Search PubMed⌕ Search

Biomedical subjects

R Martini

Publications and source records attributed to R Martini.

At least 91 records · Page 5Linked to original sources
PubMed1995

Pretranslational down regulation of cytochrome P450 2C11 in vitamin A-deficient male rat liver: prevention by dietary inclusion of retinoic acid.

Manipulation of vitamin A intake has been associated with altered rates of cytochrome P450 (P450)-mediated microsomal drug oxidation. Dietary vitamin A deficiency reportedly results in decreased rates of P450-dependent substrate oxidation, but the mechanisms underlying these changes remain unclear. In this study, the effects of dietary vitamin A modulation, as well as dietary inclusion of all-trans-retinoic acid (ATRA), on major constitutive P450s were defined. Total microsomal P450 in deficient male rats was decreased to 72% of control (0.63 +/- 0.07 vs. 0.88 +/- 0.08 nmol/mg of protein; P < .05); this was prevented by inclusion of ATRA (12 micrograms/g) in the deficient diet. Dietary vitamin A deficiency decreased rates of P450 2C11-mediated testosterone 2 alpha- and 16 alpha-hydroxylation in rat liver to 44 and 47% of respective adequate control, whereas rates of 6 beta- and 7 alpha-hydroxylation of the steroid were unaltered; inclusion of ATRA into the deficient diet prevented the loss of 2C11 activities. Immunoblot and RNA analysis revealed decreases in P450 2C11 apoprotein and its corresponding mRNA in liver from deficient rats that was prevented by inclusion of ATRA in the deficient diet. Serum testosterone concentrations were reduced in deficient rats and this also was prevented by dietary ATRA. To discern whether this was a direct effect of vitamin A on P450 2C11 regulation, further experiments evaluated the effect of ATRA administration to male rats maintained on standard rat chow (vitamin A-adequate). Dose- and time-dependent decreases in P450 2C11 activity were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

The L2/HNK-1 carbohydrate is carried by the myelin associated glycoprotein and sulphated glucuronyl glycolipids in muscle but not cutaneous nerves of adult mice.

We have previously shown that myelinating Schwann cells associated with motor, but not sensory, axons in peripheral nerves of adult mice express the L2/HNK-1 carbohydrate epitope. This carbohydrate structure carried by glycolipids and neural cell adhesion molecules has been suggested to specifically foster regrowth of motor as opposed to sensory axons after infliction of a lesion. To determine which molecular components may be the carriers of the L2 carbohydrate in motor axon-associated myelinating Schwann cells, we have isolated the purely sensory, cutaneous branch and the mixed sensory and motor muscle branch of the femoral nerve of adult mice, isolated the myelin fraction thereof and analysed the molecules expressing the L2 carbohydrate by several immunochemical methods. L2 immunoreactivity in myelin of the muscle branch was four to five times higher than that of the cutaneous branch. The 110 kDa L2-immunoreactive glycoprotein in myelin of the muscle branch, which is not L2-immunoreactive in the cutaneous branch, was identified as the myelin-associated glycoprotein by a combination of immunoprecipitation and Western blot analysis. Myelin extraction with organic solvents additionally revealed the two L2-carrying glycolipids, which amounted to approximately 40 ng glycolipid/mg dry weight in myelin of the muscle branch, whereas no significant amounts of the L2 glycolipids were found in myelin of the cutaneous branch. These observations suggest an astonishing degree of differential regulation of carbohydratesynthesizing activities in myelinating Schwann cells.

Animals↗
PubMed1994

Suppression of the constitutive microsomal cytochrome P450 2C11 in male rat liver during dietary vitamin A deficiency.

The effect of dietary vitamin A deficiency on hepatic microsomal cytochrome P450 (P450) and associated oxidase activities was examined in the male rat. Intake of a deficient diet by weanling rats over 10 weeks led to a pronounced decline in hepatic and serum vitamin A concentrations to levels that were beneath the limits of detection. These changes occurred concurrently with a decrease in total microsomal P450 to 77% of vitamin A adequate control. Measurement of microsomal androstenedione metabolism revealed respective decreases in 16 alpha- and 6 beta-hydroxylation pathways to 61 and 71% of adequate control; 7 alpha-hydroxylation was not significantly decreased. Immunoquantitation of the principal catalyst of steroid 16 alpha-hydroxylation, the androgen-dependent P450 2C11, indicated a significant decrease in the microsomal content of the enzyme to 78% of control (13.7 +/- 0.9 ng/micrograms protein in deficient rat liver versus 17.5 +/- 0.5 in adequate control; P < 0.005). Serum testosterone appeared lower in vitamin A deficient male rats, but did not attain statistical significance. Administration of a diet containing excess vitamin A (500 IU/g) to rats for 10 weeks produced marked increases in hepatic vitamin A stores, but did not increase P450 2C11 activities. Thus, the expression and function of P450 2C11 is not related directly to hepatic vitamin A levels. The trend toward lower circulating androgen levels in male rats maintained on the deficient diet for 10 weeks may have a role in P450 2C11 down regulation, but other regulatory factors may also be disrupted in these animals.

Androstenedione↗
PubMed1994

Inhibition of microsomal 17 beta-hydroxysteroid oxidoreduction activities in rat liver by all-trans-, 9-cis- and 13-cis-retinoic acid.

Retinoids and steroid hormones mediate their biological effects through nuclear receptors. However, retinoids may alter the intracellular availability of ligands for steroid receptor activation by modulating the activity of biotransformation enzymes. This study investigated the modulation of NAD(H)-linked steroid oxidoreductases in rat hepatic microsomes by retinoids. 13-cis-Retinoic acid inhibited testosterone 17 beta-dehydrogenation (Ki 2.4 +/- 0.5 microM; Km/Ki ratio 0.34 +/- 0.06) but androstenedione reduction was less susceptible to inhibition (Ki 27 +/- 13 microM; Km/Ki ratio 0.045 +/- 0.12). All-trans-retinoic acid was less potent than the 13-cis-isomer and 9-cis-retinoic acid was of intermediate potency. In vivo administration of all-trans-retinoic acid (60 mg/kg i.p. for 7 days) decreased hepatic microsomal oxidoreduction activity, but exposure over shorter periods and 13-cis-retinoic acid were without effect. Thus, all-trans-retinoic acid elicits direct inhibition and may also alter the normal regulation of the oxidoreductase under certain conditions. Three geometric isomers of retinal were potent inhibitors of testosterone dehydrogenation (IC50s approximately 6 microM), but were ineffective against androstenedione reduction. These findings suggest that certain anti-hormonal effects of retinoids may be attributable in part to modulation of endobiotic biotransformation prior to receptor binding and activation.

17-Hydroxysteroid Dehydrogenases↗
PubMed1994

Retinal dehydrogenation and retinoic acid 4-hydroxylation in rat hepatic microsomes: developmental studies and effect of foreign compounds on the activities.

All-trans-retinoic acid (RA) regulates the transcription of a number of mammalian genes and is therefore important in the control of many cellular processes. RA is formed and deactivated within the cell so that biotransformation modulates RA availability. This study investigate the relationship between the formation of RA from retinal and its metabolism by 4-hydroxylation in rat hepatic microsomes. From kinetic studies the Michaelis constants for RA formation and 4-hydroxylation were 52 and 24 microM, respectively, and the maximal reaction velocities were 33 and 136 pmol/min/mg protein, respectively. Thus, 4-hydroxylation was the more efficient process. In microsomes from 1-week-old rats, RA formation was very low (approximately 2 pmol/min/mg protein) but was several-fold greater in adults of both sexes (approximately 10 pmol/min/mg protein). In contrast, 4-hydroxylation was quantitatively more significant at all ages examined between 1 and 15 weeks; by 10 and 15 weeks a sexual dimorphism was apparent (M > F). Thus, the ratio of RA 4-hydroxylation to RA formation was comparatively large in microsomes from 1-week-old rats and declined to a stable value around 4-6 weeks of age. With the exception of dexamethasone, which decreased the activity, administration of foreign compounds to male rats had little effect on RA formation. Both dexamethasone and phenobarbital induced RA 4-hydroxylation but DMSO and beta-naphthoflavone were without effect. From these findings, 4-hydroxylation, particularly in very young animals, may be an effective means of controlling RA production. RA 4-hydroxylation, like other cytochrome P450 activities, was inducible in rat liver but no evidence was found for induction of the microsomal retinal dehydrogenase.

Aging↗
PubMed1994

Restricted localization of L1 and N-CAM at sites of contact between Schwann cells and neurites in culture.

Schwann cell-axon contacts in developing and regenerating peripheral nerve in situ contain high levels of the recognition molecules L1 and N-CAM, while the molecules are not detectable at the ab-axonal cell surface of Schwann cells. To investigate whether Schwann cells, axons, or both contribute to the localization of the molecules at Schwann cell-axon contacts, a heterologous cell culture system consisting of Schwann cells from mice and neurons from chicken was investigated by immunoelectron microscopy using species-specific L1 and N-CAM antibodies. We showed that Schwann cells expressed both molecules only at sites of contact between Schwann cells and neurites and other Schwann cells. Schwann cells not in contact with other cells expressed both molecules on their entire cell surface. In contrast, neurites expressed G4, an L1-related molecule in chicken, on their entire cell surface independently of whether they were in contact with other cells or not. Thus, cultured Schwann cells localize L1 and N-CAM selectively at cell contact sites and may thereby stabilize their attachment to the neighboring cellular partners.

Animals↗
PubMed1994

Myelin-associated glycoprotein is not detectable in perikaryal myelin of spiral ganglion neurons of adult mice.

The expression of the adhesion molecules N-CAM (neural cell adhesion molecule), L1, myelin-associated glycoprotein (MAG), and P0 has been investigated by postembedding-immunoelectron microscopy in spiral ganglia of adult mice in which both axons and neuronal cell bodies are myelinated. L1 was absent from both axonal and perikaryal myelin of spiral ganglion neurons but was expressed on unmyelinated nerve fibers. P0 was expressed in compacted parts of both types of myelin but was absent from non-compacted myelin. MAG was not detectable in perikaryal myelin but was strongly expressed in axonal myelin both periaxonally and in non-compacted regions. Conversely, N-CAM was detectable at the interface between myelin and neuronal perikarya and in non-compacted regions of perikaryal myelin, whereas it was hardly detectable in axonal myelin. This inverse expression of MAG and N-CAM in perikaryal and axonal myelin points to the possibility that N-CAM may functionally replace MAG in perikaryal myelin of spiral ganglion neurons.

Animals↗
PubMed1994

Expression and functional roles of neural cell surface molecules and extracellular matrix components during development and regeneration of peripheral nerves.

By combining both immunocytochemical and functional investigations, a hypothetical framework will be developed for the molecular mechanisms underlying neuron-glia interactions during development and regeneration of peripheral nerves. In particular, the immunoglobulin-like molecules L1, N-CAM, MAG and P0, the extracellular matrix molecules laminin and tenascin, and the carbohydrates PSA and L2/HNK-1 will be considered. During early stages of limb bud innervation in embryos, L1 and N-CAM are expressed on axons and Schwann cells and are involved in axonal fasciculation, whereas tenascin is thought to be involved in forming a scaffold around the nerve possibly preventing axons and/or Schwann cells from leaving the nerve. PSA has been shown to be involved in pathway selection at initial stages of limb bud innervation. Later on, when motor axons enter muscles, the carbohydrates determine the branching pattern of the nerves. During myelination, L1 appears to play a pivotal role during the formation of the first Schwann cell loops around the prospective myelin-containing axons. MAG and P0 appear also to be functionally involved at initial stages of myelin formation. Additionally, MAG may contribute to the formation and maintenance of non-compacted myelin and axon-Schwann cell apposition whereas P0 is involved in myelin compaction. Under regenerative conditions, L1, N-CAM, laminin, and tenascin are strongly up-regulated by denervated Schwann cells. In vitro observations strongly suggest that these molecules might foster axonal regeneration. The carbohydrate PSA is confined to regrowing axons and is also a candidate to support axonal regrowth. L2/HNK-1, which is found on motor axon-associated Schwann cells, may provide regenerating motor axons with a selective advantage over others resulting in appropriate reinnervation of motor pathways. Since many of the functional studies this review refers to have been performed in vitro, some of the conclusions drawn need reexamination in vivo. Gene manipulations, such as the generation of null mutants followed by a thorough morphological and immunocytochemical investigation may be a powerful tool to resolve this problem.

Animals↗
PubMed1994

Mice deficient for the myelin-associated glycoprotein show subtle abnormalities in myelin.

Using homologous recombination in embryonic stem cells, we have generated mice with a null mutation in the gene encoding the myelin-associated glycoprotein (MAG), a recognition molecule implicated in myelin formation. MAG-deficient mice appeared normal in motor coordination and spatial learning tasks. Normal myelin structure and nerve conduction in the PNS, with N-CAM overexpression at sites normally expressing MAG, suggested compensatory mechanisms. In the CNS, the onset of myelination was delayed, and subtle morphological abnormalities were detected in that the content of oligodendrocyte cytoplasm at the inner aspect of most myelin sheaths was reduced and that some axons were surrounded by two or more myelin sheaths. These observations suggest that MAG participates in the formation of the periaxonal cytoplasmic collar of oligodendrocytes and in the recognition between oligodendrocyte processes and axons.

Animals↗
PubMed1994

Iloprost, stable analogue of the prostacyclin, is able to improve the tissue resistance to ischaemia.

On 10 patients, suffering from peripheral arterial disease, with critical limb ischaemia, the CO2 production during ischaemia has been evaluated at 1st and at 28th day of treatment with iloprost. The study demonstrated that the drug is able to improve the tissue resistance to ischaemia, with a significant (p < 0.05) reduction of the CO2 production. The authors underline that this study is one of the first confirmations, in vivo and on the man, of the previous experimental findings, made in isolated arterial tissue.

Arterial Occlusive Diseases↗
PubMed1994

The L2/HNK-1 carbohydrate is preferentially expressed by previously motor axon-associated Schwann cells in reinnervated peripheral nerves.

The carbohydrate epitope L2/HNK-1 (hereafter designated L2) is expressed in the adult mouse by myelinating Schwann cells of ventral roots and muscle nerves, but rarely by those of dorsal roots or cutaneous nerves. Since substrate-coated L2 glycolipids promote outgrowth of cultured motor but not sensory neurons, L2 may thus influence the preferential reinnervation of muscle nerves by regenerating motor axons in vivo. In the present study, we have analyzed the influence of regenerating axons on L2 expression by reinnervated Schwann cells by directing motor or sensory axons into the muscle and cutaneous branches of femoral nerves of 8-week-old mice. We observed that regenerating axons from cutaneous branches did not lead to immunocytochemically detectable L2 expression in muscle or cutaneous nerve branches. Axons regenerating from muscle branches led to a weak L2 expression by few Schwann cells of the cutaneous branch, but provoked a strong L2 expression by many Schwann cells of the muscle branch. Myelinating Schwann cells previously associated with motor axons thus differed from previously sensory axon-associated myelinating Schwann cells in their ability to express L2 when contacted by motor axons. This upregulation of L2 expression during critical stages of reinnervation may provide motor axons regenerating into the appropriate, muscle pathways with an advantage over those regenerating into the inappropriate, sensory pathways.

Animals↗
PubMed1993

Participation of P450 3A enzymes in rat hepatic microsomal retinoic acid 4-hydroxylation.

Cytochrome P450-mediated 4-hydroxylation is an important pathway in the termination of the biological action of retinoids. Several purified mammalian hepatic P450s have been shown to catalyze the 4-hydroxylation of all-trans-retinoic acid (retinoic acid) in reconstituted enzyme systems, but the nature of the activity in untreated rat liver microsomes has not been defined. In the present study, microsomal retinoic acid 4-hydroxylation was characterized in untreated liver from rats of both sexes and after a series of induction treatments. Thus, dexamethasone and phenobarbital, but not beta-naphthoflavone or dimethyl sulfoxide, increased the activity in male and female rats. An immunoglobulin G (IgG) fraction raised against P450 3A1 decreased the rate of retinoic acid 4-hydroxylation in untreated rat hepatic microsomes, but IgG directed against the P450s 2C11, 2B1, and 2C6 were noninhibitory. In vivo administration of triacetyloleandomycin, which has been shown to form a metabolite intermediate complex with P450 3A, followed by potassium ferricyanide oxidation in vitro, reactivated retinoic acid 4-hydroxylation and androst-4-ene-3,17-dione 6 beta-hydroxylation similarly (to 154 and 152% of the respective activities in the absence of potassium ferricyanide). Finally, exogenous retinoic acid (60 mg/kg ip for three days) markedly increased the rate of retinoic acid 4-hydroxylation in hepatic microsomes from male and female rats (3.8- and 3.7-fold, respectively). This occurred without comparable increases in other P450 activities. Despite these findings, the age- and sex-related profiles of microsomal retinoic acid 4-hydroxylation were clearly different from those measured for other P450 activities. Thus, on the basis of xenobiotic pretreatment, developmental, and immunochemical studies, the enzyme(s) involved in constitutive retinoic acid 4-hydroxylation appears distinct from a number of well-described P450s in untreated and induced rat liver. The data are consistent with the partial involvement of P450(s) from the 3A subfamily in retinoic acid 4-hydroxylation, but it seems clear that P450s 3A1 and 3A2 do not participate in this activity.

Age Factors↗
PubMed1993

Kinetic evidence for the involvement of a common enzyme in the microsomal reduction of retinal and androstenedione in rat liver.

Androst-4-ene-3,17-dione (androstenedione) was found to be a potent competitive inhibitor of the NADH-supported reduction of retinal in rat hepatic microsomes (Ki 42 microM, Km/Ki ratio 1.1). Similarly, the NADH-mediated reduction of androstenedione was inhibited in mixed fashion by retinal (Ki 12 microM, Km/Ki ratio 0.34). In subsequent experiments the cofactor NADH exhibited an identical Km (8 microM) in the microsomal reductions of both substrates. Acidic pH markedly stimulated the microsomal reduction of androstenedione to testosterone and was also found to enhance retinal reduction to retinol, although the latter reaction exhibited a distinct pH optimum between 6.0 and 6.5. These results suggest that a common enzyme may participate in the reduction of both substrates but at least one other enzyme probably participates in hepatic microsomal testosterone production.

17-Hydroxysteroid Dehydrogenases↗
PubMed1993

Three-month therapy with calcium-heparin in comparison with ticlopidine in patients with peripheral arterial occlusive disease at Leriche-Fontaine IIb class.

Forty patients with a mean age of 62.6 +/- 6 years, 36 men and 4 women, with peripheral arterial occlusive disease (PAOD) at Leriche-Fontaine IIb class, were randomly allocated to one of two treatment groups, receiving either 12,500 IU/day of subcutaneous (sc) calcium-heparin (CAE) or 250 mg/day of oral ticlopidine, each given for ninety days. The following parameters were evaluated before the start of the active treatment period and after thirty and ninety days of treatment: pain-free walking distance (PWD), maximum walking distance (WDmax), systolic and diastolic blood pressure (BP), posterior tibial arterial pressure and Winsor index at rest and after exercise (treadmill), transcutaneous oxygen and carbon dioxide pressures at rest (TcPO2 and TcPCO2 respectively), and time to 50% TcPO2 recovery after three-minute ischemia. Both treatments induced an improvement in PWD/WDmax, which, at the end of the study, were increased by 50.7/58.7% and 31.7/36.2%, respectively, for CAE and ticlopidine treatments, respectively.

Arterial Occlusive Diseases↗
PubMed1993

Analysis of genetic markers by random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR).

RAPD-PCR is a new technique that, starting from genomic DNA allows, with the use of a single primer of "random" base composition to amplify a variable number of sequences that can give important informations if analyzed for linkage studies, gene mapping or phylogenetic purposes. In order to detect the possible application of this simple way of DNA-fingerprinting in individual identification and in cell lineages characterization we analyzed human and non-human Primates DNA. Six different single primers of variable length were used and resulted in individual or specific electrophoretic patterns. As already reported we found a better resolution using "short" primers. The individual electrophoretic patterns obtained by RAPD-PCR can be a simple and reliable approach to DNA analysis.

Animals↗
PubMed1992

Mouse P0 gene disruption leads to hypomyelination, abnormal expression of recognition molecules, and degeneration of myelin and axons.

We have used homologous recombination in embryonic stem cells to generate mice carrying a mutation in the gene encoding P0, an immunoglobulin-related recognition molecule and the major protein of peripheral nervous system myelin. These mice are deficient in normal motor coordination and exhibit tremors and occasional convulsions. Axons in their peripheral nerves are severely hypomyelinated and a subset of myelin-like figures and axons degenerate. The mutation leads to an abnormal regulation of some, but not all, molecules involved in myelination. These results demonstrate that P0 is essential for the normal spiraling, compaction, and maintenance of the peripheral myelin sheath and the continued integrity of associated axons. They further suggest that this protein conveys a signal that regulates Schwann cell gene expression.

Animals↗