Antioxidants and cancer. I. Selenium in the blood of normals and cancer patients

The effect of income on selenium intake and status in Utah County, Utah

Foodstuffs produced and/or purchased locally were analyzed for Se. The effect of income and gender on Se intake and status of Utah County residents was evaluated by measurement of the following indicators: erythrocyte (RBC) and plasma Se concentration, and activity of Se-glutathione peroxidase (Se-GSH-Px) (EC 1.11.1.9) in RBCs, platelets, and plasma. A Random Digit Dialing procedure was employed to stratify subjects according to gender and annual family income (less than +10,000, +10,000-20,000, greater than +20,000) in a 2 x 3 factorial design, seven subjects per cell. The weekly consumption of 44 foods shown to contribute over 90% of the Se intake of U.S. subjects was recorded for each study participant. The estimated minimum daily intake for this sample was 76.0 +/- 4.5 micrograms Se/day (mean +/- SEM). Available grain products are not produced locally, and their Se content is lower than average values reported by the U.S.D.A. Locally produced meat and dairy products had higher than average Se contents. In spite of lower grain Se and higher meat Se concentrations, subjects in this study derived more Se from grain and dairy products, and less from meat products than did subjects in a nationwide sample. The Se status of Utah County residents is similar to several other populations in the United States. There were no significant differences in Se status or intake due to gender or income. The results suggest that consumption of other foods produced in a "high Se" area can maintain Se intake and status in spite of reduced consumption of meat products generally viewed as more reliable sources of dietary Se.

Chemoprevention of cancer: selenium

1. Selenium intake (in the form of selenite, selenate, selenomethionine, etc.) protects the organism against the action of some kinds of carcinogens. 2. People and animals having less Se in their blood are at a higher risk of acquiring cancer than those whose blood contains more of this element. 3. This chemopreventive action is probably due to antioxidant properties of Se, its involvements in the enzyme glutathione peroxidase as well as in the inhibition of enzymes converting carcinogens to their ultimate forms in the cell. 4. An intake of 150-300 micrograms of Se daily is considered to be adequate to protect the human organism without exhibiting the toxic properties of this element.

Plasma selenium levels in patients with advanced upper gastrointestinal cancer

Plasma selenium levels were determined at various intervals during hospitalization of 71 patients with upper gastrointestinal and other malignancies. These patients often require frequent nutritional as well as surgical or medical intervention. Attempts were made to identify, evaluate, and compensate for numerous confounding variables at each of the 374 plasma selenium determinations. Selenium levels in stable patients who were neither receiving aggressive antineoplastic therapy, nor septic, nor taking corticosteroids and who had no clinically significant metabolic imbalance were then separately analyzed. In 55 stable patients selenium levels were 28% lower than those found in 20 normal controls (mean 61.8 micrograms/L, P less than 0.0005). An analysis of all the readings showed that selenium levels were substantially decreased by recent radiotherapy or sepsis, by regional tumor spread and increased tumor burden, and by intravenous and/or enteral hyperalimentation and intravenous lipids. In contrast to these findings, levels were relatively higher in patients with an adequate oral diet or with a lesser tumor burden. The comparison between selenium levels in stable and in aggressively treated or septic patients supports the importance of the relationship of nutrition to selenium levels in cancer patients.

Blood and liver selenium concentrations in patients with liver diseases

To study the relation between blood and liver selenium levels in hepatic disorders we measured the selenium concentrations of whole blood, serum and liver tissue obtained at laparoscopy in 17 patients with different kinds of liver diseases. As compared to healthy controls the mean concentration of selenium was decreased by 24% (p less than 0.001) in the whole blood of the patients (n = 15). Similarly, the mean concentration of selenium in serum was 35% lower in the patients than in the controls (p less than 0.001). As compared to the control samples obtained at autopsy the selenium content of liver was decreased by 13% (p less than 0.05) in the patients. Significant positive correlations were found between the selenium content of the liver and the whole blood (r = 0.62, p less than 0.05) as well as also between liver and serum (r = 0.52, p less than 0.05) selenium concentrations. In conclusion, the present study suggests that in patients with liver disorders the selenium concentrations are decreased not only in the blood but also in the liver tissue. Whether this means a decreased activity of hepatic glutathione peroxidase and, further, an increased possibility of oxidative cell injury, remains open.

Selenium concentrations in the blood and urine of a healthy Polish sub-population

Selenium (Se) levels in whole blood, red blood cells, and plasma taken from 199 healthy subjects were investigated and found to be 101.1 micrograms/1 (whole blood), 133.1 micrograms/1 (packed red blood cells), and 78.0 micrograms/1 (plasma). In 62 samples of urine, the selenium level, expressed as micrograms/g creatinine, was 11.4. The mean whole blood selenium concentration was significantly higher in men than women: 104.5 +/- 23.2 vs. 96.9 +/- 21.2 micrograms/1. No differences were found in red blood cells, plasma and urine between male and female subjects. A strong linear correlation was observed between red blood cell and whole blood selenium levels (r = 0.879; p less than 0.001) as well as between selenium levels in whole blood and plasma (r = 0.806; p less than 0.001). A weaker but still significant linear correlation was found between urine and whole blood as well as between urine and plasma selenium concentrations. The relatively low levels of the element in the blood and urine are probably due to its deficiency in the diet.

Diminished blood selenium levels in renal failure patients on dialysis: correlations with nutritional status

Selenium deficiency has been implicated as contributing to the development of cardiovascular disease, skeletal muscle myopathy, anemia, increased cancer risk, and deranged immune function. Since these problems may also be associated with renal failure, and the kidney plays an important role in selenium homeostasis, we measured selenium and compared it with nutritional status in 24 stable hemodialysis patients, 12 chronic intermittent peritoneal dialysis patients, and 29 healthy controls. Whole blood and plasma selenium was determined by a spectrofluorometric method. For whole blood the mean (+/- SD) selenium levels were 0.11 +/- 0.02 micrograms/ml in controls vs. 0.071 +/- 0.01 micrograms/ml in hemodialysis cases and 0.052 +/- 0.006 micrograms/ml in peritoneal dialysis (p less than 0.005). Significant decreases were seen also for plasma and red blood cell selenium in all groups respectively. Pre- and postdialysis plasma and whole blood selenium levels showed no significant changes in both dialysis groups. However, predialysis residual peritoneal fluid did contain selenium (0.029 +/- 0.005 micrograms/ml). Some evidence of protein-energy undernutrition was noted in both dialysis groups compared with controls. However, no significant differences in nutritional parameters were noted between hemodialysis and peritoneal dialysis patients. When all groups were combined, significant correlations were found between whole blood selenium and serum albumin (r = 0.61; p less than 0.001), triceps skin fold in females (r = 0.62; p less than 0.001), and midarm muscle circumference in males (r = 0.71; p less than 0.001). We conclude that low blood selenium is present in renal failure patients undergoing hemodialysis. This abnormality is even greater in peritoneal dialysis cases.(ABSTRACT TRUNCATED AT 250 WORDS)

Selenium, vitamin E, fiber, and the incidence of human cancer: an epidemiologic perspective

It has been hypothesized that selenium, vitamin E, and fiber reduce the risk of specific human cancers. Evidence for a role of selenium is based primarily on animal studies, inverse geographic correlations between intake and site-specific cancer incidence, and an inverse association between serum selenium and subsequent risk of cancer. Certain geographic areas with high fiber intakes have lower rates of colon cancer and, in several case-control studies, consumption of fruits and vegetables has been associated with a lower risk of large bowel cancer. Suspicion that vitamin E might reduce the risk of human cancer is largely theoretical; a protective association has been observed in only 1 small study of breast cancer. The evidence that these 3 dietary factors reduce the risk of human cancer remains incomplete. Future epidemiologic investigations should simultaneously assess a wide variety of dietary factors to address potential confounding and interacting effects. Prospective study designs should be used whenever possible to avoid any influence of cancer on dietary intake or its measurement.

Protective effect of selenium on lung cancer in smelter workers

A possible protective effect of selenium against lung cancer has been indicated in recent studies. Workers in copper smelters are exposed to a combination of airborne selenium and carcinogens. In this study lung tissue concentrations of selenium, antimony, arsenic, cadmium, chromium, cobalt, lanthanum, and lead from 76 dead copper smelter workers were compared with those of 15 controls from a rural area and 10 controls from an urban area. The mean exposure time for the dead workers was 31.2 years, and the mean retirement time after the end of exposure 7.2 years. Lung cancer appeared in the workers with the lowest selenium lung tissue levels (selenium median value 71 micrograms/kg wet weight), as compared with both the controls (rural group, median value 110; urban group, median value 136) and other causes of death among the workers (median value 158). The quotient between the metals and selenium was used for comparison: a high quotient indicating a low protective effect of selenium and vice versa. The median values of the quotients between antimony, arsenic, cadmium, lanthanum, lead, chromium, and cobalt versus selenium were all numerically higher among the cases of lung cancer, the first five significantly higher (p less than 0.05) in 28 of the 35 comparisons between the lung cancer group and all other groups of smelter workers and controls. The different lung metal concentrations for each person were weighted according to their carcinogenic potency (Crx4 + Asx3 + Cdx2 + Sbx1 + Cox1 + Lax1 + Pbx1) against their corresponding selenium concentrations. From these calculations the protective effect of selenium was even more pronounced.

Decreased activity of liver glutathione peroxidase in human hepatocellular carcinoma

Glutathione peroxidase (GSH-Px) activity, one of the scavenger enzymes of oxygen active radicals, has been measured in hepatocellular carcinoma (HCC) of 17 patients and the values compared with the activity of adjacent tumor-free tissue and with those of 30 histologically normal livers. The results demonstrate a reduced GSH-Px activity in neoplastic tissue (21.19 vs 33.74 U/g prot.; P less than 0.001). However, the adjacent tumor-free liver also had a reduced activity when compared with normal tissue (23.15 vs 33.74 U/g prot.; P less than 0.01), but this value did not differ from that of HCC tissue. These data suggest that HCC might develop in a GSH-Px-deficient condition.

Diet and cancer: value of different types of epidemiological studies

Diet and nutrition are increasingly recognized as likely to be major determinants of cancer, notably cancers of the gastrointestinal tract, breast, endometrium, ovary, and prostate. Dietary factors may collectively account for a greater proportion of all cancers that occur in contemporary Western society than does any other category of environmental exposure (1). With the development of knowledge of the protective properties of certain components of food, links with diet have been suggested for other cancer sites (2). The epidemiological evidence for the association of diet and cancer is, however, not uniformly convincing; also, the likely biological pathways are not always clear. In this paper, we comment on some current hypotheses in this area and examine the best epidemiological methods to test them.

Diminished blood selenium levels in alcoholics

Plasma, whole blood, and red blood cell selenium levels were determined by spectrofluorometry in 30 patients with chronic heavy ethanol ingestion (group I) and 20 normal controls (group II). Nutritional and general medical evaluations were also performed. The mean plasma selenium level was 0.065 microgram/ml +/- 0.012 (SD) for group I versus 0.100 +/- 0.016 for group II (p less than 0.0001). Whole blood levels were 0.076 microgram/ml +/- 0.011 versus 0.114 +/- 0.015 (p less than 0.0001), and red blood cell levels were 0.092 microgram/ml +/- 0.016 compared with 0.130 +/- 0.025 (p less than 0.0001), respectively. Mean triceps skin fold was 8.2 mm +/- 3.5 for group I males versus 12.3 mm +/- 5.0 (p less than 0.005) for group II males but was not well correlated with whole blood selenium status (r = 0.33). Nutritional parameters of percentage of ideal body weight, midarm muscle circumference, serum albumin, and total lymphocyte count revealed no differences. Mildly elevated serum aspartate aminotransferase and/or alkaline phosphatase values occurred in 53% of alcoholics, but selenium levels in these patients were no different from those with normal liver tests. We conclude that depressed blood selenium levels occur frequently in patients with chronic heavy ethanol ingestion even in the absence of overt malnutrition. Since selenium deficiency can produce a spectrum of organ injury which resembles that associated with chronic alcoholism, the relationship of selenium deficiency to alcohol-induced organ injury deserves further study.

Blood selenium concentration in residents of areas in China having a high incidence of lung cancer

Data concerning the blood selenium level and its relation to the mortality from lung cancer are reported. There were 353 samples of blood collected from workers at the Yannan Tin Mine (Yun-Xi) and 75 samples from Beijing residents for comparison. An inverse correlation between blood selenium levels and lung cancer mortalities was observed. The average selenium concentration in whole blood from Beijing residents (age-adjusted mortality rate from lung cancer for males: 12/100,000) and Yun-Xi miners (age-adjusted mortalty from lung cancer for males: 108/100,000) were 12.3 and 8.8 μg/100 mL, respectively. A similar inverse correlation was also observed among young people of comparable sex and age groups. In Yun-Xi, the tin miners working underground with an average lung cancer death rate of 250/100, 000 for males had lower blood selenium concentrations than those working above ground, where the average lung cancer death rate for males was 42/100,000. Workers frequently exposed to arsenic exhibited lower blood selenium contents. Selenium levels in the blood of patients with lung cancer were lower (6.2 μg/100 mL) than those of healthy controls.

Influence of dietary selenium on the mutagenic activity of perfusate and bile from rat liver, perfused with 1,1-dimethylhydrazine

The mutagenic effect of 1,1-dimethylhydrazine (UDMH) was studied in the liver perfusion/cell culture system. Male Wistar rats, fed a selenium-deficient diet with or without selenium supplementation in the drinking water, were used as liver donors. UDMH caused an increased mutation frequency in Chinese hamster V79 cells exposed in the perfusate. The effect was statistically significant with both selenium-deficient and selenium-supplemented livers. With selenium-deficient livers, a significant mutagenic effect was also obtained when V79 cells were treated with bile collected after the administration of UDMH. Bile flow and bile acid excretion were not affected by UDMH treatment of selenium-deficient or selenium-supplemented livers. There was a tendency towards reduced C-oxygenation of N,N-dimethylaniline in microsomes from selenium-deficient livers perfused with UDMH. The lactate/pyruvate ratio in the perfusate was increased by UDMH, the effect being more pronounced with selenium-deficient than selenium-supplemented livers.

Low serum selenium concentration in patients with cervical or endometrial cancer

Serum concentrations of selenium were determined in 37 patients with cervical and 64 patients with endometrial cancer. The patients had lower (P less than 0.001) serum concentrations of selenium than the age-, weight- and place of residence-matched paired control women. There was no difference in the selenium concentration between various age groups or different clinical stages of cervical or endometrial cancer. A low serum concentration of selenium might be a contributing factor in uterine carcinogenesis.

Serum and hair selenium levels in hereditary nonpolyposis colorectal cancer

Since low selenium (Se) levels have been identified in some individuals with colon cancer, we evaluated Se levels as a potential marker for this malignancy in a kindred subject to hereditary nonpolyposis colorectal cancer, an autosomal dominant disease. Unaffected family members and spouses were selected randomly for testing. Serum Se levels were performed on dialyzed sera using the neutron activation technique. Hair Se assays were determined by a spectrofluorometric method. Family members were classified as having low, intermediate, or high risk for colon cancer based on family history. There was no correlation between serum and hair Se measurements. There was also no significant difference in hair or serum Se levels between any of the groups, suggesting that serum Se levels do not correlate with hereditary risk for colon cancer. Prospective studies are in progress to evaluate tissue Se levels and serial Se measurements in high risk patients to establish whether Se levels change with the development of colon cancer.

Diet and the epidemiology of human breast cancer

There are substantial data on breast tumorigenesis in animals that suggest that diet may be an important factor in human breast cancer etiology. The promotional effects of dietary fat, and, in particular, unsaturated fats, on mammary tumors in rodents is well established. The geographic distribution of breast cancer in humans correlates with international differences in average fat intake. Differences in dietary habits among populations in the United States and their breast cancer risk also have been observed. In the United States, the trend has been toward increased total fat consumption and increased use of polyunsaturated fats. However, breast cancer incidence among white women in the United States has changed very little. Case-control studies of dietary intake and breast cancer risk have shown inconsistent results, and prospective studies of breast cancer mortality and serum cholesterol and serum lipids show no differences in risk between women with high levels of cholesterol and serum lipids compared with women with low levels. Laboratory studies also suggest the possibility that natural inhibitors of breast cancer may occur in the diet as well. Antioxidants, inducers of microsomal enzyme activity, and retinoids, all have been implicated in the metabolic epidemiology of breast cancer. Research results at Roswell Park memorial Institute have associated lower levels of intake of dietary vitamin A with a slightly elevated risk of breast cancer. To date, the epidemiologic data do not indicate with confidence that any specific dietary risk factor may be associated with breast cancer risk in the United States population. Additional epidemiologic studies on inhibition or promotion of breast cancer following the leads of previous laboratory research may clarify the nature and practical significance of the relationship between diet and breast cancer.

Elevated serum selenium in diabetic children

Twenty-seven diabetic children, 16 girls and 11 boys, 5-18 years of age, with a duration of the disease ranging from 2-15 years, comprised the study group. Thirteen children with a similar age and sex distribution, living in the same area served as healthy controls. All 40 children had a normal growth pattern. The mean serum selenium concentration in the diabetic children, determined by neutron activation analysis, was 7.4 +/- 0.8 micrograms/100 ml (mean +/- SD) and in the healthy controls 6.5 +/- 0.8 micrograms/100 ml. The difference between the two groups was statistically highly significant (p less than 0.01). Boys and girls in both groups had nearly identical mean serum selenium levels and no correlation was observed between the selenium concentrations and either the age, weight or height of the children or the indicators of diabetic control. The selenium status in diabetic children has not been reported previously. The possibility of elevated serum selenium in diabetic children in response to altered lipid metabolism is discussed.

Prediagnostic serum selenium and risk of cancer

Selenium levels in serum samples collected in 1973 from 111 subjects in whom cancer developed during the subsequent 5 years were compared with those in serum samples from 210 cancer-free subjects matched for age, race, sex, and smoking history. The mean selenium level of cases (0.129 +/- SEM 0.002 micrograms/ml) was significantly lower than that of controls (0.136 +/- 0.002 micrograms/ml). The risk of cancer for subjects in the lowest quintile of serum selenium was twice that of subjects in the highest. Multivariate adjustment for geographical area and serum levels of lipids, vitamins A and E, and carotene, did not alter this relation. The association between low selenium level and cancer was strongest for gastrointestinal and prostatic cancers. Serum levels of vitamins A and E compounded the effect of low selenium; relative risks for the lowest tertile of selenium were 2.4 and 3.9 in the lowest tertiles of vitamins E and A, respectively.

Decreased serum selenium in alcoholics--a consequence of liver dysfunction

The serum concentration of selenium was decreased by 17 and 48% in non-cirrhotic and cirrhotic alcoholics, respectively, as compared to healthy controls. In these alcoholics the serum selenium correlated positively with the serum albumin and plasma prothrombin time and inversely with the serum bilirubin, alkaline phosphatase and gamma-glutamyl transpeptidase. Abstinence from ethanol for two weeks was without effect on the serum selenium level in non-cirrhotic alcoholics and acute alcohol intake did not change the serum selenium concentration in non-alcoholic volunteers. In patients with primary biliary cirrhosis the serum concentration of selenium was similar to that in the alcoholic cirrhotics. In patients with hypoalbuminaemia of renal origin the serum selenium was normal. In conclusion our results show that the deterioration of liver function, irrespective of its aetiology, leads to the decrease in serum selenium levels. Whether a defect in removal of lipoperoxides is associated with this decrease in serum selenium concentration remains to be decided by further studies.

The selenium status of Belgian population groups : I. Healthy adults

A moderate level of selenium (Se) was demonstrated in the blood (123 ng/mL), erythrocytes (RBC) (161 ng/mL), and plasma (97 ng/mL) of 110 male and 54 healthy female Belgian adults by using hydride-generation atomic absorption spectrometry. These values agree well with those found in neighboring countries. The study is the first one to report on normal values for these parameters in Belgians.Glutathione peroxidase (GSH-Px) activity has also been assayed. The group in considered nondeficient. Neither the concentration of Se in blood, plasma, or RBC, nor the activity of GSH-Px in the latter, were related to age, sex, blood pressure, or smoking habits. Oral contraception was associated with elevated plasma Se levels as compared to controls (P<0.01).A statistically significant positive relationship existed between the Se concentrations in whole blood or in red blood cells and red blood cell GSH-Px activity (r=0.31,p<0.005).

Selenium levels in blood and plasma, and glutathione peroxidase activity in blood of breast cancer patients during adjuvant treatment with cyclophosphamide, methotrexate and 5-fluorouracil

Glutathione peroxidase activity in whole blood and selenium levels in whole blood and plasma from breast cancer patients, were measured during combination chemotherapy with cyclophosphamide, methotrexate and 5-fluorouracil. No significant change in either glutathione peroxidase activity or selenium levels was observed. Comparison with matched controls showed no significant differences for either parameter.

Red blood cell and serum selenium concentrations as influenced by age and selected diseases

Red blood cell and serum selenium concentrations were investigated to determine normal concentrations for our geographic area and if potential differences existed in patients with selected diagnoses (hepatic, renal, malignant, and chronic diseases). Selenium was quantified in samples of red blood cells, serum and urine by neutron activation analysis. The results were analyzed by comparing 1) pooled data from all ages for each disease with normal values, and 2) normal values with age-matched patients in each disease category. Decreases in red blood cell selenium concentrations (P less than 0.05) occurred in normal subjects over 60 years of age without concurrent significant decreases in serum selenium. Although differential results were noted in age-matched groups, overall results showed that decreased concentrations of selenium in both red cells and in serum occurred with alcoholic cirrhosis, malignancies, and chronic renal failure (P less than 0.025). Red blood cell selenium concentrations also were decreased in patients with stable chronic disease. Decreased serum selenium concentrations were positively correlated with albumin concentrations in patients with cirrhosis. There was no correlation between serum selenium and bilirubin concentrations in patients with liver disease or between serum selenium and creatinine concentrations in patients with chronic renal failure whose urinary excretion of selenium was far below control levels.

Clinical consequences of low selenium intake and its relationship to vitamin E

Great differences in dietary selenium intake have resulted in naturally occurring human selenium deficiencies and toxicities in certain parts of the world. Most North American diets, however, provide levels of selenium that fall within the estimated safe and adequate range of intake (50 to 200 microgram/day for adults) as established by the U.S. National Research Council. Low selenium status may develop in individuals fed certain therapeutic diets or given total parenteral nutrition. Attempts have been made to link low selenium intake with cancer and heart disease, but additional research is needed in this area. Selenium, as a constituent of glutathione peroxidase, plays a role in the antioxidant defense systems of the body, but other metabolic roles for selenium may yet be discovered.

Selenium, estradiol 17 beta, nitrites, and human breast cancer

Breast cancer is the most common cancer in women in the United States. Although there is a large body of studies dealing with selenium, estrogens and nitrites in relation to cancer, most of them are correlated singly and the dynamics of carcinogenesis are overly simplified. The epidemiologic and etiologic effects of selenium, estrogens and nitrites in human breast cancer are traced in their important dimensions. A hypothesis for the interaction of these factors, especially in relation to the erythrocyte is presented within a multi-stage focus of carcinogenesis. A biochemical process for breast cell carcinogenesis in general is postulated and the erythrocyte interaction with breast cancer is diagramed. An enzyme "X" is postulated (estradiase) as a facilitator in vivo of the necessary biochemical conversion of estradiol 17 to a carcinogen.

Factors influencing the inhibitory effect of selenium on mice inoculated with Ehrlich ascites tumor cells

Selenium, administered to mice with Ehrlich ascites tumors, effectively limited tumor growth. The response was dependent on the chemical form and dose of selenium administered. At the doses administered, there were no detectable adverse effects to the host.

Glutathione-peroxidase and glutathione-reductase activities of normal and pathologic human liver: relationship with age

Liver glutathione-peroxidase (L-GSH-Px) and glutathione-reductase (GSSG-Red) activities were measured in supernatants of liver tissues obtained from a total of 36 subjects. Sixteen of these patients had a functionally normal liver (control group), whereas of the remaining 20 patients, 10 were cirrhotic and 10 had a liver disease other than cirrhosis. The mean value of L-GSH-Px of the control group was 33.12 +/- 12.66 U/g protein, a value similar to that found in patients with liver disease. The L-GSH-Px of the control group was positively correlated with the age of the subjects (r = 0.620; p less than 0.02). In contrast, in patients with liver disease an opposite behaviour of the two parameters was noted (r = -0.497; p less than 0.05). L-GSH-Px activity tended to be higher in males than in females, whereas the erythrocyte glutathione-peroxidase (E-GSH-Px) of the same patients was higher in females, albeit not significantly. L-GSH-Px and E-GSH-Px were not correlated either in normal or in liver disease. The mean GSSG-Red of the control group was 40.63 +/- 11.10 U/g protein, which is not different from that of the group of liver patients. GSSG-Red was not correlated with L-GSH-Px or with the age of patients. In two patients with hepatoma, the GSH-Px activity of the cancer tissue was low and the GSSG-Red activity high.

Serum selenium levels in malignant lymphoproliferative diseases

Serum selenium levels were measured in 38 patients with malignant lymphoproliferative diseases (MLD) and in 34 non-hospitalized healthy individuals. Selenium was determined by proton induced x-ray emission. In Hodgkin's disease and non-Hodgkin malignant lymphoma the mean serum levels of selenium were not different from those of the control group. On the contrary lowered mean serum selenium concentrations were observed in the group with chronic lymphocytic leukaemia (5.2 +/- 0.7 microgram/100 ml) as compared to normal individuals (7.9 +/- 0.3 microgram/100 ml). The difference is highly significant (P less than 0.005). A second selenium test was made in 11 out of the 38 patients within 8 weeks from the beginning of radiotherapy or chemotherapy; unchanged levels were found.

Magnesium (and trace substance) deficiencies in the pathogenesis of cancer

Except for a few experimental models of magnesium (Mg)-deficiency-induced neoplasms, less attention has been paid in the past quarter century in the Western world to this macromineral than to the trace elements; e.g., selenium (Se) and zinc (Zn), and to vitamins, deficiencies of which are each considered probable factors in oncogenesis. Although early epidemiologic studies showed an inverse correlation between the amount of Mg in soil and water and the incidence of (gastric) cancer, and several animal studies supported the premise that Mg has a prophylactic effect against induction of cancer, other studies showed that Mg supplementation increased the growth of established experimental tumors. Thus, enthusiasm for this approach subsided. The early epidemiologic findings have since been confirmed, and there have been studies demonstrating the importance of Mg in maintaining immunocompetence, and others indicating that immunodeficiencies increase susceptibility to the development of cancer. Evidence has now accrued that indicates that Mg deficiency increases susceptibility to chemical oncogens. The abnormal metabolism of tryptophan (yielding a carcinogenic metabolite) that indicates functional or absolute pyridoxine deficiency is an indirect clue to Mg deficiency. Vitamin B6-activated enzymes require Mg as a cofactor. However, the early warnings against the use of Mg as part of an antineoplastic program against established cancer were justified, since rapidly metabolizing cells (such as cancers) are dependent on Mg.There are similarities between experiences with Mg and with Se and Zn. All three are required for normal metabolism; Se also protects against free radicals in the environment. Mg and Zn have increased established tumor growth, and their depletion has been applied to antineoplastic programs, with risks comparable to those of using antimetabolic agents.

Selenium and total parenteral nutrition

Despite the increasing recognition of selenium (Se) as an essential trace element in man, little is known about its metabolism during total parenteral nutrition (TPN) and the possible development of Se deficiency in high risk patients. From a general population known by its geographical location to have low Se blood levels, we studied a group of 23 surgical patients receiving TPN for at least one week. Whole blood Se levels were less than in the normal general population and, being some of the lowest observed in adult man, approached levels observed in animals with Se-responsive syndromes. Se continued to be lost predominantly in the urine although the Se content of the TPN fluids was very low (less than 0.6 micrograms/24 hr). Patients with excessive volumes of gastrointestinal excretion lost more Se. Se supplementation may be required in some patients receiving TPN.