Kirsti Rouvinen-Watt

Fatty acid composition and development of hepatic lipidosis during food deprivation--mustelids as a potential animal model for liver steatosis.

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome characterized by asymptomatic hepatic steatosis. It is present in most cases of human obesity but also caused e.g., by rapid weight loss. The patients have decreased n-3 polyunsaturated fatty acid (PUFA) proportions with decreased percentages of 18:3(n-3), 20:5(n-3) and 22:6(n-3) and an increased n-6/n-3 PUFA ratio in liver and/or white adipose tissue (WAT). The present study examined a new experimental model to study liver steatosis with possible future applications to NAFLD. Ten European polecats (Mustela putorius), the wild form of the domestic ferret, were food-deprived for 5 days with 10 fed animals as controls. The food-deprived animals showed micro- and macrovesicular hepatic steatosis, decreased proportions of 20:5(n-3), 22:6(n-3) and total n-3 PUFA and increased n-6/n-3 PUFA ratios in liver and WAT. At the same time, the product/precursor ratios decreased in liver. The observed effects can be due to selective fatty acid mobilization preferring n-3 PUFA over n-6 PUFA, decreased Δ5 and Δ6 desaturase activities, oxidative stress, decreased arginine availability and activation of the endocannabinoid system. Hepatic lipidosis induced by food deprivation was manifested in the fatty acid composition of the polecat with similarities to human NAFLD despite the different principal etiologies.

Response to Fasting in an Unnaturally Obese Carnivore, the Captive European Polecat Mustela putorius

The European polecat (Mustela putorius) is a naturally lean carnivore prone to excessive weight gain in captivity. This study assessed its suitability to investigate the natural history of the obese phenotype displayed in overweight humans, domestic animals, and seasonally obese wild mammals. Ten farm-bred polecats were subjected to a 5-day fast with 10 controls. Obesity (40% body fat) was associated with an unfavorable plasma lipid profile and high glucose and insulin concentrations. The polecats were in phase II of fasting with normoglycemia, low liver carbohydrate stores, and decreased plasma concentrations of urea and most amino acids. Although the plasma nonesterified fatty acid (NEFA) levels were elevated, the adipose tissue lipase activities suggested a blunted lipolytic response. Lipid mobilization was more efficient from intraabdominal fat. The animals developed hepatic lipidosis with elevated NEFA influx into the liver and losses of n-3 polyunsaturated fatty acids and arginine as hypothetical etiological factors. The plasma leptin, insulin, and triiodothyronine levels decreased but were not accompanied by reduced sex steroid or increased stress hormone concentrations. The blunted lipolytic response often encountered in obesity suggests that the organism is trying to defend the obese phenotype. Liver lipidosis and decreased insulin and triiodothyronine levels seem to be among the most consistent responses to fasting manifested in diverse mammalian orders and different levels of body fatness. The polecat could be recommended as an easily accessible carnivorean model to study the natural history of the obese phenotype and its comorbidities.

Effects of methylmercury on epigenetic markers in three model species: mink, chicken and yellow perch

We previously reported that methylmercury (MeHg) exposure is associated with DNA hypomethylation in the brain stem of male polar bears. Here, we conveniently use archived tissues obtained from controlled laboratory exposure studies to look for evidence that MeHg can disrupt DNA methylation across taxa. Brain (cerebrum) tissues from MeHg-exposed mink (Neovison vison), chicken (Gallus gallus) and yellow perch (Perca flavescens) were analyzed for total Hg levels and global DNA methylation. Tissues from chicken and mink, but not perch, were also analyzed for DNA methyltransferase (DNMT) activity. In mink we observed significant reductions in global DNA methylation in an environmentally-relevant dietary exposure group (1 ppm MeHg), but not in a higher group (2 ppm MeHg). DNMT activity was significantly reduced in all treatment groups. In chicken or yellow perch, no statistically significant effects of MeHg were observed. Dose-dependent trends were observed in the chicken data but the direction of the change was not consistent between the two endpoints. Our results suggest that MeHg can be epigenetically active in that it has the capacity to affect DNA methylation in mammals. The variability in results across species may suggest inter-taxa differences in epigenetic responses to MeHg, or may be related to differences among the exposure scenarios used as animals were exposed to MeHg through different routes (dietary, egg injection), for different periods of time (19-89 days) and at different life stages (embryonic, juvenile, adult).

The Role of Food Peptides in Lipid Metabolism during Dyslipidemia and Associated Health Conditions

Animal and human clinical studies have demonstrated the ability of dietary food proteins to modulate endogenous lipid levels during abnormal lipid metabolism (dyslipidemia). Considering the susceptibility of proteins to gastric proteolytic activities, the hypolipidemic functions of proteins are possibly due, in part, to their peptide fragments. Food-derived peptides may directly modulate abnormal lipid metabolism in cell cultures and animal models of dyslipidemia. The peptides are thought to act by perturbing intestinal absorption of dietary cholesterol and enterohepatic bile acid circulation, and by inhibiting lipogenic enzymatic activities and gene expression in hepatocytes and adipocytes. Recent evidence indicates that the hypolipidemic activities of some peptides are due to activation of hepatic lipogenic transcription factors. However, detailed molecular mechanisms and structural requirements of peptides for these activities are yet to be elucidated. As hypolipidemic peptides can be released during enzymatic food processing, future studies can explore the prospects of combating metabolic syndrome and associated complications using peptide-rich functional food and nutraceutical products.

Methylmercury accumulation and elimination in mink (Neovison vison) hair and blood: Results of a controlled feeding experiment using stable isotope tracers

Concentrations of metals in hair are used often to develop pharmacokinetic models for both animals and humans. Although data on uptake are available, elimination kinetics are less well understood; stable isotope tracers provide an excellent tool for measuring uptake and elimination kinetics. In the present study, methylmercury concentrations through time were measured in the hair and blood of mink (Neovison vison) during a controlled 60-d feeding experiment. Thirty-four mink were fed a standard fish-based diet for 14 d, at the end of which (day 0), 4 mink were sacrificed to determine baseline methylmercury (MeHg) concentrations. From day 0 to day 10, the remaining mink were fed a diet consisting of the base diet supplemented with 0.513 ± 0.013 µg Me(199) Hg/g and 0.163 ± 0.003 µg Me(201) Hg/g. From day 10 to day 60, mink were fed the base diet supplemented with 0.175 ± 0.024 µg Me(201) Hg/g. Animals were sacrificed periodically to determine accumulation of Me(201) Hg in blood and hair over the entire 60-d period and the elimination of Me(199) Hg over the last 50 d. Hair samples, collected from each mink and cut into 2.0-mm lengths, indicate that both isotopes of MeHg appeared in the hair closest to the skin at approximately day 10, with concentrations in the hair reaching steady state from day 39 onward. The elimination rate of Me(199) Hg from the blood was 0.05/d, and the ratio of MeHg in the hair to blood was 119. A large fraction of MeHg (22% to >100%) was stored in the hair, suggesting that in fur-bearing mammals the hair is a major route of elimination of MeHg from the body.

Manifestations of Fasting-Induced Fatty Liver and Rapid Recovery from Steatosis in Voles Fed Lard or Flaxseed Oil Lipids

Long-chain n-3 polyunsaturated fatty acids (PUFA) can have beneficial effects against fat deposition, cardiovascular diseases, and liver steatosis. We investigated how diets based on lard (predominantly saturated and monounsaturated fatty acids) or flaxseed oil (rich in 18:3n-3) affect liver fat-% and fatty acid profiles of tundra voles (Microtus oeconomus). We also studied potential participation of hyaluronan (HA) in the pathology of fatty liver and whether the development and recovery of fasting-induced steatosis are influenced by n-3 PUFA. The dietary fatty acid composition was manifested in the liver fatty acid signatures. Fasting for 18 h induced macrovesicular steatosis and the liver fat-% increased to 22% independent of the preceding diet. Fasting-induced steatosis did not involve inflammation or connective tissue activation indicated by the absence of both leukocyte accumulation and increased HA. Food deprivation modified the liver fatty acid signatures to resemble more closely the diets. Fasting reduced the proportions of long-chain n-3 PUFA in both dietary regimes and n-3/n-6 PUFA ratios in the lard-fed voles. Decreases in long-chain n-3 PUFA may promote lipid accumulation by modulating the expression of lipid-metabolizing genes. Dietary 18:3n-3 did not prevent the development or attenuate the manifestation of steatosis in the fasted voles or promote the recovery.

Partitioning and kinetics of methylmercury among organs in captive mink (Neovison vison): A stable isotope tracer study

Despite the importance of methylmercury (MeHg) as a neurotoxin, we have relatively few good data on partitioning and kinetics of MeHg among organs, particularly across the blood-brain barrier, for mammals that consume large quantities of fish. The objective of this study was to determine the partition coefficients between blood and brain, liver and kidney and fur for MeHg under steady-state conditions and to measure the half-lives for MeHg in these organs. Captive mink (Neovison vison) were fed a diet enriched with two stable isotopes of Hg, Me(199)Hg and Me(201)Hg for a period of 60 days. After a period of 10 days the diet was changed to contain only Me(201)Hg so that, between days 10 and 60, we were able to measure both uptake and elimination rates from blood, brain, liver kidney and fur. Liver and kidney response was very rapid, closely following changes in blood concentrations but there was a small lag time between peak blood concentrations and peak brain concentrations. Half-lives for MeHg were 15.4, 10.2 and 13.4 days for brain, liver and kidney, respectively. There was no measurable conversion of the MeHg to inorganic Hg (IHg) in the brain over the 60 day period, unlike in liver and kidney.

Ideal body condition improves reproductive performance and influences genetic health in female mink

Selection for large body size in mink (Neovison vison) can result in obesity, which is associated with poor reproduction and metabolic disorders. Caloric restriction is effective in diminishing oxidative stress and delaying aging-related diseases. This study investigated the effects of moderate diet restriction on body condition, health, and reproductive success of mink breeder females. One-hundred control females were fed according to conventional feeding practice, while the feed allowance of their 100 sister-pair females was restricted in order to maintain an ideal body condition during the fall and eliminate the need for drastic slimming prior to breeding. Repeated measures analyses revealed that body weight gain during the fall and weight loss prior to breeding was significantly less for the restricted females. The restricted females had significantly larger live litters (5.88 kits) than the control dams (4.62 kits; P<0.05). They were also able to maintain their body weight and condition during early lactation and were able to regain weight and condition post-lactation, unlike their control sisters. Based on their comet scores (restricted: 88; control: 116), the restricted primiparous females experienced less DNA damage (P<0.05), while no significant differences were apparent for the multiparous females (restricted: 170; control: 153). No changes in telomere length were observed among the dams. Moderate diet restriction of mink breeder females during the fall eliminated extreme fluctuations in body weight and condition throughout the seasonal production cycle and improved their litter size, and in primiparous females, lessened DNA damage.

High feeding intensity increases the severity of fatty liver in the American mink (Neovison vison) with potential ameliorating role for long-chain n-3 polyunsaturated fatty acids

BackgroundRapid body fat mobilization, obesity, and an inadequate supply of n-3 polyunsaturated fatty acids (PUFA) have been suggested to play roles in the etiology of fatty liver in the American mink (Neovison vison). This study examined the effects of feeding intensity and dietary fat source on fatty liver induced by fasting. In a multi-factorial design, 3 different fat sources (herring oil, rich in n-3 PUFA, soya oil, rich in n-6 PUFA, and canola oil, rich in n-9 monounsaturated fatty acids) were fed to mink at a low and high feeding intensity for 10 weeks, followed by an overnight or a 5-day fasting treatment to induce fatty liver.ResultsFasting led to the development of fatty liver with increased severity in the mink fed at the high feeding intensity. The herring oil diet, high in long-chain n-3 PUFA, was found to decrease the severity of fatty liver in the mink at the high feeding intensity.ConclusionPreventing excessive weight gain and increasing dietary intake of n-3 long-chain PUFA may help prevent excessive lipid accumulation during prolonged periods of fasting or inappetence by promoting hepatic fatty acid oxidation.

Uptake of selenium and mercury by captive mink: Results of a controlled feeding experiment.

Captive, juvenile, ranch-bred, male mink (Neovison vison) were fed diets containing various concentrations of methyl-mercury (MeHg) and selenium (Se) for a period of 13 weeks and then sacrificed to determine total Hg levels in fur, blood, brain, liver and kidneys and total Se concentrations in brain tissue. As MeHg concentrations in the diet increased, concentrations of total Hg in the tissues also increased with the highest level occurring in the fur > liver = kidney > brain > blood. Concentrations of Hg in the fur were correlated (r(2) > 0.97) with liver, kidney, blood and brain concentrations. The addition of Se to the mink diet did not appear to affect most tissue concentrations of total Hg nor did it affect the partitioning of Hg between the liver:blood, kidney:blood and brain:blood; however, partitioning of Hg between fur and blood was apparently affected.