Nutritional evaluation of the trypsin (EC 3.4.21.4) inhibitor from cowpea (Vigna unguiculata Walp.)

Proteinase inhibitors in legume herbivore defense: from natural to genetically engineered protectants

Proteinase inhibitors (PIs) from legumes have the potential for use as protectants in response to pests and pathogens. Legumes have evolved PIs that inhibit digestive proteinases upon herbivory resulting in delayed development, deformities, and reduced fertility of herbivorous insects. Legume PIs (serine proteinase inhibitors and cysteine proteinase inhibitors) have been overexpressed in plants to confer plant protection against herbivores. Recently, the co-expression of multiple PIs in transgenic plants enhanced host defense over single PI expression, i.e., in an additive fashion. Therefore, a synthetic PI could conceivably be designed using different inhibitory domains that may provide multifunctional protection. Little attention has yet given to expanding PI gene repertoires to improve PI efficacy for targeting multiple proteinases. Also, PIs have been shown to play an important role in response to abiotic stresses. Previously published papers have presented several aspects of strategic deployment of PIs in transgenic plants, which is the focus of this review by providing a comprehensive update of the recent progress of using PIs in transgenic plants. We also emphasize broadening the potential usefulness of PIs and their future direction in research, which will likely result in a more potent defense against herbivores.

Consumption of diets containing raw soya beans (Glycine max), kidney beans (Phaseolus vulgaris), cowpeas (Vigna unguiculata) or lupin seeds (Lupinus angustifolius) by rats for up to 700 days: effect on body composition and organ weights

Feeding trials have been done with rats to assess the effects of long-term (700 d) consumption of diets based on raw cowpeas (Vigna unguiculata; moderate Bowman–Birk inhibitor content, low lectin content), lupin seeds (Lupinus angustifolius; low lectin and protease inhibitor content) or soya beans (Glycine max; high Kunitz inhibitor content, moderate Bowman–Birk inhibitor content, moderate lectin content) or diets containing low levels of raw kidney bean (Phaseolus vulgaris; high lectin content, low Bowman–Birk inhibitor content) on body weight and composition and organ weights. All the legume-based diets reduced feed conversion efficiency and growth rates during the initial 250 d. However, after 250 d the weight gains by rats given legume-based diets were similar to those of controls given the same daily feed intake. Long-term consumption of diets containing low levels of kidney bean significantly altered body composition of rats. The levels of lipid in the body were significantly reduced. As a result, carcasses of these rats contained a higher proportion of muscle/protein than did controls. Small-intestine relative weight was increased by short- and long-term consumption of the kidney-bean-based diet. However, the increase in relative pancreatic weight observed at 30d did not persist long term. None of the other legume-based diets caused any significant changes in body composition. However, long-term exposure to a soya-bean- or cowpea-based diet induced an extensive increase in the relative and absolute weights of the pancreas and caused an increase in the incidence of macroscopic pancreatic nodules and possibly pancreatic neoplasia. Long-term consumption of the cowpea-, kidney-bean-, lupin-seed- or soya-bean-based diets by rats resulted in a significant increase in the relative weight of the caecum and colon.

Effect of supplementation on the feed intake and performance of confined and scavenging crossbred growing chickens in Burkina Faso

An experiment was conducted to evaluate the performance of crossbred growing chickens (Rhode Island Red x indigenous Burkina Faso hens) from 6 to 17 weeks of age, under five feeding/management regimes: (1) CMx(+), confined and given a mixed feed containing cracked maize and cowpea and a vitamin-mineral premix ad libitum; (2) CS(+), confined and offered ad libitum a choice of cracked maize and cowpea with the premix; (3) ScS(+), scavenging from 09:00 to 16:00 with the diet in treatment (2) available from 16:00 to 09:00; (4) ScS(-), treatment (3) but without the premix; and (5) ScO, scavenging only, with no supplements provided. Daily dry matter (DM) intake was highest for CS(+) (43.5 g), and lowest for CMx(+) (33.6 g) (p < 0.05), with intermediate intakes for ScS(+) and Sc(-) of 36.7 g and 36.2 g, respectively. The ratios of intakes of cowpea to maize were 50:50, 21:79, 27:73 and 22:78 for CMx(+), CS(+), ScS(+) and ScS(-), respectively (p < 0.05). Dietary concentrations of crude protein (CP) were 15.7%, 11.5%, 12.3% and 11.6% of DM for CMx(+), CS(+), ScS(+) and ScS(-), respectively. Average daily gains (ADG) were 8.15 g, 5.24 g, 6.03 g, 5.36 g and 4.45 g for CMx(+), CS(+), ScS(+), ScS(-) and ScO, respectively, and were significantly higher for CMx(+) (p < 0.05). Feed conversion ratio was highest for CS(+) and lowest for CMx(+). ADG of the males (6.44 g) was significantly (p < 0.05) higher than that of the females (5.86 g). Breast and thigh muscle weights were highest for ScS(+) (p < 0.05).

Prima facie evidence that a phytocystatin for transgenic plant resistance to nematodes is not a toxic risk in the human diet

A protein-engineered rice cystatin (OcIDeltaD86) provides transgenic, partial crop resistance to plant nematodes. This study determined whether its oral uptake has adverse effects on male Sprague-Dawley rats when they are administered by oral gavage 0.1-10 mg OcIDeltaD86/kg body weight daily for 28 d. Body weight and water and food intakes were unaltered for most of the study. The only significant changes in fresh weight of nine organs were for the liver (4% decrease; P < 0.05) and the empty cecum (14% increase; P < 0.05) at the two lowest doses and the highest dose of OcIDeltaD86, respectively. No abnormalities in either organ were detected by histochemistry. There were no changes in the urine or in hematological variables measured, and blood serum revealed no dose-dependent responses for any of 17 variables measured. OcIDeltaD86 was degraded by boiling with a 50% loss of its inhibition of papain after 9.2 +/- 8.0 min. It also showed >95% loss of such inhibition after 15 s in simulated gastric fluid. The results suggest that the no effect level (NOEL) for OcIDeltaD86 is >10 mg/(kg. d). This provides a range of dietary exposure >200-2000 fold depending upon the promoter used to control its expression in potato.

Engineering plants for nematode resistance

Biotechnology offers sustainable solutions to the problem of plant parasitic nematode control. There are several possible approaches for developing transgenic plants with improved nematode resistance; these include anti-invasion and migration strategies, feeding-cell attenuation, and antinematode feeding and development strategies. The essential elements of an effective control strategy are (a) genes that encode an antinematode effector protein, peptide or interfering RNA and (b) promoters that direct a specific pattern of expression for that effector. This review summarizes information on effectors that act directly against the nematode as well as those aimed at disrupting the nematode feeding site. We discuss patterns of promoter activity that could deliver expression of these effectors in a restricted and directed manner. Societal opposition to the technology of GM-nematode control is also discussed.

Parasitic nematodes, proteinases and transgenic plants

Parasite proteinases have important functions in host-parasite interactions. Consequently, they have been investigated as targets for the control of both plant and animal parasites. Plant parasitic nematodes cause estimated annual losses to world agriculture of US$100 billion and, currently, their control often relies on highly toxic nematicides, with associated environmental risks. The potential of disrupting digestive proteinases for plant parasitic nematode control, via expression of proteinase inhibitors in transgenic plants, is summarized here by Catherine Lilley, Pauline Devlin, Peter Urwin and Howard Atkinson. They then consider whether the approach of expressing antinematode proteins in plants can be adapted for control of certain animal parasitic nematodes.

Expression of the insecticidal bean alpha-amylase inhibitor transgene has minimal detrimental effect on the nutritional value of peas fed to rats at 30% of the diet

The effect of expression of bean alpha-amylase inhibitor (alpha-AI) transgene on the nutritional value of peas has been evaluated by pair-feeding rats diets containing transgenic or parent peas at 300 and 650 g/kg, respectively, and at 150 g protein/kg diet, supplemented with essential amino acids to target requirements. The results were also compared with the effects of diets containing lactalbumin with or without 0.9 or 2.0 mg bean alpha-AI, levels equivalent to those in transgenic pea diets. When 300 and 650 g peas/kg diet were fed, the daily intake of alpha-AI was 11.5 or 26.3 mg alpha-AI, respectively. At the 300 g/kg level, the nutritional value of the transgenic and parent line peas was not significantly different. The weight gain and tissue weights of rats fed either of the two pea diets were not significantly different from each other or from those of rats given the lactalbumin diet even when this was supplemented with 0.9 g alpha-AI/kg. The digestibilities of protein and dry matter of the pea diets were slightly but significantly lower than those of the lactalbumin diet, probably due to the presence of naturally occurring antinutrients in peas. The nutritional value of diets containing peas at the higher (650 g) inclusion level was less than that of the lactalbumin diet. However, the differences between transgenic and parent pea lines were small, possibly because neither the purified recombinant alpha-AI nor that in transgenic peas inhibited starch digestion in the rat small intestine in vivo to the same extent as did bean alpha-AI. This was the case even though both forms of alpha-AI equally inhibited alpha-amylase in vitro. Thus, this short-term study indicated that transgenic peas expressing bean alpha-AI gene could be used in rat diets at 300 g/kg level without major harmful effects on their growth, metabolism and health, raising the possibility that transgenic peas may also be used at this level in the diet of farm animals.

Low nutritional quality of unconventional tropical crop seeds in rats

As the search for alternative sources of food to alleviate hunger continues, this study was undertaken to determine the biological value in growing rats (BV) of proteins of some lesser known tropical seeds gathered in Nigeria. Antinutritional factors (trypsin inhibitors, phytic acid, oxalate, tannin, alkaloids) and amino acid compositions were also determined, and protein digestibility-corrected amino acid score (PDCAAS) was calculated using the amino acid requirement pattern of the preschool child and individual seed-specific correction factors for crude protein. A rat growth and balance study was conducted to determine digestibility, nitrogen-, and energy balance by feeding as the only unsupplemented protein source milled and heat-treated seeds of Adansonia digitata (Bombacaceae) and Prosopis africana, Lonchocarpus sericeus, Enterolobium cyclocarpium, Sesbania pachycarpa and Pterocarpus osun (Leguminosae) in comparison to casein fortified with methionine (control). Diets containing P. africana and L. sericeus seeds caused poor feed intake and weight loss in rats and were excluded from the nitrogen-balance test. Among the seed samples, S. pachycarpa followed by A. digitata showed the most advantageous nutritional quality [amino acid composition, digestibility, BV and net protein utilization (NPU)]. True digestibility was 82.9 and 74.5 vs. 98.5, BV was 64.6 and 70.0 vs. 90.4, and NPU was 53.5 and 52.1 vs. 89.0 for S. pachycarpa and A. digitata vs. casein (control), respectively. In terms of PDCAAS, lysine was the first limiting amino acid for S. pachycarpa (88%) and for A. digitata (58%). The PDCAAS of all essential amino acids was below 100% for E. cyclocarpium (e.g., cysteine + methionine: 37%) and for P. africana (e.g., threonine: 46%, except valine and a very high content of cysteine and methionine). In conclusion, all seeds tested in the rat balance trial were of inferior quality compared to casein. Before these tropical seeds could be used as food components or feed supplements, safety studies and proper processing to remove antinutritional factors and possible toxic constituents were required.

Novel dietary strategy for overcoming the antinutritional effects of soyabean whey of high agglutinin content

A diet-switching experiment, which aimed to improve the utilization of soyabean whey was carried out for 61 d with young rats. Feeding was arranged in such a way that after a few days on the soyabean diet, the rats were switched to a high-quality lactalbumin diet for a short period, after which the cycle was repeated several times. The weights of the rats at the end of the soyabean phases were significantly less than those of animals pair-fed on a high-quality diet throughout. However, the test group regained the weight loss after switching to the lactalbumin diet. After three cycles there were no significant differences between the weights of the test rats fed on a poor soyabean diet for over a third of the experiment and those fed on the lactalbumin diet throughout. Feed conversion was always significantly higher with test rats in the lactalbumin period than with continually pair-fed controls. Similarly, faecal N losses were significantly higher for test rats in the soyabean phase, but these differences disappeared after switching to the lactalbumin diet. At the end of the experiment there were no significant differences in body protein or lipids between the groups although the pancreas was significantly heavier while the liver was lighter in soyabean-fed rats. The high destruction of trypsin inhibitors in the gut suggests that they probably had little effect on protein digestion in the gut. In contrast, as selective depletion of the agglutinin from soyabean whey removed the nutritional benefit in the lactalbumin part of the cycle, the improved feed conversion in this period must have been the result mainly of the survival and functionality of soyabean agglutinin and the benefits due to the hyperplastic growth and faster renewal of the gut surface it induced. As processing is unnecessary, this novel method is cheap and can be easily adapted for the use of soyabean whey, regarded as a waste product.

Pancreatic enlargement is evident in rats fed diets containing raw soybeans (Glycine max) or cowpeas (Vigna unguiculata) for 800 days but not in those fed diets based on kidney beans (Phaseolus vulgaris) or lupinseed (Lupinus angustifolius)

Pancreatic weights and composition were studied with rats fed diets containing raw legume seeds for up to 800 d. Rapid pancreatic enlargement was induced by dietary soybeans (Glycine max) (high Kunitz and Bowman-Birk trypsin inhibitor contents, moderate lectin content) during the initial 150 d. Over the next 200 d the rate of pancreatic growth was similar to that in controls. After 350 d a second period of rapid pancreatic growth occurred. Macroscopic pancreatic nodules were evident in a number of rats fed soybeans for 500 d or more. A similar pattern of pancreatic growth was observed in rats fed dietary cowpeas (Vigna unguiculata) (high Bowman-Birk inhibitor content, low lectin content). Extensive pancreatic growth was also found in young rats fed moderate dietary levels of kidney beans (Phaseolus vulgaris) (low Bowman-Birk inhibitor content, high lectin content). However, the trophic effects diminished with time, and from 100 d onwards, little enlargement was evident. Consumption of a lupinseed (Lupinus angustifolius) diet (low trypsin inhibitor, low lectin content) did not cause pancreatic enlargement. The initial pancreatic growth induced by dietary soybeans seemed to be due to the lectins and trypsin inhibitors, whereas the second period of pancreatic growth was possibly due primarily to the trypsin inhibitors.

Insect pest control by copying nature using genetically engineered crops

A 'copy Nature' strategy for insect pest control is presented which aims to be relatively sustainable and environmentally friendly. Many higher plant genes encoding insecticidal proteins exist in Nature which can be expressed in transgenic plants in a tissue or development-specific manner, or in response to environmental stimuli. These genes can either be expressed singly or in combination so as to enhance host resistance to insect pests. The results so far, which have been obtained mainly in the growth-room, are discussed in both a scientific and applied context. The feasibility of this technology, either as a partial substitution technology for synthetic chemicals or as a component in IPM systems, now needs to be evaluated in the farmer's field. If proven there, its long-term use may depend on promoting agronomic and farm management which minimizes the build-up of resistance in insect populations.