Seminal fluid and sperm diluent affect sperm metabolism in an insect: Evidence from NAD(P)H and flavin adenine dinucleotide autofluorescence lifetime imaging

Research output: Contribution to journalResearch articleContributedpeer-review



Sperm metabolism is fundamental to sperm motility and male fertility. Its measurement is still in its infancy, and recommendations do not exist as to whether or how to standardize laboratory procedures. Here, using the sperm of an insect, the common bedbug, Cimex lectularius, we demonstrate that standardization of sperm metabolism is required with respect to the artificial sperm storage medium and a natural medium, the seminal fluid. We used fluorescence lifetime imaging microscopy (FLIM) in combination with time-correlated single-photon counting (TCSPC) to quantify sperm metabolism based on the fluorescent properties of autofluorescent coenzymes, NAD(P)H and flavin adenine dinucleotide. Autofluorescence lifetimes (decay times) differ for the free and protein-bound state of the co-enzymes, and their relative contributions to the lifetime signal serve to characterize the metabolic state of cells. We found that artificial storage medium and seminal fluid separately, and additively, affected sperm metabolism. In a medium containing sugars and amino acids (Grace's Insect medium), sperm showed increased glycolysis compared with a commonly used storage medium, phosphate-buffered saline (PBS). Adding seminal fluid to the sperm additionally increased oxidative phosphorylation, likely reflecting increased energy production of sperm during activation. Our study provides a protocol to measure sperm metabolism independently from motility, stresses that protocol standardizations for sperm measurements should be implemented and, for the first time, demonstrates that seminal fluid alters sperm metabolism. Equivalent protocol standardizations should be imposed on metabolic investigations of human sperm samples.


Original languageEnglish
Pages (from-to)398-411
Number of pages14
JournalMicroscopy research and technique
Issue number1
Publication statusPublished - Jan 2022

External IDs

Scopus 85114357377
unpaywall 10.1002/jemt.23914
Mendeley 58ff35d7-eb5d-3515-bd98-c2053fba8c7f


Subject groups, research areas, subject areas according to Destatis


  • Animals, Bedbugs, Flavin-Adenine Dinucleotide, Male, Microscopy, Fluorescence, Multiphoton, NADP, Sperm Motility, Spermatozoa/drug effects, FLIM, bedbug, metabolic mapping, spermatozoa, Cimex lectularius, multiphoton microscopy, FLIRR

Library keywords