Chirality effects at each amino acid position on tripeptide self-assembly into hydrogel biomaterials

Hydrogels formed by ultrashort peptides are emerging as cost-effective materials for cell culture. However, L-peptides are labile to proteases, while their D-isomers are thought to not support cell growth as well. In contrast, the self-assembly behaviour and biological performance of heterochiral peptides (i.e., made of both d and l amino acids) are largely unknown. In this study, we evaluate the effects of amino acid chirality on tripeptide self-assembly and hydrogelation at physiological pH, and cytocompatibility in fibroblast cell culture. A series of uncapped hydrophobic tripeptides with all combinations of d, l amino acids was prepared, tested for self-assembly under physiological conditions, and analysed by circular dichroism, FT-IR, cryo-TEM, AFM, and Thioflavin T fluorescence imaging. Amino acid chirality has a profound effect on the peptides' supramolecular behaviour. Only selected isomers form hydrogels, and of amyloid structure, as confirmed by rheology and XRD. Importantly, they are able to maintain the viability and proliferation of fibroblasts in vitro. This study identifies two heterochiral gels that perform well in cell culture and will assist in the design of innovative and cost-effective peptide gel biomaterials.

BASHH Scotland/Scottish HIV and AIDS group national audit 2009-2010: sexual health care for people living with HIV

A national Scottish audit of 282 patients with HIV infection attending 11 clinics showed the following levels of performance against quality improvement Scotland Sexual Health Services Standards: syphilis serology was offered in the previous six months to 55% of patients (range: 12-97% of patients in individual clinics), sexual history documented within four weeks of initial HIV diagnosis in 67% (12-100%) and offer of tests for sexually transmitted infections (STIs) documented within four weeks of HIV diagnosis in 45% (4-96%). Considerable variation in performance exists between clinics. The audit prompted interventions to further improve the sexual health care of people living with HIV infection.

Unzipping the role of chirality in nanoscale self-assembly of tripeptide hydrogels

Change of chirality is a useful tool to manipulate the aqueous self-assembly behaviour of uncapped, hydrophobic tripeptides. In contrast with other short peptides, these tripeptides form hydrogels at a physiological pH without the aid of organic solvents or end-capping groups (e.g. Fmoc). The novel hydrogel forming peptide (D)Leu-Phe-Phe ((D)LFF) and its epimer Leu-Phe-Phe (LFF) exemplify dramatic supramolecular effects induced by subtle changes to stereochemistry. Only the d-amino acid-containing peptide instantly forms a hydrogel in aqueous solution following a pH switch, generating long fibres (>100 μm) that entangle into a 3D network. However, unexpected nanostructures are observed for both peptides and they are particularly heterogeneous for LFF. Structural analyses using CD, FT-IR and fluorescent amyloid staining reveal anti-parallel beta-sheets for both peptides. XRD analysis also identifies key distances consistent with beta-sheet formation in both peptides, but suggests additional high molecular order and extended molecular length for (D)LFF only. Molecular modelling of the two peptides highlights the key interactions responsible for self-assembly; in particular, rapid self-assembly of (D)LFF is promoted by a phenylalanine zipper, which is not possible because of steric factors for LFF. In conclusion, this study elucidates for the first time the molecular basis for how chirality can dramatically influence supramolecular organisation in very short peptide sequences.

Anal cytology screening in HIV-positive men who have sex with men: experience in a city centre HIV clinic

The objectives of this study were to describe the findings of anal cytology screening during the first year of a unit protocol offering yearly screening to all HIV-positive men who have sex with men (MSM). Of 285 patients seen, 75% were offered anal cytology screening. Sixty-two percent of patients offered screening accepted and 21% of anal smears performed were reported as abnormal. Anal cytology screening may lead to earlier detection of anal intraepithelial neoplasia allowing for treatment before progression to cancer. This study revealed potential difficulties in follow-up of patients with high-grade precancerous disease and highlighted potential resource implications of implementing a routine screening programme.

Nocardia farcinica brain abscesses in an HIV-positive patient

We present a case of Nocardia farcinica brain abscesses in an HIV-positive patient, initially misdiagnosed as cerebral toxoplasmosis. The correct diagnosis was eventually confirmed by brain biopsy. It is debatable as to whether surgical intervention is necessary for diagnosis and treatment of Nocardia abscesses. This case highlights the importance of early neurosurgical input and biopsy to aid correct and timely diagnosis.

Late diagnosis of HIV: could this be avoided?

Many patients with HIV infection present at a late stage of disease. Late diagnosis is associated with increased morbidity and mortality. One strategy to encourage earlier HIV diagnosis is the promotion of HIV testing outside of a specialist HIV setting. This study aimed to determine whether the diagnosis of HIV could be made sooner by non-HIV specialists consulting HIV-positive patients in the year preceding diagnosis. A case note review of all newly diagnosed HIV-positive patients seen over a 12-month period ending in September 2006, was performed to analyse whether patients had consulted a doctor in the year prior to diagnosis, whether they were offered HIV testing and whether they had symptoms or risk factors suggesting HIV infection. Fifty-one newly diagnosed HIV-positive patients were seen during the study period. Twenty-nine of these patients had consulted a doctor in the year prior to diagnosis. Of these, 10 were offered HIV testing and 19 were not. All patients who were not offered HIV testing had risk factors for-, or symptoms of HIV infection. The majority of newly diagnosed HIV patients had consulted a doctor in the year prior to diagnosis. Most were not offered HIV testing despite having risk factors for HIV infection. HIV diagnosis may have been made earlier by testing for HIV outside of a specialist setting.

Completion of a British Association for Sexual Health and HIV regional audit loop: HIV testing in genitourinary medicine clinics in Scotland in 2004 and 2008

In 2004, the British Association for Sexual Health and HIV Scottish Branch audited HIV testing in new attendees diagnosed with a sexually transmitted infection at genitourinary medicine clinics in Scotland. In 2008 the audit loop was completed. Large increases were seen in rates of test offer and uptake, particularly in health boards with low baseline levels of testing. Overall rates of testing remain below those recommended and wide variability between boards persists.