Aging of collagen: comparative rates in four mammalian species

Cross-linking of the extracellular matrix by the maillard reaction in aging and diabetes: an update on "a puzzle nearing resolution"

The aging extracellular matrix is characterized by an age-related increase in insolubilization, yellowing, and stiffening, all of which can be mimicked by the Maillard reaction in vitro. These phenomena are accelerated in metabolic diseases such as diabetes and end-stage renal disease, which have in common with physiological aging the accumulation of various glycation products and cross-links. Eight years ago we concluded that the evidence favored oxidative cross-linking in experimental diabetes [Monnier, V.M. et al. 1996. The mechanism of collagen cross-linking in diabetes: a puzzle nearing completion. Diabetes 45(Suppl. 3): 67-72] and proposed a major role for a putative non-UV active cross-link derived from glucose. Below, we provide an update of the field that leads to the conclusion that, while oxidation might be important for Maillard reaction-mediated cross-linking via Strecker degradation and allysine formation, the single most important collagen cross-link known to date in diabetes and aging is glucosepane, a lysyl-arginine cross-link that forms under nonoxidative conditions.

Green tea extract suppresses the age-related increase in collagen crosslinking and fluorescent products in C57BL/6 mice

Collagen crosslinking during aging in part results from Maillard reaction endproducts of glucose and oxoaldehydes. Because of the tight link between oxidative and carbonyl stress, we hypothesized that natural antioxidants and "nutriceuticals" could block collagen aging in C57BL/6 mice. Six groups of young and adult mice received vitamin C, vitamin E, vitamin C&E, blueberry, green tea extract (GTE), or no treatment for a period of 14 weeks. Body weights and collagen glycation were unaltered by the treatment. However, GTE or vitamin C&E combined blocked tendon crosslinking at 10 months of age (p < 0.05, adult group). GTE also blocked fluorescent products at 385 and 440 nm (p = 0.052 and < 0.05, respectively) and tended to decrease skin pentosidine levels. These results suggest that green tea is able to delay collagen aging by an antioxidant mechanism that is in part duplicated by the combination of vitamin C and E.

Cervical range of motion in the elderly

This study was conducted to establish normative cervical range of motion values for the elderly and to compare those values to standard young adult cervical range of motion values. Differences in range of motion between men and women were also assessed. A gravity goniometer was used to measure six cervical motions in 42 subjects aged 70 to 90 years and 31 subjects aged 20 to 30 years. The elderly group had significantly less motion than the younger group for all six motions measured (p < .001). A comparison of the mean range of motion values between the two groups found that the elderly group had approximately 12% less flexion, 32% less extension, 22% less lateral flexion, and 25% less rotation. The elderly group also had a wider variation of cervical range of motion values as compared to the younger group. Women had greater cervical range of motion values than men in both age groups.

Iatrogenesis in the elderly. Factors of immobility

Mobility of elderly patients is a consequence of the interaction between factors including biological health, sensory-perceptual capacity, motor skills, cognitive capacity, and ego-strength; and environmental resources including physical and architectural features, medical regimens, institutional policies, resident and staff characteristics, and social support availability. Impaired mobility, whether self- or other-imposed, places the elderly at risk for a multitude of negative physiological and psychological consequences that can affect health, well-being, and quality of life. Understanding the basic mechanisms underlying the physiological and psychological consequences of immobility, the relative time-frame in which they can develop, and the concomitant changes associated with aging provides the basis for interventions aimed at preventing or minimizing them. A multitude of factors that influence the elderly's state of mobility are within nursing's realm of practice. Although elderly patients may present a special challenge, the negative consequences of immobility can be avoided, to a significant extent, with astute and vigilant nursing management.

Morphometric analysis of dermal collagen fibers in normal human skin as a function of age

A quantitative study of dermal collagen as a function of age was carried out by computerized digital image analysis. Fast Green-Syrius Red stained sections were obtained of skin biopsies taken from the upper inner arm of 33 healthy women and 38 healthy men. The Leitz texture Analysis System (Leitz-TAS) and mathematical morphology (Serra, 1982) were used for the evaluation of the data. Collagen was studied in the superficial dermis and also in the reticular dermis using the same program. There were significant correlations, firstly between the percentage of collagen measured by the morphometric method and the concentration of collagen analysed biochemically (microg/mm(2) of tissue section) (r = 0.79, p < 0.001) and secondly between the decreased concentration of collagen and age (r = 0.58, p < 0.05). The morphometrical measurements have shown that the relative percentage of collagen bundles (surface of collagen fibers as a function of the dermal area analyzed) was 93.35% in the superficial dermis and 89.2% in the reticular dermis. Although this value is higher than the chemically determined ratio of collagen to other proteins (over 70%), this may be due to the relatively uniform distribution pattern of (type I and III) collagen through the dermis covering most other components of the skin. As the collagen fiber density per unit dermal surface did not change with age, the decrease in collagen content of the skin may be ascribed to the loss of about 6% of dermal mass per decade (Branchet, 1990), although large individual variations exist. The histogram of the diameter distribution of collagen fiber bundles of the reticular dermis showed thinner diameters in persons between 20 and 40 years of age than in older persons. The histogram of the distribution of interfiber spaces did not show any variation with age in the superficial dermis, while in the reticular dermis there was a predominance of smaller interspaces in persons older than 50 years.

Analysis of age-associated changes in collagen crosslinking in the skin and lung in monkeys and rats

The present study was designed to address a specific question: can we define collagen aging in vivo in terms of alterations in collagen crosslinking? In order to assess the complete spectrum of change throughout life, tissues from rats, monkeys and (where available) humans were examined at ages ranging from fetal to old. Skin and lung were selected in order to include all of the crosslinks derived from lysyl oxidase-generated aldehydes that have been identified thus far, both reducible and nonreducible. Crosslinks analyzed included hydroxylysinonorleucine, dihydroxylysinorleucine, histidinohydroxymerodesmosine, hydroxypyridinium, lysyl pyridinium, and a deoxy analogue of hydroxypyridinium found in skin that differs structurally from lysyl pyridinium. Tissues from both a short-lived species (rats) and a long-lived species (monkeys) were analyzed to test further the hypothesis that changes in crosslinking are linked predominantly to biological age of the animal, rather than temporal aging. We found that biological aging seems to regulate certain predictable changes during the first part of the lifespan: the disappearance postnatally of dihydroxylysinonorleucine in skin, the rapid decrease in difunctional crosslink content in lung and skin during early growth and development, and the gradual rise in hydroxypyridinium and lysyl pyridinium in lung tissue. Changes in crosslinking were far less predictable during the second half of the lifespan. Although hydroxypridinium content continued to rise or reached a plateau in rat and monkey lungs, respectively, it showed a decrease in human lungs. The analogous trifunctional crosslink in skin, the so-called 'pyridinoline analogue', decreased dramatically in both rats and monkeys in later life. Our data suggest that caution must be taken in drawing inferences about human connective tissue aging from experiments performed in short-lived species such as rodents. Furthermore, the finding that there may be fewer total lysyl oxidase-derived crosslinks per collagen molecule in very old animals as compared with young animals suggests that we may need to expand our concepts of collagen crosslinking.

The rate of collagen maturation in rat and human skin

Hydrothermal Isometric Tension (HIT) relaxation was observed at the boiling point in rat, cat and human skin samples of different ages, after raising the temperature from 37 degrees to 100 degrees C at a rate of 1.15 degrees C/min. A Maxwellian relaxation to nearly zero was observed at the boiling point. A given velocity constant characterized a given tissue whether experiments were performed under pressure or under tensile stress. However, the velocity constant of the relaxation decreased as a function of age for all three species during the period studied. Moreover, the velocity constant decreased at the same constant rate for skin samples of cats aged 1 to nearly 5 years, of rats aged from 9 to 28 months and of children from birth to 10 years. We propose a model, based on the well known rubber-elastic properties of the denatured collagen network. In this model (1) HIT decreases as an exponential function of time during bond scission along the polymeric chains; (2) the velocity constant of the relaxation process is proportional to the rate of bond rupture and inversely proportional to the number of stable polymeric chains originally present per unit volume; (3) the evolution of the velocity constant as a function of aging finds an explanation. The HIT test should find useful applications in pathology and pharmacology, since it provides rapid, precise information on the stable state of collagen reticulation in small biopsies.