The in vivo inhibition of collagen synthesis and the reduction of prolyl hydroxylase activity by 3,4-dehydroproline

cis-trans-Amide isomerism of the 3,4-dehydroproline residue, the 'unpuckered' proline

Proline (Pro) is an outstanding amino acid in various biochemical and physicochemical perspectives, especially when considering the cis–trans isomerism of the peptidyl-Pro amide bond. Elucidation of the roles of Pro in chemical or biological systems and engineering of its features can be addressed with various Pro analogues. Here we report an experimental work investigating the basic physicochemical properties of two Pro analogues which possess a 3,4-double bond: 3,4-dehydroproline and 4-trifluoromethyl-3,4-dehydroproline. Both indicate a flat pyrroline ring in their crystal structures, in agreement with previous theoretical calculations. In solution, the peptide mimics exhibit an almost unchanged equilibrium of the trans/cis ratios compared to that of Pro and 4-trifluoromethylproline derivatives. Finally we demonstrate that the 3,4-double bond in the investigated structures leads to an increase of the amide rotational barriers, presumably due to an interplay with the transition state.

Conformational preferences of substrates for human prolyl 4-hydroxylase

Prolyl 4-hydroxylase (P4H) catalyzes the posttranslational hydroxylation of (2 S)-proline (Pro) residues in procollagen strands. The resulting (2 S,4 R)-4-hydroxyproline (Hyp) residues are essential for the folding, secretion, and stability of the collagen triple helix. Even though its product (Hyp) differs from its substrate (Pro) by only a single oxygen atom, no product inhibition has been observed for P4H. Here, we examine the basis for the binding and turnover of substrates by human P4H. Synthetic peptides containing (2 S,4 R)-4-fluoroproline (Flp), (2 S,4 S)-4-fluoroproline (flp), (2 S)-4-ketoproline (Kep), (2 S)-4-thiaproline (Thp), and 3,5-methanoproline (Mtp) were evaluated as substrates for P4H. Peptides containing Pro, flp, and Thp were found to be excellent substrates for P4H, forming Hyp, Kep, and (2 S,4 R)-thiaoxoproline, respectively. Thus, P4H is tolerant to some substitutions on C-4 of the pyrrolidine ring. In contrast, peptides containing Flp, Kep, or Mtp did not even bind to the active site of P4H. Each proline analogue that does bind to P4H is also a substrate, indicating that discrimination occurs at the level of binding rather than turnover. As the iron(IV)-oxo species that forms in the active site of P4H is highly reactive, P4H has an imperative for forming a snug complex with its substrate and appears to do so. Most notably, those proline analogues with a greater preference for a C (gamma)- endo pucker and cis peptide bond were the ones recognized by P4H. As Hyp has a strong preference for C (gamma)- exo pucker and trans peptide bond, P4H appears to discriminate against the conformation of proline residues in a manner that diminishes product inhibition during collagen biosynthesis.

Design and Synthesis of a 3,4-Dehydroproline Amide Discovery Library

The synthesis of a discovery library of 80 3,4-dehydroproline amides was achieved in a four-step reaction sequence from easily accessible 3-aminoallene-3-carboxylate methyl esters. Diversification of these proline mimics was introduced at five different sites: the substituents at the 3-pyrroline unit (R1, R2, R3), at the nitrogen (R4), and the C-terminus (R5). The 3-pyrroline scaffold was synthesized in excellent yields by a silver-catalyzed intramolecular cyclization of aminoallenes, followed by N-functionalization reactions. Maximum diversity was introduced in the final step of the reaction sequence by taking advantage of the carboxylic acid handle of the 3-pyrroline subunit. Amide coupling reactions using polystyrene-carbodiimide (PS-carbodiimide) and 1-hydroxybenzotriazole (HOBt) under microwave irradiation led to 3,4-dehydroproline amides that were obtained in purities greater than 85% by LC/MS/ESLD after scavenging the excess HOBt on a silica-bound carbonate SPE cartridge.

Alteration in the conformational stability of collagen caused by the incorporation of the lysine analogue S-2-aminoethylcysteine

We studied the effects of the lysine analogue S-2-aminoethylcysteine on the activation of lysyl tRNA and on the secretion and conformational stability of newly synthesized type I collagen in embryonic chick tendon fibroblasts. The analogue competed efficiently with lysine for activation onto tRNA without affecting significantly the activation of other amino acids (Km for lysine: 1.6 microM; Ki for S-2-aminoethylcysteine: 1.4 microM). The analogue also profoundly inhibited the synthesis and secretion of [14C]procollagen but did not affect the synthesis or secretion of non-collagenous proteins. Although the [14C]proline-labeled procollagen synthesized in the presence of S-2-aminoethylcysteine contained normal levels of hydroxyproline, it was susceptible to digestion with pepsin at 25 degrees C, indicating that incorporation of the analogue altered the conformational stability of the collagen triple helix. This analogue should be a powerful tool to further study the role of lysine on collagen structure and to determine how altered collagen structure affects its synthesis and secretion. Furthermore, this analogue may be a potent and selective inhibitor of collagen accumulation in pathologic conditions accompanied by tissue fibrosis.

Keloids: scar revision

The treatment of keloids can be a long-term, and at times, vexing, dermatologic surgical management problem arising in both white and non-white patients. This paper reviews a number of conventional, as well as novel, therapeutic approaches for the management of this disease of uncontrolled scar growth. Additionally, fundamental aspects of this disease are covered, including clinical, histologic, biochemical, immunologic, endocrinologic, and epidemiologic factors. An understanding of these latter aspects may be useful to the clinician in realizing the best possible therapeutic results. It must be emphasized that, regardless of the technique employed, an observation period of at least 2 years is necessary to effectively limit the chance and degree of recurrence.

Effects of bleomycin on 14C-proline uptake, its incorporation into proteins and hydroxylation in collagenous proteins of hamster lung slices

The uptake of 14C-proline by lung slices and its incorporation into trichloroacetic-acid (TCA)-insoluble proteins and hydroxylation in collagenous proteins were studied. They were found to be linearly increased with the incubation time for as long as 8 h. The effects of different concentrations of bleomycin on these parameters were subsequently investigated. Bleomycin at 10(-3) M significantly reduced the uptake of 14C-proline to 75% of the control value. The incorporation of 14C-proline into TCA-insoluble proteins was reduced to 84%, 78% and 75% of the control at 2.5 X 10(-4) M, 5 X 10(-4) M and 10(-3) M concentrations of bleomycin, respectively. Bleomycin failed to alter the proline pool size of the lung slices at any of these concentrations. In addition, bleomycin also inhibited the hydroxylation of 14C-proline into collagen to 72% and 69% of the control at 5 X 10(-4) M and 10(-3) M, respectively. These findings show that bleomycin-induced increases in collagen synthesis in vivo is probably secondary to inflammatory reactions of the lung and bleomycin per se has little effect on increased collagen synthesis responsible for lung fibrosis.

Collagen metabolism and spicule formation in sea urchin micromeres

The role of collagen or collagen-like protein(s) in the in vitro formation of the sea urchin embryonic skeleton was investigated using isolated micromeres of Strongylocentrotus purpuratus. Micromeres were cultured in sea water containing 4% horse serum on tissue culture plastic or an extracellular matrix of type I collagen. The effect of proline analogs and an inhibitor of collagen hydroxylation on in vitro spicule formation in both culture systems was monitored. When micromeres are cultured in the presence of proline analogs L-azetidine-2-carboxylic acid and L-3, 4-dehydroproline which disrupt collagen metabolism, spicule formation is significantly less inhibited on a collagen substratum than on plastic. Culturing micromeres on plastic in the presence of alpha, alpha'-dipyridyl, an inhibitor of collagen hydroxylation, resulted in almost complete inhibition of spicule formation. The inhibition by alpha, alpha'-dipyridyl can be overcome by culturing micromeres on collagen substratum. These results do not support the idea of collagen being the calcified organic matrix of the spicule. Rather, they suggest that micromeres synthesize a collagen-like extracellular matrix which is necessary for spicule formation. Inhibition of this activity by proline analogs or a collagen processing inhibitor can be overcome by providing the cells with a previously deposited extracellular matrix.

The effect of L-3, 4-dehydroproline on the antitumor activity and toxicity of bleomycin

Pulmonary fibrosis is a serious side effect that limits the therapeutic utility of bleomycin (BLM). Recently, it has been demonstrated that L-3, 4-dehydroproline (DHP), a proline analog, significantly reduced the extent of pulmonary fibrosis in rats administered BLM intratracheally. The present studies were performed to determine the effect of DHP on the oncolytic and toxicologic effects of BLM. DHP (25 mg/kg/day) administered sc concomitantly with BLM (4 mg/kg/day) for 9 consecutive days following a sc inoculation of B16 melanoma cells in BDF1 had no effect on tumor growth inhibition by BLM when tumor growth rate was assessed by tumor volume and by tumor weight. To determine the effect of DHP on the toxicity of BLM, DHP (25 mg/kg/day) and BLM (10 mg/kg/day) were administered to Sprague-Dawley rats for 5 consecutive days followed by 2 days of rest and 5 additional days of drug administration. BLM administration produced decreased body weight gain, acute leukocytopenia, delayed elevation in blood nitrogen levels, chronic lung and kidney disease, and alopecia. Animals administered BLM plus DHP had a similar toxicologic profile. One striking difference was that no animal administered BLM plus DHP developed alopecia, whereas five of eight rats administered BLM alone displayed this untoward effect. These results suggest that DHP neither diminishes the oncolytic activity nor exacerbates the nonpulmonary toxicity of BLM, DHP would appear, therefore, to be a potential candidate as an antifibrotic adjunct to BLM therapy.

Inhibition of prolyl hydroxylase activity and collagen biosynthesis by the anthraquinone glycoside, P-1894B, an inhibitor produced by Streptomyces albogriseolus

P-1894B, a potent prolyl hydroxylase inhibitor produced by Streptomyces albogriseolus subsp. No. 1894, inhibited about 50% of the activity of purified chick embryo prolyl hydroxylase at a concentration of 2.2 x 10(-6) M. The inhibition was noncompetitive with respect to (Pro-Pro-Gly)5 with a Ki of 1.8 x 10(-6)M. When excess amounts of ferrous ions or ascorbate were added to the reaction mixture, the inhibition was slightly reversed. P-1894B at a dose of 0.15 mg/kg reduced the hydroxylation of peptidyl proline and caused a significant inhibition of collagen biosynthesis in the uterus of the immature rat stimulated by the administration of estradiol-17 beta.

Pharmacologic control of surface scarring in human beings

A hypothetical basis for control of surface scar in human beings is: lathyrism produces poorly cross-linked collagen in healing wounds; poorly corss-linked collagen is more susceptible to digestion by tissue collagenase than is normally cross-linked collagen; and colchicine stimulates tissue collagenase activity. Therefore, treatment of patients with abnormal deposits of surface scar by excising the scar, inducing lathyrism, and administering colchicine should tend to correct abnormal balance between collagen synthesis and collagenolysis and result in a small scar with improved physical properties. Ten patients with massive keloids, resistant to conventional therapy by excision, grafting, and/or intralesional injection of steroids, have been treated by excising the keloid, grafting the defect, inducing lathyrism with Beta aminopropionitrile fumurate or penicillamine and administering colchicine. Patients were followed for 18 months to five years. No toxicity or untoward side effects from therapy were observed. No patients developed recurrent keloids while undergoing treatment. All patients showed some change in the amount of scar which persisted during the period of study. This data supports the hypothesis that lathyrism and colchicine therapy exert a measurable beneficial effect on surface scar in human beings.

Limb anomalies produced by 2,2'-dipyridyl in rats

The teratogenicity of 2,2'-dipyridyl (DIP), a chelator for ferrous iron, was investigated by administration of single dose of 60 or 75 mg/kg intraperitoneally to pregnant SD rats on days 11.5-14.5. Fetuses examined on day 21 were decreased in weight, and had defects chiefly in the limb. The type and incidence of limb defects differed according to day of treatment. Digital malformations in the forelimb and long-bone defects in the hindlimb were produced with high incidence by treatment on day 12.5, and the frequency of digital malformations in the hindlimb was increased by treatment on day 13.5. Light and electron microscopic examinations revealed the delay of mesenchymal condensation and destruction of mesenchymal cells in the forelimb bud in the early stage after day 12.5 treatment. The normal increase of DNA, protein, collagen and glycosaminoglycan contents in the forelimb bud was markedly inhibited by the treatment. The incorporation activities for [14C]proline and [14C]glucosamine of the forelimb bud were reduced to 50-60% of the control. These results indicate that DIP has potent teratogenic and cytotoxic effects on the development of the rat limb bud.