TUMOR-GROWTH MODIFIES INTRAVASCULAR POLYAMINE TRANSPORT BY PLASMA-LIPOPROTEINS IN THE MOUSE

Polyamines are polycationic compounds which are implicated in cell div ision and tumor growth. We have evaluated the potential role of plasma lipoproteins in the transport of major polyamines, spermine, spermidi ne and putrescine, and the effect of tumor growth on such transport. P lasmas of healthy male BL6/DBA2 mice and of mice bearing Lewis lung ca rcinoma (3LL) were fractionated by isopycnic density gradient ultracen trifugation, and polyamine content determined in lipoprotein fractions . Spermidine was the most abundant polyamine in the lipoproteins of bo th control and tumor-bearing mice and was principally associated with HDL (d: 1.046-1.136 g/ml); approx. 40% of total plasma polyamines was lipoprotein-associated in control mice and 60% in cancerous mice. Only minor amounts were transported by LDL (< 10% of total lipoprotein-ass ociated polyamines), while VLDL were devoid of these substances, Marke d elevations of circulating levels of LDL were found in 3LL grafted mi ce: in these particles however, the contents of spermidine and spermin e were significantly reduced. A preferential uptake of polyamines by r ed blood cells could in part explain this marked reduction of LDL poly amine content, but the consequence of this reduction on the net electr ical charge and biochemical function of LDL remains unknown. Elevation s of plasma LDL and HDL levels in 3LL-grafted mice underlie the findin g that only minor modification was detected in the putrescine content of these particles. However, it is evident that elevated total amounts of putrescine were present in the plasma of such animals. Finally, th e density profile of polyamines was modified in cancerous mice in whic h a shift to transport in lighter apo.AI-containing HDL particles was observed for spermidine; an even more marked shift was found for sperm ine. In conclusion, our data demonstrate that HDL particles constitute the major plasma vehicle for polyamine transport in both control and in tumor-bearing mice. (C) 1997 Elsevier Science B.V.