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Our results do not support the hypothesis that systemic Cpn, HSV or CMV- infection or evidence of Cpn-, HSV- or CMV-DNA in carotid plaques causes plaque destabilization and cerebral thromboembolism. Plaque infection could only be observed in cases with advanced atherosclerosis.

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Sialic acid is the common name for acylated derivatives of neuraminic acid. The most commonly occurring of these is N-acetylneuraminic acid (NeuAc), a nine-carbon sugar. NeuAc is an important constituent of the oligosaccharide chains found in the glycoproteins and glycolipids of the cell coats and membranes of animal tissue.It has been suggested that increased level of NeuAc found in the sera of patients with tumours is due to an increased release and breakdown of sialoglycoconjugates from tumour cell membranes [ 11. Recent studies by Debray et al. [2] have shown that there is an increase in highly branched oligosaccharides in transformed human tumour cells. However, altered levels of serum sialic acid have been associated with several non-neoplastic disorders 131, thus casting doubts on its specificity as a tumour marker.It has been suggested that the levels of the lipid-bound subfraction of sialic acid (LSA) might be a more useful and discriminating marker for tumour detection than total NeuAc concentration 14, 51. However, other results have indicated that LSA serum levels are not sufficiently sensitive or specific for the screening of tumour patients 161.We wished to evaluate total serum NeuAc and LSA as tumour markers, using a mouse model. In these experiments the Landschutz ascites tumour (LAT) was used. One group of mice received 1 X lo5 LAT cells in 1.0 ml of phosphatebuffered saline (PBS), pH 7.3, whereas those in the control groups received only PBS (1.0 ml). Each group contained four male Schofield mice. The mice were injected intraperitoneally. Blood samples were taken before and after injection of LAT cells or PBS. Total serum NeuAc was analysed using the colorimetric thiobarbituric acid method described by Warren [7] and serum LSA values were determined by the procedure of Katopodis & Stock [8].Total serum NeuAc results showed no correlation with tumour burden. The increase in the number of tumour cells was not accompanied by a corresponding increase in serum NeuAc levels. Fluctuations in NeuAc levels in the tumour group were accompanied by very similar changes in the PBS control group, thus indicating a non-tumour-associated effect.In the LAT bearing mice, NeuAc levels peaked after 3 days but then fell dramatically after a further 3 days. An initial peak was also observed in the PBS control group after 3 days. The magnitude of the peak in the LAT group was compared with that of the control by using Student's t test. This was based on the comparison between the average changes in NeuAc levels from day -1 (the day before injection) to day 3. A small difference was found t o exist between the LAT peak and that of the PBS control. The rapid increase in total sialic acid in mice bearing the LAT suggests that the sialic acid is produced by the host in response to the Abbreviations used: Neu Ac. N-acetylneuraminic acid; LSA, lipid-bound sub-fraction of sialic acid; LAT, Landschutz ascites turnour; PBS, phosphate-buffered saline. x 102 7.60 7.20 6.80 . z . 2-2 6.40c 2 6.00--l -5.60. 5.20 / 4.80 J 7 -0.10 ...

Sialic acid, a family of acylated derivatives of neuraminic acid, is widely distributed in mammals and usually occurs as a terminal component at the non-reducing end of carbohydrate chains of glycoproteins and glycolipids [ 11. The most commonly occuring of these is N-acetylneuraminic acid (NANA). Elevated levels of total serum NANA have been associated with tumour burden, especially in cases of advanced disease [2]. However, other work has shown that the extent of tumour burden may not be reflected in total serum NANA levels [3,4]. Significant increases have also been associated with non-neoplastic disorders, including bacterial infections and rheumatoid arthritis (51. It has been suggested that sialic acid associated with gangliosides, known as lipid-bound sialic acid (LSA), is a more useful and discriminating tumour marker than total NANA levels [6]. However, the specificity of the method most commonly used to serum LSA levels [7] has been questioned [8]. A procedure which claims to extract only gangliosidic sialic acid has been developed [9]. Early methods of NANA quantitation were colourimetric. Warren developed the thiobarbituric acid method [ 101. More recent methods have included fluorometric analysis [ 111, high performance liquid chromatography 1121, and enzymatic assays [ 131. Our aim was to modify and improve the Warren thiobarbituric acid method. In the original method NANA was subjected to periodate oxidation. After terminating this reaction with arsenite the oxidation product (b-formylpyruvate) was further reacted with thiobarbituric acid to form a pink chromophore. The colour was developed by placing the tubes in a boiling water-bath for 25 minutes. This was extracted into cyclohexanone. The purpose of this was to increase the solubility, stability, and colour intensity of the chromophore. The upper organic layer was then removed. To determine NANA levels, optical densities were measured at two wavelengths (549nm & 532nm), and then inserted into a formula devised by Warren. 2-Deoxyribose, a contaminant in cellular material from dead cells, forms an interfering chromophore in the assay and the formula is necessary to correct for this interference.The modified Warren assay was used to determine total serum NANA levels in patients suffering from cancer of the prostate and was as follows.The initial periodate oxidation was unchanged. After addition of the thiobarbituric acid and colour development a solution containing 5% (v/v) hydrochloric acid (HCI) in ethanol was added to each tube. The temperature of the tubes was maintained at 50°C. Optical densities were then measured at 560nm. Serum NANA levels were determined from a standard curve. The elimination of the use of cyclohexanone and the associated tedious and time consuming extraction step was a major improvement. The use of 50°C as the reaction temperature also eliminated cloudiness in samples, a problem often associated with the original method. The new solvent fulfilled all the requirements that had previously necessitated the use of cyclohexa...