Modulation of renal tubular cell function by RGS3

The recently discovered family of regulators of G protein signaling (RGS) accelerates the intrinsic GTPase activity of certain Galpha subunits, thereby terminating G protein signaling. Particularly high mRNA levels of one family member, RGS3, are found in the adult kidney. To establish the temporal and spatial renal expression pattern of RGS3, a polyclonal antiserum was raised against the COOH terminus of RGS3. Staining of mouse renal tissue at different gestational stages revealed high levels of RGS3 within the developing and mature tubular epithelial cells. We tested whether RGS3 can modulate tubular migration, an important aspect of tubular development, in response to G protein-mediated signaling. Several mouse intermedullary collecting duct (mIMCD-3) cell lines were generated that expressed RGS3 under the control of an inducible promoter. Lysophosphatidic acid (LPA) is a potent chemoattractant that mediates its effects through heterotrimeric G proteins. We found that induction of RGS3 significantly reduced LPA-mediated cell migration in RGS3-expressing mIMCD-3 clones, whereas chemotaxis induced by hepatocyte growth factor remained unaffected by RGS3. Our findings suggest that RGS3 modulates tubular functions during renal development and in the adult kidney.

The polycystic kidney disease 1 gene product mediates protein kinase C alpha-dependent and c-Jun N-terminal kinase-dependent activation of the transcription factor AP-1

Autosomal dominant polycystic kidney disease (ADPKD) is a common hereditary disorder that accounts for 8-10% of end stage renal disease. PKD1, one of two recently isolated ADPKD gene products, has been implicated in cell-cell and cell-matrix interactions. However, the signaling pathway of PKD1 remains undefined. We found that the C-terminal 226 amino acids of PKD1 transactivate an AP-1 promoter construct in human embryonic kidney cells (293T). PKD1-induced transcription is specific for AP-1; promoter constructs containing cAMP response element-binding protein, c-Fos, c-Myc, or NFkappaB-binding sites are unaffected by PKD1. In vitro kinase assays revealed that PKD1 triggers the activation of c-Jun N-terminal kinase (JNK), but not of mitogen-activated protein kinases p38 or p44. Dominant-negative Rac-1 and Cdc42 mutations abrogated PKD1-mediated JNK and AP-1 activation, suggesting a critical role for small GTP-binding proteins in PKD1-mediated signaling. Several protein kinase C (PKC) inhibitors decreased PKD1-mediated AP-1 activation. Conversely, expression of the C-terminal domain of PKD1 increased PKC activity in 293T cells. A dominant-negative PKC alpha, but not a dominant-negative PKC beta or delta, abrogated PKD1-mediated AP-1 activation. These findings indicate that small GTP-binding proteins and PKC alpha mediate PKD1-induced JNK/AP-1 activation, together comprising a signaling cascade that may regulate renal tubulogenesis.

Risk factors and outcome of 107 patients with decompensated liver disease and acute renal failure (including 26 patients with hepatorenal syndrome): the role of hemodialysis

The prognosis of acute renal failure in patients with preexisting liver decompensation is poor, and hemodialysis is considered futile, especially for hepatorenal syndrome (HRS). Since we observed a more favorable outcome in some patients, we retrospectively evaluated 107 patients with decompensated liver disease and acute renal failure (serum creatinine > 200 mumol/L) treated at the medical department of a university hospital in a 10-year period (1980-1990). HRS in the strict sense (urine-Na < 20 mmol/L while on furosemide) was diagnosed in 26 of 107 patients (24%). Renal function remained compensated in 25 patients, while 82 patients fulfilled the criteria for dialysis treatment (creatinine > 500 mumol/L and/or diuresis < 500 mL/day). In contrast to the current doctrine, 38 of the 82 patients were given hemodialysis (46%). Using the Cox proportional hazard model, the relative risk (presence vs. absence of a risk factor) of dying was increased 8.2-fold (3.9-17.2) in patients with thrombocytopenia < 100/nL, 3.9-fold (1.4-11.3) in those with hepatic encephalopathy and prothrombin time < 30%, 2.8-fold (1.6-4.8) in patients with malignoma, and 2.7-fold (1.5-4.8) in patients not submitted to dialysis despite its indication. In the CART statistics (classification and regression trees), the 33 patients with the poorest outcome were characterized exclusively by thrombocytopenia < 100/nL. HRS in the strict sense was not an independent risk factor. The CART group of 43 patients with favorable prognosis (compensated renal failure or treatment by hemodialysis, absent malignancy) had a 1-year survival rate of 38%. We conclude that thrombocytopenia, encephalopathy, and malignoma, but not HRS per se, are fatal signs that make hemodialysis futile in patients with acute renal failure and decompensated liver disease.

Effects of diltiazem upon metabolism and immunosuppressive action of cyclosporine in kidney graft recipients

It is widely believed that calcium antagonists such as diltiazem exert immunosuppressive effects in kidney graft recipients--however, the mechanism is unclear. In a randomized controlled trial, kidney graft recipients who received diltiazem during transplantation and for an average of 12 months thereafter experienced significantly fewer rejection episodes than patients treated with cyclosporine and steroids alone. Furthermore, 1-year (97% vs. 85%) and 4-year (80% vs. 70%) graft survival rates were higher in diltiazem-treated patients, but the difference was not statistically significant. In vitro, diltiazem had little immunosuppressive activity. Concentrations of diltiazem which blocked the proliferation of PHA-stimulated human peripheral blood mononuclear cells, or prevented activation-associated accumulation of interleukin-2 mRNA, or p50- and p70-IL-2 receptor mRNA exceeded pharmacological concentrations by more than 100-fold. Both, CsA and high doses of diltiazem caused an increase of IL-6 mRNA. In contrast to these findings, the IL-6 plasma concentrations were comparable in both groups, whereas the serum concentration of soluble IL-2 receptors was decreased in patients treated with diltiazem. Administration of diltiazem caused an alteration of CsA metabolism. The whole-blood concentration of CsA metabolite 17 was significantly increased in diltiazem-treated patients, resulting in a five-times-higher concentration of this metabolite in the cellular blood compartment compared with the parent drug. Changes in metabolites 1, 8, and 18 levels were less pronounced. Although direct immunosuppressive properties of diltiazem are unlikely, diltiazem could support immunosuppression by altering CsA metabolism, and promoting accumulation of certain metabolites.

Outcome prediction of acute renal failure in medical intensive care

Data acquired prospectively from 134 patients with acute renal failure requiring dialysis in a medical intensive care unit (ICU) were analysed in order to derive indicators predicting ICU-survival. Mortality in the ICU was 56.7%. Linear discriminant analysis correctly predicted outcome in 79.9% at the start of dialysis, and 84.7% at 48 h after the first dialysis. The most important predictive variables were mechanical ventilation and low blood pressure. On the other hand, the total correct classification rates achieved by a standardised system for scoring ICU-patients (APACHE II) did not exceed 58.2%. It is concluded that outcome prediction by APACHE II and even by the discriminant functions is too inaccurate to become the basis for clinical decisions either concerning the initiation or the continuation of dialysis treatment in ARF.

Outcome prediction models on admission in a medical intensive care unit: do they predict individual outcome?

Prospectively acquired data from 941 patients staying greater than 24 h in a medical ICU were analyzed to determine the relevance of scoring on ICU admission by the following methods of outcome prediction: Acute Physiology and Chronic Health Evaluation (APACHE II), Simplified Acute Physiology Score (SAPS), and Mortality Prediction Model (MPM). Analysis was performed separately for all patients (group A) and for a subsample (group B), obtained by excluding coronary care patients. Calculation of risk and classification of patients were carried out as recommended in the literature for MPM, APACHE II, and SAPS. In group A, sensitivities (correct prediction of hospital mortality) were 44.7%, 51.1%, and 21.2% and specificities (correct prediction of survival) were 84.5%, 85.4%, and 96.8%, respectively; overall correct classification rates were 73.3%, 75.8%, and 75.6%. In group B, sensitivities were slightly higher, but total correct classification rates did not reach group A levels. Goodness-of-fit testing showed low levels of fit for all methods in both groups. Application of APACHE II to diagnostic subgroups, using disease-adapted risk calculations, revealed marked inconsistencies between the estimated risk and the observed mortality. We conclude that the estimation of risk on admission by the three methods investigated might be helpful for global comparisons of ICU populations, although the lack of disease specificity reduces their applicability for severity grading of a given illness. The inaccuracy of these methods makes them ineffective for predicting individual outcome; thus, they provide little advantage in clinical decision-making.

Impairment of renal function in medical intensive care: predictability of acute renal failure

Acute causes and chronic risk factors for the development of acute renal failure were analyzed in prospective acquired data of 261 patients in a medical ICU. The population was divided into a group requiring dialysis treatment for established renal failure (n = 95) and a collective maintaining mild renal insufficiency (n = 166). Bivariate and linear discriminant analyses revealed that, above all, variables related to bacterial infections (sepsis and administration of antibiotic agents) and pancreatitis contributed to the discrimination, followed by bleeding, volume depletion, and chronic liver disease in the discriminant function. Bivariate analysis also yielded significant results for mechanical ventilation, CNS depression, and surgery. The importance of the nephrotoxic properties of aminoglycosides may be outweighed by their role as an indicator of severe infectious disease. The overall correct classification rate of the discriminant function was 78.5%, which reflects the importance of the predictor variables, but does not allow individual predictions.

[Acute myocardial infarct: aspects of changed mortality at the intensive care unit. Results of a prospective study from 1985 to 1987]

Between 1975 and 1987 the mortality rate among 3143 patients with acute myocardial infarction admitted to an intensive care unit fell from 25% to below 10%. Among 829 patients examined prospectively during three consecutive years, the rate was 12.5% in 1985, 13.1% in 1986, and 9.3% in 1987 (mean of 11.6%). In addition to higher age, other risk factors were identified (mortality in brackets): female sex (14.6%), heart failure (20.6%), and diabetes (19.7%). Hypertension (11.2%) and previous infarct (12.8%) had no influence on mortality rate. The mortality rate was significantly reduced (P less than 0.0003) among 290 patients who had received intravenous fibrinolytic treatment, but this effect was marked only among women, elderly patients and those without risk factors. It is concluded that many measures had led to the observed reduction in acute death rate to about 10%. It is not yet possible to determine which of the different interventions played a part.

Cyclosporin drug monitoring: comparison of four immunoassays and HPLC

Cyclosporin blood trough levels were measured with four different immunoassays and high-performance liquid chromatography in 12 patients receiving low-dose steroids and CsA after kidney transplantation. These patients represent a selection with an uncomplicated posttransplant course and received no drugs with a known influence on CsA pharmacokinetics. The use of specific antibodies against the parent drug yielded levels comparable to those detected by HPLC. CsA levels measured with nonspecific antibodies exceeded those measured with specific ones by a factor of two to three. All immunoassay-detected CsA levels correlated significantly with the HPLC-determined CsA levels. In addition, blood levels of the CsA metabolites 1, 17, 18, and 21 were determined by HPLC. In one additional patient, who was under tuberculostatic treatment and had a transitory deterioration of liver function, levels of nonspecific-antibody-determined CsA rose, as confirmed by rising levels of metabolite 17, while those of the parent drug fell. We conclude that routine drug monitoring should include at least one immunoassay with a specific antibody detecting the unchanged CsA, and a supplementary immunoassay with a nonspecific antibody detecting a composition of cross-reacting metabolites plus the unchanged substance. If available, HPLC should be used to confirm levels of CsA and its metabolites in patients with suspected alteration of their CsA metabolism.