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Macroamylases: differences in activity against various-size substrates
Abstract:
Hyperamylasemia caused by macroamylases can lead to the overdiagnosis of acute pancreatitis. We examined whether interference from macroamylase is less in assays that use high-molecular-weight rather than oligosaccharide substrates. We hypothesized that high-molecular-weight substrates would be sterically excluded from macroamylasemic complexes and thus would be hydrolyzed less efficiently. Eighteen macroamylasemic samples were assayed by using red-dyed amylopectin or blue-dyed starch as polysaccharide substrates or by using maltoheptaose or maltotetraose as oligosaccharide substrates. The oligosaccharide substrates gave comparable results (y = 0.81x + 83); we observed consistently lower activities for amylopectin than for maltotetraose (y = 0.32x + 38). We observed no bias among methods when nonmacroamylasemic specimens were analyzed. The mechanism of this difference was examined by adding anti-human pancreatic amylase antibodies to hyperamylasemic serum samples from patients without macroamylasemia and purified human pancreatic or salivary isoamylases. In each case, polyclonal and monoclonal antibodies lowered amylase activity more in assays with complex polysaccharides than in those with oligosaccharides. The use of high-molecular-weight substrates diminishes interference, and detection of suspected macroamylasemia may be possible through comparison of activities determined from automated methods that use different substrates.
Insights
Macroamylasemia can cause false acute pancreatitis diagnoses. Using high-molecular-weight substrates in amylase assays reduces interference, aiding in accurate macroamylasemia detection.
Area of Science:
- Biochemistry
- Clinical Chemistry
- Medical Diagnostics
Background:
- Macroamylasemia, a condition involving macroamylase, can lead to elevated serum amylase levels.
- Elevated amylase levels (hyperamylasemia) are often indicative of acute pancreatitis, but macroamylasemia can cause overdiagnosis.
Purpose of the Study:
- To investigate if high-molecular-weight substrates reduce interference in amylase assays compared to oligosaccharide substrates in the presence of macroamylase.
- To determine if substrate type influences amylase activity measurements in macroamylasemic samples.
Main Methods:
- Assayed 18 macroamylasemic samples using different substrates: red-dyed amylopectin (polysaccharide), blue-dyed starch (polysaccharide), maltoheptaose (oligosaccharide), and maltotetraose (oligosaccharide).
- Compared amylase activities obtained with polysaccharide versus oligosaccharide substrates.
- Investigated the mechanism by adding anti-human pancreatic amylase antibodies to hyperamylasemic serum and purified isoamylases.
Main Results:
- Oligosaccharide substrates yielded comparable amylase activity results.
- Polysaccharide substrates showed consistently lower amylase activities compared to oligosaccharide substrates in macroamylasemic samples.
- No method bias was observed when analyzing non-macroamylasemic specimens.
- Antibody addition demonstrated greater reduction in amylase activity with complex polysaccharides than with oligosaccharides.
Conclusions:
- High-molecular-weight substrates diminish assay interference caused by macroamylase.
- Comparing amylase activities from automated methods using different substrates may enable detection of suspected macroamylasemia.
- This approach can help prevent the overdiagnosis of acute pancreatitis due to macroamylasemia.