A Nanostructured Lipid System as a Strategy to Improve the in Vitro Antibacterial Activity of Copper(II) Complexes

Abstract

Abstract:The aim of this study was to construct a nanostructured lipid system as a strategy to improve the in vitro antibacterial activity of copper(II) complexes. New compounds with the general formulae [CuX 2 (INH) 2 ]¨nH 2 O (X = Cl´and n = 1 (1); X = NCS´and n = 5 (2); X = NCO´and n = 4 (3); INH = isoniazid, a drug widely used to treat tuberculosis) derived from the reaction between the copper(II) chloride and isoniazid in the presence or absence of pseudohalide ions (NCS´or NCO´) were synthesized and characterized by infrared spectrometry, electronic absorption spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, elemental analysis, melting points and complexometry with 2,2 1 ,2 11 ,2 111 -(Ethane-1,2-diyldinitrilo)tetraacetic acid (EDTA). The characterization techniques allowed us to confirm the formation of the copper(II) complexes. The Cu(II) complexes were loaded into microemulsion (MEs) composed of 10% phase oil (cholesterol), 10% surfactant [soy oleate and Brij 58 (1:2)] and 80% aqueous phase (phosphate buffer pH = 7.4) prepared by sonication. The Cu(II) complex-loaded MEs displayed sizes ranging from 158.0˘1.060 to 212.6˘1.539 nm, whereas the polydispersity index (PDI) ranged from 0.218˘0.007 to 0.284˘0.034. The antibacterial activity of the free compounds and those that were loaded into the MEs against Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922, as evaluated by a microdilution technique, and the cytotoxicity index (IC 50 ) against the Vero cell line (ATCC CCL-81 TM ) were used to calculate the selectivity index (SI). Among the free compounds, only compound 2 (MIC 500 µg/mL) showed activity for S. aureus. After loading the compounds into the MEs, the antibacterial activity of compounds 1, 2 and 3 was significantly increased against E. coli (MIC's 125, 125 and 500 µg/mL, respectively) and S. aureus (MICs 250, 500 and 125 µg/mL, respectively). The loaded compounds were less toxic against the Vero cell line, especially compound 1 (IC 50 from 109.5 to 319.3 µg/mL). The compound 2-and 3-loaded MEs displayed the best SI for E. coli and S. aureus, respectively. These results indicated that the Cu(II) complex-loaded MEs were considerably more selective than the free compounds, in some cases, up to 40 times higher.

Nanostructured lipid carriers for incorporation of copper(II) complexes to be used against <em>Mycobacterium tuberculosis</em>

“…Silva et al15,17 performed cytotoxicity assays (IC 50 ) of complexes 1, 2, and 3 using Vero (ATCC ® CCL-81), J774A.1 (ATCC ® TIB-67), and MRC-5 (ATCC ® CCL-171) cell lines. No toxic effects of the complexes were identified.…”

“…All the solutions were prepared using deionized water from a Millipore filtration system (EMD Millipore Billerica). The copper(II) complexes [CuCl 2 (INH) 2 ]·H 2 O (1), [Cu(NCS) 2 (INH) 2 ]·5H 2 O (2), and [Cu(NCO) 2 (INH) 2 ]·4H 2 O (3) were synthesized according to Silva et al15…”

“…Evaluation of the antimicrobial activity showed the activity and selectivity of the copper(II) complexes against bacteria, such as Staphylococcus aureus and Escherichia coli , were increased after the incorporation of the complexes into these systems, by analysis of cellular viability 15. Another study conducted by the same group showed that the copper(II) complexes loaded into nanostructured lipid systems also exhibited increased activity against M. tuberculosis 17.…”

“…However, the low solubility of metallic compounds in water makes their application in several in vivo experiments unfeasible 15. To minimize this problem, nanostructured systems have been developed in order to increase the solubility of the active substance and create a controlled-release system, which maintains the drug plasma concentration within the therapeutic range for several hours or days, and results in decreased toxicity and increased patient compliance 16…”

Antibacterial Activity of 7-Epiclusianone and Its Novel Copper Metal Complex on Streptococcus spp. Isolated from Bovine Mastitis and Their Cytotoxicity in MAC-T Cells

“…Historically, Chinese and Arabs used zinc to promote wound healing, while Egyptians used copper to sterilize water [ 15 ]. There is growing interest in Cu 2+ complexes [ 16 ]. Among metallic ions, copper and its compounds have been used as effective agents against bacteria, fungi, viruses, and mollusks.…”