor function continuously diminishing with aging (Baur et al., 2006; Yankner et al., 2008) and although corn oil increased longevity, it is important to know whether the quality of life was maintained. We evaluated the ability to perform on a rotarod, a classic method of testing balance and motor coordination. While the time on the rod was significantly decreased as mice aged in the N group (decreased from 115 s at month 14 to 80 s at month 25), the
171
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E R
R
150 120
N C O
169 170
U
167 168
Time on rod(s)
161 162
T
163
(Fig. 2B). This may be a result of the texture of the HF diet, which has the consistency of paste. Some days an oily liquid would form on the top of the rodent feeding jars, while the N diets were typical pellets. Interestingly, there was no significant difference in energy intake between these two groups (Fig. 2C).
E
Fig. 2. Curves of body weight (A), food intake (B) and energy intake (C) in normal diet (N) and high corn oil diet (HF) mice for 13–15 months. There initially was 31 mice/group. *P b 0.05.
*
90 60 30 0
N HF Mo: 14
N HF Mo: 25
Fig. 3. Corn oil maintained rotarod performance in both normal diet (N) and high corn oil diet (HF) mice at 14 and 25 months of age. Data are means ± SE, n = 12 mice/group. *P b 0.05.
HF group maintained their motor skills until they were 25 months of 172 age (Fig. 3). 173 3.4. Improved Hepatic Pathology
174
Histological examination of liver sections stained with hematoxylin and eosin revealed a loss of cellular integrity and the accumulation of large lipid droplets in the livers of the N group, but the HF group reduced the size of intracytoplasmic lipid vacuoles. Blinded scoring of the liver sections for overall pathology on a scale of 0–4 (with 4 being the most severe) gave mean values of 2.5 for the N group, 1.8 for the HF group and 0.8 for the YC group (Fig. 4).
175
3.5. Lowered Serum Lipids
182
Circulating lipid abnormalities are increasingly recognized as playing an important role in the aging process and age-related disorders such as diabetes and vascular dysfunction (Labinskyy et al., 2006). Compared to the YC group, serum triglyceride, total cholesterol and LDL-cholesterol were significantly increased in the N group; however, all these three serum lipids were reversed in the HF group as shown in Table 2.
183 184
3.6. Decreased Serum Inflammatory Cytokines
190
Consistent with observations of the pathological alterations in the liver and remarkably shortened lifespan of mice in the N group, circulating levels of cytokines including IL-1β, IL-6, IFN-γ and MCP-1 were significantly elevated in the N group compared to those in the YC group (Table 3). However, dietary consumption of corn oil significantly reduced these pro-inflammatory markers (Table 3), indicating that corn oil may suppress chronic inflammation caused by aging. In addition, GSR activity in the livers of the N group was significantly decreased
191
Please cite this article as: Si, H., et al., High corn oil dietary intake improves health and longevity of aging mice, Exp. Gerontol. (2014), http:// dx.doi.org/10.1016/j.exger.2014.09.001
176 177 178 179 180 181
185 186 187 188 189
192 193 194 195 196 197 198
4
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1.0 0
YC
N
HF
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Fig. 4. Corn oil improved hepatic pathology in aging mice. Hematoxylin and eosin stained slides of liver (three sections from each mouse) from young control (YC), normal diet (N) and high corn oil diet (HF) mice were scored and the number of mice at relevant categories based on the levels of vacuolar change (hydropic degeneration or lipidosis for the liver) was reported. A set of representative images and bar graphs (means ± SE, n = 12–14/group) were shown. The arrows point to intracytoplasmic lipid vacuoles. 200× magnification. Scale bar = 50 um. *P b 0.05.
C
T
Q2
R O
2.0
*
P
3.0
O
4.0
D
HF
F
N
Pathological alterations of liver ( arbitrary unit)
YC
compared to that in the YC group, whereas the activity of this enzyme was reversed in the HF group (data no shown).
201
4. Discussion
202 203
218
Aging is well-known as an inevitable process that is physiologically characterized as a progressive, generalized systematic dysfunction of almost or all organs, giving rise to the escalated vulnerability to environmental challenges and resulting in increased risks of disease and death. Indeed, aging is associated with a greatly increased metabolic and oxidative stress, elevated chronic, low-grade inflammation, and accumulated DNA mutations as well as increased levels of its DNA damages (Frisard and Ravussin, 2006; Heininger, 2000a,b). It is established that calorie restriction delays age-associated organ disorders and increases longevity as well as improves inflammation and oxidative stress in a wide range of species, suggesting that targeting nutrient-sensing and energy metabolism pathways may be an effective approach to delay the aging process and age-related diseases. In the present study, we found that high level of corn oil (58.6% FDC) intake improved health and longevity of aging mice, which may be associated with reversing aging-increased blood lipids and pro-inflammatory makers as well as aging-damaged rotarod performance test and liver function. To our
t2:1 t2:2
Table 2 Blood lipid levels (mg/dL).
210 211 212 213 214 215 216 217
R
R
O
C
208 209
N
206 207
U
204 205
E
199 200
t2:3
Group
Triglyceride
Total cholesterol
LDL
HDL
t2:4 t2:5 t2:6
YC N HF
115 ± 9 142 ± 15 124 ± 12
197 ± 19 314 ± 26⁎ 171 ± 15
135 ± 22 240 ± 23⁎ 113 ± 11
39 ± 1 52 ± 7 40 ± 3
t2:7 t2:8
Values are means ± SE (n = 12–14 per group). ⁎ P b 0.05.
knowledge, the present study is the first study that shows that if total calorie intake is kept in the normal range, long-term very high level of corn oil intake can improve health and increase longevity of aging mice. A large body of evidence indicates that increased generation of reactive oxygen species (ROS) which are chemically reactive molecules with most of them containing oxygen and unpaired electrons is one of the major triggers of aging. There is a strong correlation between chronological age and the levels of ROS generation and oxidative damage of tissues. ROS are primarily produced by mitochondria during energy production (about 2% of total oxygen consumption was funneled to ROS) (Chance et al., 1979). Extra amounts of ROS induces oxidation of fatty acids and proteins and causes oxidative damage of DNA that may lead to cellular senescence, functional alterations, and pathological conditions (Harman, 1972; Linnane et al., 1989). This extra amount of ROS is deactivated to water and oxygen by endogenous enzymes including superoxide dismutase (SOD), catalase or glutathione peroxidases (Chang et al., 2004). Endogenous antioxidant glutathione (GSH) and exogenous antioxidants including vitamins C and E are also important ROS scavengers. Reducing ROS is proposed as a leading strategy to delay aging and related degenerative diseases. Corn oil is one of the highest natural sources of vitamin E (62.01 mg/100 g oil) and is just a little less than cottonseed oil (62.37 mg/100 g oil). This high content of vitamin E may prevent aging-increased ROS and extend the lifespan of aging mice. This is supported by our results showing that a decreased GSR activity, a critical endogenous antioxidant enzyme, was reversed by corn oil intake (data not shown). Aging-induced ROS also contributes to low-grade chronic inflammation (Brod, 2000), a crucial player of the process of aging and agerelated diseases in older adults. Indeed, chronic pro-inflammatory markers including IL-6, MCP-1 and TNF-α are consistently elevated with age in the absence of acute infection or other physiological stress (Ferrucci et al., 2005). Consequently, the sustained increases of these
Please cite this article as: Si, H., et al., High corn oil dietary intake improves health and longevity of aging mice, Exp. Gerontol. (2014), http:// dx.doi.org/10.1016/j.exger.2014.09.001
219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 Q6 243 244 245 246 247 248 249 250
H. Si et al. / Experimental Gerontology xxx (2014) xxx–xxx Table 3 Serum inflammatory cytokines (pg/ml). IL-1β
IL-6
IL-10
IFNγ
TNFα
KC
MCP-1
26.3 ± 10.8 43.4 ± 15.9⁎ 26.2 ± 8.4
17.5 ± 6.7 57.7 ± 11.6⁎ 20.2 ± 9.6
1.9 ± 0.0 4.9 ± 1.0 13.1 ± 4.0
43.9 ± 10.2 110.0 ± 28.5⁎ 99.0 ± 24.7
9.1 ± 3.9 6.8 ± 2.2 6.4 ± 2.0
42.2 ± 16.2 43.5 ± 6.6 55.3 ± 3.3
62.2 ± 15.2 310.0 ± 27.5⁎ 198.0 ± 18.3
pro-inflammatory molecules impair the function and integrity of various tissues and organs and thus accelerate aging and aging-related chronic diseases, although this increase is still in the sub-acute range (Chung et al., 2006). Interestingly, calorie restriction significantly attenuates the increase of these pro-inflammatory markers while extending the lifespan (Chung et al., 2006; Zou et al., 2004), suggesting that anti-inflammatory agents may have the potential to extend a healthy lifespan. Results from the present study show that dietary intake of corn oil significantly reversed the increase of circulating proinflammatory markers including IL-1β, IL-6, IFN-γ and MCP-1 in aging mice and therefore increased longevity. Elevated LDL-cholesterol is well known as one of the major risks of cardiovascular disease and reducing blood LDL is recommended to lower cardiovascular disease as well as other aging-related chronic diseases (NCEP, 2002). Corn oil has been found to be highly effective in lowering blood cholesterol, particularly LDL-cholesterol (Ahrens et al., 1957; Hill et al., 1979). Our results are in line with these previous studies that corn oil lowers LDL-cholesterol, total cholesterol and triglyceride. This effect may be due to the high PUFA, which is supported by evidence that corn oil is more effective than olive oil in lowering LDL-cholesterol because corn oil has higher PUFA (58.7 g/100 g oil) than olive oil (8.4 g/100 g oil) (Dupont et al., 1990; Howell et al., 1998). Corn oil has a plant sterol content of 128 mg/1000 kcal vs. 66 mg/1000 kcal for olive oil, and these plant sterols can reduce cholesterol absorption from the gut which in turn lowers body pools and enhances synthesis rate through de-suppression of cellular hydroxymethylglutaryl-CoA reductase activity (Howell et al., 1998). A lower ratio of omega-6/omega-3 fatty acids (n−6/n−3) is recommended to reduce the risk of many highly prevalent chronic diseases in Western societies (ratio of n−6/n−3 in Western diets is 15/1–16.7/1 (Simopoulos, 2002). Mammalian cells cannot convert omega-6 to omega-3 fatty acids because they lack the converting enzyme, omega3 desaturase. These two classes of essential fatty acids (EFAs) are not interconvertible, are metabolically and functionally distinct and have opposing physiological functions. Therefore, too much omega-6 may be detrimental for cells. Corn oil is not a good source for EFAs because the ratio of omega-6/omega-3 fatty acids from corn oil is 83, which is much higher than the recommended ratio (1/1 to 4/1) (Simopoulos, 2002). However, the present study and other studies show that high corn oil intake improves health and longevity in mice and rats (10 mg/kg/d by oral gavage) (NTP, 1994). One explanation is that majority of omega-6 PUFA from corn oil is used for energy, and is not used to produce thrombi and atheromas, which are required for cardiovascular disease development. Moreover, high levels of vitamin E (majorly γ-tocopherol) (Elmadfa and Park, 1999) and plant sterols (0.77% by weight) (Ostlund et al., 2002) may counter the bad effects of omega-6 PUFA of corn oil. For example, γ-tocopherol, the major form of vitamin E in the corn oil, and its metabolite have more anti-inflammatory properties than α-tocopherol, the predominant form of vitamin E in the tissues and most supplements (Jiang and Ames, 2003). Taken together, if total calorie intake is kept in a normal range, long-term very high intake of corn oil (58.6% FDC) reverses agingincreased blood lipids and circulating pro-inflammatory cytokines as well as aging-damaged rotarod performance test and liver function, and thus increases longevity of aging mice. These health benefits of corn oil may result from the combinations of the high levels of PUFA,
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vitamin E and plant sterols. Therefore, corn oil, even at a high energy 307 percentage (58%), is a favorable replacement of animal fats in the 308 human diet if the total energy intake is controlled. 309
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Values are means ± SE (n = 12–14 per group). ⁎ P b 0.05.
The authors declare that there are no conflicts of interest associated 311 with this manuscript. 312 Acknowledgments
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We are grateful for the support of the National Institute of Food and 314 Agriculture of USDA, Evans-Allen program (TENX-1103-FS, to H. Si) for 315 this work. 316
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