Increased fatty acid oxidation and mitochondrial proliferation in liver are associated with increased plasma kynurenine metabolites and nicotinamide levels in normolipidemic and carnitine-depleted rats

Preliminary investigation on the impact of salty and sugary former foods on pig liver and plasma profiles using OMICS approaches

Replacing cereals with food leftovers could reduce feed-food competition and keep nutrients and energy in the food chain. Former food products (FFPs) are industrial food leftovers no more intended for human but still suitable as alternative and sustainable feedstuffs for monogastric. In this study, omics approaches were applied to evaluate the impact of dietary FFPs on pig liver proteome and plasma peptidome. Thirty-six Swiss Large White male castrated pigs were randomly assigned to three dietary treatments [control (CTR), 30% CTR replaced with salty FFP (SA), 30% CTR replaced with sugary FFP (SU)] from the start of the growing phase (22.4 ± 1.7 kg) until slaughtering (110 ± 3 kg). The low number of differentially regulated proteins in each comparison matrix (SA/SU vs. CTR) and the lack of metabolic interaction indicated a marginal impact on hepatic lipid metabolism. The plasma peptidomics investigation showed low variability between the peptidome of the three dietary groups and identified three possible bioactive peptides in the SA group associated with anti-hypertension and vascular homeostasis regulation. To conclude, the limited modulation of liver proteome and plasma peptidome by the SA and SU diets strenghtened the idea of reusing FFPs as feed ingredients to make pig production more sustainable.

Dietary supplementation with tryptophan increases the plasma concentrations of tryptophan, kynurenine, and melatonin in Yili mares

Context Tryptophan (Trp) is the precursor of melatonin (MT) and the latter plays vital physiological roles in mares. Aims The purpose of this experiment was to investigate the effects of dietary Trp supplementation on the plasma Trp, kynurenine (Kyn), 5-hydroxytryptophan (5-HT), and melatonin (MT) concentrations in female Yili horses. Methods Twenty Yili mares aged 2 years with mean bodyweight (BW) of 263.5 ± 14.77 kg and of similar stature were selected and randomly allocated to the control (CON; basal diet), basal diet plus Trp at 20 mg/kg BW (TRP1), basal diet plus Trp at 40 mg/kg BW (TRP2), or basal diet plus Trp at 60 mg/kg BW (TRP3) group. Key results The plasma total Trp, Kyn, and MT concentrations in all Trp groups steadily increased, reached their peak values, and gradually decreased after Trp supplementation between 0 h and 12 h. However, the plasma 5-HT concentration displayed the opposite trend. Peak plasma total Trp and 5-HT concentrations were attained between 1 h and 3 h, while those of KYN and MT appeared between 4 h and 6 h after Trp supplementation. The plasma total Trp and Kyn concentrations were significantly higher in TRP2 and TRP3 than in CON between 1 h and 12 h (P < 0.05) after Trp supplementation. The plasma 5-HT concentration was significantly (P < 0.05) lower in TRP1 than in CON at 3 h, 4 h, 6 h, 9 h, and 12 h after Trp supplementation. The plasma MT concentrations in TRP1 and TRP2 were significantly (P < 0.05) higher than in CON at 3 h, 4 h, and 12 h, and at 0 h, 1 h, and 12 h after Trp supplementation (P < 0.05). Conclusions Dietary Trp supplementation can increase the plasma total Trp, Kyn, and MT concentrations in Yili mares and the optimal Trp dosage was 20 mg/kg BW. Implication The addition of Trp to a basal diet or feed may increase the plasma total Trp, Kyn, and MT concentrations in female horses.

Untargeted Metabolomics Identifies Biomarkers for MCADD Neonates in Dried Blood Spots

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most common inherited mitochondrial metabolic disease of fatty acid β-oxidation, especially in newborns. MCADD is clinically diagnosed using Newborn Bloodspot Screening (NBS) and genetic testing. Still, these methods have limitations, such as false negatives or positives in NBS and the variants of uncertain significance in genetic testing. Thus, complementary diagnostic approaches for MCADD are needed. Recently, untargeted metabolomics has been proposed as a diagnostic approach for inherited metabolic diseases (IMDs) due to its ability to detect a wide range of metabolic alterations. We performed an untargeted metabolic profiling of dried blood spots (DBS) from MCADD newborns (n = 14) and healthy controls (n = 14) to discover potential metabolic biomarkers/pathways associated with MCADD. Extracted metabolites from DBS samples were analyzed using UPLC-QToF-MS for untargeted metabolomics analyses. Multivariate and univariate analyses were used to analyze the metabolomics data, and pathway and biomarker analyses were also performed on the significantly identified endogenous metabolites. The MCADD newborns had 1034 significantly dysregulated metabolites compared to healthy newborns (moderated t-test, no correction, p-value ≤ 0.05, FC 1.5). A total of 23 endogenous metabolites were up-regulated, while 84 endogenous metabolites were down-regulated. Pathway analyses showed phenylalanine, tyrosine, and tryptophan biosynthesis as the most affected pathways. Potential metabolic biomarkers for MCADD were PGP (a21:0/PG/F1alpha) and glutathione, with an area under the curve (AUC) of 0.949 and 0.898, respectively. PGP (a21:0/PG/F1alpha) was the first oxidized lipid in the top 15 biomarker list affected by MCADD. Additionally, glutathione was chosen to indicate oxidative stress events that could happen during fatty acid oxidation defects. Our findings suggest that MCADD newborns may have oxidative stress events as signs of the disease. However, further validations of these biomarkers are needed in future studies to ensure their accuracy and reliability as complementary markers with established MCADD markers for clinical diagnosis.

Kynurenic Acid Acts as a Signaling Molecule Regulating Energy Expenditure and Is Closely Associated With Metabolic Diseases

Kynurenic acid (KYNA) is an important bio-active product of tryptophan metabolism. In addition to its well-known neuroprotective effects on mental health disorders, it has been proposed as a bio-marker for such metabolic diseases as atherosclerosis and diabetes. Emerging evidence suggests that KYNA acts as a signaling molecule controlling the networks involved in the balance of energy store and expenditure through GPR35 and AMPK signaling pathway. KYNA plays an important role in the pathogenesis and development of several endocrine and metabolic diseases. Exercise training promotes KYNA production in skeletal muscles and increases thermogenesis in the long term and limits weight gain, insulin resistance and inflammation. Additionally, KYNA is also present in breast milk and may act as an anti-obesity agent in infants. Although we are far from fully understanding the role of KYNA in our body, administration of KYNA, enzyme inhibitors or metabolites may serve as a potential therapeutic strategy for treating metabolic diseases. The present review provides a perspective on the current knowledge regarding the biological effects of KYNA in metabolic diseases and perinatal nutrition.

L-Theanine affects intestinal mucosal immunity by regulating short-chain fatty acid metabolism under dietary fiber feeding

To investigate the effects of l-Theanine (LTA) on intestinal mucosal immunity and the regulation of short-chain fatty acid (SCFA) metabolism under dietary fiber feeding, a 28-day feeding experiment was performed in Sprague-Dawley rats. The results show that LTA increased the proportion of Prevotella, Lachnospira, and Ruminococcus while increasing the total SCFA, acetic acid, propionic acid, and butyric acid contents in the feces. LTA also increased IgA, IgE, and IgG levels in the ileum, and increased villi height and crypt depth. Moreover, LTA upregulated the mRNA and protein expression of acetyl-CoA carboxylase 1, sterol element-binding protein 1c, fatty acid synthase, and 3-hydroxy-3-methylglutaryl coenzyme A reductase in the liver, while downregulating the expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase 1 in the colon. Our study suggests that LTA can affect intestinal mucosal immunity by regulating SCFA metabolism under dietary fiber feeding.

Hepatic Energy Metabolism Underlying Differential Lipidomic Responses to High-Carbohydrate and High-Fat Diets in Male Wistar Rats

BACKGROUND

Low-carbohydrate diets are suggested to exert metabolic benefits by reducing circulating triacylglycerol (TG) concentrations, possibly by enhancing mitochondrial activity.

OBJECTIVE

We aimed to elucidate mechanisms by which dietary carbohydrate and fat differentially affect hepatic and circulating TG, and how these mechanisms relate to fatty acid composition.

METHODS

Six-week-old, ∼300 g male Wistar rats were fed a high-carbohydrate, low-fat [HC; 61.3% of energy (E%) carbohydrate] or a low-carbohydrate, high-fat (HF; 63.5 E% fat) diet for 4 wk. Parameters of lipid metabolism and mitochondrial function were measured in plasma and liver, with fatty acid composition (GC), high-energy phosphates (HPLC), carnitine metabolites (HPLC-MS/MS), and hepatic gene expression (qPCR) as main outcomes.

RESULTS

In HC-fed rats, plasma TG was double and hepatic TG 27% of that in HF-fed rats. The proportion of oleic acid (18:1n-9) was 60% higher after HF vs. HC feeding while the proportion of palmitoleic acid (16:1n-7) and vaccenic acid (18:1n-7), and estimated activities of stearoyl-CoA desaturase, SCD-16 (16:1n-7/16:0), and de novo lipogenesis (16:0/18:2n-6) were 1.5-7.5-fold in HC vs. HF-fed rats. Accordingly, hepatic expression of fatty acid synthase (Fasn) and acetyl-CoA carboxylase (Acaca/Acc) was strongly upregulated after HC feeding, accompanied with 8-fold higher FAS activity and doubled ACC activity. There were no differences in expression of liver-specific biomarkers of mitochondrial biogenesis and activity (Cytc, Tfam, Cpt1, Cpt2, Ucp2, Hmgcs2); concentrations of ATP, AMP, and energy charge; plasma carnitine/acylcarnitine metabolites; or peroxisomal fatty acid oxidation.

CONCLUSIONS

In male Wistar rats, dietary carbohydrate was converted into specific fatty acids via hepatic lipogenesis, contributing to higher plasma TG and total fatty acids compared with high-fat feeding. In contrast, the high-fat, low-carbohydrate feeding increased hepatic fatty acid content, without affecting hepatic mitochondrial fatty acid oxidation.

NAD+ Metabolism, Metabolic Stress, and Infection

Nicotinamide adenine dinucleotide (NAD⁺) is an essential metabolite with wide-ranging and significant roles in the cell. Defects in NAD⁺ metabolism have been associated with many human disorders; it is therefore an emerging therapeutic target. Moreover, NAD⁺ metabolism is perturbed during colonization by a variety of pathogens, either due to the molecular mechanisms employed by these infectious agents or by the host immune response they trigger. Three main biosynthetic pathways, including the de novo and salvage pathways, contribute to the production of NAD⁺ with a high degree of conservation from bacteria to humans. De novo biosynthesis, which begins with l-tryptophan in eukaryotes, is also known as the kynurenine pathway. Intermediates of this pathway have various beneficial and deleterious effects on cellular health in different contexts. For example, dysregulation of this pathway is linked to neurotoxicity and oxidative stress. Activation of the de novo pathway is also implicated in various infections and inflammatory signaling. Given the dynamic flexibility and multiple roles of NAD⁺ intermediates, it is important to understand the interconnections and cross-regulations of NAD⁺ precursors and associated signaling pathways to understand how cells regulate NAD⁺ homeostasis in response to various growth conditions. Although regulation of NAD⁺ homeostasis remains incompletely understood, studies in the genetically tractable budding yeast Saccharomyces cerevisiae may help provide some molecular basis for how NAD⁺ homeostasis factors contribute to the maintenance and regulation of cellular function and how they are regulated by various nutritional and stress signals. Here we present a brief overview of recent insights and discoveries made with respect to the relationship between NAD⁺ metabolism and selected human disorders and infections, with a particular focus on the de novo pathway. We also discuss how studies in budding yeast may help elucidate the regulation of NAD⁺ homeostasis.