Taylor Dispersion Analysis to Gain an Insight into Formulation Buffer Salts on the Stability and Aggregation Behaviour of Proteins

Wendy L. Hulse, Robert T. ForbesBiopharmaceutical Formulation Group, School of Life Sciences, University of Bradford, Bradford UK.

Email: w.l.hulse1@bradford.ac.uk

ObjectivesObjectives

Actipix TDA 200Actipix TDA 200

MethodsMethods

ConclusionsConclusions AcknowledgementsAcknowledgements

ResultsResultsTo explore the use of Taylor Dispersion Analysis to size

lysozyme in the presence of different formulation buffers and additives and to detect protein aggregation potential with

time.

To compare the results obtained with those from the conventional size measuring technique of dynamic light

scattering (DLS) and thermal analysis.

TDA200 Coupled to PrinCE CE system TDA200 Coupled to HP CE system

The band is imaged at two points, the first on entry to and the second on exit from a loop in the capillary. The hydrodynamic radius is calculated from the measured differences between peak times (first moments) and variances (second moments) at the two windows.

The TDA200 instrument uses UV area imaging and Taylor dispersion analysis (TDA) for determining diffusion coefficients and hydrodynamic radii of proteins in solution. The detector monitors broadening of a band of a therapeutic protein or small molecule solution injected into a stream of buffer solution and driven through a fused-silica capillary.

Band broadening due to Taylor dispersion is calculated from absorbance versus time data using the peak centre times at the first and second window, t1 and t2 respectively, and the

corresponding standard deviations, t1 and t2 (band broadening).

TDA analysis was carried out using 60nl of sample injected using a flow-rate of 2 mm s-1, capillary size was 75:360 ID:OD

with a total length of 143cm.

DLS analysis was carried out using a Malvern Nano-S system.

Thermal analysis was carried out using a VP-DSC with a heating and cooling rate of 1°C/min.

The authors wish to thank the EPSRC and TSB for financial support

Buffer salt selection is important and TDA demonstrates that it can notably alter the hydrodynamic radius of proteins. The TDA is a useful complement to DSC in buffer selection. The inherent, intricate behaviour of proteins in solution is complicated further by buffer systems. Both the ion and the ionic strength can affect the proteins behaviour in solution. Additional buffer systems of different salt and

ionic strength are being investigated.

Figure 1. TDA results for Lysozyme hydrodynamic radius in phosphate buffer.

Figures 4 and 5 show the TDA and DLS results for different lysozyme concentrations in acetate buffer (pH 4.5, 0.1M) which displays a narrower size range in hydrodynamic radius with increasing lysozyme concentration for TDA. The VP-DSC in Figure 6 does shows that unlike in the phosphate system, lysozyme

shows an unfolding enthalpy in the second heating cycle.

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Biopharmaceutical

Formulation

Group

1.75

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Lysozyme conc. (mg/ml)

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Acetate initial

Acetate 6 months

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Hy

dro

dy

na

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diu

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) Acetate initial

Acetate 6 months

y = 0.5219Ln(x) + 0.2015

R2 = 0.9992

y = 0.4086Ln(x) + 0.7436

R2 = 0.9932

0.50

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0.90

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Phosphate initial

Phosphate 6 months

Figure 2. DLS results for Lysozyme hydrodynamic radius in phosphate buffer. Figure 3. VP-DSC results for Lysozyme in phosphate buffer (black trace initial heating cycle, blue trace second heating cycle).

Figure 4. TDA results for Lysozyme hydrodynamic radius in acetate buffer. Figure 5. DLS results for Lysozyme hydrodynamic radius in acetate buffer. Figure 6. VP-DSC results for Lysozyme in acetate buffer (black trace initial heating cycle, blue trace second heating cycle).

Figure 7. TDA results for Lysozyme hydrodynamic radius in phosphate buffer with and without added sodium chloride.

Figure 8. VP-DSC results for Lysozyme in phosphate buffer with 2mg/ml sodium chloride added to buffer

(black trace initial heating cycle, blue trace second heating cycle).

Figure 1 shows the TDA results for different Lysozyme concentrations in phosphate buffer (pH 4.5, 50 mM) which show that increasing lysozyme concentration results in an increased hydrodynamic radius. All TDA and most DLS data points show that the hydrodynamic radius had increased

after storage. Figure 3 shows the two VP-DSC heating cycles for lysozyme (10mg/ml). No unfolding enthalpy is present in the re-heat cycle indicating that lysozyme may be irreversibly unfolded by the first heating cycle.

30 40 50 60 70 80 90 100

-0.006

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al/

o C)

Temperature (oC)

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al/

o C)

Temperature (oC)

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al/

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Phosphate 6 months

Figure 7 shows the TDA results of lysozyme (phosphate) with added sodium chloride in differing concentrations. The data indicates that addition of

NaCl produces a more consistent average hydrodynamic radius with protein concentration

than without. Secondly, the hydrodynamic radius by TDA was little influenced by salt level for this system

over 2-100mg/ml. The VP-DSC thermal profile of lysozyme in the

presence of NaCL (fig. 8) is different to that obtained without NaCl present (fig. 3), reflecting the

conformational size related changes observed using TDA.

y = 0.5219Ln(x) + 0.2015

R2 = 0.9992

0.00

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Phosphate initial Phosphate plus NaCl 2mg/ml

Phosphate plus NaCl 40 mg/ml Phosphate plus NaCl 100 mg/ml