Low and high molecular weight poly(l-lysine)s/poly(l-lysine)–DNA complexes initiate mitochondrial-mediated apoptosis differently

P. Symonds, J.C. Murray, A.C. Hunter, G. Debska, A. Szewczyk, S.M. Moghimi

Research output: Contribution to journalArticlepeer-review


Poly(l-lysine)s, PLLs, are commonly used for DNA compaction and cell transfection. We report that, although PLLs of low (2.9 kDa), L-PLL, and high (27.4 kDa), H-PLL, Mw in free form and DNA-complexed cannot only cause rapid plasma membrane damage in human cell lines, phosphatidylserine “scrambling” and loss of membrane integrity, but later (24 h) initiate stress-induced cell death via mitochondrial permeabilization without the involvement of processed caspase-2. Mitochondrially mediated apoptosis was confirmed by detection of cytochrome c (Cyt c) release, activation of caspases-9 and -3, and subsequent changes in mitochondrial membrane potential. Plasma membrane damage and apoptosis were most prominent with H-PLL. Cytoplasmic level of Cyt c was more elevated following H-PLL treatment, but unlike L-PLL case, inhibition of Bax channel-forming activity reduced the extent of Cyt c release from mitochondria by half. Inhibition of Bax channel-forming activity had no modulatory effect on L-PLL-mediated Cyt c release. Further, functional studies of isolated mitochondria indicate that H-PLL, but not L-PLL, can directly induce Cyt c release, membrane depolarization, and a progressive decline in the rate of uncoupled respiration. Combined, our data suggest that H-PLL and L-PLL are capable of initiating mitochondrially mediated apoptosis differently. The observed PLL-mediated late-phase apoptosis may provide an explanation for previously reported transient gene expression associated with PLL-based transfection vectors. The importance of our data in relation to design of novel and safer cationic non-viral vectors for human gene therapy is discussed.
Original languageEnglish
Pages (from-to)6191-6198
Number of pages8
JournalFebs Letters
Issue number27
Publication statusPublished - Nov 2005


  • Apoptosis
  • Bax channel
  • Gene transfer systems
  • Mitochondria
  • Phosphatidylserine
  • Polyamines
  • Poly(l-lysine)
  • Poly(ethylenimine)


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