In vitro complement activation favoring soluble C5b-9 complex formation alters myocellular sodium homeostasis

Pegylated Nanocapsules Produced by an Organic Solvent-Free Method: Evaluation of their Stealth Properties

PURPOSE

To develop from an original process, a novel generation of stealth lipidic nanocapsules in order to improve the lipophilic drug delivery in accessible sites.

MATERIALS AND METHODS

Nanocapsules covered by PEG1500 stearate were obtained by a low energy emulsification method. Conductivity measurements and ternary diagram were performed to describe the formulation mechanism. Hemolytic dosage CH50 and pharmacokinetic study in rats have been achieved in order to study the stealth properties of nanocapsules.

RESULTS

Transition from an O/W emulsion to a w/O/W emulsion was necessary to produce PEG1500 stearate nanocapsules. Interestingly nanocapsules with a size around 26 nm and a polydispersity index inferior to 0.1 were obtained. The CH50 test has revealed a very weak complement consumption in the presence of such nanocapsules. Moreover, after intravenous injection into rats, PEG1500 stearate nanocapsules exhibited long circulating properties. The experimental data support the concept of steric repulsion of the surface towards proteins, displayed by nanocapsules covered with PEG1500 stearate. These in vivo results were in agreement with the PEG1500 density calculated at the nanocarrier surface.

CONCLUSIONS

Injectable drug carriers have been developed. Their long-circulating properties could confer them a strong potential for lipophilic drug targeting.

Activation of multiple signaling pathways by terminal complement complexes involved in myocellular sodium homeostasis

Soluble C5b-9 complexes (SC5b-9), hemolytically inactive end-products of complement activation have long been considered to be irrelevant. Recent investigations, however, have demonstrated that SC5b-9 induces numerous biological effects via a series of intracellular signal transduction events. We have previously demonstrated that SC5b-9 enriched sera increased intracellular Na+ in rat skeletal muscles. This study was purposed to determine if the protein kinase C (PKC) or mitogen-activated protein kinase (MAPK) signaling pathway mediates the effects of SC5b-9. Fast-twitch extensor digitorum longus (EDL) muscles isolated from infant rats were incubated at 30 degrees C for 60 minutes with 10% zymosan-activated rat sera (ZARS) as a source of complement. Heat-inactivated rat sera (HIRS) were used as a control. The muscles were also incubated with ZARS or HIRS in the presence of specific inhibitors against PKC (GF109203X) or MAPK (PD98059 and SB202190). Intracellular Na+ and K+ contents were then measured. ZARS significantly increased intracellular Na+ and the Na+/K+ ratio in EDL muscles as compared to HIRS. GF109203X, PD98059 and SB202190 markedly attenuated increase in myocellular Na+ induced by ZARS, respectively. We concluded that SC5b-9 enriched sera alter myocellular Na+ homeostasis, at least in part, via the mechanisms linked to PKC and MAPK signal transduction pathways.

Does endotoxin-activated complement alter myocellular sodium homeostasis during sepsis?

BACKGROUND

Inappropriate complement activation is closely related to tissue injury and organ dysfunction during systemic infection. It is not clear, however, if endotoxin-induced complement activation is responsible for changes in myocellular sodium homeostasis during sepsis.

METHODS

Rats underwent cecal ligation and puncture (CLP) or sham operation. Twenty-four hours after operation, fast-twitch extensor digitorum longus (EDL) muscles were isolated, incubated at 30 degrees C for 1 hour in Krebs-Henseleit buffer (KHB) (pH 7.4), and used to measure intracellular Na+ and K+ contents. Blood samples were collected to measure serum hemolytic complement activity and endotoxin levels. In addition, EDL muscles isolated from normal animals were incubated at 30 degrees C for 1 hour with zymosan-activated (10 mg/mL at 37 degrees C for 1 hour) rat sera, with lipopolysaccharide (LPS)-activated (LPS from Escherichia coli 055:B5, 10 or 200 microg/mL at 37 degrees C for 30 minutes) rat sera, with heat-inactivated (56 degrees C for 30 minutes) rat sera, with LPS (1 or 20 microg/mL), or in KHB. EDL muscles isolated from normal animals were also incubated with septic sera collected 6 or 24 hours after CLP with or without administration of soluble complement receptor type 1 (20 mg/kg, intraperitoneally). Myocellular Na+ and K+ contents ([Na+]i and [K+]i) were assayed using "washout" technique. Soluble C5b-9 complex levels in zymosan-activated or LPS-activated human sera were determined by enzyme-linked immunosorbent assay to evaluate the degree of complement activation induced by zymosan or LPS.

RESULTS

Myocellular [Na+]i and [Na+]i/[K+]i ratios increased significantly 24 hours after CLP as compared with sham operation and were associated with decreased serum hemolytic complement activity and increased serum endotoxin levels. Zymosan-activated rat sera at sublytic concentrations markedly increased [Na+]i and [Na+]i/[K+]i ratios in isolated EDL muscles relative to heat-inactivated rat sera. LPS-activated rat sera, however, did not alter these two indices. In addition, myocellular [Na+]i and [Na+]i/[K+]i ratios were equivalent among normal EDL muscles incubated with septic sera, soluble complement receptor type 1-treated septic sera, or KHB.

CONCLUSION

These results collectively suggest that polymicrobial sepsis, as produced by CLP, alters sodium homeostasis in fast-twitch skeletal muscles in association with changes in systemic complement activation and circulating endotoxin levels. Although endotoxin can activate the complement cascade, endotoxin-induced complement activation does not appear to be responsible for changes in myocellular sodium homeostasis observed during sepsis in rats.

Complement activation alters myocellular sodium homeostasis during polymicrobial sepsis

OBJECTIVE

To determine whether complement activation alters sodium homeostasis in fast-twitch skeletal muscles during sepsis, and if protein kinase-C is involved in this process.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

Research laboratory.

SUBJECTS

Male Sprague-Dawley rats weighing 60-75 g.

INTERVENTIONS

Rats underwent cecal ligation and puncture (CLP) or sham-operation with or without soluble complement receptor-1 treatment. Soluble complement receptor-1 (20 mg/kg) was administered intraperitoneally 5 mins before operation. Twenty-four hours after operation, fast-twitch extensor digitorum longus muscles were isolated and incubated in normal Krebs-Henseleit buffer (pH 7.4). In addition, extensor digitorum longus muscles isolated from normal rats were incubated for 1 hr in the Krebs-Henseleit buffer media containing normal rat sera, zymosan-activated (4 or 10 mg/mL) rat sera, or heat-inactivated rat sera. Ten percent diluted rat sera were used as a complement source in all groups. Last, extensor digitorum longus muscles isolated from normal rats were incubated for 1 hr in the Krebs-Henseleit buffer media containing zymosan-activated or heat-inactivated rat sera in the presence of protein kinase-C inhibitors (i.e., 4 microM GF109203X or 5 microM rottlerin). Soluble C5b-9 complex concentrations in zymosan-activated human sera were determined by enzyme-linked immunosorbent assay to evaluate the degree of complement activation induced by zymosan.

MEASUREMENTS AND MAIN RESULTS

Incubated extensor digitorum longus muscles from CLP, sham-operated, or normal rats were used to measure intracellular Na+ and K+ contents ([Na+]i or [K+]i). Polymicrobial sepsis, as produced by CLP, markedly increased [Na+]i and [Na+]i/[K+]i ratios in fast-twitch extensor digitorum longus muscles 24 hrs after CLP compared with sham operation. Administration of soluble recombinant complement receptor 1 before operation significantly decreased myocellular [Na+]i and [Na+]i/[K+]i ratios. Zymosan profoundly elevated soluble C5b-9 concentrations in human sera in vitro. Sublytic zymosan-activated rat sera significantly increased myocellular [Na+]i and [Na+]i/[K+]i ratios relative to heat-inactivated rat sera. No difference in myocellular [Na+]i and [Na+]i/[K+]i ratios was observed when we used 4 mg/mL compared with 10 mg/mL of zymosan for activation. Last, incubation of extensor digitorum longus muscles with GF109203X or rottlerin significantly attenuated increases in myocellular [Na+]i and [Na+]i/[K+]i ratios induced by sublytic zymosan-activated rat sera.

CONCLUSIONS

Polymicrobial sepsis alters sodium homeostasis in fast-twitch skeletal muscles, which is significantly attenuated by administration of soluble complement receptor 1. Protein kinase-C inhibition completely blocks changes in myocellular [Na+]i and [Na+]i/[K+]i ratios induced by sublytic zymosan-activated rat sera. Collectively, these results suggest that an inappropriate activation of complement is, at least in part, responsible for changes in skeletal muscle sodium homeostasis during sepsis, and activation of PKC is one of the intracellular signaling pathways by which complement activation alters myocellular sodium homeostasis.