The biphasic poroviscoelastic behavior of articular cartilage: role of the surface zone in governing the compressive behavior

Surface fibrillation of articular cartilage is an early sign of degenerative changes in the development of osteoarthritis. To assess the influence of the surface zone on the viscoelastic properties of cartilage under compressive loading, we prepared osteochondral plugs from skeletally mature steers, with and without the surface zone of articular cartilage, for study in the confined compression creep experiment. The relative contributions of two viscoelastic mechanisms, i.e. a flow-independent mechanism [Hayes and Bodine, J. Biomechanics 11, 407-419 (1978)], and a flow-dependent mechanism [Mow et al. J. biomech. Engng 102, 73-84 (1980)], to the compressive creep response of these two types of specimens were determined using the biphasic poroviscoelastic theory proposed by Mak. [J. Biomechanics 20, 703-714 (1986)]. From the experimental results and the biphasic poroviscoelastic theory, we found that frictional drag associated with interstitial fluid flow and fluid pressurization are the dominant mechanisms of load support in the intact specimens, i.e. the flow-dependent mechanisms alone were sufficient to describe normal articular cartilage compressive creep behavior. For specimens with the surface removed, we found an increased creep rate which was derived from an increased tissue permeability, as well as significant changes in the flow-independent parameters of the viscoelastic solid matrix. permeability, as well as significant changes in the flow-independent parameters of the viscoelastic solid matrix. From these tissue properties and the biphasic poroviscoelastic theory, we determined that the flow-dependent mechanisms of load support, i.e. frictional drag and fluid pressurization, were greatly diminished in cartilage without the articular surface. Calculations based upon these material parameters show that for specimens with the surface zone removed, the cartilage solid matrix became more highly loaded during the early stages of creep. This suggests that an important function of the articular surface is to provide for a low fluid permeability, and thereby serve to restrict fluid exudation and increase interstitial fluid pressurization. Thus, it is likely that with increasing severity of damage to the articular surface, load support in cartilage under compression shifts from the flow-dependent modes of fluid drag and pressurization to increased solid matrix stress. This suggests that it is important to maintain the integrity of the articular surface in preserving normal compressive behavior of the tissue and normal load carriage in the joint.

Fluoroalkylethyl silane coating as a moisture barrier for dental ceramics

The performance of dental ceramics is reduced in wet environments due to stress-corrosion limiting restoration lifetime. As analysis suggests that fracture is typically initiated from the internal surface, placement of a thin coating before a restoration is cemented to place may prevent fracture if it acts as a moisture barrier. Of coatings we tested, a fluoroalkylethyl silane (du Pont MPD-7680) showed promise. This study aimed to test a range of concentrations on glass and to determine any strength improvement on dental ceramics. Glass slides (n = 8-9) were indented (29-N load) stored 24 h, etched, coated with 100, 50, and 25% fluorosilane in isopropyl alcohol, and air-cured for 24 h. The slides were fractured on a biaxial fixture in water at 0.5 mm/min and maximum stresses calculated. Uncoated controls were tested in water and liquid N2 to determine the inert strength without stress-corrosion. Results showed increasing mean strength from uncoated (53.6 MPa) to 100% (68.0 MPa) which compared to the 80.4 MPa inert strength. ANOVA showed P < .05. Subsequently the experiment was repeated on discs of three dental ceramics (n = 7-10): feldspathic (Ceramco), glass-ceramic (Dicor MGC), high-leucite (Optec) with the 100% solution only. Mean strength was significantly (P < .01) enhanced in the feldspathic (56.2 MPa, untreated, 70.7 MPa, treated) but not the high-leucite (83.1, 83.0) or the glass-ceramic (283.9, 271.4). Fluoroalkylethyl silane coating reduced stress-corrosion in glass and feldspathic porcelain. It may be a practical approach to reducing fracture of ceramic restorations.

Compressive properties of the cartilaginous end-plate of the baboon lumbar spine

The viscoelastic behavior of the cartilaginous end-plate of the baboon (Papio anubis) was studied in an experiment on compressive creep. Data were analyzed with the biphasic poroviscoelastic constitutive theory to assess the relative contributions of flow-dependent and flow-independent viscoelastic mechanisms to the observed creep behavior. Material coefficients describing the equilibrium compressive behavior (HA) and both flow-independent (c, tau 1, and tau 2) and flow-dependent (k) viscoelastic effects were determined for the end-plate by the curve-fitting of the theoretical solution to the experimental creep data. Biochemical analyses were performed to test for potential relationships between material properties and composition which may give rise to the viscoelastic behavior of the end-plate. The results indicate that the cartilaginous end-plate has a hydraulic permeability of 14.3 x 10(-14) m4/N-s, which is associated with rapid transport and pressurization of the interstitial fluid in response to loading and an increased emphasis on flow-independent viscoelastic effects. Biochemical analyses for water, sulfated glycosaminoglycan content, and hydroxyproline indicate that the end-plate of the baboon is compositionally similar to the cartilaginous end-plate in humans. Interpretation of the mechanical and compositional data suggests that fluid pressurization in the cartilaginous end-plate may be important in the maintenance of a uniform stress distribution across the boundary between vertebral body and intervertebral disc.

A retroviral sequence of the Chinese hamster ovary cell line

A partial cDNA (B52) molecule with the characteristics of retroviral sequences was isolated from the Chinese hamster ovary (CHO) K1 cell line. The B52 cDNA contains 1184 nucleotides. The first 452 nucleotides (nt) are 71% homologous to the env gene of Moloney murine leukemia virus (MMLV) and murine endogenous retroviruses. The 139 amino acids predicted from the 452 nt have 82% homology with the carboxy-terminal amino acids of the env protein of MMLV. The remaining 732 nt have several features of a typical retroviral long terminal repeat (LTR). For example, the first 14 nt are identical to the 5' inverted repeat of the retroviral LTRs. The 41-nt sequence at the 3' end is common to the R region of retroviral LTRs. The 732-nt sequence was shown to have promoter activity. The activity is approximately twofold higher than that of the Rous sarcoma virus LTR, and 1.5-fold lower than that of the early promoter of SV40 virus. Two species of mRNA of 5.2 and 2.7 kb in size were readily detected by B52 cDNA in the CHO K1 cells.

Differential gene expression in wild-type and X-ray-sensitive mutants of Chinese hamster ovary cell lines

Complementary DNA cloning, differential screening and Northern hybridization techniques were used to study differential gene expression in the wild-type Chinese hamster ovary (CHO) K1 cell line and its two X-ray sensitive mutants, xrs-5 and xrs-6. 11 species of mRNAs were found underexpressed in the two independently isolated mutants. The steady-state levels of those mRNAs are 3-26-fold less in the two mutants, depending on the particular species. 6 of the underexpressed mRNAs have been identified by comparing the sequences of the cloned cDNAs to the known sequences in GenBank. 4 of them code for the structural proteins of ferritin heavy chain, nonmuscle myosin light chain 3nm, ribosomal protein S17 and L7, respectively. The other two have strong homology with mouse B2 or retroviral sequences. The remaining 5 mRNAs did not show significant homology with any of the known sequences and apparently represent newly isolated species. The effect of 137Cs gamma-rays on the expression of the 11 mRNAs has been studied. Radiation inhibited the expression of the B2-like gene in the mutants but not in the wild-type CHO cells. The levels of the other 10 mRNAs were not affected by radiation. The underexpression of this group of genes in both xrs-5 and xrs-6 mutants seems to be related to their radiation-sensitive phenotype, although the specific gene responsible has not been identified. Two models are proposed to explain the mechanism of underexpression. It is suggested that a cellular factor or/and chromosome structural changes are involved.

[Expression and secretion of alpha-amylase gene from Bacillus subtilis in E. coli]

The E. coli which carrying the alpha-amylase gene fragment cloned from B. subtilis secreted the gene products into the medium. The reason is the exogenous gene fragment act on the cell wall of E. coli by some way, gives rise to the change of its structure. It leads up to the alpha-amylase and some periplasm proteins passing through the cell wall into the medium. It also causes the change of host colonial morphology. The secrete process are non-specific.

Distribution of the neuropeptide galanin in the cat heart and coexistence with vasoactive intestinal peptide, substance P and neuropeptide Y

The neuropeptide galanin (GAL) has been detected in the peripheral and central nervous systems. However, little is known about its distribution and localization in heart, and the possible coexistence of GAL with other neuropeptides in the heart is not established. The present immunocytochemical study describes the distribution of GAL in nerves of the feline heart and its colocalization with vasoactive intestinal peptide (VIP), substance P (SP), and neuropeptide Y (NPY). GAL-like immunoreactivity was widely distributed in the atrial and ventricular myocardium and around coronary arteries. Colocalization of GAL with VIP, SP and NPY was observed in many nerve fibers. Further, GAL and NPY were colocalized in nerve cell bodies of intracardiac ganglia. Since these neuropeptides have been found to be associated with sensory and autonomic innervation in the heart, the present findings provide evidence that GAL is shared by functionally different neuronal populations in the heart and that GAL may participate in controlling cardiac function by combined action with other neuropeptides.

Retinoic acid-regulated expression of proteolipid protein and myelin-associated glycoprotein genes in C6 glioma cells

The effect of retinoic acid (RA) on the expression of myelin-specific genes, i.e., proteolipid protein (PLP) and myelin-associated glycoprotein (MAG) in rat glioma C6 cells, was analyzed by Northern blot hybridization. RA-treatment increased the steady-state level of the PLP-specific messages within one day after RA administration and the upregulation reached a maximum on the third day. Concomitantly, the expression of MAG-specific messages in the RA-treated C6 cells dropped below the detectability limit. The expression of the PLP gene was directly related to the RA concentration increasing to approximately 44-fold over the control (untreated cells) level at 10(-6) M RA. The stimulatory effect was vitiated by cycloheximide indicating the involvement of intermediate genes in the PLP gene activation. The total cellular RNA content and the level of cyclophilin mRNA was not changed by the RA-treatment. The present data indicate that RA can be a potent modulator of the myelin-specific gene expression. Furthermore, the reciprocal response of PLP versus MAG genes to RA demonstrates that these two genes utilize different regulatory mechanisms.

Cyclic AMP-induced upregulation of proteolipid protein and myelin associated glycoprotein gene expression in C6 cells

A model culture system of C6 rat glioma cells was used to test the involvement of cAMP in the regulation of the myelin PLP and MAG genes. The treatment of cells with isoproterenol (10(-5) to 10(-8) M) upregulated the expression of the PLP and MAG genes in a concentration-dependent manner. The mRNA for PLP reached a maximum (sevenfold higher than in control cells) after about 12-24 hr, then declined to approximately fourfold over the control level. The response of MAG gene was delayed by at least 36 hr, and the level of MAG mRNA reached a maximum of approximately 48-fold over the control level on the fourth day in culture. The co-administration of propranolol blocked the effect of isoproterenol, whereas 10(-5) M forskolin simulated the effect of isoproterenol, indicating a role of cAMP in the signal transduction cascades leading to upregulation of the myelin genes. However, the dissimilarity in the timing and the extent of upregulation of the PLP and MAG genes by cAMP-stimulating agents indicate the existence of different intracellular mechanisms for the activation of these two genes. Cycloheximide blocked the stimulatory effect of isoproterenol on both the PLP and MAG genes, indicating that the effect of cAMP on the myelin genes is mediated by protein product(s) of other cAMP-response gene(s).

China strives to limit population to 1.294 billion by 2000

Mme. Peng Peiyun, minister of the State Family Planning Commission, said that China must strive to limit its total population to 1.294 billion by the end of the century as set by the 8th 5-Year Population Plan and the 10-Year Population Program. The average annual net increase of population in the country in this decade will need to drop to 15.1 million with an annual rate of natural increase of no more than 12.49/1000. According to these goals, the total fertility rate of women at childbearing age must be reduced from 2.3 in 1990 to 2.1 in 1995 and continue to decline below the present average in developed countries. These figures were announced at the National Conference for Commending Advanced Units and Model Individuals for Publicity on Family Planning held in Beijing on September 25, 1991. It is very arduous to reach the goals, admitted Minister Peng, because: First,China has a large population base and is at present confronted with the 3rd baby boom since 1949. There will be 19 million planned births each year during the 8th 5-Year Plan (1991-95). Second, the implementation of the family planning program is uneven in the country. During the 1980s, the total fertility rate of urban women was kept below 1.5 while that of rural women was around 2.8. The 1990 national population census shows that the proportion of 3rd and higher parity births is still as high as 19.32%. Facing the present grave situation of population growth, we have to increase the emphasis on publicity and education about population and family planning to better facilitate implementation of the family planning program. At the conference 365 advanced units and 485 model individuals were commended. Mr. Wang Renzhi, head of the Publicity Department of the Party's Central Committee, and Mme. Peng Peiyun attended the awarding ceremony for commendation.

[Echocardiographic changes in 91 patients with acromegaly]

Echocardiography was performed in 91 patients with acromegaly. Left ventricular internal diameter, wall thickness and left ventricular mass were measured and calculated. 76 patients with active acromegaly (GH greater than 5 ng/ml) were analysed. The result revealed that the incidence of acromegalic cardiomyopathy was 85.5% and the left ventricular mass of active acromegaly was 339.1 +/- 85.6 g and 188.8 +/- 46.7 g/m2. Most of them had left ventricular hypertrophy (LVH) or/and left ventricular dilation. Right ventricular hypertrophy was rarely detected. Most of LVH were symmetric and about a quarter of the patients with LVH was asymmetric (septum was thicker than LV posterior wall). LV mass in the active acromegaly group was larger than that in the normal group and the inactive acromegaly group. These indicate that acromegalic cardiomyopathy is related to growth hormone.

Effect of culture conditions on PLP and MAG gene expression in rat glioma C6 cells

The effects of culture conditions on the expression of myelin-specific genes, i.e. proteolipid protein (PLP) and myelin-associated glycoprotein (MAG) in rat glioma C6 cells was studied. Early passage (40-46) cells had higher steady-state level of PLP- and MAG-specific mRNA than late (100) passage cells when grown in defined (serum-free) medium. The PLP gene expression was increased whereas the MAG gene expression was reduced in the presence of 10% fetal calf serum in either passage. The level of both PLP- and MAG-specific messages was also directly related to the cell density indicating cell contact-induced stimulation of the gene expression. Furthermore, the cells apparently secrete factors into the medium, which upregulate the gene expression in autocrine fashion. The results also indicate a dissimilarity of regulatory mechanisms involved in the expression of the PLP and MAG genes.

Epidermolytic acanthoma does not contain human papillomavirus DNA

The histologic changes of epidermolytic acanthoma can mimic those of human papillomavirus infection. Sections from paraffin-embedded tissues identified histologically as epidermolytic acanthoma were examined for the presence of human papillomavirus (HPV) types 6, 11, 16, 18, and 33 using the polymerase chain reaction followed by dot-blot analysis with specific radiolabelled detecting probes. Although present in appropriate controls, human papillomavirus DNA was not detected in epidermolytic acanthoma. We conclude that epidermolytic acanthoma is not a skin lesion that is associated with human papillomavirus infection.

The density and strength of proteoglycan-proteoglycan interaction sites in concentrated solutions

Rheological flow properties of link-stable and link-free proteoglycan (PG) aggregates in concentrated solutions were measured using a cone-on-plate viscometer. A second-order constitutive model, based upon the statistical-network theories of Lodge, [Rheol. Acta 7, 379-392 (1968)] and De Kee and Carreau [J. Non-Newtonian Fluid Mech. 6, 127-143 (1979)], was developed to describe the measured steady and transient flow responses exhibited by the PG solutions. Our measurements confirmed previous experimental findings that the complex shear modulus of PG solutions depends on the frequency of the imposed small-amplitude oscillatory shear, and the apparent viscosity and primary normal-stress difference depend nonlinearly on the shear rate under steady-shear flow conditions [Mow et al., J. Biomechanics 17, 325-338 (1984b); Hardingham et al., J. orthop. Res. 5, 36-46 (1987)]. In the present study, we found that PG solutions exhibit pronounced stress overshoot responses and large hysteresis loop effects. These transient responses were shown to be sensitive to acceleration strain (i.e. the second rate of strain) as well as PG structure (i.e. link-protein stabilization). The model parameters were determined by curvefitting of the second-order constitutive model and experimental data from steady, oscillatory and transient shear flow measurements. Using this network model, we calculated the density of the idealized interaction sites existing in the PG network, and the average strength of these interaction sites. The results indicate that link-protein stabilization of PG aggregates does not change the density of interaction sites formed in the PG network, rather, it increases the average strength of these interaction sites.

The influence of link protein stabilization on the viscometric properties of proteoglycan aggregate solutions

The dynamic, steady-shear and transient shear flow properties of precisely prepared link-stable (s0 136, 66% aggregate) and link-free (s0 93, 59% aggregate) proteoglycan aggregate solutions at concentrations ranging from 10 to 50 mg/ml were determined using a cone-on-plate viscometer in a mechanical spectrometer. All proteoglycan solutions tested possessed: (1) linear viscoelastic properties - as measured by the dynamic complex modulus under small amplitude steady oscillatory conditions (1 less than or equal to omega less than or equal to 100 rad/s) - and (2) nonlinear shear-rate dependent apparent viscosities and primary normal stress difference under steady shearing conditions (0.25 less than or equal to gamma less than or equal to 250 s-1). Our transient flow data show that all proteoglycan aggregate solutions exhibited transient stress overshoot effects in shear stress and normal stress. From these steady and transient flow data, we conclude that link protein stabilized aggregates have significant effects on their dynamic and steady-shear properties as well as transient flow properties. The transient stress overshoot data provide a measure of the energy per unit volume of fluid required to overcome the proteoglycan networks in solution from a resting state. Thus we found that link-stable aggregates form much stronger networks than link-free aggregates. This is corroborated by the fact that link-stable aggregates form more elastic (lower than delta) and stiffer (higher [G*]) networks than link-free aggregates. The complete spectrum of viscometric flow data is entirely compatible with the proposed role of link protein in adding structural stability to the proteoglycan-hyaluronate bond. In cartilage, the enhanced strength of the networks formed by link-stable aggregates may play an important role in determining the material properties of the tissue and thereby contribute to the functional capacity of cartilage in diarthrodial joints.