Oxalate-Induced Damage to Renal Tubular Cells

Our own studies and those of others have shown that the incidence of calcium oxalate stones and plaques is markedly increased by nephrotoxins. The possible role of oxalate as a nephrotoxin has not been fully appreciated. However, recent studies in experimental animals and in cultured cells support this possibility. The results of these studies led us to hypothesize that hyperoxaluria promotes stone formation in several ways: by providing a substrate for the formation of the most common form of renal stones, calcium oxalate stones, and by inducing damage to renal epithelial cells. Damaged cells in turn would produce an environment favorable for crystal retention and provide membranous debris that promotes crystal nucleation, aggregation and adherence. The present report summarizes evidence for oxalate nephrotoxicity and discusses the potential importance of oxalate toxicity in the pathogenesis of stone disease

The brain tissue response to implanted silicon microelectrode arrays is increased when the device is tethered to the skull

The influence of tethering silicon microelectrode arrays on the cortical brain tissue reaction was compared with that of untethered implants placed in the same location by identical means using immunoflourescent methods and cell type specific markers over indwelling periods of 1–4 weeks. Compared with untethered, freely floating implants, tethered microelectrodes elicited significantly greater reactivity to antibodies against ED1 and GFAP over time. Regardless of implantation method or indwelling time, retrieved microelectrodes contained a layer of attached macrophages identified by positive immunoreactivity against ED1. In the tethered condition and in cases where the tissue surrounding untethered implants had the highest levels of ED1+ and GFAP+ immunoreactivity, the neuronal markers for neurofilament 160 and NeuN were reduced. Although the precise mechanisms are unclear, the present study indicates that simply tethering silicon microelectrode arrays to the skull increases the cortical brain tissue response in the recording zone immediately surrounding the microelectrode array, which signals the importance of identifying this important variable when evaluating the tissue response of different device designs, and suggests that untethered or wireless devices may elicit less of a foreign body response. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56096/1/31138_ftp.pd

Induction of Neuronal Death by Microglial AGE-Albumin: Implications for Alzheimer’s Disease

Advanced glycation end products (AGEs) have long been considered as potent molecules promoting neuronal cell death and contributing to neurodegenerative disorders such as Alzheimer’s disease (AD). In this study, we demonstrate that AGE-albumin, the most abundant AGE product in human AD brains, is synthesized in activated microglial cells and secreted into the extracellular space. The rate of AGE-albumin synthesis in human microglial cells is markedly increased by amyloid-β exposure and oxidative stress. Exogenous AGE-albumin upregulates the receptor protein for AGE (RAGE) and augments calcium influx, leading to apoptosis of human primary neurons. In animal experiments, soluble RAGE (sRAGE), pyridoxamine or ALT-711 prevented Aβ-induced neuronal death in rat brains. Collectively, these results provide evidence for a new mechanism by which microglial cells promote death of neuronal cells through synthesis and secretion of AGE-albumin, thereby likely contributing to neurodegenerative diseases such as AD

Two Populations Of Muscarine Receptors

This work provides evidence for two distinct populations of muscarine receptors in mammalian tissues, M1 and M2, and for two states of M2 receptors.The differences between the two receptors are summarized as follows. (1) M1 receptors have higher affinity for most antagonists than do M2 receptors. For example pirenzepine (apparent K(,d) for M1 = 1.65 x 10(\u27-8) M, for M2 = 5.6 x 10(\u27-7) M) shows 35-fold selectivity for M1. Exceptions to this rule are gallamine (apparent K(,d) for M1 = 3 x 10(\u27-8) M, for M2 = 1.0 x 10(\u27-8)-1.3 x 10(\u27-8) M) and pancuronium (apparent K(,d) for M1 = 5.2 x 10(\u27-8), for M2 = 2.3 x 10(\u27-8)) which are 11-fold selective for M2. (2) M2 receptors have higher affinity for most agonists than do M1 receptors. For example carbachol (apparent K(,d) for M1 = 1.8 x 10(\u27-5) M, for M2 = 5.0 x 10(\u27-7) M) shows 36-fold selectivity. While some agonists do not exhibit selectivity (e.g. MCN-A-343-11, apparent K(,d) = 3 x 10(\u27-7)) I did not find any which select for M1. (3) M1 receptors are located in forebrain regions (hippocampus, striatum, and cortex) and glands (e.g. intestinal mucosa and submaxillary glands). M2 receptors are located in brainstem regions (medulla-pons and cerebellum), heart, and smooth muscle (e.g. ileum). (4) In the presence of 1 mM Mn(\u27++), but not EDTA, M2 but not M1 receptors show a high affinity agonist-binding state which disappears in the presence of GppNHp. Alkaline extraction of membranes also prevents the formation of this high affinity state of M2, without affecting M1. These observations imply the presence of ternary complexes of agonist-M2 plus a guanine nucleotide binding protein, which are destabilized by GppNHp. The presumptive coupled form has (TURN)30-fold higher affinity than free M2. (5) M1 but not M2 receptors undergo a 10-fold increase in agonist affinity in the presence of 1 mM Mn(\u27++) plus 0.1 mM GppNHp.Thus M1 and M2 differ in location and affinity for agonists and antagonists and it is probable that they have different mechanisms of action

Oxalate toxicity in LLC-PK1 cells: Role of free radicals

Oxalate toxicity in LLC-PK1 cells: Role of free radicals. Oxalate, the most common constituent of kidney stones, is an end product of metabolism that is excreted by the kidney. During excretion, oxalate is transported by a variety of transport systems and accumulates in renal tubular cells. This process has been considered benign; however, recent studies on LLC-PK1 cells suggested that high concentrations of oxalate are toxic, inducing morphological alterations, increases in membrane permeability to vital dyes and loss of cells from the monolayer cultures. The present studies examined the basis for oxalate toxicity, focusing on the possibility that oxalate exposure might increase the production/availability of free radicals in LLC-PK1 cells. Free radical production was monitored in two ways, by monitoring the reduction of nitroblue tetrazolium to a blue reaction product and by following the conversion of dihydrorhodamine 123 (DHR) to its fluorescent derivative, rhodamine 123. Such studies demonstrated that oxalate induces a concentration-dependent increase in dye conversion by a process that is sensitive to free radical scavengers. Specifically, addition of catalase or superoxide dismutase blocked the oxalate-induced changes in dye fluorescence/absorbance. Addition of these free radical scavengers also prevented the oxalate-induced loss of membrane integrity in LLC-PK1 cells. Thus it seems likely that free radicals are responsible for oxalate toxicity. The levels of oxalate that induced toxicity in LLC-PK1 cells (350 µm) was only slightly higher than would be expected to occur in the renal cortex. These considerations suggest that hyperoxaluria may contribute to the progression of renal injury in several forms of renal disease

Role of substance P in several models of bladder inflammation

Substance P (SP) is a peptide found in the sensory nervous system which has multiple biologic effects including stimulation of muscle contraction, pain nociception, immune cell functions, plasma extravasation and a constellation of inflammatory effects. Here we investigate the role of SP in several animals models of bladder inflammation. Using the female Lewis rat, inflammation was induced using either xylene, lipopolysaccharide (LPS) or polyinosinic-polycytidylic acid (polyIC). Inflammation occurred rapidly (4 h) and was maintained in each model for at least 7 days. Each of these protocols decreased the bladder content of immunoreactive SP by approximately 50%, suggesting enhanced release. There was no change in the urinary frequency of these animals over 3 weeks, suggesting that urinary frequency changes are not mediated by acute inflammation. We also found that the SP receptor (NK1) antagonist, (-)CP96345, was unable to block the inflammation produced by polyIC, suggesting that SP is not an obligatory mediator of immune cell stimulation in this model