As any other tissue injury, open biopsies can be expected to elicit prompt inflammatory responses (1). was the same in 15 subjects who had biopsies compared with 15 different subjects who did not. Conclusion:Open, sc fat biopsies produced inflammation, hypoxia, ER stress, and decreased expression of adiponectin and leptin. These changes remained confined to the biopsy site for at least 4 h. Open, subcutaneous fat biopsies cause acute and localized inflammation, hypoxia, and Ionomycin calcium endoplasmic reticulum stress in human subjects. Open biopsies are frequently needed for diagnostic or research purposes. As any other tissue injury, open biopsies can be expected to elicit prompt inflammatory responses (1). They may also produce endoplasmic reticulum (ER) stress because tissue injuries create cellular calcium and redox state imbalances and produce an accumulation of reactive oxygen species (ROS), conditions that are known to cause ER stress (2). ER stress in turn activates intracellular pathways, collectively called the unfolded protein response (UPR), which generally assist in restoring tissue homeostasis Ionomycin calcium and integrity but that can also cause inflammation (reviewed in Ref.3). ER stress/UPR, therefore, may be one mechanism by which tissue injury is sensed and transformed into inflammation. It is presently not known whether an acute tissue injury such as an open fat biopsy is associated with ER stress. It was, therefore, the objective of this study to determine whether ER stress (indicated by a rise in UPR mRNAs) develops in adipose tissue after an open sc fat biopsy in healthy human Ionomycin calcium subjects. == Subjects and Methods == Five healthy obese volunteers [two males, three females, age 34 5 yr, body mass index (BMI) 34 1.7 kg/m2] underwent three open sc fat biopsies at 4-h intervals. In addition, insulin-stimulated glucose uptake was measured during 4 h euglycemic-hyperinsulinemic clamping in 30 healthy subjects. Of those, 15 (13 males, two females, age 33.5 2.9 yr, PIK3CG BMI 25.2 1.1 kg/m2) had two open sc fat biopsies (before and after clamp) and the other 15 (11 males, four females, 28.7 1.6 yr, BMI 24.1 1.0 kg/m2) were not biopsied. None of the participants had a family history of diabetes or other endocrine disorders or were taking medications. Their body weights were stable for at least 2 months before the biopsies. Informed written consent was obtained from all subjects after explanation of the nature, purpose, and the potential risks of these studies. The study protocol was approved by the Institutional Review Board of Temple University Hospital. == Fat biopsies == The subjects were admitted to the Temple University Hospital Clinical Research Center on the day before the studies. At approximately 0800 h on the day after admission, venous blood samples were obtained and an open sc fat biopsy was performed by a surgeon from the lateral aspect of one upper thigh (15 cm above the patella). The skin was cleaned with betadine and anesthetized with 1% lidocaine (without epinephrine) in a field block pattern (at 2 3 in.). An incision (1 in.) was made through the skin, and 200300 mg sc fat was excised (4). The excised fat was dropped immediately into isopentane and kept at its freezing point (160 C) by liquid nitrogen. The wound was then temporarily closed with adhesive tape. Four hours later, another fat biopsy was obtained approximately 3 in. above the first biopsy site, and a third biopsy was obtained from the contralateral leg. The frozen fat was stored at 80 C until analyzed. ==.