Dietary apple polyphenols increase skeletal muscle capillaries in Wistar rats

Dietary apple polyphenols enhance mitochondrial turnover and respiratory chain enzymes

Previous studies have demonstrated the beneficial effects of apple polyphenol (AP) intake on muscle endurance. Since mitochondria are critical for muscle endurance, we investigated mitochondrial enzyme activity, biogenesis, degradation and protein quality control. Twenty-four Wistar rats were randomly fed a 5% AP diet (5% AP group, n = 8), a 0.5% AP diet (0.5% AP group, n = 8), or a control diet (control group, n = 8). After a 4-week feeding period, the expression level of peroxisome proliferator-activated receptor γ coactivator-1α, a mitochondrial biosynthetic factor, did not increase, whereas that of transcription factor EB, another regulator of mitochondrial synthesis, significantly increased. Moreover, the mitochondrial count did not differ significantly between the groups. In contrast, mitophagy-related protein levels were significantly increased. The enzymatic activities of mitochondrial respiratory chain complexes II, III and IV were significantly higher in the AP intake group than in the control group. We conclude that AP feeding increases the activity of respiratory chain complex enzymes in rat skeletal muscles. Moreover, mitochondrial biosynthesis and degradation may have increased in AP-treated rats. NEW FINDINGS: What is the central question of this study? Does the administration of apple polyphenols (AP) affect mitochondrial respiratory chain complex enzyme activity, biogenesis, degradation and protein quality control in rat skeletal muscles? What is the main finding and its importance? AP feeding increases respiratory chain complex enzyme activity in rat skeletal muscle. Moreover, AP administration increases transcription factor EB activation, and mitophagy may be enhanced to promote degradation of dysfunctional mitochondria, but mitochondrial protein quality control was not affected.

Electrically stimulated contractile activity-induced transcriptomic responses and metabolic remodeling in C2C12 myotubes: twitch vs. tetanic contractions

The contraction of myotubes using electrical pulse stimulation is a research tool used to mimic muscle contractile activity and exercise in rodents and humans. Most protocols employed in previous work used low-frequency twitch contractions. However, high-frequency tetanus contractions that are more physiologically relevant to muscle contractions in vivo are poorly characterized. In this report, the similarities and differences in acute responses and chronic adaptations with different contractile modes using twitches (2 Hz, continuous, 3 h) and tetanus (66 Hz, on: 5 s/off: 5 s, 3 h) were investigated. RNA sequencing-based transcriptome analysis and subsequent bioinformatics analysis suggest that tetanus may promote bioenergetic remodeling rather than twitch. Based on in silico analyses, metabolic remodeling after three contractile sessions of twitch and tetanus were investigated. Although twitch and tetanus had no significant effect on glycolysis, both types of contraction upregulated glucose oxidation capacity. Both twitch and tetanus qualitatively caused mitochondrial adaptations (increased content, respiratory chain enzyme activity, and respiratory function). The magnitude of adaptation was much greater under tetanus conditions. Our findings indicate that the contraction of myotubes by tetanus may be a useful experimental model, especially in the study of metabolic adaptations in C₂C₁₂ myotubes.

Grape Polyphenols Ameliorate Muscle Decline Reducing Oxidative Stress and Oxidative Damage in Aged Rats

A large number of studies have demonstrated the implication of oxidative stress (OxS) in the pathogenesis of ageing-related muscle decline and atrophy. The key mechanism is related to the OxS-induced production of free radicals, with the consequent increase in oxidative damage, resulting in affected muscle quality and strength. The present study aimed to evaluate the efficacy of a grape polyphenol-based nutraceutical formulation (Taurisolo^®) in reducing the OxS in muscle of aged rats. A group of 16 aged (20 months) rats were orally administered with Taurisolo^® (n = 8; 100 mg/kg Taurisolo^®) or placebo (n = 8; 50 mg/kg maltodextrin); an additional group of eight young (three months) rats were also treated with placebo. All the treatments were orally administered for 30 days. The activities of antioxidant enzymes, the levels of malondialdehyde (MDA) and nitrotyrosine (N-Tyr) and the expression of OxS- and inflammation-related genes were evaluated on the gastrocnemius muscle. In muscle samples of the treated-group, increased activity of antioxidant enzymes, reduced MDA and N-Tyr levels and increased expression of antioxidant and anti-inflammatory genes were observed in respect to the placebo. Data herein presented suggest that the chronic treatment with Taurisolo^® significantly reduces oxidative damage and improves muscle performance in aged rats.

Acetaldehyde dehydrogenase 2 deficiency increases mitochondrial reactive oxygen species emission and induces mitochondrial protease Omi/HtrA2 in skeletal muscle

Acetaldehyde dehydrogenase 2 (ALDH2) is an enzyme involved in redox homeostasis as well as the detoxification process in alcohol metabolism. Nearly 8% of the world’s population have an inactivating mutation in the ALDH2 gene. However, the expression patterns and specific functions of ALDH2 in skeletal muscles are still unclear. Herein, we report that ALDH2 is expressed in skeletal muscle and is localized to the mitochondrial fraction. Oxidative muscles had a higher amount of ALDH2 protein than glycolytic muscles. We next comprehensively investigated whether ALDH2 knockout in mice induces mitochondrial adaptations in gastrocnemius muscle (for example, content, enzymatic activity, respiratory function, supercomplex formation, and functional networking). We found that ALDH2 deficiency resulted in partial mitochondrial dysfunction in gastrocnemius muscle because it increased mitochondrial reactive oxygen species (ROS) emission (2′,7′-dichlorofluorescein and MitoSOX oxidation rate during respiration) and the frequency of regional mitochondrial depolarization. Moreover, we determined whether ALDH2 deficiency and the related mitochondrial dysfunction trigger mitochondrial stress and quality control responses in gastrocnemius muscle (for example, mitophagy markers, dynamics, and the unfolded protein response). We found that ALDH2 deficiency upregulated the mitochondrial serine protease Omi/HtrA2 (a marker of the activation of a branch of the mitochondrial unfolded protein response). In summary, ALDH2 deficiency leads to greater mitochondrial ROS production, but homeostasis can be maintained via an appropriate stress response.

Effects of Dietary Apple Polyphenols Supplementation on Hepatic Fat Deposition and Antioxidant Capacity in Finishing Pigs

Simple Summary

Excessive fat deposition (5–10%) in the liver could lead to liver damage and nonalcohol fatty liver disease (NAFLD). However, there is no satisfactory safe and effective measure of preventive and therapeutic treatments so far. Thus, the prevention of excessive fat deposition through diet modification might be a better strategy to protect humans from metabolic diseases. Due to the anatomical and physiological similarities between humans and pigs, the present study took the finishing pig as an animal model to investigate the effects of apple polyphenols on hepatic fat deposition and antioxidant capacity and their mechanisms. The present study indicated that apple polyphenols might be an effective dietary supplementation for decreasing the excessive fat deposition in liver tissue, improving lipid profiles and increasing the antioxidant capacity of finishing pigs. This study provides a better preventive strategy to protect humans from excessive fat deposition in the liver.

Abstract

Excessive fat deposition in the liver could lead to fatty liver and an increased risk of many metabolic diseases. Apple polyphenols (APPs), the major antioxidants in apples, possess wide-ranging beneficial biological functions. The present study aimed to investigate the effects of APPs on hepatic fat deposition and antioxidant capacity in finishing pigs, and their mechanisms. Results showed that APPs improved lipid profiles, increased antioxidant enzyme activities and reduced the fat deposition in the liver. In the liver, SOD1, CAT, GPX1, GST, NF-E2-related nuclear factor 2 (Nrf2), hormone sensitive lipase (HSL), carnitine palmitoyl transferase-1b (CPT1b), peroxisome proliferator-activated receptor α (PPARα), cholesterol 7α-hydroxylase (CYP7A1) and low-density lipoprotein receptor (LDL-R) mRNA levels were increased by APPs, while Kelch-like ECH-associated protein 1 (Keap1) mRNA level, C16:0 and C20:4n-6 proportions and Δ9-18 dehydrogenase activity were decreased. In conclusion, this study indicated that APPs might be an effective dietary supplementation for improving lipid profiles, increasing antioxidant capacities and decreasing fat deposition in the liver.

Effects of dietary apple polyphenol supplementation on carcass traits, meat quality, muscle amino acid and fatty acid composition in finishing pigs

As health awareness is increasing, consumers have changed their focus with a desire to purchase safer, healthier, and higher quality and nutritional value meat. The aim of this study was to investigate whether dietary apple polyphenol (APP) supplementation in finishing pigs could provide pork with high quality and nutritional value. In the present study, 36 castrated Duroc × Landrace × Yorkshire pigs with an average body weight of 71.25 ± 2.40 kg were randomly divided into three treatments and fed with a basal diet supplemented with 0, 400, or 800 mg kg^-1 APPs for 7 weeks. The results showed that dietary 800 mg kg^-1 APP supplementation not only decreased backfat thickness and abdominal adipose tissue index but also decreased L* (lightness) and b* (yellowness) in the longissimus dorsi (LD) muscle. The LD muscle crude protein content, the proportions of essential amino acids, flavor amino acids, and total amino acids, as well as the amino acid transporter (SLC7A1, SLC7A2, SLC7A7, SLC1A2) mRNA levels were increased by 800 mg kg^-1 APPs. The proportions of docosahexaenoic acid and n-3 polyunsaturated fatty acid (PUFA) and the ratio of PUFA to saturated fatty acid in LD muscle were increased by 400 mg kg^-1 APPs. Meanwhile, dietary 400 mg kg^-1 and 800 mg kg^-1 APP supplementation decreased the contents of blood urea nitrogen and total cholesterol, as well as increased the content of inosinic acid in LD muscle. In conclusion, these results suggested that dietary 800 mg kg^-1 APP supplementation improved the carcass traits, meat color, and meat flavor in finishing pigs. These results also suggested that dietary 400 mg kg^-1 and 800 mg kg^-1 APP supplementation improved the meat nutritional value in finishing pigs. The present study provides effective evidence for the application of APP supplementation for healthy high-quality and nutritional value pork production.

Cast immobilization of hindlimb upregulates sarcolipin expression in atrophied skeletal muscles and increases thermogenesis in C57BL/6J mice

Mechanical unloading impairs cytosolic calcium (Ca²⁺) homeostasis in skeletal muscles. In this study, we investigated whether sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) itself or one of the regulators of the Ca²⁺ SERCA pump, sarcolipin (SLN), is altered to deregulate Ca²⁺ homeostasis in cast immobilized, atrophied muscles. Hindlimb muscles of 8-wk-old male C57BL/6J mice were subjected to bilateral cast immobilization for 2 wk. Two-week-cast immobilization induced both body weight and skeletal muscle loss. Highly phosphorylated Ca²⁺/calmodulin-dependent protein kinase II in the atrophied muscles suggested that cytosolic Ca²⁺ concentration was elevated. Extremely high expression levels of SLN mRNA and protein were observed in the atrophied muscles. Upregulation of SLN at the transcriptional level was supported by low RCAN1 expression, which is a negative regulator of SLN. We treated C₂C₁₂ cells with dexamethasone to mimic muscle atrophy in vitro and showed a direct relationship between high SLN mRNA expression and low Ca²⁺ uptake by sarcoplasmic reticulum. Since SLN reportedly plays a role in nonshivering thermogenesis, we performed a cold tolerance test of the whole body. As a result, we found that mice with cast immobilization showed high cold tolerance, suggesting that cast immobilization promoted whole body thermogenesis. Although the activity level was decreased during cast immobilization without change in food intake, adipose tissue weights also decreased significantly after cast immobilization. Concomitantly, we conclude that cast immobilization of hindlimb increased thermogenesis in C57Bl/6J mice, probably via high expression of SLN.

Dietary apple polyphenols supplementation enhances antioxidant capacity and improves lipid metabolism in weaned piglets

Apple polyphenols (APPs) are biologically active flavonoids that have antioxidant, anti-inflammatory, improving insulin sensitivity, hypocholesterolaemic effect and antiviral properties. This study was conducted to explore effects of dietary APPs supplementation on antioxidant activities and lipid metabolism in weaned piglets. Fifty-four weaned piglets (half male and female) were randomly divided into three groups with six replicates in each group and three piglets in each repetition. Piglets were fed control diet (basal diet) or a control diet supplemented with 400 mg/kg or 800 mg/kg APPs for 6 weeks. Blood and liver samples were collected to determine biochemical, antioxidant and lipid metabolism parameters. Here we showed that dietary APPs supplementation increased HDL-C and decreased T-CHO, TG and LDL-C concentrations. Dietary APPs supplementation increased antioxidative capacity in serum and CAT activity in liver, and significantly increased the mRNA expressions of CAT, GST and SOD1 in liver. ACC mRNA level and LPL activity were tended to decrease by APPs. HMG-CoAR, CTP7A1, CD36 and FATP1 mRNA levels were decreased by APPs, while LDL-R, PGC-1α, Sirt1 and CPT1b mRNA levels were increased by 400 mg/kg APPs. No alterations in growth performance were found in all treatments. This study firstly provided the evidence that dietary APPs supplementation could enhance systemic antioxidant capacity and improve lipid metabolism in weaned piglets. The mechanism by which APPs improve lipid metabolism might be through regulating hepatic cholesterol metabolism and increasing fatty acid oxidation, and decreasing fatty acid uptake and de novo synthesis.