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Biomedical subjects

Branko Braam

Publications and source records attributed to Branko Braam.

31 records · Page 2Linked to original sources
PubMed2004

Broadly altered gene expression in blood leukocytes in essential hypertension is absent during treatment.

We assessed whether large-scale expression profiling of leukocytes of patients with essential hypertension reflects characteristics of systemic disease and whether such changes are responsive to antihypertensive therapy. Total RNA from leukocytes were obtained from untreated (n=6) and treated (n=6) hypertensive patients without apparent end-organ damage and from normotensive controls (n=9). RNA was reverse-transcribed and labeled and gene expression analyzed using a 19-K oligonucleotide microarray using dye swaps. Samples of untreated and of treated patients were pooled for each sex and compared with age- and sex-matched controls. In untreated patients, 680 genes were differentially regulated (314 up and 366 down). In the treated patients, these changes were virtually absent (4 genes up, 3 genes down). A myriad of changes was observed in pathways involved in inflammation. Inflammation-dampening interleukin receptors were decreased in expression. Intriguingly, inhibitors of cytokine signaling (the PIAS family of proteins) were differentially expressed. The expression of several genes that are involved in regulation of blood pressure were also differentially expressed: angiotensin II type 1 receptor, ANP-A receptor, endothelin-2, and 3 of the serotonin receptors were increased, whereas endothelin-converting enzyme-1 was decreased. Strikingly, virtually no changes in gene expression could be detected in hypertensive patients who had become normotensive with treatment. This observation substantiates the long-standing idea that hypertension is associated with a complex systemic response involving inflammation-related genes. Furthermore, leukocytes display differential gene expression that is of importance in blood pressure control. Importantly, treatment of blood pressure to normal values can virtually correct such disturbances.

Adult↗
PubMed2004

Fibronectin is a hypoxia-independent target of the tumor suppressor VHL.

The von Hippel-Lindau (VHL) tumor suppressor gene regulates the extracellular matrix by controlling fibronectin deposition. To identify novel VHL target genes, we subjected mRNA from VHL-deficient RCC cells (786-0-pRC) and a transfectant re-expressing wildtype VHL (786-0-VHL) to differential expression profiling. Among the differentially expressed genes, we detected that fibronectin is upregulated in the presence of VHL, while it is not affected by hypoxia. Thus regulation of fibronectin deposition by VHL occurs at the transcriptional level, irrespective of oxygen levels.

Carcinoma, Renal Cell↗
PubMed2004

Regulation of gene expression by dietary Ca2+ in kidneys of 25-hydroxyvitamin D3-1 alpha-hydroxylase knockout mice.

BACKGROUND: Pseudovitamin D deficiency rickets (PDDR) is an autosomal disease, characterized by undetectable levels of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), rickets and secondary hyperparathyroidism. Mice in which the 25-hydroxyvitamin D3-1 alpha-hydroxylase (1 alpha-OHase) gene was inactivated, presented the same clinical phenotype as patients with PDDR. METHODS: cDNA Microarray technology was used on kidneys of 1 alpha-OHase knockout mice to study the expression profile of renal genes in this Ca2+-related disorder. Genome wide molecular events that occur during the rescue of these mice by high dietary Ca2+ intake were studied by the use of 15K cDNA microarray chips. RESULTS: 1 alpha-OHase knockout mice fed a normal Ca2+ diet developed severe hypocalcemia, rickets and died with an average life span of 12 +/- 2 weeks. Intriguingly, 1 alpha-OHase-/- mice supplemented with an enriched Ca2+ diet were normocalcemic and not significantly different from wild-type mice. Inactivation of the 1 alpha-OHase gene resulted in a significant regulation of +/- 1000 genes, whereas dietary Ca2+ supplementation of the 1 alpha-OHase-/- mice revealed +/- 2000 controlled genes. Interestingly, 557 transcripts were regulated in both situations implicating the involvement in the dietary Ca2+-mediated rescue mechanism of the 1 alpha-OHase-/- mice. Conspicuous regulated genes encoded for signaling molecules like the PDZ-domain containing protein channel interacting protein, FK binding protein type 4, kinases, and importantly Ca2+ transporting proteins including the Na+-Ca2+ exchanger, calbindin-D28K and the Ca2+ sensor calmodulin. CONCLUSION: Dietary Ca2+ intake normalized disturbances in the Ca2+ homeostasis due to vitamin D deficiency that were accompanied by the regulation of a subset of renal genes, including well-known renal Ca2+ transport protein genes, but also genes not previously identified as playing a role in renal Ca2+ handling.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed2004

Temporary losartan or captopril in young SHR induces malignant hypertension despite initial normotension.

BACKGROUND: Exposure of normotensive rats to angiotensin-converting enzyme (ACE) inhibitors in early life causes hypertrophy of intrarenal arteries. Similar defects have been found in knockout mice lacking angiotensinogen, ACE, or angiotensin II type 1 (AT1) receptors. On the other hand, transient inhibition of the renin-angiotensin system from 2 weeks of age in spontaneously hypertensive rats (SHR), either with ACE inhibitors or with AT1 receptor antagonists partially prevents the increase in blood pressure. However, permanent treatment of SHR from conception onwards with ACE inhibitors completely prevents hypertension. Although these studies demonstrated protection from hypertension-induced changes in the heart and large arteries, renal arteries were not studied and follow-up did not extend beyond 6 months of age. We postulated that while brief exposure to ACE inhibitors or AT1 receptor antagonists in young SHR would temporarily decrease blood pressure, it would also be associated with development of intrarenal arterial malformation, and ultimately have deleterious effects. METHODS: Direct effects on intrarenal arterial morphology of an ACE inhibitor (captopril, 100 mg/kg/day) and an AT1 receptor antagonist (losartan, 50 mg/kg/day), administered from the last week of gestation until 8 weeks of age were examined in SHR. After stopping treatment at 8 weeks, we continued to monitor blood pressure until spontaneous death. RESULTS: Systolic blood pressure at 8 weeks was normalized by captopril and losartan (SHR control 187 +/- 8 mm Hg; captopril 118 +/- 5 mm Hg; and losartan 120 +/- 9 mm Hg). However, by 30 weeks, blood pressure had increased to control SHR levels. At 4 weeks, the media of renal arteries and arterioles was hypertrophied. Marked smooth muscle cell hyperplasia of cortical arteries resulted in significantly increased wall thickness by 8 weeks, despite similar external diameter. Arterial wall structure was disrupted, with fragmentation of elastic fibers and irregular distribution of collagen type I fibers. After stopping treatment, the rats gradually began to show poor health and all had died by 1 year of age, while all 1-year-old control SHR females were in good health. The cause of morbidity and mortality in the rats treated in early life was clearly malignant hypertension. Severe hypertrophy of renal arterioles was found, as well as cerebral hemorrhage. CONCLUSION: Despite initial normalization of blood pressure interference with the renin-angiotensin system during a crucial stage of development in SHR can initiate marked smooth muscle cell hyperplasia and disruption of the wall structure of the intrarenal arteries. Subsequent progression of this intrarenal process after cessation of treatment suggests an independent process that eventually results in malignant hypertension and early death.

Animals↗
PubMed2004

Endothelial progenitor cell dysfunction: a novel concept in the pathogenesis of vascular complications of type 1 diabetes.

Type 1 diabetes is associated with reduced vascular repair, as indicated by impaired wound healing and reduced collateral formation in ischemia. Recently, endothelial progenitor cells (EPCs) have been identified as important regulators of these processes. We therefore explored the concept that EPCs are dysfunctional in diabetes. The number of EPCs obtained from type 1 diabetic patients in culture was 44% lower compared with age- and sex-matched control subjects (P < 0.001). This reduction was inversely related to levels of HbA(1c) (R = -0.68, P = 0.01). In addition, we demonstrated that patient EPCs were also impaired in function using an in vitro angiogenesis assay. Conditioned media from patient EPCs were significantly reduced in their capacity to support endothelial tube formation in comparison to control EPCs. Therefore, despite culturing the EPCs under normoglycemic conditions, functional differences between patient and control EPCs were maintained. Our findings demonstrate that adverse metabolic stress factors in type 1 diabetes are associated with reduced EPC numbers and angiogenicity. We hypothesize that EPC dysfunction contributes to the pathogenesis of vascular complications in type 1 diabetes.

Adult↗
PubMed2003

Human proximal tubular cell responses to angiotensin II analyzed using DNA microarray.

Angiotensin II has been shown to exert complex effects on proximal tubular cell function and growth. To assess some of the direct effects on proximal tubular cells, changes in gene expression of selected cellular pathways were determined after exposure to angiotensin II. We used DNA microarrays to analyze multiple gene expression responses to increasing angiotensin II concentrations. Human proximal tubular cells were grown in flasks, and the presence of angiotensin type 1 receptor was confirmed by Western blot analysis. At passages 4-6, these cells were exposed to angiotensin II and harvested 4 h later and mRNA of the cells was extracted; 2 microg of mRNA was fluorescently conjugated for cDNA microarray hybridization. A custom-made DNA microarray was designed by selecting 300 human genes from 10 different functional systems and amplifying clones using polymerase chain reaction. Cells were subjected to 10 and 100 nM angiotensin II with paired untreated cells as controls. RNA was isolated, reverse transcribed, labeled and hybridized to the arrays and the ratios calculated. Ratios of > or =2.0 and < or =0.5 were considered significant. Coordinated changes were observed in genes of the hepatocyte nuclear factor 3 family (NHF3; HNF3A, HNF3B and HNF3G), in the E2F genes (E2F1, E2F3) and the interferon regulatory factors IRF1 and IRF5. Induction of the expression of transcription factors points towards complex regulation of gene expression upon angiotensin II exposure. Three genes involved in the dampening of oxidative stress were enhanced. Taken together, brief exposure of human tubular epithelial cells to angiotensin II elicited a marked induction of nuclear factors, antioxidant genes and hormones and hormone receptor genes. The quick activation of transcription factors by angiotensin II indicates that angiotensin II can directly initiate a cascade of expressional events in proximal tubular cells.

Angiotensin II↗
PubMed2003

NO dependency of RBF and autoregulation in the spontaneously hypertensive rat.

In the spontaneously hypertensive rat (SHR), renal blood flow (RBF) has been reported to be very dependent on nitric oxide (NO); however, autoregulation is normal, albeit shifted to higher perfusion pressures. To test the hypothesis that in the SHR NO dependency of RBF autoregulation is diminished, we investigated RBF autoregulation in anesthetized young male SHR and normotensive Wistar-Kyoto (WKY) rats before and during acute intravenous NO synthase (NOS) inhibition with N(omega)-nitro-L-arginine (L-NNA) and urinary excretion of nitrate plus nitrite (U(NOx)V) at different renal perfusion pressures (RPP). Under baseline conditions, SHR had higher mean arterial pressure (147 +/- 4 mmHg) and renal vascular resistance (16 +/- 1 U) than WKY (105 +/- 4 mmHg and 10 +/- 0.5 U, respectively, P < 0.05). RBF was similar (9.4 +/- 0.5 vs. 10.3 +/- 0.1 ml x min(-1)x g kidney wt(-1)). Acute NOS blockade increased mean arterial pressure similarly, but there was significantly more reduction in RBF and hence an enhanced increase in renal vascular resistance in SHR (to 36 +/- 3 vs. 17 +/- 1 U in WKY, P < 0.001). The renal vasculature of SHR is thus strongly dependent on NO in maintaining basal RBF. The lower limit of autoregulation was higher in SHR than WKY in the baseline situation (85 +/- 3 vs. 71 +/- 2 mmHg, P < 0.05). Acute L-NNA administration did not decrease the lower limit in the SHR (to 81 +/- 3 mmHg, not significant) and decreased the lower limit to 63 +/- 2 mmHg (P < 0.05) in the WKY. The degree of compensation as a measure of autoregulatory efficiency attained at spontaneous perfusion pressures was comparable in SHR vs. WKY but with a shift of the curve toward higher perfusion pressures in SHR. Acute NOS blockade only increased the degree of compensation in WKY. Remarkably, U(NOx)V was significantly lower at spontaneous RPP in SHR. After reduction of RPP, the observed decrease in U(NOx)V was significantly more pronounced in WKY than in SHR. In conclusion, the renal circulation in SHR is dependent on high levels of NO; however, the capacity to modulate NO in response to RPP-induced changes in shear stress seems to be limited.

Animals↗
PubMed2003

Hypoxanthine plus xanthine oxidase causes profound natriuresis without affecting renal blood flow autoregulation.

BACKGROUND: Enhanced superoxide (O2-.) production by xanthine oxidase in ischemia/reperfusion has been implicated in structural damage. The reperfusion phase is accompanied by decreased tubular sodium reabsorption, which has been partly attributed to enhanced action of O2-. In the present study we assessed whether intrarenal increases of O2-. accomplished by concomitant intrarenal hypoxanthine and intravenous xanthine oxidase (HX/XO) infusion would decrease or increase sodium excretion, and whether HX/XO infusion could be responsible for the diminished efficacy of renal blood flow (RBF) autoregulation in ischemia/reperfusion. METHODS: In the first group of Sprague-Dawley rats, renal sodium handling was measured before and during O2-. infusion. In the second group, renal hemodynamics and RBF autoregulation were assessed. RESULTS: Intrarenal O2-. infusion dramatically increased urine flow from 14.5 +/- 2.0 microL/min to 46.3 +/- 4.4 microL/min, urinary excretion of sodium (UNaV) from 1.7 +/- 0.4 micromol/min to 8.6 +/- 0.9 micromol/min, and fractional excretion of sodium FENa from 1.2 +/- 0.4% to 7.6 +/- 1.2%. Urinary excretion of thiobarbituric acid reactive substances (TBARS), a measure of lipid peroxidation, increased during HX/XO infusion. These changes were completely reversible. Glomerular filtration rate (GFR) decreased from 1.12 +/- 0.08 during baseline to 0.79 +/- 0.06 during HX/XO (P < 0.05) and tended to increase toward baseline during recovery (0.84 +/- 0.06 mL/min/g kidney weight). HX/XO did not significantly affect mean arterial pressure (MAP). HX/XO decreased RBF in the second group from 8.4 +/- 0.6 mL/min/g kidney weight to 7.4 +/- 0.5 mL/min/g kidney weight (P < 0.05) and renal vascular resistance (RVR) slightly increased from 13.8 +/- 0.9 units under baseline conditions to 15.1 +/- 1.1 units during HX/XO infusion (P < 0.05). HX/XO did not significantly affect RBF autoregulation. Proteinuria and glucosuria were absent and light microscopy revealed no renal morphologic changes. CONCLUSION: Intrarenal O2-. infusion (1) dramatically increased sodium and volume excretion and (2) did not affect autoregulation of RBF. Thus, superoxide can markedly affect glomerulotubular balance by diverging actions on renal hemodynamics and reabsorptive function and could mediate the functional tubular consequences of ischemia/reperfusion.

Animals↗
PubMed2003

Hypoalbuminaemia enhances the renal vasoconstrictor effect of lysophosphatidylcholine.

BACKGROUND: Lysophosphatidylcholine (LPC) causes vascular dysfunction in vitro. Lipoprotein LPC is increased in hypoalbuminaemia. Albumin binds LPC and restores LPC-induced abnormalities. We hypothesized that in vivo LPC impairs blood flow more in hypoalbuminaemia than in normoalbuminaemia. METHODS: Increasing concentrations of LPC were infused intra-renally in Nagase analbuminaemic rats (NAR) and Sprague-Dawley rats (controls). RESULTS: Intra-renal LPC (0.1 micromol/min, 20 min) reduced renal blood flow (RBF) more (P < 0.01) in NAR (from 8.3 +/- 0.3 to 4.0 +/- 1.1) than in controls (from 7.7 +/- 0.7 to 5.8 +/- 0.5 ml/min/g kidney). Lysophosphatidylethanolamine had no effect. After stopping LPC, RBF recovery was delayed in NAR [median 90 (range: 70-90) vs 45 min (40-60), P < 0.01]. Intravenous bovine serum albumin (BSA) prevented LPC-induced vasoconstriction in both strains. Prolonging LPC for 60 min delayed recovery of RBF. In this setting, intra-renal BSA completely restored RBF in 75 min (30-90), while intra-renal saline over 75 min only resulted in 33 +/- 13% recovery (P < 0.01). Baseline renal LPC content was unchanged in NAR. However, intra-renal LPC infusion doubled renal LPC content in NAR, but had no effect in controls. CONCLUSIONS: In NAR, baseline RBF and renal LPC content are normal. However, exposure of NAR to LPC results in much more vasoconstriction and accumulation of LPC than in normoalbuminaemia. Addition of albumin prevents and restores LPC-induced vasoconstriction.

Animals↗
PubMed2002

Visualizing tubular lipid peroxidation in intact renal tissue in hypertensive rats.

An imbalance between production of reactive oxygen species (ROS) and antioxidant defense is involved in the pathogenesis of diverse chronic parenchymatous diseases. To identify the primary site of such increased oxidative stress, a lipophilic ROS-sensitive probe (C11-Bodipy 581/591) is introduced, which allows the visualization and quantification of oxidative injury using confocal fluorescence microscopy in living cells. The properties of this probe are such that its emission wavelength irreversibly shifts from red to green upon oxidation. This probe was used to identify the spatiotemporal distribution of lipid peroxidation in the rat kidney during chronic NOS inhibition, a model associated with hypertension and proteinuria. Chronic NOS inhibition resulted in increased lipid peroxidation in renal tubules but hardly any in glomeruli or blood vessels. This peroxidation preceded the loss of renal function characteristic of the model and was accompanied by parallel changes in thiobarbituric acid reactive substances in the renal cortex. Furthermore, the increase in oxidation was dependent on angiotensin II and NADPH oxidase and prevented by vitamin E. Induction of cytoprotective heat-shock protein 70 preceded lipid peroxidation, rise in BP, or proteinuria. These findings challenge the paradigm that the vascular wall is the source and target of oxidative stress in chronic parenchymatous renal disease associated with hypertension.

Angiotensin II↗
PubMed2001

Vitamin E alleviates renal injury, but not hypertension, during chronic nitric oxide synthase inhibition in rats.

Chronic nitric oxide (NO) synthase inhibition in rats causes hypertension, renal vascular injury, and proteinuria. NO deficiency increases superoxide (O(2)(-)) activity, but the effects of antioxidant treatment on renal injury have not been studied in this model. Exposure of rats to N omega-nitro-L-arginine (L-NNA) for 4 d markedly decreased NO-dependent relaxation in aortic rings and increased glomerular and renal interstitial monocyte influx, but renal O(2)(-) activity was not increased. After 7 d, BP and proteinuria were significantly increased. After 21 d of L-NNA treatment, rats displayed severe hypertension, decreased GFR, marked proteinuria, glomerular ischemia, renal vascular and tubulointerstitial injury, and complete loss of NO-dependent relaxation. Renal O(2)(-) activity was markedly increased [lucigenin-enhanced chemiluminescence (LEC), 279 +/- 71 versus 50 +/- 7 counts/10 mg, P < 0.01; electron paramagnetic resonance spectroscopy, 0.57 +/- 0.05 versus 0.34 +/- 0.04 U/10 mg, P < 0.05]. Apocynin, a specific inhibitor of NADPH oxidase, and diphenyleneiodonium, an inhibitor of flavin-containing enzymes, completely inhibited LEC signals in vitro, whereas allopurinol had no effect, indicating that NAD(P)H oxidase plays a major role in superoxide production in the kidney. Endothelial function remained impaired during cotreatment with alpha-tocopherol and there was no effect on hypertension or tubulointerstitial injury, but glomerular ischemia, decreases in GFR, and renal vascular injury were prevented and proteinuria was ameliorated. Renal LEC signals were intermediate between control and L-NNA-alone values (181 +/- 84 counts/10 mg). Chronic NO synthase inhibition in rats results in marked increases in renal cortical O(2)(-) activity, mediated by flavin-dependent oxidases. The absence of early increases in renal O(2)(-) activity, in the presence of endothelial dysfunction and macrophage influx, indicates that increased renal O(2)(-) activity is neither attributable to NO deficiency per se nor solely related to macrophage influx. The improvement of glomerular function and amelioration of renal vasculitis and proteinuria with vitamin E cotreatment indicate that oxidants are involved in the pathogenesis of renal injury in this model. However, markedly impaired endothelial function and unabated hypertension persist with vitamin E treatment and seem to be directly attributable to NO deficiency.

Animals↗
PubMed2000

Impaired renal blood flow autoregulation in two-kidney, one-clip hypertensive rats is caused by enhanced activity of nitric oxide.

Increases in renal perfusion pressure will induce shear stress-mediated nitric oxide (NO) release, which could oppose autoregulation of renal blood flow (RBF). Although cardiac, cerebral, and mesenteric autoregulation is enhanced during nitric oxide (NO) synthesis inhibition, this has not been reported for renal autoregulation of blood flow. In the present study, the lower limit and efficiency of RBF autoregulation (as assessed by the degree of compensation) were studied before and during NO inhibition in normotensive Sprague Dawley rats (control; n = 9) and in the non-clipped kidney of two-kidney, one-clip Goldblatt hypertensive animals (2K1C; n = 9; 3 wk; 0.25-mm silver clip). In both groups, renal autoregulation curves were obtained before and during infusion of N(G) -nitro-L-arginine (L-NNA) (bolus 1.5 mg/kg intravenously, infusion 10 microg/kg per min intravenously), using a transit-time flow probe around the left renal artery. In control rats, mean arterial pressure (MAP) increased, RBF decreased, and renal vascular resistance (RVR) increased in response to L-NNA infusion. The lower limit of autoregulation in control animals did not significantly change during L-NNA infusion (78 +/- 3 to 70 +/- 2 mmHg). The degree of compensation in these rats slightly increased during L-NNA infusion, however, this was only significant below 90 mmHg. The 2K1C rats had elevated MAP under baseline conditions. L-NNA infusion resulted in a decrease in RBF and an increase in MAP and RVR. During L-NNA infusion, RVR in 2K1C rats greatly exceeded RVR in control rats. A significant decrease was observed in the lower limit of autoregulation from 85 +/- 3 to 72 +/- 5 mmHg (P < 0.05). In the contralateral kidney of 2K1C rats, the degree of compensation was lower than in control rats under baseline conditions. L-NNA infusion resulted in significantly higher degrees of compensation compared to baseline. In conclusion, the contralateral kidney displayed a high NO dependency, as RBF greatly decreased and RVR dramatically increased in response to L-NNA infusion. The contralateral kidney of 2K1C rats exhibited impaired RBF autoregulation, which was improved by NO inhibition, as judged from a decrease in the lower limit of autoregulation and an increase in the degree of compensation. This study indicates that perfusion pressure-dependent NO release can oppose autoregulation in the kidney. However, the enhanced influence of NO on pressure-dependent RBF may facilitate the preservation of renal function in the nonclipped kidney of 2K1C rats.

Analysis of Variance↗