Polyol pathway and NADPH-dependent reductases in dog leukocytes

Area of Science:

• Biochemistry
• Immunology
• Cell Biology

Background:

• Recent reports link excess sugar alcohols to leukocyte dysfunction in diabetes.
• The polyol pathway's role in leukocytes remains unclear.
• Investigating sugar alcohol metabolism in leukocytes is crucial for understanding diabetes-related complications.

Purpose of the Study:

• To investigate NADPH-dependent reductases and sugar alcohol formation in dog leukocytes.
• To determine the specific reductases involved in sugar alcohol synthesis.
• To assess the in vivo and in vitro implications of sugar alcohol accumulation in leukocytes.

Main Methods:

• Isolation of mononuclear and polymorphonuclear leukocytes from dogs.
• Enzyme activity assays using DL-glyceraldehyde as a substrate.
• 19F nuclear magnetic resonance (NMR) spectroscopy to confirm in vitro glucose conversion.
• Gas chromatography to quantify in vivo sugar alcohol accumulation.
• Assessment of NADPH oxidase activity in neutrophils.

Main Results:

• NADPH-dependent reductase activity was found in both leukocyte types, primarily aldehyde reductase.
• In vitro, glucose was confirmed to convert to sorbitol and fructose in leukocytes.
• In vivo, galactitol accumulated in mononuclear cells more than polymorphonuclear leukocytes from galactose-fed dogs.
• Neutrophil NADPH oxidase activity was reduced in galactose-fed dogs.

Conclusions:

• Dog leukocytes convert glucose to sorbitol and fructose via the polyol pathway.
• Sugar alcohol accumulation and enzyme activity differ between mononuclear and polymorphonuclear leukocytes.
• These findings suggest a potential mechanism for leukocyte dysfunction in diabetes related to sugar alcohol metabolism.