Comparative Arterial Blood Gas Analysis in Post Septoplasty Patients with Conventional Nasal Packs Versus Nasal Packs with Airway

To evaluate levels of arterial blood gases in patients undergoing septoplasty, with conventional nasal packing versus those with nasal packing with airway. The current prospective comparative study was conducted on 68 patients undergoing septoplasty, who were divided randomly into two groups-conventional nasal packs (ANP) and nasal packs with airway (ANP-A). Arterial blood gas analysis alongwith objective symptoms of patients were recorded and evaluated. The difference between pre and post operative values of SpO2 (ANP = 6.73 ± 1.17, ANP-A = 2.84 ± 0.91) and pO2 (ANP = 15.09 ± 4.34, ANP-A = 3.46 ± 1.49) between the two groups was statistically significant (p = 0.001). Differences in post operative pH, pCO2 and HCO3 between the two groups was not statistically significant. Significant difference between the two groups was observed in patients' objective symptoms as well. Nasal packs with airway have lesser perturbing effects on septoplasty patients as compared to conventional nasal packs.

Extracellular phosphate ions cause apoptosis of terminally differentiated epiphyseal chondrocytes

Epiphyseal chondrocytes end their life cycle through apoptosis. While this event provides a mechanism for the removal of terminally differentiated cells from cartilage, agents that promote this physiological process have not been defined. To address this issue, using a cell culture technique that models events that take place in the growth plate, we asked the following questions: Can agents that promote chondrocyte maturation and cartilage mineralization serve as specific triggers for cell death? Are chondrocytes susceptible to apoptogens at a singular developmental stage? Treatment of embryonic tibial chondrocytes with inorganic phosphate (Pi) induced death in a dose- and time-dependent manner. Within 48 hr, 3 mM Pi increased chondrocyte death by 30%; lower concentrations of Pi induced death after 48 hr. To ascertain if death was due to apoptosis, we evaluated Pi-induced death by a number of different methods and compared the results to those induced by the apoptogen, staurosporine. Analysis of the death process indicated that cartilage cells shared many of the common biological features of the apoptotic process. Thus, there was DNA fragmentation, terminal deoxynucleotidyl transferase (TUNEL) labeling, an increase in cells in the sub-G1 fraction of the cell cycle, and morphological evidence of apoptosis. To explore the specificity of the Pi effect, the experiment was repeated using embryonic sternal cephalic and caudal chondrocytes, cells that are at an earlier developmental stage than the terminally differentiated tibial cells. We noted that these cells remained vital despite a major increase in the medium Pi content. Results of this study suggest that Pi is a stage-specific inducer of apoptosis in maturing chondrocytes and that this role may be linked to chondrocyte maturation and mineralization of the extracellular matrix.

Chondrocyte death is linked to development of a mitochondrial membrane permeability transition in the growth plate

In the companion article, we reported that the local phosphate (Pi) concentration triggers apoptosis in epiphyseal chondrocytes. The goal of the current investigation was to evaluate the apoptotic process in relationship to the energy status of cells in the growth plate. For these studies, we used sections of the adolescent growth plate, as well as cells isolated from the tissue. We found that there was a maturation-dependent loss of mitochondrial function in growth plate chondrocytes and these cells generated energy by glycolysis. Since treatment with the uncoupler 2,4-dinitrophenol as well as the site-specific inhibitors antimycin A and rotenone failed to elicit a further increase in the activity of the glycolytic pathway, we concluded that oxidative metabolism was minimum in these cells. Flow cytometric studies of growth plate cells and confocal microscopy of growth plate sections using the mitochondrial probes Rh123 and DiOC6(3) provided unequivocal evidence that there was loss of mitochondrial membrane potential in hypertrophic cells. Furthermore, the intrinsic fluorescence of the flavoprotein lipoamide dehydrogenase complex of the electron transport chain revealed that the mitochondria were in an oxidized state. Finally, we assessed Bcl-2 expression in these cells. Although immunohistochemical and Western blot analysis showed that the chick cells contained a low level of the anti-apoptotic protein Bcl-2, reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated that transcripts were present in chondrocytes. Based on these observations, we suggest that terminally differentiated chondrocytes undergo a maturation-dependent loss of mitochondrial function. In concert with the low expression of Bcl-2, they become sensitive to signals for programmed cell death. We hypothesize that Pi triggers apoptosis in these energy-compromised cells by promoting a mitochondrial membrane transition, thereby inducing the death process.

Developmental expression of creatine kinase isoenzymes in chicken growth cartilage

We have shown previously that creatine kinase (CK) activity is required for normal development and mineralization of chicken growth cartilage and that expression of the cytosolic isoforms of CK is related to the biosynthetic and energy status of the chondrocyte. In this study, we have characterized changes in isoenzyme activity and mRNA levels of CK (muscle-specific CK, M-CK; brain-type CK, B-CK; and mitochondrial CK subunits, MiaCK and MibCK) in the growth plate in situ and in chondrocyte culture systems that model the development/maturation program of the cartilage. The in vitro culture systems analyzed were as follows: tibial chondrocytes, which undergo hypertrophy; embryonic cephalic and caudal sternal chondrocytes, which differ from each other in their mineralization response to retinoic acid; and long-term micromass cultures of embryonic limb mesenchymal cells, which recapitulate the chondrocyte differentiation program. In all systems analyzed, B-CK was found to be the predominant isoform. In the growth plate, B-CK expression was highest in the most calcified regions, and M-CK was less abundant than B-CK in all regions of the growth plate. In tibial chondrocytes, an increase in B-CK expression was seen when the cells became hypertrophic. Expression of B-CK increased slightly over 15 days in mineralizing, retinoic acid-treated cephalic chondrocytes, but it decreased in nonmineralizing caudal chondrocytes, while there was little expression of M-CK. Interestingly, in limb mesenchyme cultures, significant M-CK expression was detected during chondrogenesis (days 2-7), whereas hypertrophic cells expressed only B-CK. Finally, expression of MiaCK and MibCK was low both in situ and in vitro. These observations suggest that the CK genes are differentially regulated during cartilage development and maturation and that an increase in CK expression is important in initiating chondrocyte maturation.

Identification of N(G)-methylarginine residues in human heterogeneous RNP protein A1: Phe/Gly-Gly-Gly-Arg-Gly-Gly-Gly/Phe is a preferred recognition motif

Three sites of N(G),N(G)-arginine methylation have been located at residues 205, 217, and 224 in the glycine-rich, COOH-terminal one-third of the HeLa A1 heterogeneous ribonucleoprotein. Together with the previously determined dimethylated arginine at position 193 [Williams et al., (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 5666-5670], it is evident that all four sites fall within a span of sequence between residues 190 and 233 that contains multiple Arg-Gly-(Gly) sequences interspersed with phenylalanine residues. These RGG boxes have been postulated to represent an RNA binding motif [Kiledjian and Dreyfuss (1992) EMBO J. 11, 2655-2664]. Dimethylation of HeLa A1 appears to be quantitative at each of the four positions. Arginines 205 and 224 have been methylated in vitro by a nuclear protein arginine methyltransferase using recombinant (unmethylated) A1 as substrate. This suggests A1 may be an in vivo substrate for this enzyme. Examination of sequences surrounding the sites of methylation in A1 along with a compilation from the literature of sites that have been identified in other nuclear RNA binding proteins suggests a methylase-preferred recognition sequence of Phe/Gly-Gly-Gly-Arg-Gly-Gly-Gly/Phe, with the COOH-terminal flanking glycine being obligatory. Taken together with data in the literature, identification of the sites of A1 arginine methylation strongly suggests a role for this modification in modulating the interaction of A1 with nucleic acids.

Adaptation of chondrocytes to low oxygen tension: relationship between hypoxia and cellular metabolism

In endochondral bone, the growth cartilage is the site of rapid growth. Since the vascular supply to the cartilage is limited, it is widely assumed that cells of the cartilage are hypoxic and that limitations in the oxygen supply regulate the energetic state of the maturing cells. In this report, we evaluate the effects of oxygen tension on chondrocyte energy metabolism, thiol status, and expression of transcription elements, HIF and AP-1. Imposition of an hypoxic environment on cultured chondrocytes caused a proportional increase in glucose utilization and elevated levels of lactate synthesis. Although we observed a statistical increase in the activities of phosphofructokinase, pyruvate kinase, lactate dehydrogenase, and creatine kinase after exposure to lowered oxygen concentrations, the effect was small. The cultured cells exhibited a decreased utilization of glutamine, possibly due to down regulation of mitochondrial function and inhibition of oxidative deamination. With respect to total energy generation, we noted that these cells are quite capable of maintaining the energy charge of the cell at low oxygen tensions. Indeed, no changes in the absolute quantity of adenine nucleotides or the energy charge ratio was observed. Hypoxia caused a decrease in the glutathione content of cultured chondrocytes and a concomitant rise in cell and medium cysteine levels. It is likely that the fall in cell glutathione level is due to decreased synthesis of the tripeptide under reduced oxygen stress and the limited supply of glutamate. The observed rise in cellular and medium cysteine levels probably reflects an increase in the rate of degradation of glutathione and a decrease in synthesis of the peptide. To explore how cells transduce these metabolic effects, gel retardation assays were used to study chondrocyte HIF and AP-1 binding activities. Chondrocyte nuclear preparations bound an HIF-oligonucleotide; however, at low oxygen tensions, no increase in HIF binding was observed. In addition, we found that AP-1 binding activities in chondrocytes exposed to low oxygen tensions was elevated, although the response was lower than that exhibited by fibroblasts exposed to the same range of oxygen concentrations. We compared these results to HIF and AP-1 binding by cells in the growth plate. There was strong HIF and AP-1 binding throughout the plate, but no evidence of selective binding to any one zone. The results of the study lend strong support to the view that chondrocytes are very well adapted to low oxygen tensions; thus, under hypoxic conditions, there is a high level of expression of both HIF and AP-1, and energy conservation appears to be near-maximum.

Retinoic acid modulation of glutathione and cysteine metabolism in chondrocytes

The major objective of this investigation was to determine the thiol status of chondrocytes and to relate changes in the level of glutathione and cysteine to maturation of the cells as they undergo terminal differentiation. Chondrocytes were isolated from the cephalic portion of chick embryo sterna and treated with all-trans retinoic acid for one week. We found that the addition of 100 nM retinoic acid to the cultures decreased the intracellular levels of glutathione and cysteine from 6.1 to 1.6 and 0.07 to 0.01 nmol/microgram DNA respectively; retinoic acid also caused a decrease in the extracellular concentration of cysteine. The decrease in chondrocyte thiols was dose and time dependent. To characterize other antioxidant systems of the sternal cell culture, the activities of catalase, glutathione reductase and superoxide dismutase were determined. Activities of all of those enzymes were high in the retinoic acid-treated cells; the conditioned medium also contained these enzymes and the cytosolic isoenzyme of superoxide dismutase. We probed the specificity of the thiol response by using immature caudal chondrocytes. Unlike the cephalic cells, retinoic acid did not change intracellular glutathione and extracellular cysteine levels, although the retinoid caused a reduction in the intracellular cysteine concentration. Finally, we explored the effect of medium components on chondrocyte thiol status. We noted that while ascorbate alone did not change cell thiol levels, it did cause a 4-fold decrease in the extracellular cysteine concentration. When retinoic acid and ascorbic acid were both present in the medium, there was a marked decrease in the level of glutathione. In contrast, the phosphate concentration of the culture medium served as a powerful modulator of both glutathione and cysteine. Results of the study clearly showed that there is a profound decrease in intracellular levels of both cysteine and glutathione and that thiol levels are responsive to ascorbic acid and the medium phosphate concentration. These findings point to a critical role for thiols in modulating events linked to chondrocyte maturation and cartilage matrix synthesis and mineralization.

Structural specificity of substrate for S-adenosylmethionine:protein arginine N-methyltransferases

The enzymatic methylation of polypeptides on the guanidino group of internal arginine residues by S-adenosylmethionine:protein arginine N-methyltransferase (protein methylase I) yields NG-monomethylarginine, NG,NG-dimethylarginine and NG,NG-dimethylarginine. It has commonly been observed that these arginine residues are present in glycine-and-arginine rich motifs. To understand structural features which are essential for serving as the methyl acceptor for protein methylase I, we have investigated substrate capacities of several synthetic oligopeptides whose sequences are homologous and/or analogous to the methyl acceptor region of the naturally occurring arginine-methylated proteins. These studies have led to the following conclusions. (i) The preferred amino-acid sequence of methyl-accepting peptides was shown to be an arginine-containing peptide with glycine in both the N- and C-flanking positions. While a tetrapeptide with such a sequence (residues 106-109 of bovine myelin basic protein) exhibited almost negligible substrate activity, an overlapping hexapeptide was a moderate substrate. (ii) Substitution of the C-flanking glycine in GKGRGL (residues 104-109 of myelin basic protein) with histidine, phenylalanine, lysine or aspartic acid completely abolished the ability of these hexapeptides to serve as substrates. (iii) A heptapeptide with a repeated glycine-arginine motif (GRGRGRG) was an excellent substrate for the enzyme. (iv) A cyclic octapeptide (CGKGRGLC), which was formed by cyclization of GKGRGL by introduction of disulfide bridge to cross-link N- and C-terminus of the hexapeptide, was an even better substrate than the hexapeptide. (v) Upon HPLC amino-acid analysis, all enzymatically methyl-14C-labeled oligopeptides were found to yield predominantly NG-monomethylarginine with a minor fraction of NG,NG-dimethylarginine in certain peptide samples. However, no NG,NG-dimethylarginine formation was detectable. (vi) The recombinant hnRNP protein A1 (residues 1-320) is known to be methylated at arginine-194 by nuclear-protein/histone protein methylase I (Rajpurohit et al. (1994) J. Biol. Chem. 269, 1079-1082). However, the hexapeptide (SSSQRG) which corresponds to residues 189-194 of protein A1 containing the methylatable arginine residue was relatively inert as a substrate. Furthermore, the N-terminal fragment of protein A1 (residues 1-196) generated by controlled trypsin digestion was also completely inactive as a substrate for the enzyme. These results indicate that the remainder of the A1 protein molecule plays an important though not yet understood role in enzymatic methylation of the arginine-194.

Effect of enzymic methylation of heterogeneous ribonucleoprotein particle A1 on its nucleic-acid binding and controlled proteolysis

Recombinant unmethylated heterogeneous nuclear ribonucleoprotein particle (hnRNP) protein A1 was enzymatically methylated by nuclear protein/histone protein methylase I [Rajpurohit, Lee, Park, Paik and Kim (1994) J. Biol. Chem. 269, 1057-1082] and the effect of methylation on several physiocochemical properties was studied. The relative binding-affinity of methylated and unmethylated protein A1 to nucleic acid was quite different. This was observed by the elution behaviour of the protein A1 on a single-stranded DNA/cellulose column; the concentration of NaCl required to release the bound protein A1 was 0.59 M for the methylated and 0.63 M for the unmethylated, respectively. Employing isoelectrofocusing, pI values of the methylated and unmethylated proteins were found to be 9.41 and 9.48, respectively. Maximum fluorescence quenching of protein A1 in the presence of coliphage MS2-RNA was found to be 40% with methylated and 45% with unmethylated. When both species of protein A1 were subjected to controlled trypsin digestion, t1/2 of the methylated protein was 1.31 min and the unmethylated, 1.63 min. The difference in their t1/2 values was much greater in the presence of MS2-RNA; 2.4 min for the former and 4.3 min for the latter, indicating that the methylated species was less stabilized by the RNA than the unmethylated. All of the above results consistently suggested that the binding-property of hnRNP protein A1 to single-stranded nucleic acid was significantly reduced subsequent to its arginine-methylation. The biological significance of this observation is discussed.

Purification and characterization of S-adenosylmethionine-protein-arginine N-methyltransferase from rat liver

A protein methylase I (S-adenosylmethionine-protein-arginine N-methyltransferase; EC 2.1.1.23), with a high specificity for recombinant heterogeneous nuclear ribonucleoprotein particle (hnRNP) protein A1, was purified from rat liver. The purification method is simple and rapid; a single initial step of DEAE-cellulose DE-52 chromatography resulted in a 114-fold enrichment from the cytosol, and subsequent Sephadex G-200 chromatography and f.p.l.c. yielded a homogeneous preparation. Ouchterlony double-immunodiffusion analysis indicated that the rat liver enzyme is immunologically different from an analogous enzyme from the calf brain, nuclear protein/histone-specific protein methylase I [Ghosh, Paik and Kim (1988) J. Biol. Chem. 263, 19024-19033; Rajpurohit, Lee, Park, Paik and Kim (1994) J. Biol. Chem. 269, 1075-1082]. The purified enzyme has a molecular mass of 450 kDa on Superose chromatography and 110 kDa on SDS/PAGE, indicating that it is composed of four identical-size subunits. The Km values for protein A1 and S-adenosyl-L-methionine were 0.54 x 10(-6) and 6.3 x 10(-6) M respectively. S-Adenosyl-L-homocysteine and sinefungin were effective inhibitors of the enzyme with Ki values of 8.4 x 10(-6) M and 0.65 x 10(-6) M respectively. Bivalent metal ions such as Zn2+, Mn2+ and Ni2+ were particularly toxic to the enzyme; at 1 mM Zn2+, 99% of the activity was inhibited. In addition, 50% of the enzyme activity was lost by treatment with 0.12 mM p-chloromercuribenzoate, indicating a requirement for a thiol group for enzyme activity. Glycerol, a compound often used to prevent enzyme inactivation, inhibited over 80% of the activity when present in the reaction mixture at a concentration of 20%.

Enzymatic methylation of recombinant heterogeneous nuclear RNP protein A1. Dual substrate specificity for S-adenosylmethionine:histone-arginine N-methyltransferase

We have previously reported the existence of two different molecular species of protein methylase I (S-adenosylmethionine:protein-arginine N-methyltransferase, E.C. 2.1.1.23) in calf brain, one specific for myelin basic protein and the other for histone (Ghosh, S. K., Paik, W. K., and Kim, S. (1988) J. Biol. Chem. 263, 19024-19033). In the present study, however, we report that heterogeneous ribonucleoprotein particle protein A1 is most likely an in vivo substrate for the "histone-specific protein methylase I." The unmethylated recombinant protein A1 has been found to be a much superior methyl acceptor for the enzyme than histone with a Km value two orders of magnitude lower (0.19 microM) than that for histone (21 microM). Myelin basic protein, a specific inhibitor for histone protein methylase I, exhibited a lower IC50 for protein A1 methylation (IC50 = 33 microM) compared with histone methylation (IC50 = 220 microM) and competitively inhibited the former with a Ki value of 1.3 x 10(-6) M. The extent of inhibition of protein A1 and histone methylation by the polyclonal antibodies prepared against purified "histone protein methylase I" was identical. Maximally, 1.08-mol methyl groups were incorporated per mol of protein A1, which was 27-fold higher than that of histone (0.04 mol/mol of histone). HPLC analysis of the enzymatically methylated amino acid residues in protein A1 revealed the formation of NG-monomethylarginine and NG,NG-dimethylarginine. The ratio of NG,NG-dimethylarginine/NG-monomethylarginine increased as a function of incubation period; however, NG,N'G-dimethylarginine was not detectable. Proteolytic cleavage of the methyl-3H-labeled recombinant protein A1 by trypsin and Staphylococcus aureus V8 endoprotease indicated that protein A1 possesses multiple sites for methylation, one of which was identified as residue 194 arginine, which coincided with the in vivo methylation site.

Enzymatic methylation of heterogeneous nuclear ribonucleoprotein in isolated liver nuclei

Protein N-methyltransferase activity has been studied in the rat liver nuclei, using recombinant heterogeneous nuclear ribonucleoprotein particle protein A1 and histone as the methyl acceptors. The hydrolysates of these two enzymatically [methyl-3H]-labeled proteins, however, yielded different patterns of methylated amino acids on HPLC analysis: NG-monomethylarginine (92%) and NG-NG-dimethyl (asymmetric) arginine (6.5%) were the major methylated amino acids identified in the protein A1, whereas epsilon-N-methylated lysine derivatives constituted a predominant portion (71%) of the methylated amino acids in histone. When liver extracts isolated from rats fed a methyl deficient diet were assayed, the methyl accepting activity of protein A1 increased 64% over the control (rats fed normal diet), while that of histone increased 260%. Partial hepatectomy induced a 7.9-fold and 2.3-fold increase in the protein A1 methylase activity after 24 and 48 h of regeneration, respectively. These results, together with the fact that myelin basic protein-specific protein methylase I does not significantly methylate protein A1, indicate the presence of an enzyme in the rat liver nuclei which methylates the protein A1.

In vivo and in vitro methylation of lysine residues of Euglena gracilis histone H1

We have earlier identified and purified two protein-lysine N-methyltransferases (Protein methylase III) from Euglena gracilis [J. Biol. Chem., 260, 7114 (1985)]. The enzymes were highly specific toward histone H1 (lysine-rich), and the enzymatic products were identified as epsilon-N-mono-, di- and trimethyllysines. These earlier studies, however, were carried out with rat liver histone H1 as the in vitro substrate. Presently, histone H1 has been purified from Euglena gracilis through Bio-Rex 70 and Bio-Gel P-100 column chromatography. The Euglena histone H1 showed a single band on SDS-polyacrylamide gel electrophoresis and behaved like other histone H1 of higher animals, whereas it had a much higher Rf value than the other histones H1 in acid/urea gel electrophoresis. When the Euglena histone H1 was [methyl-3H]-labeled in vitro by a homologous enzyme (one of the two Euglena protein methylase III) and analyzed on two-dimensional gel electrophoresis, three distinctive subtypes of histone H1 were shown to be radiolabeled, whereas five subtypes of rat liver histone H1 were found to be labeled. Finally, by the combined use of a strong cation exchange and reversed-phase Resolve C18 columns on HPLC, we demonstrated that Euglena histone H1 contains approximately 9 mol% of epsilon-N-methyllysines (1.40, 1.66, and 5.62 mol% for epsilon-N-mono-, di- and trimethyllysines, respectively). This is the first demonstration of the natural occurrence of epsilon-N-methyllysines in histone H1.

Food restriction and short-term effects of aflatoxin B1 feeding on putative preneoplastic biochemical markers

The susceptibility of experimental rats to Aflatoxin B1, a well known hepatocarcinogen, during chronic food restriction was studied, using a few putative preneoplastic biochemical markers. Gamma-Glutamyl transpeptidase was the most sensitive among the various enzymes studied, at the dose of 10 micrograms/day/100 gm body weight of Aflatoxin B1 fed over a period of three weeks after a twelve chronic food restriction in experimental rats. It was significantly elevated in the underfed untreated group, thus suggesting that preneoplastic changes may be precipitated during chronic undernutrition and carcinogen exposure.

Differences in response of glucuronide and glutathione conjugating enzymes to aflatoxin B1 and N-acetylaminofluorene in underfed rats

Changes in the hepatic drug/xenobiotic-metabolizing enzymes in underfed rats exposed to aflatoxin B1 and N-acetylaminofluorene were investigated. Neither carcinogen, fed at the level of 10 micrograms and 0.667 mg per 100 g body weight, respectively, over a period of 3 wk, had any significant influence on cytochrome P-450 and aryl hydrocarbon hydroxylase in the undernourished rats. Significantly low activities of UDP-glucuronyltransferase and glutathione S-transferase were observed in food-restricted animals fed on aflatoxin B1. N-acetylaminofluorene, on the other hand stimulated both the enzyme activities in the underfed group, to as much observed in the respective well-fed treated group. UDP-Glucuronyltransferase and glutathione S-transferase in undernutrition seem to respond differently to aflatoxin B1 and N-acetylaminofluorene. Further studies are needed to assess the possible consequences of such alterations.

Hepatic drug metabolising enzymes in undernourished men

The influence of the nutritional status of the individual on the hepatic drug metabolising enzymes in human wedge-biopsy liver samples was investigated. The aryl hydrocarbon hydroxylase (AHH) was found to be elevated although there was no change in the cytochrome P-450 levels in the undernourished groups. Conjugating enzymes viz. UDP glucuronyl transferase (UDPGT) and glutathione-S-transferase (GST) were not found to be different. The increase in AHH activity as compared to UDPGT and GST activities suggests that the activation processes may possibly be increased in the undernourished segment of the population.