Electron transport chain defect and inefficient respiration may underlie pulmonary hypertension syndrome (ascites)-associated mitochondrial dysfunction in broilers

Comparative Metabolomics in Single Ventricle Patients after Fontan Palliation: A Strong Case for a Targeted Metabolic Therapy

Most studies on single ventricle (SV) circulation take a physiological or anatomical approach. Although there is a tight coupling between cardiac contractility and metabolism, the metabolic perspective on this patient population is very recent. Early findings point to major metabolic disturbances, with both impaired glucose and fatty acid oxidation in the cardiomyocytes. Additionally, Fontan patients have systemic metabolic derangements such as abnormal glucose metabolism and hypocholesterolemia. Our literature review compares the metabolism of patients with a SV circulation after Fontan palliation with that of patients with a healthy biventricular (BV) heart, or different subtypes of a failing BV heart, by Pubmed review of the literature on cardiac metabolism, Fontan failure, heart failure (HF), ketosis, metabolism published in English from 1939 to 2023. Early evidence demonstrates that SV circulation is not only a hemodynamic burden requiring staged palliation, but also a metabolic issue with alterations similar to what is known for HF in a BV circulation. Alterations of fatty acid and glucose oxidation were found, resulting in metabolic instability and impaired energy production. As reported for patients with BV HF, stimulating ketone oxidation may be an effective treatment strategy for HF in these patients. Few but promising clinical trials have been conducted thus far to evaluate therapeutic ketosis with HF using a variety of instruments, including ketogenic diet, ketone esters, and sodium-glucose co-transporter-2 (SGLT2) inhibitors. An initial trial on a small cohort demonstrated favorable outcomes for Fontan patients treated with SGLT2 inhibitors. Therapeutic ketosis is worth considering in the treatment of Fontan patients, as ketones positively affect not only the myocardial energy metabolism, but also the global Fontan physiopathology. Induced ketosis seems promising as a concerted therapeutic strategy.

Integrated transcriptome analysis for the hepatic and jejunal mucosa tissues of broiler chickens raised under heat stress conditions

Background

Heat stress (HS) is one of the most important threats for the current poultry industry. Therefore, many efforts have been made to ameliorate the adverse effect of HS on poultry production; however, physiological and molecular mechanisms pertaining to HS are still limited in poultry. Therefore, the objective of the current study was to investigate functional alterations based on individual and integrated transcriptomes in the liver and jejunal mucosa tissues of broiler chickens exposed to HS conditions.

Results

Broiler chickens exposed to HS showed decreased growth performance and increased corticosterone concentrations in the feather. In the transcriptome analysis, the number of differentially expressed genes (DEGs) were identified in the liver and jejunal mucosa by HS conditions. In the liver, genes related to amino acid oxidation, tryptophan metabolism, lipid metabolism, oxidative phosphorylation, and immune responses were altered by HS, which support the reason why heat-stressed poultry had decreased productive performance. In the jejunal mucosa, genes related to defense systems, glutathione metabolism, detoxification of xenobiotics, and immune responses were differently expressed by HS conditions. The integrated transcriptome analysis with DEGs found in the liver and jejunal mucosa showed a considerable connectivity between the core nodes in the constructed networks, which includes glutathione metabolism, xenobiotic metabolism, carbon metabolism, and several amino acid metabolisms.

Conclusions

The core network analysis may indicate that increased requirement of energy and amino acids in the jejunal mucosa of broiler chickens exposed to HS conditions is likely compromised by increased oxidation and synthesis of amino acids in the liver. Therefore, our results may provide comprehensive insights for molecular and metabolic alterations of broiler chickens raised under HS conditions, which can aid in the development of the novel strategies to ameliorate the negative effect of HS on poultry productivity and health.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00734-y.

NaHCO3, L-arginine, and vitamin C supplemented vegetable diet ameliorates tachycardia and polycythemia in the broiler chicken

The study aimed to investigate if vegetable-based high-energy mash diets supplemented with NaHCO₃, L-arginine + vitamin C, and vegetable oils were effective against tachycardia and polycythemia in the broiler chicken. A total of 256 Ross-308 day-old male broiler chicks were randomly distributed into eight dietary treatment groups in a three-way ANOVA with 2 × 2 × 2 factorial arrangement (three factors, i.e., NaHCO₃, L-arginine + vitamin C, and vegetable oil each with two levels, e.g., 0 and 0.1% of NaHCO₃ and L-arginine + vitamin C; 3 and 4% of vegetable oil supplemented with basal diet) for a period of 35 days. Iso-caloric and iso-nitrogenous diets were formulated and supplied ad libitum. The final live weight (FLW), average daily feed intake (ADFI), average daily gain (ADG), feed efficiency (FE), carcass traits, cardio-pulmonary morphometry, total protein (TP), hemoglobin (Hb), triiodothyronine (T₃), incidence of tachycardia, and polycythemia were examined. Supplementation of NaHCO₃ increased 2.2% ADFI, 5.5% FE, and 23.2% TP. The L-arginine + vitamin C increased 2.4% FLW and decreased 1.9% heart rate. Vegetable oil increased 1.3% ADFI, 4.2% ADG, 8.6% FE, 23.1% Hb, and 15.5% PCV. The NaHCO₃, L-arginine + vitamin C, and vegetable oil additively interacted to increase 31.5% T₃ at the expense of 21.1% of the weight of the right ventricle (RV). The RV:TV, carcass traits, and hemato-biochemical indices remained within normal range irrespective of the levels of the supplementations of the test ingredients. It was concluded that vegetable-based high-energy mash diets were not susceptible to tachycardia and polycythemia. The addition of NaHCO₃ and L-arginine + vitamin C ameliorated the propensity of tachycardia and polycythemia without deteriorating performance, carcass traits, and hemato-biochemical indices of the broiler chicken in a dose-dependent manner.

Rule of UA on Cardiac Myocytes Uric Acid Differently Influence the Oxidative Damage Induced by Acute Exposure of High Level of Glucose in Chicken Cardiac Myocytes

Background: Uric acid (UA) is a potent scavenger of oxidants in mammalian and avian species. In humans, hyperglycemia with simultaneous hyperuricemia may exert additional damage to the cardiovascular system. Chickens naturally have hyperglycemia (10.1–11.0 mmol/L) and hyperuricemia (100–900 μmol/L), which makes them an interesting model.

Methods: The aim of this study was to investigate the effects of UA on the oxidative damage induced by acute exposure of high level of glucose in chicken cardiac myocytes.

Results: Cell viability and the concentrations of thiobarbituric acid reactive substance (TBARS) were decreased by glucose treatment in a dose- and time-dependent manner. After acute exposure to high level of glucose (300 mM), a moderate level of UA (300 μM) increased cell viability and reduced TBARS and glutathione (GSH) content. Compared to the control or to independent high glucose (300 mM) or UA (1,200 μM) treatment, the concurrent treatment of high glucose and high UA significantly increased the TBARS, protein carbonyl contents, and ROS concentration, whereas it decreased the cell viability, superoxide dismutase (SOD) activity, and GSH content. In the presence of high glucose and UA, the nucleic protein expression of nuclear factor erythroid 2-related factor 2 (Nrf2) was decreased and the mRNA levels of the genes cat, sod1, sod2, gss, and gclc were downregulated.

Conclusion: In conclusion, acute exposure of high level of glucose induced oxidative damage in the cardiac myocytes of chicken. The present result suggests that an adequate level of uric acid is helpful in alleviating the acute oxidative damage that is induced by high glucose, whereas the inhibition of the Nrf2 pathway by a high level of uric acid may render the cardiac myocytes more vulnerable to suffering from oxidative damage.

Further investigation of mitochondrial biogenesis and gene expression of key regulators in ascites- susceptible and ascites- resistant broiler research lines

We have extended our previous survey of the association of mitochondrial prevalence in particular tissues with ascites susceptibility in broilers. We previously reported that in breast muscle of 22 week old susceptible line male birds had significantly higher mtDNA copy number relative to nuclear copy number (mtDNA/nucDNA), compared to resistant line male birds. The higher copy number correlated with higher expression of PPARGC1A mRNA gene. Ascites is a significant metabolic disease associated with fast-growing meat-type chickens (broilers) and is a terminal result of pulmonary hypertension syndrome. We now report the mtDNA/nucDNA ratio in lung, liver, heart, thigh, and breast of both genders at 3, and 20 weeks old. At 3 weeks the mtDNA/nucDNA ratio is significantly higher in lung, breast, and thigh for susceptible line males compared to the resistant line males. Conversely, we see the opposite for lung and breast in females. At 20 weeks of age the differences between males from the two lines is lost for lung, and thigh. Although there is a significant reduction in the mtDNA/nucDNA ratio of breast from 3 weeks to 20 weeks in the susceptible line males, the susceptible males remain higher than resistant line males for this specific tissue. We assessed relative expression of five genes known to regulate mitochondrial biogenesis for lung, thigh and breast muscle from males and females of both lines with no consistent pattern to explain the marked gender and line differences for these tissues. Our results indicate clear sex differences in mitochondrial biogenesis establishing a strong association between the mtDNA quantity in a tissue-specific manner and correlated with ascites-phenotype. We propose that mtDNA/nucDNA levels could serve as a potential predictive marker in breeding programs to reduce ascites.

Liver mitochondrial dysfunction and electron transport chain defect induced by high dietary copper in broilers

Copper is an important trace mineral in the diet of poultry due to its biological activity. However, limited information is available concerning the effects of high copper on mitochondrial dysfunction. In this study, 72 broilers were used to investigate the effects of high dietary copper on liver mitochondrial dysfunction and electron transport chain defect. Birds were fed with different concentrations [11, 110, 220, and 330 mg of copper/kg dry matter (DM)] of copper from tribasic copper chloride (TBCC). The experiment lasted for 60 d. Liver tissues on d 60 were subjected to histopathological observation. Additionally, liver mitochondrial function was recorded on d 12, 36, and 60. Moreover, a site-specific defect in the electron transport chain in liver mitochondria was also identified by using various chemical inhibitors of mitochondrial respiration. The results showed different degrees of degeneration, mitochondrial swelling, and high-density electrons in hepatocytes. In addition, the respiratory control ratio (RCR) and oxidative phosphorylation rate (OPR) in liver mitochondria increased at first and then decreased in high-dose groups. Moreover, hydrogen peroxide (H2O2) generation velocity in treated groups was higher than that in control group, which were magnified by inhibiting electron transport at Complex IV. The results indicated that high dietary copper could decline liver mitochondrial function in broilers. The presence of a site-specific defect at Complex IV in liver mitochondria may be responsible for liver mitochondrial dysfunction caused by high dietary copper.

Hypoxia-induced pulmonary hypertension in type 2 diabetic mice

Hypoxia-induced pulmonary hypertension (HPH) is a progressive disease that is mainly caused by chronic exposure to high altitude, chronic obstructive lung disease, and obstructive sleep apnea. The increased pulmonary vascular resistance and increased pulmonary arterial pressure result in increased right ventricular afterload, leading to right heart failure and increased morbidity. There are several clinical reports suggesting a link between PH and diabetes, insulin resistance, or obesity; however, it is unclear whether HPH is associated with diabetes as a progressive complication in diabetes. The major goal of this study is to examine the effect of diabetic "preconditioning" or priming effect on the progression of HPH and define the molecular mechanisms that explain the link between diabetes and HPH. Our data show that HPH is significantly enhanced in diabetic mice, while endothelium-dependent relaxation in pulmonary arteries is significantly attenuated in chronically hypoxic diabetic mice (DH). In addition, we demonstrate that mouse pulmonary endothelial cells (MPECs) isolated from DH mice exhibit a significant increase in mitochondrial reactive oxygen species (ROS) concentration and decreased SOD2 protein expression. Finally, scavenging mitochondrial ROS by mitoTempol restores endothelium-dependent relaxation in pulmonary arteries that is attenuated in DH mice. These data suggest that excessive mitochondrial ROS production in diabetic MPECs leads to the development of severe HPH in diabetic mice exposed to hypoxia.

Liver mitochondrial oxygen consumption and proton leak kinetics in broilers supplemented with dietary copper or zinc following coccidiosis challenge

Mitochondrial respiration was assessed in sixteen 7-day-old broilers as a subset of a larger study assessing the effects of Cu and Zn supplementation above requirements with a coccidiosis challenge on gain/feed ratio. The birds were selected from four treatments (four birds/treatment): a control diet (Cu 15 mg/kg and Zn 60 mg/kg) + coccidiosis challenge (CC), a Cu diet with 245 mg/kg Cu from tribasic copper chloride (TBCC) + CC, a negative control diet (Cu 15 mg/kg and Zn 60 mg/kg) - CC and a Zn diet with 2000 mg/kg Zn from ZnO. The diets were composed of 49% corn, 40% soybean meal, 6.2% vegetable oil (diet dry matter = 90.62%, crude protein = 21.37%, fat = 7.7%, metabolizable energy = 12.1 MJ/day) and were fed for 14 days. Birds were dissected, and approximately one gram of liver tissue was used for mitochondrial oxygen consumption and proton leak kinetics assays. Respiratory control ratio and mitochondrial proton leak assessed by calculating rates of oxygen consumption at 175mV membrane potential were greater for the negative control group, but there were no differences in average gain/feed among treatments. In summary, broilers that did not undergo coccidiosis challenge had lower proton leak and higher respiratory control ratio. However, the impact of supplementation of Cu and Zn above requirements did not appear to prevent changes in respiratory control ratio and proton leak kinetics with coccidiosis challenge.

Homocysteine injures vascular endothelial cells by inhibiting mitochondrial activity

The aim of the present study was to investigate the role of homocysteine (Hcy) in the pathogenesis of pulmonary embolism (PE) and the associated molecular mechanisms in human umbilical vein endothelial cells (HUVECs). Hcy contents were detected with high-performance liquid chromatography. Apoptosis was detected by flow cytometry using Annexin-V staining. Cytochrome c oxidase (COX) activity was assessed with an enzyme activity assay, and the expression levels of COX 17 were determined by western blot analysis. Intracellular reactive oxygen species levels were measured using a microplate reader with a fluorescence probe. The results demonstrated that, compared with the control group, the serum Hcy levels were significantly elevated in the PE group, suggesting that Hcy may be an indicator for PE. Following treatment with Hcy, the apoptosis rate was markedly elevated in HUVECs. Moreover, Hcy decreased COX activity and downregulated the expression of COX 17 in HUVECs. Furthermore, Hcy increased the ROS levels in these endothelial cells. However, all the above-mentioned physiopathological changes induced by Hcy in HUVECs could be restored by folic acid. In conclusion, the results of the present study demonstrated that Hcy inhibited COX activity, downregulated COX 17 expression, increased intracellular ROS levels and enhanced apoptosis in endothelial cells.

Effects of dietary DL-2-hydroxy-4(methylthio)butanoic acid supplementation on growth performance, indices of ascites syndrome, and antioxidant capacity of broilers reared at low ambient temperature

This study examined the effects of dietary DL-2-hydroxy-4(methylthio)butanoic acid (DL-HMTBA) supplementation on growth performance, antioxidant capacity, and ascites syndrome (AS) in broilers reared at low ambient temperature (LAT) from 7 to 28 days of age. Eight hundred 7-day-old broilers were randomly assigned to two ambient temperatures (LAT and normal ambient temperature [NAT]), four supplemental DL-HMTBA levels (0.17, 0.34, 0.51, and 0.68 %) of the basal diet in a 2 × 4 factorial arrangement (ten replicate pens; ten birds/pen). LAT and NAT indicate temperatures of 12-14 and 24-26 °C in two chambers, respectively, and broilers were reared at these temperatures from 7 to 28 days of age. LAT significantly decreased body weight gain (P < 0.001), serum glutathione (GSH) content (day 14, P = 0.02; day 28, P = 0.045), glutathione peroxidase (GSH-Px) activity, and total antioxidant capacity (T-AOC) at 21 days (P = 0.001, 0.015) and 28 days (P = 0.017, 0.010) and increased feed conversion ratio (FCR) (P < 0.001), serum malondialdehyde (day 21, P = 0.000) and protein carbonyl Level (day 14, P = 0.003; day 21, P = 0.035). As for incidence of AS, there were significant effects of LAT on red blood cell (RBC) count (P < 0.05), hematocrit (HCT) (P < 0.05), and the right to total ventricular weight ratio (RV/TV) at 21 days (P = 0.012) and 28 days (P = 0.046). Supplementation of DL-HMTBA markedly decreased RV/TV at day 28 (P = 0.021), RBC (day 21, P = 0.008), HCT (day 21, P < 0.001), mean cell hemoglobin (day 14, P = 0.035; day 21, P = 0.003), and serum protein carbonyl level (day 21, P = 0.009), while significantly increased serum GSH content (day 14, P = 0.022; day 28, P = 0.001), SOD and GSH-Px activities at 21 days of age (P < 0.001 and P = 0.037). The optimal supplemental DL-HMTBA levels in basal diet of broilers aged from 7 to 28 days under low or normal temperatures were similar, so the authors recommended supplemental of DL-HMTBA level was 0.46 %.

The effect of allopurinol administration on mitochondrial respiration and gene expression of xanthine oxidoreductase, inducible nitric oxide synthase, and inflammatory cytokines in selected tissues of broiler chickens

Birds have a remarkable longevity for their body size despite an increased body temperature, higher metabolic rate, and increased blood glucose concentrations compared to most mammals. As the end-product of purine degradation, uric acid (UA) is generated in the xanthine/hypoxanthine reactions catalyzed by xanthine oxidoreductase (XOR). In the first study, Cobb × Cobb broilers (n = 12; 4 weeks old) were separated into 2 treatments (n = 6); control (CON) and allopurinol (AL) 35 mg/kg BW (ALLO). The purpose of this study was to assess mitochondrial function in broiler chickens in response to potential oxidative stress generated from the administration of AL for 1 wk. There was a significant reduction in state 3 respiration (P = 0.01) and state 4 respiration (P = 0.007) in AL-treated birds compared to the controls. The purpose of the second study was to assess the effect of AL on gene expression of inflammatory cytokines interferon-γ (IFN)-γ, IL-1β, IL-6, and IL-12p35, as well as inducible nitric oxide synthase and XOR in liver tissue. Cobb × Cobb broilers were separated into two groups at 4 wk age (n = 10); CON and ALLO. After 1 wk AL treatment, half of the birds in each group (CON 1 and ALLO 1) were euthanized while the remaining birds continued on AL treatment for an additional week (CON 2 and ALLO 2). A significant increase in gene expression of XOR, IFN-γ, IL-1β, and IL-12p35 in ALLO 2 birds as compared to birds in CON 2 was detected. Liver UA content was significantly decreased in both ALLO 1(P = 0.003) and ALLO 2 (P = 0.012) birds when compared to CON 1 and CON 2, respectively. The AL reduced liver UA concentrations and increased expression of inflammatory cytokines. Additional studies are needed to determine if AL causes a direct effect on mitochondria or if mitochondrial dysfunction observed in liver mitochondria was due indirectly through increased oxidative stress or increased inflammation.

Relationship between Liver Mitochondrial Respiration and Proton Leak in Low and High RFI Steers from Two Lineages of RFI Angus Bulls

The objective of this research is to evaluate liver mitochondrial oxygen consumption and proton leak kinetics in progeny from two lineages of Angus bulls with high and low residual feed intake (RFI). Two Angus bulls were selected based on results from a genetic test for RFI and were used as sires. Eight offspring at 10-11 months of age from each sire were housed in individual pens for 70–105 days following a diet adaptation period of 14 days. Progeny of the low RFI sire had 0.57 kg/d (P = 0.05) lower average RFI than progeny of the high RFI sire. There was no difference in dry matter intake between low and high RFI steers, but low RFI steers gained more body weight (P = 0.02) and tended to have higher average daily gains (P = 0.07). State 3 and State 4 respiration, RCR, and proton leak did not differ between high and low RFI steers (P = 0.96, P = 0.81, P = 0.93, and P = 0.88, resp.). Therefore, the increase in bodyweight gain which distinguished the low RFI steers from the high RFI steers may be associated with other metabolic mechanisms that are not associated with liver mitochondrial respiration and proton leak kinetics.

Effects of Dietary L-carnitine Supplementation on Growth Performance, Organ Weight, Biochemical Parameters and Ascites Susceptibility in Broilers Reared Under Low-temperature Environment

The objective of this study was to investigate the effects of L-carnitine on growth performance, organ weight, biochemical parameters of blood, heart and liver, and ascites susceptibility of broilers at different ages reared under a low-temperature environment. A total of 420 1-d-old male Ross 308 broilers were randomly assigned to two dietary treatments with fifteen replicates of fourteen broilers each. Treatment diets consisted of L-carnitine supplementation at levels of 0 and 100 mg/kg. At 11-d of age, low temperature stress was used to increase ascites susceptibility. Blood, heart and liver samples were collected at different ages for analysis of boichemical parameters. The results showed that, there was no significant difference in growth performance with L-carnitine supplementation, but the mortality due to ascites was significantly decreased. Dietary L-carnitine supplementation significantly reduced heart index (HI) and ascites heart index (AHI) on d 21, lung index (LUI) on d 35 and liver index (LI) on d 42. The broilers fed diets containing L-carnitine had significantly lower red blood cell counts (RBC), hemoglobin (HGB) concentration and hematocrit (HCT) on d 42. Dietary L-carnitine supplementation significantly reduced malondialdehyde (MDA) content of heart tissue on d 21 and 35, and significantly increased total superoxide dismutase (T-SOD) and Glutathione peroxidase (GSH-Px) activity of the heart on d 21 and 42. L-carnitine supplementation significantly reduced serum triglyceride (TG) content on d 28 and 35 and serum glucose (GLU) on d 35 and 42, and significantly increased serum total protein (TP) and globulin (GLO) content on d 42. L-carnitine supplementation significantly enhanced liver succinodehydrogenase (SDH), malic dehydrogenase (MDH) and Na⁺-K⁺-ATPase activity on d 28, and tended to reduce the lactic acid (LD) level of liver on d 35 (p = 0.06). L-carnitine supplementation significantly reduced serum uric acid (UA) content on d 28, 35 and 42. Based on the current results, it can be concluded that dietary L-carnitine supplementation reduced organ index, red blood cell counts and hematocrit, enhanced antioxidative capacity of the heart, enhanced liver enzymes activity involved in tricarboxylic acid cycle, and reduced serum glucose and triglyceride. Therefore, it is suggested that L-carnitine can potentially reduce susceptibility and mortality due to ascites.

The effects of turmeric supplementation on antioxidant status, blood gas indices and mortality in broiler chickens with T(3)-induced ascites

1. A total of 320 one-day-old Ross male broiler chickens were used to investigate the effects of 0·0, 2·5, 5·0 and 7·5 g/kg turmeric rhizome powder (TRP) in the diet, on antioxidant status, biochemical gas indices and mortality in broiler chickens with triiodothyronine (T(3)) induced ascites. 2. The TRP supplementation had no effect on blood pH, pO(2) or pCO(2) during the whole period of study. Moreover, supplementation of TRP did not influence the heart weight, right ventricle, left ventricle, or total ventricle weights, all relative to total live weight; RV/TV (right ventricle to total ventricle) ratio; or serum GPX (glutathione peroxidase) or SOD (superoxide dismutase) activities at week 6. 3. TRP supplementation influenced the blood [Formula: see text] and O(2) saturation during the whole period of study, total mortality due to ascites, and serum total tocopherol and malondialdehyde (MDA) contents. Blood [Formula: see text] and serum total tocopherol increased linearly as dietary TRP level increased. Blood O(2) saturation increased quadratically as dietary TRP increased. 4. Total ascites mortality and serum MDA content decreased linearly with increasing TRP level to 5 mg/kg and then reached a plateau. 5. The results of the study indicate that the addition of 5·0 g/kg TRP is sufficient to increase the blood O(2) saturation and bicarbonate ([Formula: see text]) concentration, and reduce the mortality due to ascites and serum MDA content.

Effect of early feed restriction on hepatic lipid metabolism and expression of lipogenic genes in broiler chickens

The study was conducted to investigate the effect of early feed restriction (ER) on lipid metabolism and mitochondrial function in the liver of broiler chickens. Newly hatched broiler chickens were randomly allocated into control and ER group which was subjected to feed restriction with feed provided on alternate days from hatch to 14 days of age (14 d), followed by ad libitum feeding until the end of the experiment on 63 d. ER group exhibited significantly lower body weight throughout the experiment. Serum concentrations of total cholesterol (TC) and high density lipoprotein cholesterol (HDLC) were significantly higher in ER group at 14 d (P<0.05), and the higher serum TC level in ER group was also observed at 63 d. In contrast, the contents of triglyceride (TG), TC and lipoprotein lipase (LPL) activity in liver were significantly lower in ER group at 14 d (P<0.05). At 14 d no significant difference was detected for the mRNA expression of the acetyl-CoA carboxylase-α (ACC-α), carnitine palmitoyltransferase I (CPT-I), sterol regulatory element binding protein-1c (SREBP-1c) or peroxisome proliferator-activated receptors α (PPAR-α) between control and ER group. At 63 d ACC-α mRNA expression was significantly down-regulated accompanied with a significantly up-regulated CPT-ImRNA and a decreased tendency of SREBP-1c mRNA expression in ER group (P=0.09). Swollen mitochondria with fragmented and reduced cristae were observed in liver of ER group at 14 d. Meanwhile the inner mitochondria membrane viscidity increased and hepatic mitochondrial superoxide dismutase (SOD) activity decreased at 14 d. The results suggest that feed restriction at early postnatal stage may produce long-term effect on lipid metabolism of broiler chicken, probably through, at least in part, alterations in mitochondria morphology and function.

Association of mitochondrial function and feed efficiency in poultry and livestock species

As grain prices have increased dramatically in the past year, understanding the fundamental genetic, cellular, and biochemical mechanisms responsible for feed efficiency (FE; g of gain/g of feed) or residual feed intake (RFI; an alternative feed efficiency trait that quantifies interanimal variation in DMI that is unexplained by differences in BW and growth rate) in livestock and poultry is extremely important with respect to maintaining viable meat production practices in the United States. Although breed and diet have long been known to affect mitochondrial function, few studies have investigated differences in mitochondrial function and biochemistry due to interanimal phenotypic differences in FE or RFI (i.e., variation among animals of the same breed and fed the same diet). This paper reviews existing literature on relationships of mitochondrial function and biochemistry with FE and RFI in poultry and livestock. The overall goal of all of this paper is to assist the development of tools (e.g., genetic markers or biomarkers) to aid commercial breeding companies in genetic selection that, in turn, will help maintain viable livestock and poultry industries in the United States and around the world.

Membrane potential and H2O2 production in duodenal mitochondria from broiler chickens (Gallus gallus domesticus) with low and high feed efficiency

Increased hydrogen peroxide (H2O2) production was observed in duodenal mitochondria obtained from broiler chickens with low feed efficiency (FE). As a decrease in mitochondrial membrane potential (Deltapsi(m)) due to mild uncoupling of oxidative phosphorylation reduces reactive oxygen species production, this study was conducted to evaluate the effect of uncoupling on Deltapsi(m) and H2O2 production in duodenal mitochondria isolated from broilers with low (0.48+/-0.02) and high (0.68+/-0.01) FE. Membrane potential and H2O2 production were measured fluorometrically and in the presence of different levels of an uncoupler, carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP). The Deltapsi(m) was higher (P<or=0.05) in high FE mitochondria at 0 to 600 nM FCCP. A decrease in Deltapsi(m) was observed at 600 and 1000 nM FCCP in the low and high FE groups, respectively. H2O2 generation was higher in the low FE mitochondria at all FCCP levels except at 200 nM. Adding 200 to 800 nM FCCP decreased H2O2 production in low but not in high FE mitochondria. These results showed that FCCP-induced uncoupling lowered H2O2 production in low FE but not in high FE duodenal mitochondria and suggest that Deltapsi(m) may influence H2O2 production in low FE mitochondria.

Effects of dietary L-carnitine and coenzyme Q10at different supplemental ages on growth performance and some immune response in ascites-susceptible broilers

Effects of dietary L-carnitine and coenzyme Q10 (CoQ10) at different supplemental ages on performance and some immune response were investigated in ascites-susceptible broilers. A 3 x 2 x 2 factorial design was used consisting of L-carnitine supplementation (0, 75, and 100 mg/kg), CoQ10 supplementation (0 and 40 mg/kg) and different supplemental ages (from day 1 on and from day 10 on). A total of 480 one-day-old Arbor Acre male broiler chicks were randomly allocated to 12 groups, every group had five replicates, each with eight birds. The birds were fed a corn-soybean based diet for six weeks. From day 10-21, all the birds were exposed to a low ambient temperature (12-15 degrees C) to increase the susceptibility to ascites. No significant effects were observed on growth performance by L-carnitine, CoQ10 supplementation, and different supplemental ages. Packed cell volume was significantly decreased by L-carnitine supplementation alone, and ascites heart index and ascites mortality were decreased by L-carnitine, CoQ10 supplementation alone, and L-carnitine + CoQ10 supplementation together (p < 0.05). Heart index of broilers was significantly improved by L-carnitine, CoQ10 supplementation alone during 0-3 week. Serum IgG content was improved by L-carnitine supplementation alone (p < 0.05), but lysozyme activity was increased by L-carnitine + CoQ10 supplementation together (p < 0.05). A significant L-carnitine by supplemental age interaction was observed in lysozyme activity. L-carnitine supplementation alone had no effects on the peripheral blood lymphocyte (PBL) proliferation in response to concanavalin A (ConA) and lipopolysaccharide, but supplemental CoQ10 alone and L-carnitine+ CoQ10 together decreased the PBL proliferation in response to ConA (p < 0.05). The present study suggested that L-carnitine + CoQ10 supplementation together had positive effects on some immune response of ascites-susceptible broilers, which might benefit for the reduction of broilers' susceptibility to ascites.

Effects of dietary coenzyme Q10supplementation on hepatic mitochondrial function and the activities of respiratory chain-related enzymes in ascitic broiler chickens

1. One hundred and sixty 1-d-old Arbor Acre male broiler chicks were fed with maize-soybean based diets for 6 weeks in a 2 x 2 factorial experiment. The factors were CoQ10 supplementation (0 or 40 mg/kg) and Escherichia coli lipopolysaccharide (LPS) challenge (LPS or saline). 2. CoQ10 was supplemented from d 1. From d 18, the chickens received three weekly i.p. injections of LPS (1.0 mg/kg BW) or an equivalent amount of sterile saline as control. From d 10 on, all chickens were exposed to low ambient temperature (12 to 15 degrees C) to induce ascites. 3. The blood packed cell volume and ascites heart index of broiler chickens were reduced by dietary CoQ10 supplementation. Mitochondrial State 3 and State 4 respiration, respiratory control ratio and phosphate oxygen ratio were not changed, but H+/site stoichiometry of complex II + III was elevated by dietary CoQ10 supplementation. 4. Cytochrome c oxidase and H+-ATPase activity were increased by CoQ10 supplementation, whereas NADH cytochrome c reductase and succinate cytochrome c reductase were not influenced. Mitochondrial anti-ROS capability was increased and malondialdehyde content was decreased by CoQ10 supplementation. 5. The work suggested that dietary CoQ10 supplementation could reduce broiler chickens' susceptibility to ascites, which might be the result of improving hepatic mitochondrial function, some respiratory chain-related enzymes activities and mitochondrial antioxidative capability.

Feed efficiency and mitochondrial function

Studies have been conducted in our laboratory to assess differences in mitochondrial function and biochemistry in male broilers with high and low feed efficiency (FE) from the same genetic line and fed the same diet. Mitochondria obtained from broilers with low FE exhibited greater uncoupling of the electron transport chain (ETC) that was apparently due to site-specific defects in electron transport resulting in higher amounts of reactive oxygen species (ROS) compared with high FE mitochondria. Higher amounts of ROS production in Low FE mitochondria were likely responsible for higher protein carbonyl levels, indicative of higher protein oxidation compared with High FE mitochondria and tissue. In turn, higher protein damage in Low FE mitochondria may have contributed to lower activity of electron transport chain complexes relative to values observed in high FE mitochondria. Low FE mitochondria did not exhibit a compromised ability to carryout oxidative phosphorylation, and although there were differences in expression of certain electron transport chain proteins, there was nothing that would indicate that differences in coupling and respiratory chain activity could be due to a general decrease in protein expression between low and high FE mitochondria. The results of these studies provide insight into understanding cellular mechanisms associated with the phenotypic expression of feed efficiency in broilers.

Effects of early feed restriction and cold temperature on lipid peroxidation, pulmonary vascular remodelling and ascites morbidity in broilers under normal and cold temperature

Two experiments were conducted to evaluate the effects of early feed restriction on lipid peroxidation, pulmonary vascular remodelling and ascites incidence in broilers under normal and low ambient temperature. In experiment 1, the restricted birds were fed 8h per day either from 7 to 14 d or from 7 to 21 d, while the controlled birds were fed ad libitum. In experiment 2, the restricted birds were fed 80 or 60% of the previous 24-h feed consumption of full-fed controls for 7 d from 7 to 14 d. On d 14, half of the birds in each treatment both in experiment 1 and experiment 2 were exposed to low ambient temperature to induce ascites. Body weight and feed conversion ratio were measured weekly. The incidences of ascites and other disease were recorded to determine ascites morbidity and total mortality. Blood samples were taken on d 14, 21, 28, 35 and 42 to measure the plasma malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). On d 42, samples were taken to determine the right/total ventricular weight ratio (RV/TV), vessel wall area/vessel total area ratio (WA/TA) and mean media thickness in pulmonary arterioles (mMTPA). Low-temperature treatment increased plasma MDA concentration. When broilers were exposed to a cool environment for 3 weeks, plasma SOD and GSH-Px activity were decreased compared with normal-temperature chicks. RV/TV, WA/TA and mMTPA on d 42 were increased in birds exposed to cold, consistent with the increased pulmonary hypertension and ascites morbidity. Early feed restriction markedly decreased plasma MDA concentration. The plasma SOD and GSH-Px activity of feed-restricted birds were markedly higher than those fed ad libitum on d 35 and d 42. All early feed restriction treatments reduced ascites morbidity and total mortality. On d 42, the RV/TV, WA/TA and mMTPA of feed-restricted broilers were lower than that of the ad libitum-fed broilers. The results suggested that early feed restriction alleviated the lipid peroxidation, promoted the activity of enzymatic antioxidant and inhibited pulmonary vascular remodelling. These changes might be associated with reduced ascites incidence.

Compromised liver mitochondrial function and complex activity in low feed efficient broilers are associated with higher oxidative stress and differential protein expression

Variations in broiler growth and efficiency have been explained in part by differences in mitochondrial function and biochemistry in broilers. To further our knowledge in this regard, 2 experiments were carried out to determine the relationships of a) mitochondrial function and activities of various electron transport chain (ETC) complexes; b) production of H2O2, a reactive oxygen species (ROS), and its association with protein oxidation; and c) mitochondrial protein expression in liver of a single line male broilers with low or high feed efficiency (FE, n = 5 to 8 per group). Mitochondrial function and complex activities were measured polarographically and spectrophotometrically, respectively. H2O2 was measured fluorimetrically, whereas oxidized protein (carbonyls) and specific mitochondrial proteins were analyzed using Western blots. Mitochondrial function (ETC coupling) and activities of ETC complexes (I, II, III, and IV) were higher in high FE compared with low FE broilers. H2O2 and protein carbonyls were higher in the livers of low FE broilers than in high FE broilers. Whereas the expression of 4 immunoreactive proteins [NAD3 (complex I), subunit VII (complex III), cytochrome c oxidase subunits (COX) II, and COX IVb (complex IV)] were higher in low FE liver mitochondria and 2 proteins [subunit 70 (complex II) and a-ATP synthase (complex V)] were higher in high FE birds, there were no differences between groups in the expression of 18 other mitochondrial proteins. In conclusion, increases in oxidative stress in low FE broilers were caused by or may contribute to differences in mitochondrial function (ETC coupling and complex activities) or the differential expression of steady-state levels of some mitochondrial proteins in the liver. Understanding the role of oxidative stress in Low FE broilers will provide clues in understanding the cellular basis of feed efficiency.

Differential expression of cardiac muscle mitochondrial matrix proteins in broilers from ascites-resistant and susceptible lines

Ascites is a metabolic disorder of modern broilers that is distinguished by cardiopulmonary insufficiency in the face of intense oxygen demands of rapidly growing tissues. Broilers with ascites exhibit sustained elevation of pulmonary arterial pressure and right ventricular hypertrophy, the end result of which is heart failure. It has been shown that mitochondrial function is impaired in broilers with ascites. In the current study, mitochondrial matrix protein levels were compared between ascites-resistant line broilers and ascites-susceptible line broilers with and without ascites using two-dimensional (2-D) gel electrophoresis. One hundred seventy-two protein spots were detected on the gels, and 9 of the spots were present at different levels in the 4 groups of broilers. These 9 protein spots were selected for identification by mass spectrometry. Two of the spots were found to contain single mitochondrial matrix proteins. Both mitochondrial matrix proteins, the dihydrolipoamide succinyltransferase component of the 2-oxoglutarate dehydrogenase complex and the alpha-subunit of mitochondrial trifunctional enzyme, were present at higher levels in ascites-resistant line broilers with ascites in the present study. The elevated levels of 2 key proteins in aerobic metabolism in ascites-resistant line broilers with ascites observed in the present study suggests that the mitochondria of broilers with this disease may respond inappropriately to hypoxia.

Glutathione and respiratory chain complex activity in duodenal mitochondria of broilers with low and high feed efficiency

We previously observed increased reactive oxygen species (ROS) production in intestinal mitochondria obtained from broiler breeder males with low feed efficiency (FE, gain-to-feed). Because antioxidants are critical for combating ROS-mediated oxidative stress and preserving mitochondrial function, the objectives of this study were 1) to determine levels of reduced glutathione (GSH), a major antioxidant in mitochondria, 2) to measure activities of GSH recycling enzymes: GSH peroxidase and GSH reductase, and 3) to establish relationships between antioxidants and respiratory chain complex activities (complexes I, II, III, IV, and V) in broiler breeder males with low and high FE. Duodenal mitochondria were isolated from broilers with low (0.62 +/- 0.01, n = 8) and high (0.80 +/- 0.01, n = 8) FE. Activities of respiratory chain complexes, GSH peroxidase, and GSH reductase, and levels of GSH were measured by UV spectrophotometry. There were no differences in GSH peroxidase or reductase activities or in individual complex activities between groups but GSH levels tended to be higher (P = 0.075) and oxidized to reduced glutathione ratio tended to be lower (P = 0.077) in broilers with high FE. Regression analysis revealed significant correlations (P < or = 0.05) between mitochondrial GSH and activities of complexes II, IV, and V with R2 values of 0.35, 0.56, and 0.49, respectively. These data suggest that GSH may be important in maintaining or enhancing the activity of certain respiratory chain complexes and could be involved in the phenotypic expression of feed efficiency in broilers.

Determination of mitochondrial function and site-specific defects in electron transport in duodenal mitochondria in broilers with low and high feed efficiency

Duodenal mitochondria were isolated from broiler breeder males with high (0.79+/-0.01, n = 9) and low (0.63+/-0.02, n = 9) feed efficiency (FE) to assess relationships of FE with duodenal mitochondrial function and site-specific defects in electron transport. Sequential additions of adenosine diphosphate (ADP) resulted in 1) higher respiratory control ratio (RCR; an index of respiratory chain coupling) in high FE mitochondria provided succinate, and 2) higher ADP to oxygen ratio (ADP:O; an index of oxidative phosphorylation) in low FE mitochondria provided NADH-linked substrates (malate, pyruvate, or both). Basal electron leak, measured as H2O2 production, was greater in low FE mitochondria provided succinate (P = 0.08) or NADH-linked substrates. As H2O2 levels were elevated in low FE compared with high FE mitochondria by complex I (P+/-0.07) and complex II inhibition, the higher basal electron leak in low FE mitochondria was apparently due to site-specific defects in electron transport at complexes I and II. Elevations in H2O2 above basal levels indicated that high FE mitochondria may also exhibit electron transport defects at complexes I and III. Despite an ability to produce adenosine triphosphate (ATP) that was equal or superior to that demonstrated in high FE duodenal mitochondria, low FE mitochondria exhibited a greater inherent degree of electron leak. The results provide insight into the role that duodenal mitochondria play in the phenotypic expression of FE in broilers.

Reduction of ascites mortality in broilers by coenzyme Q10

Effects of coenzyme Q10 (CoQ10) supplementation on growth performance and ascites were studied in broilers. One hundred eighty 1-d-old Arbor Acre male broiler chicks were randomly allocated into 3 groups with 6 replicates each. From d 8, the diets were supplemented with CoQ10 at levels of 0, 20, and 40 mg/kg, respectively. From d 15 to 21, all the chicks were exposed to low ambient temperature (15 to 18 degrees C) to induce ascites. Average feed intake, BW gain, and feed conversion ratio of the broilers during 0 to 3 wk, 3 to 6 wk, and 0 to 6 wk were measured. The results showed that there were no influences observed on broilers' growth performance, but the mortality due to ascites was reduced by CoQ10 supplementation (P < or = 0.05). Erythrocyte osmotic fragility (EOF) was significantly decreased by 40 mg/kg CoQ10 compared with the control, but no significant changes were observed on blood packed cell volume (PCV) among the treatments. Pulmonary arterial diastolic pressure was significantly decreased on d 36, but no significant changes were observed on right ventricular pressure (RVP), pulmonary arterial systolic pressure, and the maximum change ratio of right intraventricular pressure (+/- dp/ dtmax). Ascites heart index (AHI) was significantly decreased by 40 mg/kg CoQ10 supplementation (P < or = 0.05). The results of this study suggested that CoQ10 has a beneficial effect in reducing ascites mortality in broilers, and 40 mg/kg CoQ10 seems to be more effective than 20 mg/ kg CoQ10.

Differential expression of mitochondrial electron transport chain proteins in cardiac tissues of broilers from pulmonary hypertension syndrome-resistant and -susceptible lines

Pulmonary hypertension syndrome (PHS) is a metabolic disease associated with the rapid growth rate of modern broilers. Broilers susceptible to PHS experience sustained elevation of pulmonary arterial pressure leading to right ventricular hypertrophy and ultimately heart failure. Previous studies have shown that mitochondrial function is defective in broilers with PHS; they use oxygen less efficiently than broilers without PHS. In this study mitochondrial electron transport chain (ETC) protein levels were compared in cardiac tissues from PHS resistant and susceptible line broilers using quantitative immunoblots. Seven of 9 anti-mammalian mitochondrial ETC protein antibodies tested exhibited cross-species reactivity. Six ETC proteins were differentially expressed in the right ventricles of broilers raised under simulated high altitude conditions (2,900 m above sea level). Four ETC proteins were present at higher levels in resistant line birds without PHS than in resistant line birds with PHS or in susceptible line birds with or without PHS. One ETC protein was present at higher levels in broilers without PHS than in broilers with PHS in both lines, and one ETC protein was present at lower levels in susceptible line birds without PHS than in susceptible line birds with PHS or in resistant line birds with or without PHS. Interestingly, differential expression of mitochondrial ETC proteins was not observed in the right ventricles of broilers raised at local altitude (390 m above sea level) nor was it observed in the left ventricles of broilers exposed to simulated high altitude. These results suggest that higher levels of mitochondrial ETC proteins in right ventricle cardiac muscle may be correlated with resistance to PHS in broilers.

Investigation of proton conductance in liver mitochondria of broilers with pulmonary hypertension syndrome

We previously reported an impaired ability to regulate hepatic mitochondrial state 4 respiration rate in response to sequential additions of adenosine diphosphate in pulmonary hypertension syndrome (PHS). As proton conductance is a major contributor to State 4 respiration, the major goal of this study was to investigate the nature of proton conductance in hepatic mitochondria isolated from broilers with and without PHS. Broilers were placed on floor litter in environmental chambers and exposed to cold temperatures (15 degrees C) from 3 to 7 wk of age to induce PHS. Liver mitochondria were isolated from birds that exhibited PHS (cyanosis, right ventricular weight ratio > 0.30) or from birds that appeared healthy (no cyanosis, right ventricular weight ratio < 0.27). Isolated mitochondria were placed in a chamber equipped with the ability to measure oxygen content and mitochondrial membrane potential. The mitochondrial membrane potential was assessed by an ion sensitive electrode to measure the distribution of methyltriphenylphosphonium across the inner mitochondrial membrane. Proton conductance was assessed by simultaneously measuring State 4 oxygen consumption rate as respiration was progressively inhibited with increasing concentrations of malonate. The addition of cardiolipin, a lipid found in high concentrations in mitochondrial membranes that can alter proton conductance, had no affect on respiration or mitochondrial membrane potential in either group. The relationship of curves depicting State 4 respiration and mitochondrial membrane potential indicates that PHS mitochondria exhibit impaired substrate oxidation and reduced proton conductance relative to controls. These findings provide further characterization of the altered cellular oxygen utilization in broilers with PHS.

Low Feed Efficient Broilers Within a Single Genetic Line Exhibit Higher Oxidative Stress and Protein Expression in Breast Muscle with Lower Mitochondrial Complex Activity

The objectives of this study were to determine the effects of low or high feed efficiency (FE) on a) protein oxidation, b) the activities of various respiratory chain complexes, and c) expression of various mitochondrial proteins in male broilers within a single genetic line. Tissue homogenate or mitochondria were isolated from breast muscle of broilers with high (0.80 +/- 0.01) and low FE (0.62 +/- 0.02). The complex activities were measured spectrophotometrically, and the levels of oxidized protein (carbonyl) and immunoreactive mitochondrial proteins were analyzed using Western blots. Protein carbonyl levels were higher in low FE compared with high FE broilers breast muscle, which indicated enhanced protein oxidation in low FE mitochondria. Activities of all respiratory chain complexes (I, II, III, IV) were higher in high FE compared with low FE broilers for breast mitochondria. Whereas the expression of immunoreactive proteins was higher in low FE muscle mitochondria for 5 mitochondrial proteins [core I, cyt c1, cyt b (complex III), COX II (cytochrome c oxidase subunit II, complex IV), and adenine nucleotide translocator (ANT1)], there were no differences between groups in the expression of 9 other respiratory chain protein subunits associated with complexex I, II, III, IV, and V. SDS-PAGE revealed a protein band of 47 kDa that was expressed at a higher level in low FE compared with high FE mitochondria. The differential expression of certain mitochondrial proteins and the 47-kDa band might be a compensatory response either to the lower complex activities or increased protein oxidation observed in low FE birds.

Essential role of complex II of the respiratory chain in hypoxia-induced ROS generation in the pulmonary vasculature

In the pulmonary vasculature, the mechanisms responsible for oxygen sensing and the initiation of hypoxia-induced vasoconstriction and vascular remodeling are still unclear. Nitric oxide (NO) and reactive oxygen species (ROS) are discussed as early mediators of the hypoxic response. Here, we describe a quantitative analysis of NO- and ROS-producing cells within the vascular walls of murine lung sections cultured at normoxia or hypoxia. Whereas the number of NO-producing cells was not changed by hypoxia, the number of ROS-generating cells was significantly increased. Addition of specific inhibitors revealed that mitochondria were the source of ROS. The participation of the individual mitochondrial complexes differed in normoxic and hypoxic ROS generation. Whereas normoxic ROS production required complexes I and III, hypoxic ROS generation additionally demanded complex II. Histochemically demonstrable succinate dehydrogenase activity of complex II in the arterial wall decreased during hypoxia. Inhibition of the reversed enzymatic reaction, i.e., fumarate reductase, by application of succinate, specifically abolished hypoxic, but not normoxic, ROS generation. Thus complex II plays an essential role in hypoxic ROS production. Presumably, its catalytic activity switches from succinate dehydrogenase to fumarate reductase at reduced oxygen tension, thereby modulating the directionality of the electron flow.

Immunohistochemical evidence of cytochrome C oxidase subunit II involvement in pulmonary hypertension syndrome (PHS) in broilers

Defects and variation in the relative amount of protein subunits in the mitochondrial electron transport chain (ETC) have been hypothesized to be involved, in part, in the pathogenesis of pulmonary hypertension syndrome (PHS), a costly metabolic disease. Thus, the major objective of this study was to determine whether differences in relative amounts of cytochrome c oxidase subunit I and II (COX I and II) can be detected by immunohistochemistry and digital image analysis in muscle tissue of broilers with PHS compared to control broilers. Cross sections of the breast muscle (pectoralis major) were stained with monoclonal antibodies for COX I and II. Relative areas of multiple microscope viewing fields (400x) per tissue section of COX I and II were quantified by counting immunopositive pixels on the digital images. Whereas the number of immunopositive pixels for COX II was higher in PHS birds compared to controls, there were no difference for COX I. The amount of COX II was positively correlated with the right to total ventricular weight ratio (RV:TV), suggesting that there may be increased expression of COX II associated with severity of pulmonary arterial hypertension. Thus, it is possible that COX II expression in PHS broiler may be involved in the pathogenesis of PHS.

Heart and breast muscle mitochondrial dysfunction in pulmonary hypertension syndrome in broilers (Gallus domesticus)

This study was conducted to determine function and defects in electron transport in muscle mitochondria of meat chickens (broilers) with pulmonary hypertension syndrome (PHS). The respiratory control ratio (RCR, indicative of respiratory chain coupling) was higher in the control than in PHS breast and heart muscle mitochondria, but there were no differences in the ADP/O (an index of oxidative phosphorylation). Sequential additions of ADP improved the RCR in the control breast muscle mitochondria and the ADP/O in PHS breast and heart muscle mitochondria. Basal hydrogen peroxide production, (an indicator of electron leak), was higher in PHS breast and heart muscle mitochondria than in controls and differences in electron leak in PHS mitochondria were magnified by inhibiting electron transport at Complex I and III (cyt b(562)). Complex I activity was lower in PHS heart mitochondria but there was no difference in Complex II activity. Thus, compared to controls, PHS mitochondria exhibited site-specific defects in electron transport within Complex I and III that could contribute to lower respiratory chain coupling. Additionally, it appears that healthy broilers may exhibit higher basal levels of electron leak compared to other avian species. Together, these findings provide insight into inefficient cellular use of oxygen that may contribute to the development of PHS in broilers.

Association of mitochondrial function with feed efficiency within a single genetic line of male broilers

Studies were conducted to determine relationships between feed efficiency and mitochondrial function and biochemistry. After feed efficiency (FE; gain:feed) was determined in broiler breeder males between 6 and 7 wk of age, mitochondria were isolated from breast and leg muscle from birds with high FE (0.83+/-0.01, n = 6) and low FE (0.64+/-0.01, n = 7). Respiratory chain coupling, assessed by the respiratory control ratio (RCR), was greater in high FE breast, and leg mitochondria provided NADH-linked, but not FADH-linked, energy substrates. There were no differences, however, in the adenosine diphosphate to oxygen (ADP:O) ratio (an index of oxidative phosphorylation) when mitochondria were provided either energy substrate. Electron leak, as determined by generation of H202, was greater in the low FE than in high FE breast mitochondria. Electron leak increased following inhibition of electron transport at Complex I (with rotenone) and Complex III (with antimycin A) in low FE but not in high FE breast mitochondria. There were no differences in basal electron leak in leg mitochondria between groups, but H202 generation was elevated (P < 0.07) compared to basal values in low FE leg mitochondria after Complex I inhibition. The activities of Complexes I and II were greater in high FE breast and leg muscle mitochondria compared to those in low FE mitochondria. The results indicate that lower respiratory chain coupling in low FE muscle mitochondria may be due to lower activities of Complexes I and II and defects in electron leak and provide insight into cellular mechanisms associated with the phenotypic expression of feed efficiency in broilers.

Antioxidant enzyme activities and mitochondrial fatty acids in pulmonary hypertension syndrome (PHS) in broilers

Major objectives of this study were to assess antioxidant protection and fatty acid profile in lung mitochondria and whole liver in broilers with pulmonary hypertension syndrome [(PHS; with and without high dietary vitamin E (VE)] (Experiment 1) and in broilers that did not develop PHS but were genetically selected (S) or not selected (NS) for resistance to PHS (Experiment 2). In Experiment 1, lung mitochondrial glutathione peroxidase (GSH-Px) activity was elevated in broilers with PHS compared to controls, broilers fed high VE, and broilers fed high VE with PHS (VE-PHS), but there were no differences in GSH reductase (GSH-Rd) among groups. In liver tissue, GSH-Px was also elevated by PHS but was lower in VE and VE-PHS groups than in controls. There were no differences in liver GSH-Rd, superoxide dismutase (SOD), or gamma-glutamylcysteine synthetase (gamma-GCS) activities with the exception that gamma-GCS was higher in the VE-PHS group than in the other groups. In Experiment 2, S lung mitochondria exhibited lower GSH-Px and higher GSH-Rd compared to NS broilers. In the liver, there were no differences in GSH-Px, GSH-Rd, or gamma-GCS, but SOD was lower in S compared to the NS broilers. High VE increased the percentage of saturated fatty acids and decreased the percentage of unsaturated fatty acids in lung mitochondria in Experiment 1; there were no differences in fatty acid content between S and NS mitochondria in Experiment 2. Thus, it appears that GSH recycling enzyme activities are affected by PHS and high VE presumably in response to differences in oxidative stress and that genetic resistance to PHS is associated with an inherently better capability to metabolize oxidants in lung mitochondria. The increase in saturation of lung mitochondrial fatty acids with high dietary VE would presumably make them more resistant to oxidative stress and, thus, reduce the level of PHS-induced oxidative stress.

Lung mitochondrial dysfunction in pulmonary hypertension syndrome. II. Oxidative stress and inability to improve function with repeated additions of adenosine diphosphate

The major objective of this study was to examine lung mitochondrial dysfunction and antioxidants in pulmonary hypertension syndrome (PHS) in broilers. Lung mitochondria were obtained from broilers fed diets containing 15 IU (control) and 100 IU dl-alpha-tocopherol acetate, i.e., vitamin E (VE)/kg with and without PHS; the four treatment groups were control, VE, PHS, and VE-PHS, respectively (Experiment 1), or from healthy broilers genetically selected or not selected for resistance to PHS (Experiment 2). Mitochondrial function was assessed with sequential additions of adenosine diphosphate (ADP) to mimic a repeated demand for energy. Compared to controls, PHS mitochondria in Experiment 1 exhibited mitochondrial dysfunction [lower respiratory control (RCR) and ADP:O ratios and an inability to improve function with repeated energy demand] and oxidative stress [lower alpha-tocopherol and reduced glutathione (GSH) and higher oxidized glutathione levels (GSSG)]. High dietary alpha-tocopherol had no effect on lung mitochondrial function in healthy broilers (VE vs. controls) but attenuated dysfunction in VE-PHS mitochondria. In Experiment 2, there were no differences in selected and nonselected mitochondrial function following a single addition of ADP, but nonselected mitochondria exhibited lower RCR and ADP:O values with repeated energy demand. Higher GSSG levels were also observed in nonselected lung. The results indicate that lung mitochondrial dysfunction present in broilers with PHS was associated with oxidative stress and may be attenuated by high dietary vitamin E. Furthermore, genetic resistance to PHS was associated with more efficient oxidative phosphorylation in lung mitochondria and an inherently lower degree of oxidative stress.