Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.6.1.2 (alanine aminotransferase)
 26,722 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several hepatotoxic agents damage Ca++ regulation and produce toxic cell death in a manner consistent with a cause-and-effect relationship; however, vital targets of Ca++ remain unidentified. Recent results show that DNA may be the chief Ca++ target during apoptosis, a form of cell death considered distinct from toxic cell death or necrosis. The present studies explored whether nuclear Ca++ regulation is lost before dimethylnitrosamine-induced necrosis, whether DNA is attacked by Ca(++)-dependent endonucleases and whether inhibitors of Ca(++)-endonuclease activity and the DNA repair enzyme poly(ADP-ribose)polymerase affect necrosis. Adult male ICR mice received 100 mg/kg of dimethylnitrosamine i.p. By 2 to 4 hr, total nuclear Ca++ reached 150 to 180% of control and DNA fragmentation was 140 to 170% of control. Electrophoresis of DNA revealed a sharp decline in genomic DNA with the appearance of DNA fragments in a ladder-like pattern. Ca++ elevation and DNA fragmentation preceded toxic cell death by 4 hr or more and reached peak values at 18 to 24 hr, coincident with maximal alanine aminotransferase leakage. Aurintricarboxylic acid, a Ca(++)-endonuclease inhibitor, reduced toxicity 67%. 3-Aminobenzamide, nicotinamide adenine dinucleotide and theophylline, inhibitors of poly(ADP-ribose)polymerase-mediated DNA repair, potentiated liver damage 2-fold. These results support the hypothesis that DNA fragmentation plays a contributing role in toxic cell death induced by dimethylnitrosamine. Furthermore, the findings suggest that new opportunities may exist to moderate the toxicity of alkylating hepatotoxins by altering DNA regulation.
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PMID:Ca(++)-activated DNA fragmentation and dimethylnitrosamine-induced hepatic necrosis: effects of Ca(++)-endonuclease and poly(ADP-ribose) polymerase inhibitors in mice. 132 12

Little is known about the replicative forms of hepatitis B virus (HBV) in the liver in chronic liver disease. We therefore analyzed HBV DNA and the changes in DNA signals after endonuclease digestion in liver tissues taken from 64 patients with hepatitis B surface antigen-positive chronic liver disease. The "active" replication pattern, which included various replicative intermediates, was seen in 36 of 38 (95%) hepatitis B e antigen-seropositive patients. This pattern was also found in 5 of 26 (19%) hepatitis B e antigen-seronegative patients who showed the highest mean serum alanine aminotransferase level (403 +/- 184 mU/ml). Most of them had advanced liver disease. Episomal viral DNA of an "inactive" type having only the supercoiled form was found in 3 patients; they showed the lowest mean serum alanine aminotransferase level (27 +/- 7 mU/ml) and only mild liver disease. As with duck HBV infection, episomal replicative forms of human HBV could be resolved by Southern blot analysis and seem to have clinical implications in human HBV infection.
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PMID:Active and inactive replication of hepatitis B virus deoxyribonucleic acid in chronic liver disease. 401 3

Ca2+ accumulates in the nucleus and DNA undergoes enzymatic cleavage into internucleosome-length fragments before acetaminophen and dimethylnitrosamine produce hepatic necrosis in vivo and toxic cell death in vitro. However, Ca(2+)-endonuclease fragmentation of DNA is characteristic of apoptosis, a type of cell death considered biochemically and functionally distinct from toxic cell death. The present studies investigate DNA fragmentation as a critical event in toxic cell death by testing whether the Ca(2+)-calmodulin antagonist chlorpromazine and the Ca2+ channel blocker verapamil prevent acetaminophen-induced hepatic necrosis by inhibiting Ca2+ deregulation and DNA damage. Acetaminophen overdose in mice produced accumulation of Ca2+ in the nucleus (358% of control) and fragmentation of DNA (250% of control) by 6 h, with peak release of ALT occurring at 12-24 h (38,000 U/l). Pretreatment with chlorpromazine prevented increases in nuclear Ca2+ and DNA fragmentation and nearly abolished biochemical evidence of toxic cell death. Verapamil pretreatment also decreased Ca2+ accumulation and DNA damage while attenuating liver injury. The Ca2+ antagonists did not protect against toxic cell death through hypothermia because neither produced the delay in toxicity that is customarily associated with hypothermia. Nor did chlorpromazine or verapamil protect through inhibiting acetaminophen bioactivation. Chlorpromazine failed to diminish glutathione depletion in whole liver and isolated nuclei. Verapamil (250 microM) also failed to alter glutathione depletion in whole liver and had no effect on acetaminophen-glutathione adduct formation by mouse liver microsomes and by cultured mouse hepatocytes. Collectively, these results support the hypothesis that Ca(2+)-induced DNA fragmentation plays a significant role in cell necrosis produced by acetaminophen and may contribute to toxic cell death caused by other alkylating hepatotoxins.
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PMID:Ca2+ antagonists inhibit DNA fragmentation and toxic cell death induced by acetaminophen. 846 87

Several molecular events in the apoptotic or necrotic death of hepatocytes induced by acetaminophen (AAP) now appear to be well defined. Recent studies also indicate that select expression of bcl-Xl is possibly modified during AAP-induced liver injury. The purpose of this study was several-fold: (i) to examine the hepatoprotective ability of short-term (3-day) and long-term (7-day) exposures of a grape seed proanthocyanidin extract (GSPE) on AAP-induced liver injury and animal lethality; (ii) to monitor effects of GSPE on one of the prime targets of AAP, i.e., hepatocellular genomic DNA and associated apoptotic and necrotic death; and (iii) to unravel changes in the pattern of expression of an antiapoptotic gene, bcl-Xl in the liver. In order to investigate these events, male ICR mice (30-40 g) were administered nontoxic doses of GSPE (3 or 7 days, 100 mg/kg, po), followed by hepatotoxic doses of AAP (400 and 500 mg/kg, ip), and sacrificed 24 h later. Serum was analyzed for alanine aminotransferase activity (ALT) and the liver for histopathological diagnosis of apoptosis/necrosis. The ability of AAP to promote apoptotic DNA fragmentation and its counteraction by GSPE in the liver was also evaluated quantitatively (by a sedimentation assay) and qualitatively (by agarose gel electrophoresis). Portions of livers were also subjected to Western blot analysis (27,000g fraction of liver homogenates) to examine the pattern of expression of cell death inhibitory gene bcl-Xl. Results indicate that 7-day GSPE preexposure induced dramatic protection and markedly decreased liver injury and animal lethality culminated by AAP, when compared to a short-term 3-day exposure. Abrogation of toxicity was also mirrored in DNA fragmentation. Histopathological evaluation of liver sections showed remarkable counteraction of AAP-toxicity by this novel GSPE and substantial inhibition of both apoptotic and necrotic liver cell death. Agarose gel electrophoresis revealed that 7-day GSPE preexposure prior to AAP administration completely blocked Ca(2+)/Mg(2+)-Ca(2+)/Mg(2+)-dependent-endonuclease-mediated ladder-like fragmentation of genomic DNA and significantly altered the bcl-Xl expression. The most dramatic changes observed in this study were: (i) substantial increase in the expression of bcl-Xl in the liver by 7-day GSPE exposure alone; (ii) significant modification bcl-Xl expression by AAP alone; and (iii) dramatic inhibition of AAP-induced modification of bcl-Xl (phosphorylation?) expression by GSPE. In summary, these observations demonstrate that GSPE preexposure may significantly attenuate AAP-induced hepatic DNA damage, apoptotic and necrotic cell death of liver cells, and, most remarkably, antagonize the influence of AAP-induced changes in bcl-Xl expression in vivo.
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PMID:A novel proanthocyanidin IH636 grape seed extract increases in vivo Bcl-XL expression and prevents acetaminophen-induced programmed and unprogrammed cell death in mouse liver. 1046 39

Grape seed extract, primarily a mixture of proanthocyanidins, has been shown to modulate a wide-range of biological, pharmacological and toxicological effects which are mainly cytoprotective. This study assessed the ability of IH636 grape seed proanthocyanidin extract (GSPE) to prevent acetaminophen (AAP)-induced nephrotoxicity, amiodarone (AMI)-induced lung toxicity, and doxorubicin (DOX)-induced cardiotoxicity in mice. Experimental design consisted of four groups: control (vehicle alone), GSPE alone, drug alone and GSPE+drug. For the cytoprotection study, animals were orally gavaged 100 mg/Kg GSPE for 7-10 days followed by i.p. injections of organ specific three drugs (AAP: 500 mg/Kg for 24 h; AMI: 50 mg/Kg/day for four days; DOX: 20 mg/Kg for 48 h). Parameters of study included analysis of serum chemistry (ALT, BUN and CPK), and orderly fragmentation of genomic DNA (both endonuclease-dependent and independent) in addition to microscopic evaluation of damage and/or protection in corresponding PAS stained tissues. Results indicate that GSPE preexposure prior to AAP, AMI and DOX, provided near complete protection in terms of serum chemistry changes (ALT, BUN and CPK), and significantly reduced DNA fragmentation. Histopathological examination of kidney, heart and lung sections revealed moderate to massive tissue damage with a variety of morphological aberrations by all the three drugs in the absence of GSPE preexposure than in its presence. GSPE+drug exposed tissues exhibited minor residual damage or near total recovery. Additionally, histopathological alterations mirrored both serum chemistry changes and the pattern of DNA fragmentation. Interestingly, all the drugs, such as, AAP, AMI and DOX induced apoptotic death in addition to necrosis in the respective organs which was very effectively blocked by GSPE. Since AAP, AMI and DOX undergo biotransformation and are known to produce damaging radicals in vivo, the protection by GSPE may be linked to both inhibition of metabolism and/or detoxification of cytotoxic radicals. In addition, its' presumed contribution to DNA repair may be another important attribute, which played a role in the chemoprevention process. Additionally, this may have been the first report on AMI-induced apoptotic death in the lung tissue. Taken together, these events undoubtedly establish GSPE's abundant bioavailability, and the power to defend multiple target organs from toxic assaults induced by structurally diverse and functionally different entities in vivo.
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PMID:In vivo protection of dna damage associated apoptotic and necrotic cell deaths during acetaminophen-induced nephrotoxicity, amiodarone-induced lung toxicity and doxorubicin-induced cardiotoxicity by a novel IH636 grape seed proanthocyanidin extract. 1133 64

Acetaminophen (AAP), the analgesic hepatotoxicant, is a powerful inducer of oxidative stress, DNA fragmentation, and apoptosis. The anti-apoptotic oncogene bcl-XL, and the pro-apoptotic oncogene p53 are two key regulators of cell cycle progression and/or apoptosis subsequent to DNA damage in vitro and in vivo. This study investigated the effect of AAP on the expression of these oncogenes and whether agents that modulate DNA fragmentation (chlorpromazine, CPZ) and DNA repair through poly(ADP-Ribose) polymerase (PARP) activity (4-AB: 4-aminobenzamide) can protect against AAP-induced hepatotoxicity by inhibiting oxidative stress, DNA fragmentation, and/or by altering the expression of bcl-XL and p53. In addition, the protective effect of supplemental nicotinamide (NICO), known to be depleted in cells with high PARP activity during DNA repair, is similarly evaluated. Male ICR mice (3 months old) were administered vehicle alone; nontoxic doses of 4-AB (400 mg/kg, ip), NICO (250 mg/kg, ip) or CPZ (25 mg/kg, ip), hepatotoxic dose of AAP alone (500 mg/kg, ip), or AAP plus one of the protective agents 1 h later. All animals were sacrificed 24 h following AAP administration. Serum alanine aminotransferase activity (ALT), hepatic histopathology and lipid peroxidation, DNA damage, and expression of bcl-XL and p53 (western blot analysis) were compared in various groups. All of the three agents significantly prevented AAP-induced liver injury, lipid peroxidation, DNA damage, and associated apoptotic and necrotic cell deaths, 4-AB being the most effective and NICO the least. Compared to control, there was a considerable decrease in bcl-XL expression, and an increase in p53 expression in AAP-exposed livers. The effect of AAP on bcl-XL was antagonized and that on p53 was synergized by the PARP-modulator 4-AB as well as NICO, whereas the endonuclease inhibitor CPZ was without effect on either bcl-XL or p53 expression. These results suggest that the hepatotoxic effect of AAP involves multiple mechanisms including oxidative stress, upregulation of endonuclease (or caspase-activated DNAse) and alteration of pro- and anti-apoptotic oncogenes. The observed antagonism of AAP-induced hepatocellular apoptosis and/or necrosis by modulators of multiple processes including DNA repair suggests the likelihood that a more effective therapy against AAP intoxication should involve a combination of antidotes.
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PMID:Ca(2+)-calmodulin antagonist chlorpromazine and poly(ADP-ribose) polymerase modulators 4-aminobenzamide and nicotinamide influence hepatic expression of BCL-XL and P53 and protect against acetaminophen-induced programmed and unprogrammed cell death in mice. 1146 65

In the absence of telomerase, telomeres erode, provoking accumulation of DNA damage and death by senescence. Rare survivors arise, however, due to Rad52-based amplification of telomeric sequences by homologous recombination. The present study reveals that in budding yeast cells, postsenescence survival relying on amplification of the TG(1-3) telomeric repeats can take place in the absence of Rad52 when overelongated telomeres are present during senescence (hence its designation ILT, for inherited-long-telomere, pathway). By growth competition, the Rad52-independent pathway was almost as efficient as the Rad51- and Rad52-dependent pathway that predominates in telomerase-negative cells. The ILT pathway could also be triggered by increased telomerase accessibility before telomerase removal, combined with loss of telomere protection, indicating that prior accumulation of recombination proteins was not required. The ILT pathway was dependent on Rad50 and Mre11 but not on the Rad51 recombinase and Rad59, thus making it distinct from both the type II (budding yeast ALT [alternative lengthening of telomeres]) and type I pathways amplifying the TG(1-3) repeats and subtelomeric sequences, respectively. The ILT pathway also required the Rad1 endonuclease and Elg1, a replication factor C (RFC)-like complex subunit, but not Rad24 or Ctf18 (two subunits of two other RFC-like complexes), the Dnl4 ligase, Yku70, or Nej1. Possible mechanisms for this Rad52-independent pathway of telomeric repeat amplification are discussed. The effects of inherited long telomeres on Rad52-dependent recombination are also reported.
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PMID:Telomerase- and Rad52-independent immortalization of budding yeast by an inherited-long-telomere pathway of telomeric repeat amplification. 1904 70

Replication forks frequently stall at regions of the genome that are difficult to replicate or contain lesions that cause replication blockage. An important mechanism for the restart of a stalled fork involves endonucleolytic cleavage that can lead to fork restoration and replication progression. Here, we show that the structure-selective endonuclease MUS81-EME2 is responsible for fork cleavage and restart in human cells. The MUS81-EME2 protein, whose actions are restricted to S phase, is also responsible for telomere maintenance in telomerase-negative ALT (Alternative Lengthening of Telomeres) cells. In contrast, the G2/M functions of MUS81, such as the cleavage of recombination intermediates and fragile site expression, are promoted by MUS81-EME1. These results define distinct and temporal roles for MUS81-EME1 and MUS81-EME2 in the maintenance of genome stability.
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PMID:MUS81-EME2 promotes replication fork restart. 2481 86

A likely mechanism of chromosomal rearrangement formation involves joining the ends from two different chromosomal double-strand breaks (DSBs). These events could potentially be mediated by either of two end-joining (EJ) repair pathways [canonical nonhomologous end joining (C-NHEJ) or alternative end joining (ALT-EJ)], which cause distinct rearrangement junction patterns. The relative role of these EJ pathways during rearrangement formation has remained controversial. Along these lines, we have tested whether the DNA damage response mediated by the Ataxia Telangiectasia Mutated (ATM) kinase may affect the relative influence of C-NHEJ vs. ALT-EJ on rearrangement formation. We developed a reporter in mouse cells for a 0.4-Mbp deletion rearrangement that is formed by EJ between two DSBs induced by the Cas9 endonuclease. We found that disruption of the ATM kinase causes an increase in the frequency of the rearrangement as well as a shift toward rearrangement junctions that show hallmarks of C-NHEJ. Furthermore, ATM suppresses rearrangement formation in an experimental condition, in which C-NHEJ is the predominant EJ repair event (i.e., expression of the 3' exonuclease Trex2). Finally, several C-NHEJ factors are required for the increase in rearrangement frequency caused by inhibition of the ATM kinase. We also examined ATM effectors and found that H2AX shows a similar influence as ATM, whereas the influence of ATM on this rearrangement seems independent of 53BP1. We suggest that the contribution of the C-NHEJ pathway to the formation of a 0.4-Mbp deletion rearrangement is enhanced in ATM-deficient cells.
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PMID:Contribution of canonical nonhomologous end joining to chromosomal rearrangements is enhanced by ATM kinase deficiency. 2805 60