Phloretin is a much weaker inhibitor of SGLT1 than phloridzin, but it blocks GLUT2, a transporter responsible for removing glucose from enterocytes into the circulation, and GLUT1, responsible for glucose uptake in various tissues (which may affect glucose utilization). Therefore, after oral administration, phloridzin may inhibit only SGLT1 leading to a decrease of gut glucose absorption its other activities result from the activity of the aglycone-phloretin. Phloridzin, however, is a glycoside that is broken down by lactase hydrolase in the brush border membrane of the small intestine epithelial cells to phloretin and glucose. Both the effects on glucose absorption and glucose excretion decrease serum blood glucose concentration. Blockade of SGLT2 inhibits glucose reabsorption in the kidneys, increasing its excretion. Blockade of SGLT1 leads mainly to inhibition of glucose absorption from the small intestine as a result of the reduction of active transcellular glucose uptake. Phloridzin inhibits competitively SGLT1 and SGLT2. SGLT cotransporters are membrane proteins involved in the sodium-dependent glucose transport, especially the absorption of glucose in the small intestine (SGLT1) and the reabsorption of glucose from the glomerular filtrate in the kidneys (SGLT2 and, to a lesser extent, SGLT1).
Phloridzin has become the precursor of a new class of antidiabetic drugs-SGLT2 (sodium-glucose cotransporter 2) inhibitors. The most intensively studied were the effects of phloridzin on glucose absorption and excretion, and diabetes.
Phloridzin was first isolated from the apple tree bark by De Koninck in 1835. Moreover, old apple cultivars contain bigger amounts of phloridzin than newer ones. Unpeeled apples are a richer source of phloridzin than peeled ones, since phloridzin content in apple peel is 12–418 mg/kg, whereas in apple pulp-4–20 mg/kg. Phloridzin is mainly present in apple leaves and bark, but also, in lower amounts, fruits.
Phloridzin is a glycoside of phloretin (phloretin 2′-O-glucoside), a flavonoid belonging to the chemical class of dihydrochalcones. One of the most recognized apple polyphenols is phloridzin (phlorizin). fruit) consumption may be associated with a decreased risk of cancer, cardiovascular diseases or type 2 diabetes, because apples are a rich source of many compounds, such as flavonoids, phenolic acids, vitamins, that have health-promoting effects. It is commonly believed that apple (Malus × domestica Borkh. Results of the study indicate the possibility of unfavorable effects of phloridzin on the musculoskeletal system in conditions of hyperglycemia. Phloridzin at 20 mg/kg markedly augmented the unfavorable effects of diabetes on the muscle mass and strength and decreased growth of bones, whereas, at 50 mg/kg, it did not affect most of the investigated musculoskeletal parameters. The HFD/STZ rats developed hyperglycemia, with decreases in the muscle mass and strength and profound osteoporotic changes. Serum biochemical parameters, muscle mass and strength, bone mass, density, histomorphometric parameters and mechanical properties were determined. The experiments were performed on mature female Wistar rats, divided into control rats (fed a standard laboratory diet), HFD/STZ control rats, and HFD/STZ rats receiving phloridzin (20 or 50 mg/kg/day per os) for four weeks. The aim of the study was to investigate the effects of phloridzin on musculoskeletal system in rats with type 2 diabetes induced by a high-fat diet (HFD) and streptozotocin (STZ). Phloridzin and phloretin were reported to exert some favorable skeletal effects in estrogen-deficient rats and mice. One of the most known apple compounds is phloridzin, a glucoside of phloretin. It is believed that apple fruits contain components with health-promoting effects, including some antidiabetic activity.
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