Role of monoamine oxidase in aminopropionitrile-induced neurotoxicity

Optical molecular imaging of lysyl oxidase activity - detection of active fibrogenesis in human lung tissue

A fluorogenic probe provides real-time measurement of lysyl oxidase activity in ex vivo asinine and human lung tissue.

Aberrant fibrogenesis is a feature of many diseases in multiple organ systems. The lysyl oxidase family of enzymes are central to tissue homeostasis and elevated lysyl oxidase activity is implicated in fibroproliferation as well as in cancer stroma. We have synthesised a novel fluorogenic reporter for monitoring lysyl oxidase activity that generates a 3–5 fold increase in fluorescence following probe activation in ventilating fibrotic ex vivo asinine lung and ex vivo human lung tissue. The probe termed “oLOX” can provide real-time measurement of lysyl oxidase activity in a number of biological settings and is tractable from an in vitro setting to man.

Reaffirmation that metabolism of polyamines by bovine plasma amine oxidase occurs strictly at the primary amino termini

Oxidation of the biologically important polyamines spermine and spermidine by plasma amine oxidase (PAO) was specified many years ago to occur at the terminal primary rather than internal secondary amine positions. However, the finding of sequential enzymatic conversion of spermine to spermidine and then to putrescine (1, 4-butanediamine) is superficially suggestive of metabolism at the secondary amine positions, and a recent publication (Houen, G., Bock, K., and Jensen, A. L. (1994) Acta Chem. Scand. 48, 52-60) claimed that the original interpretation of preferential "terminal" deamination does not stand up to scrutiny with modern methods of analysis. We herein demonstrate that the findings cited in support of secondary amine deamination can arise artifactually from spontaneous elimination/addition reactions following initial metabolism at the terminal positions of 3-(aminopropyl)amines. We further find no evidence for the ability of PAO to metabolize the secondary amine position in homospermidine, which is devoid of such complicating side reactions. Our results support the original claimed specificity of PAO for the primary amino termini of polyamines, all of which are consistent with the general finding that the quinone-dependent copper amine oxidases specifically metabolize primary amines.

Characterization of the effects of N-hydroxy-IDPN on the auditory, vestibular, and olfactory systems in rats

The mechanism of neurotoxicity of 3,3'-iminodipropionitrile (IDPN) has been widely debated, with either the parent compound or putative metabolites implicated in various studies. The N-hydroxylated form of IDPN (HO-IDPN) has been reported to cause the excitation with choreiform and circling (ECC) syndrome in rats at doses approximately one-eighth of that required to cause comparable signs in rats treated with IDPN. Because of the similarity of symptoms induced by HO-IDPN and IDPN, we investigated the effect of HO-IDPN on other aspects of the nervous system affected by IDPN, specifically the auditory, vestibular, and olfactory systems. In addition, ECC symptoms were quantified to replicate the previous findings. HO-IDPN was administered ip in saline for 3 consecutive days to two different cohorts of young adult male Sprague-Dawley rats. The first cohort (60, 80, 100, and 120 mg/kg; n = 2/group, except for the 120 mg/kg group, where n = 1) was used in a dose range-finding study. After making the neurobehavioral assessments, animals were sacrificed for olfactory mucosal histopathology. Based on the outcome of the first study, the second cohort (n = 10/group) received saline or HO-IDPN at 100 mg/kg/day for 3 consecutive days. Two animals from each of these groups were sacrificed for olfactory mucosal histopathology; the remaining animals were tested for neurobehavioral effects 3 weeks after the last dose. Animals in the second cohort lost approximately 8% of their pretreatment body weight. All rats receiving the 100 mg/kg/day dose of HO-IDPN (and the rat receiving 120 mg/kg/day) developed the ECC syndrome and signs of vestibular dysfunction within 4 days after the last dose. HO-IDPN caused a large decrease in the acoustic startle response and markedly elevated auditory thresholds at all frequencies tested. The threshold for the ECC syndrome and olfactory mucosal damage was 100 mg/kg. These studies extend previous findings on the neurotoxicity of HO-IDPN and point to the need for determining whether HO-IDPN is an in vivo metabolite of IDPN.

In vitro and in vivo inhibition of lysyl oxidase by aminopropionitriles

Inhibition of lysyl oxidase (protein-lysine 6-oxidase, EC 1.4.3.13) decreases the rate of collagen and elastin cross-link formation and produces osteolathyrism in animals. Organic nitriles, including beta-aminopropionitrile (BAPN), have been shown to irreversibly inhibit lysyl oxidase in vitro. Both BAPN and 3,3'-iminodipropionitrile (IDPN) have been shown to produce osteolathyric changes when administered to animals. To date compounds that have been reported to inhibit this enzyme possess a primary amine functional group. In this study a series of primary and substituted aminopropionitriles was studied for their ability to inhibit lysyl oxidase activity both in vitro and in vivo. Our results show that of the compounds tested, BAPN was the most potent inhibitor of the enzyme. Reversible inhibition of lysyl oxidase in vitro was found with two secondary aminonitriles, IDPN and monomethylaminopropionitrile (MMAPN). There was no inhibition of enzyme activity associated with the tertiary compound 3,3'-dimethylaminopropionitrile (DMAPN) or propionitrile, a compound lacking an amine functional group. IDPN was found to produce a slight irreversible inhibition of the enzyme both in vitro and in vivo. Pretreatment of rats with pargyline, an inhibitor of monoamine oxidase, was found to increase the inhibitory potential of BAPN (p < or = .1). Pargyline pretreatment did not alter the inhibitory potential for any of the other aminonitriles tested. These results suggest that the presence of a primary amino functional group is not a strict requirement for inhibition of lysyl oxidase. In addition, reversible and irreversible mechanisms of inhibition may be involved in the production of osteolathyric changes associated with IDPN exposure.