Progression of medial compartmental osteoarthritis 2-8 years after lateral closing-wedge high tibial osteotomy

PURPOSE

The primary purpose of this study is to investigate the progression of medial osteoarthritis (OA) following lateral closing-wedge high tibial osteotomy (HTO). Secondary outcomes included functional and pain scores.

METHODS

This prospective cohort study analysed 298 patients treated with lateral closing-wedge HTO surgery for medial compartmental OA. OA progression was measured by comparing the minimum joint space width (mJSW) and Kellgren-Lawrence (KL) score on radiographs preoperatively and postoperatively. The WOMAC score and NRS score for pain were obtained preoperatively and postoperatively to assess secondary outcomes. Failure was defined as revision surgery; survival was estimated.

RESULTS

Mean follow-up was 5.2 ± 1.8 years (range 2-8.5). Mean preoperative mJSW was 3.4 ± 1.6 mm, which changed nonsignificantly (p = 0.51) to 3.4 ± 1.7 mm postoperatively. Mean annual joint space narrowing was 0.02 ± 0.34 mm/year. Progression to 1 KL grade or more was seen in 132 (44 %) patients, and annual risk of KL progression was 8.6 %. No KL progression was seen in 56 % of patients. Mean NRS decreased from 7.3 ± 1.5 to 3.5 ± 2.5 (p < 0.001). WOMAC scores decreased from 48.0 ± 17.2 to 23.6 ± 19.7 (p < 0.001). Failure was seen in 21 patients.

CONCLUSION

Compared to demographic data in the literature, valgus high tibial osteotomy seems to reduce the progression of OA, reduces pain and improves knee function in patients with medial compartment OA and a varus alignment.

LEVEL OF EVIDENCE

III.

Identification and localization of three photobinding sites of iodoarylazidoprazosin in hamster P-glycoprotein

P-glycoprotein is an ATP-dependent drug-efflux pump which can transport a diverse range of structurally and functionally unrelated substrates across the plasma membrane. Overexpression of this protein may result in multidrug resistance and is a major cause of the failure of cancer chemotherapy. The most commonly used photoreactive substrate is iodoarylazidoprazosin. Its binding domains within the P-glycoprotein have so far been inferred from indirect methods such as epitope mapping. In this study, the binding sites were refined and relocalized by direct analysis of photolabeled peptides. P-glycoprotein-containing plasma membrane vesicles of Chinese hamster ovary B30 cells were photoaffinity-labeled with iodoarylazidoprazosin. After chemical cleavage behind tryptophan residues or enzymatic cleavage behind lysine residues, the resulting 125I-labeled peptides were separated by tricine/PAGE and HPLC and subjected to Edman sequencing. The major photoaffinity binding sites of iodoarylazidoprazosin were localized in the amino-acid regions 248-312 [transmembrane segment (TM)4 to TM5], 758-800 (beyond TM7 to beyond TM8) and 1160-1218 (after the Walker A motif of the second nucleotide-binding domain). Therefore the binding pocket of iodoarylazidoprazosin is made up of at least three binding epitopes.

Iodomycin and iodipine, a structural analogue of azidopine, bind to a common domain in hamster P-glycoprotein

Both the overexpression of P-glycoprotein and the broad range of substrates of this ATP-binding cassette (ABC) transporter induce the phenomenon of multidrug resistance, one major cause of the failure of cancer chemotherapy in humans. This study reports that [125I]iodipine, a structural analogue of the 1,4-dihydropyridine azidopine, shares a common binding site with iodomycin, a Bolton-Hunter derivative of the anthracycline daunomycin. This binding site is different from that described for iodoarylazidoprazosin, which is presumed to share a common binding site with azidopine. Edman sequencing revealed that [125I]iodipine had photolabelled the same peptide as iodomycin and spans the primary sequence of hamster isoform pgp1 from amino acid 230 to amino acid 312.

Localization of the iodomycin binding site in hamster P-glycoprotein

P-glycoprotein, the overexpression of which is a major cause for the failure of cancer chemotherapy in man, recognizes and transports a broad range of structurally unrelated amphiphilic compounds. This study reports on the localization of the binding site of P-glycoprotein for iodomycin, the Bolton-Hunter derivative of the anthracycline daunomycin. Plasma membrane vesicles isolated from multidrug-resistant Chinese hamster ovary B30 cells were photolabeled with [125I]iodomycin. After chemical cleavage behind the tryptophan residues, 125I-labeled peptides were separated by electrophoresis and high performance liquid chromatography. Edman sequencing revealed that [125I]iodomycin had been predominantly incorporated into the fragment 230-312 of isoform I of hamster P-glycoprotein. According to models based on hydropathy plots, the amino acid sequence 230-312 forms the distal part of transmembrane segment 4, the second cytoplasmic loop, and the proximal part of transmembrane segment 5 in the N-terminal half of P-glycoprotein. The binding site for iodomycin is recognized with high affinity by vinblastine and cyclosporin A.

Competitive inhibition of photoaffinity labelling of P-glycoprotein by anticancer drugs and modulators including S9788

The affinity of the multidrug resistance modulator S9788 to interact with P-glycoprotein was characterized by its ability to inhibit the photoaffinity labelling of plasma membranes of multidrug resistant chinese hamster ovary B30 cells by iodomycin. This iodinated analogue of daunomycin specifically photolabels P-glycoprotein in membrane vesicles as well as in intact cells. The multidrug resistance reversing agents verapamil and cyclosporin and the cytotoxic drugs vinblastine and daunomycin which are known to be recognized by P-glycoprotein competed with iodomycin for its binding site on P-glycoprotein. Vinblastine and cyclosporin bound with high affinity, S9788 and verapamil with medium affinity to P-glycoprotein.

Cystic fibrosis-type mutational analysis in the ATP-binding cassette transporter signature of human P-glycoprotein MDR1

Members of the ATP-binding cassette transporter superfamily such as the P-glycoproteins (MDR) and the cystic fibrosis transmembrane conductance regulator (CFTR) share conserved sequence motifs in their nucleotide binding fold that are the major targets for CFTR mutations in patients with cystic fibrosis. Cystic fibrosis-type mutations were introduced at analogous positions into the human MDR1 gene. Heterologous expression of wild-type or mutated MDR1 revealed similar mRNA transcript levels in Chinese hamster ovary K1 recipients, but the subsequent processing was defective for all mutations that give rise to severe cystic fibrosis in the case of CFTR. Functional multidrug transporter MDR1, however, was obtained when amino acid substitutions were introduced into a less conserved position of the ATP-binding cassette transporter signature (codon 536 in MDR1). The profile of cross-resistance and chemosensitization was modulated in these codon 536 variants, which suggests that this region is involved in the drug transport function of P-glycoprotein.

Reversal of multidrug resistance in Chinese hamster ovary cells by the immunosuppressive agent rapamycin

The ability of cyclosporin A, FK506, and rapamycin to overcome multidrug resistance was investigated in Chinese hamster ovary cells in vitro by growth inhibition experiments. 1-30 microM of immunosuppressant sensitized drug-resistant cells and their drug-sensitive parents in a dose-dependent manner to adriamycin (2-2000-fold), colchicine (2-260-fold), and vinblastine (2-120-fold). The multidrug resistance-reversing activity increased in the order rapamycin < FK506 < cyclosporin A, irrespective of whether the resistant cells overexpressed hamster or human P-glycoprotein. The interaction of the three macrolides with P-glycoprotein was characterized by their ability to competitively inhibit the photoaffinity labelling of plasma membranes of resistant CHRB30 cells by iodomycin. The three immunosuppressants bound with high affinity to P-glycoprotein.