A potent small molecule, nonpeptide inhibitor of cathepsin K (SB 331750) prevents bone matrix resorption in the ovariectomized rat

Inhibition of the cyteine proteinase, cathepsin K (E.C. 3.4.22.38) has been postulated as a means to control osteoclast-mediated bone resorption. The preferred animal models for evaluation of antiresorptive activity are in the rat. However, the development of compounds that inhibit rat cathepsin K has proven difficult because the human and rat enzymes differ in key residues in the active site. In this study, a potent, nonpeptide inhibitor of rat cathepsin K (K(i) = 4.7 nmol/L), 5-(2-morpholin-4-yl-ethoxy)-benzofuran-2-carboxylic acid ((S)-3-methyl-1-(3-oxo-1-[2-(3-pyridin-2-yl-phenyl)-ethenoyl]-azepan-4-ylcarbanoyl)-butyl)-amide (SB 331750), is described, which is efficacious in rat models of bone resorption. SB 331750 potently inhibited human cathepsin K activity in vitro (K(i) = 0.0048 nmol/L) and was selective for human cathepsin K vs. cathepsins B (K(i) = 100 nmol/L), L (0.48 nmol/L), or S (K(i) = 14.3 nmol/L). In an in situ enzyme assay, SB 331750 inhibited osteoclast-associated cathepsin activity in tissue sections containing human osteoclasts (IC(50) approximately 60 nmol/L) and this translated into potent inhibition of human osteoclast-mediated bone resorption in vitro (IC(50) approximately 30 nmol/L). In vitro, SB 331750 partially, but dose-dependently, prevented the parathyroid hormone-induced hypercalcemia in an acute rat model of bone resorption. To evaluate the ability of SB 331750 to inhibit bone matrix degradation in vivo, it was administered for 4 weeks at 3, 10, or 30 mg/kg, intraperitoneally (i.p.), u.i.d. in the ovariectomized (ovx) rat. Both 10 and 30 mg/kg doses of compound prevented the ovx-induced elevation in urinary deoxypyridinoline and prevented the ovx-induced increase in percent eroded perimeter. Histological evaluation of the bones from compound-treated animals indicated that SB 331750 retarded bone matrix degradation in vivo at all three doses. The inhibition of bone resorption at the 10 and 30 mg/kg doses resulted in prevention of the ovx-induced reduction in percent trabecular area, trabecular number, and increase in trabecular spacing. These effects on bone resorption were also reflected in inhibition of the ovx-induced loss in trabecular bone volume as assessed using microcomputerized tomography (microCT; approximately 60% at 30 mg/kg). Together, these data indicate that the cathepsin K inhibitor, SB 331750, prevented bone resorption in vivo and this inhibition resulted in prevention of ovariectomy-induced loss in trabecular structure.

Cobalamin (vitamin B(12)) positively regulates interleukin-6 levels in rat cerebrospinal fluid

We have previously demonstrated that the repeated intracerebroventricular (i.c.v.) microinjection of interleukin-6 (IL-6) prevented the myelinolytic lesions of cobalamin-deficient (Cbl-D) central neuropathy [or subacute combined degeneration (SCD)] in totally gastrectomized (TGX) rats. We therefore hypothesized that cobalamin (Cbl) may actually regulate IL-6 levels in rat cerebrospinal fluid (CSF). We measured IL-6 levels in the CSF of rats made Cbl-D by means of total gastrectomy (TG) or chronic feeding with a Cbl-D diet and killed at different times from the beginning of the experiment, and found that IL-6 levels significantly and progressively decreased over time. Chronic 2-month Cbl administration started 1 week after surgery prevented the decrease in IL-6 levels and, when it was started 2 months after surgery, it significantly increased IL-6 levels, but not to presurgical values. We also investigated whether IL-6 decrease might be ultimately due to the Cbl-deficiency-linked decrease in epidermal growth factor (EGF) synthesis. Repeated i.c.v. administrations of EGF to TGX rats did not modify CSF IL-6 levels. These results, together with those of a previous study showing the preventive effect of IL-6 treatment on SCD lesions, demonstrate that: (i) Cbl selectively regulates CSF IL-6 levels; and (ii) decreased IL-6 availability plays a role in the pathogenesis of the experimental SCD, in which no evidence of inflammatory and/or immunological reaction has been observed.

Low levels of cobalamin, epidermal growth factor, and normal prions in multiple sclerosis spinal cord

We have previously demonstrated that multiple sclerosis (MS) patients have abnormal cerebrospinal fluid (CSF) levels of the key myelin-related molecules cobalamin (Cbl), epidermal growth factor (EGF), and normal cellular prions (PrP(C)s), thus confirming that some CSF abnormalities may be co-responsible for remyelination failure. We determined the levels of these three molecules in post-mortem spinal cord (SC) samples taken from MS patients and control patients. The control SC samples, almost all of which came from non-neurological patients, did not show any microscopic lesions of any type. All of the samples were supplied by the U.K. MS Tissue Bank. The Cbl, EGF, and PrP(C) levels were determined using enzyme-linked immunosorbent assays. The SC total homocysteine level was determined using a competitive immunoenzymatic assay. CSF samples, taken from a further group of MS patients, were used for the assay of holo-transcobalamin (holo-TC) levels. The Cbl, EGF, and PrP(C) levels were significantly decreased in MS SCs in comparison with controls and, paradoxically, the decreased Cbl levels were associated with decreased SC levels of homocysteine, a biochemical marker of Cbl deficiency. The trends of EGF and PrP(C) levels paralleled those previously found in CSF, whereas that of Cbl was the opposite. There was no significant difference in CSF holo-TC levels between the MS patients and the controls. Given that we have previously demonstrated that Cbl positively regulates central nervous system EGF levels, it is conceivable that the low EGF levels in the MS SC may be causally related to a local decrease in Cbl levels. Only PrP(C) levels were invariably decreased in both the SC and CSF regardless of the clinical course of the disease. These findings suggest that the simultaneous lack of Cbl, EGF, and PrP(C)s may greatly hamper the remyelination process in MS patients, because they are key molecules of the machinery for remyelination.

[Genotyping and phylogenetic analysis of HIV-1 isolates circulating in Russia]

HIV-1 genetic subtypes were analyzed by the heteroduplex mobility assay (HMA) in 125 samples derived in 1995-1996 from residents of the European part of Russia. The results indicate the prevalence of six subtypes (A, B, C, D, G, and H) in the Russian Federation, with four types (A, B, C, and G) predominating (95%). The viruses belonging to subtypes A, B, and C spread via heterosexual contacts, subtype B mainly through homosexual intercourse. The majority of subtype G isolates are epidemiologically linked with previously reported nosocomial infection of children and their mothers with HIV-1 in Southern Russia. Nucleotide sequence analysis of env encoded region confirmed the results of HMA.