The role of microorganisms in prostate cancer development

Prostate cancer is the most common cancer among Swedish men, but the aetiology of this disease is largely unknown. There is evidence for a linkage between chronic inflammation and prostate cancer. The mechanisms causing prostate inflammation and how this could promote tumour development and progression are however largely unknown. Chronic inflammatory infiltrates are common findings in prostate tissue samples and infection is proposed to be one possible cause for this inflammation. Inflammatory cells release free radicals, cytokines, and growth factors that facilitate increased cell proliferation, DNA damage, mutations, and angiogenesis. However, the present literature on the presence of microbes in prostate tissue and their possible linkage to inflammation and cancer development is limited. Therefore, the aim of this thesis was to investigate if microorganisms are present in prostate tissue and to evaluate their role in inducing prostatitis and prostate epithelial neoplasia. The presence of microorganisms (virus, bacteria and fungi) was studied in clinical prostate tissue samples to evaluate whether or not the occurrences of microorganisms were different in patients that later developed cancer compared with matched controls that did not. Viruses, bacteria and fungi were found in prostate tissues. Out of eight different viruses investigated, EBV and JC virus were detected, but there were no differences in occurrence in the case group compared to the control group. The fungus Candida albicans was present in a very small proportion of the prostate tissue samples. The predominant bacterium was Propionibacterium acnes and the second most prevalent was Escherichia coli. The presence of Propionibacterium acnes was associated with inflammation and subsequent prostate cancer development. Propionibacterium acnes was further evaluated for its capacity to induce an inflammatory response both in vitro and in vivo. Live Propionibacterium acnes induced a strong immune reaction in prostate epithelial cells in vitro with up-regulation of inflammatory genes and secretion of pro-inflammatory cytokines. Infection with Propionibacterium acnes in rat prostate resulted in a lobe specific inflammation with the most intense inflammation in the dorso-lateral prostate, lasting up to 3 months post-inoculation. Propionibacterium acnes inflammation was also associated with altered epithelial cell morphology, signs of DNA damage and increased cell proliferation. Taken together, this thesis shows that different viruses and bacteria can be found in prostate tissue. Propionibacterium acnes, the most abundant among the bacteria detected and more prevalent in the cancer than in the control group, exhibits strong prostatitis promoting properties both in vitro and in vivo. In addition, Propionibacterium acnes can induce some of the epithelial changes known to occur during prostate neoplasia formation. This thesis therefore suggests that Propionibacterium acnes induced chronic prostatitis could promote prostate cancer development. Further studies are needed to elucidate the molecular interplay linking Propionibacterium acnes induced inflammation and the formation of a pre-neoplastic state that could evolve into prostate cancer

Propionibacterium acnes infection induces upregulation of inflammatory genes and cytokine secretion in prostate epithelial cells

Background: The immune stimulating bacterium Propionibacterium acnes is a frequent colonizer of benign and malignant prostate tissue. To understand the pathogenesis of the earliest phase of this infection, we examined the P. acnes triggered immune response in cultivated prostate epithelial cells. Results: Prostate epithelial cells are triggered to secrete IL-6, IL-8 and GM-CSF when infected with P. acnes. The secretion of cytokines is accompanied by NFκB related upregulation of the secreted cytokines as well as several components of the TLR2-NFκB signaling pathway. Conclusions: P. acnes has potential to trigger a strong immune reaction in the prostate glandular epithelium. Upon infection of prostate via the retrograde urethral route, the induced inflammatory reaction might facilitate bacterial colonization deeper in the prostate tissue where persistent inflammation may impact the development of prostate diseases as hyperplasia and/or malignancy

Visualization of <i>P. acnes</i> in infected prostate.

<p>Sequential sections of DLP from infected animals at 5 days (A), 3 weeks (B) and 3 months (C) after instillation, stained with H&E (1) and <i>P. acnes-</i> specific immunofluorescence (2). Pictures A3, B3 and C3 are created by overlaying 1 & 2. Pictures A4, B4 and C4 are close-ups of pictures A2, B2 and C2 captured with confocal microscopy. Magnification: 1–3∶100X, 4∶630X.</p

Degree of prostatic inflammation.

<p>Degree of inflammation in rats 5 days, 3 weeks (1A), 3 weeks (mix), 3 months and 6 months after instillation with <i>P. acnes</i> or PBS. Diagrams A & B show the distribution of scores among rats in each group, with n denoted in the bars. A) Left ventral prostate lobe (VPL), B) Dorso-lateral prostate lobe (DLP). C) Quantitative assessment of the spatial extent of focal inflammation in inflamed DLP. The diagram shows the individual distribution and means for the five groups (n = 5, 4, 3, 2, 2).</p

Inflammation scores.

<p>Panel of H&E-stained slides of infected prostate glands that illustrates the histological correlates of the inflammation score criteria, A) minimal inflammation, B) moderate inflammation, C) severe inflammation, D) focal inflammation, E) diffuse inflammation. Magnification: A–C: 100X, D–E: 40X.</p

Recovered <i>P. acnes</i> during infection.

<p>Amount of <i>P. acnes</i> CFU and genome equivalents retrieved from left ventral prostate lobe (VP_L) and dorso-lateral prostate lobe (DLP) 5 days, 3 weeks (1A), 3 weeks (mix), 3 months and 6 months after bacterial instillation. The number of CFU was determined by cultivation on solid agar and genome equivalents were determined by QPCR. Bars represent mean values, and the error bars represent standard deviation. (n = 2–3).</p

Corpora amylacea 6 months post infection.

<p>H&E-staining of inflamed foci in DLP 6 months after <i>P. acnes</i> instillation. Polymorphonuclear leukocytes are forming inflammatory infiltrate that surround structures resembling corpora amylacea. Magnification 400X.</p

Serum levels of CRP.

<p>Serum levels of CRP in rats 5 days, 3 weeks 1A, 3 weeks mix, 3 months and 6 months after instillation with <i>P. acnes</i> and PBS control. Bars represent mean values, and error bars represent standard deviation (n = 9).</p

Rat serum content of anti-<i>P. acnes</i> IgG.

<p>Serum levels of anti-<i>P. acnes</i> IgG in rats 5 days, 3 weeks (1A), 3 weeks (mix), 3 months and 6 months after instillation. The level of anti-<i>P. acnes</i> IgG was scored in four steps, from 0 (non-detectable) to 3 (maximum level). The diagram shows the distribution of scores among infected rats (n = 9).</p