Growth promotion by homocysteic acid.

Homocysteic acid, H03SCH2CH2CHNH2CO2H, promotes growth of hypophysectomized rats, assayed by observation of increased thickness of epiphyseal cartilage of the tibia and by observation of tail growth. Doses of homocysteic acid as low as 1 microgram per day for 4 days in the tibia assay and 2.5 milligrams per kilogram per day for 5 weeks in the tail assay were effective in promoting growth. Serum somatomedin activity, determined by the porcine cartilage disk assay, was also increased by homocysteic acid. These findings relate an area of sulfur amino acid metabolism to the physiological action of growth hormone, accelerated growth in homocystinuria, initiation of arteriosclerosis, and control of cellular growth.

Tumor growth: suppression in mice by submanidibular gland extirpation.

Transplanted A-10 breast adenocarcinomas grew more slowly in young-adult male A/HeJ mice from which the submandibular glands had been extirpated than in sham-operated or unoperated control mice of the same strain. The mitotic index was lower in tumors from experimental animals than in those from controls. Vascularization about the tumor margins was also less prominent. The C1300 neuroblastoma grew more slowly in sialoadenectomized mice than in controls. Modulation of tumor growth by factors of salivary gland origin may have been responsible for these effects.

Homocysteine thiolactone metabolism in malignant cells.

Since abnormal homocysteine metabolism is associated with several disorders of growth, including neoplasia, the metabolic fate of homocysteine thiolactone was studied in cell cultures from several malignant tumors, established cell lines, cell lines transformed by oncogenic viruses, and normal skin cells. In all of the cultures of malignant cells homocysteine thiolactone becaome incorporated in peptide linkage with cellular proteins (thiolation). Normal cells incorporated homocysteine thiolactone in peptide linkage, but homocysteine thiolactone was released by acid hydrolysis. The findings suggest the speculative possibility that malignant cells are deficient in a homocysteine thiolactone derivative that prevents thiolation of proteins by homocysteine thiolactone. This hypothetical substance may also catalyze the synthesis of methionine and release acrolein, a growth-regulatory substance, in normal cells. The growth characteristics and tumorigenicity of cultured cells may be related to depletion of the hypothetical substance, and its identification, synthesis, and administration to animals would be expected to affect growth of malignant neoplasms.

Homocysteine metabolism and the oxidative modification of proteins and lipids.

Altered homocysteine metabolism is implicated as a pathogenic factor in atherogenesis, neoplasia, and aging. Hereditary enzymatic deficiencies and nutritional deficiencies of folate, pyridoxine, or cobalamin are associated with elevated blood homocysteine, accelerated atherosclerosis, and manifestations of aging. The failure of malignant cells to metabolize homocysteine thiolactone to sulfate is attributed to deficiency of thioretinaco, a complex containing cobalamin, homocysteine thiolactone, and retinoic acid. The sulfhydryl group of homocysteine is believed to act catalytically with ferric or cupric ions in a mixed function oxidation system to generate hydrogen peroxide, oxygen radicals, and homocysteinyl radicals. These reactive species may interact with the active site of enzyme protein to cause inactivation of catalytic activity. Homocysteine thiolactone is oxidized to sulfate by a process involving ascorbate, thioretinamide, and superoxide, under the control of thyroxine and growth hormone. Thioretinaco is believed to be the active site of adenosine triphosphate (ATP) binding in oxidative phosphorylation with the participation of oxygen, ascorbate, proton gradient, and electron transport. Depletion of thioretinaco from mitochondrial and microsomal membranes may be associated with increased formation and release of radical oxygen species within neoplastic and senescent cells. Specific proposals are made for investigating the importance of homocysteine metabolism in the oxidative modification of proteins and lipids.

Homocystine, atherosclerosis and thrombosis: implications for oral contraceptive users.

PIP: Individuals with homocystinuria have been found to suffer from several types of inherited enzymatic deficiencies. Experiments indicated that vascular changes were subsequent to the metabolic effects of homocysteine derivatives in the tissues. Experimental studies in animals showed that homocysteine thiolactone, methionine, homocysteic acid, and homocystine cause fibrous arteriosclerotic plaques, arterial thrombosis or venous thrombosis with pulmonary embolism. The type which develops depends on the particular homocystine derivative, the dose, and the route of administration. The use of oral contraceptives causes similar alterations in nutrient metabolism. This fact suggests the possibility of increased risk of atherosclerosis, thrombosis, and embolism among long-term oral contraceptive users. Pyridoxine supplementation may reduce the risk. Further research is needed to assess the degree of risk involved.^ieng

Homocysteine content of lipoproteins in hypercholesterolemia.

In order to study the connection between homocysteine and lipid metabolism in atherosclerosis, homocysteine was determined in lipoprotein fractions from men with hypercholesterolemia. All lipoprotein fractions contain a considerably higher level of homocysteine in hypercholesterolemia, compared to normolipemic men, varying from 2.2 to 7.2 times higher estimated per unit volume of serum used for lipoprotein isolation, and from 2.4 to 4.1 times higher, estimated per gram protein. The largest difference in homocysteine content, estimated per gram protein, is present in the LDL fraction, amounting to 4.1 times higher in the hypercholesterolemic than the normolipemic group. In contrast, cholesterol is not higher in hypercholesterolemic than normolipemic men in any lipoprotein fraction, estimated per gram protein, and cholesterol is higher in hypercholesterolemic men only in the LDL fraction, estimated per unit volume. In both LDL and VLDL fractions homocysteine is correlated with cholesterol (r = 0.78, P less than 0.001; r = 0.59, P less than 0.01, respectively) and with protein (r = 0.72, P less than 0.01; r = 0.78, P less than 0.001, respectively). The atherogenic index for homocysteine, LDLHCy/HDLHCy, is 3.5 times higher in the hypercholesterolemic than the normolipemic group. The atherogenic index for cholesterol, LDLChol/HDLChol, is 2.2 times higher in the hypercholesterolemic than the normolipidemic group. The results suggest that analysis of the homocysteine content of the serum and lipoprotein fractions may prove to be useful for assessing risk, prognosis and response to therapy in persons with atherosclerosis.

Homocysteine theory of arteriosclerosis.

Arteriosclerotic plaques were found in the aorta and arteries of rabbits given homocysteine thiolactone, methionine or homocysteic acid, both parenterally and in a synthetic diet. Animals given large doses of parenteral methionine or homocysteine thiolactone died of pulmonary embolism and pulmonary infarct. Pyridoxine prevented thrombosis and pulmonary embolism but did not prevent arteriosclerotic plaques. These findings and previous work, showing a new matabolic pathway for sulfate ester synthesis from methionine, the somatotrophic activity of homocysteic acid, and control of cellular growth and intercellular matrix synthesis by homocysteine derivatives, suggest a theory to explain aspects of the pathogenesis of arteriosclerosis.

Homocysteine and lipid metabolism in atherogenesis: effect of the homocysteine thiolactonyl derivatives, thioretinaco and thioretinamide.

In order to study the relation of homocysteine and lipid metabolism to atherogenesis, rabbits were fed a synthetic atherogenic diet and treated with parenteral thioretinaco (N-homocysteine thiolactonyl retinamido cobalamin), thioretinamide (N-homocysteine thiolactonyl retinamide) or homocysteine thiolactone hydrochloride. All three substances were found to increase dietary atherogenesis. Thioretinaco and thioretinamide increase total homocysteine of serum, but there is no effect of parenteral homocysteine thiolactone hydrochloride on serum homocysteine. The synthetic diet with corn oil significantly lowers serum homocysteine, compared either to baseline chow diet or to the synthetic diet with butter. Atherogenesis is correlated with total homocysteine, total cholesterol and LDL + VLDL cholesterol, and serum homocysteine is correlated with total cholesterol, LDL + VLDL, and HDL cholesterol in the total sample. Both synthetic diets elevate serum cholesterol, triglycerides and LDL + VLDL, but not HDL, compared to baseline values. Thioretinamide causes significant elevation of cholesterol and LDL + VLDL, compared to controls. The results show that increased dietary saturated fat and cholesterol cause deposition of lipids within the arteriosclerotic plaques produced by homocysteine, converting fibrous to fibrolipid plaques. Facilitation of atherogenesis is attributed to the effect of homocysteine on artery wall, either from parenteral homocysteine or from the increased synthesis of homocysteine from methionine, produced by thioretinaco and thioretinamide.

Plasma glucosamine and galactosamine in ischemic heart disease.

Because of the importance of glycosaminoglycans and glycoproteins in the pathogenesis of atherosclerosis, the hexosamine concentrations of plasma were determined in 28 male survivors of acute myocardial infarction and in 50 healthy males aged 30-60 years. Glucosamine and galactosamine were determined by ion-exchange chromatography of hydrolyzed whole plasma and hydrolyzed deproteinized plasma. Considerably higher plasma levels of non-protein-bound hexosamine (500 nmol/ml) and lower levels of protein-bound hexosamines (3770 nmol/ml) were observed in the ischemic heart disease group, compared with the plasma levels of non-protein-bound hexosamine (320 nmol/ml) and protein-bound hexosamine (4260 nmol/ml) of the control group. This difference is due to changes in glucosamine concentration. The galactosamine concentration is similar in the two groups. The ratio of non-protein-bound to protein-bound hexosamines in patients is about twice as high as the ratio found in controls. The glucosamine/galactosamine ratio of protein-free plasma is significantly higher in patients (12.1) than in controls (8.3). These changes in plasma hexosamines correlate with increased plasma homocysteine, cholesterol, and triglycerides observed in the patient group. The findings show that characteristic quantitative and qualitative changes in plasma hexosamine levels accompany atherosclerosis. Determination of these substances may be helpful in diagnosis and management of patients with atherosclerosis.

Reduction of plasma lipid and homocysteine levels by pyridoxine, folate, cobalamin, choline, riboflavin, and troxerutin in atherosclerosis.

Elevated plasma homocysteine and lipid levels are risk factors for atherosclerosis. The plasma levels of homocysteine, determined in acid hydrolyzates of plasma, were found to be correlated with total cholesterol (r = 0.47, P less than 0.001), triglycerides (r = 0.40, P less than 0.01), and body mass index (r = 0.42, P less than 0.01) in 52 males, aged 30-60. A group of 12 male survivors of acute myocardial infarction was given pyridoxine, folate, cobalamin, choline, riboflavin, and troxerutin for 21 days. The plasma concentrations of homocysteine and alpha-amino adipic acid declined to 68% (P less than 0.001) and 57% (P less than 0.001) of the pretreatment values, and the cholesterol, triglycerides, and LDL apo B declined to 79% (P less than 0.001), 68% (P less than 0.01), and 63% (P less than 0.001) of the pretreatment values, respectively. The results suggest a new strategy for control of the metabolic abnormalities in atherosclerosis through the use of naturally occurring, non-toxic nutrients which minimize homocysteine accumulation.

Homocystinuria, arteriosclerosis, methylmalonic aciduria, and methyltransferase deficiency: a key case revisited.

The original case of Cb1 C disease with homocystinuria, cystathioninuria, methylmalonic aciduria, and hypomethioninemia was reexamined because of its importance in the discovery of the homocysteine theory of arteriosclerosis. The vascular lesions in the case consist of proliferative fibrous intimal plaques and focal necrosis of the artery wall, which are attributed to effects of excess homocysteine thiolactone on aggregation of low-density lipoproteins (LDL) and on respiration of endothelial cells. Atrophic, metaplastic, and dysplastic changes within the gastric mucosa are attributed to effects of excess homocysteine thiolactone on synthesis of keratin, sulfomucins, and nucleoproteins within affected cells. The case illustrates how investigation of an inborn error of metabolism illuminates pathophysiological disease processes, normal metabolic pathways, and important aspects of cellular function.

Fish oil decreases serum homocysteine in hyperlipemic men.

BACKGROUND: Because of the inverse relation between dietary fish consumption and coronary heart disease and because of the importance of serum homocysteine as an independent risk factor for atherosclerosis, the effect of fish oil on serum homocysteine was studied in hyperlipemic men. METHODS: Fifteen men with either type IIa or IIb lipoproteinemia or hypertriglyceridemia were maintained on a controlled, balanced diet and given either fish oil or olive oil supplements, 12 g/d for 3 weeks, followed by a cross-over period of 3 weeks during which the olive oil or fish oil supplements were given in reverse order. Serum homocysteine was determined by liquid chromatography of acid hydrolyzates of whole serum. RESULTS: Fish oil was found to diminish serum homocysteine levels in 14 of 17 subjects (P < 0.01). Serum homocysteine was 48% +/- 33% less than control values in seven of nine patients and 36% +/- 22% less than values in seven of eight subjects who had first received olive oil. There was no effect of olive oil supplements on serum homocysteine, compared with control values, but olive oil produced an increase in serum homocysteine in those who had first received fish oil. Serum triglycerides and very low-density lipoprotein were decreased by fish oil in patients who were first given olive oil, in agreement with previous studies. There was no effect of either fish oil or olive oil on total cholesterol, apolipoprotein B, low-density lipoprotein, or high-density lipoprotein. CONCLUSIONS: The protection against coronary heart disease afforded by a diet rich in fish may be attributed to the lowering of serum homocysteine levels by the n-3 polyunsaturated fatty acids of fish oils.

Atherosclerosis, serum cholesterol and the homocysteine theory: a study of 194 consecutive autopsies.

A retrospective study examined 194 consecutive autopsies to determine the proportion of cases of atherosclerosis without elevated serum cholesterol, diabetes mellitus, or hypertension. The study cases were classified into four groups, according to the cause of death and the degree of atherosclerosis. Cases in Group 1, in which death resulted from complications of severe atherosclerosis, have a mean serum cholesterol of 186.7 +/- 41.8 mg/dL, and the cholesterol is less than 200 in 65% and less than 250 in 92% of cases. Cases in Group 2, with severe atherosclerosis dying of other diseases, have a mean serum cholesterol of 174.6 +/- 60.4 mg/dL, and the cholesterol is less than 200 in 79% of cases and less than 250 in 89% of cases. Cases in Groups 3 and 4, with moderate and minimal atherosclerosis, respectively, have mean serum cholesterol values of 172.3 +/- 54.8 and 143.5 +/- 47.8 mg/dL, and the cholesterol is less than 200 in 71% and 92% and less than 250 in 92% and 96% of cases, respectively. Serum cholesterol is significantly associated with severity of atherosclerosis in the total sample (P = 0.01). Three fourths of all cases (147/194) have neither diabetes nor hypertension, and in 74% of these cases (109/147) the cholesterol is less than 200 and in 92% (135/147) the cholesterol is less than 250. In 66% (80/122) of the cases with severe atherosclerosis, the disease developed without evidence of elevated serum cholesterol, diabetes, or hypertension. Blood homocysteine, which has been shown by other studies to be an independent risk factor for atherosclerosis, is recommended for assessing prognosis in these cases.

Chemical pathology of homocysteine. I. Atherogenesis.

The atherogenic properties of homocysteine were discovered by observation of arteriosclerosis in children with homocystinuria caused by inherited deficiency of three different enzymes. Hyperhomocysteinemia is generally recognized as an independent risk factor for coronary, cerebral, and peripheral atherosclerosis. Hyperhomocysteinemia is caused by heterozygosity for homocystinuria, micronutrient deficiency from dietary imbalance, toxins, drugs, hormones, and other factors, explaining many key observations concerning the epidemiology of atherosclerosis. The etiological factors for atherosclerosis are believed to increase conversion of methionine to homocysteine thiolactone, the reactive cyclic internal lactone of homocysteine. The free amino groups of low density lipoprotein (LDL) are thiolated by homocysteine thiolactone, causing aggregation and increased uptake of LDL by macrophages, explaining lipid deposition in atheromas. Homocysteine thiolactone, released from homocysteinylated LDL within vascular wall, promotes intimal injury, oxidation of cholesterol and unsaturated lipids, platelet aggregation, thrombogenic factors, myointimal hyperplasia, deposition of sulfated glycosaminoglycans, fibrosis and calcification of atherosclerotic plaques.

Chemical pathology of homocysteine. II. Carcinogenesis and homocysteine thiolactone metabolism.

Abnormalities of methionine metabolism in malignancy include carcinogenicity of methionine deficiency, methionine auxotrophy of cultured malignant cells, deficient methylation of DNA, and aerobic glycolysis that is reversed by methionine. Cells from children with homocystinuria form an aggregated sulfated extracellular matrix and grow in a pattern similar to cultured malignant cells. Normal cells metabolize homocysteine thiolactone to sulfate, but malignant cells accumulate homocysteine thiolactone, which thiolates proteins and other cellular macromolecules. Thioretinamide, the amide of retinoic acid homocysteine thiolactone, and its cobalamin complex, thioretinaco, are antineoplastic and chemopreventive against carcinogenesis. Deficiency of these compounds in malignant cells is believed to increase conversion of methionine to homocysteine thiolactone and thioco, its cobalamin complex. These compounds are believed to participate in oxidative phosphorylation by formation of thioretinaco ozonide disulfonium complexes that are the active sites of adenosine triphosphate (ATP) binding in mitochondrial membranes. Hypothetical deficiency of thioretinaco may explain important metabolic abnormalities of malignant cells.

Chemical pathology of homocysteine. III. Cellular function and aging.

The homocysteine thiolactonyl derivative, thioretinaco ozonide, is believed to function as an electron acceptor in oxygen metabolism and as the binding site for adenosine triphosphate (ATP) synthesis by mitochondria, preventing damage by free radical oxidants in resting cells. During cell division, methionine is converted to homocysteine thiolactone, converting thioretinaco to thioco, increasing free radical oxidants, and oxidizing cellular glutathione and ascorbate. Homocysteic acid has growth hormone activity and releases insulin-like growth factor in hypophysectomized rats, promoting oxidation of homocysteine thiolactone to sulfated glycosaminoglycans of cartilage. The free base of homocysteine thiolactone produces keratinization, squamous metaplasia, dysplasia, and carcinogenesis in normal mouse tissues. The efficiency of homocysteine thiolactone metabolism declines with aging, explaining decreased formation of adenosyl methionine in aging and suggesting loss of thioretinaco ozonide from membranes of aging cells. The effects of aging on enzyme activity, connective tissues, lipid synthesis, auto-immune diseases, atherogenesis and carcinogenesis are related to these changes in homocysteine metabolism.

Growth disorders and homocysteine metabolism.

Inherited disorders of homocysteine metabolism produce accelerated growth and arteriosclerosis with myointimal hyperplasia. The growth of cell cultures from cystathionine synthetase deficient individuals with homocystinuria is characterized by abnormal contact inhibition and production of an aggregated proteoglycan matrix which binds excess sulfate. Homocysteic acid, a precursor of sulfate ester, increases the growth rate of normal guinea pigs. Synthesis of homocysteic acid from homocysteine thiolactone is more rapid in the livers of young animals than adults, and hypophysectomy results in a pattern of homocysteine thiolactone metabolism resembling that in liver of adult animals. Homocysteine thiolactone metabolism differs in guinea pig, an herbivorous species, and in rat, an omnivorous species. Sulfate binding by cultured human cells is slightly increased when homocysteic acid is present in the culture medium. These observations suggest a relationship between homocysteic acid and somatomedin, a serum polypeptide which mediates the action of growth hormone. The growth disorders associated with homocystinuria, including arteriosclerosis and accelerated growth, are believed to result from increased conversion of methionine to homocysteine thiolactone and homocysteic acid.

Studies of the pathogenesis of arteriosclerosis induced in rats by intrarenal injection of a carcinogen, nickel subsulfide.

Widespread arteriosclerotic lesions were detected by histological examinations of rats killed at seven or nine weeks after an intrarenal (ir) injection of nickel subsulfide (Ni3S2, 5 mg per rat). Arteriosclerotic plaques were readily visualized by administering hematoporphyrin derivative (HPD) iv to rats at 24 hours before sacrifice. At necropsy, the major arteries were inspected under ultraviolet light, revealing patches of intense HPD-fluorescence in the arterial endothelium of Ni3S2-treated rats, but not in control rats. Consistent with previous reports, the Ni3S2-treated rats developed pronounced erythrocytosis; blood hematocrit values averaged 70 +/- 4 percent at seven weeks after ir injection of Ni3S2 (P less than 0.001 vs corresponding value of 49 +/- 2 percent in vehicle controls). At seven weeks, blood platelet counts averaged 17 percent lower and serum glucose concentrations averaged 23 percent lower in Ni3S2-treated rats than in controls; serum lipids, lipoproteins, non-protein nitrogen constituents, electrolytes, proteins, and enzymes were not significantly affected. Body weights and systolic blood pressures of rats at two, four, and six weeks after ir injection of Ni3S2 did not differ from corresponding values in controls. Addition of egg yolk to the diet caused mild hypercholesterolemia, but it did not enhance the incidence or severity of arterial lesions in Ni3S2-treated rats. These findings exclude hypertension and hyperlipidemia as pathogenic factors in Ni3S2-induced arteriosclerosis.

Ga-67 studies in a patient with acquired immunodeficiency syndrome and disseminated mycobacterial infection.

A well-documented case of acquired immunodeficiency syndrome (AIDS) with diffuse lymphadenopathy and disseminated mycobacteriosis in whom serial Ga-67 studies were performed is presented.