In vitro correlation of ultrastructural morphology and creatine phosphokinase release in L6 skeletal muscle cells after exposure to parenteral antibiotics

Effect of daptomycin on primary rat muscle cell cultures in vitro

Daptomycin is a lipopeptide antibiotic that has strong bactericidal activity against Gram-positive bacteria and that was previously reported to exhibit minor side effects on skeletal muscle. This study was designed to further characterize the effect of daptomycin on skeletal muscle through the use of primary cultures of muscles from rats. Our investigations demonstrated that daptomycin has a concentration-dependent and time-dependent effect on the plasma membrane of primary cultures of differentiated, spontaneously contracting rat myotubes. No effects were evident in non-differentiated myoblasts or other mononucleated cells present in cultures even at the highest daptomycin concentrations tested (6,000 microg/mL). In cultures treated with daptomycin at a concentration of 2,000 microg/mL, plasma membrane damage was observed in approximately 20-30% of differentiated myotubes; no myotube damage was detected at concentrations of 1,000 microg/mL and below. A transient loss of spontaneous myotube contractions was evident at 750 microg/mL, while at 2,000 microg/mL and above, a permanent loss of spontaneous contractility was observed. These results suggest that the putative targets for daptomycin effects on skeletal muscle are structures on the plasma membrane of highly differentiated myotubes.

Dp71, utrophin and beta-dystroglycan expression and distribution in PC12/L6 cell cocultures

Function of dystrophin Dp71 isoforms is unknown but seems related to neurite outgrowth and synapse formation. To evaluate Dp71 role in myoneural synapses, we established a coculture model using PC12 cells and L6 myotubes and analyzed expression and localization of Dp71 and related proteins, utrophin and beta-dystroglycan, in PC12 cells. Confocal microscopy showed Dp71d isoform in PC12 nuclei, golgi-complex-like and endoplasmic reticulum-like structures, whereas Dp71ab concentrates at neurite tips and cytoplasm, colocalizing with beta-dystroglycan, utrophin, synaptophysin and acetylcholine receptors. Evidences suggest that Dp71ab isoform, unlike Dp71d, may take part in neurite-related processes. This is the first work on Dp and members of Dp-associated protein complex roles in a cell-line based coculturing system, which may be useful in determining Dp71 isoforms associations.

Acute amphotericin B overdose

OBJECTIVE

To report the clinical course of a woman with cryptococcal meningitis and no previous cardiac disease who developed a fatal cardiac arrhythmia after an acute overdose of amphotericin B and to review its toxicity.

CASE SUMMARY

A 41-year-old woman with a history of proliferative glomerulonephritis from systemic lupus erythematosus was admitted with a diagnosis of cryptococcal meningitis. Liposomal amphotericin B was prescribed at the standard dose of 5 mg/kg/day; however, amphotericin B deoxycholate 5 mg/kg was inadvertently administered (usual dose of the deoxycholate formulation is 0.5-0.8 mg/kg/day). The patient developed cardiac arrhythmias, acute renal failure, and anemia. The medication error was noticed after she had received 2 doses of amphotericin B deoxycholate, and it was then discontinued. Despite treatment in the intensive care unit, the woman died on the sixth day after admission.

DISCUSSION

Amphotericin B deoxycholate has been reported to produce significant cardiac toxicity, with ventricular arrhythmias and bradycardia reported in overdoses in children and in adults with preexisting cardiac disease, even when administered in conventional dosages and infusion rates. Use of the Naranjo probability scale indicated a highly probable relationship between the observed cardiac toxicity and amphotericin B deoxycholate therapy in this patient.

CONCLUSIONS

Given the fulminant course of amphotericin B deoxycholate overdosage and lack of effective therapy, stringent safeguards against its improper administration should be in place.

An in vitro model for assessing muscle irritation of antibiotics using rat primary cultured skeletal muscle fibers

This study examined the possibility of using rat primary cultured skeletal muscle fiber to estimate the muscle irritation of antibiotics. The cells were exposed to cefaloridine (CER), cefazolin sodium (CEZ), flomoxef sodium (FMOX), cefamandole sodium (CMD), latamoxef sodium (LMOX), or cefalotin sodium (CET) at concentrations of 0 (control), 31.25, 62.5, 125, and 250 mg/ml in culture medium for 1 hr on Day 11 of culture. Cellular creatine kinase (CK) activity was measured as an indication of cell injury. The concentration of the antibiotic, at which CK activity decreased to 50% of the control (depletion concentration 50%, DC50), was utilized as an index of cytotoxicity. DC50s of CER, CEZ, FMOX, CMD, LMOX, and CET were estimated to be 406.7, 311.1, 211.6, 132.7, 114.2, and 56.5 mg/ml, respectively. There was a good correlation between DC50 obtained in the present in vitro test and the irritation volume in the in vivo test. These results suggest that the in vitro system using rat primary cultured skeletal muscle fibers is a useful alternative model for in vivo rabbit study to evaluate muscle irritation.