Synthetic gel of carotid artery plaque.

Atherosclerosis is a complex disease that affects medium and large arteries, leading to the formation and progression of plaque. In this process the proteins play an essential role and as a consequence, proteomic-based strategies examining the protein content of cells or tissues could offer a useful approach for the study of plaque proteins. Due to the heterogeneous cell composition of plaque, proteome analysis of whole lesions is difficult, besides being also complicated by the presence of plasma proteins that cannot be completely eliminated. A good way to study variations in protein expression among series of gels is to construct a synthetic gel. This type of gel is obtained by averaging the positions, shapes and optical densities of spots in a given set of gels. To be included in the synthetic gel, spots must be found in at least three gels. To obtain a profile representative of the proteome of atherosclerotic plaque, cancelling its high variability, we constructed a synthetic gel using an average of ten carotid plaque samples. We then compared it with an equivalent synthetic gel constructed using ten plasma samples from the same carotid surgery patients. For the comparison of two synthetic gels (plasma/plaque) we could discriminate plasma proteins from plaque proteins. Besides analysis of spots common to plasma, the synthetic gel is useful to detect spots exclusive to plaque, thus simplifying a very complex mixture.

Nitric oxide generation is associated with an unbalance of protein tyrosine phosphatases during liver transplantation.

Organ dysfunction secondary to ischemia-reperfusion (I/R) injury still represents a major problem in liver transplantation. Apoptosis has been observed in hepatocytes and sinusoidal endothelial cell, following I/R injury and it has been postulated as a contributing factor in ischemia-reperfusion graft dysfunction, involving a complex series of events, as changes of protein tyrosine-kinase phosphorylation. We evaluated hepatic purine metabolites, protein tyrosine phosphatases (PTPs), nitrate plus nitrite levels (NOx), caspase-3 (C-3) activity and DNA fragmentation in the time course of twelve pig orthotopic liver transplantation. Biopsies were taken before explantation (t0), after cold ischemic storage (t1) and 30 min from reperfusion (t2). During the ischemic period we observed a reduction of high energy phosphates and an increase of purine bases; PTP activity was largely increased. At t2 high energy phosphates showed a tendency to increase with respect to t1, with a partial restoration of phosphorylation potential, measured as ATP/ADT ratio. PTP activity was significantly reduced, with a concomitant increase of NOx production and C-3 activity; in a considerable number of cases we observed a sustained DNA fragmentation. We speculate that NOx production could be related to nitrosative stress, which in turn leads to dynamic alteration in PTP balance and cell signalling, regulating the activity of a number of proteins implicated in apoptotic cell death. These findings could be of interest in new potential strategy to prevent and treat I/R injury.

Circulating gastrin and ghrelin levels in patients with colorectal cancer: correlation with tumour stage, Helicobacter pylori infection and BMI.

Many studies have pointed out a possible role of gut peptides, including gastrin and ghrelin, in the pathogenesis and natural history of gastrointestinal malignancies, one of the most common death cause in the Western world. The objective of this work is to check gastrin and ghrelin serum levels in patients with colorectal cancer according to tumour's location, stage, Helicobacter pylori infection and BMI, in order to understand the two peptides' behaviour through the tumour's natural history and evaluate their assay's use in research and clinical practice. Twenty-nine subjects affected by colorectal cancer and 50 healthy controls were studied. Circulating gastrin and ghrelin levels and H. pylori serum antibodies were assessed by radioimmunologic assay and ELISA method. Gastrin and ghrelin serum levels were respectively slightly higher and significantly lower in colon cancer patients than in controls. Gastrin levels were higher in patients carrying left colon cancer and H. pylori infection while ghrelin levels were lower in both these groups. Both hormones' serum levels decreased from tumour earlier to later stages. Significant differences persisted in the correlation between BMI and ghrelin levels in controls but not in patients. Additional studies are necessary to ascertain the significance of gastrin and ghrelin opposite behaviour in colon cancer probably linked with interferences in endocrine pathways involving other gut peptides in this compromised condition.

Adenosine kinase from rat liver: new biochemical properties.

Adenosine kinase is a well-known enzyme which catalyzes the phosphorylation of adenosine to AMP: Its metabolic and kinetic properties are well studied. Here, we report new properties of rat liver enzyme, demonstrating a new reaction: ADP can be a phosphate donor instead ATP, according to the reaction: adenosine + ADP --> 2AMP) demonstrating the efficiency of AdK to phosphorylate adenosine, also starting from ADP. Cells could exploited this property in situations in which ATP levels are strongly decreased and ADP decreases slowly.

Purine metabolism in B-cell lymphocytic leukemia: a microarray approach.

B-cell chronic lymphocytic leukemia (B-CLL) is an adult-onset highly heterogeneous malignancy characterized by a cells resistance to apoptosis rather than to highly proliferative cells. In previous research, we evidenced an imbalance of purine metabolism in B-CLL cells. Since the extracellular adenosine has been proved to induce apoptosis via A2b receptor, enzymes involved in adenosine metabolism could play an important role in apoptosis resistance of B-CLL cells. We prepared a microarray chip for the analysis of 50 selected genes that could be of interest in B-CLL: enzymes of purine de-novo, salvage and catabolic pathway, oxidative stress enzymes, and apoptotis-related proteins. Preliminary results identify many genes of purine metabolism that exhibit low or high expression, while genes involved in signal transduction and apoptosis exhibit lower alterations even if of remarkable interest. This application of microarray technique seems promising and at least a subset of these genes will be valid candidates for further studies.

Purine catabolism in advanced carotid artery plaque.

This study was carried out on carotid artery plaque and plasma of 50 patients. We analyzed uric acid, hypoxanthine, xanthine, and allantoin levels to verify if enzymatic purine degradation occurs in advanced carotid plaque; we also determined free radicals and sulphydryl groups to check if there is a correlation between oxidant status and purine catabolism. Comparing plaque and plasma we found higher levels of free radicals, hypoxanthine, xanthine, and a decrease of some oxidant protectors, such as sulphydryl groups and uric acid, in plaque. We also observed a very important phenomenon in plaque, the presence of allantoin due to chemical oxidation of uric acid, since humans do not have the enzyme uricase. The hypothetical elevated activity of xanthine oxidase in atherosclerosis could be reduced by specific therapies using its inhibitors, such as oxypurinol or allopurinol.

[Evaluation of ambulatory medical care in Milan]. / Analisi del consumo di prestazioni ambulatoriali nella città di Milano.

Ambulatory procedures are an essential component of health care both for their number and for their cost. We aim therefore to identify and to quantify the volume of ambulatory procedures performed in Milan during 2003. The data come from the Outpatient Care Information Report that collect much information by characteristics of patient, health care institution and procedure categories. The analyses in this report are based on absolute measures, utilization rates and concentration index. During the year 2003 nearly 20 millions of ambulatory procedures were performed in the public and private outpatient facilities of Milan for the resident population. The average annual rate was 15 procedures per person. Utilization varied according to patient age and sex, higher in women and in the elderly group, statistically significant variability is observed (p<0.001). Outpatient care accounts for high density supply (124 specialty points for 100,000 inhabitants). Utilization rate was not homogenous both for the medical specialties and for the geographical district distribution, all that, it seems depending on the activity concentration differences and complexity supply of services than on a different distribution of health needs. This analysis may be useful as methodological starting point for further investigating current outpatient care data and for identifying those sectors in need of corrective actions.

Effect of testosterone on purine synthesis de novo in rat perineal muscle in vivo.

We examined in vivo the influence of testosterone on purine synthesis de novo, in the levator ani and gastrocnemius muscles of the rat. The hypoxanthine, adenine and guanine contents and the rate of incorporation of [14C]formate into these purine bases were determined in castrated adult and prepubertal rats (groups 1 and 2) both before and after orchiectomy and, in the second case, at different times after testosterone treatment. Substantially similar behavior was found in both groups, with some specific differences. The results showed an increase in the basal levels after castration (except for a dramatic decrease in adenine and a rise in the Gua/Ade molar ratio in prepubertal rats) and a return to basal levels after hormone administration, which was also accompanied by variations in the Gua/Ade molar ratio. The kinetics of purine nucleotide synthesis de novo in vivo and, specifically, of the overall reactions: IMP formation from PRib-PP, IMP----AMP and IMP----GMP, were followed by evaluating the incorporation curves of [14C]formate into hypoxanthine, adenine and guanine. Our results show that testosterone administration enhanced the incorporation rate and gave characteristic patterns: a diphasic cyclic oscillation of the Ade values in adult castrated rats, and single peaks having a specific shape in the other cases. The Gua/Ade labeling ratio was unchanged in castrated rats and increased in both groups during the first 5 days after testosterone treatment, after which values even fell below normal; in most cases, values overlapped the pattern of the Gua/Ade molar ratio. The specific profile of the curves indicated that testosterone initially accelerated the turnover of guanylic acid and in the second phase re-established the normal behavior and ratio of AMP and GMP formation. These results indicate that the 'inosinic branch point' was subject to regulation by testosterone. The profiles of the incorporation curves and of the Gua/Ade ratio were indicative of a primary and secondary response to hormone action.

Double inhibition of L-threonine dehydratase by aminothiols.

The inhibition of highly purified rat liver L-threonine dehydratase (L-threonine hydro-lyase (deaminating), EC 4.2.1.16) by aminothiols (L-cysteine, D-cysteine, cysteamine) has been studied. Single inhibition experiments evaluated by Lineweaver-Burk and Dixon plots showed, in a given concentration range, partially (parabolic) competitive inhibitions, indicating two binding sites for each inhibitor. Double inhibition experiments revealed that the inhibition was antagonistic, the two inhibitors weakening each other's effect. Formation of EI1 and EI2 binary complexes, and ESI1, ESI2 and EI1I2 ternary complexes was demonstrated, while formation of the quaternary complex ESI1I2 was ruled out. It is assumed that one inhibitor-binding site coincides with the substrate-binding center while the second inhibitor-binding (allosteric, regulatory) site may comprise the pyridoxal-phosphate-binding SH group(s). The comparison between Km and Ki values and the evaluation of intracellular concentrations of L-threonine, L-cysteine and cysteamine suggest a possible physiological role of the inhibition.

Synthesis of adenine and guanine nucleotides at the 'inosinic branch point' in lymphocytes of leukemia patients.

The synthesis of purine nucleotides has been studied in human peripheral blood lymphocytes from healthy subjects and patients affected by B-cell chronic lymphocytic leukemia (B-CLL). The rate of the synthesis was measured by following the incorporation of 14C-formate into the nucleotides of lymphocyte suspensions. The whole sequence AMP-->ADP-->ATP was found reduced in B-CLL lymphocytes; in the case of guanylates only the last step of the sequence GMP-->GDP-->GTP was significantly lower in the same cells. From the analysis of these results, combined with previous data, we conclude that purine metabolism undergoes an imbalancement during CLL, which is partially compensated, and point out the importance of studying concomitantly purine metabolism and nucleic acid synthesis in leukemia cells.

Behavior of L-threonine-degrading enzymes during liver regeneration.

We examined the effects of a two-thirds hepatectomy in the adult rat on the activities of the three L-threonine-degrading enzymes, L-threonine dehydratase, L-threonine aldolase and L-threonine dehydrogenase. Noticeable variations were observed which did not occur in either sham-operated or turpentine-treated rats and were not linked to food intake. They were considered specific to the regenerating liver. When the reactions were followed in vitro, L-threonine deaminase and L-threonine aldolase were significantly lower for the first 12-24 h: L-threonine dehydrogenase decreased only after 48 h. These results are linked to a decrease in the enzyme concentration in the tissue. L-Serine and L-threonine liver concentrations increased 2-3-fold during the same periods. When the activities were evaluated in vivo, the levels of the first two enzymes remained constant for 24 h, but increased after 48 h; L-threonine dehydrogenase increased between 12 and 48 h. The in vivo activity of the enzymes was reflected by total L-threonine degradation, which had a single sharp peak at 48 h. The asynchronous variations in enzyme activity are related to the differences in protein metabolism which occur in the regenerating liver, and are the consequence of a new transient differential control. The changes observed are significant in liver regeneration; they regulate the consumption and the serum and liver levels of L-serine and L-threonine, setting them aside for protein synthesis. They minutely control the flux of amino acids toward gluconeogenesis, since, during the first 48 h after partial hepatectomy, the production of glucose is ensured principally by lactate; the contribution of L-threonine seems to be more significant only at 48 h. These findings are useful in the study of the regulation of the enzymes involved in amino acid metabolism during liver regeneration.

The regulation of alanine and aspartate aminotransferase by different aminothiols and by vitamin B-6 derivatives.

We examined the effects on alanine aminotransferase and aspartate aminotransferase of different aminothiols (L-cysteine, D-cysteine, cysteamine, L-cysteine ethyl ester, L-cysteine methyl ester) and several vitamin B-6 derivatives (pyridoxal, pyridoxamine, pyridoxol, pyridoxol 5'-phosphate), before and after treatment with KOCN, which transforms these molecules into the corresponding carbamoyl derivatives. Only GPT, and not GOT, was specifically inhibited by L-cysteine and, to a lesser extent, by D-cysteine. The association reaction: PLP + apo GPT<-->holo GPT was inhibited by the vitamin B-6 derivatives, and this inhibition was prevented by pretreatment of the vitamin B-6 derivatives with KOCN. All the observed effects occurred at pH 7, 37 degrees C, at mM and even lower concentrations of reagents. Hence, they all potentially play a physiological role, in the regulation of the PLP dependent enzymes and of the vitamin B-6 levels in the cell.

The inhibition of rat liver threonine dehydratase by carbamoyl-phosphate. The formation of carbamoylpyridoxal 5'-phosphate.

The effects exerted by carbamoyl phosphate (CP) and cyanate (KCNO) on rat liver L-threonine deaminase have been studied. The two compounds showed that same effects, inhibiting through a competitive mechanism both the holoenzyme and the dialyzed enzyme; inhibition was more evident for the latter. Ki values, both for L-threonine and pyridoxal 5'-phosphate (PLP), were lower for the apoenzyme and the inhibitors also affected the Km of the apoenzyme for PLP. The effects of CP and KCNO are mainly due to an interference in the association reaction apoenzyme + PLP in equilibrium holoenzyme This was clearly demonstrated by the fact that, when PLP was incubated with CP or KCNO, it failed to enhance the activity of the holoenzyme nor did it reactivate the resolved apoenzyme. Such interference of CP and KCNO in the L-threonine deaminase activity was mainly due to a specific mechanism, the formation of a new derivative of PLP. The reaction of PLP with either CP or KCNO occurred readily, at low concentrations, under physiological conditions. The new compound was identified as 3,4-dihydro-2H-pyrido[3,4-e]1,3-oxazin-2-one derivative by ultraviolet-visible spectra, elemental analysis, infrared, NMR and MS spectra. In this paper we formulate the hypothesis that this compound is involved in the regulation of the CP and PLP intracellular content and in the control of PLP dependent enzymes.

Purine nucleotide metabolism: specific aspects in chronic lymphocytic leukemia lymphocytes.

The metabolism of purine nucleotides was studied in human peripheral blood lymphocytes from healthy subjects and patients with B-cell chronic lymphocytic leukemia. Nucleotide content was determined by HPLC. The rate of de novo synthesis of purine nucleotides was measured kinetically by following the incorporation of 14C-formate into the nucleotides of a lymphocyte suspension. The patterns of the main enzymes involved in purine nucleotide metabolism (those of the salvage pathway and catabolism) were estimated by a radiochemical method. Although the data expressed in relation to cells and protein showed some discrepancies, several common differences were evident in both cases. The main differences were an increase in NAD and IMP, a sharp decrease in 5'-nucleotidase activities and in total guanylate content and synthesis, and an increase in the A/G ratio in lymphocytes of patients with respect to controls. The changes in these parameters in CLL indicate an imbalance in purine metabolism and may play a specific role in the biology of the leukemia cell. They are also potential biochemical markers of lymphoid malignancies and may be useful in chemotherapic applications.

Identification of a mitochondrial inhibitor of rat liver L-threonine dehydrogenase.

In a previous paper, we showed inhibition of rat liver L-threonine dehydrogenase by a preparation obtained by dialysis and concentration from rat liver mitochondria stored at -20 degrees C for 7-10 days (Pagani, R., Leoncini, R., Guerranti, R. and Marinello, E. (1990) It. J. Biochem. 39, 106-114). The chemical composition of the fraction containing the unknown 'inhibitor' has now been studied and identified as D-3-hydroxybutyrate (D3HB).

Quantitative separation of uric acid and allantoin from rat liver tissue.

A simple procedure is described for the assay of liver uric acid and allantoin and their specific radioactivity after administration of a radioactive precursor. Uric acid was quantified by the uricase reaction in liver trichloroacetic acid (TCA) extracts. The 'true' allantoin content of the liver could be estimated only after precipitation with Hg-acetate, a step by which the standard allantoin was also quantitatively recovered. Crude extracts lead to the evaluation of 'apparent' allantoin. For the determination of specific radioactivity, the Hg-acetate precipitate was further purified by ion-exchange chromatography. The purity of the two metabolites was confirmed by ultraviolet absorbance spectra, HPLC, constancy of specific radioactivity and the absence of amino acids. The incorporation of [14C]formate into uric acid and allantoin in the liver was studied by this procedure. The radioactivity in allantoin was several-fold higher than that in uric acid up to 60 min after administration of the precursor. This quite unexpected result is not easily explained on the basis of current knowledge.

Restoration of rat liver L-threonine dehydratase activity by pyridoxamine 5'-phosphate: the half-transaminating activity of L-threonine dehydratase and its regulatory role.

When a highly purified preparation of rat liver l-threonine deaminase (l-TDH, EC 4.2.1.16) was 99% inactivated by dialysis, removing bound pyridoxal 5'-phosphate (PLP), the apoenzyme was reactivated not only by PLP but also by pyridoxamine 5'-phosphate (PMP). When purified by HPLC, the commercial PMP used in the incubation mixture was found to contain only extremely small amounts of PLP, which could not account for restoration of l-threonine dehydratase activity. HPLC analysis of the assay mixtures showed that during incubation, sufficient PLP had been formed for reactivation of the apoenzyme. The apoenzyme evidently bound PMP and triggered transamination between PMP and the keto acids, which either contaminated, or were formed by the minimal amount of PLP-holoenzyme always present even in the dialyzed preparation. When sufficient PLP was formed, the PLP-holoenzyme and the original 'true' l-threonine dehydratase activity were restored. When PMP was incubated with the apoenzyme in the presence of small quantities of keto acids (pyruvate or 2-oxobutyrate) small amounts of l-alanine or l-aminobutyrate were formed. The reaction was not reversible; l-alanine and l-aminobutyrate did not react with the PLP-holoenzyme. No transaminating activity occurred with other amino acids. These results show that l-threonine dehydratase exists in two forms: the well known stable apoenzyme-PLP (hydrolase deaminating) and the transient apoenzyme-PMP (non-reversible half-transaminating). Half-transamination has the biological role of keeping the activity of the 'true' l-TDH constant and of regulating intracellular levels of pyruvate, alanine, oxobutyric acid, l-aminobutyric acid, l-threonine and l-serine.

Inhibition and regulation of rat liver L-threonine dehydrogenase by different fatty acids and their derivatives.

Rat liver L-threonine dehydrogenase is a mitochondrial enzyme which transforms L-threonine either into aminoacetone or into acetyl-CoA. We show that it is inhibited by several fatty acids and their derivatives: short chain fatty acids, L-2-hydroxybutyrate and D-3-hydroxybutyrate, long chain fatty acids, such as lauric acid, myristic acid, palmitic and stearic acids, bicarboxylic acids such as malonic acid and its derivatives methyl- and hydroxymalonic acids. The inhibition occurs at low and physiological concentrations of such compounds, which are normally present and metabolized in mitochondria. It presumably plays a role in the physiology of acetyl-CoA-dependent formation of fatty acids and ketobodies, in L-threonine-dependent gluconeogenesis, and in the regulation of L-threonine metabolism by L-threonine dehydrogenase and L-threonine deaminase.

Nitrogen metabolism during liver regeneration.

Nitrogen metabolism was investigated in regenerating liver-bearing rats through the following parameters: (1) liver aminoacid content, (2) plasma and urinary urea and creatinine, (3) plasma and urinary oxypurines, uric acid and allantoin. Two groups of aminoacids were considered: (1) the essential aminoacids (phenylalanine, tyrosine, isoleucine, lysine, leucine, valine, arginine, histidine and methionine); (2) the non-essential aminoacids (aspartic acid, asparagine, glutamic acid, glutamine, alanine, glycine, serine, threonine and proline). Some of the first group tended to decrease, and those of the second group to increase, immediately after partial hepatectomy. Few ketogenic aminoacids are probably oxidized to provide energy. The flux of aminoacids for gluconeogenesis is minutely controlled, therefore, those of the second group being spared at first and set aside for protein synthesis, which increases on the second and third days after partial hepatectomy. Plasma and urinary urea, oxypurines, uric acid and allantoin did not show any significant variations after partial hepatectomy. The conclusion emerging from the present research is that, although variations in aminoacid composition and metabolism and in purine nucleotide metabolism have been demonstrated to occur in the regenerating liver, the overall nitrogen catabolism, as reflected by the principal end products, does not undergo substantial variations. The remaining liver is able to fulfil this function.

The behavior of free purine nucleotides in lymphocytes infected with HIV-1 virus.

The purine nucleotide content was examined in various cells before and after HIV-1 virus infection: healthy peripheral blood lymphocytes (PBL) and cultured PBL after infection; the PBL of asymptomatic, ARC and AIDS patients. In all cases, changes in purine nucleotide concentrations were observed. The pattern of purine nucleosides and nucleobases was also evaluated by HPLC in PBL of controls and patients. The analysis was integrated by following the incorporation of a labelled precursor ([14C]formate) into purine nucleotides, which was investigated as an indication of the rate of purine metabolism in these cells. Many interesting variations in the catabolic and of anabolic pathways were observed, demonstrating that the viral penetration affects purine nucleotide metabolism. These results suggest interesting perspectives in AIDS research.