Garden Cress Seed and Custard Apple Leaf Extracts Lower Blood Sugar in Diabetic Rats

A combination of ethanolic extracts from garden cress seeds (Lepidium sativum) and custard apple leaves (Annona squamosa) brought fasting blood glucose, insulin resistance and glucose tolerance back to near-normal levels in rats with chemically induced diabetes, according to a new open-access study published in Food Production, Processing and Nutrition. The work, led by Karima Said Mohamed Hammad, Nashwa Fathy Sayed Morsy and Nesren Elsayed of Cairo University, is the first in vivo evaluation of these two plant extracts used together, and it suggests that pairing them may deliver a stronger antidiabetic effect than either plant alone.

The researchers induced diabetes in adult male albino rats with two consecutive low doses of streptozotocin, or STZ, a compound that progressively destroys the insulin-producing beta cells of the pancreas. This two-dose approach was chosen deliberately: according to the authors, a single high dose of STZ causes rapid, extensive beta-cell damage accompanied by acute toxicity, whereas two consecutive low doses achieve gradual beta-cell destruction while avoiding toxicity. Rats whose fasting blood glucose exceeded 250 mg/dL after induction were classified as diabetic and entered the treatment phase of the experiment.

Forty-eight rats were divided into eight groups of six animals each, the maximum permitted under the ethics committee’s guidelines and the 3Rs principles of replacement, reduction and refinement. One group of non-diabetic rats and one diabetic group received only distilled water by oral gavage. The remaining six diabetic groups received, for 21 days, either garden cress seed extract at 200 or 400 mg per kilogram of body weight per day, custard apple leaf extract at the same two doses, or the two extracts combined at 100 or 200 mg of each per kilogram per day. The freeze-dried extracts were suspended in distilled water and given orally. Notably, the protocol included no drug-treated positive control, so all effects were measured relative to the untreated diabetic group rather than against a conventional antidiabetic medication.

Before testing the extracts in animals, the team characterized their chemistry. Total phenolic content, measured with the Folin-Ciocalteu reagent, was 13.29 mg gallic acid equivalents per gram of dry extract for the seed extract and 53.46 mg/g for the leaf extract. High-performance liquid chromatography detected twelve polyphenols and flavonoids in the seed extract and nineteen in the leaf extract. Benzoic acid, ellagic acid, vanillic acid and vanillin dominated the seed extract, while p-coumaric acid at 26.92 µg/mL and benzoic acid at 23.43 µg/mL were the most prominent compounds in the leaf extract. Myricetin was the most abundant flavonoid in both, with the seed extract containing 102.58 µg/mL, more than eight times the level found in the leaf extract. Ellagic acid reached 19.65 µg/mL in the seed extract but was absent from the leaf preparation.

The metabolic results were striking. Untreated diabetic rats saw fasting blood glucose climb from 5.24 mmol/L before induction to 27.52 mmol/L after three weeks. Treatment with garden cress seed extract at 400 mg/kg per day, or with the combined extracts at 200 mg of each per kilogram per day, reduced fasting glucose to values statistically indistinguishable from those of the non-diabetic control group. Custard apple leaf extract at both doses and the lower-dose combination significantly improved blood glucose but did not restore it fully to the normal range. Doubling either single extract from 200 to 400 mg/kg produced no significant additional glucose reduction, and the seed extract proved more than twice as effective as the leaf extract at equivalent concentrations.

Insulin and insulin sensitivity told a parallel story. Plasma insulin fell significantly in all diabetic groups except the rats receiving the high-dose seed extract, whose insulin levels returned to values not significantly different from normal controls. The combination at 200 mg of each extract also significantly improved insulin levels, though not fully to normal. HOMA-IR, a calculated index of insulin resistance, improved significantly toward control values in the rats given seed extract at either dose and in the high-dose combination group. On an oral glucose tolerance test performed on day 20, the seed extract at 200 mg/kg and the leaf extract at 400 mg/kg improved impaired glucose tolerance by 54.3 percent and 52.5 percent respectively, while the high-dose seed extract and the high-dose combination reduced glucose intolerance to the level of the non-diabetic rats. Plasma fructosamine, a marker of glycemic control over roughly three weeks, was normalized by the seed extract at both doses and by the leaf extract at the higher dose.

The lipid profile shifted as well. Streptozotocin-induced diabetes raised total cholesterol, triglycerides and LDL cholesterol by 125, 75 and 300 percent respectively while cutting HDL by half. The seed extract at both doses significantly lowered cholesterol, triglycerides and LDL and raised HDL. The leaf extract at 200 mg/kg produced even larger percentage reductions in cholesterol, triglycerides and LDL, but curiously, the 400 mg/kg dose of the leaf extract failed to significantly lower cholesterol or triglycerides, an outcome the authors attribute to higher levels of alkaloids, tannins and acetogenins that may reduce the bioavailability of active compounds. The low-dose combination significantly improved all four lipid measures, whereas the high-dose combination lowered triglycerides and LDL but did not significantly reduce total cholesterol.

Kidney and pancreatic tissue showed measurable protection. Serum creatinine, an indicator of kidney dysfunction, was significantly reduced by the high doses of both individual extracts, while serum albumin was unaffected by diabetes or treatment. Under the microscope, untreated diabetic rats displayed severe kidney damage, including tubular vacuolation, pyknotic nuclei, hyaline casts, hemorrhage and glomerular atrophy. In the liver, the high-dose combination largely restored normal histological patterns. The authors suggest these structural recoveries, together with improved glycemic markers, indicate that the extracts reduce beta-cell destruction and support beta-cell structural recovery, likely through polyphenols such as p-coumaric acid, rutin, naringenin and myricetin that have been reported to enhance insulin secretion.

The authors frame the combination’s advantage as synergy: at 200 mg of each extract, the mixture restored fasting glucose, glucose tolerance and insulin sensitivity in a way that the seed extract alone at the same total dose did not, achieving comprehensive glycemic control with less of each individual extract. However, they are careful to enumerate the limitations. The effects were assessed only in a streptozotocin-induced rat model, which does not fully mimic human diabetes; the absence of a positive control group prevents comparison with conventional drugs; the dose range and three-week duration preclude conclusions about long-term safety; molecular mechanisms were not investigated; and oxidative stress biomarkers were not measured, leaving the proposed antioxidant pathway unvalidated. Because the findings derive entirely from an experimental animal model, the authors conclude that further studies are required before any clinical relevance can be established.

Subject of Research: Antidiabetic effects of garden cress seed and custard apple leaf extracts in diabetic rats

Article Title: Comparative studies on the antidiabetic effects of extracts of Lepidium sativum L. seeds and Annona squamosa L. leaves on Streptozotocin-induced diabetic rats

Article References: Hammad, K. S. M., Morsy, N. F. S., & Elsayed, N. (2026). Comparative studies on the antidiabetic effects of extracts of Lepidium sativum L. seeds and Annona squamosa L. leaves on Streptozotocin-induced diabetic rats. Food Production, Processing and Nutrition, 8(1), Article 65. https://doi.org/10.1186/s43014-026-00415-7

Image Credits: AI Generated

DOI: 10.1186/s43014-026-00415-7

Keywords: diabetes, garden cress, custard apple, plant extracts, streptozotocin, rats, polyphenols, insulin resistance, HOMA-IR, histopathology, blood glucose, lipid profile