Abstract 1485: Tissue Specific Activation of cGMP by an Alternatively Spliced Form of BNP
Background: Intravenous administration of B-type natriuretic peptide (BNP) has vasorelaxing as well as diuretic and natriuretic properties. This vasorelaxing property may lead to hypotension and restrict its clinical utility. We recently identified an alternatively spliced form of BNP (ASBNP) which contains a unique carboxy terminus due to intronic retention. Based on structural considerations, we designed a truncated form of ASBNP referred to as ASBNP.1 as a potential biologic therapeutic. We have previously shown that ASBNP.1 maintained the renal properties of BNP but had no vasoactive properties in a canine model of congestive heart failure. We aimed to define the mechanism of this effect.
Methods and Results: In vitro, compared with BNP, ASBNP.1 fails to stimulate cGMP in human endothelial or vascular smooth muscle cells at equimolar doses (at 10−8 M, 10 fmol/well by BNP vs 2 fmol/well by ASBNP.1, p<0.05). BNP stimulates vasorelaxation of vascular rings (60~70%). ASBNP.1 failed to dilate preconstricted canine arterial rings (<10%). Similar findings were seen with human arterial and venous rings. However, in freshly isolated canine glomeruli and in primary human kidney mesangial cells ASBNP.1 has similar ability to stimulate cGMP to that of BNP (BNP: 1.55±0.1 vs ASBNP.1: 1.70±0.1 fmol/ul in glomeruli, NS; BNP: 28.7±4 vs ASBNP.1: 24.9±4.2 fmol/well in mesangial cells, NS). These data suggest that ASBNP.1 retains the ability of BNP to stimulate cGMP in renal cells but lacks the effects on vascular cells and intact vascular rings.
Conclusions: These findings support the hypothesis that the differential effects of ASBNP.1 in the vasculature and kidney are due to differnces in activating cGMP in these target tissues. The differential effects of ASBNP.1 suggest that uncoupling of the potent effects of BNP is possible. This uncoupling may be the result of tissue specific differences in receptor density or signaling cascades, the presence alternative receptors or subtypes, or tissue specific processing of the peptide. The specificity of ASBNP.1 should provide the opportunity to distinguish these mechanisms.