Origin and Appearance of HITS Induced by Prosthetic Heart Valves: An in vitro Study

Patients with mechanical heart valve prostheses show significantly enhanced numbers of HITS detected by transcranial Doppler ultrasound. In order to assess the origin of HITS formation, an in vitro study was set out to quantify valve induced microemboli for mechanical and bioprosthetic valves under various circulatory conditions by means of Ultrasound-Doppler-Sonography. At the same time the influence of CO2 partial pressure on HITS rate vas investigated. It can be summarised that for mechanical heart valve prostheses a strong correlation exists between left ventricular dp/dtmax and the detected HITS rates. It was also demonstrated that a bioprosthesis generates significantly less HITS than a mechanical valve. The origin of HITS is gaseous since the tests were carried out using a cell-free filtered water-glycerol test fluid. The HITS rate could be increased by increasing the amount of dissolved gas within the test fluid. The results support the hypothesis that cavitation is the key factor in the appearance of gaseous microemboli at heart valve prostheses.

[Medicinal or instrumental (corrected) therapy of renal artery stenosis?]

Arteriosclerotic renal artery stenosis (RAS) has an increased incidence in patients with cardiovascular risk factors. Clinically RAS presents in some patients as secondary, sometimes resistant arterial hypertension and in others as chronic renal insufficiency, sometimes with acute renal failure and in a third group both symptoms are observed. Doppler ultrasound plays a central role in the diagnosis of RAS. Therapeutically, it is important to identify hemodynamically relevant RAS before interventional therapy is initiated. The therapy of RAS has been under intensive debate since the publication of randomized controlled trials (RCT) which showed that only a subset of RAS can be successfully treated by interventional therapy. Since then the medicinal therapy of RAS has gained more and more impact. The following questions are raised: which forms of RAS can be treated by which therapy? What is the best medicinal therapy to treat RAS? What substances are recommended?

Chronic treatment with angiotensin-(1-7) improves renal endothelial dysfunction in apolipoproteinE-deficient mice

BACKGROUND AND PURPOSE

ApolipoproteinE-deficient [apoE (-/-)] mice, a model of human atherosclerosis, develop endothelial dysfunction caused by decreased levels of nitric oxide (NO). The endogenous peptide, angiotensin-(1-7) [Ang-(1-7)], acting through its specific GPCR, the Mas receptor, has endothelium-dependent vasodilator properties. Here we have investigated if chronic treatment with Ang-(1-7) improved endothelial dysfunction in apoE (-/-) mice.

EXPERIMENTAL APPROACH

ApoE (-/-) mice fed on a lipid-rich Western diet were divided into three groups and treated via osmotic minipumps with either saline, Ang-(1-7) (82 µg·kg(-1) ·h(-1) ) or the same dose of Ang-(1-7) together with D-Ala-Ang-(1-7) (125 µg·kg(-1) ·h(-1) ) for 6 weeks. Renal vascular function was assessed in isolated perfused kidneys.

KEY RESULTS

Ang-(1-7)-treated apoE (-/-) mice showed improved renal endothelium-dependent vasorelaxation induced by carbachol and increased renal basal cGMP production, compared with untreated apoE (-/-) mice. Tempol, a reactive oxygen species (ROS) scavenger, improved endothelium-dependent vasorelaxation in kidneys of saline-treated apoE (-/-) mice whereas no effect was observed in Ang-(1-7)-treated mice. Chronic treatment with D-Ala-Ang-(1-7), a specific Mas receptor antagonist, abolished the beneficial effects of Ang-(1-7) on endothelium-dependent vasorelaxation. Renal endothelium-independent vasorelaxation showed no differences between treated and untreated mice. ROS production and expression levels of the NAD(P)H oxidase subunits gp91phox and p47phox were reduced in isolated preglomerular arterioles of Ang-(1-7)-treated mice, compared with untreated mice, whereas eNOS expression was increased.

CONCLUSION AND IMPLICATIONS

Chronic infusion of Ang-(1-7) improved renal endothelial function via Mas receptors, in an experimental model of human cardiovascular disease, by increasing levels of endogenous NO.

Nephrolithiasis and hematuria--sometimes a stony road to diagnosis

We report a case of a young man with a history of kidney stones. Occurrence of gross hematuria several months after the extracorporeal shock wave, lithotripsy (ESWL) treatment lead to hospitalization. By ultrasound and abdominal CT scan, the urologist could exclude post-renal causes of the gross hematuria and acute renal failure. After transfer to a department of nephrology hemodialysis was started, an immediate kidney biopsy was performed and prednisolone was administered on the same day. The kidney biopsy revealed an anti-glomerular basement membrane (GBM) disease. The renal function did not recover and the patient remained on hemodialysis. In the literature it has been hypothesized that ESWL-treated patients are prone to develop anti-GBM disease by liberation of glomerular basement antigen through the ESWL high energy shock waves. An additional hypothesis considering the higher susceptibility for anti-GBM disease among certain HLA-tissue types is discussed with regard to our case. Unfortunately, the prolonged track to diagnosis and delayed immunosuppressive treatment could not prevent poor clinical outcome. Although anti-GBM disease is a rather rare disease, it should be included as a differential diagnosis for hematuria--especially months after ESWL treatment. Otherwise early diagnosis may be missed and as in our patient immunosuppressive treatment will remain unsuccessful to recover renal function.

Dihydrotachysterol therapy for hypoparathyroidism: consequences of inadequate monitoring. Five cases and a review

BACKGROUND

The half synthetic Vitamin D analogue dihydrotachysterol (DHT) is widely used for hypocalcaemic hypoparathyroidism following surgical removal of parathyroids. Such treatment generally initiated by surgeons right after surgery has to be continued in clinical practice. Unfortunately, the required careful monitoring of calcium metabolism is often lacking and as demonstrated may lead to life-threatening conditions.

PATIENTS AND METHODS

Here we report on five patients referred to our nephrology unit because of unknown impairment of renal function during therapy with DHT. All patients had clinical signs of hypercalcaemia. Since most symptoms are nonspecific they were not perceived by primary care physicians. In fact DHT treatment was continued for 4 - 50 years. In all cases calcium levels were determined after inadequate long intervals ranging from 3.08 to 4.97 mmol/l. Creatinine levels ranged from 277 to 365 micromol/l. All patients suffered from symptoms of severe hypercalcaemia, three of them needing intensive care unit treatment.

RESULTS

All patients were treated effectively with a regimen consisting of intravenous saline, a loop diuretic, and application of bisphosphonates. As confirmed by renal biopsy persisting alleviation of renal function was due to calcifications. After discontinuation of DHT therapy patients were safely switched to shorter acting vitamin D derivates maintaining a normal calcium level.

CONCLUSIONS

In comparison to short acting vitamin-D derivates hypercalcaemic episodes with DHT appear to last longer and may therefore occur with higher incidence. A future option could be the use of synthetic parathyroid hormone (s-PTH) recently shown to be safe and effective. Nevertheless a customized therapy and careful monitoring is indispensable in any case to prevent irreversible organ damage.

14-3-3 interacts with regulator of G protein signaling proteins and modulates their activity

Regulator of G protein signaling (RGS) proteins function as GTPase-activating proteins (GAPs) that stimulate the inactivation of heterotrimeric G proteins. We have recently shown that RGS proteins may be regulated on a post-translational level (Benzing, T., Brandes, R., Sellin, L., Schermer, B., Lecker, S., Walz, G., and Kim, E. (1999) Nat. Med. 5, 913-918). However, mechanisms controlling the GAP activity of RGS proteins are poorly understood. Here we show that 14-3-3 proteins associate with RGS7 and RGS3. Binding of 14-3-3 is mediated by a conserved phosphoserine located in the Galpha-interacting portion of the RGS domain; interaction with 14-3-3 inhibits the GAP activity of RGS7, depends upon phosphorylation of a conserved residue within the RGS domain, and results in inhibition of GAP function. Collectively, these data indicate that phosphorylation-dependent binding of 14-3-3 may act as molecular switch that controls the GAP activity keeping a substantial fraction of RGS proteins in a dormant state.

Origin and appearance of HITS induced by prosthetic heart valves: an in vitro study

Patients with mechanical heart valve prostheses show significantly enhanced numbers of HITS detected by transcranial Doppler ultrasound. In order to assess the origin of HITS formation, an in vitro study was set out to quantify valve induced microemboli for mechanical and bioprosthetic valves under various circulatory conditions by means of Ultrasound-Doppler-Sonography. At the same time the influence of CO2 partial pressure on HITS rate vas investigated. It can be summarised that for mechanical heart valve prostheses a strong correlation exists between left ventricular dp/dtmax and the detected HITS rates. It was also demonstrated that a bioprosthesis generates significantly less HITS than a mechanical valve. The origin of HITS is gaseous since the tests were carried out using a cell-free filtered water-glycerol test fluid. The HITS rate could be increased by increasing the amount of dissolved gas within the test fluid. The results support the hypothesis that cavitation is the key factor in the appearance of gaseous microemboli at heart valve prostheses.

Upregulation of RGS7 may contribute to tumor necrosis factor-induced changes in central nervous function

The central nervous dysfunctions of lethargy, fever and anorexia are manifestations of sepsis that seem to be mediated by increased cytokine production. Here we demonstrate that tumor necrosis factor (TNF)-alpha, an essential mediator of endotoxin-induced sepsis, prevents the proteasome-dependent degradation of RGS7, a regulator of G-protein signaling. The stabilization of RGS7 by TNF-alpha requires activation of the stress-activated protein kinase p38 and the presence of candidate mitogen-activated protein kinase phosphorylation sites. In vivo, RGS7 is rapidly upregulated in mouse brain after exposure to either endotoxin or TNF-alpha, a response that is nearly abrogated in mice lacking TNF receptor 1. Our findings indicate that TNF-mediated upregulation of RGS7 may contribute to sepsis-induced changes in central nervous function.

Interaction between RGS7 and polycystin

Regulators of G protein signaling (RGS) proteins accelerate the intrinsic GTPase activity of certain Galpha subunits and thereby modulate a number of G protein-dependent signaling cascades. Currently, little is known about the regulation of RGS proteins themselves. We identified a short-lived RGS protein, RGS7, that is rapidly degraded through the proteasome pathway. The degradation of RGS7 is inhibited by interaction with a C-terminal domain of polycystin, the protein encoded by PKD1, a gene involved in autosomal-dominant polycystic kidney disease. Furthermore, membranous expression of C-terminal polycystin relocalized RGS7. Our results indicate that rapid degradation and interaction with integral membrane proteins are potential means of regulating RGS proteins.

Cellular activation triggered by the autosomal dominant polycystic kidney disease gene product PKD2

Autosomal dominant polycystic kidney disease (ADPKD) is caused by germ line mutations in at least three ADPKD genes. Two recently isolated ADPKD genes, PKD1 and PKD2, encode integral membrane proteins of unknown function. We found that PKD2 upregulated AP-1-dependent transcription in human embryonic kidney 293T cells. The PKD2-mediated AP-1 activity was dependent upon activation of the mitogen-activated protein kinases p38 and JNK1 and protein kinase C (PKC) epsilon, a calcium-independent PKC isozyme. Staurosporine, but not the calcium chelator BAPTA [1,2-bis(o-aminophenoxy)ethane-N,N,N', N'-tetraacetate], inhibited PKD2-mediated signaling, consistent with the involvement of a calcium-independent PKC isozyme. Coexpression of PKD2 with the interacting C terminus of PKD1 dramatically augmented PKD2-mediated AP-1 activation. The synergistic signaling between PKD1 and PKD2 involved the activation of two distinct PKC isozymes, PKC alpha and PKC epsilon, respectively. Our findings are consistent with others that support a functional connection between PKD1 and PKD2 involving multiple signaling pathways that converge to induce AP-1 activity, a transcription factor that regulates different cellular programs such as proliferation, differentiation, and apoptosis. Activation of these signaling cascades may promote the full maturation of developing tubular epithelial cells, while inactivation of these signaling cascades may impair terminal differentiation and facilitate the development of renal tubular cysts.

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.

Effects of combination antihypertensive therapy on baroreflex sensitivity and heart rate variability in systemic hypertension

Earlier studies have shown that cardiovascular autonomic regulation is impaired in untreated or poorly controlled systemic hypertension. The purpose of this double-blind, randomized parallel trial was to evaluate whether improved blood pressure (BP) control can reverse this impairment. The study group consisted of 33 patients (age 45 to 63 years) with poor BP control who received randomized metoprolol or enalapril monotherapy. Baroreflex sensitivity (BRS) was assessed by phenylephrine test and time- and frequency-domain measurements of heart rate variability (HRV) were analyzed from 24-hour ambulatory electrocardiographic recordings during monotherapy and after 10 weeks of combination therapy with metoprolol + felodipine or enalaril + hydrochlorothiazide to lower casual BP to < 140/90 mm Hg. Intensified treatment decreased 24-hour systolic and diastolic BP from 139 +/- 12/86 +/- 8 mm Hg to 126 +/- 8/80 +/- 7 mm Hg (p <0.0001). BRS improved from 6.2 +/- 3.2 ms/mm Hg to 8.9 +/- 4.1 ms/mm Hg (p <0.0001) and measurements of HRV (e.g., SD of all RR intervals from 128 +/- 45 ms to 145 +/- 46 ms, p <0.001) improved significantly during the combination therapy. Changes in BRS and HRV were similar in magnitude in both treatment arms. Mean RR intervals were comparable before and after intensive antihypertensive therapy (850 +/- 124 ms vs 937 +/- 279 ms, p = NS). These data indicate that adequate BP control with modem antihypertensive combination therapy can improve cardiovascular autonomic function, which may partially explain the reduced cardiac mortality observed in patients with intensified antihypertensive therapy.