In 1988, the National Institute on Aging launched a 10-year program aimed at identification of biomarkers of aging. Previous results from our laboratory showed that pentosidine, an advanced glycation product, formed in skin collagen at a rate inversely related to maximum life span across several mammalian species. As part of the Biomarkers Program, we investigated the hypothesis that longitudinal determination of glycation and glycoxidation rates in skin collagen could predict longevities in ad libitum-fed (AL) and caloric restricted (CR) mice. C57BL/6NNia male mice were biopsied at age 20 months and at natural death. Glycation (furosine method) was assessed by gas chromatography/mass spectrometry (GC/MS) and the glycoxidation products carboxymethyllysine (CML) and pentosidine were determined by GC/MS and HPLC, respectively. CR vs. AL significantly (P<0.0001) increased both mean (34 vs. 27 months) and maximum (47 vs. 31 months) life spans. Skin collagen levels of furosine (pmol/micromol lysine) were approximately 2.5-fold greater than CML levels and 100-fold greater than pentosidine. Individual accumulation rates modeled as linear equations were significantly (P<0.001) inhibited by CR vs. AL for all parameters and in all cases varied inversely with longevity (P<0.1 to <0.0001). The incidence of three tissue pathologies (lymphoma, dermatitis, and seminal vesiculitis) was found to be attenuated by CR and the latter pathology correlated significantly with longevities (r=0.54, P=0. 002). The finding that markers of skin collagen glycation and glycoxidation rates can predict early deaths in AL and CR C57BL/6NNia mice strongly suggests that an age-related deterioration in glucose tolerance is a life span-determining process.

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SUMMARYTo facilitate detection of tumor cells at the highest resolution in any organ in athymic nude mouse model systems, a histochemical marker gene [bacterial lacZ or human placental alkaline phosphatase (ALP)] was transfected into specified transformed/tumor cells (fibrosarcoma or neuroblastoma). The fates of tumor cells were followed qualitatively and quantitatively by histochemical staining of whole organs or organ sections. Primary tumors developed initially via formation of "curly-haired" complexes of cells in the subcutis or dermis, followed by division of a large fraction of cells. When two tumor classes were mixed before injection, outgrowth occurred in regional concentrations of the primary tumor. Blood microvessels were detectable within 72 hr of injection, growing into tumor regions. IV injection routinely yielded multicellular foci in the lungs within minutes as precursors of experimental metastases. Micrometastasis was further resolved with cells "inactivated" by different treatments and by co-injection of two different tagged cell types. These approaches using different histochemical marker genes to "tag" different tumor cell classes, along with more advanced molecular biological approaches, permit us to characterize gene expression and its reversibility during the earliest stages of primary tumor formation and micrometastasis to virtually any organ in the recipient animal.