**5. Conclusions and perspectives**

At present the use of NLs as autonomous carriers of genetic material in human gene therapy can be considered an opportunity that needs extensive exploration to become a real alternative to CLs. Considering the many limits the latter still meet, particularly in the *in vivo* applications, and their slow progress, it seems important to take also the parallel way of NLs as possible autonomous carriers: lack of toxicity and high stability in serum are important characteristics in their favour. Some of the results outlined here are worth interesting developments. It has been found that complexes reflect the structure and symmetry of the parent lipids and that the different bivalent metal cations are equally active in promoting the DNA condensation into the ternary complexes; these achievements will provide structure-composition correlation, that may be used in designing at the best these materials as non-viral DNA carriers in HGT. Additional developments of the research in this field, currently investigated in our laboratories, concern the use of pegylated NLs in the management of brain related diseases, where CLs have started being experimented (Zhang et al., 2002; Pardridge, 2007; Boardo, 2007). Better results could be perhaps obtained with NLs, thanks to their ability to reduce opsonisation. The recent interest in the so-called intelligent carriers which is developing on CLs (Voinea & Simionescu, 2002; Shi et al., 2002; Alvarez-Lorenzo et al., 2009) could also represent an interesting opportunity for NLs. The structural knowledge of complexes of DNA with NLs is only one of the aspects which will presumably affect the transfection: many other aspects, such as Z-potential values, complex size, and efficient DNA entrapment are all very important acquisitions to be obtained. The entry of NLs in the world of HGT and the consequent opportunity to compare properties and activity with the ones of cationic and anionic liposomes will lead to a better understanding of that processes. In this connection is encouraging to quote the opinion of Rädler, one of the most outstanding experts in cationic lipids: "the resources devoted to creating less toxic cationic-DNA complexes, may perhaps, in the future be balanced by research exploiting the possibility of creating comparable complexes from entirely non toxic components such as the NLs/DNA/M2+ complexes".
