modification of commercial elisa kit for quantification of total ghrelin
TRANSCRIPT
Modification of Commercial Kit Assay Conditions May Be Necessary for
Increasing the Sensitivity of Biomarker Quantification: A Case StudyMatalin Shine, Deborah Martin and Masood Khan - KCAS, Shawnee, Kansas 66216 USA
Ghrelin is an appetite-stimulating peptide hormone. Several
commercial kits are available for quantification of Total and
Active Ghrelin. We set out to identify, select, and perform a Fit-
for-Purpose Validation of a commercial kit-based assay for
reliable quantification of Total Ghrelin in human plasma.
Appetite-stimulating peptide hormone Ghrelin exists in both
Active acylated [octanoyl group on serine-3] and Inactive un-
acylated forms. Metabolic effects of Ghrelin are mediated by
Active Ghrelin. Ratios of Total and Active Ghrelin are measured
as biomarkers in a variety of studies. In our quest for a reliable
kit for quantification of Ghrelin, we evaluated two commercial
kits from the same vendor. Though the kit for Active Ghrelin
worked well under assay conditions specified by the kit
manufacturer, significant changes in incubation conditions were
required to achieve optimum sensitivity of the ELISA kit for Total
Ghrelin. In this case study, a fit-for purpose modification of the
Total Ghrelin assay is described and analytical method
qualification characteristics of the assay are presented.
OBJECTIVE
INTRODUCTION
METHOD
RESULTS
Fig. 1: Ghrelin: An Appetite Biomarker
RESULTS (CONT.)RESULTS (CONT.)
CONCLUSION
Fig. 2: LLOQ Evaluation: Original Condition (A)
Fig. 3 : LLOQ Evaluation: Modified Condition (B)
Table 1: Dynamic Range of Quantification
Table 2: Precision of Measurements (Assay Controls)
Table 4: Assay Specificity
Table 7: Dilutional Linearity (Spiked Human Plasma)
Table 5: Short and Long-Term Stability in Human Plasma
• An ELISA kit for quantification of Total Ghrelin in human plasma
was used essentially as instructed by the manufacturer
(Condition A: 2 hours, RT). The kit manufacturer claimed a
theoretical minimum detectable concentration of 100 pg/mL.
However, assay sensitivity (LLOQ) at even 300 pg/mL could not
be achieved under these conditions.
• Alteration of the incubation conditions dramatically improved the
assay LLOQ to 200 pg/mL (Condition B: Overnight, 4 oC).
• Stabilized plasma control samples showed excellent
Inter- and Intra-assay precision of measurements.
• Concentrations determined in plasma control
samples were used as nominal concentration when
these samples were used for stability evaluation
experiments.
Table 6: Assay Selectivity (Addition Recovery)
• LQC and HQC samples were assayed in the absence (Baseline) and presence of Test Compounds (Glucagon and Insulin) at concentrations of 1200 and 4800 pg/mL, respectively.
Table 3: Precision of Measurements (Plasma Controls)
* Anchor Point
• Caution should be exercised in taking face value of assay
sensitivity claimed by the kit manufacturer. This may be a
theoretical value rather than the LLOQ of the assay.
• It may be necessary to have a clear understanding of the
assay design in order to make significant modifications in
assay conditions to achieve optimal method performance for
the intended use.
• The modified method must then undergo a formal analytical
method qualification (Fit-for-Purpose Validation) prior to use
for study sample analysis.
• Khan, M., Adaptation of fit-for-purpose biomarker assay validation using
commercial kits: A CRO perspective. Drug Research 11/12: 33-34, (2010).
• Lee, JW et. al., Fit-for-Purpose Method Development and Validation for
Successful Biomarker Measurements. Pharm Research 23 (2): 312-28
(2006).
REFERENCES
Plasma Sample Stabilization• Active Ghrelin is extremely unstable in blood / plasma.
• Blood samples are drawn into chilled EDTA Vacutainer tubes
preloaded with Aprotinin (500 KIU/mL).
• The blood is promptly centrifuged and the plasma separated and
acidified with 100 µL of 1 N HCl/mL. Aliquots of stabilized plasma
samples are stored frozen at a temperature ≤-20 oC.
• Condition A: (Original Condition): Lower Limit of
Quantification (LLOQ) could not be achieved even at
300 pg/mL.
• Condition B: (Modified Condition): LLOQ dramatically
improved to 200 pg/mL.
* Nominal Conc. = 1750.9 pg/mL
S-GHRL- Stomach Ghrelin
H-GHRL – Hypothalamus Ghrelin
R – Receptor
AgRP-Agouti-Related Peptide
NPY - Neuropeptide Y
LEPT - Leptin * % Baseline conc. (981.1 & 1750.9 pg/mL for Control-1 and Control-2, respectively)