Decrease of testosterone level during an experimental African trypanosomiasis: involvement of a testicular LH receptor desensitization

Bioluminescent imaging of Trypanosoma brucei shows preferential testis dissemination which may hamper drug efficacy in sleeping sickness

Monitoring Trypanosoma spread using real-time imaging in vivo provides a fast method to evaluate parasite distribution especially in immunoprivileged locations. Here, we generated monomorphic and pleomorphic recombinant Trypanosoma brucei expressing the Renilla luciferase. In vitro luciferase activity measurements confirmed the uptake of the coelenterazine substrate by live parasites and light emission. We further validated the use of Renilla luciferase-tagged trypanosomes for real-time bioluminescent in vivo analysis. Interestingly, a preferential testis tropism was observed with both the monomorphic and pleomorphic recombinants. This is of importance when considering trypanocidal drug development, since parasites might be protected from many drugs by the blood-testis barrier. This hypothesis was supported by our final study of the efficacy of treatment with trypanocidal drugs in T. brucei-infected mice. We showed that parasites located in the testis, as compared to those located in the abdominal cavity, were not readily cleared by the drugs.

Genetic resistance to infection influences a male's sexual attractiveness and modulation of testosterone

Females may be attracted to males genetically resistant to infectious diseases, and one potential mechanism for this mating bias is that such males may be better able to maintain high testosterone. To test these two hypotheses, we collected scent-marks from male house mice (Mus domesticus) genetically resistant and susceptible to Salmonella due to a single locus (Nramp 1, also known as Slc11a1). We tested whether females are more attracted to the scent-marks of resistant males, and whether such males are better able to maintain testosterone concentrations during an experimental Salmonella infection. We found that females preferred the scent-marks of genetically resistant males compared to susceptible ones; but they showed no preferences 5d after males were infected. As predicted, genetically resistant males maintained their testosterone concentrations during the experimental infection, whereas susceptible males showed a significant decline 14 d after inoculation. These differences in the males' ability to modulate testosterone, however, do not explain females' attraction to resistant males. Thus, our results indicate that females sometimes prefer males genetically resistant to infection, and they provide the first evidence that males modulate their testosterone depending upon their genetic resistance to infection; however, we found no evidence to link these two findings.

Effect of experimental infection with Trypanosoma congolense and scrotal insulation on Leydig cell steroidogenesis in the ram

Testicular steroid content and Leydig cell steroidogenesis in vitro were investigated in rams on Days 28 and 58 after Trypanosoma congolense infection and were compared with those of rams in which testicular temperature had been raised artificially by insulation of the scrotum for 58 d. Testicular testosterone content increased significantly on Day 28 after infection but was lower than that of controls on Day 58 while it increased in scrotal-insulated rams compared with that of controls by Day 58. Testicular progesterone was undetectable in the control and trypanosome-infected groups throughout the experiment, but it increased in the insulated rams by day 58. Basal (unstimulated) Leydig cell testosterone production in the infected rams was similar to that of control rams on Day 28 but was significantly lower on Day 58. Stimulation of Leydig cell testosterone production with hCG or 22R-hydroxycholesterol (22ROHC) significantly reduced in infected rams at both 28 and 58 d after infection as well as in scrotal-insulated rams on Day 58. It is concluded that the increase in testicular testosterone content in the infected and scrotal-insulated rams on Days 28 and 58, respectively, was induced by elevation of testicular temperature by trypanosome infection, perhaps through an effect on testicular blood flow. Reduced testosterone production by Leydig cells from infected and scrotal-insulated rams in response to hCG and 22ROHC suggests that trypanosome-induced pyrexia might be involved in reducing Leydig cell steroidogenesis and subsequent plasma testosterone levels, possibly by affecting enzymes involved in steroid biosynthesis.

Pyroglutamyl peptidase type I from Trypanosoma brucei: a new virulence factor from African trypanosomes that de-blocks regulatory peptides in the plasma of infected hosts

Peptidases of parasitic protozoans are emerging as novel virulence factors and therapeutic targets in parasitic infections. A trypanosome-derived aminopeptidase that exclusively hydrolysed substrates with Glp (pyroglutamic acid) in P1 was purified 9248-fold from the plasma of rats infected with Trypanosoma brucei brucei. The enzyme responsible was cloned from a T. brucei brucei genomic DNA library and identified as type I PGP (pyroglutamyl peptidase), belonging to the C15 family of cysteine peptidases. We showed that PGP is expressed in all life cycle stages of T. brucei brucei and is expressed in four other blood-stream-form African trypanosomes. Trypanosome PGP was optimally active and stable at bloodstream pH, and was insensitive to host plasma cysteine peptidase inhibitors. Native purified and recombinant hyper-expressed trypanosome PGP removed the N-terminal Glp blocking groups from TRH (thyrotrophin-releasing hormone) and GnRH (gonadotropin-releasing hormone) with a k(cat)/K(m) value of 0.5 and 0.1 s(-1) x microM(-1) respectively. The half-life of TRH and GnRH was dramatically reduced in the plasma of trypanosome-infected rats, both in vitro and in vivo. Employing an activity-neutralizing anti-trypanosome PGP antibody, and pyroglutamyl diazomethyl ketone, a specific inhibitor of type I PGP, we demonstrated that trypanosome PGP is entirely responsible for the reduced plasma half-life of TRH, and partially responsible for the reduced plasma half-life of GnRH in a rodent model of African trypanosomiasis. The abnormal degradation of TRH and GnRH, and perhaps other neuropeptides N-terminally blocked with a pyroglutamyl moiety, by trypanosome PGP, may contribute to some of the endocrine lesions observed in African trypanosomiasis.

Testosterone correlates with Venezuelan equine encephalitis virus infection in macaques

Here we briefly report testosterone and cytokine responses to Venezuelan equine encephalitis virus (VEEV) in macaques which were used as part of a larger study conducted by the Department of Defense to better characterize pathological responses to aerosolized VEEV in non-human primates. Serial samples were collected and analyzed for testosterone and cytokines prior to and during infection in 8 captive male macaques. Infected animals exhibited a febrile response with few significant changes in cytokine levels. Baseline testosterone levels were positively associated with viremia following exposure and were significantly higher than levels obtained during infection. Such findings suggest that disease-induced androgen suppression is a reasonable area for future study. Decreased androgen levels during physiological perturbations may function, in part, to prevent immunosuppression by high testosterone levels and to prevent the use of energetic resources for metabolically-expensive anabolic functions.

Neuroendocrine-immune aspects of accelerated aging in rheumatoid arthritis

The normal process of aging brings about changes in immune function, hormonal status, overall metabolism, and enhanced occurrence of neuropsychiatric disorders. These alterations are also evident at an accelerating pace in chronic inflammatory diseases. Treatment with immunosuppressive therapeutics is often not sufficiently effective. Treating neuroendocrine-immune alterations to regain homeostasis might enhance remission inducing and maintaining effects. This paper summarizes the phenomena related to normal aging and related to chronic inflammatory disease. Furthermore, a multimodal concept is being proposed to control more effectively chronic inflammatory disease on a neuroendocrine-immune basis.

Adaptive variation in testosterone levels in response to immune activation: empirical and theoretical perspectives

High testosterone levels reflect investment in male reproductive effort through the ability to produce and maintain muscle tissue and thus augment mate attraction and competitive ability. However, high testosterone levels can also compromise survivorship by increasing risk of prostate cancer, production of oxygen radicals, risk of injury due to hormonally-augmented behaviors such as aggression, violence and risk taking, reduced tissue and organ maintenance, negative energy balance from adipose tissue catabolism, and suppression of immune functions. Here, I briefly discuss how inter- and intra-individual variation in human male testosterone levels is likely an adaptive mechanism that facilitates the allocation of metabolic resources, particularly in response to injury, illness or otherwise immune activation. Maintaining low testosterone levels in resource-limited and/or high pathogen-risk environments may avoid some immunosuppression and suspend energetically-expensive anabolic functions. Augmenting testosterone levels in the presence of fertile and receptive mates, areas of high food resource availability, and low disease risk habitats will function to maximize lifetime reproductive success.

Testosterone-mediated immune functions and male life histories

Recent advances in human life history theory have provided new insights into the potential selection pressures that were instrumental in the evolution of human and non-human primate males. However, gaps remain in our understanding of how primate males regulate and allocate energetic resources between survivorship and reproductive effort. Defense against parasitic infection is an important force shaping life history evolution. Proper performance of immunological responses against infection is influenced by many physiological systems, including metabolic, reproductive, and stress hormones. Because androgens influence and modulate immune, reproductive, and somatic metabolic functions, assessing changes in testosterone and immune factors during infection may yield insight into male physiological ecology. In this review, we examine male life history trade-offs between immune and reproductive endocrine functions as well as provide a comprehensive review of testosterone-immunocompetence relationships. Emphasis is placed on testosterone because it is a primary hormone shown to be crucial to energy-allocation processes in vertebrates. Non-primate species have been used more extensively in this research than humans or non-human primates, and therefore this extensive literature is organized and reviewed in order to better understand potential parallel relationships in primates, especially humans. Furthermore, we attempt to reconcile the many inconsistent results obtained from field studies on immune-endocrine interactions as well as detail various methodologies that may be used to forward this research in evolutionary anthropology.

Plasma luteinizing hormone levels in response to gonadotropin-releasing hormone agonist and clonidine in Trypanosoma congolense-infected female goats

Trypanosomiasis, a parasitic disease of humans and animals, occurs over a wide area of Africa and imposes a large socioeconomic burden on the people. In the present study, we investigated whether trypanosomiasis-induced reproductive disorders were due to pituitary or hypothalamic dysfunction by determining plasma luteinizing hormone (LH) response to gonadotropin-releasing hormone (GnRH) agonist or clonidine in Trypanosoma congolense-infected female goats. With GnRH agonist administration, the total amount of LH secreted over a 140-min sampling period on day 23 and day 60 postinfection was consistently higher (71 and 21%, respectively) in infected goats compared to controls. In contrast, clonidine administration to infected goats on day 28 and day 69 postinfection failed to significantly alter the LH pulse frequency or the mean LH pulse amplitude over a 80-min sampling period. The results, especially the lack of response to clonidine, indicate that trypanosomiasis impairs GnRH release from the hypothalamus.

How schistosomes profit from the stress responses they elicit in their hosts

Results obtained with the model Trichobilharzia ocellata-Lymnaea stagnalis have confirmed the hypothesis that the physiological effects evoked by schistosomes in their snail host--castration and giant growth--are brought about by them interfering with the neuroendocrine systems (NES) regulating the physiological processes concerned. As soon as differentiating cercariae are present in the daughter sporocysts a factor can be detected in the haemolymph of the snail host, called schistosomin, which acts both at the central and the peripheral parts of the NES involved in regulation of reproduction and growth. Schistosomin appears to be a host-derived factor, which is probably released by cells of the internal defence system, the haemocytes, and by connective tissue cells, the telo-glial cells. It meets the criteria of having a cytokine-like function although its molecular structure does not show sequence homology with any of the vertebrate-type cytokines identified to date. Its cytokine nature explains why schistosomin can interfere with different neuroendocrine regulatory systems both at the central and peripheral--target--level, namely after binding to its own receptor. Schistosomin is probably not only responsible for the effects exerted by the parasite on female reproduction but also for those on male reproduction and on growth so that energy and space become available for the continuous production of cercariae. The nature of the humoral cercarial factor, which induces schistosomin release, is as yet unknown. Based on its hydrophobic character and on the fact that it can pass through the wall of the daughter sporocyst, it is supposed to be a diffusible molecule or a protonephridial excretion product. It does not seem to be a vertebrate-type steroid, an ecdysteroid or an eicosanoid. Results obtained in vitro have indicated that schistosomin might have a suppressive effect on haemocyte activity. Plasma from snails 5-6 weeks post-exposure showed a tendency to inhibit phagocytic activity of haemocytes from non-infected snails, that is preparatory to the escape and migration of cercariae. Once shedding has started this effect of schistosomin is overrruled by a strong activation of haemocyte activity coinciding with the tissue damage that the cercariae cause in the host. The cercariae escape from being attacked by masking their surface coat with host molecules. As the physiological effects caused by schistosomes resemble those observed during stress in mammals, experiments were carried out to find out whether schistosomin is also released in non-parasitized snails during stress resulting in an inhibiting effect on reproduction.(ABSTRACT TRUNCATED AT 400 WORDS)

Unusual cleavage of peptidic hormones generated by trypanosome enzymes released in infested rat serum

Gonad and thyroid dysfunctions are often observed in human and experimental models during african trypanosomiasis. The enzymatic activity of components released by the trypanosomes towards peptide hormones (e.g. GnRH, TRH) have consequently been studied. The incubation products of GnRH by (i) healthy or infested rat serum: (ii) trypanosomal components released by using a specific procedure; (iii) infested and normal rat brain extracts have been analysed by RP-HPLC fractionation. The peptide cleavage has been assessed by determination of either the amino acid compositions or relative molecular weight (by FAB mass spectrometry) of the different resolved HPLC fractions. Different protease inhibitors and a reducing agent have also been tested and a serine, cation-sensitive, thiol-dependent endopeptidase activity has been predominantly identified to be released by the trypanosomes in host circulation. It has been shown that the peptidase activity(ies) is(are) able to: (i) degrade the peptide hormones (GnRH, TRH) considered as important neuromodulators and neurotransmitters; (ii) generate an unusual N-terminal tetrapeptide (GnRH1-4) appearing to be still active towards the gonadal hypothalamo-pituitary axis.