A combination of dietary protein depletion and PHA-induced gut growth reduce the mass of a murine non-Hodgkin lymphoma

Polyamines and the intestinal tract

Owing to their high turnover, the intestinal mucosal cells have a particularly high requirement for polyamines. Therefore, they are an excellent charcol for the study of polyamine function in rapid physiological growth and differentiation. After a cursory introduction to the major aspects of polyamine metabolism, regulation, and mode of action, we discuss the contribution of the polyamines to the maintenance of normal gut function, the maturation of the intestinal mucosa, and its repair after injuries. Repletion of cellular polyamine pools with (D,L)-2-(difluoromethyl)ornithine has considerably improved our understanding of how the polyamines are involved in the regulation of normal and neoplastic growth. Unfortunately, the attempts to exploit polyamine metabolism as a cancer therapeutic target have not yet been successful. However, the selective inactivation of ornithine decarboxylase appears to be a promising chemopreventive method in familial adenomatous polyposis. Presumably, it relies on the fact that ornithine decarboxylase is a critical regulator of the proliferative response of the protooncogene c-myc, but not of its apoptotic response.

Antinutritional properties of plant lectins

Lectins are carbohydrate binding (glyco)proteins which are ubiquitous in nature. In plants, they are distributed in various families and hence ingested daily in appreciable amounts by both humans and animals. One of the most nutritionally important features of plant lectins is their ability to survive digestion by the gastrointestinal tract of consumers. This allows the lectins to bind to membrane glycosyl groups of the cells lining the digestive tract. As a result of this interaction a series of harmful local and systemic reactions are triggered placing this class of molecules as antinutritive and/or toxic substances. Locally, they can affect the turnover and loss of gut epithelial cells, damage the luminal membranes of the epithelium, interfere with nutrient digestion and absorption, stimulate shifts in the bacterial flora and modulate the immune state of the digestive tract. Systemically, they can disrupt lipid, carbohydrate and protein metabolism, promote enlargement and/or atrophy of key internal organs and tissues and alter the hormonal and immunological status. At high intakes, lectins can seriously threaten the growth and health of consuming animals. They are also detrimental to numerous insect pests of crop plants although less is presently known about their insecticidal mechanisms of action. This current review surveys the recent knowledge on the antinutritional/toxic effects of plant lectins on higher animals and insects.

A mistletoe lectin (ML-1)-containing diet reduces the viability of a murine non-Hodgkin lymphoma tumor

In this study we show that the characteristics of non-Hodgkin lymphoma (NHL) tumors in female Naval Medical Research Institute (NMRI, USA) mice fed mistletoe lectin (ML)-containing diets were different from those in mice fed control diet. The non-Hodgkin lymphoma tumor was originally established from a spontaneous tumor which developed in the inguinal region of a male mouse. Mice (five animals per group) were fed a lactalbumin (LA)-based control diet or a diet which provided up to 10 mg lectin per day. At the highest daily intake (10 mg lectin) the degree of mitotic activity in tumors was reduced by 75% and the nuclear area had diminished by 21%. The overall level of lymphocyte infiltration (CD3 positive cells) in tumors from mistletoe lectin fed mice was increased by a factor of two. Other morphological studies showed a high incidence of apoptotic bodies in non-Hodgkin lymphoma tumors obtained from mice fed mistletoe lectin diets. The feeding of such diets thus produced several identifiable changes in the morphology of non-Hodgkin lymphoma tumors. These were consistent with the observed reduction in tumor mass. In 4/15 mice fed a mistletoe lectin diet for 11 days there was no longer evidence of viable tumor. The results show that this lectin exerts powerful anti-tumor effects when provided by the oral route.

The growth of an established murine non-Hodgkin lymphoma tumour is limited by switching to a phytohaemagglutinin-containing diet

The growth of a non-Hodgkin lymphoma, developing subcutaneously as a solid tumour in NMRI mice, is markedly diminished by including phytohaemagglutinin (PHA), a lectin present in raw kidney bean (Phaseolus vulgaris), in the diet. In the experiment described in this communication the effect of first allowing tumours to develop for 5 days before switching the mice to a diet containing PHA at different concentrations was tested to establish whether or not feeding the lectin at late times also resulted in reducing tumour growth. This switch of diet indeed proved to be effective in slowing down growth of the lymphoma tumour. The reduced rate of growth occurs in a dose-dependent manner. We have suggested that a competition between the gut epithelium undergoing PHA-stimulated hyperplasia and the developing tumour may occur for polyamines and other nutrients from a common body pool and this could be an important contributory factor with regard to the observed low level of tumour growth following the feeding of PHA-containing diet. Recent data which showed that the level of hyperplasia of the small bowel in response to feeding the PHA diets was higher in non-injected mice compared to those which had been injected with tumour cells substantiated the concept of competition between gut and tumour for nutrients and other requirements for growth.