Nitric oxide synthase activity in muscle foods

S-nitrosoproteomics profiling elucidates the regulatory mechanism of S-nitrosylation on beef quality

This study aimed to quantitively profile the S-nitrosylation in beef semimembranosus (SM) with different treatments (nitric oxide donor or nitric oxide synthase inhibitor) by applying iodoTMT-based nitrosoproteomics. Results showed that 2096 S-nitrosylated cysteine sites in 368 proteins were detected in beef SM. Besides, differential SNO-modified proteins were screened, some of which were involved in crucial biochemical pathways, including calcium-releasing-related proteins, energy metabolic enzymes, myofibrils, and cytoskeletal proteins. GO analysis indicated that differential proteins were localized in a wide range of cellular compartments, such as cytoplasm, organelle, and mitochondrion, providing a prerequisite for S-nitrosylation exerting broad roles in post-mortem muscles. Furthermore, KEGG analysis validated that these proteins participated in the regulation of diverse post-mortem metabolic processes, especially glycolysis. To conclude, changes of S-nitrosylation levels in post-mortem muscles could impact the structure and function of crucial muscle proteins, which lead to different levels of muscle metabolism and ultimately affect beef quality.

Targeted energy metabolomics analysis of postmortem pork in an in vitro model as influenced by protein S-nitrosylation

For exploring the effect of protein S-nitrosylation on the energy metabolism of early postmortem pork (within 24 h postmortem), the six Longissimus thoracis (LT) muscle homogenates were treated with nitric oxide donor (NOR-3, (±)-(E)-4-Ethyl-2-(E)-hydroxyimino-5-nitro-3-hexenamide), nitric oxide synthase (NOS) inhibitor (L-NAME, Nω-nitro-L-arginine methyl ester hydrochloride) and control (0.1 M K₂HPO₄, pH 7.4) in the in vitro buffer system for 24 h, respectively. The western blotting result showed that NOR-3 treatment led to a greater level of protein S-nitrosylation (p < 0.05). However, S-nitrosylation levels had no significant difference between L-NAME and control groups (p > 0.05). In addition, results showed that 16 significantly differential energy metabolites were identified by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and clearly separated among three groups in the principal component analysis. Four pathways (glycolysis, tricarboxylic acid cycle, purine metabolism and pentose phosphate pathway) related to energy metabolism were significantly influenced by different levels of protein S-nitrosylation. Furthermore, the correlation analysis of metabolites demonstrated that metabolites were in dynamic equilibrium with each other. These results indicate that protein S-nitrosylation can participate in and regulate energy metabolism postmortem pork through glycolysis and tricarboxylic acid (TCA) cycle.

Arginine supplementation may improve color and redox stability of beef loins through delayed onset of mitochondrial-mediated apoptotic processes

The objective of this study was to evaluate the effects of arginine (ARG) and/or lysine (LYS) supplementation on meat quality and oxidative stability of beef loins. Steers (n = 40) were split among four dietary treatments (control, ARG, LYS or ARGLYS). The loins (longissimus lumborum) were obtained at 1 day postmortem and aged either 14 or 28 days prior to cutting of steaks for 7 days of display. No impacts of diet treatments on instrumental tenderness, water-holding capacity and fatty acid profiles were found (P > 0.05). Extended aging significantly decreased lipid oxidative stability, color stability and reducing ability of loins. However, steaks from ARG and ARGLYS maintained superior color stability coupled with lower mitochondrial membrane permeability and higher cytochrome c redox stability compared to control (P < 0.05). These results indicate that ARG supplementation can improve color stability of beef loins possibly through delayed onset of mitochondrial-mediated apoptotic processes.

Comparison of activity, expression and S-nitrosylation of glycolytic enzymes between pale, soft and exudative and red, firm and non-exudative pork during post-mortem aging

The activity, expression and S-nitrosylation of glycogen phosphorylase (GP), phosphofructokinase (PFK) and pyruvate kinase (PK) was compared between pale, soft and exudative (PSE) and red, firm and non-exudative (RFN) pork. The nitric oxide synthase (NOS) activity of RFN pork was higher than PSE pork (P < 0.05). Glycogen and lactic acid content were significantly different between PSE and RFN samples at 1 h postmortem (P < 0.05). Compared to PSE pork, RFN pork had lower activities and higher S-nitrosylation levels of GP, PFK and PK (P < 0.05). Moreover, GP expression in RFN pork was lower (P < 0.05) while no significant differences of PFK and PK expression were observed between these two groups. These data suggest that protein S-nitrosylation can presumably regulate glycolysis by modulating glycolytic enzymes activities and then regulate the development of PSE pork.

Effect of nitric oxide on myofibrillar proteins and the susceptibility to calpain-1 proteolysis

This study was designed to investigate the nature of modification of myofibrillar proteins by nitric oxide (NO) and the extent to which S-nitrosylation alters their susceptibility to calpain-1 proteolysis. Isolated myofibrils from porcine semimembranosus muscle were incubated with the NO donor S-nitrosoglutathione (GSNO) at 0, 20, 50, 250, 1000 µM for 30 min at 37 °C and then incubated with purified calpain-1. GSNO treatment decreased the thiol content of myofibrillar proteins and increased their intensity and amount of S-nitrosylation. GSNO caused the formation of proteins cross-linkage through intermolecular disulfide. More desmin and titin (T2, the degraded fragment of original titin) were degraded by calpain-1 when myofibrils were incubated with 1000 µM GSNO. Incubation with 250 and 1000 µM GSNO suppressed calpain-1-catalyzed cleavage of troponin-T. The data suggest that NO could change the redox state of myofibrillar proteins and subsequently affect the extent of proteolysis by calpain-1 in a protein-dependent manner.

Effect of protein S-nitrosylation on autolysis and catalytic ability of μ-calpain

The effect of S-nitrosylation on the autolysis and catalytic ability of μ-calpain in vitro in the presence of 50μM Ca(2 +) was investigated. μ-Calpain was incubated with different concentrations of nitric oxide donor S-nitrosoglutathione (GSNO) and subsequently reacted with purified myofibrils. Results showed that the amount of 80kDa μ-calpain subunit significantly decreased as GSNO increased from 0 to 300μM, but increases of GSNO to 300, 500 and 1000μM did not result in further inhibition. The catalytic ability of nitrosylated μ-calpain to degrade titin, nebulin, troponin-T and desmin was significantly reduced when the GSNO concentration was higher than 300μM. The cysteine residues of μ-calpain at positions 49, 351, 384, and 592 in the catalytic subunit and at 142 in small subunit were S-nitrosylated, which could be responsible for decreased μ-calpain activity. Thus, S-nitrosylation can negatively regulate the activation of μ-calpain resulting in decreased proteolytic ability on myofibrils.

Effects of infusing nitric oxide donors and inhibitors on plasma metabolites, muscle lactate production and meat quality in lambs fed a high quality roughage-based diet

As nitric oxide (NO) is postulated to be a mediator of the effects of pre-slaughter stress on meat quality the aims of this experiment were to investigate the effects of modulating NO pharmacologically on meat quality of sedentary lambs. As pharmacological NO donors are prohibitively expensive to use in the lamb model L-Arginine, the substrate for NO synthase (NOS) was infused into lambs and increased NO production by ~30%. In a 2 × 2 factorial design we infused either L-Arginine (500 mg/kg) or the NOS inhibitor L-N(G) nitroarginine methyl ester hydrochloride (L-NAME, 30 mg/kg) 190 min pre-slaughter and investigated meat quality in the Longissimus thoracis lumborum (LTL) or Semimembranosus (SM). The principal outcome of the experiment was that L-NAME inhibited proteolysis and reduced tenderness in the SM. These data indicate that events pre-slaughter that affect NO synthesis can influence meat tenderness, potentially via altered muscle metabolism or modulation of proteolytic enzymes.

Effect of nitric oxide on μ-calpain activation, protein proteolysis, and protein oxidation of pork during post-mortem aging

The aim of the current research was to examine the influence of nitric oxide (NO) on calpain activation, protein proteolysis, and oxidation in post-mortem pork. Five longissimus muscles were removed from carcass after slaughter, and samples were incubated with water, nitric oxide synthase (NOS) inhibitor, or NO donor for 24 h at 4 °C. The samples were taken out and then stored under 4 °C for 1, 4, and 7 d. Results showed that autolysis of μ-calpain increased by incubation with NOS inhibitor after storage for 1 d (P<0.05). Degradation of titin and nebulin increased by treatment of NOS inhibitor among three treatments (P<0.05). Higher levels of protein oxidation were observed after samples incubated with NO donor than treatment of NOS inhibitor (P<0.05). These data indicated that NO could participate in regulating calpain activation and its proteolysis activity during post-mortem aging.

Breast meat quality of broiler chickens can be affected by managing the level of nitric oxide

The objective of this study was to investigate the effects of nitric oxide (NO) on the quality of broiler chicken meat during postmortem storage. Eighteen broiler chickens were slaughtered and breast meat was randomly assigned to 1 of 3 treatments including the control group, nitric oxide synthase (NOS) inhibitor group, and NO enhancer group. The breast samples were incubated with water, NO enhancer, and NO inhibitor for 1 d and then stored at 4°C under atmospheric conditions for 4 and 7 d. Left side of breast meat was used to determine protein oxidation, lipid oxidation, water-holding capacity, and pH, whereas the right side was used for the measurement of color and drip loss. Breast meat from NO enhancer group showed the lowest water-holding capacity during refrigerated storage, whereas drip losses were not significantly (P > 0.05) different among 3 treatments. Lipid oxidation showed a significant difference (P < 0.05) only at 7 d in which NOS inhibitor group showed the highest, whereas the NO enhancer group showed the lowest levels of lipid oxidation. Carbonyl content in NO enhancer group was significantly higher than the control and NOS inhibitor treatment at 1 and 4 d of refrigerated storage. Lightness of breast meat in the NOS inhibitor group was greater, whereas redness was lower than the control and NO enhancer group at 4 and 7 d of refrigerated storage. The ultimate pH of 3 treatments was not significantly (P > 0.05) different from one another. These data indicate that NO could play a significant role in modulating the quality of fresh broiler breast meat during refrigerated storage.

Inhibition of nitric oxide release pre-slaughter increases post-mortem glycolysis and improves tenderness in ovine muscles

The aim of this experiment was to determine the effect of inhibiting the release of nitric oxide (NO) pre-slaughter in lambs on post-slaughter muscle metabolism and meat quality. Exercise was used as a positive control as NO is known to be released in skeletal muscle during exercise. Forty Border Leicester×Merino lambs were assigned to the treatments L-NAME (NO synthase inhibitor) infusion (0mg/kg vs. 30mg/kg, 135min pre-slaughter) and exercise (none vs. 15min immediately pre-slaughter). The inhibition of NO release using L-NAME reduced Warner-Bratzler shear force (WBSF) in the longissimus thoracis et lumborum (LTL) after 3days of ageing, while the Semimembranosous (SM) was unaffected. Inhibition of NO release with L-NAME resulted in altered glucose metabolism as indicated by reduced plasma glucose pre-slaughter particularly in exercised lambs, reduced LTL and SM glycogen of non-exercised lambs post-slaughter and increased SM lactate in exercised lambs post-slaughter. In conclusion, inhibition of NO Synthase with L-NAME pre-slaughter increases post-mortem glycolysis and improves tenderness in the loin muscle.

The significance of diet, slaughter weight and aging time on pork colour and colour stability

The objective of the present study was to investigate the effect of a diet with a low content of digestible starch, slaughter weight and subsequent aging time on meat colour and colour stability. Pork colour was determined as the extent of blooming of M. longissimus thoracis (LT) and M. semimembranosus (SM) after 1, 2, 4, 8 and 15 days postmortem and as colour stability during a subsequent storage period in air for 6 days. Compared to the control diet, the experimental diet resulted in a significantly lower postmortem muscle temperature (1°C; p<0.0001). Moreover, high slaughter weight (110kg) resulted in a higher postmortem temperature in LT (p<0.001) compared to low weight (85kg). Independent of feeding strategy and slaughter weight, the extent of blooming decreased during the first 2-4 days of aging in LT, however, the effect was more pronounced in meat from experimentally fed pigs and pigs with high slaughter weight. This effect was not seen in SM, where a gradual increase in blooming took place throughout the aging period. The colour stability was found to be superior in aged pork from experimentally fed pigs. The discoloration rate was faster in SM compared to LT. In conclusion, the present study shows that the diet composition can be used as a tool to control meat colour and colour stability in pork.

Evaluation of NO-suppressing activity of several Mediterranean culinary spices

Excess nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) is implicated in the development of a number of diseases. Due to the absence of any natural specific enzymatic defense system in vivo, the consumption of certain foods which exhibit selective suppressive ability as regards NO overproduction might boost the host's protective effects against NO-mediated toxicity. Spices, rich in phenolics, are speculated conceivably to act as potential NO-scavengers or iNOS suppressors. The relative NO-suppressing activity of methanol extracts deriving from nine Mediterranean culinary spices was determined by measuring their inhibitory effect upon NO production for lipopolysaccharide (LPS)-activated RAW 264.7 macrophages. In addition, the specifics of the suppressing mechanism were further explored. All of the spices tested, with the exception of clove, displayed a rather linear dose-dependent NO-suppressing effect without there appearing to exist any effect upon cell viability. Furthermore, the NO-suppressing capacity of certain spices was able to be ranked based upon their IC(50) (the concentration of spice extracts is required to cause 50% inhibition of NO production by LPS-activated RAW 264.7 cells), the ranking appearing as: rosemary (0.031%)>tarragon (0.052%)>cinnamon (0.059%)>oregano (0.106%)>basil (0.162%)>marjoram (0.236%)>allspice (0.269%)>and thyme (0.270%). Only cinnamon displayed excellent NO-scavenging ability, whereas all of the other spices demonstrated moderate to poor activities in this regard. Moreover, the inhibitory effect of tested spices upon the iNOS protein level was almost equivalent to their suppressive effect upon NO production. It would appear that inhibition of iNOS expression was the primary mechanism of action of spices as regards their exerting NO-suppressing activity.