I love details!

November 15th, 2018

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Fungi and prostate cancer

PSP94 is a human antimicrobial protein that specifically targets fungi (Edstrom et al 2012). It is strongly associated with prostate cancer: more PSP94 in the prostate implies lower cancer risk (Thomas et al 2008; Eeles et al 2008; Xu et al 2010), raising the possibility that a fungal infection in the prostate could be contributing to prostate cancer (Stott-Miller et al 2013; Sutcliffe et al 2014).

Chronic idiopathic inflammation of the prostate is exceedingly common and is suspected of contributing to prostate cancer (De Marzo et al 2007). Although sexually transmitted infections and uropathogens have been widely studied for nearly a century in association with prostatic inflammation (Visher 1929; Catterall 1961) and prostate cancer (Sfanos et al 2008; Hrbacek et al 2012), no consistently strong association has been found with specific microbes.

Scant effort has gone into studying fungal infections of the prostate (Sutcliffe et al 2014). In our preliminary metagenomics studies of the prostate, the only fungi we encountered were Malassezia restricta and Malassezia globosa. These two facultatively intracellular fungi are known to colonize our skin from birth (Nagata et al 2012). We initially dismissed these as contaminants (Laurence et al 2014), even though PSP94 is active only against intracellular fungi in the prostate (Sutcliffe et al 2014), whereas most fungi are extracellular.

Fungi and spondyloarthritis

The strongest epidemiologic association for prostatic inflammation is with spondyloarthritis: nearly all male ankylosing spondylitis and reactive arthritis patients have prostatic inflammation (Catterall 1961). Though few recent studies consider such an association, studies from the 1950s established this link beyond doubt (Laurence et al 2018). Sacral lymph vessels—which drain from the prostate to lymph nodes near the sacroiliac joint in the spine—have long been suspected of allowing inflammation to spread from the prostate to the spine, thus causing ankylosing spondylitis (Visher 1929).

Spondyloarthritis consists of one or more of the following: sacroiliitis, spondylitis, acute anterior uveitis, peripheral arthritis, inflammatory bowel disease (Crohn’s disease and ulcerative colitis) and psoriasis (Laurence et al 2018). Each of these conditions has strong links with an immune response against fungi  (Laurence et al 2018). Functional polymorphisms in CARD9 and IL23R, two genes needed to mount an immune response against fungi, are associated with all these conditions  (Laurence et al 2018). Elevated antibodies against fungi are associated with all these conditions  (Laurence et al 2018). Enteric Candida colonization is a risk factor for psoriasis, and many oral antifungals reduce symptoms (Laurence et al 2018). Links with fungi have been most thoroughly studied in Crohn’s disease: antibodies against three conserved fungal cell wall sugars (mannan, beta-glucan and chitin) are associated with Crohn’s disease (Main et al 1988; Dotan et al 2006). Phagocyte receptors recognizing mannan and beta-glucan are upregulated in Crohn’s disease (Baram et al 2014). Many recent studies have reported genetic and metagenomic links between fungi and Crohn’s disease (Laurence et al 2018). While these studies suggest a fungal etiology, they do not reveal which species are causative.

Functional polymorphisms in ERAP genes have also been associated with spondyloarthritis, and these polymorphisms interact with MHC class I alleles such as HLA-B*27 in modulating disease risk (Evans et al 2011). ERAP proteins are active within cells, where they trim peptides bound to MHC class I molecules, meaning that presentation of intracellular peptides to CD8+ T cells is occurring in spondyloarthritis, and thus an intracellular fungal etiology is likely—as we suspected for prostate cancer.

Circumstantial evidence for Malassezia

Monozygotic twin concordance in ankylosing spondylitis exceeds 50% (Brown et al 1997), which means any necessary fungal infection in spondyloarthritis would have to be present in well over half the population (Ruutu et al 2012). Malassezia are the only known fungi in humans which are often intracellular and highly prevalent. Fungal species putatively causing spondyloarthritis would have to be present on the skin to account for psoriasis. The only known fungal genus which is prevalent on the skin is Malassezia (Findley et al 2013). Though Malassezia species have traditionally been considered restricted to the skin, recent studies have found them in other organs, including in the mouth, gut, nose, breast, brain and lungs (Laurence et al 2018). This raises the possibility that Malassezia may be present in all spondyloarthritis sites, providing antigenic stimulation to spondyloarthritis-causing lymphocytes in each affected organ (Laurence et al 2018).

Direct evidence for Malassezia

Lysed Malassezia suspensions applied to healthy skin provoked psoriasis lesions in 10/10 psoriasis patients, while provoking similar lesions in only 2/10 controls (Lober et al 1982).

Antibodies against two Malassezia proteins were associated with psoriasis in 11/15 patients, while no such association was found in control groups (Squiquera et al 1994). No association was found with Candida proteins. This study was unique because it excluded conserved fungal antigens using a western blot, revealing an unambiguous link between psoriasis and Malassezia. Many other studies have associated antibodies against fungi with spondyloarthritis-associated conditions, but no strong conclusion could be drawn as to possible causative species because these studies included conserved fungal sugars which are present on all fungi.

As compared to healthy controls, peripheral blood mononuclear cells from psoriasis patients produced a strong Th1 response when exposed to Malassezia furfur (14/15 vs. 3/15), but no difference could be seen when exposed to Candida albicans (Kanda et al 2002). This study provides a third specific link between psoriasis and Malassezia.

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Malassezia restricta’s presence in gut biopsies was very strongly associated with pediatric granulomatous Crohn’s disease (odds ratio 25.2, 95% confidence interval [2.45–259.24], P=0.0025) (Kellermayer et al 2012). Similar studies in psoriasis fail to reveal an association because Malassezia are present on everyone’s skin from birth: psoriasis susceptibility seems to be a function only of genetic predisposition and other environmental factors. In contrast to the skin, Malassezia are not universally present in teenagers’ digestive tracts, enabling this small case-control study to find a clear association.

Finally, relative Malassezia levels in stool increase markedly during ulcerative colitis flares (Richard 2018), suggesting CD8+ T cells in ulcerative colitis are lysing gut epithelial cells containing Malassezia, releasing this fungus in stool.

Recent studies using vedolizumab in isolated Crohn’s disease suggest that antigens recognized by lymphocytes in the gut are also present in the sacroiliac joint, peripheral joints and skin, because about 10% of Crohn’s disease patients using vedolizumab subsequently develop sacroiliitis, peripheral arthritis or psoriasis (Laurence et al 2018). Vedolizumab binds to α4β7 integrin, preventing lymphocytes which activated in the gut from returning there during recirculation and forcing them into other organs. This result suggests that when lymphocytes recognizing Malassezia in the gut are forced into the spine, joints or skin, they often find Malassezia in these other organs, respectively causing sacroiliitis, peripheral arthritis and psoriasis.

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[Update March 8th 2019: Crohn's, Limon et al 2019, see this blog post]

[Update April 10th 2019: uveitis, Jayasudha et al 2019]

[Update October 9th 2019: pancreatic cancer, Aykut et al 2019]

Terbinafine and itraconazole

These findings satisfy Koch’s postulates for disease causation, albeit scattered across several related diseases. It is imperative to conduct the missing studies needed to definitely establish Malassezia as the cause of all these debilitating conditions. Malassezia require a lipid-rich environment for growth. Of commonly used antifungal drugs, the two most lipophilic are terbinafine and itraconazole. A twelve week course of oral terbinafine (250 mg/day) can clear Malassezia sympodialis from the skin, but not Malassezia globosa or Malassezia restricta: these two species are about ten times more resistant to antifungals than Malassezia sympodialis (Leeming et al 1997). Oral terbinafine and itraconazole, used in combination or at high doses, may be able to clear Malassezia globosa and Malassezia restricta from the body, quite possibly curing Crohn’s disease and other forms of spondyloarthritis. One small study reported that four out of five Crohn’s patients using oral itraconazole alone entered remission despite discontinuation of other therapies (Samuel et al 2010).