The effect of mannitol and dopamine on the renal response to thoracic aortic cross-clamping

A Process for the Design and Development of Novel Bone Morphogenetic Protein-7 (BMP-7) Mimetics With an Example: THR-184

Growth Factors have been evaluated as therapeutic targets for the treatment of a broad spectrum of diseases. Because they are proteins with pleiotropic effects, the quest to harness their beneficial effects has presented challenges. Most Growth Factors operate at the extracellular-receptor level and have natural feedback mechanisms that modulate their effects. As proteins, they are difficult and expensive to manufacture. Frequently proteins must be administered parenterally, may invoke an immune response, and may be neutralized by naturally occurring inhibitors. To circumvent these limitations, we have undertaken an effort to develop mimetics for the Bone Morphogenetic Protein (BMP) signaling pathway effects that incorporate the beneficial effects, eliminate the deleterious effects, and thereby create effective drug-like compounds.To this end, we have designed and tested a family of small peptide BMP mimetics. The design used the three-dimensional structure of BMP-7 to identify likely active surface regions. Lead sequences were then optimized based on in vitro assays that examine the selective binding to BMP receptors, demonstrate the phosphorylation of Smad-1,5,8, detect anti-apoptosis and anti-inflammation, and block the epithelial to mesenchymal transition (EMT) in renal tubular epithelial cells. These sequences were further optimized using in vivo assays of the attenuation of acute kidney injury in a rat-model of unilateral clamp ischemic reperfusion. This process uses a Structure Variance Analysis algorithm (SVA) to identify structure/activity relationships. One member of this family, THR-184, is an agonist of BMP signaling and a potent antagonist of TGFβ signaling. This small peptide mimetic inhibits inflammation, apoptosis, fibrosis and reverses epithelial to mesenchymal transition (EMT) by regulating multiple signaling pathways involved in the cellular injury of multiple organs. Its effects have been shown to control Acute Kidney Injury (AKI). THR-184 has progressed through phase I and II clinical trials for the prevention of Cardio-Vascular Surgery (CVS) associated AKI. This work provides a roadmap for the development of other growth factor mimetics and demonstrates how we might harness their therapeutic potential.

Organ protection during aortic cross-clamping

Open surgical repair of an aortic aneurysm requires aortic cross-clamping, resulting in temporary ischemia of all organs and tissues supplied by the aorta distal to the clamp. Major complications of open aneurysm repair due to aortic cross-clamping include renal ischemia-reperfusion injury and postoperative colonic ischemia in case of supra- and infrarenal aortic aneurysm repair. Ischemia-reperfusion injury results in excessive production of reactive oxygen species and in oxidative stress, which can lead to multiple organ failure. Several perioperative protective strategies have been suggested to preserve renal function during aortic cross-clamping, such as pharmacotherapy and therapeutic hypothermia of the kidneys. In this chapter, we will briefly discuss the pathophysiology of ischemia-reperfusion injury and the preventative measures that can be taken to avoid abdominal organ injury. Finally, techniques to minimize the risk of complications during and after open aneurysm repair will be presented.

Efficacy and safety of high dose versus low dose furosemide with or without dopamine infusion: the Dopamine in Acute Decompensated Heart Failure II (DAD-HF II) trial

AIMS

The role of low-dose dopamine infusion in patients with acute decompensated heart failure (ADHF) remains controversial. We aim to evaluate the efficacy and safety of high- versus low-dose furosemide with or without low-dose dopamine infusion in this patient population.

METHODS AND RESULTS

161 ADHF patients (78 years; 46% female; ejection fraction 31%) were randomized to 8-hour continuous infusions of: a) high-dose furosemide (HDF, n=50, 20mg/h), b) low-dose furosemide and low-dose dopamine (LDFD, n=56, 5mg/h and 5 μg kg(-1)min(-1) respectively), or c) low-dose furosemide (LDF, n=55, furosemide 5mg/h). The main outcomes were 60-day and one-year all-cause mortality (ACM) and hospitalization for HF (HHF). Dyspnea relief (Borg index), worsening renal function (WRF, rise in serum creatinine (sCr) ≥ 0.3mg/dL), and length of stay (LOS) were also assessed. The urinary output at 2, 4, 6, 8, and 24h was not significantly different in the three groups. Neither the ACM at day 60 (4.0%, 7.1%, and 7.2%; P=0.74) or at one year (38.1%, 33.9% and 32.7%, P=0.84) nor the HHF at day 60 (22.0%, 21.4%, and 14.5%, P=0.55) or one year (60.0%, 50.0%, and 47%, P=0.40) differed between HDF, LDFD, and LDF groups, respectively. No differences in the Borg index or LOS were noted. WRF was higher in the HDF than in LDFD and LDF groups at day 1 (24% vs. 11% vs. 7%, P<0.0001) but not at sCr peak (44% vs. 38% vs. 29%, P=0.27). No significant differences in adverse events were noted.

CONCLUSIONS

In ADHF patients, there were no significant differences in the in-hospital and post-discharge outcomes between high- vs. low-dose furosemide infusion; the addition of low-dose dopamine infusion was not associated with any beneficial effects.

'Low-dose' dopamine worsens renal perfusion in patients with acute renal failure

'Low-dose' dopamine is frequently used in intensive care units (ICU) for its presumed renoprotective effects, but prospective and retrospective studies have so far not proven prevention or amelioration of renal injury. Data on renal perfusion following dopamine infusion are limited. In order to circumvent the problem of patient heterogeneity in the ICU setting, we used a crossover design in a prospective, double-blind randomized controlled study to investigate the effect of 'low-dose' dopamine on renal resistance indices, as determined by Doppler ultrasound. Forty patients, 10 without and 30 with acute renal failure (ARF, defined as doubling of baseline creatinine or an increase above 2 mg/dl), were included. Dopamine (2 mug/kg min) or placebo was given intravenously in alternating sequence for four subsequent periods of 60 min, starting randomly with either dopamine or placebo. Resistive (RI) and pulsatility index (PI) were closely correlated, positively related to serum creatinine values at baseline and highly reproducible during the two paired infusion periods. Dopamine reduced renal vascular resistance in patients without ARF (median RI/PI from 0.70 to 0.65/1.20 to 1.07, P<0.01) but increased resistance indices in patients with ARF (median RI/PI from 0.77 to 0.81/1.64 to 1.79, P<0.01) in the absence of effects on systemic hemodynamics. Subgroup analysis of patients with ARF revealed that dopamine induced renal vasoconstriction above 55 years (n=22) and in patients not receiving norepinephrine (n=20). In conclusion 'low-dose' dopamine can worsen renal perfusion in patients with ARF, which adds to the rationale for abandoning the routine use of 'low-dose' dopamine in critically ill patients.

Evidence-based renal protection in cardiac surgery

Acute renal dysfunction is a common serious complication of cardiac surgery. Although a diversity of mechanisms exist by which the kidney can be damaged during cardiac surgery, atheroembolism, ischemia-reperfusion, and inflammation are believed to be primary contributors to perioperative renal insult. In addition, the high metabolic demands of active tubular reabsorption and the oxygen diffusion shunt characteristic of renal circulation make the kidney particularly vulnerable to ischemic injury. Remote effects of acute renal injury likely contribute to the strong association of this condition with other major postoperative morbidities and mortality and justify the search for renoprotective agents, even when dialysis is never required. Nonpharmacologic preventive strategies include procedure planning that is based on risk stratification, avoidance of nephrotoxins, and meticulous perioperative clinical care, including optimizing intravascular volume and attention to modifiable risk factors such as minimizing hemodilution. Although numerous pharmacologic interventions to prevent or treat acute renal injury have shown promise in animal models, randomized placebo-controlled clinical trials that have looked at measures of significant adverse outcomes such as death and dialysis have not confirmed a benefit.

Complications of major aortic and lower extremity vascular surgery

Atheromatous disease and invasive intervention of the aortoiliac and distal arteries are common. Morbidity and mortality have been reduced through understanding and management of patient risk factors. Complications of this form of treatment affect all organ systems; mortality is most frequently caused by a cardiovascular complication (eg, myocardial infarction). Infection, leading to aortoenteric fistula is a dreaded complication, and paraplegia, though rare, is a devastating outcome. Multiorgan failure and death may result from a systemic inflammatory response syndrome. Vascular surgery for infrainguinal disease also has a significant cardiovascular complication rate. Resulting complications may affect all organs; loss of an extremity may occur. The first part of this article reviews perioperative and postoperative complications of open aortic repair and lower-extremity revascularization and addresses the issue of regional anesthesia for major vascular surgery. The second part reviews endovascular aortic repair (EVAR). EVAR is a new intervention that combines surgery and radiology. Complications of EVAR are similar to open repair, but early results suggest they may be less frequent. New technology leads to new complications; endoleaks, migration of the endoprosthesis, and surgical conversion are unique to EVAR. The benefits of EVAR may be less blood loss, shorter hospitalization, and less cardiovascular stress; the risks may be aneurysm recurrence, prolonged surveillance and repeated secondary procedures. The development of EVAR, the complications, and the anesthesia-related concerns of EVAR, including its use in management of acute abdominal aortic aneurysm are reviewed.

Should we use diuretics in acute renal failure?

Because oliguria is a bad prognostic sign in patients with acute renal failure (ARF), diuretics are often used to increase urine output in patients with or at risk of ARF. From a pathophysiological point of view there are several reasons to expect that loop diuretics also could have a beneficial effect on renal function. However, clinical trials on the prophylactic use of loop diuretics rather point to a deleterious effect on parameters of kidney function. In patients with established ARF loop diuretics have been shown to increase urine output, which may facilitate patient management. A beneficial effect on renal function has, however, not been demonstrated. On the other hand, such an effect cannot be excluded because the available trials lack statistical power. Possible explanations for the absence of a renoprotective effect are discussed. The evidence for a renoprotective effect of mannitol is restricted to the setting of renal transplantation.

Fenoldopam infusion associated with preserving renal function after aortic cross-clamping for aneurysm repair

BACKGROUND

Cross-clamping of the descending aorta during operative repairs causes sudden, significant reductions in renal function that may persist well beyond arterial clamp release. Commonly used agents, such as dopamine and mannitol, have not consistently affected renal outcome in these high-risk patients. Fenoldopam mesylate is a novel, highly selective dopamine type-1 agonist that preferentially dilates the renal and splanchnic vasculature, but has not been investigated in patients undergoing prolonged aortic clamping for whom adverse renal outcomes should be more likely.

METHODS AND RESULTS

Twenty-two adult patients without significant pre-existing renal dysfunction and presenting for elective repairs of abdominal aortic aneurysms were studied. Fenoldopain mesylate was infused after obtaining baseline values ranging from 0.1 to 1.0 microg/kg/min for the first 24 hours postoperatively to maintain mean arterial pressure +/-25% baseline. Serial renal function indices, including creatinine clearance and electrolyte fractional excretions, were measured at baseline, at aortic clamping and unclamping, and post-clamp release, and were estimated through hospital discharge. Creatinine clearance fell during abdominal exploration and clamping, reaching a nadir with clamp removal. Partial recovery occurred by 2 hours after clamp removal, and returned to baseline values by postoperative day 1 and thereafter. Fractional excretions rose rapidly throughout the operative phase. Total fenoldopam dose was directly related to the baseline creatinine clearance; after clamp removal, creatinine clearance was directly related to the mean arterial pressure at the lowest dose of fenoldopam, and inversely related to the mean arterial pressure at clamp release.

CONCLUSIONS

In elderly patients with severe vascular disease undergoing aneurysmal repairs, the use of a fenoldopam infusion in this open-label, uncontrolled trial was associated with a relatively rapid return of renal function to baseline values, despite profound decreases during aortic cross-clamping. Further studies will be necessary to investigate how fenoldopam infusions compare with traditional therapies.

Oliguria in the ICU. Systematic approach to diagnosis and treatment

Perioperative oliguria is common but rarely implies acute renal failure. We should interpret oliguria as a sign of intravascular hypovolemia and treat it as prerenal until proven otherwise. On the other hand, the absence of oliguria does not exclude acute renal failure. The most reliable clinical indicator of progressive renal dysfunction is a serial decline in creatinine clearance estimation, a measure of glomerular filtration rate.

Intraoperative management of renal function in the surgical patient at risk. Focus on aortic surgery

Although the search for effective methods of renal prophylaxis during aortic surgery spans many decades, definitive answers are scarce. The literature is voluminous, yet the amount of work clearly relevant to the specific clinical situation of perioperative prophylaxis is small. Given the significant morbidity and subsequent mortality involved with perioperative ARF, it is difficult to sit back and do nothing when pharmacologic agents empirically are believed to possibly benefit the patient. Care must be taken to apply data from different clinical scenarios in the literature to the situation at hand. Drugs felt to be innocuous, even in low doses, may be insidiously counterproductive or damaging if they are not managed properly. Maintaining an adequate preload and stable hemodynamics seems to be the most logical universal approach at this time. Furosemide treatment without maintaining an adequate volume status once diuresis commences may be detrimental, which is true with the diuretic effects induced by mannitol or dopamine. The tachycardia resulting from a relative hypovolemia and from the beta effects of dopamine can cause myocardial ischemia from increased oxygen demand. Low urine output does not portend a negative outcome in the face of an adequate intravascular volume any more than an induced diuresis prevents renal injury. Currently, minimization of renal ischemia and maintenance of an adequate intravascular volume and renal hemodynamics are the keys to optimizing renal outcome during aortic surgery. Other maneuvers are not definitive and should be cautiously undertaken.

Low-dose "renal" dopamine

Low dose renal dopamine continues to be infused in patients at risk for renal dysfunction or as a therapy after acute renal failure has been established. This article reviews the impact of acute renal failure on patients and reviews the history and use of dopamine therapy for patients. A discussion of the rationale, positive and equivocal evidence, side effects, and possible clinical indications for low-dose renal dopamine therapy is included.

The patient at risk for acute renal failure. Recognition, prevention, and preoperative optimization

Despite major advances in critical care medicine and extracorporeal renal support, the treatment of established postoperative ARF remains unsatisfactory and costly. The essential elements of perioperative renal preservation are early recognition of high-risk patients, preoperative optimization of fluid status and cardiovascular performance, intraoperative maintenance of renal perfusion, and avoidance of nephrotoxins. Pharmacologic interventions directed at preventing postoperative ARF are under intense investigation but presently are limited to renal transplant surgery.

Effect of YM435, a dopamine DA1 receptor agonist, in a canine model of ischemic acute renal failure

1. The effects of (-)-(S)-4-(3,4-dihydroxyphenyl)- 1,2,3,4-tetrahydroisoquinoline-7,8-diol monohydrochloride monohydrate (YM435), a dopamine DA1 receptor agonist, were evaluated in a canine model of ischemic acute renal failure (ARF). 2. ARF was induced by clamping the left renal artery for 1 hr and subsequent reperfusion of the left kidney in anesthetized uninephrectomized dogs. 3. After 1-hr complete renal artery occlusion, an intravenous infusion of either YM435 (0.3 microg/kg/ min) or 0.9% saline (vehicle) was begun and continued for 1 hr. 4. In the vehicle group, renal ischemia markedly decreased glomerular filtration rate, urine flow and urinary sodium excretion. The YM435 group was characterized by significant recoveries in glomerular filtration rate, urine flow, and urinary sodium excretion as compared with the vehicle group. 5. These results indicate that YM435 can facilitate recovery in glomerular filtration rate, urine flow, and urinary sodium excretion in a canine model of ARF induced by ischemia. YM435 may be useful in the preservation of renal function in ischemia-induced ARF.

Comparative effects of dopexamine and dopamine on glycerol-induced acute renal failure in rats

Acute renal failure (ARF) was induced in rats by intramuscular injection of 50% glycerol, 10 mL/kg body weight. Rats were given isotonic saline (1.5 mL/h) dopexamine hydrochloride (dopexamine, 100 microg/h) or dopamine (100 microg/h), commencing either immediately after glycerol administration and maintained during all the observation time (90 min, acute studies) or 20 min before administration of glycerol and during 60 min (chronic studies). Renal function was assessed during 90 min after induction of ARF in anesthetized rats and during 3 days following ARF induction in conscious animals. In anesthetized rats treated with dopexamine or dopamine, the reduction in insulin and para-aminohippuric acid clearance was markedly lower than that observed in untreated animals. In conscious animals, urinary flow and creatinine clearance were higher in rats treated with dopamine or dopexamine than in the non-treated group. Rats treated with dopexamine had higher renal Na+ and K+ excretion than dopamine-treated rats. Survival was higher in the dopexamine group than in either of the other two groups. These results demonstrate that pretreatment with dopexamine or dopamine significantly improves the course of ARF, with better survival after treatment with dopexamine.

Some Recent Controversies in Intensive Care

The ability of dopamine to reverse oliguria has led to its ubiquitous renal protective use in patients at risk of acute renal failure. However, this diuresis is due primarily to inhibition of distal tubular sodium reabsorption and not renal vasodilation. Recent controlled clinical studies have been unable to demonstrate a renal protective effect independent of changes in cardiac output.

Selective decontamination of the digestive tract (SDD) has the appealing theoretical ability to minimize upper gastrointestinal colonization with gram-negative bacteria and fungi, and subsequently reduce nosocomial infection and mortality. Such modification of flora does occur, but the initial studies showing a reduction in lower respiratory tract infections have not been supported by recent large double-blind randomized controlled trials. A reduction in mortality or length of stay of general intensive care patients given SDD has never been demonstrated, and it remains an experimental therapy with possible application for some patient subgroups.

Upper gastrointestinal hemorrhage (UGH) in the critically ill is associated with prolonged ventilatory support and coagulopathy, but clinically important bleeding is now uncommon. Prophylaxis with agents that increase gastric pH is effective in reducing UGH, but may be associated with a higher incidence of nosocomial pneumonia than occurs with alternatives such as sucralfate. Prophylaxis does not alter mortality, and it is now controversial which patients, if any, should routinely receive such treatment.

Acute renal failure as a complication in the critically ill animal

Acute renal failure is associated with a high morbidity and mortality in the intensive care animal. The two most common causes are ischemic/reperfusion injury and insult from nephrotoxins. Damage to the renal cells (e.g., endothelial, tubular, or mesangial cells) and altered hemodynamics result in reduced glomerular blood flow, tubular backleak, tubular obstruction, and/or decreased glomerular permeability. Recognition of ARF during the initiation stage provides the optimal chance for recovery. Adequate circulatory blood volume and systemic blood pressure must be established prior to pharmacologic intervention. Once ARF is in the maintenance phase, metabolic consequences of uremia must be managed.