Investigating the Role of Ischemia vs. Elevated Hydrostatic Pressure Associated with Acute Obstructive Uropathy

Abstract

Obstructive uropathy can cause irreversible renal damage. It has been hypothesized that elevated hydrostatic pressure within renal tubules and/or renal ischemia contributes to cellular injury following obstruction. However, these assaults are essentially impossible to isolate in vivo. Therefore, we developed a novel pressure system to evaluate the isolated and coordinated effects of elevated hydrostatic pressure and ischemic insults on renal cells in vitro. Cells were subjected to: (1) elevated hydrostatic pressure (80 cm H(2)O); (2) ischemic insults (hypoxia (0% O(2)), hypercapnia (20% CO(2)), and 0 mM glucose media); and (3) elevated pressure + ischemic insults. Cellular responses including cell density, lactate dehydrogenase (LDH) release, and intracellular LDH (LDH(i)), were recorded after 24 h of insult and following recovery. Data were analyzed to assess the primary effects of ischemic insults and elevated pressure. Unlike pressure, ischemic insults exerted a primary effect on nearly all response measurements. We also evaluated the data for insult interactions and identified significant interactions between ischemic insults and pressure. Altogether, findings indicate that pressure may sub-lethally effect cells and alter cellular metabolism (LDH(i)) and membrane properties. Results suggest that renal ischemia may be the primary, but not the sole, cause of cellular injury induced by obstructive uropathy.

In Vitro Models for Glaucoma Research: Effects of Hydrostatic Pressure

“…Hence, it was not hydrostatic pressure, per se, that affected cellular behavior, but rather changes in the dissolved gas concentration in the medium. Our conclusions are broadly similar to those recently reported by Russ et al, 26 who also designed equipment to independently evaluate the effects of pressure and hypoxia on cultured proximal tubule epithelial cells and observed no direct effect of ϳ60 mm Hg pressure. Our conclusions also agree with the results of Obazawa et al, 15 who measured optineurin and myocilin expression in trabecular meshwork cells after exposure to an elevated pressure of 33 mm Hg for various times, which did not result in any observed changes between control and pressurized cultures.…”

“…In light of these potentially complex effects, it would be valuable, when studying pressure effects on cultured cells, to include robust controls along the lines of those we have used here or those reported by Russ et al 26 More specifically, we recommend that future studies should include an in-dwelling oxygen sensor so that oxygen tensions at the level of the cells can be directly measured. We particularly emphasize that an in-dwelling sensor is preferable to approaches where samples of media are withdrawn and analyzed, since this technique likely creates unrealistic mixing (during sampling) and equilibration of gases in the sample with the atmosphere (while the sample is being prepared for analysis).…”

The effect of the rate of hydrostatic pressure depressurization on cells in culture

“…Once the effects of hypoxia were controlled for, no effect of hydrostatic pressure on cell behavior was observed in these studies. Other methods of application of hydrostatic pressure, such as use of a pressurized chamber [ 2 , 5 , 11 , 13 , 26 , 34 ] and use of a pump-driven flow system [ 6 , 15 , 21 ] are not subject to this hypoxia artifact. Use of a pressurized chamber alters the gas composition in equilibrium with the culture medium [ 35 ], but the magnitude of these changes are small for modest changes in hydrostatic pressure.…”