The squalestatins: inhibitors of squalene synthase. Enzyme inhibitory activities and in vivo evaluation of C3-modified analogues.

Squalestatin analogues modified at C3 were prepared and evaluated for their ability to inhibit rat liver microsomal squalene synthase in vitro. While the 4,6-dimethyloctenoate ester group at C6 was maintained, a number of modifications to the C3 carboxylic acid were well tolerated. However, in the absence of the C6 ester group, similar modifications to the C3 carboxyl group caused loss of activity. Selected compounds were evaluated for their ability to inhibit cholesterol biosynthesis in vivo in rats 1 and 6 h postadministration. Analogues of squalestatin 1 (S1) modified at C3 were found to possess a shorter duration of effect in vivo which is reflected in their substantially reduced ability to lower serum cholesterol levels in marmosets. Significant cholesterol lowering (up to 62%) for the C3 hydroxymethyl analogue 1b was observed only when this compound was dosed three times a day for 3 days.

Impact of adrenalectomy on 5-HT6 and 5-HT7 receptor gene expression in the rat hippocampus.

Both glucocorticoid excess and decreased serotonergic (5-HT) transmission may cause depression. The recently cloned 5-HT6 and 5-HT7 receptors have high affinity for antidepressants. Here, we show that pharmacological adrenalectomy increases 5-HT6 and 5-HT7 receptor mRNA expression in specific hippocampal subfields, effects partly reversed by corticosterone replacement. Increased 5-HT6 and 5-HT7 receptor expression may provide a basis, in part, for the therapeutic actions of adrenal steroid synthesis inhibitors in resistant depression.

The relationship between opacity factor and M protein in Streptococcus pyogenes.

Lancefield acid extracts of Streptococcus pyogenes, type 22 (T12, M22, OF positive) gave good yields of M protein and little opacity factor (OF), but sodium dodecyl sulphate (SDS) extracts contained high titres of OF (greater than 20000) and little M protein. Acid-extracted OF could be separated from M protein by Sepharose 4B chromatography, but some of the OF-positive fractions that did not precipitate with the absorbed homologous anti-M rabbit serum, were able to neutralise opsonic antibodies present in human serum. The isoelectric-focusing profiles of the two antigens showed partial similarity. Some strains of the OF-positive serotypes, e.g., M-types 22 and 49, lost both M antigen and OF activity on serial transfer in Todd-Hewitt broth, but this was not seen in a representative of M-type 60, and no M-negative OF-negative variants could be detected after six subcultures. Among the OF-negative serotypes some, e.g., M-types 5 and 6, were completely stable, whereas others, e.g., M-types 12, 55 and 57, lost their M antigens after serial subculture. One explanation is that the genes that code for M antigen are plasmid borne in some serotypes and, moreover, are carried on the same plasmid as the gene for OF in some OF-positive serotypes. However, analysis of cell lysates by agarose-gel electrophoresis failed to demonstrate the presence of plasmid DNA in any of the strains tested.

The opacity factor of group-A streptococci.

Cell-bound opacity factor (OF) was extracted with sodium dodecyl sulphate (SDS) to yield stable extracts with titres of greater than 20 000. The mol.-wt distributions of extracellular and SDS-extracted OF, determined by ultrafiltration or chromatography on Sepharose 4B, suggested that the high mol. wt (1 x 10(6)) of extracellular OF is due to aggregation, because cell-bound and extracellular OF in the presence of SDS had an average mol. wt of only 2 x 10(5). At least four apparent multiple-molecular forms (mol. wt 7.4-12.0 x 10(4)) of OF were detected by SDS polyacrylamide-gel electrophoresis. It seemed more probable that these were due to aggregation rather than the existence of different stable conformations. To explain the molecular-size distribution, the subunit would have to be as small as 1 x 10(4) but this was supported by the finding that OF can be detected after passing through a dialysis membrane provided that its "substrate", alpha 1-lipoprotein, is present on the other side. This raises the possibility that OF is associated with a carrier molecule. The isoelectric-focusing profiles of OF were complex and differed markedly with the method used to prepare OF. Extracellular OF had a simple profile with an isoelectric point of 4.0, whereas Triton-extracted OF was the most complex and formed three peaks, the position of which varied depending on whether the detergent was present or absent during focusing runs.

Immunological heterogeneity among the M-associated protein antigens of group-A streptococci.

Different serotypes of group-A streptococci share common antigens that are closely associated with the type-specific determinant of M protein. By the use of selected human sera containing antibody to these M-associated antigens, we have shown that group-A streptococci can be divided into three categories. The majority of the opacity-factor-negative respiratory serotypes possess a shared M-associated antigen or antigens, to which high titres of antibody are common in patients with rheumatic fever, or patients recovering from upper respiratory infections with certain opacity-factor-negative serotypes. The antibody in these sera has a demonstrable but limited affinity for the M-associated antigens of strains belonging to a second category of M types, the majority of which are opacity-factor-positive serotypes of "throat" or "skin" origin. A third group, consisting mainly of opacity-factor-negative pyoderma serotypes, gave variable results and seemed to be intermediate between the other two categories. Complement-fixation-inhibition tests and absorption studies showed a marked degree of cross-reactivity between the M-associated antigens of the three categories.

Partial Resistance to Septoria Tritici Blotch (Mycosphaerella graminicola) in Wheat Cultivars Arina and Riband.

ABSTRACT Partial resistance to Septoria tritici blotch (STB) and its inheritance were investigated in a doubled-haploid population of a cross between cvs. Arina and Riband. The former has good partial resistance whereas the latter is susceptible. In adult plant trials in polytunnels, STB disease scores were negatively correlated with heading date. Resistance was not specific to any of the three fungal isolates used in these tests. A quantitative trait locus (QTL) for partial resistance to STB was identified in Riband on chromosome 6B and is named QStb.psr-6B-1. No QTL controlling a major part of the Arina resistance was identified, suggesting that its resistance may be dispersed and polygenic. There was no correlation between the lines' mean disease scores at the seedling and adult stages, implying that partial resistance to STB is developmentally regulated. Seedling resistance to the isolate IPO323 was isolate-specific and controlled by a single gene in Arina, probably allelic with the Stb6 gene in cv. Flame that confers resistance to the same isolate. The implications of these results for wheat breeding programs are discussed.

Streptococcal antibodies in patients with burn injuries.

Serum samples from 14 patients whose burns had become infected with streptococci of groups A (11 patients), C (one patient) or G (two patients), and from 19 burned patients without bacteriological evidence of streptococcal infection were examined for anti-streptococcal antibodies. Tests were made for anti-streptolysin O (ASO), anti-hyaluronidase (AH), anti-deoxyribonuclease B (anti-DNAase B) and antibody against M-associated protein (MAP). Sera from the patients with streptococcal infections were also examined, when this was practicable, for 'bactericidal' (anti-M) antibody and for antibody against the opacity factor (OF) of the infecting serotype. In patients infected with group A streptococci, the ASO response was generally poor, except in patients infected with strains of type T12/M12, and the AH response was rather similar, but most of the patients gave a rapid and vigorous anti-DNAase B response, except when the burn was small or colonization occurred very late. Antibody to the M and MAP antigens, and to OF (when the infecting strain formed this), was weak and transient, or absent, except in three of four patients infected with streptococci of type T12/M12.

Predominance of immunoglobulin G sub-class 3 among the complement-fixing antibodies to streptococcal M-associated protein.

During investigation of the absorption of group-A streptococcal antibodies from human sera by a protein A-positive Staphylococcus aureus strain, we found that the complement-fixing antibodies to M-associated protein (MAP) were only partially absorbed from the majority of sera tested, although they were shown to belong to the immunoglobulin G (IgG) class by density gradient centrifugation. In contrast, other streptococcal antibodies: anti-streptolysin O (ASO), anti-deoxyribonuclease B (anti-DNAase B), 'bactericidal' M antibody and anti-opacity factor (anti-OF), were completely absorbed from all but a minority of sera. We suggest that the complement-fixing antibodies to MAP may be of restricted heterogeneity and have an abnormal IgG sub-class distribution, with a marked predominance of IgG3 (the only sub-class that does not interact with protein A) over the IgG1 and IgG2 sub-class; IgG4 does not participate in complement fixation. The concentration and relative porportions of IgG sub-classes are believed to be genetically influenced, so our findings may have some bearing on the immune responsiveness of different individuals to streptococcal infection, and possibly have important implications in the development of the secondary sequelae.

Superior mesenteric artery bypass for chronic mesenteric ischaemia: a DGH experience.

This article evaluates the results of single vessel bypass surgery for symptomatic chronic mesenteric ischaemia (CMI) in 6 patients undergoing a total of 8 superior mesenteric artery (SMA) bypass operations, all with good post-operative symptom relief. Post-prandial pain and weight loss was present in 5 out of 6 patients. Epigastric bruit was present in only two patients and 4 out of 6 patients had diarrhoea. The patients had varying degrees of peripheral vascular disease, ischaemic heart disease and hypertension. All patients had occlusion of the SMA on angiography and bypassing the occluded segment resulted in disappearance of the symptoms and weight gain. The vascular graft was sutured end to side to the front of the infra-renal aorta and end to side to the SMA, distal to the origin of the middle colic artery. Two patients had recurrence of symptoms due to graft occlusion at 3 and 4 years, respectively; they were successfully treated with repeat SMA bypass. There were no major complications or deaths related to the procedure in this study; one patient developed an incisional hernia requiring elective repair. Thus, early restoration of SMA circulation by bypass grafting in patients with CMI is sufficient to alleviate symptoms and prevent intestinal infarction with its high mortality rate.

Inhibition of beta-haemolysis by opacity factor in group A streptococci.

Group-A streptococci belonging to opacity-factor (OF)-positive M types were poorly haemolytic on horse-blood agar, but members of OF-negative M types, and M-negative variants of OF-positive strains gave good haemolysis. Horse-serum extracts of strains of OF-negative serotypes 6 and 12, and M-negative variant cultures of OF-positive serotypes 4 and 49, had higher titres of streptolysin S than did similar extracts of OF-positive, M-positive cultures of types 4 and 49. However, much larger amounts of streptolysin S could be extracted with ribonuclease (RNAase)-digested yeast ribonucleic acid (RNA) and M-positive OF-positive cultures treated in this way gave extracts at least as strong as did their M-negative variants or the OF-negative strains. Extraction of streptolysin S from OF-negative strains by serum could be inhibited by previous incubation of the serum with extracellular OF, suggesting that the production of diffusable OF by M-positive variants of OF-positive serotypes interferes with the extraction of streptolysin S by serum and leads to poor haemolysis on blood agar. The haemolysis of all strains on blood agar was greatly improved by the incorporation of 0-1% (w/v) RNAase-digested yeast RNA into the medium, but the improvement was most marked in OF-positive serotypes.

An M-associated protein antigen (MAP) of group A streptococci.

A streptococcal antigen that is closely associated with the M-antigen, but is not type specific can be detected by means of a complement-fixation test in extracts of M-positive, but not of M-negative, variants of group A streptococci. Purification of acid extracts results in a concomitant increase in the purity both of the type-specific M-antigen and of the M-associated protein (MAP). Antibody to MAP is present in the sera of patients who have had streptococcal infection. The highest titres are found in patients with rheumatic fever.

Antibody to streptococcal opacity factor in human sera.

Two tests are described for detecting antibody to the type-specific opacity factor (OF) of group A streptococci. This antibody was detected among patients convalescent from streptococcal sore throat in two communities in which outbreaks due to opacity factor-producing strains of group A streptococci occurred.In an outbreak due to streptococci of M-type 22 there was a close correspondence between the distribution of anti-OF and of bactericidal M-antibody for the type. In a smaller outbreak due to M-type 58 streptococci, however, M-antibody was detected more often than antibody to OF.