Makings of a brittle bone: Unexpected lessons from a low protein diet study of a mouse OI model.

Glycine substitutions in type I collagen appear to cause osteogenesis imperfecta (OI) by disrupting folding of the triple helix, the structure of which requires Gly in every third position. It is less clear, however, whether the resulting bone malformations and fragility are caused by effects of intracellular accumulation of misfolded collagen on differentiation and function of osteoblasts, effects of secreted misfolded collagen on the function of bone matrix, or both. Here we describe a study originally conceived for testing how reducing intracellular accumulation of misfolded collagen would affect mice with a Gly610 to Cys substitution in the triple helical region of the α2(I) chain. To stimulate degradation of misfolded collagen by autophagy, we utilized a low protein diet. The diet had beneficial effects on osteoblast differentiation and bone matrix mineralization, but also affected bone modeling and suppressed overall animal growth. Our more important observations, however, were not related to the diet. They revealed how altered osteoblast function and deficient bone formation by each cell caused by the G610C mutation combined with increased osteoblastogenesis might make the bone more brittle, all of which are common OI features. In G610C mice, increased bone formation surface compensated for reduced mineral apposition rate, resulting in normal cortical area and thickness at the cost of altering cortical modeling process, retaining woven bone, and reducing the ability of bone to absorb energy through plastic deformation. Reduced collagen and increased mineral density in extracellular matrix of lamellar bone compounded the problem, further reducing bone toughness. The latter observations might have particularly important implications for understanding OI pathophysiology and designing more effective therapeutic interventions.

Deficiency of CRTAP in non-lethal recessive osteogenesis imperfecta reduces collagen deposition into matrix.

Deficiency of any component of the ER-resident collagen prolyl 3-hydroxylation complex causes recessive osteogenesis imperfecta (OI). The complex modifies the α1(I)Pro986 residue and contains cartilage-associated protein (CRTAP), prolyl 3-hydroxylase 1 (P3H1) and cyclophilin B (CyPB). Fibroblasts normally secrete about 10% of CRTAP. Most CRTAP mutations cause a null allele and lethal type VII OI. We identified a 7-year-old Egyptian boy with non-lethal type VII OI and investigated the effects of his null CRTAP mutation on collagen biochemistry, the prolyl 3-hydroxylation complex, and collagen in extracellular matrix. The proband is homozygous for an insertion/deletion in CRTAP (c.118_133del16insTACCC). His dermal fibroblasts synthesize fully overmodified type I collagen, and 3-hydroxylate only 5% of α1(I)Pro986. CRTAP transcripts are 10% of control. CRTAP protein is absent from proband cells, with residual P3H1 and normal CyPB levels. Dermal collagen fibril diameters are significantly increased. By immunofluorescence of long-term cultures, we identified a severe deficiency (10-15% of control) of collagen deposited in extracellular matrix, with disorganization of the minimal fibrillar network. Quantitative pulse-chase experiments corroborate deficiency of matrix deposition, rather than increased matrix turnover. We conclude that defects of extracellular matrix, as well as intracellular defects in collagen modification, contribute to the pathology of type VII OI.

[Potentially dangerous photosensitizers among drugs and medicinal plant extracts]. / Potentsial'no opasnye fotosensibilizatory sredi lekarstvennykh veshchestv i ékstraktov lekarstvennykh rastenii.

The review deals with photosensitizing properties of drugs and plant extracts. Some compounds are able to cause side effects such as phototoxicity and photoallergy. Revealing and study of harmful photosensitizers is actual problem in connection with changing photoecological situation.

[Phenothiazine drugs as photosensitizers and photoprotectors]. / Lekarstvennye preparaty iz riada fenotiazinov kak fotosensibilizatory ifotoprotektory.

The photosensitizing properties of eight N-alkylated phenothiazine neuroleptic drugs were studied. The experiments were carried out in a model system based on photooxidative chemiluminescence of Gly-Trp peptide in aqueous solution. Under irradiation with light longer than 280 nm, all the studied phenothiazine derivatives decrease the chemiluminescence intensity at low concentrations and enhance it at high concentrations. Phenothiazine derivatives is likely to be due to superoxide and/or Gly-Trp free peroxide radicals. Photosensitization begins to dominate over protection at concentrations which are different for various phenothiazine derivatives compounds and lie in the range 10(-6)-10(-5) M. The photosensitizing efficiency decreases in the order: Thioproperazine, Trifluoperazine Hydrochloride, Alimezine, Thioridazine Hydrochloride, Levomepromazine Hydrochloride, Promethazine Hydrochloride, Periciazine, Chlorpromazine Hydrochloride. It was shown that photooxidation of Gly-Trp sensitized by phenothiazine derivatives occurs via singlet oxygen formation.

[Photosensitization and photoprotection by some drugs, metabolites and other compounds]. / Fotosensibiliziruiushchie i fotoprotektornye svoistva nekotorykh lekarstvennykh preparatov, metabolitov i drugikh veshchestv.

Photosensitizing and photoprotecting efficiency of about a hundred of compounds, mainly drugs, was studied. The method based on chemiluminescence occurred along with photooxidation of glycyltryptophan under irradiation in UVB range in solution was used for testing. As a measure of photosensitizing efficiency the concentration of photosensitizer which induced two-fold increase of chemiluminescence intensity was chosen. The most effective photosensitizers are riboflavin, FAD, furagin, psoralene, vicasol, benzobarbital, mydocalm, angelicyn, furadonin, ethacridin, diazolin, folic acid. With regard to pharmacological doses of drugs in organism more dangerous sensitizers (in descending order) are p-aminosalicylic acid, furagin, riboflavin, benzobarbital, thiopental, chloramphenicol, nicodin, mydocalm, furadonin, oxolonic acid, furazolidone, psoralene, nicotinamide and diazolin. Photoprotecting effect was described by the concentration at which chemiluminescence intensity decreased twice. The most effective photoprotectors are etamsilat, quercetin, ftivazid, chlorpromazine, diprazine, thioridazine, aminophenazone, oxaphenamide. Concentration dependence for some of these drugs (etamsilat, chlorpromazine, diprazine, thioridazine) is non-monotonous: they inhibit photooxidation in low concentration (about 10(-7)-10(-6) M), but at higher concentrations (10(-5)-10(-4) M) photosensitization dominates over photoprotection.

[Photosensitizing properties and antioxidant activity of furagin--an antimicrobial drug that is a derivative of nitrofuran]. / Fotosensibiliziruiushchie svoistva i antioksidantnaia aktivnost' furagina--antimikrobnogo lekarstvennogo preparata, proizvodnogo nitrofurana.

Photosensitizing effect of antimicrobial drug nitrofuran derivative--furagin N-(5-nitro-2-furil)-allylidencamino-hydantoin) under irradiation with light longer than 280 nm was found. The method of investigation is based on photochemiluminescence of Gly-Trp peptide in aqueous solution. Maximum photosensitizing efficiency was observed at the furagin concentration 0.08 mM when chemiluminescence yield was 33 times greater than photochemiluminescence of Gly-Trp peptide in absence of drug. It was shown that photochemiluminescence sensitized by furagin occurred via free radical way. Life time of the triplet state of furagin determined by flash photolysis was 40 microseconds. A comparison of experimental data with kinetic calculation allowed us to estimate the rate constant of triplet quenching by oxygen ((2.2 +/- 0.3)10(8) M-1.s-1) and the total rate constants of physical quenching and chemical reaction with Gly-Trp peptide ((2.0 +/- 0.4)10(8) M-1.s-1). It was also found in experiments with photochemiluminescence of Gly-Trp peptide sensitized by riboflavin (irradiation with monochromatic light 436 nm) that furagin possesses antioxidant properties twice reducing the intensity of chemiluminescence at the drug concentration 0.029 mM.