Suramin Affects the Renal VEGF-A/VEGFR Axis in Short-Term Streptozotocin-Induced Diabetes

**Background:** Diabetic nephropathy (DN) accounts for approximately 50% of end-stage renal diseases and affects up to 40% of patients with diabetes. Vascular endothelial growth factor A (VEGF-A) is thought to be a critical mediator of vascular dysfunction in DN, but its role remains unclear due to conflicting reports showing both deleterious and protective effects. The lack of pharmacological tools to modify renal VEGF-A concentrations has hindered understanding of its role in DN pathogenesis. Suramin, a broad-spectrum antagonist of P2 purinoreceptors used clinically in African trypanosomiasis and investigated in cancer and inflammatory diseases, is known to interfere with growth factor signaling and accumulates primarily in the kidneys. Previous work by this group showed suramin increases urinary VEGF-A excretion without significantly changing blood VEGF-A concentrations in diabetic rats.

**Methods:** Twenty-eight male Wistar rats were randomly allocated into four groups (n=7 each): non-diabetic controls (CON), suramin-treated non-diabetic (SUR), diabetic untreated (STZ), and diabetic suramin-treated (STZ+SUR). Diabetes was induced by a single intraperitoneal injection of streptozotocin (60 mg/kg) on day -7. Suramin (10 mg/kg, ip) or saline was administered on days 0 and +7. Experiments were performed on day +14. VEGF-A protein expression was evaluated by western blot of isolated glomeruli and by immunofluorescence of renal cortex sections. Vegfr1 and Vegfr2 mRNA expression in renal cortex was quantified by real-time RT-PCR, normalized to β-actin. Serum concentrations of soluble adhesion molecules sICAM-1 and sVCAM-1 were measured by ELISA. Endothelium-dependent vasorelaxation of renal interlobar arteries was assessed using wire myography with cumulative acetylcholine concentrations (10⁻⁹ to 10⁻⁵ M) on phenylephrine-precontracted arteries. Glomerular filtration rate was estimated from serum creatinine and urea concentrations.

**Key Results:** Diabetic rats showed a 54% reduction in VEGF-A protein levels in isolated glomeruli compared to controls (0.18 ± 0.02 vs. 0.33 ± 0.03, F₁,₂₂ = 11.86, p = 0.0023). Western blot analysis did not show a statistically significant effect of suramin on VEGF-A in isolated glomeruli. However, immunofluorescence revealed that suramin significantly reduced VEGF-A expression in glomeruli by 40% in both non-diabetic and diabetic rats (7.19 ± 0.37 vs. 11.81 ± 0.84, F₁,₂₈ = 20.83, p < 0.0001), and altered its intraglomerular distribution, with signal shifting from the central glomerulus to peripheral areas corresponding to parietal epithelial cells. No significant changes in Vegfr1 mRNA expression were observed across groups. Diabetic rats had elevated Vegfr2 mRNA levels, and suramin reduced Vegfr2 mRNA by 84% in diabetic rats (p = 0.0001) to non-diabetic levels, with no effect in non-diabetic rats (p = 0.9787). Serum sVCAM-1 concentrations were reduced by approximately 52% in diabetic rats compared to non-diabetic rats (F₁,₂₃ = 21.21, p = 0.0001), with no significant effect of suramin. No differences in sICAM-1 were observed among groups. Endothelium-dependent relaxation of interlobar arteries to acetylcholine was significantly impaired in diabetic rats (maximal relaxation ~19%) compared to controls (~50%, p < 0.05). Suramin administration to diabetic rats restored maximal relaxation to approximately 53% (p = 0.01), not significantly different from control values. Estimated GFR was 13% lower in diabetic rats compared to controls (2078 ± 108 µL/min vs. 2377 ± 123 µL/min, F₁,₁₅ = 9.366, p = 0.0079), with no effect of suramin.

**Clinical Implications:** This study demonstrates that suramin modulates the renal VEGF-A/VEGFR axis in short-term diabetes by reducing VEGF-A expression in the renal cortex, decreasing elevated VEGFR-2 expression, and restoring endothelium-dependent vasorelaxation of renal arteries. The finding that suramin reduced VEGF-A expression in both diabetic and non-diabetic rats suggests this effect is not dependent on hyperglycemia. The restoration of acetylcholine-induced vasorelaxation to non-diabetic levels is particularly noteworthy, as endothelial dysfunction is an early hallmark of diabetic microvascular complications. These results position suramin as a potential pharmacological tool for investigating VEGF-A's role in early diabetic nephropathy, though the mechanism by which suramin improves endothelial function—whether through VEGF-A/VEGFR modulation or other pathways—remains to be elucidated. The study is limited by its short-term duration (3 weeks) and animal model, and further research is needed to determine whether these effects translate to human diabetic kidney disease and whether long-term suramin treatment would be beneficial or harmful.