Stimulation of growth and mucopolysaccharide synthesis by insulin treatment of chick embryo chondrocytes in cell culture

Knee Osteoarthritis in Type 2 Diabetes Mellitus: Does Insulin Therapy Retard Osteophyte Formation?

OBJECTIVE

The aim of this study was to investigate whether or not radiographic changes observed in knee osteoarthritis (OA) in type 2 diabetes mellitus (T2DM) patients on insulin therapy differed from those not on insulin.

MATERIAL AND METHODS

A cross-sectional study was performed in 311 subjects: 211 T2DM patients and 100 without diabetes (controls) in Mubarak Hospital, Kuwait. Patients were categorized into 3 groups: T2DM patients not on insulin (G1, n = 99), T2DM patients on insulin (G2, n = 112) and a nondiabetic control group (G3, n = 100). Plain X-ray of both knees was used to assess the changes of knee OA and graded using the Kellegren-Lawrence scale (0-4) and the Osteoarthritis Research Society International Atlas grading scale (0-3). A total of 622 knee X-rays were evaluated. SPSS version 21.0 was used for data analysis.

RESULTS

A highly significant association (p < 0.0001) was observed for joint space narrowing (JSN) as well as for osteophyte formation between the three groups. Comparing G2 and G3, a highly significant association (p < 0.0001) was retained for JSN [201 (89.7%) vs. 199 (99.5%)] and for osteophyte formation [26 (11.7%) vs. 72 (36.0%)]. Comparing G1 and G2, significantly less osteophyte formation was noted in G2 patients compared to G1 patients [26 (11.7%) vs. 39 (19.7%), p = 0.02]. Multivariate logistic regression analysis showed that the G2 group had less chance of osteophyte formation than either the G1 group or G3 control group (OR = 0.294, p = 0.008 and OR = 0.098, p < 0.001, respectively).

CONCLUSION

Our findings show that T2DM patients with OA knees on insulin therapy have less radiographic osteophytes compared to T2DM patients not on insulin.

A slow release formulation of insulin as a treatment for osteoarthritis

OBJECTIVE

To examine the potential of insulin, in a sustained delivery system, as a treatment for arthritis.

DESIGN

The effect of insulin on matrix synthesis, matrix breakdown, and nitric oxide production in primary cartilage explants was examined. The activity of insulin on diseased cartilage from Dunkin Hartley guinea pigs, diabetic mice, and osteoarthritic patients was measured. The specificity of insulin stimulation was compared to that of IGF-I using osteoblasts and fibroblasts. Finally, the stability of insulin in a biologically relevant system was tested, and a slow-release formulation of insulin was developed and characterized.

RESULTS

In articular cartilage explants, insulin stimulated proteoglycan (PG) synthesis, inhibited PG release and nitric oxide production, and overcame the detrimental effects of interleukin 1 (IL-1). The mechanism whereby insulin decreased matrix breakdown was through inhibition of aggrecanase activity. Insulin was active on cartilage at concentrations at which insulin does not cross-react with insulin-like growth factor I (IGF-I) receptors nor stimulate proliferation of other cells types. The response of cartilage to insulin did not diminish with age or disease. Insulin stimulated matrix synthesis in osteoarthritic cartilage and local treatment with insulin overcame endogenous suppression of matrix synthesis in diabetic cartilage. Poly-lactic-coglycolic acid (PLGA) was found to be an effective carrier for delivery of insulin, and PLGA-Insulin was active on articular cartilage in vitro and in vivo.

CONCLUSIONS

As the incidence of arthritis increases with the aging population, an effective therapy to induce repair of cartilage is needed. Based on its biological activities, insulin appears to be an attractive protein therapeutic candidate. Maximum insulin effectiveness may require a sustained delivery system.

Altered proteoglycan synthesis via the false acceptor pathway can be dissociated from beta-D-xyloside inhibition of proliferation

beta-D-Xylosides have been used to perturb proteoglycan (PG) synthesis to elucidate the function of PGs in a number of cellular processes, including proliferation, migration, and differentiation. This study was designed to examine whether specific xylosides affect the proliferation of several different cell types and, if so, whether this effect is dependent on altered PG synthesis via the false acceptor pathway. Both methylumbelliferyl beta-D-xylopyranoside and p-nitrophenyl beta-D-xylopyranoside (PNP beta-xyloside) inhibit cell proliferation and modulate PG synthesis; however, the alpha form of PNP xyloside which does not perturb PG synthesis inhibits the proliferation of cultured cells on a molar basis equally as well as the beta form. Conversely, beta-methyl xylopyranoside stimulates the synthesis of free glycosaminoglycan chains equally as well as PNP beta-xyloside and yet has no measurable effect on cell proliferation at comparable doses, indicating that cells can grow normally while experiencing disruption of their proteoglycan metabolism. At doses ranging from 0.5 to 5 mM, PNP beta-xyloside arrests cells in the G1 phase of the cell cycle at the same time point as serum starvation. It also delays the exist of cycling cells from the S phase. This treatment is not cytotoxic and is rapidly reversed by the replacement of PNP beta-xyloside containing medium with control medium. Dimethyl sulfoxide, the most commonly used solvent for beta-xyloside in proteoglycan studies, potentiates the inhibitory effect of PNP beta-xyloside on cell proliferation. These results indicate that the perturbation of PG synthesis via the false acceptor pathway can be uncoupled from control of cell proliferation.

Impairment of osteophyte formation in hyperglycemic patients with type II diabetes mellitus and knee osteoarthritis

OBJECTIVE

Since insulin is a potent growth factor for connective tissue, the present study was designed to investigate whether radiographic features of knee osteoarthritis (OA) in patients with poorly controlled, insulin-resistant type II diabetes mellitus differ from those in nondiabetic controls with knee OA.

METHODS

Radiographs from 25 female patients with diabetes and knee OA were compared with those from 48 female controls who were similar with respect to age, weight, and duration of OA symptoms.

RESULTS

Although the 2 groups were similar with respect to the frequency and severity of joint space narrowing, subchondral sclerosis, and geodes, osteophytes were less common in the patients with diabetes (P = 0.044), and spurring, when present, tended to be "marked" less often in the diabetic patients than in the controls.

CONCLUSION

The data suggest that diminished availability of insulin at the cellular level or diabetic microvascular disease attenuates the chondro- and osteogenesis required for osteophyte formation in the joints of patients with OA.

Stimulation of proteoglycan biosynthesis by serum and insulin-like growth factor-I in cultured bovine articular cartilage

The addition of foetal calf serum to explant cultures of adult bovine articular cartilage is known to stimulate proteoglycan synthesis in a dose-dependent manner. We have now shown the activity in serum responsible for this effect to be heat- and acid-stable, to be associated with a high-Mr complex in normal serum but converted to a low-Mr form under acid conditions. The activity has an apparent Mr approximately 10,000 and isoelectric points similar to those reported for insulin-like growth factors (IGFs). Addition of a monoclonal antibody against insulin-like growth factor-I (IGF-I) prevented foetal calf serum from stimulating proteoglycan synthesis. Physiological concentrations of recombinant IGF-I or pharmacological levels of insulin when added to cartilage cultures mimicked the proteoglycan-stimulatory activity of serum. IGF-I appeared to act by increasing the rate of proteoglycan synthesis and did not change the nature of the proteoglycan synthesized nor the rate of proteoglycan catabolism by the tissue, suggesting that IGF-I may be important in the regulation of proteoglycan metabolism in adult articular cartilage. Furthermore, IGF-I can replace foetal calf serum in the culture medium, thereby allowing the use of a fully-defined medium which will maintain the synthesis and tissue levels of proteoglycan in adult articular cartilage explants for up to 5 days.

In vitro effects of insulin on macromolecular events in newt limb regeneration blastemata

This work provides data demonstrating a stimulatory effect of insulin on macromolecular events occurring in cultured regeneration blastemata and demonstrates a synergistic interdependence between nerves and insulin in newt limb regeneration. The current experiments provide evidence for the following: (1) Insulin is paramount for expression of the mitogenic effect of nerves on cultures blastemata. (2) Insulin stimulates the incorporation of (3H)uridine into the acid-insoluble fraction of blastemal homogenates, but it does not alter the turnover rate of incorporated labeled uridine. (3) Insulin also stimulates the incorporation of 35SO4 and (3H)leucine into both chondroitinase-sensitive and chondroitinase-resistant blastemal proteoglycans. (4) Insulin increases the uptake of radiolabeled precursors by the blastemata, namely, (3H)leucine, (3H)uridine, 35SO4, (3H)alpha-aminoisobutyrate, and (3H)2-deoxy-D-glucose. The importance of insulin in the regulation of newt limb regeneration is discussed.

Effect of low density lipoprotein on glycosaminoglycan secretion by cultured human smooth muscle cells and fibroblasts. Influence of serum concentration and cell proliferation rate

Glycosaminoglycan (GAG) secretion was studied in cultures of human fibroblasts and arterial smooth muscle cells. Supplementation of culture medium with whole human serum increased the secretion of GAG but this effect disappeared as cell density increased. Lipoprotein-free serum (LFS) supported cell growth but led to a decrease in GAG secretion and in cell cholesterol. Addition of human low density lipoprotein (LDL) to the medium containing 10% LFS produced increases in GAG secretion (200%) and cell cholesterol (300%) and a decrease (60%) in cell population. The effects of LDL were considerably smaller in medium containing 5% LFS; this was related to the lower rate of proliferation in this medium, since there was a close relationship between rate of proliferation and stimulation of GAG secretion by LDL independent of serum concentration. In addition, fetal smooth muscle cells showed a qualitatively different response to LDL in 5% LFS, with a biphasic dose-response of GAG secretion and cell number. It is concluded that: (1) whole human serum stimulates GAG secretion by sparse cell cultures, (2) LFS can support cell growth but not GAG secretion, (3) LDL stimulates GAG secretion but has a cytotoxic effect, (4) the degree of GAG stimulation by LDL is dependent on the proliferative state of cells, (5) at low serum concentrations fibroblasts and fetal smooth muscle cells show differences in response to LDL which are not evident at higher serum concentration.

The effect of serum on biosynthesis of proteoglycans by bovine articular cartilage in culture

Proteoglycan synthesis by slices of adult bovine articular cartilage is stimulated two-to threefold when tissue is cultured in the presence of fetal calf serum for 5-6 days. After this, essentially steady-state conditions are achieved for up to 14 days in which the high synthetic rates are maintained and the amount of proteoglycan in the tissue remains nearly constant. In the absence of fetal calf serum, synthesis declines to a lower level and there is a gradual, net loss of proteoglycan from the tissue. Tissue maintained without serum for several days rapidly increases synthetic rates to the higher levels over 2-3 days after transferring into medium with serum, and vice versa, indicating that the response of the chondrocytes to serum factors is reversible. The structures of the proteoglycans synthesized under all medium conditions were typical for cartilage. Only small differences in glycosaminoglycan chain sizes and a consistent decrease in the relative amount of keratan sulfate to chondroitin sulfate during the first days in the culture were observed. The net capacity of the cells for chondroitin sulfate synthesis, as estimated by incubation in the presence of exogenous beta-xyloside acceptor, increased (or decreased) in parallel with the changes in endogenous proteoglycan synthesis when cultures were transferred from medium without to medium with serum (or vice versa), suggesting that changes in the net amounts of the enzymes for chondroitin sulfate synthesis are closely coordinated with changes in the amount of core protein being processed to proteoglycans. The responses of calf articular cartilage in the same system were somewhat different. Serum in the medium was required to maintain initial high levels of synthesis. The proteoglycans synthesized contained a lower proportion of keratan sulfate than those initially synthesized in the adult tissue, and there was no change in this proportion with time in culture. The maintenance of steady-state conditions for proteoglycan metabolism by either adult or calf tissue in the presence of serum in these cultures should provide a useful model for studying the regulation of synthesis and catabolism of proteoglycans by chondrocytes residing in a nearly normal extracellular matrix for long periods of time.

Divergent effects of long acting cyclic nucleotides and lysine vasopressin on the release of matrix sulfated proteoglycans into the medium of fetal rat chondrocytes in monolayer culture

Release of sulfated proteoglycans into the medium of fetal rat chondrocytes in monolayer culture was studied by contrasting the effects of 10% calf serum, long-acting cyclic nucleotides (8 Br-cAMP or DBcAMP), and lysine vasopressin (LVP). Eight hours after initiation of the experiment, the monolayer was pulsed for 2 hours with Na2[35SO4=], the radioactivity was chased, and the monolayer was reincubated for 6 hours with conditioned medium from replicate cultures. Immediately after labelling, the amount of newly synthesized sulfated proteglycans was invariably higher in the insoluble matrix than in the medium compartment. Both additives selectively enhanced sulfate incorporation into chondroitin sulfate of the matrix when compared to serum controls, but only LVP stimulation caused increases in the medium. Remodeling (loss of cell layer and release into the medium at 6 hours) was suppressed by cAMP analogues and increased by LVP. This process was more active in cultures of lower cell density. Utilizing calibrated gel columns, no size difference of the glycosaminoglycans was found between the medium and cell layer compartments of the three treatment groups at the two time points. Because the cAMP analogues inhibit, while LVP stimulates cell division, our observations imply that the rate of degradation of the constraining matrix is increased when replication is favored, even when chondriotin sulfate synthesis is selectively stimulated.

Effect of insulin on glucose oxidation and amino isobutyric acid transport and binding of insulin in chicken thymocytes

In chicken thymocytes isolated from 15--40 day-old chickens, after a 2 h incubation at 37 degrees C, insulin stimulated amino isobutyric acid uptake (maximal response: 40--50% of increase at 1 microgram insulin/ml and half maximal response at 60 ng/ml) by specifically stimulating the influx without altering the efflux. Insulin also stimulated glucose oxidation (maximal response: 11% of increase at 1 microgram insulin/ml). Binding of 125I-labelled chicken insulin to thymocytes was rapid and higher at 15 degrees C than at 37 degrees C. At steady state, (90 min at 15 degrees C), chicken, porcine and goose insulins were equipotent in inhibiting the binding of 125I-labelled chicken insulin. Maximal binding capacity was estimated at 1250 pg insulin/10(8) cells, i.e., 1250 binding sites/cell with an apparent dissociation constant of 200 ng insulin/ml at 15 degrees C. Degradation of 125I-labelled chicken insulin in the incubation medium was negligible at 15 degrees C but very noticeable at 37 degrees C. Therefore, the low level of insulin binding at 15 degrees C reflects a true scarcity of insulin receptors in chicken thymocytes as compared to rat thymocytes.

Long acting cAMP analogues enhance sulfate incorporation into matrix proteoglycans and suppress cell division of fetal rat chondrocytes in monolayer culture

The relationship between replication and the synthesis of matrix sulfated proteoglycans was investigated with fetal rat chondrocytes grown in monolayer culture. The effect of N6 O2' dibutyryl adenosine 3', 5' cyclic monophosphate (DBcAMP), adenosine 3', 5' cyclic monophosphate (cAMP), 8 Bromo adenosine 3', 5' cyclic monophosphate (8 Br-cAMP), sodium butyrate and hydroxyurea was examined. Between 0.05 and 0.5 mM DBcAMP, a dose related inhibition of cell division and stimulation of [35SO=/4] incorporation into matrix proteoglycans was demonstrated. At the higher concentrations of DBcAMP, cell division was completely inhibited and the enhancement of [35SO=/4] incorporation into matrix proteoglycans ranged between 40 and 120% (P less than 0.01). Utilizing 14C-glucosamine and photometric determination of proteoglycans with Alcian Blue, it was demonstrated that the increase in sulfate incorporation reflected enhanced accumulation of extracellular matrix. The effects of DBcAMP were mimicked by 8 Br-cAMP, suggesting they were mediated by the adenylyl cyclase system. cAMP (0.05-0.5 mM), sodium butyrate (0.1-0.5 mM) and hydroxyurea (0.5-5 mM) partially or fully inhibited cell division, but either failed or only slightly enhanced sulfate incorporation. The enhanced sulfated proteoglycan deposition promoted by DBcAMP began 8 to 12 hours after serum stimulation, its onset occurred prior to thymidine incorporation and the effect persisted for 28 hours. Determination of cell volume demonstrated an increase in size of DBcAMP treated chondrocytes between 8 to 12 hours, coincident with the onset of increased sulfate incorporation. These results are consistent with a model where matrix sulfated proteoglycan deposition by chondrocytes is mediated by intracellular cAMP levels and occurs in the G1 phase of the cell cycle.

Age-related decline in the synthesis of glycosaminoglycans by cultured human fibroblasts (WI-38)

A gradual decline in the synthesis of glycosaminoglycans, as evidenced by reduced rates of incorporation of [35S]-sulfate and [14C]-glucosamine into total cellular and extracellular glycosaminoglycans, occurred during the last 4 to 5 passages (1 : 2 splits) of WI-38 cultures before phase out. While labelling of cellular glycosaminoglycans by both radioactive precursors was reduced to about the same extent, a relatively greater decline in [35S]-sulfate than in [14C]-glucosamine incorporation into extracellular glycosaminoglycans was observed during the last passages. These changes in glycosaminoglycan metabolism are interpreted as an expression of cellular aging and a function of glycosaminoglycans in growth regulation (and possibly in the process of cellular senescence) is discussed.