Lipopolysaccharide-induced renin–angiotensin system (RAS) inhibition in human mesangial cells (HMC) is blocked by high ambient glucose

Background

Hyperactivation of the systemic RAS during sepsis and the intrarenal RAS in diabetes is well documented. We have previously identified the mRNA expression of all members of the RAS in immortalized HMC.

Aim

The present study evaluates the direct effect of lipopolysaccharide (LPS) on HMC RAS in the presence of high ambient glucose, a model mimicking diabetes.

Methods

Quiescent immortalized HMC kept for 24 hours in 0.5% serum-containing medium were incubated with vehicle, Escherichia coli LPS (100 μg/ml), glucose (30 mM), LPS + glucose, mannitol (30 mM), or LPS + mannitol. After 72 hours, angiotensin I and angiotensin II intracellular and extracellular concentrations (pg/mg protein) were determined by mass spectrometry analysis.

Results

LPS significantly reduced angiotensin II concentrations (mean ± SEM, vehicle vs LPS: intracellular, 910 ± 33 vs 272 ± 12; extracellular, 668 ± 62 vs 251 ± 17; P < 0.05, n = 3–6). This effect was markedly blocked by high ambient glucose, but not by mannitol, while glucose alone did not modify basal concentrations of angiotensin II. Similar results were obtained for angiotensin I. In a separate series of experiments, we measured the enzymatic activity of angiotensin I-converting enzyme and renin in protein extracts from HMC treated with LPS or glucose. LPS, but not glucose, significantly decreased ACE activity in HMC (-36%; P < 0.01, n = 4), while renin activity remained unaffected.

Conclusions

These preliminary data suggest that the intrarenal RAS is regulated in opposite directions by LPS and glucose. The LPS inhibitory effect on the RAS can be partially explained by modifications in HMC angiotensin I-converting enzyme activity. These findings are potentially related to development of and/or recovery from acute renal failure in the context of sepsis, alone or superimposed to hyperglycemia. Additional studies are underway to better characterize the mechanisms involved in this phenomenon.