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Biomedical subjects

C S Loh

Publications and source records attributed to C S Loh.

44 records · Page 3Linked to original sources
PubMed1992

Photodynamic therapy of the normal rat stomach: a comparative study between di-sulphonated aluminium phthalocyanine and 5-aminolaevulinic acid.

Dysplasia in the upper gastrointestinal tract carries a risk of invasive malignant change. Surgical excision of the affected organ is the only treatment available. Photodynamic therapy has been shown to be promising in the treatment of early and superficial tumours and may be useful for the ablation of dysplastic mucosa. Because of the diffuse nature of the disease, such treatment would necessarily involve destruction of large areas of mucosa and it is desirable to confine its effect to the mucosa in order that safe healing can take place. By means of photometric fluorescence microscopy, we have studied the pattern of photosensitisation in the normal rat stomach using di-sulphonated aluminium phthalocyanine (AlS2Pc) and 5-aminolaevulinic acid (ALA) as photosensitisizers. AlS2Pc resulted in a panmural photosensitisation of the gastric wall with the highest level encountered in the submucosa. The mucosa and muscularis propria were sensitised to equal extent. Following light exposure, a full thickness damage resulted. ALA is a natural porphyrin precursor and exogenous administration gave rise to accumulation of protoporphyrin IX (PPIX) in the cells. The resultant pattern of photosensitisation was predominantly mucosal and its photodynamic effect was essentially confined to the mucosa. ALA produced a selective photosensitisation of the gastric mucosa for its photodynamic ablation with sparing the underlying tissue layers.

Aminolevulinic Acid↗
PubMed1991

Aspartic acid 50 and tyrosine 108 are essential for receptor binding and cytotoxic activity of tumour necrosis factor beta (lymphotoxin).

Single amino acid substitutions were generated in predicted hydrophilic loop regions of the human tumour necrosis factor beta (TNF-beta) molecule, and the mutant proteins were expressed in Escherichia coli and purified. Mutants with single amino acid changes at either of two distinct loop regions, at positions aspartic acid 50 or tyrosine 108, were found to have greatly reduced receptor binding and cytotoxic activity. These two regions in TNF-beta correspond to known loop regions where mutations also result in loss of biological activity of TNF-alpha, a related cytokine which shares the same cellular receptors with TNF-beta. The two distinct loops at positions 31-34 and 84-89 in the known three-dimensional structure of TNF-alpha (equivalent to positions 46-50 and 105-110 respectively in TNF-beta), lie on opposite sides of the TNF-alpha monomer. When the TNF-alpha monomer forms a trimer, the two loops, each from a different subunit of the trimer, come together and lie in a cleft between adjacent subunits. Together, these findings suggest that a TNF receptor binds to a cleft between subunits via surface loops at amino acid residues 31-34 and 84-89 in TNF-alpha, and similarly via surface loops including amino acids aspartic acid 50 and tyrosine 108 in TNF-beta.

Amino Acid Sequence↗
PubMed1989

Transurethral resection of the prostate and bladder tumour without withdrawal of warfarin therapy.

Twelve resections of prostate and 1 extensive bladder tumour were performed in patients on long-term anticoagulation without withdrawal of warfarin therapy. The mean preoperative prothrombin index was 2.3. Four patients required blood transfusion. There were no major complications. The effects of surgery and infusion of fresh frozen plasma (FFP) on the level of anticoagulation were monitored. FFP reduced the prothrombin index by 0.25/unit. Transurethral resection can be carried out safely by an experienced urologist on patients anticoagulated with warfarin, reducing the risk of serious thromboembolic complications associated with withdrawal of anticoagulation.

Aged↗
PubMed1989

Surgical decompression for thoracic outlet syndrome.

Fifty consecutive surgical decompression operations for thoracic outlet syndrome (TOS) were performed in 43 patients over a 7-year period. Of these, 54% presented with neurological symptoms alone; the others complained of symptoms of vascular or combined origin. Operations for decompression consisted of excisions of 14 cervical ribs, 22 first ribs, and 14 soft tissue or fibrous bands. In six limbs, cervical sympathectomy was also performed for patients who had secondary Raynaud's phenomenon. Surgery resulted in complete relief of symptoms in 37 limbs (74%) and an improvement was achieved in another 10 (20%). In three limbs (6%) surgery gave no benefit. There was no mortality. Thoracic outlet decompression via the supraclavicular approach gave good results in 94% of the patients.

Female↗