Search PubMed⌕ Search

Biomedical subjects

A J Hunt

Publications and source records attributed to A J Hunt.

30 records · Page 2Linked to original sources
PubMed1991

Hemoglobin polymerization in sickle cells studied by circular polarized light scattering.

We have studied intracellular polymerization of hemoglobin S in suspensions of small populations of sickle cells using circular polarized light scattering. We argue that the preferential scattering of right circular polarized light (as expressed by measurements of the S14 Mueller scattering matrix element) directly reflects the amount of polymer inside cells. This technique has made it possible to investigate the effect of oxygen tension, cell density and osmotic stress on intracellular hemoglobin polymerization. Using S14 to determine hemoglobin polymer, we show that the polymer increases with deoxyhemoglobin concentration, that cells containing higher hemoglobin concentrations show significantly more polymer than cells containing less hemoglobin, and that polymerization occurs in sickle-trait cells in hypertonic solutions as the oxygen tension in the suspension is reduced. We also present kinetic measurements of polymerization, including that induced by osmotic shock. Finally, we demonstrate that the total light scattered (S11 Mueller scattering matrix element) that is routinely measured simultaneously with S14 can be used to estimate the percent of reduced (deoxy) Hb in the sample. These experiments demonstrate the potential of this technique to monitor hemoglobin polymerization simultaneously with oxygen dissociation under a wide variety of physiological conditions.

Erythrocytes↗
PubMed1991

Inhibition of tumor growth in mice by an analogue of platelet factor 4 that lacks affinity for heparin and retains potent angiostatic activity.

An analogue of human platelet factor 4 (PF4) lacking affinity for heparin was specifically designed to evaluate the importance of this property in the antitumor effects of recombinant PF4. The purified protein, recombinant PF4-241 (rPF4-241), failed to bind heparin but retained the ability to suppress the growth of tumors in mice. Daily intralesional injections of rPF4-241 significantly inhibited the growth of the B-16 melanoma in syngeneic mice without direct inhibitory effects on B-16 cell growth in vitro. Similar antitumor effects were observed with the human colon carcinoma, HCT-116, grown in nude mice, indicating that the inhibitory activity was neither tumor-type specific nor T-cell dependent. rPF4-241 inhibited endothelial cell proliferation in vitro with dose dependence similar to the native sequence rPF4. Both rPF4 and rPF4-241 inhibited angiogenesis in the chicken chorioallantoic membrane. The analogue, however, was inhibitory at lower concentrations than rPF4 in the chorioallantoic membrane system and its inhibitory effects were not abrogated by the presence of heparin. The present findings support the conclusion that both rPF4 and rPF4-241 inhibit tumor growth by suppression of tumor-induced neovascularization. The finding that this activity is independent of heparin binding may allow the development of PF4-based angiostatic agents with reduced toxicity and improved bioavailability. These results also suggest that PF4 may play a more specific role in modulation of blood vessel development than previously recognized.

Amino Acid Sequence↗
PubMed1991

Condom use in a large cohort of homosexually active men in England and Wales.

As part of a prospective study of the seroprevalence of HIV, a cohort of 930 men were interviewed regarding their condom use. Of the 270 respondents that engaged in insertive anal intercourse in the month preceding interview 38.9% always used a condom, 49.6% never used one, and 11.5% sometimes used one. Of the 254 respondents that engaged in receptive anal intercourse in the same time period 42.5% always used a condom, 45.7% never used one, and 11.8% sometimes used one. Compared to other research the proportion of respondents who always use a condom for anal intercourse is relatively high, though use is by no means universal. Condom use is more widespread and consistent with casual rather than regular sexual partners, and it is significantly more common within open rather than monogamous relationships. Out of a wide range of other factors only geographical location (London against outside), marital status, perceived HIV status, number of sexual partners, and how seriously respondents take safer sex are correlated with condom use.

Adult↗
PubMed1991

Sexual partners, penetrative sexual partners and HIV risk.

This paper argues that the notion of sexual partners per se is insufficient for estimating levels of HIV risk behaviour or changes in HIV risk over time, even though it is a crucial element of most epidemiological models of HIV. The concept of a penetrative sexual partner (PSP) is introduced as a considerably more accurate measure of HIV risk. Using data from a longitudinal study of 930 homosexually active men in England and Wales, this paper demonstrates that variation in numbers of PSPs (and thus HIV risk) is not related to variation in the gross numbers of sexual partners.

Adolescent↗
PubMed1990

Inhibition of angiogenesis by recombinant human platelet factor-4 and related peptides.

Recombinant human platelet factor-4 (rhPF4), purified from Escherichia coli, inhibited blood vessel proliferation in the chicken chorioallantoic membrane in a dose-dependent manner. Treatment of several cell types with rhPF4 in vitro suggested that the angiostatic effect was due to specific inhibition of growth factor-stimulated endothelial cell proliferation. The inhibitory activities were associated with the carboxyl-terminal, heparin-binding region of the molecule and could be abrogated by including heparin in the test samples, an indication that sulfated polysaccharides might modulate the angiostatic activity of platelet factor-4 in vivo. Understanding of the mechanisms of control of angiogenesis by endogenous proteins should facilitate the development of effective treatments for diseases of pathogenic neovascularization such as Kaposi's sarcoma, diabetic retinopathy, and malignant tumor growth.

Animals↗
PubMed1990

Heterosexual behaviour in a large cohort of homosexually active men in England and Wales.

This paper seeks to outline the range and type of heterosexual behaviour in a large non-clinic cohort of homosexually active males. A cohort of 930 homosexually active men were interviewed as part of a prospective study of the seroprevalence of HIV. The paper indicates that over 60% of these men have had at least one sexual experience with a female and that about 90% of these males have engaged in vaginal intercourse with a female. Twelve per cent of the cohort had sexual contact with females in the last year, and 5% had sex with females, in the month preceding interview. Amongst these behaviourally bisexual males the number of female partners is significantly lower than the number of male partners. However, the proportion of female partners with whom penetration occurs is very much higher than for male partners.

Adult↗
PubMed1990

Reentrant tachycardia in a thin layer of ventricular subepicardium: effects of d-sotalol and lidocaine.

Ventricular tachycardia (VT) was induced by premature stimulation or fast pacing in 14 Langendorff-perfused rabbit hearts whose left ventricular endocardial and intramural cells had been selectively killed by freezing. VTs were caused by apparent reentrant excitation in the surviving thin (1 mm thick) subepicardial layer of anisotropically oriented cells having ostensibly normal membrane characteristics. During VT, 100 microM d-sotalol (seven hearts) or 30 microM lidocaine (seven hearts) was added to the perfusate. Electrophysiological variables were measured before and during drug exposure at both slow (S1 = 300 ms) and fast (S1 = 150-180 ms) pacing rates. Sotalol prevented VT reinduction in six of seven preparations, compared to only two of seven with lidocaine. Lidocaine prolonged the functional refractory period (FRP) and slowed conduction velocity (CV). Lidocaine prolonged the wavelength of the cardiac impulse (= FRP x CV) by 18% at slow rates but reduced it by 21% at fast rates. Sotalol, however, since it increased the FRP without reducing CV, caused wavelength prolongation at both rates (43% at slow rates, 26% at fast rates). Thus, this VT model may provide an important contrast of class I and class III drug action, with the drug effects on wavelength predicting susceptibility to VT induction.

Action Potentials↗
PubMed1990

Seroprevalence of HIV-1 infection in a cohort of homosexually active men.

A non-clinic cohort of 525 homosexually active men from London and South Wales were recruited in 1988 for a study by interview of sexual behaviour. A sample of blood was tested for HIV-1 antibodies. Seropositivity in London was 9.2% compared with 3.4% in South Wales. Men who were not regular STD clinic attenders had a lower rate of seropositivity than did those who were regular attenders. Men who were seropositive reported more sexual partners with whom they had anal intercourse and also reported more episodes of syphilis. Overall, rates of seropositivity were lower than those reported by studies from STD clinics.

Adolescent↗
PubMed1989

Induction of antigen-specific antibody responses in primed and unprimed B cells. Functional heterogeneity among Th1 and Th2 T cell clones.

CD4+ T cells have been recently divided into two subsets. The functions of these subsets are thought to be distinct: one subset (Th1) is responsible for delayed type hypersensitivity responses and another (Th2) is primarily responsible for induction of antibody synthesis. To more precisely define the roles of both subsets in humoral immune responses, we examined the ability of a panel of nominal antigen specific Th1 and Th2 clones to induce anti-TNP specific antibody synthesis in TNP-primed or unprimed B cells. Four of nine Th1 clones induced little or no antibody synthesis with TNP-primed B cells. However, five other Th1 clones were very effective at inducing IgG anti-TNP plaque-forming cell (PFC) responses in primed B cells. One of these Th1 clones was analysed in detail and found to also provide helper function for unprimed B cells. Cognate B-T cell interaction was required for induction of both primary and secondary responses with this clone, indicating that a Th1 clone could function as a "classical" Th cell. The seven IL-4 producing Th2 clones examined were also heterogeneous in their ability to induce antibody secretion by TNP-primed B cells. Although four of the Th2 clones induced IgG and IgM anti-TNP PFC responses, two Th2 clones induced only IgM and no IgG antibody, and another clone failed to induce any anti-TNP PFC. All Th2 clones failed to induce any anti-TNP PFC. All Th2 clones produced high levels of IL-4, but "helper" Th2 clones produced significantly greater amounts of IL-5 than "non-helper" Th2 clones. These studies indicate that some IL-2- and some IL-4-producing T cell clones can induce TNP-specific antibody in cell clones can induce TNP-specific antibody in primed and unprimed B cells, and that Th1 and Th2 clones are heterogeneous in their ability to induce Ig synthesis. Therefore, although T cell clones can be classified as Th1 or Th2 types according to patterns of IL-2, IFN-gamma, or IL-4 synthesis, the functional capacity to induce antibody synthesis cannot be predicted solely by their ability to secrete these lymphokines.

Animals↗
PubMedDate not supplied

Expression and purification of active recombinant platelet factor 4 from a cleavable fusion protein.

A synthetic gene for human platelet factor 4 (hPF4) has been expressed at high levels as a fusion protein in Escherichia coli. The hPF4 sequence has been cleaved from the fusion protein by cyanogen bromide treatment and purified by column chromatography. Like hPF4, our recombinant hPF4 (rhPF4) is tetrameric under physiological conditions, binds heparin, and inhibits angiogenesis. Extensive purification to remove trace amounts of uncleaved fusion protein completely from the desired product rhPF4 was difficult. We have exploited recombinant DNA technology by modifying the fusion moiety to accomplish separation. This type of modification, which did not affect expression level, could be applied to other recombinant fusion proteins.

Amino Acid Sequence↗