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Consideration of Important Preanalytical Conditions for the Assessment of Circulating Matrix Metalloproteinase-9

We thank Drs. John and Jung for their comments on our article (1). We agree that the significance of blood collection is an important preanalytical determinant for the measurement of the concentration of circulating matrix metalloproteinase (MMP)-9. In our study we measured the serum levels of MMP-9 and compared levels between obese control subjects and patients with obstructive sleep apnea syndrome. Serum samples were collected using tubes without clot activator from all subjects. Serum levels of MMP-9 were measured with an ELISA kit obtained from Amersham Biosciences that can detect the pro–MMP-9 and pro–MMP-9–TIMP-1 complexes. The MMP-9 detection kit had < 3% cross-reactivity with pro–MMP-1, pro–MMP-2, and pro–MMP-3. We agree that MMP-9 levels may differ significantly between serum and plasma samples. In addition, it will be important to investigate the effect of different blood sampling techniques on the activity of circulating MMP-9.

Kenji Minoguchi

Showa University, Tokyo, Japan

FOOTNOTES

Conflict of Interest Statement: K.M. does not have a financial relationship with a commercial entity that has an interest in the subject of this letter.

REFERENCES

1. Tazaki T, Minoguchi K, Yokoe T, Samson KTR, Minoguchi H, Tanaka A. Watanabe Y, Adachi M. Increased levels and activity of matrix metalloproteinase-9 in obstructive sleep apnea syndrome. Am J Respir Crit Care Med 2004;170:1354–1359.[Abstract/Free Full Text]

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