Rapamycin delays but does not prevent recovery from acute renal failure: role of acquired tubular resistance.

BACKGROUND: We reported that rapamycin impairs recovery after acute renal failure (ARF) in rats. The objective of this study was to determine if recovery will eventually occur after ARF despite continued rapamycin treatment. METHODS: ARF was induced in rats by renal artery occlusion. Glomerular filtration rate (GFR), morphology, and tubular cell proliferation were assessed either 2, 4, 6, or 7 days later. Rats were treated daily with rapamycin or vehicle throughout the study. Cultured mouse proximal tubular (MPT) cells were used to compare the antiproliferative effects of rapamycin after exposure for 1 and 7 days. RESULTS: Two days after ARF, GFR was reduced severely but comparably in vehicle and rapamycin rats. In controls, GFR began to increase after day 2 and was normal by day 6. In rapamycin rats, GFR did begin to improve until after day 4 and reached normal values by day 7. In controls, many proliferating tubular cells were present in outer medulla on day 2, after which proliferation progressively decreased. By contrast, in rapamycin rats, proliferating cells were sparse on day 2, but then increased substantially through days 4 and 6. Cultured MPT cells exposed to rapamycin for 7 days were approximately 10-fold more resistant to the antiproliferative effects of rapamycin than cells exposed for 1 day. CONCLUSIONS: Rapamycin delays but does not prevent renal recovery after ARF. MPT cells become resistant to rapamycin after prolonged exposure. We speculate that the ultimate recovery of renal function after ARF is due to the development of acquired tubular cell resistance to rapamycin.

A comparison of the acute hemodynamic and delayed effects of 50% exchange transfusion with two different cross-linked hemoglobin based oxygen carrying solutions and Pentastarch.

BACKGROUND: Hemoglobin based oxygen carrying solutions (HBOC) have been designed to combine the beneficial effects of colloidal solutions with oxygen carrying capacity. Clinical trials in humans using HBOCs have had variable results. METHODS: We used a rodent 50% exchange model to compare Hemolink and Hemopure HBOC to autologous blood and Pentastarch solution. We monitored hemodynamic parameters, hemoglobin clearance, weight gain and hematocrit over a five-day period. RESULTS: Acute hemodynamic effects between the two HBOCs were similar with mild vasoconstriction. Cardiac output, systemic vascular resistance and renal function were similar to that seen with blood. HBOC's were associated with hemoglobinuria with a half-life in the circulation of 13.8 hrs for Hemolink and 19.2 hrs for Hemopure. Animals resuscitated with HBOCs exhibited delayed weight gain. CONCLUSION: Hemodynamic effects in rodents exchange-transfused with blood, Hemolink, or Hemopure were similar. The delayed weight gain observed with the HBOCs must be investigated.

Rapamycin ameliorates proteinuria-associated tubulointerstitial inflammation and fibrosis in experimental membranous nephropathy.

Proteinuria is a risk factor for progression of chronic renal failure. A model of proteinuria-associated tubulointerstitial injury was developed and was used to examine the therapeutic effect of rapamycin. Two studies were performed. In study A, proteinuric rats were given sheep anti-Fx1A to induce experimental membranous nephropathy; control rats received normal sheep serum. Four weeks later, groups were subdivided and underwent laparotomy alone (two kidneys), nephrectomy alone (one kidney), or nephrectomy with polectomy (0.6 kidney). Renal function and morphology were evaluated 4 wk later. Whereas control rats never developed proteinuria, anti-Fx1A induced severe proteinuria. Proteinuria was unaffected by renal mass reduction. Proteinuric rats developed tubulointerstitial disease that was most severe in rats with 0.6 kidneys. Renal function (GFR) was reduced by loss of renal mass and was reduced further in proteinuric rats with 0.6 kidneys. In study B, the effect of rapamycin on the expression of candidate proinflammatory and profibrotic genes and the progression of proteinuria-associated renal disease were examined. All rats received an injection of anti-Fx1A and were nephrectomized and then divided into groups to receive rapamycin or vehicle. Gene expression, renal morphology, and GFR were evaluated after 4, 8, and 12 wk. Rapamycin reduced expression of the proinflammatory and profibrotic genes (monocyte chemotactic protein-1, vascular endothelial growth factor, PDGF, TGF-beta(1), and type 1 collagen). Tubulointerstitial inflammation and progression of interstitial fibrosis that were present in vehicle-treated rats were ameliorated by rapamycin. Rapamycin also completely inhibited compensatory renal hypertrophy. In summary, rapamycin ameliorates the tubulointerstitial disease associated with chronic proteinuria and loss of renal mass.

Comparison of the effects of a 50% exchange-transfusion with albumin, hetastarch, and modified hemoglobin solutions.

We compared the hemodynamic effects of replacing 50% of the blood volume of anesthetized rats with an equal volume of five solutions: human serum albumin (HSA), hetastarch, unmodified hemoglobin, diaspirin-crosslinked hemoglobin, and o-raffinose-crosslinked hemgolobin. Control rats were exchange-transfused with their own blood. HSA and hetastarch caused a severe reduction in systemic vascular resistance (SVR), hypotension, and acute renal failure immediately after the exchange-transfusion. Unmodified and diaspirin-crosslinked hemoglobins caused comparable and severe increases in SVR, whereas vasoconstriction induced by o-raffinose-crosslinked hemoglobin was minimal. The increased SVR induced by all hemoglobin solutions resolved over a 2-day period as the hemoglobin was cleared from plasma. Body weight was monitored for 5 days after the exchange transfusion as a measure of the relative long-term efficacy of the exchange solutions tested and increased substantially in control rats (that received blood). Rats that received both crosslinked hemoglobin solutions gained a comparable amount of weight as the control group. By contrast rats that received HSA, hetastarch and unmodified hemoglobin failed to gain weight or lost weight over the same period. In summary: i) HSA and hetastarch are relatively ineffective as resuscitative fluids when administered after the loss of a large volume of blood; ii) diaspirin-crosslinked hemoglobin causes severe vasoconstriction, comparable in intensity to that induced by unmodified hemoglobin; iii) o-raffinose-crosslinked hemoglobin induces minimal vasoconstriction; iv) the vasoactive effects of all hemoglobin solutions are reversible. We conclude, that of all solutions tested, both the short- and long-term effects of an exchange-transfusion with whole blood are most closely reproduced by an exchange with o-raffinose-crosslinked hemoglobin.