Repeated cures with paracetamol worsen sarcopenia in old rats with suboptimal food intake

The availability of all amino acids is of prime importance to prevent the ageing-associated decrease in skeletal muscle mass i.e. sarcopenia. Cysteine is the precursor of sulfate and glutathione that are both utilized in the liver to detoxify paracetamol (APAP). Cysteine availability could become limiting under repeated cures with APAP, especially when food intake is suboptimal. The aim of the study was to determine whether repeated cures with APAP could worsen sarcopenia. Twenty-two-month-old male Wistar rats received 3 two-week-long cures of APAP (1% of the diet) intercalated with washout periods of two weeks (APAP group). They were compared to untreated control rats euthanatized prior to the experiment (CT group) and rats pair-fed to the APAP group (PF group). Skeletal muscle mass and protein metabolism, as well as plasma amino acids and glutathione were assessed at the end of the third cure. APAP cures reduced food intake by 33, 23 and 33 % during the successive cures leading to an overall body weight loss of 8%. APAP rats lost lean mass during the experiment (-11%). This loss tended (P = 0.09) to be higher than in the PF group (-9%). The mass of hind limb muscles and the absolute synthesis rate of muscle proteins were 13 and 17% lower in the APAP group than the PF group, respectively. Plasma free cyst(e)ine (i.e. all free forms of cysteine not bound to proteins) and glutathione were 25% lower in the APAP group than the PF group. Repeated cures with APAP worsened sarcopenia in old rats with suboptimal food intake likely as a consequence of the APAP-induced shortage in cysteine/glutathione. Clinical studies are needed to clarify the effect of repeated treatments with paracetamol on skeletal muscle mass in older persons having suboptimal or insufficient dietary intakes.

Oligonucleotide covalent modifications by estrogen quinones evidenced by use of liquid chromatography coupled to negative electrospray ionization tandem mass spectrometry

Liquid chromatography coupled to tandem mass spectrometry has been used for the detection and the structural characterization of T-rich model oligonucleotides covalently modified by estradiol-2,3-quinone. After separation by gradient elution, adducts were analyzed by negative electrospray mass spectrometry, enabling to evidence and localize the modifications in the oligonucleotide sequence. Modifications by one molecule of estrogen were evidenced on purines (A, G) whereas no reaction was observed on pyrimidic bases (T). Isomeric adducts were differentiated using tandem mass spectrometry, and energy resolved mass spectrometry allowed to underline differences in the behavior of the adducts towards collisional excitation into an ion trap device.

Methionine transsulfuration is increased during sepsis in rats

Methionine transsulfuration in plasma and liver, and plasma methionine and cysteine kinetics were investigated in vivo during the acute phase of sepsis in rats. Rats were infected with an intravenous injection of live Escherichia coli, and control pair-fed rats were injected with saline. Two days after injection, the rats were infused for 6 h with [(35)S]methionine and [(15)N]cysteine. Transsulfuration was measured from the transfer rate of (35)S from methionine to cysteine. Liver cystathionase activity was also measured. Infection significantly increased (P < 0.05) the contribution of transsulfuration to cysteine flux in both plasma and liver (by 80%) and the contribution of transsulfuration to plasma methionine flux (by 133%). Transsulfuration measured in plasma was significantly (P < 0.05) higher in infected rats than in pair-fed rats (0.68 and 0.25 micromol. h(-1). 100 g(-1), respectively). However, liver cystathionase specific activity was decreased by 17% by infection (P < 0.05). Infection increased methionine flux (16%, P < 0.05) less than cysteine flux (38%, P < 0.05). Therefore, the plasma cysteine flux was higher than that predicted from estimates of protein turnover based on methionine data, probably because of enhanced glutathione turnover. Taken together, these results suggest an increased cysteine requirement in infection.

Metabolism of cysteine is modified during the acute phase of sepsis in rats

In vivo cysteine metabolism during the inflammatory state has been studied minimally. We investigated cysteine metabolism (i.e. taurine, sulfate and glutathione formation) using a single dose of [35S] cysteine in septic rats that had been injected with live Escherichia coli into the tail vein and in control, pair-fed rats. Cysteine metabolites were separated by ion exchange chromatography, and radioactivity was counted in the different fractions. Radioactivity incorporated in tissue proteins was also measured after protein precipitation. [35S]Sulfate production was significantly lower in septic rats than in pair-fed rats. [35S]Taurine contents were significantly lower only in kidneys, spleen and gastrointestinal tract of septic rats. The higher production of [35S] taurine in the livers (the major site of taurine production) of septic rats could have a protective effect against oxidation. Glutathione concentrations were also significantly greater in liver, spleen, kidneys and gastrocnemius muscle of septic rats, presumably in order to combat oxidative stress induced by sepsis. [35S]Cysteine incorporation in glutathione was significantly higher in spleen and kidneys but not in liver of septic rats compared to pair-fed rats. This could be explained by the fact that, in liver, a greater amount of labeled glutathione had been utilized for host defense, or by a high level in glutathione turnover. Finally, [35S]cysteine incorporation into protein, in septic rats, was significantly greater than in pair-fed rats in spleen, lung and particulary in whole plasma proteins other than albumin, which mainly represent the acute-phase proteins. These data suggest an increased requirement for cysteine during sepsis in rats.

Modulation of skeletal muscle lactate metabolism following bacteremia by insulin or insulin-like growth factor-I: effects of pentoxifylline

Hyperlactatemia is a frequent complication of sepsis. We investigated the effect of pentoxifylline on plasma lactate concentrations and lactate release by epitrochlearis incubated in vitro following intravenous injection of Escherichia coli. Plasma lactate concentrations were elevated on day 2 postinfection and remained elevated for at least another 4 days. Lactate production by incubated epitrochlearis was not increased in septic rats on day 2 postinfection, and lactate production from muscles incubated with insulin (2 nM) or insulin-like growth factor-I, (10 nM) was similar in control and septic rats. On day 6 postinfection, lactate production was augmented 1.8-fold in muscles from septic rats and both insulin and IGF-I caused an exaggerated stimulation of lactate production compared with control. Pentoxifylline decreased plasma TNF concentrations 100-fold following injection of bacteria and prevented the sepsis-induced hyperlactatemia and increase in lactate production by incubated muscles in presence or absence of insulin or IGF-I. Thus, pentoxifylline prevented the sepsis-induced abnormalities in skeletal muscle lactate production and plasma lactate concentrations.

Muscle wasting in a rat model of long-lasting sepsis results from the activation of lysosomal, Ca2+ -activated, and ubiquitin-proteasome proteolytic pathways

We studied the alterations in skeletal muscle protein breakdown in long lasting sepsis using a rat model that reproduces a sustained and reversible catabolic state, as observed in humans. Rats were injected intravenously with live Escherichia coli; control rats were pair-fed to the intake of infected rats. Rats were studied in an acute septic phase (day 2 postinfection), in a chronic septic phase (day 6), and in a late septic phase (day 10). The importance of the lysosomal, Ca2+ -dependent, and ubiquitin-proteasome proteolytic processes was investigated using proteolytic inhibitors in incubated epitrochlearis muscles and by measuring mRNA levels for critical components of these pathways. Protein breakdown was elevated during the acute and chronic septic phases (when significant muscle wasting occurred) and returned to control values in the late septic phase (when wasting was stopped). A nonlysosomal and Ca2+ -independent process accounted for the enhanced proteolysis, and only mRNA levels for ubiquitin and subunits of the 20 S proteasome, the proteolytic core of the 26 S proteasome that degrades ubiquitin conjugates, paralleled the increased and decreased rates of proteolysis throughout. However, increased mRNA levels for the 14-kD ubiquitin conjugating enzyme E2, involved in substrate ubiquitylation, and for cathepsin B and m-calpain were observed in chronic sepsis. These data clearly support a major role for the ubiquitin-proteasome dependent proteolytic process during sepsis but also suggest that the activation of lysosomal and Ca2+ -dependent proteolysis may be important in the chronic phase.