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PubMed2001

The wear pattern in metal-on-metal hip prostheses.

The accumulated data suggest that there is a strong correlation between polyethylene wear and osteolysis, which ultimately leads to prosthetic loosening. Second-generation metal-on-metal prostheses have been introduced, with an eye toward resolving this wear-induced osteolysis problem. The metal particles and ions are biologically active and can affect the cell homeostasis. Thus, defining the wear pattern and ratio of a given metal-on-metal prosthesis system is desirable. An early high-wear or run-in phase followed by a low-wear phase or steady state has been suggested for metal-on-metal hip prostheses. The aim of this study was to define the wear pattern of metal-on-metal bearings. The prosthesis systems were tested in a joint simulator. An early accelerated wear phase transformed to a slower wear phase after 700,000 cycles. The run-in and steady-state wear rates for combined head and liner averaged 2.22 mm(3)/Mc and 1.0 mm(3)/ million cycles, respectively. The metal-on-metal prosthesis featured a biphasic wear trend with the wear ratio in run in being more than twofold higher than the steady-state phase.

Biocompatible Materials↗
PubMed2006

Current in vivo wear of metal-on-metal bearings assessed by exercise-related rise in plasma cobalt level.

Baseline metal ion levels are elevated in patients with metal-on-metal (MOM) hip arthroplasty. Interpretation of baseline levels is difficult as measurements are influenced by wear, corrosion, and metal ion release from stored metal in the body. Schmalzried et al. demonstrated that "wear is the function of use, not time." The specific research question we asked was: Does physiological exercise increase the wear of metal-on-metal articulation which can be measured from the plasma metal ion levels? Patients with three different well functioning MOM bearings [two types of resurfacing (BHR 46.8 mm and Cormet 48 mm) and Metasul 28 mm] were included. Blood samples were taken immediately before, immediately after, and 1 h after exercise to determine cobalt and chromium levels. A significant increase (p<0.005) in serum cobalt and chromium of 13% and 11%, respectively, was noticed after the exercise. Rise of cobalt levels in patients with a resurfacing MOM was 8.5 times (BHR group) or 6.5 times (Cormet group) larger than in those with a Metasul MOM (p=0.021 and p=0.047). Neither rise of metal levels nor baseline levels correlated with any other factor (p>0.27). Exercise-related elevations of plasma cobalt level provides information on current in vivo wear production that cannot be inferred from a baseline measurement of cobalt levels. Chromium levels cannot provide reliable information on the in vivo wear of the devices. Diameter was the important feature of the implant in determining exercise-related elevations of plasma cobalt level. Exercise-related elevations of plasma cobalt level is a potential in vivo tool to understand and improve the tribology of metal-metal bearings.

Adult↗
PubMed1999

Correlation between the Limiting pH of Metal Ion Solubility and Total Metal Concentration.

As an alternative to species distribution diagrams (pM vs pH curves in aqueous solution) drawn for a fixed total metal concentration, this work has developed simple linear models for correlating the limiting pH of metal ion solubility-in equilibrium with the least soluble amorphous metal hydroxide solid phase-to the total metal concentration. Thus adsorptive metal removal processes in complex systems can be better designed once the limiting pH of heavy metal solubility (i.e., pH*) in such a complex environment can be envisaged by simple linear equations. pH* vs pMt (Mt = total metal concentration that can exist in aqueous solution in equilibrium with M(OH)2(s)) linear curves for uranyl-hydroxide, uranyl-carbonate-hydroxide, and mercuric-chloride-hydroxide simple and mixed-ligand systems and cupric-carbonate-hydroxide complexes in equilibrium with mixed hydroxide solid phases may enable the experimental chemist to distinguish true adsorption (e.g., onto hydrous oxide sorbents) from bulk precipitation removal of the metal and to interpret some anomalous metal fixation data-usually attributed to pure adsorption in the literature-with precipitation if the pMt at the studied pH is lower than that tolerated by pH* vs pMt curves. This easily predictable pH* corresponding to a given pMt may aid the design of desorptive mobilization experiments for certain metals as well as their adsorptive removal with the purpose of simulating metal adsorption and desorption cycles in real complex environments with changing groundwater pH. Copyright 1999 Academic Press.

Journal Article↗
PubMed1994

Cobalt bioavailability from hard metal particles. Further evidence that cobalt alone is not responsible for the toxicity of hard metal particles.

Hard metal is an alloy of tungsten carbide (WC) in a matrix of cobalt metal (Co). The inhalation of hard metal dust can cause an alveolitis which may progress to interstitial fibrosis. This study was undertaken to compare, both in vivo and in vitro, the bioavailability of cobalt metal when mixed or not with WC and to assess whether this factor had any influence on the cellular toxicity of hard metal particles. In vivo, non-toxic doses of cobalt metal were administered intratracheally in the rat, alone (Co, 0.03 mg/100 g) or mixed with tungsten carbide (WC-Co, 0.5 mg/100 g containing 6.3% of cobalt metal particles). Sequential measurements of cobalt in the lung and in urine demonstrated that the retention time of the metal in the lung was longer in Co- than in WC-Co-treated animals. In vitro, the cellular cobalt uptake was higher when the metal was presented to the macrophages as WC-Co. However, there was no relationship between the cellular uptake of cobalt and the occurrence of toxicity, since the intracellular concentration of cobalt associated with the occurrence of a cytotoxic effect of WC-Co particles was insufficient to exert the same effect when resulting from exposure to Co alone. This clearly indicates that increased bioavailability of cobalt is not the mechanism by which hard metal particles exhibit their cellular toxicity. These observations confirm and extend our previous findings supporting the view that cobalt is not the only component responsible for the toxicity of hard metal particles which should be considered as a specific toxic entity.

Administration, Inhalation↗
PubMed2005

[Can metal-on-metal bearings improve the longevity of total hip prostheses?].

PURPOSE OF THE STUDY: In total hip arthroplasty (THA), inter-series comparative clinical results cannot be considered worthy before at least 10 years of average follow-up, as shown in the Swedish Arthroplasty Register experience (1978-1993). Last generation metal-on-metal bearings were introduced in France only nine years ago (1995). To date, using mid term information, data from the literature, and our experience, one could assume that this bearing material has the capacity to improve THA longevity. Three types of information were analyzed: 1) comparative radiographic and EBRA studies published on early migration (<2 years) of acetabular implants; 2) preliminary comparative data on wear and osteolysis at the 8-year maximum follow-up; 3) clinical data on dislocation frequency and in vitro and in vivo observations of bearing separation and sliding. Study no 1: primary stability of these metal-on-metal acetabular cups was better than for polyethylene (PE) cups or alumina liners; study no 2: no detectable wear and less osteolysis were observed to date with metal-on-metal bearings versus their alumina-on-PE counterparts. Study no 3: less dislocation and less head sliding were measured with the metal-on-metal versus alumina-on-PR bearings possibly due to the interfacial forces provided by lubricating fluid (suction fit). CONCLUSION: According to current knowledge, this metal-on-metal bearing still represent, with alumina-on-alumina and highly crosslinked PE, a competitive and comprehensive option to improve THA longevity. The real pending problem concerns the frequency and above all the intensity of metal delayed hypersensitivity reaction and their potential effect on implant loosening.

Aluminum↗
PubMed1996

Long-duration metal-on-metal total hip arthroplasties with low wear of the articulating surfaces.

The 20-year performance of metal-on-metal hip articulations has not been reported. Five McKee-Farrar total hip prostheses and one Sivash prosthesis were obtained at revision surgery after a mean implantation time of 21.3 years. A radiographic, histologic, implant, and wear analysis was performed on these total hip implants with cobalt-chrome metal-on-metal articulations. All cases were associated with femoral component loosening, but the bearing surfaces performed remarkably well. The worst case estimate of combined femoral and acetabular linear wear was 4.2 microns per year, about 25 times less than that typically seen with polyethylene. Metal particles and foreign-body inflammation were seen in all cases, but the volume of reactive tissue was small compared with what is generally seen at revision of hips with a polyethylene acetabular bearing. This may be due to a reduced particle burden or a decreased inflammatory reaction to particulate metal, or both. In addition to articular wear, other sources of metal particles included femoral neck impingement on the acetabular rim, stem burnishing, and corrosion. Prosthetic hip reconstructions can fail for many reasons, including suboptimal femoral stem and/or acetabular cup design and/or fixation. By today's standards, the McKee-Farrar and Sivash stem and acetabular component designs are suboptimal; however, after more than 20 years of use, the metal-on-metal bearing surfaces in these cases demonstrated low wear and do not appear to be the cause of failure. Recent advances in total hip arthroplasty, which include improved implant design, materials, manufacturing, and fixation, combined with a better understanding of the mechanisms of implant loosening and failure, suggest that the cobalt-chrome metal-on-metal bearing be reexamined as an alternative to polyethylene when exceptional durability is required.

Adult↗
PubMed2002

Factors affecting metal-metal bonding in the face-shared d(3)d(3) bioctahedral dimer systems, MM'Cl(9)(5-) (M, M' = V, Nb, Ta).

Density functional theory (DFT) calculations have been used to investigate the d(3)d(3) bioctahedral complexes, MM'Cl(9)(5-), of the vanadium triad. Broken-symmetry calculations upon these species indicate that the V-containing complexes have optimized metal-metal separations of 3.4-3.5 A, corresponding to essentially localized magnetic electrons. The metal-metal separations in these weakly coupled dimers are elongated as a consequence of Coulombic repulsion, which profoundly influences (and destabilizes) the gas-phase structures for such dimers; nevertheless, the intermetallic interactions in the V-containing dimers involve significantly greater metal-metal bonding character than in the analogous Cr-containing dimers. These observations all show good agreement with existing experimental (solid state) results for the chloride-bridged, face-shared dimers V(2)Cl(9)(5-) and V(2)Cl(3)(thf)(6)(+). In contrast to the V-containing dimers, complexes featuring only Nb and Ta have much shorter intermetallic distances (approximately 2.4 A) consistent with d-electron delocalization and formal metal-metal triple bond formation; again, good agreement is found with available experimental data. Calculations on the complexes V(2)(mu-Cl)(3)(dme)(6)(+), Nb(2)(mu-dms)(3)Cl(6)(2-), and Ta(2)(mu-dms)(3)Cl(6)(2-), which are closely related to compounds for which crystallographic structural data exist, have been pursued and provide an insight into the intermetallic interactions in the experimentally characterized complexes. Analysis of the contributions from d-orbital overlap (E(ovlp)) stabilization, as well as spin polarization (exchange) stabilization of localized d electrons (E(spe)), has also been attempted for the MM'Cl(9)(5-) dimers. While E(ovlp) clearly dominates over E(spe) as a stabilizing factor in those dimers containing only Nb and Ta metal atoms, detailed assessment of the competition between E(ovlp) and E(spe) for V-containing dimers is obstructed by the instability of triply bonded V-containing dimers against Coulombic explosion. On the basis of the periodic trends in E(ovlp) versus E(spe), the V-triad dimers have a greater propensity for metal-metal bonding than do their Cr-triad or Mn-triad counterparts.

Journal Article↗
PubMed2005

Metal-metal interactions in mixed-valence [M2Cl9]2- species: electronic structure of d1d2 (V, Nb, Ta) and d4d5 (Fe, Ru, Os) face-shared systems.

The molecular and electronic structures of mixed-valence d1d2 (V, Nb, Ta) and d4d5 (Fe, Ru, Os) face-shared [M2Cl(9)]2- dimers have been calculated by density functional methods in order to investigate metal-metal bonding in this series. General similarities are observed between d1d2 and d4d5 systems and can be considered to reflect the electron-hole equivalence of the individual d1-d5 and d2-d4 configurations. The electronic structures of the dimers have been analyzed using potential energy curves for the broken-symmetry and other spin states resulting from the d1d2 and d4d5 coupling modes. In general, a spin-doublet (S = 1/2) state, characterized by delocalization of the metal-based electrons in a metal-metal bond with a formal order of 1.5, is favored in the systems containing 4d and 5d metals, namely, the Nb, Ta, Ru, and Os dimers. In contrast, the calculated ground structures for [V2Cl9]2- and [Fe2Cl9]2- correspond to a spin-quartet (S = 3/2) state involving weaker coupling between the metal centers and electron localization. In the case of [Ru2Cl9]2-, both the spin-doublet and spin-quartet states are predicted to be energetically favored suggesting that this species may exhibit double-minima behavior. A comparison of computational results across the (d1d1, d1d2, d2d2) [Nb2Cl9]z- and [Ta2Cl9]z- and (d4d4, d4d5, d5d5) [Ru2Cl9]z- and [Os2Cl9]z- series has revealed that, in all four cases, the shortening of the metal-metal distances correlates with an increase in formal metal-metal bond order.

Journal Article↗
PubMed2006

A DFT/CDM Study of metal-carboxylate interactions in metalloproteins: factors governing the maximum number of metal-bound carboxylates.

The number of negatively charged metal-bound Asp/Glu residues determines the net charge of the carboxylate-rich metal-binding site, which has been found to play a role in enhancing the affinity and/or selectivity of a protein cavity for a given metal cofactor. Therefore, it is of interest to know the maximum number of carboxylates that could bind to a given metal (M(q)()(+)) of charge q and the key factors determining this upper limit in protein cavities, which are usually relatively buried. Using density functional theory combined with the continuum dielectric method to compute the H(2)O --> CH(3)COO(-) exchange free energies, the maximum number of carboxylates bound to M(q)()(+) in a relatively buried metal-binding site is found to depend on (i) the metal charge, q, (ii) the carboxylate-binding mode, and (iii) the first-shell carboxylate-second-shell ligand interactions. The maximum number of carboxylates bound to M(q)()(+) in a fully/partially solvent inaccessible protein cavity would not likely exceed q + 2 if (a) the metal-bound Asp/Glu side chains are hydrogen bonded to a Lys/Arg side chain or several peptide backbone amides/Asn/Gln side chains in the metal's second coordination shell or (b) at least one acidic residue binds bidentately, as opposed to monodentately, to the metal cofactor. This number is reduced to q + 1 in the absence of stabilizing interactions from outer-shell ligand(s) and if all the carboxylates are bound monodentately to the metal cofactor in a buried cavity. The computational results are consistent with findings from a PDB survey of uni-, di-, and trivalent metal-binding sites containing Asp/Glu residues.

Aspartic Acid↗
PubMed1996

Tissue reaction to metal on metal total hip prostheses.

The periprosthetic tissue reaction to polyethylene wear debris in metal on polyethylene total hip replacements is strongly implicated as the cause of osteolysis. This has led to a renewed interest in metal on metal total hip replacements. However, little is known about the role of wear debris in failures of these prostheses. Capsular and interface tissues from 9 long and short term metal on metal total hip replacement retrievals were studied to assess the tissue reaction around these prostheses. As compared with metal on polyethylene cases, the extent of the granulomatous inflammatory reaction and the presence of foreign body type giant cells was much less intense in metal on metal cases, likely because of the lower numbers and overall smaller size of metal wear debris particles. This may lead to a better transport of the particles from the joint tissues and a lower incidence of periprosthetic osteolysis around metal on metal hip replacement.

Adult↗
PubMed1999

Metal arrays in structural units based on anion-centered metal tetrahedra.

Structural units based on anion-centered metal tetrahedra (XA(4); X = O, N; A = metal) are described as eutactic metal fragments with anions in tetrahedral interstices. In this respect these units may be subdivided into fluorite derivatives and units based on stellae quadrangulae (tetrahedral stars). To describe the geometry of the metal arrays a set of tetrahedrally packed metal radii, r(tp), is derived for A = Cu, Pb, Bi, and some rare-earth metals from the systematic analysis of the A.A distances within (XA(4)) tetrahedra. Analysis of these radii and of the structural geometry of the units shows that the insertion of anions into tetrahedral interstices of the metal fragment causes its expansion and distortions by nonbonded anion-anion repulsions. The main effect is owing to the linkage of (XA(4)) tetrahedra via edges, which leads to compression of the shared A.A edges and stretching of the unshared edges. The geometry of this effect is described by some empirical expressions. It is suggested that the eutactic arrangement of metal atoms in structural units based on anion-centered metal tetrahedra is caused by the closed-shell metal-metal bonding interactions

Journal Article↗
PubMed2001

Orthopaedic implant related metal toxicity in terms of human lymphocyte reactivity to metal-protein complexes produced from cobalt-base and titanium-base implant alloy degradation.

Metal toxicity from sources such as orthopaedic implants was investigated in terms of immune system hyper-reactivity to metal implant alloy degradation products. Lymphocyte response to serum protein complexed with metal from implant alloy degradation was investigated in this in vitro study using primary human lymphocytes from healthy volunteers (n = 10). Cobalt chromium molybdenum alloy (Co-Cr-Mo, ASTM F-75) and titanium alloy (Ti-6Al-4V, ASTM F-136) beads (70 microm) were incubated in agitated human serum at 37 degrees Celsius to simulate naturally occurring metal implant alloy degradation processes. Particulate free serum samples, which were incubated with metal, were then separated into molecular weight based fractions. The amounts of soluble Cr and Ti within each serum fraction were measured and correlated with lymphocyte proliferation response to the individual serum fractions. Lymphocytes from each subject were cultured with 11 autologous molecular weight based serum fractions either with or without added metal. Two molecular weight ranges of human serum proteins were associated with the binding of Cr and Ti from Co-Cr-Mo and Ti implant alloy degradation (at < 30 and 180-330 kDa). High molecular weight serum proteins (approximately 180 kDa) demonstrated greater lymphocyte reactivity when complexed with metal released from Co-Cr-Mo alloy and Ti alloy than with low (5-30 kDa) and midrange (30-77 kDa) serum proteins. When the amount of lymphocyte stimulation was normalized to both the moles of metal and the moles of protein within each fraction (Metal-Protein Complex Reactivity Index, MPCRI), Cr from Co-Cr-Mo alloy degradation demonstrated approximately 10 fold greater reactivity than Ti in the higher molecular weight serum proteins (approximately 180-250 kDa). This in vitro study demonstrated a lymphocyte proliferative response to both Co-Cr-Mo and Ti alloy metalloprotein degradation products. This response was greatest when the metals were complexed with high molecular weight proteins, and with metal-protein complexes formed from Co-Cr-Mo alloy degradation.

Adult↗
PubMed1995

The benefits of metal-on-metal total hip replacements.

The Müller's cast prosthesis with a concentric metal-on-metal articulation and 3 sliding bearings was used in Switzerland from 1965 to 1967. During the next 10 to 15 years, a number of hips in which the metal-to-metal systems were implanted were revised. Rather than osteoporosis and cranial migration occurring, the acetabular roofs were often sclerotic and the components showed no or only minor migration. At surgery, the capsule was almost normal and without signs of inflammation. Histologically, the capsule did not show the usual masses of giant cells associated with polyethylene particles. In the mid-1980s, different designs of metal-on-metal articulations were tested. From 1987 to 1990, this author developed, together with the biomaterial division of Sulzer Medical Technology, a pure titanium shell with a polyethylene-backed 28-mm forged cobalt-chromium liner insert. This combination has been successful, with no revisions required to date. In summary, with the present metal-on-metal articulations it is now possible to stop using the polyethylene. The successful long-term results of the cast cobalt-chromium metal-on-metal articulations of 1966 hold much promise for the future of the new-forged, more-precise, metallic socket.

Hip Prosthesis↗
PubMed2005

Effects of industrial metals on wild fish populations along a metal contamination gradient.

The purpose of this study was to examine relationships among water, sediment, and fish tissue metal concentrations as they relate to fish diversity, tissue metal accumulation, and fish morphometric and reproductive condition. Fish were captured in 12 lakes near Sudbury, Ontario, Canada, that ranged in their degree of metal contamination. In general, metal concentrations in water and sediment decreased with increasing distance from industrial operations. However, only Cu and Ni demonstrated this trend in sediments. Although 20 fish species were identified in the 12 lakes, only one species, yellow perch (Perca flavescens), was common to all 12 lakes. Fish diversity was only associated with sediment metals, suggesting that short-term processes are much less important than long-term processes for fish community recovery in metal-contaminated lakes. Multivariate characterization of water metal concentrations resulted in three lake clusters: Group 1 consisted of reference lakes; Group 2 lakes had high alkalinity, conductivity, hardness, pH, waterborne metals (especially Se), and sediment Cu and Ni concentrations; Group 3 lakes had high pH, waterborne and sediment Cu, and sediment Ni, intermediate alkalinity, conductivity, and waterborne metals (except Al and Fe), and low hardness and waterborne Al and Fe. Liver Cd, Cu, Ni, Pb, and Zn, muscle Zn, and intestinal Cd and Zn were highest, and muscle Cu and male gonadosomatic index (GSI) were lowest, in Group 3 fish. Liver, muscle, and intestinal Se concentrations, and Fulton's condition factor (FCF), hepatosomatic index (HSI), and male GSI were highest in Group 2 fish. Group 1 fish had the highest muscle Hg concentrations and female GSI. Muscle Se appeared to have an antagonistic effect on muscle Hg accumulation as a function of distance from smelting operations. Neither Cu nor Ni, both metals of concern in the Sudbury area, was useful for predicting fish condition, probably because of homeostatic regulatory control. Liver Cd accumulation, which was negatively related to FCF (r = -0.16; P < 0.05), exhibited strong, nonlinear inhibition (r2 = 0.99; P < 0.0001) as a function of water hardness. Because Cd was not detected in water samples in this study, we suspect that branchial Ca2+ uptake may play some role in reducing dietary Cd uptake in hard water lakes. Selenium has received relatively little attention in the contaminated systems around Sudbury, yet our results demonstrated that tissue Se was related to all condition metrics studied. Moreover, evidence was provided that suggests that there is a gender-specific interaction between dietary Se and Cu uptake that may contribute to decreased female reproductive condition in wild yellow perch.

Animals↗
PubMed1998

Effect of heavy metals and storage time on two types of forest litter: basal respiration rate and exchangeable metals.

Two types of forest litter, MOR and MULL, were treated with 0 (control), 25, 100, 400, 1600, and 6400 mg kg-1 Cd, Cu, Pb, or Zn after different storage times (35, 75, and 125 days at approx 5 degreesC). Highly significant effects on respiration rate were observed for dose of heavy metals, type of litter, type of metal, and storage time. The respiration rate of untreated MULL litter was lower than that of untreated MOR in all incubations, and the slope of the relation to the dose of metals was steeper for MOR. Respiration rates after storage were lower than in fresh litter, and the slope of the relation between respiration rate and metal dose was less steep after storage. In the first incubation, MULL litter was more sensitive to Cd, Cu, and Pb and less sensitive to Zn than MOR litter. After 125 days of storage, no single significant effect was found in MULL litter, whereas in MOR litter all metals still inhibited respiration rate significantly. The relative toxicity of metals was similar for both litter types, and the average EC50respiration values were (mg kg-1) Cu=3880, Zn=5610, Cd=6320, and Pb=24800. The percentages of exchangeable metals (1 M NH4OAc, pH=7) in MULL litter were lower on average than in MOR litter, and the order of solubility of the metals was Cd>Zn>Pb>Cu. Storage caused no significant difference in the average percentage of exchangeable metal. The highest doses of heavy metals increased the amounts of Ca, K, Mg, and Na extracted.

Cadmium↗
PubMed2005

Leachability of protein and metals incorporated into aquatic invertebrates: are species and metals-exposure history important?

To partially simulate conditions in fish intestinal tracts, we leached six groups of metals-contaminated invertebrates at pH 2 and pH 7, and analyzed the concentrations of four metals (Cd, Cu, Pb, and Zn) and total protein in the leachates. Four of the groups of invertebrates were benthic macroinvertebrates collected from metals-contaminated rivers (the Clark Fork River in Montana and the Coeur d'Alene River in Idaho, USA); the other two groups of invertebrates (one of which was exposed to metals in the laboratory) were laboratory-reared brine shrimp (Artemia sp.). Additionally, we fractionated the pH 2 leachates using size-exclusion chromatography (SEC). Protein content was 1.3 to 1.4x higher in Artemia than in the benthic macroinvertebrates, and leachability of metals and protein differed considerably among several of the groups of invertebrates. In SEC fractions of the pH 2 leachates from both groups of Artemia, Cu and protein co-eluted; however, Cu and protein did not co-elute in SEC fractions of the leachates from any of the benthic macroinvertebrate groups. Although none of the other three metals co-eluted with protein in any of the pH 2 leachates, one or more of the metals co-eluted with lower-molecular-weight molecules in the leachates from all of the groups of invertebrates. These results suggest fundamental differences in metal-binding properties and protein leachability among some invertebrates. Thus, different invertebrates and different histories of metals exposure might lead to different availability of metals and protein to predators.

Animals↗
PubMed2005

Sub-cellular partitioning of metals (Cd, Cu, Zn) in the gills of a freshwater bivalve, Pyganodon grandis: role of calcium concretions in metal sequestration.

Indigenous unionid molluscs, Pyganodon grandis, were collected from nine lakes in the Rouyn-Noranda area (Quebec, Canada) along a polymetallic concentration gradient (Cd, Cu, Zn). After excision, the gills were gently homogenised and the cellular compartments were separated by a differential centrifugation procedure that yielded the following particulate fractions: "nuclei + cellular debris", "mitochondria", "lysosomes + microsomes" and "granules". The supernatant remaining after the final ultracentrifugation step, i.e., the operationally-defined cytosol, was separated into a "heat-denaturable proteins" (HDP) fraction and a "heat-stable proteins" (HSP) fraction containing metallothionein (MT). The Cd, Cu and Zn content of each particulate and cytosolic fraction was determined and gill metallothionein was quantified independently by a mercury saturation assay. Cytosolic Cd concentrations were significantly related to the dissolved Cd concentrations at each site, but cytosolic Cu and Zn (essential metals) were not related to their respective ambient dissolved metal concentrations. Metallothionein concentrations increased along the metal contamination gradient and were related to cytosolic Cd (and Zn) in a concentration-dependent manner. However mass balance calculations showed that binding to metallothionein could only account for a small proportion of total gill metal ( approximately 10% Cd; approximately 3% Cu; approximately 1% Zn). Under these chronic exposure conditions, the three metals (Cd, Cu and Zn) were mainly located in calcium concretions present in the gills (respectively 58 +/- 13% of the total gill Cd, 64 +/- 6% of the total gill Cu and 73 +/- 6% of the total gill Zn). The overall contribution of granules to the total gill dry weight remained relatively constant among the different lakes, suggesting that lake-to-lake variations in granule synthesis were independent of the metal contamination gradient, i.e., these constituent elements of unionid gills act as non-inducible metal sinks at the cellular level. Metal concentrations increased proportionally in both the granules and the MT pool along the polymetallic gradient, suggesting a constant partitioning between these two compartments. Overall, despite an increase in Cd in the "mitochondria" fraction, metal sequestration mechanisms seem to be reasonably effective in detoxifying cadmium: in the cytosol, Cd concentrations in the potentially metal-sensitive HDP fraction remained relatively low and constant, even in specimens collected from the most contaminated lakes.

Animals↗
PubMed2004

Cementless metal-on-metal hip arthroplasty in patients less than 50 years of age: comparison with a matched control group using ceramic-on-polyethylene after a minimum 5-year follow-up.

Thirty-nine cementless hip arthroplasties using metal-on-metal articulation were consecutively implanted in 30 patients less than 50 years of age and compared with a matched control group (by age, diagnosis, Devane activity, and Harris hip scores) of cementless arthroplasties using ceramic-on-polyethylene articulation. The Harris hip score at follow-up (minimum 5 years) for the metal-on-metal was 94.9 (range, 74-100). After the same follow-up, the results of the ceramic-on-polyethylene were significantly worse: 9 osteolyses and 7 surgical revisions related to wear (none in the metal-on-metal). Five-year survival rates were 97% +/-2% for the ceramic-on-polyethylene and 100% for the metal-on-metal. The metal-on-metal may be recommended to prevent wear problems in younger and more active patients; however, a longer follow-up is required to confirm this encouraging data.

Adult↗