Biomedical subjects

Hartmut Osswald

Publications and source records attributed to Hartmut Osswald.

31 records · Page 2Linked to original sources

PubMed2004

Nephroprotection by theophylline in patients with cisplatin chemotherapy: a randomized, single-blinded, placebo-controlled trial.

The aim of the present study was to assess the possible prevention of cisplatin-induced impairment of GFR by theophylline in patients with various malignancies. The trial design was parallel, randomized, single blinded, and placebo controlled. Patients received cisplatin at a dosage of 50 mg/m(2) either combined with etoposide, ifosfamide, and epirubicin or with paclitaxel and 5-fluorouracil/folinic acid with the usual precautions, including a standard hydration scheme before application of cisplatin in both arms. In the control arm, placebo was administered; in the verum arm, patients received theophylline in a loading dose of 4 mg/kg intravenously over 30 min before cisplatin, followed by 0.4 mg/kg per min over a minimum of 6 h, and then 350 mg three times daily orally for 4 consecutive days after completion of chemotherapy. GFR of each patient was assessed by renal clearance of inulin within 3 d before and at day 5 after cisplatin chemotherapy. Despite usual precautions, patients in the placebo group had a 21% decrease (range, 11 to 31%) of inulin clearance after a single cycle of cisplatin-containing chemotherapy (92.9 +/- 3.4 versus 71.8 +/- 3.5 ml/min; P < 0.01). Patients who received theophylline had no deterioration of GFR (91.5 +/- 3.7 versus 90.0 +/- 3.8 ml/min; P > 0.05). No adverse effects have been observed during theophylline application. Conventional precautions such as hydration and osmotic diuresis cannot prevent a significant decrease of GFR after a single cycle of cisplatin-containing chemotherapy. The prophylactic application of theophylline as an intravenous loading dose and oral maintenance regimen may preserve kidney function in terms of GFR.

Adult↗

PubMed2004

Regulation of renal adenosine excretion in humans--role of sodium and fluid homeostasis.

BACKGROUND: Adenosine is a vasoactive metabolite of ATP hydrolysis that is involved in the regulation of renal haemodynamics, tubular reabsorption and renin release. Elevated tissue levels are found under conditions of increased metabolic load, ischaemia or renal injury. Urinary adenosine excretion (EADO) may therefore provide a sensitive marker of renal functional impairment in allograft rejection and kidney disease. To provide a basis for evaluation of EADO in clinical settings, we investigated, in an intra-individual, crossover clinical trial the physiological variability and regulation of EADO in response to altered sodium and fluid balance. METHODS: Twelve healthy volunteers were randomized to normal (ad libitum), low (<5 g/day) or high (supplementation of 100 mg/kg/day) sodium chloride diets for 8 days prior to assessment of renal haemodynamics and tubular function in standard clearance investigations. Following baseline periods, fluid homeostasis was altered independently by acute oral water load. EADO was determined in 24 h urine collections and during clearance investigations. RESULTS: Mean EADO in humans was 3.2+/-0.2 micromol/ 24 h during euvolaemia and normal sodium intake. A weak correlation was found between sodium load and EADO. In clearance experiments, variation in EADO was <1.3-fold, despite profound alterations in sodium intake. EADO was independent of urinary flow rate. Renal haemodynamics were not significantly altered by dietary regimen or by acute volume load. CONCLUSION: In summary, the physiological variability of EADO is remarkably small in humans. We demonstrate that even profound alterations in sodium and fluid homeostasis do not significantly affect EADO. These data provide a basis for evaluation of elevated EADO as a marker of renal injury in various clinical settings.

Adenosine↗

PubMed2004

Influence of an altered methylation potential on mRNA methylation and gene expression in HepG2 cells.

S-adenosylhomocysteine (AdoHcy), a by-product and inhibitor of S-adenosylmethionine (AdoMet)-dependent methylation reactions, is removed by AdoHcy hydrolase. The ratio of AdoMet and AdoHcy, also termed methylation potential (MP), is a metabolic indicator for cellular methylation status. In the present study, we have investigated the influence of hypoxia and inhibition of AdoHcy hydrolase on MP in HepG2 cells. Furthermore, we studied the impact of deviations in MP on mRNA and DNA methylation and the expression of selected genes: erythropoietin, VEGF-A, AdoHcy hydrolase, cyclophilin, and HIF-1alpha. Under hypoxic conditions, the MP raised from 53.4 +/- 3.3 to 239.4 +/- 24.8, which is the result of increased AdoMet and decreased AdoHcy levels. Inhibition of AdoHcy hydrolase by adenosine-2',3'-dialdehyde leads to a 40-fold reduction of the MP under both normoxic and hypoxic conditions. Hypoxia increases erythropoietin (2.7-fold) and VEGF-A (5-fold) mRNA expression. During a reduced MP erythropoietin mRNA expression is lowered under normoxia and hypoxia by 70%, whereas VEGF-A mRNA expression is only reduced under hypoxic conditions by 60%. The mRNA expression of AdoHcy hydrolase, HIF-1alpha, and cyclophilin is insensitive to an altered MP. Furthermore, decreased MP leads to a highly significant decrease in overall mRNA methylation. Our results show that the mRNA levels of the studied genes respond differentially to changes in MP. This implies that genes with a slower transcription rate and mRNAs with a slower turnover are insensitive to short-term changes in MP.

Adenosine↗

PubMed2004

S-Adenosylhomocysteine hydrolase as a target for intracellular adenosine action.

S-Adenosylhomocysteine hydrolase (AdoHcyase) controls intracellular levels of S-adenosylhomocysteine (AdoHcy). AdoHcy is a potent product inhibitor of some S-adenosylmethionine-dependent methyltransferases. Pharmacological modulation of AdoHcyase to indirectly inhibit methyltransferases can be guided by the fact that adenosine binds with high affinity to AdoHcyase and inhibits enzyme activity. cAMP can compete with adenosine and can counteract the adenosine-induced inhibition of AdoHcyase. Thus, the ratio between adenosine and cAMP, which can vary under different physiological conditions, might result in changes in, for example, DNA promoter methylation and therefore transcription.

Adenosine↗

PubMed2004

Effect of two amino acids in TM17 of Sulfonylurea receptor SUR1 on the binding of ATP-sensitive K+ channel modulators.

The sulfonylurea receptor (SUR) is the important regulatory subunit of ATP-sensitive K+ channels. It is an ATP-binding cassette protein comprising 17 transmembrane helices. SUR is endowed with binding sites for channel blockers like the antidiabetic sulfonylurea glibenclamide and for the chemically very heterogeneous channel openers. SUR1, the typical pancreatic SUR isoform, shows much higher affinity for glibenclamide but considerably lower affinity for most openers than SUR2. In radioligand binding assays, we investigated the role of two amino acids, T1285 and M1289, located in transmembrane helix (TM)-17, in opener binding to SUR1. These amino acids were exchanged for the corresponding amino acids of SUR2. In competition experiments using [3H]glibenclamide as radioligand, SUR1(T1285L, M1289T) showed much higher affinity toward the cyanoguanidine openers pinacidil and P1075 than SUR1 wild type. The affinity for the thioformamide aprikalim was also markedly increased. In contrast, the affinity for the benzopyrans rilmakalim and levcromakalim was unaffected; however, the amount of displaced [3H]glibenclamide binding was nearly doubled. The binding properties of the opener diazoxide and the blocker glibenclamide were unchanged. In conclusion, mutation of two amino acids in TM17 of SUR1, especially of M1289, leads to class-specific effects on opener binding by increasing opener affinity or by changing allosteric coupling between opener and glibenclamide binding.

ATP-Binding Cassette Transporters↗

PubMed2003

Adenosine binding sites at S-adenosylhomocysteine hydrolase are controlled by the NAD+/NADH ratio of the enzyme.

S-Adenosylhomocysteine hydrolase (AdoHcy hydrolase) catalyzes the reversible hydrolysis of S-adenosylhomocysteine (AdoHcy) to adenosine (Ado) and homocysteine. On the basis of the kinetics of Ado binding to AdoHcy hydrolase we have shown that AdoHcy hydrolase binds Ado with different affinities [Kidney Blood Press. Res. 19 (1996) 100]. Since AdoHcy hydrolase in its totally reduced form binds Ado with high affinity we determined in the present study the Ado binding characteristics of purified AdoHcy hydrolase from bovine kidney (native form) and of reconstituted forms with defined NAD(+)/NADH ratios. AdoHcy hydrolase in its native form and at a ratio of 50% NAD(+) and 50% NADH exhibits two binding sites for Ado with a K(D1) of 9.2+/-0.6 nmol/L and a K(D2) of 1.4+/-0.1 micromol/L, respectively. Binding of Ado to AdoHcy hydrolase in its NADH form and in its NAD(+) form exhibits only one binding site with high affinity 48.3+/-2.7 nmol/L for the NADH form and with a low affinity of 4.9+/-0.3 micromol/L for the NAD(+) form. To identify these two Ado binding sites, AdoHcy hydrolase was covalently modified with [2-3H]-8-azido-Ado. After irradiation of the native AdoHcy hydrolase two different photolabeled peptides were isolated and identified as Asp(307)-Val(325) and Tyr(379)-Thr(410). When the reconstituted AdoHcy hydrolase in its NADH and in its NAD(+) form was irradiated with [2-3H]-8-azido-Ado only one peptide was identified as Asn(312)-Lys(318) from the NADH form and as Asp(391)-Ala(396) from the NAD(+) form. Based on the crystallographic data, the labeled peptide Asp(391)-Ala(396) (low affinity binding site), appears to belong to the catalytic domain of AdoHcy hydrolase, whereas the labeled peptide, identified as Asn(312)-Lys(318) (high affinity binding site), is located in the NAD domain. In conclusion, our data show that AdoHcy hydrolase has two different Ado binding sites which are dependent upon the enzyme-bound NAD(+)/NADH ratios.

Adenosine↗

PubMed2003

Role of the renin-angiotensin system in the compensation of quinpirole-induced blood pressure decrease.

The dopamine D(2)-like receptor agonist quinpirole has been reported to lower blood pressure. This effect appears to be mediated via activation of presynaptic D(2)-like receptors inhibiting the stimulated neural norepinephrine release. The aim of the present study was to investigate the role of renal nerves and the renin-angiotensin system (RAS) in the blood pressure lowering effect of quinpirole. Therefore, clearance experiments using different doses of quinpirole (0.3 to 100 microg/kg/min) were performed in thiopental-anesthetized rats with intact kidneys (INN) or 5 to 7 days after bilateral renal denervation (DNX). The functional involvement of the RAS in the blood pressure lowering effect of quinpirole was determined in rats pretreated with a subpressor dose of angiotensin II (10 microg/kg/min) or in rats pretreated with the angiotensin II (AT(1)) receptor antagonist losartan, in a subdepressor dose (10 microg/kg/min). Quinpirole dose-dependently decreased mean arterial blood pressure (MAP) by up to 29%. This blood pressure lowering effect of quinpirole was observed at lower doses in DNX rats when compared with INN animals (ED(50): 0.98 microg/kg/min in DNX vs. 6.02 microg/kg/min in INN animals). Quinpirole in a dose of 3 microg/kg/min, which did not affect MAP in vehicle treated INN rats, significantly reduced MAP in rats with losartan pretreatment. In DNX rats pretreated with angiotensin II the MAP-response to the infusion of 3 microg/kg/min quinpirole was clearly attenuated in comparison with untreated DNX animals. Our data show that stimulation of dopamine D(2)-like receptors dose-dependently decreased blood pressure, which was potentiated by both interruption of the renal innervation and AT(1) receptor blockade, while exogenous ANG II restored the enhancement of the blood pressure response to quinpirole. We conclude that the increased vasodilatory effect of quinpirole after renal denervation might depend on a decreased activity of the RAS.

Anesthesia↗

PubMed2003

Dopamine D3 receptor mRNA and renal response to D3 receptor activation in spontaneously hypertensive rats.

Defective dopamine receptors may be involved in the development of hypertension. Recently, it has been shown that gene expression and function of the renal dopamine D3 receptor is impaired in salt-sensitive Dahl rats, a model of salt-dependent hypertension. Here, the functional response to D3 receptor activation was investigated in spontaneously hypertensive rats (SHR) and their normotensive Wistar-Kyoto rats (WKY). In addition, expression of the D3 receptor gene was studied in both rat strains. In clearance experiments, Ringer solution was infused at baseline in thiopental-anesthetized SHR and WKY (each n = 8), followed by an infusion of R(+)-7-hydroxy-dipropylaminotetralin (DPAT), a specific D3 receptor agonist. DPAT was infused in two consecutive doses of 0.01 and 0.1 microg/min per kg body weight. During the entire experiment mean arterial blood pressure was significantly higher (1.5-fold) in adult SHR when compared to age-matched WKY. In both groups DPAT infusion induced a similar dose-dependent increase in urinary flow rate and sodium excretion by a maximum of 2.3-fold and 3.5-fold, respectively. DPAT also increased the glomerular filtration rate in both SHR and WKY. Reverse transcription-polymerase chain reaction studies of whole kidney samples showed no significant differences between young prehypertensive and adult hypertensive SHR when compared to age-matched normotensive WKY. In summary, pharmacological dopamine D3 receptor activation induces a uniform renal response in SHR and WKY. Together with the similar D3 receptor gene expression in both rat strains, which is independent of age or blood pressure levels, the results do not support the notion that the dopamine D3 receptor system is involved in the pathogenesis of hypertension in the SHR model.

Animals↗

PubMed2002

Characterization of the cAMP binding site of purified S-adenosyl-homocysteine hydrolase from bovine kidney.

The enzyme S-adenosyl-homocysteine hydrolase (AdoHcyase) which catalyzes the reversible hydrolysis of AdoHcy to adenosine and homocysteine is an adenosine binding protein. In the present study we examined the characteristics of [(3)H]cAMP binding to purified AdoHcyase from bovine kidney in comparison with the high affinity adenosine binding site of AdoHcyase. AdoHcyase exhibits one [(3)H]cAMP binding site with an affinity of K(d)=23.1+/-1.1nM and a B(max) of 116.6+/-3.8pmol/mg protein. Binding of [(3)H]cAMP obeyed a monophasic reaction with a k(+1) value of 0.035min/M. The dissociation of AdoHcyase-[(3)H]cAMP complex exhibited a time- and temperature-dependent character. After a 240min incubation at 0 degrees only 5-10%, however, at 20 degrees 90% were displaceable. Adenosine and cAMP displace each other with similar affinities of EC(50) 57nM vs. EC(50) 65nM. 2'-Deoxyadenosine, N(6)-methyladenosine, and NECA displace 25nM [(3)H]cAMP and 10nM [(3)H]adenosine with EC(50) values of 94, 90 and 80nM, respectively. All other nucleosides studied, adenine, inosine, adenosine-2',3'-dialdehyde, 2-chloroadenosine, aristeromycin, and adenine nucleotides were only week competitors for [(3)H]cAMP and [(3)H]adenosine. These compounds displace [(3)H]cAMP and [(3)H]adenosine with equal potencies. Our data indicate that the binding site for nanomolar concentrations of cAMP and adenosine at the AdoHcyase appears to be identical. The physiological implications of a cAMP binding site at the AdoHcyase remain to be established.

Adenosylhomocysteinase↗

PubMed2002

The preventive effect of sodium pentosan polysulfate against renal stone formation in hyperoxaluric rats.

Sodium pentosan polysulfate (SPP), a semi-synthetic glycosaminoglycan, was administered to rats with hyperoxaluria, induced by a vitamin B6 deficient diet, as a model of calcium oxalate stone formation. We studied the preventive effects of SPP on stone formation as well as its inhibitory effects on stone growth by autoradiography and radioluminography after intravenous injection of (14)C-oxalate. The rats were divided into non-treated and SPP-treated groups. The non-treated rats were divided into three groups: one group was fed a regular diet, while the other two groups were fed a vitamin B6 deficient diet for 2 and 4 weeks, respectively. The SPP-treated rats were divided into two groups: one group was intravenously injected with SPP from the start of the vitamin B6 deficient diet for a total of 4 weeks and the other group was injected with the same amount of SPP after 2 weeks of the diet for 2 weeks. (14)C-oxalate renal macroautoradiograms were prepared, and calcium oxalate deposits in the renal tissues were compared between the non-treated and SPP-treated groups. The preventive effects on calcium oxalate stone formation were clearly observed in the group injected with SPP for 4 weeks. Even in the other SPP-treated group, in which the administration of SPP was started at 2 weeks after the start of the diet when calcium oxalate stone formation was already observed, the size of the calcium oxalate deposits observed after 4 weeks was smaller than that in the non-treated group fed a vitamin B6 deficient diet for 4 weeks. In conclusion, our results show that SPP has not only preventive effects on calcium oxalate stone formation but also growth inhibitory effects on stones in hyperoxaluric rats.

Animals↗

PubMed2002

Tissue levels of S-adenosylhomocysteine in the rat kidney: effects of ischemia and homocysteine.

Most S-adenosylmethionine (AdoMet)-dependent methyltransferases are regulated in vivo by the AdoMet/S-adenosylhomocysteine (AdoHcy) ratio, also termed as "methylation potential." Since adenosine inhibits in vitro AdoHcy hydrolysis and since adenosine tissue levels increase during hypoxia, it can be predicted that AdoHcy levels may increase in the rat kidney in parallel of those of adenosine. Therefore, the present investigation was performed to assess changes of renal AdoHcy and AdoMet tissue contents during ischemia and after administration of adenosine and homocysteine or both in the ischemic rat kidney. In anesthetized rats ischemia of the kidney was induced by renal artery occlusion for various time intervals. Adenosine and homocysteine were infused into the renal artery of the ischemic kidney. To induce a hyperhomocysteinemia homocysteine was continuously infused. The kidneys were removed and immediately snap-frozen. Tissue contents of AdoHcy, AdoMet, adenosine and adenine nucleotides were analyzed by means of HPLC. Under normoxic condition the tissue contents of AdoHcy, AdoMet and adenosine were 0.7+/-0.05, 44.1+/-1.0 and 3.8+/-0.1nmol/g wet weight, respectively. Renal ischemia for 30min resulted in an increase of AdoHcy levels from 0.7+/-0.05 to 9.1+/-0.6nmol/g wet weight and in a dramatic decrease of the AdoMet/AdoHcy ratio and energy charge from 65.1+/-5.6 to 2.8+/-0.2 and from 0.87+/-0.01 to 0.25+/-0.01, respectively. Application of exogenous adenosine into the ischemic kidney did not result in further AdoHcy accumulation. However, when homocysteine was infused into the ischemic kidney, AdoHcy increased five-fold above control levels, during 5min ischemia. Systemic infusion of homocysteine leads to a reduction of the methylation potential also in the normoxic kidney. We conclude that (i) the methylation potential in the kidney is markedly reduced during ischemia, mainly due to accumulation of AdoHcy; (ii) elevation of AdoHcy tissue content during ischemia is the result of the inhibition of AdoHcy hydrolysis; (iii) homocysteine is rate limiting for AdoHcy synthesis in the ischemic kidney; (iv) under normoxic conditions hyperhomocysteinemia can affect the methylation potential in the renal tissue.

Adenosine↗

PubMed2002

Differential renal response to Nomega-nitro-L-arginine methyl ester and L-arginine in rats with hypertensive or diabetic nephropathy.

The present experiments were designed to assess the renal functional response to alterations in nitric oxide formation in animals with different forms of nephropathy. To address this issue, the effects of Nomega-nitro-L-arginine methyl ester (L-NAME) or L-arginine were assessed in animal models exhibiting arterial hypertension due to chronic nitric oxide inhibition (L-NAME, 50 mg/l in drinking water for 12 weeks) or diabetes mellitus (streptozotocin, 60 mg/kg IP). Vehicle-treated, age-matched animals served as controls. Following 12 weeks of pretreatment, mean arterial pressure (MAP), renal hemodynamics, urinary albumin, and electrolyte excretion were determined in standard clearance experiments prior to and following infusion of L-NAME (50 microg/kg/min), l-arginine (5 mg/kg/min), or saline vehicle. In control animals, L-NAME resulted in an increase in MAP and renal vascular resistance and a decline in glomerular filtration rate and renal plasma flow, as expected. L-arginine had no effect on renal hemodynamics. In nitric oxide-depleted hypertensive animals, L-NAME had no additional effect on MAP or renal hemodynamics. Infusion of L-arginine reduced elevated MAP but did not reverse changes in renal hemodynamics. Diabetic rats demonstrated glomerular hyperfiltration and proteinuria. No significant changes in MAP or renal hemodynamics were observed following infusion of L-NAME or L-arginine, respectively. However, L-NAME increased urinary albumin excretion in the absence of hemodynamic changes. The effects of nitric oxide on vascular tone were shown to be dependent on the vascular bed and the underlying disease. Variations in local nitric oxide formation and susceptibility may account for the differential response of the systemic and renal vasculature and contribute to the degree of renal functional impairment observed in different systemic diseases.

Animals↗

PubMed2002

Age dependency of renal function in CD-1 mice.

Renal function was studied in mice of different ages. In metabolic cage experiments, the renal electrolyte excretion was similar in young (n = 8; 5- to 7-wk-old) and adult (n = 6; 20- to 22-wk-old) CD-1 (ICR) BR mice, whereas spontaneous drinking volume and urinary flow rate were significantly higher in the adult compared with the young mice. Subsequently, the renal functional reserve was investigated by amino acid (AA) infusion (10%) in anesthetized young (n = 8) and adult (n = 6) mice. Because the body weight of adult mice was significantly higher than that of young animals, one group of adult mice (n = 8) received 12.5% AA to ensure that the dose of AA related to body weight was similar in both groups. Young animals constantly infused with Ringer solution served as time controls (n = 8). Glomerular filtration rate (GFR) at baseline was similar in each group. Because of AA, GFR significantly increased in young mice but not in both groups of adult animals, whereas in time controls GFR remained constant. Urinary flow rate and sodium excretion were elevated by AA in young and adult mice. We conclude that in CD-1 mice the first signs of age-related changes in kidney function concern alterations in renal hemodynamics, whereas renal tubular function appears to be preserved.

Aging↗