Objective To determine whether anatomical thigh muscle cross-sectional areas (MCSAs) and strength differ between osteoarthritis (OA) knees with frequent pain compared with contralateral knees without pain, and to examine the correlation between MCSAs and strength in painful versus painless knees. Methods 48 subjects (31 women; 17 men; age 45–78 years) were drawn from 4796 Osteoarthritis Initiative (OAI) participants, in whom both knees displayed the same radiographic stage (KLG2 or 3), one with frequent pain (most days of the month within the past 12 months) and the contralateral one without pain. Axial MR images were used to determine MCSAs of extensors, flexors and adductors at 35% femoral length (distal to proximal) and in two adjacent 5 mm images. Maximal isometric extensor and flexor forces were used as provided from the OAI data base. Results Painful knees showed 5.2% lower extensor MCSAs (p=0.00003; paired t-test), and 7.8% lower maximal extensor muscle forces (p=0.003) than contra-lateral painless knees. There were no significant differences in flexor forces, or flexor and adductor MCSAs (p>0.39). Correlations between force and MCSAs were similar in painful and painless OA knees (0.44

Objective To determine whether lower thigh muscle specific strength increases risk of incident radiographic knee osteoarthritis (RKOA), and whether there exists a sex-specific relationship between thigh muscle specific strength and BMI. Methods 161 Osteoarthritis Initiative participants (62% female) with incident RKOA (Kellgren-Lawrence grade 0/1 at baseline, developing an osteophyte and joint space narrowing grade ≥1 by year 4) were matched to 186 controls (58% female) without incident RKOA. Thigh muscle anatomical cross-sectional areas (ACSAs) were determined at baseline using axial MRI scans. Isometric extensor and flexor muscle strength were measured at baseline and specific strength (strength÷ACSA) calculated. Logistic regression assessed risk of incident RKOA associated with muscle specific strength (with and without adjustment for BMI). Results Lower knee extensor and flexor specific strength significantly increased the risk of incident RKOA in women (OR 1.47 [95%CI 1.10, 1.96] and 1.41 [1.06, 1.89], respectively) but not in men. The significant relationship in women was lost after adjustment for BMI. Lower specific strength was associated with higher BMI in women (r=−0.29, p<0.001), but not in men; whereas (absolute) strength was associated with BMI in men (r=0.28, p=0.001), but not in women. Conclusion Lower thigh muscle specific strength predicts incident RKOA in women, with this relationship being confounded by BMI. The sex-specific relationship between muscle specific strength and BMI provides a possible explanation why women with muscle strength deficits typically have a poorer prognosis than men with similar strength deficits.

MRI-based analysis of quadriceps muscles ACSAs appears to be more sensitive to longitudinal change than isometric extensor strength and is suggestive of greater loss in limbs with structurally progressive KOA than in non-progressive controls.

In the regurgitate (foregut content) of Spodoptera larvae we found high concentrations (0.5-5 mM) of 8-hydroxyquinoline-2-carboxylic acid (8-HQA). In a survey of different lepidopteran species, this compound was only detected in species belonging to the family of Noctuidae. 8-HQA was shown to derive from tryptophan metabolism. The amount of 8-HQA in the regurgitate was strongly dependent on the tryptophan content of the diet. In the insect 8-HQA is generated from tryptophan via kynurenine and 3-hydroxykynurenine. 8-HQA is produced by the larvae and not by their commensal gut bacteria. Analysis of different life stages of Spodoptera larvae revealed that 8-HQA is formed during the larval stage, probably acting as an iron chelator to control the gut microbiome.