Newer PASs, for example, SSP+ and Composol, can maintain PLT integrity and moderate metabolism similarly to plasma but offer consistently lower PLT recoveries and limited osmotic balance.

S. liquefaciens can be detected more quickly in PAS-suspended PCs (PAS-PCs) than in plasma-PCs by colony counting. Furthermore, reduced biofilm formation by S. liquefaciens and S. epidermidis during storage in PAS-PCs increases bacteria availability for sampling detection. Culture-based detection remains the earliest indicator of bacterial presence in PAS-PCs, while changes of PLT quality can herald S. liquefaciens contamination when in excess of 10(8) CFUs/mL.

Peptides containing Arg-Gly-Asp (RGD) sequences are known to bind to integrins which mediate cell adhesion and therefore have been utilized in applications such as antithrombotics and tissue engineering. Although RGD and related peptides show promise, their unfavourable pharmacokinetic profiles and susceptibility to in vivo proteolysis hinder their clinical usefulness. Peptide-polymer conjugates can address one of these challenges by extending the peptide’s residence in plasma. Hyperbranched polyglycerols (HPGs) are biocompatible polyether polyols with very long plasma circulation half-lives (t1/2 ∼ 60h) and as such are ideally suited to be carriers in such conjugates. HPGs of three different molecular weights were conjugated with RGD peptides at various substitution levels. Some of the terminal hydroxyl groups of polyglycerols were converted to vinyl sulfone groups which were subsequently utilized to couple cysteine terminated RGD peptides. The following conjugates were made: 515 kDa with substitution levels of 100:1, 500:1 and 1000:1; 100 kDa with substitution levels of 100:1 and 1000:1; and 3 kDa with substitution levels of 1:1, and 10:1. RGD-coupled HPG inhibited fibrinogen binding to platelet glycoprotein IIb-IIIa as detected by flow cytometry using anti-fibrinogen. Compared to free RGD (Ic50 = 5 x 10-5 M), inhibition of fibrinogen binding increased with increasing HPG molecular weight and increasing RGD-substitution for the high MW conjugates: Ic50 for the 515 kDa conjugates were 6.3 x 10−8 M for the 100:1 substitution, 4.7 x 10-8 M for the 500:1 substitution, and 4.1 x 10−8 M for 1000:1 substitution; Ic50 for the 100 kDa conjugates were 7.0 x 10−7 M for the 100:1 substitution and 1.2 x 10−7 M for the 1000:1 substitution. Ic50 for the 3 kDa conjugates were 2 x 10−5 M for the 1:1 substitution, 2 x 10−4 M for 10:1 substitution. Similarly, platelet function, as demonstrated by MnCl2-initated aggregation was inhibited in a dose- and molecular weight-dependent manner by HPG-RGD conjugates. Platelet aggregate formation and aggregate size were confirmed by microscopy. However, unsubstituted HPG had no effect on platelet fibrinogen binding and neither conjugated nor unconjugated HPG increased platelet CD62 surface expression. Trypsin digestion (but not SBTI-treated trypsin) removed the inhibitory activity of the conjugates and thus confirmed that both fibrinogen binding and aggregation-inhibition were dependent on the RGD peptide sequence. Such multi-determinant peptide-HPG conjugates represent a new approach to the development of antithrombotic drugs.

The use of platelet additive solutions (PAS) for the storage of buffy-coat derived platelet concentrates (PC) could conserve plasma resources and reduce post-transfusion reactions. However, PASs are difficult to handle in a production environment where their relative low viscosity produces an unstable interface between the platelet rich plasma and the red cell pellet. In the current study, a comparison is drawn between buffy-coat derived PCs (4 buffy-coats per pool) stored over 7 days either in plasma or in a novel Viscous PAS that contains 26 % plasma as a by-product of the buffy-coat pooling process. The increased viscosity (1.18 cp at 37°C) of the PAS results in a stable interface during processing. Similar, though more consistent platelet recoveries from buffy-coat pools (BCP) are achieved by the Viscous PAS (77.0 ± 2.6%) as compared to plasma (73.7 ± 5.9 %). These are significantly higher (p<0.05) than recoveries using conventional PASs (64.5 ± 2.1 %). On day 7, platelet concentration, mean platelet volume (MPV), and soluble protein concentration in PCs stored using Viscous PAS (782 ± 87 x 109 cells/L, 9.1 ± 0.5fL, 15.0 ± 1.6 mg/L, respectively) and plasma (840 ± 104 x 109 cells/L, 9.0 ± 0.7fL, 56.09 ± 9.2 mg/L, respectively) were not significantly different from their corresponding day 1 parameters (837 ± 84 x 109 cells/L, 9.1 ± 0.3 fL, 13.5 ± 0.2 mg/L) respectively for Viscous PAS and (830 ± 73 x 109 cells/L, 8.3 ± 0.5 fL, 56.6 ± 6.5 mg/mL) and for plasma. This indicates that Viscous PAS and plasma maintain platelet integrity to a similar degree during 7-day storage. Both storage media maintain pH around 7.20 until day 7. However, the rate of glucose consumption and lactate production of PCs stored in Viscous PAS (0.3365 mmol/L.day, and 0.7591 mmol/L.day) was roughly half that of the rate exhibited by PCs stored in plasma (0.8447 mmol/L.day, and 1.4258 mmol/L.day). As lactate production and glucose consumption are correlated with in vivo platelet recovery (Goodrich et al., 2006) this augurs well for platelets stored in Viscous PAS. Monitoring the extent of shape change (ESC) and morphology scores for PCs in either of the storage media showed no significant difference on day 7. However, CD62 surface expression and the hypotonic shock response (HSR) were significantly better at day 7 (p<0.05) for platelets stored in the Viscous PAS (37.43 ± 3.31% and 75.76 ± 10.95%, respectively) than stored in plasma (58.37 ± 11.71% and 49.79 ± 15.34%, respectively). We have developed a PAS that is easy to handle in a production environment and because of its osmotic balance and realtive viscosity exhibits equivalent or better storage parameters over a 7 day period than does plasma.