Christian Fleck

Serum concentrations of asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in patients with chronic kidney diseases.

BACKGROUNDnNO synthesis is inhibited by the dimethylarginine (DMA) ADMA, which accumulates, similar to SDMA, in the plasma of patients suffering from chronic renal failure (CRF). ADMA and possibly SDMA contribute to hypertension and atherosclerosis in patients with chronic renal disease: ADMA inhibits directly eNOS, whereas SDMA competes with the NO precursor arginine for uptake into the cells.nnnMETHODSnIn 26 control persons and 221 patients with kidney diseases of different stage as were CRF, end stage renal disease (ESRD), and patients after renal transplantation (RT), the plasma concentrations of ADMA (c(ADMA)), SDMA (c(SDMA)) and 20 endogenous amino acids (AA) were measured by HPLC and correlated to blood pressure, cardiac events, endothelial dysfunction, and diabetes mellitus.nnnRESULTSnBoth ADMA (1.04+/-0.04 vs. 0.66+/-0.04 microM) and SDMA (2.69+/-0.12 vs. 0.49+/-0.03 microM) were significantly (p<0.001) elevated in all patients compared to healthy controls, whereas arginine concentration (51.4+/-2.3 vs. 76.0+/-5.2 microM) was decreased in dependence on the degree of kidney disease. In RT patients, SDMA levels were significantly decreased, but c(ADMA) remained enhanced. A strong correlation was found between SDMA and both serum urea and creatinine in CRF and RT patients. A linear correlation was found between ADMA and cholesterol concentrations in RT patients. Hypertension in CRF was accompanied by a further increase in the concentration of DMAs. There was no relation between DMAs and the occurrence of peripheral arterial occlusive disease or cerebrovascular diseases. In patients with cardiac diseases, c(SDMA) was additionally increased only in the CRF group.nnnCONCLUSIONSnIn patients with chronic kidney disease, c(ADMA) and c(SDMA) are significantly increased but cardiovascular diseases are evidently not correlated to changes in DMA concentrations in this group of patients.

Design, synthesis and biological evaluation of D-ring opened galantamine analogs as multifunctional anti-Alzheimer agents.

Facing the multifactorial nature of Alzheimers disease, twelve dibenzofuran/carbazole derivatives, which can be considered as the D-ring opened analogs of galantamine, have been designed and synthesized as multifunctional anti-Alzheimer agents. In vitro tests revealed that compounds 3 and 5, which bear a nitrate moiety in the molecule, showed a potent inhibition activity towards AChE and compound 3 showed a good Aβ42 aggregation inhibitory activity. Moreover, 3 and 5 could also release a relative low concentration of NO in vitro and they did not show toxicity to neuronal cells, while exerted a neuroprotective effect against the Aβ-induced toxicity. More importantly, compound 3 showed a significant spatial memory improving effect in vivo, and a good safety in the ex vivo toxicity study.

Current progresses of novel natural products and their derivatives/ analogs as anti-Alzheimer candidates: an update.

Alzheimers disease (AD) is one of the most threatening diseases affecting the aged with high incidence. Though AD has been defined for more than 100 years, it is still incurable. The drugs clinically used for the treatment of this disease, such as acetylcholinesterase inhibitors (AChEIs) and N-methyl-D-aspartate (NMDA) receptor antagonist, can only provide a limited therapeutic effect. The need of effective drugs has stimulated the search for new compounds with potential clinical utility. Natural products are rich and unexplored sources for discovering novel leading compounds. Currently, a great number of natural products have been found possessing anti-AD property counteracting different etiological factors of AD. This review will give an update demonstration on the novel anti-AD natural products and their derivatives/analogues, which have been divided into five subgroups according to their different action mechanisms: AChEIs, antioxidants, neuroprotective agents, monoamine oxidase (MAO) inhibitors, and tau hyperphosphorylation inhibitors. We put special emphasis on the findings in the past 5 years. Besides, the drug design strategy as well as the structure-activity relationship of the relevant compounds is also discussed when it is possible.

Protective Effects of Methimazole against Cisplatin-induced Nephrotoxicity in Rats

In adult rats 6 mg kg−1 body wt. cisplatin given i.p. was nephrotoxic. Four days of i.p. treatment with 40 mg kg−1 body wt. methimazole, which started 1 day before CP, prevented increases in blood urea nitrogen and in the renal excretion of proteins. Furthermore, methimazole treatment reduced the oliguric effect of cisplatin and the depression of renal sodium excretion. However, it had no effect on the increased formation of lipid peroxides in cisplatin‐damaged kidneys, although repeated treatment with methimazole enhanced the renal glutathione content. Methimazole acts as a radical scavenger, maintaining the glutathione pool in the kidney. ©u20091997 by John Wiley & Sons, Ltd.

Renal handling of drugs and amino acids after impairment of kidney or liver function—Influences of maturity and protective treatment

Renal tubular cells are involved both in secretion and in reabsorption processes within the kidney. Normally, most xenobiotics are secreted into the urine at the basolateral membrane of the tubular cell, whereas amino acids are reabsorbed quantitatively at the luminal side. Under different pathological or experimental circumstances, these transport steps may be changed, e.g., they may be reduced by renal impairment (reduction of kidney mass, renal ischemia, administration of nephrotoxins) or they may be enhanced after stimulation of transport carriers. Furthermore, a distinct interrelationship exists between excretory functions of the kidney and the liver. That means liver injury can influence renal transport systems also (hepato-renal syndrome). In this review, the following aspects were included: based upon general information concerning different transport pathways for xenobiotics and amino acids within kidney cells and upon a brief characterization of methods for testing impairment of kidney function, the maturation of renal transport and its stimulation are described. Similarities and differences between the postnatal development of kidney function and the increase of renal transport capacity after suitable stimulatory treatment by, for example, various hormones or xenobiotics are reviewed. Especially, renal transport in acute renal failure is described for individuals of different ages. Depending upon the maturity of kidney function, age differences in susceptibility to kidney injury occur: if energy-requiring processes are involved in the transport of the respective substance, then adults, in general, are more susceptible to renal failure than young individuals, because in immature organisms, anaerobic energy production predominates within the kidney. On the other hand, adult animals can better compensate for the loss of renal tissue (partial nephrectomy). With respect to stimulation of renal transport capacity after repeated pretreatment with suitable substances, age differences also exist: most stimulatory schedules are more effective in young, developing individuals than in mature animals. Therefore, the consequences of the stimulation of renal transport can be different in animals of different ages and are discussed in detail. Furthermore, the extent of stimulation is different for the transporters located at the basolateral and at the luminal membranes: obviously the tubular secretion at the contraluminal membrane can be stimulated more effectively than reabsorption processes at the luminal side.

Methods in testing interrelationships between excretion of drugs via urine and bile

The liver and kidney are largely responsible for inactivating and eliminating drugs and other chemicals. As the excretory capabilities of the two organs overlap, a damage of one system might be compensated by the other. Because of the specificity of both renal and hepatic elimination mechanisms such an alternative excretion route is not possible generally. Several interferences are possible to characterize the relation between hepatic and renal excretion of drugs and xenobiotics. Firstly, the simultaneous assay of excreted drug amounts in urine and bile can give some information concerning the main transport routes of this drug. Thereafter the total interruption of liver or kidney function elucidates the general possibility of alternative excretion routes. But it is important for clinical practice to distinguish between different localizations of organ damages. Today some experimental possibilities exist to exclude partial functions of both kidney and liver separately. Thus it can be clarified why a compound might be excreted via liver or kidney. Moreover it can be characterized whether or not a compensation for the loss of one main excretion organ is possible or not. Such investigations are of some practical importance. Dosing guidelines for drug therapy must be completed for cases of renal or hepatic failure. Moreover the developmental pattern of both elimination routes has consequences for drug use in paediatrics as well as geriatrics. Beside this point of view such investigations are necessary for the prediction of changes in the toxicity of drugs after renal or hepatic insufficiency.

RT-PCR-based evidence for the in vivo stimulation of renal tubular p-aminohippurate (PAH) transport by triiodothyronine (T3) or dexamethasone (DEXA) in kidney tissue of immature and adult rats

Our previous studies have shown that a pre-treatment of rats with triiodothyronine (T3) or dexamethasone (DEXA) increases renal PAH excretion significantly. This stimulation was accompanied by an enhanced protein synthesis within the renal cortex. To explore the molecular basis for this sub-chronic induction process, we investigated the stimulation of PAH accumulation in renal cortical slices as well as the expression level of organic anion transporter 1 (OAT1), the recently cloned renal basolateral PAH-transporter, using RT-PCR techniques under the applied conditions. 10- and 55-day-old Han:WIST rats were treated in vivo with T3 (20 microg/100 g b.wt.) or DEXA (60 microg/100 g b.wt.), both for 3 days, once daily. Renal cortical slices were incubated for 2 hours in Cross-Taggart medium and PAH uptake into kidney tissue was measured time dependently (slice to medium ratio, QS/M). The accumulation capacity is comparable between immature and mature rats (control-QS/M: 6.7 +/- 0.1 vs. 6.9 +/- 0.2, respectively). Both age groups showed a significant increase of PAH accumulation capacity after T3 treatment (10-day-old rats: 15.0 +/- 0.2; 55-day-old rats: 11.7 +/- 1.3). After DEXA pre-treatment, PAH accumulation was only slightly changed (10-day-old rats: 5.9 +/- 0.2; 55-day-old rats: 8.2 +/- 1.3). Semi-quantitative measurements of OAT1 mRNA expression level showed a significant increase of OAT1 mRNA after pre-treatment with both T3 and DEXA in the two age groups. Thus, this is the first evidence that T3 and DEXA pre-treatment induces the expression of OAT1.

Fibronectin Splice Variants – Prognostic Markers for the Stage of Renal Interstitial Fibrosis in the Rat

Background/Aims: Renal interstitial fibrosis (RIF) is the main cause for progressive renal failure, but its pathogenic factors are not well known. In animal models of renal fibrogenesisdone thus far an increase of total fibronectin (FN) mRNA has been proved. Recent studies have pointed to a key role of the splice variant EIIIA+-FN and EIIIB+-FN for the development of organ fibrosis. However, a broader knowledge of the distribution of these different FN mRNA isoforms is still lacking. Our aim was to study the particular expression of the EIIIA+-FN and EIIIB+-FN during the process of fibrogenesis in two rat models and to evaluate the FN isoforms as diagnostic/prognostic marker for the stage of interstitial damage in rat kidneys. Methods: Kidneys of unilateral ureteral obstruction (UUO) and control rats were removed in intervals of 5, 14 or 21 days after surgery. For the investigation of kidney damage due to uranyl nitrate (UN), rats obtained a single i.p. dose of 5 mg/kg body weight UN and were killed 2, 10 and 20 weeks thereafter. The quantitative RT-PCR method was used to estimate the total FN, EIIIA+-FN and EIIIB+-FN transcription rate. Results: In the UUO model, a significant augmentation of both isoforms was obtained in the kidneys in the first 5-day interval, which was more pronounced at the 21-day interval. In the UN-treated kidneys there appeared only a continuous increase of EIIIA+-FN and the splice variant EIIIB+-FN failed to show a shift in these animals as compared to the controls. Conclusion: Both animal models generated fibrogenic damages of the tubulointerstitium, whereas only the UUO resulted in progressive fibrosis. Absence of EIIIB+-FN seems to enhance the progression of fibrogenesis.

9-Methyl-β-carboline-induced cognitive enhancement is associated with elevated hippocampal dopamine levels and dendritic and synaptic proliferation.

J. Neurochem. (2012) 121, 924–931.

Use of gene chip technology for the characterisation of the regulation of renal transport processes and of nephrotoxicity in rats.

Gene expression profiling using microarrays (rat-specific array RG-U34A, Affymetrix, U.S.A.) was employed for the investigation of: (1) hormonal regulation of renal function and (2) nephrotoxicity. For this purpose about 8,800 genes were analysed in kidney and, additionally, in liver tissue. Ad 1.) Kidney functions develop during postnatal life. Thus, in vivo transport and accumulation of p-aminohippurate (PAH) was investigated on renal cortical slices (RCS) from 10- and 55-day-old rats. The animals were treated with dexamethasone (DEXA; 60 microg/100 g b.wt./day) for 3 days, which caused a significant reduction in the accumulation of PAH in 10-day-old rats (42 +/- 5% whereas it was only slightly reduced in 55-day-old rats (70 +/- 8%). To further clarify the regulation of renal function by DEXA, results were compared with those obtained previously after in vitro stimulation with DEXA. RCS were incubated for 24 hours in DEXA-containing medium (10(-9) M). Under these conditions DEXA significantly increased the PAH uptake capacity in RCS obtained from 10- and 55-day-old rats up to 126 and 136%, respectively. Thus a stimulation of tubular transport capacity is possible in vitro. The effect of DEXA treatment on the gene expression of the kidney (in vivo) was moderate. Focussing especially on transporters, ion channels, ATPases, glucuronyltransferases, glutathione-S-transferase and cytochrome P450, the expression of only few genes were significantly changed (3 to 50-fold up- or down-regulation). Moreover, distinct age differences were found after in vivo administration of DEXA. The investigation of in vitro effects of DEXA is currently been performed. Ad 2.) The kidney is threatened by nephrotoxins because of its ability to accumulate them. We used a single administration of uranyl nitrate (UN; 0.5 mg/100 g b.wt.) as a model for chronic renal failure (CRF). Clearance experiments were performed 10 weeks after UN administration (maximal symptoms of CRF) in adult female rats. As expected, UN induced interstitial cicatrices with reduced GFR and diminished PAH transport capacity. Despite the impressive morphological and functional changes in the kidney after exposure to UN, the gene expression profiles in the kidneys were only minimally affected: we found significantly changed expression levels for only 20 genes (5 genes were up-regulated [e.g. transgelin], 15 down-regulated [among these the Na-K-Cl-symporter, insulin-like growth factor, kallikrein, and ornithine decarboxylase). The lack of agreement between gene expression data and the nephrotoxic effects of UN can probably be explained by the long time interval between dosing and the assessment of the effect. The results confirm that primary genomic responses are likely to be strongest transiently after exposure and then decrease in intensity.