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Biomedical subjects

G Marra

Publications and source records attributed to G Marra.

At least 37 records · Page 2Linked to original sources
PubMed2001

Revision rotator cuff repair: factors influencing results.

BACKGROUND: Revision rotator cuff repair is a surgical challenge, and the results have generally been inferior to those of primary repair. We examined the results of revision rotator cuff repair in a large series of patients and assessed which subgroups of patients had the greatest chance for a satisfactory functional outcome. METHODS: A revision rotator cuff repair was performed in eighty patients after the failure of a previous operative repair. The average age of the patients at the time of the revision was fifty-nine years. Prior to revision, the average pain score was 7.4 points (with 0 points indicating no pain and 10 points, severe pain) and the active range of motion of the shoulder averaged 105 degrees of elevation, 39 degrees of external rotation, and internal rotation to the eleventh thoracic vertebra. All patients underwent repeat repair of the rotator cuff tendons to bone. Additional procedures included revision acromioplasty (fifty-three patients; 66%) and distal clavicular excision (twenty-six patients; 33%), among others. RESULTS: After an average duration of follow-up of forty-nine months, the result was rated as satisfactory (excellent, good, or fair) in fifty-five patients (69%) and as unsatisfactory (poor) in twenty-five (31%). At the time of the latest follow-up, the average pain score had improved to 3.0 points and the active range of motion averaged 130 degrees of elevation, 53 degrees of external rotation, and internal rotation to the tenth thoracic vertebra. Improved results were associated with an intact deltoid origin, good-quality rotator cuff tissue, preoperative active elevation of the arm above the horizontal, and only one prior procedure. All seventeen patients who met all four of these criteria had a satisfactory result. CONCLUSIONS: The results of revision rotator cuff repair are inferior to those of primary repair. While pain relief can be reliably achieved in most patients, the functional results are improved principally in patients with an intact deltoid origin, good-quality rotator cuff tissue, preoperative elevation above the horizontal, and only one prior procedure.

Adult↗
PubMed2000

Mismatch recognition and DNA-dependent stimulation of the ATPase activity of hMutSalpha is abolished by a single mutation in the hMSH6 subunit.

The most abundant mismatch binding factor in human cells, hMutSalpha, is a heterodimer of hMSH2 and hMSH6, two homologues of the bacterial MutS protein. The C-terminal portions of all MutS homologues contain an ATP binding motif and are highly conserved throughout evolution. Although the N termini are generally divergent, they too contain short conserved sequence elements. A phenylalanine --> alanine substitution within one such motif, GXFY(X)(5)DA, has been shown to abolish the mismatch binding activity of the MutS protein of Thermus aquaticus (Malkov, V. A., Biswas, I., Camerini-Otero, R. D., and Hsieh, P. (1997) J. Biol. Chem. 272, 23811-23817). We introduced an identical mutation into one or both subunits of hMutSalpha. The Phe --> Ala substitution in hMSH2 had no effect on the biological activity of the heterodimer. In contrast, the in vitro mismatch binding and mismatch repair functions of hMutSalpha were severely attenuated when the hMSH6 subunit was mutated. Moreover, this variant heterodimer also displayed a general DNA binding defect. Correspondingly, its ATPase activity could not be stimulated by either heteroduplex or homoduplex DNA. Thus the N-terminal portion of hMSH6 appears to impart on hMutSalpha not only the specificity for recognition and binding of mismatched substrates but also the ability to bind to homoduplex DNA.

Adenosine Triphosphatases↗
PubMed2000

Decreased UV sensitivity, mismatch repair activity and abnormal cell cycle checkpoints in skin cancer cell lines derived from UVB-irradiated XPA-deficient mice.

Xeroderma pigmentosum group A gene (XPA)-deficient mice are defective in nucleotide excision repair (NER) and are therefore highly sensitive to ultraviolet (UV)-induced skin carcinogenesis. We established cell lines from skin cancers of UVB-irradiated XPA-deficient mice to investigate the phenotypic changes occurring during skin carcinogenesis. As anticipated, the skin cancer cell lines were devoid of NER activity but were less sensitive to killing by UV-irradiation than the XPA(-/-) fibroblast cell line. The lines were also more resistant to 6-thioguanine (6-TG) than XPA(-/-) and XPA(+/+) fibroblasts, which was suggestive of a mismatch repair (MMR) defect. Indeed, in vitro mismatch binding and MMR activity were impaired in several of these cell lines. Moreover, these cell lines displayed cell cycle checkpoint derangements following UV-irradiation and 6-TG exposure. The above findings suggest that MMR downregulation may help cells escape killing by UVB, as was seen previously for methylating agents and cisplatin, and thus that MMR deficient clones are selected for during the tumorigenic transformation of XPA(-/-) cells.

Animals↗
PubMed2000

Mutation in the magnesium binding site of hMSH6 disables the hMutSalpha sliding clamp from translocating along DNA.

In human cells, binding of base/base mismatches and small insertion/deletion loops is mediated by hMutSalpha, a heterodimer of hMSH2 and hMSH6. In the presence of ATP and magnesium, hMutSalpha dissociates from the mismatch by following the DNA contour in the form of a sliding clamp. This process is enabled by a conformational change of the heterodimer, which is driven by the binding of ATP and magnesium in the Walker type A and B motifs of the polypeptides, respectively. We show that a purified recombinant hMutSalpha variant, hMutSalpha 6DV, which contains an aspartate to valine substitution in the Walker type B motif of the hMSH6 subunit, fails to undergo the conformational change compatible with translocation. Instead, its direct dissociation from the mismatch-containing DNA substrate in the presence of ATP and magnesium precludes the assembly of a functional mismatch repair complex. The "translocation-prone" conformation of wild type hMutSalpha could be observed solely under conditions that favor hydrolysis of the nucleotide and mismatch repair in vitro. Thus, whereas magnesium could be substituted with manganese, ATP could not be replaced with its slowly or nonhydrolyzable homologues ATP-gammaS or AMPPNP, respectively. The finding that ATP induces different conformational changes in hMutSalpha in the presence and in the absence of magnesium helps explain the functional differences between hMutSalpha variants incapable of binding ATP as compared with those unable to bind the metal ion.

Adenosine Triphosphatases↗
PubMed2000

Osteolysis of the distal clavicle: long-term results of arthroscopic resection.

PURPOSE: The purpose of this study was to evaluate the outcome of arthroscopic distal clavicle resection by the direct superior approach for treatment of isolated osteolysis of the distal clavicle. TYPE OF STUDY: Case series. MATERIALS AND METHODS: Forty-one shoulders in 37 patients underwent arthroscopic resection of the distal clavicle. Thirty-three patients were male and 4 female, with an average age of 39 years. All patients complained of pain localized to the acromioclavicular joint region. Symptoms began after a traumatic event in 18 shoulders and were associated with repetitive stressful activity in 23 shoulders. RESULTS: At an average follow-up of 6.2 years, 22 shoulders had excellent results, 16 had good results, and 3 were failures. All 3 failures occurred in patients with a traumatic etiology. CONCLUSIONS: Arthroscopic resection for osteolysis of the distal clavicle has results comparable to open excision with low morbidity. Patients with a traumatic etiology had slightly worse results compared with patients with a microtraumatic etiology.

Adult↗
PubMed2000

Lack of association between carotid intima-media thickness and methylenetetrahydrofolate reductase gene polymorphism or serum homocysteine in non-insulin-dependent diabetes mellitus.

We assessed the contribution of the serum homocysteine (Hcy) level, an independent risk factor for vascular disease, and methylene tetrahydrofolate reductase (MTHFR) gene polymorphism to the variability of intimal-medial thickness (IMT) of the common carotid artery in middle-aged non-insulin-dependent diabetes mellitus (NIDDM) subjects. One hundred thirty NIDDM patients (60 males and 70 females) with a mean age of 53 +/- 10 years and a mean diabetes duration of 11.3 +/- 7.9 years were enrolled for the study. Exclusion criteria included liver, heart, kidney, or other major-organ disease. Fasting total serum Hcy, folate, and vitamin B12 and clinical chemistry analyte levels were measured. MTHFR polymorphism was determined by polymerase chain reaction (PCR). IMT and plaques or stenosis in the common carotid were measured by ultrasonography. Serum Hcy was inversely correlated with vitamin levels and was slightly higher in subjects with the Val/Val genotype versus Ala/Val and Ala/Ala (P = .02); no differences in genotype were found in subjects with folate or vitamin B12 at or above the median level. In univariate analysis, common carotid IMT was significantly associated with age (P = .00001), the body mass index ([BMI] P = .0003), uric acid (P = .004), systolic blood pressure (P = .03), glycemia (P = .03), and total cholesterol (P = .04). No significant association was found between serum Hcy or MTHFR polymorphism and IMT. In multiple regression analysis, age (P = .0001), uric acid (P = .03), glycemia, and the BMI (P = .05) were independently associated with IMT and explained about 42% of IMT variability. In 130 NIDDM patients without nephropathy, basal levels of serum Hcy, as well as MTHFR polymorphism, did not predict significant changes in common carotid IMT.

Arteriosclerosis↗
PubMed2000

Mismatch repair is required for O(6)-methylguanine-induced homologous recombination in human fibroblasts.

O:(6)-methylguanine is responsible for homologous recombination induced by N:-methyl-N:'-nitro-N:-nitrosoguanidine (MNNG) [H. Zhang et al. (1996) CARCINOGENESIS:, 17, 2229]. To test the hypothesis that mismatch repair is causally involved in this process, we generated mismatch repair-deficient strains from a human fibroblast line containing a substrate for detecting intrachromosomal homologous recombination. The four strains selected for study exhibited greatly increased resistance to the cytotoxic effects of MNNG, which was not affected by depletion of O:(6)-alkylguanine-DNA alkyltransferase, and greatly increased sensitivity to the mutagenic effect of MNNG, suggesting that the mutagenic base modifications induced in these four cell strains by MNNG persist in their genomic DNA. Tests showed that their extracts are deficient in the repair of G:T mismatches. The frequency of homologous recombination induced by MNNG in three of these strains was significantly (5-7-fold) lower than that induced in the parental cell strain. This was not the result of a generalized defect in recombination, because when (+/-)-7beta,8alpha-dihydroxy-9alpha,10alpha-epox y-7,8,9, 10-tetrahydrobenzo[a]pyrene was used to induce recombination, all three lines responded with a normal or even a somewhat higher frequency than that observed in the parental strain. The lack of recombination displayed by the fourth strain was shown to result from the loss of part of the recombination substrate. The results strongly suggest that functional mismatch repair is required for MNNG-induced homologous recombination.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed2000

Traumatic pseudoaneurysm of the brachial artery.

Detection and treatment of vascular injuries in extremity and pelvic trauma can be challenging. Angiography, while no longer routinely used in asymptomatic patients, is still a primary means of diagnosis. Appropriate patient selection based on physical examination, along with other less invasive imaging modalities, can decrease the need for angiography while still detecting the vast majority of clinically significant injuries. Angiography also plays a definitive therapeutic role in most cases of significant hemorrhage in the pelvis through precise identification and selective embolization of bleeding vessels.

Aneurysm, False↗
PubMed2000

Antisense inhibition of hMLH1 is not sufficient for loss of DNA mismatch repair function in the HCT116+chromosome 3 cell line.

We have reported that transfer of chromosome 3 (Chr3) containing a single wild-type copy of the hMLH1 gene into HCT116 colon cancer cells, a cell line deficient in DNA mismatch repair (MMR) activity attributable to inactivating hMLH1 mutations, corrects all of the aspects of the MMR repair-deficient phenotype. We inhibited the expression of the wild-type hMLH1 gene using antisense RNA in HCT116+Chr3 cells to determine if this would result in reversion to the MMR-deficient phenotype. Despite profound inhibition of hMLH1 expression, DNA MMR activity and alkylation sensitivity were not impaired in the antisense-transfected HCT116+Chr3 cells. Additionally, arrest of the cell cycle at the G2 phase with alkylation damage occurs in these cells, a phenotype associated with MMR proficiency. These results indicate that even with a reduction in the expression of hMLH1 protein below the limits of detection by Western blotting, DNA MMR activity remained fully functional (by direct DNA MMR activity assay). We would speculate that hMLH1 is expressed in substantially greater abundance than would be minimally necessary for DNA MMR and that minor reductions in the expression of this protein would not be sufficient to permit DNA MMR dysfunction. Alternatively, Chr3 may contain a second hMLH1 homologue that might overlap with the function of hMLH1.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Identification of hMutLbeta, a heterodimer of hMLH1 and hPMS1.

hMLH1 and hPMS2 function in postreplicative mismatch repair in the form of a heterodimer referred to as hMutLalpha. Tumors or cell lines lacking this factor display mutator phenotypes and microsatellite instability, and mutations in the hMLH1 and hPMS2 genes predispose to hereditary non-polyposis colon cancer. A third MutL homologue, hPMS1, has also been reported to be mutated in one cancer-prone kindred, but the protein encoded by this locus has so far remained without function. We now show that hPMS1 is expressed in human cells and that it interacts with hMLH1 with high affinity to form the heterodimer hMutLbeta. Recombinant hMutLalpha and hMutLbeta, expressed in the baculovirus system, were tested for their activity in an in vitro mismatch repair assay. While hMutLalpha could fully complement extracts of mismatch repair-deficient cell lines lacking hMLH1 or hPMS2, hMutLbeta failed to do so with any of the different substrates tested in this assay. The involvement of the latter factor in postreplicative mismatch repair thus remains to be demonstrated.

Adaptor Proteins, Signal Transducing↗
PubMed1999

JC virus DNA is present in the mucosa of the human colon and in colorectal cancers.

JC virus (JCV) is a polyoma virus that commonly infects humans. We have found T antigen DNA sequences of JCV in the mucosa of normal human colons, colorectal cancers, colorectal cancer xenografts raised in nude mice, and in the human colon cancer cell line SW480. A larger number of viral copies is present in cancer cells than in non-neoplastic colon cells, and sequence microheterogeneity occurs within individual colonic mucosal specimens. The improved yield of detection after treatment with topoisomerase I suggests that the viral DNA is negatively supercoiled in the human tissues. These results indicate that JCV DNA can be found in colonic tissues, which raises the possibility that this virus may play a role in the chromosomal instability observed in colorectal carcinogenesis.

Animals↗
PubMed1999

Recognition of DNA alterations by the mismatch repair system.

Misincorporation of non-complementary bases by DNA polymerases is a major source of the occurrence of promutagenic base-pairing errors during DNA replication or repair. Base-base mismatches or loops of extra bases can arise which, if left unrepaired, will generate point or frameshift mutations respectively. To counteract this mutagenic potential, organisms have developed a number of elaborate surveillance and repair strategies which co-operate to maintain the integrity of their genomes. An important replication-associated correction function is provided by the post-replicative mismatch repair system. This system is highly conserved among species and appears to be the major pathway for strand-specific elimination of base-base mispairs and short insertion/deletion loops (IDLs), not only during DNA replication, but also in intermediates of homologous recombination. The efficiency of repair of different base-pairing errors in the DNA varies, and appears to depend on multiple factors, such as the physical structure of the mismatch and sequence context effects. These structural aspects of mismatch repair are poorly understood. In contrast, remarkable progress in understanding the biochemical role of error-recognition proteins has been made in the recent past. In eukaryotes, two heterodimers consisting of MutS-homologous proteins have been shown to share the function of mismatch recognition in vivo and in vitro. A first MutS homologue, MSH2, is present in both heterodimers, and the specificity for mismatch recognition is dictated by its association with either of two other MutS homologues: MSH6 for recognition of base-base mismatches and small IDLs, or MSH3 for recognition of IDLs only. Mismatch repair deficiency in cells can arise through mutation, transcriptional silencing or as a result of imbalanced expression of these genes.

Base Composition↗
PubMed1999

Purine metabolites and malondialdehyde in platelets of diabetic patients.

The concentration of some of the purine nucleotides and their metabolites together with that of malondialdehyde (MDA) have been measured in resting and stimulated platelets of type 1 and type 2 diabetic patients. While control platelets show a net decrease of guanosine triphosphate (GTP) (3.1 vs. 2.3 nmol per 10(9) platelets) and guanosine diphosphate (GDP) (3.0 vs. 2.0 nmol per 10(9) platelets) and a significant increase of adenosine (0.04 vs. 0.55 nmol per 10(9) platelets) with platelet stimulation, platelets of type 1 and type 2 diabetic patients have a lesser change of these metabolites (GTP, 2.6 vs. 2.4; GDP, 2.3 vs. 2.4; adenosine, 0.04 vs. 0.30 (P < 0.05 vs. control) nmol per 10(9) platelets in type 1 diabetics; GTP, 2.4 vs. 2.7; GDP, 2.4 vs. 2.1; adenosine, 0.08 vs. 0.32 (P < 0.05 vs. control) nmol per 10(9) platelets in type 2 diabetics). These results indicate that the change (stimulated minus resting) of GTP, GDP and adenosine in diabetic platelets is significantly different from that of controls (P < 0.001). Moreover, the amount of MDA produced during platelet activation seems to be lower than controls only in type 2 diabetes (1.81 vs. 2.86 nmol per 10(9) platelets, P < 0.05). These results seem to indicate that a difference in the pattern of platelet nucleotides could be an important feature even in well-controlled diabetes, while MDA is probably modified only in association with the late vascular complications of diabetes.

Adenosine↗
PubMed1999

hMSH6 deficiency and inactivation of the alphaE-catenin invasion-suppressor gene in HCT-8 colon cancer cells.

Transition from an epithelioid (E) to a round (R) morphotype, in the human colon cancer cell line HCT-8, is associated with loss or truncation of alphaE-catenin and acquisition of invasiveness in organ culture. In E clones, like in parental HCT-8 cells, one allele of the alphaE-catenin gene (CTNNA1) is mutated. HCT-8 cells have also a 'Microsatelite Instability-High' (MSI-H) phenotype presumably due to a mutated hMSH6 gene. Fusion of E type cells doubles the wild type CTNNA1 alleles and prevents the loss of alphaE-catenin. Introduction of an extra chromosome 2, carrying a wild type hMSH6 gene, restores post-replicative mismatch repair and also prevents the frequent inactivation of the remaining wild type CTNNA1 allele.

Alleles↗
PubMed1999

Efficacy and safety of acarbose in the treatment of Type 1 diabetes mellitus: a placebo-controlled, double-blind, multicentre study.

AIMS: The aim of the study was to evaluate the efficacy and safety of acarbose in patients with Type 1 diabetes mellitus (DM). METHODS: A multicentre double-blind, randomized, placebo-controlled study was performed. After a 6-week run-in, 121 patients were randomized to acarbose or placebo and to high- or low-fibre diet for 24 weeks. Acarbose dose was 50 mg t.d.s. for the first 2 weeks and 100 mg t.d.s. for the subsequent weeks. RESULTS: At the end of 24 weeks of treatment the intention to treat analysis showed that acarbose compared with placebo decreased 2 h postprandial plasma glucose levels (12.23 +/- 0.83 vs. 14.93 +/- 0.87 mmol/l; F = 6.1, P < 0.02) (least square means +/- SEM). No significant effect of acarbose was recorded on HbA1c or on the number of hypoglycaemic episodes. The effect of acarbose on blood glucose control was not influenced by the amount of carbohydrate and/or fibre intake. The incidence of adverse events were 75% and 39% in acarbose and placebo groups, respectively; they were mild and confined to the gastrointestinal tract. CONCLUSIONS: The use of acarbose in combination with insulin reduces postprandial plasma glucose levels in Type 1 diabetic patients who are not satisfactorily controlled with insulin alone but without significant effect on HbA1c.

Acarbose↗
PubMed1999

Effect of hMSH6 cDNA expression on the phenotype of mismatch repair-deficient colon cancer cell line HCT15.

Mismatch recognition in human cells is mediated primarily by a heterodimer of hMSH2 and hMSH6. Cells mutated in both alleles of the hMSH6 gene are deficient in the correction of base/base mispairs and insertion/deletion loops of one nucleotide and thus exhibit a strong mutator phenotype, evidenced by elevated mutation rates and microsatellite instability, as well as by tolerance to methylating agents. The decrease in replication fidelity associated with a loss of mismatch correction implies that with each division, these cells are likely to acquire new mutations throughout their genomes. Should such secondary mutations occur in genes linked to replication fidelity or involved in the maintenance of genomic stability, they might contribute to the observed mutator phenotype. The human colon tumour line HCT15 represents one such case. Although it carries inactivating mutations in both hMSH6 alleles, it has also been shown to contain a missense mutation in the coding sequence of the proofreading domain of the polymerase-delta gene. In an attempt to find out whether the phenotype of HCT15 cells was indeed brought about solely by the lack of hMSH6, we stably transfected them with a vector carrying the wild-type hMSH6 cDNA. Our results show that although the levels of transgenic hMSH6 were low, expression of the wild-type protein resulted in a substantial restoration of mismatch binding, mismatch repair capacity and the stability of mononucleotide repeats, as well as in the reduction of mutation rates. Although methylation tolerance of the hMSH6-expressing cells was not markedly affected, the G2 cell cycle checkpoint, absent in N-methyl-N'-nitro-N-nitrosoguanidine-treated control cells, was restored.

Base Pair Mismatch↗