Effects of pentosan polysulfate on human mesenchymal precursor stem cell differentiation: mineralisation assay. Primary mesenchymal precursor stem cells (MPCs) were cultured in non-osteoinductive growth media (media control) or in osteoinductive conditions in the absence or presence of pentosan polysulfate (PPS) at the indicated concentrations. n = 3 for each PPS concentration studied. (a) Concentration of acid-solubilised calcium per well determined relative to the total amount of DNA per well. Data expressed as mean ± standard error of the mean for day 28. (b) Phase-contrast photomicrographs of cultures showing absence of mineralisation in the co-cultures with PPS (× 20). A statistically significant decrease (P < 0.01) in mineralised matrix formation was observed for PPS concentrations of 5 and 10 μg/ml. *P < 0.01 relative to controls.