The effect of liposomal charge on the distrubution of liposomes to the liver, brain, lungs and kidneys in a rat model

Abstract

English:Gentamicin was selected out of three drugs as the most appropriate liposomal marker based on its properties There after, a simple method for preparation of charged Iiposomes by rotary evaporation and hydration was adopted. Surface charge was induced by varying the lipid composition whereby neutral liposomes were prepared using phosphatidyl choline and cholesterol (9.7:6.9, molar ratio), negative and positive liposomes were prepared by addition of dieetyl phosphate (5: I :0.5, molar ratio) and stearylamine (5: I :0.5, molar ratio) to the neutral liposomes, respectively. The distribution of the encapsulated gentamicin to the specified organs in liposome treated groups was compared to a control group treated with free gentamicin at the following intervals: 1, 2, 4, 6 and 8 hours post injection. Gentamicin (60 mg/kg) free and liposome entrapped was administered intraperitoneally and five rats of each group were utilised at each time interval. Under ether anaesthesia, a blood sample was drawn and the relevant organs were harvested. The sodium hydroxide digestion method was used to extract gentamicin from the organs, and gentamicin in plasma and organ extracts was measured by fluorescence polarisation immunoassay. Liposomal characterisation revealed multilammelar Iiposomes with a mean internal diameter of 3.17 ± 1.9 urn, and encapsulation efficiency greater than 15 %. In the animal studies, liposomes delayed elimination of the encapsulated drug. The half life was 2.02 ± 0.5, 1.76 ± 0.1 and 2.04 ± 0.3 hours for the negative, positive and neutral liposome treated groups, respectively, . versus 1.53 ± 0.02 hours for the control group. Peak plasma gentamicin concentrations were higher with positive liposomes than negative and neutral liposomes at 1 hour, while the negative Iiposomes depicted a sustained release pattern between 4 and 8 hours. Distribution of liposomes to the brain and liver was dependent on liposomal surface charge. Liposomes improved gentamicin concentrations in the brain with positive liposomes highest in this regard. A biphasic pattern of distribution to the brain, with lowest gentamicin concentration at 4 hours was observed in the three liposome groups, and this was more marked in the negative liposome group. Generally, hepatic gentamicin concentrations were higher with liposomes than the control. Although, the average hepatic gentamicin concentrations were highest for positive liposomes, the negative liposomes were preferred for the liver because the concentrations were more consistent and increased with time. Uptake of gentamicin by the lungs was not enhanced by liposomes and was independent of surface charge of the liposomes. Renal concentrations of gentamicin were lower (3 to 5 folds) with liposomes, and uptake was not charge dependent. In conclusion, a simple method for preparation of liposomes was adopted. The distribution studies suggested that positively charged liposomes had highest affinity for the brain and the negative liposomes for the liver. Also, liposomes irrespective of charge exhibited reduced renal concentration of gentamicin.

Afrikaans: Gentamisien is uit drie middels gekies as die beste liposoommerker. 'n Eenvoudige metode is aangepas vir die voorbereiding van liposome met lading deur middel van rotasieverdamping en hidrering. Oppervlaklading is moontlik gemaak deur die lipiedsamestelling van die liposome te varieer. Neutrale liposome is voorberei deur fosfatidielcholien en cholesterol (9.7:6.9, mol verhouding) te gebruile Negatiewe en positiewe liposome is voorberei deur byvoeging van disetielfosfaat (5: 1:0.5, mol verhouding) en stearielamien (5:1 :0,5, mol verhouding) by neutrale liposome onderskeidelik. Die verspreiding van die gekapsileerde gentamisien na die spesifieke teikenorgane in die liposoombehandelde groepe is vergelyk met 'n kontrole groep wat behandel is met vrye gentamisien met tydsintervalle van 1, 2, 4, 6 en 8 ure na toediening. Vry gentamisien (60 mg/kg) en gentamisien bevattende liposome is intraperitoriaal toegedien en vyf rotte van elke groep is gebruik tydens elke tydsinterval. Bloedmonsters is tydens eterverdowing geneem en die spesifieke organe is verwyder. 'n Natrium Hidroksied verterings metode is gebruik om die gentamisien uit die organe te ekstraheer en die gentamisien in die plasma en organe is bepaal deur fluoreserende polarisasie immunobepaling. Liposoomkarakterisering toon 'n veelvoudige laag liposoom met '11 gemiddelde radius van 3.17 ± 1.9 urn met 'n inkapselering effektiwiteit van meer as 15 %. Tydens die dierestudies het die liposome die eliminasie van die gekapsileerde middel vertraag. Die half-leeftyd was 2.02 ± 0.5, 1.76 ± 0.1 en 2.04 ± 0.3 ure vir die negatiewe, positiewe en neutrale liposoombehandelde groepe onderskeidelik teenoor 1.53 ± 0.02 ure vir die kontrole groep. Die plasma gentamisien konsentrasies was hoër vir die positiewe Iiposome as vir die negatiewe en neutrale liposome by 1 uur, terwyl die negatiewe liposome 'n konstante vrystellingspatroon tussen 4 en 8 ure getoon het. Die verspreiding van die Jiposome na die brein en die lewer was afhanklik van die oppervlaklading van die liposome. Liposome met 'n positiewe lading verbeter die gentamisienkonsentrasie in die brein. 'n Dubbelfasige verspreidingspatroon na die brein indie drie liposoomgroepe is waargeneem met die laagste gentamisien konsentrasie by 4 ure. Die patroon was meer sigbaar in die negatiewe liposoomgroep. In die algemeen is die hepatiese gentamisien konsentrasie hoër in die teenwoordigheid van liposome as in die kontrole groep. Die gemiddelde hepatiese gentamisien konsentrasie was die hoogste vir die positief gelaaide liposome. Dit blyk egter dat die lewer die negatiewe liposome verkies, omdat die verhoogde gentamisien konsentrasie in die lewer meer konstant is gedurende die tydsinterval. Die opname van gentamisien deur die longe was nie verhoog deur die liposome nie en was onafhanklik van die oppervlaklading van die liposome. Gentamisienkonsentasie in die niere was drie tot vyf maal laer in die teenwoordigheid van liposome en is dus nie ladingafhanklik nie. In gevolgtrekking is 'n eenvoudige metode vir die voorbereiding van liposome aangepas. Die verspreidingstudies toon dat liposorne met positiewe lading die hoogste affiniteit het vir die brein en die negatiewe liposome vir die lewer. 'n Verlaagde gentamisienkonsentrasie is in die niere waargeneem ongeag die oppervlaklading van die liposome.