Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0086543 (cataract)
 29,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cataractogenic potential of the thiazolidinedione ciglitazone (CIG) was investigated in vivo and in vitro. In the rat, CIG caused a dose-dependent (30-300 mg/kg/day) increase in incidence and severity of nuclear cataract formation during a 3-month nonclinical safety assessment study. Potential mechanisms of toxicity were surveyed using whole rat lens explants exposed to CIG with or without various inhibitors of cataract formation. In vitro, CIG caused a concentration-(0.375-30 muM) and time-dependent (3-24 h) change in biochemical [ATP content or mitochondrial reduction of the tetrazolium dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) and reduced glutathione (GSH) content] and morphometric (lens wet weight and clarity) markers of damage. Within 3 h of exposure, 7.5 muM CIG decreased lens ATP content 37 +/- 7% (percentage of difference from control, p < 0.05). After 24 h of exposure, lens ATP content, MTT reduction, and GSH content declined 57 +/- 5, 30 +/- 28, and 42 +/- 8%, respectively. Lens wet weight increased 17 +/- 4% with a concomitant decrement in lens clarity. Pretreating lenses with the mitochondrial calcium uniport inhibitor ruthenium red (RR) partially or fully protected lenses from toxicity. In contrast, the antioxidant dithiothreitol, aldose reductase inhibitor sorbinil, and selective cell-permeable calpain inhibitors [calpain II inhibitor and (2S,3S)-trans-epoxysuccinyl-l-leucylamido-3-methylbutane ethyl ester (E64d)] were ineffective in providing protection under the present testing conditions. Early and selective changes in lenticular ATP content and the partial or full protective effect of RR suggest that alterations in lens bioenergetics may play an important role in CIG-induced cataract formation. Lens explant cultures were successfully used to select two thiazolidinediones that lacked cataractogenic activity when evaluated in 3-month rat safety assessment studies.
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PMID:Ciglitazone-induced lenticular opacities in rats: in vivo and whole lens explant culture evaluation. 1552 2

Calpain was first discovered 30 years ago. Two major isoforms were subsequently isolated and purified. The presence of an endogenous protein inhibitor, calpastatin, was later discovered. Calpain activity is tightly regulated by Ca(2+). At physiological levels of Ca(2+), the role of calpain remains poorly understood, but is believed to be involved in mitosis and muscle cell differentiation. Calpain has also been implicated in various membrane fusion events through remodeling of the cytoskeletal network. Calpain activation has been shown to be increased during normal aging and in muscular dystrophy, cataract, arthritis and Alzheimer's disease, and in acute traumas such as traumatic brain injury (TBI), spinal cord injury and cerebral and cardiac ischemia. Early work on calpain inhibitors was limited to protein inhibitors and other nonselective enzyme inhibitors. Peptidyl aldehydes such as leupeptin and antipain are also among the earliest reported calpain inactivators. Irreversible inhibitors such as the E64 family have also been studied, and peptidyl halomethanes and diazomethanes have long been used as protease inhibitors. A variety of calpain inhibitors are under development. From a therapeutic perspective, calpain inhibitors may have several advantages over other more conventional targets such as ion channel blockers and glumate antagonists, since calpain proteolysis represents a later component of a pathway mediating cell death initiated by excitotoxicity and elevated Ca(2+) levels. Although the potential clinical utility of calpain inhibitors seems well established, a number of important considerations remain to be addressed. The role of other proteolytic cascades contributing to neuronal cell damage following TBI must also be considered.
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PMID:Potential contribution of proteases to neuronal damage. 1561 63

Lens-specific Lp82 and ubiquitous m-calpain are neutral, calcium-activated, cysteine proteases. Both calpains are activated during rodent lens maturation and cataract formation. Lp85 calpain (Lens protein with MW=85 kDa) is a slightly larger splice variant of Lp82. Lp85 contains a 28 amino acid insert peptide (IS3) in calcium binding domain IV. Theoretically, the insert could alter the properties of Lp85 and influence proteolytic activity. The purpose of the present experiment was to compare the biochemical properties of Lp85 to Lp82 and m-calpain. Recombinant Lp85 and Lp82 were separately expressed using the baculovirus system and partially purified using Co2+ affinity and DEAE chromatographies. Calcium activation, pH dependency, and susceptibility to calpain inhibitors were assessed in a protease assay using BODIPY fluorescence-labeled casein substrate. Hydrolysis of lens proteins was assessed by SDS-PAGE and immunoblotting. Cleavage site analysis was performed by mass spectroscopy and Edman sequencing. Computer-based homology modeling was used to predict the influence of the IS3 region on the 3-dimensional structure of Lp85. Compared to m-calpain, Lp85 showed a lower calcium-activation requirement (K(50%act)=20 microM), marked insensitivity to, and cleavage of, the endogenous tissue inhibitor of calpains-calpastatin, and different preferred cleavage sites on alphaA-crystallin (five amino acid C-terminal truncation) and on aquaporin 0 (G239 and N246). Although the IS3 insert was predicted to form a loop protruding from the calcium binding region of Lp85, the biochemical properties of Lp85 studied were nearly identical to those of Lp82. Lp85 and Lp82 did not catalyze hydrolysis of each other, but both hydrolyzed m-calpain. Lp85 seems to be the enzymatic equivalent of Lp82. Both calpains could become active at lower cellular calcium levels than m-calpain. Lp85/Lp82 may have different functions than m-calpain since they cleave substrates at different sites. Lp85/Lp82 may regulate m-calpain activity by catalyzing the hydrolysis of calpastatin. The function of the IS3 insert on Lp85 remains unknown but is speculated to control subcellular distribution.
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PMID:Biochemical properties of lens-specific calpain Lp85. 1605 32

Globally, cataract accounts for the majority of cases of treatable blindness and the lens opacification associated with cataract is primarily due to the insolubilisation of crystallins, proteins essential for the transparency of the lens. Recent studies have suggested that a major cause of this insolubilisation may be the unregulated proteolysis of crystallins by calpains. These are intracellular cysteine proteases whose activation requires the presence of Ca2+ and elevated levels of lens Ca2+ is a condition strongly associated with cataract. Calpain 2 appears to be the major calpain involved in animal cataractogenesis and the strongest candidate of the calpains for a role in human cataractogenesis but despite intensive study, the mechanism(s) underlying activation of the enzyme both in cataractogenesis and normal lens function are unclear. Recently, the high-resolution structure of calpain 2 was recently solved and a structural basis for the Ca2+-dependence of the enzyme's activity has been putatively established. Other recent studies have suggested that membrane interaction(s) may play a role in lowering the Ca2+-requirements of calpain 2 activation and most recently, strongly supporting this suggestion, several lipid interactive regions in the enzyme have been identified. Here, we review progress in understanding of the role played by calpain 2 in cataractogenesis and the possible use of inhibitors of the enzyme as anti-cataract agents.
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PMID:Calpains: enzymes of vision? 1612 77

The calpains represent a well-conserved family of calcium-dependent cysteine proteases. They consist of several ubiquitous and tissue specific isoforms and exhibit broad substrate specificity influencing many aspects of cell physiology including migration, proliferation and apoptosis. Calpain activity in vivo is tightly regulated by its natural endogenous inhibitor calpastatin. Calpastatin specifically inhibits calpain and not other cysteine proteases by interaction with several sites on the calpain molecule. Inappropriate regulation of the calpain-calpastatin proteolytic system is associated with several important human pathological disorders including muscular dystrophy, cancer, Alzheimer's disease, neurological injury, ischaemia/reperfusion injury, atherosclerosis, diabetes and cataract formation. Recent advances in elucidating the tertiary structures of calpain 2 and its regulatory domain calpain 4, together with identification of new modes of regulating calpain activity provide new opportunities for the design of novel calpain inhibitors. Several classes of inhibitors, including peptidyl epoxide, aldehyde, and ketoamide inhibitors, targeting the active site have proven effective against the calpains and are in the process of evaluation in animal models of human disease. However, a major limitation to the clinical use of such inhibitors is their lack of specificity among cysteine proteases and other proteolytic enzymes. The development of a new class of calpain inhibitors that interact with domains outside of the catalytic site of calpain may provide greater specificity and therapeutic potential.
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PMID:Calpain inhibition: a therapeutic strategy targeting multiple disease states. 1647 52

The human genome contains 14 genes for 80 kDa catalytic subunit of the calcium-activated protease calpain (EC 34.22.17), yet no calpain-like cleavage sites have been detected on human lens crystallins in vivo. The purpose of the present study was to provide a comprehensive study of calpain activation in human and macaque lenses developing experimental cataract due to lens culture in ionophore A23187. Zymography was used to measure calpain activity; SDS-PAGE and immunoblotting were used to detect hydrolysis of potential lens protein substrates. Quantitative PCR was used to measure transcripts for calpains and the endogenous inhibitor calpastatin. We found that the lack of appreciable calpain-induced proteolysis in primate lenses is most likely due to relatively low levels of endogenous calpain activity compared to the high levels of endogenous calpain inhibitor, calpastatin.
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PMID:Low activity by the calpain system in primate lenses causes resistance to calcium-induced proteolysis. 1668 19

Calpains are intracellular calcium-activated cysteine proteases whose unregulated proteolysis following the loss of calcium homeostasis can lead to acute degeneration during ischemic episodes and trauma, as well as Alzheimer's disease and cataract formation. The determination of the crystal structure of the proteolytic core of mu-calpain (muI-II) in a calcium-bound active conformation has made structure-guided design of active site inhibitors feasible. We present here high-resolution crystal structures of rat muI-II complexed with two reversible calpain-specific inhibitors employing cyclic hemiacetal (SNJ-1715) and alpha-ketoamide (SNJ-1945) chemistries that reveal new details about the interactions of inhibitors with this enzyme. The SNJ-1715 complex confirms that the free aldehyde is the reactive species of the cornea-permeable cyclic hemiacetal. The alpha-ketoamide warhead of SNJ-1945 binds with the hydroxyl group of the tetrahedral adduct pointing toward the catalytic histidine rather than the oxyanion hole. The muI-II-SNJ-1945 complex shows residue Glu261 displaced from the S1' site by the inhibitor, resulting in an extended "open" conformation of the domain II gating loop and an unobstructed S1' site. This conformation offers an additional template for structure-based drug design extending to the primed subsites. An important role for the highly conserved Glu261 is proposed.
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PMID:Calpain inhibition by alpha-ketoamide and cyclic hemiacetal inhibitors revealed by X-ray crystallography. 1676 40

The photoswitchable N-terminal diazo and triazene-dipeptide aldehydes 8a-d, 10a,b, and 17a,b present predominantly as the (E)-isomer, which purportedly binds deep in the S3 pocket of calpain. All compounds are potent inhibitors of m-calpain, with 8b being the most active (IC50 of 35 nM). The diazo-containing inhibitors 8a, 8c, and 10a were irradiated at 340 nm to give a photostationary state enriched in the (Z)-isomer, and in all cases, these were less active. The most water soluble triazene 17a (IC50 of 90 nM) retards calpain-induced cataract formation in lens culture.
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PMID:Investigation into the P3 binding domain of m-calpain using photoswitchable diazo- and triazene-dipeptide aldehydes: new anticataract agents. 1749 40

Calpains are intracellular cysteine proteases that catalyze the cleavage of target proteins in response to Ca(2+) signaling. When Ca(2+) homeostasis is disrupted, calpain overactivation causes unregulated proteolysis, which can contribute to diseases such as postischemic injury and cataract formation. Potent calpain inhibitors exist, but of these many cross-react with other cysteine proteases and will need modification to specifically target calpain. Here, we present crystal structures of rat calpain 1 protease core (muI-II) bound to two alpha-ketoamide-based calpain inhibitors containing adenyl and piperazyl primed-side extensions. An unexpected aromatic-stacking interaction is observed between the primed-side adenine moiety and the Trp298 side chain. This interaction increased the potency of the inhibitor toward muI-II and heterodimeric m-calpain. Moreover, stacking orients the adenine such that it can be used as a scaffold for designing novel primed-side address regions, which could be incorporated into future inhibitors to enhance their calpain specificity.
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PMID:Cocrystal structures of primed side-extending alpha-ketoamide inhibitors reveal novel calpain-inhibitor aromatic interactions. 1870 62

Recent investigations have shown that phytochemical antioxidants can scavenge free radicals and prevent various diseases. Cataract is the leading cause of blindness and is associated with oxidative damage of the lens. Selenite-induced cataract in rat pups is an excellent mimic of oxidative stress-induced cataract. Selenite cataract is associated with oxidative stress, loss of calcium homeostasis, calpain activation and protein insolubilization in the lens. Our present study focuses on the isolation of flavonoids from Vitex negundo and to assess its efficacy in preventing these changes in the lens of selenite-induced cataract models. Eight-day-old Sprague-Dawley rat pups were used for the study and divided into four groups: Control (G I), Sodium selenite-induced (G II), Sodium selenite+quercetin treated (G III), Sodium selenite+flavonoids from Vitex negundo (FVN) (G IV). Cataract was induced by a single subcutaneous injection of Sodium selenite (4 mg/Kg body weight) on the 10th day. Treatment groups received quercetin (1.0mg/Kg body weight) and FVN (1.0mg/Kg body weight) intraperitoneally from 8th to 15th day. Cataract was visualized from the 16th day. Morphological examination of the rat lenses revealed no opacification in G I and mild opacification in G III and G IV (stage 1) whereas dense opacification in G II (stage 4-6). The activities of superoxide dismutase (SOD), catalase, Ca(2+)ATPase, concentration of reduced glutathione (GSH) and protein sulfhydryl content were significantly increased in G III and G IV compared to G II, while decreased activities of calpains, lower concentration of calcium and thiobarbituric acid reactive substances (TBARS) were observed in G III and IV as compared to G II. Lens protein profile of water soluble proteins showed normal levels of expression in treated groups compared to that of selenite-induced rats. These results indicate good antioxidant and therapeutic potential of FVN in modulating biochemical parameters against selenite-induced cataract, which have been reported in this paper for the first time.
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PMID:Vitex negundo attenuates calpain activation and cataractogenesis in selenite models. 1909 87


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