Effects of dietary fish oil on thyroid hormone signaling in the liver

Effects of maternal supplementation of fish oil during late gestation and lactation on growth performance, fecal microbiota structure and post-weaning diarrhoea of offspring piglets

Homeostasis of gut microbiota is a critical contributor to growth and health in weaned piglets. Fish oil is widely reported to benefit health of mammals including preventing intestinal dysfunction, yet its protective effect during suckling-to-weaning transition in piglets remains undetermined. Low (30 g/d) and high (60 g/d) doses of n-3-rich fish oil were supplemented in sows from late gestation to lactation. Serum indicators and gut microbiota were determined to evaluate the effects of maternal fish oil on growth performance, immunity and diarrhea of piglets. DHA and EPA in the colostrum as well as serum of suckling and 1-week post-wean piglets were significantly and linearly increased by maternal supplementation of fish oil (P < 0.05). IGF1 and T3 in nursing and weaned piglets were significantly elevated by maternal fish oil (P < 0.05), and the increase of IGF1 was concerning the dosage of fish oil. Colostrum IgG, plasma IgG, IgM in suckling piglets, IgG, IgM and IgA in weaned piglets were significantly increase as maternal replenishment of fish oil increased (P < 0.05). Additionally, cortisol was significantly reduced in weaned pigs (P < 0.05), regardless of dosage. 16S rRNA sequencing revealed that α-diversity of fecal microbiota in nursery piglets, and fecal Lactobacillus genus, positively correlated with post-weaning IgA, was significantly increased by high dosage. Collectively, maternal fish oil during late pregnancy and lactation significantly promoted growth, enhanced immunity, and reduced post-weaning diarrhea in piglets, therefore facilitated suckling-to-weaning transition in piglets, which may be partially due to the altered gut microbial community.

Liver acts as a metabolic gate for the traumatic brain injury pathology: Protective action of thyroid hormone

Clinical evidence indicates that injury to the brain elicits systemic metabolic disturbances that contributes to the brain pathology. Since dietary fructose is metabolized in the liver, we explored mechanisms by which traumatic brain injury (TBI) and dietary fructose influence liver function and their possible repercussions to brain. Consumption of fructose contributed to the detrimental effects of TBI on liver operation, in terms of glucose and lipid metabolism, de novo lipogenesis, lipid peroxidation. Thyroid hormone (T4) is metabolized in the liver and found that T4 supply improved lipid metabolism by reducing de novo lipogenesis, lipid accumulation, lipogenic enzymes (ACC, AceCS1, FAS), lipid peroxidation in liver in response to fructose and fructose-TBI. T4 supply also helped to normalize glucose metabolism and improve insulin sensitivity. Furthermore, T4 counteracted elevations of the pro-inflammatory cytokines, Tnfα and Mcp-1 after TBI and/or fructose intake in liver and circulation. T4 also exerted an effect on isolated primary hepatocytes by potentiating phosphorylation of AMPKα and AKT substrate, AS160, leading to increased glucose uptake. In addition, T4 restored the metabolism of DHA in the liver disrupted by TBI and fructose, adding important information to optimize the action of DHA in therapeutics. The overall evidence seems to indicate that the liver works as a gate for the regulation of the effects of brain injury and foods on brain pathologies.

The MAP-Kinase HOG1 Controls Cold Adaptation in Rhodosporidium kratochvilovae by Promoting Biosynthesis of Polyunsaturated Fatty Acids and Glycerol

The aim of this study was to investigate the role of RKHog1 in the cold adaptation of Rhodosporidium kratochvilovae strain YM25235 and elucidate the correlation of biosynthesis of polyunsaturated fatty acids (PUFAs) and glycerol with its cold adaptation. The YM25235 strain was subjected to salt, osmotic, and cold stress tolerance analyses. mRNA levels of RKhog1, Δ^12/15-fatty acid desaturase gene (RKD12), RKMsn4, HisK2301, and RKGPD1 in YM25235 were detected by reverse transcription quantitative real-time PCR. The contents of PUFAs, such as linoleic acid (LA) and linolenic acid (ALA) was measured using a gas chromatography-mass spectrometer, followed by determination of the growth rate of YM25235 and its glycerol content at low temperature. The RKHog1 overexpression, knockout, and remediation strains were constructed. Stress resistance analysis showed that overexpression of RKHog1 gene increased the biosynthesis of glycerol and enhanced the tolerance of YM25235 to cold, salt, and osmotic stresses, respectively. Inversely, the knockout of RKHog1 gene decreased the biosynthesis of glycerol and inhibited the tolerance of YM25235 to different stresses. Fatty acid analysis showed that the overexpression of RKHog1 gene in YM25235 significantly increased the content of LA and ALA, but RKHog1 gene knockout YM25235 strain had decreased content of LA and ALA. In addition, the mRNA expression level of RKD12, RKMsn4, RKHisK2301, and RKGPD1 showed an increase at 15 °C after RKHog1 gene overexpression but were unchanged at 30 °C. RKHog1 could regulate the growth adaptability and PUFA content of YM25235 at low temperature and this could be helpful for the cold adaptation of YM25235.

Fish and the Thyroid: A Janus Bifrons Relationship Caused by Pollutants and the Omega-3 Polyunsaturated Fatty Acids

Benefits of the omega-3 polyunsaturated fatty acids (PUFA) on a number of clinical disorders, including autoimmune diseases, are widely reported in the literature. One major dietary source of PUFA are fish, particularly the small oily fish, like anchovy, sardine, mackerel and others. Unfortunately, fish (particularly the large, top-predator fish like swordfish) are also a source of pollutants, including the heavy metals. One relevant heavy metal is mercury, a known environmental trigger of autoimmunity that is measurable inside the thyroid. There are a number of interactions between the omega-3 PUFA and thyroid hormones, even at the level of the thyroid hormone transport proteins. Concerning the mechanisms behind the protection from/amelioration of autoimmune diseases, including thyroiditis, that are caused by the omega-3 PUFA, one can be the decreased production of chemokines, a decrease that was reported in the literature for other nutraceuticals. Recent studies point also to the involvement of resolvins. The intracellular increase in resolvins is associated with the tissue protection from inflammation that was observed in experimental animals after coadministration of omega-3 PUFA and thyroid hormone. After having presented data on fish consumption at the beginning, we conclude our review by presenting data on the market of the dietary supplements/nutraceuticals. The global omega-3 products market was valued at USD 2.10 billion in 2020, and was projected to go up at a compound annual growth rate of 7.8% from 2020 to 2028. Among supplements, fish oils, which are derived mainly from anchovies, are considered the best and generally safest source of omega-3. Taking into account (i) the anti-autoimmunity and anti-cancer properties of the omega-3 PUFA, (ii) the increasing incidence of both autoimmune thyroiditis and thyroid cancer worldwide, (iii) the predisposing role for thyroid cancer exerted by autoimmune thyroiditis, and (iv) the risk for developing metabolic and cardiovascular disorders conferred by both elevated/trendwise elevated serum TSH levels and thyroid autoimmunity, then there is enough rationale for the omega-3 PUFA as measures to contrast the appearance and/or duration of Hashimoto's thyroiditis as well as to correct the slightly elevated serum TSH levels of subclinical hypothyroidism.

Molecular mechanisms underlying fructose-induced cardiovascular disease: exercise, metabolic pathways and microRNAs

NEW FINDINGS

What is the central question of this study? What are the mechanisms underlying the cardiac protective effect of aerobic training in the progression of a high fructose-induced cardiometabolic disease in Wistar rats? What is the main finding and its importance? At the onset of cardiovascular disease, aerobic training activates the p-p70S6K, ERK and IRβ-PI3K-AKT pathways, without changing the miR-126 and miR-195 levels, thereby providing evidence that aerobic training modulates the insulin signalling pathway. These data contribute to the understanding of the molecular cardiac changes that are associated with physiological left ventricular hypertrophy during the development of a cardiovascular disease.

ABSTRACT

During the onset of cardiovascular disease (CVD), disturbances in myocardial vascularization, cell proliferation and protein expression are observed. Aerobic training prevents CVD, but the underlying mechanisms behind left ventricle (LV) hypertrophy are not fully elucidated. The aim of this study was to investigate the mechanisms by which aerobic training protects the heart from LV hypertrophy during the onset of fructose-induced cardiometabolic disease. Male Wistar rats were allocated to four groups (n = 8/group): control sedentary (C), control training (CT), fructose sedentary (F) and fructose training (FT). The C and CT groups received drinking water, and the F and FT groups received d-fructose (10% in water). After 2 weeks, the CT and FT rats were assigned to a treadmill training protocol at moderate intensity for 8 weeks (60 min/day, 4 days/week). After 10 weeks, LV morphological remodelling, cardiomyocyte apoptosis, microRNAs and the insulin signalling pathway were investigated. The F group had systemic cardiometabolic alterations, which were normalised by aerobic training. The LV weight increased in the FT group, myocardium vascularisation decreased in the F group, and the cardiomyocyte area increased in the CT, F and FT groups. Regarding protein expression, total insulin receptor β-subunit (IRβ) decreased in the F group; phospho (p)-IRβ and phosphoinositide 3-kinase (PI3K) increased in the FT group; total-AKT and p-AKT increased in all of the groups; p-p70S6 kinase (p70S6K) protein was higher in the CT group; and p-extracellular signal-regulated kinase (ERK) increased in the CT and FT groups. MiR-126, miR-195 and cardiomyocyte apoptosis did not differ among the groups. Aerobic training activates p-p70S6K and p-ERK, and during the onset of a CVD, it can activate the IRβ-PI3K-AKT pathway.

The Role of the Thyroid Axis in Fish

In all vertebrates, the thyroid axis is an endocrine feedback system that affects growth, differentiation, and reproduction, by sensing and translating central and peripheral signals to maintain homeostasis and a proper thyroidal set-point. Fish, the most diverse group of vertebrates, rely on this system for somatic growth, metamorphosis, reproductive events, and the ability to tolerate changing environments. The vast majority of the research on the thyroid axis pertains to mammals, in particular rodents, and although some progress has been made to understand the role of this endocrine axis in non-mammalian vertebrates, including amphibians and teleost fish, major gaps in our knowledge remain regarding other groups, such as elasmobranchs and cyclostomes. In this review, we discuss the roles of the thyroid axis in fish and its contributions to growth and development, metamorphosis, reproduction, osmoregulation, as well as feeding and nutrient metabolism. We also discuss how thyroid hormones have been/can be used in aquaculture, and potential threats to the thyroid system in this regard.

Fish oil supplementation during adolescence attenuates metabolic programming of perinatal maternal high-fat diet in adult offspring

Perinatal maternal high-fat diet (HFD) increases susceptibility to obesity and fatty liver diseases in adult offspring, which can be attenuated by the potent hypolipidaemic action of fish oil (FO), an n-3 PUFA source, during adult life. Previously, we described that adolescent HFD offspring showed resistance to FO hypolipidaemic effects, although FO promoted hepatic molecular changes suggestive of reduced lipid accumulation. Here, we investigated whether this FO intervention only during the adolescence period could affect offspring metabolism in adulthood. Then, female Wistar rats received isoenergetic, standard (STD: 9 % fat) or high-fat (HFD: 28·6 % fat) diet before mating, and throughout pregnancy and lactation. After weaning, male offspring received the standard diet; and from 25 to 45 d old they received oral administration of soyabean oil or FO. At 150 d old, serum and hepatic metabolic parameters were evaluated. Maternal HFD adult offspring showed increased body weight, visceral adiposity, hyperleptinaemia and decreased hepatic pSTAT3/STAT3 ratio, suggestive of hepatic leptin resistance. FO intake only during the adolescence period reduced visceral adiposity and serum leptin, regardless of maternal diet. Maternal HFD promoted dyslipidaemia and hepatic TAG accumulation, which was correlated with reduced hepatic carnitine palmitoyl transferase-1a content, suggesting lipid oxidation impairment. FO intake did not change serum lipids; however, it restored hepatic TAG content and hepatic markers of lipid oxidation to STD offspring levels. Therefore, we concluded that FO intake exclusively during adolescence programmed STD offspring and reprogrammed HFD offspring male rats to a healthier metabolic phenotype in adult life, reducing visceral adiposity, serum leptin and hepatic TAG content in offspring adulthood.

Thyroid Function Disruptors: from nature to chemicals

The modern concept of thyroid disruptors includes man-made chemicals and bioactive compounds from food that interfere with any aspect of the hypothalamus-pituitary-thyroid axis, thyroid hormone biosynthesis and secretion, blood and transmembrane transport, metabolism and local action of thyroid hormones. This review highlights relevant disruptors that effect populations through their diet: directly from food itself (fish oil and polyunsaturated fatty acids, pepper, coffee, cinnamon and resveratrol/grapes), through vegetable cultivation (pesticides) and from containers for food storage and cooking (bisphenol A, phthalates and polybrominated diphenyl ethers). Due to the vital role of thyroid hormones during every stage of life, we review effects from the gestational period through to adulthood, including evidence from in vitro studies, rodent models, human trials and epidemiological studies.

Perinatal maternal high-fat diet promotes alterations in hepatic lipid metabolism and resistance to the hypolipidemic effect of fish oil in adolescent rat offspring

SCOPE

Maternal high-fat diet (HFD) promotes obesity and metabolic disturbances in offspring at weaning and adult life. We investigated metabolic consequences of maternal HFD in adolescent rat offspring and the potential benefic effects of fish oil (FO) (n-3 polyunsaturated fatty acid source).

METHODS AND RESULTS

Female rats received isocaloric, standard diet (STD: 9% fat) or HFD (28.6%) before mating, and throughout pregnancy and lactation. After weaning, male offspring received standard diet and, from 25th to 45th day, received oral administration of soybean oil (SO) or FO. HFD offspring showed higher body weight and adiposity, which was not attenuated by FO. In STD offspring, FO reduced serum triglyceride and cholesterol, as expected, but not in HFD offspring. Liver of HFD offspring groups showed increased free cholesterol and FO-treated HFD group showed lower expression of Abcg8, suggesting decreased cholesterol biliary excretion. HFD offspring presented higher hepatic expression of lipogenic markers, Srebf1 mRNA and acetyl CoA carboxylase (ACC). Serum n-3 PUFA were decreased in FO-treated HFD compared to FO-treated STD offspring, which may explain the reduced hypolipidemic FO effect.

CONCLUSION

Maternal HFD impaired the ability of FO to reduce adiposity and serum lipids in adolescent offspring, suggesting a potential predisposition to future development of metabolic disorders.

Cinnamon extract improves the body composition and attenuates lipogenic processes in the liver and adipose tissue of rats

Cinnamon attenuates lipogenic processes, regulating the expression of key enzymes, transcriptional factors and their target genes in the liver and adipose tissue.

Iodine plus n-3 fatty acid supplementation augments rescue of postnatal neuronal abnormalities in iodine-deficient rat cerebellum

High prevalence of hypothyroxinaemia in iodine-deficient (ID) mothers has serious implications for mental health of the progeny. Independent supplementation of iodine and n-3 fatty acids (FA) markedly improves growth and cognitive performance of school children. Discerning effects of n-3 FA and iodine on the developing cerebellum have not been ascertained. The present study investigates effects of these two micronutrients separately as well as together in an ID rat model. We studied the effects of these micronutrients on progeny of ID dams by instituting the following supplementation diets: (1) low-iodine diet (LID), (2) LID+potassium iodide (KI), (3) LID+n-3 FA and (4) LID+KI+n-3 FA. Pups were investigated for morphological and biochemical parameters at the peak of cerebellar histogenesis on postnatal day (P) 16 and for neurobehavioural as well as motor coordination parameters at P40. Results indicate that n-3 FA alone, without improvement in circulating thyroid hormone (TH), significantly improves functional, morphological and biochemical indices of the developing cerebellum. Further, results show that co-supplementation with iodine and n-3 FA rescues not only the loss of neurotrophic support, but also salvages motor coordination, memory and learning. This additive effect results in significantly improving neurotrophic support and seems to be mediated by parallel significant increase in TH receptor (TR)α and normalisation of TRβ, retinoic orphan receptor α and p75 neurotrophin receptor, as well as noteworthy prevention of apoptotic cell death and strengthening of anti-oxidative defence. The overall results indicate important mitigating role that n-3 FA may play in enhancing TH nuclear receptor-mediated signalling in the developing cerebellum.

Prevention of liver ischemia reperfusion injury by a combined thyroid hormone and fish oil protocol

Several preconditioning strategies are used to prevent ischemia-reperfusion (IR) liver injury, a deleterious condition associated with tissue resection, transplantation or trauma. Although thyroid hormone (T₃) administration exerts significant protection against liver IR injury in the rat, its clinical application is controversial due to possible adverse effects. Considering that prevention of liver IR injury has also been achieved by n-3 polyunsaturated fatty acid (n-3 PUFA) supplementation to rats, we studied the effect of n-3 PUFA dietary supplementation plus a lower dose of T₃ against IR injury. Male Sprague-Dawley rats receiving fish oil (300 mg/kg) for 3 days followed by a single intraperitoneal dose of 0.05 mg T₃/kg were subjected to 1 h of ischemia followed by 20 h of reperfusion. Parameters of liver injury (serum transaminases, histology) and oxidative stress (liver contents of GSH and oxidized proteins) were correlated with fatty acid composition, NF-κB activity, and tumor necrosis factor-α (TNF-α) and haptoglobin expression. IR significantly modified liver histology; enhanced serum transaminases, TNF-α response or liver oxidative stress; and decreased liver NF-κB activity and haptoglobin expression. Although IR injury was not prevented by either n-3 PUFA supplementation or T₃ administration, substantial decrease in liver injury and oxidative stress was achieved by the combined protocol, which also led to increased liver n-3 PUFA content and decreased n-6/n-3 PUFA ratios, with recovery of NF-κB activity and TNF-α and haptoglobin expression. Prevention of liver IR injury achieved by a combined protocol of T₃ and n-3 PUFA supplementation may represent a novel noninvasive preconditioning strategy with potential clinical application.

The Δ337T mutation on the TRβ causes alterations in growth, adiposity, and hepatic glucose homeostasis in mice

Mice bearing the genomic mutation Δ337T on the thyroid hormone receptor β (TRβ) gene present the classical signs of resistance to thyroid hormone (TH), with high serum TH and TSH. This mutant TR is unable to bind TH, remains constitutively bound to co-repressors, and has a dominant negative effect on normal TRs. In this study, we show that homozygous (TRβΔ337T) mice for this mutation have reduced body weight, length, and body fat content, despite augmented relative food intake and relative increase in serum leptin. TRβΔ337T mice exhibited normal glycemia and were more tolerant to an i.p. glucose load accompanied by reduced insulin secretion. Higher insulin sensitivity was observed after single insulin injection, when the TRβΔ337T mice developed a profound hypoglycemia. Impaired hepatic glucose production was confirmed by the reduction in glucose generation after pyruvate administration. In addition, hepatic glycogen content was lower in homozygous TRβΔ337T mice than in wild type. Collectively, the data suggest that TRβΔ337T mice have deficient hepatic glucose production, by reduced gluconeogenesis and lower glycogen deposits. Analysis of liver gluconeogenic gene expression showed a reduction in the mRNA of phosphoenolpyruvate carboxykinase, a rate-limiting enzyme, and of peroxisome proliferator-activated receptor-γ coactivator 1α, a key transcriptional factor essential to gluconeogenesis. Reduction in both gene expressions is consistent with resistance to TH action via TRβ, reproducing a hypothyroid phenotype. In conclusion, mice carrying the Δ337T-dominant negative mutation on the TRβ are leaner, exhibit impaired hepatic glucose production, and are more sensitive to hypoglycemic effects of insulin.

Thyroid hormone contributes to the hypolipidemic effect of polyunsaturated fatty acids from fish oil: in vivo evidence for cross talking mechanisms

n-3 polyunsaturated fatty acids (n-3 PUFA) from fish oil (FO) exert important lipid-lowering effects, an effect also ascribed to thyroid hormones (TH) and TH receptor β1 (TRβ1)-specific agonists. n-3 PUFA effects are mediated by nuclear receptors, such as peroxisome proliferator-activated receptors (PPAR) and others. In this study, we investigated a role for TH signaling in n-3 PUFA effects. Euthyroid and hypothyroid adult rats (methimazole-treated for 5 weeks) received FO or soybean oil (control) by oral administration for 3 weeks. In euthyroid rats, FO treatment reduced serum triglycerides and cholesterol, diminished body fat, and increased protein content of the animals. In addition, FO-treated rats exhibited higher liver expression of TRβ1 and mitochondrial α-glycerophosphate dehydrogenase (mGPD), at protein and mRNA levels, but no alteration of glutathione S-transferase or type 1 deiodinase. In hypothyroid condition, FO induced reduction in serum cholesterol and increase in body protein content, but lost the ability to reduce triglycerides and body fat, and to induce TRβ1 and mGDP expression. FO did not change PPARα liver abundance regardless of thyroid state; however, hypothyroidism led to a marked increase in PPARα liver content but did not alter TRβ1 or TRα expression. The data suggest that part of the effect of n-3 PUFA from FO on lipid metabolism is dependent on TH signaling in specific steps and together with the marked upregulation of PPARα in liver of hypothyroid rats suggest important in vivo consequences of the cross-talking between those fatty acids and TH pathways in liver metabolism.

Cross-regulation of hepatic glucose metabolism via ChREBP and nuclear receptors

There is a worldwide epidemic of obesity and type 2 diabetes, two major public health concerns associated with alterations in both insulin and glucose signaling pathways. Glucose is not only an energy source but also controls the expression of key genes involved in energetic metabolism, through the glucose-signaling transcription factor, Carbohydrate Responsive Element Binding Protein (ChREBP). ChREBP has emerged as a central regulator of de novo fatty acid synthesis (lipogenesis) in response to glucose under both physiological and physiopathological conditions. Glucose activates ChREBP by regulating its entry from the cytosol to the nucleus, thereby promoting its binding to carbohydrate responsive element (ChoRE) in the promoter regions of glycolytic (L-PK) and lipogenic genes (ACC and FAS). We have previously reported that the inhibition of ChREBP in liver of obese ob/ob mice improves the metabolic alterations linked to obesity, fatty liver and insulin-resistance. Therefore, regulating ChREBP activity could be an attractive target for lipid-lowering therapies in obesity and diabetes. However, before this is possible, a better understanding of the mechanism(s) regulating its activity is needed. In this review, we summarize recent findings on the role and regulation of ChREBP and particularly emphasize on the cross-regulations that may exist between key nuclear receptors (LXR, TR, HNF4α) and ChREBP for the control of hepatic glucose metabolism. These novel molecular cross-talks may open the way to new pharmacological opportunities. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

Female mice target deleted for the neuromedin B receptor have partial resistance to diet-induced obesity

Previous studies have proposed a role for neuromedin B (NB), a bombesin-like peptide, in the control of body weight homeostasis. However, the nature of this role is unclear. The actions of NB are mediated preferentially by NB-preferring receptors (NBRs). Here we examined the consequences of targeted deletion of NBRs in female mice on body weight homeostasis in mice fed a normolipid diet (ND) or a high-fat diet (HFD) for 13 weeks. Body weight and food ingestion of neuromedin B receptor knockout (NBR-KO) mice fed a normolipid diet showed no difference in relation to wild-type (WT). However, the high-fat diet induced an 8.9- and 4.8-fold increase in body weight of WT and NBR-KO, respectively, compared to their controls maintained with a normolipid diet, even though the mice ingested the same amount of calories, regardless of genotype. Comparing mice fed the high-fat diet, NBR-KO mice accumulated approximately 45% less fat depot mass than WT, exhibited a lower percentage of fat in their carcasses (19.2 vs. 31.3%), and their adipocytes were less hypertrophied. Serum leptin and leptin mRNA in inguinal and perigonadal fat were lower in HFD NBR-KO than HFD WT, and serum adiponectin was similar among HFD groups and unaltered in comparison to ND-fed mice. HFD-fed WT mice developed glucose intolerance but not the HFD-fed NBR-KO mice, although they had similar glycaemia and insulinaemia. NBR-KO and WT mice on the normolipid diet showed no differences in any parameters, except for a trend to lower insulin levels. Therefore, disruption of the neuromedin B receptor pathway did not change body weight homeostasis in female mice fed a normolipid diet; however, it did result in partial resistance to diet-induced obesity.