White lupin (Lupinus albus, L.), a widely cultivated crop that has been consumed for many years in Western Europe, may provide a useful alternative for individuals wishing to substitute animal with plant proteins for cardiovascular disease prevention. Lupin seeds have a very low content of isoflavones, and lupin protein isolates are essentially isoflavone free. In rats fed a casein-based cholesterol + cholic acid diet, a relatively low daily intake (50 mg/d by gavage for 2 wk) of total lupin protein extract reduced plasma total and VLDL + LDL cholesterol concentrations by 21 and 30%, respectively (both P < 0.001). In an attempt to elucidate the lipid-lowering mechanism, LDL receptor activity was evaluated in a human hepatoma cell line (HepG2). In this model, the lupin total protein extract was essentially inactive, whereas one purified minor protein component, conglutin γ, had a remarkable upregulatory effect, with maximal increases of 53 and 21% (both P < 0.05) for LDL uptake and degradation, respectively. This initial study indicates that lupin, although isoflavone free, has hypocholesterolemic activity similar to that of other leguminous proteins in an established animal model. Further, the cholesterol reduction appears to be associated with stimulation of LDL receptors by a well-defined protein component of the lupin seeds as demonstrated by in vitro studies.

The aim of the present study was to evaluate the effect of a chronic oral γ-conglutin treatment in male Sprague–Dawley rats in which hyperglycaemia had been induced by supplying 10 %d-glucose in drinking-water. A γ-conglutin dosage of 28 mg/kg body weight was daily administered to animals for 21 d. Plasma glucose, insulin and glucose overloading were monitored. Chronic administration of glucose resulted in a statistically significant (P < 0·05) increase in fasting blood glucose (2·5-fold) and insulin (2·7-fold)v.the values recorded in control rats. Simultaneous treatment with γ-conglutin attenuated the rise in plasma glucose (1·9-fold) and insulin (1·8-fold) levels in the glucose-fed rats (P < 0·05). Fasting insulin and homeostasis model of insulin resistance were decreased by 34 and 48 % (P < 0·05), respectively, in the γ-conglutin-treated ratsv.the values found in pair-fed animals. To confirm these results with a different approach, HepG2 cells, grown for 24 and 48 h in Dulbecco's minimum essential medium containing different glucose concentrations (5·5, 11·1 and 16·5 mmol/l), were exposed to 10 μmol/l γ-conglutin with or without 10 mmol/l metformin or 100 nmol/l insulin. γ-Conglutin increased glucose consumption (from 1·5- to 2·5-fold) in HepG2 cells, under all experimental conditions; this effect was more evident after 48 h incubation. Moreover, in thisin vitromodel, the addition of γ-conglutin potentiated the activity of insulin and metformin in cell glucose consumption. These findings extend the previous ones and suggest the potential use of lupin γ-conglutin in the control of glycaemia.