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K Baumann

Publications and source records attributed to K Baumann.

At least 37 records · Page 2Linked to original sources

Neuronal localization of presenilin-1 and association with amyloid plaques and neurofibrillary tangles in Alzheimer's disease.

Mutations in the presenilin-1 (PS1) gene is a cause of early- onset familial Alzheimer's disease (AD). Endogenous PS1 is associated with the endoplasmic reticulum in the cell body of undifferentiated SH-SY5Y neuroblastoma cells. At early stages of neuronal differentiation in rat hippocampal culture, PS1 appears in all neuritic processes and in growth cones. In mature differentiated neurons, PS1 is concentrated in the somatodendritic compartment but is also present at lower levels in axons. A similar localization of PS1 is observed in vivo in neurons of the adult human cerebral cortex. In sporadic AD, PS1 appears in the dystrophic neurites of mature amyloid plaques and co-localizes with a subset of intraneuronal neurofibrillary tangles (NFTs). About 30% of hippocampal NFTs are labeled with a highly specific antibody to the PS1 C-terminal loop domain but not with an antibody to the PS1 N terminus. This observation is consistent with a potential association of the PS1 C-terminal fragment with NFTs, because PS1 is constitutively cleaved to N- and C-terminal fragments in neurons. These results suggest that PS1 is highly expressed and broadly distributed during early stages of neuronal differentiation, consistent with a role for PS1 in neuronal differentiation. Furthermore, the co-localization of PS1 with NFTs and plaque dystrophic neurites implicates a role for PS1 in the diverse pathological manifestations of AD.

Alzheimer Disease↗

Toxic effect of concomitant administration of cyclosporin A and acyclovir on renal function and morphology in rats.

The immunosuppressive agent cyclosporin A (CyA) and the antiviral drug acyclovir may cause renal functional impairment. CyA-induced immunosuppression increases the rate of viral infections. Therefore we were interested to determine whether short-term co-administration of CyA and acyclovir involves an increased nephrotoxic risk. Male Wistar rats were treated with CyA (20 mg/kg body wt., s.c., once daily for 8 days), acyclovir (15 mg/kg body wt., s.c., 3-times daily for the last 5 days) or a combination of CyA and acyclovir. Blood levels of CyA were determined after a single dose. Urine was monitored for volume, osmolality, total protein and N-acetyl-beta-D-glucosaminidase (beta-NAG). Concentrations of blood urea nitrogen (BUN) and plasma-creatinine were determined (day 9). Renal cortical slices were monitored for accumulation of weak organic acids (para-aminohippurate, PAH) and bases (tetra-ethylammonium, TEA) and for malondialdehyde (MDA) content. Renal histology was also examined. CyA induced a decrease in body and kidney weight, in urine osmolality and in the excretion of total protein. Plasma-creatinine and BUN as well as MDA content of renal tissues were increased by CyA. Acyclovir alone did not induce significant changes. In comparison to CyA values, urine volume and beta-NAG excretion were enhanced and TEA accumulation depressed by the concomitant administration of CyA and acyclovir. CyA- or acyclovir-treatment alone did not result in significant morphological changes. In the group co-administered CyA/acyclovir, the kidneys showed mild to moderate signs of tubulopathy. Short-term co-administration of CyA and acyclovir was concluded to have possibly increased nephrotoxic potential.

Acetylglucosaminidase↗

Human mononuclear cells express 12-LX: coordinated mRNA regulation with 5-LX and FLAP genes.

Lipoxygenases (LXs) catalyze formation of leukotrienes and hydroxy-eicosatetraenoic acids (HETEs), proinflammatory, and spasmogenic autacoids that are critical for host defense systems. We studied the expression and regulation of LX genes (12-LX, 5-LX, and 15-LX) and the 5-lipoxygenase activating protein (FLAP) in human mononuclear cells (MNC) and granulocytes using a quantitative reverse transcription polymerase chain reaction (RT-PCR) technique. We show that 12-LX mRNA is constitutively expressed in resting platelet-free MNC. 12-LX gene expression was upregulated by activation with lipopolysaccharide (LPS). The formation of 12-HETE was inducible with ionophore in MNC, as assessed by high-performance liquid chromatography (HPLC) and gas chromatography, and increased after LPS pretreatment. In addition to 12-LX, resting MNC expressed the genes for 5-LX and FLAP constitutively. Quantitative time course analyses of 12-LX, 5-LX, and FLAP gene expression suggested coregulation of 12-LX and FLAP mRNAs, and reciprocal regulation of 5-LX and FLAP mRNAs. During cell stimulation with LPS 5-LX mRNA levels remained unchanged, whereas FLAP gene expression increased. No 15-LX mRNA expression or 15-HETE formation was detectable in unstimulated and activated MNC. In contrast to MNC, quantitative RT-PCR mRNA analysis showed intermittent intraindividual expression of the 5-LX and FLAP genes in resting granulocytes. mRNAs for 12-LX and 15-LX were not expressed. On stimulation of granulocytes ex vivo, mRNA expression of 5-LX and FLAP was upregulated. Stimulation by LPS differed from that by ionophore A23187. Neither LPS nor ionophore induced gene expression of 12-LX or 15-LX in granulocytes. Our data indicate that resting human MNC and granulocytes express LX and FLAP genes in a cell-specific manner. Cell activation induces coordinated upregulation of 12-LX and FLAP genes in MNC, and 5-LX and FLAP genes in granulocytes, respectively. The constitutive expression of 12-LX mRNA, its upregulation on cell activation, and the formation of 12-HETE clearly indicate the presence of a functional 12-LX in human MNC.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

Domains of tau protein, differential phosphorylation, and dynamic instability of microtubules.

The dynamic instability of microtubules is thought to be regulated by MAPs and phosphorylation. Here we describe the effect of the neuronal microtubule-associated protein tau by observing the dynamics of single microtubules by video microscopy. We used recombinant tau isoforms and tau mutants, and we phosphorylated tau by the neuronal kinases MARK (affecting the KXGS motifs within tau's repeat domain) and cdk5 (phosphorylating Ser-Pro motifs in the regions flanking the repeats). The variants of tau can be broadly classified into three categories, depending on their potency to affect microtubule dynamics. "Strong" tau variants have four repeats and both flanking regions. "Medium" variants have one to three repeats and both flanking regions. "Weak" variants lack one or both of the flanking regions, or have no repeats; with such constructs, microtubule dynamics is not significantly different from that of pure tubulin. N- or C-terminal tails of tau have no influence on dynamic instability. The two ends of microtubules (plus and minus) showed different activities but analogous behavior. These results are consistent with the "jaws" model of tau where the flanking regions are considered as targeting domains whereas the addition of repeats makes them catalytically active in terms of microtubule stabilization. The dominant changes in the parameters of dynamic instability induced by tau are those in the dissociation rate and in the catastrophe rate (up to 30-fold). Other rates change only moderately or not at all (association rate increased up to twofold, rates of rescue or rapid shrinkage decreased up to approximately twofold). The order of repeats has little influence on microtubule dynamics (i.e., repeats can be re-arranged or interchanged), arguing in favor of the "distributed weak binding" model proposed by Butner and Kirschner (1991); however, we confirmed the presence of a "hotspot" of binding potential involving Lys274 and Lys281 observed by Goode and Feinstein, 1994. Phosphorylation of Ser-Pro motifs by cdk5 (mainly Ser 202, 235, and 404) in the flanking regions had a moderate effect on microtubule dynamics while phosphorylation at the "Alzheimer"-site Ser262 MARK eliminated tau's interactions with microtubules. In both cases the predominant effects of phosphorylation are on the rates of tubulin dissociation and catastrophe whereas the effects on the rates of association or rescue are comparatively small.

Amino Acid Sequence↗

A beta-turn in alpha-amanitin is the most important structural feature for binding to RNA polymerase II and three monoclonal antibodies.

Four amatoxin-binding proteins with KD values in the nanomolar range, 3 monoclonal antibodies and RNA polymerase II, were studied with respect to their affinities to 24 alpha-amanitin derivatives with modified side chains. From KD values we estimated the amounts of binding energy that single side chains of the amatoxins contribute to complex formation. Ile6, previously identified by X-ray analysis to be part of a beta-turn (Kostansek EC, Lipscomb WN, Yocum RR, Thiessen WE, 1978, Biochemistry 17:3790-3795) proved to be of outstanding importance in all complexes. Replacement of the isoleucine with alanine reduced the affinity to all binding proteins to < 1%, suggesting a strong hydrophobic interaction. A strong effect was also seen when Gly5 was replaced with alanine, suggesting that the absence of a side chain in proximity to the beta-turn is likewise important. In addition to the beta-turn, each of the proteins showed at least 2 other points of strong contact formed by hydrogen bonds. Donors are the indole NH of 6'-hydroxy-Trp4 and OH of hydroxy-Pro2 and dihydroxy-Ile3. All the antibodies, but not RNA polymerase II, recognized the indole nucleus of 6'-hydroxy-Trp4. The geometric arrangement of the 4 strongest contact points suggests that the amatoxin binding site is different in each of the 4 proteins, except for the 2 antibodies raised in the same animal. Here, most of the contact points were identical but differed in strength of interaction. The method of structural analysis presented in this study is useful for identifying contact sites in complexes of proteins with peptides of rigid conformation. Furthermore, the method complements X-ray data by providing information on the amount of binding energy contributed by single structural elements.

Amanitins↗

Hormonal carcinogenesis in breast cancer: cellular and molecular studies of malignant progression.

We have established and characterized a series of variant cell lines in which to identify the critical factors associated with E2-induced malignant progression, and the acquisition to tamoxifen resistance in human breast cancer. Sublines of the hormone-dependent MCF-7 cell line (MCF7/MIII and MCF7/LCC1) form stable, invasive, estrogen independent tumors in the mammary fat pads of ovariectomized athymic nude mice. These cells retain expression of both estrogen (ER) and progesterone receptors (PGR), but retain sensitivity to each of the major structural classes of antiestrogens. The tamoxifen-resistant MCF7/LCC2 cells retain sensitivity to the inhibitory effects of the steroidal antiestrogen ICI 182780. By comparing the parental hormone-dependent and variant hormone-independent cells, we have demonstrated an altered expression of some estrogen regulated genes (PGR, pS2, cathepsin D) in the hormone-independent variants. Other genes remain normally estrogen regulated (ER, laminin receptor, EGF-receptor). These data strongly implicate the altered regulation of a specific subset or network of estrogen regulated genes in the malignant progression of human breast cancer. Some of the primary response genes in this network may exhibit dose-response and induction kinetics similar to pS2, which is constitutively upregulated in the MCF7/MIII, MCF7/LCC1 and MCF7/LCC2 cells.

Adenocarcinoma↗

Abnormal Alzheimer-like phosphorylation of tau-protein by cyclin-dependent kinases cdk2 and cdk5.

We have shown earlier that certain proline-directed kinases such as MAP kinase or GSK-3 can phosphorylate tau protein in an abnormal manner reminiscent of tau from Alzheimer paired helical filaments [Drewes et al. (1992); Mandelkow et al. (1992)]. Both kinases are abundant in brain tissue and associate physically with microtubules through several cycles of assembly and disassembly. In this report we show that cdk2/cyclin A incorporates = 5 Pi into recombinant tau, and that it also induces the MR shift and antibody reactivity typical of Alzheimer tau. However, since there is no cdk2 in brain [Meyerson et al. (1992)] we looked for other members of this family of kinases. Using an antibody against the conserved N-terminus we isolated a cdk-like kinase from brain which was capable of inducing the Alzheimer-like characteristics in tau by phosphorylation. Its size (31 kDa), target specificity (proline-directed), chromatographic behavior, and abundance in brain suggest that this kinase is similar or identical to the neuronal cdc2-like kinase nclk alias PSSARLE or cdk5 [Hellmich et al. (1992); Meyerson et al. (1992); Xiong et al. (1992); Tsai et al. (1993)]. This was confirmed by an antibody specific for cdk5. Like MAP kinase and GSK-3, this kinase is physically associated with microtubules and can be enriched by cycles of microtubule assembly and disassembly. Thus, cdk5 should be regarded as another kinase that could be held responsible for the changes in tau protein during Alzheimer disease progression.

Alzheimer Disease↗

Dephosphorylation of tau protein and Alzheimer paired helical filaments by calcineurin and phosphatase-2A.

We have shown previously that brain tissue contains protein kinases which can phosphorylate tau protein to a state reminiscent of the pathological state of Alzheimer paired helical filaments (PHFs); these include proline-directed kinases which phosphorylate SP or TP motifs (such as MAP kinase and GSK-3) [Drewes et al. (1992); Mandelkow et al. (1992)], as well as a novel kinase which phosphorylates S262 of tau protein and thereby strongly reduces the binding of tau to microtubules [Biernat et al. (1993)]. Here we report on the corresponding phosphatases in brain which normally keep the 'pathological' sites free of phosphate. The major phosphatases acting on tau are calcineurin and PP-2A, but not PP-1. Both are present and active in brain extracts, they can dephosphorylate recombinant tau after prior phosphorylation with either MAP kinase, GSK-3, or brain extract, and the course of dephosphorylation can be monitored with antibodies diagnostic of the pathological state of tau. Both phosphatases also act directly on PHF tau isolated from Alzheimer brains.

Alzheimer Disease↗

Identification of structural features involved in binding of alpha-amanitin to a monoclonal antibody.

Twenty-four derivatives of the cyclic octapeptide alpha-amanitin were assayed for their affinities to the monoclonal antibody beta A1/1. The derivatives were of natural, semisynthetic, and synthetic origin and had KD values ranging from 2 nM to > 70 microM. In the majority of the derivatives the chemical modifications had no detectable influence on the overall shape of the double-ring peptide. Given this condition, binding factors could be calculated from KD values of the amatoxin derivatives, which were valid for all amatoxins for estimating the contribution made by single structures to complex formation. The complex between alpha-amanitin and the immunoglobulin involves at least eight sites of contact. Four of them are responsible for strong interactions: (1) the OH group of hydroxyproline2 (binding factor 413), (2) the lipophilic side chain of isoleucine6 (binding factor 131), (3) the -CH2- moiety of the adjacent glycine5 or the absence of a side chain in this position (binding factor 361), and (4) the proton at the indole nitrogen of hydroxytryptophan4 (binding factor 140). The residual four interactions are hydrogen bonds of lower strength corresponding to binding factors of 1.5-8. The key role of the unique conformation of the amatoxins in determining their binding properties was shown by two amatoxin derivatives in which changes in the conformation were associated with virtually complete loss of affinity. For all amatoxin derivatives with conformations similar or identical to that of alpha-amanitin, we found empirical evidence that those structures of the peptide involved in binding make their contributions virtually independent of each other. It is a consequence of this rule that structural features that cooperate in binding could be characterized by the numerical product of their binding factors.

Amanitins↗

The B7 adhesion molecule is expressed on activated human T cells: functional involvement in T-T cell interactions.

The B cell antigen B7 delivers a strong co-stimulatory signal for the activation of T cells by binding to its ligands CD28 and CTLA4. Here we demonstrate the surface expression of the B7 molecule on activated human T cells in vitro and under certain conditions in vivo and its functional importance in T-T cell interactions. B7 was detected by flow cytometry on antigen-specific CD4+ and allospecific CD8+ cloned T cells from different donors with anti-B7 monoclonal antibody (mAb) or a soluble CTLA4-C gamma 1 chimera molecule and by reverse transcription-polymerase chain reactions. The expression of B7 was up-regulated following restimulation of the T cell clones and peaked after 7-9 days. Moreover, we show that the B7 molecule on T cells is functionally involved in T-T cell interactions: mAb to CD28 and the CTLA4-Ig fusion protein could inhibit the proliferation of specific T cell clones in response to T cells as antigen-presenting cells (APC) or the proliferation of peripheral blood mononuclear cells in a primary allostimulation with activated T cells as stimulator cells. Finally, we found that B7 can be expressed on freshly isolated circulating T cells since in a preliminary study with a limited number of patients, B7 was present on a subset of CD3+ cells. B7 was expressed on activated T cells (CD4+ and CD8+) of certain human immunodeficiency virus (HIV)-infected individuals (0.5-20% B7+CD8+ cells) or some patients with autoimmune diseases whereas CD3+ cells of healthy individuals did not express B7. The coexpression of major histocompatibility complex class II molecules and B7 may be relevant for the capacity of activated T cells to function as APC. The expression of B7 on T cells in vivo in autoimmune diseases and in HIV infection may be important for a better understanding of these diseases.

Antigens, Surface↗

Nephrotoxicity of acyclovir and cis-diamminedichloroplatinum(II)--effect of co-administration in rats.

The effect of co-administration of acyclovir and cis-diamminedichloroplatinum(II) (cisplatin) on nephrotoxicity in male Wistar rats was investigated. Animals received acyclovir (15 mg/kg body weight, s.c., three times per day for 5 days) or cisplatin (5 mg/kg body weight, i.p., one single injection) or a combination of both drugs. Acyclovir plasma levels were determined after one single acyclovir s.c. injection. Urines were monitored for volume, pH, osmolality and excretion of N-acetyl-beta-D-glucosaminidase (NAG), lysozyme and total protein. Concentrations of blood urea nitrogen and plasma creatinine were determined on day 6. Renal cortical slices were monitored to assess the accumulation of weak organic bases (tetraethylammonium) and acids (p-aminohippurate). Cisplatin induced a marked increase in the excretion of NAG, lysozyme and total protein and an increase in urine volume, plasma creatinine and blood urea nitrogen. Urine osmolality and accumulation of p-aminohippurate were depressed by cisplatin. Acyclovir treatment alone caused no significant symptoms of nephrotoxicity. Co-administration did not impair renal function more than cisplatin treatment alone, excepting a slight rise in lysozyme excretion on day 6. Short-term antiviral therapy with acyclovir, concomitant to cisplatin treatment, may bring, if at all, a slightly increased nephrotoxic risk.

Acyclovir↗

Active autoimmune gastritis without total atrophy of the glands.

To date, autoimmune gastritis has been diagnosed for the most part only when total atrophy of the oxyntic glands is detected. On the basis of 40 patients without total atrophy of the glands, and with parietal cell antibodies in the serum, we show that the diagnosis of type A gastritis is also possible in the pre-atrophic stage. The histological criteria for the diagnosis of active autoimmune gastritis without total atrophy of the glands are 1. usually dense, diffuse locally emphasized lymphocytic infiltration of the lamina propria between the glands in the oxyntic mucosa, 2. focal destruction of individual glands in the corpus of the stomach by lymphocytes, and 3. reactive pseudohypertrophy of the parietal cells. A comparison with a group of patients with autoimmune gastritis and total atrophy of the glands shows that in active autoimmune gastritis, too, women are more frequently affected than men (in both groups, the sex ratio is approximately 3:1). Patients without atrophy of the glands are, on average, about 12 years younger than those with "burnt out" type A gastritis (average age 69.98:57.80 years). While in the case of burnt out type A gastritis, no colonisation with Helicobacter pylori was to be found, such colonisation was demonstrated for the corpus mucosa in 22.5%, and for the antral mucosa in 15.0%. In 27.5% a minimal or low-grade inactive superficial gastritis, as may be seen after eradication of Helicobacter pylori, was additionally diagnosed in the antrum. A knowledge of the histological appearance of the pre-atrophic stage of type A gastritis might be of importance for the possible prevention of pernicious anaemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Iron- and ascorbic acid-induced lipid peroxidation in renal microsomes isolated from rats treated with platinum compounds.

Renal microsomes isolated on day 3 from cisplatin (CDDP, single i.p. injection, 4 or 6 mg/kg)-treated rats were monitored for their susceptibility to lipid peroxidation as compared with microsomes from rats treated with carboplatin (CBDCA, 30 mg/kg), transplatin (TDDP, 6 mg/kg) or CDDP hydrolysis products (4 or 6 mg/kg) or from control animals. Cephaloridine (1 g/kg daily for 4 days, i.p. injection) was used as a positive control. The effect of CDDP on renal microsomal glucose-6-phosphatase activity was investigated in vivo and in vitro. Following treatment with CDDP and CDDP hydrolysis products vs CBDCA and TDDP treatment, microsomes revealed an enhanced susceptibility to lipid peroxidation in a Fe2+ and/or ascorbic acid stimulation system. Increased lipid peroxidation, expressed as an increase in malondialdehyde (MDA) generation, paralleled the alterations in body and kidney weight and the elevations of plasma creatinine and blood urea nitrogen concentrations. Injection of the antioxidant N,N'-diphenyl-p-phenylenediamine (DPPD, 0.5 g/kg, i.p.) at 24 h prior to CDDP treatment abolished the increased vulnerability of renal microsomes to lipid peroxidation. In vivo, only CDDP hydrolysis products exhibited a significant inhibitory effect on renal glucose-6-phosphatase activity. In vitro, rat renal and hepatic microsomal glucose-6-phosphatase activity was decreased by CDDP both time- and concentration-dependently. Nephrotoxicity induced by CDDP and CDDP hydrolysis products might be attributable to iron-dependent lipid peroxidation and microsomes might represent target organelles on a subcellular level.

Animals↗

[Diabetic neuropathy].

Neuropathy is a frequent late complication of diabetes. The severity and duration of hyperglycaemia are probably the principal causal factor. The consequences of the effects of neuropathy on the lower-limb and the autonomic nervous system are major causes of morbidity. Apart from glycaemic control, no specific treatment is yet available, but measures for symptomatic alleviation of certain painful and visceral manifestations of diabetic neuropathy exist and are outlined in these guidelines. The guidelines also describe simple diagnostic strategies for detecting potentially threatening neurological signs, notably reduction or loss of lower-limb sensation which expose the patient to the risk of ulceration, unnoticed trauma and amputation. The guidelines also summarize the preventive educational measures required to minimize these risks.

Diabetic Neuropathies↗

Nephrotoxicity of cisplatin, carboplatin and transplatin. A comparative in vitro study.

The present study was designed to compare the nephrotoxicity induced by the three platinum compounds cisplatin (CDDP), carboplatin (CBDCA) and transplatin (TDDP) in vitro and to obtain information to elucidate the mechanism of platinum compound-induced nephrotoxicity. Rat or rabbit renal cortical slices were incubated for different periods of time in platinum compound-containing media (0.42 or 1.67 mM) and thereafter monitored for platinum content, tetraethylammonium(TEA) and paraaminohippurate(PAH) accumulation and gluconeogenesis. Malondialdehyde(MDA) content of slices was determined as a parameter of lipid peroxidation. Activity of glucose-6-phosphatase of rat renal microsomes was investigated after platinum-compound exposure. In all series of experiments the effect of the antioxidant N,N'diphenyl-p-phenylenediamine (DPPD) was tested. CBDCA showed no effects on all parameters of renal cell function at all concentrations and all time points investigated, except for the activity of glucose-6-phosphatase, which was slightly affected by CBDCA. CBDCA-induced MDA production was lower, compared to CDDP, which showed marked toxic effects on TEA and PAH accumulation, gluconeogenesis and glucose-6-phosphatase activity. The onset of CDDP-induced alterations was dependent on drug concentration. MDA production was reduced by DPPD. Protection against the platinum compound-induced decrease in TEA and PAH accumulation was observed after the use of DPPD. DPPD had no protective effect on CDDP-induced inhibition of gluconeogenesis and glucose-6-phosphatase, which might indicate an effect on gluconeogenesis by direct inhibition of glucose-6-phosphatase. DPPD did not alter uptake of platinum compounds in rat renal cortical slices. TDDP showed different in vitro properties compared to in vivo conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Effect of cyclosporine A on accumulation of tetraethylammonium and p-aminohippurate, and on lipid peroxidation in rat renal microsomes and cortical slices.

The effect of cyclosporine A (CsA) on lipid peroxidation (LPO) was assessed in renal cortical slices and renal microsomes. Cortical slices were incubated with 1500 micrograms/ml CsA and microsomes with 0.5-20 micrograms/ml under identical conditions (pH 7.4, 37 degrees C) for 3 hours, and LPO monitored by the formation of malondialdehyde (MDA). CsA at concentrations of 3 micrograms/ml and higher caused a significant increase MDA in microsomes and renal cortical slices showed a time dependent release of MDA into the incubation medium. The influence of CsA on tetraethammonium (TEA) and p-aminohippurate (PAH) accumulation in renal cortical slices was investigated for up to 3 hours with concentration of CsA from 10 to 1000 micrograms/ml. CsA caused a time- and concentration-dependent decrease of TEA accumulation and higher concentrations of CsA decreased PAH accumulation in renal cortical slices. The results add further evidence to the suggestion that lipid peroxidation participate in CsA-induced impairment of kidney function.

Animals↗