The prostatic antibacterial factor: identity and significance.

Abstract

Normal human prostaticfluid possesses pronounced antibacterial activity. This activity is absent or markedly diminished in the fluid of men with chronic bacterial prostatitis. Ion-probe and mass spectrographic analysis of this antibacterialfactor has shown it to be a zinc salt. ProstaticfEuid zinc levels in 15 men with chronic bacterial prostatitis averaged 50 pg. per milliliter (range 0 to 139 pg. per milliliter). The zinc level in the expressed prostate secretion (EPS) of49 control men averaged 448 pg. per milliliter (range 150 to 1,000 pg. per milliliter). There was no overlap in the range of zinc values between the two groups. The decrease in EPS zinc concentration in the patient population was not secondary to a decreased serum zinc level. Exogenous zinc given orally did not increase the EPS zinc level. The decrease in EPS zinc was not limited to infected prostaticfEuid cultures and may precede the entry of bacteria into the prostate. The data presented suggest that zinc may serve as an in vivo defense mechanism against prostatic invasion and subsequent urinary tract infections in men. Urinary tract infections occur more frequently in adult females than males. The reason for this dif- ference is unknown. In adult males the majority of urinary tract infections are secondary to an initial prostatic infection which later ascends to infect the bladder urine.' For several years, we and others have been investigating the biochemical properties of prostatic fluid and have dem- onstrated that the normal human, canine, and rat prostatic secretions possess pronounced an- tibacterial activity. 2-6 These observations have led to the purification and isolation of PAF (prostatic antibacterial factor) from prostatic fluid and se- men. 7 Positive identification of PAF by mass spec- troscopy and ion-probe analysis has confirmed that the bactericidal activity of PAF is directly related to the total zinc concentration of the fluid and no other antibacterial agent was identified. *This study was supported in part by Research Grant No. 5 ROl A110668, National Institute of Allergy and Infectious Disease, National Institutes of Health, U.S. Public Health Service. Studies involving patients with bacteriologi- cally documented chronic bacterial prostatitis demonstrated a marked diminution or total ab- sence of zinc in the EPS (expressed prostate se- cretion) of these patients as compared with nor- mal males. This suggests that the cation may serve as an in vivo antibacterial defense mechanism against prostatic and urinary tract infections in humans.