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OBJECTIVE: The effects of free fatty acids (FFA), leptin, tumour necrosis factor (TNF) alpha and body fat distribution on in vivo oxidation of a glucose load were studied in two South African ethnic groups. DESIGN AND MEASUREMENTS: Anthropometric and various metabolic indices were measured at fasting and during a 7 h oral glucose tolerance test (OGTT). Body composition was measured using bioelectrical impedance analysis and subcutaneous and visceral fat mass was assessed using a five- and two-level CT-scan respectively. Glucose oxidation was evaluated by measuring the ratio of (13)CO(2) to (12)CO(2) in breath following ingestion of 1-(13)C-labelled glucose. SUBJECTS: Ten lean black women (LBW), ten obese black women (OBW), nine lean white women (LWW) and nine obese white women (OWW) were investigated after an overnight fast. RESULTS: Visceral fat levels were significantly higher (P<0.01) in obese white than black women, despite similar body mass indexes (BMIs). There were no ethnic differences in glucose oxidation however; in the lean subjects of both ethnic groups the area under the curve (AUC) was higher than in obese subjects (P<0.05 for both) and was found to correlate negatively with weight (r=-0.69, P<0.01) after correcting for age. Basal TNF alpha concentrations were similar in all groups. Percentage suppression of FFAs at 30 min of the OGTT was 24+/-12% in OWW and -38+/-23% (P<0.05) in OBW, ie the 30 min FFA level was higher than the fasting level in the latter group. AUC for FFAs during the late postprandial period (120--420 min) was significantly higher in OWW than OBW (P<0.01) and LWW (P<0.01) and correlated positively with visceral fat mass independent of age (r=0.78, P<0.05) in the OWW only. Leptin levels were higher (P<0.01) both at fasting and during the course of the OGTT in obese women from both ethnic groups compared to the lean women. CONCLUSIONS: Glucose oxidation is reduced in obese subjects of both ethnic groups; inter- and intra-ethnic differences were observed in visceral fat mass and FFA production and it is possible that such differences may play a role in the differing prevalences of obesity-related disorders that have been reported in these two populations.

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Because of the antithrombotic and anti-inflammatory properties of the n-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are found in large quantities in marine fish, the fatty acid composition of the flesh of 18 different species of fresh-water fish found in South Africa was analysed by capillary gas chromatography. In general all the fish studied had low percentages of EPA and DHA and fairly high percentages of arachidonic acid and linoleic acid when compared with some marine fish. The saturated fats constituted 33% of total fatty acids and the mono-enes averaged 35%. The fish studied are therefore not as good a source of n-3 fatty acids as marine fish.

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In order to assess the feasibility of using stable 13C as a tracer for studying cholesterol metabolism in vivo the 13C content of some commonly consumed foods and the stability of the 13C content of human serum cholesterol has been investigated. A procedure is described for the extraction and purification of cholesterol from food, tissues and serum suitable for 13C analysis by mass spectrometry. The method caused no significant isotope fractionation effects. Generally, there was very little difference between the carbon isotope composition of the diet, the cholesterol and the tissue from which it was derived. However, the difference in 13C composition between tissue and cholesterol of prawns from different parts of the world was considerable, indicating a possible peculiarity in the metabolism of cholesterol by this species. The 13C content of human serum cholesterol on a normal diet did not alter significantly with time, suggesting that stable isotope tracer techniques could be used to measure certain aspects of cholesterol metabolism in vivo.

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Human chondrosarcoma of low-grade malignancy was cultured in the presence of 35S-sulphate and 3H-glucosamine. The glycosaminoglycans isolated were fractionated on Ecteola cellulose and electrophoresed on cellulose acetate membranes before and after treatment with chondroitinase AC or Streptomyces hyaluronidase. The results demonstrated the in vitro synthesis of hyaluronate, chondroitin sulphate and keratan sulphate. The presence of keratan sulphate of large average chain length (congruent to 15 monosaccharides) supports the contention that chain length of keratan sulphate is inversely proportional to the degree of malignancy.

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Glycosaminoglycans of human chordoma and a metastasis were studied. The glycosaminoglycans were derived from the extracellular matrix and consisted of chondroitin 4- and 6-sulphate, keratan sulphate and hyaluronate. The ratio of chondroitin sulphate to keratan sulphate was much lower in the metastasis than in the primary. Proteoglycan extracted with 4M guanidinium chloride and purified by associative density-gradient centrifugation was assessed on Sepharose 2B before and after reduction and alkylation. The result of this experiment suggested that only a small proportion of the proteoglycans were aggregated.

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Articular cartilage of fetal calves, calves, and steers together with normal and osteoarthrotic human cartilage was analyzed for hyaluronate. The hyaluronate content increased with maturation in healthy tissue, particularly in regions of maximum contact, but was low in diseased cartilage.

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The distribution of water and glycosaminoglycan in different functional regions of bovine immature articular cartilage were studied. There was always more water in each articulating than in the corresponding growing zone, but there was less water in both zones in the areas of maximum contact. There was more hyaluronate and much more keratan sulphate in the articulating areas of maximum contact than in the minimum contact areas. In the growing zone the distribution of these two glycosaminoglycans did not vary as significantly but there was slightly more keratan sulphate in the area of maximum contact. Regional variations in chondroitin sulphate content were also present although not as striking as those of keratan sulphate. The results suggest that some keratan sulphate may be synthesized as a reaction to load.

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Quantitative and qualitative variations in glycosaminoglycan content were studied in fibrillated, intact, and osteophytic cartilage of the human femoral head in osteoarthrosis. Total glycosaminoglycan content was reduced in fibrillated, unchanged in intact, and raised in osteophytic cartilage. In fibrillated and osteophytic cartilage the ratio of chondroitin sulphate to keratan sulphate was high and therefore resembled immature cartilage. Hyaluronic acid was present in reduced amount in all osteoarthrotic material. Proportionally more proteoglycans were extractable by 0-15 M NaCl and 4 M guanidinium chloride from the diseased cartilage than from normal cartilage, and all proteoglycans irrespective of buoyant density were carbohydrate deficient. It is postulated that the changes described are compatible with collagen and matrix disruption due to focal overloading and the general attempt at repair.

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The glycosaminoglycans and proteoglycans of a human chondrosarcoma have been studied. Glycosaminoglycans were fractionated and identified by cetylpirdium chloride (CPC) cellulose chromatography, ECTEOLA cellulose ion-exchange chromatography and electrophoresis on cellulose acetate. Proteoglycans were extracted by low ionic strength solutions and by 4 M guanidinium chloride and fractioned by equilibrium density-gradient centrifugation and gel chromatography on Sepharose 2B. The tumour matrix contained both the 4- and 6-sulphate isomers of chondroitin sulphate and a high concentration (12% of hexosamine) of hyaluronic acid. Proteoglycans were poor in carbohydrate moieties and proportion were capable of aggregation. Amino acid analysis of the fractionated proteoglycans suggested the presence of a single protein core. A substance with the characteristic amino acid composition of glycoprotein link was recovered from the top of the dissociative density gradient.

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