Changes in kinetics of carnitine palmitoyltransferase in liver and skeletal muscle of dogs (Canis familiaris) throughout growth and development

Myostatin serum levels depends on age and diet in athletic and no athletic dogs

Myostatin is a growth factor related to muscular mass atrophy via mTOR pathway inhibition. Mutations in this gene have been correlated with high muscular mass development in different species of mammals, including human and dogs. Different studies have shown that sport practice increases myostatin gene expression. Some of them were conducted in canine breeds selected for different sport practices, including mushing sports. In this study, body weight, muscular mass, and serum levels of myostatin were analysed in different canine breeds, selected, and not selected for sprint and middle-distance racing, and the effect on epidemiological factors was evaluated. Sex, reproductive status, and canine breed affects body weight and muscular mass, being higher in males, and in sled canine breed. Age has an effect in body weight and myostatin serum levels, being lower in elder dogs. Sport practice and type of diet had an effect in muscular mass development but not in myostatin serum levels. Results showed a high positive correlation between muscular mass and body weight but not with myostatin levels. These results suggest that independent-myostatin mechanisms of mTOR pathway regulation could be related to muscular mass development in dogs.

Intestinal Carnitine Status and Fatty Acid Oxidation in Response to Clofibrate and Medium-Chain Triglyceride Supplementation in Newborn Pigs

To investigate the role of peroxisome proliferator-activated receptor alpha (PPARα) in carnitine status and intestinal fatty acid oxidation in neonates, a total of 72 suckled newborn piglets were assigned into 8 dietary treatments following a 2 (±0.35% clofibrate) × 4 (diets with: succinate+glycerol (Succ), tri-valerate (TC5), tri-hexanoate (TC6), or tri-2-methylpentanoate (TMPA)) factorial design. All pigs received experimental milk diets with isocaloric energy for 5 days. Carnitine statuses were evaluated, and fatty acid oxidation was measured in vitro using [1-¹⁴C]-palmitic acid (1 mM) as a substrate in absence or presence of L659699 (1.6 µM), iodoacetamide (50 µM), and carnitine (1 mM). Clofibrate increased concentrations of free (41%) and/or acyl-carnitine (44% and 15%) in liver and plasma but had no effects in the intestine. The effects on carnitine status were associated with the expression of genes involved in carnitine biosynthesis, absorption, and transportation. TC5 and TMPA stimulated the increased fatty acid oxidation rate induced by clofibrate, while TC6 had no effect on the increased fatty acid oxidation induced by clofibrate (p > 0.05). These results suggest that dietary clofibrate improved carnitine status and increased fatty acid oxidation. Propionyl-CoA, generated from TC5 and TMPA, could stimulate the increased fatty acid oxidation rate induced by clofibrate as anaplerotic carbon sources.

Ontogeny of carnitine biosynthesis in Sus scrofa domesticus, inferred from γ-butyrobetaine hydroxylase (dioxygenase) activity and substrate inhibition

γ-Butyrobetaine hydroxylase (γ-BBH) is the last limiting enzyme of the l-carnitine biosynthesis pathway and plays an important role in catalyzing the hydroxylation of γ-butyrobetaine (γ-BB) to l-carnitine. To study the developmental effect of substrate concentration on the enzyme's specific activity, kinetics of γ-BBH were measured in liver and kidney from newborn and 1-, 7-, 21-, 35-, 56-, and 210-day-old domestic pigs. Fresh tissue homogenates were assayed under nine concentrations of γ-BB from 0 to 1.5 mM. Substrate inhibition associated with age was observed at ≥0.6 mM of γ-BB. Hepatic activity was low at birth but increased after 1 day. By 21 days, the activity rose by 6.6-fold (P < 0.05) and remained constant after 56 days. Renal activity was higher than in liver at birth but remained constant through 35 days. By 56 days, the velocity increased by 44% over the activity at birth (P < 0.05). The apparent K_m for γ-BB at birth on average was 2.8-fold higher than at 1 day. The K_m value was 60% higher in kidney than liver during development but showed no difference in adult pigs. The total organ enzyme activity increased by 130-fold for liver and 18-fold for kidney as organ weight increased from birth to 56 days. In conclusion, age and substrate affect γ-BBH specific activity and K_m for γ-BB in liver and kidney. Whereas the predominant organ for carnitine synthesis is likely the kidney at birth, the liver appears to predominate after the pig exceeds 7 days of age.

Ontogeny and kinetics of carnitine palmitoyltransferase I in hepatopancreas and skeletal muscle of grass carp (Ctenopharyngodon idella)

The ontogeny and kinetics of carnitine palmitoyltransferase I (CPT I) were investigated in hepatopancreas and muscle throughout four developmental stages (newly hatched larvae, 1-month-old juvenile, 3-month-old, and 6-month-old, respectively) of grass carp Ctenopharyngodon idella. In hepatopancreas, the maximal velocity (Vmax) significantly increased from hatching to 1-month-old grass carp and then gradually declined at 6-month-old grass carp. In muscle, CPT I activity was the highest at 1-month-old grass carp, nearly twofold higher than that at hatching (P < 0.05). The Michaelis constant (Km) value was also the highest for 1-month-old in both tested tissues. Carnitine concentrations (FC, AC and TC) were the lowest for 3-month-old grass carp and remained relatively constant in both tissues from fish under the other developmental stages. The FC concentration in hepatopancreas and muscle at four developmental stages were less than the respective Km, indicating that grass carp required supplemental carnitine in their food to ensure that CPT I activity was not constrained by carnitine availability.

Effects of waterborne copper exposure on carnitine composition, kinetics of carnitine palmitoyltransferases I (CPT I) and mRNA levels of CPT I isoforms in yellow catfish Pelteobagrus fulvidraco

The present study was conducted to determine the effect of waterborne copper (Cu) exposure on carnitine concentration, carnitine palmitoyltransferases I (CPT I) kinetics, and expression levels of four CPT I isoforms in the liver, muscle and heart of yellow catfish Pelteobagrus fulvidraco. Yellow catfish were exposed to four waterborne copper (Cu) concentrations (2 (control), 24 (low), 71 (medium), 198 (high) μg Cu/l, respectively) for 6weeks. Waterborne Cu exposure increased maximal reaction rates (Vmax) in the liver and muscle, but not in the heart. Michaelis-Menten constants (Km) tended to increase in the liver, but decreased in the heart after Cu exposure. The contents of total carnitine (TC) and acylcarnitine (AC) in the liver, and free carnitine (FC) in the muscle increased with increasing waterborne Cu concentrations, while FC content in the muscle declined with the increase of Cu levels. Waterborne Cu exposure also significantly influenced carnitine composition and profiles in heart. The mRNA expression of CPT Iα1a, CPT Iα1b and CPT Iα2a in the liver, and CPT Iα1a, CPT Iα1b and CPT Iβ in the muscle as well as CPT Iα1a in the heart were up-regulated by Cu exposure. Additionally, correlations were observed in the expression levels of CPT I isoforms and Km for carnitine, and between CPT I isoform expression and CPT I activity. To our knowledge, for the first time, the present study provided evidence that waterborne Cu exposure could influence carnitine composition, CPT I kinetics and mRNA levels of four CPT I isoforms in yellow catfish, which served to increase our understanding of the mechanisms underlying lipid catabolism during Cu exposure.

Differential effects of dietary Cu deficiency and excess on carnitine status, kinetics and expression of CPT I in liver and muscle of yellow catfish Pelteobagrus fulvidraco

The present study was conducted to determine the effect of dietary Cu deficiency and excess on carnitine status, kinetics and expression of CPT I in the liver and muscle of juvenile yellow catfish Pelteobagrus fulvidraco. To this end, yellow catfish were fed 0.76 (Cu deficiency), 4.18 (adequate Cu) and 92.45 (Cu excess) mg Cu kg(-1) diet, respectively, for 8 weeks. In the liver, Cu deficiency did not significantly affect the contents of FC, TC and AC, and the ratios of AC/FC and FC/TC. However, Cu excess reduced FC, TC and AC contents, and the ratio of AC/FC, but increased FC/TC ratio. In the muscle, dietary Cu levels showed no significant effects on the contents of FC, TC and AC as well as the ratio of FC/TC, but Cu excess significantly increased the ratio of AC/FC. Compared to the adequate Cu group, dietary Cu deficiency did not significantly affect the Vmax and Km values, and the ratio of Vmax/Km in the liver and muscle. However, Cu excess decreased Vmax and Vmax/Km ratio in the liver, and increased Vmax in the muscle. The mRNA expression of CPT Iα1a, CPT Iα1b, CPT Iα2a and CPT Iβ in the liver and muscle was influenced by dietary Cu levels. To our knowledge, the present study provided, for the first time, evidence that dietary Cu deficiency and excess differentially influenced carnitine status, kinetics and expression profiles of CPT I of yellow catfish, which would extend our understanding on Cu nutrition in fish.

Differential effects of dietary Cu deficiency and excess on carnitine status, kinetics and expression of CPT I in liver and muscle of yellow catfish Pelteobagrus fulvidraco

The present study was conducted to determine the effect of dietary Cu deficiency and excess on carnitine status, kinetics and expression of CPT I in the liver and muscle of juvenile yellow catfish Pelteobagrus fulvidraco. To this end, yellow catfish were fed 0.76 (Cu deficiency), 4.18 (adequate Cu) and 92.45 (Cu excess) mg Cu kg(-1) diet, respectively, for 8 weeks. In the liver, Cu deficiency did not significantly affect the contents of FC, TC and AC, and the ratios of AC/FC and FC/TC. However, Cu excess reduced FC, TC and AC contents, and the ratio of AC/FC, but increased FC/TC ratio. In the muscle, dietary Cu levels showed no significant effects on the contents of FC, TC and AC as well as the ratio of FC/TC, but Cu excess significantly increased the ratio of AC/FC. Compared to the adequate Cu group, dietary Cu deficiency did not significantly affect the Vmax and Km values, and the ratio of Vmax/Km in the liver and muscle. However, Cu excess decreased Vmax and Vmax/Km ratio in the liver, and increased Vmax in the muscle. The mRNA expression of CPT Iα1a, CPT Iα1b, CPT Iα2a and CPT Iβ in the liver and muscle was influenced by dietary Cu levels. To our knowledge, the present study provided, for the first time, evidence that dietary Cu deficiency and excess differentially influenced carnitine status, kinetics and expression profiles of CPT I of yellow catfish, which would extend our understanding on Cu nutrition in fish.

Differential effects of the chronic and acute zinc exposure on carnitine composition, kinetics of carnitine palmitoyltransferases I (CPT I) and mRNA levels of CPT I isoforms in yellow catfish Pelteobagrus fulvidraco

The present study is conducted to determine the effect of acute and chronic zinc (Zn) exposure on carnitine concentration, carnitine palmitoyltransferases I (CPT I) kinetics, and expression levels of CPT I isoforms in liver, muscle and heart of yellow catfish Pelteobagrus fulvidraco. To this end, yellow catfish are subjected to chronic waterborne Zn exposure (0.05 mg Zn L(-1), 0.35 mg Zn L(-1) and 0.86 mg Zn L(-1), respectively) for 8 weeks and acute Zn exposure (0.05 mg Zn L(-1) and 4.71 mg L(-1)Zn, respectively) for 96 h, respectively. Reduced Michaelis-Menten constants (Km) and maximal reaction rates (Vmax) values in liver and muscle are observed in fish exposed to chronic Zn concentration. In contrast, Vmax and Km values in heart increase with increasing Zn concentration. Chronic Zn exposure also significantly influences the contents of free carnitine (FC), total carnitine (TC) and acylcarnitine (AC) in liver and heart, but not in muscle. The acute Zn exposure significantly increases FC, AC, TC contents in liver and muscle, but reduces their contents in heart. The chronic and acute Zn exposure influences the mRNA levels of four CPT I isoforms (CPT Iα1b, CPT Iβ, CPT Iα2a and CPT Iα1a) in liver, muscle and heart. Furthermore, correlations are observed in the mRNA levels between CPT I isoforms and Km, and between isoforms expression and activity of CPT I. Thus, chronic and acute Zn exposure shows differential effects on carnitine content, CPT I kinetics and mRNA levels of four CPT I isoforms in yellow catfish, which provides new mechanism for Zn exposure on lipid metabolism and also novel insights into Zn toxicity in fish.

trans-10,cis-12 conjugated linoleic acid improved growth performance, reduced lipid deposition and influenced CPT I kinetic constants of juvenile Synechogobius hasta

trans-10,cis-12 (t10c12) Conjugated linoleic acid (CLA) reduced body lipid deposition in various experimental animals, but the mechanisms involved were still emerging. Carnitine palmitoyltransferase I (CPT I) catalyzes an important regulatory step in lipid metabolism. At present, no studies, to our knowledge, have evaluated the kinetic constants influenced by dietary CLA in fish. In the present study, we tested the hypothesis that changes in body lipid content in fish as a response to dietary t10c12 CLA was related to the change of CPT I kinetic constants [Michaelis constant (K m), maximal velocity and catalytic efficiency for carnitine and palmitoyl-CoA]. Juvenile Synechogobius hasta were fed three experimental diets with fish oil replaced with 0 (control), 1, or 2 % t10c12 CLA for 8 weeks. Weight gain, specific growth rate and protein efficiency rate increased with dietary t10c12 CLA level. Dietary t10c12 CLA addition significantly reduced lipid contents both in liver and muscle. Dietary CLA addition also improved CPT I activities in muscle but did not significantly influence hepatic CPT I activity. CPT I kinetic parameters (K m, V max and catalytic efficiency) were significantly influenced by t10c12 CLA. CPT I catalytic efficiencies with carnitine and palmitoyl-CoA as substrates were higher in muscle and liver of fish fed increasing t10c12 CLA. For the first time, the findings demonstrated effect of dietary CLA addition on CPT I kinetics in fish and supported our starting hypothesis that dietary t10c12 CLA addition induced alterations in CPT I kinetic constants of muscle and liver. Increased CPT I catalytic efficiency might be the main reason for reduced lipid deposition in these tissues by dietary t10c12 CLA supplementation.

The effect of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) on fatty acid oxidation in hepatocytes isolated from neonatal piglets

In the present study, the effect of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) on long-chain fatty acid oxidation by hepatocytes isolated from suckled neonatal pig liver (a low ketogenic and lipogenic tissue) was tested. Incubation of hepatocytes with AICAR (0.5 mM) in the presence of 1 mM of carnitine and 10 mM of glucose for 1 hour at 37°C had no significant effect on total [1-¹⁴C]-palmitate (0.5 mM) oxidation (¹⁴CO₂ and ¹⁴C-Acid soluble products (ASP)). Consistent with the fatty acid oxidation, carnitine palmitoyltransferase I activity and inhibition of its activity by malonyl-CoA (10 μM) assayed in cell homogenate also remained constant. However, addition of AICAR to the hepatocytes decreased ¹⁴CO₂ production by 18% compared to control (p < 0.06). The reduction of labeled carboxylic carbon accumulated in CO₂ caused a significant difference in distribution of oxidative products between ¹⁴CO₂ and ¹⁴C-ASP (p < 0.03) compared with the control. It was also noticed that acetyl-CoA carboxylase (ACC) was increased by AICAR (p < 0.03), indicating that ACC might drive acetyl-CoA toward fatty acid synthesis pathway and induce an increase in distribution of fatty acid carbon to ¹⁴C-ASP. Addition of insulin to hepatocyte incubations with AICAR did not change the oxidative product distribution between CO₂ and ASP, but further promoted ACC activity. The increased ACC activity was 70% higher than in the control group when citrate was absent in the reaction medium and was 30% higher when citrate was present in the medium. Our results suggest that AICAR may affect the distribution of metabolic products from fatty acid oxidation by changing ACC activity in hepatocyte isolated from suckled neonatal piglets; however, the basis for the increase in ACC activity elicited by AICAR is not apparent.

Maternal dietary L-carnitine supplementation influences fetal carnitine status and stimulates carnitine palmitoyltransferase and pyruvate dehydrogenase complex activities in swine

Effects of increasing maternal L-carnitine on carnitine status and energy metabolism in the fetus were evaluated by feeding pregnant swine a corn-soybean-based diet containing either 0 or 50 mg/kg added L-carnitine (n = 10/treatment) during the first 70 d of gestation. Carnitine, carnitine palmitoyltransferase (CPT), and pyruvate dehydrogenase complex (PDHC) activities were analyzed in tissues collected from fetuses on d 55 and 70. Maternal L-carnitine supplementation increased both fetal free and long-chain carnitine concentrations by 45% in liver and free carnitine by 31% in heart tissues but did not affect kidney tissue. Elevations in free and acylcarnitines increased with gestational age from 55 to 70 d in liver but not in heart and kidney. The increased carnitine concentrations resulted in a 45% increase in PDHC activity in heart and liver on d 70 of gestation but did not affect kidney and liver on d 55 of gestation. The increases in carnitine concentrations were accompanied by a 70% increase in hepatic CPT activity in 70-d-old fetuses, but activities in heart and kidney were unaffected. The Michaelis constant (K(m)) of CPT for carnitine in fetal tissues was not influenced by carnitine supplementation (P > 0.1). Notably, the concentrations of carnitine measured on d 70 were only 25-40% of the K(m) values in liver, 60-70% in heart, and 30-40% in kidney (P < 0.001). We conclude that carnitine ingestion during pregnancy increases fetal carnitine concentrations and stimulates heart PDHC and liver CPT activity without altering carnitine K(m).

Ontogeny of carnitine palmitoyltransferase I activity, carnitine-Km, and mRNA abundance in pigs throughout growth and development

Carnitine palmitoyltransferase (CPT) I catalyzes an important regulatory step in lipid metabolism; however, no studies, to our knowledge, have evaluated the molecular and kinetic [maximal velocity and Michaelis constant (K(m)) for carnitine] ontogeny of CPT I and prevailing tissue concentrations of carnitine in pigs. To this end, hepatic and skeletal muscle tissues were examined at various ages: birth; 24 h; 1, 3, 5, and 8 wk of age; and adult. Hepatic and skeletal muscle CPT I specific activities were low at birth and increased 100 and 70%, respectively, during the first week of life (P < 0.05). Skeletal muscle transcript amounts were 2.7-fold greater (P < 0.001) in 24-h-old pigs relative to newborns, whereas hepatic CPT I mRNA remained constant at each age studied. The apparent K(m) for carnitine decreased 48% (P < 0.05) during the initial 3 wk of life in liver and decreased 40% (P < 0.05) during the first week of life in skeletal muscle. Plasma and liver free carnitine concentrations increased 95 and 62%, respectively, within 24 h after birth (P < 0.05) and hepatic carnitine concentrations remained constant through 5 wk of age. Consequently, hepatic carnitine concentrations were 20-80% greater (P < 0.05) than the K(m) for carnitine during the suckling period. Skeletal muscle carnitine met or exceeded the apparent K(m) for carnitine at each stage of development. Collectively, these findings suggest that postnatal increases in CPT I activity during the suckling period are accompanied by increased tissue carnitine; however, the lack of hepatic CPT I mRNA induction and low activity reported in both tissues prior to 1 wk of age may limit postnatal lipid utilization during the piglet's transition to extra-uterine life.

Metabolic Effects of Abomasal l-Carnitine Infusion and Feed Restriction in Lactating Holstein Cows

L-Carnitine is required for mitochondrial fatty acid oxidation, but the effects of carnitine supplementation on nutrient metabolism during dry matter intake depression have not been determined in dairy cows. Studies in other species have revealed responses to L-carnitine that may be of specific benefit to dairy cows during the periparturient period. Eight lactating Holstein cows (132 +/- 36 d in milk) were used in a replicated 4 x 4 Latin square experiment with 14-d periods. Treatments were factorial combinations of abomasal infusion of either water or L-carnitine (20 g/d; d 5 to 14) and either ad libitum or restricted intake (50% of previous 5-d dry matter intake; d 10 to 14) of a balanced lactation diet. Liver and muscle biopsies were obtained on d 14 of each period. Feed restriction induced negative balances of energy and metabolizable protein. In feed-restricted cows, carnitine infusion increased 3.5% fat-corrected milk yield compared with those infused with water. Total carnitine concentration in liver was increased in feed-restricted cows infused with carnitine but not in feed-restricted cows infused with water. Carnitine infusion stimulated in vitro oxidation of [1-(14)C] palmitate to acid-soluble products and decreased the proportion of [1-(14)C] palmitate that was converted to esterified products by liver slices. Feed-restricted cows infused with carnitine had lower liver total lipid concentration and tended to have decreased triglyceride accumulation compared with feed-restricted cows infused with water. Plasma nonesterified fatty acid concentration was not altered by carnitine infusion but was increased by feed restriction; serum beta-hydroxybutyric acid was increased by carnitine infusion in feed-restricted cows. In cows fed for ad libitum intake, carnitine infusion affected beta-hydroxybutyric acid, insulin, and urea N in serum, liver glycogen concentration, and in vitro alanine oxidation by liver slices, suggesting that hepatic and peripheral nutrient metabolism was influenced. L-Carnitine infusion effectively decreased liver lipid accumulation during feed restriction as a result of greater capacity for hepatic fatty acid oxidation. Further research examining dietary supplementation of L-carnitine during the periparturient period is warranted.