Effects of dietary vegetable oils on behavior and drug responses in mice

Rapeseed (canola) oil aggravates metabolic syndrome-like conditions in male but not in female stroke-prone spontaneously hypertensive rats (SHRSP)

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Canola oil shortens life of male SHRSP.

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Testis is the target of canola oil toxicity.

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Inhibition of negative regulation by testosterone of aldosterone production may be a trigger of canola oil toxicity.

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Facilitation of hypertension by aldosterone may lead to life-shortening.

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Increased plasma lipids by canola oil have no relevance to life-shortening.

This study was conducted to investigate whether or not there are sex differences in canola oil (CAN)-induced adverse events in the rat and to understand the involvement and the role of testosterone in those events, including life-shortening. Stroke-prone spontaneously hypertensive rats (SHRSP) of both sexes were fed a diet containing 10 wt/wt% soybean oil (SOY, control) or CAN as the sole dietary fat. The survival of the males fed the CAN diet was significantly shorter than that of those fed the SOY diet. In contrast, the survival of the females was not affected by CAN. The males fed the CAN diet showed elevated blood pressure, thrombopenia and insulin-tolerance, which are major symptoms of metabolic syndrome, whereas such changes by the CAN diet were not found in the females. Plasma testosterone was significantly lower in animals of both sexes fed the CAN diet than in those fed the SOY diet, but interestingly, the lowered testosterone was accompanied by a marked increase in plasma aldosterone only in the males. These results demonstrate significant sex differences in CAN-toxicity and suggest that those sex differences may be attributable to the increased aldosterone level, which triggers aggravation of the genetic diseases specific to SHRSP, that is, metabolic syndrome-like conditions, but only in the males. The present results also suggest that testosterone may negatively regulate aldosterone production in the physiology of the males, and the inhibition of that negative regulation caused by the CAN diet is one of the possible causes of the adverse events.

Fully hydrogenated canola oil extends lifespan in stroke-prone spontaneously hypertensive rats

Background

Canola oil (Can) and several vegetable oils shorten the lifespan of stroke-prone spontaneously hypertensive rats (SHRSP). Although similar lifespan shortening has been reported for partially hydrogenated Can, the efficacy of fully hydrogenated oils on the lifespan remains unknown. The present study aimed to investigate the lifespan of SHRSP fed diets containing 10 % (w/w) of fully hydrogenated Can (FHCO) or other oils.

Methods

Survival test: Upon weaning, male SHRSP were fed a basal diet for rodents mixed with one of the test oils —i.e., FHCO, Can, lard (Lrd), and palm oil (Plm) throughout the experiment. The animals could freely access the diet and drinking water (water containing 1 % NaCl), and their body weight, food intake, and lifespan were recorded.

Biochemical analysis test: Male SHRSP were fed a test diet with either FHCO, Can, or soybean oil (Soy) under the same condition, except to emphasize effects of fat, that no NaCl loading was applied. Soy was used as a fat source in the basal diet and was set the control group. Blood pressures was checked every 2 weeks, and serum fat levels and histological analyses of the brain and kidney were examined after 7 or 12 weeks of feeding.

Results

During the survival study period, the food consumption of FHCO-fed rats significantly increased (15–20 % w/w) compared with that of rats fed any other oil. However, the body weight gain in the FHCO group was significantly less (10–12 %) than that in the control group at 9–11 weeks old. The FHCO (> 180 days) intervention had the greatest effect on lifespan, followed by the Lrd (115 ± 6 days), Plm (101 ± 2 days), and Can (94 ± 3 days) diets. FHCO remarkably decreased the serum cholesterol level compared with Can and the systolic blood pressure from 12 to 16 weeks of age. In addition, while some rats in the Can group exhibited brain hemorrhaging and renal dysfunction at 16 weeks old, no symptoms were observed in the FHCO group.

Conclusion

This current study suggests that complete hydrogenation decreases the toxicity of Can and even prolongs the lifespan in SHRSP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-021-01540-7.

Defective adaptive thermogenesis contributes to metabolic syndrome and liver steatosis in obese mice

Fatty liver diseases are complications of the metabolic syndrome associated with obesity, insulin resistance and low grade inflammation. Our aim was to uncover mechanisms contributing to hepatic complications in this setting. We used foz/foz mice prone to obesity, insulin resistance and progressive fibrosing non-alcoholic steatohepatitis (NASH). Foz/foz mice are hyperphagic but wild-type (WT)-matched calorie intake failed to protect against obesity, adipose inflammation and glucose intolerance. Obese foz/foz mice had similar physical activity level but reduced energy expenditure. Thermogenic adaptation to high-fat diet (HFD) or to cold exposure was severely impaired in foz/foz mice compared with HFD-fed WT littermates due to lower sympathetic tone in their brown adipose tissue (BAT). Intermittent cold exposure (ICE) restored BAT function and thereby improved glucose tolerance, decreased fat mass and liver steatosis. We conclude that failure of BAT adaptation drives the metabolic complications of obesity in foz/foz mice, including development of liver steatosis. Induction of endogenous BAT function had a significant therapeutic impact on obesity, glucose tolerance and liver complications and is a potential new avenue for therapy of non-alcoholic fatty liver disease (NAFLD).

Testosterone-lowering activity of canola and hydrogenated soybean oil in the stroke-prone spontaneously hypertensive rat

Canola and some other types of oil unusually shorten the survival of stroke-prone spontaneously hypertensive rats (SHRSP), compared with soybean oil, perilla oil and animal fats. Since differential effects of canola and soybean oil on steroid hormone metabolism were suggested by a preliminary DNA microarray analysis as a reason for this, the steroid hormone levels in the serum and tissues of SHRSP fed different oils were investigated. The testosterone levels in the serum and the testes were found to be significantly lower in the canola oil group than in the soybean oil group, while no significant differences were detected in the corticosterone and estradiol levels in tissues. In a second experiment, it was found that hydrogenated soybean oil, with a survival-shortening activity comparable to that of canola oil, also decreased the testosterone level in testes to a similar degree. The testosterone-lowering activity of canola and hydrogenated soybean oil observed in SHRSP was considered in relation to other factors possibly affecting the physiology of SHRSP.

Safflower extracts functionally regulate monoamine transporters

Safflower (HH), the dry flower of Carthamus tinctorius L., has long been used to empirically treat neuropsychological disorders such as stroke and major depression in traditional Chinese medicine, and recently been proven effective for regulating levels of dopamine and serotonin in new-born rat brain. The present study assessed whether HH would be bioactive for functionally regulating monoamine transporters using in vitro drug-screening cell lines. Our current results showed that all solvent-extracted HH fractions, in different degrees, markedly increased both dopamine uptake by Chinese hamster ovary (CHO) cells stably expressing dopamine transporter (DAT) and norepinephrine uptake by CHO cells expressing norepinephrine transporter (NET), and also showed that chloroform (HC), ethyl acetate (HE), and n-butyl alcohol extract strikingly depressed serotonin uptake by CHO cells expressing serotonin transporter (SERT); wherein, the potencies of ethanol extract, HC, HE, and aqueous extract to up-regulate dopamine/norepinephrine uptake and potency of HE to inhibit serotonin uptake were relatively stronger. Further investigation revealed that the enhancement of dopamine/norepinephrine uptake by HC and HE was dependent of DAT/NET activity, and the HE-induced inhibition of serotonin uptake was typical of competition. Thus, HH extracts are novel monoamine transporter modulators functioning as DAT/NET activators and/or SERT inhibitors, and would likely improve neuropsychological disorders through regulating monoamine-transporter activity.

Factors other than phytosterols in some vegetable oils affect the survival of SHRSP rats

Unusual survival-shortening activities of some vegetable oils were detected in stroke-prone spontaneously hypertensive (SHRSP) rats, and phytosterol (PS) in the oils and the tissue tocopherol status have been suggested to be the factors for the activities. Here, we re-evaluated the contribution of PS to the survival-shortening, and examined the hepatic tocopherol status. A basal diet for rodents and a test oil were mixed at a 9:1 ratio, and the diet was given to male SHRSP rats upon weaning. The total and major PS contents of the diets and tissue lipids did not correlate with relative survival time. The free fatty acid fractions obtained by lipase and alkaline hydrolyses of canola oil (Can) and the original Can contained PS in comparable amounts but the free fatty acid fractions did not exhibit survival-shortening activities compared with the soybean oil (Soy) group. The activity was not detected in the ethyl acetate extracts of the aqueous phase after the hydrolysis. When a commercially available PS preparation was added to the Soy diet at an amount 2.8-fold higher than that in the Can diet, the mean survival time was shortened but was still significantly longer than that of the Can group. The hepatic tocopherol level was significantly higher in the Can group than in the hydrogenated Soy group and Soy group, but the former two groups exhibited a survival-shortening activity. These results indicate that factors other than PS, tocopherol status and fatty acid composition in some vegetable oils are critical for the survival-shortening activity observed in SHRSP rats.

Dietary canola and soybean oil fed to SHRSP rat dams differently affect the growth and survival of their male pups

Canola oil (Can), as well as some other oils, shortens the survival of SHRSP rats compared with soybean oil (Soy). Although detrimental factors other than phytosterols have not been identified, they are likely to be hydrophobic and transmissible to pups. To test this possibility, female SHRSP rats (F0) were fed a diet supplemented with Can or Soy and mated at 11 wk of age. The growth of suckling pups (F1) from the Can-fed dams was significantly retarded compared with that of pups from the Soy-fed dams. Half of the male pups (F1) were weaned to the same diet as their dams (Can-->Can and Soy-->Soy groups) and the rest were weaned to the other diet (Can-->Soy and Soy-->Can groups). The survival rate of the male pups (F1) was significantly lower in the Can-->Can group than in the Soy-->Can group, and in the Can-->Soy group than in the Soy-->Soy group, indicating that the oils fed to dams differently affected the growth and survival of pups. There were fewer pups per dam in the Can-fed dams (F0) than in the Soy-fed dams, and in the dams (F1) of the Can-->Can and Soy-->Can groups than in those of the Can-->Soy and Soy-->Soy groups. Although Can is nutritionally detrimental to SHRSP rats compared with Soy, no direct evidence has been obtained thus far relating these observations to human nutrition.

Pathophysiological effects of dietary essential fatty acid balance on neural systems

Dietary fatty acid balance has been revealed to affect neural functions as well as chronic diseases such as cancer, cerebro- and cardiovascular diseases, and allergic hyper-reactivity. In this review, we focused on the pathophysiological effects of n-6 and n-3 fatty acids on brain functions. Long-term n-3 fatty acid deficiency in the presence of n-6 fatty acids has been shown to affect learning behavior, drug sensitivity and retinal functions. Some membrane enzymes and ion channel functions have been shown in experimental animals to be regulated by membrane fatty acid modifications. We also summarized the effects of these fatty acids in diets on human psychotic aspects and brain diseases. Although biochemical mechanisms remain to be elucidated, investigations on the effect of dietary fatty acids on neural networks may provide an important clue to clarify complex brain functions.

Unusual effects of some vegetable oils on the survival time of stroke-prone spontaneously hypertensive rats

Preliminary experiments have shown that a diet containing 10% rapeseed oil (low-erucic acid) markedly shortens the survival time of stroke-prone spontaneously hypertensive (SHRSP) rats under 1% NaCl loading as compared with diets containing perilla oil or soybean oil. High-oleate safflower oil and high-oleate sunflower oil were found to have survival time-shortening activities comparable to that of rapeseed oil; olive oil had slightly less activity. A mixture was made of soybean oil, perilla oil, and triolein partially purified from high-oleate sunflower oil to adjust the fatty acid composition to that of rapeseed oil. The survival time of this triolein/mixed oil group was between those of the rapeseed oil and soybean oil groups. When 1% NaCl was replaced with tap water, the survival time was prolonged by approximately 80%. Under these conditions, the rapeseed oil and evening primrose oil shortened the survival time by approximately 40% as compared with n-3 fatty acid-rich perilla and fish oil; lard, soybean oil, and safflower oil with relatively high n-6/n-3 ratios shortened the survival time by roughly 10%. The observed unusual survival time-shortening activities of some vegetable oils (rapeseed, high-oleate safflower, high-oleate sunflower, olive, and evening primrose oil) may not be due to their unique fatty acid compositions, but these results suggest that these vegetable oils contain factor(s) which are detrimental to SHRSP rats.