Pumpkin (Cucurbita moschata Duch), an annual herbaceous plant of the family Cucurbitaceae, is widely grown and consumed in the world. The fruit of pumpkin is rich in polysaccharides, carotene, minerals, vitamins, and other components beneficial to health. Pumpkin polysaccharides have been reported by various studies to have a diversity of biological effects including antioxidant activities, antimicrobial effects, and hypoglycemic effects (1-5).

 

    The glycosidic bonds of polysaccharides can be broken by acid or enzyme treatment, which can derive oligosaccharides hydrolysates. Such breakdown oligosaccharides could exhibit better bioactivities due to their higher bioavailability and easier absorbency in living organisms. In addition, the hydrolyzed components may have some novel biological activities because of their different physicochemical properties and molecular structures (1).

 

    One study (1) examined the antioxidant and antidiabetic activities of pumpkin polysaccharides and their acid hydrolysates in a rat model of diabetes. Pumpkin polysaccharides were extracted from dried pumpkin pulps, and pumpkin polysaccharides were then further hydrolyzed using acid to get smaller sizes of polysaccharides as pumpkin polysaccharides hydrolysates. Pumpkin polysaccharides and pumpkin polysaccharides hydrolysates were both the heteropolysaccharide and composed of rhamnose, arabinose, glucose, and galactose, their molecular weight was 104.27 kDa and 37.58 kDa, respectively.

 

    The rats were divided into 5 groups randomly (n = 5) as follows: Group 1: control group, normal rats were orally administered with saline; Group 2: the diabetic model group, the diabetic rats orally administered with saline; Group 3: the positive control group, the diabetic rats orally administered with acarbose (a drug to reduce blood glucose) melted in saline; Group 4: pumpkin polysaccharides group, the diabetic rats orally administered with pumpkin polysaccharides at 150 mg/kg body weight/day. Group 5: pumpkin polysaccharides hydrolysates group, the diabetic rats were orally administered with pumpkin polysaccharides hydrolysates at 150 mg/kg body weight/day.

 

    After 3 weeks of pumpkin polysaccharides and pumpkin polysaccharides hydrolysates administration, fasting blood glucose levels of the diabetic rats decreased by 76.17% and 87.06%, respectively, compared to the levels before the treatment. Compared to the diabetic model group, pumpkin polysaccharides and pumpkin polysaccharides hydrolysates feeding for 3 weeks significantly reduced fasting blood glucose levels (10.66±5.14 and 10.36±3.32 in pumpkin polysaccharides and pumpkin polysaccharides hydrolysates groups vs 16.60±2.91 mmol/L), prevented the weight loss in diabetic rats and enhanced the activities of the antioxidant enzymes (catalase and glutathione reductase, p < 0.01, and the glutathione, p < 0.05). Besides, pumpkin polysaccharides hydrolysates could significantly decrease the level of malondialdehyde (MDA, a marker for oxidative stress) (p < 0.05).

 

    Pumpkin polysaccharides had a distinct effect on the suppression of body weight loss compared to diabetic model rats at 21 days. Weight loss in diabetes is typical due to accelerated protein hydrolysis and fat hydrolysis for glucose generation which then resulted in a reduction in muscle and adipose tissue. Both pumpkin polysaccharides and pumpkin polysaccharides hydrolysates could help diabetic rats recover their body weight to a certain extent, and slow down weight loss (1).

 

    The liver glycogen levels of pumpkin polysaccharides and pumpkin polysaccharides hydrolysates raised significantly compared to the diabetic model rats (p < 0.05), indicating that both pumpkin polysaccharides and pumpkin polysaccharides hydrolysates could inhibit glycogen output, increase glycogen content, and improve glucose metabolism. The liver is the organ that regulated the amount of blood glucose in the body. Glycogen output is positively correlated with fasting blood glucose in the state of diabetes, and it is the primary cause of fasting hyperglycemia. Increasing liver glycogen storage thus can lower blood glucose levels.

 

    One of the main pathogenic mechanisms of diabetes is the production of excessive reactive oxygen species caused by oxidative stress, thus it is crucial to enhance the antioxidant capability aiming at relieving oxidative stress. Glutathione and the primary antioxidant enzymes catalase and glutathione reductase could scavenge free radicals effectively and improve oxidative damage in cells or organisms. Therefore, the enhanced levels and activities of these enzymes may provide an efficient defense against free radicals damaging.

 

    In another study (2), the effects of pumpkin polysaccharides that were extracted using a commercial a-amylase-assisted method were evaluated in KKAy mice (a rodent model of diabetes). Twenty-four KKAy mice were divided into two groups: the control was fed a high-fat diet; while the pumpkin polysaccharides group was fed a high-fat diet with the addition of pumpkin polysaccharides at the same time, for 6 weeks. Pumpkin polysaccharides diet (pumpkin polysaccharides are included as 10% of the diet by weight) significantly reduced body weight gain, the levels of plasma insulin, triglyceride, cholesterol, low-density lipoprotein cholesterol, and fasting blood glucose in mice and improved the level of high-density lipoprotein cholesterol and liver glycogen (p<0.05).

 

    For fasting blood glucose, the control group had an initial level of ~ 12 mmol/L which continuously increased to ~16 mmol/L by the end of the 6-week study, while the pumpkin polysaccharides group had the glucose level decreased from the initial ~12 mmol/L to ~ 8 mmol/L by the end of the study, a level roughly 50% of that in the control group. By the end of the study, the levels of insulin (17.9 ± 0.78 vs 13.7 ± 0.71 mU/L), triglyceride (1.3 ± 0.06 vs 0.6 ± 0.05 mmol/L), cholesterol (3.6 ± 1.54 vs 2.1 ± 0.02 mmol/L), low-density lipoprotein cholesterol (1.5 ± 0.07 vs 0.7 ± 0.04 mmol/L), high-density lipoprotein cholesterol (2.6 ± 5.37 vs 3.5 ± 5.92 mmol/L) and liver glycogen (1.8 ± 0.23 vs 4.3 ± 0.71 mg/g)  in the control group vs pumpkin polysaccharides group were significantly different. These results can suggest that pumpkin polysaccharides/pumpkin can be promising hypoglycemic and hypolipidemic agents for diabetes management (2).

 

    In a rabbit study (3), alloxan-induced diabetic rabbits were given pumpkin polysaccharides for 21 days to assess their effects on pancreatic islet tissue morphology. After 21 days, the weights of the alloxan-induced diabetic and non-diabetic rabbits fed with a diet containing pumpkin polysaccharides were significantly increased as compared to the control group. Compared with the diabetic control group, the pumpkin polysaccharides diet significantly reduced blood glucose (8.07 ± 2.54 vs 17.43 ± 2.76 mM, p<0.01), cholesterol (2.02 ± 0.17 vs 4.93 ± 0.23 mM, p<0.01), triglyceride (1.85 ± 0.49 vs 4.47 ± 0.38 mM, p<0.01), and glycosylated hemoglobin (HbA1c)(6.89 ± 0.62 vs 11.62 ± 0.28, p<0.01). Observing the pancreatic tissue of the diabetic rabbits revealed that pumpkin polysaccharides could promote the regeneration of damaged pancreatic islets by stimulating cell proliferation, which was accompanied by a decrease in plasma glucose levels. These results indicated that pumpkin polysaccharides had effects on lowering glucose and lipid levels and protecting the pancreas from injuries for better diabetes management.

 

    In a preliminary study (4), the effects of ethanolic extracts of three vegetable peels from the Cucurbitaceae family were studied at 250 and 500 mg /kg/day for 15 days on blood glucose and hepatic lipid peroxidation in mice. The effective and safe concentration of each peel was administered for 10 consecutive days and then on the 11th and 12th days alloxan was administered along with peel extracts. The treatment was continued up to the 15th day. In the end, all three peel extracts nearly reversed most of these changes induced by alloxan suggesting their possible role in ameliorating diabetes mellitus and related changes in serum lipids. Pumpkin peel was found to be the most effective. Pumpkin peel reduced hepatic lipid peroxidation (p< 0.001) and increased the antioxidant enzymes superoxide dismutase and catalase significantly. Pumpkin peel extract also decreased the levels of cholesterol, triglycerides, VLDL-cholesterol, and LDL-cholesterol, and increased HDL-cholesterol levels significantly (p<0.001). The doses of pumpkin peel extract at 250 and 500 mg/kg/day resulted in a significant reduction in blood glucose levels from 102.42±14.28 mg/dL to 94.11±7.08 (-8.11%) and 74.36±6.77 (-27.1%) mg/dL, respectively. 

 

    The Cucurbita genus has received a renowned interest in recent years. This plant species has been used in worldwide folk medicine for its many health benefits including the hypoglycemic effect (5). However, few recent studies have studied the effects of pumpkins on humans. This is probably due to the already wide consumption of pumpkin as food, and its health benefits have been well-known. For people who have high blood glucose and diabetes, including pumpkin as part of the diet would help to reduce blood glucose levels and to benefit diabetes management.

 

References:

1. Lu, A., Yu, M., Fang, Z., Xiao, B., Guo, L., Wang, W., Li, J., Wang, S., Zhang, Y. (2018). Preparation of the controlled acid hydrolysates from pumpkin polysaccharides and their antioxidant and antidiabetic evaluation. International Journal of Biological Macromolecules. doi:10.1016/j.ijbiomac.2018.09.158

2. Song H, Sun Z. Hypolipidaemic and hypoglycaemic properties of pumpkin polysaccharides. 3 Biotech. 2017 Jul;7(3):159. doi: 10.1007/s13205-017-0843-1. Epub 2017 Jun 29. PMID: 28660447; PMCID: PMC5489452.

3. Zhang Y, Chen P, Zhang Y, Jin H, Zhu L, Li J, Yao H. Effects of polysaccharide from pumpkin on biochemical indicator and pancreatic tissue of the diabetic rabbits. Int J Biol Macromol. 2013 Nov;62:574-81. doi: 10.1016/j.ijbiomac.2013.09.044. Epub 2013 Oct 1. PMID: 24095662.

4. Dixit, Y., & Kar, A. (2010). Protective Role of Three Vegetable Peels in Alloxan Induced Diabetes Mellitus in Male Mice. Plant Foods for Human Nutrition, 65(3), 284–289. doi:10.1007/s11130-010-0175-3

5.  Salehi, B., Capanoglu, E., Adrar, N., Catalkaya, G., Shaheen, S., Jaffer, M., Giri, L., Suyal, R., Jugran, A. K., Calina, D., Docea, A. O., Kamiloglu, S., Kregiel, D., Antolak, H., Pawlikowska, E., Sen, S., Acharya, K., Selamoglu, Z., Sharifi-Rad, J., . . .  Capasso, R. (2019). Cucurbits Plants: A Key Emphasis to Its Pharmacological Potential. Molecules, 24(10). https://doi.org/10.3390/molecules24101854

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​Photo by Marius Ciocirlan on Unsplash