Sorbitol

Sorbitol

• A 69-year-old man presents to your clinic with a chief complaint of changes in his vision.  He has a past medical history of diabetes mellitus type II and medication non-compliance.  The patient states that after a very large meal in which he consumed a family-sized bucket of chicken, a glass of maple syrup, and an entire wedding cake, he noticed that his vision became very blurry. He notes that this tends to happen whenever he eats a large meal.

Overview

• Pathway
  • alternative method of trapping glucose in the cell
    • tissues with sorbitol dehydrogenase
      • liver
      • ovaries
      • seminal vesicles
      • lens (at low level of activity)
    • tissues without sorbitol dehydrogenase
      • Schwann cells
      • retina
      • kidneys
  • note: galactose can also be converted to an aldose
    • see Galactose Metabolism topic 
• Clinical relevance
  • prolonged hyperglycemia
    • commonly caused by uncontrolled diabetes mellitus
    • pathophysiology
      • glucose enters cells and is converted to sorbitol
        • in tissues without sorbitol dehydrogenase or low levels of activity
          • sorbitol trapped in cell and is osmotically active
    • presentation
      • pathology directly linked to which tissues have aldose reductase but lack sorbitol dehydrogenase 
        • peripheral neuropathy
        • cataracts
        • retinopathy
        • all symptoms of chronic diabetes

Introduction

Sorbitol is a type of sugar alcohol commonly used as a sweetener and humectant in various food and pharmaceutical products. It is derived from glucose and is also naturally found in fruits such as apples, pears, and peaches.

In the context of the USMLE exam, sorbitol may be relevant in several areas of study, including biochemistry, pharmacology, and pathology. For example, it may be important to understand the metabolism of sorbitol in the liver, as defects in this pathway can lead to conditions such as hereditary fructose intolerance.

Studies

• Metabolism: A study published in the Journal of Clinical Investigation investigated the role of sorbitol in the pathogenesis of diabetic complications. The study found that elevated levels of sorbitol in tissues can lead to oxidative stress and tissue damage.
• Food industry: Sorbitol is widely used as a sugar substitute in food products. A study published in the Journal of Food Science and Technology evaluated the sensory properties of ice cream made with sorbitol and found that it was a suitable substitute for sugar, resulting in a similar taste and texture.
• Pharmaceutical industry: Sorbitol is commonly used as an excipient in pharmaceutical formulations due to its good solubility and low toxicity. A study published in the Journal of Pharmaceutical Sciences investigated the effects of sorbitol on the dissolution and bioavailability of a poorly water-soluble drug and found that sorbitol can enhance the dissolution rate and bioavailability of the drug.
• Dental industry: Sorbitol is used in many sugar-free chewing gums and mints due to its non-cariogenic properties. A study published in the Journal of Dental Research found that sorbitol-sweetened chewing gum can reduce plaque formation and promote oral health.

Complications

While sorbitol is generally recognized as safe for consumption, there are potential complications associated with its use, particularly when consumed in large quantities. Here are some examples:

• Gastrointestinal distress: Sorbitol is a type of sugar alcohol that is not completely absorbed in the small intestine, which can lead to osmotic diarrhea, bloating, and abdominal discomfort in some individuals.
• Increased calorie intake: While sorbitol has fewer calories than sugar, it still contains calories and can contribute to overall calorie intake if consumed in excess.
• Dental issues: Sorbitol can promote tooth decay if consumed in the form of candies or gum, as bacteria in the mouth can ferment the sorbitol and produce acids that erode tooth enamel.
• Allergic reactions: Some individuals may have an allergic reaction to sorbitol, which can manifest as hives, itching, or difficulty breathing.
• Metabolic disorders: Sorbitol metabolism is closely linked to glucose metabolism, and defects in the sorbitol pathway can lead to metabolic disorders such as hereditary fructose intolerance.

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