Homing of negatively charged albumins to the lymphatic system - General implications for drug targeting to peripheral tissues and viral reservoirs

The present study shows the lymphatic distribution of the negatively charge d anti-HIV-l agents succinylated or aconytilated human serum albumins (HSAs ) in rats. Quantitation of blood and lymphatic concentrations of these prot eins was performed through fluorescence detection of the fluorescein isothi ocyanate (FITC)-labeled proteins. At several time points after i.v. injecti on, samples were taken from the cannulated thoracic duct and the carotid ar tery. Distribution of the negatively charged albumins (NCAs) to lymph was m uch more rapid than that of albumin itself and was dependent on the total n et negative charge added to the protein: the half-life times of lymphatic e quilibration were 15, 30, and 120 min for FITC-labeled aconytilated HSA, FI TC-labeled succinylated HSA, and FITC-labeled HSA, respectively. Lymph to b lood concentration ratios of the studied compounds obtained at steady state approached unity. In addition, the fluorescence in both body fluids was sh own to represent unchanged labeled proteins. It was therefore inferred that the NCAs efficiently passed the endothelial barrier from blood to the inte rstitial compartment. Subsequently, we studied whether a specialized proces s was involved in the endothelial passage of the NCAs to the lymph. The fol lowing observations supported such a mechanism: a) preinjection of the scav enger receptor blockers polyinosinic- and formaldehyde treated HSA reduced the transport from blood to the lymphatic compartment of FITC-labeled acony tilated HSA by more than 90%; b) the rate of lymphatic distribution was lar gely reduced when the body temperature of the rat was lowered to 28 degrees ; and c) pre-administration of chloroquine resulted in a significant reduct ion in the lymphatic distribution of the NCAs. These data collectively indi cate that a scavenger receptor-mediated process is involved in the transend othelial transport of NCAs. In situ localization in lymph nodes of the rat showed that FITC -labeled aconytilated and succinyrated HSA are mainly pres ent in the germinal center and parafollicular zones. The efficient distribu tion of these anionized proteins to the lymphatic system is of particular i nterest for HIV therapy, taking into account that replication of HIV mainly takes place in the lymphoid system. The observation that macromolecules, t hrough charge modification, can extravasate through a receptor-mediated tra nscytotic process is potentially of major importance for the delivery of dr ugs with macromolecular carriers to cells not directly in contact with the blood. (C) 1999 Elsevier Science Inc.